Textured organic optical data storage media and methods of preparation

Provided is an optical data storage medium suitable for use with optical recording and playback apparatus and a method of producing the same. The optical data storage medium according to the present invention comprises a textured surfaced information layer comprised of at least one encapsulated dye. The texturing is accomplished without additional treatment steps in the formation of the surface irregularities. Not only does the optical data storage medium of the present invention provide for a high degree of contrast between the medium and recorded information but also allows for the recording of a higher density of information.

BACKGROUND OF THE INVENTION 
This invention relates to an optical data storage medium and a method of 
producing the same. More particularly, the present invention relates to an 
optical data storage medium, preferably in the form of a disk or in tape 
format, suitable for use with optical recording and playback apparatus, 
which optical data storage medium comprises a textured surfaced 
information layer comprised of at least one encapsulated dye. 
Various optical recording media and methods for recording information 
thereon are known in the prior art. For example, the recording of 
information in the form of deformations or ripples in a thermoplastic film 
is known, with techniques for achieving such deformations involving the 
steps of (1) forming a charge pattern on the surface of the thermoplastic 
film in accordance with the information to be recorded, (2) heating the 
thermoplastic to its melting point so as to permit the electrostatic 
forces produced by the charges to form a deformation pattern in the 
thermoplastic film corresponding to the charge pattern and thus to the 
information to be recorded, and (3) then cooling the thermoplastic film 
below its melting point to fix the thus formed deformation pattern in the 
film. Reading of the plastic film may be accomplished using well-known 
optical techniques. See, e.g., U.S. Pat. No. 3,952,146. 
Optical recording methods in which light from a laser or other suitable 
light source is focused upon the surface of a recording medium with 
sufficient intensity to cause the formation of deformations in the surface 
material have also been proposed. In such methods, an information 
representative pattern of deformations, e.g., pits, is formed in the 
surface of the recording medium by suitably controlling the intensity of 
the focused light in accordance with the information to be recorded while 
relative motion is established between the recording medium and the 
focused light spot. 
In recent years, attention has been increasingly paid to the information 
recording method in which information is written in a thin film of metal 
or the like formed on a substrate by using a laser ray or beam. According 
to such a method, the recording of information has been accomplished by 
forming holes or recesses in the metallic thin film under the action of a 
thermal energy beam such as a laser beam. See, e.g., U.S. Pat. No. 
4,238,803. 
Attention has also been paid to the use of dye layers, polymer layers, or 
dye/polymer layers as recording layers for optical information media. For 
example, Spong, U.S. Pat. No. 4,097,895, describes a recording medium 
which comprises a light reflecting material, such as aluminum or gold, 
coated with a light absorbing layer, such as fluorescein, which is 
operative with an argon laser light source. The thickness of the light 
absorbing layer is chosen so that the structure has minimum reflectivity. 
An incident light beam then ablates, vaporizes or melts the light 
absorbing layer, leaving a hole and exposing the light reflecting layer. 
After recording at the wavelength of the recording light, maximum contrast 
between the minimum reflectance of the light absorbing layer and the 
reflectance of the light reflecting layer exists. In this regard, note 
also U.S. Pat. No. 4,219,826. 
Carlson, in U.S. Pat. No. 3,475,760, discloses a system for directly 
recording information in a thermoplastic film as a deformation by using a 
high energy laser scanning beam of small diameter. 
Slaten, U.S. Pat. No, 4,310,919, discloses a video disk comprising an 
information storage layer. The information storage layer is comprised of a 
plastic such as polymethylmethacrylate, or blends thereof, with other 
resins. Included among the suitable resins for blending and use in the 
information storage layer are polyvinyl chloride, polyvinylidine fluoride 
and styrene copolymers such as styrene acrylonitrile. 
Kido et al, U.S. Pat. No, 4,032,691, discloses a recording material which 
comprises a support and a heat sensitive recording layer thereon, which 
heat sensitive layer is thermally deformed, foams, colors, discolors, 
sublimes, evaporates or becomes transparent, translucent or opaque when 
exposed to radiation. The heat sensitive recording layer may comprise a 
metal, dye or synthetic. 
Kido et al, U.S. Pat. No. 4,415,650, discloses optical recording media 
wherein the recording layer comprises a polymer, a dye, or a combination 
of both. The recording layer may be coated on a metallic layer supported 
by a substrate. Polymers usable for the recording layer include thioureas, 
thiocarbazides, thiocarbanic acid, trizoles and tetrazoles, and 
polyamides. 
Lewis, U.S. Pat. No. 4,296,158, discloses information carrying media 
comprised of a substrate having an information bearing layer derived from 
15 to 100% by weight of at least one polyacryloyl-containing heterocyclic 
monomer. Besides the heterocyclic monomer, the information layer can 
contain up to 85% of an ethylenically unsaturated monomer such as 
acrylonitrile. The information is encoded on the information carrying 
layer as depressions, protuberances and/or grooves. The information layer 
is then exposed to ultraviolet radiation in order to photopolymerize the 
monomers and harden the layer. The use of polyacrylonitrile in a layer 
into which information is to be recorded, however, is not disclosed. 
Further, there is a recognition in the art of the use of surface structure 
to increase the contrast between recorded data and the surrounding disc 
surface. 
For example, Craighead et al, U.S. Pat. No. 4,422,159, discloses the use of 
a disc which contains preformed column structures to obtain extremely high 
contrast. Information is written onto the disc by ablating the material 
from the uppermost surface of the column revealing a reflective medium 
below. Before treatment the material appeared black when viewed through 
the microscope and for each pulse a reflective region was produced. 
U.S. Pat. No. 4,084,185, issued to de Lang et al, discloses an optical disc 
which utilizes diffraction gratings as the source of information, as 
opposed to a laser ablated "pit." The disc contains alternating concentric 
tracts of gratings which are angled to diffract light in different 
directions. This effectively doubles the amount of storage capacity 
because the two tracks adjacent to the track being read will diffract 
light away from the detector. In this manner a data track can act as a 
space or "land" allowing for an "optimum discrimination between the 
radiation originating from the various types of gratings." The surface 
diffraction of the disc is not, however, a construction part of the disc 
which is later ablated to reveal a bright, reflective pit. Instead, it is 
a structure that is added to the disc simultaneously with the addition of 
information. 
In all of the foregoing techniques, there is involved the formation of a 
data storage medium and a distinct step for forming the surface 
irregularities. 
Despite all of the techniques used in the optical recording of information 
and the various materials used in the construction of the information 
layer of such media, the search for new materials which are useful in the 
information layer and which provide excellent contrast and sensitivity, 
and the ability to record a much higher density of information, is 
continually on-going. 
Accordingly, it is a major objective of the present invention to provide a 
novel optical data storage medium which is stable and on which information 
can be readily and effectively recorded. 
It is further an object of the present invention to provide an optical data 
storage medium capable of extremely high density data storage. 
It is another object of the present invention to provide a recording medium 
which comprises an information layer which is highly textured. 
It is still another object of the present invention to provide a recording 
medium which comprises an information layer which is highly textured and 
comprised of at least one microencapsulated dye. 
It is still another object of the present invention to provide a recording 
medium which comprises an information layer which is highly textured and 
comprised of at least one encapsulated dye. 
Yet another object of the subject invention is to provide a novel method 
for the production of an optical data storage medium as described above 
which does not require an additional step for the formation of a textured 
surface. 
These and other objects, as well as the scope, nature and utilization of 
the invention, will be apparent to those skilled in the art from the 
following description and the appended claims. 
SUMMARY OF THE INVENTION 
In accordance with the foregoing objectives, provided herewith is such a 
novel textured optical data storage medium, and a method for producing the 
same. The optical data storage medium is comprised of a thermally stable 
substrate and an organic information layer thereon. The information layer 
has a highly textured surface and is comprised of capsules of at least one 
encapsulated dye. By at least one encapsulated dye it is understood that 
the information layer can be comprised of one or a plurality of 
encapsulated dyes, each of which is responsive to different optical 
wavelengths. More specifically, the information layer can be subject to 
optically detectable changes upon the focusing of a laser beam of specific 
wavelength thereon. In a preferred embodiment the capsules of encapsulated 
dye exist as microcapsules having an average diameter or relative size of 
between about 1 micrometer and about 25 micrometers. In a particularly 
preferred embodiment, the capsules of encapsulated dye exist as 
nanocapsules having an average diameter or relative size of between about 
1.times.10.sup.-9 and about 1.times.10.sup.-6 meters. 
A method for the production of the aforementioned optical data storage 
medium comprises the steps of (1) providing a dispersion comprised of 
capsules of at least one encapsulated dye; and (2) spin coating the 
dispersion onto a thermally stable substrate to thereby form an 
encapsulated dye containing layer thereon which has a textured surface. In 
so doing, an optical data storage medium is produced which has a highly 
textured surface capable of dispersing light. This texturing is obtained 
without the need to specially treat either the substrate or the recording 
layer, but is rather a direct consequence of the use of an encapsulated 
dye as the recording layer. In a preferred embodiment, the dispersion is 
comprised of microcapsules of at least one microencapsulated dye, wherein 
said microcapsules have a relative size of between about 1 micrometer and 
about 25 micrometers. In a particularly preferred embodiment, the 
dispersion is comprised of nanocapsules of at least one nanoencapsulated 
dye, wherein said nanocapsules have a relative size of between about 
1.times.10.sup.-9 and 1.times.10.sup.-6 meters

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
An optical data storage medium is a medium on which information can be 
written with a suitable light means, e.g., a laser, and from which 
information can be read with a suitable light means. Simplistically, an 
optical data storage medium in accordance with the present invention may 
comprise a thermally stable substrate having thereon an organic 
information layer. 
In accordance with the present invention, the organic information layer is 
comprised of at least one encapsulated dye. The presence of the 
encapsulated dye provides the information layer with a highly textured 
surface, which in turn acts as a dispersant, scattering incident light 
away from a detector. In general, the size of the capsules of dye can be 
any suitable size for use in optical recording and the reading of optical 
information. It is preferred, however, that the capsules be microcapsules 
or nanocapsules. More specifically, in a preferred embodiment of the 
present invention, the encapsulated dye exists as microcapsules having an 
average diameter or relative size of between about 1 micrometer and 25 
micrometers. In a more preferred embodiment, the encapsulated dye exists 
as nanocapsules having an average size or relative size of between about 
1.times.10.sup.-9 and 1.times.10.sup.-6 meters (from one nanometer to one 
micrometer). By average diameter or relative size it is understood that on 
the average, the diameter of the particles of encapsulated dye shall be 
within the ranges defined above. 
The encapsulated dye is chosen so that it strongly absorbs at a specific 
wavelength. The capsule is constructed so that upon exposure to a laser of 
correct wavelength and intensity, the dye absorbs that laser beam, heats, 
ruptures the encapsulant and allows the molten dye to flow. The dye then 
solidifies, forming a highly reflective pool which can be read as a change 
in the reflectance of a lower intensity read laser. In its simplest form, 
the optical data storage medium of the present invention involves an 
optical data storage medium containing only one encapsulated dye. This 
construction allows for a typical binary information encoding system. 
For example, consider the light intensity reflected from the undisturbed 
textured surface of an optical data storage medium as being the standard 
or base-line and the amount of light reflected at a data point (a pool of 
melted and reformed dye) as being either greater or less than that of its 
surrounding or standard. Assigning symbols to these, the surface or 
standard intensity can be characterized as zero (0) and the dye spot or 
data point can be characterized as a plus (+). Therefore, any specific 
area of the disc can have only one of two encoded states, zero or plus. 
This is a binary system. When two data points are considered, there are 
four possible information configurations. 
______________________________________ 
Data Point A Data Point B 
______________________________________ 
0 0 
0 + 
+ 0 
+ + 
______________________________________ 
Thus, the two data points can encode four bits of information. 
The present invention is not limited to binary encoding applications. In 
fact, the present invention provides the ability to encode a great deal 
more information because it allows for a greater number of encoded states. 
This is accomplished by the use of a plurality of encapsulated dyes and a 
plurality of corresponding read and write lasers. 
For example, consider an organic information layer in accordance with the 
present invention comprised of two encapsulated dyes, one of which 
strongly absorbs at 780 nm and the other of which strongly absorbs at 830 
nm. This construction would provide the basis of four encoded states. As 
before, a specific data point is created by the use of a specific laser of 
sufficient intensity. For example, if the 780 nm laser was used, it would 
heat the 780 nm responsive dye and cause to rupture the encapsulant 
allowing that dye to form a data spot. It is important, however, that the 
830 nm responsive dye remain encapsulated while the 780 nm dye is 
irradiated. Conversely, a data spot can be created by the use of an 830 nm 
laser without disturbing the 780 nm responsive dye. Alternatively, a data 
spot could be produced by the simultaneous application of both the 780 and 
830 nm lasers. This would cause the rupturing of the microcapsules 
containing both dyes and the formation of a spot which is a mixture of the 
two. The four possible encoded states are, therefore: (1) the reflectance 
from the undisturbed texturized surface; (2) the reflectance from a data 
spot formed exclusively from dye responsive to laser light of 780 nm; (3) 
the reflectance of a data spot formed exclusively from dye responsive to 
laser light of 830 nm; and (4) the reflectance of a data spot resulting 
from the combination of both dyes. 
If it is generally assumed that the number of decimal numbers or bits of 
information that can be encoded by a given number of data points is given 
by the equation N.sub.s =S.sup.k, where S is the number of encoded states 
possible for any one data point and k is the number of data points 
considered, in the present context, since four potential data rendering 
configurations are possible for any one data spot (S=4) and we are 
considering only two data points (K=2), 16 bits of information can be 
encoded (N.sub.s =16). Of course, the present invention is not limited to 
a two encapsulated dye embodiment, but encompasses the use of a plurality 
of encapsulated dyes, including both microencapsulated dyes and 
nanoencapsulated dyes as well as mixtures thereof. 
As noted above, the preferred dyes will have very distinct light absorption 
and reflection characteristics. For example, if the writing of data is to 
be achieved with a helium/neon laser of 633 nm, then Oil Blue N dye color 
index 61555, lambda max 637 nm, would be a suitable dye for encapsulation 
and incorporation in the information layer. If, however, an argon laser is 
used which provides an output of a wavelength of about 456 nm, an organic 
dye such as fluorescein which is highly absorptive at the light frequency 
of the argon laser can be advantageously used. Particularly preferred dyes 
include naphthalocyanine dyes and phthalocyanine dyes, as well as 
porphyrin dyes. Most preferred are the naphthalocyanine dyes and 
phthalocyanine dyes which absorb irradiation and have a lambda max at 
between about 750 and 850 nm and between about 600 and 700 nm respectively 
and porphyrin dyes which have a lambda max at between about 400 and 500 
nm. 
The terms "capsule" and "encapsulated" as used herein refer to both 
capsules having a discrete capsule wall and capsules formed in a so-called 
open phase system wherein the internal phase constituents are simply 
dispersed in a binder and their equivalents. But these terms are not 
limited thereto. The terms "capsule" and "encapsulated" may include 
micelles, microemulsions, monolayers, bilayers and vesicles such as those 
described in Acc. Chem. Res. 1984, 17, 3-8 "Polymerized Surfactant 
Aggregates: Characterization and Utilization", by Janos H. Fendler; Ind. 
Eng. Chem. Prod. Res. Dev., 1985, 24, 107-113, "Potentials of Polymerized 
Surfactant Assemblies in Membrane Research", by Janos H. Fendler; Polymer 
Preprints (American Chemical Society, Division of Polymer Chemistry), 
1985, Vol. 26(1), "Polymerized Vesicles and Some of their Ghosts", by 
Steven L. Regen, Jae-Sup Shin and Kazuo Yamaguchi; and C & E News, Jan. 2, 
1984, "Membrane Mimetic Chemistry" by Janos H. Fendler. Both microcapsules 
and nanocapsules are similarly defined, except for size. 
Microcapsules are filled with an internal phase containing a photosensitive 
dye composition as previously described and are not visible to the unaided 
eye, since the mean size of the microcapsules generally ranges from 
approximately 1-25 microns or micrometers. Nanocapsules are similar, 
however the mean size of nanocapsules generally ranges from approximately 
1.times.10.sup.-9 to about 1.times.10.sup.-6 meters. 
Dyes used in the present invention may be either hydrophilic or 
hydrophobic. Consequently, the types of encapsulant and the methods of 
forming capsules according to the present invention contemplates both 
circumstances. If, for example, a hydrophobic dye is to be used, capsules 
may be prepared by: (1) preparing a partially condensed, aqueous 
thermosetting resin syrup; (2) emulsifying a water-immiscible 
(hydrophobic) dye in an aqueous colloidal solution of an amphophilic 
emulsifying agent; and (3) slowly admixing the resin syrup and the 
emulsion under conditions of brisk agitation to precipitate the resin and 
encapsulate minute liquid emulsion droplets as described in Vassiliades, 
U.S. Pat. No. 3,993,831, which is hereby incorporated by reference. 
The admixing causes the condensation product to separate from the aqueous 
medium in solid particle form as a precipitate about a nucleus of oil in 
water upon dilution with the water of the emulsion. The dilution takes 
place slowly and under conditions of brisk agitation. 
Among the thermosetting resins which can be used is that broad class of 
compositions defined as partially condensed formaldehyde condensation 
products. The term "partially condensed" as employed herein is intended to 
include resins not having reached the infusible or insoluble stage, e.g., 
B-stage resins. 
Exemplary of suitable resins are the condensation reaction products of 
formaldehyde with phenols, such as, hydroxybenzene (phenol), m-cresol and 
3,5-xylenol; carbamides, such as, urea; trazines, such as melamine; amino 
and amido compounds, such as, aniline, p-toluenesulfonamide, ethyleneurea 
and guanidine; ketones, such as acetone and cyclohexanone; aromatic 
hydrocarbons, such as, naphthalene; and heterocyclic compounds, such as 
thiophene. Under the influence of heat, these resins change irreversibly 
from a fusible and/or soluble material into an infusible and insoluble 
material. 
The preferred formaldehyde condensation products are partially-condensed 
melamine-formaldehyde, phenol-formaldehyde and urea-formaldehyde resins. 
The B-stage melamine and urea-formaldehyde resins are especially 
preferred. 
These partially condensed resins can be prepared easily according to 
conventional practices. For example, a melamine-formaldehyde partial 
condensate or syrup, which is used in the examples hereinafter presented, 
is prepared by refluxing 125 grams of melamine in 184 milliliters of 
formalin (37 percent by weight formaldehyde) neutralized to a pH of 8 with 
sodium carbonate. The mole ratio of formaldehyde to melamine in this 
reaction mixture is 2.3 to 1. The reaction continues for about 1 to 11/2 
hours at a temperature between 92.degree. and 96.degree. C. or until 1 
volume of the condensate becomes turbid when diluted with 2 to 10 volumes 
of water. The condensate can be used immediately or can be stored for 
later use by adding a small amount, about 6 to 15 percent by weight, of 
methanol to the condensate. The methanol prevents any further rapid 
condensation of the resin solution upon standing and can be evaporated 
from the syrup either prior to or during the admixing operation. 
On the other hand, if a hydrophilic dye is used, capsules may be prepared 
by the production of small or minute capsules constituted by a skin or 
thin wall of polymeric material, e.g., polyurea, polyamide, 
polysulfonamide, polyester, polycarbonate or polyurethane. This involves 
first providing an organic liquid (continuous phase liquid) containing an 
oil soluble alkylated polyvinylpyrrolidone emulsifier. A discontinuous 
(aqueous) phase liquid containing a water-soluble material, which is the 
material to be encapsulated, plus a first shell wall component, is 
dispersed in the continuous phase liquid to form a water-in-oil emulsion. 
The second shell wall component is added to the water-in-oil emulsion 
whereupon the first shell wall component reacts with the second shell wall 
component to form a solid polymeric shell wall about the material to be 
encapsulated. The capsules formed may be directly used as in the form of 
an organic suspension, i.e., a suspension of capsules in the organic 
liquid. 
Another technique, but one which is applicable to the encapsulation of 
either hydrophobic or hydrophilic dyes, is generally known as 
coacervation. Coacervation is the term applied to the ability of a number 
of aqueous solutions of colloids to separate into two liquid layers, one 
rich in colloid solute and the other poor in colloid solute. Factors which 
influence this liquid-liquid phase separation are: (a) the colloid 
concentration, (b) the solvent of the system, (c) the temperature, (d) the 
addition of another polyelectrolyte, and (e) the addition of a simple 
electrolyte to the solution. 
A unique property of coacervation systems is the fact that the solvent 
components of the two phases are the same chemical species. This is a 
major distinguishing characteristic of coacervates as compared to two 
phase systems involving two immiscible liquids. Thus, a colloidal solute 
particle migrating across the interface of a two-phase coacervate system 
finds itself in essentially the same environment on either side of the 
interface. From the viewpoint of composition, the difference between the 
two phases is a difference in concentration of solute species. 
Structurally, the two phases differ in that the colloidal solute of the 
colloid-poor phase is randomly oriented and the colloidal solute of the 
coacervate or colloid-rich phase shows a great deal of order. In all cases 
where coacervation has been observed, the solute species are geometrically 
anisotropic particles. 
Coacervation can be of two general types. The first is called "simple" or 
"salt" coacervation where liquid phase separation occurs by the addition 
of a simple electrolyte to a colloidal solution. The second is termed 
"complex" coacervation where phase separation occurs by the addition of a 
second colloidal species to a first colloidal solution, the particles of 
the two dispersed colloids being oppositely charged. Generally, materials 
capable of exhibiting an electric charge in solution (i.e., materials 
which possess an ionizable group) are coacervatable. Such materials 
include natural and synthetic macromolecular species such as gelatin, 
acacia, tragacanth, styrenemaleic anhydride copolymers, methyl vinyl 
ether-maleic anhydride copolymers, polymethacrylic acid, and the like. 
With both simple and complex coacervate systems, a necessary precondition 
for coacervation is the reduction of the charge density of the colloidal 
species. In the case of simple coacervation, this reduction of the charge 
density along with partial desolvation of the colloidal species is similar 
to that preceding the flocculation or precipitation of a colloid with the 
addition of a simple electrolyte since it is known that the addition of 
more electrolyte to a simple coacervate leads to a shrinking of the 
colloidal species. This same reduction of charge density along with 
partial desolvation of the colloidal species which precedes the 
precipitation of two oppositely charged colloids from solution may also be 
regarded to be the cause for the phase separation in a complex coacervate 
system. However, while the reduction of the charge density is a necessary 
precondition for coacervation, it is oftentimes not sufficient for 
coacervation. In other words, the reduction of the charge density on the 
colloidal particles must alter or modify the solute-solute interactions to 
such an extent that the colloidal particles will tend to aggregate and 
form a distinct, continuous liquid phase rather than a flocculent or a 
solid phase. This tendency is attributable to both coulombic and 
long-range Van der Waal's interactions of large aggregates in solution. 
Thus, in both simple and complex coacervation, two-solution phase 
formation begins with the colloidal species aggregating to form 
submicroscopic clusters, with these clusters coalescing to form 
microscopic droplets. Further coalescence produces macroscopic droplets 
which tend to separate into a continuous phase. This phase appears as a 
top or bottom layer depending upon the relative densities of the two 
layers. 
If, prior to the initiation of coacervation, an oil-in-water emulsion 
comprising oil, water and an emulsifying or thickening agent such as 
carboxymethylcellulose or gum arabic is dispersed as minute droplets in an 
aqueous solution or sol of an encapsulating colloidal material, and then, 
a simple electrolyte, such as sodium sulfate, or another, oppositely 
charged colloidal species is added to induce coacervation, the 
encapsulating colloidal material forms around each emulsion droplet, thus 
investing each of said droplets in a liquid coating of the coacervated 
colloid. The liquid coatings which surround the emulsion droplets must 
thereafter be hardened in order to produce recoverable solid-walled 
capsules having structural integrity. 
Additional methods of forming capsules, particularly microcapsules, and 
materials useful in encapsulation are discussed in U.S. Pat. Nos. 
3,864,275; 4,211,668; 4,218,409; 4,073,833; and 4,307,169. 
Nanoencapsulation may be accomplished in a number of methods, one of Which 
is disclosed in Microencapsulation, edited by J. R. Nixon of Chelsea 
College, University of London, London, England and published by Marcel 
Dekker, Inc., copyright 1976. More specifically, chapter one of 
Microencapsulation, which is entitled "Microencapsulation by Coacervating, 
Spray Encapsulation and Nanoencapsulation" by P. Speiser, discloses, at 
page 6, the manufacture and morphology of ultrafine compartments or 
nanocapsules. According to Speiser the basic principles of manufacturing 
nanocapsules are as follows. An aqueous solute solution (the solute being 
that which is to be encapsulated) is first solubilized in a weakly polar 
vehicle. Micelles of water are obtained with the solute in an organic 
outer phase. Then an amphiphilic monomer is added to the lipophilic 
external phase. These film-forming precursors are next enriched at the 
border surface and form a mixed micelle. Then the monomers are polymerized 
with the aid of suitable procedures such as ultraviolet or gamma 
radiation, heat and chemical agents. This produces solidified, hardened 
micelles with the solute molecules containing therein. 
An aqueous dispersion of nanocapsules may then be produced by replacing the 
outer lipophilic vehicle with water. At the same time the tensides and 
hydrophilic ballast materials are washed out. Finally, an ultrafine 
suspension of water in water droplets is obtained. The internal water 
phase is so small that the suspension cannot be recognized with the eye or 
with the microscope. This suspension looks like a clear aqueous solution 
with a light opalescent, Tyndall effect. By selecting the monomers and 
network agents and other auxiliary materials, it is possible to get 
tailor-made capsules between 80 and 250 nanometers. 
In another embodiment the ability of the monomers and their derivatives to 
copolymerize with unsaturated compounds permits the manufacturing of 
various coats with a three-dimensional network containing narrow or wide 
pore openings. By increasing the amount of netting agent and decreasing 
the amount of monomer we can manipulate the pore opening of the 
nanocapsules. This pore diameter can be varied between 2 nanometers and 5 
nanometers or even higher. 
The substrate is used to add dimensional stability and support to the 
organic information layer. The substrate may be optically featureless or 
may contain preformatting information (e.g., tracking grooves and/or 
encoded information in the form of readable marks). However, it is 
preferred that the substrate have a surface of suitable smoothness. The 
material of which the substrate is comprised is generally a material 
exhibiting good mechanical strength and good structural integrity against 
warping. Examples of suitable materials include aluminum, glass, 
reinforced glass, ceramics, polymethylmethacrylates, polyacrylates, 
polycarbonates, phenolic resins, epoxy resins, polyesters, polyimides, 
polyether sulfones, polyether ketones, polyolefins, polyphenylene sulfide 
and nylon. A preferred material is polycarbonate. 
The shape and size of the substrate, and hence the organic information 
layer, can vary depending upon the application. The shape and format, for 
example, may be a disc, tape, belt or drum. A disc shape or tape format is 
most preferred. Or, two substrates, having the information layer on either 
side can be combined allowing the sides having the recording layers to 
face each other at a constant distance, the combined substrate being 
sealed to prevent dust, contamination and scratches. 
The medium of this invention may also have an undercoating layer such as a 
metal reflective layer or layer of various resins on the substrate if 
necessary, with the recording layer being coated over it. In addition, 
various thermoplastic resins, thermosetting resins, UV or electron beam 
cured resins, may be used as an undercoating material. Furthermore, it may 
be advantageous to coat the organic information layer with some sort of 
protective layer such as those known in the art. This will protect the 
recording layer from dirt, dust, scratches or abrasion. 
In forming an optical data storage medium in accordance with the present 
invention, a dispersion of encapsulated dye is provided. This dispersion 
can be either purchased or prepared by one of the various methods 
previously described. Next, the dispersion of encapsulated dye is spin 
coated onto a substrate, such that it forms a highly textured information 
layer. 
Next, the dispersant is allowed to dry or evaporate and the information 
layer is allowed to set. 
Optionally, a small amount of binder material, for example hydroxy ethyl 
cellulose, may be added to the microcapsule dispersion prior to spin 
coating. 
The principles, preferred embodiments and modes of operation of the present 
invention have been described in the foregoing specification. The 
invention which is intended to be protected herein, however, is not to be 
construed as limited to the particular embodiments disclosed, since these 
are to be regarded as illustrative rather than restrictive. Variations and 
changes may be made by others without departing from the spirit and scope 
of the invention.