Preparation method and application of polytetrafluoroethylene foam

Abstract

The invention relates to a preparation method and application of polytetrafluoroethylene foam, and belongs to the technical field of foaming. The invention provides polytetrafluoroethylene foam. The polytetrafluoroethylene foam is obtained by physically foaming a foaming blank made of soluble polytetrafluoroethylene, the foaming ratio of the polytetrafluoroethylene foam is 2-50 times, the aperture of the polytetrafluoroethylene foam is 10-500 microns, and the content of soluble polytetrafluoroethylene in the polytetrafluoroethylene foam is greater than 90% by mass. The polytetrafluoroethylene foam is obtained by foaming soluble polytetrafluoroethylene through a supercritical fluid foaming technology, inherits the characteristics of heat resistance, cold resistance, flame retardance, wear resistance and the like of the soluble polytetrafluoroethylene, and also has the characteristics of low density, heat insulation, good compressibility and excellent permanent deformation resistance; the method has a huge application prospect in the fields of fine chemical engineering, medicine, aerospace and the like.

Description

Technical Field

[0001] The invention relates to a preparation method of polytetrafluoroethylene foam and application thereof, belonging to the technical field of foaming. Background Art

[0002] Polytetrafluoroethylene (PTFE) is a polymer made from tetrafluoroethylene as a monomer. Its chemical formula is (C 2 F 4 ) n PTFE is heat-resistant, cold-resistant and flame-retardant, and can be used for a long time at -180 to 260°C. In addition, PTFE is resistant to acids, alkalis and various organic solvents, and is almost insoluble in all solvents. At the same time, PTFE has an extremely low friction coefficient and excellent wear resistance.

[0003] At present, polytetrafluoroethylene has been used in many fields, for example, to make corrosion-resistant parts, wear-resistant parts, seals, insulation parts, medical equipment parts, and various parts, pipes and wires for semiconductor production. However, the high density of polytetrafluoroethylene limits its application in more fields. If the foaming of polytetrafluoroethylene can be achieved, it is expected to obtain low-density polytetrafluoroethylene foam that can inherit the performance advantages of polytetrafluoroethylene itself and has the characteristics of heat resistance, cold resistance, flame retardancy and wear resistance. This kind of foam has great application prospects in the fields of fine chemicals, medicine and aerospace. However, due to the extremely low fluidity and high difficulty of polytetrafluoroethylene, it is still impossible to directly foam polytetrafluoroethylene to achieve the foaming of polytetrafluoroethylene.

[0004] At present, conventional polymer foaming processes are divided into chemical foaming and physical foaming. Among them, the chemical foaming agent used in chemical foaming usually causes damage to the environment and will have residues in the polymer matrix. Therefore, supercritical carbon dioxide (CO 2 ) fluid and supercritical nitrogen (N 2 ) fluid and other environmentally friendly physical foaming agents. Supercritical fluid foaming technology is a polymer physical foaming technology that has emerged in recent years. Not only is the technical route itself green and environmentally friendly, and the process is non-toxic and harmless, but also, by implementing the cell nucleation and growth step by step, it greatly reduces the volume of high-pressure equipment, reduces the amount of foaming agent used and the cost of high-pressure equipment. It is urgent to develop a foaming method based on supercritical fluid foaming technology that can achieve effective foaming of polytetrafluoroethylene, so as to prepare a low-density polytetrafluoroethylene foam that can inherit the performance advantages of polytetrafluoroethylene itself and has the characteristics of heat resistance, cold resistance, flame retardancy and wear resistance. Summary of the invention

[0005] To solve the above-mentioned defects, the present invention provides a polytetrafluoroethylene foam, which is obtained by physically foaming a foamed embryonic body of soluble polytetrafluoroethylene; the polytetrafluoroethylene foam has a foaming ratio of 2 to 50 times, a pore size of 10 to 500 μm, and, in terms of mass percentage, a content of soluble polytetrafluoroethylene in the polytetrafluoroethylene foam is greater than 90%.

[0006] In one embodiment of the present invention, the method for preparing the polytetrafluoroethylene foam comprises the following steps:

[0007] Impregnation step: placing a foamed embryo made of soluble polytetrafluoroethylene (PFA) in a foaming mold with a mold cavity temperature of 250-310° C., closing the mold cavity, and introducing a gas foaming agent into the mold cavity until the pressure in the mold cavity reaches 5-50 MPa; continuously placing the foamed embryo in the mold cavity with a pressure of 5-50 MPa and a temperature of 250-310° C. until the gas foaming agent reaches a dissolution equilibrium in the foamed embryo;

[0008] Pressure relief step: after reaching the dissolution equilibrium, the pressure in the mold cavity is relieved to 0-0.5MPa to induce the nucleation and growth of the pores in the foamed embryo; after the pressure is relieved to 0-0.5MPa, the mold cavity is opened to allow the pores in the foamed embryo to continue to grow, thereby obtaining polytetrafluoroethylene foam. The mold cavity temperature in the impregnation step will affect the foaming ratio of the polytetrafluoroethylene foam. Within the range that can achieve physical foaming of soluble polytetrafluoroethylene, under the same conditions, the higher the mold cavity temperature, the higher the foaming ratio of the polytetrafluoroethylene foam. The mold cavity pressure in the impregnation step will also affect the foaming ratio of the polytetrafluoroethylene foam. Within the range that can achieve physical foaming of soluble polytetrafluoroethylene, under the same conditions, the higher the mold cavity pressure, the higher the foaming ratio of the polytetrafluoroethylene foam.

[0009] In one embodiment of the present invention, the soluble polytetrafluoroethylene is a copolymer of perfluoropropyl perfluorovinyl ether and polytetrafluoroethylene; the melt index of the soluble polytetrafluoroethylene is 0.5 to 50 g / 10 min (375° C. / 5 kg).

[0010] In one embodiment of the present invention, in the impregnation step, the time for the gas foaming agent to reach dissolution equilibrium in the foaming embryo is the impregnation time t; the impregnation time t≥H×20; where the unit of the impregnation time T is min, and H is the maximum diffusion path of the gas foaming agent in the foaming embryo, in mm. If the foaming embryo is plate-shaped, sheet-shaped or columnar, the maximum diffusion path refers to its thickness; if the foaming embryo is spherical, roll-shaped or irregular, the maximum diffusion path refers to its minimum diameter.

[0011] In one embodiment of the present invention, in the depressurization step, the depressurization rate is 1 to 300 MPa / s.

[0012] In one embodiment of the present invention, the gas foaming agent includes supercritical carbon dioxide fluid and / or supercritical nitrogen fluid.

[0013] In one embodiment of the present invention, the method for preparing the polytetrafluoroethylene foam comprises the following steps:

[0014] Impregnation step: placing a foamed embryo made of soluble polytetrafluoroethylene in a foaming mold with a mold cavity temperature of 270-305° C., closing the mold cavity, and introducing a gas foaming agent into the mold cavity until the pressure in the mold cavity reaches 8-30 MPa; continuously placing the foamed embryo in the mold cavity with a pressure of 8-30 MPa and a temperature of 270-305° C. until the gas foaming agent reaches a dissolution equilibrium in the foamed embryo;

[0015] Pressure relief step: after reaching the dissolution equilibrium, the pressure in the mold cavity is relieved to 0 MPa to induce the nucleation and growth of the pores in the foaming embryo; after the pressure is relieved to 0 MPa, the mold cavity is opened to allow the pores in the foaming embryo to continue to grow, thereby obtaining polytetrafluoroethylene foam.

[0016] In one embodiment of the present invention, the method for preparing the foamed embryo body comprises: molding a soluble polytetrafluoroethylene raw material at a molding temperature to obtain a foamed embryo body.

[0017] In one embodiment of the present invention, the molding temperature is 350-400°C.

[0018] In one embodiment of the present invention, the molding is extrusion molding, injection molding or hot pressing molding.

[0019] In one embodiment of the present invention, the foamed embryo is in the shape of a plate, a sheet, a column, a sphere, a roll or an irregular shape.

[0020] In one embodiment of the present invention, the foamed embryo is in sheet shape.

[0021] In one embodiment of the present invention, the polytetrafluoroethylene foam is a foamed plate, a foamed sheet, a foamed column, a foamed sphere, a foamed coil or an irregular foamed body.

[0022] In one embodiment of the present invention, the polytetrafluoroethylene foam is a foamed sheet.

[0023] The present invention also provides a method for preparing the above-mentioned polytetrafluoroethylene foam, the preparation method comprising: physically foaming a foaming embryo whose material is soluble polytetrafluoroethylene to obtain polytetrafluoroethylene foam; in terms of mass percentage, the content of soluble polytetrafluoroethylene in the foaming embryo is greater than 90%.

[0024] In one embodiment of the present invention, the preparation method comprises the following steps:

[0025] Impregnation step: placing a foamed embryo made of soluble polytetrafluoroethylene (PFA) in a foaming mold with a mold cavity temperature of 250-310° C., closing the mold cavity, and introducing a gas foaming agent into the mold cavity until the pressure in the mold cavity reaches 5-50 MPa; continuously placing the foamed embryo in the mold cavity with a pressure of 5-50 MPa and a temperature of 250-310° C. until the gas foaming agent reaches a dissolution equilibrium in the foamed embryo;

[0026] Pressure relief step: after reaching the dissolution equilibrium, the pressure in the mold cavity is relieved to 0-0.5 MPa to induce the nucleation and growth of the pores in the foaming embryo; after the pressure is relieved to 0-0.5 MPa, the mold cavity is opened to allow the pores in the foaming embryo to continue to grow, thereby obtaining polytetrafluoroethylene foam.

[0027] In one embodiment of the present invention, the soluble polytetrafluoroethylene is a copolymer of perfluoropropyl perfluorovinyl ether and polytetrafluoroethylene; the melt index of the soluble polytetrafluoroethylene is 0.5 to 50 g / 10 min (375° C. / 5 kg).

[0028] In one embodiment of the present invention, in the impregnation step, the time for the gas foaming agent to reach dissolution equilibrium in the foaming embryo is the impregnation time t; the impregnation time t≥H×20; where the unit of the impregnation time T is min, and H is the maximum diffusion path of the gas foaming agent in the foaming embryo, in mm. If the foaming embryo is plate-shaped, sheet-shaped or columnar, the maximum diffusion path refers to its thickness; if the foaming embryo is spherical, roll-shaped or irregular, the maximum diffusion path refers to its minimum diameter.

[0029] In one embodiment of the present invention, in the depressurization step, the depressurization rate is 1 to 300 MPa / s.

[0030] In one embodiment of the present invention, the gas foaming agent includes supercritical carbon dioxide fluid and / or supercritical nitrogen fluid.

[0031] In one embodiment of the present invention, the method for preparing the polytetrafluoroethylene foam comprises the following steps:

[0032] Impregnation step: placing a foamed embryo made of soluble polytetrafluoroethylene in a foaming mold with a mold cavity temperature of 270-305° C., closing the mold cavity, and introducing a gas foaming agent into the mold cavity until the pressure in the mold cavity reaches 8-30 MPa; continuously placing the foamed embryo in the mold cavity with a pressure of 8-30 MPa and a temperature of 270-305° C. until the gas foaming agent reaches a dissolution equilibrium in the foamed embryo;

[0033] Pressure relief step: after reaching the dissolution equilibrium, the pressure in the mold cavity is relieved to 0 MPa to induce the nucleation and growth of the pores in the foaming embryo; after the pressure is relieved to 0 MPa, the mold cavity is opened to allow the pores in the foaming embryo to continue to grow, thereby obtaining polytetrafluoroethylene foam.

[0034] In one embodiment of the present invention, the method for preparing the foamed embryo body comprises: molding a soluble polytetrafluoroethylene raw material at a molding temperature to obtain a foamed embryo body.

[0035] In one embodiment of the present invention, the molding temperature is 350-400°C.

[0036] In one embodiment of the present invention, the molding is extrusion molding, injection molding or hot pressing molding.

[0037] In one embodiment of the present invention, the foamed embryo is in the shape of a plate, a sheet, a column, a sphere, a roll or an irregular shape.

[0038] In one embodiment of the present invention, the foamed embryo is in sheet shape.

[0039] In one embodiment of the present invention, the polytetrafluoroethylene foam is a foamed plate, a foamed sheet, a foamed column, a foamed sphere, a foamed coil or an irregular foamed body.

[0040] In one embodiment of the present invention, the polytetrafluoroethylene foam is a foamed sheet.

[0041] The invention also provides application of the preparation method in preparing polytetrafluoroethylene foam.

[0042] The technical solution of the present invention has the following advantages:

[0043] 1. The present invention provides a polytetrafluoroethylene foam, which is obtained by physically foaming a foamed body of soluble polytetrafluoroethylene; the polytetrafluoroethylene foam has a foaming ratio of 2 to 50 times, a pore size of 10 to 500 μm, and, in terms of mass percentage, a content of soluble polytetrafluoroethylene in the polytetrafluoroethylene foam is greater than 90%. The polytetrafluoroethylene foam uses soluble polytetrafluoroethylene as a foaming raw material, and the soluble polytetrafluoroethylene is a copolymer of perfluoropropyl perfluorovinyl ether and polytetrafluoroethylene. Its physical properties, chemical properties, and electrical properties are similar to those of polytetrafluoroethylene. The main difference between the two is that soluble polytetrafluoroethylene can be melt-processed, while polytetrafluoroethylene cannot be melt-processed. Soluble polytetrafluoroethylene has the following performance advantages:

[0044] (1) Excellent heat resistance, cold resistance and flame retardancy, long-term use temperature -196 ~ 260 ℃, flame retardancy reaches V0 level; (2) Excellent chemical corrosion resistance, corrosion resistance to all chemicals; (3) Low friction coefficient and excellent wear resistance; (4) Excellent electrical properties, and electrical insulation is not affected by temperature; (5) Chemical resistance is similar to that of polytetrafluoroethylene and better than vinylidene fluoride; (6) Creep resistance and compression strength are better than polytetrafluoroethylene, tensile strength is high, and elongation can reach 100 ~ 300%; (7) Good dielectric properties and excellent radiation resistance.

[0045] The polytetrafluoroethylene foam of the present invention is obtained by foaming soluble polytetrafluoroethylene through supercritical fluid foaming technology. While inheriting the heat resistance, cold resistance, flame retardancy and wear resistance of soluble polytetrafluoroethylene, the polytetrafluoroethylene foam also has the characteristics of low density, heat insulation, good compressibility and excellent resistance to permanent deformation. It has great application prospects in the fields of fine chemicals, medicine, aerospace, etc. (for example, it can be used for heat insulation of high-temperature pipes in ultra-clean workshops, for heat insulation inside precision and fine equipment, for heat insulation of objects in the aerospace field that are very sensitive to quality, such as aircraft, spacecraft and space suits, and for making special heat insulation clothing and firefighting clothing, etc.).

[0046] 2. The present invention provides a method for preparing polytetrafluoroethylene foam, the preparation method comprising: placing a foaming body made of soluble polytetrafluoroethylene (PFA) in a foaming mold with a mold cavity temperature of 250-310°C, closing the mold cavity, and introducing a gas foaming agent into the mold cavity until the pressure in the mold cavity reaches 5-50MPa; continuously placing the foaming body in the mold cavity with a pressure of 5-50MPa and a temperature of 250-310°C until the gas foaming agent is A dissolution equilibrium is reached in the foamed embryo; after the dissolution equilibrium is reached, the pressure in the mold cavity is released to 0-0.5 MPa to induce nucleation and growth of pores in the foamed embryo; after the pressure is released to 0-0.5 MPa, the mold cavity is opened to allow the pores in the foamed embryo to continue to grow, thereby obtaining a polytetrafluoroethylene foam; the polytetrafluoroethylene foam has a foaming ratio of 2-50 times, a pore diameter of 10-500 μm, and, in terms of mass percentage, a soluble polytetrafluoroethylene content of greater than 90%.

[0047] The preparation method of the present invention uses soluble polytetrafluoroethylene as a foaming raw material. The soluble polytetrafluoroethylene is a copolymer of perfluoropropyl perfluorovinyl ether and polytetrafluoroethylene. Its physical properties, chemical properties and electrical properties are similar to those of polytetrafluoroethylene. The main difference between the two is that soluble polytetrafluoroethylene can be melt-processed, while polytetrafluoroethylene cannot be melt-processed. Soluble polytetrafluoroethylene has the following performance advantages:

[0048] (1) Excellent heat resistance, cold resistance and flame retardancy, long-term use temperature -196 ~ 260 ℃, flame retardancy reaches V0 level; (2) Excellent chemical corrosion resistance, corrosion resistance to all chemicals; (3) Low friction coefficient and excellent wear resistance; (4) Excellent electrical properties, and electrical insulation is not affected by temperature; (5) Chemical resistance is similar to that of polytetrafluoroethylene and better than vinylidene fluoride; (6) Creep resistance and compression strength are better than polytetrafluoroethylene, tensile strength is high, and elongation can reach 100 ~ 300%; (7) Good dielectric properties and excellent radiation resistance.

[0049] The preparation method of the present invention successfully realizes the effective foaming of soluble polytetrafluoroethylene based on supercritical fluid foaming technology. The polytetrafluoroethylene foam prepared by the preparation method of the present invention not only inherits the characteristics of soluble polytetrafluoroethylene such as heat resistance, cold resistance, flame retardancy and wear resistance, but also has the characteristics of low density, heat insulation, good compressibility and excellent resistance to permanent deformation. It has great application prospects in the fields of fine chemicals, medicine, aerospace, etc. (for example, it can be used for heat insulation of high-temperature pipes in ultra-clean workshops, for heat insulation inside precision and fine equipment, for heat insulation of objects in the aerospace field that are very sensitive to quality, such as aircraft, spacecraft and space suits, and for making special heat insulation clothing and firefighting clothing, etc.). BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 : Photograph of the polytetrafluoroethylene foam obtained in Example 1.

[0051] Figure 2 : Cell structure diagram of the internal section of the polytetrafluoroethylene foam obtained in Example 1.

[0052] Figure 3 : Flame retardant effect test diagram of the polytetrafluoroethylene foam prepared in Example 1. DETAILED DESCRIPTION

[0053] The following examples are provided for a better understanding of the present invention, but are not intended to limit the best mode of implementation, nor to limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior arts shall fall within the protection scope of the present invention.

[0054] If no specific experimental steps or conditions are specified in the following examples, the conventional experimental steps or conditions described in the literature in the field can be used. If no manufacturer is specified for the reagents or instruments used, they are all conventional reagent products that can be purchased commercially.

[0055] Example 1: A method for preparing polytetrafluoroethylene foam

[0056] This embodiment provides a method for preparing polytetrafluoroethylene foam, and the steps of the preparation method are as follows:

[0057] Molding steps: Yonghe PW-200 resin (melt index 2.2g / 10min) is selected as the raw material, and hot pressed into a plate (size 100*100*10mm) at a molding temperature of 350°C on a flat vulcanizer to obtain a foamed embryo; Yonghe PW-200 resin is soluble polytetrafluoroethylene (Polyfluoroalkoxy, PFA), which is a copolymer of perfluoropropyl perfluorovinyl ether and polytetrafluoroethylene;

[0058] Impregnation step: after placing the foamed embryo in a foaming cavity of a molding machine with a cavity temperature of 295° C., the cavity is closed, and supercritical carbon dioxide fluid is filled into the cavity until the pressure in the cavity reaches 12 MPa; the foamed embryo is continuously placed in the cavity with a pressure of 12 MPa and a temperature of 295° C. for 4 hours, so that the gas foaming agent reaches a dissolution equilibrium in the foamed embryo;

[0059] Pressure relief step: After reaching the dissolution equilibrium, the pressure in the mold cavity is relieved to 0MPa at a pressure relief rate of 15MPa / s to induce the nucleation and growth of cells in the foamed body; after the pressure is relieved to 0MPa, the molding machine is opened to allow the cells in the foamed body to continue to grow, thereby obtaining polytetrafluoroethylene foam. After the polytetrafluoroethylene foam is cooled, its density is tested in accordance with the national standard "GB T6343-2009 Determination of apparent density of foamed plastics and rubbers", and the measured density is 95kg / m 3 (The density of unfoamed Yonghe PW-200 resin is 2140kg / m 3 ).

[0060] Example 2: A method for preparing polytetrafluoroethylene foam

[0061] This embodiment provides a method for preparing polytetrafluoroethylene foam, and the steps of the preparation method are as follows:

[0062] Molding steps: DuPont PFA-440HPB resin is selected as a raw material (melt index 14g / 10min), and a plate (size 100*100*10mm) is injection molded on an injection molding machine at a molding temperature of 350°C to obtain a foamed embryo; DuPont PFA-440HPB resin is soluble polytetrafluoroethylene (Polyfluoroalkoxy, PFA), which is a copolymer of perfluoropropyl perfluorovinyl ether and polytetrafluoroethylene;

[0063] Impregnation step: after placing the foamed embryo in a foaming cavity of a molding machine with a cavity temperature of 300° C., the cavity is closed, and supercritical nitrogen fluid is filled into the cavity until the pressure in the cavity reaches 30 MPa; the foamed embryo is continuously placed in the cavity with a pressure of 30 MPa and a temperature of 300° C. for 5 hours, so that the gas foaming agent reaches a dissolution equilibrium in the foamed embryo;

[0064] Pressure relief step: After reaching the dissolution equilibrium, the pressure in the mold cavity is relieved to 0MPa at a pressure relief rate of 15MPa / s to induce the nucleation and growth of cells in the foamed embryo; after the pressure is relieved to 0MPa, the molding machine is opened to allow the cells in the foamed embryo to continue to grow, thereby obtaining polytetrafluoroethylene foam. After the polytetrafluoroethylene foam is cooled, its density is tested in accordance with the national standard "GB T6343-2009 Determination of apparent density of foamed plastics and rubbers", and the measured density is 70kg / m 3 (The density of unfoamed DuPont PFA-440HPB resin is 2150kg / m 3 ).

[0065] Example 3: A method for preparing polytetrafluoroethylene foam

[0066] This embodiment provides a method for preparing polytetrafluoroethylene foam, and the steps of the preparation method are as follows:

[0067] Molding step: Yonghe PW-200 resin is selected as the raw material (melt index 2.2g / 10min), and hot pressed into a plate (size 100*100*10mm) at a molding temperature of 350°C on a flat vulcanizer to obtain a foamed embryo;

[0068] Impregnation step: after placing the foamed embryo in a foaming cavity of a molding machine with a cavity temperature of 305° C., the cavity is closed, and supercritical carbon dioxide fluid is filled into the cavity until the pressure in the cavity reaches 15 MPa; the foamed embryo is continuously placed in the cavity with a pressure of 15 MPa and a temperature of 305° C. for 4 hours, so that the gas foaming agent reaches a dissolution equilibrium in the foamed embryo;

[0069] Pressure relief step: After reaching the dissolution equilibrium, the pressure in the mold cavity is relieved to 0MPa at a pressure relief rate of 15MPa / s to induce the nucleation and growth of cells in the foamed body; after the pressure is relieved to 0MPa, the molding machine is opened to allow the cells in the foamed body to continue to grow, thereby obtaining polytetrafluoroethylene foam. After the polytetrafluoroethylene foam is cooled, its density is tested in accordance with the national standard "GB T6343-2009 Determination of apparent density of foamed plastics and rubbers", and the measured density is 45kg / m 3 (The density of unfoamed Yonghe PW-200 resin is 2140kg / m 3 ).

[0070] Example 4: A method for preparing polytetrafluoroethylene foam

[0071] This embodiment provides a method for preparing polytetrafluoroethylene foam, and the steps of the preparation method are as follows:

[0072] Molding step: Yonghe PW-200 resin is selected as the raw material (melt index 2.2g / 10min), and hot pressed into a plate (size 100*100*10mm) at a molding temperature of 350°C on a flat vulcanizer to obtain a foamed embryo;

[0073] Impregnation step: after placing the foamed embryo in a foaming cavity of a molding machine with a cavity temperature of 270° C., the cavity is closed, and supercritical carbon dioxide fluid is filled into the cavity until the pressure in the cavity reaches 12 MPa; the foamed embryo is continuously placed in the cavity with a pressure of 12 MPa and a temperature of 270° C. for 4 hours, so that the gas foaming agent reaches a dissolution equilibrium in the foamed embryo;

[0074] Pressure relief step: After reaching the dissolution equilibrium, the pressure in the mold cavity is relieved to 0MPa at a pressure relief rate of 15MPa / s to induce the nucleation and growth of cells in the foamed body; after the pressure is relieved to 0MPa, the molding machine is opened to allow the cells in the foamed body to continue to grow, thereby obtaining polytetrafluoroethylene foam. After the polytetrafluoroethylene foam is cooled, its density is tested in accordance with the national standard "GB T6343-2009 Determination of apparent density of foamed plastics and rubbers", and the measured density is 642kg / m 3 (The density of unfoamed Yonghe PW-200 resin is 2140kg / m 3 ).

[0075] Example 5: A method for preparing polytetrafluoroethylene foam

[0076] This embodiment provides a method for preparing polytetrafluoroethylene foam, and the steps of the preparation method are as follows:

[0077] Molding step: Yonghe PW-200 resin is selected as the raw material (melt index 2.2g / 10min), and hot pressed into a sheet (size 100*100*10mm) at a molding temperature of 350°C on a flat vulcanizer to obtain a foamed embryo;

[0078] Impregnation step: after placing the foamed embryo in a foaming cavity of a molding machine with a cavity temperature of 295° C., the cavity is closed, and supercritical carbon dioxide fluid is filled into the cavity until the pressure in the cavity reaches 8 MPa; the foamed embryo is continuously placed in the cavity with a pressure of 8 MPa and a temperature of 295° C. for 4 hours, so that the gas foaming agent reaches a dissolution equilibrium in the foamed embryo;

[0079] Pressure relief step: After reaching the dissolution equilibrium, the pressure in the mold cavity is relieved to 0MPa at a pressure relief rate of 15MPa / s to induce the nucleation and growth of cells in the foamed body; after the pressure is relieved to 0MPa, the molding machine is opened to allow the cells in the foamed body to continue to grow, thereby obtaining polytetrafluoroethylene foam. After the polytetrafluoroethylene foam is cooled, its density is tested in accordance with the national standard "GB T6343-2009 Determination of apparent density of foamed plastics and rubbers", and the measured density is 174kg / m 3 (The density of unfoamed Yonghe PW-200 resin is 2140kg / m 3 ).

[0080] Comparative Example 1: A method for preparing polytetrafluoroethylene foam

[0081] This comparative example provides a method for preparing polytetrafluoroethylene foam, and the steps of the preparation method are as follows:

[0082] Molding steps: Japan Daikin LB-202 resin is selected as the raw material, and hot pressed into a sheet (size of 100*100*10mm) at a molding temperature of 350°C on a flat vulcanizer to obtain a foamed embryo; Japan Daikin LB-202 resin is polytetrafluoroethylene (PTFE), which is a high molecular polymer obtained by polymerization of tetrafluoroethylene as a monomer;

[0083] Impregnation step: after placing the foamed embryo in a foaming cavity of a molding machine at a cavity temperature of 295° C., closing the cavity, and filling the cavity with supercritical carbon dioxide fluid until the pressure in the cavity reaches 12 MPa; continuously placing the foamed embryo in the cavity at a pressure of 12 MPa and a temperature of 295° C. for 4 hours;

[0084] Pressure relief step: After 4 hours of placement, the pressure in the mold cavity is relieved to 0 MPa at a pressure relief rate of 15 MPa / s; after the pressure is relieved to 0 MPa, the molding machine is opened to obtain the final product. The results show that the surface of the PTFE sheet is bubbling, and the size has not changed significantly, and it is impossible to foam.

[0085] Comparative Example 2: A method for preparing polytetrafluoroethylene foam

[0086] This comparative example provides a method for preparing polytetrafluoroethylene foam, which is based on Example 1, and the mold cavity temperature is adjusted from 295°C to 240°C to obtain a final product. The results show that the PFA sheet has no significant change and is still a solid sheet that cannot be foamed.

[0087] Comparative Example 3: A method for preparing polytetrafluoroethylene foam

[0088] This comparative example provides a method for preparing polytetrafluoroethylene foam, which is based on Example 1, and the mold cavity temperature is adjusted from 295°C to 320°C to obtain a final product. The results show that the cells of the PFA sheet are merged and broken, and collapsed, and a normal foam product cannot be obtained.

[0089] Comparative Example 4: A method for preparing polytetrafluoroethylene foam

[0090] This comparative example provides a method for preparing polytetrafluoroethylene foam, in which the mold cavity pressure is adjusted from 12MPa to 4MPa based on Example 1 to obtain a final product. The results show that the PFA sheet has no significant change and is still a solid sheet that cannot be foamed.

[0091] Experimental Example 1: Performance Testing of Polytetrafluoroethylene Foam

[0092] This experimental example provides a performance test of polytetrafluoroethylene foam. The experimental process is as follows:

[0093] Experiment 1: The polytetrafluoroethylene foam obtained in Example 1 was observed and photographed by naked eyes. The observation and photographing results are shown in Figure 1 The internal cell structure of the polytetrafluoroethylene foam obtained in Example 1 was observed and photographed using a graduated microscope. The observation and photographing results are shown in Figure 2 .Depend on Figures 1-2 It can be seen that the polytetrafluoroethylene foam prepared in Example 1 has a microporous structure, and the pore diameter is between 100 and 300 μm. This result shows that Example 1 realizes the physical foaming of soluble polytetrafluoroethylene and gives the soluble polytetrafluoroethylene the characteristic of low density.

[0094] Experiment 2: The flame retardant effect of the polytetrafluoroethylene foam prepared in Example 1 was measured according to the UL94 flame retardant test standard. The test results are shown in Figure 3 The test results show that the flame retardant effect of the polytetrafluoroethylene foam prepared in Example 1 reaches the V-0 level, which shows that the polytetrafluoroethylene foam prepared in Example 1 has excellent flame retardant performance.

[0095] Experiment 3: The thermal conductivity of the polytetrafluoroethylene foam prepared in Example 1 was measured according to ISO 8301 standard. The test results show that the power of the polytetrafluoroethylene foam prepared in Example 1 at 0°C, 40°C and 80°C is 0.054, 0.061 and 0.073 W / (m·K) respectively, which shows that the polytetrafluoroethylene foam prepared in Example 1 has excellent thermal insulation performance.

[0096] Experiment 4: According to GB / T 8813-2020 standard, the 50% compressive stress of the polytetrafluoroethylene foam prepared in Example 1 was measured. The test results show that the 50% compressive stress of the polytetrafluoroethylene foam prepared in Example 1 is 593 KPa, which shows that the polytetrafluoroethylene foam prepared in Example 1 has good compressibility and is convenient for subsequent reprocessing.

[0097] Experiment 5: According to the national standard GB-T 6669-2008 Determination of compression permanent deformation of soft foam polymeric materials, the compression permanent deformation of the polytetrafluoroethylene foam prepared in Example 1 was measured at 25°C, a compression rate of 50% and for 6 hours. The test results are: the compression permanent deformation of the polytetrafluoroethylene foam prepared in Example 1 is 17.2% and 8.5% after 6 hours and 24 hours of recovery time, respectively. It can be seen that the polytetrafluoroethylene foam prepared in Example 1 has good resistance to permanent deformation.

[0098] Experiment 6: According to the national standard "GB / T 8811-2008 Test method for dimensional stability of rigid foam plastics", the polytetrafluoroethylene foam prepared in Example 1 was baked at 200°C for 24 hours to perform a high temperature deformation test. The test results show that the dimensional shrinkage rate of the polytetrafluoroethylene foam prepared in Example 1 after cooling is 0.92%, which shows that the polytetrafluoroethylene foam prepared in Example 1 has good heat resistance and stability and can be used for a long time in a high temperature environment.

[0099] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A polytetrafluoroethylene foam, characterized in that: The polytetrafluoroethylene foam is obtained by physically foaming a foamed embryonic body made of soluble polytetrafluoroethylene; the polytetrafluoroethylene foam has a foaming ratio of 2 to 50 times, a pore size of 10 to 500 μm, and, in terms of mass percentage, a content of soluble polytetrafluoroethylene in the polytetrafluoroethylene foam is greater than 90%.

2. The polytetrafluoroethylene foam according to claim 1, characterized in that The preparation method of the polytetrafluoroethylene foam comprises the following steps: Impregnation step: placing a foamed embryo made of soluble polytetrafluoroethylene in a foaming mold with a mold cavity temperature of 250-310° C., closing the mold cavity, and introducing a gas foaming agent into the mold cavity until the pressure in the mold cavity reaches 5-50 MPa; continuously placing the foamed embryo in the mold cavity with a pressure of 5-50 MPa and a temperature of 250-310° C. until the gas foaming agent reaches a dissolution equilibrium in the foamed embryo; Pressure relief step: after reaching the dissolution equilibrium, the pressure in the mold cavity is relieved to 0-0.5 MPa to induce the nucleation and growth of the pores in the foaming embryo; after the pressure is relieved to 0-0.5 MPa, the mold cavity is opened to allow the pores in the foaming embryo to continue to grow, thereby obtaining polytetrafluoroethylene foam.

3. The polytetrafluoroethylene foam according to claim 1 or 2, characterized in that: The soluble polytetrafluoroethylene is a copolymer of perfluoropropyl perfluorovinyl ether and polytetrafluoroethylene; the melt index of the soluble polytetrafluoroethylene is 0.5-50g / 10min.

4. The polytetrafluoroethylene foam according to claim 2 or 3, characterized in that: In the impregnation step, the time for the gas foaming agent to reach dissolution equilibrium in the foaming embryo is the impregnation time t; the impregnation time t≥H×20; wherein the unit of the impregnation time T is min, and H is the maximum diffusion path of the gas foaming agent in the foaming embryo, in mm.

5. The polytetrafluoroethylene foam according to any one of claims 2 to 4, characterized in that: In the depressurization step, the depressurization rate is 1 to 300 MPa / s.

6. The polytetrafluoroethylene foam according to any one of claims 2 to 5, characterized in that: The gas foaming agent includes supercritical carbon dioxide fluid and / or supercritical nitrogen fluid.

7. The polytetrafluoroethylene foam according to any one of claims 2 to 6, characterized in that: The preparation method of the polytetrafluoroethylene foam comprises the following steps: Impregnation step: placing a foamed embryo made of soluble polytetrafluoroethylene in a foaming mold with a mold cavity temperature of 270-305° C., closing the mold cavity, and introducing a gas foaming agent into the mold cavity until the pressure in the mold cavity reaches 8-30 MPa; continuously placing the foamed embryo in the mold cavity with a pressure of 8-30 MPa and a temperature of 270-305° C. until the gas foaming agent reaches a dissolution equilibrium in the foamed embryo; Pressure relief step: after reaching the dissolution equilibrium, the pressure in the mold cavity is relieved to 0 MPa to induce the nucleation and growth of the pores in the foaming embryo; after the pressure is relieved to 0 MPa, the mold cavity is opened to allow the pores in the foaming embryo to continue to grow, thereby obtaining polytetrafluoroethylene foam.

8. The polytetrafluoroethylene foam according to any one of claims 2 to 7, characterized in that: The method for preparing the foamed embryo body comprises: molding a soluble polytetrafluoroethylene raw material at a molding temperature to obtain a foamed embryo body; the molding temperature is 350-400°C.

9. A method for preparing the polytetrafluoroethylene foam according to any one of claims 1 to 8, characterized in that: The preparation method comprises: physically foaming a foaming embryonic body whose material is soluble polytetrafluoroethylene to obtain polytetrafluoroethylene foam; in terms of mass percentage, the content of soluble polytetrafluoroethylene in the foaming embryonic body is greater than 90%.

10. Use of the preparation method according to claim 9 in the preparation of polytetrafluoroethylene foam.

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