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CROSS-REFERENCE TO RELATED APPLICATIONS
This application is related to application Ser. No. 585,164, filed June 9,
1975, now issued U.S. Pat. No. 4,075,018, which is a continuation-in-part
of application Ser. No. 375,812, filed July 2, 1973, now issued U.S. Pat.
No. 3,926,633,, and to copending application "Fluorescent Soundtrack
Readout System" Ser. No. 088,471 of Custer and Bird filed concurrently
herewith, which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention is directed to a motion picture film wherein a layer
containing colorless, transparent ultraviolet light excitable soundtracks
is provided on one side of the film. This is a unique material bearing two
completely independent imaging systems, the familiar silver halide system
and an electrostatic system. The soundtrack images may cover the whole or
part of either the front or back of the film and are coded in digital
form. More particularly, the present invention is directed to the use of a
two layer image receiving system to record soundtracks on a film to
produce soundtracks which are substantially colorless and transparent to
visible light, but fluoresce in the visible light spectrum when exposed to
ultraviolet light. The soundtracks comprise a toner imprinted onto the
film by means of the electrostatic imaging system.
Generally, in the prior art it has become standard procedure to provide a
magnetic or optical recording track on the edge of a film adjacent the
visible image when producing sound in motion pictures. The width of the
track is a limiting factor since it can only be on an area not covered by
the photographic image, and thus must be very narrow due to the limited
width of the film. Further, when utilizing multiple analog sound tracks on
a conventional 35 mm motion picture release print, there is not sufficient
space on the film to provide reasonable soundtracks which have good signal
to noise ratio, frequency response and high information density. The
present invention, on the other hand, provides a film and a method of
using such film that admits of recording the sound on the full width of a
film, and thus provides improved reproduction of the sound.
A digital sound record requires a high density of information on the film.
For example, a single soundtrack designed to deliver sound at 90 db.
dynamic range and 0-20 KHz frequency range will require 50,000 or more
16-bit "words" or numbers per second. This amounts to more than 800,000
bit marks per second per track, or more than 4,800,000 bit marks per
second for six tracks. With auxiliary timing and positioning information,
and with some redundant information to allow for correction of individual
bit-error, a total of about 7,500,000 bits per second is required. The
area of silver halide film currently reserved for the analog soundtrack
cannot sustain this level of information recording.
It is known to use various light systems, e.g., the system shown in U.S.
Pat. No. 1,928,329 to Oswald, et al. and U.S. Pat. Nos. 3,508,015 and
3,522,388 to Miller. However, these systems apparently do not recognize
the possibility of recording both sound and images on the same area of the
film. The patent to Oswald uses a black and white film and visible light
through a lens to provide the sound system while the patents to Miller
utilize light emitting diodes of varying types. The systems thus suffer
from the same deficiency of good sound reproduction as is encountered in
the magnetic strip or variable area analog optical type of motion picture
soundtrack recording.
Further, the art sometimes accomplishes multiple sound source effects by
using separate, but synchronously run, film strips or magnetic tape. These
systems present serious technical problems such as maintaining sound and
image synchronization between the two separately run systems, especially
when the strip or tape of one of the two systems has a section removed for
repair or other purposes. This film may be of the standard 16 mm, 35 mm or
70 mm size. In the present invention and use, a plurality of digital
soundtracks imaged in a transparent, substantially colorless material
which can be excited to fluorescence by ultraviolet light are superimposed
over the visual image area. One ultraviolet soundtrack exciter source
serves to energize, or cause to fluoresce, all of the soundtracks.
Because of the intrinsically limited quality of optical and magnetic analog
soundtracks in standard use, the motion picture industry has been unable
to effectively reproduce the detailed realism, presence and aural
excitement achieved with high fidelity systems at home and at discotheques
and concerts. The accuracy of sound reproduction accepted as standard on
records and tapes cannot physically be contained in the analog optical
track standardized 50 years ago in cramped and grainy space alongside
Edison's inch-wide picture. Within this decade, given digital recording,
the art of high fidelity sound reproduction will improve still further,
putting the film industry in worse jeopardy of failing to provide sound of
equal fidelity.
Digital coding enables complete digital sound handling, including mixing
and editing, usually done on magnetic tapes, without tape hiss or noise or
degradation of the sound signal accumulating through successive
generations of the recording, mixing, editing, mastering procedure. With
the sound signal reduced to plus/minus ("yes"/"no") bits and with parity
check bits to monitor the entry of errors, the identity of successive
reproductions can be assured. Thus, the present invention is further
directed to a film having layers which accept such digitally coded
soundtrack(s) as binary number data, permitting reconstruction with
absolute precision.
The archaic analog soundtrack is a "picture" of the wave nature of sound
and the detail of the analog sound information must inevitably be mixed
together with the intrinsic defects of the recording medium. The
distortion which is characteristic of the analog recording means and the
noise imposed by the coarse silver grains of the film become inseparable
from the desired high fidelity sound.
The essential difference in the digital sound record is that the integrity
of the sound information exists separate and immune from the physical
nature of the recording medium. It is the intent of fluorescent
soundtracking to record a plurality of channels of digital sound across
the photographic image space of film as transparent and colorless
fluorescent digital words. In digital sound recording, the amplitude of
the sound wave is "sampled", or measured, at discrete intervals at a
clocked constant repetition rate, as, for example, 50,000 samples per
second to record frequencies of up to 20,000 Hz. Each sample is next
converted to, for example, 16 bit digital words with one or more parity
check bits. The 16 bits of each word used to record the wave amplitude of
the sample (the dynamic range) can write any integer between 0 and 65,535.
This is considerably more information than can be derived from the
compressed amplitude spike of the present standard optical analog
soundtrack record that is submerged among silver grains.
A simple and inexpensive system is required for imprinting or imaging the
fluorescent digital words of the system described above. One such system,
suggested for its accuracy, simplicity and ready adaptability to digital
coding, is an electrostatic imaging system. A common method for fixing the
electrostatic image on a substrate is by heat fusion of a toner comprised
of a polymer having a melting point lower than the substrate employed. For
highest optical quality the toner image may be covered with a lacquer or
polymeric overcoat which matches the visible refractive index of the toner
particles. The overcoat may further function to more securely fix the
digital image in place and to protect the data bits from abrading in the
projector or elsewhere.
It is further necessary that the fluorescent material of the toner remain
bound in the toner in order to maintain distinct markings on the film.
Difficulties are encountered, however, in obtaining such a polymer toner
which is also fluorescent. An ordinary brightener compound present at the
required concentration may suffer fluorescence quenching or may "bleed"
out of the toner particles and into the support materials. It has been
suggested in the prior art to make fluorescent polymers having the
fluorescent compound (brightener) covalently bound to a polymer backbone.
In U.S. Pat. No. 3,193,536 it is suggested to prepare a vinyl-brightener
monomer and copolymerize it into the growing backbone of a suitable
majority polymer. These teachings, however, are unsuitable for preparing
the compounds useful in the present invention. It is exceedingly difficult
to control the distribution of the brightener residues along the polymer
chain and with a high loading of the brightener, non-selective positioning
along the polymer backbone leads to severe fluorescence quenching.
Although the patent mentions systems loaded with up to 100 percent of
vinyl-brightener, no mention is made of quenching difficulties or of
strategies for avoiding them. All of the principal examples deal with
brightener loadings of 0.1-0.2 percent by weight, which do not provide
sufficient ultraviolet absorption and re-emission for a suitable toner for
the present invention.
Further problems are encountered with this approach due to the tendency for
the vinyl-brightener to self-polymerize even in the solid state and to
photoinitiate polymerization at any time. Additionally, the relative
reactivities in polymerization may be such as to incorporate all of the
vinyl-brighteners together in the first polymer chain segments formed, or
in the last chain segments. This leads to severe quenching.
A second approach to providing a fluorescent polymer suitable for the
present invention is to synthesize a polymer having reactive groups
suitable for binding to a selected group of the brightener molecule.
Problems encountered here include gross alteration of the properties of
original brightener, especially the absorption and fluorescence
wavelengths and the fluorescence quantum yield.
In this approach the monomer reactive with the brightener molecule may be a
material such as maleic anhydride, acrylyl chloride, or methacrylyl
chloride, and, subject to reasonable relative reactivities, the whole
array of ordinary vinyl monomers is available to complete the copolymer
chain. Even a sparingly soluble brightener can then be slowly coupled to
the completed polymer. This approach requires the scrupulous exclusion of
water to avoid conversion of the reactive sites to unreactive acid
functions. It also requires that one consider polymerization conditions
and monomer pairs which maximize the separation of the reactive sites, and
thus minimize possibilities for quenching.
It is the general consensus that liquid toner development gives the best
approach to high resolution electrophotography. The suspending liquid of
the toner must be moderately volatile so that it can be removed by mild
heating or evaporation at the end of the process. Additionally, it must
have a high electrical resistivity so as not to discharge the primary
images formed on exposure or contact. Additionally, the toner material
must be insoluble in the suspending liquid. The solid toner particles are
charged, all positive or all negative, with respect to the liquid vehicle.
OBJECTS OF THE INVENTION
It is an object of the present invention to provide a means for imaging
digital data on substrates, such as films, sheets or plates of plastic,
which may or may not have other visible data or graphic representations
thereon.
It is also an object of the present invention to provide a means for
applying a soundtrack to a visibly exposed and developed film by creating
an electrostatic image on the film and immediately contacting the film
with fluorescent toner.
Still another object of the present invention is to provide an unexposed
film having an image receiving system, capable of receiving the
fluorescent toner of the invention and compatible with the photographic
layers and processes for developing same.
A further object of the present invention is to provide a finished film
that has sound recording on the full width thereof and in superposition
with the visual image and that requires only a minimum of extra equipment
or modification to reproduce this sound.
It is yet another object of this invention to apply digital data to a film
by electrostatic imaging means prior to development of the visual image
layers.
It is an even further object to provide a reliable method of replaying
sound on motion picture film which may be accomplished with limited
retrofitting and addition of digital to analog circuitry to conventional
projection equipment.
A further object of the invention is to provide means for the recording of
a multiplicity of permanently synchronized digital soundtracks or channels
on a single motion picture film release print and thus create, in the
theatre, high fidelity multiple source sound effects.
It is another object of the present invention to provide a digitally coded
soundtrack data matrix, and particularly a soundtrack disposed across the
visual image space of a motion picture film.
Another object of the present invention is to provide a digitally coded
soundtrack using a colorless toner which fluoresces in the visible light
region when exposed to ultraviolet light.
Still another object of the present invention is to provide a novel
colorless toner polymer having physical and chemical properties consistent
with the nature of the film layers and uses of the present invention.
It is also an object to provide a method of making the above-described
soundtrack and film incorporating the soundtrack.
Other objects and advantages will become apparent from the following
disclosure.
SUMMARY OF THE INVENTION
The present invention is directed to a system for recording information or
data by creating an ordered pattern of electrically charged areas on a
substrate, coating the substrate with a dry or liquid electrostatic
imaging toner which is transparent under visible light but is fluorescent
under ultraviolet light and has a charge opposite to that on the
substrate, whereby the toner adheres to the charged areas and then fixing
the toner to the substrate.
In a preferred embodiment, the present invention is directed to black and
white or color photographic films having additionally coated thereon a
light insensitive system or a photoconductive system capable of receiving
a transparent, colorless ultraviolet excitable fluorescent material
applied by means of an electrostatic imaging system. However, it is
possible to employ this system with other substrates, including other
plastic base image bearing films, such as those in use in aerial
reconnisance photographs and X-rays. The system can also be used as a
updatable additional record on microfilm.
The ultraviolet fluorescent material is applied in the form of digital
indicia to provide the soundtrack of the motion picture film. The visually
exposed and developed film is charged image-wise with an electrostatic
imaging means having the soundtrack digitally coded therein. The digital
electrostatic charge image is then used to collect an image deposit from a
liquid toner made up of a suspended clear, transparent fluorescent
compound(s), desirably a fluorescent polymer. The film may then be coated
with a protective layer to ensure the integrity of the soundtrack and to
eliminate light scattering from the toner deposit by overcoating and
matching the refractive index of these particles.
DESCRIPTION OF THE DRAWINGS
The following figures will serve to schematically illustrate one embodiment
of the present invention:
FIG. 1 is a cross-section of the film of the present invention in the
unexposed state;
FIG. 2 is a schematic of a method for the preparation of a master negative
and for using the master to apply an image to the final release print.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows a normal black and white or color film having a base 11 which
may be of any usual material such as polyethylene terephthalate and a
visible light sensitive emulsion 12 which may be either black and white or
color. This is, the present invention is adaptable for either black and
white films or color films. The particular type of visible image
development required, such as dye coupling, etc., is not critical. That
is, the film of the present invention may have any desired visible
light-sensitive emulsion coated thereon. Most commonly the usual silver
halide emulsions, either black and white or color types, will be employed.
The visual image producing emulsion used in the present invention may be
provided by numerous methods, one of these being the process for high
speed laying of gelatin coatings disclosed in U.S. Pat. No. 3,617,292.
The present invention resides primarily in the provision on a silver halide
film and the use of a two layer coating capable of receiving and recording
information via electrostatic imaging means, and which can collect a toner
deposit from a dry or liquid toner made up of clear, transparent material
which fluoresces in the visible light spectrum when subjected to
ultraviolet light.
The film shown in FIG. 1 has either no antihalation backing at all, a low
density antihalation layer, or a removable antihalation layer positioned
in the gelatin behind the visible light sensitive system. The absence of
any antihalation layer implies that the visual image will be "wet-gate"
printed, followed conventional methods to eliminate surface reflections
and imperfections. In addition, the usual difficulties with halation will
be eliminated by optically immersing the rear surface of the film against
a matching dark dielectric object, such as a wheel having a gray glass
surface. A two layer 13, 14 soundtrack forming system is opposite to the
visible light-sensitive emulsions 12 on the base 11. The two layers
comprise an inner conductive underlayer 13 approximately 1-2 microns thick
and a clear dielectric or photoconductive outer layer 14 approximately
5-10 microns thick. The conductive underlayer may consist of an organic
conductor such as DCR-77 (Dow Conductive Resin), a transparent evaporated
inorganic conductor such as CuI, or a polymeric suspension of a
transparent inorganic conductor. If the DCR-77 is used, the polyester film
base is preferably conditioned with a corona discharge in air to promote
adherence of the original conductor. The dielectric layer may be any of a
large class of dielectric polymers, such as polycarbonate,
styrene-methacrylate, polyester, etc. If a polymeric photoconductive outer
layer is used, it may consist of a short wavelength dye-sensitized system
such as found in Kodak SO-101 electrostatic film or in products such as
XP5-004 made by Scott Graphics/James River Graphics Co. (see Zech, Appl.
Optics, 16(6): 1642(1972)). Where possible, the use of the simpler
dielectric layer for subsequent transfer of electrostatic charge image
(TESI) is preferred, since the absorption of sensitizing dyes is absent,
and one need not be concerned with minimizing dye absorption or adding
compensating absorption to create a neutral color. (See R. M. Schaffert,
"Electrophotography," Wiley, New York, 1975, especially pp. 167-176 for a
variety of TESI techniques.) Similarly, the organic conductor is
preferred, since it involves no materials of high refractive index and
potential light reflection or light scattering.
Although it is preferred that the sound imaging system be on the back of
the film, it is also possible to put this sound imaging system on the
front, i.e., overcoat the visible emulsion with the sound emulsion. The
provision of the sound imaging system on the same surface as the visual
image emulsion requires no special processing other than the deposition of
the sound imaging layers after the processes of development, washing and
drying of the visible image, since the visible image system and the
soundtrack system do not interfere optically with each other but the toner
image is likely to interfere with permeation of water and silver halide
processing reagents. Both locations of the soundtrack system on the film,
e.g., on the back thereof and on the same surface as the image emulsion,
are encompassed in the phrase "the soundtrack is superimposed over the
photographic image area."
In FIG. 2 the process for making the soundtrack of the present invention is
schematically illustrated. The visual image is recorded on a master
negative (not shown) and the sound is usually recorded on an analog or
digital magnetic tape, not necessarily made contemporaneously with the
visual image. The sound record and photographic motion picture negative
remain two separate entities until the final release print is made. The
master visual negative is edited, spliced and used to create one or more
generations of visual image sub-masters. It should be noted that sound may
be recorded simultaneously by as many as 20-40 different microphones.
Referring to FIG. 2, the sound is recorded by a plurality of microphones
22, transmitted by wires 23 to an optional amplification systems 24 and
then by wires 27 to magnetic tape recorders 26. These sound tapes are then
converted to digital tapes by analog to digital converters 28 which
digital tapes are used for interim storage while further editing, mixing
and processing are conducted (represented at step 29) to produce a master
digital tape. As further shown in FIG. 2, the master digital tape is then
fed to the electrostatic imaging system 30 of the invention to produce a
final release print having the sub-master visual image negative on which
the digital soundtrack from the master digital magnetic tape is printed as
fluorescent indicia. It is the release print which is used in the
projection booth of a motion picture studio to produce the visual images
and soundtrack in the theater.
Superior sound recording may in some instances be obtained by eliminating
the analog magnetic tape recorder 26 and going directly through the analog
to digital converter 28 to a first digital recorder to create a
multiplicity of digital records for later editing and mixing to create the
master digital tape. The use of the finished master digital tape in
subsequent steps is unchanged by this variation.
Direct printing of the digital images may be done with existing laser
scanner printers, with cathode ray tube systems, or with optical printing,
either contact or projection, to form the master sound negative. The
master tape or edited master tape can be optically printed by projection
or contact onto a succession of copies. Alternatively, the simple
soundtrack image is projected on a charged photoconductive belt or drum,
and the remaining image-wise charge is contact transferred to the assembly
of dielectric and conductor. The imprinting is effected at a point on the
film that is a discrete number of frames from the picture contemporaneous
with the sound record, e.g., 30 to 40 frames behind the associated visual
image in 35 mm films. Thus, a film having a visual image spaced 30 to 40
frames ahead of the sound associated with it is produced. This spacing can
be used in the visual and sound reproduction of the films since it allows
spacing between the audio and visual reproducing means in a projector.
Analog to digital sound converters known in the art may be utilized in this
invention. In one embodiment of the present invention the converter codes
six channels of digital sound. The frequency-time axis of the output of
the amplifier 24 is "sampled" or separated into discrete measurements of
wave height/amplitude information at a rate more than twice the highest
frequency to be recorded. These measurements are then converted to, for
example, 16 bit digital words. The 16 bits of each word, which can
represent any integer between 0 and 65,535, provide a code comprised of
many more distinctions than can be made from the compressed amplitude
spike of the conventional analog soundtrack record. Following Nyquist's
theorem there must be more than two samples taken for each cycle of the
highest frequency to be reproduced. Thus, 50,000 samples/sec. reproduce
20,000 Hz sound.
The electrostatic imager utilized in the invention may be any of those
known in the art, as, for example, the cathode ray imaging systems shown
in Schaffert's "Electrophotography," Wiley, New York, 1975, pp. 154-155.
The conductive mosaic faceplate CRT tube, sold by the Thomas Co. may also
be used. Means for transferring the charge to the surface of the film may
also include a belt, loop or master photoconductive charge film which can
be charged, imaged and simply pressed against the two layer soundtrack
forming system on the photographic film. The final electrostatic image is
then used to collect an image deposit from a liquid toner bearing
fluorescent compounds. Methods for pre-charging, imaging and toner
processing in electrophotography are discussed in detail by Schaffert.
Toner material may be used which has the properties of being transparent
and colorless in visible light, but fluorescent in the visible spectrum
when exposed to ultraviolet light and which can be permanently inprinted
onto the soundtrack forming system by means of the electrostatic imaging
process described above. Another requirement is that the toner fluoresce
with sufficient intensity to allow very rapid and easy discrimination by,
for example, a photoelectric or photoconductive cell element. The
ultraviolet sensitive materials suitable for use as toner material in the
present invention include any material meeting these requirements.
The toner image may be further protected by an ultraviolet transparent
index matching lacquer or overcoat, as described. Acceptable coatings
include polymethylmethacrylate, polystyrene, Lexan polycarbonate (General
Electric Co.), etc. in suitable solvents.
A particularly ideal toner material comprises a substantially transparent
thermoplastic polymer or copolymer composition formed from vinyl or
vinylidene monomers and containing ultraviolet fluorescing chromophore
components, dispersed in a volatile, colorless, high resistivity liquid
which is a non-solvent for the polymer or copolymer. The fluorescent
polymer or copolymer is used in the form of substantially spherical beads
having a diameter of from about 0.3 to 1 microns, all the beads having the
same sign of electrical charge to prevent clumping and aggregation and so
that all will be of opposite charge to the electrostatic image.
Liquids suitable for dispersing the fluorescent polymer include specially
purified high resistivity kerosene, such as manufactured under the
tradenames Sohio Solvent (Standard Oil of Ohio), Isopar (Exxon Corp.,
Houston, Tex.), etc. or freons such as Freon 113
(trichlorotrifluoroethane, duPont de Nemours & Co., Wilmington, Del.).
The fluorescent polymer must be loaded with a high concentration of
brightener, for example, 1-10 weight percent, preferably 2-5 percent, and
this must be accomplished without excessive quenching of fluorescence. At
these high concentrations, it is imperative that the brigtener should not
be able to "bleed" or migrate out of the toner particles and into the film
system. Any such migration would quickly destroy the working contrast of
the digital image data. Thus, systems in which the brightener is
covalently bonded to the polymer backbone are highly preferred.
Because the classes of brighteners suitable for incorporation in the
fluorescent polymer toner of the invention are very broad, they are best
described in functional terms and properties. It is necessary that the
brightener be a strong ultraviolet light absorber, having minimal
absorption of E max=10,000 (moles/liter).sup.-1 cm.sup.-1, preferably a
value of 20,000-50,000 at a wavelength of 420 nm. The absorption must fall
away from the ultraviolet peak to an E<E max/10 at a wavelength of 420 nm.
The brightener must be stable with respect to photoreaction and slow
reactions, such as dark oxidation, and must fluoresce with a quantum yield
(photons emitted/photons absorbed) of at least 10 percent and preferably
50-100 percent. The brightener must also admit of a covalent attachment to
a polymer backbone. As discussed below, it may be reacted into a growing
polymer or, preferably, added to reactive sites on an existing polymer.
The chromophore may be formed or altered chemically according to plan in
the attachment reaction. A typical chromophore will be loaded at a level
of 1-10 percent by weight preferably 2-5 percent, relative to the polymer.
A particularly effective brightener for incorporation into the fluorescent
polymers of the invention may be obtained from the yellow, blue-green
fluorescing laser dye 3-phenyl-7-amino-coumarin (coumarin #10 in the Kodak
series of laser dyes). Upon formation of a polymer-bound 7-amido- or
7-imido-function a colorless brightener is formed.
A class of particularly stable brighteners is obtained by forming 4-amides
or 4-imides of compounds in the series of N-alkyl-4-amino naphthalimides.
A representative precursor in this class is N-2-butyl-4-aminonaphalimide.
Compounds in the additional classes of 4-aminostilbenes may similarly be
used to form bound amide or imide brighteners. Note, however, that
difunctional compounds such as 4,4'-diamino-2,2'-stilbene disulfonic acid
cannot be used at high concentration, as they will crosslink and rigidize
the toner polymer to unacceptable degree. The useful amino stilbene
derivatives will have an unreactive group on one end of the stilbene
framework, as in the following:
##STR1##
For preparation of these compounds, see Venkataraman, "Synthetic Organic
Dyes," pp. 563 and 588.
The reactive polymer may be made in anticipation of a brightener
precursor-amine being joined to any one of several amine-reactive sites.
For example, these sites may be acid halide, diacid anhydride, or aldehyde
functions derived from polymerized monomers such as acrylyl chloride,
methacrylyl chloride, maleic anhydride, or acrolein. Somewhat less
advantageously, amine sites on the polymer as derived from vinyl amine or
4-aminostyrene may be reacted with an acid chloride aldehyde or sulphonic
acid chloride brightener-precursor.
A maleic anhydride: methyl-vinylether (1:1) copolymer (Gantrez AN-149, GAF
Corp., New York, N.Y.) may be used as the backbone for the toner of the
invention. The addition reaction to form 3-phenyl-7-amido-coumarin or
3-phenyl-7-imido-coumarin bound to the polymer was performed in dry,
peroxide-free dioxane. The brightener-polymer is insoluble in heptane and
other hydrocarbon solvents. The polymer was brilliantly fluorescent, while
successive heptane washes were only very weakly fluorescent, proof that
the brightener is bound to the polymer. The recovered solid polymer is
also brilliantly fluorescent as the dried solid, and small, crushed
particles also show the brilliant fluorescence.
However, this polymer still contained the great majority of anhydride
groups which are expected to cause widely changing properties on gradual
exposure to water vapor. Storage stability is thus anticipated to be a
problem.
These problems can be overcome in two ways. First, the remaining anhydride
groups can be reacted with a primary amine. Reaction with n-butylamine
provides a brilliantly fluorescent, white, rubbery polymer suitable as the
toner for use in the present invention. A wide variety of related alkyl
vinylether monomers can be copolymerized with maleic anhydride and a
variety of primary amines can be substituted after addition of the
brightener groups to provide suitable toners.
An alternative approach to solution of the stability problem involves use
of a lower concentration of maleic anhydride and to use monomers such as
methylacrylate, methylmethacrylate, styrene, etc. as the other "majority"
component. The majority monomer is used at 95-99 mole percent in relation
to the reactive co-monomer.
If a negatively charged toner is desired the anhydride (or acid chloride)
mole fraction may be higher than the mole fraction of brightener to be
added. After brightener attachment is completed, the addition of a trace
of water will produce carboxylic acid groups on the residual acid
precursors.
The importance of the tendency of maleic anhydride not to undergo self
addition (see Handbook of Polymer Science and Technology, N. Bikales
(ed.), Vol. 1 and the entry "Acids, Maleic and Fumaric") is that it
establishes a minimum distance between chromophore units along the chain
and so prevents the formation of sandwich dimers of the chromophore. These
dimers are expected to be non-fluorescent, and to act as acceptors for
Forster energy transfer, thus quenching the neighboring non-dimerized
chromophores. A further desirable structural feature of the chromophore
which can minimize dimer formation is the presence of some group lying out
of the planar framework of the brightener group. In
3-phenyl-7-aminocoumarin this nonplanar group is the 3-phenyl group on the
outward end of the molecule. The attached polymer chain performs the same
function at the opposite end of the molecule.
The phenomenon of Forster transfer can also be used constructively to
protect a system against excessive dimer quenching. When adding brightener
to the reactive groups of a backbone polymer, it is quite easy to add a
mixture of two brightener chromophores comprising a majority
shorter-wavelength absorber to act as the Forster donor, and a minority of
a longer-wavelength Forster acceptor. Since the acceptor is present in low
concentration, very few acceptor dimers can form. This approach has been
employed with Coumarin-10 as the acceptor-fluor, and
4-methyl-7-aminocoumarin as the absorber-donor, and a brilliantly
fluorescent 1:1 maleic anhydride: methylvinylether polymer was obtained
when 3.0 weight percent of 4 methyl-7-aminocoumarin and 0.58 weight
percent of coumarin 10 were used.
The present invention may also be utilized with existing motion picture
film projectors. The standard analog optical track on the film and the
analog readout stage in the projector remains unchanged and can coexist
with the complete digital system. In using the film of the invention the
new digital sound readout stage is substituted for the disused magnetic
soundtrack station of the projector.
It is to be understood that the term "motion picture release print" as used
throughout the specification and claims includes reference to X-ray
negatives and negatives used for other purposes such as aerial
reconnaissance mapping, etc.
While the system will probably find its greatest use in connection with
photographic films, it is obvious that the transparent fluorescent data
matrices may be produced in the manner described on other substrates.
Thus, they may be deposited on transparent bases, such as glass plates or
plastic films, on opaque substrates such as ceramics, or metals coated
with an insulating film. Where a transparent film or plate is the
substrate, the face opposite the data matrix may have a graphic
representation such as a picture, drawing or a diagram, or a printed or
handwritten text. This can be projected on a screen, as by a slide
projector, without interference from the transparent data matrix. On
exposure of the data block to ultraviolet light in a readout/scanner the
data can be readout. Specific examples of these other systems include
aerial photographic military reconnaissance and surveying photographs as
well as medical records and X-ray negatives. In aerial photographic
military reconnaissance, for instance, it is necessary that each frame of
exposed film be identified by time, longitude, latitude and altitude, and
the heading and attitudes of the aircraft in relation to the ground be
recorded at the instant the picture is exposed. The corresponding binary
data matrices are photographically exposed on the film in real time to
identify and locate each frame to carry this information and to enable the
photograph to be readily retrievable from files.
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