JP7682124B2 - Anti-vibration rubber composition and anti-vibration rubber - Google Patents

Description

The present invention relates to a rubber composition and anti-vibration rubber, and, for example, to an anti-vibration rubber composition that can provide an anti-vibration rubber with excellent vibration-proofing properties, and to an anti-vibration rubber with excellent adhesion obtained by applying this anti-vibration rubber composition.

Anti-vibration rubber used in multiple types of vibration transmission systems with different frequencies and amplitudes, such as in automobile vibration isolation, is required to exhibit appropriate and effective vibration isolation characteristics so that it can respond appropriately to the various types of input vibration.

For example, in automotive anti-vibration rubber, low dynamic spring characteristics are generally required to block the transmission of vibration when relatively small amplitude vibrations in the high frequency range of 100 Hz or more are input. Also, when relatively large amplitude vibrations in the low frequency range of about 5 to 15 Hz are input, high damping characteristics are required to increase the vibration damping effect that attenuates the vibration. On the other hand, anti-vibration rubber is also required to perform a support function such as supporting heavy objects, and so the static spring characteristics (Ks) must be relatively large to withstand a certain static force.

Therefore, it is desirable to reduce the value of the dynamic magnification (=Kd100/Ks) (also called the static-dynamic ratio), which is the ratio of the dynamic spring constant (Kd100) to the static spring constant (Ks) when a small amplitude vibration of, for example, 100 Hz is input. Also, from the viewpoint of high damping characteristics, it is desirable to increase the value of the loss coefficient (tan δ; also called the loss factor) when a large amplitude vibration of, for example, 10 Hz is input.

However, it is generally known that increasing the damping characteristics results in a corresponding increase in the dynamic magnification, and conversely, decreasing the dynamic magnification results in a corresponding decrease in damping characteristics. In other words, there is a trade-off between low dynamic magnification characteristics and high damping characteristics, and there is a strong desire for anti-vibration rubber to achieve both of these characteristics.

To address these issues, anti-vibration rubber compositions have been proposed in which hydrogenated isoprene rubber is added to diene rubber (e.g., Patent Document 1), anti-vibration rubber compositions in which domains of butadiene rubber with unevenly distributed carbon black are dispersed in a matrix phase of chlorinated butyl rubber (e.g., Patent Document 2), and even anti-vibration rubber compositions made by blending liquid styrene-butadiene rubber with an unvulcanized diene rubber material mainly composed of vinyl and styrene (e.g., Patent Document 3).

On the other hand, in the case of automotive anti-vibration rubber, a blend of natural rubber (NR) and butadiene rubber (BR) (hereinafter referred to as NR/BR as appropriate) is widely used from the viewpoint of durability against repeated vibration fatigue, and while it is relatively easy to achieve a low dynamic magnification ratio with NR/BR, achieving both low dynamic magnification ratio and high damping characteristics, which is the issue mentioned above, is a difficult task to achieve.

For example, in Patent Document 4, in order to address the issue of achieving both low dynamic magnification and high damping characteristics when using NR/BR, a diene rubber containing more than 0 parts by mass and not more than 10 parts by mass of carbon black and further containing 50 parts by mass to 70 parts by mass of oil is proposed, and the use of NR/BR is described.

As mentioned above, anti-vibration rubber for automobiles is used in multiple types of vibration transmission systems with different frequencies, amplitudes, etc. For this reason, rubber materials with various hardnesses and different damping properties are used for anti-vibration rubber materials, and in order to control the hardness and damping properties of NR/BR as a rubber component, it has been conventional to adjust the amount of various carbon blacks with different particle sizes and structures added, or the amount of process oils such as naphthenic oils added.

On the other hand, as automobiles become more compact and have higher power output, the environment surrounding automotive anti-vibration rubber tends to become hotter, so there is a particular demand for improved heat resistance of anti-vibration rubber.

Moreover, many of the anti-vibration rubbers for vehicles are rubber parts with metal fittings, which are formed by integrating the metal fittings and the rubber material, and are used as connecting members between various components such as frames and engines. In such anti-vibration rubbers, an adhesive is usually used to bond the interface between the metal fittings and the rubber material. There are generally two types of bonding methods using this adhesive: a "single-component adhesive coating method" that uses one adhesive, and a "two-component adhesive coating method" that applies a primer to the metal fitting surface and then applies a topcoat adhesive. The latter two-component adhesive coating method is widely used to obtain high adhesion.

Japanese Patent Application Publication No. 07-216136 JP 2019-131761 A JP 2005-113092 A JP 2018-188522 A

However, the anti-vibration rubber composition described in Patent Document 1 tends to have insufficient rubber strength, and the anti-vibration rubber compositions described in Patent Documents 2 and 3 do not use NR/BR, so vibration durability when subjected to repeated vibrations may be insufficient.

In addition, the anti-vibration rubber composition using NR/BR described in Patent Document 4 contains a low carbon black content and a large amount of oil, which acts as a softener, so the hardness of the resulting vulcanized rubber for anti-vibration rubber is too soft, and the support function of the anti-vibration rubber may be insufficient (for example, the rubber hardness (hardness) described in the examples of Patent Document 4 is 5 to 21, which is extremely low for vulcanized rubber hardness used in anti-vibration rubber for vehicles, and is prone to insufficient support function).

Furthermore, because the content of carbon black, a reinforcing material, is low, the rubber strength is insufficient, and durability may be insufficient, for example, when heavy loads are repeatedly applied. In addition, the addition of large amounts of process oils such as aromatic oils and naphthenic oils often leads to a decrease in the heat resistance of the vibration-proof rubber.

As mentioned above, high adhesion is required for anti-vibration rubber, but depending on the anti-vibration rubber composition used, adhesion may be insufficient. In particular, adhesion is likely to be insufficient when used in severe thermal environments.

The present invention has been made in consideration of these circumstances, and aims to provide an anti-vibration rubber composition that has excellent heat resistance, sufficient support function, and is capable of achieving both low dynamic magnification and high damping properties, and an anti-vibration rubber obtained from the anti-vibration rubber composition that has excellent adhesion between metal fittings and rubber.

The present inventors have conducted extensive research to achieve the above object. They have discovered that an anti-vibration rubber composition containing natural rubber and butadiene rubber as the main rubber components with a high proportion of natural rubber by mass, and containing a specific range of butadiene-styrene random copolymers with a specific molecular weight (Mn), can achieve both good low dynamic magnification characteristics and high damping characteristics, even when the hardness of the vulcanized rubber is sufficient from the standpoint of the support function of the anti-vibration rubber (for example, when it has a sufficient static spring constant (rubber hardness of 40 to 75)), and can achieve excellent anti-vibration characteristics not found in conventional anti-vibration rubber compositions.

In other words, one aspect of the anti-vibration rubber composition of the present invention is an anti-vibration rubber composition that contains natural rubber and butadiene rubber as the main rubber components in a mass ratio of natural rubber/butadiene rubber = 50/50 to 95/5, and also contains 15 to 50 parts by mass of a butadiene-styrene random copolymer with an average molecular weight (Mn) of 3,000 to 12,000 as a softener, based on 100 parts by mass of the rubber components.

The configuration of one aspect of the above anti-vibration rubber composition makes it possible to achieve excellent high damping properties while maintaining a good low dynamic magnification, and also to achieve high adhesion.

In one embodiment of the anti-vibration rubber composition, it is preferable that the rubber component contains 15 to 70 parts by mass of carbon black per 100 parts by mass of the rubber component. This allows the rubber composition to have a sufficient support function while achieving a high level of both low dynamic magnification and high vibration damping properties.

Furthermore, in one embodiment of the anti-vibration rubber composition, the butadiene-styrene random copolymer has an average molecular weight (Mn) of 8,000 to 12,000 and a glass transition temperature (Tg) of -10°C or more and 0°C or less, and the carbon black has a nitrogen adsorption specific surface area of 15 to 80 ^m2 /g and the carbon black content is preferably 20 to 60 parts by mass per 100 parts by mass of the rubber component. Within this range, it is possible to achieve a higher level of both low dynamic magnification characteristics and high vibration damping properties while maintaining sufficient support function, and further to achieve high adhesion.

Furthermore, in one embodiment of the above vibration-proof rubber composition, the carbon black has a nitrogen adsorption specific surface area of 20 to 45 ^m2 /g, and the content of the carbon black is preferably 25 to 50 parts by mass per 100 parts by mass of the rubber component.

Furthermore, in one embodiment of the anti-vibration rubber composition, the butadiene rubber preferably has a cis-1,4-bond amount of 90% or more and a Mooney viscosity (ML ₁₊₄ ) at 100° C. of 50 to 75. This makes it possible to achieve an even better low dynamic magnification and high rubber strength.

Furthermore, in one embodiment of the anti-vibration rubber composition, it is preferable that the rubber component contains 100 parts by mass of process oil in an amount of 0 to 5 parts by mass. In this range, it is possible to achieve a high level of heat resistance while maintaining sufficient support function and achieving both low dynamic magnification characteristics and high vibration damping properties.

One embodiment of the anti-vibration rubber of the present invention is an anti-vibration rubber characterized in that both the above-mentioned anti-vibration rubber composition and a metal fitting are vulcanization-bonded via an adhesive layer formed on the surface of the metal fitting, and the two are integrally formed.

The above-mentioned configuration of one aspect of the anti-vibration rubber provides excellent adhesion between the metal fittings and the vulcanized rubber, while achieving both low dynamic magnification characteristics and high vibration damping properties.

The present invention provides an anti-vibration rubber composition that has excellent heat resistance, sufficient support function, and is capable of achieving both low dynamic magnification and high damping properties, and also provides an anti-vibration rubber obtained from the anti-vibration rubber composition that has excellent adhesion between metal fittings and rubber.

FIG. 1 is a schematic explanatory diagram of a test piece 1 formed using each of the anti-vibration rubber compositions of Examples 1 to 9 and Comparative Examples 1 to 6 according to the present invention. 1 is a graph showing the relationship between dynamic magnification (Kd100/Ks) and tan δ (10 Hz) in test piece 1 made using each of the anti-vibration rubber compositions of Examples 1 to 9 and Comparative Examples 1 to 6 according to the present invention.

The following provides a detailed explanation of the issues involved in implementing the present invention.

As mentioned above, there is a trade-off between low dynamic magnification and high damping characteristics. That is, normally, there is a fixed relationship between damping properties and dynamic magnification, and for vibration-proof rubber (rubber sample) of the same shape, the dynamic magnification will be approximately the same for a certain damping property. In this invention, low dynamic magnification and high damping properties means that this fixed relationship is violated, and for the same damping properties, the dynamic magnification will be lower than that of normal vibration-proof rubber materials. In other words, for the same dynamic magnification, the damping properties will be greater.

The content of each material (each component) applicable to the present invention may be referred to simply as parts by mass below, but parts by mass refers to the content ratio (parts by mass) of each material (each component) when the total rubber component is taken as 100 parts by mass.

The anti-vibration rubber composition of the present invention is characterized by containing natural rubber and butadiene rubber as the main rubber components in a mass ratio of natural rubber/butadiene rubber = 50/50 to 95/5, and containing 15 to 50 parts by mass of butadiene-styrene random copolymer (liquid SBR) with an average molecular weight (Mn) of 3,000 to 12,000.

In anti-vibration rubber compositions, it is common to use natural rubber as the main rubber component, blended with styrene-butadiene copolymer rubber (SBR) or butadiene rubber (BR). When anti-vibration rubber with a lower dynamic magnification and high durability is desired, a main rubber component containing natural rubber/butadiene rubber in a ratio of 50/50 to 95/5 is often used.

However, natural rubber and butadiene rubber are known to have low damping properties (also called low loss), and although it is possible to obtain anti-vibration rubber with excellent low dynamic magnification, it is an elastic body with the rubber hardness of anti-vibration rubber normally used for vehicle applications (for example, rubber hardness of about 40 to 70), and it has not been possible to obtain an anti-vibration rubber composition that achieves both low dynamic magnification and high damping properties. In other words, there was no technical idea of including natural rubber and butadiene rubber as the main rubber components in a mass ratio of natural rubber/butadiene rubber = 50/50 to 95/5, and containing 15 to 50 parts by mass of a specific butadiene-styrene random copolymer as a softener.

For this reason, it has not been possible to come up with a component composition similar to that of the anti-vibration rubber composition of the present invention, and even when a highly durable blend of natural rubber and butadiene rubber is used, it has not been possible to achieve both low dynamic magnification and high damping properties (the same level of low dynamic magnification and high damping properties as in the present invention).

The components used in the anti-vibration rubber composition of the present invention will be explained below.

[Rubber component]
The anti-vibration rubber composition according to the present invention contains natural rubber and butadiene rubber as the main rubber component in a mass ratio of natural rubber/butadiene rubber = 50/50 to 95/5 (hereinafter simply referred to as the rubber component category of the present invention). The main rubber component means that the total amount of natural rubber (NR) and butadiene rubber (BR) is 90 mass% or more of the total rubber component. Preferably, the total amount of natural rubber (NR) and butadiene rubber (BR) is 95 mass% or more of the total rubber component. When natural rubber and butadiene rubber are contained as the main rubber component within the rubber component category of the present invention, a rubber composition having high rubber strength, excellent vibration durability, and low dynamic magnification can be obtained.

There are no particular limitations on the natural rubber, and normal natural rubber used in anti-vibration rubber can be used. Specifically, for example, in sheet rubber (including crepe), all grades of RSS (RIBBED SMOKED SHEET), WHITE CREPES, PALE CREPES, ESTATE BROWN CREPES, COMP CREPES, THIN BROWN CREPES (RIMILLS), THICH BLANCKET CRAPES (AMBERS), FLAT BARK CREPES, and PURE SMOKED BLANKET CRAPES can be mentioned. Examples of block rubber include SMR (Standard Malaysian Rubber), SIR (Standard Indian Rubber), STR (Standard Thai Rubber), SSR (Standard Singapore Rubber), SCR (Standard Ceylon Rubber), and SVR (Standard Vietnamese Rubber).

The butadiene rubber (BR) used in the present invention is not particularly limited, and various commercially available butadiene rubbers used in anti-vibration rubbers can be used. In particular, from the viewpoints of low dynamic magnification, low-temperature characteristics, and durability against repeated deformation, the higher the cis 1,4-bond content, the more preferable. For example, it is preferable to use high-cis BR in which the cis 1,4-bond content is 90% or more, and more preferably 93% or more.

Furthermore, for BR of the same chemical composition, the higher the Mooney viscosity (ML ₁₊₄ ), the higher the molecular weight tends to be, and in order to improve durability, it is preferable that the Mooney viscosity (ML ₁₊₄ ) at 100°C is 50 or more, for example. On the other hand, as the Mooney viscosity (ML ₁₊₄ ) increases, the fluidity of the rubber tends to decrease, and if the Mooney viscosity (ML ₁₊₄ ) is too high, the kneading processability and molding processability of the vibration-proof rubber material composition tend to deteriorate. For this reason, the Mooney viscosity (ML ₁₊₄ ) at 100°C is preferably 75 or less, and more preferably, the Mooney viscosity (ML ₁₊₄ ) is 65 or less. That is, in the present invention, butadiene rubber (BR) having a viscosity of 50 or more and 65 or less is preferably used. Examples of such butadiene rubber include JSR BR730, JSR BR54, and JSR BR740 (all manufactured by JSR Corporation), Ubepol 390L (manufactured by Ube Industries, Ltd.), and BUNA CB21, CB22, and CB1221 (all manufactured by ARLANXEO).

The anti-vibration rubber composition of the present invention can contain rubber components other than the natural rubber and butadiene rubber described above, within a range that does not impair the effects of the present invention (for example, within the range of 10 parts by mass or less). Examples of other rubber components include isoprene rubber (IR), styrene butadiene rubber (SBR), ethylene propylene rubber (EPDM), etc.

[Butadiene-styrene random copolymer]
The anti-vibration rubber composition according to the present invention contains 15 to 50 parts by mass of a butadiene-styrene random copolymer having an average molecular weight (Mn) of 3000 to 12000 (hereinafter referred to as the copolymer category of the present invention). In the case of this copolymer category of the present invention, it is possible to achieve both appropriate flexibility, excellent vibration damping properties, and low dynamic magnification. Note that this butadiene-styrene random copolymer acts as a softening agent and does not become an elastomer even when used in combination with a sulfur-based vulcanizing agent for normal rubber, so it is not included in the rubber component and resin component in the present invention. Examples of such butadiene-styrene random copolymers include Ricon 100, Ricon 181, and Ricon 184 (all manufactured by Cray Valley), L-SBR-820, and L-SBR-841 (all manufactured by Kuraray Co., Ltd.), etc.

Preferably, the butadiene-styrene random copolymer has an average molecular weight (Mn) of 8,000 to 12,000 and a glass transition temperature (Tg) of -10°C or higher and 0°C or lower. Such a butadiene-styrene random copolymer has an even greater effect of achieving both low dynamic magnification and high vibration damping properties. Specific examples of such butadiene-styrene random copolymers include L-SBR-841 (manufactured by Kuraray Co., Ltd.).

[Carbon black]
In the anti-vibration rubber composition according to the present invention, it is preferable to contain carbon black in a ratio of 15 to 70 parts by mass (hereinafter referred to as the carbon black category of the present invention). In the case of this carbon black category of the present invention, it is easy to obtain an appropriate static spring constant for performing the support function of the anti-vibration rubber. As mentioned above, the butadiene-styrene random copolymer also acts as a softener. That is, if the carbon black content is less than 15 parts by mass, the hardness of the vulcanized rubber becomes too low, making it difficult to obtain an appropriate static spring constant. If the carbon black content is more than 70 parts by mass, the improvement in the elastic modulus at high frequency micro-amplitude becomes greater. Therefore, the low dynamic magnification effect becomes smaller.

The carbon black used is not particularly limited, and various commercially available furnace blacks for rubber and furnace blacks for coloring can be used, but among them, carbon blacks having a nitrogen adsorption specific surface area of 15 to 80 ^m2 /g are preferably used. Examples of such carbon blacks include HAF class, MAF class, FEF class, GPF class, SRF class, FT class, etc., which are known as furnace carbon blacks for rubber. The content of this carbon black is preferably 20 to 60 parts by mass, based on 100 parts by mass of the rubber component.

More preferably, the content of carbon black having a nitrogen adsorption specific surface area of 20 to 45 ^m2 /g is 25 to 50 parts by mass. Such carbon black has a large effect of low dynamic magnification and high damping. Specific examples of such carbon black include FEF grade, GPF grade, SRF grade, etc., which are known as furnace carbon black for rubber.

[Process oil]
The anti-vibration rubber composition according to the present invention may contain process oil in addition to the above components. However, process oils such as naphthene oils, aromatic oils, and paraffin oils used in diene rubber compositions such as natural rubber and butadiene rubber have the effect of lowering the elastic modulus, but are poor at increasing damping properties, and furthermore, do not have the effect of achieving both low dynamic magnification and high damping properties. In addition, the addition of a large amount of the above process oil tends to lower heat resistance. For this reason, it is preferable to set the amount of process oil to a level that adjusts the rubber hardness (for example, 5 parts by mass or less, which is a small amount added). More preferably, it is set to 3 parts by mass or less.

[Vulcanizing agent (crosslinking agent)]
The anti-vibration rubber composition according to the present invention contains a vulcanizing agent (crosslinking agent) in addition to the above-mentioned components. Known sulfur-based vulcanizing agents can be used as the vulcanizing agent (crosslinking agent). Vulcanization using sulfur or sulfur-based compounds is preferably used because it provides excellent durability to the anti-vibration rubber. Furthermore, the butadiene-styrene random copolymer with an average molecular weight (Mn) of 3,000 to 12,000 used in the present invention is hardly crosslinked by sulfur or sulfur-based compounds, and therefore cannot become an elastomer, and can act as a softener.

Specific examples of sulfur or sulfur-based compounds include sulfur, sulfur chloride, 2-(4'-morpholinodithio)benzothiazole, 4,4'-dithiodimorpholine, tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetrabutylthiuram disulfide, tetrakis(2-ethylhexyl)thiuram disulfide, tetrabenzylthiuram disulfide, and dipentamethylenethiuram tetrasulfide. In addition to sulfur or sulfur-based compounds, bismaleimide vulcanization, resin vulcanization, etc. may be used in combination.

[Filler]
The anti-vibration rubber composition according to the present invention may contain fillers other than carbon black in addition to the above-mentioned components. Examples of the fillers include inorganic fillers such as silica, clay, and calcium carbonate, and organic fillers such as polymer fillers. These may be used alone or in combination of two or more.

Examples of silica include dry process silica (fumed silica), wet process silica, colloidal silica, etc. Among these, wet process silica, which is mainly composed of hydrous silicic acid, is particularly preferred. These silicas can be used alone or in combination of two or more. The specific surface area of the silica is not particularly limited, but the nitrogen adsorption specific surface area is usually 50 to 400 ^{m 2} /g, preferably 100 to 250 m ² /g, and more preferably 120 to 220 ^{m 2} /g. Such silica is preferable because it improves the dynamic magnification and loss factor to a high level. Here, the nitrogen adsorption specific surface area is measured by the BET method in accordance with ASTM D3037-81.

[Vulcanization accelerator]
When a sulfur compound is used as a vulcanizing agent, a vulcanization accelerator can be used in combination. Specific examples of the vulcanization accelerator 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-(2,4-dinitrophenyl)mercaptobenzothiazole, 2-(2,6-diethyl-4-morpholinothio)benzothiazole, and dibenzothiazyl disulfide, and diphenyl glycerol compounds such as benzothiazole, benzothiazole, and benzothiazyl disulfide. Examples of the vulcanization accelerator include guanidine compounds such as thiuram monosulfide, triphenyl guanidine, diorthonitrile guanidine, orthonitrile biguanide, and diphenyl guanidine phthalate, and thiuram compounds such as tetramethyl thiuram monosulfide, tetramethyl thiuram disulfide, tetraethyl thiuram disulfide, tetrabutyl thiuram disulfide, tetrakis (2-ethylhexyl) thiuram disulfide, tetrabenzyl thiuram disulfide, and dipentamethylene thiuram tetrasulfide. These vulcanization accelerators may be used alone or in combination of two or more kinds, or different kinds may be used in combination. The amount of the vulcanization accelerator is preferably 0.5 to 15 parts by mass, more preferably 1 to 10 parts by mass, and even more preferably 1.2 to 8 parts by mass, when the total amount of all rubber components including the natural rubber and the butadiene rubber is taken as 100 parts by mass. In order to adjust the vulcanization rate, scorch inhibitors such as N-cyclohexylthiophthalimide and N-phenyl-N-(trichloromethylthio)benzenesulfonamide can be preferably used.

[Vulcanization aid]
In addition, when a sulfur compound is used as a vulcanizing agent, it is preferable to use a vulcanization aid such as zinc oxide (ZnO) such as zinc oxide or activated zinc oxide or composite zinc oxide in combination with a vulcanization aid such as stearic acid or zinc stearate. Here, composite zinc oxide is known to have a layer of zinc oxide (zinc oxide) on the surface and contain an inorganic metal salt inside as a core component, and examples thereof include META-Z L series (META-Z L40, L50, L60) manufactured by Inoue Sekiryo Kogyo Co., Ltd. The content of zinc oxide or composite zinc oxide is 3 parts by mass or more and 15 parts by mass or less based on 100 parts by mass of the rubber component. The content of stearic acid or zinc stearate is preferably 0.1 parts by mass or more and 3 parts by mass or less based on 100 parts by mass of the rubber component.

[Anti-aging agent]
Since the anti-vibration rubber composition of this embodiment uses natural rubber and butadiene rubber, if the ozone resistance or heat resistance is poor, it is preferable to improve it with a known antioxidant. Examples of the antioxidant include carbamate-based antioxidants, phenylenediamine-based antioxidants, phenol-based antioxidants, diphenylamine-based antioxidants, quinoline-based antioxidants, imidazole-based antioxidants, waxes, etc. These are used alone or in combination of two or more. The content of the antioxidant is preferably in the range of 1 to 15 parts by mass, more preferably in the range of 3 to 10 parts by mass, per 100 parts by mass of the rubber component.

[Processing aids]
The anti-vibration rubber composition of this embodiment may contain a processing aid for the purpose of improving processability. Compounds used in normal rubber processing may be used as the processing aid. Specific examples of the processing aid include higher fatty acids such as ricinoleic acid, stearic acid, palmitic acid, and lauric acid, salts of higher fatty acids such as barium stearate, zinc stearate, and calcium stearate, esters of higher fatty acids such as ricinoleic acid, stearic acid, palmitic acid, and lauric acid, and tackifiers such as terpene resins and coumarone resins for the purpose of imparting tackiness. These may be used alone or in combination of two or more kinds.

[Coupling Agent]
In the anti-vibration rubber composition of the present embodiment, additives such as a coupling agent between a rubber component and carbon black, a silane coupling agent between a rubber component and silica, and known rubber additives such as a reversion inhibitor can be used alone or in combination of two or more kinds for the purpose of adjusting vibration characteristics.

[Production of Anti-Vibration Rubber Composition]
Various obvious methods can be adopted when producing the anti-vibration rubber composition according to the present invention. For example, a known kneading device such as a Banbury mixer or a roll machine is used, and natural rubber, butadiene rubber, and butadiene-styrene random copolymer are respectively charged into the kneading device, and the above-mentioned rubber additives including a vulcanizing agent are blended and appropriately kneaded to prepare an unvulcanized rubber composition of the desired composition. There is no particular restriction on the kneading method of each component, and all the component raw materials may be blended and kneaded at once, or each component may be blended and kneaded in two or three stages. As a specific example, for example, materials other than the vulcanizing agent (crosslinking agent) and the vulcanization accelerator are kneaded using a Banbury mixer, and then the crosslinking agent and the vulcanization accelerator are blended and kneaded using an open roll.

[Manufacturing of anti-vibration rubber with metal fittings]
In manufacturing the metal fitting-attached anti-vibration rubber according to the present invention, various obvious methods can be adopted, one example of which is the following method.

First, the surface of the metal fitting (metal fitting designated by reference symbol 2 in FIG. 1 described later) is roughened by shot blasting or the like, and a one-component or two-component vulcanizing adhesive is applied to the portion of the roughened surface to be bonded to the anti-vibration rubber composition, and then dried. Next, the metal fitting coated with the vulcanizing adhesive is placed in a desired position in a cavity of a desired shape mold that has been heated to a temperature suitable for vulcanizing the anti-vibration rubber composition. After that, the anti-vibration rubber composition is injected into the mold cavity in which the metal fitting is placed, using a device such as an injection machine. After the anti-vibration rubber composition is injected, the mold is heated for a certain period of time, allowing the vulcanization (crosslinking) reaction of the anti-vibration rubber composition and the reaction of the vulcanizing adhesive on the surface of the metal fitting to proceed simultaneously. Then, the metal fitting is removed from the mold to obtain an anti-vibration rubber with the metal fitting.

In addition, there are no limitations on the shape or size of the anti-vibration rubber, and it can be set appropriately depending on the level of anti-vibration properties and the application, etc.

The anti-vibration rubber manufactured in this way is used, for example, as automotive anti-vibration rubber for member mounts, strut mounts, suspension bushings, body mounts, etc., by being interposed between components that make up a vibration or shock transmission system to provide vibration isolation or cushioning properties.

In the following, several examples and comparative examples will be described in order to clarify the present invention in more detail. However, the present invention is not limited in any way by the descriptions of these examples, and it goes without saying that various modifications and improvements can be made without departing from the spirit of the present invention.

<Preparation of anti-vibration rubber composition>
Anti-vibration rubber compositions were prepared by mixing and kneading various materials in the ratios shown in Tables 1 and 2. The above kneading was carried out by first mixing the materials other than the vulcanizing agent and vulcanization accelerator for 5 minutes using a Banbury mixer, then mixing the vulcanizing agent and vulcanization accelerator, and using an open roll, setting the cooling water temperature to about 20°C, adding the vulcanizing agent and vulcanization accelerator to the rubber kneaded in the Banbury mixer while cooling, and kneading for 5 minutes to prepare anti-vibration rubber compositions (Examples 1 to 9, Comparative Examples 1 to 6).

The materials listed in Tables 1 and 2 are as follows.
・Natural rubber: SVR CV60
Butadiene rubber-1: cis 1,4-bond content 94%, Mooney viscosity (ML ₁₊₄ ) 55, "BR-730" manufactured by JSR Corporation
Butadiene rubber-2: cis 1,4-bond content 96%, Mooney viscosity ML ₁₊₄ 44, "BR-01" manufactured by JSR Corporation
Butadiene-styrene random copolymer-1: average molecular weight (Mn) 4500, Tg -15°C, "RICON 100" manufactured by Clay Valley
-Butadiene-styrene random copolymer-2: average molecular weight (Mn) 10,000, Tg -6°C, "L-SBR-841" manufactured by Kuraray Co., Ltd.
Butadiene-styrene random copolymer-3: average molecular weight (Mn) 3200, Tg -65°C, Clay Valley "RICON 181"
Butadiene-styrene random copolymer-4: average molecular weight (Mn) 3200, Tg -57°C, Clay Valley "RICON 184"
Carbon black-1: nitrogen adsorption specific surface area 22 m ² /g (SRF grade), "Asahi #50HG" manufactured by Asahi Carbon Black Co., Ltd.
Carbon black-2: nitrogen adsorption specific surface area 76 m ² /g (HAF grade), "VULCAN 3D" manufactured by Cabot Japan Co., Ltd.
Carbon black-3: nitrogen adsorption specific surface area 115 m ² /g (ISAF grade), "Niteron #300" manufactured by Nippon Steel Carbon Co., Ltd.
Anti-aging agent-1: (N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine), "Nocrac 6C" manufactured by Ouchi Shinkosha
Anti-aging agent-2: (2-mercaptobenzimidazole) "Nocrac MB" manufactured by Ouchi Shinko Co., Ltd.
・Anti-aging agent-3: (wax) Nippon Seiro Co., Ltd. "Ozoace 0100"
・Composite zinc oxide: "META-Z-L60" manufactured by Inoue Lime Industry Co., Ltd.
・Stearic acid: "Camellia Stearate" manufactured by Nippon Oil & Fats Co., Ltd.
・Naphthenic oil: "Kurisef Oil H56" manufactured by ENEOS Corporation
Vulcanizing agent: Sulfur, Tsurumi Chemical Industry Co., Ltd. "Kinkaji Fine Sulfur 200 MESH"
Vulcanization accelerator-1 (N-cyclohexyl-2-benzothiazolyl sulfenamide): "Noccela CZ-G" manufactured by Ouchi Shinko Chemical Co., Ltd.
Vulcanization accelerator-2 (tetramethylthiuram disulfide): "Noccela TT-P" manufactured by Ouchi Shinko Chemical Co., Ltd.
[Preparation of 2 mm vulcanized rubber sheets for measuring tensile properties and properties after heat aging]
For each of the vibration-proof rubber compositions of Examples 1 to 9 and Comparative Examples 1 to 6 shown in Tables 1 and 2, vulcanization molding was carried out by compression molding using a 2 mm sheet mold with a cavity such that the rubber thickness was approximately 2 mm, at 160°C for a vulcanization time of 10 minutes, to obtain a vulcanized rubber sheet having a thickness of 2 mm (hereinafter simply referred to as the evaluation rubber sheet).

[Preparation of anti-vibration rubber test pieces]
In preparing the vibration-proof rubber test piece 1 shown in FIG. 1, first, two 50 mm x 50 mm iron metal fittings 2 with a bolt 3 standing at the center of one side were prepared, and the surface of each metal fitting 2 on which the bolt 3 was not standing was roughened by shot blasting. Next, Chemlock 205 (manufactured by Lord Far East Co., Ltd.) was applied as an undercoat adhesive to each of the surfaces of each metal fitting 2 on which the bolt was not standing, and dried in an 80°C atmosphere for 20 minutes to form an undercoat adhesive layer (thickness 10 μm). After cooling each metal fitting 2 on which this undercoat adhesive layer was formed to room temperature, Chemlock 6125 (manufactured by Lord Far East Co., Ltd.) was applied as an overcoat adhesive to the surface of each undercoat adhesive layer, and dried in an 80°C atmosphere for 20 minutes to form an overcoat adhesive layer (thickness 10 μm). Then, each metal fitting 2 was placed in the molding die (so that the topcoat adhesive layer of each metal fitting 2 was facing each other), and further, unvulcanized rubber was filled between each metal fitting 2 in the molding die using an injection molding machine, and vulcanized (160°C x 12 minutes) to produce a square test piece 1 with metal fitting 2 formed into a rectangular parallelepiped of 40 mm x 40 mm x 30 mm as shown in Figure 1.

Tensile properties
Each evaluation rubber sheet obtained using each of the anti-vibration rubber compositions of Examples 1 to 9 and Comparative Examples 1 to 6 was punched out with a JIS No. 3 dumbbell, and the breaking strength (TB), breaking elongation (EB), and hardness (Hs: JIS A) were measured in accordance with JIS K 6251. The results of these measurements are shown in Tables 1 and 2.

<Heat aging resistance test>
From each of the rubber sheets for evaluation obtained using each of the anti-vibration rubber compositions of Examples 1 to 9 and Comparative Examples 1 to 6, a test specimen was first punched out with a JIS No. 3 dumbbell and placed in a gear-type aging tester set to a 100°C atmosphere for 336 hours (2 weeks) to prepare a heat-aged test specimen. Next, a tensile test was performed on each test specimen in the same manner as in the above <<Tensile Properties>> to measure the breaking elongation (i.e., the breaking elongation after heat aging). Then, the rate of change in breaking elongation after heat aging (AcEB) relative to the breaking elongation before heat aging (EB) was calculated. These calculation results are shown in Tables 1 and 2.

<Vibration characteristic test>
For each test piece 1 obtained using each of the vibration-proof rubber compositions of Examples 1 to 9 and Comparative Examples 1 to 6, an axial load was first applied via each bolt 3 to compress the test piece 1 by 6 mm in the axial direction (bolt 3 axial direction), and the load was then temporarily released. This compression and release process was repeated twice. After this, the test piece 1 was compressed by 6 mm again (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 the results. Then, from the load-deflection curve, the load values P1 and P2 (unit: N) at the time when the deflection became 2 mm and 4 mm, respectively, were read, and the load values P1 and P2 were appropriately substituted into the relational expression "Ks = (P2 - P1) / 2" to calculate the static spring constant Ks (N / mm) of each test piece.

Separately, each test piece 1 was compressed 3 mm in the axial direction via each bolt 3 in the same manner as above, and a test was conducted in which a constant displacement harmonic compression vibration of amplitude ±0.05 mm was applied at a frequency of 100 Hz from one of the bolt 3 sides (e.g., the lower side in the figure) of the test piece 1 in the compressed state, centered on the position where the test piece was compressed 3 mm. The dynamic spring constant Kd100 (N/mm) at 100 Hz was calculated in accordance with the "Non-resonant method (a)" in the "Test method for rubber vibration isolation" of JIS-K-6385-2012. The dynamic magnification (=Kd100/Ks) was then calculated from the calculated dynamic spring constant (Kd100) and the static spring constant (Ks) calculated above.

In addition, in this vibration characteristic test, each test piece 1 was compressed 3 mm in the axial direction via each bolt 3 in the same manner as above, and a constant displacement harmonic compression vibration of amplitude ±1.0 mm centered on the position where the test piece 1 was compressed 3 mm was applied from one of the bolts 3 of each test piece 1 in the compressed state at a frequency of 10 Hz, and the loss factor tan σ (10 Hz) at 10 Hz was calculated. The results of these calculations are shown in Tables 1 and 2.

Furthermore, a graph showing the relationship between the dynamic magnification Kd100/Ks and the loss factor tan σ (10 Hz) for each test piece 1 calculated as described above is shown in Figure 2. This Figure 2 compares Examples 1 to 9 with Comparative Examples 1 to 6. Note that in Figure 2, the number portion (1 to 9) of Examples 1 to 9 is written adjacent to the symbol "●", and the number portion (1 to 6) of Comparative Examples 1 to 6 is written adjacent to the symbol "×".

<Heat resistance adhesion test>
For each test piece 1 obtained using each of the vibration-proof rubber compositions of Examples 1 to 9 and Comparative Examples 1 to 6, first, in the same manner as above, the test piece 1 was stretched 50% (stretched in the vertical direction in FIG. 2) via each bolt 3, and held in a 100°C atmosphere for 60 minutes, and the presence or absence of peeling of each metal fitting 2 was visually observed. After that, the test piece was held in an atmosphere heated by 10°C for 40 minutes, and the visual confirmation of the presence or absence of peeling of each metal fitting 2 was repeated, and finally, the test piece was held in a 200°C atmosphere for 40 minutes, and the presence or absence of peeling of each metal fitting 2 was confirmed, and the test was completed. In this test, it was determined that the higher the temperature at which peeling of each metal fitting 2 could be prevented, the better the heat-resistant adhesion. Tables 1 and 2 show the maximum temperature at which peeling of adhesion could be prevented. For example, if there was no peeling of adhesion at 160°C but peeling of adhesion occurred at 170°C, "160°C" was recorded in the heat-resistant adhesion column of Tables 1 and 2. In addition, when peeling was prevented even at 200°C, it was recorded as "200°C OK." In this test, two test pieces 1 were prepared for each of the anti-vibration rubber compositions of Examples 1 to 9 and Comparative Examples 1 to 6, and the test results of the two test pieces 1, whichever had the lower peeling temperature, was used as an index of the heat-resistant adhesiveness of each anti-vibration rubber composition. These test results are shown in Tables 1 and 2.

Effects of the embodiment
2, when the anti-vibration rubber compositions of Examples 1 to 9 were used (hereinafter appropriately referred to as Examples 1 to 9), the vibration characteristic test results (results showing the relationship between dynamic magnification and loss factor) were all located below the curves (dotted lines) of the vibration characteristic test results when the anti-vibration rubber compositions of Comparative Examples 1 to 6 were used (hereinafter appropriately referred to as Comparative Examples 1 to 6), indicating that the low dynamic magnification and high damping properties were excellent. Furthermore, according to the results of Tables 1 and 2, it is also evident that the rates of change in breaking elongation (AcEB) after heat aging were smaller in the cases of Examples 1 to 9 than in the cases of Comparative Examples 1 to 6, indicating that the heat aging properties were excellent.

Furthermore, from the results of Figure 2 and Table 1, it can be seen that in the cases of Example 2 and Example 9, the butadiene-styrene random copolymer has an average molecular weight (Mn) of 10,000 and a glass transition temperature (Tg) of -6°C, and the carbon black has a nitrogen adsorption specific surface area of 22 ^m2 /g and a carbon black content of 40 parts by mass per 100 parts by mass of the rubber component, and thus has the greatest low dynamic magnification and high damping effect.

In the case of Example 8, which contains a relatively high carbon black content of 80 parts by mass, the damping properties are very large, and the low dynamic magnification high damping effect is recognized, but it can be seen that the dynamic magnification is relatively high at 5.35. Furthermore, although the low dynamic magnification high damping effect is almost the same in the cases of Example 2 and Example 9, it can be seen that the rubber strength is relatively higher in the case of Example 2, which uses a butadiene rubber with a cis-1,4-bond content of 94% and a Mooney viscosity (ML1 ₊₄ ) of 55.

Furthermore, from the results in Tables 1 and 2, it can be seen that Examples 1 to 9 have superior adhesion to the metal fitting 2 compared to Comparative Examples 1 to 6. Therefore, it can be seen that Examples 1 to 9 are effective as anti-vibration rubber.

1... Test piece 2... Metal fitting 3... Bolt (support rod)

Claims (6)

The main rubber components are natural rubber and butadiene rubber in a mass ratio of natural rubber/butadiene rubber = 50/50 to 95/5,
Based on 100 parts by mass of the rubber component, the rubber composition contains 15 to 50 parts by mass of a butadiene-styrene random copolymer having an average molecular weight (Mn) of 3,000 to 12,000 as a softener, and 20 to 60 parts by mass of carbon black having a nitrogen adsorption specific surface area of 15 to 80 m ² /g;
The butadiene-styrene random copolymer has an average molecular weight (Mn) of 8,000 to 12,000 and a glass transition temperature (Tg) of -10°C or higher and 0°C or lower, in the vibration-proof rubber composition. The rubber composition contains natural rubber and butadiene rubber as main rubber components in a mass ratio of natural rubber/butadiene rubber = 50/50 to 95/5, and contains 15 to 50 parts by mass of a butadiene-styrene random copolymer having an average molecular weight (Mn) of 3,000 to 12,000 as a softener, based on 100 parts by mass of the rubber component ;
The butadiene rubber has a cis-1,4-bond content of 90% or more and a Mooney viscosity (ML ₁₊₄ ) at 100° C. of 50 to 75 . 3. The anti-vibration rubber composition according to claim 2 , further comprising 15 to 70 parts by mass of carbon black per 100 parts by mass of the rubber component. The carbon black has a nitrogen adsorption specific surface area of 20 to 45 m ² /g;
4. The anti-vibration rubber composition according to claim 1, wherein the content of the carbon black is 25 to 50 parts by mass per 100 parts by mass of the rubber component. 5. The anti-vibration rubber composition according to claim 1 , further comprising a process oil in an amount of 5 parts by mass or less, based on 100 parts by mass of the rubber component. A vibration-proof rubber comprising the vibration-proof rubber composition according to any one of claims 1 to 5 and a metal fitting, both of which are vulcanization-bonded via an adhesive layer formed on the surface of the metal fitting, so that the two are integrally formed.

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