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JP2014110595

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DESCRIPTION JP2014110595
Abstract: To provide a molding method capable of molding a piezoelectric polymer into polymer
piezoelectric materials of various shapes, a vibration generator using the polymer piezoelectric
material, and a speaker. A material formed of a piezoelectric polymer is molded at a temperature
higher than the glass transition temperature of the piezoelectric polymer and lower than the
crystallization temperature, and then heat-treated at a temperature higher than the crystallization
temperature of the piezoelectric polymer Do. Further, a piezoelectric portion 4 formed of a
piezoelectric polymer, a first electrode 14 located on a first main surface of the piezoelectric
portion 4 and a second electrode 16 located on a second main surface of the piezoelectric
portion 4 In the vibration generating device 1 having the piezoelectric element, the piezoelectric
coefficient is 1 pC / N or more, and (a) the ratio of the length in the longitudinal direction to the
thickness of the piezoelectric portion is about 100 or more, or (b) the piezoelectric portion The
ratio of the radius of curvature of the curved portion to the thickness of the curved portion is
about 10 or more, or the ratio of the longitudinal length to the radius of curvature of the curved
portion of the piezoelectric portion (c) is about 0.01 or more. [Selected figure] Figure 1
Molding method and molded body of piezoelectric polymer
[0001]
The present invention relates to a method of molding a piezoelectric polymer and a molded body
obtained by the method. The present invention also relates to a vibration generating device using
a polymeric piezoelectric material and a speaker provided with the same.
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1
[0002]
Conventionally, piezoelectric ceramics such as lead zirconate titanate (PZT) have been widely
used as piezoelectric materials, but in recent years, polyfluorinated materials have been used
because they are excellent in processability, flexibility, transparency, lightness, etc. There is a
growing interest in piezoelectric polymers such as vinylidene, polypeptides and polylactic acid.
Among them, polylactic acid having helical chirality as disclosed in Patent Document 1 does not
require poling treatment, and can exhibit relatively high piezoelectricity only by stretching
treatment, and can maintain piezoelectricity for a long time, It attracts attention as an ideal
piezoelectric polymer material.
[0003]
JP-A-5-152638 JP-A-2003-244792
[0004]
A polymeric piezoelectric material formed of a piezoelectric polymer having helical chirality is
usually obtained by orienting the molecules of the piezoelectric polymer by uniaxially stretching
a film formed of the piezoelectric polymer. Be
However, the polymeric piezoelectric material obtained by uniaxial stretching is a flat film, and
its use is limited to that obtained by processing the film.
[0005]
On the other hand, various molding methods such as vacuum molding are known as a method of
forming a polymer such as a resin into a desired shape, but when a general molding method is
applied to a piezoelectric polymer, the molecules are oriented There is a problem that good
piezoelectricity can not be obtained.
[0006]
Therefore, one object of the present invention is to provide a molding method capable of molding
a piezoelectric polymer into polymer piezoelectric materials of various shapes.
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2
[0007]
Further, it has been proposed to use the above-mentioned polymeric piezoelectric material as a
diaphragm of a piezoelectric speaker.
However, since a polymer piezoelectric material composed of a polymer having helical chirality
such as polylactic acid is shear piezoelectric, its vibration direction is in the alignment direction
of the piezoelectric polymer, that is, in the plane of the diaphragm. In the parallel direction, air
can not be strongly vibrated, and there is a problem that high sound pressure can not be
obtained.
[0008]
As a method of solving this problem, conventionally, a method of attaching a metal plate to a
piezoelectric film to convert vibration parallel to the film surface to vertical vibration or bonding
a pair of piezoelectric films to form a bimorph type There is a way to do it.
However, such a method is disadvantageous in terms of production because a process of
laminating films is required.
[0009]
As another method, it is known that, by bending and supporting a piezoelectric film diaphragm,
respiratory vibration in a direction perpendicular to the film surface is generated (Patent
Document 2). However, even with such a configuration, another problem arises that it is difficult
to flatten the sound pressure-frequency characteristic.
[0010]
Therefore, another object of the present invention is to provide a speaker which can be
manufactured by a simple method and can realize generation of high sound pressure and flat
sound pressure-frequency characteristics.
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[0011]
As a result of intensive investigations, the present inventors have shaped the piezoelectric
polymer at a specific temperature and then heat-treated at the specific temperature to impart
piezoelectricity to a molded body and obtain a desired shape. It has been found that molding can
be compatible.
[0012]
That is, according to the first aspect of the present invention, a material formed of a piezoelectric
polymer is molded at a temperature higher than the glass transition temperature and lower than
the crystallization temperature of the piezoelectric polymer, and then the above-mentioned
piezoelectricity is obtained. A method of molding a piezoelectric polymer is provided,
characterized in that heat treatment is performed at a temperature above the crystallization
temperature of the polymer.
[0013]
Moreover, as a result of intensive investigations, the inventors of the present invention can
generate vibration due to buckling in addition to piezoelectric vibration by setting the ratio in the
longitudinal direction to the thickness of the polymeric piezoelectric material to be about 10 or
more. It has been found that it is possible to realize high sound pressure generation and flat
sound pressure-frequency characteristics by using this as a diaphragm in a piezoelectric speaker.
[0014]
That is, according to the second aspect of the present invention, there is provided a piezoelectric
portion formed of a piezoelectric polymer, a first electrode located on a first main surface of the
piezoelectric portion, and a first portion of the piezoelectric portion. A vibration generating
device having a second electrode positioned on the main surface of 2, wherein a ratio of a
longitudinal length to a thickness of the piezoelectric portion is about 10 or more. Provided.
[0015]
Moreover, according to the 3rd summary of this invention, the speaker provided with the said
vibration generating apparatus as a diaphragm is provided.
[0016]
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According to the molding method of the present invention, the piezoelectric polymer can be
molded into polymer piezoelectric materials of various shapes.
Further, according to the vibration generating device of the present invention, vibration due to
buckling can be generated, and by using this as a diaphragm in the speaker, high sound pressure
can be generated and a flat sound pressure- Frequency characteristics can be realized.
[0017]
FIG. 1 is a perspective view of a piezoelectric speaker according to an embodiment of the present
invention.
FIG. 2 is a perspective view of the main body 8 of the speaker of FIG.
FIG. 3 is a cross-sectional view of the side surface 4 of the speaker of FIG. 1 taken along the line
A-A.
FIG. 4 is a graph showing sound pressure-frequency characteristics of the speakers of Example 3,
Comparative Example 2 and Comparative Example 3.
[0018]
Hereinafter, the method for forming a piezoelectric polymer of the present invention will be
described.
[0019]
In the present specification, “piezoelectric polymer” refers to a polymer that can exhibit
piezoelectricity when the molecule is uniaxially oriented.
Moreover, "polymer piezoelectric material" means a polymer material formed of the abovementioned piezoelectric polymer and having piezoelectricity.
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[0020]
According to the first aspect of the present invention, a material formed of a piezoelectric
polymer is molded at a temperature higher than the glass transition temperature and lower than
the crystallization temperature of the piezoelectric polymer, and then the above-mentioned
piezoelectric polymer A method of forming a piezoelectric polymer is provided, which comprises
heat treatment at a temperature above the crystallization temperature of
[0021]
The piezoelectric polymer used in the molding method of the present invention is a piezoelectric
polymer having helical chirality.
Examples of the piezoelectric polymer having helical chirality include polymers having chirality
such as polylactic acid, polypeptide, polymethylglutamate, polybenzylglutamate and having a
main chain having a helical structure, and include polylactic acid or lactic acid as a structural unit
Copolymers are preferred, and polylactic acid is more preferred.
The polylactic acid may be either L-form or D-form, but polylactic acid consisting of L-form which
is easily available is preferable.
[0022]
The material formed of the piezoelectric polymer to be applied to the molding method of the
present invention is a material containing the piezoelectric polymer as a main component, and
the content of the piezoelectric polymer is, for example, 50% by mass or more and 60% by mass
As mentioned above, a material containing 70% by mass or more, or 80% by mass or more, or a
material substantially consisting of a piezoelectric polymer, for example, a material having a
content of 99 to 100% by mass of the piezoelectric polymer.
[0023]
The material formed of the piezoelectric polymer to be applied to the forming method of the
present invention is not particularly limited as long as it can be applied to various forming
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methods, but is preferably in the form of a sheet or a film.
The thickness of the sheet or film is not particularly limited, and is, for example, about 1 μm to
20 mm, preferably about 0.03 to 1.0 mm, more preferably about 0.1 to 0.3 mm.
[0024]
The weight-average molecular weight of the piezoelectric polymer is not particularly limited, but
is preferably about 10,000 to 1,000,000, more preferably about 15,000 to 400,000, more
preferably, for example, polylactic acid. Is about 20,000 to 250,000.
By setting the weight average molecular weight to about 10,000 or more, mechanical strength
and elasticity of the obtained molded article (polymer piezoelectric material) can be secured. In
addition, by setting the weight average molecular weight to about 1,000,000 or less, more
oriented crystallization can be achieved.
[0025]
In the molding method of the present invention, the temperature during vacuum molding is a
temperature above the glass transition temperature of the piezoelectric polymer used and below
the crystallization temperature. For example, when polylactic acid having a weight average
molecular weight of 100,000 is used, the temperature range is about 50 ° C. to 105 ° C.,
preferably about 70 to 110 ° C., more preferably about 75 to 105 ° C. is there. By setting the
temperature to a temperature equal to or higher than the glass transition temperature, vacuum
forming becomes easy, and breakage of the film at the time of vacuum forming can be prevented.
Moreover, the piezoelectricity of the molded object obtained can be stabilized by making the said
temperature below crystallization temperature.
[0026]
The above "glass transition temperature" can be measured by differential scanning calorimetry
(DSC). Further, the “crystallization temperature” can be measured by differential scanning
calorimetry (DSC).
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[0027]
The molding method of the present invention is not particularly limited, and vacuum molding,
pressure molding, injection molding, compression molding, blow molding and the like can be
used, and preferably vacuum molding is used.
[0028]
When the molding method of the present invention is carried out by vacuum molding, it includes
(gold) molds (female mold and male mold), and the material is not limited.
Hereinafter, a material formed of a piezoelectric polymer set in a generic manner simply as “the
mold” is pressed (pushed) by the plug from the surface opposite to the mold toward the inside
of the mold, Vacuum formation may be assisted. The pressure at the time of the press is a
pressure of about 140 to 20,000 kg, preferably about 200 to 5,000 kg, more preferably about
300 to 2,000 kg per 1 cm <2> of press area. By setting the pressing pressure in the above range,
higher piezoelectricity can be obtained.
[0029]
In the method of the present invention, “vacuum” means a pressure that can be obtained using
a general vacuum pump, and specifically, it is a pressure of 1 × 10 <−3> Pa or less.
[0030]
In the molding method of the present invention, stretching is preferably performed at such a
draw ratio that the desired retardation described later can be obtained.
[0031]
The forming method of the present invention includes heat treating the obtained formed body
after vacuum forming.
The temperature of the heat treatment is not particularly limited as long as it is higher than the
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crystallization temperature and lower than the melting point or decomposition temperature of
the piezoelectric polymer used. The temperature is about 3 to 20 ° C. higher than the
crystallization temperature.
For example, when the piezoelectric polymer is polylactic acid, the temperature range is about 80
to 150 ° C., preferably about 100 to 110 ° C. By performing heat treatment in the temperature
range, crystals having a favorable orientation of the molecules of the piezoelectric polymer can
be generated, and higher piezoelectricity can be obtained.
[0032]
The above-mentioned "melting point" can be measured by differential scanning calorimetry
(DSC).
[0033]
The heat treatment can be performed at any timing after vacuum forming.
For example, after vacuum forming, the formed body may be heated before being taken out of
the mold. After vacuum forming, the formed body may be taken out of the mold and heat treated
using another heating means such as a heating furnace.
[0034]
After the heat treatment, preferably, the heated compact is quenched to a temperature below the
glass transition temperature. Such rapid cooling can suppress the formation of spherulites that
adversely affect the piezoelectricity.
[0035]
The material formed from the piezoelectric polymer used in the molding method of the present
invention may contain a softener. The use of the additive increases the flexibility of the film and
facilitates vacuum forming.
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[0036]
The softener is not particularly limited, but when the piezoelectric polymer is polylactic acid, an
elastomer having affinity or reactivity with a carboxylic acid group or hydroxyl group at the
polymer end is preferable. As such an elastomer, a styrene-based elastomer to which a functional
group having excellent affinity with a carboxylic acid group or a hydroxyl group such as an
amine, an epoxy, a carboxylic acid anhydride or the like is added (for example, SBS or SEBS
obtained by hydrogenating this And olefinic elastomers with similar functional groups, and
polyhydroxybutyrate-based soft copolymers (styrene-based elastomers having an amine end).
Specifically, block copolymers of polyalkyl methacrylate and polyalkyl acrylate, for example,
PMMA-PnBA-PMMA (polymethyl methacrylate-polyacrylic acid n-butyl-polymethacrylic acid
methyl) block copolymer can be mentioned. The block copolymer can be obtained, for example,
as LA2250 (trade name), LA2140 (trade name), LA4285 (trade name) or the like manufactured
by Kuraray Co., Ltd.
[0037]
The amount of the softening agent added is about 1 to 40% by mass, preferably about 5 to 30%
by mass, based on the total amount of the piezoelectric polymer and the softening agent. By
setting the addition amount to about 1% by mass or more, vacuum forming becomes easy.
Moreover, the fall of the elasticity modulus and piezoelectricity of the molded object obtained
can be suppressed by the said addition amount being about 40 mass% or less.
[0038]
Further, the material formed from the piezoelectric polymer used in the molding method of the
present invention may further contain other additives such as a colorant, a plasticizer and the
like.
[0039]
The molded body obtained by the molding method of the present invention has a piezoelectric
portion.
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10
The piezoelectric portion preferably has a retardation of 100 nm or more, more preferably 500
nm or more, and even more preferably 1,000 nm or more.
[0040]
The shape of the molded body obtained by the molding method of the present invention is not
particularly limited as long as it is a shape that can be obtained by vacuum molding, for example,
cylinders, cones, polygonal columns such as triangular prisms and quadrangular prisms,
triangular pyramids and square pyramids The shape may be a polygonal pyramid, a dome shape,
or any combination of these, but a shape capable of stretching the piezoelectric polymer more
uniformly, for example, a cylindrical shape is preferable.
[0041]
The molded article obtained by the molding method of the present invention can ensure high
transparency.
[0042]
The molded body obtained by the molding method of the present invention has piezoelectricity
and can be of any shape.
Therefore, the molded body obtained by the molding method of the present invention can be
used, for example, for a piezoelectric speaker, an actuator, a vibration generator, a haptics and
the like.
[0043]
According to a second aspect of the present invention, there is provided a piezoelectric portion
formed of a piezoelectric polymer, a first electrode located on a first main surface of the
piezoelectric portion, and a second portion of the piezoelectric portion. It is a vibration generator
which has the 2nd electrode located in the principal surface, and piezoelectricity is 0.5 or more
pC / N, and the following (a)-(c): (a) Thickness of the above-mentioned piezoelectric part The
ratio of the longitudinal length to the length is about 100 or more, (b) the ratio of the radius of
curvature of the curved portion to the thickness of the piezoelectric portion is about 10 or more,
(c) the curvature of the piezoelectric portion A vibration generator is provided, characterized in
that the ratio of the longitudinal length to the radius of curvature of the part satisfies at least one
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of about 0.01 or more.
[0044]
The piezoelectric coefficient of the piezoelectric portion is 0.5 pC / N or more, preferably 2 pC /
N or more, more preferably 3 pC / N or more, and still more preferably 5 pC / N or more.
[0045]
The ratio of the longitudinal length to the thickness of the piezoelectric portion is about 100 or
more, preferably about 1,000 or more.
By setting this ratio to about 100 or more, it is possible to generate a vibration due to buckling.
[0046]
The ratio of the radius of curvature of the curved portion to the thickness of the piezoelectric
portion is about 10 or more, preferably about 30 or more, more preferably 50 or more, and still
more preferably 100 or more.
By setting this ratio to about 10 or more, it is possible to generate a vibration due to buckling.
[0047]
The ratio of the longitudinal length to the radius of curvature of the curved portion of the
piezoelectric portion is about 0.01 or more, preferably about 0.1 or more, and more preferably 1
or more.
By setting this ratio to about 0.01 or more, it is possible to generate a vibration due to buckling.
[0048]
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12
In the present invention, at least one of the above conditions (a) to (c) may be satisfied, but it is
preferable to simultaneously satisfy two, and it is more preferable to satisfy all three. In addition,
it is preferable to satisfy at least the condition (b). For example, only the condition (b), the
conditions (a) and (b), the conditions (b) and (c), or all the conditions (a) to (c) It is preferable to
satisfy.
[0049]
In the piezoelectric portion, the piezoelectric polymer is preferably oriented in the longitudinal
direction of the piezoelectric portion.
[0050]
The above-mentioned "buckling" is a phenomenon that a deflection occurs due to a stress caused
by the piezoelectric polymer stretching in the orientation direction due to shear deformation.
Vibration due to this deformation (deflection) is called vibration due to buckling.
[0051]
According to a third aspect of the present invention, there is provided a speaker including the
above-described vibration generating device of the present invention as a diaphragm.
[0052]
The speaker according to the present invention preferably includes a piezoelectric portion
formed of a piezoelectric polymer, a first electrode located on a first main surface of the
piezoelectric portion, and a second main surface of the piezoelectric portion. A speaker having a
second electrode positioned on the piezoelectric portion, wherein (i) the piezoelectric coefficient
is 2 pC / N or more, (ii) at least a portion is curved, and (iii) the elastic modulus in the
piezoelectric portion Is 0.1 GPa or more, and (iv) the following (a ') to (c'): (a ') the ratio of the
longitudinal length to the thickness of the piezoelectric portion is about 100 or more, b ') The
ratio of the radius of curvature of the curved portion to the thickness of the piezoelectric portion
is about 10 or more. (c') The ratio of the longitudinal length to the radius of curvature of the
curved portion of the piezoelectric portion is approximately It is characterized in that it satisfies
at least one of 0.01 or more.
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[0053]
In the present invention, at least one of the above conditions (a ') to (c') may be satisfied, but it is
preferable to simultaneously satisfy two, and it is more preferable to satisfy all three.
In addition, it is preferable to satisfy at least the condition (b '). For example, only the condition
(b'), the conditions (a ') and (b'), the conditions (b ') and (c'), or the conditions (a ') It is preferable
to satisfy all of (c ′).
[0054]
Hereinafter, the speaker of the present invention will be described in detail with reference to the
drawings.
[0055]
The speaker 1 of this embodiment is shown in FIG. 1, the perspective view of the main body 8 is
shown in FIG. 2, and the cross-sectional view along the line AA of the side surface 4 is shown in
FIG.
In addition, in FIG. 3, although the 1st electrode 14 and the 2nd electrode 16 may be thin layers
in fact, thickness is emphasized and it has shown typically.
[0056]
As shown in FIGS. 1 and 2, the speaker 1 has a bottom portion 2 having a circular opening, and a
cylindrical side surface extending substantially perpendicularly to the bottom portion 2 from the
opening of the bottom portion 2. It has the main-body part 8 integrally formed from the part 4
and the upper surface part 6 which block | closes the upper opening part of the side part 4. As
shown in FIG.
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14
Furthermore, as shown in FIG. 3, the inner surface 10 and the outer surface 12 of the side
portion 4 have a first electrode 14 and a second electrode 16, respectively.
[0057]
In the above speaker, the main body 8 is formed of a film formed of a piezoelectric polymer. The
piezoelectric polymer is not particularly limited, but preferably includes a piezoelectric polymer
having helical chirality that can be used in the molding method of the present invention, and
more preferably polylactic acid or lactic acid A copolymer containing as a constituent unit, more
preferably polylactic acid is used.
[0058]
The film may contain additives such as softeners, colorants, plasticizers and the like.
[0059]
The side surface portion 4 has piezoelectricity, and a voltage is applied by the first electrode 14
and the second electrode 16 disposed on both main surfaces (that is, the inner surface 10 and
the outer surface 12).
By changing this voltage, the side part 4 vibrates and a sound wave is generated. That is, the side
surface 4 functions as a diaphragm.
[0060]
Said side part 4 corresponds to the "piezoelectric part" of the speaker of the present invention,
and preferably has the following four features: (i) having a piezoelectric coefficient of about 2 pC
/ N or more; (ii) at least a part is curved (Iii) the elastic modulus is about 0.1 GPa or more; and
(iv) the following (a ′ ′) to (c ′ ′): (a ′ ′) length in the longitudinal direction (height
direction of the cylinder) with respect to thickness (B ") the ratio of the radius of the cylinder to
the thickness is greater than about 10, (c") the ratio of the longitudinal length to the radius of the
cylinder is about 0. And at least one of the values is 01 or more.
[0061]
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15
The above feature (i) will be described below.
In the side surface portion 4 in the present embodiment, the piezoelectric polymer having helical
chirality that forms a film is uniaxially oriented in the height direction of the cylinder, whereby
the side surface portion 4 has piezoelectricity. By having piezoelectricity, the film is deformed
(sheared and deformed) when a voltage is applied between both main surfaces of the side surface
4. The side part vibrates by changing this voltage.
[0062]
In the present invention, the piezoelectric coefficient of the piezoelectric portion may be any
piezoelectric coefficient sufficient to deform the piezoelectric portion by application of a voltage,
for example, about 2 pC / N or more, preferably about 3 pC / N or more, More preferably, it is
about 4 pC / N or more, still more preferably about 6 pC / N or more, and particularly preferably
about 8 pC / N or more.
[0063]
Next, the above feature (ii) will be described.
The side surface 4 in the present embodiment is curved by taking a substantially cylindrical
shape. By curving in this manner, it is possible to cause vibration (shear deformation) parallel to
the film surface generated in the piezoelectric polymer film to appear on the surface of the film.
The surrounding air vibrates due to the vibration that is expressed on the surface in this way, and
becomes a sound wave.
[0064]
In the present embodiment, the radius of the cylinder of the side surface 4 is not particularly
limited. When the radius is decreased, the degree of bending is increased, and vibration caused
by shear deformation can be more efficiently expressed on the surface of the film, and sound
pressure per unit area can be increased. On the other hand, when the radius is increased, the
efficiency of causing the vibration generated by the shear deformation to appear on the surface
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16
of the film decreases, but the surface area of the side surface, that is, the surface area of the
diaphragm increases. Therefore, the radius is determined in consideration of the sound pressure
as a whole, for example, in the present embodiment, the radius of the cylinder of the side portion
4 is about 0.3 to 20 cm, preferably about 1 to 10 cm. be able to.
[0065]
In the present embodiment, the side surface portion 4 is cylindrical, but the present invention is
not limited to this aspect, and the vibration generated by the shear deformation of at least a part
of the piezoelectric portion is the surface of the piezoelectric portion It should just be curved to
such an extent that it can express. For example, but not limited to, the curved portion of the
piezoelectric portion may have a radius of curvature of about 0.05 to 100 cm, for example about
1 to 20 cm.
[0066]
Next, the above-mentioned feature (iii) will be described. In the present embodiment, the side
surface portion 4 has an elastic modulus of about 0.1 GPa or more, preferably about 0.3 GPa or
more, more preferably about 0.5 GPa or more, still more preferably 1 GPa or more, and
particularly preferably 1.5 GPa or more. Have. The surrounding air can be vibrated more strongly
by the side surface part 4 having an elastic modulus of about 0.1 GPa or more. As a result, high
sound pressure can be obtained.
[0067]
Next, the above-mentioned feature (iv) will be described. In the present embodiment, in the side
surface portion 4, the ratio of the length in the longitudinal direction (the height direction of the
cylinder) to the thickness of the following (a ′ ′) to (c ′ ′) is about 100 or more; b ") the ratio
of the radius of the cylinder to the thickness is greater than or equal to about 10; and the ratio of
the longitudinal length to the radius of the cylinder is greater than or equal to about 0.01.
[0068]
The ratio of the length in the longitudinal direction (the height direction of the cylinder) to the
thickness is about 100 or more, preferably about 1,000 or more.
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17
[0069]
The ratio of the radius of curvature of the radius of the cylinder to the thickness is about 10 or
more, preferably about 30 or more, more preferably 50 or more, and still more preferably 100 or
more.
[0070]
The ratio of the longitudinal length to the radius of the cylinder is about 0.01 or more, preferably
about 0.1 or more, more preferably 1 or more.
[0071]
By satisfying at least one of the above conditions (a ′ ′) to (c ′ ′), the side surface portion 4
can generate a vibration due to buckling.
By generating vibrations due to buckling in this manner, flat sound pressure-frequency
characteristics can be obtained over a wide frequency range.
[0072]
Although the length in the longitudinal direction of the side portion 4 is not particularly limited,
it is about 0.5 to 100 cm, preferably about 1 to 50 cm, and more preferably about 5 to 30 cm.
[0073]
Although the radius of said side part 4 is not specifically limited, It is about 0.5-30 cm, Preferably
it is about 1-20 cm, More preferably, it is about 2-10 cm.
[0074]
Although the film thickness of the above-mentioned side part 4 is not particularly limited, it is
about 1 μm to 50 mm, preferably about 0.01 to 10 mm, more preferably about 0.1 to 1 mm, still
more preferably about 0.1 to 0.3 mm It is.
[0075]
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18
The piezoelectric portion of the side surface portion 4 has a retardation of preferably 100 nm or
more, more preferably 500 nm or more, and still more preferably 1,000 nm or more.
[0076]
The speaker of the present invention utilizes vibration due to buckling to improve sound
pressure and sound pressure-frequency characteristics.
Therefore, the speaker of the present invention can improve sound pressure and sound pressurefrequency characteristics more by making it easy to generate a vibration due to buckling.
[0077]
As a method of facilitating the occurrence of vibration due to buckling, for example, applying
stress to the piezoelectric portion can be mentioned.
The stress is preferably applied in the longitudinal direction of the piezoelectric portion, in the
present embodiment, in the height direction of the cylinder.
[0078]
In the present embodiment, the side surface portion 4 has the first electrode 14 and the second
electrode 16 on the inner surface 10 and the outer surface 12 respectively.
A voltage is applied to the side portion 4 having piezoelectricity between the first electrode 14
and the second electrode 16.
[0079]
The conductive material forming the first electrode and the second electrode is not particularly
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19
limited, and examples thereof include Cu, Ag, Ni and the like.
Although the formation method of an electrode is not specifically limited, For example, the vapor
deposition method is mentioned.
[0080]
The first electrode and the second electrode may be formed on the entire main surface of each of
the piezoelectric portions, or may be formed on only a part of the respective principal surfaces.
[0081]
In the present embodiment, the bottom surface 2 and the top surface 6 do not need to have
piezoelectricity in particular, and do not themselves generate vibration, but fix the lower end and
the upper end of the side surface 4 respectively. , Contributes to stabilizing the vibration
generated in the side face portion 4, improving the strength of the vibration, and improving the
sound pressure and the sound quality.
Also, if there is a frequency range that is a relatively low sound pressure as compared to other
frequency ranges, in order to improve the sound pressure, resonance is performed in the
frequency range of the bottom portion 2 or the top surface 6. A flatter sound pressure-frequency
characteristic can be obtained as a form to cause.
[0082]
Next, a method of manufacturing the speaker 1 of the present embodiment will be described.
[0083]
The main body portion 8 of the speaker in the present embodiment can be easily manufactured
by the above-described forming method of the present invention.
That is, a film formed of a piezoelectric polymer is vacuum formed at a temperature higher than
the glass transition temperature and lower than the crystallization temperature of the
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20
piezoelectric polymer to form the shape of the main body 8, and then the piezoelectric high value
is obtained. The heat treatment can be performed at a temperature equal to or higher than the
crystallization temperature of the molecule, whereby the main body 8 can be manufactured.
[0084]
Then, a conductive metal is vapor-deposited on the inner side surface and the outer side surface
of the side surface portion 4 to form the first electrode and the second electrode, whereby the
speaker 1 of the present embodiment can be obtained.
[0085]
As mentioned above, although one embodiment of this invention was described, this invention is
not limited to the said embodiment.
[0086]
In particular, since the speaker of the present invention can be manufactured using the abovedescribed molding method of the present invention, it can have any shape that can be
manufactured by the molding method of the present invention.
Therefore, according to the molding method of the present invention, the piezoelectric polymer is
molded as, for example, a frame of a television, a case of a mobile phone or a portable game
machine, or a part thereof by giving them piezoelectricity. The function as a speaker can be
provided.
[0087]
The present invention will be more specifically described in the following examples, but the
present invention is not limited to these examples.
[0088]
Example 1 A polylactic acid film (made by Taki Chemical Co., Ltd., a sheet having a molecular
weight of 100,000 and a thickness of 1 mm) was set in a vacuum forming machine.
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The mold used had a radius of 5 cm and a depth of 12 cm.
The film was heated to 99.3 ° C. and vacuum formed while pushing the plug at a pressure of
about 2 tons from the top of the film toward the mold.
The obtained molded product is removed from the vacuum forming machine, fixed to a jig
corresponding to the shape of the molded product, heat treated at about 110 ° C. for 5 minutes
in a heating furnace, and then placed in a water-covered water tank for quenching Then, a
compact corresponding to FIG. 2 in which the dimensions of the cylindrical portion are a radius
of 5 cm and a height of 12 cm was obtained.
[0089]
Example 2 A molded article was prepared in the same manner as in Example 1 except that the
polylactic acid film used in Example 1 was changed to a polylactic acid film (Tochi Chemical Co.,
Ltd.) having a molecular weight of 60,000 and a thickness of 0.5 mm. I got
[0090]
Comparative Example 1 A molded body was obtained in the same manner as in Example 1 except
that the film temperature at the time of vacuum forming was 110 ° C. and pressing with a plug
was not performed.
[0091]
Test Example 1 A sample having a length of 120 mm and a width of 5 mm was cut out from the
cylindrical portion of the molded articles of Examples 1 and 2 and Comparative Example 1.
The piezoelectricity and retardation of upper, middle and lower parts (upper part of FIG. 2 is
upper part) obtained by dividing the sample into upper and lower three equal parts were
measured.
The results are shown in Table 1.
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[0092]
[0093]
As shown in Table 1, it was confirmed that by using the molding method of the present invention,
it is possible to obtain a molded article having high piezoelectricity and retardation.
[0094]
Example 3 A molded article was prepared in the same manner as in Example 1 except that the
polylactic acid film used in Example 1 was changed to a polylactic acid film (Tochi Chemical Co.,
Ltd.) having a molecular weight of 90,000 and a thickness of 0.1 mm. I got
Copper was vapor-deposited on both main surfaces of the side part of the obtained formed body
to form an electrode, and a speaker of the present invention was produced.
[0095]
Comparative Example 2 A molded article was prepared in the same manner as in Example 1
except that the polylactic acid film used in Example 1 was changed to a polylactic acid film (Tochi
Chemical Co., Ltd.) having a molecular weight of 60,000 and a thickness of 1.5 mm. I got
Copper was vapor-deposited on both main surfaces of the side part of the obtained formed body
to form an electrode, and a speaker of Comparative Example 2 was produced.
[0096]
Comparative Example 3 A molded body was obtained in the same manner as in Example 1 except
that the film temperature at the time of vacuum forming was 110 ° C. and pressing with a plug
was not performed.
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Copper was vapor-deposited on both main surfaces of the side portion of the obtained formed
body to form an electrode, and a speaker of Comparative Example 3 was produced.
[0097]
The dimensions of the cylindrical portions of Example 3 and Comparative Examples 2 and 3 are
shown in Table 2 below. The film thickness is a value in the middle of the cylinder.
[0098]
Test Example 2 In Example 3 and Comparative Examples 1 and 2, sound pressure-frequency
characteristics were measured using an acoustic measurement device (LA2560, Ono Sokki). The
results are shown in FIG.
[0099]
As apparent from FIG. 4, the speaker of Comparative Example 3 having a piezoelectric coefficient
of less than 1 pC / N (0.1 pC / N) has a sound pressure of less than 40 dB in almost all frequency
regions, and is used as a speaker It was inadequate.
[0100]
In addition, in Comparative Example 2 where r / d is less than 10 (8.3), a large sound pressure
peak is observed at frequencies of 1,500 Hz to 2,500 Hz, and sound pressure near frequency
1,000 Hz and frequency 2,000 Hz The sound pressure in the vicinity had a difference of about
30 dB.
This peak is considered to be due to resonance.
[0101]
On the other hand, in the speaker of Example 3, the sound pressure rises also in the region other
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than the vicinity of the resonance frequency, and the sound pressure as a whole is 70 dB or
more, and the sound pressure near 1,000 Hz and the sound pressure near 2,000 Hz It is also
confirmed that the difference between them is also suppressed to about 10 dB, and that a good
sound pressure-frequency characteristic can be obtained as a whole. It is considered that this is
because high sound pressure can be obtained even in a frequency range other than the
resonance frequency due to the vibration due to the buckling.
[0102]
The molding method of the present invention can form molded articles of piezoelectric materials
of various shapes, and such molded articles can be specified in a wide variety of applications as
speakers, actuators, and the like.
[0103]
DESCRIPTION OF SYMBOLS 1 ... Speaker 2 ... Bottom part 4 ... Side part 6 ... Top part 8 ... Main
body part 10 ... Inner side 12 ... Outer side 14 ... 1st electrode 16 ... 2nd electrode
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