Method of making flame resistant polyimide foam insulation and the resulting insulation

The method of making high efficiency flame resistant polyimide foam insulation which comprises the steps of:

• spreading a layer of a powdered polyimide foam precursor on a surface;
• heating said powder to its foaming temperature for a period sufficient to permit substantially complete and unconstrained foaming;
• trimming the resulting uneven foam sheet to the desired sheet configuration, removing substantially all rind and other density non-uniformities;
• pressing said sheet between opposed surfaces to a thickness of from about 10 to 90 per cent of the original thickness;
• heating said sheet to a temperature of from about 400.degree. to 650.degree. F. for from about 10 to 30 minutes;
• and
• whereby stabilized, higher density, uniform insulation having improved flame resistance results.

The method of making high efficiency flame resistant rigid polyimide foam insulation which comprises the steps of:

• providing a substantially uniform sheet of polyimide foam which had been foamed unconstrained;
• pressing said sheet between opposed surfaces to a thickness of from about 25 to 40 per cent of the original thickness;
• heating said sheet to a temperature of from about 425.degree. to 600.degree. F. for a period sufficient to stabilize the foam at a uniform higher density;
• providing an uncured sheet of open cell polyimide foam which has been uniformly impregnated with a liquid polyimide resin precursor and dried;
• placing said uncured sheet against said stabilized foam sheet to form a sandwich;
• heating the sandwich to the curing temperature of said impregnating polyimide resin precursor for a time sufficient to produce substantially complete cure;
• and
• whereby a high efficiency rigid insulation panel having a highly flame resistant face is produced.

The method of making high efficiency flame resistant polyimide foam insulation in tubular form which comprises the steps of:

• providing at least one thin uniform sheet of polyimide foam which had been foamed unstrained;
• pressing said sheets between opposed surfaces to thicknesses of from about 25 to 40 per cent of the original thickness;
• heating said sheets to a temperature of from about 400.degree. to 650.degree. F. for a period sufficient to stabilize the foam sheets;
• wrapping said at least one sheet at least once around a mandrel;
• surrounding said wrapped mandrel with a cover in contact with said sheets;
• heating the resulting assembly to a temperature of from about 400.degree. to 650.degree. F. for from about 60 to 90 minutes;
• and
• removing the resulting stabilized tube from said mandrel and cover.

The method of making a rigid tubular duct having high insulation efficiency and a highly flame resistant outer surface which comprises the steps of:

• providing an uncured sheet of open cell polyimide foam uniformly impregnated with a liquid polyimide resin precursor;
• wrapping said uncured sheet at least once around a collapsible mandrel;
• covering said uncured sheet with a cover having an internal configuration corresponding to said mandrel shape and spaced uniformly therefrom;
• heating the assembly at a temperature of from about 400.degree. to 650.degree. F. for a period sufficient to cure said impregnating resin;
• whereby a tubular rigid foam duct is produced;
• providing a substantially uniform low density sheet of polyimide foam which had been foamed unconstrained;
• pressing said low density sheet between opposed surfaces to a thickness of from about 25 to 40 per cent of its original thickness;
• heating said low density sheet at a temperature of from about 400.degree. to 650.degree. F. for a period sufficient to stabilize the foam at higher density;
• applying a coating of liquid polyimide resin precursor to one surface of the stabilized foam sheet;
• drying the coated surface;
• wrapping said stabilized foam sheet around said rigid foam duct with the coated surface in contact with said duct;
• holding said stabilized foam sheet in place;
• heating the resulting assembly to a temperature of from about 400.degree. to 650.degree. F. for a period sufficient to cure said coating polyimide precursor;
• and
• whereby a high efficiency rigid insulated duct having a highly flame resistant outer face is produced.