KR20060074664A - Composition for insulated coating of the grain oriented eletrical steel sheet having good contact coating and tension properties - Google Patents

Abstract

The present invention relates to a grain-oriented electrical steel sheet having a high tensile stress due to the coating and an insulating film having excellent adhesion, and to a method of manufacturing the same, the object of which is to adjust the phosphate and colloidal silica adjusted to an appropriate viscosity and the coating properties The present invention aims to provide a coating composition for forming an insulating coating, by which a chemically insulating component is improved and a chemical reaction inducing a proper reaction with a phosphate is obtained.

In order to achieve the above object, the present invention relates to a first magnesium phosphate (Mg (H ₂ PO ₄ ) ₂ ) and a first aluminum phosphate (Al (H ₂ PO ₄ ) ₃ phosphate solution, which is a main component of an insulating electrical steel sheet coating agent, To 100 g of the phosphoric acid, an insulating coating composition was prepared, which added 10-50 g of colloidal silica as a solid content, 5-15 g of chromium oxide, and 3-7 g of boric acid. Is applied to the surface of the grain-oriented electrical steel sheet so that the dry film thickness is in the range of 2-7 µm per side, and then heat-treated for 10-50 seconds at a temperature range of 550-900 ℃ to form an insulating coating of the grain-oriented electrical steel sheet Let that point be about that.

Description

Composition for insulated coating of the grain oriented eletrical steel sheet having good contact coating and tension properties

1 is a chemical formula showing a reaction between an oxide layer present on the surface of an electrical steel sheet and phosphoric acid,

2 is a chemical formula showing the reaction of aluminum monophosphate or mono magnesium phosphate with boric acid,

3 is an explanatory diagram of a film tension measuring method using a radius of curvature.

♠ Explanation of the symbols for the main parts of the drawings ♠

(Example)

A: phosphoric acid composite reacted with an electrical steel sheet oxide layer,

B: Boric acid complex reacted with monobasic aluminum phosphate or magnesium monophosphate

The present invention relates to an insulating coating composition capable of forming an insulating coating having excellent tensile properties without producing defects in the surface of the insulating coating, that is, the surface appearance of the insulating coating. In particular, in order to improve the film tension of the existing insulating coating agent to improve the adhesion between the coating material and the material and by appropriately managing the coating amount of the coating agent related to the insulating film composition of a grain-oriented electrical steel sheet having an insulating film having an insulating film having a high tensile coating properties during planarization annealing will be.

Ordinary grain-oriented electrical steel sheet contains 3.1% Si, and has grain structure in which grain orientation is aligned in the (110) [001] direction. This product has very good magnetic properties in the rolling direction. It is used as a core material for transformers, electric motors, generators and other electronic devices.

A grain-oriented electrical steel sheet is generally made of 2-4% Si and steel containing AlN and MnS as grain growth inhibitors. (Hot rolled)-(Pre-annealed)-(Single or two-annealed cold rolled)- (Decarbon annealing)-(MgO main component annealing separator applied)-(High temperature finish annealing)-(Insulation coating and planarization annealing), etc., where 'insulation coating and planarization annealing' is the primary electrical steel sheet It refers to the process of annealing after recoating on the coating, and it improves the magnetic properties of the material by the tensile stress added by the thermal expansion coefficient difference between the film and the material in the cooling process after annealing.

The excellent insulation coating should basically have a uniform color without defects in appearance, but it was mainly used to improve the electrical insulation and enhance the adhesion of the film by incorporating various techniques to provide functionality. However, with the recent commercialization of high magnetic flux density oriented electrical steel sheets, the high tensile strength of the final insulating film has been pursued, and it has been confirmed that the high tensile insulating film contributes to the improvement of the magnetic properties of the final product.

In order to improve the characteristics of the tension coating, various process factors control techniques have been applied, and currently commercialized oriented electrical steel sheets use tensile stress in the steel sheet by using the thermal expansion coefficient difference between the steel sheet and the insulation film formed on the base layer of the foliarite. By adding, it is possible to reduce the iron loss. As a typical insulating film forming method, a method using a coating liquid containing aluminum phosphate, colloidal silica and chromium oxide disclosed in Japanese Patent Application Laid-Open No. 53-28375 and Japan The method of using the coating liquid which has magnesium phosphate, colloidal silica, and chromium oxide which are disclosed by Unexamined-Japanese-Patent No. 56-52117 is mentioned. Recently, as in Japanese Patent Nos. 3098691 and 2688147, a technique of forming a high tensile oxide film on an electrical steel sheet by using alumina sol and a mixture of boric acid is proposed. In addition, by forming a first layer composed of hydrogen phosphate containing a specific metal atom and silica on the foliar base film, as shown in Korean Patent Application No. 10-0377566, induction of adhesion between the foliar base film and the insulation film is induced. On the other hand, a technique for producing a stronger film tension effect by forming a second layer containing aluminum borate as a main component thereon has been proposed. However, materials such as alumina sol have been very sensitive to oxidizing atmosphere and can change the color of steel sheet surface after insulation coating, and it has been pointed out that there is a problem in terms of stability after coating solution preparation. In addition, in order to obtain the maximum effect when constructing two or more layers of insulation coatings as described above, the coating amount of the first and second layers should be managed uniformly to the target level, and it is known that it is very difficult to stably implement them in the field. It is true.

The present inventors have conducted research and experiments on how to form an insulating film having excellent tensile properties without the defect of the surface of the insulating film, that is, the surface appearance of the insulating film in the production of oriented electrical steel sheet as described above, based on the results The present invention has been proposed. The present invention adjusts the viscosity of the phosphate, which is the main component of the insulating coating agent of the grain-oriented electrical steel sheet, and at the same time introduces boric acid to increase the adhesion between the coating agent and the material, and also by appropriately managing the coating amount of the coating agent, the film of high tension during flattening annealing An object of the present invention is to provide a grain-oriented electrical steel sheet having an insulating coating having characteristics.

In order to improve the tension imparting ability of the grain-oriented electrical steel sheet by the insulating coating, two methods for improving the adhesion between the steel sheet and the insulating coating agent and increasing the thermal expansion coefficient difference between the steel sheet and the coating agent have been proposed.

In order to achieve the above object, the present invention provides a solution of the first magnesium phosphate (Mg (H ₂ PO ₄ ) ₂ ) and the first aluminum phosphate (Al (H ₂ PO ₄ ) ₃ ) prepared by adding magnesium hydroxide or aluminum hydroxide to phosphoric acid. Insulating coating composition which adds 10-50 g of colloidal silica as a solid content with respect to 100 g of said phosphate, 5-15 g of chromium oxide, and 3-7 g of boric acid to mixed phosphate liquid of the mixed form. To provide.

In addition, the present invention is applied to the coating composition so that the dry film thickness on the surface of the grain-oriented electrical steel sheet in the range of 2-7 ㎛ per side, and then heat treated for 10-50 seconds in the temperature range of 550-900 ℃ to form an insulating film It provides a method of forming an insulating coating of a grain-oriented electrical steel sheet.

The present invention is largely dependent on the following two methods.

First, in order to improve the adhesion between the steel sheet and the insulating coating agent, the component of the phosphate, the main component of the coating agent was optimized. Phosphates used in insulating coatings are precisely named hydrogen phosphates and contain dissociable hydrogen atoms in the compound, and metal atoms have divalent and trivalent valences. As the form of hydrogen phosphate salt, there are three forms of first salt, second salt and third salt according to the dissociation state of phosphoric acid. However, in the present invention, the first magnesium phosphate (Mg (H ₂ PO ₄ ) ₂ ) and Hydrogen phosphate salt in a mixed form of aluminum monophosphate (Al (H ₂ PO ₄ ) ₃ was used, but the method of preparing such phosphate solutions or the mixing ratio therebetween is not particularly limited, but as shown in Table 1, suitable viscosity after preparation Is maintained by default.

In addition, the phosphoric acid used in the preparation of the mixed hydrogen phosphate salt of magnesium phosphate mono (Mg (H ₂ PO ₄ ) ₂ ) and aluminum monophosphate (Al (H ₂ PO ₄ ) ₃ ) is not particularly limited, and is usually used. Concentration ranges can be used.

In the present invention, hydrogen phosphate in which hydrogen phosphate in a mixed form of magnesium phosphate (Mg (H ₂ PO ₄ ) ₂ ) and aluminum monophosphate (Al (H ₂ PO ₄ ) ₃ ) is different among several hydrogen phosphates. Type, that is, mixed form of magnesium phosphate (Mg (H ₂ PO ₄ ) ₂ ) + aluminum monophosphate (Al (H ₂ PO ₄ ) ₃ ) + calcium phosphate (Ca (H ₂ PO ₄ ) ₂ ) The adhesion was better than that of hydrogen phosphate in the form of monobasic aluminum phosphate (Al (H ₂ PO ₄ ) ₃ ) or monobasic magnesium phosphate (Mg (H ₂ PO ₄ ) ₂ ) alone.

 Secondly, the formation of complexes such as Al-B or Mg-B is expected by the condensation reaction of boric acid and hydrogen phosphate, which are the main components of the coating, at low baking temperature when forming an insulating film. It is thought to induce another condensation reaction with the ceramic layer produced by the colloidal silica to form a film having a better tension than the conventional insulating film.

The colloidal silica used acts to impart tensile stress to the material by forming a ceramic layer having a low thermal expansion coefficient upon firing of the coating agent, and the amount of the added colloidal silica is 10 g or less by weight at a solid content of 100 g of phosphoric acid. It is not possible to form a tensile stress to the material is insufficient, at 50g or more, the viscosity of the coating agent increases, the workability is very bad. Therefore, in the present invention, the content of the colloidal silica is limited to the range of 10-50 g by weight when the solid content is 100 g of the phosphoric acid.

The boric acid is difficult to form an appropriate condensation reaction with magnesium or alumina present in the phosphate when added to less than 3g per 100g of phosphoric acid, and when added to 7g or more, precipitation occurs due to excessive addition. Preferably limited to 7 g.                     

 When the chromium oxide is added in less than 5g per 100g of phosphoric acid, if the corrosion resistance of the coating agent is more than 15g, it is preferable to limit to 5-15g per 100g of phosphoric acid because the oxidative defect of the insulating film is concerned.

Although the manufacturing process of grain-oriented electrical steel sheet has some process differences among manufacturers, it is common to adjust the thickness in steelmaking, manufacture slab manufacturing, reheat and hot rolling, thickness adjustment by hot roll annealing and cold pressure, decarburization and nitride annealing, and secondary recrystallization. It is usually manufactured by high temperature annealing and final insulation coating process. The establishment of such a manufacturing process is a process based on a mass production system, and an important factor of the mass production system is the establishment of a finishing high temperature annealing process. In recent years, the production of high magnetic flux oriented electrical steel sheet becomes the center of directional electrical steel sheet production. Moreover, as the center of production cost is shifted due to the commercialization of thin products, securing excellent magnetic characteristics is a key technology. The new functional role of the improvement of magnetism by hwa has been added.

In the case of 0.23mm oriented electrical steel sheet, the tension imparting ability of the conventional insulating film is 0.30 to 0.36 kg / mm ² , and the magnetic contribution to the final product is improved by about 2 to 3% even after applying the tension. It is reported that. Therefore, the increase in the amount of high tension applied to the insulating film can directly contribute to the magnetic improvement rate. The improvement of magnetism by imparting high tensile strength to the coating layer affects the iron core loss, ie iron loss in the magnet, and it is possible to improve the magnetism because the vortex loss can be reduced by the tension applied to the material.

In general, the residual stress d _RD in the rolling direction when the insulation coating film is very small compared to the material can be expressed as follows (AJMoses and JE Thompson, Proc. IEEE, 119, 1222 [1972]). .

= 온도차 (^oC),

= Si-Fe의 열팽창 계수,

= 코팅층의 열팽창 계수,

=

영역에서의 코팅층의 Young's Modulus의 평균값,

= 소재와 코팅층의 두께비,

= 압연방향에서의 Poisson's ratiohere

= Temperature difference ( ^o C),

= Thermal expansion coefficient of Si-Fe,

= Coefficient of thermal expansion of the coating layer,

=

Average value of Young's Modulus of the coating layer in the region,

= Thickness ratio of material to coating layer,

= Poisson's ratio in rolling direction

As a tensile stress improvement coefficient by the film | membrane from said Formula, the difference of the thermal expansion coefficient between a raw material and a coating agent is mentioned, The effect can be seen by increasing this value. Although the details of the operation of the present invention are unclear, it will be assumed that they will generally work through the mechanism shown in FIGS.

As shown in FIG. 1, it is thought that free phosphoric acid contained in the coating agent at low baking temperature is present in the state indicated by A in FIG. Meanwhile, the first magnesium phosphate (Mg (H ₂ PO ₄ ) ₂ ) and the first aluminum phosphate (Al (H ₂ PO ₄ ) ₃ may be present in the form as shown in FIG. 2 through condensation reaction with boric acid. Therefore, as the film formation progresses, the reaction between A and B formed at the initial stage of the insulation film formation can be predicted (eg, AA reaction, AB reaction, or BB reaction), and the resulting AA, AB, and BB composite products are insulated. It is thought that another condensation reaction with the -OH group present in the ceramic layer produced by the colloidal silica above 800 ° C at the end of the formation will form a complex product which could not be derived by the conventional method. It is believed that the composite material produced by the mechanism plays an important role in improving the adhesion of the film tension and consequently improving the film tension.

Regardless of the annealing temperature of the insulating coating agent, the chemical reaction is strongly influenced by the type of hydrogen phosphate salt used, the ratio with metal atoms, or various reaction promoters, and a large difference may occur in the final state of the reaction. It is thought that it will react with boric acid by heating with hydrogen phosphate.

In the present invention, the coating agent needs to contain silica in addition to the hydrogen phosphate salt as described above. It is preferable to use colloidal silica from a viewpoint of the uniformity of a film, and a viewpoint of a droplet ratio, and it is suitable for a silica with a comparatively small particle diameter of 7-20 nm on average especially. Although the action of the silica is not clear, it is assumed that it promotes the condensation reaction of hydrogen phosphate and also helps to form a fine film according to the form of the film.

In order to introduce boric acid into the coating agent, it is necessary to proceed in a special compounding order, based on the fact that the boric acid is added to colloidal silica and prepared in solution. If boric acid and hydrogen phosphate are added to colloidal silica at the same time to prepare a solution, boric acid may exist as a solid particle without being properly dissolved in the coating solution due to the interference of hydrogen phosphate, in which case it is difficult to achieve its intended purpose. Therefore, after completely dissolving boric acid in colloidal silica, hydrogen phosphate and chromium oxide are sequentially added to prepare a coating solution.

In the present invention, after applying the treatment liquid configured as described above to the surface of the grain-oriented electrical steel sheet so that the dry film thickness is in the range of 2-7 ㎛ per side, and heat-treated for 10-50 seconds in the temperature range of 550-900 ℃, the grain-oriented electrical steel sheet It is possible to obtain a product having excellent adhesion to the insulation coating agent and tension due to the film.

One of the factors that determine the appearance of film is the relationship between annealing temperature and time. If it is maintained at 10 seconds or less at the maximum allowable temperature of 850 ° C., it becomes a micro-dull state and the film formation is insufficient, resulting in the problem that the hygroscopicity remains. On the other hand, if the minimum allowable temperature is maintained at 550 ° C. for 50 seconds, the coating agent, which is chemically bonded to the oxide layer, is poorly colored as reddish brown to black brown due to oxidation.

Even if the film was formed by satisfying the annealing conditions after application by a roll or the like, if the thickness of the dry film according to the method of the present invention is 2 μm or less, even if the adhesion is good, the interlayer resistance characteristics and sufficient tension imparting are difficult. In the case where the thickness is larger than or equal to one, it is preferable to increase the spot ratio so that the appropriate film thickness is limited to 2 to 7 µm per side.

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

Example 1

Si: 3.1% by weight, a thickness of 0.23mm, oriented electrical steel sheet (300 × 60 mm) with a primary film annealed with a finish annealing as a test material, the coating amount of the aqueous solution of the composition shown in Table 1 5.0 ± It was applied to one surface of the sample so that 0.5 g / m ² . Thereafter, when the plate is baked at 750 ° C. for 30 seconds, the coated surface is bent in one direction as shown in FIG. 3 by the addition of tensile stress by the coating agent, and the tension due to the film can be evaluated by measuring the degree of warpage (H ′). .

Table 2 shows the film properties of the grain-oriented electrical steel sheet obtained according to the above form, that is, the tension due to the film. In addition, the comparative material was tested using the aqueous solution which has a composition of Table 1.

Table 1

number division Type of phosphate (parts by weight) Phosphate Viscosity (cp) Colloidal silica (solid parts by weight) Boric acid Chromium oxide One Comparative material Monophosphate Al + Mg + Ca (40) 640 16.2 0 4 2 Test article Monophosphate Al + Mg (40) 250 16.2 0 4 3 Test article Monophosphate Mg (40) 100 16.2 0 4 4 Test article Monophosphate Al + Mg + Ca (40) 640 16.2 1.78 4 5 Test article Monophosphate Al + Mg (40) 250 16.2 1.78 4 6 Test article Monophosphate Mg (40) 100 16.2 1.78 4

[Table 2]

number division Type of phosphate (parts by weight) Coating amount (g / m ² ) Tension imparting ability (Kg / mm ² ) One Comparative material 1 Monophosphate Al + Mg + Ca (40) 5.5 ± 0.5 0.460 2 Test article 1 Monophosphate Al + Mg (40) 5.5 ± 0.5 0.649 3 Test article 2 Monophosphate Mg (40) 5.5 ± 0.5 0.370 4 Test article 3 Monophosphate Al + Mg + Ca (40) 5.5 ± 0.5 0.623 5 Test article 4 Monophosphate Al + Mg (40) 5.5 ± 0.5 0.890 6 Test article 5 Monophosphate Mg (40) 5.5 ± 0.5 0.391

Table 2 shows the tension imparting ability according to the type of phosphate and the presence or absence of boric acid in the coating agent. As can be seen from Table 2, the tension imparting ability was different from 40 to 75% according to the kind of phosphate among the coating materials without boric acid (Comparative Materials 1, Test Materials 1, 2). In the case of phosphate (Tester 1) excluding the increase of the tension imparting ability 45% compared to the comparative material, the tension imparting ability was reduced by 20% compared to the comparative material in the type without both Al and Ca. For this reason, the adhesion between the coating agent and the material may be different according to the type of phosphate, and the optimum adhesion with the material may be obtained when the viscosity of the phosphate is appropriate.

In addition, it can be seen that the difference in the same phosphate depending on the addition of boric acid. For example, when comparing Comparative 1 and Test 3, the boric acid-added coating increased 35% in tension, 37% in Test 1 and Test 4, and Test 2 and Test 5 6% increase. It is thought that the condensation reaction occurs between aluminum monophosphate or magnesium monophosphate and boric acid when the coating agent is burned as described above, and the Al-B or Mg-B composite material produced by such condensation reaction (Fig. 2) Finally, it is thought that a condensation reaction is performed with the OH group present in the colloidal silica to form a more firm film.

As described above, in the present invention, an insulating film of a grain-oriented electrical steel sheet is formed by using a coating agent using a phosphate obtained by mixing an appropriate amount of a mixture of aluminum monophosphate and magnesium phosphate monobasic in a solution in which a suitable amount of boric acid is dissolved in colloidal silica. When formed, an insulating coating having excellent adhesion between the appearance and material of the coating and the coating could be prepared. In addition, it was confirmed that the insulation coating thus prepared is significantly improved as compared with the existing material.

Claims (3)

Insulation coating composition of oriented electrical steel sheet with excellent film adhesion and tension-bearing ability, added by the ratio of 10-50g of colloidal silica and 3-7g of boric acid in solid ratio per 100g of phosphate mixed with aluminum monophosphate and magnesium phosphate The method of claim 1, The insulating coating composition is an insulating coating composition of a grain-oriented electrical steel sheet having excellent film adhesion and excellent tension imparting ability, characterized in that 5-15g of chromium oxide is further added per 100g of phosphate. The method of claim 1, The insulating coating composition is first prepared by adding boric acid to the colloidal silica to make a solution state, and then added to the phosphate, the coating film is excellent and excellent in film adhesion, characterized in that the tension coating ability excellent insulating film composition of the electrical steel sheet

Images