JP2012122118A - Electromagnetic steel plate with chromium-free insulating coating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electromagnetic plate sheet having a chromium-free insulating film which is excellent in rust prevention property and adhesion and does not cause sticking caused by stress-relieving annealing after punching even when the annealing atmosphere is an oxidizing atmosphere.SOLUTION: An insulating film free from Cr and having a thickness of 0.1-2 μm is formed on the both surfaces of an electromagnetic steel plate. The insulating film includes fine particles being more easily oxidized than iron, preferably carbon black, in an amount of 1-10 mass% as a solid content, with the balance including 50-90 mass% of a primary phosphate of at least one kind of metal selected from Al, Mg, Ca, Sr, Ba and Zn and 5-50 mass% of an organic resin or including 40-90 mass% of the primary phosphate, 5-50 mass% of an organic resin, and 5-10 mass% of silica.

Description

  The present invention relates to an electrical steel sheet with an insulating film and a method for producing the same. In the electrical steel sheet with an insulating film of the present invention, the insulating film does not contain hexavalent chromium, and at a low baking temperature similar to a dichromate-based film generally used as an insulating film of a conventional non-oriented electrical steel sheet. It is manufacturable, has equivalent or better performance, and has excellent anti-sticking properties after strain relief annealing.

  Electrical steel sheets are mainly used as iron cores for motors and transformers. If there is conduction between the iron plates, the iron core is the same as the thick block, and the effect of reducing the eddy current loss due to the reduced thickness of the iron plate is lost. For this reason, it coat | covers and uses the surface of an electromagnetic steel plate with an insulating film. The method of forming the iron core is a method in which an electromagnetic steel sheet with an insulating film is continuously punched into a predetermined shape and then laminated, and the laminated body is welded, or a concavo-convex portion called caulking is fitted The method of integrating by etc. is common.

  The integrated iron core may be used by being incorporated in an electric device as it is, or may be incorporated in an electric device after being annealed at a temperature of about 700 ° C. to 800 ° C. The latter annealing is called strain relief annealing, and it removes or reduces the shear strain introduced into the steel sheet during punching / shearing, thermal strain generated by welding of the end faces, and plastic deformation strain of the caulking portion by annealing. The purpose is to enhance the magnetic properties of the iron core.

  Therefore, the insulation film of magnetic steel sheets used for iron cores such as motors and transformers is not only for inter-layer resistance (insulation) but also for user convenience, punchability, weldability, film adhesion, heat resistance Various performances such as performance are required.

  Insulating coatings are (1) inorganic coating that resists strain relief annealing with emphasis on weldability and heat resistance, and (2) mixed inorganic / organic coating that resists strain relief annealing with the aim of achieving both punchability and weldability. (Also called semi-organic film), (3) It is roughly divided into three types of organic film for special use and not capable of strain relief annealing. In general, the insulating film (1) or (2) that can be strain-annealed is used, and the semi-organic insulating film (2) is markedly more punchable than the inorganic insulating film (1). Because it is excellent, it is most often used.

  Hitherto, dichromate has been widely used as an inorganic component of a treatment liquid for forming an inorganic or semi-organic insulating film because a film satisfying the above performance can be formed. The treatment liquid for forming an insulating film containing dichromate is prepared by mixing an organic reducing agent such as ethylene glycol or glycerin with an aqueous solution containing hexavalent chromium and a polyvalent metal salt. After this treatment liquid is applied to both surfaces of the electrical steel sheet, it can be baked at a temperature of 200 ° C. to 330 ° C., and hexavalent chromium can be reduced to trivalent chromium, thereby forming an insulating film. However, as is well known, hexavalent chromium used in the treatment liquid is highly toxic and is not preferred from the viewpoint of environmental measures. Further, trivalent chromium contained in the insulating film is much less toxic than hexavalent chromium, but it cannot be said that it is not toxic. Therefore, it is required to form an insulating film on the electromagnetic steel sheet without using any chromium compound.

  As in the case of dichromate, phosphate is an inorganic component used for forming an insulating film. Phosphate aqueous solution is one of the few aqueous solutions of inorganic compounds that can be formed into a film, and can be obtained at relatively low cost. Therefore, it has been studied as an inorganic component for forming inorganic and semi-organic insulating films (for example, Patent Document 1).

  Patent Document 2 discloses a phosphate-based treatment liquid for non-oriented electrical steel sheets having excellent coating properties, including primary phosphate Al, an emulsion resin, and an additive OH group-containing organic compound. This patent document states that the addition of an organic acid salt improves the moisture absorption resistance after baking and improves the seizure resistance during strain relief annealing.

  In Patent Documents 3 to 5, film formation can be performed at a baking temperature as low as that of dichromate, and even in such a case, various performances required for an insulating coating for an electrical steel sheet such as excellent water resistance, adhesion, and insulation are provided. A treatment liquid for forming a phosphate-based insulating film of an electrical steel sheet having excellent film forming properties is disclosed.

  Patent Document 6 discloses an Al / Ca phosphate, an emulsion resin containing at least 20% by mass of an ultrafine particle emulsion resin having a particle size of 0.04 to 10 μm, and Ni, Co, Sr, Fe, Cu, and Mn. Surface treatment liquid for non-oriented electrical steel sheet, containing one or more metal compounds selected from water-soluble organic compounds, hydroxides, and oxides (water-soluble substances or particles having an average particle diameter of 3 μm or less). Is disclosed. This document states that the metal compound improves stickiness due to free phosphoric acid, corrosion resistance deterioration, seizure property during annealing, and the like.

  Patent Document 7 describes that an insulating film containing an oxide sol, boric acid, and a silane coupling agent is excellent in sticking resistance by performing strain relief annealing in an oxidizing atmosphere.

Patent Document 8 contains phosphate as an inorganic component, has a BET specific surface area of 10 m ² / g or more, and has a 50% cumulative particle size of 5 μm or less and 90% cumulative measured by a laser scattering diffraction particle size distribution meter. Contains inorganic powder (specifically, oxides of alumina, silica, magnesia, titania, zirconia, etc.) having a particle size distribution of 15 μm or less in a proportion of 1 to 50% by mass with respect to the solid content of the phosphate A processing solution is disclosed. This document states that inorganic powder can eliminate stickiness and adhesion caused by free phosphoric acid.

  However, in these conventional technologies, it cannot be said that the required performance is sufficiently satisfied depending on the usage conditions in the consumer. In particular, in applications in which strain relief annealing is performed by a customer in order to remove strain after punching, sticking (seizure between stacked steel plates) is likely to occur due to strain relief annealing.

Japanese Patent Publication No.53-28375 JP-A-11-152579 JP 2001-107261 A Japanese Patent Laid-Open No. 2002-47576 JP 2002-249881 A Japanese Patent Laid-Open No. 2004-322079 JP 2009-235530 A International Publication WO09 / 154139

  An object of the present invention is to provide an electrical steel sheet that has an insulating film that does not contain chromium, has excellent performance such as rust prevention and adhesion, and does not cause sticking due to strain relief annealing after punching. It is to provide.

  The present invention is an electrical steel sheet having an insulating film having a thickness of 0.1 to 2 μm that does not contain Cr on both surfaces of the steel sheet, and the insulating film has a solid content of fine particles that are more oxidizable than iron. It is an electrical steel sheet with an insulating film, characterized in that it is contained in an amount of mass%.

In a preferred embodiment, the present invention further satisfies one or more of the following 1) to 4):
1) Carbon black is a finer particle that is easier to oxidize than iron.
2) As the solid content, the solid content of at least one metal salt or oxide selected from Al, Mg, Ca, Sr, Ba and Zn is 50 to 90% by mass, and the organic resin is 5 to 50% by mass. Formed from an aqueous treatment liquid containing
3) As the solid content, the solid content of at least one metal salt or oxide selected from Al, Mg, Ca, Sr, Ba and Zn is 40 to 90% by mass, and the organic resin is 5 to 50% by mass. And an aqueous processing solution containing 5 to 10% by mass of silica,
4) A part or all of the salt or oxide is a primary phosphate.

  The electrical steel sheet with an insulating film of the present invention is excellent in sticking resistance because an easily oxidizable element in the insulating film suppresses oxidation of the surface of the steel sheet even when strain relief annealing is performed. In addition, the insulation film can be formed at the same low baking temperature as the conventional dichromate film, and the same or better performance can be achieved. However, since the insulation film does not contain chromium, it can be used safely. be able to.

  The electrical steel sheet of the present invention has an insulating film having a thickness of 0.1 to 2 μm that does not contain Cr on both surfaces of the steel sheet, and this insulating film has a solid content of fine particles that are more oxidizable than iron. It is contained in an amount of 10% by mass.

  Examples of the “fine particles easier to oxidize than iron” include carbon black and silicon fine particles. Carbon black is preferred because of its price and availability of fine particles.

  The mechanism by which sticking occurs due to strain relief annealing is estimated as follows. The strain relief annealing is usually performed in a nitrogen atmosphere. Here, even in the nitrogen atmosphere, a small amount of oxygen, moisture, etc. cannot be avoided in industrial implementation, and is actually an oxidizing atmosphere for iron. For this reason, the surface of the steel plates stacked by strain relief annealing is oxidized, and sticking occurs due to this oxidation.

  Therefore, by adding a predetermined amount of fine particles that are easier to oxidize than iron (hereinafter also simply referred to as “easily oxidizable fine particles”) to the insulating film, the strain relief annealing atmosphere has an oxidizing property with respect to iron. However, the oxidizable element in the insulating film suppresses the oxidation of the steel sheet surface and suppresses the oxidation of iron, so that the sticking resistance of the electromagnetic steel sheet with the insulating film is remarkably improved.

  The amount of the oxidizable fine particles in the insulating film is in the range of 1 to 10% by mass. Therefore, the oxidizable fine particles are added to the water-based treatment liquid for forming the insulating film at a ratio of 1 to 10% by mass based on the total solid content. When the oxidizable fine particles are obtained in the form of a dispersion, they may be added so that the amount of the oxidizable fine particles as a solid content falls within the above range. If the amount of the easily oxidizable fine particles is less than 1% by mass, the effect of suppressing sticking in the strain relief annealing in an oxidizing atmosphere cannot be sufficiently obtained. On the other hand, if this amount exceeds 10% by mass, the conductivity of the film increases, and there is a possibility that it will not function as an insulating film. A preferable addition amount of the oxidizable fine particles is 2.5% or more and 7.5% or less in mass%.

  The smaller the particle diameter of the oxidizable fine particles, the better. This is because if the particle size is too large, the conductivity of the film may be increased or the rust prevention property may be adversely affected. The oxidizable fine particles preferably have an average particle size of less than 0.1 μm (= 100 nm). Here, the average particle size means the primary particle size of the particles. The more preferable average particle diameter of the oxidizable fine particles is 5 nm or more and 50 nm or less. If the oxidizable fine particles are ultrafine particles having an average particle size of less than 5 nm, the particles are likely to aggregate, leading to deterioration of the film properties. Since carbon black having an average particle diameter of about 10 to 20 nm can be easily obtained, it is suitable as oxidizable fine particles. It is preferable that the insulating film does not contain particles having an average particle size exceeding 0.1 μm in a substantial amount (amount of 0.5% or more).

  The electrical steel sheet of the present invention is an aqueous system in which the insulating film contains a metal compound and an organic resin which are at least one metal salt or oxide selected from Al, Mg, Ca, Sr, Ba and Zn, and optionally further silica. It is preferably formed from a treatment liquid. The preferred proportion of each component in the aqueous treatment liquid (mass%, the solid content ratio of the components based on the total solid content in the treatment liquid) is 50% to 90% of the metal compound in the absence of silica, The organic resin is 5 to 50%. When the aqueous processing liquid further contains silica, the metal compound is 40 to 90%, the organic resin is 5 to 50%, and the silica is 5 to 10%. This aqueous processing liquid further contains the oxidizable fine particles at a ratio of 1 to 10%.

  A metal compound which is a metal salt or oxide selected from Al, Mg, Ca, Sr, Ba and Zn functions mainly as a binder in the insulating film. It is preferable that at least a part, preferably all of these salts or oxides are primary phosphates.

The primary phosphate is a metal dihydrogen phosphate. For example, primary magnesium phosphate is Mg (H ₂ PO ₄ ) ₂ , and primary aluminum phosphate is Al (H ₂ PO ₄ ) ₃ . Represented by the chemical formula. However, the primary phosphate is industrially produced by reacting phosphoric acid (orthophosphoric acid) with an appropriate amount of metal hydroxide, and by changing the amount of metal hydroxide, the atomic ratio of metal / P. It is possible to produce phosphates with varying s. In the present invention, the primary phosphates of Mg, Ca, Sr, Ba and Zn which are divalent metal salts include those having a metal / P atomic ratio of 0.7 / 2 to 1.2 / 2. The primary aluminum phosphate which is a trivalent metal salt includes those having an Al / P atomic ratio of 0.7 / 3 to 1.2 / 3.

  As the primary phosphate, it is preferable to use one or both of primary aluminum phosphate and primary magnesium phosphate. More preferably, both an aluminum salt and a magnesium salt are used for the reason that a treatment solution with a high concentration is easily obtained and industrially inexpensive.

  The concentration of the primary phosphate in the treatment liquid is preferably in the range of 1 to 50% by mass, more preferably 2 to 30% by mass. If this concentration is less than 1% by mass, the film forming property of the treatment liquid is poor, and the water resistance of the formed film tends to be lowered. On the other hand, when the concentration exceeds 50% by mass, the stability of the treatment liquid is lowered, solid matter sedimentation and viscosity increase occur, and it becomes difficult to form a uniform film.

  Inclusion of the organic resin is mainly aimed at improving the punchability of the electrical steel sheet. As the organic resin, an aqueous synthetic resin is preferable. The aqueous synthetic resin may be any emulsion type, water-dispersible type, or water-soluble type. Specific examples of synthetic organic resins include acrylic resins, acrylic-styrene resins, alkyd resins, polyester resins, silicone resins, fluorine resins, polyolefin resins, styrene resins, vinyl acetate resins, epoxy resins, phenol resins, urethane resins, melamine resins, etc. 1 type, or 2 or more types can be used.

  The insulating film can contain silica if desired. As the silica, it is preferable to use fine particle silica having a colloidal particle diameter, and either liquid phase silica (colloidal silica) or gas phase silica (fumed silica) may be used, and a plurality of types of silica may be used. When the insulating film contains silica, the corrosion resistance and interlayer resistance of the insulating film tend to increase.

  In addition to the components described above, the treatment liquid for forming an insulating film used in the present invention is not limited to the various components that have been added to the treatment liquid for forming an insulating film so far as long as the properties of the insulating film are not substantially adversely affected. Small amounts of ingredients can be included. Examples of such components include corrosion inhibitors, antifoaming agents, dispersants, stabilizers and the like. Moreover, in order to color an insulating film, a coloring agent can also be contained in a process liquid. Since it is an aqueous processing solution, the solvent is water, but a water-miscible organic solvent (eg, alcohol) in a smaller amount than water may be blended for the purpose of promoting drying.

  The thickness of the insulating film is in the range of 0.1 to 2 μm, and preferably 0.5 μm or more and 1.5 μm or less. When the film thickness is less than 0.1 μm, both the insulating properties and the rust preventive properties are lowered. On the other hand, when the film thickness exceeds 2 μm, the cost increases and the adhesion of the film decreases.

  The insulating film according to the electrical steel sheet of the present invention can be formed by applying and baking the above-described treatment liquid on both surfaces of the electrical steel sheet. The coating method of the treatment liquid is not particularly limited, and various coating methods such as roll coater, curtain flow coater, spray coating, knife coater, and dipping that are generally used industrially can be applied. A preferable baking temperature is 250 to 300 ° C. as the maximum temperature reached by the steel sheet. As for the heating method, various known methods such as hot air heating, infrared heating, induction heating and oven heating can be used.

  There is no particular limitation on the electromagnetic steel plate of the processing original plate, and a steel plate having appropriate magnetic properties according to the application can be used. A typical electromagnetic steel sheet is a Si-containing steel sheet, but is not limited thereto. The electromagnetic steel sheet may be unidirectional or non-directional. Before forming the insulating film according to the present invention, pretreatment such as alkali degreasing and pickling may be performed.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not restrict | limited by these Examples. Unless otherwise specified, “%” and “parts” in the examples are “% by mass” and “parts by mass” in terms of solid content based on the insulating film and thus the total solid content of the treatment liquid.

An electromagnetic steel plate having a thickness of 0.5 mm containing 0.1% Si was used as the processing original plate.
The treatment liquid for forming the insulating film was prepared by adding and dispersing the following particles in the amounts shown in Table 1 based on the following liquid A or liquid B.

[base]
Liquid A: primary aluminum phosphate (Al / P atomic ratio = 0.9 / 3) 6.28%, primary magnesium phosphate (Mg / P atomic ratio = 0.85 / 2) 2.09%, water A treatment liquid containing 1.2% magnesium oxide and 2.2% (converted to solid content) of a synthetic resin (acryl-styrene emulsion).

  Liquid B: primary aluminum phosphate (Al / P atomic ratio = 0.9 / 3) 6.28%, primary magnesium phosphate (Mg / P atomic ratio = 0.85 / 2) 2.09%, water A treatment solution containing 1.2% magnesium oxide, 2.2% (converted to solid content) of synthetic resin (acryl-styrene emulsion), and 1.2% (converted to solid content) of silica (colloidal silica).

[particle]
C: Carbon black (MCF # 850 (average particle size 10-20 nm) manufactured by Mitsubishi Chemical Corporation),
Si: Silicon powder (silicon powder 4N manufactured by Kanto Chemical Co., Inc. (average particle size of 1 μm or more)),
Al ₂ O ₃ : Alumina sol (Alumina sol 200 manufactured by Nissan Chemical Co., Ltd. (average particle size: long side 100 nm, short side 10 nm))
Since alumina (Al ₂ O ₃ ) is less oxidizable than iron, alumina sol does not correspond to the oxidizable fine particles used in the present invention. Silicon is easily oxidizable. The silicon powder used in this example is not a fine particle having an average particle size of 0.1 μm or less, but was used as a reference example in order to examine the effect of the silicon powder.

The treatment liquid to which the particles were added was used in a sufficiently dispersed state using a hybrid mixer with 10 g of glass beads added to 100 g of the chemical solution before coating.
A chemical solution containing a predetermined amount of fine particles is applied to one side of a magnetic steel sheet with a bar coater so that the film thickness after baking is about 0.5 μm, and then the maximum reached plate temperature is 270 ° C. for 30 seconds. The coating film was baked by heating in an oven to form an insulating film. After baking, it was cooled with a water quench and dried with a dryer. An insulating film was formed on the opposite side of the electromagnetic steel sheet by the same operation to obtain an electromagnetic steel sheet with an insulating film having an insulating film on both surfaces of the treated original plate. The film thickness of the insulating film was calculated by measuring the intensity of P with a fluorescent X-ray analyzer and converting.

Regarding various performances of the obtained electrical steel sheet, the sticking resistance, insulation, rust prevention, and adhesion were evaluated by the following methods.
[Evaluation methods]
[Sticking resistance]
Two test pieces (30 x 50 mm) of magnetic steel sheets with insulating coatings were superposed so that the contact surface was 30 x 30 mm, a 10 kg weight was placed on the overlap (constant compression stress), and at 750 ° C in nitrogen Two hours of strain relief annealing was performed. Condition 1 overlaps the same test pieces, and Condition 2 overlaps the A1 surface. The specimen after annealing was subjected to a tensile test to measure the peel strength (unit: N), and the sticking resistance was evaluated in the following four stages. ◎, ○ are passed:
A: Peel before tensile test,
○: Peel strength less than 50,
Δ: Peel strength 50 or more, less than 100,
X: Peel strength 100 or more.

[Insulation]
Using a JIS C 2550 compliant interlayer resistance measuring machine, the interlayer resistance of the insulating film was measured under the following conditions:
Test pressure: 2MPa ± 5%
Interlayer resistance value R _A = A × (1 / I _A −1) (Ω · cm ² / sheet)
A: Contact electrode total area (cm ² ) (= 10)
I _A : Total current flowing through 10 contacts (A)
The criteria for insulation based on measured values of interlayer resistance are as follows:
○: 10Ω or more,
X: Less than 10Ω.

[Rust prevention]
After exposing a test piece of electrical steel sheet with an insulating film to a constant temperature and humidity layer adjusted to 50 ° C. and 95% RH for 144 hours, the area ratio (%) of surface rust was observed, and rust prevention was performed in the following four stages. Sex was evaluated. ◎, ○ are passed:
A: Area ratio of surface rust is 5% or less,
○: Area ratio of surface rust is more than 5%, 10% or less,
Δ: Area ratio of surface rust is more than 10%, 30% or less,
X: Area ratio of surface rust exceeds 30%.

[Adhesion]
A test piece of a magnetic steel sheet with an insulating film having a length of 50 mm and a width of 25 mm was wound around a 5 mm diameter iron bar, and a tape peeling test was conducted on the wound outer portion to determine the state of the insulating film remaining on the steel sheet (the area of the remaining film) Rate). From this area rate, the rate of occurrence of film peeling (area rate) was determined, and film adhesion was evaluated in the following four stages based on the rate of occurrence. ◎, ○ are passed:
A: No film peeling,
○: Film peeling occurred (area ratio is 5% or less),
Δ: Occurrence of film peeling (over 5% in area ratio, 30% or less)
X: Occurrence of film peeling (over 30% in area ratio).

  The test results are shown in Table 1 together with the type and amount of fine particles in the insulating film. Nos. A1 to A11 are examples in which the base is the A liquid, and Nos. B1 to B3 are examples in which the base is the B liquid. Examples No. A3 to A7 and B1 to B3 all had good performances such as sticking resistance, insulation and rust prevention.

  No. A9 to 11 shown as reference examples also had good sticking resistance. These were poor in insulation, but this is due to the fact that the particle size of the silicon powder is too large, so that if the particle size is appropriate, an insulating film with good sticking resistance can be obtained. Conceivable.

  On the other hand, No. A1 which is an example not containing easily oxidizable particles and No. A12 containing alumina fine particles which are not easily oxidizable instead of easily oxidizable fine particles have poor sticking resistance.

Claims (5)

  An electrical steel sheet having an insulating film having a thickness of 0.1 to 2 μm that does not contain Cr on both surfaces of the steel sheet, the insulating film having an amount of 1 to 10% by mass with fine particles that are more oxidizable than iron as solids An electrical steel sheet with an insulating film, characterized by comprising:   The electrical steel sheet with an insulating film according to claim 1, wherein the fine particles more easily oxidized than iron are carbon black.   The insulating film has a solid content of at least one metal salt or oxide selected from Al, Mg, Ca, Sr, Ba and Zn, 50 to 90% by mass, and an organic resin 5 to 50% by mass. The electrical steel sheet with an insulating film according to claim 1 or 2, wherein the electrical steel sheet is formed from a water-based treatment liquid.   As the solid content, the solid content of at least one metal salt or oxide selected from Al, Mg, Ca, Sr, Ba and Zn is 40 to 90% by mass, and the organic resin is 5 to 50% by mass. The electrical steel sheet with an insulating film according to claim 1 or 2, wherein the electrical steel sheet is formed from an aqueous treatment liquid containing 5 to 10% by mass of silica.   The electrical steel sheet with an insulating film according to claim 3 or 4, wherein a part or all of the salt or oxide is a primary phosphate.