Note: Descriptions are shown in the official language in which they were submitted.
'~ CA 02396949 2002-07-10
S 29469 PC
Single-component sealant based on a vinyl polymer dispersion
The invention relates to a one-component sealant based on a dispersion of
vinyl
polymers, the sealant in the wet state being substantially free from volatile
organic
compounds and in the dry state being self-adhesive. The invention further
relates to
the preparation and use of this sealant and to materials coated with this
sealant.
The joining of materials is generally subdivided into adhesive bonding and
sealing.
The sealing of materials is an application which is encountered in all
segments
from the metal-processing industry through to the construction segment. The
function of sealants is to accommodate movements which occur between
components, for example, and to close the joints. Joints must be closed in
order
that no solids, liquids or gases can penetrate to the wrong place. With
adhesives, on
the other hand, the primary function is to produce a bond and so the adhesion
properties and strength of the adhesives come to the fore. Adhering and
sealing
compositions for the joining of substrates can be differentiated according to
their
consistency: solid, elastic or plastic. With decreasing tensile shear
strength, the
extension of the composition passes through a maximum, with the composition
undergoing transition from solid via elastic through to the plastic region.
The
consistency of the composition determines whether it is referred to as an
adhesive
(solid to elastic) or a sealant (elastic to plastic). Thus an adhesive must
possess a
certain tensile strength in order that structural adhesive bonds can be
successfully
performed. With sealants, on the other hand, the compositions used are
basically
compositions with elastic properties that possess a certain expansion
capacity, in
order to be able to accommodate expansions and shrinkages, so that no cracks
or
fractures, and hence leaks, are developed. The known sealants have the
property of
curing following their application, so that no dirt remains adhering to the
surface.
In the construction segment, for the purpose of sealing polyolefin materials,
e.g.,
polyethylene films, sealants are known which are solvent-based and which
therefore contain volatile organic compounds. Because of environmental
considerations and also on account of their strong odor, sealants of this kind
are
coming up against ever increasing resistance, and more recent developments are
aiming at substantially solvent-free sealants.
Accordingly, the object on which the invention was based was to provide a
sealant
CA 02396949 2002-07-10
2
whose volatile organic compound content is as low as possible and which
achieves
effective sealing of polyolefin materials.
For achieving this object a one-component sealant is proposed which is
substantially free from volatile organic compounds, is based on a dispersion
of
vinyl polymers, and is self-adhesive in the dry state.
The invention accordingly provides a one-component sealant based on a
dispersion
of vinyl polymers, the sealant in the wet state being substantially free from
volatile
organic compounds and in the dry state being self-adhesive. The invention
further
provides for the preparation of the sealant of the invention and for its use
for
connecting and/or sealing materials, especially polyolefin materials, and also
provides materials coated with the sealant of the invention. Preferred
embodiments
of the invention are defined in the dependent claims and in the following
description.
The sealant of the invention is self adhesive in the dry state. The tackiness
of the
surface of the sealant can be measured in accordance with Test Methods for
Pressure-Sensitive Adhesives, 6th edition, Pressure sensitive tape council,
Itasca
III using a traveling ball whose path is less than about 30 cm, preferably
less than
about 20 cm. Fundamentally, the sealant of the invention after drying is
always
self-adhesive; in other words, an adhesive bond can be achieved at any time,
even
after drying, and the self-adhesive property is conserved.
Suitable vinyl polymers include all polymers based on at least one of the
monomers which are described in Handbook of Pressure Sensitive Technology,
2nd edition, Donatas Satas, 1989, Van Nostrand Reinhold, 0-442-28026-2,
page 444 to 450. Particularly suitable vinyl polymers are those based on at
least
acrylate and/or methacrylate monomers, for reasons including in particular
their
aging stability. These acrylate- and/or polymethacrylate-based polymers, if
comprising further monomers, preferably contain vinyl-based monomers, e.g.
vinyl
acetate, vinyl ethers, vinyl halides or vinylaromatic compounds, e.g., styrene
or
vinylbenzene, or aliphatic monomers, e.g., ethene, butadiene or propene.
Polyacrylates and/or polymethacrylates with ester groups having from about 1
to
about 15 carbon atoms are particularly suitable. Greatest preference is given
to
using polyacrylates based on 2-ethylhexyl acrylate and/or butyl acrylate.
Polyvinyl
compounds that are suitable in accordance with the invention are prepared by
CA 02396949 2002-07-10
3
dispersion polymerization, which is known to the skilled worker. Thus
commercially available polyacrylate dispersions customarily contain from about
30
to about 60% by weight of water and from about 40 to about 70% by weight of
polyacrylates plus additives where appropriate.
In the wet state the sealant appropriately comprises vinyl polymers dispersed
in an
aqueous medium. Inventively preferred sealants contain in the wet state from
about
to about 90% by weight, preferably from about 25 to about 80% by weight, in
particular from about 30 to about 50% by weight of vinyl polymers and from
about
10 5 to about 50% by weight, preferably from about 5 to about 40% by weight,
in
particular from about 15 to about 30% by weight of aqueous medium, based in
each case on 100% by weight of sealant in the wet state, the remainder in each
case
being additives. The aqueous medium comprises water and, where appropriate,
water-soluble additives. These additives are added for purposes including
15 improving the frost resistance of the sealant. Depending on the amount
added,
which can easily be determined by the skilled worker, the freezing temperature
can
be reduced down to -20°C. The additives in question here are preferably
water-
soluble inorganic salts, especially sodium chloride, potassium chloride,
calcium
chloride or sodium sulfate, or water-soluble solvents, especially methanol,
ethanol,
propanol or acetone, or water-soluble high-boiling and/or plasticizing
compounds,
especially ethylene glycol or propylene glycol. Said water-soluble additives
may
be used alone or as mixtures.
The sealant may comprise additives selected from inorganic fillers; organic
fillers,
especially plasticizers, tackifiers, oligomeric fillers, polymeric fillers,
and rheology
modifiers, such as thickeners or thixotropic agents, for example;
crosslinkers;
adhesion promoters; stabilizers; defoamers; surfactants; drying additives;
volatile
organic compounds (VOCs); and the abovementioned water-soluble additives. The
additives can be used alone or as mixtures. They are present in the following
amounts, based in each case on 100 parts by weight of sealant in the wet
state:
from about 0 to about 80 parts by weight of organic and/or inorganic fillers;
from
about 0 to about 60 parts by weight of plasticizers; from about 0 to about 80
parts
by weight of tackifiers; from about 0 to about 80 parts by weight of
oligomeric
and/or polymeric fillers; from about 0 to about 20 parts by weight of rheology
modifiers; from about 0 to about 15 parts by weight of crosslinkers; from
about 0
to about 10 parts by weight of adhesion promoters; from about 0 to about 15
parts
by weight of stabilizers, from about 0 to about 10 parts by weight of
defoamers;
CA 02396949 2002-07-10
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4
from about 0 to about 10 parts by weight of surfactants; from about 0 to about
20
parts by weight of drying additives; and from about 0 to about 10 pans by
weight
of volatile organic compounds (VOCs), preferably from about 0 to about 5 parts
by
weight of volatile organic compounds (VOCs), in particular from about 0 to
about
3 parts by weight of volatile organic compounds (VOCs). The respective
additives
are additives which are known to the skilled worker in this field and which
individually are not subject to any particular restrictions. Preferred
inorganic fillers
are precipitated or natural barium sulfate, titanium dioxide, precipitated or
natural
calcium carbonate (e.g., chalk), precipitated or natural kaolin, talc,
magnesium
hydroxide or aluminum hydroxide (the latter hydroxides allow the fire class to
be
adjusted), zinc oxide, zirconium salts, glass beads or hollow microbeads of
all
kinds. Preferred organic fillers are, for example, resins based on
hydrocarbons or
on rosin, tall resin, balsam resin, terpenes, oligomers, such as butylenes,
for
example, acrylates or other vinyl-based molecules having a relatively low
molecular weight, urethanes or esters having a relatively low molecular
weight, or
polyester-based polymeric plasticizers, e.g., Benzoflex. Suitable organic
fillers also
include polymeric fillers, such as impact modifiers, polymer fibers or polymer
powders of polyacrylates, polystyrene, polyester, polyamide, polyurethane,
polyvinyl chloride, polyolefins, polyvinyl acetate, polyisoprene or
poly(iso)butylene, for example, and also block copolymers thereof. The
plasticizers, in accordance with DIN 55945, are liquid or solid inert organic
substances with a low vapor pressure. On the basis of their solvency and
swelling
capacity, they reduce the hardness of the vinyl polymer and alter its
adhesion.
Examples of suitable plasticizers are phthalates, adipates, citrates,
phosphates,
trimellitic acid or sulfonic acid. The tackifiers are preferably rosin-based
or
hydrocarbon-based resins. Preferred crosslinkers are metal salts, such as zinc
acetate, magnesium acetate or zirconium salts; aziridines, glyoxalates or
triethylene
glycol divinyl ether. Preferred rheology modifiers are polyurethane
thickeners,
acrylate thickeners, cellulose thickeners, polyvinyl alcohol thickeners,
silicates,
vinyl ether/maleic anhydride or polyethylene oxide. Preferred adhesion
promoters
are pH regulators (e.g., acrylic acid); silanes, aziridines or fluorine-based
agents.
Preferred stabilizers for raising the temperature stability are sterically
hindered
phenols, such as Irganox 110, Antioxidant 330 or Cyanox 2246, and for
increasing
the UV stability preferred stabilizers are sterically hindered phenols and/or
sterically hindered amines, such as Irganox 1076 or 1010, Tinuvin P, Tinuvin
326
or 770, or Antioxidant 330, or modified titanium dioxides. Preferred defoamers
are
silicone-based, polyethylene oxide-based or liquid paraffin-based defoamers.
CA 02396949 2002-07-10
Preferred surfactants are wetting agents, such as anionic or cationic wetting
agents
or F- or Si-based wetting agents, with particularly preferred wetting agents
being
described on p. 152 and 516 in Handbook of Coatings Additives, Leonard J.
Calbo,
1987, Marcel Dekker Inc., 0-8247-7561-9. Suitable drying additives include
5 zirconium derivatives. The volatile organic compounds (VOCs) for the
purposes of
the invention are compounds having a vapor pressure of at least 0.1 mbar at
20°C
and a boiling point of not more than 240°C at 1013.25 mbar. They are
subdivided
into solvents, with a boiling point below 150°C, and high boilers, with
a boiling
point between 150 and 240°C, as also defined in the Ordinance on
Incentive Taxes
on Volatile Organic Compounds (OVOC 814.018), part of the Swiss Law on
Protection of the Environment (LPE from 1997) in the first section under Art.
1
(Definition). It is preferred to use from about 0 to about 3 parts by weight
of
volatile organic compounds, more preferably from about 0.1 to about 0.5 parts
by
weight of volatile organic compounds, based in each case on 100 parts by
weight
of sealant in the wet state. It is, however, also possible to use larger
amounts of
VOCs, as defined earlier on above. Solvents particularly suitable as VOCs are
ethanol, propanol or ethyl acetate. High boilers particularly suitable as VOCs
are
glycols, such as ethylene glycol or propylene glycol. In addition, the sealant
of the
invention may also comprise further customary additives, examples being
biocides
(preservatives), as defined in Handbook of Coatings Additives, Leonard J.
Calbo,
1987, Marcel Dekker Inc., 0-8247-7561-9, on page 195-197, or dyes.
Stabilizers are used especially when acrylate-based vinyl polymers with
aliphatic
monomers, such as vinyl acetate or butadiene, or aromatic monomers, e.g.,
styrene
or vinylbenzene, are employed. Furthermore, it is preferred when using
nonhydrogenated tackifiers to add an additional amount of stabilizers in order
to
obtain the desired aging stability. The function of the tackifiers, oligomeric
fillers,
and further organic fillers is to enhance the self-adhesiveness, cohesion, and
water
resistance of the sealant. Optimum cohesion can be achieved by the skilled
worker
through a choice of appropriate fillers and crosslinkers. In the construction
segment said cohesion should be still adequate at 70°C. In this context
the skilled
worker can fine-tune the optimum cohesion by appropriately adapting the chain
length of the vinyl polymer and the amount and quality of the fillers and
crosslinkers. Since the optimization of cohesion is always in conflict with
the
adhesion, the cohesion must be chosen so that it is not set higher than the
adhesion
permits.
CA 02396949 2002-07-10
6
The additives are present in an amount of from about 0 to about 80 parts by
weight,
in particular from about 10 to about 70 pans by weight, most preferably from
about
30 to about 60 parts by weight, based in each case on 100 parts by weight of
sealant in the wet state. The abovementioned water-soluble additives added for
the
purpose of improving the frost resistance are present preferably in an amount
of
from about 0 to about 30 parts by weight, in particular from about 0 to about
15
parts by weight, while the other additives are present preferably in an amount
of
from about 0 to about 70, in particular from about 20 to about 50 parts by
weight,
based in each case on 100 parts by weight of sealant in the wet state.
The viscosity of the sealant in the wet state in accordance with ISO 2555 is
preferably at least about SO Pas at 23°C when determined in accordance
with
Brookfield type A with a spindle 6 at 10 rpm. With preference the viscosity at
23°C is at least about 200 Pas, more preferably at least about 350 Pas,
in each
case as determined in accordance with Brookfield type A with a spindle 7 at
10 rpm. The upper limit on the viscosity is defined by the sealant still being
able to
be handled. The appropriate viscosity can be set by the skilled worker in the
course
of tests which are customary in the art, using the abovementioned rheology
modifiers and/or the other abovementioned additives. Rheology modifiers may
also be added in order to facilitate the handling of the sealant. With the aid
of
rheology modifiers, such as thickeners or thixotropic agents, for example, a
firm
fluid sealant is obtained which is easy to express from a cartridge or a
plastic bag
and to process. At the same time, these modifiers raise the instantaneous
strength,
as a result of which the sealant is able to bear the weight, for example, of a
polyolefin material. Wetting of the material to be sealed is achieved by means
of
surfactants. Since these surfactants may cause foaming, defoamers may be
admixed. Repulsion of the sealant on the material to be sealed can in turn be
prevented by increasing the viscosity using thickeners.
In accordance with the invention, the sealant in the dry state comprises at
least one
phase, which in the present specification is also referred to as the binding
matrix.
This phase contains the vinylpolymers and any additives soluble therein. The
glass
transition temperature, Tg, of the binding matrix is below about +10°C,
preferably
between about -80 and about +10°C, in particular between about -80 and
about
-40°C, the glass transition temperature, Tg, being determined by means
of DSC
(Differential Scanning Calorimetry) as follows. A sample of about 30 mg is
first
cooled at -10°C/min to -120°C and then warmed at 10°C/min
to 40°C. In the
CA 02396949 2002-07-10
?
course of warming, there is a jump in the Cp curve (Cp denotes heat capacity)
whose middle point defines the glass transition temperature, Tg. This middle
point
may also be determined by differentiating the curve. The use of plasticizers,
oligomeric fillers and/or tackifiers also makes it possible to use
vinylpolymers,
especially polyacrylates, with a glass transition temperature higher than
10°C,
since by means of said additives the glass transition temperature of the
binding
matrix can be lowered to the desired level. In general, the number of phases
is
determined by the composition of the sealant. Besides the binding matrix, the
sealant preferably comprises at least one further phase, especially two
further
phases. This (these) further phases) contains (contain) water and additives
which
are not dissolved in the binding matrix.
In accordance with the invention, the dry state is the state attained by the
sealant
one hour following its application to Si paper at a weight of about 300 g/m2
(dry)
at ?0°C. The wet state in the present specification refers to the state
in which the
sealant is obtained following its preparation and which it retains when
stored, for
example, in a plastic bag or a cartridge.
In the dry state, the sealant of the invention has a peel adhesion of at least
about
5 N/25 mm, preferably from about 5 to about 50 N/25 mm, in each case as
determined in accordance with DIN EN (European Norm [standard]) 1939 at
between 5 and 50°C on - for example - polyolefin materials. The sealant
possesses
this peel adhesion not only on polyolefin materials but also on all other
materials,
e.g., papers, nonwovens, polyamides or polyesters, but not on materials having
a
very low surface tension such as siliconized and fluorinated surfaces. The
peel
adhesion constitutes a repeated peel adhesion. This peel adhesion may be
achieved
by tailoring the polarity of the vinyl polymers, which is easy for the skilled
worker
to accomplish as part of tests which are common in the art. If the polarity of
the
vinyl polymer is too high, the affinity for a polyolefin material is too low,
while if
the polarity of the vinyl polymer is too low, there are too few double bonds
present
to achieve sufficient Van der Waals interactions with a polyolefin material.
In this
case the sealant must be formulated so that the adhesion (clinging) to
polyolefinic
materials is greater than the cohesion (internal strength) of the sealant. The
polarity
of the vinyl polymer, especially of the polyacrylate, can be tailored through
the
choice of monomers. Acrylate monomers with short ester groups, e.g., methyl or
ethyl groups, have a high polarity, while acrylate monomers with long ester
groups, e.g., stearyl acrylates, have a lower polarity. The polarity of a
polyacrylate
CA 02396949 2002-07-10
8
can also be optimized by using vinyl-based compounds, such as vinyl acetate,
vinyl ethers, vinyl halides or vinylaromatic compounds, e.g., styrene. By
adding
divinyl or tervinyl comonomers it is possible to regulate the cohesion, molar
mass,
and shear modulus of the polymer.
The dynamic shear modulus G' of the sealant in the dry state when determined
in
accordance with the measurement method below is situated preferably in the
range
from about 5-105 Pa to about 5-103 Pa at 25°C, in particular lower than
about 5-105
Pa at temperatures lower than -10°C, preferably lower than -
25°C, and higher than
about 5-103 Pa at temperatures higher than 60°C, preferably higher than
80°C, in
each case when determined in accordance with the following method. For the
purposes of the present invention the shear modulus G' is an elasticity
modulus (or
storage modulus) which is measured on a rheometer/plate/plate system at a
frequency of 1 Hz, an extension of 0.2%, and warming at 5°C/min on a
specimen
with a thickness of 800 p.m.
There are no restrictions on the preparation of the sealant. The
abovementioned
components are mixed with one another preferably at a temperature from about 5
to about 100°C, with all common mixing systems being suitable for the
mixing
operation, static or dynamic mixers for example. It is advantageous to use
mixers
with programmable speed regulation, so that the production sequence can be
specified. Preference is given to using mixers with high rotary speeds, the
precise
rotary speed being dependent on the composition of the sealant. If additives
of high
viscosity are used, it is appropriate to heat them before the mixing operation
in
order to facilitate said operation. Mixing takes place under vacuum,
preferably at a
pressure of from about 200 to about 80 mbar. The resulting paste is then
dispensed
into cartridges or plastic bags. In this packaging it can be kept for at least
one year.
For use, the sealant is pressed using a pressure gun from the cartridge or the
plastic
bag. The sealant then dries by evaporation of the water. In the dry state, the
sealant
contains from about 0 to about 20% by weight of water, in particular from
about 0
to about 10% by weight of water, based in each case on 100% by weight of the
dried sealant.
The sealant can be processed within a temperature range from about 1 to about
60°C. The preferred processing temperature is from about 5 to about
50°C. If
lower temperatures are required, suitable water-soluble additives, as
described
CA 02396949 2002-07-10
9
above, can be added in order to improve the frost resistance. In the dry
state, the
sealant fulfills its function in a temperature range from about -20 to about
+80°C.
The sealant is used for sealing and/or connecting materials, especially
connecting
materials. Since the sealant adheres to all materials, such as polyolefins,
papers,
nonwovens, polyamides, and polyesters, with the exception of siliconized and
fluorinated surfaces, it is used wherever such materials, especially
polyolefin
materials, are to be sealed, and especially where there are no exposed
surfaces. The
sealant may also, however, be employed wherever the continued presence of dirt
is
not disruptive. The sealants find use in particular in the construction
sector, for
pedestal strips, for profiles, especially polyolefin-containing profiles, or
in the
industrial sector. A special application in the construction sector is in the
roof area,
for connecting a polyolefin material to a solid substrate, e.g., a painted or
unpainted wall of wood, plaster, concrete, limestone or brick. Examples of
suitable
polyolefin materials are films, webs, injection moldings, fibers, and cables.
Accordingly, preferred sealants of the invention have the following features
and
advantages:
- substantially VOC-free, i.e., substantially solvent-free and high-boiler-
free,
and hence also low-odor;
- in the dry state, peel adhesion on polyolefinic materials of at least
5 N/25 mm (in accordance with DIN EN 1939) at both 5°C and 23°C;
- in the dry state, self-adhesive at from -20 to +80°C;
- aging-resistant, i.e., even on aging the peel adhesion does not fall below
5 N/25 mm (DIN EN 1939);
- glass transition temperature of the binding matrix below 10°C; and
- can be processed with a cartridge and press gun.
Accordingly, the invention provides a sealant which is substantially VOC-free
and
exhibits good adhesion on polyolefin materials in particular.
The invention is illustrated with reference to the following example, which
represents a preferred embodiment of the invention.
Example
60 parts by weight of a polyacrylate dispersion having a glass transition
. CA 02396949 2002-07-10
temperature Tg = -40°C, having a peel adhesion for PO materials of at
least
N/25 mm and having a solids content of 65% by weight, of which about 99.5%
by weight is polyacrylate and the remainder is emulsifiers, and containing 35%
by
weight of water are mixed with 6 parts by weight of water-soluble additive,
namely
5 6 parts by weight of sodium sulfate, and with the following further
additives at
room temperature (23°C) and 100 mbar: 9 parts by weight of resin, 7
parts by
weight of polyamide fibers, 13 parts by weight of polyisobutylene, 1 part by
weight of polyurethane thickener, 2 parts by weight of polyvinyl alcohol
thickener,
0.3 parts by weight of LTV stabilizer, 0.2 parts by weight of biocide and 0.5
parts
10 by weight of surfactant. In the wet state, the paste has a viscosity of
about 370 Pas
(according to Brookfield, type A, spindle 7, 10 rpm) at 23°C. In the
dry state, the
composition obtained has a shear modulus G' of 5105 Pa at -25°C to 5103
Pa at
100°C and a peel adhesion to polyolefin materials of 20 N/25 mm at
23°C. The
dried sealant is self-adhesive, with measurement of the surface tack giving a
15 traveling ball path of about 7 cm. The glass transition temperature of the
binding
matrix is -30°C. All measurements here were carried out in accordance
with the
methods of determination described above.
