Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
  • B29B15/00—Pretreatment of the material to be shaped, not covered by groups B29B7/00 - B29B13/00
  • B29B15/08—Pretreatment of the material to be shaped, not covered by groups B29B7/00 - B29B13/00 of reinforcements or fillers
  • B29B15/10—Coating or impregnating independently of the moulding or shaping step
  • B29B15/105—Coating or impregnating independently of the moulding or shaping step of reinforcement of definite length with a matrix in solid form, e.g. powder, fibre or sheet form
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
  • B29B11/00—Making preforms
  • B29B11/14—Making preforms characterised by structure or composition
  • B29B11/16—Making preforms characterised by structure or composition comprising fillers or reinforcement

Definitions

• the present invention relates to a method of impregnating a fibrous or filamentary network with powder, in particular for producing a composite material comprising a continuous, rigid or flexible matrix, with which said network is in intimate contact.
• This invention relates not only to the composite material obtained by this process, but also to a preform for composite material obtained by this process.
• Composite materials reinforced by fibers embedded in thermoplastic matrices are an extremely interesting category of materials, making it possible in particular to produce materials having excellent mechanical properties for masses substantially lower than those of metals.
• these materials are obtained by simple molding, after having coated the reinforcing fibers or filaments with the thermoplastic resin intended to constitute the matrix of the composite material.
• the mechanical properties of the composite material thus obtained depend on the quality of the interface between the reinforcing fibers or filaments and the matrix.
• thermoplastic resin In the conventional methods proposed for incorporating the thermoplastic resin into the fibrous or filamentary mass, the resin is melted to make it penetrate in the liquid state into the fibrous or filamentary mass to be impregnated, after which this fibrous mass can thus be molded impregnated to give it the shape of the piece of composite material that it is desired to obtain.
• the drawback of this solution stems from the difficulty of making the molten resin penetrate perfectly between the fibers or filaments due to the viscosity of these resins.
• thermoplastic matrix by a weaving process known under the name of "Comingle” according to which a woven mixture of reinforcing fibers and matrix fibers is woven. After weaving, the fabric is heated to melt the matrix in the form of fibers, then is compressed to obtain the desired piece. During heating, and during compression, it is necessary that the matrix being in the form of fibers melts, then migrates to penetrate between the reinforcing fibers. It is not obvious to obtain in this way, a homogeneous distribution of the matrix.
• Various solutions have been proposed to try to remedy this drawback and to allow the vacuum rate to be reduced.
• thermoplastic material of the thread is melted to form the matrix, so that the reinforcing fibers or filaments mixed with the fibers of thermoplastic material are embedded in the thermoplastic matrix. Since the thermoplastic fibers are intimately mixed in the composite yarn with the reinforcing fibers or filaments, the void rate of the composite material obtained is low.
• the prepreg is effectively flexible, but the sheath is fragile, if the sheath is thick it is less fragile but the prepreg is then less flexible.
• the powder must not melt inside the sheath. As a result, it can migrate into the wire during handling.
• the polymer which constitutes the sheath and which, in the final product, will contribute to the formation of the matrix, can only participate in the cohesion of the final product if it migrates sufficiently between the reinforcing fibers and if it is subjected to sufficient compression. high.
• glass fiber mats in particular. These mats are. impregnated with molten polymer, by calendering of thermoplastic films, by compression molding in compression of resin films and mats, by casting of molten polymer between two mats sandwiched by two calendered polymer films or by electrostatic projection of resin powder on the mat, followed by the melting of the matrix and compression of the whole.
• FR 2 258 254 has proposed a direct voltage electrostatic spraying method for introducing powder into a fibrous material. Such a process is similar to that of electrostatic painting. The powder sticks to the first fibers it encounters, so that it quickly clogs the pores of the network and prevents its penetration. This is confirmed by the low fiber content of the samples tested by the authors of this document.
• WO-92/15404 relates to a method of manufacturing electronic circuit substrates according to which fiber bundles are coated with electrostatic thermoplastic powder, this powder is melted so that the liquid material penetrates inside the bundles and coats the filaments. To increase the electrical conductivity of the filaments, they are moistened.
• the amount of resin is between 35 and 70% by weight of the composite material.
• this process does not allow powder to be introduced between the fibers or the filaments, since the penetration of the plastic material is obtained by infiltration of the latter in the liquid state with all the problems mentioned above.
• 2,820,716 to introduce a binder into a nonwoven, according to which the powder is charged to a potential and it is brought opposite a potential electrode. opposite by interposing the nonwoven between the powder and the electrode, so that the powder, attracted by the electrode, enters the nonwoven which is in its path.
• the powder here is preferably a thermoplastic binder softened by heating and then cooled to bind the fibers of the nonwoven web between them.
• the quantity of binder incorporated in the nonwoven can in no case be incorporated in proportions suitable for producing a matrix for composite material, otherwise the fibers or filaments of the nonwoven woven would not be bound by the binder, but embedded in it. It would then no longer be a nonwoven, the role of the binder being, as the name suggests, only to give cohesion to the nonwoven by binding the fibers or filaments at the contact points.
• EP-B1-0 502 900 a sintering process for a composite material has also been proposed, according to which powders of polymeric material and / or of mineral material to which a metal powder is added are electrostatically charged and mixed. Reinforcement fibers are sprinkled with this powder mixture, optionally stacking several successive sprinkled layers and a new electrostatic treatment is carried out to make the powder penetrate into the fibrous network.
• the object of the present invention is to provide a solution which makes it possible to distribute powdered material, in particular intended to form a matrix of a composite material reinforced by fibers or filaments, inside a fibrous mass. or filamentary, so as to offer an economical and efficient process, capable of remedying, at least partially, the drawbacks of the solutions known from the prior art.
• the present invention relates to a process for producing a composite material comprising a network of fibers or filaments and a matrix, rigid or flexible, with which said network is in intimate contact, according to which said matrix is incorporated in said network in powder form before being transformed to form said matrix, according to claim 1. It also relates to the composite material obtained according to claim 15, as well as a preform for composite material with thermoplastic matrix obtained according to the method of claim 14.
• the inventors have discovered a process, object of the present invention, according to which it is possible to penetrate into a woven or nonwoven fibrous or filamentous network an amount of powder capable of forming a matrix for material. rigid or flexible composite, by simultaneously subjecting the powder and the fibrous or filamentary network to an electrostatic field at an alternating voltage greater than 20 kV for a duration of at least 5 seconds.
• the voltage of the applied electrostatic field is an alternating voltage preferably between 20 and 150 kV.
• the particle size of the powder is less than 200 ⁇ m, preferably less than 60 ⁇ m.
• textile surfaces or volumes with a suitable porosity texture, in the form of nonwovens, fabrics, knits, braids, wicks or the like, which are designated in the present description under the name of networks, will be used. fibrous or filamentous.
• the fibrous or filamentary mass has been impregnated, it suffices to subject it to a heating operation at a temperature at which the powdered thermoplastic material melts and then to cool.
• the heating operation can be carried out in a mold intended to give this material the shape of the desired part. It is also perfectly possible to envisage carrying out the impregnation according to the present invention on a preformed fibrous or filamentary mass.
• the distance between the metal plates forming the electrodes can vary from 1 to 50 mm. As the phenomenon is sensitive to the field, the voltage must be adapted to the distance between the electrodes.
• the inter-electrode distance allows the intensity to be varied from 5 m to 50 mA. In fact, when the inter-electrode distance increases, the capacity of the capacitor formed by the two metal plates decreases, which lowers the charge, therefore the intensity.
• the granulometry of the powder as well as the density / granulometry ratio are also parameters which have an importance in the results obtained. It is also obvious that the powder must not tend to agglomerate, if we want to guarantee the best penetration of this powder inside the network of fibers or filaments. We have seen that it could be useful with certain powders to add an additive intended to improve its fluidity.
• the powder manufacturer added 0.3% by weight of alumina to prevent it from agglomerating, this additive being known under the name of "anti-caking" agent, to a powder of polyamide 12 sold under the brand Orgasol® by the company Atochem. It was also observed that it was more difficult to obtain good results with powders with a particle size greater than 200 ⁇ m. From the tests carried out, it would seem that the particle size of the powder must be lower the higher the density of the material.
• the impregnation of the powder inside a network of fibers or filaments is a function of various factors including the spacing between the fibers which can be increased or even created by the repulsion between the fibers subjected to an electric field and the particle size of the powder obviously have an important role. Consequently, the texture of the network of fibers or filaments plays a role. This is how nonwovens a priori have a texture favorable to impregnation by the powder in an electric field. Among the fabrics, it is preferable to orient oneself towards weaves in which the fibers are not too tight, such as a roving for example.
• the grammage of the fabric is less important than its texture. It can still be mentioned that better results have been found with fabrics whose grammage is> 300 g / m 2 . This is probably due to the fact that fabrics whose grammage is lower than this value often consist of very tight fine threads.
• a 700 g / m 2 woven glass fiber cloth from the firm Vetrotex was taken and six samples were formed. The results correspond to averages carried out on these samples having, moreover, consistent properties.
• the powder used is a polyamide 12 powder sold under the Orgasol ® brand by the firm Atochem. The particle size of this powder is 20 ⁇ m.
• the time during which the powder and the fabric were subjected, under the aforementioned conditions, to the electric field is 30 seconds and the distance from the electrodes between which the powder and the fabric are placed is 10 mm.
• a plate of composite material is produced by melting the powder distributed between the fibers of the fabric, then the whole is cooled until the material composite either at room temperature.
• a composite material wafer 2.3 mm thick is obtained, having an apparent density of 1.97 g / cm 3 with a void content of 0.4%, a percentage by mass of resin of 21% corresponding at a volume rate of 40%.
• the mechanical properties measured on these samples are 129 MPa for the maximum bending stress and 15.2 GPa for the modulus of elasticity in bending.
• EXAMPLE 2 The same fabric and the same powder were taken as in Example 1, the distance between the electrodes is the same, but the duration during which the powder and the glass fabric were subjected to the electric field of 30 kV in alternating voltage is 2 min. The measured results are interesting to observe since only one parameter has changed between this example and the previous one, namely the duration. The number of samples in this example is 9. The average of the results shows almost identical results for the thickness 2.3 mm, the apparent density 1.94 g / cm 3 , the percentage by mass of resin 21% and the matrix volume rate 39%.
• This example was carried out using a layer of the aforementioned nonwoven and of polypropylene powder (PP) sold under the trade name Coathylène® by Plast-Labor SA and whose particle size is between 38 and 98 ⁇ m. .
• the initial mass ratio between the powder and the nonwoven was 1.35.
• the powder and the nonwoven were subjected for 1 min. to the electrostatic field that of 30 kV under AC voltage and the distance separating the electrodes between which the powder and the nonwoven have been placed as indicated above is 10 mm. A percentage of 42% of powder in the nonwoven was measured, which constitutes a completely satisfactory quantity. In addition, the observed distribution of the powder in the nonwoven is good.
• This example was carried out with five superposed and needled layers of the same nonwoven as in the previous examples, which represents a mass of 1650 g / m 2 .
• the initial mass of powder was in a ratio of 1/1 with that of the nonwoven, but it was distributed half below the nonwoven and half above it.
• the other parameters of duration and distance were similar to those of Examples 3 to 6.
• the proportion of powder measured is 44% which is excellent and the distribution observed inside the layers is good.
• the examples carried out were limited in particular by the powders available on the market as well as by fabrics or nonwovens. However, the results obtained so far make it possible to prove the feasibility of this process and to see what are the main parameters necessary for the implementation of this process.
• this process it is also possible, in certain cases, to provide this matrix in two stages, a first stage consisting of dusting which is not necessarily carried out by electrostatic means.
• the role of this first step is to provide an amount of powder not sufficient to produce the matrix, but sufficient to allow a preform of the part to be produced, the role of this powder being to allow the network of fibers or filaments to keep, after cooling, the shape of the desired part.
• this preform is subjected to an electrostatic impregnation operation, as described above, with a view to providing in this preform the remainder of the quantity of powder necessary to produce the matrix.
• the powder used for impregnation can also be used to provide one or more additional functions to the textile.
• powder conduc ⁇ trainers powder conduc ⁇ trainers, antibacterial, antifungal, for example.
• fillers giving the material lightening and / or insulation characteristics by example of hollow balls or blowing agents.
• the powder used to provide an additional function to the material can also be provided by mixing it with that of the matrix, in the case of a composite.
• the powder used to provide an additional function to the material can also be provided by mixing it with that of the matrix, in the case of a composite.
• other powders or fillers have been incorporated.
• 42-% is incorporated by weight of PP of 60 microns in three layers of needled Unifilo ®, applying the életrostatique field for 30 seconds.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Reinforced Plastic Materials (AREA)
• Chemical Or Physical Treatment Of Fibers (AREA)
• Moulding By Coating Moulds (AREA)
• Processing And Handling Of Plastics And Other Materials For Molding In General (AREA)

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• 1997
  • 1997-11-04 EP EP19970810826 patent/EP0914916A1/fr not_active Withdrawn
• 1998
  • 1998-11-02 WO PCT/IB1998/001738 patent/WO1999022920A1/fr not_active Ceased
  • 1998-11-02 TR TR200001209T patent/TR200001209T2/xx unknown
  • 1998-11-02 DE DE69803697T patent/DE69803697T2/de not_active Expired - Lifetime
  • 1998-11-02 DK DK98949181T patent/DK1028836T3/da active
  • 1998-11-02 CA CA 2309245 patent/CA2309245C/fr not_active Expired - Fee Related
  • 1998-11-02 KR KR1020007004807A patent/KR100597525B1/ko not_active Expired - Fee Related
  • 1998-11-02 EP EP19980949181 patent/EP1028836B1/fr not_active Expired - Lifetime
  • 1998-11-02 JP JP2000518824A patent/JP4102021B2/ja not_active Expired - Fee Related
  • 1998-11-02 AT AT98949181T patent/ATE212584T1/de active
  • 1998-11-02 CN CNB988105446A patent/CN1184059C/zh not_active Expired - Fee Related
  • 1998-11-02 BR BRPI9813940-1A patent/BR9813940B1/pt not_active IP Right Cessation
  • 1998-11-02 AU AU95549/98A patent/AU9554998A/en not_active Abandoned
  • 1998-11-02 ES ES98949181T patent/ES2172211T3/es not_active Expired - Lifetime
• 2000
  • 2000-05-02 US US09/562,170 patent/US6733845B1/en not_active Expired - Lifetime

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