Process for the production of electrically insulating coatings o

Coating processes – Electrical product produced – Motor stator or core for winding

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Details

4272071, 427247, 427410, 4273884, C23C 2600

Patent

active

049420615

DESCRIPTION:

BRIEF SUMMARY
DESCRIPTION

This invention relates to a process of forming electrically insulating coatings on metallic surfaces and the use of that process for the production of electrically insulating coatings on metallic surfaces of silicon-containing steel.
This invention relates to a process of applying an electrically insulating layer to sheet steel by means of a resin-containing aqueous treating liquor, which is dried when it has been applied.
In the manufacture of iron cores, e.g., for motors, transformers and the like, it is known to provide electric sheet steel with an insulating layer, subsequently to blank the sheet steel, to stack the blanks and optionally to join them by welding at their cut edges.
Such insulating layers may be inorganic or organic and may be formed, e.g., by means of treating liquors which contain chromic acid and/or phsophoric acid and/or phosphates. Whereas such layers usually have a satisfactory insulating resistance, the wear of the blanking tools will generally be relatively high in such cases and the use of chromic acid is not desirable from the aspect of work place, hygiene and from an ecological aspect.
Insulating layers of another kind are formed by an application of treating liquors which contain organic resins and optional inorganic additives and will result in a longer edge life of the tools in many cases but their bond strength after the stress-relieving annealing and their influence on the formation of the seam weld are unsatisfactory, as a rule. Insulating layers of a still further kind are formed by an application of treating liquors based on organic resins which contain fluorides of polyvalent metals, particularly aluminum fluoride and will not permit a satisfactory welding of the coated sheets if the thickness of the insulation exceeds a certain upper limit. Besides, the combustion of insulating layers consisting of combinations of organic resins and fluorides of polyvalent metals, e.g., during conventional welding operations, may result in a release of pollutants (EP-A-209,940).
It is an object of the invention to provide for the formation of electrically insulating coatings on metallic surfaces, particularly of silicon-containing steel, a process which minimizes at least some of the disadvantages of the abovementioned processes which are known in the art.
In order to accomplish that object the process which has been described first hereinbefore is carried out in such a manner in accordance with the invention that an aqueous preparation which contains
(a) water-dilutable synthetic resin,
(b) a dispersed waxlike substance having a particle size between 0.1 and 20 .mu.m and a melting point between 80.degree. and 250.degree. C.,
(c) inorganic and/or organic pigment,
(d) borate,
(e) alkali metal hydroxide and/or ammonia and/or organic amine for adjusting a pH value between 7 to 9 quantity between 0.5 and 20 g/m.sup.2 (calculated as solids) and the moist film is subsequently dried at a (substrate) temperature between 120.degree. and 350.degree. for a time between 1 hour and 5 seconds.
In that context the term "drying" means primarily that the solvent contained in the preparation is evaporated but does not exclude the occurrence, e.g., of chemical reactions in or between the components of the preparation, such as cross-linking reactions, curing reactions and the like, and between said components and the metallic surface.
The process in accordance with the invention can be used to treat the surfaces of a very wide range of metals and has special significance for the formation of coatings on iron and ferrous alloys, particularly alloys which contain silicon as an alloying constituent, and of other substrates which are known as magnetic materials. Whereas the material to be insulated is usually provided as sheet metal in the form of strip or sheets, the process in accordance with the invention can also be applied to workpieces having other shapes.
An essential component of the aqueous preparation used in the process in accordance with the invention is a synthetic resin which can

REFERENCES:
patent: 3231462 (1966-01-01), Oswald
patent: 3642530 (1972-02-01), Webb
patent: 4268578 (1981-05-01), Bordini
patent: 4366185 (1982-12-01), Tanaka
patent: 4383055 (1983-05-01), Johannes
patent: 4510199 (1985-04-01), Brooken
patent: 4542070 (1985-09-01), Ohtani

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