FR2834928A1 - Wrapping material is composed of two film layers, bonded by an adhesive layer, with upper gathered structures over breaks in the adhesive to give a relief inscription for reading by the blind - Google Patents

Abstract

Wrapping material, with a relief writing structure (12), is formed by two films (14,16) durably bonded together by an adhesive layer (18). The adhesive layer is interrupted (19) at each zone of the relief structure. The upper film has projecting gatherings (20) over the breaks in the adhesive layer.

Description

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 The present invention relates to a sheet comprising at least one raised inscription.

 It further relates to a package comprising such a sheet and to a method of manufacturing such a sheet.

 Sheets with embossed inscriptions are known, in particular to allow people with visual impairments to read the inscriptions.

 In particular, it is known to have Braille inscriptions on a sheet. These inscriptions, consisting of a set of points arranged in a known and recognizable configuration project from the surface of the sheet. To form these projecting points, it is known to use inks which, after drying, form protuberances on the surface of the sheet. These inks are applied to the outer surface of the sheet.

 The implementation of such inks is relatively delicate, especially on polymer films used for packaging products, such as food products.

 The object of the invention is to propose a sheet comprising raised inscriptions which can be produced easily, in particular for use in packaging.

 To this end, the invention relates to a sheet of the aforementioned type, characterized in that it comprises at least a first and a second film between which is disposed, over most of their surface, a permanent bonding layer, in that, at the location of the or each inscription, the bonding layer has a discontinuity where the first and second films are not integral, and in that the first film has a gathered protrusion at the right of the discontinuity the tie layer.

 According to particular embodiments, the sheet includes one or more of the following characteristics: - the first and second films have internal constraints of opposite directions in the vicinity of the or each gathered in the areas where the first and second films are integral ;

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 the residual elastic elongation of the second film is greater than the residual elastic elongation of the first film in the vicinity of the or each gathering in the areas where the first and second films are integral; - The first and second films have residual thermal shrinkage constraints in opposite directions in the vicinity of the or each gathered in the areas where the first and second films are integral; - The first and second films have residual thermal elongation constraints of opposite directions in the vicinity of the or each gathered in the areas where the first and second films are integral; - it includes, at the location of the or each entry, in the or each discontinuity, an expansible ink or varnish or an intumescent ink; - The first film has, on its external surface, a varnish having a roughness greater than that of the external surface of the first film, which varnish is applied in at least one zone marked above the or each gathered; - The or each discontinuity of the bonding layer has the shape of a disc, the or each associated gathered gathered in the shape of a cap; - the width of the or each discontinuity is between 0.1 mm and 3 mm; - The width of the or each discontinuity between 0.1 mm and 3 mm extends in the direction of residual elastic elongation of the second film; - The bonding layer comprises a layer of glue, and the or each discontinuity of the bonding layer is formed of a region of the glue layer free of glue; and the bonding layer comprises a layer of continuous glue, and it comprises, at the location of the or each discontinuity, a repellant inhibiting the adhesive power of the glue of the layer of glue on at least one of the first and second films.

 The invention also relates to a packaging comprising a sheet as defined above.

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 Furthermore, the subject of the invention is a smooth sheet intended to form a sheet comprising at least one raised inscription, characterized in that it comprises at least a first and a second film between which is disposed, essentially their surfaces, a permanent bonding layer, the bonding layer having, at the location provided for the or each inscription in relief, a discontinuity where the first and second films are not integral, and in that the first and second films are elastically elongated, the elastic elongation of the second film being. greater than the elastic elongation of the first film.

 It also relates to a smooth sheet intended to form a sheet comprising at least one raised inscription, characterized in that it comprises at least a first and a second film between which is disposed, over most of their surface, a permanent bonding layer, the bonding layer having, at the location provided for the or each embossed inscription, a discontinuity where the first and second films are not integral, and in that the second film has a higher shrinkage rate at the shrinkage rate of the film allows for the same temporary rise in temperature.

 It also relates to a smooth sheet intended to form a sheet comprising at least one raised inscription, characterized in that it comprises at least a first and a second film between which is disposed, over most of their surface, a permanent bonding layer, the bonding layer having, at the location provided for the or each embossed inscription, a discontinuity where the first and second films are not integral, and in that the second film has a rate of elongation lower than the elongation rate of the first film for a temporary rise in their temperature.

 In addition, the subject of the invention is a method of manufacturing a sheet as defined above comprising the following steps: a) causing the elastic elongation of a first film and of a second film, the elongation elastic created in the second film being greater than the elastic elongation created in the first film;

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 b) applying a bonding layer on one of the first and second films, the bonding layer comprising a discontinuity at the intended location of the or each inscription; c) applying the first and second films still elongated one against the other with the interposition of the bonding layer; and d) ensuring the bonding of the first and second films by the bonding layer while these are still elongated.

 According to other manufacturing methods, the method is such that it has one of the following characteristics: - it comprises a step consisting in joining a first and a second film with the interposition of a bonding layer comprising a discontinuity at the 'planned location of the or each embossed inscription, the films being adapted to have different length variations during the same temporary rise in their temperature; - It includes a step consisting in releasing the elongation constraints of the first and second films combined with a sheet as defined above; and - it comprises a step consisting in temporarily raising the temperature of the first and second combined films of a sheet as defined above, at least in the region of the or each inscription, to a temperature sufficient to reveal, after cooling, the or each inscription in relief.

 The invention will be better understood on reading the description which follows, given solely by way of example and made with reference to the drawings, in which: - Figure 1 is a perspective view of a sheet according to invention; - Figure 2 is a sectional view of the sheet of Figure 1; - Figure 3 is a schematic view of an installation for the production of a sheet according to the invention; - Figures 4A to 4D are sectional views of two films illustrating successive stages of a first method of manufacturing the sheet; - Figures 5 and 6 are views identical to that of Figure 2 relating to alternative embodiments of a sheet according to the invention;

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 - Figure 7 is an elevational view of a sheet according to the invention having Braille inscriptions; - Figures 8A to 8C are sectional views of two films illustrating successive stages of a second method of manufacturing the sheet according to the invention; - Figure 9 is a curve illustrating a heat input phase during the manufacture of the sheet; - Figure 10 is a perspective view of a bag formed from a sheet according to the invention; and FIG. 11 is a section view illustrating a phase of manufacturing the sachet of FIG. 10.

 The sheet 10 shown in Figure 1 is a polymer sheet for packaging products such as food. It is intended in particular to constitute a sealing cap heat-sealed on a thermoformed tray. This sheet can also be used for making packaging bags.

 The sheet according to the invention has, on its outer surface, when it is used to form a package, raised inscriptions 12, these inscriptions projecting outwards relative to the surface of the sheet.

 The sheet 10 consists of two films 14,16 laminated one on the other and kept permanently associated by a layer of adhesive 18 interposed between the two films.

 The adhesive layer extends over most of the surface of the two films to ensure their permanent bond.

 The two films 14, 16 are preferably polymer films. The first film may however be made of another material, in particular paper.

 The first film 14 bearing the raised inscriptions 12 preferably has a thickness less than the film 16 constituting a support film suitable for being heat-sealed. The thickness of the second film 16 is generally between twice and four times the thickness of the first film 14. For example,

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 the thickness of the first film 14 is between 10 and 20 microns, the thickness of the second film 16 being between 30 and 100 microns.

 Preferably, the first film 14 is a film having a higher stiffness constant than the second film 16. However, the reverse is also suitable.

 The first film 14 is for example a polyester film having a thickness of 12 microns. This film is particularly suitable for receiving an impression.

 The second film 16 is preferably chosen to be easily weldable. This film is for example formed of polyethylene having for example a thickness of 50 microns.

 The glue layer 18 is formed of a solvent-based glue "ethyl acetate" consisting for example of polyol and isocyanate. The adhesive is deposited in such a way that, after drying and polymerization, the surface density of adhesive is equal to approximately 3 g / m2.

 The adhesive layer 18 has discontinuities 19 free of adhesive at the location of each inscription 12, as illustrated in FIG. 2. In addition, the first film 14 has, at the location of each inscription, a gathered 20 protruding outwards, which frown defines the embossed inscription 12.

 The glue-free discontinuities 19 extend very exactly over the surface of the embossed inscription 12, and in particular over the surface of the pleat 20 defined by the first film 14.

 According to a first manufacturing process, the gathers 20 are obtained by a difference in initial elastic elongation of the first and second films during the manufacture of the sheet, as will be explained, with reference to FIG. 3.

 Thus, after manufacture of the sheet and relaxation, the residual elastic elongation of the second film 16 is greater than the residual elastic elongation of the first film 14 forming the gathers 20.

 The production of a sheet according to the invention is carried out continuously from the first and second films 14, 16 delivered from reels 22, 24 installed in reels.

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 The first and second films 14, 16 are brought into contact with each other in a calendering unit 26 comprising two adjacent rollers 28 between which the two films are pressed against each other.

 Between the reel unwinding units 22,24 and the calendering unit 26 are arranged, on the path of each film 14,16, means denoted 32,34 for stretching the films by tensioning.

 These stretching means by tensioning comprise for example mobile rollers applied to the film, making it possible to cause an elongation of the film between the rollers and the calendering unit. This elongation is caused in the machine direction, that is to say in the direction of advancement of the film.

 These stretching means by tensioning are adapted to allow controlled elastic stretching of each film. By elastic elongation is meant a reversible deformation of the film which has the consequence of causing it to elongate.

 After unwinding and before passing through the calendering unit 26, the first film 14 passes through a printing unit 36, for example by heliography and a gluing unit 38 allowing the application of the discontinuous glue layer 18 on the surface of the film 14 before it is brought into contact with the film 16 in the calendering unit 26.

 The gluing unit 38 comprises a glue application cylinder 39 comprising cells for temporary glue retention in the regions to be glued and having a smooth surface devoid of cells for the formation of discontinuities 19 free of glue from the glue layer.

 A drying unit 40 is disposed at the outlet of the unit 38 for gluing the film 14.

 At the outlet from the calendering unit 26, the two complexed films forming the sheet are wound continuously to form a coil 42.

 The elongation units 32, 34 by tensioning of the two films are adapted to cause a differential elongation of the first and second films. More specifically, they are adapted to cause an

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 lengthening of the second film 16 greater than the elongation of the first film 14 having to form the gathers 20.

 In particular, for the first film, the elongation for one meter is between 0.1 mm and 4 mm, while, for the second film, the elongation for one meter is between 1 mm and 20 mm. The difference in elongation for one meter between the first and the second films is between 1 mm and 15 mm.

 In FIG. 4A are illustrated two sections of the first and second films 14 and 16 at rest, before extension by tensioning. These both have a length measured according to the machine direction denoted LO.

 After elastic elongation due to the tensioning, and as illustrated in FIG. 4B, the first film 14 has a length L 1 and the second film 16 has a length L2, greater than L 1.

 The two films are laminated on top of each other while they are still under tension.

 Thus, and as illustrated in FIG. 4C, the two films 14, 16 are joined together while they have different elongations.

 When the sheet 10 is separated from the roller 42, and the latter is no longer subjected to a tension maintaining the elongation applied to each of the films during its manufacture, the sheet tends to shrink, under the elastic action of the stretched polymer.

 In particular, and as illustrated in FIG. 4D, the least elongated film, namely film 14, returns to its original length of rest or retains a small residual elongation. The second film 16, which is initially the most elongated, retracts by an equal length. However, the latter retains a large residual elastic elongation relative to that of the first film.

 In the regions where the two films 14 and 16 are laminated one on the other, an additional retraction of the second film 16 is hampered by the action of the first film 14 which, for its part, can no longer shrink. Thus, the first film 14 maintains the second film 16 with a residual elongation imposed during manufacture.

 On the other hand, in the discontinuities 19 free of glue, the second film 16 is free to shrink, the latter not being secured to the first film

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 14. During this retraction of the second film, the first film 14, which is linked to the second film on either side of the discontinuities 19 free of glue, is caused to form a gathered 20 towards the outside, due to its inability to retract. Thus, the gathers 20 are formed in the regions free of glue, when the sheet is released.

 Advantageously, the inscriptions are such that the glue-free discontinuities 19 have a width of between 0.1 mm and 3 mm, this width being measured according to the direction of elongation of the second film 16.

 These widths for the elements constituting the inscriptions allow an easy tactile detection, and guarantee a sufficient thickness of the gathered so that it is detectable.

 In FIG. 5 is shown a first variant of a sheet as illustrated in FIGS. 1 and 2.

 In this embodiment, each gathered 20 is covered, on the external surface of the film 14, by a layer of rough varnish 50. This varnish, after drying, has a roughness greater than the surface roughness of the external face of the film 14.

 The presence of this varnish improves the tactile perception of the inscriptions in relief.

 In the alternative embodiment of FIG. 6, the discontinuities 19 free of glue from the layer of glue 18 comprise expandable inks or varnishes or intumescent inks. These inks or varnishes are applied before the application of the adhesive layer exactly in the interruptions of this layer, either between the two films, or on the outer surface of the first film 14 intended to provide the gathers. These inks are suitable for increasing volume during the manufacture of the film and thus favoring the expansion of the gathers 20 relative to the general surface of the first film 14.

 FIG. 7 shows an example of an inscription which can be formed on the surface of a sheet according to the invention. In this figure, the inscriptions are made up of Braille characters, each formed by six dots arranged in three lines and two columns. Each point is formed

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 generally a spherical cap having at the base a diameter between 1 mm and 3 mm.

 Other forms of registration can also be obtained. In particular, lines can be drawn transversely to the machine direction, that is to say transversely to the direction of initial elongation of the sheet.

 In the embodiments described above, the first and second films 14, 16 are joined to one another by a bonding layer consisting of a layer of glue which has discontinuities free of glue at the location of the gathers. .

 As a variant, the bonding layer interposed between the two films comprises a continuous adhesive layer and the discontinuities of the bonding layer are formed by a repellant applied to the adhesive layer at the location of the gathers. This repellant is adapted to inhibit the adhesive power of the adhesive on at least one of the first and second films.

The repellant is for example a repellent varnish.

 In FIGS. 8A, 8B and 8C is illustrated another method of manufacturing a sheet comprising inscriptions in relief.

 For the implementation of this method, the first and second films 14, 16 are chosen from materials which, when they are temporarily heated to the same temperature undergo different length variations after cooling. In particular, they are chosen to have different rates of shrinkage or elongation when they are subjected to a rise in temperature.

 More specifically, in the event of shrinking of the films during a rise in temperature, the second film 16 is chosen with a shrinkage rate greater than the shrinkage rate of the films 14 intended to form the gathers.

 The first film 14 is for example an oriented polyamide film which has a shrinkage rate, after being brought to 80 ° C. and then cooled, of less than 1%. The second film 16 is for example a polyethylene film which has a shrinkage rate, after being brought to 80 ° C. and then cooled, which is between 2% and 7%.

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 In the example given above, when the sheet thus formed constitutes a sealing cap for a tray, the second polyethylene film 16 is applied against the tray and constitutes a sealing film. Thus, the polyethylene of the second film is welded to the material constituting the tray. Gathers are therefore formed in the film opposite to the welding film.

 As a variant, the gathers can be formed in the welding film, which then constitutes the first film.

 The packaging sheet is then for example made up of a first film 14 formed of linear low density polyethylene of 50 p which has a shrinkage rate, after being brought to 80 ° C. and cooled, of about 0%, or even a about 0.5% elongation. The second film 16 is for example an oriented polyamide film of 15 u which has a shrinkage rate, after being brought to 80 ° C. and then cooled, of approximately 1%.

 In this case, the gathers are formed in the polyethylene film, which is also used as a welding film in order to secure the sheet forming the cover on a tray.

 Conversely, in the event of elongation of the films during a rise in temperature, the second film 16 is chosen with an elongation rate lower than the elongation rate of the first film 14 intended to form the gathers.

 In this case, the two films are assumed to be capable of undergoing shrinkage during a rise in temperature.

 According to this process, and as illustrated in FIGS. 8A, the two films are initially laminated one on the other, with the exception of certain zones forming discontinuities where the two films are not joined to each other. other. When bonding, the two films are not elongated in a differential manner.

 However, advantageously, in order to combine the effects of the method described here with the method described with reference to the preceding figures, the second film 16 has undergone, before lamination, an elastic elongation greater than the elastic elongation applied to the first film 14.

 After lamination, the two associated films are subjected to a heat supply leading to a temporary rise in their temperature according to the cycle illustrated in FIG. 9.

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 During this cycle, the temperature of the sheet is rapidly increased during a phase T1 and then is kept at a constant value during a phase T2 before being brought back to room temperature during a phase T3.

une température d'environ 20 C. Cette température est élevée jusqu'à une température de 75 C à 85 C lors de la phase T1, dont la durée est par exemple égale à 0, 3 seconde. Le maintien en température pendant la phase T2 est assuré pendant environ 1,2 seconde alors que le refroidissement a une durée T3 égale à 6 secondes. Initially, the complexed sheet is at room temperature, i.e.

a temperature of around 20 C. This temperature is raised to a temperature of 75 C to 85 C during the phase T1, the duration of which is for example equal to 0.3 seconds. The temperature is maintained during the T2 phase for approximately 1.2 seconds while the cooling has a duration T3 equal to 6 seconds.

 During the addition of heat, the first and second films are caused to shrink due to their nature.

 If the two films were not complex, each film would undergo different shrinkage, as illustrated in Figure 8B, where the two films are shown as being unbound. The second film 16 would have a length L2 after heating, less than the length L 1 of the first film after heating.

 In particular, if the first film 14 alone is brought to a temperature of 750C to 85 C, it undergoes, after cooling, a shrinkage of the order of 1% in the machine direction and of the order of 0.3 % crosswise.

 On the other hand, if the second film alone 16 is brought to a temperature of 750C to 85 C, this undergoes, after cooling, a shrinkage of 5% in the machine direction and of about 4% in the cross direction.

 With the method according to the invention, the two films 14,16 being bonded to each other in any zone other than the discontinuities free of the bonding layer, the first and second films are caused to shrink identically in the areas where these are stuck.

 On the other hand, in areas where the two films are not linked, the second film 16 shrinks more than the first film 14.

As the first film 14 is bonded to the second film 16 at the edge of the discontinuities of the bonding layer, the first film 14 is caused to form a gathered at the location of each discontinuity as illustrated in FIG. 8C.

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 More generally, the heating temperature of the films is preferably between 70 ° C. and 1200 ° C. and more particularly between 750 ° C. and 95 ° C.

 The time for supplying heat to the complexed sheet, that is to say the duration T1 + T2 is preferably between 0.2 seconds and 6 seconds.

 The film cooling time, that is to say the duration T3 is between 0.1 seconds and 30 seconds.

 Films 14 and 16 are chosen to have, at the temperature considered, a rate of shrinkage or elongation of between -25% (shrinkage) and + 50% (elongation) after an addition of heat and cooling.

More particularly, the retraction or elongation is preferably between -15% and + 20%.

 The shrinkage differential between the two films 14 and 16 is preferably between 1% and 15%.

 Preferably, the retraction differentials in the machine direction and in the transfer direction are as close as possible.

 In the embodiments described above, the first and second films 14, 16 are joined to one another by a bonding layer consisting of a layer of glue which has discontinuities free of glue at the location of the gathers. .

 As a variant, the bonding layer interposed between the two films comprises a continuous adhesive layer and the discontinuities in the bonding layer are formed by a repellant applied to the adhesive layer at the location of the gathers. This repellant is adapted to inhibit the adhesive power of the adhesive on at least one of the first and second films.

 The repellant is for example a repellent varnish.

 In Figure 10 is shown a bag 80 consisting of a packaging sheet according to the invention folded and sealed to delimit an enclosed space.

 This bag has a longitudinal weld 82 beyond which the sheet extends to form a free strip 84. The raised inscriptions 86 formed by the last method of the invention are advantageously provided on this free strip 84 along the weld longitudinal 82.

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 FIG. 11 illustrates the embodiment of the longitudinal weld and the simultaneous revelation of the raised inscriptions 86.

 The sheet forming the sachet is wound around a cylindrical shaper 90. A soldering iron 92 is applied to the two longitudinal edges of the sheet to ensure their welding. This soldering iron 92 is integral with a heating plate 98 suitable for applying to the free strip formed by the longitudinal edge of the sheet where the raised inscriptions are to be formed. The heating plate 98 brings heat to the sheet in the regions where raised inscriptions are to be formed, simultaneously with the production of the longitudinal weld.

 The position of the raised inscriptions along the longitudinal weld facilitates the production of the bag since the raised inscriptions can be revealed simultaneously with the production of the longitudinal weld. In addition, their position makes them easily accessible and perceptible to the blind, since these are not located on a main face of the bag below which the products are located.

 In the case where the packaging sheet is used as the lid of a tray, the raised inscriptions are preferably located in a region of the sheet applied to a smooth surface of the tray, for example on the edge of the tray, so that the raised inscriptions can be more easily perceived by manual contact, these then resting on a flat surface formed by the rim of the tray.

Claims (1)

 CLAIMS 1. - Sheet (10) comprising at least one raised inscription (12), characterized in that it comprises at least a first and a second film (14,16) between which is disposed, for the most part of their surface, a permanent bonding layer (18) in that, at the location of the or each inscription (12), the bonding layer (18) has a discontinuity (19) where the first and second films (14, 16) are not integral, and in that the first film (14) has a gathering (20) projecting in line with the discontinuity (19) of the bonding layer.  2. - Sheet according to claim 1, characterized in that the first and second films (14,16) have internal constraints of opposite directions in the vicinity of the or each gathered (20) in the areas where the first and second films ( 14,16) are united.  3. Sheet according to claim 2, characterized in that the residual elastic elongation of the second film (16) is greater than the residual elastic elongation of the first film (14) in the vicinity of the or each gathered (20) in the areas where the first and second films (14,16) are integral.  4.-Sheet according to claim 2 or 3, characterized in that the first and second films (14,16) have residual thermal shrinkage constraints in opposite directions in the vicinity of the or each gathered (20) in the areas where the first and second films (14,16) are integral.  5.-Sheet according to claim 2 or 3, characterized in that the first and second films (14,16) have residual thermal elongation stresses in opposite directions in the vicinity of the or each gathered (20) in the areas where the first and second films (14,16) are integral.  6.-Sheet according to any one of the preceding claims, characterized in that it comprises, at the location of the or each inscription (12), in the or each discontinuity (19), an expansible ink or varnish or intumescent ink (52).  7. - Sheet according to any one of the preceding claims, characterized in that the first film (14) has, on its external surface, a varnish (50) having a roughness greater than that of the external surface of the <Desc / Clms Page number 16>  first film (14), which varnish (50) is applied in at least one marked area above the or each gathered (20).  8. - Sheet according to any one of the preceding claims, characterized in that the or each discontinuity (19) of the bonding layer (18) has the shape of a disc, the or each gathered gathered (20) having the shape of a cap.  9. - Sheet according to any one of the preceding claims, characterized in that the width of the or each discontinuity (19) is between 0.1 mm and 3 mm.  10. - Sheet according to claims 3 and 9 taken together, characterized in that the width of the or each discontinuity (19) between 0.1 mm and 3 mm extends in the direction of residual elastic elongation of the second film (16).  11. - Sheet according to any one of the preceding claims, characterized in that the bonding layer comprises a layer of adhesive (18), and in that the or each discontinuity (19) of the bonding layer is formed of a glue-free region of the glue layer.  12. - Sheet according to any one of claims 1 to 10, characterized in that the bonding layer comprises a layer of continuous glue, and in that it comprises, at the location of the or each discontinuity, a repellant inhibiting the adhesive power of the adhesive of the adhesive layer on at least one of the first and second films.  13.-Package comprising at least one sheet (10) according to any one of the preceding claims.  14. - Smooth sheet intended to form a sheet comprising at least one raised inscription (12) according to claim 3, characterized in that it comprises at least a first and a second film (14,16) between which arranged, over most of their surface, a layer (18) of permanent connection, the bonding layer (18) having, at the location provided for the or each embossed inscription (12), a discontinuity (19 ) where the first and second films are not integral, and in that the first and second films are elastically elongated, the elastic elongation of the second film (16) being greater than the elastic elongation of the first film (14). <Desc / Clms Page number 17>  15. - smooth sheet intended to form a sheet comprising at least one raised inscription (12) according to claim 4, characterized in that it comprises at least a first and a second film (14,16) between which is arranged, over most of their surface, a permanent bonding layer (18), the bonding layer (18) having, at the location provided for the or each embossed inscription (12), a discontinuity (19) where the first and second films are not integral, and in that the second film (16) has a shrinkage rate greater than the shrinkage rate of the first film (14) for the same temporary rise in their temperature.  16. - smooth sheet intended to form a sheet comprising at least one raised inscription (12) according to claim 4, characterized in that it comprises at least a first and a second film (14,16) between which is arranged, over most of their surface, a permanent bonding layer (18), the bonding layer (18) having, at the location provided for the or each embossed inscription (12), a discontinuity (19) where the first and second films are not integral, and in that the second film (16) has an elongation rate lower than the elongation rate of the first film (14) for a temporary rise in their temperature.  17. A method of manufacturing a sheet (10) according to claim 14, comprising the following steps: a) causing the elastic elongation of a first film (14) and a second film (16), the the elastic elongation created in the second film (16) being greater than the elastic elongation created in the first film (14); b) applying a bonding layer on one of the first and second films (14,16), the bonding layer (18) comprising a discontinuity (19) at the intended location of the or each inscription (12); c) applying the first and second films (14,16) still elongated one against the other with the interposition of the bonding layer; and d) ensuring the bonding of the first and second films by the bonding layer while these are still elongated.  18. A method of manufacturing a sheet (16) according to claim 15 or 16, characterized in that it comprises a step consisting in bringing together a first and a second film (14,16) with the interposition of a layer of liai- <Desc / Clms Page number 18>  sound (18) comprising a discontinuity (19) at the intended location of the or each raised inscription (12), the films being adapted to have different length variations during the same temporary rise in their temperature.  19. A method of obtaining a sheet according to claim 3, characterized in that it comprises a step consisting in releasing the elongation stresses of the first and second combined films (14,16) of a sheet according to the claim 14.  20.-A method of obtaining a sheet according to claim 4 or 5, characterized in that it comprises a step consisting in temporarily raising the temperature of the first and second combined films (14,16) of a sheet according to the claim 15 or 16, at least in the region of the or each inscription (12), up to a temperature sufficient to reveal, after cooling, the or each inscription in relief.