Polytetrafluoroethylene and preparation method thereof, expanded polytetrafluoroethylene and application thereof

Abstract

The invention relates to the technical field of polytetrafluoroethylene preparation, and discloses polytetrafluoroethylene and its preparation method, expanded polytetrafluoroethylene and its application. The preparation method of polytetrafluoroethylene comprises: according to different instantaneous heat release at different times, obtaining in advance the instantaneous heat release Q in the conventional polytetrafluoroethylene preparation process; 瞬时 The relationship curve between Q0 and time is used to calculate the average heat release per unit time Q0 of the entire reaction process. The entire reaction is divided into different stages, including Q 瞬时 ≤Q0 at least one stage, and Q 瞬时 > at least one stage of Q0; adding the same reaction raw materials as in the conventional preparation method of polytetrafluoroethylene into the reactor for polymerization reaction; Q 瞬时 ≤Q0 stage, the temperature of the reaction liquid in the reactor is controlled to be T1, Q 瞬时 >Q0 stage, the temperature of the reaction liquid in the reactor is controlled to be T2, T2=T1-(1℃~3℃). This method can produce polytetrafluoroethylene with a narrow molecular weight distribution.

Description

Technical Field

[0001] The invention relates to the technical field of preparation of polytetrafluoroethylene, and in particular to polytetrafluoroethylene and a preparation method thereof, expanded polytetrafluoroethylene and applications thereof. Background Art

[0002] In the process of tetrafluoroethylene polymerization, the reactor suspension temperature control is generally used to produce polytetrafluoroethylene resin. However, the resin produced by controlling the temperature of the reactor suspension has a wide molecular weight distribution and small molecules. In the process of biaxial stretching, due to the wide molecular weight, the overall stretching process is stretched to the small molecular weight resin, but the large molecular weight resin is insufficiently stretched and has a large number of nodes. In the application process, due to the large number of nodes inside the expanded polytetrafluoroethylene (the creep performance nodes are much smaller than the stretched polytetrafluoroethylene mesh area), the expanded polytetrafluoroethylene has insufficient creep resistance during the application process, and causes the expanded polytetrafluoroethylene to creep during the operation of the aircraft, and the air inside the expanded polytetrafluoroethylene is discharged, so that the mouth cover-expanded material-mouth frame is in a vacuum state, which makes it difficult to disassemble.

[0003] In view of this, the present invention is proposed. Summary of the invention

[0004] The purpose of the present invention is to provide polytetrafluoroethylene and a preparation method thereof, expanded polytetrafluoroethylene and applications thereof.

[0005] The present invention is achieved in that:

[0006] In a first aspect, the present invention provides a method for preparing polytetrafluoroethylene, comprising:

[0007] According to the different instantaneous heat release at different times, the instantaneous heat release Q in the conventional preparation process of polytetrafluoroethylene is obtained in advance. 瞬时 The relationship curve with time t is used to calculate the average heat release per unit time Q0 during the entire reaction process;

[0008] According to the principle of heat conservation, the heat released in the reactor is reflected by calculating the heat taken away by the temperature-controlled water in the outer jacket of the reactor;

[0009] Instantaneous heat release Q 瞬时 Derivative formula built into computer program Calculated, where t0 is the interval time for collecting data at the jacket outlet, in seconds, T out is the jacket outlet temperature, T in is the jacket inlet temperature, c is the specific heat of water, m is the flow rate of temperature-controlled water in the jacket, in kg / s;

[0010] The heat released per unit time Δt is ΔQ=∑Q瞬时 / (Δt‌ / t0), Δt≥t0;

[0011] During the entire reaction process, the average heat released per unit time Δt is Q0=∑ΔQ / (t‌ / Δt), where t is the total reaction time;

[0012] According to the conventional polytetrafluoroethylene preparation method, the entire reaction process is divided into a heat release increasing stage including a gradual increase in instantaneous heat release and a heat release decreasing stage including a gradual decrease in instantaneous heat release;

[0013] The exothermic increase phase is divided into at least x phases, which include Q 瞬时 ≤Q0 at least one stage, and Q 瞬时 > at least one stage of Q0;

[0014] The heat release reduction phase is divided into at least y phases, which include Q 瞬时 ≤Q0 at least one stage, and Q 瞬时 > at least one stage of Q0;

[0015] Record the time required for each stage, obtain the different times corresponding to different stages, and make a timetable;

[0016] The same reaction raw materials as those used in the conventional preparation method of polytetrafluoroethylene are added into a reaction kettle to carry out polymerization reaction;

[0017] According to the timetable, the reaction temperature in the reactor is regulated, and the current time is Q 瞬时 ≤Q0 stage, the temperature of the reaction liquid in the reactor is controlled to be T1, and the current time is Q 瞬时 >Q0 stage, the temperature of the reaction liquid in the reactor is controlled to be T2, T2= T1-(1℃~3℃), 40℃≤T2<T1≤50℃;

[0018] The reaction raw materials include water, tetrafluoroethylene monomer and initiator.

[0019] In an optional embodiment, Δt is 10s~60min; x=y=4, and the heat release increase stage includes Q 瞬时 ≤Q0 in the first stage, and Q 瞬时 >Q0 stages 2, 3 and 4;

[0020] The first stage is Q 瞬时 ≤Q0, control the temperature of the reaction liquid in the reactor to T1, the second stage is Q0<Q 瞬时 ≤2Q0, control the reaction liquid in the reactor to T1-1℃, the third stage is 2Q0<Q 瞬时 ≤3 Q0, control the reaction liquid in the reactor to T1-2℃, the fourth stage is Q 瞬时>3Q0, control the reaction liquid in the reactor to T1-3℃;

[0021] The heat reduction stage includes Q 瞬时 > Q0's fifth, sixth and seventh stages, and Q 瞬时 ≤Q0 eighth stage;

[0022] The fifth stage is Q 瞬时 >3Q0, control the reaction liquid in the reactor to T1-3℃, the sixth stage is 2Q0<Q 瞬时 ≤3Q0, control the reaction liquid in the reactor to T1-2℃, the seventh stage is Q0<Q 瞬时 ≤2 Q0, control the reaction liquid in the reactor to T1-1℃, the eighth stage is Q 瞬时 ≤Q0, control the temperature of the reaction liquid in the reactor to T1.

[0023] In an optional embodiment, Δt is 10s~60min; x=y=3, and the heat release increase stage includes Q 瞬时 ≤Q0 in the first stage, and Q 瞬时 >Q0’s second and third stages;

[0024] The first stage is Q 瞬时 ≤Q0, control the temperature of the reaction liquid in the reactor to T1, the second stage is Q0<Q 瞬时 ≤2Q0, control the reaction liquid in the reactor to T1-1℃, the third stage is 2Q0<Q 瞬时 , control the reaction liquid in the reactor to T1-2℃;

[0025] The heat reduction stage includes Q 瞬时 >Q0's fourth and fifth stages, and Q 瞬时 ≤Q0 stage 7;

[0026] The fourth stage is Q 瞬时 >2Q0, control the reaction liquid in the reactor to T1-2℃, the fifth stage is 2Q0<Q 瞬时 , control the reaction liquid in the reactor to T1-1℃, the sixth stage is Q 瞬时 ≤Q0, control the temperature of the reaction liquid in the reactor to T1.

[0027] In an optional embodiment, the invention further comprises at least one of the following technical features (1) to (4):

[0028] (1) The pressure in the reactor is 0.5~1.5MPa;

[0029] (2) The initiator accounts for 0.02~0.5% of the mass of the reaction raw materials;

[0030] (3) The initiator is an organic peroxide; the organic peroxide includes at least one of dibenzoyl peroxide and diisopropylbenzene peroxide;

[0031] (4) The mass ratio of water to tetrafluoroethylene monomer is 10~20:1.

[0032] In an optional embodiment, the reaction raw materials further include a dispersant, and the dispersant accounts for 0.05-0.5% of the mass of the reaction raw materials.

[0033] In an alternative embodiment, the dispersant is ammonium perfluorooctanoate.

[0034] In an optional embodiment, the order of adding the reaction raw materials is:

[0035] First, add water corresponding to the temperature of the first stage into the reactor and keep it warm, and then add other raw materials.

[0036] In a second aspect, the present invention provides polytetrafluoroethylene, which is prepared by the preparation method of any one of the aforementioned embodiments.

[0037] In a third aspect, the present invention provides an expanded polytetrafluoroethylene obtained by biaxially stretching the polytetrafluoroethylene according to the aforementioned embodiment.

[0038] In a fourth aspect, the present invention provides use of the expanded polytetrafluoroethylene according to the aforementioned embodiment as a sealing material in aerospace equipment.

[0039] The present invention has the following beneficial effects:

[0040] The preparation method provided in the embodiment of the present invention is based on the consideration that the polymerization reaction of tetrafluoroethylene is an exothermic reaction. By studying the relationship between the exothermic change and temperature of the entire reaction process of the existing polytetrafluoroethylene preparation process, it is proposed to control the reaction system to different temperatures corresponding to different exothermic stages, so as to achieve real-time control of the temperature of the reaction point, so that the temperature of the reaction point is kept consistent as much as possible during the entire reaction process, thereby making the molecular weight distribution of the obtained polytetrafluoroethylene more concentrated. After temperature control by the method provided by the present invention, the molecular weight distribution of the obtained polytetrafluoroethylene can be made narrower than that of the existing manufacturing method.

[0041] The expanded polytetrafluoroethylene provided in the embodiment of the present invention is obtained by biaxially stretching the polytetrafluoroethylene provided in the embodiment of the present invention. Since the expanded polytetrafluoroethylene is obtained by polytetrafluoroethylene with a narrow molecular weight distribution provided in the embodiment of the present invention, it has a small number of nodes and good creep resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0043] Figure 1 The instantaneous heat release and time relationship curve obtained in Example 1;

[0044] Figure 2 The instantaneous heat release and time relationship curve obtained in Example 2;

[0045] Figure 3 This is a SEM image of the control product 1 in Example 1 after it is made into expanded polytetrafluoroethylene;

[0046] Figure 4 This is a SEM image of the control product 2 in Example 2 after being made into expanded polytetrafluoroethylene;

[0047] Figure 5 This is a SEM image of the experimental product 1 in Example 1 after it is made into expanded polytetrafluoroethylene;

[0048] Figure 6 This is the SEM picture of the experimental product 2 in Example 2 after it was made into expanded polytetrafluoroethylene. DETAILED DESCRIPTION

[0049] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0050] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0051] The method for preparing polytetrafluoroethylene provided in an embodiment of the present invention comprises:

[0052] According to the different instantaneous heat release at different times, the relationship curve between instantaneous heat release and time in the conventional polytetrafluoroethylene preparation process is obtained in advance, and the average instantaneous heat release of the entire reaction process is calculated;

[0053] According to the different instantaneous heat release at different times, the instantaneous heat release Q in the conventional preparation process of polytetrafluoroethylene is obtained in advance. 瞬时 The relationship curve with time t is used to calculate the average heat release per unit time Q0 during the entire reaction process;

[0054] According to the principle of heat conservation, the heat released in the reactor is reflected by calculating the heat taken away by the temperature-controlled water in the outer jacket of the reactor;

[0055] Instantaneous heat release Q 瞬时 Derivative formula built into the computer program Calculated, where t0 is the interval time for collecting data at the jacket outlet, in seconds, T out is the jacket outlet temperature, T in is the jacket inlet temperature, c is the specific heat of water, m is the flow rate of temperature-controlled water in the jacket, in kg / s;

[0056] The heat released per unit time Δt is ΔQ=∑Q 瞬时 / (Δt‌ / t0), Δt≥t0;

[0057] During the entire reaction process, the average heat released per unit time Δt is Q0=∑ΔQ / (t‌ / Δt), where t is the total reaction time;

[0058] According to the conventional polytetrafluoroethylene preparation method, the entire reaction process is divided into a heat release increasing stage including a gradual increase in instantaneous heat release and a heat release decreasing stage including a gradual decrease in instantaneous heat release;

[0059] The exothermic increase phase is divided into at least x phases, which include Q 瞬时 ≤Q0 at least one stage, and Q 瞬时 > at least one stage of Q0;

[0060] The heat release reduction phase is divided into at least y phases, which include Q 瞬时 ≤Q0 at least one stage, and Q 瞬时 > at least one stage of Q0;

[0061] Record the time required for each stage, obtain the different times corresponding to different stages, and make a timetable;

[0062] The same reaction raw materials as those used in the conventional preparation method of polytetrafluoroethylene are added into a reaction kettle to carry out polymerization reaction;

[0063] According to the timetable, the reaction temperature in the reactor is regulated, and the current time is Q 瞬时 ≤Q0 stage, the temperature of the reaction liquid in the reactor is controlled to be T1, and the current time is Q 瞬时 >Q0 stage, the temperature of the reaction liquid in the reactor is controlled to be T2, T2= T1-(1℃~3℃), 40℃≤T2<T1≤50℃;

[0064] The reaction raw materials include water, tetrafluoroethylene monomer and initiator.

[0065] The reactor used in the polytetrafluoroethylene reaction equipment is usually a reactor with a jacket on the outer wall. The temperature of the reaction system in the reactor is regulated by continuously injecting water of a certain temperature into the jacket. The temperature is continuously collected at the outlet of the jacket, and the instantaneous heat release is obtained by derivative calculation.

[0066] The preparation method provided in the embodiment of the present invention is based on the consideration that the polymerization reaction of tetrafluoroethylene is an exothermic reaction. By studying the relationship between the exothermic change and temperature of the entire reaction process of the existing polytetrafluoroethylene preparation process, it is proposed to control the reaction system to different temperatures corresponding to different exothermic stages, so as to achieve real-time control of the temperature of the reaction point, so that the temperature of the reaction point is kept consistent as much as possible during the entire reaction process, thereby making the molecular weight distribution of the prepared polytetrafluoroethylene more concentrated. After the temperature is controlled by the method provided by the present invention, the molecular weight distribution can be narrower than that of the existing manufacturing method without temperature control.

[0067] Optionally, Δt is 10s~60min, preferably 10~60min; x=y=3, the heat release increase stage includes Q 瞬时 ≤Q0 in the first stage, and Q 瞬时 >Q0’s second and third stages;

[0068] The first stage is Q 瞬时 ≤Q0, control the temperature of the reaction liquid in the reactor to T1, the second stage is Q0<Q 瞬时 ≤2Q0, control the reaction liquid in the reactor to T1-1℃, the third stage is 2Q0<Q 瞬时 , control the reaction liquid in the reactor to T1-2℃;

[0069] The heat reduction stage includes Q 瞬时 >Q0's fourth and fifth stages, and Q 瞬时 ≤Q0 stage 7;

[0070] The fourth stage is Q 瞬时 >2Q0, control the reaction liquid in the reactor to T1-2℃, the fifth stage is 2Q0<Q 瞬时 , control the reaction liquid in the reactor to T1-1℃, the sixth stage is Q 瞬时 ≤Q0, control the temperature of the reaction liquid in the reactor to T1.

[0071] Optionally, Δt is 10s~60min, preferably 10~60min; x=y=4, the exothermic increase stage includes Q 瞬时 ≤Q0 in the first stage, and Q 瞬时 >Q0 stages 2, 3 and 4;

[0072] The first stage is Q 瞬时 ≤Q0, control the temperature of the reaction liquid in the reactor to T1, the second stage is Q0<Q瞬时 ≤2Q0, control the reaction liquid in the reactor to T1-1℃, the third stage is 2Q0<Q 瞬时 ≤3 Q0, control the reaction liquid in the reactor to T1-2℃, the fourth stage is Q 瞬时 >3Q0, control the reaction liquid in the reactor to T1-3℃;

[0073] The heat reduction stage includes Q 瞬时 > Q0's fifth, sixth and seventh stages, and Q 瞬时 ≤Q0 eighth stage;

[0074] The fifth stage is Q 瞬时 >3Q0, control the reaction liquid in the reactor to T1-3℃, the sixth stage is 2Q0<Q 瞬时 ≤3Q0, control the reaction liquid in the reactor to T1-2℃, the seventh stage is Q0<Q 瞬时 ≤2 Q0, control the reaction liquid in the reactor to T1-1℃, the eighth stage is Q 瞬时 ≤Q0, control the temperature of the reaction liquid in the reactor to T1.

[0075] When the heat release increasing stage and the heat release decreasing stage are divided into the above-mentioned several stages for temperature control, polytetrafluoroethylene with a narrower molecular weight distribution can be produced.

[0076] Furthermore, the initiator is an organic peroxide, which includes at least one of dibenzoyl peroxide and dicumyl peroxide. The organic peroxide decomposes within the reaction temperature range defined in the present invention to generate free radicals, thereby initiating the polymerization of polytetrafluoroethylene.

[0077] Optionally, the initiator accounts for 0.02-0.5% of the mass of the reaction raw materials. The initiator content in this range can ensure that the tetrafluoroethylene monomer reacts at a suitable rate and ensure the performance of the obtained polytetrafluoroethylene.

[0078] Optionally, the reaction raw materials also include a dispersant, which accounts for 0.05-0.5% of the mass of the reaction raw materials. The addition of the dispersant can ensure that the monomers are evenly dispersed in the reactor, further improving the performance of the obtained polytetrafluoroethylene.

[0079] Optionally, the dispersant is ammonium perfluorooctanoate.

[0080] Specifically, the preparation method is:

[0081] S1. Deionized water having the same temperature as that required in the first reaction stage is injected into the reactor, and liquid heat medium having the same temperature is circulated into the heating jacket for heat preservation.

[0082] Injecting deionized water of the same temperature as required for the first reaction stage into the reactor and keeping it warm can avoid the problem of too wide molecular weight distribution of the generated polytetrafluoroethylene due to obvious temperature difference in different parts of the reaction liquid in the reactor during the heating process after the reaction starts. For example, if the temperature is raised again after the reaction starts, the temperature near the reactor wall is higher than the reaction temperature of the particles, low-polymerization polytetrafluoroethylene will be produced, and the temperature in the middle of the reactor is lower than the reaction temperature, high-polymerization polytetrafluoroethylene will be produced.

[0083] S2. Add initiator, polytetrafluoroethylene monomer and dispersant into the reactor, and at the same time adjust the pressure in the reactor to 0.5~1.5MPa.

[0084] Optionally, in order to make the reaction have a suitable reaction rate and thus obtain higher quality polytetrafluoroethylene, the mass ratio of the deionized water added to the reactor in step S1 to the tetrafluoroethylene monomer added to the reactor in this step is 10-20:1.

[0085] S3. According to a pre-prepared timetable, the reaction temperature in the reactor is regulated at different time stages, and a terminator is added to terminate the reaction after the reaction reaches a predetermined time or degree.

[0086] Optionally, the terminator is selected from at least one of hydrogen peroxide, ammonium persulfate, methanol and ethanol, and the mass ratio of the added amount to the tetrafluoroethylene monomer is 0.05-0.3:100.

[0087] The polytetrafluoroethylene provided in the embodiment of the present invention is prepared by the preparation method provided in the embodiment of the present invention. The polytetrafluoroethylene has the characteristic of narrow molecular weight distribution.

[0088] The expanded polytetrafluoroethylene provided in the embodiment of the present invention is obtained by biaxially stretching the polytetrafluoroethylene provided in the embodiment of the present invention. Since the expanded polytetrafluoroethylene is obtained by polytetrafluoroethylene with a narrow molecular weight distribution provided in the embodiment of the present invention, it has a small number of nodes and good creep resistance.

[0089] The expanded polytetrafluoroethylene provided by the present invention is used as a sealing material in aerospace equipment. Specifically, the expanded polytetrafluoroethylene has good creep resistance, so it can improve the problem that the mouth cover-expanded material-mouth frame is in a vacuum state due to poor creep resistance and easy adsorption of the expanded polytetrafluoroethylene, making it difficult to disassemble.

[0090] Example 1

[0091] The time table is obtained according to the conventional preparation method of polytetrafluoroethylene:

[0092] First, inject 100L of deionized water at a temperature of 40°C into the reactor, and at the same time, continuously inject water at a temperature of 40°C into the jacket of the reactor;

[0093] 50 g of initiator (dibenzoyl peroxide), 50 g of dispersant (ammonium perfluorooctanoate (PFOA)), and 10 kg of polytetrafluoroethylene monomer were added to the reactor in sequence. The pressure in the reactor was controlled to 4 MPa to start the reaction. After 960 minutes of reaction, hydrogen peroxide was added to terminate the reaction.

[0094] After the reaction is completed, a polytetrafluoroethylene product is obtained, and a reference product 1 is obtained.

[0095] During the reaction process, the outlet water temperature of the reactor jacket is collected in real time, and the real-time heat release is calculated by computer, and the heat release curve is drawn as shown in the figure. Figure 1 As shown;

[0096] The unit time Δt is set to 30 min, and the average heat release per unit time in the entire reaction process is calculated based on the data collected by the computer, and Q0 is 449.08 kJ;

[0097] According to the exothermic curve and Q0 value, the entire reaction process is divided into 6 stages, such as Figure 1 As shown, the first stage of the heat release increase phase Q 瞬时 ≤Q 0、 The second stage Q0<Q 瞬时 ≤2Q0, the third stage 2Q0<Q 瞬时 ; The fourth stage Q of the heat release reduction stage 瞬时 >2Q0、The fifth stage Q0<Q 瞬时 ≤2Q0, sixth stage Q 瞬时 ≤Q0. The above six stages are mapped into a timetable as shown in Table 1.

[0098] The appropriate reaction temperature of different stages was set: the temperature of the first stage was T1 at 42°C, the temperature of the second stage was T1-1°C, the temperature of the third stage was T1-2°C, the temperature of the fourth stage was T1-2°C, the temperature of the fifth stage was T1-1°C, and the temperature of the sixth stage was T1. According to this temperature setting, the reaction temperature of each stage was also recorded in Table 1.

[0099] Table 1 Time-temperature table

[0100]

[0101] New process for preparing polytetrafluoroethylene:

[0102] First, inject 100L of deionized water at a temperature of 42°C into the reactor and keep the reactor warm;

[0103] 50 g of initiator (dibenzoyl peroxide), 50 g of dispersant (ammonium perfluorooctanoate (PFOA)), and 10 kg of polytetrafluoroethylene monomer were added into the reactor in sequence, and the pressure in the reactor was controlled to 4 MPa to start the reaction.

[0104] After the reaction raw materials were added, the temperature of the entire reaction process was controlled by injecting water of different temperatures into the jacket at different time stages according to Table 1. After 960 minutes of reaction, hydrogen peroxide with a mass ratio of 0.05% to the monomer was added to terminate the reaction, so that the reaction temperature in the reactor at each stage corresponded to Table 1.

[0105] After the reaction is completed, experimental product 1 is obtained.

[0106] Comparative Example 1

[0107] The control product 1 produced during the preparation process of Example 1 is used as a control for the experimental product 1 of Example 1.

[0108] Example 2

[0109] The time table is obtained according to the conventional preparation method of polytetrafluoroethylene:

[0110] First, inject 100L of deionized water at a temperature of 50°C into the reactor, and at the same time, continuously inject water at a temperature of 50°C into the jacket of the reactor;

[0111] 50 g of initiator (dibenzoyl peroxide), 50 g of dispersant (ammonium perfluorooctanoate (PFOA)), and 10 kg of polytetrafluoroethylene monomer were added into the reactor in sequence, and the pressure in the reactor was controlled to 4 MPa to start the reaction.

[0112] After the reaction is completed, a polytetrafluoroethylene product is obtained, and a reference product 2 is obtained.

[0113] During the reaction process, the outlet water temperature of the reactor jacket is collected in real time, and the real-time heat release is calculated by computer, and the heat release curve is drawn as shown in the figure. Figure 2 As shown;

[0114] The unit time Δt is set to 30 min, and the average heat release per unit time Q0 in the entire reaction process is calculated to be 507.91 kJ based on the data collected by the computer;

[0115] According to the curve and Q0 value, the whole reaction process is divided into 8 stages, among which the first stage Q 瞬时 ≤Q 0、 The second stage Q0<Q 瞬时 ≤2Q0, the third stage 2Q0<Q 瞬时 ≤3Q0, fourth stage Q 瞬时 >3Q0; the fifth stage Q of the heat release reduction stage 瞬时 >3Q0、Sixth stage 2Q0<Q 瞬时 ≤3Q0, seventh stage Q0<Q 瞬时 ≤2Q0, eighth stage Q 瞬时 ≤Q0. The above eight stages are mapped into a timetable as shown in Table 2.

[0116] The appropriate reaction temperature of different stages was set: the temperature of the first stage was 53°C, the second stage was T1-1°C, the third stage was T1-2°C, the fourth stage was T1-3°C, the fifth stage was T1-3°C, the sixth stage was T1-2°C, the seventh stage was T1-1°C, and the eighth stage was T1. According to this temperature setting, the reaction temperature of each stage was also recorded in Table 2.

[0117] Table 2 Time-temperature table

[0118]

[0119] New process for preparing polytetrafluoroethylene:

[0120] First, inject 100L of deionized water at a temperature of 53°C into the reactor and keep the reactor warm;

[0121] 50 g of initiator (dibenzoyl peroxide), 50 g of dispersant (ammonium perfluorooctanoate (PFOA)), and 10 kg of polytetrafluoroethylene monomer were added into the reactor in sequence, and the pressure in the reactor was controlled to 4 MPa to start the reaction.

[0122] After the reaction raw materials were added, the temperature of the entire reaction process was controlled by injecting water of different temperatures into the jacket at different time stages according to Table 2, so that the reaction temperature in the reactor at each stage corresponded to Table 2. After the reaction was continued for 8-10 minutes, hydrogen peroxide with a mass ratio of 0.05% to the monomer was added to terminate the reaction.

[0123] After the reaction is completed, experimental product 2 is obtained.

[0124] Comparative Example 2

[0125] The control product 2 produced during the preparation process of Example 2 is used as a control for the experimental product 2 of Example 2.

[0126] Experimental example

[0127] Since there is no effective method for measuring the molecular weight distribution of polytetrafluoroethylene, the present application evaluates the microscopic properties of polytetrafluoroethylene by testing the properties of polytetrafluoroethylene after it is made into expanded polytetrafluoroethylene.

[0128] The polytetrafluoroethylene is made into expanded polytetrafluoroethylene by biaxial stretching, lamination and shaping, specifically:

[0129] Resin refrigeration: Store polytetrafluoroethylene in a refrigerator at below -10°C for 48 hours;

[0130] Resin balance: transfer the refrigerated resin to the transfer chamber and balance it to 10℃~15℃ for 24h;

[0131] Resin screening: Weigh the required weight of resin and place it in a vibrating screen for screening to obtain uniform and fine resin. The screen is 400 mesh;

[0132] Ingredients: Weigh the solvent oil and pour it into the resin, with the ratio of resin: solvent oil = 1:2; put it into the mixer for mixing, with a speed of 600r / min for 10 minutes;

[0133] Curing: put the mixture into the oven for heat preservation, let the resin and solvent oil be fully mixed, set the oven temperature to 40℃, and the time to 12h;

[0134] Mixture screening: The matured mixture is screened with a 400-mesh screen;

[0135] Pre-pressing: The sieved raw materials are transferred to the pre-pressing machine for pressing to make the loose raw materials into embryos. The pre-pressing pressure is 1MPa and the pressure is maintained for 2min.

[0136] Extrusion: The pre-pressed bar is transferred to the extruder for extrusion forming to obtain a continuous strip. The extrusion temperature is 315°C and the extrusion speed is 5m / min.

[0137] Calendering: The push-formed strip is sent to the upper and lower rollers of the calender for pressing. The roller spacing is controlled at 5mm and the temperature is 315℃ to obtain a thin strip.

[0138] Degreasing: Place the rolled strip in a 330°C environment to volatilize the solvent oil;

[0139] Stretching: Stretching was performed at 200°C and a line speed of 19 m / min to obtain a stretched film.

[0140] Shaping: The stretched film is subjected to high temperature treatment to fix the structure.

[0141] (1) The expanded polytetrafluoroethylene prepared from control product 1 and control product 2 is as follows: Figure 3 and Figure 4 As shown, from Figure 3 and Figure 4 It can be seen that there are many nodes, such as the expanded polytetrafluoroethylene obtained from experimental product 1 and experimental product 2. Figure 5 and Figure 6 As shown, from Figure 5 and Figure 6 It can be seen that there are almost no nodes. This shows that the molecular weight distribution of polytetrafluoroethylene prepared by the preparation method provided by the embodiment of the present invention is narrower than that of polytetrafluoroethylene prepared by the conventional preparation method.

[0142] (2) Measure the creep resistance of expanded polytetrafluoroethylene obtained from each control product and experimental product. The specific test method is: GB / T 1685-2008. Record the measured results in Table 3.

[0143] Table 3 Creep resistance of expanded polytetrafluoroethylene

[0144]

[0145] It can be seen from Table 3 that the creep resistance of the experimental product 1 after being made into expanded polytetrafluoroethylene is significantly better than that of the control product 1; the creep resistance of the experimental product 2 after being made into expanded polytetrafluoroethylene is significantly better than that of the control product 2. This shows that the preparation method provided by the present invention can make the molecular weight distribution of the prepared polytetrafluoroethylene more concentrated by regulating different temperatures in different heat release stages, and the prepared expanded polytetrafluoroethylene has better creep resistance than the prior art.

[0146] In summary, the preparation method provided by the present invention is based on the consideration that the polymerization reaction of tetrafluoroethylene is an exothermic reaction. By studying the relationship between the exothermic change and temperature of the entire reaction process of the existing polytetrafluoroethylene preparation process, it is proposed to control the reaction system to different temperatures corresponding to different exothermic stages, so as to achieve real-time control of the temperature of the reaction point, so that the temperature of the reaction point is kept consistent as much as possible during the entire reaction process, thereby making the molecular weight distribution of the obtained polytetrafluoroethylene more concentrated. After temperature control by the method provided by the present invention, the molecular weight distribution of the obtained polytetrafluoroethylene can be narrower than that of the existing manufacturing method.

[0147] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing polytetrafluoroethylene, characterized in that: include: According to the different instantaneous heat release at different times, the instantaneous heat release Q in the conventional preparation process of polytetrafluoroethylene is obtained in advance. 瞬时 The relationship curve with time t is used to calculate the average heat release per unit time Q0 during the entire reaction process; According to the principle of heat conservation, the heat released in the reactor is reflected by calculating the heat taken away by the temperature-controlled water in the outer jacket of the reactor; The instantaneous heat release Q 瞬时 Derivative formula built into the computer program Calculated, where t0 is the interval time for collecting data at the jacket outlet, in seconds, T out is the jacket outlet temperature, T in is the jacket inlet temperature, c is the specific heat of water, m is the flow rate of temperature-controlled water in the jacket, in kg / s; The heat released per unit time Δt is ΔQ=∑Q 瞬时 / (Δt‌ / t0), Δt≥t0, Δt is 10s~60min; During the entire reaction process, the average heat released per unit time is Q0=∑ΔQ / (t‌ / Δt), where t is the total reaction time; According to the conventional polytetrafluoroethylene preparation method, the entire reaction process is divided into a heat release increasing stage including a gradual increase in instantaneous heat release and a heat release decreasing stage including a gradual decrease in instantaneous heat release; The exothermic increase phase is divided into at least x phases, which include Q 瞬时 ≤Q0 at least one stage, and Q 瞬时 > at least one stage of Q0; The heat release reduction stage is divided into at least y stages, which include Q 瞬时 ≤Q0 at least one stage, and Q 瞬时 > at least one stage of Q0; Record the time required for each stage, obtain the different times corresponding to different stages, and make a timetable; Adding the same reaction raw materials as those used in the conventional preparation method of polytetrafluoroethylene into a reaction kettle to carry out a polymerization reaction; According to the timetable, the reaction temperature in the reactor is regulated, and the current time is Q according to the timetable. 瞬时 ≤Q0 stage, the temperature of the reaction liquid in the reactor is controlled to be T1, and the current time is Q 瞬时 >Q0 stage, the temperature of the reaction liquid in the reactor is controlled to be T2, T2= T1-(1°C~3°C), 40°C≤T2<T1≤50°C; The reaction raw materials include water, tetrafluoroethylene monomer and initiator.

2. The preparation method according to claim 1, characterized in that: x=y=4, the exothermic increase stage includes Q 瞬时 ≤Q0 in the first stage, and Q 瞬时 >Q0 stages 2, 3 and 4; The first stage is Q 瞬时 ≤Q0, the temperature of the reaction liquid in the reactor is controlled to be T1, and the second stage is Q0<Q 瞬时 ≤2 Q0, control the reaction liquid in the reactor to T1-1℃, the third stage is 2Q0<Q 瞬时 ≤3 Q0, control the reaction liquid in the reactor to T1-2℃, the fourth stage is Q 瞬时 >3Q0, control the reaction liquid in the reactor to T1-3℃; The heat reduction stage includes Q 瞬时 > Q0's fifth, sixth and seventh stages, and Q 瞬时 ≤Q0 eighth stage; The fifth stage is Q 瞬时 >3Q0, control the reaction liquid in the reactor to T1-3℃, the sixth stage is 2Q0<Q 瞬时 ≤3 Q0, control the reaction liquid in the reactor to T1-2℃, the seventh stage is Q0<Q 瞬时 ≤2 Q0, control the reaction liquid in the reactor to T1-1℃, the eighth stage is Q 瞬时 ≤Q0, and control the temperature of the reaction liquid in the reactor to be T1.

3. The preparation method according to claim 1, characterized in that , x=y=3, the exothermic increase stage includes Q 瞬时 ≤Q0 in the first stage, and Q 瞬时 >Q0’s second and third stages; The first stage is Q 瞬时 ≤Q0, the temperature of the reaction liquid in the reactor is controlled to be T1, and the second stage is Q0<Q 瞬时 ≤2 Q0, control the reaction liquid in the reactor to T1-1℃, the third stage is 2Q0<Q 瞬时 , control the reaction liquid in the reactor to be T1-2°C; The heat reduction stage includes Q 瞬时 >Q0's fourth and fifth stages, and Q 瞬时 ≤Q0 stage 6; The fourth stage is Q 瞬时 >2Q0, control the reaction liquid in the reactor to T1-2℃, the fifth stage is 2Q0<Q 瞬时 , control the reaction liquid in the reactor to T1-1℃, the sixth stage is Q 瞬时 ≤Q0, and control the temperature of the reaction liquid in the reactor to be T1.

4. The preparation method according to claim 1, characterized in that: It also includes at least one of the following technical features (1) to (4): (1) The pressure in the reactor is 0.5~1.5MPa; (2) The initiator accounts for 0.02-0.5% of the mass of the reaction raw materials; (3) The initiator is an organic peroxide; the organic peroxide includes at least one of dibenzoyl peroxide and diisopropylbenzene peroxide; (4) The mass ratio of the water to the tetrafluoroethylene monomer is 10-20:

1.

5. The preparation method according to claim 1, characterized in that: The reaction raw materials also include a dispersant, and the dispersant accounts for 0.05-0.5% of the mass of the reaction raw materials.

6. The preparation method according to claim 5, characterized in that: The dispersant is ammonium perfluorooctanoate.

7. The preparation method according to claim 2 or 3, characterized in that: The order of adding the reaction raw materials is: First, water corresponding to the temperature of the first stage is added into the reactor and kept warm, and then other raw materials are added.

8. A polytetrafluoroethylene, characterized in that: The method is prepared according to any one of claims 1 to 7.

9. An expanded polytetrafluoroethylene, characterized in that: Obtained by biaxially stretching the polytetrafluoroethylene as claimed in claim 8.

10. Use of the expanded polytetrafluoroethylene as claimed in claim 9 as a sealing material in aerospace equipment.

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