Note: Descriptions are shown in the official language in which they were submitted.
CA 0220~9~3 1997-0~-22
H 1611 PCT
17.11.1994
Elastomer products having acoustic damping properties
This invention relates to heat-curing reactive
compositions based on natural and/or synthetic elastomers
containing olefinic double bonds and vulcanizing agents
which have acoustic damping properties in the vulcanized
state. The invention also relates to a process for the
production of these compositions and to their use as
adhesives, sealing compounds and coatings.
Nowadays, motor vehicles, machines and appliances
are made almost exclusively from very thin metal sheets.
Mechanically moving parts or running engines unavoidably
cause these thin sheets to vibrate - often in the hearing
range of the human ear. These vibrations are propagated
in the form of mechanical vibration throughout the entire
vehicle, machine or appliance and can be radiated into
the air as troublesome noise at remote places. Accord-
ingly, to reduce sound radiation and vibration damping,
these sheets are provided with noise-damping coatings,
so-called anti-vlbration coatings, especially in automo-
bile manufacture and in the manufacture of domestic
appliances.
The conventional procedure adopted for this purpose
is to extrude mixtures of fillers of high specific
gravity and bitumen to form films from which the corre-
sponding shaped parts are then sta.~.Lped or cut. These
films are then bonded to the metal sheets in question,
optionally having to be adapted to the shape thereof by
heating. Although these bitumen films are still fre-
quently used by virtue of their low material price, they
are extremely brittle and tend to flake off the metal
sheet, particularly at low temperatures. The frequently
proposed additions of elastomers also produce only a
slight improvement which is inadequate for many applica-
CA 0220~9~3 1997-0~-22
H 1611 PCT 2
tions. In addition, preformed bitumen parts cannot be
applied to intricately shaped or awkwardly situated sheet
metal parts of machines or vehicles, for example the
inside surfaces of doors. Another disadvantage is that,
in many cases, several stamped parts are required for a
single vehicle or appliance and, accordingly, have to be
expensively stored in appropriate numbers.
Accordingly, attempts have been made to eliminate
the disadvantages of bitumen films by using other polymer
systems. For example, filler-containing aqueous polymer
dispersions of polyvinyl acetate or ethylene/vinyl
acetate copolymers have been developed and can be sprayed
onto the sheet metal parts in the necessary layer thick-
ness. Unfortunately, systems such as these are a disad-
vantage for use on an industrial scale where largenumbers are always involved because the water cannot be
removed quickly enough from the layer applied by spray-
ing, particularly in considerable layer thicknesses.
Another disadvantage of these conventional noise-damping
methods is that the materials in question serve the sole
purpose of damping noise.
In the manufacture of vehicles, machines and appli-
ances, efforts are now being made to simplify the com-
plexity of the production processes and hence to reduce
manufacturing costs.
In addition, adhesives, sealing compounds and coat-
ings are used in the manufacture of vehicles, machines
and appliances. Hitherto, the adhesives and/or sealing
compounds have been mainly selected for their primary
properties:
- strength, i.e. shear strength, peel strength
- elongation at break, flexibility
- resistance to ageing
- simple handling.
In the case of coatings, particularly underseal
CA 0220~9~3 1997-0~-22
H 1611 PCT 3
coatings, abrasion resistance is another selection
criterion.
Numerous efforts have been made to reduce the
complexity of the manufacture of vehicles, machines and
appliances and hence to reduce manufacturing costs.
Accordingly, there is a need for "multifunctional prod-
ucts", i.e. for example there is a need for adhesives,
sealing compounds and/or coatings which, besides their
main function, are capable of solving additional prob-
lems.
EP-A-358 598 and DE-A-3 444 863 describe plastisol
formulations which perform the dual function of under-
sealing (protection against abrasion) and acoustic
damping. DE-A-4 013 318 describes a two-layer underseal-
ing compound which performs the function of undersealingand absorbing the noise emanating from impacting par-
ticles (stones, chippings, water, etc.). Although these
products/processes perform the dual function of under-
sealing and noise damping extremely satisfactorily, there
is mainly a need to combine the function of an adhesive
and/or sealing compound with noise damping. This is
particularly desirable for those parts of an automobile,
a machine or an appliance which do not require any pro-
tection against abrasion, such as for example the boot
lid, the bonnet, the doors or the end wall of a vehicle.
Adhesives and sealing compounds for these parts are
normally applied at an early stage of the production
process known as "shell construction". The metal sheets
used are covered with anti-corrosion oils and drawing
oils in thicknesses of several grams per m2, so that the
adhesive/sealing compound used has to be able to absorb
these oils. Although plastisols, particularly PVC
plastisols, are used in shell construction, the plasti-
sols disclosed in EP-A-358 598 or DE-A-3 444 863 are not
suitable as adhesives/sealing compounds for shell con-
CA 0220~9~3 1997-0~-22
H 1611 PCT 4
struction. Plastisol formulations which have been speci-
fically developed for shell construction have only
m;nlm~l noise-damping properties, if any.
Another group of adhesive/sealing compounds suitable
for use in shell construction is based on rubbers, more
particularly vulcanizable compositions based on 1,4-
polybutadienes and/or 1,4-polyisoprenes. These composi-
tions preferably contain liquid polydienes of low molecu-
lar weight, sulfur and optionally accelerators for sulfur
vulcanization. In addition, these compositions may
contain high molecular weight, so-called solid rubber,
both the liquid polydienes and/or the solid rubber
optionally containing functional groups such as, for
example, hydroxyl groups, carboxyl groups, anhydride
groups or epoxy groups. This group of rubber-based
adhesive/sealing compounds is described in a number of
patent applications, for example EP-A-97 394, EP-A-309
903, EP-A-309 904, DE-A-3 834 818, DE-A-4 120 502, DE-A-4
122 849, EP-A-181 441 and EP-A-356 715.
It is apparent from DE-A-4 122 849 that the object
of bonding metal sheets in the construction of automobile
shells is inter alia to damp any vibration occurring.
Although the document in question does not provide any
particulars in this regard, it may be assumed that the
vibrations in question are low-frequency vibrations
outside the range of hearing of the human ear, such as
for example the vibrations of bonnets, boot lids and
doors where they have no suitable reinforclng frames
("antiflutter adhesives").
EP-A-181 441 describes two-component, thermally
crosslinkable compositions and processes for the produc-
tion of cold-crosslinking compositions, one binder con-
taining hydroxyl groups and the second binder containing
carboxylic acid groups or anhydride groups. The two
components have to be mixed immediately on application,
CA 0220~9~3 1997-0~-22
H 1611 PCT 5
curing taking place either by heating with ester forma-
ti~n between the hydroxyl groups and the carboxylic acid
groups or in the cold, in which case catalysts have to be
added. According to the document in question, the compo-
sitions may be used inter alia as vibration dampingcompositions or noise damping compositions. The document
does not provide any further particulars, particularly in
regard to the effectiveness of damping or--the substrates
which are to be damped.
Hitherto unpublished European patent application 93
120 384.8 describes the use of 3,4-polyisoprene in com-
bination with other curable or non-curable liquid and/or
solid rubbers and the use of these compositions for one-
component, hot-vulcanizable adhesive/sealing compounds
with acoustic damping properties.
It has been found that one-component, heat-curing
(w lcanizable) adhesive/sealing compounds based on liquid
rubbers and optionally solid rubbers can be modified in
such a way that there is no need to use the difficult-to-
obtain 3,4-polyisoprene, in spite of which extremely
effective acoustic damping is obtained with these com-
positions.
In the context of the present invention, acoustic
damping or vibration damping is understood to be the
damping of mechanical vibration which is known to reduce
the vibration of sheet metal constructions.
The effectiveness of the acoustic damping properties
of the compositions according to the invention is evalu-
ated by the flexural fatigue test according to Part 3 of
DIN 53440. To this end, steel plates are coated with the
compositions according to the invention and the coating
thus applied is cured under temperature conditions such
as prevail, for example, in car manufacture for curing
the various paint systems, i.e. at temperatures in the
range from 130~C to 220~C. The flexural fatigue test is
CA 0220~9~3 1997-0~-22
H 1611 PCT 6
then carried out at 200 Hz and at various temperatures to
be able to evaluate the effective acoustic damping effect
of these compositions in the "in-use temperature range",
i.e. between about 0~C and +40~C. Any heat-curing (vul-
canizable) compositions which, in the flexural fatiguetest according to DIN 53440, Part 3, show extremely high
damping, i.e. a loss factor of the coated sheet metal
strip d(combi) of > 0.1 and preferably 0.2 or more count
as acoustically effective in the context of the present
invention.
The compositions according to the invention contain
at least one of the following substances:
- one or more liquid rubbers and/or solid rubbers or
elastomers
- thermoplastic polymers in the form of fine-particle
powders
- fillers
- tackifiers and/or coupling agents
- extender oils
- vulcanizing agents, vulcanization -accelerators,
catalysts
- antiagers
- flow aids.
Liquid rubbers or elastomers may be selected from
the following group of homopolymers and/or copolymers:
polybutadienes, more particularly 1,4- and 1,2-poly-
butadienes, polybutenes, polyisobutylenes, 1,4-polyiso-
prenes, styrene/butadiene copolymers, butadiene/acrylo-
nitrile copolymers, these polymers optionally cont~ining
term;n~l and/or (statistically distributed) lateral
functional groups. Examples of such functional groups
are hydroxy, carboxyl, carboxylic anhydride or epoxy
groups. The molecular weight of these liquid rubbers is
typically below 20,000 and preferably in the range from
900 to 10,000. The percentage content of liquid rubber
CA 0220~9~3 1997-0~-22
H 1611 PCT 7
in the composition as a whole is determined by the
required rheology of the uncured composition and by the
required mechanical and acoustic damping properties of
the cured composition. The percentage content of llquid
rubber or elastomer normally varies between 5 and 50% by
weight of the formulation as a whole.
Suitable solid rubbers or elastomers normally have a
significantly higher molecular weight than the liquid
rubbers (100,000 or higher). Examples of suitable
rubbers are polybutadiene, preferably with a very high
percentage content of 1,4-cis-double bonds (typically
above 95%), styrene/butadiene rubber, butadiene/acrylo-
nitrile rubber, synthetic or natural isoprene rubber,
butyl rubber or polyurethane rubber.
The addition of fine-particle thermoplastic polymer
powders can produce a significant improvement in the
acoustic damping effect providing the thermoplastic
polymer has a glass transition temperature in the range
from 5~C to 50~C. Examples of suitable thermoplastic
polymers are polypropylene, polyethylene, thermoplastic
polyurethanes, methacrylate copolymers, styrene copoly-
mers, polyvinyl chloride, polyvinyl acetal and, in
particular, polyvinyl acetate and copolymers thereof.
The fillers may be selected from a number of materi-
als, including in particular chalks, natural ground orprecipitated calcium carbonates, calcium magnesium car-
bonates, silicates, heavy spar and carbon black. Lamel-
lar fillers, for example vermiculite, mica, talcum or
similar layer silicates, are also particularly suitable.
In some formulations, lamellar fillers have
significantly improved the acoustic damping effect. It
may be advisable to subject the fillers to an at least
partial surface pretreatment, coating with stearic acid
having proved to be particularly useful in the case of
the various calcium carbonates or chalks. The total
CA 0220~9~3 1997-0~-22
H 1611 PCT 8
filler content of the formulation can vary between 10 and
70~ by weight and is preferably between 25 and 60% by
weight.
Suitable tackifiers and/or coupling agents are
hydrocarbon resins, phenolic resins, terpene/phenol
resins, resorcinol resins or derivatives thereof, modi-
fied or unmodified resinic acids and esters (abietic acid
derivatives), polyamines, polyaminoamides, polyepoxy
resins, anhydrides and anhydride-containing copolymers.
The type and quantity of tackifier or coupling agent is
determined by the polymer composition of the adhesive/
sealing compound or by the coating composition, by the
strength of the cured composition and by the substrate to
which the composition is applied. Typical tackifying
resins (tackifiers), such as for example, the terpene/
phenol resins or resinic acid derivatives, are normally
used in concentrations of 5 to 20% by weight while
typical coupling agents, such as polyamines, polyamino-
amides or resorcinol derivatives, are typically used in
concentrations of 0.1 to 10% by weight.
The compositions according to the invention are
preferably free from plasticizers, more particularly
phthalic acid esters or extender oils. However, it may
be necessary to influence the rheology of the uncured
composition and/or the mechanical properties and/or the
acoustic damping effect of the cured compositions by the
addition of so-called extender oils, i.e. aliphatic,
aromatic or naphthenic oils. However, this is preferably
done by the addition of low molecular weight polybutenes,
polyisobutylenes or by the use of low molecular weight
liquid rubbers. If extender oils are used, they are used
in quantities of 5 to 20%.
Suitable curing agents or vulcanizing agents,
accelerators or catalysts are determined by the reactive
and/or functional groups of the polymers selected. Radi-
CA 0220~9~3 l997-0~-22
H 1611 PCT 9
.
cal vulcanization systems, more particularly based on
organic or inorganic peroxides, vulcanization systems
based on sulfur, more particularly in combination with
organic vulcanization accelerators and optionally zinc
compounds, are suitable for the curing reaction via the
olefinlc double bonds (vulcanization) of the liquid
and/or solid rubbers, although vulcanization systems of
quinones, dioximes or dinitrosobenzene are also suitable.
Particularly preferred vulcanization systems are
those based on powder-form sulfur, particularly in
combination with vulcanization accelerators, such as for
example mercaptobenzothiazole, dithiocarbamates, sulfen-
amides, disulfides, such as for example dibenzothiazole
disulfide and/or thiuram disulfides, aldehyde/amine
accelerators, guanidines and metal oxides, such as zinc
oxide for example. Typical rubber vulcanization auxili-
aries, for example fatty acids (for example stearic
acid), may be additionally present in the formulation.
The sulfur content may vary within wide limits and may be
up to 5% by weight and preferably up to about 10% by
weight, the lower limit preferably not being below 3% by
weight. The sulfur content depends on the reactivity of
the rubbers used, more particularly the liquid rubbers.
In addition, the maximum loss factor and the useful
temperature range for a sufficiently high loss factor can
be influenced through the sulfur content. The content of
vulcanization accelerators may vary between 0 and around
10~ by weight. The content of metal oxides is also
between 0 and 10% by weight.
Particularly suitable sulfur-free vulcanization
systems are vulcanization systems based on p-benzoquinone
dioxime which may additionally contain the above-mention-
ed vulcanization accelerators and/or metal compounds in
the quantity ranges mentioned above.
The compositions according to the invention may
~ =
CA 0220~9~3 1997-0~-22
.
H 1611 PCT 10
contain conventional stabilizers against thermal, thermo-
oxidative or ozone degradation, for example sterically
hindered phenols or amine derivatives, in quantities of -
typically - 0.1 to 5~ by weight.
Although the rheology of the compositions according
to the invention can normally be brought into the re-
quired range through the choice of the fillers and the
quantity ratio of the low molecular weight liquid rub-
bers, conventional flow aids, for example pyrogenic
silicas, Bentones or fibrillated or pulp chopped fibers,
may be used in quantities of 0.1 to 7%. In addition,
other conventional auxiliaries and additives may be used
in the compositions according to the invention.
The acoustic damping effectiveness of the composi-
tion according to the invention can be influenced towards
the specific needs of the application in regard to the
position of the m~ximllm of the loss factor and the
temperature range in which extremely effective acoustic
damping is achieved. The main in~luencing factors in
this regard are the vulcanization system (sulfur content,
vulcanization accelerator content) and the content and
reactivity of rubbers, particularly liquid rubbers. As
already mentioned, an addition of suitable thermoplastic
polymer powders can positively influence both the maximum
and the temperature range for effective acoustic damping.
To a certain extent, the choice of the type and quantity
of fillers can also influence the acoustic properties.
It has been found in this regard that lamellar fillers in
particular, such as mica for example, have a favorable
effect on the loss factor. In addition, the loss factor
can be influenced by the thickness of the coating. It is
known that foamed materials produce a higher loss factor
although this cannot be applied in cases where the
adhesive is required to show high tensile shear strength.
In most applications, it is desirable for the m~ximllm of
CA 0220~9~3 1997-0~-22
H 1611 PCT 11
the loss factor to be at around room temperature (around
20~C) and for the effective damping range (loss factor >
0.1) to extend over as broad a temperature range as
possible. The curing conditions for the adhesive/sealing
or coating compositions according to the present inven-
tion may be adapted to the particular application. As
mentioned at the beginning, a preferred application is
shell construction in the automotive industry so that the
compositions should cure in 10 to 35 minutes at a tem-
perature of 80~C to 240~C, temperatures in the range from
160 to 200~C preferably being applied in shell construc-
tion. A crucial advantage of the compositions according
to the invention over known plastisols is their so-called
"wash resistance" immediately after application of the
adhesives, i.e. they do not require pregelation like the
plastisols to be able to withstand the various washing
and phosphating baths used in shell construction. The
following Examples are intended to illustrate the inven-
tion without limiting its scope in any way.
In the Examples, the acoustic damping property of
the compositions was determined by the "Oberst" method
described in DIN 53440, Part 3, using coated steel
strips. The coating was cured in a conventional labora-
tory drying cabinet. Unless otherwise indicated, all
parts in the following Examples are parts by weight.
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CA 02205953 1997-05-22
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CA 0220~9~3 1997-0~-22
H 1611 PCT 14
Acoustic damping properties
1 mm thick spring steel strips measuring 240 mm x 10
mm were coated over a length of 200 mm with a layer of
the products of Examples 1 to 3 and Comparison Example 4,
after which the coatings were cured for 30 minutes at
180~C. The acoustic damping value (d-combi) was deter-
mined by the flexural fatigue test according to DIN
53440, Part 3, at 200 Hz. The coating weight was stand-
ardized to 50%, i.e. the weight of the coating with the
acoustically damping adhesive/sealing compound was 50% of
the weight of the metal strip.
The graph shows the dependence on temperature of the
acoustic damping d(combi) 50% of Examples 1 to 3 and
Comparison Example 4 which has a lower degree of cross-
linking.
Comparison Example 4 shows in particular that,without an adequate supply of reactive rubber, the sulfur
content of ~ 3% and the accelerator content do not lead
to the crosslinking according to the invention or, hence,
to effective acoustic damping.
