JPS61289396A - Sound absorbing material and manufacture thereof - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Summary of the invention] The present invention relates to sound absorbing materials, particularly ultrasonic sound absorbing materials.

Acoustic impedance is 0.7~L, S
0 kg/rds, and also provides a manufacturing method thereof.

[Industrial application field]

The present invention relates to a sound-absorbing material and a method for manufacturing the same, and more particularly to a sound-absorbing material for absorbing ultrasonic waves emitted by an ultrasonic diagnostic device, etc., and a method for manufacturing the same.

[Conventional technology]

In medical ultrasonic diagnostic equipment and non-destructive testing equipment for materials, the ultrasound waves emitted from these equipment are

In addition to the signal sound waves reflected from inside the subject, sound waves are reflected through various routes, so sound-absorbing materials are placed on the walls around the chamber in which the probe and the like are used.

Such sound absorbing materials are made by mixing inorganic powder such as tungsten powder with a rubber material such as silicone rubber.

A sound absorbing plate formed by thoroughly stirring such a mixed substance into a sheet shape is attached to the surface of an object that reflects unnecessary sound waves to prevent unnecessary reflections to the ultrasonic probe.

[Problem that the invention seeks to solve]

As an example of a sound absorbing material in which tungsten powder is added to the above-mentioned rubber material, the relationship between the acoustic impedance Z and the attenuation rate α exhibits an acoustic impedance attenuation rate characteristic as shown by curve A in FIG. 5, depending on the mixing ratio.

Generally, the following conditions are required to efficiently absorb ultrasound.

(a) The acoustic impedance of the sound absorbing material is approximately equal to the medium through which the sound waves travel.

(b) The attenuation rate of sound waves inside the sound absorbing material is large.

However, in the acoustic impedance-attenuation rate characteristic curve obtained in Fig. 5, the acoustic impedance is 1.5 like water.
3.0d for media of about X 10' kg/gs
B/ ** shows a damping rate α of about MH', but 1 For example, lXl0 kg/ like oil silicone oil etc.
Since the acoustic impedance cannot be made equal in a medium of rrfs or less, the above item (a) is not satisfied. However, in curve A in Figure 5, tungsten powder with a high specific gravity is mixed into silicone rubber with an acoustic impedance of about 1, so the acoustic impedance is 1 x 10' kg/rr.
The value is more than f s, but 1×10'kg/
At values near n('s, the attenuation rate is small. In other words, the above (b)
I can't satisfy the terms. Furthermore, although silicone resin alone does not cause reflection, it almost eliminates attenuation. In other words, with conventional sound absorbing materials, the acoustic impedance Z is 0 to 1.3 x 10' kg.
There is a drawback that it is not possible to provide a sound absorbing material that can obtain a sufficient sound absorbing effect in a medium as small as / rrr s.

Means for Solving Problem C] The present invention was made in view of the above-mentioned drawbacks, and its purpose is to reduce the acoustic impedance from θ to 1.3
The idea is to provide a sound absorbing material that can effectively prevent the reflection of sound waves even in a medium as small as 0 kg/m s and has a large attenuation rate inside the sound absorbing material. By mixing a low specific gravity material such as a hollow glass balloon containing a lot of air into the rubber-like resin, the acoustic impedance can be adjusted to 0.7 to 1.6 x 10' kg.
/ m s.

This is achieved by using sound-absorbing materials that are characterized by:

[For production]

In the present invention, a low specific gravity substance (generally called a filler), such as a hollow glass balloon, whose specific gravity is smaller than that of the rubber-like resin, such as silicone rubber, is mixed with the rubber-like resin to reduce the specific gravity and reduce the acoustic impedance. The purpose is to obtain a sound absorbing material which has a large attenuation rate, that is, can be used even in a medium with a small acoustic impedance.

〔Example〕

An embodiment of the present invention will be described in detail below with reference to FIGS. 1 and 2.

FIG. 1 is a perspective view showing an embodiment of a sound absorbing plate using the sound absorbing material of the present invention, and FIG. 2 is a side sectional view of a mold for explaining the method of manufacturing the sound absorbing material of the present invention. In Fig. 1, reference numeral 1 indicates an embodiment of the sound absorbing plate of the present invention, and the rubber-like resin 2 is one selected from silicone rubber, polyurethane, epoxy, etc., and has a specific gravity smaller than that of the above-mentioned rubber-like resin. After mixing hollow glass balloons, hollow carbon balloons, air bubbles, etc., which are low specific gravity substances 3 containing a large amount of air, and stirring the mixture with a stirrer for a sufficient time t1 so that the low specific gravity substances 3 are uniformly dispersed in the rubbery IF fat. The sound absorbing plate 1 shown in FIG. 1 is obtained by pouring into a mold 6 having a wedge-shaped recess 5 formed on the bottom as shown in FIG. It will be done.

The wedge-shaped protrusions 4 can be selected to have a wavelength approximately three times the wavelength of the sound wave, and the countless "wedge-shaped" protrusions formed in this way reduce the reflection of the sound waves on the surface of the sound absorbing plate.

Furthermore, the attenuation rate may be increased by mixing conventionally used tungsten powder as a filler in the above-mentioned rubber-like resin, but this can be selected by considering the relationship with the specific gravity. . In FIG. 3, soft polyurethane is selected as the rubber-like resin 2.

This is a characteristic that shows the relationship between the mixing ratio (wt%) and acoustic impedance Z when a hollow glass balloon is mixed as a low specific gravity substance 3 into the soft polyurethane. If there are many small specific gravity substances 3 mixed into the resin 2, it can be seen that the acoustic impedance Z is small.In general, the acoustic impedance Z is expressed as the product of the specific gravity e and the sound speed C, but if a small specific gravity substance is mixed. As a result, if the decrease in specific gravity is greater than the increase in sound speed, the acoustic impedance Z will be reduced.In addition, the above-mentioned sound absorbing material has a better scattering effect on sound waves due to its low specific gravity such as a hollow glass balloon.

As the sound wave path is divided, the attenuation rate α also increases, and as shown in FIG. As shown by the same characteristic curve C with a broken line in the figure, the acoustic impedance is 0.7 to 1.6
Since the attenuation rate can be increased within the range of 10 kg/t s, the acoustic impedance Z is 1 to 2XIQ'kg.
It can be seen that in the range of /nfs, an appropriate attenuation factor can be obtained by a combination of a conventional tungsten powder with a large specific gravity and a hollow glass balloon.

Below, nine examples of the present invention will be described in detail.

[Example 1] 5 to 30 (wt%) hollow glass balloons with a particle size of about 10 to 50 μm were mixed with soft polyurethane.

The hollow glass balloons were uniformly dispersed using a stirrer, poured into a mold, defoamed under vacuum, and released from the mold after curing. Assuming that the height of the "wedge-shaped" convex part of the sound-absorbing board is 1 crane, the acoustic impedance of the sound-absorbing board is 1.0 x 10 kg/rrrs.
When placed in a silicone oil medium, the reflection of sound waves is 14
It was less than 0 dB・In this case・Sufficient l without swelling with silicone oil like conventional silicone oil:! i decay was obtained.

[Example 2] A sound absorbing board obtained by mixing appropriate amounts of a foaming agent and a foam stabilizer into soft polyurethane and foaming it to control the number of bubbles also showed the same sound wave reflectance as in Example 1. .

〔Effect of the invention〕

The present invention was constructed and manufactured as described above.

A sound absorbing material having a small acoustic impedance and a high attenuation rate can be obtained, and a sound absorbing material that can be used even in a medium with a small acoustic impedance can be obtained.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a sound absorbing plate formed using the sound absorbing material of the present invention. FIG. 2 is a side sectional view of a mold for forming the sound absorbing plate shown in FIG. 1. FIG. 3 is a characteristic curve diagram showing the relationship between the mixing ratio and acoustic impedance of the sound absorbing material of the present invention. FIG. 4 is a characteristic curve diagram showing the relationship between acoustic impedance and attenuation rate of the sound absorbing material of the present invention. FIG. 5 is a characteristic curve diagram similar to the conventional one shown in FIG. 1...Sound absorbing board. 2...Rubber-like resin. 3...Low specific gravity substance. 4...Protrusion. 5... Concavity. 6...type. Figure 2 V1 combined specific gravity Figure 3 Figure □2 Acoustic input -q''
3 business 4 figure

Claims (5)

[Claims] (1) Mixing a low specific gravity substance such as a hollow glass balloon containing a lot of air into a rubber-like resin or a rubber-like resin containing a filler to increase the acoustic impedance from 0.7 to 1.6 x 1.
A sound-absorbing material characterized by its ability to reduce to 0^6kg/m^2s. (2) The sound absorbing material according to claim 1, wherein the low specific gravity substance containing a large amount of air is a hollow glass balloon. (3) The sound absorbing material according to claim 1, wherein the low specific gravity substance containing a large amount of air is a hollow carbon balloon. (4) The sound absorbing material according to claim 1, wherein the low specific gravity substance containing a large amount of air is a bubble. (5) A step of mixing 5 to 30 weight percent of a low specific gravity substance containing a lot of air into a rubbery resin or a rubbery resin containing a filler such as an inorganic or organic powder, and the mixed low specific gravity substance. a step of stirring and uniformly dispersing it in the rubber-like resin, a step of pouring the uniformly dispersed mixture into a mold and vacuum defoaming, and a step of curing and releasing it in the mold to obtain a sound absorbing plate. A method for manufacturing a sound absorbing material, characterized by comprising: