Manufacturing method for chrome-free insulating coated electrical steel sheet

Abstract

To provide a method for manufacturing a magnetic steel sheet with an insulation coating that has excellent powdering resistance under a severer condition in which a production line is simulated.SOLUTION: A method for manufacturing a magnetic steel sheet with an insulation coating includes the steps of: preparing a surface treatment liquid containing at least one kind of inorganic substances selected from the group consisting of an Si compound, an Al compound and a P compound as the principal component and containing 10-90 pts. mass of a Zr compound in terms of ZrO2 based on the total amount of 100 pts. mass of each of the inorganic substances in terms of SiO2, Al2O3 and PO4; applying the surface treatment liquid to a surface of a magnetic steel sheet; and heating and drying the magnetic steel sheet so that a maximum arrival sheet temperature reaches 240-320°C to form an insulation coating on the surface of the magnetic steel sheet with a coating weight of 0.05-2 g / m2 per single side.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing an insulating coated electrical steel sheet that does not contain a chromium compound and that is primarily composed of inorganic substances. [Background technology]

[0002] The insulating coatings of electrical steel sheets used in motors, transformers, etc. require various properties, including interlaminar resistance, ease of processing, and stability during storage and use. Because electrical steel sheets are used in a wide variety of applications, various insulating coatings have been developed to suit these applications. When electrical steel sheets are subjected to punching, shearing, bending, etc., residual strain degrades their magnetic properties. Therefore, to restore these properties, they are often subjected to stress relief annealing at temperatures of around 750-850°C. In this case, the insulating coating must be able to withstand stress relief annealing.

[0003] The insulating coating of electromagnetic steel sheets can be broadly divided into (1) Inorganic coating that emphasizes weldability and heat resistance and can withstand stress relief annealing. (2) A resin-containing inorganic coating (i.e., a semi-organic coating) that can withstand stress relief annealing and achieves both punchability and weldability. (3) Organic coatings for special applications that cannot be annealed for distortion relief However, the coatings that can withstand stress relief annealing as general-purpose products are those containing inorganic components as shown in (1) and (2) above, both of which generally contain chromium compounds. In particular, type (2) chromate-based insulating coatings containing organic resins are widely used because they can be manufactured using a one-coat, one-bake process, which allows for significantly improved punchability compared to inorganic insulating coatings.

[0004] However, with the recent rise in environmental awareness, there is growing demand from customers in the field of electrical steel sheets for chromate-free products that have an insulating coating that does not contain chromium compounds.

[0005] Therefore, electrical steel sheets with an insulation coating that does not contain chromium compounds have been developed. Patent Document 1 describes "an electrical steel sheet with an insulation coating whose main component is at least one inorganic substance selected from the group consisting of Si compounds, Al compounds, and P compounds, wherein the insulation coating contains 10 to 90 parts by mass of a Zr compound calculated as ZrO2 per 100 parts by mass of the total amount of the inorganic substances calculated as SiO2, Al2O3, and PO4, resulting in an electrical steel sheet with a chromium-free insulation coating that has excellent corrosion resistance, powdering resistance, and stickiness resistance." [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-268630 Summary of the Invention [Problem to be solved by the invention]

[0007] "Dust blowing resistance" refers to the degree to which dust blowing occurs less when a tension pad rubs against the insulating coating on a production line (how difficult the insulating coating is to peel off). The insulating-coated electrical steel sheet described in Patent Document 1 is said to have excellent dust blowing resistance. However, the insulating-coated electrical steel sheet described in Patent Document 1 still suffers from dust blowing problems in actual production lines, and there has been a demand for an insulating-coated electrical steel sheet that has excellent dust blowing resistance under more severe conditions that simulate those of a production line.

[0008] In view of the above problems, an object of the present invention is to provide a method for producing an electrical steel sheet with an insulation coating that has excellent resistance to powder blowing under more severe conditions that simulate those of a production line. [Means for solving the problem]

[0009] The present inventors have conducted extensive research to solve the above-mentioned problems, and have discovered that powder blowing resistance can be dramatically improved under harsher conditions simulating those of a production line by applying a surface treatment liquid containing, as a main component, at least one inorganic substance selected from the group consisting of Si compounds, Al compounds, and P compounds, and a predetermined amount of Zr compound to the surface of an electrical steel sheet, and then heating and drying the liquid under conditions of a specific range of peak metal temperature (PMT), thereby forming an insulating coating with a deposition amount within a specific range.

[0010] The gist and configuration of the present invention, which has been completed based on the above findings, is as follows. [1] A surface treatment solution is prepared, which contains, as a main component, at least one inorganic substance selected from the group consisting of an Si compound, an Al compound, and a P compound, and which contains 10 to 90 parts by mass of a Zr compound calculated as ZrO2 relative to 100 parts by mass of the total amount of the inorganic substances calculated as SiO2, Al2O3, and PO4; The surface treatment liquid is applied to the surface of an electrical steel sheet, and the sheet is heated and dried so that the maximum sheet temperature reaches 240 to 320°C, and a coating amount of 0.05 to 2 g / m per side is obtained on the surface of the electrical steel sheet. 2 Form an insulating coating of Manufacturing method for insulating coated electrical steel sheet.

[0011] [2] The method for producing an insulating coated electrical steel sheet according to [1] above, wherein the maximum sheet temperature is 260 to 300°C.

[0012] [3] The method for producing an electrical steel sheet with an insulation coating according to [1] or [2] above, wherein the Zr compound is water-soluble.

[0013] [4] The method for producing an electrical steel sheet with an insulation coating according to any one of [1] to [3] above, wherein the surface treatment solution further contains 50 parts by mass or less of a resin per 100 parts by mass of the total amount of each of the inorganic substances and the Zr compound calculated as SiO2, Al2O3, PO4, and ZrO2. [Effects of the Invention]

[0014] According to the method for producing an electrical steel sheet with an insulation coating of the present invention, it is possible to produce an electrical steel sheet with an insulation coating that has excellent resistance to powder blowing under more severe conditions that simulate those of a production line. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a graph showing the effect of maximum reached strip temperature (PMT) on powder blowing resistance. DETAILED DESCRIPTION OF THE INVENTION

[0016] A method for producing an electrical steel sheet with an insulation coating according to one embodiment of the present invention comprises the steps of: preparing a surface treatment liquid containing, as a main component, at least one inorganic substance selected from the group consisting of a Si compound, an Al compound, and a P compound, a predetermined amount of a Zr compound, and optionally a predetermined amount of a resin; and applying the surface treatment liquid to the surface of an electrical steel sheet, followed by heating and drying the surface so that the maximum peak temperature (PMT) falls within a predetermined range, thereby forming an insulating coating with a predetermined adhesion weight on the surface of the electrical steel sheet.

[0017] [Electromagnetic steel sheet] The electrical steel sheet (electric iron sheet) may be any steel sheet of any composition adjusted to change the resistivity and obtain the desired magnetic properties, and is not particularly limited. The surface of the electrical steel sheet on which the insulating coating is formed may be untreated or may be pretreated. Pretreatment is optional, but degreasing treatment using alkali or the like, and pickling treatment using hydrochloric acid, sulfuric acid, phosphoric acid, or the like are preferred.

[0018] [Si compound] Colloidal silica is preferably used as the Si compound. Colloidal silica is an inorganic colloid primarily composed of SiO2 and is often amorphous. The particle diameter is preferably 20 nm or less, more preferably 10 nm or less. The smaller the particle diameter, the better the coating formed, so there is no particular lower limit. It is believed that ultrafine particles, due to their large surface area, enhance interaction with other components and increase the strength of the coating. However, as the particle diameter decreases, aggregation between silica particles and other components becomes more likely, so the concentration of colloidal silica must be reduced. Taking these factors into consideration, a practical particle diameter can be set. The average particle diameter can be measured using the BET method (converted from the specific surface area measured by the adsorption method). Alternatively, the average value measured from electron microscope photographs can be used instead.

[0019] [Al compound] The Al compound is preferably an Al compound consisting of a hydroxyl group and an organic acid and / or its dehydration product, such as alumina sol. Since the aqueous surface treatment liquid is applied to the steel sheet and baked, the Al compound is preferably one that can be dissolved in water or dispersed in a colloidal or suspended state. Furthermore, the shape of the alumina may be any shape, such as feathery or spherical, as long as it does not affect the properties.

[0020] [P compound] Phosphates are applicable as P compounds, and examples thereof include aluminum phosphate, magnesium phosphate, calcium phosphate, iron phosphate, zinc phosphate, etc. Among these P compounds, aluminum phosphate is a compound containing aluminum, but in the present invention, its content is counted only as a "P compound" and not as an "Al compound."

[0021] The Si compound, Al compound, and P compound can be used alone or in combination as long as sufficient coating properties are obtained. Specific examples include composite systems of silica sol and alumina sol, phosphate and silica sol, phosphate and alumina sol, and silica sol, alumina sol, and phosphate.

[0022] [Zr compound] In the present invention, it is necessary to contain a specific amount of Zr compound. An appropriate amount is 10 to 90 parts by mass, preferably 15 to 80 parts by mass, and more preferably 20 to 70 parts by mass, per 100 parts by mass of the total amount of at least one inorganic substance selected from the group consisting of Si compounds, Al compounds, and P compounds, calculated as SiO2, Al2O3, and PO4, respectively. Zr compounds have three or more, typically four, bonds, and therefore can form a tough coating without using a chromium compound by causing a crosslinking reaction. However, significant effects can only be obtained when the specific amount of Zr compound is contained in the coating, with at least one inorganic substance selected from the group consisting of Si compounds, Al compounds, and P compounds as the main component.

[0023] When Zr compounds are used alone or as the main component, the network is not formed well due to the large number of bonds, which is thought to result in a weak coating with poor corrosion resistance, and conversely, if the amount added is small, the effect is naturally not exerted. In other words, it is thought that the effect can only be exerted in the presence of other specific inorganic substances.

[0024] The bonding forms are thought to be Al-O-Zr-O-Al, Si-O-Zr-O-Si, and PO-Zr-OP via oxygen. It is also thought that with organic resins, bonds such as CO-O-Zr-O-OC and CO-Zr-OC are formed with carboxyl groups and hydroxyl groups. It is thought that the same effect is seen with resins such as silicone.

[0025] That is, it is believed that a complex oxide coating containing at least one element selected from the group consisting of Si, Al, and P, and Zr element is formed.

[0026] Examples of Zr compounds include zirconium acetate, zirconium propionate, zirconium oxychloride, zirconium nitrate, ammonium zirconium carbonate, potassium zirconium carbonate, zirconium hydroxychloride, zirconium sulfate, zirconium phosphate, sodium zirconium phosphate, potassium zirconium hexafluoride, zirconium tetra-n-propoxide, zirconium tetra-n-butoxide, zirconium tetraacetylacetonate, zirconium tributoxyacetylacetonate, and zirconium tributoxystearate. These compounds can be selected based on their compatibility with the inorganic substance that constitutes the main component. These compounds can be used alone or in combination. Among these Zr compounds, zirconium phosphate and sodium zirconium phosphate contain phosphorus. However, in the present invention, their content is counted only as "Zr compounds" and not as "P compounds."

[0027] A water-soluble Zr compound is preferable to a water-insoluble paste compound, because the above-mentioned bond becomes stronger and a denser coating is formed.

[0028] [resin] The surface treatment solution preferably contains 50 parts by mass or less of resin per 100 parts by mass of at least one inorganic substance selected from the group consisting of Si compounds, Al compounds, and P compounds, calculated as SiO2, Al2O3, and PO4, respectively, plus the Zr compounds calculated as ZrO2. While a practically sufficient coating can be formed without the resin, adding a small amount of resin can further improve corrosion resistance. This is thought to be because inorganic components alone are prone to cracking due to shrinkage during film formation, while the addition of resin alleviates shrinkage stress. Adding resin provides excellent corrosion resistance, even when produced at low temperatures of 240 to 320°C.

[0029] To achieve this effect, it is preferable to include 10 parts by mass or more of resin per 100 parts by mass of the total amount of at least one inorganic substance selected from the group consisting of Si compounds, Al compounds, and P compounds, calculated as SiO2, Al2O3, and PO4, respectively, and the amount of Zr compounds calculated as ZrO2. On the other hand, if the amount exceeds 50 parts by mass, the coating after stress relief annealing becomes brittle and tends to peel off, so the amount is set to 50 parts by mass or less. A more preferable amount of resin specified above is 10 to 40 parts by mass.

[0030] The resin component is not particularly limited, but is preferably one or more aqueous resins (emulsion, dispersion, water-soluble) such as acrylic resin, alkyd resin, polyolefin resin, styrene resin, vinyl acetate resin, epoxy resin, phenolic resin, polyester resin, urethane resin, and melamine resin.

[0031] [Chromium-free] In the present invention, the surface treatment solution and insulating coating do not contain chromium. Note that "chromium-free" or "chromium-free" means that chromium is not intentionally added, not that chromium is completely absent. In other words, the inclusion of chromium as an impurity from raw materials is permissible as long as the amount of the Cr compound mixed in, etc., is 0.1 parts by mass or less, calculated as CrO3, per 100 parts by mass of the total amount of each of the inorganic substances and the Zr compound calculated as SiO2, Al2O3, PO4, and ZrO2.

[0032] [Other additives] To further improve the performance and uniformity of the coating, additives such as surfactants, rust inhibitors, boric acid, lubricants, and antioxidants may be added to the surface treatment solution and insulating coating as needed. In this case, the amount of additives is preferably about 10% by mass or less of the solid weight of the coating after drying in order to maintain sufficient coating properties.

[0033] [Insulating coating formation method] The insulating coating is formed by applying the above-mentioned surface treatment solution to the surface of the electrical steel sheet and baking it. The insulating coating can be formed by various methods commonly used in industry, such as a roll coater, flow coater, spray coater, or knife coater. For baking, commonly used methods such as hot air, infrared, or induction heating can be used.

[0034] In the present invention, it is important to heat-dry the surface treatment solution so that the PMT is 240 to 320°C, and more preferably so that the PMT is 260 to 300°C. If the PMT is less than 240°C, powdering resistance tends to decrease. This is thought to be because the bonding reaction (Al-O-Zr-O-Al, Si-O-Zr-O-Si, PO-Zr-OP) between the Zr compound and other inorganic compounds (Si compounds, Al compounds, and P compounds) does not proceed sufficiently, resulting in embrittlement of the coating strength. On the other hand, if the PMT exceeds 320°C, the amount of cracks formed during film formation increases, making the coating more susceptible to peeling due to sliding, again resulting in a deterioration of powdering resistance. Furthermore, if the coating contains an organic resin, a PMT exceeding 320°C initiates decomposition of the resin, increasing the amount of coating peeling.

[0035] [Amount of insulating coating] The amount of insulation coating applied is 0.05 to 2 g / m per side. 2 The adhesion amount is 0.05g / m 2 If the coating weight is less than 2g / m, not only the corrosion resistance but also the insulating properties tend to be insufficient. 2 If the coating amount exceeds 100%, the amount of coating peeling increases and powdering resistance decreases. The coating amount per side is more preferably 0.1 to 1.0 g / m 2 The coating weight, i.e., the weight of the solid content of the coating, can be measured from the weight loss after removing the coating by alkaline stripping. The insulating coating is preferably on both sides of the steel sheet, but may be on only one side depending on the purpose. [Example]

[0036] Each surface treatment solution was prepared by adding the types of base agent (at least one of Si compound, Al compound, and P compound), Zr compound, and resin shown in Table 1 to deionized water in the parts by mass (equivalent amounts) shown in Table 1. Each surface treatment solution was prepared so that the total amount of SiO2, Al2O3, PO4, and ZrO2 relative to the amount of deionized water was 50 g / L. Each surface treatment solution was applied using a roll coater to the surface of a test piece 150 mm wide and 300 mm long cut from a 0.5 mm thick electrical steel sheet. The test piece was then baked using a PMT shown in Table 1 over a direct propane gas flame, and then allowed to cool at room temperature to form an insulating coating with the coating amount shown in Table 1.

[0037] [Evaluation of dusting resistance using conventional methods] Test conditions: Felt contact surface width 20 x 10 mm, load: 2 kg / cm 2 (0.2 MPa), the coating surface was simply run back and forth for 400 m. After the test, the abrasion marks were observed and the state of peeling and powdering of the coating was evaluated. (Judgment criteria) ◎: Almost no scratches are visible ○: Slight scratches and slight powdering are observed △: The coating has peeled off to the extent that scratches and powdering are clearly visible. ×: Peeling so much that the steel substrate is exposed, causing a great deal of dust

[0038] [Evaluation of dusting resistance under severe conditions (XY stage method)] Conventional powder blowing resistance tests have not been able to adequately reproduce the powder blowing phenomenon that occurs on an actual production line. Therefore, we evaluated powder blowing resistance using the XY stage method, which more closely mimics the situation on a production line. Test conditions: Felt contact surface width 15mm x 15mm, load: 0.087MPa (0.89kgf / cm 2The surface of the insulating coating was rubbed with a felt attached to an XY plotter, and the felt was moved continuously 400 mm in the X-axis direction and 15 mm in the Y-axis direction, moving 36 m in a single stroke. The movement speed was 150 mpm. After the test, the felt was analyzed using fluorescent X-rays, and the amount of Zr, a component of the insulating coating, attached to the felt was taken as the amount of coating peeling, and powdering resistance was evaluated. Among the comparative examples that did not contain a Zr compound, the amount of Si attached to the felt was taken as the amount of coating peeling in Comparative Examples 10 and 16, and the amount of Al attached to the felt was taken as the amount of coating peeling in Comparative Examples 21 and 22, to evaluate powdering resistance. (Judgment criteria) ◎: Amount of coating peeled off is 0.10 g / m 2 less than ○: Amount of coating peeled off is 0.10 g / m 2 More than 0.15g / m 2 less than △: Amount of coating peeled off was 0.15 g / m 2 More than 0.20g / m 2 less than ×: Amount of coating peeled off was 0.20 g / m 2 End

[0039] [Table 1] TIFF0007774408000002.tif255108TIFF0007774408000003.tif255126

[0040] 1 is a graph showing the amount of coating peeling versus PMT for levels (Examples 9 to 13 and Comparative Examples 4 to 9) containing 60 parts by mass of alumina sol and 40 parts by mass of silica sol as the main components, 30 parts by mass of a Zr compound (derived from Zr acetate), and 30 parts by mass of an epoxy resin. As is clear from FIG. 1, good resistance to powdering was observed in the PMT range of 240 to 320°C, and particularly good resistance to powdering was observed in the PMT range of 260 to 300°C. [Industrial Applicability]

[0041] According to the method for producing an electrical steel sheet with an insulation coating of the present invention, it is possible to produce an electrical steel sheet with an insulation coating that has excellent resistance to powder blowing under more severe conditions that simulate those of a production line.

Claims

1. The inorganic material contains at least one inorganic substance selected from the group consisting of Si compounds, Al compounds, and P compounds as a main component, and each of the inorganic substances is SiO ２ Conversion, Al ２ O ３ Conversion and PO ４ The Zr compound was added to ZrO for a total of 100 parts by mass. ２ A surface treatment solution containing 10 to 90 parts by mass of the converted The surface treatment liquid is applied to the surface of the electrical steel sheet, and the surface is heated and dried so that the maximum sheet temperature reaches 260 to 300°C, and the coating amount per side of the electrical steel sheet is 0.05 to 2 g / m ２ Form an insulating coating of Manufacturing method for chrome-free insulating coated electrical steel sheet.

2. The method for producing an electrical steel sheet with a chromium-free insulation coating according to claim 1 , wherein the Zr compound is water-soluble.

3. The surface treatment solution is a solution containing each of the inorganic substances and the Zr compound. ２ Conversion, Al ２ O ３ Conversion, P.O. ４ Conversion, and ZrO ２ The method for producing an electrical steel sheet with a chromium-free insulation coating according to claim 1 or 2, further comprising 50 parts by mass or less of a resin per 100 parts by mass of the converted total amount.

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