Y 

// 

NASA CASE NO. J AR 14813-1 

PRINT FIG. 3 

The invention disclosed in this document resulted from research in aeronautical and 

space activities performed under programs of the National Aeronautics and Space 

Administration. The invention is owned by NASA and is, therefore, available for 

licensing in accordance with the NASA Patent Licensing Regulation (14 Code of 

Federal Regulations 1 245.2). 

To encourage commercial utilization of NASA-owned inventions, it is NASA policy to 

grant licenses to commercial concerns. Although NASA encourages nonexclusive 

licensing to promote competition and achieve the widest possible utilization, NASA 

will provide the necessary incentive to the licensee to achieve early practical 

application of the invention. 

Address inquiries and all applications for license for this invention to NASA Patent 

Counsel, Langley Research Center, Code 143, Hampton, Virginia 23681-0001. 

Serial No.: 

{NASA-Case-LAR-14812-11 

PDLY(ARYLEME ETHER TMIDAZOLE) 

SURFACING f ILMS FOR FLAT AND 

PARABOLIC STRUCTURES Patent 

Appl ication (NASA. ~angley 

Research Center) 15 p 

LaRC 
AWARDS ABSTRACT 

POLY(ARYLENE ETHER IMIDAZOLE) SURFACING FILMS 

FOR FLAT AND PARABOLIC STRUCTURES 

NASA Case No.: LAR 1 481 2-1 

Poly(arylene ether imidazole)~ (PAEI) are aromatic polymers which have high glass 

transition temperatures and high mechanical properties. Films of PAEls are prepared 

by solution casting in a dust-free environment with subsequent removal of the solvent 

by heating in a forced air oven. Films of PAEls may be used as surface modifiers for 

flat and parabolic panels made of neat resin epoxy or neat resin bismaleimide, as well 

as panels made of composites of epoxies or bismaleimides which may contain any type 

of continuous or chopped fiber or fabric. 

By the present invention, PAEls have been found to be particularly suitable for use as 

surface modifiers for neat resin epoxy or neat resin bismaleimide panels, as well as for 

graphitelepoxy or graphitelbismaleimide composite panels. This is possible because a 

molecule of PAEl contains imidazole groups along its backbone that co-cure with 

epoxies or bismaleimides during processing. 

The novelty of the invention resides within the formation of an integral structure having 

a smooth (specular) surface from a film of a PAEl polymer which co-cures with an 

epoxy or a bismaleimide during processing. As a result, there is excellent adhesion 

between the PAEl film and the epoxy or bismaleimide neat resin or composite resin 

facesheet. The film provides good adhesion and a smooth surface to the finished part 

and acts as a release agent from the mold. The PAEl film is thermally stable, resistant 

to electron radiation, and adheres tenaciously to the facesheet. 

Inventors: John W. Connell 

Address: 204 Henry Lee Lane 

Yorktown, VA 23692 

Employer: NASA LaRC 

Timothy W. Towell 

103 Yukon Street 

-- 

NASA LaRC 
Inventors: Stephen S. Tompkins 

Address: 1 17 Woodland Road 

Williamsburg, VA 231 88 

Employer: NASA LaRC 

Initial Evaluator: Terry L. St. Clair 

Serial No.: 08/238,102 

Filed: May 4, 1994 
LAR 14812-1 -1- PATENT APPLICATION 

POLY(ARYLENE ETHER IMIDAZOLE) SURFACING FILMS 

FOR FLAT AND PARABOLIC STRUCTURES 

5 Origin of lnvention 

The invention described herein was made by employees of the 

United States Government and may be manufactured and used by or for 

the Government for government purposes without the payment of any 

10 royalties thereon or thereof. 

Backaround of Invention 

- 1. Field of the Invention 

15 

This invention relates generally to structures made from neat resins 

and composites. It relates particularly to neat resin and composite 

structures comprising poly(arylene ether imidazole), PAEI, surfacing films 

chemically bonded to epoxy or bismaleimide, as well as graphitelepoxy or 

20 graphitelbismaleimide face sheets. 

- 2. Descrirstion of the Related Art 

PAEls are aromatic polymers which possess high glass transition 

25 temperatures and high mechanical properties. They are prepared from 

bis(hydroxyimidazole) monomers and activated aromatic dihalides or 

dinitro compounds under conditions described in J.W. Connell and 

P. M. Hergenrother. Hiah Performance Polvmers, Vol. 2, No. 4, 21 1-221, 

1990. Journal of Polvmer Science Part A: Polvmer Chemistry, Vol. 29. 

30 1 667-1 674 (1 991 ), U.S. Patents 5,066,811 (Nov. 1991 ) and 5,116,934 
LAR 14812-1 -2- PATENT APPLICATION 

(May 1992). Thin films of PAEls are prepared by solution casting in a 

dust-free environment with subsequent removal of the solvent by heating 

in a forced air oven. 

It is a primary object of the present invention to use films of PAEls 

5 as surface modifiers for flat and parabolic panels made of neat resin 

epoxy or neat resin bismaleimide, as well as panels made of composites 

of epoxies or bismaleimides which may contain any type of continuous or 

chopped fiber or fabric. 

Another object of this invention is to provide submicron surface 

10 smoothness to panels of neat resin epoxy andlor bismaleimide and 

composites of epoxies and/or bisrnaleimides which may contain any type 

of continuous or chopped fiber or fabric. 

Another object of this invention is to eliminate the need for mold 

release agents when processing neat resin epoxy andlor bismaleimide and 

15 composites of epoxies and/or bisrnaleimides which may contain any type 

of continuous or chopped fiber or fabric. 

Another object of this invention is to eliminate the need for postmachining or polishing of parts processed from neat resin epoxy andlor 

bismaleimide and composites of epoxies and/or bismaleimides which may 

20 contain any type of continuous or chopped fiber or fabric. 

Another object of this invention is to provide a method of preparing 

precision composite reflectors using carbonlgraphite epoxy. 

Summarv of the Invention 

25 

According to the present invention, thin films of thermoplastic 

poly(arylene ether imidazole)~ (PAEl)s have been found to be particularly 

suitable for use as surface modifiers for neat resin epoxy or neat resin 

bismaleimide panels, as well as for graphitelepoxy or 

30 graphitelbismaleimide composite panels. A molecule of PAEl includes 
LAR 14812-1 -3- PATENT APPLICATION 

imidazole groups along its backbone that co-cure, i.e., react chemically, 

with epoxies or bismaleimides during processing. This co-curing provides 

excellent adhesion between PAEl films and the neat resin epoxy or 

bismaleimide, as well as the graphitelepoxy or graphitelbismaleimide 

5 structures. 

A PAEl film is applied to such a structure during processing in a 

smooth mold, with the result that the as-processed structure has a 

smooth (specular) surface. Thus, there is no need for postmachining or 

polishing of PAEl-processed parts made of neat-resin epoxies and/or 

10 bismaleimides, or made of composites of epoxies andlor bismaleimides 

that may contain any type of continuous or chopped fibers or fabrics. 

Additionally, PAEl films are readily released from smooth glass or 

stainless-steel molds, so that no release agent is necessary. The 

adhesion between the PAEl films and the neat resin or composite 

15 structure remains even after thermal cycling from room temperature to 

about -1 96OC. PAEt films are thermally stable and resistant to 

bombardment by energetic electrons. 

Brief Description of the Drawings 

20 

For a more complete understanding of the present invention, 

including its objects and attending benefits, reference should be made to 

the Description of the Preferred Embodiments, which is set forth in detail 

below. This Description should be read together with the accompanying 

25 drawings wherein: 

FIG. 1 shows a composite structure according to the present 

invention comprising a poly(arylene ether imidazole) surfacing film upon 

which a reflective layer of aluminum followed by silicon oxide has been 

vapor deposited; and 

30 FIG. 2 is a representation of the interface between a graphitelepoxy 
LAR 14812-1 -4- PATENT APPLICATION 

facesheet and a poly(arylene ether imidazole) surfacing film according to 

the present invention. 

According to the present invention, a graphitelepoxy composite 

parabolic panel with the PAEl film as a surface modifier was fabricated. 

5 The as-processed panel had an areal weight of 5.7 kglm2 and a surface 

smoothness of 1.8 pm root mean square (RMS), both easily meeting goals 

of 10 kglmz and 3.0 pm RMS. The panel surface was highly specular and 

exhibited a mirror-like finish when coated with vapor deposited aluminum 

and silicon oxide. The use of the PAEl film eliminated fiber print through, 

10 post-polishing and use of mold release agents, which can contaminate the 

panel surface and contribute to surface roughness. The PAEl film is 

thermally stable, resistant to electron radiation, and adheres tenaciously 

to the facesheet even when thermally cycled. The irnidazole groups on 

the surface of the polymer film react chemically (co-cure) with the epoxy 

15 or bismaleimide and thereby provide excellent adhesion. Films of this 

type are used to provide stable precision surfaces on a variety of 

graphitelepoxy or graphitelbismaleimide structures. 

Having generally described the invention, a more complete 

understanding thereof can be obtained by reference to the following 

20 specific Examples, which are provided herein for the purpose of 

illustration only and do not limit the invention. 

25 The following example illustrates the use of a PAEl thermoplastic film 

in the manufacture of a precision composite reflector panel. 

A 50 pm thick PAEl film was placed directly against a precision 

convex parabolic glass tool 36 cm in diameter. The perimeter of the film 

was affixed to the glass tool using double-sided adhesive tape. A 25 cm 

30 diameter, uncured eight ply quasi-isotropic prepreg tape lay-up composed 
LAR 14812-1 -5- PATENT APPLICATION 

of T50 carbon fiber with ERL-1962 epoxy resin was placed on top of the 

PAEl film and glass tool. The entire tool and lay-up were vacuum bagged 

and heated to 177OC under 0.7 MPa pressure in an autoclave causing the 

epoxy to cure and chemically bond to the surface of the PAEl film. The 

5 cured composite laminate and tool were removed from the autoclave. A 

5 cm thick, graphitelphenolic composite honeycomb core material and a 

TBOIERL-1962 composite facesheet were adhesively bonded to the back 

of the laminate (the side without the PAEl film). After the adhesive 

cured, the entire sandwich was lifted from the glass tool and the excess 

10 PAEl film was trimmed from the edge of the panel. The resulting panel 

possessed a precision concave parabolic contour with the PAEl film 

bonded to the surface providing a "glass-like" finish. The final reflector 

surface 11, as shown in FIG. 1, was produced by vapor depositing a 

reflective layer, consisting of 500A of aluminum followed by 500A of 

15 silicon oxide, directly to the surface of the PAEl without any pretreatment or polishing. The surface accuracy of the reflector surface was 

tested with an infrared laser interferometer and was measured to be I .8 

prn RMS over the entire 25 cm diameter. The parabolic composite 

reflector had an areal weight of 5.7 kg/m2. 

20 

Exam~le 2 

The following example illustrates the use of PAEl thermoplastic film in 

the manufacture of a precision composite reflector panel. 

25 A 100 pm thick PAEl film was placed against a precision convex 

parabolic stainless steel tool 36 cm in diameter, covered with a release 

film. A 36 cm diameter, uncured eight ply quasi-isotropic prepreg tape 

lay-up composed of P75 carbon fiber with 930 epoxy resin was placed on 

top of the PAEl film and steel tool. The entire tool and lay-up were 

30 vacuum bagged and heated to 135OC under 0.7 MPa pressure in an 
LAR 14812-1 PATENT APPLICATION 

autoclave causing the epoxy to cure and chemically bond to the surface 

of the PAEl film. The cured composite laminate and tool were removed 

from the autoclave. A 5 cm thick, graphitelphenolic composite 

honeycomb core material and a P75/930 composite facesheet were 

5 adhesively bonded to the back of the laminate (the side without the PAEl 

film). After the adhesive cured, the entire sandwich was lifted from the 

steel tool and the excess PAEl film was trimmed from the edge of the 

panel. The resulting panel possessed a precision concave parabolic 

contour with the PAEl film bonded to the surface providing a "glass-like" 

10 finish. The final reflector surface was produced by vapor depositing a 

reflective layer, consisting of 500A of aluminum followed by 500A of 

silicon oxide, directly to the surface of the PAEl without any pretreatment or polishing. 

Example 3 

The following example illustrates the use of PAEl thermoplastic film in 

the manufacture of a composite reflector panel. 

A 18 cm X 18 cm, 75 pm thick PAEl film was placed directly against 

20 a stainless steel ferrotype plate. The edges of the film were taped to the 

steel plate. A 15 cm X 15 cm, uncured eight ply quasi-isotropic prepreg 

tape lay-up composed of P75 carbon fiber with 930 epoxy resin was 

placed on top of the PAEl film. The entire steel plate and lay-up were 

vacuum bagged and heated to 135OC under 0.7 MPa pressure in an 

25 autoclave causing the epoxy to cure and chemically bond to the surface 

of the PAEl film. The cured composite laminate was easily released from 

the steel plate by removing the adhesive tape. A 3 cm thick, 

glasslpolyimide composite honeycomb core material and a P751930 

composite facesheet were adhesively bonded to the back of the laminate 

30 (the side without the PAEl film). After the adhesive cured, the entire 
LAR 14812-1 PATENT APPLICATION 

sandwich was lifted from the steel tool and the excess PAEl film was 

trimmed from the edge of the panel. The resulting panel had PAEl film 

bonded to one surface providing a "glass-like" finish. A mirrored finish 

was produced by vapor depositing 500A of aluminum directly to the 

5 PAEI. 

Example 4 

The following example illustrates the strength and durability of the 

10 bond between PAEl film and a graphitelepoxy composite laminate after 

thermal cycling. 

A 18 cm X 18 cm, 50 pm thick PAEl film was placed directly against 

a flat polished glass tool. The edges of the film were taped to the glass 

tool. A 15 cm X 15 cm, uncured eight ply quasi-isotropic prepreg tape 

15 lay-up composed of P75 carbon fiber with 930 epoxy resin was placed on 

top of the PAEl film. The entire glass tool and lay-up were vacuum 

bagged and heated to 135OC under 0.7 MPa pressure in an autoclave 

causing the epoxy to cure and chemically bond to the surface of the PAEl 

film. The cured composite laminate was easily released from the glass 

20 tool by removing the adhesive tape. The resulting composite laminate 

had the PAEl film bonded to one side. The laminate was cut into five 2.5 

cm X 15 cm test strips. One of the test strips was quenched in liquid 

nitrogen from room temperature. The sample was removed from the 

liquid nitrogen and allowed to heat back to room temperature, then 

25 quenched again in the liquid nitrogen. This procedure was repeated for a 

total of five quenching. *No deterioration of the bond between the PAEl 

film and the composite could be detected. All attempts to remove the 

PAEl film from the composite resulted in either the epoxy failing at the 

surface of the composite or the PAEl tearing through the thickness of the 

30 film. Attempts to remove the film from the composite included trying to 
LAR 14812-1 -8- PATENT APPLICATION 

peal off the film from a corner, fracturing the composite in a flexural mode 

so as to leave the two fractured pieces connected by the PAEl film 

followed by an attempted peal, and scribing across the surface of the 

PAEl film with a steel scribe. Failure at the PAElIcomposite interface was 

5 not observed in any of these tests. Samples which had not been 

thermally cycled behaved in a similar manner. 

Example 5 

10 The following example illustrates the strength and durability of the 

bond between PAEl film and a graphitelepoxy composite laminate after 

thermal cycling. 

A 15 cm X 15 cm, 50 pm thick PAEl film was placed between the 

I I th and 12th plies of a 15 cm X 15 cm, twenty-two ply unidirectional 

15 composite prepreg lay-up composed of P75 carbon fiber with 934 epoxy 

resin. A release agent had been applied to one end of the film over an 

area 6.3 cm in from the edge across the 15 cm width. The composite 

laminate was heated to 177OC under 0.7 MPa pressure in an autoclave 

causing the epoxy to cure and chemically bond to either side of the PAEl 

20 film except where the release agent had been applied. The cured 

laminate was cut into five 2.5 cm X 15 cm test strips. Two of the test 

strips were quenched in liquid nitrogen from room temperature. The 

sample was removed from the liquid nitrogen and allowed to heat back to 

room temperature then quenched again in the liquid nitrogen. This 

25 procedure was repeated for a total of three quenching. The test samples 

were pealed apart along the fiber direction between the 1 I th and 12th 

plies. The portion of the film where the release agent had been applied 

did not bond to the composite and served as an initial crack through 

which the peal could be started. Failure at the PAElIcomposite interface 

30 was observed only where release agent had been applied. In all other 
LAR 14812-1 -9- PATENT APPLICATION 

regions, failure had occurred entirely in the composite leaving thin layer of 

carbon fibers and epoxy bonded to the PAEl film. This indicated the 

presence of a very strong adhesive bond between the PAEl and 

composite. Samples which had not been thermally cycled behaved in a 

5 similar manner. 

A representation of the observed interface 14 between the 

graphitelepoxy facesheet 12 and the PAEl film 13 is presented in FIG. 2. 

FIG. 2 shows a chemical reaction between the epoxy 12 and the 

PAEl film 13 which provides a more stable interface 14 than one based 

10 upon secondary adhesive forces which occur when nonreactive films, 

such as KaptonQ, are used. The interface 14 formed between the epoxy 

and the PAEl film provides for better thermal cycling behavior since a 

gradient is formed between the two layers which presumably has a 

different coefficient of thermal expansion (CTE) than either the PAEl film 

15 or the epoxy. Nonreactive films such as KaptonQ can disbond after 

prolonged thermal cycling due to stresses which accumulate caused by 

the mismatch in CTE between the epoxy and the film. 

What is claimed is: 
LAR 14812-1 9 PATENT APPLICATION 

POLY(ARYLENE ETHER IMIDAZOLE) SURFACING FILMS 

FOR FLAT AND PARABOLIC STRUCTURES 

Abstract of the Disclosure 

5 

Films of thermoplastic poly(arylene ether imidazole)~ (PAEl)s are 

used as surface modifiers for neat resin panels and composite resin 

panels. The PAEl polymer contains imidazole groups along the backbone 

which co-cure, i.e., react chemically, with epoxies or bisrnaleimides 

10 during processing and thereby provide excellent adhesion between the 

PAEl film and an epoxy or bismaleimide neat resin or composite resin 

facesheet. The film provides good adhesion and a smooth surface to the 

finished part and acts as a release agent from the mold. The asprocessed integral structures have very smooth (specular) surfaces, and 

15 since the film releases readily from a glass mold, no release agent is 

necessary. The PAEl film is thermally stable, resistant to electron 

radiation, and adheres tenaciously to the facesheet. The film maintains 

good adhesion even after thermal cycling from room temperature to 

--I 96OC.