JPWO2017002632A1 - Manufacturing method of glass substrate for display - Google Patents

Abstract

When manufacturing a glass substrate for display with a small heat shrinkage rate, cooling is performed until the temperature of the central portion in the width direction of the sheet glass formed by the forming step reaches 300 ° C. At this time, it is the cooling rate of the central region which is inside the width direction of the sheet glass with respect to both end portions in the width direction of the sheet glass and includes the central portion, and the temperature of the central portion is less than 450 ° C. 300 The average cooling rate in the temperature region of ° C. or higher is smaller than the average cooling rate of the central region in the temperature region other than the temperature region in the cooling process.

Description

  The present invention relates to a method for manufacturing a glass substrate for display.

  In the process of manufacturing a display, the glass substrate for display is thermally shrunk by heat treatment. At this time, if the thermal contraction rate of the glass substrate is large, a pitch shift in which the arrangement of elements formed on the surface of the glass substrate is shifted easily occurs. For this reason, from the viewpoint of reducing the pitch deviation, the glass substrate for display is required to have a small thermal shrinkage rate during the heat treatment.

  Methods for reducing the thermal shrinkage of the glass substrate include (1) adjusting the glass composition to increase the strain point of the glass, and (2) reducing the cooling rate of the sheet glass after the molding step. Is mentioned. For example, as a technique for reducing the thermal shrinkage rate of a glass substrate, a technique for improving the glass composition so that the strain point is 680 ° C. or higher is known (Patent Document 1).

  In addition, the cooling step is a first cooling step for cooling the sheet glass until the temperature of the central region of the sheet glass after forming reaches the annealing point, and the temperature of the central region is from the annealing point to the strain point of −50 ° C. This is divided into a second cooling step for cooling the sheet glass until the temperature reaches the center point, and a third cooling step for cooling the sheet glass until the temperature in the central region changes from the strain point of -50 ° C to the strain point of -200 ° C. At this time, the average cooling rate in the first cooling step is made faster than the average cooling rate in the third cooling step, and the average cooling rate in the third cooling step is made faster than the average cooling rate in the second cooling step. The technology is known (Patent Document 2).

Special table 2003-503301 gazette Japanese Patent No. 5153965

  However, if the composition is adjusted so as to increase the strain point in accordance with Patent Document 1, problems such as devitrification and difficulty melting are likely to occur, so there is a limit to increasing the strain point. In addition, when producing a glass substrate by the overflow down draw method, there is a problem that if the cooling rate of the sheet glass is reduced in the cooling step performed after the molding step, the slow cooling path becomes long and the cost of the slow cooling device increases. .

  According to Patent Document 2, the average cooling rate in the first cooling step is made faster than the average cooling rate in the third cooling step, and the average cooling rate in the third cooling step is changed to the average cooling rate in the second cooling step. Even if it is faster than the speed, there is a problem that there is a limit to the reduction of the heat shrinkage rate, which is not sufficient.

  A display mounted on a mobile device such as a mobile phone is required to have higher definition and lower power consumption. Therefore, in recent years, it has been increasingly demanded to further reduce the thermal shrinkage rate of the glass substrate that occurs during the heat treatment in the display manufacturing process.

  Then, an object of this invention is to provide the manufacturing method of the glass substrate for displays which can reduce the thermal contraction rate of a glass substrate compared with the former in the cooling process performed after shaping | molding.

The first aspect of the present invention is a method for producing a glass substrate for display. The manufacturing method is
A molding step of molding the molten glass into a sheet glass by a downdraw method;
A cooling step of cooling until the temperature of the central portion in the width direction orthogonal to the flow direction of the sheet glass reaches 300 ° C. when the formed sheet glass is flowed.
In the cooling step, a cooling rate of a central region that is an inner side of the sheet glass in the width direction than both ends of the sheet glass in the width direction and includes the center portion, and the temperature of the center portion Is lower than the average cooling rate in the central region in the temperature region other than the temperature region in the cooling step.

The cooling step includes
After being formed into the sheet glass, when the temperature of the center part in the width direction of the sheet glass is equal to or higher than the annealing point, the sheet glass is located on the inner side in the width direction of the sheet glass than both ends in the width direction. A first cooling step for cooling a central region, which is a region including the central portion, at a first average cooling rate;
A second cooling step of cooling the central region at a second average cooling rate when the temperature of the central portion is 450 ° C. or lower than the annealing point;
A third cooling step of cooling the central region at a third average cooling rate when the temperature of the central part is less than 450 ° C and 300 ° C or more,
The third average cooling rate is preferably smaller than the first average cooling rate and the second average cooling rate.

The cooling step further includes a fourth cooling step of cooling the central region at a fourth average cooling rate when the temperature of the central portion is less than 300 ° C. and 100 ° C. or more,
The fourth average cooling rate is preferably larger than the third average cooling rate.

Moreover, the 2nd aspect of this invention is a manufacturing method of the glass substrate for a display for performing heat processing at predetermined processing temperature and forming a thin film on the surface. The manufacturing method is
A molding step of molding the molten glass into a sheet glass by a downdraw method;
When flowing the formed sheet glass, the temperature of the central portion in the width direction perpendicular to the flow direction of the sheet glass is lower by 250 ° C. than the processing temperature, that is, (the processing temperature−250 ° C.). And a cooling step for cooling to a low temperature.
In the cooling step, a cooling rate of a central region that is an inner side of the sheet glass in the width direction than both ends of the sheet glass in the width direction and includes the center portion, and the temperature of the center portion Is less than a temperature lower by 100 ° C. than the treatment temperature, that is, less than (the treatment temperature−100 ° C.), more than a temperature lower than the treatment temperature by 250 ° C. The cooling rate is smaller than the average cooling rate of the central region in the temperature region other than the temperature region in the cooling step.

The cooling step includes
After being formed into the sheet glass, when the temperature of the center part in the width direction of the sheet glass is equal to or higher than the annealing point, the sheet glass is located on the inner side in the width direction of the sheet glass than both ends in the width direction, A first cooling step of cooling a central region, which is a region including the central portion, at a first average cooling rate;
When the temperature of the central portion is less than the annealing point and not less than 100 ° C. lower than the treatment temperature, that is, not less than (the treatment temperature−100 ° C.), the central region is cooled at the second average cooling rate. A second cooling step;
The temperature of the central portion is less than 100 ° C. lower than the treatment temperature, that is, less than (the treatment temperature−100 ° C.), 250 ° C. lower than the treatment temperature, that is, (the treatment temperature−250 ° C.) or more. A third cooling step of cooling the central region at a third average cooling rate,
The third average cooling rate is preferably smaller than the first average cooling rate and the second average cooling rate.

In the cooling step, the temperature of the central portion is further lower than a temperature lower by 250 ° C. than the processing temperature, that is, the processing temperature (° C.) is lower than −250 ° C., and is higher than a temperature lower than the processing temperature by 450 ° C. When the processing temperature (° C.) is −450 ° C. or higher, including a fourth cooling step of cooling the central region at a fourth average cooling rate,
The fourth average cooling rate is preferably larger than the third average cooling rate.

  In any of the first aspect and the second aspect, it is preferable that the first average cooling rate is larger than the second average cooling rate.

  In any of the first aspect and the second aspect, it is preferable that the third average cooling rate is 5.0 ° C./second or less.

In any of the first aspect and the second aspect, it is preferable that the thermal shrinkage rate of the glass substrate is 15 ppm or less.
However, the said heat shrinkage rate is a value calculated | required by the following formula | equation using the shrinkage amount of the glass substrate after performing the heat processing hold | maintained at 500 degreeC for 30 minutes.
Thermal shrinkage (ppm)
= {Shrinkage of glass substrate after heat treatment / length of glass substrate before heat treatment} × 10 ⁶

  In any of the first aspect and the second aspect, the strain point of the glass substrate is preferably 680 ° C. or higher.

  According to the method for manufacturing a glass substrate for display described above, the thermal shrinkage rate can be reduced as compared with the conventional method.

It is a figure which shows an example of the process of the manufacturing method of the glass substrate for displays of this embodiment. It is a schematic diagram of an example of the glass substrate manufacturing apparatus used for the manufacturing method of the glass substrate for a display of this embodiment. It is sectional drawing which shows an example of the shaping | molding apparatus in the manufacturing method of the glass substrate for displays of this embodiment. It is a side view which shows an example of the shaping | molding apparatus used with the manufacturing method of the glass substrate for displays of this embodiment. It is a figure which shows an example of a structure of the control apparatus used with the manufacturing method of the glass substrate for displays of this embodiment. It is a figure which shows the example of the temperature profile used at the cooling process of the manufacturing method of the glass substrate for displays of this embodiment. It is a figure which shows an example of the temperature history along the flow direction of the sheet glass in the manufacturing method of the glass substrate for displays of this embodiment. It is a schematic diagram of the example of several temperature history in the cooling process of the sheet glass used with the manufacturing method of the glass substrate for a display.

  Hereinafter, the manufacturing method of the glass substrate for a display of this embodiment is demonstrated. In the manufacturing method of the glass substrate for display of this embodiment, a glass substrate is manufactured using the overflow downdraw method. In the present specification, (treatment temperature−X ° C.) represents a temperature X ° C. lower than the treatment temperature (° C.) (X is a positive number).

(1) Overview of Glass Substrate Manufacturing Method First, a plurality of steps included in a display glass substrate manufacturing method and a glass substrate manufacturing apparatus 100 used in the plurality of steps will be described with reference to FIGS. 1 and 2. FIG. 1 is a diagram illustrating an example of steps of a method for manufacturing a display glass substrate according to the present embodiment, and FIG. 2 is a schematic diagram illustrating an example of a glass substrate manufacturing apparatus used in the method for manufacturing a display glass substrate according to the present embodiment. FIG.
As shown in FIG. 1, the glass substrate manufacturing method mainly includes a melting step S1, a clarification step S2, a forming step S3, and a cooling step S4.

  The melting step S1 is a step in which the glass raw material is melted. The glass raw material is prepared so as to have a desired composition, and then charged into the melting apparatus 11. The glass raw material is melted by the melting device 11 to become a molten glass FG. The melting temperature is adjusted according to the type of glass. In this embodiment, it heats so that the maximum temperature of the molten glass FG in melting process S1 may be 1500 to 1650 degreeC. The molten glass FG is sent to the refining device 12 through the upstream pipe 23.

  The clarification step S2 is a step of removing bubbles in the molten glass FG. The molten glass FG from which bubbles have been removed in the refining device 12 is then sent to the forming device 40 through the downstream pipe 24.

  Molding process S3 is a process of shape | molding molten glass FG to the sheet glass SG which is sheet-like glass. Specifically, the molten glass FG overflows from the molded body 41 after being continuously supplied to the molded body 41 (see FIG. 3) included in the molding apparatus 40. The overflowed molten glass FG flows down along the surface of the molded body 41. The molten glass FG is then merged at the lower end of the molded body 41 and formed into a sheet glass SG.

  The cooling step S4 is a step of cooling the sheet glass SG. The glass sheet is cooled to a temperature close to room temperature through the cooling step S4. In the cooling step S4, the thickness (plate thickness) of the glass substrate, the amount of warpage of the glass substrate, and the plane strain value of the glass substrate are determined according to the cooling state.

  In addition, you may provide a cutting process after cooling process S4. For example, the cutting step is a step of cutting the sheet glass SG having a temperature close to room temperature into a predetermined size by the cutting device 90.

  In addition, the sheet glass SG cut | disconnected by the predetermined | prescribed magnitude | size by the cutting process turns into a glass substrate through processes, such as an end surface process, after that. After being packed, the glass substrate is shipped to a panel manufacturer or the like. A panel manufacturer forms a device on the surface of a glass substrate to manufacture a display.

  Note that a cutting step may not be provided after the cooling step S4. That is, the sheet glass SG cooled in the cooling step S4 may be shipped as it is after being packed as it is. In this case, a panel maker manufactures a display by forming an element on the surface of the sheet glass SG and then cutting the sheet glass SG into a predetermined size and processing the end face.

  Hereinafter, the configuration of the forming apparatus 40 included in the glass substrate manufacturing apparatus 100 will be described with reference to FIGS. In the present embodiment, the width direction of the sheet glass SG means a direction that intersects a direction (flow direction) in which the sheet glass SG flows down among the in-plane directions of the surface of the sheet glass SG, that is, a horizontal direction. To do.

(2) Configuration of Molding Apparatus First, a schematic configuration of the molding apparatus 40 is shown in FIGS. FIG. 3 is a cross-sectional view of the molding apparatus 40. FIG. 4 is a side view of the molding apparatus 40.

The forming apparatus 40 has a path through which the sheet glass SG passes and a space surrounding the path. The space surrounding the passage is configured by, for example, a molded body chamber 20, a first cooling chamber 30, and a second cooling chamber 80.
In the present embodiment, the temperature along the flow direction of the sheet glass SG when the sheet glass SG flows downward from the position where the molten glass FG merges at the lower end 41a of the formed body 41 and the sheet glass SG is formed. Among the regions, the average cooling rate in the temperature region where the temperature of the central portion C (see FIG. 4) of the sheet glass SG is less than 450 ° C. and 300 ° C. or higher is, as will be described later, of the central portion C in the cooling step S4. The temperature is smaller than the average cooling rate in the temperature region other than the temperature region where the temperature is less than 450 ° C and 300 ° C or more. This point will be described later. The temperature range in which the average cooling rate and the average cooling rate of the temperature region in which the temperature of the central portion C is lower than 450 ° C. and 300 ° C. or higher is compared, for example, the temperature difference between the upstream side and the downstream side is at least 10 ° C. or higher. It is a temperature range.
In addition, the both ends of the width direction of the sheet glass SG mean the area | region in the range of the width direction from the edge of the both sides of the sheet glass SG to the position advanced 200 mm toward the inner side of the width direction of the sheet glass SG. The area | region inside the width direction of a part is called center area | region CA (refer FIG. 4) of the sheet glass SG. Both end portions R and L of the sheet glass SG are regions including a target portion to be cut and removed after manufacturing, whereas the central region CA of the sheet glass SG is a region including a target portion to make the plate thickness uniform. It is. The central area CA of the sheet glass SG is, for example, within 85% of the width in the width direction of the sheet glass SG from the center in the width direction of the sheet glass SG. The center part C refers to the center position in the width direction of the sheet glass SG. The average cooling rate is the average cooling rate of the central area CA including the center portion C, and the sheet glass SG passes through this temperature range with respect to the temperature difference in the flow direction at the same position in the width direction in the defined temperature range. It is the value divided by the transit time. In a temperature region expressed as less than X1 ° C and greater than or equal to X2 ° C, such as a temperature region less than 450 ° C and greater than or equal to 300 ° C, the temperature difference in the center C is treated as X1-X2 (° C), and the average in the center C A cooling rate is calculated. The average cooling rate of the portion other than the central portion C of the central region CA is also a value obtained by dividing the temperature difference in the temperature region by the passage time.

  The molded body chamber 20 is a space in which the molten glass FG sent from the clarification device 12 is formed into the sheet glass SG.

  The 1st cooling chamber 30 is arrange | positioned under the molded object chamber 20, and is a space for adjusting the thickness and curvature amount of the sheet glass SG. In the first cooling chamber 30, the sheet glass SG in a state where the temperature of the central portion C of the sheet glass SG is higher than the annealing point is cooled. The center portion C of the sheet glass SG is the center in the width direction of the sheet glass SG.

  The second cooling chamber 80 is a space for adjusting the warp, thermal shrinkage rate, and strain value of the sheet glass SG, which is disposed below the molded body chamber 20 and the first cooling chamber 30. In the second cooling chamber 80, the sheet glass SG that has passed through the first cooling chamber 30 is cooled to a temperature that is at least 100 ° C. lower than the strain point through the slow cooling point and the strain point. However, in the second cooling chamber 80, the sheet glass SG may be cooled to a temperature near room temperature. Note that the inside of the second cooling chamber 80 may be divided into a plurality of spaces by a heat insulating member 80b. The plurality of heat insulating members 80b are arranged on both sides in the thickness direction of the sheet glass SG between the plurality of pulling rollers 81a to 81g. Thereby, the temperature management of the sheet glass SG can be performed more accurately.

  Moreover, the shaping | molding apparatus 40 is provided with the molded object 41, the partition member 50, the cooling roller 51, the temperature adjustment unit 60, the lowering rollers 81a-81g, and the heaters 82a-82g, for example. Furthermore, the shaping | molding apparatus 40 is provided with the control apparatus 91 (refer FIG. 5). The control device 91 controls the drive unit of each component included in the molding device 40.

  Hereinafter, each component included in the molding apparatus 40 will be described in detail.

(2-1) Molded Body The molded body 41 is provided in the molded body chamber 20. The formed body 41 forms the molten glass FG into a sheet glass SG that is a sheet-like glass by causing the molten glass FG to overflow. As shown in FIG. 3, the molded body 41 has a substantially pentagonal shape (a shape similar to a wedge shape) with respect to the cross-sectional shape. The substantially pentagonal tip corresponds to the lower end portion 41 a of the molded body 41.

  Moreover, the molded object 41 has the inflow port 42 in the 1st end part (refer FIG. 4). A groove 43 is formed on the upper surface of the molded body 41. The inlet 42 is connected to the above-described downstream pipe 24, and the molten glass FG that has flowed out of the refining device 12 is poured into the groove 43 from the inlet 42. The molten glass FG poured into the groove 43 of the molded body 41 overflows from the pair of top portions 41 b and 41 b of the molded body 41 and flows down along the pair of side surfaces (surfaces) 41 c and 41 c of the molded body 41. Thereafter, the molten glass FG joins at the lower end 41a of the molded body 41 to become a sheet glass SG.

(2-2) Partition Member The partition member 50 is a member that blocks heat transfer from the molded body chamber 20 to the first cooling chamber 30. The partition member 50 is arrange | positioned in the vicinity of the confluence | merging point of the molten glass FG. Moreover, as shown in FIG. 3, the partition member 50 is arrange | positioned at the thickness direction both sides of the molten glass FG (sheet glass SG) merged at the merge point. The partition member 50 is a heat insulating material, for example. The partition member 50 blocks the movement of heat between the upper side and the lower side of the partition member 50 by partitioning the upper atmosphere and the lower atmosphere at the junction point of the molten glass FG.

(2-3) Cooling Roller The cooling roller 51 is provided in the first cooling chamber 30. More specifically, the cooling roller 51 is disposed directly below the partition member 50. Moreover, the cooling roller 51 is arrange | positioned in the thickness direction both sides of the sheet glass SG, and the position of the both ends R and L of the width direction of the sheet glass SG. The cooling rollers 51 disposed on both sides in the thickness direction of the sheet glass SG operate in pairs. That is, both ends in the width direction of the sheet glass SG are sandwiched between the two pairs of cooling rollers 51.

For example, the cooling roller 51 is cooled by an air cooling tube or a water cooling tube passed through the inside. The cooling roller 51 contacts both end portions R and L of the sheet glass SG, and rapidly cools both end portions R and L of the sheet glass SG by heat conduction. The viscosities of both end portions R and L of the sheet glass SG in contact with the cooling roller 51 are, for example, 10 ^9.0 poise or more.

  The cooling roller 51 is rotationally driven by a cooling roller drive motor 390 (see FIG. 5). The cooling roller 51 cools both end portions R and L of the sheet glass SG and also has a function of lowering the sheet glass SG downward. In addition, cooling of the both ends R and L of the sheet glass SG by the cooling roller 51 affects the uniformity of the width of the sheet glass SG and the thickness of the sheet glass SG.

(2-4) Temperature adjustment unit The temperature adjustment unit 60 is a unit which is provided in the 1st cooling chamber 30, and cools the sheet glass SG to the annealing point vicinity. The temperature adjustment unit 60 is disposed below the partition member 50 and above the top plate 80 a of the second cooling chamber 80.

  The temperature adjustment unit 60 cools the sheet glass SG until the temperature of the central portion C of the sheet glass SG becomes near the annealing point. Thereafter, the central portion C of the sheet glass SG is cooled in the second cooling chamber 80 to a temperature in the vicinity of room temperature via a slow cooling point and a strain point.

  The temperature adjustment unit 60 may include a cooling unit 61. A plurality of cooling units 61 (three here) are arranged in the width direction of the sheet glass SG and a plurality are arranged in the flow direction. Specifically, the cooling units 61 are arranged one by one so as to face each surface of both end portions R and L of the sheet glass SG, and each surface of a central area CA (see FIG. 4) described later. One is arranged so as to oppose.

(2-5) Pull-down roller The pull-down rollers 81 a to 81 g are provided in the second cooling chamber 80 and pull down the sheet glass SG that has passed through the first cooling chamber 30 in the flow direction of the sheet glass SG. The pull-down rollers 81a to 81g are arranged inside the second cooling chamber 80 at a predetermined interval along the flow direction. A plurality of pull-down rollers 81a to 81g are arranged on both sides in the thickness direction of the sheet glass SG (see FIG. 3) and on both ends R and L in the width direction of the sheet glass SG (see FIG. 4). That is, the pulling rollers 81a to 81g pull down the sheet glass SG while contacting the both ends R and L in the width direction of the sheet glass SG and both sides in the thickness direction of the sheet glass SG.

  The pulling rollers 81a to 81g are driven by a pulling roller driving motor 391 (see FIG. 5). It is preferable to increase the peripheral speed of the pulling rollers 81a to 81g as the pulling rollers 81a to 81g are installed on the downstream side. That is, among the plurality of lowering rollers 81a to 81g, the peripheral speed of the lowering roller 81a is the smallest, and the peripheral speed of the lowering roller 81g is the highest. The pull-down rollers 81a to 81g arranged on both sides in the thickness direction of the sheet glass SG operate in pairs, and the pair of pull-down rollers 81a, 81a, ... pulls the sheet glass SG downward.

(2-6) Heater The heaters 82 a to 82 g are provided inside the second cooling chamber 80 and adjust the temperature of the internal space of the second cooling chamber 80. Specifically, a plurality of heaters 82a to 82g are arranged in the flow direction of the sheet glass SG and the width direction of the sheet glass SG. For example, seven heaters are arranged in the flow direction of the sheet glass SG, and three heaters are arranged in the width direction of the sheet glass. The three heaters arranged in the width direction respectively control the temperature of the central region CA of the sheet glass SG and both end portions R and L of the sheet glass SG. The outputs of the heaters 82a to 82g are controlled by a control device 91 described later. Thereby, the atmospheric temperature in the vicinity of the sheet glass SG passing through the inside of the second cooling chamber 80 is controlled. The temperature control of the sheet glass SG is performed by controlling the atmospheric temperature in the second cooling chamber 80 by the heaters 82a to 82g. Further, the sheet glass SG transitions from the viscous region to the elastic region through the viscoelastic region by temperature control. In this way, in the second cooling chamber 80, the temperature of the sheet glass SG is cooled from the temperature near the annealing point to the temperature near room temperature by the control of the heaters 82a to 82g.

  In addition, the vicinity of the sheet glass SG may be provided with an ambient temperature detecting means (in this embodiment, a thermocouple) 380 (see FIG. 5) for detecting the ambient temperature. For example, the several thermocouple 380 is arrange | positioned in the flow direction of the sheet glass SG, and the width direction of the sheet glass SG. The thermocouple 380 can detect the temperature of the surface of the sheet glass SG. For example, the thermocouple 380 detects the temperature of the center portion C of the sheet glass SG and the temperatures of both end portions R and L of the sheet glass SG. The outputs of the heaters 82a to 82g are controlled based on the ambient temperature detected by the thermocouple 380.

(2-7) Cutting device The cutting device 90 cuts the sheet glass SG cooled to a temperature near room temperature in the second cooling chamber 80 into a predetermined size. Thereby, the sheet glass SG becomes a several glass plate. The cutting device 90 is driven by a cutting device drive motor 392 (see FIG. 5). Note that the cutting device 90 is not necessarily provided directly below the second cooling chamber 80. The sheet glass SG may not be cut by the cutting device 90, and the sheet glass SG may be wound into a roll shape to produce a roll-shaped sheet glass.

(2-8) Control Device FIG. 5 is a diagram illustrating an example of the configuration of the control device 91.
The control device 91 includes a CPU, a RAM, a ROM, a hard disk, and the like, and controls various devices included in the glass substrate manufacturing apparatus 100. Specifically, as shown in FIG. 5, the control device 91 receives signals from various sensors (eg, thermocouple 380) and switches (eg, main power switch 381) included in the glass substrate manufacturing apparatus 100. The temperature adjustment unit 60, the heaters 82a to 82g, the cooling roller driving motor 390, the pulling roller driving motor 391, the cutting device driving motor 392, and the like are controlled.

(3) Temperature management In the cooling step S4 of the glass substrate manufacturing method according to the present embodiment, the cooling rate of the central region CA, and the average cooling rate in the temperature region where the temperature of the central portion C is less than 450 ° C and 300 ° C or higher. However, it is smaller than the average cooling rate of the central region CA in the temperature region other than the temperature region in which the temperature of the central portion C is less than 450 ° C. and 300 ° C. or more in the cooling step S4. That is, in the cooling step S4, the average cooling rate in the central region CA is the smallest in the temperature region where the temperature of the central portion C is less than 450 ° C. and 300 ° C. or higher. By adjusting the average cooling rate in this way, an extremely low heat shrinkage rate can be achieved on the glass substrate production line. In this case, the adjustment of the average cooling rate is performed using the cooling roller 51, the temperature adjustment unit 60, and the heaters 82a to 82g described above. Of course, at this time, the temperature profiles TP1 to TP10 in the width direction of the sheet glass SG as shown in FIG. 6 are used as target temperature profiles in each temperature region in the flow direction, and the temperatures of the first cooling chamber 30 and the second cooling chamber 80 are set. By controlling, the thickness, warpage amount, and distortion of the sheet glass SG can be adjusted.

FIG. 6 is a diagram illustrating temperature profiles TP1 to TP10 that are examples of target temperature profiles in the cooling process. In the temperature profile TP1, the temperature of the central region CA of the sheet glass SG is uniform, and both end portions R and L of the sheet glass SG are lower than the temperature of the central region CA. Cooling of both end portions R and L of the sheet glass SG is performed using the cooling roller 51 after molding so that the sheet glass SG has this temperature profile TP1. In the temperature profiles TP <b> 2 to TP <b> 5, the temperature distribution of the central area CA is changed from a rectangular shape to a substantially parabolic shape that protrudes upward while the temperature of the entire sheet glass SG is lowered, and the degree of convexity of the substantially parabolic shape is gradually reduced. In the temperature profile TP6, the temperatures at both ends R and L and the central area CA are made constant. Thereafter, in the temperature profiles TP7 to TP10, the temperature distribution has a substantially parabolic shape convex downward, and the temperature distribution of the central region CA is increased downward while lowering the temperature of the entire sheet glass SG. The temperature of the first cooling chamber 30 and the second cooling chamber 80 is adjusted using the cooling unit 61 and the heaters 82a to 82g so that the temperature of the sheet glass SG has such a temperature profile.
In addition, when adjusting the temperature of the 1st cooling chamber 30 and the 2nd cooling chamber 80, the temperature of the sheet glass SG may use the measured value of the temperature of the sheet glass SG, and is controlled by heater 82a-82g. A value calculated by simulation based on the ambient temperature of the sheet glass SG may be used.

FIG. 7 is a diagram illustrating an example of a temperature history (change in temperature with time) along the flow direction of the sheet glass SG at the center C in the present embodiment. In FIG. 7, at the time A, the sheet glass SG is formed at the lower end portion 41 a of the molded body 41. The temperature of the sheet glass SG at this time is 1200 degreeC, for example. At time B, the temperature of the sheet glass SG becomes a slow cooling point (temperature when the viscosity of the glass is 10 ¹³ poise, for example, 775 ° C.), and at time C, the temperature of the sheet glass SG becomes 450 ° C. At the time D, the temperature of the sheet glass SG becomes 300 ° C., and at the time E, the temperature of the sheet glass SG becomes 200 ° C. or less and is cut by the cutting device 90. At this time, the temperature region of the sheet glass SG from the time point A to the time point B (a temperature region equal to or higher than the annealing point after the formation of the sheet glass SG) is defined as the first temperature region R1, and the sheet glass SG from the time point B to the time point C is elapsed. Is the second temperature region R2, and the temperature region of the sheet glass SG (the temperature region less than 450 ° C. and 300 ° C. or more) up to the time D after the time C has passed is the second temperature region R2. The temperature range of the sheet glass SG from the time point D to the time point E (temperature range of less than 300 ° C. and 100 ° C. or higher) is defined as a fourth temperature region R4. At this time, in the first to fourth temperature regions R1 to R4, the third average cooling rate in the third temperature region R3 is the first, second, fourth average of the other first, second, fourth temperature regions R1, R2, R4. Small compared to the cooling rate. The cooling process of the sheet glass SG in the first temperature region R1 is a first cooling process, and the cooling process of the sheet glass SG in the second to fourth temperature regions R2 to R4 is a second to fourth cooling process, respectively.
In the present embodiment, the third average cooling rate in the temperature region R3 is a case where the temperature region (temperature region having a temperature difference of 10 ° C. or more) is determined by arbitrarily dividing a range other than the temperature region R3. Smallest.

In addition, it is preferable that the first average cooling rate in the first temperature region R1 is larger than the second average cooling rate in the second temperature region because the thermal contraction rate can be efficiently reduced. Specifically, since the relaxation of the glass in the first temperature region R1 proceeds quickly, the heat shrinkage rate is more efficient when the cooling rate of the second to fourth temperature regions R2 to R4 is slower than the first temperature region R1. It is preferable from the viewpoint of reducing it.
Moreover, the 4th average cooling rate in 4th temperature area | region R4 of a 4th cooling process is larger than the 3rd average cooling speed in a 3rd temperature area | region, The length of the path | route of the sheet glass SG of cooling process S4 is changed. This is preferable in that it does not need to be performed and a decrease in production efficiency of the glass substrate is suppressed.
Further, the third average cooling rate in the third temperature region R3 is preferably 5 ° C./second or less from the viewpoint that the thermal shrinkage rate can be reduced. In addition, the lower limit of the third average cooling rate is not particularly limited, but it is, for example, 0.5 ° C. from the point of not changing the length of the path of the sheet glass SG or the reduction of the production efficiency of the glass substrate. / Second or more is preferable. Furthermore, the third average cooling rate is preferably 1 ° C./second to 4.5 ° C./second from the viewpoint of reducing the heat shrinkage rate while maintaining productivity.
In addition, the first average cooling rate in the first temperature region R1 is preferably, for example, 5 ° C./second to 50 ° C./second, and more preferably 15 ° C./second to 35 ° C./second. The second average cooling rate in the second temperature region R2 is, for example, 5 ° C./second or less, preferably 1 ° C./second to 5 ° C./second, and preferably 2 ° C./second to 5 ° C./second. More preferred.
Further, as in this embodiment, the fourth average cooling rate in the fourth temperature region R4 in which the temperature of the central portion C is less than 300 ° C. and 100 ° C. or higher is larger than the third average cooling rate in the third temperature region R3. It is preferable in that the path of the sheet glass SG is not lengthened and the thermal shrinkage rate is lowered.

The temperature history shown in FIG. 7 is the temperature history in the center portion C, but the time history of the temperature at the same position in the width direction of the other part of the center region CA that is out of the center portion C is also the third temperature region. The average cooling rate in R3 is the smallest.
The first to fourth average cooling rates in the first temperature region R1 to the fourth temperature region R4 are obtained by adjusting the atmospheric temperature of the first cooling chamber 30 and the second cooling chamber 80, and are naturally released at normal temperature. It is a small speed compared to cold.

  Generally, glass is amorphous, and high-temperature glass changes its molecular structure toward an optimal structure due to heat, that is, it tends to shrink due to thermal relaxation. For this reason, in order to produce a glass substrate with a small thermal shrinkage rate, it is preferable to cool slowly so that the thermal relaxation of the sheet glass SG proceeds sufficiently. When the sheet glass SG is cooled and the sheet glass SG is cooled without sufficient thermal relaxation, changes in the molecular structure in the glass are suppressed or prevented by high viscosity during the thermal relaxation. For this reason, when the glass substrate obtained from such a sheet glass SG is reheated for heat treatment, the suppression or prevention of thermal relaxation is released, and the process starts from the middle of thermal relaxation.

  By the way, glass has a plurality of relaxations having different speeds, and the relaxation of glass can be expressed by a superposition of relaxations having different relaxation speeds (hereinafter, relaxations having different relaxation speeds are referred to as relaxation “components”). Call). As described above, as the glass relaxation component, there are a large number of components that rapidly heat relax and contract, a component that gently relaxes and contracts, and a component that relaxes and contracts at an intermediate speed. For this reason, in the cooling process, it is preferable to set a temperature history such that thermal relaxation sufficiently proceeds in all of these components. However, as shown in FIG. 4, the path of the sheet glass SG in the cooling step S <b> 4 is a path from the vertical upper side to the lower side of the forming apparatus 40, and is provided in a structure such as a building. It is difficult to extend the route because it is necessary to renovate or add to the structure such as a building. For this reason, in the existing conveyance path | route, it is preferable to perform appropriately the temperature history of the sheet glass SG and to make the thermal contraction rate of the glass substrate in cooling process S4 efficiently small. In the present embodiment, the heat shrinkage rate of the glass substrate is reduced by making the average cooling rate in the third temperature region R3 smaller than the average cooling rate in the temperature region other than the third temperature region R3 in the cooling step S4. Can be efficiently reduced. The reason is assumed as follows.

  FIG. 8 is a schematic diagram of temperature histories T1 to T3 (solid lines) in the cooling process of the sheet glass SG in the cooling process S4 in which time is plotted on the horizontal axis and temperature is plotted on the vertical axis. Time points A and E in the figure correspond to time points A and E in FIG. Here, the temperature history T1 is an example of the temperature history of the present embodiment. The temperature history T2 is a high temperature state, the cooling rate is decreased with respect to the temperature history T1, and then the cooling rate is set to the temperature history T1. The cooling rate is increased to a cooling rate equivalent to the temperature history T1, and the temperature history T3 is set to a cooling rate equivalent to the temperature history T1 in a high temperature state, and then cooled to the temperature history T1. This is a mode in which the speed is reduced and then the cooling speed is increased with respect to the temperature history T1.

In the temperature histories T1 and T3, the component that slowly relaxes and contracts as described above (this component is referred to as component X) cannot follow the cooling rate in the high temperature state, and the change in the molecular structure related to component X at point P1 is Suppressed or blocked by viscosity. In the temperature history T2, since the cooling rate in the high temperature state is small, the change in the molecular structure related to the component X at the point P2 is suppressed or prevented by the viscosity.
On the other hand, in the temperature history T1, a component that quickly shrinks by thermal relaxation (this component is referred to as component Y) cannot follow the cooling rate at the point P3, and changes in the molecular structure related to the component Y (thermal relaxation) at the point P3. Is suppressed or prevented by viscosity. In the temperature history T2, the component Y cannot follow the cooling rate at the point P4, and the change (thermal relaxation) of the molecular structure related to the component Y is suppressed or prevented by the viscosity at the point P4. In the temperature history T3, the component Y cannot follow the cooling rate at the point P5, and the change (thermal relaxation) of the molecular structure related to the component Y is suppressed or prevented by the viscosity at the point P5.

  In such temperature histories T1 to T3, the temperature at which the change in the molecular structure (thermal relaxation) at points P1 and P2 is suppressed or prevented does not differ significantly between points P1 and P2, but the molecule related to component Y The temperatures at points P3 to P5 where the change in structure is suppressed are greatly different. Specifically, the temperature at the point P3 is the lowest. Therefore, in the temperature histories T1 to T3, the lower the temperature at which thermal relaxation is suppressed or prevented, the more the thermal relaxation progresses. Therefore, the lower the temperature at the time when the change in the molecular structure related to the component Y is suppressed or prevented. The heat shrinkage rate can be reduced. Therefore, among the temperature histories T1 to T3, the temperature history T1 that suppresses or prevents the change in the molecular structure related to the component Y at the lowest temperature can sufficiently perform thermal relaxation before cutting the sheet glass SG. As a result, it is possible to provide a sheet glass SG with a reduced thermal shrinkage efficiently.

  In addition, the 1st-4th average cooling rate in a 1st-4th temperature range can be set so that the thermal contraction rate of the sheet glass SG may achieve a predetermined target value. For example, the thermal shrinkage rate of the sheet glass SG is actually measured under a plurality of types of cooling conditions, and a calibration curve is created based on the obtained measurement values. Furthermore, the flow direction of the temperature profiles TP1 to TP10 which are targets in the width direction of the set sheet glass SG using the created calibration curve so that the thermal contraction rate of the sheet glass SG achieves a predetermined target value. By adjusting the temperature distribution along, the first to fourth average cooling rates in the first to fourth temperature regions can be set.

In the present embodiment, the temperature range of the third temperature region R3 is set to less than 450 ° C. and 300 ° C. or more, but when applied to a glass substrate for display for performing a heat treatment at a predetermined processing temperature to form a thin film on the surface, The third temperature region R3 may be a temperature region of less than (treatment temperature−100 ° C.) (above treatment temperature−250 ° C.) or more. In this case, the treatment temperature is preferably 300 ° C. or higher, more preferably 400 ° C. or higher.
For example, a thin film typified by a TFT such as a low-temperature polysilicon TFT (Thin Film Transistor) or an oxide semiconductor such as IGZO (indium, gallium, zinc, oxygen) is formed on the surface of a glass substrate. When forming a thin film such as a semiconductor, the glass substrate is heat-treated at a processing temperature of, for example, 300 ° C. or higher, or 400 ° C. or higher. Therefore, the glass substrate may determine the temperature range of the third temperature region R3 according to the processing temperature of this heat treatment. In addition, the processing temperature of the heat treatment at the time of forming the thin film is, for example, 300 ° C. to 700 ° C. or 400 ° C. to 650 ° C.
In this case, after the formation of the sheet glass SG, the temperature region where the temperature of the central portion C is equal to or higher than the annealing point is defined as the first temperature region R1, and the temperature of the central portion C is less than the annealing point (treatment temperature (° C.)-100 ° C. ) When the above temperature range is the second temperature range R2, the third average cooling rate in the third temperature range R3 is the first average cooling rate in the first temperature range R1 and the second average cooling rate in the second temperature range R2. Preferably less than the speed.
Further, a temperature region in which the temperature of the central portion C is less than (treatment temperature (° C.) − 250 ° C.) (treatment temperature (° C.) − 450 ° C. or more) is defined as a fourth temperature region R4, and the fourth average in the fourth temperature region R4. The cooling rate is preferably larger than the third average cooling rate in the third temperature region R3 in terms of reducing the heat shrinkage rate without lengthening the conveyance path.

In this embodiment, it is preferable from the point which can provide the glass substrate suitable for the glass substrate for a display that the thermal contraction rate of a glass substrate shall be 15 ppm or less by defining such temperature history by cooling process S4. More preferably, the thermal shrinkage of the glass substrate is 10 ppm or less.
In addition, the strain point of the glass substrate (temperature when the viscosity of the glass is 10 ^14.5 poise) is preferably 680 ° C. or higher from the viewpoint of reducing the thermal shrinkage of the glass substrate, and is 700 ° C. or higher. It is more preferable that the temperature is 720 ° C. or higher. However, since the devitrification temperature tends to increase when the glass composition is adjusted so as to increase the strain point, the upper limit of the strain point of the glass substrate is preferably 780 ° C. or less, and preferably 760 ° C. or less. More preferred.
The devitrification temperature is preferably 1280 ° C. or less, and preferably 1100 ° C. to 1270 ° C. from the viewpoint of achieving both a reduction in heat shrinkage and devitrification resistance. It is more preferable to be.

(Glass composition)
As a glass composition of the glass substrate manufactured by this embodiment, the following glass compositions are illustrated by mol% display, for example.
SiO ₂ 55~80%,
B ₂ O ₃ 0-18%,
Al ₂ O ₃ 3-20%,
MgO 0-20%,
CaO 0-20%,
SrO 0-20%,
BaO 0-20%,
RO 5-25%
(Wherein R is at least one selected from Mg, Ca, Sr and Ba),
R ′ ₂ O 0% to 2.0%
(However, R ′ is at least one selected from Li, Na and K)
including.
Although the total content of the metal oxides whose valence fluctuates in the molten glass is not particularly limited, for example, 0.05 to 1.5% may be included. _Further, it is preferred not to include _{As 2 O 3, Sb 2 O} 3 and PbO substantially.

(Application example of glass substrate)
The glass substrate produced by the method for producing a glass substrate of the present embodiment is particularly suitable as a glass substrate for a display such as a liquid crystal display, a plasma display, and an organic EL display, and a cover glass for protecting the display. The display using the glass substrate for display includes a flat panel display having a flat display surface, an organic EL display and a liquid crystal display, and a curved display having a curved display surface. The glass substrate is a glass substrate for a high-definition display, such as a glass substrate for a liquid crystal display, a glass substrate for an organic EL (Electro-Luminescence) display, an LTPS (Low Temperature Poly-silicon) thin film semiconductor, or an IGZO (Indium, Gallium, It is preferable to use as a glass substrate for display using an oxide semiconductor such as Zinc or Oxide.
As the glass substrate for display, non-alkali glass or alkali trace glass is used. The glass substrate for display has high viscosity at high temperatures. For example, the temperature of the molten glass having a viscosity of 10 ^2.5 poise is 1500 ° C. or higher. The alkali-free glass is a glass having a composition that does not substantially contain an alkali metal oxide (R ′ ₂ O). “Alkali metal oxide is not practically contained” means a glass having a composition in which an alkali metal oxide is not added as a glass raw material except for impurities mixed in from the raw material and the like. It is less than 1% by mass.

(Heat shrinkage)
The thermal contraction rate in the present embodiment is measured by performing a heat treatment.
A glass substrate is cut into a rectangle of a predetermined size, a marking line is put on both ends of the long side, and the glass is cut in half at the center of the short side to obtain two glass samples. One of the glass samples is heat-treated (at 500 ° C. for 30 minutes). Measure the length of the other glass sample without heat treatment. Further, the heat-treated glass sample and the untreated glass sample are put together to measure the deviation amount of the marking line with a laser microscope or the like, and the difference in the length of the glass sample is obtained to obtain the thermal contraction amount of the sample. be able to. Using the difference as the amount of heat shrinkage and the length of the glass sample before the heat treatment, the heat shrinkage rate is obtained by the following equation. Let the thermal shrinkage rate of this glass sample be the thermal shrinkage rate of a glass substrate.
Thermal contraction rate (ppm) = (difference) / (length of glass sample before heat treatment) × 10 ⁶

(Experimental example)
Using the glass substrate manufacturing apparatus 100 and the glass substrate manufacturing method, glass substrates of Examples 1 to 3 and Comparative Example were manufactured under the following conditions. The composition of the glass (mol%) _{is, SiO 2 70.5%, B 2} O 3 7.2%, Al 2 O 3 11.0%, K 2 O 0.2%, CaO 11.0%, SnO 2 _{They were} 0.09% and Fe ₂ O ₃ 0.01%. The devitrification temperature of the glass was 1206 ° C., and the liquidus viscosity was 1.9 × 10 ⁵ dPa · s. The annealing point of the glass was 758 ° C., and the strain point was 699 ° C. The sheet glass SG has a width of 1600 mm and a thickness of 0.7 mm (Example 1, Comparative Example 1), 0.5 mm (Example 2, Comparative Example 2), 0.4 mm (Example 3, Comparative Example 3). ). Moreover, the heat processing temperature for forming a thin film in a glass substrate was 550 degreeC.

The average cooling rate when the temperature of the central portion C in the width direction of the sheet glass SG is equal to or higher than the annealing point is the first average cooling rate, and the average when the temperature of the central portion C is 450 ° C. or higher below the annealing point. The cooling rate was the second average cooling rate, and the average cooling rate when the temperature of the central portion C was less than 450 ° C. and 300 ° C. or higher was taken as the third average cooling rate. In Examples 1 to 3, the third average cooling rate was slower than the first average cooling rate and the second average cooling rate. On the other hand, in Comparative Examples 1-3, the second average cooling rate was made slower than the second average cooling rate of Examples 1-3, and the third average cooling rate was made faster than the third average cooling rate of Examples 1-3. The second average cooling rate of Comparative Examples 1 to 3 was slower than the third average cooling rate of Comparative Examples 1 to 3. As a result, although the heat shrinkage rate of Examples 1-3 was 15 ppm or less, the heat shrinkage rate of Comparative Examples 1-3 exceeded 15 ppm.
From this, the effect of this embodiment is clear.

  As mentioned above, although the manufacturing method of the glass substrate of this invention was demonstrated in detail, this invention is not limited to the said embodiment and Example, Even if it is variously improved and changed in the range which does not deviate from the main point of this invention. Of course it is good.

DESCRIPTION OF SYMBOLS 11 Melting apparatus 12 Clarification apparatus 20 Molding body chamber 30 1st cooling chamber 40 Molding apparatus 41 Molding body 51 Cooling roller 60 Temperature control unit 80 2nd cooling chamber 80a Top plate 80b Heat insulation member 81a-81g Pulling-down roller 82a-82g Heater 90 Cutting Device 91 Control device 100 Glass substrate manufacturing device

Claims (10)

A molding step of molding the molten glass into a sheet glass by a downdraw method;
A cooling step of cooling until the temperature of the central portion in the width direction orthogonal to the flow direction of the sheet glass reaches 300 ° C. when flowing the formed sheet glass,
In the cooling step, a cooling rate of a central region that is an inner side of the sheet glass in the width direction than both ends of the sheet glass in the width direction and includes the center portion, and the temperature of the center portion The average cooling rate in the temperature region of less than 450 ° C. and 300 ° C. or more is smaller than the average cooling rate of the central region in the temperature region other than the temperature region in the cooling step, and the method for producing a glass substrate for display . A method for producing a glass substrate for display for applying a heat treatment at a predetermined treatment temperature to form a thin film on the surface,
A molding step of molding the molten glass into a sheet glass by a downdraw method;
A cooling step of cooling until the temperature of the central portion in the width direction perpendicular to the flow direction of the sheet glass is 250 ° C. lower than the processing temperature when flowing the formed sheet glass,
In the cooling step, a cooling rate of a central region that is an inner side of the sheet glass in the width direction than both ends of the sheet glass in the width direction and includes the center portion, and the temperature of the center portion However, the average cooling rate in the temperature region of less than 100 ° C. lower than the processing temperature and 250 ° C. lower than the processing temperature is the central region in the temperature region other than the temperature region in the cooling step. The manufacturing method of the glass substrate for a display small compared with the average cooling rate of. The cooling step includes
After being formed into the sheet glass, when the temperature of the center part in the width direction of the sheet glass is equal to or higher than the annealing point, the sheet glass is located on the inner side in the width direction of the sheet glass than both ends in the width direction. A first cooling step for cooling a central region, which is a region including the central portion, at a first average cooling rate;
A second cooling step of cooling the central region at a second average cooling rate when the temperature of the central portion is 450 ° C. or lower than the annealing point;
A third cooling step of cooling the central region at a third average cooling rate when the temperature of the central part is less than 450 ° C and 300 ° C or more,
The method for manufacturing a glass substrate for display according to claim 1, wherein the third average cooling rate is smaller than the first average cooling rate and the second average cooling rate. The cooling step further includes a fourth cooling step of cooling the central region at a fourth average cooling rate when the temperature of the central portion is less than 300 ° C. and 100 ° C. or more,
The said 4th average cooling rate is a manufacturing method of the glass substrate for displays of Claim 3 larger than a said 3rd average cooling rate. The cooling step includes
After being formed into the sheet glass, when the temperature of the center part in the width direction of the sheet glass is equal to or higher than the annealing point, the sheet glass is located on the inner side in the width direction of the sheet glass than both ends in the width direction, A first cooling step of cooling a central region, which is a region including the central portion, at a first average cooling rate;
A second cooling step of cooling the central region at a second average cooling rate when the temperature of the central portion is lower than the annealing point and not less than 100 ° C. lower than the processing temperature;
A third cooling step of cooling the central region at a third average cooling rate when the temperature of the central portion is lower than the temperature lower than the processing temperature by 100 ° C. or lower than the processing temperature by 250 ° C. Including
The method for producing a glass substrate for display according to claim 2, wherein the third average cooling rate is smaller than the first average cooling rate and the second average cooling rate. The cooling step further includes cooling the central region at a fourth average cooling rate when the temperature of the central portion is less than a temperature lower by 250 ° C. than the processing temperature and not less than 450 ° C. lower than the processing temperature. Including a fourth cooling step,
The said 4th average cooling rate is a manufacturing method of the glass substrate for displays of Claim 5 larger than the said 3rd average cooling rate.   The said 1st average cooling rate is a manufacturing method of the glass substrate for displays of any one of Claims 3-6 larger than a said 2nd average cooling rate.   The said 3rd average cooling rate is a manufacturing method of the glass substrate for displays of any one of Claims 3-7 which is 5.0 degrees C / sec or less. The manufacturing method of the glass substrate for a display of any one of Claims 1-8 whose heat shrinkage rate of the said glass substrate is 15 ppm or less.
However, the said heat shrinkage rate is a value calculated | required by the following formula | equation using the shrinkage amount of the glass substrate after performing the heat processing hold | maintained at 500 degreeC for 30 minutes.
Thermal shrinkage (ppm)
= {Shrinkage of glass substrate after heat treatment / length of glass substrate before heat treatment} × 10 ⁶ The strain point of the said glass substrate is a manufacturing method of the glass substrate for displays of any one of Claims 1-9 which is 680 degreeC or more.

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