GB2174671A

GB2174671A - Plastics containers for liquids

Info

Publication number: GB2174671A
Application number: GB08511830A
Authority: GB
Inventors: Guy Edric Dexter; Roger Purcell Hudspith
Original assignee: Metal Box PLC
Current assignee: Crown Packaging UK Ltd
Priority date: 1985-05-10
Filing date: 1985-05-10
Publication date: 1986-11-12
Also published as: GB8511830D0; GB2174671B

Abstract

A container for liquid or semi-liquid products, eg tomato ketchup or brown sauce, is formed at least in part of a thermoplastics polymer material which naturally is translucent. In order to counteract the undesirable effect of the polymer material on the visual appearance of the product or minute amount of a pigment is added to the material prior to moulding which eliminates the translucence. Typically the concentration of the pigment is 1% of that required to render the structure opaque. The container may be multilayered, i.e. external layers of pigmented polypropylene and a central barrier layer of ethylene-vinyl acetate copolymer adhered together by modified maleic anhydride adhesive.

Description

SPECIFICATION Containers This invention relates to containers for packaging products, in particular (but not exclusively) liquid and semi-liquid food products such as sauces, relishes and ketchups. The invention may also have application to containers for beverage products such, for example, as tomato juice.

It is well known to use thermoplastics polymer materials in the manufacture of packaging containers for food and beverage products.

The plastics materials may be chosen for their natural transparency, so as to cause little or no change in the appearance of the contents to the potential buyer and consumer, and/or they may be chosen to meet particular physical or chemical criteria such for, example, as high impact resistance or impermeability to liquids and gases. Materials falling within the latter category may be naturally translucent, but may lack the quality of transparency which is often desirable for customer appeal to show off the contents of the container to the best effect. Hitherto it has therefore been the practice to treat such materials with a suitable pigment in sufficient concentration to render the moulded container opaque so that its contents cannot be seen through the container wall.

For some products, opacity of the container is of no consequence; indeed, particularly in cases where the product is of a visually unappealing nature, it may be an advantage. For other products, however, it is preferred that the contents should be visible through the container wall, but hitherto the cloudy appearance and usually greyish cast of some plastics materials have hitherto largely precluded those materials from use except when rendered opaque as described above.

Usually (but not necessarily) the container is a unitary blow-moulded bottle with a neck region having an opening to be closed by a suitable plastics or metal closure. Because of its greater thickness of plastics material the neck region is particularly prone to giving the product the darkened, unappealing appearance with poor contact clarity caused by the cloudiness and colour cast of the plastics as mentioned above.

Applicants have discovered that by the addition of a suitable coloured pigment at a concentration typically 1% of the concentration which might be used to render the material wholly opaque, the undesirable effects which a naturally translucent plastics material has on the appearance of a product can, surprisingly, be largely removed; the packaged product (as seen through the container wall), may thereby be restored substantially to its natural colour and tone and its contact clarity be made to approximate substantially to that provided by a glass container.Moreover, in containers wherein the thickness of the plastics material varies because of the moulding operation which is employed, e.g. a blow-moulded bottle having a reduced-diameter neck, the effect of the pigment to counteract the natural cloudiness and discolouration of the plastics material will itself vary in correspondence with the variations in material thickness. The colour, tone and contact clarity of the product as seen through the material can accordingly be made substantially even and consistent over the whole area of the container visible to the potential consumer. The sales appeal of the pack is thereby increased.

The invention accordingly provides, according to a first aspect thereof, a container proposed for, or containing, a liquid or semi-liquid product, the container being formed at least in part of a thermoplastics polymer material which naturally is translucent and such as to change the visual appearance of the said product as seen therethrough, the material including a pigment additive of such optical characteristics and at such concentration that the product as seen through the material is substantially unchanged in its visual appearance.

According to a second aspect thereof, the invention provides a method for producing a container of a thermoplastics polymer material which naturally is translucent and such as to change the visual appearance of a liquid or semi-liquid product as seen therethrough, the method comprising moulding the container from said material to which is added a pigment of such optical characteristics and at such concentration that the said product as seen through the material is substantially unchanged in its visual appearance.

It should be emphasised that the addition of the pigment to the material is not with the intention of, nor does it have the effect of, giving the product an unnatural appearance. Its effect is one of correction, to counteract or offset the visually undesirable effect of naturally translucent thermoplastics polymer materials in their application to the packaging of some products. Amongst the materials for which this correction may be desirable are high density polyethylene, low density polyethylene, and polypropylene.

The invention may be used for single layer or multi-layer plastics structures, and a specific container (which is now described by way of example only) is in the form of a blow-moulded bottle proposed for a red tomato ketchup product. It conventionally has a body portion with an upper, reduced diameter neck portion which terminates in a screw thread for receiving a plastics screw closure.

The bottle is formed by blow-moulding a coextruded multilayer parison formed of outer layers of polypropylene on each side of a central, substantially gas-impermeable layer of EVOH (Saponified Ethylene-Vinyl Acetate Co polymer). These three layers are adhered together by layer of modified maleic anhydride adhesive between them, so that the bottle is a five-layer structure with polypropylene forming its two outermost layers.

The EVOH and adhesive layers are thin, and effectively transparent. The outer polypropylene layers, however, are provided to give the container desired mechanical properties such as impact resistance, and each layer is thick in comparison with the EVOH and adhesive layers. Typically, the polypropylene layers each have a thickness of 0.40mm, the EVOH layer has a thickness of 0.07mm, and the adhesive layers have a thickness of 0.04mm.

Natural polypropylene when moulded is translucent, with a cloudy appearance and greyish cast; in its application to the manufacture of blow-moulded plastics bottles it is therefore usually rendered opaque by addition of a pigment at a substantial concentration.

For a tomato ketchup product the appropriate pigment would be a red colour which matches the colour and tone of the ketchup as closely as possible. However, for commercial reasons it is desired that the bottle in accordance with the present invention should display the ketchup naturally to the potential buyer. In order, therefore, to counteract the somewhar dark and sludgy appearance which would otherwise be given to the ketchup by the polypropylene layers, the pigment (which may be added in conventional manner as a masterbatch additive to natural polypropylene granules in a common feed hopper for the two layers) is reduced to approximately one hundredth of the amount which would typically be used to render the bottle opaque.Thus a masterbatch which for opacity is used at 5% of the total content of the two outer layers is instead used at approximately 0.05% in accordance with the invention.

A particular example of the 5 layer bottle with layer thicknesses as listed above has its outer polypropylene layers formed from a mix of Solvay ELTEX KL 14 polypropylene with a masterbatch of Coles RED 25105 forming 0.05% of the mix by weight. The EVOH layer is of Nippin Cohsei SOARNOL D, and the adhesive layers are of Mitsubishi Petrochemical Co. MODIC P 300 F.

The invention may be used in relation to polymers other than polypropylene and for products other than tomato ketchup. Moreover, the colour of the pigment required for correction may not always be same as the colour of the product itself; for example, a yellow pigment may be required for a brown sauce product. For multilayer structures the pigment may be added to a layer or layers other than the layer or layers the optical characteristics of which require the correction to be made. The pigment may be added by the same methods as are conventionally used when opacity is required, possibly when modifled to make allowance for the reduced pigment levels which are involved.

The thermoplastics material, or combination of thermoplastics materials, to which the invention is applied may form the whole, or part only, of the container.

Claims

1. A container proposed for, or containing, a liquid or semi-liquid product, the container being formed at least in part of a thermoplastics polymer material which naturally is translucent and such as to change the visual appearance of the said product as seen therethrough, the material including a pigment additive of such optical characteristics and at such concentration that the product as seen through the polymer material is substantially unchanged in its visual appearance.

2. A container as claimed in claim 1, wherein the polymer material is multilayer.

3. A container as claimed in claim 2, wherein one or more, but not all, of the layers of the polymer material is or are pigmented.

4. A container as claimed in claim 2 or claim 3, wherein the polymer material includes a pigmented layer of polypropylene.

5. A container as claimed in claim 4, wherein the polymer material comprises external layers of pigmented polypropylene, and a barrier layer them between.

6. A container as claimed in any preceding claim, wherein the concentration of the polymer material is approxiamtely 1% of that required to render the polymer material opaque.

7. A plastics container proposed for, or containing, a liquid or semi-liquid product, the container having a multilayer wall structure comprising relatively thick external layers of polypropylene and a relatively thin barrier layer therebetween, the polypropylene being pigmented to a pigment concentration which is approximately 1% of that needed to render it opaque, the product as seen through the wall structure being substantially unchanged in its visual appearance.

8. A container as claimed in any preceding claim and substantially as herein particularly described.

9. A method for producing a container of a thermoplastics polymer material which naturally is translucent and such as to change the visual appearance of a liquid or semi-liquid product as seen therethrough, the method comprising moulding the container from said material to which is added a pigment of such optical characteristics and such concentration that the said product as seen through the material is substantially unchanged in its visual appearance.