Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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BACKGROUND OF THE INVENTION
. ._. .
Field of the Invention
This invention relates to a method for forming
a color image by using photoconductive toners and, more
particularly, to a method for forming a highly sensitive
color image by one shot of exposure to image-wise
light.
Description of the Prior Art
Heretofore, various methods are known in the
art for producing hard copies for preserving and handling
electrical color image signals.
For example, it is known to provide colors
corresponding to the image signals to the recording
paper at coordinate positions thereof corresponding
to original color signals, as for instance by spraying
ink of a predetermined color (ink jet printing) or
thermally developing a color on the recording paper
(thermal coloring). In these methods, since coloring
means are caused to mechanically sweep the recording
paper along coordinate axes thereof for sequential
image formation, a prolonged sweep time is required
for producing an accurate color image. Moreover, a
limitation is placed on the power of resolution-as a
function of the properties of the coloring means
employed.
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An electrophotographic process is also known
in the art for shortening the image forming time interval
and improving the power o~ resolution. However, in the
conventional~color electrophotographic process, three
color toners are sequentially exposed, developed and
fixed in three separate steps, thus complicating the
image forming operation. Moreover, color filters are
required for color separation, thus complicating the
apparatus. In addition, there is the risk of color
deviation from the original color.
For producing a color image by one shot
exposure to light, methods are also known in the art
by which particles containing colorless sublimable dyes
are electrostatically deposited on a sensitized plate
or photosensitive particles containing colorless
sublimable dyes are electrostatically deposited on a
photoconductive plate, after which the particles are
exposed to light so that the dyes are caused to develop
their color on the transfer sheet. In these methods,
color images can be formed only on a special transfer
sheet provided with a coloring layer of deposited
organic or inorganic acids for coloring the colorless
sublimable dyes, thus causing elevated costs. In
addition, there is the risk of color fading because
the dyes are only poor in durability.
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SUMMARY OF THE INV~NTION
-
It is an object of the present invention to
provide an improved method for forming a color image~
It is another object of the present invention
to provide a method for forming a color image in which
a color image can be obtained by one shot of exposure
to an image-wise light.
It is a further object of the present
invention to provide a method for forming a color
image which is clear and definite with little fogging.
It is a still further object of the present
invention to provide a method for forming a color image
at low cost_
According to one aspect of the present
invention, there is provided a method for forming a
color image which comprises the steps of:
(a) uniformly forming three kinds of photoconductive
toners on a substrate, each of said photoconductive
toners having an absorption wavelength band corres-
ponding to one of red, green and blue light components
of a natural light, each of said photoconductive toners
having a sensitization wavelength band corresponding
to one of r~d, green and blue light components of the
natural light, and each of said photoconductive toners
having said absorption wavelength band and said
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sensitization wavelength band different from each other;
(b) uniformly charging said photoconductive toners;
(c) obtaining three colors corresponding to three
primary colors, that is, red, green and blue from an
original image to be reproduced;
(d) converting said three primary colors into three
primary colors mutually different therefrom.
(e) exposing said photoconductive toners to a light
with each of the converted three primary-colors for
selectively removing charges from a portion of said
photoconductive toners; and
(f) removing toners freed of charges from said sub-
strate.
According to another aspect of the present
invention, there is provided a photosensitive material
employed in the method for forming a color image which
comprises a substrate and three kinds of photoconductive
toners uniformly formed on said substrate, each of said
photoconductive toners having an absorption wavelength
band corresponding to one of red, green and blue light
components of a natural light, each of said photo-
conductive toners having a sensitization wavelength
band corresponding to one of red, green and blue light
components of the natural light, and each of said photo-
conductive toners having said absorption wavelength band
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and said sensitization wavelength band different from
each other.
BRIEF DESCRIPTION OF THE DRA~INGS
Figs. 1 to 3 are schematic views for illus-
trating the relation between the sensiti~ation wavelength
band and the absorption wavelength band of the photo-
conductive toners, wherein Fig. lA shows the relation
for photoconductive cyan toners sensitive to red light;
Fig. lB that for photoconductive magenta toners sensi-
tive to blue light; Fig. lC that for photoconductive
yellow toners sensitive to blue color; Fig. 2A that for
photoconductive magenta color sensitive to red color;
Fig. 2B that for photoconductive yellow toners sensitive
to green light; Fig. 2C that for photoconductive cyan
toners sensitive to blue light, Fig. 3A that for photo-
conductive yellow toners sensitive to red light; Fig. 3B
that for photoconductive cyan toners sensitive to green
light; and Fig. 3C that for photoconductive magenta
toners sensitive to blue light.
Figs. 4 to 7 are diagrammatic views showing
the process for forming a color image according to the
present invention, wherein Fig. 4 shows the step of
electrically charging photoconductive toners; Fig. 5
the step of light exposure of the electrostatically
charged toners; Fig. 6 the step of removlng the toners
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from which the charges have been lost; and Fig. 7 shows
a step for thermally fixing the image on a substrate.
Fig. 8 is a diagrammatic view showing an example of a
color duplicàting apparatus adapted for continuous
formation of color images.
Fig. 9 is a chart showing light absorbance
characteristics of Tetrabromphenol Blue.
Fig. 10 is a chart showing photoconductive
characteristics of zinc oxide sensitized with Tetra-
bromphenol Blue.
Fig. 11 is a chart showing photoconductive
characteristics of photoconducting magenta toners
sensitive to red light.
Fig. 12 is a chart showing light absorbance
characteristics of Eosin.
Fig. 13 is a chart showing photoconductive
characteristics of zinc oxide sensitized with Eosin.
Fig. 14 is a chart showing photoconductive
characteristics of light conductive yellow toners
sensitive to green light.
Fig. 15 is a chart showing light absorbance
characteristics of Cyanin NK 1870.
Fig. 16 is a chart showing photoconductive
characteristics of zinc oxide sensitized with Cyanin
,
NK 1870.
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~ ig. 17 is a chart showing ~hotoconductive
cyan toners sensitive to blue lisht.
D~AIIED D~SCRIPmION O~ ~H~ T-~r~IO~
In fo~rming a color image by using the photo-
conductive toners, three-colored particles sensitive to
the light of the red, green and blue wavelength bands
are used as photoconductive toners. In this case, it
is necessary to consider the relation between the
absorption wavelength band res~onsi~le in determining
the color proper to the toner and the sensitization
wavelength band.
In the present specification, the sensitiza-
tion wavelength band or range means the wavelength band
by the irradiation of the light of which the toner is
rendered conductive and loses its electrostatic
charges.
~ Yhen the phtoconductive toners are colored
in three primary colors of the additive color system,
that is, red, green and blue, a color image composed
of three colors, i.e. red, green and blue, is obtained
as negative. However, in this case, the white and black
image signal portions, for exam le, are respectively
turned into black and white image signal p~rtions
(inversion of brightness).
On the other hand, when the light conductive
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toners are colored in the three primary colors of the
subtractive color system, that is, cyan, magenta and
yellow, a color image consisting of three colors,
viz. red, green and blue, is obtained as positive and
thus without brightness inversion.
~ Jhen the photoconductive toners are colored
in this manner in the three primary colors of the
subtractive color system, three further combinations
can be considered by takins the combination with the
light intensifiers or sensitizers into account.
A first combination is one of cyan color
photoconductive toners sensitive to red lisht, magenta
color photoconductive toners sensitive to sreen light,
and yellow color photoconductive toners sensitive to
blue light. In this case, a positive having the same
color as that of the exposure light may be obtained,
because the cyan color photoconductive toners are
selectively removed upon exposure to red light so that
a red color is exhibited by the remaining magenta and
yellow color photoconductive toners. However, the
sensitization wavelength bands a and the absorption
wavelength bands b of these toners overlap one another,
as shown diagrammatically in Figs. lA to lC. Thus, with
the cyan color photoconductive toners sensitive to red
light, both the sensitivity and absorption wavelength
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bands a, b are 600 to 700 nm, as shown in Fig. lA.
Similarly, both the sensitivity and absorption wave-
length bands a, _ of the magenta color photoconductive
toners are sao to 600 nm, while those of the yellow
color photoconductive toners are 400 to 500 nm, thus
overlapping each other in either cases.
When the sensitivity and absorption wave-
length bands thus overlap each other, the light of the
wavelength to which the toners should be sensitive is
absorbed by the toner coloring materials, so that
sensitization is markedly lowered.
A second combination is one of magenta color
photoconductive toners sensitive to red light, yellow
color photoconductive toners sensitive to green light
and cyan color photoconductive toners sensitive to blue
light.
A third combination is one of yellow color
photoconductive toners sensitive to red light, cyan
color photoconductive toners sensitive to green light
and magenta color photoconductive toners sensitive to
blue light. The sensitivity and absorption wavelength
bands a, b of the respective toners of the second
combination, are shown in Figs. 2A to 2C, whereas the
sensitivity and absorption wavelength bands a, b of the
respective toners of the third combination are shown
_ g _
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in Figs. 3A to 3C. In any of these combinations, the
sensitivity and absorption wavelength bands of the
toners are obviously not overlapped with one another.
According to our experiments, spectral
characteristics of light absorbance of the light
sensitizer (i.ç. sensitivity of the toner processed
in accordance with the present invention) are such
that toner sensitivity is suddenly lowered at the
longer wavelength side of a critical wavelength corres
ponding to maximal sensitivity, whereas it is lowered
slowly at the shorter wavelength side thereof thus
showing a skirting and showing limited sensitivity to
the light included in the skirting. Thus when the
absorption wavelength range proper to the coloring
material is set to be adjacent to the shorter wave-
length side of the sensitization wavelength range, the
material acts as filter for suppressing the sensitivity
to the shorter wavelength light of the skirting and
limiting the sensitization wavelength ranse to a narrow
one thereby improving spectral characteristics.
Therefore, the second combination, that is,
the combination of the magenta color photoconductive
toners sensitive to red light, the yellow color photo-
conductive toners sensitive to green light and the cyan
color photoconductive toners sensitive to blue light,
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is most preferred. Thus, as shown in ~ig. 2A, the
magenta color photoconauctive toner has a sensitivity
wavelength band a of 600 to 700 nm and an absorption
wavelength band b OI 500 to S00 nm adjacent to the short
wavelength side of the band a. Thus, even when the
sensitization wavelength band _ shows skirting so that
some sensitivity is exhibited to the light of the
wavelength less than ~oo nm, the band is overlap~ed
with the absorption wavelength band b thus causing
no inconvenience. The same may be said of yellow
color photoconductive toners. The cyan color has a
sensitization wavelength band of 400 to 500 nm which
is at a considerably shorter wavelength side so that
no inconvenience is caused by the aforementioned
skirting.
It should be noted that, in using the
magneta color photoconductive toners sensitive to red
light (hereafter referred to as magneta color toners),
the yellow color photoconductive toners sensitive to green
light (hereafter referred to as yellow color toners) and
the cyan color photoconductive toners sensitive to
blue light (hereafter referred to as cyan color toners),
image portions irradiated with red, green and blue
light present green, blue and red colors, respectively.
Therefore, for obtaining color matching between~the
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color image signals and the duplicated image, it is
necessary to convert red, green and blue signals into
blue, red and green lights, respectively. As means
for converting electrical color image signals into
predetermined exposure light, a laser beam scanner,
an array of light emitting diodes or a color CRT with
signal conversion means, may be employed.
The process of forming a color image in
accordance with the present invention is hereafter
explained by referring to the drawings.
As shown in Fig. 4, magenta color toners M,
yellow color toners Y and cyan color toners C are
evenly sprayed on a photoconductive substrate l, and
are charged uniformly by using a corona charger 2.
The toners are affixed to the substrate under electro-
static attraction.
Then, as shown in Fig. 5, the light converted
from electrical color image signals, such as blue light
B converted from red signals, red light R converted
from green signals and green light G converted from
blue signals, are irradiated. By such irradiation,
toners sensitive to the respective lights are selec-
tively rendered electrically conductive so that their
charges are lost and the force of electrostatic
attraction relative to the substrate 1 is similarly
~- .
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lost. ~or e~ample, in a zone irradiated with blue light
~, the cyan color toners C absorb the light so that
their charges are lost. Similarly, in a zone irradiated
with red light R and a zone irradia~ed with green
light G, charges on the magenta color toners M~ and on
the yellow color toners Y are los~.
The toner particles fro~ which the charges are
lost in this manner and whose elec~rostatic attrac-
tion is reduced to nill may then be removed b~ electrical
or mechanical means, as shown in ~ig. 6. In this manner,
a color image corresponding to the electrical color
image signals is ~ormed on the substrate 1. Thus the
zone irradiated with t'ne blue light ~ converted from
red signals presents a red color because the magenta
color toners M and the yellow color toners C remain
after removal of the cyan color toners C. Similarly,
the zone irradiated with red light R presents a green
color because of the remaining cyan color toners C and
the yellow color toners Y, while the zone irradiated
with the green light G presents a blue color because
o.f the remaining magenta color toners M and cyan color
toners C.
~ he color image thus obtained is then fixed
by a fixing roll 3, as shown in ~ig. 7.
~ he above described steps can be carried out
.i.
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in succession by using a color duplicator as shown in
Fig. 8.
A recording paper 12 is continuously supplied
from a supply roll 11, and a mixture of three color
toners M, Y and C are sprayed uniformly on the paper
12. These toners M, Y and C are charged by a corona
charger 13, after which the recording paper is exposed
with light of predetermined color converted by a
converter 16 from electrical color image signals
obtained by irradiating an object 14 with light from
a light source 15. The toner particles from which the
charges are lost upon light exposure are attracted and
removed by a nozzle 17, and the remaining toner particles
are fixed by a fixing roll 18.
It is seen from above that a color image is
formed in accordance with the present invention by using
the magenta, yellow and cyan color toners for removing
charges from selected photoconductive toners so that
extremely clear ~nd sensitive color image can be formed
by a single exposure operation.
The photoconductive toners of the present
invention may be formed by adding a light sensitizer,
coloring material and a resinous binder to the photo-
conductive material, said binder serving for fixing the
toner particles on the duplicating surface.
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l~Z5~i9;~
The photoconductive toners employed in the
present invention are described hereafter in detail.
The magenta color toner sensitive to red
light presents a hue belonging to a range of 1.0 RP
to 5.0 R in the Munsell color notation system, and
shows marked sensitivity to the visible light with
wavelength higher `than 600 nm ~red light). It has a
maximal point of sensitivity in the wavelength region
of 610 to 650 nm, and more than 80 percent of sensi-
tivity proper to the overall visible light region in
the wavelength region of 600 to 700 nm.
As practical construction of the photoconduc-
tive toner, it is advisable to use a photoconductor
exhibiting specific photoconductive properties in the
wavelength region higher than 600 nm (red light) by
addition of a red light intensifier or sensitizer, in
which the photoconductor contains a coloring material
exhibiting substantially negligible absorption of the
visible light more than 600 nm in wavelength, but
exhibiting absorptive properties for the wavelength
region less than 600 nm and presenting the magenta hue
as described above. With the above construction, the
coloring material acts as filter with respect to photo-
conductivity of the photoconductor in the region less
than 600 nm so that the photoconductor may exhibit
. -
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photoconductivity only in the limited wavelength region
of 600 to 700 nm. Since t'ne avove described ma~enta
coloring material usually e~hibits strong color absorp-
tion especially in the region of 500 to 600 nm, even
if the photoconductor should still exhibit a useless
sensitivity range towards the shorter wavelength side
of the 600 to 700 nm region after addition of the red
light intensifier, such useless sensitivity range is
filtered off due to color absorp i,ion of the coloring
material.
As photoconductor, materials such as sulphur,
selenium, oxides, sulfides or selenides of zinc, cadmium,
mercury, autimony, titanium, bismuth or lead, anthracene,
anthraquinone, polyvinyl carbazol, polyvinyl anthracene,
or polyacetylene may be used. The most preferred
material is zinc oxide.
As red light intensifiers for the photo-
conductor, such materials may be used as Tetrabromo-
phenol Blue, Bromophenol Blue, Bromocresol Purple,
Bromochlorophenol Blue, Bromocresol Blue, Bromo Thymol
Blue, Bromocresol Green, Tetraiodophenol Blue, Acid
Blue 1, Acid Blue 7, Acid Blue 9, Acid Blue 103,
Methylene Blue 5 Crystal Violet, Brilliant Green or
Malachite Green. These red light intensifiers are
added to the photoconductor in an amount of 0.01 to
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1.0 wt. percent.
Hypersensitizers may be additionally used
for promoting sensitization of the red light intensi-
fier so as to provide for so-called hypersensitization.
As these hypersensitizers, comounds showing electron
affinity, such as benzoquinone, chloranil, phthalic
anhydride, maleic anhydride, dinitrobenzoic acid or
iodine may be employed. ~hese hypersensitizer may be
used in an amount of 0.01 to 1.0 wt. percent relative
to the aforementioned photoconductor.
As coloring materials, inorganic pigments,
organic pigments, direct dyes, acid dyes, basic dyes,
disperse dyes or oil colors may be used singly or in
combination and in consideration occasionally of the
hue or the like factors. For example, inoranic pig-
ments such as iron oxide red of the Pigment Red 101;
organic pigments such as Pigment Red -1, -3, -4, -5,
- 6, - 7, - 8, -9, - 12, - 18, -22, -30, -32, - 36, - 38, -40,
-48, -49, -50, -53, -54, -57, -58, -59, -60, -63, -~4,
-67, -81~ -83, -90, -163, or -173; and organic pigments
such as oil colors, for example, Solvent Red -1, -3,
-8, -23, -24, -25, -27, -30, -49, -81, -82, -83, -84,
-100, -109 or -121. These coloring materials may be
used in amounts of 1.0 to 100 wt. percent related to
the aforementioned photoconductor.
.~
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The aforementioned photoconductors, red
light intensifiers and coloring materials are essential
ingredients of the above described photoconductive
toners. In addition to these essential ingredients,
a resinous binder may be occasionally used for binding
these ingredients to one another or promoting fixing
on the duplicating medium. As such binder, thermo-
plastic resins such as acrylic resin, styrene resin,
styrene-butadiene copolymer, polycarbonate resin, poly-
vinyl alcohol or polyvinyl acetate, or thermosetting
resins such as urethane resin, epoxy resin or melamine
resin, may be used either singly or in combination.
These resins may be used in an amount of 2 to 50 wt.
percent related to the aforementioned photoconductor.
The yellow color toner sensitive to green
light has a hue in the range of 5.0 YR to 10.0 Y in
the Munsell color notation system and sharp sensitivity
to the visible light of the wavelength in the range of
500 to 600 nm (green light). As characteristic of the
yellow color toner, it has a maximal point of sensi-
tivity in the wavelength region of 520 to 560 nm and
more t~an 80 percent of sensitivity proper to the
visible light concentrated in the wavelength region of
550 to 580 nm.
In addition, the above described toner
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should have light absorptive characteristics such that
preferably more than 8Q percent of light absorption
occurs in the visible light region with the wavelength
less than 520 nm and more preferably more than 80
percent of light absorption occurs in the visible
light region with the wavelength less than 500 nm.
As practical construction of these photo-
conductive toners, it is desira~le to use a photo-
conductor exhibiting specific photoconductive properties
in the wavelength region of 500 to 600 nm (green light)
by addition of a green light intensifier or sensitizer,
in which the photoconductor contains a yellow pigment
or dye exhibiting substantially negligible absorption
of the visible light more than 500 nm in wavelength and
strons absorptive characteristics for the wavelength
region less than 500 nm and presenting the above
described hue, and a resinous binder for fixing. In
this case, the yellow pigments or dyes act as filter
with respect to photoconductive properties of the
photoconductor in the wavelength region less than-500
nm in such a manner that the useless sensitivity range
from 500 nm towards a shorter wavelength side may be
removed and photoconductive properties of the photo-
conductor may be exhibited in effect only in the range
of 500 to 600 nm.
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As such photoconductor, materials such as
sulphur, selenium, oxides, sulfides or selenides of
zinc, cadmium, mercury, antimony, titanium, bismuth
or lead, anthracene, anthraquinone, polyvinyl carbazol,
polyvinyl anthracene or polyacethylene may be used.
~he most preferred material is zinc oxide.
Preferably, the green light intensifier or
sensitizer used for sensitizing the photoconductor has
no skirt in the wavelength region higher than ~00 n~.
As green light intensifier, materials such as eosin,
fluorescein, tetrabromofluorescein, tetrachlorofluorescein,
tetrabromotetrachlorofluorescein, phloxine, erythrosine
or Rhodamine ~ may be used. ~he green light intensifier
may be used in an amount of 0.01 to 1 wt. part to 100 wt.
parts of the photoconductive material.
Hypersensi~izers may be additionally used for
promoting sensitization of the green light intensifier
90 as to provide for so-called hypersensitization. As
these hypersensitizers, compounds showing electron
affinity such as benzoquinone, chloranil, phthalic
anhydride, maleic anhydride, dinitrobenzoic acid,
tetracyanoquinodimethane or iodine may be used in amounts
of 0.01 to 1 wt. part to 100 wt. parts of the photo-
conductor.
As coloring materials, inorganic pigments,
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organic pigments, direct dyes, acid dyes, basic dyes,
disperse dyes or oil colors may be used singly or in
combination and in consideration occasionally of the
hue or the like factors. For example, inorganic pig-
ments such as yellow iron oxide or loess of Pigment
Yellow -42 or -43, organic pigments such as Pigment
Yellow -1, -2, -3, -5, -6, -10, -12, -13, -14, -15,
-16, -23, -65, or -115, oil colors such as Solvent
Yellow -6, -14, -15, -16, -19, -21, -33, -56, -61, or
-80, or disperse dyes such as Disperse Yellow -5,-7,
-8, -23 or -60, may be used.
These coloring materials may be used in an
amount of 1.0 to 100 wt. parts to 100 wt. parts of the
aforementioned photoconductor.
A resinous binder may be occasionally added
for binding the photoconductor and the coloring material
to one another or promoting fixing on the paper and
in an amount of 2 to 50 parts to 100 wt. parts of the
aforementioned photoconductor. As such binder, thermo-
plastic resins such as acrylic resin, styrene resin,
styrene-butadiene copolymer, polycarbonate resin,
styrene-butadiene copolymer, polycarbonate resin,
polyvinyl alcohol or polyvinyl acetate or thermosetting
resins, such as urethane resin, epoxy resin or melamine
resin, may be used either singly or in combination.
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~ he cyan color toner sensitive to blue light
presents a hue belonging -to a range of 5.0 BG to 8.0 PB
in the ~iunsell color notation sys-tem and shows marked
sensitivity to the visible light with wavelength less
than 500 nm (red light). It has a ma~imal point of
sensitivity in the wavelength region less than 4~0 nm
and more t~lan 80 percent of sensiti~Jity proper to the
visible light region in the wavelength region less ~han
470 nm.
As practical construction of the photoconduc-
tive toner, it is advisable to use a photoconductor
exhibiting specific photoconductive properties in the
wavelength region less than 500 nm (blue light) by
addition of a blue light intensifier or sensitizer, in
which the toner contains a coloring material exhibiting
substantially negligible absorption of the visible light
less than 500 nm in wavelength, but exhibiting absorp-
tive properties for the wavelength region higher than
500 nm and especially higher than ~00 nm and presenting
the cyan hue as mentioned above. In this case, the
coloring material acts as filter with respect to photo-
conductivity of the photoconductive material in the
range higher than 500 nm so that the photoconductor
may exhibit photoconductivity only in the limited
wavelength region less than 500 nm. Since the above
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described cyan coloring material usually exhibits
strong color absorption in the region higher than
500 nm and especially higher than 600 nm, even if the
photoconductor should still exhibit a useless sensi-
tivity range towards the longer wavelength side of
S00 nm after addition of the blue light intensifier,
such useless sensitivity range is filtered off and
removed due to absorption proper to the coloring
material. Since the coloring material exhibits no
color absorption in the region of increased sensitivity
of the photoconductive material by the blue light
intensifier, that is, the region less than 500 nm in
wavelength, sensitivity of the photoconductive material
is not lowered.
As photoconductor, materials such as sulphur,
selenium, oxides, sulfides or selenides of zinc, cadmlum,
mercury, antimony, titanium, bismuth or lead, anthracene,
anthraquinone, polyvinyl carbazol, polyvinyl anthracene,
or polyacetylene, may be used. The most preferred
material is zinc oxide.
As blue light intensifier for the photo-
conductor, 2-~3-(2-carboxyethyl)-2(3H)-benzothiazoliden]
methyl-3-carboxylate ethyl benzothiazolium represented
by a formula
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~ + ~ -CH= / ~ ~
CH2 l H2
lH2 lH2
COO- COOH ,
2-[3-(2-carboxyethyl)-2(3H~-benzothiazolidene]methyl-3-
carboxyethylbenzothiazolium bromide, 2-t3-(2-carboxy-
methyl)-2-(3H)-benzothiazolidene]methyl-3-carboxylate-
methylbenzothiazolium, Auramine, merocyanine, Solar
Pure Yellow, Thioflavine T,Thioflavine S, Acridine
Yellow, etc. may be used. These blue intensifiers may
be used in an amount of 0.01 to 1.0 wt. percent related
to the aforementioned photoconductor.
Hypersensitizers may be additionally used for
promoting sensitization of the blue light intensifier
so as to provide for so-called hypersensitization. As
these hypersensitizers, compounds showing electron
affinity, such as benzoquinone, chloranil, phthalic
anhydride, maleic anhydride, dinitrobenzoic acid or
iodine may be used. These materials can be used in an
amount of 0.01 to 1.0 wt. percent relative to the afore-
mentioned photoconductor.
As coloring materials, inorganic pigments,
organic pigments, direct dyes, acid dyes, basic dyes,
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disperse dyes or oil colors may be used singly or in
combination and in consideration occasionally of the
hue or the like factors. For example, inorganic
pigments such as Pigment Blue-27 (prussian blue),
Pigment Blue-28 (cobalt blue), Pigment Blue-29 (ultra-
marine) or Pigment Blue-35 (cerulean blue); organic
pigments such as Pigment Blue-2, -9, -15, -16, -18, -19,
-24, -60 or -64; and organic dyes, such as oil colors,
for example, Solvent Blue-2, -11, -12, -25, -35, -36,
-55 or -73. These coloring materiali can be used in
an amount of 1.0 to 100 wt. percent related to the
aforementioned photoconductor.
The aforementioned photoconductor, blue
light intensifiers and coloring materials are essential
ingredients of the above described photoconductive
toners. In addition to these essential ingredients,
a resinous binder may be occasionally used for binding
these ingredients to one another or promoting fixing on
the duplicating medium. As such binder, thermoplastic
resins such as acrylic resin, styrene resin, styrene-
butadiene copolymer, polycarbonate resin, polyvinyl
alcohol or polyvinyl acetate, or thermosetting resins
such as urethane resin, epoxy resin or melamine resin,
may be used singly or in combination. These resins
may be used in an amount of 2 to 50 wt. percent relative
1225~i9~
to the aforementioned photocondu~to~.
~ he pnotoconductive toners of the present
in~ention may be prepared according to spray dry or
microc~psulation methods by me~ns of which the above
describea ingredients are unilormly dispersed or placed
in concen~rical spherical configurction within each
given par~icle.
mhe present invention will be d.escribed by
reference to- several specific Examples of preparing
three color toners. It should be.noted that these
~xamples are given only by w~y of illustration and are
not intended in any wæy for limiting the scope of the
invention.
Exam~le of Pre~aration of ~aEenta Color Phtoconductive
~oners sensitive_to Red ~i~ht ~
40 weight p~rts of Sazex 2000 (particles of
zinc oxide prepared by Sakai Kag2ku Kogyo EK), 0.05 weight
part of Tetrabromophenol ~lue (prepared by ~akarai Xagaku
EK) and 80 weight parts of ethyl alcohol were despersed
uniformly, ethyl alcohol used as solvent was dried, and
the above ~etrabromophenol ~lue used as light intensi-
fier was adsorbed to the above zinc oxide particles.
~ o the dried product were added 4 weight
parts of acrylic resin ~R 102 used as resinou.s binder
~prepared by Mitsubis'ni Rayon KK), 10 weight parts o~
-26-
1225~;9~
~ionol Red (prepared by Toyo Ink KK3 and 180 weight
parts of acetone. The resulting product was mixed by
a ball mill to a uniform liauid dispersion which was
then spray dried with a miniature sprayer to ?articulate
magenta color photoconductive toners.
Fig. 9 shows light absorbance characteristics
of Tetrabro~ophenol 31ue, Fig. 10 photoconductive proper-
ties of zinc oxide intensified by Tetrabromophenol and
~ig. 11 photoconductive properties of the resulting
magenta color pho~oconductive toners.
It is seen from Fig. 11 that the magenta
color photoconductive toners exhibit a sharp peak of
sensitivity in the wavelength region of 600 to 700 nm.
xam~le of PreParing Yellow Color Photoconductive moners
Sensitive to Green ~i~ht
40 weight parts of Sazex 2000 (particles of
zinc oxide prepared by Sakai Kagaku Kogyo KK), 0.2
weight part of ~osin (prepared by ,rako Junyaku KK) and
80 weight parts of eth~l alcohol were dispersed uniformly,
ethyl alcohol used as solvent was dried, and the above
Eosin used as light intensifier was adsorbed to the
zinc oxide particles.
~ o the dried product were added 4 weight
parts of acrylic resin ~R 102 used as resinous binder
(prepared by Mitsubishi Rayon KK), 10 weight parts of
-27-
1~2569~
~ionol Yellow (prepared by Toyo Ink ~K) and 1&0 weight
parts of acetone. r~he resul~ing product was mixed
toðer by a ball mill to a uniform liq-~id dispersion
which was then spray dried with a minia~ure sprayer ~o
particulate magenta color photoconductive toners.
Fig. 12 shows light absorbance character-
istics of Eosin, Eig. 13 photoconductive properties of
zinc oxide intensified by Eosin and Fig. 14 ~hotoconduc-
tive properties of the resulting yellow color photo-
conductive toners~
It is seen from ~ig. 14 that the yellow color
photoconductive toners exhibit a sharp peak of sensitivity
in the wavelength range of 500 to 580 nm.
Exam~le of Pre~aring Cyan Color Photoconductive moners
Sensitive to Blue ~ight
40 weight parts of Sazex 2000 (particles of
zinc oxide prepared by Sakai Kagaku KK), 0.2 weight
part of Cyanine NK 1870 (prepared by Nippon Kanko
Shikiso KK) and 80 weight parts of ethyl alcohol were
dispersed uniformly, ethyl alcohol used as solvent was
dried, and the above Cyanine NK 1870 used as light intensifier
was adsorbed to the zind oxide particles.
~ o the dried product were added 4 weight
parts of acrylic resin ~R 102 used as resinous binder
(prepared by Mitsubishi Rayon KK), 10 weight parts of
.
-28-
:~ZZS69~
Lionol Blue tprepared by Toyo Ink KK) and 180 weight
parts of acetone. The resulting product was mixed
together by a ball mill to a uniform liquid dispersion
which was then spray dried with a miniature sprayer
to particulate cyan color photoconductive toners.
Fig. 15 shows light absorbance character-
istics of Cyanine NK 1870, Fig. 16 photoconductive
properties of zinc oxide intensified by Cyanine NK 1870
and Fig. 17 photoconductive properties of the resulting
cyan color photoconductive toners.
It is seen from Fig. 17 that the cyan color
photoconductive toners exhibit a sharp peak of light
sensitivity in the wavelength range of 400 to 480 nm.
The three different photoconductive toners
thus prepared were sprayed on an ordinary paper sheet
and irradiated with three color light beams, that is,
red, green and blue light beams. After irradiation,
toner particles from which charges were lost were
removed and the remaining toner particles were fixed
on the paper sheet. The portions irradiated with red,
green and blue light beams were colored in green, blue
and red, respectively.
, .
- 29 -
