Patent Application
20110318506
1. Field
The present invention relates to optical tape storage technology and in particular to methods for making optical tape.
2. Description of the Related Art
The ever expanding amount of digital data provides an impetus for the continuing development of high capacity storage solutions. Technologies that are suitable for these applications include optical tape, magnetic tape, and optical disks. Of these possibilities, optical tape technology is believed to provide the greater storage capacity.
The typical optical tape medium includes a base film such as polyethylene naphthalate (PEN) over-coated with multiple layers for recording digital data. A polymeric imprint layer is usually disposed over the base film. In one type of optical tape, the imprint layer is over-coated with a reflective metallic layer that is, in turn, over-coated with a sequence of dielectric layer, phase change layer, and dielectric layer. The actual data recording and reading occurs in the phase change layer. In a typical application, a pulsed laser beam is projected from an optical head assembly onto the optical tape thereby causing a phase change in the phase change layer that results in data being encoded therein. Data encoded onto the optical tape is also read with a laser with the reflective layer reflecting light to a detector. Moreover, optical tape usually includes optical servo marks embossed into the imprint layer along the length of the tape for operating with a servo control system for controlling the optical head, Although the current optical tape technology works reasonably well, there are a number of problems related to the polymeric imprint layer.
The imprint layers tend to cause a number of detrimental effects due to dimensional changes that occur therein. For example, such dimensional changes may cause thickness variations in the metal and dielectric layers. Although these effects are believed to be due to poor mechanical and thermal properties of the imprint polymer, it is also thought that the sensitivity of the imprint layer to electron beam damage during the metal layer and dielectric layer depositions also contributes to these changes.
Accordingly, there is a need for new materials and methods for forming the imprint layer used in optical tape media.
The present invention solves one or more problems of the prior art by providing, in at least one embodiment, a method for forming an optical tape for data storage from a substrate film. The method of the present embodiment includes a step of patterning a curable liquid composition onto the substrate film. The curable liquid composition comprises a cationic photoinitiator and a polymerizable component selected from the group consisting of vinyl ethers, cyclohexene oxides, glycidyl ether epoxides, and combinations thereof. The curable liquid composition coated on the substrate film is illuminated with actinic radiation to form a patterned imprint layer disposed over the substrate film. A multilayer data recording assembly is placed over the second imprint layer side to form the optical tape. Advantageously, the imprint layer formed in the present embodiment is less susceptible to electron beam damage and has improved mechanical stability as compared to the imprint layers currently used to fabricate optical tape medium.
In another embodiment, a method for forming an optical tape for data storage from a substrate film is provided. Characteristically, the substrate film includes a first substrate side and a second substrate side. The method of the present embodiment includes a step of patterning a curable liquid composition onto the substrate film. The curable liquid composition comprises a cationic photoinitiator and a polymerizable component selected from the group consisting of vinyl ethers, cyclohexene oxides, glycidyl ether epoxides, and combinations thereof. The curable liquid composition coated on the substrate film is illuminated with actinic radiation (e.g., UV radiation) to form a patterned imprint layer disposed over the substrate film. A metal layer is deposited over the patterned imprint layer. A first dielectric layer is then deposited onto the metal layer. A phase change layer is then coated onto the first dielectric layer. Finally, a second dielectric layer is deposited onto the phase change layer.
In still another embodiment, an imprint layer formed by the methods set forth above is provided. The imprint layer includes the residues of a cationic photoinitiator and of a polymerizable component (e.g., monomer) selected from the group consisting of vinyl ethers, cyclohexene oxides, glycidyl ether epoxides, and combinations thereof. The imprint layer optionally further comprises the residues of a free radical photoinitiator.
Exemplary embodiments of the present invention will become more fully understood from the detailed description and the accompanying drawing, wherein:
Reference will now be made in detail to presently preferred compositions, embodiments and methods of the present invention, which constitute the best modes of practicing the invention presently known to the inventors. The Figures are not necessarily to scale. However, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. Therefore, specific details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for any aspect of the invention and/or as a representative basis for teaching one skilled in the art to variously employ the present invention.
Except in the examples, or where otherwise expressly indicated, all numerical quantities in this description indicating amounts of material or conditions of reaction and/or use are to be understood as modified by the word “about” in describing the broadest scope of the invention. Practice within the numerical limits stated is generally preferred. Also, unless expressly stated to the contrary: percent, “parts of,” and ratio values are by weight; the description of a group or class of materials as suitable or preferred for a given purpose in connection with the invention implies that mixtures of any two or more of the members of the group or class are equally suitable or preferred; description of constituents in chemical terms refers to the constituents at the time of addition to any combination specified in the description, and does not necessarily preclude chemical interactions among the constituents of a mixture once mixed; the first definition of an acronym or other abbreviation applies to all subsequent uses herein of the same abbreviation; and, unless expressly stated to the contrary, measurement of a property is determined by the same technique as previously or later referenced for the same property.
It is also to be understood that this invention is not limited to the specific embodiments and methods described below, as specific components and/or conditions may, of course, vary. Furthermore, the terminology used herein is used only for the purpose of describing particular embodiments of the present invention and is not intended to be limiting in any way.
It must also be noted that, as used in the specification and the appended claims, the singular form “a,” “an,” and “the” comprise plural referents unless the context clearly indicates otherwise. For example, reference to a component in the singular is intended to comprise a plurality of components.
Throughout this application, where publications are referenced, the disclosures of these publications in their entireties are hereby incorporated by reference into this application to more fully describe the state of the art to which this invention pertains.
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In some variations, the optical tape processing is paused after formation of the imprint layer. In this variation, the coated substrate may be rolled onto a spool for later processing. In other variations, the optical tape may be subjected to a slitting process in order to fit in a cartridge.
As set forth above, various embodiments of the present invention advantageously utilize a curable liquid composition that is cationically polymerized. Advantageously, the curable liquid composition has a viscosity less than about 50 cps at 25° C. In another refinement, the curable liquid composition has a viscosity less than about 30 cps at 25° C. In another refinement, the curable liquid composition has a viscosity less than about 20 cps at 25° C. In another refinement, the curable liquid composition has a viscosity less than about 10 cps at 25° C. Typically, the curable liquid composition has a viscosity greater than about 2 cps at 25° C. In another refinement, the curable liquid composition has a viscosity greater than about 5 cps at 25° C. The curable liquid composition includes a polymerizable component selected from the group consisting of vinyl ethers, cyclohexene oxides, glycidyl ether epoxides, and combinations thereof. In a refinement, the polymerizable component(s) are present in an amount from about 70 to about 99 weight percent of the total weight of the curable liquid composition. In another refinement, the polymerizable component(s) are present in an amount from about 80 to about 99 weight percent of the total weight of the curable liquid composition. In still another refinement, the polymerizable component(s) are present in an amount from about 90 to about 99 weight percent of the total weight of the curable liquid composition.
In one variation, the curable liquid composition includes a vinyl ether having formula I:
wherein R1 is a substituted or unsubstituted alkyl, substituted or unsubstituted cycloalkyl, substituted or unsubstituted alkenyl, or substituted or unsubstituted aryl.
In another variation, the curable liquid composition includes a vinyl ether having formula II:
In still another variation, the curable liquid composition includes a vinyl ether having formula III:
In still another variation, the curable liquid composition includes a cyclohexene oxide having formula IV:
wherein R2 is hydrogen, alkyl, or aryl.
In still another variation, the curable liquid composition includes a glycidyl ether epoxide having formula V:
wherein R3 is alkyl, alkenyl, or aryl.
In a particularly useful variation, the curable liquid composition includes a combination of the vinyl ether having formula II and the vinyl ether having formula III. In a refinement of this variation, the vinyl ether having formula II is present in an amount from about 55 weight percent to about 75 weight percent of the total weight of the curable liquid composition and the vinyl ether having formula III is present in an amount from about 25 weight percent to about 45 weight percent of the total weight of the curable liquid composition.
The curable liquid composition also includes a cationic photoinitiator. Examples of useful cationic photoinitiators include, but are not limited to, onium salts, such as diaryliodonium salts and triarylsulfonium salts that have non-nucleophilic anions (e.g., hexafluorophosphate, hexafluoroantimonate, tetrafluoroborate and hexafluoroarsenate). Specific examples of suitable onium salts include 4,4′-dimethyldiphenyliodonium tetrafluoroborate, phenyl-4-octyloxyphenyl phenyliodonium hexafluoroantimonate, dodecyldiphenyl iodonium, (4-octyloxyphenyl)phenyliodonium hexafluoroantimonate, dodecyldiphenyl iodonium hexafluoroantimonate, [4-[(2-tetradecanol)oxy]phenyl]phenyl iodonium hexafluoroantimonate and combinations thereof. In a refinement, the cationic photoinitiator is present in an amount from about 0.01 to about 15 weight percent of the total weight of the curable liquid composition. In another refinement, the cationic photoinitiator is present in an amount from about 0.5 to about 5 weight percent of the total weight of the curable liquid composition.
In another variation, the curable liquid composition further includes a free radical photoinitiator. Suitable free radical photoinitiators include, but are not limited to, benzophenones, acetophenone derivatives, and combinations thereof. Specific examples include, alpha-hydroxyalkylphenylketones, benzoins (e.g., benzoin alkyl ethers and benzyl ketals), monoacylphosphine oxides, bisacylphosphine oxides, and combinations thereof. The curable composition may also include a photosensitizer such as isopropyl-9H-thioxanthen-9-one (ITX) which is found to be a particularly useful free radical photosensitizer. In some variations, the wavelength for curing the curable liquid compositions is about 400 nm. Most photoinitiator chromophores are optimized to absorb around 250 nm. ITX has better absorbance at high wavelengths and it is known to transfer energy to photoinitiators. In a refinement, the free radical photoinitiator is present in an amount from about 0 to about 5 weight percent of the total weight of the curable liquid composition. In another refinement, the free radical photoinitiator is present in an amount from about 0.1 to about 5 weight percent of the total weight of the curable liquid composition. In still another refinement, the free radical photoinitiator is present in an amount from about 0.1 to about 2 weight percent of the total weight of the curable liquid composition.
The various methods of the present invention are used to form a polymeric imprint layer as set forth above. Therefore the imprint layer is characterized by including residues of a polymerizable component selected from the group consisting of vinyl ethers, cyclohexene oxides, glycidyl ether epoxides, and combinations thereof. In particular, the imprint layer includes residues of the compounds describe by Formula I to V. The imprint layer also includes residues of the cationic photoinitiator(s) set forth above. In some variations, the imprint layer also includes residues of the free radical photoinitiator(s) set forth above.
A polymeric imprint layer is made by coating a mixture having about 67.5 weight percent cyclohexyl vinyl ether, 30 weight percent 1,4-cyclohexanedimethanol divinyl ether, 2 weight percent (4-octyloxyphenyl)phenyliodonium hexafluoroantimonate, and 0.5 weight percent isopropyl-9H-thioxanthen-9-one onto a substrate film. The coated substrate film to then cured with UV light while passing over a patterning roller to form the imprint layer.
While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.
