Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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WO 98/46409 PCT/AU98/00255
INJECTION MOULDING
The present invention relates to injection moulding processes, in particular
to a process for
injection moulding articles having thin sections such as thin-walled tubular
containers as used
in the cosmetics industry for lotions, moisturisers and the like.
Thin-walled tubular containers, such as those used in the cosmetics industry,
are currently
produced by a combination of extrusion, injection moulding and welding
processes (generally
referred to herein as the extrusion process ). The body of the tube is
extruded in the form
of a continuous cylinder which is then cut into the desired length to form the
body of the
container. In a separate injection moulding process the "head and shoulders"
of the tube are
produced. The injection moulded "head and shoulders" are then welded to the
extruded tube
to form the container. Once the container is filled with product the tail end
of the container
is sealed by a further welding process. This process for producing tubes has a
number of
limitations, the main being the high equipment cost, the lack of variety of
tube shapes that
can be produced using it, no ability to provide various textured surface
finishes or embossing
as an integral part of the manufacturing process, and no ability to
incorporate
attachments/components such as closures and hooks during the manufacturing
process. Low
MFI polyethylene (MFI generally less than 2) is the preferred polymer for tube
manufacture
as it in general imparts the properties of good feel and flexibility required
by customers and
is suitable for extrusion processing. In addition, low MFI polyethylene offers
sufficient
product resistance and barrier properties to make it suitable for most
products currently
packed into tubes. In cases where the barrier properties of polyethylene are
inadequate for
particular applications, medium density polyethylene (MDPE), high density
polyethylene
(HDPE), polypropylene (PP) and multilayer polymer films are commonly used.
Wlvle the injection moulding of articles such as thin walled containers has
been proposed, it has
hitherto not been possible to injection mould such articles having relatively
long, thin sections
without the articles being too susceptible to failure to be of commercial or
practical use. The
main problems have been associated with the polymers used to injection mould
tubes, in that the
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process of moulding a cylindrical or other shaped tube requires the polymer to
simultaneously
have a high MFI to enable said polymer to flow down the long, narrow and
curved path dictated
by the tube shape without the use of excessive injection pressures, yet to
have sufficiently good
mechanical properties to be able to withstand handling and resist the stress
cracking effects of
many of the products that will be packed in it. In order to injection mould a
tube, conventional
techniques would require the polymer to have flow properties capable of
forming moulded'parts
with radii and a length/thickness ratio of 100 and often higher. Forcing a
'standard' polymer to
flow in a mould with such dimensions introduces severe stresses into the
polymer, these stresses
being "frozen" into the article thus produced when the polymer rapidly cools
below its
crystallising temperature before these stresses can be relieved. These
stresses result in the tube
having surprising different and deteriorated properties relative to the other
products moulded
from the same polymers under less severe moulding conditions.
Further stresses are introduced into the tubes when they are filled with
product and then crimped
and sealed - most often by heat sealing or ultrasonic welding. This process
involves bending the
'open' end of the tube back on itself through an angle of up to 180 to form
the fold at the edge
of the seal. This fold is in the direction of the flow of the polymer, which
direction having been
demonstrated to be the direction of maximum weakness of the moulded product.
This 'folded
and sealed' area, where the tube is required to be deformed in order to effect
a seal, is an area
of the injection-moulded tube particularly susceptible to stress and flex
cracking.
The following examples illustrate the special problems of injection moulding
such tubes. Tubes
were injection moulded using DuPont 2020T polymer, a polymer DuPont describe
as "especially
suited for injection moulded closure and extruded tubing where flexibility and
maximum
resistance to environmental stress cracking is required". These tubes were
moulded with extreme
difficulty, requiring very high injection pressures and temperatures simply to
get the 2020T to
fill the mould. In each moulding significant degrees of core shifting/flexing
were noted, due no
doubt to the extremely high injection pressures that were required. In
addition, it was noted that
the tubes had virtually no resistance to flexing in the direction of the
material flow, with
significant cracking being induced with less than 5 manual squeezes of the
tube. The
environmental stress cracking of the same tubes was tested, and in spite of
claims of "maximum
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resistance" to environmental stress cracking, was found to be totally
inadequate for moulding
thin-walled tubes by injection moulding.
In another illustration of the difficulty of injection moulding tubes, a Dow
'Dowlex' LLDPE
pamphlet advises that LLDPE has substantially better ESCR properties than an
equivalent high
pressure LDPE. To illustrate the difference, the pamphlet states that in one
comparative test a
high flow Dowlex LLDPE has an ESCR in oil some 80 times better than that
achieved by a hi~7h
pressure LDPE with the similar density and MFI (5700 hrs compared to 70 hrs): -
It further states
that the LLDPE has an ESCR approximately 10 times better than the LDPE when
immersed in
a 10% Teric solution at 50 C (225 hrs vs 26 hrs). However, contrary to these
observations, vle
have found that when these polymers are moulded in the form of thin wafled
tubes and ESCR
subsequently tested using a specially designed test method for assessing tube
ESCR, both Dow's
'Dowlex' LLDPE 2517 and Kemcor's LD 8153 (a high pressure LDPE with similar
MFI and
density) performed poorly in 10% Teric N9 at 50 C, and both failed within 20
minutes - clearly
indicating their unsuitability for tube manufacture by injection moulding.
This poor result is
illustrative of the highly unusual and difficult nature of manufacturing
injection moulded thin-
walled tubes acceptable to the market.
We have now found that it is possible to injection mould flexible thin-walled
articles having
relatively long thin-walled sections by selection of the polymers used in the
injection
moulding process having a time to failure of greater than 10 hours when tested
according to
the following procedure:
i) a plurality of strips of the polymer blend incorporatin(y
any post moulding treatment intended for the final article having the cross-
sectional dimensions of 0.65 mm in thickness and 10 mm in width are
injection moulded under high shear, long flow length conditions, similar to
those intended for use in the manufacture of the flexible thin-walled
artic:le. ;
ii) the strips are bent back upon themselves and stapled 3 mm from the bend;
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iii) the bent strips are immersed in a solution of a stress craclc agent such
as an
ethoxylated nonylphenol, e.g. a 10% solution of Teric N9 (nonylphenol
ethoxylated with 9 moles of ethylene oxide - Orica Australia Pty Ltd) and
held at a termperature of 50 C;
iv) the strips are observed for signs of cracking, any signs of craoking are
regarded as a failure; and
V) the time to failure is when 50% of the strips show signs of cracking.
Accordingly, we now provide a process for the manufacttxre of thin-walled
articles
comprising the steps of:
1) using a polymer blend having an ESCR as hereinabove defined of greater
than 10 hours when tested according to the above procedure;
2) melting said polymer blend;
i) ramming the molten polymer blend into a mould said mould having a cavity
which
produces a thin-walled article having a thin secti.on less than 1 mm in
thickness and
wherein the thin section is substantially continuous for greater thatl 50mm in
the
direction of flow of the molten polymer blend in the mould; and
4) removing from the mould the thin-walled article formed from the polymer
blend.
By "substantially continuous", it will be understood by those skilled in the
art that the
thickness of the thin section is generally maintained at less than I mm
although soirie
variation resulting in an increase in thickness is permitted, for example when
an en-ibossed,
textured or relief finish is incorporated into that article. The thickness
refers to the
thiolcness of the la.yer of polyxner blend described above and excludes any
additional layers
such as may be incorpoxated as a ru.ultilaminate. In applications where the
blend is.foamed
we refer to the notional thickness of an unfoamed material which can be
readily
determined from the density of the polymer blend.
It will be understood that throughout the specification and claims which
follow, the term
"polymer blend" refers to compositions comprising at least one polymer and
optionally
incorporating additional coinponents such as are described herein.
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It will be understood that throughout the specification and claims which
follow, the term
"copolymer" refers to polymers incorporating two or more monomer units
therein.
Generally, a polymer blend suitable for the manufacture of thin-walled
articles
has an ESCR as hereinabove defined of greater than 10 hours. Preferably
the ESCR of the polymer blend is greater than 100 hours, illustratively
greater than 200 hours and possibly greater than 360 hours. Where
the thin-walled article is a tube or other container used for the packaging of
a composition
such as a moisturiser or a shampoo which may be quite aggressive to the thin
walled article
and result in a degradation of its properties over time, it is desirable to
select a polymer blend
having an ESCR sufficiently high such that the thin walled article formed from
the blend is
able to withstand the rigours of use despite any degradation of properties
resulting from the
aggressive nature of the materials contained within the thin-walled article.
Where the thin-
walled article is used for the packaging of a relatively inert material, a
lower ESCR may be
tolerated.
The ESCR test as hereinabove defined may be conducted using a variety of
stress crack
agents. The stc-ess crack agent is Teric N9 (a 9-mole ethoxylate of
nonylphenyl ex Orica Australia
Pty Ltd) in some embodiments, other ethoxylates of nonylphenol may also
advantageously be used
Other stress crack agents may be used and will be selected based upon the
desired end-use.
Other stress crack agents include mineral oils, cationic surfactants, solvents
and other agents
which will be apparent to those skilled in the art.
Advantageously, the ESCR test as described above is conducted under molding
conditions
similar to those to be used in the manufacture of thin walled articles. For
example where it
is intended to produce the thin walled article using a moulding incorporating
melt flow
oscillation techniques, it may be advantageous to conduct the ESCR tests on
panels
produced frommouldings made by employing melt flow oscillation techniques.
The ESCR test as hereinabove defined has allowed a variety of polymer blends
to be selected
which are able to be injection moulded to form thin walled articles. In a
second aspect of the
present invention there is provided a process for injection mouloing a
thin-walled article comprising the steps of:
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1) melting a polymer blend wherein said polymer blend comprises at least one
polymer
arid at least one compatible agent and/or.at least one nucleating agent,
and wherein the polymer blend has an ESCR of greater than 10 hours when tested
according to the above procedure;
2) ramming the molten polymer blend into a mould said mould having a cavity
which
produces a thin-walled article having a thin section less than lmm in
thickness and
wherein the thin section is substantially continuous for greater than 50mm in
the
direction of flow of the molten polymer blend in the mould; and
3) removing from the mould the thin-walled article formed froin the polymer
blend.
A wide variety of polymers may be used as the base of a blend which meets the
ESCR test
as hercinabove defined or acts as the at least one polymer in the second
aspect qf the present
invention. These polymers include olefin homopolymers and copolymers, such as
ethylene
or polypropylene homopolymers and copolymers with C3-C',~o alpha or beta
olefins 'and/or
polyenes, preferably G,-Cg alpha or beta olefins, such polymers having
densities ranging from
very low to high density (density ranges between 0.85 and 0.97 g/cm3). Also
suitable for use
in embodiments ofthe pmesent invention are ethylene, propylene and butene
copolymers withtenninal vinyl
groups and ethylene, propylene and butene copolymers containing greater than
50% ethylene,
propylene or butene which are copolymerised with comonomers such as methyl
acrylates,
ethyl acrylates, acrylic acid and methacrylic acid, ionomers, and styrene-
ethylene/butene-
styrene ABA copolymers. These polymers may be made by a wide variety of
methods
including high and low pressure processes, using a wide variety of catalysts
such as Ziegler-
Natta and metallocenes, and have molecular structures ranging from linear to
highly
branched, thus included are LDPE, MDPE and HDPE. Particularly suitable for use
in
embodiments ofthe present invention are plastomers, `substantially linear' and
branched polyethylenes or
polypropylenes, copolymers of propylene and ethylene or one or more alpha-
olefins,
terpolymers of ethylene, propylene and one or more alpha-olefin (of which
Montell's Catalloy
polymers are an example) and polymers and copolymers of propylene manufactured
using
metallocene catalysts. Other polymers suitable for use in embodiments of the
present invention include
polylactic acid polymers.
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We have found that plastomers, "substantially linear polyethylen.es",
metallocene branched
polyethylene copolymers, propylene alpharolefin interpolymers a.nd-
Tnetallocene propylene
polymers and interpolymers are suitable for use in embodiments of the present
invention for the
production of thin-walled products, and especially for the production of
flexible tubes. A
key aharacteristic of plastomers, "substantially linear polyethylenes",
metaliocene
branched polyethylene copolymers, propylene alpha-olefin interpolymers and
metallocene
propylene polymers find interpolymers is their composition distribution ie.
the uniformity
of distribution of comonomer within and among the molecules of the polymer.
Plastomers,
"substantially linear polyethylenes", metallocene branched polyethyleYi.e
copolymers,
propylene alpha-olefin interpolymers and metallocene propylene polymers and
interpolymers are generally made using metallocene catalysts, which are known
to
incorporate comonomer very evenly among and along the polymer molecules they
produce. Thus most molecules of a particular plastomer, "substantially lineur
polyethylenes", metallocene branched polyethylene copolymers, propylene alpha-
olefin
interpolymers and metallocene propylene polymers and interpo2ymers will have
roughly
the same comonomer content, and within each molecule the comonomer wiA be
super-
randomly distributed. Ziegler-Natta catalysts generally yield copolyiners
having a
considerably broader composition distribtiti.on - specifically the comonomer
distribution in
polymers thus produced will vary widely among the polymer molecules, and will
also be
less randomly distributed within a given molecule.
US 5,451,450 describes plastomers as ethylene alpha-olefin copolymers
(including
ethvlene/alpha-olefin/polyeve copolymers) with a molecular weight distrlhution
in a ration
MW/M,, range of 1.5-30, illustratively in the range of 1.8-10 and possibly in
the range 2-4.
Generally, plastomer polymers comprise ethylene homopolymers and interpolymers
of
ethylene, with at least one C3-C20 a-olefin copolymers being especially
suitable. The
term "interpolymer" is used herein to indicate a copolymer or a ter polymer or
the like.
That is, at least one other comonomer is copolymerised with ethylene to make
the
interpolymer. Generally, the a-olefins suitable for copolymerisation with
ethyJane to form
plastomers contain in the range of about 2 to about 20 carbon atoms,
illustratively in the
range of about 3-16 carbons, possibly in the range of about 3-8 carbon atoms.
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Illustrative non-limiting examples of such a-olefins are propylene, 1-butene,
1-pentene, 4-
methyl-l-pentene, 1-hexene, 1 -octene, and 1-dodecene and the like. Polyene
comonomers
suitable for the copolymerisation with ethylene to form plastomers suitable
for embodiments
of the present invention have, in the main, about 3 to 20 carbon atoms,
illustratively in the range
of about 4 to about 20 carbon atoms, possibly in the range of about 4 to about
15 carbon
atoms. In one embodiment the polyene is a diene that has in the range of about
3 to about
20 carbon atoms, and may be a straight chained, branched chaxned or cyclic
hydrocarbon
diene. The diene is a non-conjugated diene in some embodiments. Non-limiting
examples of
ethylene/alpha-olefm plastomers suitable for embodiments of the present
invention include
ethylene/butene-1, ethylene/hex.ene-1, ethylene/octene-1 ana
ethylene/propylene
copolymers. Non-limiting examples of teipolymer plastomers suitable for
embodiments of the present
invention include ethylene/propylene/1, 4 hexadiene andethylene/octene-111, 4-
hexadiene.
Plastomers and. 'substantially linear polyethylenes' are produced in.ainly
with the use of
matallocene catalysts. US 5,281,679 shows a method of producing metallocene
homo and
copolymers with a broad molecular weight distribution, generally in the range
of 3-30,
which have improved tensile and impact strength relative to Ziegler-type
catalysed
polymers. They are also characterised by having considerably narrower short
chain
branching distributions, and lower hexane extractables. Such polymers are
suitable for use
in embodiments of the present invention.
In terms of densities, the plastomers suitable for use in the process of
embodiments of the present
invention are comparable to VLDPE or ULDPE, which are also copolymers of
ethylene
with a-olefins, such as butene, hexene or octene. They are generally defined
as ethylene
alpha-olefin copolymers vvith densities between 0.86 and about 0.915, The
process for
making VLDPEs is generally described in EP 1205.03. Plastomers, even those
with the
same density as VLDPEs, have greatly different physical properties due to
differences in
the manufacturing process - primarily in the use of metallocene catalysts. In
general, a
VLDPE compared to a plastomer of similar density has a significantly higher
melting point
and softening point, molecular weight/size distribut.ion higher than 3 and a
higher level of
crystallinity.
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Elastie s'ubstantially linear olefin polymers as disclosed in a number of
patents including
US 5,272,236, US 5,278,272, US 5,380,810, US 5,525,695 and US 5,665,800. As an
example of an elastic substantially linear olefin polymer, US Patent 5,578,272
describes
one type as having a critical shear rate at onset of surface melt fracture of
at least 50%
greater than the critical shear rate at onset of surface melt fracture of an
olefin polymer
having the sarne 12 and Mw/M,,. These polymers also have a processing index
(PI) less than
or equal to a comparative linear olefiti polymer at the same IZ and MW/M,,.
Elastic
substantially linear polymers comprising ethylene homopolymers and
interpolymers of
ethylene with at least one C3-C2o a-olefin copolymers a.re espeaially
preferred. The term
"interpolymer" is used herein to indicate a copolymer or a ter polymer or the
like. That is,
at least one other comonomer is copolymerised with ethylene to make the
interpolymer.
The term "substantially linear" polymers means that the polymer backbone is
substituted
with about 0.01 to about 3 long chain branches per 1000 carbons, most
preferably 0.03 to I
long chain branches per 1000 carbons. The tcrm "linear olefm polymer" means
that the
polymer does not have long-chain branches, as for example the traditional
linear low
density polyethylene or linear high dexzsi.ty polyeth.ylene polymers made
using Ziegler
polymerisation processes (eg US Pat 4076698 and 3645992).
The SCBDI (short chain branch distribution index) is defined as the weight
percent of
molecules having a comonomer content within 15% of the median total molar
comonomer
content. The SCBDI of the substantially linear polymers suitable for
embodiments of the present
invention is greater than about 30% in some embodiments, and possibly greater
than about 50%.
A unique chatacteristic of the substantially linear polymers of embodiments of
the present invention is a
highly unexpected flow property where the I10/I2 value is essentially
independent of
poIydispersity index (ie. Mw/Mõ). This is contrasted with conventional
polyethylene resins
having rheological properties such as the polydispersity index, the I1p/IZ,
increases. The
density of the ethylene or ethylene/a-olefi.n substantially linear olefin
polymers in
embodiments of the present invention is generally finm about 0.85g/cm3 to
about 0.97g/cm3, illustratively from
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about 0.85 to 0.92 g/cm3.
The substuitially linear polymers suitable for use in the process of
embodiments of the present invention
have processability substantially similar to that of high pressure LDPE, while
possessing
the strength and other physical properties similar to those of conventional
LLDPE without
the benefit of special adhesion promoters (eg processing additives such as
Viton
flouroelastomers made by Du Pont).
US Patent 5,525,695 describes, a manufacturing method for "substantially
linear
polyethylenes", and characterises them as having:
A. a density from about 0.85 g/cm3 to about 0.97 g/cm3;
B. au MI froin 0.01 g/10 inui to 1000 g/l0 min;
C. and preferably a melt flow ratio of Tlu/1-, from about 7 to 20; and
D. a molecular weight distribution preferably less than 5, especially less
than
3.5 and most preferably from about 1.5 to 2.5.
Elastic substantially linear olefin polymers can be made with broader
molecular weight
distributions by means of tlie appropriate selection of catalysts for the
polymerisation
process as described in US 5,278,272. Broader MWD material exhibits a higher
shear rate
or shear stress dependency. In other words, generally the broader the MWD, the
higher the
effective MFI at high shear, and hence the better the processing
characteristios, Broad
molecular weight "substantially linear olefin polymers", plastomers and
metallocene
branched polyethylenes are partieularly suited to the production of tubes by
the process of
embodiments of the present invention.
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Further, we have found that some types of polymers, illustratively unsaturated
polymers such as polyvinyl chloride and polystyrene, possibly polyolefins and
plastomers, 'substantially linear polyethylene', metallocene branched
pblyethylene and
polypropylene copolymers and even plastomers and `substantially linear
polyethylene'
polymers and polypropylene copolymers having densities between 0.87 and 0.92
and
MFIs above 10, illustratively above 20 and above 30 in some embodiments may,
with the
addition only of nucleating agents as a means of improving the ESCR of the
tubes, be used
to produce tubes suitable for packaging some less aggressive products.
However, the addition
of compatible polymers such as polypropylene and polypropylene copolymers to
such
polymers in addition to the nucleating agents results in better overall ESCR
resistance.
It has been established that polymers, but particularly plastomers and
substantially linear
olefins, having higher-than-normal 110/12 values which are essentially
independent of
polydispersity index (ie. Mu,.'Mõ) and metallocene polypropylene homo and
copolymers are
particularly suited to the manufacture of injection moulded tubes and other
thin-walled articles
having good ESCR and other physical/chemical properties. As discussed in US
5,281,679
`broadening the molecular
weight distribution of a polymer - and particularly polyethylene and its
copolymers - increases
the tensile strength and impact strength of products made therefrom. The main
reason for
high I,o/I, in a polymer is the presence of both high MW and low MW molecules
in the
polymer. It is believed that the high MW molecular fraction contribute
significantly to
improving the ESCR properties of the polymer, while the low MW molecular
fraction
contribute to the improved processability of the polymer by increasing the
shear sensitivity
of the polymer, thereby enabling the polymer to be molded into tubes in spite
of the
apparently low MFI (usually measured as I,) of the polymer.
High I102 polymers suitable for embodiments of the present invention may be
produced by a variety of
methods. These include:
1) intimately blending two or more polymers having different molecular
weights. in
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appropriate blending equipment;
2) producing bi or multi modal polymers with high I10/12 by means of "tandem"
reactors; and
3) producing bi or multi modal polymers with high Ilo/IZ in a single reactor
using
appropriate catalysts.
The catalysts used to produce bi or multi modal polymers with high II042 may
be selected
to produce:
1) broad molecular weight distribution polymers (eg, with molecular weight
distribution in the 3-30 range as described in US patent 5,281,679;or
2) effeetitrely two or more polymers, each having either a narrow or broad
molecular
weight distribution as desrred. US 5,539,076 describes a method of
manufacturing
bi or multi modal polyethylene polymers with densities between 0.89 and 0.97
in a
single reactor.
Other polymers suitable for injection moulding tubes are silane-grafted or
copolymerised
polymers. Suah polymers can be crosslinked post-processing, resulting in
mouldable/processable, crosslinked polymer compounds which provide the ease of
pro4essability and design/process flexibility of relatively low viscosity
polymers while
achieving the strength and other benefits of higher viscosity, cross-linked
polymers and
copolymers. These polymers also eliminate the need for prolonged cycle times
and
elevated teniperatures to aehieve in-niould crosslitiking. There are nurnerous
patents
describing various aspects of the method of preparing and crosslinking of
various silane-
based compositions that can be used in embodiments of the present invention.
Included are US Patents,
5,055,249, 4,117,063, 4,117,195, 4,413,066, 4,975,488 and, 3,646,155.
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In a further aspect of the present invention there is provided a compound in
which all the
ingredients can be mixed in a single step in an extruder immediately prior to
injection
moulding. The compound consists of one or more polymer types, such as
acrylates or
branched metallocene-catalysed ethylene alpha-olefin plastomers which is
reacted with an
organosilane compound such as vinyl trimethoxy silane in the presence of a
peroxide, such
as dicumyl peroxide, to produce a silane-grafted polymer - this r active
processing taking
place in the barrel of an injection moulder. Then, just prior to injecting the
silane grafted
polymer into a mould, a catalyst such as dibutyl tin dilaurate is introduced
into the silane-
grafted polymer in the barrel of the moulder and mixed to ensure intimate
mixing of the
catalyst and the grafted polymer. The catalyst facilitates the post-moulding
crosslinking of
the silane components on the polymer backbone in the presence of moisture by
means of
condensing the hydrolysable silane groups on different polymer backbones, thus
producing
a new polymer which has properties that are a combination of the properties of
the individual
polymers from which the silane-grafted polymers have been produced as well as
the properties
conferred by the higher molecular weight polymer molecules that result from
the above
crosslinking. The final properties of the new polymer can be varied by
changing the
proportions of the various polymers, varying the nature of either or both
polymers (eg. by
using polymers with additional functional groups such as vinyl acetate and/or
varying the
properties of the silane-containing polymer by, for example, changing the type
of
polyethylene and/or silane type chemically bound to a polymer). The fmal
properties can
further be changed by the addition of other compounds/additives such as
fillers, plasticisers
and antioxidants that are well known to anyone practised in the art of polymer
compounding.
An altsniative method of producing silane grafted polymers suitable for use in
embodimeaits of the preserit
invention is to graft the silane onto the polymer in the presence of a
peroxide or other free-
radical generator in a suitable reactor, such as an extruder as a separate
step, and to package
the resultant grafted polymer in moisture proof packaging for subsequent use.
When desired,
the grafted polymer may be introduced into the injection moulder together with
a suitable
amount of a condensation catalyst, the two components being intimately blended
together in
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the moulder, and then injection moulded and cross-linked post-processing.
The silane-containing polymer typically contains between 0.1 and 15 % of
hydrolysable silane.
The most conunon hydrolysable silanes used in the production of silane-
containing polymers
are vinyltrimethoxysilane, vinyltriethoxysilane, but can be any hydrolysable
silane that can
be incorporated into another polymer to form a silane-containing polymer.
The at least one compatible agent is a polymer in some embodiments and when
blended with the at least
one polymer results in blends having properties which, when blended is used to
mould thin-
walled articles such as flexible injection moulded tubes, are superior to the
original
constituents or the neat polymers. The at least one compatible agent may be
selected from
the group consisting of ethylene vinyl acetate; ethylene vinyl alcohol;
plasticised polyvinyl
acetate and polyvinyl alcohol; alkyl carboxyl substituted polyolefins;
copolymers of
anhydrides of organic acids; epoxy group containing copolymers; chlorinated
polyethylene;
ethylene-propylene-butylene etc. copolymers; ultra low density, very low
density, low
density, medium density and high density polyethylene; polypropylene,
polybutylene and
copolymers thereof; polyester ethers; polyether-esters (such as DuPont's
Hytrel range);
acrylonitrile-methacrylate copolymers; block copolymers having styrene end
blocks; half
esters; amino and alkoxysilane grafted polyethylenes; vinyl addition polymers;
styrene-
butadiene block copolymers; acid grafted polyolefins; vinyl pyrrolidine
grafted polyolefins;
block copolymers of dihydric monomers; propylene graft unsaturated esters;
modified
polyolefins comprising amide, epoxy, hydroxy or C2 - C6 acyloxy funetional
groups other
polymeric compatibilisers suitable for use with polyolefms; particles coated
with any of the
above; and mixtures thereof. In the above compatible agents the functional
groups are
,25 generally incorporated into the modified polyolefin as part of an
unsaturated monomer which
is either copolymerised with an olefin monomer or grafted onto a polyolefin to
form the
modified polyolefin.
Alkyl carboxyl substituted polyolefins may include substituted polyolefins
where the carboxyl
groups are derived from acids, esters, anhydrides and salts
thereof.''Carboxylic salts include
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neutralised carboxylic acids and are often referred to as ionomers (eg.
Surlyn). Typically
acids, anhydrides and esters include methacrylic acid, acrylic acid,
ethacrylic acid, glysidyl
maleate, 2-hydroxyacrylate, diethyl maleate, maleic anhydride, maleic acid,
esters of
dicarboxylic acids, etc. Examples include ethylenically unsaturated carboxylic
acid
copolymers such as polyethylene methacrylic acid and polyethylene acrylic acid
and salts
thereof.
Copolymers of anhydrides of organic acids include copolymers of maleic
anhydride as well
as copolymers of cyclic anhydrides.
Poly-2-oxazoline compounds and fliinroelastomers are also suited for use as
compatible
agents. Incorporation of 1-40%, iIlustratively 2-20% of poly-2-oxazoline
compounds is suitable in
some embodiments. These compatible agents improve the adhesion of the PE blend
to various
substrates, which may make them useful for prir~ting or labelling. The
compatibilizing agent
comprises an alpha-olefin copolymer substrate grafted with amounts of
monovinylidene
aromatic polymer. The alpha-olefin copolymer substrate is a terpolymer of
ethylene,
propylene and a non-conjugated diolefin in some embodiments.
Many copolymers of ethylene are also useful as compatible agents in the
process of
embodiments of the present invention. For example single site catalysed
polymers such as metallocene
catalysed polyethylene may be used as compatible agents in some embodiments of
the present invention.
Polypropylene suitable as compatible agents for use in the process of
embodiments of the present
invention may include isotactic, syndiotactic and attactic polypropylene and
syndiotactic polypropylene
of various MFIs, densities and cry,stallinities as would produce desired
properties in products
moulded by the process of embodiments of the present inventiorL Particularly
when blended with low
molecular weight plastomer:;, a wide variety of polypropylene polymers
possessing a very
wide range of MFIs (1-200+), densities and crystallinities will produce blends
suitable for
use in the process of embodiments of the present invention.
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Polyethylene suitable as compatible agents for use in the process of
embodiments of the present invention may
include polyethylenes of various MFIs, densities and crystallinities as would
produce desired
properties in products moulded by the process of the present invention.
Included are very
low, low, medium and high density polyethylene. Particularly when blended with
low
molecular weight plastomers, substantiatly linear polyethylenes, and
metallacocene branched
polyethylene polymers. A wide variety of polyethylene polymers possessing a
very wide
range of MFIs (1-200+), densities and crystallinities will produce blends
suitable for use in
the process of embodiments of the present invention.
Many monomers have been copolymerized with propylene to form copplymers of
propylene.
Many of tbese copolymers are suitable as compatible agents for use in
embodiments of the present inventiorL
Examples of ethylene-propylene copolymers include Montell's SMD6100P,
XMA6170P.
Further examples of polypropylene copolymers are Montell's Catalloy KS-084P
and KS-357P
- these products are believed to be terpolymers of propylene, ethylene and
butene. Other such
copolymers and/or terpolymers may be used.
lonomers provide particular advantages as compatible agents when combined with
plastomers,
substantially linear polyethylene, and branched polyethylenes as the at least
one polymer.
lonomers are typically copolymers of ethylene and acrylic or methacrylic acids
which have
been neutralised with metal ions such as sodium, lithium or zinc. One group of
ethylene
copolymers, called ionomers, are exemplified by the commercial product Surlyn
(manufactured by DuPont). Ionomers tend to behave similarly to cross linked
polymers at
ambient temperature, by. being stiff and tough, yet they can be processed at
elevated
temperatures. The blend of plastomer and ionomer is used in some embodiments,
such blends
provide polymers with increased barrier properties.
The block copolymers of dihydric monomers may include block copolymers of
dihydric
phenol monomers, a carbamate precursor and a polypropylene oxide resin.
The compatible agent is used in an amount at least sufficient to improve the
environmental
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stress crack resistance of the polymer blend. Standard tests for environmental
stress crack
resistance are of little value in determining how particular polymer blends
will perform in the
manufacture of thin walled articles such as tubes. While not wishing to be
bound by theory
it is believed that the injection moulding of thin walled articles such as
tubes introduces and
freezes unique stre.sses into mouldings. The degree and orientation of
stresses in articles such
as injection moulded tubes result in their susceptibility to environmental
stress cracking.
Accordingly, in order to demonstrate the improvement in environmental stress
crack
resistance resulting from embodiments of the present invention, the test
hereinabove described was developed.
In certain formulations, 2% or less of compatible agent is sufficient to
improve the
environmental stress crack resistance of the polymer blend relative to the
environmental stress
crack resistance of the plastomer.
The compatible agent may also be used in amounts in excess of those required
to compatiblise
the polymer blend in order to improve the viscosity characteristics of said
polymer blend so
as to optimise the moulding characteristics of said polymer blend and/or
general properties
of the moulded product such as softness and flexibility. Typically, the
compatible agent is
used in an amount of from about 2 to about 98 weight percent of the polymer
blend, although
lower amounts may be used in certain polymer blends. The optimum amount for a
specific
formulation will depend on the properties required and can be deterrnined by
experimentation.
Further it has been found that inclusion of percentages of compatible agent
that are greater
than necessary for increasing the environmental stress crack resistance of the
polymer blend
will often also enable the improvement of the polymer blend properties such as
tear and
impact strength, barrier properties, chemical resistance, processing and
product feel . For
example, the incorporation of greater than necessary percentages of
polypropylene to improve
the environmental stress crack resistance of a polyethylene blend to the
desired level may
improve the chemical resistance and reduce the water vapour and water
transmission ratio of
the polymer blend compared to polymer blends containing the minimum amount of
polypropylene required to improve the environmental stress crack= resistance
only. Further,
it has been found that the inclusion of greaterthan necessarY percentages
ofcompatible agent
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may enable the incorporation of greater percentages of other polymers than
would otherwise
be consistent with this invention. Thus, using the compatible agent in such
quantities may
enable the incorporation of greater-than-otherwise-possible amounts of such
beneficial,
essentially incompatible other polymers such as nylons and EVOH - with
concomitant
improvements in properties such as tear and impact strength, barrier
properties, chemical
resistance and product feel.
Barrier resins may be incorporated into the polymer blends of the present
invention. Barrier
resins that may be compatibilised with the at least one polymer include:
condensation
polymers such as polyamides, polycarbonates and various esters such as
polyethylene
terephthalate (PET), polybutylene .erephthalate (PBT), polyethylene
naphthalate (PEN);
polyvinylchloride (PVC); polyvinylidene chloride (PVDC); ethylene vinyl
alcohol (EVOH);
polyvinyl alcohol (PVOH); ethylene vinyl acetate (EVA); EMA, EMAA, EEA;
ionomers;
monovinylidine aromatic polymers and copolymers; ethylene, propylene and
butylene
copolymers; chlorosulfated polyethylene, polyisoprene and polychloroprene,
polyalkalenephenylene ester and ester ether; phenylformaldehyde; polyacrylate;
polyester
ethers; acrylonitrile-methacrylate copolymers; nitrile copolymers;
polyacrylonitrile;
polyurethane and polyacetyls. It will be appreciated that certain barrier
polymers will be
more or less compatible with the at least one polymer than others. For
example, EVOH with
-20 a sufficiently high ethylene content will be compatible with the at least
one polymer,
particularly when said polymer is an ethylene copolymer such as a plastomer,
while EVOH
with a relatively low ethylene content will be essentially incompatible.
Barrier properties of
the polymer blends of embodiments of the present invention may be further
enhanced by the addition of
additives capable of reacting with or absorbing deleterious chemicals such as
oxygen and
other gases.
The polymer blend may also incorporate a variety of other additives. Examples
of additional
additives include further polymers, pigments, dyes, fillers, antioxidants,
plasticisers, UV
protection, viscosity modifying agents, additives capable of reacting with or
absorbing
.30 deleterious chemicals such as oxygen and other mould release agents and
melt strength
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modifiers amongst others. These additives may be added to one or more
components of the
polymer blend or the polymer blend as a whole prior to moulding in order to
modify its
properties to suit specific applications or to achieve specific effects in the
end product.
In order to obtain the desirable barrier properties using an essentially
incompatible polymer
and without preorientation of the polymers prior to injection moulding that
the melt flow index
of the disperse phase is somewhat greater than the melt flow index of the
continuous phase at
the same shear rate in some embodiments. In particular, the barrier resin
(usually the
disperse phase) has a melt flow index in the range of from 1.1 to 3.5 times
greater than the melt
flow index of the continuous phase in some embodiments. For optimum barrier
properties it is
believed that the disperse phase droplets should distort to form sheets
(lamella structures)
when subjected to stresses inherent in the injection process. However, if the
melt flow index
of the disperse phase is much lower than that of the continuous phase the
droplets of disperse
phase will tend to resist distortion and not form the lamellar structure
desired for optimum
barrier properties. On the other hand, if the melt flow index of the disperse
phase is greater
than that of the continuous phase it will have a greater tendency to break up
under the sheer
stress of mixing thereby leading to a finer dispersion and hence smaller
sheets of barrier
material, thus reducing barrier performance. The polymer blend, including the
barrier
polymer, is subjected to no more mixing prior to moulding than is necessary to
obtain even
mixing in some embodiments. Excessive sheering may result in reduced barrier
properties.
The person skilled in the art will be able to determine the desired amounts of
mixing
necessary to obtain the optimum balance of properties: A further advantage of
the formation
ofthese lamella stn.icues inpolymer blends ofembodiments ofthe pmsent
invention is the abilityto design
the mould in order to facilitate flow of the molten polymer across the mould
as well as
directly down the core. It is believed that sucll a mould design facilitates
biaxial stretching
of the barrier materials to form lamellar structures, which further improve
the barrier
properties of the moulded articles.
Another method in which a lamellar/multilayer structure of polymers may be
promoted for
31 use in embodiments of the present invention is by prearrangement of the
pol,yrners of the blend into a
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composite stream and injecting said stream into the mould for form articles
consisting of
largely discrete, generally planar and parallel layers. This may be achieved
in a number of
ways, including the coextrusion of a composite stream of discrete, generally
planar and
parallel layers of the various polymer components of the blends of embodiments
of the present invention,
if necessary manipulating this composite sftam to form a second composite
stream having an
increased number of layers of substantially uniform thickness, and then
directly injection
moulding the final stream so as to form a multilayer plastic article.
In one embodiment of the present invention, the polymer blend comprises
at least one plastomer and at least one ionomer. These polymer blends may
advantageously
incorporate further polymer to impart barrier properties to the blend. For
example, the
incorporation of nylon in such a blend and selecting appropriate blending and
inoulding
conditions substantially reduces the hydrocarbon and gas permeability of the
plastomer. The
high degree of directional orientation caused by the moulding process is
believed to contribute
to the imparting of the highly desirable barrier properties able to be
introduced by the addition
of nylon and other essentially incompatible polymers. Nylon itself must be
stretched and
oriented to form lamellar structures in order to optimise barrier properties.
By incorporating
nylon into the blend of plastomer and ionomer the blend may be injection
moulded to form
components having barrier properties which are believed to have been derived
from the nylon
while retaining resistance to environmental stress cracking.
While not wishing to be bound by theory, we have found that the at least one
polymer appears
to have the property of being able to interact with the at least one
compatible agent whereby
the properties of both the at least one polymer and the at least one
compatible agent are
significantly and unexpectedly changed to enable the polymer blend thus
produced to be
suitable for the production of thin-walled articles.
It is believed that the interaction between the at least one polymer and the
at least one
compatible agent forms regions within the moulded articles which can be
regarded as
"joints". These "joints" appear to absorb or disperse stresses in articles
made from the
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polymer blend. The presence of these "joints" interspersed within the article
appear to absorb
or dissipate the stress which would otherwise result decreased physical
properties. It is
believed that these so called "joints" result from one or more of the
following mechanisms:
(i) the polymer and the compatible agent interact, resulting in an increase in
the number
of amorphous areas within the polymer;
(ii) the interaction between the polymer and the compatible agent results in
significant
localised reduction in crystallinity, ie. relatively amorphous regions, at the
interface
between the polymer and the compatible agent; and
(iii) interaction between the polymer and the compatible agent which, while
not resulting
in reduced crystallinity and hence more amorphous regions, nevertheless
produces a
region at the interface between the polymer and compatible agent which has a
greater
ability to absorb or disperse stresses.
In particular it has been found that when the at least one polymer is an
ethylene homo or
copolymer, and illustratively a plastomer or substantially linear
polyethylene, said polymer is
able to interact with propylene and many of its copolymers, and in doing so
the crystallinity
of said polymer is reduced. It is believed that the propylene polymers act as
crystallising
agents for the at least one polymer and in doing so increases the number of
amorphous
regions within the at least one polymer. DSC analysis shows that they also act
to significantly
reduce the overall crystallinity of the ethylene polymer, and particularly
plastomers and
substantially linear polyethylene polymers. It is further believed that these
amorphous
regions, together with the effects of the interfaces between the at least one
polymer and the
propylene polymer act to reduce or disperse the moulded-in stresses in the
moulded part, thus
increasing its ESCR. At the same time, said at least one polymer interacts
with the at least
one plastomer or substantially linear polyethylene and in doing so
significantly reduces the
crystallinity of the at least one plastomer.
It is believed that many of the polymer blends form a co-continuous lamella
structure and that
the interface between the at least one polymer and the at least one compatible
agent is
characterised by an intimate intermingling of the at least one polymer and the
at least one
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compatible agent at a microscopic level. In other words, it is believed that
the at least one
compatible agent acts as an interacting filler. It is believed that, because
of this intimate
intermingling between the at least one polymer and the at least one compatible
agent the
overall properties of the polymer blend are improved. Particularly when low
molecular
weight plastomers and substantially linear polyethylenes are the at least one
polymer, other
polymers previously regarded as substantially incompatible with polyethylene
may now be
compatibilised and blends thereof possess a range of properties which enables
the
commercially acceptable production of articles not hithertofore commercially
viable.
It has been found that many compounds known to be capable of nucleating the
crystallisation
of polymers, particularly olefin polymers and copolymers and especiolly
ethylene polvmers
and copolymers, improve the ESCR pinpeaties ofpolymers for use in embodiments
ofthe pre5ent inveaition.
Depending on the nature of the individual polymer(s), nucleating agents alone
(ie. without
the addition of compatible agents) are capable of increasing the ESCR of the
polymer(s) to
a level that enables said polymer(s) to be useful for the manufacture of
injection moulded
tubes. It is believed that nucleating agents increase the ESCR of polymers in
tube
manufacture by causing the formation of a greater number of small crystals
than would
otherwise be the case. These greater number of small crystals result in an
increase in the
number of amorphous areas within the polymer which are capable of absorbing or
dispersing
stresses introduced into the tube mouldings during injection moulding - thus
increasing the
ESCR and flex resistance of the product. Suitable nucleating compounds for use
in tube
manufacture include inorganic compounds such as talc, mica, compounds of
various metals
such as oxides and silicates as well as various organic compounds, including
various dyes and
pigments. However, for the most beneficial results 'when injection moulding
tules
nucleating agents are used in conjunction with compatible polymers in some
embodiments.
It has been found that compounds known to be capable of reducing the glass
transition
temperaWum (Td of the at least one polymer of embodiments of the present
invention, particularly olefin
polymers and copolymers and especially ethylene polymers and copolymers,
improve the ESCR
properties of polymers for use in embodiments of the present invention.
Depending on the natum of
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the individual polymer(s), Tg-reducing agents alone (ie. without the addition
of compatible
agents, nucleating agents or "high thermal density agents") are capable of
increasing the
ESCR of the polymer(s) to a level that enables said polymer(s) to be useful
for the
manufacture of injection moulded tubes. It is believed that Ta reducing agents
increase the
ESCR of polymers in tube manufacture by effectively increasing the time that
the polymer
takes to coil down to its crystalline state, thus increasing the amount of
time available for the
polymer molecules to rearrange themselves so as to reduce the moulded-in
stresses. This
results in the moulded part having lower moulded-in stresses than would the
case if its Tg had
not been reduced, thus resulting in the moulded product having a better ESCR.
A suitable
Tg reducing agent is polypropylene. However, for the most beneficial results
when
injection moulding tubes Tg-reducing agents are used in conjunction with
compatible
; agents in some embodiments, unless the Tg-reducing agent is in itself a
compatible agent.
Poly-2-oxazoline compounds and fluoroelastomers are also suitable for use as
compatible
polymers. In some embodiments, incorporaiion of 1-40%, illustrauvely 2 20% of
poly 2-oxazoline
compounds improves the ESCR of polymers (see US 4474928). These compatible
polymers also improve
the adhesion of the PE blend to various substrates, which may make them useful
for
preparation of the PE for printing or labelling.
Although the improved ESCR effects of additives such as nucleating agents and
Tg reducing
agents may not be particularly noticeable in 'normal' mouldings, it is
believed that in
mouldings such as thin walled tubes - in which the polymer is subjected to
fast cooling rates,
high injection speeds, high injection pressures, long, narrow flow paths and
radii, (and
resultant high levels of induced stresses) - the effects can be significant-
even at low levels of
additive addition. It has been found that such additives may improve the ESCR
of certain
polymers to the extent that the at least one polymer and sufficient amount of
additive alone
may be suitable for the production of injection moulded.
According to a further embodiment of the present invention, the at least one
compatible agent
may be incorporated into the at least one polymer. For instance, a polymer
having monomers
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incorporating compatibiliser groups may be copolymerised with other monomers
to form a
compatibilised polymer. For example, a monomer having a methacrylic acid group
may be
added to the polymerisation mixture of the at least one polymer to form a
compatibilised
plastomer. Alternatively, a compatibiliser group may be grafted onto the
polymer.
Advantageously, the polymer onto which a combatibiliser group is grafted is a
plastomer or
a substantially linear polyethylene.
The polymer blend may be prepared by extrusion of some or all of the
components of the
polymer blend and the resulting chopped extrusion used in the injection
moulding process of
embodiments of the present invention. Altematively, the polymer blend may be
provided in its component
form and subjected to mixing before and during the melting of the polymer
blend in the
present process.
The polymer blend may be melted by any convenient means. It is particularly
convenient Lhat
the polymer blend be melted in a conventional injection moulding machine where
a screw
rotating in a heated barrel both melts the polymer blend and rams the molten
polymer blend
into the mould. The articles formed from the polymer blend may be readily
removed from
the mould by convenient means.
The injection moulding process ofembodiments ofthe preserrt invention makes it
possible to produce irgeWon
moulded articles having surprisingly thin sections while retaining the
mechanical properties
of the polymer blend. We have found that articles having cross-sections as
thin as 0.3mm to
0.7mm may be injection moulded, such thin walled articles may have thin walls
over 50mm
in length. These articles may be readily produced without substantial
deterioration of the
mechanical properties of the plastics material.
The polymer blends of embodiments of the present invention which pemiit the
injection moulding of ariicles
having thin sections provides a number of advantages which have been
hithertofore
unattainable due to technical constraints. These technical constraints are
best illustrated in
the manufacture of thin walled tubes. These tubes, which are very commercially
important,
CA 02328700 2008-04-02
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are extruded and therefore preclude the use of control and variation in wall
thickness to
pemlit the manufacture of tubes having controlled and variable wall thickness.
Embodiments of the
present invention provide for the manufacture of articles having thin sections
where the thin sections
are capable of controlled and varied thickness. For example, in the embodiment
of an
injection moulded tube the thickness of the walls of the tube may be varied
along its length.
The wall thickness may be greater at the neck of _the tube thereby allowing
increased
flexibility towards the tail. Embodiments of the present invention may also
allow the incorporation of
embossing onto the thin walls of the tube. The embossing may take the form of
corporate logos,
trademarks, various text, as well as textures or surface finishes such as a
leather grain or
ripples.
A furtiier advantage of embodiments of the present invention which has been
hithectofore unattainable due to
technical constraints is the use of 'in-mould' labelling for decorating thin-
wal(ed tubes.
Extruded tubes cannot be decorated by in-mould labelling, which therefore
requires that any
labelling of such tubes bee-aarried out as a separate and expensive
manufacturing operation.
Tubes producsd by embodiments ofthe prresent invention can be in-mould
labelled during the one-step
moulding process, thereby avoiding the separate and expensive additional
manufacturing
operation. The placement of the labels into the cavity can be achieved by a
variety of means,
including placing the label on the core when the mould is open, closing the
mould and
transferring the label from the core to the cavity via a variety of means just
prior the injection
of the polymer to form an in-mould labelled tube.
A futtiier advantage of embodiments ofthe present invention is the ability to
apply a barrier sheath to all or
part of the core prior to moulding said barrier sheath which is transferred to
the moulded
article during the mouldiu$, process to confer iniproved barrier or other
beneficial properties
to tubes procuced by embodiments ofthe present invention. A further advantage
of embodiments ofthe
presant invention is the ability to apply a coating to either or both the core
and ca.vity ofthe mould piiorto
moulding and which is subsequently transferred during the moulding process to
relevant
surface of the moulded article. This process results in a coating to either
the external or
3 0mtcrnal mrface of the tubes produced by embodiments of the present
inverrtion. Such coatings may have a
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variety of functions, including decorative or barrier.
Embodiments of the present invention which enable the injection moulding of
thin walled
articles also provide for many variations in the shape and configuration of
articles which have
hithertot`ore been restricted due to technical difficulties in manufacturing
thin walled articles.
Again, with reference to the thin walled tube example a variety of closures,
hooks or flaps
may be incorporated into the design. Hithertofore the incorporation of such
additional
components would require separate components to be manufactured and
subsequently welded
or otherwise attached to the tubes, adding significantly to the total cost of
the tube. In
accordance with embodiments of the present invention, the use of appropriately
tool designs and/or dual
injection moulding equipment permits the one-step manufacture of tubes having
integral
closures, hooks, flaps or other appendages fonned from the same or different
polymers.
A number of modifications may be made to standard tube tooling to facilitate
the manufacture
of unitary tube/appendage mouldings, in particular unitary tube/closure
mouldings. Such
unitary tube/closure mouldings can have, if desired, a wide variety of moulded-
in hinges
(including living hinges), dispensing spouts aiid other convenience features
either moulded
in during the moulding process. In cases where the polymer is used to mould
the unitary
tube/closure is insufficiently stiff to allow for the moulding of a
conventional hinge with 'self-
closing' or 'flip' mechanism, the hinge itself may be constructed with a
radius. Provided the
polymer has sufficient elasticity, the radius combined with the elasticity of
the polymer should
result in a self-flipping feature for the closure.
An additional advantage of the process of embodiments of the present invention
is that by enabling the
production of tubes with special contours designed to receive attachments, it
enables the
relatively inexpensive and easy attachment of convenience features such as
self-sealing valves.
A typical tube/self-sealing closure combination consists of at least four and
often five
individual components - a two-part tube (tube body and head/shoulder), a
closure body, a
self-sealing valve, a retaining device for securing the valve to the body and
often a protector
for the valve to prevent discharge of the contents, particularly during
packing and delivery
CA 02328700 2008-04-02
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to retail outlets. The at least three pa.rt.4elf-sealing closure is assembled
separately and then
attached to the tube. The process of embodiments of the present invention
pemiits the production of a one-
part tube/valve receptor/flip-top protector to which the valve and retaining
device can be
easily attached. This reduces the number of parts required to be produced as
well as the
complexity and number of steps of the assembly process. This significantly
reduces the cost
of such tube/closures.
In a further embodiment, the use of the at least one compatible polymer in
accordance with
embodiments of the present invention pennits the manufactiue of aiticles such
as tubes may have protective
or barrier coatings directly applied onto the internal and/or external thin
walled sections
without the need for pretreatment such as corona discharge or flame treatment.
For example,
the incorporation of polyoxazoline compounds may improve the adhesion of
lacquers and
varnishes to the extent of eliminating the need for such pretreatment. This
may be of
particular advantage for containers for food use or for containing substances
which require
specific coatings for their containment.
Alternatively, suitable barrier and other coatings may be applied by
conventional means such
as dipping, spraying, printing, vapour or vacuum deposition, this latter
process being
particularly useful for the application of especially high barrier materials
such as metallic or
non-metallic oxides/nitrides (eg silicone oxide) or fluorine as well as carbon
and/or organic
radicals with useful properties. In addition, some coatings, such as coatings
produced by
reaction of the tube polymer with fluorine, may be further reacted with
monomers containing
various beneficial functional groups to further enhance the properties of the
coatings. For
example, hydroxyl-containing monomers may be reacted with a fluoridated
polyethylene
coating to produce a hydroxyl-containing coating.
By their nature, tubes have thin, soft and flexible walls. This lack of
rigidity in the moulded
tube makes it difficult to eject the moulded part from the core of the mould
by normal
mechanical means common in injection and Lompression moulding and processes
such as
stripper plates and injector pins, without causing potential damage to the
mouldings. A
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further disadvantage is the slow ejection rates often necessary to minimise
the chances of
damage to the tube on ejection.
We have found that using compressed gas to assist with the ejection minimises
the potential
for damage to the tube on ejection, and also allows for rapid ejection. When
the tube has
been formed in the mould cavity and has set sufficiently for the tube to be
retrieved from the
mould cavity, the male and female part of the mould are separated by
telescopically sliding
the male core part out of the female part. At the same time, or subsequently,
the moulded
tube can be separated by injecting compressed gas from within the male core
part and to allow
compressed air to communicate with the inside surface of the end part of the
moulded tube,
most preferably by lifting the tip of the core off the main section of the
core just prior to the
injecting of air in order to break the seal that often exists between the
moulded tube and the
core to facilitate easier removal of the moulded tube. This lifting of the tip
as well as
pressurisation beneath the end part will enable the moulded tube and the male
core part to be
separated by relative sliding movement of the moulded tube over the tip of
male core part.
To assist separation, the male core part may have a very slightly tampered
outside surface,
so the diameter of the male core part is greater at the end of the tube remote
from the end
portion .
Also, the outside surface of the male core part may be formed or treated so as
to have a slight
degree of surface roughness sufficient to inhibit formation of a vacuum seal
between the
moulded portion and the male core part during the introduction of the
pressurised gas. That
is, the degree of surface roughness will allow pressurised air to flow along
the outside surface
of the make core part and expand the moulded tube slightly to separate tube
from the core.
In a further improvement to assist removal of the moulded part from the
cavity, compressed
gas can be injected into the mould just prior to or during the separation of
the core from the
cavity in such a way that the gas flows between the outer surface of the
moulded part and the
interior surface of the cavity, thus assisting the separation of the moulded
part from the cavity
and its subsequent removal from the cavity while on the core of the mould.
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To assist in the polymer to flow more easily into the cavity to form the thin-
walled article
during the injection process, a vacuum may be applied to the cavity just prior
to and during
the injection of the polymer. Mould filling may be further assisted by
balancing polymer
flow within the mould by cutting longitudinal and/or lateral grooves in either
or both the core
cavity to direct and/or speed said polymer flow to selected areas within the
mould.
Fanbodiments ofthe preserrt inventionmayalso allowthe use ofexpmmlable cores
inthe mouldwhich facilitates
the release of the thin walled article from the mould and also allow the
production of thin
walled containers having wide sections adjacent the head and shoulder region
in a manner
hitherto not possible.
Embodiments of the present invention will be further described by the
following non-
limiting examples and drawings.
Figure 1 is a view of a thin-walled container made from the polymer blend of
an
embodiment of the present invention.
Figure 2 is a view of a thin-walled container made from the polymer blend of
an
embodiment of the present invention.
Figure 3 is a view of a thin-walled container made from the polymer blend of
an
embodiment of the present invention.
Figure 4 is a view of a thin-walled container made from the polymer blend of
an
embodiment of the present invention.
Figure 5 is a view of a thin-walled container made from the polymer blend of
an
embodiment of the present invention incorporating a hook integrally moulded
with the
container. The hook may conveniently be replaced with a spreader or other
desirable tool
of convenience.
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Figure 6 is a view of a thin-walled container made from the polymer blend of
an embodiment of the
present invention incorporating a flange with a hole adapted to hang the
container from a hook or
hanger, at a point of sale.
Figure 7 is a view of a thin-walled container made from the polymer blend of
an embodiment of the
present invention incorporating a hook adapted to hang the container from a
hook or hanger, at a
point of sale.
Figure 8 is a cut away view of a thin-walled container made from the polymer
blend of an embodiment of
i the present invention incorporating a barrier coating on the inside of the
container.
Figure 9 is a view of a unitary tube/closure.
Figure 10(a) and 10(b) are views of a tube with a side-pouch for receiving
item such as
15 product samples, toothbrushes or combs.
Figure 11-14 show detail of some support mechanisms for unitary
tube/appendages, and in
particular, unitary tube/closures.
.. 20 Some of the mould design modifications that can be employed to mould
unitary
tube/appendage mouldings are illustrated in Figures 11-14. In these designs:
1. is the runner for molten polymer
2. is a 'flip-top' closure hinged lid
3. is a 'pop' mushroom valve
25 4. is a core
5. is a stem for the 'pop' valve (3)
6. is a tube side-wall
7. is a living hinge
8. are channels/grooves for enhanced polymer flow to the tube side-walls
30 9. is a groove for enhanced polymer flow down the side-walls=of the tube
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10(a). is a support locating on the mushroom valve (3)
10(b). is a support shown in a retracted position
11. are support locations on the mushroom valve (3)
12(a). are supports locating on both the core (4) and the mushroom valve (3)
12(b). is a support locating on the side of the core
13. is an extendable core support shown in the extended position
14. is a support location on the female part of the mould
15. is an extendable core support shown in the non-extended position
In cases of unitary tube/appendages where core flexing or lateral core
movement will not
occur if the core is unsupported (for example, in large diameter tubes made
with high MFI
materials), figure 11(a) illustrates the longitudinal cross-section of a mould
with unsupported
core capable of producing a unitary tube/closure. Figure 11(b) is a section
plan on line X-X
of figure 11(a), and figure 11(b) is an alternative X-X to Y-Y section on
figure 11(a). In a
further enhancement of the basic tool design, the tool may have a split along
the X-X, (or X-
X) line so that the part of the tool defined by X-X, (or X-XZ) and Y-Y can be
separated from
the part of the tool defined by X-X to Z-Z. It may be replaced with an
alternative X-X, (or
X-X) to Y-Y tool part [see figure 11(c)] incorporating a different closure
design or type to
enable the manufacture of a tube with a different closure. The same principle
may be
extended to other appendage types. The ability of this general mould design to
be easily
modified by means of 'change parts' for the moulding of tubes with a variety
of different
attachments also enables, if desired and with the appropriate 'charge parts',
the moulding of
tubes with no attachments-ie. 'standard' tubes with 'head and shoulders'.
In cases of unitary tube/appendage where core flexing is likely to occur if
the core is
unsupported, a number of designs are capable of stabilising the core against
lateral movement
(and hence variable wall thickness) while still permitting the moulding of the
unitary
tube/appendage.
Figure 12) illustrates a tool design in which the core is stabilised against
flexing by the use
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of one or more supports which are projected out from the top of the female
half of the mould
and press down onto the 'pop' valve on the core of the male mould during the
injection of the
polymer to form the article. Once the polymer has been injected to fill the
mould, but prior
to the shutting off of the barrel valve, the supports are raised to allow
polymer to flow into
the gaps left by the supports, thereby ensuring the formation of completed
moulding. 10(a)
shows a support located on the 'pop' valve of the core, and 10(b) shows the
support raised
to allow polymer to flow into the gaps left by the raised support. If
appropriate, the support
may be located into a 'support location area' (11). Figure 12(b) is a section
plan on the X-X
line, showing a series of location areas for supports on the pop-valve.
Figure 13) illustrates a tool design in which the core is stabilised against
flexing by the use
of one or more supports [12(a) and 12(b)] which project out from the cavity to
support the
core from the side during the injection of the polymer to form the article. An
advantage of
support 12(b) is that it also pushes the mushroom valve (3) firmly onto the
core (4), thus
minimising the chances of it lifting under injection pressure. Once the
polymer has been
injected to fill the mould, prior to the shutting off of the barrel valve, the
supports are
retracted to allow polymer to flow into the holes left by the supports,
thereby ensuring the
formation of the completed moulding.
Figure 14) illustrates a tool design in which extendible supports within the
core are extended
and firmly located into the female part of the mould to 'anchor' the core
against lateral core
movement. Once the polymer has been injected to fill the mould, prior to the
shutting off of
the barrel valve, the support is retracted to allow polymer to flow into the
spaces left by the
retracted support, thereby ensuring the formation of the completed moulding. A
variation of
the above mechanism is to project the whole core upwards to locate it into the
female part of
the mould, and when the polymer has been injected to fill the mould, but prior
to shutting off
of the barrel valve, the entire core is retracted to allow polymer to flow
into the new cavity
left by the retracted core, thereby ensuring the formation of the completed
moulding.
Another advantage of this arrangement (ie. not locating the core through the
centre of the
closure to be formed) is that the centre of the closure is not restricted by
locating devices.
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This enables the formation of quite complex closures (eg with spouts and
membranes that
enable effective 'cut-off' of tube contents) as per some medicine bottles. In
a further
variation the mould can be designed to allow a very thin film to be formed
across the tip of
the aperture of the closure for 'tamper evident' proof.
Among the main advantages of stabilising mechanisms such as are shown in
figures 12-14 is
that the core supports are located 'off-centre' thereby allowing the injection
point to be
unimpeded in a central location. This allows for the formation of 'centrally
suited'
appendages such as apertures and flow control mechanisms that would otherwise
need to be
located 'off-centre'. If' 'off-centre' positioning of apertures and other
appendages is
acceptable or required, central location of the support is possible via a
number of
mechanisms, which are well known to those practised in the art.
Example 1
A polymer blend made from 50% Exact 4038, 20% Catalloy KS059P and 30% Montell
6100P was injection moulded to form a tubular container having a body having
the form of
a continuous cylinder 35mm in diameter and 150mm in length and a neck and
shoulder
portion adapted to receive a screw cap. The thickness of the continuous
cylinder varied from
0.8 mm adjacent to the neck and shoulder portion to 0.5mm at the remote end.
The tubular
container was found to possess properties suitable for use in, for example,
the cosmetics
industry.
Example 2
A polymer blend made from 60% Exact 4038 and 40% Montell 6100P was injection
moulded
to form a tubular container having a body having the form of a continuous
cylinder 35mm
in diameter and 150mm in length and a neck and shoulder portion adapted to
receive a screw
cap. The thickness of the continuous cylinder varied from 0.8 mm adjacent to
the neck and
shoulder portion to 0.5mm at the remote end. The tubular container was found
to possess
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properties suitable for use in, for example, the cosmetics industry.
Example 3
A polymer blend made from 24% Exact 4038, 56% Affinity 1350 and 20% Surlyn
9970 was
injection moulded to form a tubular container having a body having the form of
a continuous
cylinder 35mm in diameter and 150mm in length and a neck and shoulder portion
adapted to
receive a screw cap. The thickness of the continuous cylinder varied from 0.8
mm adjacent
to the neck and shoulder portion to 0.5mm at the remote end. The tubular
container was
found to possess properties suitable for use in, for example, the cosmetics
industry.
Example 4
A polymer blend made from 24% WSM 168 (Orica Australia Pty Ltd), 56% Affinity
1350
and 20% Surlyn 9970 was injection moulded to form a tubular container having a
body
having the form of a continuous cylinder 35mm in diameter and 150mm in length
and a neck
and shoulder portion adapted to receive a screw cap. The thickness of the
continuous cylinder
varied from 0.8 mm adjacent to the neck and shoulder portion to 0.5mm at the
remote end.
The tubular container was found to possess properties suitable for use in, for
example, the
cosmetics industry.
The ESCR Test
Six thin sections of injection moulded polymer blend, 0.65mm thickness were
used to
determine environmental stress crack resistance. Sections 10mm wide are cut
transverse to
the major direction of flow of the polymer blend in the mould and are
subsequently treated
with any post-mould treatments. Each section is bent back on itself and
stapled 3mm from
the bend. The bent sections are immersed in a 10% Teric N9 solution at 50 C
(Teric is a
trademark of Orica Australia Pty Ltd). The strips are then regularly checked
for signs of
cracking. Any sign of cracking is regarded as a failure. The time at which 50%
(3) of the
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sections have failed is regarded as the time to failure of the polymer blend.
The test is
concluded after 360 hours if the polymer has yet to fail.
Comparative Example A
Dow Affinity plastomer having a crystallinity of approximately 34% was
injection moulded
and six sections were cut from the mould and subjected to the ESCR Test. The
results are
shown in Table 1 below.
Examples 5 to 7
Dow Affinity plastomer having 34% crystallinity was compounded with
polypropylene ADP
126 (Montell ) in amounts identified in Table 1 below. The blends were
injection moulded
and six sections were cut from the mould and the ESCR Tests performed. The
results are
shown in Table 1 below.
TABLE 1
Example Dow Affinity Polypropylene ESCR Test (hr)
Plastomer ADP 126
Comparative 100% 7
A
8 97.5% 2.5% 30
9 95% 5% 60
160% 40% 360+
Examples 8 to 10
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Dow Affinity plastomer having approximately 34% crystallinity was compounded
with Surlyn
9970 (Du Pont) in amounts identified in Table 2 below. The blends were
injection moulded
and six sections were cut from the mould and the ESCR Tests performed. The
results are
shown in Table 2 below.
TABLE 2
Example Dow Affinity Surlyn 9970 ESCR Test (hr)
Plastomer Du Pont
Comparative 100% 7
A
8 97.5% 2.5% 15
9 95% 5% 30
F, 70 % 30% 360+
Example 11
A polymer blend of 80% Dow Affinity (34%), 19% nylon B3 (BASF) and 1.2% Surlyn
9970
was blended. The polymer blend was injection moulded and subjected to the ESCR
Test.
The polymer blend had an ESCR Test result of 360+ hours.
Example 12 and 13
A polymer blend of 79% Dow Affinity (approximately 34% crystallinity) and 30%
Surlyn
9970 was blended and injection moulded to form a thin-walled tube. A second
polymer blend
of 76% Dow Affinity (24% crystallinity), 20% nylon B3 (BASF) and 4% Surlyn was
blended
and injection moulded to form a thin-walled container. The thin-walled
containers were filled
with petrol and sealed. The polymer blend incorporating 20% nylon and 4%
Surlyn showed
a permeability to petrol approximately 20 times less than that of the blend
containing
plastomer and Surlyn only.
Example 14
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Dow Affinity plastomer having approximately 34% crystallinity was compounded
with Ti02
in the amount identified in Table 3 below. The blends were injection moulded
and six
sections were cut from the mould and the ESCR Tests performed. The results are
shown in
Table 3 below.
TABLE 3
Example Dow Affinity 1300 TiO2 EScr Test (hr)
A 100% 0% 7
B 96.5% 3.5% 22
Those skilled in the art will appreciate that the invention described herein
is susceptible to
variations and modifications other than those specifically described. It is to
be understood
that the invention includes all such variations and modifications which fall
within its spirit and
scope. The invention also includes all of the steps, features, compositions
and compounds
referred to or indicated in this specification, individually or collectively,
and any and all
combinations of any two or more of said steps or features.
