A method is disclosed for improving surface texture for adhesive bonding, metal bonding, substrate plating, decal substrate preparation, and biomedical implant applications. The surface to be bonded is dusted in a controlled fashion to produce a disbursed layer of fine mesh particles which serve as masks. The surface texture is produced by impinging gas ions on the masked surface. The textured surface takes the form of pillars or cones. The bonding material, such as a liquid epoxy, flows between the pillars which results in a bond having increased strength. For bonding metals a thin film of metal is vapor or sputter deposited onto the textured surface. Electroplating or electroless plating is then used to increase the metal thickness in the desired amount

Banks, B. A.

Mirtich, M. J.

Sovey, J. S.

English

NASA Technical Reports Server

Banks et al. 
[I11 4,344,996 
[45] Aug. 17, 1982 
[54] SURFACE TEXTURING OF 
FLUOROPOLYMERS 
[75] Inventors: Bruce A. Banks, Olmsted Township, 
Lorain County; Michael J. Mirtich, 
N. Olmsted; James S. Sovey, 
Strongsville, all of Ohio 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
[73] Assignee: The United States of America as 
[21] Appl. NO.: 218,588 
[22] Filed: Dec. 19, 1980 
[51] Int. ( 3 . 3  ...................... B32B 27/16; C23C 15/00; 
C23F 1/00 
[52] U.S. Cl. .................................. 428/141; 204/38 B; 
204/192 E; 204/192 EC 
[58] Field of Search .......... 204/192 E, 192 EC, 38 B; 
156/643; 428/ 14 1 
[561 References Cited 
U.S. PATENT DOCUMENTS 
4,056,395 11/1977 Sat0 et al. ............................... 96/36 
4,064,030 12/1977 Nakai et al. ..................... 204/192 E 
4,073,669 2/1978 Heinecke et al. ................... 156/643 
4,092,210 5/1978 Hoeptner ............................ 156/643 . 
4,160,045 7/1979 Longshore ............................ 427/38 
4,199,650 4/1980 Mirtich et al. ...................... 428/421 
FOREIGN PATENT DOCUMENTS 
2036627A 7/1980 United Kingdom ......... 204/192 EC 
Primary Examiner-Aaron Weisstuch 
Attorney, Agent, or Firm-Norman T. Musial; John R. 
Manning; Gene E. Shook 
1571 ABSTRACT 
This invention is concerned with providing improved 
surface texturing for adhesive bonding, metal bonding, 
substrate plating, decal substrate preparation, and bio- 
medical implant applications. The invention is particu- 
larly concerned with epoxy bonding to polymers that 
typically exhibit low adhesion and bonding metals to a 
desired thickness to a polymer substrate. 
The surface 12 to be bonded is first dusted in a con- 
trolled fashion to produce a disbursed layer of fine mesh 
particles 14 which serve as masks. The surface texture is 
produced by impinging gas ions on the masked surface. 
The textured surface takes the form of pillars or cones. 
The bonding material, such as a liquid epoxy, flows 
between the pillars which results in a bond having in- 
creased strength. For bonding metals a thin film of 
metal is vapor or sputter deposited onto the textured 
surface. Electroplating or electroless plating is then 
used to increase the metal thickness to the desired 
amount. 
14 Claims, 3 Drawing Figures 
https://ntrs.nasa.gov/search.jsp?R=19820025645 2020-03-21T17:25:15+00:00Z
. PateIIt Aug. 17, 1982 Sheet 1 of 2 4,344,996 
FIG. I 
FIG. 2 
U.S. Ih”aknt Au’g. 17, 1982 Sheet 2 of 2 4,344,996 
FIG. 3 
4,344,996 
2 
BRIEF DESCRIPTION OF THE DRAWING 
Details of the invention will be described in connec- 
tion with the accompanying drawings wherein; 
FIG. 1 is a perspective view of a surface of a polymer 
dusted in accordance with the invention prior to ion 
beam texturing; 
FIG. 2 is a schematic view of the ion beam texturiiig 
apparatus used to texture the surfaces of the polymer, 
and 
FIG. 3 is a photomicrograph of a fluoropolymer 
surface that has been ion beam textured using fine mesh 
copper particles as masks. 
BEST MODE FOR CARRYING OUT THE 
INVENTION 
Referring to the drawing, there is shown in FIG. 1 a 
substrate 10 of a polymeric material, such as a fluoro- 
polymer, having a surface 12 which is to be prepared 
for epoxy bonding. The substrate 10 may be any of a 
number of polymeric materials which may exhibit low 
adhesion characteristics. 
According to the present invention the surface 12 is 
covered with a disbursed layer of fine mesh particles 14. 
The preferred particles 14 are of a sputter-resistant 
material, such as tungsten, molybdenum, carbon, or 
tantalum. Almost any metal particle can be used as a 
mask for polymers inasmuch as the metal sputter yield is 
usually a few orders of magnitude lower than that of the 
polymer. Fine ground NaCl and Si02 also have been 
used as masks. 
The particles 14 are randomly disbursed over the 
surface 12 in a controlled fashion to form masks. In 
order to provide for the development of a satisfactory 
surface microstructure, the particles 14 have diameters 
in the range between 0.1 pm and 10 pm. 
The particles 14 can be applied to the surface 12 by 
dusting. These particles have also been sprayed onto the 
1 
SURFACE TEXTURING OF F%UOROPOLYMERS 
ORIGIN OF THE 1NVENTION 
The invention described herein was made by employ- 
ees of the U.S. Governmcnt and may be manufactured 
and used by or for the Government for governmental 
purposes without the payment of any royalties thereon 
or therefor. 
TECHNICAL FIELD 
This invention is concerned with preparing the sur- 
face of a low adhesion substrate, such as a fluoropoly- 
mer, for either adhesion bonding or metallizing. One 
such polymeric material is polytetrafluoroethylene, 
known commercially as Teflon. This fluoropolymer is 
presently used in both ground and space applications. 
Many polymers exhibit low adhesion characteristics. By 
way of example, untreated Teflon exhibits an epoxy 
bond tensile strength of less than 180 psi. 
Chemical etching of fluorocarbon polymers signifi- 
cantly increases the bond strength. However, chemical 
etchant shelf life is relatively short, and the bond must 
be made immediately after the application of the chemi- 
cal treatment to obtain maximum bond strength. Also 
chemical etching of polymers may not be acceptable for 
certain applications, such as biomedical implants, be- 
cause of potential surface contamination. 
When polymeric materials are to be used in solar 
absorbers for heating and cooling applications, various 
methods have been proposed for the surface prepara- 
tion. Among these procedures are painting, electro- 
chemical plating, evaporated or sputtered coating, and 
etching surface micropores or grooves. In fusion bond- 
ing of a polymer to a metal, the polymer is heated, and 
the polymer can change its basic physical and optical 
properties. 
BACKGROUNDART 
U.S. Pat. No. 4,064,030 to Nakai describes a process 
which employs R F  sputtering of polymers without 
masking. The surface texture, resulting from the sput- 
tering, is controlled only by the chemical nature of the 
substrate, RF forward power density, and etch time. 
This process is referred to as natural texturing. 
Hoepfner U.S. Pat. No. 4,092,210 described the pho- 
tolithographic process which utilizes layers or lami- 
nates for masking purposes. The masked material is 
removed by ion bombardment. 
DISCLOSURE OF INVENTION 
According to the method of the present invention, a 
disbursed layer of fine mesh particles is applied to the 
surface of a polymer in a controlled fashion to produce 
masks. The particles are applied by dusting, brushing, 
or more sophisticated techniques, such as those used for 
microvoid latex coatings. The masked surface is then 
treated by impinging gas ions on the surface. The resul- 
tant textured surface takes the form of pillars whose 
5 
10 
15 
20 
25 
30 
35 
4o surface 14 using a water and particle slurry. The spray 
is in the form of a fine mist, and as the water evaporates 
the particles 14 have a tendency to stick to the surface 
12. The particles 14 a!so have adhered to the substrate 
10 by pressing them onto the surfaacz 12 by ioliing or 
After the surface 12 of the substrate 10 has been cov- 
ered by the random particles 14 the surface is exposed 
to a vertical beam 16 of ions in a manner described in 
U.S. Pat. No. 4,199,650. This beam 16 is preferably from 
50 an electron bombardment ion source 18 of the type 
developed from electric propulsion technology. Such 
an ion source is described in “Advances in Electronics 
and Electron Physics” by H. R. Kaufman, vol. 36, pages 
365-373. Beam extraction is accomplished by a dished, 
55 two-grid ion optics system 20. Such a system is de- 
scribed in AIAA Paper No. 76-1017 entitled “A 30 cm 
Diameter Argon Ion Source”. Neutralization of the ion 
beam 16 can be achieved by secondary electrons re- 
leased by ion bombardment of the vacuum facility walls 
The electron bombardment ion source 18 is located in 
the vacuum facility (not shown) which is sufficiently 
large to minimize back sputtered facility material from 
45 direct pressure. 
60 or by use of a neutralizer. 
vertical dimensions may range from tens to hundreds of ‘contaminating the substrate 10. The vacuum facility is 
microns, depending on the selection of the beam en- 65 maintained at a pressure of about 4x 10-5 torr during 
ergy, ion current density, and etch time. After ion beam the operation of the ion source 18. 
processing the masked particles are removed by wash- The substrate 10 is positioned normal to the ion beam 
ing or dissolving. 16 at a location of about 20 centimeters from the ion 
3 
4,344,996 
source 18. The masked surface 12 is totally within the 
ion beam 16. 
The current density at the surface 12 is between about 
0.1 mA/cm2 and 1.0 mA/cm2 depending upon the ther- 
mal integrity of the polymers and the duration of expo- 
sure. The vertical beam 16 is uniform over the surface 
12 of the substrate 10 and has an energy in the 200 eV to 
2000 eV range. The etch time may range from seconds 
to hours, depending on the surface roughening desired. 
The resultant surface roughening or texturing of the 
surface 12 takes the form of pillars whose cross-section 
is similar to the dimensions of the masking particles 14 
as shown in FIG. 3. The vertical dimensions of these 
pillars may range from tenths to hundreds of microns, 
depending on the selection of beam energy, ion current 
density, etch time, and polymeric materials. 
After ion beam processing, the substrate 10 is re- 
moved from the vacuum facilities. The particles 14 are 
then removed by washing or being dissolved. The tex- 
tured polymer surface has superior characteristics for 
certain application such as writing or printing, decal 
applications, and bonding using adhesive tapes. The 
tape is applied to the textured polymer surface or the 
adhesive of the polymer tape is attached by ion beam 
texturing of the tape. 
Polymers textured in accordance with the invention 
may be used for biomedical applications, such as soft 
tissue implants. Biocompatible, water soluble masking 
particles such as certain soluble salts are preferably used 
during the texturing process for these biomedical appli- 
cations. 
A fluorocarbon polymer, known commercially as 
Teflon, was ion beam textured in accordance with the 
invention. The material was bonded using an epoxy 
bonding material in the form of a two part fluid that ws 
not viscous. The bonded joints had tensile yield 
strengths in excess of 2,000 psi. Also, ion beam textured 
surfaces produced stronger bond joints than those pro- 
duced by chemical etch processes. 
The process is superior to naturally ion etched poly- 
mers inasmuch as the vacuum processing times are re- 
duced. Referring to FIG. 3, the fluoropolymer features 
produced by natural texturing are only about one tenth 
the height of the pillars. This process is capable of pro- 
dilcing textured surfaces on polymers which do not 
yield significant structure upon ion etching. Moreover, 
thermal control of the polymer environment is easily 
obtained with the ion beam system. 
A metal may be bonded to the surface 12 to a desired 
thickness by first depositing a thin film of the metal 
4 
1. A method of treating the surface of a fluoropoly- 
mer for improved bonding without altering the chemis- 
try of the same, comprising the steps of 
applying a layer of randomly disbursed fine mesh 
particles of a sputter-resistant material having di- 
ameters in the range between about 0.1 pm and 10 
pm to said surface thereby masking the same, 
placing said fluoropolymer in a vacuum environment 
of about 4X 10-5 torr, 
exposing said masked surface to a beam of ions hav- 
ing an ion beam current density between 0.1 
mA/cm2 and 1.0 mA/cm2 to texture the same, 
moving said fluoropolymer from said vacuum envi- 
ronment to ambient pressure, and 
removing said masking particles from said textured 
surface. 
2. A method of treating the surface of a fluoropoly- 
mer as claimed in claim 1 wherein said masking particles 
are made of a material selected from the group consist- 
3. A method of treating the surface of a fluoropoly- 
mer as claimed in claim 2 wherein the fluoropolymer is 
pol ytetrafluoroethylene. 
4. A method of treating the surface of a fluoropoly- 
25 mer as claimed in claim 1 wherein said masking particles 
are applied to said surface of said fluoropolymer by 
dusting. 
5. A method of treating the surface of a fluoropoly- 
mer as claimed in claim 1 wherein said masking particles 
30 are applied to said surface of said fluoropolymer by 
spraying. 
6. A method of treating the surface of a fluoropoly- 
mer as claimed in claim 1 wherein said masking particles 
are applied to said surface of said fluoropolymer by 
7. A method of treating the surface of a fluoropoly- 
mer for biomedical applications as claimed in claim 1 
wherein said masking particles are biocompatible solu- 
ble salts. 
8. A method of treating the surface of a fluoropoly- 
mer as claimed in claim 1 wherein said masking particles 
are removed from said textured surface by washing the 
same. 
9. A method of treating the surface of a fluoropoly- 
45 mer as claimed in claim 1 wherein the masking particles 
are dissolved to remove them from said textured sur- 
face. 
10. A method of treating the surface of a fluoropoly- 
mer as claimed in claim 1 including the step of 
depositing a thin film of metal onto said textured 
surface subsequent to removing said masking parti- 
5 
10 
15 
20 ing of tungsten, molybdenum, carbon and tantalum. 
35 direct pressure. 
40 
50 
either by sputtering -or evaporation techniques. This 
film has a thickness of about lo00 A. 
This process bonds the metal to the etched surface of 
the polymer without using an adhesive. The metal 55 deposited to a thickness of about loo0 A. 
thickness is then increased by electroplating. This in- 
crease in thickness may be a few mils or greater. It is 
contemplated this metallization may be done using any 
metal that can be deposited by sputtering or vaporde- 
position and then electro- or electroless plated. 
While a preferred embodiment of the invention has 
been described, it is contemplated that various modifi- 
cations may be made without departing from the spirit 
of the invention or the scope of the subjoined claims. 
cles therefrom. 
11. A method of treating the surface of a fluoropoly- 
mer as claimed in claim 10 wherein the metal film is 
12. A method of treating the surface of a fluoropoly- 
mer as claimed in claim 11 wherein said metal film is 
deposited by sputtering. 
13. A method of treating the surface of a fluoropoly- 
60 mer as claimed in claim 12 wherein the thickness of the 
metal film is increased by electroplating additional 
metal. 
14. A fluoropolymer treated according to the process 
of claim 1. 
* I t * * *  We claim: 65 


Surface texturing of fluoropolymers

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