JP2009113488A - Method for stretching film made of synthetic material having slender strip shape - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for stretching a film made of a synthetic material, by which the film having increased mechanical characteristics in a longitudinal direction can be manufactured. <P>SOLUTION: In the method for stretching the film (1) made of the synthetic material having a slender strip shape, stretching of the film (1) is performed through a process of preheating the film (1), a process of stretching the film (1) in the longitudinal direction (17) and an additional process of stretching the film in a transverse direction (9). The process of stretching the film in the longitudinal direction (17) is performed after the process of stretching the film (1) in the transverse direction (9). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for stretching a film made of a synthetic material having the shape of an elongated strip.

  This type of method allows the production of films that are specifically intended for the production of packaging materials, capacitors or magnetic tapes. The film used in this way can be made of a thermoplastic such as polypropylene, polyester, polyamide, PVC or can be formed by a composite multilayer film.

  In many cases, such films are first stretched in the longitudinal direction and then in the transverse direction. In conventional methods, as described in WO 2004/088604, the liquid is circulated so that the raw material is first melted by an extruder and formed into a thick and narrow plate by a die to prevent crystallization of the film. And is continuously reheated by the cylinders to the stretching temperature so that it is stretched longitudinally between the variable speed cylinders.

  The film stretched in the longitudinal direction in this way enters the stretching device in the transverse direction, both edges of the film being held by two groups of scissors, respectively, and stretching the sheet in the transverse direction at a ratio of 2 to 10. So that they are guided by rails that are gradually separated from each other. The conventional scissors used are described in FR 2686041.

  The sheet stretched in this way is kept at a predetermined tension and temperature in a furnace in order to allow strain removal and crystallization of the film intended to fix the molecular structure. Then, as described in WO 98/25844, the film is cooled, the edges of the film are cut, and the film is wound on a winder.

  The most common reason for the aforementioned stretching sequence, i.e., stretching in the longitudinal direction, followed by stretching in the transverse direction, is that the economical production of packaging films is 4 to 10 meters wide. This is because a high-throughput apparatus capable of producing a film is required.

  Further, according to the prior art, the film is stretched in the longitudinal direction between cylinders that must be small in diameter so as to allow for a “short” stretch (see WO 2004/088604). Such a short stretch can prevent the film from shrinking during stretching in the longitudinal direction.

  As the width of the film increases, the length of the roller that allows stretching in the longitudinal direction increases and the diameter increases. As a result, it is necessary to reduce the width of the roller for stretching in the longitudinal direction so that short stretching can be performed. Therefore, the transverse stretching intended to increase the width of the film takes place after the longitudinal stretching.

  For this reason, such a device is a relatively simple design, and when stretching a narrow film, the stretching cylinder is forced to fit into a small diameter cylinder to perform a short stretching. Width.

  Conversely, a longitudinal stretching apparatus using a 6 to 8 meter wide cylinder has a fairly large cylinder diameter and cannot be adapted to a short stretch ratio. There is no such device in the prior art.

  With respect to the stretching of such films in the transverse direction, it is customarily known to use a stretching device in the transverse direction. In such a stretching device, the film is gripped at each edge by movable scissors and one scissor group moves away from the other scissor group.

  By such means, the applied mechanical member does not depend on the width of the film, so that it can be easily applied to the production of a very wide film. Today, transverse stretching means are known which allow the production of films of 6 to 10 meters wide.

  Stretching according to the above sequence (stretching in the longitudinal direction followed by stretching in the transverse direction) is the fact that in most cases the produced film requires storage of the stretched film. This has many disadvantages for the application device. This means that very high mechanical properties are still required in the final stretch that is received before crystallization.

  For this purpose, the film produced and wound according to the above sequence has mechanical properties in the transverse direction rather than in the longitudinal direction of the film. This is necessary to increase the required mechanical properties in the longitudinal direction of the film, especially if the film is not wound up to undergo printing, coating, metallization, or other forms of processing. Has the disadvantages.

  The object of the present invention is to overcome these drawbacks by proposing a method of stretching a film made of a synthetic material, which can produce a film with increased longitudinal mechanical properties. It is.

  Accordingly, the present invention is a method of stretching a film made of a synthetic material having the shape of an elongated strip, the stretching of the film comprising preheating the film and stretching the film in the longitudinal direction of the film. In a process carried out by continuously stretching the film through stretching means comprising an additional step of stretching the film in the transverse direction of the film, wherein the step of stretching in the longitudinal direction comprises: After the stretching step, the stretching method uses scissors, which are arranged to grip the first and second long edges of the film, respectively, and use movable first and second scissors groups. Each group is first guided away from each other to stretch the film in the transverse direction, and then stretched in the longitudinal direction. , As the spacing between adjacent scissors same group increases gradually to a method which is characterized in being moved parallel to the longitudinal direction of the film.

  In this way, the mechanical properties are increased in the direction of the final, ie stretching with respect to the longitudinal direction.

  In addition, the use of scissors to stretch in the longitudinal direction allows for easy application of wide films and allows considerable speed when stretching films instead of prior art rollers To. Thus, the speed of manufacturing, i.e. stretching the film, can be increased.

  Preferably, each set of scissors is divided into a group of scissors for stretching in the transverse direction and a group of scissors for stretching in the longitudinal direction.

  Effectively, during the longitudinal stretching process, the stretching of the film is performed by driving endless chains located on opposite sides of the film sandwiched between the first and second groups of scissors, Has a plurality of links articulated to each other, the links being moved away from or close to each other so that the spacing between two adjacent scissors can be increased or decreased.

  According to one aspect of the invention, the first and second groups of scissors are closed to grip the film, with the scissors closed to grip the film at opposite edges of the film. And a zone for stretching the film in the longitudinal direction and a continuous path along the closed path through which the scissors are opened and the zone for releasing the film.

  Preferably, each of the endless chains is arranged downstream of the zone for releasing the film, and first and second wheels arranged upstream of the zone for gripping the film in the direction of movement of the chain. Driven by the third and fourth wheels, the second wheel is arranged downstream of the first wheel, and the rotational speed of the second wheel is faster than the rotational speed of the first wheel, The fourth wheel is disposed on the downstream side of the third wheel, and the rotation speed of the fourth wheel is slower than the rotation speed of the third wheel.

  This aspect allows for recompression of the chain between the third and fourth wheels and the tension of the chain between the first and second wheels.

  In any case, the invention will be better understood with the aid of the following description, with reference to the accompanying schematic drawings, as an example of an embodiment of the device of this drawing.

  FIG. 1 shows a line for manufacturing the synthetic film 1. This line has an extruder that can extrude the film in the form of a wide and elongated strip.

  The film 1 is pressed against a cooling cylinder, that is, a molding drum 3 by, for example, an electrostatic press device 4. The film 1 generated from the electrostatic pressing device 4 passes through a stretching device 5 in a transverse direction and then a stretching device 6 in a longitudinal direction before being wound around a storage roller by a winder 7.

  The transverse stretching device 5 has a preheating zone 8, a zone 9 for stretching in the transverse direction, and a zone 10 for stabilizing the film 1. A furnace 11 is provided in each of the preheating zone 8 and the transverse stretching zone 9, and the temperatures of these furnaces are controlled as necessary.

  In particular, the laterally extending zone 9 has first and second scissors mounted respectively on first and second endless chains 12, 13 driven by gear wheels indicated by an axis in the drawing. Groups (not shown) are provided. These scissors are therefore movable and driven continuously along a closed path along the aforementioned continuous zones 8, 9, 10 of the transverse stretching device 5.

  The chains 12 and 13 are guided by rails arranged on both sides of the center plane of the production line at the level of each edge of the film. These rails extend away from each other at the transverse stretching zone 9 and are substantially parallel in the preheating zone 8 and the thermal stabilization zone 10.

  The scissors can be driven between a closed position and an open position. In the closed position, these scissors grip both edges of the film 1 and in the open position release these edges. A zone for gripping both edges of the film by a group of opposing scissors is located upstream of the preheating zone 8, and the zone for releasing the film is the stability of the film. It is arranged on the downstream side of the conversion zone 10.

  Therefore, during operation, the film 1 fed from the cooling roller 3 is gripped by the scissors on each of the edges 14 and 15 of the film, the preheating zone 8, the transverse stretching zone 9, and Pass through thermal stabilization zone 10. In the transverse stretching zone 9, the rails are separated from each other so as to stretch the film 1 in the transverse direction.

  The film is then directed to the longitudinal stretching device 6. The longitudinal stretching device 6 has a preheating zone 16, a zone 17 for stretching in the longitudinal direction, and a thermal stabilization zone 18. Each of these zones is provided with a furnace 11 and the temperature of these furnaces is controlled.

  The longitudinal stretching device 6 has first and second endless chains 19, 20 arranged symmetrically with respect to the longitudinal center plane A of the device as described above. These endless chains 19, 20 and their guiding means will be described with reference to FIG. 2 showing the details of the longitudinal stretching zone B and the following figures.

  Each of the chains 19, 20 consists of a series of links, indicated alternately by reference numerals 21,22. These links are articulated to one another along a vertical axis indicated alternately by reference numerals 23 and 24.

  The scissors 25 project from one side of the chain 20 and are articulated at the respective axis 23 of the articulation between the two links, ie the link 21 and the link 22, to the first rail. 26 is guided. Similarly, between each two links, but the scissors 25, i.e. at the axis 24 of each of the articulations, a guide member 27 protrudes on the other side of the chain 20 and on the second rail 28. Are articulated to move.

  The two rails 26, 28 are in the form of a monorail in the form of a vertical plate. The two rails 26 and 28 are held at a predetermined distance from each other (see the following description) by a common T-shaped support or by separate supports 29 and 30 (see FIG. 4). be able to.

  Each of the scissors 25 has a main body such as a carriage, and supports a vertical axis roller 31 that rolls on the side surface of the rail 26 and a horizontal axis roller 32 that rolls on the upper surface of the rail 26. . Similarly, each of the guide members 27 forms a carriage including a vertical axis roller 33 that rotates on the two side surfaces of the rail 28 and a horizontal axis roller 32 that rotates on the upper surface of the rail 28.

  For each of the scissors 25 body and each of the guide members 27, the lateral rollers 31, 33 are in this example two upper rollers and two on either side of the rail 26 or 28. And a lower roller. These two upper rollers, as well as the two lower rollers, may have a few vertical steps to fit each other for spacing reasons.

  The two rails 26 and 28 have a space that can change between a maximum value E (see the left side of FIG. 2) and a minimum value e (see the right side of FIG. 2). The two rails 26, 28 can be moved parallel to each other, close to each other, or further away from each other (see the central part of FIG. 2). The distance between the two rails 26 and 28 is determined by the distance between the two adjacent scissors 25.

  In particular, if the two rails 26, 28 have a maximum distance E, the links 21, 22 of the chain 20 are on the one hand between the alignment of the scissors 25 and on the one hand the alignment of the guide member 27. The zigzag structure given by the maximum distance E is formed.

  If the two rails 26, 28 are kept parallel and at a maximum distance E, the distance between the adjacent scissors also remains constant and equal to the minimum value d.

  Conversely, if the two rails 26, 28 have a minimum distance e, the chain links 21, 22 are on the one hand the alignment of the scissors 25 and on the other hand the alignment of the guide member 27. A straight line corresponding to the minimum interval. The interval between the two adjacent scissors 25 takes a maximum value D.

  If the two rails 26, 28 are parallel and have a minimum distance e, the distance between adjacent scissors 25 remains constant and equal to the maximum value D.

  On the other hand, when the distance between the two rails 26 and 28 changes, it is easily understood that the changeable distance between the two rails and the change in the distance between adjacent scissors are also determined. In particular, the change in the spacing between the two rails 26, 28 controls the opening and closing of the angle between the adjacent links 21, 22 of the chain 20, so that the two adjacent scissors 25 are closer or further apart from each other. Move to.

  Therefore, in the preheating zone 16 and the thermal stabilization zone 18 of the longitudinal stretching device 6, the rails 26, 28 are arranged substantially parallel to each other. In this thermal stabilization zone 18, these rails 26, 28 give a slight contraction of the film 1 under controlled tension, or in the transverse direction performed by the transverse stretching device 5. Can be arranged to slightly compensate for stretching.

  The length of the thermal stabilization zone 18 must be long enough to allow the film 1 to crystallize. Also, during the crystallization, the heat stabilization zone is kept under a predetermined tension by the scissors 25.

  As can be seen in FIG. 2, in the longitudinal stretching zone 17, the rails 26, 28 cause the scissors 25 to move gradually away to give the film 1 a longitudinal stretching. The film 1 and the scissors 25 move toward each other in the direction of movement.

  However, the rails 26, 28 arranged on both edges 14, 15 of the film 1 remain substantially parallel so that the width of the film 1 does not change significantly when passing through the longitudinal stretching device 6. Yes.

  As described above, the film 1 sent from the stretching device in the longitudinal direction is wound around the storage roller by the winder 7. The film thus obtained can range from 6 to 10 meters.

  The longitudinal stretching device 6 has four gear wheels on one surface of the film 1 and can drive each of the endless chains 19 and 20.

  In particular, the longitudinal stretching device 6 has first and second gear wheels 35, 36 arranged upstream of the zone for gripping the film in the direction of movement of the chains 19, 20. . The second wheel 36 is disposed on the downstream side of the first wheel 35. Further, the rotational speed of the second wheel 36 is faster than the rotational speed of the first wheel 35. The longitudinal stretching device 6 also has third and fourth gear wheels 37, 38 arranged downstream of the zone for releasing the film. The fourth wheel 38 is disposed on the downstream side of the third wheel 37. The rotational speed of the fourth gear wheel 38 is slower than the rotational speed of the third wheel 37.

  These aspects include the recompression of the chain between the third and fourth wheels and the bottle of the chain between the first and second wheels so as to define a stable equilibrium position. The purpose is to make it possible.

  The stretching method according to the present invention has the following effects. The stretching device in the transverse direction is small in size compared to the prior art and is therefore low in cost.

  Furthermore, the film sent directly from the cooling roller (that is, the forming drum) 3 has a speed corresponding to the speed of this roller, whereas in the prior art, a film oriented to stretch in the transverse direction is Usually, it corresponds to the speed of the drum to which the stretching speed in the longitudinal direction of 2 to 10 is added. In the case of the present invention, the film engaged with the transverse stretching device 5 is slow and rather thin. Therefore, such a film can be easily stretched even if the length of the stretched portion is not long. In the case of the prior art, since the film is stretched longitudinally before the transverse stretching device is applied, if the film is thin, the stretched part needs a considerable length and is therefore short. It will be apparent that it cannot withstand a sudden stretch of length.

  Furthermore, the film stretched in the transverse direction does not need to be crystallized because other stretching is also required. As a result, it is not necessary to provide a very long stabilization zone 10.

  Another effect is that the width of the film at the inlet and outlet of the longitudinal stretching device 6 is actually the same, except for the possibility of slight shrinkage or stretching.

  In this way, the various scissors 25 used to move along the rails 26, 28 are substantially parallel and can limit friction at these rails 26, 28. As a result, production rates well beyond current device speeds can be achieved without providing any system for the mechanical tension of the chain.

  The third effect of the present invention is that the two stretching operations are performed in the air, that is, without contacting the cylinder. In particular, the outer layer of the film can be formed of a low melting point polymer so that the film can be easily sealed. In the case of the present invention, such a film can be heated to avoid contact with the cylinder and damage. Furthermore, stretching in air makes it possible to reduce surface defects. This is very important for such forms of film, especially where it is necessary to enhance the optical properties.

  Needless to say, the present invention is not limited to the embodiment of the film stretching apparatus, but includes all the various embodiments and application apparatuses according to the same principle.

FIG. 1 is a schematic view from above of a production line capable of carrying out the method according to the invention. FIG. 2 is a plan view from above on an enlarged scale corresponding to zone A of FIG. FIG. 3 is a partial perspective view of the chain of the apparatus with scissors and guide members of the present invention. FIG. 4 is a sectional view of the apparatus. FIG. 5 is a side sectional view from the direction of arrow F5 in FIG.

Claims (5)

A method of stretching a film (1) made of a synthetic material having the shape of an elongated strip comprising stretching the film (1) by preheating the film (1) and The film (1) is passed through stretching means (5, 6) comprising a step of stretching in the longitudinal direction (17) and an additional step of stretching the film in the transverse direction (9) of the film. In a method performed by continuously stretching,
The step of stretching in the longitudinal direction (17) is performed after the step of stretching the film (1) in the transverse direction (9),
This stretching method uses a group of movable first and second scissors arranged to grip the first and second long edges of the film, respectively,
Each group of these scissors is first guided away from each other in order to stretch the film in the transverse direction, and then each group of scissors is stretched in the longitudinal direction. To move the film parallel to the longitudinal direction of the film as the spacing between adjacent scissors in the same group increases gradually.   Each of the sets of scissors is divided into a group of scissors for stretching the film in the transverse direction and a group of scissors for stretching the film in the longitudinal direction. The method of claim 1.   During the step of stretching in the longitudinal direction, the stretching of the film (1) is performed by endless chains (on both sides of the film (1) sandwiched between the scissors (25) of the first and second groups ( 19, 20), and each of the chains (19, 20) has a plurality of links (21, 22) articulated to each other, the links being adjacent to the two scissors (25 3. The method according to claim 2, characterized in that the distances (d, D)) can be increased or decreased, respectively, separated from each other or moved closer to each other. The first and second groups of scissors (25) are:
A zone for gripping the film, wherein the scissors (25) are closed to grip the film at the opposite edges (14, 15) of the film;
A zone for stretching (17) the film in the longitudinal direction;
4. A method according to claim 3, characterized in that the scissors (25) are moved continuously along a closed path which passes continuously through the opened zone for releasing the film. Each of the endless chains (19, 20) has first and second wheels (35) arranged upstream of the zone for gripping the film (1) in the direction of movement of the chains (19, 20). , 36) and third and fourth wheels (37, 38) arranged downstream of the zone to release the film,
The second wheel (36) is disposed downstream of the first wheel (35), and the rotational speed of the second wheel (36) is greater than the rotational speed of the first wheel (35). Further, the fourth wheel (38) is disposed downstream of the third wheel (37), and the rotational speed of the fourth wheel (38) is set to be the third wheel (37). 5. The method of claim 4, wherein the rotational speed is slower than

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