JPH0675065B2 - Acoustic damping material - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an acoustic damping material that constitutes an ultrasonic probe (transducer) used in a medical ultrasonic diagnostic apparatus, an ultrasonic flaw detector, or the like.

[Conventional technology]

As shown in FIG. 3, an ultrasonic probe used in a medical ultrasonic diagnostic apparatus used for medical diagnosis or an ultrasonic flaw detection apparatus used for flaw detection of a structure such as metal is made of silver or nickel on both sides. The piezoelectric vibrator 1 having the electrodes 1a and 1b, the acoustic matching layer 2 bonded to one side surface of the piezoelectric vibrator 1, and the acoustic damping layer 3 bonded to the other side surface of the piezoelectric vibrator 1 are mainly included. As a component.

The piezoelectric vibrator 1 has a resonance frequency corresponding to the shape and material, and when a transmission voltage pulse is applied to the electrodes 1a, 1b from the terminals 4a, 4b, ultrasonic damping vibration corresponding to the resonance frequency is performed. . This vibration passes through the acoustic matching layer 2 as an ultrasonic pulse, enters the subject, and is reflected at the tissue boundary of the subject. Then, the reflected ultrasonic pulse reaches the piezoelectric vibrator 1 again through the acoustic matching layer 2, vibrates the piezoelectric vibrator 1, and is converted into an electric signal.

The acoustic matching layer 2 usually has a one-layer or two-layer structure.
In the case of one layer, an epoxy resin is used, in the case of two layers, a gasra is used on the side closer to the piezoelectric vibrator 1 and an epoxy resin or the like is used on the side closer to the subject. In the case of a two-layer structure, the thickness of each acoustic matching layer is 1 / of the ultrasonic wavelength λ.
It is set near 4. By attaching such an acoustic matching layer 2, the ultrasonic pulse width is substantially shortened, which helps to improve the resolution in the depth direction. However, if the transmitted / received ultrasonic pulse is composed of 1 or 2 waves, the ultrasonic energy is reduced and the sensitivity is lowered.
It is composed of waves and is designed so that there is no tail pulling.

As described above, the adoption of the acoustic matching monk 2 has high sensitivity,
Although an ultrasonic pulse having a short pulse width can be obtained, usually, the acoustic damping layer 3 is provided in order to further reduce the tailing and the like and to sharpen the attenuation.

The characteristics required of the acoustic damping layer 3 are that the vibration of the piezoelectric vibrator 1 is not reflected at the boundary between the piezoelectric vibrator 1 and the acoustic damping layer 3, and the ultrasonic pulse incident on the acoustic damping layer 3 is the acoustic damping layer 3 It is completely absorbed within. Is related to making the acoustic impedance of the acoustic damping layer 3 equal to that of the piezoelectric vibrator 1, and is related to increasing the attenuation capability of ultrasonic pulses.

In addition to the above, heat resistance, chemical resistance, temperature characteristics, moisture resistance, mechanical strength, moldability, etc. are required as practical properties.

In reality, there is no material that satisfies all of these conditions. Therefore, a composite resin composition in which a large amount of tungsten powder is mixed with a thermoplastic resin such as a soft vinyl chloride resin or a thermosetting resin such as an epoxy resin is used as a material that is as close as possible to the material that satisfies the above conditions.

Tungsten used here has the highest specific gravity of 19.3 out of relatively low cost and readily available materials, and is suitable for achieving the purpose of increasing the acoustic impedance and ultrasonic pulse attenuation capability required for acoustic damping materials. Selected.

The average particle diameter of the tungsten powder varies depending on the type of the targeted acoustic damping material. In the case of an ultrasonic probe with a single element wall, it can be used with a size of several tens to 100 μm, but when it is used in an electronic scanning system device, it is necessary to use an arrayed probe, so it is average. Particles having a particle size of 10 μm or less are preferable. That is, it is necessary to set the pinch between the individual elements constituting the array to about 150 to 200 μm, and if the gap width between the elements is subtracted from this value, the width of one element may be close to 100 μm. . Therefore, the use of tungsten powder having an average particle size of 10 to 100 μm causes a large variation in characteristics between elements, which is not preferable in practice. Therefore, the tungsten powder used for the array-shaped probe is, for example, if the ultrasonic pulse has an operating frequency of about 5 MHz or more,
It is preferable to use those having an average particle diameter of 10 μm or less.

However, when the particle size of the tungsten powder is reduced, the surface area increases in proportion to the square of one particle size. Therefore, the contact area with the resin increases, the melt viscosity of the composite resin composition increases, it becomes difficult to mold, and the mechanical strength also decreases. However, the composite resin composition used for the acoustic damping layer needs to have excellent moldability and mechanical strength.

[Problems to be solved by the invention]

When injection molding of a conventional composite resin composition using a soft vinyl chloride resin is performed, corrosion of a mold or a molding machine due to dechlorination occurs. For this reason, there is a problem in that an injection molding means that is excellent in productivity and easy to process cannot be practically adopted. When compression molding is adopted, it is necessary to add an extremely large amount of plastic material in order to obtain the moldability required for compression molding, but as a result, mechanical strength such as impact strength and rigidity, machinability, etc. The post-workability and the like are greatly reduced, and the acoustic damping material obtained by molding becomes soft and brittle. Therefore, there is a problem that it is easily deformed, and even if it is damaged by a small impact, stable characteristics cannot be obtained and durability is poor. If the amount of the plasticizer added is reduced, mechanical strength such as impact strength and rigidity can be prevented from lowering and heat resistance can be improved, but the moldability is largely reduced and the productivity is significantly deteriorated. In addition, the amount of dechlorination increases, which is not practical.

On the other hand, a composite resin composition using an epoxy resin has excellent heat resistance, but further curing proceeds when exposed to high temperatures,
Mechanical strength such as rigidity changes. Therefore, the acoustic damping effect is changed. Furthermore, since the rigidity itself is high, it is a characteristic that is originally not desirable for enhancing the acoustic damping effect.

Therefore, the present invention has an excellent acoustic damping effect,
Moreover, it is an object of the present invention to provide an acoustic damping material excellent in moldability and mechanical strength.

[Means for solving problems]

The present invention is characterized by taking the following means in order to solve the above problems and achieve the object. That is, the acoustic damping material of the present invention is characterized by being formed by molding a composite resin composition in which tungsten powder and a synthetic resin containing at least an ethylene-ethyl acrylate copolymer are mixed.

The tungsten powder (A) in the present invention has an average particle size of usually about 1 to 100 μm, preferably 1 to 20 μm, although it depends on the type of acoustic damping material as described above.
Use the one.

As the ethylene-ethyl acrylate copolymer in the present invention, the content of ethyl acrylate is 5 to 35% by weight.
Usually, those of 15 to 25% by weight, which have an excellent balance of mechanical strength and heat resistance, are preferable.

As the synthetic resin (B), an ethylene-ethyl acrylate copolymer can be used alone, but it is preferable to add a polyamide or an epoxy resin because the heat resistance is improved. The proportion of ethylene-ethyl acrylate copolymer and polyamide is usually 100: 0 to 20:80 by weight,
The weight ratio of the ethylene-ethyl acrylate copolymer to the epoxy resin is usually 100: 0 to 50:50. Among them, the former is 70:30 to 40:60, and the latter is 7%.
A weight ratio of 0:30 to 50:50 is preferable from the viewpoint of excellent balance between heat resistance and mechanical strength.

As the polyamide used in the present invention, a softening temperature by the ring and ball method of 110 to 190 ° C., preferably 160 to 180 ° C., 200
The melt viscosity measured by a B-type viscometer at 2 ° C. is 2 to 50 poises, preferably 10 to 45 poises. Among them, those having rubber elasticity are particularly preferable. For example, polymerized fatty acid, that is, there is a condensate of dimer acid mainly composed of 36 carbon atoms, monomeric fatty acid and alkylenediamine, printing ink such as gravure ink and flexo ink from the past,
Some are used in lacquer paints and pot melt adhesives.

Examples of the epoxy resin used in the present invention include epoxy resins having a melting point of 60 to 160 ° C., preferably 90 to 135 ° C., and an epoxy equivalent of 400 to 3500, preferably 870 to 2200, according to the durance mercury method. For example, there are calcined condensates having two or more epoxy groups in the molecule, which are obtained by the reaction of epichlorohydrin with bisphenols or polyhydric alcohols. It is not necessary to add a curing agent such as amine and acid anhydride.

The use ratio of the above-mentioned tungsten powder, ethylene-ethyl acrylate copolymer, polyamide, and epoxy resin depends on the performance of the acoustic tamping agent required according to the application (acoustic impedance, ultrasonic attenuation capacity, heat resistance, mechanical strength, etc.). ) Or a post-processability, and can be appropriately selected in consideration of the balance of molding processability, etc., but tungsten powder (A)
The weight ratio of the synthetic resin (B) and the synthetic resin (B) is usually A / B = 93/7 to 98/2. Among them, the acoustic damping effect and the mechanical strength,
The range of 95/5 to 97.5 / 2.5 is preferable in terms of the balance of molding processability.

The acoustic damping material of the present invention is a tungsten powder (A).
And the synthetic resin (B) are kneaded by a known kneader such as a roll, a kneader, a Banbury mixer, an extruder, and then, if necessary, pelletized, powdered, sheet-shaped, etc., and then molded, and if necessary. It is obtained by post-processing such as cutting.
The molding method is not particularly limited, and injection molding or compression molding can be used, but injection molding is preferable in terms of productivity, post-processability, and the like.

Further, in the present invention, the surface of the tungsten powder (A) is treated with silane or the like in order to improve the moldability when kneading the tungsten powder (A) and the synthetic resin (B) or when performing injection molding or compression molding. Needless to say, known technical means such as surface treatment or addition of an additive such as a lubricant may be applied to smoothly perform molding, releasing, and the like.

〔The invention's effect〕

The composite resin composition containing the tungsten powder (A) and the synthetic resin (B) as the main components used in the present invention has excellent moldability, and the acoustic damping of the present invention obtained by molding the same. The material is excellent in mechanical strength, can exert an excellent ultrasonic damping effect from low temperature to high temperature, and has an effect that a stable function can be obtained without deformation, damage, change in rigidity and the like.

〔Example〕

Hereinafter, the present invention will be described more specifically by giving examples of the present invention together with comparative examples. All "parts" in the examples are weight (parts)
Is.

"Examples 1 to 6 and Comparative Examples 1 and 2" Tungsten powders (I) and (II), ethylene-ethyl acrylate copolymer (hereinafter abbreviated as EEA) (I).
And (II), polyamide, epoxy resin, soft vinyl chloride resin (I) and (II) raw materials selected in the compounding composition shown in the upper half of Table 1 and heated to 150 ℃ diameter 6 The sheet-shaped composite column fat composition was obtained by kneading with an inch two-roll for 5 minutes.

Tungsten powder (I): average particle size 5.6 μm Tungsten powder (II): average particle size 11.6 μm EEA (I): ethyl acrylate content 20% by weight Melt index 20 g / 10 min EEA (II): ethyl acrylate content 25% by weight % Melt index 20g / 10min Polyamide: Melt viscosity at softening temperature 170 ℃ and 200 ℃ 30
Poise Epoxy resin: Melting point 99 ° C, Epoxy equivalent 915 Soft vinyl chloride resin (I): Mixing 100 parts of vinyl chloride resin with a polymerization degree of 700 with 100 parts of dioctyl citrate and 1 part of dibutyl tin malate Soft vinyl chloride resin (II): A mixture of 100 parts of vinyl chloride resin having a degree of polymerization of 700 and 200 parts of dioctyl phthalate and 1 part of dibutyl tin malate.

Next, the composite resin composition was injection-molded and compression-molded under the conditions shown below, and injection-moldability and compression-moldability were evaluated. The results shown in the lower half of Table 1 were obtained. Was obtained.

"Injection molding method" Using an injection molding machine with a screw diameter of 28 mmφ, in the case of EEA, the cylinder temperature is 260 ° C, the injection pressure is 700 kg / cm ² , and the mold clamping force is 50to.
n, injection molding at a mold temperature of 80 ℃, in the case of soft vinyl chloride resin, cylinder temperature 190 ℃, injection pressure 700kg / cm ² ,
Injection molding was performed under the conditions of a mold clamping force of 50 ton and a mold temperature of 50 ° C. to obtain a disk having a diameter of 20 mm and a thickness of 5 mm.

"Compression molding method" 250 ℃ for EEA, 200 ℃ for soft vinyl chloride resin
After preheating the sheet-shaped composite resin composition cut into a disc shape according to the mold shape on the press plate heated to 150 kg /
It was formed by compression under the condition of cm ² for 2 minutes and then cooled with a water-cooling cooling press for 10 minutes to obtain a disk having a diameter of 60 mm and a thickness of 5 mm.

The moldability by such a molding method was evaluated based on the rate of occurrence of defective products such as cracks, chips, bubbles, appearance defects, and filling defects of the obtained molded products.

◎: Defect rate less than 5% ○: Defect rate 5% to less than 10% △: Defect rate 10% to less than 30% ×: Defect rate of 30% or more However, when a large amount of decomposition gas is generated, x is a small amount Was △.

Next, the plate-like molded articles obtained by the predetermined sample molding method for Examples (1) to (6) and Comparative Examples (1) and (2) having the same composition as shown in Table 1 were prepared. A test piece is prepared by cutting and cutting, and the physical properties such as acoustic impedance, ultrasonic attenuation capacity, Shore hardness (A), penetration, drop impact strength, etc. are measured by the measurement methods described below, and the cutting processing is performed. The sex was evaluated. Table 2 shows the results.

"Method of measuring acoustic impedance and ultrasonic attenuating ability" As a sample, an acoustic damping material 13 of 8 x 8 x L1 mm as shown in Fig. 1 obtained by removing the skin layer and cutting after molding was used. Using. In FIG. 1, 11 is a wideband ultrasonic transducer for transmission 12 is a wideband ultrasonic transducer for reception.

An ultrasonic pulse of MHz is sent through the acoustic damping material 13, and the sound velocity Vl is obtained by dividing the dimension L1 of the acoustic damping material 13 by the time required for transmission to reception, and this and the density ρ | Z | of the acoustic damping material 13. The acoustic impedance (Z) was calculated by performing the calculation of = Vl × ρ.

Then, the reception voltage V1 at this time was measured.

Next, the acoustic damping material 13 is further cut to obtain an acoustic damping material 23 of 8 × 8 × L2 mm as shown in FIG.
Similarly, the reception voltage V ₂ was measured, and the ultrasonic attenuation capacity α was calculated by performing the calculation α = 20logV1 / V2 × | 10 / L1-L2 |.

"Shore hardness measuring method" Measured on a scale (A).

“Measurement of penetration” In accordance with ASTM D-621, 1 mmφ needle, load 5 kg, temperature ± 1
It was measured under the condition of ° C.

“Measurement of drop impact strength” Ten samples cut to 8 × 8 × 5 mm were dropped 5 times on a concrete floor from a height of 1 m, and the number of samples with cracks or chips was determined.

The machinability was evaluated based on the ease of cutting into a shape of 10 x 10 x 5 mm using a razor blade and the presence or absence of cracks and chips.

⊚: Easy to cut, the cut surface is smooth, and there is almost no cracking or chipping.

◯: Cutting is relatively easy, but there are some cracks and chips. Incidence rate is less than 10%.

Δ: Cutting is possible, but cracks and chips often occur. Incidence rate 10% or more.

X: Uncut.

[Brief description of drawings]

FIG. 1 and FIG. 2 are plan views showing a method of measuring acoustic impedance and ultrasonic attenuating ability in the embodiment of the present invention. FIG. 3 is a side view of the ultrasonic probe shown for explaining the conventional example. 1 ... Piezoelectric vibrator, 1a, 1b ... Electrode, 2 ... Acoustic matching layer, 3 ... Acoustic damping layer, 4a, 4b ... Terminal, 11 ...
Ultrasonic transducers for wideband transmission, 12 ... Ultrasonic transducers for wideband reception, 13 and 23 ... Acoustic damping materials.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Haruhei Ono 3-11, 3-3, Takadai, Nagaokakyo-shi, Kyoto (56) References JP-A-58-73859 (JP, A) JP-A-56-104651 (JP, A)

Claims (3)

[Claims] 1. An acoustic damping material, characterized by being formed by molding a composite resin composition in which a tungsten powder and a synthetic resin containing at least an ethylene-ethyl acrylate copolymer are mixed. 2. The tungsten powder has an average particle size of 1
Claims 1 to 100 μm
The acoustic damping material described in the item. 3. The synthetic resin is an ethylene-ethyl acrylate copolymer simple substance or an ethylene-ethyl acrylate copolymer to which a polyamide or an epoxy resin is added. The acoustic damping material described in the item.