WO2024014340A1 - Mother glass sheet and method for manufacturing mother glass sheet - Google Patents

Abstract

This method for manufacturing a mother glass sheet includes a collection step P2 for collecting a mother glass sheet 8 for inspection, and a measurement step for measuring the shape accuracy of the mother glass sheet 8 for inspection, wherein: the collection step P2 is executed every prescribed period of time, and sets a plurality of rectangular first evaluation regions 41 so as to satisfy the full width of the effective portion of the collected mother glass sheet 8 for inspection; and the measurement step includes a step for measuring a front-to-back deflection difference d1 along a sheet drawing direction and width direction for each first evaluation region 41, and a step for calculating a change amount Δd3 of the front-to-back deflection difference d1 between corresponding first evaluation regions 41, 41 between mother glass sheets 8, 8 for inspection collected in two consecutive collection steps P2.

Description

Mother glass plate and method for manufacturing mother glass plate

The present disclosure relates to a mother glass plate and a method for manufacturing a mother glass plate.

An example of a glass plate that requires high flatness is a glass substrate for a hard disk drive (hereinafter referred to as an HDD substrate). Patent Document 1 discloses an example of an HDD board.

As an example of a mode of manufacturing an HDD substrate, when manufacturing a 3.5-inch HDD substrate, first, a large-area mother glass plate with a size of 1300 x 1500 mm to 2400 x 2800 mm, for example, and a small-area rectangular glass plate ( Cut out a large number of pieces (about 100mm square). Thereafter, an HDD substrate (also called a platter blank) is manufactured by processing each of the rectangular glass plates into a circular shape.

A method for measuring the shape accuracy of an HDD substrate is to measure the flatness of a rectangular glass plate before it is processed into a circular shape using an oblique incidence interferometer, targeting a circular area of the glass plate that corresponds to the HDD substrate. There is a method to measure Here, as an example, the flatness required for a 3.5-inch HDD substrate is as severe as 50 μm or less in an upright state without the influence of gravity.

Special Publication No. 2020-510950

As described above, there are strict requirements for the shape accuracy of the HDD substrate, so when manufacturing the mother glass plate that is the basis of the HDD board, it is necessary to ensure the shape accuracy of the mother glass plate by, for example, the following procedure.

First, a mother glass plate for inspection is collected from the mother glass plate production line. Next, the shape accuracy of the sampled mother glass plate for inspection is measured. Specifically, a large number of rectangular glass plates (about 100 mm square) are cut out from a mother glass plate for inspection. These many rectangular glass plates are arranged along the drawing direction and the width direction of the mother glass plate for inspection. Thereafter, the flatness of each cut rectangular glass plate is measured using an oblique incidence interferometer. If the flatness values of all the rectangular glass plates are within the allowable range, it is determined that the mother glass plate satisfies the shape accuracy standard for HDD substrates, and the shape accuracy of the mother glass plate is guaranteed. .

As described above, when ensuring the shape accuracy of the mother glass plate, the shape accuracy of the mother glass plate for inspection is measured by measuring the flatness of a large number of rectangular glass plates. The bottom line is that the above procedure involves actually cutting out a large number of rectangular glass plates corresponding to the size of the final product (HDD board) from a mother glass plate for inspection, and then ensuring that each piece has the required shape accuracy. If it satisfies the criteria, it is determined that the mother glass plate satisfies the shape accuracy criteria for HDD substrates.

When ensuring the shape accuracy of the mother glass plate using the above procedure, the number of rectangular glass plates cut out from the mother glass plate for inspection may reach several hundred pieces. For example, when using a part of a mother glass plate for inspection with a size of 2200 x 2500 mm, a total of 10 rows along the drawing direction and 25 columns along the width direction of the mother glass plate for inspection are used. This meant cutting out 250 rectangular glass plates. Then, it is necessary to measure the shape accuracy of each of the 250 sheets. Therefore, there is a problem in that it takes a lot of effort and time to measure the shape accuracy of the mother glass plate for inspection.

In view of the above-mentioned circumstances, the technical problem to be solved is that when manufacturing mother glass plates for HDD boards that require high shape accuracy, if a step of measuring the shape accuracy of the mother glass plate for inspection is included, The objective is to reduce the effort and time required for measurement while ensuring measurement accuracy.

(1) A method for manufacturing a mother glass plate to solve the above problems includes a production process in which mother glass plates are continuously produced on a production line, a sampling process in which a mother glass plate for inspection is collected from the production line, Mother glass for hard disk drives, comprising: a measurement process for measuring the shape accuracy of a mother glass plate for inspection; and a pass/fail judgment process for judging the pass/fail of a plurality of mother glass plates produced in a production process based on the results of the measurement process. In the manufacturing method, the mother glass plate has a rectangular shape having a first side along the sheet drawing direction and a second side along the width direction perpendicular to the sheet drawing direction, and and the second side each has a length of 1000 mm or more and a thickness of 0.3 mm or more and 0.7 mm or less, and the sampling process is performed at predetermined intervals, and the effective part of the sampled mother glass plate for inspection is A plurality of rectangular first evaluation regions with a side length of 300 mm or more and 700 mm or less are arranged and set in the width direction with respect to the effective part so as to satisfy the entire width. For each of the evaluation areas, the process of measuring the front and back deflection differences along the sheet drawing direction and the width direction, respectively, and the corresponding first evaluation area between mother glass plates for inspection sampled in two successive sampling processes. and calculating the amount of change in the difference in deflection between the front and back surfaces.

In the measurement process of this manufacturing method, when measuring the shape accuracy of the mother glass plate for inspection, the process (hereinafter referred to as , front and back deflection difference measuring process) is executed. According to this measurement mode, the shape accuracy can be more efficiently achieved than when measuring the shape accuracy of a mother glass plate for inspection by measuring the flatness of a large number of rectangular glass plates using an oblique incidence interferometer. can be measured. This is due to the following reasons (A) and (B). (A) The size of each first evaluation region (length of one side is 300 mm or more and 700 mm or less) can be made larger than the size of the rectangular glass plate when using a grazing incidence interferometer. The number can be significantly reduced. That is, the number of first evaluation regions can be significantly reduced compared to the number of rectangular glass plates. (B) As described above, even if the size of the first evaluation area is increased, the shape accuracy of the mother glass plate for inspection can be accurately measured. In other words, it is possible to accurately determine whether or not the mother glass plate for inspection satisfies the required standard of shape accuracy. The reason for this is as follows. The shape of a mother glass plate (mother glass plate for inspection) does not change locally in a small area, but gradually changes in a large area. Therefore, if the shape accuracy of the first evaluation area (shape accuracy based on the front and back deflection difference) can be guaranteed, the shape accuracy when cut out to a smaller size than the first evaluation area (such as the size of the final product) can also be guaranteed. . For the reasons (A) and (B) above, according to this measurement process, when measuring the shape accuracy of the mother glass plate for inspection, the number of objects to be measured can be significantly reduced, and the measurement can be performed accurately. As a result, it is possible to reduce the effort and time required for measurement while ensuring measurement accuracy.

In the measurement process of this manufacturing method, in addition to the process of measuring the front and back deflection difference, the amount of change in the front and back deflection difference between the corresponding first evaluation areas between the mother glass plates for inspection sampled in two successive sampling processes is measured. A step of calculating each (hereinafter referred to as "inter-corresponding region deflection difference change amount calculation step") is executed. After that, a pass/fail determination process is performed to determine whether or not the plurality of mother glass plates produced in the production process are acceptable based on the results of the measurement process. In this manufacturing method, a plurality of mother glass plates can be determined to be acceptable if both of the following [Condition 1] and [Condition 2] are satisfied. In addition, "multiple mother glass plates" refers to the mother glass plates for inspection that were collected in the first and second sampling processes of two successive sampling processes, respectively, as the preceding inspection plate and the subsequent inspection plate. This refers to a plurality of mother glass plates sandwiched between a preceding inspection plate and a subsequent inspection plate on a production line. [Condition 1]: Each of the mother glass plates for inspection (the plate for the preceding inspection and the plate for the subsequent inspection) collected in two successive sampling steps satisfies the required standard of shape accuracy. In detail, when measuring the front and back deflection differences along the board pulling direction and the width direction for each of the plurality of first evaluation regions for both the preceding inspection board and the subsequent inspection board (front and back deflection difference measurement step ), the values of the front and back deflection differences along the board drawing direction and width direction in all the first evaluation areas must be within the allowable range. [Condition 2]: The difference in front and back deflection between the corresponding first evaluation areas between the mother glass plates for inspection (between the preceding inspection plate and the subsequent inspection plate) sampled in two successive sampling steps. When the amount of change is calculated (when the step of calculating the amount of change in deflection difference between corresponding regions is executed), all calculated values are within the allowable range. For example, if there are seven first evaluation regions on one mother glass plate for inspection, the amount of change in the front and back deflection difference between the corresponding first evaluation regions must be within the allowable range in all seven. There is. On the other hand, if either [Condition 1] or [Condition 2] is not satisfied, the plurality of mother glass plates described above can be determined to be rejected.

(2) In the manufacturing method of (1) above, the measurement step includes a step of calculating the amount of change in the front and back deflection difference between the first evaluation regions adjacent in the width direction for each mother glass plate for inspection. It is preferable to further provide.

In this way, in the measurement step, it is possible to clarify the change in the shape of the mother glass plate for inspection along the width direction based on the amount of change in the front and back deflection difference between the first evaluation regions adjacent in the width direction. Therefore, it becomes possible to more accurately measure the shape accuracy of the mother glass plate for inspection. This is advantageous when a mother glass plate is required to have higher shape accuracy and a mother glass plate that satisfies the requirement is selected (determined as acceptable in the pass/fail determination process). For example, in addition to satisfying both Conditions 1 and 2 above, after calculating the amount of change in the front and back deflection difference between the first evaluation areas adjacent in the width direction, all of the calculated values are less than or equal to the threshold value. In this case, if the pass/fail determination step is made to determine pass, a mother glass plate with even higher shape accuracy can be obtained.

(3) In the manufacturing method of (1) or (2) above, in the sampling step, in correspondence with each of the plurality of first evaluation regions, A second evaluation area adjacent to the first evaluation area in the board drawing direction is further set, and the measuring step is a step of measuring the front and back deflection difference along the board drawing direction and the width direction for each of the second evaluation areas, respectively; The method may further include the step of calculating the amount of change in the front and back deflection difference between the corresponding first evaluation area and second evaluation area.

In this way, in the measurement process, the front and back deflections in the second evaluation area along the board drawing direction and the width direction, as well as the front and back deflections between the first and second evaluation areas adjacent in the board drawing direction, can be measured. Based on the amount of change in the difference, changes in the shape of the mother glass plate for inspection along the drawing direction can be clarified. Therefore, it becomes possible to more accurately measure the shape accuracy of the mother glass plate for inspection. This is advantageous when a mother glass plate is required to have higher shape accuracy and a mother glass plate that satisfies the requirement is selected (determined as acceptable in the pass/fail determination process). For example, in addition to satisfying both Conditions 1 and 2 above, the difference in front and back deflection along the board drawing direction and width direction in the second evaluation area, and the first evaluation area and second evaluation area adjacent to the board drawing direction. If the amount of change in the front and back deflection difference between the regions is calculated, and if all of the calculated values are below the threshold, it will be judged as passing in the pass/fail judgment process, then mother glass with even higher shape accuracy can be created. A board is obtained.

(4) In any of the manufacturing methods (1) to (3) above, in the sampling step, a plurality of third evaluation areas are further added to the width direction end area of the effective part of the sampled mother glass plate for inspection. In addition, the width of the width direction end area is 30% or less of the length of the second side, and the measurement step includes a step of measuring the flatness of each of the plurality of third evaluation regions using an optical interferometer. You may also have more.

In the width direction end area of the effective part of the mother glass plate for inspection, the shape of the mother glass plate for inspection is likely to change, such as warping easily occurring. Therefore, regarding the width direction end area, in addition to measuring the front and back deflection difference in the first evaluation area mentioned above, we also set multiple third evaluation areas and measured the flatness of the multiple third evaluation areas using an optical interferometer. By measuring each degree, the shape accuracy of the mother glass plate for inspection can be measured more accurately. Note that the plurality of third evaluation regions are set in the width direction end area of the effective portion of the mother glass plate for inspection, and are not set in the entire effective portion of the mother glass plate for inspection. Therefore, an increase in the number of measurement targets due to the setting of a plurality of third evaluation regions is suppressed to a minimum, so that it is possible to eliminate the possibility that efficient measurement of the shape accuracy of the mother glass plate for inspection will be hindered.

(5) In the manufacturing method of (4) above, the third evaluation region may have a rectangular shape with one side of 50 mm or more and 150 mm or less.

In this way, the size of the third evaluation area corresponds to the size of the HDD board (2.5 inch size or 3.5 inch size). Specifically, the size of the third evaluation area corresponds to the size of the rectangular glass plate before being processed into a circular shape. Therefore, it is advantageous in ensuring the shape accuracy of the mother glass plate for HDD substrates.

(6) In the manufacturing method of (4) or (5) above, it is preferable that the third evaluation area is a part of the first evaluation area.

In this way, when measuring the front and back deflection difference for the first evaluation area and measuring the flatness using an optical interferometer for the third evaluation area, the first evaluation area and the third evaluation area can be measured. It is no longer necessary to cut out and from separate areas of the mother glass plate for inspection. Furthermore, regarding the third evaluation area, in addition to the measurement of the front and back deflection difference carried out for the first evaluation area, which is the basis of the third evaluation area, flatness measurement will also be carried out. The shape accuracy of the mother glass plate for inspection can be measured more accurately.

(7) In any of the manufacturing methods (1) to (6) above, the mother glass plate has a defect inside, and the defect depth measurement step of measuring the depth from the main surface of the mother glass plate to the defect and a defect evaluation step of evaluating defects based on the measured depth.

In the manufacturing process of manufacturing an HDD substrate from a mother glass plate, the main surface of the glass plate cut into small pieces from the mother glass plate may be mechanically polished. Therefore, even if the mother glass plate has internal defects such as foreign objects or bubbles, if the depth from the main surface of the mother glass plate to the defect is less than a predetermined value, polishing will remove the defect. can be removed. In this way, a mother glass plate whose defects can be removed in a post-process can be used without being discarded as a defective product. Therefore, by executing the defect depth measurement process and the defect evaluation process, defects are classified into acceptable defects (defects that can be removed) whose depth is below a predetermined value and reject defects whose depth is greater than a predetermined value. By evaluating the mother glass plate based on the number, size, and type of reject defects, the yield of the mother glass plate can be improved.

(8) In addition, the mother glass plate that can be manufactured by the above manufacturing method has a rectangular shape with a first side along the sheet drawing direction and a second side along the width direction orthogonal to the sheet drawing direction. A mother glass plate for a hard disk drive having a first side and a second side each having a length of 1000 mm or more and a thickness of 0.3 mm or more and 0.7 mm or less, the mother glass plate having an effective A plurality of rectangular first evaluation areas are set so as to fill the entire width of the section. When measuring the front and back deflection differences along the board drawing direction and the width direction for each evaluation area, the values of the front and back deflection differences are all within the range of ±0.5 mm, and the front and back deflection differences are , is a value converted to a 350 mm square size.

In this mother glass plate, when converted to a 350 mm square size, the values of the front and back deflection differences along the sheet drawing direction and width direction in all the first evaluation areas are within the range of ±0.5 mm. This ensures high shape accuracy. Therefore, this mother glass plate is suitable as a mother glass plate for an HDD substrate that requires high shape accuracy.

(9) In the mother glass plate of (8) above, it is preferable that the amount of change in the front and back deflection difference between the first evaluation regions adjacent in the width direction is 0.3 mm or less, respectively.

If this is the case, the change in the shape of the mother glass plate along the width direction will be small, so it is more suitable as a mother glass plate for an HDD substrate that requires high shape accuracy.

(10) In the mother glass plate of (8) or (9) above, the position in the width direction is the same as the first evaluation area, and the first evaluation area corresponds to each of the plurality of first evaluation areas. A second evaluation area adjacent to the area in the board pulling direction is further set, and when the front and back deflection differences are measured along the board pulling direction and the width direction for each of the second evaluation areas, the value of the front and back deflection difference is determined. It is preferable that both of them fall within the range of ±0.5 mm, and that the amount of change in the front and back deflection difference between the corresponding first evaluation area and second evaluation area is each 0.3 mm or less.

If this is the case, the change in shape of the mother glass plate along the drawing direction will be small, so it is more suitable as a mother glass plate for an HDD substrate that requires high shape accuracy.

(11) In the mother glass plate according to any of (8) to (10) above, a plurality of rectangular third evaluations are performed in a range where the distance from the first side is 30% or less of the length of the second side. A region is set, each side of the third evaluation region is 100 mm, and when the flatness of all the third evaluation regions is measured using an optical interferometer, the flatness is 50 μm or less. It is preferable.

In this case, the size of the third evaluation area corresponds to the size of the HDD substrate (specifically, the size of the rectangular glass plate before being processed into a circle). Further, the flatness in all the third evaluation regions is 50 μm or less, and high flatness is ensured. Therefore, it is suitable as a mother glass plate for HDD substrates.

(12) The mother glass plate according to any one of (8) to (11) above preferably has a longitudinal elastic modulus of 80 GPa or more.

If it has a longitudinal elastic modulus of such a value, it will be more suitable as a mother glass plate for an HDD substrate.

(13) The mother glass plate according to any of (8) to (12) above may have internal defects, and the depth of the defect from the main surface of the mother glass plate is 25 μm or less. It is preferable.

If the depth of defects in the mother glass plate is 25 μm or less from the main surface, the defects can be removed by mechanically polishing the main surface in the manufacturing process of manufacturing an HDD substrate from the mother glass plate. As shown above, even if there is a defect inside the mother glass plate, as long as the depth of the defect is 25 μm or less from the main surface, it can be used as a glass plate for HDD substrates without being discarded as a defective product. Therefore, the yield can be improved.

According to the method for manufacturing a mother glass plate according to the present disclosure, when manufacturing a mother glass plate for an HDD substrate that requires high shape accuracy, if the step of measuring the shape accuracy of a mother glass plate for inspection is included, The effort and time required for measurement can be reduced while ensuring measurement accuracy. Further, the mother glass plate according to the present disclosure is suitable as a mother glass plate for an HDD substrate that requires high shape accuracy.

FIG. 3 is a plan view showing a mother glass plate. FIG. 3 is a plan view showing a mother glass plate. FIG. 3 is a plan view showing a mother glass plate. FIG. 3 is a plan view showing a mother glass plate. FIG. 3 is a plan view showing an enlarged view of the periphery of the first evaluation area on the mother glass plate. FIG. 3 is a diagram for explaining a method of measuring the difference in deflection between the front and back sides. It is a figure which shows the measurement result of the front and back deflection difference along the board drawing direction of several first evaluation areas. It is a figure which shows the measurement result of the front and back deflection difference along the width direction of several first evaluation areas. It is a figure which shows the measurement result of the front and back deflection difference along the board drawing direction of several second evaluation areas. It is a figure which shows the measurement result of the front and back deflection difference along the width direction of several second evaluation areas. It is a figure which shows the measurement result of the front and back deflection difference along the board pulling direction of a 1st evaluation area, and the measurement result of the front and back bending difference along the board pulling direction of a 2nd evaluation area. FIG. 7 is a diagram showing the measurement results of the front and back deflection difference along the width direction of the first evaluation area and the measurement result of the front and back deflection difference along the width direction of the second evaluation area. FIG. 3 is a cross-sectional view schematically showing a mother glass plate. FIG. 2 is a cross-sectional view schematically showing a glass plate cut out from a mother glass plate. It is a sectional view showing a production process in a method of manufacturing a mother glass plate. It is a schematic diagram which shows the collection process in the manufacturing method of a mother glass plate. It is a figure which shows the measurement result of a part of measurement process in the manufacturing method of a mother glass plate. It is a figure which shows the measurement result of a part of measurement process in the manufacturing method of a mother glass plate.

Hereinafter, a mother glass plate and a method for manufacturing the mother glass plate according to an embodiment will be described with reference to the attached drawings. First, I will explain the mother glass plate.

FIG. 1 shows a mother glass plate 1. The mother glass plate 1 is a glass cut from a glass ribbon formed by a down-draw method or a float method. This mother glass plate 1 is a mother glass for a product glass plate that requires high shape accuracy. When manufacturing a product glass plate, multiple product glass plates are cut from the mother glass plate 1. Specifically, the mother glass plate 1 of this embodiment is a mother glass for a 3.5-inch HDD substrate (glass substrate for a hard disk drive). Of course, the present invention is not limited to this, and the mother glass plate 1 may be a mother glass of an HDD substrate of another size (for example, 2.5 inch size).

The present mother glass plate 1 has a rectangular shape having a first side 2 along the sheet drawing direction and a second side 3 along the width direction orthogonal to the sheet drawing direction. Here, the "drawing direction" of the mother glass plate 1 is a direction that coincides with the drawing direction of the glass ribbon during molding of the glass ribbon. On the other hand, the "width direction" of the mother glass plate 1 is a direction that coincides with the width direction of the glass ribbon. The board drawing direction can be observed as a striped pattern by emitting light from a light source (for example, a xenon light) in a dark room while adjusting the angle of the mother glass plate 1 and projecting the transmitted light onto a screen. Therefore, even in the mother glass plate 1 cut out from a glass ribbon, it is possible to determine the drawing direction and the width direction.

The present mother glass plate 1 has a longitudinal elastic modulus of 80 GPa or more. The thickness of the mother glass plate 1 is 0.3 mm or more and 0.7 mm or less. The length 2y of the first side 2 and the length 3x of the second side 3 are each 1000 mm or more. Here, in this embodiment, the mother glass plate 1 is G8.5 size, the length 2y of the first side 2 is 2200 mm, and the length 3x of the second side 3 is 2500 mm. Of course, the present invention is not limited to this, and the mother glass plate 1 may have other sizes, such as G6 size, for example.

The mother glass plate 1 is preferably alkali-free glass or alkali aluminosilicate glass.

In the case of alkali-free glass, the glass composition, in mol%, is SiO ₂ 60-75%, Al ₂ O ₃ 5-20%, B ₂ O ₃ 0-15%, Li ₂ O + Na ₂ O + K ₂ O (Li ₂ O , Na ₂ O and K ₂ O) 0 to less than 1%, MgO 0 to 10%, CaO 0 to 15%, SrO 0 to 10%, and BaO 0 to 10%. The following glass composition examples (1) or (2) are particularly preferred.
(1) Glass composition: SiO ₂ 62-72%, Al ₂ O ₃ 9.5-16% (especially 11-15%), B ₂ O ₃ 1-8% (especially 2-4%) in terms of mol%. ), Li ₂ O + Na ₂ O + K ₂ O 0 to less than 1% (especially 0 to 0.5%), MgO 1 to 9% (especially 4 to 8%), CaO 2 to 10% (especially 3 to 8%), It is preferable to contain 0.1 to 5% (especially 1 to 3%) of SrO and 0.1 to 5% (especially 1 to 3%) of BaO.
(2) Glass composition: SiO ₂ 67-77%, Al ₂ O ₃ 9-14%, B ₂ O ₃ 0-3% (particularly less than 0-1%), Li ₂ O+Na ₂ O+K ₂ O 0 to less than 1% (especially 0 to 0.5%), MgO 0 to 5% (especially 2 to 5%), CaO 0 to 10% (especially 6 to 9%), SrO 0 to 5%, BaO 0 The content is preferably 7% (particularly 3 to 6%).

In the case of alkali aluminosilicate glass, the glass composition is SiO ₂ : 50-75%, Al ₂ O ₃ : 10-30%, B ₂ O ₃ : 0-12%, Li ₂ O: 0-10% in mol%. , Na ₂ O: 2 to 18%, and K ₂ O: 0 to 5%. The following glass composition examples (3) or (4) are particularly preferred.
(3) Glass composition, in mol%, SiO ₂ : 60-70%, Al ₂ O ₃ : 10-14%, B ₂ O ₃ : 0-3%, Li ₂ O: 0-1%, Na ₂ It is preferable to contain O: 12 to 18% and K ₂ O: 0 to 2%.
(4) Glass composition, in mol%, SiO ₂ : 65-75%, Al ₂ O ₃ : 10-30%, B ₂ O ₃ : 0-12%, Li ₂ O: 5-10%, Na ₂ It is preferable to contain O: 2 to 10% and K ₂ O: 0 to 3%.

In this mother glass plate 1, the entire area (total area) is an effective part. Here, the "effective area" is an area of the mother glass plate 1 that will later become a product glass plate. Note that in this embodiment, the entire area of the mother glass plate 1 is the effective portion, but this is not the case. If only a part of the area of the mother glass plate 1 becomes a product glass plate later, only the part of the area becomes an effective part.

In this mother glass plate 1, a plurality of rectangular first evaluation areas 41 (indicated by two-dot chain lines in FIG. 1) are set so as to fill the entire width of the effective portion (the full width of the mother glass plate 1). . Note that "the plurality of first evaluation areas 41 are set so as to fill the entire width of the effective part" means that all points in the width direction of the effective part are set so as to fill the entire width of the effective part. It is to be included within either range. The plurality of first evaluation areas 41 have the same size. In each first evaluation region 41, the dimension 41ay of the vertical side 41a extending in the board drawing direction and the dimension 41bx of the horizontal side 41b extending in the width direction are each 300 mm or more and 700 mm or less. In this embodiment, the dimension 41ay of the vertical side 41a is 500 mm, and the dimension 41bx of the horizontal side 41b is 400 mm. Here, the size of the first evaluation area 41 is larger than the size of the product glass plate (here, a 3.5-inch HDD substrate).

In this embodiment, there are seven first evaluation areas 41. Note that the number of first evaluation regions 41 is not limited to seven, and the number of first evaluation regions 41 may be increased or decreased as appropriate, for example, depending on the size of mother glass plate 1. Here, in the following description, the seven first evaluation areas 41 may be distinguished by being expressed as first evaluation areas A, B, . . . , F, G in the order of arrangement.

Among the seven first evaluation areas 41, five first evaluation areas B to F near the center in the width direction of the mother glass plate 1 are arranged in a line along the width direction of the mother glass plate 1 without gaps. On the other hand, the two first evaluation areas A and G located at both ends of the mother glass plate 1 in the width direction are located at positions shifted from the five first evaluation areas B to F in the sheet drawing direction. . Note that the first evaluation area A and the first evaluation area B, and the first evaluation area F and the first evaluation area G are located offset in the board drawing direction, but some areas overlap in the width direction. are doing.

In this embodiment, seven first evaluation regions 41 are located near the center of the mother glass plate 1 in the drawing direction, but the present invention is not limited to this. Each of the seven first evaluation regions 41 may be located at any position in the board drawing direction. That is, the location of each first evaluation area 41 may be shifted from the position illustrated in FIG. 1 in the board pulling direction. Therefore, as a form of setting the first evaluation area 41 on the mother glass plate 1, the form shown in FIGS. 2 and 3 may be adopted. In the form shown in FIG. 2, seven first evaluation areas 41 are arranged in a zigzag pattern. On the other hand, in the form shown in FIG. 3, all seven first evaluation regions 41 are arranged in a line without gaps along the width direction.

In this embodiment, as shown in FIG. 4, corresponding to each of the seven first evaluation regions 41, the position in the width direction is the same as that of the first evaluation region 41, and the first evaluation region 41 and the board A second evaluation area 42 (indicated by a two-dot chain line in FIG. 4) adjacent to each other in the pulling direction is further set. The second evaluation area 42 may be set above or below the first evaluation area 41 along the board drawing direction. Furthermore, the dimension 42ay of the vertical side 42a extending in the board drawing direction of the second evaluation area 42 and the dimension 42bx of the horizontal side 42b extending in the width direction are the same as the dimension 41ay of the vertical side 41a of the first evaluation area 41, and , is preferably the same as the dimension 41bx of the horizontal side 41b (see FIG. 1 for dimensions 41ay and 41bx). Here, in the following description, the seven second evaluation areas 42 may be distinguished by being expressed as second evaluation areas H, I, . . . M, N in the order of arrangement.

This mother glass plate 1 has a widthwise end area 5 (shown with diagonal lines in FIGS. 1 to 4). The widthwise end areas 5 are set at one end and the other end of the mother glass plate 1 in the width direction, respectively. The width dimension 5x of the width direction end area 5 is a dimension whose upper limit is 30% of the length 3x of the second side 3. That is, the widthwise end area 5 corresponds to a range in the mother glass plate 1 where the distance from the first side 2 is 30% or less of the length 3x of the second side 3. In the width direction end area 5, the mother glass plate 1 is likely to warp (particularly in the range where the distance from the first side 2 is up to 300 mm). In addition, when forming the glass ribbon, a thick ear portion is formed further outside the width direction end area 5 in the width direction.

As shown in FIG. 5, a plurality of rectangular third evaluation regions 6 (shown with diagonal lines in FIG. 5) are set in the width direction end area 5. Specifically, a plurality of third evaluation areas 6 are set in an area of the widthwise end area 5 that overlaps with the first evaluation area 41 . That is, each of the plurality of third evaluation areas 6 is a part of the first evaluation area 41. However, this is not limited to this, and the third evaluation area 6 may be set in a different area from the first evaluation area 41 in the widthwise end area 5 (an area that does not overlap with the first evaluation area 41). Further, the third evaluation area 6 may be positioned at any position in the board drawing direction as long as it is set within the width direction end area 5. In addition, since the width direction end areas 5 are set at one end and the other end in the width direction of the mother glass plate 1, the width of the mother glass plate 1 is also set for the plurality of third evaluation regions 6. They are set at one end and the other end in the direction, respectively.

In this embodiment, the third evaluation regions 6 are arranged in five rows along the board drawing direction and in two rows along the width direction at each of one end side and the other end side in the width direction. There is. Therefore, in this embodiment, the total number of third evaluation regions 6 set on the mother glass plate 1 is twenty. The number of rows of third evaluation regions 6 along the board drawing direction and the width direction may be increased or decreased as appropriate. As an example, there may be 5 to 10 rows in the drawing direction and 1 to 3 rows in the width direction. Here, regardless of the number of rows of the third evaluation areas 6 along the board drawing direction and the width direction, the third evaluation area 6 located at the outermost side in the width direction has no mother glass plate 1 in the area. It is preferable that the width direction edge of the (effective portion) be included.

Each side of the third evaluation region 6 is 50 mm or more and 150 mm or less. The third evaluation area 6 of this embodiment has a square shape of 100 mm square. Note that, unlike this embodiment, when the product glass plate is a 2.5-inch HDD substrate, the third evaluation area 6 may be, for example, a 75 mm square.

In the mother glass plate 1 described above, when seven first evaluation regions 41 are cut out from the mother glass plate 1, the following [shape accuracy criterion A] and [shape accuracy criterion B] are satisfied.

[Shape accuracy standard A]: For each of the seven first evaluation areas 41 (first evaluation areas A to G), two sides along the board drawing direction (two vertical sides 41a) and two sides along the width direction. When the front and back deflection differences d1 of (two horizontal sides 41b) are measured respectively (when a total of 28 front and back deflection differences d1 are measured), the values of the front and back deflection differences d1 are all within the range of ±0.5 mm. It fits. In addition, it is more preferable that the value of the front and back deflection difference d1 falls within the range of ±0.3 mm, even more preferably that it falls within the range of ±0.2 mm, and most preferably that it falls within the range of ±0.1 mm.

[Shape accuracy standard B]: The first evaluation areas 41 and 41 adjacent to each other in the width direction are considered as one set, and a total of 6 sets (set of A, B, set of B, C, . . . set of E, F, F , G), front and back deflections of two sides along the board drawing direction (two vertical sides 41a) and two sides along the width direction (two horizontal sides 41b) between the first evaluation areas 41, When the amount of change Δd1 of the difference d1 is calculated (when a total of 24 amounts of change Δd1 are calculated), each calculated value is 0.3 mm or less. In addition, it is more preferable that the calculated value of the amount of change Δd1 is 0.2 mm or less, and even more preferable that it is 0.1 mm or less. Here, "adjacent in the width direction" refers not only to the case where both the first evaluation regions 41, 41 are located right next to each other, as in the pair A and B in FIG. This includes cases where both first evaluation areas 41, 41 are located at positions shifted in the board drawing direction, as in the set A and B in FIGS. 1 and 2. Note that the calculation of the amount of change Δd1 in the front and back deflection difference d1 of the two sides along the board drawing direction may be omitted, and only the change amount Δd1 of the front and back deflection difference d1 of the two sides along the width direction may be calculated. In this case (when a total of 12 changes Δd1 are calculated), each calculated value is preferably 0.3 mm or less, more preferably 0.2 mm or less, and even more preferably 0.1 mm or less. .

Furthermore, in this mother glass plate 1, when seven second evaluation regions 42 are cut out in addition to the seven first evaluation regions 41, the following [shape accuracy criterion C] and [shape accuracy criterion D] are satisfied. It will be done.

[Shape accuracy standard C]: For each of the seven second evaluation regions 42 (second evaluation regions H to N), two sides along the board drawing direction (two vertical sides 42a) and two sides along the width direction. When the front and back deflection differences d2 of (two horizontal sides 42b) are measured respectively (when a total of 28 front and back deflection differences d2 are measured), the values of the front and back deflection differences d2 are all within the range of ±0.5 mm. It fits. In addition, it is more preferable that the value of the front and back deflection difference d2 falls within the range of ±0.3 mm, even more preferably that it falls within the range of ±0.2 mm, and most preferably that it falls within the range of ±0.1 mm.

[Shape accuracy standard D]: A total of 7 sets (sets A, H, sets B, I, ... sets F, M), with the corresponding first evaluation area 41 and second evaluation area 42 as one set. , G, N), the front and back deflection difference d1 between the four sides (two vertical sides 41a and two horizontal sides 41b) of the first evaluation area 41 and the corresponding four sides ( When calculating the amount of change Δd2 between the front and back deflection difference d2 of the two vertical sides 42a and the two horizontal sides 42b (when calculating a total of 28 amounts of change Δd2), each calculated value is 0.3 mm. The following is true. Note that it is more preferable that the calculated value of the amount of change Δd2 is 0.2 mm or less, and even more preferable that it is 0.1 mm or less. Note that only the amount of change Δd2 between the front and back deflection difference d1 between the two sides of the first evaluation area 41 along the board drawing direction and the front and back deflection difference d2 between the two sides along the board drawing direction of the second evaluation area 42 is calculated. You can also calculate it. In other words, regarding the calculation of the amount of change Δd2 between the front and back deflection difference d1 between the two sides extending in the width direction of the first evaluation area 41 and the front and back deflection difference d2 between the two sides extending in the width direction of the second evaluation area 42, May be omitted. In this case, the calculated values (when a total of 14 changes Δd2 are calculated) are each preferably 0.3 mm or less, more preferably 0.2 mm or less, and even more preferably 0.1 mm or less. preferable.

Furthermore, in this mother glass plate 1, when all the third evaluation regions 6 are cut out from each of the seven first evaluation regions 41, the following [shape accuracy criterion E] is satisfied.

[Shape accuracy standard E]: When the flatness of all third evaluation regions 6 is measured using an optical interferometer (when a total of 20 flatness measurements are taken), all flatness values are 50 μm or less. It is. The flatness value is more preferably 30 μm or less, even more preferably 20 μm or less, and most preferably 10 μm or less.

Hereinafter, details of [shape accuracy standard A] to [shape accuracy standard E] will be explained.

In determining whether or not [Shape Accuracy Standard A] and [Shape Accuracy Standard B] are satisfied, the front and back deflection difference d1 is measured according to the following procedure. As mentioned above, the front and back deflection difference d1 is measured in both the board drawing direction and the width direction for each of the seven first evaluation areas 41. Let us take as an example a case where the front and back deflection difference d1 along the front and back sides is measured.

As shown in FIG. 6, the front and back deflection difference d1 is the deflection W1 when the front surface of the front and back surfaces of the first evaluation area A is placed on the upper side (indicated by the solid line), and the deflection W1 when the back side is placed on the upper side (indicated by the dashed-dotted line). In the case shown by ), the deflection W2 is measured and W1-W2 is determined (d1=W1-W2). At this time, the first evaluation area A is supported by two support members 7, 7 extending in parallel with a distance L between them. In this embodiment, the distance L is 350 mm. Here, in order to measure the deflection along the board pulling direction, the vertical side 41a of the first evaluation area A is bridged between the two support members 7, 7. Of course, when measuring the front and back deflection difference d1 along the width direction, the horizontal side 41b of the first evaluation area A is spanned between the two supporting members 7, 7. Here, the deflection W1 and the deflection W2 are measured for each of the two sides (two vertical sides 41a) extending in the board drawing direction, and the front and back deflection difference d1 is measured for each of the two sides extending in the board drawing direction. That is, from the measurement mode shown in FIG. 6, two measured values, ie, the front and back deflection difference d1 on one side of the two vertical sides 41a and the front and back deflection difference d1 on the other side, are obtained.

Following the measurement procedure of the front and back deflection difference d1 described above, for each of the seven first evaluation areas 41, two sides along the board drawing direction (two vertical sides 41a) and two sides along the width direction (two horizontal sides) are measured. When the front and back deflection difference d1 of the side 41b) is measured, a total of 28 measured values are obtained as the front and back deflection difference d1. Note that since the values of the deflection W1 and the deflection W2 change depending on the length of the distance L, the value of the front and back deflection difference d1 may also change. Therefore, when the distance L is not 350 mm, the value of the front and back deflection difference d1 is converted to the value when the distance L is 350 mm (d1=(W1-W2)×350/L). Here, the measurement results of the front and back deflection differences d1 of the two sides along the board drawing direction of the seven first evaluation areas 41 (first evaluation areas A to G) are illustrated in FIG. The measurement results of the front and back deflection difference d1 are illustrated in FIG. In FIGS. 7 and 8, the measurement results on one of the two sides are shown connected with a solid line, and the measurement results on the other side are shown connected with a chain line.

As shown in the measurement results shown in Figures 7 and 8, a total of 28 measurements (14 in the drawing direction and 14 in the width direction) of the front and back deflection differences d1 were all within the range of ±0.5 mm. (-0.5mm≦d1≦0.5mm). As a result, [shape accuracy criterion A] is satisfied.

In addition, a total of 24 changes Δd1 (12 in the board drawing direction and 12 in the width direction) (in each of FIGS. 7 and 8, only one of the 12 calculated changes Δd1 is shown) The calculated values of are each 0.3 mm or less (|Δd1|≦0.3 mm). As a result, [shape accuracy criterion B] is satisfied.

In determining whether or not [shape accuracy standard C] and [shape accuracy standard D] are satisfied, two sides (two vertical sides 42a) along the board drawing direction of the second evaluation area 42 and along the width direction The procedure for measuring the front and back deflection difference d2 between the two sides (the two horizontal sides 42b) is the same as the procedure for measuring the front and back deflection difference d1 described above. Here, the measurement results of the front and back deflection differences d2 of the two sides along the board drawing direction of the seven second evaluation regions 42 (second evaluation regions H to N) are illustrated in FIG. The measurement results of the front and back deflection difference d2 between the two sides along the width direction (second evaluation regions H to N) are illustrated in FIG. In FIGS. 9 and 10, the measurement results on one side of the two sides are shown connected with a solid line, and the measurement results on the other side are shown connected with a chain line.

As shown in the measurement results shown in FIGS. 9 and 10, a total of 28 measurements (14 in the drawing direction and 14 in the width direction) of the front and back deflection differences d2 were all within the range of ±0.5 mm. (-0.5mm≦d2≦0.5mm). As a result, [shape accuracy criterion C] is satisfied.

Furthermore, the measurement results of the front and back deflection difference d1 of one side (one of the two vertical sides 41a) along the board drawing direction of the seven first evaluation areas 41 (first evaluation areas A to G) and the seven The measurement results of the front and back deflection difference d2 of the corresponding side (one of the two vertical sides 42a) of the second evaluation area 42 (second evaluation areas H to N) are displayed together in FIG. 11 (d1 are connected by a solid line, and d2 is connected by a chain line). In addition, the measurement results of the front and back deflection difference d1 of one side (one of the two horizontal sides 41b) along the width direction of the seven first evaluation areas 41 (second evaluation areas A to G) and the seven first evaluation areas 41 (second evaluation areas A to G) The measurement results of the front and back deflection difference d2 of the corresponding side (one of the two horizontal sides 42b) of the second evaluation area 42 (second evaluation area H to N) are displayed together in FIG. d2 is shown connected by a solid line, and d2 is shown connected by a dashed line). Calculation of a total of 14 changes Δd2 (7 in the board drawing direction and 7 in the width direction) (in each of FIGS. 11 and 12, only one of the 7 calculated changes Δd2 is shown) The values are each 0.3 mm or less (|Δd2|≦0.3 mm). As a result, [shape accuracy criterion D] is satisfied.

In determining whether the [shape accuracy criterion E] is satisfied, the flatness of each third evaluation region 6 is measured by the following method. That is, using a grazing incidence interferometer (product name: FT-17 or FT-900) manufactured by NIDEK, the flatness is measured with each third evaluation region 6 in an upright state. Specifically, the flatness of a circular region corresponding to the HDD substrate in each third evaluation region 6 is measured. Of course, other oblique incidence interferometers may be used. Then, the flatness value in the upright state is taken as the flatness value of each third evaluation region 6. A total of 20 flatness values obtained are all 50 μm or less. As a result, [shape accuracy criterion E] is satisfied.

By satisfying the above [Shape Accuracy Criteria A] to [Shape Accuracy Criteria E], the shape accuracy of the mother glass plate 1 is guaranteed. In order to guarantee the shape accuracy of the mother glass plate 1, it is essential that [shape accuracy standard A] is satisfied, while [shape accuracy standard B], [shape accuracy standard C], and [shape accuracy standard D] are satisfied. ], and whether or not [shape accuracy criterion E] are satisfied may be determined arbitrarily. That is, the amount of change Δd1 in the front and back deflection difference d1 of the first evaluation region 41, the front and back deflection difference d2 of the second evaluation region 42, the front and back deflection difference d1 of the first evaluation region 41, and the front and back deflection difference d2 of the second evaluation region 42. The amount of change Δd2 between and the flatness of the third evaluation region 6 may not be considered.

As shown in FIG. 13a, the mother glass plate 1 may have internal defects 1d represented by foreign objects, bubbles, etc. At this time, if the depth of the defect 1d from the main surface (front surface 1a or back surface 1b) of the mother glass plate 1 is less than or equal to a predetermined value, the defect 1d may be removed during the process of manufacturing the HDD substrate from the mother glass plate 1. As a result, no defect 1d remains on the finally obtained HDD substrate.

Specifically, in the process of manufacturing an HDD substrate, the main surface of each of the plurality of glass plates 1X (glass plates from which the HDD substrate is made) cut into small pieces from the mother glass plate 1 is mechanically polished. There are cases where Therefore, defects 1d existing in the surface layer portion of the mother glass plate 1 (the shaded area in FIG. 13a) that will be removed later by mechanical polishing are removed from the glass plate 1X by mechanical polishing. (Figure 13b shows the glass plate 1X after mechanical polishing). Therefore, no defect 1d remains on the HDD substrate.

Here, the depth of the defect 1d from the main surface (front surface 1a or back surface 1b) of the mother glass plate 1 is preferably 25 μm or less, more preferably 20 μm or less, still more preferably 15 μm or less, and most preferably Preferably it is 10 μm or less. Defects 1d existing at a depth within this range can be suitably removed by mechanical polishing.

Hereinafter, a method for manufacturing the above mother glass plate 1 will be explained.

This manufacturing method consists of a production process P1 (Figure 14) in which mother glass plates 1 are continuously produced on a production line, a sampling process P2 (Figure 15) in which mother glass plates 8 for inspection are sampled from the production line, and a sampling process P2 (Figure 15) in which mother glass plates 8 for inspection are sampled from the production line. It includes a measurement step of measuring the shape accuracy of the mother glass plate 8, and a pass/fail determination step of determining the pass/fail of the plurality of mother glass plates 1 produced in the production process P1 based on the results of the measurement step. Then, each of the plurality of mother glass plates 1 that passed the pass/fail determination process is obtained as a mother glass (mother glass for a 3.5-inch HDD substrate in this embodiment) with guaranteed shape accuracy.

<Production process>
As shown in FIG. 14, a manufacturing apparatus 9 is used to execute the production process P1. The manufacturing device 9 is a device that continuously molds the glass ribbon Gr. The manufacturing apparatus 9 includes a forming furnace 10 that forms the glass ribbon Gr, an annealing furnace 11 that slowly cools the glass ribbon Gr (annealing process), a cooling zone 12 that cools the glass ribbon Gr to around room temperature, and these forming furnaces 10, Each of the slow cooling furnace 11 and the cooling zone 12 is provided with a pair of rollers 13 provided in a plurality of upper and lower stages.

A molded body 14 for molding a glass ribbon Gr from molten glass Gm by an overflow down-draw method is arranged in the internal space of the molding furnace 10. The molten glass Gm supplied to the molded body 14 overflows from a groove (not shown) formed in the top 14a of the molded body 14 to both sides. The overflowing molten glass Gm passes along both side surfaces 14b of the wedge-shaped molded body 14 and joins at the lower end of the molded body 14, thereby forming a glass ribbon Gr continuously. The glass ribbon Gr is in a vertical position (preferably in a vertical position), and the direction Q is the drawing direction.

The internal space of the slow cooling furnace 11 has a predetermined temperature gradient downward. The glass ribbon Gr is slowly cooled so that its temperature decreases as it moves downward through the interior space of the slow cooling furnace 11. This slow cooling reduces the internal strain of the glass ribbon Gr. The temperature gradient in the internal space of the lehr 11 can be adjusted by a heating device (for example, a heater) provided on the inner surface of the lehr 11.

The plurality of roller pairs 13 are configured to sandwich the widthwise ends of the vertically oriented glass ribbon Gr from both the front and back sides. In addition, in the internal space of the slow cooling furnace 11, etc., the plurality of roller pairs 13 may include rollers whose ends are not sandwiched. In other words, the distance between the rollers constituting the roller pair 13 may be made larger than the thickness of the end portion, so that the end portion passes between the rollers.

In this embodiment, the outside of the wall 15 that partitions the forming furnace 10, the slow cooling furnace 11, and the cooling zone 12 is surrounded by an outer enclosure 16 (for example, a building). In the space between the wall portion 15 and the outer enclosure 16, partition portions 17 and 18 (for example, the floor surface of each floor of the building) are provided at positions corresponding to the upper and lower ends of the cooling zone 12, respectively. It is being These partitions 17 and 18 divide the space between the wall 15 and the outer envelope 16 into a room R1 surrounding the lehr 11 and a room R2 surrounding the cooling zone 12.

The manufacturing device 9 includes a cutting device 19 below the cooling zone 12. The cutting device 19 is configured to sequentially cut out the glass plates Gs (the original glass of the mother glass plate 1) from the glass ribbon Gr by cutting the glass ribbon Gr in a vertical position in the width direction every predetermined length. be done.

The cutting device 19 includes a wheel cutter (not shown) that runs on one side of the glass ribbon Gr descending from the cooling zone 12 to form a scribe line S along the width direction of the glass ribbon Gr; Bending stress is applied around the scribe line S while holding the contact portion 20 that supports the area where S is formed from the other side of the glass ribbon Gr and the glass ribbon Gr in the portion corresponding to the glass plate Gs. A holding section 21 that performs an operation for this purpose (operation in the V direction) is provided.

The wheel cutter is configured to form a scribe line S over the entire width or a part of the width direction of the glass ribbon Gr while descending to follow the descending glass ribbon Gr. In this embodiment, the scribe line S is also formed at the end including the relatively thick ear, but the scribe line S does not need to be formed at the end. Note that the scribe line S may be formed by laser irradiation or the like. Further, since the end portion including the ear portion is cut and removed from the glass plate Gs in a post-process, no ear portion remains in the produced mother glass plate 1.

The contact portion 20 is composed of an elongated bar that descends to follow the descending glass ribbon Gr and comes into contact with the entire width or a portion of the glass ribbon Gr in the width direction. The contact surface with the glass ribbon Gr in the contact portion 20 may be a plane or a curved surface curved in the width direction.

The holding part 21 is composed of a chuck that holds the end of the glass ribbon Gr in the width direction from both the front and back sides. A plurality of holding parts 21 are provided at intervals in the longitudinal direction of the glass ribbon Gr. The holding portions 21 are provided for one end and the other end in the width direction of the glass ribbon Gr, respectively. All of the plurality of holding parts 21 for one side end are held by the same arm (not shown). Similarly, all of the plurality of holding parts 21 for the other end are held by the same arm (not shown). By the operation of these arms, the plurality of holding parts 21 for one side end and the other side end follow the descending glass ribbon Gr and curve the glass ribbon Gr using the contact part 20 as a fulcrum. (movement in the V direction). As a result, bending stress is applied around the scribe line S, and the glass ribbon Gr is broken along the scribe line S. Along with this breaking and cutting, a glass plate Gs is cut out from the glass ribbon Gr. Then, by repeating this breaking and cutting, glass plates Gs are continuously cut out from the glass ribbon Gr. In addition, the holding part 21 is not limited to the form in which it holds the end portion of the glass ribbon Gr, but may be in a form in which it holds either the front or back surface of the glass ribbon Gr by suction, for example.

Each glass plate Gs cut from the glass ribbon Gr includes a rectangular effective portion that will later become the mother glass plate 1, and end portions located on both sides in the width direction with the effective portion in between. The ends include thick ears. When producing the mother glass plate 1, the effective portion is cut out by cutting and removing the end portion from the glass plate Gs. In cutting out the effective part, for example, a scribe line is formed along the sheet drawing direction on the glass plate Gs (formed along the boundary between the effective part and the end part), and a break cut is performed along the scribe line. By doing so, both ends of the glass plate Gs in the width direction are cut and removed. Thereby, the effective portion is cut out from the glass plate Gs to obtain the mother glass plate 1.

Here, by appropriately annealing the glass ribbon Gr in the annealing performed in the annealing furnace 11 described above, a predetermined shape accuracy can be obtained in the glass ribbon Gr and the mother glass plate 1 obtained from this glass ribbon Gr. I can do it. At this time, if the ambient temperature of the glass ribbon Gr changes over time within the slow cooling temperature range, it will affect the shape accuracy of the glass ribbon Gr (mother glass plate 1). Therefore, by suppressing the differential pressure fluctuation between the room R1 surrounding the lehr 11 and the cooling zone 12 (inner space of the cooling zone 12 divided by the wall 15), the temperature inside the lehr 11 is kept constant. Specifically, the range of variation in the differential pressure between the room R1 surrounding the slow cooling furnace 11 and the cooling zone 12 was set to 0.5 Pa to 1.5 Pa. Note that the "fluctuation range of differential pressure" means the difference between the maximum value and the minimum value of the differential pressure between the room R1 surrounding the lehr 11 and the cooling zone 12 during the period of producing the mother glass plate 1.

<Collection process>
In FIG. 15, a plurality of mother glass plates 1 are displayed side by side in the order in which they were produced in the production process P1. The mother glass plates 1 on the right side of the row are mother glass plates 1 that were produced earlier in chronological order. From these mother glass plates 1, a test mother glass plate 8 whose shape accuracy is to be measured in the measurement process is sampled. The sampling step P2 is executed at predetermined time intervals (for example, every 2 to 24 hours). That is, the left side of the two mother glass plates 8 for inspection shown in FIG. 15 is the mother glass plate 8 for inspection taken after a predetermined time period from the right side. Here, in the following explanation, the mother glass plate 8 for inspection on the right side, which was sampled first, will be referred to as the plate for preceding inspection 8a, and the mother glass plate 8 for inspection on the left side, sampled later, will be referred to as the plate for subsequent inspection. There may be cases where a distinction is made.

Note that when the molding conditions for the glass ribbon Gr are changed in the production process P1 described above, it is preferable that the time interval for performing the collection process P2 is shorter than the time interval before the molding conditions are changed. Further, the number of mother glass plates 8 for inspection sampled in one sampling process P2 (the number of plates 8a for preceding inspection and the number of plates 8b for subsequent inspection) may be one as in this embodiment. It is also possible to use a plurality of sheets.

<Measurement process>
In the measurement process, first, a plurality of (seven in this embodiment) first evaluation regions 41 and widthwise end areas 5 are set on the preliminary inspection board 8a, as shown in FIG. , a plurality of (seven in this embodiment) second evaluation regions 42 are set as shown in FIG. A total of 20 third evaluation regions 6 (10 on each side and 10 on the other end) are set. Note that a plurality of first evaluation areas 41 may be set in the same manner as shown in FIGS. 2 and 3.

Next, the following [Step 1] to [Step 5] are performed on the preliminary inspection board 8a.

[Step 1]: For each of the seven first evaluation regions 41 (first evaluation regions A to G), the front and back deflection differences d1 along the board drawing direction and the width direction are measured. The specific procedure for measuring the front and back deflection difference d1 is the same as the procedure described above. As a result, a total of 28 front and back deflection differences d1 (14 in the board drawing direction and 14 in the width direction) are measured for one advance inspection board 8a.

[Step 2]: Adjacent first evaluation areas 41 and 41 are set as one set, totaling 6 sets (set of A, B, set of B, C, ... set of E, F, set of F, G) In this step, the amount of change Δd1 in the front and back deflection difference d1 between the first evaluation regions 41, 41 along the board drawing direction and the width direction is calculated. The manner of calculating the amount of change Δd1 is the same as the manner described above. As a result, a total of 24 change amounts Δd1 (12 in the board drawing direction and 12 in the width direction) are calculated for one advance inspection board 8a. However, in [Step 2], only the amount of change Δd1 in the front and back deflection difference d1 along the width direction may be calculated.

[Step 3]: For each of the seven second evaluation regions 42 (second evaluation regions H to N), the front and back deflection differences d2 along the board drawing direction and the width direction are respectively measured. The specific procedure for measuring the front and back deflection difference d2 is the same as the procedure described above. As a result, a total of 28 front and back deflection differences d2 (14 in the board drawing direction and 14 in the width direction) are measured for one advance inspection board 8a.

[Step 4]: With the corresponding first evaluation area 41 and second evaluation area 42 as one set, a total of 7 sets (A, H group, B, I group, . . . F, M group, G, N sets), the amount of change Δd2 between the front and back deflection difference d1 of the four sides of the first evaluation area 41 and the front and back deflection difference d2 of the corresponding four sides of the corresponding second evaluation area 42 is calculated. The manner in which the amount of change Δd2 is calculated is the same as the manner described above. As a result, a total of 28 variations Δd2 are calculated for one advance inspection board 8a. However, in [Step 4], the front and back deflection difference d1 between the two sides along the board drawing direction of the first evaluation area 41 and the front and back deflection difference between the two sides along the board drawing direction of the corresponding second evaluation area 42 are determined. Only the amount of change Δd2 with respect to d2 may be calculated.

[Step 5]: Measure the flatness of all third evaluation regions 6 using an optical interferometer. The method of measuring flatness is similar to the method described above. As a result, a total of 20 flatness values are measured for one advance inspection board 8a.

When there are a plurality of advance inspection plates 8a, the measurement of the front and back deflection differences d1 and d2, the calculation of the changes Δd1 and Δd2, and the flatness measurement are performed for each of the plurality of plates 8a.

Next, for the subsequent inspection board 8b, a first evaluation area 41, a widthwise end area 5, a second evaluation area 42, and a third evaluation area 6 were set in the same manner as the preceding inspection board 8a. Then, the above [Step 1] to [Step 5] are executed. As a result, for one subsequent inspection board 8b, a total of 28 front and back deflection differences d1, a total of 28 front and back deflection differences d2, a total of 24 changes Δd1, a total of 28 changes Δd2, and a total of 20 flatness values are measured and calculated. Of course, when there are a plurality of plates 8b for subsequent inspection, the front and back deflection differences d1 and d2 are measured, the amounts of change Δd1 and Δd2 are calculated, and the flatness is measured for each of the plurality of plates.

Next, perform the following [Step 6].

[Step 6]: Corresponding first evaluation area between the mother glass plates for inspection 8 and 8 (between the preceding inspection plate 8a and the subsequent inspection plate 8b) sampled in two consecutive sampling steps P2 41, 41 (first evaluation areas A, between A, B, between B, ... F, between F, G, along the width direction) The amount of change Δd3 in the front and back deflection difference d1 is calculated.

Here, examples of the amount of change Δd3 are shown in FIG. 16 (results for one of the two sides extending in the board drawing direction) and FIG. 17 (results for one of the two sides extending in the width direction). What is shown in FIGS. 16 and 17 by a solid line is the measurement result of the front and back deflection difference d1 for the preceding test board 8a, and what is shown by a chain line is the corresponding front and back deflection for the subsequent test board 8b. These are the measurement results of the difference d1. Note that in both figures, only the amount of change Δd3 between the corresponding first evaluation areas A and A is displayed. The amount of change Δd3 is calculated to be 28 in total (14 in the board drawing direction and 14 in the width direction) when there is one each of the preceding inspection board 8a and the subsequent inspection board 8b.

<Pass/Fail Judgment Process>
In the pass/fail judgment process, if all of the following [Criteria 1] to [Criteria 6] are satisfied, a plurality of mother glass plates 1 (preceding inspection plate 8a and subsequent inspection plate A plurality of mother glass plates 1) sandwiched between the two mother glass plates 1) and 8b are accepted. In other words, it is assumed that the quality of the mother glass plate 1 of the HDD substrate is satisfied. On the other hand, if any one of [Criteria 1] to [Criteria 6] is not satisfied, the plurality of mother glass plates 1 within the range Z are rejected. In other words, it is assumed that the quality of the mother glass plate 1 of the HDD substrate is not satisfied.

[Criteria 1]: For both the preceding inspection board 8a and the subsequent inspection board 8b, all front and back deflection differences d1 measured in [Step 1] fall within the range of ±0.5 mm (-0.5 mm≦ d1≦0.5mm). In addition, it is more preferable that all front and back deflection differences d1 fall within the range of ±0.3 mm, even more preferably that they fall within the range of ±0.2 mm, and it is preferable that they fall within the range of ±0.1 mm. most preferred.

[Criteria 2]: In both the preceding inspection plate 8a and the subsequent inspection plate 8b, all the amounts of change Δd1 calculated in [Step 2] are 0.3 mm or less (|Δd1|≦0.3 mm). In addition, it is more preferable that all the amounts of change Δd1 are 0.2 mm or less, and even more preferable that they are 0.1 mm or less.

[Criteria 3]: For both the preceding inspection board 8a and the subsequent inspection board 8b, all front and back deflection differences d2 measured in [Step 3] fall within the range of ±0.5 mm (-0.5 mm≦ d2≦0.5mm). In addition, it is more preferable that all front and back deflection differences d2 fall within the range of ±0.3 mm, even more preferably that they fall within the range of ±0.2 mm, and it is preferable that they fall within the range of ±0.1 mm. most preferred.

[Criteria 4]: In both the preceding inspection plate 8a and the subsequent inspection plate 8b, all the amounts of change Δd2 calculated in [Step 4] are 0.3 mm or less (|Δd2|≦0.3 mm). In addition, it is more preferable that all the amounts of change Δd2 are 0.2 mm or less, and even more preferable that they are 0.1 mm or less.

[Criteria 5]: All flatness values measured in [Step 5] are 50 μm or less on both the preceding inspection board 8a and the subsequent inspection board 8b. In addition, it is more preferable that all the flatness values are 30 μm or less, even more preferably 20 μm or less, and most preferably 10 μm or less.

[Criteria 6]: All the amounts of change Δd3 calculated in [Step 6] are 0.3 mm or less (|Δd3|≦0.3 mm). In addition, it is more preferable that all the amounts of change Δd3 are 0.2 mm or less, and even more preferable that they are 0.1 mm or less.

Here, in this embodiment, all of [Step 1] to [Step 6] are executed in the measurement process, but the present invention is not limited to this. Only [Step 1] and [Step 6] may be required, and whether or not to perform the other [Step 2], [Step 3], [Step 4], and [Step 5] may be optional. For example, if the molding conditions of the glass ribbon Gr in the production process P1 are changed, or if the shape accuracy of the produced mother glass plate 1 tends to deteriorate (for example, the absolute value of the front and back deflection difference d1 |d1| [Step 2], [Step 3], [Step 4], and [Step 5] may be performed only when the amount of change Δd3 tends to increase.

If only [Step 1] and [Step 6] are required in the measurement process, in the pass/fail judgment process, if only [Criterion 1] and [Criterion 6] are satisfied, the result will be within the range Z shown in Figure 15. A certain number of mother glass plates 1 may be accepted. In other words, it does not matter if it satisfies the quality requirements for the mother glass plate 1 of the HDD substrate.

In addition, in this manufacturing method, regarding defects 1d, which are typified by foreign objects, bubbles, etc. contained in the mother glass plate 1, the depth from the main surface (front surface 1a or back surface 1b) of the mother glass plate 1 to the defect 1d is measured. The method may further include a defect depth measuring step and a defect evaluation step of evaluating the defect 1d based on the measured depth. When performing both of these steps, among the plurality of mother glass plates 1 that were judged to be acceptable in the above pass/fail judgment process, only the mother glass plates 1 that were also judged to be acceptable based on the results of the defect evaluation process are selected. It can also be treated as one that satisfies the quality of the mother glass plate 1 of the HDD board.

<Defect depth measurement process>
In the defect depth measuring step, it is possible to measure the depth of the defect 1d using various known measuring methods. For example, from among the images taken of the mother glass plate 1 at a plurality of focal lengths, an image that is most focused on the defect 1d is selected, and based on the focal position of the image, the defect 1d from the main surface is (the depth along the thickness direction of the mother glass plate 1) can be calculated.

<Defect evaluation process>
In the defect evaluation process, if the depth of the defect 1d measured in the defect depth measurement process is below a predetermined value (for example, 25 μm or less, 20 μm or less, 15 μm or less, 10 μm or less), the size and type of the defect 1d are determined. Regardless, the defect 1d is determined to be an acceptable defect. At that time, a defect whose depth from one main surface is less than or equal to a predetermined value may be determined to be an acceptable defect, but a defect whose depth from one main surface is less than or equal to a predetermined value may be determined to be an acceptable defect. At the same time, it is preferable to determine a defect whose depth from the other main surface is less than or equal to a predetermined value as an acceptable defect. If the mother glass plate 1 has only acceptable defects, the mother glass plate 1 is determined to be acceptable. On the other hand, if the depth of the defect 1d is greater than a predetermined value, the defect 1d is determined to be a reject defect. Thereafter, the pass/fail of the mother glass plate 1 is determined based on the number, size, and type of reject defects included in the mother glass plate 1, and the mother glass plate 1 determined to be rejected is discarded. By performing such a defect evaluation process, it can be determined that the mother glass plate 1 having only acceptable defects satisfies the quality as the mother glass plate 1 for an HDD substrate, and the yield of the mother glass plate 1 can be improved. can do.

1 Mother glass plate 1a surface (main surface)
1b Back side (main side)
1d Defect 2 First side of mother glass plate 3 Second side of mother glass plate 41 First evaluation area 42 Second evaluation area 5 Width direction end area 6 Third evaluation area 8 Mother glass plate for inspection 8a Prior inspection plate 8b Plate for subsequent inspection d1 Front and back deflection difference Δd1 Amount of change in the front and back deflection difference d2 Front and back deflection difference Δd2 Amount of change in the front and back deflection difference Δd3 Amount of change in the front and back deflection difference P1 Production process P2 Sampling process

Claims (13)

1. A production process of continuously producing mother glass plates on a production line, a sampling process of collecting a mother glass plate for inspection from said production line, a measurement process of measuring the shape accuracy of said mother glass plate for inspection, and said measurement. A method for manufacturing a mother glass plate for a hard disk drive, comprising: a pass/fail determination step of determining pass/fail of a plurality of mother glass plates produced in the production process based on the result of the process,
   The mother glass plate has a rectangular shape having a first side along the sheet drawing direction and a second side along the width direction perpendicular to the sheet drawing direction, and the first side and the second side The length of each side is 1000 mm or more, the thickness is 0.3 mm or more and 0.7 mm or less,
   The sampling process is carried out at predetermined intervals, and is performed at intervals of a predetermined time, and in order to fill the entire width of the effective part of the sampled mother glass plate for inspection, a plurality of pieces having a side length of 300 mm or more and 700 mm or less with respect to the effective part are collected. Arrange and set the rectangular first evaluation area in the width direction,
   The measurement step includes a step of measuring the front and back deflection differences along the board drawing direction and the width direction for each of the plurality of first evaluation regions, and the test mother sample collected in the two successive sampling steps. A method for manufacturing a mother glass plate, comprising the step of calculating the amount of change in the front and back deflection difference between the corresponding first evaluation regions between the glass plates.
2. The measuring step further comprises the step of calculating the amount of change in the front and back deflection difference between the first evaluation regions adjacent in the width direction for each of the mother glass plates for inspection. Method of manufacturing mother glass plate.
3. In the sampling step, in correspondence with each of the plurality of first evaluation areas, a second evaluation area that is located at the same position in the width direction as the first evaluation area and that is adjacent to the first evaluation area in the board drawing direction is selected. further setting the evaluation area,
   The measurement step includes a step of measuring the front and back deflection differences along the board drawing direction and the width direction for each of the second evaluation regions, and a step of measuring the front and back deflection differences between the corresponding first evaluation region and the second evaluation region. 3. The method for manufacturing a mother glass plate according to claim 1, further comprising the step of calculating respective amounts of change in the front and back deflection differences.
4. In the sampling step, a plurality of third evaluation areas are further set in the widthwise end area of the effective portion of the sampled mother glass plate for inspection, and the width of the widthwise end area is set as the second evaluation area. 30% or less of the side length,
   3. The method for manufacturing a mother glass plate according to claim 1, wherein the measuring step further includes a step of measuring the flatness of each of the plurality of third evaluation regions using an optical interferometer.
5. The method for manufacturing a mother glass plate according to claim 4, wherein the third evaluation area has a rectangular shape with one side of 50 mm or more and 150 mm or less.
6. The method for manufacturing a mother glass plate according to claim 4, wherein the third evaluation area is a part of the first evaluation area.
7. The mother glass plate has an internal defect,
   Claim 1 or 2, further comprising: a defect depth measuring step of measuring the depth from the main surface of the mother glass plate to the defect; and a defect evaluation step of evaluating the defect based on the measured depth. 2. The method for manufacturing a mother glass plate according to 2.
8. A rectangular shape having a first side along the board drawing direction and a second side along the width direction perpendicular to the board drawing direction, and each length of the first side and the second side A mother glass plate for a hard disk drive having a thickness of 1000 mm or more and a thickness of 0.3 mm or more and 0.7 mm or less,
   A plurality of rectangular first evaluation areas are set on the mother glass plate so as to fill the entire width of the effective portion of the mother glass plate,
   The plurality of first evaluation regions have a side in the board drawing direction of 500 mm and a side in the width direction of 400 mm,
   For each of all the first evaluation regions, when the front and back deflection differences along the board drawing direction and the width direction are measured, the values of the front and back deflection differences are all within a range of ±0.5 mm,
   The value of the difference in deflection between the front and back surfaces is a value converted to a 350 mm square size of the mother glass plate.
9. The mother glass plate according to claim 8, wherein the amount of change in the front and back deflection difference between the first evaluation regions adjacent in the width direction is 0.3 mm or less, respectively.
10. A second evaluation area is further set corresponding to each of the plurality of first evaluation areas, the position being the same in the width direction as the first evaluation area, and adjacent to the first evaluation area in the board pulling direction. is,
    For each of the second evaluation regions, when the front and back deflection differences along the board drawing direction and the width direction are measured, the values of the front and back deflection differences are all within the range of ±0.5 mm,
    The mother glass plate according to claim 8 or 9, wherein the amount of change in the front and back deflection difference between the corresponding first evaluation area and the second evaluation area is each 0.3 mm or less.
11. A plurality of rectangular third evaluation areas are set on the mother glass plate in a range where the distance from the first side is 30% or less of the length of the second side,
    Each side of the third evaluation area is 100 mm,
    The mother glass plate according to claim 8 or 9, wherein the flatness of each of the third evaluation regions is 50 μm or less when measured by an optical interferometer.
12. The mother glass plate according to claim 8 or 9, wherein the mother glass plate has a longitudinal elastic modulus of 80 GPa or more.
13. The mother glass plate has internal defects,
    The mother glass plate according to claim 8 or 9, wherein the defect has a depth of 25 μm or less from the main surface of the mother glass plate.

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