WO2014142050A1

WO2014142050A1 - Method for molding glass substrate

Info

Publication number: WO2014142050A1
Application number: PCT/JP2014/056112
Authority: WO
Inventors: 志郎舩津; 諭金杉; 啓一郎裏地
Original assignee: 旭硝子株式会社
Priority date: 2013-03-14
Filing date: 2014-03-10
Publication date: 2014-09-18
Also published as: TW201442964A

Abstract

Provided is a method for press-molding a glass substrate using a molding die, and inexpensively obtaining a glass molded article having high molded surface smoothness and high quality. The present invention is provided with: a surface processing step for placing a glass substrate having a pair of principal faces and comprising a glass containing an alkali oxide in the composition thereof between a first electrode and a second electrode, generating a corona discharge by applying a direct-current voltage so that the first electrode is a positive electrode and the second electrode is a ground or a negative electrode, and causing at least one species of alkali ion to move toward the second principal face side, which is the ground side or the negative electrode side, in a surface part on the first principal face side, which is the positive electrode side of the glass substrate; and a molding step for placing a molding die so that a press face abuts on the first principal face of the glass substrate, the surface of which has been processed in the surface processing step, and press-molding the glass substrate while maintaining the glass substrate at a predetermined temperature. The present invention furthermore has a mold release step for cooling the glass substrate and the molding die after the molding step, and separating the press face of the molding die from the first principal face of the glass substrate.

Description

Glass substrate molding method

The present invention relates to a method for forming a glass substrate, and more particularly to a method for obtaining a glass substrate having a molding surface with high shape stability at low cost by press molding.

In recent years, as a method of manufacturing a glass optical element such as a lens or a prism, a press molding method is used in which a heat-softened glass material is pressed and molded using a mold (hereinafter also referred to as a mold). Conventionally, glass substrates for magnetic recording media and the like have been manufactured by press molding using a mold. In the press molding method, a step of heating and softening a glass material, a step of pressing and molding using a molding die, and a step of separating the molding die from the glass molded body after cooling (hereinafter referred to as mold release) are sequentially performed. By passing, for example, the press surface of the mold, for example, a highly accurate and smooth mold surface is transferred to a glass material, a smooth and high-quality molding surface can be obtained, and productivity can be reduced at low cost. Is a high method.

In such a press molding method, in order to prevent the fusion of the mold to the glass softened at high temperature, to protect the press surface processed with high precision, and at the same time to obtain a molding surface of a glass molded body with high smoothness A mold release film is applied to the press surface of the mold. The mold release film is required to have mold releasability, adhesion to the mold, surface smoothness, high hardness and the like. Conventionally, Cr plating film, Ni plating film, carbon film, Ir, Re, etc. Noble metal films were used. Further, Patent Document 1 proposes a boron nitride film as a release film that is high in hardness and excellent in durability against heat cycles, and that does not chemically react with glass containing lead in particular.

However, these release films have problems such as high cost of materials themselves and high cost of film formation.

Further, in Patent Document 2, in forming a glass substrate for a magnetic recording medium, a mold release agent layer such as a metal salt of a higher fatty acid is formed on at least the mold surface (press surface) of the mold, There has been proposed a method for improving the releasability between a mold and a glass substrate which is a molded body.

However, this method not only makes it difficult to control the film thickness of the release agent layer in order to prevent the residue of the release agent from accumulating on the press surface of the mold and being transferred to the glass substrate. Each time, a release agent must be applied to form a release agent layer having a required thickness, resulting in a problem of poor work efficiency.

Japanese Patent Laid-Open No. 5-147954 JP 2004-131315 A

The present invention has been made to solve the above-described conventional problems, and is a method for press-molding a glass substrate using a mold and obtaining a high-quality glass molded body with high molding surface smoothness at low cost. The purpose is to provide.

In the glass substrate molding method of the present invention, a glass substrate made of glass having a pair of main surfaces and containing an alkali oxide in the composition is disposed between the first electrode and the second electrode, A DC voltage is applied to generate a corona discharge so that the first electrode is a positive electrode and the second electrode is a ground or a negative electrode. In the surface portion on the first main surface side that is the positive electrode side of the glass substrate A surface treatment step of moving at least one kind of alkali ions toward the second main surface side that is the ground or negative electrode side; and the first main surface of the glass substrate surface-treated in the surface treatment step. The method further comprises a molding step in which a molding die is arranged so that the press surface comes into contact with the glass substrate and press molding is performed in a state where the glass substrate is held at a predetermined temperature.

In the glass substrate molding method of the present invention, after the molding step, the glass substrate and the mold are cooled, and the release surface separates the press surface of the mold from the first main surface of the glass substrate. It is preferable to have a process. The molding step is preferably performed in an atmosphere mainly composed of nitrogen.

In the glass substrate molding method of the present invention, in the surface treatment step, the glass substrate is separated from the first electrode by a first main surface and the second electrode is formed by a second main surface. It is preferable that a corona discharge is generated by applying a DC voltage so that the first electrode is a positive electrode and the second electrode is a ground or a negative electrode. In the surface treatment step, the first electrode is a wire-like electrode, and the wire-like electrode may be arranged with its length direction parallel to the first main surface of the glass substrate. preferable.

Further, in the surface treatment step, it is preferable that an atmosphere mainly composed of air or nitrogen is maintained between the first electrode and the second electrode. The temperature of the glass substrate is preferably from room temperature to the glass transition point Tg. Further, it is preferable that the second electrode and the glass substrate are integrated and moved in parallel with the arrangement surface of the first electrode parallel to the first main surface. Furthermore, the glass substrate is preferably made of a glass material containing a total of alkali oxides and alkaline earth oxides exceeding 15% by mass.

According to the molding method of the present invention, a high-quality glass molded body having a high surface smoothness can be obtained by press molding, and the pressing surface of the molding die is covered with the glass substrate in the mold release step after molding. Since the force required for releasing from the first main surface which is the press surface (hereinafter also referred to as releasing force) is extremely small, a release film of carbon or noble metal is formed on the pressing surface of the forming die. Molding can be performed at low cost without performing a release treatment such as applying a release agent.

Further, as described above, since the mold release force of the mold is extremely small, the pressed surface of the glass substrate is not deformed due to fixation with the mold during the mold release, and the shape stability is high. In addition, since the mechanical force of the mold is suppressed by reducing the mold release force, the service life of the mold can be extended, the cost can be reduced, and the time required for mold replacement can be saved. improves.

It is a front view which shows schematic structure of an example of the surface treatment apparatus used at the surface treatment process of embodiment of this invention. It is a top view which shows arrangement | positioning of the 1st electrode with respect to the glass substrate in an example of the surface treatment apparatus used at the surface treatment process of embodiment of this invention. It is a front view which shows schematic structure of another example of the surface treatment apparatus used at the surface treatment process of embodiment of this invention. It is a top view which shows arrangement | positioning of the 1st electrode with respect to the glass substrate in another example of the surface treatment apparatus used at the surface treatment process of embodiment of this invention. It is sectional drawing which shows an example of the shaping | molding apparatus used at the shaping | molding process of embodiment of this invention. It is a graph which shows the time-dependent change of the temperature of a shaping | molding die, and the press force in the case of the glass substrate which does not pass through a surface treatment process. In Example 1, it is a graph which shows the time-dependent change of the measured value of the temperature and press force of a shaping | molding die (upper mold | type and lower mold | type). In Example 1, it is a figure which shows the cross-sectional shape of the to-be-pressed surface (molding surface) of the glass substrate after mold release. In a comparative example, it is a graph which shows the time-dependent change of the measured value of the temperature and press force of a shaping | molding die (upper mold | type and lower mold | type). In a comparative example, it is a figure which shows the cross-sectional shape of the to-be-pressed surface (molding surface) of the glass substrate after mold release. It is a graph which shows the relationship between shaping | molding temperature and the mold release force about each glass substrate with surface treatment and without surface treatment.

In the present specification, alkali oxide means alkali metal oxide, alkali ion means alkali metal ion, alkaline earth oxide means alkaline earth metal oxide, and alkaline earth ion means alkaline earth metal ion. . Embodiments of the present invention will be described below.

The glass substrate molding method of the embodiment includes a surface treatment step and a molding step. The surface treatment step has a pair of main surfaces (first main surface and second main surface) between the first electrode and the second electrode, and is made of glass containing an alkali oxide. A first main surface that is a positive electrode side of the glass substrate by generating a corona discharge by applying a DC voltage so that the first electrode is a positive electrode and the second electrode is a ground or a negative electrode. In the surface layer portion on the side, at least one kind of alkali ions is moved toward the second main surface side that is the ground or negative electrode side. In the molding step, a molding die is arranged so that the press surface is in contact with the first main surface of the glass substrate treated in the surface treatment step, and the glass substrate is held at a predetermined temperature. It is a step of press molding. The glass substrate forming method of the embodiment further includes a mold releasing step of cooling after the forming step and separating the press surface of the forming die from the first main surface of the glass substrate.

According to the molding method of the embodiment of the present invention, in the surface treatment step, a direct current voltage is applied to the glass substrate to generate corona discharge, and the first main surface side surface layer portion that is the positive electrode side of the glass substrate. , By moving the alkali ions toward the second main surface which is the ground or negative electrode side, the alkali low concentration region in which the alkali ion content ratio is lower than other regions (for example, glass base material) It can form in the surface layer part of the said positive electrode side of a base | substrate. In this alkaline low concentration region, with the reduction of the content of the alkaline ions, the content of SiO ₂ is higher than other regions. Here, a glass base material means the glass material which comprises the glass base | substrate of the state before surface treatment. In the glass substrate, the region other than the low alkali concentration region after the surface treatment can be said to have a glass composition substantially similar to that of the glass base material.

Then, the press surface is brought into contact with the first main surface in the molding process with respect to the glass substrate on which the surface treatment is performed in this way and the surface layer portion on the first main surface side is formed with the alkali low concentration region. By placing the mold in this manner and holding the glass mold at a predetermined temperature equal to or higher than the glass transition point Tg of the glass base material (hereinafter also referred to as the molding temperature), the glass mold is pressed with a smooth press surface of the mold. The substrate is press-molded, and the first main surface, which is the pressed surface, is a highly smooth surface.

In the subsequent mold release step, the press surface of the mold is separated from the first main surface of the glass substrate (released). At this time, the release force required for release is almost as small as 0, The glass substrate that has not been surface-treated is remarkably reduced as compared with the case of press molding.

The reason why the releasing force becomes extremely small in this way is considered to be as follows.
Usually, when a glass substrate that has not been surface-treated is press-molded at the above molding temperature, the press surface of the mold and the pressed surface of the glass substrate are fused at the time of pressing, and the mold release force is increased in the mold release process. appear. This is because the temperature at which the pressing surface of the mold and the pressed surface of the glass substrate start fusing during molding (hereinafter referred to as fusing start temperature) is lower than the molding temperature.

However, according to this embodiment, the surface portion of the first main surface which is an object to be pressed surface of the glass substrate, as mentioned above, by surface treatment, the content of alkali ions is relatively SiO ₂ lower Since the content ratio is high, the fusion start temperature is higher than the fusion start temperature of the glass substrate that has not been surface-treated.

On the other hand, since the molding temperature described above depends on the glass base material, if the glass base material is the same, it is constant regardless of the presence or absence of surface treatment. Further, the molding temperature applicable to the molding of the glass base material has a predetermined range. In a glass substrate that is not surface-treated, the fusing start temperature is generally lower than the lower limit of the molding temperature range. However, in the surface-treated glass substrate, the fusion start temperature is higher than the lower limit of the molding temperature range, and the molding temperature can be appropriately set to a temperature lower than the fusion start temperature. Therefore, in the surface-treated glass substrate, the molding temperature can be set to the fusion start temperature, and press molding can be performed at a temperature lower than the fusion start temperature. No fusing occurs, and therefore the mold release force required for mold release is extremely small and almost zero. The measurement of the release force will be described in more detail later.

Thus, according to the molding method of the embodiment, the mold release force of the molding die after press molding is extremely small (almost close to 0), so the shape stability of the molding surface that is the pressed surface of the glass substrate is good. Thus, the cross-sectional shape is not deformed in the pulling direction. Furthermore, since the mechanical degradation of the mold is suppressed by such a reduction in the releasing force, the service life can be extended and the cost can be reduced.
Hereinafter, each process of embodiment of this invention is demonstrated.

[Surface treatment process]
In the surface treatment step, first, a glass substrate made of glass having a pair of main surfaces and containing an alkali oxide is disposed between the first electrode and the second electrode. The glass substrate is arranged so that one main surface (first main surface) is separated from the first electrode and the other main surface (second main surface) is in contact with the second electrode. To do. Then, a DC voltage is applied so that the first electrode is a positive electrode and the second electrode is a ground or a negative electrode to generate a corona discharge between the electrodes. The generated corona discharge causes the first electrode close to the positive electrode of the glass substrate. In the surface layer portion on the first main surface side, at least one kind of alkali ions is moved toward the second main surface side which is the ground or negative electrode side. By such movement of alkali ions, the content ratio of alkali ions (hereinafter sometimes referred to as content concentration) decreases in the surface layer portion on the first main surface side, and the content concentration of alkali ions is reduced to other regions ( For example, an alkali low concentration region lower than the glass base material is formed.

In the present embodiment, the surface treatment of the glass substrate is performed by corona discharge as described above. In the surface treatment by corona discharge, the electrode does not contact the surface to be treated of the glass substrate as described later. Therefore, according to corona discharge, the surface treatment of the glass substrate can be performed without damaging the surface to be treated.

When the glass constituting the substrate contains alkaline earth ions together with alkali ions, in the positive electrode side surface layer portion of the glass substrate, not only alkali ions but also alkaline earth ions move toward the ground or negative electrode side, In the alkali low concentration region formed in the surface layer on the positive electrode side of the glass substrate, not only the alkali ion content concentration but also the alkaline earth ion content concentration is lower than other regions. However, since the movement distance per unit time is larger for alkali ions than for alkaline earth ions, ions that move due to corona discharge are typically alkali ions. Therefore, it shall be described as a low concentration region of alkali ions.

In addition, when the glass substrate contains a plurality of types of alkali oxides in its composition, the plurality of types of alkali ions all move toward the ground or the negative electrode side, so that the concentration of any alkali ions is lower than other regions. A region is formed in the surface layer portion of the glass substrate. However, among the alkali ions, sodium ions are most likely to move, and the effect of improving the releasability by the movement is great, so the main alkali ions that are moved by corona discharge in the surface treatment process are sodium ions, and sodium ions The purpose is to form a low concentration region of ions.

<Glass substrate>
The glass substrate surface-treated in the surface treatment step is composed of a glass material having an alkali oxide in composition, that is, a glass base material. The composition of the glass base material is not particularly limited as long as it has at least one alkali oxide. From the viewpoint of easy surface treatment, the total amount of alkali oxide and alkaline earth oxide is 15% by mass. What contains it in the ratio exceeding is preferable.

As such a glass material, SiO ₂ is 50 to 80%, Al ₂ O ₃ is 0.5 to 25%, B ₂ O ₃ is 0 to 10%, Na ₂ O in terms of mass% based on oxide. 10 to 16%, K ₂ O 0 to 8%, Li ₂ O 0 to 16%, CaO 0 to 10%, MgO 0 to 12%, other SrO, BaO, ZrO ₂ , ZnO, SnO ₂ The glass which contains less than 10% in total etc. can be mentioned. Hereinafter, it describes about each component which comprises this glass. In addition, all represent mass%.

SiO ₂ is a component constituting the skeleton of glass. When the content ratio of SiO ₂ is less than 50%, the stability as glass may be lowered, or the weather resistance may be lowered. The content ratio of SiO ₂ is preferably 60% or more. More preferably, it is 62% or more, and particularly preferably 63% or more.
When the content ratio of SiO ₂ exceeds 80%, the viscosity of the glass increases, and the meltability may be remarkably lowered. The content ratio of SiO ₂ is more preferably 76% or less, and further preferably 74% or less.

Al ₂ O ₃ is a component that improves the movement speed of alkali ions. When the content ratio of Al ₂ O ₃ is less than 0.5%, the migration rate of alkali ions may decrease. The content ratio of Al ₂ O ₃ is more preferably 1% or more, further preferably 2.5% or more, particularly preferably 4% or more, and most preferably 6% or more.
If the content ratio of Al ₂ O ₃ exceeds 25%, the viscosity of the glass becomes high, and there is a possibility that homogeneous melting becomes difficult. The content ratio of Al ₂ O ₃ is preferably 20% or less. More preferably, it is 16% or less, and particularly preferably 14% or less.

B ₂ O ₃ is not an essential component, but may be contained for improving meltability at high temperatures or glass strength. When B ₂ O ₃ is contained, the content ratio is more preferably 0.5% or more, and further preferably 1% or more.
_Further, the content of B 2 _{O 3} is 10% or less. Since B ₂ O ₃ tends to evaporate due to coexistence with an alkali component, it may be difficult to obtain homogeneous glass. The content ratio of B ₂ O ₃ is more preferably 6% or less, and still more preferably 1.5% or less. In particular to improve the homogeneity of the glass, B ₂ O ₃ is preferably not contained.

Na ₂ O is a component that improves the meltability of glass and has main ions (sodium ions) that move by corona discharge. When the content ratio of Na ₂ O is less than 10%, it is difficult to obtain an alkali ion transfer effect by corona discharge. The content ratio of Na ₂ O is more preferably 11% or more, and particularly preferably 12% or more.
The content ratio of Na ₂ O is 16% or less. If it exceeds 16%, the glass transition point Tg is lowered, the strain point is lowered accordingly, and the heat resistance may be inferior, or the weather resistance may be lowered. The content ratio of Na ₂ O is more preferably 15% or less, further preferably 14% or less, and particularly preferably 13% or less.

K ₂ O is not an essential component, but may be contained because it is a component that improves the meltability of glass and that is easily moved by corona discharge. When K ₂ O is contained, the content is preferably 1% or more, more preferably 3% or more.
Further, the content of _{K 2} O is 8% or less. If the content ratio of K ₂ O exceeds 8%, the weather resistance may be lowered. More preferably, it is 5% or less.

Li ₂ O is not an essential component like K ₂ O, but may be contained because it is a component that improves the meltability of glass and is a component that easily moves by corona discharge. When Li ₂ O is contained, the content ratio is preferably 1% or more, and more preferably 3% or more.
Further, the content of Li ₂ O is 16% or less. If the content ratio of Li ₂ O exceeds 16%, the strain point may be too low. The content ratio of Li ₂ O is more preferably 14% or less, and particularly preferably 12% or less.

The alkaline earth oxide is a component that improves the meltability of the glass and is an effective component for adjusting Tg.
Of the alkaline earth oxides, MgO is not an essential component, but is a component that increases the Young's modulus of the glass to improve the strength and improve the solubility. It is preferable to contain 1% or more of MgO. The content ratio of MgO is more preferably 3% or more, and particularly preferably 5% or more.
The content ratio of MgO is 12% or less. If the MgO content exceeds 12%, the stability of the glass may be impaired. The content ratio of MgO is more preferably 10% or less, particularly preferably 8% or less.

CaO is not an essential component, but when CaO is contained, its content is typically 0.05% or more. Moreover, the content rate of CaO is 10% or less. If the CaO content exceeds 10%, the amount of alkali ions transferred by corona discharge may be reduced. The content ratio of CaO is more preferably 6% or less, further preferably 2% or less, and particularly preferably 0.5% or less.

The total content (total amount) of alkali oxide and alkaline earth oxide is preferably more than 15% in order to improve the meltability of the glass and to stabilize corona discharge by adjusting Tg. The total content of alkali oxides and alkaline earth oxides is more preferably 17% or more, particularly preferably 20% or more, and the upper limit is preferably 35%.

The glass constituting the glass substrate to be surface-treated in the surface treatment step may contain other components. When such components are contained, the total content of these components is preferably 10% or less, more preferably 5% or less. It is particularly preferable to consist essentially of the above components. Furthermore, the glass containing each of these components may appropriately contain SO ₃ , chloride, fluoride, and the like as a fining agent upon melting.

It should be noted that the glass transition temperature Tg of such a glass material is preferably in the range of about 400 to 700 ° C. However, the glass transition temperature Tg in the glass material of the glass substrate used in the molding method of the present invention is not limited to this.

The shape of the glass substrate made of such a glass material is not particularly limited as long as it has a pair of main surfaces. The flat plate shape in which the pair of main surfaces are flat surfaces or the curved plate shape in which the pair of main surfaces are curved surfaces may be used. Examples of such a glass substrate include glass substrates used as glass optical elements such as optical lenses, lens arrays, and reflectors. In this specification, these flat or curved glass substrates are also referred to as glass substrates, and an example in which the glass substrate is a glass substrate will be described below.

<First electrode and second electrode>
In the surface treatment step, for example, a first electrode and a second electrode connected to a direct current power source are arranged facing each other with a predetermined interval, and the glass substrate is arranged between these electrodes. That is, the first main surface (for example, the upper surface) of the glass substrate is separated from the first electrode by a predetermined distance, and the second main surface (for example, the lower surface) is in contact with the second electrode. Place a glass substrate. Then, a DC voltage is applied so that the first electrode is a positive electrode and the second electrode is a ground or a negative electrode to generate a corona discharge between the electrodes.

Although the distance between the upper surface of the glass substrate and the first electrode as the positive electrode varies depending on the shape of the first electrode, the applied voltage, and the like, the larger the distance, the smaller the discharge current and the weaker the corona discharge. It is larger and 30 mm or less is preferable. Furthermore, as the distance is shorter, the discharge current becomes parabolically and corona discharge becomes stronger, so that it is more preferably greater than 0 mm and not greater than 10 mm.

Here, the first electrode as the positive electrode preferably has a smaller electrode area than the second electrode as the ground or the negative electrode. The “electrode area” means the projected area on the main surface of the glass substrate that is the object to be processed for the first electrode that is the positive electrode, and the glass substrate for the second electrode that is the ground or the negative electrode. The area in contact with the second main surface. When the first electrode is an assembly of a plurality of wire-like or needle-like electrodes as will be described later, the “electrode area” is the “electrode area” for each wire-like electrode or each needle-like electrode. The sum of

As the first electrode which is a positive electrode, a wire-like electrode or a needle-like electrode having a sharp tip at the tip can be used. One of these wire-like electrodes and needle-like electrodes may be used alone, or a plurality of them may be arranged at a predetermined interval (pitch) from each other, and these aggregates may be used as the first electrode. . As described above, by using a plurality of wire-like electrodes or needle-like electrodes arranged at predetermined intervals as the first electrode, the glass substrate surface can be uniformly treated.

Examples of apparatuses used in the surface treatment process are shown in FIGS. 1A, 1B, 2A, and 2B. 1A and 2A are front views schematically showing the configuration of the surface treatment apparatus 1, and FIGS. 1B and 2B are top views of the surface treatment apparatus 1 for explaining the arrangement of the first electrodes with respect to the glass substrate. FIG. In the surface treatment apparatus 1 shown in FIG. 1A, a wire electrode 2a is provided as the first electrode 2 which is a positive electrode. In the surface treatment apparatus 1 shown in FIG. 2A, a needle electrode 2 b is provided as the first electrode 2. In FIG. 1A, FIG. 1B, FIG. 2A, and FIG. 2B, the code | symbol 3 shows the 2nd electrode which is earth | ground or a negative electrode, and the code | symbol 4 shows the glass substrate which is a to-be-processed object. Reference numeral 5 indicates a DC power source, and reference numeral 6 indicates an ammeter for monitoring a current flowing through the circuit.

In the surface treatment apparatus 1 shown in FIG. 1A, the wire-like electrode 2a as the first electrode 2 is preferably thin from the viewpoint of the ease of occurrence of corona discharge. However, in terms of strength and ease of handling, the wire-like electrode 2a The diameter of the electrode 2a is preferably 0.03 to 0.8 mm, more preferably 0.1 to 0.7 mm. Moreover, it is preferable to arrange the wire electrode 2 a so that the length method is parallel to the upper surface of the glass substrate 4. When a plurality of wire-like electrodes 2a are used as the first electrode 2, each wire-like electrode 2a has an interval larger than 0 mm and equal to the distance between the glass substrate 4 and the wire-like electrode 2a, as shown in FIG. 1B. In order to uniformly treat the upper surface of the glass substrate 4, it is preferable to dispose them on a plane parallel to each other and parallel to the upper surface of the glass substrate 4. As will be described later, when the glass substrate 4 is moved in parallel with the arrangement surface parallel to the upper surface of the glass substrate 4 of the wire electrode 2a, the processing unevenness is alleviated by the parallel movement of the glass substrate 4. The interval between the wire-like electrodes 2a can be made larger.

Further, when one wire-like electrode 2a is disposed alone as the first electrode 2, the surface of the glass substrate 4 is uniformly treated, and alkali ions in an alkali low concentration region formed on the positive electrode side surface layer portion. In order to make uniform the distribution of the concentration of the second electrode 3, the second electrode 3 integrated with the glass substrate 4 is preferably moved relative to the wire electrode 2 a that is the first electrode 2. The second electrode 3, which is the ground or the negative electrode, is moved in parallel to the arrangement surface of the wire electrode 2 a parallel to the upper surface of the glass substrate 4, that is, moved in a direction perpendicular to the discharge direction of the corona discharge. preferable. In addition, it is more preferable that the second electrode 3, which is an earth or a negative electrode, is moved in a direction perpendicular to the length direction of the wire electrode 2 a with the glass substrate 4 placed thereon. This motion is more preferably a linear motion or a reciprocating linear motion, but may be a rotational motion or a rocking motion.

Furthermore, it is preferable to provide a cylindrical or rectangular casing as in the case of a widely used charger called corotron / scorotron using corona discharge. A grid electrode may be provided. By the action of the casing and the grid electrode, the flow of ions of corona discharge can be controlled, the processing uniformity to the glass substrate can be increased, and the processing efficiency can be improved.

In the surface treatment apparatus 1 shown in FIG. 2A, the needle-like electrode 2b, which is the first electrode 2, preferably has a root portion with a diameter of 0.1 to 2 mm, and the sharp tip of the needle-like electrode 2b is formed on the upper surface of the glass substrate 4. It is preferable to arrange so that the length direction is perpendicular to the upper surface. When a plurality of needle-like electrodes 2 b are used as the first electrode 2, each needle-like electrode 2 b is parallel to each other and has a length direction perpendicular to the upper surface of the glass substrate 4, and a tip portion of the glass substrate 4. It is preferable to arrange them at equal distances from the top surface. Further, as shown in FIG. 2B, the disposition positions of the needle-like electrodes 2b are larger than 0 mm, and have a staggered or grid-like shape with an interval d that is about the same as the distance between the glass substrate 4 and the needle-like electrodes 2b. A uniform arrangement such as the above is preferable for uniformly treating the surface of the glass substrate 4. When the glass substrate 4 is moved in parallel with the surface parallel to the upper surface of the glass substrate 4 where the tip of the needle-like electrode 2b is located, the processing unevenness is alleviated by the movement of the glass substrate 4, so that each The interval between the needle-like electrodes 2b can be made larger.

As the angle (tip angle) of the tip of the needle-like electrode 2b becomes smaller and smaller, the electric field intensity directly below becomes larger. Therefore, by adjusting the tip angle of the needle-like electrode 2b, the first positive electrode as the positive electrode is obtained. The electric field strength near the electrode 2 can be adjusted. The tip angle of the needle electrode 2b is preferably 1 to 15 degrees, and more preferably 1 to 9 degrees.
In the wire-like electrode 2a and the needle-like electrode 2b, when a corrosion-resistant conductive film such as gold, platinum, or other noble metal is provided on the surface, the uniformity of electric field strength is improved and the durability as an electrode is improved. .

In the surface treatment apparatus 1 shown in FIGS. 1A and 2A, the second electrode 3 that is a ground or a negative electrode has a second main surface (lower surface) of a glass substrate 4 that is an object to be processed, such as a flat plate shape or a curved plate shape. Those having a shape adapted to the above are preferred. Moreover, the thing which contacts the glass substrate 4 uniformly in a surface, such as a mesh-shaped thing which has a perforated part, may be used.
By disposing the second electrode 3 so as to be in contact with the lower surface of the glass substrate 4, the conductivity to the glass substrate 4 is improved, so that the applied voltage can be increased. In the second electrode 3, the conductive property can be further improved by providing a conductive film such as ITO on the surface in contact with the glass substrate 4. Next, surface treatment conditions (such as glass substrate temperature and treatment atmosphere) will be described.

<Surface treatment conditions>
The glass substrate temperature in the surface treatment step is preferably from room temperature to the glass transition point Tg. By setting the temperature to Tg or lower, a sufficiently low alkali concentration region can be formed on the surface layer portion of the glass substrate without causing deformation of the glass substrate or deterioration of the processing member. In addition, the temperature range is Tg or less, and the glass exhibits a solid state having a sufficiently high viscosity, so that the alkali ions in the glass substrate do not move excessively and the movement direction of the alkali ions is the electric field direction. Since it is limited to the direction toward the side, the efficiency of the surface treatment by corona discharge is high. The temperature of the glass substrate is preferably 25 to 400 ° C, more preferably 100 to 300 ° C. However, when Tg is 400 ° C. or lower, the temperature of the glass substrate is more preferably lower.

The DC voltage applied between the first electrode and the second electrode is a voltage that generates a corona discharge between the first electrode as a positive electrode and the second electrode as a ground or a negative electrode, More specifically, it is a voltage that generates corona discharge from the first electrode that is the positive electrode. This applied voltage varies depending on the shape of the first electrode and the temperature of the glass substrate as the object to be processed, but is preferably in the range of 3 to 12 kV. When the applied voltage is less than 3 kV, corona discharge hardly occurs. When the applied voltage exceeds 12 kV, arc discharge tends to occur and it is difficult to continue corona discharge. The applied voltage is more preferably 5 to 10 kV.

In the surface treatment step, the current flowing through the glass substrate, which is the object to be processed, by applying such a DC voltage includes both a current due to the movement of electrons and a current due to the movement of cations including alkali ions. The current flowing through the glass substrate is preferably in the range of 0.01 to 1000 mA, more preferably 0.1 to 100 mA. The quantity of electricity per unit area is preferably in the range of 10 ~ 500mC / cm ^2, more preferably 50 ~ 400mC / cm ^2, more preferably 100 ~ 300mC / cm ^2.

In the surface treatment step, the treatment time, that is, the time for which the corona discharge is continued depends on the applied voltage, the distance between the first electrode and the second electrode, the shape and arrangement of the first electrode, and the like. Time is preferable, and 2 to 10 hours are more preferable.

In the surface treatment step, an atmosphere mainly composed of air or nitrogen can be maintained between the first electrode and the second electrode on which the glass substrate that is the object to be processed is disposed. Here, the “atmosphere mainly composed of air or nitrogen” refers to a gas state in which the content ratio of air or nitrogen exceeds 50% by volume of the entire atmospheric gas.
As described above, the second electrode, which is the ground or the negative electrode, is disposed so as to be in contact with the second main surface (for example, the lower surface) of the glass substrate, and the conductivity between the second electrode and the glass substrate is improved. Therefore, it is not necessary to use a plasma forming gas atmosphere such as helium or argon. That is, the surface of the glass substrate can be treated by generating corona discharge around the first electrode in an atmosphere mainly composed of air or nitrogen.

[Molding process]
In the molding step, the molding die is arranged so that the press surface (mold surface) comes into contact with the first main surface of the glass substrate that has been surface-treated in the surface treatment step and has a low alkali concentration region formed on the surface layer portion. Then, press-molding is performed by pressing the glass substrate while maintaining the glass substrate at a predetermined temperature.

<Molding device>
An example of the shaping | molding apparatus used for the shaping | molding process of embodiment is shown in FIG. FIG. 3 is a cross-sectional view schematically showing the configuration of the molding apparatus 10.
The molding apparatus 10 includes a molding die 13 having a fixed lower die 11 and an upper die 12 arranged to face the lower die 11. The upper mold 12 is configured to be movable up and down, and a mold main body 14 is provided on the lower surface facing the lower mold 11 of the upper mold 12. And the glass substrate 15 surface-treated in the surface treatment step is placed on the lower mold 11 with the second main surface down, and the first main surface (alkali low concentration region) which is the upper surface thereof. The press surface 14a of the die body 14 is held so as to abut on the main surface 15a on the side where is formed.

Further, in this molding apparatus 10, the glass substrate 15 and the mold 13 (particularly the mold body 14) are heated to a predetermined temperature at which press molding can be performed, and in order to maintain the temperature, they are in contact with or in the vicinity thereof. In addition, a heating mechanism (not shown) such as an electric heater is disposed. Further, the press surface 14a of the mold body 14 is pressed against the first main surface 15a, which is the pressed surface of the glass substrate 15, by a method such as lowering the upper mold 12 and applying a load (pressing force) downward. Pressure mechanism (not shown). Such a molding apparatus 10 is disposed in a chamber (not shown) controlled in a nitrogen atmosphere or the like. Note that in the case where molding is performed in the atmosphere, a configuration without a chamber can be employed. The heating mechanism is not limited to an electric heater, and any mechanism that can heat and hold the glass substrate 15 or the like at a predetermined temperature such as electromagnetic induction heating may be used. Further, the pressurizing mechanism may be any mechanism as long as it can press the press surface 14a of the mold body 14 against the pressed surface of the glass substrate 15.

The upper mold 12 and the lower mold 11 of the mold 13 can be made of a known mold material such as stainless steel or tungsten carbide (WC). The constituent material is not particularly limited as long as it has hardness and durability that can be used as a mold.

In the mold main body 14 provided on the lower surface of the upper mold 12 facing the lower mold 11, the press surface 14 a that is a surface that contacts and presses the glass substrate 15 is the first main surface 15 a of the glass substrate 15 to be molded. For example, it is made into a mirror surface by polishing or the like. And by pressing with this press surface 14a made into the mirror surface, the surface state of the said press surface 14a is transcribe | transferred to the 1st main surface 15a of the glass substrate 15, and the smooth surface is formed. Therefore, it is preferable that the die body 14 having the press surface 14a is made of a material having excellent heat resistance and releasability from glass, and having mechanical strength and durability. Examples of the material constituting the mold body 14 include carbon such as glassy carbon, stainless steel, silicon carbide (SiC), and tungsten carbide (WC).

In the molding process, the upper mold 12 is lowered in a state where the glass substrate 15 and the mold 13 (particularly the mold body 14) are heated to a predetermined temperature at which press molding is possible, and the press surface 14a of the mold body 14 is moved to the glass substrate 15. It presses against the 1st main surface 15a which is a to-be-pressed surface, and presses with predetermined press force.

The heating temperature (molding temperature) T at the time of molding is a temperature at which the glass material (glass base material) constituting the glass substrate 15 softens to the extent that it can be press-molded, and is 50 to 50 from the glass transition point Tg of the glass material. A temperature higher by 150 ° C. is preferable. The molding temperature T is more preferably 50 to 100 ° C. higher than Tg, particularly 70 to 80 ° C. higher than Tg in that a high-quality glass molded body with high surface smoothness can be obtained. preferable.

The atmosphere in which the glass substrate 15 is press-molded, for example, the atmosphere in the chamber (not shown) in which the molding apparatus 10 is disposed is preferably an atmosphere mainly composed of nitrogen. Here, the “atmosphere mainly composed of nitrogen” refers to a gas state in which the nitrogen content exceeds 50% by volume of the total atmosphere gas, and an atmosphere in which the nitrogen content is approximately 100% by volume is more preferable.

The pressing force on the first main surface 15a, which is the pressed surface of the glass substrate 15, is preferably in the range of 0.01 MPa to 10 MPa, more preferably 0.1 MPa to 5 MPa, as the pressing force per unit area. This applied pressure is sometimes referred to as press pressure. By setting the pressing force (pressing pressure) within this range, the smooth shape of the press surface 14a of the mold body 14 is the pressed surface of the glass substrate 15 without damaging the glass substrate 15 and the mold body 14. It can be transferred and formed satisfactorily on the first main surface 15a.

The pressing time in the molding step, that is, the pressurizing time, depends on the pressing force, the heating temperature T during molding, etc., but is preferably 1 to 900 seconds, more preferably 1 to 300 seconds.

[Release process]
In the mold release step, after the molding step, the glass base and the mold are cooled, and then, for example, the upper die is raised so that the press surface of the die body is the pressed surface (molding surface) of the glass base. Pull away from the main surface.

At this time, an alkali low concentration region is formed by surface treatment on the surface portion of the first main surface which is a pressed surface of the glass substrate. In such an alkali low concentration region, as described above, the mold release is performed. The fusion start temperature at which the force is generated is higher than that before the surface treatment, that is, compared to the region other than the low alkali concentration region of the glass substrate.

Here, the molding temperature of the glass substrate, which is a predetermined temperature equal to or higher than the Tg of the glass base material, has a predetermined temperature range, and the glass substrate that has not been surface-treated has a fusion start temperature that is generally the lower limit of the molding temperature range. The temperature is below the value. However, in the glass substrate subjected to the surface treatment, the fusion start temperature is higher than the lower limit value of the molding temperature range of the glass substrate. Thereby, in the method of this embodiment, the molding temperature of the glass substrate can be appropriately set to a temperature lower than the fusion start temperature, and the press surface of the mold body is separated from the first main surface on which the low alkali concentration region is formed. The mold release force can be close to zero. Therefore, at the time of mold release, the first main surface of the glass substrate is not deformed due to fixation with the mold body, and the shape formed in the molding process is stably held. In addition, since the release force is extremely small in this way, damage to the mold body and mechanical deterioration are prevented.

Here, the above-mentioned mold release force per unit area of the mold main body is measured by the following method, for example.
That is, a molding process in which press molding is performed using the molding apparatus 10 shown in FIG. 3, and the upper die 12 is raised after cooling after molding, and the press surface 14 a of the die body 14 is made to be the first main body of the glass substrate 15. A mold release process for separating from the surface 15a is continuously performed. At this time, when the temperature of the upper mold 12 and the lower mold 11 and the pressing force (pressing pressure) per unit area by the upper mold 12 are continuously measured, for example, in the case of a glass substrate that does not undergo a surface treatment process, A graph as shown in FIG. 4 is obtained.

In the graph showing the pressing pressure of the upper mold shown in FIG. 4, the above-mentioned predetermined pressing force (pressing pressure) P was applied in the molding process in which the upper mold 12 and the lower mold 11 show the molding temperature T of glass. Thereafter, a change portion (a) is generated in which the press pressure becomes negative and further gradually decreases, and then rapidly increases and returns to the vicinity of the original zero. This change part (a) indicates that the press surface 14a of the mold main body 14 is fixed to the first main surface 15a of the glass substrate 15 and pulled and then released in the mold release step. The absolute value of the difference between the pressing pressure at the lowest point in the changing portion (a) and the pressing pressure at the time when the pressure returns to the vicinity of the original zero can be used as the mold release force per unit area. As the unit of the release force per unit area, Pa, which is the same as the press pressure, or N / cm ² can be used. In the graph showing the press pressure of the upper die in FIG. 4, the baseline after release is not 0, but this does not indicate a pressurized state.

Examples of the present invention will be specifically described below, but the present invention is not limited to these examples.

Example 1
A surface of a barium borosilicate glass substrate (manufactured by OHARA, trade name: L-BAL42, square with a main surface of 10 mm × 10 mm and a thickness of 2 mm, Tg: 506 ° C., softening point: 607 ° C.) shown in FIG. 1A It arrange | positioned between the 1st electrode (positive electrode) 2 and the 2nd electrode (earth | ground) 3 of the processing apparatus 1, and performed the surface treatment by corona discharge.

In this surface treatment apparatus 1, the second electrode 3 is a grounded flat electrode (electrode material tungsten, electrode size 10 mm × 10 mm), and the glass of the same size is placed on the second electrode 3. The substrate 4 was placed and placed horizontally. The first electrode 2 was constituted by one wire-like electrode 2a (electrode material tungsten) having a diameter of 0.5 mm, and was arranged so that the length direction thereof was parallel to one side of the glass substrate 4. The distance between the wire electrode 2a and the upper surface of the glass substrate 4 is 5 mm, and the second electrode 3 on which the glass substrate 4 is placed is 5 mm in a direction perpendicular to the length direction of the wire electrode 2a on the horizontal plane. It was reciprocated with a stroke of 100 mm at a speed of / sec. Further, an air atmosphere was formed between the wire electrode 2a as the first electrode 2 and the second electrode 3.

In this way, a voltage of 6 kV is applied between the wire electrode 2a and the second electrode 3 by the DC power source 5 while the glass substrate 4 is heated to 200 ° C. and maintained at that temperature, and in this state for 2.4 hours. Processing continued. During the surface treatment, when the current value was measured with an ammeter 6 installed in a circuit connecting the second electrode 3 and the DC power source 5, it was constant at 0.4 mA.

Next, after press-molding the surface-treated glass substrate using the molding apparatus 10 shown in FIG. 3, the separation per unit area when the press surface 14 a of the mold body 14 is separated from the glass substrate 15. The mold force was measured by the method described above. Further, the cross-sectional shape of the first main surface 15a, which is the pressed surface of the glass substrate 15 after the mold release, was measured with a non-contact three-dimensional measuring device (manufactured by Mitaka Kogyo Co., Ltd., device name: NH-3). The cross-sectional shape was measured for a range of 7 mm at the center of a glass substrate having a side of 10 mm.

Here, the mold body 14 was made of glassy carbon, and the press surface 14a was mirror-finished by polishing. Further, the heating temperature (molding temperature) T at the time of press molding is set to 580 ° C. which is 74 ° C. higher than the glass transition point Tg of the glass material (glass base material) constituting the glass substrate 15 (Tg + 74 ° C.). The pressure was 2 MPa, and the press time was 60 seconds. Furthermore, the inside of the chamber was a nitrogen atmosphere (oxygen concentration 15 ppm).

FIG. 5 shows the changes over time in the temperature of the upper mold 12 (the mold main body 14) and the lower mold 11, and the measurement value of the press pressure by the upper mold 12. Moreover, the cross-sectional shape of the to-be-pressed surface of the glass substrate 15 after mold release is shown in FIG. From the graph of FIG. 5, it can be seen that in the glass substrate 15 of Example 1, the release force per unit area required to separate the press surface 14 a of the mold body 14 from the glass substrate 15 is almost zero. Also, from FIG. 6, the pressed surface of the glass substrate 15 after mold release is a flat surface with a height difference of about 3 μm, and the flat and smooth shape formed by press molding is retained after mold release. It can be seen that no deformation has occurred during the mold release.

Comparative Example 1
A barium borosilicate glass substrate (trade name; L-BAL42, a glass substrate having a main surface of 10 mm × 10 mm square and a thickness of 2 mm) having the same composition as in Example 1 was used. This glass substrate is subjected to press molding as it is in the same manner as in Example 1 without performing surface treatment, and then released per unit area when the press surface 14a of the mold body 14 is separated from the glass substrate 15. The force was measured as in Example 1. Further, the cross-sectional shape of the pressed surface of the glass substrate 15 after the mold release was measured by a non-contact three-dimensional measuring apparatus in the same manner as in Example 1.

FIG. 7 shows changes over time in the temperature of the upper mold 12 (the mold main body 14) and the lower mold 11 and the measured value of the press pressure by the upper mold 12. In FIG. Moreover, the cross-sectional shape of the to-be-pressed surface of the glass substrate 15 after mold release is shown in FIG. From the graph of FIG. 7, in the glass substrate 15 of the comparative example 1, the mold release force required to separate the press surface 14a of the mold main body 14 from the glass substrate 15 is about 75 N per unit area (1 cm ² ). It can be seen that force is generated. Further, from FIG. 8, the pressed surface (molding surface) of the glass substrate 15 after mold release rises in a trapezoidal shape with a central portion having a height of about 20 μm and a width of about 6 μm. It can be seen that deformation occurs on the molding surface of the glass substrate 15 after the release due to the fixing.

Example 2 and Comparative Example 2
In order to confirm that the fusion start temperature at which the above-mentioned release force is generated shifts to the high temperature side by the surface treatment by corona discharge, the following experiment was performed. That is, a glass substrate that is not subjected to surface treatment (manufactured by OHARA, trade name: L-BAL42, main surface is 10 mm × 10 mm square and 2 mm thick) is molded in a nitrogen atmosphere using the molding apparatus shown in FIG. After changing the temperature in the range of 550 to 580 ° C. and performing press molding under the conditions of a press pressure of 2 MPa and a press time of 60 seconds, the release force per unit area was measured by the above method (Comparative Example 2). Also, for the same glass substrate that was surface-treated in the same manner as in Example 1, the molding temperature was changed in the range of 580 to 600 ° C. in a nitrogen atmosphere, and the press molding was performed under the conditions of a press pressure of 2 MPa and a press time of 60 seconds. After performing, the mold release force per unit area was measured by the above method (Example 2).

The measurement results are shown in FIG. FIG. 9 is a graph showing the relationship between the molding temperature and the mold release force for each glass substrate with and without surface treatment. From this graph, in Comparative Example 2, when a glass substrate without surface treatment was used, when press molding was performed at a molding temperature T of 580 ° C. (Tg + 74 ° C.), 0.8 MPa (80 N / cm ² ) or more. In contrast to the large mold release force per unit area, in Example 2, when a surface-treated glass substrate is used, the mold release force is almost generated at a molding temperature of 580 ° C. It was confirmed that they did not.

According to the molding method of the present invention, a high-quality glass molded body having a high surface smoothness can be obtained by press molding, and the pressing surface of the molding die is covered with the glass substrate in the mold release step after molding. The mold release force that separates from the first main surface, which is the press surface, is extremely small. Therefore, a mold release treatment such as forming a release film of carbon or noble metal on the press surface of the mold, or applying a release agent. It can be molded at low cost without applying. Therefore, it is suitable as an inexpensive and highly reliable molding method for obtaining a glass optical element or the like.

DESCRIPTION OF SYMBOLS 1 ... Surface treatment apparatus, 2 ... 1st electrode (positive electrode), 2a ... Wire-like electrode, 2b ... Needle-like electrode, 3 ... 2nd electrode (earth or negative electrode), 4 ... Glass substrate, 5 ... DC power supply, DESCRIPTION OF SYMBOLS 10 ... Molding apparatus, 11 ... Lower mold, 12 ... Upper mold, 13 ... Mold, 14 ... Mold main body, 14a ... Press surface, 15 ... Glass substrate.

Claims

A glass substrate made of glass having a pair of main surfaces and containing an alkali oxide in the composition is disposed between the first electrode and the second electrode, and the second electrode is used as the positive electrode. A corona discharge is generated by applying a DC voltage so that the electrode is grounded or a negative electrode, and at least one kind of alkali ions is grounded in the surface layer portion on the first main surface side which is the positive electrode side of the glass substrate. Or a surface treatment step of moving toward the second main surface which is the negative electrode side;
A molding step in which a molding die is disposed so that a press surface is in contact with the first main surface of the glass substrate surface-treated in the surface treatment step, and the glass substrate is press-molded while being held at a predetermined temperature. ,
A method of forming a glass substrate, comprising:
The said glass substrate and the said mold are cooled after the said shaping | molding process, It has a mold release process which separates the said press surface of the said mold from the said 1st main surface of the said glass base. A method for forming a glass substrate.
The glass substrate forming method according to claim 1 or 2, wherein the forming step is performed in an atmosphere mainly composed of nitrogen.
In the surface treatment step, the glass substrate is disposed such that a first main surface is separated from the first electrode and a second main surface is in contact with the second electrode, The glass substrate forming method according to any one of claims 1 to 3, wherein a corona discharge is generated by applying a DC voltage so that one electrode is a positive electrode and the second electrode is a ground or a negative electrode.
In the surface treatment step, the first electrode is a wire-like electrode, and the wire-like electrode is disposed with its length direction parallel to the first main surface of the glass substrate. A method for forming a glass substrate according to 1.
The glass substrate forming method according to claim 4 or 5, wherein, in the surface treatment step, an atmosphere mainly composed of air or nitrogen is maintained between the first electrode and the second electrode.
The glass forming method according to any one of claims 4 to 6, wherein, in the surface treatment step, the temperature of the glass substrate is from room temperature to a glass transition point Tg.
In the surface treatment step, the second electrode and the glass substrate are integrated, and are moved in parallel with an arrangement surface of the first electrode parallel to the first main surface. The method for molding a glass substrate according to any one of the above.
The glass forming method according to any one of claims 1 to 8, wherein the glass substrate is made of a glass material containing a total amount of alkali oxide and alkaline earth oxide exceeding 15% by mass.