The present invention relates to food packaging comprising a polymer
blend of polyketone and PVC in particular uPVC.
For the purposes of this patent, polyketones are defined as linear
polymers having an alternating structure of (a) units derived from carbon monoxide
and (b) units derived from one or more olefinically unsaturated compounds.
Such polyketones have the formula:
where the R groups are independently hydrogen or hydrocarbyl groups, and m is a
large integer; they are disclosed in several patents e.g. US 3694412. Processes
for preparing the polyketones are disclosed in US 3694412 and also in EP 181014
and EP 121965. Although for the purposes of this patent polyketones correspond
to this idealised structure, it is envisaged that materials corresponding to this
structure in the main but containing small regimes (i.e. up to 10 wt%) ofthe corresponding
homopolymer or copolymer derived from the olefinically unsaturated compound, also
fall within the definition.
Polyketones particularly those prepared using ethylene and CO have
high melting points which are close to the temperatures at which they undergo chemical
degradation. EP 213671 teaches that polyketones comprising carbon monoxide, ethylene
and an alpha olefin (eg propylene) units have lower melting points than corresponding
copolymers comprised only of carbon monoxide and ethylene units.
Although polyketones are known to exhibit good barrier properties,
in particular oxygen barrier properties, it is desirable to improve these properties.
It has now been found that the addition of PVC, in particular uPVC can be used
to enhance the oxygen barrier performance of polyketones without serious deterioration
of its moisture barrier performance.
Thus according to the present invention, there is provided food packaging
comprising a blend of polyketone and PVC.
Blends of polyketone and PVC are particularly advantageous when used
for food packaging since polyketones can be used to improve the thermal properties
of PVC, while at the same time retaining good barrier properties.
As noted above for the purposes of this patent, polyketones are defined
as linear polymers having an alternating structure of (a) units derived from carbon
monoxide and (b) units derived from one or more olefinically unsaturated compounds.
Suitable olefinic units are those derived from C2 to C12 alpha-olefins
or substituted derivatives thereof or styrene or alkyl substituted derivatives
of styrene. It is preferred that such olefin or olefins are selected from C2
normal alpha-olefins and it is particularly preferred that the olefin
units are either derived from ethylene or most preferred of all from a mixture
of ethylene and one or more C3 to C6 normal alpha-olefin(s)
especially propylene. In these most preferable materials it is further preferred
that the molar ratio of ethylene units to C3 to C6 normal
alpha-olefin units is greater than or equal to I most preferably between 2 and
30. Typically, the polyketone will be a terpolymer of ethylene/propylene/CO where
the units derived from propylene are present in the range 5-8% e.g. 6% by weight
of the polymer. The Melt Flow Rate (5kg load at 240°C) is typically in the range
5-200 preferably 10-150, more preferably 20-100 for example 40-80g/10 mins.
The polyketone will suitably have a number average molecular weight
of between 40,000 and 1,000,000 preferably between 50,000 and 250,000 for example
60,000 to 150,000. A preferred polyketone is a ethylene/propylene/CO terpolymer
having a number average molecular weight in the range 60,000 to 150,000.
As regards the PVC it can be either Plasticised (Flexible) PVC or
unplasticised (rigid) PVC (uPVC); it is particularly with uPVC that this invention
is concerned. Where uPVC is used, it may contain a small amount for example up
to 20% but preferably less than 5% by weight of plasticisers; however where a more
flexible material is needed, plasticised PVC will be used. Typical plasticisers
are phthalates, phoshates, and trimellitates.
As regards the Molecular Weight of PVC, this is measured by its K-value.
PVCs will typically have a K-value in the range 45 to 100, preferably 50 to 80
especially 55 to 75, e.g. 60 to 70.
The PVC may comprise conventional additives such as heat stabilisers,
blowing agents (for foams) filler, lubricants and pigments.
The polymer blend composition of the present invention can be prepared
using conventional techniques and equipment for batch or continuous blending.
The weight ratio of polyketone to PVC is suitably in the range 1:10
to 10:1 preferably 1:3 to 3:1 more preferably 1:1.5 to 1.5:1 for example 1:1. However,
it is preferred to use 1-50% by weight of PVC preferably 1-20 more preferably5-15%
e.g 10% (i.e. a polyketone to PVC ratio of 9:1). Other polymers may be blended
with the blend composition of the present invention; the nature and amount of
such a polymer will depend upon what modifications of the polymer properties are
required. Furthermore the blends of the present invention may contain conventional
polymer additives such as anti-oxidants, stabilisers, and mould release agents.
The scope of the present invention extends to articles for example
moulded articles comprising the blends as defined hereinbefore insofar as they
are for use with food.
In a further aspect of the present invention there is provided foodstuff
contained in packaging made from a blend of polyketone and PVC.
In yet another aspect of the present invention there is provided the
use of a blend of polyketone and PVC to package foodstuffs.
In another aspect of the present invention there is provided packaging
made from polyketone and PVC and instructions for use with foodstuffs.
The invention is illustrated by the following examples.
Window profile grade from Elf-Atochem, barium/cadmium stabiliser
package, acrylic impact modifiers and calcium carbonate filler, with a K value of
A series of EPCO/uPVC blends were prepared using an APV (15mm) twin
screw extruder. Blends containing 10, 20, 30, 50, 70% w/w uPVC were subsequently
compression moulded into ∼ 500µm plaques using the 40 tonne Komtek Press.
Differential scanning calorimetry (DSC) was carried out using a Perkin-Elmer
Series (7) Thermal Analyser. A heating rate of 10°C/min up to 230°C was used to
condition each material, then the sample was cooled from 230 to - 40°C at the same
rate; each cycle was performed under a nitrogen purge. A proportioned weight of
uPVC was placed in the reference pan in order that the EPCO phase could be studied
in isolation. The melting point (Tm) and the heat of fusion (ΔHf) were evaluated
from the second heating (10°C/min) endotherm. The results are shown in Table 1.
The oxygen and moisture barrier performance was measured using the
Oxtran (1000) ASTM D3985 and Permatran (W1) ASTM F-1249-89 respectively. The 10cm
x 10cm x (∼500µm) moulded plaques samples were initially assessed using the
Oxtran (1000) at 23°C and 0, 75 and 90% Relative Humidity (RH) and subsequently
using the Permatran (WIA) at 38°C, 90% RH. The results are shown in Table 2.
CHARACTERISATION OF EPCO/uPVC BLENDS Material Melting Point (°C) Heat of Fusion ΔHf (J/g) EPCO20656.5 + 10% uPVC19453.4 + 20% uPVC18947.0 + 30% uPVC18533.0 + 50% uPVC18532.7 + 70% uPVC18032.5 uPVCN/AN/A