U.S. patent application number 12/369600 was filed with the patent office on 2010-01-21 for imaging system.
This patent application is currently assigned to Zink Imaging, Inc.. Invention is credited to Peter K. CHU, Chien LIU, Stephen J. TELFER.
Application Number | 20100016154 12/369600 |
Document ID | / |
Family ID | 32962569 |
Filed Date | 2010-01-21 |
United States Patent
Application |
20100016154 |
Kind Code |
A1 |
CHU; Peter K. ; et
al. |
January 21, 2010 |
IMAGING SYSTEM
Abstract
There are disclosed imaging members wherein a chemical compound
in a crystalline form is converted, at least partially, and
preferably substantially completely or completely, to a liquid in
the amorphous form, the liquid having intrinsically a different
color from the crystalline form. Also described are imaging methods
utilizing the imaging members. The conversion of the compound from
the crystalline form to the liquid form can be effected by the
application of thermal energy or by other imaging techniques.
Inventors: |
CHU; Peter K.; (Acton,
MA) ; LIU; Chien; (Wayland, MA) ; TELFER;
Stephen J.; (Arlington, MA) |
Correspondence
Address: |
FOLEY & LARDNER LLP
111 HUNTINGTON AVENUE, 26TH FLOOR
BOSTON
MA
02199-7610
US
|
Assignee: |
Zink Imaging, Inc.
|
Family ID: |
32962569 |
Appl. No.: |
12/369600 |
Filed: |
February 11, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11656267 |
Jan 22, 2007 |
7504360 |
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12369600 |
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10789648 |
Feb 27, 2004 |
7176161 |
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11656267 |
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60451208 |
Feb 28, 2003 |
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Current U.S.
Class: |
503/200 |
Current CPC
Class: |
B41M 5/3275 20130101;
C07D 311/02 20130101; C09B 67/006 20130101; C09B 11/24 20130101;
B41M 5/385 20130101; B41M 5/284 20130101; C07D 493/10 20130101;
Y10S 430/145 20130101; Y10S 430/146 20130101; B41M 5/34 20130101;
B41M 5/1455 20130101 |
Class at
Publication: |
503/200 |
International
Class: |
B41M 5/28 20060101
B41M005/28 |
Claims
1. A color imaging member comprising at least a first color-forming
layer, wherein said first color-forming layer comprises a first
chemical compound in a crystalline form, said crystalline form
being capable of being converted to a liquid in the amorphous form,
said liquid form of said first chemical compound having
intrinsically a different color from said crystalline form.
2-25. (canceled)
Description
REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation application of U.S.
application Ser. No. 11/656,267, filed Jan. 22, 2007, which is a
continuation of U.S. application Ser. No. 10/789,648, filed Feb.
27, 2004, which claims the benefit of provisional application Ser.
No. 60/451,208, filed Feb. 28, 2003, the contents of all are hereby
incorporated by reference in their entireties.
[0002] This application is related to the following commonly
assigned, United States patent applications and patents, the entire
disclosures of which are hereby incorporated by reference herein
their entirety:
[0003] U.S. patent application Ser. No. 10/789,566, filed on Feb.
27, 2004, (Attorney Docket No. C-8586AFP) issued as U.S. Pat. No.
7,279,264;
[0004] U.S. patent application Ser. No. 10/788,963, filed on Feb.
27, 2004, (Attorney Docket No. 8587AFP) issued as U.S. Pat. No.
7,008,759;
[0005] U.S. patent application Ser. No. 10/789,276, filed on Feb.
27, 2004, (Attorney Docket No. 8588AFP) issued as U.S. Pat. No.
6,951,952;
[0006] U.S. patent application Ser. No. 10/789,600, filed on Feb.
27, 2004, (Attorney Docket No. 8589AFP) issued as U.S. Pat. No.
7,282,317;
[0007] U.S. patent application Ser. No. 10/151,432, filed May 20,
2002 (United States Patent Application Publication No.
US2003/0125206 A1), issued as U.S. Pat. No. 6,801,233; and
[0008] U.S. Pat. No. 6,537,410 B2.
FIELD OF THE INVENTION
[0009] This invention relates to imaging members, imaging methods
for forming an image and a method for manufacturing a thermal
imaging member and, more particularly, to imaging members and
methods wherein formation of an image occurs when a chemical
compound in a crystalline form is converted, at least partially, to
a liquid, or amorphous, form, the liquid having intrinsically a
different color from the crystalline form.
BACKGROUND OF THE INVENTION
[0010] The development of thermal print heads (linear arrays of
individually-addressable resistors) has led to the development of a
wide variety of thermally-sensitive media. In some of these, known
as "thermal transfer" systems, heat is used to move colored
material from a donor sheet to a receiver sheet. Alternatively,
heat may be used to convert a colorless coating on a single sheet
into a colored image, in a process known as "direct thermal"
imaging. Direct thermal imaging has the advantage over thermal
transfer of the simplicity of a single sheet. On the other hand,
unless a fixing step is incorporated, direct thermal systems are
still sensitive to heat after thermal printing. If a stable image
is needed from an unfixed direct thermal system, the temperature
for coloration must be higher than any temperature that the image
is likely to encounter during normal use. A problem arises in that
the higher the temperature for coloration, the less sensitive the
medium will be when printed with the thermal print head. High
sensitivity is important for maximum speed of printing, for
maximizing the longevity of the print head, and for energy
conservation in mobile, battery-powered printers. As described in
more detail below, maximizing sensitivity while maintaining
stability is more easily achieved if the temperature of coloration
of a direct thermal medium is substantially independent of the
heating time.
[0011] Thermal print heads address one line of the image at a time.
For reasonable printing times, each line of the image is heated for
about ten milliseconds or less. Storage of the medium (prior to
printing or in the form of the final image) may need to be for
years, however. Thus, for high imaging sensitivity, a high degree
of coloration is required in a short time of heating, while for
good stability a low degree of coloration is required for a long
time of heating.
[0012] Most chemical reactions speed up with increasing
temperature. Therefore, the temperature required for coloration in
the short heating time available from a thermal print head will
normally be higher than the temperature needed to cause coloration
during the long storage time. Actually reversing this order of
temperatures would be a very difficult task, but maintaining a
substantially time-independent temperature of coloration, such that
both long-time and short-time temperatures for coloration are
substantially the same, is a desirable goal that is achieved by the
present invention.
[0013] There are other reasons why a time-independent coloration
temperature may be desirable. It may, for example, be required to
perform a second thermal step, requiring a relatively long time of
heating, after printing. An example of such a step would be thermal
lamination of an image. The temperature of coloration of the medium
during the time required for thermal lamination must be higher than
the lamination temperature (otherwise the medium would become
colorized during lamination). It would be preferred that the
imaging temperature be higher than the lamination temperature by as
small a margin as possible, as would be the case for
time-independent temperature of coloration.
[0014] Finally, the imaging system may comprise more than one
color-forming layer and be designed to be printed with a single
thermal print-head, as described in the above-mentioned patent
application Ser. No. 10/151,432. In one embodiment of the imaging
system, the topmost color-forming layer forms color in a relatively
short time at a relatively high temperature, while the lower layer
or layers form color in a relatively long time at a relatively low
temperature. An ideal topmost layer for this type of direct thermal
imaging system would have time-independent temperature of
coloration.
[0015] Prior art direct thermal imaging systems have used several
different chemical mechanisms to produce a change in color. Some
have employed compounds that are intrinsically unstable, and which
decompose to form a visible color when heated. Such color changes
may involve a unimolecular chemical reaction. This reaction may
cause color to be formed from a colorless precursor, the color of a
colored material to change, or a colored material to bleach. The
rate of the reaction is accelerated by heat. For example, U.S. Pat.
No. 3,488,705 discloses thermally unstable organic acid salts of
triarylmethane dyes that are decomposed and bleached upon heating.
U.S. Pat. No. 3,745,009 reissued as U.S. Reissue Pat. No. 29,168
and U.S. Pat. No. 3,832,212 disclose heat-sensitive compounds for
thermography containing a heterocyclic nitrogen atom substituted
with an --OR group, for example, a carbonate group, that decolorize
by undergoing homolytic or heterolytic cleavage of the
nitrogen-oxygen bond upon heating to produce an RO+ ion or RO'
radical and a dye base or dye radical which may in part fragment
further. U.S. Pat. No. 4,380,629 discloses styryl-like compounds
that undergo coloration or bleaching, reversibly or irreversibly,
via ring-opening and ring-closing in response to activating
energies. U.S. Pat. No. 4,720,449 describes an intramolecular
acylation reaction that converts a colorless molecule to a colored
form. U.S. Pat. No. 4,243,052 describes pyrolysis of a mixed
carbonate of a quinophthalone precursor that may be used to form a
dye. U.S. Pat. No. 4,602,263 describes a thermally-removable
protecting group that may be used to reveal a dye or to change the
color of a dye. U.S. Pat. No. 5,350,870 describes an intramolecular
acylation reaction that may be used to induce a color change. A
further example of a unimolecular color-forming reaction is
described in "New Thermo-Response Dyes: Coloration by the Claisen
Rearrangement and Intramolecular Acid-Base Reaction Masahiko
Inouye, Kikuo Tsuchiya, and Teijiro Kitao, Angew. Chem. Int. Ed.
Engl. 31, pp. 204-5 (1992).
[0016] In all of the above-mentioned examples, control of the
chemical reaction is achieved through the change in rate that
occurs with changing temperature. Thermally-induced changes in
rates of chemical reactions in the absence of phase changes may
often be approximated by the Arrhenius equation, in which the rate
constant increases exponentially as the reciprocal of absolute
temperature decreases (i.e., as temperature increases). The slope
of the straight line relating the logarithm of the rate constant to
the reciprocal of the absolute temperature is proportional to the
so-called "activation energy". The prior art compounds described
above are coated in an amorphous state prior to imaging, and thus
no change in phase is expected or described as occurring between
room temperature and the imaging temperature. Thus, as employed in
the prior art, these compounds exhibit strongly time-dependent
coloration temperatures. Some of these prior art compounds are
described as having been isolated in crystalline form.
Nevertheless, in no case is there mentioned in this prior art any
change in activation energy of the color-forming reaction that may
occur when crystals of the compounds are melted.
[0017] Other prior art thermal imaging media depend upon melting to
trigger image formation. Typically, two or more chemical compounds
that react together to produce a color change are coated onto a
substrate in such a way that they are segregated from one another,
for example, as dispersions of small crystals. Melting, either of
the compounds themselves or of an additional fusible vehicle,
brings them into contact with one another and causes a visible
image to be formed. For example, a colorless dye precursor may form
color upon heat-induced contact with a reagent. This reagent may be
a Bronsted acid, as described in "Imaging Processes and Materials",
Neblette's Eighth Edition, J. Sturge, V. Walworth, A. Shepp, Eds.,
Van Nostrand Reinhold, 1989, pp. 274-275, or a Lewis acid, as
described for example in U.S. Pat. No. 4,636,819. Suitable dye
precursors for use with acidic reagents are described, for example,
in U.S. Pat. No. 2,417,897, South African Patent 68-00170, South
African Patent 68-00323 and Ger. Offenlegungschrift 2,259,409.
Further examples of such dyes may be found in "Synthesis and
Properties of Phthalide-type Color Formers", by Ina Fletcher and
Rudolf Zink, in "Chemistry and Applications of Leuco Dyes",
Muthyala Ed., Plenum Press, New York, 1997. The acidic material may
for example be a phenol derivative or an aromatic carboxylic acid
derivative. Such thermal imaging materials and various combinations
thereof are now well known, and various methods of preparing
heat-sensitive recording elements employing these materials also
are well known and have been described, for example, in U.S. Pat.
Nos. 3,539,375, 4,401,717 and 4,415,633.
[0018] Prior art systems in which at least two separate components
are mixed following a melting transition suffer from the drawback
that the temperature required to form an image in a very short time
by a thermal print-head may be substantially higher than the
temperature required to colorize the medium during longer periods
of heating. This difference is caused by the change in the rate of
the diffusion needed to mix the molten components together, which
may become limiting when heat is applied for very short periods.
The temperature may need to be raised well above the melting points
of the individual components to overcome this slow rate of
diffusion. Diffusion rates may not be limiting during long periods
of heating, however, and the temperature at which coloration takes
place in these cases may actually be less than the melting point of
either individual component, occurring at the eutectic melting
point of the mixture of crystalline materials.
[0019] Despite the many prior art examples of direct thermal
imaging systems, therefore, there are none in which the temperature
of image formation is substantially time-independent. In
particular, there has not previously been described a method for
producing an image in which a crystalline chemical compound is
converted to a liquid, or amorphous, form, the liquid form having
intrinsically a different color from the crystalline form.
SUMMARY OF THE INVENTION
[0020] It is therefore an object of this invention to provide a
novel imaging method.
[0021] Another object of the invention is to provide a thermal
imaging method wherein the temperature at which an image is formed
is time independent.
[0022] It is another object to provide an imaging method wherein an
image is formed by converting a solid chemical compound in the
crystalline form, at least partially, to a liquid in the amorphous
form.
[0023] Still another object is to provide a multicolor thermal
imaging method wherein at least one color separation image is
formed by converting a solid chemical compound in the crystalline
form at least partially to a liquid in the amorphous form.
[0024] Yet another object of the invention is to provide novel
imaging members.
[0025] Another object of the invention is to provide a method for
the manufacture of a direct thermal imaging member.
[0026] According to one aspect of the invention there are provided
imaging methods wherein a chemical compound in a crystalline form
is converted, at least partially, and preferably substantially
completely or completely, to a liquid in the amorphous form, the
liquid having intrinsically a different color from the crystalline
form. The conversion to the liquid form can be carried out by
applying heat to the thermal imaging member by any of the
techniques known in thermal imaging such as from a thermal print
head, a laser, a heated stylus, etc. In another embodiment, the
conversion to the liquid form may be effected by applying a solvent
ink jet for the crystalline solid such as from an imaging apparatus
to at least partially dissolve the crystalline material. In another
embodiment, one or more thermal solvents, which are crystalline
materials, can be incorporated in the thermal imaging member. The
crystalline thermal solvent(s), upon being heated, melt and
dissolve or liquefy, and thereby convert, at least partially, the
crystalline image-forming material to the liquid amorphous form to
form the image.
[0027] The conversion of the crystalline form to the liquid or
amorphous form upon heating or dissolving the crystalline compounds
of the present invention may produce a material of high or low
viscosity. Typically, liquid or amorphous materials with
viscosities higher than 10 12 Pas are referred to as glasses. It
may be that melting of the crystalline form produces a free-flowing
liquid that, upon cooling, becomes a glass. The temperature at
which the viscosity reaches 10 12 Pas upon cooling is referred to
as the glass transition temperature, or Tg. In order to form an
image having a desirable degree of stability, it is preferred that
recrystallization of the liquid or amorphous form into the
crystalline form not occur. It is more likely that
recrystallization will be slow when the liquid or amorphous form is
a glass, i.e., at a temperature below its Tg. For this reason it is
preferred that the Tg of the liquid or amorphous form of the
compounds of the present invention be substantially above room
temperature. Preferred Tg's are about 50.degree. C. or greater
[0028] In another aspect of the invention there are provided novel
thermal imaging members. The thermal imaging members of the
invention generally comprise a substrate carrying at least one
image-forming layer including a compound in the crystalline form,
which can be converted, as described previously, at least partially
to a liquid in the amorphous form, the liquid having intrinsically
a different color from the crystalline form. The thermal imaging
member may be monochrome or multicolor and the temperature at which
an image is formed in at least one of the image-forming layers is
time independent.
[0029] The multicolor thermal imaging members of the invention may
include at least one image-forming layer including a compound in
the crystalline form, which can be converted, as described
previously, at least partially to a liquid in the amorphous form,
the liquid having intrinsically a different color from the
crystalline form and at least one image-forming layer including
materials which form a color by a different mechanism.
[0030] Preferred thermal imaging members according to the invention
are those having the structures described in commonly assigned U.S.
Pat. No. 6,537,410 B2, which is hereby incorporated herein by
reference in its entirety and made a part of this application.
[0031] Other preferred thermal imaging members are those having the
structures described in prior, co-pending commonly assigned U.S.
patent application Ser. No. 10/151,432 filed May 20, 2002 (Patent
Application Publication No. US2003/0125206), issued as U.S. Pat.
No. 6,801,233, which is hereby incorporated herein by reference in
its entirety and made a part of this application.
[0032] Further preferred thermal imaging members are those having
the structures described in U.S. Pat. No. 6,054,246 which is hereby
incorporated herein by reference in its entirety and made a part of
this application.
[0033] In another aspect of the invention there is provided a
method for manufacturing the thermal imaging members of the
invention. Generally, the method includes the steps of forming a
dispersion of the crystalline solid and optionally a binder, in a
solvent in which the compound is insoluble or only sparingly
soluble by any suitable method such as by grinding, attriting, etc.
and forming a layer of the image-forming material on a substrate by
any suitable method such as, for example, by coating the fluid onto
the substrate using any of the techniques well-known in the coating
art. These include slot, gravure, Mayer rod, roll, cascade, spray,
and curtain coating techniques. The image-forming layer so formed
is optionally overcoated with a protective layer or layers.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] For a better understanding of the invention as well as other
objects and advantages and further features thereof, reference is
made to the following detailed description of various preferred
embodiments thereof taken in conjunction with the accompanying
drawings wherein:
[0035] FIG. 1 illustrates two different chemical mechanisms, Types
I and II, by which images can be formed according to the present
invention;
[0036] FIG. 2 illustrates a proton transfer equilibrium
characteristic of materials which undergo the Type I mechanism
shown in FIG. 1; and
[0037] FIG. 3 illustrates a chemical mechanism characteristic of
materials which undergo the Type II mechanism.
DETAILED DESCRIPTION OF THE INVENTION
[0038] Compounds in the crystalline state commonly have properties,
including color, that are very different from those of the same
compounds in an amorphous form. In a crystal, a molecule is
typically held in a single conformation (or, more rarely, in a
small number of conformations) by the packing forces of the
lattice. Likewise, if a molecule can exist in more than one
interconverting isomeric forms, only one of such isomeric forms is
commonly present in the crystalline state. In amorphous form or
solution, on the other hand, the compound may explore its whole
conformational and isomeric space, and only a small proportion of
the population of individual molecules of the compound may at any
one time exhibit the particular conformation or isomeric form
adopted in the crystal. These phenomena are exploited in three
similar ways in the compositions, imaging methods and imaging
members of the present invention.
[0039] Referring now to FIG. 1, there are seen two types of
chemical equilibria which are exploited according to the present
invention, designated Types I and II. The first type takes
advantage of the fact that certain dye molecules exhibit
tautomerism in solution (i.e., they exist as different,
interconverting isomers at equilibrium). This is shown in FIG. 1,
Type I, as the equilibrium between interconverting chemical
entities A and B. Only two chemical species are shown in FIG. 1,
Type I, but this is for the sake of simplicity only, and is not
intended to limit the scope of invention in any way. The discussion
provided herein applies equally to any number of interconverting
tautomers. In the crystalline state, as described above, only one
of the possible tautomeric forms will usually be present. Thus,
crystallization of the mixture of A and B can produce crystals of
pure A, or pure B, depending upon the conditions used.
[0040] Different tautomers may have different electronic structures
from one another, and therefore different absorption of
electromagnetic radiation. It is not unusual, therefore, for
different tautomers to have different colors. The equilibrium
distribution of tautomers will depend upon the polarity of the
medium in which they are dissolved. Thus, a polar tautomer will be
favored in a polar medium, while a less polar tautomer will be
favored in a less polar medium. If a dye molecule exhibiting
tautomerism can be crystallized into a single tautomeric form, the
crystalline state will exhibit the color of that particular
tautomer. If such a crystalline form is heated and converted to the
liquid form or dissolved in a solvent, the tautomeric equilibrium
will be re-established, so that at least some of the tautomer or
tautomers not present in the crystal will be present, in relative
amounts dependent upon the polarity of the molten state or
solution. Since contributions from tautomers not present in the
crystal will be seen, the color of the melt or solution is likely
to be different from that of the crystal.
[0041] According to the invention, there have been identified
molecules exhibiting tautomerism in which at least one tautomeric
form is colorless, and at least another tautomeric form is colored.
This is represented in FIG. 1, Type I, provided that molecule A is
colorless, and molecule B is colored. Crystallization of the
equilibrating mixture of A and B is carried out so as to produce
colorless crystals of pure A. The solvent chosen to perform the
crystallization will typically be one of such polarity (and other
chemical properties, such as hydrogen-bonding ability) that A is
favored, either in the equilibrium between A and B in solution, or
in having lower solubility in the solvent than B. The choice of
solvent is usually determined empirically for a particular mixture
of tautomers.
[0042] Upon conversion of the pure crystalline A, the equilibrium
between tautomers A and B is re-established in the resulting
amorphous (liquid) phase. The proportion of the amorphous material
that is colored (i.e., the proportion that is in the B tautomeric
form) may vary, but is preferably at least about 10%.
[0043] The colored and colorless tautomeric forms of the molecules
of the present invention must meet certain criteria for image
quality and permanence. The colorless form, which it is preferred
be the crystalline form, should have minimal visible absorption. It
should be stable to light, heating below the melting point,
humidity, and other environmental factors such as ozone, oxygen,
nitrogen oxides, fingerprint oils, etc. These environmental factors
are well known to those skilled in the imaging art. The colored,
amorphous form should be stable also to the above mentioned
conditions, and in addition should not recrystallize to the
colorless form under normal handling conditions of the image. The
colored form should have a spectral absorption appropriate for
digital color rendition. Typically, the colored form should be
yellow (blue-absorbing), magenta (green-absorbing), cyan (red
absorbing), or black, without undue absorption in an unintended
spectral region. For nonphotographic applications, however, it may
be required that the colored form not be one of the subtractive
primary colors, but rather a particular spot color (for example,
orange, blue, etc.).
[0044] The thermal imaging members of the invention can be direct
thermal imaging members wherein an image is formed in the member
itself or they can be thermal transfer imaging members whereby
image-forming material is transferred to an image-receiving member.
The melting point of the molecules used in direct thermal imaging
members of the present invention is preferably in the range of
about 60.degree. C. to about 300.degree. C. Melting points lower
than about 60.degree. C. lead to direct thermal imaging members
that are unstable to temperatures occasionally encountered during
handling of the members before or after imaging, while melting
temperatures above about 300.degree. C. render the compounds
difficult to colorize with a conventional thermal print head. It
should be noted, however, that there are uses for certain novel
compounds of the present invention that do not require the use of
thermal print heads (for example, laser imaging).
[0045] The multicolor thermal imaging members of the invention
include those wherein all the color-forming layers are carried on
the same side of a substrate as well as those wherein at least one
color-forming layer is carried on a first side of a substrate and
at least one color-forming layer is carried on a second side of the
substrate.
[0046] A preferred tautomeric equilibrium of the present invention
involves proton transfer. As shown in FIG. 2, a molecule containing
an acidic and a basic site can exist either in the protonated acid
and unprotonated base tautomeric form, or in the unprotonated acid
and protonated base form. These two forms can have different colors
if either the acidic site or the basic site of the molecule
constitute an indicator dye. Thus, the molecule might consist of a
colorless, basic indicator dye (that becomes colored in the
presence of an acid) covalently joined to an acid, or a colorless,
acidic indicator dye (that becomes colored when deprotonated)
covalently joined to a base. Of course, the molecule may also
consist of a basic indicator dye covalently joined to an acidic
indicator dye. The strengths of the acidic and the basic sites must
be such that an equilibrium may be established that does not
overwhelmingly favor one of the two tautomers under most
conditions. This is most easily achieved if the acid and the base
are weak. An especially preferred acidic grouping is a phenol,
while the basic site may vary widely, commonly being an
electronegative heteroatom such as oxygen or nitrogen.
[0047] Preferred examples of tautomeric molecules of Type I of the
present invention include the following xanthene derivatives. Two
tautomeric forms of the xanthene-derivatives are shown (represented
by formulae I and II), but this is not meant to exclude additional
tautomeric forms of the molecule. (It should be noted that only one
of the possible tautomers of xanthene
##STR00001##
molecules is sometimes reported in the literature.)
[0048] wherein R.sub.1, R.sub.3, R.sub.4, R.sub.5, R.sub.6, and
R.sub.8 are each independently hydrogen, alkyl, aryl, halogen, or
substituted or unsubstituted oxygen, nitrogen or sulfur atoms;
[0049] R.sub.2 is hydrogen, alkyl, aryl, or is absent;
[0050] R.sub.7 is substituted or unsubstituted oxygen, nitrogen,
sulfur, or halogen;
[0051] R.sub.9, R.sub.10, R.sub.11 and R.sub.12 are each
independently hydrogen, alkyl, aryl, halogen, nitro or substituted
or unsubstituted oxygen, nitrogen or sulfur atoms, or absent;
[0052] X.sub.1 is carbonyl, methylene, or sulfonyl;
[0053] X.sub.2 is oxygen or nitrogen, substituted with hydrogen,
alkyl, aryl, or nitrogen;
[0054] X.sub.3 and X.sub.4 are each independently oxygen, sulfur,
or nitrogen; and
[0055] X.sub.5 is carbon or nitrogen.
[0056] In these compounds, the acidic grouping of formula I
comprises the group X.sub.4 bearing the hydrogen atom, and the
basic site of formula I comprises the atom X.sub.2. Transfer of a
proton from X.sub.4 to X.sub.2 gives a compound of formula II.
[0057] One preferred subgroup of xanthenes of formula I are
fluorescein compounds, wherein X.sub.4 is oxygen and R.sub.7 is
oxygen substituted with hydrogen, alkyl or aryl; and X.sub.1 is
carbonyl; X.sub.2 is oxygen; and X.sub.3 is oxygen.
[0058] Many fluorescein derivatives of the above subtype are known
in the art. One tautomeric form (corresponding to formula I) of
such compounds is colorless (absorbing in the ultraviolet region of
the electromagnetic spectrum), whereas a second tautomeric form
(corresponding to formula II) is often yellow in color Fluorescein
itself is the compound of formula I, in which R.sub.2 is absent,
R.sub.7 is a hydroxyl group, R.sub.1, R.sub.3, R.sub.4, R.sub.5,
R.sub.6, R.sub.8, R.sub.9, R.sub.10, R.sub.11 and R.sub.12 are each
hydrogen atoms, X.sub.1 is carbonyl, X.sub.2, X.sub.3 and X.sub.4
are each oxygen and X.sub.5 is carbon. It has been found that there
are difficulties with many of these prior art compounds.
Fluorescein itself is difficult to crystallize in a colorless form
and in the amorphous form exhibits complex equilibria including
several, differently colored species. A simplification may be made
if R.sub.7 is an ether grouping. Thus, the previously known
compound benzyl fluorescein, in which the substituents are as
described above for fluorescein itself except that R.sub.7 is a
benzyloxy group, is readily crystallized into a colorless form. The
amorphous form of benzyl fluorescein has a yellow color.
[0059] Benzyl fluorescein has the disadvantage that only a small
proportion of the amorphous form (about 4%) is colored (i.e., about
96% of the amorphous form is in the tautomeric form corresponding
to formula I, and about 4% in the structure corresponding to
formula II). It has been found that much higher proportions of the
colored tautomer in the amorphous form may be obtained when at
least two of R.sub.1, R.sub.3, R.sub.6 and R.sub.8 in formula I
comprise an alkyl substituent, as described in more detail in
Example 1 below.
[0060] Especially preferred fluorescein derivatives of the present
invention are derivatives of formula I in which at least two of
R.sub.1, R.sub.3, R.sub.6 and R.sub.8 comprise an alkyl group
having between one and about twelve carbon atoms, which may be
branched or linear, and which may comprise aryl or heteroatomic
substituents, R.sub.2 is absent, R.sub.4, R.sub.5, R.sub.9,
R.sub.10, R.sub.11 and R.sub.12 are each hydrogen, R.sub.7 is an
ether grouping, X.sub.1 is a carbonyl group, X.sub.2, X.sub.3 and
X.sub.4 are each oxygen and X.sub.5 is carbon.
[0061] Specific preferred compounds of formula I are those in which
R.sub.2 is absent, R.sub.4, R.sub.5, R.sub.9, R.sub.10, R.sub.11
and R.sub.12 are each hydrogen, X.sub.1 is carbonyl, X.sub.2,
X.sub.3 and X.sub.4 are each oxygen, X.sub.5 is carbon, and the
other substituents are as follows:
[0062] Compound F-1: R.sub.1 and R.sub.8 are each hydrogen, R.sub.3
and R.sub.6 are each n-hexyl and R.sub.7 is benzyloxy;
[0063] Compound F-2: R.sub.1 and R.sub.8 are each hydrogen, R.sub.3
and R.sub.6 are each n-hexyl and R.sub.7 is ethoxy;
[0064] Compound F-3: R.sub.1 and R.sub.8 are each hydrogen, R.sub.3
and R.sub.6 are each ethyl and R.sub.7 is benzyloxy;
[0065] Compound F-4: R.sub.1 and R.sub.8 are each hydrogen, R.sub.3
and R.sub.6 are each n-hexyl and R.sub.7 is ethoxy;
[0066] Compound F-5: R.sub.1 and R.sub.8 are each methyl, R.sub.3
and R.sub.6 are each hydrogen and R.sub.7 is benzyloxy;
[0067] Compound F-6: R.sub.1 and R.sub.8 are each methyl, R.sub.3
and R.sub.6 are each hydrogen and R.sub.7 is 2-methoxyethoxy;
[0068] Compound F-7: R.sub.1 and R.sub.8 are each hydrogen, R.sub.3
and R.sub.6 are each ethyl and R.sub.7 is 3-methylbut-1-oxy;
[0069] Compound F-8: R.sub.1 and R.sub.8 are each hydrogen, R.sub.3
and R.sub.6 are each ethyl and R.sub.7 is 2-methylbenzyloxy;
[0070] Compound F-9: R.sub.1 and R.sub.8 are each hydrogen, R.sub.3
and R.sub.6 are each ethyl and R.sub.7 is 3-methylbenzyloxyt;
[0071] Compound F-10: R.sub.1 and R.sub.8 are each hydrogen,
R.sub.3 and R.sub.6 are each benzyl and R.sub.7 is benzyloxy;
[0072] Compound F-11: R.sub.1 and R.sub.8 are each hydrogen,
R.sub.3 and R.sub.6 are each propyl, and R.sub.7 is benzyloxy;
and
[0073] Compound F-12: R.sub.1 and R.sub.8 are each hydrogen,
R.sub.3 and R.sub.6 are each benzyl and R.sub.7 is
3-methylbut-1-oxy.
[0074] Certain of compounds F-1 through F-12 are novel compounds
described and claimed in commonly assigned U.S. patent application
Ser. No. 11/856,341, filed on Sep. 17, 2007, (Attorney Docket No.
C-8586AFP) published as U.S. Pub. No. US 2008/0058524, the entire
disclosure of which is hereby incorporated by reference herein and
made a part of this application.
[0075] A second preferred subgroup of xanthenes of formula I are
rhodol-type compounds, wherein X.sub.4 is oxygen, R.sub.2 is absent
and R.sub.7 is nitrogen bearing two substituents each of which may
independently be hydrogen, alkyl or aryl; X.sub.1 is carbonyl; and
X.sub.2, X.sub.3 and X.sub.4 are each oxygen.
[0076] Preferred compounds of the rhodol type are those in which
R.sub.1 is hydrogen, halogen, or alkyl; R.sub.2 is absent; R.sub.3
is an electron-withdrawing substituent such as halogen, sulfonyl or
nitro; R.sub.7 is nitrogen bearing at least one aryl substituent;
R.sub.4, R.sub.5, R.sub.6, R.sub.8, R.sub.9, R.sub.10, R.sub.11 and
R.sub.12 are each hydrogen; X.sub.1 is carbonyl; X.sub.2, X.sub.3
and X.sub.4 are each oxygen; and X.sub.5 is carbon. It has been
found that rhodol-type compounds can afford good magenta
(green-absorbing) chromophores provided that R.sub.3 is an
electron-withdrawing substituent such as a halogen, sulfonyl or
nitro and R.sub.7 is nitrogen bearing at least one aryl
substituent. Absent the electron-withdrawing substituent at
R.sub.3, or the aryl substituent on the nitrogen atom at R.sub.7,
the wavelength of absorption is shorter, and the colored tautomer
of the molecule exhibits a red, rather than a magenta, color.
[0077] Specific preferred rhodol-type compounds of formula I are
those in which R.sub.2 is absent; R.sub.4, R.sub.5, R.sub.6,
R.sub.8, R.sub.9, R.sub.10, R.sub.11 and R.sub.12 are each
hydrogen; X.sub.1 is carbonyl; X.sub.2, X.sub.3 and X.sub.4 are
each oxygen; X.sub.5 is carbon; and the other substituents are as
follows:
[0078] Compound Rh-1: R.sub.1 is hydrogen, R.sub.3 is bromine and
R.sub.7 is phenylamino;
[0079] Compound Rh-2: R.sub.1 is hydrogen, R.sub.3 is bromine and
R.sub.7 is N-ethyl-N-phenylamino;
[0080] Compound Rh-3: R.sub.1 is hydrogen, R.sub.3 is bromine and
R.sub.7 is N-butyl-N-phenylamino;
[0081] Compound Rh-4: R.sub.1 is hydrogen, R.sub.3 is bromine and
R.sub.7 is N-hexyl-N-phenylamino;
[0082] Compound Rh-5: R.sub.1 is hydrogen, R.sub.3 is bromine and
R.sub.7 is N-benzyl-N-phenylamino;
[0083] Compound Rh-6: R.sub.1 is hydrogen, R.sub.3 is bromine and
R.sub.7 is N,N-diphenylamino;
[0084] Compound Rh-7: R.sub.1 is methyl, R.sub.3 is bromine and
R.sub.7 is N-hexyl-N-phenylamino;
[0085] Compound Rh-8: R.sub.1 is hydrogen, R.sub.3 is hydrogen and
R.sub.7 is N-indolinyl; and
[0086] Compound Rh-9: R.sub.1 is hydrogen, R.sub.3 is bromine and
R.sub.7 is N-hexadecyl-N-phenylamino.
[0087] Certain of the compounds Rh-1 through Rh-9 are novel
compounds and are described and claimed in commonly assigned U.S.
patent application Ser. No. 10/789,276, filed on Feb. 27, 2004,
(Attorney Docket No. [[C-]]8588AFP) issued as U.S. Pat. No.
6,951,952, the entire disclosure of which is hereby incorporated by
reference herein and made a part of this application.
[0088] A third preferred subgroup of xanthenes of formula I are
rhodamine-type compounds, in which R.sub.1, R.sub.3, R.sub.4,
R.sub.5, R.sub.6, R.sub.8, R.sub.9, R.sub.10, R.sub.11 and R.sub.12
are each hydrogen, alkyl, aryl or halogen, R.sub.2 is hydrogen,
alkyl or aryl and R.sub.7 is nitrogen bearing two substituents each
of which independently may be hydrogen, alkyl or aryl, or oxygen
bearing an alkyl or aryl substituent; X.sub.1 is carbonyl; X.sub.2
is oxygen; X.sub.3 is oxygen; X.sub.4 is nitrogen; and X.sub.5 is
carbon.
[0089] Specific preferred rhodamine-type compounds of formula I are
those in which R.sub.1, R.sub.3, R.sub.4, R.sub.5, R.sub.6,
R.sub.8, R.sub.9, R.sub.10, R.sub.11 and R.sub.12 are each
hydrogen; X.sub.1 is carbonyl; X.sub.2 and X.sub.3 are each oxygen;
X.sub.4 is nitrogen; X.sub.5 is carbon; and the other substituents
are as follows:
[0090] Compound R-1: R.sub.2 is phenyl and R.sub.7 is
phenylamino;
[0091] Compound A-2: R.sub.2 is 2-methylphenyl and R.sub.7 is
2-methylphenylamino;
[0092] Compound R-3: R.sub.2 is 2-ethylphenyl and R.sub.7 is
2-ethylphenylamino;
[0093] Compound R-4: R.sub.2 is 2,4,6-trimethylphenyl and R.sub.7
is 2,4,6-trimethylphenylamino;
[0094] Compound R-5: R.sub.2 is 2-chlorophenyl and R.sub.7 is
2-chlorophenylamino.
[0095] Another specific preferred rhodamine-type compound of
formula I is Compound R-6, in which R.sub.1, R.sub.3, R.sub.4,
R.sub.5, R.sub.6, and R.sub.8 are each hydrogen, R.sub.2 is a
2-methyl-4-octadecyloxyphenyl group, R.sub.7 is an N-indolinyl
group, R.sub.9, R.sub.10, R.sub.11 and R.sub.12 are each fluorine,
X.sub.1 is carbonyl, X.sub.2 and X.sub.3 are each oxygen, X.sub.4
is nitrogen, and X.sub.5 is carbon.
[0096] Certain of the compounds R-1 through R-6 are novel compounds
and are described and claimed in commonly assigned U.S. patent
application Ser. No. 11/369,805, filed on Mar. 6, 2006, (Attorney
Docket No. C-8587AFP) issued as U.S. Pat. No. 7,220,868, the entire
disclosure of which is hereby incorporated by reference herein and
made a part of this application. the entire disclosure of which is
hereby incorporated by reference herein and made a part of this
application.
[0097] Two problems commonly occur in designing molecules for use
according to the mechanism of Type I. Firstly, it may turn out to
be impossible to crystallize the colorless tautomeric form of the
molecule. For example, many of the rhodol-type compounds described
above cannot readily be crystallized in a colorless form. Secondly,
the colorless form may be able to be crystallized, but may exhibit
a non-ideal melting point. To change the melting point would
require complete redesign of the molecule, a long and tedious
process. However, as described in U.S. Pat. No. 4,097,288, it is
well known that certain phenolic or amino compounds readily form
co-crystals with hydrogen-bonding acceptors or donors. Such
hydrogen-bonding acceptors or donors are hereinafter referred to as
"complexing agents". A co-crystal of a given molecule of the
present invention in conjunction with a hydrogen-bonding completing
agent does not necessarily have the same melting point as either
the complexing agent or the molecule of the present invention on
its own.
[0098] As mentioned above, in each of the preferred types of
formula I, atom X.sub.4 bears a hydrogen substituent. This hydrogen
atom, besides being the internal acid used to produce the colored
tautomeric form of the molecule, is also available to be complexed
by a hydrogen-bonding acceptor. Complexation, as described above,
not only may enable crystallization of the colorless tautomeric
form of the molecule in cases where this would otherwise be
difficult to achieve, but may also allow control of the melting
point. Preferred complexing agents are amino compounds, especially
heterocyclic materials such as pyridines. Specific preferred
complexing agents include phenanthroline,
2,9-dimethylphenanthroline, 4,5,6,7-tetramethylphenanthroline,
methyl picolinate, ethyl picolinate, pyrazine, 4,4'-bispyridine,
2,2'-bispyridine, terephthalamides such as
N,N,N',N'-tetramethylterephalamide and the corresponding tetrabutyl
derivative, and cyclic oxalamides such as
1,4-dimethyl-2,3-dioxopiperazine. Example 4 below illustrates the
effect of complexation to crystallize the colorless tautomeric form
of rhodol-type compounds used in the present invention and to
tailor the melting point of these and other molecules of the
present invention.
[0099] Novel complexes which are useful in the imaging members and
methods of the invention are described and claimed in commonly
assigned U.S. patent application Ser. No. 11/859,363, filed on Sep.
21, 2007,s (Attorney Docket No. C-8589AFP) published as U.S. Pub.
No. US 2008/0058525, the entire disclosure of which is hereby
incorporated by reference herein and made a part of this
application.
[0100] The present invention is not limited to compounds that exist
in different tautomeric forms. In a second embodiment of the
invention, illustrated in FIG. 1, Type II, the equilibrium
established is between a colorless adduct, shown as C, and its two
constituents, shown as D and E. D is colored dye, while E is a
colorless molecule that can add to D and render it colorless.
Typically, D is a cationic dye (an electrophile) and E is a
nucleophile. During crystallization of C, the concentration of E
may be made sufficiently high (and much higher than that of D) that
very little of D is present. When D is melted, however, the
concentration of D and E will be the same. The position of the
equilibrium may thus be different in the amorphous form resulting
from melting of C than it was in the solution from which C was
crystallized in the first place. FIG. 3 shows two examples of
equilibria that can be used for Type II of the present invention.
Scheme 1 of FIG. 3 shows the equilibrium between a hemicyanine dye
and a colorless adduct formed by addition of a tertiary amine.
Scheme 2 shows a similar equilibrium established between a xanthene
dye and a tertiary amine. A wide variety of nucleophilic molecules
may be used to establish equilibria such as those shown in FIG. 3,
but it is preferred that the adduct formed between the dye and the
nucleophile have the same charge as the final dye. If this is not
the case, for example if the adduct is neutral but the dye is
positively charged, in order to maintain charge balance the
nucleophile in the dissociated state must be negatively charged. In
this case, it is likely that the nucleophile will remain closely
associated with the dye due to electrostatic attraction. The adduct
and the dye will both be positively charged if the dye is
positively charged and the nucleophile is a tertiary amine, a
tertiary phosphine, or a thioether, for example.
[0101] To form a direct thermal imaging system, the crystalline,
colorless form of the compound of Types I and II described above is
made into a dispersion in a solvent in which the compound is
insoluble or only sparingly soluble, by any of the methods known in
the art for forming dispersions. Such methods include grinding,
attriting, etc. The particular solvent chosen will depend upon the
particular crystalline material. Solvents that may be used include
water, organic solvents such as hydrocarbons, esters, alcohols,
ketones, nitriles, and organic halide solvents such as chlorinated
and fluorinated hydrocarbons. The dispersed crystalline material
may be combined with a binder, which may be polymeric. Suitable
binders include water-soluble polymers such as poly(vinyl alcohol),
poly(vinylpyrollidone) and cellulose derivatives, water-dispersed
latices such as styrene/butadiene or poly(urethane) derivatives, or
alternatively hydrocarbon-soluble polymers such as polyethylene,
polypropylene, copolymers of ethylene and norbornene, and
polystyrene. This list is not intended to be exhaustive, but is
merely intended to indicate the breadth of choice available for the
polymeric binder. The binder may be dissolved or dispersed in the
solvent.
[0102] Following preparation of the dispersion of the compound of
the present invention, and optional addition of a polymeric binder,
the resultant fluid is coated onto a substrate using any of the
techniques well-known in the coating art. These include slot,
gravure, Mayer rod, roll, cascade, spray, and curtain coating
techniques. The image-forming layer so formed is optionally
overcoated with a protective layer or layers.
[0103] Where materials of the present invention are used to prepare
an imaging medium of the type described in copending U.S. patent
application Ser. No. 10/151,432 filed May 20, 2002, issued as U.S.
Pat. No. 6,801,233, the process described above is followed for
each of the imaging layers. Successive layers may be coated
sequentially, in tandem, or in a combination of sequential and
tandem coatings.
[0104] The invention will now be described further in detail with
respect to specific embodiments by way of examples, it being
understood that these are intended to be illustrative only and the
invention is not limited to the materials, amounts, procedures and
process parameters, etc. recited therein. All parts and percentages
recited are by weight unless otherwise specified.
Example 1
[0105] This example describes the preparation and properties of
novel fluorescein derivatives of formula I.
[0106] A. Novel fluorescein derivatives were prepared in the
following general manner (exemplified by the preparation of
Compound F-11).
Preparation of 4-propyl-1,3-dihydroxybenzene
[0107] i. 1,3-Dihydroxy-4-propanoylbenzene (10 g; 60.2 mmol) and
trifluoroacetic acid (10 eq., 0.6 mol; 68.4 g) were stirred at room
temperature until all the material was dissolved. To the resultant
solution there was added triethylsilane (2.5 eq., 0.15 mol; 17.5 g)
slowly at room temperature. After the addition, the reaction
mixture was stirred with heating at 75.degree. C. for 4 hours. The
mixture was cooled to room temperature, quenched into water and
extracted with dichloromethane to give two layers of oil product.
The upper layer (excess triethylsilane) was decanted off and to the
residual oil product there was added a mixture of hexane and
dichloromethane (ca. 7:3 ratio) with heating to give a solid
product. The product (7.3 g; 80% yield), whose structure was
confirmed by .sup.1H NMR and Electrospray mass spectrometry (ES MS)
was used for the next step without further purification.
ii. Preparation of 2,7-dipropylfluorescein
[0108] To a mixture of 4-propyl-1,3-dihydroxybenzene (6.0 g; 40
mmol, prepared as described in (i) above) and phthalic anhydride
(20 mmol; 3.0 g) there was added 73% (w/w) concentrated sulfuric
acid at room temperature and the mixture was then stirred with
heating at 150.degree. C. for 3 hours. After cooling, the mixture
was poured into water (200 mL) with stirring in the beaker,
filtered, and washed with water several times to give yellow
product with a quantitative yield. The structure of the product was
confirmed by .sup.1H NMR and ES MS.
iii. Preparation of compound F-11
[0109] 2,7-Dipropylfluorescein (3 g; 7.2 mmol, prepared as
described in (ii) above) and anhydrous potassium carbonate (4 eq.,
28.8 mmol) were dispersed in dimethylformamide (DMF, 35 mL) at room
temperature and the mixture was then stirred with heating at
100.degree. C. until reddish clear solution appeared. To the
resultant solution was added benzyl bromide (4 eq., 28.8 mmol; 4.9
g) dissolved in DMF (5 mL) slowly for 10 min. After the addition
had been completed the mixture was further stirred at 100.degree.
C. for another 3 hours. After cooling the mixture to room
temperature it was poured into water (400 mL) to give a
precipitate. The crude product (monoether, monoester) was
hydrolyzed without further purification. The monoether monoester
product was dissolved in a mixture of acetone (60 mL) and water (20
mL) and to this solution there was added aqueous sodium hydroxide
(4 eq., 28.8 mmol; 1.2 g; 12 mL a 10% aqueous solution). The
mixture was stirred at room temperature overnight. After
evaporation of acetone the mixture was diluted with water (200 mL)
and filtered. The filtrate was neutralized with dilute hydrochloric
acid to give pale yellow precipitate. The crude product was
purified by silica gel column chromatography (eluted with 3%
methanol in dichloromethane) followed by recrystallization from a
mixture of hexane and acetone to give colorless crystals (1.75 g,
48% yield; mp 202-203.degree. C.).
[0110] B. The fluorescein derivatives so prepared, having
structures described hereinabove, exhibited the following
properties:
TABLE-US-00001 Melting Range Compound Color of melt Melting point
(.degree. C.) (.degree. C.) F-1 Yellow 111* -- F-2 Yellow 225* --
F-3 Yellow 230* -- F-4 Yellow 107 7.2 F-5 Orange 220* -- F-6 Orange
251 5.4 F-7 Yellow 194 5.0 F-8 Yellow 115* -- F-9 Yellow 160* --
F-10 Yellow 219 4.6 F-11 Yellow 210 5.3 F-12 Yellow 207 4.6 Unless
indicated by (*), melting points were determined by differential
scanning calorimetry (DSC) at a temperature ramp rate of 4.degree.
C./min. *Indicates that melting points were obtained using a
capillary melting point apparatus.
Example 2
[0111] This example describes the preparation of novel rhodol-type
derivatives of the invention Derivatives Rh-1-Rh-7 were prepared in
the following general manner (exemplified by Rh-7).
[0112] ia. Preparation of 2-(5-bromo-2,4-dihydroxybenzoyl)benzoic
acid (starting material for Rh-1-Rh-6 and Rh-9).
[0113] Aluminum chloride (8.48 .mu.g, 64 mmol) was added to a
stirring suspension of phthalic anhydride (2.36 g, 16 mmol) in
tetrachloroethane (40 mL) under nitrogen. Nitromethane (6 mL) was
added to dissolve the reactants. 4-Bromoresorcinol (3 g, 16 mmol)
was added and the mixture continued to stir under nitrogen. The
reaction was monitored by high performance liquid chromatography
(HPLC) over a period of 2 hours. It was observed that the reaction
had ceased within the first 30 minutes, with starting materials
remaining. The solution was diluted with ethyl acetate (.about.150
mL) and washed with 1M hydrochloric acid (2.times.100 mL). The
product was extracted from the organic layer into a saturated
solution of sodium bicarbonate in water (200 mL). The basic aqueous
phase was acidified with 3M hydrochloric acid to a pH of 5. The
product was extracted from the aqueous phase into ethyl acetate
(150 mL), washed with brine (2.times.100 mL), dried over magnesium
sulfate and concentrated to give an orange oil which solidified
upon standing for about 10 minutes. The solid was slurried in
dichloromethane (20 mL) and filtered to give a mixture of the
desired product and phthalic acid. Slurrying in water (20 mL)
followed by filtration gave the desired product as a beige powder
(1.72 g, 5.1 mmol, 32% yield).
[0114] ib. Alternative preparation, illustrated for
2-(5-bromo-2,4-dihydroxy-3-methylbenzoyl)benzoic acid (starting
material for Rh-7).
[0115] Step 1: Aluminum chloride (21.4 g, 161 mmol) was added to a
stirring suspension of phthalic anhydride (6 g, 40 mmol) in
tetrachloroethane (200 mL) under nitrogen.
1,3-Dihydroxy-2-methylbenzene (5 g, 40 mmol) was added and the
mixture quickly thickened. After the precipitates were broken up
with a spatula the reaction continued for 1 hour. The solution was
diluted with ethyl acetate (.about.600 mL) and washed with 1M
hydrochloric acid (2.times.200 mL). The product was extracted from
the organic layer into a saturated solution of sodium bicarbonate
in water (600 mL). The basic aqueous phase was acidified with 3M
hydrochloric acid to a pH of 5. The product was extracted from the
aqueous phase into ethyl acetate (400 mL), washed with brine
(2.times.100 mL), dried over magnesium sulfate and concentrated to
give a brownish solid. The solid was slurried in dichloromethane
(20 mL) and filtered to give
2-(2,4-dihydroxy-3-methylbenzoyl)benzoic acid as an off white
powder (4.6 g, 1.6.9 mmol, 42% yield).
[0116] Step 2: Bromine (2.6 g, 16.9 mmol) was dripped into a
stirring solution of the product from Step 1 (4.6 g=16.9 mmol)
dissolved in acetic acid (42 mL). Monitoring by HPLC showed
complete bromination within 1 hour. The solution was concentrated
to give a yellow powder. Slurrying in dichloromethane followed by
filtration gave the desired product as an off white powder (5 g,
14.3 mmol, 85% yield).
[0117] ii. Preparation of Compound Rh-7.
[0118] 2-(5-Bromo-2,4-dihydroxybenzoyl)benzoic acid (prepared as
described in ia above, 1 g, 2.86 mmol) was dissolved in acetic acid
(14 mL). N-hexyl-N-(3-hydroxyphenyl)phenylamine (0.77 g, 2.86 mmol)
was added to the solution followed by methanesulfonic acid (8.58
mmol). The solution was stirred at reflux for 4 hours. The solution
was diluted with ethyl acetate (100 mL), washed with water
(2.times.50 mL), a pH 7 phosphate buffer (2.times.30 mL) and brine
(2.times.30 mL), dried over anhydrous magnesium sulfate and
concentrated to a dark purple solid. Purification by silica gel
column chromatography eluted the product with 5% acetone in
dichloromethane (0.75 g, 1.28 mmol, 45% yield, .lamda..sub.max=548
nm). The structure of the product was confirmed by .sup.1H NMR and
ES MS.
[0119] Other rhodol derivates were prepared in an analogous
manner:
[0120] Rh-1: 3.08 g of 2-(5-bromo-2,4-dihydroxybenzoyl)benzoic acid
and 1.69 g of 3-hydroxydiphenylamine afford 3.45 g (76% yield) of
Compound Rh-1.
[0121] Rh-2: 1.5 g of 2-(5-bromo-2,4-dihydroxybenzoyl)benzoic acid
and 1.0 g of N-ethyl-N-(3-hydroxyphenyl)phenylamine were reacted to
afford 1.78 g (77% yield) of Compound Rh-2.
[0122] Rh-3: 418 mg of 2-(5-bromo-2,4-dihydroxybenzoyl)benzoic acid
and 300 mg of N-butyl-N-(3-hydroxyphenyl)phenylamine were reacted
to afford 401 mg (59% yield) of Compound Rh-3.
[0123] Rh-4: 1.0 g of 2-(5-bromo-2,4-dihydroxybenzoyl)benzoic acid
and 0.83 g of N-hexyl-N-(3-hydroxyphenyl)phenylamine were reacted
to afford 1.2 g (71% yield) of Compound Rh-4.
[0124] Rh-5: 413 mg of 2-(5-bromo-2,4-dihydroxybenzoyl)benzoic acid
and 340 mg of N-benzyl-N-(3-hydroxyphenyl)phenylamine were reacted
to afford 343 mg (59% yield) of Compound Rh-5.
[0125] Rh-6: 2-(5-Bromo-2,4-dihydroxybenzoyl)benzoic acid and
N-phenyl-N-(3-hydroxyphenyl)phenylamine were reacted to afford
0.410 gms (15% yield) of Compound Rh-6 (.lamda..sub.max=542
nm).
[0126] Rh-9: 467 mg of 2-(5-bromo-2,4-dihydroxybenzoyl)benzoic acid
and 480 mg of N-hexadecyl-N-(3-hydroxyphenyl)phenylamine were
reacted to afford 435 mg (44% yield) of Compound Rh-9.
Example 3
[0127] This example describes the preparation and properties of
novel rhodamine-type derivatives. General procedure (exemplified
for Compound R-2)
[0128] A mixture of dichlorofluoran (5.55 g, 15 mmol), o-toluidine
(5.2 g, 48 mmol), anhydrous zinc chloride (4.5 g) and zinc oxide
(1.5 g) was stirred at 200.degree. C. for 1.5 hours. The still-hot
reaction mixture was then quenched with stirring into 8%
hydrochloric acid solution (300 mL) and stirred at 90.degree. C.
for 30 minutes, then filtered. The filter cake was washed with
water (100 mL), dried, and dissolved in warm methanol (100 mL). The
solution was made basic by addition of a solution of concentrated
ammonia solution (7 mL) in methanol (15 mL), then quenched with
stirring into cold water (700 mL). The slurry was filtered, and the
filter cake was washed with water (150 mL) and dried overnight
under reduced pressure to give a dark purple solid (22 g). This
material was triturated with hot methylene chloride (100 mL) and
filtered. The filtrate was purified by column chromatography on
silica gel with dichloromethane/methanol as eluant. The slightly
impure resulting material was further purified by recrystallization
from toluene to give pale purple prisms (2.6 g). The solids from
the dichloromethane trituration were heated with refluxing toluene
(25 mL), filtered hot, diluted with heptane (20 mL), cooled to
20.degree. C., and filtered to give a further 1.2 g of pale purple
prisms. The residual solids from the toluene hot filtration were
taken up in refluxing xylenes (15 mL) and cooled to deposit an
additional 1.0 g of pale purple solid.
[0129] Compounds R1-R5 exhibited the following properties. In most
cases, solvent of crystallization was incorporated into the
crystals.
TABLE-US-00002 Melting point .lamda..sub.max Solvent of (capillary,
(methanol, Compound crystallization .degree. C.) nm) R1 None 268
544 R2 Toluene 170 526 R2 Dichloromethane 147 526 R3
Dichloromethane 117 526 R4 Dichloromethane 184 522 R5 Toluene 122
520
Example 4
[0130] This example describes the preparation and properties of
complexed materials.
General Procedure A:
[0131] The complexing agent (1.0 or 0.5 equivalents) was combined
with the color forming agent and dissolved in an appropriate blend
of hot methyl ethyl ketone and cyclohexane. When successful, the
complex crystallized from the hot solution as it cooled as
colorless or nearly colorless crystals. The crystals were collected
by suction filtration and washed with an appropriate blend of
methyl ethyl ketone/cyclohexane. This wash must be carefully done
to avoid the precipitation of colored materials on the surface of
the crystals. Analysis by .sup.1H NMR spectroscopy defined the
composition of the complex. Integral ratios of 1:1 and 2:1 of dye
to complexing agent were most commonly observed and depended both
on the structure of the dye and the structure of the complexing
agent.
General Procedure B:
[0132] The complexing agent (1.0 or 0.5 equivalents) and color
forming agent were combined and ground with an agate mortar and
pestle. The resulting intimate mixture was then slurried on the
mortar in a small amount of cyclohexane and the grinding was
continued. Small amounts of methyl ethyl ketone were then added to
facilitate dissolution of the components into the solvent and aid
crystal growth. The grinding was continued until a colorless
complex was formed. Often the stronger solvent (methyl ethyl
ketone) was allowed to slowly evaporate during the grinding process
until a critical concentration was achieved. At this point
crystallization often proceeded. Once crystallization had occurred
additional cyclohexane/methyl ethyl ketone was added and the slurry
of crystals was transferred either to a container for further
ripening (heating and stirring) or directly collected by suction
filtration. The crystals were then carefully washed with an
appropriate mixture of cyclohexane/methyl ethyl ketone to avoid
precipitating colored dye on the surface of the crystals. Crystals
from this procedure could be used to seed crystallizations using
procedure A.
TABLE-US-00003 m.p. Dye Complexing Agent Procedure Ratio (DSC,
.degree. C.) Benzylfluorescein 1,10- A 1:1 201 phenanthroline
Benzylfluorescein 2,9-Dimethyl- A 1:1 185 1,10- phenanthroline
Benzylfluorescein 4,4'-bipyridyl A 2:1 109 Benzylfluorescein
Pyrazine A 1:1 125* Benzylfluorescein Ethylpicolinate A 1:1 138 F-3
4,4'-bipyridyl B 2:1 191 F-4 4,4'-bipyridyl B 2:1 215 F-9
4,4'-bipyridyl B 2:1 165 F-10 4,4'-bipyridyl B 2:1 198 Rh-1
2,9-Dimethyl- A 1:2 244* 1,10- phenanthroline Rh-1 4,4'-bipyridyl A
1:1 187 Rh-2 4,4'-bipyridyl B 2:1 210 Rh-4 2,9-Dimethyl- A 1:1 109
1,10- phenanthroline Rh-4 2,9-Dimethyl- B 1:1 108 1,10-
phenanthroline Rh-4 4,4'-bipyridyl B 160 Rh-6 4,4'-bipyridyl B 2:1
260 Rh-8 4,4'-bipyridyl A 2:1 180 Rh-8 2,9-Dimethyl- A 1:1 142
1,10- phenanthroline Rh-8 Cyclic Oxalamide A 1:2 145 (*indicates
capillary melting point.)
Example 5
[0133] This example illustrates thermal imaging members and thermal
imaging methods according to the invention. The thermal imaging
members provide yellow (imaging members 5A and 5B) and magenta
(imaging member 5C) colors.
[0134] The following materials were used in this example:
Topas 8D07, a copolymer of ethylene and norbornene, available from
Ticona, 90 Morris Avenue, Summit, N.J. 07901; Airvol 540, a grade
of poly(vinyl alcohol) available from Air Products and Chemicals,
Inc., Allentown, Pa.; Zonyl FSA, a surfactant, available from
DuPont Corporation, Wilmington, Del.; Hymicron ZK-349, a grade of
zinc stearate available from Cytech Products, Inc., Elizabethtown,
Ky.; Klebosol 30V-25, a silica dispersion available from Clariant
Corporation, Muttenz, Switzerland; Glyoxal, available from Aldrich
Chemical Co., Milwaukee, Wis.; Melinex 534, a white poly(ethylene
terephthalate) film base of approximately 96 microns' thickness,
available from DuPont Teijin Films U.S. Limited Partnership, 1
Discover Drive, P.O. Box 411, Hopewell, Va. A. An image-forming
layer was prepared as follows:
[0135] A compound of the present invention (0.15 g) was dispersed
in admixture comprising Topas 8007 (0.15 g of a 10% solution in
methylcyclohexane) and methylcyclohexane (1.2 g), using an attriter
equipped with glass beads, stirred for 18 hours at room
temperature. The total solid content of the resulting dispersion
was 11%.
[0136] The above dispersion was used to make the coating fluid for
the dye-forming layer in proportions stated below. The coating
composition thus prepared was coated onto Melinex 534 using a #18
Mayer rod, and dried. The intended coating thickness was 3.9
microns.
TABLE-US-00004 Ingredient % solids in dried film Dispersion 1.5 g
10% Topas 0.493 g 8007/methylcyclohexane Methylcyclohexane 0.15
g
[0137] B. A barrier layer was coated onto the imaging layer by
applying a 10% solution of Topas 8007 in methylcyclohexane using a
#12 Mayer rod, for an intended thickness of approximately 2.6
microns.
[0138] C. A slip overcoat was coated on the barrier layer. The
overcoat was prepared in proportions stated below. The overcoat
coating composition applied using a #18 Mayer rod for an intended
thickness of 1.6 microns.
TABLE-US-00005 Ingredient % solids in dried film Glyoxal 9.59%
Hymicron ZK-349 31.42% Klebosol 30V-25 23.53% Zonyl FSA 3.89%
Airvol 540 31.57%
[0139] The resulting imaging member was printed using a laboratory
test-bed printer equipped with a thermal head, model KYT106-12PAN13
(Kyocera Corporation, 6 Takedatobadono-cho, Fushimi-ku, Kyoto,
Japan).
[0140] The following printing parameters were used:
TABLE-US-00006 Printhead width: 4 inches Pixels per inch: 300
Resistor size: 70 .times. 80 microns Resistance: 4047 Ohm Line
Speed: 7 milliseconds per line Pressure: 1.5-2 lb/linear inch Dot
pattern: Rectangular grid.
[0141] The following results were obtained from imaging members
prepared using:
Imaging Member 5A: benzyl fluorescein (mp 191.degree. C.); Imaging
Member 5B: a novel fluorescein compound of the present invention
(F-11, mp 210.degree. C.); and Imaging Member 5C: a novel complex
of the present invention prepared from the novel rhodol-type
compound Rh-4 end 2,9-dimethyl-1,10-phenanthroline (mp 109.degree.
C.)
TABLE-US-00007 Voltage = 14 V Voltage = 16 V Density Density Energy
(J/cm.sup.2) (blue) Energy (J/cm.sup.2) (blue) Imaging Member 5A
4.01 0.07 5.24 0.51 3.61 0.06 4.72 0.31 3.21 0.04 4.19 0.15 2.81
0.04 3.67 0.08 2.41 0.01 3.14 0.07 2.01 0.04 2.62 0.04 1.61 0.04
2.10 0.04 1.20 0.04 1.57 0.04 0.80 0.04 1.05 0.04 0.40 0.04 0.52
0.04 0.00 0.04 0.00 0.04 Imaging Member 5B 4.01 0.13 5.24 1.1 3.61
0.1 4.72 1.03 3.21 0.08 4.19 0.71 2.81 0.08 3.67 0.42 2.41 0.07
3.14 0.16 2.01 0.07 2.62 0.1 1.61 0.07 2.10 0.07 1.20 0.07 1.57
0.06 0.80 0.07 1.05 0.07 0.40 0.07 0.52 0.06 0.00 0.06 0.00 0.06
Imaging Member 5C Voltage = 14 V Voltage = 16 V Density Density
Energy (J/cm.sup.2) (green) Energy (J/cm.sup.2) (green) 4.01 0.67
5.24 0.51 3.61 0.48 4.72 0.48 3.21 0.52 4.19 0.7 2.81 0.42 3.67
0.47 2.41 0.28 3.14 0.53 2.01 0.19 2.62 0.34 1.61 0.11 2.10 0.29
1.20 0.1 1.57 0.17 0.80 0.1 1.05 0.09 0.40 0.09 0.52 0.08 0.00 0.09
0.00 0.09
[0142] The following conclusions may be drawn:
[0143] a. The density with no printing energy applied was, for the
three imaging members, 0.04, 0.06 and 0.09, indicating that the
unmelted crystalline dispersions coated to form the color-forming
layer were initially substantially colorless;
[0144] b. The maximum densities achieved for the three imaging
members were, respectively, 0.51, 1.1 and 0.7. As described above,
the only active components in the three color-forming layers were
benzyl fluorescein, F-11, and the complex formed between Rh-4 and
2,9-dimethyl-1,10-phenanthroline, respectively. No developers or
other chemical adjuvants were present. Therefore, the color formed
must have arisen through intrinsic color change of these
materials.
[0145] c. For imaging members A and B, whose melting points were
191.degree. C. and 210.degree. C., respectively, imaging occurred
when 16V was applied to the print head whereas very little color
change was observed with 14 V applied. On the other hand, for
imaging member C, with melting point 109.degree. C., substantial
color change was observed under both 16V and 14V printing
conditions. The amount of energy applied during printing at 14V is
lower than that applied while printing at 16V, and consequently the
temperature achieved in the color-forming layer is lower for 14V
printing than for 16 V printing. Whether or not color is formed can
therefore be concluded to depend upon the melting point of the
color-forming layer and the temperature of heating.
[0146] d. The maximum density achieved in Imaging Member A (0.51)
is lower than that achieved in Imaging Member B (1.1). Imaging
Member A comprises benzyl fluorescein, a known compound, whereas
Imaging Member B comprises F-11, a preferred, novel, fluorescein
derivative of the invention.
Example 6
[0147] This example illustrates a thermal imaging member and
thermal imaging method according to the invention. The thermal
imaging member provides a cyan color.
[0148] In addition to the materials described in Example 5 above,
the following materials were used in this example:
Piccotac 1115, available from Eastman Chemical Company, 100 North
Eastman Road, P.O. Box 511, Kingsport, Tenn.; Melinex 6265, a white
poly(ethylene terephthalate) film base of approximately 96 microns'
thickness, available from. DuPont Teijin Films U.S. Limited
Partnership, 1 Discover Drive, P.O. Box 411, Hopewell, Va.
[0149] A. An image-forming layer was prepared as follows:
Compound R-6 of the present invention (0.08 g) was dispersed in a
mixture comprising Topas 8007/Piccotac 1115 (ratio 1:1.25, 0.08 g
of a 10% solution in methylcyclohexane) and methylcyclohexane (0.76
g), using an attriter equipped with glass beads, and stirred for 18
hours at room temperature. The total solid content of the resulting
dispersion was 10%.
[0150] The above dispersion was used to make the coating fluid for
the dye-forming layer in proportions stated below. The coating
composition thus prepared was coated onto Melinex 6265 using a #9
Mayer rod, and dried. The intended coating thickness was
approximately 2 microns.
TABLE-US-00008 Ingredient % solids in dried film Dispersion 0.93 g
10% Topas 1.63 g 8007: Piccotac 1115/methylcyclohexane
Methylcyclohexane 0.09 g
[0151] B. A barrier layer was coated onto the imaging layer by
applying a 10% solution of 1:1.25 Topas 8007/Piccotac 1115 in
methylcyclohexane using a #12 Mayer rod, for an intended thickness
of approximately 2.6 microns.
[0152] C. A slip overcoat was coated on the barrier layer. The
overcoat was prepared in proportions stated below. The overcoat
coating composition applied using a #18 Mayer rod for an intended
thickness of 1.5 microns.
TABLE-US-00009 Ingredient % solids in dried film Glyoxal 9.59%
Hymicron ZK-349 31.42% Klebosol 30V-25 23.53% Zonyl FSA 3.89%
Airvol 540 31.57%
[0153] The resulting imaging member was printed using a laboratory
test-bed printer equipped with a thermal head, model KYT106-12PAN13
(Kyocera Corporation, 6 Takedatobadono-cho, Fushimi-ku, Kyoto,
Japan).
[0154] The following printing parameters were used:
TABLE-US-00010 Printhead width: 4 inches Pixels per inch: 300
Resistor size: 70 .times. 80 microns Resistance: 4291 Ohm Line
Speed: 7 milliseconds per line Pressure: 1.5-2 lb/linear inch Dot
pattern: Rectangular grid.
The following results were obtained:
TABLE-US-00011 Voltage = 16.5 V Energy (J/cm.sup.2) Density (red)
5.88 1.13 5.29 1.10 4.71 1.05 4.12 0.79 3.53 0.52 2.94 0.30 2.35
0.14 1.76 0.1 1.18 0.1 0.59 0.1 0.00 0.1
Example 7
[0155] This example illustrates a thermal imaging member comprising
more than one color-forming layer, designed to be printed with a
single thermal print-head as described in above-mentioned patent
application Ser. No. 10/151,432, issued as U.S. Pat. No. 6,801,233.
In this example the topmost layer, printed in a relatively short
time at a relatively high temperature, comprises a material of the
present invention. The lower layer, printed in a relatively long
time at a relatively low temperature, comprises a prior art
color-forming composition in which two compounds (a leuco dye and
an acid developer) that react together to form color are brought
together by melting and diffusing.
[0156] In addition to materials described in Examples 5 and 6
above, the following materials were used in this Example: [0157]
Leuco dye Red 40, 3,3-bis(1-n-butyl-2-methyl-indol-3-yl)phthalide
(available from Yamamoto Chemical Industry Co., Ltd., Wakayama,
Japan); [0158] Acid Developer TGSA,
bis(3-allyl-4-hydroxyphenyl)sulfone, available from Nippon Kayaku
Co., Ltd, Tokyo, Japan; [0159] Airvol 205, a grade of poly(vinyl
alcohol) available from Air Products and Chemicals, Inc.,
Allentown, Pa.; [0160] Airvol 325, a grade of poly(vinyl alcohol)
available from Air, Products and Chemicals, Inc., Allentown, Pa.;
[0161] Zonyl FSN, a surfactant, available from DuPont Corporation,
Wilmington, Del.; [0162] Elvacite 2045, a grade of poly(isobutyl
methacrylate), available from Lucite International Inc., 7275
Goodlett Farms Parkway, Cordova, Tenn.; [0163] Aerosol OT-100, a
surfactant available from Cytec Industries, Inc., West Paterson,
N.J.
[0164] A white, reflective layer was coated onto the back of a
clear polyethylene terephthalate) substrate of 125 micron thickness
(Cronar 512, available DuPont Teijin Films U.S. Limited
Partnership, 1 Discover Drive, P.O. Box 411, Hopewell, Va.). The
following layers were applied to the opposite side of the
substrate:
[0165] A. Prior Art Color-Forming Layer, Affording a Magenta
Color.
[0166] An aqueous dispersion of a magenta color-former (Red 40),
poly(vinyl alcohol) (Airvol 205) and a surfactant (Zonyl FSN) was
mixed with an aqueous dispersion of an acid developer (TGSA),
poly(vinyl alcohol) (Airvol 205) and a surfactant (Zonyl FSN). A
solution of poly(vinyl alcohol) binder (Airvol 540) in water was
added and the resultant fluid was coated for a dried coverage of
Red 40: 300 mg/m.sup.2, TGSA 1139 mg/m.sup.2, Zonyl FSN 13
mg/m.sup.2, and combined poly(vinyl alcohol) (Airvol 205 and Airvol
540) 661 mg/m.sup.2.
[0167] B. A Thermally-Insulating Interlayer.
[0168] A solution of Elvacite 2045 in methylcyclohexane was coated
to a dried coverage of 8016 mg/m.sup.2.
[0169] C. Yellow Color-Forming Layer of the Present Invention.
[0170] A dispersion of Compound F-11 of the present invention was
prepared as follows:
[0171] Compound F-11 (600 g), surfactant Aerosol OT-100 (30 g),
heptanes (1.1 kg) and ethyl acetate (600 g) were combined and
transferred into a 1S-Attritor containing 6.3 kg mullite beads. The
jacket temperature was set to 10.degree. C. and the attritor was
run at 100 rpm for 24 hours. The grinding media was filtered off
and washed with heptanes (500 g). The resulting suspension of
crystalline Compound F-11 was concentrated to dryness yielding 620
g of white solid. This solid was redispersed in an aqueous solution
of poly(vinyl alcohol) (Airvol 540) containing a surfactant (Zonyl
FSN) to produce a coating fluid, which was coated to a dried
coverage of Compound F-11: 1184 mg/m.sup.2, Aerosol OT-100: 59.2
mg/m.sup.2, Airvol 540: 344 mg/m.sup.2, and Zonyl FSN 11
mg/m.sup.2.
[0172] D. An Oxygen Barrier Layer.
[0173] The following materials were coated from aqueous solution to
give the indicated dried coverages: poly(vinyl alcohol.) (Airvol
325, 1454 mg/m.sup.2), boric acid crosslinker (125 mg/m.sup.2) and
Zonyl FSN (32 mg/m.sup.2)
[0174] E. A UV-Absorbing Barrier Layer.
[0175] An aqueous fluid was coated to provide the following dried
coverages: nanoparticulate zinc oxide (UV absorber, 2153
mg/m.sup.2), poly(vinyl alcohol) (Airvol 325, 1615 mg/m.sup.2),
Zonyl FSN (32 mg/m.sup.2)
[0176] F. A Slip Coat.
[0177] An aqueous coating fluid was coated to give the following
dried Coverages: Hymicron ZK-349 (312 32 mg/m.sup.2), Airvol 540
(635 32 mg/m.sup.2), Klebosol 30V-25 (517 32 mg/m.sup.2) and Zonyl
FSN (32 32 mg/m.sup.2).
[0178] The resulting imaging member was printed using a laboratory
test-bed printer equipped with a thermal head, model KP163 (Kyocera
Corporation, 6 Takedatobadono-cho, Fushimi-ku. Kyoto, Japan)
[0179] The following printing parameters were used:
TABLE-US-00012 Pixels per inch: 300 Resistor size: 70 .times. 120
microns Resistance: 3135 Ohm Line Speed: 11.1 milliseconds per line
Pressure: 1.5-2 lb/linear inch Voltage: 40.9 V Dot pattern:
Rectangular grid.
[0180] The time taken to print each line was divided into 667 equal
time elements. Energy was supplied to the print head for a
proportion of each of these time elements referred to as the "duty
cycle". For high average power in printing, the duty cycle was a
high proportion of the total duration of the time element, while
for low average power the duty cycle was a low proportion of the
total duration of the time element. Because of both the time taken
for thermal diffusion and the large size of the resistor relative
to the distance traveled by the imaging element during each time
element, the thermal pulses of each of the time elements were not
resolved as individual dots on the imaging element. Instead, the
imaging element experienced an averaging of the power of the
individual pulses.
[0181] The following results were obtained:
TABLE-US-00013 Time elements energised Density Density (667
maximum) (blue) (Green) High power, short time Duty cycle = 0.74 0
0.155 0.17 16 0.195 0.172 18 0.259 0.18 20 0.399 0.202 23 0.621
0.239 25 0.799 0.277 27 0.936 0.306 29 1.095 0.343 32 1.221 0.386
34 1.30 0.433 36 1.326 0.425 Low power, long time Duty cycle = 0.08
0 0.156 0.173 250 0.187 0.192 292 0.205 0.225 335 0.226 0.303 377
0.266 0.467 419 0.33 0.725 462 0.418 1.065 504 0.518 1.361 546
0.627 1.597 589 0.69 1.679 631 0.693 1.703
[0182] It is readily apparent that in the high power, short time
printing condition the blue density exceeds the green density
(i.e., the yellow color predominates over the magenta color). In
the low power, long time printing condition the green density
exceeds the blue density (i.e., the magenta color predominates over
the yellow color). The unwanted green density observed when
printing yellow is mostly due to absorption of green light by the
yellow dye. Likewise, the unwanted blue density observed while
printing the magenta dye is mostly due to absorption of blue light
by the magenta dye. Thus, Compound F-11 of the present invention
can serve efficiently as an element in a thermal imaging member
comprising more than one color-forming layer, designed to be
printed with a single thermal print-head as described in
above-mentioned patent application Ser. No. 10/151,432, issued as
U.S. Pat. No. 6,801,233.
Example 8
[0183] This example illustrates the time-independence of the
color-forming temperature of a thermal imaging member according to
the invention.
[0184] The color-forming layer of Imaging Member A described in
Example 5 above was subjected to heating using a thermal pressure
laminator/sealer available from Sencorp Equipment, Hyannis, Mass.
This device allows for the independent control of the time and
temperature of heating of a sample. The optical densities (blue)
obtained were as follows:
TABLE-US-00014 Temperature Time (seconds) (.degree. C.) 0.01 .1 1
10 90 188 .49 .59 .47 -- -- 182 .35 .58 .55 -- .28 177 .36 .29 .35
.41 .19 166 .11 .08 .09 .08 .18 160 .04 .06 .04 .05 .07
[0185] It can be seen that over about four orders of magnitude in
heating time, color change occurred between nominal 160 and nominal
177.degree. C.
[0186] Although the invention has been described in detail with
respect to various preferred embodiments thereof, it will be
recognized by those skilled in the art that the invention is not
limited thereto but rather that variations and modifications can be
made therein which are within the spirit of the invention and the
scope of the amended claims.
* * * * *