DE102007009495A1 - Production of flat glass, especially thin film transistor glass, by float process uses dross box, into which inert gas is fed so that it is at higher pressure than that in the float bath chamber - Google Patents

Abstract

Production of flat glass, especially thin film transistor glass, by the float process uses a dross box (10), into which an inert gas is fed so that it is at a higher pressure than that in the float bath chamber (1). Independent claims are included for: (A) dross boxes for use in the process which are fitted with one or more injectors (21) for gas; and (B) float bath units fitted with the dross box.

Description

The Invention relates to a process for the production of flat glass, in particular of TFT glass, according to the preamble of claim 1. Furthermore, the invention relates to a Drossbox and a Floatbadvorrichtung.

The production of flat glass by the float process, known as float glass, has been known since the last century and is essentially based on the fundamental intellectual property rights of Pilkington ( US 3,083,551 . DE 147 19 50 ).

At the Float method is allowed to liquid glass, which means a gutter is brought from the work tub on a bath of molten metal, generally tin flow. The flow rate of the glass is via a movable slide, with its adjustment, among other things, the glass thickness is set. In the direction of flow of the glass seen behind the Slider is the pouring lip, from which the molten glass flowing continuously to the metal bath where the molten glass is formed into a dimensionally stable glass ribbon and solidifies. Subsequently, the solidified glass ribbon from the metal bath away. For this purpose, behind the float bath tub is a lifting device arranged.

The Float glasses made in this way usually have a thickness of less than 1.5 mm used as a thin glass substrate among other things for the production of flat screens, z. B. of plasma screens (PDP = plasma Display Panel), field emission screens (FED = Field Emission Display), TFT Liquid Crystal Displays (TFT = Thin Film Transistor), STN Liquid Crystal Displays (STN = Super Twisted Nematic), Plasma Assisted Liquid Crystal Displays (PALC = plasma assisted liquid crystal), electro-luminescence displays (EL) and the like or for the production of thin-film solar cells.

at The flat screens will vary depending on the type of display two glass panes either a thin layer of a liquid crystal compound introduced or it will be on the front and back of the rear or front disc respectively applied dielectric layers from which cells are formed in which phosphors are housed.

It Here it is important that the layer thickness of the liquid crystal layer or the thickness of the dielectric layer is strictly adhered to, so especially with large dimensions of a screen no disturbing color distortions or similarity deviations occur. Since the layer thicknesses, currently about 30 microns, always smaller and the screens are getting bigger, This condition is becoming increasingly important.

Even though Float glass due to its fire polished surface excellent is suitable for display applications, it is with these days required large substrate formats with edge lengths from above 1800 mm not yet possible, display glass after the float process whose thickness differences under 50 um.

The Floatbadvorrichtung essentially comprises the Floatbadwanne with Bottom wall and tub side walls in which the molten Metal is located, the Floatbaddach (Roof) and the side walls (Side ceilings), which are attached to the roof. Between the sidewalls of the roof and the sides of the bath are side wall boxes with openings provided, z. B. for performing top scooters.

The Floatbadvorrichtung thus has a box-shaped Floatbadgehäuse which stands in a production hall. Before the float bath device are other facilities for the production of molten glass and behind the Floatbadvorrichtung are facilities for processing arranged the produced glass ribbon.

the Floatbadgehäuse is the so-called Drossbox downstream, the device for lifting the glass ribbon from the float bath having. This device for lifting the glass ribbon comprises usually rollers for horizontal transport of the glass ribbon, the Also referred to as a lift-out scooter. Furthermore, this Drossbox serves also as a lock chamber, because the discharge opening of the Floatbadgehäuses at the same time the entrance opening the throttle box is.

at the known Floatbadvorrichtungen is in the Floatbadkammer a Forming gas, which usually consists of nitrogen and hydrogen, introduced. In the Floatbadkammer is by continuous gas supply with a predetermined throughput maintained an overpressure, to an influx of oxygen-containing gas from the outside to prevent in the Floatbadkammer. Oxygen in the float bath housing leads to Zinnoxidationen with considerable disadvantages for the surface quality of the glass ribbon to be produced.

Due to the overpressure in the Floatbadkammer the forming gas flows, inter alia, through the discharge in Floatbadgehäuse in the Drossbox. In order to avoid gas losses, various solutions have been developed in the past to seal the discharge opening. The DE-OS 27 16 174 . DE-PS 18 04 295 and the DE-OS 1 909 921 , which represent only a selection of a variety of fonts, deal with appropriate Abdichtmaßnahmen in the region of the discharge, z. B. in the form of curtains.

For additional sealing it is from the GB 1,017,713 it is known to arrange a tube at the lower end of the dividing wall between the float bath and the Drossbox, from which protective gas flows onto the glass ribbon and subsequently in the feed direction of the glass ribbon.

The Outflow of Formiergas from the Floatbadgehäuse in the Drossbox has the further disadvantage that in the Formiergasatmosphere located tin and tin oxide containing Particles because of the large distance to be covered increased to the discharge opening on the glass ribbon surface can knock down where they have surface defects cause. To an outflow of Formiergasatmosphäre over At least reducing the Drossbox are in the sidewalls the Floatbadgehäuses exhaust pipes (so-called venting-out facilities) attached, over which the Formiergasatmosphäre is sucked in a controlled manner. This ensures, on the one hand, that the tin, which is in the forming gas atmosphere, and tin oxide particles are detected early and removed and on the other hand, the gas content that is above the discharge openings into the Drossbox, reduced. Here, the supplied Gas quantity and the extracted gas volume are consistent, so that the desired overpressure within the Floatbadgehäuses is guaranteed. Gas losses via the Drossbox are still inevitable and can not be complete be prevented.

task The invention therefore relates to a process for the production of flat glass to provide with which the surface defects of the glass ribbon should be reduced. It is also task a corresponding Specify Drossbox and a Floatbadvorrichtung.

These The object is achieved by a method for producing flat glass, in which in the Drossbox an inert gas-containing, oxygen-free gas introduced and overpressure in the Drossbox the atmosphere in Floatbadgehäuse set becomes.

through the inert gas-containing gas with overpressure opposite the Floatbadgehäuse is the outflow of Formiergasatmosphäre from the Floatbadgehäuse at least reduced, whereby the Formiergasatmosphäre primarily over the provided in Floatbadgehäuse Suction (venting-out device) is sucked. Harmful particles such as tin or tin oxide particles that are in the float bath atmosphere can accumulate when using a tin bath Accordingly, only a short time in the atmosphere and are therefore removed faster. The glass band quality is significantly improved by this measure.

While so far about 60% of the Floatbadatmosphäre in the Drossbox reached, this value could be reduced to about half become.

One Another advantage is that no sealing measures to Floatbadgehäuse and the Drossbox are required.

Preferably in the Drossbox a pressure is set, which is around 0.03 mbar to 0.06 mbar above the atmospheric pressure of the Floatbadgehäuses lies. In particular, a pressure is set which is around 0.04 to 0.05 mbar above the atmospheric pressure of the Floatbadgehäuses lies.

It has shown that a slight overpressure is sufficient to the proportion of Floatbadatmosphäre, the over the Drossbox flows out, on under half of To reduce the amount that usually flows out. The surface defects of the glass ribbon go in the same way Dimensions back.

The upper limit of 0.06 mbar overpressure compared to the float bath atmosphere should preferably not be exceeded, so that not too much inert gas-containing gas flows into the Floatbadgehäuse, in particular, if this is pure nitrogen. The Formiergasatmosphäre located in Floatbadgehäuse usually has a hydrogen content of about 12 to 15 vol.%, Which is necessary for the reduction of the oxygen in the Floatbadatmosphäre. Although there is no danger that the surface of the glass ribbon is affected by the influx of gas from the Drossbox in the Floatbadkammer, because this gas contains no harmful particles, but on the other hand, by the incoming gas, in particular when it is pure nitrogen, the H ₂ content is reduced, so that the proportion of bound oxygen also decreases.

It has been shown to be at an overpressure under the Value of 0.06 mbar, this effect is negligible is.

Preferably different overpressures are set in at least two zones of the Drossbox. In this case, it is preferable to face in the float bath housing Zone of Drossbox the biggest overpressure adjust.

The zones of the Drossbox are preferably separated by curtains above the rollers. If multiple zones are provided, the overpressure will change from zone to zone, starting with the Zone adjacent to the float bath tub, gradually reduced. The gas consumption is reduced by this measure.

each Inert gas is suitable for introduction into the Drossbox. Nitrogen is preferred because of its good availability.

Preferably a gas mixture is introduced, consisting of nitrogen and hydrogen consists. The addition of hydrogen has the advantage that eventually into the Drossbox penetrating oxygen is bound to water, which then evaporates within the Drossbox.

Preferably, the composition of this gas mixture corresponds to the forming gas, which is also introduced into the Floatbadgehäuse. Accordingly, the hydrogen content is preferably less than 20% by volume. Such a gas mixture flowing into the float bath housing has the advantage that the H ₂ content in the float bath housing is not reduced.

Preferably, 200 m ³ (i.N.) / h to 400 m ³ (i.N.) / h of gas are introduced into the Drossbox. Particularly preferred is a gas amount of 250 m ³ (i.N.) / h to 350 m ³ (i.N) / h.

The m ³ (i.N) designation denotes a standard cubic meter, which is specified in DIN 1343. A standard cubic meter is the quantity corresponding to one cubic meter of gas at a pressure of 1.01325 bar, a relative humidity of 0% (dry gas) and a temperature of 0 ° C.

Preferably is set to a temperature of 600 ° C to 700 ° C heated gas introduced. The preheating has the advantage that by the contact with the gas in the glass ribbon no Tensions arise due to temperature differences and the Glass does not break. In this respect, it is advantageous the gas temperature to match the glass ribbon temperature within the Drossbox.

One Another advantage is that at these temperatures the gas volume is several times greater than the gas volume increased at 0 ° C, allowing for generation the desired overpressure only one accordingly small amount of gas is needed.

For the cooling of the outlet area of the float bath housing, in particular, the exit lip at the end of the float bath tub is preferably also used a gas. This gas heats up in the Usually at 150 ° -200 ° C. This gas can for the introduction of the Drossbox be used. Possibly. becomes the gas preheated before discharging when the recirculated Gas does not have the required temperature. In this way it is possible to save corresponding amounts of gas.

The Process is particularly suitable for the production of Borosilicate glasses, alkali-free glasses, aluminosilicate glasses, Alumolithiumsilikatgläsern and precursor glasses for glass ceramic.

Particularly suitable is the method for producing borosilicate glass, z. For fire protection applications, having a composition of (all of the following in terms of weight percent based on oxide):
SiO ₂ 70-85, B ₂ O ₃ 7-13, Na ₂ O + K ₂ O + Li ₂ O 3-8, MgO + CaO + SrO 0-3, Al ₂ O ₃ 2-7,
for the preparation of alkali-free alumino (boro) silicate glass with a composition of
SiO ₂ 50-70, B ₂ O ₃ ≤15, Al ₂ O ₃ 10-25, MgO 0-10, CaO 0-12, SrO 0-12, BaO 0-15, with MgO + CaO + SiO + BaO 8 -26, ZnO 0-10, ZrO ₂ 0-5, TiO ₂ 0-5, SnO ₂ 0-2,
z. B. for the production of display glass, in particular with a composition of
SiO ₂ > 55-65, B ₂ O ₃ 5-11, Al ₂ O ₃ > 14-25, MgO 0-8, CaO 0-8, SrO 0-8, BaO ≤ 10 with MgO + CaO + SrO + BaO 8-21, ZnO 0-5, ZrO ₂ 0-2, TiO ₂ 0-3, SnO ₂ 0-2,
in particular SiO ₂ > 58-65, B ₂ O ₃ > 6-10.5, Al ₂ O ₃ > 14-25, MgO 0 - <3, CaO 0-9, BaO> 3-8 with MgO + CaO + BaO 8-18, ZnO 0 - <2, As ₂ O ₃ -free, Sb ₂ O ₃ -free,
preferably Zn oxide, Ce oxide, Zr oxide, Ti oxide free

It is also particularly suitable for the production of various green glasses for glass-ceramic, such. B. with
SiO ₂ 55-69, Al ₂ O ₃ 19-25, Li ₂ O 3-5, Na ₂ O 0-1.5, K ₂ O 0-1.5, Σ Na ₂ O + K ₂ O 0.2 -2, MgO 0.1-2.2, CaO 0-15, SrO 0-1.5, BaO 0-2.5, Σ MgO + CaO + SrO + BaO below 6, ZnO 0-1.5, TiO ₂ 1-5, ZrO ₂ 1-2.5, SnO ₂ 0 to less than 1, Σ TiO ₂ + SrO + SnO _{2 2} 2.5-5, P ₂ O ₅ 0-3
or a glass-ceramic precursor glass having a composition of
SiO ₂ 55-75, Al ₂ O ₃ 15-30, Li ₂ O 2.5-6, Σ Na ₂ O + K ₂ O less than 6, Σ MgO + CaO + SrO + BaO less than 6, B ₂ O ₃ 0 to less than 4, ΣTiO ₂ + ZrO ₂ less than 2
or a glass-ceramic precursor glass having a composition of
SiO ₂ 60-72, Al ₂ O ₃ 18-28, Li ₂ O 3-6, Σ Na ₂ O + K ₂ O 0.2-2, Σ MgO + CaO + SrO + BaO less than 6, ZnO 0-1 , 5, B ₂ O ₃ 0 to less than 4, SnO 0.1-1.5, ΣTiO ₂ + ZrO ₂ less than 2, P ₂ O ₅ 0-3, F 0-2.

The Task is also solved by a Drossbox, which thereby characterized in that means for introducing a gas is provided, which arranged at least one in the interior of the Drossbox Gas injector and a gas supply device comprises, to the the gas injector is connected.

The gas delivery rate of the gas introduction device is preferably 200-400 m ³ (I.N.). This is si ensured that in the Drossbox the desired pressure in the order of 0.03 mbar to 0.06 mbar compared to the Floatbadatmosphäre can be adjusted.

Preferably is at least in the upper housing part of the Drossbox in space at least one gas injector is arranged above the rollers. If the Room in the upper housing part is divided into zones is at least in the zone that neighbors the float bath enclosure is arranged at least one gas injector.

According to one Another embodiment can also in the lower housing part at least in the space between the rollers at least one gas injector be arranged. Preferably, by the in the lower housing part arranged gas injectors pure nitrogen introduced what the Advantage is that the scrapers of the rollers are spared. The Presence of hydrogen in this area has the disadvantage that the scrapers, which are usually made of graphite, due can burn off the high temperatures. In that sense will by introducing nitrogenous or pure nitrogen gas also introduced a protective gas for the scrapers.

Of the Gas injector includes a parallel to the rollers extending Pipe with gas outlet openings. This tube is in the Usually mounted in the side wall of the Drossbox and out there, where the connection to the gas supply device takes place.

Preferably both pipe ends are connected to the gas supply device. This means that the tubes are over the entire width of the Drossbox from one side wall to the opposite side wall extend. In that the introduction from both sides into the Pipe takes place, the incoming gas is more uniform distributed in the Drossbox. It is advantageous if the tube in divided into two chambers. The symmetrical introduction of the gas in the Drossbox is thereby further improved.

The Gas inlet device is preferably to a gas heating device connected to the gas to the desired temperature to be able to bring, so that no tension in the glass ribbon occur can.

Preferably the gas heating device comprises a cooling device the end Floatbadwand. In this cooling device, is introduced into the likewise inert gas-containing gas, the Gas is heated due to the cooling effect and can thus again be used for the introduction into the Drossbox. As the temperature of the leaving the cooling device Gas is around 150-200 ° C, it is recommended that this already preheated gas another gas heater feed to the desired temperature of 700-800 ° C to reach.

The object is also achieved with a float bath apparatus comprising a float bath housing and a downstream Drossbox, wherein in the Floatbadgehäuse an atmospheric pressure P _F and in the Drossbox an atmospheric pressure P _D prevails, where P _D > P _F. Preferably, the atmospheric pressure P _D is 0.03 to 0.06 mbar above the atmospheric pressure P _F within the Floatbadgehäuses.

exemplary Embodiments of the invention are described below explained in more detail in the drawings. Show it:

1 a section through a Floatbadgehäuse and a Drossbox,

2 a section along the line II-II through the in 1 shown throttle box,

3 an enlarged view of the transition region between Floatbadwanne and Drossbox and

4 a plan view of the in the 3 shown cooling device with utilities.

In the 1 is a float bath housing 1 shown schematically, in which a Floatbadkammer 2 is arranged. Inside the float bath enclosure 1 there is a Formiergasatmosphäre with the pressure P _F. In the lower area is the Floatbadwanne 3 with the metal bath 4 , which usually consists of liquid tin. In the left part of the Floatbadgehäuses 1 becomes the glass melt 5 on the metal bath 4 infused and there to a glass ribbon 6 formed, the Floatbadende through the discharge opening 7 in a so-called Drossbox 10 is introduced. Inside the Drossbox 10 there are rollers 16 which are also known as lift-out scooters. By means of these rollers 16 becomes the partially solidified glass ribbon 6 from the metal bath 4 lifted and fed to other processing stations (not shown).

The Drossbox consists of an upper housing part 11 and a lower housing part 12 , The room above the glass band 6 is in the illustration shown here in 3 zones 14a , b, c split. The separation of the individual zones 14a , b, c takes place by means of curtains 15 coming from the upper housing part 11 hang down and a slight distance in cm range to the glass ribbon 6 exhibit. As a result, a sealing effect is achieved, which is the outflow of gas from the one into the dane zone is largely prevented.

In the lower housing part 12 are the rollers 16 with their scrapers underneath 17 , These scrapers also subdivide zones in the lower area that do not necessarily have to match the zones in the upper housing part.

Both in the upper housing part 11 as well as in the lower housing part 12 are gas injectors 21 arranged, being in each zone 14a , b, c only one gas injector is shown for reasons of clarity. In the lower area there are two gas injectors 21 in the area between the rollers 16 ,

These gas injectors 17 are part of a gas inlet device 20 schematically in the 2 is shown.

The 2 shows a section along the line II-II through the in 1 shown Drossbox 10 , This gas injectors 21 extend across the Drossbox 10 and consist essentially of a tube with gas outlet openings 22 , In the 2 are both above the glass band 6 as well as under the glass band in each case a gas injector 21 shown. These gas injectors 21 are via supply lines 23 to a gas supply device 30 connected, which promotes the required amount of gas into the gas injectors, so that within the Drossbox 10 an overpressure relative to the Floatbadgehäuse can be generated. The pressure P _D within the Drossbox 10 is about 0.3 to 06 mbar above the atmospheric pressure P _F Floatbadgehäuses.

The gas supply device 30 is a gas heater 31 upstream, with the gas tank 32 communicates. About the gas heater 31 the gas is heated to a temperature of 600-700 ° C.

In the 3 is the end of the float bath tub 3 shown enlarged. The end-side end wall 8th is with a cooling device 40 equipped in the 4 can be seen schematically in a sectional view. It is a kind of metal bag into which gas is introduced.

In the in 4 As shown, this cooling device consists 40 from two chambers, in the bottom gas from a gas tank 32 is initiated. Within the bag labyrinth-like passages are provided, so that the gas has a sufficiently large residence time to the end wall 8th to cool and to warm up on this occasion accordingly. The heated gas flows via lines 41 to the gas heater 31 where the already preheated gas is brought to the final temperature of 600-700 ° C. Thereafter, the gas enters the gas supply device described above 30 and is over the supply lines 32 the gas injectors 21 fed.

1

Floatbadgehäuse

2

Floatbadkammer

3

Floatbadwanne

4

metal

5

molten glass

6

glass tape

7

discharge

8th

end-side bulkhead

10

Drossbox

11

upper housing part

12

lower housing part

13

inner space

14a, b, c

Zone

15

curtain

16

roller

17

Abstreiter

20

Gaseinleiteinrichtung

21

injector

22

Gas ride opening

23

feed

30

Gas supply means

31

Gasaufheizeinrichtung

32

gas tank

40

cooling device

41

management

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - US 3083551 [0002]
• - DE 1471950 [0002]
• DE 2716174 A [0012]
• - DE 1804295 [0012]
• DE 1909921A [0012]
• - GB 1017713 [0013]

Claims (23)

Process for the production of flat glass, in particular of TFT glass, according to the float process, in which a glass melt ( 5 ) to a float bath housing having an atmosphere ( 1 ) located metal bath ( 4 ) and continuously added to a glass ribbon ( 6 ) and in which the molded glass ribbon ( 6 ) at the end of the Floatbadgehäuses ( 1 ) by means of a lifting device from the metal bath ( 4 ), which is located in a Floatbadgehäuse ( 1 ) downstream throttling box ( 10 ), characterized in that in the Drossbox ( 10 ) an inert gas-containing, oxygen-free gas is introduced and that in the Drossbox ( 10 ) an overpressure relative to the atmosphere in Floatbadgehäuse ( 1 ) is set. Method according to claim 1, characterized in that in the Drossbox ( 10 ) a pressure is set, which is 0.03 mbar to 0.06 mbar above the atmospheric pressure of the Floatbadgehäuses ( 1 ) lies. Method according to claim 2, characterized in that in the Drossbox ( 10 ), a pressure is set which is 0.04 to 0.05 mbar above atmospheric pressure in the Floatbadgehäuse ( 1 ) lies. Method according to one of claims 1 to 3, characterized in that in at least two zones ( 14a , b, c) of the Drossbox ( 10 ) different overpressures are set. A method according to claim 4, characterized in that in the Floatbadgehäuse ( 1 ) facing zone ( 14a ) of the Drossbox ( 10 ) the largest overpressure is set. Process according to Claims 1 to 5, characterized that a nitrogen-containing gas is introduced. A method according to claim 6, characterized in that N _{2 is} introduced. Method according to one of claims 1 to 6, characterized in that a mixture of nitrogen and hydrogen is initiated. Method according to one of claims 1 to 8, characterized in that 200 m ³ (i.N.) / h to 400 m ³ (i.N) / h gas in the Drossbox ( 10 ) be initiated. A process according to claim 9, characterized in that 250 m ³ (i.N.) / h to 350 m ³ (i.N) / h of gas are introduced. Method according to one of claims 1 to 10, characterized in that a to a temperature of 600 ° C Gas heated to 700 ° C is introduced. Method according to one of claims 1 to 11, characterized in that the output region of the Floatbadgehäuses ( 1 ) is cooled with a gas and that this gas then into the Drossbox ( 10 ) is initiated. Drossbox ( 10 ) with a housing from an upper housing part ( 11 ) and a housing lower part ( 12 ) and with an in-housing lifting device with rollers ( 16 ) for horizontal transport of a in a Floatbadgehäuse ( 1 ) produced glass ribbon ( 6 ), characterized in that a device ( 20 ) is provided for introducing a gas, the at least one in the interior ( 11 ) of the Drossbox ( 10 ) arranged gas injector ( 21 ) and a gas supply device ( 30 ) to which the gas injector ( 21 ) connected. Drossbox according to claim 13, characterized in that the gas delivery rate of the gas inlet device ( 20 ) Is 200 to 400 m ³ (IN) / h. Drossbox according to claim 13 or 14, characterized in that at least in the upper housing part ( 11 ) in the space above the rollers ( 16 ) at least one gas injector ( 21 ) is arranged. Drossbox according to one of claims 13 to 15, characterized in that in the lower housing part ( 12 ) at least in the space between the rollers ( 16 ) at least one gas injector ( 21 ) is arranged. Drossbox according to one of claims 13 to 16, characterized in that the gas injector ( 21 ) parallel to the rollers ( 16 ) extending tube with gas outlet openings ( 22 ). Drossbox according to claim 17, characterized in that both pipe ends of the gas injector ( 21 ) with the gas supply device ( 30 ) are connected. Drossbox according to claim 18, characterized that the tube is divided into two chambers. Drossbox according to one of claims 1 to 19, characterized in that the introduction device ( 20 ) to a gas heating device ( 31 ) connected. Drossbox according to claim 20, characterized in that the gas heating device ( 31 ) a cooling device ( 40 ) of the end Floatbadwand ( 8th ). Floatbadvorrichtung with a Floatbadgehäuse ( 1 ) and a downstream throttle box ( 10 ), wherein in the Floatbadgehäuse ( 1 ) an atmospheric pressure P _F and in the Drossbox ( 10 ) there is an atmospheric pressure P _D , characterized in that P _D > P _F. Floatbadvorrichtung according to claim 22, characterized in that the atmospheric pressure P _D is 0.03 to 0.06 mbar above the atmospheric pressure P _F.