WO2000069749A1

WO2000069749A1 - Packaging containing goods under inert gas comprising at least one player of polyketone

Info

Publication number: WO2000069749A1
Application number: PCT/GB2000/001274
Authority: WO
Inventors: Anthony Keith Powell
Original assignee: Bp Chemicals Limited
Priority date: 1999-05-18
Filing date: 2000-04-05
Publication date: 2000-11-23
Also published as: AU3977300A; GB9911560D0

Abstract

Packaging containing goods under an atmosphere of an inert gas wherein the packaging comprises (i) a mono-layer of a polyketone composition or (ii) a multi-layered structure comprising at least one layer of a polyketone composition; and the inert gas is selected from the group consisting of nitrogen, carbon dioxide, helium, neon, argon and krypton.

Description

PACKAGING CONTAINING GOODS UNDER INERT GAS COMPRISING AT LEAST ONE PLAYER OF POLYKETONE

The present invention relates to packaging, and in particular to packaging comprising (i) a mono-layer of a polyketone composition or (ii) a multi-layered structure comprising at least one layer of a polyketone composition wherein goods contained in the packaging are under an atmosphere of an inert gas. 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 Ri, R₂, R₃ and R» groups are independently hydrogen or hydrocarbyl groups, and m is a large integer; they are disclosed in several patents e.g. US 3,694,412. Processes for preparing the polyketones are disclosed in US 3,694,412 and also in EP-A-0181014 and EP-A-0121965. 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%) of the corresponding homopolymer or copolymer derived from the olefinically unsaturated compound, also fall within the definition.

EP-A-0213671 teaches that polyketones comprising units derived from carbon monoxide, ethylene and an alpha olefin (e.g. propene or butene) have lower melting points than corresponding copolymers comprised only of units derived from carbon monoxide and ethylene. A quantitative relationship is shown to exist between the proportion of units derived from propene in the polyketone and the melting point. The most preferred range of melting points is said to be from 195 to 235°C, corresponding to a specific range of ethylene:propene ratios. Within this preferred range, examples are given of terpolymers comprising units derived from carbon monoxide, ethylene and propene having melting points of 214°C and 220°C respectively (estimated to correspond to contents of units derived from propene of about 4.5 and 3.7 mol% respectively with respect to the total polymer composition). There is no discussion of the oxygen barrier properties of these polyketones.

Although polyketones are known to exhibit good barrier properties, in particular against oxygen, it is desirable to improve these properties. It is known to do this by altering the manufacturing process of the polyketone. US 4,895,689 discloses polyketone terpolymers including as the third component units derived from propene, of which the barrier properties are improved by cooling a heated solution cast film of the polyketone at a selected rate. Ethylene/propene/CO terpolymers having melting points of from 214°C to 224°C (estimated to correspond to contents of units derived from propene of between about 4.5 and 3.5 mol% respectively) are disclosed, having oxygen permeabilities at 30°C and 0% relative humidity (RH) increasing from 1.5 x 10^"12 cc.cm cm^"2 s^"! cmHg^"1 for 224°C melting point (3.5 mol% propene) to 5.3 x 10^"12 cc.cm cm^"2 s^"1 cmHg^"1 for 214°C melting point (4.5 mol% propene). US 5,077,385 describes a melt processed polymer material having improved oxygen, water and/or carbon dioxide barrier properties comprising a polymer comprisiηg at least one ethylenically unsaturated hydrocarbon which has been heat treated to a temperature in the range of 2-40°C above the melting point of the linear alternating polymer then cooled at a rate of about 1 to 20° per minute. It is stated that there appears to be good results using compression moulding temperature 5-15°C above the resin melting point. 15°C above the resin melting point is said to be best. Polyketone polymers usable in US 5,077,385 have preferred melting points of between about 210-260°C (an estimated maximum content of units derived from propene of 4.5 mol%). Specifically disclosed are ethylene/propene/CO terpolymers having a content of units derived from propene of 0, 4.7, 5.0, 8.5, 8.9 and 10.5 %.

An alternative to altering the manufacturing process is to blend the polyketone with a further polymer. EP-A-0759458 discloses blends of polyketones and PNC; in this disclosure, a carbon monoxide/ethylene/propene terpolymer having a melting point of 206°C is shown to have an oxygen permeability at 23 °C and 75% relative humidity (RH) of 0.053 cc.mm/m²/day/atm, or 0.81 x 10^"13 cc.cm cm^"2 s^'1 cmHg^'1. However the addition of 10% uPNC to the polyketone reduces the permeability to 0.010 cc.mm/m²/day/atm. No other data for unblended polyketones is given. The content of units derived from propene of this terpolymer has subsequently been measured as 6.6mol%.

Surprisingly, it has now been found that where polyketones are used in packaging applications as oxygen barriers, very low oxygen permeabilities can be achieved filling the packaging with an inert gas selected from the group consisting of nitrogen, carbon dioxide, helium, neon, argon and krypton.

According to the present invention there is provided a packaging containing goods under an atmosphere of an inert gas characterised in that:

(A) the packaging comprises (i) a mono-layer of a polyketone composition or (ii) a multi- layered structure comprising at least one layer of a polyketone composition; and (B) the inert gas is selected from the group consisting of nitrogen, carbon dioxide, helium, neon, argon and krypton.

By "an atmosphere of an inert gas" is meant that any headspace or other voids in the packaging contain an inert gas.

The present invention is based on the unexpected finding that the oxygen permeability of the polyketone composition is significantly reduced when any headspace or other voids in the packaging contain an inert gas selected from the group consisting of nitrogen, carbon dioxide, helium, neon, argon and krypton. Without wishing to be bound by any theory, it is believed that the inert gas interferes with the transportation of oxygen through the packaging. The inert gas may arise from many sources, for example, the inert gas may be carried over from a product processing stage; the packaging may be flushed with an inert gas; the packaging, containing the goods, may be evacuated and subsequently filled with an inert gas before being sealed or closed; the inert gas may be entrapped during closure or sealing of the packaging; or the inert gas may be released from the goods during storage. In a further aspect of the present invention there is provided a sealed packaging containing goods characterised in that the packaging comprises (i) a mono-layer of a polyketone composition or (ii) a multi-layered structure comprising at least one layer of a polyketone composition, and at least a portion of the inner surface of (i) the mono-layer or (ii) the multi-layered structure is in contact with an inert gas selected from the group consisting of nitrogen, carbon dioxide, helium, neon, argon and krypton.

Preferably, the goods which are contained in the packaging are goods which are sensitive to oxygen, including foodstuffs (for example meat products), beverages (for example beer), household goods, chemicals, healthcare products, medical products and pharmaceuticals.

Where the goods are chemicals, medical products or pharmaceuticals, the inert gas is preferably selected from nitrogen and argon. Where the goods are foodstuffs or beverages, the inert gas is preferably selected from carbon dioxide and nitrogen.

Where the inert gas comprises carbon dioxide, it is preferred that the inert gas comprises a mixture of carbon dioxide and at least one further inert gas, preferably nitrogen. Preferably, carbon dioxide comprises less than 50% by volume, more preferably less than 25% by volume, most preferably, less than 15% by volume of the inert gas.

For goods which are highly sensitive to oxygen (e.g. certain chemicals) it is important that the concentration of any oxygen impurity in the inert gas is low, for example, at ppm levels. For goods which are less sensitive to oxygen (e.g. foodstuffs and beverages) it is envisaged that oxygen may be present at a higher concentration in the inert gas, for example, at concentrations of up to 15% by volume. However, it is preferred that the inert gas comprises less than 10% by volume, more preferably less than 5% by volume, most preferably, less than 2.5% by volume of oxygen.

Preferably, the polyketone composition has an oxygen permeability of less than 2 x 10^'13 cc.cm cm^"2 s^"1 cmHg^"1 at 21°C, 75% relative humidity (RH), more preferably less than 0.8 x 10^"13cc.cm cm^"2 s^"1 cmHg^"1, most preferably less than 0.5 x 10^"13 cc.cm cm^"2 s^"1 cmHg^'1. Although figures quoted here are for 21°C and 75% RH, the low permeability is observed over the full range of humidities and thus the invention is not limited in this respect.

Preferably, the polyketone composition comprises a linear polyketone polymer having an alternating structure of (a) units derived from carbon monoxide, and (b) units derived from (i) ethylene and (ii) optionally a further alpha olefin selected from the group consisting of propene, butene, pentene and hexene. Preferably, the polyketone polymer is a carbon monoxide/ethylene/propene terpolymer or a carbon monoxide/ethylene/butene terpolymer.

The maximum amount of units derived from the further alpha olefin in the polyketone polymer is preferably no more than 8 mol%, more preferably no more than 6.5 mol%, most preferably no more than 6.0 mol%, typically, no more than 5.5 mol%. For carbon monoxide/ethylene/propene or carbon monoxide/ethylene/butene terpolymers, the optimum amount of units derived from propene or butene is no more than 5.5 mol %.

It is envisaged that the polyketone composition may comprise a blend of one or more polyketone polymers.

The polyketone composition may also comprise a blend of a polyketone polymer with another polymer, for example, polyethylene, polypropylene, polyamides, fluoropolymers (for example, polychlorotrifluoroethylene), ethylene vinylalcohol copolymers, polyvinylchloride, polystyrene, nitrile resins, polyvinylidenechloride and polyesters. The nature and amount of such a polymer will depend upon what modifications of the polyketone polymer properties are required. However, sufficient polyketone polymer should be present in the blend to achieve the desired barrier performance. Furthermore, the polyketone composition may contain conventional polymer additives such as anti-oxidants, stabilisers, pigments, fillers, mould release agents and processing aids (such as internal and external lubricants).

The polyketone polymers can be prepared using conventional batch or continuous reactor techniques.

The Melt Flow Rate (5kg load at 240°C, 2.095 diameter die) of the polyketone polymer is typically in the range 5-200, preferably 10-150, more preferably 20-100, for example, 40-80g/10 mins.

The polyketone polymer will suitably have a weight average molecular weight of between 20,000 and 1,000,000, preferably between 30,000 and 250,000, for example, 40,000 to 180,000.

In yet a further aspect, the present invention provides a process for packaging goods which are sensitive to oxygen in packaging comprising (i) a mono-layer of a polyketone composition or (ii) a multi-layered structure comprising at least one layer of a polyketone composition which process comprises:

(a) partially filling the packaging with the goods so that at least one void is present within the packaging which void(s) is in communication with (i) the monolayer of the polyketone composition or (ii) the multi-layered structure;

(b) filling the void(s) in the packaging with an inert gas selected from the group consisting of nitrogen, carbon dioxide, helium, neon, argon and krypton; and

(c) sealing the packaging. Where the goods are particularly sensitive to oxygen, step (a) may be carried out under an atmosphere of the inert gas in which case step (b) takes place concurrently with step (a).

Where the goods are liquids, the package will have a headspace (void) filled with an inert gas. Where the goods are particulate solids, voids between the solid particles as well as any headspace will be filled with the inert gas.

Suitably, the voids in the packaging may be filled with the inert gas by flushing the packaging containing the goods with the inert gas.

Alternatively, the packaging containing the goods may be evacuated before filling the void(s) with the inert gas in step (b). It is also envisaged that the goods may be prepared and packaged under an environment of an inert gas in which case the packaging will contain an inert gas prior to being filled with the goods i.e. step (b) takes place concurrently with step (a).

According to yet a further aspect of the present invention there is provided the use of packaging comprising (i) a mono-layer of a polyketone composition or (ii) a multi- layered structure comprising at least one layer of a polyketone composition to package goods which are sensitive to oxygen, wherein the goods are contained in the packaging under an atmosphere of an inert gas selected from the group consisting of nitrogen, carbon dioxide, helium, neon, argon and krypton.

The packaging may comprise a film, for example, a sealed pouch or a seal for a tray, bowl, pot or other receptacle (in which case the receptacle has a low permeability to oxygen) or may be a moulded article (for example, a sealed receptacle such as a sealed tray, sealed bowl, sealed bottle or a sealed pot). Also, the packaging may comprise a sealed receptacle having a liner comprising (i) a mono-layer of the polyketone composition or (ii) a multi-layered structure comprising at least one layer of a polyketone composition fitted internally to the receptacle.

The packaging is preferably formed from a multi-layered structure. Such multi- layered structures may be prepared by co-extrusion e.g. multi-layered film produced by co-extrusion or by lamination. Typically, the multi-layered structure comprises 2 to 12 layers, preferably 3 to 7 layers. Preferably, the multi-layered structure comprises 3 or 6 layers, having an internal layer which is a polyketone composition. The layer(s) of the polyketone composition, suitably has a thickness of at least 3 μm and up to 1000 μm, preferably in the range 5 to 500 μm, more preferably in the range 5 to 50 μm. The other layers of the multi-layered structure may comprise a polymer composition selected from the group consisting of polyolefin compositions, polyester compositions, polystyrene compositions, polyamide compositions, ethylenevinylalcohol compositions, polyvinylidene chloride compositions, paperboard, aluminium films, or metallised films. Tie-layers may be required to bond the different layers of the multi-layer structure as will be evident to the person skilled in the art.

Although, in the Examples below, the samples of the polyketone compositions are processed by compression moulding, the packaging can also be made by extrusion processes to produce films, receptacles, and closures (for receptacles). Extrusion techniques can result in lower permeabilities than compression moulding, as is well known, due to molecular orientation.

The invention is illustrated by the following Examples. Characterisation

For barrier performance evaluation, 11cm diameter and 150 micron thick films of the polymer were compression moulded between two polished aluminium sheets using a KOMTEC 40 tonne press. The polymer was initially held at 240°C for 3 minutes at a dial pressure of 0.2MPa, following which the dial pressure was increased to 18MPa and simultaneously a cooling rate of 15°C/minute applied until the film reached a temperature of about 30°C. The dial pressure was maintained at a constant 18MPa during the cooling cycle.

The melting point of the ex-reactor powder was determined by differential scanning calorimetry (DSC). This was carried out using a DuPont DSC Model No. 990315. A heating rate of 10°C/min from -50°C up to 240°C was used under a nitrogen purge, followed by cooling at a rate of 10°C/min back down to -50°C. A second heating cycle at the same rate was then applied: the melting point (T_m) was evaluated from the second heating endotherm. The result is shown in the Example.

The content of units derived from propene was determined by proton 1H NMR using a JEOL GSX 270 spectrometer. The polymer was analysed as a solution in HFiP/CD₂Cl₂. The content of units derived from propene is expressed in mole % of the total polymer composition.

Oxygen permeabilities were measured using a MOCON Oxtran (1000) instrument following the procedure of ASTM D3985. According to ASTM D3985 a film of polymer is mounted as a sealed semi-barrier between two chambers at ambient atmospheric pressure. One chamber is slowly purged by a stream of an inert gas (carrier gas) and the other chamber contains oxygen or a mixture of oxygen and an inert gas. As oxygen gas permeates through the film into the carrier gas, it is transported to a coulometric detector where it produces an electric current, the magnitude of which is proportional to the amount of oxygen flowing into the detector per unit time.

Oxygen permeabilities were also measured using a vacuum technique according to the following procedure. A 50 mm diameter disc of a film of polymer (hereinafter referred to as "sample") was sealed in the sample chamber of a gas diffusion apparatus which was based on a Spectramass DAQ 100/DXM quadrupole mass spectrometer so as to the divide the sample chamber into a first and a second compartment. This procedure is described by Webb et al in J. Appl. Polym. Sci.: Part B: Polym. Phys. 31, 747, 1993 which is herein incorporated by reference. The sample was initially held at room temperature. The temperature of the sample was then increased to 30°C ± 0.2°C and was maintained at this temperature during the course of the permeability measurements. The first and second compartments of the sample chamber were evacuated (pumped down) and punrping was continued until all permeants absorbed in the sample had been fully desorbed (about two days) and a stable high vacuum level (of 3 x 10^"7 mbar) had been achieved in the compartments of the sample chamber. Oxygen or a mixture of oxygen and nitrogen (test gas) was introduced into the first compartment to a measured pressure of 850 mbar, and the partial pressure of oxygen which diffused through the sample into the second compartment was recorded using an Elonex PC-320X computer over a period of time (of up to several days).

The results are shown in Tables 1 and 2. Example 1

A carbon monoxide/ethylene/propene terpolymer was prepared under the following conditions: 80 ml dichloromethane and 20g propene were charged to a mechanically stirred autoclave having a volume of 300 ml. The contents of the autoclave were brought to a temperature of 73°C. A 1 : 1 carbon monoxide/ethylene gas mixture was introduced until a pressure of 50 barg was reached. A boron solution was then introduced into the autoclave, consisting of 0.3mmol of tris(pentafluorophenyl)boron in 20 ml of dichloromethane. This was followed by addition of a catalyst solution comprising: O.Olόmmol [Pd(dppp)(PhCN)₂](BF )₂ (dppp = l,3-bis(diphenylphosphino)propane) in 20 ml of dichloromethane.

The autoclave pressure was maintained at 50 barg by introducing under pressure a 1 : 1 carbon monoxide/ethylene gas mixture. Polymerisation was stopped after 1.25 hours by depressurising the autoclave. The polymer was filtered, washed with methanol and dried at 40°C. 18.2 g of terpolymer was produced having a melting point determined by DSC of 210°C. The content of units derived from propene was determined as 5.1 mol % by NMR.

Table 1 - Oxygen Barrier Results using an Oxtran 1000 Instrument

Table 2 - Oxygen Barrier Results using a Vacuum Technique

These results demonstrate that when the chambers of the Oxtran 1000 instrument are purged with an inert gas (as exemplified by nitrogen, helium and argon) a marked reduction in oxygen permeability is observed compared with measurements made using a vacuum technique (where the polyketone film is not contacted with an inert gas). In addition, the data indicates that the presence of a second gas on the permeant side of the test sample also improves the oxygen barrier performance of the test sample, particularly in the case of nitrogen.

Claims

Claims:

1. A packaging containing goods under an atmosphere of an inert gas characterised in that:

2. A sealed packaging containing goods characterised in that the packaging comprises (i) a mono-layer of a polyketone composition or (ii) a multi-layered structure comprising at least one layer of a polyketone composition, and at least a portion of the inner surface of (i) the mono-layer or (ii) the multi-layered structure is in contact with an inert gas selected from the group consisting of nitrogen, carbon dioxide, helium, neon, argon and krypton.

3. Packaging as claimed in Claims 1 or 2 wherein the goods contained in the packaging are sensitive to oxygen and are selected from foodstuffs, beverages, household goods, chemicals, healthcare products, medical products and pharmaceuticals. 4. Packaging as claimed in any one of the preceding claims wherein the polyketone composition of (i) the mono-layer or (ii) the multi-layered structure has an oxygen permeability of less than 2 x 10^'13 cc.cm cm^'2 s^"1 cmHg^"1 at 21°C, 75% relative humidity (RH).

5. Packaging as claimed in Claim 4 wherein the polyketone composition of (i) the mono-layer or (ii) the multi-layered structure has an oxygen permeability of less than 0.5 x 10^'13 cc.cm cm^"2 s^"1 cmHg^"1 at 21°C and 75% RH.

6. Packaging as claimed in any one of the preceding claims wherein the polyketone composition of (i) the mono-layer or (ii) the multi-layered structure comprises a polymer having an alternating structure of (a) units derived from carbon monoxide, and (b) units derived from (i) ethylene and (ii) optionally a further alpha olefin selected from the group consisting of propene, butene, pentene and hexene. 7 Packaging as claimed in Claim 6 wherein the polyketone composition of (i) the mono-layer or (ii) the multi-layered structure comprises a carbon monoxide/ethylene/propene terpolymer or a carbon monoxide/ethylene/butene terpolymer.

8 Packaging as claimed in Claim 7 wherein the polyketone composition of (i) the mono-layer or (ii) the multi-layered structure comprises a carbon monoxide/ethylene/propene terpolymer or a carbon monoxide/ethylene/butene terpolymer having no more than 5 5 mol% of units derived from propene or butene respectively

9 Packaging as claimed in any one of the preceding claims wherein the packaging comprises a film, a moulded receptacle or a liner for a receptacle formed from (i) the mono-layer of a polyketone composition or (ii) the multi-layered structure comprising at least one layer of a polyketone composition.

10 A process for packaging goods which are sensitive to oxygen in packaging comprising (i) a mono-layer of a polyketone composition or (ii) a multi-layered structure comprising at least one layer of a polyketone composition which process comprises

(a) partially filling the packaging with the goods so that at least one void is present within the packaging which void(s) is in communication with (i) the monolayer of the polyketone composition or (ii) the multi-layered structure,

(b) filling the void(s) in the packaging with an inert gas selected from the group consisting of nitrogen, carbon dioxide, helium, neon, argon and krypton, and

(c) sealing the packaging 1 1 A process as claimed in Claim 10 wherein step (a) is carried out under an atmosphere of the inert gas

12 A process as claimed in Claims 10 or 11 wherein the void(s) in the packaging are filled with the inert gas in step (b) by flushing the packaging containing the goods with the inert gas 13 A process as claimed in Claims 10 or 11 wherein the packaging containing the goods is evacuated before filling the void(s) with the inert gas in step (b) 14 A process as claimed in any one of Claims 10 to 13 wherein the goods are sensitive to oxygen and are selected from foodstuffs, beverages, household goods, chemicals, healthcare products, medical products and pharmaceuticals.

15. A process as claimed in any one of Claims 10 to 14 wherein the polyketone composition of (i) the monolayer or (ii) the multi-layered structure is as defined in any one of claims 4 to 8.

16. Use of packaging comprising (i) a mono-layer of a polyketone composition or (ii) a multi-layered structure comprising at least one layer of a polyketone composition to package goods which are sensitive to oxygen, wherein the goods are contained in the packaging under an atmosphere of an inert gas selected from the group consisting of nitrogen, carbon dioxide, helium, neon, argon and krypton.