Vibration-damping rubber composition and vibration-damping rubber

Abstract

To provide a technology capable of contributing to making it easier to achieve both vibration-proof properties and heat resistance / thermal settling resistance as desired.SOLUTION: There is provided a vibration-proof rubber composition comprising a natural rubber (NR) and / or an isoprene rubber (IR) and a butadiene rubber (BR) as main rubber components, which comprises, when the total amount of all rubber components is defined as 100 pts.mass, 1.8 to 5 pts.mass of 2-mercapto benzimidazole zinc salt, 0.2 to 1.1 pts.mass of N,N'-di-2-naphthyl-p-phenylenediamine, 0.2 to 0.7 pts.mass of sulfur as a vulcanizing agent and 2 to 7 pts.mass of tetrakis(2-ethylhexyl)thiuram disulfide as a sulfur donor compound.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a vibration-damping rubber composition that can be used, for example, in vibration-damping rubber such as bushings in vehicles such as automobiles, and which has excellent vibration damping properties against vibration, as well as excellent heat resistance (heat aging resistance), heat deformation resistance, etc., and to a vibration-damping rubber that has excellent heat adhesion using the vibration-damping rubber composition. [Background technology]

[0002] Conventionally, in various vehicles such as automobiles, various vibration-damping rubbers have been placed in parts that are sources of vibration to block and suppress vibration transmission, thereby reducing the intrusion of vibration and noise into the vehicle interior and reducing the diffusion of noise into the surrounding environment, for example, in order to improve the comfort of passengers.

[0003] It is known that reducing the dynamic spring constant (Kd) is effective in improving the vibration isolation properties of vibration-damping rubber, that is, in blocking vibration transmission. However, since vibration-damping rubber is required to withstand a certain static force, such as supporting heavy objects, the static spring properties (Ks) must be large to some extent. Therefore, it is desirable that the dynamic magnification (=Kd / Ks), which is the ratio of the dynamic spring constant (Kd) to the static spring constant (Ks), be small (i.e., have a low dynamic magnification). Furthermore, it is desirable that vibration-damping rubber possesses desired material properties, such as high durability against deformation due to repeated vibrations.

[0004] To meet these performance requirements (low dynamic magnification and high durability), diene-based blend rubber (hereinafter simply referred to as diene-based rubber) made by blending natural rubber (NR) and / or isoprene rubber (IR) with butadiene rubber (BR) is often used as the rubber component in vibration-damping rubber for vehicles. Furthermore, vibration-damping rubber is required to withstand heat, such as in extremely hot environments or from heat sources, and therefore must have heat resistance (heat aging resistance) and heat degradation resistance. However, diene-based rubber made by blending natural rubber (NR) and / or isoprene rubber (IR) with butadiene rubber (BR) is known to have poor heat resistance.

[0005] To address this problem, various proposals have been made for various anti-aging agents and vulcanization systems (vulcanization accelerators and vulcanizing agents) to improve the heat resistance of the above-mentioned diene-based rubber. For example, a diene-based rubber composition (Patent Document 1) has been proposed in which the blending ratio of anti-aging agents is set so that the amount of amine-based anti-aging agent is in the range of 0.5 to 3 moles per mole of benzimidazole group of benzimidazole-based anti-aging agent, and the total amount of anti-aging agents is in the range of 1 to 10 parts by weight per 100 parts by weight of rubber component. In addition, vibration-damping rubber compositions (Patent Document 2) have been proposed, which are blends of natural rubber containing specified amounts of 2-mercaptobenzimidazole zinc salt and 4,4'-bis(α,α-dimethylbenzyl)diphenylamine with butadiene rubber, and vibration-damping rubber compositions (Patent Document 3) that contain a compound having a carbon-carbon double bond at the end and a carbonyl group at the α-position, and an imidazole-based anti-aging agent.

[0006] As for vulcanization systems (vulcanization accelerators and vulcanizing agents), there is a known technique for improving heat resistance by crosslinking (vulcanizing) using sulfur donor compounds (sulfur donors) such as tetramethylthiuram disulfide (TMTD) or 4,4'-dithiodimorpholine, either by including a small amount of sulfur or by not including sulfur. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2002-194140 [Patent Document 2] Japanese Patent Application Publication No. 11-116733 [Patent Document 3] Japanese Patent Publication No. 2015-025060 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] As mentioned in the above proposal, it is well known that butadiene rubber is included in the rubber component to obtain desired vibration isolation characteristics (such as low dynamic magnification). However, the inclusion of an anti-aging agent often increases the dynamic magnification, and depending on the type and amount of anti-aging agent used, it can be difficult to achieve the desired balance between vibration isolation characteristics and heat resistance and heat degradation resistance.

[0009] For example, Patent Document 1 describes using a rubber component containing terminally modified butadiene rubber to achieve both heat resistance and low dynamic magnification, and using 2-mercaptobenzimidazole zinc salt as an imidazole-based antioxidant and N,N'-di-β-naphthyl-p-phenylenediamine as an amine-based antioxidant. It also describes setting the blending ratio of the antioxidants to a range of 0.5 to 3 moles of the amine-based antioxidant per mole of benzimidazole group of the benzimidazole-based antioxidant.

[0010] Here, 2-mercaptobenzimidazole zinc salt is given by the following formula:

[0011] [ka]

[0012] This compound, represented by [formula], has two imidazole groups in one molecule and a molecular weight of 397.85.

[0013] N,N'-di-β-naphthyl-p-phenylenediamine is given by the following formula

[0014] [ka]

[0015] It is a compound with a molecular weight of 360.45, as shown by [formula].

[0016] In the case of Patent Document 1, since it is specified that 0.5 to 3 moles of an amine-based antioxidant are blended per mole of the benzimidazole group of the benzimidazole-based antioxidant, the blending amount of N,N'-di-β-naphthyl-p-phenylenediamine with respect to 1 part by mass of zinc 2-mercaptobenzimidazole (2 moles of imidazole group) is in the range of [0.5×360.45 / (397.85 / 2)=] 0.906 part by mass to [3×360.45 / (397.85 / 2)=] 5.436 parts by mass. In other words, with respect to 1 part by mass of N,N'-di-β-naphthyl-p-phenylenediamine, zinc 2-mercaptobenzimidazole (2 moles of imidazole group) should be blended in the range of 0.184 part by mass to 1.104 parts by mass.

[0017] However, as a result of the inventors' detailed examination, when N,N'-di-β-naphthyl-p-phenylenediamine is contained in the anti-vibration rubber composition in an amount of a certain level or more, the dynamic magnification factor may increase, and further improvement may be required to achieve both heat resistance and anti-vibration characteristics (dynamic magnification factor). In Patent Document 1, when the content of N,N'-di-β-naphthyl-p-phenylenediamine is set relatively low (for example, set to 1 part by mass or less), and when the content of zinc 2-mercaptobenzimidazole is set relatively high (for example, set to 1 part by mass or more), there is no disclosure or even suggestion regarding the heat resistance improvement effect.

[0018] In Patent Document 2, in order to improve low dynamic magnification and sag resistance, it describes a composition containing a butadiene rubber having a cis-1,4 bond content of 97% or more, and containing zinc salt of 4,4'-bis(α,α-dimethylbenzyl)diphenylamine and 2-mercaptobenzimidazole, or a methylated derivative thereof as an antioxidant for improving heat resistance.

[0019] However, as a result of the inventors' detailed examination, when 4,4'-bis(α,α-dimethylbenzyl)diphenylamine is contained in the anti-vibration rubber composition in an amount of a certain level or more, it not only increases the dynamic magnification factor, but depending on the respective contents, the long-term heat resistance may be insufficient.

[0020] In Patent Document 3, a vibration damping rubber composition containing a compound having a carbonyl group at the α-position and an imidazole-based antioxidant for diene rubber is described.

[0021] However, as a result of the inventors' study, although a compound having a carbonyl group at the α-position can greatly contribute to damping properties as described in Patent Document 3, the vulcanization rate increases when added to a vibration damping rubber composition, and the scorch stability tends to decrease significantly (the scorch time becomes shorter). There were also cases where scorch (premature vulcanization) occurred during storage of the vibration damping rubber composition, or where vulcanization progressed during injection in injection molding, making molding difficult. Furthermore, although a compound having a carbonyl group at the α-position can greatly contribute to improving damping properties as described in Patent Document 3, the dynamic magnification factor increases significantly, so the low dynamic magnification factor may be insufficient.

[0022] The present invention has been made in view of the above circumstances, and an object thereof is to provide a technology that can contribute to easily achieving both vibration damping characteristics and heat resistance, and heat resistance sag resistance as desired.

Means for Solving the Problems

[0023] The inventors of the present invention have intensively studied to obtain a vibration damping rubber composition that achieves the above object.

[0024] As a result, in a vibration damping rubber composition having natural rubber (NR) and / or isoprene rubber (IR) and butadiene rubber (BR) excellent in low dynamic magnification factor and durability as main rubber components, when the total rubber component is 100 parts by mass, 1.8 to 5 parts by mass of zinc 2-mercaptobenzimidazole and 0.2 to 1.1 parts by mass of N,N'-di-2-naphthyl-p-phenylenediamine are contained, and 0.2 to 0.7 parts by mass of sulfur is contained as a vulcanizing agent and a specific amount of a compound serving as a sulfur donor (sulfur giver) is contained, a vibration damping rubber composition and a vibration damping rubber that achieve the above object were obtained, and the invention was completed.

[0025] In other words, the following [1] to [4] are examples of the vibration-damping rubber composition and vibration-damping rubber of the present invention.

[0026] [1] A vibration-damping rubber composition comprising natural rubber (NR) and / or isoprene rubber (IR) and butadiene rubber (BR) as the main rubber components, characterized in that, when the total rubber components are 100 parts by mass, it contains 1.8 to 5 parts by mass of 2-mercaptobenzimidazole zinc salt, 0.2 to 1.1 parts by mass of N,N'-di-2-naphthyl-p-phenylenediamine, 0.2 to 0.7 parts by mass of sulfur, and 2 to 7 parts by mass of tetrakis(2-ethylhexyl)thiuram disulfide.

[0027] [2] A vibration-damping rubber composition comprising natural rubber (NR) and / or isoprene rubber (IR) and butadiene rubber (BR) as the main rubber components, characterized in that, when the total rubber components are 100 parts by mass, it contains 1.8 to 5 parts by mass of 2-mercaptobenzimidazole zinc salt, 0.2 to 1.1 parts by mass of N,N'-di-2-naphthyl-p-phenylenediamine, 0.2 to 0.7 parts by mass of sulfur, and 1 to 3 parts by mass of 2-(4-morpholinodithio)benzothiazole.

[0028] [3] The above [1] or [2] is a blend of natural rubber (NR) and butadiene rubber in which the main rubber component is a blend of natural rubber (NR) and butadiene rubber in an NR / BR ratio of 90 / 10 to 60 / 40, wherein the butadiene rubber has a Mooney viscosity (ML) at 100°C. 1+4 It is preferable to use a vibration-damping rubber composition in which the ratio is 50 to 75.

[0029] [4] The vibration-damping rubber is characterized in that the vibration-damping rubber composition described in any of [1] to [3] above is vulcanized and bonded to the surface of the metal fitting via an adhesive layer provided on the surface of the metal fitting, so that the metal fitting and the vulcanized rubber made of the vibration-damping rubber composition are integrally formed. [Effects of the Invention]

[0030] According to the present invention, it is possible to make it easier to achieve a desired balance between vibration damping characteristics, heat resistance, and heat degradation resistance. [Brief explanation of the drawing]

[0031] [Figure 1] This is a schematic diagram illustrating test piece 1, which is made using each of the vibration-damping rubber compositions from Examples 1 to 13 and Comparative Examples 1 to 15. [Modes for carrying out the invention]

[0032] The following describes in detail matters related to the implementation of the present invention.

[0033] As described above, the vibration-damping rubber composition of the present invention is a vibration-damping rubber composition mainly composed of natural rubber (NR) and / or isoprene rubber (IR) and butadiene rubber (BR), wherein, when the total rubber components are 100 parts by mass, it contains 1.8 to 5 parts by mass of 2-mercaptobenzimidazole zinc salt and 0.2 to 1.1 parts by mass of N,N'-di-2-naphthyl-p-phenylenediamine, 0.2 to 0.7 parts by mass of sulfur as a vulcanizing agent and 2 to 7 parts by mass of tetrakis(2-ethylhexyl)thiuram disulfide as a sulfur donor compound.

[0034] With this configuration, it is possible to provide a vibration-damping rubber composition for manufacturing vibration-damping rubber that has desired heat resistance (heat aging resistance), heat degradation resistance, etc., while suppressing an increase in dynamic magnification.

[0035] Furthermore, instead of containing tetrakis(2-ethylhexyl)thiuram disulfide as the sulfur donor compound, the composition may also contain 2-(4-morpholinodithio)benzothiazole (1 to 3 parts by mass). This makes it possible to provide a vibration-damping rubber composition that suppresses the increase in dynamic magnification while possessing desired heat resistance, heat fatigue resistance, etc., and furthermore, exhibiting small changes in vibration characteristics (spring constant) even when exposed to a thermal environment for a long period of time.

[0036] Furthermore, the vibration-damping rubber composition may be vulcanized and bonded to the surface of the metal fitting via an adhesive layer provided on the metal fitting surface, thereby making it possible to provide a vibration-damping rubber with excellent heat resistance and adhesion in which the metal fitting and the vulcanized rubber of the vibration-damping rubber composition are integrally formed.

[0037] Next, we will describe each component applicable to the vibration-damping rubber composition and vibration-damping rubber (rubber molded product) of this embodiment. Hereafter, when indicating the content of all components (materials), we may simply refer to it as parts by mass, which means the parts by mass of the component when the total rubber components are assumed to be 100 parts by mass.

[0038] [Rubber components] In the vibration-damping rubber composition according to this embodiment, natural rubber (NR) and / or isoprene rubber (IR) and butadiene rubber (BR) are used as the main rubber components in the rubber composition. This main rubber component means that the total amount of natural rubber (NR) and / or isoprene rubber (IR) and butadiene rubber (BR) is 90% by mass or more of the total rubber components.

[0039] Regarding the rubber component, it is preferable that natural rubber be included, for example, from the viewpoint of the stability of rubber strength and the durability of the vibration-damping rubber. There are no particular restrictions on the natural rubber, and for example, ordinary natural rubber used in vibration-damping rubber can be used. Specifically, for example, sheet rubber (including crepes) includes all grades such as RSS (RIBBED SMOKED SHEET), WHITE CREPES, PALE CREPES, ESTATE BROWN CREPES, COMP CREPES, THIN BROWN CRAPES (RIMILLS), THICH BLANKET CRAPES (AMBERS), FLAT BARK CREPES, and PURE SMOKED BRANKET CRAPES. Block rubber includes SMR (STANDARD MALAYSIAN RUBBER), SIR (STANDARD INDONESIAN RUBBER), STR (STANDARD THAI RUBBER), SSR (STANDARD SINGAPOREAN RUBBER), SCR (STANDARD CEYLON RUBBER), and SVR (STANDARD VIETNAMESE RUBBER).

[0040] Furthermore, the rubber component preferably includes butadiene rubber (BR) from the viewpoint of low dynamic magnification and durability. That is, it is preferable to have a diene-based rubber blend of natural rubber (NR) and butadiene rubber (BR). The blending ratio of natural rubber (NR) and butadiene rubber (BR) can be set as appropriate, and as an example, the natural rubber (NR) / butadiene rubber (BR) ratio can be in the range of 90 / 10 to 50 / 50 (mass ratio), preferably in the range of 90 / 10 to 60 / 40. In this range, it is possible to obtain vibration-damping rubber with excellent durability and low dynamic magnification. In natural rubber (NR) / butadiene rubber (BR), as the proportion of natural rubber (NR) increases, the vulcanized rubber strength is higher and more stable, and the variation in durability decreases. On the other hand, as the proportion of butadiene rubber (BR) increases, it becomes easier to obtain a vibration-damping rubber composition with even better low dynamic magnification.

[0041] There are no particular restrictions on the butadiene rubber (BR) applicable in this embodiment; for example, ordinary butadiene rubber used in vibration-damping rubber can be used. When durability against repeated deformation is important, a higher cis-1,4-bond content is preferable. For example, butadiene rubber with a cis-1,4-bond content of 90% or more (high-cis BR) is preferred, and high-cis BR with a cis-1,4-bond content of 93% or more is even more preferred.

[0042] Furthermore, for butadiene rubber (BR) with the same chemical composition, Mooney viscosity (ML) 1+4 The higher the Mooney viscosity (ML) at 100°C, the higher the molecular weight tends to be, and the better the durability, so for example, the Mooney viscosity (ML) at 100°C. 1+4 It is preferable to use one with a Mooney viscosity (ML) of 50 or more. 1+4 As the Mooney viscosity (ML) increases, the fluidity of the rubber tends to decrease, and Mooney viscosity (ML) 1+4 If the Mooney viscosity (ML) at 100°C is too high, the kneadability and moldability of the rubber material composition may decrease. 1+4 It is preferable to use a Mooney viscosity (ML) of 75 or less, and more preferably a Mooney viscosity (ML) of 75 or less. 1+4 One example is applying those with a value of 65 or less.

[0043] Specific examples of such butadiene rubbers include BR730, BR54, BR740 (all manufactured by ENEOS Material Co., Ltd.), Ubepol 390L (manufactured by Ube Industries, Ltd.), and BUNA CB21, CB22, CB1221 (all manufactured by Alantheo Co., Ltd.). On the other hand, when a lower dynamic magnification is required, for example, a terminally modified butadiene rubber with N-methylpyrrolidone groups at the ends (e.g., Nipol 1250H manufactured by Nippon Zeon Co., Ltd.) can be suitably used.

[0044] Isoprene rubber (IR) exhibits performance similar to natural rubber (NR), contains fewer impurities such as foreign substances, and can often be used as a substitute for natural rubber (NR). On the other hand, in terms of the stability of rubber strength and durability, natural rubber (NR) often yields better results and can therefore be preferred.

[0045] Furthermore, for purposes such as improving processability, there is no particular problem with appropriately including other rubber components other than diene rubbers, such as styrene-butadiene rubber (SBR) or EPDM (for example, in small amounts within the range of 10 parts by mass or less).

[0046] [Anti-aging agent] The vibration-damping rubber composition used in the rubber molded product of this embodiment contains 2-mercaptobenzimidazole zinc salt and N,N'-di-2-naphthyl-p-phenylenediamine as essential components as antioxidants.

[0047] 2-Mercaptobenzimidazole zinc salt is known as a secondary anti-aging agent and is generally used in combination with various amine-based and phenol-based anti-aging agents, which are primary anti-aging agents, at a concentration of 1 part by mass or less.

[0048] On the other hand, in this embodiment, the 2-mercaptobenzimidazole zinc salt is contained in an amount ranging from 1.8 parts by mass to 5 parts by mass. If the content of 2-mercaptobenzimidazole zinc salt is less than 1.8 parts by mass, the long-term improvement in heat resistance may not be sufficiently obtained. On the other hand, if the content of 2-mercaptobenzimidazole zinc salt is more than 5 parts by mass, no further improvement in heat resistance is obtained, and rather the compression set resistance tends to increase. A more preferable content of 2-mercaptobenzimidazole zinc salt is in the range of 1.9 parts by mass to 4 parts by mass.

[0049] Similar anti-aging agents, such as benzimidazole-based anti-aging agents, include 2-mercaptobenzimidazole and 2-mercaptomethylbenzimidazole. However, in a vibration-damping rubber composition as described in this embodiment, which mainly consists of natural rubber (NR) and / or isoprene rubber (IR) and butadiene rubber (BR), and contains 0.2 to 0.7 parts by mass of sulfur as a vulcanizing agent and a vulcanization accelerator that acts as a sulfur donor, 2-mercaptobenzimidazole has a smaller long-term improvement effect on heat resistance compared to 2-mercaptobenzimidazole zinc salt, and may also increase the compression set resistance. Furthermore, while 2-mercaptomethylbenzimidazole may provide a significant improvement in heat resistance, similar to 2-mercaptobenzimidazole zinc salt, it tends to increase the compression set resistance and is therefore unsuitable as a vibration-damping rubber.

[0050] The vibration-damping rubber composition used in the rubber molded product of this embodiment contains 0.2 to 1.1 parts by mass of N,N'-di-2-naphthyl-p-phenylenediamine as an amine-based anti-aging agent. This N,N'-di-2-naphthyl-p-phenylenediamine is known to have low volatility upon heating and to remain in the vulcanized rubber for a long period of time, making it suitable for use from the viewpoint of long-term heat resistance. Furthermore, when N,N'-di-2-naphthyl-p-phenylenediamine is used in combination with 2-mercaptobenzimidazole zinc salt, the combined effect may be such that even with a small amount of N,N'-di-2-naphthyl-p-phenylenediamine, a sufficient improvement in long-term heat resistance can be obtained.

[0051] On the other hand, if the content of N,N'-di-2-naphthyl-p-phenylenediamine becomes too high, it may increase the dynamic magnification of the vibration-damping rubber. Therefore, when 2-mercaptobenzimidazole zinc salt is used in combination (containing 1.8 to 5 parts by mass) as described above, even if the content of N,N'-di-2-naphthyl-p-phenylenediamine exceeds 1.1 parts by mass, no further improvement in heat resistance can be obtained.

[0052] Furthermore, in vibration-damping rubber prepared using a vibration-damping rubber composition containing an amine-based antioxidant in the proportions shown in Patent Document 1, the dynamic magnification tends to increase in most cases, and the improvement effect on heat resistance under long-term thermal conditions (e.g., exposure to heat at 100°C for 500 hours or more) is often insufficient.

[0053] Furthermore, as described in Patent Document 3, antioxidants having a carbonyl group at the α-position are known as reactive antioxidants and have excellent long-term heat resistance. However, vibration-damping rubber made using a vibration-damping rubber composition containing such an antioxidant has a carbonyl group at the α-position tends to have an increased dynamic magnification, which is undesirable. Moreover, since it often reduces resistance to compression set, it is preferable not to include it in this embodiment.

[0054] It is known that diene rubbers have poor ozone resistance. Therefore, when the purpose is to impart ozone resistance, it is preferable to include, for example, N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine and / or N-phenyl-N'-isopropyl-p-phenylenediamine (for example, in an amount between 2 parts by mass and 5 parts by mass).

[0055] [Sulfur and sulfur donor compounds (sulfur donors)] The vibration-damping rubber composition of this embodiment contains sulfur as a vulcanizing agent in an amount of 0.2 to 0.7 parts by mass (preferably 0.3 to 0.6 parts by mass) and a specific amount of a specific sulfur donor compound.

[0056] It is known that some vulcanization accelerators possess both vulcanization accelerator and sulfur donor (crosslinking agent) effects for low-sulfur (low sulfur content) rubber compositions, and some of these are classified as vulcanization accelerators, but in the description of this embodiment, they may be referred to as sulfur donor compounds.

[0057] Generally, a known technique for improving the heat resistance of rubber compositions is to crosslink (vulcanize) them with sulfur donor compounds such as tetramethylthiuram disulfide (TMTD) without containing sulfur (sulfur-free vulcanization method). However, detailed investigations by the present inventors revealed that rubber compositions obtained by this sulfur-free vulcanization method often do not maintain sufficient heat resistance in the long term. The reason for this is likely that even if the rubber composition vulcanized by this sulfur-free vulcanization method reaches a heat-resistant crosslinked form, it contains a large amount of unreacted components and reaction residues derived from the sulfur donor compound, which reduces its long-term heat resistance.

[0058] On the other hand, by including a small amount of sulfur (0.2 to 0.7 parts by mass) in the vibration-damping rubber composition of this embodiment, it is possible to reduce reaction residue and unreacted residue derived from the sulfur donor compound, which is expected to improve long-term heat resistance.

[0059] The sulfur used in this embodiment is not particularly limited, but for example, known sulfurs used as compounding materials for rubber can be used. Specific examples include powdered sulfur, precipitated sulfur, surface-treated sulfur obtained by surface treatment of powdered or precipitated sulfur, and insoluble sulfur.

[0060] Suitable sulfur donor compounds include tetrakis(2-ethylhexyl)thiuram disulfide, tetrabenzylthiuram disulfide, 2-(4'-morpholinodithio)benzothiazole, 4,4'-dithiodimorpholine, tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetrabutylthiuram disulfide, and dipentamethylenethiuram tetrasulfide. Among these, tetrakis(2-ethylhexyl)thiuram disulfide, tetrabenzylthiuram disulfide, and 2-(4'-morpholinodithio)benzothiazole are preferred. In particular, tetrakis(2-ethylhexyl)thiuram disulfide is more preferred from the viewpoint of heat resistance, compression set resistance, and heat adhesion resistance. The content of tetrakis(2-ethylhexyl)thiuram disulfide is set within the range of 2 to 7 parts by mass.

[0061] When tetrakis(2-ethylhexyl)thiuram disulfide is used, it tends to exhibit superior long-term heat resistance compared to when other thiuram-based sulfur donor compounds are used. This is likely because the reaction activity of unreacted components and reaction residues derived from the sulfur donor compound is kept low, so even if the vibration-damping rubber composition is exposed to a thermal environment for a long period of time, unnecessary reactions are less likely to occur.

[0062] In general, the thermal degradation mechanism of rubber is often explained by auto-oxidation (degradation due to high-temperature auto-oxidation) that occurs in the presence of oxygen in the air. Even in the case of vibration-damping rubber, it is extremely important to suppress the degradation of the rubber in the parts exposed to the surface (hereinafter simply referred to as exposed parts as appropriate).

[0063] However, in the case of vibration-damping rubber that has parts covered with metal, such as rubber bushings (hereinafter simply referred to as non-exposed parts as appropriate) or thick parts (for example, parts with a rubber thickness of 4 mm or more), changes in the properties of the rubber in the non-exposed parts and the rubber inside the thick parts will affect the vibration characteristics, even if they are not exposed to air. For this reason, in the case of general vibration-damping rubber, the rubber in the exposed parts was prone to oxidative degradation and surface hardening due to long-term thermal aging.

[0064] Therefore, in the vibration-damping rubber of this embodiment, when the aim is to further reduce the change in vibration characteristics due to long-term heat exposure, 2-(4'-morpholinodithio)benzothiazole is used as the sulfur donor compound. With a vibration-damping rubber composition using 2-(4'-morpholinodithio)benzothiazole as the sulfur donor compound in this way, the change in rubber hardness in the internal parts of the vibration-damping rubber is small, and the change in vibration characteristics is suppressed by the balance between the degree of hardening of the rubber surface in exposed and non-exposed parts and the small change in rubber hardness in the interior (for example, the interior of the thick parts).

[0065] In the vibration-damping rubber composition of this embodiment, the content of 2-(4-morpholinodithio)benzothiazole is in the range of 1 to 3 parts by mass, preferably 1.2 to 3 parts by mass. If the content of 2-(4-morpholinodithio)benzothiazole exceeds 3 parts by mass, the heat-resistant adhesiveness may decrease, which is undesirable.

[0066] Furthermore, m-phenylenedimaleimide can also be used as a vulcanizing agent in combination with sulfur and sulfur donor compounds.

[0067] [Vulcanization accelerator] Furthermore, it is preferable to appropriately use known vulcanization accelerators, such as those used as compounding materials for sulfur-vulcanized rubber, in the vibration-damping rubber composition of this embodiment. The vulcanization accelerator is not particularly limited, and specific examples include sulfenamide compounds such as N-cyclohexyl-2-benzothiazole sulfenamide, N-oxydiethylene-2-benzothiazole sulfenamide, and N,N-diisopropyl-2-benzothiazole sulfenamide; thiazole compounds such as 2-mercaptobenzothiazole, 2,2'-dibenzothiazolyl disulfide, zinc salt of 2-mercaptobenzothiazole, and cyclohexylamine salt of 2-mercaptobenzothiazole; guanidine compounds such as diphenylguanidine, triphenylguanidine, diorsonitrile guanidine, orthonitrile biguanide, and diphenylguanidine phthalate; and thiuram compounds such as tetramethylthiuram monosulfide.

[0068] Furthermore, to adjust the vulcanization rate and delay the scorch time, anti-scorch agents such as N-cyclohexylthiophthalimide and N-phenyl-N-(trichloromethylthio)benzenesulfonamide can be preferably used.

[0069] [Carbon Black] The vibration-damping rubber composition of this embodiment can use carbon black as appropriate, and known types can be used as one example, but it is not particularly limited. Specific examples include FT-grade, SRF-grade, GPF-grade, FEF-grade, MAF-grade, HAF-grade, ISAF-grade, and SAF-grade carbon blacks. Among these, FEF-grade, MAF-grade, and HAF-grade carbon blacks are preferred because they offer a good balance of rubber strength, durability, and low dynamic magnification. Furthermore, from the viewpoint of support performance for automobile vehicles and low dynamic magnification, for example, SRF-HS grade carbon black, which has a well-developed structure, is preferred.

[0070] [Filler] The vibration-damping rubber composition of this embodiment may contain fillers for the purpose of adjusting hardness and improving processability. For example, fillers commonly used in rubber compositions, such as silica (wet silica, dry silica, colloidal silica, etc.), calcium carbonate, clay, and talc, can be used as appropriate. These fillers can be used alone or in combination of two or more.

[0071] [Process oil] The vibration-damping rubber composition of this embodiment may contain process oil for the purpose of adjusting hardness and improving processability. Examples of process oils include naphthenic oils, paraffinic oils, and aromatic oils. These process oils can be used individually or in combination of two or more. The amount of process oil can be set as appropriate, but it is preferable to set it within the range of 0 to 20 parts by mass. If the amount of process oil exceeds 20 parts by mass, the long-term heat resistance may decrease, which is undesirable.

[0072] [Sulfurization aid] The vibration-damping rubber composition of this embodiment preferably contains a vulcanization aid of zinc oxide (ZnO) or a composite zinc oxide, and it is even more preferable to include it together with other vulcanization aids (e.g., stearic acid, zinc stearate, etc.).

[0073] In the case of composite zinc oxide, there are known types that have a layer of zinc oxide (zinc oxide) on the surface and contain an inorganic metal salt as a core component. One example of this is the META-Z L series (META-Z L40, L50, L60) manufactured by Inoue Lime Industry Co., Ltd.

[0074] The content of zinc oxide or composite zinc oxide can be set as appropriate, but for example, it is preferably 3 parts by mass or more and 15 parts by mass or less per 100 parts by mass of rubber component.

[0075] The content of stearic acid or zinc stearate can be set as appropriate, but for example, it is preferably 0.1 to 2 parts by mass per 100 parts by mass of rubber component.

[0076] [Processing aid] The vibration-damping rubber composition of this embodiment may contain processing aids for the purpose of improving processability. Compounds commonly used in the processing of rubber can be appropriately applied as processing aids. Examples include various additives such as lubricants, tackifiers, dispersants, compatibilizers, and homogenizers.

[0077] [Method for preparing vibration-damping rubber composition] The vibration-damping rubber composition of this embodiment can be prepared by kneading the essential components described above—the rubber component, the anti-aging agent component, the vulcanizing agent component (and other materials listed above as needed)—using a kneader such as a pressure kneader, Banbury mixer, Intermix mixer, or open roll.

[0078] The vibration-damping rubber of this embodiment is obtained by vulcanizing the vibration-damping rubber composition described above. The vibration-damping rubber composition can be appropriately vulcanized (for example, vulcanized at a vulcanization temperature of 145 to 170°C for 3 to 30 minutes) to become an elastic body for vibration-damping rubber.

[0079] In other words, the vibration-damping rubber made from an elastic body obtained by vulcanizing the vibration-damping rubber composition of this embodiment exhibits excellent long-term heat resistance, a low compression set, and a low dynamic magnification, resulting in superior vibration isolation. For this reason, it can be suitably used as vibration-damping rubber in vehicles such as automobiles and various types of machinery where harsh thermal environments and vibration isolation performance from vibration sources are required. [Examples]

[0080] The following are examples of this embodiment (Examples 1 to 13), but the present invention is not limited to these examples.

[0081] <<Preparation of vibration-damping rubber composition>> The vibration isolation rubber compositions of Examples 1 to 13 and Comparative Examples 1 to 15 were prepared by kneading various materials at the ratios shown in Tables 1 to 4. In the kneading, first, materials other than the vulcanizing agent, sulfur donor compound, and vulcanization accelerator were kneaded using a Banbury mixer for 5 minutes to obtain a kneaded product. Next, in the kneaded product, while cooling using an open roll (cooling with the cooling water temperature in the open roll set to about 20°C), the vulcanizing agent, sulfur donor compound, and vulcanization accelerator were added and kneaded for 5 minutes to prepare each vibration isolation rubber composition.

[0082]

Table 1

[0083]

Table 2

[0084]

Table 3

[0085]

Table 4

[0086] The various materials described in Tables 1 to 4 are as follows. · Natural rubber: SVR CV60 · Butadiene rubber - 1: cis 1,4 - bond content 96%, Mooney viscosity (ML 1+4 ) 63, "BUNA - CB21" manufactured by ARLANXEO Corporation · Butadiene rubber - 2: cis 1,4 - bond content 96%, Mooney viscosity (ML 1+4 ) 44, "BR - 01" manufactured by ENEOS MATERIAL Co., Ltd. · Butadiene rubber - 3: cis 1,4 - bond content 35%, Mooney viscosity (ML 1+4)59. Nippon Zeon Co., Ltd. "BR1250H" • Anti-aging agent-1: N,N'-di-2-naphthyl-p-phenylenediamine, manufactured by Ouchi Shinko Co., Ltd. in "Nocrac White" • Anti-aging agent - 2:2-mercaptobenzimidazole zinc salt, manufactured by Ouchi Shinko Co., Ltd., "Nocrac MBZ" • Anti-aging agent-3: (N-phenyl-N'-(1,3-dimethylbutyl)-P-phenylenediamine), manufactured by Ouchi Shinko Co., Ltd., "Nocrac 6C" • Anti-aging agent - 4:2-mercaptobenzimidazole, manufactured by Ouchi Shinko Co., Ltd. "Nocrac MB" • Anti-aging agent - 5:2-mercaptomethylbenzimidazole, manufactured by Ouchi Shinko Co., Ltd., "Nocrac MMB" • Anti-aging agent-6: N-phenyl-N'-(3-methacryloyloxy-2-hydroxypropyl)-p-phenylenediamine, manufactured by Ouchi Shinko Co., Ltd. "Nocrac G-1" • Vulcanizing agent: Sulfur, "Kinka-jirushi Fine Powdered Sulfur 200MESH" manufactured by Tsurumi Chemical Industries Co., Ltd. • Sulfur donor compound-1: Tetrakis(2-ethylhexyl)thiuram disulfide, manufactured by Ouchi Shinko Co., Ltd. "Noxellar TOT-N" • Sulfur donor compound - 2:2-(4-morpholinoditio)benzothiazole, manufactured by Ouchi Shinko Co., Ltd., "Noxella MDB-P" • Sulfur donor compound-3: Tetramethylthiuram disulfide, manufactured by Ouchi Shinko Co., Ltd. "Noxellar TT-P" • Sulfur donor compound - 4:4,4'-dithiodimorpholine, manufactured by Ouchi Shinko Co., Ltd., "Balnock R" • Vulcanization accelerator-1: (N-cyclohexyl-2-benzothiazolyl sulfenamide), manufactured by Ouchi Shinko Chemical Co., Ltd., "Noxellar CZ-G" • Vulcanization accelerator - 2: 1,3-diphenylguanidine, manufactured by Ouchi Shinko Chemical Co., Ltd., "Noxellar DP" • Carbon Black-1: Nitrogen adsorption specific surface area 47 m² 2 / g (MAF class), manufactured by Nippon Steel Carbon Co., Ltd. "Nitelon #10" • Carbon Black-2: Nitrogen adsorption specific surface area 22 m² 2 / g (SRF-HS grade), manufactured by Asahi Carbon Co., Ltd. "Asahi #52" • Paraffin wax: (Wax) Nippon Seiro Co., Ltd. "Ozo Ace 0100" • Composite zinc oxide: "META-Z-L60" manufactured by Inoue Lime Industry Co., Ltd. • Stearic acid: "Stearic Acid Tsubaki" manufactured by Nippon Oil & Fats Co., Ltd. • Naphthenic oil: "Crysef Oil H56" manufactured by ENEOS Corporation.

[0087] <<Preparation of evaluation samples (vulcanized rubber)>> [Preparation of vulcanized rubber sheets for measuring tensile properties and properties after heat aging] In each of the vibration-damping rubber compositions shown in Tables 1 to 4, Examples 1 to 13 and Comparative Examples 1 to 15, vulcanization molding was performed at 160°C for a vulcanization time of 10 minutes using a mold for 2 mm thick sheets with a cavity thickness of approximately 2 mm, to obtain a 2 mm thick vulcanized rubber sheet (hereinafter appropriately referred to simply as the evaluation rubber sheet).

[0088] [Preparation of vulcanized rubber test specimens for compression set testing] Each of the vibration-damping rubber compositions shown in Tables 1 to 4, Examples 1 to 13 and Comparative Examples 1 to 15, was vulcanized at 160°C for 15 minutes by compression molding using a cylindrical mold for creating test specimens with a diameter of 29.0 mm and a height of 12.5 mm, to obtain cylindrical vulcanized rubber test specimens (hereinafter simply referred to as rubber test specimens) with a diameter of 29.0 mm and a height of 12.5 mm for Type A durometer hardness and compression set testing.

[0089] [Preparation of test pieces for vibration-damping rubber] To prepare the vibration-damping rubber test piece 1 shown in Figure 1, two 50mm x 50mm iron fittings 2, each with a bolt 3 erected in the center of one side, were first prepared. The side of each fitting 2 without the bolt 3 was shot-blasted to create a rough surface. Next, Chemlock 205 (manufactured by Rhode Far East Co., Ltd.) was applied as a primer adhesive to each side of each fitting 2 without the bolt 3, and dried in an 80°C atmosphere for 20 minutes to form a primer adhesive layer (10 μm thick). After the fittings 2 with this primer adhesive layer were cooled to room temperature, Chemlock 6125 (manufactured by Rhode Far East Co., Ltd.) was applied as a topcoat adhesive to the surface of the primer adhesive layer, and dried in an 80°C atmosphere for 20 minutes to form a topcoat adhesive layer (10 μm thick). Then, each metal fitting 2 was placed inside the molding die (positioned so that the top adhesive layers of each metal fitting 2 faced each other), and further, using an injection molding machine, unvulcanized rubber (vibration-damping rubber composition) was filled between each metal fitting 2 inside the molding die and vulcanized (160°C for 15 minutes) to produce a test piece 1 of a rectangular vibration-damping rubber with metal fittings 2, which was formed into a rectangular parallelepiped measuring 40 mm × 40 mm × 30 mm as shown in Figure 1.

[0090] ≪Test methods, evaluation methods, and judgments for vibration-damping rubber compositions (vulcanized rubber)≫ The test methods and evaluation methods for the vibration-damping rubber compositions (vulcanized rubber) of Examples 1-13 and Comparative Examples 1-15, as described in Tables 1-4, are as follows. The evaluation results and judgment results are shown in accordance with Tables 5-8 below.

[0091] [Initial physical properties: Type A durometer hardness] Each evaluation rubber sheet obtained using the vibration-damping rubber compositions described in Tables 1 to 4 (Examples 1 to 13 and Comparative Examples 1 to 15) was prepared in sets of four and laminated to obtain a laminated sheet (i.e., a four-layer laminated sheet with a thickness of approximately 8 mm). The hardness (HA) of each laminated sheet was then measured using a Type A durometer in accordance with JIS K6253-3 (2012).

[0092] [Initial physical properties: Tensile properties] Each evaluation rubber sheet obtained using the vibration-damping rubber compositions described in Tables 1 to 4 (Examples 1 to 13 and Comparative Examples 1 to 15) was punched out using a JIS No. 3 dumbbell, and the elongation at break (EB) and tensile strength at break (TB) were measured in accordance with JIS K 6251.

[0093] [Compression set rate] For each rubber test specimen obtained using the vibration-damping rubber compositions described in Tables 1 to 4 (Examples 1 to 13 and Comparative Examples 1 to 15), in accordance with JIS K6262 (2013), the specimen was compressed to 25.0% in the height direction (height 9.38 mm) using a jig and left for 22 hours in a gear-type aging tester (forced circulation type thermal aging tester) at an ambient temperature of 100°C. After that, the specimen was removed along with the jig and immediately released. After this release, the specimen was left on a wooden stand at an ambient temperature of 23°C for 30 minutes, and the height (h1) of the rubber test specimen was measured to calculate the compression set CS (%).

[0094] The method (formula) for calculating the compression set CS conforms to JIS K6262 (2013) and is as shown in formula (1) below.

[0095] CS(%)=((h0-h1) / (h0-hs))×100 ……(1) In equation (1), h0 represents the thickness of the rubber test piece before compression (mm), h1 represents the thickness of the rubber test piece after removal from the compression device (mm), and hs represents the thickness of the spacer used (mm).

[0096] The smaller the value of the compression set CS calculated using equation (1), the lower the compression set rate and the better the heat resistance to deformation. Therefore, as an evaluation criterion, a compression set CS (%) of less than 30% was judged as "◎", a CS (%) between 30% and 35% was judged as "〇", and a CS (%) of 35% or more was judged as "×".

[0097] [Heat aging resistance-1] Each evaluation rubber sheet obtained using the vibration-damping rubber compositions described in Tables 1 to 4, Examples 1 to 13 and Comparative Examples 1 to 15, was first punched out using a JIS No. 3 dumbbell, and then subjected to a thermal aging test in accordance with JIS K 6257 by holding it in a gear-type aging tester (forced-circulation thermal aging tester) at an ambient temperature of 100°C for various holding times (72 hours, 168 hours, 240 hours, 336 hours, 500 hours, 1000 hours, 1500 hours).

[0098] Next, the hardness (HA), elongation at break (EB), and tensile strength at break (TB) after the thermal aging test were measured using the same method as described in the previous section [Initial Physical Properties].

[0099] Then, AHA (Duro-A) was determined from the difference in hardness (HA) before and after the thermal aging test. In addition, the rate of change (percentage change from the value before the thermal aging test to the value after the aging test) AcEB(%) and AcTB(%) were determined from the elongation at break (EB) and tensile strength at break (TB) before and after the thermal aging test.

[0100] Furthermore, as part of the evaluation criteria, a rating of "○" was given if both AcEB(%) and AcTB(%) were 50% or less at a holding time (heat aging time) of 1000 hours. Among those rated as "○", a rating of "◎" was given if the AcEB(%) at a holding time of 1500 hours was 60% or less. In addition, even if either or both of the AcEB(%) and AcTB(%) at a holding time of 1000 hours exceeded 50%, a rating of "△" was given if both AcEB(%) and AcTB(%) were 60% or less, as it was considered that the material could potentially be used as heat-resistant rubber. In addition, a rating of "×" was given if the AcEB(%) at a holding time of 1000 hours exceeded 60%.

[0101] [Initial vibration characteristics: Static characteristics Ks, Dynamic characteristics Kd100, Dynamic magnification] For each test piece 1 obtained using the vibration-damping rubber compositions of Examples 1-13 and Comparative Examples 1-15, first, in accordance with JIS K 6385 (2012), an axial load was applied through each bolt 3 to compress it by 5 mm in the axial direction (in the direction of the bolt 3) (compression at a displacement rate of 10 mm / min), and then the load was reduced (reduced at a displacement rate of 10 mm / min). This compression and reduction process was repeated twice. After this, the test piece was compressed again by 5 mm (i.e., the third loading process), and the load-deflection characteristics at the time of compression (third loading process) were measured, and a load-deflection curve was created based on this. Then, from the load-deflection curve, the load values ​​P1 and P2 (in N) when the deflection was 2 mm and 4 mm were read, respectively, and the static spring constant Ks (N / mm) was calculated by appropriately substituting these load values ​​P1 and P2 into the relational expression "Ks = (P2 - P1) / 2".

[0102] Separately, each test piece 1 was compressed axially by 3 mm via each bolt 3, as described above. A constant displacement harmonic compression vibration with an amplitude of ±0.05 mm centered on the 3 mm compressed position was applied at a frequency of 100 Hz from one bolt 3 side of the compressed test piece 1 (for example, the lower side shown in the figure). The dynamic spring constant Kd100 (N / mm) at 100 Hz was determined in accordance with the "Non-resonant method (a)" in the "Test method for vibration-damping rubber" of JIS-K-6385-2012. The dynamic magnification (=Kd100 / Ks) was then calculated from the determined dynamic spring constant (Kd100) and the static spring constant (Ks) calculated above.

[0103] As mentioned above, the dynamic magnification is a value that varies greatly depending on the type and content of the polymer and carbon black used. A lower dynamic magnification is desirable, but a balance with reinforcing properties is necessary. Therefore, in the evaluation, the dynamic magnification (1.56) when using the vibration-damping rubber composition of Example 1 was defined as the judgment criterion value, and a dynamic magnification of +8% or less from the judgment criterion value (i.e., 1.68 or less) was judged as "○", and a dynamic magnification of more than +8% from the judgment criterion value (i.e., greater than 1.68) was judged as "×".

[0104] [Heat aging resistance-2] Each test piece 1 obtained using the vibration-damping rubber compositions of Examples 1 to 13 and Comparative Examples 1 to 15 was first subjected to a thermal aging test by holding it in a gear-type aging tester (forced-circulation thermal aging tester) at an ambient temperature of 100°C for various holding times (72 hours, 168 hours, 240 hours, 336 hours, 500 hours, 1000 hours, and 1500 hours).

[0105] Next, after the thermal aging test (after removing test piece 1 from the gear-type aging tester), test piece 1 was left at an ambient temperature of 23°C for 16 hours to 3 days, and then the static spring constant (Ks) was measured in the same manner as in the item [Initial Vibration Characteristics] above.

[0106] Then, the rate of change (the percentage change between the value before the thermal aging test and the value after the thermal aging test) AcKs(%) was calculated from the difference in static spring constants (Ks) before and after the thermal aging test.

[0107] For evaluation purposes, a "◎" rating was given if the AcKs(%) for the heat aging test holding time (heat aging time) from 72 hours to 1500 hours was always +25 or less. Additionally, a "〇" rating was given if, although not meeting the "◎" criteria, the AcKs(%) at 1000 hours was +30 or less, and the AcKs(%) at 1500 hours was +40 or less. Furthermore, a "×" rating was given if the AcKs(%) at 1000 hours exceeded +30, and / or the AcKs(%) at 1500 hours exceeded +40.

[0108] [Heat-resistant adhesion test - 1, 2] In Heat Resistance Adhesion Test-1, each test piece 1 obtained using the vibration-damping rubber compositions of Examples 1-13 and Comparative Examples 1-15 was first stretched by 50% (stretched vertically in Figure 1) via each bolt 3, as described above, and held for 60 minutes in a gear-type aging test machine (forced circulation type thermal aging test machine) at an ambient temperature of 100°C. The presence or absence of adhesive delamination of each fitting 2 was visually observed. Subsequently, the test pieces were held for 30 minutes in each atmosphere, with the temperature further increased by 10°C, and the presence or absence of adhesive delamination of each fitting 2 was repeatedly visually checked in each atmosphere. Finally, the test pieces were held for 30 minutes in a 200°C atmosphere to confirm the presence or absence of adhesive delamination of each fitting 2, and the test was completed.

[0109] In this heat-resistant adhesion test-1, the higher the temperature at which delamination of each metal fitting 2 was prevented, the better the heat-resistant adhesion was judged to be. Tables 5 to 8 show the highest temperature at which delamination was prevented. For example, if there was no delamination at 160°C but delamination occurred at 170°C, "160°C" is written in Tables 5 to 8. If delamination was prevented even at 200°C, "200°C OK" is written.

[0110] Furthermore, in this heat-resistant adhesion test-1, two test pieces 1 were prepared for each vibration-damping rubber composition in Examples 1 to 13 and Comparative Examples 1 to 15. Of the test results of these two test pieces 1, the one with the lower peeling temperature was adopted as the indicator of heat-resistant adhesion in the heat-resistant adhesion test-1.

[0111] Next, in the heat-resistant adhesion test-2, each test piece 1, the same as in the heat-resistant adhesion test-1, was first stretched by 40% (stretched vertically in Figure 1) via each bolt 3, as described above, and then held in a gear-type aging test machine (forced-circulation type thermal aging test machine) at an ambient temperature of 100°C for various holding times (24 hours, 48 ​​hours, 72 hours). After each holding time had elapsed, the presence or absence of delamination of the adhesive on each fitting 2 was visually observed.

[0112] Furthermore, for test piece 1 in which no adhesive peeling was observed even after the holding time was set to 72 hours (after 72 hours had elapsed), the test piece was subsequently held in the test machine at an ambient temperature of 100°C for several days (30 days from the time it was first placed in the test machine), and then the presence or absence of adhesive peeling of each metal fitting 2 was visually observed.

[0113] In this heat-resistant adhesion test-2, two test pieces 1 were prepared for each vibration-damping rubber composition in Examples 1-13 and Comparative Examples 1-15. The result of the test piece 1 that showed earlier delamination was adopted as the indicator of heat-resistant adhesion in the heat-resistant adhesion test-2. In Tables 5-8, "30 days ○" indicates that there was no delamination of the adhesive of each metal fitting 2 after being held in the testing machine for 30 days.

[0114] For evaluation purposes, a test was judged as "◎" if the heat resistance limit temperature (the highest temperature at which delamination was prevented) in Heat Resistance Adhesion Test-1 was 170°C or higher, and a "30-day ○" result was obtained in Heat Resistance Adhesion Test-2. Furthermore, even if the heat resistance limit temperature in Heat Resistance Adhesion Test-1 was below 170°C, a "30-day ○" result was obtained in Heat Resistance Adhesion Test-2, it was judged as "○". Additionally, if a "30-day ○" result was not obtained in Heat Resistance Adhesion Test-2 (i.e., delamination occurred before 30 days had elapsed in the test machine), it was judged as "×".

[0115] [Overall Judgment] If any of the evaluation criteria above resulted in a "×" rating, the overall rating was determined to be "×". Furthermore, if there were no "×" ratings in any of the evaluation criteria, and there was one or fewer "△" ratings (with other items being "〇" or "◎"), the overall rating was determined to be "〇".

[0116] [Table 5]

[0117] [Table 6]

[0118] [Table 7]

[0119] [Table 8]

[0120] <<Verification results based on comparison of Examples 1-13 and Comparative Examples 1-15>> Based on the mixing ratios of various materials shown in Tables 1 to 4 and the results shown in Tables 5 to 8, the following can be observed.

[0121] First, each of the vibration-damping rubber compositions in Examples 1 to 8 has natural rubber (NR) and / or isoprene rubber (IR) and butadiene rubber (BR) as the main rubber components, and when the total rubber components are 100 parts by mass, it contains 1.8 to 5 parts by mass of 2-mercaptobenzimidazole zinc salt and 0.2 to 1.1 parts by mass of N,N'-di-2-naphthyl-p-phenylenediamine, and also contains 0.2 to 0.7 parts by mass of sulfur as a vulcanizing agent and 2 to 7 parts by mass of tetrakis(2-ethylhexyl)thiuram disulfide as a sulfur donor compound (hereinafter, these will be appropriately referred to simply as the "Examples 1 to 8 category compositions").

[0122] Furthermore, it can be seen that the configurations in Examples 1 to 8 yielded extremely excellent results in terms of compression set rate (thermal fatigue resistance), heat resistance (small deterioration of material properties due to long-term thermal aging in item [thermal aging resistance-1]), initial vibration characteristics (low dynamic magnification), and heat-resistant adhesion. In addition, the change in vibration characteristics (change in vibration isolation characteristics due to long-term thermal aging in test piece 1 (thick-walled vibration isolation rubber) in item [thermal aging resistance-2]) was also small, indicating that extremely excellent heat-resistant vibration isolation rubber compositions and heat-resistant vibration isolation rubbers can be obtained.

[0123] On the other hand, in each of the vibration-damping rubber compositions in Comparative Examples 1 to 8, the composition differs from that of the compositions in Examples 1 to 8 in that at least one of the types or amounts of the antioxidant, sulfur, or sulfur donor compound is different, and at least one of the evaluation criteria shown in Table 7 is judged as "×".

[0124] Next, in each of the vibration-damping rubber compositions of Examples 9 to 13, the main rubber component is natural rubber (NR) and / or isoprene rubber (IR) and butadiene rubber (BR), and when the total rubber component is 100 parts by mass, it contains 1.8 to 5 parts by mass of 2-mercaptobenzimidazole zinc salt and 0.2 to 1.1 parts by mass of N,N'-di-2-naphthyl-p-phenylenediamine, and also contains 0.2 to 0.7 parts by mass of sulfur as a vulcanizing agent and 1.2 to 3 parts by mass of 2-(4-morpholinodithio)benzothiazole as a sulfur donor compound (hereinafter, these will be appropriately referred to simply as the Example 9 to 13 category compositions).

[0125] Furthermore, according to the configurations in Examples 9 to 13, the change in vibration characteristics (change in vibration isolation characteristics due to long-term thermal aging in Test Piece 1 (thick-walled vibration isolation rubber) for item [Heat Aging Resistance-2]) is extremely small, indicating that superior results are obtained. In addition, in terms of compression set rate (heat sag resistance) and heat resistance (item [Heat Aging Resistance-1]), the deterioration of physical properties is small up to 1000 hours of holding time at an ambient temperature of 100°C, indicating excellent heat resistance. Regarding heat-resistant adhesion, while adhesion may be insufficient in hot atmospheres significantly exceeding 100°C, sufficient adhesion is obtained even when tensile stress is continuously applied for 30 days in a hot atmosphere of 100°C, indicating that it can be used as a heat-resistant vibration isolation rubber composition. Furthermore, the compression set rate (heat sag resistance) and initial vibration characteristics (low dynamic magnification) also show sufficiently good results.

[0126] On the other hand, in each of the vibration-damping rubber compositions in Comparative Examples 9 to 15, at least one of the types or contents of the antioxidant, sulfur, and sulfur donor compounds differs from the compositions in Examples 9 to 13, and it can be seen that at least one of the evaluation criteria shown in Table 8 is judged as "×".

[0127] Furthermore, while the vibration-damping rubber compositions in Comparative Examples 12 and 15 contained large amounts of 2-(4-morpholinodithio)benzothiazole or 4,4'-dithiodimorpholine as sulfur donor compounds, in the test pieces 1 prepared for each, peeling occurred easily between the metal fitting 2 and the rubber portion with just hand pressure. Therefore, these were deemed unsuitable as vibration-damping rubber with metal fittings, and the tests using these test pieces 1 were discontinued.

[0128] Focusing on the butadiene rubber used in the vibration-damping rubber compositions of Examples 1 to 13, in the compositions of Examples 1 to 8 and Examples 9 to 13, the Mooney viscosity (ML) of the butadiene rubber at 100°C was observed. 1+4 By setting the value to be within the range of 50 to 75, we were able to confirm that vibration isolation characteristics (low dynamic magnification) and rubber strength are further improved, resulting in more favorable results.

[0129] Based on the results above, the vibration-damping rubber compositions in Examples 1 to 8 exhibit minimal deterioration of material properties even under extremely long-term thermal environments (for example, 1500 hours at 100°C), and also demonstrate excellent heat resistance, vibration characteristics, and heat-resistant adhesion. Therefore, they can be considered extremely superior vibration-damping rubber compositions.

[0130] Furthermore, the vibration-damping rubber compositions in Examples 9 to 13 exhibit minimal changes in vibration characteristics even under extremely long-term thermal conditions (for example, 1500 hours at 100°C), and also show minimal deterioration of material properties even under long-term thermal conditions (for example, 1000 hours at 100°C). They also exhibit excellent heat resistance, vibration characteristics, and, regarding heat-resistant adhesion, do not experience delamination even when subjected to continuous tensile stress under extremely long-term thermal conditions (for example, 30 days at 100°C). Therefore, they can be considered superior vibration-damping rubber compositions. [Explanation of Symbols]

[0131] 1…Test piece 2… Metal fittings 3… Bolt (support rod)

Claims

1. A vibration-damping rubber composition comprising natural rubber (NR) and / or isoprene rubber (IR) and butadiene rubber (BR) as the main rubber components, A vibration-damping rubber composition characterized by containing 1.8 to 5 parts by mass of 2-mercaptobenzimidazole zinc salt, 0.2 to 1.1 parts by mass of N,N'-di-2-naphthyl-p-phenylenediamine, 0.2 to 0.7 parts by mass of sulfur, and 2 to 7 parts by mass of tetrakis(2-ethylhexyl)thiuram disulfide, based on 100 parts by mass of total rubber components.

2. A vibration-damping rubber composition comprising natural rubber (NR) and / or isoprene rubber (IR) and butadiene rubber (BR) as the main rubber components, A vibration-damping rubber composition characterized by containing 1.8 to 5 parts by mass of 2-mercaptobenzimidazole zinc salt, 0.2 to 1.1 parts by mass of N,N'-di-2-naphthyl-p-phenylenediamine, 0.2 to 0.7 parts by mass of sulfur, and 1.2 to 3 parts by mass of 2-(4-morpholinodithio)benzothiazole, based on 100 parts by mass of the total rubber components.

3. The main rubber component is a blend of natural rubber (NR) and butadiene rubber (BR), with an NR / BR ratio of 90 / 10 to 60 / 40. The butadiene rubber has a Mooney viscosity (ML) at 100°C. １＋４ The vibration-damping rubber composition according to claim 1 or 2, characterized in that the ratio is 50 to 75.

4. A vibration-damping rubber characterized in that the vibration-damping rubber composition according to claim 1 or 2 is vulcanized and bonded to the surface of the metal fitting via an adhesive layer on the surface of the metal fitting, thereby integrally forming the metal fitting and the vulcanized rubber made of the vibration-damping rubber composition.

5. A vibration-damping rubber characterized in that the vibration-damping rubber composition according to claim 3 is vulcanized and bonded to the surface of the metal fitting via an adhesive layer on the surface of the metal fitting, so that the metal fitting and the vulcanized rubber made of the vibration-damping rubber composition are integrally formed.

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