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United States Patent Application |
20050180284
|
Kind Code
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A1
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Hay, Grant
;   et al.
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August 18, 2005
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Radial tilt reduced media
Abstract
A storage media having a radial deviation of less than or equal to about
1.15 degrees at a radius of 55 mm is disclosed. In one embodiment, the
storage media comprises: a plastic substrate, an optical layer and a data
storage layer disposed therebetween. A reflective layer is disposed
between the data storage layer and the substrate.
Inventors: |
Hay, Grant; (Evansville, IN)
; Alizadeh, Azar; (Wilton, NY)
; Bushko, Wit; (Niskayuna, NY)
; Dris, Irene; (Clifton Park, NY)
; Feist, Thomas; (Clifton Pary, NY)
|
Correspondence Address:
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CANTOR COLBURN, LLP
55 GRIFFIN ROAD SOUTH
BLOOMFIELD
CT
06002
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Serial No.:
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101833 |
Series Code:
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11
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Filed:
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April 8, 2005 |
Current U.S. Class: |
369/53.21; 369/275.3; G9B/7.159; G9B/7.172 |
Class at Publication: |
369/053.21; 369/275.3 |
International Class: |
G11B 007/09 |
Claims
1-50. (canceled)
51. A storage media, comprising: a plastic substrate having a substrate
composition comprising a polyarylene ether and having a substrate
thickness; an optical layer having an optical layer composition different
from the substrate composition; 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.
52. The storage media of claim 51, 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.
53. The storage media of claim 51, 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.
54. The storage media of claim 51, wherein a stiffness ratio of the
optical layer to the substrate is about 0.5 to about 5 measured in
tensile deformation at room temperature.
55. The storage media of claim 51, wherein a swell ratio of the optical
layer to the substrate is about 0.5 to about 5.0.
56. The storage media of claim 51, wherein the optical layer thickness is
about 0.2 micrometers to about 120 micrometers.
57. The storage media of claim 51, wherein the optical layer composition
is selected from the group consisting of polycarbonates, acrylic
polymers, epoxies, silicones, and copolymers and combinations comprising
at least one of the foregoing optical layer compositions.
58. The storage media of claim 57, wherein the optical layer composition
comprises poly(alkyl acrylate).
59. The storage media of claim 57, wherein the optical layer composition
comprises silicones.
60. The storage media of claim 51, wherein the substrate composition
further comprises polystyrene.
61. The storage media of claim 60, wherein the polyarylene ether comprises
a polyphenylene ether selected from the group consisting of polyphenylene
ether derived from 2,6-dimethylphenol, polyphenylene ether derived from
2,6-dimethylphenol copolymerized with 2,3,6-trimethyiphenol, and reaction
products, combinations, and composites comprising at least one of the
foregoing polyphenylene ethers.
62. The storage media of claim 51, wherein the radial deviation is less
than or equal to about 1.0 degree.
63. The storage media of claim 62, wherein the radial deviation is less
than or equal to about 0.5 degrees.
64. The storage media of claim 51, further comprising a dielectric layer
disposed between the optical layer and the substrate, wherein the
dielectric layer is selected from the group consisting of silicon
nitride, aluminum nitride, aluminum oxide, silicon carbide, and
combinations comprising at least one of the foregoing dielectric layers.
65. The storage media of claim 51, further comprising an adhesive layer
disposed between the optical layer and the substrate, wherein the
adhesive layer is selected from the group consisting of 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 combinations comprising at
least one of the foregoing adhesives.
66. The storage media of claim 51, further comprising an adhesive layer
disposed between the optical layer and the substrate, wherein the
adhesive layer is selected from the group consisting of a UV curable
adhesive, a pressure sensitive adhesive, and combinations comprising at
least one of the foregoing.
67. The storage media of claim 51, further comprising a lubrication layer,
wherein the lubrication layer is selected from the group consisting of
fluoro oils, and fluoro greases, and combinations comprising at least one
of the foregoing.
68. The storage media of claim 51, wherein the optical layer composition
is selected from the group consisting of ethylene-tetrafluoroethylene
copolymers, polyvinyl fluoride, polyvinylidene fluoride, polyvinylidene
chloride, and polytetrafluoroethylene, and reaction products, and
combinations comprising at least one of the foregoing optical layer
compositions.
69. A storage media, comprising: a plastic substrate having a substrate
composition comprising a polyarylene ether and having a substrate
thickness; an optical layer having an optical layer composition different
from the substrate composition; and wherein the storage media has a
radial deviation over time of less than or equal to about 1.15 degrees at
a radius of 55 mm when exposed to humidity, a stiffness ratio of the
optical layer to the substrate of about 0.5 to about 5 measured in
tensile deformation at room temperature, a swell ratio of the optical
layer to the substrate of about 0.5 to about 5.0; and wherein the storage
media is capable of storing greater than or equal to about 20 GB of data;
and wherein the storage media is capable of reflecting an energy field.
70. The storage media of claim 69, further comprising a reflective layer
disposed between the optical layer and the substrate, and 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.
71. The storage media of claim 69, wherein a stiffness ratio of the
optical layer to the substrate is about 0.5 to about 5 measured in
tensile deformation at room temperature.
72. The storage media of claim 69, wherein a swell ratio of the optical
layer to the substrate is about 0.5 to about 5.0.
73. The storage media of claim 69, wherein the optical layer thickness is
about 0.2 micrometers to about 120 micrometers.
74. The storage media of claim 69, wherein the optical layer composition
is selected from the group consisting of polycarbonates, acrylic
polymers, epoxies, silicones, and copolymers and combinations comprising
at least one of the foregoing optical layer compositions.
75. The storage media of claim 69, wherein the optical layer composition
comprises poly(alkyl acrylate).
76. The storage media of claim 69, wherein the optical layer composition
comprises silicones.
77. The storage media of claim 69, wherein the substrate composition
further comprises polystyrene.
78. The storage media of claim 69, wherein the polyarylene ether comprises
a polyphenylene ether selected from the group consisting of polyphenylene
ether derived from 2,6-dimethylphenol, polyphenylene ether derived from
2,6-dimethylphenol copolymerized with 2,3,6-trimethylphenol, and reaction
products, combinations, and composites comprising at least one of the
foregoing polyphenylene ethers.
79. The storage media of claim 69, wherein the radial deviation is less
than or equal to about 1.0 degree.
80. The storage media of claim 79, wherein the radial deviation is less
than or equal to about 0.5 degrees.
81. The storage media of claim 69, wherein the optical layer composition
is selected from the group consisting of ethylene-tetrafluoroethylene
copolymers, polyvinyl fluoride, polyvinylidene fluoride, polyvinylidene
chloride, and polytetrafluoroethylene, and reaction products, and
combinations comprising at least one of the foregoing optical layer
compositions.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application 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 having a radial deviation of
less than or equal to about 1.15 degrees at a radius of 55 mm. In one
embodiment, the storage media comprises: a plastic substrate, an optical
layer and a data storage layer disposed therebetween. A reflective layer
is disposed between the data storage layer and the substrate.
[0009] The above described and other features are exemplified by the
following figures and detailed description.
DESCRIPTION OF THE DRAWINGS
[0010] Referring now to the drawings, wherein like elements are numbered
alike:
[0011] FIG. 1 is a cross-sectional illustration of a prior art low areal
density system employing an optically clear substrate.
[0012] 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.
[0013] 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).
[0014] FIG. 4 is a graphical illustration of dynamic curvature of a
substrate during desorption and adsorption.
[0015] FIG. 5 is a graphical illustration of the effect of thickness on
structure curvature range during absorption and subsequent desorption.
[0016] FIG. 6 is a curvature ratio contour map at a diffusion ratio of
1.5.
[0017] FIG. 7 is a curvature ratio contour map at a diffusion ratio of
1.0.
[0018] 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
[0019] 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.
[0020] 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 gigabites (Gb) in storage and
having data transfer rates of approaching or even exceeding 100 megabites
per second (Mbps). Thinner readthrough 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.
[0021] 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.
[0022] 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.
[0023] 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.
[0024] 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: 1 BeamSpotDiameter [ NA ]
[0025] where
[0026] .lambda.=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: 2
TiltMargin [ d NA 3 ]
[0029] where
[0030] d=thickness of readthrough medium
[0031] 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.
[0032] Referring to FIG. 2, for example, data retrieval comprises
contacting the data storage layer(s) 102 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.
[0033] 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: 3 _ ( t ) = l
1 / 2 - 1 / 2 c ( z , t ) z
[0034] where:
[0035] .epsilon.=strain
[0036] z=thickness direction
[0037] l=thickness
[0038] c=concentration
[0039] .beta.=swell coefficient where .epsilon.(t)=.beta.C(Z,t)
[0040] The curvature of the substrate is related to the first moment of
the water distribution in the disk as shown below: 4 ( t ) = 12
l 1 1 / 2 - 1 / 2 c ( z , t ) z z
[0041] 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: 5 ( t ) - ( 0 ) = 6 1 s 1 l
1 f ( t ; , , , q )
[0042] where
[0043] t=time
[0044] .DELTA..phi.=change in relative humidity 6 = l 2 l 2 =
[0045] ratio of layer thickness, 7 = E 2 1 - v 2 E 1 1 -
v 1 =
[0046] ratio of mechanical stiffness, 8 = 2 s 2 1 s 1
= 2 .infin. 1 .infin. =
[0047] ratio of water strains, 9 q = D 2 D 1 =
[0048] ratio of diffusivities
[0049] subscript "2" refers to the film and subscript "1" refers to the
substrate
[0050] 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.
[0051] 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.
[0052] The maximum in the dynamic curvature on absorption and desorption
of water for a single substrate is given by the following relation: 10
( t ) - ( 0 ) = 6 1 s 1 l 1
[0053] 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:
[0054] Max Radial Tilt Range (rad) 11 Max Radial Tilt
Range ( rad ) = r = 1.92 rh sr
t = 1.92 rh r t
[0055] where:
[0056] K is the curvature (length.sup.-1);
[0057] .DELTA.rh is step relative humidity;
[0058] .beta.is strain/mass fraction water at a given temperature(T);
[0059] s is mass fraction water at relative humidity (rh)=1 and T;
[0060] .epsilon.=.beta.s is water strain at rh=l and T;
[0061] t is substrate thickness; and
[0062] r is radius of interest.
[0063] 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.
[0064] FIG. 4 outlines the dynamic curvature in absorption and
subsequently in desorption normalized by 12 6 1 s 1 l 1
[0065] 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.
[0066] 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.
[0067] 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.
1 TABLE 1
Ratios Value
Thickness .rho. 0.09
Stiffness .gamma. 3
Swell .delta.
1.01
Diffusivity q 0.15
Minimum Range 0.11
[0068] 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.
[0069] 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
[0070] 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 a 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.
[0071] 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.
[0072] Non-limiting examples of thermosetting resins are epoxies,
phenolics, alkyds, 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.
[0073] 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(alkylene terephthalate)s (particularly
poly[ethylene terephthalate] and poly[butylene terephthalate]) containing
soft-block segments of poly(alkylene 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.
[0074] 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: 1
[0075] wherein R.sup.16 is hydrogen or C.sub.1-4 alkyl, optionally in
combination with structural units of the formula II: 2
[0076] 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.
[0077] 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.
[0078] Possible polycarbonates include those comprising structural units
of the formula III: 3
[0079] 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[1 H-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. 4,217,438.
[0080] More preferably, R.sup.18 is an aromatic organic radical and still
more preferably a radical of the formula IV: 4
[0081] 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.
[0082] 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.
[0083] 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): 5
[0084] 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.
[0085] 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-methyl-
phenyl)cycloheptane; 1,1 -bis(4-hydroxy-3-methylphenyl)-3,3,5-trimethylcyc-
lohexane (DMBPI); and mixtures comprising at least one of the foregoing
units.
[0086] 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).
[0087] 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): 6
[0088] 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.
[0089] 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.
[0090] The polyphenylene ethers are polymers comprising a plurality of
structural units of the formula (VIII) 7
[0091] 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.
[0092] 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.
[0093] 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.
[0094] 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.
[0095] 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 comprises 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.
[0096] 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.
[0097] 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.
[0098] 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.
[0099] 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). 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.
[0100] The dielectric layer(s) which are often employed as heat
controllers, can typically have a thickness of up to or exceeding about
1000 .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.
[0101] 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.
[0102] 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 micrometers 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.
[0103] 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.
[0104] 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 mismatched
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
[0105] 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.
[0106] 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).
[0107] 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
2TABLE 2
Stiffness ratio Swell ratio Radial Tilt
Range
Film Material (film to substrate) (film to 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
[0108] 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
[0109] 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).
3TABLE 3
Stiffness ratio Swell ratio Radial Tilt
(film to (film to Range
Substrate 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
[0110] 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
[0111] 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.
4TABLE 4
Stiffness
ratio Swell ratio
Radial Tilt
Film Substrate (film to (film to 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%
[0112] 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.
[0113] 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 mismatched compositions contribute in enabling higher areal
density storage (about 20 Gb or greater) when compared to a disc without
a mis-matched composition of the optical film and the substrate.
[0114] 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.
* * * * *