Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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A PRoCEæs FOR THE PRODUCTION OF HEAT-ACTI~ATABLE MAT~
F~E~ FROM ~UPPORT~ ~ND RELEASE AGENTS AND THEIR USE ~OR
BONDING V~RIOUS ~UBSTRATES
This invention relates to a process for the produc-
tion of heat-activatable mats based on hydroxyl polyester
polyurethanes which are free from supports and release
agents and to their use for bonding various substrates.
It is known that various substrates can be bonded
with solvent-containing adhesive systems or with solvent-
less adhesive systems based on hydroxyl polyester poly-
urethanes, for example by using hotmelt films (see, for
example, H.J. Studt in Coating 2/93, pages 34 et seq.).
The disadvantage of solvent-containing adhesive systems
lies on the one hand in the pollution of the environment
by solvents which are released during the bonding process
and, on the other hand, in their long processing cycles
which entail high subsequent costs. Accordingly, there
is a tendency for economic and anti-pollution reasons to
use solventless adhesive systems for bonding various
substrates.
In the case of solventless adhesive systems, for
example where heat-activatable films based on hydroxyl
polyester polyurethanes are used, disadvantages include
their low permeability to gases and their feel-hardening
effect, which is particularly noticeable in the bonding
of textiles, and also the relatively high weight per unit
area which involves higher material costs.
For the reasons mentioned above, therefore, the use
~of heat-activatable films based on hydroxyl polyester
polyurethanes is confined to industrial applications, for
example laminated parts for the interior trim of motor
vehicles. Although, in this field of application, more
adhesive has to be continuously applied for some com-
posite structures, for example to arrest elastic forces
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of thermoformed flexible PVC films, there are sufficient
potential applications where adhesive can be applied in
relatively small quantities and a continuous, film-like
surface structure of the adhesive applied is a disad-
vantage.
The heat-activatable films to be used for bonding
various substrates may be produced by various methods.
The production of elastomeric films, for example
from polyurethanes, by co-extrusion is generally known
(DE-A 2 114 065, US 3,880,691). The flat materials
obtained do not contain any release agents or spacers.
A major disadvantage of this process lies in the complex
process technology involved (2 extruders and a blowing
head with 2 concentric annular nozzles~ and in the
accumulation of a release film which cannot be put to any
subsequent use.
The production of films from thermoplastic elas-
tomers, for example polyurethanes, by monofilm extrusion
blow molding is also known.
To enable the advantage of this process in terms of
lower capital investment in machinery to be fully util-
ized, an internal release agent or spacer has to be added
to the relatively very tacky thermoplastics before blow
molding of the film because otherwise the lengths of film
stick to one another after laying flat by means of a
squeezing roller and can no longer be separated there-
after.
In addition, these release agents or spacers are
used to avoid blocking of the wound and separated lengths
of film as a result of post-crystallization. At present,
waxes and/or organic additives, as described for example
in
A) H. Saechtling, Kunststoff-Taschenbuch, 25th Edition,
Carl-Hanser-Verlag
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B) Becker/Braun, Kunstst~ff-Handbuch Vol. 7, Polyure-
thane, Carl-Hanser-Verlag
C) Xunststoffe 80 (7), pages 827 et seq. (1990)
D) Gachter/Muller, Kunststoffadditive, 3rd Edition,
Carl-Hanser-Verlag,
are suitable spacers or release agents. However, it is
also known that, with certain substrates, the addition of
release agents or spacers results in a reduction in
adhesive strength. Polymeric spacers as described, for
example, in EP 0 526 858 are also used. They are at-
tended by the disadvantage that the mechanical properties
of the resulting sheet-form materials can be undesirably
affected. In addition, a distinct change in activat-
ability compared with the starting material used andchanges in the specific adhesion to certain substrates
cannot be ruled out.
Accordingly, the problem addressed by the present
invention was to avoid the above-mentioned disadvantages
attending the use of solvent-containing adhesives and
also the use of solventless adhesives, such as films.
Some of the disadvantages mentioned can be avoided by
using heat-activatable mats in the bonding of various
substrates, particularly where the melt blowing process
(for example REICOFIL~ melt blowing process) is used to
produce the mats.
Accordingly, the present invention relates to a
process for the production of heat-activatable mats based
on hydroxyl polyester polyurethanes which are free from
supports and release agents and which have viscosities of
600 to 3500 mPa.s, measured as solution viscosity in
methyl ethyl ketone (15%), and weights per unit area of
5 to 200 g/m', characterized in that the mats are pro-
duced by melt blowing (for example REIC0FILX melt blowing
process) at melt temperatures in the range from 230 to
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260OC using a receiving conveyor belt of which the
constituent material has a surface tension of 18.5x10-5
N/cm to 46x105 N/cm.
The present invention also relates to the use of the
mats produced by the described method for bonding or
coating various substrates.
The heat-activatable mats free from supports and
release agents produced by the process according to the
invention preferably have weights per unit area of 8 to
50 g/m2 and, more preferably, in the range from 10 to 30
g/m2. The weights per unit area of the mats are deter-
mined by the substrates used in the bonding process and,
if required, may even extend to relatively high weights
per unit area, particularly when any unevenness is to be
made level in the bonding process.
The raw materials based on hydroxyl polyester poly-
urethanes used in the process according to the invention
preferably a viscosity of 1500 to 2100 mPa.s, measured as
solution viscosity (15%) in methyl ethyl ketone (Brook-
field LVT viscosimeter, spindle 3, 60 r.p.m., 23OC3.
Particularly suitable hydroxyl polyester polyure-
thanes are those obtainable by reaction of organic iso-
cyanates with preferably difunctional polyester polyols
containing alcoholic hydroxyl groups and low molecular
weight diols as chain extending agents, an NCO:OH equiva-
lent ratio of 0.9:1 to 0.999:1 being maintained during
the reaction, as described in EP 0 158 086 and in DE-PSS
1 256 822, 2 161 340 and 3 502 379.
Particularly suitable dihydroxypolyesters are those
having a molecular weight above 600, preferably in the
range from 1200 to 6000 and more preferably in the range
from 2000 to 4000 g/mol, which may be obtained in known
manner from alkane dicarboxylic acids preferably contain-
ing 6 carbon atoms and alkanediols preferably containing
at least 4 carbon atoms. Suitable dicarboxylic acids
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are, for example, adipic acid, sebacic acid, pimelic
acid, suberic acid, azelaic acid, sebacic acid. Suitable
alkanediols are, for example, butane-1,4-diol, pentane-
1,5-diol and hexane-1,6-diol. ~he chain extending agents
are, in particular, diols or diol mixtures with molecular
weights in the range from 62 to 300 and preferably in the
range from 62 to 150 g/mol. Suitable diols such as these
are, for example, alkanediols preferably containing 4 to
6 carbon atoms, such as butane-1,4-diol, pentane-1,5~diol
and hexane-1,6-diol.
Examples of suitable diisocyanates are 1,6-diiso-
cyanatohexane,1,4-diisocyanatocyclohexane,1-isocyanato-
3-isocyanatomethyl-3,5,5-trimethylcyclohexane,methylene
bis-(4-isocyanatocyclohexane), 2,4- and optionally 2,6-
diisocyanatotoluene, 4,4'-diisocyanatodiphenyl methane,
4,4'-diisocyanatodiphenyl-2,2-propane and mixtures of
such isocyanates. In a particularly preferred embodi-
ment, 4,4'-diisocyanatodiphenyl methane is used as a
reaction component.
As already mentioned, the mats according to the
invention are produced by melt blowing, more particularly
using melt temperatures (measured before the spinning
nozzles) of 230 to 260C. The melt blowing process is
described in detail in DE-OS 19 64 060 and in DE-OS 23 08
242 and consists essentially of a specially designed
forming tool for polymer filaments which follows an
extruder and of which the principal feature lies in the
fact that a directed, heated airstream is associated with
each individual nozzle, ensuring that the issuing polymer
filaments are highly stretched and broken under con-
trolled conditions. The hot air can be directed onto the
polymer melt from slots closely adjacent on 2 sides or,
alternatively, the polymer melt can flow from an annular
bore around the inner melt bore.
The issuing filaments are deposited onto a moving
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receiving surface, for example in the form of a circulat-
ing conveyor helt.
In the process according to the invention, it is
important to use a conveyor belt of which the constituent
material has a surface tension of preferably 18.5x10-5 to
33x105 N/cm. Teflon-coated textiles, for example, may be
used as constituent materials for the conveyor belt.
The bonding of various substrates may of course also
be carried out by directly coating the substrate to be
bonded with the mat produced by the process according to
the invention and initiating the bonding of the sub-
strates by heat activation of the mat (for example by
exposure to infrared radiation or by contact heat).
Various methods may be used for bonding substrates
with the mat produced by the process according to the
inventlon .
In the case of precoated substrates (for example
flexible PVC foam sheets, TPU sheets), vacuum forming,
thermoforming, vacuum thermoforming, are used for the
production of molded articles for roof elements, side
panel elements or back-foamable composites for the
production of seats, etc. Such processes are known and
are described in detail, for example, in Saechtling
"Kunststoff Taschenbuch", 21st Edition, 1979, pages 140
25 to 184.
A large number of substrates can be bonded to
substrates of the same kind or to substrates of different
kinds with the mat produced by the process according to
the invention. In addition to the flexible PVC and TPU
surface sheets mentioned, such substrates include in
particular various textile materials based on cotton,
cotton/wool blends, wool, wool blends, polyester and
polyamide fabrics and polyolefins.
It was surprising to find that hydroxyl polyester
polyurethanes could be processed to mats by melt blowing
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because the high melt temperatures required for melt
blowing, which are about 500C above the temperatures
applied in conventional film production processes, had
been expected to lead in hydroxyl polyester polyurethanes
to such a pronounced shift in equilibrium in favor of the
starting components that at best oligomeric products
which could not longer be hardened to form a mat would be
obtained.
In addition, it had been expected that cohesive
strength would no longer be sufficiently present in bonds
formed with the mats through degradation of the polymer.
This is not the case.
In the prior art, there is a limited number of known
raw materials which can be made into mats by melt blow-
ing. The raw materials in question are, in particular,polymers which completely solidify in amorphous or partly
crystalline form, such as for example polypropylene and
polystyrene. The polymers mentioned generally have the
property of developing a completely tack-free surface
immediately after falling below a temperature of around
70C. Hydroxyl polyester polyurethanes with a segmented
soft segment/hard segment structure show more critical
behavior in this regard. Thus, recrystallization of the
hydroxyl polyester polyurethane processed by extrusion
requires a much longer time compared with the polymers
mentioned above and, in any event, requires a temperature
below a melt temperature of 50c in the extrudate. This
behavior of segmented polyester urethanes generally leads
to the above-mentioned disadvantages of production in the
presence of release agents or spacers and blocking of the
extrudates on the roll.
It has surprisingly been found that the hydroxyl
polyester polyurethanes mentioned, which are deposited as
random fibers, develop a tack-free surface shortly after
deposition onto the conveyor belt of the melt blowing
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machine, so that the melt-blown mat obtained can then be
directly delivered to a winding unit; the mat does not
block on the roll.
By virtue of the minimal fiber denier (approximately
O.l dtex), the mat obtained is distinguished by high
surface coverage (covering power), even when applied in
small quantities. Even if it is applied in large quanti-
ties of 30 g/m2 to textiles, a soft feel is maintained.
Permeability to air can be selectively established,
depending on the quantity applied.
Examples
The tests described in the following were carried
out in a commercial REICOFIL~ melt blowing machine (prod-
uction width 1 meter). The thermoplastic elastomeric
hydroxyl polyester polyurethanes were predried for 12
hours in a SOMOS~ air dryer.
Example 1
The extruder and mold temperature were adjusted to
give a melt temperature of 250C before the spinning
nozzles. The hydroxyl polyester polyurethane (solution
viscosity 2000 mPa.s) was extruded at a screw speed of 5
r.p.m. The output of the spinning pump was adjusted to
4 r.p.m. The resultinq extruder output was 22 kg/h and
the resulting extruder/nozzle melt pressure was 40~16
bar. After stretching by the compressed air preheated to
220C and the controlled filament breakage, the polymer
filaments issuing from the melt nozzles were deposited
30 ~ onto a circulating conveyor belt with a surface tensionof 30-10-5 N/cm and delivered from there to an inter-
mediate takeoff station where the edges were cut. The
mat was then wound onto 1000 mm cardboard tubes. Dif-
ferent weights per unit area were adjusted by varying the
rate of travel of the mat and/or the throughput. The mat
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was wound onto the tubes in lengths of 200 meters per ~ `
test. The mats could readily be offwound from the tubes
at any time.
Bxample 2
The extruder and mold temperature were adjusted to
give a melt temperature of 250C before the spinning
nozzles. The hydroxyl polyester polyurethane (solution
viscosity 1200 mPa.s) was extruded at a screw speed of 4
r.p.m. The output of the spinning pump was adjusted to
4 r.p.m~ The resulting extruder output was 22 kg/h and
the resulting extruder/nozzle melt pressure was 40/30
bar. After stretching by the compressed air preheated to
220C and the controlled filament breakage, the polymer
filaments issuing from the melt nozzles were deposited
onto a circulating conveyor belt with a surface tension
of 30-10-5 N/cm and delivered from there to an inter-
mediate takeoff roller where the edges were cut. The mat
was then wound onto 1000 mm cardboard tubes. Different
weights per unit area were adjusted by varying the rate
of travel of the mat and/or the throughput. The mat was
wound onto the tubes in lengths of 200 meters per test.
The mats could readily be offwound from the tubes at any
time.
Exampl~ 3 -
In the same way as described in Example 1, the
hydroxyl polyester polyurethane was directly applied as
a mat to a TPU surface sheet (thickness 100 ~m). In this
case, too, the mats were wound onto 1000 mm cardboard
tubes after the intermediate takeoff and edge trimming
stations. The mats could readily be offwound at any
time.
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Example 4
The procedure was as described in Example 3 using a
flexible PVC (foam) sheet. The adhesion of the melt
blown mat of the hydroxyl polyester polyurethane was
sufficient to guarantee problem-free winding and offwind-
ing of the coated mat.
Example 5
As in Example 3, the hydroxyl polyester polyurethane
was directly applied in the form of a mat to a cotton
fabric. The adhesion of the mat to the cotton fabric was
again excellent. Bonds between this cotton fabric coated
with varying quantities of material and an uncoated
cotton Iabric produced the peel strengths shown in Table
1 below.
Table 1:
Bonding Sample Quantity Peel
temperature code applied strength
(C) ~~~~ (g/mZ) (N/5 cm)
100 PUR Example 1 10 12.5
100 PUR Example 1 24.0
100 PUR Example 1 30 38.5
120 PUR Example 1 10 16.5
120 PUR Example 1 20 31.0
120 PUR Example 1 30 35.0
140 PUR Example 1 10 16.5
, I
140 PUR Example 1 20 35.0
140 PUR Example 1 30 41.5
.
160 PUR Example 1 10 20.0
160 PUR Example 1 20 39.0
160 PUR Example 1 30 51.5
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¦ 100 PUR Example 2 10 13.5
100 PUR Example 2 20 27.5
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100 PUR Example 2 30 46.0
I
¦ 120 PUR Example 2 10 16.5
120 PUR Example 2 20 29.0
I
120 PUR Example 2 30 42.5
140 PUR Example 2 10 14.0
140 PUR Example 2 20 30.0
140 PUR Example 2 30 43.5
160 PUR Example 2 10 16.0
160 PUR Example 2 20 36.0
160 PUR Example 2 30 53.5
,:
Pressure applied: 1 bar : ~:
Pressing time: 20 seconds
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