Films of thermoplastic poly(arylene ether imidazole)s (PAEIs) are used as surface modifiers for neat resin panels and composite resin panels. The PAEI polymer contains imidazole groups along the backbone which co-cure, i.e., react chemically, with epoxies or bismaleimides during processing and thereby provide excellent adhesion between the PAEI 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 as-processed integral structures have very smooth (specular) surfaces, and since the film releases readily from a glass mold, no release agent is necessary. The PAEI 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 approximately -196 C

Connell, John W.

Towell, Timothy W.

English

NASA Technical Reports Server

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 E T H E R  TMIDAZOLE)  
SURFACING f ILMS FOR FLAT AND 
PARABOLIC  STRUCTURES P a t e n t  
Appl ication (NASA. ~angley 
Research C e n t e r )  15 p 
LaRC 
https://ntrs.nasa.gov/search.jsp?R=19950007726 2020-06-17T23:53:16+00:00Z
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 post- 
machining 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 p m  root mean square (RMS), both easily meeting goals 
of 10 kglmz and 3.0 p m  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  p m  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 pre- 
treatment 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 p m  thick PAEl film was placed against a precision convex 
parabolic stainless steel tool 3 6  cm in diameter, covered with a release 
film. A 3 6  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 pre- 
treatment 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 p m  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 t h  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 t o  177OC under 0.7 MPa pressure in an autoclave 
causing the epoxy t o  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 t h  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 as- 
processed 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. 




Poly(arylene ether imidazole) surfacing films for flat and parabolic structures

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