FR3091828A1 - Semi-finished products comprising a thermoplastic resin - Google Patents

Abstract

The invention relates to a method of manufacturing a semi-finished product, comprising the following steps: providing reinforcing fibers and a thermoplastic resin having a crystallization temperature of Tcresin; mixing the reinforcing fibers with the thermoplastic resin; heating to effect the melting of the thermoplastic resin and to bring it to a temperature above the melting temperature of the resin; and optionally, a calendering step; the semi-product being characterized by a crystallization temperature Tcsemi-product, the Tcsemi-product being greater than or equal to Tcresin. The invention also relates to a process for manufacturing a composite part from these semi-finished products, as well as to the composite part obtained from this process. No Figure.

Description

Semi-finished products comprising a thermoplastic resin

Field of invention

The present invention relates to a semi-finished product comprising reinforcing fibers and a thermoplastic resin. The present invention also relates to a process for manufacturing the semi-finished product, a process for manufacturing a composite part, and the composite part obtained from this semi-finished product.

Technical background

Composite materials associating a thermoplastic resin with reinforcing fibers are, because of their excellent mechanical properties for a low weight, of great interest in many fields, in particular in the aeronautical and space industry, but also in the automotive industry. and sports equipment.

These composite materials, which may have long, continuous or short fibres, for example, can be obtained by conventional processes for transforming composites using liquid resins (thermosetting or thermoplastic) or plastics processes (injection, resin transfer molding (RTM), injection molding, compression molding, (thermo)stamping, filament winding, etc…).

These composite materials are generally manufactured by assembling/stacking and consolidating semi-finished products consisting of reinforcing fibers coated with resin such as prepregs in the form of unidirectional sheets, rovings or wovens.

These semi-finished products can be obtained for example by impregnating the fibers which are generally continuous unidirectional with the resin. There are various processes, in which the resin can be either melted, or dissolved in a solvent, or in powder form, in a fluidized bed, or dispersed in an aqueous solution. The impregnated fibers are then, where appropriate, stripped of the solvent or of the aqueous solution and then heated in order to melt the resin retained and form the semi-finished product. It is also possible to provide the thermoplastic resin within the reinforcing fibers by intimately mixing (comeling) reinforcing fibers with thermoplastic fibers brought to be melted to form the resin surrounding the reinforcing fibers This semi-finished product is characterized by a homogeneous distribution of the resin (then called matrix) around the reinforcing fibers.

The paper by Iyer et al. in Journal of Thermoplastic composite materials, 1990 (p.325-355) describes the parameters which are essential for the development of a process for impregnating fibers with a dry powder of thermoplastic material.

Document US 3,742,106 describes a process for the manufacture of a semi-finished product comprising passing glass fibers spread through a powder bed of thermoplastic material and heating the fibers so as to melt the thermoplastic material and form a matrix of thermoplastic material around the fibers.

The Miller et al. in Composites Part A , 1998 (p.773-782) describes two methods of impregnating the fibers with a thermoplastic material: the first method comprising mixing the reinforcing fibers with the thermoplastic material in the form of fibers and the second method comprising the mixing reinforcing fibers with the thermoplastic material in powder form.

The article by Funck et al. in Composites Manufacturing, 1995 (p.189-192) describes improved methods of heating a thermoplastic strip (pre-impregnated strip) by laser or by direct flame heating.

The document “ Thermal Degradation Effects on Consolidation and Bonding in the Thermoplastic Fiber-Placement Process ” by Fink et al. (Army Research Laboratory-ARL-TR-2238, June 2000) relates to the effects of thermal decomposition of polyetherketoneketone (PEKK) during a semi-finished product consolidation process.

The article by Tadini et al. in Aerospace Science and Technology , 2017 (p.106-116) relates to the analysis of the chemical degradation of PEKK-based composites for aeronautical components at high temperature.

The article by Patel et al. in Polymer Degradation and Stability, 2010 (p.709-718) presents different PEEK decomposition mechanisms and different products formed due to this decomposition.

The article by Vasconcelos et al. in Materials Research, 2013 (p.227-235) concerns the evaluation of the decomposition kinetics of PEEK in nitrogen as well as in synthetic air atmospheres.

There is still a need to provide a semi-finished product having good properties, in particular good flow properties, and having minimal degradation, in particular thermal, for the manufacture of high-quality composite materials.

• la fourniture de fibres de renfort et d’une résine thermoplastique ayant une température de cristallisation Tc_résine;
• le mélange des fibres de renfort avec la résine thermoplastique ;
• le chauffage pour effectuer la fusion de la résine thermoplastique et pour la porter à une température supérieure à la température de fusion de la résine ; et
• optionnellement, une étape de calandrage ;

The invention relates firstly to a method for manufacturing a semi-finished product, comprising the following steps:

• providing reinforcing fibers and a thermoplastic resin having a crystallization temperature Tc _resin ;
• mixing the reinforcing fibers with the thermoplastic resin;
• heating to effect melting of the thermoplastic resin and to bring it to a temperature above the melting temperature of the resin; and
• optionally, a calendering step;

the semi-finished product being characterized by a crystallization temperature Tc _{semi-finished product} , the _semi- finished product Tc being greater than or equal to the _resin Tc.

In certain embodiments, the melting of the thermoplastic resin is carried out by heating the reinforcing fibers, or the thermoplastic resin, or all the reinforcing fibers and the thermoplastic resin.

In certain embodiments, the heating is carried out by infrared irradiation, UV irradiation, microwave irradiation, laser irradiation, convection heating or heating by high frequency waves, and preferably by infrared irradiation.

In some embodiments, at least a portion of the thermoplastic resin melting step is performed under an inert atmosphere.

In certain embodiments, during the step of melting the thermoplastic resin, all the reinforcing fibers and the thermoplastic resin are supplied with a power per unit of mass of 10 to 1600 kW/kg, preferably of 20 to 1400 kW/kg.

In some embodiments, the heating of the thermoplastic resin to a temperature above its melting temperature is carried out up to a temperature of 320 to 420°C, and preferably 360 to 400°C.

In certain embodiments, the _semi- finished Tc is higher than the _resin Tc by 1 to 10°C, and preferably by 4 to 8°C.

In certain embodiments, the thermoplastic resin is one or more polyaryletherketones chosen from polyetherketones, polyetheretherketones, polyetherketoneketones, polyetheretherketoneketones, polyetherketoneetherketoneketones, polyetheretherketoneetherketones, polyetheretherketones, and polyetherdiphenyletherketones, polyetheretherketones, and preferably chosen from polyetherketones, polyetherketoneketones, and polyetheretherketones.

In some embodiments, the reinforcing fibers are carbon fibers and/or glass fibers.

The invention also relates to a semi-finished product obtained according to the process described above.

• la fabrication d’au moins deux semi-produits selon le procédé décrit ci-dessus ;
• l’empilement des semi-produits en au moins deux couches de semi-produits ;
• la consolidation des couches de semi-produits, et
• le refroidissement des couches de semi-produits consolidés afin d’obtenir la pièce composite.

The invention also relates to a method for manufacturing a composite part comprising the following steps:

• the manufacture of at least two semi-finished products according to the process described above;
• stacking the semi-finished products into at least two layers of semi-finished products;
• the consolidation of layers of semi-finished products, and
• the cooling of the layers of consolidated semi-finished products in order to obtain the composite part.

In certain embodiments, the composite part is characterized by a crystallization temperature Tc _composite , where Tc _composite ≥ Tc _resin – 5°C.

• la fourniture d’au moins deux semi-produits comme décrits ci-dessus ;
• l’empilement des semi-produits en au moins deux couches de semi-produits ;
• la consolidation des couches de semi-produits, et
• le refroidissement des couches de semi-produits consolidés afin d’obtenir la pièce composite.

The invention also relates to a method for manufacturing a composite part comprising the following steps:

• the supply of at least two semi-finished products as described above;
• stacking the semi-finished products into at least two layers of semi-finished products;
• the consolidation of layers of semi-finished products, and
• the cooling of the layers of consolidated semi-finished products in order to obtain the composite part.

In certain embodiments, the composite part is characterized by a crystallization temperature Tc _composite , where Tc _composite ≥ Tc _{semi-finished} – 10°C.

The invention also relates to a composite part obtained according to one of the methods described above.

In certain embodiments, the composite part has a thickness of 0.05 to 150 mm, and/or a length of 0.01 to 100 m, and/or a width of 0.005 to 5 m.

In certain embodiments, the composite part is a part of an aerial or space locomotion vehicle, or a part of a drilling installation, or a part intended to be positioned in contact with or near a vehicle or engine, or a part intended to be subjected to friction.

The present invention makes it possible to meet the need expressed in the state of the art. It more particularly provides a semi-finished product having good properties, in particular good flow properties, and having minimal degradation, in particular thermal, for the manufacture of high-quality composite materials.

It has been discovered by the present inventors that the manufacture of high quality composite materials is highly dependent on the properties of the semi-finished products. Indeed, the obtaining of semi-finished products having an absence of degradation or a minimal degradation makes it possible to obtain the properties suitable for the manufacture of composite parts having few defects. Degradation will be qualified here as a mechanism which tends to slow down initially, then to interfere with the capacity of the semi-finished product to crystallize. This mechanism may be linked to an increase in molecular masses by branching of polymer chains. This degradation, which in the context of the invention is mainly thermal degradation of the resin in the semi-finished product, must be minimal. The suitable properties of the semi-finished product produced according to the present invention and making it possible to obtain composite parts free from defects are mainly a good flow property as well as a good ability to crystallize. The present inventors have found that the crystallization temperature of the semi-product is an indicator of the good properties of the semi-product as well as of its degradation and that a semi-product crystallization temperature Tc _semi-product greater than or equal to the temperature crystallization of the thermoplastic resin alone Tc _resin (before the manufacture of the semi-finished product) makes it possible to obtain semi-finished products having good properties and exhibiting minimal degradation.

The present inventors have also discovered that when these semi-finished products are used for the manufacture of composite parts, the crystallization temperature of the composite part Tc _composite can also be an indicator of the good properties and of the minimal degradation of the composite part.

Brief description of figures

represents differential scanning calorimetry (DSC) analysis diagrams for a PEKK resin (A = first heating, B = second heating, C = cooling), where the temperature is represented on the abscissa (°C) and the flow of heat is represented on the ordinate (W/g).

represents differential scanning calorimetry (DSC) analysis diagrams for a PEKK resin (A = first heating, B = second heating, C = cooling), where the temperature is represented on the abscissa (°C) and the flow of heat is represented on the ordinate (W/g).

represents a DSC analysis diagram for a semi-finished product according to the invention (A = first heating, B = second heating, C = cooling), where the temperature is represented on the abscissa (°C) and the heat flux is represented on the ordinate (W/g).

represents a DSC analysis diagram for a composite part according to the invention (A = first heating, B = second heating, C = cooling), where the temperature is represented in abscissa (°C) and the heat flux is represented in ordinate (W/g).

represents a DSC analysis diagram for a semi-finished product according to a comparative example (A = first heating, B = second heating, C = cooling), where the temperature is represented on the abscissa (°C) and the heat flow is represented on the ordinate (W/g).

represents a DSC analysis diagram for a composite part according to a comparative example (A = first heating, B = second heating, C = cooling), where the temperature is represented in abscissa (°C) and the heat flow is represented in ordinate (W/g).

detailed description

The invention is now described in more detail and in a non-limiting manner in the description which follows.

Process for manufacturing a semi-finished product

“ Semi-finished product ” means a product comprising a resin and reinforcing fibers, which is used as an intermediate product in the manufacture of composite materials. The semi-finished products according to the invention are prepregs (or tapes) in the form of a layer of fibers in a resin matrix. The reinforcing fibers preferably have an essentially unidirectional orientation in the semi-finished product.

The resin of the semi-finished product is a thermoplastic resin which may comprise one or more thermoplastic materials. Similarly, the reinforcing fibers can be made up of fibers of the same nature or fibers of a different nature, both in terms of chemical nature (organic, inorganic, mineral, natural, biosourced, etc.) and dimensions (diameter, number ).

The thermoplastic material can be one or more polyaryletherketones (PAEK).

• Ar et Ar’ désignent chacun un radical aromatique divalent ;
• Ar et Ar’ peuvent être choisis, de préférence, parmi le 1,3-phénylène, 1,4-phénylène, le 4,4'-biphénylène, le 1,4-naphthylène, le 1,5-naphthylène et le 2,6-naphthylène, éventuellement substitués ;
• X désigne un groupe électroattracteur, qui peut être choisi, de préférence, parmi le groupe carbonyle et le groupe sulfonyle ;
• Y désigne un groupe choisi parmi un atome d’oxygène, un atome de soufre, un groupe alkylène, tel que notamment -CH₂- et l’isopropylidène.

By “ PAEK ” is meant the polymers comprising units of formula (-Ar-X-) as well as units of formula (-Ar'-Y-), in which:

• Ar and Ar' each designate a divalent aromatic radical;
• Ar and Ar' can preferably be chosen from 1,3-phenylene, 1,4-phenylene, 4,4'-biphenylene, 1,4-naphthylene, 1,5-naphthylene and 2, 6-naphthylene, optionally substituted;
• X denotes an electron-withdrawing group, which can preferably be chosen from among the carbonyl group and the sulphonyl group;
• Y denotes a group chosen from an oxygen atom, a sulfur atom, an alkylene group, such as in particular —CH ₂ — and isopropylidene.

Among the X units, at least 50 mol.%, preferably at least 70 mol.% and more particularly, at least 80 mol.% of the X units represent a carbonyl group. In certain embodiments, all the X units denote a carbonyl group.

Among the Y units, at least 50 mol.%, preferably at least 70 mol.% and more particularly at least 80 mol.% of the Y units represent an oxygen atom. In some embodiments, all Y units denote an oxygen atom.

Thus, in certain embodiments, the PAEK is a polymer comprising, or preferably consisting of, units of formula (-Ar-CO-) as well as units of formula (-Ar'-O-), the units Ar and Ar' being as defined above.

In certain embodiments, the PAEK is a poly-ether-ketone-ketone (PEKK), comprising a succession of repeated units of the -(Ar ₁ -O-Ar ₂ -CO-Ar ₃ -CO) _n - type, each Ar ₁ , Ar ₂ and Ar ₃ independently representing a divalent aromatic radical, preferably a phenylene.

In the formula above, as in all the formulas that follow, n represents an integer.

The bonds on either side of each Ar ₁ , Ar ₂ and Ar ₃ unit can be of the para, or meta, or ortho type (preferably of the para or meta type).

In certain embodiments, the PEKK comprises a succession of repeating units of formula (IA) and/or of formula (IB) as follows:

(IA)

(IB)

The units of formula (IA) are units derived from isophthalic acid (or I units), while the units of formula (IB) are units derived from terephthalic acid (or T units).

In the PEKK used in the invention, the mass proportion of T units relative to the sum of the T and I units can vary from 0 to 5%; or 5 to 10%; or 10 to 15%; or 15 to 20%; or 15 to 20%; or 20 to 25%; or 25 to 30%; or 30 to 35%; or 35 to 40%; or 40 to 45%; or 45 to 50%; or 50 to 55%; or 55 to 60%; or 60 to 65%; or 65 to 70%; or 70 to 75%; or 75 to 80%; or 80 to 85%; or 85 to 90%; or 90 to 95%; or 95 to 100%.

Ranges of 35 to 100%, in particular from 55 to 85% and even more specifically from 60 to 80%, are particularly suitable. In all the ranges set out in this application, the terminals are included unless otherwise stated.

In certain embodiments, the PAEK is a poly-ether-ether-ketone (PEEK), comprising a succession of repeated units of the type -(Ar ₁ -O-Ar ₂ -O-Ar ₃ -CO) _n -, each Ar ₁ , Ar ₂ and Ar ₃ independently representing a divalent aromatic radical, preferably a phenylene.

The bonds on either side of each Ar ₁ , Ar ₂ and Ar ₃ unit can be of the para, or meta, or ortho type (preferably of the para or meta type).

In certain embodiments, the PEEK comprises a succession of repeated units of formula (II):

(II)

and/or a succession of repeated units of formula (III):

(III)

and/or a succession of repeated units of formula (IV):

(IV)

and/or a succession of repeating units of formula (V):

(V)

In certain embodiments, the PAEK is a poly-ether-ketone (PEK), comprising a succession of repeated units of the -(Ar ₁ -O-Ar ₂ -CO) _n - type, each Ar ₁ and Ar ₂ representing independently a divalent aromatic radical, preferably a phenylene.

The bonds on either side of each Ar ₁ and Ar ₂ unit can be of the para, or meta, or ortho type (preferably of the para or meta type).

In certain embodiments, the PEK comprises a succession of repeating units of formula (VI):

(VI)

In certain embodiments, the PEK comprises a succession of repeated units of formula (VII):

(VII)

In this formula, as in the following formulas, x and y represent whole numbers.

In certain embodiments, the PEK comprises a succession of repeated units of formula (VIII):

(VIII)

In certain embodiments, the PAEK is a poly-ether-ether-ketone-ketone (PEEKK), comprising a succession of repeating units of the type -(Ar ₁ -O-Ar ₂ -O-Ar ₃ -CO-Ar ₄ -CO) _n -, each Ar ₁ , Ar ₂ , Ar ₃ and Ar ₄ independently representing a divalent aromatic radical, preferably a phenylene.

The bonds on either side of each Ar ₁ , Ar ₂ , Ar ₃ and Ar ₄ unit can be of the para, or meta, or ortho type (preferably of the para or meta type).

In certain embodiments, the PEEKK comprises a succession of repeating units of formula (IX):

(IX)

In certain embodiments, the PAEK is a poly-ether-ether-ether-ketone (PEEEK), comprising a succession of repeating units of the type -(Ar ₁ -O-Ar ₂ -O-Ar ₃ -O-Ar ₄ -CO) _n -, each Ar ₁ , Ar ₂ , Ar ₃ and Ar ₄ independently representing a divalent aromatic radical, preferably a phenylene.

The bonds on either side of each Ar ₁ , Ar ₂ , Ar ₃ and Ar ₄ unit can be of the para, or meta, or ortho type (preferably of the para or meta type).

In certain embodiments, the PEEEK comprises a succession of repeating units of formula (X):

(X)

In certain embodiments, the PAEK is a poly-ether-ketone-ether-ketone-ketone (PEKEKK), comprising a succession of repeating units of the type -(Ar ₁ -O-Ar ₂ -CO-Ar ₃ -O- Ar ₄ -CO-Ar ₅ -CO) _n -, each Ar ₁ , Ar ₂ , Ar ₃ , Ar ₄ and Ar ₅ independently representing a divalent aromatic radical, preferably a phenylene.

The bonds on either side of each Ar ₁ , Ar ₂ , Ar ₃ , Ar ₄ and Ar ₅ unit can be of the para, or meta, or ortho type (preferably of the para or meta type).

In certain embodiments, the PAEK is a poly-ether-ether-ketone-ether-ketone (PEEKEK), comprising a succession of repeating units of the type -(Ar ₁ -O-Ar ₂ -O-Ar ₃ -CO- Ar ₄ -O-Ar ₅ -CO) _n -, each Ar ₁ , Ar ₂ , Ar ₃ , Ar ₄ and Ar ₅ independently representing a divalent aromatic radical, preferably a phenylene.

The bonds on either side of each Ar ₁ , Ar ₂ , Ar ₃ , Ar ₄ and Ar ₅ unit can be of the para, or meta, or ortho type (preferably of the para or meta type).

In certain embodiments, the PAEK is according to the most general formula indicated below, in which certain Ar and/or Ar' units represent a divalent radical derived from diphenyl or biphenol.

In certain embodiments, the PAEK is a poly-ether-diphenyl-ether-ketone (PEDEK), comprising a succession of repeating units of the type -(Ar ₁ -ODO-Ar ₂ -CO) _n -, each Ar ₁ and Ar ₂ independently representing a divalent aromatic radical, preferably a phenylene, and D representing a divalent radical derived from diphenyl.

The bonds on either side of each Ar ₁ and Ar ₂ unit can be of the para, or meta, or ortho type (preferably of the para or meta type).

In certain embodiments, the PEDEK comprises a succession of repeating units of formula (XI):

(XI)

Blends of the above PAEKs can also be used, as well as copolymers of the above PAEKs.

The PAEK resin may comprise one or more additional polymers not belonging to the PAEK family.

Preferably, the mass content of PAEK in the PAEK resin is greater than or equal to 50%, preferably 60%, more preferably 70%, more preferably 80% and more preferably 90%.

In some embodiments, the PAEK resin consists essentially of one or more PAEKs.

Advantageously, the thermoplastic resin comprises PEK, PEEK or PEKK as the thermoplastic material. PEKK is particularly preferred.

In some embodiments, the thermoplastic resin may have a glass transition temperature Tg of 120 to 200°C, preferably 140 to 170°C. The Tg is determined by differential scanning calorimetry (DSC) according to standard EN ISO 11357-4: 2014.

In some embodiments, the thermoplastic resin may have a melting temperature Tm of 250 to 400°C, preferably 300 to 350°C. The Tf is determined by differential scanning calorimetry (DSC) according to standard EN ISO 11357-4: 2014.

In some embodiments, the thermoplastic resin may have a Tc _resin crystallization temperature of 220 to 310°C, preferably 245 to 285°C. This crystallization temperature can also be determined by differential calorimetric analysis (DSC) according to standard EN ISO 11357-4: 2014 but with cooling at 20° C./min.

The reinforcing fibers used for the manufacture of the semi-finished products can be chosen from among all the fibers capable of being used as reinforcement in the manufacture of parts made of composite materials.

Thus, it may in particular be glass fibers, quartz fibers, carbon fibers, graphite fibers, silica fibers, metal fibers such as steel fibers, aluminum fibers or boron fibers, ceramic fibers such as silicon carbide or boron carbide fibers, synthetic organic fibers such as aramid fibers or poly(p-phenylene benzobisoxazole) fibers, better known by the acronym PBO, or PAEK fibers, or mixtures of such fibers.

Preferably, they are carbon fibers or glass fibers, and more particularly carbon fibers.

The fibers are preferably unsized. When they are sized, the sizing is preferably adapted to the resin, in particular in that it does not lead to harmful degradation products for the resin.

The average diameter of the reinforcing fibers can be in particular from 2 to 20 μm, preferably from 4 to 15 μm, more preferably from 6 to 10 μm. Average fiber diameter can be measured by microscopic analysis

• la fourniture des fibres de renfort et d’une résine thermoplastique telles que décrites ci-dessus;
• le mélange des fibres de renfort avec la résine thermoplastique ;
• le chauffage pour effectuer la fusion de la résine thermoplastique et pour élever la température de la résine thermoplastique à une température supérieure à la température de fusion de la résine; et
• optionnellement une étape de calandrage.

The method for manufacturing a semi-finished product according to the invention may comprise the following steps:

• providing reinforcing fibers and a thermoplastic resin as described above;
• mixing the reinforcing fibers with the thermoplastic resin;
• heating to effect melting of the thermoplastic resin and to raise the temperature of the thermoplastic resin to a temperature above the melting temperature of the resin; and
• optionally a calendering step.

The second stage and the third stage thus allow the impregnation of the reinforcing fibers with the thermoplastic resin.

Thus, the semi-finished products according to the invention can be manufactured by unwinding in an aligned manner and by putting under tension rovings of fibers initially wound in reels, arranged adjacent to each other; then by carrying out the impregnation with the resin.

The number of rovings arranged adjacently may in particular be from 10 to 300, preferably from 20 to 200, more preferably from 30 to 100, for example approximately 50. Each roving may in particular comprise from 300 to 50,000 fibers, from preferably 1,000 to 50,000 fibers, more preferably 3,000 to 50,000 fibers, more preferably 6,000 to 50,000 fibers, more preferably 6,000 to 48,000 fibers, more preferably 6,000 to 24,000 fibers, more preferably 12,000 to 24,000 fibres, for example about 12,000 fibres.

The mixing can be carried out by introducing and circulating the reinforcing fibers in a bath of aqueous dispersion of resin. The fibers mixed with thermoplastic resin powder are then taken out of the bath and freed of water, for example by drying in an infrared oven. Then, melting the thermoplastic resin and then raising the temperature of the thermoplastic resin to a temperature above its melting temperature allows the fibers to be coated with the resin. The coated fibers obtained are then if necessary shaped, for example by calendering. This step can make it possible to texturize and ensure the sizing of the semi-finished product.

Alternatively, the mixing can be carried out by introducing and circulating the reinforcing fibers in a bath of resin dissolved in a solvent, then by drying, evaporation of the solvent and melting of the thermoplastic resin and calendering as described above.

Alternatively, the mixture can be carried out by placing the reinforcing fibers in a fluidized bed of resin powder, then melting the thermoplastic resin and calendering as described above.

The heating mentioned above may consist of heating the reinforcing fibers (which itself makes it possible to heat the thermoplastic resin), or directly heating the thermoplastic resin, or heating all the reinforcing fibers and thermoplastic resin.

Thus, the heating can be carried out by infrared irradiation, UV irradiation, microwave irradiation, laser irradiation, convection heating, high frequency wave heating or hot air heating. Preferably, the heating is carried out by infrared irradiation.

For example, the heating may be heating of the reinforcing fibers by infrared irradiation, or heating of the thermoplastic resin by convection.

The heating can be carried out in several stages, for example by applying different powers from one stage to another. It is for example possible to use several ovens each having a different power, or an oven having distinct heating zones. By “ heating power ” is meant here the electrical power consumed by the oven.

Preferably, the heating is of decreasing intensity, that is to say that a first heating power is applied first (for example of infrared irradiation), then a second heating power (for example of infrared irradiation) lower than the first, then optionally a third heating power (for example infrared irradiation) lower than the first, and possibly so on.

Preferably, the reinforcing fibers are at a distance of 2 to 25 cm, and preferably 6 to 15 cm from the radiation source.

The heating can for example be carried out at a maximum power of 25 to 60 kW, preferably of 30 to 50 kW.

The heating time (from the start of heating until the moment when no more heating is applied) can be in particular from 3 to 150 seconds, and preferably from 10 to 80 seconds. Thus, the heating time may in particular be from 3 to 10 seconds; or 10 to 20 seconds; or 20 to 30 seconds; or 30 to 40 seconds; or 40 to 50 seconds; or 50 to 60 seconds; or 60 to 70 seconds; or 70 to 80 seconds; or 80 to 90 seconds; or 90 to 100 seconds; or 100 to 110 seconds; or 110 to 120 seconds; or 120 to 130 seconds; or 130 to 140 seconds; or 140 to 150 seconds.

During heating, the power absorbed per kg of all the reinforcing fibers and the thermoplastic resin makes it possible to bring the thermoplastic resin to its melting temperature and to exceed it to bring the resin to a temperature above its temperature of fusion to obtain the semi-finished product. This power can in particular be from 10 to 1600 kW/kg, preferably from 20 to 1400 kW/kg. Thus, this absorbed power can be from 10 to 100 kW/kg; or from 100 to 200 kW/kg; or from 200 to 300 kW/kg; or from 300 to 400 kW/kg; or from 400 to 500 kW/kg; or from 500 to 600 kW/kg; or from 600 to 700 kW/kg; or 700 to 800 kW/kg; or 800 to 900 kW/kg; or from 900 to 1000 kW/kg; or from 1000 to 1100 kW/kg; or from 1100 to 1200 kW/kg; or from 1200 to 1300 kW/kg; or from 1300 to 1400 kW/kg; or from 1400 to 1500 kW/kg; or from 1500 to 1600 kW/kg.

This absorbed power can be calculated using the following formula:

Power per unit mass P is measured in kW/kg. Cp represents the heat capacity of all the reinforcing fibers and the thermoplastic resin, and it is expressed in J/kg.°C, Tf represents the melting point of the resin in °C, Vm represents the volume rate of reinforcing fibers, ΔHf represents the enthalpy of fusion of the resin in J/kg (can be determined by DSC according to standard EN ISO 11357-4: 2014) and Dm represents the mass flow rate of semi-finished product expressed in kg/ s.

During the heating step, a line speed of 2 to 80 m/min, preferably 5 to 40 m/min, for example 10 to 20 m/min can be used.

During the heating step, the thermoplastic resin must reach a temperature above its melting point to allow the manufacture of the semi-finished product. This temperature may in particular be from 320 to 420°C, preferably from 360 to 400°C. Also, the reinforcing fibers can reach a maximum temperature of 300 to 440°C, preferably 360 to 400°C in the case of the impregnation of thermoplastics of the PAEK type. The temperature of the reinforcing fibers can be measured using a pyrometer or a thermal camera.

According to certain embodiments, at least part of the melting of the thermoplastic resin is carried out under an inert atmosphere. Preferably, the entire step of melting the thermoplastic resin is carried out under an inert atmosphere.

By " melting under an inert atmosphere " is meant a melting in which the product to be melted is brought into contact with a gaseous mixture essentially devoid of oxygen. Melting under an inert atmosphere can take place, for example, in an enclosure filled with nitrogen or another inert gas mixture, or else in an enclosure filled with air but with a sweep of an inert gas mixture (for example nitrogen) on the molten product.

The calendering step can be carried out in particular by a heating calendering device. The temperature during the calendering can in particular be from 20 to 350° C., preferably from 140 to 240° C.

• une épaisseur de 0,05 à 1 mm, de préférence de 0,15 à 0,4 mm ;
• une longueur de 0,01 m à 25.000 m pour des produits à base de fibres de verre par exemple et à 10.000 m pour des tapes à base de fibres de carbone.
• une largeur de 0,005 m à 5 m, de préférence de 0,01 m à 5 m.

The semi-finished product generally comes in the form of a more or less wide ribbon (one can speak of a web or sheet from a certain width) and more or less thick. These semi-finished products preferably have the following dimensions:

• a thickness of 0.05 to 1 mm, preferably 0.15 to 0.4 mm;
• a length of 0.01 m to 25,000 m for products based on glass fibers for example and 10,000 m for tapes based on carbon fibers.
• a width of 0.005 m to 5 m, preferably 0.01 m to 5 m.

Preferably, the semi-finished products according to the invention comprise from 1 to 99% by weight, preferably from 30 to 90%, in particular from 50 to 80% by weight, and in particular from 60 to 70% by weight of fibers reinforcement.

Preferably, the semi-finished products according to the invention comprise from 1 to 99% by weight, preferably from 10 to 70%, in particular from 20 to 50% by weight, and in particular from 30 to 40% by weight of resin .

The semi-finished products according to the invention may have a _{semi-finished product} crystallization temperature Tc of 220 to 320° C., preferably of 245 to 295° C. determined by differential calorimetric analysis (DSC) according to standard EN ISO 11357-4: 2014 when cooling at 20°C/min.

The _{semi-finished Tc of the semi-} finished products according to the invention is greater than or equal to the _resin Tc (that is to say at the crystallization temperature of the thermoplastic resin alone before the manufacture of the semi-finished product).

According to some embodiments, the Tc _semi-product is equal to Tc _resin . Alternatively, the _semi- finished Tc is higher than the _resin Tc by 1 to 10°C and preferably by 4 to 8°C. The Tc _semi-product can for example be from 1 to 2°C; or 2 to 4°C; or 4 to 6°C; or 6 to 8°C; or 8 to 10°C greater than or equal to the Tc _resin .

The semi-finished products of the invention may also further comprise fillers (other than the reinforcing fibers) and/or functional additives. Among the functional additives, it is possible in particular to include one or more surfactants, UV stabilizers, thermal stabilizers, light stabilizers, impact modifiers, plasticizers, expanding agents and/or biocidal agents, thermally and/or electrically conductive particles, dyes, flame retardants, flame retardants, etc.

The fillers can in particular be mineral fillers such as alumina, silica, calcium carbonate, titanium dioxide, glass beads, carbon black, graphite, graphene and carbon nanotubes.

The total quantity of fillers and additives is preferably less than or equal to 5% by weight, more preferably 2% by weight, more preferably 1% by weight in the semi-finished product.

Additives and/or fillers, when present, can preferably be incorporated during impregnation with the resin.

Composite parts manufacturing process

• l’empilement d’au moins deux semi-produits ;
• la consolidation des semi-produits, et
• le refroidissement des semi-produits afin d’obtenir la pièce composite.

The manufacturing process of a composite part involves:

• the stacking of at least two semi-finished products;
• the consolidation of semi-finished products, and
• the cooling of the semi-finished products in order to obtain the composite part.

The thermoplastic resin can be identical or different from one semi-finished product to another forming the same composite part. Preferably, the thermoplastic resin is of the same nature (for example PEK or PEKK or PEEK) in all the semi-finished products of the composite part. It may possibly include a different grade from one semi-finished product to another, for example a different viscosity, a different molecular weight or a different melting temperature. Alternatively, the grade of the thermoplastic resin is the same in all the semi-finished products of the composite part.

The composite part obtained from this process is characterized by a _composite crystallization temperature Tc.

When the thermoplastic resin of the different semi-products is the same, or when the semi-products are the same, the _composite Tc temperature can be compared with the _resin Tc temperature of the starting resin, or with the _semi-product Tc temperature of the semi-finished products used to manufacture the part.

Thus, in embodiments, Tc _composite ≥ Tc _resin – 5°C. Thus, the difference between the Tc _resin and the Tc _composite can be less than 5°C; or less than 4°C; or less than 3°C; or less than 2°C; or less than 1°C.

In embodiments, Tc _composite ≥ Tc _semi-product – 10°C. Thus, the difference between the _semi- finished Tc and the _composite Tc can be less than 10°C; or less than 9°C; or less than 8°C; or less than 7°C; or less than 6°C; or less than 5°C; or less than 4°C; or less than 3°C; or less than 2°C; or less than 1°C.

The _composite Tc of a composite part according to the invention can be from 210 to 320° C. and preferably from 245 to 295° C. determined by differential calorimetric analysis (DSC) according to standard EN ISO 11357-4: 2014 during cooling at 20°C/min.

Composite parts are obtained, for example, by first manufacturing a preform, in particular by placing or draping pre-impregnated semi-finished products in a mould. The composite part is then obtained by consolidation, a step during which the preform is heated, generally under pressure in an autoclave, so as to assemble the semi-finished products by fusion. Preferably, the semi-finished products produced according to the invention can be consolidated outside the autoclave, for example under a vacuum tank placed in an oven. Such equipment is more economical than an autoclave, and therefore advantageous to use. However, it allows a lower level of compression than an autoclave.

Thus, when the consolidation is carried out in an autoclave, the pressure applied in the autoclave can be from 1 to 20 bar and preferably from 7 to 10 bar. Thus, the pressure applied in the autoclave can in particular be from 1 to 1.5 bar; or 1.5 to 2 bar; or from 2 to 2.5 bar; or 2.5 to 3 bar; or from 3 to 3.5 bar; or 3.5 to 4 bar; or 4 to 4.5 bar; or 4.5 to 5 bar; or 5 to 5.5 bar; or 5.5 to 6 bar; or 6 to 6.5 bar; or 6.5 to 7 bar; or 7 to 7.5 bar; or 7.5 to 8 bar; or 8 to 8.5 bar; or 8.5 to 9 bar; or 9 to 9.5 bar; or 9.5 to 10 bar; or 10 to 10.5 bar; or from 10.5 to 11 bar; or 11 to 11.5 bar; or from 11.5 to 12 bar; or from 12 to 12.5 bar; or from 12.5 to 13 bar; or from 13 to 13.5 bar; or 13.5 to 14 bar; or from 14 to 14.5 bar; or 14.5 to 15 bar; or 15 to 15.5 bar; or 15.5 to 16 bar; or 16 to 16.5 bar; or 16.5 to 17 bar; or from 17 to 17.5 bar; or from 17.5 to 18 bar; or from 18 to 18.5 bar; or from 18.5 to 19 bar; or from 19 to 19.5 bar; or 19.5 to 20 bar.

When the consolidation is carried out in a vacuum tank, the pressure applied in the vacuum tank can be from 50 to 900 mbar and preferably from 300 to 800 mbar. Thus, the pressure applied in the vacuum tank can in particular be from 50 to 100 mbar; or 100 to 150 mbar; or 150 to 200 mbar; or 200 to 250 mbar; or from 250 to 300 mbar; or from 300 to 350 mbar; or from 350 to 400 mbar; or from 400 to 450 mbar; or from 450 to 500 mbar; or from 500 to 550 mbar; or from 550 to 600 mbar; or from 600 to 650 mbar; or from 650 to 700 mbar; or from 700 to 750 mbar; or from 750 to 800 mbar; or from 800 to 850 mbar; or 850 to 900 mbar.

During the consolidation of the preform, the temperature of the semi-products can increase to a maximum temperature, higher than the melting temperature of the thermoplastic resin, and then remain constant.

The maximum temperature is preferably set at a value which is 5 to 50°C higher than the melting temperature of the resin, preferably 10 to 40°C higher than the melting temperature of the resin, preferably 20 at 30° C. higher than the melting point of the resin, and for example higher by 25° C. than the melting point of the resin.

The maximum temperature may be, depending on the case, 300 and 450°C, preferably 320 to 400°C, and for example 375°C. In some embodiments, the maximum heating temperature may be 300 to 320°C; or 320 to 340°C; or 340 to 360°C; or 360 to 380°C; or 380 to 400°C; or 400 to 420°C; or 420 to 450°C.

The consolidation of a preform is followed by its cooling in order to solidify the composite part. Thus, the temperature is decreased to a temperature below the melting temperature of the resin.

In the processes for manufacturing composite parts, the semi-finished products or preforms are subjected to various thermal cycles under pressure or under vacuum in order to assemble them together to form the composite part and/or to shape it.

• une épaisseur de 0,05 à 1 mm, de préférence de 0,15 à 0,4 mm ;
• une longueur de 0,01 à 100 m, de préférence de 0,1 à 10 m ;
• une largeur de 0,005 à 5 m, de préférence de 0,01 à 5 m.

In some embodiments, a number of semi-finished products may be positioned side-by-side and edge-to-edge on a plane. In this case, the reinforcing fibers of the semi-finished products can be oriented in the same direction. Thus, the semi-finished products can form a layer of thickness which corresponds to the thickness of a semi-finished product. In some embodiments, the plane on which the semi-finished products are positioned may be curved. In certain embodiments, the semi-finished products can be positioned on a mandrel, circular for example. In other embodiments, the semi-finished products can be positioned in such a way that a slight overlap is possible on each of the edges of the semi-finished products. These placements of semi-finished products can be made, for example, using an automated laying means of the AFP (Automated Fiber Placement) type. Alternatively, these placements can be made using a filament winding process. Thus, a layer of semi-finished products can be made up of one or more semi-finished products positioned next to each other. This layer of semi-finished products preferably has the following dimensions:

• a thickness of 0.05 to 1 mm, preferably 0.15 to 0.4 mm;
• a length of 0.01 to 100 m, preferably 0.1 to 10 m;
• a width of 0.005 to 5 m, preferably 0.01 to 5 m.

A preform is an assembly of a certain number of layers of semi-finished product. The number of layers in a preform can vary from 1 to 200, preferably from 6 to 48.

Thus, the number of layers in a preform can vary from 1 to 150 layers, preferably from 4 to 100, and ideally from 6 to 48.

Thus, a preform according to the invention can for example comprise from 1 to 10; or from 10 to 20; or from 20 to 30; or from 30 to 40; or from 40 to 50; or from 50 to 60; or 60 to 70; or 70 to 80; or 80 to 90; or from 90 to 100; or from 100 to 110; or from 110 to 120; or from 120 to 130; or from 130 to 140; or 140 to 150 layers of semi-finished products.

The reinforcing fibers preferably have an essentially unidirectional orientation in each layer of semi-finished products. The unidirectional orientation of the reinforcing fibers can be the same from one layer to another, i.e. two adjacent layers of semi-finished products have unidirectional orientations of the reinforcing fibers which essentially form an angle of 0° to each other. Preferably, however, the unidirectional orientation of the reinforcing fibers differs from one layer of semi-finished products to another. More preferably, two layers of adjacent semi-finished products have unidirectional orientations of reinforcing fibers which essentially form an angle of about 90° with respect to each other; or which substantially form an angle of approximately 45° to each other.

In certain embodiments, two layers of adjacent semi-finished products can present unidirectional orientations of reinforcing fibers which essentially form an angle of 0° to 20°; or from 20 to 45°; or 45 to 60°; or 60 to 90° to each other; these angles being able to be counted positively and/or negatively.

The composite parts thus manufactured by consolidating the preforms can be further transformed, in order to obtain assemblies of complex composite parts. Thus, it is possible to co-consolidate composite parts, a process generally carried out in an autoclave using a new thermal cycle, or to weld parts together by local heating.

The composite parts which are obtained with the process according to the invention can be parts of an aerial or space locomotion machine, or parts of a drilling installation (for hydrocarbon fields), or any part located in contact or in the vicinity of an engine (for example an engine of a maritime, land or air vehicle) or a reactor, and in particular seals, connectors, sheaths and structural parts. They may also be parts intended to be subjected to friction, i.e. parts in moving contact with one or more surfaces, in use. Such parts can in particular be supports, rings, valve seats, gears, pistons, piston rings, valve guides, compressor blades, seals and engine components.

Examples

The following examples illustrate the invention without limiting it.

Example 1 – Manufacture of semi-finished product and composite part according to the invention

To study the properties and degradation of a semi-finished product comprising carbon fibers and PEKK as the thermoplastic resin, as well as of a composite part also comprising carbon fibers and the same thermoplastic resin, the crystallization temperature of the PEKK resin alone was first measured at Tc _resin =263°C by DSC analysis as illustrated in Figure 1 (C).

Then, a semi-finished product was manufactured from this PEKK resin and carbon fibers by a powder fluidized bed impregnation process as described in document WO 2018/115736.

Heating of the impregnated carbon fibers was carried out in an infrared oven with 40% power for 2 s, 20% power for 3.5 s and 0% power for 3.5 s. The powers indicated are percentages of the maximum power delivered by the infrared modules, ie 36 kW for the first IR oven and 48 kW for each of the following two.

The speed of the semi-finished product in the infrared oven was 5 m/min and the total energy supplied during heating was 2.2 kW.min.

The calendering was carried out at a calender temperature of 230° C., the product itself being maintained at a temperature above its melting point, ie 380° C.

The DSC analysis of the semi-product obtained according to this process made it possible to measure the crystallization temperature of the semi-product Tc _semi-product =268° C. as illustrated in FIG. 2 (C).

_Semi- finished Tc is therefore superior to _resin Tc.

A composite part was then fabricated from semi-finished products as fabricated above. It results from the assembly by juxtaposition and the consolidation of 23 folds in orientation 0°. Each ply consists of tapes 12 mm wide and 0.25 mm thick. These folds were deposited using an automated tape placement robot equipped with LASER heating. Consolidation was carried out in an autoclave at a plateau temperature of 375° C. for 30 min (temperature rise with a ramp at 10° C./min and cooling at -10° C./min). The nitrogen pressure in the autoclave was kept constant (7 bars), the vacuum level applied at the level of the part being fixed at 100 mbar.

The DSC analysis of the composite part made it possible to measure the crystallization temperature of the composite part Tc _composite =261° C. as illustrated in FIG. 3 (C).

The Tc _composite therefore has a difference of 2°C with the Tc _resin .

Example 2 – Comparative example

Another semi-finished product was made from a PEKK resin (having a crystallization temperature Tc _resin of 273°C according to DSC analysis and as shown in Fig. 4 (C)) and carbon fibers.

The same mode of impregnation as in Example 1 was used.

Heating of the impregnated carbon fibers was carried out in an infrared oven with 65% power for 2 s, 65% power for 3.5 s and 55% power for 3.5 s. The power percentages correspond to the power emitted by the infrared modules, this power being indicated as being a maximum percentage of the power that a module can provide. Here each module has a maximum power of 48 kW.

The speed of the semi-finished product in the infrared oven was 5 m/min and the total energy supplied during heating was 10.3 kW.min.

The calendering was carried out at a temperature of 230°C.

The DSC analysis of the semi-product obtained according to this process made it possible to measure the crystallization temperature of the semi-product Tc _semi-product =267° C. as illustrated in FIG. 5 (C).

The _semi- finished Tc is in this case lower than the Tc _resin .

A composite part was then manufactured from semi-finished products as manufactured above using the same process as in the previous example.

The DSC analysis of the composite part made it possible to measure the crystallization temperature of the composite part Tc _composite =249° C. as illustrated in FIG. 6 (C).

The Tc _composite therefore has a difference of 25°C with the Tc _resin .

Claims (17)

Process for manufacturing a semi-finished product, comprising the following steps:

• providing reinforcing fibers and a thermoplastic resin having a crystallization temperature Tc _resin ;
• mixing the reinforcing fibers with the thermoplastic resin;
• heating to effect melting of the thermoplastic resin and to bring it to a temperature above the melting temperature of the resin; and
• optionally, a calendering step;

the semi-finished product being characterized by a crystallization temperature Tc_{semi-finished product}, the CT_{semi-finished product}being greater than or equal to the Tc_resin. Process according to claim 1, in which the melting of the thermoplastic resin is carried out by heating the reinforcing fibers, or the thermoplastic resin, or the assembly of the reinforcing fibers and the thermoplastic resin. Manufacturing process according to claim 2, wherein the heating is carried out by infrared irradiation, UV irradiation, microwave irradiation, laser irradiation, convection heating or high-frequency wave heating, and preferably by infrared irradiation. Manufacturing process according to one of Claims 1 to 3, in which at least part of the step of melting the thermoplastic resin is carried out under an inert atmosphere. Process according to one of Claims 1 to 4, in which, during the step of melting the thermoplastic resin, the assembly of the reinforcing fibers and the thermoplastic resin is supplied with a power per unit mass of 10 to 1600 kW/kg, preferably from 20 to 1400 kW/kg. Process according to one of Claims 1 to 5, in which the heating of the thermoplastic resin to a temperature above its melting point is carried out up to a temperature of 320 to 420°C, and preferably of 360 to 400° vs. Process according to one of Claims 1 to 6, in which the Tc _semi-product is higher than the Tc _resin by 1 to 10°C, and preferably by 4 to 8°C. Process according to one of Claims 1 to 7, in which the thermoplastic resin is one or more polyaryletherketones chosen from polyetherketones, polyetheretherketones, polyetherketoneketones, polyetheretherketoneketones, polyetheretherketoneketoneketones, polyetheretherketoneetherketones, polyetheretherketones, and polyetherdiphenyletherketones, polyetheretherketones, and preferably chosen from polyetherketones, polyetherketoneketones and polyetheretherketones. Method according to one of Claims 1 to 8, in which the reinforcing fibers are carbon fibers and/or glass fibres. Semi-finished product obtained according to the process of one of claims 1 to 9. Process for manufacturing a composite part comprising the following steps:

• the manufacture of at least two semi-finished products according to the method of one of claims 1 to 9;
• stacking the semi-finished products into at least two layers of semi-finished products;
• the consolidation of layers of semi-finished products, and
• the cooling of the layers of consolidated semi-finished products in order to obtain the composite part.

Method according to claim 11, in which the composite part is characterized by a crystallization temperature Tc _composite , where Tc _composite ≥ Tc _resin – 5°C. Process for manufacturing a composite part comprising the following steps:

• providing at least two semi-finished products according to claim 10;
• stacking the semi-finished products into at least two layers of semi-finished products;
• the consolidation of layers of semi-finished products, and
• the cooling of the layers of consolidated semi-finished products in order to obtain the composite part.

Method according to claim 13, in which the composite part is characterized by a crystallization temperature Tc _composite , where Tc _composite ≥ Tc _{semi-finished product} – 10°C. Composite part obtained according to the method of one of claims 11 or 12, or according to the method of one of claims 13 or 14. Composite part according to Claim 15, having a thickness of 0.05 to 150 mm, and/or a length of 0.01 to 100 m, and/or a width of 0.005 to 5 m. Composite part according to one of Claims 15 or 16, which is a part of an aerial or space locomotion device, or a part of a drilling installation, or a part intended to be positioned in contact with or near a vehicle engine or a reactor, or a part intended to be subjected to friction.