KR19980038067A - Coating composition for forming non-oriented electrical steel sheet insulation coating with excellent appearance and corrosion resistance - Google Patents

Abstract

The present invention relates to a coating composition for forming an insulating film used to form an insulating film on the surface of a non-oriented electrical steel sheet, the composition and the content of the inorganic insulating film forming treatment liquid is appropriately adjusted and the production of the insulating film accordingly The present invention relates to a coating composition for forming an insulating film of a non-oriented electrical steel sheet excellent in appearance and corrosion resistance prepared by controlling the conditions appropriately.

Description

Coating composition for forming non-oriented electrical steel sheet insulation coating with excellent appearance and corrosion resistance

The present invention relates to a coating composition for forming an insulating film used to form an insulating film on the surface of a non-oriented electrical steel sheet, and more particularly to a coating composition for forming an insulating film excellent in appearance and corrosion resistance.

Non-oriented electrical steel sheet used as an iron core for electric equipment such as a small electric motor, transformer, etc. forms an insulating film on the surface in order to suppress the generation of eddy current and to reduce the power loss. These insulating coatings are classified into three types of organic, inorganic, and mixtures of organic and inorganic according to the demands of various use characteristics of the demand, and the film formation is completed by applying and drying the treatment liquid continuously to the surface of the electrical steel sheet. .

However, recently, the demand demanded electrical steel sheet manufacturers that color (green preference) among the characteristics of insulation coatings of electrical steel products, and that the surface is beautiful because there is no unreacted coating component (hereinafter, these items are called 'appearance'). It is a trend.

In addition, the coiled product is continuously punched out into a predetermined shape by a mold at a demand price and then subjected to stress relief annealing, which is excellent in corrosion resistance since it is exposed to the air from this process, that is, from product shipment to stress relief heat treatment. It is essential to do

As a technique for the conventional method of forming an insulating coating of non-oriented electrical steel sheet, the present inventors have applied for a patent in Korea and published and registered in Korea Patent No. 31208 (Notification No. 89-3582), this patent The present invention relates to a method for forming an organic and inorganic mixed insulating film, and although they have a compounding stability effect therebetween, they have the following problems.

That is, the reason why calcium oxide is added to the aqueous solution in which chromic anhydride is dissolved is added at a chemical equivalent or more per 100 parts by weight of chromic anhydride to 28.7-31.0 parts by weight is to increase the PH of the calcium dichromate salt solution produced by adding the chemical equivalent or more. It is intended to suppress the sudden reaction with the resin, the effect is reasonable. However, an extreme exothermic phenomenon occurs during the reaction between chromic anhydride and calcium oxide, which requires a separate cooling operation to smoothly perform the filtration work and the blending with the resin, and the inorganic composition (A ′) hereinafter Calcium bicarbonate salt solution, which is produced by adding more than chemical equivalent, is left unreacted in the auxiliary composition (A '). There is a problem that causes a deterioration of the appearance of the formed film and a problem of low corrosion resistance by the use of the acrylic resin of the emulsion type.

In order to solve the above-mentioned disadvantages, the present inventors firstly, the unreacted calcium particles added in the preparation of the dichromate solution are rapidly deposited by gravity while being in the liquid coating solution before being delivered to the coating, which causes the appearance defect. Secondly, when the acrylic resin of emulsion type used as organic resin is dried on the surface of steel sheet after coating treatment in field machine, water existing between large particles is also released. It is estimated that moisture in the air enters the voids during the final productization, resulting in a problem of lowering corrosion resistance, and researches and experiments are carried out to adjust the type of inorganic dichromate to minimize the types of components and resins used. Of course, the above problems can be solved, as a non-oriented electrical steel sheet Other general characteristics can be also been proposed the present invention on the basis of the fact that to meet.

Accordingly, an object of the present invention is to provide a coating composition for forming an insulating coating having excellent appearance and corrosion resistance by appropriately adjusting the components and contents thereof in the insulating coating forming treatment liquid and controlling the manufacturing conditions of the insulating coating accordingly. .

In order to achieve the above object, in the present invention, the acrylic resin of the water-soluble tarpaulin in solid content in 100 g of chromic anhydride in the inorganic composition (A) in magnesium dichromate salt (A) containing 100 g of chromic anhydride and 23.6 to 30.1 g of magnesium oxide. Provided is a coating composition for forming an electrically insulating film having excellent appearance and corrosion resistance on the surface of an non-oriented electrical steel sheet comprising 21 to 110 g, 5 to 45 g of glycerin, and 3 to 10 g of mica powder.

Hereinafter, the present invention will be described in detail with reference to preferred embodiments of the present invention.

Appearance and excellent in corrosion resistance insulating coating film-forming composition of the present invention, the inorganic composition (A) prepared by adding the magnesium oxide in 23.6-30.1g chromic anhydride 100g, the composition (A) water-soluble relative to 100g of CrO ₃ It is formed by adding 21-110 g of acrylic resin as a solid, 5-45 g of glycerin, and 3-12 g of powdered mica.

In addition, an insulating coating having excellent appearance and corrosion resistance can be produced using the coating composition of the present invention. To the inorganic composition (A) prepared by adding magnesium oxide 23.6-30.1 g to 100 g of chromic anhydride, To the surface of the non-oriented electrical steel sheet, an insulating film-forming treatment liquid formed by adding 21-110 g of water-soluble acrylic resin, 5-45 g of glycerin, and 3-12 g of powdered mica was added to 100 g of CrO _3. After coating so that a film thickness may be 0.5-5.0 micrometers per side | surface, an insulating film can be manufactured by the manufacturing method which consists of annealing for 10 to 70 second in the temperature range of 350 degreeC-850 degreeC.

Hereinafter, the roles, functions, preparation methods, and limitations on the amount of each component will be described.

In the present invention, the treatment liquid is constituted as follows. The dichromate metal salt added in order to provide adhesion and corrosion resistance to the film should increase the pH to suppress the decomposition of the resin by inhibiting the reaction between the resin and the chromic acid added thereto. In order to produce such an effect, the addition amount of magnesium oxide needs to be more than the chemical equivalent required for reaction with magnesium dichromate salt. In this case, at 23.6 g or less of magnesium oxide, the purpose of excessive addition of magnesium oxide cannot be achieved. On the other hand, when it exceeds 30.1 g, the appearance of the magnesium oxide particles remaining unreacted may deteriorate the appearance of the film. It is effective to make an appropriate addition amount into 23.6-30.1 g with respect to 100 g of chromic anhydrides.

The organic reducing agent glycerin added in order to reduce the chromium hexavalent to chromium trivalent and to make the annealing condition fast and stable is large in the amount of remaining chromium hexavalent in the film when the amount of the organic reducing agent glycerin is added to 5 g or less with respect to 100 g of CrO ₃ in the inorganic composition (A) The presence of a yellowish brown surface is poor, and when the content is 45 g or more, the treatment solution is easily gelled, and thus the solution stability is deficient.

When water-soluble acrylic resin that improves adhesion with the material and gives flexibility to the film is not obtained sufficient film adhesion when added to the solid content of resin 21g or less with respect to 100g of CrO ₃ in the inorganic composition (A) in the treatment liquid, sufficient film adhesion is not added. The problem of powdering after SRA occurs, so 21-110g is appropriately added.

The ultrafine mica powder added to improve the electrical insulation of the coating is less than 3g with respect to 100g of CrO ₃ in the dichromate in the treatment liquid, and the effect of improving the insulation is insufficient. It is disadvantageous that the mica added within days generates a layer separation phenomenon due to precipitation and is applied, and even after application by stirring by forced stirring, the appearance is not uniform after annealing, so it is preferable to limit the range to 3-12 g.

On the other hand, in the present invention, after coating the coating composition for forming an insulating film formed as described above on the surface of the non-oriented electrical steel sheet so that the dry film thickness is in the range of 0.5 to 5.0㎛ per one side, in the temperature range of 350 ℃ to 850 ℃ It is preferable to anneal for 10 to 70 seconds, for the following reason.

One of the factors that determine the amount of chromium 6 remaining in the film and the surface color of the film is the relationship between the annealing temperature and time. When the annealing temperature is lower than 350 ° C., a large amount of chromium hexavalent is present in the film, thereby making it easy to absorb moisture. On the other hand, when it is higher than 850 ℃, the annealing temperature becomes difficult to control, resulting in non-uniform reduction, which makes it difficult to control the surface quality such as appearance defects, which makes it difficult to work industrially stably. It is preferable to limit to the temperature range of 350 degreeC-850 degreeC.

When the annealing time is shorter than 10 seconds, a large amount of chromium hexavalent is present in the film, so that the moisture is easily absorbed, and the surface color becomes yellowish brown, and when it is 70 seconds or more, the surface color is reduced due to deterioration of product productivity and overdrying. Since there is a problem that this yellowish brown color becomes poor, it is preferable to limit the annealing time to 10 to 70 seconds.

Even if the film is formed after the roll is applied to meet the annealing conditions, if the thickness of the dry film according to the method of the present invention is 0.5 μm or less, the required insulation cannot be obtained and the surface color is almost grayed out as the base plate. It is a factor that avoids the use itself from the demand price. When the thickness is 5.0 μm or less, problems such as powder removal, welding characteristics, and drop rate after stress relief annealing arise. Therefore, it is preferable to limit the dry film thickness to be in the range of 0.5 μm to 5.0 μm per side.

Hereinafter, the present invention will be described in more detail with reference to Examples.

(Example)

After 10 days of blending the insulating coating liquid having the composition as shown in Table 1, using a synthetic rubber roll, uniformly coated on the surface of the non-oriented electrical steel sheet (containing 0.4% of Si, plate thickness: 0.5 mm), and then heating and annealing them. An electrically insulating film was formed, respectively. Comparative Example 8 of the coating composition was excluded from the coating property test due to the loss of coating workability due to gelation and delamination.

Table 1

Film properties of the electrically insulating film formed as described above were measured, and the measurement results are shown in Table 2 below.

TABLE 2

In Table 2, the stress relief annealing was heat-treated at 750 ℃ X 2 hours in a dry 100% N ₂ gas atmosphere, the insulation (Amps.) When the current through the input 0.5 V, 1.0 A (amps) under 300 PSI pressure The adhesion current (mmψ) is the minimum arc diameter without film peeling when the specimen is bent by 180 ° after contact with a circular arc of 10, 20, 30-100mmψ after annealing. The surface color is good when there is almost no remaining chromium hexavalent in the formed film, and when the chromium trivalent is present at a predetermined amount or more to become a dark green insoluble chromium oxide, the remaining chromium hexavalent is It is a defect that a brown film is produced by a large amount present, and the external appearance makes a state in which unreacted divalent oxide etc. remain on the steel plate surface. The amount of chromium hexavalent eluate is measured by immersing a 100 cm 2 coated sample in boiling water for 1 hour and measuring the amount of chromium hexavalent (μg). Corrosion resistance was visually observed for rust on the surface of the coating after 8 hours of salt spray test (5% NaCl, 35 ° C) .Inorganic composition (A) solution prepared by reacting magnesium oxide with chemical equivalent or more Inventive Examples 1, 2, and 3 obtained by annealing an electrical steel coating composition made by adding water-soluble acrylic resin, glycerin, and mica powder to an appropriate treatment condition were added to glycerin, titrated annealing, and formed to a predetermined film thickness. Since there is almost no hexavalent value and proper reduction is made, most of the film is changed to chromium trivalent, so it turns into green insoluble chromium oxide and has a good color, and the additive composition of the coating composition and the range of addition are different (Comparative Examples 1, 4, 5, 6,8) It can be seen that the appearance and corrosion resistance are superior to those of the comparative examples of the annealing treatment and manufacturing (Comparative Examples 2, 3, and 7) improperly. It is extremely difficult to clarify the mechanism to be obtained, but an acrylic resin of water-soluble type (e.g. 0.01 μm) which has a smaller average resin particle size than an emulsion type acrylic resin (e.g. 1.50 μm) made of a resin having a large average particle size. It is presumed that this is possible by minimizing the pores after water has escaped during the formation of the film on the surface of the electrical steel sheet and deriving the effect of suppressing moisture penetration into the atmosphere.

Therefore, as mentioned above, according to the coating composition for electrical insulation film formation which shows the outstanding external appearance and corrosion resistance on the surface of the non-oriented electrical steel plate of this invention, the mixed coating which has the acrylic resin of a water-soluble type | mold in the dichromate magnesium liquid as a main component By using the liquid, there is an advantageous characteristic for improving the appearance and improving the corrosion resistance, and it is only effective to form an insulating film on the surface of the non-oriented electrical steel sheet that can also satisfy the characteristics generally required such as insulation, adhesion and heat resistance. Rather, it is possible to increase the work efficiency due to the exclusion of the time required for cooling the inorganic composition, which was required as a pretreatment process when combining the organic and inorganic compositions of the prior art.

Claims (1)

To the magnesium dichromate salt solution (A) containing 100 g of chromic anhydride and 23.6 to 30.1 g of magnesium oxide, the acrylic resin of the water-soluble type is 21 to 110 g in solid content, 5 to 45 g of glycerin, and mica relative to 100 g of chromic anhydride in the inorganic composition (A). A coating composition for forming an electrically insulating film, which exhibits excellent appearance and corrosion resistance on a non-oriented electrical steel sheet characterized by an organic and inorganic mixed coating liquid containing 3 to 12 g of powder.