Perfected tubular support for the winding of material in sheets and method for its production

Abstract

A tubular support for winding a material in sheet form includes a corrugated tubular element, wherein the corrugated tubular element is positioned inside at least one outer coating element in sheet form. The internal corrugated tubular element has outer longitudinal portions and inner longitudinal portions connected by annular radial walls which form an inner corrugated wall. The internal corrugated tubular element and the outer coating element in sheet form are connected at the outer longitudinal portions. In a different embodiment, a corrugated tubular element is positioned between two coating elements in sheet form, in outer and internal positions respectively.

Description

FIELD OF THE INVENTION

The present invention relates to a perfected tubular support for the winding of material in sheets, and a method for its production.

BACKGROUND OF THE INVENTION

The term “material in sheets” means an extendable film for packaging, such as film made of LLDPE (liner low density polyethylene), film made of PP (polypropylene), film made of PET (polyester), film made of PA (polyamide), coextruded or laminated film and similar derivatives, produced in in-line and off-line production plants.

In the present state of the art, this material in sheets (produced in continuous by extrusion, calendering, or any other process) is wound onto a tubular support, called core, with a full wall made of cardboard or plastic, prevalently PVC (polyvinylchloride).

These cores however have drawbacks, in particular with respect to the weight/resistance ratio. This is due to the fact that the sheet of plastic film wound onto them is spooled by applying a certain tension to the same, in order to guarantee a good geometry of the bobbins thus obtained; the visco-elastic nature of the materials prevalently forming said continuous sheet ensures that, after the winding, there is a certain elastic return of the sheet, with the result that a crushing force is exerted in a radial direction on the surface of the cores.

This crushing leads to the consequent collapsing of the support or core, with the impossibility of using the bobbin wound thereon, as, in order to apply the same to any winding system, whether it be automatic or manual, the circularity and dimensional constancy of the internal diameter of the core or support must be guaranteed.

In order to sustain this pressure, the present state of the art is compelled to considerably increase the thickness of the cores, consequently increasing their weight and reducing the useful volume available for the sheet wound thereon, as the outer diameter of said bobbins is also restricted for transportation reasons (dimension of the storage pallets).

There are also additional problems directly connected to the type of material of the support or core.

Supports produced in PVC, for example, have the disadvantage of not being compatible with the materials wound (LLDPE), with obvious consequences relating to the recyclability of the whole packaging in the case of its grinding.

Supports made of cardboard, on the other hand, have known limits of use in the case of open environments, due to the fact that they cannot guarantee adequate performances in the case of adverse atmospheric conditions as they absorb humidity and water.

Furthermore, these supports also have problems with respect to their recyclability due to the high content of silicates.

Finally, the types of supports currently present on the market require the application of special ferrules to be inserted at the ends in the case of manual use, to allow them to be held by the operator, to prevent his hands from being “burnt” during the unwinding of the bobbin due to friction with the smooth surface of the cores (in the case of PVC cores) or with the cardboard.

Cores consisting of a tubular element corrugated on its surface or side wall, are also known.

In this case, a greater crushing resistance is obtained thanks to the presence of the radial ribs of the corrugated tube. These radial ribs of the tubular element which forms the core, however, are subject to buckling, by absorbing the mechanical action exerted by the continuous sheet element wound onto it. The radial ribs are therefore plastically deformed and create an angle of less than 90° with respect to the axis of the core or support. This deformation, which is in any case inevitable regardless of the height and thickness of said radial ribs, causes an increase in the total length of the core or support and a reduction in the outer and inner diameters. This leads to the lack of a fundamental characteristics required by the cores, i.e. the constancy and regularity of the inner diameter, together with a significant deformation in an axial direction.

For a better understanding, the effect of a radial force F on a core or support A only consisting of a supporting element with a corrugated internal wall, can be clearly seen in FIG. 1 relating to a section of a core or support of the known type.

It can be observed, in fact, that the original dimensions “a”, “b” and “c”, respectively corresponding to the outer diameter of the tube, the inner diameter of the tube and the axial length, after the application of the crushing force F (uniformly distributed on all the surfaces in contact with the wound sheet) vary by a quantity “Δa”, “Δb” and “Δc”, with the consequences previously described.

EP 0 729 911 discloses a tubular support including a metallic tubular element having triangle-shaped ribs coupled each other in order that continuous outer and inner surfaces are formed.

SUMMARY OF THE INVENTION

A general objective of the present invention is therefore to provide a solution which is both economical, ecocompatible and at the same time easy to produce and with an adequate resistance, which eliminates all the drawbacks indicated above.

A further objective is to provide a supporting element which is capable of substituting the known cores.

In view of the above objectives, according to the present invention, a tubular support has been conceived, for the winding of material in sheets, having the characteristics described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

The structural and functional characteristics of the present invention and its advantages with respect to the known art will appear even more evident from the following description, referring to the enclosed drawings, which, among other things, show two embodiments of a tubular support for the winding of material in sheets produced according to the invention.

In the drawings:

FIG. 1 is a section of half of a portion of a tubular support or core of the known type under the effect of a radial force F;

FIG. 2 is a perspective view of a section of a tubular support for the winding of material in sheets produced according to a first embodiment of the invention;

FIG. 3 is a section of half of a portion of the tubular support of FIG. 2 ;

FIG. 4 is a section of a portion of a tubular support produced according to a second embodiment of the invention;

FIG. 5 is a perspective view illustrating the section of tubular support of FIG. 4.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

With reference to FIGS. 2 and 3, these illustrate a schematic view of a section of a tubular support for the winding of material in sheets produced according to the invention, indicated as a whole with 11. This tubular support 11 forms a core and is composed of an internal tubular element 12 or corrugated tube and at least an outer coating element in sheets 13. The internal tubular element 12 forms a continuous internal corrugated wall, in order to increase the moment of inertia of the support 11 contemporaneously reducing its weight, and consequently the quantity of material used for its production. The outer coating element in sheets 13 forms a continuous smooth outer wall to guarantee the dimensional and geometrical regularity of the product wound in sheets (not shown) and eliminates some of the drawbacks of the known art which will be discussed hereunder.

This new combination solves the technical problems of the known art and, in particular, the corrugated form of the internal part of the support 11 provides resistance against the mechanical action exerted by the elastic return of the material wound thereon (not shown). The deformation and consequent “collapsing” of the support is completely avoided, thanks to the action exerted by the coating element 13, which is subjected to alternating traction and compression axial forces, avoiding repetition of the situation illustrated in FIG. 1.

In particular, FIG. 3 represents a portion in an enlarged longitudinal section of the internal tubular element 12 externally carrying the outer coating element in sheets 13.

The internal tubular element 12 has outer longitudinal portions 14 and internal longitudinal portions 15 which, connected by annular radial walls 16, form an inner corrugated wall.

Two annular radial walls 16, when connected by an outer longitudinal portion 14, define inner annular interspaces 17, whereas two annular radial walls 16, when connected by an inner longitudinal portion 15, define outer annular interspaces 18.

These interspaces 17 and 18 have a substantially rectangular profile according to the axial section, whereas the longitudinal dimension X of the interspace 17 is substantially equal to that of the interspace 18.

For purely illustrative purposes, the whole internal wall of the inner tubular element 12 has a form which is substantially similar to a square wave.

The overall length of the internal tubular element 12, substantially consisting of a plurality of alternating interspaces 17 and 18, can vary in relation to the final use.

Analogously, the thickness of the internal corrugated wall of the core, identified with the dimension Y, can vary significantly depending on the resistance degree to be given to the support 11, object of the invention, which in turn depends on the crushing force exerted by the sheet wound thereon in rolls (not shown).

FIG. 2 illustrates the inner tubular element 12 also complete with the outer coating element in sheets 13 forming the support 11 of the invention.

The outer longitudinal portions 14 of the inner tubular element 12 are closely joined to the outer coating element in sheets 13 by contact present on the longitudinal dimensions X of the interspaces 17.

The presence of this outer coating element in sheets 13 is fundamental for guaranteeing specific characteristics of the support 11, object of the invention, which substantially eliminate the problems deriving from the sole use of the known tubular element with a corrugated wall.

The annular radial ribs 16 subject to buckling due to the crushing force exerted by the material in sheets wound externally (not shown), tend, in fact, to have an angle different from 90° with respect to the axis of the support, as shown in FIG. 1, with a consequent deformation of the dimensions characteristic of the support (“a”, “b” and “c”); the presence of the coating element 13 eliminates this drawback, as, thanks to its resistance to traction to which it is subjected in the dimension X between two longitudinal portions 14 (in which it is closely bound to the inner tubular element 12), it specifically guarantees the perpendicularity of the radial ribs 16 with respect to the axis of the support.

Regardless of the height and thickness of the ribs 16, this determines the constancy of the total length of the support without any reduction in its outer and inner diameters.

In this way, the constancy and regularity of the support is maintained, according to the invention, even if subjected to stress.

It should be repeated that the presence of the outer longitudinal portions 14 closely connected to the outer coating element in sheets 13 by contact, allows the plastic deformation of the radial ribs 16 to be annulled or drastically limited, further increasing their moment of inertia and above all eliminating or maintaining the deformation in an axial direction within absolutely acceptable limits with respect to the state of the art.

In this way, it is possible to maintain a geometrical form of the support 11 after the elastic return of the element in sheets wound thereon (not shown) within tolerances absolutely comparable to what is proposed by other supports of the present state of the art, and consequently accepted by the market.

A second fundamental advantage ensured by the presence of the smooth outer coating element in sheets 13 is represented by the possibility of guaranteeing a flat and constant winding surface of the continuous sheet (not shown), which definitely favours the formation of a final bobbin having a regular geometrical form.

The thickness Z of the outer coating element in sheets 13 can naturally vary significantly in relation to the mechanical action exerted by the sheet wound thereon (not shown), which in turn depends on its very nature and winding procedure, obviously in addition to the quantity wound.

For purely illustrative purposes, as the dimensional measurements of the support 11 as described in the present invention can vary considerably in relation to the application envisaged, it can be said that a support 11 having an outer diameter of about 59-63 mm and an internal diameter of about 50 mm (a typical application is the winding of extendable LLDPE film onto bobbins having a weight of about 2.5 kg for manual use in an industrial area) it would have an overall weight of about 90 g, against the approximate 300 g of a known cardboard support for an analogous application or 480 g of a traditional support made of PVC, the mechanical resistance characteristics naturally being considered as being the same.

A fundamental aspect of the product naturally also relates to the materials of which it is formed, which represent an essential element for its characterization.

In particular, the internal tubular element 12 substantially consists of a mixture, in a widely variable percentage, of glass fibre and polypropylene and/or polyethylene and/or polystyrene and/or polyamide and/or polyester and/or other similar products.

The polypropylene can, in turn, be a block copolymer, a random copolymer, a homopolymer or terpolymer, and can be a virgin or regenerated material, depending on the characteristics to be conferred to the core.

The same polyethylene can be a low-density, medium-density, high-density polyethylene, linear or metallocene, and can analogously be virgin or regenerated.

For applications in which a relatively reduced mechanical crushing resistance is required, the glass fibre can be substituted with talc, in order to further reduce the final cost of the product.

The smooth outer coating element in sheets 13 in turn substantially consists of a polypropylene and/or polyethylene and/or polystyrene and/or polyamide and/or polyester and/or other similar products.

The polypropylene can in turn be a block copolymer, a random copolymer, a homopolymer or terpolymer, and can be a virgin or regenerated material, depending on the characteristics to be conferred to the support 11.

The same polyethylene can be a low-density, medium-density, high-density polyethylene, linear or metallocene, and can analogously be virgin or regenerated.

In short, the continuous production process of the support 11 consists of the extrusion of a smooth tube through a horizontal extrusion head, said tube being thermoformed when it is still in the molten state by means of a so-called corrugator, which gives the desired form to the tubular element 12 through a forming process which also envisages the contemporaneous cooling of the melt.

The cooling of the tubular element 12 is effected contemporaneously with its forming by means of a series of moulds having the desired shape, equipped with a cooling system by cooled water or cold air conduction.

The thermoforming can be effected by:

mechanical action (male mould and female mould which interlock continuously creating the desired form) ;

by pressure (the tube in the molten state is “thrust” by a gush of pressurized air against the walls of the female mould, thus acquiring the desired form);

vacuum (the tubular element in the molten state is sucked towards the walls of the female mould, thus acquiring the desired form).

The above three systems can substantially all be used for the present invention, offering advantages and disadvantages, depending on the cases and sizes to be produced, and can therefore be chosen in the definition phase of the characteristics of the support to be produced.

Following the forming and cooling of the tubular element 12, there is a second extrusion head, called “square”, i.e. having the axis of the outlet die of the melt perpendicular with respect to the axis of the extruder connected to it.

The above head has a passage coaxial to the extrusion die, and therefore perpendicular to the axis of the extruder, in which the corrugated tubular element 12 which has just been formed, passes.

The outer coating element in sheets 13 is then deposited on the tubular element 12 by direct extrusion; the fact that this is poured directly while it is still in the molten state avoids the use of any type of glue or other adhesive for firmly binding the tubular element 12, and in particular the longitudinal portions 14, with the outer coating element in sheets 13.

After this extrusion, a cooling tank can be present, for bringing the outer coating element in sheets 13 to room temperature, and also for disposing of the heat supplied by the outer coating element in sheets 13 to the corrugated tubular element 12 by contact.

The presence or absence of this cooling tank depends on the productivity of the line in terms of kg/h and thicknesses in question.

The last step of the production relates to the pulling and cutting unit of the continuous support thus formed, consisting of a pulling device with belts or wheels and a circular cutting system which allows a surface to be obtained which is absolutely perpendicular to the axis of the support 11 produced.

The production process can also be equipped with various accessories, such as dosing and gravimetric weighing systems to determine the effective flow-rate of the line and produce mixtures of different materials (such as, for example, colored masterbatches) in continuous, surface defect control systems.

FIGS. 4 and 5 illustrate a further possible embodiment of the invention, where the same parts as those illustrated in FIGS. 1-3 are indicated with the same reference numbers increased by 100.

As can be clearly seen from the drawings, in this further embodiment of the invention, the corrugated tubular element 112 is equipped with two coating elements 113 and 113′, outer and inner respectively. The specific characteristics, already described previously, of the support according to the invention, are thus enhanced.

In any case, variations and modifications of details can be also be applied to the embodiments of the support described, all included in the scope of the same invention.

The forms of the structure for producing the support of the invention, as also the materials and assembly procedures, can obviously differ from those shown for purely illustrative and non-limiting purposes in the drawings.

The protection scope of the invention is therefore delimited by the enclosed claims.

Claims

1. A tubular support (11) for the winding of material in sheets comprising a corrugated tubular element (12) characterized in that said corrugated tubular element (12) is positioned inside at least one outer coating element in sheets (13).

2. The tubular support (11) according to claim 1, characterized in that said inner corrugated tubular element (12) has outer longitudinal portions (14) and inner longitudinal portions (15) connected by annular radial walls (16) which form an inner corrugated wall.

3. The tubular support (11) according to claim 2, characterized in that said inner corrugated tubular element (12) and said at least one outer coating element in sheets (13) are connected in correspondence with said outer longitudinal portions (14).

4. The tubular support (11) according to one or more of the previous claims, characterized in that two annular radial walls (16), when connected by an outer longitudinal portion (14), define inner annular interspaces (17), whereas two annular radial walls (16), when connected by an inner longitudinal portion (15), define outer annular interspaces (18).

5. The tubular support (11) according to claim 4, characterized in that said interspaces (17, 18) have a substantially rectangular profile according to the axial section.

6. The tubular support (11) according to claim 4, characterized in that the longitudinal dimension (X) of the interspace (17) is substantially equal to that of the interspace (18).

7. The tubular support (11, 111) according to one or more of the previous claims, characterized in that said inner corrugated tubular element (12, 112) is positioned between two coating elements in sheets (113, 113′), inner and outer respectively.

8. The tubular support (11, 111) according to one or more of the previous claims, characterized in that said inner corrugated tubular element (12, 112) substantially consists of a mixture, in a widely variable percentage, of fibre glass and polypropylene and/or polyethylene and/or polystyrene and/or polyamide and/or polyester and/or similar, wherein said polypropylene can be a block copolymer, a random copolymer, a homopolymer or a terpolymer, and it can be a virgin or regenerated material, according to the desired characteristics to be conferred to said support (11, 111), and wherein said polyethylene can be low-density, medium-density, high-density polyethylene, linear or metallocene, and can also be virgin or regenerated.

9. The tubular support (11, 111) according to one or more of the previous claims, characterized in that said coating element in sheets (13, 113) substantially consists of polypropylene and/or polyethylene and/or polystyrene and/or polyamide and/or polyester and/or similar, wherein said polypropylene can be a block copolymer, a random copolymer, a homopolymer or a terpolymer, and it can be a virgin or regenerated material, according to the desired characteristics to be conferred to said support (11, 111) and wherein said polyethylene can be low-density, medium-density, high-density polyethylene, linear or metallocene, and can also be virgin or regenerated.

10. A method for producing a support (11) according to one or more of claims 1 to 6, characterized in that it comprises, in succession:

extrusion of a smooth pipe by means of a horizontal extrusion head;

thermoforming of the pipe when it is still in the molten state by means of a corrugator, which confers the desired form to the tubular element (12) with contemporaneous cooling;

extrusion, by means of a second extrusion head having the axis of the outlet die perpendicular with respect to the axis of a first extrusion head, of said at least one outer coating element in sheets (13) directly pouring it onto said tubular element (12) when it is still in the molten state;

cooling of said support (11) effected for disposing of the heat of the outer coating element in sheets (13) of the corrugated tubular element (12); and

pulling and cutting the continuous support (11) thus formed, to obtain a surface absolutely perpendicular to the axis of the support (11).

11. The method for producing a support (111) according to one or more of claims 7 to 9, characterized in that it comprises, in succession:

extrusion of a smooth pipe by means of a horizontal extrusion head;

thermoforming of the pipe when it is still in the molten state by means of a corrugator which confers the desired form to the tubular element (112) with contemporaneous cooling;

extrusion by means of a second extrusion head having the axis of the outlet die perpendicular with respect to the axis of a first extrusion head of said outer coating element in sheets (113) directly pouring it onto said tubular element (112) when it is still in the molten state;

extrusion by means of a third extrusion head having the axis of the outlet die coaxial with respect to the axis of said first head of said inner coating element in sheets (113′) in contact with said tubular element (112) when it is still in the molten state;

cooling of said support (111) effected for disposing of the heat of the outer and inner coating element in sheets (113, 113′) of the corrugated tubular element (112); and

pulling and cutting the continuous support (111) thus formed, to obtain a surface absolutely perpendicular to the axis of the support (111).