Method for manufacturing electromagnetic steel sheet with insulating film

Abstract

Provided is a method for manufacturing an electromagnetic steel sheet with an insulating film, the sheet such having excellent punchability and weldability under severe evaluation conditions. This method for manufacturing an electromagnetic steel sheet with an insulating film is characterized by including: a step of preparing a water-based coating material; and a step of applying the water-based coating material on a surface of an electromagnetic steel sheet and heating and drying said coating material to form an insulating film. The method is further characterized in that: the water-based coating material contains a resin, an inorganic component, an optional organic reducing agent, an optional compound B, and water; 50 mass% or more of the resin is composed of one or both of an emulsion resin and a dispersion resin; and the water-based coating material has a viscosity of 1.0 mPa·s or more.

Description

Manufacturing method for insulating coated electrical steel sheet

[0001] The present invention relates to a method for manufacturing an insulating coated electrical steel sheet.

[0002] Insulation-coated electrical steel sheets naturally have excellent magnetic properties, which are their basic characteristic, but various other properties are also required in the manufacturing process of motors, transformers, etc. Properties required in the manufacturing process of such products include, for example, punchability, weldability (welding of end faces), coating adhesion, and corrosion resistance. It is well known that adding a resin component to the insulation coating is effective in improving punchability, but adding resin can cause blowholes during welding, so achieving both punchability and weldability has been a challenge.

[0003] Patent Document 1 describes a "method for producing an insulating coated electrical steel sheet having excellent weldability and punchability, characterized by applying an aqueous coating liquid containing a resin and an inorganic component to the surface of the electrical steel sheet, and then heating and baking the coating from the steel sheet side."

[0004] Japanese Patent Application Laid-Open No. 2003-213444

[0005] In Patent Document 1, although the weldability and punchability were improved, there was still room for improvement in terms of achieving both weldability and punchability under stricter evaluation conditions.

[0006] In view of the above problems, an object of the present invention is to provide a method for manufacturing an electrical steel sheet with an insulation coating that is excellent in both punchability and weldability under stricter evaluation conditions.

[0007] As a result of intensive research conducted by the present inventors to achieve this object, they have newly discovered that by maintaining the viscosity of the water-based paint containing a resin and an inorganic component used to form the insulating coating within an appropriate range, it is possible to obtain an insulating-coated electrical steel sheet that is excellent in both punchability and weldability under stricter evaluation conditions. It has also been found that the effect of improving punchability and weldability by maintaining the viscosity of the water-based paint applied to the electrical steel sheet within an appropriate range is not limited to heating from the steel sheet side by induction heating as described in Patent Document 1, but can also be obtained when heating is performed from the surface of the coating film formed by the water-based paint, as in a gas furnace or electric furnace.

[0008] The present invention, which was completed based on the above findings, is summarized as follows: [1] A method for producing an electrical steel sheet with an insulating coating, comprising the steps of preparing a water-based paint, and applying the water-based paint to the surface of an electrical steel sheet and drying it by heating to form an insulating coating, wherein the water-based paint contains a resin, an inorganic component, an optional organic reducing agent, an optional boron compound (B compound), and water, 50 mass % or more of the resin is composed of one or both of an emulsion resin and a dispersion resin, and the water-based paint has a viscosity of 1.0 mPa s or more.

[0009] [2] The method for producing an electrical steel sheet with an insulating coating according to [1], wherein the water-based paint has a viscosity of 40 mPa·s or less.

[0010] [3] The method for producing an electrical steel sheet with an insulating coating according to [1], wherein the water-based paint has a viscosity of 10 mPa·s or less.

[0011] [4] The method for producing an electrical steel sheet with an insulation coating according to any one of [1] to [3], wherein one or both of the emulsion resin and the dispersion resin in the water-based paint have particle sizes of 30 nm or more.

[0012] [5] The method for producing an electrical steel sheet with an insulation coating according to any one of [1] to [4], wherein the solid content mass ratio of the resin to the total mass of the resin, the inorganic component, the organic reducing agent, and the B compound in terms of solid contents in the water-based paint is 0.5 mass% or more and 50 mass% or less.

[0013] 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 is excellent in both punchability and weldability under stricter evaluation conditions.

[0014] Hereinafter, an embodiment of the method for manufacturing an electrical steel sheet with an insulation coating according to the present invention will be described. Note that the embodiment described below is an example of a specific embodiment of the present invention, and the configuration of the present invention is not limited to this specific example.

[0015] A method for producing an insulating coated electrical steel sheet according to one embodiment of the present invention comprises the steps of preparing a water-based paint and applying the water-based paint to the surface of an electrical steel sheet and drying it by heating to form an insulating coating, wherein the water-based paint contains a resin, an inorganic component, an optional organic reducing agent, an optional B compound, and water, wherein 50 mass % or more of the resin is an emulsion resin and / or a dispersion resin, and the water-based paint has a viscosity of 1.0 mPa s or more.

[0016] There are no particular restrictions on the electrical steel sheet that serves as the base for the insulating coating, but it is preferable to adjust the composition appropriately depending on the desired properties. For example, increasing the resistivity is effective in improving iron loss, so it is preferable to add elements that improve resistivity, such as Si, Al, Mn, Cr, P, and Ni. The proportions of these elements can be determined depending on the desired magnetic properties.

[0017] The C and S contained in electrical steel sheets are elements that are disadvantageous to weldability, and it is also desirable to reduce their contents in terms of magnetic properties. Therefore, the C content in electrical steel sheets is preferably 0.01 mass% or less. Furthermore, the S content in electrical steel sheets is preferably 0.01 mass% or less. There are no particular restrictions on the other trace elements, segregated elements such as Sb and Sn, and inevitable impurities contained in electrical steel sheets.

[0018] There are no particular restrictions on the manufacturing method of the electrical steel sheet, and various conventionally known methods can be applied. Furthermore, the surface roughness of the steel sheet is not particularly restricted, but when emphasis is placed on the space factor, it is preferable to set the three-dimensional surface roughness SRa to 0.5 μm or less. Furthermore, there are no particular restrictions on the final thickness of the steel sheet, and various thicknesses can be applied, but from the viewpoint of magnetic properties, it is preferable to set the thickness to 0.8 mm or less.

[0019] The water-based paint contains a resin and an inorganic component. These resins and inorganic components have the property of being soluble or dispersible in water. The water-based paint may also contain one or both of an organic reducing agent and a B compound. Any type of coating treatment liquid may be used for the water-based paint, such as a coating treatment liquid containing at least a chromate and a resin, a coating treatment liquid containing at least a phosphate and a resin, or a coating treatment liquid containing at least an inorganic colloid and a resin. Various components may also be added to the water-based paint to improve heat resistance or corrosion resistance.

[0020] The type of resin contained in the water-based paint is not particularly limited, and may be one or more selected from acrylic resins, epoxy resins, urethane resins, phenolic resins, styrene resins, amide resins, imide resins, urea resins, vinyl acetate resins, alkyd resins, polyolefin resins, and polyester resins. These may be used alone, as copolymers, or as mixtures. Of the total resin amount (solid content) in the water-based paint, 50% by mass or more is resin with particle size, i.e., one or both of emulsion resins and dispersion resins. When the mass ratio of one or both of emulsion resins and dispersion resins in the resins contained in the water-based paint is 50% by mass or more and 100% by mass or less, this means that the mass ratio of completely water-soluble resins without particle size is 0% by mass or more and 50% by mass or less. If the mass ratio of completely water-soluble resins without particle size exceeds 50% by mass, the effect of improving punchability is not satisfactory. In the present invention, when calculating the mass ratio of one or both of the emulsion resin and the dispersion resin in the total resin amount, so-called monomers such as water-soluble acrylic acid, which are components of the resin, are also included in the calculation as "resin."

[0021] It is preferable that one or both of the emulsion resin and the dispersion resin in the water-based paint have a particle size of 30 nm or more. When the particle size of one or both of the emulsion resin and the dispersion resin is 30 nm or more, the resin area that adheres to the mold end surface and covers the mold tip during punching is suitable, the adhesive wear suppression effect between the mold end surface and the workpiece is suitable, and punching properties are obtained favorably. Note that there is no particular upper limit for the particle size of the resin, but when the space factor is important, it is preferable that the particle size of the resin be 1 μm or less. The particle size of the resin can be measured by dynamic light scattering in accordance with JIS 8828:2013.

[0022] In the water-based paint, the solid content mass ratio of the resin to the total mass of the resin, inorganic components, organic reducing agent, and B compound in terms of solid content is preferably 0.5% by mass or more and 50% by mass or less. When the solid content mass ratio of the resin is 0.5% by mass or more, the above-mentioned effect of improving punchability (adhesive wear suppression effect) is preferably obtained. When the solid content mass ratio of the resin is 50% by mass or less, the amount of organic matter that decomposes and vaporizes during welding is suitable, blowholes in the weld bead can be suppressed, and suitable weldability can be obtained. It is even more preferable that the solid content mass ratio of the resin is 40% by mass or less.

[0023] Inorganic components contained in the water-based paint include Cr compounds, P compounds, Si compounds, etc. Cr compounds include chromates and dichromates containing at least one metal selected from Ca, Mg, Zn, K, Na, Al, etc., and one or more of these can be used. Phosphates are applicable as P compounds, and examples thereof include aluminum monophosphate, magnesium phosphate, calcium phosphate, iron phosphate, and zinc phosphate, and one or more of these can be used. Si compounds include colloidal silica, fumed silica, and plate-like silica, and one or more of these can be used. Colloidal silica, fumed silica, and plate-like silica exist in particulate form in the insulating coating. Multiple types of inorganic compounds may also be contained.

[0024] From the viewpoint of improving the insulating properties and corrosion resistance of the insulating coating, the solid mass ratio of the inorganic component to the total mass of the resin, inorganic component, organic reducing agent, and compound B converted into solid content is preferably 30 mass % or more, and more preferably 60 mass % or more. Furthermore, if the ratio of the inorganic component is too high, there is a concern that punching properties may deteriorate, so this mass ratio is preferably 80 mass % or less.

[0025] The water-based paint contains an organic reducing agent. By including an organic reducing agent, the reduction reaction of chromium can be favorably promoted. The type of organic reducing agent is not particularly limited, but it is preferable to use at least one selected from diols and sugars. In particular, it is more preferable to use one or more diols selected from ethylene glycol and 1,4-butanediol, and one or more sugars selected from glycerin, polyethylene glycol, sucrose, lactose, sucrose, glucose, and fructose.

[0026] When the water-based coating material contains an organic reducing agent, from the viewpoint of fully obtaining its effect, the solid mass ratio of the organic reducing agent to the total mass converted to solid contents of the resin, inorganic components, organic reducing agent, and Compound B is preferably 10 mass% or more. Furthermore, if the content of the organic reducing agent is too high, the coating properties after annealing deteriorate, so the mass ratio is preferably 30 mass% or less.

[0027] The water-based paint contains a B compound. By including the B compound, coating cracking that may occur during stress relief annealing can be effectively alleviated, and powdering resistance can be suitably improved. Examples of such B compounds include boric acid, orthoboric acid, metaboric acid, tetraboric acid, sodium metaborate, sodium tetraborate, etc., and these can be used alone or in combination. The B compound is not limited to these compounds, and may be, for example, a compound that dissolves in water to generate borate ions, and the borate ions may be linearly or cyclically polymerized.

[0028] When the water-based coating material contains Compound B, from the viewpoint of fully obtaining its effects, the solid mass ratio of Compound B to the total mass of the resin, inorganic components, organic reducing agent, and Compound B converted to solid content is preferably 5 mass% or more. Moreover, if the content of Compound B is too high, the coating properties after annealing deteriorate, so this mass ratio is preferably 30 mass% or less.

[0029] The water-based paint must have a viscosity of 1.0 mPa·s or greater. If the viscosity of the water-based paint is less than 1.0 mPa·s, the resin particles tend to settle in the paint and form heterogeneous aggregates, resulting in insufficient weldability under more stringent evaluation conditions. The cause of the deterioration of weldability due to heterogeneous aggregates is unclear, but it is believed that the presence of heterogeneous aggregates of resin particles makes it difficult to remove low-boiling-point components in the water-based paint (coating film), whether the coating is heated from the steel sheet side or the coating film surface side. Maintaining the viscosity of the water-based paint within an appropriate range allows the resin particles to be uniformly dispersed in the paint, thereby suppressing the formation of aggregates. Furthermore, the viscosity of the water-based paint is preferably 40 mPa·s or less, and more preferably 10 mPa·s or less. A viscosity of 10 mPa·s or less effectively suppresses streak-like coating defects known as roping when forming a coating on a steel sheet.

[0030] The solids concentration of the aqueous paint may be adjusted to achieve the desired viscosity, or a viscosity modifier may be added. The type of viscosity modifier is not particularly limited, and commonly used viscosity modifiers such as acrylic polymers and urethane-modified polyethers may be used.

[0031] The viscosity of the water-based paint in the present invention is a value measured after mixing the components in a predetermined ratio and adjusting to the desired solid content concentration. The viscosity is also a value measured in accordance with JIS K 6901:2021. For example, it can be measured using a BM type viscometer (manufactured by Tokyo Keiki Co., Ltd.) at a test temperature of 25°C.

[0032] The method for applying the water-based paint may be any method that can apply the water-based paint to the steel sheet, and various methods such as a roll coater method, a bar coater method, an air knife method, and a spray coater method can be applied.

[0033] The heating method for the coating film is not particularly limited, and a general baking method using a gas furnace or electric furnace may be used. However, it is preferable to use an induction heating method that utilizes eddy currents generated when an electric current is passed through the steel sheet for heating. There are no particular limitations on the frequency or heating rate of the induction heating, and these may be selected appropriately depending on the heating time and efficiency, which are limited by equipment constraints, and the properties of the electrical steel sheet (sheet thickness, magnetic permeability, etc.). The heating temperature, i.e., the maximum sheet temperature, may be the temperature required to form the insulating coating. However, since a water-based paint is used, it is preferably 100°C or higher, and more preferably 150°C or higher. By setting it to 100°C or higher, residual water can be suitably suppressed. Furthermore, the maximum sheet temperature is preferably 350°C or lower. By setting it to 350°C or lower, thermal decomposition of the resin can be suitably suppressed.

[0034] The coating is preferably heated from the steel sheet side (the lower layer of the coating). Heating from the lower layer of the coating results in favorable punchability and weldability. The reasons for this are unclear, but the inventors believe the following: 1) When heating from the lower layer of the coating, convection occurs within the unsolidified coating, and resins that are not completely dissolved but have a particulate form, such as emulsion resins and dispersion resins, are concentrated near the surface, increasing the amount of resin in the outermost layer and improving punchability. 2) When heating from the surface of the coating, the surface dries first, and low-boiling-point components tend to remain inside the coating, which turns into gas during welding and causes blowholes. However, when heating from the steel sheet side (the lower layer of the coating), the low-boiling-point components are effectively removed from the coating, resulting in stable weldability.

[0035] The dry weight of the insulating coating is 0.05 g / m ２ The weight of the insulating coating is preferably 0.05 g / m or more. ２In the above cases, the coating is uniformly applied and the coating performance is stable. In addition, the coating weight of the insulating coating is 7.0 g / m2 in dry weight. ２ It is preferable that the density is 7.0 g / m or less. ２ By setting the following, the coating adhesion can be suitably obtained.

[0036] The resins, inorganic components, organic reducing agents, and B compounds shown in Tables 1 and 2 were added to deionized water and mixed to give the mass % (solids content equivalent) shown in Tables 1 and 2 to prepare water-based paints. Although ethylene glycol, used as the organic reducing agent, is liquid at room temperature, its content was calculated as solids. The solids concentration of the water-based paints was 3 mass %. Thickener A-10H (manufactured by Toa Gosei Co., Ltd.) was added to the water-based paints as a viscosity adjuster, so that the water-based paints of each example had the viscosities shown in Tables 1 and 2.

[0037]

[0038]

[0039] These water-based paints were applied with a roll coater to the surface of test pieces cut out from 0.5 mm thick electrical steel sheets to a width of 150 mm and a length of 300 mm, and the pieces were baked using an induction heating method (Table 1) and a hot air furnace heating method using a gas furnace (Table 2) to the sheet temperatures shown in Tables 1 and 2, and then allowed to cool at room temperature to form insulating coatings. The coating weight of each insulating coating was 0.5 g / m2 in dry weight. ２ was unified into.

[0040] The appearance, weldability and punchability of the insulating coating were evaluated as follows, and the results are shown in Tables 1 and 2.

[0041] [Evaluation of coating appearance] The appearance of the steel sheet surface after painting was visually observed to check for the presence or absence of roping. (Evaluation criteria) ◎: No roping occurred ◯: Slight roping occurred, but no effect on coating performance ×: Severe roping occurred, resulting in deterioration of coating performance

[0042] [Weldability Evaluation] Steel plates were stacked to a thickness of 3 cm, and TIG welding was performed under the following conditions, evaluating the maximum welding speed at which blowholes did not occur. In Patent Document 1, evaluation was performed at a current value of 120 A, but this time, in order to evaluate under more severe welding conditions, the welding test was performed with a current value of 150 A. Electrode: Th-W 2.6 mmφ Pressing force: 10 N / mm ２ Current: 150A Shielding gas: Ar (6 liters / min) (Evaluation criteria) ◎: 120cm / min or more 〇: 80cm / min or more but less than 120cm / min ×: Less than 80cm / min

[0043] [Punchability evaluation] A continuous punching test was performed under the following conditions, adjusting the die so that the initial burr height was 10 μm, and the number of punches until the burr height reached 50 μm was used. 15 mmφ steel die use clearance: 5% Punching oil: used (Evaluation criteria) ◎: 1 million or more times 〇: 500,000 or more times to less than 1 million times ×: Less than 500,000 times

[0044] Table 1 shows that the inventive examples, in which the viscosity of the water-based paint was 1 mPa·s or higher, were superior to the comparative examples in terms of appearance, weldability, and punchability. Comparing Tables 1 and 2, it can be seen that induction heating from the bottom of the coating provided better weldability than heating using a gas furnace. Even in the case of a gas furnace, controlling the viscosity of the water-based paint improved performance. This clearly demonstrates that the effects of the present invention can be achieved regardless of the heating method.

[0045] According to the present invention, it is possible to provide a method for manufacturing an electrical steel sheet with an insulation coating that is excellent in both punchability and weldability under stricter evaluation conditions.

Claims

1. preparing a water-based paint; a step of applying the water-based paint to a surface of an electrical steel sheet and drying it by heating to form an insulating coating; having The water-based paint contains a resin, an inorganic component, an optional organic reducing agent, an optional boron compound (B compound), and water; 50% by mass or more of the resin is composed of one or both of an emulsion resin and a dispersion resin, 4. A method for producing an electrical steel sheet with an insulating coating, wherein the water-based paint has a viscosity of 1.0 mPa·s or more.

2. The method for producing an electrical steel sheet with an insulating coating according to claim 1 , wherein the water-based paint has a viscosity of 40 mPa·s or less.

3. The method for producing an electrical steel sheet with an insulation coating according to claim 1 , wherein the water-based paint has a viscosity of 10 mPa·s or less.

4. 4. The method for producing an electrical steel sheet with an insulation coating according to claim 1, wherein one or both of the emulsion resin and the dispersion resin in the water-based paint have a particle size of 30 nm or more.

5. 4. The method for producing an electrical steel sheet with an insulation coating according to claim 1, wherein a solid content mass ratio of the resin to a total mass of the resin, the inorganic component, the organic reducing agent, and the B compound in terms of solid contents in the water-based paint is 0.5 mass% or more and 50 mass% or less.

6. A method for manufacturing an insulating coated electrical steel sheet as described in claim 4, wherein the solid mass ratio of the resin to the total mass converted into solid contents of the resin, the inorganic component, the organic reducing agent, and the B compound in the water-based paint is 0.5 mass% or more and 50 mass% or less.