Hydroxyl vinyl ether modified low-temperature-resistant fluororubber and preparation method thereof

Abstract

The invention discloses hydroxyl vinyl ether modified low-temperature-resistant fluororubber and a preparation method thereof.The preparation method comprises the following steps that vinylidene fluoride and hexafluoropropylene are mixed to serve as an initial mixed monomer to be subjected to a polymerization reaction, in the polymerization reaction process, the mixed monomer and a hydroxyl vinyl ether monomer are supplemented for multiple times to continue to be subjected to the polymerization reaction, and the hydroxyl vinyl ether modified low-temperature-resistant fluororubber is obtained; the fluororubber raw rubber product is the hydroxyl vinyl ether modified low-temperature-resistant fluororubber. According to the invention, the low-temperature resistance of the fluororubber is improved by adding the low-cost hydroxyl vinyl ether comonomer into the structure of common fluororubber; meanwhile, high-cost iodine or bromine perfluoroalkane is replaced as a crosslinking point monomer; a fluorine-free nonionic surfactant which is good to the environment is used for replacing PFOA perfluorooctanoic acid salt to carry out emulsion polymerization reaction.

Description

Technical Field

[0001] The invention relates to the field of rubber, and in particular to a hydroxy vinyl ether modified low-temperature resistant fluororubber and a preparation method thereof. Background Art

[0002] Fluororubber refers to a polymer elastomer with special properties that has fluorine atoms attached to the carbon atoms of the main chain or side chain. This emerging polymer material has excellent properties such as high temperature resistance, chemical resistance, aging resistance, and good physical and mechanical properties. It is widely used in many fields such as aviation, aerospace, automobiles, ships, and petroleum. However, general fluororubber has very poor low-temperature resistance. For example, the maximum temperature at which general fluororubber (types 26 and 246) can maintain rubber elasticity and act as a seal is -15 to -20°C, and it cannot be used well in cold areas.

[0003] The low temperature resistance of rubber refers to the ability of rubber to maintain its elasticity and normal operation at a specified low temperature, which mainly depends on two basic processes of polymers: glass transition and crystallization. The glass transition temperature is the transition temperature of the molecular chain segments of rubber from motion to freezing, and the segment motion is achieved by the rotation within the single bond of the main chain. Therefore, the flexibility of the molecular chain helps to improve the low temperature performance of the material, and increasing the polarity of the molecular chain helps to improve the oil resistance of the material.

[0004] In order to improve the low-temperature resistance of general-purpose fluororubber, three approaches can be taken: (1) changing the copolymer composition to increase the VF2 content in the fluororubber; (2) introducing low-temperature resistant modified copolymer monomers, such as perfluoroalkyl vinyl ether (PAVE), mainly PMVE; or perfluoroalkoxyalkyl vinyl ether (PAAVE), introducing flexible ether bonds in the side chains of fluoroelastomers to reduce Tg; (3) adding low molecular weight fluorinated polymers with lower Tg to the compound.

[0005] However, the high content of vinylidene fluoride in fluororubber will cause fluororubber products to be not alkali-resistant, not hot water-resistant and not water vapor-resistant. The cost of low-temperature-resistant modified monomers, such as perfluoroalkyl vinyl ether (PAVE for short) and perfluoroalkoxyalkyl vinyl ether (PAAVE for short) is high. At the same time, in order to realize the curing of fluororubber polymerized by low-temperature-resistant modified monomers, it is also necessary to introduce crosslinking point monomers with higher costs, such as fluorine-containing chlorine-containing, fluorine-containing bromine-containing or fluorine-containing iodine-containing organic compounds. The fluororubber prepared in this way is very expensive, which seriously limits the promotion and application of low-temperature-resistant fluororubber. Adding low-relative molecular weight fluorine-containing polymers with lower Tg in the rubber compound will cause the mixing process to be difficult, and the vulcanization process is difficult to control, and the aging resistance of fluororubber products will also be reduced.

[0006] The ammonium salt and metal salt of perfluorooctanoic acid (PFOA) is an ionic emulsifier that has been used since the development of tetrafluoroethylene dispersion polymerization. It is also widely used in the emulsion polymerization of fluorinated rubber. Because its molecular structure fluorocarbon chain has strong hydrophobicity, and one end of the carboxylic acid has strong hydrophilicity, it has the property of forming micelles in the medium. Fluorinated monomers have strong hydrophobicity due to the fluorine atom wrapping and are extremely difficult to dissolve in water. The use of perfluorocarboxylate surfactants can minimize the surface tension of water, capture fluorinated monomers, and form micelles, greatly increasing the monomer concentration of fluorinated monomers in micelles. When the triggered free radicals come into contact with the micelle permeable water film, sufficient conditions are provided for the chain growth reaction of the emulsion polymerization reaction, and the chain growth reaction is carried out in the micelle until a high molecular weight fluoropolymer is generated, and the micelle particles filled with polymers are stably present in the water phase. This is the main reason why PFOA has been successfully used as a dispersant used in fluoroolefin emulsion polymerization for decades. PFOA is one of the most difficult organic pollutants found in the world. It has the potential for persistent bioaccumulation and long-range migration, which affects human health and the living environment. Due to the above reasons, PFOA has been listed as a candidate for persistent organic pollutants. Therefore, it is also an urgent task to use non-PFOA substances as dispersants in the polymerization process of fluororubber.

[0007] Commonly used fluororubber cross-linking systems include organic diamines, bisphenols and organic peroxides. The cost of organic diamine cross-linking agents is relatively low, and the prepared fluororubber has good heat and oil resistance, but poor compression deformation resistance, easy aging, poor physical properties, and the generated carbon-nitrogen bonds are easily hydrolyzed; the fluororubber compound of the bisphenol cross-linking agent system has good scorch resistance, and the prepared fluororubber has small compression deformation, but requires a promoter to remove -HF- and form double bonds to enable cross-linking. At the same time, the residual unreacted double bonds are likely to cause fluororubber aging, and an acid absorber is also required to remove HF gas; the fluororubber prepared by organic peroxide has excellent water resistance and acid resistance, excellent aging performance, good chemical medium resistance and compression deformation resistance, but it also needs a free radical scavenger such as TAIC for assistance, and the stability and processing fluidity of the fluororubber compound of the peroxide vulcanization system are poor.

[0008] Therefore, it is desirable to provide a cost-effective low-temperature resistant fluororubber and a suitable cross-linking system to meet its application requirements in cold regions. Summary of the invention

[0009] The purpose of the present invention is to provide a hydroxy vinyl ether modified low temperature resistant fluororubber and a preparation method thereof, which improves the low temperature resistance of fluororubber by adding low-cost comonomers to the structure of ordinary fluororubber; finds suitable cross-linking point monomers to replace the use of high-cost cross-linking point monomers. At the same time, finds a new dispersant to replace PFOA perfluorooctanoate for emulsion polymerization. Furthermore, a suitable cross-linking system can be provided to prepare rubber products with excellent performance.

[0010] In one aspect of the present invention, the present invention proposes a method for preparing a hydroxy vinyl ether modified low temperature resistant fluororubber. According to an embodiment of the present invention, the method comprises the following steps: vinylidene fluoride and hexafluoropropylene are mixed as initial mixed monomers for polymerization reaction, and mixed monomers and hydroxy vinyl ether monomers are added multiple times during the polymerization reaction to continue the polymerization reaction, the polymerization reaction uses water as the reaction medium, and the polymerization reaction system also includes any one or more of a dispersant and an initiator to obtain a fluororubber raw rubber product, namely the hydroxy vinyl ether modified low temperature resistant fluororubber.

[0011] In addition, the method for preparing a hydroxy vinyl ether modified low-temperature resistant fluororubber according to the above embodiment of the present invention may also have the following additional technical features:

[0012] In some embodiments of the present invention, the molar ratio of vinylidene fluoride and hexafluoropropylene in the added mixed monomer is (90:10)-(60:40), the molar ratio of the hydroxy vinyl ether monomer and the mixed monomer is (0.5-50):100, and the solid content of the fluororubber raw rubber product is 5wt%-50wt%.

[0013] In some embodiments of the present invention, the hydroxy vinyl ether monomer is one or more of hydroxybutyl vinyl ether, hydroxyethyl vinyl ether, vinyl diethylene glycol ether, 2-methyl-2-acrylic acid-2,3-dihydroxypropyl ester, vinyloxybutyl polyethylene glycol, 4-allyloxybenzyl alcohol, butanediol monoallyl ether, diethylene glycol monoallyl ether, ethylene glycol monoallyl ether, diethylene glycol vinyl ether, 2-methylallyl alcohol, 3-methyl-2-butene-1-ol, and ethylene glycol vinyl ether. Preferably, hydroxybutyl vinyl ether is used.

[0014] In some embodiments of the present invention, the amount of the additional mixed monomer is sufficient to maintain the polymerization pressure of the polymerization reaction, and the polymerization pressure is 2.0-4.0 MPa.

[0015] In some embodiments of the present invention, the processes of adding the mixed monomer and adding the hydroxy vinyl ether monomer are performed alternately and separately, and the polymerization reaction temperature is 70-100°C.

[0016] The polymerization reaction uses water as a reaction medium, and the polymerization reaction system also includes any one or more of a dispersant and an initiator.

[0017] In some embodiments of the present invention, the dispersant is a fluorine-free nonionic surfactant, and the fluorine-free nonionic surfactant is a polyol nonionic surfactant, such as ethylene glycol ester, glycerol ester, polyglycerol ester, pentose and tetrol ester, sorbitol ester, sorbitol ester, sucrose ester and polyoxyethylene polyol ester, or a mixture thereof. Preferably, the nonionic surfactant is polyoxyethylene sorbitan monostearate (CAS No.: 9005-67-8 ). The amount of the dispersant added is 0.01%-10% of the mass of the reaction medium.

[0018] The initiator is one or both of ammonium persulfate and potassium persulfate, and the added amount of the initiator is 0.1%-15% of the mass of the reaction medium.

[0019] In another aspect of the present invention, the present invention provides a hydroxy vinyl ether modified low temperature resistant fluororubber prepared according to the preparation method of the hydroxy vinyl ether modified low temperature resistant fluororubber, wherein the hydroxy vinyl ether is used as the cross-linking point monomer. The structural formula is as follows:

[0020]

[0021] In another aspect of the present invention, the present invention provides a fluororubber composition. According to an embodiment of the present invention, the fluororubber composition comprises the following components in parts by weight: 100 parts of hydroxy vinyl ether modified low temperature resistant fluororubber, 30 parts of carbon black N9900, 0-10 parts of magnesium oxide, 0-10 parts of calcium hydroxide, and 0.5-10 parts of vulcanization accelerator.

[0022] In addition, a fluororubber composition according to the above embodiment of the present invention may also have the following additional technical features:

[0023] In some embodiments of the present invention, the vulcanization accelerator is a dehydration catalyst, including alkyl tin, fatty acid tin, fatty acid stannous, fatty acid alkyl tin, organic titanium compound, zirconate, bismuth alkyl acid, benzenesulfonic acid, benzenesulfonated acetyl, specifically dibutyltin dilaurate, dibutyltin laurate maleate, di-n-octyltin dilaurate, dodecylbenzenesulfonic acid, dodecylbenzenesulfonic acetyl, toluenesulfonic acid, toluenesulfonic acetyl methanesulfonated acetyl, teasulfonic acid, tetrapropylbenzenesulfonic acid, stannous octoate, organic titanium compound (ZL-928), tetrabutyl zirconate, dibutyltin diacetate, di-n-butyltin bis(monooctyl maleate), p-toluenesulfonic acid, dodecylbenzenesulfonic acid, bismuth isooctanoate, and one or more thereof are selected; preferably dibutyltin dilaurate (DBTDL).

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) Hydroxy vinyl ether is used as a comonomer, and a copolymer structure containing an ether bond is added to the structure of ordinary fluororubber to improve the low-temperature resistance of fluororubber. The hydroxy vinyl ether modified low-temperature resistant fluororubber provided by the present invention has a low glass transition temperature and a low TR-10. Compared with fluororubber, the other properties of the obtained hydroxy vinyl ether modified low-temperature resistant fluororubber remain basically unchanged, which can ensure its application in the low-temperature field.

[0026] (2) The hydroxy vinyl ether modified low-temperature resistant fluororubber provided by the present invention has low cost. Compared with perfluoroalkyl vinyl ether (PAVE) and perfluoroalkoxyalkyl vinyl ether (PAAVE), the present invention uses hydroxy vinyl ether as a cross-linking point monomer to replace the use of bromine-containing and iodine-containing cross-linking point monomers with higher costs, which can improve the flexibility of the molecular chain, help improve the low-temperature performance of the material, and reduce costs.

[0027] (3) The present invention introduces an ether structure into the added hydroxy vinyl ether monomer, and the molar ratio of the hydroxy vinyl ether monomer in the added monomer to the mixed monomer is preferably (0.5-50):100; within this range, the content of perfluoromethyl vinyl ether monomer in the obtained hydroxy vinyl ether modified low-temperature resistant fluororubber segment can be 1-20%, and a small amount is added and added alternately and separately, and evenly distributed in the flexible segment; if the amount of hydroxy vinyl ether monomer added is too high, the content of hydroxy vinyl ether monomer connected to the low-temperature resistant fluororubber segment is too high, and the high temperature resistance of the fluororubber will be reduced; if the amount of hydroxy vinyl ether monomer added is too low, the effective content of hydroxy vinyl ether monomer connected to the fluororubber molecular segment cannot be met, which also affects the low temperature resistance and curing performance of the product.

[0028] (4) Since hydroxy vinyl ether is used as a polymerization monomer in the polymerization process of low-temperature resistant fluororubber, polar hydroxyl groups are introduced into the molecular chain of fluororubber. On this basis, polyols in polyol nonionic surfactants are used instead of PFOA perfluorooctanoate as dispersants for emulsion polymerization. Using polyol nonionic surfactants as dispersants can attract the hydroxyl groups on the grafted hydroxy vinyl ethers in the polymers at the early stage of polymerization, and then form micelles; the polymers in the micelles can capture fluorinated monomers; at the same time, the hydroxyl groups of the polyol nonionic surfactants can form hydrogen bonds with the hydroxyl groups of the hydroxy vinyl ethers, attracting free hydroxy vinyl ethers, providing sufficient conditions for the chain growth reaction of the emulsion polymerization reaction, and carrying out chain growth reactions in the micelles until high molecular weight fluoropolymers are generated, and the micelle particles filled with polymers are stably present in the aqueous phase.

[0029] (5) The present invention introduces a hydroxy vinyl ether structure into the fluororubber polymer structure, adopts a non-ionic surfactant to replace PFOA perfluorooctanoate as a dispersant, and carries out an emulsion polymerization reaction, thereby providing a method for replacing PFOA as a dispersant for the preparation of fluoropolymers and expanding the PFOA replacement route.

[0030] (6) The present invention uses one or more of a dehydration catalyst such as alkyl tin, fatty acid tin, fatty acid stannous, fatty acid alkyl tin, organic titanium compound, zirconate, alkyl acid bismuth, benzenesulfonic acid, and benzenesulfonated acetyl as a vulcanization (cross-linking) accelerator, and dibutyltin dilaurate (DBTDL) is suitable as a cross-linking accelerator. At a certain temperature, the cross-linking accelerator can act as a dehydration catalyst to promote the reaction of two hydroxyl groups to release one water molecule H2O to form an ether bond, thereby allowing the hydroxy vinyl ether modified low-temperature resistant fluororubber to form a three-dimensional cross-linked structure. Compared with the above three fluororubber cross-linking systems, a dehydration catalyst is used as a cross-linking accelerator for hydroxy vinyl ether modified fluororubber. Combined with the hydroxyl group of hydroxy vinyl ether modified fluororubber, dehydration is used to form ether bonds for cross-linking. The ether bonds have good flexibility, and the prepared ether-bond cross-linked fluororubber has excellent low-temperature resistance. At the same time, the ether bonds are relatively stable, and the prepared fluororubber has good heat resistance, oil resistance and aging resistance. Although a water absorbent is needed to remove moisture generated by the dehydration reaction, the magnesium oxide present in the vulcanization system has a water absorption function itself, and the magnesium hydroxide generated after absorbing water can be used as a filler. No other accelerators are needed in the vulcanization system to remove hydrofluoric acid HF in the molecular chain, and unstable double bonds will not be formed. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] Example 1

[0033] A method for preparing hydroxy vinyl ether modified low-temperature resistant fluororubber comprises the following steps:

[0034] (1) Add 13 L of deionized water to a 20 L reactor. The reactor should be evacuated. When the oxygen content is ≤30 ppm, add 15 g of polyoxyethylene sorbitan monostearate and heat the contents of the reactor to 90° C.

[0035] (2) Add vinylidene fluoride VDF and hexafluoropropylene HFP in a molar ratio of 75:25 as the initial mixed monomers into the reactor, and raise the reactor pressure to 2.5MPa; and add 10g of potassium persulfate to carry out polymerization reaction. When the pressure in the reactor is lower than 2.48MPa, add a mixed monomer of vinylidene fluoride and hexafluoropropylene in a molar ratio of 75:25, so that the pressure in the reactor reaches 2.5MPa; then inject hydroxybutyl vinyl ether into the reactor (the molar ratio of hydroxybutyl vinyl ether to the introduced mixed monomer is 15:100). When the solid content of the emulsion reaches about 30wt%, the polymerization reaction is terminated, and the unreacted monomers are recovered to obtain an emulsion containing hydroxyvinyl ether modified low-temperature resistant fluororubber;

[0036] (3) The emulsion is placed in a coagulation barrel, and then a certain amount of MgCl2 is added for coagulation, and then vacuum dried at about 110°C to obtain about 4 kg of hydroxy vinyl ether modified low-temperature resistant fluororubber.

[0037] Example 2

[0038] A method for preparing hydroxy vinyl ether modified low-temperature resistant fluororubber comprises the following steps:

[0039] (1) Add 13 L of deionized water to a 20 L reactor. The reactor should be evacuated. When the oxygen content is ≤30 ppm, add 15 g of polyoxyethylene sorbitan monostearate and heat the contents of the reactor to 90° C.

[0040] (2) Add vinylidene fluoride and hexafluoropropylene in a molar ratio of 90:10 as the initial mixed monomers into the reactor, and raise the reactor pressure to 2.5MPa; and add 10g of potassium persulfate to carry out polymerization reaction. When the pressure in the reactor is lower than 2.48MPa, add a mixed monomer of vinylidene fluoride and hexafluoropropylene in a molar ratio of 90:10, so that the pressure in the reactor reaches 2.5MPa; then inject hydroxybutyl vinyl ether into the reactor (the molar ratio of hydroxybutyl vinyl ether to the introduced mixed monomer is 15:100). When the solid content of the emulsion reaches about 30wt%, the polymerization reaction is terminated, and the unreacted monomers are recovered to obtain an emulsion containing hydroxyvinyl ether modified low-temperature resistant fluororubber;

[0041] (3) The emulsion is placed in a coagulation barrel, and then a certain amount of MgCl2 is added for coagulation, and then vacuum dried at about 110°C to obtain about 4 kg of hydroxy vinyl ether modified low-temperature resistant fluororubber.

[0042] Example 3

[0043] A method for preparing hydroxy vinyl ether modified low-temperature resistant fluororubber comprises the following steps:

[0044] (1) Add 13 L of deionized water to a 20 L reactor. The reactor should be evacuated. When the oxygen content is ≤30 ppm, add 15 g of polyoxyethylene sorbitan monostearate and heat the contents of the reactor to 90° C.

[0045] (2) Add vinylidene fluoride and hexafluoropropylene in a molar ratio of 60:40 as the initial mixed monomers into the reactor, and raise the pressure of the reactor to 2.5MPa; and add 10g of potassium persulfate to carry out polymerization reaction. When the pressure in the reactor is lower than 2.48MPa, add a mixed monomer of vinylidene fluoride and hexafluoropropylene in a molar ratio of 60:40, so that the pressure in the reactor reaches 2.5MPa; then inject hydroxybutyl vinyl ether into the reactor (the molar ratio of hydroxybutyl vinyl ether to the introduced mixed monomer is 15:100). When the solid content of the emulsion reaches about 30wt%, the polymerization reaction is terminated, and the unreacted monomers are recovered to obtain an emulsion containing hydroxyvinyl ether modified low-temperature resistant fluororubber;

[0046] (3) The emulsion is placed in a coagulation barrel, and then a certain amount of MgCl2 is added for coagulation, and then vacuum dried at about 110°C to obtain about 4 kg of hydroxy vinyl ether modified low-temperature resistant fluororubber.

[0047] Example 4

[0048] A method for preparing hydroxy vinyl ether modified low-temperature resistant fluororubber comprises the following steps:

[0049] (1) Add 13 L of deionized water to a 20 L reactor. The reactor should be evacuated. When the oxygen content is ≤30 ppm, add 15 g of polyoxyethylene sorbitan monostearate and heat the contents of the reactor to 90° C.

[0050] (2) Add vinylidene fluoride and hexafluoropropylene in a molar ratio of 75:25 as the initial mixed monomers into the reactor, and raise the reactor pressure to 2.5 MPa; and add 10 g of potassium persulfate to carry out the polymerization reaction. When the pressure in the reactor is lower than 2.48 MPa, add a mixed monomer of vinylidene fluoride and hexafluoropropylene in a molar ratio of 75:25, so that the pressure in the reactor reaches 2.5 MPa; then inject hydroxybutyl vinyl ether into the reactor (the molar ratio of hydroxybutyl vinyl ether to the introduced mixed monomer is 7.5:100). When the solid content of the emulsion reaches about 30 wt%, the polymerization reaction is terminated, and the unreacted monomers are recovered to obtain an emulsion containing hydroxy vinyl ether modified low-temperature resistant fluororubber;

[0051] (3) The emulsion is placed in a coagulation barrel, and then a certain amount of MgCl2 is added for coagulation, and then vacuum dried at about 110°C to obtain about 4 kg of hydroxy vinyl ether modified low-temperature resistant fluororubber.

[0052] Example 5

[0053] A method for preparing hydroxy vinyl ether modified low-temperature resistant fluororubber comprises the following steps:

[0054] (1) Add 13 L of deionized water to a 20 L reactor. The reactor should be evacuated. When the oxygen content is ≤30 ppm, add 15 g of polyoxyethylene sorbitan monostearate and heat the contents of the reactor to 90° C.

[0055] (2) Add vinylidene fluoride and hexafluoropropylene in a molar ratio of 75:25 as the initial mixed monomers into the reactor, and raise the reactor pressure to 2.5MPa; and add 10g of potassium persulfate to carry out polymerization reaction. When the pressure in the reactor is lower than 2.48MPa, add a mixed monomer of vinylidene fluoride and hexafluoropropylene in a molar ratio of 60:40, so that the pressure in the reactor reaches 2.5MPa; then inject hydroxybutyl vinyl ether into the reactor (the molar ratio of hydroxybutyl vinyl ether to the introduced mixed monomer is 30:100). When the solid content of the emulsion reaches about 30wt%, the polymerization reaction is terminated, and the unreacted monomers are recovered to obtain an emulsion containing hydroxyvinyl ether modified low-temperature resistant fluororubber;

[0056] (3) The emulsion is placed in a coagulation barrel, and then a certain amount of MgCl2 is added for coagulation, and then vacuum dried at about 110°C to obtain about 4 kg of hydroxy vinyl ether modified low-temperature resistant fluororubber.

[0057] Comparative Example 1

[0058] A method for preparing hydroxy vinyl ether modified low-temperature resistant fluororubber comprises the following steps:

[0059] (1) Add 13 L of deionized water to a 20 L reactor. The reactor should be evacuated. When the oxygen content is ≤30 ppm, add 15 g of sodium perfluorooctanoate and heat the contents of the reactor to 90 °C.

[0060] (2) Add vinylidene fluoride and hexafluoropropylene in a molar ratio of 75:25 as the initial mixed monomers into the reactor, and raise the reactor pressure to 2.5 MPa; and add 10 g of potassium persulfate to carry out the polymerization reaction. When the pressure in the reactor is lower than 2.48 MPa, add a mixed monomer of vinylidene fluoride and hexafluoropropylene in a molar ratio of 75:25, so that the pressure in the reactor reaches 2.5 MPa; then inject hydroxybutyl vinyl ether into the reactor (the molar ratio of hydroxybutyl vinyl ether to the introduced mixed monomer is 15:100). When the solid content of the emulsion reaches about 30 wt%, the polymerization reaction is terminated, and the unreacted monomers are recovered to obtain an emulsion containing hydroxy vinyl ether modified low-temperature resistant fluororubber;

[0061] (3) The emulsion is placed in a coagulation barrel, and then a certain amount of MgCl2 is added for coagulation, and then vacuum dried at about 110°C to obtain about 4 kg of hydroxy vinyl ether modified low-temperature resistant fluororubber.

[0062] Comparative Example 2

[0063] A method for preparing hydroxy vinyl ether fluororubber comprises the following steps:

[0064] (1) Add 13 L of deionized water to a 20 L reactor. The reactor should be evacuated. When the oxygen content is ≤30 ppm, add 15 g of sodium perfluorooctanoate and heat the contents of the reactor to 90 °C.

[0065] (2) Add vinylidene fluoride and hexafluoropropylene in a molar ratio of 75:25 as the initial mixed monomers into the reactor, and raise the reactor pressure to 2.5 MPa; and add 10 g of potassium persulfate to carry out polymerization reaction. When the pressure in the reactor is lower than 2.48 MPa, add a mixed monomer of vinylidene fluoride and hexafluoropropylene in a molar ratio of 75:25, so that the pressure in the reactor reaches 2.5 MPa. When the solid content of the emulsion reaches about 30 wt%, the polymerization reaction is terminated, and the unreacted monomers are recovered to obtain an emulsion containing hydroxy vinyl ether modified low-temperature resistant fluororubber;

[0066] (3) The emulsion is placed in a coagulation barrel, and then a certain amount of MgCl2 is added for coagulation, and then vacuum dried at about 110°C to obtain about 4 kg of hydroxy vinyl ether modified low-temperature resistant fluororubber.

[0067] Performance Testing

[0068] The Mooney viscosity, fluorine content and glass transition temperature of the hydroxy vinyl ether modified low temperature resistant fluororubber provided in the test examples and comparative examples are tested in the following manner:

[0069] Mooney Viscosity: Measured in accordance with ASTM D1646 using a L (large) spindle at 121°C (unless otherwise stated) with a one minute preheat time and a 10 minute spindle run time.

[0070] Fluorine content: using NMR nuclear magnetic resonance F19 fluorine spectroscopy.

[0071] Glass transition temperature: GB / T19466.2 Plastics Differential Scanning Calorimetry (DSC) Part 2: Determination of glass transition temperature.

[0072] The Mooney viscosity, fluorine content and glass transition temperature of the rubber products of Examples 1-5 and Comparative Examples 1-2 are shown in the following table.

[0073] Table 1 Rubber properties of Examples 1-5 and Comparative Examples 1-2

[0074]

[0075] Example 6

[0076] A fluororubber composition is prepared from the hydroxy vinyl ether modified low temperature resistant fluororubber of Examples 1-5 and Comparative Examples 1-2. The specific formula and preparation method are as follows:

[0077] The formula of the fluororubber composition of Examples 1-5 and Comparative Example 1 includes the following components in parts by weight: 100 parts of fluororubber, 10 parts of N990 carbon black, 8 parts of magnesium oxide, 4 parts of calcium hydroxide, 2 parts of dibutyltin dilaurate (DBTDL), and 2 parts of palm oil.

[0078] The formula of the fluororubber composition of Comparative Example 2 includes the following components in parts by weight: 100 parts of fluororubber, 10 parts of N990 carbon black, 8 parts of magnesium oxide, 4 parts of calcium hydroxide, 2 parts of bisphenol AF, 2 parts of BPP, and 2 parts of palm oil.

[0079] The first stage vulcanization is 175℃×10min, and the second stage vulcanization is 175℃×24h; the compression test conditions are: 25% compression rate, 200 degrees, 72 hours.

[0080] The performance test method is as follows:

[0081] Tensile properties: GB / T528 Determination of tensile stress-strain properties of vulcanized rubber or thermoplastic rubber.

[0082] Compression set: GB / T7759 Determination of compression set of vulcanized rubber and thermoplastic rubber at room temperature, high temperature and low temperature.

[0083] TR-10 Temperature: ASTM D1053 test method.

[0084] Table 2 Performance results of fluororubber compositions prepared from Examples 1-5 and Comparative Examples 1-2

[0085] sample Tensile strength, MPa Pressure change, % TR-10,℃ Example 1 15.6 18.5 -32.1 Example 2 15.4 18.9 -32.1 Example 3 14.5 19.2 -32.3 Example 4 12.3 17.3 -26.8 Example 5 19.5 23.1 -38.2 Comparative Example 1 15.2 17.4 -32.3 Comparative Example 2 11.3 16.5 -15.8

[0086] As can be seen from Table 2, the performance of the hydroxy vinyl ether modified low-temperature resistant fluororubber is compared with that of the ordinary fluororubber (Example 1 and Comparative Example 2), the tensile strength is improved, the TR-10 brittle temperature is significantly increased, and the pressure change is also improved. It can be considered that the hydroxy vinyl ether modified low-temperature resistant fluororubber can meet the use requirements of fluororubber; at the same time, hydroxybutyl vinyl ether, as a cross-linking point monomer, can achieve cross-linking of the hydroxy vinyl ether modified low-temperature resistant fluororubber under the action of the dehydration catalyst vulcanization system.

[0087] By using polyoxyethylene sorbitan monostearate as a dispersant (Example 1) and sodium perfluorooctanoate as a dispersant (Comparative Example 1) as a dispersant for comparison, the performance of the obtained hydroxy vinyl ether modified low temperature resistant fluororubber is slightly different. This shows that the performance of the hydroxy vinyl ether modified low temperature resistant fluororubber can reach the level of Comparative Example 1, but the cost is much lower, and perfluorooctanoate is not used in the synthesis process, which is more environmentally friendly.

[0088] The changes in the composition of the mixed monomers of VDF and HFP (Example 1, Example 2 and Example 3) have little effect on the performance of the hydroxy vinyl ether modified low-temperature resistant fluororubber.

[0089] Similarly, the change of alternating feeding time has a certain influence on the performance of hydroxy vinyl ether modified low temperature resistant fluororubber. When the alternating feeding interval time increases, the tensile strength decreases, the TR-10 brittle temperature decreases, and the pressure change increases; when the alternating feeding interval time decreases, the tensile strength increases, the TR-10 brittle temperature increases, and the pressure change decreases.

[0090] The feeding ratio of hydroxybutyl vinyl ether (Example 1, Example 4 and Example 5) has a great influence on the performance of hydroxy vinyl ether modified low temperature resistant fluororubber. When the feeding ratio of hydroxybutyl vinyl ether is high (Example 5), the tensile strength of hydroxy vinyl ether modified low temperature resistant fluororubber is improved, the TR-10 brittle temperature is reduced, but the pressure change is increased. When the feeding ratio of hydroxybutyl vinyl ether is low (Example 4), the tensile strength of hydroxy vinyl ether modified low temperature resistant fluororubber is reduced, the TR-10 brittle temperature is increased, and the pressure change is slightly reduced.

[0091] In summary, the molar ratio of VDF:HFP in the mixed monomer is 75:25, the molar ratio of the mixed monomer to hydroxybutyl vinyl ether is 100:15, and polyoxyethylene sorbitan monostearate is used as a dispersant. The prepared hydroxy vinyl ether modified low-temperature resistant fluororubber has good cost performance.

[0092] The above contents are merely examples and explanations of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the structure of the present invention or exceed the scope defined by the claims, they shall all fall within the protection scope of the present invention.

Claims

1. A method for preparing a hydroxy vinyl ether modified low temperature resistant fluororubber, characterized in that: The following steps are involved: Vinylidene fluoride and hexafluoropropylene are mixed as initial mixed monomers for polymerization reaction, and mixed monomers and hydroxy vinyl ether monomers are added during the polymerization reaction to continue the polymerization reaction. The polymerization reaction uses water as a reaction medium, and the polymerization reaction system also includes any one or more of a dispersant and an initiator to obtain a fluororubber raw rubber product, namely the hydroxy vinyl ether modified low-temperature resistant fluororubber.

2. The method for preparing a hydroxy vinyl ether modified low temperature resistant fluororubber according to claim 1, characterized in that: The molar ratio of vinylidene fluoride to hexafluoropropylene in the mixed monomer is (90:10)-(60:40), the molar ratio of the hydroxy vinyl ether monomer to the mixed monomer is (0.5-50):100, and the solid content of the fluororubber raw rubber product is 5wt%-50wt%.

3. The method for preparing a hydroxy vinyl ether modified low temperature resistant fluororubber according to claim 1, characterized in that: The hydroxy vinyl ether monomer is one or more of hydroxybutyl vinyl ether, hydroxyethyl vinyl ether, vinyl diethylene glycol ether, 2-methyl-2-acrylate-2,3-dihydroxypropyl ester, vinyloxybutyl polyethylene glycol, 4-allyloxybenzyl alcohol, butanediol monoallyl ether, diethylene glycol monoallyl ether, ethylene glycol monoallyl ether, diethylene glycol vinyl ether, 2-methylallyl alcohol, 3-methyl-2-butene-1-ol, and ethylene glycol vinyl ether.

4. The method for preparing a hydroxy vinyl ether modified low temperature resistant fluororubber according to claim 1, characterized in that: The mixed monomer is added to maintain the polymerization pressure of the polymerization reaction, and the polymerization pressure is 2.0-4.0 MPa; the addition of the mixed monomer and the addition of the hydroxy vinyl ether monomer are performed alternately and separately, and the polymerization temperature is 70-100°C.

5. The method for preparing a hydroxy vinyl ether modified low temperature resistant fluororubber according to claim 1, characterized in that: The dispersant is a fluorine-free nonionic surfactant, and the added amount of the dispersant is 0.01%-10% of the mass of the reaction medium; the initiator is one or both of ammonium persulfate and potassium persulfate, and the added amount of the initiator is 0.1%-15% of the mass of the reaction medium.

6. The method for preparing a hydroxy vinyl ether modified low temperature resistant fluororubber according to claim 5, characterized in that: The fluorine-free nonionic surfactant is a polyol nonionic surfactant.

7. The method for preparing a hydroxy vinyl ether modified low temperature resistant fluororubber according to claim 1, characterized in that: The hydroxy vinyl ether is used as a cross-linking point monomer.

8. A hydroxy vinyl ether modified low temperature resistant fluororubber prepared by the method for preparing hydroxy vinyl ether modified low temperature resistant fluororubber according to any one of claims 1 to 7.

9. A fluororubber composition, characterized in that: The invention comprises the following components in parts by weight: 100 parts of the hydroxy vinyl ether modified low-temperature resistant fluororubber as claimed in claim 8, 30 parts of carbon black N9900, 0-10 parts of magnesium oxide, 0-10 parts of calcium hydroxide and 0.5-10 parts of a vulcanization accelerator.

10. A fluororubber composition according to claim 9, characterized in that: The vulcanization accelerator is a dehydration catalyst.

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