U.S. patent application number 12/169495 was filed with the patent office on 2008-11-06 for thermoformable acoustic sheet.
This patent application is currently assigned to I.N.C. Corporation Pty Ltd. Invention is credited to Michael William Coates, Marek Kierzkowski.
Application Number | 20080274274 12/169495 |
Document ID | / |
Family ID | 3822893 |
Filed Date | 2008-11-06 |
United States Patent
Application |
20080274274 |
Kind Code |
A1 |
Coates; Michael William ; et
al. |
November 6, 2008 |
THERMOFORMABLE ACOUSTIC SHEET
Abstract
A thermoformable acoustic sheet formed by a compressed fibrous
web includes high melt fibres and adhesive thermoplastic fibres in
which the adhesive fibres are at least partially melted so that in
the compressed web the adhesive fibres at least partially coat the
high melt fibres and reduce the interstitial space in the fibre
matrix. Also included are methods of producing a thermoformable
acoustic sheet which includes heating a fibre web including high
melt and adhesive thermoplastic fibres to at least partially melt
the adhesive fibres and compressing the web to form a sheet so that
the adhesive fibres at least partially coat the high melt fibres to
reduce the interstitial space in the fibre matrix.
Inventors: |
Coates; Michael William;
(Glen Iris, AU) ; Kierzkowski; Marek; (Ferntree
Gully, AU) |
Correspondence
Address: |
SEED INTELLECTUAL PROPERTY LAW GROUP PLLC
701 FIFTH AVE, SUITE 5400
SEATTLE
WA
98104
US
|
Assignee: |
I.N.C. Corporation Pty Ltd
South Dandenong
AU
|
Family ID: |
3822893 |
Appl. No.: |
12/169495 |
Filed: |
July 8, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11786463 |
Apr 10, 2007 |
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12169495 |
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10333385 |
Sep 19, 2003 |
7226656 |
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PCT/AU2001/000880 |
Jul 19, 2001 |
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11786463 |
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Current U.S.
Class: |
427/180 |
Current CPC
Class: |
B29C 43/28 20130101;
B60R 13/08 20130101; D04H 1/4382 20130101; B29K 2067/00 20130101;
B29K 2105/06 20130101; Y10T 428/24 20150115; G10K 11/162 20130101;
D04H 1/58 20130101; B29C 51/004 20130101; D04H 3/16 20130101; B29K
2067/046 20130101; D04H 1/4291 20130101; D04H 1/559 20130101; Y10T
428/24636 20150115; D04H 1/55 20130101; Y10T 428/249921 20150401;
D04H 1/541 20130101; Y10T 428/249953 20150401; D04H 1/435 20130101;
Y10T 428/24322 20150115; D04H 1/60 20130101; D04H 1/593 20130101;
D04H 1/46 20130101; D04H 1/54 20130101; B29C 43/228 20130101; Y10T
428/249924 20150401 |
Class at
Publication: |
427/180 |
International
Class: |
B05D 1/12 20060101
B05D001/12 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 19, 2000 |
AU |
PQ 8830 |
Claims
1-25. (canceled)
26. A method of producing a thermoformable acoustic sheet including
the steps of heating a fibre web including high melt and adhesive
thermoplastic fibres to at least partially melt the adhesive fibres
and compressing the web to form a sheet so that the adhesive fibres
at least partially coat the high melt fibres and reduce the
interstitial space in the fibre matrix.
27. A method of producing a thermoformable acoustic sheet according
to claim 26 wherein the thermoplastic fibres are treated with an
adhesive coating to increase the air flow resistance.
28. A method of producing a thermoformable acoustic sheet according
to claim 27 wherein the adhesive coating is applied as a powder at
a rate of from 10 to 80 g/m.sup.2.
29. A method of producing a thermoformable acoustic sheet according
to claim 26 wherein the thermoplastic fibres are treated with a
coating formed by one or more further webs of thermoplastic
fibres.
30. A method of producing a thermoformable acoustic sheet according
to claim 27 wherein the fibre web including high melt and adhesive
thermoplastic fibres and the coating formed by one or more further
webs of thermoplastic fibres are compressed concurrently.
31. A method of producing a thermoformable acoustic sheet according
to claim 26 wherein the sheet has a total air flow resistance
between 275 and 1100 mks Rayls.
32. A method of producing a thermoformable acoustic sheet according
to claim 31 wherein the sheet has a total air flow resistance
between 600 and 1100 mks Rayls.
33. A method of producing a thermoformable acoustic sheet according
to claim 32 wherein the sheet has a total air flow resistance
between 900 and 1000 mks Rayls.
34. A method of producing a thermoformable acoustic sheet according
to claim 26 wherein the sheet has a low sag modulus at temperatures
up to 150.degree. C.
35. A method of producing a thermoformable acoustic sheet according
to claim 26, wherein the high melt fibre has a melting point above
about 220.degree. C.
36. A method of producing a thermoformable acoustic sheet according
to claim 26, wherein the adhesive fibre has a melting point between
100 and 160.degree. C.
37. A method of producing a thermoformable acoustic sheet according
to claim 36 wherein the adhesive fibre has a melting point between
120 and 150.degree. C.
38. A method of producing a thermoformable acoustic sheet according
to claim 37 wherein the adhesive fibre has a melting point between
135 and 145.degree. C.
39. A method of producing a thermoformable acoustic sheet according
to claim 2 wherein the high melt fibres are about 6 denier or
below.
40. A method of producing a thermoformable acoustic sheet according
to claim 39 wherein the high melt fibres are about 4 denier or
below.
41. A method of producing a thermoformable acoustic sheet according
to claim 26 wherein the adhesive fibres are about 6 denier or
below.
42. A method of producing a thermoformable acoustic sheet according
to claim 41 wherein the adhesive fibres are about 4 denier or
below.
43. A method of producing a thermoformable acoustic sheet according
to claim 42 wherein the adhesive fibres are about 2 denier.
44. A method of producing a thermoformable acoustic sheet according
to claim 26 wherein the web of thermoplastic fibres is produced
from non-woven vertically aligned high loft thermally bonded
fibres.
45. A method of producing a thermoformable acoustic sheet according
to claim 26 wherein the thermoplastic fibres are selected from
polyethylene terephthalate (PET), polyethylene butylphthalate
(PBT), polyethylene 1,4-cyclohexanedimethanol (PCT), polylactic
acid (PLA) and/or polypropylene (PP).
46. A method of producing a thermoformable acoustic sheet according
to claim 26 wherein the web of thermoplastic fibres has a web
weight of about 1000 g/m.sup.2 or below.
47. A method of producing a thermoformable acoustic sheet according
to claim 46 wherein the web of thermoplastic fibres has a web
weight of about 800 g/m.sup.2 or below.
48. A method of producing a thermoformable acoustic sheet according
to claim 47 wherein the web of thermoplastic fibres has a web
weight of about 600 g/m.sup.2 or below.
49. A method of producing a thermoformable acoustic sheet according
to claim 48 wherein the web of thermoplastic fibres has a web
weight of about 400 g/m.sup.2 or below.
50. A method of producing a thermoformable acoustic sheet according
to claim 26 wherein the web of thermoplastic fibres have 50% or
more of adhesive fibres or adhesive component fibres and is
compressed at a temperature between 180-220.degree. C. for a period
between 1 and 3 minutes.
51-52. (canceled)
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to materials for acoustic absorption.
More particularly it relates to thermoformable acoustic sheets.
[0002] Sounds absorption is required in a wide variety of
industrial and domestic applications. In many of these applications
it is desirable that the acoustic material conforms to the shape of
a surface for example or otherwise retains a particular shape. In
such applications it is desirable that the acoustic sheet can be
heat moulded to the required shape to provide relative ease and
speed of production. Sound absorption can be a function of depth of
air space, air flow resistance, mass, stiffness and the acoustic
impedance of any porous media behind the acoustic sheet. Therefore,
adding a third dimension for example by moulding to a required
shape increases stiffness and can add practical and aesthetic
value. Importantly a three dimensionally shaped material provides
its own air space. The shape therefore has a major influence on
sound absorption and stiffness. One particular application for heat
mouldable or thermoformable acoustic sheets is in the automotive
industry, in particular, in under bonnet insulators for motor
vehicles. Existing under bonnet insulators use moulded flibreglass
insulators for sound absorption. In these products resinated
fibreglass, or felt is sandwiched between two layers of non-woven
tissue and subsequently heat molded to form a so called "biscuit"
with sealed edges. The difficulties associated with this product
include the fact that the moulding process is relatively slow
taking up to 21/2 minutes per moulded part. Additionally, the use
of resinated fibreglass is undesirable because of is inherent
undesirable handling problems while the resins can release toxic
gases during the moulding process.
[0003] Other examples of applications for thermoformable sheets in
the automotive industry include wheel arch linings, head linings
and boot linings.
[0004] Attempts to produce a suitable thermoformable material from
thermoplastic textile for underbonnet insulator have been
unsuccessful due to one or more of the failure of the materials to
meet requirements of low sag modulus typically encountered at
operating temperatures, unsuitable moulding performance, and lack
of uniformity of air flow resistance required for acoustic
absorption performance.
[0005] It is an object of this invention to provide a
thermoformable acoustic sheet and a method of producing such a
sheet that will at least provide a useful alternative.
SUMMARY OF THE INVENTION
[0006] In one aspect this invention provides a thermoformable
acoustic sheet formed by a compressed fibrous web including high
melt and adhesive thermoplastic fibres. During forming the adhesive
fibres are at least partially melted so that in the compressed web
the adhesive fibres at least partially coat the high melt fibres
and reduce the interstitial space in the fibre matrix.
[0007] In one form of the invention, the thermoplastic fibres are
treated with an adhesive coating to increase the airflow
resistance.
[0008] In another form of the invention, the thermoplastic fibres
are treated with a coating formed by one or more further webs of
thermoplastic fibres to increase the air flow resistance.
[0009] Preferably the further web contains a substantial amount of
adhesive fibre.
[0010] In another aspect this invention provides a method of
producing a thermoformable acoustic sheet including the steps of
heating a fibre web including high melt and adhesive thermoplastic
fibres to at least partially melt the adhesive fibres and
compressing the web to form a sheet. In the compressed sheet the
adhesive fibres at least partially coating the high melt fibre to
reduce the interstitial space in the fibre matrix.
[0011] In one form of the method of the present invention, the
sheet is treated with an adhesive coating to increase the air flow
resistance.
[0012] In another form of the method of the present invention, the
thermoplastic fibres are treated with a coating formed by one or
more further webs of thermoplastic fibres to increase the air flow
resistance.
[0013] The compression of the fibrous material under heat and
pressure results in the at least partial melting of the adhesive
fibre which acts as a heat activatable binder to at least partially
coat and join to the high melting fibre thus reducing interstitial
space in the fibre matrix and creating a labyrinthine structure
that forms a tortuous path for air flow through the fibre matrix.
The high melting fibre remains substantially intact, although some
softening is acceptable and can act as a reinforcement in the
acoustic sheet.
[0014] Preferably, the acoustic sheet has a total air flow
resistance of between 275 and 1100 mks Rayl, more preferably
600-1100 mks Rayl and even more preferably 900-1000 mks Rayl. Such
air flow resistance values of the acoustic sheet result in
effective absorption of sound for applications such as hood or
under bonnet insulation. In this regard the acoustic sheet produced
in accordance with the present invention exhibit the acoustic
behaviour of a porous limp sheet. Porous limp sheets display
superior sound absorption at low frequencies.
[0015] Preferably, the thermoformable acoustic sheet has a low sag
modulus at temperatures up to about 150.degree. C.
[0016] The fibrous material can be a combination of fibres of
various denier. The high melt fibres are 12 denier or below, 6
denier or below and/or 4 denier or below. The adhesive fibres are 8
denier or below, 6 denier or below, 4 denier or below and/or at
about 2 denier.
[0017] The fibrous material can be selected from, but not limited
to, polyester, polyethylene terephthalate (PET), polyethylene
butylphthalate (PBT), polyethylene 1,4-cyclohexanedimethanol (PCT),
polylactic acid (PLA) and/or polypropylene (PP). Fibre with special
characteristics such as high strength or very high mailing point
can also be used. Examples include Kevlar.TM., Nomex.TM. and
Basofil.TM.. Alternatively, the high melting point fibres may be
substituted by natural fibre such as wool, hemp, kanet etc.
[0018] The web of fibrous material used to produce the acoustic
sheet of this invention can be produced from a non-woven vertically
aligned high loft thermally bonded material formed by the
STRUTO.TM. process under Patent WO 99/61693. Suitable low and high
melt materials can be used to provide the respective fibres.
[0019] The web of fibrous material used to produce the acoustic
sheet of this invention can also be produced by cross-lapping and
thermal bonding. The web can also be produced by carding fibres and
consolidation by needle punching. According to another option the
web can be produced by other non-woven textile manufacturing
methods such as melt blown, spun bond etc.
[0020] Adhesive fibres are also known as low melt, bonding or
binding fibres. Various materials can be used for the high melt and
adhesive fibres so long as the adhesive fibre can be partially
melted without substantially melting the high melt fibre. Some
softening of the high melt fibre is acceptable. The high melt fibre
preferably has a melting point above about 220.degree. C. The
adhesive fibre preferably has a melting point between 100 and
160.degree. C., more preferably 120-150.degree. C. and even more
preferably 135-145.degree. C. It will be appreciated that
thermoplastic fibres are available in mono and bi component form. A
bicomponent fibre can be formed of discrete low and high melting
point portions. Heating such a bicomponent fibre ("adhesive
bicomponent fibre") results in at least partial melting of the low
melting point portion leaving the higher melting point portion
intact. Therefore in the method of the present invention, heating a
fibre web results in at least partial melting of the adhesive
fibres and/or the low melting point portion of any adhesive
bicomponent fibres present in the web to at least partially coat
and join to the high melting fibre. The higher melting point fibres
and high melting point portions of any adhesive bicomponent fibre
remain intact after the compaction process.
[0021] The web of fibrous material used to produce the acoustic
sheet preferably has a web weight 1000 g/m.sup.2 or below, more
preferably 800 g/m.sup.2 or below, even more preferably 600
g/m.sup.2 or below and even further preferably 400 g/m.sup.2 or
below. The web is typically compressed by between 15 and 25
times.
[0022] The compression step of the method of the present invention
can be undertaken in any suitable known manner, for example in any
flat bed laminator or calendar.
[0023] In one embodiment the fibrous material is produced as a
single layer with a high proportion, preferably greater than 50% of
adhesive and/or adhesive bicomponent fibre. This may be compacted
in a Meyer.TM. flat bed laminator at 180-220.degree. C., preferably
at 190-200.degree. C., for a period of 1-3 minutes, preferably
1.5-2 minutes. The processing conditions can be varied to alter the
thickness and/or other characteristics and the subsequent air flow
resistance of the acoustic sheet.
[0024] In one form of the invention, the thermoplastic fibres are
treated with an adhesive coating. The coating treatment can be
effected in any suitable known manner, for example by the
application of an adhesive film or an adhesive powder and
subsequent heating. The amount of adhesive treatment can be
adjusted to control the total air flow resistance of the
thermoformable acoustic sheet. The adhesive can be a crosslinking
adhesive powder. The application rate of powder is dependent on
particle size, melting point, melt flow properties and polymer
type. These types of adhesive have an initial curing temperature
that can be exceeded after curing and cooling without remelting of
the adhesive Suitable adhesives include the product SURLYN.TM.
manufactured by DuPont. Typical polymers for the adhesive film
and/or powder are co-polyester, polyethylene and/or
polypropylene.
[0025] In one form of the invention, where the adhesive coating is
an adhesive powder, a layer of non-woven fabric or other material
may be laminated to the compressed thermoplastic sheet using the
adhesive powder.
[0026] Preferably the compression and coating treatment steps are
performed in a single process. That is, heating required prior to
the compression and for adhesive melting (to form the coating) can
be a single step before compression.
[0027] In another form of the invention, the compression of the
thermoplastic fibre and the lamination to the non-woven fabric are
achieved in a single process. Preferably a compression and adhesive
melting temperature of about 200.degree. C. is used.
[0028] In another form of the invention, the coating by use of a
web of thermoplastic fibres may be effected by the application of
multiple webs of fibrous material which are introduced in parallel
into the compaction process, and compacted concurrently.
Alternatively, the web(s) can be introduced in one or more further
compacting steps after the first web of fibrous material including
adhesive and high melt thermoplastic fibres has been compacted. The
further web(s) of fibrous material can include adhesive fibre,
adhesive bicomponent fibre and/or high melt fibre. The amount and
type of additional fibrous material can be adjusted to control the
total air flow resistance of the thermoformable acoustic sheet.
[0029] In one form of the invention the thermoformable acoustic
sheet can be formed from a first web preferably comprising 10-40%,
further preferably 20% high melting point fibre and a second web of
fibrous material, preferably comprising 60-100% further preferably
more than 70%, even further preferably 100% adhesive or adhesive
melt bicomponent fibre. The two webs can be compacted concurrently
and adhere to each other without the need for an adhesive
layer.
[0030] In another form of the invention the thermoformable acoustic
sheet may be formed from two webs in which one of the webs may have
a relatively low proportion of adhesive or adhesive bicomponent
fibre, such as 10-60% preferably 20-25%. The webs can be compacted
as described above. However, in this embodiment, a thermoplastic
adhesive layer may be required to be introduced between the two
webs, in the form of a powder. The addition rate of the powder is
preferably within the range 10 and 80 g/m.sup.2, more preferably
40-60 g/m.sup.2. If a film is used rather than a powder it must be
thin enough to become permeable during the compaction process,
preferably from 15-25 microns thick. The adhesive may be required
if the compressed webs exhibit recovery after compaction, or if
they do not compact sufficiently for adequate sound absorption.
[0031] The mouldable acoustic sheet according to this invention has
been found to be particularly suitable for use in automotive
applications and In particular as an under bonnet acoustic liner.
The thermoformable acoustic sheet can be readily formed using a
moulding temperature of between 150.degree. and 180.degree. C. and
may require use of flame retardant fibres or an additional flame
retardant treatment. Suitable additives as flame retardants are
deca-bromodiphenyloxide as supplied by Great Lake Chemicals. High
melt fibres having improved inherent flame retardant
characteristics may be used, for example a grafted polyester such
as Trevira.TM. CS. The moulded sheet substantially retains the air
flow resistance of the unmoulded sheet and thus its acoustic
properties. Moreover, the sheet has a low sag modulus at
temperatures up to about 150.degree. C. and is suitable for use as
an under bonnet insulator or liner.
[0032] For hood insulator applications, the appearance must be
consistent and low gloss. Appearance can be influenced by the fibre
properties and binder fibres tend to develop gloss during
compaction and subsequent molding. To minimise gloss, the option of
using an additional layer of fibrous material as the coating with
each layer having significantly different fibre blend ratios is
preferred. A face web should have a relatively low proportion of
binder fibre, preferably 10-20% and a back web should have a very
high binder ration, from 60-100%, preferably 80%. The back web will
significantly contribute to flow resistance to assure excellent
sound absorption, whilst the facing web assists in resisting
marring during the process.
[0033] The thermoformable material of this invention is also
suitable for use in wheel arch linings, head linings and boot
linings. In most applications the selected air flow resistance of
the moulded sheet can be used in combination with an acoustic
cavity or space behind the sheet to achieve desired acoustic
absorption.
[0034] In another form of the invention the uniform air flow
resistance can be at least partially achieved by laminating a
textile layer with selected air flow resistance to the compressed
sheet. The layer can for example be a slit or perforated
thermoplastic film or textile layer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] The invention will now be described by way of example only
with reference to the accompanying drawings and examples, in
which:
[0036] FIG. 1 is a schematic diagram of a flat bed laminating
machine;
[0037] FIG. 2 is a plot of normal incidence sound absorption
coefficient against frequency for tested samples of this
invention;
[0038] FIG. 3 is a plot of flow resistance versus fibre formulation
for samples having a high melt/adhesive fibre ratio of 1:1 and web
weight of 600 g/m.sup.2;
[0039] FIG. 4 is a plot of flow resistance versus powder additive
weight for samples having a high melt (6 denier)/adhesive (4
denier) fibre ratio of 1:1, and a web weight of 600 g/m.sup.2;
[0040] FIG. 5 is a plot of sound absorption versus flow resistance
for a range of samples with a web weight of 600 g/m.sup.2 at a
frequency of 1000 Hz and a 60 mm air gap; and
[0041] FIG. 6 is a plot of sound absorption versus product weight
for a range of samples with an air flow resistance of 600 mks Rayls
at a frequency of 500 Hz and an air gap 50 mm.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0042] The present invention can be implemented using a known
laminating machine such as a Meyer laminating machine schematically
illustrated in FIG. 1. As shown in the drawing the laminating
machine 1 includes a web supply roll 2.
[0043] The web 3 is fed to a heat contact system 9, which is
readily known to those in the art as including heaters 10
positioned on either side of two opposed parallel belts 11 and 12.
The belts 11, 12 are thus heated and in turn heat the web 3 to
about 200.degree.. A pair of adjustable pressure rollers 13, 14
bear against the respective belts 11, 12 to compress the web 3. A
subsequent cooling system 15 is provided to cool the compressed
product.
[0044] In the case of a product made using a thermoplastic adhesive
powder, the web 3 is fed from the supply roller through a scatter
head 4 which applies the thermoplastic adhesive powder to the
surface of the web 3. A winding system 5 for thermoplastic adhesive
film 6 is also provided in the machine 1. It will be apparent to
those skilled in one art one or other of the scatter head system 4
or unwinding system 5 for thermoplastic adhesive film 6 is to place
adhesive in contact with web 3. As described above, the web 3 then
continues through heat contact system 9 where the thermoplastic
adhesive powder is melted under the action of heated belts 11, 12
as the web 3 is simultaneously compressed under the action of
pressure rollers 13, 14. Cooling system 15 cools the final product
as described above.
[0045] Where a further fabric layer or web is to be provided, a
supply of fabric or web 7 is stored on a roll 8 prior to entry into
the heat contact system 9 so that the fabric web 7 is fed to the
heat contact system 9 simultaneously with web 3. Where a
thermoplastic adhesive has been deposited on web 3 by scatter head
system 4 or unwinding system 5, the heated belts 11, 12 heat the
fabric 7 and web 3 to melt the adhesive. Pressure rollers 13, 14
bear against the respective belts 11, 12 to force fabric 7 into
contact with web 3 and the melted adhesive. Again, as described
above, the web 3 is compressed and the cooling system 15 cools the
compressed and laminated product.
Test Results
Example 1
[0046] A sample was prepared using the above described machine and
tested using an impedance tube with a 50 mm air gap to ASTME E
1050-90. The properties of the sample were: [0047] carrier
formulation 30% polypropylene (adhesive fibre) and 70% polyester
(high melt); [0048] web material was a needle punched mixture in
roll form; [0049] carrier web weight 450 g/m.sup.2; and [0050]
polyester non-woven fabric facing web weight 50 g/m.sup.2 adhered
with a small (15-20 g) of polypropylene powder.
[0051] The average air flow resistance of the sample was 300-400
mks Rayls.
[0052] FIG. 2 is a plot of average incident sound absorption versus
frequency for six randomly selected samples prepared according to
this example.
Example 2
[0053] A sample was prepared and tested in the same manner as in
Example 1 with the following specifications: [0054] 50% high melt
fibre of 6 denier; [0055] 50% adhesive fibre of 4 denier; and
[0056] web weight 700 g/m.sup.2.
[0057] The air flow resistance of the sample was in the range of
300-400 mks Rayls.
Example 3
[0058] A sample was prepared and tested in the same manner as in
Example 1 with the following specifications; [0059] 30% high melt
polyester fibre of 6 denier, [0060] 70% adhesive polyester fibre of
4 denier; [0061] web weight 600 g/m.sup.2.
[0062] The air flow resistance of the sample was in the range of
700-850 mks Rayls.
Example 4
[0063] A sample was prepared and tested in the same manner as in
Example 1 with the following specifications: [0064] 50% high melt
polyester fibre of 6 denier; [0065] 50% adhesive bicomponent
polyester fibre of 4 denier; and [0066] web weight 600
g/m.sup.2.
[0067] As shown in FIG. 3, the air flow resistance of the sample
was in the range of 275-375 mks Rayls.
Example 5
[0068] A sample was prepared and tested in the same manner as in
Example 1 with the following specifications: [0069] 50% staple high
melt polyester fibre of 6 denier, [0070] 50% adhesive bicomponent
polyester fibre of 2 denier; and [0071] web weight 600
g/m.sup.2.
[0072] As shown in FIG. 3, the air flow resistance of the sample
was in the range of 450-600 mks Rayls.
Example 6
[0073] A sample was prepared and tested in the same manner as in
Example 1 with the following specifications: [0074] 50% high melt
polyester fibre of 3 denier; [0075] 50% adhesive polyester fibre of
2 denier; and [0076] web weight 600 g/m.sup.2.
[0077] As shown in FIG. 3, the air flow resistance of the sample
was in the range of 550-750 mks Rayls.
Example 7
[0078] A sample was prepared and tested in the same manner as in
Example 1 with the following specifications: [0079] 30% high melt
polyester fibre of 4 denier; [0080] 70% adhesive bicomponent
polyester fibre of 2 denier; [0081] web weight 250 g/m.sup.2;
[0082] spun bonded non-woven fabric polyester with a web weight of
100 g/m.sup.2; [0083] polyethylene thermoplastic powder at an
application rate of 20 g/m.sup.2; and [0084] dibromophenyloxide
flame retardant additive at an application of 25 g/m.sup.2.
[0085] The air flow resistance of the sample was in the range of
700-900 mks Rayls.
Example 8
[0086] A sample was prepared and tested in the same manner as in
Example 1 using two webs of fibrous material with the following
specifications: [0087] 180 g/m.sup.2 30% bicomponent polyester
fibre of 2 denier and 70% high melt black 4 denier polyester fibre;
and [0088] 300 g/m.sup.2 100% 2 denier bicomponent fibre.
[0089] The two webs of the above specification were introduced to a
Meyer laminator at the following settings. [0090] pressure 15 KPa;
[0091] distance between top and bottom belt 1 mm; [0092] first bank
of heaters temperature 175.degree. C.; and [0093] second bank of
heaters temperature 190.degree. C.
[0094] This resulted in a flow resistance of 900-1100 mks
Rayls.
Example 9
[0095] A sample was prepared and tested in the same manner as in
Example 8:
Web 1
[0096] 85% high melt polyester fibre with 4 denier; [0097] 15%
adhesive bicomponent polyester fibre of 2 denier; and [0098] web
weight 180 g/m.sup.2.
Web 2
[0098] [0099] a 30% staple high melt polyester fibre of 4 denier;
[0100] 70% adhesive bicomponent polyester-fibre of 2 denier; and
[0101] web weight 250 g/m.sup.2.
[0102] The airflow resistance of the sample was in the range of
700-900 mks Rayls.
Example 10
[0103] Samples were prepared and tested in the same manner as in
Example 1 with the following specifications: [0104] 50% high melt
polyester fibre of 6 denier; [0105] 50% adhesive polyester fibre of
4 denier: [0106] web weight 600 g/m.sup.2; and [0107] varying
application rates of LDPE adhesive powder.
[0108] Eight samples were made, each with the application rate of
the adhesive powder varying from 10 g/m.sup.2 to 80 g/m.sup.2 in 10
g/m.sup.2 intervals. A plot of the resulting air flow resistance of
each sample is shown in FIG. 4.
[0109] Test results for a range of acoustic sheets made in
accordance with the invention are illustrated in FIGS. 5 and 6. In
FIG. 5, a range of samples with a web weight 600 g/m.sup.2 were
tested at a frequency of 1000 Hz with a 50 mm air gap between the
sample and a solid surface for their sound absorption coefficient
against the air flow resistance. FIG. 6 illustrates the sound
absorption coefficient against product weight (g/m.sup.2) for a
range of samples having an air flow resistance of 600 mks Rayls.
The sound absorption coefficients were measured at a frequency of
500 Hz with a 50 mm air gap between the samples and a solid
surface.
[0110] The air flow resistance is dependent on the ratio of binder
mat to high melt fibre. If a low air flow resistance is required,
then a smaller amount of binder is required. For a high air flow
resistance, the binder ratio is significantly higher.
[0111] Air flow resistance can vary with fibre size and geometry.
Larger diameter fibres result in lower air flow resistance through
a higher porosity.
[0112] The foregoing describes a limited number of embodiments of
the invention and modifications can be made without departing from
the scope of the invention.
* * * * *