Composite carbon fiber material and method of making same

A composite carbon fiber material is formed of one or more layers of carbon fiber material in which the carbon fibers are aligned all in the same direction and a mat of nonwoven, woven, or off-axis unidirectional carbon fibers are laminated together. Layers may be used individually or as a hybrid. The layers can be preimpregnated or impregnated during processing using thermoplastic or thermosetting resins. A layer of thermoplastic resin is applied either over the surface or within the composite structure, and the resin permeates the material so as to provide a more stable mechanical structure once the resin is processed. The material combines good mechanical strength with improved electrical current carrying properties when compared with the aligned carbon fiber layer alone. The layering sequence, layer type, and resin type can be specified to tailor electrical properties, mechanical properties, durability, and wear resistance. The resultant material achieves these results in substantially smaller material thickness than previously available.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to a thin-gauge composite material formed of layers of specialized carbon fibers and polymeric resins and, more particularly, to a composite carbon fiber material that is useful in an electrical contact assembly typically used in an electromechanical device.

2. Description of the Background

The use of carbon fiber material for structural applications is well known. Typically, this material is composed of multiple layers of either woven fabric or layers of unidirectional, continuous carbon fibers that are laminated together. The orientation and number of layers are chosen to meet the stiffness, strength, and dimensional stability requirements of the particular application. In typical aerospace applications the thin gauge material has between four to eight plies, with a thickness in the range of 0.030 to 0.060 inches. Various processing methods for applying heat and pressure to consolidate the layers of the carbon fiber reinforced thermoplastic and thermosetting composites include the use of autoclaves, presses, and pultrusion. These carbon fiber materials can be formed or shaped by stamping, cutting and machining. The thermoplastic composites can be successively processed, for example, consolidation can be followed by forming and welding. Although thin-gauge composite materials exist, they are not suitable for microelectronic applications presently under consideration.

In U.S. patent application Ser. No. 09/498,872, assigned to the assignee of this application and the disclosure of which is incorporated herein by reference, it is proposed that an electrical contact be formed of carbon fibers that are arranged in a side by side fashion and embedded in an electrically conductive matrix. Nevertheless, both the electrical characteristics and the mechanical characteristics of this carbon fiber electrical contact are seen to be subject to improvement.

Therefore, the need arises for improvements in carbon fiber materials.

OBJECTS SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide an improved carbon fiber composite material that has similar mechanical properties as existing composites but with a smaller thickness, as well as providing good electrical conductivity, and in which the material is a composite formed of carbon fiber materials and elastomeric resin layers.

It is another object of the present invention to provide a composite carbon fiber material having a layer of aligned carbon fibers that has arranged on both flat sides thereof a nonwoven carbon fiber mat, woven fabric or off-axis unidirectional layers with the outer surfaces of the carbon fiber mats being finely coated with a polymeric resin.

A further object of the present invention is to provide a composite carbon fiber material having multiple layers of the carbon fibers that are aligned in a polymeric matrix and adhered together with the multiple layers then being laminated with mats formed of nonwoven carbon fibers, woven fabric or off-axis unidirectional layers, with the exterior surfaces of the mats being coated with a polymeric resin for forming the composite material into a stable structure.

In accordance with one aspect of the present invention the carbon fibers that are aligned and bound in a polymeric matrix are combined between two nonwoven carbon fiber mats, woven fabric or off-axis unidirectional layers. The nonwoven carbon fiber mats, woven fabric, or off-axis unidirectional layers provide improved mechanical strength and stability to the aligned carbon fiber layer and also provide a primary current carrying capability to aid in the overall electrical conductivity of the composite material. Unidirectional electrical conductivity can be achieved by using two methods: carbon fiber to carbon fiber contact between the individual layers that is applicable to both non-conductive and conductive polymers; and/or by adding conductive materials to the resin layer or layers. The fabrication techniques utilized in making the composite material create a network of connections between the differently oriented carbon fibers to provide the desired electrical conductivity. The extent of this conductivity is regulated by the resin volume fraction and may be increased by introducing conductive particles into the resin layer or layers of the composite.

The unidirectional carbon fiber layer is used for carrying electrical current along a primary axis as well as creating mechanical stability along that axis. Used alone, however, this material provides no off-axis electrical conductivity and has virtually no off-axis mechanical stability. The present invention teaches the use of a nonwoven fabric, woven fabric and off-axis unidirectional layer of carbon fibers to provide off axis current carrying capabilities, as well as adding off-axis mechanical stability.

The layer or layers of resin provide additional bonding material for the additional carbon fiber layers and control the overall composition of the material. By varying the ratio of insulative resin to carbon fiber, the mechanical and electrical properties of the composite can be tailored to meet a variety of applications. Also, by introducing and varying the ratio of conductive particles to the resin layer or layers the total electrical conductivity can be increased to be above that which can be achieved by the network of carbon fibers alone.

The invention can contain one or more layers of each of the above-described components depending on the desired electrical and mechanical properties specified and the material layering pattern may be changed depending on the application requirements. By using the above layers of carbon fibers and elastomerics, the resulting composite material can be fabricated at a thickness of less than 0.010 inch.

The above and other objects, features and advantages of the present invention will become apparent from the following detailed description of illustrative embodiments thereof to be read in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

InFIG. 1an exploded view of the inventive composite carbon fiber material is shown in which a central layer20is formed of aligned carbon fibers that are held together by a plastic matrix. Arranged on either side of the central layer20are mats22and24that are formed of nonwoven carbon. These mats22,24are ultrathin carbon fiber material that is extremely light weight and uniform and is substantially isotropic, because there is almost no directionality of the fibers in the plane of the nonwoven carbon fiber fabric.

As noted, the nonwoven carbon fiber mat is an ultrathin material and is generally available having a thickness from 0.08 mm to 0.79 mm. In that regard, one commercial source for this nonwoven carbon fiber mat or material is the Hollingsworth & Vose Company, 112 Washington Street, East Walpole, Mass. 02032.

The composite material is formed as shown inFIG. 2, in which following the arrangement of the mats22,24over the aligned carbon fiber central layer20a thermoplastic resin or polymer is coated over the exterior surfaces of each mat. This forms layer26over mat24and layer28over mat22. The thermoplastic resin layers28and30serve to bind or adhere the nonwoven carbon fiber mats22,24to the respective outer surfaces of the central layer20formed of the aligned carbon fibers.

In another embodiment of the present invention, the central layer of carbon fibers is duplicated, however, the direction of the carbon fibers is changed so that the carbon fibers are at right angles to each other in the successive central layers. More specifically, as shown inFIG. 3, a central layer of aligned carbon fibers40is provided and a second central layer of aligned carbon fibers42is placed to be coextensive with the first layer, however, in layer42the direction of the longitudinal length of the carbon fibers is substantially perpendicular to the direction of the longitudinal length of the carbon fibers in layer40. The two layers40and42may be adhered to each other with a small amount of thermoplastic resin. Thereafter a nonwoven carbon layer44is arranged over the aligned carbon fiber layer40and a second nonwoven carbon fiber mat46is arranged over the aligned carbon fiber layer42.

It is understood that the showing inFIG. 3is an in-process assembly and is not the final composite material, which in fact is shown in an edge view inFIG. 4. As seen inFIG. 4, a thermoplastic resin layer48is applied over the nonwoven carbon fiber mat44and a similar thermoplastic resin layer50is applied over the nonwoven carbon fiber layer46. The effect of these thermoplastic resin layers48,50is to form a stable material by causing adherence between each mat and its respective carbon fiber layer. Some of that same material, although not seen inFIG. 4would also be applied between the respective carbon fiber layers40,42to bond those two layers to each other.

In another embodiment shown inFIG. 5, multiple layers of the aligned carbon fibers are again provided. In this embodiment, both layers of the aligned carbon fiber structure have the fibers aligned in the same direction. Specifically, a first carbon fiber layer60is provided and a second carbon layer62is provided, however, a nonwoven carbon fiber mat64is interposed between the two carbon fiber layers60,62. As in the previous embodiment, a small amount of thermoplastic resin, not seen inFIG. 5, would be applied to both sides of the nonwoven carbon fiber mat64in order to form a centrally arranged composite material. Thereafter, additional carbon fiber mats are provided on the outer surfaces of the carbon fiber layers60and62. More particularly, a nonwoven carbon fiber mat66is provided on an exterior surface of aligned carbon fiber layer60and a second nonwoven carbon fiber mat68is provided on an exterior surface of the aligned carbon fiber layer62, in which the fibers are aligned in the same direction as carbon fiber layer60.

FIG. 6shows the composite material finally assembled in the order of the layers as shown inFIG. 5, in which a thermoplastic resin layer70is applied on the exterior surface of nonwoven carbon fiber mat66and a thermoplastic resin layer72is applied on an exterior surface of nonwoven carbon fiber mat68.

One advantageous use for the above-described composite carbon fiber material is the manufacture of electrical contacts that conduct electricity and have a dynamic relationship to a resistive path. Therefore, the inventive composite carbon fiber material has been found to provide improved current carrying capabilities because the nonwoven carbon fiber mats provide a primary current carrying capability and, moreover, the composite carbon fiber material has improved mechanical strength so that the resiliency required of such electrical contacts is improved by use of this composite material.

It should be understood that, although not seen in the edge views ofFIGS. 2,4, and6, a small amount of the thermoplastic resin that forms the exterior coatings of the composite material may also be applied between the internal layers in order to make certain that all layers are firmly bonded, one to another.

It is understood of course that the foregoing description is presented by way of example only and is not intended to limit the spirit or scope of the present invention, which is to be defined by the appended claims.