U.S. patent application number 11/652940 was filed with the patent office on 2007-06-14 for resin-molded component and method for manufacturing thereof as well as diaphragm for loudspeaker.
This patent application is currently assigned to Sony Corporation. Invention is credited to Kunihiko Tokura, Masaru Uryu.
Application Number | 20070132131 11/652940 |
Document ID | / |
Family ID | 33296859 |
Filed Date | 2007-06-14 |
United States Patent
Application |
20070132131 |
Kind Code |
A1 |
Tokura; Kunihiko ; et
al. |
June 14, 2007 |
Resin-molded component and method for manufacturing thereof as well
as diaphragm for loudspeaker
Abstract
A resin-molded component such as a loudspeaker diaphragm, in
which rigidity is enhanced while light weight and high specific
modulus of elasticity are maintained, is formed by applying carbon
dioxide gas with a predetermined pressure to a thermoplastic resin
in which crystallization is facilitated in the resin flowing
direction to fill a mold. After the resin is filled, injection
molding is performed by somewhat moving the mold to form five
layers of: oriented minute-foaming layers, having approximately
cylindrical foams, the length of which is twice the diameter
thereof in the resin flowing direction in the mold, an unfoamed
core layer positioned between both the foaming layers, and unfoamed
skin layers formed on the front and rear surfaces.
Inventors: |
Tokura; Kunihiko; (Tokyo,
JP) ; Uryu; Masaru; (Chiba, JP) |
Correspondence
Address: |
LERNER, DAVID, LITTENBERG,;KRUMHOLZ & MENTLIK
600 SOUTH AVENUE WEST
WESTFIELD
NJ
07090
US
|
Assignee: |
Sony Corporation
Tokyo
JP
|
Family ID: |
33296859 |
Appl. No.: |
11/652940 |
Filed: |
January 12, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10860739 |
Jun 3, 2004 |
|
|
|
11652940 |
Jan 12, 2007 |
|
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Current U.S.
Class: |
264/45.5 ;
264/85 |
Current CPC
Class: |
B32B 27/06 20130101;
Y10T 428/249989 20150401; Y10T 428/1317 20150115; Y10T 428/249981
20150401; B32B 27/32 20130101; B32B 5/18 20130101; Y10T 428/249988
20150401; H04R 7/10 20130101; Y10T 428/13 20150115; Y10T 428/249978
20150401; Y10T 428/249992 20150401; Y10T 428/249991 20150401; B32B
27/065 20130101; B32B 2398/20 20130101; Y10T 428/1376 20150115;
H04R 2307/029 20130101 |
Class at
Publication: |
264/045.5 ;
264/085 |
International
Class: |
B32B 37/00 20060101
B32B037/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 11, 2003 |
JP |
P2003-167006 |
Claims
1. A method for manufacturing a resin-molded component, comprising
the steps of: applying carbon dioxide gas with a predetermined
pressure continuously to a thermoplastic resin, in which
crystallization is facilitated in a resin flowing direction, to
fill a mold, and performing injection molding by moving the mold
after said filling to form a five-layer structure of: a first
foaming layer and a second foaming layer having substantially
cylindrical foams, a length of said foams being twice or more a
diameter thereof in the resin flowing direction in the mold, an
unfoamed core layer positioned between the first foaming layer and
the second foaming layer, and unfoamed skin layers formed as front
and rear surfaces of the component.
2. The method for manufacturing a resin-molded component according
to claim 1, wherein said thermoplastic resin in which
crystallization is facilitated in the resin flowing direction is a
resin material substantially composed of polyolefin composition
containing ultra-high molecular polyolefin.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. application Ser.
No. 10/860,739, filed on Jun. 3, 2004, the disclosure of which is
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention related to a resin-molded component, a
method for manufacturing thereof, and a resin-molded diaphragm used
in a loudspeaker.
[0004] 2. Description of the Related Art
[0005] Conventionally, there has been known a diaphragm for a
loudspeaker, which is composed of a resin-molded component.
Hereupon, in order to expand the piston movement area, a diaphragm
is required to have a large specific modulus E/.rho. (E: elasticity
modulus, .rho.: density) and a large internal loss to obtain a flat
frequency characteristic. Therefore, in the case of a diaphragm
composed of a resin-molded component, in order to improve an
elasticity modulus, a material in which high-modulus fiber or
filler is highly filled in thermoplastic resin having comparatively
large internal loss has been conventionally used through injection
molding or sheet forming. However, due to the increase in the
amount of those additives relative density of materials increases,
which causes the rising of the specific modulus and reduces a resin
streak length in injection molding to makes it difficult to be
thinly loaded. Accordingly, the above described characteristics of
large specific modulus and large internal loss have been limited in
improvement thereof.
[0006] In order to improve the specific modulus, conventionally a
method to reduce the density has been taken. It is known that in a
diaphragm made of a polymeric material, chemical foaming agent is
added to obtain a molded diaphragm. As a result of foaming, light
weight can be realized; however, the diameter of foams becomes
large to considerably decline Young's modulus and improvement in
specific modulus can not be obtained. Moreover, foamed shape is not
uniform so that outer appearance may be unattractive, which is one
of problems. Lately, a foamed diaphragm, in which injection
molding, chemical foaming, and reinforcing fiber are combined, is
proposed.
[0007] On the other hand, with respect to resin-molding technology,
micro cellular technology is lately known as a method for forming a
pored foamed cell, in which supercritical fluid is used to
uniformly disperse the foamed cells with the foaming density of
10.sup.9/cm.sup.2 or more. According to the method, resin-molded
products can be made light in weight without deteriorating the
strength thereof.
[0008] Patent document 1 discloses the art relating to the above
described micro cellular technology.
[0009] Also, Patent document 2 discloses the art relating to the
above described foamed diaphragm in which injection molding,
chemical foaming, and a reinforcing fiber are combined to be
used.
[Patent document 1]
[0010] Japanese Translation of PCT International Application No.
H6-506724
[Patent document 2]
[0011] Japanese Published Patent Application No. H8-340594
[0012] In a foamed diaphragm formed by combining injection molding,
chemical foaming, and a reinforcing fiber, since cells are foamed
longitudinally in the plane thickness direction within a skin layer
of the diaphragm when injection molding is performed, effectiveness
of reinforcing the skin layer is attained. However, each of the
foamed cells has a large diameter such as several hundred .mu.m due
to chemical foaming, so that it is extremely difficult to control
the size thereof and to obtain the state in which the whole plane
is uniformly foamed. In order to compensate the above situation, a
reinforcing fiber is also employed; however, the fiber does not act
to reinforce the inside foaming cells and there remains limits on
improvement in the specific modulus.
[0013] On the other hand, a diaphragm of sheet form obtained by
means of a method employing the micro-cellular technology has been
known, in which a crystalline thermoplastic resin sheet is
impregnated with supercritical carbon dioxide gas to form
simultaneously with pressure release a uniform micro-cellular sheet
of approximately 10 .mu.m. The above diaphragm of sheet form has
uniformity compared to conventional foamed sheet and also has a
superior appearance. However, since a sheet made of a single
material such as polyester resin is used as an unfoamed crystalline
resin, elastic modulus thereof is low compared to materials used
for conventional diaphragms and the elastic modulus is further
deteriorated after foaming. Accordingly, although specific gravity
is small, elastic modulus is greatly declined, which becomes a
problem when used as a diaphragm.
[0014] Further, an injection-molded diaphragm, to which this
technology is applied, is also known. In the case of the
micro-cellular technology, carbon dioxide gas is fed to the inside
of a cylinder of a forming machine in a supercritical condition (at
7.4 MPa or higher pressure, at 31.degree. C. or higher temperature)
to form a solvent resin in which dissolved carbon dioxide is
oversaturated, and simultaneously with the forming in a mold,
pressure is released to cause minute foams. However, when for
example a thin diaphragm is injection-molded, resin tends to
solidify rapidly, so that it becomes extremely difficult to form a
uniformly-foamed body on injection molding as proposed.
[0015] The object of the present invention is to provide a
resin-molded component and a resin-molded loud-speaker diaphragm,
in which the above problems are solved, light-weight is
facilitated, specific modulus is maintained at a high level, and
rigidity is enhanced.
SUMMARY OF THE INVENTION
[0016] In the present invention, carbon dioxide gas is continuously
applied at a predetermined pressure to a thermoplastic resin in
which crystallization is facilitated in the flowing direction of
the resin to fill a mold; and after the resin is filled, the mold
is moved by a certain amount to perform injection-molding by which
are formed five layers of: a first and second foaming layers each
having approximately cylindrical foams, the length of which is
twice or more the diameter thereof in the flowing direction of the
resin in the mold, an unfoamed core layer positioned between both
the foaming layers, and unfoamed skin layers formed on the front
and rear surfaces.
[0017] Accordingly, specific modulus and rigidity are maintained at
higher levels to form a resin-molded component in light weight,
having preferable characteristics when for example used as a
diaphragm of a loud speaker.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a perspective view showing the shape of a
diaphragm according to an embodiment of the present invention;
[0019] FIG. 2 is a sectional view showing a cross section in the
resin flowing direction of a diaphragm according to an embodiment
of the present invention;
[0020] FIG. 3 is a sectional view showing a cross section in the
direction perpendicular to the resin flowing direction of a
diaphragm according to an embodiment of the present invention;
[0021] FIG. 4 is an explanatory view showing an example of the
construction of an injection-molding machine according to an
embodiment of the present invention;
[0022] FIG. 5 is a table showing the measurement results of
physicality with respect to a diaphragm according to the present
invention and the other diaphragms;
[0023] FIG. 6 is a micrograph corresponding to FIG. 2; and
[0024] FIG. 7 is a micrograph corresponding to FIG. 3.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] Hereinafter, an embodiment of the present invention will be
described with reference to FIGS. 1 to 7.
[0026] As an example of a resin-molded component according to the
embodiment, the example in which the present invention is applied
to a diaphragm of a loud speaker is explained. FIG. 1 shows an
example of the shape of the diaphragm of this embodiment. A
diaphragm 100 according to this embodiment is a cone-shape
diaphragm of 110 mm in outer diameter, 30 mm in inner diameter, and
0.30 mm in thickness. When the diaphragm is formed, resin is filled
from a cold gate of the mold disposed at a forming apparatus
through a film gate using a resin injecting portion 101a on a
central portion 101 to uniformly spread over a thin vibrating
portion 102 from the central portion 101a. In this example,
thermoplastic resin in which crystallization is facilitated in the
resin flowing direction is used as a resin to be formed into the
diaphragm 100; and by dissolving carbon dioxide gas when molded, a
foaming layer having minute foaming cells is formed within resin
itself constituting the diaphragm 100. Processing to form the
foaming layer will later be described.
[0027] FIGS. 2 and 3 show the cross sections of the vibrating
portion 102 of the diaphragm 100 shown in FIG. 1. FIG. 2 shows the
cross section in the resin flowing direction, that is, in the X
direction shown in FIG. 1, and FIG. 3 shows the cross section in
the direction perpendicular to the resin flowing direction, that
is, in the Y direction shown in FIG. 1. Further, FIG. 6 is a
micrograph corresponding to FIG. 2 and FIG. 7 is a micrograph
corresponding to FIG. 3. The resin foaming structure of the
vibrating portion 102 has five layers of: an unfoamed core layer 1
formed in the center, oriented minute-foaming layers 2, 3 formed on
both surfaces of the core layer 1, and unfoamed skin layers 4, 5
each positioned outside the oriented minute-foaming layers, and the
whole thickness is approximately 0.1 mm to 1 mm.
[0028] Each of the foaming cells formed in the oriented
minute-foaming layers 2, 3 has a cylindrical-shape of 50 .mu.m or
less in diameter and the length of twice or more the diameter.
Specifically, when the cross section is shown in the X direction,
that is the direction of flowing resin on forming, of FIG. 2, each
of the foaming cells has an elongate shape; and when the cross
section is shown in the Y direction, each of the foaming cells has
an approximately circular shape. The diameter of circular cells
shown in FIG. 3 is 50 .mu.m or less. Numerous foaming cells are
dispersed in the oriented minute foaming portion, which constitutes
50% or less of the whole thickness of the diaphragm. Those foaming
cells exist only in the oriented minute-foaming layers 2, 3, and
are not formed in the core layer 1 and the skin layers 4, 5
similarly containing carbon dioxide gas.
[0029] Hereinafter, the principle of generating foaming cells of
the above cylindrical shape will be described. Conventionally, in
the case where thinly-molded products such as a diaphragm are
manufactured, resin solidifies rapidly, so that even if carbon
dioxide gas is dissolved, resin viscosity sufficient to generate
foams can not be obtained. However, in the case of this embodiment
where thermoplastic resin, in which crystallinity is facilitated in
the resin flowing direction, is used and crystal orientation is
underway on filling the resin, the resin portion is fibrillated to
cause the dissolved carbon dioxide gas to specifically foam in the
resin flowing direction.
[0030] Only such resin materials as capable of forming a crystal
oriented portion when forming a thin product such as a diaphragm
can be selected to use among thermoplastic resin materials in which
crystallinity is facilitated in the resin flowing direction.
Particularly, it is preferable to use polyolefin containing
ultra-high molecular polyolefin or the like, in which a crystal
layer can be easily formed and elastic modulus is largely improved.
Specifically, it is preferable that the resin is mainly made of
polyolefin composition obtained by multistage-polymerization of
ultra-high molecular polyolefin having an intrinsic viscosity of 10
to 40 dl/g in a decalin solution at 135.degree. C. and ultra-high
molecular polyolefin having an intrinsic viscosity of 1 to 5 dl/g
in a decalin solution at 135.degree. C.
[0031] A diaphragm according to this embodiment is formed by an
injection molding method. FIG. 4 shows an outline of an injection
molding apparatus to be used. The injection molding apparatus
having a carbon dioxide gas injecting portion 14 capable of
injecting carbon dioxide gas with pressure provided behind a hopper
taking portion 13 is used, and resin as an ingredient is taken from
a hopper 12 to be heated and melted in a plasticization screw
portion 11. Carbon dioxide gas is injected into the plasticization
screw portion 11 and is infiltrated into resin in a molten state in
a plasticization cylinder 15. At this time, if the pressure of
carbon dioxide supplied from a steel bottle 16 is lower than that
of resin, injection will be difficult. Therefore, while the
pressure of resin is detected, the pressure of gas needs to be
adjusted and injected using a pressurizing pump 17. Although the
pressure is not particularly specified as long as carbon dioxide is
a gaseous body, is in a super-critical state or the like, solvent
power of carbon dioxide gas for the resin needs to be high, so that
the high pressure is preferable. However, more pressure increase
than required will be a cause to generate large blisters on the
surface of formed products, which is unfavorable.
[0032] Since resin at high pressure with carbon dioxide gas
dissolved is injected into molds 18, 19 at a high speed, counter
pressure or the like is given thereto while the molds are closed.
In order to adjust the pressure inside the molds, it is preferable
to have changed the inside pressure into that equivalent to the
injected resin by feeding a pressure-adjusting gas injection
portion 20 with carbon dioxide gas from the pressurizing pump 17,
for example. Hence, it is preferable that the molds be
packing-sealed with rubber or the like so that dissolved carbon
dioxide gas cannot escape from the molds when resin is
injected.
[0033] Further, a mold-clamping mechanism 21 of the injection
molding apparatus uses hydraulic pressure of a direct pressure
type, of an electric driving type or the like and is capable of
releasing the molds to an extent of intended thickness immediately
after the resin is injected so as to control the thickness of
foaming. In this embodiment, the injection molding apparatus is a
high-speed molding apparatus that includes an injecting unit of
adjusted values of maximum injection pressure 2800 kg/cm.sup.2,
maximum injection speed 1500 mm/s, and rate of rise 10 ms.
[0034] Hereinafter, practice examples in which a diaphragm
according to the embodiment of the present invention is formed, and
comparative examples thereof will be explained.
PRACTICE EXAMPLE 1
[0035] Specialized polyolefin resin (brand name: LUBMER.RTM. L3000
manufactured by Mitsui Chemicals) made by multistage-polymerizing
ultra-high molecular polyolefin and other high molecular
polyolefin, which is one of the resin materials in which an
oriented minute-foaming layer is apt to form on injection molding,
was used in a practice example 1. Resin was injected from the
hopper 12 and was heated to 280.degree. C. and melted in the
plasticization screw portion 11; and liquefied carbon dioxide gas
from the steel bottle 16 was pressurized by the pressurizing pump
17 up to 6 Mpa and injected into the plasticization screw portion
11. The molds 18, 19 were filled with resin at a temperature of
80.degree. C. and at an injection speed of 800 mm/s, pressure was
maintained, and then the molds 18, 19 were opened by 0.2 mm to be
cooled and a diaphragm was taken out.
[0036] As a result, a favorable molded product was obtained in
which on the outer appearance skin layers were formed, and the
whole of the diaphragm was uniformly foamed as shown in FIGS. 2 and
3. The thickness of the diaphragm obtained was 0.49 to 0.52 mm that
was approximately similar to the amount of opening of the molds,
and an expansion ratio of approximately 1.7 times was confirmed.
When the diaphragm is cut in the direction perpendicular to the
resin flowing direction and shown, foamed cells of a cylinder shape
are exclusively generated in an oriented minute-foaming layer under
the skin layer and those are not seen in the core layer. Each of
the foamed cells has a cylindrical shape along the resin flowing
direction and the diameter thereof is 50 .mu.m or less. It is
understood that because high-speed thin forming is performed,
crystal orientation is facilitated in this portion.
PRACTICE EXAMPLE 2
[0037] The same resin as used in the practice example 1 was used
for molding, and after resin was filled, molds were opened by the
amount of 0.4 mm to further improve the expansion ratio. The
thickness of the diaphragm obtained was approximately 0.7 mm, and
the shape of foams was similar to those of the practice example
1.
PRACTICE EXAMPLE 3
[0038] The same resin as used in the practice examples 1 and 2 were
used, and after resin was filled, molds were opened by the amount
of 0.6 mm to mold a diaphragm. Though uniformity was not obtained
on the surface of a diaphragm due to generation of a sink, similar
shape to those of practice examples 1 and 2 was obtained with
respect to the state of foams.
[0039] With those results of practice examples 1 to 3, it is
recognized that resin was foamed without exceeding a predetermined
extent even if carbon dioxide gas was dissolved, and a portion
capable of foaming was limited to the oriented minute-foaming
layers 2, 3, which was confirmed when seeing the cross section.
Accordingly, it is understood that when resin is molded 1 mm or
less in thickness, a favorable foaming condition can be obtained on
molding.
COMPARATIVE EXAMPLE 1
[0040] The same resin as that of the practice example 1 was used to
mold a diaphragm without opening the molds after filling the resin.
Although carbon dioxide gas was dissolved in the resin, due to the
thin thickness the resin solidified without any foams
generated.
COMPARATIVE EXAMPLE 2
[0041] General-purpose polypropylene resin (hereinafter called PP)
was used as a material to be filled at a temperature of 240.degree.
C. and at an injection speed of 800 mm/s. Similarly to the practice
example 1, after the resin was filled, molds were opened by the
amount of 0.2 mm and the pressure was released. As a result, the
foaming phenomenon was hardly recognized and the thickness remained
0.3 mm of the initial state; in addition, since the molds were
opened, uniformity could not be obtained with respect to the outer
appearance thereof. In a system in which mica or other inorganic
filler was added to PP, the result was the same as the above, and
foams of carbon dioxide gas dissolved in resin could not be
obtained on thin molding at a high speed and at a high pressure. As
a result, it is understood that when using a general-purpose resin
material in which carbon dioxide gas is dissolved, the foaming
phenomenon can not be recognized in a thinly molded product such as
a diaphragm, because resin tends to solidify rapidly. However, as
shown in the embodiments of the present invention, with respect to
the resin materials in which the fibrillation phenomenon is
observed accompanied by crystalline orientation, the foaming
phenomenon can be facilitated.
COMPARATIVE EXAMPLE 3
[0042] Similar PP to the above comparative examples was prepared,
and a chemical foaming material of 0.1 pts.wt. was dry-blended
therein to mold a diaphragm. A temperature on molding and a
temperature of molds are set to 200.degree. C. and 80.degree. C.,
respectively; and resin is filled and after maintaining the
pressure, the molds were opened by 0.2 mm to generate foams. While
the foaming material generated nitrogen gas by decomposition at a
predetermined temperature, a foamed product of approximately 0.5 mm
was obtained though outer appearance was not favorable. When seen
the cross section thereof, the diameter of foams was 100 .mu.m or
more, which is not small, and the shape was almost spherical to be
randomly arranged by several numbers.
[0043] The measurement results of physical properties of the above
practice examples 1 to 3 and comparative examples 1 and 3 measured
by the vibration reed method are shown in FIG. 5. Samples for the
measurement are prepared by cutting a diaphragm of 7 mm in the
resin flowing direction thereof. Further, rigidity of samples are
compared by regarding an unfoamed state of the comparative example
1 as the reference of rigidity 1.
[0044] According to the measurement results, though each specific
modulus of practice examples 1 to 3 declines as the expansion ratio
(the amount of opening of molds) increases, rigidity thereof
greatly increases. Compared to that, a diaphragm of the comparative
example 3 in which a foaming agent is added to PP has low specific
modulus and low rigidity. Accordingly, when the embodiments of the
present invention are employed, a diaphragm with favorable
properties can be obtained by selecting an appropriate expansion
ratio.
[0045] It should be noted that in the above embodiments
explanations were given to a case in which a loudspeaker diaphragm
was resin-molded; however, it may also possible to perform similar
processing and obtain a minute foaming cell in a uniform state as
shown in FIGS. 2 and 3, when other resin-molded components are
formed.
[0046] According to the present invention, in the state in which a
skin layer and a core layer are uniformly formed over the whole of
a resin-molded component, minute foaming cells can be formed
between the layers to form a oriented minute-foaming layer by the
crystalline orientation in thin molding, so that high rigidity and
high specific modulus can be maintained along with lighter weight
obtained.
[0047] Consequently, when a resin-molded component obtained
according to the present invention is applied to, for example, a
diaphragm for use in a loudspeaker, such effectiveness as high
resonance frequency of a diaphragm, expansion of reproduction
frequency band, and the like can be obtained.
[0048] Having described preferred embodiments of the invention with
reference to the accompanying drawings, it is to be understood that
the invention is not limited to those precise embodiments and that
various changes and modifications could be effected therein by one
skilled in the art without departing from the spirit or scope of
the invention as defined in the appended claims.
* * * * *