One common beverage is beer. However, the yeast and bacteria in beer adhere significantly to dispensing equipment made of synthetic plastics used in the beverage industry, especially at the point of serving, i. e. in bars, restaurants, etc. The delivery pipes and tubes (often termed"lines") in a bar should be cleaned at least once a week, and the lines are generally replaced completely every two years or so. Such cleaning and replacement involves considerable time and effort, as well as expense. The delivery lines for other beverages such as'soft'drinks, or soft drinks components, also require regular cleaning.

According to one aspect of the present invention, a plastic tubing is provided for passage of a potable liquid, the tubing having a wall structure comprising one or more concentric layers in one or more of which an antimicrobial substance is included, the substance being able to migrate inwardly through the tubing and be controllably released from the tubing bore in use. The use of multiple layers for the tubing provides significant flexibility in how and where the antimicrobial substance is located, the general physical properties of the tubing, and how the antimicrobial substance is released.

In this regard, one objective of the present invention is to control the rate of release of the antimicrobial substance from the bore of the tubing.

Controlled rate of release provides at least two advantages. Firstly, some assurance that the concentration of antimicrobial substance in the potable liquid does not exceed a desired maximum, thus avoiding any possible toxicity problems. Secondly, that the expected time period of the antimicrobial substance release can be estimated, such that the expected life span of the effectiveness of the tubing can be estimated. Timing for the replacement of the tubing can then be estimated.

Preferably, one or more of the layers of the wall structure of the tubing have a rate of migration of an antimicrobial substance through said layer or layers which is different to the rate of migration of the antimicrobial substance thorough one or more other layers of the tubing.

With differential rates of migration through the layers of the wall structure of the tubing, the rate of release of the antimicrobial substance into the bore may be further controlled.

The layers of the tubing may be made from any suitable thermoplastic polymer material. Those generally used having had regulation approval for the passage of potable liquids include polyethylene, polyethylene vinyl acetate (eva), nylon, and polyvinyldifluorene (PVDF). These materials provide different properties, and also have different costs. Two or more layers of the wall structure of the tubing may be of the same material.

The width of each layer of the tubing may also vary according to the properties desired. As with the width of each layer, the amount or concentration of antimicrobial substance in the relevant layer or layers may vary as desired or necessary. Two or more antimicrobial substances may be used, in the same or different layers of the wall structure of the tubing.

A number of antimicrobial substances are known which have fond to have the required properties for the present invention, including being able to be included with a plastic in the forming of a tube. One particular substance is Triclosan (RTM), a well known antimicrobial agent, which has a broad antimicrobial spectrum at low concentration, and which is known to be active against yeast and fungi.

According to a second aspect of the present invention, there is provided a method of making plastic tubing as defined above, wherein each layer is extruded and an antimicrobial substance is incorporated into the tubing by admixing the substance into one or more layers of the tubing before or during their extrusion.

The present invention preferably provides plastic tubing having a constant rate of release of antimicrobial substance from the tubing bore in use. Hence, based on the amount of use of the tubing, the effective time period of antimicrobial activity can be estimated. Such estimation is easier where the tubing is in constant use. Once all the antimicrobial substance is expected or is known to have been released, the tubing could be replace with new tubing.

The present invention provides tubing adapted to prevent or reduce the adhesion of bacteria and other unwanted micro-organisms and substances to its bore. The adhesion of such substances to the bore of tubing carrying a potable liquid has obvious infection risks. Such adhesion also leads to "furring"of the bore, with reduced flow and possible biockage. The yeasts in beer are particularly noted for their adhesion to plastic tubing.

The tubing of the present invention may be used for the passage or transfer of any potable liquid, whether still or carbonated, alcoholic or non- alcoholic, fresh or stored. The present invention is particularly suitable for the passage of drinking water, still and carbonated flavoured beverages including soft drinks and soft drinks components, and beers, ciders, etc. The uses of the tubing extend to wherever potable liquids are made, supplie sold, and/or delivered, e. g. bars, restaurants, factories, caravans, boats Embodiments of the present invention will now be described, by way of example with reference to the accompanying drawings, in which:- Fig. 1 is a cross-sectional view of a first plastic tubing according to the present invention showing one wall structure; Fig. 2 is a cross-sectional view of a second plastic tubing showing a second wall structure; Fig, 3 is a cross-sectionat view of a third plastic tubing showing a third wall structure; Fig. 4 is a cross-sectional view of a fourth plastic tubing showing a fourth wall structure; Fig. 5 is a cross-sectional view of a fifth plastic tubing showing a fifth wall structure; Referring to Fig. 1 of the drawings, in a first embodiment a first plastic tubing 2 is provided for the passage of a potable liquid, e. g. soda water or beer. The wall structure of the first tubing 2 has two concentric layers, an outer layer 4 and an inner layer 6 with the inner layer 6 defining a central bore 8 for the liquid.

The outer layer 4 is formed from medium density polyethylene (MDP), which is easy to mould, provides flexibility, and is also relatively inexpensive.

The inner layer 6 is made from a copolymer with an antimicrobial substance, for example Triclosan (RTM), included therein at a concentration of e. g. 3% by weight. Although many of the copolymers used in the beverage industry are possibly more expensive than e. g. MDP, organisms such as bacteria and yeast are known to have considerably less adhesion to such copolymers.

Thus, the inhibitory effect of such copolymers, along with the inhibitory effect of the antimicrobial substance, may outweigh the cost of such an inner layer, in order to provide much cleaner tubing, and a much greater life span of tubing before it needs replacing.

In use, as liquid flows along the tubing bore 8, the antimicrobial substance is released from the inner layer 4, thereby helping to prevent the build up of any bacteria or other unwanted substances on and along the bore 8. As the antimicrobial substance at the edge of the inner 4 is released, the substance behind it migrates forward towards the bore 8. Hence all the substance is eventually released over a period of time.

In a second embodiment as shown in Fig. 2, a second tubing 20 has a wall structure comprising an outer layer 22 and an inner layer 24 with a bore 26 being defined by the inner layer 24. The inner layer 24 includes the substance at a concentration of 0.5% by weight. The outer layer 22 also includes the substance, but at a concentration of 3-5% by weight. Hence, once the substance in the inner layer 24 is released into the bore 26, the substance in the inner layer 24 will be replenished by the substance in the outer layer 22. The rate of replenishment, and thus also possibly the long- term rate of release of the substance from the inner layer 22 into the bore 26, may depend upon the difference in the concentrations of the substance in the inner and outer layers 24,22, and the rates of migration of the substance across the inner and outer layers 24,22. In this way, it should be possible to vary the rate of release.

For instance, the inner layer 24 could be of a material which has a rate of migration of the substance therethrough which is different to that of the outer layer 22; preferably a lower rate of migration. With a lower rate of migration, it is the inner layer 24 which controls the rate of release of the substance from the inner layer 24 into the bore 26 of the second tubing 20.

The outer layer 22 acts as the reservoir of the substance. The outer layer 22 could also be formed from a plastics material which is able to support a high concentration of the substance, thereby creating a significant reservoir, and significant effective life span of the substance release.

In a third embodiment as shown in Fig. 3, a third plastic tubing has a wall structure of only one layer 30, of MDP with a bore 32 defined therein.

The antimicrobial substance used is at a concentration of 2% by weight.

In a fourth embodiment as shown in Fig. 4, a fourth plastic tubing has a wall structure of three concentric layers, an inner layer 40 of nylon an intermediate layer 42 of eva and an outer layer 44 of nylon with a bore 46 defined by the inner layer 40. The inner layer 40 includes the antimicrobial substance at a concentration of 1 % by weight. Also, the intermediate layer 42 includes the antimicrobial substance at a concentration of 2% by weight.

In a fifth embodiment as shown in Fig. 5, a fifth plastic tubing has a wall structure similar to the fourth plastic tubing and like parts and denoted by like numerals. The difference in this embodiment is that the intermediate layer 42 does not have any antimicrobial substance.

In all embodiments, the inner layer, at least, of the wall structure is of material having regulatory approval for the passage of potable liquids.

Clearly the width of the layers in the above examples can be varied as desired or necessary, as can the concentration of antimicrobial substance in each layer, within manufacturing and toxicity limits. A wider layer may be desired for greater strength, and increased antimicrobial substance inclusion.

The width and nature of each layer may also be gauged against cost, where e. g. MDP is significantly cheaper than eg. PVDF.

The present invention provides plastic tubing, which, whilst preferably maintaining the known desired properties for its use, e. g. longitudinal flexibility, ease of forming and handling, also provides significant flexibility and control in the rate of release of an antimicrobial substance therefrom. There is also control over the cost of different materials and time span of release. In particular, the rate of release of an antimicrobial substance into the bore of the tubing can be readily controlled by using an inner layer of rate-determining material.

Variations and modifications can be made without departing from the scope of the invention described above and as claimed hereinafter.