Preparation method of nitrile rubber with improved oil resistance

Abstract

The invention relates to a preparation method of high-oil-resistance nitrile rubber, which at least comprises the following steps of: adding butadiene, acrylonitrile, water, a composite emulsification system, a part of molecular weight regulator and an initiator into a polymerization kettle, and synthesizing nitrile rubber cement by adopting an intermittent feeding mode of replenishing the molecular weight regulator in batches and a thermal polymerization process, and adding a terminating agent and an anti-aging agent, degassing, condensing, washing and drying to obtain the high-strength nitrile rubber product. The nitrile rubber has Mooney viscosity # imgabs0 # tensile strength of more than or equal to 27.5 MPa and elongation at break of more than or equal to 450%, and can meet the application requirements in the fields of automobiles, aerospace, sealing washers and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of rubber preparation, and in particular relates to a method for preparing nitrile rubber with improved oil resistance. Background Art

[0002] Nitrile Butadiene Rubber (NBR) is widely used in the fields of automobiles, aerospace, sealing gaskets, etc. due to its excellent oil resistance, benzene resistance, heat resistance and physical and mechanical properties. The above fields have more stringent performance requirements on rubber, and have higher requirements on rubber's oil resistance, bonded acrylonitrile, Mooney viscosity, etc.

[0003] In the polymerization process, in the Japanese patent with publication number JPH05222267A, by appropriately adjusting the polymerization temperature, using potassium persulfate as an initiator, anionic surfactants such as potassium oleate and sodium dodecylbenzene sulfonate or non-ionic surfactants such as polyoxyethylene alkyl ether as emulsifiers, and dodecyl mercaptan as a regulator, NBR is obtained. The molecular weight distribution index is 30-150, the molecular weight distribution index is 5-8, the gel content is less than 5%, and the combined acrylonitrile content is 10%-45%, which is used in rubber products such as rubber rollers. In the Chinese invention patent with publication number CN103665265B, by properly adjusting the polymerization temperature, using diisopropylbenzene hydroperoxide as an initiator, rosin acid soap, sodium salt of naphthalenesulfonic acid and formaldehyde condensate as an emulsifier, and dodecane mercaptan as a regulator, NBR is obtained. The content of acrylonitrile is 18% to 46%, the tensile strength is 10 to 22 MPa, and it is used in rubber products industries such as rubber rollers.

[0004] In the prior art, the acrylonitrile content of nitrile rubber is mostly less than 40%, which cannot meet the demand for rubber in the fields of automobiles, aerospace, sealing gaskets, etc., and the monomer conversion rate during the polymerization process is about 75%, which is not high enough. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing highly oil-resistant nitrile rubber, which solves the problem in the prior art that the combined acrylonitrile content is less than 40% and the conversion rate is not high enough. The present invention achieves the improvement of the polymerization conversion rate while ensuring that the rubber properties are not affected by accurately controlling the pH value of the polymerization system. On the basis of the prior art, a nitrile rubber with high oil resistance, higher combined acrylonitrile and better Mooney viscosity is prepared.

[0006] The technical scheme adopted by the present invention is: a method for preparing nitrile rubber with improved oil resistance, after adding polymerization monomers, water, emulsifiers, initiators and molecular weight regulators, high-temperature emulsion polymerization is carried out at a pH of 10.0-11.5 to obtain nitrile rubber mortar; the molecular weight regulator is added in at least two batches, the polymerization monomers are butadiene and acrylonitrile, the emulsifier includes dodecylbenzenesulfonic acid and naphthalenesulfonic acid formaldehyde condensate sodium salt, wherein, by weight, the amount of dodecylbenzenesulfonic acid is 2-4.5 parts, and the amount of naphthalenesulfonic acid formaldehyde condensate sodium salt is 0.4-1 part; a terminator and an antioxidant are added to the nitrile rubber mortar, and then the nitrile rubber is obtained after degassing, coagulation, washing and drying in sequence.

[0007] The present invention does not particularly limit the specific ratio of the polymerization monomers butadiene and acrylonitrile. The ratio commonly used in the prior art for preparing oil-resistant nitrile rubber can be used, such as 50 to 60 parts of butadiene and 40 to 50 parts of acrylonitrile, more preferably 50 to 55 parts of butadiene and 45 to 50 parts of acrylonitrile. The acrylonitrile content can be higher, and the polymerization formula can be adjusted according to product requirements. The present invention does not particularly limit the addition method of the monomers. The monomers can be added once or multiple times. For example, when the acrylonitrile ratio is high and the butadiene ratio is low, the butadiene monomer can be added in batches multiple times or continuously, and the present invention does not particularly limit it.

[0008] The synthesis scheme of the nitrile rubber of the present invention is high-temperature emulsion polymerization. The polymerization temperature used in the high-temperature emulsion polymerization commonly used in the technical field can be any, and is not particularly limited, such as 25 to 45° C., etc. The polymerization reaction temperature is preferably controlled at 30 to 40° C., and more preferably higher than 30° C.

[0009] The present invention does not particularly limit the initiator system and the amount of addition. The initiator usually used in the high-temperature emulsion polymerization of nitrile rubber can be used. For example, the initiator system can use persulfates, such as potassium persulfate, ammonium persulfate and other water-soluble initiators, and the amount of addition is usually 0.2 to 1.0 parts. The type and amount of terminator and antioxidant are also not particularly limited. General terminators and antioxidants can be used. For example, the terminator can be at least one of sodium nitrite, hydroxylamine sulfate and diethylhydroxylamine. Other terminators can also be used. The amount of terminator added is usually 0.05 to 0.5 parts. The antioxidant can be polybutylbisphenol, diphenylamine derivatives and other antioxidants, and the amount of antioxidant added is usually 0.5 to 2 parts.

[0010] The present invention does not particularly limit the timing of adding the terminator, and the desired nitrile rubber mortar can be selected to achieve different ranges of conversion rates according to product requirements. The present invention preferably adds the terminator when the reaction conversion rate reaches 85-90%.

[0011] The present invention also does not particularly limit the molecular weight regulator and the amount thereof. The molecular weight regulator and the amount thereof commonly used in nitrile rubber can be used. Common molecular weight regulators include tert-dodecyl mercaptan, n-dodecyl mercaptan, regulator 4, etc., and tert-dodecyl mercaptan is preferably used as the molecular weight regulator. The molecular weight regulator is usually used in an amount of 0.2 to 1 part, more preferably 0.3 to 0.7 part, and the amount thereof can be adjusted according to the product performance requirements and the type of molecular weight regulator.

[0012] In the present invention, the molecular weight regulator is used multiple times in the emulsion polymerization, such as adding the molecular weight regulator in batches for more than 2 times, such as adding the molecular weight regulator in different polymerization kettles according to the polymerization conversion rate in continuous polymerization, and preferably adding the molecular weight regulator in 3 times in intermittent polymerization. The present invention does not particularly limit the proportion of the molecular weight regulator added in batches. When adding twice, it is preferred to add the molecular weight regulator when the reaction conversion rate reaches 35-40%; when the reaction conversion rate reaches 50-55%, add the molecular weight regulator again. More preferably, based on the total amount of the molecular weight regulator added as 100%, it is preferred that the first addition amount is 20-35%, and the second addition amount is 20-35%.

[0013] In the present invention, the pH value of the polymerization system needs to be controlled to be 10.0-11.5, and the more preferred pH value is 10.0-11.0; if the pH value is not within the range required by the present invention, being too high or too low will prolong the polymerization reaction time and reduce the physical and mechanical properties of the product.

[0014] The present invention requires the use of a composite emulsification system, and the composite emulsifier contains at least dodecylbenzenesulfonic acid and naphthalenesulfonic acid formaldehyde condensate sodium salt, wherein the amount of dodecylbenzenesulfonic acid is 2 to 4.5 parts, and the amount of naphthalenesulfonic acid formaldehyde condensate sodium salt is 0.4 to 1 part. When the amount of naphthalenesulfonic acid formaldehyde condensate sodium salt is too low, such as only 0.3 parts, the stability of the polymer emulsion will be reduced, and the phenomenon of glue hanging will be easy to occur during the polymerization process.

[0015] The present invention needs to add 2 to 4.5 parts of dodecylbenzene sulfonic acid in the composite emulsification system. The dodecylbenzene sulfonic acid and sodium dodecylbenzene sulfonate have different effects. Only sodium dodecylbenzene sulfonate is added without adding dodecylbenzene sulfonic acid, and its effect is different from the present invention, because sodium dodecylbenzene sulfonate is a saponification product of dodecylbenzene sulfonic acid. Due to the use of dodecylbenzene sulfonic acid, not only sodium dodecylbenzene sulfonate exists in the reaction system, but also part of dodecylbenzene sulfonic acid is not saponified, and a synergistic effect will be generated between the two, so that the stability of the entire polymerization system is improved, and the polymerization reaction efficiency is improved. Therefore, dodecylbenzene sulfonic acid in the composite emulsification system of the present invention cannot be replaced by sodium dodecylbenzene sulfonate.

[0016] The present invention does not exclude the addition of other emulsifiers in addition to dodecylbenzenesulfonic acid and naphthalenesulfonic acid formaldehyde condensate sodium salt to the composite emulsification system, such as potassium oleate, potassium stearate, etc. The usage amount of the composite emulsifier is preferably 2.4 to 6 parts, more preferably 2.5 to 5.5 parts.

[0017] The present invention also does not exclude the addition of other commonly used additives for nitrile emulsion polymerization into the polymerization system, such as soft water, electrolytes, reducing agents, etc., and the addition amount range is the general addition amount range.

[0018] Unless otherwise specified, the parts described in the present invention refer to 100 parts by mass of the total amount of polymerized monomers. The present invention also provides a more preferred method for preparing nitrile rubber, comprising the following steps:

[0019] The invention discloses a method for preparing the invention, based on 100 parts by weight of butadiene and acrylonitrile, comprising 250-280 parts of soft water, 50-55 parts of butadiene and 45-50 parts of acrylonitrile; an emulsifier is a composite system containing dodecylbenzenesulfonic acid and sodium salt of naphthalenesulfonic acid formaldehyde condensate, wherein the amount of dodecylbenzenesulfonic acid is 2-4.5 parts and the amount of sodium salt of naphthalenesulfonic acid formaldehyde condensate is 0.4-1 parts; an initiator is a persulfate, and the amount thereof is 0.1-0.5 parts; a reducing agent such as triethanolamine is 0.1-0.3 parts; and a reducing agent such as triethanolamine is 0.1-0.3 parts. parts; the molecular weight regulator is added in an amount of 0.3 to 0.7 parts in three times; the above raw materials are mixed to cause polymerization reaction, and the pH value of the polymerization system is 10.0-11.5; when the reaction conversion rate reaches 35 to 40%, a secondary molecular weight regulator is added; when the reaction conversion rate reaches 50 to 55%, a tertiary molecular weight regulator is added, and when the reaction conversion rate reaches 85 to 90%, a terminator and an antioxidant are added, and the nitrile rubber is obtained after degassing, coagulation, washing and drying.

[0020] More preferably, the preparation method of nitrile rubber comprises the steps of:

[0021] The invention relates to a method for preparing a preparation method of the present invention. The preparation method comprises 275 parts of soft water, 50-55 parts of butadiene and 45-50 parts of acrylonitrile based on 100 parts by weight of the addition amount of butadiene and acrylonitrile. The emulsifier is a composite system of dodecylbenzenesulfonic acid and naphthalenesulfonic acid formaldehyde condensate sodium salt, and the emulsifier is used in an amount of 2.5-5 parts, wherein the dodecylbenzenesulfonic acid is used in an amount of 2-4.5 parts, and the naphthalenesulfonic acid formaldehyde condensate sodium salt is used in an amount of 0.4-1 part. The initiator is a persulfate, and the amount thereof is 0.1-0.5 parts. The triethanolamine is 0.1 parts. The addition amount of the molecular weight regulator is 0.3-0.7 parts, and the addition is divided into three times.

[0022] The above raw materials are mixed to cause polymerization reaction, and the pH value of the polymerization system is 10.0-11.0; when the reaction conversion rate reaches 35-40%, a secondary molecular weight regulator is added; when the reaction conversion rate reaches 50-55%, a tertiary molecular weight regulator is added, and when the reaction conversion rate reaches 85-90%, the material is discharged after cooling to 20-25°C, a terminator and an antioxidant are added, and the nitrile rubber is obtained after degassing, condensation, washing and drying. The polymerization conversion rate of the nitrile rubber of the present invention can reach 85-90% at most, further improving the primary utilization rate of the monomer, reducing the energy consumption of monomer recovery, and increasing the production capacity of the polymerization equipment.

[0023] The beneficial effect of the present invention is that the present invention uses sodium salt of dodecylbenzenesulfonic acid and naphthalenesulfonic acid formaldehyde condensate containing a specific ratio as a composite emulsification system, controls the pH value of the polymerization system, and adopts a thermal emulsion polymerization process to synthesize highly oil-resistant nitrile rubber. The nitrile rubber produced by the present invention can meet the application requirements of the fields of automobiles, aerospace, sealing gaskets, etc.; in addition, when the present invention is used to synthesize the mortar, the polymerization process is stable and the energy consumption is low. The preferred high oil-resistant nitrile rubber product indicators are: a combined acrylonitrile content of 40-45%, Mooney viscosity 90~120, tensile strength ≥27.5MPa, elongation at break ≥450%. DETAILED DESCRIPTION

[0024] The present invention is described in detail below in conjunction with specific implementation modes.

[0025] The invention discloses a method for preparing highly oil-resistant nitrile rubber. The method adopts an emulsifying system compounded with sodium salt of dodecylbenzenesulfonic acid and naphthalenesulfonic acid formaldehyde condensate, controls the pH value of the polymerization system and uses a thermal intermittent emulsion polymerization process to prepare the highly oil-resistant nitrile rubber.

[0026] The monomer composition is (based on 100 parts by weight of butadiene and acrylonitrile, the same below) 50-55 parts of butadiene, 45-50 parts of acrylonitrile, the emulsifier is a composite system containing dodecylbenzenesulfonic acid and naphthalenesulfonic acid formaldehyde condensate sodium salt, and the amount of dodecylbenzenesulfonic acid is 2-4.5 parts, the amount of naphthalenesulfonic acid formaldehyde condensate sodium salt is 0.4-1 part, and the pH value of the polymerization system is 10.0-11.5. The monomer and initiator are added once, the molecular weight regulator is added three times, and the intermittent emulsion polymerization is adopted, and the polymerization temperature is 30-40°C.

[0027] Butadiene and acrylonitrile are used as polymerization monomers, and the emulsification system contains sodium salt of dodecylbenzenesulfonic acid and naphthalenesulfonic acid formaldehyde condensate. The pH value of the polymerization system is controlled by sodium (potassium) hydroxide, and the initiation system uses persulfates, such as potassium persulfate, ammonium persulfate and other water-soluble initiators, and the molecular weight regulator is selected as tert-dodecyl mercaptan, etc., and the intermittent feeding method of adding the molecular weight regulator in batches is adopted to synthesize the nitrile rubber slurry, add the terminator, and obtain a highly oil-resistant nitrile rubber after degassing, coagulation, washing and drying.

[0028] After the polymerization kettle is evacuated, soft water, emulsifier, part or all of the monomers and reducing agent are added. After the temperature is raised to 30-40°C, an initiator is added. When the reaction conversion rate reaches 35-40%, a molecular weight regulator is added for the second time. When the reaction conversion rate reaches 85-90%, the material is discharged after the temperature is lowered to 20-25°C, a terminator and an antioxidant are added, and a highly oil-resistant nitrile rubber is obtained after degassing, condensation, washing and drying.

[0029] The high oil-resistant nitrile rubber produced by the invention has an acrylonitrile content of 40-45%, and has high tensile strength and elongation at break, and can meet the application requirements in the fields of automobiles, aerospace, sealing gaskets, etc.

[0030] The test methods for rubber use conventional test methods: total solids test uses SH / T1154-92 standard; combined acrylonitrile test uses SH / T1157-1997 standard; Mooney viscosity The test adopts GB / T1232.1-2000 standard; the tensile strength test adopts GB / T528-1998 standard; the elongation at break test adopts GB / T528-1998 standard.

[0031] Effect of the invention: The nitrile rubber produced by the present invention meets the application requirements in the fields of automobiles, aerospace, sealing gaskets, etc.; in addition, when the mortar is synthesized using this patent, the polymerization process is stable and the energy consumption is low.

[0032] More specifically, it can be seen from the examples that the technology of the present invention can produce acrylonitrile content of 40-45% and Mooney viscosity 90~120, tensile strength ≥27.5MPa, elongation at break ≥450% of high performance, highly oil-resistant nitrile rubber.

[0033] Example 1

[0034] The polymerization kettle was evacuated and replaced with nitrogen until the vacuum degree reached -0.1Mpa. 260 parts of soft water, 55 parts of butadiene, 45 parts of acrylonitrile, emulsifier (including 2.5 parts of dodecylbenzenesulfonic acid, 0.5 parts of sodium salt of naphthalenesulfonic acid formaldehyde condensate), 0.1 parts of triethanolamine, 0.15 parts of molecular weight regulator were added in sequence. The pH value of the polymerization system was 10.3. Then the temperature was raised. When the reaction temperature reached 30°C, 0.2 parts of initiator potassium persulfate were added. When the reaction conversion rate reached 35-40%, 0.15 parts of molecular weight regulator were added for the second time. When the reaction conversion rate reached 50-55%, 0.15 parts of molecular weight regulator were added for the third time. When the reaction conversion rate reached 88%, the temperature was lowered to 20-25°C and the material was discharged. Terminator and antioxidant were added. After degassing, condensation, washing and drying, a highly oil-resistant nitrile rubber was obtained. Among them, triethanolamine is the initiator.

[0035] Example 2

[0036] The polymerization kettle is evacuated and replaced with nitrogen until the vacuum reaches -0.1Mpa. 275 parts of soft water, 52 parts of butadiene, 48 parts of acrylonitrile, emulsifier (including 3 parts of dodecylbenzenesulfonic acid and 0.5 parts of sodium salt of naphthalenesulfonic acid formaldehyde condensate), 0.15 parts of triethanolamine, 0.2 parts of molecular weight regulator are added in sequence. The pH value of the polymerization system is 10.5. Then the temperature is raised. When the reaction temperature reaches 31°C, 0.3 parts of initiator ammonium persulfate are added. When the reaction conversion rate reaches 35-40%, 0.15 parts of molecular weight regulator are added for the second time. When the reaction conversion rate reaches 50-55%, 0.15 parts of molecular weight regulator are added for the third time. When the reaction conversion rate reaches 88%, the material is discharged after cooling to 20-25°C, terminator and antioxidant are added, and a highly oil-resistant nitrile rubber is obtained after degassing, condensation, washing and drying.

[0037] Example 3

[0038] The polymerization kettle is evacuated and replaced with nitrogen until the vacuum reaches -0.1Mpa. 270 parts of soft water, 53 parts of butadiene, 47 parts of acrylonitrile, emulsifier (including 2 parts of dodecylbenzenesulfonic acid, 0.8 parts of sodium salt of naphthalenesulfonic acid formaldehyde condensate, and 0.4 parts of potassium oleate) are added in sequence, 0.07 parts of triethanolamine, 0.15 parts of molecular weight regulator, and the pH value of the polymerization system is 10.5. Then the temperature is raised. When the reaction temperature reaches 33°C, 0.15 parts of initiator ammonium persulfate are added. When the reaction conversion rate reaches 35-40%, 0.1 parts of molecular weight regulator are added for the second time. When the reaction conversion rate reaches 50-55%, 0.15 parts of molecular weight regulator are added for the third time. When the reaction conversion rate reaches 86%, the material is discharged after cooling to 20-25°C, terminator and antioxidant are added, and a highly oil-resistant nitrile rubber is obtained after degassing, condensation, washing and drying.

[0039] Example 4

[0040] The polymerization kettle is evacuated, replaced with nitrogen, and the vacuum degree reaches -0.1Mpa. 255 parts of soft water, 51 parts of butadiene, 49 parts of acrylonitrile, emulsifier (including 2.3 parts of dodecylbenzenesulfonic acid, 0.8 parts of naphthalenesulfonic acid formaldehyde condensate sodium salt), 0.12 parts of triethanolamine, 0.25 parts of molecular weight regulator are added in sequence, and the pH value of the polymerization system is 10.6. Then the temperature is raised, and when the reaction temperature reaches 35°C, 0.25 parts of initiator potassium persulfate are added. When the reaction conversion rate reaches 35-40%, 0.1 parts of molecular weight regulator are added for the second time, and when the reaction conversion rate reaches 50-55%, 0.1 parts of molecular weight regulator are added for the third time. When the reaction conversion rate reaches 88%, the material is discharged after cooling to 20-25°C, terminator and antioxidant are added, and a highly oil-resistant nitrile rubber is obtained after degassing, condensation, washing and drying.

[0041] Example 5

[0042] The polymerization kettle is evacuated, replaced with nitrogen, and the vacuum degree reaches -0.1Mpa. 265 parts of soft water, 54 parts of butadiene, 46 parts of acrylonitrile, emulsifier (including 2.5 parts of dodecylbenzenesulfonic acid, 0.8 parts of naphthalenesulfonic acid formaldehyde condensate sodium salt), 0.1 parts of triethanolamine, 0.2 parts of molecular weight regulator are added in sequence, and the pH value of the polymerization system is 10.8. Then the temperature is raised, and when the reaction temperature reaches 32°C, 0.2 parts of initiator potassium persulfate are added. When the reaction conversion rate reaches 35-40%, 0.15 parts of molecular weight regulator are added for the second time, and when the reaction conversion rate reaches 50-55%, 0.1 parts of molecular weight regulator are added for the third time. When the reaction conversion rate reaches 90%, the material is discharged after cooling to 20-25°C, terminator and antioxidant are added, and a highly oil-resistant nitrile rubber is obtained after degassing, condensation, washing and drying.

[0043] Comparative Example 1

[0044] The polymerization kettle is evacuated, replaced with nitrogen, and the vacuum degree reaches -0.1Mpa. 260 parts of soft water, 55 parts of butadiene, 45 parts of acrylonitrile, emulsifier (including 2.5 parts of sodium dodecylbenzene sulfonate and 0.5 parts of sodium salt of naphthalenesulfonic acid formaldehyde condensate), 0.1 parts of triethanolamine, 0.15 parts of molecular weight regulator are added in sequence, and the pH value of the polymerization system is 10.3. Then the temperature is raised, and when the reaction temperature reaches 30°C, 0.2 parts of initiator potassium persulfate are added. When the reaction conversion rate reaches 35-40%, 0.15 parts of molecular weight regulator are added for the second time, and when the reaction conversion rate reaches 50-55%, 0.15 parts of molecular weight regulator are added for the third time. When the reaction conversion rate reaches 88%, the material is discharged after cooling to 20-25°C, terminator and antioxidant are added, and a highly oil-resistant nitrile rubber is obtained after degassing, condensation, washing and drying.

[0045] Comparative Example 2

[0046] The polymerization kettle is evacuated and replaced with nitrogen until the vacuum reaches -0.1Mpa. 275 parts of soft water, 52 parts of butadiene, 48 parts of acrylonitrile, emulsifier (including 3 parts of dodecylbenzenesulfonic acid and 0.3 parts of sodium salt of naphthalenesulfonic acid formaldehyde condensate), 0.15 parts of triethanolamine, 0.2 parts of molecular weight regulator are added in sequence. The pH value of the polymerization system is 10.5. Then the temperature is raised. When the reaction temperature reaches 31°C, 0.3 parts of initiator ammonium persulfate are added. When the reaction conversion rate reaches 35-40%, 0.15 parts of molecular weight regulator are added for the second time. When the reaction conversion rate reaches 50-55%, 0.15 parts of molecular weight regulator are added for the third time. When the reaction conversion rate reaches 88%, the material is discharged after cooling to 20-25°C, terminator and antioxidant are added, and a highly oil-resistant nitrile rubber is obtained after degassing, condensation, washing and drying.

[0047] Comparative Example 3

[0048] The polymerization kettle is evacuated and replaced with nitrogen until the vacuum reaches -0.1Mpa. 270 parts of soft water, 53 parts of butadiene, 47 parts of acrylonitrile, emulsifier (including 2 parts of dodecylbenzenesulfonic acid and 0.4 parts of potassium oleate), 0.07 parts of triethanolamine, 0.15 parts of molecular weight regulator are added in sequence. The pH value of the polymerization system is 10.5. Then the temperature is raised. When the reaction temperature reaches 33°C, 0.15 parts of initiator ammonium persulfate are added. When the reaction conversion rate reaches 35-40%, 0.1 parts of molecular weight regulator are added for the second time. When the reaction conversion rate reaches 50-55%, 0.15 parts of molecular weight regulator are added for the third time. When the reaction conversion rate reaches 86%, the material is discharged after cooling to 20-25°C, terminator and antioxidant are added, and a highly oil-resistant nitrile rubber is obtained after degassing, condensation, washing and drying.

[0049] Comparative Example 4

[0050] The polymerization kettle is evacuated, replaced with nitrogen, and the vacuum degree reaches -0.1Mpa. 255 parts of soft water, 51 parts of butadiene, 49 parts of acrylonitrile, emulsifier (including 2.3 parts of dodecylbenzenesulfonic acid, 0.8 parts of naphthalenesulfonic acid formaldehyde condensate sodium salt), 0.12 parts of triethanolamine, 0.25 parts of molecular weight regulator are added in sequence, and the pH value of the polymerization system is 9.8. Then the temperature is raised, and when the reaction temperature reaches 35°C, 0.25 parts of initiator potassium persulfate are added. When the reaction conversion rate reaches 35-40%, 0.1 parts of molecular weight regulator are added for the second time. When the reaction conversion rate reaches 50-55%, 0.1 parts of molecular weight regulator are added for the third time. When the reaction conversion rate reaches 88%, the material is discharged after cooling to 20-25°C, terminator and antioxidant are added, and a highly oil-resistant nitrile rubber is obtained after degassing, condensation, washing and drying.

[0051] Comparative Example 5

[0052] The polymerization kettle is evacuated and replaced with nitrogen until the vacuum reaches -0.1Mpa. 265 parts of soft water, 54 parts of butadiene, 46 parts of acrylonitrile, emulsifier (including 2.5 parts of dodecylbenzenesulfonic acid and 0.8 parts of naphthalenesulfonic acid formaldehyde condensate sodium salt), 0.1 parts of triethanolamine, 0.45 parts of molecular weight regulator are sequentially added. The pH value of the polymerization system is 10.8. Then the temperature is raised. When the reaction temperature reaches 32°C, 0.2 parts of initiator potassium persulfate are added. When the reaction conversion rate reaches 90%, the material is discharged after cooling to 20-25°C, terminator and antioxidant are added, and a highly oil-resistant nitrile rubber is obtained after degassing, condensation, washing and drying.

[0053] The nitrile rubber produced by the present invention has high tensile strength and elongation at break, and can meet the application requirements in the fields of automobiles, aerospace, sealing gaskets, etc.

[0054] As shown in Table 1, the high oil-resistant special nitrile rubber prepared in Examples 1-5 and the experimental conditions in Comparative Examples 1-5 are compared. The test results of the performance of the nitrile rubber are shown in Table 2 below: As can be seen from Table 2, the nitrile rubber is synthesized by using a composite emulsification system of dodecylbenzenesulfonic acid and naphthalenesulfonic acid formaldehyde condensate sodium salt and a thermal emulsion polymerization process. The Mooney viscosity 90~120, tensile strength ≥27.5MPa, elongation at break ≥450%.

[0055] Table 1

[0056]

[0057]

[0058] Table 2

[0059]

[0060] In the present invention, as the polymerization conversion rate of the nitrile rubber emulsion polymerization increases, the rubber-bound acrylonitrile content increases and the Mooney viscosity increases, but as the conversion rate increases, the rubber performance deteriorates. The present invention achieves the improvement of the polymerization conversion rate while ensuring that the rubber performance is not affected by the precise control of the pH value of the polymerization system.

Claims

1. A method for preparing a nitrile rubber having improved oil resistance, characterized in that: include: After adding polymerization monomers, water, emulsifiers, initiators and molecular weight regulators, high temperature emulsion polymerization is carried out at a pH of 10.0-11.5 to obtain nitrile rubber; the molecular weight regulator is added in at least two batches, the polymerization monomers are butadiene and acrylonitrile, the emulsifier includes dodecylbenzenesulfonic acid and naphthalenesulfonic acid formaldehyde condensate sodium salt, wherein the amount of dodecylbenzenesulfonic acid is 2-4.5 parts by weight, and the amount of naphthalenesulfonic acid formaldehyde condensate sodium salt is 0.4-1 part by weight; A terminator and an antioxidant are added to the nitrile rubber mortar, and then the nitrile rubber is obtained after degassing, coagulation, washing and drying in sequence.

2. The preparation method according to claim 1, characterized in that: The amount of butadiene added is 50-60 parts, and the amount of acrylonitrile added is 40-50 parts; more preferably, the amount of butadiene added is 50-55 parts, and the amount of acrylonitrile added is 45-50 parts.

3. The preparation method according to claim 1, characterized in that: The reaction temperature of the high-temperature emulsion polymerization reaction is 25-45°C, and the amount of the emulsifier added is 2.4-6 parts; preferably, the reaction temperature of the high-temperature emulsion polymerization reaction is 30-40°C, and the amount of the emulsifier added is 2.4-6 parts; more preferably, the reaction temperature of the high-temperature emulsion polymerization reaction is higher than 30°C, and the amount of the emulsifier added is 2.5-5.5 parts.

4. The preparation method according to claim 1, characterized in that: The initiator is a persulfate initiator system, preferably a potassium persulfate water-soluble initiator and an ammonium persulfate water-soluble initiator; the added amount of the initiator is 0.1 to 0.5 parts.

5. The preparation method according to claim 1, characterized in that: The molecular weight regulator is one of tert-dodecyl mercaptan, n-dodecyl mercaptan and regulator D, preferably tert-dodecyl mercaptan; the total addition amount of the molecular weight regulator is 0.2 to 1 part, preferably 0.3 to 0.7 part.

6. The preparation method according to claim 1 or 5, characterized in that: The molecular weight regulator is added in three batches, and the timing of adding each batch is: Before the high-temperature emulsion polymerization reaction begins, the molecular weight regulator is added for the first time; when the reaction conversion rate of the high-temperature emulsion polymerization reaction reaches 35-40%, the molecular weight regulator is added for the first time; when the reaction conversion rate of the high-temperature emulsion polymerization reaction reaches 50-55%, the molecular weight regulator is added for the second time; More preferably, based on the total amount of the molecular weight regulator added being 100%, the first additional amount is 20 to 35%, and the second additional amount is 20 to 35%.

7. The preparation method according to claim 1, characterized in that: The step of adding a terminator and an antioxidant to the nitrile rubber comprises: When the reaction conversion rate of the high-temperature emulsion polymerization reaction reaches 85-90%, a terminator and an antioxidant are added to the nitrile rubber mortar.

8. The preparation method according to claim 1 or 7, characterized in that: The terminator is one of sodium nitrite, hydroxylamine sulfate and diethylhydroxylamine, and the antioxidant is polybutylbisphenol or diphenylamine derivative; the added amount of the terminator is 0.05 to 0.5 parts, and the added amount of the antioxidant is 0.5 to 2 parts.

9. The preparation method according to claim 1, characterized in that: When preparing the nitrile rubber slurry, a reducing agent is also added; The adding of polymerization monomers, water, emulsifiers, initiators and molecular weight regulators comprises: Taking 100 parts by weight of butadiene and acrylonitrile as the added amount, the added amount of water is 250-280 parts, the added amount of butadiene is 50-55 parts, the added amount of acrylonitrile is 45-50 parts, the added amount of dodecylbenzenesulfonic acid is 2-4.5 parts, and the added amount of naphthalenesulfonic acid formaldehyde condensate sodium salt is 0.4-1 part; the initiator adopts persulfate, and the added amount is 0.1-0.5 parts; the reducing agent is 0.1-0.3 parts; the total added amount of molecular weight regulator is 0.3-0.7 parts, which is added in three batches; when the reaction conversion rate of high-temperature emulsion polymerization reaches 35-40%, the molecular weight regulator is added for the first time; when the reaction conversion rate of high-temperature emulsion polymerization reaches 50-55%, the molecular weight regulator is added for the second time; The step of adding a terminator and an antioxidant to the nitrile rubber comprises: When the reaction conversion rate of the high temperature emulsion polymerization reaction reaches 85-90%, a terminator and an antioxidant are added.

10. The preparation method according to claim 9, characterized in that: When preparing the nitrile rubber, triethanolamine is also added; After adding the polymerization monomer, water, emulsifier, initiator and molecular weight regulator, a high temperature emulsion polymerization reaction is carried out at a pH of 10.0-11.5 to obtain the nitrile rubber slurry, comprising: Based on 100 parts by weight of butadiene and acrylonitrile, the amount of water added is 275 parts, the amount of butadiene added is 50-55 parts, and the amount of acrylonitrile added is 45-50 parts; the emulsifier is a composite system composed of dodecylbenzenesulfonic acid and naphthalenesulfonic acid formaldehyde condensate sodium salt, the amount of the emulsifier added is 2.5-5 parts, wherein the amount of dodecylbenzenesulfonic acid added is 2-4.5 parts, and the amount of naphthalenesulfonic acid formaldehyde condensate sodium salt added is 0.5-1 part; the initiator adopts persulfate , the addition amount is 0.1-0.5 parts; the addition amount of triethanolamine is 0.1 parts; the total addition amount of molecular weight regulator is 0.3-0.7 parts, which is added in three batches; when the reaction conversion rate of high temperature emulsion polymerization reaches 35-40%, the molecular weight regulator is added for the first time; when the reaction conversion rate of high temperature emulsion polymerization reaches 50-55%, the molecular weight regulator is added for the second time; at a pH of 10.0-11.0, high temperature emulsion polymerization is carried out to obtain nitrile rubber; The step of adding a terminator and an antioxidant to the nitrile rubber slurry comprises: When the reaction conversion rate of the high temperature emulsion polymerization reaches 85-90%, the material is discharged after cooling to 20-25°C, and a terminator and an antioxidant are added.

Images