Modified polytetrafluoroethylene dispersion resin and preparation method thereof

Abstract

The invention discloses a modified polytetrafluoroethylene dispersion resin and a preparation method thereof, and relates to the technical field of high polymer materials, and the preparation method comprises the following steps: taking a polytetrafluoroethylene aqueous dispersion liquid, and carrying out pre-dispersion treatment by adopting ultrasonic waves to obtain a pre-dispersed polytetrafluoroethylene emulsion; dissolving a tri-functionalized fluorine-containing siloxane modifier in an organic solvent to form a modifier solution, and dropwise adding the modifier solution into the pre-dispersed polytetrafluoroethylene emulsion while stirring to form a mixed solution; transferring the mixed solution into a reaction kettle, adding an initiator, and carrying out a grafting reaction in a gradient heating mode under the protection of nitrogen; and after the reaction is finished, cooling a product, carrying out suction filtration, washing, and then carrying out vacuum drying to obtain the modified polytetrafluoroethylene dispersion resin. According to the modified polytetrafluoroethylene resin disclosed by the invention, the bonding strength with a matrix and the dispersion stability in the resin are remarkably improved, meanwhile, the processing temperature is reduced, and the material is endowed with excellent performance retention rate after damp-heat aging and batch stability of industrial production.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer materials, in particular to a modified polytetrafluoroethylene dispersion resin and a preparation method thereof. Background Art

[0002] Polytetrafluoroethylene (PTFE) is a polymer material with excellent comprehensive properties. Due to its outstanding chemical corrosion resistance, excellent high and low temperature stability, and excellent dielectric insulation properties, it has gained an indispensable application position in many high-tech fields such as chemical industry, electronics, kitchenware, and medical treatment. However, the molecular structure of PTFE gives it extremely low surface energy, which exhibits strong hydrophobic and oleophobic properties. On the one hand, this is the source of its non-stickiness, but on the other hand, it also leads to extremely poor adhesion between it and most other materials, such as metals, inorganic non-metallic materials, or common matrices such as epoxy resins. This inherent low adhesion makes it difficult for PTFE to adhere firmly to the surface of the substrate as a coating or to form a strong composite interface with the resin matrix as a filler, greatly limiting its application expansion in the fields of high-performance composite materials and functional coatings. In addition, when PTFE is used in the form of an aqueous dispersion, its particles are highly inert and lack effective electrostatic or steric stabilization mechanisms. They are very easy to agglomerate and quickly settle in the dispersion medium, resulting in poor stability of the dispersion system and difficulty in achieving uniform and controllable coating or blending processing. At the same time, the high melt viscosity and crystallinity of polytetrafluoroethylene make its molding and processing temperature very high, usually requiring sintering above 350 degrees Celsius. This not only means huge energy consumption, but also makes it impossible to apply to many substrates that are not resistant to high temperatures, further narrowing its application range.

[0003] In order to overcome the above technical bottlenecks, the existing technology has made a variety of modification attempts, but all of them have obvious limitations. For example, although physical methods such as plasma treatment and high-energy ray irradiation can activate the surface of polytetrafluoroethylene to a certain extent and introduce oxygen-containing polar groups to temporarily increase its surface activity, this modification effect is usually unstable and easily decays over time, that is, there is a "time-effectiveness" problem, and the related equipment investment is huge and the process is complicated, which is not suitable for large-scale industrial production. The method of physical blending modification, that is, melt blending it with other polymers, often leads to serious two-phase separation due to the huge compatibility difference between polytetrafluoroethylene and other polymers, and it is impossible to achieve effective performance complementarity and improvement at the molecular level. The chemical etching method using strong acids, strong bases or molten alkali metals, although it can form a carbonized layer on the surface of the material through defluorination reaction or introduce functional groups, significantly improving adhesion, but this treatment process is intense and the conditions are harsh, which usually inevitably destroys the CF main chain structure of polytetrafluoroethylene, resulting in its inherent core advantages such as mechanical strength, weather resistance and chemical stability being severely weakened, which is not worth the loss. Therefore, developing a mild and efficient modification method that can significantly improve the adhesion and dispersibility of polytetrafluoroethylene, reduce its processing temperature, and at the same time not damage its main structure and performance is a technical problem that needs to be solved urgently in the current field of materials science. Summary of the Invention

[0004] The purpose of the present invention is to provide a modified polytetrafluoroethylene dispersion resin and a preparation method thereof, which solve the problems existing in the background technology.

[0005] To solve the above technical problems, the present invention provides a method for preparing a modified polytetrafluoroethylene dispersion resin, comprising the following steps:

[0006] Taking a polytetrafluoroethylene aqueous dispersion, and pre-dispersing it by ultrasonic treatment to obtain a pre-dispersed polytetrafluoroethylene emulsion;

[0007] Dissolving a trifunctional fluorinated silicone modifier in an organic solvent to form a modifier solution, and adding the modifier solution dropwise to a pre-dispersed polytetrafluoroethylene emulsion under stirring to form a mixed solution;

[0008] The mixed solution was transferred to a reactor, an initiator was added, and the mixture was heated to 120-140°C in a gradient heating manner under nitrogen protection to carry out the grafting reaction;

[0009] After the reaction is completed, the product is cooled, filtered, washed with deionized water and anhydrous ethanol, and then vacuum-dried at 60-80° C. to obtain a modified polytetrafluoroethylene dispersion resin.

[0010] Preferably, the preparation method of the trifunctional fluorinated silicone modifier comprises:

[0011] Step (a) In a reaction vessel equipped with a reflux condenser, perfluorooctylethyl iodide and anhydrous toluene are mixed, heated to 80° C., triethoxysilane is added dropwise under nitrogen protection, and after the addition is complete, Karstedt catalyst is added, and the reaction is maintained at 80° C. for 8 hours. After the reaction is completed, the mixture is subjected to reduced pressure distillation to obtain a fluorocarbon silane intermediate;

[0012] Step (b) mixing the fluorocarbon silane intermediate and anhydrous ethanol, heating to 60° C., adding concentrated sulfuric acid dropwise, and then slowly adding vinyldimethylethoxysilane dropwise, and continuing the reaction at 60° C. for 4 hours. The reactants are neutralized, extracted, dried and rotary evaporated to obtain a trifunctional fluorosiloxane modifier.

[0013] Preferably, based on 100 parts by weight of the solid content of polytetrafluoroethylene, the amount of the trifunctional fluorinated silicone modifier is 1-5 parts by weight, and the amount of the initiator is 0.2-1.0 parts by weight.

[0014] Preferably, the initiator is dicumyl peroxide or benzoyl peroxide.

[0015] Preferably, the rate of the gradient temperature increase is 3-8°C / min.

[0016] Preferably, while the modifier solution is being added dropwise, an ethanol dispersion of the double-crosslinked core-shell stabilizer is added; and the grafting reaction is heated and temperature-controlled using a pulsed microwave-assisted reaction process instead of a gradient heating process.

[0017] Preferably, the preparation method of the double cross-linked core-shell stabilizer comprises: adding ammonia water as a catalyst to an alcohol aqueous solution, and uniformly adding a precursor mixture consisting of phenyltriethoxysilane, vinyltriethoxysilane and (3-glycidyloxypropyl)trimethoxysilane to the alcohol aqueous solution in a 40°C water bath and under stirring, to carry out a hydrolysis condensation reaction, and after the reaction is completed, centrifuging, washing and drying to obtain the stabilizer.

[0018] Preferably, the parameters of the pulsed microwave-assisted reaction process are: microwave frequency 2.45 GHz, a pulse working cycle of heating for 30 seconds and pausing for 30 seconds, and the microwave power is adjusted by real-time temperature monitoring to maintain the reaction temperature at 130±1°C.

[0019] Also provided is a modified polytetrafluoroethylene dispersion resin, which is prepared by the above-mentioned preparation method of the modified polytetrafluoroethylene dispersion resin.

[0020] Also provided is a use of a modified polytetrafluoroethylene dispersion resin in preparing a polytetrafluoroethylene composite material or coating with high bonding strength or high dispersion stability.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] By chemically grafting polytetrafluoroethylene at the molecular level, functional active groups were successfully introduced into its inert surface, fundamentally improving the interfacial affinity between polytetrafluoroethylene and heterogeneous materials, enabling it to form strong and lasting chemical bonds with various matrices such as metals and resins. Whether used as a coating or a filler in composite materials, it exhibits excellent bonding strength, ensuring the integrity and reliability of the composite interface under complex stresses, and solving the problem of weak bonding strength of traditional polytetrafluoroethylene materials due to surface inertness.

[0023] The dispersion behavior of polytetrafluoroethylene particles in liquid media is significantly improved. After modification, an effective steric hindrance layer is formed on the surface of the particles, which can effectively prevent the agglomeration and sedimentation of the particles, thereby obtaining a long-lasting and stable high-solid content dispersion system, which is crucial to ensure the uniformity of the internal structure of the coating or composite material, ensuring the uniformity and predictability of the macroscopic performance of the final product, and effectively reducing the melt viscosity of the material, so that its molding and sintering temperature can be significantly reduced. This not only saves energy consumption in the production process, but also broadens its application prospects on heat-sensitive substrates.

[0024] By introducing a unique synergistic stabilization mechanism and advanced process control methods, the long-term service reliability of modified polytetrafluoroethylene materials has achieved a qualitative leap. The prepared resin can still maintain extremely high performance stability in harsh accelerated aging environments such as high temperature and high humidity, effectively avoiding the problem of bonding failure caused by environmental factors. The heating method adopted realizes uniform and precise energy input to the reaction system, fundamentally ensuring the high consistency between product batches in industrial-scale production, and laying a solid technical foundation for the preparation of high-end polytetrafluoroethylene products with stable performance and reliable quality. DETAILED DESCRIPTION

[0025] Comparative Example 1

[0026] This comparative example is intended to illustrate the performance limitations of unmodified polytetrafluoroethylene materials in the prior art. Specifically, 1000 g of a 25 wt% aqueous polytetrafluoroethylene dispersion (brand D-1, 250 g solids content) was used directly in subsequent performance tests without any modification.

[0027] The composite material was prepared by mixing it with epoxy resin and testing its dispersion stability. It was then coated on a sandblasted aluminum alloy surface and sintered at 370°C to form a film, and its lap shear strength was tested.

[0028] Results showed that after mixing the unmodified polytetrafluoroethylene with epoxy resin, it settled significantly within two hours of standing, failing to form a stable dispersion. The lap shear strength of the unmodified polytetrafluoroethylene with the aluminum alloy matrix was only 2.5 ± 0.3 MPa, indicating a very weak bond. Furthermore, the sintering temperature required for its formation was as high as 370°C, resulting in high energy consumption.

[0029] Example 1

[0030] This embodiment provides a method for preparing a modified polytetrafluoroethylene dispersion resin;

[0031] The key raw material used in this method, trifunctional fluorinated silicone modifier (TFSM), is prepared in advance by the method disclosed in the technical solution of the present invention;

[0032] The specific steps of the preparation method are:

[0033] 1000 g of a 25 wt% aqueous polytetrafluoroethylene dispersion (brand D-1, solid content 250 g) was pre-dispersed using an ultrasonic wave with a power of 500 W and a frequency of 20 kHz for 15 minutes to obtain a pre-dispersed polytetrafluoroethylene emulsion.

[0034] Dissolve the trifunctional fluorosilicone modifier in 50 mL of anhydrous ethanol to form a modifier solution; add the solution dropwise to the pre-dispersed polytetrafluoroethylene emulsion under stirring; the amount of the trifunctional fluorosilicone modifier used is 1 part by weight (i.e., 2.5 grams) based on 100 parts by weight of the polytetrafluoroethylene solid content;

[0035] The mixture was transferred to an autoclave, and 0.2 parts by weight (i.e., 0.5 g) of dicumyl peroxide (DCP) as an initiator was added. Under nitrogen protection, the mixture was heated in a gradient heating manner at a heating rate of 3°C / min, and finally heated to 120°C for a grafting reaction for 3 hours.

[0036] After the reaction is completed, the product is cooled, filtered, washed with deionized water and anhydrous ethanol, and then vacuum-dried at 60° C. to obtain the modified polytetrafluoroethylene dispersion resin of this embodiment;

[0037] The modified resin prepared in this example was used to prepare composite materials and coatings; the results showed that, thanks to the trifunctional fluorinated silicone modifier grafted on the surface of polytetrafluoroethylene, its dispersion stability in the epoxy resin was improved, and it could still maintain a relatively good uniform state after standing for 24 hours; when it was applied to the surface of aluminum alloy to prepare an anti-corrosion and wear-resistant coating, the bonding strength of the coating was significantly improved compared with that of Comparative Example 1, and the lap shear strength reached 5.8±0.4 MPa; at the same time, the sintering temperature of the material was reduced to 345°C, and the adaptability to heat-sensitive substrates was improved.

[0038] Example 2

[0039] This embodiment provides a method for preparing a modified polytetrafluoroethylene dispersion resin;

[0040] The specific steps of the preparation method are:

[0041] The ultrasonic pre-dispersion treatment steps are the same as those in Example 1;

[0042] In the dropwise addition step, the amount of the trifunctional fluorosilicone modifier was increased to 2.5 parts by weight (i.e., 6.25 g) based on 100 parts by weight of the solid content of polytetrafluoroethylene;

[0043] In the grafting reaction step, the initiator dicumyl peroxide (DCP) was added in an amount of 0.5 parts by weight (i.e., 1.25 g); the temperature was heated in a gradient manner at a heating rate of 5°C / min, and finally heated to 130°C for a grafting reaction for 3 hours;

[0044] The post-treatment steps were the same as in Example 1, except that the vacuum drying temperature was 70°C;

[0045] The modified polytetrafluoroethylene dispersion resin prepared in this example was used to prepare high-demand electronic packaging composite materials. The results showed that it exhibited good dispersibility in the epoxy resin matrix and remained uniform and stable without sedimentation after standing for 72 hours, which is crucial for ensuring the uniformity of the dielectric properties of the packaging material. Its lap shear strength with the aluminum alloy substrate was increased from 2.5 MPa of the unmodified form to 9.5±0.5 MPa, demonstrating its applicability in the preparation of polytetrafluoroethylene composite materials with high bonding strength. In addition, the sintering temperature was successfully reduced from 370°C to 320°C, reducing production energy consumption.

[0046] Example 3

[0047] This embodiment provides a method for preparing a modified polytetrafluoroethylene dispersion resin;

[0048] The specific steps of the preparation method are:

[0049] The ultrasonic pre-dispersion treatment steps are the same as in Example 1;

[0050] In the dropwise addition step, the upper limit of the amount of the trifunctional fluorinated silicone modifier is 5 parts by weight (i.e., 12.5 g) based on 100 parts by weight of the solid content of polytetrafluoroethylene.

[0051] In the grafting reaction step, an initiator, dicumyl peroxide (DCP), was added in an amount of 1.0 part by weight (i.e., 2.5 g); a gradient heating method was used, with a heating rate of 8°C / min, and finally heated to 140°C for a grafting reaction for 3 hours;

[0052] The post-treatment steps were the same as in Example 1, except that the vacuum drying temperature was 80°C;

[0053] The modified resin of this example was used to prepare a non-stick coating. The results showed that a higher amount of modifier resulted in a stronger bond between the coating and the metal substrate, with a lap shear strength of up to 9.8±0.4 MPa. However, compared with Example 2, the performance improvement was limited, but the cost of the modifier increased significantly, suggesting that in practical applications, the amount of modifier should be balanced based on cost and performance requirements. Its dispersion stability was comparable to that of Example 2, and the sintering temperature could be further reduced to 315°C.

[0054] Example 4

[0055] This embodiment provides a method for preparing a modified polytetrafluoroethylene dispersion resin, wherein the initiator used is benzoyl peroxide (BPO);

[0056] The specific steps of the preparation method are:

[0057] The ultrasonic pre-dispersion treatment steps are the same as in Example 1;

[0058] The amount of the trifunctional fluorinated silicone modifier used is the same as in Example 2, 2.5 parts by weight (i.e., 6.25 g);

[0059] During the grafting reaction step, 0.5 parts by weight (i.e., 1.25 grams) of benzoyl peroxide (BPO) was added as an initiator. Due to the low decomposition temperature of BPO, a gradient heating method was used at a rate of 5°C / minute to a final temperature of 95°C, and the reaction time was extended to 5 hours.

[0060] The post-processing steps are the same as in Example 1;

[0061] This example is intended to verify the feasibility of using different initiators. The modified resin prepared by this method was applied to a non-stick coating for cookware, and its performance was essentially equivalent to that of the product prepared in Example 2. The lap shear strength with aluminum alloy was 9.3±0.5 MPa, and it remained stable in epoxy resin for 72 hours at a sintering temperature of 325°C. This demonstrates the flexibility of the preparation method of the present invention, allowing the selection of different initiator systems based on equipment and cost requirements.

[0062] Example 5

[0063] This embodiment provides a preparation method of modified polytetrafluoroethylene dispersion resin that is further optimized based on the basic preparation method. The method introduces a double cross-linked core-shell stabilizer and adopts a pulsed microwave-assisted reaction process.

[0064] The dual cross-linked core-shell stabilizer (DCCS) and trifunctional fluorosilicone modifier (TFSM) used in this example were prepared in advance according to the method disclosed in the technical solution section of the present invention;

[0065] The specific steps of the preparation method are:

[0066] The ultrasonic pre-dispersion treatment steps are the same as those in Example 1;

[0067] 2.5 parts by weight of TFSM were dissolved in ethanol; while adding the modifier solution dropwise, 0.1 parts by weight (ie, 0.25 g, accounting for 0.1% of the solid content of polytetrafluoroethylene) of a double cross-linked core-shell stabilizer (DCCS) in ethanol were added;

[0068] The mixed solution was transferred to an industrial-grade microwave chemical reactor, and 0.5 parts by weight of initiator DCP was added. The grafting reaction was heated and temperature-controlled using a pulsed microwave-assisted reaction process. The parameters of the pulsed microwave-assisted reaction process were set as follows: microwave frequency of 2.45 GHz, a duty cycle of "heating for 30 seconds, pause for 30 seconds", and the reaction temperature was maintained at 130 ± 1°C using real-time monitoring by an optical fiber thermometer and adjustment of microwave power by a PID controller. The reaction was continued for 3 hours.

[0069] The post-processing steps are the same as in Example 1;

[0070] The modified polytetrafluoroethylene dispersion resin prepared in this embodiment is applied to the weather-resistant coating of the components inside the automobile engine compartment; this application scenario has strict requirements on the long-term service reliability of the material; the initial performance is close to that of Example 2, with a lap shear strength of 9.6±0.3MPa and a sintering temperature of 320°C; the key is that thanks to the hydrolysis-resistant three-dimensional cross-linked network formed by the double cross-linked core-shell stabilizer after curing, and the highly uniform grafting brought about by the pulsed microwave-assisted reaction process, the coating exhibits excellent aging resistance; after aging for 1000 hours in a wet and hot environment at 150°C and 85% relative humidity, the lap shear strength retention rate with the substrate is as high as more than 95%, while the strength of the sample in Example 2 decreases by more than 30%; this proves that the technical solution of this embodiment can effectively solve the problem of performance attenuation under high-temperature and wet-heat aging, and is suitable for large-scale industrial production with stable batches.

[0071] Performance Comparison

[0072] The following table summarizes the key parameters and performance test results of the above comparative examples and embodiments:

[0073]

[0074]

[0075] The above are merely preferred embodiments of the present invention and do not limit the present invention in any other form. Any technician familiar with the profession may use the technical content disclosed above to change or modify it into an equivalent embodiment with equivalent changes and apply it to other fields. However, any simple modification, equivalent change and modification made to the above embodiment based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing a modified polytetrafluoroethylene dispersion resin, characterized in that: The following steps are involved: Taking a polytetrafluoroethylene aqueous dispersion, and pre-dispersing it by ultrasonic treatment to obtain a pre-dispersed polytetrafluoroethylene emulsion; Dissolving a trifunctional fluorinated silicone modifier in an organic solvent to form a modifier solution, and adding the modifier solution dropwise to a pre-dispersed polytetrafluoroethylene emulsion under stirring to form a mixed solution; The mixed solution was transferred to a reactor, an initiator was added, and the mixture was heated to 120-140°C in a gradient heating manner under nitrogen protection to carry out the grafting reaction; After the reaction is completed, the product is cooled, filtered, washed with deionized water and anhydrous ethanol, and then vacuum-dried at 60-80° C. to obtain a modified polytetrafluoroethylene dispersion resin.

2. The method for preparing a modified polytetrafluoroethylene dispersion resin according to claim 1, wherein: The preparation method of the trifunctional fluorinated silicone modifier comprises: Step (a) In a reaction vessel equipped with a reflux condenser, perfluorooctylethyl iodide and anhydrous toluene are mixed, heated to 80° C., triethoxysilane is added dropwise under nitrogen protection, and after the addition is complete, Karstedt catalyst is added, and the reaction is maintained at 80° C. for 8 hours. After the reaction is completed, the mixture is subjected to reduced pressure distillation to obtain a fluorocarbon silane intermediate; Step (b) mixing the fluorocarbon silane intermediate and anhydrous ethanol, heating to 60° C., adding concentrated sulfuric acid dropwise, and then slowly adding vinyldimethylethoxysilane dropwise, and continuing the reaction at 60° C. for 4 hours. The reactants are neutralized, extracted, dried and rotary evaporated to obtain a trifunctional fluorosiloxane modifier.

3. The method for preparing a modified polytetrafluoroethylene dispersion resin according to claim 1, wherein: Based on 100 parts by weight of the solid content of polytetrafluoroethylene, the amount of the trifunctional fluorinated silicone modifier is 1-5 parts by weight, and the amount of the initiator is 0.2-1.0 parts by weight.

4. The method for preparing a modified polytetrafluoroethylene dispersion resin according to claim 1, wherein: The initiator is dicumyl peroxide or benzoyl peroxide.

5. The method for preparing a modified polytetrafluoroethylene dispersion resin according to claim 1, characterized in that: The rate of the gradient temperature increase was 3-8°C / min.

6. The method for preparing a modified polytetrafluoroethylene dispersion resin according to claim 1, characterized in that: While adding the modifier solution dropwise, add the ethanol dispersion of the double cross-linked core-shell stabilizer; In addition, the grafting reaction adopts a pulsed microwave-assisted reaction process for heating and temperature control to replace the gradient temperature increase.

7. The method for preparing a modified polytetrafluoroethylene dispersion resin according to claim 6, characterized in that: The preparation method of the double cross-linked core-shell stabilizer includes: adding ammonia water as a catalyst to an alcohol aqueous solution, and uniformly adding a precursor mixture consisting of phenyltriethoxysilane, vinyltriethoxysilane and (3-glycidyloxypropyl)trimethoxysilane to the alcohol aqueous solution under stirring in a 40°C water bath to carry out a hydrolysis condensation reaction. After the reaction is completed, the stabilizer is centrifuged, washed and dried to obtain the stabilizer.

8. The method for preparing a modified polytetrafluoroethylene dispersion resin according to claim 6, characterized in that: The parameters of the pulsed microwave-assisted reaction process are as follows: microwave frequency 2.45 GHz, a pulsed working cycle of heating for 30 seconds and pausing for 30 seconds, and the microwave power is adjusted by real-time temperature monitoring to maintain the reaction temperature at 130±1°C.

9. A modified polytetrafluoroethylene dispersion resin, characterized in that: The modified polytetrafluoroethylene dispersion resin is prepared by adopting the preparation method of the modified polytetrafluoroethylene dispersion resin according to any one of claims 1 to 8.

10. Use of the modified polytetrafluoroethylene dispersion resin according to claim 9 in preparing a polytetrafluoroethylene composite material or coating with high bonding strength or high dispersion stability.

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