U.S. patent application number 10/449474 was filed with the patent office on 2003-09-18 for chemical reinforced glass substrate having desirable edge profile and method of manufacturing the same.
This patent application is currently assigned to HOYA CORPORATION. Invention is credited to Isono, Hideki, Miyamoto, Takemi.
Application Number | 20030172677 10/449474 |
Document ID | / |
Family ID | 17629849 |
Filed Date | 2003-09-18 |
United States Patent
Application |
20030172677 |
Kind Code |
A1 |
Miyamoto, Takemi ; et
al. |
September 18, 2003 |
Chemical reinforced glass substrate having desirable edge profile
and method of manufacturing the same
Abstract
In a method of manufacturing a chemical reinforced glass
substrate, consideration is previously made about a relationship
between conditions of chemical reinforcement for a glass substrate
and deformation caused by the chemical reinforcement at an edge
portion of the glass substrate. The glass substrate is chemically
reinforced on the basis of the relationship so that an edge profile
is shaped into a desirable edge profile during the chemical
reinforcement. The resultant chemical reinforced glass substrate is
flat and smooth in a wide area and effective to improve a recording
density and to avoid head crashes.
Inventors: |
Miyamoto, Takemi;
(Nakakoma-gun, JP) ; Isono, Hideki; (Kitakoma-gun,
JP) |
Correspondence
Address: |
SUGHRUE, MION, ZINN, MACPEAK & SEAS
2100 Pennsylvania Avenue, N.W.
Washington
DC
20037-3202
US
|
Assignee: |
HOYA CORPORATION
|
Family ID: |
17629849 |
Appl. No.: |
10/449474 |
Filed: |
June 2, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10449474 |
Jun 2, 2003 |
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09676664 |
Oct 2, 2000 |
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6595028 |
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Current U.S.
Class: |
65/30.14 |
Current CPC
Class: |
C03C 19/00 20130101;
C03C 21/002 20130101 |
Class at
Publication: |
65/30.14 |
International
Class: |
C03C 015/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 30, 1999 |
JP |
280779/1999 |
Claims
What is claimed is:
1. A method of manufacturing a glass substrate for an information
recording medium, the glass substrate having an edge portion
adjacent to an outer and/or an inner peripheral side end,
comprising the steps of: previously finding a relationship between
chemical reinforcement conditions and that profile variation at the
edge portion of the glass substrate which results from chemical
reinforcement; and performing the chemical reinforcement of the
glass substrate on the basis of the relationship to obtain a
chemically reinforced glass substrate.
2. A method of manufacturing a glass substrate for an information
recording medium, the glass substrate having an edge portion
adjacent to an outer and/or an inner peripheral side end,
comprising the steps of: previously finding a relationship between
chemical reinforcement conditions and that profile variation at the
edge portion of the glass substrate which results from chemical
reinforcement; deciding a profile on the edge portion by predicting
the profile variation of the edge portion to obtain, as a glass
substrate prior to chemical reinforcement, an glass substrate prior
to chemical reinforcement which has a decided profile and which is
not subjected to the chemical reinforcement; and performing the
chemical reinforcement of the glass substrate prior to chemical
reinforcement to obtain the glass substrate which has a desired
profile at the edge portion.
3. A method as claimed in claim 1, wherein the chemical
reinforcement performing step is performed on conditions such that
the profile variation on the edge portion becomes small.
4. A method as claimed in claim 1, wherein the chemical
reinforcement performing step is performed under the chemical
reinforcement condition such that a compressive stress layer formed
on a surface layer of the glass substrate by the chemical
reinforcement reaches to a depth between 3 and 100 .mu.m and has a
compressive stress of 1-15 kg/mm.sup.2 and that a tensile stress
caused by the chemical reinforcement within the glass substrate is
not larger than 4.5 kg/mm.sup.2.
5. A method as claimed in claim 1, wherein the chemical
reinforcement condition defines a processing temperature and a
processing time during the chemical reinforcement.
6. A method as claimed in claim 5, wherein the processing
temperature and the processing time fall with a range between
280.degree. C. and 400.degree. C. and a duration between 0.5 and 5
hours, respectively.
7. A method as claimed in claim 2, the glass substrate prior to
chemical reinforcement having a main surface chamfered and polished
together with the edge portion adjacent to the outer and/or the
inner peripheral side end, wherein the previously finding step
previously finds, as the relationship, a relationship between a
polishing condition of the main surface and an edge profile
obtained on the basis of the polishing condition; wherein: the
deciding step obtains the glass substrate prior to chemical
reinforcement by controlling the polishing condition of the main
surface on the basis of the above-mentioned relationship between
the polishing condition and the edge profile.
8. A method as claimed in claim 7, wherein the polishing condition
is determined such that the edge portion is polished to be put into
a surface down state lowered relative to the main surface of the
glass substrate.
9. A method as claimed in claim 8, wherein the polishing condition
determined for the surface down state is defined such that use is
made about a soft polisher of a hardness between 60 and 80
(Asker-C) and a surface pressure to the glass substrate is kept at
a range between 40 and 150 kg/cm.sup.2 during polishing.
10. A glass substrate which is subjected to chemical reinforcement
and which is for use in an information recording medium, the glass
substrate chemically reinforced having a main surface and an edge
portion adjacent to an outer and/or an inner peripheral side end
and contiguous to the main surface, the edge portion of the glass
substrate which is chemically reinforced having a predetermined
region defined by an edge profile which falls within .+-.0.35 .mu.m
in relation to a flat portion of the main surface determined as a
reference surface (zero).
11. A glass substrate as claimed in claim 10, the glass substrate
being subjected to chemical reinforcement and defined as a glass
substrate after chemical reinforcement, the main surface of the
glass substrate after chemical reinforcement having a glide area
which includes a recording area located inside of the glide area,
the glide area having a glide outer periphery while the recording
area has a recording area outer periphery inside the glide outer
periphery and a flat area, wherein: the edge profile chemically
reinforced has, within an area extended from the glide outer
periphery to an inside of the recording area, a ski-jumped point
which is the highest point with respect to a reference surface
(zero) defined by the flat area and which has a ski-jump value not
greater than .+-.0.35 .mu.m at the skl-jump point; the edge profile
also having, at a roll-off point defined by a position of the glide
outer periphery, a roll-off value not greater than .+-.0.35 .mu.m
with respect to the reference surface.
12. A glass substrate as claimed in claim 10, wherein the glass
substrate chemically reinforced has a compressive stress layer
within a surface layer which is caused by the chemical
reinforcement and which has a depth between 3 and 100 .mu.m and a
compressive stress of 1-15 kg/mm.sup.2; the glass substrate
chemically reinforced also having a tensile stress not greater than
4.5 kg/mm.sup.2 within an inside of the glass substrate.
13. A method of manufacturing an information recording medium from
the glass substrate claimed in claim 1, further comprising the step
of: depositing a recording layer on the main surface of the glass
substrate.
14. An information recording medium manufactured from the glass
substrate claimed in claim 10, further comprising a magnetic layer
over the main surface.
15. An information recording medium as claimed in claim 14, the
information recording medium being a magnetic recording medium of a
LUL drive type.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to a chemical reinforced glass
substrate and an information recording medium including the glass
substrate and also to a method of manufacturing the chemical
reinforced glass substrate and the information medium.
[0002] As one of information recording media, a magnetic disk
mounted on a hard disk drive (HDD) is known in the art.
[0003] Recently, it is strongly required to increase storage
capacity of the magnetic disk. As a result, an extension of a
recording region on the magnetic disk and a high recording density
of the recording become an emergency matter.
[0004] The hard disk drive includes a magnetic head that faces a
recording surface of the magnetic disk and flies over the recording
surface to write/read information to/from the magnetic disk. It is
desirable that a flying height or an interval between the magnetic
head and the recording surface is lower and lower because the
recording density of the magnetic disk can be increased.
[0005] Two methods are known as a driving method for driving the
hard disk drive. One is a CSS (Contact Start and Stop) method and
the other is an LUL (Load/Unload) method. Because the LUL method
permits a reduction of the interval between the magnetic head and
the recording surface in comparison with the CSS method, the former
enables an increase of the recording density in comparison with the
CSS method.
[0006] On the other hand, the recording surface of the magnetic
disk must be flat and smooth to stabilize a flight of the magnetic
head. That is, the magnetic disk must have a substrate that has a
flat and smooth surface. As the substrate, attention has been
directed to a glass substrate for the magnetic disk because its
main surface can be made very flat and very smooth.
[0007] The main surface of the glass substrate is polished by a
soft polisher to even or smooth them. However, polishing by the use
of the soft polisher causes a surface down or a surface rise to
occur at an outer edge portion and/or an inner edge portion of the
glass substrate. In the LUL method, the magnetic head stays at the
outside in a radial direction of the magnetic disk when the
magnetic disk is not driven. When the magnetic disk is driven, the
magnetic head moves toward the center of the magnetic disk to
write/read information to/from the magnetic disk and faces the
recording surface of the magnetic disk. Accordingly, the surface
down and/or the surface rise at the outer edge portion make the
flight of the magnetic head unstable. In the worst case, the
magnetic head clashes with the surface of the magnetic disk. In
addition, the down and/or the rise limits the recording area of the
magnetic disk. This is because an extent of the recording area
depends on a flat area of the main surface of the glass
substrate.
[0008] To solve the above-mentioned problems, several proposals
have already been made. For example, a technique for reducing the
surface down and the surface rise is disclosed in Japanese
Unexamined Patent Publication (JP-A) No. H05-89459. The technique
provides appropriate polishing conditions (i.e. polishing pressure
and polishing time). Moreover, another technique for stabilizing
the flight of the magnetic head is disclosed in Japanese Unexamined
Patent Publication (JP-A) No. H05-290365. The technique provides an
appropriate radius of curvature at the outer edge portion of the
glass substrate.
[0009] By the way, the glass substrate is often subjected to
chemical reinforcement or treatment used by chemical solution after
the polishing process to improve mechanical strength and
durability. Such a glass substrate will be called a chemical
reinforced glass substrate hereinafter. The chemical reinforcement
partially replaces specific ions included in the surface of the
glass substrate with other ions larger than the specific ions in
ionic radii.
[0010] According to the inventors' experimental studies, it has
been found out that the chemical reinforced glass substrate can not
accomplish a stable flight of a magnetic head due to head crashes
and the like and therefore makes it impossible to widen a recording
area of the magnetic recording medium manufactured from the
chemical reinforced glass substrate.
SUMMARY OF THE INVENTION
[0011] It is therefore an object of this invention to provide a
chemical reinforced glass substrate which is subjected to chemical
reinforcement and which has desirable edge shapes or profiles at
outer and inner edges.
[0012] It is another object of this invention to provide a chemical
reinforced glass substrate of the type described having a high
mechanical strength and a flat and smooth surface.
[0013] It is still another object of this invention to provide a
chemical reinforced glass substrate which can widen a recording
area formed on its main surface.
[0014] It is further still another object of this invention to
provide a chemical reinforced glass substrate used for an
information recording medium which can be properly clamped by a
clamp for an information recording apparatus.
[0015] It is yet another object of this invention to provide a
chemical reinforced glass substrate used for an information
recording medium which enables a writing/reading head to fly stably
over its recording surface.
[0016] The ski-jump portions at the outer edge portion of the glass
substrate make the flight of the magnetic head unstable and limit
the recording area. In addition, it is unavoidable to enlarge the
interval between the magnetic head and the recording surface of the
magnetic disk because the ski-jump portions at the outer edge
portion might bring about the head clashes with the magnetic
disk.
[0017] On the other hand, the ski-jump portions at the inner edge
portion of the glass substrate inclines the magnetic disk against a
clamp for clamping the magnetic disk. There is a case where the
ski-jump portions at the inner edge portion distort or destroy the
magnetic disk when it is clamped by the clamp.
[0018] Herein, description will be made about principles of this
invention for a better understanding of this invention. Heretofore,
a chemical reinforced glass substrate is rarely used for
manufacturing a magnetic recording medium or has not been
investigated about characteristics of the chemical reinforced glass
substrate. According to the inventors' experimental studies, it has
been found out that the magnetic recording medium which includes a
chemical reinforced glass substrate can not accomplish a stable
flight of a magnetic head and often causes head crashes to occur
during read/write operation. As a result, it is difficult to
accomplish a low flight operation of the magnetic head and to
expand a recording area of the magnetic recording medium.
[0019] Further inventors' research has revealed that the glass
substrate is undesirably deformed at inner and outer edge portions
of a main surface when the glass substrate is subjected to chemical
reinforcement. It has been also found out that deformed portions
appear in the form of projections or recesses at the inner and the
outer edge portions. In any event, such projections and recesses
provide inner and/or outer edge profiles and will be referred to as
ski-jump portions and roll-off portions, respectively. The ski-jump
portions at the outer edge portion of the glass substrate make the
flight of the magnetic head unstable and limit the recording area.
In addition, it is unavoidable to enlarge the interval between the
magnetic head and the recording surface of the magnetic disk
because the ski-jump portions at the outer edge portion might bring
about the head clashes with the magnetic disk.
[0020] On the other hand, the ski-jump portions at the inner edge
portion of the glass substrate inclines the magnetic disk against a
clamp for clamping the magnetic disk. This means that the ski-jump
portions at the inner edge portion distort or destroy the magnetic
disk when it is clamped by a clamp.
[0021] The ski-jump portions at the outer edge portion of the glass
substrate make the flight of the magnetic head unstable and limit
the recording area. In addition, it is unavoidable to enlarge the
interval between the magnetic head and the recording surface of the
magnetic disk because the ski-jump portions at the outer edge
portion might bring about the head clashes with the magnetic
disk.
[0022] According to a first aspect of this invention, a method is
for use in manufacturing a glass substrate for an information
recording medium, the glass substrate having an edge portion
adjacent to an outer and/or an inner peripheral side end. The
method comprises the steps of previously finding a relationship
between chemical reinforcement conditions and that profile
variation at the edge portion of the glass substrate which results
from chemical reinforcement and performing the chemical
reinforcement of the glass substrate on the basis of the
relationship to obtain a chemically reinforced glass substrate.
[0023] As mentioned before, consideration is previously made about
the relationship between the profile variation caused by the
chemical reinforcement and the chemical reinforcement conditions.
The profile variation may occur, for example, on the edge portion
adjacent to the outer peripheral side end and may appear in a
thickness direction. In this event, the profile variation may be
represented by a variable component in the thickness direction. At
any rate, the chemical reinforcement is performed on the basis of
the relationship previously detected or found and, as a result, the
profile variation on the edge portion adjacent to the outer
peripheral side end can be controlled by the chemical reinforcement
condition. This applies to the edge portion adjacent to the inner
peripheral side end.
[0024] The chemical reinforcement may be performed, for example, by
a first method of chemically reinforcing a glass substrate by using
ion exchange and by a second method of chemically reinforcing the
glass substrate by using a de-alkali process. Specifically, the
first method realizes the chemical reinforcement of the glass
substrate by exchanging ions included in a surface layer of the
glass substrate for ions which are included in a chemical
reinforcement solution and which have diameters greater than the
ions of the surface layer. With this method, expansion takes place
in an in-plane direction of the glass substrate and a profile
variation component on the main surface is represented by a
positive value. Such a positive value of the profile variation
component brings about a surface rise area.
[0025] On the other hand, the second method which uses the
de-alkali process shrinks the glass substrate in the in-plane
direction and the profile variation component is represented by a
negative value. This brings about a surface down area. In addition,
it is confirmed that the profile variation component of the edge
portion adjacent to the inner peripheral side end is smaller than
that of the outer peripheral side end by 10% -20%.
[0026] According to a second aspect of this invention, a method is
for use in manufacturing a glass substrate for an information
recording medium. The glass substrate has an edge portion adjacent
to an outer and/or an inner peripheral side end. The method
comprises the steps of previously finding a relationship between
chemical reinforcement conditions and that profile variation at the
edge portion of the glass substrate which results from chemical
reinforcement, deciding a profile on the edge portion by predicting
the profile variation of the edge portion to obtain, as a glass
substrate prior to chemical reinforcement, a glass substrate prior
to chemical reinforcement which has a decided profile and which is
not subjected to the chemical reinforcement, and performing the
chemical reinforcement of the glass substrate prior to chemical
reinforcement to obtain the glass substrate which has a desired
profile at the edge portion.
[0027] In addition to the merits mentioned in conjunction with the
first aspect, the second aspect of this invention predicts the
profile variation components caused by the chemical reinforcement
and uses the glass substrate prior to chemical reinforcement that
can cancel them. With this method, it is possible to strictly and
precisely control an outer peripheral contour of the glass
substrate subjected to the chemical reinforcement. This applies to
an inner peripheral contour of the glass substrate.
[0028] According to a third aspect of this invention, the chemical
reinforcement performing step is performed on conditions such that
the profile variation on the edge portion becomes small. For
example, the chemical reinforcement is carried out so that the
profile variation becomes small on the outer peripheral side end.
In this case, it is possible to suppress, on the outer peripheral
side end, the profile variation which might occur due to the
chemical reinforcement, if the glass substrate prior to chemical
reinforcement is flat on the outer peripheral side end.
[0029] Alternatively, even when use is made of the glass substrate
prior to chemical reinforcement which can cancel the profile
variation, as mentioned in the second aspect, a profile variation
extremely becomes small between the glass substrate prior to
chemical reinforcement and the glass substrate. This means that the
outer edge profile can readily be controlled as compared with a
large profile variation and stable processing can be executed with
the profile variation kept small. These apply to the inner
peripheral side end of the glass substrate.
[0030] According to a fourth aspect of this invention, the chemical
reinforcement performing step is performed under the chemical
reinforcement condition such that a compressive stress layer formed
on a surface layer of the glass substrate by the chemical
reinforcement reaches to a depth between 3 and 100 .mu.m and has a
compressive stress of 1-15 kg/mm.sup.2 and that a tensile stress
caused by the chemical reinforcement within the glass substrate is
not larger than 4.5 kg/mm.sup.2.
[0031] As mentioned before, the compressive stress layer at first
reaches to the depth between 3 and 100 .mu.m. This makes it
possible to keep desirable mechanical strength of the glass
substrate and to reduce the profile variation component on the
outer peripheral side end when the chemical reinforcement is
performed.
[0032] When the depth of the compressive stress layer is thinner
than 3 .mu.m, the mechanical strength becomes undesirably weak in
durability and against breakage. When the depth of the compressive
stress layer exceeds 100 .mu.m, the profile variation component
becomes large when the chemical reinforcement is performed.
Preferably, the depth of the falls within a range between 40 and 80
.mu.m and more preferably, within a range between 50 and 70
.mu.m.
[0033] Second, the compressive stress caused in the surface layer
of the glass substrate by the chemical reinforcement is selected
between 1 and 15 kg/mm.sup.2 while the tensile stress caused within
the glass substrate is not greater than 4.5 kg/mm.sup.2. This
serves to improve the strength of the glass substrate and the
durability against breakage based on aging. The compressive stress
less than 1 kg/mm.sup.2 undesirably weakens the strength of the
glass substrate (deterioration of the durability against defects
and the characteristics withstanding breakage) while the
compressive stress over 15 kg/mm.sup.2 enlarges the profile
variation components and makes it difficult to control the outer
edge profile.
[0034] The tensile stress over 4.5 kg/mm.sup.2 also enlarges the
profile variation components and make the control of the outer edge
profile difficult.
[0035] At any rate, the above-mentioned merits are more excellent
by setting the depth of the compressive stress layer, the
compressive stress, and the tensile stress into optimum values.
These are true of the inner peripheral side end.
[0036] According to a fifth aspect of this invention, the chemical
reinforcement condition defines a processing temperature and a
processing time during the chemical reinforcement. By rendering the
processing temperature and the processing time of the chemical
reinforcement condition into predetermined ranges, it is possible
to reduce the profile variation components which appear on the
outer and/or the inner peripheral side ends during the chemical
reinforcement processing.
[0037] In addition to the processing temperature and time, the
chemical reinforcement condition may be specified by a species of
fused salts and a mixing ratio of the fused salts. However, the
processing temperature and time can be readily adjusted in
comparison with the species and the mixing ratio of the fused
salts. Accordingly, controlling the processing temperature and time
is very effective on massproduction and in workability.
[0038] According to a sixth aspect of this invention, it is
preferable that the processing temperature and the processing time
fall with a range between 280.degree. C. and 400.degree. C. and a
duration between 0.5 and 5 hours, respectively. If the processing
temperature is lower than 280.degree. C., the processing
temperature is undesirably lower than a melting point of the fused
salt or salts. On the other hand, the processing temperature higher
than 400.degree. C. undesirably shortens the processing time and
gives rise to a reduction of workability. The processing time
shorter than 0.5 hour becomes worse in workability while the
processing time over 5 hours undesirably worsen productivity.
[0039] Preferably, the processing temperature and the processing
time may fall within ranges between 340 and 360.degree. C. and
between 1 and 4 hours, respectively, so as to lower the profile
variation components on the outer and/or the inner peripheral side
ends of the chemically reinforced glass substrate, although they
can not be uniquely determined because of depending upon glass
compositions of the glass substrate, compositions of the chemical
reinforcement solution, and so on.
[0040] According to a seventh aspect of this invention, the glass
substrate prior to chemical reinforcement has a main surface
chamfered and polished together with the edge portion adjacent to
the outer and/or the inner peripheral side end. In addition, the
previously finding step previously finds or predicts, as the
relationship, a relationship between a polishing condition of the
main surface and an edge profile obtained on the basis of the
polishing condition. Moreover, the deciding step obtains the glass
substrate prior to chemical reinforcement by controlling the
polishing condition of the main surface on the basis of the
above-mentioned relationship between the polishing condition and
the edge profile. Specifically, the glass substrate prior to
chemical reinforcement has the main surface chamfered along the
outer and/or the inner peripheral side ends each adjacent to the
edge portion. Prediction is made about the relationship between the
polishing condition of polishing the main surface of the glass
substrate subjected to a chamfering process and the profile of the
edge portion adjacent to the outer and/or the inner peripheral side
end. It is posssible to obtain the glass substrate prior to the
chemical reinforcement, (may be called an unreinforced or a
provisional glass substrate), which has desired outer and/or inner
edge profiles by controlling the polishing condition of the main
surface on the basis of the above-mentioned relationship.
[0041] According to an eighth aspect of this invention, the
polishing condition is determined such that the edge portion is
polished to be put into a surface down state lowered relative to
the main surface 2 of the glass substrate 1, as illustrated in FIG.
1. Such a polishing condition of rendering the main surface 2 into
the surface down state makes it possible to simply and precisely
obtain the provisional glass substrate which has the outer edge
profile removed by or cancelled by a profile variation caused by
the chemical reinforcement. This is true of the inner peripheral
side end of the provisional glass substrate.
[0042] According to a ninth aspect of this invention, the polishing
condition determined for the surface down state is defined such
that use is made about a soft polisher of a hardness between 60 and
80 (Asker-C) and a surface pressure to the glass substrate is kept
at a range between 40 and 150 kg/cm.sup.2 during polishing. The
above-mentioned polishing condition makes it possible to readiyl
and precisely attain the glass substrate prior to the chemical
reinforcement, which stably keeps the surface down state and to
readily control the outer edge profile. In addition, it has been
found out that the outer edge profile of the edge portion tends to
be rendered into the surface down state as the polisher or a
polishing pad is hardened with the other conditions kept intact.
The outer edge profile is liable to become the surface rise state
as the polishing pressure becomes high while the outer edge profile
is rendered into the surface down state as the polishing rotation
speed becomes high.
[0043] The outer edge profile is varied in dependency upon
polishing conditions determined by a structure, a size, and an
amount of abrasive materials of a polishing machine. However,
controlling the outer edge profile by the hardness of the polisher
has a good controllability and is readily executed over a wide
range. Under the circumstances, it is preferable that the outer
edge profile may be mainly controlled by the hardness of the
polisher and subordinately controlled by the polishing pressure and
the polishing speed.
[0044] According to a tenth aspect of this invention, a glass
substrate is subjected to chemical reinforcement and is for use in
an information recording medium. The glass substrate chemically
reinforced has a main surface and an edge portion which is adjacent
to an outer and/or an inner peripheral side end and which is
contiguous to the main surface, The edge portion of the glass
substrate which is chemically reinforced has a predetermined region
defined by a profile which falls within .+-.0.35 .mu.m in relation
to a flat portion of the main surface determined as a reference
surface (zero). With this structure, it is possible to make a
magnetic head stably float and run without any head crashes with a
low height left and to widen a recording area. At any rate, high
density recording and reproducing can be achieved. This means that
the glass substrate after the chemical reinforcement is kept flat
in the outer edge profile to the exent that no problem takes place
in connection with the extension of the recording area and the high
density recording and reproducing. This is very effective in a
magnetic recording medium of a LUL type.
[0045] In the meanwhile, the predetermined region adjacent to the
outer peripheral side end may be optionally determined along the
outer peripheral side end. However, it is preferable that the
predetermined region may be defined by a region which is largely
deviated from a reference surface which is determined by a flat
portion of the main surface and which is roughened in flatness.
[0046] Specifically, it is possible to define, as the predetermined
region, a region between an outer periphery of a recording area (an
area of the main surface usually keeping flatness) on the main
surface and an outermost periphery of a glide region determined on
the main surface. Alternatively, the predetermined region may be
determined by a region from a side end wall of the glass substrate
to an inside of the outer periphery of the recording area.
[0047] Herein, it is to be noted that the recording area is
generally included within the glide region but may be identical
with the glide region.
[0048] At any rate, It is preferable that the outer edge profile
falls within a range of .+-.0.20 .mu.m (namely, between -0.20 .mu.m
and +0.20 .mu.m) and more preferably, a range of .+-.0.10 .mu.m
(-0.10.mu.m and +0.10.mu.m). This also applies to the inner
peripheral side end.
[0049] According to an eleventh aspect of this invention, the glass
substrate is subjected to chemical reinforcement and defined as a
glass substrate after chemical reinforcement. The main surface of
the glass substrate after chemical reinforcement has a glide area
which includes a recording area located inside of the glide area.
The glide area has a glide outer periphery while the recording area
has a recording area outer periphery inside the glide outer
periphery and a flat area. The edge profile chemically reinforced
has, within an area extended from the glide outer periphery to an
inside of the recording area, a ski-jumped point which is the
highest point with respect to a reference surface (zero) defined by
the flat area and which has a ski-jump value not greater than
.+-.0.35 .mu.m at the ski-jump point. In addition, the edge profile
also has, at a roll-off point defined by a position of the glide
outer periphery, a roll-off value not greater than .+-.0.35 .mu.m
with respect to the reference surface.
[0050] As mentioned above, the ski-jump point and the roll-off
point are defined in the area which is extended from the glide
outer periphery to an inside of the recording area. This means that
it is possible to render the ski-jump value and the roll-off value
into less than +0.35 .mu.m and more than -0.35 .mu.m, respectively,
with respect to the reference surface, The edge profile which has
the above-mentioned ski-jump value and roll-off value can attain
the merits mentioned with reference to the tenth aspect before. In
addition, it is possible to readily manage products by executing
numerical control in consideration of the ski-jump point and the
roll-off point.
[0051] Specifically, the ski-jump value represents a value of the
ski-jump point which is the highest point on the edge profile, with
respect to the reference to the flat surface of the glass substrate
while the roll-off value represents a value of the roll-off point
determined on a border line drawn at a position of the glide outer
periphery, as mentioned before. The roll-off value is also decided
with respect to the reference surface.
[0052] Both the ski-jump value and the roll-off value are measured
in the following manner.
[0053] As shown in FIG. 2, consideration is made about a section of
the glass substrate cut by a plane which is perpendicular to the
main surface of the glass substrate and which passes through a
center of the glass substrate of a disk shape. Within the section,
two reference points are determined within the recording area of
the main surface on an outline of the recording area and are
successively named ?R1 and ?R2 from the order near to the center of
the glass substrate. In addition, an additional point ?R3 is
determined on a line extended from the recording area outer
periphery in an outer direction and is remote from the recording
area outer periphery by a predetermined distance. The additional
point R3 defines a position of the glide outer periphery of the
glide area.
[0054] Next, the reference points R1 and R2 are connected to each
other by a line which is extended outwards of the glass substrate.
The extended line is drawn by a broken line in FIG. 2. Within an
area between R2 and R3, measurement is made about a distance
between the line R1R2 (or the extended line) and each point set on
the outline of the glass substrate. The ski-jump point (represented
by S) on the outline of the glass substrate is defined by a highest
point at which the distance is the highest in a positive direction.
The distance s at the ski-jump point is the ski-jump value.
[0055] On the other hand, the roll-off point is defined by a point
R which corresponds to R3 and which is placed on the outline of the
glass substrate while a distance r between point R and the straight
line R1R2 (or the extened line) is representative of the roll-off
value.
[0056] As shown in FIG. 3, it happens that the ski-jump value s
slightly takes a negative value. In this case, the ski-jump
specifies the surface down state. As shown in FIG. 4, the roll-off
value r also often takes a positive value, which specifies a
surface rise state of the glass substrate. Moreover, the ski-jump
value s may become equal to the roll-off value r, as shown in FIG.
4.
[0057] The reference points R1 and R2 and the point R3 may be
optionally selected with reference to a size of the glass
substrate. For example, when the glass substrate has an outside
diameter of 2.5 inches, 3.0 inches, and 3.5 inches, the point R3
may be determined at a position which is placed at 1 mm from the
outer peripheral side end on an inside of the glass substrate. In
the case of the glass substrate of 2.5 inches (65 mm in diameter),
the reference points R1 and R2 and the roll-off point R3 may be
determined, for example, at the positions of 23 mm, 27 mm, and 32.5
mm from the center of the glass substrate, respectively. The
roll-off point R3 in the above-mentioned example is determined on
the outer peripheral side end.
[0058] When the ski-jump value exceeds the range of .+-.0.35 .mu.m,
the magnetic disk can not accomplish stable floating and gives rise
to head crashes. This make it difficult to install the magnetic
recording medium within a magnetic disk drive.
[0059] The roll-off value over the range of .+-.0.35 .mu.m also
deteriorates floating stability of the magnetic head and gives rise
to head crashes.
[0060] Preferably, each of the ski-jump value and the roll-off
value falls within a range of .+-.0.20 .mu.m and more preferably,
within a range of .+-.0.10 .mu.m.
[0061] According to a twelfth aspect of this invention, the glass
substrate after chemical reinforcement has a compressive stress
layer within a surface layer which is caused by the chemical
reinforcement and which has a depth between 3 and 100 .mu.m and a
compressive stress of 1-15 kg/mm.sup.2,
[0062] Moreover, the glass substrate after chemical reinforcement
also has a tensile stress not greater than 4.5 kg/mm.sup.2 within
an inside of the glass substrate.
[0063] The depth of the compressive stress layer between 3 and 100
.mu.m makes it possible to manufacture an information recording
medium glass substrate which has preferable mechanical strength.
The depth less than 3 .mu.m weakens the mechanical strength of the
glass substrate (durability against defects and characteristic
withstanding breakage). When the depth of the compressive stress
layer exceeds 100 .mu.m, the profile variation component becomes
large when the chemical reinforcement is performed. Preferably, the
depth of the falls within a range between 40 and 80 .mu.m and more
preferably, within a range between 50 and 70 .mu.m.
[0064] Second, the compressive stress caused in the surface layer
of the glass substrate by the chemical reinforcement is selected
between 1 and 15 kg/mm.sup.2 while the tensile stress caused within
the glass substrate is not greater than 4.5 kg/mm.sup.2. This
serves to improve the strength of the glass substrate and the
durability against breakage based on aging. The compressive stress
less than 1 kg/mm.sup.2 undesirably weakens the strength of the
glass substrate (deterioration of the durability against defects
and the characteristics withstanding breakage) while the
compressive stress over 15 kg/mm.sup.2 enlarges the profile
variation components and makes it difficult to control the outer
edge profile.
[0065] The tensile stress over 4.5 kg/mm.sup.2 also enlarges the
profile variation components and make the control of the outer edge
profile difficult.
[0066] At any rate, the above-mentioned merits are more excellent
by setting the depth of the compressive stress layer, the
compressive stress, and the tensile stress into optimum values.
These are true of the inner peripheral side end.
[0067] According to a thirteenth aspect of this invention, a method
of manufacturing an information recording medium from the glass
substrate comprises the step of depositing a recording layer on the
main surface of the glass substrate. The information recording
medium thus manufactured has the glass substrate flat on the outer
edge profile and a wide recording area. In such an information
recording medium, the glass substrate has a flat inner edge profile
also and can avoid breakage. In any event, the information
recording medium can be appropriately mounted onto a magnetic
memory device.
[0068] According to a fourteenth aspect of this invention, an
information recording medium manufactured from the glass substrate
comprises a magnetic layer over the main surface. The information
recording medium has a high recording density because the glass
substrate has a flat outer edge profile and can widen a recording
area. The glass substrate which has the flat inner edge profile can
avoid breakage. In any event, the information recording medium can
be appropriately mounted onto a magnetic memory device.
[0069] According to a fifteenth aspect of this invention, the
information recording medium is available for a magnetic recording
medium of a LUL drive type which can realize an extremely low
floating operation of the magnetic head. Therefore, this invention
is very effective when it is applied to the LUL drive type magnetic
recording medium.
BRIEF DESCRIPTION OF THE DRAWING
[0070] FIG. 1 is a sectional view for use in describing a polished
glass substrate which has an outer edge profile put in a surface
down state;
[0071] FIG. 2 is a sectional view for use in describing an edge
profile in detail;
[0072] FIG. 3 is a sectional view for use in exemplifying a
ski-jump and a roll-off at an edge portion of a glass
substrate;
[0073] FIG. 4 is a sectional view for use in exemplifying another
ski-jump and another roll-off at an edge portion of a glass
substrate;
[0074] FIG. 5A is a sectional view of an edge profile of a glass
substrate prior to a chemical treatment;
[0075] FIG. 5B is a sectional view of an edge profile of a chemical
reinforced glass substrate after the chemical treatment;
[0076] FIG. 6 is a flow chart of a method of manufacturing a
chemical reinforced glass substrate according to a preferred
embodiment of this invention;
[0077] FIG. 7 is a table shows measured results for finding
reinforcement relationships with regard to 3.5 inch glass
substrates;
[0078] FIG. 8 is a table shows measured results for finding
reinforcement relationships with regard to 2.5 inch glass
substrates;
[0079] FIG. 9 is a table shows measured results for finding
polishing relationships; and
[0080] FIG. 10 is a graph shows a part of the measured results of
FIG. 9.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0081] Referring to FIGS. 5A and 5B, description will be at first
directed to a glass substrate and a chemical reinforced glass
substrate, respectively, for a better understanding of this
invention.
[0082] FIG. 5A shows an outer edge portion of a glass substrate 10
prior to chemical reinforcement. The glass substrate 10 prior to
chemical reinforcement may be simply called a glass substrate. The
illustrated edge portion is assumed to have an ideal edge profile
or shape. The glass substrate 10 has a main surface 11, an outer
peripheral surface 12, and a chamfer 13 between the main surface 11
and the side surface 12.
[0083] When the glass substrate 10 is immersed in a chemical
reinforcement solution (not shown), specific ions in the surfaces
of the glass substrate 10 are replaced with other ions which are
larger than the specific ions in ionic radii. As a result, each
surface of the glass substrate 10 slightly expands as shown by
arrows in FIG. 5A. Consequently, the glass substrate 10 is treated
or processed into a chemical reinforced glass substrate 10' as
illustrated in FIG. 5B.
[0084] As shown In FIG. 5B, it has been confirmed that a swell or a
bump 14 is formed between the main surface 11' and the chamfer 13'.
When the chemical reinforced glass substrate 10' is used for a
magnetic disk of a hard disk drive, a magnetic head of the hard
disk drive flies over the bump 14. As a result, the flight of the
magnetic head becomes unstable. Moreover, it is hard to fly the
magnetic head at a low height because the magnetic head clashes
with the magnetic disk. In addition, the ski-jump portion 14 limits
a flat area of the main surface 11'. The flat area is used for a
recording area of the magnetic disk.
[0085] Additionally, though another bump portion (not shown) is
formed between the outer peripheral surface 12' and the chamfer
13', it is unrelated to the flight of the magnetic head and the
recording area of the magnetic disk. Therefore, explanation of the
bump portion between the outer peripheral surface 12' and the
chamfer 13' will be omitted hereinafter.
[0086] According to Applicants' experimental studies of the
chemical reinforcement for the glass substrate, it has been found
out that the bump portion of the outer edge portion of the chemical
reinforced glass substrate could be controlled by changing chemical
reinforcement conditions. In addition, the applicants have found
that changing polishing conditions could control the outer edge
profile of the glass substrate having a chamfer. Taking this into
consideration, the applicants have completed a method according to
this invention related to the chemical reinforced glass substrate
on the basis of the above-mentioned facts.
[0087] Furthermore, the applicants have found out that the flight
of the magnetic head became stable and could becomes lower without
clash with the magnetic disk including the chemical reinforced
glass substrate when the bump portion is appropriately controlled
within a desirable size. Then the applicants have completed another
method according to this invention related to the magnetic disk
having the chemical reinforced glass substrate on the basis of the
findings.
[0088] Referring to FIG. 6, the description will proceed to a
method of manufacturing a chemical reinforced glass substrate
according to a preferred embodiment of this invention.
[0089] At the step S201 of FIG. 6, a plurality of glass substrates
are provided to be polished under various polishing conditions.
Each of the glass substrates has a disk shape and a center hole.
Namely, each of the glass substrates has an outer edge portion and
an inner edge portion. Hereinafter, though the description is
mainly made about the outer edge portion, the inner edge portion
can be also processed in a similar manner. Generally, the glass
substrate has a main surface, an outer peripheral surface, and a
chamfer between the main surface and outer peripheral surface. The
main surfaces of the glass substrates are polished under the
various polishing conditions to be changed to polished glass
substrates with polished edge profiles (i.e. smooth or undeformed
edge profiles). Polishing relationships between the polishing
conditions and the polished edge profiles are found prior to
chemical reinforcement.
[0090] At the step S202, the polished glass substrates (or other
polished glass substrates) are provided to be chemically reinforced
under various reinforcement conditions. The polished glass
substrates are chemically reinforced under the various
reinforcement conditions to be chemically reinforced to obtain
chemical reinforced glass substrates having reinforced edge
profiles (i.e. deformed edge profiles). Treatment relationships
between the treatment conditions and the treated edge profiles are
found.
[0091] At the step S203, to obtain a chemical reinforced glass
substrate having a desirable edge profile, a combination of one of
the polished edge profiles and one set of reinforcement conditions
is decided or selected on the basis of the reinforcement
relationships found at the step S202.
[0092] At the step S204, another glass substrate is provided and
polished on the basis of the polishing relationships found at the
step S201. As a result, a polished glass substrate is obtained
which has the decided edge profile decided at the step S203.
[0093] At the step S205, the polished glass substrate is chemically
reinforced under the condition of the set decided at the step S203.
Ideally, as a result, the polished glass substrate is rendered into
the chemical reinforced glass substrate having the desirable edge
profile.
[0094] Thus, the chemical reinforced glass substrate having the
desirable edge profile is obtained. For mass production, the steps
S203-S205 are repeated or the steps 204 and 205 may be repeated
once the desirable edge profile is determined at the step 203.
[0095] Then, the chemical reinforced glass substrate is sent to a
next process. At the step S206, at least a recording layer is
deposited on the main surface of the chemical reinforced glass
substrate to form a magnetic disk. The recording layer including a
magnetic layer.
[0096] Finally, at the step S207, the magnetic disk is assembled
into a hard disk drive.
[0097] According to the above-mentioned method, it is readily
understood that deformed portions, namely, the bump 14 (FIG. 2)
caused by the chemical reinforcement at the edge portions can be
controlled by changing the reinforcement conditions. This is
because the reinforcement relationships between the deformed
portions (especially, in a direction of thickness) and the
reinforcement conditions are previously found. The deformed
portions have the edge profiles in the direction of thickness.
[0098] Herein, the chemical reinforcement is for strengthening or
reinforcing the glass substrate. As already described before, the
chemical reinforcement enhances mechanical strength and durability
of the glass substrate. As the chemical reinforcement, an ion
exchange method and a de-alkalization method are known. In the ion
exchange method, specific ions included in surfaces of the glass
substrate are replaced with other ions in a chemical reinforcement
solution. Because the other ions are larger than the specific ions
in ionic radii, the surfaces of the glass substrate expand. As a
result, the edge portion tends to swell.
[0099] On the other hand, in the de-alkalization method, alkali
ions are removed from the surfaces of the glass substrate.
Consequently, the edge portion tends to become small. The
deformation at the inner edge portion is almost equal to 80-90
percent of that at the outer edge portion.
[0100] Moreover, according to the method, the reinforced edge
profile can be strictly controlled by selecting the polished glass
substrate. This is because the deformation caused by the chemical
reinforcement can be adjusted by polishing the glass substrate on
the basis of the reinforcement relationships and polishing
relationships.
[0101] In addition, according to the above mentioned method, a
desirable polished edge profile can be easily and precisely
obtained by selecting the polishing conditions. This is because the
polishing relationships are previously found and detected.
[0102] The desirable polished edge profile is, for example, as
shown in FIG. 3. That is, the outer edge portion has a surface down
without a surface rise. Such an edge profile is suitable for
offsetting deformation caused by the chemical treatment. The edge
profile shown in FIG. 3 is easily and precisely obtained by using
soft polisher having hardness of 60-80 (Asker-C) with a surface
pressure 40-150 g/cm.sup.2 at the main surface of the glass
substrate. When the hardness of the polisher becomes hard and other
polishing conditions are fixed, the edge portion becomes lower.
Similarly, when a polishing rotation speed becomes fast with other
polishing conditions kept constant, the edge portion becomes lower.
When the polishing pressure becomes large, the edge portion becomes
higher.
[0103] The hardness of the polisher can readily changed by
exchanging the polisher for another one. The hardness of the
polisher can be finely changed by the exchange. The control of the
polishing by the exchange of the hardness of the polisher can be
precisely performed in a wide range.
[0104] On the other hand, when the reinforcement conditions are
selected so that the deformation is smaller and the edge profile of
the polished glass substrate is flat, the deformation is
considerably suppressed. If the deformation is small, the edge
profile is easy to control. Consequently, it is readily possible to
manufacture large number of the chemical reinforced glass
substrates having even quality.
[0105] When a compressive stress layer caused by the chemical
treatment has a depth of 3-100 .mu.m, the chemical reinforced glass
substrate has necessary strength and the deformation at the outer
edge portion is suppressed. When the compressive stress layer has
the depth smaller than 3 .mu.m, the chemical reinforced glass
substrate can not withstand friction and is easily broken. When the
compressive stress layer has the depth larger than 100 .mu.m, the
deformation is large and hard to control. A desirable depth of the
compressive stress layer falls within a range of 40 .mu.m to 80
.mu.m and a more desirable depth falls within a range of 50 .mu.m
to 70 .mu.m.
[0106] Moreover, when the compressive stress layer has a
compressive stress 1-15 kg/mm.sup.2 and a tensile stress caused by
the compressive stress layer in the glass substrate except for the
compressive stress layer is under 4.5 kg/mm.sup.2, the glass
substrate is improved in the strength and the durability.
[0107] When the compressive stress is lower than 1 kg/mm.sup.2, the
glass substrate cannot withstand friction and is easily broken.
When the compressive stress is larger than 15 kg/mm.sup.2, the
deformation is large and hard to control the edge profile. When the
tensile stress is larger than 4.5 kg/mm.sup.2, the deformation is
large and hard to control the edge profile.
[0108] The depth of the compressive stress layer, the compressive
stress, and the tensile stress may be adjusted to improve the
strength and the durability of the glass substrate and to simplify
the control of the edge profile. For example, it is desirable that
the depth of the compressive stress layer is 40-80 .mu.m, the
compressive stress is 3-14 kg/mm.sup.2, and the tensile stress
layer is under 2.5 kg/mm.sup.2.
[0109] The reinforcement conditions include reinforcement or
treatment temperature, reinforcement or treatment time, a
combination of fused salts, a mixed ration of the fused salts, and
so on. The treatment temperature and the treatment time are easy to
change and effective in mass production of the glass substrate.
Namely, it is easy to suppress the deformation of the edge portion
within a predetermined range by suitably selecting the treatment
temperature and the treatment time. For example, the treatment
temperature is 280-400.degree. C. and the treatment is 0.5-5 hours.
If the treatment temperature is lower than 280.degree. C., it is
lower than the fusion points of the fused salts. If the treatment
temperature is higher than 400.degree. C., the treatment time must
be shortened and must be strictly controlled. On the other hand,
when the treatment time is shorter than 0.5 hours, it must be
strictly controlled and an operation is hard to be performed. When
the treatment time is longer than 5 hours, productivity is
decreased. The treatment temperature and the treatment time must be
changed according to components of the glass substrate and
components of the chemical reinforcement treatment solution.
Accordingly, the treatment temperature and the treatment time for
suppressing the deformation cannot be generalized. However, an
desirable example is cited soon. It is desirable that the treatment
temperature is 320-380.degree. C. (more desirably, 340-360.degree.
C.) and the treatment time is 1-4 hours.
[0110] As already described in conjunction with FIG. 4, the
deformation on the edge portion can be specified by the edge
profile that can be represented by the ski-jump and the
roll-off.
[0111] Referring FIGS. 7 through 10, description will be made about
examples of this invention, taking the above into account.
EXAMPLE 1
[0112] In a first example, the reinforcement relationships are
measured. The measurement is performed about the chemical
reinforcement conditions (i.e. the chemical reinforcement
temperature and the chemical reinforcement time), variations on the
basis of the deformation (i.e. variations of the outside diameter
and the inside diameter), a thickness (or depth) of the compression
stress layer, the compressive stress, the tensile stress, and
transverse rupture strength.
[0113] Glass substrates prior to chemical reinforcement (simply
called glass substrates) are prepared for the measurement. Samples
1-1 to 1-7 of FIG. 7 have 3.5 inches (i.e. 95 mm) in diameter while
samples 2-1 to 2-8 of FIG. 8 have 2.5 inches (i.e. 65 mm) in
diameter. These glass substrates are polished and substantially
have flat main surfaces. Under the circumstances, measurement is
made about both of the ski-jump value s and the roll-off value r of
each glass substrate which are defined in conjunction with FIG. 4
and which are about zero.
[0114] The roll-off point R is decided (see FIG. 4) at a position
placed inside by 1 mm from the outer peripheral surface while the
reference point R2 is decided at a position remote by 5.5 mm from
the outer peripheral surface in connection with each glass
substrate. In each of the 3.5 inch sample glass substrates, the
point R3 is located at a position remote by 46.5 mm from the center
and the reference point R2 is located at a position remote by 42 mm
from the center.
[0115] In each of the 2.5 inch sample glass substrates, the point
R3 is located at a position distant by 31.5 mm from the center and
the point R2 is located at a position remote by 27 mm from the
center.
[0116] A height of the outer edge portion is successively measured
along the outline of the outer edge portion by a surface roughness
measuring apparatus (SURFTEST SV-624 manufactured by Mitutoyo Co.).
The height of the outer edge portion of the chemical reinforced
glass substrate is different from the that of the glass substrate
prior to chemical reinforcement. Herein, the highest point and its
value of the edge profile between the points R2 and R3 is defined
as the ski-jump point S and the ski-jump value s, respectively, as
mentioned before, and the ski-jump value s is determined at every
one of the chemical reinforced glass substrates.
[0117] The outside and the inside diameters are measured by a
micrometer. to obtain a first outside diameter prior to chemical
reinforcement and a second outside diameter of the chemical
reinforced glass substrate. The first outside diameter is different
from the second diameter. Thus, a variation between the first and
the second outside diameters is obtained. Similarly, measurement is
made about the inside diameters of the glass substrates prior to
chemical reinforcement and after chemical reinforcement to obtain
first and second inside diameters, respectively. As a result, the
first inside diameter is different from the second inside diameter.
Thus, a variation between the first and the second inside diameters
is obtained.
[0118] In the above-mentioned example, a mixture of potassium
nitrate (60 wt %) and sodium nitrate (40 wt %) is used as the
chemical reinforcement solution.
[0119] Results of the measurement are shown in FIGS. 7 and 8.
[0120] As easily understood from FIGS. 7 and 8, as the
reinforcement temperature becomes high, each variation of the
outside diameter, inside diameter, and the ski-jump value s becomes
large. Similarly, as the reinforcement time becomes long, each
variation of the outside diameter, inside diameter, and the
ski-jump value s becomes large. The transverse rupture strength
becomes also large as the treatment temperature and/or the
treatment time becomes high and/or long.
[0121] Taking the above into consideration, it is possible to
obtain the desirable edge profile of the chemical reinforced glass
substrate in the following manner. Namely, the chemical
reinforcement conditions are at first determined within a range
that satisfies mechanical and chemical durability required for the
glass substrate for the magnetic disk or the magnetic recording
medium. Thereafter, a ski-jump value depending upon the chemical
reinforcement conditions is predicted in accordance with a
correlation between the determined chemical reinforcement
conditions mentioned above and a variation of the ski-jump values.
Under the circumstances, the edge profile of the glass substrate
prior to chemical reinforcement is determined as the desirable edge
profile in consideration of both the lapping process and the
polishing process. Thus, the edge profile of the chemical
reinforced glass substrate can be strictly controlled.
[0122] Required transverse rupture strength of the glass substrate
for the magnetic disk of 3.5 inches falls within a range between 15
and 20 kgf. All of the samples 1-1 through 1-7 have the transverse
rupture strength falling within the above-mentioned range. From
this fact, it is concluded that the variation of the outer edge
profiles can be reduced or suppressed by performing the chemical
reinforcement under the chemical reinforcement conditions that the
reinforcement temperature and the time fall within the range
between 340 and 360.degree. C. and the range between 1.5 and 2
hours, respectively, and the variation of the ski-jump values is
small and falls within a range between 0 and 0.010 .mu.m. More
desirable conditions are specified by combinations of the
reinforcement temperature of 340.degree. C. and the reinforcement
time 1.5-2 hours.
[0123] On the other hand, the required transverse rupture strength
of the glass substrate for the magnetic disk of 2.5 inches is about
10-15 kgf. In this case, all of the samples 2-1 through 2-8 satisfy
the required transverse rupture strength. Then, the desirable
conditions which can suppress the variation are combinations of the
reinforcement temperature of 340-360.degree. C. and the
reinforcement time 0.6-2 hours.
[0124] From the above-mentioned results, conclusion may be made
about the facts that the preferable chemical reinforcement
conditions for satisfying the required mechanical strength with the
ski-jump value kept small are that the depth of the compressive
stress layer caused by the chemical reinforcement is present
between 40 and 80 .mu.m, the compressive stress is between 3 and 14
kg/mm.sup.2, and the tensile stress is not greater than 2.5
kg/mm.sup.2. The tensile stress is caused by the compression stress
layer in the chemical reinforced glass substrate except for the
compression stress layer.
EXAMPLE 2
[0125] In a second example, the polishing relationships are
measured. A plurality of polishers having different hardness is
prepared for measuring the roll-off value r. For each of polishers,
one hundred of the glass substrates unpolished are provided. Each
unpolished glass substrate has a flat surface and 3.5 inches in
diameter. In this event, an amount of each polisher and a polishing
pressure are kept constant. In each unpolished glass substrate, the
point R3 is decided at a position remote by 1 mm from the outer
peripheral side surface. Under the circumstances, the roll-off
value r at the point R3 is determined or measured which represents
an amount of deviation of the outline point R from the reference
line or surface.
[0126] Results of the measurement are shown in FIGS. 9 and 10. As
easily understood from FIGS. 9 and 10, when the hardness is smaller
than 60 (Asker-C), the roll-off value r is positive. With an
increase of the hardness, the roll-off value r becomes low.
[0127] As mentioned before, it is readily understood that the
ski-jump value s becomes positive by chemical reinforcement when
the glass substrate is subject to the chemical reinforcement.
Taking this into account, it is necessary to put the edge profile
of the glass substrate prior to the chemical reinforcement (namely,
the glass substrate after the polishing process) into the surface
down state in relation to the main surface of the above-mentioned
glass substrate in order to keep the edge profile of the chemical
reinforced glass substrate in a flat or excellent state.
Accordingly, the polisher must have the hardness over 60 (Asker-C).
Desirable hardness of the polisher is 60-80 (Asker-C). More
desirable hardness of the polisher is between 66 and 80 (Asker-C)
because the mean value of the roll-off values r is negative.
EXAMPLE 3
[0128] In the example 3, a chemical reinforced glass substrate is
manufactured and a magnetic disk is manufactured by the use of the
chemical reinforced glass substrate.
[0129] (1) ROUGH LAPPING PROCESS
[0130] At first, melted glass (e.g. aluminosilicate glass) is
pressed by an upper mold, a lower mold, and a body mold to form a
glass substrate having 96.0 mm in diameter and 1.8 mm in thickness.
The aluminosilicate glass comprises, as main components, silicon
dioxide (SiO.sub.2:58-75 wt %), aluminum oxide
(Al.sub.2O.sub.3:5-23 wt %), lithium oxide (Li.sub.2O: 3-10 wt %),
and sodium oxide (Na.sub.2O:4-13 wt %). For example, the
aluminosilicate glass includes SiO.sub.2 of 63.5 wt %,
Als.sub.2O.sub.3 of 14.2 wt %, Li.sub.2O of 5.4 wt % Na.sub.2O of
10.4 wt %, ZrO.sub.2 (zirconium dioxide) of 6.0 wt %,
Sb.sub.2O.sub.3 (diantimony trioxide) of 0.4wt %, and
As.sub.2O.sub.3 (diarsenic trioxide) of 0.1 wt %.
[0131] The glass substrate may be obtained by grinding or cutting a
sheet glass with a grinder. The sheet glass is formed by, for
example, a down flow method or a float method.
[0132] Next, the glass substrate is lapped by a lapping machine.
Namely, the glass substrate is mounted on a carrier of the lapping
machine. Then, both sides (upper and lower main surfaces) are
lapped by the use of abrasive grains having a particle size of
#400. The abrasive grains are, for example, aluminum oxide. In this
process, the glass substrate is loaded with 100 kg. Thus, the
substrate is changed into a roughly lapped glass substrate having
profile irregularity of 0-1 .mu.m and surface roughness of 6 .mu.m
in Rmax (based on JIS B 0601).
[0133] (2) SHAPING PROCESS
[0134] An opening is formed at the center of the roughly lapped
glass substrate by a cylindrical whetstone and an inner peripheral
surface is exposed. Moreover, an outer peripheral surface of the
roughly lapped glass substrate is ground so that the outside
diameter becomes 95 mm. In addition, chamfers are formed between
each main surface and the inner peripheral surface and between each
main surface and the outer peripheral surface. The inner peripheral
surface, the outer peripheral surface, and chamfers have surface
roughness 4 .mu.m in Rmax. Thus, the roughly lapped glass substrate
is rendered into a shaped glass substrate.
[0135] (3) MIRROR FINISHING PROCESS FOR EDGES
[0136] While the shaped glass substrate is rotated, the inner
peripheral surface, the outer peripheral surface, and the chamfers
are brushed with slurry of cerium dioxide abrasive grains. Thus,
mirror finish for the inner peripheral surface, the outer side
surface, and the chamfers is completed. The inner peripheral
surface has surface roughness of 0.17 .mu.m in Rmax and 0.02 L m in
Ra. The chamfers of the inner edge portion have surface roughness
of 0.60 IL m in Rmax and 0.08 .mu.m in Ra. The outer peripheral
surface has the same surface roughness as the inner peripheral
surface has. The chamfers of the outer edge portion have surface
roughness of 0.77 .mu.m in Rmax and 0.10 .mu.m in Ra. The surface
roughness is measured by a measurement apparatus of Tencor P2
(manufactured by KLA-Tenkor Co.)
[0137] Then the mirror finished glass substrate are washed with
water.
[0138] (4) LAPPING PROCESS
[0139] The mirror finished glass substrate is lapped by the lapping
machine with abrasive grains having a particle size of #1000. By
this process, the mirror finished glass substrate changes into a
smooth lapped glass substrate having flatness of 3 .mu.m and
surface roughness of about 2.0 .mu.m in Rmax and 0.2 .mu.m in Ra.
The surface roughness is measured by an AFM (interatomic force
microscope).
[0140] Then, the smooth lapped glass substrate is soaked in neutral
detergent liquid and water in order and washed.
[0141] (5) POLISHING PROCESS
[0142] The smooth lapped glass substrate is polished by polishing
machine to remove flaws and warps that cannot be removed by the
above-mentioned lapping process. This process is performed on the
basis of the results of the examples 1 and 2. For example, the
ski-jump value s increases by 0.004 .mu.m when the chemical
reinforcement treatment is performed at 340.degree. C. for 2 hours.
In this case, if the polishing is performed so that the ski-jump
value s is about 0 .mu.m and the roll-off value r is about -0.004
.mu.m, the edge profile becomes almost flat. Namely, the polishing
conditions that the ski-jump value s is about 0 .mu.m and the
roll-off value r is about -0.004 .mu.m are selected. Additionally,
the points 2 and 3 correspond to those of Examples 1 and 2.
[0143] The selected polishing conditions are enumerated below.
[0144] Polishing Fluid: cerium dioxide (mean particle diameter=1.0
.mu.m) (free abrasive grains+water),
[0145] Polisher: Soft Polisher (hardness of 68 (Asker-C)),
[0146] Load: 200 kg (surface pressure: 66 g/cm.sup.2),
[0147] Polishing Time: 80 minutes,
[0148] Removing thickness: 50 .mu.m,
[0149] Rotation Speed of Upper Table: 20 rpm,
[0150] Rotation Speed of Lower Table: 26 rpm,
[0151] Revolution (orbital motion) Speed of Carrier: 3 rpm, and
[0152] Rotation Speed of Carrier: 3 rpm.
[0153] After the polishing under the above mentioned conditions is
performed, the polished glass substrate is successively soaked in
neutral detergent liquid, first pure water (demineralized water),
second pure water, first isopropyl alcohol, and second isopropyl
alcohol (steam and drying) in order.
[0154] The ski-jump value s and the roll-off value r of the
polished glass substrate are measured by the surface roughness
measuring apparatus (SURFTEST SV-624 manufactured by Mitutoyo Co.).
The ski-jump value s is equal to +0.002 .mu.m while the roll-off
value r is equal to -0.005 .mu.m. It can be recognized that the
edge portion practically has a surface down without a surface
rise.
[0155] (6) CHEMICAL REINFORCEMENT TREATMENT PROCESS
[0156] The polished glass substrate is heated to 300.degree. C. and
soaked in chemical reinforcement solution heated to 340.degree. C.
for 2 hours. The chemical reinforcement solution is a mixture of
potassium nitrate (60%) and sodium nitrate (40%).
[0157] Next, the chemical reinforced glass substrate is soaked in
water of 20.degree. C. for 10 minutes to cool it quickly. In this
event, the chemical reinforced glass substrate is broken if it has
minute cracks on the surfaces. That is, this process enables
elimination of a defective article.
[0158] Then, the chemical reinforced glass substrate is soaked in
sulfuric acid having concentration of 10 wt %, neutral detergent
liquid, first pure water, second pure water, and isopropyl alcohol
in order to wash it.
[0159] The ski-jump value s and the roll-off value r of the
chemical reinforced glass substrate are measured. The ski-jump
value s and the roll-off value r are equal to +0.002 .mu.m and
+0.005, respectively. This means that the surface of the chemical
reinforced glass surface between the points R2 and R3 falls within
a range of -0.005 .mu.m and +0.005 .mu.m from the reference
surface. That is, the chemical reinforced glass surface has a
nearly flat surface at the edge portion.
[0160] Moreover, the chemical reinforced glass substrate has the
compression stress layer of 79.8 .mu.m thick, the compressive
stress of 13.8 kg/mm.sup.2, and the tensile stress of 2.0
kg/mm.sup.2. The values are equal to those of the sample 1-2 of
FIG. 7.
[0161] Furthermore, the chemical reinforced glass substrate has the
surface roughness Ra of 0.51 nm and Rmax of 5.20 nm on the main
surface, waviness Wa of 0.43 nm at the main surface, and
mircowaviness Wa (Ra) of 0.50 measured at a microscopic area of the
edge portion. Additionally, the surface roughness Ra and Rmax are
measured by the interatomic force microscope. The waviness Wa is
measured by a multifunction disk interferometer (e.g. OPTIFLAT
manufactured by PHASE SHIFT TECHNOLOGY Co.). The measurement of the
waviness Wa is performed about an area (about 115400 pixels) of
20.3 mm to 45.0 mm remote from the center in a radius direction.
The microwaviness Wa (Ra) is measured by a multifunction surface
analyzing machine (e.g. MicroXAM manufactured by PHASE SHIFT
TECHNOLOGY Co.). The measurement of the waviness Wa (Ra) is
performed to a square area (about 250000 pixels) of about 500 .mu.m
in length and about 600 .mu.m in width.
[0162] The vaviness Wa and the microwaviness Wa (Ra) are provided
as follows.
[0163] The microwaviness Wa (Ra) and the waviness Wa are calculated
by scanning a predetermined area of the substrate surface by the
use of white light (wavelength: about 550 nm) and etc., by
synthesizing reflection light from the substrate surface with
reflection light from a reference surface, and by using
interference fringes appearing at a synthesized point.
[0164] The microwaviness Wa (Ra) on the micro-area has a waviness
period of about 2 .mu.m to 4 mm and is represented by an average of
an absolute value of a deviation from a center line to a measured
curve. Herein, the center line is defined by a straight line such
that, when a parallel straight line is drawn which is parallel to
an average line of the measured curve, an area surrounded by the
parallel straight line and the measured curve becomes equal to each
other on both sides of the parallel straight line. The
microwaviness Wa (Ra) and the waviness Wa may be measured by any
other light than white light.
[0165] A plurality of measuring points is decided on the measuring
curve. Each of the measuring points has a measuring point value.
The measuring point value is a distance from a standard straight
line which is suitably decided. The microwaviness Wa (Ra) (or
waviness Wa) is given by: 1 Wa ( Ra ) ( or Wa ) = 1 N i = 1 N | Xi
- X _ |
[0166] where N is the number of the measuring points, Xi is the
measuring point value at the i-th measuring point, and {overscore
(X)} is the mean of all of the measuring point values X.
[0167] It is preferable that the microwaviness Wa (Ra) and the
waviness Wa have the microwaviness period from 2 .mu.m to 4 mm, as
mentioned before, and a waviness period from 300 .mu.m to 5 mm,
respectively.
[0168] (7) MANUFACTURING PROCESS FOR MAGNETIC DISK
[0169] A nickel-aluminum seed layer, a chrome-molybdenum
underlayer, a cobalt-chrome-platinum-tantalum magnetic layer, and
carbon hydride protective layer are deposited in order on the both
sides (upper and lower main surfaces) of the chemical reinforced
glass substrate by a sputtering apparatus of an inline type. A
perfluoropolyether lubricant layer is formed each carbon hydride
protective layer by the use of a dip method. Thus, a magnetic disk
is completed.
[0170] The magnetic disk is mounted on a hard disk drive of the LUL
method. In the hard disk drive, a magnetic head can fly stably
without clash with the magnetic disk. Because the surface roughness
Ra and Rmax and the waviness Wa and the microwaviness Wa (Ra) are
all small, a touch-down-height is preferably not greater than 10
nm. Thus, the recording area can be expanded. ?
COMPARATIVE EXAMPLE 1
[0171] A chemical reinforced glass substrate is manufactured by a
manner similar to the example 3. However, the polishing process is
performed so that the roll-off value r becomes positive by
adjusting especially the outer edge profile. In addition, the
chemical treatment process is performed at 380.degree. C. for 4
hours.
[0172] Though the chemical reinforced glass substrate has the
surface roughness Ra and Rmax that are similar to those of the
example 3, the ski-jump value s and the roll-off value r are equal
to +0.421 .mu.m and +0.420 .mu.m, respectively. When the chemical
reinforced glass substrate is used for a magnetic disk of a hard
disk drive, a magnetic head clashes with the magnetic disk.
[0173] The chemical reinforced glass substrate has a compression
stress layer of 140.8 .mu.m in depth, a compressive stress of 20.5
kg/mm.sup.2 in compression stress layer, a tensile stress 2.7
kg/mm.sup.2 in the chemical reinforced glass substrate. These
values are equal to those of the samples 1-7 of FIG. 7. Moreover,
the chemical reinforced glass substrate has the waviness Wa of 1.85
nm and the microwaviness Wa (Ra) of 0.93 nm.
[0174] As understood from comparison of Example 3 with the
comparative example 1, it is to be noted that the chemical
reinforcement conditions are decided in Example 3 in relation the
required mechanical strength and durability and the polishing
conditions are decided so as to cancel the deformation caused by
the chemical reinforcement. In addition, the chemical reinforced
glass substrate is manufactured in Example 3 on the basis of the
decided polishing condition and the decided chemical reinforcement
conditions. As a result, it is proved that the magnetic head does
not clash with the magnetic disk that uses the chemical reinforced
glass substrate (Example 3) and that is driven by the hard disk
drive adopting the LUL method. However, when the polishing
conditions are not considered like in the comparative example, the
chemical reinforced glass substrate can not be used for the
magnetic disk driven by the LUL method.
[0175] Moreover, it is understood from the comparison of the
example 3 with the comparative example 1 that the ski-jump value s
and the waviness Wa and the microwaviness Wa (Ra) become large when
the deformation becomes large (the reinforcement time becomes long
and/or reinforcement temperature becomes high).
EXAMPLE 4
[0176] A chemical reinforced glass substrate is manufactured by a
manner similar to the example 3. However, the polished glass
substrate is soaked in hydosilicofluoric acid after the polishing
process. The chemical reinforced glass substrate is used for a
magnetic disk of a hard disk drive adopting the CSS
(contact-start-stop) method.
[0177] The chemical reinforced glass substrate has the ski-jump
value s and the roll-off value r that are the same as those of the
Example 3. The surface roughnesses Rmax and Ra of the chemical
reinforced glass substrate are influenced by the hydosilicofluoric
acid and equal to 7.8 nm and 0.83 nm, respectively.
[0178] In the hard disk drive, a magnetic head can fly stably
without clash with the magnetic disk using the chemical reinforced
glass substrate. Moreover, it is possible to widen the recording
area by using the chemical reinforced glass substrate according to
Example 4.
EXAMPLE 5
[0179] A chemical reinforced glass substrate is manufactured by a
manner similar to the example 3. Herein, it is to be noted that the
polishing conditions are selected so that the ski-jump value s and
the roll-off value r become about 0 .mu.m and about -0.035 .mu.m,
respectively, by expecting or considering the ski-jump value s and
the roll-off value r which are obtained during the chemical
reinforcement performed under the chemical reinforcement conditions
(380.degree. C. and 4 hours) mentioned in conjunction with Example
1. The chemical reinforcement is performed under the chemical
reinforcement conditions (380.degree. C. and 4 hours) after the
polishing process is performed under the above-mentioned polishing
conditions.
[0180] Practically, the polishing process is performed by the use
of a polisher having hardness of 80 (Asker-C). The load, the
polishing time, and other conditions are appropriately
adjusted.
[0181] The chemical reinforced glass substrate has the ski-jump
value s of +0.03 .mu.m and the roll-off value r of -0.04 .mu.m both
of which are worse than those of the example 3. This is because the
deformation caused by the chemical reinforcement is too large to be
controlled by the polishing.
[0182] Though the ski-jump value s and the roll-off value r are
worse than those of the example 3, a magnetic head can fly stably
without clash with a surface of a magnetic disk using the chemical
reinforced glass substrate in a LUL type hard disk drive. In
addition, the recording area can be widened in Example 5 also.
[0183] Plural chemical reinforced glass substrates were
manufactured by the processes of the example 3 and the example 5.
It was confirmed that the chemical reinforced glass substrates
manufactured by the example 3 had a small variation in the edge
profile in comparison with the chemical reinforcement glass
substrates according to the example 5 when measurement was made
about the edge profile. Consequently, the chemical reinforcement
glass substrates according to the example 3 had the edge profiles
which were uniform and excellent as compared with the example
5.
[0184] While this invention has thus for been described in
conjunction with the preferred embodiment thereof, it will readily
be possible for those skilled in the art to put this invention into
practice in various other manners.
[0185] For example, this invention may be applied to not only the
outer edge portion but also the inner edge portion.
[0186] Moreover, the treatment conditions may include not only the
treatment temperature and the treatment time but also the kind of
the chemical reinforcement treatment solution. For example, the
mixture ratio of the potassium nitrate and sodium nitrate may be
changed. Moreover, the potassium nitrate or the sodium nitrate may
be used as the chemical reinforcement treatment solution.
Furthermore, sodium sulfate (Na.sub.2SO.sub.4), potassium sulfate
(K.sub.2SO.sub.4), sodium bromide (NaBr), potassium bromide (KBr),
KNO.sub.2, and NaNO.sub.2 may be selectively used as the chemical
reinforcement solution.
[0187] Furthermore, the chemical reinforcement may be a
de-alkalization process. In this case, it is desirable that the
polishing is performed so that the ski-jump value s and the
roll-off value r become positive.
[0188] Still furthermore, other polishing may be performed to the
main surface of the chemical reinforced glass substrate. In this
case, the treatment conditions are adjusted so that the desirable
edge profile is obtained after the other polishing.
[0189] In addition, the chemical reinforced glass substrate may be
used for an optical disk, a magneto-optical disk, and the like.
* * * * *