FR2871164A1 - Thermoplastic composition, used for manufacture of flat alveolar elements, comprises a polymer and/or copolymer resin comprising hot fluidity index of 0.8-40 g/minute and further comprises natural and/or synthetic fibers - Google Patents

Abstract

Thermoplastic composition (A) for manufacture of flat alveolar elements with one or two walls comprising transversal partitions of width 50-5000 mu m (where the flat alveolar elements is obtained by extrusion and calendering), comprises at least a polymer and/or copolymer resin comprising hot fluidity index of 0.8-40 g/minute and further comprises at least a type of natural and/or synthetic fibers. Thermoplastic composition (A) for manufacture of flat alveolar elements with one or two walls comprising transversal partitions of width 50-5000 mu m (where the flat alveolar elements is obtained by extrusion and calendering) comprises at least a polymer and/or copolymer resin comprising hot fluidity index of 0.8-40 g/minute and further comprises at least a type of natural and/or synthetic fibers (having a length of 10-105> mu m and diameter, which is lower than the length) in suspension in the resin, such that the hot fluidity index of (A) is 0.1-0.8 g/minute for polyolefin and 1-8 g/minute for styrenic polymers. An independent claim is also included for a material (B) (in plate or sheet form) with a alveolar structure comprising: two walls (7, 10) (one assembled with other), which forms the main sides of (B); and a series of partitions (5) (having a width of 50-5000 mu m) perpendicular to the walls and connecting the walls (where: the first wall (7) having a base (6) and partitions are lugged from one of the sides of the base constituting the partitions; the second wall (10) is connected to the free ends (13) of the partitions of the first wall (7); the base (6) of the first wall (7) is constituted by a hot fluid thermoplastic resin comprising natural and/or synthetic fibers (having a length of 10-105> mu m and diameter lower than the length of the fibers); and if the partitions of the first wall (7) are constituted by the same thermoplastic resin, then the wall comprises fibers whose length is more than 50%, which is lower than the width of the partitions and the diameter is lower than the length).

Description

The present invention relates to a thermoplastic composition for

  the manufacture of extruded cellular elements by extrusion then calendering and the cellular material obtained from this composition.

  "Flat cellular elements" means plates or sheets comprising two parallel walls which form the main faces of the material, and a series of partitions, parallel to each other and most often perpendicular to these walls, which connect these walls. between them.

  It is known to manufacture honeycomb plates by extrusion then calendering, as described for example in the patent application filed by the applicant and published under the number FR 2 828 132 A1. This method comprises the steps of: - extruding a thermoplastic composition by means of a conventional type extruder and a conventional flat die conforming this one-ply thermoplastic composition; - To use a shell having at least one cylinder in which are formed grooves of width I, I may be between 50 pm and 5000 pm, and to pass said layer against the cylinder while the material of this layer is to the plastic state, so that this passage develops, by creep of the material in said grooves, partitions on one of the faces of this layer, thus forming said first layer; to use two assembly cylinders located downstream of the grooved cylinder, and to pass said first layer thus formed between these cylinders, and to supply said second layer between these two assembly cylinders so that this second layer passes between these cylinders substantially at the same speed as the first layer and comes intimately in application on the free ends of the partitions of this first layer.

  The manufacturing method cited above provides the advantage, compared to conventional die extrusion processes, to give, if desired, a non-rectilinear appearance to the walls of the material, thanks to calendering. This makes it possible to improve the compressive strength of the material obtained as well as the folding resistance for a folding edge in the longitudinal direction of the grooves.

  However, this method does not improve the mechanical characteristics of the material when the partitions are straight and parallel to each other, and above all, this process retains the disadvantage of extrusion processes, namely the almost inevitable formation of shrinkage at right of the partitions during the cooling of the plates at the output of the manufacturing machine. This greatly limits the quality of the printing that can be obtained on the surface of the cellular material, because of the poor flatness thereof.

  In addition, in the extrusion-calendering manufacturing process as described above, the thermoplastic composition used is a material, generally polyolefinic, of the so-called "extrusion grade" grade, that is to say having a Melt flow index is generally included, for example for polyolefins between 0.1 and 0.8 g / min or between 1 and 8 g / min for styrenic polymers. Such a composition is therefore relatively viscous. This poses the problem of improper filling of the grooves of the calendering roll during the calendering operation, which can lead to a cellular material whose partitions are incomplete, and which is therefore weakened.

  The object of the present invention is therefore to provide a thermoplastic composition intended for the manufacture by calendering of flat cellular elements, which on the one hand makes it possible to limit the phenomena of shrinkage of material during its cooling, and thus improves the printability by limiting or even avoiding the use of surface preparation techniques of the elements thus produced with Corona type processes, and secondly, allows to strengthen the compressive strength of the resulting plate.

  The object mentioned above is achieved with a composition intended for the manufacture of single-walled or double-walled cellular elements having transverse partitions of width I between 50 μm and 5000 μm, these cellular flat elements being obtained by extrusion then calendering, said composition comprising at least one polymer and / or copolymer resin, characterized in that: (i) the melt flow index of said resin is between 0.8 and 40 g / min., and in that (ii) said composition further comprises at least one type of natural and / or synthetic fibers suspended in the resin, the length of which is between 10 μm and 105 μm and the diameter of which is less than the length, so that the melt flow rate of the composition is between 0.1 and 0.8 g / min for polyolefins and between 1 and 8 g / min for styrenic polymers.

  During the manufacture of a cellular sheet material by extrusioncalandrage, the composition according to the invention is first extruded in the form of a continuous sheet, then the latter passes between two calendering rollers, one of which has grooves to be able to form partitions, approximately of width I, to one of the faces of said plate, as explained above.

  According to the invention, during the calendering operation, the resin, of low viscosity, will flow very easily into the grooves, filling them quickly and completely. This very fluid resin comprises and carries with it in particular a majority of short fibers whose length is less than the width I. These fibers are of sufficiently small size to be able to pass into the grooves of the calender roll. In contrast, the majority of the longer fibers, of length greater than I, are retained at the base of the grooves of the calendering roll, and remain trapped in the base of the plastic layer thus formed.

  The high density of long fibers in the base makes it possible to limit or even eliminate sinkholes during cooling, and the low density, or even the absence, of long fibers in the partitions makes it possible to stiffen them and to increase the resistance. compression of the obtained material. In addition, the grooves of the calendering cylinder being correctly filled with a plastic material of high fluidity, the risk of poorly formed partitions is eliminated.

  In another advantageous version of the invention, the fibers of the composition are only fibers of length greater than the width I of the partitions so as to have in the partitions practically only pure resin which is therefore very fluid, which increases even more. the probability of filling the partitions even for very thin walls.

  According to a preferred embodiment of the invention, the melt index of the composition is between 0.3 and 0.5 g / min for polyolefins and 3 to 5 g / min. for styrenic polymers.

  Advantageously, the resin is chosen from the group of polyethylene resins, polypropylene, polycarbonate, polyvinyl chloride, polyamide, or styrenic polymers.

  In addition, the composition according to the invention preferably comprises between 5% and 50% of fibers, preferably between 15% and 50% of fibers, as a percentage of the weight of the composition.

  Preferably, the fibers are hollow fibers.

  Likewise, the fibers are preferentially chosen from the group of cellulosic fibers.

  Finally, according to a preferred variant of the invention, the composition further comprises at least one inorganic filler, for example chalk or talc and / or an expansion agent of the type for example diazocarbonamide or aluminum hydroxide. , the mineral fillers that can contribute to the internal sliding of the material, its rigidity and its printability, and the blowing agent, besides the well-known advantage of the corresponding lightening and material gain bringing here the advantage of a better guarantee of filling the grooves thanks to the thrust of the gases.

  The present invention also relates to a sheet or sheet material with a so-called "cellular" structure, that is to say comprising two walls joined to one another which form the main faces of the material and a series of partitions, perpendicular to these walls, which connect these walls to one another: - the first wall having a base and partitions of width between 50 and 5000 pm projecting from one of the faces of this base, which constitute said partitions, and the second wall being connected to the free ends of the walls of the first wall, characterized in that the base of the first wall is made of a very fluid thermoplastic resin hot (grade "injection") comprising natural fibers and / or synthetic materials of lengths between 10 pm and 105 pm and whose diameter is less than the length, so that the melt index of the composition is between 0.1 and 0.8 g / min for polyolefins and between 1 and 8 g / min for styrenic polymers, and in that the partitions of the first wall consist of the same thermoplastic resin and comprise fibers whose length is, for more 50% of them, less than the width I of the partitions, and whose diameter is less than the length.

  In a preferred embodiment of the invention, the partitions of the first wall consist of the same thermoplastic resin and comprise fibers whose length is, for all of them, less than the width I of the partitions, i.e. short fibers.

  In addition, and according to a preferred embodiment of the invention, the ribs of the first wall consist of the same thermoplastic resin and comprise less than one third of the total amount of fibers in the material.

  Preferably, the fibers used in this material are hollow fibers of cellulosic type and optionally, as said above, additives of the mineral fillers and / or expansion agent (s) type will advantageously be included in the material composition of this first and possibly second wall (s).

  Because of the length of fibers of the composition, greater than the width of the partitions, for the majority of said fibers, it is observed firstly that the long fibers, that is to say longer than I, are in very large numbers. lower in the partitions, compared to the number of long fibers present in the first wall, and secondly the total number of fibers in the partitions is much lower than the number of fibers in the wall of the material.

  This makes it possible to obtain good geometrical properties of these partitions, as well as a good demolding of the material obtained, out of the calendering roll.

  For a good understanding, the invention will now be described in detail, with reference to the attached schematic drawing, showing by way of non-limiting example, a particular embodiment of a foam material plate, obtained from a composition according to the invention.

  Figure 1 is a side view of a device for manufacturing a honeycomb plate by extrusion and calendering; Figure 2 is an enlarged sectional view of a cellular foam material obtained from a thermoplastic composition according to the invention.

  The composition according to the invention described here by way of example is a thermoplastic composition for the manufacture of flat elements by extrusion then calendering. It comprises a thermoplastic polypropylene resin whose melt index also called "MFI" for Melt Flow Index is 1.5 g / min.

  This composition further comprises hemp fibers suspended in the resin, whose length is between 10 and 2000 μm and whose diameter is between 1 μm and 150 μm, so that the melt index of the composition is about 0.25 g / min.

  The percentage of fibers in total weight of the composition is then about 30%, the remaining 70% being constituted by resin.

  During the manufacture of the extrusioncalandar cellular sheet material, as shown in FIG. 1, the composition according to the invention is first extruded in the form of a layer, from an extruder 1 provided with a flat die 2.

  Then there is used a calender having two cylinders 3, 4 in which are provided grooves here width 0.4 mm (400 pm), and the extruded layer is passed against this cylinder while the material of this layer is in the plastic state, so that this passage develops, by creep of the material in said grooves, partitions 5 on one of the faces 6 of this layer, thus forming a first ribbed layer 7.

  Two assembly cylinders 8, 9, located downstream of the grooved cylinder 4, are then used, and the first ribbed layer 7 thus formed is passed between these cylinders.

  Finally, a second layer 10 is fed simultaneously between these two assembly cylinders 8, 9 so that this second layer 10 passes between these cylinders at substantially the same speed as the first ribbed layer 7 and comes into close contact with the ends. free partitions 5 of this first ribbed layer. Fixing the second layer 10 on the free end of the partitions 5 of the first layer 7 is made possible by heating the surface of said second layer 10 by means of a heating system 11 which raises. locally the surface temperature of the second layer, thereby making it plastic and thus suitable for assembly with the first layer. The cellular material consisting of the two layers 7, 10 is then planified by passage between two sets of rollers 12 whose respective axes are located in two parallel planes.

  According to the invention, during the calendering operation between the rollers 3, 4, the resin, of low viscosity, will flow very easily to the inside of the grooves, filling them quickly and completely.

  This very fluid resin comprises in particular short fibers whose length is between 10 and 400 pm and whose diameter is here between 1 and 50 pm. These fibers are of sufficiently small size to be able to pass through the grooves of the calendering roll 4. On the other hand, the majority of the longest fibers, having a size of between 400 and 2000 μm, and a diameter of between 10 and 150 μm, are retained at the base of the grooves of the calendering roll, and remain imprisoned in particular by expansion in the base of the layer of plastic material thus formed.

  The present invention also relates to a sheet or sheet material with a so-called "alveolar" structure obtained from a composition as described above, at the end of the extrusion-calendering process described above.

  Such a foamed cellular material is shown in FIG. 2, and comprises the two layers 7, 10 forming the walls of the material and a series of partitions of width at the base I, I which may be between 50 and 5000 μm, perpendicular. to these walls, which connect these walls to each other.

  The first wall 7 is constituted by the base 6 and the partitions 5 projecting from one of the faces of this base 6, which constitute said partitions, and the second wall 10 is connected to the free ends of the partitions 5 of the first wall 7 .

  According to the invention, the base 6 of the first wall 7 consists of a thermoplastic resin comprising natural fibers whose length is between 10 μm and 5 times the width I and whose diameter of said fibers is less than their length. . In addition, since the base 6 and the partitions 5 are integrally formed in one piece by calendering as described above, the partitions 5 are made of the same polypropylene-based resin as that used for the base 6. Nevertheless, the partitions 5 comprise, in particular, fibers whose length is mainly between 10 μm and 400 μm, and therefore fibers shorter than that which may be found in the base, as illustrated in FIG. 2.

  It should be noted that the density of fibers in the partitions is lower than the density of fibers in the base of the first layer; the latter being advantageously greater than 30% by weight of the composition in this portion of the layer. The high density of long fibers in the base advantageously makes it possible to limit the appearance of shrinkage on cooling.

  It goes without saying that the invention is not limited to the examples given above, but that it encompasses all variants. Thus, in particular, the partitions may be rectilinear, or not, for example of sinusoidal shape, which will enhance the compressive strength or folding of the cellular material obtained.

Claims (13)

  1. Thermoplastic composition for the manufacture of flat single or double-walled cellular elements comprising transverse partitions of width I between 50 μm and 5000 μm, these cellular flat elements being obtained by extrusion then calendering, said composition comprising at least a polymer and / or copolymer resin, characterized in that: (i) the melt flow index of said resin is between 0.8 and 40 g / min., and in that (ii) said composition further comprises at least minus one type of natural and / or synthetic fibers suspended in the resin, whose length is between 10 μm and 105 μm and whose diameter is less than the length, so that the melt index of the composition is between 0.1 and 0.8 g / min for polyolefins and between 1 and 8 g / min for styrenic polymers.   2. Thermoplastic composition according to claim 1, characterized in that the fibers entering the composition are all longer than the width I of the transverse partitions.   3. Thermoplastic composition according to claim 1 or 2, characterized in that the melt index of the composition is between 0.3 and 0.5 g / min for polyolefins and 3 to 5 for styrenic polymers.   4. Thermoplastic composition according to claims 1 to 3, characterized in that the resin is selected from the group of polyethylene resins, polypropylene, polycarbonate, polyvinyl chloride, polyamide, or styrenic polymers.   5. Thermoplastic composition according to any one of claims 1 to 4, characterized in that it comprises from 5 to 50% of fibers, preferably between 15% and 50% of fibers, by weight of the composition.   6. Thermoplastic composition according to any one of claims 1 to 5, characterized in that the fibers are hollow fibers.   7. Thermoplastic composition according to any one of claims 1 to 6, characterized in that the fibers are of cellulosic type.   8. Thermoplastic composition according to any one of claims 1 to 7, characterized in that it further comprises at least one mineral filler.   9. Thermoplastic composition according to any one of claims 1 to 8, characterized in that it further comprises at least one blowing agent.   10. Material in sheet or sheet with structure called "alveolar", that is to say comprising two walls (7, 10) assembled to one another which form the main faces of the material and a series of partitions of width I between 50 pm and 5000 pm, perpendicular to these walls (7, 10), which connect these walls (7, 10) between them: - the first wall (7) having a base (6) and partitions (5). ) protruding from one of the faces of this base, which constitute said partitions (5), and - the second wall (10) being connected to the free ends (13) of the partitions (5) of the first wall (7) characterized in that the base (6) of the first wall (7) consists of a hot-melt thermoplastic resin comprising natural and / or synthetic fibers having a length of between 10 μm and 105 μm and diameter is less than the length of said fibers, so that the melt index of the compositio n is between 0.1 and 0.8 g / min for polyolefins and between 1 and 8 g / min for styrenic polymers, and in that the partitions (5) of the first wall (7) consist of the same thermoplastic resin and comprise fibers whose length is, for more than 50% of them, less than the width I of the partitions, and whose diameter is less than the length.   11. Material according to claim 10, characterized in that the partitions (5) of the first wall (7) consist of the same thermoplastic resin and comprise fibers whose length is, for all of them, less than the width I of the partitions.   12. Material according to any one of claims 10 or 11, characterized in that the ribs (5) of the first wall (7) consist of the same thermoplastic resin and comprise less than one third of the total amount of fibers in the material.   13. Material according to claims 10 to 12, characterized in that the fibers are hollow fibers of cellulosic type.