Title of Invention

A PLASMA PROCESS FOR SURFACE MODIFICATION OF BRASS FOR BRASS TO RUBBER BONDING

Abstract

A plasma process for surface modification of brass for brass to rubber bonding, which comprises the following steps: a) holding the brass article in a vacuum maintaining sub atmospheric pressure in the range of 10 torrto 5 X 10‾³; b) introducing a gas in an enclosed space for generating oxidative plasma between brass article surface supported on a cathode and an electrode at ground potential and said being in an enclosed space; c)supplying electric power to the said electrodes d) the gas being directed from plasma generating region towards the surface of brass to be treated so that the gas impinges against the brass surface for effecting surface modification for bonding with rubber.

Full Text

FORM 2THE PATENTS ACT, 1970(39 of 1970)& The Patents Rules, 2003COMPLETE SPECIFICATION [See Section 10 and rule 13] 1. TITLE OF THE INVENTION : "A PLASMA PROCESS MODIFICATION OF BRASS FOR BRASS TO RUBBER BONDING" FOR SURFACE 2. APPLICANT(S)(a) NAME: INSTITUTE FOR PLASMA RESEARCH(b) NATIONALITY: INDIAN(c) ADDRESS : A Government of India body, of B-15-17/P, Sector-25,Estate, Gandhinagar - 382 044 Gujarat, India. GIDC Electronics 3. PREAMBLE TO THE DESCRIPTION COMPLETEThe following specification particularly describes the invention and the manner in which it is to be performed. DESCRIPTION FIELD OF INVENTION This invention relates to an environment friendly plasma process that activates the brass surface. It provides nano-structured dendrites and partially oxidizes the brass surface, which improve the metal to rubber bonding. The novel plasma process is cost effective and provides excellent rubber to brass bonding after the surface modification of brass. BACKGROUND OF INVENTION Use of chemicals (solvents, acids etc.) is a common practice in industries to clean and activate the surface of metals and alloys (brass). The clean and activated surface is required to get good bonding with the adhesive/rubber. The chemicals provide non-uniform etching as well as pollute the environment. The chemicals used to activate the surface of brass should be disposed off safely using effluent treatment plant. This makes the process quite cumbersome. The industries are facing tough problems because the government rules are becoming stringent for polluting processes. For cleaning purpose one can use ultrasonic cleaners. It has been observed that it cleans the surface to a certain extent only. In order to improve metal to metal or metal to polymer or rubber bonding, it requires other treatments Advanced techniques such as laser, dielectric barrier discharge, corona discharge, atmospheric pressure plasma torches, inductive plasmas etc. can be used for the cleaning and surface activation purpose. However, these techniques are either not suitable for three-dimensional objects or they are expensive. To overcome the basic problems a plasma process is developed which is environment friendly, cost effective and provides excellent rubber to brass bonding after the surface modification of brass. PRIOR ART Generally, specific primers and adhesives are used for bonding of rubbers to metal. In order to reduce the emissions of volatile organic compounds, a large number of aqueous rubber to metal adhesives were commercialized. The rubber to metal bonding mechanism is very complex as there are several reactions occur simultaneously that is in a short duration. An important requirement for good bonding is proper surface preparation of metal in particular brass. In 1862, Sanderson submitted a British patent application describing the use of electro-deposited brass as an intermediary for bonding rubber to steel. L. Daft patented in US -for alloys containing antimony and claimed that the use of alloys of copper and zinc with bismuth and arsenic form bonding with rubber during vulcanization process. Different researchers reviewed rubber to brass bonding topic. Van Ooij described rubber to brass bonding for tyre applications and used organic plasma polymerized films as primers for bonding steel to rubber and for the first time got good rubber to steel bonding using organofunctional silanes. Various examples results revealed that reaction of brass with rubber results in the formation of both CuxS and ZnS. The amount of CuxS formed must be carefully controlled. It improves the adhesion as a result of a catalytic effect on the rubber vulcanization. However, excessive CuxS formation leads to embrittlement of the interfacial CuxS/ZnS film and a loss of adhesion. Formation of CuxS during the vulcanization is very important and can be explained on the basis of the cohesive strength of epitaxial CuxS films as a function of their thickness. Thin films are strong and adherent, but they change their composition and modification as they grow thicker. Their cohesive strength decreases with thickness due to lattice contraction. The optimum CuxS film thickness is of the order of 30-40 nm. The surface modification of brass using oxidizing plasma is not explored in any prior art to improve rubber to brass bonding. We have developed a plasma process to oxidize the brass surface to enhance rubber to brass bonding. OBJECT OF THE INVENTION The prime object of the present invention is to propose a plasma process for surface modification of brass for brass to rubber bonding which increases the surface area by providing a nano structured dentrides and also partially oxidizes the brass surface. Another object of the present invention is to propose a plasma process for surface modification of brass for brass to rubber bonding which is environment friendly and cost effective. Further object of the present invention is to propose a plasma process for surface modification of brass for brass to rubber bonding which is suitable for three dimensional objects at low cost. DETAILED DESCRIPTION OF INVENTION The brass surface preparation involves two main steps: (i) cleaning step to remove dirt, oil and other surface contaminants using degreasing agents (ii) surface activation of brass. The surface activation involves: (a) removal of contaminants such as rust, scale and pre-existing corrosion by products, which are bound to the metal surface, (b) increase the surface area of the brass to provide an active surface for bonding. Conventionally, chemicals and adhesives are used to get good bonding between metal and rubber. Recently, plasma polymerized organo-functional coatings were applied on metal to improve metal to rubber bonding. Mechanism of brass-ruhber bonding: Brass reacts with sulfur-containing intermediates resulting in the formation of interfacial non-stoichiometric sulfides. During vulcanization, brass is corroded by sulfur-containing species resulting in the formation of duplex sulfide films. The sulfide film consists of non-stoichiometric CuxS at the sulfide-rubber interface and ZnS at the sulfide-metal interface. These sulfides, especially the CuxS, grow into the rubber matrix when it is in the flowing condition during the process of vulcanization. Optimum time should be available for these sulfide dendrites to grow into the rubber matrix. Further, this rubber-brass bond is very durable and has high resistance to dynamic and thermal aging (during service, the inside of the tire can reach a temperature of about 120°C). According to the present invention there is provided a plasma process for surface modification of brass for brass to rubber bonding, which comprises the following steps: a) holding the brass article in a vacuum maintaining sub atmospheric pressure in the range of 10 torrto5X10-3; b) introducing a gas in an enclosed space for generating oxidative plasma between brass article surface supported on a cathode and an electrode at ground potential and said being in an enclosed space; c) supplying electric power to the said electrodes d) the gas being directed from plasma generating region towards the surface of brass to be treated so that the gas impinges against the brass surface for effecting surface modification for bonding with rubber. According to another aspect of the present invention there is provided an apparatus for modification of the brass surface by oxidative plasma for brass to rubber bonding which comprises a vacuum chamber, connected to a vacuum pump for maintaining sub atmospheric pressure in the range of 10 torr to 5 X 10-3 , a cathode working as brass article surface mounting device, and electrode at ground potential and said electrodes are fitted in the said chamber to generate oxidative plasma and connected to a means for supply of electric power,a means for supply gas between a electrodes, the means for gas supply configured to direct gas from plasma generating region towards the surface of brass article to be treated to enable gas to impinge against the brass surface for providing nano structured dendrites and so increase surface area for effecting surface modification of brass for brass to rubber bonding. DETAILS OF FIGURES. Figure 1 shows a schematic diagram of plasma equipment Figure 1 shows a schematic diagram of plasma equipment used to modify the surface of brass used for three dimensional articles for example valves for brass to rubber bonding. Apparatus consists of a cathode (1) working as (brass)valve mounting device, electrode (2) is at ground potential, power supply by a power supply means (3), vacuum chamber(4) of steel, a gas feeding means (5) for generating oxidative plasma. The power supply means is DC, AC, pulsed DC, low or medium frequency or radio frequency power supply for treatment of brass valve for brass to rubber bonding. The suitable distance between the valve and the cathode working as mounting device is maintained in the range from 1 to 10 cm. Gas feeding means is a gas source having any one of the gas; nitrogen, air, hydrogen, hydrogen oxide, carbon dioxide, carbon tetra chloride, and any other gas which is generating oxidative plasma. The said gas source is connected by a pipe to the vacuum chamber, The temperature in the vacuum chamber is maintained such that the brass valve is maintained at the temperature in the range of 50 top 100°C for good bonding with rubber. The subatmospheric pressure in the vacuum chamber is maintained in between from 10 torr to 5 X 10-3 . preferably 10 torr to 1 X 10-2 by a vacuum pump (6). Brass used in the valve must have 55% to 75 % copper. The rubber used for molding must have 0.5% to 5% sulphur content. The modification of the brass surface with oxidative plasma, will provide nano structured dendrites and so increase surface area for effecting surface modification of brass for brass to rubber bonding .After modification of the brass surface molding of rubber is obtained by maintaining the temperature during the process from 100 °C to 200°C for time period 10 to 60 minutes. Finally aging of the valve is done at elevated temperature from 60°C to 200°C for 1 to 6 hours. A plasma process for surface modification of brass for rubber-brass bonding, is obtained by (a)holding the three dimensional brass articles such as valves in a vacuum maintaining sub atmospheric pressure in the range of 10 torr to 5 X 10-3 by a vacuum pump;(b) introducing a gas for generating oxidative plasma between brass surface as cathode and an electrode at ground potential and said being in an enclosed space;(c) supplying electric power to the said electrodes;(d) the gas being directed from plasma generating region towards the surface of brass to be treated so that the gas impinges against the brass surface for effecting surface modification for bonding with rubber and then molding rubber on the brass surface at temperature from 100°C to 200°C for 10 to 60 minutes. The brass articles (valves) are exposed to oxidative plasma that oxidized Cu and Zn partially and provide specific nano-structure at the brass surface. The formation of non-stoichiometric copper oxide and the specific surface morphology plays very important role in improving brass to rubber bonding. After the process optimization we did not observe the failure of rubber to brass bond in the plier test which was conducted few thousand times. Experimental procedure: Pre-cleaned three dimensional brass articles such as valves are placed on a specially designed valve mounting arrangement. The arrangement is placed in a vacuum chamber and works as cathode. The top electrode is at ground potential (It is shown in Figure). The chamber is evacuated by a vacuum pump to sub-atmospheric pressure (1X10-2 torr). Plasma forming gas is introduced in the chamber and plasma is generated using a power supply. The valves are exposed in the plasma for particular time duration (10 -60 minutes). Subsequently, the valves are molded with the rubber. Chemical reactions: Cu/Zn+ oxidative plasma Þ CuxO + ZnxO ….(I) CuxO + Sx -Rubber Þ CuxS -Rubber ....(2) (At the brass surface) WE CLAIM: l.A plasma process for surface modification of brass for brass to rubber bonding, said process comprising the following steps: a) holding the brass article in a vacuum maintaining sub atmospheric pressure in the range of 10 torrto5X10-3; b) introducing a gas in an enclosed space,for generating oxidative plasma between brass article surface supported on a cathode and an electrode at ground potential c) supplying electric power to the said electrodes d) the gas being directed from plasma generating region towards the surface of brass to be treated so that the gas impinges against the brass surface for effecting surface modification for bonding with rubber. 2. A plasma process as claimed in claim 1 where in gas for generating oxidative plasma is Nitrogen, Argon, Air, Oxygen, H20, C02 or any gas for oxidative plasma. 3. A plasma process as claimed in claim 1 where in sub atmospheric pressure in the said enclosed is 10 torr tol X 10-2 . 4. A plasma process as claimed in claim 1 where in brass surface is kept at elevated temperature ranging from 50 to 100 °C. 5. A plasma process as claimed in claim 1 where in rubber used for bonding is having sulphur content as 0.5% to 5%. 6. An apparatus for modification of the brass surface by oxidative plasma for brass to rubber bonding comprising a vacuum chamber, connected to a vacuum pump for maintaining sub atmospheric pressure in the range of 10 torr to 5 X 10-3 , a cathode working as brass article surface mounting device, and electrode at ground potential and said electrodes are fitted in the said chamber to generate oxidative plasma and connected to a means for supply of electric power,a means for supply gas between a electrodes, the means for gas supply configured to direct gas from plasma generating region towards the surface of brass article to be treated to enable gas to impinge against the brass surface for providing nano structured dendrites and so increase surface area for effecting surface modification of brass for brass to rubber bonding. 7 An apparatus for modification of the brass surface as claimed in claim & used for three dimensional article such as valve. 8. A plasma process for surface modification of brass for brass to rubber bonding substentially as herein before described with the help of accompanying drawing. 9.An apparatus for modification of the brass surface by oxidative plasma for brass to rubber bonding substentially as herein before described with the help of accompanying drawing. Dated this 29th day of June, 2006 (R. C. DHAWAN) OF LALL LAHIRI & SALHOTRA AGENT FOR THE APPLICANTS ABSTRACT A PLASMA PROCESS FOR SURFACE MODIFICATION OF BRASS FOR BRASS TO RUBBER BONDING A plasma process for surface modification of brass for brass to rubber bonding, which comprises the following steps: a) holding the brass article in a vacuum maintaining sub atmospheric pressure in the range of 10torrto5X10-3; b) introducing a gas in an enclosed space for generating oxidative plasma between brass article surface supported on a cathode and an electrode at ground potential and said being in an enclosed space; c) supplying electric power to the said electrodes d) the gas being directed from plasma generating region towards the surface of brass to be treated so that the gas impinges against the brass surface for effecting surface modification for bonding with rubber.

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1044-MUM-2006-CLAIMS(30-6-2006).pdf

1044-MUM-2006-CLAIMS(AMENDED)-(6-5-2013).pdf

1044-mum-2006-claims.doc

1044-mum-2006-claims.pdf

1044-mum-2006-correspondance-received.pdf

1044-MUM-2006-CORRESPONDENCE(14-8-2006).pdf

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1044-MUM-2006-CORRESPONDENCE(IPO)-(30-6-2006).pdf

1044-mum-2006-description (complete).pdf

1044-MUM-2006-DRAWING(30-6-2006).pdf

1044-MUM-2006-FORM 1(2-6-2010).pdf

1044-MUM-2006-FORM 18(2-6-2010).pdf

1044-MUM-2006-FORM 2(COMPLETE)-(30-6-2006).pdf

1044-MUM-2006-FORM 2(TITLE PAGE)-(30-6-2006).pdf

1044-MUM-2006-FORM 2(TITLE PAGE)-(6-5-2013).pdf

1044-MUM-2006-FORM 26(14-8-2006).pdf

1044-mum-2006-form-1.pdf

1044-mum-2006-form-2.doc

1044-mum-2006-form-2.pdf

1044-mum-2006-form-3.pdf

1044-MUM-2006-REPLY TO EXAMINATION REPORT(6-5-2013).pdf

1044-MUM-2006-SPECIFICATION(AMENDED)-(6-5-2013).pdf

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1044-MUM-2006DESCRIPTION(COMPLETE)-(30-6-2006).pdf