Composite material sheet and process for manufacturing the same

Abstract

A composite material sheet or panel is obtained by extruding a mixture composed of at least one thermoplastic material, particularly of the polyolefin family, and of mineral fibers having predetermined dimensional characteristics (diameter and length). The extrusion process is performed with parameters sufficient to generate in the sheet a three-dimensional structure embedded in the thermoplastic material.

Claims

1. A process for manufacturing a composite material sheet comprising the following steps: providing a thermoplastic material as granules or powder; providing non-vegetable fibers as groups or bundles of fibers having a predetermined length width and thickness; mixing the thermoplastic material and the fibers to develop a mixture, and disgregating the bundles of fibers during the mixing; feeding the mixture of the thermoplastic material and the fibers to an extruder, forming a sheet by extruding the mixture through an extrusion die of the extruder, the sheet comprising a three-dimensional fiber structure in which the fibers are entangled on themselves, the fiber structure being embedded in the thermoplastic material, wherein a distribution percentage of an orientation of the fibers versus a direction of extrusion is set between a ratio of 1:1 to a ratio of 6:1, the ratio being between a percentage of the fibers oriented in a direction of extrusion and the ratio of the fibers directed in a direction perpendicular to the direction of extrusion.

2. The process according to claim 1, wherein the distribution percentage of the orientation of the fibers relative to the direction of extrusion is set by varying alternatively or in combination temperatures of the mixture of the thermoplastic material and the fibers and a length of a die plate between 30 to 150 cm.

3. The process according to claim 1, wherein the distribution percentage of the orientation of the fibers between the direction perpendicular to the direction of extrusion and a direction parallel to the direction of extrusion varies continuously according to a polynomial function having a degree of two or higher.

4. The process according to claim 1, wherein the fiber bundles comprise groups of individual fibers adherent to each other, the individual fibers having a length between 2 to 20 mm bundles being shaped as bars or cylinders with a thickness ranging from 0.5 to 2 mm.

5. The process according to claim 4, further comprising a step of generating the fiber bundles from individual bundles.

6. The process according to claim 1, further comprising a step of grinding the composite material sheet and of adding recycled material to the thermoplastic material and the fibers in a quantity sufficient to maintain a same starting formulation.

7. The process according to claim 1, wherein the steps of mixing and extruding are performed in the extruder with an output flat die, wherein the fibers entangle with each other due to a mechanical action exerted by mixing screws and the die, thus generating a three-dimensional fiber structure contemporaneously with the step of mixing and extruding.

8. The process according to claim 7, wherein fiber bundle disgregation is obtained by the mechanical action exerted by the mixing screws, and an entangling and fiber orientation distribution is generated by the mechanical action exerted by the extrusion die opening and aligning individual fiber of the bundles.

9. An extruded composite material sheet or panel comprising: a thermoplastic material; non-vegetable fibers embedded in the thermoplastic material and having a predetermined length and forming a three-dimensional fiber structure, wherein the fibers are entangled on themselves, the of the three dimensional fiber structure showing a distribution percentage of an orientation of the fibers relative to a direction of extrusion which is between a ratio of 1:1 to a ratio of 6:1 between a percentage of the fibers oriented in the direction of extrusion and the ratio of the fibers directed in a direction perpendicular to the direction of extrusion.

10. The extruded composite material sheet according to claim 9, wherein the sheet has a thickness, and wherein the distribution percentage of the orientation of the fibers relative to the direction of extrusion varies along the thickness of the sheet.

11. The extruded composite material sheet according to claim 10, wherein about half a number of the fibers, within a layer of the sheet forming surfaces of the sheet at two opposed faces, has an orientation between a direction +60 and 60 relative to the direction of extrusion, and wherein a ratio of the distribution percentage of the orientation of the fibers relative to the direction of extrusion, between the orientation of the fibers along the directions at +60 or 60 relative to the direction of extrusion and an orientation of the fibers parallel to the direction of extrusion being between a ratio of 1:1 and a ratio of 6:1

12. The extruded composite material sheet according to claim 9, wherein said three-dimensional fiber structure comprises a combination of the fibers mainly arranged in the direction of extrusion, and for a part, at a same time, exhibiting isotropy in two other directions of a plane, due to a mechanical action exerted by an extrusion opening and an aligning individual fiber bundles.

13. The extruded composite material sheet according to claim 9, wherein the thermoplastic material belongs to the group consisting of polyethylene, polypropylene, or mixtures of polyolefins.

14. The extruded composite material sheet according to claim 9, wherein the non-vegetable fibers comprise glass fibers.

15. The extruded composite material sheet according to claim 9, wherein the thermoplastic material and the fibers are present substantially in a same proportion.

16. A composite panel comprising: one or more extruded composite material sheets comprising: a thermoplastic material; and non-vegetable fibers embedded in the thermoplastic material and having a predetermined length and forming a three-dimensional fiber structure, wherein the fibers are entangled on themselves, the of the three dimensional fiber structure showing a distribution percentage of an orientation of the fibers relative to a direction of extrusion which is between a ratio of 1:1 to a ratio of 6:1 between a percentage of the fibers oriented in the direction of extrusion and the ratio of the fibers directed in a direction perpendicular to the direction of extrusion.

Description

[0028] Examples of the present invention are described hereinafter by means of the following figures in which:

[0029] FIG. 1 illustrates a graphic representation of the percentage of the distribution of the orientation of the fibers in relation to the extrusion direction which corresponds to an angle of 90 and for different settings of the temperature and of the length of the extrusion die of platform in a direction of extrusion.

[0030] FIG. 2 illustrate a similar graph as in FIG. 1 but the measurement is limited to a layer of about 0.5 mm depth along each of the two opposite surfaced of the sheet.

[0031] FIG. 3, is a graph putting in relation the ratio of the flexural modulus along the direction of extrusion and perpendicular to the direction of extrusion of the sheets according to the examples of the FIGS. 1 and 2 with the peak values of the graphs of FIGS. 1 and 2.

[0032] In the following some examples will be described with the help of the annexed drawings.

[0033] An extruded sheet comprising a blend of poliolefine resins and of glass fibres according to the present invention has been extruded. The sheet thickness is of 2.2 mm.

[0034] The length of the die in the direction of extrusion has been varied in four steps between 40 and 100 mm.

[0035] The temperature of the material being extruded is between 200 and 220 degrees C.

[0036] FIG. 1 shows the curves of distribution of the fibres relatively to their orientation in respect to the direction of extrusion and expressed in percent.

[0037] The measurement of the data has been carried out by evaluating the fibres oriented along a certain angle with respect to the direction of extrusion which coincides with a 90 angle in FIG. 1.

[0038] Maximum angle of orientation of the fibres is 0 and 180 which corresponds to an orientation of the fibres perpendicular to the direction of extrusion and in the two directions starting from the direction of extrusion.

[0039] Measurement has been carried out by means of an RX tomography which has been angularly displaced each time of 0.5 relatively to a centre of rotation falling on an axis oriented in the direction of extrusion.

[0040] At each angle of acquisition, the corresponding percentage of fibres oriented along the said angle has been determined.

[0041] The curves have been rescaled in order that their integral from 0 to 180 corresponds to the 100% of the fibers comprised in the sheet.

[0042] The different curves relate to different length of the extrusion die starting from 30 cm up to 100 cm.

[0043] The four curves are identified by symbols and by a name 2141PDC, 2141PSS, 2141PSC, 2141PDD.

[0044] As it appears form the curves by varying the length of the die, the distribution of the fibres becomes more and more non isotropic. The curve defined as 2141PDC is the flattest one. This means that the fibres are isotropically oriented in relation to the direction of extrusion.

[0045] This has an effect on the ratio of flexural modulus values in longitudinal and in transverse direction as referred to the direction of extrusion and where this direction is parallel to the longitudinal direction.

[0046] The ratio of the distributions at the maximum of the curve to the minimum of the curve relating to the example 2141PDC is about 1.2.

[0047] By varying the length of the die a higher number of fibres are aligned in the direction parallel to the direction of extrusion. The curve relating to the example 2141PDD shows the higher dynamic in range and indicates a ratio of the distributions at the maximum of the curve to the minimum of the curve of about 5.7:1.

[0048] This means that in this case a higher percentage of the fibers are oriented in a direction parallel to the direction of extrusion than the ones oriented transversally to it. In this case the ratio between longitudinal and transversal flexural modulus as defined above is different and the higher so that the sheet has a higher resistance against flexural stresses in the longitudinal direction.

[0049] FIG. 2 shows what happens to the distribution of the orientation of the fibres in respect to the direction to extrusion in a thin superficial layer of about 0.5 mm depth from a surface of the sheet.

[0050] Again the measurements are taken in relation to the direction of extrusion corresponding to the 90 angle in the graph and using the same RX tomography as for FIG. 1.

[0051] Four sheets obtained with four die length has been scanned as explained above. The form sheets and the relative curves are identified as already done above.

[0052] In reading the curves it appears that varying the die length has the effect not only of flattening the curve, meaning having a higher degree of isotropy or unisotropy of the fibres orientation distribution, but it varies also the angular width of the possible orientation of the fibres centered along the direction of extrusion (90). Curve 2141PDC is more flattened and most fibres will be distributed in a isotropic way along directions comprised between about 50 and +50 relatively to the direction of extrusion (90). Curve 2141PDD shows a more unisotropic distribution of the fibres on the different orientations but the angular width of the possible orientations is reducing to about 30 to +30 relatively to the direction of extrusion. Examples 2141 Psc and Pss show an intermediate behavior between 2141PDC and 2141PDD.

[0053] Although the above examples are limited to a variation in the length of the dye, experiments has shown also a similar influence on the distribution of the fibres on different angular orientations in respect to the direction of extrusion determined by varying the temperature of the mixture being extrused.

[0054] FIG. 3 shows the ratio of the longitudinal flexural modulus to the transverse flexural modulus on sheets according to the present invention showing different distributions of the fibres along different orientations with respect of the direction of extrusion.

[0055] As already indicated above the term longitudinal direction means here parallel to the direction of extrusion, while the term transverse direction means a direction perpendicular to the direction of extrusion.

[0056] Two further examples have been added to the one indicated by 2141 and discussed in relation to the four cases of FIGS. 1 and 2.

[0057] As it appears from the above description, the invention allows to optimize the mechanical properties of the sheet in relation to two different directions (longitudinal and transverse) parallel and perpendicular to the direction of extrusion of the sheet. This is achieved without the need of modifying the composition of the sheet material or the thickness of the sheet but only setting different distribution of the fibers onto different orientations in relation to the direction of extrusion by varying only some parameters of the extrusion process and particularly length of the extrusion die and/or temperature of the mass of material to be extruded.