FR2633215A1 - Method and device for the continuous shaping of thermoplastic sheets or films - Google Patents

Abstract

Method for the continuous shaping of thermoplastic sheets or films, characterised by the succession of the following operations: - the thermoplastic film 1, especially having a lacunate structure, is continuously unwound from a storage reel 1a and is led via guide rollers so as to run into a chamber 3 provided with heating means, for a duration and at a temperature such that the film is brought, upon leaving the chamber, via thermal softening, into a plastically deformable state; - and the film is made to pass in this state over lap rollers 5 and working rollers 6, 10, 11 where it undergoes operations involving physical deformations bringing it into the desired final state, especially an elongation with molecular orientation of the material, or lamination of a sheet or filament 18, printing or setting into relief or even creation of rupture initiators. The invention also relates to the plant for implementing the method and the products obtained thereby.

Description

The present invention relates to a method and a device for carrying out this method, and allowing the shaping and continuous working of materials in the form of sheets 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 as to interrupt by zones and momentarily the flow of extruded thermoplastic material, thereby causing perforations distributed over the surface. of the tablecloth.

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

Such products have multiple applications, in particular for constituting barriers, fences, warning and detection 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 ply 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 make additional openings in this ply by sectioning certain zones. or to incorporate into the primary ply, a elongated element (linear or itself in the form of a film or sheet), so as to result in more elaborate products and meeting 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, cutting, or addition of added, suitable elements. to fulfill a more specific use 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 characterized by 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 over rolls of call and work where it undergoes operations leading to physical deformations bringing it to the 'desired end state.

According to a first embodiment, the film consists of a plastic grid of incomplete structure with square or diamond mesh
More specifically and according to one embodiment of the invention, the sheet of thermoplastic material is called, at the exit from 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 11 stretching and elongation. of the tablecloth.

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 carried out so as to cause a molecular reorientation of the long polymerized chains constituting the thermoplastic material, thereby causing the alignment of these molecular chains in the same direction and 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 a deformation of the sheet by creating unevenness in relief on the latter.

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

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

According to yet another characteristic, the operations to which the ply is subjected constitute in the supply and the joining to the surface of said primary ply, of a secondary element called up and added continuously by constituting a multilayer ply.

For example, the secondary element attached to a structure of sheets or sheets and the two sheets respectively primary and secondary are laminated one on the other by two calendar rollers.

And in this case, according to a characteristic of the process thus implemented, the secondary ply is brought into contact with the primary ply (in the thermiquerent softened and plastically deformable state), being itself heated so as to cause its surface softening to thus perfect the adhesion of the two plies for the proàucvion of a complex multilayer ply.

And the secondary tablecloth can consist of a sheet of continuous structure, while the primary tablecloth consists of a discontinuous gap structure; the secondary state tablecloth, for example produced itself from a synthetic film, paper tablecloth, nonwoven or textile.

According to another embodiment, the element attached to the primary ply is itself of filIform linear structure.

And it may especially be a coated metallic cable, the coating, for example lul-meme thermoplastic, allowing after heating of this coating, an intimate adhesion of the coated wire on the primary ply.

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

And according to a variant, the device also comprises rollers for working the ply, rollers comprising heating means suitably distributed.

 The heating rollers may in the first instance conduct heat over all of their surfaces.

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 the links located opposite the heating points to break.

According to a variant of the device, there is provided at the exit from the sheet at least one roller comprising heating means and this roller comprises an annular groove allowing the insertion of a wire, the groove being of suitable diameter so as to allow a part of the wire to the outside, the heating roller making it possible to secure the connection of the wire to the primary ply.

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, the filiform elements of which constitute the sides of the meshes have undergone stretching, causing the reorientation of the polymer molecules constituting the material with a reinforcement of these elements.

The invention also relates to complex lacunar structures, on which a continuous filiform or sheet element is attached, secured to the primary ply by calendar rollers supplied with the primary ply in its softened state at the exit from the heating enclosure.

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

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

Figure 2 and Figure 3 show two details mont-rant heating rollers capable of allowing the work of the primary sheet leaving the heating chamber.

Considering all of the figures, it can be seen that the primary ply 1 consisting of a film or mesh extruded in thermoplastic material and wound on the storage reel 1a.

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

The primary then passes into a heating enclosure 3; the heating means can be of any suitable nature and consist of a fluid arlieu (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 primary sheet, on leaving this enclosure, to be brought to a state of thermal softening corresponding to a plastically deformable state.

To this end, the ply 1 passes over one, or possibly several deflection 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 V ′ greater than 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 decrease the density of material within the grid consequently to increase, 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 dobby 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 engravings or notched peggs 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 Impressions 16,17 (figure>).

According to an alternative embodiment, which can be combined with the previous ones, the softened and plastically deformable primary sheet leaving the heating enclosure is to add a counter-sheet or a second element unwound and called continuously and which is itself secured to the primary ply.

This added element can be a secondary sheet coming from the coil 5 and passing between the calendering rollers 1Q and li.

One or both of the cylinders 10 and 11 may themselves include heating means so as to ensure a good adhesion of the two sheets or sheets which are both brought to a neighboring state of roll-up allowing their mutual joining to form a multi-layer sheet.

The secondary ply may be of any suitable material, in particular be itself formed of a grid of different characteristics or else of a ply having a continuous surface; this sheet may be made of paper, cellulose, nonwoven fabric, fabrics or even a film of synthetic material.

According to a variant, the primary ply receives the contribution of a filiform element which can be positioned for example along the ply; just as a plurality of parallel threadlike elements can be added.

These elements joined continuously on the sheet allow the introduction of reinforcement means.

One can in particular thus secure a metal cable; and advantageously the metal cable will be provided with an outer sheath made of synthetic material, in particular thermoplastic, and this outer sheath itself subject to softening will, by timing, adhere to the primary ply which is facing it being itself softened by effect thermal at the exit of the heating enclosure.

 In this case, it is advantageously possible to use a roller as shown in FIG. 2 and provided with a groove; the roller internally includes heating means acting in particular at the level of said groove; the groove 15 is designed to receive the wire and the roller 14 is applied against a counter-roller, so that the pressure of the filiform element (sheathed cable) on the primary ply in the softened state allows them to be joined mutual.

It is understood that the groove should have a diameter slightly less than the diameter of the sheathed cable so that the meeting of the two rollers results in a pressure at the sheathed cable on the primary ply.

Claims (13)

CLAIMS I - Process for the continuous shaping of sheets or films of thermoplastic material characterized by the succession of the following operations. - the thermoplastic film is unwound continuously from a storage reel and it is driven 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 leaving the enclosure, by thermal softening, in a plastically deformable state, - and the film is led in this state to pass on rolls of call and work where it undergoes operations causing physical deformations bringing it to the state desired end. 2 - Process according to claim 1, characterized in that the film consists of a plastic grid of incomplete structure with square meshes or diamonds. 3 - Method according to one of claims 1 or 2, characterized in that the sheet of thermoplastic material is called, at the outlet of the heating enclosure, by rollers driving this sheet at a traveling speed greater than the speed of upstream rollers, by pulling on the softened sheet itself causing the stretching and elongation of the sheet.  4 - Method according to one of claims 1,2 or 3, characterized in that the stretching of the sheet in the state of thermal softening, is carried out so as to cause a molecular recreating of the long polymerized chains constituting the thermoplastic material , thus causing the alignment of these molecular chains in the same direction and parallel to the stretching of the sheet, thus causing a strengthening of the latter. 5 - Method according to one of claims 1 or 2, characterized in that the operations to which is subjected the softened sheet leaving the heating chamber, causes a deformation of the sheet by creating unevenness in relief on the latter.  6 - Method according to claim 5, characterized in that said unevenness in relief causes a hollow or raised inscription on the surface of the sheet. 7 - Method according to one of claims 1 or 2, characterized in that the operations to which the softened sheet is subjected cause zones or lines of weakness in the sheet in particular incipient ruptures in the links or corsons constituting the meshes of the gap table. 8 - Method according to one of claims 1 or 2, characterized in that the operations to which the sheet is subjected constitute in the supply and the joining to the surface of said primary sheet, of a secondary element called and reported continuously by constituting a multilayer web. 9 - Method according to claim 8, characterized in that the added secondary element has a structure of sheets or sheets and the two sheets respectively primary and secondary are laminated one on the other by two calendaring rollers. 10 - Method according to one of claims 8 or i, characterized in that the secondary ply is brought into contact with the primary ply (in 11 thermally softened and plastically deformable state), being itself heated so as to cause its softening surface so as to perfect the adhesion of the two plies for the production of a complex multi-layer ply.  it - Method according to one of claims 8,9 or 10, characterized in that the secondary ply consists of a sheet of continuous structure, while the primary ply consists of a discontinuous gap structure; the secondary ply being for example itself made of a synthetic film, paper ply, nonwoven or textile. 12 - Process according to claim 8, characterized in that the element attached to the primary ply is lul-meme of linear thread-like structure and it is in particular made up of a metallic cable with coating, the coating for example lul-meme thermoplastique1 allowing after warming of this coating, an intimate adhesion of the coated wire on the primary web. 13 - Device for the implementation of the method according to one of claims î to 12, characterized in that it comprises a storage coil (la) of the primary web (i) thermoplastic, a plurality of rollers guide t2), a heating enclosure (3) and means for guiding the primary ply (i) for an appropriate time within this enclosure, where the primary ply undergoes thermal softening, rollers (5) for driving and possibly stretch the primary sheet out of the heating chamber.  14 - Device according to claim 13, characterized in that it also comprises rollers (10) for working the ply, at least one of said rollers comprising heating means distributed suitably. 15 - Device according to claim 13, characterized in that the heating roller or rollers (10) 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 links located opposite the heating points. 16 - Device according to claim 15, characterized in that at least one roller (10) provided with the heating means comprises an annular groove allowing the insertion of a wire, the groove being of suitable diameter so as to allow an overflow part of the wire to the outside, the heating roller making it possible to secure the connection of the wire to the primary ply.  17 - Tablecloth of thermoplastic material of incomplete structure, forming grid or net, characterized in that the 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, according to one of claims 1 to 4. 18 - Complex sheet, characterized in that it consists of a primary ply of thermoplastic material with a lacunar structure, on which a continuous filiform or sheet element is attached, secured to the primary ply by calendar rollers supplied with primary sheet in its softened state at the outlet of a heating enclosure, according to one of claims 8 to 12.