A polymeric substrate is coated with a metal oxide film to provide oxidation protection in low Earth orbital environments. The film contains about four volume percent polymer to provide flexibility

Banks, Bruce A.

Mirtich, Michael J.

Sovey, James S.

English

NASA Technical Reports Server

United States Patent 1191 [ i l l  Patent Number: 4,664,980 
Sovev et al. 1451 Date of Patent: May 12, 1987 
[54] OXIDATION PROTECTION COATINGS FOR [52] US. CI. .................................... 428/421; 428/422; 
POLYMERS 428/447; 42W473.5; 428/702 
[75] Inventors: 
[73] Assignee: 
[21] Appl. No.: 
[22] Filed: 
James S. Sovey, Strongsville; Bruce 
A. Banks, Olmsted Township, 
Cuyahoga County; Michael J. 
Mirtich, North Olmsted, all of Ohio 
The United States of America as 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
834,977 
Feb. 27, 1986 
[58] Field of Search .................. 427/397.7; 42W473.5, 
428/421,422,441, 202 
1561 References Cited 
U.S. PATENT DOCUMENTS 
3,514,388 5/1970 Brumfield et al. .................. 204/192 
3,984,581 10/1976 Dobler et al. ......................... 427/35 
4,112,137 9/1978 Zega ...................................... 427/38 
4,574,879 3/1986 DeGree et al. .............. 42W473.5 X 
4,091,138 5/1978 Takagi et al. ....................... 428/209 
4,199,650 4/1980 Mirtich et al. ...................... 428/421 
Primary Examiner-Michael R. Lusignan 
Attorney, Agent, or Firm-Gene E. Shook; John R. 
Manning 
P I  ABSTRACT 
A polymeric substrate 10 is coated with a metal oxide 
film 22 to provide oxidation protection in low earth 
orbital environments. The film contains about four vol- 
ume percent polymer to provide flexibility. 
Related U.S. Application Data 
[62] Division of Ser. No. 761,235, Jul. 31, 1985, Pat. No. 
4,604,181, ,,,hi& is a division of Ser. No, 649,330, Sep, 
14, 1984, Pat. No. 4,560,577. 
[51] Int. Cl.4 ........................ B32B 9/04; B32B 27/00; 
B32B 27/06 14 Claims, 4 Drawing Figures 
https://ntrs.nasa.gov/search.jsp?R=19870014303 2020-03-23T15:18:06+00:00Z
U.S. Patent May 12,1987 Sheet 1 of2 4,664,980 
14 
16 
FIG. I 
i 
FIG. 2 
uo s o  Patent May 12,1987 Sheet 2 of 2 4,664,980 
FIG. 3 
50 
L 
FIG. 4 
4,664,980 
1 2 
beam, and the ionized molecules are deposited on the 
Takagi U.S. Pat. No. 4,091,138 discloses a coating 
method wherein a metal is ionized in the crucible. This 
5 metal is deposited on a film material, such as a poly- 
OXIDATION PROTECTION COATINGS FOR substrate. 
POLYMERS 
ORIGIN OF THE INVENTION 
The invention described herein was made by employ- 
ees of the U.S. Government and may be manufactured 
and used by or for the Government for governmental 
purposes without the payment of any royalties thereon 
or therefor. 
10 
imide or other thermoplastic resin, to form an electri- 
cally conducting insulated coating. 
Zega U.S. Pat. No. 4,112,137 is directed to a coating 
method wherein a metal source is bombarded by an 
electron beam. This nrfetal is used to coat glass surfaces. 
Brumfield et a1 U.S. Pat. No. 3,514,388 is concerned 
STATEMENT OF COPENDENCY with a metal plating method for coating a large number 
of metal and nonmetal parts at the same time using a 
metal. A~~~~ gasses are employed in the ion plating 
None of the prior art patents discloses a coating for 
oxidation protection. Moreover, none of these patents 
employs an ion beam for cleaning the substrate prior to 
coating. 
DISCLOSURE OF THE INVENTION 1. Technical Field 
This invention relates to the protection of polymeric A polymer material is exposed to an ion beam to clean 
materials, such as polyimides. The invention is particu- absorbed gasses and contaminants from its surface. The 
larl y concerned with providing an oxidation protection ion cleaned polymer surface is then immediately ion 
barrier to these materials when they are exposed to low 25 beam sputter coated with a protective thin film. Materi- 
earth orbital environments. als may be co-sputtered to form a coating containing 
Various polymers exhibit weight loss when exposed both metal oxides and polymers. 
to a near earth orbital environment. The mechanism The substrate shape, ion specie, ion energy and ion 
appears to be oxidation by the energetic incidence of beam current density utilized can be varied. No substan- 
atomic oxygen 'atoms associated with high relative ve- 30 tial change in the polymer or materials characteristics is 
locity of near earth spacecraft and the high abundance hvolved. BY Providing the Polymer with a lightweight 
of atomic oxygen in low earth orbit. It has been demon- thin flexible film, all of the demonstrated advantages Of 
strated that organic polymers, such as polyimides, have the substrate material can be utilized with the added 
high rates of weight loss in this environment. oxidation protection of the oxide polymer coating. 
BRIEF DESCRIPTION OF THE DRAWINGS 
tural or thermal blankets, a problem develops because 
This application is a division of application Ser. No. 
761,235 filed July 31, 1985 and now U.S. Pat. No. 15 apparatus. 
4,604,181 which is a division of application Ser. No. 
649,330 filed SePt. 14, 1984 and now US. Pat. No. 
4,560,577. 
20 
DESCRIPTION 
Because many of these polymers are used as struc- 35 
these materials become so thin through oxidation that 
they lose their structural or thermal integrity. In partic- 
The advantages and features Of the invention 
be more apparent from the 
description when read in connection with the accompa- 
40 nying drawings wherein like numerals are used 
throughout to identify like parts. 
FIG. is a schematic view showing a polymer sheet 
being ion beam cleaned in accordance with the present 
invention; 
FIG. is a schematic viaw showing the ion cleaned 
polymer surface of FIG. being immediately ion beam 
sputter-coated with a protective thin film; 
is a schematic view showing a single ion 
is a schematic view showing an alternate em- 
ular, a polyimide is typically used as a solar array blan- 
ket material. If this material is exposed long enough, 
mechanical and electrical failures are encountered in 
the spacecraft power system. 
Alternatives to polymers which oxidize have been 
considered by filling these materials with additives that 45 
reduce their oxidation rates. Other solutions have been 
proposed, such as using alternate materials, including 
silicon rubber and polytetrafluoroethylene, which ex- 
hibit lower oxidation rates. All of these solutions to the 
orbital oxidation problem represent major changes in 5o 
design. These solutions also sacrifice other important bodiment of the invention utilizing multiple ion 
polymer characteristics, such as strength, weight, opti- for ion cleaning and codeposition. 
cal absorptance, emittance, tearing, creep, and adhesion 
properties. BEST MODE FOR CARRYING OUT THE 
INVENTION 
provide oxidation protection for POlYXtIeriC materials, Referring now to the drawings there is shown in 
such as polyimides, in a low earth orbital environment. FIG. 1 a film or sheet 10 ofa  polymeric material such as 
2. Prior Art a polyimide known commercially as Kapton having a 
Mirtich and Sovey U.S. Pat. No. 4,199,650 discloses surface 12 that is to be covered with an oxidation barrier 
the treating of polyimide and fluorinated ethylene prop- 60 for exposure to a low earth orbital environment. The 
ylene polymers using an electron bombardment argon surface 12 of the sheet 10 is exposed to a beam 14 of 500 
source. This treatment modifies the electrical and opti- eV to 2 0 0  eV argon ions at current densities of 0.1 
cal properties of the polymers. mA/cm2 to 10 mA/cm2. 
Dobler et a1 U.S. Pat. No. 3,984,581 discloses a The argon ion beam 14 is furnished by an electron 
method wherein multilayer coatings of silicon oxide and 65 bombardment ion source 16 of the type developed for 
another metal oxide are provided on the surface of an electric propulsion technology. Argon gas from a suit- 
organic polymeric plastic material for antireflective able source, not shown, is fed through a line 18 to a 
purposes. The oxides are vaporized by an electron cathode in a chamber within the source 16 where the 
FIG. 
FIG. 
for both ion cleaning and codepos~t~on; and 
It is, therefore, an object of the present invention to 55 
4,664,9 80 
3 
gas is ionized. The argon ions are retained within this 
chamber which also contains an anode about its outer 
periphery. Such an ion source is described in “Ad- 
vances in Electronic and Electron Physics” by H. R. 
Kaufman, vol. 36, pages 265-373 (1974). It will be ap- 
preciated that other gases, in addition to argon can be 
used to form the bombarding ions in the beam 114. For 
example, xenon and hydrogen may be used, and even 
hydrocarbons may be provided in the ion source 16. 
Extraction of the beam 14 is accomplished by a two 
grid ion optic system 20. Such a system is described in 
AIAA Paper No. 76-1017 entitled “A 30 cm Diameter 
Argon Ion Source”. Such a double grid system includes 
both the screen grid and accelerator grid. The screen 
grid serves to contain the discharge plasma while form- 
ing the necessary ion optics to prevent direct impinge- 
ment of the accelerated ions into the accelerator grid. 
Ions in the near vicinity of the screen grid have a high 
probability of being accelerated through the openings in 
the screen and the accelerator grids because of the high 
electric fields present at the grids. 
Neutralization of the ions is achieved by the interjec- 
tion of electrons into the beam 14. A suitable neutralizer 
in the form of a downstream cathode provides these 
electrons. 
The electron bombardment ion source 16 is located in 
the vacuum facility which is sufficiently large to pre- 
vent back sputtered facility materials from contaminat- 
ing the process. The operating pressure within the vac- 
uum facility during sputtering is about 1 X 1 0 - 4  torr or 
lower. 
Immediately after cleaning the polymer sheet 10 is 
mounted in the vacuum chamber in the position shown 
in FIG. 2. The ion cleaned surface 12 is then ion sputter 
coated with a protective thin film 22 having a thickness 
between about 50 angstroms and about 800 angstroms. 
This is accomplished by mounting a sputter target 24 in 
the ion beam 14. 
The sputter target 24 is composed of two tvDes of 
5 
10 
15 
20 
25 
30 
35 
materials. A metaloxide, such ai Si02 or A1203,’forms 40 
a larger portion 26. A flexible polymer with a low oxi- 
dation rate, such as polytetrafluoroethylene or silicone 
rubber, forms a small portion 28. 
These target material portions 26 and 28 may be ei- 
ther spatially separated or overlapping. The purpose of 45 
the metal oxide-materials is to piovide an aiready oxi- 
dized surface on the polymer to be protected. A protec- 
tive coating 22 consisting essentially of 100% metal 
oxide may not have suitable flexibility to retain good 
integrity without cracking or spalling on substrates 10 
that are expected to be bent over a small radii of curva- 
ture. Thus, the purpose of the polymer portion 28 of the 
sputter target 24 is to provide a small amount, i.e. less 
than about 20 volume percent, of molecularly mixed 
polymer content to the protecting film 22 to give it 
additional flexible properties. 
The area of the polymer target portion 28 is typically 
much smaller than the metal oxide target portion 26 
because only a small amount of the polymer produces a 
large gain in film flexibility. Also, it is desirable to have 
the oxidation protection dominated by the metal oxide 
of the larger portion 26. 
Alternate Embodiments of the Invention 
Referring now to FIGS. 3 and 4, there is shown reel 
to reel production of a coated polymer material in 
coiled form. In the embodiment of FIG. 3 the same ion 
beam is used for both sputter cleaning and film deposi- 
50 
55 
60 
65 
4 
tion in the manner shown in FIGS. 1 and 2. In the em- 
bodiment of FIG. 4 separate ion beams are used for 
cleaning and film deposition. 
Referring now to FIG. 3 a coil of polymer material 30 
to be coated passes from a payout reel 32 over a roller 
34 to a takeup reel 36. The roller 34 is located in the ion 
beam 14. A target of the type shown in FIG. 2 is like- 
wise mounted in the ion beam 14. 
As the polymer material 30 moves from the payout 
reel 32 to the roller 34, a surface portion 38 is ion beam 
cleaned in the manner described above in connection 
with FIG. 1. After the ion beam cleaned surface portion 
passes over the roller 34, a predetermined surface por- 
tion 40 is coated in a manner described above in connec- 
tion with the embodiment shown in FIG. 2. 
In the embodiment of FIG. 4 a coil of polymer mate- 
rial 42 to be coated is fed from a payout reel 44 to a 
takeup reel 46 in a manner similar to that described 
above in connection with the embodiment shown in 
FIG. 3. A beam 48 of argon ions from a source 50 cleans 
a surface portion 52 of the polymer material 42 in the 
manner described above in connection with the embodi- 
ment of FIG. 1. 
A pair of ion sources 54 and 56 provide ion beams 58 
and 60, respectively, to bombard a target 62 in the man- 
ner discussed above in connection with FIG. 2. The 
target 62 is similar to the target 24 in that it includes a 
metal portion 64 and a polymer portion 66. A surface 
portion 68 of the polymer material 42 is coated in the 
manner described above in connection with FIG. 2 as 
the material moves between the reel 44 and the reel 46. 
In all the aforementioned embodiments the deposited 
films are typically 50 angstroms-800 angstroms thick. 
This thickness provides desirable flexibility and surface 
protection. 
By way of example, a polymer material was covered 
with a coating comprising 96 volume percent of Si02 
and 4 volume percent polytetrafluoroethylene in accor- 
dance with the present invention. This coating reduced 
oxidation rates of the polyimide material by a factor of 
at least five hundred in shuttle orbiter tests. 
While several embodiments of the invention have 
been described it will be appreciated that various modi- 
fications can be made without departing from the spirit 
of the invention or the scope of the subjoined claims. 
For example, the metal oxide portions 26 and 64 of the 
targets 24 and 62 may be any oxide whose mechanical, 
optical, electrical and adhesion properties are desirable. 
Conductive metal oxides, such as indium and/or tin 
oxide, may be used to provide a conductive as well as an 
oxidation protecting surface. It is further contemplated 
that the metal oxide and/or polymer sputter deposited 
coating 22 may be a mixture of one or more oxides 
and/or polymers. 
In certain applications the sputter cleaning and metal 
oxide deposition could be accomplished by W F  sputter 
cleaning and W F  sputter deposition. Also, B.C. sputter 
deposition or electron beam evaporation may be used 
instead ~f the ion beam cleaning and ion beam deposi- 
tion of metal oxides. For some polymers, thermal evap- 
oration might be used instead of the ion beam sputter- 
ing. Such a thermal evaporation step could be used with 
polytetrafluoroethylene, for example. 
The arrangement of the ion sources as described in 
FIGS. 1 through 4 and the sputter targets may be spa- 
tially varied. Also, the ratio of polymer to metal oxides 
can be varied. This ratio may be varied from 100% 
metal oxide to 100% polymer. 
4,664,980 
5 6 
We claim: 
1. A coated material comprising 
a substrate of a polyimide material, and 
a metal oxide coating on said substrate forming an 
oxidation barrier, said coating containing less than 
about 20 volume percent of a molecularly mixed 
flexible polymer to provide additional flexibility. 
2. A coated material as claimed in claim 1 wherein the 
metal oxide coating contains a flexible polymer having 
a low oxidation rate. 
3. A coated material as claimed in claim 2 wherein 
said coating contains about 96 volume percent metal 
oxide and about 4 volume percent flexible polymer. 
coating is an oxide of a metal selected from the group 
consisting essentially of silicon, aluminum, indium, and 
tin. 
5. A coated material as claimed in claim 4 wherein the 
coating is a metal 
ing essentially of Si02 and A1203. 
6. A coated material as claimed in claim 2 wherein the 
coating contains a flexible polymer selected from the 
and silicone rubber. 
7. A coated material as claimed in claim 6 wherein the 
coating contains about four volume percent of the flexi- 
ble polymer. 
metal oxide coating has a thickness between about 50 
angstroms and about 800 angstroms. 
9. A coated material as claimed in claim 1 wherein the 
metal oxide coating contains a small amount of several 
molecularly mixed flexible polymers. 
lo. A coated 
a substrate Of a polymeric 
a flexible coating on said substrate for forming an 
oxidation barrier, said flexible coating containing 
about 96 volume percent of a metal oxide selected 
from the group consisting essentially of Si02 and 
and about 4 volume percent of a flexible 
polymer selected from the group consisting essen- 
tially of polytetrafluoroethylene and silicone rub- 
ber molecularly mixed with said metal oxide. 
11. A coated material as claimed in claim 10 wherein 
4. A coated material as claimed in claim 2 wherein the 15 the flexible coating comprises about 96 volume percent 
Si02 and about 4 volume percent polytetrafluoroethyl- 
ene thereby reducing the oxidation rates of the poly- 
meric material by a factor of at least five hundred in 
12. A coated material as claimed in claim 10 wherein 
the flexible coating comprises an oxide of a conductive 
metal containing a small amount of a molecularly mixed 
flexible polymer. 
13. A coated material as claimed in claim 12 wherein 
metal selected from the group consisting essentially of 
indium and tin containing a small of a molecu- 
larly mixed flexible polymer. 
14. A coated material as claimed in claim 10 wherein 
8. A coated material as claimed in claim 1 wherein the 30 the flexible coating has a thickness between about 50 
comprising 
and 
Orbiter tests. 
selected from the group consist- 20 
group Of polytetrafluoroethylene 25 the flexible coating comprises an oxide of a conductive 
angstroms and about 800 angstroms. * * * * *  
35 
40 
45 
50 
55 
60 
65 


Oxidation protection coatings for polymers

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