|Title of Invention||
A PROCESS FOR THE ELECTRO DEPOSITION OF EXPOXY RESINS OVER METALLIC SUBSTRATES
|Abstract||Electrodeposition of epoxy resin over mild steel and aluminium which comprises applying a voltage of 50-200V through a bath prepared by the process such as herein described, where the anode to be coated is mild steel or aluminium and cathode is mild steel, passing the current for a period ranging from 1-2 minutes at a temperature in the range of 30-35°C rinsing with deionised water and baking at a temperature in the range of 130 to 150°C for a period ranging from 20 to 30 minutes.|
|Full Text||This invention relates to a process for electrodeposition of epoxy resin over metallic substrates. The deposition is carried out using a bath containing novel epoxy ester resin.
A few water soluble resins are available for electrodeposition, like linseed oil maleic anhydride resins, castor oil maleic anhydride resins, alkyd resins shellac etc. They have got poor corrosion resistance of less than 500 hrs in salt spray chamber. Hence there is a need to develop resins which will produce coatings with better properties such as epoxy esters which possess desirable corrosion resistant and weather-resistant properties.
A process for the preparation of novel epoxy ester resins having better corrosion resistance and weather resistance properties is a subject matter of our copending application No.864/D/90 from which this application has been divided out. An electrodeposition bath containing novel epoxy resin which is useful for the electrodeposition of the primer on mild steel or aluminium is made a subject matter of our application No.426/DEL/95 which has also been divided out of application No.864/D/90. The object of the present invention is to provide a process for the electrodeposition of a primer on mild steel or aluminium using the said bath. The coatings obtained by the electrodeposition have the desired properties like hardness, flexibility and corrosion resistance. These are useful as primer coatings for automobile components.
Accordingly, the present invention provides a process for the preparation of new epoxy resins useful for electrodeposition on mild steel or aluminium is prepared by reacting 100-150 parts by weight of an epoxy resin having an epoxy equivalent of 450-900, 40-60 parts of butyl cellosolve, 10-30 parts of propylene glycol, 50-75 parts of linseed fatty acid and 10-20 parts of maleic anhydride at a temperature in the range of 140°C - 170°C. The new resin produced by the above said process in be used for the preparation of bath useful for electrodepositing the resin on to metal substrate to prevent corrosion.
The electrodeposition bath is prepared by adding an organic amine to the resin prepared by the process described above and dissolving in deionised water, the pH of the resulting bath being adjusted in the range of 7.0 to 7.5.
The organic amine used for the preparation of the bath may be selected for triethanol amine, triethyl amine.
Accordingly the invention provides a process for the electrodeposition of epoxy resin over metallic substrates which comprises applying a voltage of 100-200 V through bath prepared by the process as claimed in copending application such as herein described, passing the current for a period ranging from 1-2 minutes ,rinsing with deionized water and baking at a temperature in the range of 100 to 150°C for a period ranging from 20-30 minutes.
The coating thus obtained is found to be uniform and adherent with a thickness of 25-30 um.
The invention is illustrated by the following examples which should not be construed to limit the size of the invention. Example: 1
This example relates to the preparation of resin:
100 parts of epoxy resin, 40 parts of butyl cellosolve and 12 parts of propylene glycol are refluxed along with 50 parts of linseed fatty acid at a temperature of 160°C for 60 mts. The temperature is then reduced to 130°C and 20 parts of maleic anhydride added and again refluxed for 60-90 mts at 140 °C. Then it is allowed to cool to produce water soluble resin.
10 parts of the above said resin is solubilised in water by adding 1 part otriethanol amine to make upto 100 parts; the pH being 7.5 which forms rhe systematic electrodeposition bath. From this bath, anodic electrodeposition is
carried out on mild steel and aluminium sheets by applying a voltage of 100 using the sheet to be coated as the anode and mild steel plate as the cathode, the coating time being 2 mts at a temperature of 30°C-35°C. Acid pickled and sand blasted mild steel substrates can be used ana in the case of aluminium alkali cleaning is done prior to electrodeposition. The coating is then rinsed with deionised water and baked at 150°C for 20 mts. The coating is then rinsed with deionised water and baked at 150°C for 20 mts. The coating thus obtained is uniform and adherent with a thickness of 25-30 urn.
Example : 3
To the bath described in example 2, is added 4 parts of micaceous iron oxide pigment and dispersed well and electrocoating taken at a voltage of 100 V for 2 mts at a temperature of 30-35°C. The coating is then baked at 130°C for 20 mts. A reddish brown deposit is obtained. The coating has got a thickness of 25 and withstands salt spray test for over 500 hrs.
Example : 4
The bath described in example 2 is pigmented with 3-5 parts rutile titanium dioxide pigment. Electrodeposition is carried out at 150 volts for 2 mts. A white coating is obtained on mild steel or aluminium with a thickness of 25 um.
The process of the present invention produces electrocoatings with more corrosion resistance (more than 500 hours salt spray resistance) than the electrocoatings produced by the processes already developed earlier (less than 500 hours salt spray resistance).
1. A a process for the electrodeposition of epoxy resin over metallic substrates which comprises applying a voltage of 100-200 V through bath prepared by the process as claimed in copending application such as herein described, passing the current for a period ranging from 1-2 minutes ,rinsing with deionized water and baking at a temperature in the range of 100 to 150°C for a period ranging from 20-30 minutes.
2. A process for the electrodeposition of epoxy resin over metallic substrates substantially as here in described with reference to the examples 2 & 4.
|Indian Patent Application Number||425/DEL/1995|
|PG Journal Number||33/2003|
|Date of Filing||14-Mar-1995|
|Name of Patentee||COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH|
|Applicant Address||RAFI MARG, NEW DELHI-110001 INDIA|
|PCT International Classification Number||C23C 20/00|
|PCT International Application Number||N/A|
|PCT International Filing date|