Abstract:
A pre-impregnated material including a textile substrate and resin adhered to the textile substrate, the pre-impregnated material being characterized in that the resin has a uniformity of thickness having a variation of less than 5% of its average thickness. Pre-impregnated materials with other properties are also disclosed.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to pre-impregnated materials generally.  
       BACKGROUND OF THE INVENTION  
       [0002]     The following U.S. Patent Documents are believed to represent the current state of the art: U.S. Pat. Nos. 6,656,316; 6,620,243; 5,911,932; 5,895,622; 5,820,941; 5;800,615; 5,639,307; 5,409,757; 5,360,661; 5,310,582; 5,302,419; 5,296,064; 5,198,281; 5,171,630; 5,094,883 and 4,634,058.  
       SUMMARY OF THE INVENTION  
       [0003]     The present invention seeks to provide improved pre-impregnated materials.  
         [0004]     There is thus provided in accordance with a preferred embodiment of the present invention a pre-impregnated material including a textile substrate and resin adhered to the textile substrate, the pre-impregnated material being characterized in that the resin has a uniformity of thickness having a variation of less than 5% of its average thickness.  
         [0005]     There is also provided in accordance with another preferred embodiment of the present invention a pre-impregnated material including a textile substrate and resin adhered to the textile substrate, the pre-impregnated material being characterized in that the resin has an impregnation depth of at least 60% of the thickness of the textile substrate.  
         [0006]     There is further provided in accordance with still another preferred embodiment of the present invention a pre-impregnated material including a textile substrate and resin adhered to the textile substrate, the pre-impregnated material being characterized in that the resin has a thickness exceeding 300 microns.  
         [0007]     There is yet further provided in accordance with another preferred embodiment of the present invention a pre-impregnated material including a textile substrate and resin adhered to the textile substrate, the pre-impregnated material being characterized in that the weight of the resin is at least 70% of the weight of the pre-impregnated material.  
         [0008]     There is even further provided in accordance with yet another preferred embodiment of the present invention a pre-impregnated material including a textile substrate and resin adhered to the textile substrate, the pre-impregnated material being characterized in that the resin has a thickness less than 50 microns.  
         [0009]     There is still further provided in accordance with still another preferred embodiment of the present invention a pre-impregnated material including a textile substrate and resin adhered to the textile substrate, the pre-impregnated material being characterized in that the weight of the resin is less than 10% of the weight of the pre-impregnated material.  
         [0010]     There is also provided in accordance with another preferred embodiment of the present invention a pre-impregnated material including a textile substrate and resin adhered to the textile substrate, the pre-impregnated material being characterized in that the resin includes particles having a size spectrum which extends over at least two orders of magnitude.  
         [0011]     There is further provided in accordance with yet another preferred embodiment of the present invention a pre-impregnated material including a textile substrate and resin adhered to the textile substrate, the pre-impregnated material being characterized in that the resin includes particles having a density spectrum which extends over at least one order of magnitude.  
         [0012]     In accordance with another preferred embodiment of the present invention the resin has a uniformity of thickness having a variation of less than 5% of its average thickness. In accordance with another preferred embodiment of the present invention the resin has a uniformity of thickness having a variation of less than 2% of its average thickness. In accordance with yet another preferred embodiment of the present invention the resin has a uniformity of thickness having a variation of less than 2% of its average thickness along its width.  
         [0013]     In accordance with another preferred embodiment of the present invention the resin has an impregnation depth of at least 60% of the thickness of the textile substrate. In accordance with yet another preferred embodiment of the present invention the resin has an impregnation depth of at least 80% of the thickness of the textile substrate.  
         [0014]     In accordance with another preferred embodiment of the present invention the weight of the resin is less than 5% of the weight of the pre-impregnated material.  
         [0015]     In accordance with another preferred embodiment of the present invention the resin is fully melted. In accordance with yet another preferred embodiment of the present invention the resin is partially melted and partially in particulate form. In accordance with still another preferred embodiment of the present invention the resin is formed as a plurality of resin layers. In accordance with another preferred embodiment of the present invention the resin is formed as a plurality of resin layers having different thicknesses. In accordance with yet another preferred embodiment of the present invention the resin is formed as a plurality of resin layers formed of different resin materials.  
         [0016]     There is also provided in accordance with another preferred embodiment of the present invention a laminate formed of a plurality of layers of pre-impregnated material, at least one of the plurality of layers of pre-impregnated material including a textile substrate and resin adhered to the textile substrate, the pre-impregnated material being characterized in that the resin has a uniformity of thickness having a variation of less than 5% of its average thickness.  
         [0017]     There is further provided in accordance with yet another preferred embodiment of the present invention a laminate formed of a plurality of layers of pre-impregnated material, at least one of the plurality of layers of pre-impregnated material including a textile substrate and resin adhered to the textile substrate, the pre-impregnated material being characterized in that the resin has a thickness exceeding 300 microns.  
         [0018]     There is even further provided in accordance with still another preferred embodiment of the present invention a laminate formed of a plurality of layers of pre-impregnated material, at least one of the plurality of layers of pre-impregnated material including a textile substrate and resin adhered to the textile substrate, the pre-impregnated material being characterized in that the weight of the resin is at least 70% of the weight of the pre-impregnated material.  
         [0019]     There is yet further provided in accordance with another preferred embodiment of the present invention a laminate formed of a plurality of layers of pre-impregnated material, at least one of the plurality of layers of pre-impregnated material including a textile substrate and resin adhered to the textile substrate, the pre-impregnated material being characterized in that the resin has a thickness less than 50 microns.  
         [0020]     There is still further provided in accordance with yet another preferred embodiment of the present invention a laminate formed of a plurality of layers of pre-impregnated material, at least one of the plurality of layers of pre-impregnated material including a textile substrate and resin adhered to the textile substrate, the pre-impregnated material being characterized in that the weight of the resin is less than 10% of the weight of the pre-impregnated material.  
         [0021]     There is also provided in accordance with still another preferred embodiment of the present invention a laminate formed of a plurality of layers of pre-impregnated material, at least one of the plurality of layers of pre-impregnated material including a textile substrate and resin adhered to the textile substrate, the pre-impregnated material being characterized in that the resin includes particles having a size spectrum which extends over at least two orders of magnitude.  
         [0022]     There is further provided in accordance with another preferred embodiment of the present invention a laminate formed of a plurality of layers of pre-impregnated material, at least one of the plurality of layers of pre-impregnated material including a textile substrate and resin adhered to the textile substrate, the pre-impregnated material being characterized in that the resin includes particles having a density spectrum which extends over at least one order of magnitude.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]     The present invention will be appreciated more fully from the following detailed description, taken in conjunction with the drawings in which:  
         [0024]      FIG. 1  is a simplified sectional illustration of a pre-impregnated material constructed and operative in accordance with a preferred embodiment of the present invention, showing uniformity of resin thickness;  
         [0025]      FIG. 2  is a simplified sectional illustration of a pre-impregnated material constructed and operative in accordance with another preferred embodiment of the present invention, showing uniformity of resin thickness;  
         [0026]      FIG. 3  is a simplified sectional illustration of a pre-impregnated material constructed and operative in accordance with a preferred embodiment of the present invention, showing impregnation depth;  
         [0027]      FIG. 4  is a simplified sectional illustration of a pre-impregnated material constructed and operative in accordance with a preferred embodiment of the present invention, showing high resin thickness;  
         [0028]      FIG. 5  is a simplified sectional illustration of a pre-impregnated material constructed and operative in accordance with a preferred embodiment of the present invention, showing low resin thickness;  
         [0029]      FIG. 6  is a simplified sectional illustration of a pre-impregnated material constructed and operative in accordance with another preferred embodiment of the present invention, showing uniformity of resin thickness;  
         [0030]      FIG. 7  is a simplified sectional illustration of a pre-impregnated material constructed and operative in accordance with another preferred embodiment of the present invention, showing uniformity of resin thickness;  
         [0031]      FIG. 8  is a simplified sectional illustration of a pre-impregnated material constructed and operative in accordance with a preferred embodiment of the present invention, showing impregnation depth;  
         [0032]      FIG. 9  is a simplified sectional illustration of a pre-impregnated material constructed and operative in accordance with a preferred embodiment of the present invention, showing high resin thickness;  
         [0033]      FIG. 10  is a simplified sectional illustration of a pre-impregnated material constructed and operative in accordance with a preferred embodiment of the present invention, showing low resin thickness;  
         [0034]      FIG. 11  is a simplified sectional illustration of a laminate formed of a plurality of layers of pre-impregnated material constructed and operative in accordance with a preferred embodiment of the present invention; and  
         [0035]      FIG. 12  is a simplified sectional illustration of a laminate formed of a plurality of layers of pre-impregnated material constructed and operative in accordance with a preferred embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0036]     Reference is now made to  FIG. 1 , which is a simplified sectional illustration of a pre-impregnated material constructed and operative in accordance with a preferred embodiment of the present invention, showing uniformity of resin thickness. As seen in  FIG. 1 , a fabric  100  is shown impregnated with a resin forming at least one resin layer  102  having a high degree of uniformity of thickness, having a variation of less than 5% and preferably approximately 1%. The illustrated embodiment includes two layers  102 , on opposite surfaces of the fabric  100 , each layer preferably of thickness about 100 microns.  
         [0037]     The fabric  100  may be any suitable type of fabric, woven as shown in  FIG. 1  or alternatively non-woven or formed in any other suitable manner. The term “fabric” as used throughout the specification and claims, includes also an array of fibers which may or may not be interengaged and which may or may not extend along parallel directions. The array of fibers may or may not be homogeneous and may or may not include fibers of different materials and/or configurations and/or sizes.  
         [0038]     The resin may be any suitable type of impregnatable resin, including, inter alia, thermosetting and/or thermoplastic materials, such as PP, PA, PPS, PEEK, PEKK, PBT, PEI, PAI, Epoxies, Phenolics and Polyimides. The resins may include both organic and non-organic materials. Preferably, the resins are impregnated in the form of powders having a particle size of between 1 and 200 microns.  
         [0039]     It is seen that in the illustrated example, warp fibers  110  and weft fibers  112  and the interstices  114  therebetween each have formed thereon and therein a pair of opposite-facing resin layers  102  whose thickness is uniform to a high degree, having a variation of less than 5% and preferably approximately 1%. Typically each of warp fibers  110  and weft fibers  112  is formed of a multiplicity of individual fiber strands  116 .  
         [0040]     The pre-impregnated material of  FIG. 1  is preferably realized by accelerated impingement of a stream of resin particles onto the fabric  100  followed by the application of heat, in accordance with the teachings of applicant/assignee&#39;s Published PCT Patent Application WO 03/024609, the disclosure of which is hereby incorporated by reference.  
         [0041]     Reference is now made to  FIG. 2 , which is a simplified sectional illustration of a pre-impregnated material constructed and operative in accordance with another preferred embodiment of the present invention, showing uniformity of resin thickness. The essential difference between the embodiment of  FIG. 2  and that of  FIG. 1 , described hereinabove, is in the amount of resin impregnated into the fabric.  
         [0042]     As seen in  FIG. 2 , a fabric  200  is shown fully impregnated with a resin and forming a fully impregnated fabric layer  202  having a high degree of uniformity of thickness, having a variation of less than 5% and preferably approximately 1%. The thickness is preferably about 500 microns.  
         [0043]     The fabric  200  may be any suitable type of fabric, woven as shown in  FIG. 2  or alternatively non-woven or formed in any other suitable manner. The term “fabric” includes also an array of fibers which may or may not be interengaged and which may or may not extend along parallel directions. The array of fibers may or may not be homogeneous and may or may not include fibers of different materials and/or configurations and/or sizes.  
         [0044]     The resin may be any suitable type of impregnatable resin, including, inter alia, thermosetting and/or thermoplastic materials, such as PP, PA, PPS, PEEK, PEKK, PBT, PEI, PAI, Epoxies, Phenolics and Polyimides. The resins may include both organic and non-organic materials. Preferably, the resins are impregnated in the form of powders having a particle size of between 1 and 200 microns.  
         [0045]     Turning to  FIG. 2 , it is seen that in the illustrated example, warp fibers  210  and weft fibers  212  and the interstices  214  therebetween each are fully impregnated such that layer  202  has thickness which is uniform to a high degree, having a variation of less than 5% and preferably approximately 1%. Typically each of warp fibers  210  and weft fibers  212  is formed of a multiplicity of individual fiber strands  216 .  
         [0046]     It is appreciated that the embodiment of  FIG. 2  is typically more rigid than the embodiment of  FIG. 1 .  
         [0047]     The pre-impregnated material of  FIG. 2  is preferably realized by accelerated impingement of a stream of resin particles onto the fabric  200  followed by the application of heat, in accordance with the teachings of applicant/assignee&#39;s Published PCT Patent Application WO 03/024609, the disclosure of which is hereby incorporated by reference.  
         [0048]     Reference is now made to  FIG. 3 , which is a simplified sectional illustration of a pre-impregnated material constructed and operative in accordance with another preferred embodiment of the present invention. The difference between the embodiment of  FIG. 3  and that of  FIG. 1 , described hereinabove, is in the fact that the fabric is coated only on one side thereof.  
         [0049]     As seen in  FIG. 3 , similarly to that described hereinabove with reference to  FIG. 1 , a fabric  300  is shown impregnated with a resin forming a resin layer  302  having a high degree of uniformity of thickness, having a variation of less than 5% and preferably approximately 1%. The illustrated embodiment includes a single layer  302 , typically of thickness approximately 200 microns.  
         [0050]     The fabric  300  may be any suitable type of fabric, woven as shown in  FIG. 3  or alternatively non-woven or formed in any other suitable manner. The term “fabric” as used throughout the specification and claims, includes also an array of fibers which may or may not be interengaged and which may or may not extend along parallel directions. The array of fibers may or may not be homogeneous and may or may not include fibers of different materials and/or configurations and/or sizes.  
         [0051]     The resin may be any suitable type of impregnatable resin, including, inter alia, thermosetting and/or thermoplastic materials, such as PP, PA, PPS, PEEK, PEKK, PBT, PEI, PAI, Epoxies, Phenolics and Polyimides. The resins may include both organic and non-organic materials. Preferably, the resins are impregnated in the form of powders having a particle size of between 1 and 200 microns.  
         [0052]     It is seen that in the illustrated example, warp fibers  310  and weft fibers  312  and the interstices  314  therebetween each have formed thereon and therein a resin layer  302  whose thickness is uniform to a high degree, having a variation of less than 5% and preferably approximately 1%. Typically each of warp fibers  310  and weft fibers  312  is formed of a multiplicity of individual fiber strands  316 .  
         [0053]     The pre-impregnated material of  FIG. 3  is preferably realized by accelerated impingement of a stream of resin particles onto the fabric  300  followed by the application of heat, in accordance with the teachings of applicant/assignee&#39;s Published PCT Patent Application WO 03/024609, the disclosure of which is hereby incorporated by reference.  
         [0054]     Reference is now made to  FIG. 4 , which is a simplified sectional illustration of a pre-impregnated material constructed and operative in accordance with a preferred embodiment of the present invention, showing high resin thickness. The essential difference between  FIG. 4  and  FIG. 2  described hereinabove lies in the overall resin thickness.  
         [0055]     As seen in  FIG. 4 , a fabric  400  is shown fully impregnated with a resin and forming a fully impregnated fabric layer  402  having a high degree of uniformity of thickness, having a variation of less than 5% and preferably approximately 1%. The thickness is preferably above 500 microns and may reach up to approximately 6 mm.  
         [0056]     The fabric  400  may be any suitable type of fabric, woven as shown in  FIG. 4  or alternatively non-woven or formed in any other suitable manner. The term “fabric” includes also an array of fibers which may or may not be interengaged and which may or may not extend along parallel directions. The array of fibers may or may not be homogeneous and may or may not include fibers of different materials and/or configurations and/or sizes.  
         [0057]     The resin may be any suitable type of impregnatable resin, including, inter alia, thermosetting and/or thermoplastic materials, such as PP, PA, PPS, PEEK, PEKK, PBT, PEI, PAI, Epoxies, Phenolics and Polyimides. The resins may include both organic and non-organic materials. Preferably, the resins are impregnated in the form of powders having a particle size of between 1 and 200 microns.  
         [0058]     Turning to  FIG. 4 , it is seen that in the illustrated example, warp fibers  410  and weft fibers  412  and the interstices  414  therebetween each are fully impregnated and additional resin is formed thereover, preferably on both surfaces of the fabric, such that layer  402  has thickness which is uniform to a high degree, having a variation of less than 5% and preferably approximately 1%. Typically each of warp fibers  410  and weft fibers  412  is formed of a multiplicity of individual fiber strands  416 .  
         [0059]     The pre-impregnated material of  FIG. 4  is preferably realized by accelerated impingement of a stream of resin particles onto the fabric  400  followed by the application of heat, in accordance with the teachings of applicant/assignee&#39;s Published PCT Patent Application WO 03/024609, the disclosure of which is hereby incorporated by reference.  
         [0060]     Reference is now made to  FIG. 5 , which is a simplified sectional illustration of a pre-impregnated material constructed and operative in accordance with a preferred embodiment of the present invention, showing a relatively low resin thickness. The essential difference between the embodiment of  FIG. 5  and that of  FIG. 1 , described hereinabove, is in the amount of resin impregnated into the fabric. In the embodiment of  FIG. 5 , a relatively small amount of resin is impregnated into the fabric, producing relatively thin, but highly uniform, layers of resin.  
         [0061]     As seen in  FIG. 5 , a fabric  500  is shown impregnated with a resin forming at least one resin layer  502  having a high degree of uniformity of thickness, having a variation of less than 5% and preferably approximately 1%. The illustrated embodiment includes two layers  502 , on opposite surfaces of the fabric  500 , each layer preferably of thickness about 30 microns.  
         [0062]     The fabric  500  may be any suitable type of fabric, woven as shown in  FIG. 5  or alternatively non-woven or formed in any other suitable manner. The term “fabric” as used throughout the specification and claims, includes also an array of fibers which may or may not be interengaged and which may or may not extend along parallel directions. The array of fibers may or may not be homogeneous and may or may not include fibers of different materials and/or configurations and/or sizes.  
         [0063]     The resin may be any suitable type of impregnatable resin, including, inter alia, thermosetting and/or thermoplastic materials, such as PP, PA, PPS, PEEK, PEKK, PBT, PEI, PAI, Epoxies, Phenolics and Polyimides. The resins may include both organic and non-organic materials. Preferably, the resins are impregnated in the form of powders having a particle size of between 1 and 200 microns.  
         [0064]     It is seen that in the illustrated example, warp fibers  510  and weft fibers  512  and the interstices  514  therebetween each have formed thereon and therein a pair of opposite-facing resin layers  502  whose thickness is uniform to a high degree, having a variation of less than 5% and preferably approximately 1%. Typically each of warp fibers  510  and weft fibers  512  is formed of a multiplicity of individual fiber strands  516 .  
         [0065]     The pre-impregnated material of  FIG. 5  is preferably realized by accelerated impingement of a stream of resin particles onto the fabric  500  followed by the application of heat, in accordance with the teachings of applicant/assignee&#39;s Published PCT Patent Application WO 03/024609, the disclosure of which is hereby incorporated by reference.  
         [0066]     Reference is now made to  FIG. 6-10 , which are similar to  FIGS. 1-5 , but differ therefrom in that a lesser amount of heat has been applied to the resin following impregnation of the fabric, thereby producing a partially-particulate, partially melted resin matrix, as distinguished from a fully melted resin matrix in the embodiments of  FIGS. 1-5 . In the embodiments of  FIGS. 6-10 , the resin layers lie outside of the fabric to a somewhat greater degree than in the embodiments of  FIGS. 1-5 .  
         [0067]     Reference is now made to  FIG. 6 , which is a simplified sectional illustration of a pre-impregnated material constructed and operative in accordance with a preferred embodiment of the present invention, showing uniformity of resin thickness. As seen in  FIG. 6 , a fabric  600  is shown impregnated with a resin forming at least one resin layer  602  having a high degree of uniformity of thickness, having a variation of less than 5% and preferably approximately 1%. The illustrated embodiment includes two layers  602 , on opposite surfaces of the fabric  600 , each layer preferably of thickness about 100 microns.  
         [0068]     The fabric  600  may be any suitable type of fabric, woven as shown in  FIG. 6  or alternatively non-woven or formed in any other suitable manner. The term “fabric” as used throughout the specification and claims, includes also an array of fibers which may or may not be interengaged and which may or may not extend along parallel directions. The array of fibers may or may not be homogeneous and may or may not include fibers of different materials and/or configurations and/or sizes.  
         [0069]     The resin may be any suitable type of impregnatable resin, including, inter alia, thermosetting and/or thermoplastic materials, such as PP, PA, PPS, PEEK, PEKK, PBT, PEI, PAI, Epoxies, Phenolics and Polyimides. The resins may include both organic and non-organic materials. Preferably, the resins are impregnated in the form of powders having a particle size of between 1 and 200 microns.  
         [0070]     It is seen that in the illustrated example, warp fibers  610  and weft fibers  612  and the interstices  614  therebetween each have formed thereon and therein a pair of opposite-facing resin layers  602  whose thickness is uniform to a high degree, having a variation of less than 5% and preferably approximately 1%. Typically each of warp fibers  610  and weft fibers  612  is formed of a multiplicity of individual fiber strands  616 .  
         [0071]     The pre-impregnated material of  FIG. 6  is preferably realized by accelerated impingement of a stream of resin particles onto the fabric  600  followed by the application of heat, in accordance with the teachings of applicant/assignee&#39;s Published PCT Patent Application WO 03/024609, the disclosure of which is hereby incorporated by reference.  
         [0072]     As noted above, in the embodiments of  FIGS. 6-10 , the resin layers lie outside of the fabric to a somewhat greater degree than in the embodiments of  FIGS. 1-5 . In the above-described embodiment of  FIG. 6 , it is seen that approximately 60% of the thickness of each of the resin layers  602  lies outside of the fabric, while in  FIG. 1  approximately 40% of the resin layers  102  lies outside the fabric.  
         [0073]     Reference is now made to  FIG. 7 , which is a simplified sectional illustration of a pre-impregnated material constructed and operative in accordance with another preferred embodiment of the present invention, showing uniformity of resin thickness. The essential difference between the embodiment of  FIG. 7  and that of  FIG. 6 , described hereinabove, is in the amount of resin impregnated into the fabric.  
         [0074]     As seen in  FIG. 7 , a fabric  700  is shown fully impregnated with a resin and forming a fully impregnated fabric layer  702  having a high degree of uniformity of thickness, having a variation of less than 5% and preferably approximately 1%. The thickness is preferably about 500 microns.  
         [0075]     The fabric  700  may be any suitable type of fabric, woven as shown in  FIG. 7  or alternatively non-woven or formed in any other suitable manner. The term “fabric” includes also an array of fibers which may or may not be interengaged and which may or may not extend along parallel directions. The array of fibers may or may not be homogeneous and may or may not include fibers of different materials and/or configurations and/or sizes.  
         [0076]     The resin may be any suitable type of impregnatable resin, including, inter alia, thermosetting and/or thermoplastic materials, such as PP, PA, PPS, PEEK, PEKK, PBT, PEI, PAI, Epoxies, Phenolics and Polyimides. The resins may include both organic and non-organic materials. Preferably, the resins are impregnated in the form of powders having a particle size of between 1 and 200 microns.  
         [0077]     Turning to  FIG. 7 , it is seen that in the illustrated example, warp fibers  710  and weft fibers  712  and the interstices  714  therebetween each are fully impregnated such that layer  702  has thickness which is uniform to a high degree, having a variation of less than 5% and preferably approximately 1%. Typically each of warp fibers  710  and weft fibers  712  is formed of a multiplicity of individual fiber strands  716 .  
         [0078]     It is appreciated that the embodiment of  FIG. 7  is typically more rigid than the embodiment of  FIG. 6 .  
         [0079]     The pre-impregnated material of  FIG. 7  is preferably realized by accelerated impingement of a stream of resin particles onto the fabric  700  followed by the application of heat, in accordance with the teachings of applicant/assignee&#39;s Published PCT Patent Application WO 03/024609, the disclosure of which is hereby incorporated by reference.  
         [0080]     Reference is now made to  FIG. 8 , which is a simplified sectional illustration of a pre-impregnated material constructed and operative in accordance with another preferred embodiment of the present invention. The difference between the embodiment of  FIG. 8  and that of  FIG. 6 , described hereinabove, is in the fact that the fabric is coated only on one side thereof.  
         [0081]     As seen in  FIG. 8 , similarly to that described hereinabove with reference to  FIG. 6 , a fabric  800  is shown impregnated with a resin forming a resin layer  802  having a high degree of uniformity of thickness, having a variation of less than 5% and preferably approximately 1%. The illustrated embodiment includes a single layer  802 , typically of thickness approximately 200 microns.  
         [0082]     The fabric  800  may be any suitable type of fabric, woven as shown in  FIG. 8  or alternatively non-woven or formed in any other suitable manner. The term “fabric” as used throughout the specification and claims, includes also an array of fibers which may or may not be interengaged and which may or may not extend along parallel directions. The array of fibers may or may not be homogeneous and may or may not include fibers of different materials and/or configurations and/or sizes.  
         [0083]     The resin may be any suitable type of impregnatable resin, including, inter alia, thermosetting and/or thermoplastic materials, such as PP, PA, PPS, PEEK, PEKK, PBT, PEI, PAI, Epoxies, Phenolics and Polyimides. The resins may include both organic and non-organic materials. Preferably, the resins are impregnated in the form of powders having a particle size of between 1 and 200 microns.  
         [0084]     It is seen that in the illustrated example, warp fibers  810  and weft fibers  812  and the interstices  814  therebetween each have formed thereon and therein a resin layer  802  whose thickness is uniform to a high degree, having a variation of less than 5% and preferably approximately 1%. Typically each of warp fibers  810  and weft fibers  812  is formed of a multiplicity of individual fiber strands  816 .  
         [0085]     The pre-impregnated material of  FIG. 8  is preferably realized by accelerated impingement of a stream of resin particles onto the fabric  800  followed by the application of heat, in accordance with the teachings of applicant/assignee&#39;s Published PCT Patent Application WO 03/024609, the disclosure of which is hereby incorporated by reference.  
         [0086]     As noted above, in the embodiments of  FIGS. 6-10 , the resin layers lie outside of the fabric to a somewhat greater degree than in the embodiments of  FIGS. 1-5 . In the above-described embodiment of  FIG. 8 , it is seen that approximately 60% of the thickness of each of the resin layers  802  lies outside of the fabric, while in  FIG. 3  approximately 40% of the resin layers  102  lies outside the fabric.  
         [0087]     Reference is now made to  FIG. 9 , which is a simplified sectional illustration of a pre-impregnated material constructed and operative in accordance with a preferred embodiment of the present invention, showing high resin thickness. The essential difference between  FIG. 9  and  FIG. 7  described hereinabove lies in the overall resin thickness.  
         [0088]     As seen in  FIG. 9 , a fabric  900  is shown fully impregnated with a resin and forming a fully impregnated fabric layer  902  having a high degree of uniformity of thickness, having a variation of less than 5% and preferably approximately 1%. The thickness is preferably above 500 microns and may reach up to approximately 6 mm.  
         [0089]     The fabric  900  may be any suitable type of fabric, woven as shown in  FIG. 9  or alternatively non-woven or formed in any other suitable manner. The term “fabric” includes also an array of fibers which may or may not be interengaged and which may or may not extend along parallel directions. The array of fibers may or may not be homogeneous and may or may not include fibers of different materials and/or configurations and/or sizes.  
         [0090]     The resin may be any suitable type of impregnatable resin, including, inter alia, thermosetting and/or thermoplastic materials, such as PP, PA, PPS, PEEK, PEKK, PBT, PEI, PAI, Epoxies, Phenolics and Polyimides. The resins may include both organic and non-organic materials. Preferably, the resins are impregnated in the form of powders having a particle size of between 1 and 200 microns.  
         [0091]     Turning to  FIG. 9 , it is seen that in the illustrated example, warp fibers  910  and weft fibers  912  and the interstices  914  therebetween each are fully impregnated and additional resin is formed thereover, preferably on both surfaces of the fabric, such that layer  902  has thickness which is uniform to a high degree, having a variation of less than 5% and preferably approximately 1%. Typically each of warp fibers  910  and weft fibers  912  is formed of a multiplicity of individual fiber strands  916 .  
         [0092]     The pre-impregnated material of  FIG. 9  is preferably realized by accelerated impingement of a stream of resin particles onto the fabric  900  followed by the application of heat, in accordance with the teachings of applicant/assignee&#39;s Published PCT Patent Application WO 03/024609, the disclosure of which is hereby incorporated by reference.  
         [0093]     Reference is now made to  FIG. 10 , which is a simplified sectional illustration of a pre-impregnated material constructed and operative in accordance with a preferred embodiment of the present invention, showing a relatively low resin thickness. The essential difference between the embodiment of  FIG. 10  and that of  FIG. 5 , described hereinabove, is in the amount of resin impregnated into the fabric. In the embodiment of  FIG. 10 , a relatively small amount of resin is impregnated into the fabric, producing relatively thin, but highly uniform layers of resin.  
         [0094]     As seen in  FIG. 10 , a fabric  1000  is shown impregnated with a resin forming at least one resin layer  1002  having a high degree of uniformity of thickness, having a variation of less than 5% and preferably approximately 1%. The illustrated embodiment includes two layers  1002 , on opposite surfaces of the fabric  1000 , each layer preferably of thickness about 30 microns.  
         [0095]     The fabric  1000  may be any suitable type of fabric, woven as shown in  FIG. 10  or alternatively non-woven or formed in any other suitable manner. The term “fabric” as used throughout the specification and claims, includes also an array of fibers which may or may not be interengaged and which may or may not extend along parallel directions. The array of fibers may or may not be homogeneous and may or may not include fibers of different materials and/or configurations and/or sizes.  
         [0096]     The resin may be any suitable type of impregnatable resin, including, inter alia, thermosetting and/or thermoplastic materials, such as PP, PA, PPS, PEEK, PEKK, PBT, PEI, PAI, Epoxies, Phenolics and Polyimides. The resins may include both organic and non-organic materials. Preferably, the resins are impregnated in the form of powders having a particle size of between 1 and 200 microns.  
         [0097]     It is seen that in the illustrated example, warp fibers  1010  and weft fibers  1012  and the interstices  1014  therebetween each have formed thereon and therein a pair of opposite-facing resin layers  1002  whose thickness is uniform to a high degree, having a variation of less than 5% and preferably approximately 1%. Typically each of warp fibers  1010  and weft fibers  1012  is formed of a multiplicity of individual fiber strands  1016 .  
         [0098]     The pre-impregnated material of  FIG. 10  is preferably realized by accelerated impingement of a stream of resin particles onto the fabric  1000  followed by the application of heat, in accordance with the teachings of applicant/assignee&#39;s Published PCT Patent Application WO 03/024609, the disclosure of which is hereby incorporated by reference.  
         [0099]     As noted above, in the embodiments of  FIGS. 6-10 , the resin layers lie outside of the fabric to a somewhat greater degree than in the embodiments of  FIGS. 1-5 . In the above-described embodiment of  FIG. 10 , it is seen that approximately 60% of the thickness of each of the resin layers  1002  lies outside of the fabric, while in  FIG. 5 , approximately 40% of the resin layers  502  lies outside the fabric.  
         [0100]     Reference is now made to  FIG. 11 , which illustrates a laminate formed of a plurality of layers of pre-impregnated material, preferably of the type described above with respect to any of  FIGS. 1, 5 ,  6  and  10 . This laminate is preferably formed by applying heat and pressure to a plurality of layers of the pre-impregnated material in a mold. As seen in  FIG. 11 , the application of pressure deforms the warp and weft fibers, here designated by reference numerals  1100  and  1102  respectively, spreading out the individual fiber strands thereof, respectively designated by reference numerals  1110  and  1112 . In such a case, the resin layers of the various layers of pre-impregnated material become fused together, and the fibers of various layers of pre-impregnated material also tend to be merged. It is a particular feature of the present invention that due to the high degree of uniformity of thickness of the resin layers, voids in the laminate are avoided to a significant extent and highly uniform laminate surfaces are realized. The laminate of  FIG. 11  is particularly suitable for use in resin transfer molding (RTM) in which additional resin is added during the final molding process.  
         [0101]     Reference is now made to  FIG. 12 , which illustrates a laminate formed of a plurality of layers of pre-impregnated material, preferably of the type described above with respect to any of  FIGS. 2, 4 ,  7  and  9 . This laminate is preferably formed by applying heat and pressure to a plurality of layers of the pre-impregnated material in a mold. As seen in  FIG. 12 , the application of pressure deforms the warp and weft fibers, here designated by reference numerals  1200  and  1202  respectively, spreading out the individual fiber strands thereof, respectively designated by reference numerals  1210  and  1212 . In such a case, the resin layers of the various layers of pre-impregnated material become fused together, and the fibers of various layers of pre-impregnated material also tend to be merged. It is a particular feature of the present invention that due to the high degree of uniformity of thickness of the resin layers, voids in the laminate are avoided to a significant extent and highly uniform laminate surfaces are realized. The laminate of  FIG. 12  is suitable for molding which does not involve the addition of resin to the laminate.  
         [0102]     It will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described hereinabove. Rather the scope of the present invention includes both combinations and subcombinations of various features described and shown in the foregoing description as well as modifications and variations thereof which would occur to a person of ordinary skill in the art upon reading the foregoing description and which are not in the prior art.