CN1290665A

CN1290665A - Glass substrate for information rocord medium and information record medium using sail glass substrate

Info

Publication number: CN1290665A
Application number: CN00133866A
Authority: CN
Inventors: 桥本和明; 渡边隆
Original assignee: Hoya Corp
Current assignee: Hoya Corp
Priority date: 1999-09-08
Filing date: 2000-09-08
Publication date: 2001-04-11
Also published as: KR20010070063A; JP2001076336A; KR100557262B1

Abstract

The invention provides a glass substrate for information recording medium, which consists of glass sufficiently satisfying required physical properties for the substrate of information recording medium. The glass substrate consists of the glass containing 0.0001-10 mol% stannic oxide and/or cerium oxide based on the total amount of the glass component other than the refined agent or the glass obtained from a glass material containing 1-10 mol% at least one selected from C, SO3 and H2O based on the total amount of the glass component as the refined agent. The information recording medium comprises this substrate and a magnetic layer formed on at least a part of the substrate surface.

Description

Glass substrate for information recording medium and information recording medium using the same

The present invention relates to a glass substrate for an information recording medium and an information recording medium using the same. And more particularly, to a glass substrate for an information recording medium, which can fully satisfy the physical properties required for the information recording medium without containing arsenic and antimony compounds, which are generally used as refining agents but are harmful to the environment, and an information recording medium using the same.

In recent years, due to the development of electronics technology, particularly, information technology represented by computers, the demand for information recording media such as magnetic disks, optical disks, and magneto-optical disks has rapidly increased. The main components of a magnetic memory of a computer and the like are a magnetic recording medium and a magnetic head for reproducing magnetic recording data. As magnetic recording media, floppy disks and hard disks are known. Substrate materials for hard disks (magnetic disks) include aluminum substrates, glass substrates, ceramic substrates, carbon substrates, and the like. However, the fact that the use of aluminum substrates and glass substrates depends mainly on capacity and use. Recently, the size of hard disk drives for notebook computers is decreasing and the magnetic recording density thereof is increasing, so that the floating gap of the magnetic head is decreasing. The surface smoothness of the magnetic disk substrate is required to satisfy high accuracy. However, the hardness of aluminum alloy is low, and if an aluminum disk is polished using a high-precision abrasive and a polishing machine, the polished surface undergoes plastic deformation, so it is difficult to produce a flat surface with a precision level higher than a specific level. For example, even if the surface of an aluminum alloy is plated with nickel-phosphorus, it is impossible to produce a surface having an average surface roughnessRa of 20 angstroms or less. Further, as the size and thickness of hard disk drives are reduced, there is also a strong demand to reduce the thickness of substrates for magnetic disks. However, because aluminum alloys are low in strength and low in rigidity, it is difficult to reduce the thickness of the magnetic disk for maintaining a predetermined strength required by the specifications of the hard disk drive.

Under such circumstances, glass substrates having high strength, high rigidity, high shock resistance, and high surface smoothness have begun to be used for magnetic disks. Glass substrates are excellent in surface smoothness and mechanical strength, and thus have attracted attention as current and promising substrates.

Therefore, many glasses have been studied as glass substrates for information recording media. For example, JP-B-47-1949, JP-A-5-32431 and JP-A-10-1329 disclose chemically increasableStrong glass and chemically strengthened glass, JP-A-9-356234 discloses ｃA glass in which the main crystal phases are formed by solid solution of ｃA lithium disilicate phase and either β -spodumene phase or β -spodumene, and JP-A-11-116267 discloses ｃA specific modulus of at least 36X 10⁶Nm/kg glassGlass.

Meanwhile, it is common practice to use arsenic and antimony compounds as refining agents for molten glass. Although these compounds are excellent in the effect of removing bubbles, they may have a harmful effect on the environment in the step of producing glass and the step of recycling, so that their use is limited.

Thus, for example, JP-A-10-72238 discloses chemically strengthenable alumino-silicｃA glasses having ｃA specific composition in which SnO is incorporated₂And F₂Substantially free of incorporation of As₂O₃And Sb₂O₃As a refining agent.

However, as for the glass used as the above-mentioned glass substrate for an information recording medium, it is true that there is no glass containing no arsenic compound or antimony compound.

Accordingly, an object of the present invention is to provide a glass substrate for an information recording medium which does not contain arsenic and antimony compounds as refining agents and can satisfy physical properties required for a substrate for information recording, such as excellent surface smoothness, high young's modulus, high specific modulus and the like, and an information recording medium to which the above glass substrate is applied.

The present inventors have made an effort to achieve the above objects and have found the following results. A substrate formed of a glass containing a predetermined amount of a specific component and containing tin oxide and cerium oxide in a specific quantity ratio based on the total amount of the above specific component, or a glass containing C, SO in a specific quantity ratio₃And H₂O, a substrate formed of glass can satisfy the above-mentioned object as a glass substrate for an information recording medium. Thus, the present invention has been completed on the basis of the above findings.

That is, according to the present invention, there is provided a recording medium for informationThe glass substrate of (1), which is formed of a glass having the following composition (mol%): the glass contains 35-70% SiO₂0-15% of Al₂O₃3-30% of Li₂O+Na₂O, 1-45% of CaO, 3-45% of CaO + MgO and 0.1-30% of TiO₂And contains tin oxide and/or cerium oxide (hereinafter referred to as "glass substrate I") in an amount of 0.0001 to 10mol% based on the total amount of the above glass components.

According tothe present invention, there is also provided a glass substrate for an information recording medium, the glass substrate being formed of a glass having a composition (mol%) of 60 to 75% of SiO₂2-10% of Al₂O₃8-20% of Li₂O, 3-15% of Na₂O and 2-10% ZrO₂，Na₂O／ZrO₂A molar ratio of 0.1 to 8, and Al₂O₃／ZrO₂A molar ratio of 0.2 to 5, and contains 0.0001 to 10mol% of tin oxide and/or cerium oxide (hereinafter referred to as "glass substrate II") based on the total amount of the above glass components.

According to the present invention, there is also provided a glass substrate for an information recording medium, the glass substrate being made of a material containing SiO₂-Al₂O₃-R₂Chemically strengthened glass of O (wherein R is an alkali metal) having the following composition, the glass containing SiO in a total amount of 98 mol% or more₂、Al₂O₃And R₂O and containing radicals based onTin oxide and/or cerium oxide (hereinafter referred to as "glass substrate III") in an amount of 0.0001 to 10mol% based on the total amount of the glass components.

According to the present invention, there is also provided a glass substrate for an information recording medium, the glass substrate being formed of a glass having a composition (mol%) containing 45 to 85% of SiO₂4-32% of Al₂O₃8-30% of Na₂O+Li₂O (provided that Li is₂The amount of O does not exceed Na₂O and Li₂70% of total O) and 2-13% of ZnO and F₂Or both (provided that F is present)₂In an amount of less than 8%), (Li)₂O+Na₂O)／Al₂O₃The molar ratio is 2/3-4/1, SiO₂、Al₂O₃、Na₂O、Li₂O、F₂And ZnO in a total amount of at least 90 mol%, and contains tin oxide and/or cerium oxide in an amount of 0.0001 to 10mol% based on the total amount of the above glass components (hereinafter referred to as "glass substrate IV").

According to the present invention, there is also provided a glass substrate for an information recording medium, the glass substrate being formed of a glass having a composition (mol%) of 35 to 65% of SiO₂5-25% of Al₂O₃10-40% of MgO and 5-15% of TiO₂0.8-10% of Y₂O₃And 0-3% of ZrO₂And contains 0.0001 to 10mol% of tin oxide and/or cerium oxide based on the total amount of the above glass components (hereinafter referred to as "glass substrate V").

According to the present invention, there is also provided a glass substrate for an information recording medium, the glass substrate being formed of a glass having a composition (mol%) containing 25 to 52% of SiO₂5-35% of Al₂O₃0-7% of Li₂O, 15-45% of MgO and 0-17% of Y₂O₃0-25% of TiO₂0-8% of ZrO₂1-30% of CaO and 0-5% of B₂O₃+P₂O₅，Y₂O₃、TiO₂、ZrO₂And CaO in a total amount of 5 to 30 mol%, and contains 0.0001 to 10mol% of tin oxide and/or cerium oxide based on the total amount of the above glass components (hereinafter referred to as "glass substrate VI").

According to the present invention, there is also provided a glass substrate for an information recording medium, the glass substrate being formed of a glass having a composition (mol%) of 60 to 70% of SiO₂2-15% of Al₂O₃6-20% of Li₂O, 2-9% of Na₂O, 0-3% of K₂O, 0-5% of MgO, 1-7% of CaO, 0-5% of SrO, 0-2% of BaO and 0-5% of TiO₂0-2% of Fe₂O₃0-1% of MnO, 0-5% ofZrO₂And 0-2% of Y₂O₃，Li₂O、Na₂O and K₂The total content of O is 10-25 mol%, the total content of MgO, CaO, SrO and BaO is 2-15 mol%, TiO₂、Fe₂O₃And MnO in a total amount of 0.01 to 3 mol%, and contains 0.0001 to 10mol% of tin oxide and/or cerium oxide (hereinafter referred to as "glass substrate VII") based on the total amount of the above glass components.

According to the present invention, there is also provided a glass substrate for an information recording medium, which is made of a glass containing lithium disilicate (Li) as a main crystal phase₂O·2SiO₂) The glass of (1), the glass (mol%)Contains 65-85% of SiO₂8-30% of Li₂O, l-10% Al₂O₃And 0-5% of P₂O₅And contains 0.0001 to 10mol% of tin oxide and/or cerium oxide (hereinafter referred to as "glass substrate VIII") based on the total amount of the above glass components.

According to the present invention, there is also provided a glass substrate for an information recording medium, the glass substrate being formed of a glass having a composition (mol%) containing 30 to 65% of SiO₂5-35% of Al₂O₃5 to 35 percent of ZnO, 0 to 20 percent of MgO, 0.5 to 25 percent of CaO, SrO, BaO and B₂O₃+La₂O₃+Y₂O₃+Gd₂O₃+Ta₂O₅+Nb₂O₅+WO₃+Bi₂O₃(As long as the CaO + SrO + BaO content is 0-20%, B₂O₃0-10% of La₂O₃+Y₂O₃+Gd₂O₃In an amount of 0-20% and Ta₂O₅+Nb₂O₃+WO₃+Bi₂O₃0-10%) of 1-15% of TiO₂0-7% of ZrO₂+P₂O₅+SnO₂(provided that ZrO is present₂In an amount of 0-2%, and P₂O₅0 to 5%), and 0 to 5% of F which is a fluoride of at least one metal element constituting the above metal oxideAnd contains 0.0001 to 10mol% of tin oxide and/or cerium oxide (hereinafter referred to as "glass substrate IX") based on the total amount of the above glass components.

According to the present invention, there is also provided a glass substrate for an information recording medium, which is formed of a glass obtained from a glass material containing 1 to 10mol% of at least one selected from C, SO as a refining agent based on the amount of the glass component₃Or H₂O (hereinafter "glass substrate X").

According to the present invention, there is also provided an information recording medium having a magnetic layer formed on at least a part of a surface of any one of the above-mentioned glass substrates for an information recording medium.

Best mode for carrying out the invention

The glass substrate for an information recording medium of the present invention comprises glass substrates I to X, and each glass substrate is formed of a glass composition containing a predetermined amount of a glass selected from SiO except for a refining agent₂、Al₂O₃、Li₂O、Na₂O、K₂O、CaO、MgO、SrO、BaO、ZnO、Bi₂O₃、ZrO₂、Y₂O₃、La₂O₃、Gd₂O₃、Ta₂O₅、Nb₂O₅、WO₃、Bi₂O₃、Fe₂O₃、MnO、P₂O₅、B₂O₃And F. Further, the glass composition of each of the glass substrates I to IX contains 0.0001 to 10mol%of tin oxide and/or cerium oxide as a refining component based on the total amount of the above glass components, and the glass composition for the glass substrate X contains 1 to 10mol% of at least one selected from the group consisting of C, SO based on the total amount of the glass components₃Or H₂And O is used as a refining agent.

In the glass of the glass substrate I-IX of the present invention, the tin oxide used as a refining agent is usually SnO or SnO₂And cerium oxide is usually Ce₂O₃Or CeO₂. These refining agents may be used alone or in combination. Further, the essences will be described belowThe refining agent can be mixed with C, SO₃Or H₂O is used in combination.

As for refining agents₂O₃And Sb₂O₃Refining in, for example, melting of glass raw materialsAs at the initial stage of formation₂O₃To As₂O₅Showing As₂O₃The refining effect of (1). Although the co-presence of nitrates is said to promote As₂O₃To As₂O₅(JP-A-11-49520), but the coexistence of nitrate causes Nitrogen Oxide (NO)_x) Problems arise and cost increases.

On the contrary, it is assumed that SnO and SnO used in the present invention₂The refining of (A) is based on the following reaction scheme (I).

Despite the above-mentioned SnO and SnO₂Refining effect of (2) with As₂O₃The effect is the same, but the effect is poor. When they are added in a large amount, a sufficient refining effect can be expected. However, when they are added in too large an amount, there may be caused a bad situation in which the quality of the glass is poordue to the formation of non-molten substances. The content of tin oxide in the glass is 0.0001 to 10mol%, preferably 0.0001 to 7 mol%, more preferably 0.0001 to 5 mol% based on the total amount of glass components other than the refining agent, from the viewpoints of refining effect and prevention of the formation of non-molten substances.

Ce is also considered to be₂O₃And CeO₂The refining effect of (A) is based on the following reaction scheme (II).

Despite the above Ce₂O₃And CeO₂Refining effect of (2) with As₂O₃The refining effect of (2) is the same, but the effect is poor. They are relatively preferred for acid glasses (containing a large amount of silicic acid). However, as the basicity increases (because the content of alkali metal and alkaline earth metal oxides increases), the effect thereof tends to decrease. When Ce is added in a large amount₂O₃And CeO₂In time, it can be expected to achieve chargingRespectively refining effect. However, when they are added in too large an amount, the glass starts to deteriorate in devitrification and causes coloring of the glass and increase in density. In view of the refining effect and physical properties of the glass, the content of cerium oxide in the glass is 0.0001 to 10mol%, preferably 0.0001 to 7 mol%, more preferably 0.0001 to 5 mol%, based on the total amount of glass components other than the refining agent.

When the above tin oxide and the above cerium oxide are used in place of As₂O₃And Sb₂O₃When used as a refining agent, not only is there an advantage that no harmful influence is exerted on the environment, but also the following advantage is expected.

(1) The allowable range of the amounts of tin oxide and cerium oxide is larger than As₂O₃And Sb₂O₃So that the refining action can be controlled more easily. As may be added₂O₃Is usually about 0.1 to 0.6 mol%, Sb may be added₂O₃The content of (B) is usually about 0.1 to 1 mol%. As described above, when the content of tin oxide and/or cerium oxide is 0.0001 to 10mol% and the addition amount thereof is about 10mol%, it is observed that the physical properties of the glass are not substantially lowered.

(2) The nitrate content may be reduced or nitrate may not be used.

(3) In addition to the pull-down forming method and the press forming method, a float forming method may be applied. When As₂O₃Or Sb₂O₃When used as a refining agent, there is a limitation that the float forming method cannot be used. In the float forming process, glass is flowed in a metallic tin bath to form a glass article. In this case, tin diffuses into the glass. For example when using As₂O₃In the process, a reduction reaction is carried out according to a reaction flow (III),

(Ⅲ)

also, the metal in the glass such As As or Sb precipitates causes discoloration or quality change of the glass, so that the float forming method cannot be applied to a glass containing As₂O₃Or Sb₂O₃In the glass of (2). In contrast, when tin oxide or cerium oxide is used, such a problem is not involved, and a float molding method may be used.

In the glass substrate I-IX of the present invention, As may be doped₂O₃And/or Sb₂O₃Is incorporated into the glass together with the above-mentioned tin oxide and the above-mentioned cerium oxide in an amount of less than 0.05 mol% based on the total amount of the glass components other than the refining agent.

In the glass lining X of the invention, at least one C, SO₃And H₂O is used as a refining agent. These refining agents may be used alone or in combination of two or all. Further, these refining agents may be used in combination with the above tin oxide and/or the above cerium oxide. Among the above-mentioned refining agents, C and CO are used at the initial stage of glass melting and at high temperatures₂By the production of CO₂The gas exhibits refining activity. When the content of C is too large, a bad situation may be caused in which the glass is strongly colored due to the change of the redox balance, or when the glass is formed using a platinum crucible, it is alloyed with platinum. In view of its refining effect and the above-mentioned reason, the content of C in the glass material is 1 to 10mol%, preferably 1 to 5 mol%, based on the total amount of glass components other than the refining agent.

SO₃There is a high solubility in glass at low temperatures and a low solubility at high temperatures. When containing SO₃When the glass melt is heated to a high temperature, SO₃Production of SO₂And O₂The refining effect is shown. When SO is increased₃When the content of (A) is small, or when SO is reduced₃The content of (B) does not greatly affect the properties of the glass. However, when SO₃When the content of (b) is too large, floating non-molten sulfate appears on the surface of the molten glass, or white bubbles are left, which deteriorates the quality of the glass. Further, as the gas component increases, the workability is caused to deteriorate during melting of the glass. SO in glass material in view of refining effect, glass quality and workability₃Is contained in an amount of 1 to 10mol%, preferably 1 to 7 mol%, based on the total amount of glass components except the refining agent。SO₃Is provided in the form of a sulfate or sulfuric acid.

Furthermore, H₂O is supplied in the form of hydroxide, molecular water or hydrate, and generates a large amount of moisture at the initial stage of melting of the glass raw material. However, in the initial stage of melting, at relatively low temperatures, alkali metal silicates, carbonates, nitrates and the like sometimes react to form a melt and are therefore formedThe melt has a high viscosity, so that the release of gas from the glass melt is sometimes suppressed. Because in the initial stage of melting H₂O generates a large amount of water vapor, stirring the formed melt, so that H₂O has a refining effect. When H is added₂When the amount of O is too large, the content of the gas component increases, so that deterioration of workability in the melting process and deterioration of glass quality are caused. H in the glass material in view of refining effect and glass quality₂The content of O (based on the total amount of glass components other than the refining agent) is 1 to 10mol%, preferably 1 to 7 mol%.

When at least one C, SO₃And H₂O instead of As₂O₃Or Sb₂O₃When used as a refining agent, not only has an advantage of causing no harmful effects on the environment, but also brings the following advantages. Because C, SO₃And H₂The allowable range of the amount of O is larger than that of As₂O₃Or Sb₂O₃And so the refining characteristics can be easily controlled. Further, similarly to the use of the above-described tin oxide and cerium oxide, the content of nitrate may be reduced, or nitrate may not be used, and a float forming method may be used in addition to the down-draw forming method and the press forming method.

When the above tin oxide and/or the above cerium oxide is used as a refining agent, the content thereof is based on the value of a glass component other than the refining agent in the obtained glass. When C, SO₃And H₂When any of O is used as a refining agent, since these refining agents are reduced by volatilization, the content thereof is based on the value of a glass component other than the refining agent in a glass material (raw material of glass).

In the present inventionLess than 0.05 mol% of As based on the total amount of glass components other than the refining agent in the bright glass substrate X₂O₃And/or Sb₂O₃May be used in combination with C, SO described above₃And H₂Any of O is incorporated into the glass together.

The glass component other than the refining agent in the glass for a glass substrate for an information recording medium of the present invention will be described below.

SiO₂Is a component which acts as a glass network former oxide and increases the stability of the glass network, i.e. crystallization stability and devitrification. Furthermore, SiO₂With oxides such as Al₂O₃The incorporation can improve mechanical properties required for the substrate for an information recording medium, such as glass strength, rigidity, and the like, and it can also improve heat resistance of the glass.

Al₂O₃Is a very important component for imparting high heat resistance and high durability to glass, and is compatible with SiO₂Bonding is a component that increases the stability and rigidity of the glass network. Especially when Al is present₂O₃Replacing a portion of SiO₂When incorporated into glass, Al₂O₃The glass is incorporated into a network of glass and has a great effect of improving the Young's modulus and heat resistance of glass as a network-forming substance. That is, Al₂O₃It is essential to improve the Young's modulus of glass and the heat resistance of glass.

Li₂O is a glass group suitable for improving the meltability of glass without lowering the Young's modulus of the glassAnd it is also a glass component that can strengthen glass by chemical strengthening. And Na₂O has the effect of lowering the Young's modulus, and is a component that can significantly reduce the liquidus temperature of the glass. K₂O is a component which improves the meltability of the glass, and in chemically strengthened glass, it has the effect of reducing the surface pressure stress after ion exchange.

CaO is a component suitable for producing glasses having a high Young's modulus and having a low liquidus temperature. However, CaO has an effect of increasing the specific gravity of the glass. MgO is also a suitable component for producing glass having a high Young's modulus and has the effect of raising the liquidus temperature compared to CaO. In addition, MgO has the effect of reducing the specific gravity of the glass. SrO and BaO are effective components not only for improving the meltability of the glass but also for lowering the liquidus temperature of the glass. However, these components have the effect of increasing the specific gravity of the glass.

ZnO is a component which, when incorporated in larger amounts, reacts with Al₂O₃The components together produce gahnite as the main crystal under the heat treatment condition of the glass material, thereby improving the hardness and heat resistance of the glass.

TiO₂It is a component which reduces the high-temperature viscosity of the glass to improve the meltability of the glass and to improve the stability and durability of the glass network. When it is incorporated into glass, it has the effect of greatly increasing the Young's modulus of the glass without greatly increasing the specific gravity of the glass.

ZrO₂Is a component that mainly improves the durability and rigidity of the glass. When less ZrO is doped₂When it is used, it has the effect of improving the heat resistance of the glass, and it improves the crystallization stability of the glass to prevent devitrification. When ZrO₂Too large of (b) causes deterioration of meltability of the glass at high temperature and also causes deterioration of surface smoothness of the glass.

Y₂O₃Is a component for improving the Young's modulus of glass, improving the crystallization stability of glass, and improving the durability and meltability of glass at high temperatures. Especially when Al is introduced into a large amount of glass₂O₃To improve the bending strength and shock resistance of the glass, Y₂O₃As molten Al₂O₃The adjuvant of (2) has excellent effect.

La₂O₃、Gd₂O₃、Ta₂O₅、Nb₂O₅、WO₃And Bi₂O₃Is an effective component for improving physical properties of the glass such as meltability, hardness, chemical durability and the like. When the content of these is too large, the glass is loweredThe quality of (c).

Fe₂O₃In the molten glass at Fe²⁺And Fe³⁺And these ions have a large influence on the light transmittance of the molten glass, particularly the transmittance in the infrared region. When the content is too large, the absorption in the infrared region is large, so that it is difficult to control the glass temperature distribution during melting and glass formation. MnO being a modification of Fe²⁺And Fe³⁺And effective components that interact to change the light transmittance. However, when the content of MnO is too large, deterioration in quality of the glass is caused.

P₂O₅And B₂O₃Is a component for adjusting the meltability of glass at high temperatures. For example, when a small amount of P is added₂O₅Or B₂O₃When incorporated into glass, the specific modulus of the glass does not change much, but the high-temperature viscosity of the glass is greatly reduced, so that it has a large influence on the easy-to-melt glass.

F is usually introduced in the form of fluoride and is a component effective as a dissolving agent for glass materials and for adjusting crystallization. When the content thereof is too large, it is difficult to obtain uniform glass, the glass is liable to devitrification, and it is difficult to form glass.

In the glass substrates I to IX of the present invention, the contents of glass components other than the refining agent are as follows. In the following, in the glass substrate, "%" represents "mol%".

Glass substrate I:

the glass contains 35-70% SiO₂0-15% of Al₂O₃3-30% of Li₂O+Na₂O, 1-45% of CaO, 3-45% of CaO + MgO and 0.1-30% of TiO₂Preferably 40-65% SiO₂2-10% of Al₂O₃3-27% of Li₂O+Na₂O, 1-20% CaO, 5-40% CaO + MgO and 1-20% TiO₂. In the above glasses, Y may be used₂O₃Or ZrO₂Replacing part of TiO₂。

The above-mentioned glasses, which can be applied in glass substrates, can be chemically strengthened by known methods.

Glass substrate ii:

the glass contains 60-75% SiO₂2-10% of Al₂O₃8-20% of Li₂O, 3-15% of Na₂O and 2-10% ZrO₂And Na₂O／ZrO₂A molar ratio of 0.1 to 8, and Al₂O₃／ZrO₂A molar ratio of 0.2 to 5, preferably 65 to 75% SiO₂8-10% of Al₂O₃10-17% of Li₂O, 5-12% of Na₂O and 2-7% ZrO₂And Na₂O／ZrO₂A molar ratio of 0.5 to 4.0, and Al₂O₃／ZrO₂The molar ratio is 0.3-4.0.

The glass described above, which can be used in the glass substrate II, can be chemically strengthened in a known manner.

Glass substrate III:

the glass is a glass containing SiO₂-Al₂O₃-R₂Chemically strengthenable glass of O (wherein R is an alkali metal) whose composition contains more than 98 mol% in total of SiO₂、Al₂O₃And R₂O。

The glass is a chemically strengthened glass, can be chemically strengthened by a known method, and can be applied to a glass substrate III.

A glass substrate IV:

the glass composition contains 45-85% of SiO₂4-32% of Al₂O₃8-30% of Na₂O+Li₂O(provided that Li is contained therein)₂The content of O is not more than Na₂O and Li₂70% of total O) and 2-13% of ZnO and F₂Or both (provided that F is present)₂Less than 8%), (Li)₂O+Na₂O)／Al₂O₃A molar ratio of 2/3-4/1, a total content of at least 90% SiO₂、Al₂O₃、Na₂O、Li₂O、F₂And ZnO.

The glass described above, which can be used in the glass substrate iv, can be chemically strengthened by known methods.

A glass substrate V:

the glass composition contains 35-65% of SiO₂5-25% of Al₂O₃10-40% of MgO and 5-15% of TiO₂0.8-10% of Y₂O₃And 0-3% of ZrO₂Preferably 37-60% SiO₂7-22% of Al₂O₃12 to 38 percent of MgO and 5.5 to 14 percent of TiO₂1-8% of Y₂O₃And 0-3% of ZrO₂. The above glass is a crystallized glass.

Glass substrate vi:

the glass transition composition contains 25-52% SiO₂5-35% of Al₂O₃0-7% of Li₂O, 15-45% of MgO and 0-17% of Y₂O₃0-25% of TiO₂0-8% of CaO, 1-30% of CaO and 0-5% of B₂O₃+P₂O₅Y in a total content of 5 to 30%₂O₃、TiO₂、ZrO₂And CaO, preferably 30 to 50% SiO₂7-32% of Al₂O₃0.5-6% of Li₂O, 22-40% MgO, O.5-15% Y₂O₃1-20% of TiO₂0.5-6% of ZrO₂2 to 27 percent of CaO and 0.5 to 3.5 percent of B₂O₃+P₂O₅Y in a total content of 5.5-27%₂O₃、TiO₂、ZrO₂And CaO. The glass is high elastic glass.

Glass substrate VII:

the glass composition contains 60-70% SiO₂2-15% of Al₂O₃6-20% of Li₂O, 2-9% of Na₂O, 0-3%of K₂O, 0-5% of MgO, 1-7% of CaO, 0-5% of SrO, 0-2% of BaO and 0-5% of TiO₂0-2% of Fe₂O₃0-1% of MnO and 0-5% of ZrO₂And 0-2% of Y₂O₃Total content of10-25% of Li₂O、Na₂O and K₂O, MgO, CaO, SrO and BaO with the total content of 2-15%, and Bi with the total content of 0.01-3%₂O₃、Fe₂O₃And MnO.

The above-mentioned glasses, which can be used in the glass substrate VII, can be chemically strengthened by known methods.

Glass substrate viii:

the glass contains lithium disilicate (Li) as a main crystal phase₂O·2SiO₂) And the composition of which contains 65-85% of SiO₂8-30% of Li₂O, 1-10% of Al₂O₃And 0-5% of P₂O₅Preferably, lithium disilicate (Li) is contained as a main crystal phase₂O·2SiO₂) And the composition of which contains 65-85% of SiO₂、8-20% of Li₂O, 5-10% of Al₂O₃And 1-5% of P₂O₅。

The glass is a glass containing lithium disilicate (Li)₂O·2SiO₂) Li as the predominant crystalline phase₂O-SiO₂-Al₂O₃A glass-ceramic. In order to lower the melting and forming temperature of the glass and to suppress devitrification of the glass during forming, the glass may contain Na in an amount of not more than 10%, preferably not more than 5%, as required₂O or K₂O。

Glass substrate IX:

the glass composition contains 30-65% of SiO₂5-35% of Al₂O₃5 to 35 percent of ZnO, 0 to 20 percent of MgO, 0.5 to 25 percent of CaO, SrO, BaO and B₂O₃+La₂O₃+Y₂O₃+Gd₂O₃+Ta₂O₅+Nb₂O₅+WO₃+Bi₂O₃(As long as the CaO + SrO + BaOBaO content is 0-20%, B₂O₃0-10% of La₂O₃+Y₂O₃+Gd₂O₃In an amount of 0-20% and Ta₂O₅+Nb₂O₅+WO₃+Bi₂O₃0-10%) of 1-15% of TiO₂0-7% of ZrO₂+P₂O₅+SnO₂(provided that ZrO is present₂Is 0-2% and P₂O₅0 to 5%), and 0 to 5% of F which is a fluoride of at least one metal element constituting the above metal oxide. SnO mentioned above₂The component serves as a nucleating agent as an auxiliary component.

When a chemically strengthened glass is used for the above glass substrates I, II, III, IV and VII, the chemical strengthening method is not particularly limited. The chemical strengthening can be carried out by subjecting the chemically strengthened glass to an ion exchange treatment by known methods, for example, in a treatment bath containing Na ions and/or K ions. The above treatment is carried out at a temperature substantially equal to or lower than the heat distortion temperature of the glass and at a temperature at which the molten salt does not decompose. Since the treatment bath contains Na ions and/or K ions, it is preferable to use a sodium nitrate and/or potassium nitrate bath. However, the use of nitrate is not compulsorily limited, and sulfate, bisulfate, carbonate, bicarbonate, or halide may be used. When Na ions are contained in the treatment bath, the Na ions are ion-exchanged with Li ions in the glass. When K ions are contained in the treatment bath, the K ions are ion-exchanged with Li ions and Na ions in the glass. Further, when Na ions and K ions are contained in the treatment bath, the Na ions and K ionsare ion-exchanged with Li ions and Na ions in the glass. Due to the above ion exchange, alkali metal ions in the surface portion of the glass are replaced with alkali metal ions having a larger ion radius to form a deformation layer in the surface portion of the glass, thereby forming compressive stress on the surface of the glass and tensile stress inside the glass. The glass can thus be strengthened chemically.

In the glass substrate for an information recording medium (glass substrate I-X) provided by the present invention, the Young's modulus of the glass is preferably at least 70 GPa. When the young's modulus is less than 70GPa, the strength of the glass is insufficient, so that it is difficult to obtain a very reliable glass substrate. The young's modulus of the glass preferably has at least 80GPa in view of the reliability of the glass substrate.

Furthermore, the specific modulus of the glass preferably has a value of at least 30X 10⁶Nm/kg. Equivalent modulus less than 30 x 10⁶Nm/kg, it is difficult to obtain a highly reliable glass substrate which can cope with high-speed rotation of a driving device, and can reduce the thickness and increase the recording density of a recording medium. The specific modulus of the glass preferably has a value of at least 32X 10 in view of reliability of the glass substrate⁶Nm/kg. The term "specific modulus" means "young's modulus/specific gravity", and young's modulus means a value obtained by measurement according to a method described later.

Further, the glass substrate preferably has a maximum surface roughness (Rmax) of 7 μm or less. When Rmax exceeds 7 μm, it is difficult to achieve a higher recording density. In view of a higher recording density, Rmax is more preferably 5 μm or less.

The glass (glass substrates I to X) of the glass substrate for the information recording medium is generally colored, and the transmittance at a wavelength of 400nm is generally less than 10%. Such a glass can be used for improving the temperature increasing ability of a glass substrate in the process of manufacturing an information recording medium, and for improving the visibility during a defect test of a glass substrate for an information recording medium.

When producing an information recording medium, a layer made of a metal, an alloy, a metal compound, or the like, such as a magnetic layer, is formed on a glass substrate. This layer is preferably formed by a sputtering method. In the sputtering method, a glass substrate is generally heated to 200 ℃ or more by a condenser with a halogen lamp. The wavelength of light emitted from the light source is 250nm or more, and the substrate made of the colored glass absorbs light of the heating source, so that the glass substrate can be heated to a predetermined temperature for a short period of time. Therefore, the cycle time for manufacturing the information recording medium can be reduced.

The liquidus temperature of the above glass is preferably 1400 ℃ or less, particularly preferably 1360 ℃ or less. In this case, the glass substrate for an information recording medium can be easily produced by press forming or draw down forming. Further, in the present invention, the glass substrate can be produced by a float forming method, since the glass is not required to containHas As₂O₃And Sb₂O₃As refining agents have already been described.

The glass substrate for information recording medium (glass substrates I-X) provided by the present invention is composed of one of the above glasses. The method of producing the glass substrate is not limited, and any known method may be used. For example, the glass is directly formed into a disk shape by a direct pressing method. Further, the glass is formed into a sheet bya down-draw forming method, a melting method or a float method, and the glass in the form of a sheet is processed into a disk shape. Then, the glass thus shaped is ground and polished to produce a glass substrate for an information recording medium having a desired size and a desired shape.

The grinding and polishing step generally comprises step (1): rough grinding, (2) grinding (fine grinding), (3) first polishing (buffing) and (4) second buffing (final buffing). By these precise polishing steps, a glass substrate having a maximum surface roughness (Rmax) of 7 μm or less can be obtained, and a glass substrate having a maximum surface roughness (Rmax) of 5 μm or less can also be obtained.

In a glass substrate used for an information recording medium, the surface of the glass substrate may be textured by wet etching treatment with a mixture of hydrofluoric acid and nitric acid, by forming an uneven aluminum layer or the like, or by forming a rough surface by means of laser light or irradiation with ultraviolet rays, as necessary.

When the glass substrate of the information recording medium is used for a standard information recording medium having a diameter of 2.5 inches or less, it is preferable that the maximum flatness value deviating from full flatness be 3.0 μm or less when the thickness h of the glass substrate is 1.0 mm, and the flatness be 2.0 μm or less when the thickness h of the glass substrate is 0.7 mm or less.

The glass substrate of the present invention is used as a substrate for an information recording medium such as a magnetic disk, a magneto-optical disk or an optical disk. The glass substrate of the present invention is particularly preferable as a substrate for a magnetic disk. The magnetic disk is not particularly limited. For example, the glass substrate of the present invention can be preferably used for a magnetic disk compatible with a low flying height head, or for a magnetic disk compatible with a Magnetoresistive (MR) head or a Giant Magnetoresistive (GMR) head.

The information recording medium of the present invention has the above glass substrate and a magnetic layer formed on at least a part of the surface of the glass substrate. The information recording medium of the present invention can be produced generally by successively forming an underlayer, a magnetic layer, a protective layer and a lubricant layer on the above glass substrate.

In the information recording medium of the present invention, the underlayer can be appropriately selected depending on the magnetic layer formed thereon. For example, in the magnetic layer made of Co as a main component, the underlayer is preferably made of a Cr simple substance or a Cr alloy from the viewpoint of improving magnetic properties.

The underlayer is made of at least one material selected from nonmagnetic metals such as Cr, Mo, Ta, Ti, W, V, B, Al, and the like. In the magnetic layer made of Co as a main component, the underlayer is preferably made of a simple substance of Cr or a Cr alloy from the viewpoint of improving magnetic properties. Further, the base layer is not limited to a single layer, and it may have a plurality of layers of the same or different types of layered structures. For example, the multilayer layered structure includes a multilayer underlayer such as Cr/Cr, Cr/Cr/Mo, Cr/CrV, CrV/CrV, Al/Cr/CrMo, Al/Cr/Cr, Al/Cr/CrV, Al/CrV/CrV.

In the present invention, between the glass substrate and the magnetic layer, or on the magnetic layer, an irregularly shaped layer may be formed to prevent adhesion of the magnetic head and the information recording medium. When the irregular shaped layer is provided as described above, the adhesion of the magnetic head and the information recording medium does not occur by appropriately adjusting the surface roughness of the information recording medium, so that a very reliable information recording medium can be obtained.

Many types of raw materials for irregularly shaped layers and methods of forming the same are known, but the materials and methods for forming irregularly shaped layers are not limited. It is preferable to use a material having a higher melting point than the above glass substrate of the present invention, or the like. The material for the irregularly shaped layer is selected from metals such as Al, Ag, Ti, Nb, Ta, Bi, Si, Zr, Cr, Cu, Au, Sn, Pd, Sb, Ge and Mg, and alloys thereof. These metals and alloys may be used alone or in combination. Furthermore, the above materials may also be selected from oxides, nitrides or carbides of the above metals.

In view of the easiness of forming irregularly shaped layers and the effect thereof, the material is preferably an Al simple substance or a metal containing aluminum as a main component such as Al alloy, aluminum oxide, or aluminum nitride.

Further, in view of head adhesion, the surface roughness of the irregularly shaped layer is preferably Rmax =50 to 300 angstroms, and preferably Rmax =100 and 200 angstroms.

When the above Rmax is less than 50 angstroms, the surface of the information recording medium is nearly flat. Therefore, it is undesirable that the magnetic head and the information recording medium adhere to each other, with the result that the magnetic head and the information recording medium may be damaged or the adhesion may cause a head crash. Further, when Rmax exceeds 300 angstroms, it is undesirable that the sliding height starts to become large, with the result that the recording density is reduced.

In the information recording medium of the present invention, the material for the magnetic layer is not limited, and it may be selected from known materials as needed. The magnetic layer includes a magnetic thin film made of a material containing Co as a main component, such as CoPt, CoCr, CoNi, CoNiCr, CoCrTa, CoPtCr, and CoNiPt, or a magnetic thin film of CoNiCrPt, CoNiCrTa, CoCrTaPt, and CoCrPtSiO. The magnetic layer may have a multilayer structure (e.g., CoPtCr/CrMo/CoPtCr or CoCrTaPt/CrMo/CoCrTaPt) in which magnetic films are separated by nonmagnetic thin films (e.g., Cr, CrMo, or CrV) to reduce noise.

The magnetic layer compatible with the magnetoresistive head (MR head) or giant magnetoresistive head (GMR head) also includes a magnetic layer formed by doping an impurity element selected from Y, Si, rare earth element, Hf, Ge, Sn, or Zn, or an oxide film of any of these impurity elements into a Co-containing alloy.

Further, the magnetic layer may be a ferrite-containing magnetic layer, an iron-rare earth element-containing magnetic layer, or a magnetic layer made of SiO₂BN, etc. in a nonmagnetic layer, and a granular magnetic layer formed by dispersing magnetic powder of Fe, Co, FeCo, CoNiPt, etc. Further, the magnetic layer may be of any recording type such as a longitudinal recording type or a perpendicular recording type.

In the information recording medium of the present invention, the protective layer is not particularly limited, and may include a Cr thin film, a Cr alloy thin film, a carbon film, a zirconia thin film, and a silica thin film. The protective layer, the underlayer, the magnetic layer, and the like can be formed continuously with the in-line sputtering apparatus. The protective layer may have a single-layer structure or a multi-layer structure of the same or different types.

In the present invention, another protective layer may be formed on the protective layer, or in place of the protective layer. For example, instead of the above-described protective layer, Silica (SiO) formed by this method may be provided by diluting tetraalkoxysilane with an alcohol solvent, preparing a coating solution in which colloidal silica fine particles are dispersed, coating the coating solution, and calcining the coated solution₂) A film.

In the information recording medium of the present invention, the lubricating layer is not particularly limited. For example, perfluoropolyether (PEPE) as a liquid lubricant is diluted with an olefin solvent to prepare a coating solution, the coating solution is applied to the surface of a medium by a dipping method, a spin coating method, or a spraying method, and the applied coating layer is selectively heated, thereby forming a lubricating layer.

Examples

The present invention will be described in further detail hereinafter with reference to examples, which should not be construed as limiting the invention thereto.

The physical properties of the glass were measured or evaluated by the following methods.

(1) Young's modulus

A fully annealed specimen having dimensions of 20 mm. times.20 mm. times.100 mm was used to measure the longitudinal wave velocity of 5MHz ultrasonic waves. The Young's modulus was calculated according to the following formula.

Young's modulus = (4G)²-3G·V₁ ²·ρ)／(G-V₁ ²·ρ)

G=V_s ²·ρ

Wherein G = modulus of rigidity, V₁= longitudinal wave velocity (m/s), Vs = transverse wave velocity (m/s), ρ = density (g/cm)³)。

(2) Specific modulus

Specific modulus =young's modulus/specific gravity

(3) Coefficient of thermal expansion

The samples were measured with a thermomechanical analyzer (TMA) and the average thermal expansion coefficient was determined from 100 to 300 ℃.

(4) Maximum surface roughness (Rmax)

Measured with AFM Man Scope3A supplied by Digital Instruments Inc.

(5) Liquidus temperature

The sample was placed in a platinum container and left in a gradient temperature furnace for 30 minutes, and then the crystals on the surface and inside of the sample were observed by an optical microscope. The lowest temperature at which no crystals precipitate is considered the liquidus temperature.

(6) Transmittance at wavelength of 400nm

The transmittance of a 1.00 mm thick glass plate at a wavelength of 400nm was measured with "MPS-2000" supplied by Shimadzu Corporation.

Examples 1 to 28

Raw materials such as oxides, hydroxides, carbonates, nitrates, chlorides, sulfates, refining agents were weighed so as to form the oxide compositions shown in tables 1 to 5, and mixed to prepare a mixture of raw materials. The raw material mixtures were separately placed in platinum crucibles, heated to 1, 450-. Then, the obtained molten glass was cast into a mold made of iron, and annealed to make a glass. Tables 1-5 show the physical properties of the glasses.

With regard to the glass oxide composition, examples 1 to 16 relate to the glass of the glass substrate I, example 17 to the glass of the glass substrate II, example 18 to the glass of the glass substrate III, examples 19 to 21 relate to the glass of the glass substrate VII, examples 22 and23 relate to the glass of the glass substrate VIII, examples 24 to 25 relate to the glass of the glass substrate IX, example 26 relates to the glass of the glass substrate V, example 27 relates to the glass of the glass substrate VI and example 28 relates to the glass of the glass substrate IV.

The physical properties of the glasses in examples 1 to 21 and 28 were obtained from chemically strengthened glasses.

TABLE 1

		Examples
		Examples						1	2	3	4	5	6
		Glass Oxide compound Composition of (mol％)	SiO₂	55．5	58．5	53．0	58．5	1	2	3	4	5	6	52．5	45．0
Al₂O₃	7．0		SiO₂	55．5	58．5	53．0	58．5	6．0	6．0	3．0	6．5	10．0		52．5	45．0
Al₂O₃	7．0		B₂O₃	-	-	-	-	6．0	6．0	3．0	6．5	10．0	-	-
P₂O₅	-		B₂O₃	-	-	-	-	-	-	-	-	-	-	-
P₂O₅	-		Li₂O Na₂O K₂O	9．5 - -	11．5 - -	9．5 - -	11．4 4．0 -	-	-	-	-	-	9．5 - -	9．0 - -
MgO CaO SrO BaO	14．0 4．0 - -		Li₂O Na₂O K₂O	9．5 - -	11．5 - -	9．5 - -	11．4 4．0 -	6．0 8．0 - -	10．5 11．0 - -	6．0 6．0 - -	8．0 12．0 - -	15．0 5．0 - -	9．5 - -	9．0 - -
MgO CaO SrO BaO	14．0 4．0 - -		ZnO TiO₂ Y₂O₃ ZrO₂	- 5．5 2．0 2．5	- 8．0 2．0 -	- 7．0 3．0 -	- 8．5 0．5 2．5	6．0 8．0 - -	10．5 11．0 - -	6．0 6．0 - -	8．0 12．0 - -	15．0 5．0 - -	- 7．0 2．5 2．0	- 15．0 1．0 -
Refining agent	Species of Amount (based on glass oxide) mol％)		ZnO TiO₂ Y₂O₃ ZrO₂	- 5．5 2．0 2．5	- 8．0 2．0 -	- 7．0 3．0 -	- 8．5 0．5 2．5	SnO₂ 0．5	SrO 1．0	Ce₂O₃ 0．5	CeO₂ 1．5	SnO₂ 1．0	- 7．0 2．5 2．0	- 15．0 1．0 -	SO₃ 5．0
	Species of Amount (based on glass oxide) mol％)	Species of Amount (based on glass oxide) mol％)	C 0．5	- -	- -	- -	- -	SnO₂ 0．5	SrO 1．0	Ce₂O₃ 0．5	CeO₂ 1．5	SnO₂ 1．0	- -		SO₃ 5．0
	Refining performance		C 0．5	- -	- -	- -	- -	Good effect	Good effect	Good effect	Good effect	Good effect	- -	Good effect
Colour of glass			Brown colour	Y^*	O^*	O^*	Y^*	Good effect	Good effect	Good effect	Good effect	Good effect	Brown colour	Good effect
Colour of glass		Article (A) Theory of things Property of (2) Can be used for	Brown colour	Y^*	O^*	O^*	Y^*	Young's modulus (GPa)	107	104	110	102	Brown colour	111	107
Specific gravity of	2．8		2．75	2．9	2．7	2．9	2．8	Young's modulus (GPa)	107	104	110	102		111	107
Specific gravity of	2．8		2．75	2．9	2．7	2．9	2．8	Specific modulus (. times.10)⁶Nm／Kg)	38	38	38	37	38	38
Coefficient of thermal expansion (ppm/. degree.C.)	69		7．7	7．9	8．0	7．8	7．0	Specific modulus (. times.10)⁶Nm／Kg)	38	38	38	37	38	38
Coefficient of thermal expansion (ppm/. degree.C.)	69		7．7	7．9	8．0	7．8	7．0	Maximum surface roughness [ Rmax](μm)	3	5	4	3	3	4
Transmittance at 400nm (%)	80		80	75	65	80	70	Maximum surface roughness [ Rmax](μm)	3	5	4	3	3	4
Transmittance at 400nm (%)	80		80	75	65	80	70	Liquidus temperature (. degree.C.)	1240	1065	1170	1120	1240	1110

Y = yellowish, O = orange

TABLE 2

		Examples
		Examples						7	8	9	10	11	12
		Glass Oxide compound Composition of (mol％)	SiO₂	47．0	60．5	45．5	45．5	7	8	9	10	11	12	58．0	56．0
Al₂O₃	4．0		SiO₂	47．0	60．5	45．5	45．5	2．0	2．0	2．0	4．0	9．0		58．0	56．0
Al₂O₃	4．0		B₂O₃	-	-	-	-	2．0	2．0	2．0	4．0	9．0	-	-
P₂O₅	-		B₂O₃	-	-	-	-	-	-	-	-	-	-	-
P₂O₅	-		Li₂O Na₂O K₂O	19．0 7．0 -	15．5 5．0 -	9．5 6．5 -	10．5 2．0 -	-	-	-	-	-	5．0 1．0 -	18．0 - -
MgO CaO SrO BaO	4．0 1．0 - -		Li₂O Na₂O K₂O	19．0 7．0 -	15．5 5．0 -	9．5 6．5 -	10．5 2．0 -	4．0 4．0 - -	10．0 15．0 - -	10．5 10．5 - -	16．0 3．0 - -	3．0 5．0 - -	5．0 1．0 -	18．0 - -
MgO CaO SrO BaO	4．0 1．0 - -		ZnO TiO₂ Y₂O₃ ZrO₂	- 12．0 1．0 5．0	- 5．0 3．0 1．0	- 10．5 1．0 -	- 9．0 - 10．0	4．0 4．0 - -	10．0 15．0 - -	10．5 10．5 - -	16．0 3．0 - -	3．0 5．0 - -	- 8．0 1．0 4．0	- 3．0 60 -
Refining agent	Species of Amount (based on glass oxide) mol％)		ZnO TiO₂ Y₂O₃ ZrO₂	- 12．0 1．0 5．0	- 5．0 3．0 1．0	- 10．5 1．0 -	- 9．0 - 10．0	SnO 1．0	Ce₂O₃ 0．1	SnO₂ 0．0001	SnO₂ 2．0	CeO₂ 0．0001	- 8．0 1．0 4．0	- 3．0 60 -	H₂O 5．0
	Species of Amount (based on glass oxide) mol％)	Species of Amount (based on glass oxide) mol％)	CeO₂ 1．0	- -	- -	H₂O 3．0	H₂O 2．0	SnO 1．0	Ce₂O₃ 0．1	SnO₂ 0．0001	SnO₂ 2．0	CeO₂ 0．0001	- -		H₂O 5．0
	Refining performance		CeO₂ 1．0	- -	- -	H₂O 3．0	H₂O 2．0	Good effect	Good effect	Good effect	Good effect	Good effect	- -	Good effect
Colour of glass			YB^*	Y^*	Brown colour	Y^*	Brown colour	Good effect	Good effect	Good effect	Good effect	Good effect	Y^*	Good effect
Colour of glass		Article (A) Theory of things Property of (2) Can be used for	YB^*	Y^*	Brown colour	Y^*	Brown colour	Young's modulus (GPa)	107	100	108	121	Y^*	103	104
Specific gravity of	2．8		2．7	2．8	3．2	2．8	2．7	Young's modulus (GPa)	107	100	108	121		103	104
Specific gravity of	2．8		2．7	2．8	3．2	2．8	2．7	Specific modulus (. times.10)⁶Nm／Kg)	38	37	38	38	37	38
Coefficient of thermal expansion (ppm/. degree.C.)	11．5		9．6	9．6	9．2	7．8	8．6	Specific modulus (. times.10)⁶Nm／Kg)	38	37	38	38	37	38
Coefficient of thermal expansion (ppm/. degree.C.)	11．5		9．6	9．6	9．2	7．8	8．6	Maximum surface roughness [ Rmax](μm)	4	5	3	4	3	5
Transmittance at 400nm (%)	70		75	80	85	80	85	Maximum surface roughness [ Rmax](μm)	4	5	3	4	3	5
Transmittance at 400nm (%)	70		75	80	85	80	85	Liquidus temperature (. degree.C.)	1000	990	1120	1230	1120	1020

YB = light yellow-brown, Y = light yellow-brown

TABLE 3

		Examples
		Examples						13	14	15	16	17	18
		Glass Oxide compound Composition of (mol％)	SiO₂	65．0	40．5	45．5	59．5	13	14	15	16	17	18	66．0	68．0
Al₂O₃	5．0		SiO₂	65．0	40．5	45．5	59．5	3．0	2．0	2．0	9．5	10．5		66．0	68．0
Al₂O₃	5．0		B₂O₃	-	-	-	-	3．0	2．0	2．0	9．5	10．5	-	-
P₂O₅	-		B₂O₃	-	-	-	-	-	-	-	-	-	-	-
P₂O₅	-		Li₂O Na₂O K₂O	4．0 - -	7．0 - -	11．5 3．0 -	14．5 3．0 -	-	-	-	-	-	12．0 9．5 -	11．0 10．5 -
MgO CaO SrO BaO	7．0 7．0 - -		Li₂O Na₂O K₂O	4．0 - -	7．0 - -	11．5 3．0 -	14．5 3．0 -	21．5 18．0 - -	12．0 12．0 - -	6．0 6．0 - -	- - - -	- - - -	12．0 9．5 -	11．0 10．5 -
MgO CaO SrO BaO	7．0 7．0 - -		ZnO TiO₂ Y₂O₃ ZrO₂	- 1．0 6．0 5．0	- 4．0 5．0 1．0	- 12．0 - 2．0	- 6．0 1．0 3．0	21．5 18．0 - -	12．0 12．0 - -	6．0 6．0 - -	- - - -	- - - -	- - - 3．0	- - - -
Refining agent	Species of Amount (based on glass oxide) mol％)		ZnO TiO₂ Y₂O₃ ZrO₂	- 1．0 6．0 5．0	- 4．0 5．0 1．0	- 12．0 - 2．0	- 6．0 1．0 3．0	C 2．0	CeO₂ 2．0	SnO 2．0	CeO₂ 2．0	Ce₂O₃ 2．0	- - - 3．0	- - - -	SnO 1．0
	Species of Amount (based on glass oxide) mol％)	Species of Amount (based on glass oxide) mol％)	SO₃ 0．5	H₂O 3．0	- -	H₂O 3．0	- -	C 2．0	CeO₂ 2．0	SnO 2．0	CeO₂ 2．0	Ce₂O₃ 2．0	CeO₂ 1．0		SnO 1．0
	Refining performance		SO₃ 0．5	H₂O 3．0	- -	H₂O 3．0	- -	Good effect	Good effect	Good effect	Good effect	Good effect	CeO₂ 1．0	Good effect
Colour of glass			Brown colour	Brown colour	Y^*	Y^*	Brown colour	Good effect	Good effect	Good effect	Good effect	Good effect	Brown colour	Good effect
Colour of glass		Article (A) Theory of things Property of (2) Can be used for	Brown colour	Brown colour	Y^*	Y^*	Brown colour	Young's modulus (GPa)	102	115	112	102	Brown colour	83	81
Specific gravity of	2．9		3．0	2．9	2．8	2．5	2．5	Young's modulus (GPa)	102	115	112	102		83	81
Specific gravity of	2．9		3．0	2．9	2．8	2．5	2．5	Specific modulus x 10⁶Nm／Kg)	35	37	39	37	33	32
Coefficient of thermal expansion (ppm/. degree.C.)	7．2		8．9	9．3	8．3	8．8	8．7	Specific modulus x 10⁶Nm／Kg)	35	37	39	37	33	32
Coefficient of thermal expansion (ppm/. degree.C.)	7．2		8．9	9．3	8．3	8．8	8．7	Maximum surface roughness [ Rmax](μm)	5	6	4	2	4	2
Transmittance at 400nm (%)	85		60	80	60	65	70	Maximum surface roughness [ Rmax](μm)	5	6	4	2	4	2
Transmittance at 400nm (%)	85		60	80	60	65	70	Liquidus temperature (. degree.C.)	1130	1240	1220	1080	930	890

Y = light yellow

TABLE 4

		Examples
		Examples						19	20	21	22	23	24
		Glass Oxide compound Composition of (mol％)	SiO₂	59．0	65．0	67．0	72．0	19	20	21	22	23	24	72．0	47．0
Al₂O₃	2．0		SiO₂	59．0	65．0	67．0	72．0	9．0	10．5	1．0	3．0	12．0		72．0	47．0
Al₂O₃	2．0		B₂O₃	-	-	-	3．0	9．0	10．5	1．0	3．0	12．0	-	6．0
P₂O₅	-		B₂O₃	-	-	-	3．0	-	-	-	1．0	-	-	6．0
P₂O₅	-		Li₂O Na₂O K₂O	17．0 3．0 -	9．0 14．0 -	8．5 7．0 -	18．0 1．0 2．0	-	-	-	1．0	-	20．0 - 2．0	- - -
MgO CaO SrO BaO	4．0 4．0 4．0 -		Li₂O Na₂O K₂O	17．0 3．0 -	9．0 14．0 -	8．5 7．0 -	18．0 1．0 2．0	- 2．0 - -	2．5 4．0 0．5 -	1．0 1．0 1．0 -	2．0 - - -	- 3．0 3．0 5．0	20．0 - 2．0	- - -
MgO CaO SrO BaO	4．0 4．0 4．0 -		ZnO TiO₂ Y₂O₃ ZrO₂	- 3．0 1．0 3．0	- - - -	- - - -	- - - -	- 2．0 - -	2．5 4．0 0．5 -	1．0 1．0 1．0 -	2．0 - - -	- 3．0 3．0 5．0	- - - -	17．0 5．0 1．0 1．0
Refining agent	Species of Amount (based on glass oxide) mol％)		ZnO TiO₂ Y₂O₃ ZrO₂	- 3．0 1．0 3．0	- - - -	- - - -	- - - -	CeO₂ 2．0	Ce₂O₃ 4．0	Ce₂O₃ 4．0	SnO₂ 1．0	SnO₂ 1．0	- - - -	17．0 5．0 1．0 1．0	SnO 2．0
	Species of Amount (based on glass oxide) mol％)	Species of Amount (based on glass oxide) mol％)	- -	- -	- -	CeO₂ 1．0	CeO₂ 1．0	CeO₂ 2．0	Ce₂O₃ 4．0	Ce₂O₃ 4．0	SnO₂ 1．0	SnO₂ 1．0	- -		SnO 2．0
	Refining performance		- -	- -	- -	CeO₂ 1．0	CeO₂ 1．0	Good effect	Good effect	Good effect	Good effect	Good effect	- -	Good effect
Colour of glass			Brown colour	Brown colour	Brown colour	Brown colour	Brown colour	Good effect	Good effect	Good effect	Good effect	Good effect	Y*	Good effect
Colour of glass		Article (A) Theory of things Property of (2) Can be used for	Brown colour	Brown colour	Brown colour	Brown colour	Brown colour	Young's modulus (GPa)	95	77	78	78	Y*	81	104
Specific gravity of	2．8		2．5	2．6	2．4	2．4	3．0	Young's modulus (GPa)	95	77	78	78		81	104
Specific gravity of	2．8		2．5	2．6	2．4	2．4	3．0	Specific modulus (. times.10)⁶Nm／Kg)	34	31	30	33	34	35
Coefficient of thermal expansion (ppm/. degree.C.)	7．9		8．7	8．0	7．8	7．6	4．9	Specific modulus (. times.10)⁶Nm／Kg)	34	31	30	33	34	35
Coefficient of thermal expansion (ppm/. degree.C.)	7．9		8．7	8．0	7．8	7．6	4．9	Maximum surface roughness [ Rmax](μm)	3	3	4	3	3	4
Transmittance at 400nm (%)	60		35	40	70	70	65	Maximum surface roughness [ Rmax](μm)	3	3	4	3	3	4
Transmittance at 400nm (%)	60		35	40	70	70	65	Liquidus temperature (. degree.C.)	970	990	950	1050	1100	1350

Y = light yellow

TABLE 5

		Examples
		Examples				25	26	27	28
		Glass Oxide compound Composition of (mol％)	SiO₂	55．0	46．0	25	26	27	28	47．0	64．0
Al₂O₃	12．0		SiO₂	55．0	46．0	10．0	6．0	8．5		47．0	64．0
Al₂O₃	12．0		B₂O₃	-	-	10．0	6．0	8．5	-	3．0
P₂O₅	-		B₂O₃	-	-	-	-	-	-	3．0
P₂O₅	-		Li₂O Na₂O K₂O	- - -	- - -	-	-	-	5．0 - -	9．0 9．0 -
MgO CaO SrO BaO	12．0 3．0 1．0 1．0		Li₂O Na₂O K₂O	- - -	- - -	30． - - -	25．0 - - -	4．0 2．5 - -	5．0 - -	9．0 9．0 -
MgO CaO SrO BaO	12．0 3．0 1．0 1．0		ZnO TiO₂ Y₂O₃ ZrO₂	12．0 4．0 - -	- 11．0 1．0 2．0	30． - - -	25．0 - - -	4．0 2．5 - -	- 7．0 10．0 -	- - - -
Refining agent	Species of Amount (based on glass oxide) mol％)		ZnO TiO₂ Y₂O₃ ZrO₂	12．0 4．0 - -	- 11．0 1．0 2．0	SnO 2．0	H₂O 4．0	H₂O 4．0	- 7．0 10．0 -	- - - -	SnO₂ 1．0
	Species of Amount (based on glass oxide) mol％)	Species of Amount (based on glass oxide) mol％)	Ce₂O₃ 2．0	- -	- -	SnO 2．0	H₂O 4．0	H₂O 4．0	- -		SnO₂ 1．0
	Refining performance		Ce₂O₃ 2．0	- -	- -	Good effect	Good effect	Good effect	- -	Good effect
Colour of glass			Brown colour	DB^*	DB^*	Good effect	Good effect	Good effect	C-Less^*	Good effect
Colour of glass		Article (A) Theory of things Property of (2) Can be used for	Brown colour	DB^*	DB^*	Young's modulus (GPa)	99	117	C-Less^*	132	77
Specific gravity of	2．9		2．9	3．4	2．5	Young's modulus (GPa)	99	117		132	77
Specific gravity of	2．9		2．9	3．4	2．5	Specific modulus (. times.10)⁶m／Kg)	34	40	39	39
Coefficient of thermal expansion (ppm/. degree.C.)	4．7		5．6	4．2	8．5	Specific modulus (. times.10)⁶m／Kg)	34	40	39	39
Coefficient of thermal expansion (ppm/. degree.C.)	4．7		5．6	4．2	8．5	Maximum surface roughness [ Rmax](μm)	3	5	3	3
Transmittance at 400nm (%)	60		75	85	90	Maximum surface roughness [ Rmax](μm)	3	5	3	3
Transmittance at 400nm (%)	60		75	85	90	Liquidus temperature (. degree.C.)	1020	1320	1350	980

DB = dark brown, C-Less = colorless

Note: SO (SO)₃As a sulfate salt such as Na₂SO₄、Li₂SO₄Or MgSO 2₄Is provided in the form of₂O is a hydroxide or hydrate such as Al (OH)₃、Mg(OH)₂、Ca(OH)₂、MgCl₂·6H₂Provided in the form of O.

Example 29

A glass having the same composition as that of the glass of example 1 was made into a glass substrate having a diameter of 2.5 inches and a thickness of 0.8 mm by a direct pressing method, and the glass substrate was chemically strengthened. On the surface of each of the above glass substrates, an AlN texture layer, a CrMo underlayer, a CoPtCrTa magnetic layer and a carbon protective layer were successively shaped by an in-line sputtering apparatus to fabricate a magnetic disk.

The thus-obtained magnetic disk was subjected to a sliding test, showing that neither collision (the magnetic head scratches the projections on the surface of the magnetic disk) nor chipping (the magnetic head collides with the projections on the surface of the magnetic disk) occurred.

The glass substrate for an information recording medium had an average surface roughness (Ra) of 5 angstroms and a flatness of 1 μm.

Example 30

The same glass substrate as in example 29 was used. An underlayer composed of Al (layer thickness 50A)/Cr (1, 000A)/CrMo (100A), a magnetic layer made of CoPtCr (120A)/CrMo(50A)/CoPtCr (120A), and a Cr (50A) protective layer were successively formed on the surface of each glass substrate by an in-line sputtering apparatus.

The above substrate was immersed in an organosilicon compound solution (a mixture of water, isopropanol, and tetraethoxysilane) in which SiO was contained₂Particles (particle size 100 angstroms) have been dispersed therein, and the substrate taken out of the solution is calcined to form SiO having a texture effect on each side₂And a protective layer. Further, the surface of each protective layer was subjected to a dipping treatment with a lubricant made of perfluoropolyether to obtain a magnetic disk compatible with the MR head.

The discs thus obtained were subjected to a sliding test, showing neither collision nor breakage. It was also found that there were no defects in the layers, such as the magnetic layer.

Example 31

A magnetic disk was produced in the same manner as in example 30, except that the original underlayer was replaced with an underlayer made of Al/Cr/Cr and the original magnetic layer was replaced with a magnetic layer made of CoNiCrTa. The disk had the same result as in example 30.

According to the present invention, a glass substrate made of glass that fully satisfies the physical properties required for a substrate for an information recording medium can be obtained without using conventional arsenic and antimony compounds that are used as refining agents but have a detrimental effect on the environment. Such a glass substrate for an information recording medium is suitable as a substrate for a magnetic disk, a substrate for a magneto-optical disk, and a substrate for an optical disk, for example.

Claims

1. A glass substrate for an information recording medium, which is formed of a glass having a composition (mol%) containing 35 to 70% of SiO₂0-15% of Al₂O₃3-30% of Li₂O+Na₂O, 1-45% CaO, 3-45% CaO + MgO, and 0.1-30% TiO₂And contains 0.0001 to 10mol% of tin oxide and/or cerium oxide based on the total amount of the above glass components.

2. A glass substrate for an information recording medium, the glass substrate being formed of a glass having a composition (mol%) containing 60 to 75% of SiO₂2-10% of Al₂O₃8-20% of Li₂O, 3-15% of Na₂O and 2-10% ZrO₂，Na₂O／ZrO₂A molar ratio of 0.1 to 8, and Al₂O₃／ZrO₂A molar ratio of 0.2 to 5, and contains 0.0001 to 10mol% of tin oxide and/or cerium oxide based on the total amount of the above glass components.

3. A glass substrate for an information recording medium, the glass substrate being made of a material containing SiO₂-Al₂O₃-R₂Chemically strengthened glass of O (wherein R is an alkali metal) in a total amount of 98SiO in an amount of not less than mol%₂、Al₂O₃And R₂O and contains 0.0001 to 10mol% of tin oxide and/or cerium oxide based on the total amount of the above glass components.

4. A glass substrate for an information recording medium, the glass substrate being formed of a glass having a composition (mol%) containing 45 to 85% of SiO₂4-32% of Al₂O₃8-30% of Na₂O+Li₂O (provided that Li is₂The amount of O does not exceed Na₂O and Li₂70% of total O) and2-13% of ZnO and F₂Or both (provided that F is present)₂In an amount of less than 8%), (Li)₂O+Na₂O)／Al₂O₃The molar ratio is 2/3-4/1, SiO₂、Al₂O₃、Na₂O、Li₂O、F₂And ZnO in a total amount of at least 90 mol%, and contains tin oxide and/or cerium oxide in an amount of 0.0001 to 10mol% based on the total amount of the above glass components.

5. A glass substrate for an information recording medium, the glass substrate being formed of a glass having a composition (mol%) containing 35 to 65% of SiO₂5-25% of Al₂O₃10-40% of MgO and 5-15% of TiO₂0.8-10% of Y₂O₃And 0-3% of ZrO₂And contains 0.0001 to 10mol% of tin oxide and/or cerium oxide based on the total amount of the above glass components.

6. A glass substrate for an information recording medium, the glass substrate being formed of a glass having a composition (mol%) containing 25 to 52% of SiO₂5-35% of Al₂O₃0-7% of Li₂O, 15-45% of MgO and 0-17% of Y₂O₃0-25% of TiO₂0-8% of ZrO₂1-30% of CaO and 0-5% of B₂O₃+P₂O₅，Y₂O₃、TiO₂、ZrO₂And the total content of CaOIn an amount of 5 to 30 mol%, and contains 0.0001 to 10mol% of tin oxide and/or tin oxide based on the total amount of the above glass componentsAnd (3) cerium.

7. A glass substrate for an information recording medium, the glass substrate being formed of a glass having a composition (mol%) containing 60 to 70% of SiO₂2-15% of Al₂O₃6-20% of Li₂O, 2-9% of Na₂O, 0-3% of K₂O, 0-5% of MgO, 1-7% of CaO, 0-5% of SrO, 0-2% of BaO and 0-5% of TiO₂0-2% of Fe₂O₃0-1% of MnO and 0-5% of ZrO₂And 0-2% of Y₂O₃，Li₂O、Na₂O and K₂The total content of O is 10-25 mol%, the total content of MgO, CaO, SrO and BaO is 2-15 mol%, TiO₂、Fe₂O₃And MnO in a total amount of 0.01 to 3 mol%, and 0.0001 to 10mol% of tin oxide and/or cerium oxide based on the total amount of the above glass components.

8. A glass substrate for an information recording medium, the glass substrate being made of a material containing lithium disilicate (Li)₂O·2SiO₂) Formed as a glass having a main crystal phase, the glass containing (mol%) 65-85% SiO₂8-30% of Li₂O, 1-10% of Al₂O₃And 0-5% of P₂O₅And contains 0.0001 to 10mol% of tin oxide and/or cerium oxide based on the total amount of the above glass components.

9. A glass substrate for an information recording medium, the glass substrate being formed of a glass having a composition containing (mol%) 30 to 65% of SiO₂5-35% of Al₂O₃5 to 35 percent of ZnO, 0 to 20 percent of MgO, 0.5 to 25 percent of CaO, SrO, BaO and B₂O₃+La₂O₃+Y₂O₃+Gd₂O₃+Ta₂O₅+Nb₂O₅+WO₃+Bi₂O₃(As long as the CaO + SrO + BaO content is 0-20%, B₂O₃0-10% of La₂O₃+Y₂O₃+Gd₂O₃Is 0-20% and Ta₂O₅+Nb₂O₅+WO₃+Bi₂O₃0-10%) of 1-15% of TiO₂0-7% of ZrO₂+P₂O₅+SnO₂(provided that ZrO is present₂The content of (b) is 0-2%, and P₂O₅0 to 5%), and 0 to 5% of F constituting a fluoride of at least one metal element of the above metal oxides, and contains 0.0001 to 10mol% of tin oxide and/or cerium oxide based on the total amount of the above glass components.

10. A glass substrate for an information recording medium, the glass substrate being formed of a glass material containing 1 to 10mol% of at least one selected from the group consisting of C, SO based on the total amount of glass components₃Or H₂And O is used as a refining agent.

11. The glass substrate of any of claims 1-10, having a young's modulus of at least 70 GPa.

12. The glass substrate of any of claims 1-11 having a specific modulus of at least 30 x 10⁶Nm／kg。

13. The glass substrate according to any one of claims 1 to 12, having a maximum surface roughness (Rmax) of 7 μm or less.

14. The glass substrate of any of claims 1-13, having a transmittance at 400nm of less than 10%.

15. The glass substrate of any of claims 1-14, having a liquidus temperature of 1, 400 ℃ or less.

16. An information recording medium having a glass substrate according to any one of claims 1 to 15, and a magnetic layer formed on at least a part of a surface thereof.