WO2005090072A1

WO2005090072A1 - Multilayer composite plates and methods of producing composite plates

Info

Publication number: WO2005090072A1
Application number: PCT/US2005/008471
Authority: WO
Inventors: Christopher Toto; George Rawa
Original assignee: Greene, Tweed Of Delaware, Inc.
Priority date: 2004-03-15
Filing date: 2005-03-15
Publication date: 2005-09-29

Abstract

A multilayer composite plate includes at least one continuous fiber layer constructed of a thermoplastic polymer resin and a plurality of continuous fibers and at least one short fiber layer constructed of a thermoplastic polymer resin and a plurality of short fibers, wherein the layers are consolidated to form a sandwich composite plate.

Description

TITLE OF THE INVENTION [0001] Multilayer Composite Plates and Methods of Producing Composite Plates

CROSS-REFERENCE TO RELATED APPLICATIONS [0002] This Application claims the benefit of U. S. Provisional Patent Application No. 60/553,076, filed March 15, 2004, the entire disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION [0003] Medical devices and tools are traditionally made from metals, such as aluminum, stainless steel and titanium. Metals have been selected for these uses for several reasons including their amenability to sterilization procedures (by heat or chemical agents) and because they are non-antigenic. Metal also possesses the physical properties necessary for many medical device and tool applications, such as strength and a relatively high flexural modulus, e.g., 10,000,000 lbs per square inch (68,948 MPa) for aluminum.

[0004] However, metals, while useful, are not a disadvantage-free material for the fabrication of medical devices and tools. Metal tools and devices can be heavy and consequently, unwieldy, potentially hindering a surgeon's dexterity in performance of a procedure. A patient fitted with a metal-containing medical device, e.g., a halo, may experience additional discomfort because of the mass of the device, the cold feel of metal against the skin, and/or the potential for certain types of metal to discolor the skin. Moreover, a patient implanted with a metal-containing device may be subject to inconvenient and potentially embarrassing searches at security checkpoints in, for example, airports, sporting venues, and other public places. More significantly when considered from the perspective of patient care, metal is not radiolucent. Devices implanted or otherwise secured to a patient obstruct the passage of diagnostic X-rays, potentially hindering the physician in diagnosis and treatment of the patient. [0005] Plastics (thermoplastics and thermosets) are radiolucent, can be subjected to most sterilization procedures, and can be formed so as to not invoke immune responses in humans. They are not, however, feasible replacements for the many medical device and tool applications requiring relatively high tensile strength and flexural modulus. For example, bone fixators used to support bone fractures during the healing process must be sufficiently strong and stiff to maintain a proper alignment of the bone despite rigorous forces exerted on the area. Plastics do not generally exhibit sufficient tensile strength and/or flexural modulus to be effective for this task.

[0006] Because many medical device and tool applications require the physical properties of metal as well as radiolucency, attempts have been made to increase the physical properties of plastic polymers by incorporating various fillers. However, these prior art reinforced plastics are deficient in that increased physical properties are often non-uniform throughout the finished material — for example, sufficiently strong only in the direction parallel to the long axis of the reinforcing fiber or filler. Thus, the orientation of the fiber or filler is significant, and the production processes that necessarily involve the monitoring of the placement and orientation of the fibers are costly, labor intensive, and time consuming.

[0007] Multilayer composites having reinforcement are also known in the art. For example, in the aerospace industry composites constructed of an aluminum honeycomb core having outer polymer sheath layers are known. These composites are desirable for their strength and are light weight, due to the fact that the core strengthens while allowing open spaces internally which are filled with air. However, such composites are not readily adaptable to medical uses because they are not radiolucent due to the metal content.

[0008] Thus, there is still a need in the art for a material that possesses acceptable or comparable physical properties (e.g., strength and flexural modulus similar to metal) yet which remains radiolucent. Such material would have preferred varied applications including medical device and tool applications, aerospace applications, container transportation applications, and other uses where radiolucent, relatively light weight, yet strong and stiff materials are desired.

BRIEF SUMMARY OF THE INVENTION [0009] The invention includes a multilayer composite plate comprising at least one continuous fiber layer that comprises at least a thermoplastic polymer resin and a plurality of continuous fibers and at least one short fiber layer comprising a thermoplastic polymer resin and a plurality of short fibers. The layers are consolidated to form a multilayer composite plate. [0010| The present invention also includes a multilayer composite plate comprising at least two continuous fiber layers, each comprising a thermoplastic polymer resin and continuous fibers; at least one short fiber layer, comprising a thermoplastic polymer resin and short fibers; wherein the at least one of the short fiber layers is positioned between at least two of the continuous fiber layers.

[0011 ] A method of preparing a multilayer composite plate is also included herein. The method comprises consolidating at least two layers, wherein at least one of the layers includes a thermoplastic polymer resin and continuous fibers and at least one of the layers includes a thermoplastic polymer resin and short fibers.

[0012] A preferred embodiment included herein is a sandwich composite plate comprising a first outer layer comprising continuous carbon fibers impregnated with a thermoplastic; a second outer layer comprising continuous carbon fibers impregnated with a thermoplastic; and an inner layer comprising short carbon fibers impregnated with a thermoplastic. The first and second outer layers are situated on either side of the inner layer so as to form a sandwich configuration and the sandwich composite plate is formed by compression molding the layers. DETAI LED DESCRIPTION OF THE INVENTION

[0013] As described herein preferred embodiments of a multilayer composite plate for use in applications requiring a radiolucent, relatively strong and stiff materials, methods for making such plates and devices and tools that include such plates. [0014] The multilayer composite plate includes at least two layers. One or more of the at least two layers is a short fiber layer ("SF layer") and at least one of the layers is a continuous fiber layer ("CF layer"). The CF layer or layers comprises a polymer resin and a plurality of continuous fibers. The SF layer comprises a polymer resin and a plurality of short fibers. The layers are then consolidated to form a multilayer composite plate. It is preferred that the multilayer plate comprises two CF layers. Generally, a short fiber is defined herein as a fiber of less than about 0.5 inches (1.27 cm), and a continuous fiber is defined herein as being greater than about 0.5 inches (1.27 cm).

[0015] Each of the SF layer(s) and the CF layer(s) includes a polymer resin. Thermoplastic resins are preferred. Additional layers may be formed of either thermoplastic or thermoset, or mixtures or blends of those polymers. In addition, thermosetting resins may be provided in certain circumstances where application warrant such use as blending materials in the SF and/or CF layers. Within a CF layer, continuous fibers can be present as individual fibers (such as impregnated continuous fibers made by, for example, pultrusion) or multiple plies of continuous woven fibers in stacked form. Thermoplastic resins in mixtures/blends of resins are preferred such that predominantly thermoplastic resins are used (e.g. it is preferred to have 90% by weight of the total resin portion or greater). Suitable thermoplastic resins for use in the multilayer composite plate of the invention include all those known or to be developed in the art and may be varied depending on the specific properties desired in the end product multilayer composite plate. [0016] Exemplary thermoplastic polymer resins suitable for use in the CF and or SF layers of the invention include the following: polyethylene, polyethylene chlorinates, polyaryl ether ketones (such as polyetherketone, polyetherketoneketone and polyetheretherketone), polyamides (such as NYLON 6, NYLON 12), acrylonitrile-butadiene-styrene (ABS), cellulosic resins (such as ethyl cellulose, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, and cellulose nitrate), ethylene vinyl alcohol (EVOH), fluoroplastics (such as polytetrafluoroethylene (PTFE), fluorinated ethylene propylene copolymer (FEP), perfluoro-alkylalkane (PFA), poly(chlorotrifluoroethylene), ethyl chlorotrifluoroethylene (ECTFE), ethyltrifluoroethylene (ETFE), and polyvinylidene fluoride (PVDF)), polyvinyl chlorides (PVC), polyvinylidene chlorides, thermoplastic elastomers (such as ethylene propylene diene elastomers (EPDM), ethylene-propylene rubber (EPR) and polyurethane elastomers), liquid crystalline polymer (LCP), thermoplastic polyesters, ionomers, polyacetals, polyacrylates, polyacrylonitirile, polyamideimides, polybutadienes, polybutylenes, polycarbonates, polyketones, polyetheramides, polysulfones (such as polysulfone, polyethersulfone and polyphenylsulfone), polyimides, polymethylpentenes, polyphenylene oxides, polyphenylene sulfides, polyphthalamides, polypropylenes, polystyrenes, polyurethanes, and/or co-polymers and/or derivatives of these or any other known or to be developed thermoplastic polymers.

[0017] The selected thermoplastic polymer in the SF or CF layers may also be a mixture, blend, alloy, or copolymerized random, block or graft copolymer of two or more of the above polymers or their monomer constituents. Preferred polymers for the CF and SF layers include polyaryl ether ketones, polysulfone, polyphenyl sulfones, polyphenylene sulfides, polyether sulfones, polyetherimides, polyamides, liquid crystalline polymer and their derivatives and copolymers. [0018] Suitable thermosetting resins for use as blending materials or additives in the CF and or SF layers or for use in forming additional optional layers include epoxy resins, phenolic resins, urea-formaldehyde resins, melamine-formaldehyde resins, polybenzoxazole resins, acetylene terminated polyimide resins, silicones, triazines, alkyds, vinyl ester resins, vinyl esters, and xylene resins and/or compolymers and/or derivatives of these or any other known or to be developed thermosetting resins. [0019] Each of the layers in the multilayer composite may contain a different or the same thermoplastic resin, or mixtures or blends of thermoplastic resins. For example, one layer may contain polyetherketoneketone, a second layer may contain an FEP copolymer, and a third layer may contain a blend of polyetheretherketone and polyetherketoneketone. [0u-.U| in addition, me resin seiecteα for one or more of the layers of the invention may also include any fillers or additives known or to be developed in the art useful in altering and/or enhancing the end product's physical or chemical properties or in modifying the processing behavior of the resin when the individual layers are being formed. Exemplary fillers may include but are not limited to glass spheres and/or fibers, carbon spheres and/or fibers, carbon black, silicates, fiberglass, calcium sulfate, asbestos, boron fibers, ceramic fibers, thermoplastic reinforcing fibers (such as those polyamide type fibers sold under the trademark KEVLAR , available from E.I. du Pont de Nemours & Co., Inc., Wilmington, Delaware), aluminum hydroxide, barium sulfate, calcium carbonate, magnesium carbonate, silica, alumina, aluminum nitride, borax (sodium borate), activated carbon, pearlite, zinc terephthalate, Buckyballs, graphite, talc, mica, synthetic Hectorite, silicon carbide platelets, wollastonite, calcium terephthalate, ceramic compounds, silicon carbide whiskers, or fullerene tubes, depending on the specific properties desired in the end product. One may also include plasticizers, flame retardants, conductive materials, and/or colorants (such as pigments or dyes) in the polymer resin from which the layers are prepared.

[0021] Other fillers or combinations of fillers may be used as is known or to be developed in the art in order to enhance or modify the properties of the resultant composite, including mechanical properties, thermal properties, and/or electrical properties, or to improve the processability of the selected resin(s), for example, by altering the rheological properties of the material.

[0022] The SF layer(s) and the CF layer(s) are preferably unfilled polymer resin and fiber. Alternatively, regarding the SF layer, it preferably includes short fibers (including chopped fibers, stretch-broken and/or milled fibers). The short fibers may be inorganic fibers, ceramic fibers, carbon fibers, glass fibers, graphite fibers, and/or plastic fibers (thermoset or thermoplastic). Carbon fibers are preferred, with carbon chopped fibers being the most preferred. As will be understood to a person skilled in the art, if plastic fibers are selected, the selected plastic fibers preferably have a greater glass transition temperature (T_g) than that of the resin into which it is incorporated and/or the temperature at which the plate and/or SF layer is prepared. [00231 The specifications and physical properties, such as lengths and diameters, of the short fibers included in the SF layer will necessarily vary depending on the end application into which the multilayer composite plate is to be used, and the physical properties one wishes the multilayer composite plate to exhibit. [0024] Fibers of any desired diameter and/or length, including nano fibers and even nanotubes may be used. In general, however, it is preferred that the selected short fiber has a length of about 100 microns to about 1.27 cm (about 0.5 inches). Other preferred lengths include about 0.254 cm to about 1.106 cm (about 0.1 inches to about 0.4 inches), about 0.0588 cm to about 0.762 cm (about 0.02 inches to about 0.3 inches), about 0.0762 cm to about 0.508 cm

(about 0.03 inches to 0.2 inches), and about 0.8128 cm to about 0.9398 cm (about 0.32 inches to about 0.37 inches).

[0025] Suitable short fibers having diameters of about 0.1 microns are preferred, as are fibers having diameters of about 5 microns to about 15 microns, and about 7 microns to about 10 microns. More than one type of short fiber may be incorporated into the SF layer. For example, the short fiber may include a mixture of chopped fibers of varying aspect ratios and/or milled fibers of varying aspect ratios.

[0026] The short fibers may be about 10% to about 90% by volume of any SF layer. It is preferred that the short fibers are about 40% to about 80% by volume of an SF layer, and more preferred that they are about 50% to about 70% by volume of an SF layer. It is most preferred that the short fibers are about 60% by volume of an SF layer.

[0027] The CF layer preferably contains fibers which may be inorganic, ceramic, glass, graphite, carbon and/or plastic (thermoplastic and thermoset) fibers. More preferably, the fibers are carbon fibers. The continuous fibers may be unidirectional or bi-directional continuous fibers (preferably bidirectional fibers would have approximately 50% of the fibers in the parallel direction and approximately 50% of the fibers in the perpendicular direction), stretch-broken, braided fibers and/or woven continuous fibers. In using stacked, woven fibers, such as for example, carbon fibers woven into a fabric ply, where the woven fabric ply is about 0.015 inch (0.381 mm) thick or less, it is preferred that from 1-250 such woven fabric plies, more preferably 10-50, and most preferably 20-40 such woven fabric plies are used in about a 1 inch (2.54 cm) to about a 2 inch (5.08 cm) thickness of a CF layer of the composite as measured in the transverse direction. Additionally, the fibers are preferably braided or commingled fibers. Preferred diameters for the continuous fibers include about 0.1 microns, about 5 to about 15 microns, and about 7 to about 10 microns. [0028] It is preferred that the continuous fibers independently make up about 30% to about 90% by volume of any CF layer. It is more preferred that the continuous fibers are about 40% to about 80% by volume of a CF layer, and most preferred that they are about 50% to about 70% by volume of a CF layer. [0029] In addition to the continuous fibers, the CF layer may also contain any of the short fibers listed above for additional reinforcement, if desired. Indeed, in one version of the invention, a single layer containing both short fibers and continuous fibers, for example in fabric plies, arranged in strata, is prepared. [0030] Any of the individual layers may be pre-formed prior to consolidation as a multilayer composite plate. The pre-forming of the layers may be carried out by any suitable method known or to be developed in the art, including by extrusion, pultrusion, injection molding, compression molding, rolling, and/or autoclaving. For example, a CF layer may be prepared by compression molding the selected polymer resin (into which any desired additives have already been compounded) around the selected woven fiber sheet ply or plies.

[0031] An SF layer may be prepared, for example, by extrusion of the selected polymer resin (into which any desired additives have already been compounded) into a sheet or plate-like form. Alternatively, in a composite of at least three layers, having an SF layer on the inside layer, one may form the SF layer by placing short fiber-containing resin flakes, resin pellets, and/or resin powders between pre-formed CF layers and heat laminating the entire plate to consolidate and simultaneously produce the SF layer inside the multilayer structure.

[0032] A method of preparing a multilayer composite plate includes consolidating at least two layers. At least one of the layers comprises a thermoplastic polymer resin and continuous fibers and at least one of the layers comprises a thermoplastic polymer resin and short fibers. Consolidation of the plate may be achieved in any manner known or to be developed in the art as long as the layers are securely fixed into a consolidated plate. The processes will necessarily be variable, depending, for example, on the number of layers the finished consolidated plate will contain. The attachment of the layers to one another may be accomplished through thermal/chemical means (such as heat lamination, use of intervening adhesive layers), by physical fixation (such as staples, rivets, or stitching) or by a combination of such exemplary methods. As discussed above, the layers may be pre-formed and subsequently consolidated or they may be simultaneously formed and consolidated into the finished multilayer composite plate. [0033] The layers may be arranged in any order. The arrangement will be variable depending on such factors as availability and cost of materials, method of consolidation to be applied and intended end use of the plate. Additional layers may be present in the multilayer composite plate, either as intervening layers or added to the top or bottom surface of the plate. The additional layer(s) may be of any suitable material described herein. Preferably, they are repeating layers of one or more of the CF and/or SF layers described above. They may also be, for example, adhesive layers, decorative layers or films, neat polymer layers, insulating layers, or metal or ceramic layers or coatings, For example, a finished multilayer composite plate may include ( 1 ) a CF layer, (2) a SF layer, (3) an additional SF layer, (4) a CF layer, (5) an adhesive layer, (6) a layer of neat thermoplastic resin, (7) an additional SF layer, and (8) a final CF layer. Variations of such structures using different layers can be devised as is desired. However, it is most preferred that a composite plate have a "sandwich configuration" in that at least three of its layers would include a configuration which is: (1 ) CF layer; (2) SF layer; and (3) CF layer. Although, additional layers on the top and bottom would also be within the scope of the invention. [0034] The thickness of each individual layer may vary. However, it is generally preferred that the SF layer(s) be about 20% to about 80% by volume of the total volume of the plate, more preferred that it is about 30% to about 70% of the total volume, and most preferred that it is about 40% to about 60% of the total volume. It is generally preferred that the CF layer(s) be about 20%) to about 80% by volume of the total volume of the plate, more preferred that it is about 30%) to about 70% of the total volume, and most preferred that it is about 40% to about 60% of the total volume.

[0035] In a preferred embodiment of the invention, a sandwich composite plate has at least three layers that are compression molded together. The first outer layer is a CF layer having continuous carbon fibers that are impregnated with a thermoplastic; the second outer layer is a CF layer that has continuous carbon fibers that are impregnated with a thermoplastic; and an inner layer is an SF layer having short carbon fibers impregnated with a thermoplastic. The first and second outer layers are situated on either side of the inner layer so as to form a sandwich. The sandwich configuration is then compression molded to form a laminate composite (the sandwich composite plate). In a further preferred embodiment, the continuous carbon fibers are woven into a fabric like structure(s). No particular pattern need be followed. In an even further preferred embodiment, the CF layers include multiple plies of fabric like structures which are made of woven continuous carbon fibers, and the fabric like structures are in stacked form. The preferred thermoplastics include polyaryl ether ketones (such as polyetheretherketone and polyetherketoneketone), polyamides (such as NYLON 6, and NYLON 12), polyimides, liquid crystalline polymer, polysulfones (such as polysulfone, polyethersulfones and polyphenylsulfones), polyphenylene sulfides and derivatives and copolymers thereof. The thermoplastics can be used alone or in combination with one or more of the others. [0036] In the sandwich composite, the combined volume of the first and second outer layers ranges from about 10% to about 75% of the total volume. The preferred volume of the first and second outer layers combined ranges from about 40% to about 60%> of the total volume. The inner layer ranges from about 5% to about 75% of the total volume. The preferred volume of the inner layer ranges from about 40% to about 60%> of the total volume. Therefore, the volumetric ratio of the sandwich composite of the combination of the first and second outer layers to the inner layer ranges from about 1 : 15 to about 15: 1. Preferably the range is from about 3:2 to about 2:3. Also, various additives described herein may be added in depending on the application for which the composite will be used.

[0037] The multilayer composite plate of the invention may be used to make medical devices and tools, such as halos, X-ray cassettes, nail guides, X-ray accessories, MRI tables, bone fixators of all types, bone screws, bone plates, stabilizers, braces, structural components of casts, surgical tools including drills, scalpels, forceps, tweezers, and retractors. Other applications include use of the multilayer composite plate to make parts for use in aerospace applications, fluid handling applications, industrial applications, medical and biotechnological applications, oilfield applications, and semiconductor applications and shipping containers. [0038[ The composite is capable of being machined into various parts for use in the above applications. Additionally, the muitilayered composite is capable of having a hole bored through the sandwich composite plate layers at least in the transverse or z-direction and is also capable of having the holes threaded in order to accommodate a bolt-like or a screw-like member. The transverse direction, also known as the z-direction, is defined as being perpendicular to the layer interface. The layer interface being the plane where two layers of the composite meet. [0039[ O^ne of the goals of the present invention was to create a more cost effective composite that had substantially similar properties to prior art plates that are constructed of a composite including only continuous fiber in the form of many woven fabric plies. By incorporating at least one SF layer, the composite costs significantly less to make on an equal volume basis while retaining comparable physical properties.

[0040] Prior art plates exist that are constructed of multiple plies of woven continuous carbon fibers that are impregnated with a thermoplastic polymer. Such composites comprise about 100-120 plies of woven carbon fiber fabric per inch of plate, and are impregnated with TM PEEK. They are marketed commercially as Orthtek , available from Greene Tweed & Co., Inc., Kulpsville, PA. The prior art composite exhibits a strength of approximately 9400 psi

(41 ,830 N) in the transverse or z-direction using a transverse tensile test and exhibits a strength 2 of about 9600 psi (675 kg/cm ) in a short-beam shear test as prescribed by ASTM D2344. [00411 Aspects of the invention will now be described witn respect to tfte tollowing non- limiting examples: Example 1

[00421 The composite used in this example is constructed of three layers that are compression molded together. The outer layers are CF layers formed from plies of continuous carbon fiber woven fabrics that are impregnated with PEEK. The inner layer includes short carbon fibers dispersed in a PEEK matrix. The volume of short carbon fibers in the inner layer on a volume basis is 60 % of the SF layer. The lengths of the short carbon fibers vary in length and are less than about 0.5 inches (about 1.27 cm).

[0043] A short beam shear test was performed based on Standardized Test ASTM D2344.

The samples were 6.0 in. (15.2 cm) long. The load was applied with a crosshead speed of 0.05 in/min. The test temperature was 72.3 °F (22.4 °C) and the relative humidity was 25%). Instron

Model 4206 was used.

[0044] The strength of the composite was comparable to a plate of equal size that is made of TM only compression molded multiple plies of Orthtek material as described above with no short fiber layers. Having the inner core constructed of short carbon fibers dispersed in a PEEK matrix resulted in a significant reduction of the total cost of the composite with the short fiber layer replacing as many as 220 or so woven fabric plies in a prior art composite as described above for an equivalent thickness while achieving comparable properties.

Example 2

[0045] The transverse tensile strength of a set of polyetheretherketone (PEEK) based sandwich composite plates of a similar construction as above in Example 1 , was tested using an Instron Machine Model Number 4206. The samples were 1.0 in. (2.54 cm) in thickness. [0046] As in the above Example 1 , the strength was also comparable to a laminate of equal TM size that includes only multiple plies of Orthtek material with no short fiber layer.

[0047] It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.

Claims

CLAIMSWe claim:

1. A multilayer composite plate comprising at least one continuous fiber layer comprising a thermoplastic polymer resin and a plurality of continuous fibers and at least one short fiber layer, comprising a thermoplastic polymer resin and a plurality of short fibers, wherein the layers are consolidated to form a multilayer composite plate.

2. The multilayer composite plate according to claim 1 , comprising two continuous fiber layers.

3. The multilayer composite plate according to claim 1, wherein the thermoplastic polymer resin of the at least one continuous fiber layer is selected from the group consisting of polyaryl ether ketones, polysulfones, polyetherimides, polyphenylene sulfides, polyamides, liquid crystalline polymer, and derivatives and copolymers thereof.

4. The multilayer composite plate according to claim 1 , wherein the polymer resin of the at least one short fiber layer is independently selected from the group consisting of polyaryl ether ketones, polysulfones, polyetherimides, polyphenylene sulfides, polyamides, liquid crystalline polymer, and derivatives and copolymers thereof.

5. The multilayer composite plate according to claim 1, wherein the short fibers are selected from the group consisting of carbon fibers, glass fibers, graphite fibers, ceramic fibers, and plastic fibers.

6. The multilayer composite plate according to claim 1 , wherein the continuous fibers are selected from the group consisting of ceramic, carbon fibers, glass fibers, graphite fibers, ceramic fibers, and plastic fibers.

7. The multilayer composite plate according to claim 1 , wherein the continuous fibers are selected from the group consisting of unidirectional fibers, bidirectional fibers, co- mingled fibers, braided fibers, and woven continuous fibers.

8. The multilayer composite plate according to claim 1 , wherein the short fibers are selected from chopped fibers and milled fibers.

9. The multilayer composite plate according to claim 1 , wherein the continuous fibers of the continuous fiber layer are woven.

10. The multilayer composite plate according to claim 1 , wherein the continuous fibers are present in the at least one continuous fiber layer in an amount of about 30% to about 90% by volume.

1 1. The multilayer composite plate according to claim 1, wherein the short fibers are present in the at least one short fiber layer in an amount of about 10%> to about 90% by volume.

12. The multilayer composite plate according to claim 1 , wherein the continuous fibers are present in at least one continuous fiber layer in an amount of about 40% to about 80% by volume.

13. The multilayer composite plate according to claim 1, wherein the one short fibers are present in the at least one short fiber layer in an amount of about 50% to about 70% by volume.

14. The multilayer composite plate according to claim 1, wherein the continuous fibers are present in the at least one continuous fiber layer in an amount of about 50% to about 70%) by volume.

15. The multilayer composite according to claim 1, wherein there is one inner short fiber layer and two outer continuous fiber layers such that the composite comprises a sandwich configuration.

16. A multilayer composite plate comprising: (a) at least two continuous fiber layers, each comprising a thermoplastic polymer resin and continuous fibers; (b) at least one short fiber layer, comprising a thermoplastic polymer resin and short fibers; wherein at least one of the at least one short fiber layers is positioned between at least two of the continuous fiber layers.

17. A method of preparing a multilayer composite plate comprising consolidating at least two layers, wherein at least one of the layers comprises a thermoplastic polymer resin and continuous fibers and at least one of the layers comprises a thermoplastic polymer resin and short fibers.

18. A sandwich composite plate comprising a first outer layer comprising continuous carbon fibers impregnated with a thermoplastic; a second outer layer comprising continuous carbon fibers impregnated with a thermoplastic; an inner layer comprising short carbon fibers impregnated with a thermoplastic; wherein the first and second outer layers are situated on either side of the inner layer so as to form a sandwich configuration and the sandwich composite plate is formed by compression molding the layers.

19. The sandwich composite plate according to claim 18, wherein the thermoplastic in each layer may be the same or different and each is selected from the group consisting of polyetheretherketone, polyetherketoneketone, polyamides, polyimides, liquid crystalline polymer, polysulfones, polyphenylene sulfides and derivatives and copolymers thereof.

20. The sandwich composite plate according to claim 18, wherein the continuous carbon fibers are woven fibers.

21. The sandwich composite plate according to claim 18, wherein the first and second outer layers comprise multiple plies of sheets comprise woven continuous carbon fibers.

22. The sandwich composite plate according to claim 18, wherein a volumetric ratio of a combination of the first and second outer layers to the inner layer ranges from about 1 : 15 to about 15: 1.

23. The sandwich composite plate according to claim 18, wherein a volumetric ratio of a combination of the first and second outer layers to the inner layer ranges from about 3:2 to about 2:3.