GB2245706A

GB2245706A - Product monitoring

Info

Publication number: GB2245706A
Application number: GB9013905A
Authority: GB
Inventors: Christopher Marcus
Original assignee: Cintex Ltd
Current assignee: Cintex Ltd
Priority date: 1990-06-22
Filing date: 1990-06-22
Publication date: 1992-01-08
Also published as: WO1992000229A1; IE912123A1; GB9013905D0; AU8003591A; EP0535071A1; CA2086001A1

Abstract

A method of detecting metallic foreign bodies in products (4) contained within a wrapper having a metallic coating is characterised in that the metallic coating (3) is constructed to have discontinuities (6) to thereby enable any metallic foreign body (5) to be detected through the metallic coating, such discontinuities being typically in the form of either corrugations in the film or gaps in the metallic coating.

Description

PRODUCT MONITORING This invention relates to a method and apparatus for monitoring a series of products and is related to the method and apparatus disclosed in our UK patent application 8907229.2 and our international patent application No GB90/00469.

In those applications a method and apparatus is disclosed by which mass-produced food products can be monitored in order to detect any metallic foreign bodies which may be contained in them.

There are certain food products where it is required to keep them in storage for significant periods of time, for exale up to one year, without them deteriorating. In order to achieve this it is known to wrap such products in a single or multi-layer plastic film incorporating a metallised or metal oxide coating or layer in order to protect the product from various aspects of the environment including air, gas and ultra-violet radiation.

There can be as many as seven layers. The presence of such a metallised or metal oxide coating or layer can form a screen which presents the effective operation of the method and apparatus of our above mentioned patent applications. The present invention is concerned with overcoming this problem.

The general approach adopted by the applicants has been to investigate the possibility of in effect breaking-up the surface of the metallised sheet in the sense of how it is "seen" by the drive and detection signals so that to some extent areas of the metallised layer will appear to be transparent as far as the drive and detection signals are concerned.

According to the present invention a method of enabling the method as claimed in our aforesaid copending patent applications to be used to detect metallic foreign bodies within products wrapped inside a film having a metallised or metal oxide coating or layer comprises treating the said coating or layer to render it discontinuous whereby said coating or layer becomes to some extent transparent to the detection signal.

According to one aspect of the present invention the aforesaid relative transparency is achieved by providing the coating or layer with one or more areas which are uncoated such areas being relatively very small in relation to the total area of the coating or layer film and such as to not substantially effect the sealing properties of the film.

According to a second aspect of the present invention the aforesaid relative transparency is achieved by corrugating the said coating or layer.

How the invention may be carried out will now be described, by way of example only, and with reference to the accompanying drawings in which: Figure 1 shows a very enlarged fragmentary view of a metallised wrapper film constructed according to a first aspect of the present invention; Figure 2 is a similar view to figure 1 showing a metallised wrapper film constructed according to a second aspect of the present invention; and Figure 3 is a very enlarged fragmentary cross-sectional view of a wrapper film constructed according to a third aspect of the present invention.

The general method and apparatus to which the present invention is applicable is disclosed in our copending UK patent application No 8907229.2 and international patent application No GB90/00469. The details of this method and apparatus will therefore not be described in this application.

The essence of that method and apparatus is the use of the phase difference which exists between the detection signal and the drive signal for a particular product coupled with the use as a datum of the signal generated by a satisfactory product having no metallic foreign body to judge whether the next subsequent product being monitored is free from a metallic foreign body or not.

Figure 1 illustrates, on an extremely large scale a very small portion of a film wrapper 1 having a substrate 2 and a metallic coating 3, the wrapping film 1 containing a food powder 4.

The substrate 2 is made of a plastics material such as Mylar (Registered Trade Mark) and the metallic coating 3 is aluminium.

In this example the metallic coating 3 is relatively thin having a thickness of a few microns. The plastic substrate is typically 0.1 mm thick.

The effect of corrugating the wrapping film 1, and thus. the metallic coating 3 is to influence the.

above mentioned detection and drive signals in such a way that the metallic coating in effect becomes transparent to some extent to those signals thus enabling a metallic foreign body, indicated by 5 in figure 1, to be detected. The exact mechanism is not known to the applicants but it is thought that the corrugations sufficiently affect the crystalline structure of the coating to render it "transparent" at these points.

Although a specific form of corrugation is shown in figure 1 other forms of corrugation could be employed.

The term "corrugation" is intended to have a broad meaning to include any formation of irregularities or irregular pattern in the surface of the film and thus the metallic coating 3, the effect of which would be to enable the aforementioned signals to effectively detect a metallic foreign body contained within the product enclosed by the wrapping, i.e. to enable the signals to, as it were "see" through the wrapping.

Figure 2 illustrates an alternative approach which is particularly appropriate where the metallic coating 3 is substantially thicker than that indicated in connection with figure 1 and where the approval of Figure 1 does not give a satisfactory result. In this embodiment the same reference numerals have been used to illustrate the equivalent elements to those shown in figure 1. However, the effective "transparency" of the metallic coating 3 is achieved by providing it with a series of mutually parallel gaps or stripes 6 which are relatively narrow compared with the metallic material between adjacent stripes 6. For example each stripe may be only 0.1 mm wide.

The distance between adjacent stripes is a compromise between sealing and detection capabilities. Sealing capability is generally inversely proportional to the number of stripes.

In contrast the detection effectiveness appears to be proportional to the square of the number of stripes employed. Thus by doubling the number of stripes the detection effectiveness is increased by a factor of four. It has also been found that for maximum detection effectiveness the stripes 6 should run parallel to the direction of travel of the product as it passes through the detection apparatus.

The total area of the stripes 6 in relation to the total area of the metallic coating 3 would be typically only one to two per cent. It has been found that although this enables effective monitoring of metallic foreign bodies to be carried out, it is not sufficient to significantly affect the sealing effect of the wrapper 1 as a whole.

Although figure 2 illustrates an arrangement of stripes 6 which consists of mutually parallel straight lines other arrangements and shapes of stripe 6 could be employed. Furthermore other forms of discontinuity in the metallised coating, which achieved the objective of adequately sealing the product whilst at the same time enabling effective monitoring of foreign bodies, could be employed.

The embodiment of figure 3 illustrates the application to a multi-layer wrapper of an approval similar to that shown in figure 2.

In this embodiment there are three layers of plastic film 2 a , 2 b and 2 c and two sets of metallic stripes 3 a and 3 b sandwiched between the plastic film layers.

The stips on each set overlap with those in the other set and are insulated from one-another by the plastic film layer 2 b With this overlapping the effective sealing function of the wrapper is maintained whilst at the same time creating the required discontinuity in the metallised areas to enable the effective detection of foreign bodies within the wrapped product to be carried out.

In the folllowing claims the term "discontinuity" is intended to cover any arrangement in which the surface of the metallic coating is either shaped or configured to render it partially transparent to the detection signal.

Claims

1. A method of enabling the method as claimed in our aforesaid copending patent applications to be used to detect metallic foreign bodies within products wrapped inside a film having a metallised or metal oxide coating or layer comprises treating the said coating or layer to render it discontinuous whereby said coating or layer becomes to some extent transparent to the detection signal.

2. A method as claimed in claim 1 in which the discontinuity is achieved by providing the film with one or more areas which are uncoated such areas being relatively very small in relation to the total area of the film and such as to not substantially effect the sealing properties of the film.

3. A method as claimed in claim 2 in which the said areas comprise a plurality of gaps or stripes so that the substrate is uncoated in those gaps or stripes.

4. A method as claimed in claim 1 in which the discontinuity is achieved by corrugating the film.

5. A method as claimed in claim 2 or 3 in which there are a plurality of layers of film between which are sandwiched a plurality of sets of discontinuous metallied or metal oxide coatings.

6. A method as claimed in claim 5 in which the sets of said coatings overlap with one another.

7. A method substantially as hereinbefore described with reference to and as shown in either figure 1 or figure 2 or figure 3 of the accompanying drawings.