JP2019032918A - Glass substrate for magnetic recording medium - Google Patents

Abstract

To provide a glass substrate for a magnetic recording medium which does not easily cause deflection or fluttering during high-speed rotation and matches thermal expansion coefficient of a spindle material (for example, stainless steel or the like).SOLUTION: In a glass substrate for a magnetic recording medium of the present invention, an average linear thermal expansion coefficient in the temperature range of 30 to 380°C is 30×10/°C or more, and Young's modulus is 80 GPa or more.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a glass substrate for a magnetic recording medium.

  The magnetic recording apparatus includes a magnetic recording medium in which a magnetic layer is formed on a magnetic recording medium substrate, and information can be recorded using the magnetic layer. Conventionally, an aluminum alloy substrate has been used as a substrate for a magnetic recording medium used in a magnetic recording apparatus, but now, with the demand for higher recording density, the hardness, flatness and smoothness are higher than those of an aluminum alloy substrate. A glass substrate having excellent properties is mainly used.

  In recent years, in order to meet the need for further higher recording density, a magnetic recording medium using an energy-assisted magnetic recording method, that is, an energy-assisted magnetic recording medium has been studied. As for the energy-assisted magnetic recording medium, a glass substrate is used, and a magnetic layer or the like is formed on the surface of the glass substrate. In the energy-assisted magnetic recording medium, an ordered alloy having a large magnetic anisotropy coefficient Ku (hereinafter referred to as “high Ku”) is used as the magnetic material of the magnetic layer.

  In order to increase the degree of ordering (ordering degree) of the magnetic layer and increase the Ku, the base material including the glass substrate is heated at a high temperature of about 600 ° C. to 700 ° C. during or before the formation of the magnetic layer. Heat treatment may be performed, and after the magnetic layer is formed, the substrate including the glass substrate may be irradiated with laser. Such heat treatment and laser irradiation also have the purpose of increasing the annealing temperature and coercive force of the magnetic layer containing the FePt-based alloy or the like.

  By the way, a glass substrate for a magnetic recording medium is required to have a high rigidity (Young's modulus) so as not to be greatly deformed during high-speed rotation.

  More specifically, in a disk-shaped magnetic recording medium, information is written and read along the rotation direction while rotating the magnetic head around the central axis and moving the magnetic head in the radial direction. In recent years, the rotational speed for increasing the writing speed and the reading speed has been increasing from 5400 rpm to 7200 rpm, and further to 10000 rpm. However, in a disk-shaped magnetic recording medium, depending on the distance from the central axis in advance. Since a position for recording information is assigned, if the glass substrate is deformed during rotation, the magnetic head is displaced and accurate reading becomes difficult.

  Further, in recent years, by mounting a DFH (Dynamic Flying Height) mechanism on the magnetic head, the gap between the recording / reproducing element portion of the magnetic head and the surface of the magnetic recording medium has been significantly narrowed (low flying height) has been achieved. A higher recording density is being achieved. The DFH mechanism is a mechanism in which a heating unit such as a very small heater is provided in the vicinity of the recording / reproducing element unit of the magnetic head, and only the periphery of the element unit is thermally expanded toward the medium surface. By providing such a mechanism, the distance between the magnetic head and the magnetic layer of the medium is reduced, so that signals of smaller magnetic particles can be picked up, and high recording density can be achieved. On the other hand, since the gap between the recording / reproducing element portion of the magnetic head and the surface of the magnetic recording medium is extremely small, for example, 2 nm or less, the magnetic head may collide with the surface of the magnetic recording medium even with a slight impact. is there. This tendency becomes more prominent as the rotation speed becomes higher. Therefore, during high-speed rotation, it is important to prevent the glass substrate from being bent or fluttering, which causes this collision.

  Further, the glass substrate for a magnetic recording medium is also required to have an appropriate thermal expansion coefficient in order to increase the reliability of recording and reproduction of the magnetic recording medium. More specifically, an HDD (hard disk drive) incorporating a magnetic recording medium has a structure in which the magnetic recording medium itself is rotated by pressing a central portion with a spindle of a spindle motor. For this reason, if the difference between the thermal expansion coefficients of the glass substrate and the spindle material is too large, the magnetic recording medium is deformed because the thermal expansion and contraction of the two differ with respect to the surrounding temperature change. When such a phenomenon occurs, the written information cannot be read out by the magnetic head, and the reliability of recording and reproduction may be impaired. Therefore, it is desirable that the glass substrate for a magnetic recording medium has a thermal expansion coefficient that matches the thermal expansion coefficient of the spindle material (for example, stainless steel).

  Therefore, the present invention has been made in view of the above circumstances, and its object is to prevent the occurrence of bending and fluttering (fluttering) during high-speed rotation, and to match the thermal expansion coefficient of the spindle material (for example, stainless steel). The idea is to create a glass substrate for recording media.

As a result of repeating various experiments, the inventor has found that the above technical problem can be solved by increasing the thermal expansion coefficient and Young's modulus of the glass substrate to a predetermined value or more, and proposes the present invention. It is. That is, the glass substrate for a magnetic recording medium of the present invention is characterized in that an average linear thermal expansion coefficient in a temperature range of 30 to 380 ° C. is 30 × 10 ⁻⁷ / ° C. or more and a Young's modulus is 80 GPa or more. Here, the “average linear thermal expansion coefficient in the temperature range of 30 to 380 ° C.” can be measured with a dilatometer. The “Young's modulus” can be measured by a well-known resonance method.

The glass substrate for magnetic recording media of the present invention regulates the average linear thermal expansion coefficient in the temperature range of 30 to 380 ° C. to 30 × 10 ⁻⁷ / ° C. or higher. In this way, since the difference in thermal expansion coefficient between the glass substrate and the spindle material is reduced, the thermal expansion and contraction of both of the glass substrate and the spindle material are easily matched to the surrounding temperature change. As a result, the magnetic recording medium is hardly deformed, and the reliability of recording / reproducing of the magnetic recording medium can be improved. Further, when heat treatment or laser irradiation is performed to achieve high Ku, the difference in thermal shrinkage between the glass substrate and the spindle material can be reduced.

  Furthermore, the glass substrate for magnetic recording media of the present invention regulates the Young's modulus to 80 GPa or more. This makes it difficult for the glass substrate to be bent or fluttered during high-speed rotation, thus preventing collision between the information recording medium and the magnetic head.

  The glass substrate for a magnetic recording medium of the present invention preferably has a softening point of 700 ° C. or higher. In this way, even if heat treatment or laser irradiation is performed at a high temperature, the glass substrate is hardly distorted, and the Ku of the magnetic layer can be easily increased. If distortion occurs in the glass substrate during heat treatment or laser irradiation, this distortion may cause a collision between the glass substrate and the magnetic head. Here, the “softening point” refers to a value measured based on the method of ASTM C336.

Further, the glass substrate for a magnetic recording medium of the present invention has a glass composition, in _{mass%, SiO 2 53~66%, Al} 2 O 3 7~34%, B 2 O 3 0~8%, MgO 0~22 %, CaO 1 to 15%, Y ₂ O ₃ + La ₂ O ₃ + ZrO ₂ 0 to 20% are preferably contained. Here, “Y ₂ O ₃ + La ₂ O ₃ + ZrO ₂ ” refers to the total amount of Y ₂ O ₃ , La ₂ O ₃ and ZrO ₂ .

  The glass substrate for a magnetic recording medium of the present invention preferably has a surface roughness Ra of 1.0 nm or less. This makes it possible to improve the magnetic characteristics even if the bit size is reduced for higher recording density. Here, the “surface roughness Ra of the surface” refers to the surface roughness Ra of the main surface (both surfaces) excluding the end face, and can be measured by, for example, an atomic force microscope (AFM).

  The glass substrate for a magnetic recording medium of the present invention preferably has an average linear transmittance of 70% or more in an optical path length of 1 mm and a wavelength range of 350 to 1500 nm. In this way, when the laser irradiation is performed to increase the Ku, the laser beam is sufficiently irradiated to the magnetic layer, so that the magnetic recording medium can be efficiently increased in recording density. Here, the “average linear transmittance in an optical path length of 1 mm and a wavelength range of 350 to 1500 nm” can be measured with a commercially available spectrophotometer. For example, a spectrophotometer UV-3100 manufactured by Shimadzu Corporation can be used.

  The glass substrate for a magnetic recording medium of the present invention preferably has a disk shape, that is, a disk shape, and a shape in which a circular opening is formed at the center (see FIG. 1).

It is an upper perspective view for showing a disk shape.

In the glass substrate for magnetic recording medium of the present invention, the average linear thermal expansion coefficient in the temperature range of 30 to 380 ° C. is 30 × 10 ⁻⁷ / ° C. or more, preferably 31 × 10 ⁻⁷ to 70 × 10 ⁻⁷ /. C, 32 × 10 ^{−7 to} 65 × 10 ⁻⁷ / ° C., 36 × 10 ^{−7 to} 62 × 10 ⁻⁷ / ° C., 37 × 10 ^{−7 to} 60 × 10 ⁻⁷ / ° C., 38 × 10 ⁻⁷ to 55 × 10 ⁻⁷ / ° C., 40 × 10 ^{−7 to} 53 × 10 ⁻⁷ / ° C., 42 × 10 ^{−7 to} 51 × 10 ⁻⁷ / ° C., particularly preferably 42 × 10 ⁻⁷ to 50 × 10 ⁻⁷ / ° C. If the average linear thermal expansion coefficient in the temperature range of 30 to 380 ° C. is too low, the difference in thermal expansion coefficient between the glass substrate and the spindle material will increase, so that the thermal expansion and contraction of both will match the ambient temperature change. It becomes difficult to do. As a result, the magnetic recording medium is easily deformed, and the recording / reproducing reliability of the magnetic recording medium is likely to be lowered.

  In the glass substrate for magnetic recording media of the present invention, the Young's modulus is 80 GPa or more, preferably 84 GPa or more, particularly preferably 87 to 120 GPa. If the Young's modulus is too low, the glass substrate is likely to be bent or fluttered during high-speed rotation, and the information recording medium and the magnetic head are likely to collide.

The glass substrate for magnetic recording media of the present invention has, as a glass composition, mass%, SiO ₂ 53 to 66%, Al ₂ O ₃ 7 to 34%, B ₂ O ₃ 0 to 8%, MgO 0 to 22%, _{CaO 1~15%, Y 2 O 3} + La 2 O 3 + is more preferably contains ZrO 2 0 to 20%. The reason for limiting the content of each component as described above will be described below. In addition, in description of content of each component,% display represents the mass% unless there is particular notice.

SiO ₂ is a component that forms a network of glass. The content of SiO ₂ is preferably 53 to 66%, 55 to 64%, 56 to 62%, particularly 57 to 60%. When the content of SiO ₂ is too small, it becomes difficult to vitrify and heat resistance tends to decrease. On the other hand, if the content of SiO ₂ is too large, it tends to decrease. Meltability and moldability, and the thermal expansion coefficient becomes too low.

Al ₂ O ₃ is a component that increases Young's modulus and weather resistance. The content of Al ₂ O ₃ is preferably 7 to 34%, 8 to 26%, 9 to 24%, 11 to 23%, 12 to 22%, 14 to 21%, particularly 16 to 21%. When the content of Al ₂ O ₃ is too small, the Young's modulus and the heat resistance is liable to decrease. On the other hand, when the content of Al ₂ O ₃ is too large, the melting properties, formability, and resistance to devitrification tends to drop.

B ₂ O ₃ is a component that forms a glass network, but is a component that lowers the Young's modulus and heat resistance. Therefore, the content of B ₂ O ₃ is preferably 0 to 8%, 0.1 to 7%, 1 to 6%, particularly 3 to 5%.

  MgO is a component that greatly increases the Young's modulus, and is a component that decreases the high-temperature viscosity and improves the meltability and moldability. The content of MgO is preferably 0 to 22%, 0.5 to 21%, 1 to 20%, 2 to 19%, 3 to 18%, 4 to 16%, 5 to 16%, 7 to 16%, 8 to 14%, especially 9 to 12%. When there is too little content of MgO, it will become difficult to receive the said effect. On the other hand, when there is too much content of MgO, devitrification resistance will fall easily.

  CaO is a component that increases the meltability and moldability by lowering the high-temperature viscosity. The content of CaO is preferably 1 to 15%, 2 to 12%, 3 to 10%, particularly 5 to 8%. When there is too little content of CaO, it will become difficult to receive the said effect. On the other hand, when there is too much content of CaO, devitrification resistance will fall easily.

Y ₂ O ₃ , La ₂ O ₃ and ZrO ₂ are components that increase the Young's modulus. The total amount of Y ₂ O ₃ , La ₂ O ₃ and ZrO ₂ is preferably 0-20%, 0.1-18%, 0.5-16%, 1-15%, 1-14%, 1- 12%, 1.2 to 10%, 1.3 to 8%, especially 1.5 to 5%. When Y ₂ O _3, the total amount of _La 2 _{O 3} and ZrO ₂ is too high, devitrification resistance is liable to decrease. The content of Y ₂ O ₃ is preferably 0-15%, 0.1-14%, 0.5-13%, 0.5-12%, 0.5-10%, 0.5-8% 0.5-6%, especially 1-4%. The content of La ₂ O ₃ is preferably 0 to 6%, 0 to 4%, particularly 0 to 2%. The content of ZrO ₂ is preferably 0 to 10%, 0.1 to 6%, 0.5 to 4%, particularly 1 to 3%. When the content of Y ₂ O ₃ is too large, it tends to decrease. Devitrification resistance, also raw material cost is likely to rise. When the content of La ₂ O ₃ is too large, it tends to decrease. Devitrification resistance, also raw material cost is likely to rise. When the content of ZrO ₂ is too large, the devitrification resistance is liable to decrease.

  In addition to the above components, for example, the following components may be added.

Li ₂ O, Na ₂ O, and K ₂ O are components that lower the high-temperature viscosity and improve the meltability and moldability, but are components that reduce water resistance and weather resistance. From the viewpoint of meltability and moldability, the total amount of Li ₂ O, Na ₂ O, and K ₂ O is preferably 0.01 to 10%, 0.05 to 8%, 0.1 to 5%, and 0.005. 3 to 3%, especially 0.5 to less than 1%. The respective contents of _Li 2 O, Na ₂ O and _{K 2} O is preferably 0.01 to 10% from 0.05 to 8%, 0.1% to 5%, from 0.3 to 3%, in particular 0.5 to less than 1%. From the viewpoint of water resistance and weather resistance, it is ˜15%, 0 to 10%, 0 to 5%, 0 to 1%, particularly less than 0.1 to 1%. The content of each of The _Li 2 O, Na ₂ O and _{K 2} O is preferably less than 0-10%, 0-5%, in particular 0.1% to 1%.

  SrO and BaO are components that lower the high-temperature viscosity and improve the meltability and moldability. SrO and BaO are 0 to 15%, 0.1 to 12%, particularly 0.5 to 10%, respectively.

  ZnO is a component that lowers the high-temperature viscosity and significantly increases the meltability. The content of ZnO is preferably 0 to 7%, 0.1 to 5%, particularly 0.5 to 3%. When there is too little content of ZnO, it will become difficult to receive the said effect. In addition, when there is too much content of ZnO, it will become easy to devitrify glass.

TiO ₂ is a component that enhances water resistance and weather resistance, but is a component that colors glass. Therefore, the content of TiO ₂ is preferably 0 to 0.5%, particularly 0 to less than 0.1%. When the content of TiO ₂ is too large, the average linear transmittance in the wavelength range 350~1500nm tends to decrease.

As a fining agent, 0.05 to 0.5% of one or more selected from the group of SnO ₂ , Cl, SO ₃ and CeO ₂ (preferably a group of SnO ₂ and SO ₃ ) may be added. .

Fe ₂ O ₃ is a component that is inevitably mixed as an impurity in the glass raw material, and is a coloring component. Therefore, the content of Fe ₂ O ₃ is preferably 0.5% or less, 0.001 to 0.1%, 0.005 to 0.07%, 0.008 to 0.03%, particularly 0.01 -0.025%. When the content of Fe ₂ O ₃ is too large, the average linear transmittance in the wavelength range 350~1500nm tends to decrease.

V ₂ O ₅ , Cr ₂ O ₃ , CoO ₃ and NiO are coloring components. Therefore, the respective contents of V ₂ O ₅ , Cr ₂ O ₃ , CoO ₃ and NiO are preferably 0.1% or less, particularly less than 0.01%. When the content of each of _{V 2 O 5, Cr 2 O} 3, CoO 3 and NiO is too large, the average linear transmittance in the wavelength range 350~1500nm tends to decrease.

From the environmental consideration, it is preferable that the glass composition does not substantially contain As ₂ O ₃ , Sb ₂ O ₃ , PbO, Bi ₂ O ₃ and F. Here, “substantially does not contain” means that the glass component does not actively add an explicit component, but allows it to be mixed as an impurity. It indicates that the content is less than 0.05%.

  The glass substrate for a magnetic recording medium of the present invention preferably has the following characteristics.

  The softening point is preferably 700 ° C. or higher, 800 ° C. or higher, 900 ° C. or higher, 930 ° C. or higher, particularly 950 to 1150 ° C. If the softening point is too low, the glass substrate is likely to be distorted when heat treatment or laser irradiation is performed at a high temperature, making it difficult to increase the Ku of the magnetic layer. Further, this distortion may cause a collision between the glass substrate and the magnetic head.

  The average linear transmittance in an optical path length of 1 mm and a wavelength range of 350 to 1500 nm is preferably 70% or more, 80% or more, particularly 90% or more. If the average linear transmittance in the optical path length of 1 mm and the wavelength range of 350 to 1500 nm is too low, the laser light is not sufficiently irradiated to the magnetic layer when laser irradiation is performed, and it is difficult to increase the Ku of the magnetic layer.

The liquidus temperature is preferably 1250 ° C. or lower, 1200 ° C. or lower, 1180 ° C. or lower, 1160 ° C. or lower, particularly 1130 ° C. or lower. The liquid phase viscosity is preferably 10 ^3.8 dPa · s or more, 10 ^4.4 dPa · s or more, 10 ^4.6 dPa · s or more, 10 ^4.8 dPa · s or more, particularly 10 ^5.0 dPa · s or more. s or more. In this way, devitrified crystals are less likely to precipitate during molding, and it becomes easier to mold into a plate shape. Therefore, the arithmetic average Ra of the surface roughness is set to 1. without polishing the surface or by a small amount of polishing. It can be 0 nm or less, particularly 0.2 nm or less. As a result, it is possible to improve the magnetic characteristics by reducing the bit size. Moreover, the manufacturing cost of the glass substrate can be reduced by reducing the devitrification crystal and the amount of polishing. Here, the “liquid phase temperature” is obtained by passing the standard sieve 30 mesh (500 μm) and putting the glass powder remaining on the 50 mesh (300 μm) in a platinum boat, and holding it in a temperature gradient furnace for 24 hours. It can be calculated by measuring the temperature at which precipitation occurs. “Liquid phase viscosity” refers to the viscosity of glass at the liquidus temperature and can be measured by the platinum ball pulling method.

The temperature at a high temperature viscosity of 10 ^2.5 dPa · s is preferably 1550 ° C. or lower, 1500 ° C. or lower, 1480 ° C. or lower, 1200 to 1450 ° C., particularly 1300 to 1440 ° C. or lower. When the temperature at a high temperature viscosity of 10 ^2.5 dPa · s is too high, the meltability and formability are lowered, and the production cost of the glass substrate is increased. Here, the “temperature at a high temperature viscosity of 10 ^2.5 dPa · s” can be measured by a platinum ball pulling method.

  The surface roughness Ra of the surface is preferably 1.0 nm or less, 0.7 nm or less, 0.4 nm, particularly 0.2 nm or less. If the surface roughness Ra is too large, improvement in magnetic characteristics cannot be expected even if the bit size is reduced for higher recording density.

  The plate thickness is preferably 1.5 mm or less, 1.2 mm or less, 0.2 to 1.0 mm, particularly 0.3 to 0.9 mm. When the plate thickness is out of the above range, it becomes difficult to use it as the base material of the magnetic recording medium.

  The method for producing the glass substrate for a magnetic recording medium of the present invention is, for example, as follows. First, a glass raw material prepared to have a desired glass composition is put into a continuous melting furnace, heated and melted at 1500 to 1700 ° C., clarified, and then supplied to a molding apparatus and molded into a plate shape. It is preferable to cool. A well-known method can be adopted as a method of cutting into a predetermined dimension after forming into a plate shape. Various methods can be adopted as a method for forming the glass substrate. For example, an overflow down draw method, a slot down method, a roll out method, a redraw method, a float method, an ingot molding method, or the like can be adopted. In particular, the overflow downdraw method is preferable from the viewpoint of improving the flatness and smoothness of the surface.

  Hereinafter, the present invention will be described based on examples. The following examples are merely illustrative. The present invention is not limited to the following examples.

  Tables 1 to 9 show examples (sample Nos. 1 to 86) and comparative examples (sample No. 87) of the present invention.

First, after putting the glass batch which prepared the glass raw material into a platinum crucible so that it might become the glass composition in a table | surface, it melted, clarified, and homogenized at 1500-1700 degreeC for 24 hours. In melting the glass batch, the mixture was stirred and homogenized using a platinum stirrer. Next, the molten glass was poured onto a carbon plate and formed into a plate shape, and then slowly cooled at a temperature near the annealing point for 30 minutes. About each obtained glass substrate, density Density, average linear thermal expansion coefficient CTE _{30-380 degreeC} in the temperature range of 30-380 degreeC, Young's modulus Young's Modulus, rigidity modulus Shear modulus, Poisson's ratio Poisson's ratio, strain point Ps, gradual Cold point Ta, softening point Ts, temperature at high temperature viscosity 10 ^4.0 dPa · s, temperature at high temperature viscosity 10 ^3.0 dPa · s, temperature at high temperature viscosity 10 ^2.5 dPa · s, liquidus temperature TL, liquid The phase viscosity log η was evaluated. In the table, “NA” represents unmeasured.

  The density is a value measured by Archimedes method.

Average linear thermal expansion coefficient CTE in the temperature range of _{30 to 380 ° C. 30 to 380 ° C.} is a value measured with a dilatometer.

  The Young's modulus, rigidity, and Poisson's ratio refer to values measured by the resonance method.

  The strain point, annealing point, and softening point are values measured based on the methods of ASTM C336 and C338.

The temperature at a high temperature viscosity of 10 ^4.0 dPa · s, 10 ^3.0 dPa · s, and 10 ^2.5 dPa · s is a value measured by a platinum ball pulling method.

As is apparent from the table, sample No. Nos. 1 to 86 have an average linear thermal expansion coefficient CTE in the temperature range of _{30 to 380 ° C. 30 to 380 ° C.} is 33.2 × 10 ⁻⁷ / ° C. or more, and Young's modulus is 80.0 GPa or more. It is suitable as a glass substrate. On the other hand, sample No. 87 had an average linear thermal expansion coefficient CTE in the temperature range of 30 to 380 ° C. of _{30 to 380 ° C.} of 35.0 × 10 ⁻⁷ / ° C. and a Young's modulus of 76 GPa.

  Sample No. in the table. After putting a glass batch prepared with glass raw materials into a melting furnace so as to have a glass composition of 1 to 87, melting, clarifying and homogenizing at 1500 to 1700 ° C. for 24 hours so that the plate thickness becomes 0.675 mm Then, it was formed into a plate shape by the overflow down draw method. It was 0.10-0.20 nm when surface roughness Ra of the surface of the obtained glass substrate was measured with the atomic force microscope (AFM). Furthermore, when the average linear transmittance | permeability in optical path length 1mm and wavelength range 350-1500nm was measured with the spectrophotometer UV-3100 made from Shimadzu about the obtained glass substrate, all were 90% or more.

Claims (6)

An average linear thermal expansion coefficient in a temperature range of 30 to 380 ° C. is 30 × 10 ⁻⁷ / ° C. or more, and a Young's modulus is 80 GPa or more.   The glass substrate for a magnetic recording medium according to claim 1, wherein the softening point is 700 ° C or higher. As a glass composition, in _{mass%, SiO 2 53~66%, Al} 2 O 3 7~34%, B 2 O 3 0~8%, MgO 0~22%, CaO 1~15%, Y 2 O 3 + La _{3. The} glass substrate for a magnetic recording medium according to claim 1, comprising ₂ O ₃ + ZrO ₂ 0 to 20%.   The glass substrate for a magnetic recording medium according to any one of claims 1 to 3, wherein the surface roughness Ra of the surface is 1.0 nm or less.   5. The glass substrate for a magnetic recording medium according to claim 1, wherein an average linear transmittance in an optical path length of 1 mm and a wavelength range of 350 to 1500 nm is 70% or more.   The glass substrate for a magnetic recording medium according to any one of claims 1 to 5, wherein the glass substrate is in a disk shape.