Plastic surfaces can be improved physically and optically by treating them with a plasma of boron trifluoride. The trifluoride can be the sole reactant or be part of a mixture also containing an organic monomeric substance such as perfluorobutene-2 or an organosilane. The boron trifluoride-containing coating can also serve as an intermediate coating between the plastic surface and a plasma deposited organic polymer

Kubacki, R. M.

English

NASA Technical Reports Server

350-169 SR 
5623178 XR 4 9091 9 166 
United States Patent [191 
Kubacki 
[54] BORON TRIFLUORIDE COATINGS FOR 
THERMOPLASTIC MATERIALS AND 
METHOI) OF APPLYING SAME IN GLOW 
DISCHARGE 
[75] Inventor: Ronald Michael Kubacki, Rancho La 
[73] Assignee: The United States of America as 
Costa, Calif., by Alan M. Lovelace 
represented by the Administra tor of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
[21] Appl. No.: 807,762 
[22] Filed: Jun. 17, 1977 
[51] 
[52] 
Int. c1.2 ............................................... B05D 3/06 
U.S. c1. .................................... 428/411; 350/165; 
350/175 NG; 427/40; 427/41; 427/164; 
428/412; 428/422; 428/447; 428/515; 428/523; 
428/538 
[58] Field of Search ....................... 427/38, 39, 40, 41, 
427/163, 164; 428/538,422,447,412,411; 
350/164, 165, 175 NG 
11 11 4,091,166 
[45] May 23, 1978 
1561 References Cited 
U.S. PATENT DOCUMENTS 
3,811,753 SA974 Onoki et al. .................. 350/175 NG 
3,847,652 11/1974 Fletcher et al. ....................... 427/41 
4,049,861 9/1977 N o d  .................................. 428/447 
Primary Examiner-John H. Newsome 
Attorney, Agent, or Firm-Armand McMillan; John R. 
Manning; Darrell G. Brekke 
1571 ABsTRAm 
Plastic surfaces can be improved physically and opti- 
cally by treating them with a plasma of boron trifluo- 
ride. The trifluoride can be the sole reactant or be part 
of a mixture also containing an organic monomeric 
substance such as perfluorobutene-2 or an organosilane. 
The boron trifluoride-containing coating can also serve 
as an intermediate coating between the plastic1 surface 
and a plasma deposited organic polymer. 
11 claims, No Drawings 
. . . . .  -. c _ _  - 
https://ntrs.nasa.gov/search.jsp?R=19780023290 2020-03-20T13:26:06+00:00Z
4,09 1,166 
1 2 
conditions, using electron bombardment to vaporize a 
BORON TRIFLUORIDE COATINGS FOR material which is glass in the Addis process and silicon 
THERMOPLASTIC MATERIALS AND METHOD oxide in the Dobler process. The use of elevated tem- 
OF APPLYING SAME IN GLOW DISCHARGE peratures is avoided. 
An object of the present invention is to provide a new 
type of inorganic coating for optical or other thermo- ORIGIN OF THE INVENTION 
The invention described herein was made in the per- plastic substrates. Another object is to provide an inter- 
formance of work under a NASA contract and is sub- mediate coating which will enhance the adherence of 
ject to the provisions of Section 305 of the National certain organic polymeric materials to said substrates. A 
Aeronautics and Space Act of 1958, Public Law 85-568 10 further object is to provide a material which can be 
(72 Stat. 435; 42 U.S.C. 2457). plasma coated simultaneously with suitable organic 
monomeric substances to improve the properties of the 
resulting Dolvmeric coatinn. 
5 
PRIOR ART 
1. . - 
SUMMARY O F  THE INVENTION Synthetic plastic optical components are generally made from organic resins such as acrylics, polystyrenes, 15 
polycarbonates and the like. Although they possess It has now been discovered that these and other ob- 
several advantages over the more traditional glass and jects which will become apparent as the process of the 
crystalline materials in terms of weight, resistance to invention is described, can be accomplished by subject- 
thermal shock and mechanical stresses, cost, etc., they ing a plastic substrate to a boron trifluoride low temper- 
are particularly vulnerable to abrasion, scratching and 20 ature plasma. The process may be used to form a single 
environmental conditions. This vulnerability often re- inorganic coating of the material on the plastic surface 
sults in impairment, if not complete destruction of their or to form a coating which combines the boron trifluo- 
optical capabilities. ride with an organic polymeric coating substance. Al- 
Numerous attempts have been made to correct these ternately, the coating obtained by exposure to a boron 
defects. These attempts have often consisted in applying 25 trifluoride plasma may serve as an intermediate binding 
some scratch resistant layer of material on the compo- layer between the plastic and an outer organic poly- 
nents by conventional methods which have included meric coating. 
DETAILED DESCRIPTION 
dip coating, electronic beam coating, ultraviolet poly- 
merization and varnishing of the components' surface 
with a solution of the coating material followed by 30 The coating processes that constitute the present 
evaporation of the solvent. While some progress has invention may be carried out in any of the plasma reac- 
been accomplished in these manners, the compositions tors described in U.S. Pat. No. 3,847,652. The configu- 
and processes employed have tended to create addi- ration actually employed for the preparations disclosed 
tional problems with respect to cost, uniformity, adhe- in the present specification involved an internal elec- 
sion, orientation and directionality requirements be- 35 trode parallel plate arrangement deposition system, 
tween the substrate and the coating composition. To with the deposition taking place within the plasma be- 
illustrate the shortcomings of the methods of the art, tween the electrodes. The reactor, 25.4 cm in diameter 
one can consider the dip coating process which consists and 30.5 cm long, was connected to a liquid nitrogen 
in immersing a substrate into a coating liquid, removing trap in train with a vacuum pump. Except as shall be 
it from the liquid and drying it. One problem with this 40 otherwise noted, the reactor and its accessory equip- 
process is that the thickness of the resulting film is virtu- ment were set up and operated substantially in the man- 
ally beyond control. Furthermore, not only do films so ner described in U.S. Pat. No. 3,847,652. 
prepared not show any durability at thicknesses under The plastic material to be coated, e.g., polished cast 
about 1 micron, but also they are generally too thick sheet stock of a bisphenol A-phosgene polycarbonate 
and not sufficiently uniform for use as optical coatings 45 resin, can be cleaned before coating, although this was 
on a substrate having the complex geometry of a lens. found not to be necessary in the case of boron trifluo- 
Thick coatings (> 2 microns) in fact never exhibit both ride coating due to the high adhesion of that substance 
abrasion resistance and anti-reflective properties over to the plastic substrate. In any event, the cleaning, when 
the entire range of the visible spectrum (- 4OOO to 7000 done, generally consisted in (1) dipping the plastic 
A). 50 pieces in Freon solvent T-WD 602, a water dispersion 
Recent developments in the art of coating plastic of trichlorotrifluoroethane having an initial boiling 
substrates have involved the utilization of plasma or point of 47" C at 760 mm; (2) rinsing them in a second 
glow discharge polymerization of various organic mon- solvent, e.g., trichlorotrifluoroethane; and (3) degreas- 
omers which include organo-silanes and perfluorobu- ing them in vapors of the latter liquid. Other established 
tene-2. These processes have yielded thin uniform opti- 55 techniques such as pretreatment of the plastic surfaces 
cally clear coatings which may possess, depending on with water, ammonia, oxygen and the like can also be 
the monomer selected and the conditions employed, advantageously employed to enhance the properties of 
various desirable properties such as abrasion resistance some of the fdms that can be produced by the process of 
and antireflectivity. the invention. 
The coating process is initiated by positioning the 
thermoplastic elements to achieve increased scratch or plastic substrate near the center of the reactor in an 
abrasion resistance. Thus, Cormia (U.S. Pat. No. aluminum frame supported by Teflon legs. The reactor 
3,458,342), Onoki (US. Pat. No. 3,811,753) and Chang is evacuated to a background pressure 0.67 N/m2 of 
et al. (US. Pat. No. 3,991,234) all disclose applying a mercury and the coating agent allowed to flow in at a 
vitreous coating on plastic lenses by simple evaporation, 65 suitable rate and pressure. Radio frequency power, e.g., 
preferably in a vacuum. Dobler (U.S. Pat. No. at 13.56 MHn is then applied either continuously or, if 
3,984,581) and Addis (U.S. Pat. No. 3,953,652), on the desired, in a pulsed mode, for example in an on-off cycle 
other hand, suggest coating a plastic lens under vacuum of 1.5 millisecond. Although a large number of power 
Thin inorganic coatings have also been applied to 60 
3 
4,091,166 
settings and pressure combinations can be employed to 
achieve some coating of BF3 on plastic substrates, pre- 
ferred pressures and power settings range between 
about 9.3 to 20 N/m2 and 30 to 75 W, respectively. 
The boron trifluoride coating obtained in this manner 
can serve as the sole protection of the plastic surface or, 
alternately, it may serve as a base upon which organic 
polymeric coatings are deposited to augment the pro- 
tection afforded to the plastic surface and to increase 
the adhesion of said organic polymeric coatings to the 
plastic surface. These organic coatings may be applied 
in any conventional manner but plasma deposition is 
preferred for the obtention of thin transparent uniform 
films of controlled thickness. Among the materials that 
can be used to overcoat the boron trifluoride film are: 
perfluorobutene-2; organosilanes such as vinyltrichlo- 
rosilane, tetraethoxysilane, vinyltriethoxysilane, hexa- 
methyldisilazane, tetramethylsilane, vinyldimethyle- 
thoxysilane, vinyltrimethyoxysilane, tetravinylsilane, 
vinyltriacetoxysilane, and methyltrimethoxysilane; 
ethylene-nitrogen gas mixtures, and the like. These 
materials may be employed singly or in any combina- 
tion desired. 
A further alternative to employment of the boron 
trifluoride coating as an intermediate film between the 
plastic surface and the outer organic polymeric coating, 
is to combine the boron trifluoride with the organic 
monomer gas and carry out the deposition of a film with 
that mixture. 
Finally, any coating thus obtained can be further 
treated in a plasma of inorganic gas or vapors, including 
nitrogen, oxygen, ammonia and the like, to convert as 
much of the coating substance as possible to oxides, 
nitrides and other appropriate resistant linkages. 
Examples will now be provided to illustrate specific 
non-limiting embodiments of the processes just de- 
scribed. 
EXAMPLE 1 
A piece of optically clear polymethylmethacrylate 
was placed in a boron trifluoride plasma in an apparatus 
of the type already described. The pressure of boron 
trifluoride, the lone reactant, was set at 9.3 N/m2 and 
the power, at 50 W. Under these conditions, a clear film 
was deposited onto the substrate at a rate in the order of 
about 0.25 to 0.50 Angstrom per second. The film, even 
at thicknesses as small as 600 A for example, exhibited a 
strong blue color, indicating an index of refraction 
smaller than that of the polymethylmethacrylate (1.492 
N,) with good uniformity. Adhesion of the film to the 
substrate was excellent as determined by tape pull test in 
accordance with MIL-SPEC C675A. The film however 
lacked durability in that on wiping with lens cleaning 
tissue, severe scratching and smearing occurred. This 
latter shortcoming as well as the low deposition rate 
achieved can be improved by varying the pressure and 
the power employed. The film obtained is advanta- 
geously used as an intermediate layer to increase the 
adherence of polymerized organic films such as poly- 
perfluorobutene-2 to the plastic surface. 
EXAMPLE 2 
In this preparation, boron trifluoride was mixed with 
nitrogen gas in a ratio of 2 to 1. The total pressure was 
about 20 N/m2and the power at 35-75 W. A blue film 
was obtained and, again, at a very low deposition rate, 
Infrared spectrum data showed absorption at the B-N 
bond wavelength. Adhesion of the film to the substrate 
4 
was very good while durability was poor. The thickness 
of the film was measured by interferometry. It was thus 
determined that at 35 watts of power, the deposition 
rate was 0.62 A per second. The coating showed signs 
5 of incipient opacity at power settings greater than 60 
watts. 
EXAMPLE 3 
In this preparation, boron trifluoride was deposited in 
10 combination with perfluorobutene-2. The total pressure 
of the gas mixture was 20 N/m2 and their ratio, 2 to 1 
respectively. The power used was 50 W. Under these 
conditions, the rate of deposition increased to about 2 
A/second and the film obtained showed good adhesion 
and moderate durability. The coating however did not 
pass a hand cleaning test with lens tissue. 
A comparison of infrared spectra taken from the 
present film and from one prepared with perfluorobu- 
tene-2 as the sole reactant indicated that while both 
2o coatings showed one absorption peak at 9 p (C-F), that 
obtained from the film of the present example was con- 
siderably larger. Incorporation of boron was also evi- 
dent. 
25 EXAMPLE 4 
The plasma coated plastic substrate of Example 3 was 
given a nitrogen post-treatment which consisted in 
evacuating the apparatus to the background pressure 
3o and creating a nitrogen plasma for 500-700 seconds at a 
pressure of 13.3 N/m2and a power of 50 W. The dura- 
bility of the treated film was markedly improved. The 
product successfully passed the tape pull test for adhe- 
sion. It was also free of degradation after having been 
35 subjected to 20 and 40 rubs with an eraser under 2.2 psi 
pressure, as specified by MIL SPEC-C-675A. This data, 
according to the standard procedure, was obtained by 
visual inspection of the coating, as the specification 
requires. Further, inspection under 40 magnification 
and white-light illumination failed to detect any degra- 
dation. Also, immersion for up to 24 hours in distilled 
water or in Freon TF (trichlorotrifluoroethane) and 
acetone showed the coating to be insoluble. 
Although the present invention has been disclosed 
45 generally in terms of its preferred parameters and em- 
bodiments, it will be understood that many variations in 
compositions and processes can be carried out by the 
man skilled in the art without departing from its spirit 
and scope as defined by the following claims. 
50 What is claimed is: 
1. A method for depositing a single layer coating on 
a plastic substrate, comprising the step of subjecting the 
substrate to bombardment by boron trifluoride in 
plasma form. 
2. A method of claim 1 wherein the boron trifluoride 
is employed at a pressure within the range of 9.3 to 20 
N/m2and the plasma is maintained by a radio frequency 
voltage within the range of about 30 to 75 watts. 
3. The method of claim 1 wherein the boron trifluo- 
60 ride plasma comprises a nitrogen-containing gas. 
4. The method of claim 1 wherein the boron trifluo- 
ride plasma comprises an organic monomeric substance. 
S. The method of claim 1 wherein the single layer 
coating obtained is further subjected to a plasma of an 
6. The method of claim 5 wherein the organic mono- 
meric substance is selected from the group consisting of 
organosilanes and perfluorobutene-2, 
55 
65 organic monomeric substance. 
4,091,166 
5 
7. The method of claim 6 wherein the coated sub- 
strate is further treated in a nitrogen plasma. 
8. A plastic surface coated with a layer of plasma 5 
deposited boron trifluoride. 
9. The boron trifluoride coated plastic surface of 
10 
15 
20 
25 
30 
6 
claim 8 which carries an outer layer of a plasma poly- 
merized organic monomeric compound. 
10. The plastic surface of claim 9 wherein the outer 
layer consists of a plasma polymerized mixture of an 
organic monomeric compound and boron trifluoride. 
11. The plastic surface of claim 9 which has been 
subjected to a further treatment by a nitrogen plasma. * * * * *  
35 
40 
45 
50 
55 
65 


Boron trifluoride coatings for thermoplastic materials and method of applying same in glow discharge

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