KR100530066B1 - Insulating film composition having improved appearance and coating property and method for forming an insulating film on a nonoriented silicon steel sheet using it - Google Patents

Abstract

The present invention relates to a coating composition used for forming an insulating coating of non-oriented electrical steel sheet and a method for forming an insulating coating using the same. An organic / inorganic mixed coating composition for forming an insulating coating having excellent coating workability and coating properties, and non-oriented using the same. It is an object of the present invention to provide a method for forming an insulating film of electrical steel sheet.

According to the present invention, 12-68 g of an aqueous type of chromic acid-based acrylic resin, 5-27 g of glycerin and a non-silicone leveling organic additive per 100 g of chromate (CrO ₃ ) in a chromate solution containing boric acid 3.5 to 6.1% by weight A coating composition made up by the addition of 0.9-9.4 g is provided. In addition, the coating composition is applied to the surface of the non-oriented electrical steel sheet so that the dry coating thickness is in the range of 0.7-2.8 ㎛ per side and heat-treated at a temperature of 370-800 ℃ for 10-70 seconds to form an insulating film Provided is a method for forming an insulating coating of an non-oriented electrical steel sheet.

According to the present invention, even after the stress relief annealing, an insulating coating that provides excellent appearance and insulation, adhesion, corrosion resistance, weldability, and the like can be formed on the surface of the non-oriented electrical steel sheet.

Description

INSULATING FILM COMPOSITION HAVING IMPROVED APPEARANCE AND COATING PROPERTY AND METHOD FOR FORMING AN INSULATING FILM ON A NONORIENTED SILICON STEEL SHEET USING IT}

The present invention relates to an organic and inorganic composite insulating film forming composition composed of chromate and an aqueous solution type of chromic acid resistant acrylic resin, and a method of forming an insulating film on the surface of a non-oriented electrical steel sheet using the same. The present invention relates to an insulating film forming composition having excellent appearance and continuous roll coating workability without streaking after stress relief annealing (SRA) on a surface of a steel sheet and a method for forming an insulating film using the same.

Non-oriented electrical steel sheets used as iron cores for electric machines such as small electric motors and transformers are provided to the demand after forming an insulating film on the surface to suppress eddy currents and minimize power loss. Coil-oriented non-oriented electrical steel sheet, which is available on demand, is usually used for forming a series of iron cores, such as punching, stress relief annealing for the purpose of stress relief annealing, automatic lamination and welding, etc. Do the work. Therefore, the insulating film is required to improve the work productivity due to the no peeling of the formed film during the stress relief heat treatment carried out at a high temperature and heat resistance to maintain intrinsic electrical insulation. In addition, a beautiful appearance is required in consideration of the fact that the coating process for forming the insulating film is a finishing process for finally providing the electrical steel sheet product to the demand price. In addition, it is required to have excellent adhesion, weldability, corrosion resistance, and continuous roll coating workability.

Insulation coating formation coating composition that requires such characteristics are classified into three types, organic, inorganic and organic-inorganic mixture, and the coating is formed by supplying the treatment liquid continuously to the surface of the electrical steel sheet and then applying and drying. The dual organic-inorganic mixed composition has both the advantages of the inorganic coating composition and the advantages of the organic coating composition.

Currently, research on the coating composition for forming an insulating coating which can secure the advantages of the inorganic coating composition and the organic coating composition at the same time has been conducted. As a part of the research, the present inventors have disclosed Korean Patent Application No. 86-10301. Proposed as shown in The coating composition proposed in Patent Application No. 86-10301 has good general coating properties of the inorganic and organic mixed compositions. First, however, foaming is generated from the solution storage tank under the cotarol, which supplies and recovers the coating composition solution according to the recent improvement of the working environment, such as the increase in the size of cotarol and the high speed of work progress. If the work is carried out in the same time, the continuous roll coating work that shows surface defects is impossible. Second, the appearance of fine streaks on the surface during stress relief annealing of electrical steel products causes new defects. Have drawbacks

Accordingly, an object of the present invention is an insulating film having excellent roll coating workability and coating properties by adding a non-silicone leveling organic additive based on an aqueous type chromic acid-based acrylic resin to a chromate-based aqueous solution containing boric acid instead of colloidal silica. To provide an oil-inorganic mixed coating composition for forming.

Another object of the present invention is to provide a method for forming an insulating coating by applying the coating composition to the non-oriented electrical steel sheet.

According to one aspect of the invention,

In a chromate solution containing 3.5 to 6.1% by weight of boric acid,

Stress relief annealing (SRA) characterized in that it is made by adding 12-68 g of an aqueous type chromic acid resistant acrylic resin, 5-27 g of glycerin, and 0.9-9.4 g of a non-silicone leveling organic additive per 100 g of chromate (CrO ₃ ) in the aqueous solution. After the coating, the organic and inorganic mixed coating composition for forming an insulating film having excellent appearance, roll coating workability and coating properties is provided.

According to another aspect of the present invention,

In a chromate solution containing 3.5 to 6.1 wt% of boric acid, 12-68 g of an aqueous type chromic acid resistant acrylic resin, 5-27 g of glycerin, and a non-silicone leveling organic additive 0.9-9.4 per 100 g of chromate (CrO ₃ ) in the aqueous solution. The organic and inorganic mixed coating composition comprising g is applied on the surface of the non-oriented electrical steel sheet so that the dry film thickness is in the range of 0.7-2.8 μm per side and heat-treated for 10-70 seconds at a temperature of 370-800 ° C. There is provided a method for forming an insulating film of an non-oriented electrical steel sheet, characterized by forming a film.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

The present inventors use boric acid-containing chromate instead of colloidal silica as an inorganic component, and use an aqueous type of chromic acid-resistant acrylic resin, that is, exclude an emulsion type and set it as an aqueous solution type. In addition, by adding an appropriate amount of a non-silicone leveling organic additive and a glycerin for water-based paints, and appropriately controlling the insulating film forming conditions, as the chromate and acrylic resin solidifies, a dense and beautiful film appearance is obtained to form an excellent insoluble film. It was found that the effect appeared.

The organic and inorganic mixed insulation coating composition of the present invention is characterized by adding an aqueous solution-type chromic acid-resistant acrylic resin prepared synthetically without using an emulsifier to a chromate-based aqueous solution containing boric acid. As in the coating composition proposed in Korean Patent Application No. 86-10301, in the case of using an aqueous emulsion type acid-soluble acrylic resin prepared synthetically using an emulsifier, the added emulsifier may cause defects in appearance during application and drying treatment. Since there is a concern, the synthetic resin form is replaced with an aqueous solution type without emulsifier rather than an emulsion type with emulsifier.

In addition, the coating composition of the present invention does not exclude the colloidal silica used in the Patent No. 86-10301, and adds a non-silicone leveling organic additive into the chromate-based aqueous solution to prevent streaking after stress relief annealing. It is characterized by providing an effect.

The chromate solution in the present invention added in order to impart corrosion resistance to the coating means a single or mixed solution of a solution in which calcium oxide and / or magnesium oxide are dissolved in an aqueous solution of chromic acid. The production method and the formulation of the chromate aqueous solution is not limited to this, but generally used chromate aqueous solution, in order to impart a gloss effect, the boric acid solution containing 3.5-6.1% by weight. If the boric acid is less than 3.5% by weight does not exhibit a sufficient gloss, and when added to more than 6.1% by weight is not preferable because the precipitate begins to occur.

The aqueous chromic acid-based acrylic resin functions to enhance adhesion to the material and to impart flexibility to the film. The aqueous type chromic acid-based acrylic resin, which is synthesized without using an emulsifier, is present in the form of an aqueous solution, and the amount of addition is less than 12 g per 100 g of CrO _{3 in the} chromate-based aqueous solution. Appearance defects and insufficient film adhesion can not be obtained, the effect of the addition of organic resin is lowered, when the addition of more than 68g, the weldability and heat resistance degradation phenomenon appears, so 12-68g to the appropriate addition amount.

The glycerin serves to reduce the annealing conditions quickly and stably by reducing chromium hexavalent to chromium trivalent as a reducing agent. The glycerin is added at 5-27 g per 100 g of CrO _{3 in the} chromate solution, and if it is added below 5 g, a large amount of remaining chromium hexavalent in the film is present, resulting in a yellowish brown surface color, and more than 27 g. In this case, the treatment liquid tends to gel, and defects in solution stability are undesirable.

In addition, in order to give an effect of exhibiting excellent appearance without streaking after stress relief annealing, 0.9-9.4 g of non-silicone leveling organic additive is added per 100 g of CrO _{3 in the} chromate solution. If the non-silicone leveling organic additive is added at less than 0.9g per 100g of CrO _{3 in the} chromate-based aqueous solution, a stripe pattern appears after stress relief annealing, and if it is added at more than 9.4g, surface defects begin to appear. I do not. The non-silicone leveling organic additive useful in the present invention includes, for example, a non-silicone leveling organic additive wherein the main component is a nonionic acrylic copolymer solution and the solvent is dipropylene glycol monomethyl ether.

As described above, the composition of the organic and inorganic mixed coating composition is coated on the surface of the non-oriented electrical steel sheet so that the dry film thickness is in the range of 0.7-2.8 μm per one side, and heat-treated for 10-70 seconds in the temperature range of 370-800 ° C. (Annealed), an insulating film having an excellent appearance can be formed. In this way, the formed organic and inorganic mixed insulating film, as well as the insulation properties, adhesion, corrosion resistance and weldability, which are essential requirements to be provided as the insulating film of the steel sheet, as well as streaks do not occur after the stress relief annealing. This property is due to the excellent continuous roll coating workability of the coating composition of the present invention.

The temperature and time of annealing are important in determining the properties of the envelope appearance. If the annealing temperature is lower than 370 ° C. in the present invention, a large amount of chromium hexavalent element is present in the film, thereby making it easy to absorb moisture, and the surface color is also yellowish brown. In addition, when the annealing temperature is higher than 800 ° C., it is difficult to control the annealing temperature, resulting in non-uniform reduction, so that appearance defects are likely to occur, and surface quality control becomes difficult. On the other hand, when the annealing time is 10 seconds or less, a large amount of chromium hexavalent element is present in the film, so that the moisture is easily absorbed, and the color of the surface tends to turn yellowish brown. There is a problem that the surface color appears yellowish brown and becomes poor.

In addition, even if the film is formed by satisfying the annealing condition after application, if the dry coating thickness is less than 0.7 μm on the surface of the steel sheet, the required insulation and corrosion resistance cannot be obtained, and the surface color appears to be almost grayish as the small support plate. It is a factor to avoid the user. In addition, when the dry coating thickness is 2.8 µm or more, the welding properties are deteriorated, so that the dry coating thickness is in the range of 0.7-2.8 µm per side.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Example

The coating composition for forming an insulating film having the composition as shown in Table 1 was applied to the surface of the non-oriented electrical steel sheet (containing 0.4 wt% of Si) having a thickness of 0.5 mm uniformly and continuously (cota roll) as shown in Table 1 below. Under the conditions of heat annealing, an electrically insulating film was formed, respectively. Comparative Example 4, which was carbon-annealed by over annealing in the coating composition, Comparative Example 5, in which a large amount of chromium hexavalent elements remained in the film due to insufficient annealing treatment conditions, and a sufficient reducing effect was not obtained using less organic reducing agent glycerin. In Comparative Example 6, all of the surface appearance was yellowish brown, and thus excluded from the film coating evaluation.

On the other hand, gelation began to occur as the elapsed treatment time and as the frictional heat between the co-tarols increased, and the comparative example 7 (borate and glycerin was observed with the naked eye at the same time for 3 hours continuous application). For the coating composition of the case in which an excessive amount was added) and the coating composition of Comparative Example 8 (in the case of addition of the emulsion type acrylic resin and colloidal silica), which started to generate extreme bubbles from the solution storage tank after 2 hours of continuous application. The above process is omitted.

The film properties of the electrical insulating film formed as described above were measured, and the measurement results are shown in Table 2 below.

⁽¹⁾ Stress Relief Annealing (SRA): The electrically insulating coating material was heat-treated at 750 ° C. for 2 hours in a dry 100% N ₂ gas atmosphere.

^{(2) The} insulation was evaluated by the storage current value (Amps.) When the input voltage was 0.5V and the current was 1.0A under 300PSI pressure.

⁽³⁾ Adhesion (mmψ) was evaluated as the minimum arc diameter without film peeling when the specimen was bent 180 ° after being annealed around an annular bar having an arc of 10, 20, 30-100mmψ after annealing.

⁽⁴⁾ Corrosion resistance was shown by visual observation of rust on the surface after 8 hours of salt spray test (5% NaCl, 35 ℃).

⁽⁵⁾ Weldability: appearance shape and blow hole appearing in the weld bead part after TIG welding (welding current: 150A, electrode: pure-W (3.2mmψ), electrode gap: 0.35mm, welding speed: 15mm / sec) It was evaluated by visual observation of the formation of holes).

₍₆₎ The surface appearance after SRA was evaluated by visual observation of the occurrence of streaks.

The results of the above embodiment will be described below based on Tables 1 and 2. Inventive examples a and b, which satisfy the conditions of the present invention, have excellent roll coating continuous workability (more than 24 hours), and have excellent appearance characteristics that do not cause streaks on the surface after stress relief annealing, insulation, adhesion, The characteristics required as a film, such as corrosion resistance and weldability, were favorable. On the contrary, in the case of Comparative Examples 1-3, in which the composition of the coating composition was outside the composition range of the present invention, or improperly applied and annealed, the product utilization value was poor due to the appearance defects in which the stripe shape appeared larger after annealing compared to Examples a and b. Was lost. In Comparative Example 2 in which the insulating film was treated with a thick film, the weldability was poor, and in Comparative Example 3 in which the insulating film was extremely thin, the insulation and the corrosion resistance were poor.

The organic-inorganic mixed coating composition according to the present invention does not use colloidal silica, but an appropriate amount of a non-silicone leveling organic additive and glycerin is added by using a boric acid-containing chromate and an acrylic resin of an aqueous solution of chromic acid. Even after the stress relief annealing, an insulating coating that provides excellent appearance and insulation, adhesion, corrosion resistance, and weldability can be formed on the surface of the non-oriented electrical steel sheet.

Claims (2)

In a chromate solution containing 3.5 to 6.1% by weight of boric acid, Stress relief annealing (SRA) characterized in that it is made by adding 12-68 g of an aqueous type chromic acid resistant acrylic resin, 5-27 g of glycerin, and 0.9-9.4 g of a non-silicone leveling organic additive per 100 g of chromate (CrO ₃ ) in the aqueous solution. ) Organic, inorganic mixed coating composition for forming insulation film with excellent appearance, roll coating workability and coating properties. In a chromate solution containing 3.5 to 6.1 wt% of boric acid, 12-68 g of an aqueous type chromic acid resistant acrylic resin, 5-27 g of glycerin, and a non-silicone leveling organic additive 0.9-9.4 per 100 g of chromate (CrO ₃ ) in the aqueous solution. The organic and inorganic mixed coating composition comprising g is applied on the surface of the non-oriented electrical steel sheet so that the dry film thickness is in the range of 0.7-2.8 μm per side and heat-treated for 10-70 seconds at a temperature of 370-800 ° C. A method for forming an insulating film of an non-oriented electrical steel sheet, characterized by forming a film.