Composite laminate and its use in sport articles such as shoes

The field of the invention is that of composite materials, and more specifically composite laminates based on fibers organized or not in fabrics or in layers and immobilized in matrices made of polymer resin.

More specifically, the invention relates to a composite laminate in the form of a thin sheet, usable in the manufacture of sporting goods such as sports shoes (sole, upper / upper), roller skates, skis , surfboards, skateboards, golf clubs, scooters, cycles (frames, wheels), fishing rods, snowshoes, helmets, cross-country ski poles, backpacks, tents ...

Composite materials are materials comprising a thermosetting or thermoplastic polymer matrix and a fibrous reinforcement, and optionally granular fillers and adjuvants. The polymer matrix acts as a binder for the reinforcing fibers. It distributes and ensures the transmission of forces to the fibers. The oriented fibrous reinforcement (woven or non-woven) or random (non-woven) provides the properties of strength and mechanical rigidity to the final composite. These composites are used as raw materials in the automotive industry, shipyards, the aeronautical industry, the textile industry, the sporting goods industry (shoes, skis, golf clubs ...). 65% of the composites produced are polyester or vinylester resins reinforced with glass fibers, and obtained using the open molding technique. The remaining 35% is formed by special resins (phenolic, polyurethane and silicone) reinforced with carbon or aramid fibers.

The composites can be in the form of sandwich or laminate constructions, formed by a plurality of superposed fibrous layers and embedded in the matrix. In these composite laminates (sandwich), there is a central structure also called core or composite core, linked by each of its faces to an outer composite skin. These sandwich or laminate composite constructions have the characteristic of being relatively light and extremely rigid. This stiffness is such that the <i>deformability</i> is very small. It is therefore easy to understand that such mechanical characteristics make it difficult to shape and shape parts produced in composite laminates.

The American patent <b>3 873 168</b> describes a composite laminate article comprising a core 14 constituted by a crosslinkable polyimide resin and reinforced by a glass fabric. This core is interposed between two composite skins, the matrix of which is also made of crosslinkable polymer resin and the fibrous reinforcement of which is formed by a graphite fabric. The composite laminate according to US 3 873 168 suffers from too great rigidity and a relatively high cost. Indeed, the fibers used are high performance fibers or fiber fabrics and therefore expensive.

The American patent <b>3 779 851</b> discloses a composite laminate comprised of a plurality of sheets of graphite fabric impregnated with epoxy resin. This laminate is presented as having a ratio<i>mechanical resistance</i>/<i>weight</i> very high, as well as very low thermal expansion characteristics. Such specifications are sought for applications of these composite laminates for the manufacture of optical instruments (mirror). Again, these are extremely rigid composite laminates. The total thickness of the composite laminates according to US 3,779,851, is for example 3.6 mm, or even at least 3 mm (12 inches x 0.254). The folds used to make this laminate are sheets pre-impregnated with carbon fibers in an epoxy resin matrix. This composite laminate has a stiffness that is too great to be used as a raw material in the manufacture of sporting goods, for example shoes, where a certain deformability or ability to bend in the longitudinal direction is required. In addition, the fibrous reinforcement consists exclusively of carbon fibers. This results in a prohibitive price for fields of application such as that of sporting goods which are produced on a large scale and at very low cost, contrary to what can be found in advanced technological fields, such as aeronautics or aerospace.

Furthermore, it is known to use in sports articles, in particular sliding members, such as skis, ice skates, roller skates, snowboards, damping means constituted by laminate structures comprising composites.

Thus, the French patent application <b>n ° 2 742 063</b> discloses a frame of roller skates comprising a damping means, constituted by a laminate successively comprising a layer of rigid stress and a visco-elastic layer. The laminate can include one or more pairs of<i>rigid layer</i>/<i>visco-elastic layer.</i> The rigid layer is made from plastic with a high modulus of elasticity, from composite fibers or from aluminum, these materials being chosen for their rigidity and lightness. The visco-elastic layer is made of rubber or synthetic elastomer. To have the desired damping effect, the composite-rubber laminate according to FR 2 742 063 necessarily has a thickness greater than or equal to 3 mm. In addition, this composite laminated damping means remains perfectible in terms of deformability, cost and weight saving.

French patent application <b>n ° 2 730 416</b> describes a golf club handle consisting of a laminate comprising an outer composite layer of reinforced resin:<ul id="ul0001" list-style="bullet" compact="compact"><li>by carbon fibers, a central core (or core) made of polymer foam, synthetic or natural resin, cork, wood or others,</li><li>and by a composite inner layer of resin reinforced with glass fibers.</li></ul>The density of the internal and external composite layers is greater than 1.2 kg / dm³ and their longitudinal Young's modulus E1 is greater than 20 GPa. The polymer foam core has a density less than 1.2 kg / dm³ and a longitudinal Young's modulus E3 of less than 20 GPa. This composite laminate has a thickness of between 0.2 and 9 mm. Here again, it could be seen that the compromise <i>stiffness</i>/<i>deformability</i>/<i>lifetime</i>/<i>weight gain</i> is not completely satisfactory for this composite / polymer foam / composite laminate according to this French patent application No. 2,730,416. Document GB-A-2-256-784 describes a rubber shoe sole provided with a reinforcement composite not having a sandwich structure. Document WO96 / 2665 describes a polyurethane sole provided, in its thickness, with one or more layers of polyaramid fibers.

It emerges from this review of the prior art that the manufacturers of sporting goods are still waiting for a raw material having the mechanical properties of composites in terms of maximum stiffness and minimum deformability, combined with a capacity vibration damping, low cost, and low weight. These manufacturers also expect this raw material to be easily feasible and industrially formable and finally that it retains its mechanical properties in a sustainable manner over time.

Under these circumstances, one of the essential objectives of the present invention is to propose a new basic material for the manufacture of manufactured articles, in particular sports articles, having drastic mechanical requirements, a very low cost price. and as light as possible.

These objectives, among others, are achieved by the present invention which firstly relates to a composite laminate comprising a sandwich structure made of a core interposed between two skins, characterized in that:<ul id="ul0002" list-style="dash" compact="compact"><li>the soul and the two skins are composite,</li><li>at least a portion of the fibers of the core are fibers whose mechanical strength is significantly lower than that of at least a portion of the fibers of one and / or the other skin.</li></ul>

It is to the credit of the inventors to have been able to demonstrate, after long and painstaking work and in a completely surprising and unexpected manner, that the fact of producing a fully composite microsandwich structure in which the core comprises a resin reinforced by fibers whose mechanical properties are less than those of reinforcing fibers of composite skins placed on either side of the core. Indeed, against all expectations, this introduction of fibers having no mechanical strength and having a low economic value, did not harm the mechanical qualities of the laminated composite material.

Thanks to the invention, there is thus a laminated composite material, light, economical and endowed with high mechanical qualities.

The invention also relates to one of the methods of manufacturing the above-mentioned laminate, the use of said laminate for the manufacture of sporting articles - in particular shoes -, and the article thus formed.

The invention will be better understood in the light of the following detailed description of preferred embodiments of the laminate according to the invention, with reference to the accompanying drawings in which:<ul id="ul0003" list-style="dash" compact="compact"><li>FIG. 1 is a partial schematic representation in section of the laminate according to the invention,</li><li>FIGS. 2A and 2B are explanatory diagrams of a test Tf for evaluating the mechanical strength of composite laminate,</li><li>FIGS. 3A and 3B are views from above and in longitudinal section, respectively, of an element of the lower part of a shoe (sole assembly) - in this case first of assembly - constituted by the composite microsandwich according to the invention,</li><li>Figures 4 to 6 are graphs showing the evolution of the mechanical resistance compared to a standard (100%) composite of carbon fibers as a function of the ratio of the thickness of the core to the average of the thicknesses of the skins ( or average skin thickness value),</li><li>FIG. 7 represents a damping curve of a laminate according to the invention relative to a standard laminate of carbon fiber composite, as a function of time in seconds,</li><li>FIG. 8 is a histogram giving the surface density of two composite laminates according to the invention relative to a one-piece carbon fiber composite.</li></ul>

Figure 1 shows the composite laminate 1 according to the invention. This consists of a sandwich structure comprising a core or core 2 inserted or sandwiched between two skins 3 and 4. This core 2 and these skins 3 and 4 are of a composite nature, that is to say formed by a polymer resin matrix - preferably the same for all three - reinforced by fibers (fibrous material). The fibrous material of the skins 3 and 4 is constituted by high performance fibers, while the fibrous material of the core 2 comprises fibers with low mechanical characteristics and preferably inexpensive.

Advantageously, the fibrous material of the core and / or the skins is present:<ul id="ul0004" list-style="dash" compact="compact"><li>in the form of continuous linear assemblies of (micro) fibers united into threads or rovings of different shapes (basic threads, single threads, cabled threads, rovings);</li><li>in the form of non-linear (discontinuous) yarns, chopped basic yarns or crushed fibers;</li><li>in the form of mats: mat with cut or continuous threads, surface mat, needled mat;</li><li>or in the form of fabrics with canvas or taffeta reinforcement, satin reinforcement, twill reinforcement, high-modulus reinforcement, unidirectional reinforcement, or ribbon reinforcement.</li></ul>

According to a preferred arrangement of the invention, the core 2 and the skins 3 and 4 each consist of a plurality of plies - in this case 3 for the core 2 (2₁, 2₂, 2₃) and 4 for skins 3 and 4 (respectively 3₁, 3₂, 3₃, 3₄ ; 4₁, 4₂, 4₃, 4₄) -. In practice, the core 2 and / or the skin or skins 3 and 4 are obtained by superposition of several plies of fibrous and / or composite materials. Thus, the composite laminate 1 according to the invention is characterized in that it has one or more folds constituting the core and one or more folds constituting the skins, these folds being formed by sheets of woven or nonwoven microfibers, oriented or not, pre-impregnated or not with resin.

In a preferred feature of the invention, the laminate has a total thickness "e" of 3 mm or less, preferably less than 2.5 mm.

The thickness e₂ of the core 2 is advantageously less than or equal to 2 mm, preferably 1.5 mm.

Furthermore, it is preferable that the ratio of the thickness of the core e₂, on the total thickness of the two skins e₃ + e₄ is defined as follows: <maths id="math0001" num=""><math display="block"><mrow><mrow><mrow><msub><mi mathvariant="normal">e</mi><mn>2</mn></msub></mrow><mo>/</mo><mrow><mstyle scriptlevel="+1"><mfrac><mrow><mi mathvariant="normal">e</mi><mn>3</mn><mo>+</mo><mi mathvariant="normal">e</mi><mn>4</mn></mrow><mn>2</mn></mfrac></mstyle></mrow></mrow><mo>≤</mo><mn>5</mn></mrow></math><img file="EP1199155B1_D0001.tif" /></maths> preferably <maths id="math0002" num=""><math display="block"><mrow><mrow><mrow><msub><mi mathvariant="normal">e</mi><mn>2</mn></msub></mrow><mo>/</mo><mrow><mstyle scriptlevel="+1"><mfrac><mrow><mi mathvariant="normal">e</mi><mn>3</mn><mo>+</mo><mi mathvariant="normal">e</mi><mn>4</mn></mrow><mn>2</mn></mfrac></mstyle></mrow></mrow><mo>≤</mo><mn>4</mn></mrow></math><img file="EP1199155B1_D0002.tif" /></maths> and more preferably still <maths id="math0003" num=""><math display="block"><mrow><mn>0</mn><mo>,</mo><mn>1</mn><mo>≤</mo><mrow><mrow><msub><mi mathvariant="normal">e</mi><mn>2</mn></msub></mrow><mo>/</mo><mrow><mstyle scriptlevel="+1"><mfrac><mrow><mi mathvariant="normal">e</mi><mn>3</mn><mo>+</mo><mi mathvariant="normal">e</mi><mn>4</mn></mrow><mn>2</mn></mfrac></mstyle></mrow></mrow><mo>≤</mo><mn>3</mn><mo>,</mo><mn>5.</mn></mrow></math><img file="EP1199155B1_D0003.tif" /></maths>

Regarding the nature and structure of the fibrous material of the core 2, it should be noted that the reinforcing fibers of this core 2 are woven or not, are oriented or not in one or more directions, and are preferably chosen from the group including:<ul id="ul0005" list-style="bullet" compact="compact"><li>textile (micro) fibers made of:<ul id="ul0006" list-style="dash" compact="compact"><li>synthetic polymers: polyamides (NYLON), polyolefin, polyesters, polyesterimides ...</li><li>natural polymers: silk, cotton, linen, jute, hemp,</li></ul></li><li>cellulosic fibers.</li></ul>It is optionally possible to envisage using mixtures of these fibers.

By way of examples of fibrous reinforcement for the core 2, mention may be made of all natural or synthetic fabrics, in particular silk, polyamides (NYLON®) such as, for example, a textile used as lining in clothing and consisting of a non-woven material made of nylon microfibers (Cambrelle®), or other textiles such as linen, cotton, jute, boss cloth, BEMBERG®, any type of paper: watercolor paper, blotting paper, kraft paper, absorbent paper, toilet paper, newspaper ..., any type of cardboard ....

In fact, all the fibrous materials likely to be in the form of thin sheets may be suitable and <i>impregnable</i> by polymer resin, and capable of forming the fibrous reinforcement of the core 2 of the laminate according to the invention, provided that its market value is low.

As regards the fibrous reinforcement of the skins, it is preferable according to the invention that the fibers which constitute it, whether woven or not, oriented or not in one or more directions, are selected from the group of (micro) high performance fibers including:<ul id="ul0007" list-style="dash" compact="compact"><li>carbon (micro) fibers;</li><li>glass (micro) fibers;</li><li>(micro) fibers of synthetic polymers, in particular polyolefins, more especially high density polyethylene fibers oriented DYNEEMA® and drawn, polyamide fibers KEVLAR® TEVARON® or other fibers such as VECTRAN® or SPECTRAL®;</li><li>metallic (micro) fibers, in particular, aluminum, titanium or boron (micro) fibers;</li><li>natural (micro) fibers such as silk.</li></ul>It is optionally possible to envisage using mixtures of these fibers.

Preferably, the fibers of the skins are glass fibers (for example E glass, R or S glass, D glass, silica), carbon fibers, high density polyethylene fibers, oriented and drawn ( DYNEEMA®), aluminum fibers or polyamide (KEVLAR®).

As indicated above, one of the essential characteristics of the invention is based on the choice of a fibrous reinforcement for the core 2 of the microsandwich, of lower quality or mechanical resistance compared to the fibrous reinforcement of the outer skins 3 and 4. Within the meaning of the invention, this notion of lower quality or mechanical strength can be understood through at least one of the following mechanical characteristics specific to the fibers constituting the fibrous reinforcement of the core 2 and of the skins:<ul id="ul0008" list-style="none" compact="compact"><li>□ the microfibers of the core 2 woven or not, oriented or not in one or more directions have a characteristic of tensile stress in longitudinal traction CR (in MPa) such as: CR ≤ 1500 preferably CR ≤ 1000 and more preferably still CR ≤750</li></ul>

Another criterion for selecting the fibers of the core 2 is linked to their price. Thus the fibers of the core 2 are preferably chosen from the fibers having an average market value at least 2 times, preferably at least 5 times and more preferably still at least 10 times less than that of the fibers of the skin or skins.

The fibrous reinforcements of the core 2 and / or of the skins 3 and 4 may be in the form of continuous threads or more or less sophisticated semi-products, such as dry fibers, dry fabrics, prepreg fabrics, products pultruded.

According to an advantageous characteristic of the invention, the core 2 of the composite laminate has vibration dissipation properties (damping).

For obvious reasons of ease of manufacture, preference will be given to embodiments in which the matrix of the core 2 and of the skins 3 and 4 is constituted by a single product.

Thus, these matrices / binders are, for example, chosen from organic thermosetting or thermoplastic resins:<ul id="ul0009" list-style="none" compact="compact"><li>o phenolic</li><li>o polyester,</li><li>o vinylester</li><li>o polyesterimide</li><li>o polyaramid</li><li>o epoxy,</li><li>o polyimide</li><li>o polycarbonate</li><li>o polyterephthalate</li><li>o phenylene polyoxide</li><li>o polyacetal</li><li>o polyamide</li><li>o polysulfurized</li><li>o polyolefin</li></ul>

By way of practical examples, mention may be made of epoxy resins, phenolic resins, vinyl ester resins and polyester resins.

Depending on the applications and therefore the mechanical properties sought, it is possible to introduce fillers or additives into the composites of the core 2 or of the skins 3 and 4 of the laminate 1 according to the invention. These fillers / additives are for example selected from the group comprising: catalysts, accelerators, mold release agents, flame retardants, anti UV, fungicides, chalk, silica, kaolin, titanium oxide, glass, short fibers, metallic powders, quartz, mica.

According to another interesting variant of embodiment of the invention, at least one of the skins of the laminate 1 is transparent so as to make the core 2 visible, the latter advantageously comprising decorative elements. This variant could be implemented for applications such as skis, snowboards, skateboards, roller skates, surfboards, among others.

The laminate or microsandwich 1 according to the invention can also be defined through a stiffness characteristic R measured in a bending test <u style="single">Tf</u>.

The test procedure <u style="single">Tf</u> is the following:<ul id="ul0010" list-style="none" compact="compact"><li>Rectangular specimens of dimensions 90 x 50 mm are used. The dimensions of the test are fixed whatever the test specimen.</li><li>The figure shows the width I equal to 50 mm of the test piece 5.</li><li>These specimens are tested in three-point bending on a conventional tensile machine. The device used is shown in side view in Figure 2A and in top view in Figure 2B.</li><li>The rectangular 90 x 50 mm test piece is designated by the reference 5. This test piece 5 rests on two cylindrical bars 6-7, parallel, transverse, of diameter equal to 10 mm and of length substantially equal to the width of the test piece. or 50 mm. These cylindrical metal bars 6,7 define support lines 8, 9 respectively, shown in FIG. 2B.</li><li>A force F is applied by means of a third cylindrical metallic bar 10 identical and parallel to the bars 6,7 and resting on the upper face of the test piece 5, so as to define a support line 11. The latter is arranged substantially in the middle of the distance <u style="single">d</u> separating the support lines 8, 9 from the support cylinders 6, 7. The distance<u style="single">d</u> between the support lines 8 and 9 is 80 mm. This Tf test makes it possible to complete the Young's module of the test piece, which can be in composite microsandwich laminate 1 according to the invention. One can also thus assess its resistance to rupture, as well as its deflection deflection. From these results, the stiffness R of the test piece is given in an unconventional unit, namely: N / mm. This corresponds to the effort required to obtain a millimeter of arrow measured at the start of the flexion. The results are expressed relative to a control / standard test piece, which is made of carbon fibers of nature T 700 and from TORAY. The carbon fibers used are in the form of a prepreg fabric having the following characteristics: 193 g / m² and marketed under the name VICOTEX® from HEXCEL Composites. The matrix resin is an M10 epoxy resin from HEXCEL Composites.</li></ul>

Thus, according to a preferred characteristic of the invention, the laminate according to the invention has a characteristic of resistance to rupture R in a bending test Tf compared to a control specimen in composite carbon fibers of the same shape and stiffness as those test pieces tested, such as: R≥50, preferably R ≥ 60, and more preferably still R ≥ 70.

As regards the manufacture of the composite laminates 1 according to the invention, it is possible to have recourse to all the processes known to those skilled in the art of composites. As examples, we can cite:<ul id="ul0011" list-style="dash" compact="compact"><li>manual processes by contact or projection,</li><li>medium series processes by vacuum molding or injection (RTM),</li><li>processes by press molding, low pressure and cold, medium pressure and hot, or high pressure and hot (SMC-TER),</li><li>processes by continuous stratification by pultrusion, by self-molding or by injection of thermoplastics,</li><li>reaction injection molding (RIM) processes applied in particular to polyurethane (pure RIM, R-RIM, S-RIM).</li></ul>

In cases where the assembly of the different layers of the composite laminate is not obtained by the above-mentioned methods, it is possible instead or in addition to use bonding assemblies using suitable adhesives. .

Without this being limiting, there will be mentioned in this presentation, two modes of implementation of a process for manufacturing the composite laminate according to the invention.

In the first embodiment, use is made of fibrous reinforcements (mats, plies of threads oriented in one or more directions, fabrics) dry. The fibrous reinforcement of the core 2 is thus constituted by one or more superimposed sheets (for example of paper) or of fabrics (eg silk) or of nonwovens for example CAMBRELLE® = nylon microfibers. Each skin 3 and 4 a fibrous reinforcement consists of one or more plies of fibrous material (carbon fibers oriented or not, woven or not). All or part of the skin folds 3-4 and possibly the core 2 are impregnated with crosslinkable resin, using a crosslinkable resin (for example epoxy). The stack of plies impregnated with resin is subjected to a high pressure (for example 8 bars). Advantageously, it is heated to accelerate the cross-linking (for example at 150 ° C.). Preferably, the dry core is placed between the skins and the two skins are then impregnated with the resin.

According to the second embodiment of the method, the ply or plies constituting the skin (s) 3-4 and / or the core 2, are constituted by a fibrous material pre-impregnated with resin. The stacking is then carried out, making it possible to obtain the microsandwich, it is pressurized and optionally heated as provided in the first embodiment. For the skins, the prepreg fabric used can be a multidirectional or unidirectional fabric of carbon threads on which the resin is deposited. The excess resin is removed by passing between heated or unheated rollers (timing). Before use, the product must be stored cold, generally at least 18 ° C to avoid polymerization of the resin. The fabrics must be brought to room temperature to be usable. When the fiber reinforcement of skins 3-4 is not made of carbon fibers but of high density polyethylene fibers, the pressure used is 2 bars and the temperature is 100 ° C. In any case, a person skilled in the art is able to adjust these parameters according to the nature of the materials used.

According to another of its aspects, the invention relates to the use of laminate as defined above for the manufacture of sporting goods and in particular:<ul id="ul0012" list-style="dash" compact="compact"><li>shoes, in particular sole or upper, and more particularly sports shoes,</li><li>sporting goods, in particular roller skates, skis, surfboards, skateboards, shaft or "shaft" and head of golf clubs, scooters, cycles, fishing rods, rackets, helmets, ski poles (bottom), frames backpack, tents ...</li></ul>

In addition, the invention also relates to articles, and in particular sports articles as obtained by the use of the microsandwich composite laminate mentioned above.

Finally, the laminate according to the invention can be used to produce a composite laminate skin, in particular of the type of those having a thickness greater than 3 mm.

Example 1:

By way of illustration, the following describes the preparation of a constituent element of the lower part (sole assembly) of a shoe, for example a sport shoe: insole, first insole, first fitting ... FIGS. 3A and 3B show this sole element 12 consisting of a composite laminate according to the invention. The latter includes the two outer skins 3, 4 and an inner core 2. The fibrous reinforcements used are:<ul id="ul0013" list-style="dash" compact="compact"><li>for skins 3-4: sheets of carbon fabric pre-impregnated and having a surface density of 193 g / m², thickness equal to 0.19 mm and marketed under the name VICOTEX® / HEXCEL. The orientation of the fibers in the carbon fabric is as follows 0 ° / 90 °</li><li>for core 2: a nonwoven of polyamide microfibers (NYLON®), of thickness equal to 0.32 mm and marketed under the name CAMBRELLE® PBS 3.</li></ul>

Using a punch tool having the shape of the element 12 of FIG. 3A, six plies of prepreg carbon fabric and four plies of Cambrelle are cut. Three plies of prepreg carbon fabric are stacked to form the outer skin 4, then four plies of Cambrelle to form the core 2, and finally three plies of prepreg carbon fabric to form the other outer skin 3. This stack or this superposition of folds is then placed in the female part of a mold of suitable shape, then the male part of this mold is applied to the stack or the superposition of folds, using a press. tray type of those sold by the SATIM Company, heating at 150 ° C for 10 minutes and under a pressure of 4 bars. The composite laminate sole element 12 is extracted from the mold, allowed to cool for 10 minutes, and then the finishing operations such as deburring are carried out. The sole element 12 thus produced is light, economical and has the expected mechanical qualities in terms of longitudinal flexion and transverse stiffness.

Example 2: manufacture of rectangular test pieces of composite laminate and of a control test piece / evaluation of these test pieces in the rigidity test Tf and in a damping test then measurement of the lightness of the laminate

2.1)

Manufacture of test pieces

The test pieces produced are rectangular parallelepipeds of dimensions 80 x 50 mm. They are obtained in the same way as the sole elements 12, the manufacture of which is described above. These test pieces have the same constitution and the same thickness as this sole element 12 manufactured as described above. The only difference between the test pieces is the nature of the fibrous reinforcement of the core 2 which is varied.

The carbon fiber standard / control specimen has the same dimensions and shape as the composite laminate test specimens tested. Its manufacture is described above, in conjunction with the Tf test procedure.

2.2)

Rigidity R

The stiffness R of nine composite laminates according to the invention was measured with respect to a control or reference standard constituted by a one-piece carbon fiber test piece as defined above, as a function of the thickness of the core by in relation to the thickness of the skins. We thus obtain 9 curves,<u style="single">at</u> at <u style="single">i</u>, shown in Figure 4. Table 1 below gives the nature of the test pieces of composite laminate tested.<tables id="tabl0001" num="0001"><table frame="all"><title>TABLE 1</title><tgroup cols="3" colsep="1" rowsep="1"><colspec colnum="1" colname="col1" colwidth="17mm" colsep="1" /><colspec colnum="2" colname="col2" colwidth="57mm" colsep="1" /><colspec colnum="3" colname="col3" colwidth="49mm" colsep="1" /><thead><row><entry namest="col1" nameend="col1" align="center" valign="top"><b>Curve</b></entry><entry namest="col2" nameend="col2" align="center" valign="top"><b>Nature of the fibrous reinforcement of the core 2</b></entry><entry namest="col3" nameend="col3" align="center" valign="top"><b>Origin / Trade name</b></entry></row></thead><tbody><row><entry namest="col1" nameend="col1" align="center" valign="top"><b>at</b></entry><entry namest="col2" nameend="col2" align="center" valign="top">Silk</entry><entry namest="col3" nameend="col3" align="center" valign="top">Garment fabric</entry></row><row><entry namest="col1" nameend="col1" align="center" valign="top"><b>b</b></entry><entry namest="col2" nameend="col2" align="center" valign="top">Polyamide microfiber nonwoven</entry><entry namest="col3" nameend="col3" align="center" valign="top">CAMBRELLE PBS3</entry></row><row><entry namest="col1" nameend="col1" align="center" valign="top"><b>vs</b></entry><entry namest="col2" nameend="col2" align="center" valign="top">Linen</entry><entry namest="col3" nameend="col3" align="center" valign="top">Garment fabric</entry></row><row><entry namest="col1" nameend="col1" align="center" valign="top"><b>d</b></entry><entry namest="col2" nameend="col2" align="center" valign="top">Woven with polyamide microfibers</entry><entry namest="col3" nameend="col3" align="center" valign="top">BONTEX BONSTITCH NXT 0.9</entry></row><row><entry namest="col1" nameend="col1" align="center" valign="top"><b>e</b></entry><entry namest="col2" nameend="col2" align="center" valign="top">Polyamide microfiber nonwoven</entry><entry namest="col3" nameend="col3" align="center" valign="top">CAMBRELLE PBS4</entry></row><row><entry namest="col1" nameend="col1" align="center" valign="top"><b>f</b></entry><entry namest="col2" nameend="col2" align="center" valign="top">Jute</entry><entry namest="col3" nameend="col3" align="center" valign="top">Garment fabric</entry></row><row><entry namest="col1" nameend="col1" align="center" valign="top"><b>g</b></entry><entry namest="col2" nameend="col2" align="center" valign="top">Pattern canvas</entry><entry namest="col3" nameend="col3" align="center" valign="top">Garment fabric</entry></row><row><entry namest="col1" nameend="col1" align="center" valign="top"><b>h</b></entry><entry namest="col2" nameend="col2" align="center" valign="top">Cotton</entry><entry namest="col3" nameend="col3" align="center" valign="top">Garment fabric</entry></row><row><entry namest="col1" nameend="col1" align="center" valign="top"><b>l</b></entry><entry namest="col2" nameend="col2" align="center" valign="top">Synthetic silk</entry><entry namest="col3" nameend="col3" align="center" valign="top">BEMBERG</entry></row></tbody></tgroup></table></tables>

Figure 4 shows that for ratios <maths id="math0004" num=""><math display="inline"><mrow><mrow><mrow><msub><mi mathvariant="normal">e</mi><mn>2</mn></msub></mrow><mo>/</mo><mrow><mstyle scriptlevel="+1"><mfrac><mrow><mi mathvariant="normal">e</mi><mn>3</mn><mo>+</mo><mi mathvariant="normal">e</mi><mn>4</mn></mrow><mn>2</mn></mfrac></mstyle></mrow></mrow></mrow></math><img file="EP1199155B1_D0004.tif" /></maths> of the order of 0.5, the properties of the composite laminates 1 of the invention are comparable to those of the carbon fiber standard.

Figure 5 attached shows the results obtained for fibrous reinforcements of the core of the composite laminate according to the invention, in silk of different natures. Table 2 below specifies the nature and origin of the silks used.<tables id="tabl0002" num="0002"><table frame="all"><title>TABLE 2</title><tgroup cols="3" colsep="1" rowsep="1"><colspec colnum="1" colname="col1" colwidth="17mm" colsep="1" /><colspec colnum="2" colname="col2" colwidth="56mm" colsep="1" /><colspec colnum="3" colname="col3" colwidth="44mm" colsep="1" /><thead><row><entry namest="col1" nameend="col1" align="center" valign="top"><b>Curve</b></entry><entry namest="col2" nameend="col2" align="center" valign="top"><b>Nature of the fibrous reinforcement of the core 2</b></entry><entry namest="col3" nameend="col3" align="center" valign="top"><b>Origin / Trade name</b></entry></row></thead><tbody><row><entry namest="col1" nameend="col1" align="center" valign="top">◆</entry><entry namest="col2" nameend="col2" align="center" valign="top">Silk</entry><entry namest="col3" nameend="col3" align="center" valign="top">CONFECTION</entry></row><row><entry namest="col1" nameend="col1" align="center" valign="top">■</entry><entry namest="col2" nameend="col2" align="center" valign="top">Wild silk</entry><entry namest="col3" nameend="col3" align="center" valign="top">TUSSAH 6342</entry></row><row><entry namest="col1" nameend="col1" align="center" valign="top">▲</entry><entry namest="col2" nameend="col2" align="center" valign="top">Silk</entry><entry namest="col3" nameend="col3" align="center" valign="top">SHAPPE 11122</entry></row><row><entry namest="col1" nameend="col1" align="center" valign="top">•</entry><entry namest="col2" nameend="col2" align="center" valign="top">Silk</entry><entry namest="col3" nameend="col3" align="center" valign="top">TWILL ADC 79095</entry></row><row><entry namest="col1" nameend="col1" align="center" valign="top">∇</entry><entry namest="col2" nameend="col2" align="center" valign="top">Silk velvet 200 g</entry><entry namest="col3" nameend="col3" align="center" valign="top">CONFECTION</entry></row></tbody></tgroup></table></tables>

FIG. 6 also gives results of the relative rigidity of laminated compounds whose core A has a fibrous paper reinforcement compared to a control standard made of carbon fibers. Table 3 of the papers used for the core of the composite laminate according to the invention.<tables id="tabl0003" num="0003"><table frame="all"><title>TABLE 3</title><tgroup cols="2" colsep="1" rowsep="1"><colspec colnum="1" colname="col1" colwidth="17mm" colsep="1" /><colspec colnum="2" colname="col2" colwidth="57mm" colsep="1" /><thead><row><entry namest="col1" nameend="col1" align="center" valign="top"><b>Curve</b></entry><entry namest="col2" nameend="col2" align="center" valign="top"><b>Nature of the fibrous reinforcement of the core 2</b></entry></row></thead><tbody><row><entry namest="col1" nameend="col1" align="center" valign="top">◆</entry><entry namest="col2" nameend="col2" align="center" valign="top">Absorbent paper towels</entry></row><row><entry namest="col1" nameend="col1" align="center" valign="top">■</entry><entry namest="col2" nameend="col2" align="center" valign="top">Newspaper</entry></row><row><entry namest="col1" nameend="col1" align="center" valign="top">▲</entry><entry namest="col2" nameend="col2" align="center" valign="top">Paper designs</entry></row><row><entry namest="col1" nameend="col1" align="center" valign="top">X</entry><entry namest="col2" nameend="col2" align="center" valign="top">Blotting paper</entry></row><row><entry namest="col1" nameend="col1" align="center" valign="top">□</entry><entry namest="col2" nameend="col2" align="center" valign="top">Watercolor paper</entry></row><row><entry namest="col1" nameend="col1" align="center" valign="top">●</entry><entry namest="col2" nameend="col2" align="center" valign="top">Kraft</entry></row></tbody></tgroup></table></tables>

2.3) Damping properties

The damping properties of the test pieces of composite laminates according to the invention are evaluated, in which the fibrous reinforcement of the core is made of silk. These specimens are parallelepipedic, of dimensions 70 x 8 cm for a thickness less than 3 mm. The test piece is fixed to a support by one of its ends. The free end is bent by a value equal to 65 mm relative to the rest position of the test piece, then the test piece is allowed to oscillate by measuring the path of the free end. Figure 7 attached shows the curve <u style="single">k</u> damping A as a function of time t. This curve <u style="single">k</u> is to be compared with depreciation A as a function of time (curve <u style="single">j</u>) obtained for a standard test piece of the same dimensions and the same shape as the test piece of the laminated composite to be tested, with the difference that the standard consists of a carbon fiber composite of the same type as those used for the test control of rigidity R for the Tf test described above. The composite resin is identical for the composite laminate tested and for the carbon fiber control test piece. Comparison of curves<u style="single">k, i</u> shows that the composite laminate with fibrous silk reinforcement for the core, has much better damping properties A than the control standard whose fibrous reinforcement is made of high performance carbon fibers.

2.4)

Lightness

Figure 8 gives in the form of a histogram the surface density ds of:<ul id="ul0014" list-style="dash" compact="compact"><li>the carbon fiber standard test piece of Examples 2.1 and 2.2. : block C-ds = 1733 g / m².</li><li>the test piece of the composite laminate according to the invention with a fibrous silk reinforcement for the core, as used in Example 2.2: block S-ds = 1698 g / m²,</li><li>the composite laminate test tube whose core has a fibrous reinforcement in CAMBRELLE PBS3 curve b figure 4 example 2.1: block PA-ds = 1341 g / m².</li></ul>

This FIG. 8 highlights the qualities of lightness of the laminated compound according to the invention.