Stock material or miscellaneous articles – Composite – Of metal
Reexamination Certificate
2001-11-15
2003-12-23
Jackson, Monique R. (Department: 1773)
Stock material or miscellaneous articles
Composite
Of metal
C428S450000, C428S457000, C428S461000, C428S462000, C427S387000, C427S388100, C427S388400, C524S261000, C524S377000, C524S417000, C524S429000
Reexamination Certificate
active
06667105
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a coating composition for forming insulating films, a non-oriented electrical steel sheet with the coating composition coated thereon, and a method for forming the insulating films on the steel sheet. More specifically the present invention relates to an organic-inorgarnic mixed coating composition for forming insulating films, a non-oriented electrical steel sheet with the coating composition coated thereon, and a method for forming the insulating films on the steel sheet, in which the roll spreading workability and the films characteristics are superior, and the aesthetics is excellent.
BACKGROUND OF THE INVENTION
Generally, non-oriented electrical steel sheets are used as the steel core for small electric motors and for transformers. These non-oriented electrical steel sheets are coated with insulating films before being supplied to users, so that the power loss due to the generation of eddy currents can be minimized.
The non-oriented electrical steel sheets which are supplied to the users after forming the insulating films generally undergo further processing, such as punching, high temperature annealing for relieving stress, automatic stacking, welding and the like so as to provide a shape to the steel sheets.
During the high temperature annealing for relieving the stress, the insulating films should not peel off, and should be highly heat resistant so as to maintain its insulating properties even at a high temperature. Further, the non-oriented electrical steel sheets are supplied directly to the users after forming the insulating films, and therefore, the aesthetics of the steel sheets has to be superior. In addition, it is required that the film adherence, corrosion resistance and continuous roll spreading workability be superior.
The conventional insulating films which are coated on non-oriented electrical steel sheets are roughly classified into: organic, inorganic, and organic-inorganic mixed insulating films.
The inorganic insulating films are superior in heat resistance compared with the organic and organic-inorganic mixed insulating films, but the punchability is not adequate. The organic insulating films are superior in punchability and adherence, but the films decompose and are destroyed during stress relieving annealing, with the result that the film adherence is aggravated.
Accordingly, there has been a demand for the development of organic-inorganic mixed insulating films which have the merits of the inorganic insulating films and the organic insulating films. Examples of this are disclosed in Korean Patents 25106, 31208 and 31219.
The composition of the organic-inorganic mixed insulating films generally contains chromic acid so as to ensure the requisite characteristics such as corrosion resistance, adherence and the like. Chromic acid thus contained not only gives harmful effects to humans during the manufacture of the coating composition and during the coating operation, but also causes environmental contamination such as water contamination and the like.
Accordingly, there has been researched and developed an insulating film which does not contain the chrome compound, and one example of this is disclosed in Japanese Patent Application Laid-open No. Hei-6-330338. In this technique, the main ingredient is an emulsion of primary aluminum phosphate and an organic resin having a particle size of 0.3~3.0 &mgr;m. Further, there are added boric acid and colloidal silica. Particularly, the particle size of the organic resin is controlled so that the heat resistance and the like can be improved.
Other examples in which the chrome compound is excluded are Japanese Patent Application Laid-open No. Hei-7-41913 and Hei-7-166365. In these cases, the main ingredients are an organic resin of a particle size of 0.3~3.0 &mgr;m and one or two selected from the group consisting of: aluminum phosphate, calcium phosphate and zinc phosphate. Further, boric acid is added.
The above techniques do not contain a chrome compound, and therefore, the films are said to be environmentally friendly, as well as being not harmful to humans, but their aesthetics are not desirable.
SUMMARY OF THE INVENTION
The present invention is intended to overcome the above described disadvantages of the conventional techniques.
Therefore it is an object of the present invention to provide an organic-inorganic mixed coating composition for forming an insulating film, in which the main ingredient is a phosphate and an acid-soluble emulsion type acrylic-syrenic copolymer, and there are further added the optimum amounts of elements for improving the coating characteristics, thereby making the roll spreading workability, the film characteristics and the aesthetics superior, as well as preventing the environment from being contaminated.
It is another object of the present invention to provide a non-oriented electrical steel sheet in which the coating composition composed of the ingredients is coated thereon, and therefore, the insulating properties of the coated film are superior, and the aesthetics is excellent.
It is still another object of the present invention to provide a method for forming the insulating films on non-oriented electrical steel sheet, in which the same properties as mentioned above are obtained.
Conventional coating compositions in which a chrome compound is used are not only harmful to humans, but also are undesirable environmentally. Therefore, organic-inorganic mixed coating compositions have been developed in which the use of the chrome compound is excluded. However, there is a limit to forming a reliable insulating film having superior film characteristics.
Accordingly, the present inventors carried out repeated research and studies to develop an organic-inorganic coating composition in which the use of the chrome compound is excluded, and in which superior film characteristics can be obtained. As a result, the inventors found that there can be obtained superior film characteristics if the main ingredients are composed of organic-inorganic mixed substances consisting of a phosphate and a low foamable and acid-soluble emulsion-type acrylic-styrenic copolymer resin, and if additives such as zinc nitrate, silicon, a non-ionic surfactant, and ethylene glycol are added in proper amounts.
In the present invention, the above cited additives are added in proper amounts to the main ingredients composed of organic-inorganic mixed substances consisting of a phosphate and a low foamable and acid-soluble emulsion-type acrylic-styrenic copolymer resin. Thus, when the coating composition is spread on the electrical steel sheet, the respective additives act to solidify the phosphate and the acrylic resin, and act to form an insoluble film exhibiting superior aesthetics. The superior film characteristics and continuous roll spreading workability cannot be obtained by simply using the respective additives. The proper proportions of each additive must be used to obtain these superior results.
In achieving the above objects, the coating composition according to the present invention includes for each 100 g of phosphoric acid of a primary aluminum phosphate solution: 28~98 g (solid weight) of an acid-soluble emulsion type acrylic-styrenic copolymer resin; 6~18 g of zinc nitrate; 4~13 g of a silicon additive; 18~35 g of ethylene glycol; and 3~11 g of non-ionic surfactant.
In another aspect of the present invention, the non-oriented electrical steel sheet according to the present invention is coated with the above coating composition.
In still another aspect of the present invention, the method for coating the insulating film according to the present invention includes the steps of: preparing a coating composition by adding the above stated ingredients; spreading the coating composition on a non-oriented electrical steel sheet; and subjecting the electrical steel sheet (thus coated) to a heat treatment at a temperature of 150~800° C. for 14~45 seconds.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
First, the coating composition for forming an ins
Chang Sam-Kyu
Lee Seok-Joo
Yoo Young-Jong
Jackson Monique R.
Pohang Iron & Steel Co. Ltd.
Webb Ziesenheim & Logsdon Orkin & Hanson, P.C.
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