Abstract: A heat-shrinkable polyimide film which comprises a polyimide film prepared by converting at least about 50% by weight of polyamide acid obtained by reacting a biphenyltetracarboxylic acid dianhydride represented by the general formula ##STR1## with an aromatic diamine into polyimide, and stretched in at least one direction to provide heat-shrinkability, and a process for producing the film.

Abstract: An internal combustion engine ignition system comprises: (a) a capacitive discharge ignition device having a voltage transformer which converts a low DC voltage into a corresponding AC voltage and boosts and rectifies the AC voltage into a first higher DC voltage for discharging each of the spark plugs sequentially, boosts and rectifies the AC voltage into a second higher DC voltage for generating arc-sustaining ignition energy, and rectifies the AC voltage into a third higher DC voltage; (b) an ignition signal generating means which generates and outputs an ignition signal whenever the engine rotates through a predetermined engine rotational angle offset by an angular interval determined by the engine speed and engine load; (c) an ignition coil means having a primary winding and secondary winding, one end of the primary winding thereof receiving the first DC voltage from the DC-DC converting means, the other end of the primary winding thereof being grounded when the ignition signal is received from the ignit

Abstract: A process for producing a polyimide tube which comprisesapplying a solution of polyamide acid obtained by reacting a biphenyltetracarboxylic acid dianhydride represented by the general formula ##STR1## with an aromatic diamine in an organic polar solvent to at least one surface of a polyimide film,drying thereafter the film with heating to convert a part of the polyamide acid into the imide form while controlling the volatile material content to about 5 to 60% by weight, by which a compound film having a heat-fusible layer composed of a polyimide precursor is obtained,winding the compound film on a heat resistant core material,heating to unify the compound film by the heat-fusible layer, and removing the heat resistant core material to obtain the polyimide tube.

Abstract: A heat-fusible polyimide compound film which comprises a polyimide film and a heat-fusible layer composed of a polyimide precursor having a volatile material content of about 5 to about 50% by weight which is prepared by converting a part of a polyamide acid obtained by reacting a biphenyltetracarboxylic acid dianhydride represented by the general formula ##STR1## with an aromatic diamine into imide, provided on at least one surface of the polyimide film, and a process for producing the film.

Abstract: A coated article comprising a metal support and a baked layer of a water soluble heat-resistant insulating varnish containing a resin comprising ester groups and imide rings in the molecule dissolved in water using a volatilizable basic compound, the resin comprising the reaction product of(A) a carboxyl-containing polyesterimide resin having an acid value of about 30 to 150 obtained by reacting (a) a polyhydric alcohol component comprising at least one organic polyhydric alcohol and containing about 10 to 60 mol % of an imide ring-containing glycol of the general formula (I): ##STR1## wherein R.sub.1 is a trivalent aromatic group, R.sub.

Abstract: A water-soluble heat-resistant insulating varnish containing a resin comprising ester groups and imide rings in the molecule dissolved in water using a volatilizable basic compound, the resin comprising the reaction product of(A) a carboxyl-containing polyesterimide resin having an acid value of about 30 to 150 obtained by reacting (a) a polyhydric alcohol component comprising at least one organic polyhydric alcohol and containing about 10 to 60 mol % of an imide ring-containing glycol of the general formula (I): ##STR1## wherein R.sub.1 is a trivalent aromatic group, R.sub.2 is a divalent organic group, and n is an integer of 1 to 3, with (b) a polycarboxylic acid component comprising at least one trivalent or divalent organic carboxylic acid or the anhydride thereof, where about 30 to 100 mol % of which comprises an aromatic tricarboxylic acid or the anhydride thereof so that the equivalent ratio (OH/COOH) between the polyhydric alcohol component and the polycarboxylic acid component is about 1.0 to 2.

Abstract: An aqueous insulating varnish which comprises an aqueous medium containing dissolved therein a resin containing ester groups, imide groups and free carboxyl groups in the resin molecule, with a volatile base selected from the group consisting of ammonia and a volatile organic amine to render the resin soluble, the resin comprising the reaction product ofA. a carboxyl group containing polyol (containing ester groups in the molecule) comprising the reaction product of1. an organic carboxylic acid component comprisingA. about 15 to 100 mol% of at least one of an aromatic tricarboxylic acid and the anhydride thereof in which up to 30 mol% of the aromatic tricarboxylic acid and the anhydride thereof can be replaced by at least one of an aromatic tetracarboxylic acid and the anhydride thereof, andB. about 0 to 85 mol% of at least one of a dicarboxylic acid and the anhydride thereof; and2. an organic alcohol component comprising at least one organic polyhydric alcohol;B.

Abstract: An aqueous insulating varnish which comprises an aqueous medium containing dissolved therein a polyester resin having an acid value of about 20 to 200 with a volatile basic compound, the resin being obtained by reactingA. an organic polycarboxylic acid component comprisingA. at least 30 mol% of at least one of an aromatic tricarboxylic acid and the anhydride thereof, in which up to about 30 mol% of the tricarboxylic acid and anhydride thereof can be replaced by at least one of an aromatic tetracarboxylic acid and the anhydride thereof, andB. about 0 to 70 mol% of at least one of a dicarboxylic acid and the anhydride thereof, andB. an organic polyhydric alcohol component containing at least 20 mol% of a polyethylene terephthalate oligomer represented by the formula ##STR1## wherein n is an integer of 1 to 5, in a OH/COOH equivalent ratio of about 1.0 to 2.0.

Abstract: Aqueous baking varnishes having a low viscosity and a high concentration suitable for coating conductors which compriseA. a carboxyl group containing polyester resin having an acid number of about 10 to 150 comprising the reaction product of1. an organic carboxylic acid component comprisingA. about 15 to 100 mol% of at least one of an aromatic tricarboxylic acid and the anhydride thereof in which up to 30 mol% of the aromatic tricarboxylic acid and the anhydride thereof can be replaced by at least one of an aromatic tetracarboxylic acid and the anhydride thereof, andB. about 0 to 85 mol% of at least one of a dicarboxylic acid and the anhydride thereof, and2. an organic alcohol component comprising at least one organic polyhydric alcohol; andB.