U.S. patent application number 11/926910 was filed with the patent office on 2008-03-13 for polyolefin film, tape or yarn.
This patent application is currently assigned to Lankhorst Indutech B.V.. Invention is credited to Johannes Antonius Joseph Jacobs, Joachim Loos, Antonius Andreas Johannes Maria Peijs, Tilo Schimanski.
Application Number | 20080063846 11/926910 |
Document ID | / |
Family ID | 26076958 |
Filed Date | 2008-03-13 |
United States Patent
Application |
20080063846 |
Kind Code |
A1 |
Loos; Joachim ; et
al. |
March 13, 2008 |
POLYOLEFIN FILM, TAPE OR YARN
Abstract
The invention is directed to monoaxially drawn polyolefin
multilayer film, tape or yarn of the AB or ABA type, having a
stretch ratio of more than 12, having an E-modulus of at least 10
GPa, substantially consisting of a central layer (B) of a
polyolefin selected from polyethylene and polypropylene, and one or
two other layers (A) of a polyolefin from the same class as the
material of the central layer B, the DSC melting point of the
material of the said other layers (A) being lower than the DSC
melting point of the material of the said central layer (B),
wherein the central layer (B) is between 50 and 99 wt. % of the
material and the other layers (A) between 1 and 50 wt. %. The
present invention further relates to a method of manufacturing such
a tape, film or yarn.
Inventors: |
Loos; Joachim; (Nuenen,
NL) ; Jacobs; Johannes Antonius Joseph; (Heerenveen,
NL) ; Peijs; Antonius Andreas Johannes Maria;
(Veldhoven, NL) ; Schimanski; Tilo;
(Schweitenkirchen, DE) |
Correspondence
Address: |
PEARNE & GORDON LLP
1801 EAST 9TH STREET
SUITE 1200
CLEVELAND
OH
44114-3108
US
|
Assignee: |
Lankhorst Indutech B.V.
Prinsengracht 2
Sneek
NL
|
Family ID: |
26076958 |
Appl. No.: |
11/926910 |
Filed: |
October 29, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10483927 |
Jun 28, 2004 |
7318961 |
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PCT/NL02/00487 |
Jul 19, 2002 |
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11926910 |
Oct 29, 2007 |
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Current U.S.
Class: |
428/212 ;
264/210.1; 264/210.7; 428/221; 428/373; 442/200; 442/364 |
Current CPC
Class: |
B32B 27/32 20130101;
B32B 2323/10 20130101; B29C 48/91 20190201; B32B 2323/04 20130101;
B32B 7/02 20130101; Y10T 442/641 20150401; B32B 2250/242 20130101;
B32B 2307/704 20130101; Y10T 442/656 20150401; B29C 48/911
20190201; B29C 55/065 20130101; D01F 8/06 20130101; B29K 2023/00
20130101; Y10T 428/2495 20150115; B29C 55/023 20130101; B32B 27/08
20130101; Y10T 428/2929 20150115; B32B 37/153 20130101; Y10T
428/31913 20150401; B32B 27/327 20130101; B29C 48/05 20190201; D01D
5/253 20130101; Y10T 428/24942 20150115; B29K 2223/00 20130101;
B29C 48/18 20190201; B32B 2307/516 20130101; D01D 5/426 20130101;
Y10T 442/3033 20150401; B29C 48/08 20190201; B32B 2405/00 20130101;
B32B 2250/40 20130101; Y10S 428/91 20130101; Y10T 442/608 20150401;
Y10T 428/249921 20150401; Y10T 442/3154 20150401; Y10T 442/3146
20150401 |
Class at
Publication: |
428/212 ;
264/210.1; 264/210.7; 428/221; 428/373; 442/200; 442/364 |
International
Class: |
B32B 7/02 20060101
B32B007/02; D01D 5/12 20060101 D01D005/12; D02G 3/00 20060101
D02G003/00; D03D 15/00 20060101 D03D015/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 19, 2001 |
EP |
01202757.9 |
Oct 4, 2001 |
EP |
01203764.4 |
Claims
1-21. (canceled)
22. Monoaxially drawn polyolefin multilayer film, tape or yarn of
the AB or ABA type, having a total stretch ratio of more than 12,
having an E-modulus of at least 10 GPa, substantially consisting of
a central layer (B) of a polyolefin selected from polyethylene and
polypropylene, and one or two other layers (A) of a polyolefin from
the same class as the material of the central layer (B), the DSC
melting point of the material of the said other layers (A) being
lower than the DSC melting point of the material of the said
central layer (B), wherein the central layer (B) is between 50 and
99 wt. % of the material and the other layers (A) between 1 and 50
wt. %.
23. Film, tape or yarn according to claim 22, wherein the stretch
ratio is at least 15.
24. Film, tape or yarn according to claim 22, wherein the stretch
ratio is at most 50.
25. Film, tape or yarn according to claim 22, wherein the material
of the central and other layers is based on polypropylene.
26. Film, tape or yarn according to claim 22, wherein the material
of the central and other layers is based on polyethylene.
27. Film, tape or yarn according to claim 22, wherein the material
of the central layer is a crystalline polymer having a weight
average molecular weight of at least 250,000 g/mol.
28. Film, tape or yarn according to claim 22, wherein the outer
layer or layers (A) at least consist of a random copolymer.
29. Film, tape or yarn according to claim 22, wherein the outer
layer or layers A comprise a metallocene catalyzed homopolymer or
metallocene catalyzed copolymer.
30. Film, tape or yarn according to claim 22, wherein the material
of the central layer is a crystalline polymer having a weight
average molecular weight of at least 250 000 g/mol, and wherein the
outer layer or layers (A) at least consist of a propylene ethylene
copolymer, having an ethylene content of between 1 and 25 mol. %
and a propylene content of between 75 mol % and 99 mol %.
31. Film, tape or yarn according to claim 22, wherein the material
of the central and other layers is based on polyethylene, and
wherein the outer layer or layers (A) at least consist of an
ethylene propylene copolymer, having an ethylene content of between
75 mol % and 99 mol % and a propylene content of between 1 and 25
mol. %.
32. Film, tape or yarn according to claim 22, having a thickness of
between 25 and 300 .mu.m.
33. Film, tape or yarn according to claim 22, having an E-modulus
of at least 12.5 GPa.
34. Woven or non-woven composite prepared from a film, tape or yarn
according to claim 22, optionally having been heat treated.
35. Composite material comprising a matrix material reinforced with
film, tape or yarn according to claim 22.
36. Composite material comprising a matrix material reinforced with
a woven or non-woven composite according to claim 30.
37. Method for manufacturing a monoaxially drawn polyolefin
multilayer film, tape or yarn of the AB or ABA type having a total
stretch ratio of more than 12, wherein (i) a film, tape or yarn of
the AB or ABA type, substantially consisting of a central layer (B)
of a polyolefin selected from polyethylene and polypropylene, and
one or two other layers (A) of a polyolefin from the same class as
the material of the central layer (B), the DSC melting point of the
material of the said other layers (A) being lower than the DSC
melting point of the material of the said central layer (B),
wherein the central layer (B) is between 50 and 99 wt. % of the
material and the other layers (A) between 1 and 50 wt. % is
provided by co-extrusion, and (ii) the co-extruded film, tape or
yarn is subjected to a single stage or multi-stage stretching at a
temperature below the melting point of the central layer B.
38. Method for manufacturing a monoaxially drawn polyolefin
multilayer film, tape or yarn according to claim 37, having an
E-modulus of at least 10 GPa.
39. Method according to claim 37, wherein at least one of the
stretching stages is performed at a temperature in the range of
25-70.degree. C.
40. Method according to claim 39, wherein the film, tape or yarn is
first stretched at temperature in the range of 25-70.degree. C. and
thereafter stretched at a higher temperature.
41. Method according to claim 37, wherein the tape, film or yarn is
stretched to a total stretch ratio of at least 15.
42. Method according to claim 37, wherein a monoaxially drawn
polyolefin multilayer film, tape or yarn of the AB or ABA type,
having a total stretch ratio of more than 12, having an E-modulus
of at least 10 GPa, substantially consisting of a central layer (B)
of a polyolefin selected from polyethylene and polypropylene, and
one or two other layers (A) of a polyolefin from the same class as
the material of the central layer (B), the DSC melting point of the
material of the said other layers (A) being lower than the DSC
melting point of the material of the said central layer (B),
wherein the central layer (B) is between 50 and 99 wt. % of the
material and the other layers (A) between 1 and 50 wt. % is
prepared.
43. Tape, film or yarn, obtainable by a method according to claim
37.
44. Film, tape or yarn according to claim 22, wherein the stretch
ratio is at least 20.
45. Method according to claim 37, wherein the tape, film or yarn is
stretched to a total stretch ratio of at least 20.
46. Method according to claim 37, wherein the tape, film or yarn is
stretched to a total stretch ratio of at most 50.
Description
[0001] The invention is directed to a polypropylene multilayer
film, tape or yarn, suitable for producing reinforcing woven and
non-woven type materials, especially for strengthening and/or
stiffening of products. Polyolefin films of mono- or multiplayer
type are generally produced by blown film or cast film extrusion.
At some stage of the production process the material can be
stretched in order to increase the strength and stiffness of the
material.
[0002] Polyolefin tapes and yarns are generally produced from
polyolefin films of mono- or multilayer type, by cutting the film
to the desired width. At some stage of the production process the
material can be stretched in order to increase the strength and
stiffness of the material.
[0003] U.S. Pat. No. 6,578,370 describes a thermoplastic composite
material formed of a polypropylene film that is coated with a layer
of an ethylene copolymer further comprising propylene units. The
coated layer has a lower softening point than the polypropylene
core. The publication describes the stretching of the material to a
draw ratio of 20:1 in a hot air oven. The examples indicate that
composites of the material may have a mean tensile modulus of
elasticity of up to 2.5 GPa.
[0004] JP-A 2000-8244 describes a flat yarn cloth for reinforcing
laminated layers, prepared from a composite yarn of the ABA type,
wherein the B layer is a polypropylene and the A layers are based
on an ethylene-.alpha.-olefin copolymer or a blend of two
ethylene-.alpha.-olefin copolymers. The yarns are produced by
co-extruding the two materials, slitting the film and stretching it
to a stretch ratio of 3-12. After weaving, the material is heat
treated to weld the yarns together.
[0005] EP-A 336,210 describes a three-ply drawn polyolefin laminate
comprising a core layer of polypropylene and/or LLDPE and top
layers from butene-1 polymers. The material can be used in the
packaging area. This material has poor mechanical properties.
[0006] EP-A 776,762 describes a polyolefin tape or yarn based on a
co-extruded polyolefin material, having a stretch ratio of 6 to 10.
This material is described as being suitable for preparing all
kinds of cloths, strappings and the like.
[0007] Although the properties of the material according to the
above citations are quite good, especially with respect to tensile
strength, there is a need for further improvement. It is a first
object of the present invention to provide a tape or yarn having
improved mechanical properties.
[0008] In composite materials yarns and cloths are often used for
reinforcing. Most commonly used are glass fibre materials. However,
glass fibre materials have the disadvantage that they make it very
difficult to recycle the materials in which they are incorporated.
It would be very useful if the glass fibres could be replaced by
polymeric fibres or other polymeric reinforcement components,
thereby making it easier to recycle the composite materials. One of
the strong advantages of glass fibres reside in the stiffness
thereof, which is generally one of the weak aspects of polymeric
fibres or other reinforcement components. Accordingly, it is a
further object of the invention to provide polymeric materials that
have sufficient stiffness to be able to replace glass fibres in
composite materials.
[0009] With respect to recycling of the products produced from
polyolefin films, tapes and yarns it would be an advantage if all
components of the material could be classified as the same
material, such as polypropylene or polyethylene (including
copolymers thereof wherein propylene respectively ethylene forms
the majority of the monomeric units). The advantage thereof would
be that the resulting recycled material would still be one
material, instead of a blend of various components (no
contamination).
[0010] The present invention is directed to a monoaxially drawn
polyolefin multilayer film, tape or yarn of the AB or ABA type
having a stretch ratio of more than 12, having an E-modulus of at
least 10 GPa, substantially consisting of a central layer (B) of a
polyolefin selected from polyethylene and polypropylene, and one or
two other layers (A) of a polyolefin from the same class as the
material of the central layer B, the DSC melting point of the
material of the said other layers (A) being lower than the DSC
melting point of the material of the said central layer (B),
wherein the central layer (B) is between 50 and 99 wt. % of the
material and the other layers (A) between 1 and 50 wt. %.
[0011] Surprisingly it has been found that this multilayer material
(also referred to as laminate) has excellent properties with
respect to mechanical strength, stiffness and the like. Because of
its composition, it can be qualified as a mono-component material
being either polyethylene or polypropylene, which is an advantage
in recycling. More in particular it is possible to recycle
production scrap as part of the central layer component. Further,
in view of the requirements to manufacturers of consumer goods,
such as cars and the like, concerning the possibility of recycling
of the components after the useful life of the product, it is
important that components consist of one class of material
only.
[0012] The E-modulus as used herein is the value as measured by ISO
527.
[0013] By combining the material composition of the laminate
(film/tape/yarn) with the extremely high total stretch ratio, more
than 12, preferably more than 15, such as at least 20 and even up
to 50 or more, a material has been created that can be used
advantageously for all kinds of reinforcements, that can replace
e.g. glass fibres in various reinforcing applications and that can
be used in various higher temperature applications, such as
automotive or aerospace applications. In general, the material of
the invention especially suitable for (lightweight) construction
applications, high pressure applications and medical applications.
It is possible to apply the material in the construction of houses,
ships, cars, and the like, but also as reinforcement in high
pressure parts, such as tubes (for oil production and the like), or
in the production of or theses.
[0014] In the context of this invention, the material has been
defined as meeting a minimum level of the total stretch ratio
(TSR). TSR is defined as the degree of stretching from an isotropic
melt to the final tape or film. This is at least in part defined by
the difference in speed between the stretch rollers. The actual
value of the TSR can be determined from the birefringence and/or
the E-Modulus of the final film, tape or yarn (in stretching
direction). The TSR applies especially to the central layer, which
preferably is a highly crystalline material. The material of the
other layer will generally be less crystalline. The function of the
other layer is especially the provision of the possibility to weld
the films, tapes, fibres or yarns together when a woven, non-woven
or staple/stack of the material is heat treated.
[0015] The basic materials to be used in the production of the
film, tape or yarn according to the invention are polypropylene or
polyethylene.
[0016] In case of the use of polypropylene as the material for the
film, tape, yarn or fibre, the material for the central, or core,
layer B will preferably be a homopolypropylene, preferably having a
relatively high molecular weight, such as a weight average
molecular weight (MW) of at least 250 000 g/mol, as determined gel
permeation chromatography (GPC), and a melting temperature of at
least 160.degree. C. It is to be noted that the central layer
preferably consists of one material only, but that in case of
recycle of production scrap, minor amounts of the material of the
other layer may also be present in the core layer. This will
generally not exceed 10 wt. %.
[0017] In an embodiment wherein the core layer (B) is a
polypropylene, the material of the outer layers in this embodiment
is, as indicated above, also a polypropylene, preferably a
copolymer of propylene with ethylene or another .alpha.-olefin. An
important aspect thereof is that the softening point of the
material, generally indicated by the DSC melting point as defined
in ISO 11357-3 is lower than the softening point of the central
layer, the difference being at least 10.degree. C. The maximum
difference between softening points of the layer B and the layer(s)
A is not particularly critical. For practical reasons, the
difference will usually be less than about 70.degree. C. Very good
results have inter alia been achieved with a film, tape or yarn
wherein the difference in softening points is in the range of
15-40.degree. C.
[0018] Very good results have been achieved with a random
copolymer, such as a propylene-ethylene random copolymer, as the
outer layer(s) A. Instead of a copolymer or in combination
therewith, a polyolefin, preferably a polypropylene homopolymer or
polypropylene copolymer, prepared by making use of a metallocene
catalyst is used as the outer layer(s) A. Particular good results
have been achieved with such a metallocene based statistical
polymer. A suitable example of a metallocene is
rac-[Me2Si(2-Me-4-(1-Naphtyl)Ind)2]ZrCl2 H. (described in H.
Brintzinger, D. Fischer, R. Mulhaupt, B. Rieger, R. Waymouth,
Angew. Chem. 107 (1995) 1255 and in W. Kaminsky, Macromol. Chem.
Phys. 197 (1996) 3907).
[0019] As the product of the invention is generally used in a form
where the films, tapes or fibres are at angle to each other (woven,
non-woven materials), the outer layer makes it possible to heat
treat the woven, stacked or stapled material, thereby welding
together the individual films/fibres/yarns or tapes to create a
composite material (e.g. a woven material) of very high structural
integrity. By selecting the softening point at a sufficiently large
distance from the softening point of the central layer, it is
possible to have a heat treatment which does not impair the
properties of the material itself.
[0020] In an embodiment of the invention, the outer layer or layers
A at least consist of a ethylene propylene copolymer, having an
ethylene content of between 75 mol % and 99 mol % and a propylene
content of between 1 and 25 mol. %. Particular good results have
been achieved with such an outer layer or layers in an embodiment
wherein the central layer B is a polyethylene.
[0021] It is preferred to use a propylene ethylene copolymer,
having an ethylene content of between 1 and 25 mol. % and a
propylene content of between 75 mol % and 99 mol %, as the material
for the outer layers A, in particular if the central layer is a
polypropylene. Such a copolymer (as outer layer(s) A), in
particular such a random copolymer, has been found to adhere highly
satisfactorily to the central layer. Further a composite of tape,
yarn or film comprising such a copolymer has been found to have a
very good strength, impact resistance and abrasion resistance. It
is also possible to use blends of two of these materials.
[0022] In case of the use of polyethylene, basically the same
considerations apply. As the central layer an HDPE is preferably
used, i.e. a polyethylene having a density of at least 950
kg/m.sup.3. The weight average molecular weight (MW), as determined
by GPC, is preferably at least 250 000 g/mol and the melting point
is 130.degree. C. or higher. It is to be noted that the central
layer preferably consists of one material only, but that in case of
recycle of production scrap, minor amounts of the material of the
other layer may also be present in the core layer. This will
generally not exceed 10 wt. %.
[0023] The material of the other layer is characterised in that it
will also be a polyethylene, but now with a lower melting point,
the difference being at least 10.degree. C. Suitable polyethylenes
are random or block ethylene copolymers, LLDPE, LDPE, VLDPE and the
like.
[0024] For both types of layer materials it is to be noted that
they will generally contain conventional additives, including but
not limited to dyes and pigments, flame retarders, UV-stabilisers,
anti-oxidants, carbon black and the like.
[0025] In a less preferred option of the general approach to the
present invention, each of the outer layers at itself consists of
two or more separate layers. It is also possible that in the
three-layer configuration (ABA), the two outer layers have a
slightly different composition.
[0026] The major part of the product of the invention consists of
the central layer (B). In a preferred embodiment the amount of
central layer is between 50 and 99 wt. %, preferably between 60 and
90 wt. %. The balance of the material consist of the outer layers
(A).
[0027] In practice, the thickness of the tape, film or yarn will
generally be up to 300, preferably between 25 and 300 .mu.m. This
is governed by the original film thickness and the stretch ratio,
in this case the ratio of the speed of the stretch rollers. The
width of the tapes can vary over a wide range, such as from 25
.mu.m up to 50 cm or more. The width of the films can also vary
over a wide range, e.g. from 1 cm up to 150 cm or more.
[0028] As indicated above, the material of the invention has very
good mechanical properties. For example, the E-modulus will be at
least 10 GPa, preferably at least 12.5 GPa. The tensile strength
can easily be at least 0.25 GPa, even up to at least 0.4 GPa (value
as measured by ISO 527). The upper limit for the strength that can
be obtained in the materials of the present invention is about half
of the theoretical value. This means that for polypropylene a value
of 1 GPa and for polyethylene a value of 5 GPa will generally be
the upper limit.
[0029] A film, tape or yarn according to the invention can be used
to produce all kinds of materials, such as those discussed in the
introduction.
[0030] One of the preferred embodiments of the use of the film
according to the invention is the production of a reinforcing
material for example by winding or stapling/stacking, and/or
compacting it from the film. Preferably, the material is then heat
treated and pressed. By this heat treatment the individual films
are welded together. In this way the structural integrity of the
stapled/stacked material will be guaranteed. The said heat
treatment will be done at a temperature between the softening point
of the material of the outer layers (A) and the material of the
central layer (B). A surprising property of the heat treated
material is the improved abrasion resistance and the resistance
against delamination of the individual films.
[0031] During the heat treatment preferably a pressure is applied,
in particular if the heat treatment involves subjecting a
plate-like material or shaped article to a temperature at which the
material of the central layer (B) has a tendency to shrink (due to
disorientation of the polymer chains to a more random
configuration). For example, polypropylene tends to shrink at a
temperature above 100-115.degree. C. Preferably such a pressure is
at least 5 bar. Very good results with respect to mechanical
properties of the resulting materials have been obtained by
compacting the material at a pressure in the range of 20-70
bar.
[0032] Alternatively or in combination with applying a pressure,
the material may be clamped during heat treatment, in order to
avoid shrinking.
[0033] One of the preferred embodiments of the use of the tape or
yarn according to the invention is the production of a
(reinforcing) cloth for example by weaving, winding, chopping and
stapling, and/or compacting it from the tape, fibre or yarn.
Preferably, the material is then heat treated and pressed. By this
heat treatment the individual fibres are welded together. In this
way the structural integrity of the cloth will be guaranteed. The
said heat treatment will be done at a temperature between the
softening point of the material of the outer layers (A) and the
material of the central layer (B). A surprising property of the
heat treated material is the improved abrasion resistance and the
resistance against delamination of the individual fibres.
[0034] The production of the material of the invention will
generally be done by co-extruding the various layers. Generally
cast extrusion is used, whereby the extruder has a flat dye plate,
without profile. When a film is manufactured the material may be
stretched, after co-extrusion and cooling the material. In case a
tape or yarn is manufactured, the material will be slit into the
required width of the individual strands (after co-extrusion and
cooling), followed by stretching.
[0035] The stretching can be a single stage or a multi-stage
stretching. The stretch ratio in each step may be between 1.1 and
50--preferably in the range of 2 to 10, more preferably in the
range of 3 to 8--the total draw ratio being important for
determining the TSR, as defined herein. Very good results, with
respect to mechanical properties of the stretched tape, yarn or
film, have been achieved in a multi-stage stretching process
wherein the stretch ratio in the first stretching stage of the
tape, film or yarn is 4-5.
[0036] It is preferred to stretch the material at a temperature
between 20 and 250.degree. C. Preference is given to stretching at
a temperature below the DSC melting point of the material used for
the central layer B (herein after "cold stretching"). Very good
results have been achieved with a cold-stretching method wherein at
least one of the stretching stages are carried out at a temperature
below the DSC melting point of the outer layer, the temperature
being in the range of 25-75.degree. C., more preferably between 30
and 60.degree. C. In case of multi-stage stretching, the first
stretching is preferably carried out a relatively low temperature,
more in particular in the range of 30-60.degree. C., and the
subsequent stretching stage or stages are preferably carried at a
relatively high temperature, for example at a temperature between
60.degree. C. and the DSC melting point of the outer layer. Thus an
a high as possible stretch can be achieved. Good results have been
obtained with a subsequent stretching at a temperature of at least
100.degree. C. It is highly preferred to carry out the subsequent
stretching at a temperature at which the stretch ratio until
breakage (during the stretching process) is essentially maximised.
It has been found that a temperature relatively close to the
temperature at which the stretching is maximised, a film, tape or
yarn is produced with very good mechanical properties, such as a
very high E-modulus. The temperature at which the stretching is
maximised can routinely be determined by the skilled person.
[0037] Between two stretching steps an annealing step may be
included. This can also be done after the final stretching.
[0038] The material of the invention, both the individual films,
tapes, yarns/fibres or a cloth or stapled/stacked material prepared
thereof can suitably be used for incorporation in a matrix
material, for example as reinforcing material. Examples thereof are
various composite materials such as fibre reinforced plastics,
automotive applications such as bumpers, dashboards, engine covers
and the like, application in the aerospace industry, such as
construction materials for aeroplanes and the like. Other
applications have been discussed here above.
[0039] The invention is now elucidated on the basis of the
following examples, which are not to be construed as limiting the
invention.
EXAMPLE 1
[0040] Using a co-extrusion line, a film was prepared consisting of
a core layer B of polypropylene having a DSC softening temperature
of 152.degree. C. and two top layers A of a propylene random
copolymer having a DSC softening temperature of 135.degree. C.
(ABA-structure). The weight ratio A:B:A was 5:90:5.
[0041] The film was stretched at 55.degree. C. in a ratio of 1:5
followed by stretching at 128.degree. C. in a ratio of 1:3.4,
thereby producing a stretched film that had a stretch ratio of 1:17
and a thickness of 70 .mu.m.
[0042] The elasticity modulus of the stretched film was 15.8 GPa
and the strength was 585 MPa.
EXAMPLE 2
[0043] Some of the films of Example 1 were processed into yarns of
a width of 2.1 mm. The yarns were woven to produce a fabric
material (tissue material), which was subsequently heat treated at
150.degree. C. to consolidate the structure. The final material had
quasi isotropic stiffness of 7 GPa (determined by ASTM 3039-76) and
a tensile strength of more than 270 MPa. (determined by ISO
527).
EXAMPLE 3
[0044] Some of the films of Example 1 were stapled/stacked and
subsequently heat treated at 150.degree. C. to consolidate the
structure. The final material had quasi isotropic stiffness of 7
GPa and a tensile strength of more than 270 MPa.
EXAMPLE 4
[0045] A film was prepared as described in example 1 except for the
stretching stages being carried out at a temperature of 128.degree.
C. The material (having a stretch ratio of 1:14 and a thickness of
70 Elm) had an elasticity modulus of 11.5 GPa and a tensile
strength of 450 MPa.
* * * * *