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JP2001268686

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DESCRIPTION JP2001268686
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
diaphragm for an electroacoustic transducer and a method of manufacturing the same. More
particularly, the present invention relates to a diaphragm for an electroacoustic transducer made
of a synthetic resin manufactured using a molding method in which the cavity volume is
expanded after injection compression, and a method for manufacturing the same.
[0002]
BACKGROUND ART The physical properties required for diaphragms for electroacoustic
transducers such as speakers (sometimes referred to simply as diaphragms), in particular
diaphragms for low to mid-range and all bands, have a specific elastic modulus (E / ρ ), Specific
flexural rigidity (E / ρ3) is large (that is, high modulus, low density), has adequate internal loss,
is resistant to mechanical fatigue, and has good weather resistance. Furthermore, in recent years,
waterproofness has become one of the important characteristics, mainly for vehicles. In order to
meet such demands, materials such as various metals, ceramics, synthetic resins, synthetic fibers,
natural fibers and the like have conventionally been proposed, processed using various
processing methods, and used.
[0003]
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1
Among the materials conventionally used, metals and ceramics have high elastic modulus but
high density and low internal loss, so they are relatively excellent for high-frequency
reproduction. However, it was unsuitable for the low to mid range and all bands where light
weight and high rigidity are required. In addition, so-called paper diaphragms using cellulose
fibers such as wood pulp as the main raw material have a relatively low density and have
sufficient elastic modulus and appropriate internal loss for general performance, so they are
balanced. It has been used for a long time as a diaphragm that has been removed. However, this
paper diaphragm also has problems such as poor waterproofness and the fact that the main raw
material is a natural fiber and the change in physical properties due to changes in manufacturing
conditions is large, so the product performance is not stable.
[0004]
On the other hand, a synthetic resin diaphragm is mainly formed by using an injection molding
method, mixing a filler such as mica or carbon fiber with an olefin-based resin such as
polypropylene as a base. Since the diaphragm made of synthetic resin by injection molding has
excellent waterproofness, can be produced with a relatively high elastic modulus and less
variation, it can be said that it is a diaphragm superior to the paper-made diaphragm in these
points. Since the density is high compared to the paper diaphragm, when the weight is reduced
to the same extent as the paper diaphragm, the diaphragm becomes too thin, and there is a
disadvantage that a sufficient bending rigidity can not be obtained.
[0005]
From the above points, in order to obtain an excellent diaphragm for low to mid range and all
bands that can also be used for automotive applications where waterproofing is required, the
paper diaphragm is waterproofed or injection molded. It is necessary to lower the density of the
synthetic resin diaphragm by For waterproofing of paper diaphragms, various methods have
been proposed for filling with resin such as silicone or fluorine, or forming a synthetic resin film
on the diaphragm surface, but the waterproofness is not sufficient. In addition, mass increase,
product variation, cost increase, etc. were all not complete.
[0006]
Further, as a method for lowering the density of a synthetic resin diaphragm by injection
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2
molding, a method of forming cells using a foaming agent and providing a space in the
diaphragm is proposed in JP-A-8-340594. The diaphragm by this method is excellent when the
physical properties (specific bending stiffness etc.) are evaluated as a structure (plate), but as the
diaphragm for an electroacoustic transducer, there exists an independent space by cells,
Furthermore, since the film is thin and the cell system becomes relatively large, the cell resonates
and as a result, the sound quality of the speaker is deteriorated. In addition, when the thin plate
is formed as thin as a diaphragm, the cell diameter varies due to slight variations in forming
conditions, so that the variation in acoustic performance becomes large.
[0007]
The object of the present invention is made in view of the above-mentioned point, and uses a
molding method which makes independent space as small as possible, and enlarges the cavity
volume after injection compression of a structure close to a paper diaphragm (three dimensional
structure by fibers). A diaphragm made of synthetic resin, which is lightweight, has high rigidity,
has a suitable internal loss, is excellent in waterproofness, is excellent in sound quality, and is
also excellent in productivity, and a diaphragm for an electroacoustic transducer, It is in
providing the manufacturing method.
[0008]
[Means for Solving the Problems] In order to achieve the above object, the diaphragm for an
electroacoustic transducer according to the present invention is formed by injection compression
of a resin material in which a synthetic resin and a glass fiber are mixed, and then the cavity
volume is enlarged and molded. In the diaphragm for electro-acoustic transducer, the resin
material is provided with a continuous gap formed by utilizing a reaction force of the glass fiber
when the resin material is expanded.
[0009]
According to the diaphragm for electro-acoustic transducer with this configuration, since there is
a continuous void made of glass fiber and resin inside, the density is lower than that of a normal
synthetic resin diaphragm, and further glass fiber And the resin is firmly bound, so it is
lightweight and highly rigid.
In addition, although the internal foam structure can not be expected to improve the internal loss
due to the ordinary foam structure, the diaphragm for the electroacoustic transducer of the
present invention has a large thermal conversion rate of energy due to the movement of the glass
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3
fiber. The internal loss can be improved compared to the
Furthermore, since a skin layer is formed on the diaphragm surface by the injection compression
molding method, that is, since a skin layer / expansion layer / skin layer is sequentially formed in
the thickness direction, the waterproofness is excellent and the production is stable. It is possible
to obtain a diaphragm for an electroacoustic transducer excellent in quality, and furthermore,
since there is no cell resonance which tends to occur in a foamed product, a high quality sound
quality with little distortion can be obtained.
[0010]
In the above, the average expansion magnification of the whole diaphragm at the time of
expansion of the resin material is 1.1 to 4.0 times, preferably 1.5 to 3.0 times. If the expansion
ratio is less than 1.1 times, the specific elastic modulus is further improved, but the specific
flexural rigidity can not be obtained sufficiently. In addition, when the expansion ratio exceeds
4.0 times, the specific flexural rigidity is further improved, but the specific elastic modulus can
not be sufficiently obtained, and furthermore, a good appearance can not be obtained.
[0011]
Moreover, content of glass fiber is 15 to 70 weight%, Preferably it is 20 to 50 weight%. When the
content of glass fiber is less than 15% by weight, the expansibility, strength, rigidity and heat
resistance are not sufficient, and when the content of glass fiber exceeds 70% by weight, the
fluidity at the time of melting decreases. Expandability, moldability is reduced, and a good
appearance can not be obtained.
[0012]
Moreover, in the diaphragm of the present invention, it is made of a thermoplastic resin
containing 15 to 70% by weight of fibers having a weight average fiber length of 0.5 to 4 mm,
the thickness of the main part is less than 1.2 mm, and the porosity Is preferably 10 to 75%.
[0013]
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The weight reduction of the diaphragm depends on the type and content of fibers contained and
the required properties of the desired molded product, but the porosity (average) is 10 to 75%,
preferably 20 to 60%. It is selected.
If the porosity is less than 10%, the effect of weight reduction is small, and if it exceeds 75%, the
surface smoothness is reduced, and the dense skin layer on the surface becomes thin and weak in
strength. The porosity (%) can be expressed as [(volume of molded product−volume without
void) / volume of molded product] × 100.
[0014]
The weight average glass fiber length in the molded article after molding is in the range of 0.5 to
10 mm, preferably 0.5 to 4 mm. It is advantageous to keep the glass fiber length as long as
possible in terms of strength and springback properties, but for example, in the case of a thin
diaphragm like the diaphragm of the embodiment described later, 0.3 mm before expansion,
expansion Even after that, since it is as thin as 0.6 mm, it is difficult to hold the glass fiber to 10
mm or more, and the appearance is slightly deteriorated. In consideration of strength, springback
property, and appearance, it is preferable to keep it at 4 mm or less. When it is less than 0.5 mm,
it becomes difficult to expand.
[0015]
The method for producing a diaphragm for an electroacoustic transducer according to the
present invention has a glass fiber content of 15 to 70% by weight, the glass fibers are parallel to
each other, and the length is 2 to 100 mm. Glass fiber-containing thermoplastic resin pellet or
glass fiber-containing thermoplastic resin pellet having a glass fiber content of 15 to 90% by
weight, glass fibers parallel to each other, and a length of 2 to 100 mm A mixture containing a
thermoplastic resin other than the thermoplastic resin and melt-kneading a mixture so that the
glass fiber content in the glass fiber-containing thermoplastic resin pellet is 15 to 70% by weight
of the whole, and a mold cavity corresponding to a final molded product The molten resin is
injected into an open mold so as to be larger than the volume, and the mold cavity volume is
equal to the volume of the final molded product just before, immediately after, or at the
completion of the injection of the molten resin. After the molten resin is filled into the mold
cavity by advancing the movable mold to small position, characterized in that retracting the
movable mold to a position corresponding to the volume of the final molded article.
[0016]
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According to the method of manufacturing the diaphragm for an electroacoustic transducer
according to this configuration, the glass fiber-containing thermoplastic resin pellet or the
mixture containing the glass fiber-containing thermoplastic resin pellet is melt-kneaded, and
widely opened in the mold cavity The molten resin is injected, and then the movable mold is
advanced to a position where the mold cavity volume is smaller than the volume of the final
molded product just before, immediately after, or at the completion of the injection of the molten
resin.
Thus, after the molten resin is filled in the mold cavity, the movable mold is retracted to expand
the volume of the mold cavity to a position corresponding to the volume of the final molded
product. Then, the molten thermoplastic resin expands to an enlarged volume due to a spring
back phenomenon due to the entanglement of the contained glass fibers, so that a diaphragm
having a continuous void inside is obtained.
[0017]
Here, as a molding material, the average fiber length of the glass fiber is 2 to 100 mm, preferably
4 to 50 mm, more preferably 5 to 20 mm, having a length equal to the total length, and arranged
parallel to each other Fiber-reinforced thermoplastic resin pellets containing 15 to 90% by
weight, preferably 20 to 80% by weight of glass fibers, wherein the glass fibers are 15 to 70% by
weight, preferably 20 to 50% by weight of the entire molding material Using the molding
material. That is, the fiber-reinforced thermoplastic resin pellet can be used alone or as a mixture
with another thermoplastic resin.
[0018]
If this fiber reinforced thermoplastic resin pellet is used, even if it is plasticized / kneaded with a
screw of an injection device, breakage of the fiber does not easily occur, and the dispersibility
also becomes good. Furthermore, the spring back phenomenon of the molten resin in the cavity
becomes better, the fiber length remaining in the final molded product becomes longer, the
physical properties are improved, and the surface appearance is improved. As a plasticizing
screw of an injection molding machine, the use of a relatively low type having a compression
ratio of 2.3 or less, particularly 2 or less, is preferable from the viewpoint of suppressing fiber
breakage.
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[0019]
Further, as a mold, for example, a mold capable of reducing and expanding the volume (mold
distance) of the mold cavity is used. In this case, the structure is not limited to the structure in
which the entire surface of the cavity is compressed or expanded, and depending on the shape of
the molded product, only the main part may be advanced or retracted. When manufacturing the
diaphragm by reducing and enlarging the volume of the mold cavity, the distance between the
mold cavities of the main part of the mold at the start of resin filling is 0.2 to 10 mm, preferably
3 to 5 mm, It is desirable to use a mold cavity that narrows to 0.1 to 1.1 mm when filled with
resin. Here, the diaphragm may not necessarily be a uniform plate-like molded product, and the
distance between the main parts is within the above range. Further, this mold cavity distance can
be appropriately determined by calculating the target thickness of the diaphragm and the
apparent density.
[0020]
Under the above conditions, the mold temperature is (Tc-50 ° C) to (Tc) based on the
crystallization temperature (Tc) in the case of crystalline resin, or the glass transition
temperature in the case of non-crystalline resin Based on (Tg), it is desirable to carry out molding
under a temperature range of (Tg-50 ° C) to (Tg), and further under a molding condition in
which the injection filling time is in the range of 1 second or less. That is, the mold temperature
is set to a relatively higher temperature than in the case of general molding. The mold
temperature is preferably lower in the case of ordinary molded products from the viewpoint of
cooling efficiency after molding and molding cycle, but in molding of the diaphragm of the
present invention, the mold is relatively high. It is desirable to set the temperature in order to
enhance the expansivity.
[0021]
The crystallization temperature of the crystalline thermoplastic resin can be measured in
accordance with JIS K7121. Specifically, the crystalline thermoplastic resin is heated at a
temperature rising rate of 10 ° C./minute using DSC-7 made by Perkin-Elmer, and kept at 230
° C. for 3 minutes, then 10 ° C./minute It is obtained as a peak temperature when cooled at a
temperature drop rate of The glass transition temperature of the amorphous thermoplastic resin
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can be determined as a known method, for example, a gradient in measurement of the
relationship between specific volume and temperature, that is, a change point of the specific
volume temperature coefficient.
[0022]
The temperature of the mold is, of course, appropriately determined in consideration of other
manufacturing conditions such as the type of molding material, the content of fibers, the melt
flowability, the cavity spacing at the time of injection filling, and the degree of weight reduction.
For example, when a polypropylene resin is used as the thermoplastic resin, the temperature is
75 ° C. to a crystallization temperature (Tc), preferably 80 ° C. to 120 ° C.
[0023]
Next, the injection filling time of the molten resin containing glass fiber into the mold cavity is
not particularly limited, but is 1 second or less, preferably 0.5 seconds or less, more preferably
0.1 second or less. The injection filling time is the time from the start of injection of the molten
resin into the mold cavity to the complete filling of the molten resin in the mold cavity. This time
can be suitably selected by factors such as other various molding conditions as in the case of the
above-mentioned mold temperature. However, if it exceeds 1 second, even if the molding die
temperature is set high, the resin amount is small and it is easy to cool, and the space between
the molding die cavities is very narrow, so the movable die which is the next step In some cases,
the expansion of the mold cavity is not sufficient due to the retraction of the mold cavity, making
it difficult to manufacture a desirable diaphragm.
[0024]
With regard to the flowability of the thermoplastic resin, among conventional injection molding
materials, it is preferable to use a resin having a melt index (MI) of super-better flow grade or
higher. In particular, low molecular weight, super flowable resins can be used in the present
invention, which themselves have low strength and can not be used for injection molding.
Although this MI changes measurement conditions with each thermoplastic resin, MI is 80-800 g
/ 10 minutes, Preferably it is 100-600 g / 10 minutes on the general measurement conditions of
each thermoplastic resin. This MI can be determined from the resin in the fiber-reinforced
thermoplastic resin pellet, the raw resin, and the MI of other pellets.
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[0025]
In the case of a polypropylene resin to which the present invention can preferably be applied, the
MI is specifically 80 to 800 g / 10 min, preferably 100 to 600 g / 10 min, more preferably 200
to 500 g / 10 min. If the MI is less than 80 g / 10 min, the flowability may be reduced, which
may make it difficult to form the diaphragm. If the MI exceeds 800 g / 10 min, the strength of
the diaphragm may be insufficient. In addition, measurement of MI of a polypropylene resin is
the value (following, the same) measured according to JISK7210 (230 degreeC, 2.16 kg load).
[0026]
Here, the ultra-high fluidity polypropylene-based resin used in the present invention is the type,
length, and content of fibers contained, temperature of molding die, cavity spacing during
injection or injection compression, cavity shape, nozzle The MI can be appropriately selected
according to the flow length (area) from (gate), other forming conditions, and the like. In this
case, resins different in MI can also be mixed and used. However, it is not necessary to use an
extremely large MI as long as the formability is satisfied.
[0027]
The synthetic resin to be used in the present invention is not particularly limited. For example,
polypropylene, propylene-ethylene block copolymer, propylene-ethylene random copolymer,
polyolefin resin such as polyethylene, polystyrene, rubber modified impact resistance
Polystyrene, polystyrene resins such as polystyrene having syndiotactic structure, ABS resin,
polyvinyl chloride resin, polyamide resin, polyester resin, polyacetal resin, polycarbonate resin,
polyaromatic ether or thioether resin, poly Thermoplastic resins such as aromatic ester resins,
polysulfone resins and acrylate resins can be employed. Here, although the said thermoplastic
resin can also be used independently, you may use it in combination of 2 or more types.
[0028]
Among such thermoplastic resins, polypropylene-based resins such as polypropylene, block
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copolymers of propylene and other olefins, random copolymers, or a mixture thereof are
preferable. The polypropylene-based resin is preferably a polypropylene-based resin containing
an unsaturated carboxylic acid such as maleic anhydride or fumaric acid, or an acid-modified
polyolefin-based resin modified with a derivative thereof. In addition, other thermoplastic resins
such as high density polyethylene, low density polyethylene, ethylene-α-olefin copolymer resin,
polyamide resin, and impact strength improvement such as ethylene-α-olefin copolymer
elastomer can be used for polypropylene resin. Elastomers can also be formulated.
[0029]
In addition, antioxidants such as phenol, phosphorus and sulfur, light stabilizers, UV absorbers,
weathering agents, crosslinkers, nucleating agents, colorants, short fibers, talc, calcium
carbonate, etc. should be added. You can also. These additives are generally added as other
thermoplastic resins or further additive masterbatches separately from the above-mentioned
fiber-reinforced thermoplastic resin pellets.
[0030]
As glass fiber, it is glass fiber of E-glass or S-glass, Comprising: The thing whose average fiber
diameter is 25 micrometers or less, Preferably the thing of the range of 3-20 micrometers can be
employ | adopted preferably. If the diameter of the glass fiber is less than 3 μm, the glass fiber
does not conform to the resin at the time of production of the glass fiber reinforced pellet, and
impregnation of the resin becomes difficult, but if it exceeds 20 μm, cutting and breakage easily
occur during melt kneading. . 100 to 10,000, preferably 150 to 5,000, of the glass fibers are
surface-treated with a coupling agent for producing pellets by using the thermoplastic resin and
the glass fibers by a pultrusion method or the like. It is desirable to bundle in the range of
[0031]
As a coupling agent, it can select suitably from what is conventionally, as a silane coupling agent
and a titanium coupling agent. In particular, it is preferable to use an amino-based silane
compound.
[0032]
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10
As a convergence agent, a urethane type and an olefin type are employable, for example. It is
preferable that the urethane type focusing agent is generally contained in a proportion of 50% by
weight or more of polyisocyanate obtained by the polyaddition reaction of a diisocyanate
compound and a polyhydric alcohol. On the other hand, a modified polyolefin resin modified with
an unsaturated carboxylic acid or a derivative thereof can be employed as the olefin scavenger.
[0033]
A glass fiber reinforced pellet is manufactured by adhering and impregnating a thermoplastic
resin to the glass fiber converged with the above-mentioned focusing agent. As a method of
attaching and impregnating a thermoplastic resin to glass fiber, for example, a method of passing
a fiber bundle into a molten resin and impregnating the fiber with resin, a method of
impregnating a fiber for coating through a fiber bundle, or For example, a method may be
employed in which the molten resin attached around the fibers is spread and impregnated into
the fiber bundle. Here, in order to make the fiber bundle and the resin fit well, that is, to improve
the wettability, the molten resin is pulled out through the tensioned fiber bundle inside the die
provided with the concavo-convex portion on the inner periphery. Alternatively, after the fiber
bundle is impregnated, a pultrusion method may be employed in which a step of pressing the
fiber bundle with a pressure roller is incorporated. In addition, if the glass fiber and the molten
resin are well compatible with each other and have good wettability, the molten resin is easily
impregnated into the glass fiber and the production of the pellet becomes easy. The process to be
performed may be omitted. Here, as a method of making the resin blend well, it is possible to
impart polarity to the resin, graft a functional group that reacts with the coupling agent on the
surface of the glass fiber, or raise the fiber bundle to the melting temperature of the molten resin
such as liquid paraffin. It is effective to pre-treat with a liquid having a boiling point of
[0034]
When a long fiber bundle (strand etc.) impregnated with resin is cut along the longitudinal
direction of the fiber by the above method, a fiber reinforced resin pellet containing long fibers
having the same length as the entire length of the pellet You can get Under the present
circumstances, as a resin pellet, a fiber bundle is made into a strand, and not only what cut |
disconnected the resin containing long fiber bundle whose cross-sectional shape became
substantially circular shape, a sheet form, a tape by arranging fibers flatly. The resin-containing
long fiber bundle in the shape of a band or a band may be cut into a predetermined length. Thus,
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fiber-reinforced resin pellets are obtained.
[0035]
BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the diaphragm according to
the present invention will be described below with reference to the drawings. (Regarding the
Diaphragm) FIG. 1 is a partial cross-sectional view showing the diaphragm of the present
embodiment. FIG. 2 is a partially enlarged cross-sectional view of FIG. The diaphragm 10 of the
present embodiment includes a cone-shaped diaphragm main body 11 made of synthetic resin,
and a rubber edge 12 attached to the outer periphery of the diaphragm main body 11.
[0036]
The cone-shaped diaphragm main body 11 is formed by expanding a cavity volume after
injection compression of a resin material in which a synthetic resin and a glass fiber are mixed,
that is, by retracting a movable mold, and internally When the material is expanded, a continuous
air gap 13 is formed by utilizing the reaction force of the glass fiber, a skin layer (unexpanded
layer) 14 is formed on the surface, and the thickness of the main portion is 1.2 mm. Less than
formed. Here, the void ratio (rate of the void 13) is adjusted to 10 to 75%. Further, the average
expansion coefficient of the resin material when the movable mold is retracted after the injection
compression is 1.1 to 4.0.
[0037]
As the synthetic resin, various materials described above can be used, but unsaturated carboxylic
acids-modified polyolefin-containing α-olefin resins having an MI of 80 to 800 g / 10 minutes
are preferable. Although the material mentioned above can be used also about glass fiber, the
weight average glass fiber length after shaping | molding is 0.5-4 mm. Further, the content of
glass fiber is 15 to 70% by weight, preferably 20 to 50% by weight of the whole molding
material.
[0038]
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12
According to such a diaphragm, since there is a continuous void 13 composed of glass fiber and
resin inside, the density is lower than that of a normal synthetic resin diaphragm, and further
glass fiber and resin are used. It is lightweight and highly rigid because it is firmly bonded. In the
ordinary foam structure, improvement in internal loss due to foaming can not be expected, but in
the diaphragm of this embodiment, since the thermal conversion rate of energy by the movement
of the glass fiber is large, compared with the unexpanded one. Internal losses can be improved.
Furthermore, since a skin layer is formed on the diaphragm surface by the injection compression
molding method, a diaphragm excellent in waterproofness and excellent in production stability
can be obtained, and a cell which tends to occur in a foamed product Because there is no
resonance of, good sound quality with little distortion can be obtained.
[0039]
(Method of Manufacturing a Vibrating Plate) FIG. 3 is a cross-sectional view of a mold
conceptually showing an embodiment of the method of manufacturing a vibrating plate of the
present embodiment, immediately after the start of injection and filling of molten resin into a
mold cavity. Indicates the state of FIG. 4 shows the condition immediately after completion of
injection filling in which the mold cavity is reduced and the molten resin is compressed and filled.
FIG. 5 shows a state in which the mold cavity is enlarged and the molten resin is expanded to
form a molded product. In FIGS. 3, 4 and 5, 1 is a fixed mold, 2 is a movable mold, 3 is a mold
cavity, 4 is a sprue, 7 is an injection nozzle, 8 is an injection molten resin, and 9 is a diaphragm. .
[0040]
In the manufacture of the diaphragm of the present embodiment, as shown in FIGS. 3 to 5, the
movable mold 2 is advanced and retracted relative to the fixed mold 1 to change the space
(volume) of the mold cavity. It is possible to Although the one shown in FIGS. 3 to 5 shows one in
which the movable mold 2 compresses and enlarges the entire surface of the cavity, depending
on the shape of the molded product, only the main part may be advanced or retracted. The
movable mold can be advanced and retracted independently of the direct-pressure mold opening
/ closing mechanism and the injection molding machine, and can advance and retract the sliding
mold provided between the movable platen and the movable mold or inside the movable mold. It
can be implemented by incorporating a mold moving device.
[0041]
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13
Next, the manufacturing method will be described based on the movement of the mold. In the
case of filling the molten resin by injection compression, as shown in FIG. 3, the fixed mold 1 and
the movable mold 2 are placed in a state where the cavity distance D1 is obtained, and the
molten resin containing glass fiber in this state Start the injection of Thereafter, as shown in FIG.
4, the movable mold 2 is advanced to compress the molten resin and fill the cavity 3
simultaneously with and / or after the start of injection. The injection amount of the molten resin
in this case is a volume corresponding to the cavity interval D2 (D1> D2).
[0042]
The mold incorporates a device (not shown) for controlling the mold temperature of the mold
surface of the mold cavity. As described above, the molding die has an upper limit for each
temperature based on the crystallization temperature (Tc) or glass transition temperature (Tg) of
the thermoplastic resin, and the lower limit is lower by 50 ° C. than each temperature. It is
adjusted to a relatively high temperature which is a temperature range to be taken. In the
method of manufacturing the diaphragm of this embodiment, the mold temperature is set
relatively high because the thickness of the mold cavity is thin.
[0043]
The mold temperature is 70 to 120 ° C., preferably 80 to 115 ° C. when a polypropylene resin
is used. If the mold temperature is less than 70 ° C., unfilled portions of the molten resin may
occur, or expansion may not be uniform. In addition, if the mold temperature is too high, it may
be difficult to cool and demold the molded article. However, in the present embodiment, even if
the mold temperature is relatively high, the rigidity of the molded product is high, and molding
can be performed as well as general molded products.
[0044]
A molten thermoplastic resin containing glass fibers melted, kneaded, plasticized and measured
by a plasticizing device (not shown) to the mold cavity is injected from the injection nozzle 7
through the sprue 4 and the molten resin is melted. It will be eight. Then, the injected molten
resin usually advances the movable mold 2 so that the cavity distance becomes the position of
D2 from before the completion of injection, compresses the molten resin, and fills and fills the
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mold cavity 3.
[0045]
For this purpose, a plasticized, melted and metered molten resin having a volume corresponding
to a cavity distance D2 is injected. The advancing of the movable mold 2 in this case may be
performed by position control or may be controlled by pressure. In the case of pressure control,
it is preferable to leave a clearance when the movable mold 2 advances and compression of the
resin is completed. As a result, even when the volume of the injection resin slightly fluctuates and
runs short, the compressive force of the movable mold acts and the entire cavity can be reliably
filled.
[0046]
In this embodiment, as described above, it is necessary to inject and fill the injection filling at a
relatively high speed of 1 second or less, preferably 0.5 seconds or less, and more preferably 0.1
seconds or less. The injection molding in the mold cavity and compression by the movable mold
ensure that the molten resin transfers the shape of the mold, fine irregularities such as emboss
on the surface of the mold, and the like. The molten resin starts to cool at the contact portion
with the mold. In the present embodiment, at the same time as or after the completion of the
filling of the molten resin, as shown in FIG. 5, the movable mold 2 is moved to the position where
the thickness of the final molded product is D3 (D3> D2). Set back. Due to the backward
movement of the movable mold 2, the glass fiber-containing thermoplastic resin in a molten state
is expanded by a spring back phenomenon due to the entanglement of the contained glass fibers,
and the final molded product is formed. It is pressed against the wall and shaped. That is, a
diaphragm provided with a continuous air gap formed by the reaction force of the glass fiber
inside is obtained.
[0047]
Here, the movable die is preferably retracted after the formation of the surface layer is
completed, depending on the molding conditions, the molding material, and the shape of the
mold although the process of filling the molten resin is completed. That is, when the cooling
progresses and the viscosity of the molten resin becomes high, the expansion of the molten resin
becomes difficult to follow the retraction of the movable mold, and there is a possibility that the
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volume of the final molded product can not be reliably formed. is there.
[0048]
EXAMPLES (1) Preparation of material Glass fiber reinforced polypropylene pellets (Mostrone L)
which were pultrusion molded and cut to a predetermined length (8 mm in this example) and
polypropylene with improved fluidity for thin wall molding (MI = And 500) were dry-blended so
that the glass fiber was 30% by weight of the whole raw material. By using this method, molding
with less fiber breakage is possible, so that in the skin layer, the reinforcing effect of the glass
fiber is increased, and in the core portion, a large springback phenomenon causes a large
expansion phenomenon to occur. Thus, a diaphragm with a high modulus of elasticity and a low
density is obtained.
[0049]
(2) Molding The resin prepared in the above (1) was introduced into an injection compression
molding machine, and a diaphragm was molded in the following procedure. The resin
temperature was 200 ° C., and the mold temperature was 80 ° C. Before injection, the movable
mold was opened by a predetermined amount from the normal mold clamping position (in this
example, 1 mm open), and injection standby was made at that position. The resin is injected at a
speed of about 300 mm / sec while maintaining the open mold position a predetermined amount,
and the movable mold is quickly moved to the normal mold clamping position almost
simultaneously (after about 0.01 seconds) with the end of injection. (About 0.06 seconds),
pressed at a pressure of 50 t (490 kN). The die gap at the completion of pressing was 0.3 mm.
Further, the injection results were injection pressure 480 kg / cm 2 (4704 × 100000 Pa), and
the filling time was 0.04 seconds. Immediately after pressing, the movable mold was quickly
opened by a predetermined amount before the inside of the molded product was solidified, and
the molded product was expanded by the reaction force of the glass fiber. The opening time was
about 0.05 seconds, and the opening amount was 0.36 mm (the product thickness is 0.6 mm).
After cooling for about 8 seconds, the diaphragm was removed from the mold. The molded
product had continuous voids obtained by the expansion of the glass fibers inside, and the both
side surfaces were unexpanded layers (see FIG. 2).
[0050]
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(3) Incorporation into a Speaker and Performance Evaluation A rubber edge was attached to the
diaphragm (diaphragm main body) manufactured in the above (2), incorporated into a speaker,
and frequency-sound pressure characteristics and sound quality were evaluated. For comparison,
a diaphragm that was about twice foamed using an organic blowing agent (ADCA) was used. Of
course, the specifications of the base resin, the diaphragm shape and the speaker were the same
as those of the present invention. [Physical Properties] The two resins were molded into flat
plates having a thickness of 0.6 mm, and the physical properties were measured. The
performance evaluation results are as shown in Table 1 below. From Table 1, the product of the
present invention exhibited physical properties superior to that of the conventional product in all
items.
[0052]
[Sound Pressure-Frequency Characteristic and Sound Quality] The results of measuring the sound
pressure-frequency characteristic and the sound quality of the product of the present invention
and the conventional product are shown in FIGS. 6 and 7. Since the product of the present
invention has higher specific elastic modulus (sound velocity), specific flexural rigidity, and
internal loss compared to conventional products (foamed with organic blowing agent), the high
frequency reproduction limit is extended, and the sound pressure is further increased. The
number of peaks and valleys is also reduced (see FIGS. 6 and 7). In addition, the actual hearing
results were good, and natural sound quality with less distortion was obtained compared to the
conventional products.
[0053]
According to the diaphragm for electro-acoustic transducer of the present invention, since there
is a continuous void made of glass fiber and resin inside, the density is lower than that of a
normal synthetic resin diaphragm. Further, since the glass fiber and the resin are firmly bound,
the weight is light and the rigidity is high. In addition, although the internal foam structure can
not be expected to improve the internal loss due to the ordinary foam structure, the diaphragm
for the electroacoustic transducer of the present invention has a large thermal conversion rate of
energy due to the movement of the glass fiber. The internal loss can be improved compared to
the Furthermore, since a skin layer is formed on the surface of the diaphragm at the time of
injection compression, it is possible to obtain a diaphragm for an electroacoustic transducer
which is excellent in waterproofness and excellent in production stability. Since there is no
resonance of the small cell, a high quality sound with little distortion can be obtained.
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