NZ217893A - Heat shrinking wrappings on articles between two conveyors - Google Patents

Description

217893 Priority Dato(s): .. . Pi1?.

Compreio Specification Fiied: ^3^!.9.$^ Class: g(6.e?3/c2, Publication Date: 3. P. ...

P.O. Journal, No: NEW ZEALAND PATENTS ACT. 1953 No.: Dite: COMPLETE SPECIFICATION "SHRINK TUNNEL WITH OVERHEAD CONVEYOR' A 13 OCT 1986 XK/We, W R GRACE & CO, a corporation organized and existing under the laws of the State of Connecticut, USA, of 1114 Avenue of the Americas, New York, NY 10036, United States of America, hereby declare the invention for which >tx^ we pray tuat a patent may be granted to)t*i©yus, and the method by which it is to be performed, to be particularly described in and by the following statement:- 217893 £ hi f 12FEBWB8 SHRINK TUNNEL WITH OVERHEAD CONVEYOR FIELD OF THE INVENTION The present invention relates to a shrink tunnel for shrinking a thermoplastics film around a product, and more specifically a shrink tunnel for shrinking a film around a product which is prone to curling or buckling during the shrinking cycle.

BACKGROUND OF THE INVENTION Shrinkable films are often useful in packaging food and nonfood products. These thermoplastics films are characterized by the ability to shrink upon the application of heat, providing shrinkability and shrink tension to the film and in turn providing a product which is packaged tightly by the thermoplastics film and generally has good clarity and optical properties while protecting the packaged product from environmental abuse and handling during the distribution cycle.

Shrink tunnel apparatus have been available in the marketplace for many years. These are generally designed to convey the packaged product, already wrapped in a shrinkable film, through a tunnel or other means where recirculating hot air effects shrinking of the film around the 404/850619/1/1 -7 o ^ 21789y 2FEB)98g product. Exposure to the hot air is generally for a feiX. seconds, £or a time sufficient to shrink the film around the product. The product is typically carried through the shrink tunnel or other means by a roller or belt type conveyor.

Certain products lend themselves to the use of shrinkable film, and consequently the use of a shrink tunnel or other means to actually shrink the film around the respective product. These products are relatively insensitive to the actual shrink tension imparted by the thermoplastics film during the shrinking cycle.

However, other products are more sensitive to the shrinking cycle, and yet it is desirable to utilize shrinkable films with respect to these products as well. Such products are for example record album jackets, and other paper products or relatively flat products which utilize a cardboard backing or sheet or other relatively flat cardboard or 15 paper base to hold the product. These products are characterized by a low flexural modulus. It is desirable to shrink wrap these products to provide the aesthetic appeal of a tightly wrapped, high clarity consumer item, but the use of such thermoplastics shrinkable films can sometimes result in curling or buckling of the product due to the shrink tension of 20 the thermoplastics film being used in the shrinking process. The curling phenomenon is detrimental in many respects, including the possible loss of value of the product to be packaged, or at least the production of a finished product with less aesthetic appeal for the consumer than a product in which no curling is present.

One possible solution to this curling or buckling problem is the use of thermoplastics films which are characterized by lower shrink tension 404/850619/1/2 r*\ < .• O 4 217893 and other shrink properties such as free shrink or shrink force. An example of such films are films made from polyvinyl chloride (PVC). However, some of the most suitable thermoplastics films and laminates currently available, which are useful for their physical properties such 5 as high tensile strength, low tear propagation, and other properties, would thereby be eliminated from use with products prone to curling. These include polyolefin films. These thermoplastics films just mentioned often also have good optical qualities and exhibit good toughness, both desirable characteristics in a thermoplastics film to be used in packaging 10 consumer products.

It would also be advantageous to use these polyolefin films in lieu of PVC in order to avoid the relatively corrosive effect of PVC on shrink tunnel hardware, and to take advantage of the excellent machinability of the polyolefin films.

In the past, solid belts such as solid belts made of teflon and other materials have been used as overhead conveyors in conjunction with roller or belt type conveyors, for use with polyethylene film. These solid belt configurations have proven to be ineffective in properly shrinking many shrink films in part because of the lack of proper heat 20 distribution.

It is therefore an object of the present invention to provide a shrink tunnel apparatus wherein curl-sensitive products such as cardboard-based or cardboard-backed products, or other products of low flexural modulus, may be wrapped with heat shrinkable films and yet exhibit little or no curling or buckling of the product as the ff vr-if<K heat shrinking procedure. I r oo 1 02F EBW88/ 404/850619/1/3 V <3/ 217893 It is still another object of the present invention to provide a shrink tunnel apparatus for reducing or eliminating curling or buckling of curl-sensitive products during the shrinking cycle while still making use of thermoplastics shrinkable films having relatively high shrink tension and other shrink properties.

SUMMARY OF THE INVENTION In one aspect of the present invention, in an apparatus for heat shrinking a thermoplastics film wrapped around a product to be packaged, said apparatus including a first driven roller-type conveyor, means for supporting said conveyor, means for advancing the wrapped product along the conveyor from a point of entry to a point of exit, means for circulating hot air through the conveyor to and around the wrapped product, and tunnel means for housing the circulating means and substantially confining the flow of air within the apparatus, the improvement comprises a second conveyor, of a type permitting the circulation of hot air through said second conveyor to the wrapped product, disposed substantially parallel to and in alignment with the first conveyor to permit the wrapped product to advance along the first conveyor while in contact with the second conveyor, in order to substantially reduce curling or buckling of the wrapped product.

In another aspect of the present invention, a method of substantially reducing curling of wrapped products during a heat shrink cycle comprises advancing a wrapped product along a first conveyor of a heat shrink apparatus; simultaneously bringing the wrapped product into contact 'A tN 1 with a second conveyor disposed substantially parallel to in alii ?nt /W 404/850619/1/4 ^(12FEB^8 fc 217S93 with the first conveyor; and introducing heated air through the first and second conveyors to the wrapped article.

DESCRIPTION OF THE DRAWINGS In the drawings which are attached hereto and form a part hereof: FIG. 1 is a perspective view of a heat shrink apparatus including the apparatus of Che present invention; and, FIG. 2 is a schematic view of a preferred embodiment of che apparatus according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to FIG. 1, a heat shrink apparatus 10 includes a first roller-type conveyor 12, a supporting means 14 for supporting said conveyor, and an advancing 16 means for advancing a wrapped produce 18 (see FIG. 2) along the first conveyor 12. The supporting means 14 may include any suitable framework for housing the first roller type conveyor 12 and advancing means 16. The advancing means 16 may include a chain driven by a motor or other suitable apparatus for advancing a conveyor. A tunnel means 20 encompasses substantially all of the conveyor means 12 and houses a set of air chambers (not shown) for che passage of hot air from typically an electric resistance unit or units to che wrapped product IS.

Various controls, also well known in the art, may be u the speed of first conveyor 12, the temperature and v 404/850619/1/5 tilized •/ V* elocitsy of che 217S93 air circulating within tunnel means 20, and che other variables of the heat shrink apparatus 10. For example, controls may regulate air velocity and air temperature respectively. Typically air temperatures for use in shrinking wrapped products in accordance with the present Invention range from about 260°F to about 325°F. Additional controls may include a disconnect switch and a control for conveyor speed. Typical conveyor speeds may range from 0 to 120 feet per minute.

The foregoing generally describes apparatus readily available and commercialized, and well known in the arc, for heat shrinking products wrapped in heat shrinkable thermoplastics films. The wrapped product 18 is placed at a point of entry 22 (Fig 2) i.e. one end of the conveyor 12, a advanced along and by the conveyor 12 and through tunnel means 20 where recirculated hot air raises che cemperacure of the wrapped product to an extent sufficient to induce shrinkage of the thermoplastics film around the product. The now heat-shrunk wrapped product is advanced further to the point of exit 24 (Fig 2) or opposite end of the conveyor where the product transferred for further processing or shipped for distribution.

It has been found that when the heat shrinking apparatus is used as shown, products wrapped in thermoplastics films having relatively high shrink tensions and other indicia of shrink energy will sometimes exhibit curling or buckling, especially if the products have relatively weak structural strength, or low flexural modulus such as cardboard-based or cardboard-backed products e.g. record albums, packages for paper products, pillow cases and linens .and greeting cards, in these situations, it is desirable to find a way of reducing or eliminating this curling or buckling problem in order to provide an aestheticall^appealing product, and to reduce loss of product due to faul^ ^packagrrvgV In <1CCD IQfifi 217893 accordance with the present invention, and as a solution to this curling or buckling phenomenon, a second conveyor 26 is superimposed above the first conveyor 12. Second conveyor 26 is of a type which permits the circulation of hot air through the conveyor 26 and towards the wrapped product 18. Individual rollers 28 of first conveyor 12 and individual rollers 30 of second conveyor 26 sequentially contact the wrapped product 18 as It is advanced through tunnel means 20. These rollers 28 and 30 are preferably covered with silicone rubber, and are preferably driven by passage over rails 32 and 34 respectively around their individual axes and provide more efficient and uniform shrinkage of the chermoplastics wrapping material (See FIG. 2). Second conveyor 26 is advanced by advancing means 36 which may be similar to advancing means 16 of first conveyor 12. Adjusting means 38 allows for the pre-selection of -an appropriate gap between second conveyor 26 and first conveyor 12 to adjust for the thickness of the product to be heat-shrunk. Typically, only slight pressure exerted on the wrapped product 18 by the second conveyor 26 is necessary to prevent or substantially reduce curling and buckling of the wrapped product during the shrink cycle.

In a preferred embodiment, second conveyor 26 is disposed above first conveyor 12, and displaced therefrom a distance sufficient to provide contact between rollers 28 of first conveyor 12, and rollers 30 of second conveyor 26, and wrapped product 18, without exerting excessive pressure on wrapped product 18 as it passes through tunnel means 20.

Conveyors 12 and 26 are preferably substantially flush with respect to horizontal alignment in the heat shrink apparatus 10 at point of entry 22, but first conveyor 12 preferably projects some^ffe^#a^ther horizontally than second conveyor 26 at point of esft' 24 V.N 404/850619/1/7 °1 \f 12 FEB 1988 v ... . ..,_■■<•/ •-•••' * ••' q 217893 facilicaces incroducclon of a wrapped producc 18 becween rollers 28 and 30 ac poinc of ancry 22, well before subjecting wrapped producc 18 co che shrinking accion of che heaced air while allowing easy access co and transfer of che shrunk producc at poinc of exic 24.

While che lnvencion as described above relaces primarily co a heac shrink apparacus in which a firsc and second conveyor are in subscan-cially horizoncal arrangemenc, wich che second conveyor sicuaced vertically above che firsc conveyor, it is clear chac wich suicable modifications che firsc and second conveyors may be used in any arrangemenc including a tilced or vertical arrangement.

Referring now Co figure 2, a schemacic side- view of che firsc conveyor 12 and second conveyor 26 shows individual rollers 28 of firsc conveyor 12 and individual rollers 30 of second conveyor 26. A wrapped product 18 is shown with an exaggeraced thickness for purposes of claricy.

Firsc conveyor 12 may be a belc having cransverse "live" rolls excended becween a pair of linked chains disposed in a parallel relationship. The construction and use of such a conveyor is well known in the art and currently used in many heat-shrinking apparatus designs.

Second conveyor 26 is preferably constructed similar to first conveyor 12, but need not be identical to first conveyor 12. An important characteristic of second conveyor 26 is the ability to apply slight pressure to a wrapped product during the heat-shrink cycle while allowing circulating hot air to pass through and around the live roLJ^of second E N r \ conveyor 26 Co pass around Che wrapped product 18.

'In 12 FEB 1988 404/850619/1/8 217893 Conveyors 12 and 26 may be driven by suitable advancing means well known in che arc and may include a chain driven by a mocor or ocher apparaCus for advancing che conveyors. An example is a 3/4 horse power mocor running at 1500 rpm and driving Che respective conveyors at speeds up Co 120 feec per minuce. Variable gears and sprockecs may be appropriacely used in Che advancing means in connection with a drive mocor.

Hot air may be incroduced and recirculaCed chrough che cunnel means 16 by various means and by various air paths well known in che arc. Typically air is incroduced Co che cunnel means 20 after having been heaced for example by electric resistance heacing. The air is circulated by fan means to che wrapped producc, for example" from inlet ducts positioned on four sides of the wrapped product 18.

It is well within the purview of one skilled in the art Co appropriately utilize circulaCing hoc air at temperatures and velocities suitable for the particular application.

In addition to substantially reducing or eliminating the curling problem, the present invention provides better control of temperature than in standard heat shrinking apparatus. The driven rollers tend to distribute the recirculated hot air more effectively and more evenly over the wrapped product and help to reduce the variability in shrinkage which can result from a scandard heac shrinking apparatus.

Although the present invention has been described in connection with a preferred embodiment, it is to be understood that modifications and 404/850619/1/9 12 FEB 1988 '« 217893 variations may be utilized without departing from the principles and scope of the invention, as readily understood by Chose skilled in che arc.

Claims (9)

\7, 21789J WHAT UE CLAIM IS:

1. An apparatus for heat shrinking a thermoplastics film wrapped around a product to be packaged, said apparatus including a first conveyor having a series of parallel individual driven rollers (hereafter "roller-type conveyor") , means for supporting said conveyor, means for advancing the wrapped product along the conveyor from a point of entry to a point of exit, means for circulating hot air through the conveyor to and around the wrapped product, and cunnel means for housing the circulating means and substantially confining che flow of air within the apparatus, a second conveyor permitting -the circulation of hoc air through said second conveyor to the wrapped product, disposed substantially parallel to and in alignment with the first conveyor to permit che wrapped produce Co advance along -che first conveyor while in contact wich the second conveyor, in order ca substantially reduce curling or buckling of the wrapped product.

2. The apparatus ; according to claim 1 wherein the second conveyor is a roller-type conveyor.

3. The roller-type conveyor of claim 2 wherein individual rollers of the first and second conveyors in contact wich the wrapped product are driven about their respective axes.

4. The apparatus according co claim 1 wherein che second conveyor is connected to adjusting means for providing a pre-selected gap between the first and second conveyor. ■ t-,v' ' u \

5. The apparatus according to claim 1 wherein the first- and / , ^ V \ second conveyors have a substantially horizontal flowpath u -J 404/850619/1/L1 21789C 13,

6. A method of substantially reducing curling of a product, wrapped with a thermoplastics film, during a heat-shrink cycle comprising: having a series of parallel individual driven rollers (hereafter "roller-type OOnveyar") of a heat shrink apparatus; contact with a second roller-type conveyor disposed substantially parallel Co and in alignment wich che first conveyor; and c) introducing heaced air chrough che firsc and second conveyors Co Che wrapped producc.

7. The method according co claim 6 wherein individual rollers of che firsc and second roller-cype conveyors are driven as che wrapped producc is advanced chrough che heat shrink apparatus.

8. An apparatus as claimed in any one of claims 1-5 substantially as hereinbefore described with reference to any one of the drawings herein.

9. A method as claimed in either one of claims 6 and 7 substantially as hereinbefore described with or without reference to any one of the drawings herein. a) advancing the wrapped proauct along a fo-rat conveyor b) simultaneously bringing the wrapped product into i 404/850619/1/12