Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
1993-02-22
2001-07-10
Le, H. Thi (Department: 1773)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S690000, C428S690000, C428S690000, C428S447000
Reexamination Certificate
active
06258471
ABSTRACT:
The invention relates to unique coating compositions suitable for preparing master media for anhysteretic recording and a process for making them. More particularly, the invention relates to coating compositions which provide master media having superior durability and anhysteretic recording characteristics notwithstanding surface roughness and coercivities significantly less than three times those of copy media.
BACKGROUND OF THE INVENTION
Conventionally, contact printing has been used as a system for the high speed duplication of audio and/or video signals prerecorded on a master. In contact printing, the master medium must have a coercivity three times higher than that of the copy tape. To attain high duplicating speeds, generally more than one hundred times normal speed, the master and copy are wrapped around something like a transfer drum so that the coated surfaces of each face one other. Air pressure is generally used to press the master and copy together and a bias field is applied using a stationary transfer bias head. The mirror image of the magnetic pattern on the master becomes transferred onto the copy.
Devices for printing or copying signals by tape-to-tape copying processes from a master magnetic tape on which the signals are already recorded in a mirror image to a slave or copying magnetic medium such as a tape using either a magnetic printing or thermal printing method have been described, for example, in U.S. Pat. Nos. 3,592,977; 4,755,888 and the like. Other devices for anhysteretic recording are also known for tape-to-tape copying as well as for copying from a tape to photographic film base or from magnetically recorded layers onto transparent magnetic layers on a copying substrate such as transparent magnetic layers in the cellulose acetate base of photographic film.
Currently available master tapes which provide sufficient signal to transfer a mirror image to a copy medium, particularly a photographic layer, are quite fragile. When attempts were made to record to photographic film, the commercial master failed so quickly that it was not possible to evaluate the record/playback apparatus to be used. The commercial master was brittle and had poor adhesion to base with particularly rapid failure at the edges.
To function adequately, a master must not only have high durability but it must also function without scratching or otherwise damaging the magnetic, photographic, or other layers of the copying medium. High coercivity (2000 Oe) master tapes are generally used with low coercivity (650 Oe) copy media.
Further, the master must function without “pre-exposure” of the receiving sensitized layers due to sparks from electrostatic discharge of charges accumulated during the transport and transfer processes when film webs are driven, brought together, and parted at high speed. In magnetic transfer from a master to a magnetic film base, such problems are resolved by back coating the master with a conductive layer, preferably a thin and durable conductive carbon containing layer. However, mobile components transfer from the magnetic layer and back coat on contact with the receiving medium during high speed copying. While such mobile components as well as volatile molecules or particulate debris in the air flow do not generally present a significant problem during transfer to magnetic receiving media, they are quite detrimental to a photographic layer since static changes anywhere in the system can destroy the photograhic properties of a photosensitive layer.
SUMMARY OF THE INVENTION
It has now been found that coating compositions for high durability, non-brittle, and adherent master media for anhysteretic transfer of magnetically recorded information to a copy medium, particularly to a photographic layer, comprise from about 59 to about 69% of a magnetic pigment, preferably from about 64 to about 68%, most preferably 64%; from about 2.9 to about 6.9% of an abrasive powder, preferably from about 3.8 to about 5.4, most preferably 5.36%; from 0 to about 5.5% of a colloidal inorganic powder, preferably from about 1 to about 3%, most preferably 1.34%; from about 2.9 to about 4.5% of a wetting agent, preferably from about 3.3 to about 4.4, most preferably 3.8%; from about 0.7 to about 3.1% of a lubricant, preferably from about 0.8 to about 2.3, most preferably 1.54%; from about 14.1 to about 35.6% of a binder, preferably from about 20 to about 25.5%, most preferably 21%, at least about 85% of which is a polyurethane and from 0.05 to about 15% of which is a polyisocyanate crosslinking agent, preferably about 10%. (All percentages of the components of the coating composition described herein are by weight based on the total dry weight of the coating composition except the polyurethane and crosslinking agent, which are percent by weight of the binder.)
The coating compositions of invention can be disposed on a substrate or support, preferably back-coated with a composition containing from about 15 to about 25% of carbon black, from about 15 to about 25% of an inorganic filler, from about 0.5 to about 2% by weight of an abrasive, from about 20 to about 30% of a vinyl copolymeric binder, from about 15 to about 25% of a polyurethane binder, from about 7.5 to about 17.5% of a crosslinking agent, from about 0.9 to about 2% of a lubricant, from about 0.06 to about 0.6% of a coating aid. All percentages are by weight of the dry weight of the backcoating which is preferably applied to provide a dry coating thickness of from about 0.3 to about 1.5 microns, most preferably about 0.5 micron. The backcoating composition is applied as a dispersion, preferably containing from about 8 to about 15% by weight of solids, most preferably 10%, in any suitable solvent such as any of those described herein, preferably mixtures thereof, most preferably approximately 4:3:3 mixtures of methylethylketone:methylisobutylketone:cyclohexanone.
Backcoating compositions which obviate the problems caused by electrostatic charges which arise during the transport and transfer processes generally in signal transfer to a magnetic film base do not behave satisfactorily when a signal is being transferred to a photographic layer. The backcoating of the invention obviates pre-exposure problems associated with sparks from electrostatic discharge of charges accumulated when webs are driven, brought together, and parted at high speed. Problems arising from mobile component transfer including volatile molecules or particulate debris in the air which can be detrimental to a photographic receiving layer are obviated when the backcoat of the invention is used.
The master media of the invention have good durability and electrical and recording performance characteristics. The master media of the invention, which generally have a coercivity of at least about 2000 Oe, efficiently and effectively transfer signals to copy media having coercivities ranging as high as from about 850 to about 1000 Oe. The master media of the invention have similar output characteristics to known high coercivity master tapes but, because they provide thinner coatings, the master media of the invention have better overwrite. They also have superior adhesion to substrates, particularly polyester substrates whether subbed or unsubbed, with none of the brittleness noted with prior master media. Also, the ability to use a thicker film base improves handling and transport characteristics. In addition, scratches and other damage to copying media, particularly the magnetic layers of cellulose acetate or polyester photographic film base, are reduced or prevented using the master media of the invention.
The magnetic coating compositions of the invention are prepared by an essentially three-step process involving a wet-out stage, a grind stage, and a let-down stage. The process involves wetting out by mixing magnetic pigment, abrasive powder, colloidal inorganic or carbon powder, and wetting agent with a solvent, grinding the wet-out mixture, letting down the wet-out/grind mixture by adding binder, lubricant and polyisocyanate crosslinking agent thereto an
James Robert O
Sherwood Harry J
Verdone Joseph A
Eastman Kodak Company
Le H. Thi
Wells Doreen M.
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