GB2293132A

GB2293132A - Polyketone films

Info

Publication number: GB2293132A
Application number: GB9517095A
Authority: GB
Inventors: Anthony Keith Powell; James Graham Bonner
Original assignee: BP Chemicals Ltd
Current assignee: BP Chemicals Ltd
Priority date: 1994-08-26
Filing date: 1995-08-21
Publication date: 1996-03-20
Also published as: GB9517095D0; GB9417382D0

Abstract

A method for processing polyketone comprises heating a polyketone or a polyketone/polymer blend to a temperature not greater than 15 DEG C above its melting point prior to thermo forming the polyketone or polyketone/polymer blend, the polyketone or polyketone/polymer blend being preferably essentially free of any additives.

Description

POLYMER FILMS This invention relates to polymer films, in particular films comprising polyketones and processes for making such films.

For the purpose 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. 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 lOwt%) of the corresponding homopolymer or copolymer derived from the olefinically unsaturated compound, also fall within the definition.

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.

Polyketones can be used in a variety of applications including, for example, packaging. It is important in the case of polymers used in some packaging applications for example film applications to improve the optical properties of the polymer.

In the case of polyolefins e.g. polyethylene, to obtain good optical properties e.g. clarity, the polyolefin is processed at temperatures very much higher (e.g. > 100"C) than its melting point This is in order to minimise crystallinity on cooling. However, in the case of polyketones we have surprisingly found that the optical properties are improved by processing the polymer as close to its melting point as possible.

Therefore according to the present invention, there is provided a method for processing polyketone which comprises heating a polyketone or a polyketone/polymer blend to a temperature not greater than 15"C above its melting point prior to thermoforming the polyketone or polyketone/polymer blend, the polyketone or polyketone/polymer blend being preferably essentially free of any additives.

For the purposes of describing the present invention, the term --polyketone can also mean a blend of polyketone with at least one other polymer. The essential features of the present invention is that the polyketone or polyketone/polymer blend should be heated to a temperature no greater than 15"C preferably no greater than 10 , particularly no greater than 5"C above its melting point. A preferred feature of the present invention is that the polyketone is essentially free of any additives.

Conventionally a polymer will comprise one or more additives when being processes; such conventional additives include thermal stabilisers, antioxidants, lubricants, UV stabilisers. However in the present invention it is preferred that no additives are present in the polyketone while processing; where additives are present it is preferred that the total amount of all additives is less than 0.5 parts per hundred (pph) by weight more preferably less than O.lpph.

However, it is understood that the polyketone may unavoidably contain impurities derived from the reagents used it its manufacture (e.g.

palladium metal, solvent etc.).

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 to C6 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 1 most preferably between 2 and 30. Typically, the polyketone will be a copolymer of ethylene/propylene/CO where the propylene is in the range 5-8% e.g. 6Z by weight of the polymer. The Melt Flow Rate (5kg load at 240 C) is typically in the range 10-150 preferably 20-100, more preferably 40-80.

-It is contemplated that blends of polyketones with other polymer are encompassed within the present invention. It is preferred that such blends will contain at least 50%, preferably at least 70% more preferably at least 90X by weight of polyketone.

Suitable polymers which may be included in polyketone blends include polyethylene, (e.g. LDPE, LLDPE, HDPE) polypropylene and polycarbonate.

The equipment used to thermoform the polyketone will be conventional equipment, well known to those skilled in the art.

Since the present invention relates to a method for processing transparent, semi-transparent or opaque products, the equipment used will typically be film extruders, blow moulders etc.

In a further aspect of the present invention there is provided a product comprising polyketone or a polyketone/polymer blend which has been processed by heating a polyketone or a polyketone/polymer blend to a temperature not greater than 15"C above its melting point prior to thermoforming the polyketone or polyketone/polymer blend which is preferably substantially free of any additives.

Such thermoformed products will be either colourless, "water clear" and transparent or semi-transparent or opaque with high gloss where the improved optical properties will be advantageous. Such product will suitably be film, transparent bottles and containers, or transparent sheeting for thermoforming into containers. Since polyketones are known to have superior barrier properties to other thermoplastics, a preferred application for polyketones is food packaging e.g. film packaging.

The invention will now be illustrated with reference to the following Examples.

Ethylene/Propylene/CO polyketone (EPCO) prepared using a palladium catalyst and incorporating 5-6% by weight of propylene (melting point 204"C) was used for all examples.

Example 1 EPCO powder which had been washed and dried was processed on a Plasticisers Film/Fibre Single screw extruder using a screw speed of 30rpm, haul-off speed of 15ft/min and temperature profile (hopper to -die) of 180, 205, 215 and 215"C. The film produced was measured for haze according to ASTM D1003-61 (1988) the result is given in Table 1.

Example 2 Example 1 was repeated, except that the EPCO was precompounded prior to film processing using an APV co-rotating 15mm twin screw compounding extruder using a screw speed of 150rpm, an output rate of O.Skg/hr, with the temperature of the barrel and die being 215"C.

The haze measurement is given in Table 1.

Example 3 Example 2 was repeated except that lpph of pseudoboehmite (aluminium oxide hydroxide) was added to the EPCO powder prior to precompounding.

Example 4 Example 3 was repeated except that the temperature profile of the film extruder was 180, 200, 240 and 240"C.

Examples 5 and 6 Linear low density polyethylene (LLDPE) and low density polyethylene (LDPE) were, also processed into film using the conditions shown in Example 1. The haze measurements for Examples 2 6 are given in Table 1.

Table 1

Example Haze (X) 1 5 2 10 3 16 4 32 5 16 6 15 The results show that improved optical properties are obtained by thermoforming the product (the film) at a temperature close to the melting point of the starting polyketone and also by reducing the amount of stabiliser added.

Claims

Claims:

1. A method for processing polyketone which comprises heating a polyketone or a polyketone/polymer blend to a temperature not greater -than 15"C above its melting point prior to thermo forming the polyketone or polyketone/polymer blend, the polyketone or polyketone/polymer blend being preferably essentially free of any additives.