Electricity: conductors and insulators – Insulators
Reexamination Certificate
1999-12-14
2001-09-11
Reichard, Dean A. (Department: 2831)
Electricity: conductors and insulators
Insulators
C428S383000, C427S207100, C174S1100SR, C174S1200SR
Reexamination Certificate
active
06288342
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a round or flat insulated wire used as magnet wires for various kinds of electric coils in electric and electronic equipment.
2. Description of the Related Art
In recent years, combined with down-sizing and weight reducing tendency for equipment in various fields such as in the automobile and electric or electronic industries, the demand has grown for reduced size and weight of coils used in such equipment as well as low cost manufacturing while maintaining high performance such as electric characteristics, mechanical characteristics and long lasting heat resistance. Therefore, it is necessary for forming coils to wind magnet wires around a smaller core at a higher density and at a higher speed, which results in damaging the insulation film for the magnet wires, thereby deteriorating the electromechanical characteristics of equipment or lowering the production yield.
For coping with the problems, countermeasures have been taken for the insulation film of insulated wires such as (1) improvement of mechanical strength, (2) improvement of flexibility, (3) improvement of lubrication and (4) improvement of adhesion with conductors. For example, Japanese Patent Application Laid-Open No. 196025/1994 (a) describes the technique of improving the resistance to fabrication of a heat resistant insulation film made of polyamideimide, polyimide or aromatic polyamide by properly setting the tensile strength, tensile modulus of elasticity, adhesion and static friction coefficient to piano wires. Further, Japanese Patent Application Laid-Open No. 58519/1987 (b) discloses a flat insulated wire formed by coating and baking an enamel prepared by adding a polyisocyanate block material blocked with a polyesterimide and a phenolic compound to a polyetherimide. Further, Japanese Patent Application Laid-Open No. 34828/1983 (c) discloses a blend of a polyamideimide and a polyetherimide, to obtain a material having mechanical characteristics comparable with those of the polyetherimide and excellent in solvent resistance, abrasion resistance and long lasting heat resistance.
However, in the technique disclosed in (a), while the insulation film is constituted taking into consideration the improvements (1), (3) and (4), the flexibility is not always sufficient. In the technique disclosed in (b) the problems of degradation due to fabrication and lowering of thermal impact resistance of insulation film caused by rolling an insulated wire to have a flat square shape by combining the flexibility of the polyetherimide, the heat resistance and the adhesion of the polyesterimide to the conductor, and the solderability of phenolic compound-blocked polyisocyanate, but the film does not have sufficient flexibility since elongation at the break of the polyesterimide is inadequate (for example, refer to Comparative Example 7 in this specification). Each of the blend materials obtained in (c) has low glass transition temperature (refer to Table 2 of the patent publication (c)), and the heat resistance is not sufficient to be used as a heat resistant magnet wire material.
As has been described above, although the related art as in (a), (b) and (c) described above can solve the given subjects respectively as the magnet wire material, they are not yet completely satisfactory for obtaining further excellent winding fabricability while maintaining high heat resistance. It may be attributable to the provision of different characteristics which is intended in any of the prior arts is done basically by combining various materials in a single layered structure.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a novel insulated wire excellent in flexibility of an insulation film, suffering from no cracking to the film even undergoing severe winding fabrication or rolling fabrication, having excellent fabricability together with high heat resistance and, more preferably, excellent weldability of the insulation film near the welded portion in that it neither causes blister due to heat upon welding nor increases a discoloration length in the step of welding terminal ends of an insulated wire.
The present inventors have studied in earnest a method capable of making high heat resistance and fabricability compatible while taking various problems into consideration and, as a result, found that the foregoing subjects can be solved by a method as described later, leading to the accomplishment of this invention.
That is, this invention provides an insulated wire, which comprises a first insulation layer (A) comprising a thermosetting resin having a glass transition temperature of 250° C. or higher as a main ingredient formed on a conductor; and a second insulation layer (B) comprising a resin, as a main ingredient, formed by mixing a thermosetting resin (B1) having a glass transition of 250° C. or higher with 10 to 90% by weight of a thermoplastic resin (B2) having a glass transition temperature of 140° C. or higher, formed on the first insulation layer (A), wherein the insulation film comprising the first insulation layer (A) and the second insulation layer (B) has an elongation at break of 40% or more and an adhesion to the conductor of 30 g/mm or more.
Further, this invention provides an insulated wire in which the mixing ratio of the thermoplastic resin (B2) having a glass transition temperature of 140° C. or higher in the second insulation layer (B) is from 30 to 70% by weight, and a ratio (T
1
/T
2
) of a thickness T
1
of the first insulation layer (A) to a thickness T
2
of the second insulation layer (B) is within a range of from 5/95 to 40/60.
Furthermore, a residual amount of a solvent in the insulation film is preferably 0.05% by weight or less based on the total amount of the insulation film in this invention.
It is considered that the foregoing object can be attained in accordance with this invention by the reasons described below.
(1) By setting the adhesion of the insulation film to the conductor to 30 g/mm or more and setting the elongation at break of the insulation film to 40% or more, flexibility of the film capable of withstanding severe winding fabrication can be attained. Even if the elongation at break of the insulation film is 40% or more, if the adhesion to the conductor is less than 30 g/mm, the film of the insulated wire is exfoliated from the conductor, or the film is creased to cause cracking in the film when put to a flexibility test. On the other hand, even if the adhesion to the conductor is 30 g/mm or more, if the elongation at break of the insulation film is less than 40%, the film is cracked by the flexibility test in a similar manner as described above.
(2) In addition to the condition described above, the flexibility and the heat resistance of the insulation film can be made compatible by forming the first insulation layer (A) with a thermosetting resin having a glass transition temperature of 250° C. or higher and forming the second insulation layer (B) with a resin formed by mixing a thermosetting resin (B1) having a glass transition temperature of 250° C. or higher with a thermoplastic resin (B32) having a glass transition temperature of 140° C. or higher, with a mixing ratio of (B2) to (B1) being set within a range from 10 to 90% by weight. The heat resistance mentioned herein is evaluated by a heat softening temperature measured by a method described later, and it is necessary that the softening temperature is 400° C. or higher.
(3) Balance between the adhesion to the conductor and the elongation at break of the insulation film, which is thus far difficult to attain by the single layer structure, can be obtained, and the flexibility can be improved for the entire insulation film, by combining the first insulation layer (A) and the second insulation layer (B). Existent insulated wires often cause a problem that though the flexibility can be satisfied in round wires, the flexibility cannot be satisfied when they are rolled into a flat square shape. However, the flexibility is not deteriorated in th
Asai Hiromitu
Hashimoto Hideyuki
Kurata Masaharu
Matsubara Shinichi
Matsuura Yuki
Reichard Dean A.
Smith , Gambrell & Russell, LLP
Sumitomo Electric Industries Ltd.
Walkenhorst W. David
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