WO2020025511A1

WO2020025511A1 - Biosourced composite panel having a controlled-roughness surface, and corresponding methods of production

Info

Publication number: WO2020025511A1
Application number: PCT/EP2019/070291
Authority: WO
Inventors: Moussa KHALFALLAH; Erwan GROSSMANN
Original assignee: Kairos
Priority date: 2018-07-28
Filing date: 2019-07-27
Publication date: 2020-02-06
Also published as: FR3084280B1; FR3084280A1

Abstract

The present invention relates to composite panels (10) which can be sandwich-type panels and comprise at least one composite skin (12A, 12B), a core (11), said skin (12A, 12B) having at least two layers of a composite material (30A, 31A; 30B, 31B), and the composite material comprising at least one strengthening fibre of natural origin and a matrix of at least one biosourced polymer, characterized in that a1) the skin (12A, 12B) of said composite panel (10) further comprises, on its outer side, at least one layer of at least one biosourced, semi-crystalline, thermoplastic polymer (40A, 40B) having a crystallinity less than 20%; b1) said at least one layer of biosourced, semi-crystalline thermoplastic polymer (40A, 40B) has a surface finish without visible defects; c1) between the adjacent layers of composite material there are positioned layers comprising a sheet of cellulose material (50A, 50B) having a mass per unit area of between 20 g/m² et 250 g/m²; and/or d1) between two adjacent layers included in the skins (12A, 12B) of the composite panel, and between the core (11) and each of the skins (12A, 12B), there are positioned layers with a thickness of between 20 micrometers and 1 mm of at least one biosourced polymer (221A, 222A, 223A; 221B, 222B, 223B) that ensure that all of the layers adhere to each other and that the skins adhere to the spacer element.

Description

Bio-sourced composite panel having a surface of controlled roughness and associated manufacturing methods

The present invention relates to a composite panel of the type commonly called a “sandwich”, that is to say comprising a spacer, also called a “core”, preferably positioned between at least two “skins”. The present invention thus generally relates to a multilayer composite panel.

When the spacer is positioned between two skins, the skins can be generally identical, that is to say that the construction of the panel can have symmetry with respect to the median plane of the retractor.

These skins can be made from a composite material, hence the name given to the composite panel assembly, even if generally the core is not itself made of composite material.

Generally, a composite material is a material composed of reinforcing fibers associated with a "matrix". The matrix, generally a thermoplastic or thermosetting polymer, fills the space between the reinforcing fibers while ensuring adhesion (which can be excellent) with the latter thus allowing the transfer to the reinforcing fibers of the stresses suffered by the panel during its use. Conventionally, the reinforcing fibers have the distinction of having a high Young's modulus, generally much higher than that of the matrix.

The spacer, for its part, is typically chosen from weakly dense materials, however having good resistance to compression to allow sufficient pressure when it is assembled with the skins.

The skins are typically associated on the spacer by gluing, which is provided by the resin present in the skins themselves or by a specific glue added. This type of “sandwich” construction allows good rigidity for an overall low density.

There are many uses for these composite panels, in particular as Point-of-Sale Advertising products (known as POS products). However, this type of PLV composite panel is often made from synthetic materials such as fiberglass, resins and spacer based on petro-sourced polymers (from petroleum) or mono material, even example in the form of plates of polymethacrylate, degrading with difficulty, even very hardly, and leaving a significant environmental impact.

This is why bio-based alternatives have been proposed, for example by the use of PLA (polylactic acid). Such a composite panel has the advantage of having extremely low environmental impacts, determined by LCA (Life Cycle Analysis).

On the other hand, the existing POS panels support very variable surface treatments such as prints, assemblies with decorative films, as well as shaping by folding, bending, etc., for the production of display stands and advertising stands.

Thus, for an acceptable visual rendering, it is preferable that this type of panel has a “mirror polished” surface state as well as particular profiles, for example rounded edges, while advantageously being very easily machinable by mechanical means or by cutting. laser.

Different quality criteria are thus defined: wavelets, porosity or even cracks.

Wavelets are visible defects essentially in low-angle light having nested rounded shapes originating from variations in thickness of the polymer (s) present on the surface of the panel, whereas, moreover, the surface roughness can be satisfactory.

The porosities are in the form of small craters and arise from the bursting of gas bubbles, essentially water vapor from the layers of composites internal to the panel during manufacture.

The cracks form lines with excess thicknesses or hollows and arise from the release of internal tensions of the polymer during the manufacture of the composite panel. In addition, such panels can reach large dimensions. For example, one of the most common formats corresponds to a rectangular surface of 1220 mm x 2440 mm for a thickness of 3 mm.

Furthermore, it is advantageous for this type of panel to have a constant thickness, good flatness despite its large dimensions, suitable mechanical resistance as well as a scratch resistance expressed through a Shore D hardness which must be between 60 and 90, this at processing temperatures up to 70 ° C.

Thus US2012170649 describes a composite based on the use of natural fibers and PLA but without any specific requirements as to the quality of the surface.

CN103302864 describes a bio-composite based on natural fibers and PLA. The surface layers are made entirely from PLA. However, it is not a multilayer sandwich type structure. In addition, the PLV application with its level of requirement is not considered.

EP2729289 describes composite structures having a controlled roughness, however the level of roughness is not that of the mirror polish. In addition, the fibers used are not natural fibers.

Thus, until now, it has not been possible to produce such composite panels, in particular PLV, based on bio-sourced materials fully meeting all of the requirements mentioned above. In fact and more specifically, the POS panels based on bio-sourced materials hitherto offered cannot present the required levels of flatness, nor claim to a surface appearance free of a certain number of defects such as " wavelets ”,“ porosities ”and“ cracks ”mentioned above.

The present invention therefore intends to propose a sandwich type panel based on bio-sourced materials that fully meet, thanks to a particular construction, the specifications of the PLV type panels.

The present invention therefore intends to propose:

bio-sourced composite panels that are economically and qualitatively competitive compared to existing POS panels;

bio-degradable or compostable POS panels; a solution to the use of spacers made from recycled bio-sourced materials;

use of a retractor obtained from recycled bio-sourced sandwich panels; and or

simple and economical processes for the industrial production of bio-sourced POS panels.

SUMMARY OF THE INVENTION

To this end, the subject of the invention is a composite panel of the aforementioned type (“sandwich”) comprising at least one composite skin, preferably two composite skins which can be on either side of a spacer (also called core), said or said skins comprising at least two layers of composite material (identified as first layer (s) and second layer (s) of composite material), said composite material comprising at least one reinforcing fiber of natural origin and a matrix of at least one bio-sourced polymer, characterized in that:

al) (the) the skins of said composite panel further comprise on their outer face, which is not in contact with the retractor, at least one layer of at least one semi-crystalline bio-sourced thermoplastic polymer having a crystallinity rate of less than 20%, preferably less than 10%; bl) said at least one layer of semi-crystalline bio-sourced thermoplastic polymer has a surface condition without visible defects, in particular without defects of "wavelets", "porosities" or "cracks", with a "mirror polish" ", That is to say has a surface roughness of less than 0.8 micrometers according to standard ISO 4287;

cl) between the adjacent layers of composite material either between (the) first layers of composite material on the one hand and (the or the second layers of composite material on the other hand are positioned at least one layer comprising at least one sheet of cellulosic material (50A, 50B) having a surface mass of between 20 g / m ² and 250 g / m ² and optionally a Young's modulus in the preferred direction of orientation of the fibers greater than 2 Giga Pascal; and or dl) between two adjacent layers included in (the) the skins of said composite panel, as well as between the spacer and each (of the or skins), are positioned (one or more layers of a thickness between 20 micrometers and 1 mm of at least one bio-sourced polymer ensuring the bonding of all the layers together as well as the bonding (of the skin (s)) with the spacer.

Thus, the object of the present invention therefore also relates to a panel as defined above, characterized in that said panel has at least one composite skin, but does not have a second composite skin on another face of the spacer (also called soul).

The object of the present invention further relates to a composite skin as defined above, that is to say comprising at least two layers of composite material, said composite material comprising at least one reinforcing fiber of natural origin. and a matrix of at least one bio-sourced polymer, and

a'I) which may further comprise on at least one of its external faces at least one layer of at least one semi-crystalline bio-sourced thermoplastic polymer having a degree of crystallinity of less than 20%, preferably less than 10% ;

b'I) said at least one layer of semi-crystalline bio-sourced thermoplastic polymer has a surface condition without visible defects, in particular without defects of "wavelets", "porosity" or "cracks", with a "polish "mirror", that is to say has a surface roughness of less than 0.8 micrometers according to standard ISO 4287; and or

c'I) between the adjacent layers of composite material or between the first layer of composite material on the one hand and the second layer of composite material on the other hand are positioned at least one layer comprising at least one sheet of cellulosic material having a surface mass of between 20 g / m ² and 250 g / m ² and optionally a Young's modulus in the preferred direction of orientation of the fibers greater than 2 Giga Pascal; and I) optionally on a surface of the skin is positioned at least one layer with a thickness of between 20 micrometers and 1 mm at least a bio-sourced polymer capable of ensuring the bonding of the skin with a support such as a retractor (also called core).

The object of the present invention thus relates to a process for manufacturing a composite panel as described above, comprising the following steps:

a2) the superposition of at least two plates, for example of metal having a mirror polish on their face (s) in contact with the stack formed, of at least one film and / or a film precursor based on '' at least one bio-sourced polymer, at least one comélé, at least one retractor and optionally at least one cellulosic sheet preferably having a moisture content of less than 5%;

b2) placing the stack according to step a2) in a heating press at a temperature between 160 and 230 ° C, preferably at a temperature of 200 ° C;

c2) the optional implementation in the heating press of a degassing step, comprising for example at least 3 degassing cycles comprising: a first cycle at a first pressure of between 0.4 and 0.6 bar, preferably 0, 5 bar, for a duration of between 1 and 3 minutes, followed by degassing of a duration of between 1 and 5 seconds; a second cycle at a second pressure of between 0.6 and 0.8 bar, preferably 0.7 bar, for a duration of between 1 and 3 minutes, followed by degassing of a duration of between 1 and 5 seconds; a third cycle at a third pressure of between 0.9 and 1.5 bar, preferably 1 bar, for a duration of between 2 and 3 minutes, followed by degassing of a duration of between 1 and 5 seconds;

d2) the cooling of at least one plate of a temperature between 160 and 230 ° C, preferably at a temperature of 200 ° C, at a temperature between 10 and 50 ° C, preferably 30 ° C, for a period at least 100 seconds, preferably between 100 seconds and 150 seconds; and

e2) recovering the composite panel obtained, for example by extracting the composite panel from a cooling press used in step d2); characterized in that said at least one film and / or a film precursor based on at least one biosourced polymer is placed in the stack in step a1) so as to:

- be included in the surface layers, and / or

- participate in the bonding of the layers together.

In addition, the subject of the present invention relates to a method for producing a composite panel comprising the following steps:

a3) superimposition between at least two plates, for example of metal having a mirror polish on their face (s) in contact with the stack formed, of at least one film and / or a film precursor based on at least one bio-sourced polymer, at least one comele, and optionally at least one cellulosic sheet, preferably having a moisture content of less than 5%;

b3) placing the stack according to step a3) in a heating press at a temperature between 160 and 230 ° C, preferably at a temperature of 200 ° C;

c3) optional implementation in the heating press of a degassing step which may include, for example, at least 3 degassing cycles comprising: a first cycle at a first pressure of between 0.4 and 0.6 bar, preferably 0.5 bar, for a duration of between 1 and 3 minutes, followed by degassing of a duration of between 1 and 5 seconds; a second cycle at a second pressure of between 0.6 and 0.8 bar, preferably 0.7 bar, for a duration of between 1 and 3 minutes, followed by degassing of a duration of between 1 and 5 seconds; a third cycle at a third pressure of between 0.9 and 1.5 bar, preferably 1 bar, for a duration of between 2 and 3 minutes, followed by degassing of a duration of between 1 and 5 seconds;

d3) cooling of at least one plate of a temperature between 160 and 230 ° C, preferably at a temperature of 200 ° C, at a temperature between 10 and 50 ° C, preferably 30 ° C, for a period d '' at least 100 seconds, preferably between 100 seconds and 150 seconds; and e3) recovering the composite panel obtained, for example by extracting the composite panel from a cooling press used in step d3);

characterized in that said method comprises an additional step f3) where a YOM mat is inserted before the press between at least one of the plates enclosing the stack according to step a3) and a plate of the press.

In a particular embodiment, the YOM mat is interposed between a sheet and a press plate, which makes it possible to improve the surface condition of the panel according to the present invention, if a “polished” type of surface is desired. - mirror ". The panel is then in contact with the sheet during its formation.

In a particular embodiment, the YOM mat can be bare or interposed between a release sheet (such as a silicone sheet in contact with the panel during its formation) and a press plate, which allows a less polished appearance of the sign.

The object of the present invention thus relates to a composite panel capable of being obtained according to one of the methods described herein which can for example be characterized by a presence of less than 10% V / V of cavities, preferably less than 1% V / V of cavities and / or in that said panel has a flatness measured according to standard NF EN 10029 of ± 1%.

The object of the present invention further relates to the use of at least one bio-sourced thermoplastic polymer to produce a surface layer for composite panel characterized in that said surface layer of bio thermoplastic polymer (s) -sourced (s) is semi-crystalline with a degree of crystallinity of less than 20%, preferably less than 10%.

The object of the present invention also relates to a surface layer for a composite panel comprising at least one bio-sourced thermoplastic polymer characterized in that said layer is semi-crystalline with a degree of crystallinity of less than 20%, preferably less than 10% .

The object of the present invention further relates to the use of a sheet of cellulosic material, preferably having a surface mass of between 20 g / m ² and 250 g / m ² and optionally a Young's modulus in the preferred direction d fiber orientation greater than 2 Giga Pascal, to reduce irregularities linked to the use of at least one bio-sourced comele in a composite panel.

The object of the present invention thus relates to a composite panel comprising at least one bio-sourced comele in combination with at least one sheet of cellulosic material, preferably having a surface mass of between 20 g / m ² and 250 g / m ² and optionally a Young's module in the preferred direction of fiber orientation greater than 2 Giga Pascal.

The object of the present invention also relates to the use of a YOM mat in the thermoforming manufacture of a composite panel for distributing the pressure uniformly over the surface of thermoforming tools, such as thermoforming molds in contact. with said composite panel.

The object of the present invention further relates to a press for manufacturing a composite panel comprising a YOM mat interposed between a mold and a press plate.

DEFINITIONS

In the present description, the ISO 4287 standard is applied in particular according to the geometric specification criteria of the products, surface finish profile method, definition terms and surface finish parameters according to the Al amendment of August 2009.

In this description, the ISO 1133 standard is applied in particular according to the criteria of ISO 1133-1: 2011 and ISO 1133-2: 2011, namely: Plastics - Determination of the hot melt index of thermoplastics, in mass (MFR) and in volume (MVR) - Partial: normal method, and Part 2: method for materials sensitive to time-temperature history and / or humidity. In this description, ISO 535 is applied in particular according to the criteria of FIS0535: 20l4, namely: Paper and cardboard - Determination of water absorption - Cobb method.

In this description, the European standard NF EN 10029 is applied in particular for the determination of flatness according to the criteria of NF EN 10029 February 2011.

In the context of the present invention, the expression “film precursor” includes any conventional compound that a person skilled in the art may have at his disposal. arrangement for obtaining a film, for example the desired film compound may be in the form of a liquid (more or less viscous for the implementation of the present invention), powder, granule, fiber, fabric, comel, etc. and under the effect of heat, a chemical reaction and / or pressure becomes a film.

The term "V / V" denotes "volume over volume", therefore a ratio of a volume of cavities, here relative to a total volume of layer of composite material considered, such as a skin according to the present invention.

DETAILED DESCRIPTION

In a particular embodiment, the invention relates to a composite panel of the aforementioned type characterized in that said composite panel as described above, comprises the characteristic al).

In a particular embodiment, the invention relates to a composite panel of the aforementioned type characterized in that said composite panel as described above is characterized in that it comprises the characteristic b1).

In a particular embodiment, the invention relates to a composite panel of the aforementioned type characterized in that said composite panel as described above comprises characteristic cl).

In a particular embodiment, the invention relates to a composite panel of the aforementioned type characterized in that said composite panel as described above comprises the characteristic dl).

In a particular embodiment, the invention relates to a composite panel of the aforementioned type characterized in that said composite panel as described above, comprises the characteristic al) and b 1).

In a particular embodiment, the invention relates to a composite panel of the aforementioned type characterized in that said composite panel as described above, comprises the characteristic a1) and c1).

In a particular embodiment, the invention relates to a composite panel of the aforementioned type characterized in that said composite panel as described above, includes the characteristic a1) and dl).

In a particular embodiment, the invention relates to a composite panel of the aforementioned type characterized in that said composite panel as described above, comprises the characteristic bl) and cl). In a particular embodiment, the invention relates to a composite panel of the aforementioned type characterized in that said composite panel as described above, includes the characteristic bl) and dl).

In a particular embodiment, the invention relates to a composite panel of the aforementioned type characterized in that said composite panel as described above, comprises the characteristic cl) and dl).

In a particular embodiment, the invention relates to a composite panel of the aforementioned type characterized in that said composite panel as described above, comprises the characteristic a1), b 1) and cl).

In a particular embodiment, the invention relates to a composite panel of the aforementioned type characterized in that said composite panel as described above, comprises the characteristic a1), b1) and d1).

In a particular embodiment, the invention relates to a composite panel of the aforementioned type characterized in that said composite panel as described above, comprises the characteristic a1), cl) and dl).

In a particular embodiment, the invention relates to a composite panel of the aforementioned type characterized in that said composite panel as described above, includes the characteristic bl), cl) and dl).

In addition, the invention relates to a composite panel of the aforementioned type comprising two skins on either side of a spacer, said skins being made up of at least two layers of a composite material consisting of reinforcing fibers of natural origin and in a matrix of a bio-sourced polymer, characterized in that:

- the skins of said composite panel have on their outer face, which is not in contact with the retractor, layers of a semi-crystalline bio-sourced polymer having a crystallinity rate of less than 20;

- said layers of semi-crystalline bio-sourced polymer have a surface condition with no visible defects, in particular without defects of "wavelets", "porosities" or "cracks", with a "mirror polish", that is ie has a surface roughness of less than 0.8 micrometers according to ISO standard 4287;

- between the adjacent layers of composite material or between the layer are positioned layers consisting of a sheet of cellulosic material having a surface mass of between 20 g / m ² and 250 g / m ² and a Young's modulus in the preferred direction of orientation of the fibers greater than 2 Giga Pascal;

- between two adjacent layers constituting the skins of said composite panel, as well as between the spacer and each of the skins, are positioned layers of a bio-sourced polymer ensuring the bonding of the layers together and of the skins with the spacer d '' a thickness between 20 micrometers and 1 mm.

More particularly, the invention relates to a fully bio-sourced multilayer composite panel (sandwich), that is to say that all of its constituents, fibers, resin, glue and spacer come from biomass. In addition, the panel according to the invention is recyclable, bio-degradable or compostable.

Advantageously, the invention relates to a composite sandwich panel the spacer of which is obtained by recycling of bio-sourced materials.

According to preferred embodiments of the invention, the composite panel also has one or more of the following characteristics, taken in isolation or according to any technically possible combination (s):

the semi-crystalline bio-sourced polymer constituting the surface layers of the skins has a degree of crystallinity of between 1% and 20%, preferably between 2% and 15%, more preferably between 3% and 12%, for example between 5% and 10% or between 10% and 20%;

- The surface layers of the skins have a Shore D hardness of between 60 and 90;

- the semi-crystalline biobased polymer constituting the surface layer of the skins is chosen from poly lactic acid (PLA), the group consisting of homopolymers of hydroxyalkanoates and copolymers of hydroxyalkanoates, as well as their derivatives and their mixtures ;

- the polymer constituting the surface layer of the skins has an MFI according to the ISO 1133 standard understood between, 5 g / lO min and 90 g / lO min as well as a TG between 45 ° C and 90 ° C;

- The fibers constituting the composite materials are chosen from cellulosic fibers such as flax, hemp, jute, ramie, banana, cotton, viscose and regenerated cellulose fibers; - The matrix constituting the composite materials is chosen from poly lactic acid (PLA), homopolymers of hydroxyalkanoates and copolymers of hydroxyalkanoates, as well as their derivatives and their mixtures;

- The matrix constituting the composite material has an MFI measured according to ISO 1133 standard between 1.5 g / 10 min and 90 g / 10 min and a glass transition temperature (TG) between 45 ° C and 90 ° C;

- The polymer constituting the bonding layers has an MFI measured according to ISO 1133 standard between 1.5 g / 10 min and 90 g / 10 min and a glass transition temperature (TG) between 45 ° C and 90 ° C;

- The polymer constituting the bonding layers has an MFI measured according to ISO 1133 standard between 6 g / 10 min and 38 g / 10 min and a TG between 45 ° C and 70 ° C;

- the cellulosic sheets consist of Kraft paper with a surface mass of between 20 g / m ² and 250 g / m ² ;

- the cellulosic sheets consist of a nonwoven based on natural fiber with a surface mass of 20 g / m ² to 150 g / m ² , preferably between 30 g / m ² to 125 g / m ² ;

- the cellulosic sheets have a COBB 60 index determined according to ISO standard 535 of between 80% and 100% of the surface mass of said cellulosic sheets;

- the cellulosic sheets are completely impregnated with the polymer of the adjacent bonding layers;

- the spacer (11) is based on bio-sourced material

- the retractor is made of cork granules;

- The retractor consists of all or part of particles from the recycling of the composite panel according to the invention;

- the panel according to the invention has a flatness measured according to standard NF EN 10029 of ± 10%, preferably ± 1%;

- The panel according to the invention has a coloring produced by pigments which can for example be uniformly distributed in the composite layers. The invention also relates to a composite skin made up of the assembly of first layers of composite materials and second layers of materials composites, and of cellulose sheets bonded together by the layers of a bio-sourced polymer ensuring the bonding of all the layers together as well as the bonding (of the skin or skins) with the retractor, if necessary.

The subject of the invention is also a composite skin consisting of the assembly of first layers of composite materials and second layers of composite materials, and of cellulose sheets bonded together by the layers of a bio-sourced polymer ensuring the bonding of all of the layers together as well as the bonding of the skin (s) with the retractor, where appropriate, having, in addition, a coloration produced by pigments, preferably uniformly distributed in the first and second composite layers

The invention also relates to methods for producing a composite panel, in particular suitable for POS applications having the characteristics described herein.

A first process consists of:

- the supply of precursor layers in the form of fibers of natural origin and fibers of a bio-sourced polymer, films (and / or film precursor (s)) based on an organic polymer -sourced intended for bonding layers, films (and / or film precursor (s)) of a bio-sourced polymer intended to constitute the layers of surfaces, of cellulose sheets and of a spacer;

- drying the cellulose sheets so that they have a humidity rate of less than 5%;

- the superimposition, between two metal plates having a mirror polish on its face in contact with the stack, comele, film (s) and / or a precursor (s) of film (s), sheets and spacer in the '' following order:

* a film and / or a surface polymer film precursor;

* a comélé;

* a film and / or a precursor of a bonding polymer film;

* a cellulosic sheet;

* a film and / or a precursor of a bonding polymer film

* a comélé;

* a film and / or a precursor of a bonding polymer film;

* the retractor; * a film and / or a precursor of a bonding polymer film;

* a comélé;

* a film and / or a precursor of a bonding polymer film;

* a cellulosic sheet;

* a comélé;

* a film and / or a surface polymer film precursor;

- the placement of the above stack with the two metal plates in a heating press at 200 ° C;

- a degassing step for example by the implementation in the heating press of at least 1 degassing cycle (preferably 3 degassing cycles) consisting of:

* a (first) cycle at 0.5 bar lasting between 1 to 3 min, followed by degassing between 1 to 5 s;

* a (second) cycle at 0.7 bar lasting between 1 to 3 min, followed by degassing between 1 to 5 s; and or

* a (third) cycle at 1 bar lasting between 2 to 3 min, followed by degassing between 1 to 5 s;

- transfer of the stack to a cooling press;

- cooling the metal plates from 200 ° C to 30 ° C for a period of 100s to 150s;

- extracting the composite panel from the cooling press.

A second process consists of:

- the supply of precursor layers in the form of fibers of natural origin and fibers of a bio-sourced polymer, films (and / or film precursor (s)) of a bio-sourced polymer intended for build up the layers of surfaces, cellulose sheets and a spacer;

- drying the cellulose sheets so that they have a moisture content of less than 5%;

- the superimposition, between two metal plates having a mirror polish on its face in contact with the stack, comele, films (and / or film precursor (s)), sheets and spacer in the following order: * a film (and / or a film precursor) of surface polymer;

* a comélé;

* a cellulosic sheet;

* a comélé;

* the retractor;

* a comélé;

* a cellulosic sheet;

* a comélé;

* a film (and / or a film precursor) of surface polymer;

- placement of the above stack in a heating press at 200 ° C;

* a (first) cycle at 0.5 bar with a duration between 1 to 3 mm, followed by degassing between 1 to 5 s;

- transfer of the stack to a cooling press;

- extracting the composite panel from the cooling press.

Preferably, the method for producing a composite panel according to the two methods described above may consist in interposing a YOM mat between a metal plate enclosing the stack leading to the composite panel and a plate of the cooling press.

Other characteristics and advantages of the invention will appear on reading the description which follows, given solely by way of example and made with reference to the appended drawings, in which: [Fig. 1] is a sectional view of a panel according to the invention.

[Fig. 2] is a block diagram explaining the phases of the process leading to the panel according to the invention.

The invention therefore relates to a sandwich type panel having a spacer and bio-sourced composite skins which must meet the specifications requiring POS panels.

Such a panel has a thickness of between 2 mm and 50 mm.

The panel according to the invention consists of the superposition of different materials, the nature of which we will hereinafter specify.

As seen above, the construction of the panel is preferably symmetrical with respect to the median plane of the spacer. This ensures that the tensions are balanced when the panel is manufactured and maintains the flatness of the panel during its use.

However, in particular cases where one seeks for example a bending or the panel may be asymmetrical, that is to say that the skins on either side of the spacer may be of different construction, for example having a different number of plies or be of different natures, that is to say for example not having the same polymer or the same nature of fibers.

To simplify the point, we will consider below that the panel is of symmetrical construction with respect to the median plane of the retractor.

Referring to FIG. 1 which presents a section of the composite panel 10 according to the invention, it is noted that each of the skins 12 A, 12B has two faces 123, 124 and 125, 126 respectively.

The faces 123 and 125 are facing the spacer 11.

More precisely, the face 123 of the skin 12A is turned towards the face 111 of the retractor while the face 125 of the skin 12B is turned towards the face 112 of the retractor. Between the face 111 of the retractor and the face 123 of the skin 12A is a bonding layer 221 A.

Similarly between the face 112 of the spacer and the face 125 of the skin 12B is a bonding layer 221B.

The skin 12A, 12B consists, in contact with the bonding layer 221 A, 221 B, of a first layer of composite material 30A, 30B assembled with a sheet cellulosic 50A, 50B via a bonding layer 222A, 222B, which cellulosic sheet 50A, 50B being associated on its other face with a second layer of composite materials 31 A, 31B via a second layer adhesive 223 A, 223B.

On this second layer of composite material 223A, 223B is the surface layer 40 A, 40B.

It is understood that the invention is not limited to the composite panel of FIG. 1. In fact the number of composite layers in each of the skins can be greater, the presence of an additional composite layer resulting in the presence of a layer of cellulosic sheet and an additional bonding layer.

Now the components of the bio-sourced composite panel according to the invention will be described in detail.

With regard to the spacer 11, all types of spacers based on bio-sourced materials are possible, such as honeycomb spacers based on cellulosic fibers (generally paper or cardboard), spacers based on corrugated cardboard, balsa spacers, bio-sourced foam spacers, bamboo leaves, spacers based on agglomerated cellulosic particles, etc.

The surface mass of the spacer 11 is chosen between 50 kg / m ³ and 350 kg / m ³ , preferably between 200 kg / m ² and 300 kg / m ³ .

The type of spacer preferred for bio-sourced sandwich constructions according to the invention consists of cork particles, preferably recycled cork. As a supplier of this type of retractor suitable for the invention, the company Agglolux can be mentioned.

The different intermediate bonding layers 221 A, 222A, 233A; 221B, 222B, 223B are based on a bio-sourced semi-crystalline thermoplastic polymer having an MFI determined according to ISO 1133 standard between 1.5 g / lO min and 90 g / lO min, a glass transition temperature included between 45 ° C and 75 ° C as well as a degree of crystallinity between 0% and 40%. Its melting temperature is between 155 ° C and 180 ° C. Mention may be made, as polymers suitable for the invention, of poly lactic acid (PLA), homopolymers of hydroxyalkonates, copolymers of hydroxyalkanoates, their derivatives and mixtures thereof.

The bonding layers have a thickness of between 0.03 mm and 0.5 mm. An example of a polymer suitable for the invention is the PLA supplied in the form of a 0.35 mm film. We can cite the film PLA 04010 from the company INFIANA.

The degree of crystallinity of the polymer in the finished product is less than 40%.

The composite layers consist of reinforcing fibers "embedded" in a matrix of thermoplastic polymer.

The composite layers 30A, 31 A; 30B, 31B come from precursor or semi-finished textile tablecloths called “comélés”.

Comele is understood to mean an intimate mixture of fibers of different natures. In this case, these are reinforcing fibers mixed with fibers based on bio-sourced thermoplastic polymers.

After fusion of the fibers and compression, the polymer from the fibers will fill the space between the reinforcing fibers and thus constitute the matrix of the composite layer.

Such haze may be obtained by needling at the end of a nonwoven manufacturing line called by "dry process" consisting of a working-mixing / carding / coating. Such mixes are, for example, available under the trade name of ECOLINE® supplied by the company NORAFIN.

Other binding methods can be envisaged as an alternative to needling, for example binding methods by water jet more suitable for short fibers and low weight comélés. Products produced by this process are available under the name of ECOLINE SL® and supplied by the company NORAFIN.

It can also be "UniDirectional" tablecloths of flax fibers available under the brand Flaxtape® from the company LINEO.

Fabrics made from yarns consisting of mixtures of reinforcing fibers and thermoplastic fibers can also be used. Mention may be made here of the products known under the name BIOTEX from the company Composite Evolution.

Particular types of fabrics differing in their weave, that is to say in the way in which the warp and weft threads intersect, can be chosen according to the desired mechanical performance for the composite panel. We can quote for example taffetas supplied by the company LINEO, twills of the company Depestele or the bi-biases of Terre de Lin.

The reinforcing fibers, derived from comellates, present in the composite layers are fibers of natural origin preferably Liberian such as flax, hemp, jute, but all the other vegetable fibers can also be used, such as coconut fibers, bamboo, banana, ramie raffia, sisal, etc.

We will however favor flax and hemp fibers for their higher Young modulus.

The length of the reinforcing fibers is between 5 mm and 30 mm.

The preferred mixtures for the invention have a surface mass of between 20 g / m ² and 1500 g / m ² .

The polymers derived from the thermoplastic fibers constituting the comélés and serving as matrices for the composite layers are for their part chosen from the bio-sourced semi-crystalline thermoplastic polymers having a PWM determined according to ISO 1133 standard between 1.5 g / lO min and 90 g / 10 min, a glass transition temperature between 45 ° C and 85 ° C as well as a crystallinity rate of less than 40%.

Their melting point is between 155 ° C and 210 ° C.

The mass percentage of thermoplastic fibers relative to the reinforcing fibers is between 10% and 95%, preferably between 40 and 60%.

As thermoplastic fibers suitable for the invention, mention may be made of Ingeo ™ Biopolymer 6201D fibers from the company Nature Works.

As we will see, the bonding layer can consist of an "excess" of polymer coming from the composite layers and not systematically by the addition of a film. In this case, the mass percentage of thermoplastic fibers will be higher, greater than 50%.

Mention may be made, as bio-sourced thermoplastic polymers suitable for the production of fibers intended to serve as a matrix for poly lactic acid (PLA), homopolymers of hydroxyalconoates, copolymers of hydroxyalconoates, their derivatives and mixtures thereof. The density of each composite layer in the finished product is between 1.15 kg / m ³ and 1.35 kg / m ³ .

The layer consisting of the cellulosic sheet preferably consists of a paper, and more particularly a Kraft paper.

This type of paper is defined by its composition based on 100% natural cellulosic fibers (or wood pulp) coming mainly from pine or fir trees, not chemically treated (brown in color) and therefore biodegradable and recyclable. It has a rubbed and laid appearance.

A Kraft paper suitable for the invention is the laid Kraft paper from the company HERMET.

Its basis weight is between 20 g / m ² and 250 g / m ² .

As an alternative to Kraft paper, it is possible to use “dry” nonwovens based on natural fibers with a surface mass of between 50 and 150 g / m ² . For example, a type of nonwoven suitable for the invention is SL ECOLINE® from the company NAROFIN.

Products linked by water jets commonly called "Spunlace" may also be suitable such as Spunlace 100% viscose or Spunlace 100% linen from the company NORAFIN.

The surface layers 40A, 40B of the panel consist of a thermoplastic polymer chosen from biosourced semi-crystalline polymers having an MFI determined according to ISO 1133 standard between 1.5 g / lO min and 90 g / lO min, a glass transition temperature between 45 ° C and 90 ° C and a crystallinity of less than 40%.

Its melting temperature is between 155 ° C and 210 ° C.

The degree of crystallinity of the surface layers 40A, 40B in the finished product is less than 10%.

When it is said that the bonding layers, the surface layers or the matrix of the composite layers are based on bio-sourced polymers it means that they can be mixed with different adjuvants such as also bio-sourced plasticizers or fillers inert of vegetable, mineral or organic origin.

These additives can make it possible to significantly reduce the cost price of the composite panel but essentially have the role of improving the properties mechanical, thermal, resistance to UV (Ultraviolet Radiation), to prevent yellowing or to allow coloring of the composite panel.

In particular, the thermoplastic fibers based on bio-sourced polymer constituting the comele can be dyed in the mass, that is to say that colored pigments can be added during the production of the “compounds” used for the extrusion of said said fibers.

Such a coloring in the mass of the thermoplastic fibers of the comélés makes it possible to produce composite layers 30A, 30B; 31 A, 31B also homogeneously colored and therefore a panel of uniformly colored appearance without the need for subsequent operations in its manufacture, such as paints or lacquers, the choice of the degree of crystallinity of the surface layers 40A, 40B allowing , in fact, to adapt the gloss of the composite panel.

By “homogeneous”, it is understood in the context of the present invention that the coloring is distributed in a uniform and / or regular manner, for example so that a standard 10 ° observer does not perceive any significant variation per portion of 0, lm ² , or even 0.0lm ² portion, of product analyzed.

We have seen that the attempts at bio-sourced panels presented a number of crippling defects for the type of use intended.

In order to better understand the invention, it is useful at this stage to analyze in detail the reasons for these defects and to place them in perspective in relation to the solutions proposed by the invention.

"Porosity" fault

The raw materials used, natural fiber, cork or PLA in the form of film have a whole rate of moisture uptake between 0.1% and 30%.

This means that an average percentage of 20% of water may be present in the stack at the time of introduction into the oven.

Even extensive degassing does not allow the various layers to be completely dried, hence the migration of water vapor leading to porosity defects on the surface of the panel. When the temperature in the oven exceeds the melting temperature of the polymers present, the stack becomes completely porous, because the films (and / or film precursors) possibly initially introduced for the bonding layers disappear as such by the effect of withdrawal.

The use of sheets of cellulosic material 50A, 50B positioned between two adjacent layers of comele brings to this surprising effect to block this migration of water vapor.

Without feeling bound by a precise interpretation, the inventors think that, by its hydrophilic nature, the cellulosic sheet adsorbs and / or absorbs the "remainder" of water vapor still circulating through the stack at the end of degassing.

This adsorption or absorption is all the more effective since the sheet has a high affinity for water. A commonly used indicator to qualify the hydrophilic character of a cellulosic sheet is the COBB 60 index determined according to ISO standard 535.

Thus, the COBB 60 index of the cellulose sheets used for the invention is between 50% and 100%, advantageously between 80% and 100% of the surface mass of said sheet.

This adsorption or even absorption is made even more effective if the cellulosic sheets are placed in an oven so as to dry them as much as possible just before their use in the stack.

While the percentage of humidity of the cellulosic sheets varies between 5 to 10% under ordinary storage conditions (20 ° C, 60% relative humidity), it is less than 5% when the cellulosic sheets are placed in the within the stack.

Lack of flatness, lack of "wavelets"

The flatness of the panel is determined by thickness measurements using a HEIDENHAIN type probe according to standard NF EN 10029.

For the PLV application, the specifications impose a flatness of class A and B resulting in a tolerance of ± 1% over the entire surface of the panel.

Generally, the main problems related to the use of matter of bio-sourced origin relate to G inhomogeneity.

This inhomogeneity manifests itself on two levels.

- at the level of the materials themselves. As we have seen, the retractor is preferably made of cork recyclas, cork being a material having good compatibility with adhesives based on bio-sourced polymer such as PLA, in the form of granules of variable sizes than the 'It is possible to choose so as to give the retractor the optimum compressive strength properties. These particles are of a random shape, generally approximately spherical with a FERET diameter (Df) of between 0.5 and 7 mm, linked together by an adhesive, preferably a bio-sourced adhesive.

For the retractor, a mixture consisting of 10% to 50% of cork granules with a diameter Df of between 3 mm to 5 mm and from 50% to 90% of granules having a diameter Df between 2 mm and 4 mm is preferred. .

We can thus give the retractor a compressive strength of up to 7 bars and make it accept deformations of reversible thickness up to 30%.

The compression stiffness determined according to standard NF ISO 7322 is between 80 N / mm and 150 N / mm, preferably greater than 135 N / mm.

Furthermore, it is thus possible to give the retractor very great ease of machining, whether by cutting tools, by scraping or sanding, but also by laser cutting.

It results from this choice of particle size, necessary for good resistance to compression, a particularly rough surface condition of the spacer. The average roughness determined according to ISO 4288 is approximately Ra 0.35 mm and is generally between 0.2 mm and 0.8 mm.

Likewise, this irregularity manifests itself with regard to the plant fibers, in particular the bast fibers preferentially used in the context of the invention, which can be made up of a different number of elementary fibers and therefore also have a very variable diameter understood. between 20 micrometers and 300 micrometers.

- at the level of the semi-finished product.

Whatever the process envisaged above for the manufacture of comele, and by the very fact of the intrinsic inhomogeneity of the materials, the precursor plies exhibit significant irregularities, all the more important as their density is low. Thus, the density of the needle-punched comelé of the ECOLINE NP® brand used in an embodiment of the invention has a standard deviation of ± 0.02 g / cm ³ for a product with an average surface density of 350 g / m ² and a standard deviation of ± 0.01 g / cm ³ for a product with an average surface mass of 700 g / m ² .

This problem of non-uniformity will in particular be expressed at the level of flatness. In fact, during the compression of the skins, the high roughness of the surface of the retractor and the irregularity due to the density of the streaks will “add up” to create variations in density throughout the thickness of each of the skins. .

This will consequently lead to a variable thickness of the skins and therefore to a defect in the flatness of the panel.

In addition, this variation in density will induce an equally variable distribution of the surface polymer, which will lead to these ripple effects.

Furthermore, the problems of wavelets encountered on the surface of the panels are also due to the excess thickness of the bio-sourced thermoplastic material which tends to shrink when hot. This phenomenon called "shrinkage" is essentially due to the reorganization of the polymer during cooling. The cooling rate and the holding pressure applied to compensate for this shrinkage do not play their role sufficiently in the compression process, hence the meeting of "wavelet" surface defects, characterized by a sagging of the material in the thick areas and large.

To overcome this problem, the inventors first tried to use YOM (Yamauchi Original Mat) "carpets" from Yamauchyi Corp. during the forming of the composite panel.

This type of "mat" is made of rubber reinforced with glass fibers and allows the pressure to be distributed relatively evenly over the surface of thermoforming tools for the manufacture of laminates.

EP0978528, as well as JPH06278153 describe such mats in particular for thermoforming. On the other hand, until the present invention, such carpets were used for the manufacture of small parts, such as printed circuits, but not for POS materials. The "YOM" mats are upholstery mats resistant to temperatures up to 250 ° C and pressures up to 15MPa. So advantageous, the effect of cushioning ("cushioning" in English) is between 100 and 1700mth, preferably between 200 and 1000 mth, more preferably between 300 and 700 pm, such as 400 ± 50 pm, 500 ± 50 pm, or 600 ± 50 pm. In addition, advantageously, the heat resistance of such carpets can be between 0.5 and 6 ° C / J, preferably between 1 and 5 ° C / J, more preferably between 1.5 and 3 ° C / J, such as 1.7 ± 0.2 ° C / J, 2.0 ± 0.2 ° C / J, or 2.2 ± 0.2 ° C / J. Thus in a particular embodiment according to the present invention, the “YOM” padding mat used has a padding effect of between 300 and 700 μm and a heat resistance of between 1.5 and 3 ° C./D.

By positioning this mat between the platens of the forming press and the metal plate in contact with the panel being formed, the inventors have indeed observed an improvement in flatness.

For example, it is possible to put a layer of cork in place of the PLA surface film (glued with the PLA of the comele), to make it a material with a cork appearance and to have flat plates (increased flatness) incorporating cork to the core, flax / PLA in the skins and a thin layer of cork on the surface (respecting the steps of the process according to the invention). Thus, in this case the carpets will be used directly in contact with the cork without adding sheet, for example.

In the context of the present invention, it makes it possible to locally adapt the pressure to the density and thus to minimize flatness defects.

However, this improvement proved insufficient to obtain panels with PLA on the surface with a mirror-polished finish.

At this stage, the only way known to those skilled in the art to remedy the flatness problem is to significantly increase the surface mass of the streaks so as to decrease the value of the standard deviation of the surface mass of the precursor layers. .

However, such a solution would lead to a prohibitive cost of the panel.

The solution proposed in the context of the invention results from a surprising effect which makes it possible not to inconsiderately increase the weights of the materials used. It has in fact been found that the cellulosic intermediate sheet placed between two successive layers of composite for the purpose of adsorption of water vapor also has this effect of "smoothing" the irregularities linked to the use of bio-sourced comele.

The insertion of the cellulosic layer also makes it possible, by dividing the volume of the polymer into small thin layers which generates a "barrier" effect on the reorganization of the polymer, to reduce its volume shrinkage.

Surprisingly, these effects only take place if the cellulosic sheet is placed between two layers of composite material and if the composite layers have a surface mass greater than 100 g / m ² .

To be completely effective from this point of view, the surface mass of such a cellulosic sheet must be between 20 and 250 g / m ² .

Machining faults, delamination of layers

One would think that the presence of a cellulosic sheet would lead to weakening the stack and would facilitate its delamination, particularly during machining operations.

This problem can be avoided by the nature of the polymer used for the bonding layer, which will be chosen with an MFI sufficient to allow complete wetting of the cellulosic sheet.

As we have seen, the cellulosic sheet has a high COBB 60 of 80% and 100% of its surface mass.

If COBB 60 determines the hydrophilic nature of a material, it can also characterize the affinity of a material for any type of liquid with a low viscosity.

This is the reason why, as we saw above, the polymer of the film (and / or of the film precursor) used for the bonding layer is chosen between 1.5 g / 10 min and 90 g / 10 min, preferably more than 20 g / 10 min.

Furthermore, to ensure good cohesion between the layers and to allow good machining behavior, it has been established that the cellulosic sheets must have a Young's modulus greater than 2 Giga Pascal measured in the preferred direction of orientation of the cellulosic fibers. As we have seen, alternatively the paper is replaced by a nonwoven which will therefore have a COBB 60 in the same range.

The latter solution which is a priori less economically advantageous, however, cannot be excluded in particular cases, for example in cases of very large deformations where the paper, even impregnated with polymer, would have difficulty withstanding the shearing forces.

Thus, the combined choices of the particle size of the spreader granules with that of the suitable MFI bonding polymer guarantee sufficient machinability compatible with the uses in particular of the PLV type of the composite panel according to the invention.

Figure 3 and Figure 4 are sectional views taken with a scanning electron microscope of a panel according to the present invention (Figure 3) and of a panel not having the skins according to the present invention (Figure 4). It can be seen that in Figure 3 the core remains mostly porous, while in Figure 4, the matrix of the composite material enters the core (cork, here). It follows that the material of Figure 4 does not have the surface qualities of the material of Figure 3. The skins of the material according to Figure 4 are less homogeneous in surface than those of the material of Figure 3. The material according to the figure 3 also includes better insulating properties (the porosities of the core, in cork here, are preserved). In Figure 3, the cellulosic layer is visible, the outer layer is homogeneous while the inner layer (core) has many porosities. The composite material of the skins is here in PLA-Lin.

Defects in cracks, uncontrolled roughness.

The "2P" mirror polish thus called because of its high reflectivity surface is characterized by Ra less than 0.8 micrometers according to standard EN 10088-2.

In the context of the present invention, it is the surface films (and / or surface film precursors) which, when they solidify after reaching their melting temperature (if any) in contact with the plates, must have this mirror polish.

It is known that by rapidly cooling a semi-crystalline polymer, an amorphous or quasi-amorphous polymer is obtained, therefore without the risks of internal tensions which are created between the crystals in the case of a highly crystalline polymer and which lead to defects in cracks. However, for PLV applications, a completely amorphous surface finish is not acceptable for the reasons of machinability and resistance to scratching mentioned above.

It has been determined that operating conditions allowing a crystallinity level of between 5% and 10% to be obtained make it possible both to avoid the problems of cracking, which leads to the desired mirror polish, while guaranteeing a hardness in the required range.

These operating conditions will be specified below.

The process for obtaining the panel according to the invention will now be described with reference to FIG. 2.

We will describe more precisely the process leading to the product of figure 1.

In a first step 100, the layers which will constitute the panel are provided: the layers of comele, the films (and / or the film precursors) of polymer allowing the intermediate bonding of the layers together, the cellulose sheets, the films (and / or film precursors) and finally two metal plates (not shown in Figure 1).

The cellulose sheets are placed in an oven in a second step 110 to be completely dried.

It is understood that the number of layers of comele and consequently the number of bonding films (and / or the quantity of film precursor (s)) as well as the number of cellulose sheets may be greater than the layers of the product of Figure 1. An additional layer of comele causing the addition of a layer of film (and / or a film precursor) bonding as well as a layer of a cellulose sheet.

It is also understood that it is possible not to systematically use a film (and / or a film precursor) for the bonding between the layers. The bonding layer can indeed come from the polymer present in the composite layer. In this case the percentage of thermoplastic fibers in the comele is greater than 50%. These layers are stacked, during step 120, in the following order:

a first film (and / or film precursor) of surface polymer which will lead to the surface layer 40B in the finished product constituting the first element of the skin 12B; - A first comélé which will lead to the composite layer 31B;

- A first film (and / or film precursor) of bonding polymer leading to the bonding layer 223B;

- a first cellulosic sheet 50B;

- A second comele leading to the composite layer 30B and constituting the last element of the skin 12A;

- A second film (and / or film precursor) of bonding polymer leading to the bonding layer 222B between the skin 12B and the spacer i l;

- the spacer 11;

- a third bonding film (and / or precursor) leading to the bonding layer 221 A for assembling the skin 12A on the spacer 11;

- A third comele leading to the composite layer 30A constituting the first element of the skin 12A;

- a fourth bonding film (and / or precursor) for the bonding layer 222A;

- a second cellulosic sheet 50A;

- a fourth comélé for the composite 31 A;

- a second film (and / or film precursor) of surface polymer leading to the surface layer 40A;

- Two metal plates (not shown in Figure 1) preferably in stainless steel with a thickness of 0.5 mm to 3 mm with dimensions close to the dimensions corresponding to the surface of the panel to be produced and having a mirror polish on their face in contact with the films (and / or precursor (s) of surface film (s)) are positioned on either side of the stack thus formed.

In step 130, the stack is then placed in a heating press at 200 ° C. and is subjected to a pressure / degassing cycle consisting of:

- a first cycle at 0.5 bar lasting between 1 to 3 min, followed by degassing between 1 to 5 s

- a second cycle at 0.7 bar lasting between 1 to 3 min, followed by degassing between 1 to 5 s - a third cycle at 1 bar lasting between 2 to 3 min, followed by degassing between 1 to 5 s

- a last heating cycle for 2 to 5 minutes.

This cycle is essential to limit any migration of air or water vapor to the surfaces of the panel responsible for porosity defects.

The heating of the material is preferably carried out by conduction in order to ensure temperature uniformity and to ensure rapid distribution of the calories.

The temperature of the heating press leads to the melting of the polymers, which in particular allows the polymer initially present in the form of fibers in the comele, by virtue of its suitable viscosity, to wet the reinforcing fibers and to wet the cellulose sheets.

The stack with the two steel plates is then transferred to the cooling press during step 140 where the actual forming will take place and where it undergoes compression of the order of 0.5 to 7 bars depending the thickness of the panel and the number of composite layers making it up.

This cooling press consists essentially of two perfectly flat plates regulated at a temperature between 15 ° C to 40 ° C.

As we have seen, preferably, between each of the steel plates and one of the flat plates of the cooling press is positioned a YOM mat (not shown in FIG. 1).

In contact with the two plates, through the YOM mats, the plates surrounding the stack cool quickly. They go from 200 ° C to 30 ° C for a period of between 100 s and 150 s. This cooling time is chosen so as to allow the layer of polymer from surface films (and / or film precursors) to reach a crystallinity rate of less than 20%, and preferably between 10% and 20 %.

The thickness of the plates of 3 mm makes it possible to guarantee their flatness while limiting the time necessary for cooling in the cooling press.

After this cooling time, the various polymer strata have cooled sufficiently to have solidified and ensure the overall cohesion of the composite panel according to the invention, which allows it to be removed from the cooling press giving rise to the last step 150. Left at room temperature (around 20 ° C), the polymers present in the internal layers, composite layers and bonding layers, will continue to crystallize for several days without compromising the flatness of the panel over time.

On leaving the mold, the composite panel has a thickness that is at least 10% less than the thickness of the initial stack.

The presence of the cellulose sheets 50A, 50B has surprisingly avoided the phenomena of porosity and wavelets and allowed excellent flatness.

The polymer derived from the bonding films (and / or precursor (s) of film) or present in excess in the precursors of the composite layers 30A, 31A and 30B, 31B has, for its part, allowed perfect assembly between said layers. of composites, the cellulose sheets 50A, 50B and as well as between the skins 12A, 12B and the retractor 11.

Preferably, the polymer derived from the bonding films (and / or precursor (s) of film) fully impregnated with the cellulosic layers ensuring good behavior of the composite panel (10) in a humid environment and preventing delamination of said panel during operations. subsequent machining.

Thus, the type of construction described by the invention makes it possible to obtain a fully bio-sourced panel perfectly suited to POS applications.

Furthermore, it should be noted that the skin 12 A, 12B consists of the assembly of layers of composite materials such as 30A, 31A; 30B, 31B and of cellulose sheets such as 50A, 50B bonded together by the layers of a bio-sourced polymer such as 221A, 222A, 223A; 221B, 222B, 223B can by itself constitute a composite material usable for multiple applications including for POS applications in particular when the latter do not require the manufacture of panels having large surfaces and not requiring too severe mechanical performance, which turns out to be often the case for the construction of displays.

In the case of the latter application, panels based on composite skins such as 12A, 12B have the advantage, when the composite materials 30A, 31 A; 30B, 31B the constituents are dyed in the mass, to present single-colored sides. This is not the case for a sandwich panel according to the invention for which the spacer 11 will always have a shade corresponding to the nature of the particles or of the constituent sheets, generally brownish.

Thus the aesthetic rendering of such displays made of skins alone will be more attractive.

The method of manufacturing the skin-based panel such as 12 A, 12B alone is in every respect similar to that of the sandwich panel 10, with this ready of course that a spacer 11 is not inserted in the stack before introduction in the heating press. The number of layers of composite materials such as 30A, 31 A; 30B, 31B is determined by the mechanical properties required and is generally greater than three.

It should also be noted that the panels according to the invention can be very easily recycled.

Indeed, the entirety of a panel can be crushed until granules with an average diameter of 3 mm can be assembled, possibly with cork particles, virgin or itself recycled, to constitute spacers capable of use in new POS panels.

The process used does not lead to significant investments since presses exerting a pressure of less than 10 bars are sufficient. In addition, the percentage of recycled material that can be high, the panel according to the invention proves to be particularly economical.

It should also be noted that the panel according to the invention is completely compostable. Thus, panels from 3 mm to 20 mm thick with a spacer whose thickness varies from 2.5 mm to 19 mm have obtained the M4 classification according to the protocol of standard NF P 92-501: 1995.

Claims

1. Composite panel (10) of the “sandwich” type comprising at least two composite skins (12A, 12B) on either side of a spacer (11), said skins (12A, 12B) comprising at least two layers of composite material (3 OA, 31 A;

30B, 31B), said composite material comprising at least one reinforcing fiber of natural origin and a matrix of at least one bio-sourced polymer, characterized in that:

al) the skins (12A, 12B) of said composite panel (10) further comprise on their outer face, which is not in contact with the spacer (11), at least one layer of at least one bio thermoplastic polymer - semi-crystalline source (40A, 40B) having a degree of crystallinity of less than 20%, preferably less than 10%;

bl) said at least one layer of semi-crystalline bio-sourced thermoplastic polymer (40A, 40B) has a surface condition without visible defects, in particular without defects of "wavelets", "porosities" or "cracks", with a “mirror polish”, that is to say has a surface roughness of less than 0.8 micrometers according to ISO standard 4287;

cl) between the adjacent layers of composite material either between the layer (30A) and the layer (31 A) on the one hand and the layer (30B) and the layer (31B) on the other hand are positioned layers comprising a sheet a cellulosic material (50A, 50B) having a surface mass of between 20 g / m ² and 250 g / m ² and optionally a Young's modulus in the preferred direction of orientation of the fibers greater than 2 Giga Pascal; and or

dl) between two adjacent layers included in the skins (12A, 12B) of said composite panel, as well as between the spacer (1 1) and each of the skins (12A, 12B), are positioned layers with a thickness between 20 micrometers and 1 mm of at least one bio-sourced polymer (221 A, 222A, 223A; 221B, 222B, 223B) ensuring the bonding of all the layers together as well as the bonding of the skins with the spacer.

2. Panel according to claim 1 characterized in that said at least one semi-crystalline bio-sourced thermoplastic polymer included in the layers of skin surface (40A, 40B) has a degree of crystallinity of between 5% and 10%.

3. Panel according to claims 1 and 2 characterized in that the surface layers of the skins (40A, 40B) have a Shore D hardness of between 60 and 90.

4. Panel according to any one of the preceding claims, characterized in that said at least one semi-crystalline biosourced polymer included in the surface layer of the skins (40 A, 40B) is chosen from poly lactic acid (PLA ), the group comprising homopolymers of hydroxyalkanoates and copolymers of hydroxyalkanoates, as well as their derivatives and mixtures.

5. Panel according to any one of the preceding claims, characterized in that the polymer included in the surface layer of the skins (40A, 40B) has an MFI according to standard ISO 1133 of between 1.5 g / 10 min and 90 g / 10 min as well as a TG between 45 ° C and 90 ° C.

6. Panel according to any one of the preceding claims, characterized in that the fibers included in the composite materials (30A, 31 A and 30B, 31B) are chosen from cellulosic fibers such as flax, hemp, jute fibers, ramie, banana, cotton, viscose and / or regenerated cellulose.

7. Panel according to any one of the preceding claims, characterized in that the matrix of the composite material included in the composite layers (30A, 31A and 30B, 31B) is chosen from PLA (Poly Lactic Acid), homopolymers of hydroxyalkanoates and copolymers of hydroxyalkanoates, as well as their derivatives and mixtures.

8. Panel according to any one of the preceding claims, characterized in that the matrix included in the composite material of the composite layers (30A, 31 A and 30B, 31B) has an MFI measured according to ISO 1133 standard between 1.5 g / 10 min and 90 g / 10 min and a glass transition temperature (TG) between 45 ° C and 90 ° C.

9. Panel according to any one of the preceding claims, characterized in that the polymer included in the bonding layers (221 A, 222 A, 223 A and 221B, 222B, 223B) has an MFI measured according to ISO 1133 between 1 5 g / 10 min and 90 g / 10 min and a glass transition temperature (TG) of between 45 ° C and 90 ° C.

10. Panel according to any one of the preceding claims, characterized in that the polymer included in the bonding layers (221 A, 222 A, 223 A and 221B, 222B, 223B) has an MFI measured according to ISO 1133 between 6 g / 10 min and 38 g / 10 min and a TG of between 45 ° C and 70 ° C.

11. Panel according to any one of the preceding claims, characterized in that the cellulose sheets (50A, 50B) comprise a Kraft paper with a surface mass of between 20 g / m ² and 250 g / m ² .

12. Panel according to any one of the preceding claims, characterized in that the cellulosic sheets (50A, 50B) comprise a nonwoven based on natural fiber with a surface mass of between 20 g / m ² and 150 g / m ² .

13. Panel according to any one of the preceding claims, characterized in that the cellulosic sheets (50A, 50B) have a COBB 60 index determined according to ISO standard 535 between 80% and 100% of the surface mass of said cellulosic sheets (50A , 50B).

14. Panel according to any one of the preceding claims, characterized in that the cellulosic sheets (50A, 50B) are completely impregnated with said at least one polymer from the adjacent bonding layers (222 A, 223 A; 222B, 223B).

15. Panel according to any one of the preceding claims, characterized in that the spacer (11) is based on bio-sourced material.

16. Panel according to any one of the preceding claims, characterized in that the spacer (11) comprises cork granules.

17. Panel according to any one of the preceding claims, characterized in that the spacer (11) comprises particles resulting from the recycling of the composite panel according to any one of claims 1 to 16.

18. Panel according to any one of the preceding claims, characterized in that said panel has a flatness measured according to standard NF EN 10029 of ± 10%, preferably ± 1%.

19. Panel according to any one of the preceding claims, characterized in that said panel has a coloration by pigments uniformly distributed in the composite layers (30A, 30B; 31 A, 31B).

20. Panel according to any one of the preceding claims, characterized in that said panel has at least one composite skin (12A), but does not have a second composite skin (12B) on another face of the spacer (11) .

21. Composite skin (12A, 12B) as defined in any one of claims 1 to 20.

22. Method for manufacturing a composite panel (10) according to any one of claims 1 to 20 comprising the following steps:

a2) the superposition of at least two plates, for example of metal having a mirror polish on their face (s) in contact with the stack formed, of at least one film and / or a film precursor based on '' at least one bio-sourced polymer, at least one comélé, at least one spacer (11) and optionally at least one cellulosic sheet preferably having a moisture content of less than 5%;

d2) cooling at least one plate with a temperature between 160 and 230 ° C, preferably at a temperature of 200 ° C, at a temperature between 10 and 50 ° C, preferably 30 ° C, for a period of at least 100 seconds, preferably between 100 seconds and 150 seconds; and

e2) recovering the composite panel obtained, for example by extracting the composite panel from a cooling press used in step d2); characterized in that said at least one film and / or a film precursor based on at least one bio-sourced polymer is placed in the stack in step a1) so as to:

- be included in the surface layers, and / or

- participate in the bonding of the layers together.

23. The manufacturing method according to claim 22, characterized in that the stack obtained in step a2) comprises the following order: a film and / or a film precursor of surface polymer (s); a comele; a cellulosic sheet; a comele; the retractor; a comele; a cellulosic sheet; a comele; and a film and / or a surface polymer film precursor.

24. The manufacturing method according to claim 23, characterized in that the stack obtained in step a2) further comprises at least one film and / or a film precursor of bonding polymer (s) preferably in the order next: a film and / or a film precursor of surface polymer (s); a comele; a film and / or a film precursor of bonding polymer (s); a cellulosic sheet; a comele; a film and / or a film precursor of bonding polymer (s); the retractor; an adhesive polymer film and / or precursor; a comele; an adhesive polymer film and / or precursor; a cellulosic sheet; a comele; and a film and / or a surface polymer film precursor.

25. A method of producing a composite panel according to any one of claims 22 to 24 comprising an additional step f2) where a YOM mat is interposed between at least one of the plates, preferably metallic, enclosing the stack according to l 'step a2) and a press plate, before the press.

26. A method of producing a composite panel comprising the following steps: a3) superimposition between at least two plates, for example of metal having a mirror polish on their face (s) in contact with the stack formed, of at least one film and / or a film precursor based on at least one bio-sourced polymer, at least one comele, and optionally at least one cellulosic sheet, preferably having a moisture content of less than 5%; b3) placing the stack according to step a3) in a heating press at a temperature between 160 and 230 ° C, preferably at a temperature of 200 ° C;

c3) optional implementation in the heating press of a degassing step, comprising for example at least 3 degassing cycles comprising: a first cycle at a first pressure of between 0.4 and 0.6 bar, preferably 0.5 bar, for a duration of between 1 and 3 minutes, followed by degassing of a duration of between 1 and 5 seconds; a second cycle at a second pressure of between 0.6 and 0.8 bar, preferably 0.7 bar, for a duration of between 1 and 3 minutes, followed by degassing of a duration of between 1 and 5 seconds; a third cycle at a third pressure of between 0.9 and 1.5 bar, preferably 1 bar, for a duration of between 2 and 3 minutes, followed by degassing of a duration of between 1 and 5 seconds;

d3) cooling of at least one plate of a temperature between 160 and 230 ° C, preferably at a temperature of 200 ° C, at a temperature between 10 and 50 ° C, preferably 30 ° C, for a period d '' at least 100 seconds, preferably between 100 seconds and 150 seconds; and

e3) recovering the composite panel obtained, for example by extracting the composite panel from a cooling press used in step d3); characterized in that said method comprises an additional step O) where a YOM mat is inserted before the press between at least one of the plates enclosing the stack according to step a3) and a press plate.

27. The manufacturing method according to claim 26, characterized in that the stack obtained in step a3) comprises between 2 and 20 layers of comele, for example between 5 and 15 layers of comele.

28. The manufacturing method according to claims 26 or 27, characterized in that the stack obtained in step a3 comprises at least one film and / or a film precursor of bonding polymer (s), preferably based on at least one bio-sourced polymer.

29. Manufacturing process according to any one of claims 26 to 28, characterized in that the stack obtained in step a3 comprises a film and / or a film precursor of surface polymer (s), preferably based at least one bio-sourced polymer.

30. The manufacturing method according to any one of claims 26 to 29, characterized in that the stack obtained in step a3 comprises the following order: if necessary at least one film and / or a film precursor surface polymer (s); a succession of at least one comélé with optionally at least one film and / or a film precursor of bonding polymer (s) and / or a cellulose sheet; and optionally at least one film and / or a film precursor of surface polymer (s).

31. Manufacturing process according to any one of claims 22 to 28, characterized in that the stack obtained in step a2) or a3) comprises at least coloring pigment, for example deposited between at least two layers before press or previously included in at least one layer before stacking, such as for example in at least one film and / or a film precursor based on at least one bio-sourced polymer.

32. Composite panel capable of being obtained according to the method according to any one of claims 22 to 25, or the method according to any one of claims 26 to 31.

33. Composite panel capable of being obtained according to the method according to claim 32, characterized by a uniform coloring in its thickness and / or over the extent of its surface.

34. Composite panel according to claim 32 or 33, characterized by a presence of less than 10% V / V of cavities, preferably less than 1% V / V of cavities.

35. Composite panel according to any one of claims 32 to 34, characterized in that said panel has a flatness measured according to standard NF EN 10029 of ± 1%.

36. Composite panel according to any one of claims 32 to 35, characterized by a thickness between 0.5 mm and 20 cm, preferably between 2 mm and 1 cm.

37. Use of at least one bio-sourced thermoplastic polymer to produce a surface layer for composite panel characterized in that said surface layer of bio-sourced thermoplastic polymer (s) is semi-crystalline with a degree of crystallinity of less than 20%, preferably less than 10%.

38. Surface layer for composite panel comprising at least one bio-sourced thermoplastic polymer characterized in that said layer is semi-crystalline with a degree of crystallinity less than 20%, preferably less than 10%.

39. Use of a sheet of cellulosic material, preferably having a surface mass of between 20 g / m ² and 250 g / m ² and optionally a Young's modulus in the preferred direction of orientation of the fibers greater than 2 Giga Pascal, to reduce irregularities related to the use of at least one bio-sourced comele in a composite panel.

40. Composite panel comprising at least one bio-sourced comele in combination with at least one sheet of cellulosic material, preferably having a surface mass of between 20 g / m ² and 250 g / m ² and optionally a Young's module in the direction preferred fiber orientation greater than 2 Giga Pascal.

41. Use of a YOM mat in the thermoforming manufacture of a composite panel to distribute the pressure uniformly over the surface of thermoforming tools, such as thermoforming molds in contact with said composite panel.

42. Press for manufacturing a composite panel comprising a YOM mat interposed between a mold and a press plate.