Butadiene-acrylonitrile rubber composition

Abstract

The present invention provides a nitrile rubber composition, which contains 0.2 to 1.6 parts by weight of sulfur, 2 to 6 parts by weight of an organic peroxide, and 1 to 7 parts by weight of a vulcanization accelerator, with respect to 100 parts by weight of nitrile rubber. The nitrile rubber composition is excellent in storage stability of unvulcanized compound even in the absence of a vulcanization retarder, and can provide a cushioning member which can satisfy high properties required for a cushioning member, such as a cushioning member mounted in a power steering device of an automobile or the like, in good balance, while ensuring sufficient processability and moldability.

Description

Technical Field

[0001] This invention relates to a nitrile rubber composition. More specifically, it relates to a nitrile rubber composition that exhibits excellent rubber stability while providing effective vulcanized molded articles for use as impact stoppers and the like. Background Technology

[0002] Rubber impact stops, as components (buffers) that absorb impacts from repeated operation, are assembled in various mechanical devices. In particular, the rubber materials used for impact stops in automotive power steering systems are required to have a cushioning function that absorbs impacts under specified displacement, as well as heat resistance and durability that do not undergo significant changes in properties even after repeated use at high temperatures.

[0003] To improve the impact resistance of rubber buffer components such as impact stops, one could consider increasing the size of the buffer or its weight. However, these methods contradict the trend of smaller space and lighter weight in automobile development in recent years and are therefore difficult to adopt.

[0004] In addition, one could cite the use of metal or resin to increase hardness in order to improve cushioning. While this method is effective against several high impacts, from the perspective of softness, it is considered difficult to meet the long-life requirements of repeated impacts.

[0005] The applicant has proposed an NBR composition for use as a molding material for cushioning components, comprising NBR, a specific grade of carbon black, a vulcanization retarder, thiazole-based and thiuram-based vulcanization accelerators, and a sulfur-based vulcanizing agent (Patent Document 1). While the cushioning components obtained from this composition exhibit excellent processability of the rubber compound and hardness of the vulcanized rubber, further improvements are desired from the viewpoint of the storage stability and heat resistance of the unvulcanized rubber compound.

[0006] Here, as the molding material for cushioning components, the stability of uncured rubber compounds during storage is also an important factor in improving productivity. While choosing high-hardness rubber materials as the material for cushioning components requiring load resistance is effective, on the other hand, high-hardness rubber materials may often pose obstacles in production aspects such as processability and molding. Furthermore, if high hardness is achieved solely through crosslinking using a common sulfur crosslinking system, the storage stability of the uncured rubber compound cannot always be guaranteed.

[0007] As described above, there is a need for a nitrile rubber composition whose uncured compound exhibits excellent storage stability, ensures adequate processability and moldability, and can provide vulcanized molded articles with the high properties required for cushioning components, such as conventional physical properties, load characteristics, and heat resistance.

[0008] [Existing Technical Documents] [Patent Documents] [Patent Document 1] Japanese Patent No. 7236591 [Patent Document 2] Japanese Patent No. 6045935 Summary of the Invention [The technical problem that the invention aims to solve] The present invention was made in view of the above-mentioned technical problems, and provides a nitrile rubber composition that provides excellent storage stability of uncured rubber, ensures sufficient processability and moldability, and provides a cushioning component that can uniformly meet the high characteristics required for conventional physical properties, load characteristics and heat resistance, such as those required for cushioning components assembled in automotive power steering systems.

[0009] [Methods for solving technical problems] The object of the present invention is achieved by the following nitrile rubber composition, wherein, relative to 100 parts by weight of nitrile rubber, it contains 0.2 to 1.6 parts by weight of sulfur, 2 to 6 parts by weight of organic peroxide and 1 to 7 parts by weight of vulcanization accelerator.

[0010] [Invention Effects] The nitrile rubber composition of this invention exhibits the following excellent effects: vulcanized rubber articles formed from this composition possess well-balanced load-bearing capacity and heat resistance without compromising conventional physical properties. Furthermore, while ensuring sufficient processability and moldability, it also maintains the storage stability of unvulcanized rubber compounds even without the use of vulcanization retarders. Detailed Implementation

[0011] While there are no particular limitations on the nitrile rubber used, acrylonitrile-butadiene rubber with a bound acrylonitrile content of 15-48%, preferably 22-42%, can be used. In practice, commercially available products can be used directly, such as NIPOL DN3335 from Zeon Corporation, and N240S and N241 from JSR Corporation. The nitrile rubber composition of this invention is prepared by adding sulfur, organic peroxides, and a vulcanization accelerator as essential components to this nitrile rubber.

[0012] Sulfur is used at a ratio of 0.2 to 1.6 parts by weight, preferably 0.4 to 1.2 parts by weight, relative to 100 parts by weight of nitrile rubber. If sulfur is used at a ratio lower than the above ratio, the load-bearing characteristics will deteriorate; on the other hand, if sulfur is used at a ratio higher than the above ratio, the storage stability and heat resistance of the uncured rubber compound will deteriorate.

[0013] As organic peroxides, 1,1-di(tert-butylperoxy)-3,3,5-trimethylcyclohexane, di-tert-butyl peroxide, tert-butylisopropylbenzene peroxide, diisopropylbenzene peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexyn-3, 1,3-bis(tert-butylperoxyisopropyl)benzene, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, tert-butylperoxybenzoate, tert-butylperoxyisopropyl carbonate, n-butyl-4,4'-di(tert-butylperoxy)valerate, etc., can be used in a ratio of 2 to 6 parts by weight, preferably 3 to 5 parts by weight, relative to 100 parts by weight of nitrile rubber. If organic peroxides are used in proportions lower than those mentioned above, the load characteristics and heat resistance will deteriorate. Furthermore, if the sulfur content is increased without the use of organic peroxides, the storage stability of the uncured rubber compound will decrease. On the other hand, if they are used in proportions higher than those mentioned above, the elongation at break will deteriorate.

[0014] As vulcanization accelerators, thiuram-based vulcanization accelerators such as tetramethylthiuram monosulfide, tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetrabutylthiuram disulfide, tetra(2-ethylhexyl)thiuram disulfide, and bispentamethylenethiuram tetrasulfide are used; thiazole-based vulcanization accelerators such as 2-benzothiazole disulfide, N-cyclohexyl-2-benzothiazole sulfenamide, 2-thiol-benzothiazole, zinc salts or cyclohexylamine salts of 2-thiol-benzothiazole, 2-(N,N'-diethylthiocarbamoylthio)benzothiazole, and 2-(4'-morpholinodithio)benzothiazole are used, with thiuram disulfide-based vulcanization accelerators being preferred. These vulcanization accelerators are used in a ratio of 1 to 7 parts by weight, preferably 2 to 6 parts by weight, relative to 100 parts by weight of nitrile rubber. If the vulcanization accelerator is used in a proportion lower than the above ratio, the heat resistance will deteriorate; on the other hand, if it is used in a proportion higher than the above ratio, the elongation at break will deteriorate.

[0015] It should be noted that Patent Document 2 discloses a crosslinked rubber composition for cushioning components. This rubber composition contains a crosslinking accelerator and a crosslinking delay agent comprising di-2-benzothiazole disulfide, N-cyclohexyl-2-benzothiazole sulfenamide, and tetraalkylthiuram disulfide in the rubber component containing NBR. However, in this rubber composition, if even one of the three components of the crosslinking accelerator is not included, extremely high impact resistance cannot be obtained. Furthermore, although it is generally described that sulfur crosslinking systems, organic peroxide crosslinking agents, etc., can be used as crosslinking systems, in practice, only sulfur is used in the various embodiments. Moreover, without the crosslinking delay agent, which is an essential component, the impact resistance of the cushioning component will be significantly worse. Therefore, it does not provide any inspiration for the structure of the present invention.

[0016] In addition to the essential components mentioned above, the composition preferably contains appropriate reinforcing agents, fillers, oxides or hydroxides of divalent metals, antioxidants, processing aids, plasticizers, light stabilizers, flame retardants, antistatic agents, and other compounding agents commonly used in the rubber industry, without impairing their properties.

[0017] As a reinforcing agent, carbon black, silica, activated calcium carbonate, etc. can be used, with carbon black being preferred. From the viewpoint of achieving high hardness while ensuring processability and formability, its proportion is usually about 120 parts by weight or less relative to 100 parts by weight of NBR, preferably about 50 to 90 parts by weight.

[0018] The composition is prepared as follows: in addition to the above-mentioned components, fillers such as talc and calcium silicate, plasticizers such as dioctyl sebacate (DOS), and other necessary components are added, and the mixture is compounded using a mixing machine such as an Intermix, kneader, Banbury mixer, or open mixing mill. Vulcanization is carried out using an injection molding machine, compression molding machine, or vulcanizing press, typically at approximately 160–190°C for about 3–20 minutes.

[0019] Example The present invention will now be described in detail through embodiments. It should be noted that the present invention, including its effects, is not limited to these embodiments.

[0020] Example 1 Nitrile butadiene rubber (NIPOL DN3335, produced by Zeon Corporation of Japan; AN content 33%) 100 parts by weight HAF Carbon Black (Cabot Japan Product VULCAN 3L) 84 parts by weight Zinc oxide (Hyster product) 10 parts by weight Anti-aging agent (Seiko Chemicals Nonflex RD) 1.5 parts by weight Plasticizer (DOS product from Taoka Chemical Industry) 5 parts by weight Sulfur (Tsurumi Chemical Industry product) 1.2 parts by weight Organic peroxide (dicumyl peroxide) 4 parts by weight 4 parts by weight of thiuram-based vulcanization accelerator (Nocceler TBZTD, a product of Dainei New Chemical Industry) The above-mentioned components were mixed using a kneader and an open-type rubber mixing mill. The mixture was then subjected to pressure vulcanization at 180°C for 4 minutes to prepare test vulcanized molded products. The following evaluations and measurements were performed using the mixture and the obtained test vulcanized molded products.

[0021] Storage stability of uncured rubber compounds: in accordance with JIS K6300 corresponding to ISO 289. Under storage conditions of 30℃, 80% humidity, and 30 days, calculate the difference in minimum Mooney viscosity Vm between the uncured rubber compound before and after storage, as ΔVm. ΔVm is expected to be less than 20M.

[0022] Characteristics of uncured rubber compounds: based on JIS K6300 corresponding to ISO 289. The scorch time t5 (minutes) in the Mooney scorch test (125°C) was determined. The expected t5 value is 6.5 minutes or more.

[0023] Standard physical properties: according to JIS K6251 corresponding to ISO 37 and JIS K6253 corresponding to ISO 7619-1. Instantaneous hardness Hs and elongation at break (%) were measured. The expected instantaneous hardness Hs is above 80, and the expected elongation at break is above 120%.

[0024] Load characteristics: in accordance with JIS K6262 corresponding to ISO 815-1 Using a large test specimen with a diameter of φ29±5mm and a thickness of 12.5±5mm, the compressive stress was measured at a constant compression rate of 10mm / min. The expected compressive stress at 30% compression is above 4.1kN.

[0025] Heat resistance test: according to JIS K6257 corresponding to ISO 188. Calculate the rate of change of elongation at break after 70 hours at 120℃. The expected rate of change of elongation is within -54%.

[0026] Example 2 In Example 1, the sulfur content was changed to 0.8 parts by weight.

[0027] Example 3 In Example 1, the amount of sulfur was changed to 0.4 parts by weight.

[0028] Example 4 In Example 1, the sulfur content was changed to 1.6 parts by weight.

[0029] Example 5 In Example 1, the amount of organic peroxide was changed to 2 parts by weight.

[0030] Example 6 In Example 1, the amount of organic peroxide was changed to 6 parts by weight.

[0031] Example 7 In Example 1, the dosage of the thiuram-based sulfurization accelerator was changed to 1 part by weight.

[0032] Example 8 In Example 1, the dosage of the thiuram-based sulfurization accelerator was changed to 7 parts by weight.

[0033] Comparative Example 1 In Example 1, no organic peroxides were used, and the sulfur content was changed to 1.8 parts by weight.

[0034] Comparative Example 2 In Example 1, sulfur is not used.

[0035] Comparative Example 3 In Example 1, the sulfur content was changed to 2.4 parts by weight.

[0036] Comparative Example 4 In Example 1, no organic peroxides are used.

[0037] Comparative Example 5 In Example 1, the amount of organic peroxide was changed to 8 parts by weight.

[0038] Comparative Example 6 In Example 1, no thiuram-based vulcanization accelerator was used.

[0039] Comparative Example 7 In Example 1, the dosage of the thiuram-based sulfurization accelerator was changed to 12 parts by weight.

[0040] The results obtained in the above embodiments and comparative examples are shown in Tables 1 to 2 below.

[0041] Table 1

[0042] Table 2

Claims

1. A nitrile rubber composition, characterized in that, Relative to 100 parts by weight of nitrile rubber, it contains 0.2 to 1.6 parts by weight of sulfur, 2 to 6 parts by weight of organic peroxide, and 1 to 7 parts by weight of vulcanization accelerator.

2. The nitrile rubber composition according to claim 1, characterized in that, The vulcanization accelerator is a thiuram-based vulcanization accelerator or a thiazole-based vulcanization accelerator.

3. The nitrile rubber composition according to claim 1, characterized in that, It does not contain vulcanization delay agents.

4. A vulcanized molded article, characterized in that, The nitrile rubber composition of claim 1 is a vulcanized molded article.

5. The vulcanized molded article according to claim 4, characterized in that, According to JIS K-6262, the load characteristics measured by the compressive stress of a large test piece with a diameter of φ29±5mm and a thickness of 12.5±5mm when compressed at a constant speed of 10mm / min are above 4.1kN at 30% compression.

6. A buffer element, characterized in that, It is composed of the vulcanized molded article as described in claim 4 or 5.

7. The buffer according to claim 6, characterized in that, An impact stop component installed in the power steering system of an automobile.

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