Note: Descriptions are shown in the official language in which they were submitted.
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Transparent polypropylene containers for packaging shoes
The present invention relates to the use of containers made of transparent
polypropylene for
packaging or storing articles from the area of clothing, sports articles, toys
or home worker articles
and in particular shoes, specifically transparent polypropylene containers
suitable for packaging
shoes and also systems comprising containers made of a transparent polymer
which are suitable
for packaging or storing articles from the area of clothing, sports articles
or toys.
Two part cardboard boxes consisting of a box and a lid are frequently used for
packaging articles
from the area of clothing, sports articles or toys and in particular for
packaging shoes. A
disadvantage of this type of packaging is its often unsatisfactory mechanical
stability, particularly
when many such cardboard boxes are stacked on top of one another, as is
customary in many
shoe shops. Furthermore, it is not unusual for the packaging and especially
the lid to be damaged
when lower boxes are pulled out from a stack of cardboard boxes, since the lid
is frequently
grasped for pulling out the box.
A further disadvantage of cardboard packaging is that the contents of the box
cannot be seen.
This means that it is either necessary to take the goods from the cardboard
box to enable them to
be displayed in a shop or the customers and the sales staff can obtain
information on the contents
only from inscriptions on the outside of the cardboard box. This is also
disadvantageous in places
where shoes regularly have to be taken from the cardboard boxes and then put
back in, since
incorrectly positioned shoes are not easy to find and when errors are
discovered, it is a
complicated procedure to restore the original order.
25' A further disadvantage of such cardboard packaging is its low reuse value.
Such packaging is
thus essentially disposable packaging which has to be disposed of either by
the purchaser or by
the vendor of the articles, which is associated with considerable costs.
Reusable packaging, in particular for shoes, made of plastic is known, for
example, from
EP-A 659 649. The containers disclosed there have a foldable frame and side
sections made of a
flexible material which can be folded together.
Shoe boxes made of a transparent or translucent plastic are described in WO
86/07576.
However, the plastics from which the shoe boxes can be produced particularly
advantageously
are not disclosed.
Polypropylenes constitute a class of plastics which is frequently well-suited
to packaging
applications. These generally have advantageous mechanical properties such as
satisfactory
hardness, stiffness and dimensional stability. They are also economically
advantageous.
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However, the toughness, in particular at low temperatures, the stress
whitening behavior, the
distortion and especially the transparency frequently leaves something to be
desired.
It is an object of the present invention to overcome the abovementioned
disadvantages of the
prior art and to find containers which are suitable for packaging articles
from the area of clothing,
sports articles or toys and have good mechanical properties, enable the
packaging to be handled
easily and can be produced economically and with low distortion.
We have found that this object is achieved by the use of containers comprising
transparent
polypropylene for packaging or storing articles from the area of clothing,
sports articles, toys or
home worker articles, with the containers having wall thicknesses of at least
0.8 mm, wherein the
transparent polypropylene is a propylene homopolymer or propylene copolymer
which has a haze
value of <_40%, based on a thickness of the polypropylene of 1 mm and measured
on injection-
molded test specimens, and has a tensile modulus of >_700 MPa and a Charpy
notched impact
strength at 0°C of >_3 kJ/mz.
Furthermore, we have found containers comprising transparent polypropylene
which are suitable
for packaging purposes and also systems comprising containers comprising a
transparent
polymer which are suitable for packaging or storing articles from the area of
clothing, sports
articles, toys or home worker articles.
According to the present invention, a transparent polypropylene is used for
producing the
containers. For the present purposes, the term polypropylene refers to a
polymer produced from
monomers comprising at least 50% by weight of propylene. Possible comonomers
are, in
particular, a-olefins, i.e. hydrocarbons having terminal double bonds.
Preferred a-olefins are
linear or branched CZ-CZO-1-alkenes other than propylene, in particular linear
Cz-C,o-1-alkenes or
branched C2-Coo-1-alkenes such as 4-methyl-1-pentene, conjugated and
nonconjugated dienes
such as 1,3-butadiene, 1,4-hexadiene or 1,7-octadiene or vinylaromatic
compounds such as
styrene or substituted styrene. Further suitable olefins are ones in which the
double bond is part
of a cyclic structure which may comprise one or more ring systems. Examples
are cyclopentene,
norbornene, tetracyclododecene and methylnorbornene and dienes such as 5-
ethylidene-2-
norbornene, norbornadiene or ethylnorbornadiene. It is also possible for
mixtures of two or more
olefins to be copolymerized with propylene. Particularly preferred olefins are
ethylene and linear
C4-C,o-1-alkenes such as 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-
decene and in
particular ethylene and/or 1-butene.
The transparent polypropylene used according to the present invention for
producing the
containers has a haze value, based on a thickness of the polypropylene of 1 mm
and measured
on injection-molded test specimens in accordance with the standard ASTM D
1003, of <_40%,
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preferably __<25%, particularly preferably <_15% and very particularly
preferably <_12%. The haze
value is a measure of the opacity of the material and is thus a parameter
which characterizes the
transparency of the material. The lower the haze value, the higher the
transparency.
The transparent polypropylene also has an advantageous combination of
stiffness and
toughness. The tensile modulus of the transparent polypropylene is >_700 MPa
and preferably
>_800 MPa, measured in accordance with ISO 527-2:1993. To determine the
tensile modulus,
preference is given to injection molding a test specimen of type 1 having a
total length of 150 mm
and a parallel section of 80 mm at a melt temperature of 250°C and a
tool surface temperature of
30°C. To allow further crystallization to occur, the test specimen is
then stored for 7 days under
standard conditions of 23°C/50% atmospheric humidity. The strain rate
in the determination of the
modulus should be 1 mm/min. The toughness of the transparent polypropylene,
determined as
the Charpy notched impact strength at 0°C, is >_3 kJ/m2, preferably >_4
kJ/m2 and particularly
preferably >_6 kJ/m2. The Charpy notched impact strength is measured in
accordance with the .
standard ISO 179-2/1 eU.
The transparent polypropylene also displays good stress whitening behavior.
For the present
purposes, stress whitening is the occurrence of whitish discoloration in the
stressed region when
the polymer is subjected to mechanical stress. It is generally believed that
the whitening is caused
by small voids being formed in the polymer under mechanical stress. Good
stress whitening
behavior means that no or only very small regions of whitish discoloration
occur under mechanical
stress.
One method of quantifying stress whitening behavior is to subject defined test
specimens to a
defined impact stress and then to measure the size of the resulting white
spots. Accordingly, the
dome indenter method involves allowing a falling dart to drop onto a test
specimen using a falling
dart apparatus in accordance with DIN 53443 part 1. A falling dart having a
mass of 250 g and an
impact head diameter of 5 mm is used here. The dome radius is 25 mm and the
height from which
the dart is dropped is 50 cm. Injection-molded round disks having a diameter
of 60 mm and a
thickness of 2 mm are used as test specimens, and each test specimen is
subjected to only one
impact test. The stress whitening is reported in mm as the diameter of the
visible stress whitening
mark, and the value reported is the mean of in each case 5 test specimens,
with the individual
values being determined on the side of the round disk opposite the side on
which impact occurs
as a mean of the two values in the flow direction on injection molding and
perpendicularly thereto.
The transparent polypropylene displays no or only very little stress whitening
at 23°C, determined
by the dome indenter method. In the case of preferred transparent
polypropylenes, a value of
from 0 to 8 mm, preferably from 0 to 5 mm and in particular from 0 to 2.5 mm,
is determined at
23°C using the dome indenter method.
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Suitable transparent polypropylenes are homopolymers of propylene or
preferably copolymers of
propylene obtained using catalyst systems based on metallocene compounds.
Suitable transparent polypropylenes can also be heterophase propylene
copolymers, also known
as multiphase propylene copolymers or as propylene block copolymers. Such
compositions
usually have demixed phases, generally with a polyolefin having a relatively
low stiffness being
dispersed in the matrix of a propylene polymer having a higher stiffness.
Heterophase propylene copolymers suitable as transparent polypropylenes are,
for example,
ones comprising a copolymer of ethylene and 1-butene as soft phase.
Particularly useful heterophase propylene copolymers are copolymers comprising
a propylene
polymer A forming the matrix and a propylene copolymer B dispersed therein,
with the
heterophase propylene copolymers having been prepared using catalyst systems
based on
metallocene compounds.
The propylene polymer A can be a propylene homopolymer or a copolymer of
propylene with up
to 15% by weight and preferably up to 10% by weight of olefins other than
propylene, with
preferred propylene copolymers containing from 1.5 to 7% by weight, in
particular from 2.5 to 5%
by weight, of olefins other than propylene. As comonomer, preference is given
to using ethylene
or linear C4-Coo-1-alkenes or mixtures thereof, in particular ethylene and/or
1-butene.
The propylene copolymers B usually contain from 5 to 40% by weight of olefins
other than
propylene. It is also possible for two or more different propylene copolymers
which may differ both
in respect of the comonomer content and in respect of the type of the olefins)
other than
propylene to be used as component B. Preferred comonomers are ethylene and
linear C4-Coo-1-
alkenes or mixtures thereof, in particular ethylene and/or 1-butene. In a
further preferred
embodiment, monomers containing at least two double bonds, e.g. 1,7-octadiene
or
1,9-decadiene, are additionally employed. The content of olefins other than
propylene in the
propylene copolymers is generally from 7 to 25% by weight, preferably from 10
to 20% by weight,
particularly preferably from 12 to 18% by weight and in particular from 14% by
weight to 17% by
weight, based on the propylene copolymer B.
The weight ratio of propylene polymer A to propylene copolymer B can vary. It
is preferably from
90:10 to 60:40, particularly preferably from 80:20 to 60:40 and very
particularly preferably from
70:30 to 60:40, with propylene copolymers B being able to be all propylene
copolymers forming
the component B.
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Such a preferred transparent polypropylene preferably has a narrow molar mass
distribution
MH,/M~. For the purposes of the invention, the molar mass distribution MW/M"
is the ratio of the
weight average molar mass MW and the number average molar mass M~. The molar
mass
distribution MW/M~ is preferably in the range from 1.5 to 3.5, particularly
preferably in the range
5 from 1.8 to 2.5 and in particular in the range from 2 to 2.3.
The average molar mass M" of such.a preferred transparent.polypropylene is
preferably in the
range from 20 000 glmol to 500 000 g/mol, particularly preferably in the range
from 50 000 g/mol
to 200 000 g/mol and very particularly preferably in the range from 80 000
g/mol to 150 000 g/mol.
To prepare such a preferred transparent polypropylenes, preference is given to
using catalyst
systems based on metallocene compounds of transition metals of group 3, 4, 5
or 6 of the
Periodic Table of the Elements.
Particular preference is given to catalyst systems based on metallocene
compounds having the
formula (I),
L M (I)
~X
**
T, ~ Rz
where
M is zirconium, hafnium or titanium, preferably zirconium,
X are identical or different and are each, independently of one another,
hydrogen or
halogen or an -R, -OR, -OSOzCF3, -OCOR, -SR, -NRz or -PRz group, where R is
linear or branched C,-Czo-alkyl, C3-Czo-cycloalkyl which may bear one or more
C,-C,o-
alkyl radicals as substituents, C6-Czo-aryl, C~-Czo-alkylaryl or C~-Czo-
arylalkyl and may
contain one or more hetero atoms of groups 13-17 of the Periodic Table of the
Elements
or one or more unsaturated bonds and is preferably C~-C,o-alkyl such as
methyl, ethyl,
n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tent-butyl, n-pentyl, n-
hexyl, n-heptyl or
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n-octyl or C3-Czo-cycloalkyl such as cyclopentyl or cyclohexyl, where the
radicals X may
also be joined to one another and preferably form a C4-C4o-dienyl ligand, in
particular a
1,3-dienyl ligand, or an -OR'O-, group in which the substituent R' is a
divalent group
selected from the group consisting of C,-C4o-alkylidene, C6-C4o-arylidene, C~-
C4o-
alkylarylidene and C~-C4o-arylalkylidene,
where X is preferably a halogen atom or an -R or -OR group or the two radicals
X form
an -OR'O- group and X is particularly preferably chlorine or methyl,
is a divalent bridging group selected from the group consisting of C,-CZO-
alkylidene,
C3-CZO-cycloalkylidene, C6-CZO-arylidene, C,-CZO-alkylarylidene and C,-Czo-
arylalkylidene
radicals which may contain hetero atoms of groups 13-17 of the Periodic Table
of the
Elements, or is a silylidene group having up to 5 silicon atoms, e.g. -SiMez-
or -SiPhz-,
where L is preferably a radical selected from the group consisting of -SiMez-,
-SiPh2-,
-SiPhMe-, -SiMe(SiMe3)-, -CHz-, -(CHZ)z-, -(CHz)3- and -C(CH3)2,
R' is linear or branched C,-Czo-alkyl, C3-CZO-cycloalkyl, which may bear one
or more
C,-C,o-alkyl radicals as substituents, Cs-CZo-aryl, C~-CZO-alkylaryl or C~-CZO-
arylalkyl and
may contain one or more hetero atoms of groups 13-17 of the Periodic Table of
the
Elements or one or more unsaturated bonds, where R' is preferably unbranched
in the a
position and is preferably a linear or branched C,-C,o-alkyl group which is
unbranched in
the a position, in particular a linear C,-C4-alkyl group such as methyl,
ethyl, n-propyl or
n-butyl,
R2 is a group of the formula -C(R3)ZR', where
R3 are identical or different and are each, independently of one another,
linear or branched
C,-Czo-alkyl, C3-C2o-cycloalkyl which may bear one or more C,-C,o-alkyl
radicals as
substituents, C6-Czo-aryl, C~-Czo-alkylaryl or C~-CZO-arylalkyl and may
contain one or
more hetero atoms of groups 13-17 of the Periodic Table of the Elements or one
or
more unsaturated bonds, or two radicals R3 may be joined to form a saturated
or
unsaturated C3-CZO ring,
where R3 is preferably a linear or branched C,-C,o-alkyl group, and
R4 is hydrogen or linear or branched C,-CZO-alkyl, C3-Czo-cycloalkyl which may
bear one or
more C,-C,o-alkyl radicals as substituents, C6-Czo-aryl, C~-CZO-alkylaryl or
C~-CZO-
arylalkyl and may contain one or more hetero atoms of groups 13-17 of the
Periodic
Table of the Elements or one or more unsaturated bonds,
where R4 is preferably hydrogen,
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T and T' are divalent groups of the formulae (II), (III), (IV), (V) or (VI),
Rs Rs Rs Rs Rs Rs
~S ** ** Rs ~ Rs ** Rs
Rs ~ Rs \ ** s Rs
* ~N / ~ R Rs
Rs ~ Rs * * s
s * R
R Rs Rs Rs Rs Rs Rs Rs
(1l) (Ill) (IV) (v) (v1)
where
the atoms denoted by the symbols * and ** are in each case bound to the atoms
of the compound
of the formula (I) which are denoted by the same symbol, and
Rs are identical or different and are each, independently of one another,
hydrogen or
halogen or linear or branched C,-CZO-alkyl, C3-Czo-cycloalkyl which may bear
one or
more C,-C,o-alkyl radicals as substituents, Cs-CZO-aryl, C~-CZO-alkylaryl or
C,-CZO-
arylalkyl and may contain one or more hetero atoms of groups 13-17 of the
Periodic
Table of the Elements or one or more unsaturated bonds,
where Rs is preferably hydrogen or a linear or branched C,-C,o-alkyl group, in
particular
a linear C,-C4-alkyl group such as methyl, ethyl, n-propyl or n-butyl, and
Rs are identical or different and are each, independently of one another,
halogen or linear
or branched C,-CZO-alkyl, C3-CZO-cycloalkyl which may bear one or more C,-C,o-
alkyl
radical as substituents, Cs-C2o-aryl, C~-C2o-alkylaryl or C~-CZO-arylalkyl and
may contain
one or more hetero atoms of groups 13-17 of the Periodic Table of the Elements
or one
or more unsaturated bonds,
where Rs is preferably an aryl group of the formula (VII),
R' R'
(VII)
R' ~ R'
R8
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where
R' are identical or different and are each, independently of one another,
hydrogen or
halogen or linear or branched C,-Czo-alkyl, C3-Czo-cycloalkyl which may bear
one or
more C~-C,o-alkyl radicals as substituents, Cs-CZO-aryl, C~-CZO-alkylaryl or
C~-Czo-
arylalkyl and may contain one or more hetero atoms of groups 13-17 of the
Periodic
Table of the Elements or one or more unsaturated bonds, or two radicals R' may
be
joined to form a saturated or unsaturated C3-C2o ring,
where R' is preferably a hydrogen atom, and
R8 is hydrogen or halogen or linear or branched C,-CZO-alkyl, C3-CZO-
cycloalkyl which may
bear one or more C,-C,o-alkyl radicals as substituents, Cs-Czo-aryl, C~-C2o-
alkylaryl or
C~-CZO-arylalkyl and may contain one or more hetero atoms of groups 13-17 or
the
Periodic Table of the Elements or one or more unsaturated bonds,
where Rg is preferably a branched alkyl group of the formula -C(R9)3, where
R9 are identical or different and are each, independently of one another, a
linear or
branched C,-C6-alkyl group or two or three radicals R9 are joined to form one
or more
ring systems.
Preference is given to at least one of the groups T and T being substituted by
a radical R6 of the
formula (VII), and particular preference is given to both groups being
substituted by such a
radical. Very particular preference is given to at least one of the groups T
and T being a group of
the formula (IV) which is substituted by a radical R6 of the formula (VII) and
the other having either
the formula (II) or (IV) and likewise being substituted by a radical R6 of the
formula (VII).
Very particular preference is given to catalyst systems based on metallocene
compounds of the
formula (VIII),
35
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Rs
Rs
R
Rs
(VIII)
\X
R2
R
Particularly useful metallocene compounds and processes for preparing them are
described, for
example, in WO 01/48034 and the international patent application No.
PCT/EP02/13552.
It is also possible to use mixtures of various metallocene compounds or
mixtures of various
catalyst systems. However, preference is given to using only one catalyst
system comprising one
metallocene compound, with this being used for the polymerization of the
propylene polymer A
and the propylene copolymer B.
Examples of suitable metallocene compounds are
dimethylsilanediyl-(2-ethyl-4-(4'-tert-butylphenyl)indenyl)-(2-isopropyl-4-(4'-
tert-butylphenyl)-
indenyl)zirconium dichloride,
dimethylsilanediyl-(2-methyl-4-(4'-tert-butylphenyl)indenyl)-2-isopropyl 4-(1-
naphthyl)indenyl)-
zirconium dichloride,
dimethylsilanediyl-(2-methyl-4-phenyl)-1-indenyl)-(2-isopropyl-4-(4'-tert-
butylphenyl)-1-indenyl)-
zirconium dichloride,
dimethylsilanediyl-(2-methylthiapentenyl)-(2-isopropyl-4-(4'-tert-
butylphenyl)indenyl)zirconium
dichloride,
dimethylsilanediyl-(2-isopropyl-4-(4'-tert-butylphenyl)indenyl)-(2-methyl-4,5-
benzindenyl)zirconium
dichloride,
dimethylsilanediyl-(2-methyl-4-(4'-tert-butylphenyl)indenyl)-(2-isopropyl-4-
(4'-tert-butylphenyl)
indenyl)zirconium dichloride,
dimethylsilanediyl-(2-methyl-4-(4'-tert-butylphenyl)indenyl)-(2-isopropyl-4-
phenylindenyl)zirconium
dichloride,
dimethylsilanediyl-(2-ethyl-4-(4'-tert-butylphenyl)indenyl)-(2-isopropyl-4-
phenyl)indenyl)zirconium
dichloride or
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dimethylsilanediyl-(2-isopropyl-4-(4'-tert-butylphenyl)indenyl)-(2-methyl-4-(1-
naphthyl)indenyl)-
zirconium dichloride
or mixtures thereof.
5 In addition, the preferred catalyst systems based on metallocene compounds
generally further
comprise compounds capable of forming metallocenium ions as cocatalysts.
Suitable cocatalysts
include strong, uncharged Lewis acids, ionic compounds having Lewis-acid
cations and ionic
compounds containing Bronsted acids as cation. Examples are
tris(pentafluorophenyl)borane,
tetrakis(pentafluorophenyl)borate and salts of N,N-dimethylanilinium. Further
compounds which
10 are suitable as compounds capable of forming metallocenium ions and thus as
cocatalysts are
open-chain or cyclic aluminoxane compounds. These are usually prepared by
reacting
trialkylaluminum with water and are generally present as mixtures of both
linear and cyclic chain
molecules of various lengths or cage molecules of various sizes. The preferred
catalyst systems
based on metallocene compounds are usually employed in supported form.
Suitable supports are,
for example, porous organic or inorganic inert solids such as finely divided
polymer powders or
inorganic oxides, for example silica gel. The metallocene catalyst systems may
further comprise
organometallic compounds of the metals of groups 1, 2 and 13 of the Periodic
Table, e.g.
n-butyllithium or aluminum alkyls.
In the preparation of the particulary preferred heterophase compositions,
preference is given to
firstly polymerizing the propylene polymer A in a first stage by polymerizing,
based on the total
weight of the mixture, from 90% by weight to 100% by weight of propylene, if
desired in the
presence of further olefins, usually at from 40°C to 120°C and
pressures in the range from 0.5 bar
to 200 bar. In a second stage, a mixture of from 2 to 95% by weight of
propylene and from 5% to
98% by weight of further olefins is subsequently polymerized onto the polymer
obtainable by the
reaction of the first stage, usually at from 40°C to 120°C and
pressures in the range from 0.5 bar
to 200 bar. The polymerization of the propylene polymer A is preferably
carried out at from 60 to
80°C, particularly preferably from 65 to 75°C, and a pressure of
from 5 to 100 bar, particularly
preferably from 10 bar to 50 bar. The polymerization of the propylene
copolymer B is preferably
carried out at from 60 to 80°C, particularly preferably from 65 to
75°C, and a pressure of from 5 to
100 bar, particularly preferably from 10 bar to 50 bar.
Customary additives, for example molar mass regulators such as hydrogen or
inert gases such as
nitrogen or argon, can also be used in the polymerization.
The composition of the propylene copolymers B of such preferred transparent
polypropylenes
prepared using catalyst systems based on metallocene compounds is preferably
uniform. They
comprise little comonomer incorporated in blocks. The expression "incorporated
in blocks" is used
to mean that two or more comonomer units follow one another directly. In
preferred propylene
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11
copolymers B obtained from propylene and ethylene, the structure can be
determined by
'3C-NMR spectroscopy. Evaluation of the spectra is prior art and can be
carried out by a person
skilled in the art using, for example, the method of H.N. Cheng,
Macromolecules 17 (1984),
pp. 1950-1955, or L. Abis et al., Makromol. Chemie 187 (1986), pp. 1877-1886.
The structure can
then be described by the proportions of "PEX' and of "PEP", where PEx refers
to propylene-
ethylene units having ?2 successive ethylene units and PEP refers to propylene-
ethylene units
having an isolated ethylene unit between two propylene units. Preferred
propylene copolymer
compositions obtained from propylene and ethylene have a PEP/PEx ratio in the
range from 0.75
to >_1, preferably the range from 0.85 to >_1.4 and particularly preferably in
the range from 0.85
to 1.2 and in particular in the range from 0.9 to 1.1.
In the case of the preferred use of ethylene as comonomer, particular
preference is given to an
ethylene content of the propylene copolymers B of from 10 bis 20% by weight,
in particular from
12 to 18% by weight and particularly preferably about 16% by weight. The
transparency of the
propylene copolymer compositions used according to the present invention is
virtually
independent of the proportion of propylene copolymer B present.
Particularly useful heterophase propylene copolymers suitable as transparent
polypropylenes are
also ones comprising
A) from 50 to 98, preferably from 60 to 95% by weight of a crystalline
propylene homopolymer,
or a crystalline random copolymer of propylene with ethylene and/or C4-Coo-1-
alkenes,
containing from 0.5 to 15% by weight of ethylene and/or C4-C,o-1-alkenes; and
B) from 2 to 50, preferably from 5 to 40% by weight of (i) an elastomeric
copolymer of ethylene
with one or more C4-C,o-1-alkenes (copolymer (a)), containing from 60 to 85%
by weight of
ethylene, or (ii) a blend of copolymer (a) with a copolymer of propylene with
more than 15%
up to 40% of ethylene (copolymer (b)), Wherein the weight ratio (a)/(b) is
preferably from 1/4
to 4/1.
Examples of C4-C,o-1-alkenes that can be used as comonomers in Fractions A and
B are
1-butene, 1-pentene, 1-hexene and 4-methyl-1-pentene. Particularly preferred
is 1-butene.
The MFR (230°C/2.16 kg) determined according to ISO 1133 of such
heterophase propylene
copolymers is preferably from 0.1 to 100 g/10 min.
Such useful heterophase propylene copolymers are typically prepared by
sequential
copolymerization of the monomers in the presence of stereospecific Ziegler-
Natta catalysts
supported on magnesium dihalides. The polymerization is carried out in at
least two steps: in the
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first stage, one carries out the synthesis of the polymer of Fraction A, in
the second one, the
synthesis of the polymer of Fraction B. The synthesis of the latter occurs in
the presence of the
polymer obtained and the catalyst used in the preceding stage. Reaction times
and temperatures
relative to the two steps are not critical and are advantageously in the range
from 0.5 to 5 hrs, and
from 50 °C to 90 °C respectively. Regulation of the molecular
weight is done by using molecular
weight regulators commonly used, e.g. hydrogen and ZnEt2.
Suitable stereospecific catalysts comprise the product of the reaction
between:
i) a solid component, containing a titanium compound and an electron-donor
compound (internal electron-donor) supported on magnesium chloride;
ii) an aluminum alkyl compound (cocatalyst); and, optionally,
iii) an electron-donor compound (external electron-donor).
Said catalysts are preferably capable of producing homopolymer polypropylene
having an
isotactic index higher than 90%.
Catalysts having the above mentioned characteristics are well known in the
patent literature;.
particularly advantageous are the catalysts described in US-A 4,399,054 and EP-
A 45977.
The solid catalyst component (i) contains as electron-donor a compound
generally selected
among the ethers, ketones, lactones, compounds containing N, P and/or S atoms,
and mono-
and dicarboxylic acid esters.
Particularly suited are phthalic acid esters and succinic acid esters. Other
electron-donors
particularly suited are the 1,3-diethers, as illustrated in published European
patent applications
EP-A 361 493 and EP-A 728 769.
As cocatalysts (ii), one preferably uses the trialkyl aluminum compounds, such
as AI-triethyl,
AI-triisobutyl and AI-tri-n-butyl.
The electron-donor compounds (iii) that can be used as external electron-
donors (added to the
AI-alkyl compound) comprise the aromatic acid esters (such as alkylic
benzoates), heterocyclic
compounds (such as the 2,2,6,6-tetramethylpiperidine and the 2,6-
diisopropylpiperidine), and in
particular silicon compounds containing at least one Si-OR bond (where R is a
hydrocarbon
radical). The previously said 1,3- diethers are also suitable to be used as
external donors. In the
case that the internal donor is one of the said 1,3-diethers, the external
donor can be omitted.
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13
The particularly useful transparent polypropylenes obtained by using catalyst
systems based on
metallocene compounds or by using stereospecific Ziegler-Natta catalysts
supported on
magnesium dihalides are preferably prepared in a multistage polymerization
process having at
least two polymerization stages connected in series, generally in the form of
a reactor cascade. I'
is possible to use the customary reactors employed for the polymerization of
propylene. The
polymerization can be carried out in a known manner in bulk, in suspension, in
the gas phase or
in a supercritical medium. It can be carried out batchwise or preferably
continuously. Solution
processes, suspension processes, stirred gas-phase processes or gas-phase
fluidized-bed
processes are all possible. As solvent or suspension medium, it is possible to
use inert
hydrocarbons, for example isobutane, or else the monomers themselves. It is
also possible for
one or more stages of the process employed according to the present invention
to be carried out
in two or more reactors. The size of the reactors is not of critical
importance for the process
employed according to the present invention. It depends on the output which is
to be achieved in
the reaction zone or in the individual reaction zones.
Preference is given to processes in which the polymerization in the second
stage, in which the
propylene copolymers) B or fraction B are formed, takes place from the gas
phase. The previous
polymerization of the propylene polymers A or fraction A can be carried out
either in bulk, i.e. in
liquid propylene as suspension medium, or likewise from the gas phase. If all
polymerizations take
place from the gas phase, the process is preferably carried out in a cascade
of stirred gas-phase
reactors which are connected in series and in which the pulverulent reaction
bed is kept in motion
by means of a vertical stirrer. The reaction bed generally comprises the
polymer which is
polymerized in the respective reactor. If the initial polymerization of the
propylene polymers A is
carried out in bulk, the process is preferably in a cascade comprising one or
more loop reactors
and one or more gas-phase fluidized-bed reactors. The preparation can also be
carried out in a
multizone reactor.
The amount of monomers added in the individual stages and the process
conditions such as
pressure, temperature or the addition of molar mass regulators such as
hydrogen are chosen so
that the polymers formed have the desired properties.
Customary additives, for example molar mass regulators such as hydrogen or
inert gases such as
nitrogen or argon, can also be used in the polymerization.
The transparent polypropylenes generally further comprise additives known to
those skilled in the
art, e.g. stabilizers, lubricants and mold release agents, fillers, nucleating
agents, antistatics,
plasticizers, dyes, pigments or flame retardants, in customary amounts. These
are generally
incorporated during granulation of the pulverulent product obtained in the
polymerization.
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Customary stabilizers are antioxidants such as sterically hindered phenols,
processing stabilizers
such as phosphites or phosphonites, acid scavengers such as calcium stearate
or zinc stearate or
dihydrotalcite, sterically hindered amines or UV stabilizers, In general, the
propylene copolymer
compositions used according to the present invention contain one or more
stabilizers in amounts
of up to 2% by weight.
Suitable lubricants and mold release agents are, for example, fatty acids,
calcium or zinc salts of
fatty acids, fatty acid amides or low molecular weight polyolefin waxes, which
are usually used in
concentrations of up to 2% by weight.
Possible fillers are, for example, talc, chalk or glass fibers, which can
usually be used in amounts
of up to 50% by weight.
Suitable nucleating agents are, for example, inorganic additives such as talc,
silica or kaolin, salts
of monocarboxylic or polycarboxylic acids, e.g. sodium benzoate or aluminum
tert-butylbenzoate,
dibenzylidenesorbitol or its C,-C8-alkyl-substituted derivatives such as
methyldibenzylidenesorbitol, ethyldibenzylidenesorbitol or
dimethyldibenzylidenesorbitol or salts
of diesters of phosphoric acid, e.g. sodium 2,2'-methylenebis(4,6-di-tert-
butylphenyl) phosphate.
The content of nucleating agents in the propylene polymer composition is
generally up to 5% by
weight.
Such additives are generally commercially available and are described, for
example, in
Gachter/Muller, Plastics Additives Handbook, 4th Edition, Hansa Publishers,
Munich, 1993.
In a preferred embodiment, the transparent polypropylenes contain from 0.1 to
1 % by weight,
preferably from 0.15 to 0.25% by weight, of a nucleating agent, in particular
dibenzylidenesorbitol
or a dibenzylidenesorbitol derivative, particularly preferably
dimethyldibenzylidenesorbitol.
The containers are used for packaging or storing articles from the area of
clothing, sports articles,
toys or home worker articles. For example, they are suitable for packaging or
storing footwear of
all types, e.g. shoes, sandals, boots, sports shoes, roller blades or ski
boots, laundry, tennis
articles, toys such as toy cars or building blocks or home worker articles
such as tools, screws or
nails. In particular, the containers are used for packaging or storing shoes.
The containers have wall thicknesses of at least 0.8 mm and preferably at
least 1.0 mm. The wall
thickness of the containers is generally approximately equal in all regions of
the containers.
However, they can also have reinforced regions or ribs. The containers
generally have
dimensions which make it possible to pack the articles, in particular the
shoes, easily.
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Preferred containers are made up of two parts and consist of a box-shaped
receptacle and a lid.
The receptacle and the lid can be joined to one another, in particular via a
film hinge. The box-
shaped receptacle and the lid are preferably configured so that in the closed
state of the
containers the receptacle and the lid lock into place.
5
Furthermore, the receptacles are preferably configured so that they can be
stacked inside one
another in the empty state. This is usually achieved by giving the receptacles
a conical shape.
Preference is also given to the upper rim of the receptacles being reinforced
around the outside to
provide stiffening. In addition, this makes it simpler to achieve a locking
into place of receptacle
10 and lid in the closed state of the containers.
A possible design of a preferred container made up of a box-shaped receptacle
and a lid is shown
in the attached figure.
15 The lids are preferably designed with short side parts which are usually
between 10 and 20 mm
high. Preference is also given to the lower rim of the lid being reinforced
around the inside to
provide stiffening. In addition, this makes it simpler to achieve a locking
into place of receptacle
and lid in the closed state of the containers.
The containers are preferably produced by injection molding. However, the
containers can also be
obtained by forming, for example folding, extruded sheets and in particular
extruded corrugated
sheets.
The present invention further~provides containers comprising transparent
polypropylene, with the
containers having wall thicknesses of at least 0.8 mm, wherein the transparent
polypropylene is a
propylene homopolyme~ or propylene copolymer which has a haze value of <_ 40%,
based on a
thickness of the polypropylene of 1 mm and measured on injection-molded test
specimens, and
has a tensile modulus of _> 700 MPa and a Charpy notched impact strength at
0°C of >_ 3 kJ/m2
and the containers are provided at the bottom with a material which has a
coefficient of sliding
friction which is greater than that of the transparent polypropylene. This
material prevents, or at
least reduces, slipping of the packed or stored articles such as shoes.
Examples of suitable
materials having a coefficient of sliding friction which is higher than that
of the transparent
polypropylene are elastomers or thermoplastic elastomers such as thermoplastic
polyolefins or
styrene oligoblock copolymers. Suitable thermoplastic polyolefins are
marketed, for example, by
Basell under the name Adflex. In general, the containers are provided at the
bottom with the
material having the increased coefficient of sliding friction only in some
regions. These regions
can be, for example, oval, in the form of rectangular strips or also in the
shape of a foot.
Production can be carried out, for example, by two-component injection
molding. However, it is
also possible to manufacture the containers and moldings of the material
having the increased
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16
coefficient of sliding friction separately and then to fix the moldings to the
container, for example
by adhesive bonding.
The present invention further provides systems for packaging or storing
articles from the area of
clothing, sports articles, toys or home worker articles, with at least two
objects being present in a
package, wherein the objects are surrounded by a container comprising a
transparent polymer
and having a wall thickness of at least 0.8 mm and at least two objects are
separated from one
another by a transparent flexible film. Such systems make it possible to
readily see articles which
consist of at least two objects and are packaged in a form which ensures that
the objects are
protected from impact against one another or with the walls of the package
during transport of the
packaging systems.
Examples of suitable transparent polymers which can be used for producing the
containers of the
systems are polystyrene, polycarbonate, styrene-butadiene block copolymers and
polypropylene,
with the above-described transparent polypropylenes being particularly useful.
Preferred transparent films are flexible and have a low stiffness.
Furthermore, preferred
transparent films are produced from a material which has a coefficient of
sliding friction which is
higher than that of the transparent polymer. Suitable transparent films can be
produced, for
example, from thermoplastic polyolefins, e.g. from thermoplastic polyolefins
as are marketed by
Basell under the name Adflex.
The present invention further provides reusable packaging systems for
packaging clothing, sports
articles, toys or home worker articles and in particular shoes wherein
containers comprising a
transparent polymer and having a wall thickness of at least 0.8 mm are used
for packaging the
clothing, sports articles, toys or home worker articles and smaller containers
which fit accurately
into the containers or can be hung into the containers are made available for
reuse of the
containers. These inserts are preferably made of the same transparent polymer
from which the
containers are made. The inserts can also be configured as sorting containers
having a plurality of
compartments, for example from 2 to 10, preferably from 4 to 8, compartments..
Suitable inserts can be sold empty as supplements for the further use of the
containers originally
serving as packaging material. However, the inserts can also be sold already
filled, i.e. then as
reusable packaging for other articles. Suitable articles which can be sold
packed in such inserts
are, for example, shoe care products such as tubes of polish, cleaning
equipment or cleaning
cloths or sewing requisites such as needles, yarns or buttons.
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Suitable transparent polymers which can be used for producing the containers
of the systems are,
for example, polystyrene, polycarbonate, styrene-butadiene block copolymers of
polypropylene,
with the above-described transparent polypropylene being particularly useful.
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