Note: Descriptions are shown in the official language in which they were submitted.
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Sprayable acoustic compositions
The invention relates to sprayable acoustic
compositions, production processes and uses.
Surfaces set in vibration emit sound. This can be
highly desirable, for example in the case of musical
instruments; however, it can also be regarded as
problematic, especially if this sound is perceived as
noise.
By way of example, sheet metal in the bodywork of
automobiles is excited via the engine, the road surface
or stone impact to produce vibrations which are
perceived as rumble in the interior of the vehicle.
In order to damp these undesired sheet metal
vibrations, the automobile industry often applies
bitumen mats to the sheet metal. Although this is a
successful method of sound-deadening for the interior,
it has at the same time a large number of
disadvantages.
A stock of the bitumen mats trimmed to size in the
correct shape has to be held for every surface; when a
plurality of shapes of mat have to be provided for
various vehicle models this represents a challenge in
terms of logistics and stock management.
Manual labour is used to apply the mats by adhesive
bonding, and this is naturally a cause of quality
variations.
Furthermore, there are some toxicological reservations
about bitumen.
Sprayable or extrudable compositions have been
discussed for some years as replacement for these
bitumen mats, and in many respects are superior to the
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bitumen mats.
These compositions applied by robots can be applied
even to complex-shaped or curved sheet metal without
difficulty.
It is very easy to make adjustments for altered
requirements or change of model.
Automation can achieve a reduction in the amount of
manual labour and an improvement in process quality.
Compositions of this kind have been previously
described and are to some extent also now used in small
quantities in automobile production. However, materials
of this type have not yet achieved a breakthrough,
since all of the systems proposed hitherto have
disadvantages which inhibit their adoption.
Firstly, materials based on PVC or on chlorinated
thermoplastics have been proposed, for example in the
form of plastisol in EP 0456473 or EP 766714, or in the
form of a composition requiring hot processing in
EP 1277823. However, chlorine-containing plastics are
disadvantageous for environmental reasons, since they
can form HCl and highly toxic dioxins on incineration,
and this also has attendant disadvantages especially
during recycling. In the case of the compositions
disclosed in EP 1277823, another disadvantage is the
need for hot processing.
Aqueous dispersions have moreover been described, which
on drying give a film having the desired damping
property; materials of this type are described by way
of example in the publications EP 1457530 and
EP 1520865. Specifically in the case of relatively
thick layers such as those needed for good damping
action, however, these materials require long drying
times in order to remove the water from the sprayed-on
layer. Associated with this there is the risk of
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undesired formation of bubbles, especially if the
drying procedure is accelerated.
Compositions based on epoxy resins have likewise been
widely proposed; examples are provided by the publi-
cations EP 0407157, EP 1023413 and EP 1500690. However,
there are some reservations about the constituents of
these resins, and they are often allergenic or even
mutagenic and carcinogenic. Since these coatings are
often very hard and brittle they are mostly unsuitable
for external use. Repair in the event of damage is also
very difficult with this material.
Finally, plasticizers have also been described with
binders based on (meth)acrylate, for example in
EP 0702708 or in EP 1090067.
The term (meth)acrylate here and hereinafter means not
only the esters of inethacrylic acid but also the esters
of acrylic acid, and also mixtures of the two. Examples
of these monomers are methyl methacrylate, butyl meth-
acrylate, hydroxyethyl methacrylate, ethyl acrylate and
butyl acrylate.
The term (meth)acrylate plastisols is used hereinafter
to describe plastisols whose polymeric constituents are
composed to a substantial extent of (meth)acrylates.
However, these (meth)acrylate plastisols require very
high contents of plasticizers in order to ensure
sufficient processibility. These can evaporate to a
limited extent out of the coating, especially in new
vehicles. If these plastisols are used in vehicle
interiors, this leads to an increased level of fogging,
i.e. deposition of these vapours on the windowpanes of
the vehicle. Fogging is undesired and problematic,
since it impairs the view through the windowpanes,
especially in sunlight or other types of glare.
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The object therefore consisted in providing a material
for vibration damping which excludes all of the disad-
vantages revealed in the prior art. The object also
consisted in improvement of existing plastisol
materials. The intention is to provide plastisols which
comprise less volatile constituents, these being
responsible for fogging.
These objects, and also other objects which, although
not explicitly stated, are readily deducible or
derivable from the circumstances discussed in the
introduction to this specification, are achieved via a
formulation, comprising
a) from 1 to 60% by weight of oligomers whose molar
mass is smaller than 20 000 g/mol,
b) from 0 to 60% by weight of solvents for the
oligomers a),
c) from 5 to 60% by weight of pulverulent polymers
whose molar mass is greater than 100 000 g/mol,
and
d) other fillers, auxiliaries and/or additives,
where components a) to c) make up at least 20% of
the formulation. Components a) to c) preferably
make up 40% of the formulation.
It has been possible to reduce fogging via replacement
of the entire amount, or of a part, of the plasticizer
usually used in plastisols by oligomers, in particular
(meth)acrylate oligomers.
The inventive formulations have excellent
processibility.
Surprisingly, it has also been found possible to
observe a marked improvement in the damping properties
of the coating.
The use of (meth)acrylate plastisols meets the require-
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ment of flexibility in dealing with various surface
shapes and curvatures; another result is optimized
stock management of the damping materials.
The oligomers a) encompass monomer constitutions which
can not only be composed of various types of monomer
but can also comprise various chain lengths
corresponding to the distribution curves.
The molar mass MW of the oligomers a) is
< 20 000 g/mol, preferably < 10 000 g/mol, particularly
preferably < 5000 g/mol, and they preferably contain at
least 30% by weight of (meth)acrylates, particularly
preferably at least 60% by weight of (meth)acrylates.
The oligomers a) have preferably been selected from the
group of the (meth)acrylates, such as alkyl
(meth)acrylates of straight-chain, branched, or cyclo-
aliphatic alcohols having from 1 to 22 carbon atoms,
examples being methyl (meth)acrylate, ethyl (meth)-
acrylate, n-butyl (meth)acrylate, isobutyl (meth)-
acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl
(meth)acrylate, stearyl (meth)acrylate, lauryl (meth)-
acrylate, cyclohexyl (meth)acrylate, isobornyl
(meth)acrylate, aryl (meth)acrylates, such as benzyl
(meth)acrylate or phenyl (meth)acrylate, each of which
can be unsubstituted or can have mono- to tetra-
substituted aryl radicals, mono(meth)acrylates of
ethers, of polyethylene glycols, of polypropylene
glycols, or their mixtures having from 5 to 80 carbon
atoms, e.g. tetrahydrofurfuryl methacrylate,
methoxy(m)ethoxyethyl methacrylate, 1-butoxypropyl
methacrylate, cyclohexyloxymethyl methacrylate, benzyl-
oxymethyl methacrylate, furfuryl methacrylate,
2-butoxyethyl methacrylate, 2-ethoxyethyl methacrylate,
allyloxymethyl methacrylate, 1-ethoxybutyl meth-
acrylate, 1-ethoxyethyl methacrylate, ethoxymethyl
methacrylate, poly(ethylene glycol) methyl ether
(meth)acrylate, poly(propylene glycol)methyl ether
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(meth)acrylate, styrene, and substituted styrenes, e.g.
4-vinylbenzoic acid.
The inventive oligomers have to have no reactive groups
of any kind, because their role in the processible form
of the formulation is that of a solvent and their role
in the fully gelled form is that of a binder.
However, it can be advantageous in specific embodiments
to modify the physical properties of the oligomers,
such as the properties of hydrophilicity or of
polarity, via incorporation of additional functional
groups; examples which may be mentioned are hydroxy
groups (e.g. via the use of hydroxyethyl methacrylate
or hydroxypropyl methacrylate as comonomer), acid
groups (e.g. via the use of acrylic acid or methacrylic
acid or hydroxypropyl methacrylate as comonomer) or
amide groups (e.g. via the use of acrylamide or meth-
acrylamide as comonomer).
Processes known to the person skilled in the art are
used to synthesize the oligomers. They are generally
prepared via solution polymerization using chain
transfer agents; typical chain transfer agents are
sulphur compounds, such as mercaptans (e.g. 1-dodecane-
thiol, 1-butanethiol, etc.). For certain monomers it is
also possible to use catalytic chain transfer agents;
examples of these CCT catalysts are cobalt(II) com-
plexes with porphyrin ligands or with glyoximine
ligands (e.g. 5,10,15,20-tetrakis(4-methoxyphenyl)-
21H,23H-porphyrin-cobalt(II), 2,3,7,8,12,13,17,18-octa-
ethyl-21H,23H-porphyrincobalt(II), bis[(difluoroboryl)-
diphenylglyoxime]cobalt(II) or bis[(difluoroboryl)-
diphenylglyoxime]cobalt(II)). In the cases where this
is possible the use of catalytic chain-transfer agents
is particularly preferred.
The formulation can be prepared either with solvents or
else without solvents. Solvents that can be used are
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liquids or mixtures of liquids which in the binary
mixture with the respective oligomers in the
quantitative proportioning intended in the respective
formulation form an optically clear solution which
exhibits no separation or phase formation even after
24 hours of standing at 20 C.
Less preference is given to liquids which in this
mixture with the oligomers exhibit clouding immediately
or within 24 hours, but without any settling or
creaming of any of the components, but they can never-
theless be used in specific embodiments.
Particular mention may be made of the following
solvents, but the list can be extended as desired and
is not to be understood as limiting:
esters of phthalic acid, e.g. diundecyl phthalate,
diisodecyl phthalate, diisononyl phthalate, dioctyl
phthalate, diethylhexyl phthalate, di-C7-Cll-n-alkyl
phthalate, dibutyl phthalate, diisobutyl phthalate,
dicyclohexyl phthalate, dimethyl phthalate, diethyl
phthalate, benzyl octyl phthalate, butyl benzyl
phthalate, dibenzyl phthalate, and tricresyl phosphate,
dihexyldicapryl phthalate.
Hydroxycarboxylic esters, e.g. esters of citric acid
(for example tributyl 0-acetylcitrate, triethyl
0-acetylcitrate), esters of tartaric acid or esters of
lactic acid.
Aliphatic dicarboxylic esters, e.g. esters of adipic
acid (for example dioctyl adipate, diisodecyl adipate),
esters of sebacic acid (for example dibutyl sebacate,
dioctyl sebacate, bis(2-ethylhexyl) sebacate) or esters
of azelaic acid.
Esters of trimellitic acid, e.g. tris(2-ethylhexyl)
trimellitate. Esters of benzoic acid, e.g. benzyl
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benzoate.
Esters of phosphoric acid, e.g. tricresyl phosphate,
triphenyl phosphate, diphenyl cresyl phosphate,
diphenyl octyl phosphate, tris(2-ethylhexyl) phosphate,
tris(2-butoxyethyl) phosphate.
Alkylsulphonic esters of phenol or of cresol, dibenzyl-
toluene, diphenyl ether.
Preference is given to use of phthalates, adipates,
phosphates or citrates; particular preference is given
to phthalates.
Use of volatile solvents, such as low-boiling hydro-
carbons or their mixtures (e.g. petroleum ether) is
less preferred but also certainly advisable in specific
embodiments. Use of volatile solvents is targeted
particularly at exterior applications, for example in
underbody protection, where fogging is not relevant.
The solvents mentioned and other solvents can also be
used in the form of mixtures.
The molar mass of the polymers c) is usually
>100 000 g/mol, preferably >400 000 g/mol. These
polymers can by any of the processes known to the
person skilled in the art (e.g. free-radical poly-
merization, anionic polymerization, cationic poly-
merization, polyaddition or polycondensation). Free-
radical polymerization is preferred.
Accordingly, it is possible to use monomers - or else
monomers in mixtures - accessible to any of these poly-
merization reactions. Preference is given to
ethylenically unsaturated compounds, e.g. (meth)-
acrylates, styrene and its derivatives, unbranched or
branched alkenes, vinyl esters and other compounds.
(Meth)acrylates are particularly preferred.
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It is preferable to use compounds selected from the
group of the methyl (meth)acrylates, ethyl (meth)-
acrylates, propyl (meth)acrylates, isopropyl (meth)-
acrylates, n-butyl (meth)acrylates, isobutyl (meth)-
acrylates, tert-butyl (meth)acrylates, 2-ethylhexyl
(meth)acrylates, hexyl (meth)acrylates, cyclohexyl
(meth)acrylates, pentyl (meth)acrylates, heptyl
(meth)acrylates, octyl (meth)acrylates, 1,4-butanediol
(meth)acrylates, 2-butoxyethyl (meth)acrylates, 2-
ethoxyethoxymethyl (meth)acrylates, 2-ethoxyethyl
(meth)acrylates, tetrahydrofurfuryl (meth)acrylates,
vinyloxyethoxyethyl (meth)acrylates, methoxyethoxyethyl
(meth)acrylates, 1-butoxypropyl (meth)acrylates, 1-
methyl-(2-vinyloxy)ethyl (meth)acrylates,
cyclohexyloxymethyl (meth)acrylates,
methoxymethoxyethyl (meth)acrylates, benzoyloxymethyl
(meth)acrylates, furfuryl (meth)acrylates, 2-
butoxyethyl (meth)acrylates, 2-ethoxyethoxymethyl
(meth)acrylates, R-carboxyethyl acrylates, 2-
ethoxyethyl (meth)acrylates, allyloxymethyl (meth)-
acrylates, 1-ethoxybutyl (meth)acrylates, methoxymethyl
(meth)acrylates, 1-ethoxyethyl (meth)acrylates, ethoxy-
methyl (meth)acrylates, 2,3-epoxybutyl (meth)acrylates,
3,4-epoxybutyl (meth)acrylates, glycidyl (meth)-
acrylates, 2-(dimethylphosphato)propyl (meth)acrylates,
2-(ethylenephosphito)propyl (meth)acrylates, dimethyl-
phosphinomethyl (meth)acrylates, dimethylphosphonoethyl
(meth)acrylates, diethyl methacryloylphosphonates,
dipropyl methacryloylphosphates, ethylsulphinylethyl
(meth)acrylates, 4-thiocyanatobutyl (meth)acrylates,
ethylsulphonylethyl (meth)acrylates, thiocyanatomethyl
(meth)acrylates, methylsulphinylmethyl (meth)acrylates,
bis(methacryloyloxyethyl) sulphides, trimethyloyl-
propane tri(meth)acrylates, 1-hexenes, 1-heptenes,
cyclohexenes, vinylcyclohexanes, 3,3-dimethylpropenes,
3-methyl-l-diisobutylenes, 4-methyl-l-pentenes, vinyl
acetates, styrenes, a-methylstyrenes, a-ethylstyrenes,
vinyltoluenes, p-methylstyrenes, esters or diesters of
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maleic acid, 9-vinylcarbazoles, 3-vinylcarbazoles,
4-vinylcarbazoles, vinyloxolanes, vinylfurans, vinyl-
thiophenes, vinylthiolanes.
It is preferable that at least one of the polymers c)
is composed of more than 60% by weight, particularly
preferably more than 80% by weight, of (meth)acrylates.
In one particular embodiment, each of the polymers c)
is composed of more than 60% by weight, preferably more
than 80% by weight, of (meth)acrylates.
In another preferred embodiment, at least one of the
polymers c) is composed of more than 60% by weight,
particularly preferably more than 80% by weight, of
methyl methacrylate.
The polymers c) are usually composed of more than 60%
by weight of (meth)acrylates.
For good further processibility, an oligomer a) and/or
a polymer c) can bear one or more functional groups
which can give post-crosslinking. Examples of
functional groups that can be used are hydroxy,
mercapto, amino, carboxy, carbonyl, sulphonyl, epoxy,
(3-ketoester and isocyanate groups.
These can, if appropriate, also be present in protected
form, e.g. the isocyanate group reacted with, for
example, alcohols, with phenols, with oximes, with
caprolactams, with amines or with C-H-acidic compounds.
Hydroxy groups are preferred.
The polymers can be prepared via emulsion
polymerization, suspension polymerization, solution
polymerization or bulk polymerization. Preparation via
emulsion polymerization is preferred.
In the case of preparation via emulsion polymerization,
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the polymers are produced in the form of polymer
particles dispersed in water. These have to be
converted to a dry powder; the usual methods are
suitable for this purpose, examples being coagulation,
spray drying and freeze drying. Spray drying is
preferred.
The preferred preparation process by means of emulsion
polymerization and spray drying gives powder particles
whose average particle diameter is usually from 1 to
500 pm, these being composed of individual polymer
particles whose average particle diameter is usually
from 200 to 1200 nm. Powders of this type are
particularly suitable for preparation of the inventive
formulations.
(Unless otherwise stated, "average particle diameter"
here and hereinafter means the volume-average of the
particle size distribution of the specimen. These
values can be measured by way of example via laser
diffraction, e.g. with the aid of a Coulter LS 13 320
manufactured by Beckmann-Coulter.)
An emulsion polymerization procedure known to the
person skilled in the art can also prepare polymer
particles which have a core and have one or more shells
around the core, and all of the polymers here which
form the core and, respectively, form each of the
shells can have different monomeric constitutions
(core/shell particles).
A similar method can also be used to prepare particles
whose monomeric constitution changes continuously from
the centre of the particle to its surface,
corresponding in some ways to a core-shell particle
with very many shells. In this case another term used
is particles with gradient morphology or "gradient
latices".
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As is well known, polymers and oligomers are
practically always composed of mixtures of various
molecules, their properties having a distribution
around one or more maxima. An example of these
properties is molecular weight, which is characterized
via average values, the molecular weights of the
individual polymer molecules having a distribution - of
varying breadth and also sometimes polymodal - around
this average value.
Another example relates to chemical constitution. For
example, copolymers (specifically in free-radical poly-
merization) are mostly produced via random
incorporation of the available monomers. If, by way of
example, a certain monomer A has 2% presence in a
monomer mixture its rate of incorporation into an
oligomer which is composed of an average of 50 monomer
units is statistically once per oligomer. In fact,
oligomers without this monomer A will be found, as will
oligomers having 2 or 3 of this type of monomer unit,
than if oligomers having exactly one incorporated
monomer A form the majority.
The intention here is to make it expressly clear that
when polymers and oligomers are used materials used are
always in a certain sense mixtures, but are not usually
perceived and specified as such. (For better
comprehensibility and for demarcation, these
"inevitable" mixtures are termed polymer material and,
respectively, oligomer material in the description
hereinafter).
However, the expressions "polymers" and "oligomers" in
this specification moreover expressly mean mixtures of
a plurality of polymer materials or of a plurality of
oligomer materials: by way of example, two or more
separately prepared materials with different molecular
weight distributions or with different monomer
constitutions can be mixed. Materials used as polymers
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and, respectively, oligomers can moreover also comprise
those mixed after they have been obtained by different
preparation processes (e.g. an emulsion polymer and a
suspension polymer).
Polymer particles which have core-shell or gradient
morphology and which have been prepared via emulsion
polymerization are moreover also mixtures of different
polymer materials, since this structure is specifically
manifested via different materials.
The possibility not only of adjusting the properties of
individual polymer materials or oligomer materials as
desired but also of mixing different materials
permitting a targeted approach to all of the
requirements of any specific application.
The usual fillers, auxiliaries and/or additives can be
added to the formulation.
Commonly used fillers are inter alia calcium carbonate
(in various versions, e.g. naturally occurring or
precipitated, surface-treated, etc.), barium sulphate
(baryte) and silicates, e.g. mica, bentonites,
montmorillonite, talc or vermiculite. Barium sulphate
is particularly preferred.
Among the auxiliaries and additives are colour
pigments, antioxidants, rheology additives, blowing
agents and other materials.
Blowing agents are added to the formulations
particularly for the foaming of plastisols. Examples of
commonly used blowing agents are azo compounds (e.g.
azodicarbamide), N-nitroso compounds (e.g. dinitroso-
pentamethylenetetramine), sulphonyl hydrazides (e.g.
4,4'-oxybis(benzenesulphonic hydrazide)) or sulphonyl-
semicarbazides (p-toluenesulphonylsemicarbazides).
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Carbon blacks are often used as colour pigment.
If appropriate, auxiliaries for post-crosslinking can
also be added. These auxiliaries are generally
compounds having two or more functional groups which
form mutual bonds and/or form bonds with other
components of the formulation. For this it can, if
appropriate, be necessary to add an initiator or a
catalyst, and/or to supply energy, for example in the
form of heat, UV radiation, or another form.
Examples of reactive components that can be used are
hydroxy, mercapto, amino, carboxy, carbonyl, sulphonyl,
epoxy, (3-ketoester, isocyanate, and vinyl groups;
isocyanates are preferred.
These can, if appropriate, also be present in protected
form, e.g. the isocyanate group reacted with, for
example, alcohols, with phenols, with oximes, with
caprolactams, with amines or with C-H-acidic compounds.
The formulations have a wide field of application and
can advantageously be used wherever the intention is to
damp the vibration of a surface.
Examples of these applications in private households
are the cladding of household devices, such as washing
machines, refrigerators, kitchen machines and air-
conditioning systems, and also the cladding of personal
computers.
Examples in construction and engineering materials are
pipes, floors and wallcoverings.
It is readily possible to conceive of a large number of
other applications and application sectors. The
surfaces to be coated can themselves be composed here
of various materials, e.g. plastic, wood, ceramic,
cardboard, or chip- and wood-fibre-based materials.
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Commonly encountered and particularly preferred
surfaces are sheet metal surfaces.
Particular preference is given to the coating of
bodywork parts in automobile construction. If the
coatings are used externally in the underbody region
and wheel-arch region of the motor vehicle, noise from
impact of stones, sand and water is reduced, in
addition to the damping of the vibrations of the sheet
metal.
The same formulation can also be used to fill cavities,
for example those occurring in automobile construction,
for example in the roof struts or in A columns, in B
columns and in C columns. Foamable formulations are
often used for these applications. Alongside the
damping of vibrations of sheet metal here, onset of
vibration of any air columns included in these cavities
is also prevented.
