JP2013040091A - Glass plate including light incidence surface having light scattering function and reflection control function - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a glass plate including a glass surface having unevenness suitable for improving both light scattering function and reflection control function.SOLUTION: The glass plate 1 includes a glass surface 11 to be a light incidence surface. The glass surface 11 includes minute salient 31 whose diameter is 20 to 250 nm and unevenness 20 represented by an arithmetic mean roughness Ra of 0.08 to 0.8 micron, a maximum height Ry of 0.3 to 7.0 microns, and an average spacing Sm of 0.3 to 10.0 microns. The unevenness 20 and 30 of the glass plate can be formed by etching processing using an etching solution containing hydrofluoric acid and fluoride salts such as potassium fluoride.

Description

  The present invention relates to a glass plate having a light incident surface having a light scattering function and a reflection suppressing function. More specifically, the present invention relates to a glass plate disposed on the light incident side of a thin film solar cell, a cover glass disposed on the light incident side of a crystalline solar cell, a front glass of a reflective liquid crystal display device, a building, The present invention relates to a glass plate suitable for use as a window or partition of a moving object.

  In some cases, the surface of the glass plate serving as the light incident surface is required to scatter incident light on the surface and suppress reflection of incident light. For example, the front glass plate of a thin-film solar cell is desired to scatter incident light to lengthen the optical path in the photoelectric conversion layer and suppress reflection of incident light to increase the amount of light reaching the photoelectric conversion layer. Yes. The cover glass placed on the light incident side of the crystalline solar cell also scatters the light so that the reflected light does not feel dazzling to the residents of the surrounding building, suppressing the reflection of the incident light, and the photoelectric conversion layer It is desired to increase the amount of light that reaches.

  In consideration of the above, it has been proposed to form a film made of silica fine particles and a binder on the light incident surface of a glass plate (for example, Patent Document 1). By this film, a light scattering function and a reflection suppressing function are imparted to the light incident surface of the glass plate. A film made of silica fine particles and a binder is formed by a sol-gel method. As measured in the Example section of Patent Document 1, the light scattering function can be evaluated based on the haze rate, and the reflection suppression function can be evaluated based on the reflectance or transmittance of incident light.

  A film composed of silica fine particles and a binder is excellent in that the influence of incident surface irregularities on incident light can be controlled by appropriately selecting the particle size of the silica fine particles. However, the technique using silica fine particles is not suitable for causing surface irregularities suitable for light scattering and surface irregularities suitable for reflection suppression to coexist in the same region of the surface of the glass plate. When a particle having a relatively large particle size suitable for light scattering and a particle having a relatively small particle size suitable for reflection suppression are arranged in the same region, a particle having a small particle size is interposed between particles having a large particle size. It is for burying. There is a limit in enhancing both of these functions by imparting a light scattering function and a reflection suppressing function to a glass plate using a film composed of silica fine particles and a binder.

  Currently, a template glass is mainly used as a cover glass of a solar cell having a light scattering function. Template glass is mass-produced by the so-called roll-out method. Surface irregularities constituted by the glass itself, such as the surface of the template glass, are basically more advantageous than the surface irregularities constituted by the film in terms of manufacturing cost. However, a glass plate having a surface unevenness suitable for enhancing both of these functions while having a light scattering function and a reflection suppressing function while being constituted by glass itself has not been known so far.

  By the way, as a method for imparting irregularities to the surface of a glass plate, an etching method is known in which the surface is eroded using a hydrofluoric acid-based etchant (etchant). For example, in the field of decorative glass, a technique for providing irregularities on the surface of a glass plate by an etching method combined with a sandblasting method is frequently used. Since the degree of light scattering cannot be increased by processing only by etching using a normal etchant, the glass surface to which etching is applied is roughened in advance by sandblasting in this technique. In the field of magnetic disks, a technique is known in which minute projections are formed on the surface of a glass plate serving as a disk substrate by an etching method using hydrofluoric acid and potassium fluoride (for example, Patent Document 2). . The minute convex portion is formed to reduce the friction between the magnetic head and the magnetic disk when the magnetic disk device is started. However, the height of the micro-projections formed for this purpose is less than about 100 nm (the height is 5 nm to 70 nm in the claims of Patent Document 2), and sufficient light scattering is applied to the surface of the glass plate. It does not bring.

  In Patent Document 3, the transmittance of a glass plate is limited to a limited range (0 by an etching process using a special etching solution containing ammonium dihydrogen phosphate, aluminum fluoride, and aluminum chloride together with hydrofluoric acid. .12 to 0.28%), but improved (see Tables 1 and 2). However, the surface unevenness of the glass surface subjected to this etching treatment is very small (expressed by an average surface roughness Ra of about 0.6 nm or less) and does not cause sufficient light scattering.

JP 2001-278737 A Japanese Unexamined Patent Publication No. 63-225919 JP 2005-179132 A

  In view of the above circumstances, an object of the present invention is to provide a glass plate that is constituted by glass itself and has surface irregularities suitable for improving both the light scattering function and the reflection suppressing function.

The present invention is a glass plate provided with a glass surface serving as a light incident surface,
The glass surface has minute convex portions having a diameter of 20 nm to 250 nm, an arithmetic average roughness Ra of 0.08 μm to 0.8 μm, a maximum height Ry of 0.3 μm to 7.0 μm, and 0.3 μm A glass plate having irregularities indicated by an average interval Sm of ˜10.0 μm is provided.

  ADVANTAGE OF THE INVENTION According to this invention, the glass plate provided with the structure suitable for improvement of both a light-scattering function and a reflection suppression function is provided.

It is a perspective view which shows one form of the glass plate of this invention with the partial enlarged view of the glass surface which is the main surface. It is a figure which shows an example of the surface roughness curve of a glass surface. It is sectional drawing which shows another one form of the glass plate of this invention. It is a figure which shows the state which observed the glass surface of the glass plate produced by Example 2 using the scanning electron microscope (SEM). It is another figure which shows the state which observed the glass surface of the glass plate produced by Example 2 using SEM. It is another figure which shows the state which observed the glass surface of the glass plate produced by Example 2 using SEM. It is another figure which shows the state which observed the glass surface of the glass plate produced by Example 2 using SEM. It is a figure which shows the state which observed the glass surface of the glass plate produced by Example 17 using SEM. It is a figure which shows the state which observed the glass surface of the glass plate produced by Example 42 using SEM.

  In light of the fact that the light scattering function and the reflection suppressing function are mainly required in the wavelength range from the visible range to the near infrared range, typically in the wavelength range of 380 nm to 1100 nm, Basically, light in the above wavelength range is targeted.

  In FIG. 1, one form of the glass plate of this invention and the shape of the surface asperity are shown. The glass plate 1 includes a glass surface 11 serving as a light incident surface as its main surface, and irregularities 20 are formed on the glass surface 11. In order to distinguish from fine irregularities 30 having a short cycle, which will be described later, the irregularities 20 having a relatively large period may be referred to as “long-period irregularities”.

  The long-period unevenness 20 is a surface texture that can be formed by retreating the glass surface 11 by an etching process, and includes a convex portion 21 and a concave portion 22 that is a space between the convex portions 21. The convex portions 21 constituting the long-period irregularities 20 are not formed by adding a material different from the glass constituting the glass plate 1. The glass surface 11 is subjected to etching treatment and further modification by application of chemical strengthening treatment performed as necessary, and the composition may be slightly changed (alkaline ions on the surface layer of the glass surface 11 are changed). It may be reduced by elution or may be replaced with another kind of ions), and basically comprises a glass surface formed by exposing the glass constituting the glass plate itself. The long-period unevenness 20 can be formed over the entire glass surface 11 that functions as a light incident surface.

  As will be described later, since the fine irregularities (short-period irregularities) 30 having a short period are too small to scatter light, the light scattering on the glass surface 11 is substantially caused by the long-period irregularities 20. Yes. On the other hand, since the long-period unevenness 20 is too large for forming the pseudo optical layer, it is considered that the light reflection suppression on the glass surface 11 is substantially caused by the short-period unevenness 30. However, the long-period irregularities 20 may also contribute to suppression of reflection of incident light through multiple scattering of light, enlargement of the surface area of the glass surface, and the like depending on the shape and the like.

  The light incident on the glass surface 11 is incident or reflected on the inside of the glass plate 1 while being changed in optical path by the long-period irregularities 20. In general, the degree of light scattering due to surface irregularities is evaluated based on the haze ratio. As is well known, the haze ratio is a ratio of diffuse light transmittance to total light transmittance. Due to the long-period irregularities 20 on the glass surface 11, the haze rate Hz of light incident on the glass surface 11 can be increased to, for example, 10% or more, preferably 30% or more. The haze rate Hz may be 32% or more, further 35% or more, particularly 40% or more, 50% or more in some cases, and 60% or more if necessary. Although there is no particular reason for limiting the upper limit of the haze rate, the haze rate Hz is, for example, 95% or less, more preferably 90% or less, and particularly preferably 80% or less.

  However, depending on the application, a glass plate having a haze ratio Hz that is not too high may be required. According to the study of the present inventor, for example, in a cover glass of a solar cell, a glass plate having a haze ratio of 10 to 30% has a desirable influence on the characteristics of the solar cell rather than a glass plate having a haze ratio Hz exceeding 30%. There is a case. In addition, a glass plate having a haze ratio in the range of about 10 to 30% may be desired from the viewpoint of appearance.

The average height H _av of the convex portions 21 constituting the long-period irregularities 20 is 0.1 μm to 5.0 μm, preferably 0.2 μm to 3.0 μm, and more preferably 0.3 μm to 2.5 μm. The average bottom length L _av of the convex portion 21 is 0.2 μm to 10.0 μm, preferably 0.3 μm to 7.0 μm, and more preferably 0.4 μm to 5.0 μm.

Here, with reference to FIG. 2, the measuring method of the height H of the convex part 21 and the bottom part length L is demonstrated. FIG. 2 is a profile of the glass surface that appears in the cross section when the glass surface 11 is observed from the cross sectional direction of the glass plate 1. This profile can be measured, for example, as a surface roughness curve obtained by scanning the glass surface along a predetermined direction. In FIG. 2, the center line 40 is set according to the area standard. That is, the center line 40 is set such that the peak 41 protruding upward from the center line 40 and the valley protruding downward are of equal area. More specifically, the center line 40 is set so that the total area of the areas defined by the curve and the center line 40 above and below the center line 40 is equal. And regarding the peak part 41 which has an apex above the center line 40 and has a bottom part below the center line 40, the length of the line segment which connects between the bottom parts is made into the bottom part length L, and the apex of the peak part 41 A distance (shortest distance) between the line segment and the line segment is defined as a height H. The average height H _av and the average bottom length L _av are determined by the average value (number average value) of the height H and the bottom length L.

  The peak portion 42 whose top portion is below the center line 40 is often a profile in the vicinity of the lower portion of the bottom of the convex portion 21, and there is a high possibility that the height of the convex portion 21 is not appropriately reflected. For this reason, in the above description, when the height H and the bottom length L are determined, only the peak portion 41 having the top portion above the center line 40 is handled as a convex portion.

  In determining the height H and the bottom length L, it is based on a surface roughness curve having a measurement length of 50 μm (the length of the center line 40 is 50 μm) measured at an arbitrary part of the glass surface 11. The number of peak portions 41 (the number N of convex portions) existing in this length range is preferably 3 to 15, particularly 5 to 10. The surface roughness curve is, for example, a non-contact three-dimensional measuring apparatus of a stage scanning laser probe system (for example, manufactured by Mitaka Kogyo Co., Ltd.) equipped with a laser autofocus microscope for measuring the Z-axis height and a high-precision XYZ stage NH series).

  The irregularities formed on the glass surface 11 preferably have the following characteristics. In addition, all the following parameters are prescribed | regulated to JISB0601: 2001, For example, it can obtain by measuring the glass surface 11 using the above-mentioned non-contact three-dimensional measuring apparatus.

Arithmetic mean roughness Ra: 0.08 μm to 0.8 μm, preferably 0.09 μm to 0.5 μm, more preferably 0.1 μm to 0.4 μm

Maximum height Ry: 0.3 μm to 7.0 μm, preferably 0.5 μm to 5.0 μm, more preferably 0.6 μm to 3.0 μm

Average spacing Sm: 0.3 μm to 10.0 μm, preferably 0.8 μm to 10.0 μm, more preferably 1.0 μm to 10.0 μm, and in some cases 3.0 μm to 10.0 μm, for example 4.3 μm to 9.0 μm, for example, 4.3 μm to 8.0 μm

  A characteristic shape that is considered to be derived from an etching process to be described later may appear on the individual protrusions 21 constituting the long-period unevenness 20 (see FIG. 1). The convex portion 21 has, on a number basis, a plurality of linear ridge portions 24 that extend downward, with 50% or more, further 70% or more, and in some cases 80% or more, branched downward from the top portion 25 in some cases. And a flat mountainside (slope) 23 that spreads downward with the peak 24 as the upper side.

  Finer short-period irregularities 30 are formed on the glass surface constituting the long-period irregularities 20. In FIG. 1, the short-period unevenness 30 is drawn only in the region D, but the unevenness 30 is also formed in regions other than the region D. The short-period irregularities 30 can be formed on the glass surface 11 partially or over the entire area. As shown in FIG. 1, the glass surface 11 can have the long-period irregularities 20 and the short-period irregularities 30 separately in different areas, but in a superimposed manner in the same area.

  Similarly to the long-period unevenness 20, the short-period unevenness 30 can also be formed by retracting the glass surface 11 by an etching process. The short period unevenness 30 is also a surface texture constituted by the glass itself. The etching process for forming the short period unevenness 30 need not be performed separately from the etching process for forming the long period unevenness 20. That is, as will be described later, the long-period irregularities 20 and the short-period irregularities 30 can be formed on the glass surface 11 by a single etching process.

  Since the height and period of the short-period irregularities 30 are sufficiently smaller than the wavelength of light that is a problem in this specification (see the above-described wavelength range), the glass surface 11 on which the short-period irregularities 30 are formed is the glass plate 1. It can function as a pseudo optical layer having an apparent refractive index smaller than that of the bulk portion. The pseudo optical layer has a refractive index of glass (typical) for light having a wavelength sufficiently larger than the degree of fluctuation due to minute fluctuations at the interface between the glass and a substance in contact with the glass (usually air) in the layer. Specifically, it functions as a low refractive index layer having a refractive index between 1.52) and the refractive index of the substance (1 in the case of air). And it is thought that reflection of the light which injects into the glass surface 11 is suppressed by presence of this layer.

  By the reflection suppressing function mainly derived from the short-period unevenness 30, it is possible to improve the transmittance of light incident on the glass surface 11. The transmittance improvement ΔT can be 0.1% or more, further 0.3% or more, particularly 0.5% or more, especially 0.7% or more, and in some cases 1.0% or more. The effect of improving the transmittance is directly obtained by the short-period unevenness 30, but as described above, the increase in surface area due to the long-period unevenness 20 may contribute to the increase. The improvement in transmittance is the same glass plate as the glass plate 1 except that the glass surface 11 is a smooth surface, specifically, the glass surface is a smooth surface having no irregularities, and has the same thickness and composition. Evaluation can be made based on a glass plate. When the glass plate is subjected to the chemical strengthening treatment, the same composition is determined based on the glass composition inside the glass plate not affected by the chemical strengthening treatment. Further, in this specification, the “smooth surface” specifically refers to a so-called fire-making surface manufactured by a manufacturing method such as a float method or an overflow downdraw method, and is subjected to processing such as etching processing or chemical strengthening processing. It means not a glass surface.

The diameter DT of the minute protrusions 31 constituting the short period unevenness 30 is preferably in the range of 20 nm to 250 nm, more preferably 50 nm to 200 nm. The height PV of the minute protrusions 31 is preferably in the range of 30 nm to 150 nm, more preferably 50 nm to 100 nm. The number TN of the fine protrusions 31 is preferably 50 to 2000, more preferably 100 to 1000, per 1 μm ² of the glass surface as the main surface.

  The diameter DT, the height PV, and the number TN can be determined based on the observation result with a scanning electron microscope (SEM). The diameter DT of the minute convex portion 31 is determined by the diameter when the outer edge of the convex portion is regarded as a circle of equal area. Further, the height PV is determined by the method described with reference to FIG. 2 based on the profile obtained from the cross-sectional observation of the glass surface by SEM. As this profile, a profile measured over a total length of 0.5 μm along the glass surface is used.

  Note that a characteristic shape that is considered to be derived from an etching process to be described later may appear in the minute recess 32 that constitutes the short-period unevenness 30 together with the minute protrusion 31. That is, the minute recess 32 is typically a crater-like depression hole in which the outer edge of the hole appearing on the glass surface is substantially circular.

  Strictly speaking, the “period” that distinguishes the long-period irregularities 20 and the short-period irregularities 30 can be specified by the average value of the interval W (see FIG. 2) of the apexes of the peaks 41 in the surface roughness curve. As the mountain portion 41, as described above, only those having a top portion located above the center line 40 which is an equal area line and a bottom portion located below are selected. In addition, the surface roughness curve about the short period unevenness | corrugation 30 shall use the curve of the measurement length of 0.5 micrometer obtained by cross-sectional observation of the glass surface using SEM.

  The period of the long-period unevenness 20 is on the order of microns, and is, for example, 0.5 μm to 8.0 μm. On the other hand, the period of the short-period irregularities 30 is on the order of submicrons, and is, for example, 50 nm to 500 nm, for example, 50 nm to 200 nm. Since the period of both the unevennesses 20 and 30 is greatly different as described above, the unevennesses 20 and 30 can be clearly distinguished.

  The glass surface 12 opposite to the glass surface 11 serving as the light incident surface is usually a light emitting surface. The glass surface 12 may be a smooth surface having no surface irregularities such as the long-period irregularities 20 and the short-period irregularities 30, and has the long-period irregularities 20 and the short-period irregularities 30 as with the glass surface 11. It may be a surface. In addition, the glass surfaces 11 and 12 of a glass plate are a pair of main surfaces which have the largest area in the surface of a glass plate, and the thickness of a glass plate will be decided by the distance between them.

  Hereinafter, one form of the manufacturing method of the glass plate 1 provided with the glass surface 11 which has the long period unevenness | corrugation 20 and the short period unevenness | corrugation 30 superimposed is demonstrated. As described above, the etching process is used in this embodiment.

  First, a glass plate is prepared. As the glass plate, it is sufficient to use a glass plate of mass-produced general-purpose composition, typically a soda lime silica glass manufactured by the float process. However, the glass plate is not limited to this, and a glass plate obtained by various production methods such as an overflow downdraw method may be used. The type of glass plate is not limited to the above, and glass plates having various compositions such as borosilicate glass and aluminosilicate glass can also be used. The glass plate preferably has a glass composition in which silicon dioxide is the main component of the network forming component, particularly the main component of all components, in order to supply silicon necessary for the progress of the chemical reaction described below. In the present specification, the “main component” means a component occupying 50% by mass or more according to common usage.

  What is necessary is just to select the thickness of a glass plate suitably according to a use, and there is no special restriction | limiting in the range. For example, a suitable thickness when used as a front glass substrate of a solar cell is 2 mm to 6 mm, particularly 3 mm to 5 mm. An appropriate thickness when used as a cover glass of a solar cell is 0.1 mm to 6 mm, particularly 0.1 mm to 1.5 mm.

The composition of soda lime silica glass is shown below as an example of the glass composition suitable for the glass plate. Below, the content rate of each component is displayed by the mass%. _{SiO 2: 65~80%, Al 2} O 3: 0~5%, MgO: 0~10%, CaO: 5~15%, MgO + CaO: 5~15%, Na 2 O: 10~18%, K 2 O: 0 to 5%, Na ₂ O + K ₂ O: 10 to 20%, B ₂ O ₃ : 0 to 5%, other trace components: 0 to 1%. Here, examples of “other trace components” include colored components represented by Fe ₂ O ₃ and clarified components represented by SO ₃ .

  An etchant (etchant) to be prepared together with the glass plate is prepared containing hydrofluoric acid (hydrofluoric acid) and a fluoride salt. The fluoride salt is preferably at least one selected from potassium fluoride, ammonium fluoride and sodium fluoride. This etching solution can be prepared, for example, by mixing hydrofluoric acid and an aqueous fluoride salt solution.

  In the etching process, erosion of the surface of the glass plate is performed while depositing a silicofluoride salt. For example, when an etching solution containing hydrofluoric acid and potassium fluoride is brought into contact with the surface of the glass plate, the reaction of the formula (1) involving silicon oxide eluted from the glass plate into the etching solution proceeds, and the produced silicon fluoride is generated. Potassium halide precipitates. When the etching solution containing hydrofluoric acid and ammonium fluoride is brought into contact with the glass plate, the reaction of the formula (2) proceeds and the produced ammonium silicofluoride is precipitated. Similarly, when sodium fluoride is used, the reaction of formula (3) proceeds and the produced sodium silicofluoride precipitates.

SiO ₂ + 4HF + 2KF → K ₂ SiF ₆ ↓ + 2H ₂ O (1)
SiO ₂ + 4HF + 2NH ₄ F → (NH ₄ ) ₂ SiF ₆ ↓ + 2H ₂ O (2)
SiO ₂ + 4HF + 2NaF → Na ₂ SiF ₆ ↓ + 2H ₂ O (3)

  When etching proceeds with a silicofluoride salt such as potassium silicofluoride or ammonium silicofluoride deposited on the glass surface, fine irregularities appear on the surface of the glass plate. The fine surface irregularities are also formed in the region where the silicofluoride salt is adhered. From this fact, it is considered that the fine surface irregularities were formed by the non-uniform progression of erosion caused by etching by the silicofluoride salt adhering to the surface of the glass plate as a porous body.

  Conventionally, minute projections formed on a glass plate by using an etching solution containing hydrofluoric acid and a fluoride salt such as potassium fluoride have been mainly used for manufacturing a magnetic disk substrate. In this application, a minute convex portion having a height of about 5 nm to 70 nm is used as a protrusion for preventing the magnetic head from adhering to the substrate. Since a glass plate as a substrate for a magnetic disk is basically required to have a smooth surface, in the technical field of magnetic disks, the etching process using the etching solution exceeds the above-mentioned minute convex portions. It has been considered appropriate to carry out under conditions such that the convex portions are not formed.

  If etching proceeds further with silicic acid salts such as potassium silicofluoride deposited on the surface of the glass plate, erosion due to etching proceeds non-uniformly according to local differences in the amount of silicic acid salt deposited. However, larger irregularities appear than the fine surface irregularities described above. Thus, surface irregularities (long-period irregularities 20) having a relatively large period and long periods are formed together with surface irregularities (short-period irregularities 30) having a relatively small period and a short period. In order to obtain a glass plate having a glass surface having both surface irregularities 20 and 30, it is important to apply conditions under which the erosion by etching proceeds sufficiently and appropriately on the glass surface to which the deposited silicofluoride salt has adhered. It is. Erosion due to etching can be sufficiently achieved by comprehensively adjusting the temperature of the etching solution, the time of the etching process, the concentration of hydrofluoric acid and fluoride salt in the etching solution, the composition of the glass plate, etc. in consideration of the mutual influences. And it can proceed appropriately.

  The temperature of the etching solution during the etching process is slightly higher than room temperature (20 to 25 ° C.), for example, 28 ° C. or more, and preferably 30 to 35 ° C. The time for the etching process depends on the temperature to be applied, but for example, 10 seconds or more, and further 30 to 600 seconds are appropriate. The concentration of hydrofluoric acid in the etching solution is preferably 1 to 10% by mass. Further, the concentration of a fluoride salt such as potassium fluoride is preferably 1 to 25% by mass, and in some cases 10 to 20% by mass. However, the concentration of hydrofluoric acid and fluoride salt should be adjusted as appropriate according to the applied temperature and time.

  By the etching treatment, a silicofluoride salt such as potassium silicofluoride adheres to the glass surface, and in some cases, the entire glass surface is covered with the silicofluoride salt. This silicic acid salt is washed away in a cleaning process (attachment removal process) performed subsequent to the etching process for performing the etching process. As the cleaning solution used in the cleaning step, various acids such as hydrochloric acid, nitric acid, and sulfuric acid can be used. Surface irregularities 20 and 30 are formed on the glass surface exposed through the cleaning process. After washing with an acid, the glass surface may be washed with water as appropriate in order to wash away the adhering acid. The glass plate 1 in which the surface irregularities 20 and 30 are formed on the glass surface 11 is obtained through a glass plate drying process that is further performed as necessary. If water is used as the cleaning liquid, the attached substances cannot be completely removed unless washing is performed for a long time while applying a physical force. Therefore, the acid exemplified above is suitable as the cleaning liquid.

  The etching process may be applied to both glass surfaces 11 and 12 of the glass plate 1 or may be applied to only one glass surface 11. In the latter case, surface irregularities 20 and 30 are imparted to the glass surface 11, and the glass surface 12 is held as a smooth surface.

  Thereafter, if necessary, the glass plate is subjected to a film forming process, a chemical strengthening process, and the like. In the film forming step, for example, a transparent conductive film, an overcoat film, a protective film, and the like are formed on the glass surface 12 opposite to the glass surface 11 on which the surface irregularities 20 and 30 are formed. These films may be formed after the base film is formed. As shown in FIG. 3, one glass surface 11 is constituted by a glass surface having long-period irregularities 20 and short-period irregularities 30, and an underlying film 52 is formed on the other glass surface 12 as necessary. The glass plate 2 on which the transparent conductive film 51 is formed is particularly suitable for use as a front glass plate of a thin film solar cell. That is, in the preferred embodiment of the present invention, the glass surface having the short period unevenness 30 on the glass surface 11 forms the long period unevenness 20 and the thin film type in which the transparent conductive film 51 is formed on the glass surface 12. A front glass plate of a solar cell is provided.

  The base film 52 is formed as necessary for adjusting the optical characteristics of the glass plate 2 and for preventing diffusion of alkali components from the glass plate 2. The underlayer 52 may be composed of a single layer, but may be composed of two or more layers, and is preferably composed of a first underlayer and a second underlayer. The first underlayer formed in contact with the glass plate 2 is preferably composed mainly of tin oxide, silicon oxide, titanium oxide, zinc oxide or silicon oxycarbide, and particularly preferably composed mainly of tin oxide. . The second underlayer is preferably composed mainly of silicon oxide or aluminum oxide, and particularly preferably composed mainly of silicon oxide. A preferable film thickness of the first underlayer is 10 nm to 100 nm, particularly 20 nm to 70 nm. The preferred film thickness of the second underlayer is 5 nm to 80 nm, particularly 10 nm to 40 nm.

  For example, the transparent conductive film 51 may be a film made of zinc oxide doped with fluorine-doped tin oxide (FTO), tin-doped indium oxide (ITO), boron, aluminum, gallium, indium, or the like. The preferred film thickness of the transparent conductive film 51 is, for example, 400 nm to 900 nm, preferably 500 nm to 800 nm, although it depends on the material constituting the film. The conductivity of the transparent conductive film 51 is expressed by a sheet resistance value, for example, 30Ω / □ or less, particularly 5 to 20Ω / □ or less is suitable. These films can be formed by a known thin film forming method represented by a CVD (chemical vapor deposition) method and a sputtering method.

The chemical strengthening step is preferably performed in order to ensure the necessary strength, particularly when the glass plate to be used is thin. The chemical strengthening treatment is generally included in the vicinity of the surface of the glass plate by exchanging alkali metal ions, for example, by replacing lithium ions (Li ⁺ ) contained in the vicinity of the surface of the glass plate with sodium ions (Na ⁺ ). This is carried out by replacing sodium ions with potassium ions (K ⁺ ), and is typically carried out by ion exchange between sodium ions contained in the glass plate and potassium ions contained in the treatment liquid. Examples of the treatment liquid for performing this ion exchange include molten salts of potassium salts represented by potassium nitrate. That is, the chemical strengthening treatment can be preferably performed by immersing the glass plate in a molten salt containing potassium ions and performing ion exchange between potassium ions and sodium ions contained in the glass plate. The conditions of the chemical strengthening treatment, for example, the temperature of the molten salt and the dipping time of the glass plate may be appropriately selected from known conditions. For example, the temperature of the molten salt is 380 to 480 ° C., particularly 380 to 460 ° C. The immersion time is 30 minutes to 1440 minutes. The chemical strengthening treatment is suitable as a treatment for imparting practical strength to the cover glass for solar cells in which a thin glass plate is used.

  Thus, a glass plate having the characteristic surface irregularities 20 and 30 realized by the above-described etching process and having a glass surface into which compressive stress is introduced by ion exchange in the chemical strengthening process is obtained. The shape of the short period unevenness 30 tends to increase its pitch by the chemical strengthening treatment. Since the increase in the transmittance may be slightly reduced by the chemical strengthening process, it is preferable to perform the etching process in anticipation of this decrease. The haze rate often increases slightly due to the chemical strengthening treatment.

  Note that the etching process may be performed after the film forming process is performed in advance. In this case, the surface irregularities 20 and 30 are formed on only one glass surface 11 by etching. Further, the etching step may be performed after the chemical strengthening step is performed in advance. However, since the compressive stress layer formed by chemical strengthening may be removed when the chemical strengthening step is performed first, it is preferable to perform the etching step first.

  In order to reduce the weight of solar cells, there is an increasing demand for thin cover glass. A thin glass plate originally has low strength and cannot be tempered by air cooling. Therefore, in order to provide practical strength as a cover glass, there is nothing but chemical strengthening. However, if surface irregularities are imparted by a film made of silica fine particles and a binder formed on the surface of the glass plate, this film becomes an obstacle, so that ion exchange cannot be performed on the surface of the glass plate. It is also conceivable to form a film on the surface of a glass plate that has been subjected to chemical strengthening treatment in advance. However, in order to fix the silica fine particles with the binder using the sol-gel method, it is necessary to heat at a high temperature. For example, the heating temperature (baking temperature) applied in the example of Patent Document 1 is 610 ° C. When heated to such a high temperature, ions on the surface of the glass plate move due to diffusion, and the strength improved by the chemical strengthening treatment is greatly reduced. Since it is difficult to apply both chemical strengthening treatment and film formation by the sol-gel method, a mass production technique has not been established for a cover glass having a suitable unevenness on the surface and a thin plate thickness.

  If the etching process mentioned above is applied, the glass plate which has a glass surface which has a light-scattering function and a reflection suppression function, and has the intensity | strength required practically can be mass-produced. This is because it is not necessary to form a film that impedes chemical strengthening on a glass plate that realizes both functions on the glass surface. Subsequent to the etching process, the chemically strengthened glass plate has characteristics particularly suitable as a cover glass for solar cells. According to a preferred embodiment of the present invention, the haze ratio is 10% or more, preferably 30% or more, when compared to a glass plate that differs in that the glass surface is a smooth surface but is the same in thickness and composition. And a transmittance of 0.1% or more, preferably 0.3% or more, and a relatively high transmittance, and the thickness is, for example, 0.1 mm to 1.5 mm, preferably 0.3 mm to 1.1 mm. Thus, a glass plate that has been subjected to chemical strengthening treatment, particularly a glass plate suitable for a cover glass of a solar cell can be provided. Here, the measured values in the wavelength region of 380 nm to 1100 nm are adopted as the haze ratio and transmittance.

  Specifically, the etching treatment is performed after removing deposits that have been deposited with the etching treatment so that the degree of increase in the transmittance and the haze ratio is within a desired range in the finally obtained glass plate. It is preferable to carry out by appropriately adjusting the etching conditions such as the etching time so that the degree of increase in the haze ratio is in the above range. In this case, the glass plate used as the calculation reference for the increase width of the transmittance can be a glass plate to be subjected to the etching process.

As is apparent from the above description of the production method, the present invention is directed to another aspect thereof.
Etching solution containing hydrofluoric acid and fluoride salt on the surface of a glass plate containing silicon oxide, preferably a glass plate having a thickness of 0.1 mm to 6 mm, more preferably 0.1 mm to 1.5 mm. An etching step of eroding the surface and imparting irregularities to the surface while precipitating silicofluoride salt on the surface by contacting,
A deposit removing step (for example, a step of cleaning the surface using an acid) to remove the silicofluoride salt adhering to the surface of the glass plate,
In the etching step, the haze ratio for incident light having a wavelength range of 380 nm to 1100 nm incident on the surface of the glass plate obtained after the deposit removing step reaches 10% or more, preferably 30% or more, and the incident light The transmittance is about 0.1% or more, preferably 0.3% or more than the transmittance for incident light in the wavelength region that is incident on the surface before the etching step and the deposit removal step are performed. , More preferably 0.5% or more, to develop the unevenness on the surface until it becomes high,
Provided is a method for producing a glass plate, particularly a method for producing a glass plate suitable for a cover glass of a solar cell.

  The above-described manufacturing method may further include a strengthening step for chemically strengthening the glass plate, which is performed after the deposit removing step, in addition to the etching step and the deposit removing step.

  As described above, according to a preferred embodiment of the present invention, the glass surface that is the light incident surface has fine irregularities that reduce the reflectance of incident light, and the irregularities have a longer period than the fine irregularities. In addition, it is possible to provide a glass plate in which irregularities constituted by convex portions having a size contributing to scattering of incident light are formed.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not restrict | limited by a following example. The evaluation method of characteristics was as follows.

[Haze rate Hz, transmittance T]
Measurement was performed using a spectrophotometer “UV3100” manufactured by Shimadzu Corporation with a measurement wavelength range of 380 to 1100 nm.

[Arithmetic average roughness Ra, maximum height Ry, average interval Sm]
Measurement and analysis were performed using a non-contact three-dimensional measuring device “NH-3N” manufactured by Mitaka Kogyo Co., Ltd.

[Average height H _av , average bottom length L _av , number of protrusions N]
Based on the surface roughness curve obtained above, it was specified according to the calculation method described above. The surface roughness curve is obtained by scanning the glass surface over a length of 50 μm.

[Diameter DT, convex height PV, convex number TN of (short-period irregularities)]
From the observation result using SEM, it specified according to the above-mentioned calculation method. Here, the diameter DT and the number TN were determined based on the result of observing an area of 1.2 μm × 0.9 μm on the glass surface at a magnification of 100,000 times. The height PV was determined from a profile obtained by cross-sectional observation of the vicinity of the glass surface at a magnification of 100,000 times. This profile was obtained with a measurement length of 0.5 μm.

Example 1
A soda lime silica glass plate having a thickness of 1.1 mm manufactured by a float method as a glass plate to be etched, and an aqueous solution containing 5% by mass hydrofluoric acid (hydrofluoric acid) and 20% by mass potassium fluoride as an etching solution, respectively. Got ready. The etching solution was kept at 30 ° C., and the glass plate was immersed in this etching solution for 30 seconds to carry out the etching treatment. During the etching process, the glass plate was allowed to stand and the etching solution was not stirred. Next, the glass plate taken out from the etching solution was immersed in 5% by mass of sulfuric acid to perform a cleaning process to remove the adhering potassium silicofluoride. During the cleaning process, the glass plate was rocked in sulfuric acid. Furthermore, the glass plate taken out from the sulfuric acid was washed with water to obtain a glass plate having surface irregularities formed on both glass surfaces.

(Example 2)
A glass plate on which surface irregularities were formed was obtained in the same manner as in Example 1 except that the etching treatment time was 2 minutes.

(Example 3)
A glass plate having surface irregularities was obtained in the same manner as in Example 2 except that the concentration of hydrofluoric acid in the etching solution was 1.2 mass% and the concentration of potassium fluoride was 11.6 mass%.

(Comparative Example 1)
A glass plate on which surface irregularities were formed was obtained in the same manner as in Example 2 except that the concentration of potassium fluoride in the etching solution was 40% by mass.

(Examples 4 to 21, Comparative Examples 2 to 3)
A glass plate on which surface irregularities were formed was obtained in the same manner as in Example 1 except that the etching treatment time and the concentrations of hydrofluoric acid and potassium fluoride in the etching solution were changed to the values shown in Table 1.

(Examples 41 to 43, Comparative Example 4)
The chemical strengthening treatment was applied to the glass plates obtained in Examples 1 to 3 and Comparative Example 1. This treatment was performed by immersing the glass plate in molten potassium nitrate maintained at 460 ° C. for 30 minutes. The glass plate taken out from the potassium nitrate molten salt was washed with water to obtain a glass plate having surface irregularities and chemically strengthened.

(Reference Example 1)
A soda-lime-silica glass plate having a thickness of 1.1 mm before the etching treatment was used as a measurement target. The transmittance T for Reference Example 1 was 89.1%.

(Reference Example 2)
The measurement object was a soda-lime silica glass plate having a thickness of 1.1 mm to which the chemical strengthening treatment was applied under the above conditions without performing the etching treatment. The transmittance T for Reference Example 2 was 88.9%.

  The measurement result about the glass plate obtained by each Example and each comparative example is shown in Tables 1-3.

  Under the etching conditions applied in each example and comparative example, the reduction in the thickness of the glass plate is limited to a very limited range (about 2 μm or less). It is clear that the change in transmittance in each example and comparative example is not due to a decrease in thickness. This is because the light absorption of the glass plate having a thickness of about 1.1 mm is extremely small and substantially equal to 0, and thus the change in transmittance due to the reduction in thickness becomes a value that can be ignored.

  The observation result by SEM of the glass plate obtained by Example 2 is shown as FIG. 4A-FIG. 4D. The observation result by the SEM of the glass plate obtained by Example 17 is shown as FIG. A large number of convex portions 21 having the above-described characteristics were formed on the surface of the glass plate, and fine convex portions 31 were formed on the surface of each convex portion 21. In Example 2, the period of the long-period irregularities determined according to the above-described method was 3.2 μm, and the period of the short-period irregularities was 70 nm. Further, the surface of the glass plate obtained by each of the examples other than those described in Table 3 by observation using SEM, the convex portions 21 and the minute convex portions having dimensions similar to those of the examples described in Table 3. It was confirmed that 31 was formed.

  The observation result by the SEM of the glass plate obtained by Example 42 is shown as FIG. The irregularities on the surface of the glass plate are slightly deformed by being affected by the chemical strengthening treatment. However, even after the chemical strengthening treatment, the values of Ra, Ry and Sm on the glass surface were within the above-mentioned preferred ranges. When the chemical strengthening treatment was performed, it was confirmed that the haze rate Hz increased by about 1% and the transmittance T decreased by about 0.3% to 0.5% compared to before the chemical strengthening treatment. However, if the etching process conditions are set appropriately, the transmittance T can be improved to compensate for the decrease in the transmittance T.

  If the concentration of potassium fluoride is too high, erosion of the glass surface does not proceed sufficiently, and the haze rate Hz does not increase (each comparative example). The same etching treatment as in Example 1 was performed except that ammonium fluoride was used instead of potassium fluoride. Further, the same treatment as in Example 1 was performed except that sodium fluoride was used instead of potassium fluoride. As a result of performing this etching process, it was confirmed that both long-period surface irregularities and short-period surface irregularities were formed as in Example 1.

(Example 51)
The solar cell R in which the cover glass of the prototype solar cell was replaced with the glass plate of Reference Example 1, and the glass plate obtained in Example 11 from the cover glass of the solar cell (haze ratio 15.0%, transmittance increase width 0) The short circuit current Isc was measured with respect to the solar cell A1 replaced with 3%). It was confirmed that the Isc of the solar cell A1 is 0.51% larger than the Isc of the solar cell R.

(Example 52)
The short circuit current Isc was measured for the solar cell A2 in which the cover glass of the solar cell was replaced with the glass plate obtained in Example 17 (haze ratio 40.2%, transmittance increase width 0.3%). It was confirmed that the Isc of the solar cell A2 is 0.12% larger than the Isc of the solar cell R.

(Example 53)
A glass plate with surface irregularities formed in the same manner as in Example 1 except that the etching treatment time was 20 seconds and the concentrations of hydrofluoric acid and potassium fluoride in the etching solution were 3% and 24%, respectively. Obtained. The haze rate Hz of this glass plate was 20.0%, and the increase ΔT of the transmittance T was 0.1%. The short circuit current Isc was measured for the solar cell A3 in which the cover glass of the solar cell was replaced with the glass plate obtained in Example 17. It was confirmed that the Isc of the solar cell A3 is 0.89% larger than the Isc of the solar cell R.

  In addition, although the said Example is a prototype, even if it is a commercially available solar cell, it is clear that a characteristic is improved by using the glass plate by this invention as a cover glass.

1, 2 Glass plate 11, 12 Glass surface (main surface)
20 Long-period unevenness 21 Convex part 22 Concave part 23 Mountainside part 24 Peak part 25 Top part 30 Short-period uneven part 31 Micro convex part 32 Micro concave part 40 Center lines 41 and 42 Mountain part 51 Transparent conductive film 52 Base film

Claims (11)

A glass plate having a glass surface as a light incident surface,
The glass surface has minute convex portions having a diameter of 20 nm to 250 nm, an arithmetic average roughness Ra of 0.08 μm to 0.8 μm, a maximum height Ry of 0.3 μm to 7.0 μm, and 0.3 μm The glass plate which has the unevenness | corrugation shown by the average space | interval Sm of -10.0 micrometers.   The glass plate of Claim 1 whose haze rate of the incident light of the wavelength range 380 nm-1100 nm which injects into the said glass surface is 10% or more.   The glass plate according to claim 2, wherein the haze ratio is 30% or more.   The transmittance of incident light in the wavelength range of 380 nm to 1100 nm is 0.1% or more higher than that of a glass plate having a smooth surface with no irregularities and the same thickness and composition. The glass plate as described in.   The glass plate according to claim 4, wherein the transmittance is 0.3% or more.   The glass plate in any one of Claims 1-5 in which the said micro convex part and the said unevenness | corrugation are formed by the etching.   The glass plate in any one of Claims 1-6 whose height of the said micro convex part is 30 nm-150 nm.   The glass plate in any one of Claims 1-7 whose thickness is 0.1-6 mm.   The glass plate of Claim 8 whose thickness is 0.1 mm-1.5 mm.   The glass plate in any one of Claims 1-9 to which the chemical strengthening process was performed. The solar cell provided with the glass plate in any one of Claims 1-10.