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BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
acoustic damping material constituting an ultrasonic probe (transducer) used in a medical
ultrasonic diagnostic apparatus, an ultrasonic flaw detector or the like. [Prior Art] Ultrasonic
probes used in medical ultrasonic diagnostic devices used for medical diagnosis and ultrasonic
flaw detection devices used for flaw detection of structures such as metals are double-sided as
shown in FIG. A piezoelectric vibrator 1 having electrodes 1a and 1b made of silver and nickel, an
acoustic matching layer 2 joined to one side of the piezoelectric oscillator 1, and an acoustic
damping joined to the other side of the piezoelectric oscillator 1 Layer 3 is the main component.
The piezoelectric imaging element 1 has a resonant frequency corresponding to the shape and
material, and when a transmission voltage pulse is applied to the electrodes 1a and 1b from the
terminals 4a and 4b, ultrasonic attenuation vibration corresponding to the resonant frequency is
generated. Do. 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 again reaches the piezoelectric vibrator 1 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, and in the case of two layers, Gazla is used on the side closer to the piezoelectric
vibrator 1 and the epoxy resin or the like is used on the side closer to the object. In the case of
the two-layer structure, the thickness of each acoustic matching layer is set to about 1⁄4 of the
ultrasonic wavelength λ. 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 transmission / reception ultrasonic pulse is composed of 1 to 2 fatigue, the
ultrasonic energy is reduced and the sensitivity is reduced, so it is usually designed to be
composed of 3 to 4 waves and to be free from tailing. As described above, ultrasonic pulse with
high sensitivity and short pulse width can be obtained by adopting the acoustic matching
capacitor 2, but usually the acoustic damping layer 3 is used to make the tailing and the like
further smaller and to make the attenuation rapidly. Grant The characteristics required for 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; ■ the
ultrasonic pulse incident on the acoustic damping layer 3 is acoustic damping It is two points
that it is completely absorbed in the layer 3. As to {circle around (3)}, the acoustic impedance of
the acoustic damping layer 3 is made equal to that of the piezoelectric vibrator 1, and as to
{circle around (4)}, the damping ability of the ultrasonic pulse is increased.
In addition to the above-mentioned {circle over (1)} and {circle over (2)}, other practical
properties, such as heat resistance, chemical resistance, temperature characteristics, moisture
resistance, mechanical strength, and molding processability, are required. There is no material
that satisfies all the conditions of 1 to 4 in reality. 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 as close as
possible to the material satisfying the above conditions. Tungsten used here has the highest
specific gravity of 19.3 among relatively low cost 1- and readily available materials, and achieves
the purpose of increasing the acoustic impedance and ultrasonic pulse attenuation required for
acoustic damping materials. A suitable one is selected. The average particle size of the tungsten
powder varies depending on the type of the target acoustic damping material. In the case of an
ultrasonic probe with a single element wall, the size of a mark of several tens to 100 gv can be
used, but when it is used for an electronic scanning system, it is necessary to use an arrayed
probe Those having an average particle size of 10 pn or less are preferable. That is, the pinch
between the individual elements constituting the above array needs to be about 150 to 200 Ifn,
and if the gap width between the elements is subtracted from this value, the width of one
element may be close to 1007 ffi . Therefore, if tungsten powder having an average particle
diameter of 10 to 100 pl is used, the variation in characteristics among the elements becomes
large, which is not preferable in practical use. Therefore, it is preferable to use a tungsten powder
having an average particle diameter of 10 pn or less if the ultrasonic pulse has an operating
frequency of about 5 MHz or more, for example, as the tungsten powder used for the arrayed
probe. However, as the particle size of the tungsten powder is reduced, the surface area increases
in proportion to the square of the single particle size. As a result, the contact area with the resin
is increased, the melt viscosity of the composite resin composition is increased, the molding
becomes difficult, and the mechanical strength is also reduced. However, the composite resin
composition used for the acoustic damping layer is required to be excellent in 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 and a molding machine occurs due to dechlorination. For this reason, there is
a problem that index forming means which is excellent in productivity and easy to process can
not be practically adopted. In addition, when compression molding is employed, it is necessary to
add a very large amount of plastic material to obtain the formability necessary for compression
molding, but as a result, mechanical strength such as impact resistance and rigidity,
machinability, etc. The post-processability etc. is greatly reduced, and the acoustic damping
material obtained by molding becomes soft and brittle.
Therefore, there is a problem that stable characteristics can not be obtained, such as easy
deformation, even breakage with a small impact, and the durability is inferior. In addition, if the
addition amount of the plasticizer is reduced, the decrease in mechanical strength such as the
impact resistance strength and the rigidity is suppressed and the heat resistance is also
improved, but the decrease in formability is large and the productivity is significantly
deteriorated. In addition, it is not practical because the amount of dechlorination increases. On
the other hand, the composite resin composition using an epoxy resin is excellent in heat
resistance, but when it is exposed to a high temperature, curing progresses further and
mechanical strength such as rigidity changes. This results in a change in the acoustic damping
effect. Furthermore, since the rigidity itself is high, it is a characteristic originally undesirable for
enhancing the acoustic damping effect. Then, an object of the present invention is to provide an
acoustic damping material which has excellent acoustic damping effect and is also excellent in
moldability and mechanical strength. [Means for Solving the Problems] The present invention is
characterized by solving the above problems and taking the following means in order to achieve
the object. That is, the acoustic damping material of the present invention is (A> tungsten powder
(B) ethylene-ethyl acrylate copolymer alone or a mixture of ethylene-ethyl acrylate copolymer
and polyamide or epoxy resin (hereinafter referred to as synthetic resin (B)) It is characterized in
that a composite resin composition containing as a main component is molded. As the tungsten
powder (A) in the present invention, although it varies depending on the type of the acoustic
damping material as described above, the average particle diameter is usually about 1 to 100%,
preferably 1 to 20%. As the ethylene-ethyl acrylate copolymer in the present invention, one
having a content of ethyl acrylate of 5 to 35% by weight is usually used, and in particular, 15 to
25% by weight having an excellent balance of mechanical strength and heat resistance. Is
preferred. Although an ethylene-ethyl acrylate copolymer can be used alone as the synthetic
resin (B), it is preferable to further add a polyamide or an epoxy resin because heat resistance is
improved. The weight ratio of ethylene-ethyl acrylate copolymer to polyamide is usually 100: O
to 20:80. The weight ratio of the ethylene-ethyl acrylate-1 copolymer to the epoxy resin is
usually 100: O to 50:50. Among them, 70:30 to 40:60 in the former case and 70 in the latter
case. It is preferable to use a weight ratio of 30 to 50:50 in terms of the balance 1 between heat
resistance and mechanical strength.
The polyamides used in the present invention have a softening temperature of 110 to 190 ° C.,
preferably 160 to 180 ° C. according to the ring and ball method, and a melt viscosity of 2 to
50 poises preferably 2 to 50 poises at 200 ° C. Although 45 Boise thing etc. are mentioned,
what has rubber elasticity especially is especially preferable. For example, there are polymerized
fatty acids, that is, condensation products of dimer acids having a carbon number of 36,
monomer fatty acids, and alkylene diamines, and conventionally, printing inks such as gravure
inks and flexo inks, lacquers, pot melt adhesives, etc. There is something used. As the epoxy resin
used in the present invention, an epoxy resin 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, can
be mentioned. For example, there is a compacted condensate having two or more epoxy groups
in the molecule obtained by the reaction of epichlorohydrin and a bisphenol or polyhydric
alcohol. There is no need to add a curing agent such as amine or acid anhydride. The proportions
of the above-mentioned tungsten powder, ethylene-ethyl acrylate copolymer, polyamide and
epoxy resin are the performances of the acoustic tamping agent required according to the
application (acoustic impedance, ultrasonic attenuation ability, heat resistance 9 mechanical
strength Etc. and post-processability etc. can be appropriately selected in consideration of the
balance of molding processability etc., but the weight ratio of tungsten powder (A) to synthetic
resin (B) is usually A / B = 93/7 to 98/98. It is preferably in the range of 9515 to 97.5 / 2.5 in
view of the balance between the acoustic damping effect and the mechanical strength and the
molding processability. The acoustic damping material of the present invention is a roll of a
tungsten powder (A) and a synthetic resin (B), kneader. The mixture is kneaded with a known
mixer such as a Banbury mixer-1 extruder, and, if necessary, in the form of a pellet or powder. It
can be obtained by forming it into a sheet or the like and then performing post-processing such
as cutting if necessary. The molding method is not particularly limited, and it can be molded by
injection molding or compression molding, but injection molding is preferable in terms of
productivity, post-processability and the like. Furthermore, in the present invention, the surface
of the tungsten powder (A> is made of silane or the like in order to enhance molding
processability when kneading the tungsten powder (A) and the synthetic resin (B) or performing
injection molding or compression molding. It goes without saying that known technical means
may be applied such as surface treatment and addition of additives such as lubricants in order to
smoothly carry out molding processing, mold release and the like.
[Effects of the Invention] The composite resin composition containing the tungsten powder (A)
and the synthetic resin (B) used in the present invention as main components is excellent in
moldability, and obtained by molding and processing this. The acoustic damping material of the
present invention is excellent in mechanical strength, can exhibit excellent ultrasonic damping
effect from low temperature to high temperature, and is deformed. There is an effect that a stable
function can be obtained without damage or a change in rigidity. EXAMPLES The present
invention will be described more specifically by referring to examples of the present invention
together with comparative examples. All parts in the examples are by weight. "Examples 1 to 6
and Comparative Examples 1 to 2" Tungsten powders (I) and (■), ethylene-ethyl acrylate
copolymer (hereinafter abbreviated as EEA) (■) and (■), polyamide, epoxy resin, Raw materials
selected from soft vinyl chloride resins (I) and (II) are mixed according to the composition shown
in the upper half of Table 1 and kneaded for 5 minutes with a 2-inch roll of 6 inch diameter
heated to 150 ° C. Thus, a sheet-like composite column fat composition was obtained. Tungsten
powder (1): Average particle size 5.6 parts m Tungsten powder (II): Average particle size 11.67
REEA (I): Ethyl acrylate content 20% by weight Melt index 20 g / 10 m 1 n EEA (I [): Ethyl
acrylate content Amount 25% by weight Melt index 209/10 mn Polyamide: softening
temperature 170 ° C, melt viscosity 30 Boise at 200 ° C Epoxy resin: melting point 99 ° C,
epoxy equivalent 915 flexible vinyl chloride resin (1) vinyl chloride having a degree of
polymerization of 700 100 parts of resin mixed with 100 parts of dioctyl phthalate and 1 part of
dibutyltin maleate Soft vinyl chloride resin (■) 200 parts of dioctyl phthalate with 1 part of
dioctyl phthalate to 100 parts of vinyl chloride resin having a degree of polymerization of 700 Of
ours. Next, the composite resin composition was injection-molded and compression-molded
under the conditions shown below, and the injection moldability and compression moldability
were evaluated. The results shown in the lower half of Table 1 are as follows: It was obtained.
Injection method: using an injection molding machine with a screw diameter of 28 mmφ,
injection in the case of EEA at cylinder temperature 260 ° C, injection pressure cuff 00 9 / cA,
clamping force 50tOn, mold temperature 80 ° C In the case of a soft vinyl chloride resin, the
cylinder temperature is 190 ° C., the injection pressure cuff 00 b / cJ, and the clamping force 5
oton. Injection molding was carried out under conditions of a mold temperature of 50 ° C. to
obtain a disc with a diameter of 20 mm and a thickness of 5 #, respectively.
“Compression molding method” EEA: 250 ° C., and soft vinyl chloride resin: 200 ° C. A
sheet-like composite resin composition cut into a disk shape according to the mold shape on a
press plate heated to 200 ° C. After preheating, the product was compression-formed under the
conditions of 150 K9 / ci for 12 minutes, and then cooled for 10 minutes with a water-cooled
cooling press to obtain a 60 mm diameter disk having a thickness of 5 #. About the moldability
by such a molding method, a crack, a chip, a bubble, appearance defect of the obtained molded
article. It evaluated on the basis of the incidence rate of the inferior goods which have a filling
defect etc. :: Defect rate less than 5% O: Defect rate 5% to less than 10% Δ: Defect rate 10% to
less than 30% ×: Defect rate 30% or more However, if a large amount of cracked gas is
generated, x, If a small amount Is △. Next, plate-like molded articles obtained by the
predetermined sample forming method for Examples (1) to (6) and Comparative Examples (1)
and (2) having the same composition as shown in Table 1 were obtained. A test piece is prepared
by cutting and cutting, and physical properties such as acoustic impedance, ultrasonic
attenuation ability, Shore hardness (A), penetration degree, and drop impact strength are
measured by the measurement method described below, and also cut. The sex was evaluated.
Table 2 shows the results. [Measurement Method of Acoustic Impedance and Ultrasonic
Attenuation Ability] As a sample, an 8 × 8 × 11 M acoustic damping material 13 as shown in
FIG. 1 obtained by removing 1 skin layer after molding and cutting was used. In FIG. 1, reference
numeral 11 denotes a transmitting broadband ultrasonic transducer 12 which is a receiving
broadband ultrasonic transducer. The ultrasonic pulse of MHz is sent through the acoustic
damping material 13 and the velocity L ° of the acoustic damping material 13 is divided by the
time required for transmission and reception to obtain the sound velocity V ° C. This and the
density ll Z of the acoustic damping material 13 The acoustic impedance (Z) was calculated by
performing an operation of l = VffiXρ. Then, the received 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 XL 2 m as shown in FIG. 2, and similarly, the reception voltage 2 is measured, α-2 o /!
The ultrasonic attenuation ability α was calculated by performing an operation of 0Qvl / V2 ×
110 / L1−L2. [Measurement of Shore Hardness] Measured on a scale (A). "Measurement of
penetration" 1 # φ needle according to ASTM D-621. It measured on the conditions of load 5 Kti
and temperature +/- 1 degreeC. [Measurement of Drop Impact Strength] Ten samples cut to a
size of 8 × 8 × 5 # were dropped 5 times onto a concrete floor from a height of 1 m, and the
number of samples in which cracking or chipping occurred was determined.
With regard to machinability, the ease when cutting into a 10 × 10 × 5 # shape using a razor
blade. It evaluated on the basis of the existence of a crack and a chip. :: Easy to cut, smooth cut,
and almost no cracking or chipping. ○: Cutting is relatively easy, but there are some cracks and
chips. Occurrence rate less than 10% Δ: Cutting is possible, but cracking and chipping occur
frequently. Occurrence rate 10% or more. X: It is impossible to cut.
Brief description of the drawings
1 and 2 are plan views showing methods of measuring acoustic impedance and ultrasonic
attenuation in an embodiment of the present invention.
FIG. 3 is a side view of the ultrasonic probe shown to explain the conventional example.
DESCRIPTION OF SYMBOLS 1 ... Piezoelectric vibrator, 1a, 1b ... Electrode, 2 ... Acoustic matching
layer, 3 ... Acoustic damping layer, 4a, 4b ... Terminal, 11 ... Ultrasonic transducer for broadband
transmission , 12: ultrasonic transducers for broadband reception, 13 and 23: acoustic damping
material. Applicant agent Patent attorney Tsuboi
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