MXPA00004516A

MXPA00004516A - Flaw detector for package closures

Info

Publication number: MXPA00004516A
Application number: MXPA/A/2000/004516A
Authority: MX
Inventors: Sighinolfi Eugenio
Original assignee: Tetra Laval Holdings&Ampfinance Sa*
Priority date: 1999-05-14
Filing date: 2000-05-10
Publication date: 2001-11-21

Abstract

A control unit (1) interacting with a strip packaging material to which are applied, to close respective openings (3) in the packaging material, a number of patch elements (5) and a number of tear-off tongues (6) heat sealed to respective patch elements (5). To determine the integrity of the patch elements (5), the unit has at least one contact surface (21) at an operating electric potential (Va) and cooperating with the side of the packaging material (4) having the patch elements (5) to define one plate of a capacitor (23), the other plate of which is defined by an aluminium film (4a) of thepackaging material (4), and the dielectric of which is defined by the heat-seal plastic material interposed between the plates;and a detecting circuit (26) connected to the contact surface (21) and to the aluminium film (4a) to detect an electric quantity related to variations in the dielectric strength of the dielectric of the capacitor (23) and so determine the presence of any microholes in the patch elements (5).

Description

CONTROL UNIT TO INSPECT THE INTEGRITY OF DEGREEABLE CLOSURE DEVICES APPLIED TO RESPECTIVE OPENINGS IN PACKAGING MATERIAL IN STRIPS TO PRODUCE ASEPTIC SEALED PACKAGES OF FOODSTUFFS THAT CAN BE POURED DESCRIPTION OF THE INVENTION The present invention is concerned with a control unit for inspecting the integrity of tear-off closure devices applied to respective openings in strip packaging material to produce aseptic sealed packages of pourable food products. As is known, many pourable food products, such as fruit juice, UHT milk (treated at ultra high temperature), wine, tomato sauce etc., are sold in packages made of sterilized packaging material. A typical example of such packaging is the parallelepiped packing for liquid or pourable food products known by the name of Tetra Brik Aseptic (registered trademark), which is formed by folding and sealing packaging material rolled into strips or bands. The packaging material has a multilayer structure comprising a layer of fibrous material, for example, paper covered on both sides with layers of plastic material of REF .: 119056 thermal sealing, for example polyethylene. In the case of aseptic packaging for long-term storage products such as UHT milk, the packaging material comprises a layer of barrier material defined for example by an aluminum film which is superimposed on a layer of heat sealing plastic material and it is in turn covered by another layer of heat sealing plastic material that defines the inner face of the package that inevitably comes into contact with the food product. As is known, such packages are produced in fully automatic packaging machines in which a continuous tube is formed from the packaging material supplied in the form of a strip. The strip of packaging material is sterilized in the packaging machine, for example by the application of a chemical sterilizing agent such as a hydrogen peroxide solution; following the sterilization, the sterilizing agent is removed, for example vaporized by heating, from the surfaces of the packaging material and the strip or band of packaging material thus sterilized is kept in a closed sterile environment and is folded and sealed longitudinally to form a tube. The tube is filled with the sterilized or sterile processed food product and is sealed in equally spaced cross sections along which it is then cut into pillow-shaped packages that are subsequently folded < 38 $ mechanically to form the finished packages, for example substantially parallelepipeds. The finished package comprises an opening through which the product can be poured and a tear closure device applied to the opening. The openings are formed and the respective closure devices are applied to the packaging material in strips or bands before the material is folded to the vertical tube and filled with the food product. More specifically, each closure device comprises a "patch" element defined by a small sheet of heat sealing plastic material ~ and applied to close the respective opening, next to the packing material that inevitably defines the interior of the package and a tongue. of tear applied to the opposite side of the packaging material and thermally sealed to the patch element. The tongue comprises an aluminum layer and a layer of heat sealing plastic material, usually polyethylene, which is sealed to the patch element. By virtue of the patch element and the tab which adhere to each other, the portion of the patch element sealed to the tongue is also removed, thus exposing the opening, when the tongue is torn. In the course of the operation of the heat seal, tears or microholes are formed in the superheated patch element, particularly as a result of the patch element interacting with the normally quite irregular edges of the opening formed in the packing material. The presence of microholes in the patch element can deteriorate the integrity and asepsis of the package by allowing outside air to enter the package. It is an object of the present invention to provide a control unit for inspecting the integrity of the tear closure devices applied to the respective openings in the packaging material in strips and providing a quality control application of the closing devices to the packaging material. It is a further object of the present invention to allow the inspection to be carried out during the operation of the packaging machine. In accordance with the present invention, a control unit is provided for inspecting the integrity of tear closure devices applied to the respective openings in a strip packaging material to form aseptic sealed packages of pourable food products.; the material of The packing has a multilayer structure that comprises at least one electrically conductive sheet of covered barrier material. on opposite sides with respective layers of heat sealing plastic material; each closure device comprises a laminar patch element made of plastic heat sealing material and applied to close a respective opening, to one side of the packaging material that inevitably defines the interior of the package and a tear-off tab also made of plastic material of heat seal and which is applied to an opposite face of the packaging material and sealed to the patch element; the unit is characterized in that it comprises: at least one contact surface at an electrical operating potential and which cooperates with the packing material in the patch elements to define one plate of one capacitor, the other plate of which is defined by the sheet of the barrier material and the dielectric material of which is defined by the plastic heat sealing material of the patch elements and the layer of the packaging material interposed between the sheet of barrier material and the patch elements and detection means connected to the contact surface and to the barrier material sheet of the packaging material to detect an electrical quantity related to variations in the dielectric strength of the dielectric material of the capacitor and thus determine the presence of any microholes in the patch elements. A preferred non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings in which: Figure 1 shows a side elevation view of a control unit according to the present invention for inspecting the integrity of tear closure devices applied to respective openings in the strip packaging material; Figure 2 shows a front elevation view of the control unit of Figure 1; Figure 3 shows an enlarged section of a closure device applied to a respective opening of the packaging material. No. 1 of the accompanying drawings indicates, as a whole, a unit for inspecting the integrity of the tear closure devices 2 applied to respective openings 3 in the strip packing material 4 fed along a path P. unit 1 can be incorporated into a packaging machine (not shown) to continuously produce, from the packaging material 4 in strips or bands, aseptic sealed packages (not shown) of pourable food products, such as pasteurized milk or UHT, fruit juice, wine, etc. In particular, the packing material 4 is folded and longitudinally sealed in a known manner to form a vertical tube, which is filled with the sterilized or sterilized food product, is sealed along a similarly spaced cross section and is then mechanically folded to form the finished packages. The unit 1 is located along the path P of the packing material 4, downstream of a known station (not shown) to apply closure devices 2 to respective openings 3 in the packing material 4 and upstream of a station to form the vertical tube of the packaging material. The packaging material 4 has a multilayer structure and substantially comprises a layer of fibrous material, for example paper, covered on both sides with respective layers of heat sealing plastic material, for example polyethylene. inevitably defines the internal face of the package and that therefore comes into contact with the food product, is also provided with a layer of electrically conductive barrier material defined for example by an aluminum sheet 4a which is in turn covered on both sides with respective layers of heat sealing plastic material, for example polyethylene.

With particular reference to Figure 3, each closure device 2 comprises a patch element 5 defined by a small sheet of heat sealing plastic material and applied to close a respective opening 3 to the face of the packaging material 4 which inevitably defines the Inside the package and a tear-off tongue 6 which is also made of heat-sealing plastic material, is applied to the opposite side of the packing material 4 and is thermally sealed to the patch element 5. In particular, the patch element 5 and the tongue 6 is joined along a sealing area extending close to and inward of a side edge of the respective opening 3 and defining a tearing portion of the patch 5 when the tongue 6 is torn. The tongue 6 also has a multilayer structure and comprises a layer of heat sealing plastic material, for example polyethylene, one face of which is attached to the patch element 5 and a layer of barrier material, usually aluminum, which is fixed to the layer of the heat sealing plastic material on the side opposite the patch element 5. With reference to Figures 1 and 2, the unit 1 substantially comprises an external, substantially parallelepiped, box 8 made of the plastic material and having side openings opposite 9, 10 for the passage of the packaging material 4 in strips and two inactive rollers 11, 12, which are housed inside the box 8 with respective axes A, B parallel to the packaging material 4, are supported in a rotational manner by respective pairs of brackets or brackets 13, 14 projecting from a side wall of the box 8 and cooperating on opposite sides with the packing material 4 in the elements of patch 5 and tab 6 respectively. More specifically, the roller 11 is equipped, in a rotary or rotatable manner about the respective axis A, to the free ends of brackets or brackets 13, while the roller 12 is equipped in a rotary manner around the respective axis B, to the other end of a rocker lever 15 hinged in a point "intermediate the brackets or brackets 14 and the opposite end of which is connected to the bottom wall of the box 8 by a cylindrical coil spring 16 which consequently exerts a torque on the lever 15 for keeping the roller 12 in contact with the packing material 4. Each roller 11, 12 comprises a cylindrical intermediate portion 40 of diameter d and opposite end portions 41 rounded, convex outwardly with a radius of curvature r which fluctuates from between 0.25 and 0.5 times the diameter d of the intermediate portion 40.

The roller 11 is connected to an adjustable high-voltage generator 20, such that an external surface 21 of the roller 11 that comes into contact with the packing material 4 is at an operating potential Va while the aluminum film 4a of packing material 4 is at ground potential. The surface 21 of the roller 11 and the aluminum film 4a of the packing material 4 define respective plates of a capacitor 23, the dielectric element of which is defined by the thermal seal plastic material of the patch elements 5 and the layer of the packaging material 4 interposed between the aluminum film 4a and the patch elements 5. To ensure a secure ground connection of the aluminum film 4a of the packaging material 4, an additional idle roller 24 is provided which is housed inside of the box 8 for rotating about a respective axis C perpendicular to the packing material 4, has an external annular groove 25 cooperating with and contacting laterally with a peripheral edge of the packing material 4 and is connected to ground. An important aspect of the present invention is that the unit 1 also comprises a detection circuit 26 to detect variations in the dielectric strength of the packing material 4 equipped with the closing devices 2 and thus determine the presence of any microholes (figure 3) in the patch elements 5. More specifically, on account of the different insulating properties of the air and the material defining the patch elements 5, tests have shown that, when the closure devices 2 are perfectly integral, the dielectric strength of the packing material 4 equipped with closure device 2 is equal to a first value Dl - in the example shown 20 KV / mm - and assumes a second value D2 - in the example shown of 3 KV lower than the value Dl in the presence of microholes in the patch element 5. detection circuit 26 provides detection of the flow of electrical current through the dielectric material of the capacitor 23, which is presented as a function of the Va value of the operation potential supplied by the generator 20 and when the dielectric strength of the packing material 4 equipped with closing devices 2 passes from the value of 1 to the value of 2, that is in the presence of micro-holes in the patch element 5. In particular, the operating potential n It is supplied by the generator 20 is selected to produce no flow of electrical current through the dielectric material of the capacitor 23 when the patch elements 5 are perfectly integral, but sufficient to produce such a current flow in the presence of microholes in the elements of patch 5. With particular reference to Figure 1, the detection circuit 26 comprises a resistor 28 having a first terminal 29 connected to the generator 20 and a second terminal 30 connected to the roller 11 and a comparator 31 having a first input 32 connected to the terminal 29 via the interposition of a voltage reducer 33 that supplies a measurement potential Vm related to the potential of the terminal 29 and consequently to the operation potential Va, a second input 34 that receives a reference potential Vf and a output 35 which supplies a logic state signal Sp indicating the presence / absence of microholes in the Relative patch element 5 and assumes a high logic level (Sp =? ") when the measurement potential Vm is smaller than the reference potential Vf and a low logic level (Sp = 0) under other conditions. In real service, the generator 20 supplies a potential for square wave operation, which assumes high values in the vicinity of each closing device 2 and low values in the areas of the packaging material 4 interposed between two successive openings 3 for producing, in such areas, no electric current flow possibly caused by the presence of small fissures in the layers of the heat seal plastic material which comes into contact with the aluminum layer and which may deteriorate the packing material 4. In the case of a micro-hole (figure 3) in the patch element 5 traveling between the rollers 11 and 12, the dielectric strength of the material interposed between the roller 11 and the aluminum film 4a of the packing material 4 falls from the value of 1 to the value of 2 such that, in the presence of a value of Va of high operating potential of the generator 20, the current flows through the packing material 4 resulting in í a fall in the measurement potential Vm. As the measurement potential Vm falls below the reference potential Vf, the state signal Sp changes from a low logic level to a high logic level to indicate the presence of a miCro hole in the patch element 5. When the measurement potential Vm falls below a minimum threshold value related to the dielectric strength D2 of the material interposed between the roller 11 and the aluminum film 4a of the packing material 4, no electric current flows through the packing material 4, in such a way that the potential Vm is increased to a maximum threshold value above which the electric current flows again through the dielectric material of the capacitor 23; such a phenomenon is repeated until the micro-hole reaches beyond the rollers 11 and 12, this is for a time interval dependent on the travel speed of the packing material 4. When the micro-hole reaches beyond the rollers 11 and 12 , the measurement potential Vm returns to the nominal value and from here, the state signal Sp assumes a low logic level. Conversely, if the patch element 5 traveling between the rollers 11 and 12 is perfectly integral, no electrical current flows through the packing material 4 equipped with closing devices 2, so that the measurement potential Vm remains in the nominal value and does not fall below the reference potential Vf and the signal Sp remains at the low logic level (Sp = 0). The advantages of the unit 1 according to the present invention will be clear from the above description. In particular, the unit 1 provides the quality control of the operations carried out on the packaging material 4 to form openings 3 and apply respective closing devices 2. The information contained in the status signal Sp indicating the presence of micro-holes in the patch elements 5 can be used to reject, at a subsequent stage in the operation cycle of the packaging machine, at least the packages formed from the portion of the packaging material 4 comprising defective patch elements 5 . Clearly, changes can be made to unit 1 as described and illustrated herein without departing from the scope of the appended claims. In particular, the roller 11 connected to the generator 20 can be connected to the box 8 by the rocker lever 15 and the spring 16 and the roller can be equipped in a fixed position to the box 8. It is noted that, with regard to on this date, the best method known by the applicant to carry out the aforementioned invention is the conventional one for the manufacture of the objects to which it refers.

Claims

CLAIMS Having described the invention as above, the content of the following claims is claimed as property: 1. A control unit for inspecting the integrity of tear closure devices applied to respective openings in a strip packing material to form sealed packages aseptic food products that can be poured; the packaging material having a multilayer structure comprising at least one electrically conductive sheet of barrier material covered on opposite sides with respective layers of heat seal plastic material; each closing device comprises a laminar patch element made of plastic heat sealing material and applied to close a respective one of the openings to one side of the packaging material that eventually defines the inside of the package and a tearing tab also made of material heat sealing plastic and which is applied to an opposite face of the packaging material and sealed to the patch element; the unit is characterized in that it comprises: at least one contact surface at an electrical operating potential and which cooperates with the packing material in the patch elements to define one plate of one capacitor, the other plate which is defined by the sheet of the barrier material and the dielectric material which is defined by the plastic heat sealing material of the patch elements and the layer of the packaging material interposed between the sheet of the barrier material and the patch elements and detection means connected to the contact surface and the sheet of the barrier material of the packaging material to detect an electrical quantity related to variations in the dielectric strength of the dielectric material of the capacitor and thus determine the presence of any microholes in the patch elements.
2. A unit according to claim 1, characterized in that the detection means comprise indicating means for indicating the electric current flow through the dielectric material of the capacitor.
A unit according to claim 1 or 2, characterized in that the detection means comprise comparison means having a first input that receives a reference signal indicating a reference potential, a second input that receives a measurement signal indicator of a measurement potential related to the electrical potential of operation and an output that supplies a status signal indicating the presence of microholes in a relative patch element . ? », * Erji in the case of a predetermined relationship between the measurement signal and the reference signal. .
A unit according to claim 3, characterized in that the status signal is a logic signal that assumes a first logical level indicating the presence of microholes in the relative patch element when the measurement potential is less than the reference potential.
5. A unit according to any of the preceding claims, characterized in that the contact surface is connected to voltage generating means that supply the electrical potential of operation and because the detection means comprise resistance means interposed between the voltage generating means. and the contact surface. -
6. A unit according to any of the preceding claims, characterized in that it comprises a first and a second idle rollers, having respective axes parallel to the packaging material and cooperating on opposite sides with the "packaging material in the elements of patch and tongues respectively, the contact surface is defined by the external surface of the first idle roller
7. A unit according to claim 6, characterized in that the first and second idle rollers each comprise a cylindrical intermediate portion and portions of the same. rounded end, opposite, convex outward that have a radius of curvature that fluctuates between 0.25 and 0.5 times the diameter of the intermediate portion.
8. A unit according to any of the preceding claims, characterized in that it comprises a third inactive roller having an axis perpendicular to the packaging material, which laterally cooperates with a peripheral edge of the packaging material and is at ground potential.
9. A unit according to any of the preceding claims, characterized in that each tab has a multilayer structure comprising a layer of barrier material. Control that interacts with a packaging material in strip or band to which they are applied, to close respective openings (3) in the packaging material, a number of patch elements (5) and a number of tear tabs (6). ) thermally sealed to respective patch elements (5). To determine the integrity of the patch elements (5), the unit has at least one contact surface (21) at an electrical operating potential (Va) and cooperating with the side of the packing material (4) having the patch elements (5) to define a plate of a capacitor (23), the other plate which is defined by an aluminum film (4a) of the packing material (4) and the dielectric material which is defined by the " heat sealing plastic material interposed between the plates and a detection circuit (26) connected to the contact surface (21) and to the aluminum film (4a) to detect an electrical quantity related to variations in the dielectric strength of the dielectric material of the capacitor (23) and thus determine the presence of any microholes in the patch elements (5).