|Title of Invention||
A PROCESS FOR PREPARING CAPS AND CLOSURES FOR CARBONATED DRINKS "
|Abstract||A process for preparing caps and closures for carbonated drinks is disclosed. The process for preparing caps and closures for carbonated drinks with a bimodal high density polyethylene (HDPE) resin produced with a catalyst system comprises a bisindenyl-based catalyst component and wherein said HDPE resin has a density, measured following the method of standard test ASTM 1505 at a temperature of 23°C, of from 0.945 to 0.965 g/cm3, a melt index MI2, measured following the method of standard test ASTM D 1238 at a temperature of 190°C and under a load of 2.16 kg, of from 1 to 10 dg/min, and a molecular weight distribution, defined by the polydispersity index D that is the ratio Mw/Mn of the weight average molecular weight Mw over the number average molecular weight Mn, of at least 3.|
|Full Text||The present invention relates to caps and closures for carbonated and stiil drinks
prepared with bimodal high density polyethylene resins.
Polyethylene resins prepared with Ziegler-Natta (ZN) catalyst systems are generally
used for preparing caps and closures for carbonated drinks. These resins have a
reasonably high stress crack resistance, but they leave room for improvement. Such
resins are for example Hostalen® GD4755 commercialised by Basell, or Eltex®
B4020N commercialised by Inovene.
Metallocene-prepared resins having a narrow monomodal polydispersity index have
also been tested in that field but they do not offer ideal mechanical properties
because of their limited stress crack resistance.
There is thus a need to prepare resins that can be used to produce caps and
closures for carbonated drinks.
It is an aim of the present invention to produce caps and closures for carbonated
drinks that have high environmental stress crack resistance.
It is also an aim of the present invention to produce caps and closures for
carbonated drinks with a resin that is easy to process by injection moulding or by
it is another aim of the present invention to produce caps and closures for
carbonated drinks that have a good rigidity.
it is yet another aim of the present invention to provide caps and closures for
carbonated drinks that have good tightness.
It is a further aim of the present invention to prepare caps and closures for
carbonated drinks that have a good dimensional stability.
It is yet a further aim of the present invention to prepare caps and closures for
carbonated drinks that have a good creep resistance.
it is also an aim of the present invention to produce caps and closures for
carbonated drinks that are easy to open.
It is yet a further aim of the present invention to prepare caps and closures for
carbonated drinks that have good organoleptical and food contact properties
because they have a very little content of volatile organic compounds (VOC).
Accordingly, the present invention discloses caps and closures for carbonated drinks
produced by injection moulding or by compression moulding with a bimodal high
density polyethylene (HDPE) resin.
The bimodal HDPE resin can be prepared from a physical blend or from a chemical
blend. The chemical blend can result for example from a single catalysts system
used in a double loop reactor wherein the loops are operated under different
polymerisation conditions or from two or more catalyst systems used in a single or in
a double loop reactor.
When a double loop reactor is used, it can be operated under various modes:
- hydrogen split wherein different concentrations of hydrogen are used in the
different reactors in order to produce a low molecular weight fraction in a
reactor and wherein the polydispersity is broadened in the other reactor;
- comonomer split wherein different comonomer concentrations are used in the
different reactors in order to produce a low comonomer concentration in a
reactor and a high comonomer concentration in the other reactor;
- comonomer/hydrogen split wherein a high molecular weight and high
comonomer concentration is produced in one reactor and a low molecular
weight, low comonomer concentratrion is produced in the second reactor. In
the direct configuration, the high comonomer concentration is produced in the
first reactor and vice versa, in the inverse configuration, the low comonomer
concentration is produced in the first reactor.
The first mode, in direct configuration, is preferred in the present invention.
Preferably, the bimodal HDPE resin is prepared with a catalyst system based on a
bridged bisindenyl catalyst component. The catalyst component is of general formula
wherein (Ind) is an indenyhor an hydrogenated jndenyl, substituted or unsubstituted,
R" is a structural bridge between the two indenyls to impart stereorigidity that
comprises a C1-C4 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
transition metal Group 4 of the Periodic Table or vanadium.
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 or in the cyclohexenyl ring and the bridge.
Each substituent on the indenyl may be independently chosen from those of formula
XRV in which X is chosen from Group 14 of the Periodic Table, 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 not 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 CH3. More preferably, at
least one and most preferably both cyclopentadienyl rings are unsubstituted.
In a particularly preferred embodiment, both indenyls are unsubstituted, and most
preferably they are unsubstituted hydrogenated indenyls. Most preferably it is
isopropyledenebis(tetrahydroindenyl) zirconium dichloride.
The active catalyst system used for polymerising ethylene comprises the above-
described catalyst component and a suitable activating agent having an ionising
Suitable activating agents are well known in the art: they include aluminium alkyls
aluminoxane or boron-based compounds.
Optionally, the catalyst component can be supported on a support.
This catalyst system is preferably used in a liquid full double loop reactor wherein
the loops are operated under different conditions in order to produce a bimodal
resin. The double loop reactor can be operated either in direct configuration wherein
the high comonomer concentration copolymer is prepared in the first reactor or in
inverse configuration wherein the low comonomer concentration homopolymer is
prepared in the first reactor.
The bimodal resins of the present invention have densities of from 0.940 to 0.965
g/cm3, preferably of from 0.945 to 0.955 g/cm3 and more preferably of about 0.950
g/cm3. They have a melt index MI2 of from 1 to 50 dg/min, preferably of from 1 to 10
dg/min, more preferably of from 1.5 to 8 dg/min, most preferably from 1.5 to 4
dg/min. They have a polydispersity index that is preferably of at least 3, more
preferably from 3.0 to 4.0 and most preferably from 3.1 to 3.6. The molecular
weights are determined by GPC-DRI. In solution, long-branched polymers assume a
more compact configuration than linear chains and their molecular weight can thus
be slightly underestimated. Density is measured following the method of standard
test ASTM 1505 at a temperature of 23 °C. Melt flow indices MI2 and HLMI are
measured following the method of standard test ASTM D 1238 at a temperature of
190 °C and respectively under loads of 2.16 and 21.6 kg. Poiydispersity index D is
defined as the ratio Mw/Mn of the weight average molecular weight Mw over the
number average molecular weight Mn and the molecular weights are determined by
gel permeation chromatography (GPC).
The caps and closures of the present invention are prepared by injection moulding
or by compression moulding. The injection moulding cycle may be decomposed
into three stages: filling, packing-holding, and cooling. During filling, polymer melt is
forced into an empty cold cavity; once the cavity is filled, extra material is packed
inside the cavity and held under high pressure in order to compensate for density
increase during cooling. The cooling stage starts when the cavity gate is sealed by
polymer solidification; further temperature decrease and polymer crystallisation
takes place during the cooling stage. Typical temperatures for the filling step are of
from 160 to 280 °C, preferably of from 230 to 260 °C. Compression moulding is
carried out under similar conditions.
Different approaches have been developed for evaluating resin processability in
injection moulding processes.
A first approach for testing flow in runners and in mould cavities during filling is to
measure the viscosity at high shear rates and in isothermal conditions. Viscosity at
high shear rates is the most important physical property that influences mould
filling. The appropriate strain rates depend on the resin, the injection pressure and
the mould geometry, but typical strain rates are above 1500 - 2500 s-1. It is also
important to take into account the viscosity differences caused by the temperature
differences inside the mould, wherein the central temperature is higher than the
A second approach involves non-isothermal tests that simulate the injection
moulding process. In these tests, the rheologjcal, crystellisation and thermal
properties of polymers are taken into account. The test however does not yield
values of physical properties but gives a purely empirical, apparatus-dependent
measure of processability. It is the spiral flow test that consists in measuring the
spiral flow length before freeze-up of melted polymer injected into a standard
mould under standard filling conditions.
The caps and closures according to the present invention are characterised by a
remarkably low content of volatile organic compounds.
Figure 1 represents the molecular weight distribution of the resins tested.
Figure 2 represents the complex viscosity expressed in Pas as a function of
frequency expressed in rad/s for several resins.
Figure 3 represents the flow length FL expressed in mm as a function of injection
pressure expressed in bars.
Several resins have been tested in the production of caps and closures for
They were selected as follows.
Resin R1 is a monomodal high density polyethylene (HDPE) resin prepared with
isopropylidene-bis(tetrahydroindenyl) zirconium dichloride.
Resins R3 to R5 are bimodal HDPE resins prepared with isopropylidene-
bis(tetrahydroindenyl) zirconium dichloride (THI) in a double loop reactor in inverse
configuration, i.e. wherein the homopolymer is prepared in the first reactor.
Resin R2, R6 and R9 are bimodal HDPE resins prepared with isopropylidene-
bis(tetrahydroindenyl) zirconium dichloride (THI) in a double loop reactor in direct
configuration, i.e. wherein the copolymer is prepared in the first reactor.
Resins R7 and R8 are conventional, commercially available, Ziegler-Natta HDPE
Their properties are summarised in Table I.
The curves representing the molecular weight distribution for all resins are
represented in Figure 1. As expected, the molecular weight distribution of all the
resins prepared with a Ziegler-Natta catalyst system are significantly broader than
those of all the metallocene-prepared resins. In addition, they include very long
chains that are characterised by a high molecular weight fraction above 106 daltons
at variance with all the metallocene-prepared resins, both monomodal and bimodal
that do not contain very long chains.
The molecular architecture of the resins has also been investigated and the amount
of short chain branching and long chain branching has been evaluated for each
resin. All samples were very crystalline.
The short chain branching content was measured by NMR. The results for all resins
are displayed in Table II as well as the nature of the short branches.
The long chain branching content was determined by the long chain branching index
(LCBI) method. The method is described by Schroff R.N. and Mavridis H. in
Macromolecules, 32, 8454 (1999) and LCBI is given by empirical formula
wherein no is the zero shear viscosity expressed in Pa.s and [n] is the intrinsic
viscosity in solution expressed in g/mol. This method is more sensitive than the usual
Dow Rheological Index (DRI) or NMR methods and is independent of the
polydispersity. It was developed for substantially linear polyethylene such as typically
obtained in metallocene catalysis and it only requires the measurement of intrinsic
viscosity of a dilute polymer solution and the zero shear viscosity. It is equal to zero
for linear chains and deviates from zero when long chain branching is present. The
intrinsic viscosity values were calculated from the Mark-Houwink relationship that
was developed for linear chains and it must be noted that this method only applies to
resins having a small content of long chain branching. The zero shear viscosity was
obtained by Carreau-Yasada fitting. The results are displayed in Table II and they
show that the resins prepared with Ziegler-Natta catalyst systems have no long chain
branching and that the bimodal metallocene-prepared resins have the highest level
of long chain branching.
The complex viscosity curves as a function of angular frequency are presented in
Figure 2. Plate-plate rheometer data were used because they are more precise and
more reliable. It is known in the art that shear thinning or pseudo-plastic behaviour is
influenced by the presence of long chain branching or by broadening of the
molecular weight distribution. As can be seen from figure 2, the bimodal resins
prepared with THI have the most pronounced pseudo-plastic behaviour due to the
combined effects of the presence of long chain branching and fairly broad molecular
The temperature dependence of the viscosity can be described by formula
wherein aT is the time shift factor, T is the temperature and p and p0 are the densities
respectively at temperatures T and T0. Far from the glass transition temperature, as
is the case for the polyethylene of the present invention, the flow activation energy
Ea can be derived from the Arrhenius relationship:
The calculated values are reported in Table III. It was observed that the activation
energy of all resins prepared with THI had much higher values of the activation
energy than those obtained for the resins prepared with Ziegler-Natta catalyst
systems: this is due to the presence of long chain branching.
A standard mouldability test has been carried out. Melted polymer was injected into a
standard mould having a simple spiral geometry involving a long flow path. The
moudability index is defined as the flow length, meaning the length of mould filled
before freeze-up under standard filling conditions. The injection pressure and
temperature have been varied. Flow lengths (FL) for several resins have been
reported as a function of increasing injection pressure at a temperature of 210 °C in
Figure 3. For resin R6, the spiral flow lengths (SFL) have been measured at a
temperature of 210 °C and respectively under injection pressures of 500, 800 and
1000 bars: they were respectively of 131,182 and 231 mm. Bimodal resins present
high FL values, in agreement with viscosity results. Bimodal THI resins have a low
viscosity at high shear rate as a result of their pronounced shear thinning behaviour.
Several injection trials were carried out to prepare caps and closures with these
resins. The injection machine had the following characteristics:
- Engel ES250 6340 device, equipped with a barrier screw having a diameter D
of 55 mm and a ratio length over diameter L/D of 24;
- maximum hydrauloc pressure of 172 bars;
- mould having 48 cavities;
- caps and closures having a diameter of 28 mm and a weight of 2.8 g
The experimental injection conditions were as follows:
- cycle time of about 6 s;
- residence time of the material into the screw of about 2 shots, a shot being
the average time between two cycles;
- screw rotation speed of 400 rpm;
- temperature profile: 25/240/245/250/255/260 °C;
- holding pressure of 60 bars;
- clamping force of 2400 N
The results are summarised in Table IV
wherein Pinj is the maximum injection pressure expressed in bars, dem-com are the
demoulding comments and dem-index is the demoulding index ranking from i for
easy demoulding to 5 for difficult demoulding. Easy de-moulding of the caps
prepared according to the present invention is the result of the excellent dimensional
stability of metallocene prepared resins.
In conclusion, the processability of all bimodal mPE was comparable to that of the
prior art commercial ZNPE grades. The maximum injection was slightly higher for the
bimodal mPE than for the reference conventional ZNPE, but the cycle time was
similar to that of prior art resins and demoulding was easy. The maximum injection
pressure was in line with viscosity and spiral flow observations.
The characterisation of solid state properties were carried out as follows on two
types of specimens:
A) compression-moulded specimens for the evaluation of rigidity by the flexion
test following the method of standard test ISO 178.
B) injected caps for the evaluation of:
a) stress crack resistance by specific pressure tests;
b) dimensional stability with a micrometer;
c) tightness by a high pressure test
All caps were prepared in the same injection conditions and on the same
machine in order to minimise thermo-mechanical and cap design effects.
Pressure inside carbonated drink bottles can cause excessive deformation of
caps and closures. Rigidity is thus a crucial parameter in order to avoid such
deformation. The flexural modulus was measured following the method af
standard test ISO 178. The results are displayed in Table V. The values of the
flexural modulus are very similar for all resins.
Stress cracking in caps and closure occurs in two possible ways: either pressure
crack at the top of the cap or capping torque crack at the contouring of the cap.
Pressure tests were carried out using a method developed in-house. It consists in
applying a pressure on a cap screwed on a pre-form/bottle.
Five caps were screwed respectively on five bottles at a torque of 1.8 N.m The
cap/bottle systems were placed under a constant air relative pressure of 6 bars at
a temperature of 45 °C. During the test, the pressure was continuously measured
and the appearance of macro-cracks was visually checked once a day. The test
was stopped when pressure inside the bottles had decreased to atmospheric
pressure because of the presence of cracks.
The results are presented in Table V. They show that the superiority of bimodal mPE
resins over prior art reference resin R7.
It is known in the art that increasing the molecular weight and short-chain branching
(SCB) improves stress crack resistance because there are more tie molecules and
more effective tie molecule entanglement and anchoring in the crystalline lamellae.
Incorporation of comonomer is also known to increase the content of tie molecules
and the efficiency of entanglements. The metallocene-prepared polyethylene resins
of the present invention are characterised by long chains, high level of SCB and
optimised distribution of SCB along the long chains. As a consequence, they have
improved stress crack resistance.
The height and lips of caps were measured about 24 hours hours after injection with
a micrometre. They were all within specifications but the mPE resins presented
slightly lower shrinkage than the other resins.
All the caps prepared according to the present invention were also tested for
tightness: they were submitted to a pressure of 10 bars during one minute. They all
passed the test.
In this table, Efl lis the flexural modulus expressed in Mpa, F50a is the average failure
time expressed in days as determined by the in-house method.
In addition opening torque results and taste results have shown equivalent behaviour
for all the resins tested.
The volatile organic compounds (VOC) have much smaller concentrations for
metallocene-prepared resins than for the Ziegler-Natta resins. Polymer samples
were analysed by Automated Thermal Desorption (ATD)/Gas chromatography (GC)
method with quantitative analysis by Flame Induction Decay (FID) method. This
technique consisted in a thermic desorption, at a temperature of 150 °C, of the
volatile organic compounds contained in the polymer. The organic compounds were
carried along by a stream of helium and were trapped by adsorbent TENAX® cooled
down to a temperature of -40 °C. The volatile compounds were then injected in a
chromatographic separation column by heating the trap to a temperature of 240 °C.
Quantification was carried out using an external calibration line and identification was
carried out on the basis of retention time. The VOC results from Table V show that
Ziegler-Natta grades have a much higher concentration of volatile organic
compounds than all metallocene-prepared resins according to the present invention.
As a consequence of their low content of volatiles, the organoleptic properties (taste
and odour) of the resins according to the present invention were excellent. They
were measured by the procedure described as follows. 25 g of pellets were
contacted with 1 L of water at a temperature of 60 °C for 48 hr, followed by 48 hr of
the same water at a temperature of 20 °C. Several dilutions of that water were then
tested by a panel of 8 tasters according to the following dilution scheme.
% test water Stage
The test is negative and the sample water is declared not conform if a taste or odour
is perceived at stages A5 or A7.
The use of bimodal metallocene-prepared polyethylene resins is thus a very
attractive alternative to reference Ziegler-Natta resins. They offer improved stress
crack resistance and VOC with respect to reference resins whereas they keep the
same level of processability, rigidity, opening torque and taste as prior art resins.
The bimodal HDPE of the present invention can be used in various applications such
as for example,
- in injection or compression moulding for caps closure used for beverage,
cosmetics or food;
- in blow moulding for milk bottles;
- in extrusion for raffia;
- in cable jacketing.
1. A process for preparing caps and closures for carbonated drinks with a bimodal high
density polyethylene (HDPE) resin produced with a catalyst system comprising a
bisindenyl-based catalyst component and wherein said HDPE resin has a density, measured
following the method of standard test ASTM 1505 at a temperature of 23°C, of from 0.945
to 0.965 g/cm3, a melt index MI2, measured following the method of standard test ASTM
D 1238 at a temperature of 190°C and under a load of 2.16 kg, of from 1 to 10 dg/min, and
a molecular weight distribution, defined by the polydisperslty index D that is the ratio Mw/
Mn of the weight average molecular weight Mw over the number average molecular
weight Mn, of at least 3.
2. The process as claimed in claim 1 wherein the bimodal high density polyethylene
(HDPE) resin is produced with a bisindenyl-based catalyst system in a double loop reactor
wherein the loops are operated under different polymerisation conditions.
3. The process as claimed in claim 2 wherein the HDPE resin is prepared with the
bisindenyl-based catalyst system in a double loop reactor in direct configuration.
4. The process as claimed in claim 2 wherein the HDPE resin is prepared with the
bisindenyl-based catalyst system in a double loop reactor in inverse configuration.
5. The process as claimed in any one of claims 1 to 4 wherein the bisindenyl-based
catalyst component is based on an unsubstituted bistetrahydroindenyl component.
6. The process as claimed in claim 5 wherein the bisindenyl-based catalyst component
is isopropylidenebis(tetrahydroindenyl) zirconium dichloride.
A PROCESS FOR PREPARING CAPS AND
CLOSURES FOR CARBONATED DRINKS
A process for preparing caps and closures for carbonated drinks is disclosed. The
process for preparing caps and closures for carbonated drinks with a bimodal high density
polyethylene (HDPE) resin produced with a catalyst system comprises a bisindenyl-based
catalyst component and wherein said HDPE resin has a density, measured following the
method of standard test ASTM 1505 at a temperature of 23°C, of from 0.945 to 0.965
g/cm3, a melt index MI2, measured following the method of standard test ASTM D 1238 at
a temperature of 190°C and under a load of 2.16 kg, of from 1 to 10 dg/min, and a
molecular weight distribution, defined by the polydispersity index D that is the ratio
Mw/Mn of the weight average molecular weight Mw over the number average molecular
weight Mn, of at least 3.
|Indian Patent Application Number||2161/KOLNP/2007|
|PG Journal Number||37/2012|
|Date of Filing||13-Jun-2007|
|Name of Patentee||TOTAL PETROCHEMICALS RESEARCH FELUY|
|Applicant Address||ZONE INDUSTRIELLE C, B-7181 SENEFFE(FELUY)|
|PCT International Classification Number||C08L 23/06|
|PCT International Application Number||PCT/EP2005/057021|
|PCT International Filing date||2005-12-21|