REINFORCEMENT FIBER IMPREGNATION PROCESS WITH POLYARYLETHERCETONES AND

SEMI-PRODUCTS THUS OBTAINED

[Technical area]

The present patent application relates to the field of the manufacture of semi-finished products comprising a thermoplastic matrix and reinforcing fibers. It also relates to such semi-finished products as well as their use for the manufacture of composite parts.

[Prior art]

Composite materials combining a thermoplastic resin with reinforcing fibers have, because of their excellent mechanical properties for a low weight, a 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 are generally manufactured by consolidating semi-finished products made up of reinforcing fibers coated with resin such as prepregs in the form of unidirectional sheets, wicks or woven fabrics.

These semi-products can be obtained by impregnation of the fibers with the resin. There are various processes, in which the resin can be melted, dissolved in a solvent, or else in the form of powder, either in a fluidized bed or dispersed in an aqueous solution. The impregnated fibers are then if necessary freed from the solvent or from the aqueous solution and then heated in order to melt the resin retained and form the semi-product.

For polymers with a high melting point such as polyaryletherketones (PAEK), impregnation in an aqueous dispersion bath is advantageous from an economic and environmental point of view.

However, in order to obtain impregnation at the heart of the resin fibers, this process requires ensuring a homogeneous distribution of the resin in the dispersion.

Thus, patent application WO 88/03468 proposes to stabilize the suspension by making it very viscous (at least 50 Pa-s) and also by adding, where appropriate, a surfactant. The document further proposes to add a minor amount of organic liquid miscible with water in order to accelerate the elimination of the aqueous medium after impregnation.

With a similar approach, US Pat. No. 5,236,972 proposes to add a water soluble polymer, a wetting agent, and further a biocide, a plasticizer and an anti-foam agent to the dispersion.

US Pat. No. 5,888,580 proposes, on the contrary, to use a low viscosity dispersion containing little dispersing agent, and to regulate the charge of the resin fibers by means of the resin concentration of the dispersion and the residence time. However, composite parts made from such semi-finished products exhibit high porosity and suboptimal mechanical properties.

In order to remedy this problem, application FR 3 034 425 proposes to disperse the thermoplastic resin by means of a specific surfactant alkoxylated alcohol, namely stearyl alcohol ethoxylated 100 times, and to combine a stirring device to maintain the homogeneous suspension. Thus, the authors claim to be able to consolidate composite products without porosities. However, this invention does not solve all the difficulties associated with the viscosification of the resin, and can lead to subsequent forming defects. In fact, in the molten state, the too viscous polymeric resin is no longer able to flow properly. Therefore, it is difficult to achieve composite parts having the desired shape, properties and surface appearance.

In particular, it is common to observe the appearance of wrinkles on the surface and problems with the strength of the welds produced during the assembly of composite parts into complex parts. These defects are exacerbated when consolidation is carried out at a pressure of less than 5 bars.

In general, it is advantageous to be able to manufacture composite parts without having to resort to high pressure, since this requires the use of very expensive autoclaves.

The aim of the invention is to remedy these problems and to propose a process for preparing semi-finished products capable of being transformed into composite parts which do not exhibit the above-mentioned defects.

It also aims to provide a process for the preparation of semi-finished products capable of being consolidated under low vacuum, outside an autoclave.

More specifically, the object of the invention is to propose such a process for the preparation of semi-finished products in which the resin has a viscosity and a crystallinity which changes little following the thermal cycles required for the manufacture of composite parts.

[Summary of the invention]

The objects mentioned above have been achieved by a process according to the invention, in which the reinforcing fibers are impregnated in an aqueous dispersion of pulverulent PAEK resin comprising a minimum amount of surfactant.

Indeed, it has been found that it is possible to limit the amount of surfactants and / or thickening agents by adding volatile organic compounds miscible with water. Indeed, these compounds

make it possible to increase the viscosity of the dispersion and to stabilize it. On the other hand, these compounds do not remain in the resin because of their volatility.

It has also been found that these volatile organic compounds miscible with water can have an anti-foaming effect, which makes it possible to further reduce the presence of additives such as anti-foam agents. In fact, these additives can also be harmful during consolidation and can also hinder the adhesion between the fiber and the matrix.

Indeed, the present invention is based on the observation that the quality of composite parts based on PAEK resins depends in particular on the viscosity of the resin in the semi-finished product and on its subsequent development. However, at the high temperatures required for the manufacture and consolidation of PAEK-based semi-products (temperatures generally above 300 ° C), the compounds introduced during the process can decompose into reactive species, which can generate reactions of PAEK chain lengthening including connections. The resulting increase in molecular weight then increases the viscosity of the resin.

However, the systematic study of the various agents likely to be present in the PAEK-based semi-product revealed on the one hand that the additives used in the dispersion were a main factor in the increase in viscosity after a thermal cycle and on the other hand that this effect was very variable according to their dosage.

On this basis, it was possible to validate that the use of a low dosage surfactant makes it possible to limit the evolution of the viscosity of the resin and to obtain composite parts of the required quality.

Without wishing to be bound by this hypothesis, it is assumed that many compounds, in particular organic, decompose in the PAEK resin under the effect of the high temperature required to melt it. The reactive species formed during the decomposition, in particular the radicals, can then react with the polymer and cause chain extension reactions including branching, which increase the molecular mass of the polymer and therefore also its viscosity. However, when the resin has a high viscosity, it is no longer able to impregnate and coat the fibers well, to ensure good adhesion of the semi-products to each other, or to match the mold walls, this which affects the quality of the composite products obtained. The presence of

Also, according to a first aspect, the subject of the invention is a process for preparing a semi-finished product comprising a PAEK-based resin and reinforcing fibers, comprising the steps of:

at. Preparation of a dispersion comprising a PAEK-based resin in pulverulent form dispersed in an aqueous phase comprising at least one volatile organic compound and optionally a surfactant;

b. Contacting the reinforcing fibers with said aqueous dispersion;

vs. Drying of the fibers impregnated with dispersion; and

d. Heating the impregnated fibers to a temperature sufficient for the melting of the resin, so as to form a semi-product,

characterized in that,

the aqueous phase of the dispersion has a dynamic viscosity, measured at 25 ° C. under shear stress of 6.8 s "1 on a Brookfield DV2T Extra viscometer, is less than 25 Pa s; and that

when the surfactant is present, its content is less than 1% by weight relative to the mass of dispersed resin.

Preferably, the volatile organic compound is chosen from alcohols, ketones, aldehydes, esters of carboxylic acids, glycols and ethers, in particular an alcohol chosen from methanol, ethanol, isopropanol, n-propanol, n-butanol, 2-butanol, tert. butanol, 1-methoxy-2-propanol, 1-ethoxy-2-propanol and their mixtures, a glycol chosen from ethylene glycol, propylene glycol and their mixtures, a ketone such as acetone, an ether, a carboxylic acid ester chosen from methyl acetate, ethyl acetate and propyl acetate, and mixtures thereof.

Advantageously, the volatile organic compound forms with the water of the aqueous phase an azeotrope.

Preferably, the reinforcing fibers are carbon fibers.

The aqueous phase of the dispersion preferably has a dynamic viscosity, measured at 25 ° C under shear stress of 6.8 s "1 on a Brookfield DV2T Extra viscometer, is 0.1 to 5, in particular 0.300 to 3 and all particularly from 0.5 to 2 Pa s.

The process of the invention is particularly useful when the PAEK resin is selected from the group consisting of poly-ether-ketone (PEK), polyether-ether-ketone (PEEK), poly-ether-ether-ketone-ketone (PEEKK) , poly-ether-ether-ketone-ketone (PEKK), poly-ether-ketone-ether-ketone-ketone (PEKEKK), poly-ether-ether-ketone-ether-ketone (PEEKEK), poly-ether-ether- ether-ketone (PEEEK), and poly-ether-diphenyl-ether-ketone (PEDEK), their mixtures and their copolymers with each other or with other members of the PAEK family. In particular, the PAEK resin can be a PEKK having a percentage by weight of terephthalic units relative to the sum of the terephthalic and isophthalic units of between 35 and 100%. Advantageously, the pulverulent PAEK resin in the dispersion has a median diameter D50 of 1 to 300 μm,

Advantageously, the semi-finished product prepared is chosen from a prepreg or a tape.

Furthermore, according to a second aspect, the subject of the invention is a dispersion useful in the preparation of a semi-product, comprising:

at. 1 - 50% by weight of PAEK-based resin having a number-average particle size of between 1 and 300 μιη;

b. 0 - 1% by weight, calculated based on the weight of the resin, of at least one surfactant; vs. 1 - 50% by weight of at least one volatile organic compound;

d. 0 - 1% by weight of other additives; and

e. the rest of the water,

it being understood that the total of additives (c) and (d) in the aqueous phase represents less than

4% by weight of the dispersion.

Preferably, the dispersion of the invention comprises 15-35% by weight of PAEK-based resin.

According to a third aspect, the invention relates to a semi-finished product comprising a resin based on a PAEK and reinforcing fibers, capable of being obtained by the process of the invention. Advantageously, the semi-product is characterized in that the weight-average molecular mass M w of the PAEK resin, as measured by size exclusion chromatographic analysis, does not increase by more than 100% after heat treatment to 375. ° C for 20 minutes.

Finally, according to a fourth aspect, the subject of the invention is the use of a semi-finished product as described above for the manufacture of composites.

[Brief description of the figures]

The invention will be better understood with regard to the following description and the figure, which shows:

Fig. unique appearance of the dispersions according to Examples 12 to 14 after vigorous stirring and standing

5 minutes (left: dispersion according to Comparative Example 12, medium: dispersion according to Example 13, right: dispersion according to Example 14).

[Description of the embodiments]

Definition of terms

The term “semi-finished product” is understood to denote products comprising a resin and reinforcing fibers used as intermediate products in the manufacture of composite materials. These products can in particular be prepregs in the form of unidirectional sheets of wicks, of woven fabrics, or else of fiber-matrix mixtures.

Semi-finished products can then be assembled, for example by manual or automated draping or by automated fiber placement, and shaped by consolidation, for the manufacture of composite parts. The composite parts thus produced can be further processed, in order to obtain complex composite part assemblies. Thus, it is possible to co-consolidate composite parts, a process generally carried out in an autoclave by means of a new thermal cycle, or to come and weld parts to each other by local heating.

The term “resin” is intended to denote a composition mainly comprising one or more polymers added, where appropriate, with conventional additives, in particular fillers and functional additives.

The term “dispersion” is understood to denote a heterogeneous composition comprising a liquid phase and a solid phase. In the dispersion used in the process of the invention, the liquid phase is aqueous and contains a thermally stable surfactant as well as other additives, if necessary. The solid phase comprises or consists essentially of the PAEK resin in powder form.

The term “surfactant” is intended to denote a compound having a hydrophilic part and a lipophilic part, and capable of dispersing the resin powder in the liquid phase and of maintaining it in suspension in the presence or absence of agitation. This compound can also aid in the wetting of the fibers by the dispersion.

The term “organic compound” is understood to denote a compound containing at least the element carbon and one or more of the following elements: hydrogen, halogens, oxygen, sulfur, phosphorus, silicon or nitrogen, with the exception of carbon oxides. and carbonates and bicarbonates.

The term “volatile compound” is understood in the context of this description to mean a compound whose boiling point at atmospheric pressure is less than 200 ° C, and preferably less than 150 ° C, more preferably less than 120 ° C. and very particularly less than 100 ° C.

The dispersion

The dispersion implemented in the proposed process comprises according to the invention an aqueous phase in which is dispersed a PAEK resin in powder form.

The PAEK resin essentially comprises at least one polyaryletherketone (PAEK) polymer. Poly- (aryl-ether-ketones) (PAEK) contain the units of the following formulas:

in which :

Ar and Ari each denote a divalent aromatic radical;

Ar and Ari can be chosen, preferably, 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; it can be chosen, preferably, from the carbonyl group and the sulfonyl group,

Y denotes a group chosen from an oxygen atom, a sulfur atom, an alkylene group, such as -CH 2 - and isopropylidene.

In these X and Y units, at least 50%, preferably at least 70% and more particularly, at least 80% of the groups X are a carbonyl group, and at least 50%, preferably at least 70% and more particularly at least. minus 80% of the Y groups represent an oxygen atom. According to a preferred embodiment, 100% of the X groups denote a carbonyl group and 100% of the Y groups represent an oxygen atom.

More preferably, the poly-arylene-ether-ketone (PAEK) can be chosen from:

- a poly-ether-ketone-ketone, also called PEKK, comprising units of formula IA, of formula IB and their mixture:

a poly-ether-ether-ketone, also called PEEK, comprising units of formula II:

The sequences can be totally para (Formula II). In the same way, it is possible to introduce, partially or totally, meta linkages into these structures at the level of ethers and ketones according to the two examples of formulas III and IV below:

Or sequences in ortho according to formula V:

- a poly-ether-ketone, also called PEK, comprising units of formula VI

In the same way, the sequence can be totally para but we can also introduce partially or totally meta chains (formulas VII and VIII):

Formula VII

a poly-ether-ether-ketone-ketone, also called PEEKK, comprising units of the IX:

In the same way, we can introduce meta chains into these structures at the level of ethers and ketones.

a poly-ether-ether-ether-ketone, also called PEEEK, comprising units of formulas

X:

In the same way, we can introduce meta linkages in these structures at the level of ethers and ketones but also biphenol or diphenyl linkages according to formula XI (type D units in the next names, formula XI thus corresponds to the name PEDEK):

Other arrangements of the carbonyl group and the oxygen atom are also possible.

Preferably, the PAEKs used in the invention are chosen from the group consisting of poly-ether-ketone (PEK), polyether-ether-ketone (PEEK), poly-ether-ether-ketone-ketone (PEEKK), poly- ether-ether- ketone-ketone (PEKK), poly-ether-ketone-ether-ketone-ketone (PEKEKK), poly-ether-ether-ketone-ether-ketone (PEEKEK), poly-ether-ether-ether-ketone (PEEEK), and poly-ether-diphenyl-ether-ketone (PEDEK), their mixtures and their copolymers with each other or with other members of the PAEK family. PEEK and PEKK as well as their mixtures are particularly preferred.

Advantageously, the stability of the PAEK in the molten state can be improved by adding one or more phosphates or phosphate salts.

Preferably, the PAEK resin comprises at least one polyether-ketone-ketone (PEKK) which represents more than 50%, preferably more than 60%, in particular more than 70%, more preferably more than 80% and in particular more than 90%. Mass% of resin, terminal included. The remaining 10 to 50% by mass may be constituted by other polymers belonging or not to the PAEK family.

More preferably, the PAEK resin consists essentially of PEKK.

Advantageously, the PEKK has a percentage by weight of terephthalic units relative to the sum of the terephthalic and isophthalic units from 35 to 100%, in particular from 40 to 95%, more preferably from 50 to 90%, preferably from 60 to 80% , and in particular, this ratio is 65 to 75%.

The resin can moreover, as discussed above, additionally comprise other usual additives such as fillers. Furthermore, the resin may optionally contain minor amounts of functional additives. Preferably, the resin is nonetheless devoid of additives liable to decompose under the effect of heat in order to limit the risk of changes in viscosity.

The particle size of the PAEK resin powder can have an impact on the stability of the suspension. It can also influence the resin impregnation quality of the reinforcing fibers. In order to ensure optimum homogeneity of the suspension and good impregnation, it is preferred that the resin powder is finely divided. More specifically, it is preferred that the PAEK powder has a median diameter D50 is located in a range from 1 to 300 μιη, preferably from 5 to 100 and most particularly from 10 to 50 μιη as measured according to the ISO 13 320 standard. .

Preferably, the PAEK resin powder content of the dispersion is advantageously between

I and 50%, preferably between 10 and 40% and very particularly 25 to 35% by weight relative to the weight of the finished dispersion.

As mentioned above, the process according to the invention is characterized in that the dispersion furthermore comprises at least one surfactant.

As surfactant, it is possible to choose an ionic or nonionic surfactant. Preferably, it is an ionic surfactant, and in particular an anionic surfactant.

According to a particularly preferred embodiment, the surfactant comprises a phosphate group. Indeed, phosphates seem less prone to react with PAEK resins than other surfactants when used in the aqueous dispersion impregnation process.

More specifically, mention may in particular be made of surfactants from the family of ethoxylated alcohols, such as ethoxylated alcohols and their mono- or di-esters with phosphoric acid. The ethoxylated alcohols are in particular alcohols comprising 6 to 24 and in particular 10 to 16 carbon atoms. Preferably, they are monoesters of phosphoric acid and ethoxylated alcohols. Particularly preferred are the alkyl ether phosphates and alkylaryl ether phosphates.

Among these surfactants, preference will be given to those having a minimum of oxide units of short alkyls, in particular of C 1 to C 3 alkyls. In fact, the methylene oxide, ethylene oxide and propylene oxide units are particularly thermally sensitive and capable of generating radicals.

It has in fact been demonstrated that a reduction in the content of short alkyl oxide units improves the quality of the PEKK in consolidation in the molten state. Such a reduction can be obtained by controlling the amount of surfactant on the one hand and by choosing a surfactant with a low content of short alkyl oxide units on the other hand.

Now, these alkyl oxide units are also particularly effective for ensuring good dispersion of the PAEK powder. Thus, it is estimated that a content of 0.15, preferably 0.20 and in particular 0.30% by weight of short alkyl oxide units relative to the weight of PAEK is particularly advantageous.

In terms of stability, preference will be given to surfactants having a low number of alkyl oxide units, in particular less than 50, in particular from 5 to 40, and more preferably between 10 and 30.

Particularly preferred are the surfactants of formula below:

As mentioned above, the number of alkyl oxide units (number n) in these formulas is preferably less than 50, in particular 5 to 40, and more preferably between 10 and 30.

As compounds of this family, there may be mentioned in particular the surfactants sold under the name Lanphos PE35 by the company Lankem, Cecabase T by the company CECA France and Klearfac AA270 by the company DeWolf.

This surfactant can be used in the form of free acid, but it is preferably neutralized. Neutralization can be carried out beforehand or in situ in the dispersion by adding an appropriate amount of sodium or potassium hydroxide.

According to the invention, the dispersion comprises not more than 1%, preferably not more than 0.5%, in particular not more than 0.4%, and very particularly not more than 0.3% by weight of surfactant, calculated with respect to the weight of resin to disperse.

It may be advantageous to add several surfactants. In particular, it is possible to choose a surfactant making it possible to ensure good dispersion of the PAEK resin powder and another surfactant in order to improve the affinity of the reinforcing fibers with the PAEK resin powder.

According to a particular embodiment of the invention, the dispersion does not contain a surfactant.

The aqueous phase of the dispersion can, if necessary, comprise minor amounts of other conventional additives such as thickening agents, anti-foaming agents, biocidal agents. In order to limit the presence of additives in the semi-finished products and the associated potential problems, the dispersion nevertheless comprises a preferably minimum content of other additives. Preferably, however, the aqueous phase of the dispersion does not contain other conventional additives, in particular no thickening agents. Preferably, the amount of other additives will not exceed 4% by weight, in particular 3% and very particularly 2% by weight of the finished dispersion.

The aqueous phase of the dispersion consists mainly of water. The aqueous phase of the dispersion comprises at least 60% by weight, preferably 70%, more preferably 80% and very particularly 90% by weight of water. The water used to prepare the dispersion is preferably demineralized water.

According to the invention, the dispersion further comprises one or more volatile organic compounds. These compounds can be chosen in particular from the families of alcohols, ketones, aldehydes, esters of carboxylic acids, glycols and ethers.

Preferably, the volatile organic compound is an alcohol chosen from ethanol, isopropanol, n-propanol, n-butanol, 2-butanol, tert. butanol, 1-methoxy-2-propanol, 1-ethoxy-2-propanol and their mixtures, a glycol selected from ethylene glycol, propylene glycol and their mixtures, a ketone selected such as acetone, an ether , a carboxylic acid ester chosen from methyl acetate, ethyl acetate and propyl acetate, and mixtures thereof.

Particularly preferred are volatile organic compounds forming an azeotrope with water, facilitating their elimination, such as ethanol, methyl acetate, propyl acetate and mixtures thereof.

As already mentioned, it has been observed that the addition of such volatile organic compounds to the aqueous phase makes it possible to reduce or even eliminate the content of surfactant required to stabilize the PAEK resin in the dispersion, which makes it possible to limit the harmful thermal degradations in the dispersion. the PAEK during the consolidation stage. Moreover, these compounds can make it possible to increase the viscosity of the dispersion by ensuring better wetting of the dispersed particles. However, their volatility ensures that they do not remain in the resin, unlike the usual non-volatile additives which then run the risk of being broken down into species reactive to the melting of the resin.

The aqueous phase of the dispersion preferably comprises 1 to 50, in particular 5 to 40, more preferably 10 to 30 and very particularly 15 to 25% by weight of one or more volatile compounds.

The dispersion obtained preferably has a dynamic viscosity, as measured at 25 ° C under shear stress of 6.8 s "1 on a Brookfield DVT2T Extra viscometer, from 0.1 Pa-s to 20 Pa-s, in particular from 0.1 to 5, in particular from 0.3 to 3 and very particularly from 0.5 to 2 Pa s.

The process for preparing the dispersion can be carried out in a manner known per se. More specifically, the dispersion can for example be prepared by introducing the required quantity of water into a container of suitable volume and fitted with a suitable stirring device, then by then adding the surfactant as well as the other additive (s), if applicable. appropriate. If necessary, the mixture is stirred until a homogeneous solution is obtained. The powdery PAEK resin is then introduced into the aqueous solution, followed by stirring until a stable dispersion is obtained.

Reinforcement fibers

The reinforcing fibers can in principle be any fibers customarily used in the manufacture of semi-finished products.

In accordance with the invention, the reinforcing fibers can be chosen from 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 else PAEK fibers, or alternatively mixtures of such fibers.

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

According to a preferred embodiment, the fibers do not induce, in combination with the other compounds, a significant change in the viscosity of PAEK in the semi-finished product and in the composite.

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

The reinforcing fibers used for the manufacture of semi-finished products by impregnation by means of aqueous dispersion are generally continuous.

Preferably, they are in the form of unidirectional fibers, for example in the form of threads grouping together several thousand elementary filaments (typically from 3000 to 48000) measuring, for example, 6 to 10 μιη in diameter for the carbon fibers. This type of fiber is known by the name of rovings (in English "rovings").

The fibers can nevertheless also be organized in a different manner, for example in the form of a mat, or alternatively of textiles obtained by weaving wicks.

The semi-finished manufacturing process

The manufacturing process according to the invention can be carried out in a conventional manner, on the usual equipment, by implementing the dispersion as described above. As indicated above, the presence in the dispersion of a low dosage surfactant makes it possible to limit the formation of reactive species capable of increasing the molecular mass of the resin and therefore its viscosity, and thereby reducing the appearance of defects in composite parts.

More specifically, the semi-finished products are obtained by introducing and circulating the reinforcing fibers in an aqueous dispersion bath as described above. The fibers impregnated with PAEK resin are then taken out of the bath and freed from water, for example by drying in an infrared oven. The dried impregnated fibers are then heated until the resin melts, in order to allow the fibers to be coated with the PAEK resin. The coated fibers obtained are then, where appropriate, shaped, for example by calendering. This step can make it possible to texture and ensure the sizing of the semi-finished product.

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

Advantageously, these semi-products are characterized in that the weight average molecular mass Mw of the PAEK resin, as measured by size exclusion chromatographic analysis, does not increase by more than 100% after heat treatment at 375 ° C for 20 minutes in air.

The semi-products obtained according to the process of the invention can be used in particular for the manufacture of composite parts.

The composite parts are obtained, for example, by first manufacturing a preform, in particular by placing or draping the prepreg semi-products in a mold. 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-products by fusion. Preferably, the semi-finished products manufactured according to the invention can be consolidated outside an autoclave, for example in a vacuum tank placed in an oven.

The semi-finished products manufactured according to the process of the invention are characterized in particular by a resin whose viscosity has changed little despite the high temperatures required for their manufacture in order to melt the resin.

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

The composite products manufactured according to the process of the invention are characterized in particular by a resin whose viscosity has changed little despite the high temperatures required for their manufacture.

During these steps, a not too high viscosity of the die is essential in order to ensure that the semi-products conform to the shapes of the mold. The viscosity of the matrix also makes it possible to ensure good flow during consolidation and thus avoid surface defects such as wrinkles.

The invention will be explained in more detail in the examples which follow.

[EXAMPLES]

Example 1 to 9: Evolution of the crystallization temperature according to the surfactant dosage

The impact of the thermal cycle on a PEKK resin (KEPSTAN 7002 marketed by the company Arkema France) was studied for variable dosages of different surfactants by measuring the crystallization temperature. The crystallization temperature is, like the viscosity, affected by the elongation reactions including those of branching. Indeed, when the average molecular mass of the polymer increases, the viscosity increases and the crystallization temperature decreases.

The following surfactants have been studied:

Brij S 100, sold by the company Sigma Aldrich: Monooctadecyl ether of polyethylene glycol (100) - Lanphos PE35, sold by the company Lankem: monoester of phosphoric acid and C13 alcohol

Lanphos PE35 neutralized: Lanphos PE35 neutralized by adding sodium hydroxide solution according to the following protocol:

Preparation of an aqueous solution of PE35 Na at 1% by mass

Lamphos PE35 (lg) and a 1 mol / L NaOH solution (1.3g) are introduced into a beaker, made up with distilled water (97.7g) and the mixture is stirred vigorously for 10 minutes until obtaining a clear solution. The quantity of 1M NaOH solution corresponds to 0.95 equivalent of sodium hydroxide (determined by acid-base determination of an aqueous solution of PE 35).

PEKK samples impregnated with these surfactants were prepared as follows:

An aqueous solution of X% by weight of surfactant is prepared by introducing into a flask (1000-X) g of water as well as Xg of the surfactant. The aqueous solution is homogenized for 10 minutes using a homogenizer mill.

Then, 3g of PEKK powder (marketed under the name Kepstan 7002PT by the company Arkema France, D50 = 20μιη) is introduced at (3 X) g of a 1% by weight solution of surfactant prepared in a single neck flask of 250mL of so that the surfactant / PEKK mass ratio is X%). Then added lOmL of distilled water and stirred vigorously for 10 minutes using a magnetic stirrer.

Finally, the water is evaporated from the dispersion obtained using a rotary evaporator and the powder is dried under vacuum at 120 ° C. for 2 hours in order to recover a PEKK powder impregnated with surfactant.

As an example, for example 3:

3g of PEKK

- 3 x 0.8 = 2.4g of Brij S100 aqueous solution at 1% by weight

10g distilled water

The crystallization temperature of PEKK is measured by scanning calorimetry (DSC) after a thermal cycle in which the sample of powder impregnated with surfactant is heated at 380 ° C. for 30 minutes under nitrogen.

The results in Table 1 below show a notable decrease in the crystallization temperature after thermal cycling for all the samples. It can reasonably be assumed that the viscosity of the resin increases in the same proportion, causing difficulties in processing the semi-finished product obtained.

Moreover, for a given surfactant, the crystallization temperature after thermal cycle decreases markedly more when the dosage increases, for the contents examined between 0.25 and 1.25% by weight.

Table 1: Crystallization temperature of PEKK impregnated with surfactant

* mass of surfactant / mass of PEKK

Finally, we note that at equal dosage, the effect on the crystallization temperature depends on the surfactant chosen: the surfactant Lanphos PE35 generates a very moderate decrease while the decrease is very marked for the surfactant Brij S100 which has a proportion by mass of high ethylene oxide

In view of these results, it therefore appears advantageous to choose a suitable surfactant and to use a low dosage of surfactant.

Example 10: Effect of a volatile organic compound on the stability of the dispersion

When the amount of surfactant is reduced beyond a certain threshold, the dispersion can no longer be properly stabilized, which can cause difficulties during the manufacture of semi-finished products such as prepregs.

However, it has been observed that the addition of certain volatile organic compounds such as alcohols makes it possible to reduce the dosage of surfactant or even to eliminate it required to stabilize a dispersion of PAEK powder in an aqueous medium.

In order to study this effect in more detail, aqueous dispersions containing 33% by weight of PEKK powder and varying contents of surfactant and isopropanol were prepared. The preparation protocol is explained below for a dispersion containing 30% by weight of isopropanol relative to the aqueous phase and 1% by weight of surfactant, relative to the weight of PEKK.

6g of PEKK (Kepstan 7002PT sold by the company Arkema France, D50 = 20μηι) are introduced into a suitable container fitted with a stirring means and Xg of surfactant is added (X being such that the surfactant / PEKK mass ratio = X%). Then, 12 g of water / isopropanol mixture (100-n / n (n being the percentage of isopropanol, n = 0 - 30) are added to the solution and the dispersion obtained is stirred vigorously for 30 minutes using a magnetic stirrer The mixtures thus produced are then dried for 12 hours under vacuum at 120 ° C.

Each dispersion prepared is then judged in terms of its stability after 60 minutes of its preparation. Dispersion is considered to be:

stable (+) when the PEKK is perfectly dispersed in the solution,

fairly stable (o) when the PEKK is well dispersed but settles a little on the walls, and - inhomogeneous (-) when the PEKK is not completely dispersed.

The composition and the stability of the various dispersions produced are collated in Table 2 below.

Table 2: Stability of PEKK powder dispersions

The series of tests was repeated using fert-butanol as the alcohol, with equivalent results.

These results demonstrate that part, or even all of the surfactant can be replaced by an alcohol such as isopropanol or te / t-butanol as a dispersant of the PEKK powder.

Example 11: Effect of a thickening agent on the crystallization temperature

The impact of the presence of thickening agents on the evolution of the crystallization temperature after thermal cycling was studied as follows.

A PEKK powder impregnated in a 0.1% by weight solution of surfactant was prepared as indicated in Example 1, but adding to the solution of surfactant in addition 6% by weight of sodium polyacrylic acid.

The dispersion is very thick (viscosity of about 10 Pa-s) and must be degassed before use due to the presence of numerous bubbles.

The PEKK powder impregnated with surfactant and thickening agent further exhibits very low thermal stability. In fact, after having undergone the thermal cycle mentioned in Example 1, the sample has a much lower crystallization temperature than an equivalent sample prepared with a surfactant content of 1% by weight.

It is thus found that the thickening agent can be as harmful as a surfactant, or even more, for a PAEK resin exposed to high temperatures.

In order to prepare semi-products having a good behavior in the subsequent transformation into composite materials, it is therefore preferable to use baths of aqueous dispersion of PAEK powder devoid of thickening agent.

Example 12 - 21: Adjusting the viscosity

In order to study the effect of the volatile organic compound on the viscosity of the aqueous phase of the dispersion, dispersions with variable contents of surfactant and of isopropanol were prepared, according to the protocol indicated in Example 10.

The dynamic viscosity of the dispersions was measured at 25 ° C. on a Brookfield viscometer model DV2T Extra under shear stress of 6.8 s- 1 .

The results are collated in Table 3 below.

Table 3: Dynamic viscosity as a function of the surfactant and isopropanol content

* comparison example

The results demonstrate that a suitable choice of the content of surfactant and of isopropanol makes it possible to vary the viscosity of the aqueous phase of the dispersion over a wide range.

In the exemplified case, it is thus possible to adjust the viscosity between 60 and 1000 mPa-s by adjusting these two parameters.

Example 22: Anti-foaming effect of alcohol in the dispersion

In order to study the anti-foaming effect of the volatile organic compound in the aqueous surfactant solution, the dispersions of Examples 12 to 14 were stirred vigorously for 3 minutes. After allowing the dispersions to stand for 5 minutes, the appearance of the dispersions was photographed (see Fig. 1).

Note that the solution in the container on the right (20% by weight of isopropanol) has markedly less foam than the container on the left (0% by weight of isopropanol) or that in the middle (10% by weight of isopropanol). ). In this mixture, isopropanol therefore acts as an anti-foaming agent.

In the presence of PEKK powder, this effect is even more marked, since 10% by weight of isopropanol is sufficient to obtain a satisfactory anti-foam effect.

An alcohol added to the aqueous phase of PAEK powder dispersions can therefore also act as an effective anti-foaming agent, and thus avoid the addition of an additional additive.

It can be seen from all of the studies reported above that the dosage of the surfactant constitutes an essential factor concerning the evolution of the viscosity of a PAEK resin subjected to a thermal cycle representative of that required for the consolidation of a semi-solid. produced in composite parts. Furthermore, the above examples demonstrate the advantage of adding an alcohol to the aqueous phase of the dispersion. This is because it can have a triple function: partially compensating for the omitted surfactant, modulating the viscosity without adding a thickening agent, and replacing a possible anti-foaming agent.

The use of a low dosage surfactant, optionally coupled with an alcohol, and the elimination of other additives as far as possible in the dispersion of PAEK used during the manufacture of semi-products according to the process of the invention thus makes it possible, while preserving the viscosity of the PAEK resin, to ensure good quality of the composite parts obtained from them.

[List of documents cited]

WO 88/03468

US 5,236,972

US 5,888,580

F 3,034,425

Claims

1. Process for preparing a semi-finished product comprising a PAEK-based resin and reinforcing fibers, comprising the steps of:

at. Preparation of a dispersion comprising a PAEK-based resin in pulverulent form dispersed in an aqueous phase comprising at least one volatile organic compound and optionally a surfactant;

b. Contacting the reinforcing fibers with said aqueous dispersion;

vs. Drying of the fibers impregnated with dispersion; and

d. Heating the impregnated fibers to a temperature sufficient for the melting of the resin, so as to form a semi-product,

characterized in that the aqueous phase of the dispersion has a dynamic viscosity, measured at 25 ° C under shear stress of 6.8 s "1 on a Brookfield DV2T Extra viscometer, is between 0.1 and 25 Pa-s; and that

when the surfactant is present, its content is less than 1% by weight relative to the mass of dispersed resin.

2. Preparation process according to claim 1, wherein the volatile organic compound is selected from alcohols, ketones, aldehydes, esters of carboxylic acids, glycols and ethers.

3. Preparation process according to one of claims 1 to 2, wherein the volatile organic compound is an alcohol chosen from methanol, ethanol, isopropanol, n-propanol, n-butanol, 2- butanol, tert. butanol, l-methoxy-2-propanol, l-ethoxy-2-propanol and their mixtures, a glycol chosen from ethylene glycol, propylene glycol and their mixtures, a ketone such as acetone, an ether, a carboxylic acid ester chosen from methyl acetate, ethyl acetate and propyl acetate, and mixtures thereof.

4. Preparation process according to one of claims 1 to 3, wherein the volatile organic compound forms with the water of the aqueous phase an azeotrope.

5. Preparation process according to one of claims 1 to 4, wherein the reinforcing fibers are carbon fibers.

6. Preparation process according to one of claims 1 to 5, wherein the aqueous phase of the dispersion has a dynamic viscosity, measured at 25 ° C under shear stress of 6.8 s "1 on a Brookfield DV2T Extra viscometer. , is from 0.1 to 5, in particular from 0.300 to 3 and very particularly from 0.5 to 2 Pa-s.

7. Preparation process according to one of claims 1 to 6, wherein the PAEK resin is chosen from the group consisting of poly-ether-ketone (PEK), polyether-ether-ketone (PEEK), poly-ether-ether. -ketone-ketone (PEEKK), poly-ether-ether-ketone-ketone (PEKK), poly-ether-ketone-ether-ketone-ketone (PEKEKK), poly-ether-ether-ketone-ether-ketone (PEEKEK) , poly-ether-ether-ether-ketone (PEEEK), and poly-ether-diphenyl-ether-ketone (PEDEK), their mixtures and their copolymers with each other or with other members of the PAEK family.

8. Preparation process according to one of claims 1 to 7, wherein the PAEK resin is a PEKK having a percentage by weight of terephthalic units relative to the sum of the terephthalic and isophthalic units of between 35 and 100%.

9. Preparation process according to one of claims 1 to 8, wherein the pulverulent PAEK resin in the dispersion has a median diameter D50 of 1 to 300 μιη, preferably 5 to 100 and most particularly 10 to 50 μιη such than measured according to ISO 13 320.

10. Preparation process according to one of claims 1 to 9, wherein the semi-finished product is chosen from a prepreg or a tape.

11. Dispersion useful in the preparation of a semi-finished product, comprising:

at. 1 - 50% by weight of PAEK-based resin having a number-average particle size of between 1 and 300 μιη;

b. 0 - 1% by weight, calculated based on the weight of the resin, of at least one surfactant; vs. 1 - 40% by weight of at least one volatile organic compound;

d. 0 - 1% by weight of other additives; and

e. the rest of the water,

it being understood that the total of additives (c) and (d) in the aqueous phase represents less than 4% by weight of the dispersion, and that the aqueous phase has a dynamic viscosity, measured at 25 ° C under shear stress of 6 , 8 s "1 on a Brookfield DV2T Extra viscometer, is between 0.1 and 25 Pa s.

12. The dispersion of claim 11 comprising 15-35% by weight of PAEK-based resin.

13. Semi-finished product comprising a resin based on a PAEK and reinforcing fibers, obtainable by the process as defined in claims 1 to 10.

14. The semi-product of claim 13, wherein the weight-average molecular mass M w of the PAEK resin, as measured by size exclusion chromatography analysis, does not increase by more than 100% after heat treatment to 375. ° C for 20 minutes.

Use of a semi-finished product according to Claim 13 or 14 for the manufacture of composite materials.