MANUFACTURING PROCESS FOR GLUE-LESS MULTI-LAYER DECORATED FILM AND THERMOFORMED PRODUCT OBTAINED THEREWITH

Abstract

A manufacturing process for composite film for thermoformed products, including the steps of manufacturing a first plastic substrate film in the amorphous state, by extrusion, causing said first plastic substrate film to undergo a decoration/metal-finish process, causing said first plastic substrate film, to undergo a lamination step, characterized in that before said lamination step, on said first amorphous substrate film a layer of molten plastic material is laid, corning out of an extrusion head, and in that said first plastic film coupled with the layer of molten plastic material, immediately downstream of said extrusion head pass between an entry cylinder and a master cylinder of a lamination unit furthermore comprising at least an exit cylinder, the thickness of said first substrate film being in the range of 150-800μ and the thickness of said molten layer being in the range of 150-1200μ after lamination, said entry cylinder, master cylinder and exit cylinder being heat adjusted on temperatures in the range 20-55° C., with growing temperatures from the entry cylinder, to the master cylinder to the exit cylinder.

Claims

1. A process for manufacturing a composite film for thermoformed product, comprising the steps of: manufacturing a first plastic substrate film in the amorphous state (S.sub.1), by extrusion, causing said first plastic substrate film (S.sub.1) to undergo a decoration/metal-finish process (M), causing said first plastic substrate film (S.sub.1) to undergo a lamination step, characterized in that before said lamination step, on said first amorphous substrate film (S.sub.1) a layer of molten plastic material (S.sub.2) is laid, corning out of an extrusion head (4a), and in said first plastic film (S.sub.1) coupled with the layer of molten plastic material (S.sub.2), immediately downstream of said extrusion head (4a) pass between an entry cylinder (5a) and a master cylinder (5b) of a lamination unit (5) furthermore comprising at least an exit cylinder (5c), the thickness of said first substrate film (S.sub.1) being in the range of 150-800μ and the thickness of said molten layer (S.sub.2) being in the range of 150-1200μ after lamination, said entry cylinder (5a), master cylinder (5b) and exit cylinder (5c) being heat adjusted on temperatures in the range 20-55° C., with growing temperatures from the entry cylinder (5a), to the master cylinder (5b) to the exit cylinder (5c).

2. The process as in claim 1, wherein said cylinders (5) are independently heat adjusted, the entry cylinder (5a) from 20° to 30° C., the master cylinder (5b) from 30° to 42° C. and the exit cylinder (5c) from 45° to 55° C.

3. The process as in claim 1, wherein said extruded molten film layer (S.sub.2) is laid on said first substrate film (S.sub.1) on the side on which the decoration/metal-finish (M) is found.

4. The process as in claim 1, wherein said first plastic film coupled with the layer of molten plastic material arrive tangential in the nip area between said entry cylinder (5a) and said master cylinder (5b).

5. The process as in claim 1, wherein upstream of said extrusion head (4a), said first substrate film (S.sub.1) passes on one or more rubber-coated transfer cylinders and at least one side-extending cylinder (3).

6. The process as in claim 1, wherein said first film (S.sub.1) comes from the top and descends to the bottom before passing in the proximity of the extruder head (4a) which is arranged so as to convey said molten plastic material (S.sub.2) in the lower part of said first film, before the nip area between said entry cylinder (5a) and master cylinder 5b).

7. The process as in claim 1, wherein said layer of molten plastic material (S.sub.2) is laid at a temperature ranging from 230° to 280° C.

8. The process as in claim 1, wherein said first substrate film and said extruded molten plastic material are PET-based.

9. The process as in claim 1, wherein said layer of molten plastic material (S.sub.2) coming out of the extrusion head (4a) is laid having on a width greater than the width of said first substrate film (S.sub.1), forming lateral bands which laterally extend beyond said first substrate film (S.sub.1) by at least 6 cm.

10. The process as in claim 1 further comprising a composite plastic film for the production of thermoformed products, characterized in that it is obtained by a process as in any one of the preceding claims and it consists of a first substrate plastic film in the amorphous state, with an completely decorated/metalized surface whereon a layer of amorphous extruded plastic material is coupled, the thickness of said first substrate film being in the range of 150-800μ and the thickness of said layer of said amorphous extruded plastic material being in the range of 150-1200μ.

11. The process as in claim 1 further comprising a thermoformed product with a decorated/metalized plastic film, characterized in that said film has a composite structure obtained by the stable coupling of a first substrate of amorphous plastic material and a second layer of amorphous plastic material between which a metal-finish/decoration veil is arranged, the coupling between said first amorphous substrate whereon the metal-finish/decoration veil is laid and said second amorphous layer being obtained by lamination with the second amorphous layer in the molten state at a temperature in the range 230-280° C. and the perimeter trimming of the product being obtained by a hot blade apt to weld said first substrate of amorphous plastic material with said second layer of amorphous plastic material internally constraining said metal-finish/decoration veil.

12. The process as in claim 10 further comprising a thin thermoformed product, wherein at least said first substrate is made of PET.

13. The process as in claim 12, wherein a product is manufactured with the plastic film.

14. The process as in claim 13 further comprising a food serving tray, characterized in that it is obtained by thermoforming of the thermoformed product.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0026] Further features and advantages of the invention will in any case be more evident from the following detailed description of a preferred embodiment, given purely as a non-limiting example and illustrated in the attached drawings, wherein

[0027] FIG. 1 represents a schematic elevation side view of a plant for the process according to the invention; and

[0028] FIG. 2 is a schematic cross section view, enlarged in an exaggerated manner, of a film according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] For ease of explanation, in the following the manufacturing process of a composite film and a relative thermoformed tray is described, or other wide-surface support, of metalized plastic material. It is understood that from the process of the invention different decorated products can also be obtained.

[0030] In an initial step, a first film of clear, coloured or colourless plastic material must be produced, with amorphous structure, for example PET, obtained by extrusion. This first step may occur according to methodologies known per se, without practicing the conventional stretching and elongation process which would otherwise produce an orientation of the macro-molecules of the plastic material. The film must be cooled and stored for the time necessary to stabilise the amorphous structure thereof.

[0031] The thickness of the first film of amorphous plastic material is normally in the order of 150-250μ but, in case it is necessary to obtain high final thicknesses, this range of thicknesses may be extended up to 800μ.

[0032] This first film undergoes a decoration process, in particular metallic finishing, on one side thereof. The metallic finishing process is known per se and occurs, for example, through deposition processes of metallic vapours, such as particles of aluminum, copper, alloys of copper, zinc, silver, gold or other, accomplishing an optic density or absorbance suitable to the desired reflectance, lower than 3 and, normally ranging between 1.2 e 2.00.

[0033] Once the metal finish has been stabilised, the film is wound on a bobbin—with the side on which the decoration/metal finish is applied facing inwards—and transferred onto a reel support spindle from which it can be unwound at will.

[0034] According to the embodiment illustrated in FIG. 1, the decorated film is caused to progress towards an extrusion station, accurately avoiding that the decorated/metal finish side be contaminated or scratched during the path. For such purpose, a structure equipped with a tension-controlled support spindle 1, with rubber-coated transfer cylinders 2 and with at least one side-extending cylinder (banana roll or Mink) 3 is provided, upstream of an extrusion unit 4, so as to ensure that the amorphous metal-finish film reaches extruder 4 and a lamination assembly 5 in a perfectly extended condition.

[0035] Compared to the representation of FIG. 1, please notice that the decorated/metal-finish side of the base film faces left, that is, the side on which the extruder die is also arranged.

[0036] According to a variant of this embodiment, upstream (along the film path) of lamination assembly 5, a heat-adjustable preheating tunnel (not shown) is furthermore provided, with infra-red light or other equivalent system, through which the first film is caused to pass. The pre-heating tunnel may be used for heat-adjusting the temperature of the first film before it comes in contact with the extruded material and the lamination cylinders, since that may affect the adhesion conditions of the composite laminate.

[0037] As mentioned above, the plant furthermore provides an extrusion/lamination station which consists of an extrusion head 4a, suitably supplied by an actual extruder 4b, and of a series of cylinders 5—typically at least three cylinders, an entry cylinder 5a, a master cylinder 5b and an exit cylinder 5c—independently heat-adjusted on different temperature ranges, for example from 20 to 30° C. entry cylinder 5a, from 30 to 42° C. master cylinder 5b and from 45 to 55° C. exit cylinder 5c. The heat-adjusted cylinders have the function, in addition to laminating the product at the desired thickness, also of progressively absorb heat, progressively cooling and stabilising the laminated product.

[0038] In the extrusion station a layer of clear (coloured or colourless) or partly dull (light barrier) plastic material, extruded in the molten state, for example PET, is deposited onto the first decorated/metal-finish film, on the side on which the decoration/metal finish is found. The thickness of this second film of amorphous plastic material is in the order of 150-1,200μ, depending on the final desired thickness; the sum of the two ranges of thicknesses of the first and second film allows to reach thicknesses up to 2,000μ, values which are out of reach with the bi-oriented/amorphous technology, since the bi-oriented film reaches at most thicknesses of 50μ.

[0039] In particular, in the extrusion station, the veil of extruded plastic material is deposited on the decorated/metal finish side of the first film at a short distance upstream (in the progress direction of the film on the plant) of the nip between entry cylinder 5a and master cylinder 5b.

[0040] Preferably the first substrate film coupled with the molten plastic material come tangential on the line of closest proximity (nip) between entry cylinder 5a and master cylinder 5b.

[0041] For such purpose, preferably side-extending cylinder 3 is adjustably mounted in position, so as to be able to adjust the arrival angle of the first film at the extrusion head 4a and then at the entry of the gap between entry cylinder 5a and master cylinder 5b. The first film can furthermore pass on one side or on the opposite side of side-extending cylinder 3, so as to change the angle of the path thereof. In the embodiment illustrated in FIG. 1 it can be noticed that stretching cylinder 3 is mounted vertically sliding at the lower end of support arms, which in turn can slide horizontally on the reference frame of the plant: the combination of the two horizontal and vertical movements supplies the desired adjustment displacement on the vertical plane.

[0042] In the embodiment illustrated in FIG. 1, support spindles 1 are arranged advantageously in the upper part of the plant, therefore the first film comes from above and goes downwards before passing in the proximity of the extruder.

[0043] The extruder is located so as to convey the extruded material into the lower part of the first film, before the entry between entry cylinder 5a and master cylinder 5b.

[0044] On the extrusion head, in the extrusion die, adjustable side decklings are provided, which allow to adjust the width of the extrusion lip so as to produce a web of molten material of a width at least substantially equal to the one of the first substrate film, so that through a subsequent lateral trimming a coupled composite film may be obtained of the desired nominal dimensions.

[0045] In particular, it should be noted that an uneven thickness of the molten material occurs in the proximity of the lateral edges, which unevenness is further amplified by the presence of the first film entering the calenders which, with its own thickness, affect the extruding thin area. This portion of the material having irregular thickness would be unuseful.

[0046] Hence, preferably the side decklings of the extruder are arranged so that the second layer of extruded material has a greater width than that of the first film by at least 6-7 cm on each side, preferably between 6 cm and 10 cm depending on the thickness of the first metal-finish film.

[0047] These lateral bands of extruded material, which overhang beyond the lateral edges of the film have a twofold advantage. On the one hand, these lateral bands during the extrusion step absorb the fluctuations of molten material and avoid that irregularities propagate on the useful part of the coupled product; in actual fact it has been detected that the effect is excellent and the process reaches regime conditions in a very short time and with little wasted material. On the other hand, the lateral bands of even material (that is, the second molten material) allow to perform a trimming operation of 5-6 cm of the film externally to the metal-finish part, hence obtaining an easily recyclable waste and coupled material bobbins having perfectly even and flat edges.

[0048] Finally, the lateral bands of the second material laterally constrain the thin layer of metal finish, determining an advantageous contribution to the consolidation of the various layers. The final product hence has a crosswise section as illustrated in FIG. 2, wherein it is clearly perceived how the veil of metal finish M is embedded in the plastic material between the first layer of substrate S.sub.1 and the second layer of molten material S.sub.2. When the material is trimmed, a short portion of lateral band nevertheless remains which performs the same function. In the finished product of course the band of material without metal finish must not be present: for such purpose, after thermoforming, the edge of the product is trimmed again with hot blades, which engrave in the area wherein the coupled film also has the metal finish/decoration layer: in this step, the hot blades create a sort of local suture welding of the plastic material, which locally recreates a perimeter constraint between the two layers of plastic material having sandwiched therebetween the decoration/metal finish layer. The perimeter suture welding joined to the fact that the thermoformed material is consolidated by the same foldings of the finished product, virtually remove any risk of delamination of the coupled film.

[0049] Returning to the process mode, it must be noted that the second layer of extruded plastic material is advantageously laid on the first film at a temperature preferably in the range 230-280° C.

[0050] Thereby, a new layer of plastic material is obtained with amorphous structure on the previous first substrate (first substrate film), also having an amorphous structure.

[0051] This range of temperatures ensures the best coupling affinity between the two layers of amorphous plastic material, preferably PET, so as to avoid the forming of internal tensions or the embedding of air.

[0052] Immediately downstream of the extrusion station, the first decorated/metal-finish substrate film and the extruded layer laid thereon in the molten state are caused to pass into the assembly of heat adjusted laminating cylinders 5 which, in the path indicated in FIG. 1, combine pressures and temperatures until they steadily couple the two layers and calibrate the thickness of the final film thereby obtained.

[0053] With the range of usable thicknesses the perfect coupling of the films in lamination requires precisely a passage through the path designed by the assembly of laminating cylinders 5.

[0054] For such purpose, preferably, the two coupled layers (first substrate film and extruded layer in the molten state), after having passed through the position where the entry cylinder 5a and the master cylinder 5b are tangential, continue the lamination path remaining adherent to the master cylinder for at least 180°, more preferably at least 200°, before passing into the position where master cylinder 5b and exit cylinder 5c are tangential. The coupled composite film remains adherent also to exit cylinder 5c for at least further 90° before definitively coming out of lamination/calendering assembly 5.

[0055] This path, wherein the composite film, after the extrusion passage, runs adherent to lamination cylinders 5, ensures a correct calibration of the final product and, especially, a progressive cooling which determines a perfect adhesion of the two layers, without producing anomalous deformations of the decoration/metal-finish and excessive risks of delamination between the two layers.

[0056] As a result, upon the increase of the thicknesses, the lamination speed must be reduced, to allow correct cooling and a stable adhesion between the two films. Typically, the range of film progress speeds lies between 20 m/min (high thicknesses) and 60 m/min (lower thicknesses).

[0057] At the end of the lamination/calendering step, an even coupled composite film is obtained, consisting of two plastic layers, both with an amorphous structure, between which the decoration/metal-finish veil (visible at least through the clear layer/s) is embedded. The colour of the layers of plastic film determines the type of metal effect obtained, starting from transparent (silver), passing from various hues of grey (from platinum to lead), as far as amber which covers the range of copper to all the varieties of gold (yellow, pink, red). In order to obtain the same colour result from both surfaces it is necessary that the colour effect of the two layers of plastic film is the same regardless of the thickness thereof.

[0058] Decorative variants, alternative to the metal finish are obtained with a first substrate film—always strictly amorphous and better if made of PET—decorated as marble, wood, with advertising or of a different nature images.

[0059] The perfect affinity between the two amorphous layers, joined and intimately consolidated by the high-temperature coupling followed by lamination, ensures a fully neutral behaviour and devoid of tensioning. The shrinkage rates typical of the two layers are fully equivalent, which property makes the composite film devoid of any drawback in the subsequent thermal treatments.

[0060] Unlike the previous technology, which had stretching difficulties due to the “resistance” opposed by the bi-oriented layer, in the present case of the invention the material faithfully follows the details of the moulds.

[0061] Hence, once cooled, the coupled composite film can be used as it is or cut to measure of a blank and undergo a thermoforming process in a mould, producing a desired final product, such as a serving tray. Precisely because the material of the invention is capable of accurately following the mould details, to obtain a quality finished product, it is suitable that the moulds are finished smooth, that is with an even or in any case low roughness value, using then 0.3-0.5-millimetre holes for air extraction.

[0062] By this process it is possible to mould a tray of any perimeter shape and especially with any surface shape, because the coupled semi-finished product of two amorphous layers endures very well even high deformations, without risks of cracks or delaminations. The absence of anomalous flows of the material during thermoforming leaves also fully unimpaired the evenness and uniformity of the metal-finish layer, which is hence of better quality and appearance, even though undergoing high stretching rates or high moulding temperatures. The best results are obtained with forming systems combined with the aid of compressed air in a range from 3 to 5 bar, and the use of sandwich-like heating ovens with differentiated temperatures, hotter on the greater thickness and less hot on the thinner one.

[0063] Better results are obtained thermoforming the composite film in a condition in which the thinner layer is on the part at sight.

[0064] At the end of the thermoforming, in a way known per se, the final product (for example a food serving tray) is laterally trimmed to remove thermoforming trimmings and swarfs by shearing systems or punching systems, preferably with cutting blades heated at about 140-150° C. The final hot-blade trimming perfectly cauterizes/welds the perimeter edge of the product, stabilising it.

[0065] Once cooled, since the shrinkages of the two layers are identical and no tensions remain due to elastic form “memory”, the final product maintains the desired shape—as it is imparted by the thermoforming—and remains perfectly stable in time.

[0066] Due to a construction structure which comprises two layers of amorphous plastic material, with the thin layer of metal finish or decoration arranged in between, the product thermoformed according to the invention perfectly achieves the desired results.

[0067] It is nevertheless understood that the invention must not be considered limited to the particular arrangements illustrated above, which make up exemplifying embodiments, but that different variants are possible, all within the reach of a person skilled in the field, without departing from the scope of protection of the invention, as defined by the following claims.

[0068] For example, although the preferred manufacturing plant provides that the substrate film is unwound from top to bottom, it is not ruled out in line of principle that the substrate film may come also from the bottom to the extruder. For example, the film coming from the bottom could wound on the entry cylinder and the melt material would fall above the film on its decorated/metalized surface.

[0069] This solution evidently implies plant and accessibility discomfort, but it is not ruled out that the coupling with the extruded material may occur in an equally effective manner or that this solution could be advantageous due to other plant requirements. Similarly, the same extruder could be arranged to transfer the molten material according to a vertical plane instead of on a substantially horizontal plane.