JP7323928B2 - Acrylic rubber composition and vibration damping material - Google Patents

Description

The present invention relates to an acrylic rubber composition and a vibration damping material.

A vibration damping material based on acrylic rubber is known (see, for example, Patent Document 1). This type of vibration damping material is more cost effective than silicone rubber-based vibration damping materials, and has been attracting attention in recent years. The vibration damping material is required to have heat resistance, cold resistance, etc., in addition to the vibration damping property for damping vibration.

JP 2005-187772 A

Conventional vibration damping materials based on acrylic rubber sometimes have a problem of processability (workability) in the manufacturing process. Specifically, the acrylic rubber composition, which is the raw material of the vibration damping material, sticks to the kneader (pressure kneader, roll mill, etc.) with a strong adhesive force during kneading, and it is difficult to remove it from the kneader. Sometimes it took a long time.

An object of the present invention is to provide a vibration damping material or the like based on acrylic rubber, which is excellent in heat resistance, cold resistance, and workability.

Means for solving the above problems are as follows. Namely
<1> 25 to 85 parts by mass of an acrylic rubber having a glass transition temperature of −40° C. or less and containing a cross-linking point, and ethylene acrylic having a glass transition temperature of −40° C. or less and containing the same kind of cross-linking point as the above-mentioned cross-linking point 15 to 75 parts by mass of rubber (where the total of the acrylic rubber and the ethylene acrylic rubber is 100 parts by mass), 15 to 30 parts by mass of a polyether ester plasticizer, and 80 to 140 parts by mass of a metal hydroxide , 15 to 25 parts by mass of a phosphorus-based flame retardant, 0.5 to 3.5 parts by mass of a lubricant, 0.1 to 5 parts by mass of a cross-linking agent, and 0.1 to 10 parts by mass of a cross-linking aid. system composition.

<2> The acrylic rubber composition according to <1>, further comprising 5 to 15 parts by mass of carbon black.

<3> The acrylic rubber composition according to <1> or <2>, wherein the acrylic rubber and the ethylene acrylic rubber contain a carboxyl group as the cross-linking point.

<4> The acrylic rubber composition according to any one of <1> to <3>, wherein the cross-linking agent comprises an aliphatic amine compound, and the cross-linking aid comprises a guanidine compound.

<5> A vibration damping material comprising a crosslinked product of the acrylic rubber composition according to any one of <1> to <4>.

According to the present invention, it is possible to provide a vibration damping material or the like based on an acrylic rubber that is excellent in heat resistance, cold resistance, and workability.

Explanatory diagram schematically showing the configuration of the vibration test equipment

[Acrylic rubber composition]
The acrylic rubber composition of the present embodiment mainly contains acrylic rubber, ethylene acrylic rubber, plasticizer, metal hydroxide, phosphorus-based flame retardant, lubricant, cross-linking agent, and cross-linking aid.

As the acrylic rubber, one having a glass transition temperature of −40° C. or less is used. As the acrylic rubber, one having a cross-linking point that is cross-linked using a cross-linking agent and a cross-linking aid is used. Specifically, an acrylic rubber having a crosslinkable group (crosslinking point) (for example, an acrylic rubber containing a carboxyl group) is used.

Such an acrylic rubber comprises, for example, a polymer of a monomer composition containing at least one (meth)acrylate and a carboxyl group-containing monomer having a carboxyl group. In addition, in this specification, "(meth)acrylate" means "methacrylate and/or acrylate." "Methacrylate and/or acrylate" means either or both of "acrylic" and "methacrylic".

Examples of the (meth)acrylates include alkyl (meth)acrylates and alkoxyalkyl (meth)acrylates.

Examples of the alkyl (meth)acrylate include alkyl (meth)acrylate having a linear or branched alkyl group having 1 to 18 carbon atoms (preferably 1 to 8 carbon atoms, more preferably 1 to 4 carbon atoms). ) acrylates. Such alkyl (meth)acrylates include, for example, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, i-propyl (meth)acrylate, n-butyl (meth)acrylate, i -Butyl (meth) acrylate, n-pentyl (meth) acrylate, i-pentyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-hexyl (meth) acrylate, octyl (meth) acrylate, i-octyl (meth) ) acrylate, nonyl (meth) acrylate, i-nonyl (meth) acrylate, i-decyl (meth) acrylate, lauryl (meth) acrylate, tridecyl (meth) acrylate, i-myristyl (meth) acrylate, stearyl (meth) acrylate , i-stearyl (meth)acrylate and the like.

Examples of the alkoxyalkyl (meth)acrylates include alkoxyalkyl (meth)acrylates in which the alkoxy group has 1 to 4 carbon atoms and the alkyl group has 1 to 4 carbon atoms. Such alkoxyalkyl (meth)acrylates include methoxymethyl (meth)acrylate, methoxyethyl (meth)acrylate, methoxypropyl (meth)acrylate, ethoxymethyl (meth)acrylate, ethoxyethyl (meth)acrylate, ethoxypropyl ( meth)acrylate, butoxyethyl (meth)acrylate and the like.

The carboxyl group-containing monomer is not particularly limited as long as it has a carboxyl group and is copolymerizable with the (meth)acrylate. Examples include (meth)acrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, monoalkyl esters thereof, and the like. Acid anhydrides of these carboxyl group-containing monomers (for example, acid anhydride group-containing monomers such as maleic anhydride and itaconic anhydride) can also be used as carboxyl group-containing monomers.

For polymerization of the acrylic rubber, known techniques (e.g., emulsion polymerization method, suspension polymerization method, bulk polymerization method, solution polymerization method) can be used. etc. are also appropriately selected and used from known ones.

Commercially available acrylic rubbers include, for example, "NOXTITE (registered trademark) PA-524" (glass transition temperature: -44°C, manufactured by Unimatec Co., Ltd.).

The amount of acrylic rubber compounded in the acrylic rubber-based composition is set to 25 to 85 parts by mass when the total amount of acrylic rubber and ethylene acrylic rubber compounded is 100 parts by mass.

Ethylene acrylic rubber having a glass transition temperature of −40° C. or less is used. As the ethylene acrylic rubber, one having a cross-linking point that is cross-linked using a cross-linking agent and a cross-linking aid is used. Specifically, ethylene acrylic rubber having the same type of crosslinkable groups (crosslinking points) as acrylic rubber (for example, ethylene acrylic rubber containing a carboxyl group) is used.

Such ethylene acrylic rubber comprises, for example, a polymer of a monomer composition containing at least one (meth)acrylate, an ethylene monomer, and a carboxyl group-containing monomer having a carboxyl group.

As the (meth)acrylate, for example, the above-mentioned alkyl (meth)acrylate, alkoxyalkyl (meth)acrylate, etc., which are used for acrylic rubber may be used. As for the carboxyl group-containing monomer having the carboxyl group, the above-mentioned carboxyl group-containing monomer used for acrylic rubber may be used.

For the polymerization of the ethylene acrylic rubber, known techniques (e.g., emulsion polymerization method, suspension polymerization method, bulk polymerization method, solution polymerization method) can be used. Solvents and the like are appropriately selected and used from known ones.

Commercially available products of the ethylene acrylic rubber include, for example, "Vamac (registered trademark) VMX-4017" (glass transition temperature: -41°C, manufactured by DuPont).

The amount of ethylene acrylic rubber compounded in the acrylic rubber-based composition is set to 15 to 75 parts by mass when the total amount of acrylic rubber and ethylene acrylic rubber compounded is 100 parts by mass.

A polyether ester plasticizer is used as the plasticizer. Polyether ester plasticizers include, for example, polyethylene glycol butanoic acid ester, polyethylene glycol isobutanoic acid ester, polyethylene glycol di(2-ethylbutyric acid) ester, polyethylene glycol (2-ethylhexylic acid) ester, polyethylene glycol decanoic acid ester, Dibutoxyethanol adipate, di(butyldiglycol) adipate, di(butylpolyglycol) adipate, di(2-ethylhexyloxyethanol) adipate, di(2-ethylhexyldiglycol) adipate, diadipate (2-ethylhexylpolyglycol), dioctoxyethanol adipate, di(octyldiglycol) adipate, di(octylpolyglycol) adipate, and the like. These may be used alone or in combination of two or more.

The freezing point (°C) of the plasticizer used is, for example, -50°C or lower. Further, the molecular weight of the plasticizer used is, for example, 450 or more (preferably 500 or more). When such a plasticizer is used, it does not harden in a low-temperature environment (for example, -45°C) and can impart flexibility to a base resin containing acrylic rubber or ethylene acrylic rubber. Moreover, such a plasticizer is difficult to volatilize even in a high temperature environment (for example, 150° C.) and can remain in the base resin.

The amount of the plasticizer compounded in the acrylic rubber-based composition is set to 15 to 30 parts by mass with respect to a total of 100 parts by mass of the acrylic rubber and the ethylene acrylic rubber.

Metal hydroxides are used for the purpose of imparting flame retardancy, imparting vibration damping properties, etc., and are in the form of particles. The metal hydroxide is not particularly limited as long as it does not impair the purpose of the present invention. For example, aluminum hydroxide is used. As the aluminum hydroxide, a low soda aluminum hydroxide having a soluble sodium content of 100 ppm or less is particularly preferable. As used herein, the amount of soluble sodium is the amount of sodium ions (Na ⁺ ) dissolved in water when the low-soda aluminum hydroxide and water are brought into contact.

The average particle size of the metal hydroxide is, for example, preferably 5 μm to 15 μm, more preferably 5 μm to 12 μm.

The amount of the metal hydroxide compounded in the acrylic rubber-based composition is set to 80 to 140 parts by mass with respect to a total of 100 parts by mass of the acrylic rubber and the ethylene acrylic rubber. Metal hydroxides are cheaper in material cost and have better heat resistance than phosphorus-based flame retardants.

Phosphorus-based flame retardants are flame retardants containing phosphorus (P) in the compound, and are used to impart flame retardancy to acrylic rubber-based compositions. Phosphorus-based flame retardants have higher flame retardancy than metal hydroxides. The phosphorus-based flame retardant of the present embodiment is used for imparting vibration damping properties to the acrylic rubber-based composition in addition to imparting flame retardancy. As the phosphorus-based flame retardant, for example, a metal phosphinate flame retardant, an organic phosphorus flame retardant, ammonium polyphosphate, and the like are used. Among these, metal phosphinate flame retardants are preferred. Examples of the metal in the metal phosphinate flame retardant include Al, Mg, Ca, Ti, Zn, and Sn.

The amount of the phosphorus-based flame retardant compounded in the acrylic rubber-based composition is set to 15 to 25 parts by mass with respect to 100 parts by mass in total of the acrylic rubber and the ethylene acrylic rubber.

The lubricant is blended with the acrylic rubber composition for the purpose of improving workability (kneader dischargeability, roll adhesion, etc., which will be described later) and vibration damping.

Fatty acid esters (higher fatty acid esters, etc.), aliphatic amines (aliphatic primary amines, etc.), etc. are used as lubricants. These lubricants may be used alone or in combination of two or more. As the lubricant, it is preferable to use a combination of a fatty acid ester and an aliphatic amine. When a fatty acid ester and an aliphatic amine are used in combination in this way, processability (e.g. kneader dischargeability, roll dischargeability, etc.) is particularly excellent.

Examples of commercially available lubricants include "STRACTOL WB222" (higher fatty acid ester (an example of fatty acid ester), manufactured by S&S Japan Co., Ltd.), "STRACTOL WB18" (aliphatic primary amine (an example of aliphatic amine ), manufactured by S&S Japan Co., Ltd.) and the like.

The blending amount of the lubricant in the acrylic rubber-based composition is set to 0.5 to 3.5 parts by mass when the total blending amount of the acrylic rubber and the ethylene acrylic rubber is 100 parts by mass. When the blending amount of the lubricant is within such a range, the processability, vibration damping properties, etc. of the acrylic rubber-based composition are easily ensured. When the total amount of the acrylic rubber and the ethylene acrylic rubber is 100 parts by mass, the amount of the lubricant compounded in the acrylic rubber composition is preferably 1.5 parts by mass or more, and more preferably 2.2 parts by mass or more. preferable.

The amount of the lubricant (fatty acid ester) compounded in the acrylic rubber composition is preferably 3.0 parts by mass or less, and 2.5 parts by mass when the total amount of acrylic rubber and ethylene acrylic rubber compounded is 100 parts by mass. Part or less is more preferable.

Further, the amount of the lubricant (aliphatic amine) compounded in the acrylic rubber composition is preferably 1.8 parts by mass or less, and 1.5 parts by mass when the total amount of the acrylic rubber and the ethylene acrylic rubber is 100 parts by mass. Part by mass or less is more preferable.

The cross-linking agent is not particularly limited as long as it can cross-link the acrylic rubber and the ethylene acrylic rubber. For example, an aliphatic amine compound is used.

Examples of aliphatic amine compounds include aliphatic diamine compounds such as hexamethylenediamine, hexamethylenediamine carbamate, and N,N'-dicinnamylidene-1,6-hexanediamine. Among these, hexamethylenediamine carbamate is preferred.

The amount of the cross-linking agent in the acrylic rubber composition is 0.1 to 5.0 parts by mass, preferably 0.2 to 3.0 parts by mass, with respect to 100 parts by mass of acrylic rubber and ethylene acrylic rubber. set.

The cross-linking aid is used together with the cross-linking agent and has a function of promoting cross-linking of the acrylic rubber and the ethylene acrylic rubber. The cross-linking aid is not particularly limited as long as it can cross-link the acrylic rubber and the ethylene acrylic rubber. For example, a guanidine compound is used.

Guanidine compounds include, for example, guanidine, tetramethylguanidine, dibutylguanidine, 1,3-o-tolylguanidine, 1,3-diphenylguanidine and the like. Among these, 1,3-diphenylguanidine is preferred.

The amount of the cross-linking aid compounded in the acrylic rubber composition is set to 0.1 to 10 parts by mass, preferably 0.5 to 5 parts by mass, with respect to 100 parts by mass of acrylic rubber and ethylene acrylic rubber in total. .

In addition to the components described above, the acrylic rubber composition may contain other components as long as the object of the present invention is not impaired. Specific other components include fillers, processing aids, anti-aging agents, tackifying resins, rust inhibitors, antioxidants, corrosion inhibitors, colorants, foaming agents, ultraviolet absorbers, surfactants, and the like. mentioned.

Examples of substances constituting the filler include metals such as iron, copper, and aluminum, or alloys thereof, talc, glass, inorganic materials such as glass, graphite (carbon black), minerals, and the like.

The amount of carbon black compounded in the acrylic rubber-based composition is not particularly limited as long as it does not impair the object of the present invention. is preferably set.

The acrylic rubber-based composition is uniformly kneaded using a general rubber kneading device.

The acrylic rubber composition is heat-press molded into a predetermined shape, and further heat-treated in an oven for a predetermined period of time, so that a cross-linking reaction proceeds and a vibration consisting of a cross-linked product (cured product) of the acrylic rubber-based composition is obtained. A damping material is obtained.

In the acrylic rubber composition, a cross-linking reaction (primary cross-linking reaction, amidation reaction) proceeds during heat press molding, and further a cross-linking reaction (secondary cross-linking reaction, imidization reaction) proceeds during heat treatment. By doing so, a crosslinked product of the acrylic rubber-based composition is obtained.

[Vibration damping material]
The vibration damping material is excellent in heat resistance (for example, usable at 150° C.), cold resistance (for example, usable at −45° C.), and vibration damping property (loss factor at 23° C. of 0.4 or more).

Also, the vibration damping material is excellent in workability. When manufacturing a vibration damping material from the above acrylic rubber composition, the acrylic rubber composition has strong adhesion to a kneader (pressure kneader, roll mill, etc.) in the kneading process of the acrylic rubber composition. sticking is suppressed. The container-shaped kneading unit of a pressure kneader and the rolls of a roll mill are made of metal, and conventional acrylic rubber-based compositions stick to such kneaders with strong adhesive force. . On the other hand, the acrylic rubber-based composition (and the vibration damping material) of the present embodiment is easy to peel off from the kneader (the kneading section, etc.) in the kneading step, and is excellent in processability (workability).

The acrylic rubber-based composition of the present embodiment can ensure heat resistance, cold resistance, vibration damping properties, etc., even if it contains a lubricant or the like as described above.

In addition, the vibration damping material is excellent in flame retardancy (equivalent to V-0 in UL94V standard). In addition, the vibration damping material is based on acrylic rubber and ethylene acrylic rubber, and has excellent oil resistance. The hardness of the vibration damping material is preferably A50 or less, and more preferably A20 or more and A50 or less. The hardness of the vibration damping material is measured according to JIS K6253.

Vibration damping materials are used, for example, in equipment that incorporates a vibration source such as a motor, and equipment that incorporates precision parts to block the transmission of vibration from the outside. In particular, the vibration damping material can be suitably used in locations such as the engine compartment of an automobile, which are likely to reach high temperatures and in some cases may reach low temperatures (for example, when used in cold climates). Moreover, although oil resistance is also required for such a portion, the vibration damping material of this embodiment can be used without any problem because it is based on acrylic rubber and ethylene acrylic rubber.

The vibration damping material may be formed in a sheet shape, or may be molded into a predetermined shape using a mold or the like.

The present invention will be described in more detail below based on examples. In addition, the present invention is not limited at all by these examples.

[Examples 1 to 5 and Comparative Examples 1 to 6]
(Production of acrylic rubber composition)
In each example and each comparative example, acrylic rubber, ethylene acrylic rubber, polyether ester plasticizer, aluminum hydroxide, metal phosphinate flame retardant, carbon black, lubricant A, lubricant B, cross-linking agent and cross-linking aid were blended in proportions (parts by mass) shown in Table 1, and the mixture was charged into a pressure kneader and kneaded at 70°C for 5 minutes to obtain an acrylic rubber composition.

The materials used in each example are as follows.
"Acrylic rubber": trade name "NOXTITE (registered trademark) PA-524", Tg = -44°C, manufactured by Unimatec "Ethylene acrylic rubber": trade name "Vamac (registered trademark) VMX-4017", Tg = - 41 ° C., DuPont Co., Ltd. "Polyether ester plasticizer": trade name "ADEKAIZER (registered trademark) RS-700", molecular weight = about 550, freezing point = -53 ° C., ADEKA Co., Ltd. "Aluminum hydroxide" ( Example of metal hydroxide): Low soda aluminum hydroxide, trade name “BF083”, average particle size = 10 μm, manufactured by Nippon Light Metal Co., Ltd. “Metal phosphinic acid salt flame retardant” (an example of phosphorus flame retardant): Product Name "Exolit (registered trademark) OP1230", phosphorus content = about 23% by mass, manufactured by Clariant Chemicals Co., Ltd. "Carbon black": trade name "Asahi #35", average particle size = 78 nm, manufactured by Asahi Carbon Co., Ltd. "Lubricant A”: higher fatty acid ester (fatty acid ester type), trade name “STRACTOL WB222”, manufactured by S&S Japan Co., Ltd. “Lubricant B”: primary aliphatic amine (aliphatic amine type), trade name “STRACTOL WB18” , S&S Japan Co., Ltd. "Cross-linking agent": hexamethylenediamine carbamate (an example of an aliphatic diamine compound), trade name "CHEMINOX AC-6", Unimatec Co., Ltd. "Cross-linking aid": 1,3-diphenylguanidine ( An example of a guanidine compound), trade name “Noccellar D”

(Production of vibration damping material)
Next, the acrylic rubber composition was kneaded with a two-roll mill (distance between rolls: 2 mm) for an additional 3 minutes, and then the composition was heat-press molded into a plate using a heat press and a mold. During this heat press molding, the composition is primarily crosslinked. The molding temperature was 180° C., the molding pressure was 30 MPa, and the molding time was 10 minutes. Further, the composition after heat pressing is left to stand in an oven at 175 ° C. for 4 hours to perform secondary cross-linking, and then taken out from the oven to form the plate-shaped vibration damping material of each example and each comparative example. got

〔evaluation〕
(Processability evaluation 1: Kneader dischargeability)
In each example and each comparative example, it was evaluated whether or not the acrylic rubber composition was easily discharged from the container-shaped kneading section of the pressure kneader during production of the acrylic rubber composition. Evaluation criteria are as follows. The results are shown in Table 1.
<Evaluation Criteria>
When the acrylic rubber composition (kneaded product) can be taken out in less than 10 minutes on a 10 L kneader scale.
When the acrylic rubber composition (kneaded product) can be removed in 10 minutes or more and less than 30 minutes on the 10 L kneader scale ・・・「〇」
When the acrylic rubber composition (kneaded product) can be taken out in 30 minutes or more on the 10 L kneader scale ・・・「×」

(Processing evaluation 2: roll tackiness)
In each example and each comparative example, when the acrylic rubber composition was kneaded in a two-roll mill, the ease of peeling off the composition from the rolls (the ease of peeling) was evaluated. Evaluation criteria are as follows. The results are shown in Table 1.
<Evaluation Criteria>
When about 60 kg of the acrylic rubber composition can be peeled off from the roll in less than 30 minutes.
When about 60 kg of the acrylic rubber composition can be peeled off from the roll within 30 minutes or more and less than 60 minutes: "○"
When about 60 kg of the acrylic rubber composition can be peeled off from the roll in 60 minutes or longer.

(hardness)
In each example and each comparative example, a test piece of a predetermined size (length 50 mm, width 50 mm, thickness 6 mm) was cut out from the obtained vibration damping material, and the hardness of the test piece was measured according to JIS K6253. (JIS A hardness) was measured (constant pressure load within 1 second). The results are shown in Table 1.

(Hardness change after heating)
In each example and each comparative example, the test piece used in the hardness measurement was heated at a temperature of 150° C. for 24 hours. Then, the hardness (JIS A hardness) of the heated test piece was measured (constant pressure load within 1 second) in accordance with JIS K6253 in the same manner as the hardness measurement (hardness measurement before heating). Then, the hardness change amount (hardness increase amount) before and after heating was obtained from the hardness after heating and the hardness before heating. The results are shown in Table 1. In addition, when the hardness change amount (hardness increase amount) is 5 or less, it can be said that the heat resistance is excellent.

(Compression set after heating)
In each example and each comparative example, a test piece of a predetermined size (diameter 13 mm, thickness 6 mm) was cut out from the obtained vibration damping material, and the compression set was measured using the test piece (thickness D) according to JIS. Measured according to K6262. Specifically, the test piece after heating is compressed by 25% in the thickness direction using a predetermined compression device (compression jig) (thickness D1), and in that state, an environmental tester (constant temperature bath) at 150 ° C. placed inside and left there for 22 hours. After that, take out the test piece from the environmental tester, release the compression device that compresses the test piece, leave it on the wooden board at room temperature for 30 minutes or more, and then measure the thickness (D2) of the test piece. The compression set (%) was calculated from (D−D2)/(D−D1)×100. The results are shown in Table 1. When the compression set (%) value is 50 or less, it can be said that the heat resistance is excellent.

(Simple low temperature embrittlement test)
In each example and each comparative example, a test piece of a predetermined size (length 40 mm, width 6 mm, thickness 2 mm) was cut out from the obtained vibration damping material, and one end of the test piece was attached to a simple low temperature embrittlement test jig. installed. Place the simple low temperature embrittlement test jig in a test environment set at a predetermined temperature for 1 hour, then take it out and at the same time impact the free end side of the test piece with the impact jig attached to the simple low temperature embrittlement test jig. was added, and the presence or absence of damage to the test piece was confirmed. Temperatures were set in 1° C. intervals. The results are shown in Table 1. Table 1 shows the minimum temperature at which the test piece did not crack. If it does not crack down to -45°C (if it cracks at a temperature lower than -45°C), it can be said that it has excellent cold resistance.

(Loss factor)
In each example and each comparative example, four test pieces each having a length of 5 mm, a width of 5 mm, and a thickness of 3 mm were cut out from the obtained vibration damping material. Next, a vibration test apparatus 10 shown in FIG. 1 was prepared. FIG. 1 is an explanatory diagram schematically showing the configuration of the vibration test apparatus 10. As shown in FIG. As the vibration tester 10, "F-300BM/A" (manufactured by Emic Co., Ltd., fully automatic vibration tester) was used. The vibration test device 10 is a device that generates a vibration frequency of a predetermined frequency to vibrate the vibration table 11 . The vibration direction is the vertical direction (thickness direction of the test piece S) in FIG. The vibration test apparatus 10 includes a mounting plate 12 and the like in addition to the vibration table 11 . The mounting plate 12 has a square shape in a plan view, and has a mass of 1000 g. The damping property test using the vibration test apparatus 10 was performed under a room temperature environment of 23°C.

As shown in FIG. 1, the four test pieces S are arranged at the four corners of the mounting plate 12, and are sandwiched between the mounting plate 12 and the vibration table 11. As shown in FIG. That is, the mounting plate 12 is supported by the test piece S at four points on the vibration table 11 .

In this state, the vibration table 11 was vibrated under the conditions of an acceleration of 0.4 G, a frequency of 5 Hz to 1000 Hz, and a sweep speed of 1 oct/min. Vibration of the mounting plate 12 was detected by the acceleration pickup 13 attached to the mounting plate 12, and a resonance curve was created based on the detection results.

Next, based on the resonance frequency f0 (Hz) indicating the peak value (resonance magnification) of the resonance curve and the frequencies f1 and f2 (f1<f0<f2) indicating values 3 dB lower than the peak value , the loss factor tan δ was calculated from the following formula (1) (half width method).
tan δ=(f2−f1)/f0 (1)

Table 1 shows the loss factor tan δ of each example and each comparative example. When the loss factor tan δ is 0.4 or more (23° C.), it can be said that the vibration damping property is excellent.

(Flame retardance)
In each example and each comparative example, a test piece of a predetermined size (length 125 mm, width 13 mm, thickness 1 mm) was cut out from the obtained vibration damping material, and the test piece was cut into a vertical flame retardant conforming to the UL94V standard. did the test. The results are shown in Table 1. In Table 1, the case where the flame retardancy achieved "V-0" was indicated as "V-0", and the case where it was not achieved was indicated as "x".

As shown in Table 1, it was confirmed that the acrylic rubber compositions of Examples 1 to 3 were particularly excellent in kneader dischargeability and roll adhesion. In Examples 1 to 3, no part of the acrylic composition (kneaded product) remained stuck to the kneading part when the kneader dischargeability was evaluated. Examples 1 to 3 are cases where lubricants (lubricants A and B) are blended in the acrylic rubber composition. Further, it was confirmed that the vibration damping materials of Examples 1 to 3 are excellent in heat resistance, cold resistance, vibration damping property and flame retardancy.

Examples 4 and 5 are cases in which the blending amount of the lubricant is smaller than those of Examples 1-3. Moreover, Example 4 is a case where only lubricant B is contained as a lubricant, and Example 5 is a case where only lubricant A is contained as a lubricant. In the case of Example 4, the acrylic rubber composition (kneaded product) could not be removed within 10 minutes, but the acrylic rubber composition was removed within 10 minutes or more and less than 30 minutes. It was possible to take out the product (kneaded product). In addition, in the case of Example 4, a part of the acrylic rubber composition (kneaded material) was stuck to the kneading part and remained in the evaluation of the kneader dischargeability. In addition, in the case of Example 4, as in Examples 1 to 3, particularly excellent results were obtained with respect to roll adhesion. Further, in the case of Example 5, during evaluation of roll tackiness, the acrylic rubber composition could not be peeled off from the roll within 30 minutes or less, but within 30 minutes or more and less than 60 minutes. Moreover, it was possible to peel off the acrylic rubber-based composition from the roll. In addition, in the case of Example 5, as in Examples 1 to 3, particularly excellent results were obtained with respect to kneader dischargeability. It was also confirmed that the vibration damping materials of Examples 4 and 53 are excellent in heat resistance, cold resistance, vibration damping property and flame retardancy.

Comparative Example 1 is a case where the compounding amount of the phosphorus-based flame retardant is small and the lubricant (lubricants A and B) is not included. In such Comparative Example 1, there was a problem in roll adhesion. The kneader dischargeability of Comparative Example 1 was about the same as that of Example 4. In addition, Comparative Example 1 had a loss factor smaller than 0.4 and had a problem with vibration damping.

Comparative Example 2, like Example 1 and the like, contains a predetermined amount of lubricant (lubricants A and B), but the amount of the phosphorus-based flame retardant compounded is small. Although Comparative Example 2 was excellent in processability (ejectability from kneader and roll adhesion), the loss factor was smaller than 0.4 and there was a problem in vibration damping. In addition, it was found that Comparative Example 2 had an increased value of the loss factor as compared with Comparative Example 1, and the vibration damping property was improved by containing the lubricant.

Comparative Example 3 is a case where only acrylic rubber is included as the resin component. In Comparative Example 3, the result of the simple low-temperature embrittlement test was -44°C, indicating a problem with cold resistance. Moreover, in the case of Comparative Example 3, there were problems with workability (kneader dischargeability, roll stickiness). The acrylic rubber composition of Comparative Example 3 had a strong adhesive force to the kneader (kneading section), making it difficult to take out the acrylic composition (kneaded product), resulting in a long time required for the takeout work. . Further, in the case of Comparative Example 3, part of the acrylic composition (kneaded product) was stuck to the kneading unit during evaluation of the kneader discharge property, and all the acrylic composition (kneaded product) was removed from the kneading unit. could not be removed from the Moreover, in the case of Comparative Example 3, there was also a problem with roll adhesion. Specifically, it was difficult to peel off the acrylic rubber-based composition of Comparative Example 3 from the roll, resulting in a long peeling operation.

Comparative Example 4 is a case where the amount of acrylic rubber compounded is small and the amount of ethylene acrylic rubber compounded is large. Similar to Comparative Example 3, Comparative Example 4 had problems in workability (ejectability from kneader, roll stickiness). Moreover, in the case of Comparative Example 4, the loss factor was smaller than 0.4, and there was a problem in vibration damping.

Comparative Examples 5 and 6 are cases where the blending amount of the lubricant is too large. In the case of Comparative Example 5, the result of the simple low temperature embrittlement test was -43°C, indicating a problem with cold resistance. In Comparative Example 5, the blending amount of lubricant A (fatty acid ester) was 4 parts by mass, which is also a case where the blending amount of lubricant A is too large. Moreover, in the case of Comparative Example 6, the compression set was 52, and there was a problem in heat resistance. In Comparative Example 6, the blending amount of lubricant B (aliphatic amine) was 2 parts by mass, and the blending amount of lubricant B was too large.

DESCRIPTION OF SYMBOLS 10... Vibration test apparatus, 11... Shaking table, 12... Mounting plate, 13... Acceleration pick-up, S... Test piece (vibration damping material)

Claims (5)

25 to 85 parts by mass of an acrylic rubber having a glass transition temperature of −40° C. or lower and containing cross-linking points;
15 to 75 parts by mass of ethylene acrylic rubber having a glass transition temperature of −40° C. or lower and containing the same type of cross-linking point as the cross-linking point (provided that the total of the acrylic rubber and the ethylene acrylic rubber is 100 parts by mass);
15 to 30 parts by mass of a polyether ester plasticizer,
80 to 140 parts by mass of metal hydroxide,
15 to 25 parts by mass of a phosphorus-based flame retardant,
0.5 to 3.5 parts by mass of a lubricant;
0.1 to 5 parts by mass of a cross-linking agent;
An acrylic rubber composition containing 0.1 to 10 parts by mass of a cross-linking aid. The acrylic rubber composition according to Claim 1, further comprising 5 to 15 parts by mass of carbon black. 3. The acrylic rubber composition according to claim 1, wherein said acrylic rubber and said ethylene acrylic rubber contain a carboxyl group as said cross-linking point. The acrylic rubber composition according to any one of claims 1 to 3, wherein the cross-linking agent comprises an aliphatic amine compound, and the cross-linking aid comprises a guanidine compound. A vibration damping material comprising a crosslinked product of the acrylic rubber composition according to any one of claims 1 to 4.

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