WO2005014263A1

WO2005014263A1 - Method and plant for producing a release sheet provided with a predetermined pattern

Info

Publication number: WO2005014263A1
Application number: PCT/EP2003/013836
Authority: WO
Inventors: Franco Caltabiano
Original assignee: Favini S.P.A.
Priority date: 2003-08-05
Filing date: 2003-12-03
Publication date: 2005-02-17
Also published as: AU2003292207A1; TW200505683A; ITMI20031606A1

Abstract

A method and a plant (1) for producing a release sheet (2) provided with a predetermined pattern, particularly but not exclusively intended for the preparation of sheet synthetic products, such as for example synthetic leathers, synthetic fabrics and the like, are described. The method according to the invention comprises the steps of forming a film of polymeric material (4), providing a supporting substrate (5), coupling the film of polymeric material (4) to the supporting substrate (5), and transferring the pattern onto the film of polymeric material (4) so coupled to the supporting substrate (5), wherein the step of transferring the pattern is carried out by means of a transfer roll (8) provided on at least one radially outer portion (13) thereof with a pattern having a shape mating the pattern of the release sheet (2), and wherein the above-mentioned at least one radially outer portion (13) is substantially constituted by a mouldable material substantially incompatible with the polymeric material of the film (4). Advantageously, the features of the method of the invention allow to increase the 15 production flexibility of the release sheet (2) and, with the same, the production flexibility of the desired sheet synthetic product.

Description

METHOD AND PLANT FOR PRODUCING A RELEASE SHEET PROVIDED WITH A PREDETERMINED PATTERN

DESCRIPTION

Field of the invention

In a first aspect thereof, the present invention relates to a method for producing a release sheet provided with a predetermined pattern, particularly but not exclusively intended for manufacturing sheet synthetic products, such as for example synthetic leathers, synthetic fabrics and the like.

The present invention also relates to a plant for producing such release sheet.

Release sheets provided with a predetermined pattern are used in a wide variety of processes for producing synthetic products, such as for example processes for producing synthetic leathers and some types of synthetic fabrics and processes for imprinting a mark or another sign on synthetic materials.

In the present description and in the subsequent claims, the term "pattern" is used to indicate any design, such as a design in high relief, in which case the release sheet is of the so-called embossed type, a design in low relief, a design having an opaque effect and the like.

With reference to leathers and synthetic fabrics, in order to attain high quality levels, these must reproduce as faithfully as possible the look of the natural leathers, such as for example kid, calf, lamb and buffalo skins, and, respectively, the texture of natural fabrics, such as cotton, linen, hemp, including special textures such as that of jeans fabric.

Such synthetic fabrics are prepared by applying a suitable material, for example adapted to constitute the leather or the synthetic fabric which has to be produced, to a multi- layered release sheet typically comprising a polymeric film and a supporting substrate, generally of the paper type, in which the polymeric film has a pattern mating the pattern which has to be obtained on the synthetic final product. Thus, if the release sheet is of the embossed type, i.e. if it is provided with a desired pattern in high relief, the synthetic final product will have a pattern in low relief and vice versa. Thus, for example, in the case of synthetic leather, a pattern (in low relief) mating that provided on the embossed release sheet (in high relief) is obtained, so as to reproduce as faithfully as possible the look of natural leather, by coating a material adapted to constitute the synthetic leather on the embossed release sheet after interposition of an adhesive layer.

At the end of the process of coating the synthetic leather, the embossed release sheet is released from the leather so engraved and can be reused, typically tens of times, in further processes for preparing synthetic leathers.

Prior art

In the production of embossed release sheets intended to be used in the manufacture of sheet synthetic products, methods are known -as for example disclosed by British patent GB 688 637 - comprising the steps of forming a film of polymeric material, providing a supporting substrate, typically made of paper, coupling, typically by rolling, the film of polymeric material to the supporting substrate, and embossing the film of polymeric material so coupled to the supporting substrate, wherein the embossing step is carried out by means of a roll for transferring the embossing pattern, known in the art with the term of embossing roll, made of steel suitably engraved according to the desired design.

Steel has proven to be a material suitable for the purpose since steel allows to carry out both the embossing process and the subsequent release of the embossed polymeric film from the embossing roll. Although such method is substantially suitable for the purpose, in order to produce an embossing roll made of steel suitable for reproducing the desired embossing pattern on the release sheet, however, it is necessary to engrave the roll by means of mechanical engraving techniques which are very laborious, require a long actuation time and unacceptably increase the production costs of the embossed release sheet and, with these, the production costs of the synthetic leather or synthetic fabrics prepared by means of such type of sheet. Furthermore, at the end of the process of engraving the embossing roll of steel, normally carried out by lathe machining by means of an engraving tool moved along annular zones of the surface of the embossing roll according to a predetermined sequence, it is necessary to carry out a further chroming protective treatment, with a consequent further increase in the production time and costs of the embossing roll of steel.

In view of the fact that in order to obtain a production of embossed release sheets which is economically advantageous it is necessary to provide a set of batches of embossing rolls, and that the production of the synthetic leathers and synthetic fabrics is subject to changeable market demands, which require periodic and frequent variations in the embossing pattern, it is clear that it is difficult to reconcile the need of continuously providing new batches of embossing rolls with the laboriousness, the time consumption and the production costs of the embossing rolls of steel.

In other words, although the above-mentioned prior art methods for producing an embossed release sheet are substantially suitable for the purpose, firstly they have the disadvantage of being able to satisfy with extreme difficulty and at unacceptably high costs the above-mentioned need of replacing periodically and frequently the embossing rolls, which need is particularly felt in the field of the preparation of synthetic leathers and synthetic fabrics.

Secondly, the embossing rolls of steel easily get dirty and are particularly subject to impressions or smudges, which may irreversibly alter the pattern displayed on the synthetic leather or on the synthetic fabric. Such an alteration may be particularly evident and, as such, may cause undesired waste products in the case in which a design having an opaque effect, instead of a pattern in high relief or in low relief, has to be imparted to all or to a portion of the synthetic product.

Summary of the invention

The technical problem underlying the present invention is therefore that of providing a method and plant for producing a release sheet provided with a predetermined pattern which result in an increased productive flexibility so as to satisfy, in an acceptable time and with acceptable costs, the periodic and frequent need - dictated by the changeable market demands - of replacing the roll (or rolls in plants with greater productive capacity) for transferring the pattern, while allowing to obtain a release sheet provided with the desired pattern having high quality characteristics.

In accordance with a first aspect of the invention, the above-mentioned technical problem is solved by a method for producing a release sheet provided with a predetermined pattern, comprising the steps of:

a) forming a film of polymeric material;

b) providing a supporting substrate;

c) coupling said film of polymeric material to said supporting substrate; and d) transferring said pattern onto said film of polymeric material so coupled to said supporting substrate;

wherein said transfer step is carried out by means of a transfer roll provided on at least one radially outer portion thereof with a pattern having a shape mating the pattern of the release sheet, said at least one radially outer portion being substantially constituted by a mouldable material substantially incompatible with the polymeric material of the film.

In the present description and in the subsequent claims, the expression "transferring a predetermined pattern onto the film of polymeric material" is used to indicate any action of forming, on the film of polymeric material, a pattern having a shape mating the pattern formed on the transfer roll and replicating in negative the pattern to be obtained on the synthetic product, such as for example a pattern comprising at least one design in high relief, at least one design in low relief or at least one opaque zone.

In the present description and > in the subsequent claims, moreover, the expression "mouldable material" is used to indicate any material which can be shaped by conventional shaping processes, for example by moulding or casting, so as to obtain a predetermined pattern - for example comprising a design in high or low relief - on the outer surface thereof.

Thanks to the provision of a transfer roll having such features, it is advantageously possible to increase the production flexibility of the release sheet provided with a_, predetermined pattern and, with the same, the production flexibility of synthetic products, such as for example synthetic leathers or fabrics, and thus to meet the changeable market demands promptly and without affecting the production costs in an excessive manner. The use of a mouldable material, in fact, allows to reduce the production time and costs of the transfer roll with respect to the time and costs required for the production of the prior art transfer rolls made of steel.

In a preferred embodiment of the invention, the transfer roll comprises a support roll onto the outer part of which a suitably shaped cast, for example annular, made of a mouldable material substantially incompatible with the polymeric material of the film and provided with a predetermined pattern is applied.

This cast may be obtained in different ways which can be easily selected by a man skilled in the art depending on the specific requirements. Thus, for example, in order to reproduce the veins and the ridges forming the design of a natural leather or a natural fabric, the cast is preferably obtained in two steps.

In a first step, a layer of a first mouldable material is coated onto a ^'predetermined portion of these natural materials so as to obtain - after the setting of the mouldable , material - an intermediate cast carrying the negative design of the leather or of the fabric.

In a second step, a layer of a second mouldable material incompatible with the polymeric material of the film, second material which may be the same as or different from the first material constituting the intermediate cast, is coated onto the intermediate cast, so as to obtain - after the setting of the second mouldable material - a second cast carrying the same design as the leather or the fabric, second cast which shall be fixed to the outer part of the support roll.

In order to reproduce the design formed on an already formed release sheet, on the other hand, the cast is preferably obtained in a single step by coating a layer of mouldable material substantially incompatible with the polymeric material of the film on the release sheet, so as to obtain - after the setting of the mouldable material - a cast carrying the same design as the synthetic product to be produced, cast which shall be fixed to the outer part of the support roll.

In accordance with a preferred embodiment of the method of the invention, the film of polymeric material is formed by extrusion.

In accordance with the invention, the film of polymeric material may be constituted by any material adapted to be easily worked superficially and having adequate characteristics of dimensional stability so as to form the desired pattern thereon and to maintain such pattern substantially unaltered through time. For the purposes of the invention, the supporting substrate is preferably selected from the group comprising polyolefin, polyurethane, epoxy and polyester polymeric materials.

Preferably, such polyolefin polymeric materials are selected from the group comprising: polyethylene, polypropylene, polymethylpentadiene. Preferably, the film of polymeric material coupled to the supporting substrate has a thickness comprised between about 10 and about 80 μm. By selecting a thickness of the film of polymeric material within such a preferred range of values, it is advantageously possible to transfer a pattern, for example embossed, of an adequate depth (typically between about 10 and about 80 μm, i.e. substantially equal to the thickness of the film of polymeric material) onto a leather or onto a synthetic fabric. In such a way, it is possible to prepare synthetic leathers faithfully reproducing the wrinkles and the engravings of natural leather or synthetic fabrics faithfully reproducing the texture of natural fabrics.

Within the above-mentioned range of values, the thickness of the film of polymeric material may be preferably and conveniently selected as a function of the type of pattern to be reproduced on the synthetic final product.

Thus, in a first preferred embodiment of the invention used in the formation of low depth patterns with a so-called smooth look of the synthetic product, the thickness of the film of polymeric material is preferably comprised between about 10 and about 20 μm.

In a second preferred embodiment of the invention used in the formation of so-called medium depth patterns, the thickness of the film of polymeric material is preferably comprised between about 20 and about 30 μm.

In a third preferred embodiment of the invention used in the formation of so-called medium-high and high depth patterns, the thickness of the film of polymeric material is preferably comprised between about 30 and about 80 μm.

In accordance with the invention, the supporting substrate may be constituted by any sheet material to which it is possible to fix the film of polymeric material in a substantially irreversible manner.

For the purposes of the invention, the supporting substrate is preferably selected from the group comprising: paper, card, cardboard, fabric, plastic materials and combinations thereof.

In accordance with a particularly preferred embodiment of the method of the invention, the supporting substrate is of the paper-based type, such as for example paper, card and cardboard and preferably has a basic weight comprised between about 80 g/m² and about 175 g/m .

Within the above-mentioned range of values, the basic weight of the supporting substrate may be preferably and conveniently selected as a function of the type of pattern to be reproduced on the synthetic final product.

Thus, in a first preferred embodiment of the invention used in the formation of low depth patterns with a so-called smooth look of the synthetic product (with a thickness of the film of polymeric material preferably comprised between about 10 and about 20 μm), the basic weight of the supporting substrate is comprised between about 80 g/m and about 100 g/m .

In a second preferred embodiment of the invention used in the formation of so-called medium depth patterns (with a thickness of the film of polymeric material preferably comprised between about 20 and about 30 μm), the basic weight of the supporting substrate is comprised between about 100 g/m and about 150 g/m².

In a third preferred embodiment of the invention used in the formation of so-called medium-high and high depth patterns (with a thickness of the film of polymeric material preferably comprised between about 30 and about 80 μm), the basic weight of the 9 9 supporting substrate is comprised between about 150 g/m and about 175 g/m .

Alternatively, the supporting substrate may comprise a fabric, a synthetic material, such as for example a film of plastic material, a layer of the mixed type constituted by combinations of such materials, or any supporting material of another nature suitable for the purpose.

Preferably, the above-mentioned steps a) of forming the film of polymeric material and b) of providing the supporting substrate are carried out in a substantially simultaneous manner. In such a way, any undesired idle time between the above-mentioned steps of the method of the invention can be avoided.

Preferably, the above-mentioned steps c) of coupling the film of polymeric material to the supporting substrate and d) of transferring the pattern onto the film of polymeric material coupled to the supporting substrate are carried out in a substantially simultaneous manner.

Advantageously and thanks to the fact that the film of polymeric material is provided with the predetermined pattern as the film is being coupled to the supporting substrate, in such a way:

i) the production speed of a release sheet provided with a predetermined pattern, for example an embossed sheet, is increased, and ii) the number of manipulations to which the semi-finished products constituting the release sheet must be subjected is reduced, with a consequent advantageous preservation of the pattern without any sort of alterations.

In accordance with a preferred embodiment of the method of the invention, the above- mentioned steps a) of forming the film of polymeric material, c) of coupling the film of polymeric material to the supporting substrate and d) of transferring the pattern onto the film of polymeric material coupled to the supporting substrate are carried out in a substantially continuous manner.

In the following description and in the subsequent claims, the expression "in a substantially continuous manner" is used to indicate the absence of intermediate storages of the semi-finished products used in the production of the release sheet provided with a predetermined pattern between the various manufacturing steps.

As an illustrative example, the expression "forming a film of polymeric material and coupling the polymeric film to the supporting substrate in a substantially continuous manner" is used to indicate the fact that the coupling of the film of polymeric material is carried out on the film just formed, for example by extrusion.

In the same way, the expression "coupling the film of polymeric material to the supporting substrate and transferring the pattern onto the film of polymeric material coupled to the supporting substrate" is used to indicate the fact that the transfer of the pattern onto the film of polymeric material is carried out on the film just coupled to the supporting substrate, i.e., as stated above, just formed by extrusion and, as such, still in molten state, so as to faithfully reproduce on the film of polymeric material a pattern having a shape mating the pattern provided on the transfer roll.

Preferably, the transfer roll is subjected to a predetermined rotation speed, preferably comprised between about 20 m min and about 150 m/min.

By maintaining the rotation speed of the transfer roll within such a preferred range of values, it is advantageously possible to transfer the desired pattern onto the film of polymeric material in a precise manner and at a suitable production speed.

Within the above-mentioned range of values, the rotation speed of the transfer roll may be preferably and conveniently selected as a function of the thickness of the film of polymeric material, which is in turn dependent upon the type of pattern to be reproduced on the synthetic final product, thickness which determines the maximum rotation speed compatible with a correct manufacture of the release sheet.

Thus, in a first preferred embodiment of the invention used in the formation of low depth patterns with a so-called smooth look of the synthetic product (with a thickness of the film of polymeric material preferably comprised between about 10 and about 20 μm), the rotation speed of the transfer roll is comprised between about 100 m/min and about 150 m/min.

In a second preferred embodiment of the invention used in the formation of so-called medium depth patterns (with a thickness of the film of polymeric material preferably comprised between about 20 and about 30 μm), the rotation speed of the transfer roll is comprised between about 50 m/min and about 100 m/min.

In a third preferred embodiment of the invention used in the formation of so-called medium-high and high depth patterns (with a thickness of the film of polymeric material preferably comprised between about 30 and about 80 μm), the rotation speed of the transfer roll is comprised between about 20 m/min and about 50 m/min.

Preferably, the above-mentioned step c) of coupling the film of polymeric material to the supporting substrate is carried out by rolling by means of a pressure roll cooperating with the above-mentioned transfer roll.

Preferably, the pressure roll has a longitudinal axis extending substantially parallel to the longitudinal axis of the transfer roll so as to be able to exert a predetermined pressure on the transfer roll along a line of contact substantially parallel to the longitudinal axes of the two rolls.

Thanks to such type of coupling, it is advantageously possible to carry out a coupling of the film of polymeric material to the supporting substrate in a continuous manner, and consequently to produce a release sheet of indefinite length.

In accordance with a preferred embodiment of the method of the invention, the step c) of coupling the film of polymeric material to the supporting substrate is carried out by pressing the pressure roll against the transfer roll at a pressure - measured at the line of contact between the pressure roll and the transfer roll - comprised between about 50 kg/linear cm and about 400 kg/linear cm.

In such way, it is advantageously possible to obtain an adequate definition of the pattern and a thickness of polymeric film comprised within the above-mentioned preferred range of values.

The pressure exerted by the pressure roll against the transfer roll may be preferably and conveniently selected within the above-mentioned range of preferred values as a function of the type of pattern to be reproduced on the synthetic final product.

Thus, in a first preferred embodiment of the invention used in the formation of low depth patterns with a so-called smooth look of the synthetic product (with a thickness of the film of polymeric material preferably comprised between about 10 and about 20 μm), the pressure exerted by the pressure roll against the transfer roll is comprised between about 50 kg/linear cm and about 100 kg/linear cm.

In a second preferred embodiment of the invention used in the formation of so-called medium depth patterns (with a thickness of the film of polymeric material preferably comprised between about 20 and about 30 μm), the pressure exerted by the pressure roll against the transfer roll is comprised between about 100 kg/linear cm and about 200 kg/linear cm.

In a third preferred embodiment of the invention used in the formation of so-called medium-high and high depth patterns (with a thickness of the film of polymeric material preferably comprised between about 30 and about 80 μm), the pressure exerted by the pressure roll against the transfer roll is comprised between about 200 kg/linear cm and about 400 kg/linear cm.

Preferably, the mouldable material substantially incompatible with the polymeric material is selected from the group comprising mouldable elastomeric materials having mechanical and chemical-physical characteristics suitable for the purpose.

Among the mouldable elastomeric materials, silicone rubbers are particularly preferred for the purposes of the invention.

Among these, silicone rubbers with two cold cross-linkable components having a Shore A hardness at 23°C measured in accordance with standard DIN 53505 comprised between about 10 and about 70 have a particularly advantageous use.

Still more preferably, the above-mentioned silicone rubbers have a compression set at 23 °C measured in accordance with standard DIN 53517 comprised between about 5 and about 10%. Silicone rubbers of preferred use are commercially available with the names of KE 1600® (Wonpoong Corporation, Seoul, South Korea), SILASTIC® (Dow Corning Corporation, Midland, MI, U.S.A.) or ELASTOSIL® (Wacker-Chemie GmbH, Munich, Germany).

Advantageously, the use of one of such preferred materials for producing the transfer roll allows to improve the definition of the pattern on the release sheet and to enrich the contrast effects conferred to the synthetic leather or to the fabric by the release sheet, in particular where contrast effects between glossy zones and opaque zones have to be achieved.

Preferably, the method of the invention further comprises a step of cooling the polymeric film provided with the desired pattern.

Thanks to the provision of a cooling step, it is advantageously possible to achieve an increased production speed of the release sheet provided with a predetermined pattern.

Still more preferably, the cooling step is carried out in a manner substantially simultaneous with the above-mentioned step of transferring the pattern onto the film of polymeric material.

Thanks to the provision of a cooling step carried out in a manner substantially simultaneous with the step of fransferring the pattern onto the film of polymeric material, the impression of the pattern (independently of the type thereof, i.e. independently of whether the pattern is in high relief, low relief or has an opaque effect) is fixed as the pattern is being transferred onto the film of polymeric material, with a consequent advantageous achievement of a well-defined and precise pattern, as faithful as possible to the desired pattern. In such a way, it is advantageously possible to produce a release sheet provided with a predetermined design having high quality and long-lasting characteristics, which allow to reuse the sheet a large number of times, typically in the order of tens of times.

Preferably, the cooling step is carried out by cooling the transfer roll and/or the pressure roll, said rolls in this case being in heat exchange relationship with suitable cooling means.

In the case in which the cooling step is carried out by means of the transfer roll, it is advantageously possible to carry out the step of transferring the pattern onto the film of polymeric material and the step of cooling the latter by means of a single device, i.e. the transfer roll itself, thus reducing the production time.

In the case in which the cooling step is carried out by means of the transfer roll and the pressure roll, the effectiveness of the cooling can be further increased. Thanks to this, the rotation speed of the transfer roll can be advantageously increased, within the range of values given above with reference to the depth of the pattern to be formed in the release sheet, with an advantageous corresponding increase in the production speed of the latter.

Alternatively, the cooling step may be carried out by means of a coolmg roll arranged parallel to and in heat exchange relationship with the transfer roll in an opposite position with respect to the pressure roll.

In accordance with a further preferred embodiment of the method of the invention, the cooling step may be carried out by means of the above-mentioned cooling roll and a suitable transfer roll and/or a pressure roll which, in this case, are in heat exchange relationship with suitable cooling means.

In this latter case, the cooling step is advantageously carried out still more effectively, which allows to use a still higher rotation speed of the fransfer roll, again within the ranges of values given above.

Preferably, the cooling roll is made of a suitable material adapted to ensure an optimal heat exchange, such as for example steel or any other metallic material suitable for the purpose.

In the preferred embodiments described above, the transfer roll and/or the pressure roll and/or the cooling roll may be provided with respective circuits for the circulation of a cooling fluid maintained at a predetermined temperature lower than the melting temperature of the polymeric material.

When the film of polymeric material is produced by extrusion, as the film comes out from the extrusion head it may have a temperature in the order of some hundreds of degrees centigrade, whereby the temperature of the cooling fluid is preferably selected within a range of values ranging from about 2° to about 25°C and, still more preferably, in a range of values ranging from about 10° to about 20°C.

In order to increase the cooling speed of the film of polymeric material and to attain high rotation speeds of the rolls, the cooling fluid is, on the other hand, preferably maintained at a temperature comprised between about 2° and about 5°C.

Preferably and for clear reasons of availability and cost, the cooling fluid is water.

In accordance with a preferred embodiment thereof, the method of the invention further comprises the step of applying a material adapted to counterwarp the supporting substrate onto the above-mentioned supporting substrate so coupled to the polymeric film. For illustrative purposes, such material may advantageously be applied by a conventional rotogravure wetting process.

In such way, the physical properties of the release sheet provided with a predetermined pattern are advantageously preserved from possible undesired deformations, which allows to obtain a release sheet provided with a predetermined pattern reusable for an increased number of times in the preparation of synthetic leathers, synthetic fabrics or other synthetic products.

In order to carry out the above-mentioned method, the present invention provides a plant for producing a release sheet provided with a predetermined pattern, comprising:

a) an extrusion apparatus for forming a film of polymeric material;

b) means for feeding a supporting substrate;

c) means for coupling said film of polymeric material to said supporting substrate; and

d) a roll for transferring said pattern onto said film of polymeric material so coupled to said supporting subsfrate;

wherein said transfer roll is provided on at least one radially outer portion thereof with a pattern having a shape mating the pattern of the release sheet, said at least one radially outer portion being substantially constituted by a mouldable material substantially incompatible with the polymeric material of the film.

Preferably, the coupling means comprises a pressure roll cooperating with the transfer roll for coupling the film of polymeric material to the supporting subsfrate by rolling, said pressure roll having a longitudinal axis extending substantially parallel to the longitudinal axis of the transfer roll.

In accordance with a preferred embodiment of the plant of the invention, the pressure roll has a longitudinal axis extending substantially parallel to the longitudinal axis of the transfer roll and is able to exert a predetermined pressure on said transfer roll, preferably a pressure comprised between about 50 kg/linear cm and about 400 kg/linear cm.

Preferably, the transfer roll is adapted to rotate at a rotation speed comprised between about 20 m/min and about 150 m min.

In accordance with a preferred embodiment of the plant of the invention, the mouldable material substantial incompatible with said polymeric material is selected from the group comprising the elastomeric materials indicated above.

Preferably, the plant of the invention further comprises means for cooling the film of polymeric material.

In accordance with a preferred embodiment of the plant of the invention, the above- mentioned cooling means is arranged in the fransfer roll and/or in the pressure roll.

Alternatively, the above-mentioned cooling means is arranged in a cooling roll arranged parallel to and in heat exchange relationship with the fransfer roll in an opposite position with respect to the pressure roll.

In accordance with a further preferred embodiment of the plant of the invention, the above-mentioned cooling means is arranged both in the transfer roll and in the pressure roll and in a suitable cooling roll as defined above.

Preferably, the optional cooling roll is made of a suitable material adapted to ensure an optimal heat exchange, such as for example steel or any other metallic material suitable for the purpose.

In accordance with a preferred embodiment, the transfer roll and/or the pressure roll and the optional cooling roll are provided with respective circuits for the circulation of a suitable cooling fluid, such as for example water, maintained at a predetermined temperature lower than the melting temperature of the polymeric material of the film.

Preferably, the plant of the invention further comprises a gravure roll arranged downstream of the coupling means and intended to apply a material adapted to counterwarp the supporting substrate onto the supporting substrate coupled to the film of polymeric material. In the present description and in the subsequent claims, the expression "upstream" and "downstream" are used to indicate those parts of the plant of the invention which are firstly and, respectively, lastly crossed by the semi-finished products (i.e. the supporting substrate and the film of polymeric material) used to produce the release sheet provided with a predetermined pattern.

Brief description of the drawings

Additional features and advantages of the invention will become more readily apparent from the description of some embodiments of a method for producing a release sheet provided with a predetermined pattern according to the invention, made with reference to the attached drawing figure in which, for illustrative and non limiting purposes, a plant for carrying out said method is shown.

In the drawing, figure 1 schematically illustrates, in a perspective view, a plant for producing a release sheet provided with a predetermined pattern in accordance with the present invention.

Detailed description of the preferred embodiments

With reference to the diagram of figure 1, a plant according to the invention for producing a release sheet 2 provided with a predetermined pattern is generally indicated at 1. In the illustrated example, the release sheet 2 is in particular of the embossed type, i.e. provided with a design in high relief, and is intended to prepare synthetic leathers, synthetic fabrics and the like.

The plant 1 comprises an extrusion apparatus, of which only the head 3 is shown for the sake of simplicity, for forming a film 4 of polymeric material. More particularly, the film 4 of polymeric material is formed by extrusion along a predetermined extrusion direction, in the figure indicated with an arrow E. Purely for illustrative purposes, the polymeric material may consist of a polyolefin polymer, such as for example polypropylene (PP). Conveniently, the extrusion head 3 is fed with a mixture of polypropylene by means of an extrusion screw, conventional per se and not shown, and is shaped in such a way as to extrude a film of polypropylene having a predetermined width.

The plant 1 of the invention further comprises feed means, conventional per se and not shown, intended to feed a supporting subsfrate 5, such as for example a sheet of paper- based material, along a predetermined conveying direction.

In the illustrated preferred embodiment, the conveying direction of the supporting substrate 5, indicated with an arrow A in figure 1, is incident with the above-mentioned extrusion direction E, at a working position downstream of the extrusion head 3.

More particularly, in accordance with the preferred embodiment of the plant 1 of the invention shown in figure 1, a reel 11 is intended to feed the supporting substrate 5 in a first direction, indicated with an arrow F in the figure and, thanks to the provision of a deviating rod 6, in the above-mentioned second conveying direction A incident with the extrusion direction E of the film 4 of polymeric material, so as to allow, as better described hereafter, the coupling between the fihn of polymeric material 4 and the supporting substrate 5.

In accordance with the invention, the plant 1 further comprises means for coupling the film 4 to the supporting substrate 5, including for example a pressure roll 7 and a transfer roll 8 provided with a pattern having a shape mating the pattern to be transferred onto the release sheet 2, said rolls 7 and 8 cooperating with each other.

The pressure roll 7, which is preferably motorized in a way conventional per se, has a longitudinal axis extending parallel to the longitudinal axis of the transfer roll 8, also preferably motorized in a way conventional ^er se. Furthermore, the pressure roll 7 is able to exert a predetermined pressure on the fransfer roll 8, preferably a pressure comprised between about 50 kg/linear cm and about 400 kg/linear cm, so as to ensure the achievement of a suitable definition of the embossing pattern and a thickness of the film 4 comprised within a preferred range of values comprised between about 10 and about 80 μm.

In accordance with the illustrated preferred embodiment of the plant 1 of the invention, therefore, the reel 11 and the extrusion head 3 are intended to feed the supporting substrate 5 and, respectively, the film of polypropylene 4 towards the gap formed between the pressure roll 7 and the transfer roll 8.

In accordance with the invention, the transfer roll 8 is provided with a pattern having a shape mating the pattern of the release sheet 2 to be produced on at least one radially outer portion 13 substantially constituted by a mouldable material substantially incompatible with the polymeric material constituting the film 4. In the preferred embodiment illustrated in figure 1, the above-mentioned radially outer portion 13 of the transfer roll 8 substantially coincides with the entire radially outer surface of the transfer roll 8.

However, for some applications, such as for example in the manufacture of some types of fabrics to which particular effects have to be conferred exclusively in predetermined portions of the fabric, the radially outer portion 13 could occupy just a part of the radially outer surface of the transfer roll 8, for example just an annular portion or a plurality of annular portions longitudinally spaced apart from each other or one or more portions circumferentially spaced apart along the radially outer surface of the transfer roll 8.

In the preferred embodiment illusfrated in figure 1, the above-mentioned radially outer portion 13 of the transfer roll 8 is provided with a pattern in low relief, i.e. engraved, so as to obtain a so-called embossed film 4 of polymeric material and thus to allow the production of synthetic products, such as for example leathers and fabrics, provided with designs in low relief. However, in other applications, the above-mentioned at least one radially outer portion 13 of the transfer roll 8 could be provided with a pattern in high-relief, so as to correspondingly engrave the film 4 of polymeric material and to allow the production of synthetic products, such as for example leathers and fabrics, provided with designs in high relief.

In the preferred embodiment illustrated in figure 1, the transfer roll 8 comprises a radially inner support roll 12, which in the example is shown hollow, of limited size (for illustrative purposes having a diameter equal to about 200-250 mm) and of low cost, made for example of steel and coated with the above-mentioned radially outer portions 13 substantially constituted by a mouldable material substantially incompatible with the polymeric material of the film 4.

Such transfer roll 8 can therefore advantageously be made in a rapid and easy manner, for example by providing a cast of mouldable material substantially incompatible with the polymeric material of the film 4 on the support roll 12. The cast may be derived from a natural leather, from a natural fabric or from a pre-existing release sheet by methods known per se, for example by the methods illustrated above, so as to obtain a pattern which faithfully reproduces the design, for example the veins and the ridges, of the natural leather or of the natural fabric to be imitated.

Such cast made of the mouldable material is then used to coat the radially outer portion 13 of the support roll 12.

For such a purpose, the coating process of the support roll 12 can be carried out by using a cast of mouldable material substantially incompatible with the polymeric material of the film 4 having an area substantially equal to the area of the above-mentioned radially outer portion 13 of the support roll 12 or by using a plurality of casts of smaller area, which are placed side by side and joined to coat the radially outer portion 13 of the support roll 12.

The mouldable material constituting the radially outer portion 13 of the transfer roll 8 is preferably a silicone rubber, for example one of the commercially available silicone rubbers mentioned above, which is substantially incompatible with polypropylene and at the same time allows a simplified, rapid and low-cost production of the transfer roll 8, which production is capable of responding promptly to the changeable demands of the market of synthetic leather.

The transfer roll 8 is adapted to rotate at a rotation speed comprised between about 20 m/min and about 150 m/min, which is advantageously selected, as illusfrated previously, on the basis of the cooling speed of the polypropylene film 4.

In order to increase the production speed of the release sheet 2 provided with a predetermined pattern, the plant 1 further comprises means 9 for cooling the film 4. In accordance with the preferred embodiment illustrated in figure 1 and in order to increase the effectiveness of the cooling action, the cooling means 9 may be arranged in the transfer roll 8, in the pressure roll 7 and in a cooling roll 10 suitably arranged to carry out a further cooling action.

The cooling roll 10, made for example of steel, is placed parallel to and in heat exchange relationship with the fransfer roll 8 in an opposite position with respect to the pressure roll 7. Preferably, the cooling roll 10 is idle and is rotated by the transfer roll 8 in a rotation direction opposite to the latter.

In accordance with the preferred embodiment of the plant 1 illustrated in figure 1, therefore, the transfer roll 8 is positioned downstream of the extrusion head 3 between the pressure roll 7 and the cooling roll 10 which are placed at opposite sides with respect to the transfer roll 8.

In the preferred embodiment illusfrated in the figure, the cooling means 9 arranged in the pressure roll 7 arid in the cooling roll 10 comprises respective circuits, for example comprising a plurality of tubes 14 for the circulation of a suitable cooling fluid maintained at a predetermined temperature below the melting temperature of polypropylene.

Preferably, the tubes 14 have longitudinal axes parallel to the longitudinal axis of the respective roll 7, 10 in which the tubes are arranged.

In accordance with the illusfrated preferred embodiment, the cooling means 9 arranged in the transfer roll 8 comprises the above-mentioned hollow support roll 12; in which a cooling fluid can flow.

The plant 1 may further comprise, downstream of the pressure roll 7, a system, conventional per se and not shown, for cutting the edges or selvedges of the release sheet 2, which is subsequently collected in reels of predetermined size.

With reference to the plant described above, a preferred embodiment of the method according to the invention comprises the following steps.

In a first step of the method, the film 4 of polypropylene is formed. In particular, the film 4 is extruded by the extrusion head 3, preferably along the extrusion direction E. In a second step of the method, preferably carried out in a manner substantially simultaneous with the above-mentioned first step, the supporting subsfrate 5 fed by the reel 11 is provided. In particular, the supporting subsfrate 5 is firstly fed in the direction F and then, by means of the deviator rod 6, in the direction A incident with the extrusion direction E.

In a subsequent step, the film 4, once out of the extrusion head 3, is coupled to the supporting subsfrate 5. In this embodiment, the step of coupling the film 4 of polypropylene to the supporting subsfrate 5 is carried out by rolling by means of the pressure roll 7 and the fransfer roll 8, by exerting, in particular by means of the pressure roll 7, a predetermined pressure against the transfer roll 8. Preferably, a pressure of between about 50 kg/linear cm and about 400 kg/linear cm is exerted, so as to confer the film 4 a thickness preferably comprised between about 10 and about 80 μm.

At this point, in accordance with a preferred embodiment of the method of the invention, the predetermined pattern is simultaneously transferred onto the film 4 being coupled to the supporting substrate 5 by means of the fransfer roll 8 provided, on the radially outer portion 13 made of silicone rubber, with a pattern having a shape mating the pattern to be formed on the release sheet 2. In the illusfrated embodiment, more particularly, such step of forming the film 4 by extrusion, such step of coupling the film 4 being formed and such step of transferring the pattern onto the film being coupled to the supporting substrate 5 are carried out in a substantially continuous manner.

The pressure roll 7 and the transfer roll 8 are preferably subjected to a rotation speed comprised between about 20 m min and about 150 m/min.

In a further step of this preferred embodiment of the method of the invention, the film 4 is cooled, in a manner substantially simultaneous with the above-mentioned step of transferring the pattern onto the film 4 coupled to the supporting substrate 5, by feeding a cooling fluid, preferably water at a temperature comprised between about 2° and about 25°C, to the support roll 12 of the transfer roll 8 and to the tubes 14 of the pressure roll 7 and of the cooling roll 10.

At the end of the above-mentioned manufacturing steps, a release sheet 2 provided with a predetermined pattern of indefinite length is thus obtained in a substantially continuous manner, which sheet in the illusfrated embodiment is fed towards a direction out of the plant 1, indicated in the figure with the arrow O. The release sheet 2 provided with a predetermined pattern can then be trimmed at the edges by means of the above- mentioned cutting system and subsequently collected in rolls of predetermined size.

From what has been described and illusfrated above, all the advantages achieved by the invention and especially those related to the possibility of producing a release sheet provided with a predetermined pattern in a flexible manner and responding to the ever changeable market demands promptly and at low cost are immediately apparent.

The method and the plant of the invention allow, in particular, to manufacture a release sheet provided with a suitable pattern at low cost and in a simple manner and to drastically reduce the stop time of the plant necessary for the replacement of the roll carrying the pattern to be transferred which, in this case, unlike what occurs in the prior art, is the fransfer roll 8 and not the pressure roll 7, which is much more laborious to disassemble.

Of course, a man skilled in the art may carry out modifications and variants to the above-described invention in order to fulfill specific and contingent applicative requirements, variants and modifications anyhow falling within the scope defined by the subsequent claims.

Thus, for example, in the case of the production of an embossed release sheet with a pattern in high relief, the pressure roll may be provided, on at least one radially outer portion thereof, with a corresponding pattern in high relief of a shape mating the pattern engraved in low relief on at least one radially outer portion of the transfer roll.

Claims

1. Method for producing a release sheet (2) provided with a predetermined pattern, comprising the steps of:

a) forming a film of polymeric material (4);

b) arranging a supporting substrate (5);

c) coupling said film of polymeric material (4) to said supporting substrate (5); and

d) transferring said pattern onto said film of polymeric material (4) so coupled to said supporting substrate (5);

wherein said fransfer step is carried out by means of a transfer roll (8) provided on at least one radially outer portion (13) thereof with a pattern having a shape mating the pattern of the release sheet (2), said at least one radially outer portion (13) being substantially constituted by a mouldable material substantially incompatible with the polymeric material of the film (4).

2. Method according to claim 1, wherein said polymeric material is selected from the group comprising: polyolefin, polyurethane, epoxy and polyester polymeric materials.

3. Method according to claim 2, wherein said polyolefin polymeric materials are selected from the group comprising: polyethylene, polypropylene and polymethylpentadiene.

4. Method according to claim 1, wherein said film of polymeric material (4) has a thickness comprised between about 10 and about 80 μm.

5. Method according to claim 1, wherein said supporting substrate (5) is constituted by a material selected from the group comprising: paper, card, cardboard, fabric, plastic material and combinations thereof.

6. Method according to claim 1, wherein said steps a) of forming the film of polymeric material (4) and b) of providing the supporting substrate (5) are carried out in a substantially simultaneous manner.

7. Method according to claim 1 or 6, wherein said step c) of coupling the film of polymeric material (4) to the supporting substrate (5) and said step d) of transferring the pattern onto the film of polymeric material (4) coupled to the supporting subsfrate (5) are carried out in a substantially simultaneous manner.

8. Method according to claim 7, wherein said steps a) of forming the film of polymeric material (4), c) of coupling the film of polymeric material (4) to the supporting subsfrate (5) and d) of transferring the pattern onto the film of polymeric material (4) coupled to the supporting substrate (5) are carried out in a substantially continuous manner.

9. Method according to claim 1, wherein said fransfer roll (8) is subjected to a rotation speed comprised between about 20 m/min and about 150 m/min.

10. Method according to claim 1, wherein said step c) of coupling the film of polymeric material (4) to the supporting substrate (5) is carried out by rolling by means of a pressure roll (7) cooperating with said fransfer roll (8), said pressure roll (7) having a longitudinal axis extending substantially parallel to the longitudinal axis of the transfer roll (8).

11. Method according to claim 10, wherein said step c) of coupling the film of polymeric material (4) to the supporting subsfrate (5) is carried out by pressing said pressure roll (7) against said fransfer roll (8) at a predetermined pressure.

12. Method according to claim 11, wherein said predetermined pressure is comprised between about 50 kg/linear cm and about 400 kg/linear cm.

13. Method according to claim 1, wherein said mouldable material substantially incompatible with said polymeric material is selected from the group comprising elastomeric materials substantially incompatible with the polymeric material.

14: Method according to claim 1 or 10, further comprising a step of cooling the film of polymeric material (4) provided with the predetermined pattern.

15. Method according to claim 14, wherein said cooling step is carried out in a manner substantially simultaneous with said fransfer step of the pattern onto the film of polymeric material (4) coupled to the supporting substrate (5).

16. Method according to claim 14 or 15, wherein said cooling step is carried out by cooling the transfer roll (8) and/or the pressure roll (7).

17. Method according to any one of claims 14-16, wherein said cooling step is carried out by means of a cooling roll (10) arranged parallel to and in heat exchange relationship with said transfer roll (8) in an opposite position with respect to said pressure roll (7).

18. Method according to claim 17, wherein said cooling roll (10) is made of a suitable metallic material.

19. Method according to claim 16 or 17, wherein said transfer roll (8) and/or said pressure roll (7) and said optional cooling roll (10) are provided with respective circuits for the circulation of a cooling fluid maintained at a predetermined temperature lower than the melting temperature of the polymeric material of the film (4).

20. Method according to claim 19, wherein said cooling fluid is water.

21. Method according to claim 1, further comprising the step of applying a material adapted to counterwarp the supporting subsfrate (5) onto said supporting substrate (5) so coupled to said film of polymeric material (4).

22. Plant (1) for producing a release sheet (2) provided with a predetermined pattern, comprising:

a) an extrusion apparatus for forming a film of polymeric material (4);

b) means for feeding a supporting substrate (5);

c) coupling means for coupling said film of polymeric material (4) to said supporting substrate (5); and

d) a transfer roll (8) for transferring said pattern onto said film of polymeric material (4) so coupled to said supporting substrate (5);

wherein said transfer roll (8) is provided on at least one radially outer portion (13) thereof with a pattern having a shape mating the pattern of the release sheet (2), said at least one radially outer portion (13) being substantially constituted by a mouldable material substantially incompatible with the polymeric material of the film (4).

23. Plant (1) according to claim 22, wherein said coupling means comprises a pressure roll (7) cooperating with said transfer roll (8) for coupling said film of polymeric material (4) to said supporting subsfrate (5) by rolling, said pressure roll (7) having a longitudinal axis extending substantially parallel to the longitudinal axis of the fransfer roll (8).

24. Plant (1) according to claim 22, wherein said mouldable material substantially incompatible with said polymeric material is selected from the group comprising elastomeric materials substantially incompatible with the polymeric material.

25. Plant (1) according to claim 22 or 23, further comprising means for cooling (9) the film (4) of polymeric material.

26. Plant (1) according to claim 25, wherein said cooling means is arranged in the transfer roll (8) and/or in the pressure roll (7).

27. Plant (1) according to claim 25 or 26, wherein said cooling means (9) is arranged in a cooling roll (10) arranged parallel to and in heat exchange relationship with said transfer roll (8) in an opposite position with respect to said pressure roll (7).

28. Plant (1) according to claim 27, wherein said cooling roll (10) is made of a suitable metallic material.

29. Plant (1) according to claim 26 or 27, wherein said fransfer roll (8) and/or said pressure roll (7) and said optional cooling roll (10) are provided with respective circuits for the circulation of a cooling fluid maintained at a predetermined temperature lower than the melting temperature of the polymeric material of the film (4).

30. Plant (1) according to claim 22, further comprising a gravure roll arranged downstream of said coupling means and intended to apply a material adapted to counterwarp the supporting substrate (5) onto the supporting subsfrate (5) coupled to the film of polymeric material (4).