U.S. patent number 3,850,679 [Application Number 05/315,393] was granted by the patent office on 1974-11-26 for chemical vapor deposition of coatings.
This patent grant is currently assigned to PPG Industries, Inc.. Invention is credited to Krishna Simhan, John F. Sopko.
United States Patent |
3,850,679 |
Sopko , et al. |
November 26, 1974 |
CHEMICAL VAPOR DEPOSITION OF COATINGS
Abstract
A metal oxide coating is applied to a hot glass surface by
contacting the surface with a mixture of carrier air, vaporized
solvent and a vaporized metal containing reactant. The mixture is
directed against the glass through a nozzle at a Reynolds number
exceeding 2500 with the nozzle-to-glass spacing at least 1.25 times
the characteristic dimension of the nozzle.
Inventors: |
Sopko; John F. (New Kensington,
PA), Simhan; Krishna (Fischbach, DT) |
Assignee: |
PPG Industries, Inc.
(Pittsburgh, PA)
|
Family
ID: |
23224199 |
Appl.
No.: |
05/315,393 |
Filed: |
December 15, 1972 |
Current U.S.
Class: |
427/255.19;
65/60.3; 65/60.52; 118/718; 427/250; 427/255.31 |
Current CPC
Class: |
C03C
17/002 (20130101); C23C 16/453 (20130101); C03C
17/00 (20130101); C23C 16/545 (20130101); C03C
17/245 (20130101); C03C 2218/152 (20130101); C03C
2217/21 (20130101); C03C 2217/219 (20130101); C03C
2217/217 (20130101); C03C 2217/23 (20130101) |
Current International
Class: |
C03C
17/00 (20060101); C23C 16/54 (20060101); C23C
16/453 (20060101); C03C 17/245 (20060101); C03C
17/23 (20060101); C23c 011/00 () |
Field of
Search: |
;117/16R,17.2R,107.1
;118/48,49 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Rosdol; Leon D.
Assistant Examiner: Pitlick; Harris A.
Attorney, Agent or Firm: Pollock; E. Kears Lepiane; Donald
Carl
Claims
We claim:
1. A method of applying a coating to a substrate by directing a
gaseous mixture comprising at least one coating reactant through a
nozzle against a substrate comprising:
a. vaporizing the coating reactant and mixing coating reactant
vapors and a carrier gas to form said gaseous mixture; and
b. directing said gaseous mixture through said nozzle at a nozzle
exit Reynolds number of at least about 2500.
2. The method of applying a coating according to claim 1 wherein
said gaseous mixture comprises:
a. vapors of a reactive metal compound, and
b. a carrier gas comprising at least one reactant which will react
with said metal compound under conditions adjacent said
substrate.
3. The method of applying a coating according to claim 1 wherein
said gaseous mixture directed from said nozzle wets substantially
all of the interior faces of said nozzle while maintaining the
surfaces of said nozzle in facing relation to said substrate
substantially nonwetted by said gaseous mixture.
4. The method of applying a coating according to claim 1 wherein
said gaseous mixture is directed through said nozzle at a nozzle
exit Reynolds number of at least about 5000.
5. The method of applying a coating according to claim 1 wherein
said gaseous mixture flowing through said nozzle has a
substantially greater linear velocity at the exit of said nozzle
facing said substrate than at the entrance of said nozzle.
6. The method of applying a coating according to claim 1 wherein
said nozzle has an elongated shaped exit end having a major
dimension and a minor dimension and wherein said gaseous mixture
flows from said nozzle exit a distance of at least 0.5 times the
minor dimension of said nozzle exit before impinging against the
substrate.
7. The method of applying a coating according to claim 6 wherein
said gaseous mixture flows from said nozzle exit a distance of from
about 1.25 to about 5 times the minor dimension of said nozzle exit
before impinging against said substrate.
8. The method of applying a coating according to claim 6 wherein
said gaseous mixture is directed through said nozzle at a nozzle
exit Reynolds number of at least about 5000.
9. The method of applying a coating according to claim 1 wherein
the temperature of said gaseous mixture at said nozzle exit exceeds
that temperature at which said metal reactant saturates said
gaseous mixture and the temperature of said gaseous mixture at the
nozzle exit is less than that at which said metal reactant will
react to form a coating.
10. The method according to claim 1 wherein the substrate is a
ribbon of glass moving at a velocity of about greater than about
100 inches per minute.
11. The method as set forth in claim 1 wherein the substrate is a
ribbon of glass moving in a downstream direction from exit end of a
bath chamber of a float tank into an annealing lehr and wherein
said directing step is performed upstream of the annealing lehr and
downstream of the exit end of the bath chamber.
12. The method as set forth in claim 11 wherein said nozzle has an
elongated shaped exit end having a major dimension and a minor
dimension and wherein the gaseous mixture flows from the nozzle
exit a distance of about 0.5 to about 10 times the minor dimension
of the nozzle exit before impinging on the glass ribbon to coat the
glass ribbon.
13. The method according to claim 1 wherein said directing step
further comprises:
moving the gaseous mixture through a nozzle having (1) an entrance
and an exit end, and (2) having interior surfaces of monotonically
and constantly increasing radii of curvature from the entrance end
to the exit end to accelerate flow of the gaseous mixture adjacent
interior surfaces of the nozzle.
Description
CROSS REFERENCES TO RELATED APPLICATIONS
This application is related to the following copending
applications, all commonly assigned, all specifically incorporated
by reference herein and all filed on even date herewith: "Nozzle
for Chemical Vapor Deposition of Coatings", Ser. No. 315,394, filed
Dec. 15, 1972 by Krishna Simhan; "Coating Composition Vaporizer",
Ser. No. 315,395, filed Dec. 15, 1972, by John Sopko; and "Method
for Increasing Rate of Coating Using Vaporized Reactants", Ser. No.
315,384, filed Dec. 15, 1972 by Karl H. Bloss and Harald
Molketin.
This application is also related to a copending application
entitled "A Process for the Deposition of Films", Ser. No. 182,993,
filed Sept. 23, 1971 based on a convention priority date of Sept.
29, 1970, by Hans-Jurgen Goetz, Helmut Lukas and Harald Molketin.
This application is also incorporated by reference herein.
BACKGROUND OF THE INVENTION
This invention relates to coating substrates, particularly glass
substrates, with coatings comprised primarily of metal oxides. This
invention more particularly relates to contacting a hot glass
surface with the vapors of reactants which form metal oxide
coatings upon contacting the hot glass surface.
Prior to the present invention it has been known that substrates
may be coated with metal oxide coatings by contacting the
substrates with solutions comprised of metal betadiketonates and
the like dissolved in appropriate solvents. See the following U.S.
Pat. Nos.: Mochel, U.S. Pat. No. 3,202,054; Tompkins, U.S. Pat. No.
3,081,200; Donley et al, U.S. Pat. No. 3,660,061 and Michelotti et
al, U.S. Pat. No. 3,652,246. These patents have disclosed to the
public a number of chemical compositions which are suitable for the
coating of glass with metal oxide coatings. In general, the
techniques described for applying such coatings to glass taught in
the prior art are methods wherein a liquid spray of coating
composition is directed against a glass substrate surface to be
coated. While these patents cover the application of particular
metals or metal oxides to glass or other substrates, whether the
compositions are applied in liquid or vapor form, they each
disclose, as a best mode of application, contacting the substrate
with the composition in liquid form. In the development of
techniques for applying vaporized coating compositions to heated
substrates at atmospheric pressure certain difficulties have been
encountered. It has been difficult to obtain coatings which are
finely grained and uniform in appearance. Thick coatings have been
produced by contacting the substrate with a liquid spray, but it
has been extremely difficult if not impossible to obtain relatively
thick films having visible light transmittances of below about 50%
using known vapor deposition techniques.
Vapor deposition processes have been known in the past. Most
commercial embodiments of vapor deposition processes are processes
carried out under subatmospheric pressure conditions. A number of
techniques have evolved for enhancing the rate of film deposition
using these techniques, for example, electrical fields, magnetic
fields, and radio frequency or microwave excitation have been used
to increase the momentum of reactant particles in vapor coating
compositions during their applications. Also, wave guides have been
used to direct the vapors of coating compositions to particularly
confined target areas. See U.S. Pat. No. 3,114,652 to Schetky and
U.S. Pat. No. 3,561,940 to Scholes.
The applicants have now discovered that the uniformity of films
produced by chemical vapor deposition and the rate of chemical
vapor deposition or film buildup may be significantly enhanced by
directing reactant containing vapors through a nozzle against a
substrate under particular flow conditions and preferably doing so
at particular nozzle-to-substrate spacings.
SUMMARY OF THE INVENTION
A vaporizable coating reactant is vaporized into a vapor phase or
gaseous carrier and is delivered through a nozzle and directed
against a heated substrate. The substrate and reactant temperatures
are such that upon contact with the substrate the reactant reacts
to form an adherent coating on the substrate. In order to insure
rapid, efficient and uniform deposition of coating the gaseous
mixture containing the coating reactant is directed through the
nozzle with a Reynolds number of at least 2,500. For high speed
coating of a continuous ribbon or sheet of glass it is preferred
that the Reynolds number for the flowing gaseous mixture be at
least about 5,000.
The vaporizable coating reactant is generally a material which is a
solid or liquid at room temperature although the preferred
reactants are usually solids at room temperature. The reactant may
be vaporized by conventional methods, such as boiling if it is
liquid, or if the reactant is a solid it may be vaporized by
delivering it onto a heated plate, by admixing it with an inert
material, such as sand, and passing a heated carrier gas through
the mixture or by fluidizing it with a rapidly moving stream of
carrier gas and heating the fluidized mixture. In the preferred
embodiments of this invention the reactant is dissolved in an
appropriate solvent, and the solution is sprayed into a hot carrier
gas to vaporize the solvent and the reactant. A particularly
preferred method of vaporization and apparatus for carrying out the
method are the inventions of John Sopko and are the subject of his
copending application entitled "Coating Composition Vaporizer" and
filed on even date herewith.
The reactive coating materials which are preferred for use in the
present invention are the pyrolizable organo metallic salts of the
metals of Groups Ib through VIIb and of Group VIII of the Periodic
Chart of the Elements. The preferred organo metallic salts which
are employed are betadiketonates, acetates, hexoates, formates and
the like. The acetylacetonates of iron, cobalt and chromium are
particularly preferred as the reactive ingredients of the present
coating compositions.
While the coating reactants which are preferred for use in this
invention are pyrolyzable materials, other kinds of reactants may
also be employed. For example, hydrolytic reactants, such as
fluorinated betadiketonates, particularly acetylacetonates, and
metal dicumenes, may be used. Also reactants may be employed which
require the presence of substantial quantities of other cooperating
reactants such as oxygen, hydrogen, halogens or the like. As
already indicated the preferred method for vaporization involves an
initial step of solution so that the reactant or reactants employed
should be easily dissolved in a suitable solvent.
A variety of aliphatic and olefinic hydrocarbons and halocarbons
are suitable as solvents in carrying out the methods disclosed
here. Single component solvent systems, particularly a solvent
system employing methylene chloride, are effectively employed in
the present invention. Solvent systems employing two or more
solvents are also found to be particularly useful.
Some representative solvents which may be employed in carrying out
the present invention are: methylene bromide, carbon tetrachloride,
carbon tetrabromide, chloroform, bromoform, 1,1,1-trichloroethane,
perchlorethylene, 1,1,1,-trichloroethane, dichloroiodomethane,
1,1,2-tribromoethane, trichloroethylene, tribromoethylene,
trichloromonofluoroethane, hexochloroethane,
1,1,1,2-tetrachloro-2-chloroethane,
1,1,2-trichloro-1,2-dichloroethane, tetrafluorobromethane,
hexachlorobutadiene, tetrachloroethane and the like.
Other solvents may also be employed, particularly as mixtures of
one or more organic polar solvents, such as an alcohol containing 1
to 4 carbon atoms and one hydroxyl group and one or more aromatic
non-polar compounds, such as benzene, toluene or xylene. The
volatility of these materials makes their use somewhat more
difficult than the above designated group of preferred halogenated
hydrocarbons and halocarbons, but they have particular economic
utility.
In the preferred practice of this invention a solution of a
reactive organo-metallic salt in an organic solvent is directed to
a vaporizing chamber. The vaporizing chamber is constructed so as
to provide a heating element which heats the space surrounding the
element to a temperature sufficient to vaporize the coating
solution within that space rather than vaporizing the liquid only
in contact with the heating element itself. A carrier gas is
directed across and away from the heater to intercept the coating
composition to mix with it enhancing its rate of vaporization and
to carry the vapors through the heater to the substrate to be
coated.
Vapors of the solvent and reactive organo metallic salt are
directed from the vaporizer chamber to an elongated manifold
disposed across the width of a heated substrate which is to be
coated. Connected to this manifold is an elongated nozzle for
directing the vapors against the substrate.
In a preferred embodiment, which is the subject of the copending
application of Krishna Simhan entitled "Nozzle for Chemical Vapor
Deposition of Coatings", and filed on even date herewith the
elongated nozzle has as its minor cross-section a uniformly
converging shape to provide for substantially continuous
acceleration of the boundary layers of vapor passing through. The
major cross-sectional dimension of the nozzle is slightly less than
the corresponding substrate width so that a substrate placed in
facing relation to the nozzle extends beyond the major dimension of
the nozzle at both ends thereof. This relationship provides for the
maintenenace of a substantially uniform pressure drop along the
major dimension of the nozzle and prevents the escape of a
disproportionately large amount of vapors directed through the
nozzle at each end of the nozzle and thus all vapors have good
contact with the substrate.
The face of the nozzle disposed in facing relationship to a
substrate to be coated is located in a position relative to a
support for substrates to be coated such that the spacing between
the nozzle face and the surface closest thereto during coating is
at least 0.5 times the width of the nozzle at its exit. Preferably
the spacing-to-nozzle width ratio is at least 0.65 and more
preferably is between 0.9 and 5. In the most preferred embodiments
the ratio is between 1.25 and 5.
The vaporizer and manifold of the coating apparatus of this
invention are operated at sufficient pressure to cause vapor flow
through the nozzle at a Reynolds number of at least 2500 and
preferably at least about 5000 in order to insure rapid, efficient
and uniform deposition of coating.
The apparatus and method of this invention may be employed to apply
coatings to a variety of receptive substrates. Refractory
substrates, such as, glasses, glass ceramics, ceramics, porcelain
clad metals and the like are particularly amenable to coating by
the present invention. Other substrates, such as, metals, plastics,
paper and the like may also be coated according to the principles
of this invention. In particular, this invention is useful to
provide for the coating of flat glass with transparent metal oxide
coatings. The resulting metal oxide coated flat glass articles have
found particular utility in architectural applications .
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partial, cutaway, perspective view of the preferred
apparatus for practicing the present invention, showing the flow of
vapors and other fluids employed in the practice of the
invention.
FIG. 2 is a partial sectional view of the preferred vaporizer,
manifold and nozzle used in the practice of the present invention
shown in combination with a sheet of float glass supported in
facing relation to the nozzle.
FIG. 3 is a partial sectional view of the preferred device of this
invention taken along section line 3--3 of FIG. 2.
FIG. 4 is a partial sectional view of the preferred vaporizer of
this invention taken along section line 4--4 of FIG. 3 showing the
particular relationship of the heating element therein to the
chamber space with its inlets, outlets and baffling arrangement to
provide for the vaporization of the coating compositions employed
in this invention within the space of the chamber rather than for
vaporization in contact with the heating element itself.
FIG. 5 is an enlarged sectional view of the preferred nozzle used
in the practice of this invention along with a suitable manifold
for distributing vapor to the nozzle.
FIG. 6 is a sectional view of the preferred nozzle for use in the
practice of this invention taken along section line 6--6 of FIG.
5.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the practice of this invention it is important that the Reynolds
number which characterizes the flowing vapors exiting from the
nozzle and being directed against the substrate being coated be
greater than about 2,500.
While a Reynolds number of at least 1700 insures that vapor flow
will be fully turbulent, it has now been discovered that the
Reynolds number must be at least about 2500 in order for flow to be
substantially uniform throughout the area of impingement against
the substrate as evidenced by interferometric techniques and by the
uniformity of resulting deposits.
The Reynolds number is defined by the following classic
equation:
N.sub.Re = W .sup.. .sigma. .sup.. L/.eta. .
The Reynolds number is dimensionless. The symbols W, .sigma. and
.eta. represent the flow velocity, the density and the dynamic
viscosity of the flowing vapor. L is a characteristic length
defined at the point where the other variables are determined.
According to known principals of hydraulics, the characteristic
dimension L which is relevant in the defined relationship is the
hydraulic diameter which is defined as four times the
cross-sectional area of the nozzle exit divided by the wetted
perimeter of the nozzle exit. The flow, density and vapor viscosity
are all characterized in the equation as the values of these
properties at the nozzle exit.
The present invention may be more fully appreciated from a detailed
description of the apparatus and method which follows.
Referring first to FIG. 1, a substrate, for example a sheet of
glass 11, is provided for coating. The sheet of glass 11 is
generally supported, preferably in a horizontal plane, and is
generally supported by means which can translatably move or convey
the glass sheet 11 along a path such as indicated by the arrow at
the lower right of FIG. 1. Disposed in facing relation to the glass
sheet 11 is the coating apparatus of this invention comprising a
vaporizer assembly 12 and a vapor distribution assembly 13.
The vaporizer assembly 12 comprises a vaporizer chamber 14, which
in a preferred embodiment of the invention is a cylindrical chamber
containing elements for vaporizing reactants, which elements are
further described below. The vaporizer assembly 12 further
comprises means for supplying a reactant 15 and means for supplying
a carrier gas 16.
A reactant is supplied through a solution line 17 to a series of
solution feed lines 18, each of which is connected to a spray tip
19 having its discharge opening inside the vaporizer chamber 14.
The solution line 17 is jacketed with a coolant line 20, which is
divided into forward and return flow portions by a baffle 21.
Atomization gas, preferably air, is supplied to each spray tip 19
through a series of atomization feed lines 22, all of which are
connected to an atomization gas line 23.
The entire reactant supply means 15 is mounted onto the vaporizer
chamber 14 by a series of caps 24 which surround the lines and are
bolted or otherwise connected to a series of mounts 25 welded to
the vaporizer chamber 14.
The carrier gas supply means 16 comprises a carrier gas manifold 26
mounted on the vaporizer chamber 14 by a bracket 27. Connected to
the carrier gas manifold 26 are a series of carrier gas feed lines
28, each connected to a carrier gas preheater 29 which are in turn
connected to the vaporizer chamber 14 in a manner such that heated
carrier gas may be directed into the chamber. The preheaters 29 are
preferably electrical resistance heaters, each having an electric
power connection 30 connected to a source of controlled electric
power (not shown).
The vaporizer chamber 14 may be a single structure, but if it is of
extended length it is preferably of modular construction with a
series of relatively short vaporizer chambers 14 connected
end-to-end by vaporizer chamber couplings 31 which lock the
individual chambers together.
Inside the vaporizer chamber 14 are elements for vaporizing a
reactant and other materials such as a solvent. A heater 32 is
mounted within the vaporizer chamber 14 in a manner such that the
chamber is divided into two portions, one into which all incoming
materials enter and one from which departing vapors leave. The
heater 32 is so constructed that vapors may pass through it from
the entrance portions to the exit portion of the vaporization
chamber 14. A preferred heater is a fin and tube heat exchanger
having a thermally controlled heat exchange fluid supplied to its
tubes.
The heater 32 is mounted within the chamber 14 on mountings, which
are efficiently also carrier gas distribution plates 33, welded or
otherwise connected to the interior walls of the chamber 14. The
carrier gas distribution plates 33 are so shaped and connected to
the chamber 14 that an enclosed manifold space is formed with each
plate 33 and the closely spaced chamber wall. The carrier gas
distribution plates 33 are provided with a series of openings which
permit the free flow of gas out into the entrance portion of the
vaporizer chamber 14 where it mixes with sprayed reactant and
solvent vaporizing them.
The gaseous mixture containing a reactant in the entrance portion
of the vaporizer chamber 14 passes through the heater 32 which
trims or finely controls the temperature of the mixture entering
the exit portion of the vaporizer chamber 14. The heater 32
preferably has a high heat capacity relative to the mass of flowing
gaseous mixture so that thermal stability is insured.
In the exit portion of the vaporizer chamber 14 are a series of
vapor discharge lines 34, extending outward through the wall of the
vaporizer chamber 14 and having several inlet openings near their
interior ends. The interior end of each vapor discharge line 34 is
preferably covered with an umbrella 35 which deflects any
occasional particulate material, which enters the chamber or forms
in the chamber thus, preventing it from clogging the vapor
discharge line.
Surrounding the vapor discharge lines 34 is a vapor discharge
heater 36. The vapor discharge heater 36 has two cavities, an inlet
cavity and a return cavity which are connected to a recirculating
heat exchange fluid system (not shown). During operation, hot
fluid, such as oil, is circulated through the vapor discharge
heater 36 to control the temperature of the gaseous mixture being
discharged from the vaporizer chamber 14.
Connected to each vapor discharge line 34 is a coupling 37,
preferably a flexible coupling, which connects the vaporizer
assembly 12 to the vapor distribution assembly 13. The vapor
distribution assembly 13 comprises a vapor manifold or plenum 38
having two vapor channels 39 separated by a dividing wall 40 and
jacketed with inner and outer thermal control fluid cavities, 41
and 42. During operation, hot fluid, such as oil, is circulated
through the inner and outer cavities to control the temperature of
the gaseous mixture flowing through the vapor channels 39.
The vapor channels 39 of the plenum 38 open into nozzles 43,
preferably converging nozzles. Each nozzle is formed of opposing
nozzle wall members 44 connected to the plenum 38. Preferably each
nozzle wall member 44 is provided with a cavity 45 through which
hot fluid, such as oil, may be directed to precisely control the
temperature of a gaseous coating mixture being directed through the
nozzles 43 to the substrate 11.
The present coating apparatus and method may be employed in
combination with a variety of other processes and substrates, such
as paper making, metal sheet rolling and the like. The present
method may be used to coat a continuous sheet or a series of
discrete substrates. In the preferred embodiments of this invention
a continuous glass sheet is coated. This may be a sheet produced by
the plate process, by any sheet process (Colburn, Fourcault or
Pittsburgh Pennvernon Process) or by a float process. The present
invention can be used effectively to apply a coating to a substrate
in a vertical, horizontal or otherwise oriented plane, and this
feature is a particularly valuable and unique feature of this
invention.
In a particularly preferred embodiment the present invention is
used to coat a newly formed float glass ribbon. The ribbon could be
easily coated on either major surface by the principles of this
invention and the description which follows relates to coating the
top surface of the glass ribbon.
Referring now to FIGS. 2, 3 and 4 as well as to FIG. 1, the
apparatus of this invention may be observed in a particularly
preferred environment, the space between a float forming bath and
an annealing lehr.
A continuous glass ribbon 11 is shown on a bath of molten metal 46,
such as molten tin, contained in a bath chamber 47 comprising
refractory bottom, side and top walls 48 encased in metal sheathing
49.
The ribbon 11 is lifted from the molten metal 46 at the exit end of
the bath chamber 47 on lift out rolls 50, which are suitably
journaled and driven by conventional roll driving means connected
to a driving motor (not shown). Carbon blocks 51 are spring loaded
and press against the bottom of the rotating rolls 50 to remove any
materials which may become deposited on the rolls. The carbon
blocks 51 are supported within a refractory extension of the bath
chamber 52. Material removed from the rolls which falls into this
extension 52 may be easily removed on an intermittent basis.
The ribbon of glass 11 is conveyed into an annealing lehr 53 having
a plurality of lehr rolls 54 therein. Conventional driving means is
provided for rotating the rolls 54. Each lehr roll 54 exerts a
tractive force on the glass of sufficient magnitude to convey the
glass through the lehr where its temperature is controlled to
release permanent stress and strain in the glass. The rolls 54
constitute part of a means for transporting newly formed float
glass from the float bath chamber 47, through a vaporization
coating chamber 55 and then through the annealing lehr 53.
The atmosphere within the bath chamber 47 is a reducing atmosphere
containing nitrogen and a small amount of hydrogen in order to
insure that oxidation of the molten metal 46 is inhibited.
Generally the atmosphere contains about 90 to 99.9 percent nitrogen
with the remainder being hydrogen. The atmosphere is maintained at
a pressure slightly above ambient pressure, for example, 0.1 to 0.5
inch water to substantially prevent the ingress of ambient
atmosphere into the bath chamber 47.
To retain the atmosphere and to permit the passage of the glass
ribbon from the bath chamber 47, the exit end of the bath chamber
is provided with a series of curtains or drapes 56 which trail on
the glass ribbon and serve as means for segregating the slightly
pressurized atmosphere of the vaporization coating chamber 55 from
the bath chamber 47. These drapes or curtains 56 are usually made
of flexible asbestos or fiber glass material which does not mar the
glass and which withstands temperature of the environment, namely,
a temperature of approximately 1000.degree. to 1200.degree.F.
Additional drapes or curtains 57 of similar material are provided
at the entrance of the lehr 53, the latter drapes serve as means
for segregating the lehr 53 from the vaporization coating chamber
55.
The vapor coating chamber 55 is provided with vacuum hoods 58
having inlets disposed both upstream, adjacent the bath chamber,
and downstream, adjacent the lehr. The vacuum hoods 58 extend
vertically upward to a pair of exhaust pipes 59 and are
sufficiently spaced from one another to provide sufficient room for
supporting I-beams 60 and for the vapor coating apparatus
comprising vaporizer assembly 12 and vapor distribution assembly 13
along with associated equipment. The vacuum hoods 58 are movably
supported on I-beams 60 by wheels 61 which rest on the top of the
I-beams 60. The I-beams 60 are disposed transversely across the
path of the ribbon of glass 11 moving from the bath chamber 47 to
the lehr 53. The vacuum hoods are held in spaced relation by cross
brace 62. The exhaust pipes 59 are mounted on brackets 63 on which
are mounted wheels 64 which rest upon tracks 65 of a supporting
overhead beam 66. The entire vacuum hood assembly comprising the
vacuum hoods 58 and exhaust pipes 59 may be moved transverse to the
path of the glass ribbon 11 to completely remove the assembly from
the float line for maintenance and repair. This removal is
accomplished by causing the assembly to move along beams 60 and 66
while rolling on the supporting wheels 61 and 64.
The vapor coater assembly is supported within the vapor coating
chamber 55 from I-beams 60 by means of vapor coater support bracket
67. Mounted on the support bracket 67 are vapor coater support
wheels 68. Vapor coater support wheels 68 rest on I-beams 60 one of
which has a track 69 mounted on it. The shape of the track 69 and
of the support wheel 68 engaging it is such as to prevent the
lateral movement of the assembly with respect to the track and
I-beams.
The vapor coater assembly comprises, in addition to the vaporizer
asembly 12 and the vapor distribution assembly 13, a mechanical
structure for supporting these operative elements. This mechanical
structure includes a motor 70 and jacks 71 for raising and lowering
the assembly to position it closer to or farther from the substrate
to be coated.
Depending from vapor coater support bracket 67 are vapor coater
cross arms 72. Mounted on cross arms 72 are a motor support 73 and
jack supports 74. Mounted on the motor support 73 is the motor 70,
preferably a DC variable speed motor. Connected to this motor 70 is
a drive shaft 75 which is in turn connected to screw jacks 71.
Within each jack 71 there is appropriate gearing for driving a scew
shaft in a vertical motion.
Screw shafts 76 connect with the drive shaft 75 through jacks 71
connected to a gear. By driving the drive shaft 75 by motor 70 the
screw shafts 76 are caused to move vertically to raise and lower
the vapor coating assembly. Mounted on the screw shafts 76 are
yokes 77. Connected to and depending from yokes 77 are support arms
78 which connect to cross plates 79.
Mounted on cross plates 79 is a vaporizer cradle support 80 to
which is bolted or otherwise connected the vaporizer chamber
14.
As briefly described above, the preferred practice of this
invention requires that a carrier gas, preferably air, be supplied
to the vaporizer chamber 14 to mix with the atomized spray of
coating composition coming from the spray nozzle tips 19 to enhance
the rate of vaporization of the coating material and then to carry
the mixture through the heater 32 to further heat the combination
for ultimate delivery to the substrate to be coated. The carrier
gas is supplied to the vaporizer from manifolds 26 which are
preferably pipes mounted on the assembly by brackets 27. Flexible
tubing 28 is connected to the carrier gas manifold 26 and directed
through heating elements 29 to connectors passing through the wall
of the vaporizer chamber 14 and entering the space formed by air
distribution plates 33 with the wall of the vaporizer chamber.
Power is supplied to heaters 29 from an electrical cable 81 which
passes through a supporting distribution conduit 82 mounted on
brackets 27 and 83.
The internal details of the vaporizer 12 which is preferably
employed in the practice of this invention are further described in
the copending application of John Sopko entitled "Coating
Composition Vaporizer".
The structural characteristics of the presently preferred apparatus
are apparent in FIGS. 2, 3 and 4. Unreacted or excess coating
composition vapors and the carrier gas discharged from the nozzles
43 toward the substrate 11 fill the vapor coating chamber 55.
Unreacted vapors and gases are removed from the chamber by vacuum
hood 58. In order to minimize or avoid the buildup of deposits on
irregular structural surfaces which might result in deposits
flaking off and dropping onto the substrate 11 thereby causing
defects the vapor coating assembly is encased within a vapor coater
shield 84. The vapor coater shield 84 may be provided with
reinforcement plates 85. It is connected to the coater assembly by
being connected to cross plates 79. The cross plates, 79 as
indicated before, are connected to the support assembly 78 and are
further connected to the vaporizer cradle support 80. As already
indicated, the vaporizer chamber 14 is connected to the vaporizer
cradle support 80. The cross plates 79 are provided with access
holes 86. The space between the vapor coater shield 84 and the
vapor manifold 38 is preferably filled with a thermal insulation
87, such as mineral wool, asbestos or the like.
As shown in FIG. 3 the construction of a vapor coater assembly to
span the entire width of a conventionally formed glass ribbon may
be modular. Modular design is preferred for ease of maintenance and
repair of the equipment. Individual vaporizer chambers 14 with
appurtenent equipment are connected together to form an assembly
which spans the entire ribbon width.
While the vaporizer 14 may be modular in design, the vapor
distribution manifold 38 and the vapor nozzles 43 are preferably
single units. In this way vapors are uniformly distributed across
the width of the substrate which is to be coated.
Referring to FIGS. 5 and 6, the details of the vapor distribution
manifold and the vapor nozzles may be appreciated.
The coating vapors are uniformly distributed along the substrate by
the vapor manifold or plenum 38. The structure of a particularly
preferred plenum 38 and nozzle 43 combination may be appreciated
from the enlarged views of FIGS. 5 and 6. The transverse length of
the plenum or manifold 38, which spans the width of a glass ribbon
to be coated, is much greater than the width of the manifold. For
example, in order to coat a glass ribbon having a width of about 10
feet the length of the manifold, d shown in FIG. 6, will be
approximately 10 feet as well. In general, the width of the
manifold will be one foot or less.
The vapor manifold 38 comprises a plurality of vapor channels which
are elongated and separated from one another at their exit ends but
which meet in a common channel at their entrance. The plurality of
couplings 37 which bring vapors from the vaporizer 14 to the
manifold 38 are connected to the manifold 38 along this common
channel entrance.
Each vapor channel 39 may preferably be constructed with at least
two opposing curves so that the path of travel of vapors passing
through the channel must change direction at least twice. In this
manner the uniformity of vapor distribution along the length of the
channel is enhanced. While baffles may be positioned within the
channels to further interrupt the vapor flow and distribute the
vapor along the length of the channels, the simple design without
baffles but with changed flow direction is preferred. In the
preferred design there are no areas of stagnation and no protruding
bodies to create eddy flows of significant magnitude.
Surrounding the vapor channels 39 are cavities 41 and 42 for
carrying a heating or cooling fluid as desired according to the
cross current flows as illustrated in FIG. 6. These chambers 41 and
42 extend along the length of the vapor manifold 38 and are
connected to a source of heating or cooling fluid (not shown). In
the preferred embodiment hot oil is supplied to the chambers.
Connected to the vapor manifold 38 are nozzle wall members 44
forming nozzles 43 which direct the vaporized coating composition
and carrier gas toward the substrate 11 which is to be coated. The
nozzles 43 are elongated as seen in FIG. 6, and in plan view they
appear as slots. The cross-section of the nozzle openings viewed
parallel to the major slot dimension, e, illustrates that the
preferred nozzles narrow considerably from their entrance to their
exit. The contraction of each slot is such that vapor passing
through the slot is continuously accelerated along the length of
the slot. In this way the boundary layer of vapors adjacent the
slot wall is minimized, and the perimeter of the slot is uniformly
wet by the vapors such that exiting vapors are uniformly directed
against the substrate. The nozzles may be characterized by a
contraction ratio, which is the ratio of inlet area to outlet area
or in the nozzles shown in FIGS. 5 and 6 as c/a. The preferred flow
conditions for obtaining efficient and uniform coating are
described below and the conditions described are defined as the
conditions at the exit end of the nozzles. The preferred nozzles
are the subject of the copending application of Krishna Simhan
entitled "Nozzle for Chemical Vapor Deposition of Coatings".
The minor dimension of each nozzle exit, indicated as a in FIG. 5,
dictates the spacing b between the nozzle exit and the substrate.
Preferably the ratio b/a ranges from 0.75 to 10. In the most
preferred embodiments the ratio b/a is from 1.25 to 5. Within the
most preferred range of spacing as indicated by the ratio b/a the
rate of coating deposition is substantially greater than at closer
or more distant spacings.
Each vapor channel 39 preferably has a volume of at least about six
minutes times the volumetric throughput of the channel. By having
this capacity to hold up vapors passing through the channel the
channel serves as a calming section to wash out in residual
velocity variations resulting from the flow of discrete streams
exiting from the flexible couplings 37. As mentioned before, the
vapor channels 39 preferably reorient vapor flow tending to
uniformly distribute the vapor along the length of the manifold 38.
The configuration and size of the vapor channels 39 are observed to
cooperate with the shape of the nozzles 43. If the contraction
ratio, c/a, for the nozzles is increased, particularly above about
5 to 6, the capacity or volume of the vapor channels 39 may be
decreased without detrimental effect.
Each nozzle 43 is formed of two members 44, each having a curved
face, connected to the manifold 38 with their curved faces in
facing relationship. Each member may be provided with a channel 45
for carrying a fluid, such as hot oil, to control the temperature
of the vapors and gas being discharged. In the preferred embodiment
hot oil passes through parallel channels 45 and then through
channels 41 and 42. The temperature of the oil to and from the
nozzles may be measured, and the temperature calculated from such
measurements to be the nozzle temperature is the temperature
employed in defining vapor flow conditions at each nozzle exit.
The curved surfaces defining the flow region of the nozzles are
smoothly machined to avoid creating minute obstructions or
scratches that would import local disturbances to the vapor and gas
flow. In a preferred embodiment nozzle members are made of machined
steel or other base metal, and the curved interior surfaces are
plated with an easily worked metal such as gold or other precious
metal. A metal finish of at least about 64 microinch and preferably
about 16 microinch is satisfactory. When the contraction ratio, c/a
is sufficiently great the metal finish may be less smooth without
effect.
The curvature of the nozzle interior surfaces is such that the
radius of curvature is least at the entrance and greatest
(approaching infinity) at the exit. In a most preferred embodiment
the radius of curvature monotonically (and preferably constantly)
increases as a function of distance from the entrance toward the
exit of the nozzle. For ease in the construction of the apparatus
the nozzle members 44 are machined to distinctly different radii in
separate regions (I, II, III and IV for example) along the path
length of the nozzle. Each region is smoothly machined to blend
with the next.
The exit edges of the nozzle members are preferably sharp, well
defined corners so that the substrate facing portion of the nozzle
members will not be wet by exiting vapors and gas. The substrate
facing edge of each nozzle member 44 should be about 90.degree.
with respect to the face of the member and preferably will be about
87.degree. so that the edge has an angle of about 3.degree. up away
from the nozzle exit with respect to the plane of the
substrate.
The flow conditions which are maintained in the practice of this
invention are defined at each nozzle exit. With reference to FIG.
5, the following parameters are considered. The characteristic
length employed in determining the vapor discharge Reynolds number
is the hydraulic diameter of the nozzle, defined as four times the
nozzle cross-sectional area divided by wetted perimeter of the
nozzle opening:
D = 4ae/2(a+e)
Since a is much less than e the hydraulic diameter approximates 2a.
The temperature of the flowing vapor-gas mixture is considered to
be the average oil temperature across the nozzle determined from
measured inlet and outlet oil temperatures. The density and
viscosity of the vapor-gas mixture are determined to be the density
and viscosity of the mixture at the nozzle temperature and
vaporization chamber pressure. In general the properties of the
carrier gas at that temperature and pressure are satisfactory. The
flow velocity is determined from the mass flow to the vaporizer
divided by the density of the mixture as indicated further divided
by the total area of the nozzle exit openings (number of nozzles
multiplied by [a .sup.. e]).
The following examples illustrate the importance of nozzle exit
Reynolds number and nozzle-to-substrate spacing.
EXAMPLE I
An experimental apparatus having a single nozzle like that
described above having the following characteristics is employed
for the tests described below. The apparatus has a motor driven fan
capable of delivering 3000 liter/minute of gas. A 5 kilowatt
heating coil is provided downstream of the fan with the heating
coil located in the duct through which the gas flows from the fan
to the nozzle. A thermocouple is located in the wall of the duct
immediately upstream of the nozzle, and this thermocouple is
connected to a temperature regulator which is connected to and
controls the power to the heating coil. A substrate support is
positioned opposite the nozzle opening. The substrate support is
provided with means for heating the substrate, and a series of
thermocouples are provided for monitoring substrate temperature.
The support is constructed to hold a flat substrate in a plane
perpendicular to a plane defined through center of the nozzle along
the axis of discharged gas flow.
An optical interferometer (MACH-ZEHNDER) is provided in surrounding
relation to the experimental apparatus. The interferometer is
positioned so that the center of its line of sight is in the plane
defined by the axis of gas flow and is parallel to the plane of a
substrate. The interferometer employs two coherent monochromatic
light beams, each having a wavelength of 546 nanometers (mercury
arc lamp with narrow band green filter). Since the anticipated flow
fields to be studied exhibit a substantial temperature gradient, a
rotating mirror system is used in the interferometer. A rotation
rate providing for 200 orders of interference is employed. Optical
interference is recorded using a camera, and the resulting
photographs reveal temperature profiles by a comparison of fringe
shifts in terms of fringe widths in accordance with the well known
principles of interferometry. As derived from the Gladstone-Dale
relationship, a shift of n fringe spaces indicates a temperature
difference of n .sup.. .DELTA. .theta. where .DELTA. .theta. is the
difference between the local temperature at the fringe and the
reference temperature, .theta..sub.R, which is the bulk carrier gas
temperature detected under quiescent conditions.
The apparatus was operated first with a nozzle-to-substrate spacing
of two times the nozzle width (one times hydraulic diameter).
Heated air alone was discharged at several flow rates characterized
as having Reynolds numbers of 900, 1500, 2000, 2500, 4000 and
5000.
The heated gas (air) which is discharged against the substrate must
turn 90.degree. in the vicinity of the substrate. The beginning of
this turn is observed from the interferograms (the photographs of
the interfered light) to be about 0.8 times the nozzle width, a,
above the substrate. At Reynolds numbers at and above 2500 a
pronounced sharp boundary region of uniform density is observed
adjacent the substrate. This is indicative of uniform and efficient
deposition conditions. Also at and above a Reynolds number of 2500
the width of the effective flow contact with the substrate is
observed to be substantially greater than the nozzle width so that
the coating reactants can be effectively spread over the substrate
surface.
The experiments when repeated with substrate temperatures ranging
from 930.degree.F. to 1025.degree.F. reveal no significant
variation with substrate temperature.
The experiments are repeated with the nozzle-to-substrate spacing
varied. Spacing ratios of b/a = 4, b/a = 2 and b/a = 1 are
tested.
For a spacing ratio of 4 the interferograms reveal gas density maps
exhibiting a sufficiently broad region of uniformity near the
substrate for uniform coating at a Reynolds number of 5000. At
lower Reynolds numbers the region is diminished and below a
Reynolds number of about 2500 the density map suggests the
likelihood of non-uniform coating.
For a spacing ratio of 2 the interferograms reveal gas density maps
exhibiting a divergence of the flow into a uniform coating region
beginning at about 0.67 times the nozzle width above the substrate.
At this spacing ratio flow oscillations which were apparent at a
greater spacing ratio are absent and the flow and density fields
remain uniform with respect to time. Even below a Reynolds number
of 2500 a small uniform coating region is observed and above a
Reynolds number of 2500 the width of the region exceeds the nozzle
width and at a Reynolds number of 5000 the region width is about
two times the nozzle width.
For a spacing ratio of 1 the interferograms reveal gas density maps
exhibiting sharply turning flows creating variable pressure fields.
This tends to destroy the effect of the discharge flow and the
higher Reynolds numbers within the preferred range are reached with
a uniform coating region still confined to about the width of the
nozzle.
Further reduction of the spacing ratio requires higher Reynolds
numbers. Despite any a priori thought that improvements might be
made by moving the nozzle closer to the substrate any boundary
penetration which might be expected is found to be offset by
non-uniform conditions observed experimentally.
While the example described above establishes the significance of
Reynolds number and nozzle-to-substrate spacing for vapor coating
insofar as their significance may be deduced from gas density
variations and other conditions in the vicinity of a substrate, the
example which follows describes coating a glass substrate according
to the preferred embodiment of this invention.
EXAMPLE II
The apparatus shown and described above is positioned across a
float formed ribbon of glass between a float forming bath and an
annealing lehr.
A continuous ribbon of clear glass approximately ten feet wide and
about 1/4 inch thick is conveyed beneath the device at a linear
velocity of about 250 inches per minute. The glass is a
conventional soda-lime-silica glass having a visible light
transmittance of about 88 percent.
A coating solution is prepared. The solution has the following
composition on a one gallon basis.
______________________________________ Iron acetylacetonate 510
grams Chromium acetylacetonate 150 grams Cobalt acetylacetonate 55
grams Methylene chloride 1 gallon
______________________________________
The coating solution is delivered to the solution line 17 at a rate
of about 0.2 gallon per minute, at a pressure of about 10 psig and
at a temperature of about 70.degree.F. Atomization air is supplied
to the atomization gas line 23 at a pressure of about 5 psig and at
a temperature of about 70.degree.F.
Carrier air is delivered to the carrier gas manifold 26 at about 38
psig and at a rate of about 170 SCFM. The carrier is heated to
about 500.degree.F. in the preheaters 29 and is delivered to the
vaporizer chamber 14 with the air velocity through the distributor
plates 33 being about 5 to 10 feet per minute. The sensible heat in
the air is sufficient to vaporize the coating solution and to
establish the resulting air-vapor mixture temperature within the
range of about 400.degree.F. to 420.degree.F.
Hot oil is supplied to all heaters at a temperature of about
410.degree.F. Thus, the coating mixture leaving the vaporizer
chamber 14 and passing through the plenum 38 and nozzles 43 has a
stabilized temperature of about 410.degree.F. The glass temperature
beneath the nozzles is about 1050.degree.F.
The nozzle-to-substrate spacing is b/a = 2. The described
conditions provide a nozzle exit flow Reynolds number of 5000. The
Reynolds number is based on the viscosity of air at 410.degree.F.
and the density of the air-methylene chloride mixture at
410.degree.F. and one atmosphere pressure. Mass flow is directly
utilized from the known input.
The apparatus is operated for a period of 20 minutes to coat about
200 square feet of glass. The resulting coating is uniform over the
surface of the glass with the average visible light transmittance
of the coated glass being 40 percent and the variation of
transmittance being less than .+-. 2 percent except for the extreme
marginal edges of the glass extending beyond the major dimension of
the nozzles.
The coating is observed to be more uniform and have a much more
finely grained appearance than coatings produced by spray methods
using the same coating materials.
EXAMPLE III
The method of Example II is repeated several times except that in
each instance some process parameter is varied to determine its
influence upon the coatings produced.
First, the method is repeated with the exit flow having a Reynolds
number of 2500. The resulting coating is of excellent quality as in
Example II although the overall average transmittance is only 50
percent indicating somewhat less coating or deposition efficiency
than in the preferred practice of the invention.
Second, the method is repeated with the exit flow having a Reynolds
number of 2000. The resulting coating is thinner and less uniform
than in the previous example; the average transmittance is only 60
percent with the transmittance range being .+-. 5 percent which is
unacceptable for architectural applications.
Third, the method is repeated with the exit flow having a Reynolds
number of 7000. The resulting coating is of excellent quality as in
Example II.
Finally, two runs are made with the exit flow having a Reynolds
number of 5000. In one run the nozzle-to-substrate spacing is 0.9
times the nozzle width and in the other the spacing is 5 times the
nozzle width. The resulting coating in each instance is sufficient
to provide an overall average transmittance of less than 50 percent
but the variation in each instance is about .+-. 3 percent
indicating marginal quality for many architectural uses.
* * * * *