Note: Descriptions are shown in the official language in which they were submitted.
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CAVITY SEALING ARTICLE AND METHOD
TECHNICAL FILED OF THE INVENTION
This invention relates to sealing articles for cavities, and methods for
making and
using them. More particularly, this invention relates to sealing articles for
channels in
automobiles or other land vehicles, boats or other marine vehicles, aircraft
or other
aerospace vehicles, structures, including land and marine structures, and the
Like,
wherever it is desirable to seal a cavity against the passage of air,
moisture, fluids,
particuiates, and the like. In a particular aspect, this invention relates to
the sealing of
channels, such as pillars, in the body structure of automobiles and similar
vehicles; and
the invention will be discussed primarily with respect to that aspect.
BACKGROUND OF THE INVENTION
During the fabrication of automobiles, trucks, and similar vehicles, many body
components present cavities that require sealing to prevent the ingress of
moisture and
contaminants that can cause corrosion of the body parts. This is especially
true with
respect to unibody structures, where a heavy frame is replaced by a
structurally designed
space frame that inherently presents a number of moisture- and contaminant-
collecting
cavities. These cavities also serve as passages through which road and engine
noise and
other sounds may be transmitted during normal use of the vehicle. For example,
the
upright post structure of a vehicle body defining a portion of a window
opening presents
an elongated cavity that can collect moisture and contaminants and also
transmit sounds
unless the cavity is at least partially filled with a sealant material that
blocks the passage
of moisture and debris and that also serves as a baffle for muting sounds that
would
otherwise be transmitted along the length of the cavity and then radiate into
the passenger
compartment of the vehicle. There are other irregular cavities in a vehicle
body that
desirably are sealed to prevent moisture and contaminants from entering that
area and
being conveyed to other parts of the vehicle body.
Many attempts have been made to seal these cavities; and some techniques and
products for this purpose are described in US Patents Nos. 5,266,133 and
5,373,027
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(Hanley et al.), 5,212,208 and 5,160,465 (Soderberg), 5,040,803 (Cieslik et
al.), 4,989,913
(Moore, III), and 4,874,650 (Kitoh et al.), among others.
A currently favored technique in automobile cavity sealing is the use of a
heat
activated sealing foam material. Typically, a mass of a material capable of
expansion
(foaming) at elevated temperatures, i.e. a thermoplastic mixture containing
both a heat
activated foaming agent and a heat-activated crosslinking agent, is placed on
a tray or
other mechanical support, usually made from sheet metal or a molded high
temperature
thermoplastic, that is capable of being mechanically fastened within the
cavity. Because
automobile bodies are now typically coated by total immersion in phosphating,
rustproofing, electrocoating, and other paint baths to ensure that the
interiors of all open
cavities are coated, the sealing article (the tray, together with the mass of
foamable
material), should not fill the cavity cross-section before foaming, so that
the coatings may
enter the cavity during immersion and drain from it after removal from the
bath. As the
automobile body is passed through an oven to cure the coating to the metal of
the body,
1 S the foamable mass expands to fill the cavity cross-section and seal to the
walls of the
cavity. While this technique has proved generally satisfactory, it suffers
from two
principal disadvantages. First, because the foam material is not self
supporting during
foaming, it is subject to sagging before the foam crosslinks, and therefore
requires
support. This problem is particularly severe when the axis of the cavity to be
sealed is
approximately horizontal, so that the foam material (which is perpendicular to
the cavity
axis) is approximately vertical, and the sagging therefore tends to limit
expansion of the
foam toward the upper parts of the cavity walls. The tray required to support
the foam
during expansion and sealing adds to both the weight and cost of the seal.
Second,
because the foamable material is supported during expansion, interfacial
adhesion of the
molten foaming material to the support restricts lateral expansion of the
foam, so that
greater expansion occurs perpendicular to the support (along the longitudinal
axis of the
cavity rather than towards the cavity walls). As a result, sealing may be
incomplete, and a
greater amount of foamable material is used in an attempt to ensure adequate
sealing, also
adding to both the weight and cost of the seal. This problem is particularly
severe when
the cavity to be sealed is highly irregular in cross-section or has a sharply
acute angle,
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when a considerable excess of foamable material may be used to attempt to
ensure that
the foam fills the cavity cross-section and penetrates to the vertex of the
angle.
In certain uses, particularly in the sealing of the vertical pillars of
automobile
bodies, it may be desirable to be able to provide a drain passage within the
pillar. For
example, in automobiles with sunroofs, it is necessary to provide a drain
passage for
water which might otherwise accumulate in spaces around the sunroof. Usually,
this
drain passage is created by a drain tube from the sunroof area passing down
one or both of
the "A" pillars (the pillars on either side of the front window of the
automobile). Thus a
passage must be provided through any seal in that pillar. Three different
solutions are
currently used for this problem. One is to allow the pillar itself to serve as
the drain
passage and to provide a drainage plug through the cavity seal. The drainage
plug has a
tortuous path through which fluids may drain, but which is intended to reduce
sound
travel through the plug. This simple solution has the two disadvantages of
allowing
draining fluid to contact the inside of the pillar as it drains and of
allowing sound
I S infiltration, especially the infiltration of high frequency sound, through
the drain plug
since the tortuous path is still open. A second solution is to use a
conventional seal with a
hole, and a drain hose passing through the hole. Here the disadvantages of the
drain plug
are avoided, but the need for the hose to be emplaced before the vehicle frame
is fully
assembled means that a hose capable of withstanding the high temperatures
encountered
in the paint bake ovens must be used, increasing the cost. A third solution is
to leave the
pillars open through the painting process, then install a low cost hose
through the pillar
and seal it in place by injection of a foaming material, such as a two-part
urethane, into
the pillar. This solution also provides an effective seal, but at the
increased cost of capital
equipment for preparation and injection of the urethane foam, ventilation,
etc., and with
the need for an additional step in the vehicle assembly process.
It would be desirable to produce a cavity sealing article, especially a
sealing article
for use in a channel in a land, marine, or aerospace vehicle, such as a pillar
in the body
structure of an automobile or similar vehicle, that could be prepared readily
and
inexpensively, would be readily handleable and empiaceable within a cavity to
be sealed
without requiring special tooling, would be readily activatable by elevating
the cavity
temperature to such temperatures as are commonly encountered in operations on
the
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vehicle body (e.g. 115°C to 250°C for automobile paint ovens),
and, on activation, would
provide an effective seal against infiltration of air, moisture, other
undesirable fluids and
particulates, and sound. Desirably, such a sealing article would also permit
the passage of
drain hoses and the like through the seal. It would also be desirable to
produce a
multiple-layer cavity sealing article having the same ease of manufacture and
use and
providing an even more effective sound seal.
BRIEF SUMMARY OF THE INVENTION
In a first aspect, this invention provides a planar cavity sealing article
comprising:
(a) at least one driver comprising a crosslinked foamable polymer, and
(b) a sealer comprising an uncrosslinked foamable polymer in intimate contact
with
the at least one driver and substantially surrounding the at least one driver
in the
plane of the article.
In particular, in this first aspect, this invention provides a planar cavity
sealing
article for use in a longitudinally extending cavity defined by cavity walls,
the cavity
having a cross-section within the cavity walls which is to be sealed at a
predetermined
location, the article comprising:
(a) at least one driver comprising a crosslinked foamable polymer, and
(b) a sealer comprising an uncrosslinked foamable polymer in intimate contact
with
the at least one driver and substantially surrounding the at least one driver
in the
plane of the article;
the article having a size and shape such that the article incompletely
occupies the cross-
section of the cavity at the predetermined location and having expansion and
sealing
properties such that, when the article is placed at the predetermined location
within the
cavity and foamed, the foamed sealer is forced into intimate and sealing
contact with the
cavity walls.
Especially, in this first aspect, this invention provides a cavity sealing
article for
use in a longitudinally extending cavity defined by cavity walls, the cavity
having a cross-
section within the cavity walls which is to be sealed at a predetermined
location, the
article comprising:
(a) a planar cavity sealing layer comprising:
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(1) at least one driver comprising a crosslinked foamable polymer, and
(2) a sealer comprising an uncrossiinked foamable polymer in intimate contact
with the at least one driver and substantially surrounding the at least one
driver in the plane of the layer; and
(b) a support structure adapted to fit within the cavity and orient the
article within the
cross-section at the predetermined location,
the article having a size and shape such that the article incompletely
occupies the cross-
section of the cavity at the predetermined location and the sealing layer
having expansion
and sealing properties such that, when the article is placed at the
predetermined location
within the cavity and foamed, the foamed sealer is forced into intimate and
sealing
contact with the cavity walls.
In a second aspect, this invention provides a multiple-layer cavity sealing
article
comprising:
(a) a plurality of planar sealing layers, each sealing layer independently
comprising:
(a) at least one driver comprising a crosslinked foamable polymer, and
(b) a sealer comprising an uncrosslinked foamable polymer in intimate contact
with the at least one driver and substantially surrounding the at least one
driver in the plane of the layer; and
(b) a support structure supporting the plurality of sealing layers in spaced-
apart
relationship.
In particular, in this second aspect, this invention provides a multiple-layer
cavity
sealing article for use in a longitudinally extending cavity defined by cavity
walls, the
cavity having a cross-section within the cavity walls which is to be sealed at
a
predetermined location, the article comprising:
(a) a plurality of planar sealing layers, each sealing layer independently
comprising:
(a) at least one driver comprising a crosslinked foamable polymer, and
(b) a sealer comprising an uncrosslinked foamable polymer in intimate contact
with the at least one driver and substantially surrounding the at least one
driver in the plane of the layer; and
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(b) a support structure adapted to fit within the cavity and orient the
article within the
cross-section at the -predetermined location, the support structure supporting
the
plurality of sealing layers in spaced-apart relationship,
the article having a size and shape such that the article incompletely
occupies the cross-
section of the cavity at the predetermined location and the sealing layers
having
expansion and sealing properties such that, when the article is placed at the
predetermined
location within the cavity and foamed, the foamed sealers are forced into
intimate and
sealing contact with the cavity walls.
In a third aspect, this invention provides a method of sealing a cavity by use
of the
cavity sealing article of the invention.
In a fourth aspect, this invention provides a method of making the cavity
sealing
article of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross-sectional view showing a first embodiment of the cavity
sealing
article of this invention emplaced within a cavity.
FIG. 2 is a cross-sectional view along line A-A of FIG. 1, parallel to the
longitudinal axis of the cavity.
FIG. 3 is a cross-sectional view showing the cavity sealing article of FIG. 1
after
foaming.
FIG. 4 is a cross-sectional view showing a second embodiment of the cavity
sealing article of this invention emplaced within a cavity.
FIG. 5 is a cross-sectional view showing a third embodiment of the cavity
sealing
article of this invention emplaced within a cavity.
FIG. 6 is a cross-sectional view showing a fourth embodiment of the cavity
sealing article of this invention emplaced within a cavity.
FIG. 7 is a cross-sectional view showing a fifth embodiment of the cavity
sealing
article of this invention emplaced within a cavity.
FIG. 8 is a cross-sectional view showing a sixth embodiment of the cavity
sealing
article of this invention emplaced within a cavity.
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FIG. 9 is a cross-sectional view showing the first embodiment of the cavity
sealing article of this invention emplaced upon a support plate within a
cavity.
FIG. 10 is a cross-sectional view along line A-A of FIG. 9, parallel to the
longitudinal axis of the cavity.
FIG. 11 is a cross-sectional view showing a seventh embodiment of the cavity
sealing article of this invention with an aperture therethrough emplaced
within a cavity.
FIG. 12 is a cross-sectional view along line A-A of FIG. 11, parallel to the
longitudinal axis of the cavity.
FIG. 13 is a cross-sectional view showing an eighth embodiment of the cavity
sealing article of this invention with a grommet therethrough emplaced within
a cavity.
FIG. 14 is a cross-sectional view along line A-A of FIG. 13, parallel to the
longitudinal axis of the cavity.
FIG. 15 is a cross-sectional view showing a ninth, multiple-layer, embodiment
of
the cavity sealing article of this invention emplaced in a cavity, the cross-
section being
parallel to the cavity axis.
FIG. 16 is a cross-sectional view showing a tenth, multiple-layer, embodiment
of
the cavity sealing article of this invention emplaced in a cavity, the cross-
section being
parallel to the cavity axis.
FIG. 17 is a perspective view showing an eleventh, multiple-layer, embodiment
of
the cavity sealing article of this invention.
FIG. 18 is a cross-sectional view of the eleventh embodiment of the cavity
sealing
article of this invention emplaced in a cavity, the cross-section being
parallel to the cavity
axis.
FIG. I9 is a cross-sectional view of the eleventh embodiment of the cavity
sealing
article of this invention after foaming and expansion.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
For simplicity and ease of understanding, the invention will be described and
illustrated generally with respect to a cavity sealing article of this
invention having only a
single sealing layer, including the case where the sealing layer itself forms
the cavity
sealing article, and where the article or sealing layer{s) of the article
comprise only one
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driver; however, specific illustration of cavity sealing articles having more
than one .
sealing layer and articles or sealing layers having more than one driver will
also be given.
Referring to the drawings, where like numerals denote like elements of the
invention, FIG. 1 is a cross-sectional view showing a first embodiment of the
cavity
sealing article of this invention emplaced at a predetermined location within
a cavity, the
longitudinal axis of which is perpendicular to the page. The axis of the
cavity may be
oriented in any direction: horizontal, oblique, or vertical; so that the cross-
section that is
to be sealed at the predetermined location may be, correspondingly, vertical,
oblique, or
horizontal. The cavity shown generally as 10 is defined by a pair of cavity
wall forming
members 12 and 14 which may be fastened together by any suitable means (not
shown).
The planar cavity sealing article shown generally as 20 comprises a single
sealing layer of
a single crosslinked foamable polymer driver 22 surrounded in the plane of the
article by
and in intimate contact with an uncrosslinked foamable polymer sealer 24. The
article 20
is positioned within the cavity 10 by mounting on a stud 30 projecting through
one of the
1 S cavity walls. FIG. 2 shows the article of FIG. 1 in a further cross-
sectional view, where
the longitudinal axis of the cavity is parallel to the page. On activation of
the article by
the application of a sufficient temperature for a sufficient time, the driver
22 foams to
expand and force the sealer 24, which also foams and expands, into contact
with the
cavity walls, thereby sealing the cavity. FIG. 3 shows the cavity sealing
article of FIG. 1
after foaming, where the driver 22 has foamed and expanded to more
substantially fill the
cavity cross-section; and the sealer 24, which has also foamed and expanded,
has been
forced into sealing contact with the cavity walls. FIG. 4 shows a second
embodiment of
the cavity sealing article of this invention, also having only a single
driver, but where the
driver is of non-uniform shape with exaggerations or protrusions in directions
in which it
is desired to provide an especially pronounced "push" to the sealer by the
foaming and
expansion of the driver. FIGS. 5, 6, and 7 show three more embodiments of this
first,
single-layer, aspect of the cavity sealing article of this invention in cross-
section, where
each of the articles shown generally at 20 comprises a plurality of drivers 22
with a sealer
24 in intimate contact with and substantially surrounding the plurality of
drivers in the
plane of the article.
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Composition of the cavity sealing-article or sealing layer(s) of the cavity
sealing article
Suitable compositions for the cavity sealing article, or for the or each
sealing layer
of the cavity sealing article, of this invention will be foamable polymer
compositions
having a foaming temperature appropriate to the temperature range of intended
application, for example a foaming temperature within the range of
temperatures to be
encountered in bake ovens for vehicle bodies, and the like. Such compositions
will
contain a base polymer and a blowing agent to cause foaming of the polymer.
They will
typically also contain fillers, antioxidants, flame retardants, and/or other
stabilizers such
as are conventional in polymeric articles, and may contain pigments,
plasticizers,
adhesion promoters, activators for the blowing agents, and the like.
The sealer portion of the article or sealing layer(s), sometimes referred to
elsewhere in this application simply as "the sealer", may, and preferably
will, contain a
chemical crosslinking agent to strengthen the resulting foamed polymer, and
may also
contain a tackifier to maximize adhesion of the article to the cavity walls on
foaming. If
the sealer and the drivers) are not made in a unitary fashion, but are
assembled before
crosslinking of the driver(s), for example by comolding or coextrusion of the
drivers) and
sealer portions of the article or sealing layer(s), and the drivers) are to be
crosslinked by
radiation, then the sealer may contain an agent chosen to prevent radiation
crosslinking,
an "anti-rad", for example a free-radical quencher such as an amine, so that
the whole
article or sealing layer may be irradiated with only the drivers) being
crosslinked by the
radiation. The sealer is uncrosslinked before foaming, by which is meant that
it is either
totally free of crosslinking or has such a low degree of crosslinking that it
substantially
retains the foaming and adhesive characteristics of an uncrosslinked polymer.
Desirably,
the sealer becomes crosslinked on foaming, as discussed further later in the
application, as
this provides additional stability to the foam, but it is within the scope of
the invention
that the sealer may be uncrosslinked (as defined immediately above) even after
foaming.
The at least one driver portion of the article, or of the or each sealing
layer of the
article, sometimes referred to elsewhere in this application simply as "the
driver" or "the
drivers", which are crosslinked, will typically contain either or both of a
chemical
crosslinking agent and a radiation crosslinking promoter, a "pro-rad", to
enhance radiation
crosslinking of the driver. Where the at least one driver portion of the
article or layers) is
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chemically crosslinked, the crosslinking agent chosen will be one having an
activation
temperature substantially below the activation temperature of the blowing
agent so ti~at
the driver may be crosslinked before any foaming occurs. When the at least one
driver
portion is radiation crosslinked, such as by exposure to electron beam
irradiation, the
driver portion will typically contain a radiation crosslinking promoter; the
amount and
type of which may be chosen depending on the polymer composition. When the at
least
one driver is crosslinked by radiation, the extent of the irradiation will
depend on the
material of the drivers) (the polymer, additives, etc.), the type and quantity
of radiation
crosslinking promoter, the thickness of the article, etc. Typical irradiation
dosages for
electron beam irradiation will lie between 0.25 and 20 Mrad, preferably
between 0.5 and
10 Mrad, and more preferably between 2 and 6 Mrad.
If the article or sealing layer comprises a plurality of drivers, it will
generally be
convenient for all of the plurality of drivers to be crosslinked to an equal
extent so that
their expansion properties are the same. For example, in the third and fourth
embodiments of the article shown in FIGS. 5 and 6, where the drivers are of
uniform size
and are arranged regularly within the plane of the article, it will be
convenient for the
plurality of drivers to be crosslinked to an equal extent. However, it is
within the scope of
this invention that the drivers may not be crosslinked to an equal extent, if
desired. For
example, in FIG. 7, where there are two sets of drivers, an inner first set of
two drivers
221 surrounded by an outer second set of four drivers 222, it may be
advantageous for the
drivers in the inner set and outer set to be crosslinked to different extents
so that they
possess different expansion properties. This may be done, for example, by
selective
irradiation. For example, if it is desired that the . inner set of drivers be
more heavily
crosslinked, such as by being irradiated to 6 Mrad, the outer set of drivers
be less heavily
crosslinked, such as by being irradiated to 3 Mrad, and the sealer
uncrosslinked
(unirradiated), then a sheet of foamable polymeric composition forming the
article may be
cut to the desired shape for the article, masked to expose only the region
which will
become the inner set of drivers and the masked article irradiated with 3 Mrad,
the first
mask removed and a second mask, exposing those regions which will become the
inner
and outer sets of drivers, placed over the article, and the re-masked article
then irradiated
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with a further 3 Mrad. The resulting article will have two sets of drivers
having different
extents of crosslinking and an uncrosslinked sealer.
Although it is not required by this invention that the compositions of the
foamable
polymers of the at least one driver and the sealer of the article or sealing
layers) be the
same, they should be compatible so that the resulting article or layer
provides an optimal
seal when the article is used.
It may be convenient for manufacture that the compositions of the foamable
polymers of the at least one driver and sealer should be the same; and it may
be further
convenient that the article or sealing layers) should be formed from a single
piece of such
a foamable polymeric composition. Such a manufacture is discussed further
later in this
application and in the Examples. In this case, the at least one driver portion
of the article
or sealing layer will typically be crosslinked by radiation, and the foamable
polymeric
composition will contain both the chemical crosslinking agent for the sealer
and desirably
will also contain a radiation crosslinking promoter to enhance radiation
crosslinking of
the at least one driver.
Suitable base polymers may include a wide range of polymers, typically chosen
for a particular application so that the resulting article will foam at a
convenient
temperature for sealing of the cavity to be sealed and will be stable under
intended use
conditions. A suitable base polymer or mixture of polymers will thus have a
softening
point below the desired temperature of foaming in the absence of crosslinking,
for
example at a temperature at least 50°C below the desired foaming
temperature. The melt
flow index, MFI, as measured by ASTM D-1238-95, of the polymer or mixture of
polymers will desirably be from 0.5 to 10, preferably from 3 to 7, and in any
event will
desirably be chosen to give an appropriate degree of expansion of the
resulting article
during foaming.
Suitable polymers thus include olefmic polymers such as very low density
polyethylene, low density polyethylene, medium density polyethylene, high
density
polyethylene, polyethylenes or ethylene copolymers prepared by metallocene
polymerization, such as Exact [Exxon] and Engage [Dow], ethylene copolymers
such as
ethylene-vinyl acetate copolymer, ethylene-methacrylic acid copolymer,
ethylene-acrylic
acid copolymer, ethylene-butyl acrylate copolymer, ionomers, such as Surlyn
[duPont]
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and Iotek [Exxon], ethylene terpolymers such as ethylene-vinyl acetate-
methacrylic acid .
copolymer, elastomers such as ethylene-propylene rubber, EPDM, nitrite
rubbers, butyl
rubbers, chloroprene, chloropolyethylene, polyacrylate elastomers,
chlorosulfonated
polyethylene, thermoplastic elastomers, and fluoropolymers such as
polyvinylidene
fluoride, ethylene-tetrafluoroethylene copolymer, fluorinated ethylene-
propylene
copolymer, poly(chlorotrifluoroethylene), ethylene-chlorotrifluoroethylene
copolymer,
etc., and mixtures of any two or more of the above.
For example, a suitable polymer or mixture of polymers for use in a cavity
sealing
article or sealing layer for use in the automobile industry, where bake oven
temperatures
will be in the range of 115°C to 250°C, e.g. around
160°C, may have a softening point
below about 100°C, preferably below 90°C, in the absence of
crosslinking. Such
polymers may include ethylene-vinyl acetate copolymer (EVA), ethylene-methyl
acrylate
copolymer (EMA), and the like, optionally admixed with each other or with such
polymers as low density polyethylene and/or ionomers. An exemplary polymer is
EVA
having a vinyl acetate (VA) content between 5% and 45%, especially between 15
and
35%, particularly between 20% and 30%.
Suitable fillers for the composition of the sealing article or sealing layer
include
inorganic fillers such as zinc oxide, barium sulfate (Huberbrite), calcium
carbonate,
magnesium hydroxide, alumina trihydrate, and the like; at a concentration up
to about 40
parts per 100 parts of the base polymer.
The blowing agent is chosen so as to effect foaming and expansion of the
article
or sealing layers) at an elevated temperature normally present during the
manufacture of
the product containing the cavity to be sealed; for example, at a temperature
normally
present during passage of an automobile body through a paint bake oven
(typically 115°C
to 250°C). Suitable blowing agents will include from 1 to 15 parts per
100 parts of base
polymer of an azodicarbonamide or benzenesulfonyl hydrazide. Suitable
azodicarbonamide blowing agents include Celogeri AZ 130 or 3990; and suitable
modified azodicarbonamide agents include Celogeri 754 or 765, all from
Uniroyal
Chemical. Suitable benzenesulfonyl hydrazide blowing agents include p,p'-
oxybis-
(benzenesulfonyl hydrazide), sold as Celogeri OT, and p-toluenesulfonyl
hydrazide, sold
as Celogeri TSH, both also from Uniroyal. The blowing agent may also be made
up of a
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combination of agents depending on the degree of expansion desired for a
particular
application; and may also include a blowing agent activator such as diethylene
glycol,
urea, dinitrosopentamethylenetetramine (DNPT), and the like. Certain fillers,
such as
zinc oxide (Kadox), may also act as activators for the blowing agent. The
amount of
activator added will depend on the choice of blowing agent and the amount of
expansion
required.
Flame retardants may also be present, of such kinds and at such concentrations
as
will provide flame retardancy for the article. These may include halogenated
flame
retardants such as the polybrominated aromatics (e.g. decabromobiphenyl), and
the like,
for example in combination with inorganic materials such as antimony trioxide;
or may
include non-halogenated flame retardants, such as the magnesium hydroxide and
alumina
trihydrate previously mentioned as fillers.
The chemical crosslinking agent is preferably a free radical crosslinking
agent
compatible with the base polymer of the article or sealing layer(s). Preferred
chemical
crosslinking agents are peroxides, such as bis(t-
butylperoxy)diisopropylbenzene, 1,1-di-t-
butylperoxy-3,3,5-trimethylcyclohexane, 4,4-di-t-butylperoxy n-butyl valerate
(Trigonox), dicumyl peroxide (Dicup), and the like. In most cases, the
chemical
crosslinking agent is provided at 1 to S parts per 100 parts of base polymer.
The blowing agent and the chemical crosslinking agent will be chosen so that
the
chemical crosslinking agent has an activation temperature approximately that
of the
blowing agent. For example, it may have an activation temperature slightly
below that of
the blowing agent, so that the foam maintains stability during expansion,; but
desirably
the kinetics of the crosslinking and foaming reactions are such that the
sealer of the article
or sealing layers) expands and foams on heating, and adheres to the walls of
the cavity,
before the resulting foam is completely crosslinked by action of the chemical
crosslinking
agent. Desirably, the activation temperature of the blowing agent will be
chosen so that
the blowing agent is not easily accidentally activated (such as by mixing at a
temperature
above the optimal mixing temperature, during welding or other forming of a
cavity in
which the sealing article is emplaced, or during phosphating, painting or
other coating
treatments, or drying of such coatings) but is only activated when it
encounters
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temperatures in which it is desired that the sealing article should foam, such
as are present .
in bake ovens.
The radiation crosslinking promoter may be chosen from among those
conventionally used to promote the crosslinking of polymers, such as triallyl
cyanurate
(TAC), triallyl , isocyanurate (TAIC), triallyl trimellitate, triallyl
trimesate, tetraallyl
pyromellitate, the diallyl ester of 1,1,3-trimethyl-5-carboxy-3-(4-
carboxyphenyl)indane,
trimethylolpropane trimellitate (TMPTM, Sartomer 350), pentaerythritol
trimethacrylate,
tri(2-acryloxyethyl) isocyanurate, tri(2-methacryloxyethyl) trimellitate, and
the like, and
combinations thereof.
The tackifier, if present, will be chosen to enhance the tackiness of the
outside
surface of the article or sealing layer(s), in particular the periphery of the
article or sealing
layers) which will come into contact with the cavity walls, on expansion but
not such
that the outer surface exhibits tackiness after formation of the article and
before
expansion, since it is generally desirable that the outer surface of the
article should be dry
and non-tacky during initial placement of the article in the cavity.
Desirably, to enhance
the adhesive qualities of the base polymer at the temperature of expansion,
the tackifier
will have a relatively low molecular weight, no significant crystallinity, a
ring-and-ball
softening point above at least 50°C (and preferably higher, near the
softening point of the
base polymer), and will be compatible with the base polymer and other polymers
present.
The tackifier may be present in up to 30 parts per 100 parts of base polymer.
Suitable
tackifiers include novolak resins, partially polymerized rosins, tall oil
rosin esters, low
molecular weight aromatic thermoplastic resins, Picco and Piccotac~' resins
from
Hercules Chemical, and the like.
Antioxidants, adhesion promoters, plasticizers, pigments, and the like may
also be
employed in conventional amounts.
Exemplary formulations include:
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Formulation,
parts
by
weight
.
Ingredient A B C D
Evatane 28-OS (EVA) 100 100
Elvax 470 (EVA) 100 100
Irganox 1076 (antioxidant) 2 2 2 2
Kadox 911 (Zn0) 30 30
Huberbrite 7 (BaS04) 30 30
Piccotac 95 (tackifier) 30
Varox 231 XL (chemical crosslinking2.5 1.5 2.5 1.5
agent)
Celogen TSH (blowing agent) 10 10
Celogen OT (blowing agent) 10 10
Sartomer 350 (radiation crosslinking5 S 5 5
promoter)
Of these formulations, formulations A and C are particularly applicable to the
manufacture of the sealer portion of a cavity sealing article or sealing layer
of a cavity
sealing article of this invention, while formulations B and D are applicable
to the
manufacture of both the driver and sealer portions of a cavity sealing article
or sealing
layer.
The composition may be prepared by methods conventional in the art of polymer
blending, such as by mixing in a high shear mixer such as a Banbury or
Brabender type
mixer, with care being taken to ensure that the temperature of the blend does
not rise to
such an extent that the chemical crosslinking agent or blowing agent are
activated.
Typically, the base polymer, other polymers/tackifier {if present), and
antioxidant are
added first, and blended to homogeneity. The filler, adhesion promoter,
pigments (if
present) may be mixed with the base polymer, or may be added after the base
polymer has
been softened by mixing. These first mixing stages are not particularly
temperature-
sensitive. Once all ingredients other than the blowing and crosslinking agents
have been
added and fully blended, however, temperature control becomes important as
these Iast
agents are added. Accordingly, the mixer is cooled so that the temperature of
the
composition does not exceed about 95°C, and more preferably does not
exceed about
80°C; the blowing agent(s), accelerator(s), crosslinking agents, and
any plasticizers are
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added, and the resulting composition is subjected to high shear mixing under
controlled
temperature conditions until the composition is homogeneous. The composition
may then
be cooled, for example by processing through a two-roll mill with cooled
rollers.
The resulting bulk composition may then be formed into the appropriate shape
for
the cavity sealing article of this invention by any appropriate means. For
example, it may
be extruded or rolled into sheets for cutting, extruded into rods of a desired
cross-
sectional configuration to be subsequently sectioned into the articles, molded
into desired
shapes, or pelletized for later molding or extrusion.
The particular composition used to make the cavity sealing article or sealing
layers) of the cavity sealing article of this invention is not critical; and a
person of
ordinary skill in the art should have no difficulty, having regard to that
skill and this
disclosure, including the references cited here, in determining a suitable
formulation to
prepare a cavity sealing article or sealing layer of this invention or in
optimizing such a
composition for a particular application.
Manufacture of the cavity sealing article or sealing layer
Although it is within the contemplation of this invention that a single
sealing
article or sealing layer of an article of this invention may have expansion
and sealing
properties so that it may be used to seal a range of cavities of different
sizes or shapes,
more typically a cavity sealing article or sealing layer is formulated and
shaped
specifically for use in a particular cavity which is intended to be sealed.
This is especially
true in automobile or other vehicle manufacture, where cavities may be of very
different
cross-sections, and the quality of the seal is of considerable importance to
provide a
moisture, sound, and particulate barrier.
The thickness of the cavity sealing article or sealing layer of this
invention, by
which is meant the dimension perpendicular to the plane of the article or
layer prior to
foaming, will typically be between 3 mm and 13 mm, more typically between 5 mm
and 8
mm. In a single-layer article, if the article is not provided with a support
structure, such
as the support plate seen in FIG. 10, for example, a relatively greater
thickness may be
desirable to provide adequate structural rigidity during manufacture and use;
if the article
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is provided with a support structure or is a multiple-layer article, then a
relatively lesser
thickness may be appropriate.
The cavity sealing article or the sealing layers) of the cavity sealing
article of this
invention, as previously described, comprises at least one foamable
crosslinked driver
substantially surrounded by a foamable uncrosslinked sealer, the shape and
size of which
will be chosen based on the cavity cross-section and the foaming properties of
the article
or layer(s). The article or layers) will typically have a cross-section that
is comparable in
shape to the cavity to be sealed, but between about 45% and 85% of the linear
dimensions, typically about 55% to 75% of the linear dimensions, of the
cavity.
Because the filling of the cavity cross-section is provided primarily by the
at least
one driver of the article or sealing layer, rather than by the sealer (which
is much softer at
the temperature of foaming), the cross-section of the at least one driver of
the article or
sealing layer will desirably be chosen so that, on expansion, the drivers)
alone would
substantially but not completely fill the cavity cross-section; for example,
the expanded
drivers) will have linear dimensions between 40% and 100% of the cavity
dimensions,
especially between 70% and 95% of the cavity dimensions. Too small a driver or
drivers
may provide insufficient filling of the cavity cross-section for the softer
sealer portion to
fill the remaining space, while too large a driver or drivers may buckle
within the cavity
when fully expanded thereby potentially damaging the seal. For a driver
portion having a
linear expansion of 200% {a volume expansion of 800%), then, suitable linear
dimensions
for the driver may be from 20% to 50%, especially 35% to 45% of the linear
dimensions
of the cavity; for a driver having a linear expansion of 230% (a volume
expansion of
1200%), suitable linear dimensions may be from 18% to 45%, especially 30% to
40%,
etc. Especially if the cavity is of irregular shape, the configuration of the
driver portion
may be exaggerated in the direction of shape irregularities, especially
vertices, in the
cross-section of the cavity, to ensure that the sealer portion is driven
completely into these
irregularities and vertices and the resulting foam completely fills and seals
the cavity.
This is shown in FIG. 4, where, although the cross-section of the sealing
article as a
whole is the same as that of the sealing article of FIG. 1, the single driver
portion 22 of
the sealing article 20 comprises exaggerations 22A through 22F in the
direction of the
vertices of the cavity to assist in filling these vertices. The sealer will
relatively uniformly
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surround the drivers) in the plane of the article or layer and be of such a
size that it
provides sufficient sealing (i.e: as yet uncrosslinked) foam during expansion
to
completely fill all spaces between the drivers) and the cavity walls and,
desirably, adhere
to them. The optimal size of the sealer will therefore depend on such factors
as the
material of the sealer, its extent of expansion, the extent to which the
expanded drivers)
will fill the cavity, and the like.
The width of the sealer surrounding the drivers) may be varied between
different
portions of the article, depending particularly on the complexity of the shape
of the cavity
to be sealed. For example, if the cavity is of relatively regular shape and
the cavity walls
are relatively smooth (lacking in sudden changes in direction), then a
relatively greater
clearance between the periphery of the article or sealing layers) and the
cavity walls may
be desirable; such as to permit the ready flow of paint when the cavity to be
sealed is an
automobile pillar painted by total immersion. In such a case, the proportion
of the article
or layers) comprising the drivers) may generally be greater and,
correspondingly, the
width of the sealer will be less. However, if the cavity is narrow and/or of
relatively
irregular shape, then a narrower clearance between the periphery of the
article or sealing
layers) and the cavity walls may be desirable to ensure adequate filling of
the cavity; and
in such a case, the proportion of the article or layers) comprising the
drivers) may be
smaller and the sealer be of relatively greater width. Thus a cavity of
complex shape may
be filled by a cavity sealing article of this invention with different
clearance gaps between
the article or sealing layers) and the walls of the cavity and sealer widths
at different
locations in the article.
Typically, the article or sealing layers) will be sized not directly as a
proportion
of the dimensions of the cavity at the predetermined location that is to be
sealed, but by
considering a certain clearance between the article or layers) and the cavity
walls at the
predetermined location, for example from 1 mm to about 8 mm, for example,
about 3 mm
to 5 mm, depending on the size of the cavity and the complexity of the cavity
shape, and
then calculating from the desired clearance and the resulting size of the
article the extent
of expansion that will be required to seal the cavity, taking into account the
desirability of
the expanded drivers) substantially filling the cavity at the desired location
with the
sealer providing primarily the sealing between the article or layers) and the
cavity walls.
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Because the extent of expansion of the foamable polymeric material may
conveniently be
varied by both the amount of blowing agent that is used and by the extent of
crosslinking
of the driver(s), it will be possible to optimize the size and properties of
the article or
layers) to fill the cavity.
Conveniently, the cavity sealing article or the or each sealing layer of the
article is
manufactured in the form of a flat sheet having a shape corresponding
generally to the
cross-sectional shape of the cavity to be sealed, but smaller in linear
dimension. In such a
case, it is particularly convenient to manufacture the article or layers) from
a foamable
polymer composition containing both a chemical crosslinking agent for the
sealer and a
radiation crosslinking promoter for the driver portion or portions of the
article or layer(s),
as previously described. A sheet of foamable polymeric material is simply cut
to the final
dimensions of the article or layer(s), or the article or layers) are molded to
the desired
shape from the foamable polymeric material, and the driver portion or portions
are
selectively crosslinked by masking that portion of the piece which will become
the sealer
of the article or layer(s), so that only that portion of the piece that will
become the driver
or drivers of the article or layers) are crosslinked. The sealer portion and
driver
portions) of the article or layers) may also be cut separately from the same
or different
sheets of foamable polymeric material, and the resulting drivers) and sealer
assembled
into the cavity sealing article of this invention. In this case, the sheet
from which the
drivers) are cut may be crosslinked as a sheet before the drivers) are cut
from it, or the
drivers) may be crosslinked after cutting from the sheet. Other methods of
manufacturing the cavity sealing article or sealing layers) thereof are also
possible, such
as extruding a rod of the foamable polymeric material of the drivers) to a
cross-section
desired for the driver(s), crosslinking them, subsequently extruding around
those rods)
the foamable polymeric material of the sealer, then sectioning the resulting
composite rod
into a plurality of cavity sealing articles or layers; coextruding the
drivers) and sealer in
the appropriate shapes, sectioning, and crosslinking the driver(s); molding
the drivers)
and sealer either as a unitary piece of the same material or comolding two
different
materials for the drivers) and sealer, etc. It is also within the scope of
this invention that
the sealer may also surround the driver in the direction of the cavity axis as
well as in the
cavity cross-section, although such embodiments are not shown.
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It will be apparent that particular manufacturing techniques may be more .
appropriate for particular designs of the article or sealing layer(s). For
example, although
it may be convenient to physically assemble an article or sealing layer of the
article from
two separate pieces of material, one for the already-crosslinked driver and
one for the
sealer, when there is only a single driver, such a technique may be less
convenient when
an article or sealing layer is to contain a plurality of drivers, especially
in the case of an
embodiment such as that shown in FIG. 6 where there are a large number of
drivers.
However, techniques such as coextrusion and sectioning may be appropriate for
such
embodiments. A convenience in manufacturing an article or sealing layer with a
large
IO plurality of drivers, such as the embodiment of FIG. 6, may be in
manufacturing a sheet
of foamable polymeric material, irradiating it in a pattern to produce the
drivers, and then
cutting the sheet into pieces of appropriate shape for the desired article or
sealing layer.
This patterned irradiation and cutting may be done in such a way that the
drivers form a
regular pattern within the article or layer, such as is shown in FIG. 5; or it
may be done in
1 S such a way that the drivers lie in no particular orientation with respect
to the article or
layer, such as is shown in FIG. 6, where it may be seen that not all of the
periphery of the
article is provided by sealer material.
The sealer substantially surrounds the at least one driver in the plane of the
article
or sealing layer to maximize the sealing efficiency of the article or layer
when it is used,
20 as the material of the sealer typically provides greater adhesion to the
cavity walls than
the material of the driver(s). By "substantially surrounds" is meant that the
periphery of
the article or layer in the plane of the article or layer should be provided
primarily by the
sealer. In particular, when the article or layer has only a single driver, it
is desirable that
the driver be completely surrounded by the sealer in the plane of the article
or layer. Such
25 a situation is seen in FIGS. 1 and 4, for example. When the article or
layer has a plurality
of drivers, it is also desirable that the drivers be completely surrounded by
the sealer in
the plane of the article or layer; and this is seen in FIGS. S and 7. However,
for
convenience in manufacture of the article or layer when the article or layer
has a plurality
of drivers and has been cut from a sheet of foamable polymeric material that
has been
30 selectively irradiated in a patterned manner such as in FIG. 6, as
discussed above, a part
of the periphery of the article or layer may be provided by driver material.
In this
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instance, it is desirable that the patterning of the drivers on the sheet
and/or the cutting of
the article or layer from the sheet be such that an article or layer cut from
the sheet will
have less than 50%, preferably less than 30%, more preferably less than 20% of
the
periphery provided by driver material; and that no large section of the
periphery be
provided solely by driver material.
Typically, a multiple-layer cavity sealing article of this invention will have
two
sealing layers, but this invention also contemplates articles having more than
two sealing
layers. For simplicity, and because the invention and its manufacture and use
is
adequately described by an article having only two layers, the drawings
illustrate the
invention only with reference to two-layer cavity sealing articles; however, a
person of
ordinary skill in the art will have no difficulty, having regard to that skill
and this
disclosure, in manufacturing and using a multiple-layer cavity sealing article
having more
than two layers.
While it is possible that all of the sealing layers of a particular multiple-
layer
1 S cavity sealing article may be the same, it is also possible that not all
of the sealing layers
must be the same.
The use of a cavity sealing article in which each sealing layer is the same
offers
advantages in manufacture, both because only one type of sealing layer is
required to be
manufactured and because the assembly of the multiple-layer cavity sealing
article is
simplified when only one type of sealing layer is used - the sealing layer
parts of the
article are identical and no choice among different parts is required.
However, there may be circumstances in which the use of sealing layers that
are
not all the same may offer advantages in the multiple-layer cavity-sealing
article of this
invention. One example is where the cross-section of the cavity to be sealed
changes
substantially at the predetermined location, such as where the cavity changes
in cross-
sectional area, where the cavity changes in cross-sectional shape but not in
area, or where
the cavity curves or is otherwise irregular at the predetermined location. In
each of these
circumstances, it will be apparent to a person of ordinary skill in the art
that it may be
desirable that the sealing layers be of different sizes and/or shapes even if
they are
otherwise identical in composition and thickness, so that each sealing layer
may be
chosen to best seal the cross-section of the cavity at the point where it is
placed. Even if
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the cross-section of the cavity to be sealed is the same for each sealing
layer of a multiple-
layer cavity sealing article, it still may be desirable that the sizes,
compositions,
thicknesses, or degrees of expansion of the various sealing layers not all be
the same. For
example, it is highly desirable that at least one (and preferably all) of the
sealing layers of
the article completely seal the cross-section of the cavity at the point where
it is placed. If
only one sealing layer is used, then, that layer is chosen to ensure complete
sealing, and
this certainty of sealing (achieved by choice of the driver and sealer size,
degree of
expansion, etc.) may not in itself be optimal in other properties, such as
acoustic
properties. In particular, it may require that the sealing layer have a
hardness that is
greater or less than desirable for maximum acoustic benefit. In the multiple-
layer article
of this invention, it is possible to have different sealing layers optimized
for different
functions within the sealing article. For example, one sealing layer may be
optimized to
ensure complete sealing of the cavity cross-section while another sealing
layer may be
optimized to provide a more efficient acoustic burner, etc. Similarly, the
sealing layers
may be of different thicknesses, if desired. A person of ordinary skill in the
art, having
regard to that knowledge and this disclosure, will be able to determine
suitable sealing
layers for a multiple-layer sealing article of this invention and to optimize
them for a
particular application.
A person of ordinary skill in the art will be able, having regard to that
skill and
this disclosure, to select suitable materials and perform a suitable method of
manufacture
for a cavity sealing article or sealing layers) of a sealing article of this
invention.
The support structure
If the cavity sealing article of this invention comprises a support structure,
that
support structure performs two functions: first, it is adapted to fit within
the cavity to be
sealed and orient the article or sealing layers) within the cross-section of
the cavity at the
predetermined location; and second, in the case of a multiple-layer sealing
article, it
supports the sealing layers in spaced-apart relationship.
The support structure or components may be prepared from any material having
the structural integrity and durability necessary to permit storage of the
cavity sealing
article of this invention, placement of the article within a cavity to be
sealed, sealing of
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the cavity by foaming of the article, and use of the article within the
cavity, potentially for
an extended time such as the lifetime of a vehicle. This requires both
structural stability
at elevated temperatures, such as stability at temperatures of at least
150°C, preferably at
temperatures of at least 180°C, and the ability to withstand the forces
produced by
foaming of the article at those temperatures, and long-term durability
Typically, the
mounting means may be prepared from metal, such as steel, including metal
mesh,
especially when used for a support plate such as plate 42 in FIGS. 9 and 10,
or may be
prepared from a high melting point thermoplastic polymer, such as a high
temperature
polyolefin, a polyamide such as a nylon, for example, nylon 6, nylon 46, or
nylon 66, a
polyester, such as polyethylene terephthalate, an aromatic polyether,
polyether ketone, or
polyamide, a thermoset resin, or the like; especially one that may easily be
formed into
the desired shape. These polymers will typically contain fillers,
antioxidants, flame
retardants, and/or other stabilizers such as are conventional in polymeric
articles, and may
contain pigments, plasticizers, adhesion promoters, and the like. In addition,
the
polymers may contain reinforcing materials, such as glass fiber and the like,
if needed or
desired. The support structure may be formed as a single piece, such as by
molding, or
assembled from two or more pieces.
The shape of the support structure is designed so that it fits within the
cavity to
orient the article within the cross-section of the cavity at the predetermined
location,
desirably so that the sealing layers) lie perpendicular to the cavity walls,
and the support
structure will therefore be provided with features that are capable of
interaction with the
cavity walls to provide that orientation, as is discussed further below.
In addition, the shape of the support structure for a multiple-layer cavity
sealing
article is designed so that it supports the plurality of sealing layers in
spaced-apart
relationship. Thus, for each sealing layer, the support structure will provide
a support for
that layer so that it is appropriately oriented within the cavity and so that
a sealed space is
formed within the cavity between each two sealing layers when the sealing
layers of the
article have been foamed and expanded. Typically, the support structure will
support the
plurality of sealing layers in parallel spaced-apart relationship; but if the
cavity is of
irregular shape or is to be sealed at a curve, etc., it may be desirable for
the sealing layers
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to be non-parallel so that each sealing layer separately lies perpendicular to
the cavity .
walls, for example.
Thus, the support structure may comprise one or a plurality of support plates
or
trays, one for each sealing layer, which are in turn fastened in spaced-apart
relationship to
one another, and means for locating the support structure in the cavity, such
as are well-
known in the art for other foamable cavity seals.
The spacing between the or each pair of sealing layers in a multiple-layer
article
may be chosen to maximize the attenuation at a desired frequency, achieved by
spacing
the sealing layers approximately ~./4 apart, where ~, is the wavelength of the
sound at the
desired frequency. Because the sealing layers are not themselves completely
rigid, this
idealized ~,/4 spacing may not in fact be optimal, and some adjustment of the
spacings
may be appropriate to achieve the attenuation profile most desired. Such
adjustments are
within the ordinary skill of the art.
Depending on its design and intended use, the support structure may be made to
be emplaced and retained within the cavity to be sealed by any suitable means,
such as by
fastening to a wall of the cavity by a fastener of some sort such as the bolt
and nut
illustrated in FIGS. 10 and 12, or by some similar fastening means such as a
clip or stud,
and/or may be made so that features of the support structure grippingly engage
the walls
of the cavity to retain the article in the predetermined location, such as by
means of the
protrusions illustrated in FIGS. 17 through 19.
Manufacture of the supported cavity sealinu article
The supported cavity sealing article is manufactured by mounting the or each
of
the sealing layers on the support structure. Depending on the design of the
article, this
may be accomplished by mounting the or each sealing layer on the structure by
means of
one or more studs, screws, or relatively small supports. The sealing layers
may also be
provided with holes to engage protrusions, clips, or the like, formed in the
support
structure; or the support structure may be provided with adhesive surfaces by
which the
sealing layers may be fastened to it.
Because the driver portion of the or each sealing layer of the article of this
invention is crosslinked, it does not flow when heated to a temperature above
the melting
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point of the polymers comprising it, although it will soften to a certain
extent (depending .
on the materials, the extent of cross-linking, and the temperature). It is
therefore a
particular benefit of the multiple-layer sealing article of this invention
that the driver
portion of each sealing layer is relatively dimensionally stable and each
sealing layer of
the article can .therefore be emplaced on the support structure by a simple
support means
such as those described previously, rather than requiring substantial support
to prevent its
sagging during heating and foaming (especially when the cross-section to be
sealed is
vertical and sagging of the sealing layer would tend to cause the sealing
material to pull
away from the cavity wall above the sealing article. As a result, the sealing
layers of this
invention do not need expensive, complex, or precise mounting on the support
structure,
but yet will still provide an excellent seal when used.
It will be evident to one of ordinary skill in the art, having regard to that
skill and
this disclosure that a variety of means may be used to emplace the sealing
article of this
invention within a cavity to be sealed, and that all such means fall within
the scope of this
1 S invention.
Use of the cavity sealine article
The cavity sealing article of this invention is used by placement in the
cavity to be
sealed, preferably approximately centrally in the cavity cross-section and
with the cross-
section of the article approximately coincident with the cross-section of the
cavity. The
article may be emplaced in the cavity by such means as are conventional in the
art, for
example by emplacement through a hole into an already formed cavity or, more
usually,
by fastening onto one of two or more members which are subsequently fastened
together
to form the cavity. It is a feature of the cavity sealing article of this
invention that,
because of the use of the driver and sealer portions of the article to
maximize its cavity
filling and sealing efficacy, placement of the article in the cavity is not as
position-critical
as placement of prior art cavity seals. A single-layer article may be emplaced
by
mounting on a stud, screw, or other relatively small support (such as is shown
in the
previously-mentioned Soderberg patent and illustrated in FIGS. 1, 2, and 4).
In some
instances, the cavity to be sealed will have a structural part or parts which
will support the
cavity sealing article in a desired location, particularly if the article has
been molded or
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shaped to a predetermined shape for that location and/or is provided with
molded-in
features (for example, holes or protrusions) to engage those parts. In other
instances, the
article may be formed with features, such as protrusions extending from the
periphery of
the article in the plane of the article, such that the protrusions engage the
cavity to provide
correct placement of the article in the predetermined location. This is shown
in FIG. 8,
where a single-layer sealing article 20 is provided with protrusions of the
sealer 24A
through 24D shaped to engage the cavity walls. The article may also be
provided with
clips or the like, about which it has been molded, to engage holes in the
cavity walls; or
may be provided with holes to engage protrusions, clips, or the like, formed
in or attached
to the cavity walls. The article may also be emplaced by fastening to a
support structure
such as a support plate or tray (or between a pair of such support plates or
trays, although
it is a feature of the cavity sealing article of this invention that extensive
support is not
necessary), which is in turn fastened to or otherwise firmly located in the
cavity, such as
is well-known in the art for other foamable cavity seals. This is shown in
FIGS. 5, 6, 7,
11, and 13, where only one arm 40A of a support bracket is seen; and in more
detail in
FIGS. 9, 10, 12, and 14, where the support can be seen in more detail.
In FIGS. 9 and 10, a single-layer cavity sealing article 20 is fastened to a
support
structure comprising a support plate 42, only the periphery of which is
visible behind the
article, by a bolt 44 passing through a washer 46, a hole in the driver and
the support plate
and a nut 48. Here, the support plate 42 is mounted on a bracket shown
generally at 40,
having one arm 40A to which it is fastened and the other arm 40B which is
fastened to the
cavity wall 14 by a bolt 50 and nut 52, thereby positioning the support plate,
and hence
the article 20, in the cavity. It will be evident to one of ordinary skill in
the art, having
regard to that skill and this disclosure that other means may be used to
emplace the
sealing article of this invention within a cavity to be sealed, and that all
such means fall
within the scope of this invention.
Because the driver portion of the sealing article of this invention is
crosslinked, it
does not melt or flow when heated to a temperature above the melting point of
the
polymers comprising it, although it will soften to a certain extent (depending
on the
materials, the extent of cross-linking, and the temperature). It is therefore
a particular
benefit of the sealing article of this invention that the driver portion is
relatively
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dimensionally stable and the article can therefore be emplaced within the
cavity to be
sealed by a simple support, rather than requiring substantial support to
prevent its sagging
during heating and foaming (especially when the cross-section to be sealed is
vertical and
sagging of the article would tend to cause the sealing material to pull away
from the
cavity wall above the sealing article, as discussed below in Example 3 and
Comparative
Example 3). For example, the sealing article may be supported only on a single
stud or
screw (such as is shown in FIGS. 1, 2, and 4), may be effectively self
supporting (such as
is shown in FIG. 8), or may be supported on a support plate with a simple
fastener such as
a nut and bolt (such as is shown in FIGS. 9, 10, 11, and 12) or a grommet
(such as is
shown in FIGS. i 3 and 14). What is more, because the driver foams and expands
in use,
it is not necessary that the mounting of the sealing article, for example on a
support plate
such as in FIGS. 9 and 10, be a sealed mounting: the driver will expand to
seal tightly to
any mounting means (like the bolt shown) that is used. As a result, the cavity
sealing
article of this invention does not need expensive, complex, or precise
mounting within the
cavity to be sealed, but yet will still provide an excellent seal when used.
To permit the passage of drain hoses, electrical wiring, or the like objects
through
the cavity sealing article of this invention subsequent to the installation
and foaming of
the article, the cavity sealing article may be provided with one or more
apertures through
the article. These apertures) are typically provided through the drivers) of
the article, as
the drivers) have more uniform expansion and the size of the aperture after
foaming of
the article can therefore be more easily predicted. In a first method of
providing the
aperture, the driver may simply have an aperture cut into it during
manufacture. The
aperture in the driver is sized such that, on expansion of the driver, and
hence of the
aperture itself, during foaming of the article, the aperture will enlarge to
the ultimately
desired size. For example, if the driver has a linear expansion of 200% on
foaming and
the size and shape of the article is such that the expansion of the driver
will be
unconstrained by the sealer and the cavity walls, and an aperture of 1 cm
diameter is
desired in the finished seal, an aperture of 5 mm diameter will be provided in
the driver
when the sealing article is manufactured. If the expansion of the driver is
expected to be
constrained, then the aperture will be sized accordingly. This aperture may be
provided in
the driver by any suitable method, such as cutting or molding, and a
particularly
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convenient method is the simple cutting of the aperture through the driver
with a tubular .
punch of the appropriate size. The material punched out from the driver may be
removed
before the seal is installed and foamed, or it may be left in place during
installation and
foaming to provide a "knock-out" aperture which may be opened only if desired,
thereby
leaving the seal.uncompromised if a drain hose or other object is not to be
installed. FIG.
11 shows a single-layer cavity sealing article of this invention where an
aperture 54 has
been provided through the driver 22 of the sealing layer of the article 20. In
this
embodiment, the arm 40A of the bracket on which the sealing layer of the
article 20 is
mounted within the cavity is offset from the center of the article, as seen in
more detail in
FIG. 12, where it maybe seen that the other arm 40B is fastened to the cavity
wall. In a
second method of providing the aperture, a solid grommet is inserted through
the driver
during manufacturing of the sealing article. The grommet is of the desired
final size and
shape of the aperture, and may be provided with means, such as an O-ring, for
tightly
sealing to a drain hose or like object inserted through the grommet.
Typically, if a solid
grommet is to be used, it will be attached to a support that is used to retain
the cavity
sealing article in the predetermined location in the cavity. This is
illustrated in FIGS. 13
and 14, where the grommet 56 holds the cavity sealing article 20, through an
aperture in
the driver 22, to one arm 40A of a bracket 40, of which the other arm 40B is
fastened to
the cavity wall. In this instance, because the grommet provides a definite
size and shape
for the aperture, the configuration of the article or sealing layer will
desirably be chosen
so that the driver expands tightly within the grommet on foaming and expansion
of the
article. In particular, it may be desirable that the size of the article or
sealing layer and its
expansion properties be chosen so that expansion of the article on foaming is
constrained
by the cavity walls, so that the aperture within the driver through which the
grommet
passes does not expand unconstrainedly away from the grommet.
FIG. 13 is a cross-sectional view showing a ninth, multiple-layer, embodiment
of
the cavity sealing article of this invention emplaced within a cavity, the
longitudinal axis
of which is within the page. The multiple-layer cavity sealing article shown
generally as
200 comprises two sealing layers shown generally as 200A and 200B supported in
spaced-apart relationship by the support structure shown generally as 300.
Sealing layer
200A comprises a crosslinked foamable polymer driver 220A surrounded by and in
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intimate contact with an uncrosslinked foamable polymer sealer 240A; and
sealing layer
2008 likewise comprises driver 2208 and sealer 2408. Support structure 300
comprises
a generally U-shaped strap 320, the center portion of which is secured to the
inner side of
the cavity wall 120 by a bolt 340 and nut 360; with the two arms of the U
projecting into
the cavity. Each sealing layer 200A and 2008 is further supported by a support
plate
380A and 3808 respectively, and is fastened to that support plate and to the U-
shaped
strap 320 by bolts and nuts 400A and 420A and 4008 and 4208 respectively.
FIG. 14 is a cross-sectional view showing a tenth, multiple-layer, embodiment
of
the cavity sealing article of this invention emplaced within a cavity, the
longitudinal axis
of which is within the page, illustrating a different manner of fastening the
two sealing
layers 200A and 2008 to the support structure 300. In this Figure, sealing
layer 200A is
fastened to the U-shaped strap 320 by an adhesive layer 440; and sealing layer
2008 is
fastened to the U-shaped strap 320 by two expanding anchors 460A and 4608
passing
through holes in the strap 320 and the sealing layer 2008. Support plates may
also be
1 S present, if desired, but are not shown in this Figure.
FIGS. 17 through 19 illustrate an eleventh, multiple-layer, embodiment of the
cavity sealing article of this invention, using an alternative support
structure. In these
three figures, the driver and sealer portions of the sealing layers, and the
means holding
the sealing layers to the support structure, are not individually shown or
described, since
their location and function will be evident from the previous figures.
FIG. 17 is a perspective view of this eleventh embodiment, showing sealing
layers
200A and 2008 supported by the support structure shown generally as 500. The
support
structure S00 comprises support plates 520A and 520B for sealing layers 200A
and 2008,
and spacers 540 and 560 maintaining the support plates in spaced-apart
relationship. In
this embodiment, support plate 520A is shown as having flexible protrusions
580A,
600A, 620A, and 640A; and support plate 5208 is shown as having flexible
protrusions
5808, 6008, 6208, and 6408. These flexible protrusions are designed so as to
grippingly
engage the wall of the cavity to be sealed, as better illustrated in FIG. 18,
and thereby
retain the sealing article in the location within the cavity desired to be
sealed.
FIG. 18 is a cross-sectional view of the eleventh embodiment of the multiple-
layer
sealing article, with the longitudinal axis of the cavity within the page. As
can be seen,
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the flexible protrusions 580A through 640B of the support structure engage the
cavity
wall 120 to retain the sealing article in the appropriate position.
FIG. 19 is a cross-sectional view showing the eleventh embodiment of the
sealing
article after foaming and expansion. Sealing layers 200A and 200B have foamed
and
expanded to fill the cross-section of the cavity, thereby creating two seals
with a "dead
space" between them.
It will be apparent that embodiments of the cavity sealing article having
multiple
sealing layers, such as those shown in FIGS. 15 through 19, may employ sealing
layers
comprising more than one driver, such as those shown in FIGS. 5, 6, and 7 and
described
previously with regard to embodiments having a single sealing layer, and/or
may be
provided with an aperture or apertures therethrough, such as those shown in
FIGS. 11
through 14 and described previously with regard to embodiments having a single
sealing
layer; and all such variations are considered as being within the scope of
this invention.
When the article is emplaced within a cavity of a vehicle, the article is
desirably
placed such that there is substantially complete clearance around it within
the cavity
before activation and foaming, thereby permitting the phosphating,
rustproofmg,
electrochemical painting, and other treatments such as are commonly given to
vehicle
bodies. When the article is emplaced within a cavity that is not subject to
painting and
the like, such clearance is not necessary.
When it is desired to activate and foam the sealing article of this invention,
the
article is exposed to a sufficient temperature for a sufficient time to
activate the blowing
agent and the chemical crosslinking agent. Suitable times and temperatures
will depend
on the application in which the seal is to be used, aid may include
temperatures between
100°C and 300°C or greater for periods between 5 and 100
minutes. Typically, in the
case of sealing channels in new vehicle bodies, this heat activation will
occur when the
body is placed in a paint bake oven to cure previously applied paint, and such
temperatures and times are typically between 115°C and 250°C for
10 to 40 minutes, for
example 160°C for 25 minutes, but a person of ordinary skill in the art
will realize that
other temperatures and times may be appropriate. Also, the sealing article may
be
activated by other heat sources (for example, local heating such as induction
heating of
the area), for example if it is being used for repair purposes or is being
emplaced in a
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large structure. On heating, the uncrosslinked sealer of the article softens
and foams
while the crosslinked drivers) of the article foam in a uniform fashion to
push the sealer
into intimate sealing contact with the walls of the cavity. The foam of the
sealer then
chemically crosslinks, stabilizing the sealer foam so that the foamed article
forms a stable
plug filling the whole cross-section of the cavity and intimately bonded to
the cavity
walls, acting as a moisture, sound, and particulate barrier.
The invention is illustrated by the following Examples and Comparative
Examples.
EXAMPLE 1
A foamable sheet was prepared from the following formulation:
Ingredient Parts by weight
Evatane 28-OS (EVA, 28% VA, MFI 5, Atochem) 100.0
Irganox 1076 (antioxidant, Ciba-Geigy) 2.0
Kadox 911 (zinc oxide) 30.0
Varox 231 XL (peroxide crosslinker, Vanderbilt) 1.5
Celogen TSH (blowing agent, Uniroyal) 10.0
Sartomer 350 (radiation crosslinking promoter, Sartomer) 5.0
A Brabender mixer was set at 80°C; and the Evatane, Irganox, and
Kadox were
added and blended to homogeneity. The Varox, Celogen, and Sartomer were then
added
1 S and blended to homogeneity, ensuring that the temperature of the mixer
remained below
80°C during the mixing process. The mixed material was then molded, at
about 100°C
(below the decomposition temperature of the Varox and Celogen), into a sheet
of
approximately 6 mm thickness.
A test cavity was formed from a section of metal rain-gutter, of irregular but
approximately trapezoidal cross-section, approximately 105 mm on the longer of
the
parallel sides (across the top of the gutter, which was closed with a piece of
sheet metal),
70 mm across the shorter of the parallel sides (the bottom), and 75 mm high.
The interior
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of the test cavity was sprayed with light oil (WD-40~) to simulate
contamination of the
cavity and provide a more stringent test of the sealing power of the cavity
sealing article.
A piece of the foamable sheet prepared as described above was cut to
approximately the shape of the test cavity, with linear dimensions
approximately 65%
85% of those of the cavity. The piece was a trapezoid, with the longer of the
parallel
sides being 90 mm, the shorter being 47 mm, and the height being 51 mm. The
piece was
held in an acrylate jig, with an acrylate mask of approximately 13 mm
thickness placed on
top of the piece, masking an approximately 13 mm wide strip (forming the
sealer portion
of the cavity sealing article) around the edge of the piece and leaving an
exposed area also
of trapezoidal shape, with the longer of the parallel sides being 45 mm, the
shorter being
29 mm, and the height being 25 mm, forming the driver portion. The resulting
assembly
was irradiated with 1.6 Mrad of 3.0 MeV electrons to crosslink the exposed
section of the
piece (the driver), thereby producing a cavity sealing article of this
invention.
The test cavity was placed on a metal sheet so that its axis was vertical and
cross-
section horizontal, and the cavity sealing article was placed on the metal
sheet, in
approximately the center of the cavity. The resulting assembly was placed in a
157°C
oven for 25 minutes, then removed and allowed to cool.
Examination of the test cavity revealed that the crosslinked driver portion of
the
article had foamed and expanded isotropically, forming a uniform foam with
small closed
cells. This foam had forced the uncrosslinked sealer portion at the periphery
of the article
into close proximity with the walls of the test cavity. The sealer of the
article had also
foamed, although in a less uniform fashion and with open cells visible on the
surface, but,
with the driver, had completely filled the test cavity cross-section and
displayed excellent
adhesion to the cavity walls.
The resulting foamed article was non-tacky and non-moisture absorbing, and
effectively sealed the cavity.
Square test pieces of the material of the sealing article of this Example,
either
crosslinked (like the driver) or uncrosslinked (like the sealer), were foamed
for an
identical temperature and time, laid horizontally on a metal sheet but not
otherwise
externally confined. The crosslinked material expanded isotropically with a
linear
expansion of 200% in each direction (volume expansion of 800%), giving a
uniform foam
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of small cell size. The uncrosslinked material expanded anisotropically with a
linear
expansion of approximately 180% in the two horizontal directions and non-
uniform
vertical expansion of approximately 265% in the center and 100% at the edges
(volume
expansion of approximately 600%), giving a coarse cell structure.
COMPARATIVE EXAMPLE 1
Cavity sealing articles not of this invention but similar to that of Example I
were
prepared as follows:
without a radiation crosslinking promoter or crosslinking (i.e. lacking a
driver); and
with the same formulation as in Example 1, but radiation crosslinked uniformly
across its
entire area (i.e. lacking a sealer).
These articles were tested in the same manner as the cavity sealing article of
Example 1, i.e. placing them horizontally in a test cavity and foaming them in
an oven.
The non-crosslinked article foamed preferentially in the vertical direction,
probably due to
adhesion to its support, and did not fill the cross-section of the test
cavity; however,
adhesion of the foam to the cavity walls was good. The uniformly crosslinked
article
foamed isotropically; however, it did not adhere to the cavity walls and
buckled where it
came into contact with them, so that it also did not fill the cross-section of
the test cavity.
These results, taken with the results of Example 1, show that a cavity sealing
article of this invention with a crosslinked driver and uncrosslinked sealer
functions well
to seal a cavity, whereas similar articles lacking either the driver or sealer
do not function
to seal a cavity.
EXAMPLE 2
A cavity sealing article of this invention similar to that used in Example 1
was
prepared from a formulation similar to that of Example 1 but containing an
additional 30
parts by weight Piccotac 95 (tackifier, Hercules Chemical Co.). The article
was tested in
the manner described in Example 1. The sealer portion of this article flowed
to a greater
extent on foaming than the sealer of the article of Example 1; but the article
showed the
same uniform expansion of the driver, filling of the cavity cross-section, and
excellent
sealing to the cavity walls that was shown by the article of Example 1.
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The resulting foamed article was non-tacky and non-moisture absorbing, and
effectively sealed the cavity.
EXAMPLE 3
A cavity sealing article of this invention, and a test cavity, were prepared
as in
Example 1. The article was adhered by a piece of double-sided adhesive tape to
a sheet
metal support plate, having a shape and size similar to that of the article,
with flanges at
the corners of the plate so that the plate (and hence the article) was
supported centrally in
the cavity. The resulting assembly was placed in the oven with the axis of the
cavity
horizontal (the article, and the cavity cross-section, therefore being
vertical), and was
heated at 157°C for 25 minutes to foam the article.
Examination of the test cavity revealed that the crosslinked driver portion of
the
article had foamed and expanded isotropically, forming a uniform foam with
small closed
cells. This foam had forced the uncrosslinked sealer portion at the periphery
of the article
into close proximity with the walls of the test cavity. The sealer of the
article had also
foamed, although in a less uniform fashion and with open cells visible on the
surface, but,
with the driver, had completely filled the test cavity cross-section and
displayed excellent
adhesion to the cavity walls.
The resulting foamed article was non-tacky and non-moisture absorbing, and
effectively sealed the cavity.
COMPARATIVE EXAMPLE 3
A cavity sealing article not of this invention but similar to that of Example
1 was
prepared by manufacturing the article using the same procedure as in Example 1
but not
radiation crosslinking the center area, so that the article lacked a driver.
The article was
tested in the same manner as the cavity sealing article of Example 3, i.e.
placing it
vertically in a test cavity and foaming it in an oven. The article foamed
preferentially in
the horizontal direction, sagged badly away from the upper part of the cavity
walls, and
did not fill the cross-section of the test cavity; however, adhesion of the
foam to the cavity
walls was good.
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These results, taken with the results of Example 3, show that a cavity sealing
article of this invention with a crosslinked driver and uncrosslinked sealer
functions well
to seal a cavity, whereas a similar article lacking the driver does not
function to seal a
cavity.
EXAMPLE 4
A test cavity of approximately trapezoidal shape was prepared from mild steel.
The base of the trapezoid was 76 mm, the top was 70 mm, and the height was 67
mm.
The two top corners of the trapezoid were rounded, and the two base corners
were pinch
welded, forming sharp vertices.
Cavity sealing articles according to this invention were prepared generally as
in
Example 1, but with the articles each having a plurality of drivers and a
sealer in intimate
contact with and substantially surrounding the drivers. A foamable sheet was
prepared
from the following formulation:
Ingredient Parts by weight
Elvax 470 (EVA, duPont) 80
Evatane 28-OS (EVA, 28% VA, MFI S, Atochem) 20
Irganox 1076 (antioxidant, Ciba-Geigy) 2
Kadox 911 (zinc oxide) 10
OMYA-Car-UFT (calcium carbonate) 30
Raven C Ultra Beads (carbon black) 2
Piccotac 95 (tackifier, Hercules) 15
Varox DCP40KE (peroxide crosslinker, Vanderbilt) 4
Celogen OT (blowing agent, Uniroyal) 5
Sartomer 350 (radiation crosslinking promoter, Sartomer) 5
A Brabender mixer was set at 80°C; and all materials except the Varox,
Celogen,
and Sartomer were added and blended to homogeneity. The Varox, Celogen, and
Sartomer were then added and blended to homogeneity, ensuring that the
temperature of
the mixer remained below 80°C during the mixing process. The mixed
material was then
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pelletized to give pellets of a base uncrosslinked foamable polymer. Sheets
6.5 mm thick
were molded from these pellets at about 100°C (below the decomposition
temperature_of
the Varox and Celogen), and irradiated with 4.8 Mrad of 3.5 MeV electrons in
patterned
fashion to form articles of this invention.
In one example, the drivers were 3 mm squares, spaced on a square grid on 6 mm
centers; in a second, the drivers were 6 mm squares on 12 mm centers; in a
third, the
drivers were I 3 mm squares on i 9 mm centers; in a fourth, the drivers were 3
mm
diameter circles on 6 mm centers; in a fifth, the drivers were 6 mm diameter
circles on 12
mm centers; and in other embodiments, the drivers were of non-uniform shapes.
On
heating, each of these articles foamed and sealed to the walls of the test
cavity.
EXAMPLE 5 (SIMULATED MULTIPLE-LAYER CAVITY SEALING ARTICLE/
To demonstrate the characteristics of the multiple-layer cavity sealing
article of
this invention, a simulated double-layer cavity sealing article was prepared
by mounting
two single-layer cavity sealing articles in close proximity within a test
channel; and the
acoustic characteristics of various simulated double-layer articles so
prepared compared
with each other and with a single-layer article.
As an example, two sealing layers were prepared by preparing a 60 mm x 60 mm
square of 6.4 mm thick foamable polymer, of which the central 40 mm x 40 mm
section
(the "driver") was radiation cross-linked to have a linear expansion of about
150%
(volume expansion of about 340%). Each sealing layer was bolted with a 3 mm
bolt
through the center of the sealing layer to a 60 mm x 60 mm backplate of 3 mm
wire mesh,
on the other side of which was a 19 mm wide L-shaped aluminum strap, the
longer leg of
which was 50 mm long with a first hole 12 mm from the end of the longer leg,
the bolt
passing through that hole and being secured by a nut; and the shorter leg of
which was 25
mm long with a second hole I2 mm from the end of the shorter leg. The strap
was
secured to the inner wall of a 250 mm long channel made from 0.8 mm steel,
having a
75 mm x 75 mm square cross-section, by a bolt through that second hole; so
that the
sealing layer was positioned centrally in the cross-section of the channel,
with the nearer
sealing layer to the end of the channel being approximately 50 mm from the end
of the
channel. The distance between the two sealing layers could be adjusted by
placement of
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the supports within the channel. Similar sealing layers of different degrees
of expansion,
sizes, and thicknesses, were also prepared.
Acoustic testing was conducted in the manner described in Saha and Myers,
"Evaluating Acoustical Performance of Expandable Sealant Materials", SAE
Technical
Paper No. 930336, SAE International Congress and Exposition, Detroit,
Michigan, March
1-5, 1993. The channel was mounted in a fixture filling an opening located in
the wall of
a reverberation room containing a loudspeaker and source microphone, with a
small
anechoic chamber on the other side of the opening containing a receiving
microphone.
The insertion loss (in effect, the attenuation caused by the sealing article)
was measured
over the range 125 Hz - 10 KHz.
A single layer sealing article of 12.7 mm thickness, tested for comparative
purposes, using a medium expansion ( I 60% linear expansion) foam of the type
described
in Example 1 showed an insertion loss (the difference between the receiving
microphone
sound pressure levels before and after insertion of the cavity sealing
article, measured in
decibels) of 10 - 12 dB between 125 and 200 Hz, rising to about 50 dB at 500
Hz, then
dipping to about 30 dB at 800 Hz, rising again to 45 dB by 1600 Hz, then
staying in the
range of 40 - 45 dB until 10 KHz. Similar single layer sealing articles of 9.5
mm and 6.4
mm thickness showed similar performance below 500 Hz, a drop to about 20 dB
between
800 and 1250 Hz, and an insertion loss in the 2 KHz to 10 KHz range that
averaged 35 -
40 dB.
A double-layer sealing article of this invention, using two 6.4 mm thickness
sealing layers of the same foam spaced 38 mm apart, showed comparable
attenuation up
to 500 Hz, no significant drop around 1 KHz, and an insertion loss averaging
better than 6
dB greater than that of the 12.7 mm single layer sealing article in the 2.5
KHz - 10 KHz
range, with the difference increasing with increasing frequency.
A similar result was seen for high expansion (200% linear expansion) foams,
where the drop in insertion loss for the single-layer article near 1 KHz was
even greater
than for the medium expansion foam and was absent for the double-layer
article, but the
difference in high-frequency insertion loss was not quite as great. Typically,
greater
expansion, which results in a softer foam, gives better high frequency
attenuation for both
single-layer and double-layer articles.
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These data indicate that for the same total thickness of sealing layer, a
double-
layer cavity sealing article provides better acoustic performance (greater
attenuation) than
a similar single-layer cavity sealing article.
Varying the spacing between the sealing layers of a double-layer article using
S medium expansion foam from 25 mm to 38 mm had little effect on the insertion
loss,
though the greater spacing provided slightly greater and more even
attenuation.
In a test using double-layer articles with sealing layers of different
expansion
(hardness), it was found that the combination of one low expansion (125%
linear
expansion), relatively hard sealing layer and one high expansion (200% linear
expansion,
relatively soft sealing layer gave slightly greater insertion loss than was
achieved with the
same design using two identical high expansion sealing layers.
These data indicate that varying the spacing between the sealing layers, and
using
non-identical layers, in the multiple-layer cavity sealing article of this
invention enables
variation in the characteristics of the sealing article.
While this invention has been described in conjunction with specific
embodiments
and examples, it wilt be evident to one of ordinary skill in the art, having
regard to this
disclosure, that equivalents of the specifically disclosed materials and
techniques will also
be applicable to this invention; and such equivalents are intended to be
included within
the following claims.
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