U.S. patent application number 12/049535 was filed with the patent office on 2008-07-24 for thermally expandable material useful for reducing vibratioin transfer.
Invention is credited to Sylvain Germes, Laurent Tahri, Jean-Luc Wojtowicki.
Application Number | 20080176969 12/049535 |
Document ID | / |
Family ID | 35998524 |
Filed Date | 2008-07-24 |
United States Patent
Application |
20080176969 |
Kind Code |
A1 |
Tahri; Laurent ; et
al. |
July 24, 2008 |
THERMALLY EXPANDABLE MATERIAL USEFUL FOR REDUCING VIBRATIOIN
TRANSFER
Abstract
A thermally expandable material is provided that, once expanded,
has a Young's storage modulus E' between 0.1 MPa and 1000 MPa, a
loss factor of at least 0.3 (preferably, at least 1) and preferably
a shear storage modulus G' between 0.1 MPa and 500 MPa at a
temperature between -10 and +40 degrees C. in the frequency range 0
to 500 Hz. Such materials are useful in combination with a carrier
to form a dissipative vibratory wave barrier that effectively
reduces the transfer of vibrations from a vibration generator, as
may be present in a vehicle.
Inventors: |
Tahri; Laurent; (Cosne sur
Loire, FR) ; Wojtowicki; Jean-Luc; (Pouilly sur
Loire, FR) ; Germes; Sylvain; (Fontenay-le-Fleury,
FR) |
Correspondence
Address: |
HENKEL CORPORATION
1001 TROUT BROOK CROSSING
ROCKY HILL
CT
06067
US
|
Family ID: |
35998524 |
Appl. No.: |
12/049535 |
Filed: |
March 17, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11542928 |
Oct 2, 2006 |
7364221 |
|
|
12049535 |
|
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Current U.S.
Class: |
521/99 |
Current CPC
Class: |
C08J 9/06 20130101; G10K
11/16 20130101; C08J 2353/02 20130101; C08L 23/0853 20130101 |
Class at
Publication: |
521/99 |
International
Class: |
C08J 9/00 20060101
C08J009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 6, 2005 |
EP |
05292082.4 |
Claims
1. A thermally expandable material that when expanded has a Young's
storage modulus E' between 0.1 MPa and 1000 MPa and a loss factor
higher than 0.3 at a temperature between -10 and +40 degrees C. in
the frequency range 0 to 500 Hz.
2. A thermally expandable material in accordance with claim 1,
wherein said thermally expandable material comprises at least one
thermoplastic elastomer, at least one non-elastomeric
thermoplastic, at least one stabilizer or antioxidant, at least one
blowing agent, and at least one curing agent.
3. A thermally expandable material in accordance with claim 1,
wherein said thermally expandable material is comprised of at least
one peroxide curing agent.
4. A thermally expandable material in accordance with claim 1,
wherein said thermally expandable material is comprised of at least
one thermoplastic elastomer selected from the group consisting of
thermoplastic polyurethanes, styrene/butadiene block copolymers,
hydrogenated styrene/butadiene block copolymers, styrene/isoprene
block copolymers, and hydrogenated styrene/isoprene block
copolymers.
5. A thermally expandable material in accordance with claim 1,
wherein said thermally expandable material is comprised of at least
one non-elastomeric thermoplastic selected from the group
consisting of ethylene/vinyl acetate copolymers and ethylene/methyl
acrylate copolymers.
6. A thermally expandable material in accordance with claim 1,
wherein said thermally expandable material is comprised of at least
one olefinically unsaturated monomer or oligomer.
7. A thermally expandable material in accordance with claim 1,
wherein said thermally expandable material is comprised of at least
one plasticizer.
8. A thermally expandable material in accordance with claim 1,
wherein said thermally expandable material is comprised of at least
one wax.
9. A thermally expandable material in accordance with claim 1,
wherein said thermally expandable material is comprised of at least
one latent chemical blowing agent.
10. A thermally expandable material in accordance with claim 1,
wherein said thermally expandable material is comprised of at least
one tackifying resin.
11. A thermally expandable material in accordance with claim 1,
wherein said thermally expandable material is comprised of at least
one blowing agent activator.
12. A thermally expandable material in accordance with claim 1,
wherein said thermally expandable material is comprised of at least
one styrene/isoprene/styrene triblock polymer or fully or partially
hydrogenated derivative thereof with at least about 50% of the
polymerized isoprene monomer moieties having 1,2 and/or 3,4
configurations.
13. A thermally expandable material in accordance with claim 1,
wherein said thermally expandable material comprises: a). from 25
to 70% by weight of at least one thermoplastic elastomer; b). from
15 to 40% by weight of at least one non-elastomeric thermoplastic;
c). from 0.01 to 2% by weight of at least one stabilizer or
antioxidant; d). from 2 to 15% by weight of at least one blowing
agent; and e). from 0.5 to 4% by weight of at least one curing
agent.
14. A thermally expandable material in accordance with claim 1,
wherein said thermally expandable material comprises: a). from 35
to 55% by weight of at least one thermoplastic elastomer selected
from the group consisting of thermoplastic polyurethanes,
styrene/butadiene block copolymers, hydrogenated styrene/butadiene
block copolymers, styrene/isoprene block copolymers, and
hydrogenated styrene/isoprene block copolymers; b). from 20 to 35%
by weight of at least one non-elastomeric thermoplastic selected
from the group consisting of ethylene/vinyl acetate copolymers and
ethylene/methyl acrylate copolymers; c). from 0.05 to 1% by weight
of at least one stabilizer or antioxidant; d). at least one latent
chemical blowing agent in an amount effective to cause the
expandable material to expand at least 100% in volume when heated
at a temperature of 150 degrees C. for at least 20 minutes; e).
from 0.5 to 4% by weight of at least one peroxide; and f). from 0.5
to 2% by weight of at least one olefinically unsaturated monomer or
oligomer; wherein said thermally expandable material contains less
than 10% by weight filler.
15. A thermally expandable material in accordance with claim 1,
wherein said thermally expandable material comprises: a). from 25
to 70% by weight of at least one thermoplastic elastomer; b). from
15 to 40% by weight of at least one non-elastomeric thermoplastic;
c). from 0.01 to 2% by weight of at least one stabilizer or
antioxidant; d). from 2 to 15% by weight of at least one blowing
agent; e). from 0.5 to 4% by weight of at least one curing agent;
f). at least one tackifying resin, in an amount up to 10% by
weight; g). at least one wax, in an amount up to 10% by weight; and
h). at least one plasticizer, in an amount up to 5% by weight.
16. A thermally expandable material in accordance with claim 1,
wherein said thermally expandable material comprises: a). from 35
to 55% by weight of at least one styrene/isoprene block copolymer
thermoplastic elastomer selected from the group consisting of
styrene/isoprene block copolymers; b). from 20 to 35% by weight of
at least one non-elastomeric thermoplastic selected from the group
consisting of ethylene/vinyl acetate copolymers; c). from 0.05 to
1% by weight of at least one stabilizer or antioxidant; d). at
least one latent chemical blowing agent in an amount effective to
cause the expandable material to expand at least 100% in volume
when heated at a temperature of 150 degrees C. for at least 20
minutes; e). from 0.5 to 4% by weight of at least one organic
peroxide; f). from 0.5 to 2% by weight of at least one C.sub.1 to
C.sub.6 alkyl (meth)acrylate; g). at least one tackifying resin, in
an amount up to 10% by weight; h). at least one plasticizer, in an
amount up to 5% by weight; and i). at least one wax, in an amount
up to 10% by weight; wherein said thermally expandable material
contains less than 10% by weight filler.
17. A thermally expandable material in accordance with claim 16,
wherein at least about 50% of the polymerized isoprene monomer
moieties in said at least one styrene/isoprene block copolymer
thermoplastic elastomer have 1,2 and/or 3,4 configurations.
18. A thermally expandable material in accordance with claim 1,
wherein said thermally expandable material comprises: a). from 35
to 55% by weight of at least one styrene/isoprene block copolymer
thermoplastic elastomer selected from the group consisting of
styrene/isoprene block copolymers; b). from 20 to 35% by weight of
at least one non-elastomeric thermoplastic selected from the group
consisting of ethylene/vinyl acetate copolymers; c). from 0.05 to
1% by weight of at least one stabilizer or antioxidant; d). at
least one latent chemical blowing agent in an amount effective to
cause the expandable material to expand at least 100% in volume
when heated at a temperature of 150 degrees C. for at least 20
minutes; e). from 0.5 to 4% by weight of at least one curing agent
capable of inducing free radical reactions; g). at least one
tackifying resin, in an amount up to 10% by weight; and h). at
least one plasticizer, in an amount up to 5% by weight.
19. A thermally expandable material in accordance with claim 18,
wherein at least about 50% of the polymerized isoprene monomer
moieties in said at least one styrene/isoprene block copolymer
thermoplastic elastomer have 1,2 and/or 3,4 configurations.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of application Ser. No.
11/542,928, filed 2 Oct. 2006, now allowed, which claims priority
under the Paris Convention to European Patent Application No.
05292082.4, filed 6 Oct. 2005, and incorporated herein by reference
in its entirety.
FIELD OF THE INVENTION
[0002] The present invention relates to reducing the transfer of
vibrations generated by a vibration generator.
DISCUSSION OF THE RELATED ART
[0003] In a vehicle, the transfer of vibrations generated by a
dynamic force generator, such as an engine, a motor, a pump or a
gear box, via structural elements to an emitting surface such as a
panel, leads to the emission of structure borne noise.
[0004] Different solutions have been suggested in order to at least
reduce such structure borne noise. In vehicle construction, passive
measures such as the recourse to vibration dampers or dampening
mats have been proposed. Such dampening mats are often applied on
vibrating panels, e.g., in the doors or on the floor of a vehicle.
The extent of noise reduction of these methods is often
unsatisfactory.
[0005] In the conventional process, mixtures of bitumen or asphalt
and fillers with a high specific weight are extruded into sheets,
from which the appropriate shapes are punched or cut. These sheets
are then bonded to the appropriate metal sheet parts and must
sometimes also be adapted to the shape of the sheet by heating.
Although these bitumen sheets are still frequently used because of
their low material cost, they are very brittle and tend to peel off
from the metal sheet, particularly at low temperatures. Also, the
incorporation of additives which has often been proposed only
results in a slight improvement which is not sufficient for many
applications. Moreover, it is completely impossible to apply the
pre-formed bitumen parts to the complex-shaped or almost
inaccessible metal sheet parts of machines or vehicles, e.g., the
inner surfaces of the cavities of motor vehicle doors. In addition,
there is the further disadvantage that in many cases several
punched parts are required for only one vehicle or appliance and
therefore costly storage is required.
[0006] There has consequently been no lack of attempts to eliminate
the disadvantages of bitumen sheets using other polymer systems.
For example, aqueous polymer dispersions of polyvinylacetate or
ethylene-vinylacetate copolymers containing fillers were developed
which can be sprayed on to the metal sheet parts with the necessary
coating thickness. These systems are, however, disadvantageous for
industrial use when there are high rates of production because the
water cannot be removed rapidly enough from the coating that is
sprayed on, particularly when this coating is fairly thick.
[0007] The sound damping properties of polymer coatings are best in
the range of the glass transition temperature of the polymer
system, because due to the viscoelasticity of the polymer in this
temperature range the mechanical energy of the vibration process is
converted into heat by molecular flow phenomena. Conventional
sprayable coating materials based on PVC plastisols, which, e.g.,
are widely used as an underbody coating in motor vehicle
construction, have no notable sound damping effect in the
application temperature range of -20 to +60.degree. C. because the
maximum value of the glass transition is about -20.degree. C. to
-50.degree. C., depending on the proportion of plasticizer.
[0008] Attempts were therefore made to modify these conventional
PVC plastisols so that they would have better sound damping
properties in the application temperature range of -20.degree. C.
to +60.degree. C. Coatings are known from German published patent
application 3514753 which contain multiply unsaturated compounds,
e.g., di- or triacrylates, peroxide cross-linking agents and
inorganic fillers, in conventional PVC plastisols. In the hardened
state these plastisols are, however, glass-hard and brittle, and
are therefore not really suitable for use in automobile
construction because they do not have sufficient flexibility,
particularly at low temperatures. Apart from this, these
formulations have a very low loss factor tan .delta. and thus the
sound damping effect is not very marked.
[0009] Compositions are described in German published patent
application 3444863 which contain PVC or vinylchloride/vinylacetate
copolymers, optionally methylmethacrylate homopolymers or
copolymers, a plasticizer mixture and inert fillers. The
plasticizer mixture comprises plasticizers which are compatible
with the methylmethacrylate polymers and plasticizers for the
vinylchloride polymers which are incompatible with the
methylmethacrylate polymers which may be present. The plastisols
thus obtained have improved sound damping properties compared with
conventional PVC plastisols. However, particularly at temperatures
above about 30.degree. C., the sound damping effect drops again. If
an attempt is made to shift the range of the maximum loss factor
tan .delta. to higher temperatures by varying the relative
quantities of the individual components, the cold flexibility of
the coating drops very severely. A reduced cold flexibility is,
however, precisely what is disadvantageous in vehicle construction.
In addition, the loss factor decreases very severely at lower
temperatures with these formulations. These plastisol compositions
therefore have a sufficiently high loss factor only in a very
narrow temperature range.
[0010] Furthermore, active measures for reducing structure borne
noise have been developed. These measures usually employ sensors,
signal processing, actuators, and power sources to counteract or
effectively increase the dissipation of the vibration by producing
corresponding forces or strains.
[0011] Although active control measures have been shown to
effectively reduce structure borne noise, they require
sophisticated technical equipment, especially with respect to
signal processing and sensors. This does not only increase the
costs, but also leads to an increased risk of breakdown.
[0012] Therefore, there is a need for an economic means for
effectively reducing structure borne noise in a system, especially
in a vehicle.
[0013] It is therefore an object of the present invention to
overcome the drawbacks of the prior art.
BRIEF SUMMARY OF THE INVENTION
[0014] After long and extensive research work the inventors have
now found that effective reduction of structure borne noise in a
system such as a vehicle may be achieved by way of a particular
dissipative vibratory wave barrier, a particular thermally
expandable material useful for the manufacture of said dissipative
vibratory wave barrier, and a method employing said dissipative
vibratory wave barrier.
[0015] The dissipative vibratory wave barrier according to the
present invention comprises a carrier having an inner surface and
an outer surface, the carrier having a polygonal section,
especially rectangular, optionally U-shaped, and comprising on at
least one of its outer surface or its inner surface a coating
comprising a thermally expandable material selected among those
which, after expansion and at a temperature between -10 and
+40.degree. C., have a Young's storage modulus E' between 0.1 MPa
and 1000 MPa, preferably a loss modulus E'' between 0.5 and 1, a
loss factor greater than 0.3 (preferably, greater than 1) and
preferably also a shear storage modulus G' between 0.1 MPa and 500
MPa in the frequency range 0 to 500 Hz.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a schematic perspective view of a first embodiment
of a dissipative vibratory wave barrier according to the present
invention before expansion of the thermally expandable
material.
[0017] FIG. 2 is a schematic perspective view of the dissipative
vibratory wave barrier of FIG. 1 after expansion of the thermally
expandable material.
[0018] FIG. 3 is a schematic perspective view of the dissipative
vibratory wave barrier of FIG. 1 after insertion into a structural
element.
[0019] FIG. 4 is a schematic perspective view of the dissipative
vibratory wave barrier of FIG. 3 after expansion of the thermally
expandable material.
[0020] FIG. 5 is a graph showing three curves representing the
variation of the structure borne noise in a car body as a function
of frequency.
DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS OF THE INVENTION
[0021] As previously mentioned, the thermally expandable material
to be used in combination with a carrier is selected among those
which, after expansion and at a temperature between -10 and
+40.degree. C., have a Young's storage modulus E' between 0.1 MPa
and 1000 MPa, preferably a loss modulus E'' between 0.5 and 1, a
loss factor greater than 0.3 (preferably, greater than 1) and
preferably also a shear storage modulus G' between 0.1 MPa and 500
MPa in the frequency range 0 to 500 Hz.
[0022] Young's storage modulus (E') is defined as the ratio of
tensile stress to tensile strain below the proportional limit of a
material. Shear storage modulus G' is defined as the ratio of
shearing stress to shearing strain within the proportional limit
and is considered a measure of the equivalent energy stored
elastically in a material. The loss factor (also sometimes referred
to as the structural intrinsic damping or tan delta) is the ratio
of the Young's loss modulus E'' over Young's storage modulus E' for
the damping in tension compression. For the damping in shear, the
loss factor is the ratio of the shear loss modulus G'' over the
shear storage modulus G'. These values may be readily determined by
Dynamic Mechanical Analysis (DMA) of a material, which in the
context of this invention is the thermally expandable material
after expansion. As is well known in the art, Dynamic Mechanical
Analysis can be performed either by an indirect method where the
material is characterized on a carrier (Oberst's beam test) or by a
direct method where the tested sample is made only from the
material to be characterized (viscoanalyzer).
[0023] The carrier selected for use in the present invention has an
inner surface and an outer surface. In cross-section, the carrier
should be polygonal in shape. Preferably, the cross-sectional shape
of the carrier has at least three sides that are straight lines
and/or arcs. In one embodiment, the carrier is open or partially
open on one side, but in another embodiment the cross-sectional
shape of the carrier is closed. For example, the carrier in
cross-section may have a shape selected from the group consisting
of rectangular, square, pentagonal, hexagonal, U-shaped, and
D-shaped. The sides of the carrier may be equal or different in
length, with the lengths of the sides generally being selected in
accordance with the interior dimensions of the structural element
into which the dissipative vibratory wave barrier is to be inserted
or the exterior dimensions of the structural element onto which the
dissipative vibratory wave barrier is to be fixed. The carrier may
be completely hollow, but in certain embodiments could have one or
more interior elements such as braces, ribs, cross-walls and the
like. The carrier may be designed with small tabs, legs or other
protrusions on its surface(s) or edge(s) that will face the bottom
of the hollow structural element into which the dissipative
vibratory wave barrier is to be inserted. These protrusions are
configured to hold such surface(s) or edge(s) away from the lower
interior surface of the structural element, thereby allowing any of
the liquids used in vehicle assembly operations to more completely
coat or contact such lower interior surface. In the embodiment
where the dissipative vibratory wave barrier is fixed onto the
outside of the structural element, the surface of the barrier
having the coating of thermally expandable material positioned
thereon and facing the exterior surface of the surface element may
be similarly held a relatively short distance away from such
exterior surface by any suitable positioning means such as spacer
elements, clips, flanges and the like.
[0024] In one embodiment of the invention, the carrier is straight.
In other embodiments, however, the carrier may be bent or curved.
In still other embodiments, the carrier may be straight in certain
sections and curved in other sections. Each side of the carrier may
be planar (flat), but it is also possible for a side of the carrier
to be non-planar (e.g., curved or containing one or more indented
areas and/or one or more protruding sections). The carrier sides
may be continuous (free of any openings), but in certain
embodiments one or more sides of the carrier could contain one or
more openings. Generally speaking, the shape and configuration of
the carrier are selected so as to generally parallel or match the
contours or shape of the structural element into which the
dissipative vibratory wave barrier is to be inserted or onto which
the dissipative vibratory wave barrier is to be fixed and to clear
any elements within the structural element or on the exterior of
the structural element that might otherwise prevent the dissipative
vibratory wave barrier, once coated with the thermally expandable
material, from fitting within or onto such structural element. As
will be explained in more detail subsequently, it will be desirable
to allow at least some clearance room between the outer surfaces of
the dissipative vibratory wave barrier and the inner surfaces of
the structural element (in the embodiment where the barrier is to
be inserted into the structural element) or between the inner
surfaces of the dissipative vibratory wave barrier and the outer
surfaces of the structural element (in the embodiment where the
barrier is to be fixed onto the outside of the structural
element.
[0025] The carrier may be made of metal. Preferred metals are
steel, particularly galvanized steel, and aluminum.
[0026] The carrier may also be made of a synthetic material, which
may optionally be fiber reinforced (e.g., with glass fibers) and/or
reinforced with other types of fillers. Preferred synthetic
materials are thermoplastic synthetic materials having a low water
absorption and dimensionally stable up to at least 180.degree. C.
Suitable thermoplastic synthetic materials may, for example, be
selected within the group consisting of polyamides (PA),
polyphenylene sulphides (PPS), polyphenylene ethers (PPE),
polyphenylene sulfones (PPSU), polyether imides (PEI) and
polyphenylene imides (PPI). Thermoset synthetic materials such as
molding compounds, rigid polyurethanes, and the like may also be
used to construct the carrier. The carrier may be formed into the
desired shape by any suitable method, such as, for example, molding
(including injection molding), stamping, bending, extrusion and the
like.
[0027] Preferably, the carrier is relatively stiff. In one
embodiment, the carrier is at least as stiff at room temperature as
the structural element into which the dissipative vibratory wave
barrier will be inserted or onto which the dissipative vibratory
wave barrier will be fixed.
[0028] In the embodiment where the dissipative vibratory wave
barrier is to be inserted into the structural element, the coating
is applied to at least a part of the outer surface of the carrier
but may also be applied to the whole outer surface. Similarly, in
the embodiment where the dissipative vibratory wave barrier is to
be fixed onto the structural element, the coating is applied to at
least a part of the inner surface of the carrier but may also be
applied to the whole inner surface. The coating of thermally
expandable material may be continuous, although the present
invention also contemplates having two or more separate portions of
the thermally expanded material on the outer or inner surface of
the carrier. These portions may differ in size, shape, thickness,
etc.
[0029] The coating comprising the thermally expandable material may
be uniform in thickness, but may also be varied in thickness over
the outer or inner surface of the carrier. Typically, the coating
will be from 0.5 to 10 mm thick.
[0030] The thermally expandable material is a material that will
foam and expand upon heating but that is typically solid (and
preferably dimensionally stable) at room temperature (e.g., 15-30
degrees C.). In some embodiments, the expandable material will be
dry and non-tacky, but in other embodiments will be tacky. The
thermally expandable material preferably is formulated such that it
is capable of being shaped or molded (e.g., by injection molding or
extrusion) into the desired form for use, such shaping or molding
being carried out at a temperature above room temperature that is
sufficient to soften or melt the expandable material so that it can
be readily processed but below the temperature at which expansion
of the expandable material is induced. Cooling the shaped or molded
expandable material to room temperature yields a dimensionally
stable solid having the desired shape or form. Upon activation of
the blowing agent, i.e., upon being subjected to a temperature of
between about 130.degree. C. and 240.degree. C. (depending on the
exact formulation of expandable material that is used), the
expandable material will typically expand to at least about 100% or
at least about 150% or alternatively at least about 200% of its
original volume. Even higher expansion rates (e.g., at least about
1000%) may be selected where required by the desired end use. When
used in an automobile body, for example, the expandable material
typically has an activation temperature lower than the temperature
at which primer or paint is baked on the vehicle body during
manufacture.
[0031] The thermally expandable material may be applied to the
carrier surface by any suitable means such as extrusion,
co-molding, over-molding, or the like. For example, the thermally
expandable material may be heated to a temperature sufficient to
soften or melt the material without activating the blowing agent or
curing agent that may be present and the softened or melted
material then extruded as a ribbon onto the outer or inner carrier
surface. Upon cooling, the ribbon of thermally expandable material
then re-solidifies and adheres to the carrier surface.
Alternatively, sheets of the thermally expandable material may be
formed into individual portions of the desired size and shape by
die-cutting, with the individual portions then being attached to
the outer or inner surface of the carrier by any suitable means
such as mechanical fasteners or heating the surface of the portion
that is to be contacted with the carrier surface to a temperature
sufficient for the expandable material to function as a hot melt
adhesive. A separately applied adhesive layer may also be used to
attach the thermally expandable material to the outer or inner
surface of the carrier.
[0032] In an especially advantageous embodiment, the thermally
expandable material comprises:
[0033] from 25 to 70% by weight, preferably from 35 to 55% by
weight, of at least one thermoplastic elastomer (preferably a
styrene/butadiene or styrene/isoprene block copolymer or at least
partially hydrogenated derivative thereof);
[0034] from 15 to 40% by weight, preferably from 20 to 35% by
weight, of at least one non-elastomeric thermoplastic (preferably
an ethylene/vinyl acetate or ethylene/methyl acrylate
copolymer);
[0035] from 0.01 to 2% by weight, preferably from 0.05 to 1% by
weight, of at least one stabilizer or antioxidant;
[0036] from 2 to 15% by weight of at least one blowing agent,
preferably an amount effective to cause the expandable material to
expand at least 100% in volume when heated at a temperature of 150
degrees C.;
[0037] from 0.5 to 4% by weight of one or more curing agents,
optionally including from 0.5 to 2% by weight of at least one
olefinically unsaturated monomer or oligomer, and optionally;
[0038] up to 10% by weight (e.g., 0.1 to 10% by weight) of at least
one tackifying resin;
[0039] up to 5% by weight (e.g., 0.1 to 5% by weight) of at least
one plasticizer;
[0040] up to 10% by weight (e.g., 0.1 to 10% by weight) of at least
one wax;
[0041] up to 3% by weight (e.g., 0.05 to 3% by weight) of at least
one activator for the blowing agent;
as well as optionally at least one filler (although the amount of
filler is preferably less than 10% by weight, more preferably less
than 5% by weight), the percentages being expressed as weight
percentages of the total weight of the thermally expandable
material.
[0042] Generally speaking, it will be desirable to use a
thermoplastic elastomer that has a softening point no higher than
the temperature at which the blowing agent begins to be activated,
preferably at least about 30 degrees C. lower than the temperature
that the expandable material will be exposed to when it is to be
expanded. The thermoplastic elastomer is preferably selected within
the group consisting of thermoplastic polyurethanes (TPU) and block
copolymers (including linear as well as radial block copolymers) of
the A-B, A-B-A, A-(B-A).sub.n-2-B, A-(B-A).sub.n-1 and
(A-B).sub.n-Y types, wherein A is an aromatic polyvinyl ("hard")
block and the B block represents a rubber-like ("soft") block of
polybutadiene, polyisoprene or the like, which may be partly or
completely hydrogenated, Y is a polyfunctional compound and n is an
integer of at least 3. The blocks may be tapered or gradient in
character or consist entirely of one type of polymerized
monomer.
[0043] Hydrogenation of the B block removes originally present
double bonds and increases the thermal stability of the block
copolymer. Such copolymers may be preferred in certain embodiments
of the present invention.
[0044] Suitable block copolymers include, but are not limited to,
SBS (styrene/butadiene/styrene) copolymers, SIS
(styrene/isoprene/styrene) copolymers, SEPS
(styrene/ethylene/propylene/styrene) copolymers, SEEPS (styrene/
ethylene/ethylene/propylene/styrene) or SEBS
(styrene/ethylene/butadiene/styrene) copolymers.
[0045] Especially suitable block copolymers include
styrene/isoprene/styrene triblock polymers, as well as fully or
partially hydrogenated derivatives thereof, in which the
polyisoprene block contains a relatively high proportion of monomer
moieties derived from isoprene having a 1,2 and/or 3,4
configuration. Preferably, at least about 50% of the polymerized
isoprene monomer moieties have 1,2 and/or 3, 4 configurations, with
the remainder of the isoprene moieties having a 1, 4 configuration.
Such block copolymers are available from Kuraray Co., Ltd. under
the trademark HYBRAR and may also be prepared using the methods
described in U.S. Pat. No. 4,987,194, incorporated herein by
reference in its entirety.
[0046] In certain preferred embodiments of the invention the "hard"
blocks represent from about 15 to about 30 percent by weight of the
block copolymer and the "soft" blocks represent from about 70 to
about 85 percent by weight of the block copolymer. The glass
transition temperature of the "soft" blocks is preferably from
about -35 degrees C. to about 10 degrees C. while the glass
transition temperature of the "hard" blocks is preferably from
about 90 degrees C. to about 110 degrees C. The melt flow index of
the block copolymer preferably is from about 0.5 to about 6 (as
measured by ASTM D1238, 190 degrees C., 2.16 Kg). Typically, the
block copolymer will have a number average molecular weight of from
about 30,000 to about 300,000.
[0047] Examples of suitable thermoplastic polyurethanes (TPU) are
those made according to conventional processes by reacting
diisocyanates with compositions having at least two isocyanate
reactive groups per molecule, preferably difunctional alcohols.
Suitable organic diisocyanates to be used include, for example,
aliphatic, cycloaliphatic, araliphatic, heterocyclic and aromatic
diisocyanates.
[0048] Specific examples of diisocyanates include aliphatic
diisocyanates such as, for example, hexamethylene-diisocyanate;
cycloaliphatic diisocyanates such as, for example,
isophorone-diisocyanate, 1,4-cyclohexane-diisocyanate,
1-methyl-2,4- and -2,6-cyclohexane-diisocyanate and the
corresponding isomer mixtures, 4,4'-, 2,4'- and
2,2'-dicyclohexylmethane-diisocyanate and the corresponding isomer
mixtures; and aromatic diisocyanates such as, for example,
2,4-toluylene-diisocyanate, mixtures of 2,4- and
2,6-toluylene-diisocyanate, 4,4'-diphenylmethane-diisocyanate,
2,4'-diphenylmethane-diisocyanate and
2,2'-diphenylmethane-diisocyanate, mixtures of
2,4'-diphenylmethane-diisocyanate and
4,4'-diphenylmethane-diisocyanate, urethane-modified liquid
4,4'-diphenylmethane-diisocyanates and/or
2,4'-diphenylmethane-diisocyanates,
4,4'-diisocyanato-1,2-diphenyl-ethane and
1,5-naphthylene-diisocyanate. Diphenylmethane-diisocyanate isomer
mixtures with a 4,4'-diphenylmethane-diisocyanate content of
greater than 96 wt. % are preferably used, and
4,4'-diphenylmethane-diisocyanate and 1,5-naphthylene-diisocyanate
are used in particular. The diisocyanates mentioned above can be
used individually or in the form of mixtures with one another.
[0049] The compounds reactive with the isocyanate groups include,
but are not limited to, polyhydroxy compounds such as polyester
polyols, polyether polyols or polycarbonate-polyols or polyols
which may contain nitrogen, phosphorus, sulfur and/or silicon
atoms, or mixtures of these. Linear hydroxyl-terminated polyols
having on average from about 1.8 to about 3.0 Zerewitinoff-active
hydrogen atoms per molecule, preferably from about 1.8 to about 2.2
Zerewitinoff-active hydrogen atoms per molecule, and having a
number average molecular weight of 400 to 20,000 g/mol are
preferably employed as polyol. These linear polyols often contain
small amounts of non-linear compounds as a result of their
production. Thus, these are also often referred to as
"substantially linear polyols".
[0050] The polyhydroxy compounds with two or three hydroxyl groups
per molecule in the number average molecular weight range of 400 to
20,000, preferably in the range of 1000 to 6000, which are liquid
at room temperature, glassy solid/amorphous or crystalline, are
preferably suitable as polyols. Examples are di- and/or
trifunctional polypropylene glycols; random and/or block copolymers
of ethylene oxide and propylene oxide can also be used. Another
group of polyethers that can preferably be used are the
polytetramethylene glycols (poly(oxytetramethylene) glycol,
poly-THF), which are produced, e.g., by the acid polymerization of
tetrahydrofuran, the number average molecular weight range of these
polytetramethylene glycols typically lying between 600 and 6000,
preferably in the range of 800 to 5000.
[0051] The liquid, glassy amorphous or crystalline polyesters that
can be produced by condensation of di- or tricarboxylic acids, such
as, e.g., adipic acid, sebacic acid, glutaric acid, azelaic acid,
suberic acid, undecanedioic acid, dodecanedioic acid,
3,3-dimethylglutaric acid, terephthalic acid, isophthalic acid,
hexahydrophthalic acid, dimerized fatty acid or mixtures thereof
with low molecular-weight diols or triols, such as, e.g., ethylene
glycol, propylene glycol, diethylene glycol, triethylene glycol,
dipropylene glycol, 1,4-butanediol, 1,6-hexanediol, 1,8-octanediol,
1,10-decanediol, 1,12-dodecanediol, dimerized fatty alcohol,
glycerin, trimethylolpropane or mixtures thereof, are also suitable
as polyols.
[0052] Another group of polyols to be used for making the TPU's are
polyesters based on .epsilon.-caprolactone, also known as
"polycaprolactones".
[0053] However, polyester polyols of oleochemical origin can also
be used. These polyester polyols can be produced, for example, by
the complete ring opening of epoxidized triglycerides of an at
least partially olefinically unsaturated, fatty acid-containing fat
mixture with one or more alcohols with 1 to 12 C atoms and
subsequent partial transesterification of the triglyceride
derivatives to alkyl ester polyols with 1 to 12 C atoms in the
alkyl radical. Other suitable polyols are polycarbonate polyols and
dimerized diols (Henkel), as well as castor oil and its
derivatives. The hydroxyfunctional polybutadienes, as obtainable,
for example, with the trade name "Poly-bd", can be used as polyols
for making the TPU's to be used according to the invention.
[0054] Preferably, combinations of polyether polyols and glassy
amorphous or crystalline polyester polyols are used for making the
TPU's.
[0055] Preferably, the polyols have an average functionality
towards isocyanate from about 1.8 to 2.3, preferably 1.9 to 2.2,
particularly about 2.0.
[0056] The thermoplastic polyurethanes may also be made by
additionally using chain extending compounds like low molecular
weight polyols such as ethylene glycol, propylene glycol or
butadiene glycol or low molecular weight diamines such as
1,2-diaminoethylene, 1,3-diaminopropylene or 1,4-diaminobutane or
1,6-diaminohexane.
[0057] In preferred embodiments, the soft domains of the
thermoplastic polyurethane are selected from the group consisting
of poly(ethylene adipate), poly(1,4-butene adipate), poly(ethylene
1,4-butene adipate), poly(hexamethylene 2,2-dimethylpropylene
adipate), polycaprolactone, poly(diethylene glycol adipate),
poly(1,6-hexanediol carbonate) and poly(oxytetramethylene).
[0058] Other thermoplastic elastomers suitable for use in the
present invention include other types of block copolymers
containing both hard segments and soft segments such as, for
example, polystyrene/polydimethylsiloxane block copolymers,
polysulfone/polydimethylsiloxane block copolymers,
polyester/polyether block copolymers (e.g., copolyesters such as
those synthesized from dimethyl terephthalate, poly(tetramethylene
ether) glycol, and tetramethylene glycol),
polycarbonate/polydimethylsiloxane block copolymers,
polycarbonate/polyether block copolymers, copolyetheramides,
copolyetheresteramides and the like. Thermoplastic elastomers which
are not block copolymers but which generally are finely
interdispersed multiphase systems or alloys may also be used,
including blends of polypropylene with ethylene-propylene rubbers
(EPR) or ethylene-propylene-diene monomer (EPDM) rubbers (such
blends often being grafted or cross-linked).
[0059] In addition to one or more thermoplastic elastomers, it is
also preferred for the expandable material to contain one or more
non-elastomeric thermoplastics. Preferably, the non-elastomeric
thermoplastic is selected so as to improve the adhesion properties
and processability of the expandable material. Generally speaking,
it will be desirable to use a non-elastomeric thermoplastic that
has a softening point no higher than the temperature at which the
blowing agent begins to be activated, preferably at least about 30
degrees C. lower than the temperature that the expandable material
will be exposed to when such material is to be expanded.
Particularly preferred non-elastomeric thermoplastics include
olefin polymers, especially copolymers of olefins (e.g., ethylene)
with non-olefinic monomers (e.g., vinyl esters such as vinyl
acetate and vinyl propionate, (meth)acrylate esters such as C1 to
C6 alkyl esters of acrylic acid and methacrylic acid). Exemplary
non-elastomeric thermoplastics especially suitable for use in the
present invention include ethylene/vinyl acetate copolymers
(particularly copolymers containing from about 20 to about 35
weight % vinyl acetate) and ethylene/methyl acrylate copolymers
(particularly copolymers containing from about 15 to about 35
weight % methyl acrylate and/or having Vicat softening points less
than 50 degrees C. and/or melting points within the range of 60 to
80 degrees C. and/or melt flow indices of from 3 to 25 g/10
minutes, as measured by ASTM D1238, 190 degrees C., 2.16 Kg).
[0060] In certain embodiments of the invention, the weight ratio of
thermoplastic elastomer: non-elastomeric thermoplastic is at least
0.5:1 or at least 1:1 and/or not greater than 5:1 or 2.5:1.
[0061] The tackifying resin may be selected within the group
consisting of rosin resins, terpene resins, terpene phenolic
resins, hydrocarbon resins derived from cracked petroleum
distillates, aromatic tackifying resins, tall oil resins, ketone
resins and aldehyde resins.
[0062] Suitable rosin resins are abietic acid, levopimaric acid,
neoabietic acid, dextropimaric acid, palustric acid, alkyl esters
of the aforementioned rosin acids, and hydrogenation products of
rosin acid derivatives.
[0063] Examples of suitable plasticizers include C.sub.1-10 alkyl
esters of dibasic acids (e.g., phthalate esters), diaryl ethers,
benzoates of polyalkylene glycols, organic phosphates, and
alkylsulfonic acid esters of phenol or cresol.
[0064] Suitable waxes include paraffinic waxes having melting
ranges from 45 to 70.degree. C., microcrystalline waxes with
melting ranges from 60 to 95.degree. C., synthetic Fischer-Tropsch
waxes with melting points between 100 and 115.degree. C. as well as
polyethylene waxes with melting points between 85 and 140.degree.0
C.
[0065] Suitable antioxidants and stabilizers include sterically
hindered phenols and/or thioethers, sterically hindered aromatic
amines and the like.
[0066] All known blowing agents, such as "chemical blowing agents"
which liberate gases by decomposition or "physical blowing agents",
i.e., expanding hollow beads (also sometimes referred to as
expandable microspheres), are suitable as blowing agent in the
present invention. Mixtures of different blowing agents may be used
to advantage; for example, a blowing agent having a relatively low
activation temperature may be used in combination with a blowing
agent having a relatively high activation temperature.
[0067] Examples of "chemical blowing agents" include azo,
hydrazide, nitroso and carbazide compounds such as
azobisisobutyronitrile, azodicarbonamide,
di-nitroso-pentamethylenetetramine, 4,4'-oxybis(benzenesulfonic
acid hydrazide), diphenyl-sulfone-3,3'-disulfohydrazide,
benzene-1,3-disulfohydrazide and p-toluenesulfonyl
semicarbazide.
[0068] "Chemical blowing agents" may benefit from the incorporation
of additional activators such as zinc compounds (e.g., zinc oxide),
(modified) ureas and the like.
[0069] However, "physical blowing agents" and particularly
expandable hollow microbeads are also useable. Advantageously, the
hollow microbeads are based on polyvinylidene chloride copolymers
or acrylonitrile/(meth)acrylate copolymers and contain encapsulated
volatile substances such as light hydrocarbons or halogenated
hydrocarbons.
[0070] Suitable expandable hollow microbeads are commercially
available, e.g., under the trademarks "Dualite" and "Expancel"
respectively, from Pierce & Stevens (now part of Henkel
Corporation) or Akzo Nobel, respectively.
[0071] Suitable curing agents include substances capable of
inducing free radical reactions, in particular organic peroxides
including ketone peroxides, diacyl peroxides, peresters, perketals,
hydroperoxides and others such as cumene hydroperoxide,
bis(tert-butylperoxy) diisopropylbenzene, di(-2-tert-butyl
peroxyisopropyl benzene),
1,1-di-tert-butylperoxy-3,3,5-trimethylcyclohexane, dicumyl
peroxide, t-butylperoxybenzoate, di-alkyl peroxydicarbonates,
di-peroxyketals (such as
1,1-di-tert-butylperoxy-3,3,5-trimethylcyclohexane), ketone
peroxides (e.g., methylethylketone peroxide), and
4,4-di-tert-butylperoxy n-butyl valerate. The curing agent is
preferably a latent curing agent, that is, a curing agent that is
essentially inert or non-reactive at room temperature but is
activated by heating to an elevated temperature (for example, a
temperature within the range of from about 130 degrees C. to about
240 degrees C.).
[0072] In a particularly desirable embodiment, the thermally
expandable composition contains a small amount (e.g., 0.1 to 5
weight percent or 0.5 to 2 weight percent) of one or more
olefinically unsaturated monomers and/or oligomers such as C.sub.1
to C.sub.6 alkyl (meth)acrylates (e.g., methyl acrylate),
unsaturated carboxylic acids such as (meth)acrylic acid,
unsaturated anhydrides such as maleic anhydride, (meth)acrylates of
polyols and alkoxylated polyols such as glycerol triacrylate,
ethylene glycol diacrylate, triethylene glycol diacrylate,
trimethylolpropane triacrylate (TMPTA) and the like, triallyl
trimesate, triallyl trimellitate (TATM), tetraallyl pyromellitate,
the diallyl ester of
1,1,3,-trimethyl-5-carboxy-3-(4-carboxyphenyl)indene,
dihydrodicyclo pentadienyl acrylate, trimethylolpropane
trimellitate (TMPTM), pentaerythritol trimethacrylate,
phenylene-dimaleimide, tri(2-acryloxyethyl)isocyanurate, triallyl
isocyanurate (TAIC), triallyl cyanurate (TAC),
tri(2-methacryloxyethyl)trimellitate, unsaturated nitriles such as
(meth)acrylonitrile, vinyl compounds (including vinyl aromatic
compounds such as styrene), allyl compounds and the like and
combinations thereof. In one embodiment, the olefinically
unsaturated monomer(s) and/or oligomer(s) used contain only one
carbon-carbon double bond per molecule (i.e., the monomer or
oligomer is monofunctional with respect to olefinically unsaturated
functional groups). Preferably, the monomer(s) and/or oligomer(s)
are selected to be capable of undergoing free radical reaction
(e.g., oligomerization or polymerization) initiated by the curing
agent(s) present in the expandable material when the expandable
material is heated to a temperature effective to activate the
curing agent (for example, by thermal decomposition of a peroxide).
Examples of suitable fillers include ground and precipitated
chalks, talc, calcium carbonate, carbon black, calcium-magnesium
carbonates, barite and silicate fillers of the
aluminium-magnesium-calcium type, such as wollastonite and
chlorite. Preferably, however, the total amount of filler is
limited to less than 10% by weight, more preferably less than 5% by
weight. In one embodiment, the expandable material contains no
filler (defined herein as substantially inorganic particles, such
as particles of the materials mentioned above).
[0073] In certain embodiments of the invention, the components of
the thermally expandable material are selected such that the
expandable material is free or substantially free of any
thermosettable resin such as an epoxy resin (e.g., the expandable
material contains less than 5% or less than 1% by weight epoxy
resin).
[0074] Expansion of the thermally expandable material is achieved
by a heating step, wherein the thermally expandable material is
heated for a time and at a temperature effective to activate the
blowing agent and also any curing agent that may be present.
[0075] Depending on the nature of the thermally expandable material
and the line conditions at the assembly line, the heating step is
typically carried out at a temperature from 130.degree. C. to
240.degree. C., preferably from 150.degree. C. to 200.degree. C.,
with a residence time in the oven from about 10 min. to about 30
min.
[0076] It is advantageous to take benefit of the heating step that
follows the passage of the vehicle parts in the generally used
electro coating bath (E-coat bath) to cause expansion of the
thermally expandable material as the temperature during this
heating step is generally sufficient to cause the expected
expansion.
[0077] The present invention also relates to a method for reducing
the transfer of vibrations from a vibration generator to a location
to which the vibration generator is connected via a structural
element, comprising equipping said structural element with means
for dissipating vibrational energy generated by the vibration
generator, characterized in that the means for dissipating
vibrational energy comprises a dissipative vibratory wave barrier
according to the present invention as described here above.
[0078] Examples of vibration generators include motors, engines,
pumps, gear boxes, suspension dampers and springs.
[0079] The method according to the present invention is
particularly adapted for reducing structure borne noise in an
automobile vehicle. In this case the vibration generator is
connected to at least one of the constitutive parts of the
passenger compartment of said vehicle via a structural element. The
shape of the structural element is that of a tubular rail with a
polygonal, preferably rectangular, cross-section.
[0080] The method according to the present invention comprises
successively:
[0081] selecting a dissipative vibratory wave barrier according to
the present invention having dimensions such that it can be
inserted into the structural element or fixed onto the structural
element;
[0082] inserting the dissipative vibratory wave barrier into the
structural element or fixing the dissipative vibratory wave barrier
onto the structural element in a location close to the vibration
generator; and
[0083] expanding the thermally expandable material.
[0084] Advantageously, the dissipative vibratory wave barrier is
selected such that a clearance of about 1 to 10 mm between the
outer surfaces of the dissipative vibratory wave barrier and the
inner surfaces of the structural element (in the embodiment where
the barrier is inserted into the structural element) or between the
inner surface(s) of the dissipative vibratory wave barrier and the
outer surface(s) of the structural element (in the embodiment where
the barrier is fixed onto the outside of the structural element) is
obtained. Such an arrangement is desirable as it allows liquids
such as cleaning baths, conversion coating baths and electro
coating (e-coat) baths to freely contact the inner and outer
surfaces of the structural element. The inner and outer surfaces
thus can be easily treated with such liquids after introduction of
the dissipative vibratory wave barrier and prior to expansion of
the coating of thermally expandable material.
[0085] In another advantageous embodiment the cross-section of the
dissipative vibratory wave barrier has the same shape as the
cross-section of the structural element. For example, if the
structural element has a rectangular cross-section with an interior
length l and an interior width w, the exterior dimensions of the
dissipative vibratory wave barrier (where the barrier is to be
inserted into the structural element) will be l and w minus two
times the clearance necessary for the expanding material. The
longitudinal length of the dissipative vibratory wave barrier
generally should be selected so that it is no longer than the
length of the structural element into which the wave barrier is to
be inserted or onto which the wave barrier is to be fixed.
Typically, the dissipative vibratory wave barrier has a
longitudinal length that is at least as long as the longest
cross-sectional dimension of the carrier, e.g., at least two or at
least three times the length of the longest cross-sectional
dimension of the carrier. Longer lengths will permit a greater
quantity of the thermally expandable material to be introduced
between the structural element and the carrier, but generally for
cost and weight reasons the quantity of such material used is
preferably not significantly in excess of the amount needed to
achieve the desired extent of vibration transfer reduction.
[0086] The dissipative vibratory wave barrier is preferably
inserted into the structural element or fixed onto the structural
element as close as possible to the vibration generator and before
the receiving vibrating structure from which the sound is
generated. If desired, any suitable method may be used to
physically attach the dissipative vibratory wave barrier to the
structural element prior to activation of the thermally expandable
material so that the barrier is secured in the desired position
relative to the structural element, thereby preventing displacement
of the barrier while the structural element is being subjected to
further handling (as may be encountered in a vehicle assembly
operation, for example). Such attachment may be accomplished, for
example, through the use of mechanical fasteners such as clips,
pins, screws, bolts, clamps and the like as well as through the use
of flanges or tabs on one or both of the carrier and the structural
element that are welded, riveted or adhesively attached so as to
interconnect the carrier and the structural element. The
dissipative vibratory wave barrier and the structural element may
alternatively be configured in a cooperative manner so that
gravitational and/or frictional forces alone are relied on to keep
the barrier in place. For example, a U-shaped dissipative vibratory
wave barrier that is to be fixed to the outside of a rectangular
shaped structural element may be designed to have flanges extending
inward on each side of the open end of the U-shaped carrier. When
the dissipative vibratory wave barrier is fitted around the
structural element, these flanges rest on the upper outer surface
of the structural element, thereby allowing the barrier to hang
from the structural element.
[0087] Expansion of the expandable material is obtained by a
heating step.
[0088] Depending on the nature of the thermally expandable material
and the line conditions at the assembly line, the heating step is
typically carried out at a temperature from 130.degree. C. to
240.degree. C., preferably from 150.degree. C. to 200.degree. C.
with a residence time in the oven from about 10 min. to about 30
min.
[0089] To cause expansion of the thermally expandable material, it
is advantageous to take benefit of the heating step that follows
the step of passing the vehicle parts containing the dissipative
vibratory wave barrier through the generally used electro coating
bath (E-coat bath), as the temperature during this heating step is
generally sufficient to cause the desired expansion.
[0090] The amount of thermally expandable material that is applied
to the carrier is selected such that, after expansion, its volume
occupies the clearance between the carrier and the surface of the
structural element that faces the carrier. The thermally expandable
material may be formulated such that it adheres to the inner or
outer surface of the structural element after expansion.
[0091] The hereindescribed dissipative vibratory wave barriers of
the present invention can be used in any location within an
automotive vehicle frame. For instance, such locations include, but
are not limited to, pillars (including A, B, C and D pillars),
rails, pillar to door regions, roof to pillar regions, mid-pillar
regions, roof rails, windshield or other window frames, deck lids,
hatches, removable top to roof locations, other vehicle beltline
locations, motor (engine) rails, lower sills, rocker panel rails,
support beams, cross members, lower rails, and the like.
[0092] The above and other objects, features and advantages of the
present invention will become more apparent from the following
description of preferred embodiments, reference being made to the
accompanying figures, in which:
[0093] FIG. 1 is a schematic perspective view of a first embodiment
of a dissipative vibratory wave barrier according to the present
invention before expansion of the thermally expandable
material;
[0094] FIG. 2 is a schematic perspective view of the dissipative
vibratory wave barrier of FIG. 1 after expansion of the thermally
expandable material;
[0095] FIG. 3 is a schematic perspective view of the dissipative
vibratory wave barrier of FIG. 1 after insertion into a structural
element;
[0096] FIG. 4 is a schematic perspective view of the dissipative
vibratory wave barrier of FIG. 3 after expansion of the thermally
expandable material; and
[0097] FIG. 5 is a graph showing three curves representing the
variation of the structure borne noise in a car body as a function
of frequency.
[0098] The dissipative vibratory ave barrier (1) shown in FIG. 1
comprises a U-shaped carrier (2) having an inner surface (2a) and
an outer surface (2b). A coating (3) comprising a thermally
expandable material is applied to the outer surface (2b). The
initial thickness of the expandable material may be, for example,
0.5 to 10 mm, e.g., 2 mm.
[0099] The U-shaped carrier (2) is made of metal or of a synthetic
material. Preferred metals are galvanized steel and aluminium.
[0100] When using a synthetic material, these may optionally be
fiber reinforced. The synthetic materials may be selected from
those previously recited. The thickness of the carrier (2) may be,
for example, 0.2 to 5 mm, e.g., approximately 1 mm. Preferably, the
thickness of the metal or synthetic material is selected so as to
provide a carrier having a stiffness at least equal to the
stiffness of the structural element to be combined with the
dissipative vibratory wave barrier.
[0101] The following non-limiting example illustrates the invention
and the manner of practicing the same.
[0102] As shown in FIG. 3, the dissipative vibratory wave barrier
(1) is introduced into a structural element of a car body, for
example into a front member (4) having a longitudinal shape such as
a rail or pillar. The structural element may already be enclosed
when the dissipative vibratory wave barrier is introduced; for
example, the structural element may be a hydroformed pillar or rail
or a pillar or rail that has been assembled by fastening together
two or more sheet metal sections. Alternatively, the dissipative
vibratory wave barrier may be introduced into a channel-shaped
section. After inserting the dissipative vibratory wave barrier
(1), the channel-shaped section may be enclosed or sealed to form
the structural element by placing a plate (which may be flat or
formed into a nonplanar shape) on the open side of the
channel-shaped section, with the channel-shaped section and plate
being preferably secured to each other by suitable attachment means
such as welding, adhesive bonding, mechanical fasteners, or some
combination thereof.
[0103] As shown in FIG. 3, the dissipative vibratory wave barrier
may have a carrier (2) that is approximately rectangular having the
same exterior dimensions as the front member (4) minus the
clearance necessary for the expanding material (in this case minus
4 mm all around the carrier). The dissipative vibratory wave
barrier may be placed loosely (i.e., without physical attachment)
within the structural element or alternatively may be fixed in
position using one or more attachment devices such as clips, pins,
bolts, screws, and the like. For example, the edges of the carrier
(2) which come into contact with an inner surface of the structural
element (4) may have one or more clips extending therefrom which
are inserted into openings or other receptacles in said inner
surface, thereby holding the dissipative vibratory wave barrier in
place. The clips may be configured such that the edges of the
carrier (2) are positioned a small distance away from the bottom of
the structural element, thereby allowing cleaning compositions,
conversion coating compositions, paint or primer compositions or
any of the other liquids typically used during vehicle assembly
operations to more fully contact the inner surface of the
structural element.
[0104] After the insertion of the dissipative vibratory wave
barrier (1), the car body is heated to a temperature of 180.degree.
C. for 20 min in order to cause expansion of the thermally
expandable material in the space between the outer surface of the
carrier (2b) and the inner surface of the structural element. The
activated dissipative vibratory wave barrier is illustrated in FIG.
4. After the heating, the coating of now-expanded expandable
material has a thickness of 4 mm. The expansion can be realized
during the passage of the vehicle parts through an oven following
treatment of the parts in an electro coating bath.
[0105] In other examples, the dissipative vibratory wave barrier
(1) can be selected such that the clearance between the outer
surfaces of the dissipative vibratory wave barrier (1) and the
inner surfaces of the structural element is about 1 to 10 mm. In
all these cases, after the heating, the thermo-expandable material
occupies all the clearance.
[0106] FIG. 5 shows the results of an experimentation carried out
using a real car body. In this experiment, the dissipative
vibratory wave barrier is located from the end of the front member
and has a length of 52 cm.
[0107] A dynamic shaker is used as vibration generator and is
attached at the free end of the front longitudinal member in form
of a rail of the car body, with the dynamic shaker providing a wide
band excitation in the frequency range from 20 Hz up to 2000
Hz.
[0108] The injected vibration is measured by means of a force
sensor located at the entry point.
[0109] The response of the front floor and firewall panels to which
the longitudinal member is connected is measured by means of
accelerometers.
[0110] The spaced averaged mobility of the floor panels is
calculated (m/s/N) in the frequency range from 20 Hz up to 2000
Hz.
[0111] A comparison of the vibration levels is given in FIG. 5
while using the proposed invention onto the vibration transfer path
and using classical damping mats applied directly on the vibrating
panels. The curves show the variation of the spaced averaged
mobility as a function of frequency.
[0112] Three experiments are conducted:
[0113] without any added damping material on the vibrating panels
and on the vibration transfer path (curve Cl on FIG. 5).
[0114] 2.9 kg of conventional asphaltic damping mats are applied on
the vibrating panels (front floor and firewall panels) (curve C2 on
FIG. 5); this is the classical solution used on the studied car
body to damp the vibration of the panels.
[0115] the dissipative vibratory wave barrier according to the
invention as described below is used (curve C3 on FIG. 5).
[0116] The expandable material had the following composition:
[0117] 45 parts by weight SIS block copolymer, styrene content
20%
[0118] 5 parts by weight aromatic hydrocarbon resin as
tackifier
[0119] 2.5 parts by weight diisononylphthalate
[0120] 4.5 parts by weight microcrystalline wax
[0121] 27.5 parts by weight thermoplastic ethylene/vinyl acetate
copolymer (28% vinyl acetate)
[0122] 0.1 parts by weight phenolic antioxidant
[0123] 8.8 parts by weight blowing agent (azodicarbonamide)
[0124] 1.0 parts by weight
1,1-di-tert-butylperoxi-3,3,5-trimethylcyclohexane
[0125] 0.5 parts by weight methylacrylate
[0126] 1.5 parts by weight zinc oxide treated urea.
[0127] From curves C1 and C2, it appears that in the frequency
range of structure borne noise between 100 Hz and 500 Hz, the
spaced averaged mobility is reduced by an average of 5.0 dB. Since
the spaced averaged mobility is directly proportional to the
structure borne noise, noise reduction is also 44%.
[0128] By comparison of curves C3 and C2, it appears that in the
frequency range of structure borne noise between 100 Hz and 500 Hz
the spaced averaged mobility is reduced by an average of 1.4 dB,
i.e. 15%.
[0129] The superiority of the solution proposed by the invention
with respect to the most frequently used prior art solution
(vibration dampers and dampening mats) clearly appears when
comparing the reduction of noise obtained due to the invention,
i.e., 44% and the reduction obtained when using the prior art
solution, i.e., 15%.
[0130] The principal advantages of the invention are as
follows:
[0131] much less material is necessary to damp the vibration of the
vibrating panels;
[0132] the use of the dissipative vibratory wave barrier according
to the invention is much cheaper in term of process costs for the
car or machinery manufacturer compared to the application of
damping material to the vibrating panels;
[0133] the ability to work on transmission paths requires a more
in-depth analysis of the vehicle body structure but allows the
solution to be tuned on a given excitation source or frequency
range compared to a multi-purpose solution as the treatment of the
panels;
[0134] the use of the dissipative vibratory wave barrier according
to the invention may also contribute to the rigidity of the frame
thus improving the safety and comfort of the vehicle, however a
substantial contribution to the rigidity of the frame will always
reduce the efficacy of the dissipative vibratory wave barrier
property.
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