JPH0260903B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a foam composite vibration damping material that exhibits a remarkable vibration damping effect due to the presence of a solid constraining layer, and more specifically, a specific solid constraining layer is bonded to one surface of a plate-shaped foam material to form a plate-shaped foam material. By bonding the other surface to the vibrating body, it not only has a remarkable vibration damping effect, but also has excellent sound absorption performance, and is extremely practical vibration damping that can be made thinner and lighter, and has a large cost reduction effect. Regarding materials. The present inventors previously discovered that by forming polyurethane, which has low damping performance as a solid material, (i) the damping performance is slightly improved, and (ii) the damping performance has a large frequency dependence. Based on this knowledge, he conducted further research and discovered excellent vibration damping performance by adding a powdered filler to polyurethane foam, and filed a patent application (Japanese Patent Application 134215-1982). . However, when a filler is added during foaming of polyurethane, an increase in viscosity due to blending with the filler is unavoidable, and therefore there is a problem in that there is a limit to the amount of filler to be used. As a result of further research in consideration of the above points, the present inventors discovered that a foam composite vibration damping material having extremely excellent vibration damping performance could be obtained using a completely different method from the above-mentioned invention. It has arrived. In other words, the damping material of the present invention utilizes a method of combining a specific foam with a specific constraining layer to maximize the damping performance of the foam itself, which is different from that used in conventional damping materials. This method is completely different from methods that utilize the damping properties of solid viscoelastic materials such as polymers and asphalt. That is, the main point of the present invention is to derive vibration damping performance from the foam alone by attaching the foam directly to the vibrating body and further bonding the restraining layer to the foam (FIG. 1A). In other words, the vibration damping performance of the foam is small if it is simply attached to a vibrating body as an unrestricted type, but when used as a restrained type, the amount of deformation of the foam in response to vibration is greatly expanded, and The vibration damping effect is dramatically improved by the occurrence of shear deformation. Therefore, when considering the mechanism by which such vibration damping performance occurs, it is naturally desirable to use a soft foam material, and conversely, by using such a soft foam, it is possible to create a constrained type foam with excellent low frequency vibration damping performance. It can be used as a composite damping material. On the other hand, the solid material that acts as a restraining layer does not need to have vibration damping performance by itself in principle, and may simply be a heavy material that can exert restraint on the foam. However, when the damping effect of the constraining layer itself is very large, this effect is added, and the damping performance of the foam composite damping material as a whole is slightly improved. At this time, the point to be careful about when using a solid restraining layer is that if it is very hard, such as a metal plate,
This causes a significant decrease in damping performance in a certain frequency range from low frequencies to medium frequencies. Therefore, in order to exhibit excellent vibration damping performance in a wide frequency range from low frequencies to medium frequencies, the restraining layer must also be flexible. By the way, when looking at the sound absorption performance of the vibration damping material of the present invention, it is natural that it has sound absorption performance because it uses a foam as a matrix, but it has low sound absorption performance due to the presence of the solid restraining layer bonded to the foam surface. There is a tendency for high frequency sound absorption performance to decrease as frequency sound absorption performance improves. However, as the thickness of the foam material becomes thinner, the sound absorption performance of the foam material tends to decrease dramatically in the low frequency range. This helps improve sound absorption performance in the important low to medium frequency range (see examples below).
Of course, in this case, it is possible to control the frequency dependence of the sound absorption performance by providing an appropriate amount of through holes in the constraint layer. Now, in order to take noise countermeasures comprehensively and effectively, it is necessary to exhibit both a vibration damping effect and a sound absorbing effect, and a material that has both of these properties is the filler-filled foam according to the above-mentioned pending invention. Other than that, I can't find anything else at the moment. Therefore, as a practical solution, common commercially available products provide both performances by pasting a solid vibration damping material on the vibration source and then pasting foam on top of it (Figure 1B). In this case, as a matter of course, the damping performance is almost entirely due to the solid damping material, while the sound absorption performance is brought about by the foam. Therefore, in the case of such a laminated composite (commercially available), it is necessary to use a large amount of expensive damping material in order to obtain sufficient damping performance, and when you add the material cost of the foam to this, Product cost becomes very high. Compared to such commercially available bonded composites,
As mentioned above, the foam composite vibration damping material of the present invention is completely different not only in form but also in the mechanism of vibration damping performance, and should be strictly distinguished from commercially available bonded composites. Furthermore, in terms of cost,
(i) The solid constraining layer only needs to be an inexpensive and heavy material, and (ii) the thickness of the foam can be reduced as the weight of the solid constraining layer increases. This makes it possible to significantly reduce costs. Furthermore, by using a suitable material for the constraining layer, flame retardance, oil resistance, durability, etc. can be improved. As described above, the foam composite vibration damping material of the present invention can be said to be a soundproofing material that not only has novelty but also has many practical advantages. By the way, when using foam as a sound absorbing material,
The surface of the foam is coated with a thin film of aluminum or plastic to finish the surface and improve its low-frequency sound absorption performance.Furthermore, various thin films are applied to the surface of the foam as interior materials. Pasting is being done. In this case, it is desirable that the thickness of the thin film be 50μ or less so as not to impair sound absorption performance at high frequencies (Architectural Acoustics Series <Materials> 1. Sound Absorption Materials, edited by Japan Acoustic Materials Association, Masaru Koyasu, page 56). In all of these cases, no attention is paid to the vibration damping performance of the foam material, and from a performance standpoint, the thin film does not function as a restraining layer because the weight ratio of the thin film to the foam is approximately 0.1 to 0.5. There is little hope of improving vibration damping performance with thin films.
This is clearly distinguished from the foam composite damping material of the present invention. The foam material used in the present invention has a modulus (M ₂₅ value obtained by dividing the load when compressed by 25% by the compressed area) of 100 g/cm ² or less, preferably 80 g/cm ² or less when compressed by 25%, and Preferably 50g/cm ²
The following are desirable. However, in order to particularly improve vibration damping performance in the low frequency range, it is preferably 20 g/cm ² or less. In this case, if the M ₂₅ of the foam exceeds 100 g/cm ² , the effect of the constraining layer becomes less apparent. Foam materials used include regular polyurethane foam, various plastic foams such as polyvinyl chloride, polyethylene, polystyrene, and phenol resin, foams with fillers, plasticizers, flame retardants, etc. added to these foams, and general foams. Any type of foam material may be used, such as impregnated foam with an impregnating liquid added, or compressed foam obtained by compressing a general foam, but considering that it also has excellent sound absorption performance, these materials are suitable. Among these, foams with continuous pores are preferred, and polyurethane foams are particularly preferred. In principle, the solid restraining layer may be any heavy material that provides restraint to the foam at the operating temperature and does not flow easily on its own, but preferably satisfies the following conditions. That is, the dynamic storage modulus E of the solid constrained layer at 25°C is E≦1×10 ⁵ Kg/cm ² , preferably E≦6×10 ⁴ Kg/cm ² , more preferably E≦4×10 ⁴ Kg / ^cm2 . Further, it is desirable that the density ratio between the solid constrained layer and the foam is 5 or more, preferably 10 or more. Furthermore, these solid substances act as a constraining layer when the weight ratio of the constraining layer to the foam is 2.0 to 1.0×.
A range of 10 ³ is preferred. In other words, when considering the direction perpendicular to the bonding surface between the solid object and the foam, the ratio of the weight of the solid object to the weight of the foam per unit area of the bonding surface is 2.0.
If it is less than
If it exceeds 1.0×10 ³ , the foam will be crushed and will not work properly. However, more preferably the weight ratio of both is 2.5 or more and 3.0×10 ² or less. Furthermore, from the standpoint of sound absorption performance, it is desirable that the solid constraining layer has an appropriate number of through holes with an appropriate diameter. These solids can be applied to the foam surface by (i) spraying or flattening them as a liquid in some way, (ii) attaching them as a sheet on their own or with an adhesive, or (iii) Bonded by methods such as pasting as a woven fabric, non-woven fabric, or net-like material; (iv) integral molding during foaming; The foam composite vibration damping material thus obtained is used by pasting its foam side surface onto a vibrating body, but it may also be melt-bonded or integrally molded during foam foaming. The foam composite damping material of the present invention can be used for wheels, ships,
Used as vibration damping material for automobiles, aircraft, etc., railway rails, home appliances, metal processing machines, etc., as well as for buildings such as residences, offices, factories, etc., as well as for office equipment, computers, sound systems, etc. and is widely used as a sound absorbing material. Next, the present invention will be explained in more detail based on Examples. Example 1, Comparative Examples 1 to 3 The samples shown in Table 1 were pasted on a galvanized iron plate with a thickness of 1 mm, a width of 25 mm, and a length of 300 mm to serve as test specimens.
The loss coefficient η was measured using a vibration analysis device (mechanical impedance method) manufactured by Akashi Seisakusho Co., Ltd.
Note that the conditions of using a frequency of 10 to 5000 Hz and measuring at room temperature (29° C.) are common to all Examples and Comparative Examples except Example 12. Example 1 and Comparative Example 1 have the same composition and the same shape for both the foam and the constraint layer, but in accordance with the gist of the present invention, Example 1 is used as type A in FIG. 1, and comparative example is a commercially available laminate material. This is the same type B as shown in Figure 1 and is attached to the vibration source (iron plate). On the other hand, in Comparative Example 2 and Comparative Example 3, only the foam and only the restraining layer used in the above-mentioned Example 1 and Comparative Example 1 were attached to the vibration source, and the results obtained for these samples were Shown in Figure 2. The value of η of Comparative Example 1 is given as approximately the sum of each η of the foam and constraint layer used in Comparative Example 2 and Comparative Example 3. On the other hand, Example 1 shows a much higher η value than Comparative Example 1, that is, a high η value that cannot be estimated from the η values of the foam and the constrained layer, which are the constituent factors, and shows good damping performance. It is at a level that sufficiently exceeds the standard η≧0.05 (preferably η≧0.1). This confirms the special damping performance mechanism of the foam composite damping material of the present invention.

[Table] The modulus (M ₂₅ ) of the foam at 25% compression is determined by placing a circular pressure plate with a diameter of 200 mm on top of the test piece, compressing it at a speed of 100 mm/min, and stopping the disk when the strain reaches 25%. The stress value was determined after 20 seconds of rest. Examples 2, 3, Comparative Example 4 When the samples shown in Table 2 are attached as type A in Fig. 1 (all examples and comparative examples that follow are type A as far as damping performance measurement is concerned), η is The frequency dependence is shown in Figure 3. It can be seen that in the case of an iron plate whose constraining layer has a very high elastic modulus, the vibration damping performance at low frequencies is greatly reduced.

[Table] Examples 4 and 5, Comparative Example 5 The η-frequency curves of the samples given in Table 3 are shown in FIG. Compared to the vibration damping performance of the foam alone (Comparative Example 5), when the restraint type is used, the value of η is significantly improved as the weight of the restraint layer increases (Examples 4 and 5).

[Table] Example 6, Comparative Example 6 The effect of the softness of the foam itself was measured using the samples given in Table 4. The results are shown in FIG. It can be seen that even if the same constraint layer is used, the vibration damping performance is significantly improved in the case of a soft foam.

[Table] Examples 7 to 9 As another example, the η-frequency curve of the system given in Table 5 is shown in FIG. In both cases, excellent vibration damping performance is exhibited over a fairly wide frequency range.

[Table] Examples 10 and 11, Comparative Example 7 Table 6 shows the frequency dependence of the normal incidence sound absorption coefficient at room temperature (29° C.) for representative samples as shown in FIG. In this case, the sound absorption performance was measured by the normal incidence method with the material in close contact with a rigid wall (however, in the case of a constraint type foam composite damping material, the sound was set so that the sound was incident from the solid constraint layer). In the case of only a foam without a constraining layer (Comparative Example 7), the low frequency sound absorption coefficient is very low as seen in the figure. When a constraint layer is attached to this, the sound absorption performance in the practically important low and medium frequency ranges is improved (Example 10), and this curve can be further controlled by making appropriate holes in the constraint layer ( Example 11).

[Table] Example 12 The sample foam is urethane foam, M ₂₅ 16g/cm ² , thickness 5mm, and the constraint layer is filler-filled PVC, E2×10 ⁴ Kg/cm ² .
A material made of c/f23 was used. This foam composite damping material was attached to a 1 mm thick iron plate and then vibrated, the sound pressure level was measured and compared with the case of only the iron plate, as shown in Figure 8. FIG. 8 shows that the foam composite damping material of the present invention has excellent damping performance particularly in the low frequency and medium frequency regions, and it was confirmed that it is extremely useful as a damping material.

[Brief explanation of the drawing]

FIG. 1 shows a cross section of the damping material, where A is the foam composite damping material of the present invention, and B is a conventional bonding material of damping material and foam (commercially available). 2 to 6 show the frequency dependence of the loss coefficient η measured at room temperature (29° C.) using the Examples and Comparative Examples given in each table as samples. Figure 7 is room temperature (29℃)
shows the frequency dependence of the normal incidence sound absorption coefficient.
Figure 8 shows the effect of reducing the sound pressure level at 25℃ using foam composite damping material. 1... Foam, 2... Solid constraint layer, 3... Damping material, 4... Vibration source.

Claims (1)

[Claims] 1. A foam material having a compression modulus of 100 g/cm ² or less at 25% and a dynamic storage modulus of 1×10 ⁵ at 25°C on the surface opposite to the surface to be attached to the vibrating body.
Kg/cm ² or less, the density ratio with the foam is 5 or more, and the weight ratio with the foam is 2.0 or more 1×
10 ³ or less vibration damping material combined with a solid restraining layer. 2 The compression modulus at 25% is 80 g/cm ² or less, the dynamic storage modulus of the solid constrained layer at 25°C is 6 x 10 ⁴ Kg/cm ² or less, and the density ratio with the foam is
10 or more, and the weight ratio with the foam is 2.5
The damping material according to claim 1, wherein the vibration damping material is 3×10 ² or less.