U.S. patent application number 11/782994 was filed with the patent office on 2008-02-07 for radial tilt reduced media.
This patent application is currently assigned to GENERAL ELECTRIC COMPANY. Invention is credited to Azar Alizadeth, Wit Bushko, Irene Dris, Thomas Feist, Grant Hay.
Application Number | 20080032086 11/782994 |
Document ID | / |
Family ID | 21820125 |
Filed Date | 2008-02-07 |
United States Patent
Application |
20080032086 |
Kind Code |
A1 |
Hay; Grant ; et al. |
February 7, 2008 |
Radial Tilt Reduced Media
Abstract
In one embodiment, a storage media can comprise: a plastic
substrate having a substrate composition, an optical layer having
an optical layer composition different from the substrate
composition, wherein the optical layer is a spin coated or
injection molded; and a reflective layer disposed between the
optical layer and the substrate. The storage media has a radial
deviation over time of less than or equal to 1.15 degrees at a
radius of 55 mm when exposed to a cycle at 25.degree. C. of 50%
relative humidity--90% relative humidity--50% relative humidity. In
one embodiment, a method for making a data storage media,
comprises: disposing a reflective layer on a plastic substrate,
wherein the plastic layer comprises a thermoplastic, spin coating
an optical layer onto the plastic substrate, wherein the optical
layer comprises a thermoset, and disposing a protective layer on
the substrate.
Inventors: |
Hay; Grant; (US) ;
Alizadeth; Azar; (US) ; Bushko; Wit; (US)
; Dris; Irene; (US) ; Feist; Thomas;
(US) |
Correspondence
Address: |
CANTOR COLBURN LLP - SABIC (NORYL)
55 GRIFFIN ROAD SOUTH
BLOOMFIELD
CT
06002
US
|
Assignee: |
GENERAL ELECTRIC COMPANY
1 River Road
Schenectady
NY
12345
|
Family ID: |
21820125 |
Appl. No.: |
11/782994 |
Filed: |
July 25, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10024349 |
Dec 18, 2001 |
7300690 |
|
|
11782994 |
Jul 25, 2007 |
|
|
|
60316126 |
Aug 30, 2001 |
|
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60279887 |
Mar 29, 2001 |
|
|
|
Current U.S.
Class: |
428/64.4 ;
369/284; G9B/7.159; G9B/7.172 |
Current CPC
Class: |
G11B 7/2535 20130101;
G11B 7/24056 20130101; Y10T 428/2495 20150115; G11B 7/2542
20130101; G11B 2007/24312 20130101; G11B 2007/2432 20130101; G11B
2007/25711 20130101; G11B 2007/25715 20130101; G11B 2007/24314
20130101; Y10T 428/26 20150115; G11B 7/258 20130101; G11B 7/248
20130101; G11B 7/252 20130101; G11B 7/2578 20130101; Y10T 428/21
20150115; G11B 2007/25713 20130101; G11B 2007/2571 20130101; G11B
7/2585 20130101; G11B 7/2533 20130101; G11B 7/2595 20130101; G11B
7/2534 20130101; G11B 2007/2431 20130101; G11B 7/2536 20130101;
G11B 7/256 20130101; G11B 2007/24316 20130101; G11B 2007/25708
20130101; G11B 7/2433 20130101; G11B 7/2472 20130101; G11B
2007/24308 20130101; G11B 7/259 20130101 |
Class at
Publication: |
428/064.4 ;
369/284 |
International
Class: |
B32B 3/02 20060101
B32B003/02; G11B 7/24 20060101 G11B007/24 |
Claims
1. A storage media, comprising: a plastic substrate having a
substrate composition; an optical layer having an optical layer
composition different from the substrate composition, wherein the
optical layer is a spin coated or injection molded; and a
reflective layer disposed between the optical layer and the
substrate; wherein the storage media has a radial deviation over
time of less than or equal to 1.15 degrees at a radius of 55 mm
when exposed to a cycle at 25.degree. C. of 50% relative
humidity--90% relative humidity--50% relative humidity, and wherein
the storage media is capable of storing greater than or equal to
about 20 GB of data.
2. The storage media of claim 1, wherein the substrate comprises
polyarylene ether.
3. The storage media of claim 1, wherein the substrate comprises
polycarbonate.
4. The storage media of claim 1, wherein the substrate has a side
comprising surface features, and wherein the reflective layer is
disposed on the side of the substrate comprising the surface
features.
5. The storage media of claim 1, further comprising a data storage
layer disposed between the reflective layer and the optical layer,
wherein the data storage layer comprises a material selected from
the group consisting of an organic dye and an inorganic phase
change compound.
6. The storage media of claim 1, wherein the optical layer
thickness is about 0.2 micrometers to about 120 micrometers.
7. The storage media of claim 1, wherein the optical layer is a
spin coated layer and the optical layer composition comprises
acrylic polymers.
8. The storage media of claim 1, further comprising data
layers.
9. The storage media of claim 1, further comprising a data layer
comprising an organic dye.
10. The storage media of claim 1, further comprising a data layer
comprising a phase change material.
11. A storage media, comprising: a plastic substrate comprising
polycarbonate; an optical layer having an optical layer composition
different from the substrate composition, wherein the optical layer
is a spin coated; a reflective layer disposed between the optical
layer and the substrate; and a protective layer; wherein the
storage media has a radial deviation over time of less than or
equal to 1.15 degrees at a radius of 55 mm when exposed to a cycle
at 25.degree. C. of 50% relative humidity--90% relative
humidity--50% relative humidity.
12. The storage media of claim 11, further comprising data
layers.
13. The storage media of claim 11, further comprising a data layer
comprising an organic dye.
14. The storage media of claim 11, further comprising a data layer
comprising a phase change material.
15. A storage media, comprising: a plastic substrate comprising
polyarylene ether and polystyrene; an optical layer having an
optical layer composition different from the substrate composition,
wherein the optical layer is a spin coated; a reflective layer
disposed between the optical layer and the substrate; and a
protective layer; wherein the storage media has a radial deviation
over time of less than or equal to 1.15 degrees at a radius of 55
mm when exposed to a cycle at 25.degree. C. of 50% relative
humidity--90% relative humidity--50% relative humidity.
16. The storage media of claim 15, further comprising data
layers.
17. The storage media of claim 15, further comprising a data layer
comprising an organic dye.
18. The storage media of claim 15, further comprising a data layer
comprising a phase change material.
19. A method for making a data storage media, comprising: disposing
a reflective layer on a plastic substrate, wherein the plastic
layer comprises a thermoplastic; spin coating an optical layer onto
the plastic substrate, wherein the optical layer comprises a
thermoset; and disposing a protective layer on the substrate;
wherein the storage media has a radial deviation over time of less
than or equal to 1.15 degrees at a radius of 55 mm when exposed to
a cycle at 25.degree. C. of 50% relative humidity--90% relative
humidity--50% relative humidity.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation application of U.S.
patent application Ser. No. 10/024,349 filed Dec. 18, 2001, and
claims the benefit of U.S. Provisional Application Ser. No.
60/316,126 filed Aug. 30, 2001, and U.S. Provisional Application
Ser. No. 60/279,887 filed Mar. 29, 2001, which are incorporated
herein by reference.
BACKGROUND OF THE INVENTION
[0002] Optical, magnetic, and magneto-optic media are primary
sources of high performance storage technology that enables high
storage capacity coupled with a reasonable price per megabyte of
storage. Areal density, typically expressed as billions of bits per
square inch of disk surface area (Gbits per square inch
(Gbits/in.sup.2)), is equivalent to the linear density (bits of
information per inch of track) multiplied by the track density in
tracks per inch. Improved areal density has been one of the key
factors in the price reduction per megabyte, and further increases
in areal density continue to be demanded by the industry.
[0003] In the area of optical storage, advances focus on access
time, system volume, and competitive costing. Increasing areal
density is being addressed by focusing on the diffraction limits of
optics (using near-field optics), investigating three dimensional
storage, investigating potential holographic recording methods and
other techniques.
[0004] Conventional polymeric data storage media has been employed
in areas such as compact disks (CD-ROM) and recordable or
re-writable compact disks (e.g., CD-RW), and similar relatively low
areal density devices, e.g., less than about 1 Gbits/in.sup.2,
which are typically optical devices requiring the employment of a
good optical quality substrate having low birefringence.
[0005] Referring to FIG. 1, a low areal density system 1 is
illustrated having a read device 3 and a recordable or re-writable
storage media 5. The storage media 5 comprises conventional layers,
including a data layer 7, dielectric layers 9 and 9', reflective
layer 11, and protective layer 13. During operation of the system
1, a laser 15 produced by the read device 3 is incident upon the
optically clear substrate 17. The laser passes through the
substrate 17, and through the dielectric layer 9, the data layer 7
and a second dielectric layer 9'. The laser 15 then reflects off
the reflective layer 11, back through the dielectric layer 9', the
data layer 7, the dielectric layer 9, and the substrate 17 and is
read by the read device 3.
[0006] Conventionally, the above issues associated with employing
first surface, including near field, techniques have been addressed
by utilizing metal, e.g., aluminum, and glass substrates. These
substrates are formed into a disk and the desired layers are
disposed upon the substrate using various techniques, such as
sputtering. Possible layers include reflective layers, dielectric
layers, data storage layers, and protective layers. Once the
desired magnetic layers have been added, the disk may be
partitioned into radial and tangential sectors through magnetic
read/write techniques. Sector structure may also be added through
physical or chemical techniques, e.g. etching; however, this must
occur prior to the deposition of the magnetic layers.
[0007] As is evident from the fast pace of the industry, the demand
for greater storage capacities at lower prices, the desire to have
re-writable disks, and the numerous techniques being investigated,
further advances in the technology are constantly desired and
sought.
BRIEF SUMMARY OF THE INVENTION
[0008] Disclosed herein is a storage media and methods for making
the same.
[0009] In one embodiment, a storage media can comprise: a plastic
substrate having a substrate composition, an optical layer having
an optical layer composition different from the substrate
composition, wherein the optical layer is a spin coated or
injection molded, and a reflective layer disposed between the
optical layer and the substrate. The storage media has a radial
deviation over time of less than or equal to 1.15 degrees at a
radius of 55 mm when exposed to a cycle at 25.degree. C. of 50%
relative humidity--90% relative humidity--50% relative
humidity.
[0010] In one embodiment, a method for making a data storage media,
comprises: disposing a reflective layer on a plastic substrate,
wherein the plastic layer comprises a thermoplastic, spin coating
an optical layer onto the plastic substrate, wherein the optical
layer comprises a thermoset, and disposing a protective layer on
the substrate. The storage media has a radial deviation over time
of less than or equal to 1.15 degrees at a radius of 55 mm when
exposed to a cycle at 25.degree. C. of 50% relative humidity--90%
relative humidity--50% relative humidity.
[0011] The above described and other features are exemplified by
the following figures and detailed description.
DESCRIPTION OF THE DRAWINGS
[0012] Refer now to the drawings wherein like elements are numbered
alike.
[0013] FIG. 1 is a cross-sectional illustration of a prior art low
areal density system employing an optically clear substrate.
[0014] FIG. 2 is a cross-sectional illustration of a read/write
system using one possible embodiment of a storage media with a
light incident on the data storage layer without passing through
the substrate, i.e., a first surface storage media.
[0015] FIG. 3 is a graphical illustration of curvature change
induced by a humidity set from 25.degree. C. and 50% relative
humidity (rh) to 25.degree. C. and 90% rh for two matched systems
with different bonding schemes (i.e., PSA and ultraviolet (UV)
curable adhesive).
[0016] FIG. 4 is a graphical illustration of dynamic curvature of a
substrate during desorption and adsorption.
[0017] FIG. 5 is a graphical illustration of the effect of
thickness on structure curvature range during absorption and
subsequent desorption.
[0018] FIG. 6 is a curvature ratio contour map at a diffusion ratio
of 1.5.
[0019] FIG. 7 is a curvature ratio contour map at a diffusion ratio
of 1.0.
[0020] FIG. 8 is a graphical illustration of curvature change
induced by a humidity set from 25.degree. C. and 50% relative
humidity (rh) to 25.degree. C. and 90% rh for a mismatched system
(e.g., same substrate as FIG. 3 with a different composition film
than substrate).
DETAILED DESCRIPTION OF THE INVENTION
[0021] In this specification and in the Claims that follow,
reference will be made to a number of terms that shall be defined.
For example, the singular forms "a", "an" and "the" include plural
referents unless the context clearly dictates otherwise. "Optional"
or "optionally" mean that the subsequently described event or
circumstance may or may not occur, and that the description
includes instances where the event or circumstance occurs and
instances where it does not. "Tilt" as used herein refers to the
degrees by which a material bends on a horizontal axis and is
typically measured as the vertical deviation at the outer radius of
the storage medium. The "maximum radial tilt range" as used herein
is the disk curvature during absorption and subsequent desorption
of water and is hence twice the radial tilt specification as
usually specified by the developers in the industry.
[0022] High-density re-recordable optical media formats are being
developed to replace existing VHS tape recorders for consumer
entertainment consumption. The goal is to produce a removable media
format approaching or even exceeding 20 gigabytes (GB) in storage
and having data transfer rates about 35 megabytes per second (MBps)
and approaching or even exceeding 100 MBps. Thinner read-through
mediums are required for these types of media with as thin as 80
micrometers currently are being developed. Most of the formats are
asymmetric in structure with the above mentioned thin readthrough
medium being supported by a thicker substrate. Curvature in the
readthrough medium is induced by changes in the surrounding
environment. Humidity and temperature changes will induce curvature
into the total asymmetric structure and hence the readthrough
medium. The curvature induces spherical aberrations that lead to
poor performance of the optical drive. Disclosed below are ranges
of material parameters and material parameter ratios for the
substrate and film that lead to improved dimensional stability of
the total structure. This technology minimizes curvature variation
in the readthrough medium induced by environmental humidity
changes.
[0023] Optical media format developers are currently moving towards
re-recordable optical media formats that will replace the consumer
VHS market. In these formats, the areal density is increased by:
adding extra information layers, decreasing laser wavelength,
and/or increasing numerical aperture.
[0024] Both increasing the numerical aperture and decreasing the
wavelength has a detrimental impact on the magnitude of the optical
aberrations and hence read noise/errors. These aberrations are
considerably sensitive to tilt of the optical medium. Materials
utilized for manufacture of optical media generally adsorb water
that in turn causes a volume change of the material better known as
swell. Any asymmetry in the water absorption/swell will incur a
bending moment within the media. Asymmetry in the water absorption
in optical disks is caused by the need for impermeable metallic and
inorganic layers adjacent to the information layer. The bending
moment causes curvature in the media and hence the readthrough
medium.
[0025] Disc curvature is determined by measuring a laser beam
deflection off the disc surface. The angle of inclination from a
flat horizontal disc is compared to the angle of inclination of the
disc of interest; the difference in the angles is referred to as
disc tilt. From geometrical considerations, the laser beam
deflection is equal to twice the disc tilt and is commonly referred
to as radial deviation. The tilt range is defined as the maximum
range in the tilt measured on a disc at a specific disc radius on
both absorption and subsequent desorption of water.
[0026] To attain high areal densities in optical storage media the
laser beam spot diameter (i.e., the diameter of the laser light
beam that strikes the media) needs to be decreased. In the pure
diffraction limited case the beam diameter is related to the
numerical aperture and wavelength in the following way: Beam
.times. .times. Spot .times. .times. Diameter .varies. [ .lamda. NA
] ##EQU1## where .lamda.=wavelength
[0027] NA=numerical aperture
[0028] In the optical media formats, laser wavelength and/or
numerical aperture may be altered to achieve the desired density
increase. The inherent problem with moving to lower wavelengths and
higher numerical apertures is the retrospective noise tolerance
collapse; e.g., tilt tolerance, which is related to the above in
the following way: Tilt .times. .times. Margin .varies. [ .lamda. d
. NA 3 ] ##EQU2## where d=thickness of readthrough medium
[0029] In media formats being developed the thickness of the
optical medium is being reduced, relative to current formats, to
increase the disc tilt tolerance. This optical layer or optical
film is then bonded to a thicker substrate for mechanical stability
and final use in an optical drive. There are other instances where
more than one of these optical layers is bonded together to obtain
a multilayer format similar to the DVD format. The film is the
optical medium and the information layer is on the injection-molded
substrate. These thin optical mediums can be thought of as optical
films.
[0030] Referring to FIG. 2, for example, data retrieval comprises
contacting the data storage layer(s) 102 (e.g., surface features,
phase change material, or organic dye) with a light beam 110 (white
light, laser light, or other) incident on such layer(s). A
reflective layer (not shown), disposed between the data storage
layer 102 and substrate 108, reflects the light back through the
data storage layer 102, adhesive layer 106, optical layer 114, and
to the read/write device 112 where the data is retrieved.
[0031] Assuming that the structure is an elastic plate that extends
infinitely in the in-plane directions and that the material
properties are not a function of thickness then the isotropic
strain due to water absorption is given by the below expression: _
.function. ( t ) = .beta. l .times. .intg. l / 2 - l / 2 .times. c
.function. ( z , t ) .times. .times. d z ##EQU3## where:
.epsilon.=strain
[0032] z=thickness direction
[0033] l=thickness
[0034] c=concentration
[0035] .beta.=swell coefficient where .epsilon.(t)=.beta.c(z,t)
[0036] The curvature of the substrate is related to the first
moment of the water distribution in the disk as shown below:
.kappa. .function. ( t ) = 12 .times. .times. .beta. l .times.
.intg. l / 2 - l / 2 .times. c .function. ( z , t ) .times. z
.times. .times. d z ##EQU4##
[0037] For multiple layer systems the above integrals are
summations of integrals across the specific layer thicknesses
including material parameters for each layer. The concentration of
water as a function of thickness and time c(z,t) is calculated from
a solution to the diffusion equation. In the case of a two layer
system the time dependant curvature change induced by a set
humidity change is given by the below general expression: .kappa.
.function. ( t ) - .kappa. .function. ( 0 ) = 6 .times.
.DELTA..PHI..beta. 1 .times. s 1 l 1 .times. f .function. ( t ;
.rho. , .gamma. , .delta. , q ) ##EQU5## where t=time
[0038] .DELTA..PHI.=change in relative humidity .rho. = l 2 l 2 =
ratio .times. .times. of .times. .times. layer .times. .times.
thickness , .gamma. = E 2 1 - v 2 E 1 1 - v 1 = ratio .times.
.times. of .times. .times. mechanical .times. .times. stiffness ,
.times. .delta. = .beta. 2 .times. s 2 .beta. 1 .times. s 1 = 2
.infin. 1 .infin. = ratio .times. .times. of .times. .times. water
.times. .times. strains , q = D 2 D 1 = ratio .times. .times. of
.times. .times. diffusivities ##EQU6## subscript .times. .times. "
2 " .times. .times. refers .times. .times. to .times. .times. the
.times. .times. film .times. .times. and .times. .times. subscript
.times. .times. " 1 " .times. .times. refers .times. .times. to
.times. .times. the .times. .times. substrate ##EQU6.2##
[0039] If all of the material parameters are supplied, the two
layer structure dynamic curvature change can be determined. FIG. 3
exhibits validation with the above mathematical description and
experimental data on: a matched optical film/substrate
polycarbonate system (e.g., a system comprising a polycarbonate
optical film and a polycarbonate substrate) that under went a step
in environmental humidity. Meanwhile, FIG. 4 exhibits further
validation on three different systems with various bonding layers
and both matched and mismatched systems.
[0040] Optical media manufacturers specify upper and lower
specification limits on structure curvature. This requires that the
substrate curvature falls within these specification limits at all
times during any environmental humidity change. The curvature range
(FIG. 5) during an absorption and subsequent desorption should be
minimized. There are three ways to reduce the curvature range: (1)
reduce the swell/strain of the substrate on absorption of water,
(2) select a film that minimizes the curvature dynamic of the
structure, and (3) change the film thickness. An explanation of how
to reduce the curvature or tilt range of a single layer substrate
or a dual layer system by selecting materials with reduced
swell/strain on absorption of water is set forth in commonly
assigned U.S. patent Ser. No. 09/943,767.
[0041] The maximum in the dynamic curvature on absorption and
desorption of water for a single substrate is given by the
following relation: .kappa. .function. ( t ) - .kappa. .function. (
0 ) = 6 .times. .DELTA..PHI..beta. 1 .times. s 1 l 1 ##EQU7## This
shows that reducing the solubility and swell coefficient of the
material can minimize the pure substrate tilt. Consequently, an
optical film is chosen to minimize system curvature. The curvature
can be converted into a tilt and the maximum tilt range experienced
by the structure on sorption and subsequent desorption is given by
the below expression: Max .times. .times. Radial .times. .times.
Tilt .times. .times. Range .times. .times. ( rad ) = .kappa.
.times. .times. r = 1.92 .times. .times. .DELTA. .times. .times. rh
.times. .times. .beta. .times. .times. sr t = 1.92 .times. .times.
.DELTA. .times. .times. rh .times. .times. .times. .times. r t
##EQU8## where: .kappa. is the curvature (length.sup.-1);
[0042] .DELTA.rh is step relative humidity;
[0043] .beta. is strain/mass fraction water at a given temperature
(T);
[0044] s is mass fraction water at relative humidity (rh)=1 and
T;
[0045] .epsilon.=.beta.s is water strain at rh=1 and T;
[0046] t is substrate thickness; and
[0047] r is radius of interest.
The "maximum radial tilt range" as used herein is the disk
curvature during absorption and subsequent desorption of water and
is hence twice the radial tilt specification as usually specified
by the developers in the industry.
[0048] FIG. 4 outlines the dynamic curvature in absorption and
subsequently in desorption normalized by 6 .times.
.DELTA..PHI..beta. 1 .times. s 1 l 1 ##EQU9## hence arriving at a
value of one and minus one at the maximum and minimum respectively
for a substrate without film. By adding a film comprising a
different chemical composition than the substrate, the asymmetry
can be reduced, hence reducing the value of the maximum tilt.
[0049] As the thickness of the optical film (matching film and
mismatched film) is increased, the maximum tilt will also reduce to
the point where there is no tilt for a film of the same thickness
as the substrate (e.g., DVD, DVR (digital video recordings), and
the like). FIG. 5 exhibits the behavior of the curvature range with
the thickness ratio where the film and substrate are the same
material. It was disclosed that by having a matched film that is
approximately 30% of the thickness of the substrate, the tilt of
the coated substrate can be reduced to 5% of that of a substrate
without a film. Additionally at an optical film (layer) thickness
of about 20% of the substrate thickness the tilt reduction is down
to 10% of the substrate tilt. This curvature dependence on
thickness is stronger than the tilt tolerance reduction caused by
aberrations dependence on thickness. Consequently, by having an
optical film thickness of greater than or equal to about 18% of the
substrate thickness, the tilt can be reduced by greater than or
equal to about 80%, with a reduction in tilt of greater than or
equal to about 90% obtained with an optical film thickness of
greater than or equal to about 20% of the substrate thickness.
Preferably, the optical film thickness is about 20% to about 40% of
the substrate thickness, with a thickness of about 25% to about 35%
of the substrate thickness preferred.
[0050] If the thickness of the film is fixed then material
properties of the film can be optimized to reduce the tilt range.
By mismatching the material of the film to that of the substrate,
the tilt range can also be reduced. For example, Table 1 gives
ratios of parameters for a disc system (100 micrometer (.mu.m) film
and 1.1 millimeter (mm) substrate) that lead to a curvature range
that is 11% that of the substrate curvature range. This is a four
fold improvement over a matched film/substrate system for a given
thickness. TABLE-US-00001 TABLE 1 Ratios Value Thickness .rho. 0.09
Stiffness .gamma. 3 Swell .delta. 1.01 Diffusivity q 0.15 Minimum
Range 0.11
[0051] For a given film thickness the curvature is more sensitive
to the strain ratio and stiffness ratio and less sensitive to the
diffusion ratio. FIG. 6 is a contour plot outlining the normalized
curvature range as a function of the stiffness ratio and
strain/swell ratio. This contour plot is for a specific diffusion
ratio of 1.5. The optimum curvature range is obtained for the case
where the stiffness ratio is related to the strain ratio in a
hyperbolic way. This hyperbolic functionality is consistent for any
diffusion ratio as is supported by FIG. 7, which illustrates
contour plot for a specific diffusion ratio of 1.0. Preferably, the
stiffness ratio to swell ratio is within the inner contour by area
200.
[0052] Based upon the above information, the optical film can be a
plastic having the desired stiffness ratio (.gamma.) (Youngs
modulus(megapascals)/(1--Poisson ratio)), swell ratio (.delta.)
(percentage growth of the material at equilibrium), and diffusivity
ratio (q), wherein all ratios refer to the ratio of the optical
film to the substrate. The desired amounts of these parameters are
dependent upon the thickness of the optical film. The ultimate
desire is to reduce the tilt, e.g., curvature, to a radial
deviation range of less than or equal to about 1.15 degrees at a
radius of 55 mm, with less than or equal to about 1.0 degrees at a
radius of 55 mm preferred, less than or equal to about 0.80 degrees
at a radius of 55 mm more preferred, less than or equal to about
0.70 degrees at a radius of 55 mm even more preferred, less than or
equal to about 0.50 degrees at a radius of 55 mm yet even more
preferred, and less than or equal to about 0.25 degrees at a radius
of 55 mm desired. Generally, the stiffness ratio can be greater
than or equal to about 0.5, with a stiffness ratio of greater than
or equal to about 0.70 preferred, and a stiffness ratio of greater
than or equal to about 1.25 more preferred. Preferably, the
stiffness ratio is less than or equal to about 5, with a stiffness
ratio of less than or equal to about 3 preferred, and a stiffness
ratio of less than or equal to about 2.5 even more preferred. The
stiffness of the optical film and substrate is measured in tensile
deformation at room temperature using an Instron testing machine.
With respect to the swell ratio, it can be greater than or equal to
about 0.50, with greater than or equal to about 0.75 preferred, and
greater than or equal to about 1.0 more preferred. Preferably, the
swell ratio is less than or equal to about 5, with less than or
equal to about 3 more preferred, and less than or equal to about
2.5 even more preferred. The swell strain is measured using a
Thermomechanical analyzer from TA instruments. The diffusivity
ratio can be greater than or equal to about 0.05, with greater than
or equal to about 0.10 preferred. Preferably the diffusivity is
less than or equal to about 2.0, with less than or equal to about
1.0 preferred.
[0053] With respect to thickness, the optical film can have a
thickness of about 0.2 micrometers to about 0.6 mm. Within the film
thickness range, less than or equal to about 0.6 mm is preferred,
less than or equal to about 250 micrometers is more preferred, and
less than or equal to about 120 micrometers is even more preferred,
in some applications. Also preferred within this range is the
optical thickness of greater than or equal to about 0.2
micrometers, with greater than or equal to about 5 micrometers more
preferred, and greater than or equal to about 50 micrometers even
more preferred. In contrast, the substrate typically has a
thickness of greater than or equal to about 0.3 mm, with greater
than or equal to about 0.6 mm preferred, and greater than or equal
to about 1.1 mm more preferred. Also preferred is a substrate
thickness of less than or equal to about 2.5 mm, with less than or
equal to about 2.0 mm more preferred, and less than or equal to
about 1.5 mm even more preferred. Due to current equipment and due
to industry specifications, a substrate thickness of about 1.1 mm
is generally preferred. If decreased substrate thicknesses are
employed (e.g., less than about 1.2 mm), it is preferred to
maintain an optical film to substrate thickness ratio of less than
or equal to about 1, with a thickness ratio of less than or equal
to about 0.5 preferred, and less than or equal to about 0.1 more
preferred. Also preferred is a thickness ratio of greater than or
equal to about 0.001, with greater than or equal to about 0.005
more preferred, and greater than or equal to about 0.025 even more
preferred.
[0054] Possible optical film materials that can be any plastic that
exhibits appropriate properties, including thermoplastics,
thermosets, as well as homopolymers, copolymers, reaction products,
and combinations comprising at least one of the foregoing materials
including, but not limited to addition and condensation polymers.
Illustrative, non-limiting examples of thermoplastic polymers are
olefin-derived polymers such as polyethylene, polypropylene, and
their copolymers; chlorinated polyethylene, polyvinyl chloride,
polymethylpentane; ethylene-tetrafluoroethylene copolymers,
polyvinyl fluoride, polyvinylidene fluoride, polyvinylidene
chloride, polytetrafluoroethylene, ethylene-vinyl acetate
copolymers, polyvinyl acetate, diene-derived polymers such as
polybutadiene, polyisoprene, and their copolymers; polymers of
ethylenically unsaturated carboxylic acids and their functional
derivatives, including acrylic polymers such as poly(alkyl
acrylates), poly(alkyl methacrylates), polyacrylamides,
polyacrylonitrile and polyacrylic acid; alkenylaromatic polymers
such as polystyrene, poly-alpha-methylstyrene, hydrogenated
polystyrenes, syndiotactic and atactic polystyrenes, polycyclohexyl
ethylene, styrene-co-acrylonitrile, styrene-co-maleic anhydride,
polyvinyltoluene, and rubber-modified polystyrenes; polyamides such
as nylon-6, nylon-66, nylon-11, and nylon-12; polyacetals,
polyesters such as polyethylene terephthalate, polybutylene
terephthalate, and polycyclohexylmethylene terephthalate;
polycarbonates; polyestercarbonates; high heat polycarbonates,
polyethers such as polyarylene ethers especially polyphenylene
ethers derived from 2,6-dimethylphenol and copolymers with
2,3,6-trimethylphenol, polyethersulfones, polyetherethersulfones,
polyetherketones, polyetheretherketones, and polyetherimides;
polyarylene sulfides, polysulfones, and polysulfidesulfones; and
liquid crystalline polymers.
[0055] Non-limiting examples of thermosetting resins are epoxies,
phenolics, allcyds, polyesters, polyimides, polyurethanes, mineral
filled silicones, bis-maleimides, cyanate esters, multifunctional
allylic compounds such as diallylphthalate, acrylics, alkyds,
phenol-formaldehyde, novolacs, resoles, bismaleimides, PMR resins,
melamine-formaldehyde, urea-formaldehyde, benzocyclobutanes,
hydroxymethylfurans, and isocyanates benzocyclobutene resins, as
well as homopolymers, copolymers, reaction products, and
combinations comprising at least one of the foregoing thermosetting
resins. In one embodiment, the thermoset polymer further comprises
at least one thermoplastic polymer, such as, polyphenylene ether,
polyphenylene sulfide, polysulfone, polyetherimide, polyester, and
the like, as well as homopolymers, copolymers, reaction products,
and combinations comprising at least one of the foregoing
thermoplastic polymers. The thermoplastic polymer is typically
combined with a thermoset monomer mixture before curing of the
thermoset.
[0056] Both thermoplastic polyesters and thermoplastic elastomeric
polyesters can be employed. Illustrative, non-limiting examples of
thermoplastic polyesters include poly(ethylene terephthalate),
poly(1,4-butylene terephthalate), poly(1,3-propylene
terephthalate), poly(cyclohexanedimethanol terephthalate),
poly(cyclohexanedimethanol-co-ethylene terephthalate),
poly(ethylene naphthalate), poly(butylene naphthalate), and
polyarylates. Illustrative, non-limiting examples of thermoplastic
elastomeric polyesters (commonly known as TPE) include
polyetheresters such as poly(allcylene terephthalate)s
(particularly poly[ethylene terephthalate] and poly[butylene
terephthalate]) containing soft-block segments of poly(allcylene
oxide), particularly segments of poly(ethylene oxide) and
poly(butylene oxide); and polyesteramides such as those synthesized
by the condensation of an aromatic diisocyanate with dicarboxylic
acids and a carboxylic acid-terminated polyester or polyether
prepolymer.
[0057] Suitable polyarylates include, but are not limited to, the
polyphthalate esters of 2,2-bis(4-hydroxyphenyl)propane (commonly
known as bisphenol A), and polyesters consisting of structural
units of the formula I: ##STR1## wherein R.sup.16 is hydrogen or
C.sub.1-4 alkyl, optionally in combination with structural units of
the formula II: ##STR2## wherein R.sup.17 is a divalent C.sub.4-12
aliphatic, alicyclic or mixed aliphatic-alicyclic radical. The
latter polyesters may be prepared by the reaction of a
1,3-dihydroxybenzene moiety with at least one aromatic dicarboxylic
acid chloride under alkaline conditions. Structural units of
formula II contain a 1,3-dihydroxybenzene moiety which may be
substituted with halogen, usually chlorine or bromine, or
preferably with C.sub.1-4 alkyl; e.g., methyl, ethyl, isopropyl,
propyl, butyl. The alkyl groups are preferably primary or secondary
groups, with methyl being more preferred, and are most often
located in the ortho position to both oxygen atoms although other
positions are also contemplated. The most preferred moieties are
resorcinol moieties, in which R.sup.16 is hydrogen. The
1,3-dihydroxybenzene moieties are linked to aromatic dicarboxylic
acid moieties which may be monocyclic moieties, e.g., isophthalate
or terephthalate, or polycyclic moieties, e.g.,
naphthalenedicarboxylate.
[0058] In the optional soft block units of formula II, resorcinol
or alkylresorcinol moieties are present in ester-forming
combination with R.sup.17 which is a divalent C.sub.4-12 aliphatic,
alicyclic or mixed aliphatic-alicyclic radical.
[0059] Possible polycarbonates include those comprising structural
units of the formula III: ##STR3## wherein at least about 60
percent of the total number of R.sup.18 groups are aromatic organic
radicals and the balance thereof are aliphatic, alicyclic, or
aromatic radicals. Suitable R.sup.18 radicals include m-phenylene,
p-phenylene, 4,4'-biphenylene, 4,4'-bi(3,5-dimethyl)-phenylene,
2,2-bis(4-phenylene)propane,
6,6'-(3,3,3',3'-tetramethyl-1,1'-spirobi[1H-indane]),
1,1'-bis(4-phenylene)-3,3,5-trimethylcyclohexane, and similar
radicals such as those which correspond to the
dihydroxy-substituted aromatic hydrocarbons disclosed by name or
formula (generic or specific) in U.S. Pat. No. 4,217,438.
[0060] More preferably, R.sup.18 is an aromatic organic radical and
still more preferably a radical of the formula IV: ##STR4## wherein
each A.sup.1 and A.sup.2 is a monocyclic divalent aryl radical and
Y.sup.1 is a bridging radical in which one or two atoms separate
A.sup.1 and A.sup.2. For example, A.sup.1 and A.sup.2 typically
represent unsubstituted phenylene or substituted derivatives
thereof. The bridging radical Y.sup.1 is most often a hydrocarbon
group and particularly a saturated group such as methylene;
cyclohexylidene; 3,3,5-trimethylcyclohexylidene; or isopropylidene.
The most preferred polycarbonates are bisphenol A polycarbonates,
in which each of A.sup.1 and A.sup.2 is p-phenylene and Y.sup.1 is
isopropylidene. Suitable polycarbonates may be made using various
processes, including interfacial, solution, solid state, or melt
processes.
[0061] In one embodiment, the storage media comprises at least one
layer with at least one polycarbonate. In another embodiment, the
storage media comprises at least one layer with two different
polycarbonates. Homopolycarbonates derived from a single dihydroxy
compound monomer and copolycarbonates derived from more than one
dihydroxy compound monomer are encompassed.
[0062] In one embodiment, the substrate and/or at least one other
layer of the storage media comprise a polycarbonate or
copolycarbonate comprising structural units (V) or (VI): ##STR5##
where R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5, and R.sup.6 are,
independently chosen from C.sub.1-C.sub.6 alkyl and hydrogen;
R.sup.7 and R.sup.8 are, independently, C.sub.1-C.sub.6 alkyl,
phenyl, C.sub.1-C.sub.6 alkyl substituted phenyl, or hydrogen; m is
an integer of 0 to about 12; q is an integer of 0 to about 12; m+q
is an integer of about 4 to about 12; n is an integer of about 1 to
about 2; and p is an integer of about 1 to about 2.
[0063] Representative units of structure (V) include, but are not
limited, to residues of
1,1-bis(4-hydroxy-3-methylphenyl)cyclohexane (DMBPC);
1,1-bis(4-hydroxy-3-methylphenyl)cyclopentane;
1,1-bis(4-hydroxy-3-methylphenyl)cycloheptane;
1,1-bis(4-hydroxy-3-methylphenyl)-3,3,5-trimethylcyclohexane
(DMBPI); and mixtures comprising at least one of the foregoing
units.
[0064] Representative units of structure (VI) include, but are not
limited, to residues of 2,2-bis(4-hydroxy-3-methyl)propane (DMBPA);
and 4,4'-(1-phenylethylidene)bis(2-methylphenol) (DMbisAP).
[0065] In an even further embodiment, the substrate and/or at least
one other layer of the storage media can comprise polycarbonate or
copolycarbonate comprises structural units (VII): ##STR6## where
R.sup.9, R.sup.10, R.sup.13 and R.sup.14 are independently
C.sub.1-C.sub.6 alkyl, R.sup.11 and R.sup.12 are independently H or
C.sub.1-C.sub.5 alkyl, each R.sup.15 is independently selected from
H and C.sub.1-C.sub.3 alkyl and each n is independently selected
from 0, 1 and 2.
[0066] Representative units of structure (VII) include, but are not
limited to, 6,6'-dihydroxy-3,3,3',3'-tetramethyl spirobiindane
(SBI); 6,6'-dihydroxy-3,3,5,3',3',5'-hexamethyl spirobiindane;
6,6'-dihydroxy-3,3,5,7,3',3',5',7'-octamethylspirobiindane;
5,5'-diethyl-6,6'-dihydroxy 3,3,3',3'-tetramethylspirobiindane, and
mixtures comprising at least one of the foregoing units.
[0067] The polyphenylene ethers are polymers comprising a plurality
of structural units of the formula (VIII) ##STR7## wherein in each
of the units independently, each Q.sup.1 is independently halogen,
primary or secondary lower alkyl (i.e., alkyl containing up to 7
carbon atoms), phenyl, haloalkyl, aminoalkyl, hydrocarbonoxy, or
halohydrocarbonoxy wherein at least two carbon atoms separate the
halogen and oxygen atoms; and each Q.sup.2 is independently
hydrogen, halogen, primary or secondary lower alkyl, phenyl,
haloalkyl, hydrocarbonoxy or halohydrocarbonoxy as defined for
Q.sup.1. Most often, each Q.sup.1 is alkyl or phenyl, especially
C.sub.1-4 alkyl, and each Q.sup.2 is hydrogen.
[0068] Both homopolymer and copolymer polyphenylene ethers are can
be employed. Suitable copolymers include random copolymers
containing such units in combination with (for example)
2,3,6-trimethyl-1,4-phenylene ether units. Also included are
polyphenylene ethers containing moieties prepared by grafting onto
the polyphenylene ether in a known manner such materials as vinyl
monomers or polymers such as polystyrenes and elastomers, as well
as coupled polyphenylene ethers in which coupling agents such as
low molecular weight polycarbonates, quinones, heterocycles and
formals undergo reaction in known manner with the hydroxy groups of
two polyphenylene ether chains to produce a higher molecular weight
polymer, provided a substantial proportion of free OH groups
remains.
[0069] Particularly useful polyphenylene ethers for many purposes
are those that comprise molecules having at least one
aminoalkyl-containing end group. The aminoalkyl radical is
typically located in an ortho position to the hydroxy group.
Polymers containing such end groups may be obtained by
incorporating an appropriate primary or secondary monoamine such as
di-n-butylamine or dimethylamine as one of the constituents of the
oxidative coupling reaction mixture. Also frequently present are
4-hydroxybiphenyl end groups, typically obtained from reaction
mixtures in which a by-product diphenoquinone is present,
especially in a copper-halide-secondary or tertiary amine system. A
substantial proportion of the polymer molecules, typically
constituting as much as about 90% by weight of the polymer, may
contain at least one of the aminoalkyl-containing and
4-hydroxybiphenyl end groups.
[0070] It will be apparent that the contemplated polyphenylene
ethers include all those presently known, irrespective of
variations in structural units or ancillary chemical features,
including, but not limited to homopolymer and copolymer
thermoplastic polymers, and mixtures comprising at least one of the
foregoing polyphenylene ethers. Copolymers may include random,
block or graft type. Thus, for example, suitable polystyrenes
include homopolymers, such as amorphous polystyrene and
syndiotactic polystyrene, and copolymers containing these species.
The latter embraces high impact polystyrene (HIPS), a genus of
rubber-modified polystyrenes comprising blends and grafts wherein
the rubber is a polybutadiene or a rubbery copolymer of styrene in
a range between about 70% by weight and about 98% by weight and
diene monomer in a range between about 2% by weight and about 30%
by weight. Also included are ABS copolymers, which are typically
grafts of styrene and acrylonitrile on a previously formed diene
polymer backbone (e.g., polybutadiene or polyisoprene). Suitable
ABS copolymers may be produced by various methods.
[0071] In a preferred embodiment the optical film comprises
thermoplastic resins and the substrate comprises thermosetting
resins. It is also possible for the optical film to comprise
thermosetting resins while the substrate comprises thermoplastic
resins. Similarly it is possible for the optical film and the
substrate to comprise a mixture of thermoplastic and thermosetting
resins and wherein at least one element of the composition of the
optical film is different from that of the substrate.
[0072] The optical layer or film can be deposited by a variety of
techniques, including vapor deposition (e.g., plasma enhanced
chemical vapor deposition, and the like), coating (e.g.,
electrodeposition coating, meniscus coating, spray coating,
extrusion coating, spin coating, solution coating, and the like),
casting (e.g., extrusion casting, solution casting, and the like),
injection molding, film blowing, calendaring, and the like, as well
as combinations comprising at least one of the foregoing
techniques. Meanwhile, the substrate is typically manufactured by
an extrusion, molding (e.g., injection molding, extrusion molding,
compression molding, and the like), and the like, as well as
combinations comprising at least one of the foregoing
techniques.
[0073] Although the substrate is typically a polycarbonate
material, it is clearly understood that the substrate can also
comprise any plastic mentioned above in relation to the optical
film. For example, the substrate can comprise thermoplastics
wherein the thermoplastic is bisphenol A polycarbonate, copolyester
polycarbonate of bisphenol A and dodecanoic acid containing 7 mole
% of polyester and 93 mole % of bisphenol A polycarbonate, 39 mole
% of polyphenylene ether and 61 mole % polystyrene,
1,3-bis(4-hydroxyphenyl methane), 90 mole % bisphenol A and 10 mole
% disecbutyl bisphenol A, polycarbonate of tetramethyl
cyclobutanediol and high flow polycarbonate tetra xylyl
hydroquinone diphosphite, and the like, as well as mixtures
comprising at least one of the foregoing thermoplastics. Similarly,
the optical layer can comprise thermoplastics including 80 wt %
isophthalate terephthalate resorcinol-20 wt % polycarbonate,
styrene acrylonitrile, bisphenol A polycarbonate, copolyester
polycarbonate of bisphenol A and dodecanoic acid containing 7 mole
% of polyester and 93 mole % of bisphenol A polycarbonate, 39 mole
% of polyphenylene ether and 61 mole % polystyrene,
1,3-bis(4-hydroxyphenyl methane), 90 mole % bisphenol A and 10 mole
% disecbutyl bisphenol A, polycarbonate of tetramethyl
cyclobutanediol and high flow polycarbonate tetra xylyl
hydroquinone diphosphite, and the like, as well as reaction
products and mixtures comprising at least one of the foregoing
thermoplastics. Furthermore, the film for these high density
formats preferably has optical properties such as in-plane
retardations of less than or equal to about 10 nanometers (nm). The
films also have low thickness non-uniformity and surface roughness.
For a 100 micrometer film, thickness uniformity at length scales
longer than 2 centimeters (cm) is on the order of less than or
equal to about 2 micrometers and the surface roughness at the 1
millimeter (mm) length scale is on the order of less than or equal
to about 40 nm.
[0074] The substrate may further include energy absorption.
Dampening can be achieved through a variety of approaches such as
by addition of an energy absorbing component or through slip
mechanisms involving various fillers and reinforcing agents. Useful
materials that may improve the damping characteristics include
elastic materials with high damping capabilities (e.g., a damping
coefficient of greater than or equal to about 0.05), such as
vulcanized rubbers, acrylic rubbers, silicone rubbers, butadiene
rubbers, isobutylene rubbers, polyether rubbers,
isobutylene-isoprene copolymers and isocyanate rubber, nitrile
rubbers, chloroprene rubbers, chlorosulfonated polyethylene,
polysulfide rubbers and fluorine rubber, block copolymers including
polystyrene-polyisoprene copolymers such as described in U.S. Pat.
No. 4,987,194, thermoplastic elastomeric materials, including
polyurethanes, and combinations comprising at least one of the
foregoing, among others. Vibration-damping materials also include
resins in which large amounts of particles (such as ferrites,
metals, ceramics, and the like), flakes (such as of talc, mica and
the like), and various fibers (such as zinc oxide, wollastonite,
carbon fibers, glass fibers, and the like), and mixtures comprising
at least one of the foregoing, can be employed. Microfibers,
fibrils, nanotubes, and whiskers, foamed and honeycombed structures
may also be useful as are various combinations of the
foregoing.
[0075] Beside the optical layer, which is typically the top layer,
other layers which may be applied to the substrate may include one
or more data storage layer(s), lubricating layer(s), adhesive
layer(s), dielectric layer(s), reflective layer(s), insulating
layer(s), combinations comprising at least one of these layers, and
others. The data storage layer(s) may comprise any material capable
of storing retrievable data, such as an optical layer, magnetic
layer, or more preferably a magneto-optic layer, having a thickness
of less than or equal to about 600 .ANG., with a thickness of less
than or equal to about 300 .ANG. preferred. Possible data storage
layers include, but are not limited to, oxides (such as silicone
oxide), rare earth element--transition metal alloy, nickel, cobalt,
chromium, tantalum, platinum, terbium, gadolinium, iron, boron, as
well as alloys and combinations comprising at least one of the
foregoing, and others, such as organic dye (e.g., cyanine or
phthalocyanine type dyes), and inorganic phase change compounds
(e.g., TeSeSn or InAgSb). The data layer may comprise grooves,
channels, projections, depressions, ruts, lands, protrusions, pits,
etc. ("surface features"; see FIG. 2, data layer 102). Preferably,
the data layer has a coercivity of greater than or equal to about
1,500 oersted, with a coercivity of greater than or equal to about
3,000 oersted especially preferred.
[0076] The dielectric layer(s) which are often employed as heat
controllers, can typically have a thickness of up to or exceeding
about 1,000 .ANG. and as low as about 200 .ANG.. Possible
dielectric layers include nitrides (e.g., silicon nitride, aluminum
nitride, and others); oxides (e.g., aluminum oxide); carbides
(e.g., silicon carbide); and combinations comprising at least one
of the foregoing dielectric layers, among other materials
compatible within the environment and preferably not reactive with
the surrounding layers.
[0077] The reflective layer(s) should have a sufficient thickness
to reflect a sufficient amount of energy to enable data retrieval.
Typically the reflective layer(s) can have a thickness of up to and
sometimes exceeding about 700 .ANG., with a thickness of about 300
.ANG. to about 600 .ANG. generally preferred. Possible reflective
layers include any material capable of reflecting the particular
energy field, including metals (e.g., aluminum, silver, gold,
titanium, and alloys and mixtures comprising at least one of the
foregoing materials and others). The reflective layers may be
disposed on the substrate by various techniques such as sputtering,
chemical vapor deposition, electroplating and the like.
[0078] Optionally disposed between the optical layer and the data
storage layer, and/or between other layers, is an adhesive layer
that can, for example, adhere the optical film to the other layers
supported by the substrate. The adhesive layer can also be employed
to enhance the dampening of the disc, with the thickness and nature
of the adhesive determining the amount of dampening provided by the
layer. The adhesive layer, which can have a thickness of up to
about 50 micrometers (.mu.m) or so, with thicknesses of about 1
micrometer to about 30 micrometers preferred, can comprise rubber
based or elastomeric thermosets, flexible thermoplastics, and the
like. Typical adhesives are rubber-based or rubberlike materials,
such as natural rubber or silicone rubber or acrylic ester
polymers, and the like. Non-rigid polymeric adhesives such as those
based on rubber or acrylic polymers and the like have some of the
properties of elastomers, such as flexibility, creep resistance,
resilience, and elasticity, and do provide useful dampening to
enhance the quality of playback of the data storage disc. The
chemistry of non-rigid polymeric adhesives is diverse, and includes
polymers of the types of materials described herein as elastomers
and rubbers, as flexible thermoplastics, and as thermoplastic
elastomers. Suitable examples of such adhesives include
polyisoprene, styrene butadiene rubber, ethylene propylene rubber,
fluoro vinyl methyl siloxane, chlorinated isobutene-isoprene,
chloroprene, chlorinated polyethylene, chlorosulfonated
polyethylene, butyl acrylate, expanded polystyrene, expanded
polyethylene, expanded polypropylene, foamed polyurethane,
plasticized polyvinyl chloride, dimethyl silicone polymers, methyl
vinyl silicone, polyvinyl acetate, and the like, as well as
compositions comprising at least one of the foregoing adhesives.
This layer may also comprise any combination comprising at least
one of the above adhesives. Typically pressure sensitive adhesives
are preferred for use in data storage disc applications. The
adhesive layer may be added to the data storage disc by methods
such as vapor deposition, spin casting, solution deposition,
injection molding, extrusion molding, and the like.
[0079] In addition to the data storage layer(s), dielectric
layer(s), protective layer(s) and reflective layer(s), other layers
can be employed such as lubrication layer and others. Useful
lubricants include fluoro compounds, especially fluoro oils and
greases, and the like.
[0080] The storage media disclosed herein reduces tilt as compared
to a substrate without an optical layer and/or a substrate with a
matched optical layer (e.g., where the optical layer comprises the
same material as the substrate) by controlling the thickness and/or
mismatching the optical layer and substrate compositions. Some of
the advantages are illustrated in FIG. 8, which shows a substantial
reduction in radial deviation (i.e., a deviation of 0.50 degrees)
versus the matched system of FIG. 3 (e.g., a radial deviation of
1.26 degrees). Note, FIGS. 3 and 8 employ the same substrate with
different optical layers. In FIG. 3, numbers 1-3 relate to samples
comprising polycarbonate substrate and optical layer with a
pressure sensitive adhesive disposed therebetween, while samples
10, 20, 30, and 40 employ a polycarbonate substrate and optical
layer with a UV curable adhesive.
EXAMPLE 1
[0081] In this example (simulated) Bisphenol A Polycarbonate
(BPA-PC) was retained as the substrate material, while isophthalate
terephthalate resorcinol-polycarbonate (ITR-PC 80-20) blend,
styrene acrylonitrile (SAN 576) or BPA-PC was chosen as the optical
film. The optical film has a thickness of about 100 micrometers
while the substrate has a thickness of 1.1 millimeters giving a
film to substrate thickness ratio of 0.09.
[0082] Both the substrate and optical film stiffness were measured
in tensile deformation at room temperature using an Instron tensile
testing machine. The swell of a polymeric material as defined
herein is the percentage of volume growth of the totally dry
material when subjected to a 100% relative humidity environment at
a specific temperature. The swell is measured utilizing a TMA 2940
Thermomechanical Analyzer from TA instruments. A film is mounted
under a very low constant load and initially held in a dry
atmosphere. The length change is then measured upon absorption of
water when the material is exposed to 100% relative humidity. The
water strain or swell is taken to be the strain of the material
(length change divided by the original gauge length).
[0083] Table 2 below outlines the stiffness and swell ratio of the
film to substrate as well as the radial tilt range for the
different material combinations. It can be clearly seen that when
polymeric materials chosen for the optical film and the substrate
are different from each other, the radial tilt range is much
smaller than for the purely matched material system where BPA-PC
alone is used as material for the substrate and optical film
TABLE-US-00002 TABLE 2 Stiffness ratio Swell ratio (film to (film
to Radial Tilt Range Film Material substrate) substrate) (degrees)
ITR-PC 80-20 1.101 1.781 0.292 SAN 576 1.378 1.649 0.236 BPA-PC
1.000 1.000 0.560
[0084] Generally an optical film that is stiffer and has a greater
swell (water strain) than the substrate material will have better
performance when compared to a matched film/substrate system.
EXAMPLE 2
[0085] In this example BPA-PC is the polymeric material used for
the optical film and different polymeric materials were used as the
substrate as shown in Table 2. The optical film has a thickness of
about 100 micrometers while the substrate has a thickness of 1.1
millimeters giving a film to substrate thickness ratio of 0.09. The
substrate materials are listed as follows: copolyester
polycarbonate of Bisphenol A and dodecanoic acid containing 7 mole
% of polyester and 93 mole % of BPA-PC (RL-7553), 39 mole % of
polyphenylene ether and 61 mole % polystyrene (PPE/PS 101),
1,3-bis(4-hydroxyphenyl methane) (BHPM), 90 mole % bisphenol A and
10 mole % disecbutyl bisphenol A (BPA disecbutyl BPA),
polycarbonate of tetramethyl cyclobutanediol (TMCBD-PC) and blend
of BPA-polycarbonate with polycarbonate tetra xylyl hydroquinone
diphosphite (BPA-PC+1 wt % TXHQDR). TABLE-US-00003 TABLE 3
Stiffness ratio Swell ratio Substrate (film to (film to Radial Tilt
Range Material substrate) substrate) (degrees) RL 7553 (SPOQ) 1.311
1.209 0.297 PPE/PS 101 0.744 2.141 0.196 39%/61% BHPM 1.000 1.724
0.208 BPA-disecbutyl 0.908 1.560 0.284 BPA 90-10 TMCBD-PC 1.478
2.451 0.167 BPA-PC + 1 wt % 1.188 1.200 0.339 TXHQDP BPA-PC 1.000
1.000 0.560
[0086] Both the substrate and optical film stiffness were measured
in tensile deformation at room temperature using an Instron tensile
testing machine. The swell of a polymeric material as defined
herein is the percentage of volume growth of the totally dry
material when subjected to a 100% relative humidity environment at
a specific temperature. The swell is measured utilizing a TMA 2940
Thermomechanical Analyzer from TA instruments. A film is mounted
under a very low constant load and initially held in a dry
atmosphere. The length change is then measured upon absorption of
water when the material is exposed to 100% relative humidity. The
water strain or swell is taken to be the strain of the material
(length change divided by the original gauge length). Table 3 above
outlines the stiffness and swell ratio of the film to substrate as
well as the radial tilt range for the different material
combinations. Once again it can be seen that when the polymeric
material used as the optical film differs from that used for the
substrate, the radial tilt range is significantly decreased which
in turn allows for the increased storage capacity.
EXAMPLE 3
[0087] In this example, BPA-PC was replaced in both the optical
film and substrate by different materials as indicated in Table 4
below. The optical film has a thickness of about 100 micrometers,
while the substrate has a thickness of 1.1 millimeter giving a film
to substrate thickness ratio of 0.09. TABLE-US-00004 TABLE 4
Stiffness ratio Swell ratio Film Substrate (film to (film to Radial
Tilt Range Material Material substrate) substrate) (degrees) PS 101
PPE/PS 101 1.039 0.010 0.154 39%/61% BHPM PPE/PS 101 1.000 2.935
0.142 39%/61%
[0088] Here the optical film was polystyrene (PS) in one case while
1,3-bis(4-hydroxyphenyl methane) (BHPM) was used in the other. A
blend of 39 mole % of polyphenylene ether and 61 mole % polystyrene
was used as the substrate in both cases. Both the substrate and
optical film stiffness were measured in tensile deformation at room
temperature using an Instron tensile testing machine. The swell of
a polymeric material as defined herein is the percentage of volume
growth of the totally dry material when subjected to a 100%
relative humidity environment at a specific temperature. The swell
is measured utilizing a TMA 2940 Thermomechanical Analyzer from TA
instruments. A film is mounted under a very low constant load and
initially held in a dry atmosphere. The length change is then
measured upon absorption of water when the material is exposed to
100% relative humidity. The water strain or swell is taken to be
the strain of the material (length change divided by the original
gauge length). Table 4 above outlines the stiffness and swell ratio
of the film to substrate as well as the radial tilt range for the
different material combinations. Once again it can be seen that
when the polymeric material used as the optical film differs from
that used for the substrate, the radial tilt range is significantly
decreased which in turn allows for the increased storage
capacity.
[0089] The storage media disclosed herein reduces radial tilt by
mismatching the compositions of the optical film and substrate, and
by optionally employing mis-matched thicknesses of the substrate
and optical film. The mis-matched compositions contribute in
enabling higher areal density storage (about 20 GB or greater) when
compared to a disc without a mismatched composition of the optical
film and the substrate.
[0090] While the invention has been described with reference to an
exemplary embodiment, it will be understood by those skilled in the
art that various changes may be made and equivalents may be
substituted for elements thereof without departing from the scope
of the invention. In addition, many modifications may be made to
adapt a particular situation or material to the teachings of the
invention without departing from the essential scope thereof.
Therefore, it is intended that the invention not be limited to the
particular embodiment disclosed as the best mode contemplated for
carrying out this invention, but that the invention will include
all embodiments falling within the scope of the appended
claims.
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