A modified polytetrafluoroethylene dispersion resin and a method of preparation

Abstract

The application discloses a modified polytetrafluoroethylene dispersion resin and a preparation method, relates to the technical field of high polymer materials, and comprises the following steps: taking a polytetrafluoroethylene aqueous dispersion liquid, and performing pre-dispersion treatment by using ultrasonic waves to obtain a pre-dispersed polytetrafluoroethylene emulsion; dissolving a trifunctional fluorine-containing siloxane modifier in an organic solvent to form a modifier solution; under stirring, the modifier solution is added dropwise into the pre-dispersed polytetrafluoroethylene emulsion to form a mixed liquid; the mixed liquid is transferred into a reaction kettle, and an initiator is added; under nitrogen protection, a gradient heating mode is adopted to perform grafting reaction; after the reaction is completed, the product is cooled, filtered, washed, and then vacuum dried to obtain the modified polytetrafluoroethylene dispersion resin. The modified polytetrafluoroethylene resin significantly improves the bonding strength with a matrix and the dispersion stability in the resin, simultaneously reduces the processing temperature, and endows the material with excellent performance retention rate after hygrothermal aging and batch stability in industrial production.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high polymer materials, and particularly relates to a modified polytetrafluoroethylene dispersion resin and a preparation method. BACKGROUND

[0002] Polytetrafluoroethylene is a high polymer material with excellent comprehensive performance, and has obtained an indispensable application position in many high-tech fields such as chemical industry, electronics, kitchenware and medical treatment due to its outstanding chemical corrosion resistance, excellent high and low temperature stability and excellent dielectric insulation performance. However, the molecular structure of polytetrafluoroethylene endows it with extremely low surface energy, which shows strong hydrophobic and oleophobic characteristics. On the one hand, this is the source of its non-stickiness, but on the other hand, it also leads to poor adhesion between polytetrafluoroethylene and most other materials, such as metals, inorganic non-metallic materials or epoxy resin, etc. This inherent low adhesion makes it difficult for polytetrafluoroethylene to be firmly attached to the surface of the substrate as a coating, or to form a strong composite interface with the resin matrix as a filler, which greatly limits its application expansion in the field of high-performance composite materials and functional coatings. In addition, when polytetrafluoroethylene is applied in the form of aqueous dispersion, the particles are highly inert due to the surface, lack effective electrostatic or steric stabilization mechanism, and are prone to agglomeration and rapid sedimentation in the dispersion medium, resulting in poor stability of the dispersion system, and making it difficult to achieve uniform and controllable coating or blending processing. At the same time, the high melt viscosity and crystallinity of polytetrafluoroethylene make its forming processing temperature very high, usually need to be sintered above 350 degrees Celsius, which not only means huge energy consumption, but also makes it unable to be applied to many substrates that are not resistant to high temperature, further reducing its application range.

[0003] In order to overcome the above technical bottleneck, the prior art has made various modification attempts, but all have obvious limitations. For example, although physical methods such as plasma treatment and high-energy radiation can activate the surface of polytetrafluoroethylene to a certain extent, introduce oxygen-containing polar groups to temporarily improve the surface activity, but such modification effect is usually unstable and easy to decay over time, that is, there is a "time effect" problem, and the related equipment investment is huge and the process is complex, which is not suitable for large-scale industrial production. The method of physical blending modification, that is, melt blending with other polymers, often leads to serious two-phase separation due to the large compatibility difference between polytetrafluoroethylene and other polymers, and cannot effectively complement and improve the performance at the molecular level. The chemical etching method using strong acid, strong base or molten alkali metal can form a carbonized layer on the material surface or introduce functional groups through defluorination reaction, which can significantly improve the adhesion, but this treatment process is violent and the conditions are harsh, which will inevitably damage the C-F main chain structure of polytetrafluoroethylene, resulting in serious weakening of its inherent mechanical strength, weather resistance and chemical stability and other core performance advantages, which is not worth the loss. Therefore, developing a mild and efficient modification method that can significantly improve the adhesion and dispersibility of polytetrafluoroethylene while reducing its processing temperature without damaging its main structure and performance is a technical problem that needs to be solved in the field of material science. SUMMARY

[0004] The purpose of the present application is to provide a modified polytetrafluoroethylene dispersion resin and a preparation method, which solves the problems in the background art.

[0005] To solve the above technical problems, the present application provides a preparation method of a modified polytetrafluoroethylene dispersion resin, comprising the following steps:

[0006] Take the aqueous dispersion of polytetrafluoroethylene, and perform pre-dispersion treatment with ultrasonic waves to obtain a pre-dispersed polytetrafluoroethylene emulsion;

[0007] Dissolve the trifunctional fluorine-containing siloxane modifier in an organic solvent to form a modifier solution, and drop the modifier solution into the pre-dispersed polytetrafluoroethylene emulsion under stirring to form a mixed solution;

[0008] Transfer the mixed solution to a reaction kettle, add an initiator, and heat to 120-140℃ under nitrogen protection by gradient heating to perform grafting reaction;

[0009] After the reaction is completed, cool the product, perform suction filtration, and wash with deionized water and anhydrous ethanol, and then vacuum dry at 60-80℃ to obtain the modified polytetrafluoroethylene dispersion resin.

[0010] Preferably, the preparation method of the trifunctional fluorine-containing siloxane modifier comprises:

[0011] Step (a) In a reaction vessel equipped with a reflux condenser, perfluorooctyl ethyl iodine and anhydrous toluene were mixed and heated to 80°C. Triethoxysilane was added dropwise under nitrogen protection. After the addition was complete, Karstedt catalyst was added and the reaction was maintained at 80°C for 8 hours. After the reaction was completed, the intermediate fluorocarbon silane was obtained by vacuum distillation.

[0012] In step (b), the fluorocarbon silane intermediate and anhydrous ethanol are mixed, heated to 60°C, concentrated sulfuric acid is added dropwise, followed by the slow addition of vinyldimethylethoxysilane. The reaction is continued at 60°C for 4 hours. After neutralization, extraction, drying and rotary evaporation, the trifunctionalized fluorosiloxane modifier is obtained.

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

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

[0015] Preferably, the gradient heating rate is 3-8℃ / minute.

[0016] Preferably, an ethanol dispersion of a dual cross-linked core-shell stabilizer is added simultaneously with the addition of the modifier solution; and the grafting reaction is heated and temperature-controlled using a pulsed microwave-assisted reaction process to replace gradient heating.

[0017] Preferably, the preparation method of the dual crosslinked core-shell stabilizer includes: adding ammonia as a catalyst to an alcohol-water solution, and uniformly adding a precursor mixture composed of phenyltriethoxysilane, vinyltriethoxysilane and (3-glycidoxypropyl)trimethoxysilane to the alcohol-water solution under stirring in a 40°C water bath to carry out a hydrolysis-condensation reaction. After the reaction is completed, the stabilizer is obtained by centrifugation, washing and drying.

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

[0019] A modified polytetrafluoroethylene dispersion resin is also provided, which is prepared by the above-mentioned method for preparing a modified polytetrafluoroethylene dispersion resin.

[0020] The invention also provides the application of a modified polytetrafluoroethylene dispersion resin in the preparation of polytetrafluoroethylene composite materials or coatings with high adhesive strength or high dispersion stability.

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

[0022] By performing molecular-level chemical grafting modification on polytetrafluoroethylene (PTFE), functionalized active groups were successfully introduced into its inert surface, fundamentally improving the interfacial affinity between PTFE and heterogeneous materials. This enabled PTFE to form strong and durable 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. This solves the problem of weak bonding caused by the surface inertness of traditional PTFE materials.

[0023] The modification significantly improves the dispersion behavior of polytetrafluoroethylene (PTFE) microparticles in liquid media. After modification, an effective steric hindrance layer is formed on the particle surface, which can effectively prevent particle aggregation and sedimentation, thereby obtaining a long-lasting and stable high-solids content dispersion system. This is crucial for ensuring the uniformity of the internal structure of coatings or composite materials, ensuring the uniformity and predictability of the macroscopic properties of the final product. It also effectively reduces the melt viscosity of the material, resulting in a significant decrease in its molding and sintering temperature. 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 (PTFE) 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 bonding failure caused by environmental factors. The heating method adopted achieves uniform and precise energy input to the reaction system, fundamentally ensuring high consistency between product batches in industrial-scale production, laying a solid technical foundation for the preparation of high-end PTFE products with stable performance and reliable quality. Detailed Implementation

[0025] Comparative Example 1

[0026] This comparative example aims to illustrate the performance limitations of unmodified polytetrafluoroethylene (PTFE) materials in the prior art. The specific operation is as follows: 1000 grams of PTFE aqueous dispersion with a concentration of 25 wt% (brand name D-1, solid content 250 grams) is taken and used directly for subsequent performance testing without any modification treatment.

[0027] The composite material was prepared by mixing it with epoxy resin, and its dispersion stability was tested. The composite material was coated on the surface of sandblasted aluminum alloy, and after being sintered at 370℃ to form a film, its lap shear strength was tested.

[0028] The results showed that the unmodified polytetrafluoroethylene, after being mixed in epoxy resin, underwent significant sedimentation within 2 hours of standing, failing to form a stable dispersion system; its lap shear strength with the aluminum alloy matrix was only 2.5±0.3MPa, indicating very weak bonding force; in addition, the sintering temperature required for its molding 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, trifunctionalized fluorinated siloxane modifier (TFSM), is prepared in advance using the method partially disclosed in the technical solution of this invention;

[0032] The specific steps of this preparation method are as follows:

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

[0034] The trifunctionalized fluorinated siloxane modifier was dissolved in 50 mL of anhydrous ethanol to form a modifier solution; the solution was added dropwise to the pre-dispersed polytetrafluoroethylene emulsion under stirring; the amount of trifunctionalized fluorinated siloxane modifier used was 1 part by weight (i.e. 2.5 g) based on 100 parts by weight of polytetrafluoroethylene solid content.

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

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

[0037] The modified resin obtained in this embodiment was used to prepare composite materials and coatings. The results showed that, thanks to the trifunctionalized fluorosiloxane modifier grafted onto the surface of polytetrafluoroethylene, its dispersion stability in epoxy resin was improved, and it could still maintain a good uniform state after standing for 24 hours. When it was applied to the surface of aluminum alloy to prepare anti-corrosion and wear-resistant coatings, the bonding strength of the coating was significantly improved compared with Comparative Example 1, and the lap shear strength reached 5.8±0.4MPa. 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 this preparation method are as follows:

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

[0042] In the dropwise addition step, the amount of trifunctionalized fluorosiloxane modifier is increased to 2.5 parts by weight (i.e. 6.25 grams) based on 100 parts by weight of polytetrafluoroethylene solid content.

[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 increased by a gradient method at a rate of 5 °C / min, and finally heated to 130 °C for 3 hours for the grafting reaction.

[0044] The post-processing steps are the same as in Example 1, except that the vacuum drying temperature is 70°C;

[0045] The modified polytetrafluoroethylene (PTFE) dispersion resin prepared in this embodiment was used to prepare high-requirement electronic packaging composite materials. The results showed that it exhibited good dispersibility in the epoxy resin matrix and remained uniform and stable after standing for 72 hours without sedimentation, which is crucial for ensuring the uniformity of the dielectric properties of the packaging material. The lap shear strength with the aluminum alloy substrate was increased from 2.5 MPa for the unmodified resin to 9.5 ± 0.5 MPa, proving that it can be used to prepare PTFE composite materials with high adhesive 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 this preparation method are as follows:

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

[0050] In the dropwise addition step, based on the solid content of polytetrafluoroethylene per 100 parts by weight, the upper limit of the amount of trifunctionalized fluorosiloxane modifier is selected as 5 parts by weight (i.e. 12.5 grams).

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

[0052] The post-processing steps are the same as in Example 1, except that the vacuum drying temperature is 80°C;

[0053] The modified resin in this embodiment 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 an overlap shear strength of 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 the amount of modifier should be balanced between cost and performance requirements in practical applications. 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 this preparation method are as follows:

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

[0058] The amount of the trifunctional fluorosiloxane modifier is the same as in Example 2, which is 2.5 parts by weight (i.e. 6.25 grams).

[0059] In the grafting reaction step, benzoyl peroxide (BPO) initiator was added in an amount of 0.5 parts by weight (i.e. 1.25 g). Since BPO has a low decomposition temperature, a gradient heating method was used, with a heating rate of 5 °C / min, and the temperature was finally raised to 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 embodiment aims to verify the feasibility of different initiators; the modified resin prepared by this method is applied to the non-stick coating of kitchenware, and its performance is basically equivalent to that of the product prepared in Example 2; the lap shear strength with aluminum alloy is 9.3±0.5MPa, it remains stable in epoxy resin for 72 hours, and the sintering temperature is 325°C; this shows that the preparation method of the present invention has a certain degree of flexibility, and different initiator systems can be selected according to equipment and cost requirements.

[0062] Example 5

[0063] This embodiment provides a method for preparing modified polytetrafluoroethylene dispersion resin that is further optimized based on the basic preparation method. This method introduces a dual crosslinking core-shell stabilizer and adopts a pulsed microwave assisted reaction process.

[0064] The dual cross-linked core-shell stabilizer (DCCS) and the trifunctionalized fluorinated siloxane modifier (TFSM) used in this embodiment were both prepared in advance according to the methods disclosed in part of the technical solution of this invention;

[0065] The specific steps of this preparation method are as follows:

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

[0067] Dissolve 2.5 parts by weight of TFSM in ethanol; while adding the modifier solution dropwise, add 0.1 parts by weight (i.e. 0.25 g, accounting for 0.1% of the solid content of polytetrafluoroethylene) of an ethanol dispersion of dual crosslinked core-shell stabilizer (DCCS).

[0068] The mixture 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 2.45 GHz, working cycle "heating for 30 seconds, pausing for 30 seconds", and the microwave power was adjusted in real time by a fiber optic thermometer and a PID controller to maintain the reaction temperature at 130±1℃ 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 was applied to a weather-resistant coating for automotive engine compartment components. This application scenario has stringent requirements for the long-term service reliability of the material. The initial performance is similar to that of Example 2, with an overlap shear strength of 9.6 ± 0.3 MPa and a sintering temperature of 320°C. The key is that, thanks to the hydrolysis-resistant three-dimensional crosslinked network formed by the dual crosslinking 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 humid and hot environment at 150°C and 85% relative humidity, its overlap shear strength retention rate with the substrate is as high as 95% or more, while the strength of the sample in Example 2 decreased by more than 30%. This proves that the technical solution of this embodiment can effectively solve the performance degradation problem under high temperature and humid heat aging and is suitable for batch-stable large-scale industrial production.

[0071] Performance Comparison

[0072] The table below 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 are not intended to limit the present invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments that can be applied to other fields. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for producing a modified polytetrafluoroethylene dispersion resin, characterized by, The method comprises the following steps: An aqueous dispersion of polytetrafluoroethylene is prepared by ultrasonic pre-dispersion treatment to obtain a pre-dispersed polytetrafluoroethylene emulsion; The trifunctional fluorosilicone modifier is dissolved in an organic solvent to form a modifier solution, and the modifier solution is added dropwise into the pre-dispersed polytetrafluoroethylene emulsion under stirring to form a mixed solution; The mixed solution is transferred into a reaction kettle, and an initiator is added, and the grafting reaction is carried out by heating to 120-140°C under nitrogen protection in a gradient heating mode; 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; The preparation method of the trifunctional fluorosilicone modifier comprises: In step (a), a reaction container equipped with a reflux condenser is used to mix perfluorooctylethyl iodine and anhydrous toluene, and heated to 80°C. Under nitrogen protection, triethoxysilane is added dropwise. After the dropwise addition is completed, Karstedt catalyst is added, and the reaction is maintained at 80°C for 8 hours. After the reaction is completed, the fluorocarbon silane intermediate is obtained by reduced pressure distillation. In step (b), the fluorocarbon silane intermediate and anhydrous ethanol are mixed and heated to 60°C. Concentrated sulfuric acid is added dropwise, and then vinyl dimethyl ethoxysilane is slowly added. The reaction is continued at 60°C for 4 hours. After the reaction is completed, the trifunctional fluorosilicone modifier is obtained by neutralization, extraction, drying and rotary evaporation. At the same time of adding the modifier solution, an ethanol dispersion of the double crosslinking core-shell stabilizer is added; and the grafting reaction is heated and temperature-controlled by using a pulse microwave assisted reaction process instead of gradient heating. The preparation method of the double crosslinking core-shell stabilizer comprises: adding ammonia water as a catalyst in an alcohol water solution, and uniformly dropping a precursor mixture composed of phenyltriethoxysilane, vinyltriethoxysilane and (3-glycidyl ether propyl) trimethoxysilane into the alcohol water solution under stirring at 40°C water bath to carry out hydrolysis and condensation reaction. After the reaction is completed, the double crosslinking core-shell stabilizer is obtained by centrifugation, washing and drying.

2. The method for preparing a modified polytetrafluoroethylene dispersion resin according to claim 1, characterized in that, The amount of the trifunctional fluorosilicone modifier is 1-5 parts by weight based on 100 parts by weight of the solid content of the polytetrafluoroethylene, and the amount of the initiator is 0.2-1.0 parts by weight.

3. The method for preparing a modified polytetrafluoroethylene dispersion resin according to claim 1, characterized in that, The initiator is dicumyl peroxide or benzoyl peroxide.

4. The method for preparing a modified polytetrafluoroethylene dispersion resin according to claim 1, characterized in that, The rate of the gradient heating is 3-8°C / min.

5. The process for preparing a modified polytetrafluoroethylene dispersion resin according to claim 4, characterized by, The parameters of the pulse microwave assisted reaction process are: microwave frequency 2.45 GHz, pulse working cycle of heating for 30 seconds and pausing for 30 seconds, and the microwave power is adjusted by real-time monitoring of the temperature to maintain the reaction temperature at 130±1°C.

6. A modified polytetrafluoroethylene dispersion resin characterized by comprising, The modified polytetrafluoroethylene dispersion resin is prepared by the method of any one of claims 1-5.

7. The use of the modified polytetrafluoroethylene dispersion resin of claim 6 in the preparation of polytetrafluoroethylene composite materials or coatings with high bonding strength or high dispersion stability.

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