GB2174670A - Coated plastics containers - Google Patents

Abstract

A bottle of a thermoplastics polymer material, eg polyropylene, which is naturally translucent for e.g. tomato ketchup is externally coated with a polymeric coating material such as an acrylic or a polyurethene, the coating counteracting the effect of the translucent bottle wall and making it more transparent and so improving the visual appearance of the product whilst also giving the bottle a high gloss finish. Prior to coating the container, the surface is preferably heated by flame or corona discharge to render it receptive to the coating which may be acrylic, vinylidene chloride copolymer, epoxy resins, urethanes and esters. The coating may be applied by aqueous dispersion or a solvent solution laid down by dry spray flow or brush coating. After coating the container is dried by hot air or infra red heating. The container may have a multi-layer structure, eg external and internal layers of polypropylene separated by a thin, gas-impermeable layer of EVOH, the three layers being 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 a tomato juice.

Hitherto food products such as sauces, relishes and ketchups have been marketed in glass bottles or jars closed usually by metal screw-closures. These containers have a very low permeability to gases and liquids, and moreover have a high degree of transparency and contact clarity; they are therefore capable of giving their contents a long shelf life, with a high degree of customer appeal.

However, because of the brittleness and lack of flexibility of the material of which they are made, such glass containers are liable to breakage in transit, display and use, and access to their contents may present difficulty for the consumer. In an attempt to alleviate these disadvantages wholly plastics bottles have recently been introduced. These bottles have a high impact resistance and are substantially unbreakable; they are flexible and if required can be arranged to expel their contents by squeezing. Moreover, they can be of laminated construction to provide a required degree of impermeability to gases and liquids.

From the above mentioned three viewpoints, plastics bottles have proved to be satisfactory; from the viewpoint of customer appeal, however, they are at a disadvantage as compared with the more usual glass containers, in that they have had a matte exterior surface and have tended to give their contents a darkened and rather muddy appearance with relatively poor contact clarity which is offputting to the consumer at the point of sale and thereafter.

In particular, plastics bottles which have been proposed for tomato ketchup are moulded from a translucent polymer structure formed of relatively thick outer layers of polypropylene, a thin intermediate, barrier layer of EVOH (Saponified Ethylene-Vinyl Acetate Copolymer), and thin adhesive layers between the polypropylene and the EVOH. However, and largely because of the natural characteristics of the polypropylene, such a structure has a dull surface (in comparison with glass) and a slight milkiness, giving the ketchup as seen by the consumer the unappealing appearance mentioned above.

In an attempt to improve the customer appeal of plastics bottles for such food products as tomato ketchups, Applicants are proposing in their copending Patent Application of todays date (Agents' ref. E3173), 8511830, that the plastics. material should be tinted by the addition of an appropriate pigment at a low concentration such that the light transmissability of the plastics is substantially unaffected. It has surprisingly been found that by suitable choice of the colour and concentration of the pigment the colour, tone and contact clarity of the filled bottle could be improved and made to approximate closely to that of a glass bottle of the same product.

This proposal, however, inherently has albeit relatively minor drawbacks, in particular the undesirably tinted appearance given to those parts of a partly empty bottle which are free of the product, and the restraints imposed on the bottle-moulding process by the need to purge the moulding machinery and change the pigment for each change in the product which the bottles are destined to pack.

In attempting to overcome the disadvantages of the proposal of our above-mentioned copending Patent Application, Applicants have made the further surprising discovery that, by coating the plastics bottles externally with a suitable polymeric coating material, the colour, tone and contact clarity of a glass container can again be approximated but without the drawbacks mentioned above of pigmenting the polymer structure or its components; in addition to making this improvement in the visual appearance of the product as seen, the coating can be chosen to give the bottle the appealing glossy appearance of its glass counterpart.

Applicants have found that bottles treated using the above technique can be used for products of widely differing colours and compositions, there being little or no need for the bottle manufacturer to differentiate the bottles in any way in accordance with the products to be packed. Thus, appeal to the customer is combined with relative cheapness and ease of manufacture. If desired, however, the technique can be used on containers which have already been tinted in accordance with the teachings of our above-mentioned copending Patent Application.

According therefore, to one aspect of the invention, there is provided a container proposed for or including a liquid or semi-liquid food 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, and being externally coated with a polymeric coating material which substantially counteracts the effect of the polymer material on the visual appearance of the product whilst giving it a glasslike glossy appearance.

The coating may be formed in a conventional manner, by applying the coating material to the moulded container as an aqueous dispersion or a solvent solution, and thereafter drying the coating by hot air, infra-red heating or the like. The coating may be laid down on the container by dip, spray, flow or brush coating, or by any other suitable coating method. Prior to coating, the container surface to be coated may be treated in known manner, e.g. by flame or corona discharge treatment, to render it adequately receptive to the coating material.

Polymeric coating materials which have been found to be suitable are selections from acrylics, vinylidene chloride copolymers, epoxy resins, urethanes and esters. It is believed, however, that other polymers may be used.

An embodiment of the invention will now be described by way of illustrative example. A bottle for tomato ketchup was blow-moulded from a multi-layer tubular parison to have a body portion and an upper, reduced-diameter neck portion formed with a screw-thread for receiving a screw closure.

The bottle accordingly had a five-layer wall structure formed of external and internal layers of polypropylene separated by a thin but substantially gas-impermeable layer of EVOH (Saponified Ethylene-Vinyl Acetate Copolymer), the three layers being adhered together by further thin layers of modified maleic anhydride adhesive between adjacent layers.

The bottle was blow-moulded in conventional manner and subsequently flame-treated, again in conventional manner, to render its external surface receptive and adherent to ACRONAL 250D acrylic polymer (manufactured by BASF), which was flow coated onto the surface as an aqueous dispersion.

Following coating with the polymeric coating material, the bottle was passed through a hot air oven to drive off the water and form a thin but coherent coating on the exterior surface of the bottle. The coated bottle was filled with tomato ketchup and closed, the bottle then having an attractive gloss, and a product appearance with good contact clarity approximating to that of glass; in contrast with glass, however, the bottle had a high impact resistance and could be squeezed to expel the tomato ketchup product as desired.

A second bottle, manufactured and coated by substantially the same process as the first, had Holden RD 44071 urethane polymer as the coating material instead of the acrylic polymer of the first bottle.

This bottle again had a high gloss and gave a natural appearance to the product.

The invention is not limited in application to bottles having the particular polymer structure of the containers which are described above by way of example in the two preceding paragraphs. It may be used for other types of container, with single layer or multilayer polymer structures, and may involve coating onto polypropylene or other polymer surfaces.

Claims (9)

1. A container for a liquid or semi-liquid food product, which is 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, and being externally coated with a polymeric coating material which substantially counteracts the effect of the polymer material on the visual appearance of the product whilst giving it a glass-like, glossy appearance.

2. A container according to claim 1, having an exterior surface of polypropylene to which the polymeric coating material is applied as a coating thereon.

3. A container according to claim 1 or claim 2, having a multilayer polymer structure.

4. A container according to any preceding claim, wherein the polymeric coating material is an acrylic.

5. A container according to any claim of claims 1 to 3, wherein the polymeric coating material is a vinylidene chloride copolymer.

6. A container according to any claim of claims 1 to 3, wherin the polymeric coating material is an epoxy resin.

7. A container according to any claim of claims 1 to 3, wherein the polymeric coating material is a urethane.

8. A container according to any of claims 1 to 3, wherein the polymeric coating material is an ester.

9. A coated container substantially as herein described by way of example.