JP6628151B2 - Forming method of curved sheet glass - Google Patents

Description

  The present invention relates to a method for forming a curved glass sheet, and more particularly to a method for forming a curved glass sheet by bending a glass sheet.

  In recent years, portable electronic devices such as smartphones and tablet PCs have rapidly become widespread. As a plate glass used for a touch panel or the like of these devices, a conventionally used flat plate glass (hereinafter, simply referred to as a flat glass) is generally used. The adoption of a curved plate glass having a shape curved by a radius has been studied, and has actually begun to be adopted. In addition, the use of a curved glass sheet having a curved shape for a glass sheet used in a display for an automobile such as a car navigation system has begun to be studied.

  As a method of forming the curved glass sheet, a press method and a self-weight method are known roughly. Among these, the press method is to press-mold a heat-softened flat glass using an upper mold and a lower mold having a curved molding surface (see, for example, Patent Document 1), but the weight of the glass sheet is lower than its own weight. The method uses only the lower mold having a curved molding surface, and softens the flat glass placed on the lower mold by heating, so that the flat glass is deformed by its own weight to follow the molding surface of the lower mold. It is formed into a shape (for example, see Patent Document 2).

JP-A-1-24034 JP-A-9-208244

  However, any of the above-described methods for forming a curved sheet glass uses a softening phenomenon caused by heating the flat glass, and thus a mark (contact mark) generated when the sheet glass contacts the forming surface in a softened state is generated. There is a problem that remains on the surface even after molding. That is, in the pressing method, since the sheet glass is heated to at least the vicinity of the softening point, the surface of the sheet glass is in a very soft state. For this reason, contact marks with the molding surface are likely to be formed on the surface of the sheet glass. In particular, in the case of the press method, since the sheet glass is sandwiched between the upper and lower molds with a corresponding pressing force, contact marks with the molding surface are easily formed.

  In addition, in the self-weight method, since the sheet glass is basically bent to a predetermined radius of curvature only by the deformation of the sheet glass due to its own weight (usually bending deformation), it is necessary to heat the sheet glass to a temperature higher than that of press molding. For this reason, although the pressing force on the forming surface is not strong as compared with the pressing method, the point where a contact mark with the forming surface remains remains because the sheet glass itself is soft. For example, in the case of a conventional product such as a window glass for an automobile (Patent Document 1 and the like), this kind of contact mark was not so problematic, but in a high definition display application such as a smartphone or an automobile display, a display surface was used. Is considered to be a defect of the product, which may lead to a decrease in product value.

  In view of the above circumstances, in the present specification, it is a technology to be solved by the present invention to provide a curved glass sheet having good surface quality by minimizing the occurrence of a contact mark with a molding die. Subject.

The above object can be achieved by a method for forming a curved glass sheet according to the present invention. That is, in this forming method, a sheet glass placed on a lower mold is heated to obtain a curved sheet glass by its own weight deformation accompanying softening of the sheet glass.In the method of forming a curved sheet glass, the heating of the sheet glass is started after the heating of the sheet glass is started. Until the forming is completed, it is characterized in that the viscosity of the glass sheet is maintained at 10 ¹⁰ poise or more.

As described above, the present invention has been made by paying attention to the minimum viscosity of the glass sheet during the heating step when the glass sheet is formed into a curved glass sheet using the so-called weight method. That is, the conventional self-weight method, a glass sheet softening point (glass viscosity at this time is about 10 ^{7.65 poise)} and flexed sufficiently by heating to the vicinity, receiving the deflected was glass sheet with the forming surface This adjusts the final degree of curvature (for example, radius of curvature) of the sheet glass. On the other hand, according to the present invention, the sheet glass that is bent by heating the sheet glass by its own weight deformation due to softening is required to have its own weight deformation until reaching the final shape (the shape of the curved sheet glass as a molded product). The minimum required viscosity (minimum viscosity) was determined, and the minimum value of the viscosity from the start of heating to the completion of molding was defined. Thereby, while forming the sheet glass into a desired shape, a situation in which the molding surface and the sheet glass come into contact with each other more strongly than necessary is avoided, and a contact mark with the molding surface remains on the surface of the formed sheet glass (curved sheet glass). Can be prevented as much as possible. Alternatively, even if a contact mark remains, the extent (size, number, conspicuousness) can be suppressed as small as possible. Further, the higher the viscosity of the sheet glass, the harder the surface of the sheet glass. This also makes it difficult to form a contact mark with the forming surface. In particular, by maintaining the viscosity of the glass sheet at 10 ¹¹ poise or more from the start of heating the glass sheet to the completion of the molding of the glass sheet, it is more difficult to form a contact mark with the molding surface, and the curved glass sheet It is possible to reduce the size, number, etc. of the contact marks generated on the surface of the substrate. Therefore, for example, it is possible to form a curved plate glass that can satisfy high-quality surface quality for smartphones.

Further, in the method for forming a curved glass sheet according to the present invention, the time during which the viscosity of the glass sheet becomes 10 ¹³ poise or less is set to 60 minutes or less from the start of heating the glass sheet to the completion of the molding of the glass sheet. May be set, preferably set to 30 minutes or less, and more preferably set to 15 minutes or less. Further, from the viewpoint of increasing the molding accuracy, it is preferable to set the time during which the viscosity of the sheet glass becomes 10 ¹³ poise or less to 1 minute or more.

As described above, the present invention regulates the minimum viscosity of the sheet glass during the forming step of the curved sheet glass by the self-weight method, thereby enabling high-precision curve forming while generating contact marks with the forming surface. Although it is possible to prevent or suppress the situation that, in view of preventing the occurrence of contact traces on the surface of the sheet glass with a higher probability on this, it is relatively even if not reached the minimum viscosity It is desirable to keep the state of low viscosity (high temperature state) as short as possible. Therefore, as described above, by setting the minimum viscosity of the sheet glass from the start of heating to the completion of molding to 10 ¹⁰ poise or more, and setting the time for the viscosity of the sheet glass to 10 ¹³ poise or less to 60 minutes or less, Can be prevented with a higher probability, or the degree thereof (the number, size, and conspicuousness of occurrence) can be further suppressed.

Further, the molding method of bending glass sheets according to the present invention, during the period from the start of heating to sheet glass until the molding of the glass sheet is completed, the following 90 minutes of time at which the viscosity of the glass sheet is 10 ^{14.5 poise} or less May be set, preferably set to 60 minutes or less, and more preferably set to 30 minutes or less. In addition, from the viewpoint of improving the molding accuracy, it is preferable to set the time during which the viscosity of the sheet glass becomes 10 ^14.5 poise or less to 5 minutes or more.

This configuration is also defined in the same meaning as the configuration described above, and the minimum viscosity of the plate glass from the start of heating to the completion of molding is set to 10 ¹⁰ poise or more, and the viscosity of the plate glass is set to 10 ^14.5 poise. By setting the following time to 90 minutes or less, the occurrence of contact marks can be prevented with a higher probability, or the degree can be further suppressed. Needless to say, in this case, by further setting the time during which the viscosity of the plate glass becomes 10 ¹³ poise or less to 60 minutes or less, it is possible to further prevent the occurrence of contact marks.

  Further, the method for forming a curved sheet glass according to the present invention may be a method of starting heating the sheet glass in a state where a sheet softer than the lower mold is interposed between the lower mold and the sheet glass.

  By interposing a sheet softer than the lower mold in this way, the sheet glass comes into contact with this sheet, and direct contact with the lower mold is avoided. Since this sheet is softer than the lower mold, even if it comes into contact with the glass sheet, it is hardly damaged (contact mark). Further, since it is a sheet, it is flexible against deformation, and easily follows the molding surface provided on the lower mold. Therefore, even if this sheet is interposed, there is no possibility that the forming accuracy of the curved sheet glass is reduced.

  Further, in the method for forming a curved sheet glass according to the present invention, the sheet glass is placed on a lower mold, and a closed space is formed between a lower surface of the sheet glass and a molding surface provided on the lower mold, and then the closed space is depressurized. It may be something.

  As described above, by reducing the pressure in the closed space formed between the sheet glass and the molding surface provided in the lower mold, the closed position is located on the upper surface side as compared with the pressure in the space (closed space) located on the lower surface side of the plate glass. The air pressure in the space increases relatively. As a result, the sheet glass that partitions the closed space and the space located on the upper surface side is pressed from the space located on the upper surface side toward the forming surface. Accordingly, this pressing force has a shape that promotes the deformation of the sheet glass toward the forming surface, and the sheet glass can be formed into a shape following the forming surface at a lower temperature (while maintaining a high viscosity). Therefore, it is possible to more accurately form the sheet glass into a shape following the forming surface while preventing the occurrence of contact traces on the surface of the sheet glass with a higher probability or further suppressing the degree thereof.

  In this case, the curved sheet glass forming method according to the present invention may further include pressurizing a space located on the upper surface side of the sheet glass.

  As described above, in addition to reducing the pressure in the sealed space formed between the glass sheet and the molding surface, the pressure in the space located on the lower surface side of the glass sheet can be increased by pressing the space located on the upper surface side of the glass sheet. And the pressure in the space located on the upper surface side can be made larger, and the sheet glass can be pressed toward the forming surface with a larger pressing force. Therefore, even when the viscosity of the glass sheet is kept higher, the glass sheet can be formed into a shape following the forming surface. Therefore, it is possible to more accurately form the sheet glass into a shape following the forming surface while preventing the occurrence of contact traces on the surface of the sheet glass with a higher probability or further suppressing the degree thereof.

  Further, the method for forming a curved glass sheet according to the present invention may be one in which the curved glass sheet is formed by heating the glass sheet using a lower mold provided with a concave forming surface.

  If a lower mold having a concave forming surface is used, for example, only placing the sheet glass on the lower mold, the closed space can be easily formed between the lower surface of the sheet glass and the forming surface. it can. Therefore, the above configuration is particularly effective when the space located on the upper surface side of the plate glass is relatively pressurized.

  In addition, the method for forming a curved sheet glass according to the present invention, using a lower mold provided with a concave forming surface and a convex forming surface, after forming the curved sheet glass by heating the sheet glass, Inverting the curved glass sheet, placing the inverted curved glass sheet on a lower mold provided with a forming surface having a shape corresponding to the lower surface of the inverted curved glass sheet, and forming the curved glass sheet by heating. Is also good.

 The above configuration is effective when forming a curved plate glass having a concavely curved portion and a convexly curved portion. That is, when the curved sheet glass having the uneven shape as described above is molded by the method according to the present invention, the molding surface corresponding to the lower surface shape of the curved sheet glass to be molded, that is, the concave surface is formed with the molding surface having a convex shape. It is conceivable to use a lower mold provided with a molding surface. Here, when the curved sheet glass is formed by heating the sheet glass by the method (self-weight method) according to the present invention, a state in which the end portion of the portion formed on the convex forming surface of the curved sheet glass is raised. It has been found that it is difficult to accurately form a convexly curved portion.

  Therefore, in the present invention, after the sheet glass is placed on the lower mold and the curved sheet glass is formed by heating, the curved sheet glass is inverted, and a forming surface having a shape corresponding to the lower surface of the inverted curved sheet glass is provided. The curved plate glass after inversion was placed on the lower mold, and the curved plate glass was formed by heating. According to this method, the part formed in a state in which the ends are raised on the convex molding surface in the molding before the inversion is deformed by its own weight due to heat softening on the concave molding surface in the molding after the inversion. Thereby, it is re-formed into a final shape (a shape similar to a concave forming surface). Therefore, even with a curved plate glass having a concavely curved portion and a convexly curved portion, it is possible to correct the rising of the end portion and mold the glass plate with high precision.

  Further, in this case, in the method for forming a curved sheet glass according to the present invention, the lower mold used for molding after inversion may be the lower mold used for molding before inversion. Alternatively, the lower mold used for molding after inversion may be different from the lower mold used for molding before inversion.

  When the curved glass sheet to be formed is composed of a concave part and a convex part that are symmetrical to each other, the lower surface shape of the curved sheet glass after inversion is the same as the lower surface shape of the curved sheet glass before inversion. . Therefore, a common molding surface can be used before and after reversal, and even when reversing and performing further molding, only one lower die is required. In addition, even when the concave part of the curved plate glass and the convex part have an asymmetric shape, the lower mold used for molding after inversion is different from the lower mold used for molding before inversion. By separately preparing and providing a forming surface of a shape corresponding to the lower surface of the curved sheet glass after the inversion on the lower mold for the above-described inversion, the curved sheet glass of the desired shape is formed by molding twice before and after the inversion. can do. Therefore, according to the forming method according to the present invention, any shape of curved glass sheet can be accurately formed by using the lower molds having the corresponding shaped surfaces before and after the reversing operation. It is possible to do.

  In addition, the method for forming a curved sheet glass according to the present invention includes the steps of: providing a concave forming surface in a lower mold; placing plate glass having opposite lengths on two sides on the forming surface; When forming the sheet glass, the sheet glass is formed in an inclined position with respect to the horizontal direction so that the relatively short side of the sheet glass contacts the forming surface above the relatively long side. It may be placed on a surface.

  The shape of the sheet glass before the curve forming is usually rectangular, and the shape of the forming surface provided on the lower mold is often a semi-cylindrical shape. In this case, the plate glass is formed on the forming surface with the center line of the plate glass having the same distance from the two opposite sides of the plate glass coincident with the center line of the forming surface having the same distance from the two sides forming the peripheral edge of the forming surface. Place on top. At this time, the mounting posture of the plate glass is horizontal. On the other hand, in recent years, from the viewpoint of design, there has been an increasing need for a glass sheet having a non-rectangular shape such as a trapezoidal shape to be a curved glass sheet. However, when a sheet glass having such a shape is placed in a horizontal posture on the molding surface of the lower mold, as in the related art, the sheet glass is asymmetrically curved (the short side and the long side of the sheet glass are different from each other). Therefore, the value of the radius of curvature of the formed glass sheet was not stable, and it was difficult to form the curved glass sheet with required accuracy.

  On the other hand, in the present invention, the lower mold is provided with a concave forming surface, two opposite sides of the plate glass having different lengths are placed on the forming surface, and the curved plate glass is formed by heating. In doing so, the sheet glass is placed on the forming surface in a posture inclined with respect to the horizontal direction so that the relatively short side of the sheet glass contacts the forming surface above the relatively long side. I put it. By placing the non-rectangular plate glass in the inclined position on the forming surface in this manner, the center of gravity of the non-rectangular plate glass is relatively compared to the case where the plate glass is placed in the horizontal position as in the related art. The state is offset to the short side of the sheet glass. More specifically, when a non-rectangular sheet glass is placed on a molding surface in a horizontal position, the center line of the concave molding surface (here, for example, the distance from the two sides forming the peripheral edge of the molding surface is equal) The center of gravity of the sheet glass is offset to the longer side than the center line. On the other hand, as described above, the plate glass is placed in an inclined posture so that the side that becomes the short side of the sheet glass is relatively upward, so that the center of gravity of the sheet glass is closer to the short side of the center line of the forming surface than before. Can be offset. As a result, a curved glass sheet can be formed while maintaining a balance between the short side and the long side, so that the degree of curvature due to its own weight deformation is prevented from varying between the short side and the long side as much as possible. As a result, it is possible to stably form a highly accurate curved plate glass.

  In this case, in the method for forming a curved glass sheet according to the present invention, the center of gravity of the glass sheet is closer to the shorter side of the glass sheet than the center line of the molding surface where the distance from the two sides forming the peripheral edge of the molding surface is equal. The sheet glass may be placed on the forming surface in a posture inclined with respect to the horizontal direction so as to be positioned.

  As described above, by setting the position of the center of gravity of the sheet glass with respect to the forming surface, softening due to heating causes the sheet glass to undergo its own weight deformation (deflection) such that the center of gravity of the sheet glass is directed to the center line of the forming surface. This is because the short side of the glass sheet has a small contact area with the molding surface and a small frictional resistance. Therefore, by placing the plate glass as described above, it is possible to further reduce the variation in the degree of curvature between the short side and the long side, and to form a curved plate glass with higher precision.

  Further, in this case, the method for forming a curved glass sheet according to the present invention is such that the offset amount of the center line of the glass sheet having the same distance from the two sides of the glass sheet to the shorter side of the glass sheet with respect to the center line of the forming surface is equal to The distance may be set to be more than 1 and not more than 15 times the distance from the center line to the center of gravity.

  The inventors of the present invention have verified whether the center of gravity of the sheet glass is specifically offset to the center line of the forming surface, and how the offset has a favorable effect on the forming accuracy. It was found that very good results were obtained when the distance from the center line of the sheet glass to the center of gravity was set to be more than 1 and not more than 15 times. Accordingly, by setting the amount of offset of the center line of the sheet glass to the short side of the sheet glass with respect to the center line of the molding surface within the above range, the difference in curvature between the short side and the long side after bending is extremely small. In addition, it is possible to stably perform high-precision curved sheet glass forming.

  As described above, according to the present invention, it is possible to provide a curved plate glass having a good surface quality by minimizing the occurrence of contact marks with the mold.

It is a principal part sectional view of the shaping | molding apparatus of the curved sheet glass which concerns on 1st embodiment of this invention. FIG. 2 is a plan view of the mold shown in FIG. 1. It is a figure for explaining the forming method of the curved sheet glass concerning a first embodiment of the present invention, and is an important section sectional view of a forming device when a sheet glass deforms by its own weight by heating. It is a graph which shows the relationship between the heating time and the viscosity of sheet glass which concern on 1st embodiment of this invention. It is principal part sectional drawing of the shaping | molding apparatus of the curved sheet glass which concerns on 2nd embodiment of this invention. It is AA sectional drawing of the shaping | molding die shown in FIG. It is principal part sectional drawing of the shaping | molding apparatus of the curved sheet glass which concerns on 3rd embodiment of this invention. FIG. 8 is a plan view of the mold shown in FIG. 7. It is a figure for explaining the forming method of the curved sheet glass concerning a third embodiment of the present invention, and is an important section sectional view of a forming device when sheet glass deforms by its own weight by the first heating. It is a figure for explaining the forming method of the curved sheet glass concerning a third embodiment of the present invention, when a curved sheet glass formed into the shape shown in Drawing 9 is turned upside down and placed in a forming die shown in Drawing 7 It is principal part sectional drawing of the shaping | molding apparatus. It is principal part sectional drawing of the shaping | molding apparatus of the curved sheet glass which concerns on 4th Embodiment of this invention. FIG. 12 is a plan view of the mold shown in FIG. 11. FIG. 12 is a cross-sectional view of a main part of the molding die when the sheet glass is placed on the molding die shown in FIG. 11 in a horizontal posture.

  Hereinafter, a first embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 is a cross-sectional view of a main part for describing an outline of a curved sheet glass forming apparatus 10 according to a first embodiment of the present invention. The forming apparatus 10 accommodates a lower mold 11 for forming the sheet glass G1 into a predetermined curved shape, a heating apparatus 12 for heating the sheet glass G1 placed on the lower mold 11, and the lower mold 11 and the heating apparatus 12. A furnace chamber 13 is provided.

Here, the sheet glass G1 to be formed can have an appropriate composition according to its use, and the composition is not particularly limited, but, for example, SiO ₂ : 50 to 80 by mass%, for example. %, Al ₂ O ₃ : 5 to 25%, B ₂ O ₃ : 0 to 15%, Na ₂ O: 1 to 20%, and K ₂ O: 0 to 10%. In addition, a curved tempered glass sheet can be formed by chemically strengthening after being curved-formed by the forming apparatus 10.

  The size of the sheet glass G1 is not particularly limited, but, for example, its thickness may be 3.0 mm or less, preferably 2.5 mm or less, and more preferably 1.5 mm or less. , More preferably, 1.0 mm or less. On the other hand, the lower limit may be 0.1 mm or more, preferably 0.5 mm or more, from the viewpoint of moldability. This is because if the thickness is small, even if it is relatively high in viscosity, it can be easily curved and formed.

  The lower mold 11 has a forming surface 14 for forming the sheet glass G1 into a predetermined curved shape. In the present embodiment, the forming surface 14 is a concave curved surface, and as shown in FIG. 2, two opposite sides of the plate glass G1 placed on the lower mold 11 (here, the short sides G1a, G1a) can be supported over the entire width direction (here, a direction orthogonal to the bending direction; the same applies hereinafter). The shape of the molding surface 14 is formed in a shape that extends linearly in the width direction and has a single radius of curvature over the entire area in the bending direction. In the present embodiment, the bending direction is a direction along the long sides G1b, G1b of the glass sheet G1, and the width direction is a direction along the short sides G1a, G1a of the glass sheet G1 (FIG. 2).

  In the present embodiment, a sheet 15 is provided between the plate glass G1 and the molding surface 14 provided on the lower mold 11. Therefore, in this case, heating of the glass sheet G1 is started in a state where the sheet 15 is interposed between the glass sheet G1 and the forming surface 14. Here, the sheet 15 is mainly for protecting the plate glass G1 from the lower mold 11, and is formed of a material softer than the lower mold 11. Specifically, glass, carbon, or a metal (such as stainless steel) softer than the material forming the lower mold 11 can be used. They also have resistance to heating the sheet glass G1. In addition, the sheet 15 is naturally formed in a sheet shape, and is required to have a rigidity (a degree of resistance to deformation as the sheet 15) that can be deformed following the forming surface 14 when placed on the forming surface 14. . In view of this point, for example, the sheet 15 is formed of glass cloth when the sheet 15 is formed of glass, carbon cloth when the sheet 15 is formed of carbon, and stainless steel cloth when the sheet 15 is formed of stainless steel. Should be formed.

  The lower mold 11 can be formed of any material without particular limitation as long as it can withstand heating of the plate glass G1 described later, and mullite is an example. Of course, it is also possible to form the lower mold 11 from a material other than mullite, for example, alumina, zircon, or a mixture thereof (alumina zircon, zircon mullite, etc.).

  The heating device 12 is for heating the plate glass G1 placed on the lower mold 11 in the furnace chamber 13, and is, for example, a radiant heating type such as an electric heater, or convection heating the atmosphere 16 in the furnace chamber 13 with a burner. Alternatively, a type in which a gas heated by a burner is supplied into the furnace chamber 13 to convectively heat the atmosphere 16 in the furnace chamber 13 can be adopted. In the present embodiment, as shown in FIG. 1, a case where the heating device 12 is arranged at the upper part of the furnace chamber 13, more precisely, at a position facing the upper surface G <b> 1 c of the plate glass G placed on the lower mold 11. Although illustrated, of course, other arrangement modes (arrangement positions and numbers) can be adopted.

  Next, an example of a method for forming a curved sheet glass using the forming apparatus 10 having the above configuration will be described together with advantages of the present invention.

  First, as shown in FIG. 1, a sheet glass G1 to be formed is supplied into a furnace chamber 13 of a forming apparatus 10 and mounted on a lower mold 11 (a mounting step). As shown in FIG. 1, when the sheet 15 is interposed, the sheet 15 is placed on the lower mold 11 and the plate glass G1 is placed from above. When placed on the lower mold 11, the glass sheet G1 has a shape before curved deformation (for example, a flat plate shape as shown in FIG. 1). At this time, the lower mold 11 may be preheated at a predetermined temperature (for example, 200 to 300 ° C.) (a preheating step). Preheating may be performed in the furnace chamber 13 or may be performed in a furnace chamber (preheating furnace) different from the furnace chamber 13.

  After placing the plate glass G1 on the lower mold 11 in this way, the heating of the plate glass G1 by the heating device 12 is started (heating step). As a result, the sheet glass G1 is softened, and the sheet glass G1 is made to conform to the forming surface 14 by macroscopic deformation due to softening (in the present embodiment, downward bending deformation) (closely adheres to the forming surface 14). Then, as shown in FIG. 3, it is formed into a shape corresponding to the forming surface 14 (forming step). When the forming of the curved glass sheet G2 is completed, the curved glass sheet G2 is taken out of the lower mold 11 and out of the furnace chamber 13 (a take-out step). Through the above steps, the curved plate glass G2 is obtained.

FIG. 4 shows the relationship between the heating time and the viscosity of the glass sheet G1 during the heating step. As shown in FIG. 4, in the main heating step, the temperature of the sheet glass G1 (usually, the temperature of the sheet glass G1 is estimated based on the temperature of the atmosphere 16 in the furnace chamber 13 which can be easily measured) is increased at a constant gradient, After heating the glass sheet G1 to a predetermined temperature, a heat history for cooling the glass sheet G1 at a predetermined gradient is set. At this time, the heat history is set so that the maximum temperature of the glass sheet G1, that is, the minimum viscosity V _{min of the} glass sheet G1 is 10 ¹⁰ poise or more. In other words, the viscosity of the glass sheet G1 is maintained at 10 ¹⁰ poise or more from the start of heating the glass sheet G1 to the completion of the forming. Thus, while the sheet glass G1 is formed with high precision, a situation in which the forming surface 14 and the sheet glass G1 are brought into unnecessarily strong contact with each other is avoided, and the surface of the formed sheet glass G1 (curved sheet glass G2) is formed with the forming surface 14. This makes it possible to prevent contact traces from remaining as much as possible. Further, the higher the viscosity of the glass sheet G1, the harder the surface (the lower surface G1d) of the glass sheet G1. This also makes it difficult to form a contact mark with the molding surface 14.

Further, in the present embodiment, during the period from the start of heating to the forming completion, the time _{T 1} at which the viscosity of the glass sheet G1 is equal to or less than _V 1 ⁼ 10 13 poise set to 60 minutes or less, and the viscosity of the glass sheet G1 is V ₂ = ¹⁰ 14.5 poise or less become time _{T 2} was to set below 90 minutes. As described above, even if the sheet glass G1 does not reach the minimum viscosity _Vmin , by keeping the state of relatively low viscosity as short as possible, it is possible to prevent the occurrence of contact marks with a higher probability, or to the extent ( It is possible to further suppress the number of occurrences, the size, the conspicuousness, etc.). Note that in the glass sheet G1 showing the composition of an example in this embodiment, the viscosity V ₁ was equivalent to the viscosity at the annealing point, the viscosity V ₂ corresponds to the viscosity at the strain point. From this, it is possible to not only control the minimum viscosity V _min of the glass sheet G1 but also keep the time periods T ₁ and T ₂ for keeping the glass sheet G1 at a temperature equal to or higher than the annealing point and the strain point as short as possible. It can be understood that it is very effective in preventing or suppressing the occurrence of traces as much as possible.

It is preferable that the minimum viscosity V _min and the times T ₁ , T _{2 at which the} viscosities become equal to or less than the predetermined viscosities V ₁ , V ₂ are appropriately set depending on the use of the curved plate glass G2. For example, in the case of a high-definition display application for an automobile display, taking into consideration that the thickness dimension is relatively large, for example, the time T at which the minimum viscosity V _min of the sheet glass G1 becomes 10 ¹⁰ poise or more and the predetermined viscosity V ₁ or less is set. ₁ 60 minutes or less, and a predetermined viscosity _{V 2} less become time _{T 2} to preferably set below 90 minutes. In addition, in the case of a high-definition display application for a smartphone, taking into consideration that the thickness dimension is relatively small, for example, the time T _{1 at} which the minimum viscosity V _min of the plate glass G1 becomes 10 ¹¹ poise or more and the predetermined viscosity V ₁ or less. 30 minutes or less, and a predetermined viscosity V ₂ less become time T ₂ to preferably set to 60 minutes or less.

  In the present embodiment, the heating of the sheet glass G1 is started in a state where the sheet 15 softer than the lower mold 11 is interposed between the lower mold 11 and the sheet glass G1. Thereby, the sheet glass G1 comes into contact with the sheet 15, and direct contact with the lower mold 11 is avoided. Since this sheet 15 is softer than the lower mold 11, even if it comes into contact with the plate glass G1, scratches (contact marks) are less likely to be made. Further, since the sheet 15 is flexible, it is flexible against deformation, and easily follows the molding surface 14 provided on the lower mold 11. Therefore, the presence of the sheet 15 does not adversely affect the heating curve forming of the sheet glass G1, and there is no problem in terms of forming accuracy.

  As described above, the first embodiment of the method for forming curved sheet glass according to the present invention has been described. However, this forming method can take any form within the scope of the present invention.

  FIGS. 5 and 6 show an example thereof (second embodiment of the present invention). The forming apparatus 17 shown in these figures shows a state in which the sheet glass G1 is placed on the lower mold 18 and the lower surface G1d of the sheet glass G1. And a molding surface 14, a closed space 19 is formed, and the closed space 19 and the space 20 located on the upper surface G1c side of the sheet glass G1 can be partitioned. In detail, the lower mold 18 has a side portion 21 defining a closed space 19 together with the lower surface G1d of the sheet glass G1 and the forming surface 14 in a state where the sheet glass G1 is placed on the forming surface 14, thereby forming the forming surface With the plate glass G1 placed on the plate 14, a closed space 19 can be formed on the lower surface G1d side of the plate glass G1.

  The lower mold 18 has a decompression device 22 that decompresses the sealed space 19 formed on the lower surface G1d side of the glass sheet G1. Thus, the pressure in the closed space 19 can be reduced during part or all of the period during which the plate glass G1 is heated.

As described above, by reducing the pressure in the sealed space 19 formed between the sheet glass G1 and the molding surface 14, the pressure in the space (closed space 19) located on the lower surface G1d side of the sheet glass G1 is lower than the pressure in the upper surface G1c. The pressure in the space 20 in which it is located is relatively increased. Thereby, the plate glass G1 which partitions the closed space 19 and the space 20 located on the upper surface G1c side is pressed toward the forming surface 14 from the space 20 located on the upper surface G1c side. Therefore, this pressing force has a shape that promotes the deformation of the sheet glass G1 toward the forming surface 14, and the sheet glass G1 is shaped into a shape following the forming surface 14 at a lower temperature (while maintaining the minimum viscosity V _min higher). Can be molded. Therefore, it is possible to prevent the occurrence of contact marks on the lower surface G1d of the sheet glass G1 with a higher probability or to further suppress the degree thereof, and to form the sheet glass G1 into a shape that more closely follows the forming surface 14 with higher accuracy. Becomes possible. In this case, the minimum viscosity V _min of the plate glass G1 can be set to, for example, 10 ^11.5 poise or more.

In the second embodiment, although not shown, a pressurizing device for pressurizing the space 20 located on the upper surface G1c side of the sheet glass G1 may be further provided. If the closed space 19 formed between the glass sheet G1 and the molding surface 14 is depressurized and the space 20 located on the upper surface G1c side of the glass sheet G1 is further pressurized, the lower surface G1d side of the glass sheet G1 can be further pressed. The difference between the atmospheric pressure of the located space (sealed space 19) and the atmospheric pressure of the space 20 located on the upper surface G1c side can be increased, and the sheet glass G1 can be pressed toward the forming surface 14 with a larger pressing force. Therefore, even in a state where the minimum viscosity V _min of the glass sheet G1 is kept higher, the glass sheet G1 can be formed into a shape according to the forming surface 14.

  FIG. 7 is a sectional view of a main part of a molding device 23 according to the third embodiment of the present invention. As shown in FIG. 7, the molding apparatus 23 differs from the first and second embodiments in that it has a lower mold 26 provided with a concave molding surface 24 and a convex molding surface 25. I do.

  Here, both the concave forming surface 24 and the convex forming surface 25 have a constant radius of curvature, and in the present embodiment, are symmetrical (rotationally symmetric) around the boundary 27 between the two forming surfaces 24, 25. ) In this case, the radius of curvature, the width dimension, and the dimension along the bending direction (the dimension in the direction orthogonal to the width direction in FIG. 8) of each of the molding surfaces 24, 25 are all set to the same size.

  Next, an example of a method of forming a curved sheet glass using the forming apparatus 23 having the above configuration will be described together with advantages of the present invention.

  First, as shown in FIG. 7, the sheet glass G1 to be formed is supplied into the furnace chamber 13 of the forming apparatus 23 and mounted on the lower mold 26 (mounting step). At this time, as shown in FIG. 8, the sheet glass G1 is formed such that two opposing sides (short sides G1a, G1a) of the rectangular sheet glass G1 are supported by the forming surfaces 24, 25 over the entire area in the width direction. It rests on the surfaces 24 and 25. Although illustration is omitted, when the sheet 15 is interposed as in the first embodiment, the sheet 15 is placed on the lower mold 26, and the sheet glass G1 is placed from above.

  After the plate glass G1 is placed on the lower mold 26 in this manner, heating of the plate glass G1 by the heating device 12 is started (heating step). As a result, the sheet glass G1 is softened, and the sheet glass G1 is adapted to the respective forming surfaces 24 and 25 (by being macroscopically adhered to the forming surfaces 24 and 25) due to its own weight deformation accompanying the softening, as shown in FIG. Next, a curved sheet glass G3 having a concavely curved portion G3a and a convexly curved portion G3b, which is shaped according to the molding surfaces 24 and 25, is molded (molding step). At this time, the end G3b1 of the convex portion G3b tends to slightly rise from the convex molding surface 25.

  After forming the curved glass sheet G3 in this manner, the curved glass sheet G3 is inverted, and a lower mold having a molding surface corresponding to the lower surface G3c of the inverted curved glass sheet G3, here, the first time, The curved plate glass G3 is placed on the same one as the lower mold 26 used for the heat molding of FIG. Since it is inverted, the concavely curved portion G3a of the curved plate glass G3 is mounted on the convex forming surface 25, and the convexly curved portion G3b is mounted on the concave forming surface 24. State. After that, the heating of the curved sheet glass G3 by the heating device 12 is started (reheating step), and the curved sheet glass G3 is softened, and the curved sheet glass G3 is deformed by its own weight due to the softening. Reshape to the shape. At this time, the end portion G3b1 slightly raised from the convex molding surface 25 in the first heat molding is placed on the concave molding surface 24 after inversion, and its own weight is reduced in a direction to cancel the floating. Works. Therefore, the convexly curved portion G3b including the end portion G3b1 is accurately re-formed into a shape conforming to the molding surface 24 due to the downward bending deformation in the second heat molding.

Also in the present embodiment, the heat history is set so that the minimum viscosity V _min of the glass sheet G1 (curved glass sheet G3) between the first and second heating steps is 10 ¹⁰ poise or more. While forming G1 (curved glass sheet G3) with high precision, avoiding a situation where each of the forming surfaces 24, 25 and the glass sheet G1 (curved glass sheet G3) comes in contact with the glass sheet G1 (curved glass sheet G3) more than necessary. G3) A situation in which contact marks with the molding surfaces 24 and 25 remain on the surface can be prevented as much as possible.

Of course, in addition to the minimum viscosity _{V min,} the time _{T 1} at which the viscosity of the glass sheet G1 (curved plate glass G3) is equal to or less than _V 1 ⁼ 10 13 poise set to 60 minutes or less, and the glass sheet G1 (curved plate glass G3) the viscosity by setting the time _{T 2} equal to or less than _V 2 ⁼ 10 14.5 poise below 90 minutes, bear a relatively low viscosity state as much as possible in a short time, the occurrence of contact trace with higher probability It can be prevented, or the degree thereof (number of occurrences, size, conspicuousness, etc.) can be further suppressed.

  In the third embodiment, the case where the concave portion G3a and the convex portion G3b of the curved plate glass G3 to be formed are symmetrical is illustrated. It is possible to apply. In this case, although not shown, as the lower mold used for molding after inversion, a different mold from the lower mold 26 used for molding before inversion is separately prepared to correspond to the lower surface G3c of the curved glass sheet G3 after inversion. By providing the shaping surface of the shape on the lower die for inversion, the curved plate glass G3 having a desired shape can be formed by two shaping operations before and after inversion.

  In the third embodiment, the case where the curved plate glass G3 to be molded has one portion G3a having a concave shape and one portion G3b having a convex shape is exemplified. It may be a sheet glass G3. For example, although not shown, a curved plate glass G3 having a shape in which a convex portion G3b is connected to both sides of a concave portion G3a can be formed by the method according to the third embodiment described above.

  Hereinafter, a fourth embodiment of the present invention will be described with reference to FIGS.

  FIG. 11 is a sectional view of a main part of a molding apparatus 10 according to a fourth embodiment of the present invention. As shown in FIG. 11, the molding device 10 is the same as the molding device 10 used in the first embodiment. The difference lies in the shape of the plate glass G4 to be formed and the mounting mode. Hereinafter, these points will be mainly described in detail.

  As shown in FIG. 12, the plate glass G4 to be molded in the present embodiment has a so-called non-rectangular shape in which the lengths of two opposing sides G4a1 and G4a2 are different from each other. In the illustrated example, the plate glass G4 has a trapezoidal shape with the short side G4a1 as the upper base and the long side G4a2 as the lower base since the two opposite sides G4a1 and G4a2 are parallel.

  Then, the plate glass G4 having the above shape is formed in a posture inclined with respect to the horizontal plane H such that the short side G4a1 is in contact with the forming surface 14 above the long side G4a2 as shown in FIG. It is placed on the surface 14.

  Further, at this time, the center of gravity g (FIG. 12) of the sheet glass G4 is more than the center line C1 (FIG. 12) of the forming surface 14 having the same distance from the two sides 14a, 14a forming the peripheral edge of the forming surface 14. The mounting posture and position of the plate glass G4 are set so as to be located on the short side G4a1 side (FIG. 11). More specifically, the offset amount of the center line C2 (FIG. 12) of the plate glass G4 having the same distance from the two sides G4a1 and G4a2 of the plate glass G4 to the short side G4a1 side of the plate glass G4 with respect to the center line C1 of the molding surface 14. S (FIG. 11) is set to be more than 1 and not more than 15 times the distance d (FIG. 13) from the center line C2 of the glass sheet G4 to the center of gravity g. Note that the offset amount S here refers to a deviation amount of the direction of the center line C2 of the sheet glass G4 along the horizontal plane H with respect to the center line C1 of the molding surface 14, as shown in FIG.

  After the plate glass G4 is placed on the lower mold 11 as described above, heating of the plate glass G4 by the heating device 12 is started (heating step). As a result, the glass sheet G4 is softened, and the glass sheet G4 is made to conform to the molding surface 14 (macroscopically adheres to the molding surface 14) due to its own weight deformation due to the softening, and is formed into a shape similar to the molding surface 14. (Molding step).

  Here, in the present invention, the plate glass G4 is inclined with respect to the horizontal plane H such that the side that becomes the relatively short side G4a1 contacts the forming surface 14 above the side that becomes the relatively long side G4a2. It was placed on the molding surface 14 in the posture in which it was set (see FIG. 11). By placing the non-rectangular plate glass G4 in the inclined position on the forming surface 14 in this manner, the center of gravity g of the non-rectangular plate glass G4 is compared with the case where the plate glass G4 is placed in the horizontal position as in the related art. Then, the plate glass G4 is relatively offset to the short side G4a1 side (see FIGS. 11 and 13). More specifically, when the non-rectangular plate glass G4 is placed on the molding surface 14 in a posture along the horizontal plane H, as shown in FIG. 13, the center line C1 of the concave molding surface 14 (here, The center of gravity g of the glass sheet G4 is offset to the longer side G4a2 than the center line having the same distance from the two sides 14a, 14a forming the peripheral edge of the molding surface 14.) On the other hand, as described above, the plate glass G4 is placed in an inclined posture such that the side that becomes the short side G4a1 of the plate glass G4 is relatively upward, so that the center of gravity g of the plate glass G4 is formed on the molding surface 14 more than before. It can be in a state of being offset toward the center line C1. Thus, the curved sheet glass can be formed while maintaining a balance between the short side G4a1 side and the long side G4a2 side, and thus the degree of bending due to its own weight deformation (in the present embodiment, the radius of curvature after forming) is short. Variations between the side G4a1 and the long side G4a2 can be prevented as much as possible, and highly accurate curved plate glass can be stably formed.

  In particular, in the present embodiment, the side where the center of gravity g of the glass sheet G4 is on the shorter side G4a1 of the glass sheet G4 than the center line C1 of the molding surface 14 having the same distance from the two sides 14a, 14a forming the peripheral edge of the molding surface 14. Was placed on the plate glass G4. More specifically, based on the verification results by the present inventors, the offset amount S of the center line C2 of the sheet glass G4 with respect to the center line C1 of the forming surface 14 is determined by the distance d from the center line C2 of the sheet glass G4 to the center of gravity g. The position of the plate glass G4 was set so as to be more than 1 and not more than 15 times (FIG. 13). By placing the sheet glass G4 in this manner, the sheet glass G4 undergoes its own weight deformation (flexure deformation) such that the center of gravity g of the sheet glass G4 is directed toward the center line C1 of the forming surface 14 due to softening caused by heating. Therefore, by placing the plate glass G4 as described above, the variation in the degree of curvature between the short side G4a1 side and the long side G4a2 side can be further reduced, and a more accurate curved plate glass can be formed. .

Also in the present embodiment, by setting the heat history so that the minimum viscosity V _min of the sheet glass G4 during the heating step is 10 ¹⁰ poise or more, the sheet glass G4 can be formed with high accuracy. By avoiding a situation where the surface 14 and the plate glass G4 are in contact with each other more strongly than necessary, it is possible to prevent a situation in which a contact mark with the molding surface 14 remains on the surface of the formed plate glass G4 as much as possible.

Of course, in addition to the minimum viscosity _{V min,} the time _{T 1} at which the viscosity of the glass sheet G4 becomes less _V 1 ⁼ 10 13 poise set to 60 minutes or less, and the viscosity of the glass sheet G4 is _V 2 ^{= 10 14.5} by setting poise or less and comprising a time T ₂ below 90 minutes, bear a relatively low viscosity state as much as possible in a short time, the occurrence of contact trace can be prevented at a higher probability, or the degree (generation number, Size, conspicuousness, etc.) can be further suppressed.

  In the fourth embodiment, a non-rectangular plate glass G4 has a trapezoidal shape. However, the present invention can of course be applied to a plate glass having another form. For example, although not shown, the present invention can also be applied to a non-trapezoidal sheet glass such as a square shape in which two opposite sides are not parallel to each other. In this case, the side means, when viewed as a whole sheet glass, a portion which constitutes the peripheral portion linearly, and not only the complete linear shape but also the peripheral portion extending linearly with a slight curvature. Partly included.

  Further, with respect to the forming surface 14 provided on the lower mold 11, in the first, second, and fourth embodiments, for forming the plate glasses G1, G4 into a shape having a single radius of curvature over the entire area in the longitudinal direction. Although an example having a shape is illustrated, the shape is not limited to this. The forming surface 14 may be configured with a plurality of radii of curvature, whereby it is possible to form the glass sheets G1 and G4 into a curved shape having a plurality of continuous radii of curvature. Of course, a part of the plate glasses G1 and G4 can be formed in a curved shape. Further, it is not necessary that the entire surfaces of the plate glasses G1 and G4 be placed on the molding surface 14. For example, although not shown, a flat surface extending in the horizontal direction is provided around the molding surface 14, and the flat glass The periphery of G1 and G4 may be supported.

  Further, in the first to fourth embodiments, one or a plurality of lower dies 11 are fixedly arranged in the furnace chamber 13, and the sheet glasses G <b> 1 and G <b> 4 are placed on the lower dies 11 and molded at a time (so-called “first”). Although batch processing is performed), the lower mold 11 and the sheet glasses G1 and G4 are passed through a heating furnace (furnace chamber 13) while being conveyed by a conveyor or the like, so that the sheet glasses G1 and G4 are sequentially formed. Processing may be performed (so-called continuous processing may be performed).

  Hereinafter, examples of the present invention will be described. First, the experimental conditions (forming conditions, measurement conditions) will be described, and then the experimental results will be described.

(Molding condition)
In each of the examples (Examples 1 to 4) and the comparative example, a plate glass having a long side of 160 mm, a short side of 80 mm, and a thickness of 0.7 mm was used as a test piece. Then, this sheet glass was placed on a forming surface having a concave curved shape of R1000 mm so as to be curved along the long side, and was formed into a shape following the forming surface by its own weight deformation due to heat softening. The heat history at this time is as shown in Table 1.

(Measurement condition)
The number of contact marks remaining on the surface of the curved glass sheet formed as described above was measured. As a treatment before the measurement, the surface of the curved plate glass was washed with pure water in a clean room to remove removable foreign substances, and the number of contact marks was visually measured. The measurement was performed in a clean room under two conditions of (1) illuminance 700 lx and (2) illuminance 1200 lx. Table 2 shows the measurement results at this time. In addition, "countless" in Table 2 means that the number of contact marks that can be visually confirmed in the target test piece is so large as to exceed 100.

As described above, when the minimum viscosity of the sheet glass during the heating step was less than 10 ¹⁰ poise (comparative example), an unacceptable level of countless contact marks were observed on the surface of the sheet glass (curved sheet glass) after molding. On the other hand, when the minimum viscosity of the sheet glass during the heating step was set to 10 ¹⁰ poise or more (Examples 1 to 4), the number of contact marks remaining on the surface of the curved sheet glass was small. In particular, when the minimum viscosity of the plate glass is set to 10 ¹⁰ poise or more during the heating step (Examples 1 and 2), the occurrence of contact marks is not observed at least under ordinary illuminance (under 700 lx). In particular, in this case, when the time during which the viscosity of the plate glass becomes 10 ¹³ poise or less is set to 30 minutes or less, and the time when the viscosity becomes 10 ^14.5 poise or less is set to 60 minutes or less (Example 1), The occurrence of contact marks was not observed at all under the condition of further increasing the illuminance (under 1200 lx), and a curved glass sheet showing excellent molding accuracy was obtained.

10, 17, 23 Forming device 11, 18, 26 Lower mold 12 Heating device 13 Furnace chamber 14 Forming surface 15 Sheet 19 Sealed space 22 Decompression device G1, G4 Plate glass G2, G3 Curved plate glass

Claims (11)

By heating the glass sheet placed on the lower mold, to obtain a curved glass sheet by its own weight deformation due to softening of the glass sheet, in a method of forming a curved glass sheet,
From the start of heating to the glass sheet to the completion of the molding of the glass sheet, the viscosity of the glass sheet is maintained at 10 ¹⁰ poise or more, the time to be 10 ¹³ poise or less is set to 30 minutes or less, and 10. A method for forming a curved sheet glass, wherein the time during which 10 ^14.5 poise or less is set is set to 60 minutes or less . The method for forming a curved sheet glass according to claim 1, wherein heating of the sheet glass is started in a state where a sheet softer than the lower mold is interposed between the lower mold and the sheet glass. By placing the plate glass in the lower mold, after forming a sealed space between the plate underside and the molding surface of the provided in the lower mold of the glass, depressurizing the closed space, according to claim 1 or 2 For forming curved sheet glass. The method for forming a curved sheet glass according to claim 3 , further comprising pressurizing a space located on an upper surface side of the sheet glass. Using the lower mold molding surface which forms a concave is provided, performs shaping of the curved plate glass by heating to the plate glass, the molding method of the curved plate glass according to any one of claims 1-4. Using the lower mold provided with a concave forming surface and a convex forming surface, after forming the curved plate glass by heating the plate glass,
Invert the curved glass sheet, place the curved glass sheet on a lower mold having a molding surface corresponding to the lower surface of the inverted curved glass sheet, and form the curved glass sheet by the heating. The method for forming a curved sheet glass according to claim 1 or 2, which is performed. The method for forming a curved glass sheet according to claim 6 , wherein the lower mold used for molding after the inversion is a lower mold used for molding before the inversion. The method for forming a curved glass sheet according to claim 6 , wherein a lower mold used for the molding after the inversion is different from a lower mold used for the molding before the inversion. Providing a concave molding surface in the lower mold, placing the plate glass having two opposing side lengths different from each other on the molding surface, and forming the curved plate glass by heating, The glass sheet is placed on the molding surface in a posture inclined with respect to the horizontal direction so that the side of the sheet glass that is relatively short side contacts the molding surface above the side that is relatively long side. method of molding a curved plate glass according to claim 1 or 2 location. The sheet glass is inclined with respect to the horizontal direction so that the center of gravity of the sheet glass is located on a side that is a shorter side of the sheet glass than a center line of the forming surface, which is equal in distance from two sides forming a peripheral portion of the forming surface. The method for forming a curved sheet glass according to claim 9 , wherein the curved glass sheet is placed on the forming surface in an inclined position. The offset amount of the center line of the sheet glass having the same distance from the two sides of the sheet glass to the short side of the sheet glass with respect to the center line of the molding surface is 1 of the distance from the center line of the sheet glass to the center of gravity. The method for forming a curved sheet glass according to claim 10 , wherein the value is set to be more than 15 times and not more than 15 times.

Images