U.S. patent application number 10/553572 was filed with the patent office on 2007-08-02 for metallocene produced polyethylene for fibres applications.
This patent application is currently assigned to ATOFINA RESEARCH. Invention is credited to Eric Maziers, Vincent Stephenne.
Application Number | 20070178303 10/553572 |
Document ID | / |
Family ID | 32892932 |
Filed Date | 2007-08-02 |
United States Patent
Application |
20070178303 |
Kind Code |
A1 |
Maziers; Eric ; et
al. |
August 2, 2007 |
Metallocene produced polyethylene for fibres applications
Abstract
The present invention provides monofilaments or stretched tapes,
unwoven or woven into raffia, prepared with metallocene-produced
polyethylene having long chain branches.
Inventors: |
Maziers; Eric; (Seneffe,
BE) ; Stephenne; Vincent; (Rixensart, BE) |
Correspondence
Address: |
FINA TECHNOLOGY INC
PO BOX 674412
HOUSTON
TX
77267-4412
US
|
Assignee: |
ATOFINA RESEARCH
Seneffe
BE
|
Family ID: |
32892932 |
Appl. No.: |
10/553572 |
Filed: |
April 7, 2004 |
PCT Filed: |
April 7, 2004 |
PCT NO: |
PCT/EP04/50479 |
371 Date: |
October 23, 2006 |
Current U.S.
Class: |
428/375 |
Current CPC
Class: |
D01F 6/04 20130101; D01D
5/426 20130101; Y10T 428/2933 20150115 |
Class at
Publication: |
428/375 |
International
Class: |
D02G 3/00 20060101
D02G003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 16, 2003 |
EP |
03076128.2 |
Claims
1-8. (canceled)
9. Monofilaments or stretched tapes, unwoven or woven into raffia
prepared from a metallocene-produced polyethylene resin having long
chain branches.
10. The monofilaments or stretched tapes of claim 9 wherein the
metallocene component is a tetrahydroindenyl.
11. The monofilaments or stretched tapes of claim 9 produced by the
steps comprising: (a) providing a metallocene-produced medium
density polyethylene resin having long chain branches; (b)
producing a film from the polyethylene resin of step (a); (c)
orienting the film obtained from step (b) by stretching; (d)
cutting the film of step (b) into strips; and (e) optionally,
annealing the stretched film.
12. The monofilaments or stretched tapes of claim 11 wherein the
stretching is carried out at a temperature from about 10 to about
70.degree. C. lower than the melting temperature of the resin.
13. The monofilaments or stretched tapes of claim 12 wherein the
stretched film is annealed at a temperature of from about 5 to
about 10.degree. C. lower than the stretching temperature.
14. The monofilaments or stretched tapes of claim 11 wherein the
stretching is performed by passing the film over a first and second
roller and the ratio of the roller's velocities is in the range of
from about 5 to about 7.
15. The monofilaments or stretched tapes of claim 14 wherein the
stretching is carried out at a temperature from about 10 to about
70.degree. C. lower than the melting temperature of the resin and
the stretched film is annealed at a temperature of from about 5 to
about 10.degree. C. lower than the stretching temperature.
16. A process for preparing stretched tapes that comprises the
steps of: (a) providing a metallocene-produced medium density
polyethylene resin having long chain branches; (b) producing a film
from the polyethylene resin of step (a); (c) orienting the film
obtained from step (b) by stretching; (d) cutting the film of step
(b) into strips; and (e) optionally, annealing the stretched
tapes.
17. The process of claim 16 wherein step (d) is performed before
step (c).
18. The process of claim 16 wherein step (c) is performed before
step (d).
19. The process of claim 16 wherein the stretching is carried out
at a temperature from about 10 to about 70.degree. C. lower than
the melting temperature of the resin.
20. The process of claim 19 wherein the stretching is carried out
at a temperature from about 15 to about 50.degree. C. lower than
the melting temperature of the resin.
21. The process of claim 16 wherein the stretching is performed by
passing the film over a first and second roller and wherein the
ratio of the roller's velocities is in the range of from about 5 to
about 7.
22. The process of claim 21 wherein the stretching is carried out
at a temperature from about 10 to about 70.degree. C. lower than
the melting temperature of the resin.
23. The process of claim 22 wherein the stretched film is annealed
at a temperature of from about 5 to about 10.degree. C. lower than
the stretching temperature.
24. The process of claim 23 wherein the annealing is carried out
while transferring the film from the second stretcher roller to a
third roller and wherein the velocity of the third roller is less
than that of the second roller.
25. The process of claim 23 wherein the stretching is carried out
at a temperature from about 15 to about 50.degree. C. lower than
the melting temperature of the resin.
26. The process of claim 19 wherein the film is annealed at a
temperature of from about 5 to about 10.degree. C. lower than the
stretching temperature.
27. The process of claim 16 wherein the metallocene-produced resin
is produced using a tetrahydroindenyl component.
Description
[0001] This invention relates to the field of monofilaments and
stretched tapes prepared with metallocene-produced
polyethylene.
[0002] Monofilaments are uniaxially oriented wire-like polymer
strands having a circular cross section. They are manufactured by
melt spinning process and their size ranges from 0.1 to 2.5 mm in
diameter, depending upon the end use application. Polyethylene,
polypropylene, nylon and polyesters are commonly used as raw
materials for making monofilaments.
[0003] Stretched tapes are prepared from a primary film produced
either by a blown or by a cast film process. The film can be cut
into tapes and then oriented or reversely, oriented and then cut
into tapes. The orientation is carried out by stretching the film
or tapes while passing through an air oven or on a hot plate at a
temperature below the melting point. The stretching is carried out
by passing the film or tapes over two sets of rollers placed
respectively before and after the air oven/hot plate and operating
at different speeds, the speed of the second set of rellers being
larger than that of the first set of rollers.
[0004] The polymer preferably used in the market for these
applications is a high density polyethylene (HDPE) prepared with a
Ziegler-Natta catalyst, said HDPE having a MI2 smaller than 1 g/10
min such as for example Solvay Eltex A4009MFN1325 resin or Basell
Hostalen GF 7740 F1, GF7740 F2, GF7740 F3, GF7750 M2 grades or the
polyethylene resins disclosed in GB-0023662. The molecular weight
distribution MWD of these resins is quite broad which means that
the resins may include very long as well as very short chains.
[0005] Semi-crystalline polyethylene (PE) and polypropylene (PP)
have also been used as materials for monofilaments stretched tapes
and raffia, such as disclosed for example in FR-A-2814761,
JP-2001342209 or JP-2001220405. Throughout this description, raffia
is defined as woven monofilaments or woven stretched tapes. The
stretched tapes and monofilaments prepared with polyethylene
exhibit a higher elongation at rupture, a greater flexibility and a
lower tendency to fibrillation than those prepared from
polypropylene. These properties are advantageous for example in the
production of woven tape fabrics. The products prepared from
polyethylene however suffer from the disadvantage their tenacity is
much lower than that of the products prepared from polypropylene.
Tenacity increases as a function of molecular weight, density,
degree of orientation of the chains/crystallites and increases with
narrowing of the molecular weight distribution. Impact strength
increases with decreasing density, increasing molecular weight and
decreasing molecular weight distribution.
[0006] There is thus a need for monofilaments or stretched tapes,
unwoven or woven into raffia having a better balance of
properties.
[0007] It is an object of the present invention to prepare
monofilament or stretched tape products having high tenacity.
[0008] It is another object of the present invention to prepare
monofilament or stretched tape-products having high impact
strength.
[0009] It is also an object of the present invention to prepare
monofilament or stretched tape products having high elongation at
rupture.
[0010] It is a further object of the present invention to prepare
monofilament or stretched tape products having a soft touch.
[0011] It is yet another object of the present invention to prepare
monofilament or stretched tape products having great
flexibility.
[0012] Accordingly the present invention provides monofilaments or
stretched tapes, unwoven or woven into raffia prepared from
metallocene-produced polyethylene (mPE) resin having long chain
branches.
[0013] The preferred metallocene catalyst component is based on a
terahydroindenyl component or on a constrained geometry component,
more preferably on a terahydroindenyl component.
[0014] The invention also provides a process for preparing raffia
or stretched tapes with a metallocene-produced polyethylene that
comprises the steps of [0015] a) providing a metallocene-produced
medium density polyethylene resin having long chain branches;
[0016] b) producing a film from the polyethylene resin of step a)
[0017] c) orienting the film obtained from step b) by stretching;
[0018] d) cutting the stretched film of step c) into strips.
[0019] Alternatively, the primary film can first be cut into strips
and then oriented by stretching.
[0020] The film can be either a blown film or a cast film. Film
production is easier with processed material having high melt
strength such as polyethylene having long chain branches and/or
very long linear chains. Metallocene catalyst systems based on
tetrahydroindenyl components or on constrained geometry components
are particularly useful for preparing polyethylene resins having
long branches.
[0021] In the production of blown films, the resins prepared with a
terahydroindenyl catalyst component provide a very stable bubble
thereby leading to films having a uniform thickness and presenting
no or very little creases. Uneven thickness and creases are points
of weakness when the film is cut into tapes and stretched.
[0022] In the production of cast films, the resins prepared with a
terahydroindenyl catalyst component have a stable elongational
viscosity leading to a stable and regular thickness.
[0023] It is further observed that resins having long branches keep
good mechanical properties, such as traction resistance and
tenacity, at densities smaller than those of linear resins having
equivalent mechanical properties. Working at low densities has the
advantage of providing material that has improved flexibility, low
fusion temperature and good processability.
[0024] Orientation of the primary film or of the cut tapes is
carried out by stretching while passing through an air oven or over
a hot plate, maintained at a temperature below the melting
temperature. Stretching of the primary film or of the cut tapes is
done by passing said film or tapes over two sets of rollers (goddet
rollers) placed respectively before and after the air oven/hot
plate, and operating at different speeds. The stretch ratio S2/S1
is defined by the ratio of the speed of roller 2, S2 to the speed
of roller 1, S1 wherein S2 is larger than S1.
[0025] Stretching at such high temperature results in
chain/crystals orientation with a simultaneous increase of
crystallinity. These structural changes lead to an increase of
tensile strength and concurrently to a reduction of elongation. The
tensile strength increases with increasing stretch ratio and with
increasing stretching temperature. It is preferred that the
stretching-temperature is as close as possible to but smaller than
the melting temperature. For high density polyethylene, typical
values for the stretch ratio are of from 5.0 to 7.0. The typical
stretching temperatures depend upon the melting temperature of the
polyethylene resins: they must be lower than but as close as
possible to the melting temperature. Typically, they are from 5 to
70.degree. C. lower than the melting temperature of the resin,
preferably they are from 10 to 50.degree. C. lower than the melting
temperature of the resin.
[0026] Preferably, the drawn tapes are annealed immediately after
the stretching operation in order to minimise shrinkage that could
occur as a result of residual stresses in the oriented tapes.
Annealing is done by heating the stretched tapes while they are
being transferred from the second goddet rollers onto a third
roller having a speed S3 that is smaller than the speed of roller
2, S2. Preferably, speed S3 is about 95% of speed S2. The annealing
ratio AR is defined as (S2-S3)/S2) at a temperature slightly
inferior to the stretching temperature. Typically, the annealing
temperature is from 5 to 10.degree. C. lower than the stretching
temperature.
[0027] Polymers that do not include either very long linear chains
or long chain branched molecules have a better stretchability. For
example, the low density polyethylene (LDPE) having long chain
branches cannot be stretched beyond a certain degree, whereas the
purely linear polyethylene chains usually obtained with a
Ziegler-Natta catalyst have a high degree of stretchability.
[0028] The metallocene used to prepare the high density
polyethylene can be a bis-indenyl represented by the general
formula: R''(Ind).sub.2MQ.sub.2 (I) or a bis-cyclopentadienyll
represented by the formula R''(Cp).sub.2MQ.sub.2 (II) or a
constrained geometry component of formula R''(Cp)(NR')MQ.sub.2
(III) wherein (Ind) is an indenyl or an hydrogenated indenyl,
substituted or unsubstituted, Cp is a cyclopentadienyl ring
substituted or unsubstituted, R' is hydrogen or a hydrocarbyl
having from 1 to 20 carbon atoms, R'' is a structural bridge
between the two indenyls to impart stereorigidity that comprises a
C.sub.1-C.sub.4 alkylene radical, a dialkyl germanium or silicon or
siloxane, or a alkyl phosphine or amine radical, which bridge is
substituted or unsubstituted; Q is a hydrocarbyl radical having
from 1 to 20 carbon atoms or a halogen, and M is a group IVb
transition metal or Vanadium.
[0029] In formula (I), each indenyl or hydrogenated indenyl
compound may be substituted in the same way or differently from one
another at one or more positions in the cyclopentadienyl ring, the
cyclohexenyl ring and the bridge.
[0030] In formula (I), each substituent on the indenyl may be
independently chosen from those of formula XR.sub.v in which X is
chosen from group IVA, oxygen and nitrogen and each R is the same
or different and chosen from hydrogen or hydrocarbyl of from 1 to
20 carbon atoms and v+1 is the valence of X. X is preferably C. If
the cyclopentadienyl ring is substituted, its substituent groups
must be so bulky as to affect coordination of the olefin monomer to
the metal M. Substituents on the cyclopentadienyl ring preferably
have R as hydrogen or CH.sub.3. More preferably, at least one and
most preferably both cyclopentadienyl rings are unsubstituted.
[0031] In a preferred embodiment, both indenyls are unsubstituted
and the most preferred catalyst component is a
tetrahydroindenyl.
[0032] In formula (II), each cyclopentadienyl ring may be
substituted in the same way or differently from one another at one
or more positions in the cyclopentadienyl ring.
[0033] In formula (II), each substituent on the cyclopentadienyl
may be independently chosen from those of formula XR*.sub.v in
which X is chosen from group IVA, oxygen and nitrogen and each R*
is the same or different and chosen from hydrogen or hydrocarbyl of
from 1 to 20 carbon atoms and v+1 is the valence of X. X is
preferably C and the most preferred substituent is n-butyl.
[0034] R'' is preferably a C1-C4 alkylene radical (as used herein
to describe a difunctional radical, also called alkylidene), most
preferably an ethylene bridge (as used herein to describe a
difunctional radical, also called ethylidene), which is substituted
or unsubstituted.
[0035] The metal M is preferably zirconium, hafnium, or titanium,
most preferably zirconium.
[0036] Each Q is the same or different and may be a hydrocarbyl or
hydrocarboxy radical having 1 to 20 carbon atoms or a halogen.
Suitable hydrocarbyls include aryl, alkyl, alkenyl, alkylaryl or
arylalkyl. Each Q is preferably halogen.
[0037] Among the preferred metallocenes used in the present
invention, one can cite bis tetrahydro-indenyl compounds and bis
indenyl compounds as disclosed for example in WO 96/35729 or
bis(cyclopentadienyl) compounds. The most preferred metallocene
catalyst is isopropylidene-bis(4,5,6,7-tetrahydro-1-indenyl)
zirconium dichloride.
[0038] The metallocene may be supported according to any method
known in the art. In the event it is supported, the support used in
the present invention can be any organic or inorganic solids,
particularly porous supports such as talc, inorganic oxides, and
resinous support material such as polyolefin. Preferably, the
support material is an inorganic oxide in its finely divided
form.
[0039] The addition on the support, of an agent that reacts with
the support and has an ionising action, creates an active site.
[0040] Preferably, alumoxane is used to ionise the catalyst during
the polymerization procedure, and any alumoxane known in the art is
suitable.
[0041] The preferred alumoxanes comprise oligomeric linear and/or
cyclic alkyl alumoxanes represented by the formula: ##STR1## for
oligomeric, linear alumoxanes And ##STR2## for oligomeric, cyclic
alumoxanes, wherein n is 1-40, preferably 10-20, m is 3-40,
preferably 3-20 and R is a C.sub.1-C.sub.8 alkyl group and
preferably methyl. Methylalumoxane is preferably used.
[0042] One or more aluminiumalkyl(s) can be used as cocatalyst in
the reactor. The aluminiumalkyl is represented by the formula
AlR.sub.x can be used wherein each R is the same or different and
is selected from halides or from alkoxy or alkyl groups having from
1 to 12 carbon atoms and x is from 1 to 3. Especially suitable
aluminiumalkyl are trialkylaluminium, the most preferred being
triisobutylaluminium (TIBAL).
[0043] Further, the catalyst may be prepolymerised prior to
introducing it in the reaction zone and/or prior to the
stabilization of the reaction conditions in the reactor.
[0044] The polyethylene resin of the present invention has a
density ranging from 0.925 to 0.950 g/cm.sup.3, preferably, from
0.930 to 0.940 g/cm.sup.3 and most preferably about 0.935
g/cm.sup.3. The melt index MI2 is within the range 0.1 to 5 g/10
min, preferably in the range 0.2 to 1.5 g/10 min.
[0045] The density is measured following the method of standard
test ASTM D 1505 at 23.degree. C. and the melt index MI2 is
measured following the method of standard test ASTM D 1238 at
190.degree. C. and under a load of 2.16 kg.
[0046] The metallocene-prepared polyethylenes produce very strong
stretched tapes and raffia products, mainly because of their narrow
molecular weight distribution and because they have long chain
branches. The final products have improved tensile and elongation
properties and simulteneously they have improved flexibility and
processing properties.
EXAMPLE
[0047] Several resins have been tested for preparing raffia
products.
[0048] Resin R1 is a medium density polyethylene resin prepared
with isopropylidene (tetrahydroindenyl) zirconium dichloride. It
had a density of 0.934 g/cm.sup.3 and a melt index MI2 of 0.9 g/10
min. It was additivated as follows: [0049] 94.5 wt % of resin R1;
[0050] 4% red masterbatch PE 44930 from Clariant; [0051] 1% polymer
processing aid AMF 702 from Schuman; [0052] 0.5% antibloc
masterbatch B1981 from Clariant.
[0053] Resin R2 was a commercial resin prepared with a
Ziegler-Natta catalyst system: (GF7740 F1 from Hostalen). It had a
density of 0.946 g/cm.sup.3 and a melt index MI2 of 0.5 g/10
min.
[0054] These two resins were treated under the same conditions for
blown film production, and for stretching. [0055] Melt die
temperature: 220.degree. C. [0056] Thickness of primary film: 60
microns; [0057] Orientation temperature: varied progressively from
80 to 120.degree. C. [0058] Stretch ratio: 7:1
[0059] The final products, whether unwoven or woven (nets) obtained
from the metallocene-produced resin R1 had a high tenacity, an
excellent elongation at rupture and a very high break strength. It
also had a soft touch and a high flexibility.
[0060] The properties of the stretched tapes obtained from resins
R1 and R2 are summarised in Table I. TABLE-US-00001 TABLE I R1 R2
Tenacity at rupture cN/Tex 24.9 22.1 Elongation at rupture % 33.2
29.3 Strength at rupture cN 593 525 Titre Tex 23.8 20.8
[0061] The elongation, the strength and the tenacity at rupture of
the stretched tapes have been measured following the method of
standard test ISO-2062 (1993).
[0062] The titre is measured in tex or g/km: this is a measure of
the linear mass of a filament or fibre.
[0063] The properties of the woven stretched tapes or raffia are
displayed in Table II. TABLE-US-00002 TABLE II R1 R2 Elongation at
rupture % 30.6 29.4 Strength at rupture cN 997 811
[0064] The raffia products prepared according to the present
invention has thus improved properties with respect to those of the
prior art.
[0065] The elongation and strength at rupture of the raffia have
been measured following the method of standard test ISO-5081
(1977).
* * * * *