JPH0347186B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a vibration damping material that exhibits an excellent vibration damping effect in a wide temperature range from room temperature or its vicinity to high temperatures. [Prior Art] Generally, vibration damping materials, especially vibration damping steel plates, are constructed by interposing a viscoelastic material layer between two steel plates and integrating the whole structure, so that it resists steady vibrations or shocks applied to the steel plates. The original vibration energy is absorbed by the viscoelastic material layer and converted into thermal energy due to internal friction, thereby reducing noise (vibration damping effect).
This type of damping steel plate is widely used in oil pans, cylinder head covers, shielding plates, motor cases, etc. of vehicles. As mentioned above, the damping action of the damping steel plate is based on the damping action of the viscoelastic material layer itself interposed between the two steel plates.
The loss coefficient (η) is generally used as a measure of the damping effect.
is used, and the damping effect is evaluated based on the value of the loss coefficient η. It is preferable that the loss coefficient η is large and does not change over a wide range from low temperatures to high temperatures. In other words, the above-mentioned vibration damping steel plates are used in a wide temperature range from low to high temperatures. It is required to exhibit an excellent vibration damping effect even at considerably high temperatures. As described above, the performance of a damping steel plate is greatly influenced by the loss coefficient η of the viscoelastic material layer itself, and conventionally, synthetic resin or rubber has been used as the viscoelastic material layer. . Synthetic resins have unique viscoelastic characteristics, that is, the elastic modulus and loss coefficient η are highly temperature dependent. The coefficient η has a large temperature dependence, with a sharp peak near the glass transition temperature (usually at room temperature or higher), and the temperature range in which the damping effect is exerted is narrow. have. This is mainly due to the sudden decrease in the elastic modulus of the synthetic resin. Moreover, when the temperature of the synthetic resin rises and exceeds its glass transition temperature, it becomes molten, and a damping steel plate made of such a synthetic resin as a viscoelastic material layer suffers from a rapid decrease in the loss coefficient η. . Therefore, it is not possible to exhibit an excellent vibration damping effect over a wide temperature range, and only exhibits an excellent vibration damping effect at temperatures near the glass transition temperature. In particular, when the glass transition temperature is exceeded, the above-mentioned η decreases rapidly, so that it cannot be used at a considerably high temperature. In order to eliminate these drawbacks to some extent, it was proposed to use a block copolymer obtained by copolymerizing a liquid polyol and a vinyl monomer as a vibration damping material (Japanese Patent Application Laid-Open No.
50−39374). However, since all synthetic resins have high glass transition temperatures, such block copolymers also have high glass transition temperatures. Therefore, in the proposed method, although it is possible to increase the loss coefficient at high temperatures, it is not possible to increase the loss coefficient at low temperatures. That is, the damping material obtained by the proposed method has a small loss coefficient η at low temperatures, and the curve of the loss coefficient η is not a flat straight line, but a bell-shaped curve with a peak on the high temperature side. On the other hand, vibration-damping steel plates with rubber as a viscoelastic material layer also
The loss coefficient η reaches its maximum near the glass transition temperature, but since the glass transition temperature of rubber is generally below zero degrees, it cannot be used at room temperature or in the high temperature range above room temperature when it is actually used as a vibration damping steel plate. cannot exhibit an excellent vibration damping effect. However, since rubber is three-dimensionally crosslinked, even if the temperature rises and exceeds the glass transition temperature, it does not become molten, and the loss coefficient η does not drop as suddenly as in synthetic resins. The loss coefficient η-temperature curve of this rubber and the loss coefficient η-temperature curve of the synthetic resin are shown in FIG. In the figure, curve A' is for synthetic resin, and curve B' is for rubber. As is clear from Figure 1, although synthetic resins exhibit excellent vibration damping effects near the glass transition temperature in the temperature range of room temperature or higher, they cannot be used due to the high temperature dependence of the loss coefficient η. In the temperature range above, the damping effect decreases rapidly. On the other hand, rubber has a low temperature dependence of its loss coefficient η, so the vibration damping effect changes relatively little due to temperature changes. Sufficient vibration damping action cannot be obtained in the temperature range. As described above, synthetic resins and rubber have advantages and disadvantages, and even if they are used alone, an excellent vibration-damping steel plate cannot be obtained. Therefore, it has been considered to blend synthetic resin and rubber to reduce the temperature dependence of the loss coefficient η and obtain a high value of the loss coefficient η over a wide temperature range. [Problems to be Solved by the Invention] However, damping materials using a blend of synthetic resin and rubber as a viscoelastic material layer have a large loss coefficient η at the peak, but at the same time have low temperature dependence. Because of this, the intended purpose cannot be achieved. This invention has low temperature dependence of the loss coefficient η,
The purpose of the present invention is to provide a vibration damping material that exhibits an excellent damping effect over a wide temperature range by developing a viscoelastic material that can maintain a high loss coefficient η in the temperature range in which the damping material is used. [Means for Solving the Problems] In order to achieve the above object, the present invention provides a vibration damping material comprising a rigid substrate and a viscoelastic material layer formed in close contact with the surface of the substrate. The viscoelastic material layer is produced by a viscoelastic reaction between a nitrile rubber containing 15 to 60% by weight of repeating units derived from acrylonitrile and an acrylic acid compound represented by the following general formula (1) or (2). (A) on a weight basis, comprising a repeating unit (A) derived from a nitrile rubber and a repeating unit (B) derived from an acrylic compound:
(B) is mainly composed of viscoelastic reaction products in a ratio of 100:20 to 80.

【formula】

[In formulas (1) and (2), R is a monovalent organic group. ]

In other words, the viscoelastic substance in the damping material is
It is not a simple blend of rubber and resin by mechanical mixing, but a viscoelastic reaction product of the above nitrile rubber and the acrylic acid compound (monomer) represented by the above general formulas (1) and (2). It is composed mainly of. In this viscoelastic reaction product, the acrylic acid compound (monomer) itself polymerizes to form a chain structure,
It is thought that it is bonded to the double bond in the nitrile rubber molecules to form a graft polymer with the nitrile rubber, and this structure and the nitrile rubber, which is a constituent part of the graft polymer, By having the repeating unit (A) derived from the repeating unit derived from the acrylic acid compound and the repeating unit derived from the acrylic acid compound (B) in the above ratio, the viscoelastic reaction product can be used at a wide temperature range from low to high temperatures. It is expected to have a high and uniform loss factor η over the range.
Therefore, a damping material using this material exhibits an excellent damping effect in the above temperature range. The nitrile rubber used in the synthesis of the above viscoelastic reaction product is acrylonitrile copolymer (NBR), acrylonitrile-isoprene copolymer (NIR), acrylonitrile-butadiene-isoprene terpolymer (NBIR), or a combination thereof. It is necessary that they are appropriately combined and contain 15 to 60% by weight of repeating units derived from acrylonitrile. That is,
15 repeating units derived from acrylonitrile
By using a nitrile rubber with 60% by weight and the balance being repeating units derived from butadiene and isoprene, the double bonds in the nitrile rubber (present in the repeating units derived from butadiene and isoprene) ) becomes appropriate, and the acrylic acid compound chain is bonded thereto to obtain a desired graft polymer. As the acrylic acid compound (monomer) to be reacted with the nitrile rubber, those represented by the following general formula (1) or (2) are used.

【formula】

[In formulas (1) and (2), R is a monovalent organic group. ]

Specific examples of the above-mentioned monovalent organic group R include alkyl groups such as methyl group, ethyl group, butyl group,
cycloalkyl group, 2-hydroxyalkyl group,
Examples include tetrahydrofurfuryl group, allyl group, glycidyl group, and dimethylamino group. Also included are residues of polyhydric alcohols such as diethylene glycol and tetraethylene glycol. As the polymerization initiator for the above acrylic acid compound (monomer), a thermal polymerization initiator consisting of a widely used organic peroxide such as dialkyl peroxide, hydroperoxide, peroxy ester, peroxy ketal, etc. is used. It will be done. Further, as a rigid substrate on which a viscoelastic substance layer mainly composed of the above-mentioned viscoelastic reaction product is formed, a commonly used steel plate can be used.
In addition, rigid plastic plates such as FRP are also used. The damping material of the present invention is manufactured using the above-mentioned raw materials, for example, in the following manner. That is, the above nitrile rubber and acrylic acid compound (monomer) were mixed in 100 parts by weight (hereinafter "parts") of the former.
20 to 80 parts of the latter. By doing this, in the viscoelastic reaction product obtained, the repeating units (A) derived from the nitrile rubber and the repeating units (B) derived from the acrylic acid compound are (on a weight basis) ( A):(B)=100:
The ratio will be between 20 and 80. When the repeating unit (B) is below the above range, the viscoelastic reaction product becomes more rubbery and
The loss coefficient η becomes lower in the high temperature range, and the damping effect in the high temperature range becomes smaller. On the other hand, when it exceeds the above range, the viscoelastic reaction product becomes more resinous, its loss coefficient η becomes lower near room temperature, and the damping effect at room temperature becomes smaller. Therefore, the ratio of repeat units (A) and (B) is set as above (A): (B) = 100:
It is important to set the ratio to 20 to 80, and for that purpose, it is necessary to mix the nitrile rubber and the acrylic acid compound in the above ratio. In this case, appropriate amounts of an organic peroxide, a reinforcing filler, an anti-aging agent, and a softener are simultaneously added as a thermal polymerization initiator for the acrylic acid compound (monomer). Next, the above compound is rolled to form a thin sheet, which is sandwiched between two steel plates whose surfaces to which the viscoelastic material layer is coated are coated with a vulcanizing adhesive, and then vulcanized ( heat press). Through this vulcanization heating, the thermal polymerization initiator acts and the acrylic acid compound (monomer) is thermally polymerized and chained, and at the same time, it bonds to the double bond in the nitrile rubber molecules and grafts with the nitrile rubber. Forms a polymer and becomes a viscoelastic reaction product. As a result, the desired vibration damping steel plate is obtained. In addition, the above compound was dissolved in a known solvent to form a paste, and the paste was applied to the adhering surface of one of two steel plates whose adhering surface had been coated with a vulcanized adhesive, and then dried. Thereafter, the remaining steel plate may be stacked on top of the steel plate, and the steel plate may be vulcanized (heat pressed) and crimped in this state. In this case, a damping steel plate having an extremely thin layer of viscoelastic material is obtained. Note that the viscoelastic material layer is not only formed between two steel plates as described above, but may also be formed on one steel plate. In this case as well, an excellent vibration damping effect can be obtained due to the action of the viscoelastic material layer. [Operation and Effect] As described above, in this invention, the viscoelastic material layer for exerting a vibration damping effect is not composed of a simple blend of rubber and resin, but is composed of a nitrile rubber and an acrylic acid compound. , and in the reaction product, repeating units (A) derived from nitrile rubber and repeating units (B) derived from an acrylic acid compound are arranged in the above-mentioned ratio. , the loss coefficient η of the viscoelastic reaction product keeps its peak almost uniform from low to high temperatures. Therefore, a damping material using the viscoelastic reaction product exhibits the maximum damping effect at any temperature within the above temperature range. In particular, the loss coefficient η of the viscoelastic reaction product
Because it maintains its peak even in high temperature ranges exceeding 100℃, it exhibits the maximum damping effect even in high temperature ranges, and this is because damping materials are often used in areas where a considerable amount of heat is dissipated, such as in automobile engines. Taking this into account, this can be said to be an extremely important effect. Furthermore, since the viscoelastic reaction product uses nitrile rubber, which has high oil resistance, it has high oil resistance, and therefore, the vibration damping material of the present invention is highly practical. Further, since the viscoelastic reaction product has excellent mechanical strength, the damping material of the present invention can sufficiently withstand mechanical processing such as shearing. Next, examples will be described together with comparative examples. Examples 1 to 3, Comparative Example 1 The raw materials shown in Table 1 below were blended in the proportions shown in the same table, and the blend was kneaded using a Banbury mixer and passed through a forming roll to form a 0.4 mm thick ball. Formed into a sheet. This is applied to two steel plates (thickness:
0.7 mm) and heat pressed (vulcanized) at 150°C for 10 minutes to obtain a vibration damping steel plate. The structure of the obtained damping steel plate is shown in Figure 2. In the figure, 1 is a steel plate, 2
is a viscoelastic material layer.

【table】

[Comparative Example 2: Example of the proposed method]

To 50 parts of polypropylene glycol dimethacrylate obtained by reacting polypropylene glycol with a molecular weight of 3000 with methacrylic acid chloride, 50 parts of methyl methacrylate was added, and to this was added 4 parts of benzoyl peroxide (DOP 5% by weight solution).
The mixture was heated at 60°C for 2 hours, cast between metal plates prepared in advance, and left at 80°C for 2 hours to cure. This was sandwiched as an intermediate layer between two steel plates having a thickness of 0.7 mm to obtain a vibration damping steel plate. The structure of the obtained damping steel plate was as shown in FIG. The vibration damping steel plate obtained as above is 30mm wide.
Cut into lengths of 300 mm and measure the loss coefficient η at each temperature (frequency 500 Hz) using the mechanical impedance method.
was measured, and the loss coefficient η-temperature curve is shown in FIG. In the figure, curve A is Example 1, curve B
is Example 2, curve C is that of Example 3, curve D is that of Comparative Example 1, curve E is that of a commercially available damping steel plate using ethylene-vinyl acid copolymer resin as the viscoelastic material layer, and curve F is that of Comparative Example 2. be. Comparison of curves A to C and curves D to F shows that the damping steel plates of the examples, unlike those of the comparative examples, exhibit a loss coefficient η at or near the peak in a wide temperature range,
It can be seen that the maximum vibration damping effect can be exhibited within that temperature range.

[Brief explanation of drawings]

Fig. 1 is a loss coefficient η vs. temperature curve diagram of rubber and resin, Fig. 2 is a sectional view explaining the structure of an example product of the present invention, and Fig. 3 is an explanatory diagram explaining its loss coefficient η vs. temperature curve. It is. 1... Steel plate, 2... Viscoelastic material layer.

Claims (1)

[Claims] 1. A vibration damping material comprising a rigid substrate and a viscoelastic material layer formed in close contact with the surface of the substrate, wherein the viscoelastic material layer has 15 repeating units derived from acrylonitrile. It is a viscoelastic reaction product of a nitrile rubber containing ~60% by weight and an acrylic acid compound represented by the following general formula (1) or (2), and is a repeating unit derived from the nitrile rubber (A ) and a repeating unit (B) derived from an acrylic acid compound in a ratio of (A):(B)=100:20 to 80 on a weight basis. A vibration damping material characterized by: [Formula] [Formula (1) and (2), R is a monovalent organic group. 2. The damping material according to claim 1, wherein the rigid substrate is a steel plate.