DEVICE FOR STRETCHING A THERMOPLASTIC FILM SIMULTANEOUSLY IN THE LONGITUDINAL DIRECTION AND THE TRANSVERSE DIRECTION

Abstract

A device for stretching a thermoplastic film simultaneously in the longitudinal direction and the transverse direction is provided. The device includes, on each side of the film (F) to be stretched, grasping members for grasping a lateral edge of the film (F), and guide members; first and second guide rails (R1, R2), on which the members and are respectively able to move; first connecting rods connecting the grasping members and the guide members. In an embodiment, each guide member is connected to a single grasping member by one or several of said first connecting rods, and is connected to a first longitudinal adjusting member by one or several second connecting rods connected to the first longitudinal adjusting member; and the device includes adjusting means for adjusting the position and orientation of said first longitudinal adjusting member relative to said first and second guide rail (R1, R2).

Claims

1. A device for stretching a thermoplastic film simultaneously in the longitudinal direction and the transverse direction, comprising, on each side of the film to be stretched, grasping members for grasping a lateral edge of the film, in particular in the form of clamps; a first guide rail, close to the film, on which these grasping members are placed and along which these grasping members are able to move; guide members; a second guide rail, on which these guide members are placed and along which these guide members are able to move; this second rail is rigidly connected to said first rail, in that its position is not adjustable relative to this first rail in a direction transverse to the film; and first connecting rods connecting the grasping members and the guide members, the first connecting rods being movable relative to these grasping members and these guide members along first axes; wherein, on each side of the film, each guide member is connected to a single grasping member by one or several of said first connecting rods, and is connected to a first longitudinal adjusting member by one or several second connecting rods, this or these second connecting rods being movable relative to the guide member and relative to this first longitudinal adjusting member along second axes parallel to said first axes; said second connecting rod(s) of a first guide member and said second connecting rod(s) of a second guide member consecutive to said first guide member are connected to said first longitudinal adjusting member at pivot points that are combined or close on this first longitudinal adjusting member; and the device includes adjusting means for adjusting the position and orientation of said first longitudinal adjusting member relative to said first and second guide rails.

2. The device according to claim 1, wherein, on each side of the film, the device comprises a second elongated adjusting member and a series of third connecting rods, respectively homologous to said first elongated adjusting member and said second connecting rods, this second elongated adjusting member and this series of third connecting rods being situated on one side of the grasping members, first connecting rods and guide members that is opposite the side of these same grasping members, first connecting rods and guide members on which are located said first elongated adjusting member and the series of said second connecting rods.

3. The device according to claim 1, wherein each pair of said second connecting rods extends between the two said first connecting rods associated with the same guide members as this pair of second connecting rods.

4. The device according to claim 3, wherein said first elongated adjusting member, and if applicable said second elongated adjusting member, are in the form of a rail with an upside down U-shaped section, forming a guide slot for guiding the pivot which connects the two connecting rods of each pair of second connecting rods to one another.

5. The device according to claim 1, wherein each pair of second connecting rods extends over the side of said second rail opposite said first rail.

6. The device according to claim 5, wherein said first elongated adjusting member is in the form of a rail, having guide parts engaged on it and movable on it, each of these guide parts being secured to a pivot on which said second connecting rods are pivotably mounted.

7. The device according to claim 1, wherein comprises a first linear motor associated with said first longitudinal adjusting member, and if applicable, a second linear motor associated with said second longitudinal adjusting member, acting on each junction point of said second connecting rods so as to assist the movement of these second connecting rods along said longitudinal adjusting member during the longitudinal stretching operation of the film.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] FIG. 1 is an illustration of the well-known pantograph principle;

[0035] FIG. 2 is an enlarged, cross-sectional view of a known subassembly shown in FIG. 1;

[0036] FIG. 3 is a view similar to FIG. 1, in which known means allowing elastic longitudinal deformation of rails are added;

[0037] FIG. 4 is a cross-sectional view of said known subassembly and of said means allowing elastic longitudinal deformation of the rails;

[0038] FIG. 5 is a view of the known subassembly similar to FIG. 4;

[0039] FIG. 6 is a simplified top view of a known device according to a first embodiment;

[0040] FIG. 7 is a simplified top view similar to FIG. 6 of a known device according to a second embodiment;

[0041] FIG. 8 is a very simplified top view of one of the subassemblies making up this device situated on a lateral side of the film to be stretched, according to a first embodiment;

[0042] FIG. 9 is an enlarged cross-sectional view of this subassembly, according to a first implementation;

[0043] FIG. 10 is a view of the subassembly similar to FIG. 9, according to a second implementation;

[0044] FIG. 11 is a view of said subassembly similar to FIG. 8, according to a second embodiment; and

[0045] FIG. 12 is a cross-sectional view of this subassembly.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0046] FIG. 8 shows one of the lateral subassemblies 1 comprised by a device for stretching a thermoplastic film F on one side of this film, the device including a second subassembly, identical to the illustrated first subassembly 1, arranged on the other side of the film F, symmetrically to this first subassembly 1 relative to the longitudinal median axis of the film F.

[0047] It will be understood that this FIG. 8 resembles FIG. 1, and FIG. 9 resembles FIG. 2; they include: [0048] the film F; [0049] the arrow AvF depicting the direction of advance of the film F in the heating tunnel making it possible to make the material of this film malleable; [0050] the first and second guide rails R1, R2; the second rail R2 converges toward the first rail R1 towards the downstream direction; [0051] the grasping members 2, including clamps 3 for grasping a lateral edge of the film F, engaged on the first rail R1; [0052] the guide members 4 engaged on the second rail R2; [0053] first pairs of connecting rods 5 connecting a grasping member 2 to a guide member 4; [0054] the base 6 connecting the rails R1, R2 to one another; and [0055] rollers 7 equipping the grasping members 2 and the guide members 4 and rolling against the inner and outer faces and the upper and lower edges of these rails.

[0056] The subassembly is also equipped with the same means as those previously described in reference to FIGS. 3 and 4 (articulated frames C, slides Co, screws V and table T) so as to make it possible to produce an inflection of the rails R1, R2 like that shown in FIGS. 6 and 7 to allow stretching of the film F in a direction transverse to the direction of advance of this film.

[0057] As illustrated, unlike FIG. 1, each guide member 4 is connected to a single grasping member 2 by a single pair of superimposed connecting rods 5, hereinafter called first connecting rods, which is connected to an adjusting beam 10 by a pair of second connecting rods 11, having a length smaller than that of the first connecting rods 5.

[0058] The first axes along which the first connecting rods 5 are movable relative to the corresponding grasping member 2 and guide member 4 are parallel to the second axes along which the second connecting rods 11 are movable with respect to the corresponding guide members 4 and the adjusting beam 10.

[0059] On the side of the guide member 4, the second axis is formed by a pivot 15, and, on the opposite side, this second axis is formed by a pivot 16 on which two rollers 17 are mounted, these rollers being received and able to roll inside a slot formed by the beam 10.

[0060] As shown in FIG. 9, the beam 10 has an upside down U-shaped cross-section, in order to form said slot. This beam 10 has openings arranged in its central wall, in portions overlapping articulations of the frames C as shown in FIG. 3; these openings allow the transverse deformation of this beam 10 such that it can follow the inflection given to the rails R1 and R2 to perform transverse stretching of the film F.

[0061] The beam 10 is connected to posts 20, arranged at identical or similar intervals along the length of this beam. The base of the upright of each post 20 is secured to a nut 21 traversed by a screw 22 perpendicular to the direction of advance AvF of the film F; this screw 22 traverses the flank of the base 6 bearing the second rail R2 and is rotatable relative to this flank while being stopped relative thereto in the axial direction, for example by pins. Each screw 22 is connected to means for maneuvering it in rotation, such as a wheel or a motor; the actuation of the different screws 22 in one rotation direction or the other of these screws makes it possible to move the assembly formed by the posts 20 and the beam 10 in a direction perpendicular to the direction of advance AvF of the film F.

[0062] It is understood that these screws 22 and nuts 21 thus make up means for adjusting the position and orientation of the beam 10 relative to the first rail R1 and the second rail R2.

[0063] Considering FIG. 8, it appears that the beam 10 is positioned close to the first rail R1, while being substantially parallel to this rail R1; due to the convergence of the rail R2 toward the rail R1 in the downstream direction, the movement of the members 2 and 4 along these respective rails R1, R2 leads to gradually opening the angle formed by the pairs of second connecting rods 11 connected to one another, such that the distance between two consecutive members 4 increases in the downstream direction, and therefore such that, in a manner multiplied by the connecting rods 10, the distance between two consecutive members 2 increases correlatively.

[0064] Comparing FIGS. 1 and 8, it appears that, in the device according the disclosed embodiments shown in FIG. 8, the lengths of the second connecting rods 11 are added to the lengths of the first connecting rods 5 as regards to the maximum possible gap between two consecutive grasping members 2, and that they thus make it possible to obtain a substantially higher longitudinal stretching rate relative to what was allowed by the existing devices as shown in FIG. 1.

[0065] Still in reference to FIG. 8, it is understood that the orientation of the beam 10 relative to the rails R1, R2 makes it possible to influence the evolution of the gap between the grasping members 2 along the rails R1, R2, and therefore to adjust the longitudinal stretching rate of the film F, with the possibility of producing a so-called negative longitudinal stretching rate, i.e., with the two successive grasping members 2 coming closer together. Thus, if the beam 10 is oriented such that the downstream portion of this beam approaches the rail R2 in the downstream direction, said beam will make it possible to obtain a gradual opening of the angle between the successive pairs of second connecting rods 11 in the downstream direction, in addition to what is provided by the convergence of the rail R2 with the rail R1 in the downstream direction; the beam 10 will therefore make it possible to obtain an increase in the longitudinal stretching rate; on the contrary, if this same beam 10 is oriented such that a downstream portion of this beam moves away from the rail R2 in the downstream direction, said beam will provide a gradual closing of the angle between the successive pairs of second connecting rods 11 in the downstream direction, subtracted from the opening of these second connecting rods 11 provided by the convergence of the rail R2 with the rail R1 in the downstream direction; the beam 10 will therefore provide a decrease in the longitudinal stretching rate.

[0066] FIG. 10 is a view similar to FIG. 9, showing another alternative implementation in which the subassembly 1 comprises a second assembly of said second connecting rods 25 connected to a second adjusting beam 26, arranged on the side opposite that on which the first connecting rod 11/beam 10 assembly is arranged; this second assembly allows a better distribution of forces when the device is intended to withstand substantial forces. It appears that the posts 27 of the second assembly join the posts 20 of the first assembly at the nut 21 and that they can therefore be actuated simultaneously, using the same screw 22.

[0067] FIGS. 11 and 12 show a second embodiment of the device according to an invention; for simplification reasons, the parts or elements of the first embodiment already described above will be designated using the same numerical references and will not be described again. In this second embodiment, each pair of second connecting rods 11 extends on the side of the second rail R2 opposite the first rail R1. In this case, there is no beam 10, but instead, a rail 30 similar to said first or second rails R1, R2, having guide parts 31 engaged on it and movable along it, like the parts 4, each of these guide parts 31 being secured to a pivot 32 on which said second connecting rods 11 are pivotably mounted. The rail 30 is secured to bases 36 fastened to it at similar or identical intervals over its length, connected to nuts 21 engaged with screws 22, to adjust the position and orientation of the rail 30.

[0068] As appears from the preceding, the disclosed embodiments provide a device having the decisive advantages set out above relative to the similar devices of the prior art.

[0069] In particular, the device according to the disclosed embodiments allow, for optimal films, a very precise adjustment of the isotropy of the refraction index of the produced films, since for this type of film, a fixed transverse stretching rate is completely acceptable, as long as the possibility of adjusting the longitudinal stretching rate allows an orientation of the crystalline structures in the film by the desired angle, while guaranteeing extreme precision of the positioning of the clamps between the right side and the left side of the film.

[0070] For the membranes, and in particular for those intended to manufacture high-performance batteries, the device according to the disclosed embodiments make it possible to obtain perfect isotropy of the porosity of the film over the entire length of the film, which requires that for a given transverse stretching rate, which may be fixed with no drawbacks, the longitudinal stretching rate be distributed along the transverse stretching as a function of what is exactly necessary to obtain a 90 orientation over the entire film portion, and therefore the desired porosity isotropy.

[0071] The disclosed embodiments have been described above in reference to embodiments provided as examples. It is of course not limited to these embodiments, and the scope of protection is defined by the appended claims.