December 2014 Archives

#198 Electric Insulating Paint

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This type of paint has long been used for wires, coils and capacitors installed in electrical/electronic equipment.Its applications are largely classified into the electric power field and the electronics fields.

Varnish coating is used for impregnating coils in the electric power field.This has made the equipment more compact and lightweight, improved its characteristics, including reliability, reduced costs, and produced more energy-efficient devices.Unsaturated polyester coatings are used for impregnating coils installed in small power transformers.This coating was adopted for its excellent workability, for example scraping can be performed easily after curing.

Polyurethane-based insulating coatings are one of the paints widely used for communication devices and home electronic appliances.The film of this paint has superior chemical resistance and electrical characteristics. In addition, soldering on this coating can be performed without peeling off the film.
Polyurethane paints with superior painting and soldering performance were also developed to improve the productivity or the reliability of this paint.For example, a 1 mm diameter baked enamel has superior flexibility and adhesive/soldering performance.The electrical wires with this insulation coating applied are used as a wire with minimized soldering time in reducing the effect on other components in light electrical appliances and shortening the work time, as well as in the process control.

Electric insulating paints with a heat resistance property have been developed as well.While motors and transformers are becoming more compact and lightweight, they require improved reliability such as the ability to run continually. Enamel wires used for these devices need to have more enhanced heat resistance.
Enamel wires in general are manufactured by applying organic resin dissolved or dispersed in solvents onto a copper wire, followed by a baking finish.Most of them are classified as polyimide varnish, polyester varnish, polyester-imide varnish, polyamide-imide varnish, and those mixed with ladder silicone-based oligomer for the improved heat resistance.
Repeat the process of applying these varnish coatings on a copper wire with a baking finish several times. To finish, measure the finishing diameter, the conductor diameter, the coating thickness, flexibility, thermal softening temperature, heat shock (200C° x 1hr.), and overload characteristics, etc.

An example of electrical characteristics of coil impregnating varnish is shown in [Table 1].

[Table 1] Characteristics of coil impregnating varnish
ItemGeneral-purposeBrief treatmentCompact type
Volume resistivityNormal state, Ω・cm3×10153×10154×1015
Water exposure, Ω・cm8×10149×10141×1015
Insulation breakdown strengthNormal state, kv/mm20.420.821.3
Water exposure, kv/mm20.120.420.6

#197 Magnetic Paint

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Magnetic paints are used as coatings to control the magnetic field.We are surrounded by products using this type of coating.
In addition to VTR tapes, audio cassette tapes, and MTs for computers, this type of coating is used for various items that are necessary for industry and in our daily lives, such as credit cards, train tickets, commuter passes, highway passes, bus tickets, telephone cards, orange cards, etc.
Magnetic paints are comprised of a magnetic substance (powder), binder resin, additives, solvents, and other substances.A typical magnetic powder is the metal powder containing γFe2O3,CrO2, and Fe as the main ingredients.
Magnetic paints are largely classified into two categories according to the recording density: Ba ferrite,γ-Fe2O3・Fe3O4,and Co-γFe2O3・CrO2are used for horizontal recording; while metal powder・Co-FeOx, Ba ferrite・hexagonal-plate vapor deposition, and sputter・Co-Cr are used for vertical recording.
Materials such as polyurethane and vinyl chloride-vinyl acetate copolymer are used for the binder resin, which increases various characteristics such as adhesive performance with the base PET (polyethylene terephthalate), abrasion resistance, rigidity, slippage, and dispersion property of the magnetic powder.

Required characteristics for magnetic films and their predominant factors are shown in [Table 1].

Required characteristics for magnetic films and their predominant factors are shown in [Table 1].
Required characteristicsPredominant factors
Magnetic substanceBinderBaseDispersionApplicationProcessing
High sensitivity, reproduction output, and saturated/residual flux density   
Good frequency characteristics and short-wavelength recording characteristics  
Adequate coercive force     
Good SN ratio  
Small output fluctuation    
Small output fluctuation     
Small harmonic distortion rate    
Low impedance, free from static trouble    
Small temperature/secular changes in electromagnetic conversion characteristics   
Adequate flexibility    
Low wear coefficient and smooth running    
Less-wearing on the head    
Good adhesive performance with the base    
No degradation of adhesive performance in long-term storage    

The recording density is improving year after year.

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