Sound insulating structure

The disclosure relates to a sound insulating structure formed on an automobile floor panel on which at least one of a vibration and a sound is incident. This structure includes a covering layer for covering the panel and a cushioning layer for reducing an impact of the at least one of the vibration and the sound. This cushioning layer is interposed between the covering layer and the panel and made of a nonwoven fabric. This nonwoven fabric includes 5-95 wt % of a first fiber and 5-95% of a second fiber, wherein the total amount of the first and second fibers is 100 wt %. This first fiber has a fineness within a range from 1.5 to 40 deniers, a first melting point, and a first portion including polyethylene terephthalate. The second fiber has a fineness within a range from 1.5 to 15 deniers, a core portion, and a sheath portion covering the core portion. A majority of the core portion includes polyethylene terephthalate. The sheath portion includes an elastic copolyester which has a second melting point that is lower than the first melting point and is not higher than 200.degree. C. The elastic copolyester is prepared by copolymerizing polyethylene terephthalate and at least one other monomer. The sound insulating structure has a high sound-transmission-loss factor within a so-called road-noise frequency range and an adequate cushioning effect and is particularly superior in sound insulating at a normal temperature (15.degree.-40.degree. C.).

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates in general to a sound insulating structure 
for reducing an impact of vibration and/or sound which is incident on the 
structure from outside, and more particularly to a sound insulating 
structure that is suitable as an insulating floor carpet for an automobile 
floor panel, for reducing an impact of vibration and/or sound which is 
incident on the structure from the panel. 
2. Description of the Prior Art 
A conventional automobile insulating carpet, which is formed on an 
automobile floor panel, has a cushioning or insulating soft layer for 
reducing an impact of vibration and/or sound which is incident on the 
panel. Hitherto, there have been proposed various materials for the 
cushioning layer, such as felt, foamed urethane and nonwoven fabric made 
of, for example, common polyester fibers. Such felt generally used is 
prepared, for example, by at first breaking up a used cloth into fibers, 
then by matting the fibers into a woollike mass, and then by subjecting 
this mass to the needle punching treatment or by adding a binder such as 
phenol resin to this mass and then heating this binder-added mass to 
harden the same. The thus prepared felt having an apparent density from 
about 0.04 to about 0.2 g/cm.sup.3 and a thickness from about 5 to about 
30 mm is generally used. 
An important requirement for an automobile insulating carpet is to reduce 
noises such as a so-called road-noise (i.e., a noise incident on an 
automobile from road). In case that the above-mentioned felt is used for 
the cushioning layer, the resonance point (i.e., the point of frequency at 
which the sound transmission loss becomes minimum) of this cushioning 
layer falls within the road-noise frequency range (250-700 Hz). The noise 
which is incident on the cushioning layer from the floor panel and within 
the road-noise frequency range is much greater than the noise outside this 
range. Therefore, in case of the felt, the loss factor of noise becomes 
low, and thus it is not possible to obtain a sufficient damping effect and 
a good sound insulation. 
In view of the above-mentioned drawback of the felt, there has been 
proposed a urethane foamed body as another material for the cushioning 
layer. For example, Japanese Patent Unexamined First Publication 
JP-A-Hei-3-176241 discloses a method of producing an automobile floor 
carpet. This carpet has a foamed polyurethane layer 3, an outer 
polyurethane layer 4, and nylon fibers (flock) 5 formed on the layer 4 by 
electrocoating. The thus proposed foamed urethane body has a higher loss 
factor and a lower noise transmission loss at the resonance point, 
respectively than those of the above felt, common polyester nonwoven 
fabric and the like. However, the foamed urethane body has the following 
first and second drawbacks. 
The first drawback of the foamed urethane body is as follows. The spring 
constant of the foamed urethane body is higher than that of the felt, and 
the frequency of resonance point of the foamed urethane body is also 
higher than that of the felt. Therefore, in case of the foamed urethane 
body, the frequency range for the effective damping which is higher than 
the resonance point is narrower than that of the felt. Therefore, when the 
foamed urethane body has the same thickness as that of the felt, the 
former is inferior to the latter in the transmission loss within the 
overall frequency range (e.g., 250-6,400 Hz). Some measures can be taken 
for the purpose of obtaining a sufficient sound insulation. One of these 
measures is to increase the thickness of the foamed urethane body. Another 
measure is to increase the weight of a backing layer interposed between 
the carpet surface layer and the cushioning layer. With this measure, the 
resonance point is lowered, and thus the frequency range for the effective 
damping is widened. However, these measures increase the automobile's 
weight and the production cost. 
The second drawback of the foamed urethane body is as follows. The cost for 
producing the foamed urethane body is high. Furthermore, in the production 
of the foamed urethane body, it is necessary to provide an injection step 
of a polyol and an isocyanate in the form of liquid, a foaming step, and 
an bonding step. Therefore, it takes a long time and it is necessary to 
provide a large size facility with an exhaust apparatus, for producing the 
foamed urethane body. Thus, the foamed urethane body is inferior in 
productivity and economical efficiency. 
As an alternative to the above-mentioned felt and foamed urethane body, a 
nonwoven fabric has been proposed for the cushioning layer. Polyester 
fiber is very widely used to prepare this fabric, because it is high in 
Young's modulus and elastic modulus. For example, Japanese Patent 
Unexamined First Publication JP-A-Hei-7-223478 discloses a nonwoven fabric 
made of a polyester fiber comprising at least two types of polyester 
fibers (i.e., a high-melting-point polyester fiber and a low-melting-point 
polyester fiber). These at least two fibers are bonded together by heating 
these fibers at a temperature within a range from the melting point of the 
low-melting-point fiber to the melting point of the high-melting-point 
fiber. It is mentioned in this publication that the low-melting-point 
fiber preferably has a core-and-sheath structure and that the melting 
point different between these fibers is preferably at least 20.degree. C. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a sound insulating 
structure which is high in sound transmission loss factor within the 
road-noise frequency range and particularly superior in damping effect and 
sound insulation in a normal temperature range (15.degree. to 40.degree. 
C.), light in weight and suitable as an automobile insulating floor 
carpet. 
According to the present invention, there is provided a sound insulating 
structure formed on a panel on which at least one of a vibration and a 
sound is incident, said structure comprising: 
a covering layer for covering the panel; and 
a cushioning layer for reducing an impact of the at least one of the 
vibration and the sound, said cushioning layer being interposed between 
said covering layer and the panel and made of a nonwoven fabric, said 
nonwoven fabric comprising 
5-95 wt % of a first fiber having a fineness within a range from 1.5 to 40 
deniers, a first melting point, and a first portion comprising 
polyethylene terephthalate, and 
5-95 wt % of a second fiber having a fineness within a range from 1.5 to 15 
deniers and a core portion and a sheath portion covering said core 
portion, a majority of said core portion comprising polyethylene 
terephthalate, said sheath portion comprising an elastic copolyester which 
has a second melting point that is lower than said first melting point and 
is not higher than 200.degree. C., said elastic copolyester being prepared 
by copolymerizing polyethylene terephthalate and at least one other 
monomer, a total weight of said first and second fibers being 100 wt %.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In the following, a sound insulating structure according to the present 
invention will be described in detail. This sound insulating structure is 
used preferably as an automobile insulating floor carpet. 
As is seen from FIG. 1, a sound insulating structure 10 is, for example, 
formed on an automobile floor panel 12 made of steel. The structure 10 
comprises a covering layer 14 (i.e. carpet outer skin layer or carpet 
proper) for covering the panel 12 and a cushioning layer 16 for reducing 
an impact of at least one of a vibration and a sound which is incident on 
the panel 12. It is usual that the structure 10 further has a backing 
layer 18 made of a thermoplastic resin, which serves to back the covering 
layer 14 and is interposed between the cushioning layer 16 and the 
covering layer 14, and a fusible insulator layer 20 which is made of, for 
example, an asphalt sheet and interposed between the floor panel 12 and 
the cushioning layer 16. 
In the invention, the cushioning layer is made of a special nonwoven 
fabric. This fabric comprises 5-95 wt % (preferably 20-80 wt %) of a first 
fiber (i.e., a high-melting-point fiber) and 5-95 wt % (preferably (20-80 
wt %) of a second fiber (i.e., a core-and-sheath type composite or 
conjugated fiber), wherein the total amount of the first and second fiber 
is 100 wt %. The first fiber has a melting point which is higher than that 
of the second fiber and preferably at least 200.degree. C. If the amount 
of the second fiber exceeds 95 wt %, the cushioning layer becomes too hard 
or stiff. With this, the cushioning layer becomes inferior in cushioning 
action. Furthermore, too high proportion of the second fiber causes the 
production cost increase, because the second fiber is more expensive than 
the first fiber containing polyethylene terephthalate as a main component 
thereof. If the amount of the second fiber is less than 5 wt %, a shaped 
body of the nonwoven fabric is lowered in stability. 
As is mentioned hereinabove, the first fiber includes polyethylene 
terephthalate as a main component thereof. In other words, the first fiber 
may be a single component fiber made of only polyethylene terephthalate or 
an eccentric-type composite or conjugated fiber. This eccentric-type 
conjugated fiber has first and second portions which are bonded together 
and eccentrically arranged with each other in a transverse section of the 
eccentric fiber. The first portion comprises polyethylene terephthalate. 
The second portion comprises a copolymer prepared by copolymerizing 
polyethylene terephthalate and at least one monomer selected from the 
group consisting of a glycol component, a dibasic acid component, and a 
hydroxycarboxylic acid. This glycol component is different from ethylene 
glycol, and this dibasic acid component is different from terephthalic 
acid. 
Examples of the above-mentioned glycol component are trimethylene glycol, 
tetramethylene glycol, diethylene glycol, pentaerythritol, and bisphenol 
A. Examples of the above-mentioned dibasic acid component are aromatic 
dicarboxylic acids such as isophthalic acid and naphthalenedicarboxylic 
acid, fatty acid dicarboxylic acids such as glutaric acid, adipic acid and 
cyclohexanedicarboxylic acid. An example of the above-mentioned 
hydroxycarboxylic acid is para-hydroxybenzoic acid. It is preferable that 
the thus exemplified at least one monomer for the first fiber is added in 
an amount such that the above-mentioned second portion (i.e. polyethylene 
terephthalate copolymer) of the first fiber has a melting point of at 
least 200.degree. C. The above-mentioned eccentric-type conjugated fiber 
is preferably used as the first fiber, because this eccentric-type fiber 
becomes crimped by a heat treatment and thus provides the cushioning layer 
which is superior in external appearance. 
The eccentric-type conjugated fiber as the first fiber may be a solid-type 
fiber. In other words, this fiber has an inside which is free of a hallow 
space(s). However, it is preferable that this eccentric-type conjugated 
fiber is a fiber mixture comprising a first conjugated fiber portion 
having an inside which is free of a hollow space(s) and a second 
conjugated fiber portion which has an inside having a hollow space(s) and 
amounts to 20-35 wt % based on the weight of the first conjugated fiber 
portion. With this, the sound insulation efficiency is greatly increased. 
In the invention, the above-mentioned first and second fibers have a 
fineness within a range from 1.5 to 40 deniers and a fineness within a 
range from 1.5 to 15 deniers, respectively. If the fineness of the first 
or second fiber is less than 1.5 deniers, the polymer discharge amount in 
the melt spinning process becomes small and thus the spinning rate 
decreases, or the efficiency of the carding process is lowered by thread 
breakage, or the carding rate is lowered in the process of producing the 
nonwoven fabric. With this, the production cost increases. On the other 
hand, if the fineness of the first fiber is greater than 40 deniers, the 
spinning rate is relatively lowered due to the upper limit of the polymer 
discharge amount in the melt spinning process, and the difference of 
fineness between the first and second fibers becomes too much and thus the 
carding rate in the process of producing the nonwoven fabric is lowered, 
thereby increasing the production cost. If the fineness of the second 
fiber is greater than 15 deniers, the fiber number of the nonwoven fabric 
and the number of the thermally fused points in the nonwoven fabric 
decreases to an extent that the nonwoven fabric becomes insufficient in 
resilience and that the nonwoven fabric may be in a so-called fatigue to a 
great extent. 
In the invention, the second fiber has a core portion and a sheath portion 
covering the core portion. A majority of the core portion comprises 
polyethylene terephthalate. The sheath portion comprises an elastic 
copolyester which is prepared by copolymerizing polyethylene terephthalate 
(as a main copolymerizing monomer) and at least one other monomer. The 
elastic copolyester of the second fiber preferably has a tan .delta. of at 
least 0.1 within a normal temperature range (i.e., 15.degree.-40.degree. 
C.), wherein this tan .delta. is defined as a ratio of a loss elasticity 
(i.e., dynamic loss, E.sub.2) of the elastic copolyester to a storage 
modulus (i.e., dynamic modulus of elasticity, E.sub.1) of the elastic 
copolyester. Thus, the first and second fibers are preferably bonded 
together by fusing the elastic copolyester. With this, the nonwoven fiber 
becomes superior in shape stability. 
When the elastic copolyester of the second fiber has a tan .delta. of at 
least 0.1, this copolyester has a kind of phase transition in its polymer 
chain. At near the phase transition, friction between the molecular chains 
becomes great. Therefore, energy of a vibration incident on the elastic 
copolyester is efficiently transformed into thermal energy. With this, the 
cushioning layer has a good damping effect. Thus, it is considered that a 
vibration having a frequency range near the resonance point is efficiently 
suppressed, thereby improving the sound transmission loss. 
Polyethylene terephthalate, which is a polyester having a glycol component 
having a chain of two methylene groups, has a high glass transition 
temperature (Tg). Therefore, the elastic copolyester having the peak value 
of tan .delta. of at least 0.1 within or near the normal temperature range 
(15.degree.-40.degree. C.) can be obtained by copolymerizing polyethylene 
terephthalate and the at least one other monomer which is, for example, a 
glycol having a chain of at least four methylene groups. The thus prepared 
copolyester provides a superior sound insulation effect under a condition 
of actual use. In other words, as is shown in FIG. 2, when the elastic 
copolyester having a tan .delta. of at least 0.1 within a temperature 
range from 15.degree. to 40.degree. C. is used as a material for the 
sheath portion of the second fiber, the nonwoven fabric of the cushioning 
layer provides a superior damping effect within the normal temperature 
range where the sound insulating structure is actually used. Thus, as is 
shown in FIG. 3, the sound transmission loss of the sound insulation 
structure of the present invention at and near the resonance point is 
increased, relative to that of prior art. Furthermore, the cushioning 
layer becomes stable in shape. 
It is preferable that the elastic copolyester of the sheath portion is 
prepared by copolymerizing polyethylene terephthalate as a main 
copolymerizing monomer and the at least one other monomer and that the 
elastic copolyester has a heat of fusion of up to 6 cal/g and a melting 
point which is lower than the melting point of the first fiber and up to 
200.degree. C., in view of the spinning process of the second fiber and 
formability of the nonwoven fabric's shape. It is preferable that the 
above-mentioned at least one other monomer comprises a glycol having a 
chain of at least four methylene groups. Examples of the at least one 
other monomer are an ester formed by the union of a glycol having a chain 
of at least four methylene groups and terephthalic acid, such as 
polybutylene terephthalate or polyhexamethylene terephthalate, 
polycaprolactone, and a polyether as the glycol having a chain of at least 
four methylene groups, such as polytetramethylene glycol. 
In the invention, it is preferable that the cushioning layer has a hardness 
such that the cushioning layer is compressed by 25% when it receives a 
load ranging from 4 to 60 kgf. In the following, this will be referred to 
as that 25% hardness of the cushioning layer is from 4 to 60 kgf. If it is 
less than 4 kgf, the cushioning layer may become insufficient in 
resilience. If it is greater than 60 kgf, the cushioning layer may become 
too hard and may not function properly. The 25% hardness of the cushioning 
layer is more preferably from 5 to 40 kgf. 
In the invention, it is preferable that the cushioning layer has a 
thickness within a range from 2 to 50 mm. If it is less than 2 mm, the 
cushioning layer may not function properly. If it is greater than 50 mm, 
the cushioning layer may become too much in volume and weight. 
In the invention, it is preferable that the nonwoven fabric for the 
cushioning layer has an apparent density within a range from 0.03 to 0.1 
g/cm.sup.3. If it is less than 0.03 g/cm.sup.3, the cushioning layer may 
become too soft, and may be easily in fatigue (i.e. permanent deformation 
by pressure) and insufficient in resilience. Therefore, the cushioning 
layer may not function properly. If it is more than 0.1 g/cm.sup.3, the 
cushioning layer may become too hard. With this, the cushioning layer may 
not have a sufficient damping capability. 
The present invention will be illustrated with reference to the following 
nonlimitative Examples. In the following Examples and Comparative 
Examples, "part(s) by weight" will be expressed as "part(s)" for 
simplicity, unless otherwise described. 
EXAMPLE 1 
In this example, as is shown in FIG. 1, a sound insulation structure 10 
having a cushioning layer 16 of the present invention was formed on a flat 
steel plate 12 as an automobile floor panel. This steel plate 12 had a 
thickness of 0.8 mm and a surface density of 6.3 kg/m.sup.2. In general, 
an actual automobile floor panel may not have a flat shape, but may have a 
so-called bead shape to increase stiffness of the panel or may have an 
irregular shape to provide a space(s) for a heater duct and/or a wiring 
harness. However, a flat steel plate was used in this example for the 
purpose of easily determining the 25% hardness and the sound transmission 
loss. It is needless to say that a nonwoven fabric of the present 
invention for the cushioning layer can be desirably shaped by a press 
machine to correspond to the shape of the actual automobile floor panel 
which is not flat. 
In this example, a united member in which a tufted pile carpet as a 
covering layer 14 and a polyethylene sheet as a backing layer 18 had been 
previously bonded together was used. This tufted pile carpet had a weight 
per unit are (METSUKE) of 580 g/m.sup.2. The polyethylene sheet had a 
weight per unit area of 600 g/m.sup.2. As a fusible insulator layer 20, an 
asphalt sheet having a thickness of 2.5 mm and a surface density of 4.0 
kg/m.sup.2 was used. 
As the cushioning layer 16, a nonwoven fabric which is made of polyester 
and has a weight per unit area of 1,000 g/m.sup.2 at a thickness of 30 mm 
was prepared as follows. At first, this nonwoven fabric was prepared by 
mixing together the following three components as first and second fibers 
of the present invention. That is, as the first fiber, 60 parts of 
side-by-side solid-type conjugated fibers having a fineness of 2 deniers 
and a length of 51 mm, and 20 parts of side-by-side hollow-type conjugated 
fibers having a fineness of 6 deniers and a length of 51 mm were used. As 
the second fiber, 20 parts of elastic thermally-fusible conjugated fibers 
having a melting point of 170.degree. C., a fineness of 2 deniers and a 
length of 51 mm was used. This second fiber was prepared so as to have a 
core portion made of polyethylene terephthalate and a sheath portion made 
of an elastic copolyester. This copolyester was prepared by copolymerizing 
polyethylene terephthalate, polybutylene terephthalate, polycaprolactone, 
and the like. 
The thus prepared nonwoven fabric was heated at a temperature of 
190.degree. C. in an oven so as to melt the second fiber. Then, this 
fabric was shaped by a press machine to have a thickness of 20 mm and an 
apparent density of 0.05 g/cm.sup.3. The thus prepared cushioning layer 
had a 25% hardness of 10 kgf. 
Similar to Example 1, each of the shaped nonwoven fabrics according to the 
aftermentioned Examples 2-18 also had an apparent density of 0.05 
g/cm.sup.3. 
The united member of the covering layer 14 and the backing layer 18, the 
cushioning layer 16, the fusible insulator layer 20, and the steel plate 
12 were bonded together in the order shown in FIG. 1. In fact, the 
polyethylene sheet as the backing layer was melted at 130.degree. C., and 
under this condition the cushioning layer was placed on the polyethylene 
sheet, followed by cooling, to achieve a bonding therebetween. However, 
according to the present invention, a spunbonded foundation cloth or a 
thermally fusible nonwoven fabric may be used to achieve the bonding 
between the backing layer and the cushioning layer. 
Using the thus prepared sample which is a laminate of the steel plate and 
the sound insulating structure formed thereon, the following evaluation 
tests were conducted, except 25% hardness test. The results are so-called 
comparative results and shown in Table 1. In other words, in Table 1, "A" 
means that Example was much superior to Comparative Example; "B" means 
that Example was somewhat superior to Comparative Example; and "C" means 
that Example was equal to Comparative Example. For example, as shown in 
the first row of Table 1, the transmission loss result of Example 1 was 
much superior to that of Comparative Example 1, within a frequency range 
from 250 to 700 Hz, within a frequency range greater than 700 Hz, and 
within an overall frequency range from 250 to 6,400; and the cushioning 
effect of Example 1 was somewhat superior to that of Comparative Example 
1. 
1. 25% HARDNESS 
In this test, only the cushioning layer was used. In fact, according to 
need, a plurality of the cushioning layers were laminated to have a 
thickness of at least 50 mm. A load was added to the cushioning layer so 
as to compress the same by 25%, in accordance with Japanese Industrial 
Standard (JIS) K 6382-1978, using a load an aluminum disk having a 
diameter (.phi.) of 200 mm and a thickness of 5 mm. Upon this, the value 
of this load was measured and defined as 25% hardness. 
2. SOUND TRANSMISSION LOSS 
The sound transmission loss was measured in accordance with Japanese 
Industrial Standard (JIS) A 1416, using the sample. 
3. CUSHIONING EFFECT 
Using the sample, a load up to 5 kgf was added to the cushioning layer, 
with the same testing machine described in JIS K 6382-1987 and an iron 
disk having a diameter of 150 mm. Upon this, the amount of compression of 
the cushioning layer was measured. 
EXAMPLE 2 
In this example, Example 1 was repeated except in that the mixing ratio of 
the three types of fibers was modified. That is, as the first fiber, 70 
parts of the solid-type conjugated fibers and 20 parts of the hollow-type 
conjugated fibers, and as the second fiber 10 parts of the elastic 
thermally-fusible fibers were used. The shaped cushioning layer had a 25% 
hardness of 8.0 kgf. 
EXAMPLE 3 
In this example, Example 1 was repeated except in that the mixing ratio of 
the three types of fibers was modified. That is, as the first fiber, 75 
parts of the solid-type conjugated fibers and 20 parts of the hollow-type 
conjugated fibers, and as the second fiber 5 parts of the elastic 
thermally-fusible fibers were used. The shaped cushioning layer had a 25% 
hardness of 6.0 kgf. 
EXAMPLE 4 
In this example, Example 1 was repeated except in that the mixing ratio of 
the three types of fibers was modified. That is, as the first fiber, 40 
parts of the solid-type conjugated fibers and 20 parts of the hollow-type 
conjugated fibers, and as the second fiber 40 parts of the elastic 
thermally-fusible fibers were used. The shaped cushioning layer had a 25% 
hardness of 25.0 kgf. 
EXAMPLE 5 
In this example, Example 1 was repeated except in that the mixing ratio of 
the three types of fibers was modified. That is, as the first fiber, 20 
parts of the solid-type conjugated fibers and 20 parts of the hollow-type 
conjugated fibers, and as the second fiber 60 parts of the elastic 
thermally-fusible fibers were used. The shaped cushioning layer had a 25% 
hardness of 50 kgf. 
EXAMPLE 6 
In this example, Example 1 was repeated except in that, as the first fiber, 
60 parts of the solid-type conjugated fibers and 20 parts of the 
hollow-type conjugated fibers, and as the second fiber 20 parts of elastic 
thermally-fusible conjugated fibers having a fineness of 15 deniers, a 
length of 51 mm and a melting point of 170.degree. C. were used. The 
shaped cushioning layer had a 25% hardness of 8.0 kgf. 
EXAMPLE 7 
In this example, Example 6 was repeated except in that the mixing ratio of 
the three types of fibers was modified. That is, as the first fiber, 70 
parts of the solid-type conjugated fibers and 20 parts of the hollow-type 
conjugated fibers, and as the second fiber 10 parts of the elastic 
thermally-fusible fibers were used. The shaped cushioning layer had a 25% 
hardness of 6.0 kgf. 
EXAMPLE 8 
In this example, Example 6 was repeated except in that the mixing ratio of 
the three types of fibers was modified. That is, as the first fiber, 75 
parts of the solid-type conjugated fibers and 20 parts of the hollow-type 
conjugated fibers, and as the second fiber 5 parts of the elastic 
thermally-fusible fibers were used. The shaped cushioning layer had a 25% 
hardness of 4.0 kgf. 
EXAMPLE 9 
In this example, Example 6 was repeated except in that the mixing ratio of 
the three types of fibers was modified. That is, as the first fiber, 40 
parts of the solid-type conjugated fibers and 20 parts of the hollow-type 
conjugated fibers, and as the second fiber 40 parts of the elastic 
thermally-fusible fibers were used. The shaped cushioning layer had a 25% 
hardness of 20.0 kgf. 
EXAMPLE 10 
In this example, Example 6 was repeated except in that the mixing ratio of 
the three types of fibers was modified. That is, as the first fiber, 60 
parts of the solid-type conjugated fibers and 20 parts of the hollow-type 
conjugated fibers, and as the second fiber 20 parts of the elastic 
thermally-fusible fibers were used. The shaped cushioning layer had a 25% 
hardness of 40.0 kgf. 
EXAMPLE 11 
In this example, Example 1 was repeated except in that, as the first fiber, 
60 parts of the solid-type conjugated fibers and 20 parts of the 
hollow-type conjugated fibers, and as the second fiber 10 parts of the 
elastic thermally-fusible conjugated fibers and 10 parts of nonelastic 
thermally-fusible conjugated fibers having a melting point of 110.degree. 
C., a fineness of 2 deniers and a length of 51 mm were used. The shaped 
cushioning layer had a 25% hardness of 10.0 kgf. 
EXAMPLE 12 
In this example, Example 11 was repeated except in that the mixing ratio of 
the four types of fibers was modified. That is, as the first fiber, 70 
parts of the solid-type conjugated fibers and 20 parts of the hollow-type 
conjugated fibers, and as the second fiber 5 parts of the elastic 
thermally-fusible fibers and 5 parts of the nonelastic thermally-fusible 
fibers were used. The shaped cushioning layer had a 25% hardness of 8.0 
kgf. 
EXAMPLE 13 
In this example, Example 1 was repeated except in that, as the first fiber, 
60 parts of the solid-type conjugated fibers and 20 parts of the 
hollow-type conjugated fibers, and as the second fiber 10 parts of elastic 
thermally-fusible conjugated fibers having a melting point of 170.degree. 
C., a fineness of 15 deniers and a length of 51 mm and 10 parts of 
nonelastic thermally-fusible conjugated fibers having a melting point of 
110.degree. C., a fineness of 15 deniers and a length of 51 mm were used. 
The shaped cushioning layer had a 25% hardness of 8.0 kgf. 
EXAMPLE 14 
In this example, Example 13 was repeated except in that the mixing ratio of 
the four types of fibers was modified. That is, as the first fiber, 40 
parts of the solid-type conjugated fibers and 20 parts of the hollow-type 
conjugated fibers, and as the second fiber 20 parts of the elastic 
thermally-fusible fibers and 20 parts of the nonelastic thermally-fusible 
fibers were used. The shaped cushioning layer had a 25% hardness of 8.0 
kgf. 
EXAMPLE 15 
In this example, Example 1 was repeated, except in that the nonwoven fabric 
was prepared so as to have a weight per unit area of 250 g/m.sup.2 at a 
thickness of 10 mm and that the nonwoven fabric was shaped to have a 
thickness of 5 mm. The shaped cushioning layer had a 25% hardness of 10.0 
kgf. 
EXAMPLE 16 
In this example, Example 1 was repeated, except in that the nonwoven fabric 
was prepared so as to have a weight per unit area of 500 g/m.sup.2 at a 
thickness of 15 mm and that the nonwoven fabric was shaped to have a 
thickness of 10 mm. The shaped cushioning layer had a 25% hardness of 10.0 
kgf. 
EXAMPLE 17 
In this example, Example 1 was repeated, except in that the nonwoven fabric 
was prepared so as to have a weight per unit area of 1,500 g/m.sup.2 at a 
thickness of 45 mm and that the nonwoven fabric was shaped to have a 
thickness of 30 mm. The shaped cushioning layer had a 25% hardness of 10.0 
kgf. 
EXAMPLE 18 
In this example, Example 1 was repeated, except in that the nonwoven fabric 
was prepared so as to have a weight per unit area of 2,500 g/m.sup.2 at a 
thickness of 75 mm and that the nonwoven fabric was shaped to have a 
thickness of 50 mm. The shaped cushioning layer had a 25% hardness of 10.0 
kgf. 
COMATIVE EXAMPLE 1 
In this comparative example, a foamed urethane was used for the cushioning 
layer, in place of the nonwoven fabric. This foamed urethane was prepared 
as follows. A first solution consisting of 100 parts of propylene 
oxide-1,2,6-hexanetriol as a polyol, 2 parts of water, one part of a 
surface active agent and 0.5 parts of carbon black, and a second solution 
consisting of 100 parts of tolylenediisocyanato and 0.5 parts of a 
silicone oil were injected at a low pressure into a foaming mold having a 
clearance of 20 mm and then were foamed therein. The thus obtained foamed 
urethane sheet had a thickness of 20 mm, an apparent density of 0.06 
g/cm.sup.3, and a 25% hardness of 15.0 kgf. 
Similar to Comparative Example 1, each of the cushioning layers according 
to the aftermentioned Comparative Examples 2-4 also had an apparent 
density of 0.06 g/cm.sup.3. Each of the cushioning layers according to the 
aftermentioned Comparative Examples 5-18 had an apparent density of 0.05 
g/cm.sup.3. 
Using the foamed urethane sheet as a cushioning layer, a laminate of the 
steel plate and the sound insulating structure formed thereon was prepared 
in the same manner as in Example 1, except in that the foamed urethane 
sheet was bonded to the backing layer with a spray-type adhesive. 
In addition to the evaluation tests of Example 1, the following test was 
further conducted on the laminated (sample). 
4. TRANSMISSIBILITY OF VIBRATION TO THE SOLE OF A FOOT 
A load of 5 kgf equivalent to that added to the floor carpet by an average 
human foot was placed on the sample, using an iron disk having a diameter 
of 150 mm equivalent to the sole surface of an average human foot. Then, 
under this condition, the sample was subjected to a forced vibration with 
a constant force of 5N, and the transmissibility of vibration (the 
vibration transmission gain) at a frequency of 30 Hz was measured. The 
results are shown in the column of "Vibration Trans. to Foot" in Table 4. 
Similar to the results of Table 1, the comparative results of Comparative 
Example 1 as compared with another Comparative Example are shown in Table 
4. In Table 4, "D" means, for example, in the first row, that Comparative 
Example 1 is inferior to Comparative Example 2, with respect to the sound 
transmission loss within a frequency range from 400 to 1,000 Hz. In Table 
1, "Vibration Trans. to Foot" represents 
COMATIVE EXAMPLE 2 
In this comparative example, Comparative Example 1 was repeated except in 
that, as a backing layer, a sheet of ethylenevinylacetate copolymer (EVA) 
containing calcium carbonate as a filler was used, in place of the 
polyethylene sheet having a weight per unit area of 600 g/m.sup.3. This 
EVA sheet had a weight per unit area of 1,500 g/m.sup.3. The cushioning 
layer had a 25% hardness of 15.0 kgf. 
COMATIVE EXAMPLE 3 
In this comparative example, a commercial felt sheet (FELTOP (tradename) 
made by Howa Seni Kogyo Co.) was used. This felt sheet had a thickness of 
20 mm, an apparent density of 0.06 g/cm.sup.3, and a 25% hardness of 5.0 
kgf. 
Using this felt sheet as a cushioning layer a laminate of the steel plate 
and the sound insulating structure formed thereon was prepared in the same 
manner as in Example 1. 
The same evaluation tests, as those of Comparative Example 1 were conducted 
on the laminate (sample). 
COMATIVE EXAMPLE 4 
In this comparative example, Comparative Example 3 was repeated except in 
that, as a backing layer, the EVA sheet of Comparative Example 2 was used. 
The cushioning layer had a 25% hardness of 5.0 kgf. 
COMATIVE EXAMPLE 5 
In this comparative example, Example 1 was repeated except in that 20 parts 
of common nonelastic thermally-fusible conjugated fiber having a melting 
point of 110.degree. C., a fineness of 2 deniers and a length of 51 mm 
were used for preparing a nonwoven fabric, in place of the elastic 
thermally-fusible conjugated fibers, that the nonwoven fabric was heated 
up to a temperature of 175.degree. C., and that the same evaluation tests 
as those in Comparative Example 1 were conducted on the sample. The 
cushioning layer had a 25% hardness of 10.0 kgf. 
COMATIVE EXAMPLE 6 
In this comparative example, Comparative Example 5 was repeated except in 
that 70 parts of the solid-type conjugated fibers, 20 parts of the 
hollow-type conjugated fibers, and 10 parts of the nonelastic 
thermally-fusible conjugated fibers were used. The cushioning layer had a 
25% hardness of 8.0 kgf. 
COMATIVE EXAMPLE 7 
In this comparative example, Comparative Example 5 was repeated except in 
that 75 parts of the solid-type conjugated fibers, 20 parts of the 
hollow-type conjugated fibers, and 5 parts of the nonelastic 
thermally-fusible conjugated fibers were used. The cushioning layer had a 
25% hardness of 6.0 kgf. 
COMATIVE EXAMPLE 8 
In this comparative example, Comparative Example 5 was repeated except in 
that 40 parts of the solid-type conjugated fibers, 20 parts of the 
hollow-type conjugated fibers, and 40 parts of the nonelastic 
thermally-fusible conjugated fibers were used. The cushioning layer had a 
25% hardness of 25.0 kgf. 
COMATIVE EXAMPLE 9 
In this comparative example, Comparative Example 5 was repeated except in 
that 20 parts of the solid-type conjugated fibers, 20 parts of the 
hollow-type conjugated fibers, and 60 parts of the nonelastic 
thermally-fusible conjugated fibers were used. The cushioning layer had a 
25% hardness of 50.0 kgf. 
COMATIVE EXAMPLE 10 
In this comparative example, Comparative Example 5 was repeated except in 
that 60 parts of the solid-type conjugated fibers, 20 parts of the 
hollow-type conjugated fibers, and 20 parts of common nonelastic 
thermally-fusible conjugated fibers having a melting point of 110.degree. 
C., a fineness of 15 deniers and a length of 51 mm were used. The 
cushioning layer had a 25% hardness of 8.0 kgf. 
COMATIVE EXAMPLE 11 
In this comparative example, Comparative Example 10 was repeated except in 
that 70 parts of the solid-type conjugated fibers, 20 parts of the 
hollow-type conjugated fibers, and 10 parts of the nonelastic 
thermally-fusible conjugated fibers were used. The cushioning layer had a 
25% hardness of 6.0 kgf. 
COMATIVE EXAMPLE 12 
In this comparative example, Comparative Example 10 was repeated except in 
that 75 parts of the solid-type conjugated fibers, 20 parts of the 
hollow-type conjugated fibers, and 5 parts of the nonelastic 
thermally-fusible conjugated fibers were used. The cushioning layer had a 
25% hardness of 4.0 kgf. 
COMATIVE EXAMPLE 13 
In this comparative example, Comparative Example 10 was repeated except in 
that 40 parts of the solid-type conjugated fibers, 20 parts of the 
hollow-type conjugated fibers, and 40 parts of the nonelastic 
thermally-fusible conjugated fibers were used. The cushioning layer had a 
25% hardness of 20.0 kgf. 
COMATIVE EXAMPLE 14 
In this comparative example, Comparative Example 10 was repeated except in 
that 60 parts of the solid-type conjugated fibers, 20 parts of the 
hollow-type conjugated fibers, and 20 parts of the nonelastic 
thermally-fusible conjugated fibers were used. The cushioning layer had a 
25% hardness of 40.0 kgf. 
COMATIVE EXAMPLE 15 
In this comparative example, Comparative Example 5 was repeated except in 
that 60 parts of the solid-type conjugated fibers, 20 parts of the 
hollow-type conjugated fibers, and 20 parts of the nonelastic 
thermally-fusible conjugated fibers were used, that the nonwoven fabric 
was prepared so as to have a weight per unit area of 250 g/m.sup.2 at a 
thickness of 10 mm, and that the nonwoven fabric was shaped by the press 
machine to have a thickness of 5 mm. The cushioning layer had a 25% 
hardness of 10.0 kgf. 
COMATIVE EXAMPLE 16 
In this comparative example, Comparative Example 15 was repeated except in 
that the nonwoven fabric was prepared so as to have a weight per unit area 
of 500 g/m.sup.2 at a thickness of 15 mm and that the nonwoven fabric was 
shaped to have a thickness of 10 mm. The cushioning layer had a 25% 
hardness of 10.0 kgf. 
COMATIVE EXAMPLE 17 
In this comparative example, Comparative Example 15 was repeated except in 
that the nonwoven fabric was prepared so as to have a weight per unit area 
of 1,500 g/m.sup.2 at a thickness of 45 mm and that the nonwoven fabric 
was shaped to have a thickness of 30 mm. The cushioning layer had a 25% 
hardness of 10.0 kgf. 
COMATIVE EXAMPLE 18 
In this comparative example, Comparative Example 15 was repeated except in 
that 60 parts of the solid-type conjugated fibers, 20 parts of the 
hollow-type conjugated fibers, and 20 parts of the nonelastic 
thermally-fusible conjugated fibers were used, that the nonwoven fabric 
was prepared so as to have a weight per unit area of 2,500 g/m.sup.2 at a 
thickness of 75 mm and that the nonwoven fabric was shaped to have a 
thickness of 50 mm. The cushioning layer had a 25% hardness of 10.0 kgf. 
As is seen from Tables 1-3, with respect to the results of the sound 
transmission loss of the samples having the cushioning layers of the same 
thicknesses, when the samples of Examples are compared with those of 
Comparative Examples, the former was much superior to the latter, within 
the road-noise range (i.e. a frequency range from 250 to 700 Hz); and the 
former was superior to or at least equal to the latter, within the overall 
range (i.e. a frequency range from 250 to 6,400 Hz). 
As is seen from Tables 1-3, with respect to the results of the sound 
transmission loss of the samples having the cushioning layers of the same 
weight per unit area thereof, the samples of Examples were superior to or 
at least equal to those of Comparative Examples. 
As is seen from Tables 1-3, with respect to the results of the cushioning 
effect test of the samples having the cushioning layers of the same 
thickness, Examples 1-14 were superior to Comparative Examples 3 and 4 in 
which a commercial felt was used in place of the nonwoven fabric of the 
present invention. 
According to the present invention, density of the cushioning layer can be 
reduced by 10-30%, for obtaining the same sound insulation and the same 
cushioning effect, by the nonwoven fabric of the present invention, as 
those obtained by the urethane foamed body and the felt. Thus, it is 
possible to make the sound insulation structure light in weight. 
As is mentioned above, the sound insulating structure of the present 
invention is high in sound transmission loss factor within the road-noise 
frequency range and particularly superior in sound insulation at the 
normal temperature. Furthermore, the sound insulating structure of the 
present invention has an adequate cushioning effect and can be reduced in 
weight. 
TABLE 1 
__________________________________________________________________________ 
Sound Transmission Loss 
Cushioning 
250-700 Hz 
700 Hz &lt; 
250-6,400 Hz 
Effect 
__________________________________________________________________________ 
Example 1 relative to Com. Ex. 1 
A A A B 
Example 1 relative to Com. Ex. 2 
C B B B 
Example 1 relative to Com. Ex. 3 
A A A A 
Example 1 relative to Com. Ex. 4 
B B A A 
Example 1 relative to Com. Ex. 5 
A C B B 
Example 2 relative to Com. Ex. 1 
A A A B 
Example 2 relative to Com. Ex. 2 
C B B B 
Example 2 relative to Com. Ex. 3 
A A A A 
Example 2 relative to Com. Ex. 4 
B B A A 
Example 2 relative to Com. Ex. 6 
A C B B 
Example 3 relative to Com. Ex. 1 
A A A B 
Example 3 relative to Com. Ex. 2 
C B B B 
Example 3 relative to Com. Ex. 3 
A A A A 
Example 3 relative to Com. Ex. 4 
B B A A 
Example 3 relative to Com. Ex. 7 
A C B B 
Example 4 relative to Com. Ex. 1 
A A A B 
Example 4 relative to Com. Ex. 2 
C B B B 
Example 4 relative to Com. Ex. 3 
A A A A 
Example 4 relative to Com. Ex. 4 
B B A A 
Example 4 relative to Com. Ex. 8 
A C B B 
Example 5 relative to Com. Ex. 1 
A A A B 
Example 5 relative to Com. Ex. 2 
C B B B 
Example 5 relative to Com. Ex. 3 
A A A A 
Example 5 relative to Com. Ex. 4 
B B A A 
Example 5 relative to Com. Ex. 9 
A C B B 
Example 6 relative to Com. Ex. 1 
A A A B 
Example 6 relative to Com. Ex. 2 
C B B B 
Example 6 relative to Com. Ex. 3 
A A A A 
Example 6 relative to Com. Ex. 4 
B B A A 
Example 6 relative to Com. Ex. 10 
A C B B 
__________________________________________________________________________ 
TABLE 2 
__________________________________________________________________________ 
Sound Transmission Loss 
Cushioning 
250-700 Hz 
700 Hz &lt; 
250-6,400 Hz 
Effect 
__________________________________________________________________________ 
Example 7 relative to Com. Ex. 1 
A A A C 
Example 7 relative to Com. Ex. 2 
C B B B 
Example 7 relative to Com. Ex. 3 
A A A A 
Example 7 relative to Com. Ex. 4 
B B A A 
Example 7 relative to Com. Ex. 11 
A C B B 
Example 8 relative to Com. Ex. 1 
A A A B 
Example 8 relative to Com. Ex. 2 
C B B B 
Example 8 relative to Com. Ex. 3 
A A A A 
Example 8 relative to Com. Ex. 4 
B B A A 
Example 8 relative to Com. Ex. 12 
A C B B 
Example 9 relative to Com. Ex. 1 
A A A C 
Example 9 relative to Com. Ex. 2 
C B B B 
Example 9 relative to Com. Ex. 3 
A A A A 
Example 9 relative to Com. Ex. 4 
B B A A 
Example 9 relative to Com. Ex. 13 
A C B B 
Example 10 relative to Com. Ex. 1 
A A A B 
Example 10 relative to Com. Ex. 2 
C B B B 
Example 10 relative to Com. Ex. 3 
A A A A 
Example 10 relative to Com. Ex. 4 
B B A A 
Example 10 relative to Com. Ex. 14 
A C B B 
Example 11 relative to Com. Ex. 1 
A A A B 
Example 11 relative to Com. Ex. 2 
C B B B 
Example 11 relative to Com. Ex. 3 
A A A A 
Example 11 relative to Com. Ex. 4 
B B A A 
Example 11 relative to Com. Ex. 5 
A C B B 
Example 12 relative to Com. Ex. 1 
A A A B 
Example 12 relative to Com. Ex. 2 
C B B B 
Example 12 relative to Com. Ex. 3 
A A A A 
Example 12 relative to Com. Ex. 4 
B B A A 
Example 12 relative to Com. Ex. 6 
A C B B 
__________________________________________________________________________ 
TABLE 3 
__________________________________________________________________________ 
Sound Transmission Loss 
Cushioning 
250-700 Hz 
700 Hz &lt; 
250-6,400 Hz 
Effect 
__________________________________________________________________________ 
Example 13 relative to Com. Ex. 1 
A A A B 
Example 13 relative to Com. Ex. 2 
C B B B 
Example 13 relative to Com. Ex. 3 
A A A A 
Example 13 relative to Com. Ex. 4 
B B A A 
Example 13 relative to Com. Ex. 10 
A C B B 
Example 14 relative to Com. Ex. 1 
A A A B 
Example 14 relative to Com. Ex. 2 
C B B B 
Example 14 relative to Com. Ex. 3 
A A A A 
Example 14 relative to Com. Ex. 4 
B B A A 
Example 14 relative to Com. Ex. 13 
A C B B 
Example 15 relative to Com. Ex. 15 
A C B B 
Example 16 relative to Com. Ex. 16 
A C B B 
Example 17 relative to Com. Ex. 17 
A C B B 
Example 18 relative to Com. Ex. 18 
A C B B 
__________________________________________________________________________ 
TABLE 4 
__________________________________________________________________________ 
Sound Transmission Loss 
Cushioning 
Vibration 
400-1,000 Hz 
1,000 Hz &lt; 
250-6,400 Hz 
Effect 
Trans. to Foot 
__________________________________________________________________________ 
Com. Ex. 1 relative to Com. Ex. 2 
D D D C C 
Com. Ex. 1 relative to Com. Ex. 3 
D C C A A 
Com. Ex. 1 relative to Com. Ex. 4 
D D D A A 
Com. Ex. 2 relative to Com. Ex. 1 
A A A C C 
Com. Ex. 2 relative to Com. Ex. 3 
B A B A A 
Com. Ex. 2 relative to Com. Ex. 4 
D C C A A 
Com. Ex. 3 relative to Com. Ex. 1 
B C C D D 
Com. Ex. 3 relative to Com. Ex. 2 
D D D D D 
Com. Ex. 3 relative to Com. Ex. 4 
D D D C C 
Com. Ex. 4 relative to Com. Ex. 1 
A A B D D 
Com. Ex. 4 relative to Com. Ex. 2 
A C B D D 
Com. Ex. 4 relative to Com. Ex. 3 
A A A C C 
Com. Ex. 5 relative to Com. Ex. 1 
B A B B B 
Com. Ex. 5 relative to Com. Ex. 2 
D B C B B 
Com. Ex. 5 relative to Com. Ex. 3 
A A A A A 
Com. Ex. 5 relative to Com. Ex. 4 
C B B A A 
Com. Ex. 6 relative to Com. Ex. 1 
B A B B B 
Com. Ex. 6 relative to Com. Ex. 2 
D B C B B 
Com. Ex. 6 relative to Com. Ex. 3 
A A A A A 
Com. Ex. 6 relative to Com. Ex. 4 
C B B A A 
Com. Ex. 7 relative to Com. Ex. 1 
B A B B B 
Com. Ex. 7 relative to Com. Ex. 2 
D B C B B 
Com. Ex. 7 relative to Com. Ex. 3 
A A A A A 
Com. Ex. 7 relative to Com. Ex. 4 
C B B A A 
Com. Ex. 8 relative to Com. Ex. 1 
B A B B B 
Com. Ex. 8 relative to Com. Ex. 2 
D B C B B 
Com. Ex. 8 relative to Com. Ex. 3 
A A A A A 
Com. Ex. 8 relative to Com. Ex. 4 
C B B A A 
__________________________________________________________________________ 
TABLE 5 
__________________________________________________________________________ 
Sound Transmission Loss 
Cushioning 
Vibration 
400-1,000 Hz 
1,000 Hz &lt; 
250-6,400 Hz 
Effect 
Trans. to Foot 
__________________________________________________________________________ 
Com. Ex. 9 relative to Com. Ex. 1 
B A B B B 
Com. Ex. 9 relative to Com. Ex. 2 
D B C B B 
Com. Ex. 9 relative to Com. Ex. 3 
A A A A A 
Com. Ex. 9 relative to Com. Ex. 4 
C B B A A 
Com. Ex. 10 relative to Com. Ex. 1 
B A B B B 
Com. Ex. 10 relative to Com. Ex. 2 
D B C B B 
Com. Ex. 10 relative to Com. Ex. 3 
A A A A A 
Com. Ex. 10 relative to Com. Ex. 4 
C B B A A 
Com. Ex. 11 relative to Com. Ex. 1 
B A B B B 
Com. Ex. 11 relative to Com. Ex. 2 
D B C B B 
Com. Ex. 11 relative to Com. Ex. 3 
A A A A A 
Com. Ex. 11 relative to Com. Ex. 4 
C B B A A 
Com. Ex. 12 relative to Com. Ex. 1 
B A B B C 
Com. Ex. 12 relative to Com. Ex. 2 
D B C B C 
Com. Ex. 12 relative to Com. Ex. 3 
A A A A A 
Com. Ex. 12 relative to Com. Ex. 4 
C B B A A 
Com. Ex. 13 relative to Com. Ex. 1 
B A B B B 
Com. Ex. 13 relative to Com. Ex. 2 
D B C B B 
Com. Ex. 13 relative to Com. Ex. 3 
A A A A A 
Com. Ex. 13 relative to Com. Ex. 4 
C B B A A 
Com. Ex. 14 relative to Com. Ex. 1 
B A B B B 
Com. Ex. 14 relative to Com. Ex. 2 
D B C B B 
Com. Ex. 14 relative to Com. Ex. 3 
A A A A A 
Com. Ex. 14 relative to Com. Ex. 4 
C B B A A 
__________________________________________________________________________