MXPA96002309A - Reforz glass substrate - Google Patents

Abstract

The present invention relates to a glass substrate intended to be used as supports in a data storage unit, reinforced by exchanges of surface ions and whose matrix comprises the constituents below, in the following weight proportions: SiO2 of 45% to 65%; A12O3 5 to 20%; B2O3 from 0% to 5%; Na2O from 4% to 12%; K2O from 3.5 to 12%; MgO from 0% to 8%; CaO from 0% to 13%; ZrO2 from 0% at 20% the sum of the oxides SiO2, A12O3 and ZrO2 remains equal to or less than 70%, that composition possibly comprises BaO and / or SrO oxides in proportions such that: 11% equal to or less than MgO + CaO + BaO + SrO equal or less than 24%, and alkaline oxides are introduced according to weight percentages such that: 0.22 equal to or less than Na2O / Na2O + K2O equal to or less than 0.

Description

REINFORCED GLASS SUBSTRATE DESCRIPTION The invention relates to glass substrates that are used primarily as a support in the realization of data storage units. More particularly, the invention relates to glass substrates in the form of discs that are used mostly as "peripheral" memories in the computer industry. Although the invention is not limited to this application, it will be described with reference to the production of magnetic hard drives. A magnetic hard disk is generally composed of a support element shaped to have the shape of a perforated disk at its center. On this disc, it is possible to deposit a series of magnetic thin layers that are used to store data. The data is recorded and read with the help of one or more reading heads that are placed above the disk while it is animated by a rotation movement. To obtain a technical quality, data reading, the head should approach the disk as close as possible; it is then spoken of "contact recording". In effect, the signal detected by the head decreases exponentially when its height increases. In addition, current demands require an increasingly important storage density. This is translated by the storage of a given information on an increasingly smaller surface. To ensure the reading of data recorded in this way, the distance between the disk and the reading head must be reduced more and more; this distance must be less than 300 Angstrdms. Above all, substrates for the production of magnetic hard drives are described in US Pat. No. 5,316,844; It is aluminum substrates. This document also describes an important aspect of these substrates: those must present only a very small roughness. This document indicates roughness values whose Ra, or average roughness, is between 100 and 300 Angstrdms. The current requirements, linked to the growing need for storage, and therefore to a disk distance / reading head increasingly smaller, corresponding to a Ra less than 30 Angstrome. On the other hand, if the requirements that are related to the memory capacity of magnetic hard drives are increasingly important, another requirement that may seem paradox, is related to the dimensions of those hard drives. In fact, these data storage units must be as small as possible and have an equally small mass. These demands are linked, on the one hand, to the growing need for portable storage units, which are therefore bulky and light; the development of portable computing tools and programs that need large memory capacities are the basis of that need. On the other hand, always in order to increase the data storage capacities, it is interesting to be able to associate several magnetic hard disks in a given space and therefore have substrates that have a reduced thickness. A substrate that is made of aluminum can not have a thickness of less than 0.6 millimeter and at the same time present the qualities required to constitute a hard disk, especially in terms of rigidity and resistance to damage at the moment of the impact of the reading head against the disc. To remedy these drawbacks and to be able to lighten and eventually reduce the thickness of such a substrate, it has been proposed above all in the patent application EP 579 399, to make it of glass. In particular, conventional glass compositions have been used to obtain a float glass of the construction or automobile type. The floa type glass is obtained in the form of a ribbon and then it is transformed into a sheet and finally it is cut and shaped into discs of the required dimensions. Then, these are polished to obtain the desired thickness and roughness. It became clear in the course of tests, that these glass substrates are subject to different disadvantages and can not satisfy in that way, the realization of magnetic hard drives. In particular, the surface of these floa t type glass substrates is subject to a significant loss of alkalis and especially of potassium or sodium and essentially of the ion contributed by a chemical tempering. These alkalines have harmful effects on the magnetic layers deposited on the substrates. Indeed, it is clear that the regulation of alkaline in these layers, produces the destruction of recorded data and short-term more or less. The object of the invention is to reduce these drawbacks and more particularly that of providing substrates that are used as supports in the realization of storage units of a large number of information and have a limited volume and weight. The subject of the invention is also those types of substrates which have sufficient mechanical and chemical resistance and do not have the disadvantages observed for glass substrates of the type floa t, mentioned above.This objective according to the invention is achieved by means of a substrate of glass, which is intended to be used as support in data storage units, reinforced by surface ion exchange and whose matrix comprises the constituents below in the following weight proportions: Si02 from 45% to 65% A1203 from 0% to 20% B203 from 0% to 5% Na20 from 4% to 12% K20 from 3.5% to 12% MgO from 0% to 8% CaO from 0% to 13% Zr02 from 0% to 20%.

The sum of the oxides Si02, Al203 and Zr02 remains equal to or less than 70%; that composition optionally comprises the BaO and / or SrO oxides in proportions such as: 11% equal to or less than MgO + CaO + BaO + SrO equal to or less than 24% The alkali oxides are introduced according to weight percentages such as: 0.22 equal or less to Na20 / Na20 + K20 equal to or less than 0.60. The glass matrices of the substrates according to the invention advantageously comprise ZnO oxide in a weight ratio of less than 10% and preferably less than 4%. This oxide has above all the ability to improve idrolytic resistance, without increasing the viscosity at elevated temperatures. A substrate which is made from one of the compositions listed above and which were subjected to an ion exchange, especially by means of a chemical tempering treatment, can be used as a support for carrying out a data storage unit and more particularly a magnetic hard drive. In fact, the mechanical resistance and the chemical or hydrolytic resistance that are obtained, agree to this type of use. On the other hand, as already said above, there are roughness efforts also linked to those very high rotation speeds and to the relatively close position of the read head; the requirements are for a Ra less than 30 Angstroms. It is above all possible, from techniques known in the glass industry, to transform a glass sheet obtained by the floa t process and a substrate of that type that satisfies the different tolerances. These techniques consist essentially of stages of trimming, drilling and shaping of the edges (or "overflow"). Then, they follow classic polishing stages by mechanical means that allow, on the one hand, to obtain the desired thickness and, on the other hand, a roughness whose Ra is less than 30 Angstroms. It is also possible to perform a finishing polish that allows to reach a roughness whose Ra is less than 10 Angstroms. Such polishing can eventually combine several polishing steps by mechanical and / or chemical means. In a variant of the invention, it is foreseen to realize these substrates by means of a pressing technique; A mass of glass is carried in a mold where a press gives it the desired shape. Then it is possible to proceed to the different polishing stages. The invention also contemplates other methods for realizing these substrates. A non-limiting list of procedures that can be used is given below: rolling, drawing down, trimming washers. In a variant of the invention, the glass substrate has a matrix comprising the constituents below, in the following weight proportions: sio2 from 45% to 65% A1203 from 5% to 20% B203 from 0% to 5% Na20 of 4% to 12% 2o from 4% to 12% MgO from 0% to 8 CaO from 0% to 8% Zr02 from 0% to 6% According to a preferred mode of this variant of the invention, the favorable Al20 oxide by the chemical resistance, has a percentage of overall content greater than 10%. It also allows to increase the lower temperature of annealing (temperature of strain point), which is an interesting factor, especially to perform a chemical tempering at high temperatures. The content percentage in Zr02, difficult element to melt, is advantageously less than 5%. B203 oxide intervenes little in the mechanical and chemical properties of the glass matrix. On the other hand, it has the advantage of lowering the viscosity at high temperatures. The content percentage of B2O3 will advantageously be between 0 and 3%, and preferably less than 2%, to promote the homogeneity of the glass. Therefore, a glass composition selected from the following will be used: Si02 from 45% to 60% Al203 from 10% to 20% B203 from 0% to 3% Na20 from 4% to 12% K20 from 4% to 12% MgO from 0% to 8% CaO from 0% to 8% Zr02 from 0% to 5%.

The sum of the oxides Si02, Al203 and Zr02 remains equal to or less than 70%; the composition optionally comprising the Bao and / or SrO oxides in proportions such that: 14% or below CaO + MgO + BaO + SrO exceeding 22%, and the alkaline oxides are introduced as percentages by weight such that: 0.22 as or lower than Na20 / Na20 + K20 equal to or less than 0.60.

The overall percentage of alkaline earth elements is kept high enough to allow a small viscosity at high temperatures to be obtained. This is interesting especially when the glass is obtained according to the float process. The presence of these elements also favors the fusion of these glass compositions. BaO contributes to the decrease in viscosity at high temperatures. It also allows to reduce the risks of devitrification. MgO and SrO allow to increase the hydrolytic resistance of the glasses. As regards the content percentages of alkali metal oxides Na20 and 20, these are advantageously selected from a molar point of view. In effect, an alkaline-mixed phenomenon is observed which limits the migration of alkalis on the surface; it becomes clear that the migration of the ions decreases significantly when Na20 and K20 are in molar quantities more or less equivalent. The state of the surface that is obtained after the ion exchange, that is to say, for example, an absence of sodium ions over a small thickness, may persist due to the alkali-mixed effect that limits the migration of the ions.

According to another variant of the invention, the glass substrate has a matrix, which belongs to another family, which comprises the constituents below, in the following weight proportions: Si02 from 45% to 63% A1203 from 0% to 18% Na20 from 4% to 12% K20 from 3.5% to 12% MgO from 1% to 8% CaO from 1% to 13% Zr02 from 6.5% to 20%.

For this family of glass Zr02 plays a stabilizing role. This oxide increases to a certain extent, the chemical resistance of the glass and favors the increase of the annealing temperature. The percentage of Zr02 must not exceed 20% under penalty of making the merger too difficult. If this oxide is difficult to melt, it has the advantage of not increasing the viscosity of the glasses according to the invention, at high temperatures. This makes it possible to avoid introducing into these glasses oxides such as B203, of which one of the effects is that of reducing the viscosity of the glass, or of increasing the content percentage of the alkaline oxides having the same effect.

The glasses according to this variant of the invention may also contain alumina which plays a role similar to that of zirconium oxide. Alumina increases the chemical resistance of this type of glass, favors the elevation of its lower temperature of annealing. On the contrary, it is a difficult oxide to melt, and that increases the viscosity of the glass at high temperatures. In a general manner, the melting of the glasses according to this variant of the invention remains within the limits of acceptable temperatures for a production according to the floa t process, with the reservation that the sum of the SiO oxides; > , Al203 and Zr02 remain equal to or less than 70%. By acceptable limits, it is to be understood that the glass temperature corresponding to logn = 1.6 does not exceed about 1630 ° C and preferably 1590 ° C. In the glasses according to the invention, the sum of the oxides Zr02 and Al203 is advantageously equal to or greater than 8%, and preferably, comprised between 8% and 22%. Its content percentage of Zr02 is advantageously between 8% and 15%. Preferred glass compositions according to this variant of the invention, comprise the constituents below, in the following weight proportions: Si02 45% to 59% Al203 O% to 10% Na20 of 4% to 10% K20 - 3.5% to 7% MgO from 1% to 7% CaO 1% to 12% Zr02 from 8% to 15% .

According to a preferred mode of the invention, the exchanges of surface ions are obtained in a bath of KN03 that allows an exchange of sodium ions in potassium ions. In a variant, a mixed bath is used, ie a bath containing several types of alkali ions, which allows multiple ion exchange. In other variants, chemical tempering can be activated by external factors, such as the creation of an electric field or then the presence of ultrasound. Chemical tempering can also be combined with thermal pre-treatment. From an economic point of view, it is necessary to carry out this chemical tempering as quickly as possible. This tempering time is preferably less than 15 hours and even more preferably less than 7 hours. The tempering temperature is advantageously between 400 ° C and 520 ° C. A hardening carried out in conditions of this type leads to rupture modules, in annular bending, greater than 500 MPa and a tempering depth of at least 14 microns. The tempering carried out in this way has a double function. On the one hand, it reinforces the chemical resistance of the substrate; in effect, it becomes clear that the hydrolytic attack power to the tempered substrate decreases. On the other hand, tempering allows a mechanical reinforcement of the surface. It reinforces the intrinsic properties of the substrate linked with its composition. This is very interesting and allows to obtain a satisfactory mechanical resistance, especially a resistance to bending, to collisions, and to crushing, for example, due to the reading head. In addition, the authors of the present invention were able to reveal the reasons for breakages of magnetic hard drives animated by a high-speed rotation movement; At the time of drilling and shaping, especially of the inner hole, many defects appear in areas that are difficult to shape. Therefore, the "chemical" tempering makes it possible to reinforce the shaped edges of the substrate A substrate according to the invention as just described satisfies the criteria required to be used as support in the realization of a magnetic hard disk. made of the combination of the composition and the chemical tempering eventually associated with another pre-treatment, a sufficient mechanical strength, on the one hand, on the surface to withstand the crushing of the reading head and, on the other hand, on the edges, especially It also has sufficient chemical resistance and, above all, an idyllic resistance that ensures the • .- durability of a magnetic hard disk Other details and characteristics of the invention will be evident below of the description of exemplary embodiments of substrates according to the invention and of test The substrates that are made are discs that have the following dimensions: - outer diameter: 65 mm - internal diameter: 20 mm - thickness: 0.635 mm The selected compositions A, B. and C to make these substrates are the following; They are expressed in percentages by weight: The compositions are melted and transformed into glass tapes according to the floa t process, and then into glass sheets. Therefore, the substrates are obtained by trimming, shaping and then polishing. The polishing is done by classical means of mechanical nature and allows to reach a roughness whose Ra is less than 10 Angstroms. Then, a chemical tempering is carried out in a bath of potassium nitrate (K 03).

It is necessary to note that the compositions have high pore t strain temperatures, that is to say lower temperatures of annealing (of the order of 580 ° C) which allow a hardening to be carried out at a relatively high temperature; A chemical tempering is all the more effective when it is at a temperature close to that of the strain poin t. A higher temperature at the time of tempering, allows to realize this more quickly, saving a high surface effort and / or an important ion exchange depth. Other notable values of these compositions are also interesting. In fact, these compositions are selected for a formation according to the float process and must therefore meet the requirements linked to this process. These are, above all, the temperatures corresponding to the viscosities required at the moment of melting = 1.6 and at the time of entry on the tin bath logn = 3.5.

The corresponding temperatures of the selected compositions are the following: These temperatures are completely compatible with the floa t procedure. In addition, the liquidus temperatures of the compositions are: - A :: TLiq = 1120 ° C - B: TLiq = 1180 ° C - B :: TLiq = 1170 ° C Those temperatures are lower than T (logn = 3.5) and for therefore the glasses can be obtained according to the float process without risk of devitrification. Different tests were carried out that allow to characterize, on the one hand, the mechanical resistance and, on the other hand, the chemical resistance, on substrates such as just described. The first test that was performed is related to thermal shocks. This test made it possible in particular to demonstrate that the substrates which are made according to the invention are adapted to the treatments to which they must subsequently be subjected, for example, at the moment of deposition of the magnetic thin layers. At the time of the test, the substrates resisted without damage to temperature variations ranging from 350 ° C to 20 ° C. Another test that has already been mentioned in the foregoing is to rotate a substrate at high speed (7000 to 25000 rounds per minute). The substrates according to the invention gave satisfaction to this test. The reinforcement especially of the edges that was obtained after the tempering, is sufficient therefore.

The last mechanical test that was carried out consists of an annular flexion. The test device consists, on the one hand, of a hollow cylinder with a diameter of 55 mm on which the substrate rests concentrically and, on the other hand, of a hollow cylinder with a diameter of 30 mm that comes to rest on bending on the substrate; The last cylinder is also concentric in relation to the other elements. This test was performed on substrates according to the invention that were subjected to chemical tempers of different durations. It was also done on a non-tempered substrate. The results of these tests are compared to that obtained on a substrate that was subjected to a chemical tempering and whose composition is of the silica-socal-calcium type usually used for the "float" procedure. This substrate has an alkaline regulation rate that is too important to satisfy the requirements required for use as a support in a magnetic hard disk. On the contrary, its breaking module, in annular bending, or its surface stress are judged satisfactory and the rupture module can therefore serve as a reference. The current requirements that are required for this type of substrate are an average rupture modulus higher than 240 MPa with a minimum value higher than 150 MPa.

The results that were obtained are the following: The results presented in this table show that a tempering treatment of a duration that can be less than 4 hours, is satisfactory to lead to the desired mechanical strength. On the other hand, the depth of the defects of a substrate according to the invention that was not subjected to a chemical tempering treatment was estimated; this measure revealed a maximum depth of 15 micras. The depth of exchange at the time of tempering must be greater than this value, therefore. Measurements of depths of exchanges were made for composition A. These measurements were made with an electronic icrosonde. It is revealed that, after 4 hours of treatment, the value of 15 microns has already been exceeded.

They were carried out after tests in relation to the hydrolytic resistance according to the invention.

The first measurement of hydrolytic resistance was carried out on substrates according to the invention that had not been subjected to chemical tempering. This measurement is compared to that which was made on a substrate whose glass composition is of the "float" type. These measurements are made with the method D.G.G. This method consists in immersing 10 grams of crushed glass, whose grain size is between 360 and 400 microns, in 100 milliliters of water brought to a boil for 5 hours. After rapid cooling, the solution is filtered and a determined volume of the filtrate is evaporated to dryness. The weight of the dry matter that was obtained allows us to calculate the amount of glass dissolved in the water; this amount is expressed in milligrams per gram of tested glass. Results: - Substrate A: 7 mg / g - Substrate B: 6 mg / g - Substrate C: 11 mg / g - Substrate type "floa t" C: 30 mg / g These results show that the substrates according to the invention , have a hydrolytic resistance clearly superior to that of a substrate that was made from a classical composition for use according to the floa t process. In fact, the value measured, according to this method, on a substrate according to the invention corresponds almost to that which would be measured for a non-alkaline glass composition. Accordingly, the glass composition according to the invention is very interesting from the chemical resistance point of view. Another method for evaluating the hydrolytic resistance of a substrate according to the invention, which was eventually subjected to a chemical tempering treatment, consists in an aging of the substrate in a closed room for a period of one week maintained at a temperature of 80. ° C and within an atmosphere whose relative humidity rate is 80%. Then, the substrate is observed in scanning electron microscopy and the surface crystallizations are analyzed by EDX. { Energy Disperei sees K-ray). This test does not allow to quantify the regulation rate of alkalis. On the contrary, it allows to compare the different substrates. In this way, it is possible to guarantee the durability of a substrate, for example, from a reference substrate. A last method to evaluate the hydrolytic resistance of a substrate that was subjected to a chemical tempering treatment, consists of immersion of several hours (24 hours, approximately) in demineralized water at 80 ° C, followed by a dosage by means of a applicator for plasma, of the ions that passed in the solution, and more particularly of the alkalines (K +, Na +, Li +). It is clear that this test is well correlated with the test described in the foregoing. These tests were carried out on substrates according to the invention. The results obtained are satisfactory and show that the hydrolytic resistance of the substrates after chemical tempering is satisfactory for the applications to which they are intended. The results of the different tests that were presented, show the mechanical resistance and hydrolytic resistance of a substrate that was made according to the invention. In this way, they confirm the possibility of using the substrates according to the invention as a support in a data storage unit, such as a magnetic hard disk.

Claims (17)

NOVELTY OF THE INVENTION Having described the invention, we consider it as a novelty and, therefore, claim as our property, what is contained in the following clauses.

1. Glass substrate, intended to be used as a support in a data storage unit, reinforced by exchanges of surface ions and whose matrix comprises the constituents below, in the following weight proportions: Si02 from 45% to 65%, A1203 from 0% to 20%, B2 ° 3 from 0% to 5%, Na20 from 4% to 12%,? 2o from 3. 5% to 12%, MgO from 0% to 8 g. CaO from 0% to 13 o. Zr02 from 0% to 20 o,. the sum of the oxides Si02, Al203 and Zr02 remains equal to or less than 70%; that composition optionally comprises the BaO and / or SrO oxides in proportions such that: 11% equal to or less than MgO + CaO + Bao + SrO equal to or less than 24%, and the alkali oxides are introduced according to weight percentages such that: 0.22 or lower than Na20 / Na20 + K20 equal to or less than 0.60.

2. - Glass substrate according to clause 1, characterized in that the matrix comprises the constituents below, in the following weight proportions: S? 02 of 45 5% to 65%, Al203 of 0 o. or at 20 B203 of 0 g. ? to 5 % , Na20 from 4% to 12%, K20 from 4% to 12%, MgO from 0% to 8%, CaO from 0% to 8%, Zr02 of 0 g. ? to 6%; the sum of the oxides S 02, Al203 and Zr02 remains equal to or less than 70%; that composition optionally comprises the BaO and / or SrO oxides in proportions such that: 11% equal to or less than MgO + CaO + BaO + SrO equal to or less than 24%, and the alkali oxides are introduced according to weight percentages such that: 0.22 or lower than Na20 / Na20 + K20 equal to or less than 0.60.

3.- Substrate according to clause 1 or 2, characterized in that the percentage of weight content of Al203 is greater than or equal to 10%.

4. - Substrate according to any of clauses 1 to 3, characterized in that the weight content percentage of Zr02 is less than 5%.

5.- Substrate according to any of clauses 1 to 4, characterized in that the percentage of CaO content by weight is less than 3%.

6.- Substrate according to any of the preceding clauses, characterized in that the weight content percentage of B203 is less than 3%.

7. Substrate according to any of the preceding clauses, characterized in that the composition comprises the constituents below in the following weight proportions: Si02 from 45% to 60%, A1203 of 10 20 o, B203 from 0% to 3%, Na20 from 4% to 12%, K20 from 4% to 12%, MgO from 0% to 8%, CaO from 0% to 8%, Zr02 from 0% to 5%; the sum of the oxides Si02, Al203 and Zr? 2 remains equal to or less than 70%; that composition optionally comprises the BaO and / or SrO oxides in proportions such that: 14% equal to or less than CaO + MgO + BaO + SrO equal to or less than 22%, and the alkali oxides are introduced according to weight percentages such that: 0.22 alike or lower than Na20 / Na20 + K20 equal to or less than 0.60.

8. Substrate according to any of the preceding clauses, characterized in that the matrix comprises the constituents below in the following weight proportions: SiO- 53.6 A1203 10.0 B2 ° 3 2.2 Na20 5.2? 2o 6.2 MgO 4.2 CaO 6.8% SrO 7.0% BaO 2.8% ZrO 2.0%

9.- Substrate according to clause 1, characterized in that the matrix comprises the constituents below in the following weight proportions: Yes? 2 of 45% to 63 o. ? , Zr02 of 6. 5% to 20%, A1203 from 0% to 18%, Na20 from 4% to 12%,? 2o from 3.5%%, CaO of 1% at 13 q. ? I MgO of 1% to 8 o, the sum of the oxides S? 02, Al203 and Zr? 2 remains equal to or less than 70%; that composition optionally comprises the BaO and / or SrO oxides in proportions such that: 11% equal to or less than MgO + CaO + BaO + SrO equal to or less than 24%, and the alkali oxides are introduced according to weight percentages such that: 0.22 or lower than Na20 / Na20 + K20 equal to or less than 0.60.

10.- Substrate according to any of the preceding clauses, characterized in that the ion exchange is carried out by chemical tempering.

11. Substrate according to clause 10, characterized in that the chemical tempering is carried out in a bath of KN03, at a temperature comprised between 400 ° C and 520 ° C and for a time less than 24 hours.

12. Substrate according to any of clauses 10 or 11, characterized in that the chemical tempering can be activated by external factors such as an electric or ultrasound field.

13. Substrate according to any of the preceding clauses, characterized in that the floa t process is obtained by cutting, perforating and forming.

14. Substrate according to any of clauses 1 to 12, characterized in that it is obtained by pressing a glass mass, and then by drilling and shaping.

15. Substrate according to any of the preceding clauses, characterized in that it is polished in such a way that the roughness corresponds to a Ra less than 30 Angstrdms.

16. Substrate according to clause 15, characterized in that it is subjected to a finishing polish that leads to a roughness whose Ra is less than 10 Angstrdms.

17.- Use of a substrate according to any of clauses 1 to 16, as a support on a magnetic hard disk.