Note: Descriptions are shown in the official language in which they were submitted.
,~ 2123053
~lexiblo h~at-J~al~l~ m~ilayer fiLm m~o_~Qm
thermo~atic ola~tomers ~it~ ~n int-rn~l barri~r lay~
The present invention relates to heat-sealable flexible
multilayer films, the core layer and/or core layers of
which are made from barrier polymers and the outer layers
of which are made from thermoplastic elastomers. Due to its
improved barrier properties towards organic liquids, in
particular hydrocarbons and alcohols, the film is suitable
for the production of low-loss storage or transport
packages, in particular for fuels.
There are legal provisions relating to environmental
protection which cover storage containers for liquid media
hazardous to the environment. A known solution is to
install the containers within bunds or to provide double-
walled containers wherein the emphasis is upon protection
of the soil and water courses from the stored media.
DE-GM 91 09 544 provides a comprehensive review of the
embodiments of tank systems described in the relevant
patent literature.
Most known structural measures to achieve the desired
protective effect are suitable only for new tank storage
due to the involved high technical efforts. Older fuel
storage depots very often incorporate no safety measures
complying with recent regulations. Since structural
measures are often not practicable, protective systems with
an internal film bag are used ('bag in box' system).
While protection of the soil and water courses, as laid
down in Bau- und Prufgrundsatzen fur den Gewasserschutz
[Principles of construction and testing for the protection
of water courses], parts I and II, Institut fur Bautechnik,
Reichpietschufer 74-76, 10785 Berlin, Germany, is part of
the present technical state of the art, there is now also
WW 5379 - Foreign countries
- ~ ~ 2 1 2 3 0 ~ 3
an increasing concern to prevent or minimise environmental
damage caused by evaporating liquids, particularly those of
organic kind.
Pouches made from flexible films or bags as well as
internal liners installed within larger containers allow it
to enclose stored liquids and prevent further evaporation
of the liquid, which is otherwise possible by exchange of
the vapour phase above the liquid. If the film constituting
the bag is also sufficiently flexible, then the bag filled
with the material being stored can accommodate to the
volume of the stored liquid, as is for example described in
German patent DE 40 00 427 A1, such that when filling and
emptying the bag in the tank it is not necessary to expel
the vapour phase which is at equilibrium with the stored
material. In this case, it is only the surrounding air --
which does not contain any vapour of the stored liquid
which is expelled when the volume of the bubble changes.
The use of plastic films for storing high-boiling organic
liquids such as for example diesel fuel and/or for liners
for storage containers for these sub~tances has been known
for a long time and is described in the relevant
25 instructions, such as for example Technische Regel fur ~ ~-
brennbare Flussig~eiten [technical rule relating to
flammable liquids] n 501 (TRbF 501 Richtlinie/Bau- und -~ ~-
Prufgrundsatze fur Leckanzeigegerate fur Behalter
[guideline/principles for the construction and testing of
leakage indicators for containers]) edited by Verband der
Technischen Uberwachungsvereine e.V. (Technische Regeln fur
brennbare Flussig~eiten, 1991, Carl Heymann Verlag,
Luxemburger Stra~e 449, 50939 Cologne, Germany). TRbF 501
explicitly describes the construction principles for films
made from plasticised polyvinyl chloride (PVC) for such
applications. However, plasticised PVC's resistance
Ww 537g 2
:`` 2~230~3
against many organic solven~s and mineral oil pr:odwc~s is
not sufficient.
Rubber-based elastomers as well have insufficient barrier
properties and, due to their crosslinked molecular
structure, they do not offer the design-flexibility for
easy adaption of bags to existing tank containers as
thermoplastic film materials do.
In contrast, thermoplastic elastomers (TPE) are
characterised by a combination of good mechanical
properties, i.e. elevated tensile strength and tear
propagation resistance, high extensibility, together with
good flexibility at low temperatures and chemical
resistance. TPE have for a long time been known and consist
of block copolymers. The different blocks or segments in
their structure determine different properties of the TPE,
usually a distinction is being made between hard and soft
segments. The hard segment determines strength, while the
soft segment determines elasticity and flexibility. The
different blocks of the hard and soft segments separate in
the solid state which consequently exhibits a domain
structure.
The combination of the different material properties
strength and flexibility in one molecule is achieved by an
alternating arrangement of different blocks. The so-called
internal plasticisation means that elasticity or softness
are inherent to the plastic and are unaffected by a change
in additive composition, as it occurs in the case of
migration. `~
The formation of physical networks by the combination of
hard segments giving crystallites, glassy solidified
domains and/or by hydrogen bridge formation means that
these networks are thermo-reversible, i.e. these materials
WW 5379 3
: , ~ . ,
21230~3
may be processed and shaped as thermoplastics and may al~o
be heat-bonded.
An review of the structure, production, properties and
applications of TPE may be obtained from Hoffmann in
Kunststoffe 80 (1990) 10, Legge in Rubber Chemistry and
Technology 62 (1989) 529 and Goyert in Swiss Plastics 4
(1982) 7
If explosive media are stored, there is an additional
requirement for the films used to be antistatic in order to
prevent any risk of ignition. In Technische Regel fur
brennbare Flussigkeiten n 401 (TRbF 401 Richtlinie fur
Innenbeschichtungen von Behaltern zur Lagerung brennbarer
Flussigkeiten der Gruppe A Gefahrenklasse I, II und der
Gruppe B [guideline relating to internal coatings for
containers for the storage of flammable liquids of group A,
hazard class I, II and of group B]) edited by Verband der
Technischen Uberwachungsvereine e.V. obtainable from Carl
Heymans Verlag KG, Luxemburger Str. 449, 50939 Cologne,
Germany, it is inter alia mentioned that coatings do not
give rise to ignition hazards due to the formation of
electrostatic charges if their resistance does not exceed
103 Ohm.
The hazards arising from a discharge of static electricity, ~ -
together with possible preventive measures, are described
in guideline n 4 from Berufsgenossenschaft der chemischen -~
Industrie [chemicals industry employer's liability
insurance association] (ZH 1/200). It is explained there
that for solid materials the formation of hazardous charges
is not to be expected if their surface resistance is less
than or equal to 109 Ohm, measured to DIN 53 482/VDE~0303,
part 3 in a standard conditioning atmosphere at 23C and
50% relative humidity.
Ww 5379 4
:-' 212~0~3
The material properties of TPE may be modified, in a
similar manner to those of standard plastics, with
additives and fillers. Antistatic properties may
successfully be imparted to plastics by the addition of
carbon black, as explained by Hauf in Materialwissenschaft
und Werkstofftechnik 23 (1992) 157 or We~ling in Polymer
Engineering and Science 31 ~1991) 1200.
Materials with surface resistances of > 1013 Ohm, measured
to DIN 53 482, are generally described as insulators and
those with resistances of < 105 Ohm as conductors. Materials
with a resistance between these limiting values are
classified as static electricity dissipative or often
simply as antistatic materials.
The use of antistatic coatings or outer layers is variously
described in the relevant patent literature, for example
DE-GM 18 22 483 describes completely synthetic woven
fabrics sealed with polyester-urethanes, wherein a
conductive coating is applied to only one side. In
practice, coated woven fabrics have an undesirably large
number of pinholes so that microleaks cannot be eliminated
in such systems. Application of a conductive coating to
only one side is inadequate. -~
-
DE 31 03 772 A1 describes multilayer film structures with
conductive TPU outer layers. Plasticised PVC as the core
material has inadequate barrier properties for diffusing
fuel molecules. Even if more rigid grades of PVC are used,
barrier properties may only be slightly improved and film
flexibility is lost.
i
Coated or laminated woven fabrics are of a distinctly more
heterogeneous nature than films, which nature is only
unwillingly tolerated. Inherent to fabric layers is the
risk of faster lateral diffusion, so that any possible
material damage is accelerated.
WW 5379 5
21 230~3
.~`
The two-layer film structures described in JA 52-69486 have
the disadvantage that only one of the two outer layers can
be heat-sealed together.
Of particular importance is the lining of containers for
the storage of materials with high vapour pressures, as
they often occur with explosives, such as for example
fuels. These substances frequently exhibit increased
diffusion through the plastic materials used for container
linings. EP 0 461 836 A1 describes the necessity of an
additional barrier layer in polyolefin materials when
storing fuels and suggests the use of polyamides as barrier
layer materials.
Polyamide is well known for its high strength and good
chemical resistance. A comprehensive review of the
properties, production and processing of this class of
materials may be found in Kunststoff-Handbuch, vol. VI,
Polyamides, Vieweg, i~uller (eds.), Carl Hanser Verlag,
Munich 1966. However, using polyamides of a sufficient
thickness to ensure satisfactory barrier properties leads
to an undesirable reduction in flexibility.
~ .
Moreover, polyamide has barrier properties which are only
partially adequate for fuels, as explained by Leaversuch in
~odern Plastics International 12 (1991) 14.
It is known from the relevant specialist literature, such
as for example Rellmann ~ Schenck in Kunststoffe 82 (1992)
729, that barrier layer polymers such as ethylene/vinyl
alcohol copolymers (EVAl) and saponified and/or partially
saponified ethylene/vinyl acetate copolymers a~e used to
reduce loss of stored media in rigid containers. However,
the systems as for example described by Daubenbuchel in
Kunststoffe 82 ~1992) 201 are not suitable for flexible
storage containers due to their material structure.
WW 5379 6
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21230~3
.~
The object of the invention was thus to provide a film
which is capable of adapting to external shapes and is
heat-sealable to itself, i.e. is weldable, such that
flexible containers such as pouches, bags or internal
liners for cans or tanks may be shaped from it. For safety
reasons, these flexible containers should have a great
abrasion and puncture resistance in order to forestall
mechanical damage on repeated filling and emptying
operations. This means the film should exhibit high tear
strength and elongation at break, while also requiring only
low stresses for a slight elongation.
The materials used should also be resistant to fuels, and
films produced from them should moreover have good barrier
properties towards the largest possible number of organic
solvents.
It was also important to produce this film in such a way
that it is heat-sealable or weldable to itself, while
nonetheless being abrasion resistant and offering both
thermal stability and elevated chemical resistance.
The required permeability, for example of unleaded premium
petrol, should not exceed 1 g/(m2 24 h), measured to
DIN 53 532.
For the storage of oxidisable organic solvents with a high
vapour pressure, i.e. explosive media, there is the
additional object of achieving a sufficiently low surface
resistance to exclude ignition hazards from discharges of
static electricity. This resistance should be less than 10~ ;
Ohm, measured to DIN 53 482/VDE 0303, part 3, electrode ~ -
arrangement A.
Barrier properties which are largely independent of
environmental conditions should also be considered
advantageous.
WW 5379 7
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2t2~0~3
-
Despite the vigorous efforts of ~hose skilled in the art,
particularly plastic film manufacturers, to produce such a
film, none has yet been made known to those experts
interested in flexible barrier layer films.
It has now proved possible to achieve this object according
to the invention with a heat-sealable, flexible multilayer
film having at least three layers, comprising layers of
different structural polymers which is characterised in
that it has thermoplastic elastomers in the outer layers
and an EVAl barrier layer as core and the layers are joined
together by coextrusion and/or lamination.
Films suitable for the production of storage bags, pouches
or liners which have at least three layers and are made
from thermoplastic elastomers with an internal barrier
layer of EVAl, preferably have a total thickness of 0.05 to
2 mm.
In addition to the stated minimum three layers, the film
may contain further layers of other structural polymers
which allow it to further improve the properties of the
film according to the invention or to adapt it to the
requirements of particular applications.
The sum of the thermoplastic elastomer outer layers has a
content ranging from 20% to 98% related to the total weight
of the film~ Preferred films are those in which the sum of
the outer layers is at least 30% and at most 80% related to
the total weight of the film.
In a preferred embodiment, the film is of symmetrical
structure such that it may be welded to itself without loss
of properties and without regard to the layer structure.
Thermoplastic elastomers synthesised from hydrophilic raw
materials are of particular interest as constituents for
WW 5379 8
.
21230~3
,, ~
the outer layers of films used in the storage of organic
solvents and mineral oil products. Such elastomers are
thermoplastic polyurethanes (TPU) and copolyetheresters
(PEE), since they have lower affinity to hydrophobic
mineral-oil based fuels.
It is not generally necessary to introduce reinforcing
fabric into the film as the mechanical strength and
stability of the film according to the invention is
generally sufficiently high due to the use of
tear-resistant materials, in particular the thermoplastic
elastomers. By dispensing with such reinforcement, the film
according to the invention gains chemical resistance as the
penetration of possible damaging particles, which could be
contained in the material being stored, is prevented.
At least one of the heat-sealable outer layers may if
required be made antistatic. Suitable materials for ~-
imparting antistatic properties are conductive additives
such as for example carbon blacks or intrinsically
conductive polymers or metal particles. The conductive
additives are incorporated into the molten TPE using the
machines commonly used in the plastics industry such as
kneaders or extruders, in particular double screw
extruders.
':
When blending the electrically conductive additives, it
proved successful to use processing auxiliaries which have
a plasticising effect and very largely leave the polymer
matrix after finishing the blending process, wherein no
negative effects on properties remain. Such volatile
processing auxiliaries are preferably compressed gases with
an elevated plasticising action, carbon dioxide being
particularly suitable for this purpose.
Carbon blacks with a BET surface area of greater than or
equal to 600 m2/g (ASTM D-3037) and an average particle size
wW 5379 9
.: - .
---` 212~
of less than 500 nm are preferably used as the antistatic
additive. Carbon blacks fulfilling these requirements are
commercially available, for example Printex XE 2 from
Degussa or Ketjenblack EC 600 from Akzo. The preferred
carbon black content to impart antistatic properties is
suitably 5 to 20%.
Since the barrier properties of EVAl copolymers are very
highly dependent upon their moisture content or the
moisture content of their surroundings, it is advantageous
not to use these copolymers as outer layers of films, but
instead to incorporate them as core barrier layers in film - -
structures.
It proved possible, as is known from food packaging film,
to stabilise the barrier properties of the barrier layer to
a very great extent independently of environmental moisture
by introducing additional interlayers. Polyolefin materials
proved particularly suitable for the production of such
interlayers. Polyethylene polymers are used in a preferred
embodiment.
The barrier properties of the film according to the
invention against a commercial available, unleaded premium
petrol are so pronounced that the permeability of this
liquid is below 1 g/(m2 24 h~.
; , The properties of the polymer raw materials used for the
individual layers of the film according to the invention
may be further improved with regard to the use according to
the invention by the addition of suitable customary
additives in effective quantities. Additives which may be
used to this end include inter alia not only slip additives
and lubricants but also colouring pigments, biocides and
inorganic fillers or antiblocking agents, such as for
example silica.
Ww 5379 10
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t?.3n~
Preferred slip additives are not only carboxylic acid
amides such as erucic acid amides, stearic acid amides and
palmitic acid amides or polydiorganylsiloxanes, but also
fluoroelastomers and inorganic slip additives such as
molybdenum disulphide, but also stearic acid salts.
Suitable anti-blocking agents are for example organic
polymers incompatible with the film matrix or inorganic
substances such as silicates, silicon dioxide and calcium
lQ carbonate. Inorganic substances such as silicon dioxide
with an average particle size of 1 to 10 ,um have proved
particularly successful anti-blocking agents. The effective
quantity of these anti-blocking agents to be added is 0.5
to 6 wt.%, preferably 2 to 4 wt.% related to average film
iS weight.
Surprisingly, when imparting electrically conductive
properties to the outer layers of the film according to the
invention, wherein the described carbon black is preferably
used, its particles having a spacing effect, it was found
that the quantity of further anti-blocking agents added
could be reduced by the extent to which electrically
conductive additives were included in the formulation
and/or could be completely omitted.
A comprehensive description of usual additives and their
mode of action may be referred to in Gachter & Muller,
Taschenbuch der Kunststoffadditive [handbook of plastics
; additives], Carl Hanser Verlag, Munich 1989.
In order to ensure the long term stability of the
properties of the film according to the invention, it may
contain suitable additions of stabilisers in effective
quantities, preferably hydrolysis stabilisers and/or
photostabilisers and/or antioxidants.
WW 5379 11
? t) ~;~
Light-absorbing substances are suitable to achieve
photostabilisation, benzoates and/or phenysalicylates which
absorb high-energy UV light being in particular used, but
also substituted acylates and benzotriazoles. Quenchers may
also be used for photostabilisation, preferably nickel-
organyl chelates and/or nickel dithiocarbamates.
Preferably used hydrolysis stabilisers are carbodiimide9,
in particular non-migrating variants as polycarbodiimides,
but also hydroxyethyl ureas.
Suitable antioxidants for use in the film according to the
invention are both so-called primary antioxidants,
secondary phosphites or phosphonites sterically hindered by
substitution at the oxygen and/or sterically hindered
phenols and also mixtures of primary and secondary
antioxidants.
Stabiliser systems suitable for use in the plastics used in
the film according to the invention are, for example,
described by Rek and Bravar in J.Elast.Plast 12 (1980) 245.
The substances to be added may be incorporated by direct
mixing during polymer production or also by the addition of
a masterbatch or a liquid or polymer concentrate containing
the additives, in an amount corresponding to the desired
quantity to be incorporated.
All the polymer materials used for the film according to
the invention may be processed in customary plastics
processing machinery, such as for example extruders.
Generally used tools, such as flat film dies with
downstream chill rolls or downstream coating units, but
also blown film dies combined with appropriate collapsing
arrangements, may be used to form the films.
WW 5379 12
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2123053
r ~
Purpose-designed tools, for example coextrusion dies, may
be used to join the layers. If it is impossible to use a
single tool directly to process two different materials
which are necessarily used in the film according to the
invention due to very different processing behaviour, the
layers may also subsequently be bonded by thermal
lamination, for example by flame lamination, by lamination
using a suitable adhesive system or also by any other
customary lamination process.
In a preferred embodiment, polyurethane adhesives are used
to laminate differing film webs, wherein adhesive systems
are used which exhibit strong molecular crosslinking, such
that they are only slightly swollen but not dissolved by
migrating molecules of the stored substances.
Interlayer adhesion may, if necessary, be distinctly
improved by the use of bonding resins.
There is a great variety of commercially available grades
of bonding resins. These are generally copolymers with at
least two comonomers, but multipolymers with up to more
than five different comonomers are aIso used.
A preferred comonomer in the bonding resins is in
particular ethylene, which improves adhesion with non-polar -
polymers. Maleic anhydride is also preferably incorporated ~-
into bonding resins. Due to the anhydride functional group,
this substance renders a strong bond with polar,
. .
30 particularly protic groups possible. Comonomers containing -~ ~-
vinyl acetates, acrylates, methacrylates and butyl
acrylates as the acid group are also widely used, since
they have a bonding effect due to their polar organic
molecular structure, wherein butyl acrylates are preferred
comonomers.
WW 5379 13
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21230~
When using bonding resins containing maleic anhydride,
adhesion of the structure is often found to improve with
storage time of the film, a phenomenon brought about by
molecular transformations which are initiated during
5 processing, but which, due to their slow progress, only
later achieve the desired level of bonding strength.
The surface properties of the film according to the
invention may be modified on one or both sides. Suitable
10 treatments are in particular corona, plasma or fluorine
treatments. Use of these latter treatments means that the
barrier properties of the film according to the invention
may be optimally adapted to the expected contact medium or
further improved.
Such surface-treatment processes for plastic films are
comprehensively described by Dorn & Wahono in
Maschinenmarkt 96 (1990) 34-39 or Milker & Moller in
~unststoffe 82 (1992) 978-981.
The invention is illustrated in greater detail below with
examples and comparative examples.
Ex~el~ 1
A symmetrical film was coextruded using a three-layer die.
The surface layers were made from a TPU with a
poly(oxytetramethylene)diol soft segment prepared from
tetrahydrofuran and a hard segment with a Shore A hardness
30 of 86 prepared from 4,4'-diisocyanatodiphenyl-methane (MDI)
and butanediol, the core layer was made from ethylene-vinyl ;
alcohol copolymer (EVAl). The EVAl used had an ethylene
content of 38 wt.% related to the total weight of the EVAl
used. At this ethylene content, the EVAl has only slight -`~
35 barrier action, but it may be directly processed together
with the TPU due to their similar processing temperatures.
WW 5379 14
:'~
Ei~
`- 21230~3
The outer layers of the blown ~ilm were each of an average
thickness of 90 ~m and the core layer of an average
thickness of 20 ,um.
Ex~mp~ 2
A TPU was blended with 10% of an elevated surface area
carbon black, Ketjenblack EC 600 in order to obtain
conductive properties. The TPU, which had a soft segment -
prepared from adipic acid and hexa-methylenediol and a hard
segment prepared from MDI and butanediol, had a Shore A
hardness of 93 or a Shore D hardness of 47. It was
necessary to use amide waxes to incorporate the carbon
black. The conductive TPU was coextruded with a bonding
resin and an EVAl using a three-layer die to produce an
asymmetrical structure.
The ethylene content of the EVAl was 32 wt.% related to the
total weight of EVAl. The bonding resin used was a
copolymer of ethylene, butyl acrylate and maleic anhydride.
The ethylene content was provided by an LLDPE.
The TPU layer was 90 ~m thick, the bonding resin and EVAl
layers were each 10 ~m thick.
; In a further processing stage, the surfaces of the EVAl
layers were melted using an infra-red radiant heater and, -
by bringing two webs together, joined into a symmetrical
film with an EVAl core layer surrounded by bonding resin
layers and TPU outer layers.
~X~Eelo 3
A plasticised PEE raw material of Shore D hardness 60,
consisting of hard segments prepared from terephthalic acid
and ethylene glycol and soft segments of poly(oxytetra-
methylene)diol was compounded in a kneader with a -
WW 5379 15
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proportion of 8 wt.% of conductive carbon black,
Ketjenblack EC 600, in relation to the total weight of
compound obtained. No plasticising auxiliaries capable of
migrating to the film surface were used during compounding.
S A single layer blown film was extruded from this compound.
The same was done to prepare a film from an EVA1 with an
ethylene content of 29 wt.% related to the total weight of
EVAl used. The PEE and EVAl had processing temperatures
which were more than 30C apart, so that they could not be
processed in a single die. The barrier structure was
obtained by adhesive lamination of the PEE films on both
sides of the EVAl film. A crosslinking polyurethane
adhesive dissolved in an organic, polar, aprotic solvent
was applied and the films bonded together under the action
of pressure and heat using conventional laminating
equipment.
The average thickness of the conductive PEE films was
100 ,um, that of the EVAl film 15 ~um.
~~m~l~ 4
A conductive polyurethane, produced in the same manner as
in example 2, was converted into a two-layer TPU film in a -
blown film coextrusion die together with another TPU, the
soft segment of which was prepared from adipic acid and
hexamethylenediol, and the hard segment from MDI and
butanediol, of Shore A hardness 96 or Shore D hardness 54,
the layers of which film were each 50 um thick.
A coextruded three-layer film produced from polyamide 6 and
EVAl, with outer layers of polyamide and a core layer of
EVAl, was used as the barrier film. This symmetrical
barrier film was 15um in thickness, wherein the thickness
of the EVAl layer was 2 um and that of the polyamide layers
enclosing it 6.5 um each.
WW 5379 16
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Films according to the invention of thlckness 220 ~m were
produced using a crosslinking polyurethane adhesive,
wherein the two-layer TPU films described above were
laminated on both side of the barrier film. Lamination was
performed such that the layers rendered conductive with
carbon black were on the outside of the finished laminated
film structure.
~XA~ 5
A film was produced in a three-layer blown film coextrusion
die with a core of a bonding resin of 10~m in thickness.
One of the outer layers, each of which were 50 ,um thick,
consisted of a conductive TPU, the soft segment of which
was prepared from adipic acid and hexamethylenediol and the
hard segment from MDI and butanediol. The Shore A hardness
of the TPU was 93, or the Shore D hardness 47. The other
outer layer, also 50 ,um thick, consisted of a linear low
density polyethylene of density 0.93S g/cm3 and an MFI of
0.5, measured at 190C with a test weight of 2.16 kg. ~ '
A coextruded, symmetrical three-layer film produced from
polyamide 6 and EVAl was used as the barrier layer with
outer layers of polyamide and a core layer of EVAl (c.f.
example 4). This barrier film was 80 um thick, wherein the
thickness of the EVAl layer was 6 ~m and that of each of
the polyamide layers enclosing it 37 ~um.
Films according to the invention were obtained by using a
crosslinking polyurethane adhesive, wherein the first
stated three-layer films were laminated on both sides of ~i
the barrier film. Adhesive lamination of the first stated
three-layer films onto the barrier film was performed on -
the non-conductive layers of low density polyethylene, such
that the outer layers of the finished laminated film
structure consisted of carbon black filled TPU layers.
WW 537g 17
,'
Co~ar~ti~re . ~7taD~l~ l 212 3 0 ~ 3
A film was melt-processed from a commercially available
thermoplastic polyurethane with an elastic ether segment by
extrusion and subsequent casting onto a chill roll. The TPU
had a poly(oxytetramethylene)diol soft segment prepared
from tetrahydrofuran, together with a hard segment prepared
from MDI and butanediol. The polyurethane used had a Shore
A hardness of 85. 2% silicon dioxide and 0.4~ amide wax,
each related to the total quantity of film, were added as
processing auxiliaries. The thickness of the film described
was 400 ~m.
Comparativo ~xam~lo 2
An elevated surface area, electrically conductive carbon
black, Ketjenblack EC 500, was incorporated into a TPU of
Shore A hardness 93 or Shore D hardness 47 using a kneader. ~ -~
The TPU was characterised by a soft segment prepared from -
adipic acid and hexamethylenediol and a hard segment
prepared from MDI and hutanediol. The polymer was carefully ~ -
plasticised by adding amide waxes. A blown film of 200 ~m
in thickness was obtained by extrusion. -~
Co~arativ~ oxamplo 3
A calendered film produced from plasticised PVC was used as
a further comparative example~ Flexibilisation was achieved
by the addition of 20 wt.% dioctyl phthalate related to the
total weight of the film. The thickness of this comparative
film was 300 ~m.
Ç~ 4 ~-
A PEE raw material of Shore D hardness 60 consisting of
hard segments prepared from terephthalic acid and
tetramethylene glycol and soft segments of poly(oxytetra-
WW 53~9 18
~ 21230~3
methylene)diol was melted i.n a.n extruder. A Pilrn wasproduced from the melt using a blown Pilm die. After
collapsing, edge-trimming and separation, the film 50
obtained had a thickness of 200 ,um.
Ww 5379 19
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., . ,, . . '
'' ' ' ' ~ ` ' " ,.
., : , ' , , ~ ` :
.
21 230~3
T~le
~=.
Table 1Petrol Electrical Tear Elongation Softening
permeabilit~/ surface strength at break point
resistance
g/(m2 24 h~ Ohm Nlmm2 % C
Example 1 0.2 3- 101Z 55.2 360 143
Example 2 < 0.1 6 105 51.1 550 135
. .. .
Example 3 < 0.1 7 ~ 1 o6 27.6 480 157
. _
Example 4 0.2 6 105 29.2 590 135
. ._
Example 5 O.1 5 105 23.1 690 148
Comparative 10.4 3 1 ol2 72.0 480 140
example 1
_
Comparative 16.3 6 105 39.1 440 174 -
example 2 _ ~:
Comparative 33.8 6 104 12.5 170 74 ~ - -
example 3 : : -
:::
Comparative7.6 5 1 ol2 36.1 645 157 - -
. example 4
As may clearly be seen from a comparison of the examples :~ -
and the comparative examples, the films according to the :
invention are superior to the comparative films in terms of :
the desired properties.
Determination of petrol permeability
The petrol permeability of the films is determined ~:
according to DIN 53 532 "Determination of liquid
permeability of elastomer films". Pursuant to DIN 50 014,
determination was performed at a temperature of 23C in
ambient air witn a relative humidity of 50% ~standard
conditioning atmosphere 23/50). The petrol used was a
customary commercial unleaded premium petrol according to
DIN 51 607/EN 228.
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2t2~
Measurement of su~a~ re~ anc~
Electrical surface resistance i9 measured according to DIN
53 482/VDE 0303, part 3, in standard conditioning
atmosphere 23/50. Electrode arrangement A consisting of two
sprung parallel electrodes lO0 mm in length and lO mm apart
was used.
Mea~$urement of tear strength a~_elongation at break
Tear strength and elongation at break are determined
according to DIN 53 455. Standard conditioning atmosphere
23/50 is used. Test strips with a clamping distance of 50
mm must be used.
Determination of softening range
Softening range is determined on a Kofler hot plate. To
this end, a strip of film of dimensions 30 x 200 mm is laid
upon the previously calibrated Kofler heating bench.
Starting from a low temperature, the film strip is lifted
up after a waiting period of 30 seconds. The temperature -
range at which the film adheres to the Kofler heating bench
gives the softening range.
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' ~
: :
