JPH05185029A - Magnetic steel sheet having insulating coating film - Google Patents

Abstract

PURPOSE:To improve the insulating performance and adhesiveness by applying a processing soln. consisting of an aq. dispersion of the surface of a magnetic steel sheet and then baking the dispersion. CONSTITUTION:This magnetic steel sheet having an insulating coating film is appropriately used as the material for the water-wheel generator and large- sized motor. A processing soln. consisting of an aq. dispersion of high-mol.wt. epoxy resin and 1-20 pts.wt., based on 100 pts.wt. of the solid component of the dispersion, of an etherified methylolmelamine as the cross-linking agent is applied on the surface of a magnetic steel sheet and baked to form a desired coating film, and the insulating performance and adhesiveness of the coating film, adhesiveness with the additional coat and the punching property, weldability, corrosion resistance of the sheet are improved. The thickness of the coating film is controlled to 2-20mum and the epoxy resin having >=4000 number average mol.wt. is used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrical steel sheet having an insulating coating, and more particularly to an electrical steel sheet having an insulating coating having good electrical insulation and adhesion, which is preferably used as a material for turbine generators and large motors. .

[0002]

2. Description of the Related Art There are many properties required for an insulating coating of an electromagnetic steel sheet such as electric insulation, adhesion, adhesion with an additional coat, punchability, weldability, corrosion resistance and refrigerant resistance.
Many studies have been conducted to meet these requirements, and many techniques have been proposed for a method of forming an insulating coating on the surface of an electromagnetic steel sheet and an insulating coating composition.

As one of the proposals, there is a method of forming an insulating coating film using an organic resin. Although this method is excellent in electric insulation, it is used for the purpose of improving the adhesion with an electromagnetic steel sheet. It is necessary to perform chemical conversion treatment such as chromate treatment or bond treatment on the surface of the steel sheet in advance.

For example, in JP-A-60-38069, a phosphate base film is formed on the surface of an electromagnetic steel sheet, and then a polyester resin, an epoxy ester resin, or an acrylic resin is applied. A method of forming a coating film having high interlayer insulating property, high corrosion resistance, excellent adhesion property, excellent punching property, etc. on an electromagnetic steel sheet is disclosed.

However, such a chemical conversion treatment requires facilities for chemical conversion treatment, a washing facility after the treatment, a subsequent drying facility and the like, which causes an increase in the cost of the product. Therefore, the advent of a method of forming a coating film of an organic resin having sufficient adhesiveness without chemical conversion treatment is desired.

[0006]

The object of the present invention is thus to provide a magnetic steel sheet having a coating film which is excellent in adhesion to a magnetic steel sheet even when applied with an organic resin without chemical conversion treatment and which is excellent in electrical insulation. To do.

[0007]

The present inventors have focused on a method of forming a coating having sufficient adhesion to a magnetic steel sheet without chemical conversion treatment, focusing on the type of resin and its crosslinking system. As a result of intensive research, the present invention has been completed by finding that the combination of a high molecular weight epoxy resin and a specific cross-linking agent meets the above object.

That is, according to the present invention, a treatment liquid comprising an aqueous dispersion of a high molecular weight epoxy resin and 1 to 20 parts by weight of etherified methylol melamine as a crosslinking agent per 100 parts by weight of the solid content of the dispersion. Provided is an electromagnetic steel sheet having an insulating coating having good electric insulation and adhesion, which is obtained by a baking process after coating on the surface of the electromagnetic steel sheet.

The high molecular weight epoxy resins used in the present invention are 2,2-bis (4-hydroxyphenyl) propane (bisphenol A), 1,1-bis (4-hydroxyphenyl) ethane (bisphenol AD), 1, It is a high molecular weight epoxy resin derived from dihydric phenols such as 1-bis (4-hydroxyphenyl) methane (bisphenol F), hydroquinone and resorcin, and above all, bisphenol A and epichlorohydrin. The molecular weight thereof is preferably 4,000 or more in terms of number average molecular weight (Mn) from the viewpoint of adhesion, and Mn is preferably 40,000 or less from the viewpoint of maintaining the fluidity of the resin during heating.

Such a high molecular weight epoxy resin may have an epoxy group at the terminal, but even if it is present, it is in a very small amount and has a repeating unit as represented by the formula (I), so-called phenoxy resin. It also includes

[0011]

[Chemical 1] In formula (I), Ar is a dihydric phenol residue.

In the present invention, etherified methylol melamine is used as a crosslinking agent for the purpose of crosslinking a high molecular weight epoxy resin to obtain a good coating film. This particular combination gives a coating with good adhesion to electrical steel and good electrical insulation.

The amount of the cross-linking agent used is 1 to 20 parts by weight based on 100 parts by weight of the solid content of the aqueous dispersion in consideration of heat resistance and adhesion of the coating.

The etherified methylol melamine, which is one of the cross-linking agents of the present invention, is a mixture of one or two or more of six types of methylol melamine up to monomethylol melamine or hexamethylol melamine, and a carbon number. It is obtained by dehydration reaction with 1 to 4 alcohols in the presence of an acid catalyst, but it is not necessary that all the methylol groups be etherified. For example, in the case of hexamethylolmelamine, monoetherification or hexaether There are six types of compounds, and of these, one or a mixture of two or more types can be used.

The treatment liquid obtained by mixing the dispersion and the cross-linking agent is applied to the magnetic steel sheet, and the method is carried out by using a means known per se, for example, a device such as a curtain flow coater or a roll coater. ..

The magnetic steel sheet coated with the treatment liquid forms a coating film in the baking process. In the baking process, a device known per se such as a heating furnace is used and the temperature is set to 200 to 700 ° C. for 15 to 3
It is baked for 00 seconds.

The coating film is formed by the above steps. The thickness of the coating film is preferably 2 μm or more from the viewpoint of electrical insulation, punchability, corrosion resistance and the like, and 20 μm or less from the viewpoint of space factor. Preferably.

The thus obtained high-molecular weight epoxy resin is crosslinked to form a coating on the magnetic steel sheet, which is excellent in electric insulation and adhesion of the coating, and is advantageously used as a material for turbine generators and large motors.

[0019]

EXAMPLES The present invention will be specifically described below with reference to examples.

Of high molecular weight epoxy resin dispersions
Preparation method Stir an aqueous solution in which 3% of HLB15-16 polyoxyethylene alkyl ether is dissolved in 400 g of ion-exchanged water, and add a solution in which 100 g of phenoxy resin is uniformly dissolved in a mixed solvent of methyl ethyl ketone / toluene (1: 1). The suspension was dropped to obtain a suspension, and the pressure was reduced under stirring to remove methyl ethyl ketone and toluene to obtain an aqueous dispersion of a phenoxy resin.

(Examples 1 and 2) 1.8 with a plate thickness of 0.5 mm
% Si magnetic steel sheet was washed with degreased water and dried. On the other hand, the treatment liquid was prepared by blending the cross-linking material of Table 1 with the dispersion of the high molecular weight epoxy resin prepared above in a ratio shown in Table 1. This treatment liquid is coated on a magnetic steel sheet by a roll coater method so as to have a dry film thickness as shown in Table 1,
It was baked in an electric furnace. The baking conditions are shown in Table 1.

Evaluation of the interlayer resistance, adhesion, SST corrosion resistance, solvent resistance, and punchability of the coated magnetic steel sheet was carried out by the methods described below. The results are shown in Table 1.

Interlayer resistance Measured by JIS C2550 second method Adhesiveness Cellophane tape was adhered to a sample of 5 cm × 20 cm, bent 180 ° inward / outward with a 10 mmφ round bar, peeled off the tape, and judged whether the coating film was peeled or not. did. ◯: No peeling off ×: There is peeling off In Table 1, the inner curve indicates inner bending and the outer curve indicates outer bending. SST Corrosion resistance Measured by JIS Z2371 Rust rate 30
The time required to reach% is shown. Solvent resistance Xylene was dipped in gauze and reciprocated 20 times under a load of 500 g, and then the film was observed and the presence or absence of peeling was measured. ◯: No peeling off Δ: Parting peeling ×: Complete peeling Punching performance A 15 mmφ steel die was used to evaluate the number of punches until the burr height reached 50 μm at a punching speed of 500 spm.

(Comparative Examples 1 and 2) The used resin, crosslinking agent,
The baking conditions and the evaluation results are shown in Table 1.

[0025]

[Table 1]

[0026]

According to the present invention, there is provided an electromagnetic steel sheet having a coating excellent in adhesion and electric insulation. Since the steel sheet of the present invention does not require chemical conversion treatment before the painting process, it is inexpensive and can be advantageously used as a material for turbine generators and large motors.

Claims (3)

[Claims] 1. An aqueous dispersion of a high molecular weight epoxy resin, and etherified methylol melamine 1-2 as a cross-linking agent per 100 parts by weight of the solid content of the dispersion.
A magnetic steel sheet having an insulating coating having good electrical insulation and adhesion, which is obtained by applying a treatment liquid consisting of 0 parts by weight to the surface of the magnetic steel sheet and then performing a baking process. 2. The thickness of the coating is 2 to 20 μm.
The electromagnetic steel sheet described. 3. The electrical steel sheet according to claim 1, wherein the high molecular weight epoxy resin has a number average molecular weight of 4,000 or more.