Note: Descriptions are shown in the official language in which they were submitted.
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fiEX~T'~TRANSLATION Br/m/W61V26.11.1997
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An actively 6reathin~ mufti-layer film
The present inventian relates to mufti-layer, water-impermeable, actively
breathing
S films which are made of thermoplastic polyurethanes and which are produced
by
coextrusion, the characterising feature of which is that the film exhibits a
directionally-dependent permeability to water vapour.
The present invention also relates to the use of the film according to the
invention for
effecting water-impermeable, actively breathing sealing of sheet-like articles
such as
woven goods and nonwoven fibrous webs, and relates to articles of use produced
therefrom, particularly in the clothing sector, mainly relating there to
workwear or
rainwear.
The possibility of protecting porous, sheet-like articles from the ingress or
penetration
of water by means of a water-impermeable film or coating is generally known
and
forms part of the prior art.
For example, materials which actively breathe are frequently used in order to
impart a
high level of wearer comfort to articles of clothing. The actively-breathing
character
of the film is generally verified via its permeability to water vapour. To
prevent the
build-up of moisture near the wearer of articles of clothing which are
finished in this
manner, the permeability to water vapour has to be as high as possible.
High permeabilities to water vapour can be achieved for certain types of
films, for
example, by imparting microporosity as a result of biaxial stretching, as
described in
US 4,194,041. Microporous films of this type lead to problems in use, where
they are
often subjected to considerable stretching. The elbow region of outer clothing
can be
cited as an example of this. Enlargement of the pores can easily occur here,
which
results in the formation of tears and thus in the loss of impermeability to
water.
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Problems of this type are circumvented by the use of pore-free films having a
high
permeability to water vapour, such as those described in EP 0 591 782, for
example.
EP 0 658 581 describes the use of hydrophilic thermoplastic polyurethanes in
the
sphere of actively-breathing sheet-like textile articles.
Thermoplastically processable polyurethanes are thermoplastic elastomers such
as
those which are described in the review article in Rubber Chemistry and
Technology
62 (1989), pages 529 - 54. Commercially available thermoplastic polyurethanes
are
generally characterised by a cambination of good tensile strength and tear
propagation
resistance, together with a high level of extensibility over a broad
temperature range.
A review on thermoplastic polyurethanes is given by Hepburn (editor):
Polyurethane
elastomers, Applied Science Publishers, Barking (1982) pages 49 - 80. Special
extruded products can be processed to form films either via a sheet extrusion
die or
via blown film extrusion. Further information on extrusion technology is
given, for
example in Kirk - Othmer: Encyclopedia of Chemical Technology, Volume 9 (1966)
pages 232 - 241. Apart from single-layer films, it is also possible by
employing
extrusion technology to produce multi-layer films from thermoplastic
polyurethanes,
as is described in EP 0 603 680 for example.
As has already been described above, the wearer comfort of articles of
clothing to
which active breathing properties are imparted is influenced to a considerable
extent
by the permeability to water vapour thereof. The desired high permeability to
water
vapour should not, however, result in the transport of moisture from the
outside to the
inside. The object ofd the present invention is thus to provide a highly
elastic film
which is impermeable to water but which is permeable to water vapour, the
permeability of which to water vapour is directionally-dependent.
This object has surprisingly been achieved by the production of a film based
on
thermoplastic polyurethanes ('TPUs) which is produced by coextrusion.
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Accordingly, the present invention relates to a TPU film which comprises at
least two
layers and to the use thereof for the production of actively-breathing, water-
impermeable sheet-like articles which exhibit a directionally-dependent
permeability
to water vapour, characterised in that the films exhibit a different
permeability to
water vapour when a different one of the two outer layers of the film
according to the
invention faces the source of moisture when the permeability to water vapour
is
determined according to one of the customary standard methods of measurement.
Customary methods of determining permeability to water vapour are described in
DIN
53122 or ASTM E9(~ for example. These methods of determination are based on
the
penetration of water vapour from a source to a sink. The water vapour source
is
formed by a climatic chamber, a climatic solution or a defined vapour phase,
etc. The
sink is generally formed by a drying agent. The films according to the
invention
preferably consist of different TPU resin formulations in the different
layers. The
essential concept of the invention is to employ what is a preferential
transport of
moisture from the layer which exhibits the higher permeability to water vapour
to the
layer which is provided with a lower permeability to water vapour.
This object has been achieved by a multi-layer film which is characterised in
that the
individual layers are built up from linear, thermoplastically processable,
segmented
polyurethane molecules. The polyurethanes, which are comparatively
hydrophilic, are
formed from alternating blocks of soft and hard segments, wherein the soft
segments
are formed from difunctional polyols A) which are synthesised from polymerised
ethers and/or esters, and the hard segments are formed from the reaction
products of a
low molecular weight diol B), i.e. from the chain extender, and a diisocyanate
C).
These blocks are advantageously linked to each other so that the hard segment
forms
the two ends of the molecular chain in each case, and so that the reactive
cyanate
groups situated at the ends of the linear molecule can optionally be capped by
alcohols D).
The thermoplastic polyurethanes are preferably linear block copolymers which
always
comprise a certain i:raction of branches due to the allophanate-forming
secondary
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reaction which occurs during the reaction to form the urethane. The average
molecular
weight of suitable thermoplastic polyurethanes is preferably between 10,000
g/mol
and 250,000 g/mol.
Difunctional compounds, i.e. compounds which advantageously contain two
terminal
hydroxyl groups, are preferably used for the soft segment A). Compounds which
are
particularly preferred in this respect are ethylene oxide polymers and/or
copolymers,
which are also often termed polyoxyethylene glycols and/or polyethylene oxide
glycols, the monomer unit of which is characterised by the structure (-O-CHz-
CHZ-)
and-which have an average molecular weight of at least 400 g/mol and at most
2800
g/mol. In one particularly preferred embodiment, the average molecular weight
is
between 800 g/mol and 1200 g/mol. These compounds are further characterised by
a
weight ratio of carbon to hydrogen which is at least 1.3 and which is at most
2.5. The
proportion by weight of the soft segment A) to the thermoplastic elastomer
which
forms the film according to the invention ranges between 35 % and 60 %, and is
preferably between 40 % and 50 %, with respect to the total weight of
thermoplastic
polyurethane in each case. The tendency of the soft segments to crystallise
can be
reduced, and the breathing activity can optionally be increased, by
copolymerisation
of the ethylene oxide with other cyclic ethers, for example propylene oxide or
tetrahydrofuran.
The constituents of the hard segments can be selected from isocyanate and diol
components which are known for the production of film raw materials from
thermoplastic polyurethanes.
Short-chain, bifunctional substances, the molecular weight of which is between
18 and
350 g/mol, are used as diol component B). Examples thereof in the form of
dihydric
alcohols include ethylene glycol, 1,2-propylene glycol, 1,4-butylene glycol,
which is
also known as tetramethylene glycol, 2,3-butylene glycol, 1,5-pentanediol, 1,6-
hexanediol and 1,8-octanediol, as well as diethylene glycol, triethylene
glycol,
tetraethylene glycol and higher polyethylene glycols with molecular weights up
to 350
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g/mol, dipropylene glycol and higher polypropylene glycols with molecular
weights
up to 350 g/mol, and also include dibutylene glycol and higher polybutylene
glycols
with molecular weights up to 350 g/mol.
Other low molecular weight diols B) with molecular weights up to 350 g/mol
which
are suitable for the production of the polyurethanes used according to the
invention are
ester diols of general formula
HO-(CHZ)y CO-O-(CHZ)X OH
---
and
HO-(CHZ)x O-CO-R-CO-O-(CHZ)X-OH,
wherein
R denotes an alkylene radical comprising 1 to 10, preferably 2 to 6, C atoms
or a
cycloalkylene or arylene radical comprising 6 to 10 C atoms,
x is 2 to 6, and
y is3to5,
e.g. adipic acid-bis-(~i-hydroxyethyl) ester and terephthalic acid-bis-
([3hydroxyethyl)
ester.
Suitable isocyanates C) comprise aliphatic, cycloaliphatic, aromatic and
heterocyclic
diisocyanates which ~~re described by the formula
OCN-Q-NCO
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wherein
Q denotes an aliphatic hydrocarbon radical comprising 2 to 18, preferably 6 to
10, C atoms, a cycloaliphatic hydrocarbon radical comprising 4 to 15 C atoms,
or an aromatic hydrocarbon radical comprising 6 to 15, preferably 6 to 13, C
atoms.
Examples of diisocyanates such as these include 1,4-tetramethylene
diisocyanate, 1,6-
hexamethylene diisocyanate, cyclohexane 1,3- and 1,4-diisocyanate and any
mixtures
of these isomers, naphthalene 1,5-diisocyanate, 2,4- and 2,6-
diisocyanatotoluene and
any mixtures of these isomers, and diphenylmethane 2, 4'- and/or 4,4'-
diisocyanate.
Suitable alcohols D) which can be used as capping reagents include low
molecular
weight alcohols with a molecular weight of at least 32 g/mol and at most 100
g/mol.
Suitable capping reagents not only include monofunctional alcohols, but also
include
di-, tri- or higher polyols. Aliphatic short chain alcohols with a molecular
weight of at
least 32 g/mol and at most 400 g/mol are preferred.
According to the invention, polyurethane elastomers which exhibit different
degrees
of hydrophilic character or permeabilities to water vapour are used for the
individual
layers of the film. This can be achieved by the use of different soft segments
and/or
modified hard segments of the polyurethanes in the individual layers. For the
soft
segments, for example, there is an increase in hydrophilic character in the
sequence:
polyester < polytetrahydrofuran < polyethylene oxide.
Modifications can be used for the hard segments, for example, such as those
which are
sold by Bayer AG, Leverkusen and which are known as dual hydrophilic
Impraperm~
types (EP 0 525 567 and DE 4 236 569).
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In one preferred embodiment, all the layers of the film are based on
thermoplastic
polyurethane elastomers, the longer chain diol components of which are
essentially
formed from polyethers. Structures which are particularly preferred in this
respect are
those in which all the layers of the film are formed from different
thermoplastic
polyurethanes which ~~re used to build up polyether soft segments.
In one particularly preferred embodiment, the polyurethane elastomer resins
which
form the different layers of the film according to the invention have
different Shore
hardnesses. In this respect, whilst optionally retaining the same soft segment
structure,
the-soft segment content of the layers which form the film according to the
invention
is varied, so that the resins which form the individual layers exhibit
different
permeabilities to water vapour.
The thermoplastic polyurethanes which are used preferably have a Shore
hardness of
75 - 95 A, most preferably 85 - 95 A, as determined according to DIN 53 505.
Examples of thermoplastic polyurethanes which are suitable according to the
invention are those which are obtainable under the trade names of Desmopan~,
Elastollan~, Estane~, lmpraperm~, Pellethane~, Morthane~ or Texin~.
In one suitable embodiment of the film according to the invention the
individual layers
additionally contain customary additives from the group comprising:
I. anti-seizing agents, inorganic or organic separators,
II. internal lubricants or demoulding agents,
III. pigments or fillers, and
IV. stabilisers.
The total content of said additives I to IV is preferably between 1 % by
weight and 30
by weight.
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The customary additives which the film according to the invention may contain
are
described, for example, by Gachter and Muller in: Kunststoff Additive, Carl
Hanser
Verlag Munich, 3rd F;dition (1989).
The films which are preferred according to the invention are those which have
a total
thickness between 5 ~m and 500 Vim, most preferably between 5 ~m and 50 Vim.
According to the invention, the thickness of each of the individual layers can
vary
within the range from 10 % to 90 % of the total thickness. A structure is
particularly
preferred in which thc: thinner layer corresponds to a proportion between 10 %
and 49
% ef the total thickness.
In very thin actively-breathing structures, an additional backing layer, e.g.
a layer
based on polyethylene, can be used according to the invention to impart better
handling, e.g. for stiffening. In a film such as this, the thickness of the
layers) of
thermoplastic polyurethane(s;) is preferably between 5 ~m and 25 Vim, and the
thickness of the backing layer is preferably between 5 ~.m and 100 Vim.
Customary thermal shaping procedures for the processing of plastics to form
multi-
layer sheet-like articles are pwticularly suitable for the production of the
mufti-layer
film according to the invention. One such procedure which should be mentioned
here
is production by coextrusion, which is preferably effected by the blown film
process.
On account of the better composite bonding which can be achieved, coextrusion
is the
particularly preferred process of those which are suitable for the production
of multi-
layer thermoplastic sheet-like articles.
Moreover, coextrusian is preferable to the coating processes from a melt or
solution
which are known in the art, since only one pass through the machine is
necessary.
According to the prior art, the melt is distributed circularly for mufti-layer
blown film
dies by means of designs which comprise sleeves, ribbed mandrel holders,
spiral
distributors or sandwich dies (e.g. the Bramton Engineering design). Circular
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distribution of the melt based on the spiral distributor principle is
preferred according
to the present invention.
The surface properties of the films according to the invention can be modified
on one
or both sides by means of known physical and chemical methods of treatment,
such as
corona, flame, plasma or fluorine treatment for example.
On account of their properties according to the invention, the films described
here are
particularly suitable as membrane films, especially those which are used in
the
clothing sector. They are particularly suitable for use in the sphere of
workwear or
working clothes, which are often worn for long periods. In the leisurewear
sector, they
are particularly suitable for use as a wind- and weatherproof, rain-resistant
outdoor
membrane.
The films according to the invention are also suitable for applications in the
fields of
medicine and medical technology. Coverings for wounds, active ingredient
patches,
anti-allergic mattress covers and operating theatre protective clothing should
be
explicitly mentioned here.
In a most preferred embodiment, the films according to the invention are used
as
laminated composites with woven textile goods, knitted goods or nonwoven webs,
or
with wovens and nonwovens in general.
The films which are described in the context of the following examples and
comparative examples were produced by blown film coextrusion. The construction
of
endless screw tooling which is suitable for the digestion of thermoplastic
resins is
described, for example, by Wortberg, Mahlke and Effen in: Kunststoffe, 84
(1994)
1131-1138, by Pearson in: Mechanics of Polymer Processing, Elsevier
Publishers,
New York, 1985 or by the Davis-Standard company in: Paper, Film & Foil
Converter
64 (1990) pages 84 - 90. Dies for shaping the melts into films are described
by
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Michaeli in: Extrusions-Werkzeuge, Hanser Verlag, Munich, 1991, amongst other
references.
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A film was produced by means of a double-layer blown film extrusion die. Layer
(1)
of the film, which had a thickness of 20 Vim, was produced from a
thermoplastic
polyurethane of Shore hardness 90A according to DIN 53505, which exhibited an
MFR of 27 g/10 minutes as measured at 190°C using a test mass of 10 kg
, and which
was essentially synthesised from components comprising diphenylmethane 4,4'-
diisocyanate as the hard segment, polyethylene oxide as the soft segment and
1,4-
butanediol as the chain extender. 4 % by weight, with respect to the total
weight of
co~rrponents used for film processing, of a natural hydrated silica with a
particle size
between 3 ~.m and 7 ~.m, and 1 % by weight of an amide wax were added in order
to
adjust the processing properties.
The substances used in layer (2), which had a thickness of 10 Vim, comprised a
thermoplastic polyurethane of Shore hardness 85A according to DIN 53505, which
exhibited an MFR of 25 g/10 minutes as measured at 190°C using a test
mass of 10
kg, and which was essentially synthesised from components comprising
diphenylmethane 4,4'-diisocyanate as the hard segment, polytetrahydrofuran as
the
soft segment and 1,4-butanediol as the chain extender. Amounts of hydrated
silica and
amide wax were added which were the same as those used in layer ( 1 ).
The materials were each processed to form a film, in a single-screw extruder
comprising a flanged-on blown film extrusion die. Increasing temperatures of
160
190°C were set at the; extruders, which had a diameter of 45 mm. The
extrusion die
temperature was 190°C.
xa le 2
A film was produced by means of a double-layer blown film extrusion die. Layer
( 1 )
of the film, which had a thickness of 20 Vim, was produced from a
thermoplastic
polyurethane of Shore hardness 82A according to DIN 53505, which exhibited an
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MFR of 26 g/10 minutes as measured at 190°C using a test mass of 10 kg,
and which
was essentially synthesised from components comprising diphenylmethane 4,4'-
diisocyanate as the hard segment, polyethylene oxide as the soft segment and
1,4-
butanediol as the chain extender. 4 % by weight, with respect to the total
weight of
components used for film processing, of a natural hydrated silica with a
particle size
between 3 ~m and 7 um, and 1 % by weight of an amide wax were added in order
to
adjust the processing properties.
The substances used in layer (2), which had a thickness of 10 ~.m, comprised a
thermoplastic polyurethane with a Shore hardness of 85A according to DIN
53505,
which exhibited an MFR of 25 g/10 minutes as measured at 190°C using a
test mass
of 10 kg, and which was essentially synthesised from components comprising
diphenylmethane 4,4'-diisocyanate as the hard segment, polytetrahydrofuran as
the
soft segment and 1,4=butanediol as the chain extender. Amounts of hydrated
silica and
amide wax were added which were the same as those used in layer ( 1 ).
The materials were each processed to form a film, in a single-screw extruder
comprising a flanged-on blown film extrusion die. Increasing temperatures of
160
190°C were set at the extruders, which had a diameter of 45 mm. The
extrusion die
temperature was 190°C.
A film was produced as in Example 2, using a double-layer blown film extrusion
die.
Layer (1) of the film had a thickness of 36 ~m and layer (2) thereof had a
thickness of
10 Vim.
A film was produced using a three-layer extrusion die. Layer (1) of the film,
which
had a thickness of 10 Vim, was produced from a thermoplastic polyurethane of
Shore
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hardness 82A according to DIN 53505, which exhibited an MFR of 26 g/10 minutes
as measured at 190°C using a test mass of 10 kg, and which was
essentially
synthesised from components comprising diphenylmethane 4,4'-diisocyanate as
the
hard segment, polyethylene oxide as the soft segment and 1,4-butanediol as the
chain
extender. 4 % by weight, with respect to the total weight of components used
for film
processing, of a natural hydrated silica with a particle size between 3 pm and
7 p,m,
and 1 % by weight of an amide wax were added in order to adjust the processing
properties.
The--substances used in layer (2), which had a thickness of 10 Vim, comprised
a
thermoplastic polyurethane of Shore hardness 85A according to DIN 53505, which
exhibited an MFR of 25 g/10 minutes as measured at 190°C using a test
mass of 10
kg, and which was essentially synthesised from components comprising
diphenylmethane 4,4'-diisocyanate as the hard segment, polytetrahydrofuran as
the
soft segment and 1,4-butanediol as the chain extender. Amounts of hydrated
silica and
amide wax were added which were the same as those used in layer ( 1 ).
In layer (3), which had a thickness of 20 pm, a polyethylene was used which
exhibited
an MFR of 3 g/10 minutes as measured at 160°C using a test mass of 2.16
kg.
The materials were each processed to form a film, in a single-screw extruder
comprising a flanged-on blown film extrusion die. Increasing temperatures of
160-
190°C were set at the extruders, which had a diameter of 45 mm. The
extrusion die
temperature was 190"C.
om~arative example 1
A film was produces! using a single-layer extrusion die. Layer (1) of the
film, which
had a thickness of 50 pm, was produced from a thermoplastic polyurethane of
Shore
hardness 90A according to DIN 53505, which exhibited an MFR of 27 g/10 minutes
as measured at 190°C using a test mass of 10 kg, and which was
essentially
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synthesised from components comprising diphenylmethane 4,4'-diisocyanate as
the
hard segment, polyethylene oxide as the soft segment and 1,4-butanediol as the
chain
extender. 4 % by weight, with respect to the total weight of components used
for film
processing, of a natural hydrated silica with a particle size between 3 pm and
7 p.m,
and 1 % by weight of an amide wax were added in order to adjust the processing
properties.
The material was processed to form a film, in a single-screw extruder
comprising a
flanged-on blown film extrusion die. Increasing temperatures of 160-
190°C were set
at tie extruders, which had a diameter of 45 mm. The extrusion die temperature
was
190°C.
Unitsxample xampleExample ExampleComparative
1 2 3 4 example
1
ilm thickness pm 30 30 45 20 50
ermeability to g/
water
apour (source 130 720 650 1400 350
of
oisture facing (mz
layer .
(1)) d)
ermeability to g/
water
apour (source 90 700 470 1200 350
of
oisture facing (mz
layer .
d)
2))
It can be seen from Table 1 that the films according to the inventions exhibit
a
directionally-dependent permeability to water vapour, whereas this is not
observed for
the film from the comparative example. It can be seen from a comparison of
Example
2 and Example 3 in particular that the degree of directional-dependency of the
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permeability to water vapour can be adjusted in a targeted manner by the
variation
according to the invention of the layer thicknesses.
Determination of the permeability to water vapour:
The permeability to water vapour was determined according to DIN 53122. This
was
performed at a temperature of 23°C and at a relative atmospheric
humidity of 85%. In
Example 4, the permeability t:o water vapour was determined after separating
the PE
backing film or layer (3).
