Patent Application
20080182060
The invention is generally in the field of three dimensional optical data carriers and their manufacture. The optical data carriers of the invention can be used for recording and reading and in some cases are also re-writable.
Optical storage is one of the most popular data storage means. The information or data may be recorded, stored, read and erased on the three-dimensional information carrier usually having the form of a disc. Carriers may be monolithic disc-like bodies made of a transparent or translucent polymer material. The material is usually a polymer such as polymethylmethacrylate (PMMA) with bound active moieties that are capable of changing their state from one isomeric form to another upon interaction with electromagnetic energy, such as laser radiation. The information is recorded on the carrier as series of three-dimensional regular marks or oblong and tilted data marks such as disclosed in PCT application, publication No. WO 2005/015552.
The storage capacity of a three-dimensional (3D) carrier may exceed hundreds of Gigabytes and it is proportional to the volume of the carrier and particularly to the volume containing the active moiety. Because of this, the three-dimensional carriers have an active thickness that significantly exceeds the thickness of conventional discs. For example, a typical three-dimensional two-photon terabyte carrier would typically have an active thickness of 1 to 6 millimeter.
Recording and reading of information of a two photon, three-dimensional carrier may be performed by one or two laser beams termed “activation” or heating beam(s) and a recording beam. Typically, the activation beam changes the energetic state at a particular recording location (by 1-photon absorption, e.g. at about 980 nm) enabling the recording beam to change the active moiety state from one isomeric form to another or what is termed trans-cis transition (by 2-photon absorption e.g. at about 670 nm) to record or erase the information. Typically, the activating beam is a different beam than the recording beam. Alternatively, the recording beam may also the activating beam which, in turn, may be different than the read beam.
Being relatively thick, two-photon 3D optical data carriers are typically produced by casting in a manner that causes relatively small distortions in their geometry. However, injection and extrusion production methods are also known. In the latter manufacturing process, cooling of the relatively thick carrier may take a considerable amount of time and the chemical steady state would be established at a relatively high temperature resulting in a high level of residual high-level energetic transitions in the carrier. These residual transitions impart lower signal-to-noise ratio in reading signals, once put in use as data storage. Casting results gives rise to a lower amount of residual high-level energetic transitions and better carrier recording properties.
One of the problems associated with such a data carrier is that the activation beam penetrating to deeper layers of the carrier, is partially absorbed by the material's upper layers and thus the power for recording in inner layers should typically be increased, as compared to the power required for recording in outer layers. Increase in the power of the activation beam, required to compensate for the absorption is difficult to achieve.
Information or data marks may be of sub-micron size. Recording, reading or erasing of such small marks requires high mechanical accuracy of the disc, which is in case of thick discs is difficult to obtain through casting. The high rotational speed of the disc, desired for fast recording and reading of data, may give rise to further distortions of the geometry of such a disc eventually limiting the accuracy and speed of recording or reading of submicron marks. The mechanical properties of the photo-active medium may also become a limiting factor if, for example, the active material comprising the active groups is too fragile or flexible.
The ability to have the same predictable laser power for every recording or reading depth would simplify the processes.
In accordance with the invention a new optical data carrier is provided. The optical data carrier of the invention is characterized in that different layers have different concentrations of the reactive, irradiation-absorbing material. The term “layer” should be understood in its physical sense, namely as meaning volume portions that are all equidistant from the external top or bottom face of the data carrier. In other words, the data carrier of the invention is characterized in that there are different concentrations of the irradiation-absorbing material at different depths away from its upper (or lower) surface, the upper surface being that from which data is written into or read from said data carrier. The different concentrations typically give rise to a depth-related concentration gradient, with the concentration increasing (monotonically or in a step-wise fashion) in relation to the distance from (or depth) said upper surface, all regions that are equidistant from the upper surface, have substantially the same concentration of the irradiation-absorbing material.
In accordance with the invention there is thus provided a three-dimensional (3D) data carrier comprising a plurality of layers characterized in that each of said layers contains a different concentration of irradiation-absorbing material.
The term “irradiation” typically denotes infrared (IR), visible or ultraviolet (UV) light irradiation. The “irradiation-absorbing material” may be any molecule or a group of molecules that can absorb the electromagnetic, e.g. light irradiation and generate heat through non-irradiative or convection mechanisms, emit photons through a fluorescence mechanism or undergo a conformational change, e.g., a switch between cis and trans configurations.
In accordance with an embodiment of the invention, the concentration of the irradiation-absorbing material increases from one surface of the data carrier towards surfaces away therefrom. Typically, the concentration of irradiation-absorbing material in different layers is selected such as to ensure equal absorption of power of an irradiating beam at different depths of said carrier
In accordance with another preferred embodiment, the 3D data carrier is produced as a laminate assembled from a plurality of plates or sheets adhered to one another. The sheets or plates are typically adhered to one another by the use of an adhesive, which once cured should have a refractive index similar to that of the polymeric material from which the sheets or plates are made of. By one embodiment, the individual plates or sheets have different concentrations of the irradiation-absorbing material. This means that the plates or sheets comprise some sheets or plates with different concentrations of the irradiation-absorbing material than other sheets or plates in said carrier. By some embodiments, each such sheet or plate has a different concentration of said material, whereby a gradual gradient of concentrations is obtained. By another embodiment, several of the assembled sheets or plates may have one concentration of said material, several others another concentration, etc. Such a 3D data carrier thus comprises two or more groups of two or more sheets or plates each, all sheets or plates of one group have the same concentration of said material different than that of any other of said two or more groups. In said 3D carrier several sheets or plates with one concentration of said material will typically be all adjacent one another and will constitute one group, sheets with another concentration another group, etc. While there will still be a gradient of concentrations in such case, the concentration gradient throughout the medium will be less gradual or rather more a stepwise gradient.
By one embodiment of the invention, the irradiation-absorbing material is incorporated also in the adhesive. This may permit different plates or sheets in the disc of the invention to have the same concentration of the irradiation-absorbing material, the different concentration between the plates being obtained by including different concentrations thereof in the different adhesive layers that adhere different plates or sheets to one another. By some embodiments of the invention the different sheets or plates that are assembled together to form the disc have no irradiation-absorbing material and these are included only in the adhesive material.
By another embodiment of the invention the different sheets or plates are adhered to one another through light-induced melting of a boundary layer between two adjacent sheets or plates.
The thickness of each layer is typically in the range of about 100-600 μm. The thickness may be selected based on minimization of the amount of high-energy transition formed at the steady state conditions in course of polymer cooling. Thick injected-molded plates cool slowly following their injection molding and therefore if the cooling is not sufficiently rapid, the molecules of the irradiation-absorbing material may undergo a heat-induced change in their configuration, for example a switch between their cis and trans isomeric states. Thus, molding thin plates that cool faster, may at times be preferred over thicker ones.
The 3D data carrier of the invention is typically, although not exclusively, in the form of a disc.
The invention also provides methods for producing said 3D data carriers comprising assembling and adhering together different plates or sheets. This may be either through the use of an adhesive, applied on at least one of two adjacent sheets, which may include also the irradiation-absorbing material, or through a light-induced transient (namely during the adhering step) melting of a boundary layer between adjacent plates or sheets. By one embodiment, different sheets or plates that are assembled together have different concentrations of irradiation-absorbing material. In accordance with another embodiment of the method, different assembled sheets or plates have the same concentration of said material, the method comprising adhering sheets or plates by the use of an adhesive that contains the irradiation-absorbing material, different sheets or plates being adhered with adhesive compositions comprising different concentrations of said material.
A method for the manufacture of three-dimensional information carrier in accordance with an embodiment of the invention comprises (i) laminating transparent or translucent sheets of polymer, (ii) a laser beam melts the boundary layer between said sheets of polymer and the melted layer bonds said sheets to each other, and (iii) a laser beam cuts out a plurality of said carriers from said laminated sheets.
In order to understand the invention and to see how it may be carried out in practice, a preferred embodiment will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:
The structure and principles of the carrier and the assembly method described herein may be understood with reference to non-limiting exemplary embodiments depicted in the annexed drawings. In the drawings, like reference numerals in different figures denote elements with identical or similar function. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the method. As will be understood by an artisan, the depicted embodiments are but illustrative examples of the invention as disclosed and defined above.
Typical examples of active groups are stilbene derivative of the following formula (I):
Ar1(R1)C═C(R2)Ar2 (I)
wherein Ar1 and Ar2 are phenyl groups optionally independently substituted with one or more groups selected from —C1-6alkyls, —OC1-6alkyl, —SC1-6alkyl and, —C1-6OH, thiols and their salts, NR′R″, R′ and R″ being independently hydrogen or C1-6alkyl; R1 and R2 are substituents selected from nitrites selected from —(CH2)nCN, n being 0, 1 or 2, halides, RCOOH, R being C1-6alkyl, their C1-6exters, or a nitro compound selected from —(CH2)nNO2, n being 0, 1 or 2.
C1-6alkyls may be straight or branched alkyls, preferably a methyl, ethyl, propyl, isopropyl, butyl, sec-butyl or tert-butyl or pentyl groups; the nitrile is preferably a —CN group and the nitro compound is preferably an —NO2 group
The polymeric material is typically prepared from modified monomers of the following formula (II):
Ar1(R1)C═C(R2)Ar2—M (II)
wherein Ar1, Ar2, R1 and R2 are as defined above and M is a polymerizable monomeric moiety. Specific example of M are acrylic monomers such as methylmethacrylate (MMA) and methylacrylate (MA) derivatives.
Exemplary modified monomers are those of the following formula (IV):
wherein X and Y are as defined above.
Particular examples of modified monomers of the following formula (IV) and (V):
The stilbene derivatives can undergo a light-induced cis-trans isomerization and can in this way be converted from blank or unwritten form to written form upon interaction with appropriate light wavelength and energy, such as by laser irradiation.
The thickness of the plates may be chosen according to a number of different criteria, among them considerations of optimization of the cooling speed of the plates and reduction of the time in course of which steady state conditions in the polymer material would exist. Plates 174 may be produced by injection or extrusion, which have essentially higher throughput than casting, although the former means of preparation are limited to relatively thin plates.
The data is optically recorded on carrier 170 in form of marks 172 in practically any location in the 3D optical data carrier, although conveniently the marks are ‘written’ in a layered fashion to form a plurality of “virtual” layers 176. The distance between layers 176 may typically be in the range of 3-15 micron. The total thickness of the assembled carrier 170 may vary from 200 micron to more than 6 mm. Carrier 170, which is typically, as in the illustrated embodiment disk-shaped (accordingly, the optical data carrier will be referred to herein occasionally as “disc”), has a central mounting bore generally designated 182, symmetrical about rotational axis 186. The diameter of the bore may be different in different layers changing from a broader diameter in its external layers to narrower diameter D in inner ones. The portions 188 and 190, respectively at the disc's periphery and adjacent the central bore, are typically not-utilized for recording data marks, although they may be used to record auxiliary information.
Linear absorption of an electromagnetic radiation by medium, in which the radiation traverses, is proportional to the amount of encountered absorbing material, which is in turn proportional to the concentration of such absorbing material, the length (depth) of the path of the electromagnetic wave in the medium, and the (wavelength dependent) linear absorption coefficient. By way of example, if a laser beam 190a will be focused on a point 196a in the second layer, it will loose less power than beam 190b focused on a point 196b in a more inner layer, having before penetration into the medium power equal to beam 190a.
The activating laser beam activates the activating groups. The recording laser induces a change in the state of the active groups in the polymer material. The activation is performed by heating a microscopic volume of the optical data carrier 170 with a pulse of a fixed and predetermined duration. The ability to have the same predictable laser power for every recording or reading depth would simplify the processes and require less laser power. A material having a constant absorption in terms of power absorbed per optical path in the disk (Watt/cm) may provide this quality.
The focal point 196 of laser beam 190 is negligibly small relative to the disk or even plate thickness (less than a micron as compared with a few hundred microns to a few millimeters of the disc's thickness.) The intensity at the focal point of a laser beam at a certain depth is expressed in the following function (1) as:
I(x)=I*exp[−a*c(x)*x] (1)
Wherein:
I irradiation intensity at the surface of the disk
a absorption coefficient
x depth in the plate
e(x) concentration of the absorbing substance, namely that of the active groups or the activating dgrruops, as a function of depth in the plate that may be limited by saturation effects
It is desired according to a preferred embodiment of the invention that the absorbance at every depth should be constant as represented by the following function (2) as:
Constant=d/dx(I*exp[−a*c(x)*x])=−a*I*exp[−a*c(x)*x]*(x*d/dx c(x)+c(x)) (2)
The function (3) that determines the concentration of the heat absorbing material in the polymer may be as follows:
C(x)=−log(C1*a*x)/a/x (3)
Wherein C1 is a normalization constant (having units of concentration).
Substituting C(x) into the absorbance function and taking the derivatives, the attenuation gradient function (4) is obtained, as follows:
Δ=−I*C1*a (4)
As can be seen, the above exemplary attenuation gradient function is a constant (and has units of Watt/cm).
The requirement for equal power of absorption at every depth of the disc dictates a depth-related increase in the concentration of the light energy absorbing group (irradiation-absorbing material). One embodiment for producing such a disc would be to include different concentrations of the active, light-absorbing groups in different plates of the disc. Thus, external layer 174-1 may have a concentration of such groups, different, typically lower than the concentration in deeper plates, e.g. 174-10 or 174-N.
The concentration of such groups is selected such so as to have approximately equal absorption of power from the activation beam per unit of depth of the carrier or disc.
According to an embodiment of the invention, the different plates of the disc, e.g. each with its different concentration of active light-absorbing groups, may be independently prepared as separate plates for subsequent assembly to form said disc. As will be appreciated, the invention is not limited in any way to such a manner of disc production. The different plates may be adhered to one another by the use of adhesives. A variety of different transparent adhesives, preferably such having a light refraction index similar to that of the polymer, may be used to attach or laminate plates 174 to each other.
According to one embodiment, active groups are included in the adhesive and following polymerization of the adhesive become immobilized in the cured adhesive layer and are typically bound to the polymeric backbone thereof. The concentration of the active groups in the adhesive may be different than the concentration thereof in the adjacent plates. The control of the concentration of the active groups may be an effective means for achieving a depth-dependent concentration of said active groups. At times, the plates may be made without such active groups which will thus be included only in the adhesive.
Lamination of a number of plates 174 into one carrier disc 170 increases the mechanical strength of an optical disc. It is an extremely effective means for preventing tilting and other distortions in the disc's geometry and, thus, the rotational speed of the disc in the process of writing or reading may be increased. By laminating a desired number of plates it is possible also to manufacture carriers/discs having different storage capacities. For example, when an optical disc recording medium is made by laminating two plates, it would have about half of the storage capacity of a carrier made of four plates.
An apparatus for assembly of plates to one another, according to an embodiment of the invention, is depicted in a schematic manner in
The polymer material may be sensitive to abrasions and contact handling of plates may leave scratches, pits and other that may complicate recording or reading processes. Use of pickup heads or grippers for non-contact objects handling is known in the art. One example of such pick-up head or gripper is disclosed in U.S. Pat. No. 5,871,814 to Livshits, the contents of which, at least as such relating to the mode of operation relevant to the grippers depicted in
As can be seen particularly in
As can be seen in
Use of any type of reinforcing carcasses made of materials having higher strength than polymer 178 of which the recordable plates are made supports rotation of the information carrier at a speed substantially higher than carriers that do not have such reinforcing carcass. The thickness of plates 174 may thus be increased without damaging the recording/reading performance, although formation of the steady state in plates 174 should prevail over the possible plate thickness considerations.
I is possible also to assemble the different plates to form the optical data carrier disc on the carcass.
Some of carcasses illustrated above have a central part that is configured in a hub-like form. Hubs provide convenient and accurate carrier mounting means. The three-dimensional carriers are planed for multiple and long term use. Hubs that are made of material stronger than the carrier body improve the durability of the mounting elements of the carrier. The conical surfaces of the hubs may be used as assembly jigs or tools for assembly of plates of which the carrier is produced. Dynamic balancing and thermal processing of the carrier assemblies may take place after completion of the assembly, as known per se.
Dynamic balancing of the carrier assemblies may take place after completion of the assembly. Dynamic balancing and thermal processing of assembled carriers may be required.
The described above assembly processes may be automated and assembly lines operating simultaneously on a number of carriers could be built. The speed of the assembly of three-dimensional information carriers could be further improved by implementing the assembly process simultaneously on a large number (batch) of carriers.
Apparatus 350 performs lamination of plates 340 by local heating of a narrow strip 354 of the boundary layer between plates 340. One or more laser devices 356 having a wavelength similar or different to the activating laser beam heats and melts a micron thin layer 354 between sheets 340. A lamp other than laser may also be configured for heating and melting the boundary between the sheets. Simultaneously with the melting process, rollers 358 apply equal pressure across the melted strip 354. This outer surface of rollers 358 require proper surface finish and cleanliness not to damage the surface of plates 340. Regular material guiding rollers 362 may be used to handle and direct the sheets before and after the lamination process. Upon completion of the lamination process, which may include lamination of more than two plates and laminated polymer sheet 344 leaves lamination apparatus 350. Subsequent process steps or the desired capacity of the carrier dictate the thickness of laminated polymer sheet 344.
Laser 360 may be a single laser with a scanning arrangement or a plurality of lasers or laser diodes, or other suitable IR or other light sources, represented in
At subsequent step, laminated sheet assembly is transported to a cutout station 380. A plurality of lasers or laser diodes 362 are arranged to simultaneously produce circumferential cuts 389 around and concentric with bores 374. This is schematically illustrated in
In an alternative manner of cutout of optical data carrier discs the grippers are first attached to bores 374 and the cut 389 is being made only thereafter. This is illustrated in
The disclosed method of three-dimensional carriers production is a high throughput method. Methods of injection, extrusion or casting manufacturing of sheets of polymer material are well known. Each of the process stations may be implemented as an assembly line operating as a continuous process, simplifying the material handling between the stations.
| Number | Date | Country | Kind |
|---|---|---|---|
| 60643112 | Jan 2005 | US | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IL2006/000053 | 1/12/2006 | WO | 00 | 7/12/2007 |
