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JP2011178956

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DESCRIPTION JP2011178956
An object of the present invention is to satisfy the demand for downsizing and weight reduction
of a speaker by providing a foam sheet suitable for forming a diaphragm such as a speaker. The
foam sheet is formed of a resin composition having a polypropylene-based resin as a base
polymer, and is used to form a diaphragm of a speaker or a microphone, wherein the thickness is
1 mm or more and 2 mm or less, density: 0 .25 g / cm or more and 0.45 cm or less, tensile elastic
modulus: 120 MPa or more, open cell ratio: 15% or less, and the polypropylene-based resin has a
melt tension of 10 cN or more and 30 cN or less And a melt mass flow rate of 1.5 g / 10 min or
more and 5.0 g / 10 min or less. [Selected figure] None
Foam sheet
[0001]
The present invention relates to a foam sheet, and more particularly, to a foam sheet formed of a
resin composition containing a polypropylene-based resin as a base polymer and used to form a
diaphragm of a speaker or a microphone.
[0002]
2. Description of the Related Art In the past, there have been demands for smaller and lighter
speakers and microphones mounted on various types of devices including small electronic
devices such as mobile phones and notebook personal computers.
10-05-2019
1
In general, a speaker is provided with a diaphragm that vibrates to generate sound, and a
mechanism that vibrates the diaphragm, and the diaphragm is called cone paper obtained by
forming paper in a cone shape. Are widely used. Also, conversely, in the microphone, a
mechanism is used to vibrate the diaphragm by sound and convert the vibration into an electric
signal. On the other hand, it is effective to reduce the size of the mechanism for vibrating the
diaphragm by making it easier to vibrate the diaphragm and to reduce the size and weight of the
speaker and the microphone. It has been studied to form a diaphragm from a resin foam sheet
that can be vibrated by a weaker force than cone paper.
[0003]
For example, Patent Document 1 below describes the use of a foam sheet formed of a resin
composition having a polypropylene-based resin as a base polymer for a diaphragm. However,
sufficient studies have not been made to the use of such a foam sheet as a sheet for forming a
diaphragm of a speaker or a microphone so far, and a sheet suitable as a foam sheet for forming
a diaphragm is seen. It has not been issued.
[0004]
That is, in the case of speakers and microphones, it is not easy to obtain a foam sheet suitable for
forming the diaphragm, and it is difficult to satisfy the demand for smaller size and lighter
weight. There is.
[0005]
Japanese Patent Application Laid-Open No. 57-41096
[0006]
The present invention has been made in view of the problems as described above, and provides a
foam sheet suitable for forming a diaphragm, which in turn satisfies the need for smaller and
lighter speakers and microphones. The purpose is.
[0007]
The inventors of the present invention conducted intensive studies to solve the above problems,
and as a result, they found that among foam sheets formed of a polypropylene resin composition,
those having predetermined properties are suitable for forming a diaphragm. The present
invention has been completed.
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2
[0008]
That is, the present invention according to the foam sheet is a foam sheet which is formed of a
resin composition having a polypropylene-based resin as a base polymer, and is used to form a
diaphragm of a speaker or a microphone. 2 mm or less, density: 0.25 g / cm <3> or more, 0.45
cm <3> or less, tensile modulus: 120 MPa or more, open cell ratio: 15% or less, and
polypropylene The resin is characterized in that it has a melt tension of 10 cN or more and 30 cN
or less and a melt mass flow rate of 1.5 g / 10 min or more and 5.0 g / 10 min or less.
[0009]
In the present specification, “melt tension” is intended to be a value measured at 230 ° C., for
example, a value measured as follows using a capillary rheometer.
[0010]
(Melt tension measurement method) First, a polypropylene-based resin to be a sample is
accommodated in a cylinder having an inner diameter of 15 mm disposed in the vertical
direction, and heated for 5 minutes at 230 ° C. to melt it. A piston is inserted from the lower end
of the cylinder so that the extrusion speed is 0.0773 mm / s (constant) with the piston (die
diameter: 2.095 mm, die length: 8 mm, inflow angle: The molten resin is extruded in the form of
a string from 90 degrees (conical), and this string is passed through a tension detection pulley
disposed below the above-mentioned capillary, and then wound using a winding roll.
Assuming that the initial speed at the beginning of winding at this time is 4 mm / s, and the
acceleration thereafter is 12 mm / s <2>, the winding speed is gradually increased, and the
tension observed by the tension detection pulley is rapidly reduced. The velocity is taken as the
"breakpoint velocity" and the maximum tension before this "breakpoint velocity" is observed is
measured as the "melt tension".
[0011]
Furthermore, the "melt mass flow rate" in this specification intends the value measured by the
method (condition M: 230 ° C, 2.16 kg) described in JIS K 7210: 1999.
[0012]
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3
The foam sheet of the present invention has the above characteristics, is suitable as a material for
forming a diaphragm of a speaker, and is useful for reducing the size and weight of a speaker or
a microphone. It can be said.
[0013]
Hereinafter, embodiments of the present invention will be described.
The foam sheet of this embodiment is formed of a resin composition containing a polypropylenebased resin as a base polymer, and has a thickness of 1 mm or more and 2 mm or less, and a
density of 0.25 g / cm <3> or more and 0.45 cm <3. > It is important that the tensile modulus of
elasticity is 120 MPa or more and the open cell ratio is 15% or less.
The polypropylene-based resin used for the base polymer has a melt tension of 10 cN or more
and 30 cN or less, and a melt mass flow rate of 1.5 g / 10 min or more and 5.0 g / 10 min or less
(hereinafter “MFR”) It is important to have
[0014]
In addition to the case where the foam sheet of this embodiment is used as a flat diaphragm as it
is, for example, a three-dimensional shape is imparted by forming processing by a sheet forming
method such as press forming, vacuum forming, or pressure forming. It can be used as a
diaphragm.
And about the "thickness", the "density", the "tensile elastic modulus", and the "open cell rate"
prescribed | regulated above, the value in the state before being used for formation of a
diaphragm is prescribed | regulated.
However, it is preferable that the values of “thickness”, “density”, “tensile elastic
modulus” and “open cell ratio” be within the above ranges even after being processed as a
diaphragm.
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4
However, for example, even in the case where secondary foaming or partial compression is
caused in the foam sheet by the above-mentioned forming process, “thickness”, “density”,
“tensile modulus” in all the portions of the diaphragm The value of does not have to be
maintained in the above range.
[0015]
The thickness of the foam sheet can be measured based on JIS K 7248: 2005. For example, a
sample of 10 cm in width and 10 cm in length is prepared, and a dial gauge is used at several
places (for example, 5 places) of this sample. It can be determined by measuring and calculating
the average value.
It is important that the thickness of the foam sheet is within the above range. If the thickness
exceeds the upper limit (2 mm), the rigidity of the diaphragm becomes too strong or the mass
becomes too heavy, which is favorable It is because there is a possibility that the vibration can
not be obtained.
On the other hand, when the thickness is less than the lower limit value (1 mm), there is a
possibility that the rigidity of the diaphragm is insufficient, and there is a possibility that a
favorable vibration property can not be obtained.
[0016]
In addition, the density (apparent density) of the foam sheet can be measured based on JIS
K7222: 2005. For example, a sample having a width: 10 cm × length: 10 cm is prepared, and
this is based on JIS K 7248: 2005 The volume V (cm <3>) of the sample can be measured and the
mass W (g) of this sample can be measured and determined. For example, the width and length of
the sample are accurately measured with a caliper, and the volume (V = width × length ×
thickness) is calculated together with the thickness, and the mass (W) of the sample is measured,
and the following formula (1) is calculated It can be determined by calculation. Density (unit: g /
cm <3>) = W / V (1) Incidentally, it is important that the density of the foam sheet is within the
above range that the density has an upper limit value (0. When it exceeds 45 g / cm <3>, it is
because there is a possibility that the vibration property which becomes favorable as a result of
the diaphragm becoming too heavy may not be obtained. On the other hand, if the density is less
than the lower limit value (0.25 g / cm <3>), the rigidity of the diaphragm is likely to be
10-05-2019
5
insufficient, and a favorable vibration property may not be obtained.
[0017]
Moreover, about the tensile elasticity modulus of a foamed sheet, it can obtain | require based on
JISK6767-1999 "foamed plastic-polyethylene-test method." In addition, it is important that the
tensile elastic modulus of the foam sheet has the above-mentioned value that, when the tensile
elastic modulus is less than the lower limit value (120 MPa), the rigidity of the diaphragm may be
insufficient. It is because it has a possibility that it becomes impossible to obtain the good
vibration property. The upper limit value is not particularly limited, but the tensile modulus of
the foam sheet is usually 300 MPa or less.
[0018]
When a foamed sheet is produced by extrusion foaming as described later, the value of the
tensile modulus may be different between the extrusion direction (MD direction) and the
direction (TD direction) orthogonal to the extrusion direction. The term "tensile modulus" as used
herein is intended to mean the average value in the MD direction and the TD direction.
[0019]
Furthermore, the open cell ratio of the foam sheet can be measured based on JIS K7138: 2006.
For example, a sample having a width: 10 cm × length: 10 cm is prepared, and as described
above, based on JIS K 7248: 2005. The volume V (cm <3>) of this sample is measured, and the
non-aerated volume Vi (cm <3>) is measured using, for example, an air comparison type
hydrometer made by Tokyo Science Co., Ltd. ) Can be asked.
Open cell ratio (unit:% by volume) = (V−Vi) / V × 100 (2) In addition, it is important that the
open cell ratio of the foam sheet has the above value, When the open cell rate of the foam sheet
exceeds the upper limit (15%), moisture absorption is apt to occur, and there is a possibility that
the vibration state is changed in the use environment, and generally it is durable when the open
cell rate is high. It is because inferior tendency is seen.
[0020]
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6
Next, a forming material for forming such a foam sheet will be described. As described above, the
foam sheet of this embodiment is formed of a resin composition containing a polypropylenebased resin as a base polymer, and the polypropylene-based resin has a melt tension of 10 cN to
30 cN. It has a melt mass flow rate of 1.5 g / 10 min or more and 5.0 g / 10 min or less.
[0021]
As a polypropylene resin showing such melt tension, it can be easily found from among those
commercially available as high melt tension polypropylene resin (hereinafter also referred to as
"HMS-PP"). As this high melt tension polypropylene resin (HMS-PP), for example, trade names
"WB130 HMS", "WB 135 HMS", and "WB 140 HMS" from Borealis, trade names "Pro-fax F 814"
from Basell, Japan Polypropylene Commercially available under the trade names "FB 3312", "FB
5100", "FB 7200", and "FB 9100".
[0022]
Among them, HMS-PP in which long chain branching which is a free end is formed in the
molecule is easy to increase the foaming of the foamed sheet while suppressing the formation of
open cells in the extrusion foaming described later. It is suitable in point. That is, HMS-PP having
free end long chain branching is used as the base polymer in that the foamed sheet can be
produced by the efficient production method by extrusion foaming while adjusting “density”
and “open cell ratio” within the above range. It is preferable to adopt.
[0023]
As such HMS-PP, those which are partially cross-linked by irradiation of active energy rays such
as electron beam or radiation to form free end long chain branches, or free end long chain
branches are formed by chemical cross linking And the like. As a forming material of the foam
sheet of this embodiment, HMS-PP in which the long-chain branch which becomes a free end by
chemical crosslinking, such as "WB135HMS" of Borealis company, can be used suitably
especially.
[0024]
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7
In the resin composition used as the forming material of the foam sheet of this embodiment, such
HMS-PP may constitute a base polymer by one kind alone, and has a melt tension of 10 cN or
more and 30 cN or less HMS-PP having a melt mass flow rate (MFR) of 1.5 g / 10 min or more
and 5.0 g / 10 min or less may constitute a base polymer.
[0025]
The above-mentioned range is set for the melt tension of the polypropylene-based resin used for
the base polymer because the melt tension of the polypropylene-based resin is less than the
lower limit (10 cN) and foams are easily generated during foaming. While it becomes difficult to
increase the degree of foaming while suppressing the formation of C, the melt tension is too high
when the upper limit value (30 cN) is exceeded, which may make the foaming itself difficult.
[0026]
In addition, the above-mentioned range is set to the MFR of the polypropylene-based resin used
for the base polymer, because if it is less than the above lower limit value (1.5 g / 10 min), for
example, the foam sheet is There is a risk that the power load of the extruder will be excessive
during production, and if it exceeds the upper limit value (5.0 g / 10 min), the flowability of the
molten resin at the time of extrusion may be too high, resulting in discharge amount fluctuation.
In order to have
That is, in order to produce a foam sheet efficiently, it is important that MFR is in the said range.
[0027]
The polymer component of the resin composition is preferably composed only of HMS-PP in
which the melt tension and the MFR fall within the above range, but if necessary, for example,
polyethylene (PE) -based resin or HMS It is also possible to incorporate a polymer highly
compatible with HMS-PP, such as a polypropylene resin other than -PP, as a polymer component
in the resin composition.
However, even in such a case, the HMS − is such that the melt tension of the polymer mixture in
which the entire polymer component is mixed is 10 cN or more and 30 cN or less, and the MFR is
1.5 g / 10 min or more and 5.0 g / 10 min or less. It is preferable to contain polymers other than
10-05-2019
8
PP.
[0028]
Moreover, the component for foaming is contained in the resin composition for forming the foam
sheet of this embodiment normally. The components for this foaming include, for example, a gas
component that is in a gaseous state at least at the melting point of the base polymer, a
nucleating agent that serves as a core when forming bubbles by the gas component, and thermal
decomposition at the melting point of the base polymer. The thermal decomposition type
foaming agent etc. which are produced | generated and gas is generate | occur | produced are
mentioned.
[0029]
Examples of the gas component include aliphatic hydrocarbons such as propane, butane and
pentane; 1,1-dichloro-1-fluoroethane (HCFC-141b), 1-chloro-1,1-difluoroethane (HCFC-142b), 2 Freon such as chloro-1,1,1,2-tetrafluoroethane (HCFC-124), 1,1,1,2-tetrafluoroethane (HFC134a) and 1,1-difluoroethane (HFC-152a) System gas components; nitrogen, carbon dioxide,
argon, water and the like can be mentioned. These gas components may be used alone or in
combination.
[0030]
Examples of the nucleating agent include talc, mica, silica, diatomaceous earth, aluminum oxide,
titanium oxide, zinc oxide, magnesium oxide, magnesium hydroxide, aluminum hydroxide,
calcium hydroxide, potassium carbonate, calcium carbonate, magnesium carbonate, sulfuric acid
Inorganic compound particles such as potassium, barium sulfate and glass beads, organic
compound particles such as polytetrafluoroethylene, and the like can be mentioned. The
nucleating agent can be contained, for example, in the foam layer forming material in a
masterbatch method previously contained in a polyolefin resin, and the nucleating agent is
contained in an amount of 5% by mass or more and 50% by mass or less A nucleating agent can
be used more effectively by using a masterbatch dispersed in a polyolefin resin so as to become a
target.
10-05-2019
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[0031]
Furthermore, as the thermal decomposition type foaming agent, for example, azodicarbonamide,
sodium hydrogencarbonate, a mixture of sodium hydrogencarbonate and citric acid and the like
can be mentioned. The heat-degrading foaming agent is more effectively dispersed in a
polyolefin-based resin so as to have a content within the range of 10% by mass or more and 50%
by mass or less to form a masterbatch. It can be used for
[0032]
Furthermore, the resin composition includes, for example, various stabilizers such as weathering
agents, antioxidants, anti-aging agents, processing aids such as external lubricants, internal
lubricants, etc., antistatic agents, slip agents, pigments, fillers, etc. Additives can be included as
appropriate.
[0033]
In order to produce the foam sheet of this embodiment using such a material, the method of
implementing extrusion foaming using a common extruder as production equipment of a foam
sheet is mentioned.
For example, a polymer component such as a base polymer is introduced into an extruder on the
upstream side of a tandem extruder, and the polymer component is melt-kneaded in this
extruder, for example, at a temperature condition favorable to the dissolution of the gas
component. After that, a gas component such as butane, for example, is injected at a midway
point of this extruder and kneading is further performed, and the resin composition containing
the gas component is adjusted to a temperature condition suitable for extrusion by the
downstream extruder. Then, a method of extrusion foaming from a flat die or a circular die to
produce a foam sheet can be employed.
[0034]
The foam sheet thus obtained can be used as a flat diaphragm as it is, for example, it can be
molded into a box or cone shape and this molded product can be used as a diaphragm. .
[0035]
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10
By using the foam sheet according to the present embodiment as a diaphragm, the power
required for vibration can be reduced as compared to the case of using a paper diaphragm, and
the speaker can be made smaller and lighter.
[0036]
In addition, about the above effects, it is widely exhibited not only in the foam sheet illustrated
above but in the foam sheet of the present invention, and the present invention is not limited to
the foam sheet directly exemplified above. It is not limited.
[0037]
EXAMPLES The present invention will next be described in more detail by way of examples,
which should not be construed as limiting the invention thereto.
[0038]
Example 1 Preparation of Foamed Sheet First, it has a single-screw extruder (upstream side)
having a diameter of 90 mm and a single-screw extruder (downstream side) having a diameter of
115 mm connected to the single-screw extruder. A tandem extruder was prepared.
The ratio of 100 parts by mass to 100 parts by mass with respect to 100 parts by mass of the
polypropylene-based resin is 0.2 parts by mass as trade name “WB135” (melt tension: 19 cN,
MFR: 1.7 g / 10 min) manufactured by Borealis as a polypropylene-based resin Supply sodium
hydrogencarbonate-citric acid foaming agent (master batch by Dainichi Seika Co., Ltd., trade
name "Finecell Master PO410K") to the first hopper of single-screw extruder with a diameter of
90 mm on the upstream side, 200 ° After heating and melting with C, butane (isobutane /
normal butane = 35% by mass / 65% by mass), which is a gas component, was injected and
kneaded so that the ratio to 100 parts by mass of the molten resin was 5 parts by mass.
The foamable resin composition is supplied to the downstream extruder through a connecting
pipe maintained at a temperature of 195 ° C. to reduce the temperature of the resin
composition from 185 ° C. to 155 ° C., and the diameter of 140 mmφ. Extrusion foaming was
carried out at a discharge rate of 110 kg / hour from a circular die.
The cylindrical foam produced by the extrusion foaming is expanded on a cooling mandrel
10-05-2019
11
having a diameter of 414 mm and a length of 500 mm, and the outer surface is cooled by
blowing air from an air ring. Two strips of foam sheet were prepared by cutting with a cutter at
two points symmetrical (180 degrees open) in the circumferential direction of the mandrel.
[0039]
The foam sheet of Example 1 obtained in this manner has the characteristics shown in Table 1,
and the diaphragm obtained by molding the foam sheet has a beautiful appearance and a light
weight. It was confirmed that the sound quality was good when the speaker was manufactured.
[0040]
(Comparative Examples 1 and 2) Comparative Examples 1 and 2 in the same manner as Example
1 except that the addition amount of the foaming agent was changed, and the obtained
characteristics were as shown in Table 1. The foam sheet of was produced.
Although the diaphragm made of these foam sheets had a beautiful appearance, the sound
quality at the time of producing the speaker was inferior to the case of using the foam sheet of
Example 1.
[0041]
[0042]
Also from these results, it can be seen that the foam sheet of the present invention is suitable for
forming a speaker or a diaphragm of a microphone.
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