Method for preparing nitrile rubber with improved low temperature resistance

Abstract

The application discloses a preparation method of nitrile rubber with improved low-temperature resistance, which comprises the following steps: using butadiene and acrylonitrile as polymerization monomers, continuously adding acrylonitrile in batches, preferably adding more than three times; using a low-temperature emulsion polymerization method, and adding a composite emulsifier which at least contains disulfated rosin acid soap, C 10 ~C 13 linear alkyl benzene sulfonic acid, naphthalene sulfonic acid formaldehyde condensate sodium salt; preferably, the adding amount of the composite emulsifier is 2.5-5.0 parts, more preferably 2.8-4.0 parts, the molecular weight regulator is added once or more times, the nitrile rubber paste is synthesized, a terminator is added, and the nitrile rubber is prepared after degassing, coagulation, washing and drying. The nitrile rubber with acrylonitrile content of 17-20% and Mooney viscosity of 40-70 and good low-temperature resistance is produced.

Description

Technical Field

[0001] This invention belongs to the field of rubber materials technology, and specifically relates to a method for preparing nitrile rubber with improved low-temperature resistance. Background Technology

[0002] Nitrile rubber is obtained by emulsion polymerization of butadiene and acrylonitrile. Due to the presence of unsaturated double bonds and polar -CN groups in its molecular chain, it has good oil resistance and excellent physical and mechanical properties. It has been widely used in various oil-resistant products, such as O-rings, flexible hoses, gaskets, fuel tank linings, oil tank linings, printing consumables, printing rollers, insulating floor mats, hard rubber parts, oil-resistant shoe soles, fabric coatings, pump impellers, oil well brush cloths, pipe thread protective layers, wire sheaths, adhesives, rubber gloves, and food packaging films. Its development and utilization prospects are broad.

[0003] For many years, countries around the world have been conducting research on the synthesis of nitrile butadiene rubber (NBR). Currently, alkali metal salts of alkyl aryl sulfonates, alkali metal salts of fatty acids, rosin acid soaps, and their mixed soaps are commonly used as emulsifiers in emulsion polymerization. For example, Idemitsu Petrochemical Co., Ltd. of Japan has developed a highly efficient dispersant for NBR emulsion polymerization, composed of maleic acid (anhydride) and styrene sulfonate. Using this dispersant can improve the dispersibility of monomers and the stability of NBR. JSR Corporation of Japan uses nonionic surfactants such as polyethylene oxide alkyl ethers, polyethylene oxide fatty acid esters, polyethylene oxide sorbitol fatty acid esters, and ethylene oxide / propylene oxide block copolymers as emulsifiers. Zeon Corporation of Japan, by appropriately adjusting the polymerization temperature, uses potassium persulfate as an initiator, potassium oleate, sodium dodecylbenzene sulfonate, and other anionic or nonionic surfactants such as polyethylene oxide alkyl ethers as emulsifiers, and dodecyl mercaptan as a regulator to produce NBR. It has a molecular weight distribution index of 5-8, a gel content of less than 5%, and a bound acrylonitrile content of 10%-45%, and is used in the rubber products industry such as rubber rollers.

[0004] CN103450399A discloses a method for preparing nitrile rubber by emulsion polymerization. The polymerization includes at least the following steps: adding a portion of acrylonitrile, a portion of emulsifier, a portion of regulator, and an initiator to a polymerization reactor; adding butadiene under vacuum; carrying out emulsion polymerization under stirring; adding a portion of emulsifier, crosslinking agent, and acrylonitrile to the polymerization reactor when the polymerization conversion rate reaches 25-40% in the middle stage of the reaction; and adding the remaining portion of emulsifier and regulator when the polymerization conversion rate reaches 60-75% in the later stage of the reaction. The crosslinking agent is one or more of the following: triallyl isocyanurate, triallyl cyanurate, diethylene glycol diacrylate, diethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, 1,4-butanediol diacrylate, and polyethylene glycol dimethacrylate; the amount of crosslinking agent added is 0.1-3.0 parts. The emulsifier is one or more of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, potassium stearate, potassium oleate, and disproportionated rosin potassium soap. The resulting nitrile rubber has a high microgel content and low gel content, making it easy to form a three-dimensional structure during processing. This results in good physical and mechanical properties of the rubber product, increased Mooney viscosity, and consequently, improved tensile strength and 300% elongation stress. In the examples, the tensile strength is 19–24 MPa.

[0005] CN114380949A discloses a nitrile rubber, its preparation method, and its application. The preparation method includes: subjecting a raw material system containing butadiene, acrylonitrile, a reactive antioxidant N-(4-(aniline)phenyl)methylacrylamide, and a portion of a molecular weight regulator to a low-temperature polymerization reaction; when the reaction conversion rate reaches 50-55%, adding the remaining portion of the molecular weight regulator; terminating the reaction when the reaction conversion rate reaches 70-75%, to obtain nitrile rubber; the amount of acrylonitrile added is 31-33 parts; the emulsifier is a composite system composed of a sodium salt of a linear alkylbenzene sulfonic acid and a formaldehyde condensate. Using this preparation method, the Mooney viscosity of the obtained nitrile rubber is... With a temperature range of 40-60, this nitrile rubber exhibits good processing properties and excellent resistance to heat and oxygen aging.

[0006] CN111019046A relates to a method for preparing nitrile rubber, which includes the following steps: First, water, emulsifier, activator, acrylonitrile, and molecular weight regulator are added to a polymerization reactor. Then, under an inert atmosphere, an oxygen scavenger, butadiene, and an initiator are added to induce a polymerization reaction between acrylonitrile and butadiene. When the polymerization conversion rate reaches 45% or higher, a molecular weight regulator is added. Finally, when the polymerization conversion rate reaches 75% or higher, a terminator is added. The obtained nitrile latex is collected, coagulated, and dried to obtain nitrile rubber. The amount of acrylonitrile added is 40-50 parts. The emulsifier includes a primary emulsifier and a co-emulsifier, wherein: the primary emulsifier is selected from at least one of potassium disproportionated rosinate, sodium dodecylbenzene sulfonate, potassium oleate, and potassium stearate; the co-emulsifier is selected from at least one of sorbitan tristearate, polyoxyethylene sorbitan monolaurate, and sodium β-naphthalenesulfonate formaldehyde condensate. Using this preparation method, the resulting nitrile rubber has a bound acrylonitrile content of 38% to 41%, a Mooney viscosity range of 40 to 70, a tear strength > 40 KN / m, and a tensile strength > 25 MPa. This nitrile rubber has good properties, especially good oil resistance and high tear strength.

[0007] The existing methods for preparing nitrile rubber have the following main drawbacks:

[0008] Defect 1: The polymerization reaction takes a long time and the power consumption of the reaction equipment is high.

[0009] Defect 2: Low polymerization conversion rate. Increasing the polymerization conversion rate will reduce the strength of the product, thus making it impossible to obtain nitrile rubber products that meet the performance requirements.

[0010] Defect 3: Low acrylonitrile content nitrile rubber produces many fine particles during coagulation, making washing and drying difficult in the post-processing stage.

[0011] For the reasons mentioned above, further research is needed on the preparation method of nitrile rubber to solve the problems of long polymerization time, low conversion rate, and many fine rubber particles during coagulation, which make post-processing difficult. Summary of the Invention

[0012] The purpose of this invention is to provide a simple process for preparing nitrile rubber with good low-temperature resistance.

[0013] To achieve the objective of this invention, the preparation method includes at least the following:

[0014] Butadiene and acrylonitrile are used as polymerization monomers. Based on a total addition of butadiene and acrylonitrile of 100 parts by mass, the acrylonitrile content is less than 25 parts. Acrylonitrile is added in batches or continuously, preferably in three or more batches. A low-temperature emulsion polymerization method is used, employing a composite emulsion system. The composite emulsifier contains at least disproportionated rosin acid soap and C... 10 ~C13 Sodium salt of linear alkylbenzene sulfonic acid and naphthalene sulfonic acid formaldehyde condensate; preferably, the amount of composite emulsifier added is 2.5 to 5.0 parts, more preferably 2.8 to 4.0 parts, and the molecular weight regulator is added once or multiple times to synthesize nitrile rubber paste. A terminator is added, and the paste is then degassed, coagulated, washed and dried to obtain a nitrile rubber.

[0015] The present invention recommends a more preferred or more typical monomer composition ratio of: 80-85 parts butadiene and 15-20 parts acrylonitrile.

[0016] The acrylonitrile monomer of the present invention is added to the low-temperature emulsion polymerization reaction in batches or continuously, preferably in three or more batches, and more preferably in four batches.

[0017] Acrylonitrile is added in four stages: the first addition of acrylonitrile is made when the reaction conversion rate reaches 30-35%; the second addition is made when the reaction conversion rate reaches 45-55%; and the third addition is made when the reaction conversion rate reaches 60-65%. Preferably, the amount of acrylonitrile monomer added in the first stage is 30-50% of the total amount of acrylonitrile monomer added, and the remaining additions of acrylonitrile monomer are 50-70% of the total amount of acrylonitrile monomer added.

[0018] The synthesis scheme of nitrile rubber in this invention is low-temperature emulsion polymerization. The polymerization reaction temperature used in low-temperature emulsion polymerization commonly used in this technical field is not particularly limited. For example, the polymerization reaction temperature of low-temperature emulsion polymerization is 7 to 12°C, and the preferred polymerization reaction temperature is 8 to 10°C.

[0019] The present invention does not particularly limit the amount of disproportionated rosin acid soap added in the composite emulsifier. For example, based on 100 parts by mass of butadiene and acrylonitrile, the amount of disproportionated rosin acid soap in the composite emulsifier is 1.5 to 3.3 parts, preferably 1.6 to 2.5 parts.

[0020] This invention does not specifically limit the C content in the composite emulsifier. 10 ~C 13 The preferred amount of linear alkylbenzene sulfonic acid in the composite emulsifier is C, calculated based on a total of 100 parts by weight of butadiene and acrylonitrile. 10 ~C 13 The amount of linear alkylbenzene sulfonic acid used is 0.7 to 1.2 parts, more preferably 0.9 to 1.1 parts.

[0021] The present invention does not particularly limit the amount of sodium naphthalene sulfonic acid formaldehyde condensate added to the composite emulsifier. For example, it is preferred that the amount of sodium naphthalene sulfonic acid formaldehyde condensate is 0.3 to 0.5 parts, and more preferably 0.3 to 0.4 parts.

[0022] This invention does not particularly limit the initiation system or the amount added. Generally, any initiator used for low-temperature emulsion polymerization of nitrile rubber can be used. For example, the initiation system used for low-temperature emulsion polymerization is organic hydrogen peroxide-ferrous salt, preferably dicumyl hydrogen peroxide, with a preferred addition amount of 0.1 to 0.3 parts; the reducing agent used for low-temperature emulsion polymerization is preferably sodium ferric ethylenediaminetetraacetate, with a preferred addition amount of 0.01 to 0.15 parts; the chelating agent used for low-temperature emulsion polymerization is preferably disodium ethylenediaminetetraacetate, with a preferred addition amount of 0.01 to 0.05 parts.

[0023] This invention does not particularly limit the molecular weight regulator and its amount. Generally, any molecular weight regulator used for nitrile rubber can be used. Common molecular weight regulators are one of tert-dodecyl mercaptan and n-dodecyl mercaptan, with tert-dodecyl mercaptan being preferred. The preferred amount of molecular weight regulator is 0.3 to 0.8 parts, more preferably 0.4 to 0.7 parts. The preferred terminator is one of sodium nitrite, hydroxylamine sulfate, and diethylhydroxylamine. The preferred amount of terminator is 0.05 to 0.15 parts.

[0024] The present invention does not specifically limit the timing of the addition of the terminator; the terminator is added when the reaction conversion rate reaches 80-85%.

[0025] The present invention also provides a preferred method for preparing nitrile rubber, comprising the following steps:

[0026] Based on 100 parts by weight of butadiene and acrylonitrile, the monomer composition is: 80-85 parts butadiene, 15-20 parts acrylonitrile, 200-250 parts deionized water, and the composite emulsifier includes disproportionated rosin acid soap, C... 10 ~C 13 A compound emulsification system of sodium salt of linear alkylbenzene sulfonic acid and naphthalene sulfonic acid formaldehyde condensate, wherein the amount of compound emulsifier is 2.5–5.0 parts, and the amount of disproportionated rosin acid soap is 1.5–3.3 parts, C 10 ~C 13 The amount of linear alkylbenzene sulfonic acid is 0.7–1.2 parts, and the amount of sodium salt of naphthalene sulfonic acid formaldehyde condensate is 0.3–0.5 parts; the initiation system is organic hydrogen peroxide-ferrous salt, and the amount of organic hydrogen peroxide is 0.1–0.3 parts; the molecular weight regulator is tert-dodecyl mercaptan, and the amount of tert-dodecyl mercaptan is 0.3–0.8 parts; acrylonitrile is added in more than 3 portions; the polymerization temperature is 7–12℃; and the amount of composite emulsifier is preferably 2.8–4.0 parts.

[0027] The present invention also provides a more preferred method for preparing nitrile rubber, comprising the following steps:

[0028] After evacuating the polymerization reactor, deionized water, composite emulsifier, reducing agent, electrolyte, chelating agent, some monomers, and molecular weight regulator are added. The temperature is controlled at 7-12℃, and then an initiator is added. When the reaction conversion rate reaches 30-35%, a second batch of acrylonitrile is added; when the reaction conversion rate reaches 45-55%, a third batch of acrylonitrile is added; when the reaction conversion rate reaches 60-65%, a fourth batch of acrylonitrile is added; when the reaction conversion rate reaches 80-85%, a terminator is added, the material is discharged, and after degassing, coagulation, washing, and drying, a nitrile rubber is obtained.

[0029] This invention does not specifically limit C 10 ~C 13 Types of linear alkylbenzene sulfonic acids, such as C 10 ~C 13 The linear alkylbenzene sulfonic acid is dodecylbenzene sulfonic acid.

[0030] Compared with the prior art, the embodiments of the present invention have at least the following advantages: They employ an emulsification system composed of disproportionated rosin acid soap, dodecylbenzene sulfonic acid, and sodium salt of naphthalene sulfonic acid formaldehyde condensate, along with a low-temperature emulsion polymerization process. This solves the technical problems of high particle size and difficulty in washing and drying during post-processing due to the low acrylonitrile content of nitrile rubber. Furthermore, the present invention discovers that adding acrylonitrile in batches, especially in four batches, can lower the glass transition temperature of nitrile rubber, resulting in excellent low-temperature resistance. The nitrile rubber produced using the method of the present invention exhibits excellent low-temperature resistance, meeting the application requirements of oil-resistant seals in low-temperature working environments. Additionally, the polymerization process is stable and energy consumption is low when using the method of the present invention to synthesize the adhesive. As shown by the optimal production scheme in the embodiments, the technology of the present invention can produce a product with a bound acrylonitrile content of 17-20% and a Mooney viscosity of ML110+04. ℃ Nitrile rubber with a temperature range of 40-70 exhibits excellent low-temperature resistance and can be used in oil-resistant sealing applications in low-temperature working environments.

[0031] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures pointed out in the description. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] This invention discloses a method for preparing nitrile rubber with improved low-temperature resistance, comprising:

[0034] Butadiene and acrylonitrile are used as polymerization monomers. Based on a total addition of butadiene and acrylonitrile of 100 parts by mass, the acrylonitrile content is less than 25 parts. Acrylonitrile is added in batches or continuously, preferably in three or more batches. A low-temperature emulsion polymerization method is used, employing a composite emulsion system. The composite emulsifier contains at least disproportionated rosin acid soap and C... 10 ~C 13 Sodium salt of linear alkylbenzene sulfonic acid and naphthalene sulfonic acid formaldehyde condensate, wherein the disproportionated rosin acid soap comprises 1.5–3.3 parts, preferably 1.6–2.5 parts, C 10 ~C 13 The amount of linear alkylbenzene sulfonic acid is 0.7–1.2 parts, preferably 0.9–1.1 parts; the amount of sodium naphthalene sulfonic acid formaldehyde condensate is 0.3–0.5 parts, more preferably 0.3–0.4 parts; a molecular weight regulator is added once or multiple times to synthesize nitrile rubber paste; a terminator is added, and the paste is then degassed, coagulated, washed, and dried to obtain a nitrile rubber. It should be noted that all parts in this application are by weight.

[0035] In this invention, the acrylonitrile monomer content is relatively low, below 25 parts, and the polymerization formula can be adjusted according to product requirements. Excessive acrylonitrile content can easily lead to poor elasticity and compression set resistance of the vulcanized rubber, as well as low performance retention during aging, resulting in a significantly shortened service life when exposed to hot oil or hot air for extended periods. This invention recommends a more preferred or typical monomer composition ratio of 80-85 parts butadiene and 15-20 parts acrylonitrile for the synthesis of nitrile rubber.

[0036] The acrylonitrile monomer of the present invention is added to the polymerization reaction in batches or continuously, preferably in three or more batches, and more preferably in four batches; preferably, the amount of acrylonitrile monomer added for the first time is 30 to 50% of the total amount of acrylonitrile monomer added.

[0037] When acrylonitrile monomer is added to the polymerization reaction four times, the preferred method is as follows: when the reaction conversion rate reaches 30-35%, acrylonitrile is added for the first time; when the reaction conversion rate reaches 45-55%, acrylonitrile is added for the second time; and when the reaction conversion rate reaches 60-65%, acrylonitrile is added for the third time.

[0038] It is recommended that the initial addition of acrylonitrile monomer be 30-50% of the total acrylonitrile monomer addition, and the subsequent addition of acrylonitrile monomer be 50-70% of the total acrylonitrile monomer addition.

[0039] This invention has found that when the amount of acrylonitrile monomer added is less than 25 parts, if the acrylonitrile monomer is added in batches or continuously, especially in four batches, the distribution of acrylonitrile in the molecular chain segments is significantly improved, resulting in a significant reduction in the glass transition temperature of the polymer.

[0040] The synthesis scheme of nitrile rubber in this invention is low-temperature emulsion polymerization. The polymerization temperature used in low-temperature emulsion polymerization commonly used in this technical field is not particularly limited, such as 7-12°C, and preferably controlled at 8-10°C. It can be batch polymerization or continuous polymerization.

[0041] This invention does not particularly limit the initiator system or the amount added. Generally, any initiator used for low-temperature emulsion polymerization of nitrile rubber can be used. For example, the initiation system can be an organic hydrogen peroxide-ferrous salt redox initiation system, such as dicumyl peroxide-ferrous salt, cumyl peroxide-ferrous salt, etc. The amount added is usually 0.1 to 0.3 parts.

[0042] The present invention does not particularly limit the type and amount of the terminator. Any common terminator can be used, such as sodium nitrite, hydroxylamine sulfate, and diethylhydroxylamine. The amount of terminator added is usually 0.05 to 0.15 parts.

[0043] This invention does not specifically limit the timing of adding the terminator; the desired conversion rate of the nitrile rubber can be selected according to product requirements. Preferably, the terminator is added when the reaction conversion rate reaches 80% or higher; more preferably, it is added when the reaction conversion rate reaches 80-85%.

[0044] This invention does not particularly limit the molecular weight regulator or its amount. Any molecular weight regulator and amount commonly used for nitrile rubber is acceptable. Common molecular weight regulators include tert-dodecyl mercaptan and n-dodecyl mercaptan, with tert-dodecyl mercaptan being preferred. The typical amount of molecular weight regulator used is 0.3–0.8 parts, more preferably 0.4–0.7 parts, and the amount can be adjusted according to product performance requirements and the type of molecular weight regulator.

[0045] In this invention, the molecular weight regulator in emulsion polymerization can be added once, multiple times, or continuously, depending on the different performance requirements of the product.

[0046] Typically, when emulsion polymerization of nitrile butadiene rubber uses a composite emulsion system, the emulsifier includes a primary emulsifier and a co-emulsifier, wherein:

[0047] The main emulsifier can be one or more anionic emulsifiers, such as at least one of potassium disproportionated rosinate, sodium dodecylbenzene sulfonate, sodium decaalkyl sulfate, potassium oleate and potassium stearate, or other anionic emulsifiers;

[0048] The co-emulsifier can be a nonionic emulsifier, such as at least one of sorbitan tristearate, sodium β-naphthalenesulfonate formaldehyde condensate, and octylphenol polyoxyethylene ether, or other nonionic emulsifiers.

[0049] Combining anionic and nonionic emulsifiers can have a synergistic effect, improving the stability of latex.

[0050] This invention employs a specific composite emulsification system, wherein the composite emulsifier is a combination of at least three substances: disproportionated rosin acid soap, linear alkylbenzene sulfonic acid, and sodium salt of naphthalene sulfonic acid formaldehyde condensate.

[0051] In this invention, the amount of compound emulsifier added can be the amount of emulsifier used in general techniques in the art, especially when anionic emulsifiers and nonionic emulsifiers are compounded. The amount of compound emulsifier used in this invention is preferably 2.5 to 5.0 parts, more preferably 2.8 to 4.0 parts.

[0052] This invention requires the addition of disproportionated rosin acid soap, which can be either potassium or sodium soap, to the compound emulsifier. The potassium or sodium disproportionated rosin acid soap in the compound emulsification system of this invention cannot be replaced by other anionic emulsifiers such as sodium decaalkyl sulfate, potassium oleate, and potassium stearate. This is because the inventors unexpectedly discovered in experiments that, due to a synergistic effect, the addition of potassium or sodium disproportionated rosin acid soap increases the particle size of the polymer emulsion, which is particularly beneficial to the subsequent emulsion coagulation process after emulsion polymerization. The amount added can be adjusted according to the desired polymer emulsion particle size, especially the ease of emulsion coagulation after emulsion polymerization. The recommended amount of disproportionated rosin acid soap is 1.5–3.3 parts, more preferably 1.6–2.5 parts.

[0053] This invention requires the addition of C to the compound emulsifier. 10 ~C 13 Linear alkylbenzene sulfonic acid. The function of linear alkylbenzene sulfonic acid differs from that of sodium linear alkylbenzene sulfonate. Adding only sodium linear alkylbenzene sulfonate without linear alkylbenzene sulfonic acid results in a different effect than in this invention. This is because sodium alkylbenzene sulfonate is a saponification product of alkylbenzene sulfonic acid. Due to the use of alkylbenzene sulfonic acid, some alkylbenzene sulfonic acid remains incompletely saponified during its saponification process. A synergistic effect occurs between the two, improving the stability of the entire polymerization system and increasing the polymerization efficiency. Therefore, linear alkylbenzene sulfonic acid in the composite emulsion system of this invention cannot be replaced by sodium linear alkylbenzene sulfonate. As an emulsifier, C 10 ~C 13 The most commonly used linear alkylbenzene sulfonic acid is dodecylbenzene sulfonic acid. 10 ~C 13 The preferred amount of linear alkylbenzene sulfonic acid added is 0.9 to 1.1 parts.

[0054] This invention requires sodium salt of naphthalenesulfonic acid formaldehyde condensate and C 10 ~C 13 Linear alkylbenzene sulfonic acid is used concurrently, and its dosage is determined as needed; this invention does not impose any particular limitation. Failure to add it will lead to a decrease in the stability of the polymerization emulsion, and sludge formation may easily occur during polymerization. The preferred dosage of sodium naphthalenesulfonic acid formaldehyde condensate is 0.3–0.5 parts, more preferably 0.3–0.4 parts.

[0055] This invention also does not exclude the addition of other anionic emulsifiers or nonionic emulsifiers, such as potassium oleate or potassium stearate, in addition to disproportionated rosinate potassium soap or sodium soap, linear alkylbenzene sulfonic acid and naphthalene sulfonic acid formaldehyde condensate sodium salt, to the composite emulsification system.

[0056] This invention also does not exclude the addition of other commonly used auxiliaries for nitrile emulsion polymerization, such as deionized water, electrolytes, reducing agents, chelating agents, etc., to the polymerization system, provided that the addition amount is within the general addition range.

[0057] This invention does not particularly limit the type and amount of electrolyte added; any general electrolyte and general amount added are acceptable, such as potassium hydroxide, sodium pyrophosphate, sodium carbonate, etc., and the amount added can be 0.01 to 0.05 parts.

[0058] This invention does not particularly limit the type and amount of reducing agent. A general reducing agent and a general amount can be used, such as ferrous sulfate, sodium ferric ethylenediaminetetraacetate, sodium thiosulfate, etc., and the amount added can be 0.01 to 0.15 parts.

[0059] This invention does not particularly limit the type and amount of chelating agent. A general chelating agent and a general amount can be used, such as disodium ethylenediaminetetraacetate or tetrasodium ethylenediaminetetraacetate, and the amount added can be 0.01 to 0.05 parts.

[0060] Unless otherwise specified, in this invention, "part" refers to 100 parts by mass of the total amount of polymeric monomers, and "percentage" refers to the percentage by mass.

[0061] The present invention also provides a more preferred method for preparing nitrile rubber, comprising the following steps:

[0062] The monomer composition (based on 100 parts by mass of butadiene and acrylonitrile, the same below) is: 80-85 parts butadiene, 15-20 parts acrylonitrile, and 200-250 parts deionized water. The composite emulsifier includes disproportionated rosin acid soap and C... 10 ~C 13 A compound emulsification system of sodium salt of linear alkylbenzene sulfonic acid and naphthalene sulfonic acid formaldehyde condensate, wherein the amount of compound emulsifier is 2.5-5.0 parts, and the amount of disproportionated rosin acid soap is 1.5-3.3 parts, C 10 ~C13 The amount of linear alkylbenzene sulfonic acid is 0.7–1.2 parts, and the amount of sodium salt of naphthalene sulfonic acid formaldehyde condensate is 0.3–0.5 parts; the initiation system is organic hydrogen peroxide-ferrous salt, and the amount of organic hydrogen peroxide is 0.1–0.3 parts; the amount of molecular weight regulator is 0.3–0.8 parts; acrylonitrile is added in more than 3 portions; the polymerization temperature is 7–12℃; the preferred amount of composite emulsifier is 2.8–4.0 parts.

[0063] More preferably:

[0064] After evacuating the polymerization reactor, deionized water, composite emulsifier, reducing agent, electrolyte, chelating agent, some monomers, and molecular weight regulator are added. The temperature is controlled at 7-12℃, and then an initiator is added. When the reaction conversion rate reaches 30-35%, a second batch of acrylonitrile is added; when the reaction conversion rate reaches 45-55%, a third batch of acrylonitrile is added; when the reaction conversion rate reaches 60-65%, a fourth batch of acrylonitrile is added; when the reaction conversion rate reaches 80-85%, a terminator is added, the material is discharged, and after degassing, coagulation, washing, and drying, a nitrile rubber is obtained.

[0065] This invention develops a simple method for preparing nitrile rubber, employing an emulsion system composed of disproportionated rosin acid soap, dodecylbenzene sulfonic acid, and sodium salt of naphthalene sulfonic acid formaldehyde condensate, along with a low-temperature emulsion polymerization process. This solves the technical problems of high particle size and difficult washing and drying processes in nitrile rubber due to its low acrylonitrile content. Furthermore, this invention discovers that adding acrylonitrile in batches, especially in four batches, can lower the glass transition temperature of nitrile rubber, resulting in excellent oil resistance and low-temperature resistance of the polymer.

[0066] The nitrile rubber produced using the method of this invention has excellent low-temperature resistance and meets the application requirements of oil-resistant seals in high-temperature working environments. In addition, when synthesizing the adhesive using this application, the polymerization process is stable and the energy consumption is low.

[0067] As can be seen from the optimal production scheme in the examples, the technology of the present invention can produce a product with a bound acrylonitrile content of 17-20% and a Mooney viscosity. Nitrile rubber with a temperature range of 40-70 exhibits excellent low-temperature resistance and can be used in oil-resistant sealing applications in low-temperature working environments.

[0068] The testing methods for nitrile rubber are standard: total solids test follows SH / T1154-92 standard; Mooney viscosity... The tests were conducted according to GB / T1232-2000 standard; the acrylonitrile content test was conducted according to SH / T1157-1997 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.

[0069] Example 1

[0070] The 10L polymerization reactor was evacuated and purged with nitrogen to a vacuum level of -0.1 MPa. Then, 235 parts of deionized water, 80 parts of butadiene, 11 parts of acrylonitrile, a composite emulsifier (including 1.6 parts of potassium disproportionated rosinate soap, 0.9 parts of dodecylbenzene sulfonic acid, and 0.34 parts of sodium naphthalene sulfonic acid formaldehyde condensate), 0.11 parts of sodium iron ethylenediaminetetraacetate, 0.04 parts of disodium ethylenediaminetetraacetate, and 0.6 parts of tert-dodecyl mercaptan (see Table 1 for specific components).

[0071] Then, control the temperature. When the reaction temperature reaches 8°C, add 0.15 parts of the initiator diisopropylbenzene hydrogen peroxide.

[0072] When the reaction conversion rate reaches 30-35%, add 3 parts of secondary acrylonitrile; when the reaction conversion rate reaches 45-55%, add 3 parts of tertiary acrylonitrile; when the reaction conversion rate reaches 60-65%, add 3 parts of quaternary acrylonitrile; when the reaction conversion rate reaches 84%, add 0.07 parts of sodium nitrite as a terminator, discharge the material, and then degas, coagulate, wash and dry it to obtain a nitrile rubber.

[0073] The preparation methods of Examples 2-8 are the same as those of Example 1, and the differences are shown in Table 1.

[0074] The preparation methods of Comparative Examples 1-8 are the same as those of Example 1, with the differences shown in Table 2.

[0075] The performance of the nitrile rubber prepared in Examples 1-8 was tested, and the specific test results are shown in Table 3.

[0076] The performance of the nitrile rubbers prepared in Examples 1-8 was tested, and the specific test results are shown in Table 4.

[0077] Table 1 Components of the Examples

[0078]

[0079] Table 2 Comparative Examples Components

[0080]

[0081] Table 3. Performance test results of nitrile rubber in the examples.

[0082]

[0083] Table 4. Performance test results of comparative nitrile rubber.

[0084]

[0085] As can be seen from Tables 3 and 4, the technology of this invention can produce products with a bound acrylonitrile content of 17-20% and a Mooney viscosity. Nitrile rubber with a temperature range of 40-70 exhibits excellent low-temperature resistance and can be used in oil-resistant sealing applications in low-temperature working environments.

[0086] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing nitrile rubber with improved low-temperature resistance, characterized in that, The preparation method includes at least: Butadiene and acrylonitrile are used as polymerization monomers. Based on a total addition of butadiene and acrylonitrile of 100 parts by mass, the acrylonitrile content is less than 25 parts. Acrylonitrile is added in batches or continuously, preferably in three or more batches. A low-temperature emulsion polymerization method is used, employing a composite emulsion system. The composite emulsifier contains at least disproportionated rosin acid soap and C... 10 ~C 13 A sodium salt of linear alkylbenzene sulfonic acid and naphthalene sulfonic acid formaldehyde condensate is used. The amount of disproportionated rosin acid soap in the composite emulsifier is preferably 1.5 to 3.3 parts, more preferably 1.6 to 2.5 parts. A molecular weight regulator is added once or multiple times to synthesize a nitrile rubber paste. A terminator is added, and the paste is degassed, coagulated, washed and dried to obtain a nitrile rubber.

2. The method for preparing nitrile rubber according to claim 1, characterized in that, The monomer composition ratio is: 80-85 parts butadiene and 15-20 parts acrylonitrile.

3. The method for preparing nitrile rubber according to claim 1 or 2, characterized in that, The acrylonitrile is added in four stages: the first addition of acrylonitrile is made when the reaction conversion rate reaches 30-35%; the second addition of acrylonitrile is made when the reaction conversion rate reaches 45-55%; and the third addition of acrylonitrile is made when the reaction conversion rate reaches 60-65%. Preferably, the amount of acrylonitrile monomer added for the first time is 30-50% of the total amount of acrylonitrile monomer added, and the amount of acrylonitrile monomer added in the remaining stages is 50-70% of the total amount of acrylonitrile monomer added.

4. The method for preparing nitrile rubber according to claim 1, characterized in that, The polymerization reaction temperature of the low-temperature emulsion polymerization is 7-12°C, and the preferred polymerization reaction temperature is 8-10°C.

5. The method for preparing nitrile rubber according to claim 1, characterized in that, Based on a total addition of butadiene and acrylonitrile of 100 parts by mass, the amount of composite emulsifier added is 2.5 to 5.0 parts, more preferably 2.8 to 4.0 parts.

6. The method for preparing nitrile rubber according to claim 1 or 5, characterized in that, Based on a total addition of butadiene and acrylonitrile of 100 parts by mass, the C content in the composite emulsifier is... 10 ~C 13 The amount of linear alkylbenzene sulfonic acid used is 0.7 to 1.2 parts, preferably 0.9 to 1.1 parts.

7. The method for preparing nitrile rubber according to claim 6, characterized in that, The amount of sodium naphthalenesulfonic acid formaldehyde condensate in the composite emulsifier is 0.3 to 0.5 parts, preferably 0.3 to 0.4 parts.

8. The method for preparing nitrile rubber according to any one of claims 1, 2, or 4, characterized in that, The initiation system used in the low-temperature emulsion polymerization is an organic hydrogen peroxide-ferrous salt, preferably added in an amount of 0.1 to 0.3 parts; the organic hydrogen peroxide is preferably dicumyl hydrogen peroxide; the reducing agent used in the low-temperature emulsion polymerization is preferably sodium ferric ethylenediaminetetraacetate, preferably added in an amount of 0.01 to 0.15 parts; the chelating agent used in the low-temperature emulsion polymerization is preferably disodium ethylenediaminetetraacetate, preferably added in an amount of 0.01 to 0.05 parts.

9. The method for preparing nitrile rubber according to any one of claims 1, 2, or 4, characterized in that, The molecular weight regulator is one of tert-dodecyl mercaptan and n-dodecyl mercaptan, preferably tert-dodecyl mercaptan; the preferred amount of the molecular weight regulator is 0.3 to 0.8 parts, more preferably 0.4 to 0.7 parts; the preferred terminator is one of sodium nitrite, hydroxylamine sulfate, and diethylhydroxylamine; the preferred amount of the terminator is 0.05 to 0.15 parts.

10. The method for preparing nitrile rubber according to claim 9, characterized in that, Add a terminator when the reaction conversion rate reaches 80-85%.

11. The method for preparing nitrile rubber according to any one of claims 1, 2, or 4, characterized in that, The preparation method includes the following steps: Based on 100 parts by weight of butadiene and acrylonitrile, the monomer composition is: 80-85 parts butadiene, 15-20 parts acrylonitrile, 200-250 parts deionized water, and the composite emulsifier includes disproportionated rosin acid soap, C... 10 ~C 13 A compound emulsification system of sodium salt of linear alkylbenzene sulfonic acid and naphthalene sulfonic acid formaldehyde condensate, wherein the amount of compound emulsifier is 2.5–5.0 parts, and the amount of disproportionated rosin acid soap is 1.5–3.3 parts, C 10 ~C 13 The amount of linear alkylbenzene sulfonic acid is 0.7–1.2 parts, and the amount of sodium salt of naphthalene sulfonic acid formaldehyde condensate is 0.3–0.5 parts; the initiation system is organic hydrogen peroxide-ferrous salt, and the amount of organic hydrogen peroxide is 0.1–0.3 parts; the amount of molecular weight regulator is 0.3–0.8 parts; acrylonitrile is added in more than 3 portions; the polymerization temperature is 7–12℃; the preferred amount of composite emulsifier is 2.8–4.0 parts.

12. The method for preparing nitrile rubber according to any one of claims 1, 2, 4 or 11, characterized in that, The preparation method includes the following steps: After evacuating the polymerization reactor, deionized water, composite emulsifier, reducing agent, electrolyte, chelating agent, some monomers, and molecular weight regulator are added. The temperature is controlled at 7-12℃, and then an initiator is added. When the reaction conversion rate reaches 30-35%, a second batch of acrylonitrile is added; when the reaction conversion rate reaches 45-55%, a third batch of acrylonitrile is added; when the reaction conversion rate reaches 60-65%, a fourth batch of acrylonitrile is added; when the reaction conversion rate reaches 80-85%, a terminator is added, the material is discharged, and after degassing, coagulation, washing, and drying, a nitrile rubber is obtained.

13. The method for preparing nitrile rubber according to claim 11, characterized in that, The C 10 ~C 13 The linear alkylbenzene sulfonic acid is dodecylbenzene sulfonic acid.

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