A method for increasing the bulk density of a fusible polytetrafluoroethylene resin powder

Abstract

This invention provides a method for increasing the bulk density of fusible polytetrafluoroethylene (PFA) resin powder. The method includes: freezing and then thawing a PFA polymer solution, filtering to obtain a wet material, washing with water and drying, and then subjecting it to high-temperature treatment at a temperature 20-30°C below the melting point of PFA to obtain PFA powder. This invention, by subjecting the PFA polymer solution to low-temperature freezing and thawing to obtain a dried material, and then subjecting it to high-temperature treatment at a temperature 20-30°C below the melting point of PFA, removes volatile and low-molecular-weight substances, thereby effectively increasing the bulk density of the PFA powder to over 750 g / L, thus improving the processing and application performance of the powder. For example, it can effectively reduce powder dusting and adhesion to container walls, meeting the requirements of electrostatic spraying and granulation.

Description

Technical Field

[0001] This invention relates to the field of fluorochemical technology, and in particular to a method for increasing the bulk density of fusible polytetrafluoroethylene resin powder. Background Technology

[0002] Meltable polytetrafluoroethylene (PFA), also known as perfluoroalkoxy vinyl ether polymer, is the most important class of melt-processable fluoropolymers. It inherits the excellent high and low temperature resistance, aging resistance, chemical solvent resistance, electrical insulation and non-flammability of polytetrafluoroethylene, and can be processed into products in the molten state. It is widely used in aerospace, machinery, petrochemical, pharmaceutical, electronics and semiconductor fields.

[0003] PFA can be produced using emulsion polymerization, and the products are divided into fusible PTFE emulsions and fusible PTFE resins, with the resins including powder and granule products. The PFA emulsion obtained from emulsion polymerization is generally coagulated and demulsified using mechanical stirring to obtain PFA powder. However, due to its low bulk density, the powder is prone to issues such as fly shavings and orange peel when used for electrostatic spraying; when used to manufacture granules, it suffers from severe material buildup during screw granulation, incomplete filling of the screw bore, and adhesion to the container walls, resulting in low production efficiency, environmental unfriendliness, and inaccurate metering.

[0004] CN101003633A discloses a method for increasing the bulk density of poly(perfluoroethylene) propylene resin powder. The method involves high-speed stirring in an aqueous medium at a temperature of 60-115°C, and adding a volatile organic solvent to adjust the particle size, thereby increasing the bulk density. However, this method requires the addition of organic solvents, which is environmentally unfriendly, and incomplete processing can negatively impact the appearance and quality of the finished product.

[0005] Some existing technologies, such as CN109515778A and CN103707432B, improve the bulk density of powdered materials by modifying the device or equipment. For enterprises, these methods require the purchase of additional equipment, which significantly increases production costs, and there may not be corresponding equipment with good implementation effects available on the market. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method for increasing the bulk density of fusible polytetrafluoroethylene resin powder. This method is environmentally friendly and requires no additional equipment.

[0007] This invention provides a method for increasing the bulk density of fusible polytetrafluoroethylene resin powder, comprising:

[0008] The PFA polymerization liquid is frozen and then thawed, filtered to obtain wet material, washed with water and dried, and then subjected to high-temperature treatment at a temperature 20-30°C below the melting point of PFA to obtain PFA powder.

[0009] This invention employs a low-temperature freezing and thawing post-treatment method for the PFA polymerization liquid, instead of conventional mechanical stirring to cause coagulation and demulsification. This eliminates the need for electrolytes, thus avoiding the introduction of impurity ions. Following this, a high-temperature treatment is performed at a temperature 20-30°C below the melting point of PFA, which removes volatile substances (dispersants and other additives used in the polymerization process) and low-molecular-weight substances (low-molecular-weight polymers). This method effectively increases the bulk density of PFA powder, significantly improving its processing and application performance.

[0010] It should be noted that the method for increasing the bulk density of fusible polytetrafluoroethylene resin powder described in this invention is essentially a method for preparing fusible polytetrafluoroethylene resin powder, and the resulting PFA powder has a significantly higher bulk density than existing technologies.

[0011] In some embodiments of the present invention, the high-temperature treatment time is 0.5-1 hour.

[0012] In some embodiments of the present invention, the freezing temperature is -15°C, and the PFA polymer solution is frozen completely.

[0013] In some embodiments of the present invention, the thawing temperature is 80°C, and the thawing continues until all the ice melts into a liquid state.

[0014] In this invention, both freezing and thawing can be performed using a water bath. For example, freezing can be done using a -15°C salt water bath, and thawing can be done using an 80°C hot water bath. Alternatively, for more thorough heat exchange, a flowing water bath can be used.

[0015] In some embodiments of the present invention, the drying temperature is 260°C and the drying time is 3-4 hours.

[0016] In some embodiments of the present invention, the PFA polymer solution is prepared by emulsion polymerization reaction, and the solid content of the PFA polymer solution is 20-27%, for example 20%, 23%, 25%, 27%.

[0017] Specifically, in some embodiments of the present invention, the preparation steps of the PFA polymerization solution are as follows:

[0018] In a 100L horizontal high-pressure reactor equipped with a stirrer and jacket, deionized water, a fluorinated surfactant, and a buffer are added. Modifiers, chain transfer agents, and initiators are added at the reaction temperature. Tetrafluoroethylene monomer is then introduced until the reaction pressure is reached, initiating the copolymerization reaction. The reaction is stopped when the solid content reaches approximately 20-27%, yielding a fusible polytetrafluoroethylene polymer solution. The specific selection of additives, reaction temperature, and pressure are all existing technologies in this field and will not be elaborated upon further in this paper.

[0019] Furthermore, the PFA polymerization solution is first filtered through a 200-mesh sieve before freezing. This filtration is to remove demulsifiers and other impurities.

[0020] The present invention also provides a fusible polytetrafluoroethylene resin powder, which is prepared by the above method and has a bulk density of 750 g / L or higher.

[0021] The existing technology uses mechanical stirring, coagulation, and demulsification to obtain polytetrafluoroethylene resin powder, which has a bulk density of about 360-370 g / L. The present invention increases the bulk density by more than double, that is, by more than 2 times.

[0022] The fusible polytetrafluoroethylene (PTFE) resin powder provided by this invention can be used in electrostatic spraying. Before application, the PFA powder needs to be pulverized to a particle size of 20-30 μm as required for electrostatic spraying. Using the high bulk density PFA powder of this invention, phenomena such as fly shavings and orange peel are less likely to occur during electrostatic spraying.

[0023] This invention also provides a fusible polytetrafluoroethylene (PTFE) resin granule, which is obtained by granulation of the aforementioned fusible PTFE resin powder. The granulation can be performed using conventional melt extrusion granulation. Specifically, when using a screw extruder during the preparation process, phenomena such as excessive material buildup, incomplete filling of the screw bore, and adhesion to the container wall can be effectively avoided, resulting in high production efficiency. The fusible PTFE resin granules provided by this invention can meet the requirements of injection molding, extrusion, and compression molding.

[0024] This invention provides a method for increasing the bulk density of fusible polytetrafluoroethylene (PFA) resin powder. The method involves drying the PFA polymer solution by subjecting it to low-temperature freezing and thawing, followed by high-temperature treatment at a temperature 20-30°C below the melting point of PFA. This process removes volatile and low-molecular-weight substances, effectively increasing the bulk density of the PFA powder to over 750 g / L, thereby improving its processing and application performance. For example, it effectively reduces powder dispersion and adhesion to container walls, meeting the requirements for electrostatic spraying and granulation. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0026] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field, or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased through legitimate channels.

[0027] In the following examples, the steps for preparing PFA polymer solution by emulsion polymerization are as follows:

[0028] In a 100L horizontal high-pressure reactor equipped with a stirrer and jacket, deionized water, a fluorinated surfactant (a perfluorooctanoic acid substitute), and a buffer (ammonium carbonate) are added. After the oxygen analysis is qualified, a modifier (PPVE), a chain transfer agent (methanol), and an initiator (ammonium persulfate) are added. Tetrafluoroethylene monomer is introduced to the reaction pressure, and the copolymerization reaction begins in the temperature range of 65-75℃. When the solid content reaches about 25%, the reaction is stopped to obtain a fusible polytetrafluoroethylene polymer solution.

[0029] Example 1

[0030] This embodiment provides a method for increasing the bulk density of fusible polytetrafluoroethylene resin powder, the steps of which are as follows:

[0031] After filtering, 5L of PFA polymerization liquid is placed in an 8L refrigeration unit with a double jacket. First, -15℃ brine is introduced for freezing for 2 hours, and then 80℃ hot water is introduced for thawing for 1 hour. The resulting wet material is placed in a washing tank and washed 2-3 times with deionized water. It is then dried in an oven at 260℃ for 3 hours, and then heated to 285℃ for high-temperature treatment for 0.5 hours. After pulverization (if it is not to be used for electrostatic spraying, the pulverization operation can be omitted, the same below), high bulk density PFA powder is obtained.

[0032] Example 2

[0033] This embodiment provides a method for increasing the bulk density of fusible polytetrafluoroethylene resin powder, the steps of which are as follows:

[0034] After filtering, 5L of PFA polymerization liquid was placed in an 8L refrigeration unit with a double jacket. First, -15℃ brine was introduced for freezing for 2 hours, and then 80℃ hot water was introduced for thawing for 1 hour. The resulting wet material was placed in a washing tank and washed 2-3 times with deionized water. It was then dried in an oven at 260℃ for 3 hours, and then heated to 278℃ for high-temperature treatment for 1 hour. After pulverization, high-bulk-density PFA powder was obtained.

[0035] Example 3

[0036] This embodiment provides a method for increasing the bulk density of fusible polytetrafluoroethylene resin powder, the steps of which are as follows:

[0037] After filtering, 5L of PFA polymerization liquid was placed in an 8L refrigeration unit with a double jacket. First, -15℃ brine was introduced for freezing for 2 hours, and then 80℃ hot water was introduced for thawing for 1 hour. The resulting wet material was placed in a washing tank and washed 2-3 times with deionized water. After drying in an oven at 260℃ for 3 hours, the temperature was raised to 288℃ for high-temperature treatment for 0.5 hours. After pulverization, high-bulk-density PFA powder was obtained.

[0038] Comparative Example 1

[0039] This comparative example provides a method for preparing a fusible polytetrafluoroethylene resin powder, the steps of which are as follows:

[0040] After filtering 5L of PFA polymerization liquid, deionized water was added to adjust the solid content to 10%. Electrolyte (ammonium bicarbonate) was added and mechanical stirring was performed for coagulation. The resulting wet material was washed with deionized water 2-3 times, and then dried in an oven at 260℃ for 3 hours. After pulverization, PFA powder was obtained.

[0041] Comparative Example 2

[0042] This comparative example provides a method for preparing a fusible polytetrafluoroethylene resin powder, the steps of which are as follows:

[0043] After filtering 5L of PFA polymerization liquid, deionized water was added to adjust the solid content to 10%. Electrolyte was added and mechanical stirring was performed for coagulation. The resulting wet material was washed with deionized water 2-3 times, then dried in an oven at 260℃ for 3 hours, and then heated to 285℃ for 0.5 hours. After pulverization, PFA powder was obtained.

[0044] Comparative Example 3

[0045] This comparative example provides a method for preparing a fusible polytetrafluoroethylene resin powder, the steps of which are as follows:

[0046] After filtering 5L of PFA polymerization liquid (the solid content is still 25%), electrolyte is added and mechanical stirring and coagulation are carried out. The resulting wet material is washed with deionized water 2-3 times, then dried in an oven at 260℃ for 3 hours, and then heated to 285℃ for 0.5 hours. After pulverization, PFA powder is obtained.

[0047] Comparative Example 4

[0048] This comparative example provides a method for preparing a fusible polytetrafluoroethylene resin powder, the steps of which are as follows:

[0049] After filtering, 5L of PFA polymerization liquid was placed in an 8L refrigeration unit with a double jacket. First, -15℃ brine was introduced for freezing for 2 hours, and then 80℃ hot water was introduced for thawing for 1 hour. The resulting wet material was placed in a washing tank and washed 2-3 times with deionized water. It was then dried in an oven at 260℃ for 3 hours, and then heated to 275℃ for high-temperature treatment for 0.5 hours. After pulverization, PFA powder was obtained.

[0050] Comparative Example 5

[0051] This comparative example provides a method for preparing a fusible polytetrafluoroethylene resin powder, the steps of which are as follows:

[0052] After filtering, 5L of PFA polymerization liquid was placed in an 8L refrigeration unit with a double jacket. First, -15℃ brine was introduced for freezing for 2 hours, and then 80℃ hot water was introduced for thawing for 1 hour. The resulting wet material was placed in a washing tank and washed 2-3 times with deionized water. It was then dried in an oven at 260℃ for 3 hours, and then heated to 295℃ for high-temperature treatment for 0.5 hours. After pulverization, PFA powder was obtained.

[0053] Comparative Example 6

[0054] This comparative example provides a method for preparing a fusible polytetrafluoroethylene resin powder, the steps of which are as follows:

[0055] After filtering, 5L of PFA polymerization liquid was placed in an 8L refrigeration unit with a double jacket. First, -15℃ brine was introduced for freezing for 2 hours, and then 80℃ hot water was introduced for thawing for 1 hour. The resulting wet material was placed in a washing tank and washed 2-3 times with deionized water. It was then dried in an oven at 260℃ for 3 hours, and then heated to 275℃ for high-temperature treatment for 1.5 hours. After pulverization, PFA powder was obtained.

[0056] Comparative Example 7

[0057] This comparative example provides a method for preparing a fusible polytetrafluoroethylene resin powder, the steps of which are as follows:

[0058] After filtering, 5L of PFA polymerization liquid was placed in an 8L refrigeration unit with a double jacket. First, -15℃ brine was introduced for freezing for 2 hours, and then 80℃ hot water was introduced for thawing for 1 hour. The resulting wet material was placed in a washing tank and washed 2-3 times with deionized water. It was then dried in an oven at 260℃ for 3 hours, and then heated to 295℃ for high-temperature treatment for 1.5 hours. After pulverization, PFA powder was obtained.

[0059] Performance testing

[0060] The performance of the fusible polytetrafluoroethylene resin powders provided in each embodiment and comparative example was tested (including melting point, melt flow index, particle size, and bulk density). The melting point was tested according to GB / T19466.1-2004, the melt flow index according to GB / T3682-2000, and the bulk density according to HG / T 3028-1999. The average particle size was measured using a laser particle size analyzer. The results are shown in Table 1.

[0061] Table 1

[0062]

[0063]

[0064] The results above show that the meltable polytetrafluoroethylene resin powder provided by the present invention has a melting point of 308℃, a bulk density of ≥750g / L, and a melt index of 15.8-16.2. Compared with the PFA powder obtained by conventional mechanical agglomeration (Comparative Example 1), the melt index is not significantly different, and the bulk density is increased by more than 2 times. This effectively improves the processing and application performance of the powder, meets the requirements of electrostatic spraying, and the sprayed products do not have flying debris or orange peel phenomenon. It can also be further processed by melt extrusion granulation to obtain granular products that meet the processing methods of injection, extrusion, and compression molding.

[0065] It should be noted that the endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0066] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "specific implementation," or "some specific implementations," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for increasing the bulk density of fusible polytetrafluoroethylene resin powder, characterized in that, include: The PFA polymerization liquid is frozen and then thawed, filtered to obtain wet material, washed with water and dried, and then subjected to high temperature treatment at a temperature 20-30°C below the melting point of PFA to obtain PFA powder with a bulk density of more than 750 g / L; the drying temperature is 260°C.

2. The method for increasing the bulk density of fusible polytetrafluoroethylene resin powder according to claim 1, characterized in that, The high-temperature treatment time is 0.5-1 hour.

3. The method for increasing the bulk density of fusible polytetrafluoroethylene resin powder according to claim 1, characterized in that, The freezing temperature is -15°C, and the PFA polymer solution is frozen completely.

4. The method for increasing the bulk density of fusible polytetrafluoroethylene resin powder according to claim 3, characterized in that, The thawing temperature is 80°C, and the ice is thawed until it is completely melted into a liquid state.

5. The method for increasing the bulk density of fusible polytetrafluoroethylene resin powder according to any one of claims 1-4, characterized in that, The PFA polymer solution is prepared by emulsion polymerization and has a solid content of 20-27%.

6. The method for increasing the bulk density of fusible polytetrafluoroethylene resin powder according to claim 5, characterized in that, The PFA polymer solution is first filtered through a 200-mesh sieve before being frozen.

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