Title of Invention

'CARBON ARAMID FIBRE REINFORCED PLASTIC COMPOSITES AND A METHOD FOR PREPARATION THEREOF"

Abstract

This invention relates to a method for the preparation of carbon aramid fibre reinforced plastic composites. According to the method dried and cooled aramid fibre and carbon fibre is coated with resin solution modified with a modifier and re-modified with a dry modifier. The solvent is dried to remove traces, cut into pieces. The plies followed by hydraulic pressing of the stacked plies is stacked.

Full Text

FIELD OF INVENTION This invention relates to Carbon A ram id Fibre Reinforced Plastic composites and a method of preparation thereof wherein the composites prepared thereby have applications as a structural component and for ballistic protection as well as for providing opacity in wide frequency range of Electro-Magnetic emission. PRIOR ART The Electro-Magnetic radiation is the emission of Electro-Magnetic energy from the electrical and electro-magnetic equipment and components. This emission can cause disturbance to other electronics in the proximity. Electromagnetic Interference (EMI) is the impairment of the performance of an electronic system or sub-system by an unwanted electromagnetic disturbance. The need to ensure reliable operation in noisy environments of Radio frequency Interference (RFI) or Electrostatic discharge has led to the concept of electromagnetic compatibility (EMC) which is the ability of an electronic component to operate satisfactorily in the proximity of other component without itself susceptible to unacceptable interference which might cause malfunction in other components. EMC is achieved by reducing the interference below the level that disrupts the intended operation. EMI shielding requires the housings and enclosures for electronic equipment to be electrically conductive. The shielding effectiveness is a measure of the ability of a material to control radiated electromagnetic energy which is measured in decibel (dB). The conventional method of electromagnetic shielding the electronics is by housing the same inside the metallic enclosure which provides both physical and electromagnetic isolation. However, the disadvantage of the above method is that metals being heavy, add significantly to the weight of an electronic system. Another disadvantage of the above method is that the corrosion rate is accelerated by galvanic action when dissimilar metals arc used in conjunction. Another method known in the art for electromagnetic shielding is by application of certain conducting organic polymer coatings which are known to possess good EMI shielding properties. Such coatings are based on polymers such as polyaniline, polypyrole, polyacetylene, etc applied on insulating polymer surfaces or embedded in polymer matrix. However, the above method has the drawbacks of instability, poor processibility and poor mechanical properties etc. Another disadvantage of such organic polymer based coalings is (lint in dynamic movements, the conducting polymer may chip off and shielding property may be lost. Further disadvantage of the above method is that due to use of matrix media for dispersion of conductive polymers, the uniformity of conductivity is not achieved throughout the composite. Another process known in the art for KM I shielding is Metal/powder composite which provides a discontinuous metal/polymer composite with a metal layer formed from a plurality of fine metal strands. The metal and polymer may be selected so that composite is capable of being thermofornied without loss of electrical conductivity or transparency. The disadvantage of using metal powder is that it increases the weight of the component whereas for aircraft components minimum weight is required. Another disadvantage of using metal powder is that the composite may become prone to corrosion and its properties will get degraded after certain period of time. Another method known in the art involves use of electrically conducting high strength aramid composites fibre prepared by vapour phase polymerisation of pyrole usingferric chloride as an oxidant. The addition of polypyrolc to the aramid composite gives conduction to the composite fibre but its mechanical properties are affected. In the case of air-borne electronic equipment, the need to minimize the weight of equipment is of critical importance. This has resulted in search of light weight, non-metallic materials. Also in case of Naval Warship, light weight non-metallic material having good ballistic properties as well as electromagnetic shielding properties are required in its communication components and operation room. In aircraft application, metallic cabinets arc used for electronic packaging which is generally made of aluminium alloys. There is a need to minimize weight of these cabinets, especially in case of experimental aircraft where a number of electronic equipments are used on board for various studies. Studies on Fibre Reinforced Plastics (FRP) have shown (hat FRP materials can give a weight advantage of 50% over optimally designed aluminium structures. However, the limitation of FRP materials is that while these materials provide weight reduction but they are unable to provide EMI shielding. NEED OF THE PRESENT INVENTION There is therefore need lor Composite malt'iiul mid method for preparation (hereof, which provides composite material which is light weight, provides ballistic protection and EMI shielding in wide frequency range of electromagnetic emissions and which is resistant to corrosion even in humid environment. OBJECTS OF THE PRESENT INVENTION The primary object of the present invention is to provide Carbon aramid fibre reinforced plastic composites and a method for preparation thereof, wherein hybrid composite prepared thereby provides electromagnetic shielding in a wide range of frequencies of EMI emissions in the range of 100-2000MHz. Another object of the present invention is to provide Carbon a ram id fibre reinjorced plastic composites and a method for preparation thereof, wherein hybrid composite material prepared thereby provides ballistic protection, beside EMI shielding. Still another object of the present invention is to provide Carbon aramid fibre reinforced plastic composites and a method for preparation thereof, wherein the hybrid composite prepared thereby has superior mechanical properties. Further object of the present invention is to provide Carbon aramid fibre reinforced plastic composites and a method for preparation thereof, wherein hybrid the composite material prepared thereby are corrosion-resistant. Still further object of the present invention is to provide Carbon aramid fibre reinforced plastic composites and a method for preparation thereof, wherein the hybrid composite prepared thereby retains shielding effectiveness even after prolonged exposure to humid environment like marine environment; Yet further object of the present invention is to provide Carbon aramid fibre reinforced plastic composites and a method for preparation thereof, wherein the carbon aramid hybrid composite prepared thereby retains integrity and shielding effectiveness even after exposure to temperature of the' order of 60-70ºC and humidity of the order of 100%. Even further object of the present invention is to provide Carbon aramid fibre reinforced plastic composites and a method for preparation thereof, wherein the carbon aramid hybrid composite prepared thereby has the EMI shielding effectiveness of the order of 100-80dB at 100MHz to 2000 MHz frequency. Still further object of the present invention is to provide Carbon aramid fibre reinforced plastic composites and a method for preparation thereof, wherein the carbon aramid hydrid composite prepared thereby have high tensile strength and flexural strength and show immunity against small caliber bullets. STATEMENT OF INVENTION w c According to this invention there is provided a method for the preparation of carbon fabric with resin polyvinyl butyral in ethyl alcohol, modified with a modifier phenol formaldehyde and re-modified with a dry modifier hexamine, drying to remove traces of solvent, cutting into pieces, stacking the plies followed by hydraulic pressing of the stacked plies. Further according to this invention there is provided Carbon aramid fibre reinforced plastic composite comprising hydraulic pressed stacked piles of aramid and carbon fabrics coated with resin solution modified with a modifier and remodified with a dry modifier. The present invention relates to carbon aramid fibre reinforced plastic composite and a method for preparation thereof wherein the hybrid composites prepared thereby have higher toughness and superior energy absorption/dissipation capacity. The method oi preparation of composites, used polyvinyl butyral modified by phenol formaldehyde matrix resin which offer ballistic resistance and also shows opacity in the wide frequency range of electromagnetic emissions. The low density ballistic resistant composite of the present invention is environmentally resistant and also maintains shielding effectiveness of the order Of 100 -80dB at 100 to 2000MHz. In the process of the present invention, polyvinyl butyral modified by phenol formaldehyde resin, is further modified by hexamine, which improves the toughness of the composite and enhances the pot life of prepregs. These prepregs are combined to give the composites the property of ballistic resistance as well as the capability of provide opacity in the wide frequency range of Electromagnetic emissions. The processing parameters adopted for making the * composites overcome many shortcomings e.g. non-uniform resin distribution, in-built voids, low adhesion between plies, non-uniform curing etc. of the composites which are normally encountered in the processes of the known art. DESCRIPTION OF METHOD According to the present invention, the method for the preparation of carbon-aramid fibre reinforced plastic composites comprises of the following steps: a) Taking plain weave aramid fabric of (450g/m2 ) and carbon fabric (200g/m2 ) and keeping in oven for about 4-5 hours at 100- 110 ºC to remove the moisture. b) Cooling the fabric obtained by step(a) above to room temperature and then cooling with a 35% (w/w) resin solution in ethyl alcohol where resin used is polyvinyle butyral modified by phenol formaldehyde which has been further modified by a dry modifier, preferably hexamine. (c) Drying the treated fabric obtained by step (b) at room temperature for about 48 hours and removing the excess of solvent by keeping in vacuum oven. (d) Cutting the fabric into pieces, preferably of 30 cm x 30 cm ,prcpreg plies and stacking one over the other having two layers of carbon fabric on top at either side of the composites. Care is taken to keep the fibres in aligned position nnd thereafter again keeping them in a vacuum oven for about 10 minutes to remove the solvent. (e) Keeping the stacked plies between two mild steel plates kept in between PTFE coated glass fabric and heating, at slow rate, at about 160-165° C for about 2 hours at a pressure of 6.9 Mpa. (f) Taking out the laminate from the press after cooling and cutting its sides using diamond cutting saw using a cooling medium like water. The different constituents of the carbon aramid fibre composite of the present invention has synergic effect on each other as the ballistic protection and EMI shielding capability provided by the composite is not possessed by any of the individual constituents of the present invention The method of the present invention will now be illustrated with a working example which is intended to be a typical example to illustrate the working of the invention and is not intended to be taken restrictively to imply any limitation on the scope of the invention. EXAMPLE 12 meters of Aramid F'abric(450g/m2 ) woven roving plain weave and 2 meters of carbon fabric (200g/m2) plain weave were taken and kept in over at 100° C for 4 hours. The fabric was then allowed to cool at room temperature. The resin Polyvinyl butyralPVB) modified with phenol formaldehyde and further modified with hexamine, was dissolved in distilled ethyl alcohol solution so that 20% (w/w) resin content should be obtained from the prepegs. The fabrics were coated with the developed resin from both the sides and then allowed to dry at room temperature for 48 hours. This was then kept in vacuum oven for removal of the left out solvent. The fabric was cut into pieces of size 300 mm x 300 mm and plies of such fabric were taken and stacked one over the other to build lamination of different thickness. Care was taken to keep carbon layers (3-4) on top on either sides. The stacked plies were kept between two MS plates and were then placed between two plates of a hydraulic press and the temperature was applied gradually and raised to 160° C for 2 hours. The heating was kept slow so as to maintain uniform temperature throughout the laminate. The pressure of thc plate was kepi at 1000 psi (6.9 Mpa). The plates were then allowed to cool in the press itself after switching off. The pressure was then released. The plates were taken out from the press. The desired laminate was obtained. Shielding effectiveness was determined using coaxial jig process as normally carried out. The finished product on evaluation exhibits the following properties as given in Table 1 to 4:- Table 1 Mechanical properties of Carbon/Aramid/Phcnolic Composite of present invention as compared to known Aramid/glass/phenolic composite (Table Removed) Table 2 Ballistic Performance for Carbon - Aramid - Phenolic Composites (Table Removed) Table 3 Shielding Effectiveness Performance revaluation of Carbon-Aramid-Phenolic Composites (Table Removed) Table 4 Environmental test results of the Carbon-Aramid-Phenolic Composite after high temperature & humidity (Table Removed) It is to be understood that the method of the present invention is susceptible to adaptations, changes, modifications by those skilled in the art. Such changes, nodifications, adaptions, are intended to be within the scope of the present invention which is set forth by the following claims: WE CLAIM: 1. A method for the preparation of carbon aramid fibre reinforced plastic composites comprising of coating carbon aramid fabric with resin polyvinyl butyral in ethyl alcohol, modified with a modifier phenol formaldehyde and re-modified with a dry modifier hexamine, drying to remove traces of solvent, cutting into pieces, stacking the plies followed by hydraulic pressing of the stacked plies. 2. The method as claimed in claim 1 wherein the said drying of the aramid and carbon fabric is done preferably at 100-110°C for 4-5 hours to remove moisture. 3. A method as claimed in claim 1 wherein hydraulic processing of stacked plies of resin coated carbon and aramid fibres is carried out at preferably 6.9 Mpa at around 160°C to 165°C for about 2 hours. 4. A method for the preparation of carbon aramid fibre reinforced plastic composites substantially described and illustrated herein.

Documents:

141-del-2000-abstract.pdf

141-del-2000-claims.pdf

141-del-2000-correspondence-others.pdf

141-del-2000-correspondence-po.pdf

141-del-2000-description (complete).pdf

141-del-2000-form-1.pdf

141-del-2000-form-19.pdf

141-del-2000-form-2.pdf

141-DEL-2000-Form-3.pdf

141-del-2000-gpa.pdf