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Description  |
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BACKGROUND OF THE INVENTION
Color-forming di- and triarylmethane compounds possessing certain
S-containing ring-closing moieties, namely, a thiolactone, dithiolactone
or thioether ring-closing moiety are disclosed in International
Application No. PCT/US86/02685 published June 18, 1987 as International
Publication No. WO87/03541. These dye precursors are rendered colored by
contacting with a Lewis acid material capable of opening the S-containing
ring moiety. Preferably, the Lewis acid material is a metal ion of a heavy
metal with silver ion being particularly preferred.
As disclosed therein, these dye precursors and Lewis acid materials find
utility in a wide variety of color-forming applications including the
formation of dye images where color formation is brought about in an
imagewise fashion by the imagewise application of heat, pressure or other
stimulus necessary to effect contact between the dye precursor and Lewis
acid material. In a preferred embodiment, thermographic recording
materials are provided which employ these dye precursors, particularly the
thiolactones such as the thiophthalides in combination with an organic
silver salt such as silver behenate. Preferably, these recording materials
also include a polymeric binder such as polyvinylbutyral and a
heat-fusible organic acidic material such as 3,5-diisopropylsalicylic acid
or 4,4'-sulfonyldiphenol.
SUMMARY OF THE INVENTION
The present invention is concerned with the use of a particular organic
acidic material in thermographic recording materials employing thiolactone
dye precursors and silver behenate as the color-forming components and
with a one-pot coating fluid that may be employed in their preparation. In
particular, it has been found that the use of 3,5-dihydroxybenzoic acid as
the heat-fusible acidic material with these color-forming components
provides thermographic recording materials having improved Dmax/Dmin
characteristics together with good storage stability. Also, it has been
found quite unexpectedly that 3,5-dihydroxybenzoic acid can be combined
with these color-forming components to give a one-pot coating fluid stable
enough to coloration to be applied by a single delivery system in large
scale coating operations thereby obviating the need for two separately
coated layers or for blending two separate coating fluids at the time a
single imaging layer is applied. Besides the convenience and other
manufacturing advantages associated with a single coating fluid, thinner
recording layers possessing the desired density characteristics can be
obtained with lesser quantities of color-forming components and binder.
Moreover, lesser quantities of this acidic material can be used to achieve
a given Dmax in both one-pot coating compositions and inline blended
compositions.
It is, therefore, among the objects of the present invention to provide
thermographic recording materials and to provide one-pot coating
compositions that may be used in the preparation of the recording
materials.
DETAILED DESCRIPTION OF THE INVENTION
The di- and triarylmethane thiolactone compounds used as the dye precursors
in the present invention may be represented by the formula
##STR1##
wherein ring B represents a substituted or unsubstituted carbocyclic aryl
ring or rings, e.g., of the benzene or naphthalene series or a
heterocyclic ring, e.g., pyridine or pyrimidine; G is hydrogen or a
monovalent radical; and Z and Z' taken individually represent the moieties
to complete the auxochromophoric system of a diarylmethane or a
triarylmethane dye when said S-containing ring is open and Z and Z' taken
together represent the bridged moieties to complete the auxochromophoric
system of a bridged triarylmethane dye when said S-containing ring is
open, i.e., when the ring sulfur atom is not bonded to the meso carbon
atom. Usually, at least one of Z and Z' whether taken individually or
together possesses as an auxochromic substituent, a nitrogen, oxygen or
sulfur atom or a group of atoms containing nitrogen, oxygen or sulfur.
In the triarylmethane compounds represented in formula I above, the
moieties Z and Z', when taken individually, may be the same or different
and typically represent heterocyclic groups containing nitrogen, oxygen or
sulfur as the heterocyclic atom, particularly N-heterocyclic groups such
as julolidin-3-yl, indol-3-yl, pyrr-2-yl, carbazol-3-yl, and indolin-5-yl
wherein the N atom of the indolyl, pyrryl, carbazolyl and indolinyl groups
may be substituted with hydrogen or alkyl having 1 to 6 carbon atoms, or
the moieties Z and Z' typically may be carbocyclic aryl, particularly
phenyl or naphthyl groups which include an appropriately positioned
auxochromic substituent, i.e., an atom or group that produces an
auxochromic effect, which substituent is usually positioned para to the
meso carbon atom. Typically, Z and Z' when taken together represent aryl
groups bridged by a heteroatom, such as, oxygen, sulfur or nitrogen to
form, for example, 4H-chromeno [2,3-C] pyrazole and particularly represent
carbocyclic aryl groups, such as, phenyl groups bridged with a heteroatom,
preferably oxygen, sulfur or nitrogen substituted with hydrogen or an
alkyl group having 1 to 6 carbon atoms to provide a xanthene,
thioxanthene or an acridine dye, which dyes possess an auxochromic
substituent(s) para to the meso carbon atom, i.e., in the 3-position or in
the 3,6-positions or meta and para to the meso carbon atom, i.e., in the
3,7-positions.
In the diarylmethane compounds, one of Z and Z' may be a heterocyclic group
or carbocyclic aryl group as discussed above and the other of Z and Z' may
be, for example, phenoxy, thiophenoxy, alkoxy containing 1 to 20 carbon
atoms, alkylthio containing 1 to 20 carbon atoms,
-N,N-(disubstituted)amino wherein each said substituent may be alkyl
containing 1 to 20 carbon atoms, carbocyclic aryl containing 6 to 12
carbon atoms, aralkyl containing 7 to 15 carbon atoms particularly phenyl-
and naphthyl-substituted alkyl or alkaryl containing 7 to 15 carbon atoms
particularly alkyl-substituted phenyl and naphthyl. Representative alkyl
groups include methyl, butyl, hexyl and octadecyl and representative aryl
groups include phenyl and naphthyl. Representative alkaryl groups include
p-octylphenyl, o-methylnaphthyl and p-hexylphenyl, and representative
aralkyl groups include phenethyl, benzyl and naphthylmethyl.
Examples of useful auxochromic substituents include --OR.sub.1 wherein
R.sub.1 is hydrogen, alkyl usually having 1 to 6 carbon atoms, aralkyl
usually having 7 to 15 carbon atoms, alkaryl usually having 7 to 15 carbon
atoms or carbocyclic aryl usually having 6 to 12 carbon atoms; --SR.sub.2
wherein R.sub.2 has the same meaning given for R.sub.1 ; --NR.sub.3
R.sub.4 wherein R.sub.3 and R.sub.4 each represent hydrogen, alkyl usually
having 1 to 6 carbon atoms, .beta.-substituted ethyl, cycloalkyl usually
having 5 to 7 carbon atoms, aralkyl usually having 7 to 15 carbon atoms,
alkaryl usually having 7 to 15 carbon atoms or
##STR2##
wherein R.sub.5 and R.sub.6 each are hydrogen, alkyl usually having 1 to 6
carbon atoms, halo such as chloro, bromo, fluoro and iodo, nitro, cyano,
alkoxycarbonyl wherein said alkoxy has 1 to 6 carbon atoms, sulfonamido
(--NHSO.sub.2 R.sub.0), sulfamoyl (--SO.sub.2 NHR.sub.0), sulfonyl
(--SO.sub.2 R.sub.0), acyl (--COR.sub.0) or carbamyl (--CONR.sub.0)
wherein R.sub.0 usually is alkyl having 1 to 20 carbon atoms, benzyl or
phenyl and R.sub.3 and R.sub.4 taken together represent the atoms
necessary to complete a heterocyclic ring usually piperidino, pyrrolidino,
N-methylpiperidino, morpholino or
##STR3##
wherein q is an integer 2 to 5 and R.sub.7 has the same meaning as
R.sub.5,
##STR4##
wherein R.sub.8 and R.sub.9 each are hydrogen, alkyl usually having 1 to 6
carbon atoms or
##STR5##
wherein R.sub.11 and R.sub.12 have the same meaning as R.sub.5 and R.sub.6
and R.sub.10 is --COR.sub.13, --CSR.sub.13 or --SO.sub.2 R.sub.13 wherein
R.sub.13 is hydrogen, alkyl usually having 1 to 6 carbon atoms, phenyl,
--NH.sub.2, --NHR.sub.14, --N(R.sub.14).sub.2 or --OR.sub.14 wherein
R.sub.14 is hydrogen, alkyl usually containing 1 to 6 carbon atoms or
phenyl. Representative alkyl groups include methyl, ethyl, propyl, butyl
and hexyl. Representative .beta.-substituted ethyl groups include
.beta.-methoxymethoxyethyl and .beta.-2'-tetrahydropyranyloxyethyl.
Representative aralkyl groups include phenyl and naphthyl-substituted
alkyl, such as, benzyl, phenethyl and naphthylmethyl and representative
alkaryl groups include alkyl-substituted phenyl and naphthyl, such as,
o-methylphenyl, o-methylnaphthyl and p-hexylphenyl. Representative
carbocyclic aryl groups include phenyl and naphthyl and representative
cycloalkyl groups include cyclopentyl, cyclohexyl and cycloheptyl. It will
be appreciated that the auxochromic substituent(s) will be selected for a
given diarylmethane, triarylmethane or bridged triarylmethane compound to
provide the desired chromophore color upon opening of the S-containing
ring and to achieve facile color formation.
In addition to the auxochromic substituents, the subject dye precursor
compounds may possess one or more additional substituents on Z and/or Z'
and/or ring B as may be desired that do not interfere with the intended
utility for the dye. Typical substituents for Z and/or Z' and for G
include carboxy; hydroxy; cyano; thiocyano; mercapto; sulfo; nitro;
sulfonamido (--NHSO.sub.2 R.sub.0); sulfamoyl (--SO.sub.2 NHR.sub.0);
sulfonyl (--SO.sub.2 R.sub.0); acyl (--COR.sub.0); carbamyl
(--CONR.sub.0); halomethyl such as trifluoromethyl; alkyl usually having 1
to 20 carbon atoms such as methyl, octyl, hexadecyl; alkoxy usually having
1 to 20 carbon atoms such as methoxy, ethoxy, propoxy and butoxy;
alkoxycarbonyl having 1 to 20 carbon atoms such as ethoxy- and
dodecyloxycarbonyl; aralkyl usually having 7 to 15 carbon atoms, for
example, phenyl- or naphthyl-substituted alkyl such as benzyl, phenethyl
and naphthylmethyl; alkaryl usually having 7 to 15 carbon atoms, for
example, alkyl substituted phenyl or naphthyl such as o-methylphenyl,
o-methylnaphthyl and p-hexylphenyl; aralkyloxy usually having 7 to 15
carbon atoms, for example, phenyl- or naphthyl-substituted alkoxy such as
benzyloxy, phenethyloxy and naphthylmethyloxy; aryloxy usually containing
6 to 12 carbon atoms such as phenoxy and naphthoxy; thioalkyl groups,
usually having 1 to 20 carbon atoms such as methylthio, ethylthio and
hexylthio; thioaryl and thioaralkyl groups containing up to 15 carbon
atoms such as phenylthio, naphthylthio, benzylthio and phenethylthio; halo
such as chloro, bromo, fluoro and iodo; amino including mono- and
disubstituted amino such as --NR.sub.15 R.sub.16 wherein R.sub.15 and
R.sub.16 each are hydrogen, alkyl usually having 1 to 20 carbon atoms,
aralkyl usually having 7 to 15 carbon atoms and aryl having 6 to 12 carbon
atoms; and a fused substituent such as a fused benzene ring.
In a preferred embodiment, B is a benzene ring and Z and Z' taken
individually or together complete the auxochromophoric system of a
triarylmethane dye.
The dye precursor compounds used in the present invention can be monomeric
or polymeric compounds. Suitable polymeric compounds are those which, for
example, comprise a polymeric backbone chain having dye precursor moieties
attached directly thereto or through pendant linking groups. Polymeric
compounds of the invention can be provided by attachment of the dye
precursor moiety to the polymeric chain via the Z and/or Z' moieties or
the ring B. For example, a monomeric dye precursor compound having a
reactable substituent group, such as an hydroxyl or amino group, can be
conveniently reacted with a mono-ethylenically unsaturated and
polymerizable compound having a functional and derivatizable moiety, to
provide a polymerizable monomer having a pendant dye precursor moiety.
Suitable mono-ethylenically unsaturated compounds for this purpose include
acrylyl chloride, methacrylyl chloride, methacrylic anhydride,
2-isocyanatoethyl methacrylate and 2-hydroxyethyl acrylate, which can be
reacted with an appropriately substituted dye precursor compound for
production of a polymerizable monomer which in turn can be polymerized in
known manner to provide a polymer having the dye precursor compound
pendant from the backbone chain thereof.
The thiolactone dye precursors can be synthesized, for example, from the
corresponding lactones by heating substantially equimolar amounts of the
lactone and phosphorus pentasulfide or its equivalent in a suitable
solvent. The silver behenate may be prepared in a conventional manner
using any of various procedures well known in the art.
The one-pot coating compositions of the present invention are prepared by
mixing the selected dye precursor, preferably, a thiophthalide and the
3,5-dihydroxybenzoic acid with a dispersion of silver behenate and polymer
binder carried in a suitable organic liquid. The binder may be any of
those commonly employed in silver behenate/polymer dispersions and
preferably is polyvinylbutyral. The organic liquid employed preferably is
methyl ethyl ketone. In addition to these named ingredients, the coating
compositions may contain dispersing agents, surfactants, plasticizers,
cross-linking agents, coating aids or other reagents as may be desired.
The resulting coating composition may be applied to paper, plastic film,
metal foil or other support materials commonly used for recording elements
or coated on any other substrate as desired by spray, air knife, slot,
silk screen, reverse roll or other appropriate coating means. The coating
may then be dried at ambient or slightly elevated temperatures.
Besides being useful in the production of monochromes having the desired
color which is intended to include "black", the subject compositions also
are useful in the production of multilayered recording materials for
forming multicolor images. In this embodiment, the dye precursors
generally are selected to give the subtractive colors cyan, magenta and
yellow. Besides the imaging layer(s), it will be appreciated that
additional layers may be present such as subbing layers, interlayers or
barrier layers for thermally and chemically isolating the respective
imaging layers from each other, infra-red absorbing layers, antihalation
layers, antistatic layers, back coat layers, adhesive layers and so forth.
Preferably, a protective topcoat or overcoat layer is employed which layer
may contain ultraviolet absorbers, matting agents, waxes or other
materials as commonly used in such layers.
Imagewise heating of the recording element for forming the color image may
be effected by the direct application of heat by using, for example, a
thermal printing head, by conduction from heated image-markings of an
original using conventional thermographic copying techniques, by heat
generated from an electrical signal by including an electroconductive
layer or by converting electromagnetic radiation into heat, for example,
by using an infra-red laser diode as a light source and including an
infra-red absorber in the imaging layer for converting infra-red radiation
into heat. In producing multicolor images, infra-red absorbers may be
selected for the respective imaging layers that absorb at different
predetermined wavelengths so that the respective layers may be imaged
separately.
To illustrate the present invention, a number of heat-fusible organic
acidic materials were compared at the same molecular level in a single
layer containing the thiophthalide dye precursor shown below (Compound A)
and silver behenate dispersed in polyvinylbutyral binder. The molar ratios
employed were 1:2:2 dye precursor: silver: acidic material, respectively.
The layers were coated out of methyl ethyl ketone on a transparent
polyethylene terephthalate support using a #34 Meyer rod and air dried at
room temperature. The coated samples were heated at 110.degree. C. until a
Dmax was reached, and then the maximum and minimum transmission densities
(Dmax/Dmin) were measured for red (R) using a Macbeth transmission
densitometer equipped with the appropriate filter.
##STR6##
The results obtained for those acidic materials exhibiting a Dmax of at
least 1.00 are set forth below:
______________________________________
Acidic Material Dmax (R) Dmin (R)
______________________________________
2,5-Dihydroxybenzoic Acid
3.78 0.10
3,5-Dihydroxybenzoic Acid
3.35 0.03
2,3-Dihydroxybenzoic Acid
3.34 0.10
3-Phenylsalicylic Acid
3.29 0.20
3-Methyl-2-nitrobenzoic Acid
3.24 0.05
5-Chlorosalicylic Acid
3.18 0.33
5-Phenylsalicylic Acid
3.18 0.13
2-Hydroxy-3-methylbenzoic Acid
3.18 0.06
Salicylic Acid 3.17 0.08
3,5-Dibromosalicylic Acid
3.14 0.84
3-Methoxysalicylic Acid
3.12 0.07
3-Hydroxy-2-naphthoic Acid
3.05 0.14
Phthalic Acid 3.00 0.12
3-Methylsalicylic Acid
2.87 0.06
a-Hydroxynaphthoic Acid
2.82 0.09
DL-Mandelic Acid 2.80 0.04
5,5-Thiodisalicylic Acid
2.71 0.48
3,5-Diisopropylsalicylic Acid
2.68 0.05
p-Hydroxyphenoxy acetic Acid
2.53 0.03
p-Bromomandelic Acid
2.46 0.06
3-Hydroxy-4-nitrobenzoic Acid
2.32 0.04
m-Hydroxybenzoic Acid
2.27 0.02
p-Chloromandelic Acid
2.27 0.06
5-Sulfosalicylic Acid
2.18 1.88
Benzylmalonic Acid 2.15 0.05
4-Methyl-3-nitrobenzoic Acid
1.96 0.03
2,6-Dihydroxybenzoic Acid
1.94 0.26
Citric Acid 1.88 0.25
o-Chlorobenzoic Acid
1.29 0.03
3-Methy-4-Nitrobenzoic Acid
1.25 0.04
4-Dimethylaminosalicylic Acid
1.14 0.04
4,4'-Sulfonyldiphenol
1.09 0.02
2-Pyridine Aldoxime
1.07 0.03
______________________________________
From reference to the above data, it can be seen that a high Dmax together
with a low Dmin was obtained using 3,5-dihydroxybenzoic acid as the
heat-fusible acidic material in a single imaging layer prepared from a
one-pot coating composition.
In a further comparison, the pot life of inline blended fluids for forming
a single imaging layer was evaluated for the acidic materials,
3,5-dihydroxybenzoic acid and 3,5-diisopropylsalicylic acid. The amounts
of reagents used in the fluids were calculated to give the coated
coverages indicated in terms of mg/ft.sup.2. In this comparison Fluid A
comprised polyvinylbutyral (200 mg/ft.sup.2) and Compound A (30
mg/ft.sup.2) in methyl ethyl ketone, and Fluid B comprised the acidic
material (50 mg/ft.sup.2) polyvinylbutyral (100 mg/ft.sup.2) and silver
behenate (15 mg/ft.sup.2 as silver) dispersed in methyl ethyl ketone. Upon
mixing Fluids A and B, it was found that the mixture containing the
3,5-diisopropylsalicylic acid had a pot life of minutes with the onset of
color occurring after only 30 seconds. In comparison, the mixture
containing 3,5-dihydroxybenzoic acid was essentially colorless after one
week thereby obviating the need for inline blending of two separate fluids
for providing a single imaging layer.
Besides the color stability obtained by using 3,5-dihydroxybenzoic acid as
the heat-fusible organic acidic material, the quantity of binder and other
reagents employed in the one-pot composition can be reduced from the
amounts used in inline blended fluids while still achieving a given
Dmax/Dmin. As an illustration, two recording elements I and II employing
3,5-dihydroxybenzoic acid and a control element employing
3,5-diisopropylsalicylic acid were prepared by coating the imaging layers
from methyl ethyl ketone on a transparent polyethylene terephthalate
support followed by applying a topcoat layer. The protective topcoat layer
comprised polyvinylalcohol coated at a coverage of 30 mg/ft.sup.2, Quinlon
C available from du Pont Company (chromium, pentahydroxy (tetradecanato)
di-) coated at a coverage of 30 mg/ft.sup.2 and Fluorad FC-100 available
from the 3M Company (fluorochemical surfactant - fluorinated alkyl
amphoteric mixture) coated at a coverage of 1 mg/ft.sup.2. The imaging
layer for each element and the Dmax/Dmin (Red) measured by transmission
for the heated and unheated portions of each are set forth below.
Control Element
Topcoat Layer
Imaging Layer--inline blend of (1) and (2)
(1) polyvinylbutyral coated at a coverage of 200 mg/ft.sup.2 and Compound A
coated at a coverage of 30 mg/ft.sup.2 ;
(2) polyvinylbutyral coated at a coverage of 100 mg/ft.sup.2, silver
behenate coated at a coverage of 15 mg/ft.sup.2 silver and
3,5-diisopropylsalicylic acid coated at a coverage of 50 mg/ft.sup.2.
Transparent Support
Dmax/Dmin 1.3/0.04
Element I
Topcoat Layer
Imaging Layer--inline blend of (1) and (2)
(1) polyvinylbutyral coated at a coverage of 200 mg/ft.sup.2 and Compound A
coated at a coverage of 30 mg/ft.sup.2 ;
(2) polyvinylbutyral coated at a coverage of 100 mg/ft.sup.2, silver
behenate coated at a coverage of 11 mg/ft.sup.2 silver and
3,5-dihydroxybenzoic acid coated at a coverage of 25 mg/ft.sup.2
Transparent Support
Dmax/Dmin 1.3/.04
Element II
Topcoat Layer
Imaging Layer--one-pot composition-polyvinylbutyral coated at a coverage of
100 mg/ft.sup.2, silver behenate coated at a coverage of 10 mg/ft.sup.2
silver, Compound A coated at a coverage of 25 mg/ft.sup.2 and
3,5-dihydroxybenzoic acid coated at a coverage of 25 mg/ft.sup.2.
Transparent Support
Dmax/Dmin 1.4/.04
From the above comparisons, it will be apparent that using inline blended
fluids the same Dmax/Dmin was obtained with lesser amounts of silver and
acidic material when 3,5-dihydroxybenzoic acid was used as the acidic
material, the amount of the benzoic acid being less than the molecular
equivalent of 35 mg/ft.sup.2 based on 50 mg/ft.sup.2 of the salicylic
acid. Also, it will be apparent that by using the one-pot composition a
slightly higher Dmax was obtained with even lesser amounts of the
reactants and less than half the amount of binder.
In addition to its use in single imaging layers as shown above, it will be
appreciated that 3,5-dihydroxybenzoic acid also can be used advantageously
in recording elements where the reactants, i.e., the thiolactone and the
silver are in separate layers. For example, several recording elements
were prepared by coating the following layers one and two on a transparent
polyethylene terephthalate support. A protective topcoat layer having the
same composition given above was coated over layer two.
______________________________________
Topcoat Layer
**Layer Two - Red/Green/Blue/Black
Layer One - polyvinylbutyral coated at a coverage of 200
mg/ft.sup.2, *silver behenate coated at a coverage of 20
mg/ft.sup.2 silver and 3,5-dihydroxybenzoic acid coated
at a coverage of 60 mg/ft.sup.2.
Transparent Support
*silver behenate coated at a coverage of 18 mg/ft.sup.2 for
Blue
**Layer Two -
Red 100 mg/ft.sup.2 polyvinylbutyral and
50 mg/ft.sup.2 Compound B plus
15 mg/ft.sup.2 Compound C
Red-2 100 mg/ft.sup.2 polyvinylbutyral and
50 mg/ft.sup.2 Compound B
Blue 100 mg/ft.sup.2 polyvinylbutyral and
30 mg/ft.sup.2 Compound A
Green 100 mg/ft.sup.2 polyvinylbutyral and
50 mg/ft.sup.2 Compound D
Black 200 mg/ft.sup.2 polyvinylbutyral and
80 mg/ft.sup.2 Compound E plus
20 mg/ft.sup.2 Compound B
Compound B
##STR7##
Compound C
##STR8##
Compound D
##STR9##
Compound E
##STR10##
______________________________________
Control elements were prepared that were identical to those above except
that 60 mg/ft.sup.2 of 3,5-diisopropylsalicylic acid was used as the
organic acidic material. For each of the colors the Dmax obtained for the
test samples exceeded the control samples by 10 to 35%. Dmin for the test
samples in each color was at or below that of the control. Though the test
sample for blue contained 10% less silver, it still had a 15% higher Dmax
than the control sample as well as a low Dmin, and also, it exhibited
excellent performance on accelerated aging tests.
As can be seen from the foregoing, 3,5-dihydroxybenzoic acid when used as
the sole organic acidic material provides a stable one-pot coating
composition and when used in inline blended coatings and in two layer
coatings also provides recording elements having excellent imaging
characteristics. In the latter two embodiments, it will be appreciated
that 3,5-dihydroxybenzoic acid also can be used in combination with other
acidic materials if desired.
Since certain changes may be made in the herein described subject matter
without departing from the scope of the invention herein involved, it is
intended that all matter contained in the above description and examples
be interpreted as illustrative and not in a limiting sense.
* * * * *
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