U.S. patent number 3,892,569 [Application Number 05/312,216] was granted by the patent office on 1975-07-01 for photosensitive sheets comprising organic dyes and sensitizers.
This patent grant is currently assigned to General Film Development Corporation. Invention is credited to Daniel E. Speers.
United States Patent |
3,892,569 |
Speers |
July 1, 1975 |
Photosensitive sheets comprising organic dyes and sensitizers
Abstract
A copy sheet light stable under ordinary room temperature
conditions includes a low cost substrate coated with a color
forming means which is rendered photosensitive by a heat
activatable sensitizing material included in the coating. A heat
activatable desensitizer may also be present. The sensitizer is
preferably encapsulated in a heat rupturable means which is
destroyed upon heating the copy sheet to a predetermined threshold
temperature. A copy system utilizing the copy sheet need include
only a means for superimposing the original to be copied and the
copy sheet and a heat and light source.
Inventors: |
Speers; Daniel E. (Westport,
CT) |
Assignee: |
General Film Development
Corporation (Southport, CT)
|
Family
ID: |
23210416 |
Appl.
No.: |
05/312,216 |
Filed: |
December 4, 1972 |
Current U.S.
Class: |
430/541; 430/138;
430/351 |
Current CPC
Class: |
G03C
7/02 (20130101); G03C 1/002 (20130101) |
Current International
Class: |
G03C
7/02 (20060101); G03C 1/00 (20060101); G03c
001/76 (); G03c 003/00 (); G03c 001/72 () |
Field of
Search: |
;96/89,48QP,67 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Klein; David
Assistant Examiner: Schilling; Richard L.
Attorney, Agent or Firm: Parmelee, Johnson &
Bollinger
Claims
I claim:
1. An ordinarily light stable copy sheet capable of being rendered
sensitive to light upon heating above a predetermined threshold
temperature comprising a support means having thereon a coating
including a photo-sensitizable color forming organic dye
insensitive to light at ambient temperatures without a sensitizing
means but sensitive to light at ambient temperatures with a
sensitizing means, a sensitizing means selected so as to be capable
of sensitizing said color forming organic dye only upon the
application of heat to the copy sheet, said sensitizing means being
physically kept from effective contact with the color forming
organic dye until the application of the heat to the copy sheet by
a physical segregation means which is heat destructible at the
threshold temperature and a desensitizing means for rendering the
copy sheet light stable upon an application of heat greater than
that necessary for sensitization.
2. An ordinarily light stable copy sheet capable of being rendered
sensitive to light upon heating above a predetermined threshold
temperature comprising a support means, a color forming means
including an organic dye selected from the group consisting of
xanthene, thiazine, triarylmethane, azine, azo, anthraquinone,
diphenylmethane, thiazole, acridine and oxazine or a combination
thereof and a composition which upon heating above the
predetermined temperature will form, in situ, a photosensitizing
material including a substituted thiourea selected from the group
consisting of thiosinamine, diethylidene thiourea, diethyl allyl
thiourea and thiourea dioxide, all carried on the support
means.
3. A copy sheet as claimed in claim 2 further including a promoting
composition which effectively reduces the time necessary to expose
the copy sheet to light for producing an acceptable copy by 25 to
50 percent.
4. A copy sheet as claimed in claim 2 further including a
desensitizing composition effectively activatable at a temperature
greater than the temperature which effectively activates the
photosensitizing material and which renders the color forming means
stable upon the application of heat to yield such greater
temperature.
5. An ordinarily light stable copy sheet capable of being rendered
photosensitive upon heating above a predetermined threshold
temperature comprising a support means, a color forming composition
including an organic dye selected from the group consisting of
xanthene, thiazine, triarylmethane, azine, azo, anthraquinone,
diphenylmethane, thiazole, acridine and oxazine and a
photosensitizing material capable of becoming effectively active
upon the application of heat including a component selected from
the group consisting of substituted thioureas selected from the
group consisting of thiosinamine, diethylidene thiourea, diethyl
allyl thiourea and thiourea dioxide, hydrogen peroxide and
anethole, all carried on the support means.
6. A copy sheet as claimed in claim 5 wherein the photosensitizing
material is maintained segregated from sensitizing contact with the
color forming composition by a heat destructible means which is
effectively destroyed as a segregating means upon heating to a
temperature just above the threshold temperature.
7. A copy sheet as claimed in claim 6 further including a
desensitizing composition effectively activatable at a temperature
greater than the temperature which effectively activates the
photosensitizing material and which renders the color forming
composition light stable upon the application of heat to yield such
greater temperature.
8. A copy sheet as claimed in claim 7 wherein the desensitizing
composition is sulfurous acid.
9. A copy sheet as claimed in claim 5 further including a promoting
composition which effectively reduces the time necessary to expose
the copy sheet to light for producing an acceptable copy by 25 to
50 percent.
Description
BACKGROUND OF THE INVENTION
This invention relates to copy sheets for copying or reproducing an
image from an original and to methods for manufacturing the same.
In particular, this invention is directed to copy sheets
incorporating compositions which become photosensitive upon
effective sensitization by heat activatable sensitizing
compositions.
Present day industrial, business office, communications home and
other activities often evidence a need for efficient and
inexpensive copying methods and means. As a result many different
copying techniques, particularly in the office copying field, have
been suggested. However, no single approach has been fully
satisfactory from all aspects.
The most widely accepted copying methods are those based on
electrostatic techniques, particularly xerography. Nevertheless,
the complexity and sensitivity of these procedures are well known.
Presently available electrostatic equipment requires a relatively
large initial investment in hardware and, in addition, individual
copies are comparatively expensive. Furthermore, even with relative
care, equipment of this type is easily damaged thus making
maintenance costly and resulting in unproductive down time.
Photographic copying techniques utilizing light sensitive material
which is developed subsequent to exposure to light generally result
in wet copies and require the production of a negative. Also,
individual copy costs with such processes are relatively high. More
significantly, however, copy sheets utilized in processes of this
type must be stored in darkened areas in a manner similar to
photographic film, a requirement resulting in inconvenience and
inefficiency in an ordinary office.
Other techniques employ heat sensitive copy sheets, in contrast to
light sensitive copy sheets, to develop an image. These
thermographic methods, while utilizing copy sheets that need not be
stored in darkened areas and producing copies of relatively lesser
expense, experience major disadvantages in the areas of image
resolution. Since heat is readily diffused, blurring of the image
with lack of sharp, well defined copy occurs. Due to the nature of
the copy sheet material that must be used, fading, tearing and
cracking of the copy sheets after long storage is also a
problem.
The prior art has also suggested various combinations of
photography and thermography including techniques identified as
"thermophotography" and "photothermography." With the former, a
heat sensitive copy sheet is exposed to differential heating as in
conventional thermography; however, a latent image is produced
which is subsequently developed by exposure to light. Although this
procedure may render the copies more stable, the basic difficulties
of poor resolution and inability to copy colored originals,
inherent in thermographic procedures, is not obvious. In the
reverse technique, photothermography, a copy sheet is first exposed
to light, as in a conventional photographic procedure, and then
developed by heat in contrast to more conventional chemical
developing procedures. In this procedure, the original copy sheet
used is still light sensitive thus still requiring troublesome
storage in a darkened area.
The foregoing discussion, illustrative of the more commonly known
procedures for copying and exemplary of the disadvantages
associated therewith, demonstrates the need for improved copying
techniques and means which overcome the drawbacks connected with
those presently known.
SUMMARY OF THE INVENTION
The copying system and method of the present invention overcomes
the disadvantages inherent in prior art techniques by providing
inexpensive, ordinarily light stable copy sheets which are rendered
sensitive to light upon heating above a predetermined threshold
temperature. Upon sensitization, the copy sheets are capable of
producing color images having good resolution by the use of
relatively simple equipment which is comparatively easy to
maintain.
The copy sheets and copying methods and means of the present
invention provide reproductions having the high definition of
detail usually resulting from photographic techniques, wherein
light sensitive materials are the color image forming means,
without the dark room storage and chemical development difficulties
inherent in prior art uses of such techniques. At the same time,
the present invention provides the advantages of prior art
thermographic techniques since the copy sheets are stable under
ambient light and temperature conditions and dry processing is
possible. Moreover, good resolution of copies without fading and
cracking of copies is achieved along with the ability to copy
colored originals.
The copy sheets of this invention incorporate a color forming means
which is rendered light sensitive by a sensitizing material. The
sensitizing material becomes effectively active subsequent to the
application of heat to the copy sheet at a predetermined threshold
temperature. Subsequent to production of the desired image upon the
copy sheet, the color forming means may be rendered desensitized by
a desensitizing agent also included thereon. At ordinary
storageroom conditions of light and temperature the unused copy
sheets of this invention remain stable for extended periods of
time. Subsequent to sensitization and exposure to light to provide
an image, the color forming means may be desensitized to provide a
stable copy having long storage life. Thus, it is an object of this
invention to provide copy sheets which are light stable at ordinary
ambient conditions, become photosensitive upon heating above a
selected threshold temperature and produce a color image from an
original.
A further object of this invention is the provision of a copying
method and means utilizing light and heat while producing dry
copies, exhibiting good resolution and stable storage life, from
colored originals by using copy sheets stable to light and
temperature under normal ambient conditions.
The copy sheets of this invention may have color forming means
including a mixture of color forming compositions selected to
produce multicolor copies which would reproduce originals of
substantially any color. The color forming means compositions and
sensitizing material compositions may be applied to a desired
substrate and may be kept separated by heat destructable means. The
copy sheets of this invention are readily usable in simplified
apparatus involving little more than a light source, a glass plate
and a heated plate to enclose the original and copy sheet.
A further object of this invention is the provision of a method for
manufacturing photothermographic copy sheets. An additional object
is the provision of a copying technique utilizing simplified
apparatus which is inexpensive and relatively maintenance free.
Still other objects will be apparent from the following
description.
BRIEF DESCRIPTION OF THE DRAWINGS
Several embodiments are illustrated in schematic form in the
accompanying drawings as an aid to better understanding of the
invention.
FIG. 1 is a schematic view of an embodiment of a copy sheet
according to this invention;
FIG. 2 is an enlarged cross-sectional view through a portion of
another embodiment of a copy sheet according to this invention;
FIGS. 3A and 3B are enlarged cross-sectional views through a
portion of further embodiments of a copy sheet of this invention;
and
FIG. 4 is a schematic side view, partly in section, showing the
basic elements required for a copier system utilizing a copy sheet
according to this invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1, there is shown in schematic a copy sheet
illustrative of this invention. Structurally, the copy sheet
basically comprises a support element or substrate carrying a
coating material as illustrated. The support element may be formed
of any suitable substrate material such as paper, plastic sheets,
metal foils, and other adaptable materials for specialized
applications. Paper, because of its availability and low cost, is
preferred and readily usable since the relatively low temperatures
used herein are not harmful thereto.
The coating material includes a sensitizable color forming means
and a heat activatable sensitizing means to photosensitize the
color forming means. The color forming means includes a color
forming composition which is selected so as to be substantially
insensitive to light at ambient temperatures below about
35.degree.C and, in particular instances, preferably below even
somewhat higher temperatures, for example, 50.degree.C, in the
absence of a material which will activate it so as to be sensitive.
The sensitizing means includes a composition which is ineffective
to sensitize the color forming composition at ambient temperatures
and is only activated to perform its sensitizing function at or
above a threshold temperature greater than ambient temperatures,
preferably a temperature between about 35.degree.C and
175.degree.C. This latter higher limit assures that unduly high
temperatures which may possibly have a deleterious effect on the
support element are not required.
The essential criteria for a color forming composition which will
satisfy the requirements of this invention are light stability
under ordinary ambient conditions and capacity for
photosensitization, to provide a color change in areas exposed to
light, by a sensitizing means which is activated at or above a
threshold temperature beyond ambient temperatures. Knowing this,
those skilled in the art may select materials which will satisfy
these general requirements. For example, numerous organic dyes are
known and available which fit within the restrictions defined by
this invention.
Preferred dyes for use as the color forming composition in the copy
sheets of this invention are the dyes of the Xanthene class.
Xanthene dyes which have been found particularly effective include
Erythrosin B (C.I. 45,430), Rhodamine B (C.I. 45,170), Rodamine 6G
(C.I. 45,160), Pyronine G (C.I. 45,005), Eosin B (C.I. 45,400),
Uranine (C.I. 45,350), Rose Bengal (C.I. 45,435), C.I. Basic Red 11
(C.I. 45,050), Saccharein (C.I. 45,070), Rosamine (C.I. 45,090) and
Rhodamine 12GM (C.I. 45,310).
The briding carbon or aryl groups of the Xanthene dyes may be
substituted by a --COR, --COOR, --SCN, --CN or --NO.sub.3 group
which will, for the purpose of the systems to be described in more
detail hereinafter, decrease the light exposure time over the use
of a more conventional Xanthene dye by approximately 50 percent.
Examples of materials of this type may be found in U.S. Pat. Nos.
1,880,572 and 1,880,573.
Another class of particularly useful dyes are the Thiazines which
show excellent printing characteristics, most of these dyes
yielding a printing image with less than 10 seconds light exposure
time. However, these dyes are slightly less desirable than the
Xanthene dyes listed previously since, after yielding a printed
image, Thiazine dyes require more care in stabilization.
Specifically, Thiazine dyes tend to fade if exposed to a constant
light source rich in ultraviolet light. Thus, they are preferably
utilized when the duplicated copy would not be likely to be
constantly exposed to such light. Exemplary Thiazine dyes which
have been found to be particularly useful are Thionin (C.I. 52,00),
Methylene Blue (C.I. 52,015), Methylene Green B (C.I. 52,020) and
New Methylene Blue N (C.I. 52,030).
Another group of dyes useful as color forming means in accordance
with the instant invention are the Triarylmethane dyes,
particularly Malachite Green (C.I. 42,000), Victoria Blue B (C.I.
44,045), Crystal Violet (C.I. 42,555) and Erioglaucine (C.I.
42,090).
The Azine dyes are also useful according to the concepts of this
invention, one particularly desirable material in this class being
Phenosafranin (C.I. 50,200).
The Azo dyes are also found to be quite useful according to the
instant invention although it has been found that dyes of this
group bleach out faster and whiter if small quantities of sulfuric
acid are included in the sensitizing phase. Exemplary materials
within this class which are found to be particularly desirable
include Tartrazine (Monoazo -- C.I. 19,140) Chromotrope 2R (Monazo
-- C.I. 16,570), Ponceau 2R (Monazo -- C.I. 16,150), Fast Red S
(Monazo -- C.I. 15,620), Thiazol Yellow G (Monazo -- C.I. 19,540),
Buffalo Black NBR (Disazo -- C.I. 20,470), Sulfocyanin G (Disazo --
C.I. 26,410) and Sulfocyanin 5R (Disazo -- C.I. 26,360).
Anthraquinone dyes are also useful, but like the Azo dyes appear to
function better in the presence of small quantities of sulfuric
acid. Oil Blue N (C.I. 61,555) is an exemplary useful
anthraquinone. However, this dye turns dark blue instead of
bleaching, resulting in a blueprint type of copy.
Other dye classes which include useful members are Diphenylmethane
(e.g., Auramine O -- C.I. 41,000 and Auramine G -- C.I. 41,005),
Thiazol, Acridine (e.g., Phosphine -- C.I. 46,045, Acridine Yellow
-- C.I. 46,025, Flaveosine -- C.I. 46,060, Benzoflavine -- C.I.
46,065 and Aurazin G -- C.I. 46,030), and Oxazine (e.g., Capril
Blue GN -- C.I. 51,000, Capril Blue GON -- C.I. 51,015,
Galleocyamine -- C.I. 51,030 and Aminogallamine Blue -- C.I.
51,060).
The amount of color forming means utilized will vary depending upon
the color and intensity derived in the final product. The examples
set forth hereinafter indicate the amount to be used based on the
overall compositions set forth therein. Generally, the yellow dyes
such as Tartrazine generally take almost twice as much
quantitatively as the reds and blues in order to produce similar
results. Nevertheless, those skilled in the art will be able to
readily vary these compositions at will based on observations to
produce desired results. Also, the selection of the color of the
dye may be made dependent upon the particular application. In some
instances the color forming composition is bleached out or rendered
substantially colorless upon exposure to light after sensitization
whereas in other instances it changes from one color to another in
exposed areas. Additionally, as will be seen from the embodiments
set forth hereinafter, it is possible to mix color forming
compositions and thereby reproduce a colored original by a colored
copy.
The color forming composition is rendered photosensitive by a
suitably selected sensitizing material which is ineffective under
ambient light and temperature conditions but becomes effective to
photosensitize the color forming material upon heating above a
threshold temperature. This desired characteristic is designated
herein as "heat activatable" and those skilled in the art will be
capable of readily selecting sensitizing means which meet this
criteria. Preferable heat activatable sensitizing means for this
invention are the substituted thioureas such as thiosinamine,
diethylidene thiourea, diethyl allyl thiourea and thiourea dioxide.
Other sensitizers such as hydrogen peroxide and anethole may be
used with those dye materials known to be sensitive thereto. The
sensitizing means may be present together with a color forming
means or segregated therefrom only by a heat destructible
segregation means such as the heat rupturable capsules similar to
those employed in so-called carbonless copy papers made by National
Cash Register Company. Alternatively, the sensitizing material may
be formed in situ during the copying process when the copy sheet is
heated above the threshold temperature, which is then that
temperature at which the constituents chemically react to
efficiently produce the desired sensitizing material. Thus,
thiosinamine may be formed in situ by providing allyl mustard oil
in combination with ethanol and ammonia together with the color
forming composition in the coating. These constituents, when heated
sufficiently will react in situ to form thiosinamine which will
then function as the sensitizer for the color forming
composition.
The embodiment illustrated in FIG. 1 shows the coating material
incorporating both the color forming composition and the
sensitizing material as a single layer. However, the support
element can conveniently carry the coating material in the form of
several separate layers as illustrated in FIG. 2. The structural
embodiment of FIG. 2 is suitable where the sensitizing material is
to be formed in situ since the reactive constituents can then be
maintained in physical proximity to one another to facilitate
formation of the sensitizer. The formed sensitizer will then lay
adjacent the color forming means and photosensitize it. Where the
sensitizing material is present in its final form, same for
activation by heat, it may be mixed together with the color forming
composition in a single layer as in FIG. 1.
The embodiment of FIG. 3A is particularly suitable when the color
forming composition and sensitizing material are to be maintained
segregated from one another until the appropriate time by a heat
destructible means. Thus, FIG. 3A shows the support element
carrying a layer containing the color forming composition and a
separate layer containing the sensitizing means in heat rupturable
capsule form. The drawing is illustrative only and the sensitizing
material layer encapsulation may be formed according to any well
known techniques, such as those commonly used in the manufacture of
so-called carbonless carbon paper and similar element, for example,
that made by National Cash Register Company. The encapsulating
medium material should be selected so as to be rupturable or
destructible above the desired threshold temperature at which the
copy sheet is to be utilized. In most instances this is preferably
a temperature greater than about 35.degree.C. Either the color
forming composition or sensitizing material may be encapsulated in
the heat rupturable material. Also, if desired, one layer with
thorough mixing of the color forming composition and encapsulated
sensitizing means may be employed. Alternatively, a layer of heat
rupturable material such as a film or sheet may be interposed
between the color forming composition and the sensitizing material
so as to segregate the two as shown in FIG. 3B.
Heating the copy sheet above that threshold temperature which will
result in either chemically activating the sensitizing material or
destroying the heat destructible segregating means to release the
chemically reactive sensitizing material results in the color
forming composition becoming photosensitive due to the action of
the sensitizing material. However, once the color forming
composition has been exposed to light in formation of a copy image
it is desirably desensitized and rendered light stable once again.
In many instances, it is sufficient to merely reduce the
temperature of the copy sheet, after exposure, to below the
threshold temperature in order to render the copies stable,
particularly stable to ordinary ambient conditions of light and
temperature. For example, temperature reduction works well when
anethole is the sensitizing material. Copy sheets sensitized with
thiourea dioxide can be desensitized by continued heating without
the incorporation of any separate desensitizing means. However,
where some of the more sensitive dyes are used or the sensitizing
means is formed in situ, as previously described, and remains
active to continue to sensitize the color forming composition, it
is desirable to include a separate desensitizing material. This is
accomplished by incorporating certain compounds in the basic
composition which render the sensitizer ineffective following the
heating and image reproducing process. These desensitizing means
may be activated either through the action of light or additional
heat.
In a manner similar to that described for the other embodiments of
this invention, the desensitizing material can be separated from
other constituents of the coating material by segregation means
which are heat destructible. Thus, the desensitizing means can be
incorporated as a layer of heat rupturable capsules which are
destroyed at a preselected temperature which is greater than the
temperature necessary to activate the sensitizing material.
Alternatively, an intermediate heat destructible layer can be used
between the desensitizing means and the remainder of the coating
material, this layer also being effectively destroyed at a
temperature above that used to sensitize. The temperature
differential between that necessary to activate the sensitizing
material and that necessary to activate the desensitizing material
can conveniently be on the order to 5.degree. to 7.degree.C.
The desensitizing material will be selected so as to be effective
with the color forming and sensitizing compositions used. Of wide
application as a desensitizer in the compositions of this invention
is sulfurous acid either in a capsulated form or separated by heat
destructible layer or some other manner from the remainder of the
coating material. Sulfurous acid may be present in its final form
or formed in situ by incorporating sulfuryl chloride and pyridine
in the coating material. With peroxide fast dyes, hydrogen peroxide
in the presence of an alkali such as sodium hydroxide can be used
as a desensitizing means, particularly with the sensitizers
thiosinamine, or diethyl allyl thiourea. Other desensitizing
compositions are acetyl chloride dissolved in acetone, for use with
thiosinamine, Raney Nickel in alcoholic gelatin, benzoyl peroxide,
lead hydroxide, mecuric oxide, ammoniacal silver nitrate, sodium
bisulphite, acetic anhydride, alcoholic potassium hydroxide and
sodium nitroprusside. Reinecke's Salt with copper irons such as
Fehling's Solution A, iodine in ethanol, alkali bromide or iodide
compounds, cuprous chloride and ammonium chloride can also be
utilized as desensitizers. The foregoing desensitizers are useful
for incorporation in coating material in encapsulated or other form
which will cause them to be effectively released upon application
of higher temperature.
When diethyl thiourea is the sensitizing compound, mecuric oxide is
an effective desensitizer since diethyl urea, a relatively
ineffective sensitizer, is formed. In the presence of ethylamine,
triethylguanidine, an even less effective sensitizer, is formed.
Anesole is an effective desensitizer and can be utilized in benzene
solution in a gelatin overcoat. Light may be also used to
desensitize the copy sheets and this can be done by the addition to
the compositions of protoporphyrin when the sensitizing material is
a substituted thiourea. The amount of protoporphyrin added is
determined by the printing time desired. The substituted thiourea
sensitizes the color forming composition causing it to bleach under
the influence of light. However, as the light exposure continues
the protoporphyrin photo-oxidizes the substituted thiourea to
produce a material, which is ineffective as a sensitizer. For
example, when thiosinamine is the sensitizer continued light
exposure in the presence of protoporphyrin yields allyl formamidine
sulfuric acid. In some instances continued radiation that is,
irradiation of the basic composition without desensitizing
compounds following exposure to light by, x-rays or gamma rays can
desensitize by liberating sulfur from the sensitizing phase by a
chain reaction.
Various modifications of the compositions can be made by
incorporating components which catalyze or promote the systems to
either reduced heating time, exposure time or reduced overall
processing time.
The following examples are illustrative of the invention.
EXAMPLE 1
A binder is prepared consisting of 1 g of gelatin or
nitrocellulose, but preferably a mixture of these two with 15 ml of
absolute alcohol, i.e., ethanol. Certain dyes such as Benzopurpin
4B, Thiazol Yellow and Auracin, among others, require the presence
of nitrocellulose in the binder.
To the above binder solution is added 1 - 3 mg of the color forming
means, specifically for this example, Thionin, dissolved in 5 ml of
absolute alcohol and the mix is held at the lowest possible
temperature by continual stirring at 30.degree.C.
To the above dye solution is added 5 ml of allyl mustard oil or
synthetic allyl mustard oil (N.F. VIII such as manufactured by
Magnus, Mabee & Reynard of New York) and 10 ml of 30 percent
ammonia.
Paper stock, previously sized with 15 percent gelatin and 5 percent
glycerin (although other sizing materials such as pectin sugar or
can sugar may be included if desired), is coated with the above
mixture and allowed to dry at ordinary room temperatures or below.
The sizing basically reduces the porosity of the paper stock,
although certain constituents necessary to copying according to the
techniques of this invention may be included in the sizing.
EXAMPLE 2
The composition of Example 1 is basically a single layer system for
the color forming means and the sensitizing means which acts in
accordance with the basic concepts of this invention because the
constituents of the thosinamine require the presence of elevated
temperatures in order to react to form the sensitizing means in
situ. The stability of such copy sheets under ambient conditions
can be further increased by utilizing a multilayer arrangement such
as the following:
Fifteen ml of allyl mustard oil or synthetic allyl mustard oil is
added to 15 ml alcoholic solution of a 15 percent gelatin. The
mixture was run through a homogenizer at 35.degree.C. and coated
upon blank paper stock.
Two mg of Thionin in 5 ml of absolute alcohol is added to 10 ml of
a 15 percent alcoholic gelatin solution and coated upon the paper
which had previously been coated with the mustard oil solution.
Five ml of 30 percent ammonia is added to 10 ml of a 15 percent
alcoholic gelatin solution and this in turn was coated on top of
the two previous coatings.
EXAMPLE 3
Each of the above Examples incorporates the three basic
constituents necessary to the formation of thiosinamine in situ,
that is, oil of mustard, alcohol and ammonia. However, to even
further stabilize the materials against accidental sensitization of
the color forming composition under rather extreme ambient
conditions, precursors of three basic constitutents mentioned
previously can be substituted therefor. For example, the 30 percent
ammonia solution can be replaced by a mixture of 3 parts sal
ammoniac and 1 part lime or a mixture of other reactable alkali
hydroxides and ammonium salts. Upon heating as described for
sensitization ammonia is evolved in situ which then reacts with the
mustard oil and the alcohol to produce the sensitizing material,
thiosinamine.
Alternatively, the ammonia may be replaced by urea in water,
methanol or ethanol, a system including this substitution requiring
temperatures of up to about 145.degree.C. for approximately 45
seconds to form the sensitizing means to sensitize the color
forming composition.
Another substitution for the ammonia is 1 part hexaminecobaltic
chloride mixed with 3 parts distilled water. With such a system,
the paper is initially stable to light at ordinary ambient
conditions, although continued subjection of a paper including this
material to light, especially in the ultraviolet or near
ultraviolet region, results in some decomposition of the
hexaminecobaltic chloride to yield a photosensitive paper. Thus,
although such a paper will be relatively stable to accidental or
short time exposure to light, long term storage is preferably in
the dark.
A further substitution involves replacing the allyl mustard oil
with a mixture of allyl iodide and potassium thiocyanate in
absolute ethanol. This, however, requires that heating times be
approximately doubled in order to form the sensitizer
thiosinamine.
Of course, as hereinbefore disclosed, the thiosinamine may be
present in the coating material in the final form, rather than
being formed in situ, provided it is separated from the color
forming means by a segregation means of the type discussed.
A yet further substitution can result in the formation, in situ, of
the sensitizer diethylidene thiourea. For example, both the allyl
mustard oil and the ammonia are replaced by thiourea ethyl oxalate.
However, the paper stock must be previously saturated with
aldehydeammonia or aldehydeammonia must be incorporated in a
gelatin substrate. Heating produces diethylidene thiourea which in
turn sensitizes the color forming means to the action of light.
Exposure times for the material are preferably fifty percent
greater than for the thiosinamine discussed above. Copy sheets
having diethylidene thiourea as a sensitizer may exhibit some
photosensitivity at ambient temperature after several days storage
and thus are desirably used in application where they will not be
subject to ambient light and temperature conditions for extended
periods.
EXAMPLE 3A
Anethole is a sensitizer particularly useful with dyes such as
Erythrosin B, Rose Bengal, Methylene Blue, Crystal Violet and
Thionin. Preferably, blank paper stock is first floated in a
solution of 15 percent gelatin in water and Thionin. The amount of
dye in the system is determined by the shade of coloration desired
and light to pale blue is preferred. The paper is then cooled,
preferably to or below freezing, while the system dries. While
maintaining the paper in the cold state, a coating of 100 percent
anethole at or slightly above its melting point is applied by
spraying or other suitable methods. The anethole solidifies as it
strikes the paper. Several such spray coatings may be employed.
Following solidification of the anethole, the paper may be
maintained at ambient to cool temperatures until use, at which
time, it is heated and exposed to light in the same manner as the
copy sheet of Example 1.
The order of the two coatings may be reversed, if desired, but the
effectiveness of this system depends upon the degree of separation
of the two phases. Thus, an intermediate layer of gelatin or other
material may be applied, if necessary, to further segregate the
color forming means from the sensitizing means. Additionally,
certain materials such as bergamot oil may be added to the anethole
to raise its melting point and further stabilize the system.
EXAMPLE 4
Another substituted thiourea which is particularly effective as a
sensitizing means according to this invention, due to the fact that
it requires the application of heat in order to become effective,
is thiourea dioxide. This material may be prepared by cooling 30
percent hydrogen peroxide to -0.4.degree.C. and slowly adding
powdered thiourea until crystals separate from the solution. The
crystals are filtered off and dried by air at approximately
25.degree.C. since temperatures higher than about 30.degree.C. at
this point tend to render the sensitizer ineffective when
subsequently used.
One gram of these crystals is added to 5 ml of distilled water at
20.degree.C. and stirred at this temperature for 15 - 30 minutes.
The solution will appear saturated since all of the crystals do not
dissolve; however, they are left in solution. Ten ml of alcoholic
15 percent gelatin is added thereto and the temperature is raised
to 25.degree.C. Stirring is continued while a color forming means
such as an alcoholic solution of 2 mg Thionin (Thiazine dyes are
particularly good color forming means with this sensitizer) is
added thereto.
Paper stock is coated with the foregoing and dried as quickly as
possible at as low temperature as possible. Following low
temperature drying, the paper is slowly raised to ambient
temperatures. Such paper is stable if stored in a cool dry place
and kept from drastic exposures to light or temperatures. Continued
exposures to relatively high ambient temperatures will render this
paper photosensitive.
EXAMPLE 5
The methods of the various examples set forth previously may be
utilized with a mixture of dyes in a manner so as to bleach
preferentially according to light reflected from, and passed
through, colored matter to yield a colored reproduction resembling
the original.
An example of such material could include any of the aforementioned
sensitizing phases, but the following formula is given by way of
illustration.
To 10 ml of alcoholic gelatin - nitrocellulose (1 gm of each) is
added 5 ml of synthetic allyl mustard oil. The mixture is placed in
a stirring apparatus and continuously stirred while the remainder
of the components, including 10 ml of 30 percent ammonia, are
added.
In a separate container, to 5 ml of absolute alcohol is added 4 mg
phenanthrophenazonium methyl nitrate (yellow), 2 mg. Rosinduline 2B
(magenta) and 2 mg Capril Blue G O N (cyan). When thoroughly
dispersed, the dye solution is added to the above mix including the
mustard oil and the ammonia. The completed mixture is then passed
through a homogenizer and coated upon blank paper stock which is
then dried at room temperatures or below.
Exposure to light follows heating at temperatures above about
40.degree.C. at which point the dyes will bleach preferentially
according to the color of the exposing light, and following
exposure, will reflect according to the degree of bleaching.
A manner of using copy sheets formed according to this invention is
illustrated schematically in FIG. 4 showing a copying device. The
copying device includes a support, base and cover, all indicated
generally. The base includes a transparent plate such as a glass
plate and a light source therebeneath. Various light sources may be
utilized although certain coating composition may provide better
copies with different light sources. For example, a conventional
1500 watt sodium iodine lamp has been used quite satisfactorily
with the copy sheets described in the examples given below although
a 424 watt mercury vapor sun lamp developing ultraviolet energy in
the spectrum bounded by the lines 2,800 - 3,200 Angstrom units wave
length has been shown to provide better results. The type of light
source can be readily selected by one skilled in the art depending
on the particular coating composition and results desired.
In operation, the original to be copied is placed on the glass
plate and a copy sheet superimposed with respect thereto. A heated
metal plate is carried by the cover of the copying device and
lowered into contact, with the back preferably, of the copy sheet.
This function is to hold the copy sheet and original in contact
with each other and with the glass plate. The heating means is
activated to raise the temperature of the copy sheet and the
coating material thereon to the desired threshold temperature which
functions to activate the sensitizing material and sensitize the
color forming composition. Preferably such temperature is above
ordinary room ambient temperature and 35.degree.C may be considered
illustrative of a minimum threshold temperature for activation of
the sensitizing means. However, the reaction may be speeded by
decreasing heating times, and in some instances resolution
increased, by utilizing higher temperatures. An optimum temperature
for most embodiments of this invention has been found to be
approximately 70.degree.C. At this temperature the heating time
need not be greater than about 20 seconds and may in some instances
be shorter.
Once the sensitizing means has been activated the light source may
be energized automatically and the copy sheet thereby exposed to
the original and to the selected light pattern. At this temperature
the color forming composition will have been sensitized and will
change in color in areas exposed to light to produce an image
corresponding to the light pattern. If the desensitizing material
has been included in the copy sheet, heating plate may be
automatically energized subsequent to exposure to raise the
temperature slightly to that temperature which will activate the
desensitizing means. Alternatively, the heat resulting from
energizing the light source may raise the temperature of the copy
sheet and material thereon sufficiently to activate the
desensitizing means once the sensitizing means has performed its
function. The device may be cooled down in conventional manner.
The copy sheets do not require heating to extremely high
temperatures which might damage the copy and original and
necessitate excessive requirements. Generally, the materials of
this invention anticipate heat requirements yielding temperature no
greater than about 130.degree.C and in preferred embodiments, less
than about 100.degree.C. This enables the use of relatively
inexpensive support elements such as ordinary paper and low
temperature plastic sheets and economical heating equipment having
low power requirements.
The following examples are illustrative of the means and method of
using a copy sheet according to this invention.
EXAMPLE 6
A copy sheet formed according to the techniques of Example 1 is
placed in contact with an original in a copying device such as is
shown schematically in FIG. 4. Since the copy sheet is not light
sensitive until its temperature has been elevated, the heated metal
plate is energized to raise the temperature above ambient
conditions. At approximately 40.degree.C., the paper is preferably
heated for approximately 50 seconds, whereas if the temperature is
raised to approximately 70.degree.C., only 20 seconds is required
for the heating phase. Utilizing a 1500 watt sodiumiodine lamp, the
light source is then energized for approximately 10 seconds to
expose the heated copy sheet to a light pattern corresponding to
the original, although the time can be further limited or extended
for different contrasts. The paper can be removed immediately after
the light exposure, or, preferably, can remain in contact with the
heating element for an additional 10-20 seconds to insure greater
permanency.
The yield is a positive duplicate of the original.
Basically, the system defined hereinabove forms a copy in the
following manner. When the composition is mixed and retained at
ambient temperatures, the individual constituents remain relatively
stable. However, on heating the paper, the oil of mustard, absolute
alcohol and ammonia combine to form thiosinamine in situ which in
turn sensitizes the dye to the action of the light.
EXAMPLE 7
A copy sheet formed according to Example 4 is utilized for printing
by heating for approximately 10 seconds at from about 50.degree. -
90.degree.F. or for about 20 seconds at from about 40.degree. -
50.degree.C. Exposure to light for 20 seconds more or less
depending upon the contrast desired will then produce an image
corresponding to the exposure time.
With copy sheets formed in this manner, stabilization may be
achieved within 5 seconds by bringing the paper to 130.degree.C.,
by exposing the paper to steam for approximately 10 seconds or by
dipping the paper in, or flooding the same with, boiling water.
Another method of stabilizing such paper is to coat the same with
peracetic acid following exposure, although care must be taken to
avoid affecting the dye.
Various modifications may be made of the disclosed composition to
catalyze or promote the system thereby reducing either the heating
time or the exposure time, and in other instances thereby reducing
the overall processing time while still producing an acceptable
copy.
The composition of Example 1 can be further modified by inclusion
in the gelatin sizing layer or in the gelating binder of 5 ml of
50.4 grams of rhombic sulfur dissolved in 100 grams of carbon
disulfide. This additive promotes the reaction of the system,
cutting all times by approximately 25 percent. Alternatively, if
one gram of monomethylparamidophenyl sulfate is added to the
coating mixture with the dye solution, the exposure time, with the
system of Example 1, is decreased by about 50 percent to
approximately 5 seconds.
With the system of Example 3A, particularly when the color forming
means in Methylene Blue, Crystal Violet or Thionin, the addition of
0.5 g of sodium or potassium hydroxide to the dye phase will
decrease light exposure time by about 30 percent. Generally, the
inclusion of 1 - 5 grams of zinc oxide in the coating composition
or in the sizing, of the various disclosed systems of this
invention, decreases both the heating times and the exposure times
by 15 - 20 percent.
Thus there has been disclosed herein copy sheets, processes and
means for manufacturing and for utilizing the same in reproduction
techniques, having advantages over the prior art.
* * * * *