FR2827805A1 - Plastic component decorating procedure, uses motifs on continuous strip of film fed from roll, cut into sections and placed in injection mould - Google Patents

Abstract

The procedure for applying a thin film layer carrying a motif, especially a decorative motif, to an injected thermoplastic component, comprising using a continuous strip of film (F1) on which the motifs are printed in a single line in the form of labels, each motif being wider than the component but narrower than the film strip. The procedure for applying a thin film layer carrying a motif, especially a decorative motif, to an injected thermoplastic component, comprising using a continuous strip of film (F1) on which the motifs are printed in a single line in the form of labels, each motif being wider than the component but narrower than the film strip. The film strip is delivered from a roll (B1), feeding each label (31) in turn to a cutting post where it is cut out together with a surrounding zone (30). The label is then inserted into an injection mould (8, 9) with one wall corresponding to the surface to be decorated and after the mould has been closed, pinching the edge of the label and forming a weakened line in its peripheral zone and then molten thermoplastic material is injected. After cooling, the molded component with the label attached is removed from the mould and the edge of the label outside the weakened line is separated to leave a finished article.

Description

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 The present invention relates to a method of decorating a plastic part.

 The terms decoration and decorative are to be considered here with a broad meaning, not necessarily with an aesthetic meaning.

 It relates more precisely to a process for coating with a thin and flexible film bearing a pattern, in particular decorative, a part made of injected thermoplastic material, the connection of the part with the film being made directly in the injection mold, by overmolding.

 The reason in question could be purely informative.

 The invention also relates to an injection mold suitable for implementing certain steps of the process.

 The invention was more particularly conceived for the decoration of hulls of cases of portable telephones; it goes without saying, however, that it can find various applications, when it is a matter of applying a given pattern, in particular decorative and / or informative, to a piece of thermoplastic material.

 As another possible application, there may be mentioned, for example, the manufacture of a dashboard element of a motor vehicle.

 The invention aims to provide a process of the kind mentioned which is suitable for mass production, which can be implemented at a relatively low cost, this with perfect quality of finish of the products.

 These objectives are achieved, in accordance with the present invention, thanks to the fact that: on the one hand, a film in the form of a strip is used, on which are printed, at the end of the line, a repetitive series of carrier labels each of a decorative pattern, and whose width is substantially greater than that of the part to be coated, but substantially less than that of said strip, the latter being wound on a dispensing reel, and, - on the other hand, it operates as follows: a) the film is unwound from this reel to bring each label successively to a cutting station; b) a blank is cut from the strip comprising, in addition to the constituent part of the label proper, a substantially planar peripheral zone which surrounds it;

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 c) this blank is introduced into an injection mold, one of the walls of which is complementary to that of the wall to be coated, and the conformed part of the label is applied against the latter; d) the mold is closed by strongly pinching the film constituting the blank at the contour of the label part, following the connection line of the latter with said peripheral zone which surrounds it, so as to print a line of weakening; e) the molten thermoplastic material intended to constitute said part is injected into the mold, against the face of the shaped part of the label which is not applied against said wall of the mold; f) after cooling, the molded part coated with the blank is removed from the mold; g) the blank is cut out by removing said peripheral zone, by breaking said weakening line, so as to obtain a finished part.

 This process makes it possible to work at high speed; there is no untimely movement of the label in the mold during the injection, because the latter is firmly held in place by the effect of pinching; the degree of finish of the parts is remarkable because the edge of the label coincides exactly with that of the part, thanks to the removal of the peripheral zone which has become useless, along a clean and ideally positioned break line.

 There is therefore no gap between the room and its decor.

 The method can be implemented for the production of a flat part.

 It can also be used, in a particularly efficient manner, for the production of parts with curved walls, for example in the form of a bowl. This supposes an additional forming operation, so as to obtain not a planar configuration blank, but a curved blank, which will conventionally be called preform in the following description and in the claims.

 In this case, the procedure is as follows: a1) the film is unwound from the reel to bring each label successively to a forming station; bl) the label is conformed thereto, so as to give it a curve corresponding to that of the wall to be coated;

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 b2) a preform is cut from the strip comprising, in addition to the label part thus shaped, a substantially planar peripheral zone which surrounds it; c) the preform is introduced into an injection mold, one of the walls of which is complementary to that of the wall to be coated, and the shaped part of the label is applied against the latter; d) the mold is closed by strongly pinching the film constituting the preform at the level of the contour of said shaped part, along the connection line of the latter with said peripheral zone which surrounds it, so as to print a line of weakening; e) the molten thermoplastic material intended to constitute said part is injected into the mold, against the face of the shaped part of the label which is not applied against said wall of the mold; f) after cooling, the molded part coated with the preform is removed from the mold; g) the preform is cut out by removing said peripheral zone, by breaking said weakening line, so as to obtain a finished part.

 Furthermore, according to a certain number of advantageous, non-limiting characteristics of the invention: - a film of thermoplastic material is used, and the labeling of the label in step (bl) above is carried out by thermoforming ; - At least one zone of the label is isolated from heat during this thermoforming, which makes it possible to limit, or even annihilate, the deformation of the label, and of the decoration which is affixed thereto, in this zone; - As regards the formatting of a label having small footprints, such as indentations, thermoforming is carried out in two successive stages, one called the main one, during which the heat is isolated from the surface of the label in which these imprints are located, surface where the framing of the print must be perfect, the other called finishing, practiced after the label has cooled, during which all of its heat surface so that fingerprints can be made; - Said film has a thickness of between 50 and 200 micrometers approximately, and preferably between 100 and 150 micrometers (for a mobile phone application) and is made of material based on styrene, polycarbonate or polypropylene, compatible with molding with the material injected thermoplastic;

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 the injected part has a thickness of between approximately 0.5 and 5 millimeters, and preferably of the order of 0.8 to 1 millimeter (for a mobile phone application) and is made of a material based on polystyrene, polycarbonate or polypropylene, compatible with molding with the film; - The injected part is made of transparent material, and the label has at least one window, also transparent, capable of acting as a reading screen.

 This process lends itself remarkably to the manufacture of a keyboard shell with keys, in particular of a portable telephone box.

 In this case, the injection of thermoplastic material in step (f) is advantageously carried out in such a way that the abovementioned recesses are not covered with material, and are also surrounded by lines of weakness facilitating the subsequent punching of the film to be this level to form openings intended for the passage of the keys of the keyboard.

 The invention can advantageously be applied to the manufacture of a part traversed by at least one opening, for example of a window for viewing a telephone screen, in the case where it is a case of cellphone.

 In this case, there is formed in the label (before the introduction of the blank or the preform into the injection mold), a recess in the zone corresponding to this opening, and the thermoplastic material is injected into the mold in such a way that this recess is not covered with material, and is also surrounded by a line of weakness facilitating the subsequent punching of the film at this level, to form said opening.

 The invention also relates to an injection mold for the implementation of steps (d) to (g) of the process which has just been described.

 This mold comprises two complementary half molds, one of which has a peripheral edge which surrounds the mold cavity, and is suitable, when the mold is closed, for strongly pinching the film constituting the preform at the level of the contour of said shaped part. , along the connection line of the latter with said peripheral zone which surrounds it, so as to print a line of weakness therein.

 This peripheral edge therefore has a double function: on the one hand, ensuring perfect immobilization of the label (and correlatively of the decoration) during overmolding and, on the other hand, printing a breaking line allowing,

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 after molding, a clean and precise removal of the excess label, just flush with the edge of the part.

 Other characteristics and advantages of the invention will become apparent from the description which will now be made of it, with reference to the appended drawings, which very schematically represent a possible mode of implementation.

In these drawings:
Figure 1 is a general diagram illustrating the process.

 Figure 2 is a perspective view of a section of the film strip used.

 Figure 3 is a view similar to that of Figure 2, showing a thermoformed label, still secured to the strip.

 Figures 4 to 7 are sectional views showing the thermoforming operation.

 Figure 8 shows the preform cutting operation.

 Figures 9 to 11 are sectional views showing the injection molding.

 Figure 12 shows the finished part (in section).

 Figure 13 is a schematic sectional view of an injection mold according to the invention, used for the production of a flat part, one face and the peripheral edge are coated with the decorative film.

 Figure 14 shows, also in section, the part leaving this mold.

 Figure 15 is a schematic sectional view of an injection mold according to the invention, also used for the production of a flat part, only one side of which is coated with the decorative film.

 Figure 16 shows, also in section, the part leaving this mold.

 FIG. 1 very schematically illustrates the method of molding a shell of a keyboard with keys, and more particularly of a portable telephone.

 In this figure, the reference B1 designates a dispenser reel of a ribbon FI on which is pre-printed, at the tail leu leu, a repetitive set of labels bearing decorations and inscriptions corresponding to a shell.

 The labels are not necessarily identical.

 The reference E designates a station for shaping the strip FI, either by cold stamping or by thermoforming, so as to give

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 each unit of the strip, intended to cover a hull, a curve similar to that of the hull.

 In the preferred embodiment which will be described later, it is a thermoforming.

 The decorations and inscriptions are pre-printed on the IF strip, if necessary, with an anamorphosis, so that the formatting practiced at station E does not compromise the integrity of the drawing, nor the good subsequent matching decoration and different inscriptions with the keyboard shell, and in particular with the keyboard keys.

 This printing, by screen printing or offset for example, can be done in a better controlled and more precise manner than a similar operation on an injected part, and makes it possible to print relatively complex images (drawings or photos). Of course, the printing must be compatible with the temperature of the subsequent molding.

 Station D designates a station for cutting the individual labels previously shaped; at this station, the curved film blanks 3 are therefore detached from the strip FI. As will be seen below in more detail, these blanks 3 - or preforms - comprise, in addition to the shaped label part, a substantially planar peripheral zone 30 which surrounds it.

 Each preform 3 is then routed, for example using a robot, to the injection tool, of which the PI press, with its half molds 7-8 and the unit d, is shown very schematically in the figure. injection.

 The fall strip F2 is recovered on a take-up reel B2.

 In FIG. 1, the arrows f symbolize the step-by-step advance of the film strip at the forming and cutting stations.

 After molding, a shell 1 is obtained composed of a wall and an overmolded preform, the peripheral edge 30 of which is still integral with the part.

 The next station D2 ensures the trimming of the part, that is to say the separation of the zone 30 from the rest of the part, for example by means of a die-cutting tool. It also performs, as will be seen below, the punching of areas 310 of the label which are located opposite the openings intended to receive the keys of the keyboard, during assembly of the telephone.

 The finished part is then sent to a designated TU station, suitable for carrying out appropriate finishing treatments, for example the varnishing, drying and packaging of the decorated part.

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 The constituting film of the strip FI is, in the illustrated embodiment, a flexible and thin thermoplastic film. It is for example a transparent extruded film, based on styrene, having a thickness of the order of 120 micrometers, and a width of the order of 200 mm. The strip, which is very long, comprises a plurality of printed rectangular labels 100, placed end to end, while being separated by an interval 104. The long side of the labels is parallel to the edges of the strip. Their width is significantly less than that of the strip. It is for example of the order of 100 mm, while their length is of the order of 180 mm.

 Each label carries decorative and / or informative patterns 102, as well as an unprinted area left transparent, constituting a window 101.

 The lateral areas 103, 103 ′ which are not printed on the strip are used in particular for transporting it, by means of suitable advancing members (rollers or claws, for example), step by step at the stations E and Dl mentioned above with reference to the figure. 1.

 The labels can advantageously be printed by a digital offset process controlled by computer, which makes it possible to obtain great flexibility, the labels of the same series being able to be either identical or different, in whole or in part.

 The inks used for printing are obviously chosen to adhere properly to the film and to resist the stretching thereof during forming at station E, as well as the heat used, both during thermoforming ( item E) during the injection (PI press).

 The thermoforming tool is very schematically represented in FIG. 4.

 Its function is to format the flat labels 100 such as that of FIG. 2 to give it the configuration of a bowl with curved wall, such as that illustrated in FIG. 3, the shape of which corresponds to that of the shell of phone that we have to realize.

 It is represented with its opening facing down.

 This bowl, or preform, has on the top a certain number of indentations, such as circular recesses 310 and bosses 311.

 At its periphery, its wall is strongly curved - and therefore stretched -; on the contrary, its upper face is slightly deformed, especially in its central region, which is relatively flat.

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 FIG. 4 is a sectional view along a vertical and transverse plane corresponding to the line IV-IV of FIG. 3.

 In this figure, the reference 4 designates a male counter-form, the upper face 41 of which has the same curve as the part to be produced, as well as the appropriate recesses 42. At the periphery of this counter-form extends a plate 43 capable of serve as a support for a frame 5, so as to enclose and retain the film FI to be formed, over the entire periphery of the label. The tools are dimensioned in such a way that the label is then located just above the part 41 of the counterform. The clamping frame, or blank holder 5 is movable in the vertical direction, suitable control means not shown being provided for lowering it, and clamping the film or on the contrary lifting it and releasing the film after the operation.

 Just above the film FI, facing the central zone of the label, is positioned, and retained by suitable holding members, a plate 7 made of thermally insulating material. Above the latter is mounted a heating device, such as an electrical resistor, suitably supplied with electrical current by ad hoc control means. The counter form is traversed by secondary channels 400 which open upwards and are connected in the lower part to a main channel 40 connected to a suction member (vacuum source) via an appropriate control valve.

 As illustrated in FIG. 5, when the resistor 6 is energized, it heats the thermoplastic film by infrared radiation, to a temperature sufficient for it to soften; moreover, by applying the vacuum in the counterform (arrow V), it is attracted and applied strongly against the latter, by marrying the wall thereof. The deformation, by stretching the material, is especially important around the periphery of the counterform. On the other hand, it is negligible in the central region, owing to the fact that the curve is weakly pronounced there and that the film is little heated there due to the presence of the thermal screen 7. Thanks to this arrangement the patterns of the decoration affixed on the The label in this region (photos, graphics, drawings, letters or numbers) therefore does not undergo - or practically no - deformation. In most cases, there is therefore no need to provide an anamorphic print on the original film plan.

 This thermal masking however thwarts the conformation of the surface details, in particular of the recesses 310 in the bowls 42 of the counterform.

 To obtain them, the film is subjected to a second thermoforming, finishing, after having retracted the thermal cover 7 (see FIG. 6).

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 The release is then carried out by retracting the heating resistance, lifting the blank holder 5 and pneumatic blowing S in the channels 40,400 (see FIG. 7).

 Then, at the cutting station D1, the preform 3 is separated from the rest F2 of the strip, which is rewound in B2 (see Figures 1 and 8).

 Of course, the operations carried out at stations E and D1 are carried out automatically by programmable control means, in synchronism with the step-by-step advance f of the strip FI.

 According to an important characteristic of the invention, this cutting, the cutting line of which is shown by the strong dashed line L in FIG. 3-, the preform 3 comprises, in addition to the relief silhouette 31, a plane peripheral rim 30; its width, for information, is of the order of 10 to 15 mm.

 The molding tool of Figures 9 and 10 is purposely shown on a larger scale than that of the cutting tool of Figures 4 to 7.

 It is an injection mold composed of two complementary superimposed half molds 8, 9, capable of being brought together for molding (FIG. 10), or of being separated in order to placing the preform (Figure 9) or removing the molded part.

 The upper half-mold 8 has a cavity 80 whose shape of the wall corresponds to that of the raised part 31 of the preform. Known methods in the field of injection molding, such as the electrostatic effect (potential difference between the preform and the receiving half-mold 8) or the application of vacuum (suction) are provided to ensure that the part 31 and its recesses 310 are applied intimately against the wall of this cavity 80 during molding.

 The lower half-mold 9 has a male part (convex) shaped to be positioned inside the cavity 80 when the mold is closed (FIG. 10). Its wall surface 90 is then at a certain distance from the surface of the cavity 80 (and from the preform which is applied to it). The spacing corresponds to the wall thickness of the part to be molded, for example of the order of 0.8 to 1 mm.

 At their periphery, the cavity 80 of the half mold 8 and the male part of the half mold 9 have planar plates 800, respectively 900, forming the joint plane of the mold. When the mold is closed, these plates come into mutual support (see Figure 10).

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 The plate 900 borders a recess, or counterbore, 91 which surrounds the central male part 90. When the mold is closed, it is thus provided, opposite this recess, a free space, the height of which, referenced x in FIG. 10 , is greater than the thickness of the film.

 According to an important characteristic of the invention, the cavity 80 is bordered by a peripheral protuberance 81, having a sharp edge directed downwards. The protuberance 81 has a section approximately in the shape of a right triangle; its inner side is vertical and its outer side is the hypotenuse. This section therefore has an acute angle, in the shape of a point facing downwards. When the mold is closed, the edge 81 comes to wedge and compress the junction line between the outer planar part 30 of the preform, and its convex part 31. This compression is nevertheless limited because the upper mold is in abutment, by its peripheral plate 800, against the plate 900 of the lower mold.

 It is sufficient to crush the film material in the junction zone of the parts 30 and 31, just at the base of the latter, forming a closed line of peripheral weakening (grooving), referenced 32 in FIG. 11.

 The edge 30 of the preform is enclosed, but not compressed, in the free space opposite the recess 91.

 It will be noted that, in order to better distinguish the coating film from the other components, this film has been shown in broken lines in FIGS. 10 to 12.

 The wall 80 of the cavity of the half mold 8 is provided with a certain number of studs 82 positioned and dimensioned so that each stud comes to be housed in a recess 310 when the mold is closed, this to apply the recess against the wall 90 of the lower half-mold 9, in order to prevent the molten material from being inserted under said recess during the injection.

 It will be noted that each pad 82 is surrounded by a sharp edge 820, similar to the edge 81 described above.

 The mold being closed (FIG. 10), the preform part 31 is held against the bottom of the cavity 80 as explained above; the pinching produced by the edge 81 participates in the correct positioning of this part in the mold.

 The molding is carried out in a conventional manner, of molten thermoplastic material, such as a transparent polycarbonate, of crystal type, being injected into the mold by suitable supply channels 92 passing through the half-mold 9 (arrow I, FIG. 10 ).

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 After cooling, the mold is opened, and the part is extracted therefrom, composed of a body M coated with film 30-31, which adheres strongly thereto (Figure 11).

 Next, at the station called D2 in FIG. 1, the edge 30 of the film is removed, which can be detached easily and perfectly clearly along the line of weakening of material, which constitutes in a way a line of pre- cutting.

 This operation can be carried out either manually, by tearing off the edge 30, or using a conventional cutting tool. At this station, the film pellets 310 are also removed, for example by punching; this operation is also done neatly and without burrs, thanks to the weakening lines formed by the edges 820.

 The finished part 1 ′, shown in FIG. 12 has a particularly sharp edge 10 ′, which exactly coincides with the edge of the decorative coating film 31.

 The punching of the pellets 310 has released openings 0, the edges of which are also very clear, serving for the passage of the keys during the assembly of the telephone.

 The same principle can be used for the realization of any other opening.

 If one remains in the field of the phone shell, it may in particular be a window intended to come into correspondence with the screen when the latter is integrated into the underlying housing part, or with the microphone.

 If the basic material M is transparent, the window 101 mentioned above, also transparent, is however capable of serving as a screen, in which the various information displayed on the current telephone can be read. use.

 The mold illustrated in FIG. 13 is designed for the production of a flat (and planar) part, one of the faces of which, in this case the upper face, as well as the peripheral edge, or edge, are coated with the decorative film. .

 The preform 3a has the form of a deep-drawn cup, the bottom 30a of which is flat, and the depth of which corresponds to the thickness of the part to be molded. It includes a peripheral zone 31 a.

 The upper half-mold 8 ′ has a flat-bottom cavity, the opening of which faces downwards, shaped to receive the preform. This cavity is bordered by a peripheral protuberance with a sharp edge 81 ′. The half mold

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 lower 9 ', which has a channel 92' for injecting the material, has a flat upper face.

la périphérie 32a de la base du chant 300a (voir figure 14). Le pourtour de film 3 la peut ainsi être rompu et enlevé aisément, et de manière nette, le bord du film décoratif venant exactement à fleur de la face inférieure (nue) Fa de la pièce finie. As in the previous embodiment, the edge of the protuberance 81 ′ compresses the preform when the mold is closed, and during the molding of the part Ma, in order to produce a line of weakening of material to

the periphery 32a of the base of the edge 300a (see FIG. 14). The periphery of the film 3a can thus be broken and removed easily and clearly, the edge of the decorative film coming exactly flush with the lower (bare) side Fa of the finished part.

 The mold illustrated in FIG. 15 is designed for the production of a flat (and planar) part of which only one of the two faces, in this case the lower face, but not the peripheral edge, is coated with the decorative film. .

 The preform 3b here is a flat blank (cut, but not thermoformed) comprising a central zone 30b constituting the label proper, as well as a peripheral bank 31b.

 The upper half-mold 8 "has a cavity with a flat bottom, the opening of which faces downward, and the shape of which corresponds to that of the part to be produced. This cavity is bordered by a peripheral protuberance with a sharp edge 81".

 It is in this cavity that the material Mb is injected, via an 85 "supply channel.

 The lower half-mold 9 "has a flat upper face.

 As in the previous embodiment, the edge of the protuberance 81 "compresses the blank when the mold is closed, and during the molding of the part, in order to produce a line of weakening of material at the periphery 32b of the central zone 30b (see FIG. 16). The 3 lb film periphery can thus be broken and removed easily and neatly, the decorative film, which covers the underside of the part, having an edge which exactly coincides with the edge lower edge of slice Tb of the finished part.

 The flat part produced by the operations which have just been described with reference to FIGS. 13 to 16 can have any outline, regular or not.

Claims (11)

1. Method for coating with a thin and flexible film carrying a pattern, in particular decorative, a piece of injected thermoplastic material, characterized in that: - on the one hand, a film in the form of a strip (FI) is used on which are printed, at the tail leu leu, a repetitive series of labels (100) each carrying a decorative pattern, and whose width is substantially greater than that of the part to be coated, but substantially less than that of said strip (FI), the latter

 being wound on a dispensing reel (bd), and, - on the other hand, the procedure is as follows: a) the film from the reel (BI) is unwound to successively bring each label (100) to a cutting station; b) a blank is cut from the strip (FI) comprising, in addition to the label part (31) thus cut, a peripheral zone (30) which surrounds it; c) the blank is introduced into an injection mold, one of the walls of which is complementary to that of the wall to be coated, and the part constituting the label is applied against the latter; d) the mold is closed by strongly pinching the blank at the contour of the label, along the connection line of the latter with said peripheral zone (30) which surrounds it, so as to print a line of weakness therein (32); e) injecting into the mold the molten thermoplastic material intended to constitute said part, against the face of the part (31) of the label which is not applied against said wall of the mold; f) after cooling, the molded part (1), coated with the blank (3), is removed from the mold; g) the blank is cut out by removing said peripheral zone (30), by breaking said weakening line (32), so as to obtain a finished part (1 ′).  2. Method for coating with a thin and flexible film bearing a pattern, in particular a decorative pattern, a part with a curved wall, of injected thermoplastic material, characterized in that: - on the one hand, a film in the form of a strip is used (FI) on which are printed, at the tail leu leu, a repetitive series of labels (100) each carrying a <Desc / Clms Page number 14>  decorative pattern, and whose width is substantially greater than that of the part to be coated, but substantially less than that of said strip (FI), the latter being wound on a dispensing reel (B 1), and, - on the other hand , one operates as follows: a1) the film is unwound from the reel (BI) in order to bring each label (100) successively to a forming station (E); bl) the label (100) is conformed thereto, so as to give it a curve corresponding to that of the wall to be coated; b2) a preform (3) is cut from the strip (FI) comprising, in addition to the label part (31) thus shaped, a peripheral zone (30) substantially planar, which surrounds it; c) the preform is introduced into an injection mold, one of the walls of which is complementary to that of the wall to be coated, and the shaped part (31) of the label is kept pressed against the latter; d) the mold is closed by strongly pinching the film constituting the preform (3) at the contour of said shaped part (31), along the connection line of the latter with said peripheral zone (30) which surrounds it, so as to print a line of weakness therein (32); e) injecting into the mold the molten thermoplastic material intended to constitute said part, against the face of the shaped part (31) of the label which is not applied against said wall of the mold; f) after cooling, the molded part (1), coated with the preform (3), is removed from the mold; g) the preform is cut out by removing said peripheral zone (30), by breaking said weakening line (32), so as to obtain a finished part (1 ′).  3. Method according to claim 2, characterized in that a film of thermoplastic material is used, and that the shaping of the label (100) in step (bl) is carried out by thermoforming.  4. Method according to claim 3, characterized in that it isolates heat, during thermoforming, at least one area of the label (100).  5. Method according to claim 4, applied to the formatting of a label having imprints of small dimensions such as recesses (310), characterized in that the thermoforming is carried out in two successive stages, one so-called main, during which we isolate <Desc / CRUD Page number 15>  heat the area of the label in which said imprints are located, the other known as finishing, practiced after the label has cooled, during which the whole of its surface is exposed to heat so as to allow the realization prints.  6. Method according to one of claims 1 to 5, characterized in that said film has a thickness of between 50 and 200 micrometers approximately, and is made of material based on styrene, polycarbonate or polypropylene, compatible with molding with the injected thermoplastic material.  7. Method according to one of claims 1 to 6, characterized in that the injected part has a thickness of between 0.5 and 5 millimeters approximately, and is made of material based on polystyrene, polycarbonate or polypropylene, compatible to molding with the film.  8. Method according to one of claims 1 to 7, characterized in that the injected part is made of transparent material (M), and that the label (100) has at least one window (101) also transparent, capable of act as a reading window.  9. Method according to one of the preceding claims, applied to the manufacture of a keyboard shell with keys, in particular of a portable telephone box.  10. The method of claim 1 or 2, applied to the manufacture of a part traversed by at least one opening, characterized in that one forms in the label, before the introduction of the blank or the preform into the mold injection, a recess in the area corresponding to this opening, and that the thermoplastic material is injected into the mold in such a way that this recess (310) is not covered with material, and is also surrounded by a weakening line facilitating the subsequent punching of the film at this level, to form said opening.  11. Injection mold for the implementation of steps (c) to (f) of the method according to claim 1 or 2, characterized in that it comprises two complementary half-molds (8,9), one of which (8) has a peripheral edge (81) surrounding the mold cavity and adapted, when the mold (8-9) is closed, to strongly pinch the film constituting the blank or the preform (3) at the contour of the constituting part of the label (31), along the connection line of the latter with said peripheral zone (30) which surrounds it, so as to print therein a line of weakness (32).