CA1127945A

CA1127945A - Optical disc

Info

Publication number: CA1127945A
Application number: CA349,873A
Authority: CA
Inventors: James H. Sharp; Lupu Alexandru; Vlad J. Novotny; Michael A. Hopper
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1979-06-04
Filing date: 1980-04-15
Publication date: 1982-07-20
Also published as: GB2055218A; GB2055218B; JPS55161690A; DE3014677A1

Abstract

ABSTRACT OF THE DISCLOSURE

An optical recording member is provided which has a reflective substrate, and a thin dye-in-polymer layer on the substrate, the dye-in-polymer layer being made to be responsive to an optical recording apparatus so that at least the dye portion of that layer will migrate from the areas struck by the the optical recording apparatus to expose the reflective substrate. Prior to the recording process, the dye-in-polymer layer forms an anti-reflection layer to cover the reflective substrate.

Description

il~Z7~45 OPTICAL DISC

BACRGROUND OF THE INVENTION
This invention relates to a novel optical infor-mation recording member, and to methods for recording and retrieving information from such a member.
It is known in the prior art to construct an optical recording member, to record information on such a member, and to optically recover information from such a member. In Spong U. S. Patent 4,097,895, there is dis-closed an optical record, which is made of a disc-shaped substrate of glass coated with a layer of aluminum, and the aluminum layer is then overcoated with a layer of a dye.
When the layer of dye is exposed to a light source, such as a modulated laser beam, a series of pits is formed to expose the aluminum layer under the dye coating. The information thus recorded in the form of a series of pits may then be recovered by an optical playback process. The thickness of the dye layer is chosen to establish an anti-reflection condition, while the exposed aluminum layer is highly reflective. ~owever, such a system has substantial disadvantages. The thin layer of dye overcoating is formed by vapor deposition in a vacuum, and such a process is very expensive as compared to the cost of the materials in-volved. In addition, the deposited thin layer of dye poses a materials handling problem in that it is messy to handle and care must be exercised in not damaging or disturbing the integrity of that layer. ~n this respect, such a recording member is similar to the carbon paper sometimes used in the typing process.
In Bloom et al U.S. Patent 4,023,185, there is disclosed an optical recording medium similar to that of the Spong patent. The recording medium of Bloom et al is coated with a layer of dye which is said to be hydrophobic and has improved resistance to abrasion. However, the above noted disadvantages with respect to the device of 7~5 Spong are still generally applicable to the recording medium of Bloom et al.
In Landwer U. S. Patent 3,825,323, there is dis-closed apparatus for precise positioning of a focused laser beam on the surface of a moving record by capacitive means, for use in a recording process to generate a memory by localized melting of selected areas along recording tracks in the surface of the record. In the Landwer process, a thick thermoplastic film is coated on a backing substrate of high melting point material such as glass. To "write"
on such a film, a laser beam is selectively focused on the surface of the film to generate minute melted depressions thereon. When such recorded information is to be "read outl' a non-destructive laser beam is applied to the record and the amount of light energy reflected by the melted areas or grooves is sufficiently different from the amount of light energy reflected by the undisturbed areas that such difference can be sensed and converted into binary data signals corresponding to the recorded data by known means. Thus, Landwer's record has no reflective substrate for reading out the recorded information. To achieve the object of always having the focal plane of the focusing lens coincide with the surfac~ of the recording member, Landwer provides a conductive layer in the recording member between the glass substrate and the thermoplastic overcoat.
The conductive layer, together with a flat conductive metal ring, which is physically connected to the lens housing, form a capacitor whose capitance is a measure of the dis-tance between the conductive layer and the conductive ring.
By monitoring this capacitance, a differential output signal to a servo mechanism is obtained for adjusting the position of the lens to insure the coincidence of the focal plane of the lens with the recording surface. The thick-ness of the thermoplastic film disclosed by Landwer, together with the absence of any highly energy-absor~ing component, make the optical disc of I,andwer require sub-llZ7945 stantial amounts of energy for marking purposes.
SUMMARY OF THE INVENTION
It is an object of an aspect of the present inventionto provide an improved optical recording member and an im-5 proved method for recording and retrieving information fromsuch a member. It is an object of an aspect of the present invention to provide an improved optical recording member which is relatively inexpensive to make, stable under normal handling conditions, has high marking sensitivity and optical 10 contrast. It is an object of an aspect of the present inven-tion to provide a method for optically recording information which requires the use of only very low powered lasers.
These and other objects of the invention will be apparent from the following detailed disclosure.
According to one aspect of this invention there is provided an optical recording member for optically recording and retrieving of information thereon comprising a reflec-tive substrate having coated thereon a layer of a polymer having a dye dispersed therein, said dye-in-polymer layer 20 being made to be responsive to an optical recording appara-tus so that at least the dye portion of said layer will migrate from the areas worked upon by said optical record-ing apparatus to expose the reflective substrate, and said dye-in-polymer layer forms an anti-reflection layer to cover 25 said reflective substrate in other areas.
In accordance with another aspect of this invention there is provided a method for recording information on the optical recording member hereinbefore recited comprising:
providing a recording laser having a wavelength substan-30 tially matching the absorption peak of the dye-in-polymer layer of said optical recording member; precisely position-ing the dye-in-polymer layer in the path of the recording laser to receive the information to be recorded from the recording laser; and causing the migration of at least the 35 dye portion of the dye-in-polymer layer at those areas in accordance with the information to be recorded, to thus expose the reflective substrate at said areas.

, ~.

-3a-BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings:
Figure 1 is a cross-sectional view of an optical recording member in accordance with the present invention;
Figure 2 is a cross-sectional view of another em-bodiment of the optical recording member of the present invention, Figure 3 is a cross-sectional view of yet another embodiment of the optical recording member of the present invention;
Figure 4 is a cross-sectional view of a further embodiment of the optical recording member of the present invention; and ~, ~ll.Z7945 Figure 5 is a schematic diagram showing an appar-atus which may be used to record or "write" information on the optical recording member of the present invention, as well as to read the recorded information therefrom.
DETAILED DESCRIPTION
Referring to Figure 1, an optical recording member 10 in accordance with the present invention is shown to be composed of two component parts: a reflective sub-strate 11 and a thin anti-re~lective coating of a dye-in-polymer mixture 12 on the reflective substrate. In the particular embodiment illustrated in Figure 1, the reflec-tive substrate 11 is made of a base support layer 13 and a reflective layer 14. The reflective layer 14 may be suit-ably made of a thin coating of a reflective material, such as aluminum, chromium, titanium, doped and undoped poly-lS acetylene, etc. The base support layer 13 may be made of any material that is rela~ively inexpensive and yet imparts to the optical recording member 10 the requisite structural rigidity and furnishes a relatively smooth surface on which the reflective layer 14 may be deposited. Typical examples of materials which can be used for the base support layer 13 are glass, metals, and various polymeric materials such as plexiglass, polycarbonate, polypropylene, and various acrylic resins. Although the reflective substrate 11 is illustrated in Figure 1 as made of two layers 13 and 14, the entire substrate may be formed of one material so long as that material has the requisite structural strength and the ability to form a smooth surface and the necessary reflec-tivity. It should be understood that in order to attain maxium marking sensitivity, the reflective substrate 11 should be a poor heat conductor. As metals are generally heavier and more expensive than other materials, the reflective substrate 11 should not be made entirely from metal. When the reflective layer 14 is made of a metal, it is generally very thin in comparison to the thickness of the entire reflective substrate 11 or to the base support layer 13.

l~Z794S

The thin coating o dye-in-polymer is formed of a mixture of one or more dyes and one or more polymers. The selection of dyes and polymers is based in part on their compatibility with each other. Within ~he meaning of this invention, the materials are considered compatible when at least 3 percent by weight of the dyes can be dispersed in the solid polymers without forming visible aggregates. The polymer material is preferred to be a thermoplastic material such as polystyrene, polycarbonates, polyolefins, polyacrylates, polymethacrylates, polyesters, polyamides, polyvinylacetate, copolymers and block copolymers, etc.
The general requirements for the polymer component of the thin ~oating layer 12 are that it should be a stable solid at normal ambient temperature conditions and yet have low glass transition and melting temperatures. The polymer should be a solid at normal ambient temperatures so that the optical recording member of the present invention will be stable and can be easily handled and stored. The low glass transition and melting tempèratures will permit the dye-in-polymer coating 12 to be softened by a writing laser at the lowest possible temperature. This will permit the most efficient recording of information on the optical recording member, in terms of the laser power required.
The reductîon in the amount of power needed to record in-formation on the recording member of the pres~nt inventionwill also be beneficial to the problem of heat disposal or dissipation.
The dyes which are suitable for use in the dye-in-polymer coating 12 are thcse which have their spectral absorptivity or absorption peak at or very near the wave length of the laser employed. In this respect, the dye-in-polymer coating and the recording laser should be matched for maximum efficiency. We have found that Disperse ~ed 11 dye made by ICI having the structural formula:
3~

1127~45 o ~
o-ctt~

the Eastman Polyester Yellow 6G-LSW having the structural 5 formula:

\C _ Clt ~~
!~ c~ ~
A~ ~3~
and the infra red absorber IR-130 14401 Eastman Kodak, having the chemical formula:

~3 ~ 3 ~8 are examples of suitable dyes.
The proportion of dye in the thin coating 12 of dye-in-polymer should be advantageously as high as possible. The efficiency of the optical recording member of the present invention in recording information thereon will be higher when the dye concentration in the thin coat-ing 12 is high. This is because there must be sufficient amount of dye in the thin coating 12 to efficiently absorb the energy from a writing laser and to establish anti-reflection conditions. With lower concentrations of dye, even where thicker coating 12 is employed, more materials would be consumed and more power would be required of the writing laser in the recording process. However, overload ing the dye and polymer mixture with dye may cause the dye to become unstable and crystallize out. Furthermore, when optical focussing is utilized, some small reflectivity from coating 12 is desired. We have found that it is possible to 7~45 load the dye-in-polymer mixture with up to 80 percent by weight of dye without causing crystallization.
The thickness of the thin coating of dye-in-polymer is of great importance. As indicated above, this dye-in-polymer layer should be as thin as possible to increase the efficiency of the recording system, or to minimi~e the energy required for marking, but there must be sufficient amount of dye present to form an anti-reflection layer and to absorb most of the marking energy. Hereto-fore, a thin recording layer has been achieved only withsubstantially pure dyes and with vapor deposition tech-niques. When thermoplastic materials have been used in the recording layer, such recording layers have been relatively very thick. Surprisingly, it has now been found that a thin coating of dye-in-polymer in accordance with the present invention can be made to be very thin, e.g. about 100-2000 Angstroms and yet provide a very sensitive record-ing member. Moreover, the thin coating of dye-in-polymer of the present invention can be formed on the reflective substrate by inexpensive and conventional techniques such as solution coating, which includes spin coating, roll coating, and dip coating.
Referring to Figure 2, a cross-sectional view of another embodiment of the optical recording member of the present invention is shown. In this embodiment, there is provided as in the embodiment of Figure 1 above, a reflec-tive substrate 11 made of a base support layer 13 and a reflective layer 14, and a thin coating 12 of dye-in-polymer. In addition, this embodiment has an overcoat layer 15 on top of the thin coating of dye-in-polymer. In using the optical recording member of the present inven-tion, efforts will be made to keep the recording and reading apparatus as free from dust as possible. However, it will be appreciated that the optical recording member must be handled and stored. Thus, it would be virtually impossible to completely exclude the presence of dust and other minute particles from the sur~ace of the optical recording member. Since each square inch of the surface area of the optical recording member must accommodate millions of pieces of information, a single dust particle will occupy the area intended for a thousand to ten thousand bits of information. The presence of dust particles directly on the surface of the thin coating 12 will thus prevent recording or reading of information from the area involved. More important, the presence of dust particles directly on the optical recording member of the present invention may result in the reading or recording of erroneous information on the recording member. By over-coating the optical recording member with a layer 15, which should be of a material that is transparent to the record-ing laser ~nd to the reading light, dust particles will be separated from the surface of the thin coating 12 by a distanc2 which is the thickness of the overcoat 15. We have found that the overcoat layer 15 may suitably be 0.2 to 3 millimeters thick and preferably between about 0.5 to 1 millimeter thick. ~ince the recordin~ laser beam is in a sharply convergent state at this distance away from the surface of the dye-in-polymer layer 12, we have found that the presence of dust particles on the surface of the over-coat layer 15 does not appreciably interfere with the recording or r~ading of information from the optical recording member. The overcoat layer 15 may be made of the same type of materials as the base support layer 13, for example, glass, polyesters, polyamides, polyvinylalcohols, polycarbo~ates or polymethylmethacrylates, etc.
Figure 3 shows another embodiment in which the base support layer 13 and the overcoat layer 15 of Figure 2 have been combined into a single support and overcoat layer 16. ~ayer 16, which can be made of the same class of mater-ials as layer 13 and 15, ser~es to both impart structural integrity to the optical recording member and to separate dust and other particles from the surface of the dye-in-polym~r la~er 12.

~2'7~5 Figure 4 shows a further embodiment in which an air gap or space 17 is provided on top of layer 12. Air gap 17 is formed by a top layer 18, which may be made of the same type of materials as layers 13, 15 and 16, and spacers S 19. When the optical recording member is in the form of a round disc, spacers 19 may be in the form of a ring around the periphery of the disc and in the form of a column in the center of the disc. Spacers 19 may be made of practically any material, such as a polymer or a metal, since they can be non-transparent. The advantages of this embodiment are that the air gap is a poor heat conductor and that it pro-vides a space for heated or melted materials to be de-posited.
With reference to Figure 5, there is shown a schematic diagram of an apparatus which may be used to record information on the optical recording member of the present invention, as well as to read the information recorded on such a member. A beam 21 is ~enerated by a laser device 22 and goes through a focusing lens 23 into an acousto-optic modulator 24, and from there through a hole or slit 25. The A/O modulator 24 is controlled by a micro-processor 26, and it controls both the duration and the amplitude of pulse of the beam that will be permitted to go through hole 25. A single solid state laser with internal modulation can be substituted for the laser device 22, ~ens 23 and A/O modulator 24. From the hole 25, the beam is directed by a reflecting mirror 27 to a beam splitter 28.
Beam splitter 28 is basically a transmitter, and only a very slight ~mount of attenuation occurs there. ~rom beam splitter 28, the beam is directed to another beam splitter 29, deflected there through a ~ovable objective lens 30, and on to the dye-in polymer layer of the optical recording member 31 of the present invention. There is a small but constant amount of leakage through the A/O modulator ~4.
This sma~l amount of leakage is insufficient to cause writing on the optical recording member 31, but is re-flected back along the path shown in dotted line through a 11279~5 pair of cylindrical lenses 32 and 33 into a focusing detector 34. This signal will permit the focusing detector 34 to keep the movable objective lens 30 in a position to precisely focus the beam onto the optical recording member 31 through the focus control device 35.
The infor~tion is recorded on the optical recording member 31 in micron-size bits. Typically, the recording member may contain up to 108 bits of information per square centimeter.
When the information recorded on the optical recording member 31 is to be read out, a continuous, low powered beam from laser 22 is directed onto the recording member 31, and thence reflected back through beam splitter 29 into photodetector 36. The signal may be visually displayed on an oscilloscope or the signal may be sent on to the mic~oprocessor 26. The positioning of the optical recording member 31, in both the recording and reading processes, is controlled by the microprocessor, as shown.
A separate light source having a wavelength not absorbed significantly by the thin layer 12 can also be used for focusing. Tracking can be achieved by conventional means.
Although the detailed me~hanism of what takes place in the dye-in-polymer layer is not completely under-stood, it is believed that when that layer is exposed to a laser beam of suitable wave length, the dye molecules absorb the radiation which is then converted into thermal energy. This thermal energy facilitates the removal of the dye from the area struck by the laser beam either by lateral diffusion of the dye molecules or by the flow of the softened dye-polymer mixture. In any event, the migra-tion of the dye exposes the reflective layer thereunder.
The invention will be further illustrated by the following specific examples.

1127g~s EXAMPLE I
A glass substrate, spe~ifically a Corning Glass Substrate #7059, was precleaned and then suspended in soapy water in a sonic bath for thirty minutes. The su~strate was then removed from the soapy water, rinsed with deion-ized water and suspended in a sonic bath of deioni2ed water for another thirty minutes. The cleaned substrate was then suspended above refluxing ethanol for about one hour. Upon removing from the refluxing ethanol, the glass substrate was immediately dried with a heated air gun. Care must be taken to dry the substrate quickly and smoothly to avoid spotting the glass surface. The cleaned substrate was then stored in a slide tray. When the cleaned substrate is to be used in further processing, it must be carefully inspected for presence of any dust particles. If dust particles are found on the glass surface, an ionizing air gun may be used to remove the dust immediately before further processing steps.
The cleaned glass substrate was then coated with an aluminum reflective layer. The aluminum employed was of 99.999% purity, commercially available from the R. D.
Mathis Co. The aluminum is evaporated onto the glass sub-strate with a Varian NRC 3115 Evaporator. The evaporation pressure was 10 7 Torr, with a current of 290 amps. The deposition rate was 50 A per second. An aluminum layer of 300 A thickness was obtained.
A 3% solution of the polymer and dye in a solvent was prepared, although higher and lower concentrations of the poly~er and dye in the solvent may be used, depending on the particular polymer and dye and so]vent employed, the thickness of the resultant film desired, and the method of preparation, etc. 100 ml of the solvent, methylethylketone (MEK~ was mixed with 1.2 grams of polyvinylacetate and 1.8 grams of Eastman Polyester ~ye Yello-~ 6G-LSW. The mix-ture was thoroughly mixed with a magnetic stirrer for threehours at room temperature. The resultant solution was then filtered, using a syringe filter with a 1 micron fluoropore filter.
The polymer-in-dye solution was then spin coated onto the aluminum side of the substrate, using a Headway Research Photo-Resist Spinner. The spin rate was 9,000 rpm, and the duration was 100 seconds. Either the spin rate or the solution concentration may be adjusted to obtain the particular film thickness desired. The film thickness for this particular coating was 1,000 A. The polymer-in-dye film was then air dried at room temperature.
Alternatively, the polymer-in-dye film may be dried in a vacuum oven at 40C. However, immediately after the spin coating process, the polymer-in-dye film will be dry enough to be handled. The resultant dye-in-polymer film contains 60% dye.
EXAMPLE II
The procedure of Example I was repeated except that the polymer-in-dye solution was prepared by mixing 2.~
grams of the dye Eastman Polyester Yellow 6G-LSW with 0.6 grams of the polyvinylacetate in 100 ml MEK. The resultant polymer-in-dye film contained 80% dye.
EXAMPLE III
The procedure of Example I was repeated except that the dye Eastman Polyester Yellow 6G-LSW was replaced by the red dye ICI Disperse Red 11.
EXAMPLE IV
The procedure of Example I was repeated except that theJ Eastman Polyester Yellow dye was replaced by the dye IR~ 14001 Eastman Kodak.
EXAMPLE V
The procedure of Example II was repeated except that the dye Eastman Polyester Yellow was replaced by the ICI Disperse Red 11.
EXAMPLE VI
The procedure of Example I was repeated except that an overcoat of polymethylmethacrylate of 1 mm thick-~1~79i~S

-~3-ness was placed on top of the dye-in-polymer film after the film had been completely dried.
EXAMPLE VII
The optical recording members prepared in accor-dance with Examples I and II were used to record informa-tion, using the apparatus illustrated in Figure 5. The marking laser was of the helium-cadmium type with a marking wavelen~th of 4410 A, and a beam size of 1 ~ m. The writing power was varied between about 1 and 30 mW and the exposure times betwePn about 5 n sec and 10 ~Lsec. The marking energy required for the marking thresholds were as low as 0.03 nJ/per bit. The information recorded on the optical recording me~bers was retrieved by reading with the appara-tus illustrated in Figure 5. The reading laser was of the same type as the writing laser, but the power levels used were 0.1 mW and lower.
EXAMPLE VIII
The procedure of Example VII was repeated with the samples of Examples III and V except that the marking laser was of the argon-ion type with a marking wavelength of 5140A. Good marking and eead out were achieved.
~XAMPLE IX
The procedure of Example VII was repeated with the sample of Example IV except that the marking laser was of the gallîum-arsenide and the gallium aluminum arsenide types with marking wavelengths in the range from about ~150 to 8500 A~ Good results were also achieved.
While the invention has been described in detail with reference to specific preferred embodiments, it will be appreciated tha~ various modifications may be made from the speciic details wi~hout depar~ing from the spîrit and scope of the invention~

Claims

WHAT IS CLAIMED IS:

1. An optical recording member for optically recording and retrieving of information thereon comprising a reflective substrate having coated thereon a layer of a polymer having a dye dispersed therein, said dye-in-polymer layer being made to be responsive to an optical recording apparatus so that at least the dye portion of said layer will migrate from the areas worked upon by said optical recording apparatus to expose the reflective substrate, and said dye-in-polymer layer forms an anti-reflection layer to cover said reflective substrate in other areas.

2. An optical recording member according to claim 1 wherein the reflective substrate has doped or undoped polyacetylene as the reflective element.

3. An optical recording member according to claim 1 wherein the reflective substrate is formed of a support layer and a reflective layer, with the reflective layer positioned immediately adjacent the dye-in-polymer layer.

4. An optical recording member according to claim 3 wherein the support layer is made of a plastic material and the reflective layer is made of aluminum.

5. An optical recording member according to claim 1 wherein the dye is selected from the group consisting of ICI dispersed Red 11, Eastman Polyester Yellow 6G-LSW, and IR-132 14401 Eastman Kodak.

6. An optical recording member according to claim 1 wherein the polymer in the dye-in-polymer layer is a thermoplastic material.

7. An optical recording member in accordance with claim 1 wherein the polymer is polyvinylacetate.

8. An optical recording member according to claim 1 wherein the dye-in-polymer layer is about 100 to 2000 .ANG. thick.

9. An optical recording member according to claim 1 wherein the dye-in-polymer layer contains between about 3-80% by weight of dye.

10. An optical recording member according to claim 1 further comprising an overcoat layer on the dye-in-polymer layer, said overcoat layer is made of a polymeric material which is transparent to the optical apparatus for recording and retrieving information from said optical re-cording member.

11. An optical recording member according to claim 10 wherein the overcoat layer is made of poly-carbonate, polymethylmethacrylate, polyester, or polyviny-lalcohol.

12. An optical recording member according to claim 10 wherein the overcoat layer is between about 0.2 and 3 mm thick.

13. A method for recording information on the optical recording member of claim 1 comprising:
providing a recording laser having a wavelength substantially matching the absorption peak of the dye-in-polymer layer of said optical recording member;
precisely positioning the dye-in-polymer layer in the path of the recording laser to receive the infor-mation to be recorded from the recording laser; and causing the migration of at least the dye portion of the dye-in-polymer layer at those areas in accordance with the information to be recorded, to thus expose the reflective substrate at said areas.

14. The method according to claim 13 wherein the dye is Eastman Polyester Yellow 6G-LSW and the laser is a helium-cadmium laser.

15. The method according to claim 13 wherein the dye is ICI Dispersed Red 11 and the laser is an argon-ion laser.

16. The method according to claim 13 wherein the dye is IR-132 14401 Eastman Kodak and the laser is a gallium-arsenide or a gallium-aluminum-arsenide laser.

17. An optical recording member according to claim 10 wherein said overcoat layer is spaced from said dye-in-polymer layer so as to form an air gap there-inbetween.