Process for the preparation of nitrile rubber with improved oil resistance

Abstract

The present application relates to a kind of preparation methods of high oil-resistant nitrile rubber, and polymerization at least includes the following process: butadiene, acrylonitrile, water, composite emulsifying system, partial molecular weight regulator, initiator are added to polymerization kettle, using the intermittent feeding mode of batch supplementing molecular weight regulator, heat method polymerization process is synthesized butyronitrile glue pulp, termination agent and antioxidant are added, and it is after degassing, coagulation, washing and drying to obtain a kind of high-strength butyronitrile rubber product.The butyronitrile rubber has the tensile strength of Mooney viscosity ≥27.5MPa, and can meet the application requirements of automobile, aerospace, sealing washer and other fields.

Description

Technical Field

[0001] This invention belongs to the field of rubber preparation technology, specifically relating to a method for preparing nitrile rubber with improved oil resistance. Background Technology

[0002] Nitrile butadiene rubber (NBR) is widely used in the automotive, aerospace, and gasket industries due to its excellent oil resistance, benzene resistance, heat resistance, and physical and mechanical properties. These industries have more stringent requirements for rubber performance, including higher requirements for oil resistance, acrylonitrile binding, and Mooney viscosity.

[0003] Regarding the polymerization process, Japanese patent JPH05222267A discloses a method for preparing NBR by appropriately adjusting the polymerization temperature, using potassium persulfate as an initiator, potassium oleate, sodium dodecylbenzene sulfonate, or nonionic surfactants such as polyoxyethylene alkyl ethers as emulsifiers, and dodecyl mercaptan as a regulator. The molecular weight distribution index is 5-8, the gel content is less than 5%, and the bound acrylonitrile content is 10%-45%, which is suitable for use in the rubber roller and other rubber product industries. Chinese invention patent CN103665265B describes the preparation of NBR by appropriately adjusting the polymerization temperature, using dicumyl peroxide as an initiator, sodium salt of rosin acid soap, naphthalene sulfonic acid and formaldehyde condensate as an emulsifier, and dodecyl mercaptan as a regulator. With a strength of 30-95, a combined acrylonitrile content of 18%-46%, and a tensile strength of 10-22 MPa, it is used in the rubber products industry, such as rubber rollers.

[0004] In existing technologies, the acrylonitrile content of nitrile rubber is mostly below 40%, which cannot meet the rubber usage requirements of the automotive, aerospace, and sealing gasket industries. Moreover, the monomer conversion rate during polymerization is only around 75%, which is not high enough. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing high oil-resistant nitrile butadiene rubber, which solves the problem of insufficient conversion rate due to acrylonitrile content of less than 40% in the prior art. This invention improves 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. Based on the prior art, a high oil-resistant nitrile butadiene rubber with higher acrylonitrile content and better Mooney viscosity is prepared.

[0006] The technical solution adopted in this invention is as follows: a method for preparing nitrile rubber with improved oil resistance, comprising adding polymeric monomers, water, emulsifiers, initiators, and molecular weight regulators, and then carrying out a high-temperature emulsion polymerization reaction at a pH of 10.0-11.5 to obtain nitrile rubber paste; the molecular weight regulator is added in at least two batches, the polymeric monomers are butadiene and acrylonitrile, and the emulsifiers include dodecylbenzene sulfonic acid and sodium salt of naphthalene sulfonic acid formaldehyde condensate, wherein, by weight, the amount of dodecylbenzene sulfonic acid is 2-4.5 parts, and the amount of sodium salt of naphthalene sulfonic acid formaldehyde condensate is 0.4-1 parts; a terminator and an antioxidant are added to the nitrile rubber paste, and then the mixture is subjected to degassing, coagulation, washing, and drying to obtain nitrile rubber.

[0007] This invention does not particularly limit the specific ratio of the polymerizable monomers butadiene and acrylonitrile. Commonly used ratios in the preparation of oil-resistant nitrile rubber in existing technologies can be used, such as 50-60 parts butadiene and 40-50 parts acrylonitrile, more preferably 50-55 parts butadiene and 45-50 parts acrylonitrile. The acrylonitrile content can also be higher, and the polymerization formula can be adjusted according to product requirements. This invention also does not particularly limit the method of monomer addition. The monomers can be added all at once or in multiple additions. For example, when the acrylonitrile ratio is high and the butadiene ratio is low, the butadiene monomer can be added in batches or continuously. This invention does not impose any particular limitations.

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

[0009] This invention does not particularly limit the initiator system or the amount added. Any initiator commonly used in the high-temperature emulsion polymerization of nitrile rubber can be used. For example, the initiator system can be a persulfate-based water-soluble initiator, such as potassium persulfate or ammonium persulfate, with an addition amount typically of 0.2–1.0 parts. Similarly, the type and amount of the terminator and antioxidant are not particularly limited. Common terminators and antioxidants can be used. For example, the terminator can be at least one of sodium nitrite, hydroxylamine sulfate, and diethylhydroxylamine, or other terminators. The amount of the terminator added is typically 0.05–0.5 parts. The antioxidant can be polybutylene bisphenol A, diphenylamine derivatives, or other types of antioxidants, with an addition amount typically of 0.5–2 parts.

[0010] This invention does not specifically limit the timing of adding the terminator; the desired conversion rate of the nitrile rubber paste can be selected according to product requirements. Preferably, the terminator is added when the reaction conversion rate reaches 85-90%.

[0011] This invention does not particularly limit the molecular weight regulator or its dosage. Any molecular weight regulator and dosage commonly used for nitrile rubber is acceptable. Common molecular weight regulators include tert-dodecyl mercaptan, n-dodecyl mercaptan, and regulator butyl, with tert-dodecyl mercaptan being preferred. The typical dosage of the molecular weight regulator is 0.2 to 1 part, more preferably 0.3 to 0.7 parts, and the dosage can be adjusted according to product performance requirements and the type of molecular weight regulator.

[0012] This invention employs molecular weight regulators in emulsion polymerization multiple times, such as adding them in batches two or more times. For example, in continuous polymerization, the molecular weight regulator is added to different polymerization reactors according to the polymerization conversion rate. In batch polymerization, it is preferable to add the molecular weight regulator in three batches. This invention does not particularly limit the proportion of the molecular weight regulator added in batches. When adding it twice, it is preferable to add the molecular weight regulator when the reaction conversion rate reaches 35-40%, and then add it again when the reaction conversion rate reaches 50-55%. More preferably, based on the total amount of molecular weight regulator added being 100%, the first addition is preferably 20-35%, and the second addition is also preferably 20-35%.

[0013] In this invention, the pH value of the polymerization system needs to be controlled between 10.0 and 11.5, and more preferably between 10.0 and 11.0. If the pH value is not within the range required by this invention, whether too high or too low, the polymerization reaction time will be prolonged and the physical and mechanical properties of the product will decrease.

[0014] This invention requires the use of a composite emulsification system, and the composite emulsifier contains at least dodecylbenzenesulfonic acid and sodium salt of naphthalenesulfonic acid formaldehyde condensate. The amount of dodecylbenzenesulfonic acid is 2 to 4.5 parts, and the amount of sodium salt of naphthalenesulfonic acid formaldehyde condensate is 0.4 to 1 part. When the amount of sodium salt of naphthalenesulfonic acid formaldehyde condensate is too low, such as only 0.3 parts, it will lead to a decrease in the stability of the polymer emulsion and make it easy for glue to stick during the polymerization process.

[0015] In this invention, 2-4.5 parts of dodecylbenzenesulfonic acid are added to the composite emulsion system. The dodecylbenzenesulfonic acid and sodium dodecylbenzenesulfonate have different functions. Adding only sodium dodecylbenzenesulfonate without dodecylbenzenesulfonic acid results in a different effect than in this invention. This is because sodium dodecylbenzenesulfonate is a saponification product of dodecylbenzenesulfonic acid. Due to the use of dodecylbenzenesulfonic acid, the reaction system contains not only sodium dodecylbenzenesulfonate but also some unsaponified dodecylbenzenesulfonic acid. This creates a synergistic effect, improving the stability and efficiency of the entire polymerization system. Therefore, sodium dodecylbenzenesulfonate cannot be substituted for dodecylbenzenesulfonic acid in the composite emulsion system of this invention.

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

[0017] This invention also does not exclude the addition of other commonly used auxiliaries for nitrile emulsion polymerization, such as soft water, electrolytes, and reducing agents, to the polymerization system, provided that the addition amount is within the general addition range.

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

[0019] Based on 100 parts by weight of butadiene and acrylonitrile, the mixture includes 250-280 parts soft water, 50-55 parts butadiene, and 45-50 parts acrylonitrile; the emulsifier is a composite system containing sodium salt of dodecylbenzenesulfonic acid and 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 part; the initiator is a persulfate, and its amount is 0.1-0.5 parts; the reducing agent is such as triethanolamine, 0.1-0.3 parts. The raw materials are mixed in three parts; the molecular weight regulator is added in the amount of 0.3 to 0.7 parts, in three parts; after the above raw materials are mixed, a polymerization reaction occurs, and the pH value of the polymerization system is 10.0-11.5; when the reaction conversion rate reaches 35-40%, a second molecular weight regulator is added; when the reaction conversion rate reaches 50-55%, a third molecular weight regulator is added; when the reaction conversion rate reaches 85-90%, a terminator and an antioxidant are added, and after degassing, coagulation, washing and drying, nitrile rubber is obtained.

[0020] More preferably, the method for preparing nitrile rubber includes the following steps:

[0021] Based on 100 parts by weight of butadiene and acrylonitrile, the mixture includes 275 parts of soft water, 50-55 parts of butadiene, and 45-50 parts of acrylonitrile; the emulsifier is a composite system of dodecylbenzenesulfonic acid and naphthalenesulfonic acid formaldehyde condensate sodium salt, with an emulsifier dosage of 2.5-5 parts, of which dodecylbenzenesulfonic acid accounts for 2-4.5 parts and naphthalenesulfonic acid formaldehyde condensate sodium salt accounts for 0.4-1 parts; the initiator is a persulfate, with a dosage of 0.1-0.5 parts; triethanolamine is 0.1 parts; and the molecular weight regulator is 0.3-0.7 parts, added in three portions.

[0022] The above raw materials are mixed and subjected to a polymerization reaction. The pH 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. When the reaction conversion rate reaches 85-90%, the temperature is lowered to 20-25°C and the material is discharged. A terminator and antioxidant are added, and the mixture is then degassed, coagulated, washed, and dried to obtain nitrile rubber. The nitrile rubber of this invention can achieve a polymerization conversion rate of up to 85-90%, further improving the primary utilization rate of monomers, reducing monomer recovery energy consumption, and increasing the production capacity of polymerization equipment.

[0023] The beneficial effects of this invention are that it uses a sodium salt of dodecylbenzenesulfonic acid and naphthalenesulfonic acid formaldehyde condensate in a specific ratio as a composite emulsion system, and synthesizes high oil-resistant nitrile rubber using a thermal emulsion polymerization process by controlling the pH value of the polymerization system. The nitrile rubber produced using this invention can meet the application requirements of the automotive, aerospace, and sealing gasket industries; furthermore, when synthesizing the adhesive using this invention, the polymerization process is stable and energy consumption is low. The preferred indicators for the high oil-resistant nitrile rubber product are: a bound acrylonitrile content of 40-45%, and a Mooney viscosity of... 90~120, tensile strength ≥27.5MPa, elongation at break ≥450%. Detailed Implementation

[0024] The present invention will now be described in detail with reference to specific embodiments.

[0025] The present invention discloses a method for preparing high oil-resistant nitrile butadiene rubber, which uses an emulsion system composed of dodecylbenzene sulfonic acid and sodium salt of naphthalene sulfonic acid formaldehyde condensate, and prepares high oil-resistant nitrile butadiene rubber by controlling the pH value of the polymerization system and using a thermal batch emulsion polymerization process.

[0026] The monomer composition (based on 100 parts by weight of butadiene and acrylonitrile, the same below) is 50-55 parts butadiene and 45-50 parts acrylonitrile. The emulsifier is a composite system containing sodium salt of dodecylbenzenesulfonic acid and naphthalenesulfonic acid formaldehyde condensate, with 2-4.5 parts of dodecylbenzenesulfonic acid and 0.4-1 parts of naphthalenesulfonic acid formaldehyde condensate. The pH of the polymerization system is 10.0-11.5. The monomer and initiator are added at once, and the molecular weight regulator is added in three stages. The process is a batch emulsion polymerization at a polymerization temperature of 30-40℃.

[0027] Butadiene and acrylonitrile were used as polymerization monomers. The emulsion system contained sodium salts of dodecylbenzenesulfonic acid and naphthalenesulfonic acid formaldehyde condensate. The pH value of the polymerization system was controlled by sodium (potassium) hydroxide. The initiation system used water-soluble initiators such as potassium persulfate and ammonium persulfate. Tertiary dodecyl mercaptan was selected as the molecular weight regulator. A batch feeding method with partial addition of molecular weight regulator was used to synthesize nitrile rubber paste. A terminator was added, and the paste was degassed, coagulated, washed, and dried to obtain a high oil-resistant nitrile rubber.

[0028] After the polymerization reactor is evacuated, soft water, emulsifier, some or all of the monomer and reducing agent are added. After the temperature is raised to 30-40℃, 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 temperature is lowered to 20-25℃ and the material is discharged. Terminator and antioxidant are added, and the product is degassed, coagulated, washed and dried to obtain a high oil-resistant nitrile rubber.

[0029] The high oil-resistant nitrile rubber produced using this invention has an acrylonitrile content of 40-45% and exhibits high tensile strength and elongation at break, meeting the application requirements of the automotive, aerospace, and gasket industries.

[0030] The testing methods for rubber are standard: total solids testing follows SH / T1154-92 standard; combined with acrylonitrile testing follows SH / T1157-1997 standard; Mooney viscosity... The tests were conducted according to GB / T1232.1-2000 standard; the tensile strength test was conducted according to GB / T528-1998 standard; and the elongation at break test was conducted according to GB / T528-1998 standard.

[0031] Effects of the invention: The nitrile rubber produced using this invention meets the application requirements of the automotive, aerospace, and sealing gasket industries; in addition, when using this patent to synthesize the adhesive, the polymerization process is stable and the energy consumption is low.

[0032] More specifically, as can be seen from the embodiments, the technology of the present invention can produce a product with a bound acrylonitrile content of 40-45% and a Mooney viscosity. Highly oil-resistant nitrile butadiene rubber with properties ranging from 90 to 120 mm, tensile strength ≥27.5 MPa, and elongation at break ≥450%.

[0033] Example 1

[0034] The polymerization reactor was evacuated and purged with nitrogen to a vacuum level of -0.1 MPa. Then, 260 parts soft water, 55 parts butadiene, 45 parts acrylonitrile, emulsifier (including 2.5 parts dodecylbenzene sulfonic acid and 0.5 parts sodium formaldehyde condensate of naphthalene sulfonic acid), 0.1 parts triethanolamine, and 0.15 parts molecular weight regulator were added sequentially, maintaining a pH of 10.3. The temperature was then raised to 30°C, and 0.2 parts potassium persulfate initiator was added. When the reaction conversion rate reached 35-40%, 0.15 parts of the molecular weight regulator were added for the second time. When the reaction conversion rate reached 50-55%, 0.15 parts of the 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. A terminator and antioxidant were added, and the mixture was degassed, coagulated, washed, and dried to obtain a highly oil-resistant nitrile rubber. Triethanolamine was used as the initiator.

[0035] Example 2

[0036] The polymerization reactor was evacuated and purged with nitrogen to a vacuum level of -0.1 MPa. Then, 275 parts soft water, 52 parts butadiene, 48 parts acrylonitrile, emulsifier (including 3 parts dodecylbenzenesulfonic acid and 0.5 parts sodium salt of naphthalenesulfonic acid formaldehyde condensate), 0.15 parts triethanolamine, and 0.2 parts molecular weight regulator were added sequentially, maintaining the pH of the polymerization system at 10.5. The temperature was then raised to 31°C, and 0.3 parts ammonium persulfate initiator were added. When the reaction conversion rate reached 35-40%, 0.15 parts of the molecular weight regulator were added for the second time. When the reaction conversion rate reached 50-55%, 0.15 parts of the 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. A terminator and antioxidant were added, and the mixture was degassed, coagulated, washed, and dried to obtain a highly oil-resistant nitrile rubber.

[0037] Example 3

[0038] The polymerization reactor was evacuated and purged with nitrogen to a vacuum level of -0.1 MPa. Then, 270 parts soft water, 53 parts butadiene, 47 parts acrylonitrile, emulsifier (including 2 parts dodecylbenzene sulfonic acid, 0.8 parts sodium naphthalene sulfonic acid formaldehyde condensate, and 0.4 parts potassium oleate), 0.07 parts triethanolamine, and 0.15 parts molecular weight regulator were added sequentially, maintaining the pH of the polymerization system at 10.5. The temperature was then raised to 33°C, and 0.15 parts ammonium persulfate initiator were added. When the reaction conversion rate reached 35-40%, 0.1 parts of the molecular weight regulator were added for the second time. When the reaction conversion rate reached 50-55%, 0.15 parts of the molecular weight regulator were added for the third time. When the reaction conversion rate reached 86%, the temperature was lowered to 20-25°C, and the material was discharged. A terminator and antioxidant were added, and the mixture was degassed, coagulated, washed, and dried to obtain a highly oil-resistant nitrile rubber.

[0039] Example 4

[0040] The polymerization reactor was evacuated and purged with nitrogen to a vacuum level of -0.1 MPa. Then, 255 parts soft water, 51 parts butadiene, 49 parts acrylonitrile, emulsifier (including 2.3 parts dodecylbenzenesulfonic acid and 0.8 parts sodium formaldehyde condensate of naphthalenesulfonic acid), 0.12 parts triethanolamine, and 0.25 parts molecular weight regulator were added sequentially, maintaining the pH of the polymerization system at 10.6. The temperature was then raised to 35°C, and 0.25 parts potassium persulfate initiator was added. When the reaction conversion rate reached 35–40%, 0.1 parts of the molecular weight regulator were added for the second time. When the reaction conversion rate reached 50–55%, 0.1 parts of the 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. A terminator and antioxidant were added, and the mixture was degassed, coagulated, washed, and dried to obtain a highly oil-resistant nitrile rubber.

[0041] Example 5

[0042] The polymerization reactor was evacuated and purged with nitrogen to a vacuum level of -0.1 MPa. Then, 265 parts soft water, 54 parts butadiene, 46 parts acrylonitrile, emulsifier (including 2.5 parts dodecylbenzenesulfonic acid and 0.8 parts sodium formaldehyde condensate of naphthalenesulfonic acid), 0.1 parts triethanolamine, and 0.2 parts molecular weight regulator were added sequentially, maintaining the pH of the polymerization system at 10.8. The temperature was then raised to 32°C, and 0.2 parts potassium persulfate initiator was added. When the reaction conversion rate reached 35-40%, 0.15 parts of the molecular weight regulator were added for the second time. When the reaction conversion rate reached 50-55%, 0.1 parts of the molecular weight regulator were added for the third time. When the reaction conversion rate reached 90%, the temperature was lowered to 20-25°C, and the material was discharged. A terminator and antioxidant were added, and the mixture was degassed, coagulated, washed, and dried to obtain a highly oil-resistant nitrile rubber.

[0043] Comparative Example 1

[0044] The polymerization reactor was evacuated and purged with nitrogen to a vacuum level of -0.1 MPa. Then, 260 parts soft water, 55 parts butadiene, 45 parts acrylonitrile, emulsifier (including 2.5 parts sodium dodecylbenzenesulfonate and 0.5 parts sodium naphthalenesulfonic acid formaldehyde condensate), 0.1 parts triethanolamine, and 0.15 parts molecular weight regulator were added sequentially, maintaining the pH of the polymerization system at 10.3. The temperature was then raised to 30°C, and 0.2 parts potassium persulfate initiator was added. When the reaction conversion rate reached 35-40%, 0.15 parts of the molecular weight regulator were added for the second time. When the reaction conversion rate reached 50-55%, 0.15 parts of the 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. A terminator and antioxidant were added, and the mixture was degassed, coagulated, washed, and dried to obtain a highly oil-resistant nitrile rubber.

[0045] Comparative Example 2

[0046] The polymerization reactor was evacuated and purged with nitrogen to a vacuum level of -0.1 MPa. Then, 275 parts soft water, 52 parts butadiene, 48 parts acrylonitrile, emulsifier (including 3 parts dodecylbenzenesulfonic acid and 0.3 parts sodium formaldehyde condensate of naphthalenesulfonic acid), 0.15 parts triethanolamine, and 0.2 parts molecular weight regulator were added sequentially, maintaining the pH of the polymerization system at 10.5. The temperature was then raised to 31°C, and 0.3 parts ammonium persulfate initiator were added. When the reaction conversion rate reached 35-40%, 0.15 parts of the molecular weight regulator were added for the second time. When the reaction conversion rate reached 50-55%, 0.15 parts of the 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. A terminator and antioxidant were added, and the mixture was degassed, coagulated, washed, and dried to obtain a highly oil-resistant nitrile rubber.

[0047] Comparative Example 3

[0048] The polymerization reactor was evacuated and purged with nitrogen to a vacuum level of -0.1 MPa. Then, 270 parts soft water, 53 parts butadiene, 47 parts acrylonitrile, emulsifier (including 2 parts dodecylbenzenesulfonic acid and 0.4 parts potassium oleate), 0.07 parts triethanolamine, and 0.15 parts molecular weight regulator were added sequentially, maintaining the pH of the polymerization system at 10.5. The temperature was then raised to 33°C, and 0.15 parts ammonium persulfate initiator were added. When the reaction conversion rate reached 35-40%, 0.1 parts of the molecular weight regulator were added for the second time. When the reaction conversion rate reached 50-55%, 0.15 parts of the molecular weight regulator were added for the third time. When the reaction conversion rate reached 86%, the temperature was lowered to 20-25°C, and the material was discharged. A terminator and antioxidant were added, and the mixture was degassed, coagulated, washed, and dried to obtain a highly oil-resistant nitrile rubber.

[0049] Comparative Example 4

[0050] The polymerization reactor was evacuated and purged with nitrogen to a vacuum level of -0.1 MPa. Then, 255 parts soft water, 51 parts butadiene, 49 parts acrylonitrile, emulsifier (including 2.3 parts dodecylbenzenesulfonic acid and 0.8 parts sodium formaldehyde condensate of naphthalenesulfonic acid), 0.12 parts triethanolamine, and 0.25 parts molecular weight regulator were added sequentially, resulting in a polymerization system pH of 9.8. The temperature was then raised to 35°C, and 0.25 parts potassium persulfate initiator was added. When the reaction conversion rate reached 35–40%, 0.1 parts of the molecular weight regulator were added for the second time. When the reaction conversion rate reached 50–55%, 0.1 parts of the 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. A terminator and antioxidant were added, and the mixture was degassed, coagulated, washed, and dried to obtain a highly oil-resistant nitrile rubber.

[0051] Comparative Example 5

[0052] The polymerization reactor was evacuated and purged with nitrogen to a vacuum level of -0.1 MPa. Then, 265 parts soft water, 54 parts butadiene, 46 parts acrylonitrile, emulsifier (including 2.5 parts dodecylbenzenesulfonic acid and 0.8 parts sodium formaldehyde condensate of naphthalenesulfonic acid), 0.1 parts triethanolamine, and 0.45 parts molecular weight regulator were added sequentially, maintaining the pH of the polymerization system at 10.8. The temperature was then raised to 32°C, and 0.2 parts potassium persulfate initiator was added. When the reaction conversion rate reached 90%, the temperature was lowered to 20-25°C, and the material was discharged. A terminator and antioxidant were added, and the mixture was degassed, coagulated, washed, and dried to obtain a highly oil-resistant nitrile rubber.

[0053] The nitrile rubber produced using this invention has high tensile strength and elongation at break, which can meet the application requirements of automobiles, aerospace, gaskets and other fields.

[0054] Table 1 shows a comparison of the experimental conditions for the high oil-resistant special nitrile rubber prepared in Examples 1-5 and Comparative Examples 1-5. The test results for the properties of the nitrile rubber are shown in Table 2 below. Table 2 shows that the nitrile rubber synthesized using a compound emulsion system of dodecylbenzenesulfonic acid and naphthalenesulfonic acid formaldehyde condensate sodium salt and a hot emulsion polymerization process has a Mooney viscosity of [missing value]. 90~120, tensile strength ≥27.5MPa, elongation at break ≥450%.

[0055] Table 1

[0056]

[0057]

[0058] Table 2

[0059]

[0060] In this invention, as the polymerization conversion rate increases, the acrylonitrile content in the rubber increases and the Mooney viscosity increases. However, as the conversion rate increases, the rubber properties deteriorate. This invention achieves improved polymerization conversion rate while ensuring that the rubber properties are not affected by precise control of the pH value of the polymerization system.

Claims

1. A method for preparing nitrile rubber with improved oil resistance, characterized in that, include: After adding monomers, water, emulsifiers, initiators, and molecular weight regulators, a high-temperature emulsion polymerization reaction is carried out at pH 10.0-11.5 to obtain nitrile butadiene adhesive. The molecular weight regulator is added in at least two batches. The monomers are butadiene and acrylonitrile. The emulsifier includes sodium dodecylbenzene sulfonic acid and sodium naphthalene sulfonic acid formaldehyde condensate. Based on the amount of butadiene and acrylonitrile added as 100 parts by weight, the amount of dodecylbenzene sulfonic acid is 2-4.5 parts, and the amount of sodium naphthalene sulfonic acid formaldehyde condensate is 0.4-1 part. A terminating agent and an antioxidant are added to the nitrile rubber paste, and then the paste is subjected to degassing, coagulation, washing and drying in sequence to obtain nitrile rubber. The terminator is one of sodium nitrite, hydroxylamine sulfate, and diethylhydroxylamine, and the antioxidant is polybutyl bisphenol or a diphenylamine derivative; the amount of the terminator added is 0.05 to 0.5 parts, and the amount of the antioxidant added is 0.5 to 2 parts.

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.

3. The preparation method according to claim 2, characterized in that, The amount of butadiene added is 50-55 parts, and the amount of acrylonitrile added is 45-50 parts.

4. The preparation method according to claim 1, characterized in that, The reaction temperature of the high-temperature emulsion polymerization reaction is 25~45℃, and the amount of emulsifier added is 2.4~6 parts.

5. The preparation method according to claim 4, characterized in that, The reaction temperature of the high-temperature emulsion polymerization reaction is 30-40°C, and the amount of emulsifier added is 2.4-6 parts.

6. The preparation method according to claim 5, characterized in that, The amount of emulsifier added is 2.5 to 5.5 parts.

7. The preparation method according to claim 1, characterized in that, The initiator is a persulfate-based initiation system.

8. The preparation method according to claim 7, characterized in that, The initiator is a water-soluble potassium persulfate initiator and a water-soluble ammonium persulfate initiator; the amount of initiator added is 0.1~0.5 parts.

9. 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.

10. The preparation method according to claim 9, characterized in that, The molecular weight regulator is tert-dodecyl mercaptan; the total amount of molecular weight regulator added is 0.2 to 1 part.

11. The preparation method according to claim 10, characterized in that, The total amount of molecular weight regulator added is 0.3 to 0.7 parts.

12. The preparation method according to claim 1 or 9, characterized in that, The molecular weight regulator was added in three batches, with the timing of each batch addition as follows: Before the high-temperature emulsion polymerization reaction begins, a molecular weight regulator is added for the first time; when the reaction conversion rate of the high-temperature emulsion polymerization reaction reaches 35-40%, a molecular weight regulator is added again for the first time; when the reaction conversion rate of the high-temperature emulsion polymerization reaction reaches 50-55%, a molecular weight regulator is added again for the second time.

13. The preparation method according to claim 12, characterized in that, Based on a total molecular weight regulator addition of 100%, the first addition is 20-35%, and the second addition is 20-35%.

14. The preparation method according to claim 1, characterized in that, The addition of a terminator and an antioxidant to the nitrile rubber paste includes: 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 paste.

15. The preparation method according to claim 1, characterized in that, A reducing agent is also added during the preparation of nitrile rubber paste; The addition of monomers, water, emulsifiers, initiators, and molecular weight regulators includes: Based on 100 parts by weight of butadiene and acrylonitrile, the following additives are used: water 250-280 parts, butadiene 50-55 parts, acrylonitrile 45-50 parts, dodecylbenzenesulfonic acid 2-4.5 parts, and naphthalenesulfonic acid formaldehyde condensate sodium salt 0.4-1 part; persulfate initiator 0.1-0.5 parts; reducing agent 0.1-0.3 parts; total molecular weight regulator 0.3-0.7 parts, added in three batches; the first addition of molecular weight regulator when the reaction conversion rate of the high-temperature emulsion polymerization reaches 35-40%; the second addition of molecular weight regulator when the reaction conversion rate of the high-temperature emulsion polymerization reaches 50-55%. The addition of a terminator and an antioxidant to the nitrile rubber paste includes: When the reaction conversion rate of the high-temperature emulsion polymerization reaction reaches 85-90%, a terminator and an antioxidant are added.

16. The preparation method according to claim 15, characterized in that, Triethanolamine is also added during the preparation of nitrile rubber paste; After adding the polymerizing 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 nitrile butadiene rubber paste, 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 sodium salt of naphthalenesulfonic acid formaldehyde condensate, and the amount of emulsifier added is 2.5-5 parts, of which the amount of dodecylbenzenesulfonic acid added is 2-4.5 parts, and the amount of sodium salt of naphthalenesulfonic acid formaldehyde condensate added is 0.5-1 part; the initiator is a 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, added in three batches; 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; the high-temperature emulsion polymerization reaction is carried out at pH 10.0-11.0 to obtain nitrile rubber paste. The addition of a terminator and an antioxidant to the nitrile rubber paste includes: When the reaction conversion rate of the high-temperature emulsion polymerization reaction reaches 85-90%, the material is discharged after cooling to 20-25℃, and a terminator and antioxidant are added.

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