MXPA01009772A - Composite comprising structural and non structural fibers - Google Patents

Abstract

A composite comprises a structural component and a resin component, the structural component comprising structural fibres and a toughening additive comprising non-structural thermoplastic fibres and the resin component comprising a non-thermoplastic material. The structure component is a preform formed from the structural fibres and the thermoplastic fibres. The volume fraction of the structural fibres in the preform is at least 65%. The composite may be produced by forming a preform from structural fibres with non-structural thermoplastic fibres to provide a structural component. Liquid resin is then injected or infused into the structural component and cured.

Description

COMPOSITE COMPRISING STRUCTURAL AND NON-STRUCTURAL FIBERS DESCRIPTION OF THE INVENTION The present invention is concerned with a compound and with a method of manufacturing the compound. The composite materials generally comprise an array of reinforcing fibers in a resin matrix. The present global industries use composite structures, for example the aerospace industry, predominantly uses prepregs (fibrous composite material having unidirectional fibers included in a resin matrix in sheets or strips ready for deformation (acronym for pre-impregnation)), unidirectional and base of conventional fabrics. Such prepregs are commonly made by stretching continuous wicks of reinforcing fibers or fabrics through a bath of molten resin or resin dissolved in solvents. Then the prepreg is formed into a desired shape, charged to a mold that is closed and heated to cure the resin. In the last five to seven years, an alternative technology for manufacturing composite parts has emerged which is generally referred to as liquid compound molding. In the molding of liquid compound, a dry fibrous reinforcement is loaded to a mold or tool and the resin is Ref .: 132206 injected or infused to the fibers and cured. The reinforcement is termed a "preform" whose term is well known to those skilled in the art of the compounds as it indicates a set or assembly of dry fibers which constitutes the reinforcement component of a compound in a form suitable for use in a process of liquid compound molding. A preform is commonly a assembly of textile shapes such as fabrics, braids or mats, adapted or formed as necessary and assembled as a specific operation before being placed or on the mold tool. Liquid composite molding technologies, such as RTM (resin transfer molding) or vacuum infusion methods are perceived by many as the solution to the problem of composing composite parts in a variety of intractable situations, such as large aerospace primary structures and high volume structural automotive components. The benefits that liquid composite molding technologies are perceived to offer with respect to conventional prepregs are reduced waste and tear time, no dependence on falling and increased storage life properties. However, the molding of liquid compound presents its own problems, particularly, when the end use applications require high hardness and where the control of curing cycle time is critical. Structural parts require a high degree of hardness for most applications and this is especially true for primary aerospace components. The solution to introducing high hardness in an aerospace grade compound has traditionally been to harden the matrix - usually by introducing a second phase additive such as a thermoplastic polymer to the base epoxy resin matrix. Various methods have been employed for the addition of a thermoplastic material to the resin. The thermoplastic can be combined with the thermosetting resin without reacting at elevated temperatures to produce a single phase, the unreacted melt. A limitation of this procedure is the level of thermoplastic that can be added to improve hardness. As the high molecular weight thermoplastic dissolves in the resin, the viscosity of the combination gradually rises. However, the very nature of the process of introducing the resin into the reinforcing fibers requires that the rheological properties of the resins, viscosity and elasticity be such as to allow infiltration of the resin throughout the fabric preform. This is essential if the resulting composite structure will be free of voids and long injection times and high injection temperatures will be avoided. Conventional hardened epoxies are extremely viscous systems which means that high pressures and massive tools are required with the need to heat the resins and difficulties in matching the curing time and injection-fill cycles. Thermoplastic can also be added in the form of a continuous solid film that is placed between two layers of fiber. In such processes, the thermoplastic layer is generally known as the interleaving layer. A process of this type is disclosed in European Patent Application No. 0327142 which describes a composite comprising a solid continuous layer of a thermoplastic material placed between two layers of fiber impregnated with thermosetting resin. In the heating of the thermosetting layers and the interlayer layers they remain as discrete layers. A problem with the interleaving process is that the solid thermoplastic film does not dissolve to the resin during the thermal processing step. As a result, although the final compound can show the desired increase in hardness, there is a weak resin-thermoplastic interface. The weak interface between the interlayer and the matrix can cause poor resistance to creasing between folds, especially when exposed to a humid environment. The thermoplastic material can also be introduced into a powdered form. An example of this technique is disclosed in European Patent Application No. 0274899 wherein the thermoplastic material is added to the resin before the prepreg is prepared or sprayed onto the surface of the prepreg. The use of powders presents a problem since it is difficult to ensure that a uniform distribution of powder will be supplied to the resin. Consequently there is an unequal loading of the thermoplastic material with the result that the composite will have regions of different hardness. Furthermore, the incorporation of a thermoplastic material sprayed into the resin is not suitable for liquid compound molding techniques because the viscosity of the resin is increased when the particles are aggregated according to the standard Newtonian theory with all the consequent disadvantages as it is discussed previously. If the dust particles are of a size similar to the spaces between the fibers, then the process of infiltration of the resin to the fibers can also result in the thermoplastic powders being filtered out leading to an agglomeration of dust where the resin enters the mold and the resin free of dust in the volume of the final compound. Whether the sprayed thermoplastic is added to the resin or prepreg, the amount that can be incorporated is limited. Thus, too much is the hardening effect and in general, to obtain a reasonable improvement in hardness, expensive structural thermoplastics have to be used. It has been proposed in Japanese patent application 6-33329 to include thermoplastic in the form of fibers. The application discloses a blend of reinforcing fibers comprising 99-80% by weight of carbon fibers or graphite fibers and 1-20% by weight of thermoplastic resin. The compound includes only unidirectional fibers and it is described that the process is only useful in a classical prepreg technique. A good compound is one that has a combination of physical properties particularly suited to a specific application. The physical properties of the composite product are determined by, among other things, the physical properties of the solidified resin matrix material and the structural material and the uniformity of distribution of the matrix material and the structural material in the composite. Better results are obtained where the matrix material is intimately contacted with all the structural material. It is therefore desirable that the resin matrix material be of such consistency (viscosity) that it covers (moistens or wet) all the structural material and if necessary, fills the interstices formed in the structural material. Uniform wetting is particularly difficult to obtain where the structural material is of complex structure, for example where it is a preform or where the proportion of matrix material to support is particularly low. The viscosity of the matrix material is affected by the number and types of additives. Therefore, the problem arises that, although a liquid matrix material or a gel, comprising one or more additives may possess appropriate physical properties when solidified, the viscosity of the liquid or gel matrix material may be too high to facilitate its distribution uniform around the support material, particularly where the support is complex. This results in a composite product that lacks the expected physical characteristics. Normally, to obtain a good combination of properties a composite material will consist of a variety of constituents. Normally, for an aerospace grade prepreg there will be a high performance fiber reinforcement combined with a complex polymer matrix queen mix. This matrix mixture usually consists of a thermosetting resin combined with various additives. These subsequent additives improve the hardness of the basic resin. Such systems have complex flow characteristics and while they can be easily combined with fibers in a prepreg form, their use in other manufacturing techniques is limited. As an example, an attempt to use such a complex resin in a resin injection or transfer prs in a complex fiber preform may result in the filtration of additives and a non-uniform product. Accordingly, there is a need for a method of manufacturing a compound that overcomes the aforementioned problems particularly for large complex structures. According to a first aspect of the present invention there is provided a composite comprising a structural component and a resin component, the structural component comprises structural fibers and a hardening additive comprising non-structural thermoplastic fibers and the resin component comprises a non-structural material. thermoplastic and the structural component is a preform formed from structural fibers and thermoplastic fibers. According to a second aspect of the present invention, a structural reinforcement is provided for use in a composite comprising a preform formed from structural fibers and non-structural thermoplastic fibers, wherein all or part of the structural fibers are combined with the non-structural thermoplastic fibers in the preform and wherein the overall volume fraction of the structural fibers in the preform is at least 65%. The term "structural fiber" as used herein refers to fibers that add the strength of the • final composite such as glass or carbon fibers and therefore have a modulus of elasticity greater than 50 GPa. The term "non-structural fiber" as used herein refers to fibers that are not provided to increase the strength of the final composite since they have a modulus of elasticity of less than 20 GPa. These known reinforcing fibers formed from materials such as Kevlar are non-structural fibers in the terms of the present Application. The shape of the structural reinforcement allows the removal of all resin hardening additives thus allowing the use of low viscosity epoxy systems and thus making the impregnation of large parts feasible with low cost lightweight tooling sensitive to pressure and time manageable cycle. In addition, a significantly greater amount of hardening additive can be included without compromising any of the processing aspects of liquid compound molding techniques. Thus, according to a third aspect of the present invention there is provided a method of manufacturing a compound comprising forming a preform from structural fibers with non-structural thermoplastic fibers to provide a structural component, injecting a liquid resin into the structural component and cure the liquid resin component. By incorporating the hardening additive into the structural component before the addition of the resin, a lower viscosity resin, that is, a resin substantially free of the hardening additive, can be used. Hardening means the ability to increase the energy required to cause a final fracture, which can manifest itself in the ability to absorb energy during impact. Such ability or ability can be measured by appropriate impact testing methods that will be known to one skilled in the art. It is known that thermoplastic polymers increase the ability to absorb impact energy in structural compounds. By properly forming the preform they can be completely dispersed in the final composite to give homogeneous impact resistance or introduced into specific sites to provide a zone hardening mechanism as required in some composite parts. Preferably, the hardening additive is a thermoplastic material whose latent heat of fusion can absorb an exothermic curing energy ratio but which, after the completion of curing, is inverted to its solid form without loss of hardening capacity. Preferably, the curing agent, resin and thermoplastic additive are selected to provide a curing step that is carried out at least partially at a temperature lower than the melting point of the thermoplastic additive to thereby allow the absorption of some of the the curing energy in the melting or phase change of the additive if excessive heat release occurs. Preferably, the curing step is started at a temperature lower than the temperature of the melting point of the additive and can be advanced to a temperature higher than the melting point temperature during the curing cycle.

Injection of low viscosity resins (heated or otherwise) can decrease the injection-fill part of the processing cycle. However, it is also necessary to decrease the curing cycle time. This can be obtained through very active resins, higher temperatures, etc., - but the risk is always the generation of an exothermic or excessive heat release - particularly in the thick parts, which would lead to a degraded or damaged end part. Preferably, the hardening additive comprises semi-crystalline thermoplastic fibers. A very fast curing can be carried out without the risk of excessive exotherms if semi-crystalline thermoplastic fibers are used as the hardening additive. The heat generated by curing at an appropriate temperature can be used to generate the melting of the crystalline thermoplastic fibers in the fibers. The latent heat of the melting of the crystalline thermoplastic fibers will then moderate the temperature rise in the thermosetting resin. The section of hardening fibers with melting temperature of the appropriate crystalline components allows the curing time to be driven to its maximum potential without the risk of damage to the compound. The semi-crystalline fibers by themselves will be simply inverted to their original condition in the cooling and the process will not be affected by the final hardness of the parts. Preferred hardener additives include: • polyethylene, polypropylene, polyamides, polyethylene terephthalate, polyether ether ketone. Preferably, the hardening additive is sufficient to improve the impact absorption energy of the unhardened compound by at least 30%, more preferably by at least 50%. Preferably, the volume percentage of the hardening additive in the final compound is more than 2%, more preferably, more than 5%, more preferably, more than 10%. Preferably, the volume percentage of the hardening additive in the final compound is not more than 30%, more preferably, not more than 25%, more preferably, not more than 20%. It is particularly preferable that the volume percentage of the hardening additive in the final compound is not more than 15%. The volume percentage of structural fibers in the preform is preferably at least 65%. The minimum value of 65% ensures that there are enough structural fibers to give the required strength. In addition, the amount of non-structural thermoplastic fibers in the preform is insufficient to allow direct conversion of the material to the fully consolidated thermoplastic compound by a thermal processing route. However, the proportion of hardening fibers, that is, the thermoplastic fibers, is high compared to the known methods in which the thermoplastic is added in the form of particles and thus the hardening effect is commensurately much greater than that obtained with those known methods. . Preferably, the melting temperature of the hardening additive is not the same as the curing temperature of the resin component. It can be between 80- '350 ° C, more preferably 100-250 ° C, but its final selection will depend on the parameters of the base matrix material. Suitably, it may be 20 ° C higher than the curing temperature although it has been found that with some materials, at least, it may actually be preferable for the thermoplastic fibers to melt. The ability of the compound to be produced using a low viscosity resin will implicitly increase the speed at which a mold can be filled. However, the problem of controlling the curing times of the resin persists. A key factor always in resin injection is to ensure that the resin fills the mold and wet or wet the reinforcement fully before it cures. However, the filling time and curing time are linked and the resin starts to cure as soon as it is mixed before the injection and that process continues throughout the injection cycle. In a preferred embodiment, the steps of injecting and curing the process are separated by removing the curing agents from the resin formulation. A resin curing agent is instead added to the structural component before the injection of the resin component. Preferably, the curing agent is activated by temperature. The curing agent can be added to the structural component by dispersion to the thermoplastic fibers. It is now possible to obtain commercially available curing agents which are available in solid powder form and which only become active at a specific temperature. This capacity arises particularly when the curing agent is encapsulated in a thermoplastic solid with a very specific melting temperature. The micronized curing agents can be dispersed in the structural reinforcement and then the resin can be hot injected without any risk of premature reaction. The curing of the resin can then be activated when desired by simply raising the temperature to the critical temperature to activate the dispersed curing agents.

This embodiment allows the curing of the resin to be prevented before its addition to the structural component. This avoids the problems of synchronization where the viscosity of the resin rises due to curing before its addition to the structural component or during the addition process. This provides a much greater degree of control with respect to processing and also provides more flexibility in terms of composite structures because the lower viscosity resins provide less processing problems. For example, compounds with thick laminated structures can benefit while in the prior art methods difficulties were experienced in providing sufficient resin in the middle layers and areas of the layers furthest from the edges. The temperature-activated curing agents provide even greater control by providing the possibility of consummating the addition of the resin before curing and then raising the temperature to activate curing once satisfactory mixing of the components has been carried out. structural resin. This curing operation can be very fast since highly reactive resins can be used and the thermoplastic fibers provide the ability to moderate an exothermic temperature rise. In addition, it allows for the possibility of improved quality assurance by allowing the filling of the mold to be inspected and rectified if an error occurs, without the concern that the curing is already taking place. Suitable resin curing temperatures, curing agents suitable for particular resins and temperatures and melting points of thermoplastic polymers are well known to those of ordinary skill in the art. A further preferred aspect is the use of a textile web as part of the preform when being sandwiched between layers of the structural component. The web preferably has a greater proportion of absorbency than the layer (s) of the structural component either due to its thinness or the inherent absorbency or structure of the web material or a combination of these characteristics. Thus, in some embodiments, it is preferred that a layer of sandwich web be provided between the structural layers and provide means for increasing the rate of resin infiltration into the structure. Advantageously, by this means, the resin can be directed preferably to the center of the thicker structures that has been possible up to now. A web is a very thin layer of nonwoven fibrous material that is commonly produced by a papermaking route. The web will act to assist resin infiltration to the center of a preform by virtue of a higher resin absorbency rate than the rest of the preform. By sandwiching the webs between the layers of fabrics, the resin can thus be directed towards the center of thick preforms more rapidly than has been possible up to now. The web will also act to provide selective hardening by being positioned at the interface between the fabric layers which is a first site for delamination in a composite part. Preferably, the web is a thin layer of fibers produced by a papermaking route. Preferably, the web is less than 100 g / m2, more preferably less than 50 g / m2, more preferably less than 30 g / m2. The veil will provide a combination of fiber bonding with yield and deviation of cracking. The web can also provide hardening by comprising a mixture of non-structural thermoplastic fibers and structural fibers. Preferably, the web comprises no more than 70% non-structural thermoplastic fibers, more preferably no more than 60%. The web may contain a minimum of 20% non-structural thermoplastic fibers. The amount of non-structural thermoplastic fiber is however determined by the need to maintain an appropriate overall structural fiber content within the preform. The web may also contain curing agents. If the veils are distributed throughout the preform or attached to all the fabrics used in the part, then it would be possible to remove the curing agents from both the resin and the other materials used to form the preform. A preferred aspect of the web is the presence of a binder material distributed on or in the web that is preferably activated by the resin, preferably by the temperature of the resin. A suitable binder is a thermoplastic with a lower melting point than that of the incoming resin. Alternatively, the temperature of the resin may be subsequently raised at the entrance to the web to thereby activate the binder. It is also possible to coat the binder directly on the surface structure which is then placed between the layers of the structural component to be subsequently activated by temperature but this is not as convenient as incorporating it into the web. In a preferred aspect, the temperature of the incoming resin dissolves the binder but is not sufficient to begin the curing which is then carried out in a subsequent heating step. In this way, thick walled and textile fiber fabrics can be securely glued together to form the preform before the curing step. Preferably, the resin is a thermosetting resin, more preferably an epoxy resin. The preform may include a textile that can be a woven or non-woven fabric. The textile may comprise a hybrid yarn, that is structural fibers and hardening fibers interwoven in a hybrid yarn or the textile may comprise structural yarn and hardening yarn mixed in a single textile. Preferably, the hardening fibers are intermixed with the structural fibers to form the hybrid yarn. Hybrid yarns with different proportions of non-structural thermoplastic fibers and structural fibers can be used in the same fabric or textile. Similar hybrid yarns containing mixtures of different non-structural thermoplastic fibers and structural fibers can be used in the same fabric, textile or preform. The basic concept of using hybrid threads can be varied considerably. It is possible to replace all the threads in a preform with a hybrid thread or alternatively to replace only one section. In addition, a large preform may consist of areas of conventional or hardened fibers according to the needs of the part. This offers a processing advantage in that a single resin system can be used for a large part but the properties of the composite can differ in terms of hardness and temperature capacity from place to place - thus making the molding of a load of structures complex more feasible. The properties of the compound can be varied widely by making the preform in different ways. For example, with a woven fabric the configuration in which the structural fibers and the thermoplastic fibers are provided will have an effect on the overall performance of the composite. The use of a structural reinforcement in the form of a textile therefore allows greater versatility. Modes of the present invention will now be described with reference to the examples and accompanying drawings in which: The figure shows a schematic laminar compound according to the present invention; Figure Ib shows the upper layer of the laminar composite of the figure with a schematic impact region; The figure shows the schematic construction of the upper layer of the laminar compound of figure la; Figure Id shows a schematic exploded view of the yield zone 2 shown in Figure Ib; Figure 2a shows a hybrid veil sandwiched between two structural layers in a laminate; Figure 2b shows a possible construction for the hybrid veil of Figure 2a; Figure 2c shows an alternative construction for the hybrid veil of Figure 2a; Figure 3 shows the energy absorbed against the volume fraction by the thickness for several examples; and Figures 4 to 6 show graphs of impact resistance as a function of the thickness per volume fraction of fibers for a composite formed from glass fibers alone, Figure 4, glass fibers and polypropylene fibers, Figure 5 and glass fibers and polyamide fibers, figure 6. The figure reveals a composite with a laminar structure of three identical flat rectangular layers superimposed: top layer 3a; middle layer b and lower layer c. The internal structure is clearly shown by the figure which is an exploded view of the insert 4. The exploded view shows each layer formed from a hybrid fabric comprising structural fiber yarns, for example carbon fibers dispersed with yarns of thermoplastic fiber frayed in a thermosetting resin matrix. Figure Ib and figure Id show schematically the effect of an impact on the surface of the upper layer 3a. In particular, figure Ib reveals a series of diagonal linear yield zones of the theoretical impact and figure Id shows an explosion of a linear yield zone 2 and reveals that the yield zone corresponds to a thermoplastic yarn extending in the layer compound With reference to Figure 2, this shows a schematic laminar composite construction similar to that of Figure 1 but with a hybrid veil sandwiched between two textile layers. The sandwich veil introduces hardening to the textile composite. Two alternatives of the veil construction are shown in Figures 2b and c. Figure 2b schematically shows the construction of mixed structural and non-structural fibers and thermoplastic powder, while Figure 2c shows a unique construction of carbon fibers and thermoplastic powder. In both cases, resistance to delamination and some hardening is provided by bonding the fibers between the textile layers and the fibrous web. However, this is greatly improved by the presence of the thermoplastic in the veil layer.

By proper design of the interfolding web, the rate of resin flow through the web can be improved relative to the flow rate through the upper and lower structural layers and thus improve the rate of impregnation of resin injected into the composite . In both cases, the curing agent can be present with the structural components before the addition of the resin in such a way that the curing process can be activated at the appropriate temperature once a satisfactory "wetting" has been carried out. of the structural component.

Example 1 A composite was prepared from a cloth preform consisting of glass fibers blended with polypropylene fibers in a non-corrugated quadriaxial fabric. The fabric was impregnated with low viscosity unsaturated polyester resin and the laminate was cured at room temperature followed by a post-cure at 80 ° C according to the specification of the resin supplier. The plate was 3 mm thick and the volumetric fractions of the three components were as follows: glass fibers 0.2 v / v; polypropylene fibers 0.2 v / v; and polyester resin 0.6 v / v. The laminate was subjected to a weight impact test that falls to measure its energy absorption. The specific test configuration used produces absorbed energy result for glass fiber composites that fall into a main curve determined by the thickness of the laminate and the volume fraction of the fibers. The energy absorbed by the laminate prepared from the preform with polypropylene fibers added as curing agents was 100 J. In contrast, a similar laminate produced from identical polyester resin 0.8 v / v but reinforced with a cloth that was entirely produced from glass fibers of a volumetric fraction of 0.2 v / v and a thickness of 3 mm absorbed an average of approximately J. J. This demonstrates that the addition of the thermoplastic fibers to the preform provides a considerable hardness benefit.

Example 2 A glass fiber epoxy compound was prepared from an epoxy resin DGEBA (diglycidyl ether of bisphenol-A cured with an amine hardener [Shell Epikote 828 cured with aromatic amine HY932 from Ciba]) and a fabric woven from tissue full of glass fibers E. The fabric occupied approximately 50% by volume of the compound. A similar compound was prepared with the same level of fabric but where the fabric component contained 70% (by volume) of E glass fibers and 30% by volume of semi-crystalline polymer fiber, with a fiber melting temperature semi-crystalline polymer of 210 ° C. The compounds were produced by impregnating fabrics and lamination to a thickness of 6 cm thick and cured in an oven set at 190 ° C. Thermocouples embedded in the center of the laminate monitored the temperature rise in the materials as they initially equilibrated to the furnace temperature and then experienced additional temperature elevations due to the exothermic curing process. The laminate with only glass fibers exhibited a temperature rise beyond 190 ° C oven temperature that became rapid and reached a peak value of 300 ° C at which point significant degradation of the epoxy was observed. Semi-crystalline thermoplastic fiber laminate also exhibited a temperature rise due to exothermic curing but once this temperature reached the crystalline melting temperature of the thermoplastic fibers, the overall temperature rise was stopped and the epoxy resin was not degraded notably.

EXAMPLE 3 A composite of carbon fibers, 3 mm thick, was prepared from a full woven fabric and an epoxy resin (diglycidyl ether of bisphenol A cured with an amide hardener [Shell Epikote 828 cured with aromatic amine HY932 of Ciba]). The fabric contained 70% by volume of carbon fibers (Torayca T300) and 30% by volume of 6.6 nylon fibers. The cloth was impregnated with the liquid epoxy resin and cured at room temperature for 24 hours followed by a post-cure at 100 ° C for 4 hours. The cured laminate contained approximately 50% carbon fibers by volume and 21% nylon fibers by volume. The remaining 29% of the composition was cured epoxy resin. A similar compound was prepared by impregnating a cloth produced exclusively from carbon fibers. In this case, the full woven carbon fibers occupied 50% of the volume of the composite and the epoxy resin matrix occupied the remaining 50%. Both laminates were subjected to weight impact tests that dropped excess energy. The laminate comprising only carbon fibers and an epoxy matrix absorbed 50 J of energy. The laminate with carbon fibers, nylon fibers and epoxy matrix absorbed 85 J.

Examples 4 to 7 Tests have been carried out with a series of glass fiber compounds of average volume fraction that exhibit impact hardness (energy absorbed during impact of falling weight with full penetration) that is improved by a factor of 2. -3 times by the inclusion of thermoplastic fibers compared to the unmodified analogs. Tests have also shown a notable lack of sensitivity in notches in open hole stress tests on the same materials. The impact results of two materials against two control samples are shown in Figure 3 and Table 1 defines the tested materials.

Table 1 Comparison of hardened and unhardened composite laminates Each of the structural components consisted of approximately 50:50 glass to hardener additive, by volume. Figure 3 shows the impact results for Examples 4-7 as a plot of the energy absorbed against the thickness per volume of fibers. The main impact curve for SMC (lamellar molding compound), GMT (glass mat thermoplastics) and prepreg, etc., have been superimposed for comparative purposes. The energy absorbed for the compounds containing polypropylene and polyester is significantly improved compared to analogous compounds that do not have a hardening additive. Figures 4 to 6 are graphs showing the impact resistance, that is, the energy absorbed during penetration, as a function of the thickness per volumetric fraction of the fibers. Each graph has data from three different thermoshable matrices - two epoxies and one polyester. The first graph of figure 4 shows the results obtained when single glass fibers are used with the volumetric fraction of the glass fibers in the compound which is between 30 to 50%. The second and third graphs of figures 5 and 6 show the results when the portion of the glass fibers is replaced by polypropylene, figure 5 and polyamide, figure 6. The graphs show that the inclusion of thermoplastic polymers provide significant benefits in terms of of improved impact resistance. In addition, the effect is consistent with different matrices. The resins used in the study producing the graphs of Figures 4 to 6 included an unsaturated isophthalic polyester resin (UP), Crystic 272 (a product of Scott Bader foot) and two epoxy systems, EP1 was an epoxy curing resin cold (diglycidyl ether of bisphenol A cured with an amide hardener (Shell Epikote 828 cured with aromatic amide HY932 from Ciba) and EP2 was a one part low viscosity epoxy resin supplied by Cytec-Fiberite, Cycom 823, which It was cured at 120 ° C. The experimental procedure of all these tests involved the use of a drop weight test instrumented in which a striker equipped with a hemispherical tip of 20 mm in diameter is allowed to fall on a sample of plate of the test compound The composite sample is a thin plate, usually 3 mm thick and 60 ram x 60 mm in size that is simply supported on a steel ring with an internal diameter of 40 mm. The knocker is dropped from a height of 1 m and has sufficient mass in such a way that the kinetic energy is sufficient for the striker to completely penetrate the sample. The test records the forces during the impact event and the energy absorbed is calculated from the force time record and the measured speed of the striker as it makes an impact with the sample. The thermoplastic fibers used incorporated into the resin matrix provide a thermoplastic region in the thermoformable matrix that gives a mechanism for plastic deformation and yield that is not possible in the thermosetting resin without modifying itself. The low viscosity of the unmodified thermosetting resin makes it feasible to mold large parts in reasonable periods of time and use low injection pressure for the process which will also eradicate any problem with the washing of the fibers near the injection points due to the applied pressures . The invention has the potential to make a variety of composite manufacturing techniques more effective by being able to handle a greater range of matrix formulations and its efficiency with existing systems can be increased since the flow and wetting times can be reduced. This will result in a reduction in the time taken to manufacture a component. It is noted that, with regard 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 (25)

1. CLAIMS Having described the invention as above, the content of the following claims is claimed as property: 1. A compound characterized in that it comprises a structural component and a resin component, the structural component comprises structural fibers and a hardening additive comprising non-thermoplastic fibers. structural components and the resin component comprises a non-thermoplastic material and the structural component is a preform comprising an assembly or assembly formed from the structural fibers and non-structural thermoplastic fibers, characterized in that the assembly comprises non-structural thermoplastic fibers that are fiber form in the final compound.
2. 2. The compound according to claim 1, characterized in that the resin component is a thermosetting resin composition.
3. 3. The compound according to claim 1 or claim 2, characterized in that the resin component is a thermosetting resin composition of low viscosity.
4. 4. The compound according to any of the preceding claims, characterized in that the volume percentage of the hardening additive in the compound is more than 2% but less than 30%.
5. 5. The compound according to any of the preceding claims, characterized in that the volume of the hardening additive is more than 5% but less than 25%.
6. 6. The compound according to any of the preceding claims, characterized in that the volume of the hardening additive is more than 10% but less than 20%.
7. The composite according to any of the preceding claims, characterized in that the structural reinforcement component is provided in the form of a plurality of textile layers and at least one web is provided between a pair of adjacent layers, the web comprises a Thin layer of woven or non-woven material.
8. The compound according to any of the preceding claims, characterized in that the volume fraction of the structural fibers in the preform is at least 65%.
9. 9. The use of a structural reinforcement in the manufacture of a compound by molding of liquid compound, the structural part comprises a preform comprising a dry fiber assembly formed from structural fibers and non-structural thermoplastic fibers.
10. 10. A structural reinforcement for use in a composite comprising a preform, characterized in that it comprises a dry fibrous assembly formed from structural fibers and non-structural thermoplastic fibers, the volume fraction of the structural fibers in the preform is at least 65. %.
11. The structural reinforcement according to claim 10, characterized in that at least some of the thermoplastic fibers are semi-crystalline.
12. 12. The structural reinforcement in accordance with either claim 10 or claim 11, characterized in that it further comprises a resin curing agent.
13. 13. The structural reinforcement according to claim 12, characterized in that the curing agent is activatable by temperature.
14. The structural reinforcement according to any of claims 10 to 13, characterized in that the preform comprises layers of textiles and the reinforcement component additionally includes at least one web between a pair of adjacent layers, the web is formed from a thin layer of woven or non-woven material.
15. 15. The structural reinforcement according to claim 14, characterized in that the web includes thermoplastic fibers.
16. 16. The structural reinforcement according to claim 14 or claim 15, characterized in that the binder material is distributed on or in the web.
17. 17. The structural reinforcement according to any of claims 14 to 16, characterized in that the web has a higher absorbency rate for the resin than for the fibers.
18. 18. The structural reinforcement according to claims 10 to 17, characterized in that the preform includes a textile comprising a hybrid yarn of intermingled structural fibers and thermoplastic fibers or yarn of structural fibers and yarn of thermoplastic fibers.
19. A method for making a composite, characterized in that it comprises forming a preform by combining dry structural fibers with dry non-structural thermoplastic fibers in an assembly to provide a structural fabric component, injecting or infusing a liquid resin into the structural fiber component and curing the liquid resin component.
20. The method according to claim 19, characterized in that a resin curing agent is added to the structural component before the resin component.
21. The method according to claim 20, characterized in that the curing agent is encapsulated in a material that is melted at a first temperature and where the curing step involves raising the temperature to the first temperature to activate the curing agent .
22. 22. The method according to any of claims 19 to 21, characterized in that the curing step is carried out at least partially at a temperature lower than the melting point of the thermoplastic fibers.
23. 23. The method according to any of claims 19 to 22, characterized in that the preform including textile is provided in layers and a web is provided between at least one adjacent pair of layers before the addition of the resin, the Veil comprises a thin layer of woven or non-woven material.
24. 24. The method according to claim 23, characterized in that it comprises distributing binder material on or in the web.
25. 25. The method according to any of claims 19 to 24, characterized in that the resin injection process is resin transfer molding or composite resin injection molding.