U.S. patent application number 11/030960 was filed with the patent office on 2005-07-21 for molded body of thermoplastic resin having sound absorption characteristics.
Invention is credited to Hira, Akinobu, Shinohara, Mitsuru, Shioya, Satoru, Tokoro, Hisao, Yamazaki, Hiroshi.
Application Number | 20050158536 11/030960 |
Document ID | / |
Family ID | 27285957 |
Filed Date | 2005-07-21 |
United States Patent
Application |
20050158536 |
Kind Code |
A1 |
Tokoro, Hisao ; et
al. |
July 21, 2005 |
Molded body of thermoplastic resin having sound absorption
characteristics
Abstract
An expansion-molded article (foamed body) produced by using
foamed and expanded beads, and having open voids has sound
absorbing qualities, and can be used as a sound absorbing material.
However, a sound absorbing material comprising such an
expansion-molded article has been unable to attain a high sound
absorption coefficient in a wide acoustic frequency range. The
invention relates to a molded article produced by using resin
particles, and having sound absorbing qualities. The resin
particles used have through hole(s) and a porosity of 45 to 80% in
a most densely packed state. The void content of the molded article
is 10 to 60%, and the bulk density thereof is 0.01 to 0.6
g/cm.sup.3. The molded article has not less than 3 continuous
center frequency measuring points at which the sound absorption
coefficient is at least 70%, and not less than 7 continuous center
frequency measuring points at which the sound absorption
coefficient is at least 50% in the sound absorption coefficients at
the center frequencies of 250, 315, 400, 500, 630, 800, 1000, 1250,
1600, 2000, 2500 and 3150 (Hz) as determined by the measuring
method of reverberant absorption coefficient prescribed in JIS A
1409.
Inventors: |
Tokoro, Hisao;
(Utsunomiya-shi, JP) ; Yamazaki, Hiroshi;
(Kawasaki-shi, JP) ; Shioya, Satoru; (Kawachi-gun,
JP) ; Shinohara, Mitsuru; (Utsunomiya-shi, JP)
; Hira, Akinobu; (Utsunomiya-shi, JP) |
Correspondence
Address: |
SHERMAN & SHALLOWAY
415 NORTH ALFRED STREET
ALEXANDRIA
VA
22314
US
|
Family ID: |
27285957 |
Appl. No.: |
11/030960 |
Filed: |
January 10, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11030960 |
Jan 10, 2005 |
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10153649 |
May 24, 2002 |
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10153649 |
May 24, 2002 |
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09381172 |
Sep 17, 1999 |
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09381172 |
Sep 17, 1999 |
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PCT/JP98/01480 |
Mar 31, 1998 |
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Current U.S.
Class: |
428/316.6 ;
428/313.5; 428/318.4; 428/319.3; 428/319.7 |
Current CPC
Class: |
B32B 27/08 20130101;
G10K 11/16 20130101; Y10T 428/249981 20150401; B32B 27/32 20130101;
B32B 5/18 20130101; Y10T 428/249953 20150401; Y10T 428/249992
20150401; Y10T 428/249972 20150401; Y10T 428/249991 20150401; B29K
2995/0002 20130101; Y10T 428/249971 20150401; B29C 44/445 20130101;
Y10T 428/249987 20150401 |
Class at
Publication: |
428/316.6 ;
428/319.3; 428/319.7; 428/318.4; 428/313.5 |
International
Class: |
B32B 003/26 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 1, 1997 |
JP |
9-98152/1997 |
Jan 26, 1998 |
JP |
10-27811/1998 |
Claims
1-8. (canceled)
9. A sound absorbing structure of a vehicle comprising a sound
absorbing material composed of an expansion-molded article and a
skin material, incorporated into an interior material of the
vehicle, wherein the expansion-molded article being obtained by
fusing and mutually bonding small resin pieces of foamed
thermoplastic resin, and having continuous void with a void content
of about 25 to 60%, wherein the skin material is bonded or
laminated on the surface of the expansion-molded article.
10. A sound absorbing structure of a vehicle comprising a sound
absorbing material composed of an expansion-molded article and a
skin material, incorporated into an interior material of the
vehicle, wherein the expansion-molded article being obtained by
fusing and mutually bonding small resin pieces of foamed
thermoplastic resin, and having continuous void with a void content
of about 25 to 60%, wherein the skin material is bonded or
laminated on the surface of the expansion-molded article, wherein
the small resin piece has through hole(s), and wherein a ratio
(L)/(D) of the maximum length (L) of the small resin piece in
direction along the hole to the maximum diameter (D) of the small
resin piece at the section perpendicular to direction along the
hole is 0.7 to 1.2.
11. A sound absorbing structure of a vehicle according to claim 9,
wherein the skin material is woven fabric or non-woven fabric.
12. A sound absorbing structure of a vehicle according to claim 9,
wherein the skin material is synthetic resin sheet.
13. A sound absorbing structure of a vehicle according to claim 9,
wherein the skin material comprises a single-layer structure.
14. A sound absorbing structure of a vehicle according to claim 9,
wherein the skin material comprises a multi-layer structure having
foamed layer.
15. A sound absorbing structure of a vehicle according to claim 10,
wherein the skin material is woven fabric or non-woven fabric.
16. A sound absorbing structure of a vehicle according to claim 10,
wherein the skin material is synthetic resin sheet.
17. A sound absorbing structure of a vehicle according to claim 10,
wherein the skin material comprises a single-layer structure.
18. A sound absorbing structure of a vehicle according to claim 10,
wherein the skin material comprises a multi-layer structure having
foamed layer.
Description
TECHNICAL FIELD
[0001] The present invention relates to a molded body (molded
article) of a resin, which has open voids and good sound absorbing
qualities in a wide frequency range, and possesses sound absorbing
qualities useful for floor backing materials, wall backing
materials and core materials thereof, automotive interior
materials, or the like.
BACKGROUND ART
[0002] The conventional sound absorbing material is generally
produced by forming an iron plate or the like into a box, providing
openings for conducting sound absorption in the front surface
thereof and containing glass wool therein. However, a sound
absorbing and insulating panel of this kind has such drawbacks that
(i) its weight is heavy and hence very difficult to install,
[0003] (ii) glass wool used as a sound absorbing material has no
water resistance, (iii) it is difficult to fabricate it without
using other parts and the like, and its installation becomes
large-scale, and (iv) reinforcing members as a sound absorbing
member, a sound insulating member and a panel are different from
one another, and so the cost, weight and production man-hour
thereof increase.
[0004] Japanese Patent Application Laid-Open Nos. 137063/1995 and
108441/1996 describe the fact that expansion-molded articles with
open voids obtained by molding foamed particles of a specific shape
have sound absorbing qualities. These publications describe the
expansion-molded articles as having excellent sound absorbing
qualities, but this only means that the molded articles have
excellent sound absorbing qualities in a narrow acoustic frequency
range of specific wavelengths. Therefore, the publications have not
taken achievement of an excellent sound absorption coefficient in a
wide acoustic frequency range into consideration.
[0005] It is an object of the present invention to provide a molded
article of a thermoplastic resin having excellent sound absorbing
qualities in a wide frequency range.
[0006] Another object of the present invention is to provide a
molded article of a thermoplastic resin, which has open voids and
is excellent in air permeability in addition to sound absorbing
qualities.
[0007] A further object of the present invention is to provide a
molded article of a thermoplastic resin, which is excellent not
only in sound absorbing qualities, but also in air permeability and
heat insulating property.
DISCLOSURE OF THE INVENTION
[0008] According to the present invention, there is thus provided a
molded article obtained by bonding small resin pieces composed of a
thermoplastic resin to one another so as to form open voids.
Examples of the form of the small resin pieces include particles,
chips, crushed products, etc. In the present invention, one of
these or a mixture thereof is used. The void content of the molded
article according to the present invention is 10 to 60%, and the
bulk density thereof is 0.01 to 0.6 g/cm.sup.3.
[0009] The small resin pieces in the present invention are
preferably of a structure having through hole(s) or non-through
hole(s), particularly a structure having through hole(s). However,
the present invention is not always limited to those of the
structure having such hole(s). The small resin pieces may be in
various shapes. However, the small resin pieces are selected so as
to give a porosity of 45 to 80% in a most densely packed state.
When the small resin pieces are not of the structure having the
hole(s), the porosity is defined as a proportion, in terms of
percentage, of a volume occupied by the space portion given by
spaces among the small resin pieces to the apparent volume of the
small resin pieces in a most densely packed state. When the small
resin pieces are of the structure having the hole(s) on the other
hand, a volume occupied by the spaces of the holes is also
calculated as the porosity. Therefore, the porosity of this case is
defined as a proportion, in terms of percentage, of a volume
occupied by the total space portion of a space portion given by
spaces among the small resin pieces and a space portion given by
the spaces of the holes in the small resin pieces to the apparent
volume of the small resin pieces in a most densely packed
state.
[0010] In the present invention, the porosity of the small resin
pieces is 45 to 80%.
[0011] Incidentally, the reason why the void content of the molded
article may be lower than the porosity of the small resin pieces in
some cases when both of the porosity and the void content are
compared with each other is that a part of the small pieces is
melted, and the small pieces may be expanded in some cases when the
small pieces are bonded to one another to obtain a molded article.
The molded article according to the present invention features that
it has not less than 3 continuous center frequency measuring points
at which the sound absorption coefficient is at least 70%, and not
less than 7 continuous center frequency measuring points at which
the sound absorption coefficient is at least 50% in the sound
absorption coefficients at the center frequencies of 250, 315, 400,
500, 630, 800, 1000, 1250, 1600, 2000, 2500 and 3150 (Hz) as
determined by the measuring method of reverberant absorption
coefficient prescribed in JIS A 1409.
[0012] In the present invention, the small resin pieces are
preferably in the form of particles having through-hole(s). In this
case, a ratio (L)/(D) of the maximum length (L) of the through hole
in a direction along the hole thereof to the maximum diameter (D)
of the small piece at the section perpendicular to the direction
along the hole is preferably 0.7 to 1.2.
[0013] In the present invention, a polyolefin resin is preferred as
the thermoplastic resin, and the small resin pieces are preferably
formed from an expandable resin. The present invention includes the
constitution that a molded article is bonded to a skin material. In
general, the molded article and the skin material are bonded to
each other by presetting the skin material in a mold, filling a
number of the small resin pieces into the mold and heating the
small pieces, thereby producing a molded article.
[0014] In the present invention, the small resin pieces having a
porosity of 45 to 80% formed of a thermoplastic resin are used as a
material and bonded to one another so as to form open voids,
thereby forming a molded article. The void content of the molded
article is 10 to 60%, and the bulk density thereof is 0.01 to 0.6
g/cm.sup.3. The molded article according to the present invention
becomes excellent in sound absorbing qualities in a wide frequency
range making such structural features a premise condition. Its
sound absorption coefficient is greatly improved compared with the
expansion-molded articles having mere open voids.
[0015] As described above, the molded article according to the
present invention has excellent sound absorbing qualities, can
exhibit a sufficient function even in the form of a simple material
in an application field of sound absorption and sound insulation
and moreover can be applied to other wide uses such as combinations
with other sound absorbing materials. The molded article according
to the present invention can be produced by a molding process
comprising filling the small resin pieces into a mold and heating
them, thereby integrally fusion-bonding the small resin pieces to
one another.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 illustrates embodiments as to vertical sectional
forms of resin particles used in the molded articles according to
the present invention;
[0017] FIG. 2 illustrates other embodiments as to vertical
sectional forms of resin particles used in the present
invention;
[0018] FIG. 3 illustrates specific forms of resin particles used in
the present invention;
[0019] FIG. 4 diagrammatically illustrates the relationships
between frequency and sound absorption coefficient in the molded
articles of resin particles obtained in Examples 1, 5 and 6 and
Comparative Examples 1 and 2; and
[0020] FIG. 5 diagrammatically illustrates the relationships
between frequency and sound absorption coefficient in the molded
articles of resin particles obtained in Examples 2 to 4.
BEST MODE FOR CARRYING OUT THE INVENTION
[0021] The present invention will hereinafter be described n
detail.
[0022] The term "small resin pieces" as used in the present
invention means small pieces composed of a thermoplastic resin and
having an optional form such as particles, chips or a crushed
product obtained by crushing molded articles. In the present
invention, one of the particles, chips, crushed product and the
like may be chosen for use, or a mixture of two or more of these
small resin pieces may be used.
[0023] The small resin pieces used in the present invention may be
either a foamed body or an unfoamed body.
[0024] With respect to a case where the small resin pieces are in
the form of particles, i.e., resin particles, the present invention
will hereinafter be described. However, it goes without saying that
the following description applies to cases where the small resin
pieces are in the forms of other chips, crushed product and the
like than the particles. When the resin particles are unfoamed
particles, they are preferably in the form of hollow particles or
of a structure having through hole(s). When the resin particles are
foamed particles on the other hand, they are preferably of a
structure having through hole(s).
[0025] Specific examples of the structure of the resin particles
include a cylinder of L/D<2, a column or cylinder of
L/D.gtoreq.2, a polygonal prism or cylinder of L/D.gtoreq.2.5, a
prism having a cruciform section, etc. Spheres having a through
hole may also be applied to the present invention. In order to
obtain foamed particles of such a desired form in particular, there
may be mentioned (1) a process in which particles of a base resin
for foamed particles are provided and then expanded, and (2) a
process in which the base resin is extruded and at the same time
expanded. In either the foamed particles or the unfoamed particles,
the resin particles can be provided in the desired form by
selecting the form of a die orifice of an extruder.
[0026] The void content of the molded article of the resin
particles according to the present invention is 10 to 60%. The void
content A (%) of the molded article of the resin particles having
open voids is calculated in accordance with the following
equation:
A(%)=[(B-C)/B].times.100
[0027] wherein B is the apparent volume (cm.sup.3) of the molded
article of the resin particles, and C is the true volume (cm.sup.3)
of the molded article of the resin particles. The apparent volume B
is a volume calculated out from the outside dimensions of the
molded article, and the true volume C is a volume of the molded
article found from an increased volume determined by sinking the
molded article into a graduated cylinder containing alcohol.
[0028] If the void content is lower than 10%, the viscous friction
of air becomes hard to occur because such a molded article has an
air layer too little to convert sound energy into thermal energy
and vibration energy within the molded article, and so the molded
article has no air layer sufficient to propagate sound wave through
the interior of the molded article. Therefore, the molded article
undergoes lowering in sound absorption coefficient. If the void
content exceeds 60% on the other hand, sound wave penetrates into
the interior of such a molded article without resistance, and so
the contact of the sound wave with the wall surfaces of the resin
particles becomes hard to occur, whereby the propagation of energy
to the resin composition becomes hard to occur to make it difficult
to cause the attenuation of the sound energy. The molded article
can exhibit a function as a sound absorbing material so far as the
void content thereof is within a range of 10 to 60%.
[0029] The void content of the molded article having open voids
according to the present invention is preferably 25 to 50% in view
of sound absorbing qualities and stability to formation of open
voids.
[0030] The bulk density of the molded article of the resin
particles according to the present invention is 0.01 to 0.6
g/cm.sup.3. The bulk density is a value determined by dividing the
weight M (g) of the molded article of the resin particles by the
apparent volume V (cm.sup.3) thereof. The apparent volume is a
volume calculated out from the outside dimensions of the molded
article. If the bulk density is lower than 0.01 g/cm.sup.3, the
compression characteristics of such a molded article becomes poor,
and the molded article tends to become incapable of satisfying the
conditions of hole diameter, which will be described subsequently.
If the bulk density exceeds 0.6 g/cm.sup.3 on the other hand, the
weight of such a molded article becomes heavy, and moreover the
molded article involves a problem that it is difficult to become a
molded article which satisfies the above-described conditions of
void content. It is hence not preferable for the molded article to
have such a low or high bulk density.
[0031] The above-described bulk-density is preferably 0.03 to 0.09
g/cm.sup.3 from the viewpoints of the provision of a molded article
having high compressive strength and light weight, and
profitability.
[0032] In the present invention, the sound absorption coefficient
means the reverberant absorption coefficient prescribed in JIS A
1409 and measured at 250 to 3150 Hz in 1/3-octave band frequencies
based on 1000 Hz (incidentally, the measurement is conducted by
determining the area of a sample as 9.72 m.sup.2 of 3.6 m long and
2.7 m broad and arranging it on a floor surface in the center of a
reverberation chamber under conditions of room temperature,
25.degree. C. and 70% relative humidity at Tokyo Metropolitan
Industrial Technology Research Institute). In the present
invention, the molded article has not less than 3 continuous center
frequency measuring points at which the sound absorption
coefficient is at least 70%, and not less than 7 continuous center
frequency measuring points at which the sound absorption
coefficient is at least 50%. It is preferred that said at least 3
continuous center frequency measuring pints at which the sound
absorption coefficient is at least 70% should be included in said
at least 7 continuous center frequency measuring points at which
the sound absorption coefficient is at least 50%. The measurement
of the reverberant absorption coefficient will now be described in
detail. In the present invention, the sound absorption coefficient
is determined at measuring frequencies of the following center
frequencies: 250, 315, 400, 500, 630, 800, 1000, 1250, 1600, 2000,
2500 and 3150 (Hz) by the measuring method of reverberant
absorption coefficient prescribed in JIS A 1409. The molded article
according to the present invention exhibits a sound absorption
coefficient of at least 70% at not less than 3 continuous pints (at
least 3 continuous points of, for example, 630, 800 and 1000 (Hz)
or 315, 400, 500 and 630) in the above-described measuring
frequencies (Hz) and a sound absorption coefficient of at least 50%
at not less than 7 continuous pints in the above-described
measuring frequencies (Hz).
[0033] Molded articles having a sound absorption coefficient
outside the above range according to the present invention can only
exhibit an action as a sound absorbing material the sound absorbing
region of which is within a specific frequency range, and are hence
unfit to use them as sound absorbing materials for an anti-noise
policy.
[0034] In the present invention, no particular limitation is
imposed on the form of the molded article so far as it satisfies
the above-described void content, bulk density and sound absorption
coefficient. However, the resin particles as a component of the
molded article preferably have through hole(s).
[0035] In a molded article obtained by using resin particles having
no through hole, the weight thereof is liable to be too heavy when
the resin particles are unfoamed particles. When the resin
particles are foamed particles having no through hole, it is
necessary to set molding and heating conditions low in order to
control their secondary expandability. When do so, however, fusion
bonding strength among the foamed particles becomes low. Therefore,
it is necessary to set the fusion bonding strength among the foamed
particles high. When do so, however, portions to become voids are
also filled in by secondary expansion, resulting in a failure to
attain a sufficient void content. As described above, the range of
the molding conditions under which a good molded article satisfying
both void content and fusion bonding strength among foamed
particles at the same time can be provided is limited, and so it is
difficult to stably provide a molded article having the desired
void content. In the form of the above-described resin particles
having no through hole, further, the size of voids formed among the
particles tends to vary, and it is difficult to uniformly fill them
into a mold, and so a filling density varies every time the resin
particles are filled. Therefore, it is difficult to control the
void content of the resulting molded article. In addition, it is
also difficult to make the void content of the molded article
uniform to a certain extent at all positions.
[0036] As the hole diameter of the through hole in each resin
particle is smaller, or the void content of the resulting molded
article is higher, the molded article can be provided as a molded
article further excellent in sound absorption coefficient even when
its thickness is small. As the hole diameter of the through hole in
each resin particle is greater, or the void content of the
resulting molded article is lower, the molded article cannot be
provided as a molded article excellent in sound absorption
coefficient unless its thickness is made great.
[0037] In the present invention, besides the void content and bulk
density of the molded article, the porosity of the resin particles
in a most densely packed state also has an important meaning. The
porosity D (%) of the resin particles in a most densely packed
state is determined in accordance with the following equation:
D(%)=[(E-F)/E].times.100
[0038] wherein E is the apparent volume (cm.sup.3) of the resin
particles, and F is the true volume (cm.sup.3) of the resin
particles. The apparent volume E is a volume of a certain amount of
the resin particles, which is found from read by a graduated
cylinder when placing the resin particles in the most densely
packed state in the empty graduated cylinder. The true volume is a
volume of a certain amount of the resin particles, which is found
from an increased volume determined by sinking the resin particles
into a graduated cylinder containing alcohol.
[0039] The porosity in the present invention must be 45 to 80%,
preferably 50 to 70%. If the porosity is lower than 45%, the
intended void content cannot be attained in the resulting molded
article. If the porosity exceeds 80% on the other hand, the sound
absorption coefficient of the resulting molded article is lowered.
It is hence not preferable to use any resin particles having a
porosity outside the above range. When the resin particles are too
small or great, the requirements of the present invention as to the
void content cannot be satisfied. When the size of the resin
particles which satisfy the requirements of the present invention
as to the void content is expressed in terms of the weight, its
average weight amounts to 1 to 8 mg per resin particle.
[0040] When the average value of hole diameters of through holes in
the resin particles used for forming a molded article is expressed
as d, d is preferably 0.5 to 3.0 mm. If d exceeds 3.0 mm, the hole
diameter is great, the opening of the hole is wide, and the contact
portion of the wall surface sufficient for the material itself to
absorb sound energy is small, so that it is difficult to attain an
excellent sound absorption coefficient in a wide frequency range
when the material is thin-wall. If d is smaller than 0.5 mm on the
other hand, the productivity of the resin particles is
deteriorated.
[0041] The term "hole diameter" as used in the present invention
means the maximum inner diameter of the hole in sections
perpendicular to the direction of the hole in the resin particle.
FIG. 1 illustrates various forms of resin particle 1 having through
hole(s) and shows the sectional forms of the resin particles 1.
Examples of the sectional forms thereof include (a) a hollow circle
(doughnut form), (b) a hollow triangle, (c) a hollow hexagon, (d) a
form that a hollow circle is divided by a partition, (e) a form
that 2 hollow circles are arranged side by side, (f) a form that 3
hollow circles are arranged in contact with one another, (g) a
hollow circle partially having a discontinuity, (h) a hollow square
partially having a discontinuity, and (i) an indeterminate
form.
[0042] With respect to the form of the resin particles, resin
particles in which 3 to 8 branch-like projections are provided on
the peripheral surfaces of the resin particles of the
above-described structures having through hole(s), i.e., the
cylindrical structures are one of the preferred embodiments.
Examples of such forms include those always having a fixed form in
any section perpendicular to the prescribed direction as
illustrated in FIG. 2, said sectional form being (j) a hollow
circle 2 having 3 branch-like projections 3 at equally divided
positions on the peripheral surface thereof, (k) a hollow triangle
4 having 3 branch-like projections 3 at equally divided positions
on the peripheral surface thereof, (l) a hollow square 5 having 4
branch-like projections 3 at equally divided positions on the
peripheral surface thereof, (m) a hollow circle 2 having 6
branch-like projections 3 on the peripheral surface thereof, or (n)
a hollow triangle 4 having 6 branch-like projections 3 on the
peripheral surface thereof.
[0043] As embodiments of the above-described resin particles, may
be mentioned the forms illustrated in, for example, FIG. 3(o) to
FIG. 3(t).
[0044] More specifically, they are such that as illustrated in FIG.
3(o) and FIG. 3(t), any section perpendicular to the direction of
the through hole has a substantially fixed structure as illustrated
in FIG. 1(a) and FIG. 1(b), and the particle is of a straight form;
as illustrated in FIG. 3(p), the section perpendicular to the
direction of the through hole exhibits an indeterminate form as
illustrated in FIG. 1(i); as illustrated in FIG. 3(q), a plurality
of such resin particles as shown in FIG. 3(o) are combined with
each other; as illustrated in FIG. 3(r), the resin particle having
a through hole inclines; and as illustrated in FIG. 3(s), the hole
diameter of the through hole in the resin particle varies with the
section perpendicular to the direction of the through hole.
[0045] A reference character d' indicates a hole diameter of a
through hole in a resin particle, and the average value of d' is
defined as the average value d of the hole diameters. When a resin
particle has at least 2 through holes, d is determined on the basis
of the hole diameter d' of each through hole [see FIG. 3(q)]. When
the inner diameter of the through hole varies, the length of the
longest part thereof is defined as the hole diameter d' [see FIG.
3(s)]. In the case of the indeterminate form, the length of the
longest line connecting the corresponding points of the through
hole without being interrupted by a projection within the through
hole is defined as the hole diameter d' of the through hole [see
FIG. 3(p)]. Examples of the measuring points are illustrated in
FIG. 3.
[0046] When the resin particles are in the form of a cylinder,
directional property can be given to the cylindrical resin
particles by controlling air pressure upon filling the resin
particles into a mold, so that the void content, particularly, the
directional property of open voids can be controlled to some
extent.
[0047] In a resin particle always having a fixed form in any
section perpendicular to the prescribed direction, the L/D value
thereof is value obtained by dividing the maximum length (L) of the
particle in the direction perpendicular to the maximum diameter (D)
in the section of the body thereof by the maximum diameter (D). In
the case of the resin particles having through hole(s) in
particular, the L/D value is a value obtained by dividing the
maximum length (L) of the through hole by the maximum diameter (D)
in the section perpendicular to (L) (see FIG. 3). In the case where
the resin particles are in the form of, for example, a cylinder, L
and D correspond to the height and outer diameter of the cylinder,
respectively.
[0048] In the present invention, the above-described forms of the
resin particles are suitably selected, whereby a molded article
having various interior void structures can be obtained.
Incidentally, all the above-illustrated resin particles always have
a fixed form in any section perpendicular to the prescribed
direction. However, the resin particles used in the present
invention are not limited to these particles. Those the sectional
form of which is not fixed may be used. A preferred range of L/D is
0.2 to 7.0.
[0049] In the present invention, the L/D of the resin particles
having through hole(s) is preferably controlled to 0.7 to 1.2. By
controlling the L/D in this manner, the opening area of the
resulting molded article, on which sound wave is incident, becomes
wide, and the prescribed void content is attained, so that the
molded article becomes excellent in sound absorbing qualities.
[0050] As means for producing the resin particles, resin particles
in the form of a pellet are produced by, for example, a means in
which a base resin is melted and kneaded in an extruder, the melt
is then extruded into a strand, and the strand is cooled and then
chopped into the prescribed lengths, or the strand is chopped into
the prescribed lengths and then cooled. In the case where foamed
resin particles are provided, there may be used a means in which
the above resin particles are dispersed in a dispersion medium in
the presence of a foaming agent in a closed vessel to heat the
resultant dispersion to a temperature not lower than a temperature
at which the resin particles are softened, thereby impregnating the
resin particles with the foaming agent, and the vessel is then
opened at one end thereof so as to release the resin particles and
the dispersion medium at the same time into an atmosphere of a
pressure lower than the internal pressure of the vessel (usually,
under atmospheric pressure) while maintaining the internal pressure
of the vessel higher than the vapor pressure of the foaming agent,
thereby expanding the resin particles.
[0051] When the foamed particles are provided as described above,
there may be used, for example, a process in which particles of a
base resin, to which an inorganic substance such as talc, calcium
carbonate, borax, aluminum hydroxide or zinc borate has been added,
are placed together with a volatile foaming agent and/or an
inorganic gas type foaming agent in a closed vessel, the resin
particles and foaming agent are dispersed in a dispersion medium in
the closed vessel, the resultant dispersion is heated to a
temperature not lower than the softening temperature of the resin
particles, thereby impregnating the resin particles with the
foaming agent, and the vessel is then opened at one end thereof so
as to release the resin particles and the dispersion medium at the
same time into an atmosphere of a pressure lower than the internal
pressure of the vessel, thereby obtaining the foamed particles.
[0052] No limitation is imposed on the dispersion medium used in
dispersing the resin particles therein so far as it does not
dissolve the resin particles. Examples of such a dispersion medium
include water, ethylene glycol, glycerol, methanol and ethanol.
Water is generally used.
[0053] Further, an anti-fusing agent may be used for the prevention
of fusion bonding among the resin particles when the resin
particles are dispersed in the dispersion medium to heat the
resultant dispersion to a foaming temperature. Any anti-fusing
agent may be used as such an anti-fusing agent, irrespective of
inorganic or organic agent so far as it neither dissolves in water
or the like nor melts upon the heating. However, inorganic
anti-fusing agents are generally preferred. Preferable examples of
the inorganic anti-fusing agents include powders of kaolin, talc,
mica, aluminum oxide, titanium oxide, aluminum hydroxide and the
like. Besides, an anionic surfactant such as sodium
dodecylbenzenesulfonate or sodium oleate may be suitably used as a
dispersion aid. The average particle size of the anti-fusing agent
is preferably 0.001 to 100 .mu.m, particularly, 0.001 to 30 .mu.m.
In general, the amount of the anti-fusing agent to be added is
preferably 0.01 to 10 parts by weight per 100 parts by weight of
the resin particles. It is also preferable to add the surfactant in
a proportion of generally 0.001 to 5 parts by weight per 100 parts
by weight of the resin particles.
[0054] Examples of the foaming agent used generally include
volatile foaming agents such as propane, butane, hexane,
cyclobutane, cyclohexane, trichlorofluoromethane,
dichlorodifluoromethane, chlorofluoromethane, trifluoromethane,
1,2,2,2-tetrafluoroethane, 1-chloro-1,1-difluoroethane,
1,1-difluoroethane and 1-chloro-1,2,2,2-tetrafluoroethane, and
inorganic gas type foaming agents such as nitrogen, carbon dioxide,
argon and air. Of these, inorganic gas type foaming agents which
causes no ozonosphere destruction and is cheap are preferred, with
nitrogen, air and carbon dioxide being particularly preferred. The
amount of the foaming agents other than nitrogen and air to be used
is generally 2 to 50 parts by weight per 100 parts by weight of the
resin particles. When nitrogen or air is used as the foaming agent,
the amount used is such that it is introduced into a closed vessel
under a pressure within a pressure range of 5 to 60 kgf/cm.sup.2G.
The amount of these foaming agents to be used is suitably
controlled according to the relationship between the bulk density
of the foamed particles to be obtained and a foaming temperature,
or between the bulk density and a quantity of heat of fusion of the
foamed particles at a high-temperature peak. The quantity of heat
of fusion at the high-temperature peak is controlled by a foaming
temperature, a heating rate to the foaming temperature, and holding
time in the vicinity of the foaming temperature. The quantity of
heat of fusion at the high-temperature peak is preferably within a
range of 10 to 25 J/g. Incidentally, the quantity of heat of fusion
at the high-temperature peak is reflected by the heat history upon
the production of the foamed particles and is a quantity of heat
corresponding to an area of a portion surrounded by a base line
obtained by connecting points corresponding to 80.degree. C. and a
melting completion temperature on a DSC curve obtained by
differential scanning calorimetry by a straight line, a DSC curve
portion indicating a peak on a higher temperature side, and a line
drawn down to the base line in such a manner that it passes through
a peak of a valley between the peak on the higher temperature side
and a peak on a lower temperature side and crosses at right angles
with the axis of abscissa on the graph, which indicates
temperature.
[0055] The resin particles may be colored by adding a color pigment
or dye of, for example, a black, gray or brown color to a base
resin. When colored foamed particles obtained from the colored base
resin are used, a colored molded article of the resin particles can
be obtained. The color of the color pigment or dye may be suitably
selected from yellow, red, pink, green, blue, etc. in addition to
the colors exemplified above according to the use application of
the resulting molded article.
[0056] When an additive such as the color pigment or dye, or the
inorganic substance is added to the base resin, the additive may be
directly incorporated into the base resin. In general, it is
however preferable to prepare a masterbatch containing the additive
in consideration of the dispersibility and the like of the additive
and then knead this masterbatch with a base resin. The amount of
the color pigment or dye to be added may vary according to the kind
and density of a color to be colored. However, it is preferably
added in a proportion of generally 0.001 to 5 parts by weight per
100 parts by weight of the base resin. When the resin particles are
expanded into foamed particles, the addition of the inorganic
substance in the amount described above brings about the effects of
enhancing the expansion ratio of the resulting foamed particles and
controlling the cell diameter thereof to 50 to 350 .mu.m.
[0057] The resin particles for the foamed particles may be
obtained, for example, by melting and kneading a masterbatch, to
which inorganic substances and the like for addition to the base
resin have been added as described above, together with the base
resin in an extruder, extruding the melt mixture through a die
having the desired sectional form, cooling the extradite and then
cutting it into prescribed lengths. In the case where the base
resin particles are obtained in this process, the form of the resin
particles is substantially similar to the form of foamed particles
obtained by expanding the resin particles at the prescribed
expansion ratio. Therefore, the form of the foamed particles is
adjusted by adjusting the form of the resin particles.
[0058] As another process for obtaining the foamed particles, there
may be applied any conventionally known process, for example, a
process in which an extruded foam is directly obtained by means of
an extruder equipped with a die having the desired sectional form
according to a foam extrusion method, and the foam is cut into
proper lengths, thereby obtaining foamed particles.
[0059] Examples of the thermoplastic resin used in the resin
particles in the present invention include polyolefin resins;
styrene polymers such as polystyrene, poly(.alpha.-methylstyrene),
styrene-maleic anhydride copolymers, blends or graft polymers of
polyphenylene oxide and polystyrene, acrylonitrile-styrene
copolymers, acrylonitrile-butadiene-st- yrene terpolymers,
styrene-butadiene copolymers and high impact polystyrene; vinyl
chloride resins such as polyvinyl chloride, vinyl chloride-vinyl
acetate copolymers and copolymers of ethylene or propylene and
vinyl chloride; polyamide resins; and polyester resins.
[0060] Examples of the polyolefin resins include ethylene-butene
random copolymers, ethylene-butene block copolymers, polypropylene
resins such as ethylene-propylene black copolymers,
ethylene-propylene random copolymers, ethylene-propylene-butene
random terpolymers and homopolymer of propylene, polyethylene
resins such as low density polyethylene, medium density
polyethylene, high density polyethylene, linear low density
polyethylene, linear very low density polyethylene, ethylene-vinyl
acetate copolymers, ethylene-methyl methacrylate copolymers, and
ionomer resins obtained by subjecting an ethylene-methacrylic acid
copolymer to intermolecular crosslinking with an metal ion,
polybutene-1, polypentene, and ethylene-acrylic acid-maleic
anhydride terpolymers.
[0061] Although the polyolefin resin may be used without
crosslinking it, it may be crosslinked by a peroxide or radiation
before use. However, the uncrosslinked resin is preferred from the
viewpoints of the number of production processes and recycling
ability.
[0062] Among the above-mentioned base resins, low density
polyethylene, linear low-density polyethylene, polypropylene,
ethylene-propylene copolymers, propylene-butene copolymers and
ethylene-propylene-butene terpolymers are preferred in that they
provide molded articles good in recovery property and
toughness.
[0063] Of the above-mentioned base resins, ethylene-propylene
random copolymers, propylene-butene random copolymers,
ethylene-propylene-butene terpolymers are particularly preferred
from the viewpoints of heat resistance and strength.
[0064] As the polypropylene resins mentioned above as the base
resins and having a melting point of 130.degree. C. or higher, such
as polypropylene, propylene-ethylene copolymers, propylene-butene
copolymers, propylene-ethylene-butene terpolymers, etc. are
particularly preferred those obtained by using a metallocene
compound as a polymerization catalyst in that they exhibit
excellent rigidity and heat resistance compared with those obtained
by using another polymerization catalyst in the relations between
the melting point and rigidity of the resin and between the melting
point and heat resistance of the resin. Incidentally, the
metallocene compound is a compound having a structure that, for
example, a transition metal is held by unsaturated compound(s) of a
.pi. electron system, or a compound in which one or more
cyclopentadienyl groups or analogues thereof are present as a
ligand on a tetravalent transition metal such as titanium,
zirconium, nickel, palladium, hafnium or platinum.
[0065] To the base resin, may be added flame retardants of the
bromine or phosphorus type, or the like for imparting flame
retardancy, antioxidants of the phenol, phosphorus or sulfur type,
or the like for preventing deterioration, and light stabilizers of
the hindered amine or benzophenone type, or the like, and besides
for improving processability, fatty acid metal salts such as
calcium stearate as a neutralizer for catalyst and fatty acid
amides such as erucic acid amide and oleic acid amide as a
lubricant. The above-described additives may preferably be each
added in a proportion of 0.001 to 10 parts by weight per 100 parts
by weight of the resin.
[0066] In the present invention, the various polymers described
above may be used either singly or in any combination thereof as
usual. A biodegradable plastic such as polycaprolactone,
poly(.beta.-hydroxybutyri- c acid) or a copolymer thereof,
polyvinyl alcohol, or modified starch may also be used in
combination with the above-described base resin. When the
biodegradable plastic is used in combination with the base resin,
both components may be mixed in advance, or particles of both
components may be separately expanded to mix the resultant foamed
particles with each other. Further, unfoamed resin particles
composed of the biodegradable plastic may be mixed with foamed
particles composed of the base resin.
[0067] In order to impart flexibility to the base resin, a rubber
component such as ethylene-propylene rubber may be added in a
proportion of 5 to 40 wt. %.
[0068] The molded articles according to the present invention can
be produced by the following molding process. In the case where the
resin particles are, for example, foamed particles, the foamed
particles are filled into a mold, and steam is fed to the mold to
heat the foamed particles, thereby foaming and expanding them to
fusion-bond the foamed particles to one another so as to give an
expansion-molded article. When the resin particles are unfoamed
particles, they are also filled into a mold like the case where the
resin particles are foamed particles, and steam is fed to the mold
to heat the resin particles, thereby fusion-bonding the resin
particles to one another so as to give a molded article.
[0069] When the molded article according to the present invention
is formed as an expansion-molded article, a skin may be applied to
the expansion-molded article.
[0070] As a skin material, there is generally used a synthetic
resin sheet. The skin material may be used by forming it into a
desired form by injection molding, stamping molding or the like, or
by extruding it through a T-die or the like into a sheet in advance
and forming the sheet into a desired form by a method such as press
molding, air-pressure forming or vacuum forming. The skin material
may be used without shaping it in advance by sucking it upon
molding of the foamed particles or the like to bring it into close
contact with the mold, thereby shaping it. The skin material is
preferably composed of a material having fusion bonding property to
the foamed particles.
[0071] Incidentally, the skin material may be laminated on the
molded article with an adhesive or pressure sensitive adhesive.
[0072] When the foamed particles are composed of particles of a
polyolefin resin, and the base resin of the foamed particles of the
polyolefin resin is a polypropylene resin such as a
propylene-ethylene random copolymer, as a material of the skin
material, there is used a polypropylene resin containing at least
70 wt. % of a propylene component, such as a homopolymer of
propylene, ethylene-propylene block copolymer, ethylene-propylene
random copolymer, propylene-butene random copolymer or
propylene-ethylene-butene random copolymer, or a polyolefin
elastomer obtained by containing a rubber component such as
ethylene-propylene rubber (EPR) or ethylene-propylene-diene rubber
(EPDM) in such a polypropylene resin.
[0073] When the base resin of the foamed particles of the
polyolefin resin is a polyethylene resin such as linear low density
polyethylene, as a material of the skin material, there is used a
polyethylene resin such as low density polyethylene, medium density
polyethylene, high density polyethylene, linear low density
polyethylene, linear very low density polyethylene, and a
polyethylene copolymer containing at least 70 wt. % of an ethylene
component, or a polyolefin elastomer obtained by containing a
rubber component such as EPR or EPDM in such a polyethylene
resin.
[0074] The skin material is not limited to that of a single-layer
structure and may be of a multi-layer structure having a foamed
layer or the like. In the case of the skin material of the
multi-layer structure, it is necessary to form at least its inner
side with a material having fusion bonding property to the foamed
particles. As a material of its outer side, there may be used a
sheet material having a high decorative effect, such as woven
fabric or non-woven fabric.
[0075] The thickness of the skin material is preferably 0.3 to 8.0
mm.
[0076] In order to produce an expansion-molded article having a
skin according to the present invention, a skin material is first
fitted to a mold along the inner surface of the mold. After the
mold is then clamped in this state, foamed particles are filled
into the mold, and steam is fed into the mold to heat the foamed
particles, thereby foaming and expanding the foamed particles so as
to fusion-bond the foamed particles to one another and moreover to
the skin material. After this manner, an expansion-molded article
having a skin with the skin material bonded to the surface of the
expansion-molded article can be obtained.
[0077] Since the foamed particles having a porosity of at least 45%
in the most densely packed state are used in the present invention,
steam penetrates between the foamed particles from the foamed
particle side (from the side of the surface of the foamed particle
layer in no contact with the skin material) near to the skin
material even when the skin material has no steam permeability. As
a result, the foamed particles in the vicinity of the skin material
and the inner side of the skin material are sufficiently heated, so
that fusion bonding is certainly achieved among the foamed
particles in the vicinity of the skin material and between the
foamed particles and the skin material. When the foamed particles
having through hole(s) are used in particular, the penetration of
steam is further facilitated. The resultant expansion-molded
article having a skin has sound absorbing performance equivalent to
that having no skin. A skin material having high sound insulating
property may be selected for lamination. Incidentally, the
measurement of the sound absorption coefficient of the
expansion-molded article having a skin is conducted by using a side
of the molded article, on which no skin is laminated, as a sound
absorbing surface.
[0078] The molded articles of the resin particles according to the
present invention combine air permeability and heat insulating
property in addition to the sound absorbing qualities and can be
utilized in a wide variety of fields. For example, they can be used
in various use applications such as (1) heat insulating and
air-permeable sound absorbing materials in residences, (2)
composite materials with building materials in road, aeronautical
navigation, rail road, architecture and the like, (3) simplified
soundproofing panels for constructional equipment in buildings, and
(4) automotive structural materials such as interior materials and
bumpers.
[0079] The present invention will hereinafter be described in
further detail by the following examples and comparative
examples.
[0080] A base resin composed of an ethylene-propylene random
copolymer (ethylene content: 2.4 wt. %, melting point: 146.degree.
C., MFR: 10 g/10 min, expressed as EP in Table 1), aluminum
hydroxide and carbon black were heated and kneaded in an extruder,
and the thus-melted mixture was extruded into a strand through a
die. The strand was quenched in water and then chopped into the
prescribed lengths, thereby producing 5 kinds of resin particles
which were in the sectional form of a hollow cylinder and different
from one another in the combination of average hole diameter and
average particle weight. With respect to these kinds of resin
particles, foamed particles were produced in accordance with the
following process. Namely, 60 kg of the resin particles were
blended with carbon dioxide as a foaming agent, 400 g of kaolin as
a dispersing agent, 6 g of sodium dodecylbenzenesulfonate as a
surfactant, and 240 liters of water. While stirring the resultant
mixture in a closed vessel (volume: 400 liters), it was heated to
147.degree. C. without raising the temperature of the mixture
beyond 161.degree. C. that is a melting completion temperature of
the base resin, and held for 15 minutes at the same temperature.
The mixture was further heated to 0.152.degree. C. and held for 15
minutes. A back pressure equal to the equilibrium vapor pressure
within the closed vessel was then applied, and the vessel was
opened at one end thereof while keeping that pressure to release
the resin particles and water at the same time, thereby expanding
the resin particles to give gray foamed particles having a
sectional form of a hollow cylinder. Incidentally, aluminum
hydroxide and carbon black were added by the masterbatching process
to give blending amounts of 0.2 wt. % and 0.26 wt. %,
respectively.
[0081] With respect to the foamed particle samples thus obtained,
the average hole diameter d (mm), average particle weight (mg),
porosity (%) in a most densely packed state, quantity of heat (J/g)
at the high-temperature peak, bulk density (g/cm.sup.3) and L/D
were determined. The results are shown in Table 1.
[0082] The quantity of heat (J/g) at the high-temperature peak
shown in Table 1 is a quantity of heat of fusion at a peak on the
higher temperature side on a DSC curve obtained by differential
scanning calorimetry (heating rate: 10.degree. C./min) of about 2
mg of a foaming particle sample.
[0083] The thus-obtained foamed particle samples were each filled
into a mold of 1,200 mm.times.900 mm.times.50 mm, and heated with
steam of 2.8 to 3.8 kgf/cm.sup.2G to mold the foamed particles,
thereby obtaining expansion-molded articles of the propylene resin
in a plank form conforming with the mold dimensions. These molded
articles are expressed as I to V in Table 1.
[0084] With respect to the molded articles I to V, the bulk density
(g/cm.sup.3) and void content (%) were determined. The results are
shown in Table 1.
[0085] With respect to the respective molded articles, a test on
sound absorption properties was conducted to determine their sound
absorption coefficients.
EXAMPLE 1
[0086] The molded article I having a thickness of 50 mm was used as
it is to measure its sound absorption coefficient in accordance
with the measuring method of reverberant absorption coefficient
prescribed in JIS A 1409. The sound absorption coefficient was
measured by determining the area of a sample as 9.72 M.sup.2 (3.6 m
long and 2.7 m broad) and arranging it on a floor surface in the
center of a reverberation chamber under conditions of room
temperature, 25.degree. C. and 70% relative humidity at Tokyo
Metropolitan Industrial Technology Research Institute.
EXAMPLE 2
[0087] Two molded articles I were placed on each other to give a
thickness of 100 mm, thereby measuring its sound absorption
coefficient in the same manner as in Example 1.
EXAMPLE 3
[0088] Two molded articles II were placed on each other to give a
thickness of 100 mm, thereby measuring its sound absorption
coefficient in the same manner as in Example 1.
EXAMPLE 4
[0089] Two molded articles III were placed on each other to give a
thickness of 100 mm, thereby measuring its sound absorption
coefficient in the same manner as in Example 1.
EXAMPLE 5
[0090] The molded article IV having a thickness of 50 mm was used
as it is to measure its sound absorption coefficient in the same
manner as in Example 1.
EXAMPLE 6
[0091] The molded article V having a thickness of 50 mm was used as
it is to measure its sound absorption coefficient in the same
manner as in Example 1.
COMPARATIVE EXAMPLE 1
[0092] The molded article II having a thickness of 50 mm was used
as it is to measure its sound absorption coefficient in the same
manner as in Example 1.
COMPARATIVE EXAMPLE 2
[0093] The molded article III having a thickness of 50 mm was used
as it is to measure its sound absorption coefficient in the same
manner as in Example 1.
[0094] The measured results of the sound absorption coefficients in
Examples 1 to 6 and Comparative Examples 1 and 2 are shown in
Tables 2 and 3. The relationships between frequency and sound
absorption coefficient in Examples 1 to 6 and Comparative Examples
1 and 2 are diagrammatically illustrated in FIGS. 4 and 5. In these
graphs, the axis of abscissa indicates the frequency (Hz) of sound
wave, while the axis of ordinate indicates the reverberant
absorption coefficient (%).
1 TABLE 1 Foamed particles Average Quantity of Expansion-molded
article particle heat at high- Bulk Bulk Void Molded Base Sectional
d weight Porosity temp. peak density density content article resin
form (mm) (mg) (%) (J/g) (g/cm.sup.3) L/D (g/cm.sup.3) (%) I EP (a)
2.3 2 59 17.6 0.038 0.88 0.040 30 II EP (a) 4.2 6 57 18.0 0.039
0.86 0.042 23 III EP (a) 4.3 6 56 16.5 0.037 0.80 0.040 17 IV EP
(a) 2.5 2 60 18.8 0.039 0.98 0.041 42 V EP (f) 2.3 6 61 18.1 0.039
0.87 0.043 36
[0095]
2 TABLE 2 Evaluation of sound Molded article Thickness absorbing
qualities Example 1 I 50 .largecircle. 2 I 100 .largecircle. 3 II
100 .largecircle. 4 III 100 .largecircle. 5 IV 50 .largecircle. 6 V
50 .largecircle. Comp. 1 II 50 X Example 2 III 50 X Evaluation of
sound absorbing qualities: .largecircle.: Having not less than 3
continuous center frequency measuring points at which the sound
absorption coefficient is at least 70%, and not less than 7
continuous center frequency measuring points at which the sound
absorption is at least 50%; X: Having less than 3 continuous center
frequency measuring points at which the sound absorption
coefficient is at least 70%, and/or less than 7 continuous center
frequency measuring points at which the sound absorption is at
least 50%.
[0096]
3TABLE 3 Center frequency in Reverberant absorption coefficient (%)
1/3-octave Comp. Comp. band Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex.
1 Ex. 2 250 15 52 59 37 21 17 16 24 315 22 85 46 54 25 22 22 22 400
32 100 84 76 36 33 31 28 500 49 100 74 77 52 57 51 47 630 73 96 67
79 76 94 73 55 800 99 86 71 82 100 100 59 45 1000 100 87 87 82 100
78 49 38 1250 81 97 75 64 87 59 39 35 1600 65 97 66 58 65 59 43 36
2000 62 91 66 65 64 73 45 37 2500 94 97 71 75 92 74 46 38 3150 84
91 74 65 100 90 47 38
INDUSTRIAL APPLICABILITY
[0097] The molded articles according to the present invention are
excellent in sound absorbing qualities in a wide frequency range
and also in air permeability and heat insulating property, and are
useful as sound absorbing materials incorporated into walls, floors
and the like in buildings, sound absorbing materials incorporated
into interior materials for vehicles such as automobiles, etc.
* * * * *