FR2646124A1 - Method and device for the continuous shaping of sheets or films made of thermoplastic material - Google Patents

Abstract

Device for the purpose of continuously shaping a web made of thermoplastic material, and especially a plastic mesh of lacunate structure having a square or diamond-shaped mesh cell, the device being of the type comprising a reel 1a for storing the web consisting of the thermoplastic mesh 1, a plurality of guide rollers 2, a heating chamber 3 and means for guiding the web 1 for a suitable time within this chamber where it is subjected to thermal softening, take-off rollers 5 for driving and possibly stretching the primary web upon leaving the heating chamber, and the device is characterised in that it also comprises rollers 10 for working the web, at least one of the rollers comprising heating means suitable for providing an intense but localised heating effect in order to cause, at the appropriate place, a localised temperature rise leading to a physical deformation of the web bringing it into the desired final state; the web is especially a lacunate mesh which receives localised perforations consisting of rupture initiators in the links constituting the said web.

Description

The present invention relates to a process, as well as a device for the implementation of this process, and allowing the shaping and the continuous working of materials in the form of sheet or films of thermoplastic material.
Numerous processes are known which allow the production of continuous sheets wound on a reel, and made of a thermoplastic material with incomplete structures.

 in the processes generally used the thermoplastic material is extruded from a die while mechanical or pneumatic devices are actuated opposite this die so. to interrupt by zones and momentarily the flow of extruded thermoplastic material, thereby causing distributed perforations on the surface of the sheet.

Generally the tube extruded by the annular die is then split according to a generator which allows the production of a continuous strip of lacunar structure thus forming a grid, mesh or net.

Such products have multiple applications, in particular for constituting barriers, fences, warning and marking plies of pipes buried in the ground, or even product packaging.
However, it is sometimes necessary to transform, after its production, the incomplete material or thermoplastic mesh produced to give it a shape or dimensions corresponding to a particular or more specific use.

It may thus be desired to conform the continuous sheet according to a reduced material density, in particular for the purpose of economy or with a view to improved efficiency, just as it may be necessary to practice in this sheet the additional openings by cutting off certain areas of so as to end up with more elaborate products that meet specific specifications.

The invention aims to allow the shaping of plastic nets or grids in order to transform the physical state of the initial grid and to lead it to a final state, after deformation, sectioning,
suitable for a more specific job or application and for which modifications of the initial product appear necessary or desirable.

In the context of the present invention, the thermoplastic characteristics of the material are used to bring it to a physical state which will allow it to undergo the programmed modifications.

To this end, the invention relates firstly to a process for the continuous shaping of sheets or films of thermoplastic material and comprising the succession of the following operations.

the film of thermoplastic material is unrolled continuously from a storage reel and it is led by guide rollers to circulate in an enclosure provided with heating means, for a duration and at a temperature such that the film is brought to the exit from the enclosure, by thermal softening, to a plastically deformable state, - and the film is led in this state to pass on rolls of call and work where it undergoes operations leading to physical deformations bringing it to the state desired end.

According to a first embodiment, the film consists of a plastic grid of incomplete structure with square meshes or in diamonds.

More specifically and according to one embodiment of the invention, the sheet of thermoplastic material is called, at the outlet of the heating chamber, by rollers driving this sheet at a traveling speed greater than the speed of the upstream rollers, causing traction on the softened sheet itself causing stretching and elongation of the sheet.

We will prefer a speed of the take-up rollers between 1.5 and 5 times the speed of the upstream rollers.

And more especially the stretching of the sheet in the state of thermal softening, is conducted so as to cause a molecular reorientation of the long polymerized chains constituting the thermoplastic material1 thereby causing the alignment of these molecular chains in the same direction and in parallel to the stretching of the sheet thus causing a reinforcement of the latter.

According to another embodiment, the operations to which the softened sheet is subjected when leaving the heating enclosure, causes deformation of the. tablecloth by creating relief inequalities on the latter.

One can in particular provide that these unevenness in relief cause a hollow or relief inscription on the surface of the sheet.

According to one characteristic, the operations to which the softened sheet is subjected cause perforations in the sheet creating points or lines of weakness, constituting the beginnings of ruptures in its links or cords constituting the meshes of the lacunar sheet.

The invention also relates to a device for implementing the method, and this device
comprises a reel for storing the thermoplastic ply, a plurality of guide rollers, a heating enclosure and means for guiding the primary ply for an appropriate time within this enclosure, where the primary ply undergoes thermal softening, rollers of call to entrain and possibly stretch the primary sheet out of the heating unit.

And according to the invention the disposi.ti # also includes rolls for working the ply, rollers comprising these heating means distributed suitably.

Or it can be provided that the heating rollers are arranged so as to ensure an intense but occasional heating effect for example to cause at the appropriate level temporary thermal elevation effects causing a rupture of the links located opposite the heating points.
And the invention also relates to the products thus obtained.

In particular, the invention relates to a sheet of lacunar structure, forming grid or net, whose filiform elements, constituting the sides of the meshes, have undergone a stretching, causing the reorientation of the polymer molecules constituting the material with a reinforcement of these elements.

Other characteristics and advantages of the invention
will emerge from the description which follows and which is given in
report with some particular embodiments presented as examples.

FIG. 1 represents a view of a diagram of an embodiment of a first form of the invention.

Figure 2 and Figure 3 show two details showing heating rollers capable of allowing the work of the web out of the heating chamber.

By considering all the figures we see that the tablecloth
1 consisting of a film or mesh extruded in thermoplastic material and wound on the storage reel
the.

This ply 1 is guided and driven on the cylinders 2 G at a given speed W.

The tablecloth - then passes into a heating enclosure ~ 3 the heating means can "be this any suitable nature and be made up of a fluid medium (liquid or gaseous) brought to an appropriate temperature; the heating means can also act by radiation (infrared ray tube).

The passage time and the temperature of the medium in the heating enclosure are calculated so as to allow the sheet leaving this enclosure to be brought into a state of thermal softening corresponding to a plastically deformable state.

To this end, the sheet 1 passes over one, or possibly several return rollers 4 disposed within the heating enclosure 3.

Leaving the enclosure, the primary ply 1 passes over the take-up rollers 5 which are driven at a speed Vt greater than 2 V; the ratio between V 'and V can be between 1.5 and 5 or possibly more depending on requirements.

It is understood that the traction exerted on the primary ply by the take-up rollers 5, driven at a speed greater than the speed of the rollers 2, causes traction and stretching on the ply 1.

For this purpose the cylinders 2 and 5 are driven by motorized variators allowing the input and output speeds of the product to be modified at will.

Stretching makes it possible to reduce the density of material within the grid, therefore acorister, for the same weight of material, the surface, that is to say in fact the length of the usable ply.

In addition, the stretching causes an orientation of the polymer molecules of the plastic with a parallel alignment of the long chains of the polymers which were dispersed in any way during the initial extrusion operations.

 The molecular orientation provides the final web with increased tensile strength.

According to a variant or parallel to the previous stretching, the primary ply 1 can be brought to undergo other operations in particular by passing over the drum 6; the latter may include on its surface notches or notched combs mounted on a support itself heated by internal electrical resistances to the rollers.

So that the plastically deformable material, leaving the heating chamber, is easily worked by the cylinder 6 to cause local deformations or relief formations at the level of the imprint 16, i7 (Figure 3).

Claims (9)

REYENDICATIONS 1 - Device for the continuous shaping of a sheet of thermoplastic material and in particular of a plastic grid of incomplete structure with square or diamond mesh, the device being of the type comprising a storage reel (la) of the sheet made up of the thermoplastic grid (i), a plurality of guide rollers (2), a heating enclosure (3) and means for guiding the sheet (i) for an appropriate time within this enclosure where it undergoes thermal softening, take-up rollers (5) for entraining and optionally stretching the primary ply leaving the heating chamber, and the device is characterized in that it also comprises rollers (10) for working the ply, one of the rollers at least comprising heating means capable of ensuring an intense but punctual heating effect to cause at the appropriate level a punctual thermal elevation effect causing physical deformation of the sheet bringing it to the desired end state. 2 - Device according to claim 1 above, characterized in that the punctual heating means are provided to cause zones or lines of weakness in the sheet in particular the incipient ruptures in the links or cords constituting the meshes of the lacunar grid . 3 - Device according to one of claims 1 or 2 above, characterized in that it comprises a drum (6) having on its surface engravings or notched combs mounted on a support itself heated by electrical resistances internal to rollers. 4 - Device according to claim 3 above, characterized in that the notches or notched combs mounted on said drum and provided with electrical resistances are capable of causing in the grid local deformations or formations of reliefs or impressions (16, 17) . 5 - Device according to one of claims 3 or 4 above, characterized in that said engravings or notched combs mounted on the drum (6) and heated by electrical resistances are capable of causing a punctual thermal elevation effect a rupture links located opposite the heating point. 6 - Device according to one of claims 3 or 4, and for the production of incomplete structure grids for the identification of pipes, characterized in that said engravings or notched combs mounted on the drum (6) and heated by electrical resistances are capable of causing, by a pontic thermal elevation effect, perforations in the sheet creating points or lines of weakness constituting incipient fractures in the links or cords constituting the meshes of the lacunar sheet. 7 - Dispostif according to one of claims 3 or 4 above, characterized in that said engravings or notched combs. are able to cause a hollow or raised inscription on the surface of the sheet. 8 - Device according to one of claims 1 to 7 above, characterized in that the take-up rollers (5) are provided to stretch the sheet out of the heating chamber, the speed of rotation of the rollers call being greater than the speed of unwinding of the storage reel, thus causing the alignment of the molecular chains parallel to the stretching of the web and a strengthening of the latter.  g - Grid with a lacunar structure applicable in particular for the identification of pipes buried in the ground, characterized in that it is obtained by the implementation of the device according to one of claims 1 to 7 above and characterized in that '' it includes unevenness in relief and in particular primers for ruptures in the links or cords constituting the meshes of the sheet of the lacunar grid, these primers for ruptures having been obtained by passing over a drum comprising notches or notched combs provided with means heating and in particular electrical resistances.  10 - Grid of lacunar structure according to claim 9 and characterized in that the incipient fractures consist of perforations creating lines of weakness in the links or cords constituting the meshes of the lacunar sheet.