Note: Descriptions are shown in the official language in which they were submitted.
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TITLE .~-~
A METHOD AND APPARATUS FOR ~-
MANUFACTURING COATED FLAT GLASS ~ ~
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5 BACKGROUND OF THE INVENTION -- -
This invention relates to the manufacture of coated flat .
glass. More particularly, the invention relates to the
manufacture of flat glass by the float process, for example, ,;
wherein the glass is coated during the manufacture thereof to ::.
10 produce a resultant coated glass product having improved -
energy efficiencies and optical properties. - .;
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DESCRIPTION OF THE PRIOR ART ;~
In the float process for flat glass manufacture, molten
glass is delivered at a controlled rate onto one end, the hot
end, of a molten metal bath contained in an elongate tank
structure. Usually, the molten metal bath is of molten tin
or a molten tin alloy in which tin predominates. The final
ribbon of glass is discharged from the bath by traction ~-
means, usually driven traction rollers, often referred to as
lift out rollers, disposed beyond the outlet end of the bath, ;~
which traction means applies a tractive force to advance the ;~
ribbon along the path.
It has been found that certain coatings for glass are
25 designed to control the transmission and emission of energy. ~:
For example, metal oxide coatings can be employed to reduce
the emissivity of the resultant glass product in respect of
infra-red radiation; and to reduce the total energy
transmission in respect of solar radiation. The reduction of
infra-red radiation emissivity will result in the ability of
the coated glass product to conserve heat energy; and the
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reduction of solar radiation will result in the ability of
the coated glass product to reduce solar gain and glare.
Also, it has been found that when the coated glass ~ ;
35 products are utilized as a glazing for building construction ~
purposes, the product must be able to be readily handled -- -
without fear of scratching or removing the coat'ing, as well ;~
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as have an inherently uniform optical quality free from an
undesirable optical effect which would adversely affect the
aesthetic appearance of the glass.
It is known that pyrolytic coating processes are
desirable from an abrasion resistance standpoint. For
example, it is found that pyrolytic coatlngs applied to glass
can be more abrasion resistant than the surface of the glass
itself. Most of the energy efficient and optically
acceptable coatings are applied to the glass subsequent to
the manufacture thereof. Typically, the glass is cut into
blanks of desired sizes, and the blanks are then coated by
vacuum deposition, sputtering, or similar processes without
the requirement of additional heating of the glass; or by a
spray or a chemical vapor deposition process requiring
15 reheating of the glass. In the coating processes which are ~
temperature dependent, the coating must be applied in a -
temperature controlled environment. Obviously, to allow the
glass ribbon to cool following its manufacture in order to
cut it into blanks of the desired dimensions, and to then
reheat the glass blanks to prepare them for the coating, is
not energy efficient. Thus, it is believed that the
processes of the prior art have been energy inefficient and,
in many instances, too expensive to en~oy commercial success.
Accordingly, it is a main ob~ect of the present
25 invention to provide an on-line process for manufacturing a -~
glass product having an abrasion resistant, color-free,
energy-efficient coating thereon. ~`
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SUMMARY
The present invention provides a method of and apparatus
for manufacturing flat glass having an abrasion-resistant, -
colorless, energy-efficient coating formed thereon in an on-
line procedure as a ribbon of glass is advanced along and
removed from a molten metal bath. ;`'~-
It has been found that coaters, as of the chemical vapor
deposition type, for example, located within the head space ; ~ `~
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over the molten metal bath, remain clean and deposit free
since no outside oxygen is present to dilute the precursor,
such as metal oxide (tin oxide). Such dilution results in
formation of oxidized flakes at the outlet end of the coater
which militate against the deposition of a uniform film on
the glass surface.
Amongst the problems encountered in coating the glass
surface of the ribbon as it emerges from the float bath is
that the surrounding air tends to infiltrate lnto the
reaction zones in uncontrolled amounts. The rate of
infiltration is dependent, among other factors, upon the ~
speed of the glass ribbon, clearance between the outlet of ~ ;
the coater and the ad~acent surface of the glass ribbon,
sealing means ad~acent the glass ribbon, and the exhaust flow ~;
15 rate. Such an environment causes the formation of oxidized -:
flakes at the bottom, outlet end of the coater, causing
streaking and a non-uniformity in the deposition of the
coating on the glass surface. Also, it has been found that ~ ~
the uppermost surface of the glass ribbon loses heat energy -~ ~-
as it emerges from the bath, lowering the surface temperature
of the glass, and requiring a reduction in deposition speed
or a lower rate of deposition. Further, the presence of
outside air may result in ignition of the coating precursors.
In order to overcome the aforesaid problems, amongst ` -
others, it is the deslderatum of this invention to provide a
controlled atmosphere coating section ad~acent the outlet of
the bath to assure that the coater mechanism therewithin is
bathed in a substantially oxygen-free atmosphere. The
controlled atmosphere prevents the formation of undesirable
oxidized material thereon and reduces the amount of heat
energy lost by the top surface of the transient glass ribbon,
thereby increasing the deposition efficiency and enhancing `
the abrasion-resistant and colorless qualities of the film.
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STATEMENT OF THE INVENTION
In accordance with the present invention there is
provided a method of manufacturing coated glass which
comprises the steps of: a) delivering molten glass at a
controlled rate to a molten metal bath within a tank
structure having an enclosed headspace over said molten metal
bath; b) advancing the glass along the surface of the bath of
molten metal under thermal conditions assuring that a ribbon ---
of glass having an upwardly facing surface is established on
10 the bath; c) maintaining a protective atmosphere at a plenum :~
over said ribbon within said enclosed headspace; d) allowing
the ribbon of glass to cool sufficiently to be withdrawn ~
undamaged from the bath of molten metal; e) advancing the ~ ::
ribbon from said bath of molten metal on a series of traction ~`~
rolls through an immediately adjacent enclosed controlled
atmosphere chamber; and f) applying at least one coating to
the upwardly facing surface of the ribbon of glass advancing
on said rolls within said adjacent controlled atmosphere
chamber
Also in accordance with the present invention, there is :. .
provided an apparatus for depositing at least one layer of `~
coating material on the upper surface of a ribbon of float ::~
glass comprising, an elongated tank structure having inlet
and outlet ends and containing a bath of molten metal, an
25 enclosure over said tank structure defining a headspace .~:-
within which a plenum of protective atmosphere is maintained, :::
means delivering molten glass to the bath at said inlet end -
and advancing the glass along the surface of the bath to said - .
outlet end under thermal conditions assuring that a ribbon of ~:
glass having an upwardly facing surface is formed.on the
bath, a plurality of traction rolls mounted adjacent said
outlet end outside said enclosure for receiving and conveying .
said ribbon from said bath, an enclosed controlled atmosphere :-:
chamber contiguous with said tank structure and enclosure and
35 enveloping said traction rolls, and coating means within said .;.;~
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controlled atmosphere chamber for depositing at least one of
said layers on said ribbon on said traction rolls. ;
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings:
Fig. 1 is a central longitudinal sectional elevation of
apparatus embodying the invention, comprising a tank
structure for a bath of molten metal and a superimposed roof
structure, in which apparatus molten glass delivered to the
bath is withdrawn in ribbon form;
Fig. 2 is a top plan view of the tank structure of the
apparatus illustrated in Fig. l;
Fig. 3 is a transverse sectional view taken along line
3-3 of Fig. l;
Fig. 4 is a central longitudinal sectional elevational
view of a controlled atmosphere chamber ad;acent the outlet ~;
end of the apparatus illustrated in Figs. 1 through 3; and ~-~
Fig. 5 is a schematic vertical sectional view of one of
the coaters disposed in the controlled atmosphere chamber.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The drawings illustrate a preferred form of the
apparatus according to the invention for use in applying a
uniform coating to the upper surface of a ribbon of float
glass. Thus, in accordance with the invention one or more
coating stations are disposed within a controlled atmosphere
chamber contiguous with the outlet end of the bath of molten
metal and enclosing the rolls immediately ad~acent the tank
structure by which the ribbon is removed from the molten
metal.
Referring initially to the construction of the apparatus
illustrated in Figs. 1 to 3, inclusive, molten glass 10 is ~;
delivered in a conventional manner from a melting tank (not ~
shown) along a canal 12 which terminates in a spout having -
opposite side ~ambs 14 and a spout lip 16. The flow of
molten glass to the spout, usually soda-lime-silica glass, is
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controlled by a regulating gate or tweel 18. The spout
extends over an inlet end wall 20 of a tank structure
including a floor 22, an outlet end wall 24, and associated
side walls 26.
The tank structure contains a bath of molten metal 28,
usually molten tin or an alloy in which tin predominates.
The molten glass 10 is adapted to flow as illustrated at 30
over the spout lip 16 onto the surface of the molten metal
bath 28 at the inlet of the tank structure. The temperature
at the inlet is maintained at a desirable level by heaters 32
mounted beneath a roof structure 34 which is supported over -~
the tank structure and defines a head space 36 above the ` ;~
molten metal bath 28. The roof structure 34 has an inlet end
wall 38 which depends downwardly close to the surface of the --;-;
molten metal bath 28 to define an inlet 40 of restricted
height. An extension 42 of the roof structure 34 extends up
to the tweel or gate 18 to provide and define a chamber in
which the spout is enclosed.
The roof structure 34 also has a downwardly extending
outlet end wall 44. An outlet 46 for a ribbon of glass 48 ~ `
produced on the molten metal bath 28 is defined between the
lower face of the out.let end wall 44 of the roof structure 34
and the upper face of the outlet end wall 24 of the bath. '-
Driven traction or lift-out rollers 50 are mounted beyond the
outlet 46. The rollers 50 are mounted with their supporting
`surface slightly above the level of the upper surface of the ,~
bath end wall 24 so that the ribbon of glass 48 is lifted - - ;
gently from the bath surface for traction discharge
hori~ontally away from the outlet 46 onto the rollers 50. `~-~
1 A protective atmosphere comprised, for example, ~
primarily of nitrogen with a small amount of hydrogen, is j~ ,
maintained at a plenum in the head space 36 over the bath,
being supplied through ducts 52 extending downwardly through
the roof structure 34 and connected to a common header 54.
The protective atmosphere flows outwardly through the inlet
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40 to fill the chamber under the extension 42 enclosing the
spout.
A temperature gradient is conventionally maintained down
the bath from a temperature of about 1000C. at the inlet of
5 the bath 40 to a temperature on the order of 700C. at the ~ ;
outlet end 46 where the ribbon of glass 48 is removed from
the bath. At the outlet 46, the glass is thus sufficiently
stiffened to be unharmed by contact with the traction or lift ;
out rollers 50~ but still be lifted from the bath surface as
illustrated.
The molten glass 10 which flows over the spout lip 16
and onto the bath 28 as at 30, is permitted to flow laterally
on the molten metal bath 28 to form a layer 56 of molten
glass. The layer 56 is then advanced under thermal and
mechanical conditions assuring formation of the ribbon of
glass 48 which is cooled and discharged from the bath. The
width of the tank structure containing the molten metal bath -~
28 between the side walls 26 is greater than the width of the -
ribbon of glass 48. --~
In the embodiment illustrated, there are two coaters or --
gas distributor beams 58 and 60 spaced from one another along
the path of the ribbon of glass 48 within the tank structure.
The coaters 58 and 60 are employed for supplying coating
gases to the surface of the glass ribbon 48 and are located
transversely of the path of travel of the ribbon of glass 48
along the bath near the outlet end of the bath as is clearly
apparent from an examination of Figs. 1 and 2. A more
detailed description of the coaters appears hereinafter.
Mounted outside the discharge end of the tank are the
traction or lift out rollers 50. As mentioned hereinbçfore,
the rollers are disposed somewhat above the level of the i~
upper surface of the bath end wall 24 and cooperate to apply ~ -
a tractive effort to the ribbon of glass 48 moving towards
the outlet, which tracti~e effort advances the glass along
the bath. The ribbon of glass 48 passes out of the bath into
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and through the controlled atmosphere chamber 70, illustrated
in greater detail in Fig. 4, on the rollers 50.
The temperature of the molten metal bath 28 in the tank ` ~
structure is conventionally regulated from the inlet end to ~ `
the discharge end as by providing thermal regulators, not
shown, immersed in or extending over the molten metal, and by `~
the heaters 32 mounted in the roof structure 34.
The glass ribbon 48, upon leaving the outlet 46 of the
apparatus containing the molten metal bath 28, enters a
10 controlled atmosphere chamber 70 which is defined by an inlet ~ ~;
end wall 72 having an inlet opening 74, a spaced outlet end
wall 76 having an outlet opening 78, spaced apart side walls
80, and an sssociated roof 82. Typically, the controlled ;`~
atmosphere chamber 70 also will include a floor member 84, ;~
15 and suitable atmosphere may be provided to the chamber as ~`
deemed appropriate by a duct 85 from a supply (not shown). -
All of the above elements cooperate to form the chamber which
tends to completely envelope the lift-out or traction rollers
50 and the transient ribbon of glass 48 thereon.
There is provided within the chamber a coater 86, and '
preferably a pair of spaced apart coaters 86 and 86', similar ` -`~
in structure to the coaters 58 and 60 which are disposed
within the tank structure containing the molten metal bath
28. Suitable sealing means including seals 90 and 92 are .`~
25 employed to effectively seal the controlled atmosphere ~'
chamber 70 by contacting the under surface of the ribbon of ` ``~
glass 48 and the roller 50 ad~acent the outlet opening 78, `~
respectively. The seal members 90 and 92 effectively produce ``~
sufficient sealing means to maintain the desired atmosphere "~
within the chamber 70, and may typically be formed of a
graphite material capable of withstanding the temperatures to ;~
which they are exposed. `~
The physical and chemical nature of the reactants used
in the chemical vapor deposition processes of the invention
dictate that the gases, as well as the surfaces of the
coaters 58, 60, 86, and 86', be maintained within a'-.~-
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prescribed temperature range or ranges. Such regulation is
required because of condensation, premature film deposition,
decomposition, and gas phase nucleation (powder formation)
which can occur if the environment and the associated
temperatures are not correctly maintained. Typically,
coaters located within the molten metal bath 28 remain
deposit-free since outside oxygen is not present to dilute
the precursors used therein. The amount of oxygen used to
produce the metal oxide, tin oxide, for example, can be
10 precisely premixed. However, with coaters of the type ;~
described located outside of the molten metal bath 28, it has
been found that the surrounding atmosphere air tends to
infiltrate the reactor zones in undesirable and
uncontrollable quantities, causing deposits to form and the
temperature of the upper surface of the emerging ribbon of
glass to decrease. The combination results in both non-
uniform deposition of the coating and a reduction in the rate
of deposit~on of the coating. These problems are obviated by
establishment of the controlled atmosphere chamber 70.
In operation, the chamber 70 is preferably maintained at
a slightly increased internal pressure compared with the
external pressure. Thus, by admitting a suitable atmosphere
to the chamber as by the duct 85, the interior atmosphere may -`
comprise a selected composition at a pressure equal to or
greater than the external atmosphere so as to preclude
infiltration of external atmosphere. Of course, if the
atmosphere in the chamber 70 is to be the same as that within
the headspace 36, the internal pressure of the chamber 70 may
be maintained slightly less than the internal pressure within
the,interior of the head space 36 over the molten metal bath
28. The relative pressure conditions will thus result in a
flow of the atmosphere from within the head space 36 above -~
the molten metal bath 28 through the outlet 46 to the ~;
controlled atmosphere chamber 70 through inlet opening 74.
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Thus, the atmosphere within the chamber 70 is
appropriate to prevent the formation of undesirable oxides
and the like on the coaters 86 and 86'. ;~
Also, since the inlet and outlet walls 72 and 76,
5 respectively, the side walls 80, the roof 82, and the floor
84 tend to prevent the dissipation of heat energy, the
temperature of the transient ribbon of glass 48 tends to
remain within a range suitable for efficient deposition of ~;
the coating material from the coaters 86 and 86'. However,
10 if necessary, additional heat may be provided within the
chamber 70 as by heating elements 89.
It will be appreciated that a coating material may be
deposited in one or a plurality of layers, or several coating
materials may be sequentially deposited in varying ~-
combinations, by any or all of the coaters 58, 60, 86 and 86'
in accordance with the invention.
By way of example, if it were assumed that it is desired to
produce a ribbon of glass containing a colorless, abrasion ` ~-~
resistant, low-E coating in a continuous on-line manner, the .
20 following procedure could be followed. ,~
Initially, the coater 58 positioned over the molten metal
bath 28 applies a 250 angstrom thick film of doped tin oxide on ~-
the glass ribbon 48, and the coater 60 then applies on the initial -`
coating a supplemental 250 - 280 angstrom thick layer of silica. ~ -~
25 The thus coated glass ribbon 48 exits the molten metal bath 28 and ` =~
enters the controlled atmosphere chamber 70 through the inlet 72,
and is caused to travel sequentially under the coaters 86 and 86'.
The coater 86 applies a 1500 angstrom thick layer of tin oxide, ` i `
and the coater 86' applies a 1500 angstrom thick layer of doped --
30 tin oxide. Upon completion of the coating process, the coated
glass ribbon 48 exits the chamber 70 through the outlet opening 78
and is conveyed into and through an associated temperature
controlled lehr (not shown).
The coaters described above are similar in operation to the
35 coater illustrated and described in United States Patent No.
4,504,526 to Hofer et al., entitled APPARATUS AND METHOD FOR
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PRODUCING A LANINAR FLOW OF CONSTANT VELOCITY FLUID ALONG A
SUBSTRATE.
More specifically, the coaters 86 and 86' include, as
schematically illustrated in Fig. 5, a vacuum source 91 which ls
operative to effectively remove the atmosphere immediately over
the ribbon 48 in the direction of the inlet zone of the chamber
70, and an associated down stream source of precursor 93 having an
elongated outlet nozzle 94 for producing a laminar flow of
precursor of constant velocity over the width of the transient
glass ribbon 48. The coaters also include a vacuum source 96
which is operative to remove the atmosphere immediately over the
glass ribbon 48 downstream from the precursor source 93. The -
source of precursor 93 and associated elongate outlet nozzle 94
thus produce a constant velocity laminar flow of precursor fluid
over the width of the transient glass ribbon 48 both upstream and
downstream of the precursor source. ; :
It will be appreciated that the selected precursor fluid
emitted from the outlet nozzles 94 of the sequentially arranged
coaters 86 and 86' will deposit the desired film or films
20 sequentially on the upper surface of the previously formed films, -;
if any, on the glass ribbon 48. Due to the disposition of the
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respective vacuum sources 91 and 96 of the coaters, the precursor ~ ~-
emitted from the outlet nozzle 94 is deposited on the moving -
ribbon of glass, and any of the precursor which does not deposit ~ -
25 on the ribbon is caused to flow either upstream of the glass -
ribbon 48 and be removed from the surface thereof by the vacuum
source 91, or downstream with the glass ribbon 48 and be removed
therefrom by the vacuum source 96. In the manner explained, a
zone of precursor fluid is maintained over the glass ribbon 48 ~
30 under both of the sources of precursor fluid 86 and 86'. By -;
controlling the speed of the glass ribbon 48, the temperature
within the chamber 70, the quantity of precursor emitted from the
coaters 86 and 86', and/or the associated vacuum sources 91 and -
96, the thickness of the deposited layers of the precursors may be
35 controlled. ~.
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It will be appreciated that the process and apparatus herein
described are useful in the manufacture of coated glass for
various purposes. Of particular importance are coatings designed
to reduce the emissivity of coated glass in respect of infrared
radiation and those designed to reduce total energy transmissivity
of coated glass in respect of solar radiation. .
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