KR19990026911A - Coating composition for forming insulating film and method of forming insulating film of non-oriented electrical steel sheet using same - Google Patents

Abstract

The present invention relates to a coating composition for forming an insulating coating and a method for forming an insulating coating of an non-oriented electrical steel sheet using the same, and an object thereof is to use a phosphate and an acid-soluble emulsion acrylic resin as a main component instead of using a chromium compound. By applying an organic mixed composition and adding elements to improve the coating properties, it is to provide a coating composition for forming an insulating film which is advantageous in terms of pollution and excellent coating properties. The present invention is to provide a method for forming an insulating coating by applying to a grain-oriented electrical steel sheet.

The present invention for achieving the above object is when the emulsion acrylic resin is a solid content with respect to 100 g of the phosphoric acid in the phosphate solution alone or in combination of magnesium monophosphate or monobasic aluminum phosphate salt prepared by adding magnesium hydroxide or aluminum hydroxide to phosphoric acid 13.0-70.2g by weight, 1.1-6.8g by weight of colloidal alumina, 0.25-1.95g by weight of silane coupling agent (solid coupling agent), 5.1-23.8g of zinc nitrate The present invention relates to a coating composition for forming an insulating coating, which is added in an amount of water and whose concentration is adjusted with water, and a method for forming an insulating coating on the surface of a non-oriented electrical steel sheet using the coating composition.

Description

Coating composition for forming insulating film and method of forming insulating film of non-oriented electrical steel sheet using same

The present invention relates to a coating composition for forming an insulating coating and a method for forming an insulating coating of an non-oriented electrical steel sheet using the same, and more particularly, to form an insulating coating having excellent heat resistance after appearance and stress relief annealing. The present invention relates to a coating composition and a method for forming an insulating coating of an non-oriented electrical steel sheet using the same.

In manufacturing non-oriented electrical steel sheet used as iron core for electric equipments such as small electric motors and transformers, in order to suppress eddy current generation and to reduce power loss, insulation film is formed on the surface and coiled electrical steel products are in demand. The die is continuously punched into a predetermined shape by a mold or the like, and then heat treatment is usually performed at a high temperature for the purpose of stress relief annealing. Therefore, it is required to have excellent heat resistance of the insulating film during stress relief heat treatment. In addition, since the coating process is a finishing process of finally providing electrical steel sheet products to the demand price, the demand for beautiful appearance is increasing and nowadays, this is managed as an important surface quality item for creating new high value. In addition, other main performances required as an insulating film forming agent are required to be excellent in adhesion, corrosion resistance, workability, hygroscopicity, etc., and this performance must be achieved by an extremely thin film.

Since the surface treatment method of the electrical steel sheet is easily affected by the base, the smaller the silicon content in the steel, the lower the adhesiveness, and in particular, has a significant effect on the peelability after annealing. On the other hand, chromic acid is usually contained as an agent for the insulation coating treatment to impart the required characteristics of the coating, such as corrosion resistance. It is ideal to exclude use from the beginning of insulation coating liquid production because it may cause environmental problems in the process and shorten the life due to abnormal abrasion of mold when punching out due to residual chromium hexavalent.

Insulation coating for non-oriented electrical steel sheet is classified into three kinds of organic, inorganic, organic and inorganic mixture according to the demand of various usage characteristics of the non-oriented electrical steel sheet, and is formed by continuously supplying the treatment liquid to the surface of the electrical steel sheet and applying and drying it. As a method for forming an insulating coating on the surface of a non-oriented electrical steel sheet, Korean Patent Nos. 25106 (notice 87-2105), 31208 (notice 89-3582) and 31219 (limited by the inventor) Publication No. 89-3583), there is a method for forming an electrical insulating film.

These methods relate to a method of forming an organic and inorganic mixed insulating film having both the advantages of the inorganic insulating film and the advantages of the organic insulating film, and has an effect of improving adhesion before stress relief annealing. However, the methods of Korean Patent No. 25106 and Korean Patent No. 31028 are not satisfactory in improving the insulation, and in Korean Patent No. 31219, the effect of improving the insulation is excellent, but the appearance is somewhat deteriorated due to the roughness of the surface. There are also disadvantages to the rate. In addition, these methods use chromium compounds, which is a problem in terms of work or environmental pollution.

Therefore, the present invention is advantageous in terms of pollution by applying an inorganic and organic mixed composition containing phosphate and an acid-soluble emulsion acrylic resin as a main component, and adding additional elements to improve coating properties. In order to provide a coating composition for forming an insulating coating, excellent coating properties are obtained, and an object thereof is provided, and the present invention also provides a method for forming an insulating coating by applying the coating composition to a non-oriented electrical steel sheet. There is a purpose.

The present inventors do not use chromium compounds at all, but use inorganic and organic mixed compositions containing phosphate and an acid-soluble emulsion-based acrylic resin as a main component. In addition, as a result of examining various kinds of additive elements in order to rewrite the coating properties such as appearance and heat resistance, when an appropriate amount of colloidal alumina, silane coupling, and zinc nitrate was added in combination, phosphate was annealed during solid annealing. In addition, the acrylic resin was solidified to form an excellent insoluble film that became a dense and beautiful film appearance, and it was found that an excellent coating property improvement effect such as appearance, adhesion, and heat resistance that these solids could not obtain alone was obtained.

Starting from the above point of view, the present invention provides an emulsion acrylic resin with respect to 100 g of the phosphoric acid in a phosphate solution alone or in combination of magnesium monophosphate or monobasic aluminum phosphate prepared by adding magnesium hydroxide or aluminum hydroxide to phosphoric acid. 13.9-70.2g by weight of solids, 1.1-6.8g by weight of colloidal alumina, 0.25-1.95g by weight of silane coupling agent, and 5.1-zinc nitrate It is related with the coating composition for insulating film formation which adds in content of 23.8g, and adjusts concentration with water,

According to the present invention, the 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 0.8-4.2 μm per side, and then heat-treated for 14-45 seconds at a temperature range of 550-750 ° C. to form an insulating film. It relates to a method for forming an insulating coating of non-oriented electrical steel sheet.

Hereinafter, the present invention will be described in more detail.

In the present invention, the coating solution is constituted as follows.

Examples of the phosphate added to provide corrosion resistance and insulation to the film include phosphoric acid in which magnesium hydroxide, which is a divalent metal compound, or aluminum hydroxide, which is a trivalent metal compound, is added and dissolved, respectively, to a composition ratio of monobasic magnesium salt or monobasic aluminum phosphate salt. Take at least one of them. The production method of the above phosphate solutions or the compounding ratio therebetween are not particularly limited, and conventionally used solutions of monobasic magnesium phosphate and monobasic aluminum phosphate salt can be used.

Moreover, the said phosphoric acid is not specifically limited, either, The thing of the concentration range normally used can be used.

The acid-soluble emulsion acrylic resin acts to increase the adhesion to the material and to impart flexibility to the film. The addition amount (in solid content) is less than 13.9g with respect to 100g of phosphoric acid, the powdery and rough surface appearance is poor, and sufficient film adhesion is not obtained, and there is no effect of adding organic resin. This becomes bad and the film peeling and insulation fall after a stress relief annealing do not appear. Therefore, in this invention, content of the said emulsion acrylic resin is restrict | limited to the range of 13.9g-70.2g compared with 100g of said phosphoric acid.

When the colloidal alumina is added in an amount of 1.1g or less as a solid content per 100g of phosphoric acid, the adhesion and heat resistance are poor, resulting in film peeling and poor appearance after annealing the steel sheet, and when 6.8g or more is added, layer separation occurs within 1 day after compounding. Even if it is applied after stirring, an uneven film is formed. Therefore, in the present invention, the content of the colloidal alumina is preferably limited to 1.1-6.8g compared to 100g of the phosphoric acid.

The silane coupling agent is present at the interface between the organic resin and the inorganic material and acts as a crosslinking agent. The silane coupling agent is 0.25-1.95 g in terms of solid content per 100 g of phosphoric acid, that is, 0.1 mole per 100 g of phosphoric acid. 10.6-82.6 g of silane coupling agent is added. When the silane coupling agent is added in an amount of 0.25g or less as a solid content (0.1 mol of the silane coupling agent is added in 10.6g or less) When the moisture absorption resistance of the film is insufficient, and when 1.95g or more is added (0.1 mol silane coupler) When more than 82.6g of ring agent is added), it becomes difficult to make a uniform treatment bath, resulting in poor appearance and uneven insulation after coating. Therefore, in the present invention, the content of the silane coupling agent is preferably limited to 0.25-1.95 g in solid content relative to 100 g of the phosphoric acid.

When the zinc nitrate is added in an amount of less than 5.1g per 100g of phosphoric acid, the coating processability and gloss are insufficient, and when more than 23.8g is added, the zinc nitrate is partially peeled off after the stress relief annealing heat treatment. Therefore, in the present invention, the content of the zinc nitrate is preferably limited to 5.1g-23.8g compared to 100g of the phosphoric acid.

In the present invention, the treatment liquid configured as described above is applied to the surface of the non-oriented electrical steel sheet so that the dry film thickness is in the range of 0.8-4.2㎛ per side, and annealed for 14-45 seconds in the temperature range of 550-750 ℃ inorganic-organic mixture It is possible to obtain an insulating film having excellent appearance, adhesiveness, and insulation properties that should be provided as a cinnamon film.

One of the factors that determine the appearance of the film is the relationship between annealing temperature and time. If the temperature of the furnace at the maximum allowable temperature of 750 ° C. is maintained at 14 seconds or less, a problem occurs in that the hygroscopicity of the film formation becomes poor and the film formation is insufficient. On the other hand, if it is maintained at the allowable minimum temperature of 550 ° C for more than 45 seconds, the coating agent, which is chemically bound to the oxide layer, is poorly colored as blackish brown-black due to oxidation.

On the other hand, when the temperature of the furnace is maintained at 550 ° C. or lower, annealing becomes insufficient and hygroscopicity remains or a film is formed, and a long time is required, and in practice, problems of low productivity occur in industrial use. In this case, the annealing temperature is also difficult to control, resulting in nonuniform film formation, and appearance defects tend to occur.

Even if the film is formed by satisfying the annealing condition after application by a roll or the like, if the thickness of the dry film by the method of the present invention is 0.8 μm or less, the necessary interlayer resistance property cannot be obtained even if the hygroscopicity and adhesion are good. In the case of 4.2 µm or more, it is preferable to limit the appropriate coating thickness to 0.8-4.2 µm per side because welding properties and spot ratios are lowered.

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

Example

After 7 days of blending the insulating coating liquid of the composition (addition amount of emulsion acrylic resin and colloidal alumina based on solid content) as shown in Table 1, non-oriented electrical steel sheet (containing 0.4% of Si, 0.5mm thick) using synthetic rubber roll After the uniform coating on the surface of the), an electrical insulating film was formed on the basis of heat annealing as shown in Table 1 below. Comparative Example (6) in the coating composition could not be applied due to the loss of coating workability due to the delamination phenomenon.

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

At this time, stress relief annealing was heat-treated at 750 ° C x 2 hours in a dry 100% N ₂ gas atmosphere, and insulation (Amps.) Is represented as the received current value when current of 0.5V, 1.0A was input under 300PSI input. , Adhesion (mmø) is the minimum arc diameter without film peeling when the specimen is bent 180 ° after contact with an arc of 10, 20, 30 ~ 100mmø after annealing. will be. In addition, surface roughness is the value expressed by the centerline average roughness value (Ra) measured by the tactile surface roughness, and the corrosion resistance was observed by visual observation of the surface rust occurrence after 8 hours of salt spray test (5% NaCl, 35 ° C). The peeling of the film shows the presence or absence of adhesion of the peeling film that appears when peeled off with an adhesive tape (polypropylene) on the peeled film after the removal of the annealing.

As can be seen from Table 1 and Table 2, the invention examples (a, b) satisfying the conditions of the present invention as a coating such as the appearance and the heat resistance (the property that the film peeling, insulation does not decrease) after stress relief annealing The required properties were excellent.

On the other hand, in the case of Comparative Example (1-6), in which the coating composition was added in an inappropriate range or inadequately applied and annealed, the characteristics required as a film such as appearance and heat resistance after stress relief annealing compared to Examples (a and b) fell. That is, Comparative Example (1) having a low resin content in the coating composition is poor in coating workability, poor in appearance and adhesion such as streak, stress, and dark color before stress relief annealing, and excludes preparations other than phosphate-acrylic resins. In Comparative Example (2), which had insufficient appearance and corrosion resistance, and Comparative Example (3) in which the electrical insulating film was extremely thin with the treatment solution without phosphate addition, the insulation and corrosion resistance before the stress relief annealing was poor, and the peeling after the stress relief annealing was performed. The phenomenon appeared. On the other hand, Comparative Example (4) is a case where the film formation is difficult due to insufficient annealing treatment conditions, and Comparative Example (5) appeared to be in the state of carbonization in understanding the annealing treatment. Such extreme appearance defects will result in the loss of utility value.

As described above, according to the present invention, colloidal alumina is added to a mixed coating liquid obtained by adding an emulsion acrylic resin of an acid (phosphate) soluble type to a phosphate inorganic composition comprising at least one of monobasic magnesium phosphate or monobasic aluminum phosphate salt. By adding an appropriate amount of silane coupling agent and zinc nitrate in combination, a coating composition is obtained and applied to an electrical steel sheet, thereby reducing the appearance and stress of beautiful surface roughness, unlike in the chromate-resin-based insulating coating solution to which silica powder is added. After annealing, not only the effect of forming an insulating coating on the surface of the non-oriented electrical steel sheet, which can satisfy the use characteristics required as a coating such as heat resistance (such as peeling and insulating property), but also conventional chromate Pollution Caused by Excluding Chrome Chromium Compounds Effect to bridge the blown are also provided.

Claims (6)

13.9-70.2 g, colo of the acrylic acrylic resin with a solid content of 100 g of the phosphoric acid in a phosphate solution alone or in combination of magnesium monophosphate or monobasic aluminum phosphate salt prepared by adding magnesium hydroxide or aluminum hydroxide to phosphoric acid. This month, alumina is added in an amount of 1.1-6.8 g by weight in solids, silane coupling agent in a content of 0.25-1.95 g in weight by solids and zinc nitrate in 5.1-23.8 g, and the concentration is adjusted by water. Coating composition for insulating film formation The method of claim 1, The phosphoric acid is a coating composition for forming an insulating film, characterized in that the concentration of 85% The method of claim 1, The silane coupling agent is a coating composition for forming an insulating film, characterized in that the concentration of 0.1 mol 13.9-70.2 g, colo of the acrylic acrylic resin with a solid content of 100 g of the phosphoric acid in a phosphate solution alone or in combination of magnesium monophosphate or monobasic aluminum phosphate salt prepared by adding magnesium hydroxide or aluminum hydroxide to phosphoric acid. This month is a coating solution containing 1.1-6.8 g of alumina as a solid content, 0.25-1.95 g of a silane coupling agent as a solid content, and zinc nitrate in 5.1-23.8 g, and adjusting the concentration with water. Coated on the surface of the non-oriented electrical steel sheet so that the dry film thickness is in the range of 0.8-4.2㎛ per one side, and then heat-treated for 14-45 seconds in the temperature range of 550-750 ℃ to form an insulating film Method of forming insulation film of oriented electrical steel The method of claim 4, wherein The phosphoric acid is an insulating film forming method of the non-oriented electrical steel sheet, characterized in that the concentration of 85% The method of claim 4, wherein The silane coupling agent is an insulating film forming method of the non-oriented electrical steel sheet, characterized in that the concentration of 0.1 mol