Honeycomb structure and method for preparing the same

Details Honeycomb structure and method for preparing the same Honeycomb structure and method for preparing the same

1999-12-09

2001-12-18

Jones, Deborah (Department: 1775)

Stock material or miscellaneous articles

Structurally defined web or sheet

Honeycomb-like

C428S365000, C442S181000

Reexamination Certificate

active

06331340

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a honeycomb structure and a method for preparing the same.
The honeycomb structure comprises planar bulk materials of hollow prismatic cells. The heat-resistant honeycomb structure is used in, for instance, peripheral machinery and tools of engines for airplanes, sandwich panels used at portions which are exposed to a high temperature and structural members used in, for instance, airplanes and space machinery and tools which are exposed to high temperature and pressure and have high heat resistance over a long time period in an environment or at a normal service temperature of about 260° C. As base materials for honeycomb structures having a light weight and high mechanical strength and excellent in specific strength with respect to weight, there have conventionally been used, for instance, aluminum foils and kraft paper. As such base materials excellent in heat resistance as well, there have been developed, for instance, those produced by forming metal foils such as stainless steel and titanium foils into honeycomb-like structures and then subjecting the honeycomb structures to brazing process; those prepared by adhering heat-resistant resins such as resol-phenol resins to glass fibers and carbon fibers serving as base materials (fiber reinforced resin honeycomb structure); and those prepared by adhering heat-resistant resins such as resol-phenol resins to synthetic heat-resistant aromatic polyamide paper serving as base materials.
Among them, the fiber reinforced resin honeycomb structure has good specific strength and specific rigidity and therefore it has been used as aircraft parts. If it is used as parts of aircraft engine, it is required to have excellent mechanical strength at high temperature region (120 to 150° C.) and thermoformability into two-dimensional and three-dimensional surface. In order to meet mechanical strength at high temperature region and thermoformability, there has conventionally been used a thermoplastic resin having a glass transition temperature of 250° C. or higher (that is, the resin is softened at a temperature higher than 250° C. which makes the molding of the resin easy) and showing no heat deterioration of mechanical property at a temperature 100° C. lower than the glass transition temperature. However, this thermoplastic resin is solid at an ordinary temperature and does not dissolve in a suitable solvent. Accordingly, it is necessary to heat the resin to 350° C. or higher to convert it to a liquid state before it is used to make a honeycomb structure. For this purpose, a special apparatus for the manufacture of a honeycomb structure is needed, which leads to low efficiency and high cost. Further, the thermoplastic resin itself is expensive.
Moreover, a honeycomb structure comprising a carbon fiber as a base material suffers from radio obstruction problem and therefore, the use thereof is limited.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a honeycomb structure which is free of radio obstruction problem and is excellent in mechanical strength at a high temperature region ranging from 120 to 150° C. and heat formability to curved surface. It is another object to provide a method for preparing such a honeycomb structure with low cost.
The present invention provides a honeycomb structure comprising a supporting base of glass fibers impregnated with a polyamide imide resin prepolymer.
The present invention also provides a method for preparing a honeycomb structure which comprises the steps of alternately stacking a plurality of corrugated sheets, each of which is produced by corrugating a supporting base of glass fibers impregnated with a polyamide imide resin prepolymer and curing the prepolymer during or after the corrugating step, and a plurality of flat sheets, each of which is prepared by impregnating a supporting base of glass fibers with a polyamide imide resin prepolymer and then curing the prepolymer, through a node bond adhesive; heating the resin under pressure to form a crosslinked and cured laminated structure; impregnating the laminated structure with a polyamide imide resin prepolymer; and curing and crosslinking the prepolymer to obtain a honeycomb structure.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will hereinafter be explained in more detail.
The supporting bases of glass fibers used in the honeycomb structure of the present invention are preferably those having a tensile strength in crosswise direction that is 105 to 150% of that in lengthwise direction. The size of the glass fiber constituting the supporting bases of glass fibers is preferably 30 to 210 tex, more preferably 60 to 150 tex. The supporting bases of glass fibers used in the present invention may be, for instance, woven fabrics, knitting fabrics and nonwoven fabrics, more specifically, glass fiber woven fabrics of 120 to 380 g/m
2
, preferably 145 to 220 g/m
2
such as plain weave fabrics or long shaft weave fabrics. The supporting base suitably has a thickness generally ranging from about 0.15 to 0.25 mm and a width ranging from about 250 to 350 mm. In order to prepare the supporting bases of glass fibers having a tensile strength in crosswise direction (i.e., the direction parallel to shear direction of the honeycomb structure) that is 105 to 150% of that in lengthwise direction, the size (cross section) of fibers in crosswise direction may be increased by 5 to 50%, preferably 10 to 30% as compared with that in lengthwise direction, the number of fibers in crosswise direction may be increased by 5 to 50%, preferably 10 to 30% as compared with that in lengthwise direction, or combinations thereof may be used.
The supporting base of glass fibers is impregnated with a polyamide imide resin prepolymer. The amount thereof to be impregnated into the supporting base suitably ranges from 20 to 80% by weight, preferably 50% by weight as expressed in terms of the solid content thereof. Preferred examples of such polyamide imide resin prepolymer are those represented by the following general formula (1):
wherein n is a numerical value ranging from 10 to 100.
The polyamide imide resin prepolymer of the formula (1) is cured by heat to form a polyamide imide resin of the following formula (2).
The polyamide imide resin prepolymer of the formula (1) is commercially available and it may be easily prepared by the method disclosed in Die Angewandte Makromolekulare Chemie 40/41 (1974) 139-158.
The supporting base of glass fibers impregnated with the polyamide imide resin prepolymer is subjected to corrugating using corrugated rolls according to the usual method. The height and width of each corrugation of the resulting corrugated sheet suitably range from 2 to 3 mm and the pitch thereof suitably ranges from 8 to 9 mm.
The supporting base of glass fibers (flat sheet) impregnated with the polyamide imide resin prepolymer is then adhered to a corrugated rack while applying a pressure of 0.1 to 10 kgf/cm
2
, preferably 5.0 kgf/cm
2
by using adhesiveness of the resin. Then, the same type of rack is placed on the top surface of the supporting base and heated at a temperature of 150 to 450° C., preferably 250 to 300° C. at a pressure of 0.1 to 20 kgf/cm
2
, preferably 6.0 kgf/cm
2
, for 0.5 to 24 hours, preferably 6 hours to crosslink and cure the resin to thereby prepare a corrugated sheet.
A plurality (for instance, about 150 to 400 sheets each) of the corrugated sheets to which a node bond adhesive of a polyamide imide resin prepolymer is coted on the crest portions of the corrugations in an amount ranging from about 10 to 300 g/m
2
and the flat sheets (free of corrugations) of glass fiber supporting base impregnated with the polyamide imide resin prepolymer are alternately stacked and then the resulting stacked sheets are heated at a temperature ranging from about 150 to 450° C., preferably 250° C., at a pressure of 0.1 to 10 kgf/cm
2
, preferably 1.0 kgf/cm
2
, for 0.5 to 24 hours, preferably 6 hours to crosslink and cure the resin to thereby prepa

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