MXPA99010175A - Preforms for moulding process and resins therefor - Google Patents

Abstract

Binder coated fibres comprising from 80 to 99%by weight reinforcing fibres and from 1 to 20%by weight of a preform binder resin, said binder resin being in the form of particles or discrete areas on the surface of the reinforcing fibres, said binder resin comprising:from 40 to 90%by weight of the binder resin of a thermosetting resin and from 10 to 60%by weight of the binder resin of a high molecular weight engineering thermoplastic and/or an elastomer selected from vinyl addition polymer, fluororelastomers and polysiloxane elastomers, the engineering thermoplastic/elastomer being dissolved in the thermosetting resin, the binder resin being non-tacky at ambient temperature, having a softening point in the range 50 to 150°C and being heat curable at a temperature in the range 50 to 200°C.

Description

PREFORMS FOR MOLDING PROCESS AND RESINS FOR THE SAME DESCRIPTION OF THE INVENTION The present invention relates to preforms for molding processes, especially resin transfer molding processes.

(RTM) and binders for use therein. The various molding processes, such as RTM processes involve loading dry fibrous reinforcement layers into a mold, closing the mold, introducing a thermoplastic resin composition into the mold and curing the resin typically by means of of the application of heat. One of the process constraints in such a process is the loading of the fibrous reinforcement into the mold. The individual layers of fabrics must be cut and shaped to conform to the various curvatures in the mold. This can be time consuming and difficult to perform, especially for full batches involving foam cores and other core materials. It would be desirable to assemble the REF .: 32018 fibrous reinforcement out of the mold and only load that structure (or preform) into the mold at one time. The preforms used for the preparation of the composite are typically composed of multiple layers of fibrous material. These are assembled in a stack and formed prior to placement on a mold surface for impregnation with matrix resin. Known methods for preparing the dry preform layers for molding involve stacking multiple layers of the woven or knitted fabric material with the desired fiber orientation, and then joining together by stitching or stapling the layers of material together. This is to keep the alignment of the fibers uniform and stabilize the fabric to prevent fraying. The stack of the material is then cut, outside the joint or stapling, to the desired shape of the preform. The preform is then placed in a mold and the resin is injected to impregnate the fabric. These methods for the stabilization of the preform however, are limited to two-dimensional (flat) structures and the stacking of the material can not be shaped to conform to an outline of complex parts without disturbing the joining or stapling and / or causing the misalignment of the fibers. If attempts are made to flex the preform, for example, to form a curved surface, the layers may separate or break at the points of attachment. The production of complex three-dimensional preforms can involve weaving and three-dimensional braiding. These methods are very labor intensive, increasing the cost for the production of a complex shaped part. Another method for stabilizing a preform involves spraying or spraying an adhesive, for example, a hot melt adhesive, onto the surface of the layers to hold them together. Usually, the dry fabric is coated in discrete areas with a thin layer of the liquefied thermoplastic polymer or alternatively, a fibrous polymer is placed between the layers and heat is applied to melt the polymer, to provide the adhesive characteristics. Such preforms are then contoured in a preforming mold to conform to the required complex shape, by melting and resolidifying the polymer. This is achieved by the selective application and removal of an external heat source, for example, a hot air gun. This is a highly intense labor operation. Since the hot melt adhesive is a thermoplastic polymer, it has several disadvantages. Firstly, the binder may not sufficiently wet the fibers to retain the adjacent layers together, to maintain a shape after formation. Thus, if the preform is handled, such as during loading within the mold, it is possible for the fiber layers to be displaced. Also, such thermoplastic material may be detrimental to the cured mechanical operation of the thermosetting matrix resin systems, typically used to produce components by means of a resin transfer molding process. During the injection, the thermoplastic binder forms bags located within the component, which inhibit or prevent the infiltration of the thermosetting resin, reducing the strength or strength of the component. Thus, to form complex composite articles using hot melt binder, it is required to sacrifice part of the resistance and Tg. US-A-4, 992, 228 discloses a method for the preparation of preforms that comprises (1) amplification substantially uniformly on the surface of each one or more folds of a non-impregnated substrate material, one or more thermoplastic, non-sintering resinous compounds, which are substantially free of any compound that could serve as a crosslinker for said thermoplastic material, the resinous compound being in the form of a powder having a particle size of less than about 500 microns and having a melting point as determined by Differential Scanning Calorimetry of from about 50 ° C to about 70 ° C, in an amount from about 3 to about 5 weight percent based on the weight of the substrate material; (2) the melting of the resinous composite in the form of thermoplastic, powder, on the surface of said substrate material; (3) the cooling of the resinous material; (4) mounting one or more folds of the substrate material treated in this manner, and shaping said folds of the treated substrate material into a desired shape; (5) fastening the folds formed in this way from the material of the treated substrate at a temperature sufficient to melt said resinous compound; Y (6) cooling the shaped, shaped folds of the substrate material to a temperature below the melting point of the resinous compound; whereby a preformed preform is formed for use in molding processes as reinforcement material. The North American Patent -No. No. 5,080,857 describes a method of molding using a stabilized preform, comprising the steps of: a) the provision of a plurality of oriented fiber layers, b) the stacking of the layers, c) the application of a non-catalyzed thermosetting resin, solid, between each layer, d) the placement of the layers stacked on a mold surface having a desired preform shape, e) the formation of layers on the mold surface, f) the heating of the layers to melt the resin and merge slightly the layers together, g) cooling to rigidify the layers to form a preform, and h) impregnating the preform with a matrix of thermosetting resin containing a catalyst at a temperature at which the thermosetting resin uncatalyzed, solid, it will melt and mix with the resin matrix to catalyze the molten, uncatalyzed thermosetting resin with it. U.S. Patent No. US-A-5, 427, 725 describes a process for making a matrix composite comprising the steps of: 1) contacting a reinforcing substrate with a thickener, which contains either: ) a simple resin that is capable of at least partially healing itself; or b) a mixture containing resin and hardener which is capable of at least partially curing, at a temperature and for a time sufficient to partially cure the thickener, so that it adheres to the substrate but remains in the form of thermoplastic material, and is able to react later, with which a preform is elaborated; 2) placing one or more layers of the preform in a mold; 3) the injection of a second resin or curable resin composition which is capable of reacting with the thickener, inside the mold to impregnate the preform; and 4) curing the thickener of the matrix resin, whereby a composite material is formed. The processes of US Patent Nos. 5,080,857 and 5,427,725 are an improvement in terms of compatibility with the molding resin. GB-2007676 Patent, GB-2182074, EP-0309221, EP-0297674, O89 / 04335, US-5532296 and US-4377657 describes resin compositions that are suitable for use in various molding processes. However, none of these resins are described as being useful for resin transfer molding and most are liquid or thick at room temperature before curing. U.S. Patent No. 4,757,120 discloses polyimide polymers are reaction products of active methylene compounds and derivatives of N, N'-bismaleimida are improved by incorporating them with 2 to 15% by weight of a polymer polyethersulfone. The polymer blend is useful in the production of films, moils, pre-spikes, laminates, and filled composites which are particularly useful in structural components which have high temperature stability. The present invention provides an improved preform binder resin for the manufacture of a preform. According to one aspect of the present invention, binder-coated fibers comprising from 80 to 99% by weight reinforcement fibers and from 1 to 20% by weight of a preform binder resin are provided., the binder resin being in the form of discrete particles or areas on the surface of the reinforcing fibers, said binder resin comprising: from 40 to 90% by weight of the binder resin, from a thermosetting resin and from 10 to 60% by weight of the binder resin, of an engineering thermoplastic material, of high molecular weight, and / or of an elastomer selected from polymer with the addition of vinyl, fluoroelastomers and polysiloxane elastomers, the engineering design of the thermoplastic / elastomer that dissolves in the thermosetting resin, the binder resin being non-tacky at room temperature, having a softening point in the range of 50 to 150 ° C and being heat curable at a temperature in the range of 50 to 200 ° C. The invention utilizes a preform binder resin which comprises a thermosetting resin having a thermoplastic and / or engineered elastomer dissolved therein. The preform binder resin is a non-tacky or adherent solid at room temperature. The resin may be in the form of a free-flowing powder, which does not agglomerate, which generally has a particle size below 1500 μm and which typically has an average particle size in the range of 100 to 500 μm. The particulate binder can be applied to the reinforcing fibers and heated to soften the particles, causing the powder to adhere to the fibers. Alternatively, the binder resin can be applied to the reinforcing fibers from the solution by spraying, printing, etc., such that after the evaporation of the solvent particles, discrete areas or islands of the binder resin are formed. A continuous coating of the binder resin is not desired since it adversely affects the mobility of the fibers. The binder coating of the invention can be in the form of a woven or nonwoven fabric which has fibers and good mobility, and can be easily stacked and shaped, and joined by application of heat at a temperature in the range of 60 to 120. ° C to make a preform. The thermosetting resin is selected to be the same as or completely compatible with the matrix resin to be used in the RTM process. The presence of the dissolved thermoplastic / elastomer provides the solid characteristics and softening point properties to the binder resin, and also imparts desirable properties to the finished molded articles, in particular the roughness of the article is improved. It is known that the presence of a high molecular weight thermoplastic resin can improve the rigidity of the matrix resins used in RTM. However, it is not easily possible to incorporate the thermoplastic resin into the matrix resin, since the presence of the dissolved thermoplastic resin increases the viscosity of the matrix resin, such that it will not easily flow through the reinforcing fibers during the molding process. The presence of undissolved particulate thermoplastic resin in the matrix resin is not practical since the particulate resin is filtered by reinforcing fibers during the injection of the matrix resin. The fibers coated with the binder of the invention introduce the thermoplastic resin throughout the length of the preform, and therefore throughout the length of the molded article. This is in a way that easily improves the rigidity of the molded article without affecting in a harmful way the mobility of the fabrics used in the preparation of the preform. The thermosetting resins used in the invention can be selected from a wide range of resins useful in molding applications, including but not limited to bismaleimide resins (BMI), cyanate resins and epoxy resins.

Bismaleimide resins are heat curable resins that contain the maleimido group as a reactive functional group. The term "bismaleimide" as used herein includes the higher functionality mono-, bis-, tris-, tetrakis-maleimides and maleimides, and also mixtures thereof, unless otherwise noted. Bismaleimide resins with an average functionality of about 2 are preferred. Bismaleimide resins, as defined in this way, are prepared by the reaction of the maleic anhydride or a substituted maleic anhydride such as methylmaleic anhydride with an aromatic or aliphatic di- or polyamine. Examples of the syntheses can be found, for example in U.S. Patent Nos. 3,018,290, 3,018,292, 3,627,780, 3,770,691 and 3,839,358. Also useful are the closely related nadicimide resins, prepared analogously from a di- or polyamine, but wherein the maleic anhydride is replaced by a Diels-Alder reaction product of maleic anhydride or a maleic anhydride substituted with a diene such as cyclopentadiene. As used herein and in the claims, the term bismaleimide will include the nadicimide resins. Preferred di- or polyamine precursors include aliphatic and aromatic diamines. The aliphatic diamines may be straight chain, branched or cyclic, and may contain heteroatoms. Many examples of such aliphatic diamines can be found in the references cited above. Especially preferred aliphatic diamines are hexanediamine, octanediamine, decandiamine, dodecandiamine, and trimethylhexandiamine. The aromatic diamines can be mononuclear and polynuclear, and can also contain fused ring systems. Preferred aromatic diamines are phenylenediamines; the toluenediamines; the various methylenedianilines, particularly 4,4'-methylenedianiline; the naphthalenediamines; the various amino-terminated polyarylene oligomers corresponding to, or analogous to, the formula H2N-Ar [X-Ar] nNH2, wherein each Ar can independently be a mono- or poly-nuclear arylene radical, each X can be independently - 0-, ~ S-, -C02-, -S02-, -O-CO-, lower alkyl of 1 to 10 carbon atoms, halogenated alkyl of 1 to 10 carbon atoms, lower alkyleneoxy of 2 to 10 carbon atoms , arylenoxy, polyoxyalkylene or polyoxyarylene, and wherein n is an integer from about 1 to 10; and di- and polysiloxanes terminated in primary aminoalkyl. Particularly useful are mixtures of "eutectic" resin of bismaleimide containing several bismaleimides. Such mixtures generally have melting points that are considerably lower than the individual bismaleimides. Examples of such mixtures can be found in U.S. Patent Nos. 4,413,107 and 4,377,657. Several such eutectic mixtures are commercially available. The cyanate resins are heat-curable resins whose reactive functional group is the cyanate, or group -OCN. These resins are generally prepared by the reaction of a di- or polyfunctional phenolic compound with a cyanogen halide, generally cyanogen chloride or cyanogen bromide. The synthesis method for now is well known to those of skill in the art, and examples can be found in U.S. Patent Nos. 3,448,079, 3,553,244 and 3,740,348. The products of this reaction are the di- and polycyanate esters of the phenols. The cyanate ester prepolymers can be prepared by heat treatment of the cyanate functional group monomers with or without a catalyst. The degree of polymerization can be followed by the viscosity measurement. Catalysts can be used to aid polymerization. Such prepolymers and catalysts are known in the art. Suitable cyanate resins are commercially available and can be prepared from mono-phenols., di-, and polynuclear, including those that contain fused aromatic structures. The phenols can optionally be fused aromatic structures. The phenols may optionally be substituted with a wide variety of organic radicals including, but not limited to halogen, nitrol, phenoxy, acyloxy, acyl, cyano, alkyl, aryl, alkaryl, cycloalkyl, and the like. The alkyl substituents can be halogenated, particularly perchlorinated and perfluorinated. Particularly preferred alkyl substituents are methyl and trifluoromethyl. Particularly preferred phenols are mononuclear diphenols such as hydroquinone and resorcinol; the various bisphenols, such as bisphenol A, bisphenol F, and bisphenol S; the various dihydroxynaphthalenes; and the oligomeric phenol and the novolacs derived from cresol. Substituted varieties of these phenols are also preferred. Other preferred phenols are the phenolated dicyclopentadiene oligomers prepared by the Friedel-Crafts addition of the phenol or a phenol substituted to the dicyclopentadiene, as shown in US Pat. No. 3,536,734. Epoxy resins can also be used alone or as co-monomers in the resin systems with cyanate functional group or bismaleimide functional group, of the present invention. Epoxy queens are thermosetting resins that contain the oxirane or epoxy group as the reactive functional group. The oxirane group can be derived from a number of various synthesis methods, for example by the reaction of an unsaturated compound with a peroxygen compound such as peracetic acid, or by reaction of the epichlorohydrin with a compound having an active hydrogen, followed by for dehydrohalogenation. The synthesis methods are well known to those of skill in the art, and can be found for example in the Handbook of Epoxy Resins, Lee and Neville, Eds. , McGraw Hill, 1967, in chapters 1 and 2 and in the references cited therein. Epoxy resins useful in the practice of the present invention are generally those that are commercially available and substantially di- or polyfunctional resins. In general, the functionality should be from about 1.8 to about 8. Many such resins are commercially available. Particularly useful are epoxy resins that are derived from epichlorohydrin. Examples of such resins are the di- and polyglycidyl derivatives of the bisphenols, such as bisphenol A, bisphenol F and bisphenol S; the dihydroxynaphthalenes, for example 1,4-, 1,6-, 1,7-, 2,5-, 2,6- and 2,7-dihydroxynaphthalenes; 9,9-bis [hydroxyphenyl] fluorene; the phenolated and cresolated monomers and dicyclopentadiene oligomers as shown in U.S. Patent No. 3,536,734; aminophenols, particularly 4-aminophenol; various amines such as 4,4'-, 1,4'- and 3,3'-methylenedianiline and methylenedianiline analogs in which the methylene group is replaced with a lower alkyl of 1 to 4 carbon atoms substituted or unsubstituted, or by the group -0-, -S-, -CO-, -0-C0-, -0-C0-0-, -S02-, or aryl; and polyarylene oligomers terminated at amino, hydroxyl and mixed amino and hydroxyl, having the groups -0-, -S-, -CO-, -0-C0-, -0-C0-0-, -S02- , and / or lower alkyl interspersed between mono- or polynuclear aryl groups as shown in US Patent No. 4,175,175. Epoxy resins based on cresol novolacs and phenol are also suitable. Novolacs are prepared by condensing phenol or cresol with formaldehyde, and typically have more than two hydroxyl groups per molecule. The glycidyl derivatives of the novolacs can be liquid, semi-solid or solid, and in general have epoxy functionalities of about 2.2 to about 8. The hybrid resin systems can also be used. Suitable hybrid resin systems include the combination of bismaleimides and the comatomers of cyanate ester, the comonomers of epoxy and cyanate ester, and the comonomers of bismaleimide and epoxy, and the mixture thereof. The binder resin of the present invention further contains an engineering elastomer and / or thermoplastic, dissolved. Such suitable thermoplastics have high fracture strength and glass transition temperatures above 150 ° C, preferably above 200 ° C. The thermoplastic mixture can be a polyimide, polyetherimide (PEI), polyethersulfone (PES), polysulfone, polyetherketone, polyetheretherketone (PEEK), polyamide, polyamideimide, or the like. PEI is preferred. Elastomers useful in the invention include flexible vinyl addition polymers, including homopolymeric and copolymeric diene rubbers, conjugated diene derivatives of 4 to 8 carbon atoms such as butadiene, isoprene, propylene, chloroprene, and the like. These include, but are not limited to copolymers of such dienes with each other and with one or more monomers such as styrene, acrylonitrile, methacrylonitrile, acrylic acid, methacrylic acid, methyl methacrylate, and the like. Butadiene-acrylonitrile polymers and butadiene-acrylonitrile polymers with carboxylic functional group are most preferred. Suitable fluoroelastomers are described in Polym. Int., 26 (2), 69-73, 1991. Suitable polysiloxane elastomers are described J. Appl. Polym. Sci., 54 (1), 83-90, 1994. The thermoplastic / elastomeric materials are present in amounts of about 10 to about 60 weight percent, preferably 20 to 40 weight percent of the binder resin. The thermoplastics / elastomers can be easily dissolved in the thermosetting resin using a solvent, for example, methylene chloride, and after that the solvent is removed. The resulting material can be crushed to the desired particle size; alternatively, the solution can be spray dried. The exact amounts of the thermosetting resin and the thermoplastic in the binder will vary with the individual constituents. In general, the thermosetting resins are liquid and the presence of increasing amounts of dissolved thermoplastic / elastomer increases the viscosity until a solid forms at room temperature. The thermoplastic concentration is adjusted to provide a non-sticky solid having a softening point in the range of 50 to 150 ° C, typically 60 to 120 ° C. The resulting solid binder resin is non-tacky allowing it to be used in the form of a non-agglomerating, free-flowing powder. The binder resin melts or softens sufficiently at moderate temperatures in the range of 50 to 150 ° C. This allows the binder particles to bond to the surface of the fibers when they are heated in contact with the fibers and cooled. After that, the fibers coated with the binder can be shaped and bonded together to retain the desired shape by heating within the above temperature range and cooling. Preferred combinations of the thermosetting resin and the democratic material for the binder resin used in the invention include BMI / PEI, BMI / PES and epoxy / PEI. The matrix resin used in the RTM process is preferably the same as the binder thermosetting resin. The binder resin may contain up to 20% by weight of one or more additives selected from thermally conductive particles, electrically conductive particles, fire retardants, colorants, catalysts, curing agents and coupling agents. Suitable thermal conductive particles include metal particles, suitable electrically conductive particles including graphite. Preferred fire retardants include aluminum trihydrate, zinc borate and phosphorus flame retardants. Examples of coupling agents include aminosilanes. The reinforcing fibers used in the present invention include glass fibers, carbon fibers, aramid fibers, ceramic fibers, etc. and mixtures thereof. The resin binder can be applied to the rows of individual fibers which are then processed to form a fabric or a substrate, or preferably the resin binder is applied to a fabric comprising the reinforcing fibers. The resin binder can be applied to one or both surfaces of the fabric. The binder resin can be applied in the form of a powder, generally having a particle size in the range of 100 to 500 μm. Any suitable powder coating technique including spray coating, electrostatic coating, drip coating, etc. may be employed. After application of the binder resin powder, the binder is heated to a temperature in the range of 50 to 150 ° C to soften the particles, so that they bind to the fiber. The heat treatment should not be sufficient for the particles to completely melt and flow to form a continuous layer, as this will affect in a damaging way the mobility of the fabric. The binder resin powder is conveniently heated by passing the coated fabric under infrared lamps. Alternatively, the binder resin can be applied from the solution by spraying or spraying, printing, etc., to provide discrete areas of binder resin on the fibers.

The binder-coated fiber of the invention can be easily coated and stacked by applying heat and pressure, so that a consolidated preform is produced which has long-term room temperature integrity and good handling capacity. The preform can be used to prepare a composite material by introducing a thermosetting matrix resin and curing the resins at a temperature of 50 to 200 ° C. The matrix resin can be introduced into the preform by any suitable technique. In general, the preform is placed in a mold and the matrix resin introduced into the mold cavity to impregnate the preform. The thermosetting resin of the binder resin and the matrix resin are preferably, but not limited at the same time to ensure optimum compatibility, thereby allowing complete impregnation of the preform to produce a high performance compound. The presence of the thermoplastic / throemeric material dissolved in the resin binder has been found to increase the stiffness of the final cured compound, compared to the identical compound prepared without the dissolved thermoplastic. In addition, other properties of the cured compound, for example, flexural strength, flexural moduli, interlaminar shear strength, are not affected in a damaging manner by the presence of the thermoplastic material dissolved in the binder resin. The invention will now be illustrated by the following Examples.

Example 1 Preparation of a bismaleimide binder modified with PEI 2.5 kg of PEI (General Electric Ultem 1000) was dissolved in 7.5 kg of methylene chloride. 7.5 kg of bismaleimide resin (RTM Cytec 5250-4 resin) was added to the PEI solution and stirred until homogeneous. The methylene chloride was then removed in vacuo at 80 ° C. When cooled to room temperature, the resulting material was a glassy, hard solid, which was subsequently ground to a fine powder of particle size of 100 to 500 μm.

This powder is the binder for the manufacture of the preform.

Example 2 Powder coating of glass cloth The binder powder of Example 1 was powder coated on 7781-style glass cloth. The powder was uniformly applied to one side of the fabric to give a coverage of 6% by weight. The powder coated fabric was then passed under an infrared heater which softened the powder, which adhered to the surface of the cloth. Other cloth samples were coated at 1 and 3% by weight.

Example 3 Manufacture of a preform The powder coated fabric of Example 2 was used to produce a helmet shaped preform. The binder-coated fabric was accumulated within a female mold. This was then consolidated in the form by means of a bladder or rubber balloon inflated with steam. The heat and pressure generated by the steam softened the binder and allowed the fabric to fold to stick together. The helmet-shaped preform was then cooled under pressure and was a rigid, well-consolidated preform, which had integrity at room temperature in the long term.

Example 4 Evaluation of Rigidity The interlaminar fracture stiffness of a composite laminate produced from the carbon cloth coated with binder of the invention, and a commercial bismaleimide resin, was compared to an equivalent laminate produced without a binder. To produce a binder-coated fabric, a uniform coating of the binder of Example 1 was manually splashed onto both surfaces of a 3K5H carbon cloth of 283 grams. The fabric was coated to give 3.5% by weight of binder on each side of the fabric, and therefore a total binder content of 7% by weight. The fabric was then heated in an air circulation oven for 2 minutes at 120 ° C, to melt the binder on the fabric. The fabric coated with binder was then removed from the oven and allowed to cool to room temperature. The composite laminates were produced from the fabric coated with the binder and standard cloth. 96 gram bismaleimide resin films were applied to each side of the two fabrics. The resulting materials were then cut into pieces measuring 40.5 x 30.5 cm (16 x 12 inches). Ten folds of this material were then stacked together and consolidated under manual pressure. In the center of this stack or stack an FEP release film was placed between the pleats at one end, in order to produce a laminate suitable for the preparation of G? C test specimens according to Test Method 1,0005 of the AITM. The preformed laminates were then cured in an autoclave molding cycle for 6 hours at 190 ° C. the resulting composite laminates were then post-cured in an air circulation oven for 5 hours at 245 ° C. The Gic test specimens were prepared according to the 10005 test method of the AITM, with the warp fibers that were aligned to the specimen in the longitudinal direction, with the faces of the warp that were nested in the plane of the crack or fissure. . Six specimens were cut from both laminates and tested in order to acquire data. For specimens without binder the G? C value obtained was 268.6 J / m2. For the specimens with the binder the G? C value obtained was 419.9 J / m2. Gics are significantly higher for specimens that included the binder, and thus illustrate the increase in stiffness of the composite material, provided by the use of the binder resin of the invention.

Example 5 Using the samples as prepared in Example 4, the following properties of the cured laminates were evaluated: n = number of specimens tested sd = standard deviation cv = coefficient of variation The vitreous transition temperatures are the values of tan d (tangent of d) from the measurements of the dynamic-mechanical-thermal analysis (DMTA). The results show that, for the measured properties, the materials produced with the binder resin of the invention are not significantly different from those produced without the binder.

Example 6 Preparation of a PES-modified bismaleimide binder 400 g of PES (Victrex 5003P) were dissolved in 1.3 kg of methylene chloride. 600 g of bismaleimide resin (Cycom 5250-4 RTM resin) was added to the PES solution and applied until homogeneous. The methylene chloride was removed in vacuo at 80 ° C. when cooled to room temperature, the resulting material was a hard, glassy solid, which was subsequently ground to a powder of particle size less than 500 μm. This powder was suitable for the powder coating and the manufacture of the preform by techniques described in Examples 2 and 3.

Example 7 Preparation of an epoxy binder modified with phenoxy resin 70 g 'of a solid epoxy novolac resin (Ciba ECN 1273) was added to a solution of 40% solids of thermoplastic phenoxy resin material in methyl ethyl ketone (Phenoxy Associates Paphen PKHS-40). An additional 20 g of methyl ethyl ketone was added and the mixture was stirred until the epoxy novolac resin was completely dissolved. Then 5 g of a catalyst (Anjinomoto Ajicure PN23) were added and the mixture was stirred until it was homogeneous. The methyl ethyl ketone solvent was then removed in vacuo at 80 ° C. When cooled to room temperature, the resulting material was a hard solid, which was subsequently ground to a particle size of less than 500 μm. This powder can then be used as a binder resin.

Example 8 Preparation of a cloth coated with epoxy binder The binder resin of Example 7 was coated with powder on 7781-style glass cloth at a coating weight of 5% as for Example 2.

Example 9 Fabrication of an epoxy binder preform 8 pieces (30 x 15 cm) of the powder coated fabric of Example 8 were cut and stacked together. This pile of fabric was then consolidated at vacuum pressure using a vacuum bag. The vacuum bag was then placed in an oven at 80 ° C for 10 minutes to soften the binder and stack the folds of the fabric together. After cooling to room temperature the vacuum bag was removed and a well-established preform was formed, which had integrity at room temperature, in the long term.

Example 10 Evaluation of stiffness The binder of Example 6 was used to prepare the G? C specimens as for Example 4. The test was performed according to test method 1.0005 of the AITM. For specimens with binder, a value for Glc of 447.9 was obtained J / m This compares for a value with G? C of 268.6 J / m2 without binder. This demonstrates a significant increase in the rigidity of the composite material provided by the use of the binder resin of the invention.

Example 11 Preparation of a polysulfone-modified epoxy binder g of polysulfone (Amoco P1800) were dissolved in 100 g of methylene chloride. 76 g of a solid novolac resin (Ciba ECN 1273) was added to the solution and stirred until dissolved. Then 1 g of a catalyst (Ciba DY9577) was added and the mixture was stirred until it was homogeneous. The methylene chloride was then removed under vacuum at 70 ° C. When cooled to room temperature, the resulting material was a hard solid, which was subsequently ground to a particle size of less than 500 μm. This powder could then be used as a binder resin.Example 12 Preparation of a cloth coated with epoxy binder The binder resin of Example 11 was coated on carbon cloth 3K5H at a coating weight of 6% following the procedure of Example 2.

Example 13 Fabrication of an epoxy binder preform Eight pieces (33 x 18 cm) of the powder coated fabric of Example 12 were cut and stacked together. The folds were consolidated at 80 ° C following the procedure of Example 9. It resulted in a well-consolidated preform with integrity at room temperature in the long term.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (24)

RE IVINDICATIONS Having described the invention as above, the content of the following claims is claimed as property:

1. Binder-coated fibers comprising from 80 to 99% by weight of reinforcing fibers and from 1 to 20% by weight of a preform binder resin, the binder resin is in the form of discrete particles or areas on the surface of the fibers of reinforcement, the binder resin is characterized in that it comprises: from 40 to 90% by weight of the binder resin, from a thermosetting resin and from 10 to 60% by weight of the binder resin of a high molecular weight engineering thermoplastic material and / or an elastomer selected from polymer with addition of vinyl, f luoroelastomers and polysiloxane elastomers, the thermoplastic / engineering elastomer is dissolved in the thermosetting resin, the binder resin being non-stick at room temperature, and has a softening point in the range of 50 to 150 ° C and is heat curable at a temperature in the range of 50 to 200 ° C.

2. The binder-coated fibers according to claim 1, characterized in that the binder resin comprises about 75% by weight of thermosetting resin / lathe and about 25% by weight of engineering thermoplastic material.

3. The binder coated fibers according to claim 1 or claim 2, characterized in that the thermosetting resin is selected from bismaleimide resins, cyanate resins and epoxy resins.

4. The binder coated fibers according to claim 3, characterized in that the thermosetting resin is a bismaleimide resin.

5. The binder-coated fibers according to any of the preceding claims, characterized in that the engineered thermoplastic material has a Tg of at least 150 ° C and is selected from polyimide, polyetherimide, polyethersulfone, polysulfone, polyetherketone, polyetheretherketone, polyamide, polyamidoimide and phenoxy resin.

6. The binder coated fibers according to claim 5, characterized in that the engineered thermoplastic material is a polyetherimide, polyethersulfone or epoxy resin.

7. The binder coated fibers according to any of the preceding claims, characterized in that the elastomer is a homopolymer or copolymer diene rubber derived from a conjugated diene having from 4 to 8 carbon atoms.

8. The binder-coated fibers according to claim 7, characterized in that the elastomer is a butadiene-acrylonitrile polymer or a butadiene-acrylonitrile polymer with a carboxylic functional group.

9. The binder coated fibers according to any of the preceding claims, characterized in that the binder resin comprises up to 20% by weight of one or more additives selected from thermally conductive particles, electrically conductive particles, fire retardants, colorants, catalysts, curing agents and coupling agents.

10. The fibers coated with binder according to any of the preceding claims, characterized in that the reinforcing fibers are selected from glass fibers, carbon fibers, aramid fibers, ceramic fibers and mixtures thereof.

11. The binder-coated fibers according to claim 11, characterized in that the reinforcing fibers are in the form of a fabric.

12. The binder-coated fibers according to claim 11, characterized in that they comprise from 90 to 97% by weight of reinforcing fibers and from 3 to 10% by weight of a binder resin that is coated on a surface of the fabric or on both sides of the fabric.

13. The binder-coated fibers according to any of the preceding claims, characterized in that the binder resin is in the form of particles having a particle size not greater than 1500 μm.

14. The binder coated fibers according to claim 13, characterized in that the binder resin is in the form of particles having an average particle size in the range of 100 to 500 μm.

15. A binder resin in the form of a free-flowing powder, which does not agglomerate, which is a non-sticky solid at ambient temperatures, which has a softening point in the range of 50 to 150 ° C and which is curable by heat at a temperature in the range of 50 to 200 ° C, and characterized in that it comprises: from 40 to 90% by weight of a thermosetting resin and from 10 to 60% by weight of a high molecular weight engineering thermoplastic and / or an elastomer which is a vinyl-added rubber polymer, with the proviso that when the engineering plastic is polyethersulfone it is present in an amount of 20 to 60% by weight.

16. A binder resin according to claim 15, characterized in that it consists of: 40 to 90% by weight of a thermosetting resin, 10 to 60% by weight of a high molecular weight engineering thermoplastic and / or a selected elastomer of polymer with addition of vinyl, fluoroelastomers and polysiloxane elastomers, up to 20% by weight of one or more additives selected from thermally conductive particles, electrically conductive particles, fire retardants, colorants, catalysts, curing agents and coupling agents.

17. A binder resin according to claim 15 or claim 16, characterized in that the components are as defined in accordance with any of claims 2 to 8.

18. A binder resin according to any of the claims 15. at 17, characterized in that it is in the form of a free flowing powder, which does not agglomerate, having a particle size no greater than 1500 μm.

19. A binder resin according to claim 18, characterized in that it has an average particle size in the range of 100 to 500 μm.

20. A method for the preparation of a stabilized preform, characterized in that it comprises the steps of: the provision of a plurality of layers of fibers coated with binder, as defined according to any of claims 1 to 18, the formation of the layers on a surface of the mold, heating the layers to a temperature in the range of 50 to 150 ° C to melt the binder resin and fuse the layers together, and cooling to stiffen the layers to form a preform.

21. A process for the production of a composite material, characterized in that it comprises the steps of: the provision of a preform produced by the method according to claim 20, the application of a thermoset matrix resin to the preforms, and the curing of the resins at a temperature in the range of 50 to 200 ° C, whereby a composite material is formed.

22. A process according to claim 21, characterized in that the preform is placed in a mold.

23. A process according to claim 22, characterized in that the matrix resin is introduced into the mold containing the preform.

24. A process for the preparation of a composite material according to claim 23, characterized in that the matrix resin is of the same type as the binder resin thermosetting resin.