KR100368254B1 - Coating composition for forming insulating coating with excellent roll coating workability and method for forming insulating coating of non-oriented electrical steel sheet using same - Google Patents

Abstract

The present invention relates to an insulating coating coated on the surface of a non-oriented electrical steel sheet to reduce eddy current loss; Its purpose is to improve the coating performance of roll coating and to carry out continuous coating for a long time, and to further improve the general use characteristics such as insulation and adhesiveness that the insulation film should have, and to use it. The present invention provides a method of forming an insulating coating on the surface of a grain-oriented electrical steel sheet. The present invention also provides an excellent appearance of a beautiful pale golden color different from the light green color when reducing from chromium hexavalent to trivalent in the conventional chromium-containing insulating coating composition.

The present invention having such an object,

(a) 8.2-10.1 g of magnesium ions and 2.1-9.3 g of powdered fines per 100 g of phosphoric acid

To silica-containing magnesium phosphate salt containing silica;

(b) To 100 g of phosphoric acid of the silica-containing magnesium phosphate salt solution

22.4-100.2g, boric acid: 0.3-0.8g, zinc nitrate: 8.3-20.3g are added to the acid-soluble emulsion type acrylic-styrene copolymer resin by the weight basis when it is solid content,

(c) For solid content of 100 g of the acrylic-styrene copolymer emulsion resin

Monomer methacryloxy silane coupling agent: 0.3-1.0 g,

Polymeric organosilicon: Add 1.5-5.0 g and adjust the concentration as the remaining water

The technical gist of the coating composition for insulating film formation which is excellent in roll coating workability which is made is made.

Description

Coating composition for forming insulating coating with excellent roll coating workability and method for forming insulating coating of non-oriented electrical steel sheet using same

The present invention relates to an insulating coating coated on the surface of a non-oriented electrical steel sheet to reduce the eddy current loss, more specifically does not contain chromium, as well as coating composition for forming an insulating coating having excellent roll coating workability and use thereof The present invention relates to a method of forming an insulating coating on an non-oriented electrical steel sheet.

The non-oriented electrical steel sheet is punched and laminated, and then the laminated cross section is fixed and assembled by welding or the like to be used as an iron core of a motor transformer. In this case, it is preferable to form an insulating film on the surface of the steel sheet in order to prevent power loss by increasing the interlayer resistance during lamination to reduce the eddy current loss. In addition to insulation, the insulating coating requires properties such as coating appearance, corrosion resistance, adhesion, and water absorption.

Coating compositions for insulating coating formation are largely classified into three types: organic, inorganic, or organic and inorganic mixtures. The dual organic-inorganic mixed coating composition has both the advantages of the inorganic coating composition and the advantages of the organic coating composition. However, the conventional organic and inorganic mixed coating composition usually contains chromic acid in order to secure the required characteristics of the coating such as corrosion resistance, which may cause adverse effects on the human body and environmental problems due to the use of chromium. In addition, due to residual chromium hexavalent in the coating of the steel sheet may shorten the life due to abnormal wear of the mold during punching.

Accordingly, the present inventors have proposed a coating composition for forming an insulating coating which solves the problem of using chromium and improves insulation, corrosion resistance and appearance characteristics in Korean Patent Application No. 97-49228. The proposed technique does not use a chromium compound but instead contains a phosphate and an acid-soluble emulsion acrylic resin, and an appropriate amount of colloidal alumina, a silane coupling agent, and zinc nitrate is added to improve the beautiful appearance, adhesion, and heat resistance. will be.

However, the proposed coating composition has a problem in that the resin component sticks to the coating roll during the continuous coating and solution circulation operation on the surface of the non-oriented electrical steel sheet. Of course, this problem can be prevented by proceeding while replacing a new coating roll coating (Coater), there is a problem that the productivity of the coating roll coating change is reduced. In addition, in general, the demand for non-oriented electrical steel sheet demands a certain weight of the cold rolled coil products, if the continuous coating operation as described above, the weight of the cold rolled coil products will vary in weight, causing demands complaints do.

Accordingly, the present inventors conducted a multi-angle study to solve the roll coating workability problem of the coating composition of the prior art described above, confirming that the solution can be solved by securing the slip property between the coating composition and the roll. It has come to propose the present invention.

The present invention improves the roll coating coating workability and can stably carry out continuous coating work for a long time, as well as reducing the chromium hexavalent to trivalent, which appears in general use characteristics such as insulation and adhesion properties that an insulation coating should have and chromium-containing insulation coating composition. It is an object of the present invention to provide a coating composition for forming an insulating film having an excellent appearance of a beautiful pale golden color different from that of a light green color.

Furthermore, the present invention provides a film forming method of non-oriented electrical steel sheet using the coating composition of the present invention, another object.

Coating composition of the present invention for achieving the above object,

(a) 8.2-10.1 g of magnesium ions and 2.1-9.3 g of powdered fines per 100 g of phosphoric acid

To silica-containing magnesium phosphate salt obtained by adding silica;

(b) To 100 g of phosphoric acid of the silica-containing magnesium phosphate salt solution

22.4-100.2g, boric acid: 0.3-0.8g, zinc nitrate: 8.3-20.3g are added to the acid-soluble emulsion type acrylic-styrene copolymer resin by the weight basis when it is solid content,

(c) For solid content of 100 g of the acrylic-styrene copolymer emulsion resin

Monomer methacryloxy silane coupling agent: 0.3-1.0 g,

Polymeric organosilicon: Add 1.5-5.0 g and adjust the concentration as the remaining water

Is done.

The insulating film forming method of the present invention for achieving the above another object,

The coating composition of the present invention is coated on the surface of the non-oriented electrical steel sheet so as to have a dry film thickness in the range of 0.7-2.8 μm per single side, and then annealing at a temperature of 550-700 ° C. for 11-27 seconds.

Hereinafter, the present invention will be described in detail.

[Coating composition for forming organic and inorganic insulating film]

Referring to the characteristics of the coating composition of the present invention based on the problem analysis of the prior art as follows.

(1) The above-described coating composition of the prior art is a monomer type silane coupling agent is added to the resin, and these components have a sticky property when used for a long time, so that the continuous roll coating operation is impossible because they adhere to the roll coater. As a result, when the surface of the roll was coated as it is, the appearance of the film was poor.

Therefore, in the present invention, the monomer-type methacryloxy silane coupling agent and the polymer type organic silicon, which is a high molecular weight specially modified silicone which gives a slip effect, are used in combination with the acid-soluble emulsion type acrylic-styrene copolymer resin in a roll of the treatment liquid. It is the first feature of inhibiting coating adhesion.

(2) The coating composition of the prior art described above is stirred by adding powdery fine silica together with the resin after phosphate production. In this case, the insulating effect is shown, but powdered fine silica is deposited by the amount added, which causes problems in solution use.

Therefore, in the present invention, the powder silica is added during the phosphate production to easily dissolve the powder silica by the exothermic heat generated at this time, thereby securing the insulation effect and the stability of the coating composition.

(3) Furthermore, in the present invention, boric acid and zinc nitrate are added to the emulsion-type acrylic-styrene copolymer resin in combination to secure a highly insoluble film having a light golden color and beautiful appearance. .

Hereinafter, the role and function of each component in the coating composition of the present invention will be described and the reason for numerical limitation will be described.

The silica-containing monobasic phosphate salt added in order to impart heat resistance and insulation to the insulating film according to the present invention is prepared by simultaneously adding powdery fine silica in the course of adding and dissolving magnesium ions to phosphoric acid. As such, when powder silica is added during phosphate production, powdery fine silica is easily dissolved by the exothermic heat generated at this time, thereby satisfying two effects of insulation and stability of the treatment solution.

At this time, magnesium ion is added 8.2-10.1g per 100g of phosphoric acid, because when magnesium ion is less than 8.2g, it shows strong acidity pH value and poor compatibility with resin. This is because delamination due to the deposition of reactive magnesium ions occurs.

In addition, the powdery fine silica is added 2.1-9.3g with respect to 100g of phosphoric acid, because the addition of less than 2.1g appears to have insufficient insulation, and if more than 9.3g is added, the adhesion of the film is inferior. The fine powdery silica may be fine powder silica used as a general electrical steel sheet insulation coating agent, and the particle size thereof is not particularly limited.

According to the present invention, acrylic-styrene-based copolymer resins added in order to increase adhesion to steel sheets and to provide film flexibility are advantageous to use an emulsion type resin rather than a water-soluble resin in terms of compatibility with aqueous phosphate solution and stability. Do. In addition, the acryl-styrene copolymer resin is good in acid solubility in the acid mixture to improve the uniform coating properties of the coating stability and low viscosity of the emulsion. In one embodiment, an acid-soluble emulsion (average particle diameter: 0.2 mu m) type acrylic-styrene copolymer resin having a pH of 3 or less is used. In order to form an insulating coating on the surface of the non-oriented electrical steel sheet, it is uneconomical to apply a new treatment solution that meets the demand of the customer from the tip of the coil having a large weight every time the new insulation coating is formed. Therefore, it is common practice to apply the steel sheet with one kind of treatment liquid first, then stop the line and then apply the rest of the coil with another kind of treatment liquid. At this time, the used treatment liquid remaining in the cota roll is not removed, and when it is replaced with another coating liquid, the first treatment liquid and the next treatment liquid are mixed with each other. When it is lost or left for several days after use and reused, the coating operation characteristics are lost due to the gelation reaction between the inorganic components present in the solution itself. The resin used in the present invention has excellent mixing compatibility with other chromium and phosphoric acid components contained in other pure inorganic insulating coating agents or organic / inorganic mixed insulating coating agents, and can improve other product productivity in continuous operation. It is a characteristic of the acid-soluble emulsion acrylic-styrene resin that exhibits the effect of reducing the treatment liquid and minimizing the waste treatment even when reused.

The addition amount of the said acid-soluble emulsion type acrylic-styrene resin is made into 22.4-100.2g on the basis of the weight at the time of solid content with respect to 100g of phosphoric acid of a silica containing monophosphate magnesium salt. The reason is that when the amount of acid-soluble emulsion-type acrylic-styrene resin is added below 22.4g, sufficient film adhesion and good film appearance cannot be obtained, and there is no effect of adding organic resin, and when it is added above 100.2g, in terms of weldability Because of lack of practicality.

In the present invention, the boric acid plays a role of imparting a dense and beautiful appearance and gloss to the coating, and the amount of the boric acid is not more than 0.8g when the addition amount is less than 0.3g in solid content with respect to 100g of phosphoric acid. If it is added, even if applied after forced agitation, a non-uniform film is formed, so that the proper amount of addition is 0.3-0.8g.

In the present invention, zinc nitrate plays a role of imparting corrosion resistance and light golden color to the film. The amount of zinc nitrate is sufficient corrosion resistance and good when it is added in an amount of 8.3 g or less with respect to 100 g of phosphoric acid of silica-containing magnesium phosphate. If the coating color cannot be obtained and it is added more than 20.3g, it becomes difficult to make a uniform treatment bath, causing a problem of poor appearance after coating and an insulation non-uniformity, which is not practical. Therefore, the added amount is in the range of 8.3-20.3g. It is preferable to limit.

In the present invention, the monomer-type Methacryloxysilane coupling agent has a double bond in the molecular formula and is formed of a material oxide layer formed after rolling annealing during coating and annealing and acryl-styrene copolymer resin in the treatment liquid. It acts as a chemical reaction linkage between the two. By this action, the adhesion between the steel sheet and the film is improved and the corrosion resistance is improved, and by the crosslinking role between the acrylic-styrene-based copolymer resin and the polymer organosilicon, which is another additive, they are united and dried to show an uneven film appearance. It has a suppressing effect. The monomer type methacryloxy silane coupling agent does not have an additive effect when added to 0.3 g or less with respect to 100 g of the solid content of the acryl-styrene copolymer. 0.3-1.0 g is added as an appropriate amount.

In the present invention, the polymer type organosilicon is added for the purpose of improving slip property with the roll coating, and the amount of the organosilicon is 1.5 g or less with respect to 100 g of the solid content of the acryl-styrene copolymer resin. When added, acrylic-styrene copolymer resins having inherent stickiness and inherent viscosity are adhered to the surface of the roll cota. When the amount of 5.0g or more is added, the miscibility of the treatment liquid is good, but the price is high and economical. It is disadvantageous in that it is effective to set the appropriate amount of 1.5-5.0 g.

[Method for Forming Insulating Film of Non-oriented Electrical Steel Sheet]

The coating composition formed as described above 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 annealed for 11-27 seconds in the temperature range of 550-700 ° C. to form an organic-inorganic mixed system. It is possible to obtain an insulating coating having excellent appearance, adhesiveness, insulation, heat resistance and corrosion resistance as well as roll coating application work which is an essential requirement before coating as a coating.

One of the factors that determine the appearance of the film is the relationship between annealing temperature and time. If the furnace temperature is 700 ° C., which is the maximum allowable temperature, when it is maintained for 11 seconds or less, the film becomes in an dull state and the film formation is insufficient, resulting in the problem that the absorbency remains. On the other hand, if it is maintained at the allowable minimum temperature of 550 ° C. for more than 27 seconds, the coating agent, which is chemically bonded to the oxide layer, is poorly colored due to oxidation.

On the other hand, if the furnace temperature is kept below 550 ℃, water resistance and water absorption are inferior. On the other hand, if it is higher than 700 ℃, it is difficult to control the annealing temperature, resulting in uneven film formation, which makes it difficult to control surface quality. This is a difficult problem for industrially stable work.

In the present invention, even if the film is formed by satisfying the above annealing conditions after roll application, if the film thickness after annealing the electrical steel sheet is thinner than 0.7 μm, the required interlayer resistance property cannot be obtained. Since the rate is lowered, it is within the range of 0.7-2.8 μm per single side.

Hereinafter, the present invention will be described in detail through examples.

EXAMPLE

After mixing the coating composition for forming an insulating film having the composition as shown in Table 1, and after one month, using a synthetic rubber roll uniformly coated on the surface of the non-oriented electrical steel sheet having a thickness of 0.5mm and heated as shown in Table 1 After the electrical insulating film was formed under the annealing conditions, the film characteristics of the electrical insulating film were evaluated as follows, and the measurement results are shown in Table 2 below. In addition, the steel sheet formed with the electrical insulating film was stress-annealed for 750 ° C. × 2 hours in a dry 100% N ₂ gas atmosphere, and the film characteristics after the stress-relieving annealing were examined.

(1) The surface appearance is evaluated by visual observation of color, streaks, luster, etc., and the film color is bright light green, and there is no streak phenomenon and the gloss is good, the film appearance is judged to be good, and the film color is thick or dark color. The more the appearance of streaks and the less gloss, the poorer the surface appearance.

(2) The insulation property was evaluated by the storage current value (Amp) when a current of 0.5 V x 1.0 A was passed under a pressure of 300 psi.

(3) Adhesion (mmø) was evaluated by the minimum arc diameter without film peeling when the specimen was bent 180 ° after being annealed to 10, 20, 30 ~ 100mmø arc after annealing.

(4) Corrosion resistance was evaluated by observing the surface of rust after 24 hours of salt spray test (5% NaCl, 35 ℃).

(5) The water resistance was evaluated as the color difference (ΔE) before and after the application of petroleum jelly by using the coated specimen as a standard specimen, and was good when the value of ΔE was 1.0 or less and poor when a value of 2.0 or more appeared.

(6) Film peeling was evaluated by the presence or absence of adhesion of the film peeling powder which appeared when peeled off with an adhesive tape (pullypropylene) on the film after stress relief annealing.

division Composition of insulating coating liquid (g) Annealing Condition Film thickness (single side μm) Silica-containing monophosphate Emulsion Acrylic-Styrene Copolymer Resin ^② Boric acid Zinc nitrate Mono model methacryloxy silane coupling agent ^③ Polymer organosilicon ^④ water Temperature (℃) Time in seconds Phosphoric Acid (85%) Magnesium ion Powdered Silica ^① Inventive Example a 100 9.5 6 38 0.6 14 0.2 1.5 74 660 19 2.2 b 9.2 4 36 0.5 12 0.2 1.3 81 690 17 2.1 Comparative example One 1.1 ^* - ^* 40 - ^* 11 0.3 1.4 85 700 16 0.3 ^* 2 9.3 16 ^* 3 ^* 0.1 ^* 1 ^* - ^* 0.2 ^* 96 650 21 2.3 3 9.0 5 65 0.5 10 0.2 2.2 77 480 9 ^* - 4 8.6 6 44 0.4 12 0.2 1.8 92 880 ^* 27 - 5 18.2 ^* - ^* 41 3.7 ^* 35 ^* 2.1 ^* 1.8 69 700 16 - 6 9.4 4 58 0.5 12 0.9 ^* - ^* 81 Continuous application is not possible ① brand name is Aerosil 380, ② brand name is PA-P40, and the amount of addition is based on solid content ③ is brand name A-174 manufactured by union carbide of USA ④ brand name is Coatosil WB-5 In comparison example 6, the stickiness of the roll coating surface was visually observed and the roll coating workability was judged to be lost after 3 hours continuous coating treatment on the surface of the non-oriented electrical steel sheet in actual line. The * mark is outside the terms of the present invention.

division Film characteristics Before stress relief annealing After stress relief annealing Outer appearance Insulation (Amp.) Adhesiveness (mmø) Corrosion resistance (% rust) Water absorption Peeling phenomenon Adhesiveness (mmø) Inventive Example a Good 0.12 10 Good (0) Good none 10 b Good 0.14 10 Good (0) Good none 10 Comparative example One Good 0.96 10 Poor (55) Good none 10 2 Bad 0.11 40 Poor (85) Bad has exist 70 3 Bad Not measurable Not measurable 4 Bad Not measurable Not measurable 5 Bad Not measurable Not measurable

As can be seen from Table 1 and Table 2, the invention examples (a, b) satisfying the conditions of the present invention showed excellent roll coating workability, as well as the properties required as a coating such as appearance.

On the other hand, the comparative example (1-6) in which the addition range of the coating composition was inappropriately applied or improperly applied and annealed was inferior in the characteristics required as a coating such as roll coating coating property or appearance compared to the invention example.

More specifically, Comparative Example (1), which was thinly treated with a coating composition containing less magnesium ions and no powdered silica and boric acid, was inferior in insulation corrosion resistance. The acid-soluble emulsion type acrylic-styrene copolymer resin and the zinc nitrate content and the comparative example (2) which did not add the monomer type methacryloxy silane coupling agent did not have the external appearance, corrosion-resistance adhesiveness, and water absorption resistance. In addition, Comparative Example (3) is a case where film formation is difficult due to insufficient annealing treatment conditions, and Comparative Example (4) is a case where carbonized annealing is shown by annealing treatment. In Comparative Example (5), the monomer-type methacryloxy silane coupling agent, magnesium ion, boric acid, and zinc nitrate content were added in an excessive amount, and applied with agitation in an unsuitable state as an insulating coating solution, but the appearance was poor. When the value of use is lost, Comparative Example (6) has a poor phenomenon in which the resin adheres to the roll cotta surface due to the addition of high-molecular weight special modified silicone additive organosilicon added for the purpose of improving slipperiness with the coating. This is the case.

As described above, according to the present invention, there is provided a coating composition for forming an insulating coating, which improves not only the roll coating coating workability but also the general properties required for coating such as appearance, and the coating composition is used for insulating non-oriented electrical steel sheet. When applied to the film forming process, the productivity is improved according to the realization of the continuous coating operation, there is an effect that can be produced reproducibly produced a certain weight electrical steel coil in accordance with the demand of the demand.

Claims (2)

(a) Magnesium phosphate monophosphate solution containing 8.2-10.1 g of magnesium ions and 2.1-9.3 g of powdered fine silica with respect to 100 g of phosphoric acid; (b) To 100 g of phosphoric acid of the silica-containing magnesium phosphate salt solution 22.4-100.2g, boric acid: 0.3-0.8g, zinc nitrate: 8.3-20.3g are added to the acid-soluble emulsion type acrylic-styrene copolymer resin by the weight basis when it is solid content, (c) For solid content of 100 g of the acrylic-styrene copolymer emulsion resin Monomer methacryloxy silane coupling agent: 0.3-1.0 g, Polymeric organosilicon: Add 1.5-5.0 g and adjust the concentration as the remaining water A coating composition for forming an inorganic and inorganic insulating film having excellent roll coating workability. In the method for forming an insulating coating on a non-oriented electrical steel sheet, After coating the coating composition of claim 1 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㎛ per one side, the annealing for 11-27 seconds at a temperature of 550-700 ℃ Method of forming insulating film of oriented electrical steel sheet.