CA1071938A

CA1071938A - Method and apparatus for forming metal oxide coating on the surface of glass sheet

Info

Publication number: CA1071938A
Application number: CA231,023A
Authority: CA
Inventors: Katsuji Fujimoto; Hideo Mitsuno
Original assignee: Nippon Sheet Glass Co Ltd
Current assignee: Nippon Sheet Glass Co Ltd
Priority date: 1974-07-10
Filing date: 1975-07-09
Publication date: 1980-02-19
Also published as: DK311075A; CH597104A5; AT343844B; NO141751C; SE7507877L; NO141751B; AU8261275A; DE2530630C2; GB1480546A; SE398227B; FR2277785B1; NL7508161A; IT1039654B; ATA529475A; NO752463L; DK140693B; BR7504312A; ES439256A1; BE831174A; DK140693C

Abstract

ABSTRACT OF THE DISCLOSURE
A method for forming a metal oxide coating on the surface of a moving glass sheet by spraying onto the surface a solution of a heat-decomposable metal oxide wherein the amount of the solution to be sprayed is restricted at positions near both side ends of the glass sheet so as to provide a uniform coating thickness in apparatus for performing the above method is also provided which comprises a combination of a mechanism for detecting the position of a travelling spray gun and a mechanism for restricting the amount of the solution to be sprayed.

Description

~V~93~

This invention relates to a novel method ~or ~orming a coating of a metal oxide on the sur~ace o~ a glass sheet by heat deco~position, and an apparatus therefor in order to impart electric conductivity to the glass surface or to improve its optical properties.
As is wel.l known, -the heat decomposition method provides a coating of a ~etal oxide by adhering a metal compound convertible to the metal oxide by hea-t decomposition to the surface of a glass sheet kept at a temperature above the heat decomposition temperature o~ the metal compound.
Generally, the metal compound is d~ssolved in a ~uit;able solvent9 and the solu-tion is sprayed onto the glass sur~ace or the glass is immersed in the solution.
One procedure ~or treating glass sheet in -the ~bove manner involves spraying the metal compound solution to the glass surface be~ore the glass sheet fo~ned in a continuous ribbon in a forming apparatus enters a lehr, or while the temperature o~ the glass in the lehr is still sufficiently high (more than 550C.).
It has been the conventional practice to move a spray gun jetting out the metal compound solu-tion reciprocally in the widthwise direc-tion o~ the glass sheet abo~e the continuously moving glass shee-t, and thus to spray the solution to the entire sur~ace of the glass sheet. However, the conventional method suffers from the following dis-advantages ~hen the moving direction o~ the spray gun changes near both ends of the glass sheet, the spray gun stops momentarily (~or example, ~or about 0~2 second), but . .
the solution is still being jetted out during the stoppage '~ ....

2 - ~

1~7193 Accordingly, a larger amount of the solu-tion is sprayed onto both side ends o~ the glass sheet at w~ich the gun stops than onto the central portion of the glass sheet in its widthwise direction. Furthermore, the solution sprayed from the stopping gun scatters over a considerably wide range, and consequently, a thicker coating is ~ormed on both side end portions o~ the glass sheet than on the ;~
central part. Naturally, there~ore, the effective width over which a coating of uniform -thickness is fo~ed is 10 considerably smaller than the stroke of the spray g~.- ;
It may be thought that in order to increase the effective ~ wid-th, it would be feas~ble to increase the ~ of -the t ~ spray gun to the width of the glass sheet or lar~er. Such an idea, however, cannot avoid the serious de~ect that the sprayed solution markedly contaminates the glass sheet-conveying rolls and their vicinity at a part near the ends o~ the width of the glass sheet, and is therefore infeasible.
Moreover J in the method involving the spraying o~ the metal compound solution, the solvent (mainly, an organic solvent) wh.ich constitutes a grea-ter part of the solution, and a par-t oP the metal compound are gasified on th0 surface o~ the glass sheet main-tained at a high -temperature, and become noxious exhaust gases. In order ~
to remove these exhaust gases, a suction duct is provided ~ - - -near the moving path of the spray ~un. Furthermore~ in the conventiona~ appara-tus shown in Figure 5~ a side 3uction duct 21 is disposed also above bo-th ends of glass sheet l so that the ducts can suck and remove great amounts of e~aust gases generated ~rom -the sprayed solution jetted out from ,, " .

. :.. . . ' .: .............. . :
.

~ 0 ~ ~ 9 38 spray gun 6 at halt. In view of the arrangement of the side suction ducts 21, the stroke of the spray gun 6 cannot be increased.
When the stroke of the spray gun 6 is increased, the sprayed solution at the stroke end adheres to the side suction ducts 21, and drops onto the glass sheet 1. Since the gun 6 is near the duct 21, a splash of the sprayed solution leaks outside through beneath the duct 21 to cause environmental pollution. From this standpoint, too, the stroke of the spray gun 6 cannot be increased.
The maximum effective width over which a coating of uniform thick-ness can be formed is about 30 inches smaller than the stroke of the spraygun, and the current practice is to cut off large portions of both sides of the glass sheet, and therefore, in order to obtain a sheet glass with a coating of the desired width, the original glass sheet should have a consider-ably large width, and the yield obtainable is low.
Accordingly, it would be advantageous if the effective width over which a uniform coating can be formed is increased, and the sprayed solution can be utilized economically.
Accordingly, the present invention provides a method for forming a metal oxide coating on a surface of a glass sheet continuously moving at a ~0 constant speed and held at a high temperature by spraying onto the surface of the glass sheet a solution comprising at least one metal compouncl con-vertible to a metal oxide upon heat decomposition, by means of a spray gun moving reciprocally at a substantially constant speed in a direction substantially crossing the moving direGtion of the glass sheet, characterized in that the amount of solution being sprayed in the central part of the re-ciprocating path is kept at a substantially cons~ant amount and the amount of solution being sprayed in the vicinity of each extreme end of the recipro-cating path is restricted with respect to said constant amount by diverting at least a part of the flow of solution to the spray gun into a flow path separ~te from the ~low path to the spray gun so as to prevent ~xcessive metal oxide build-up on the ends of the surface of the glass sheet and to produce a glass sheet having a metal oxide film of uDiform thickness coated in the ,~,d".~ :
.... . :. .: ..

~ 3 8 ~ :

surface thereof.
In order to perform the method of this invention, there is provided :
an apparatus for forming a coating of a metal oxide on the surface of a glass sheet, which comprises a means for continuously advancing a glass sheet kept .. .. .
at a high temperature; at least one spray gun disposed above the surface of -.
said glass sheet and containing a jet nozzle for spraying a solution compris- .. -. .
ing at least one metal compound onto the surface of the glass sheet; means for reciprocating said spray gun in a direction crossing the advancing direction of said glass sheet; means for feeding said metal compound solution under pressure steadily into said spray gun; a three-way valve attached to said spray gun for restricting the amount of the spray solution in order to change the amount of the spray solution between a first sta.te in which all tho solut:ion -eed to the spray gun is jetted out from said nozzle and a sccond stato in which the amount of the spray solution fed to the spray gun is restricted and the non-sprayed solution is conducted to a flow path separate from a path to the jet nozzle a detection-operation mechanism for detecting the arrival of said spray gun at a predetermined position in the vicinity of each extreme end of the reciprocating path away from the central ~:
part to each extreme end and operating said three-way valve on the basis of . .:this detection thereby to effect the change from the first state to the :.
socond state, and for detecting the departure of the spray gun from said predetermined position to the central part of the reciprocating path and .
operating said three-way valve on the basis of this detection thereby to effect the change from the second state to the first state.

.

10'~193~3 Figures 1 to 4 of the accompanying drawings illustra~e one embodiment o~ the apparatus for performing the method of this invention. Figure 1 is a front elevation of the entire apparatus; Figure 2 is a schematic side elevation thereof; Figure 3 is an enlarged side elevation of the principal part of *he apparatus; and Figure 4 is an enlarged top plan of the principal parts of the apparatus. Figure 5 is a schematic front elevation of the conventional apparatus.
One preferred embodiment of the present invention will be described in detail with reference to the accompany-ing drawings.
Referring to Figure 2, a ribbon-like glass sheet 1 withdrawn continuously from a Eloat-type plate glass form-ing apparatus (not shown) is delivered to a lehr by means of conveyor rolls 2. While the glass sheet 1 passes over the conveyor rolls 2, a solution of a metal compound is sprayed onto the upper surface of the glass sheet.
Above the conveyor rolls 2, a beam 3 riding over the advancing path of the glass sheet 1 is provided. A solution spraying device ~ is mounted on the beam 3 so that it can reciprocate sideways along the beam 3 while it is pulled by a chain 5. A pair of spray guns 6 spaced from each other at a suitable distance in the advancing direction of the glass f~ : .
. ~;

1 ~ 7 ~ 9 3 8 sheet e~tend from the spray device ~ to a poin-t near the upper surface of the sheet glass 1. A suction duct 20 is provided on bo~h sides of the moving path of spray guns 6 to suck and remove noxious exhaust gases.
As is shown in Figure 3, each of the spray guns is composed of a feed pipe 7 for the metal compound solution and a feed pipe 8 for pressurized air in a double tube fashion, and a jet nozzle 9 for the solution at its lower end. Solution feed openings 10 are opened at the upper ends of the solution feed pipes 7 of the spray guns, and the upper ends of the two air feed pipes ~ are connected . .
to each other to form a common air feed opening 11.
At the upper part of each of the solution feed pipes 7, a three-way valve 13 for restricting the .amoun~.of the spray is provided which can change ~he amount .
of the metal compound solution to be sprayed from the first state to the second state, or from the second state to the .
first state. .~ :
The first state,.referred to herein, denotes . :
the state in which all the solution.fed into the feed pipes 7 is conveyed to the nozzle 9, and therefore, all the :.
solution fed is jetted out from the nozzle 9. The second state, referred to herein, denotes the state in which the ~:.
flowing of the solution fed into the feed pipes 7 to the :
nozzle 9 is res*ricted, and either a part of the solution is ..
conveyed to the nozzle 9 or the solution is not at all . .
conveyed to the nozzle 9, and any remainder of the solution is sent to a return pipe 12 thereby to restrict the amount of the solution to be jetted out from the nozzle 9.

.

9~8 In the preferred embodiment of ihe present invention, the second state is one in which the total amount of the solution fed into the solution feed pipes 7 is sant to the return pipe 12, and no solution is jetted out from the nozzle g.
The change of the amount of spray jet from the nozzle is performed by means of the three-way valve 13 utilizing the oscillating motion bf a lever 14. On both side ends of the beam 3, a plate-like stopper 15 having a suitable length in the moving direction A of the spray gun is disposed abuttably against ` ` `the lever 14. When the lever 14 is released from the stopper 15, the above-mentioned first state is realized.
When the lever 14 abuts against the stopper 15, the irst state is changed to the second state. This is shown in Figure 4.
The stopper 15 is securred to a bracket 1~ which is screwed into a screw shaft 16 supported in parallel to the moving direction of the spray gun and anchored by projections 18 of an auxiliary frame 17. By the manual rotating operation of the screw shaft 16, the stopper 15 can be adjusted at a predetermined position by screwing in the moving direction of *he spray gun.
Now, the operation of the apparatus of this -invention will be described in detail. Simultaneously with the delivering of the glass sheet 1, the solution ~ 9 ~

spraying device 4 is reciprocated in the widthwise direction of the sheet glass at a suitable speed corresponding to the speed of the sheet glass. During this time, the metal compound soluiion and pressurized air are fed respectively from the feed openings 10 and 11, and the solutlon is sprayed ~the first state) from the noæzles 9 of the spray guns 6 against the high tempera-ture glass sheet utilizing the pressurized air. The metal compound of the solution sprayed onto the high temperature glass decomposes by heat to become a coating of a metal oxide on the glass sheet. A part of the solvent and the metal compound is gasified to form exhaust gases which are then removed ~hrough the suction ducts 20.
When the spray gUIlS 6 reach a point near the upper part of the side ends of the glass sheet 1, the lever 14 of the three-way valve 13 abuts the stopper 15 which has been adjusted in advance as to its position.
Ihus, the three-way valve 13 operates and the amount of the spray jet from the nozzles 9 changes to the second state.
All the fed solution is let away through the return pipes 12, and collected at a pressurized solution feeding section (not shown). Accordingly, the spraying of the solution from the nozzles 9 is stopped momentarily.
When the advancing direction of the spray guns 6 changes and the l-ever 14 of the restricting mechanism 13 is disengaged from the stopper 15, the restricting mechanism 13 operates to change the amount of the spray jet from the nozzles 9 to the first state, and all the solution is again flowed through the nozzles 9 and sprayed against the glass surface.
The above operation is repeated at both side ends of the glass sheet 1, and the spraying of the solution by the spray gun 6 is effected substantially only over the width of the glass sheet. At both side ends, the spraying is momentarily stopped, and no excessive solution is sprayed against the glass sheet.
In operating the apparatus of the above construction, the following considerations should be given.
(1) Desirably, the distance between the three~way valve 13 and the nozzle 9 is as short as possible.
If the distance from the three-way valve 13 to the nozzle 9 is large, the solution in the flow path from the three-way valve 13 to the nozzle 9 still flows out even when the supply of the solution toward the nozzle 9 is interrupted at the three-way valve 13. This results in a delay in the complete stoppage of the spraying. Especially when the speed of the spray gun 6 is considerably high, the stopping of spraying requires extreme rapidity. For example, when the moving speed of the spray gun is 2 meterlsec., the precision oE the timing of the spray stopping must be adjusted to about 0.1 sec.
If, on the other hand, the three-way valve 13 is caused to approach too near the nozzle 9, there is a likelihood~ ~ -that the three-way valve 13 itself is damaged, for example~ by the heat of radiation from the high tempera-ture glass, or the metal compound coagulates within the mechanism by the action of heat, thereby causing troubles to the three-way valve 13.
Accordingly, the distance between the three-way valve 13 and the - 1 0 - ' " ' ~7 .

.

10~19~

.
glass sheet 1 musl be determined appropriately.
(2) The three-way valve 13 must be adapted ~ .
to maintain the flow of the solution even during its opera-tion. . .
In order to effect uniform spraying, the solution is automatically controlled so that its amount of feed is al~ays constant. Thus, when the flow of the solution is .~
impeded even momen-tarily, the flow amount of the solution :.
varies abruptly upon the interruption or resumption of the : .
flowing of the solution, and accordingly the automatic : ~:
control of the flow rate at a predetermined value becomes ..
impossible. Accordingly, a device which merely impedes the flow of the solution, suc}l as a shut-of:E valve, cannot be used in place of the three-way valve 13.
~3) When the first state should be changed to the second state with regard to the position of the spray gun cannot bedetermined in general terms because it differs depending upon variables such as the advancing speed of the glass sheet, the moving speed of the spray gun or the amount of the solution to be fed to the feed pipe. However, once the operating conditions have been set, those skilled in the art can easily detect, for example, by a preliminary experiment, the best position of the spray gun near both side ends of the.glass sheet 1 which will provide a substantially uniform coating of a metal oxide on the surface of the sheet glass if the change From the first state to the second state is effected when the spray gun :.:
stays at that position. Thus, the position of the spray gun . .
for effecting this change should be determined on the above ""'.

r~~`?
: ' ~7~33i3 standard.
For example, when a glass sheet having a width of ~ -145 inches advances at a rate of 200 inches/min. 9 the spray gun moves at a rate of 4080 inches/min., and the amount of the solution to be fed is 1000 cc/min., the maximum effective width can be obtained by changing the amount of the solution from the first state to the second state when the spray gun has reached a position within 5 to 10 inches from the side end of the glass sheet.
(4) The metal compound used in this invention may generally be any metal compounds which decompose to metal oxides when heated and adhere to glass. Examples of suitable metal compounds are ~diketone salts, alkoxy compounds~ and alk~l compounds of cobalt~ iron, chromium~
nickel, tin, titanium, manganese, calcium, and magnesium.
The acetyl acetonato complex salts of the above metals are especially preferred. The solvent used to form solutions of the above metal compounds may be any solvents which dissolve the above metal compounds. Generally, methanol, butanol, isopropanol, benzene, toluene~ and heptane are used~
Since excessive spraying does not take place at both ends of the solution sprayed width in the above-described treatment, the sprayed width substantially becomes an effective width, and a substantial amount of the solution which would be wasted at both ends of the sprayed width according to the conventional techniques can now be saved.
For example, in order to obtain an effective width of 100 inches, a sprayed width of 130 inches is required accorcling to the conventional apparatus, whereas according to the - 12 _ ~ 8 apparatus of the present invention, the sprayed width can be 100 inches. Thus, in order to obtain the same effective width, the amount of the solution required in accordance with the apparatus of this invention is only about 78% of that required in the conventional apparatus, thus providing a saving of 22%.
Since there is no excessive spraying of the solution, the rolls 2 and their vicinity are not contaminated.
Thus, the sprayed width can be substantially equal to the width of the glass sheet, and the effective width can be a maximum with regard to the starting glass sheet. Further-more, because the sprayed width can be changed by adjusting the position of the stopper, the eEfect:ive width can be set optionally. Por example, when it is desired to obtain a glass sheet having a small effective width, the speed of withdrawing the glass from a float glass forming apparatus is increased to reduce the width of the glass sheet and the sprayed width. This gives rise to increased productivity corresponding to the increase of the speed of withdrawing the glass sheet.
When the lever 1~ of the three-way valve 13 contacts the stopper lS, the spraying is stopped. Accordingly, the stroke of the spray gun 6 can be made equal to, or larger than, the width of the glass sheet.
Since the spraying of the solution stops at both ends of the sprayed width, the generation of exhaust gases ;~
at this part is reduced, and it is not particularly necessary to provide side suction ducts. Even when such a side duct i.s required, it may be of a small size with a reduced amount ~ -~`'1 ' :'"' . .

~ 07~L~338 of air suction. The stroke of the spray gun can thus be increased accordingly, and the sprayed width can also be increased.
In the preferred embodiment of the present inven-tion described in detail above, the jetting of the solution from the nozzle 9 is completely shut off at both ends of the sprayed width. If desired, the amount of spray can be merely reduced instead of completely shutting off the spraying from the nozzle 9, and the excessive feed can be let away through the return pipe 12.
The method of this invention has the following advantages over the prior art.
~1) Since the excessive sparying is prevented by restricting the spraying of the sOlueion at predetenmined positions on both side ends of the sprayed widthl the sprayed width can substantially become an effective width over whirh a uniform coating is formed. Coated glass sheets can be obtained in good yields by increasing the stroke of the spray gun to the width of the glass sheet or greater~
and thus increasing the effective width to nearly the entire width of the glass sheet.
(2) Since the excessive spraying at both ends of -the sprayed width is restricted, the solution can be saved correspondingly. The amount of the solution per unit effec-tive width can be reduced, and the cost of treatment can be curtailed.
When the method of this invention is performed by the apparatus of this invention, the following adv~ntages are further exhibited.

~07193~

(1) When the spraying of the solution from the spray guns is restricted ae both ends of the sprayed width, the restricted solution is let away through a separate flow path. Thus, the solution is continuously fed in a steady state even when the restriction of spraying is effected.
Thus, when the spraying is resumed, the original steady spraying state can be instantaneously caused by a simple switch-over of the flow path without involving any great change in the flow rate. As a result, the flow rate of the feed solution can be easily controlled~ and uniform spraying can be performed over the entire sprayed width whlle the amount of the feed solution is being maintained always constant.
(2) As the excessive feed solution resulting from the restriction of the amount of spray is let away through a separate flow path, this solution can be re-utilized.
This brings about an overall increase ln the efficiency of utilizing the spray solution.

_ 15 ~

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method for forming a metal oxide coating on a surface of a glass sheet continuously moving at a constant speed and held at a high temperature by spraying onto the surface of the glass sheet a solution comprising at least one metal compound convertible to a metal oxide upon heat decomposition, by means of a spray gun moving reciprocally at a sub-stantially constant speed in a direction substantially crossing the moving direction of the glass sheet, characterized in that the amount of solution being sprayed in the central part of the reciprocating path is kept at a substantially constant amount and the amount of solution being sprayed in the vicinity of each extreme end of the reciprocating path is restricted with respect to said constant amount by diverting at least a part of the flow of solution to the spray gun into a flow path separate from the flow path to the spray gun so as to prevent excessive metal oxide build-up on the ends of the surface of the glass sheet and to produce a glass sheet having a metal oxide film of uniform thickness coated in the surface there-of.

2. The method of claim 1, wherein the spraying of the solution from the spray gun is stopped in the vicinity of each extreme end of the reciprocating path.

3. An apparatus for performing the method as defined in claim 1, which comprises a means for continuously advancing a glass sheet kept at a high temperature; at least one spray gun disposed above the surface of said glass sheet and containing a jet nozzle for spraying a solution comprising at least one metal compound onto the surface of the glass sheet; means for reciprocating said spray gun in a direction crossing the advancing direction of said glass sheet; means for feeding said metal compound solution under pressure steadily into said spray gun; a three-way valve attached to said spray gun for restricting the amount of the spray solution in order to change the amount of the spray solution between a first state in which all the solution fed to the spray gun is jetted out from said nozzle and a second state in which the amount of the spray solution fed to the spray gun is restricted and the non-sprayed solution is conducted to a flow path separate from a path to the jet nozzle; a detection-operation mechanism for detecting the arrival of said spray gun at a predetermined position in the vicinity of each extreme end of the reciprocating path away from the central part to each extreme end and operating said three-way valve on the basis of this detection thereby to effect the change from the first state to the second state, and for detecting the departure of the spray gun from said predetermined position to the central part of the reciprocating path and operating said three-way valve on the basis of this detection thereby to effect the change from the second state to the first state.

4. The apparatus of claim 3 wherein said detection-operation mechanism is provided movable in the widthwise direction of the glass sheet, and wherein said three-way valve effects the change to the first state when its switch-over lever departs from said detection-operation mechanism, and it effects the change to the second state when the switch-over lever abuts said detection-operation mechanism.

5. The apparatus of claim 3 wherein said spray gun consists of a feed pipe for said metal compound solution and a feed pipe for pressurized air.

6. The apparatus of claim 3 wherein a suction duct is provided near the moving path of said spray gun.