U.S. patent number 3,668,127 [Application Number 04/836,246] was granted by the patent office on 1972-06-06 for liquid developer for electrophotography.
This patent grant is currently assigned to Kabushiki Kaisha Ricoh. Invention is credited to Hazime Machida, Zenjiro Okuno.
United States Patent |
3,668,127 |
Machida , et al. |
June 6, 1972 |
LIQUID DEVELOPER FOR ELECTROPHOTOGRAPHY
Abstract
A liquid developer for use in electrophotography, wherein a
toner comprising pigment particles and a resinous layer coated on
said pigment particles is dispersed in a carrier liquid of high
electric resistance and low dielectric constant, said developer
being characterized by the fact that the pigment particles are
coated with a resinous layer consisting of at least two layers of
which the first layer is directly coated on the particles and is
comprised of a resin insoluble in said carrier liquid while the
outermost layer comprises a resin capable of somewhat swelling up
in said carrier liquid.
Inventors: |
Machida; Hazime (Tokyo,
JA), Okuno; Zenjiro (Tokyo, JA) |
Assignee: |
Kabushiki Kaisha Ricoh (Tokyo,
JA)
|
Family
ID: |
12710819 |
Appl.
No.: |
04/836,246 |
Filed: |
June 25, 1969 |
Foreign Application Priority Data
|
|
|
|
|
Jul 1, 1968 [JA] |
|
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43/45135 |
|
Current U.S.
Class: |
430/114; 523/201;
524/474 |
Current CPC
Class: |
G03G
9/131 (20130101) |
Current International
Class: |
G03G
9/12 (20060101); G03G 9/13 (20060101); G03g
009/04 () |
Field of
Search: |
;252/62.1 ;260/33.6 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lesmes; George F.
Assistant Examiner: Brammer; J. P.
Claims
1. A liquid developer for electrophotography comprising 1-50 parts
by weight of an electrostatically charged toner dispersed in 1000
parts by weight of a carrier liquid, said carrier liquid having an
intrinsic resistivity of more than 10.sup.9 .OMEGA. cm and being
selected from the group consisting of an isoparaffinic hydrocarbon,
a paraffinic hydrocarbon and mixtures thereof, said toner
consisting of pigment particles having a first resinous layer
coated on the surface of the pigment particles and a second
resinous layer coated on the surface of the first resinous layer,
said pigment particles being selected from the group consisting of
Carbon Black (C.I.No. 77266), Spirit Black (C.I. No. 50415),
Aniline Black (C.I. No. 50440), Alkali Black (C.I. No. 42750),
Cyanine Blue (C.I. No. 26410), Fast Yellow (C.I. No. 13135), Fast
Red (C.I. No. 37125), Benzidine Orange (C.I. No. 21110) and
Methylene Blue (C.I. No. 25015), said first resinous layer
consisting of 0.5-10 parts by weight of an (A) resin, based on 1
part by weight of the pigment particles, said (A) resin being
selected from the group consisting of polystyrene,
styrene-butylmethacrylate copolymer having a molar ratio of about
7:3, styrene-laurylmethacrylate copolymer having a molar ratio of
about 9:1, styrene-hydroxymethacrylate copolymer having a molar
ratio of about 6:4, styrene-butadiene copolymer having a molar
ratio of about 8:2 and methylmethacrylate butylmethacrylate
copolymer, said second resinous layer consisting of 1-20 parts by
weight of a (B) resin, based on 1 part by weight of the pigment
particles, said (B) resin being selected from the group consisting
of styrene-laurylmethacrylate copolymer having a molar ratio of
about 1:1, styrene-butylmethacrylate-acrylic acid copolymer having
a molar ratio of about 3:7:1, butylmethacrylate homopolymer, vinyl
toluene-vinyl acetate copolymer, phenolmodified alkyd resin,
styrene-butadiene copolymer having a molar ratio of about 6.5:3.5,
laurylmethacrylate-hydroxymethacrylate copolymer having a molar
ratio of about 3:1 and styrene-butadiene
2. A liquid developer according to claim 1, wherein the carrier
liquid is a mixture of isoparaffinic and paraffinic hydrocarbons
and the toner consists of Spirit Black as the pigment,
styrene-butylmethacrylate copolymer having a molar ratio of about
7:3 as the (A) resin and
3. A liquid developer according to claim 1, wherein the carrier
liquid is a mixture of isoparaffinic and paraffinic hydrocarbons
and the toner consists of Carbon Black as the pigment, methyl
methacrylate -- butyl methacrylate copolymer as the (A) resin and
styrene -- butadiene copolymer
4. A liquid developer according to claim 1, wherein the carrier
liquid is a mixture of isoparaffinic and paraffinic hydrocarbons
and the toner consists of Carbon Black as the pigment,
methylmethacrylate -- butylmethacrylate copolymer as the (A) resin
and vinyl toluene -- vinyl
5. A liquid developer for electrophotography comprising 1-50 parts
by weight of an electrostatically changed toner dispersed in 1,000
parts by weight of a carrier liquid, said carrier liquid having an
intrinsic resistivity of more than 10.sup.9 .OMEGA. cm and being
selected from the group consisting of an isoparaffinic hydrocarbon,
a paraffinic hydrocarbon and mixtures thereof, said toner
consisting of pigment particles having a first resinous layer
coated on the surface of the pigment particles, a second resinous
layer coated on the surface of the first resinous layer, and a
third resinous layer coated on the surface of the second resinous
layer, said pigment particles being selected from the group
consisting of Carbon Black (C.I.No. 77266), Spirit Black (C.I.No.
50415), Aniline Black (C.I. No. 50440), Alkali Black (C.I. No.
42750), Cyanine Blue (C.I. No. 26410), Fast Yellow (C.I. No.
13135), Fast Red (C.I.No. 37125), Benzidine Orange (C.I.No. 21110),
and Methylene Blue (C.I.No. 25015), said first resinous layer
consisting of 0.5-10 parts by weight of an (A) resin, based on 1
part by weight of the pigment particles, said (A) resin being
selected from the group consisting of polystyrene,
styrene-butylmethacrylate copolymer having a molar ratio of about
7:3, styrene- laurylmethacrylate copolymer having a molar ratio of
about 9:1, styrene-hydroxymethacrylate copolymer having a molar
ratio of about 6:4, styrene-butadiene copolymer having a molar
ratio of about 8:2 and methylmethacrylate-butylmethacrylate
copolymer, said third resinous layer consisting of 1-20 parts by
weight of a (B) resin, based on 1 part by weight of the pigment
particles, said (B) resin being selected from the group consisting
of styrene-lauryl-methacrylate copolymer having a molar ratio of
about 1:1, styrene-butylmethacrylate-acrylic acid copolymer having
a molar ratio of about 3:7:1, butylmethacrylate homopolymer, vinyl
toluene-vinyl acetate copolymer, phenol-modified alkyd resin,
styrene-butadiene copolymer having a molar ratio of about 6.5:3.5,
laurylmethacrylate-hydroxymethacrylate copolymer having a molar
ratio of about 3:1 and styrene-butadiene copolymer having a molar
ratio of about 1:1, said second resinous layer consisting of 0.5 -
10 parts by weight of one of said (A) and (B) resins, but differing
from the resins of said first and third layers, based on 1 part by
weight of the pigment
6. A liquid developer according to claim 5, wherein the carrier
liquid is an isoparaffinic hydrocarbon and the toner consists of
Aniline Black as the pigment, styrene-lauryl methacrylate copolymer
having a molar ratio of 9:1 as the first resinous layer, butyl
methacrylate homopolymer as the second resinous layer and lauryl
methacrylate - hydroxy methacrylate copolymer having a molar ratio
of about 3:1 as the third resinous layer.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid developer for
electrophotography which is prepared by uniformly dispersing, in a
carrier liquid, a toner provided with two or more resinous layers
of different solubility in said carrier liquid, said layers being
coated on the surfaces of pigment particles.
2. Description of the Prior Art
Liquid developers in the prior art have been obtained by dispersing
pigment particles, together with an additive such as a resin
capable of controlling the polarity of pigment particles so as to
impart to them dispersibility in the carrier liquid or stability to
the toner, in a highly insulating carrier liquid to thereby cause
said pigment particles to adsorb the resin within the carrier
liquid and form a toner. Such a liquid developer has heretofore
been manufactured by dispersing pigment particles, such as Carbon
Black, in a carrier liquid, e.g., an organic solvent such as
paraffinic hydrocarbon, upon kneading and pulverizing them together
with a resin such as alkyd resin employed as a polarity-controlling
agent or a dispersion stabilizer. In order to effect development by
means of the thus obtained liquid developer, a copying material
having an electrostatic latent image is immersed in said liquid
developer to thereby cause the toner to be charged with positive or
negative polarity so as to generate electrophoresis corresponding
to the polarity of the latent image area and to adhere onto the
surface of the photo-sensitive layer, whereby there is formed a
visible image.
Since the liquid developers in the prior art are prepared by mere
dispersion of pigment particles together with a specific additive
in a carrier liquid as stated above, for some period of time
subsequent to the manufacture thereof, such matters as the resin
are relatively firmly adsorbed onto the pigment particles, the
toner displays a distinct polarity, and a sufficient dispersibility
thereof is maintained, but, with the passage of time, the
adsorbability of the pigment particles deteriorates gradually, the
adsorbed resin comes off the pigment particles, and the polarity of
the toner becomes indistinct or the toner precipitates, whereby
hampering the developing efficiency as compared with the initial
stage subsequent to manufacture thereof. The root cause for
deterioration of these qualities is the co-existence of the toner
and the extra resin not adsorbed onto pigment particles within the
carrier liquid, and the existence of such extra resin causes the
insulating property of the carrier liquid to deteriorate or the
electric charge of the toner to change, and, further in case of
copying, said resin adheres to the electrostatic latent image area
to lower the electric charge thereof, resulting in a decrease in
the amount of adhered toner, and the copied image is not
sufficiently concentrated, i.e., distinct. Besides, the amount of
resin adsorbed onto pigment particles within the carrier liquid is
comparatively small and the adhesive power of the toner for the
photo-sensitive layer surface of the copying material is weak.
Further, when the copied image obtained was utilized as an offset
master or transferred, it could hardly produce a satisfactory
effect.
SUMMARY OF THE INVENTION
The present invention is intended to provide a liquid developer
composition for use in electrophotography by mean of dispersing, in
1,000 parts by weight of a highly insulating organic solvent, from
1-50 parts by weight of a toner comprised of pigment particles
coated with multiple layers of resins having different solubilities
in the carrier liquid on the basis of the judgement that the above
stated drawbacks of liquid developers in the prior art are
attributable to the composition of the toner per se. The
electrophotography as referred to in the present invention means
producing a copy by converting an electrostatic latent image into a
visible image after forming a latent image consisting of
electrostatic charge on an appropriate electrostatic charge
carrier. The foregoing liquid developer is applicable to the
development of such electrostatic latent image.
The following is the concrete explanation of the present invention
with reference to the accompanying drawing.
FIGS. 1, 2 and 3 of the drawing respectively are enlarged
cross-sectional views of the structure of some examples of the
toner for the liquid developer for electrophotography according to
the present invention.
FIG. 1 and FIG. 3 show a toner having two resinous layers while
FIG. 2 shows a toner having three resinous layers. The toner is
respectively provided with a first resinous layer 2 formed directly
on the surface of a pigment particle 1, and on the top of said
first resinous layer there is provided a second resinous layer,
which corresponds respectively to the outermost resinous layer 3 in
relation to the pigment particle in FIG. 1, and to the middle
resinous layer 3a in FIG. 2, and to the resin-dispersed layer 3b,
viz., the outermost layer in FIG. 3. In FIG. 2, there is further
provided the outermost resinous layer 4. Further, in each toner,
the solubilities of the resins contained in respective resinous
layers thereof in the carrier liquid differs from one another. The
resinous layer closest to the pigment particle preferably is
insoluble in the carrier liquid while the outermost resinous layer
is capable of somewhat swelling up therein. Accordingly, the first
resinous layer 2, for instance, of each toner and the second
resinous layer 3a of FIG. 2 are insoluble, whereas the second
resinous layer 3 and 3b, respectively, of FIG. 1 and FIG. 3 and the
third resinous layer 4 of FIG. 2 are capable of somewhat swelling
up in the carrier liquid. Therefore, by dispersing these toners in
an appropriate carrier liquid, there can be obtained the liquid
developer for electrophotography according to the present
invention.
In other words, the present invention relates to a liquid developer
for electrophotography which is characterized in that a toner
comprising pigment particles coated with two or more resinous
layers of different solubilities in the carrier liquid is dispersed
in a highly insulating carrier liquid. To be more precise, the
resin coated directly onto the pigment particles is insoluble in
the carrier liquid while the resin contained in the outermost
resinous layer somewhat swells up in the same and the resin of
intermediary layer(s) other than the foregoing two layers is
possessed of either of these properties, and is preferably
insoluble in the carrier liquid.
In preparing the toner according to the present invention, for
instance, a toner comprising two or three resinous layers as shown
in FIG. 1 and FIG. 2, 1 part by weight of pigment is mixed with 1
part by weight -- preferably 3 parts by weight -- of the selected
1st resin and is processed for thermal fusion of kneading upon
adding a small amount of an appropriate solvent. Then, after
cooling or evaporation of solvent, the grains obtained are
pulverized to an approximate grain size of less than 150 mesh.
Subsequently, 2 parts by weight of the thus pulverized particles
and 1 part by weight of the second resin, selected as the resin for
use in forming the outermost resinous layer in case of the
two-layered toner and for use in forming the middle resinous layer
in case of the three-layered toner, are mixed and then processed
for either thermal fusion or kneading upon adding a small amount of
an appropriate solvent which will not cause the first resinous
layer formed in advance to dissolve or swell up. The thus kneaded
mixture is pulverized, after cooling or solvent evaporation in the
same way as in the foregoing, whereby there is obtained either the
desired toner when the two-layered toner is being produced or the
particle provided with the middle layer, viz., the 2nd resinous
layer when the three-layered toner is being produced. Further, when
the three-layered toner is being produced, by processing 2 parts by
weight of the aforesaid mixed particles and 1 part by weight of the
third resin selected for use in forming the outermost layer
according as the treatment applied at the step of forming the
outermost layer in case of the two-layered toner, a toner provided
with three resinous layers can be formed. When preparing the toner
provided with a resin dispersed layer as the outermost layer 3b
such as shown in FIG. 3, it will suffice to coat pigment particles
having the first resinous layer of the preliminary stage with a
solution prepared by dispersing the second resin in an appropriate
solvent, by means of spray drying and the like.
Through the uniform dispersion of the toner prepared as above in an
appropriate organic solvent having a high insulating property (such
as paraffinic or isoparaffinic hydrocarbon or a mixture thereof
having an intrinsic volume resistivity of more than 10.sup.9
.OMEGA.. cm), a desired liquid developer for electrophotography can
be obtained.
Though the pigment particles, resins and carrier liquid applicable
in the present invention are the same as that employed for
conventional liquid developers for use in electrophotography, care
should be taken in selecting and combining these materials in order
to make the toner and carrier liquid function effectively. However,
so long as this requirement in met, it is at one's option to either
select the pigment particles and resin to the carrier liquid or
select the carrier liquid to the pigment particles and resin,
providing that the resin to be selected is preferred to have its
second order transition point above 40.degree. C. in order to avoid
flowing of the toner at the time of fixing. Suitable combinations
of materials in due consideration of the foregoing are as shown in
examples hereunder, and the materials applicable in these
combinations are enumerated as follows:
As for the pigment particles, there can be used Carbon Black
(C.I.No. 77266), Spirit Black (C.I.No. 50415), Aniline Black
(C.I.No. 50440), Alkali Black (C.I.No. 42750), Cyanine Blue
(C.I.No. 26410), Fast Yellow (C.I.NO. 13135), Fast Red (C.I.No.
37125), Benzidine Orange (C.I.No. 21110), Methylene Blue (C.I.No.
25015), etc.
As for the resin for the 1st layer to coat pigment particles
directly, there can be used styrene, styrene-butylmethacrylate
copolymer (a molar ratio of 7 : 3), styrene-laurylmethacrylate
copolymer (a molar ratio of 9 : 1), styrene-hydroxymethacrylate
copolymer(a molar ratio of 6 : 4), styrene-butadiene copolymer (a
molar ratio of 8 : 2) as well as commercial resins, e.g.,
methylmethacrylate -- butylmethacrylate copolymers such as BR 60,
BR 70, BR 75, BR 80, BR 85, BR 95 (manufactured by Mitsubishi Rayon
Co. Ltd.), etc., and these are respectively employed in the
proportion of 0.5-10 parts by weight, based on pigment
particles.
As for the resin to be employed for the outermost layer, there are
styrene-laurylmethacrylate copolymer (a molar ratio of 1 : 1),
styrene-butadiene copolymer (a molar ratio of 1 : 1),
styrene-butylacrylate-acrylic acid copolymer (a molar ratio of 3 :
7 : 1) as well as commercial butylmethacrylate homopolymer such as
BR 65, BR 90, BR 121, BR 122, BR 123, BR 101, BR 105 and BR 106
(products manufactured by Mitsubishi Rayon Co. Ltd.) vinyltoluene
-- vinylacetate copolymer (manufactured by the Goodyear Tire &
Rubber Co. under the trade name of Solprene), phenol-modified alkyd
resin such as Nikanol AM, Nikanol S-101 (products manufactured by
Japan Gas-Chemical Co. Inc.), laurylmethacrylate -
hydroxymethacrylate copolymer (a molar ratio of 3:1),
styrene-butadiene copolymer such as Pliolite AC, Pliolite ACL and
Pliolite VTAC (products manufactured by the Goodyear Tire &
Rubber Co.), and these are respectively employed at the proportion
of 1-20 parts by weight of the pigment particles. As to the
respective intermediary layers, the 1st resin or the resin for the
outermost layer is employed, and the appropriate amount is in the
range of 0.5-10 parts by weight of pigment particles.
As for the carrier liquid, there can be used paraffinic or
isoparaffinic hydrocarbons or a mixture thereof such as naphtha,
Isopar H (manufactured by ESSO Standard Sekiyu K.K.), etc.
The liquid developer according to the present invention has the
feature that the polarity of the toner will not change nor will the
dispersibility thereof deteriorate, and, accordingly, the same
developing efficiency as at the initial stage subsequent to the
manufacture thereof can be always maintained satisfactorily because
the resin never comes off the toner particles. Moreover, there
being no surplus particles other than the toner particles within
the carrier liquid, there is no fear of causing deterioration of
the insulation resistance of the carrier liquid or deteriorations
of the electric charge as well as the electrophoresis of the toner
particles. Even more remarkable is that all the toner particles
have a uniform size so that they are uniformly charged in the
liquid developer, corresponding to the size thereof. Accordingly,
they generate so rapid an electrophoresis towards the potential
existing at a latent image area or a non-exposed-to-light area,
which is electrostatically charged, that they adhere firmly;
however, they do not do so towards the faint potential remaining at
a non-latent image area or a exposed-to-light area. In other words,
they adhere only along the potential line at the higher part of the
electrostatic charge density capable of generating electrophoresis,
but in the other lower part of said density they do not generate
sufficient electrophoresis in order to adhere thereto.
Accordingly, the liquid developer of the present invention is also
characterized in that the toner particles adhere selectively onto
an electrostatic latent image area corresponding to the electric
charge thereof. In this respect, the toner used in the present
invention is a new and improved type of charge selective toner
compared with the conventional ones, and accordingly the occurrence
of any stained background (non-image area) at the time of copying
can be avoided.
Further, the outermost resinous layer coated on the surface of
pigment particles being somewhat swollen up in the carrier liquid,
its adhesive property to the photo-sensitive layer of the copying
material is very much strengthened. Not only that, the toner being
composed of relatively many layers of resin, the visible image
obtained through development is ready to be transferred if an
appropriate solvent is selected, and further can be utilized as an
excellent offset-printing master by employing an appropriate
hydrophobic resin for the resinous layer of the toner.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1, FIG. 2 and FIG. 3 of the accompanying drawing are enlarged
cross-sectional views showing the structure of examples of the
toner to be employed for the liquid developer for
electrophotography according to the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Example 1
A mixture of 7 parts by weight of styrene and 3 parts by weight of
butylmethacrylate was subjected to bulk polymerization at a
temperature of 80.degree. - 100.degree. C. for 5 hours under a
nitrogen current in the presence of azobis-isobutyronitrile, a
reaction initiator, whereby there was obtained a
styrene-butylmethcrylate copolymer (having a composition ratio of
styrene resin 7: butylmethacrylate resin 3). Next, 1 part by weight
of Spirit Black and 4 parts by weight of the foregoing copolymer
were mixed with 5 parts by weight of toluene. The grains obtained
upon evaporation of toluene were pulverized to a grain size of
about 150 mesh with a ball-mill, whereby there were prepared fine
grains comprising pigment particles coated with the 1st resinous
layer. Then, 5 parts by weight of the thus obtained fine grains, 2
parts by weight of butylmethacrylate homopolymer (manufactured by
Mitsubushi Rayon Co. Ltd. and sold under the name `Standard 101`)
as the second resin and 3 parts by weight of toluene were mixed.
The grains obtained upon evaporation of toluene were pulverized to
about 150 mesh with a ball-mill, whereby there was prepared a toner
provided with two resinous layers consisting of the second resinous
layer coated on the surface of the foregoing first resinous layer.
Subsequently, 10 parts by weight of the thus prepared toner was
uniformly dispersed in a carrier liquid comprising Naphtha No. 6
(manufactured by ESSO Standard Sekiyu K.K.) and Isopar H
(manufactured by ESSO STTANDARD Sekiyu K.K.) mixed at the weight
ratio of 4 : 6, whereby there was obtained the desired liquid
developer for electrophotography.
Example 2
A mixture of 9 parts by weight of styrene and 1 part by weight of
laurylmethacrylate was subjected to bulk polymerization at a
temperature of 80.degree. -100.degree.C for 6 hours within the
nitrogen current in the presense of azobis-isobutyronitrile, a
reaction initiator, whereby there was obtained
styrene-lauryl-methacrylate copolymer (having a composition ratio
of styrene resin 9: laurylmethacrylate resin 1). Next, 1 part by
weight of Aniline Black (manufactured by Imperial Chemical
Industries Ltd.) and 3 parts by weight of the foregoing copolymer
were mixed and subjected to thermal fusion. The mixture, upon
cooling to room temperature, was pulverized to about 150 mesh with
a ball-mill, whereby there were obtained fine grains comprising
pigment particles coated with the 1st resinous layer. Then, 5 parts
by weight of the thus obtained fine grains and 2 parts by weight of
butylmethacrylate homopolymer manufactured by Mitsubish Rayon Co.
Ltd. and sold under the name `BR 105`) as the 2nd resin were mixed
and subjected to thermal fusion, and, after cooling, were
pulverized in the same way as above, whereby there were prepared
fine grains having the second resinous layer coated on the top of
the foregoing first resinous layer. Furthermore, 1 part by weight
of the thus prepared fine grains, 2 parts by weight of
laurylmethacrylate-hydroxymethacrylate resin copolymer (having a
composition ratio of laurylmethacrylate resin 3:
hydroxymethacrylate resin 1) and 5 parts by weight of a solvent
comprising the aforesaid Naphtha No. 6 and Isopar H at the weight
ratio of 3 : 7 were mixed and, after evaporation of the solvent,
the mixture was pulverized in the same way as above, whereby there
was prepared a toner provided with three resinous layers consisting
of the 3rd resinous layer coated on the surface of the foregoing
2nd resinous layer. Subsequently, 1 part by weight of thus prepared
toner was dispersed in 100 parts by weight of Isopar H, whereby
there was obtained the desired liquid developer for
electrophotography.
Example 3
One part by weight of Carbon Black (manufactured by Asahi Carbon
Mfg. K.K. and sold under the name `XG-550`), 5 parts by weight of
methylmethacrylate-butylmethacrylate copolymer (manufactured by
Mitsubishi Rayon Co. Ltd. and sold under the name `BR-95`) and 5
parts by weight of toluene were mixed and heated at a temperature
of 60.degree. -70.degree.C. The mixture grains obtained upon
cooling after evaporation of toluene were pulverized to the grain
size of less than about 150 mesh, whereby there were obtained fine
grains comprising pigment particles coated with the 1st resin. A
mixture of 1 part by weight of the thus obtained fine grains and
0.5 part by weight of styrene-butadiene copolymer of a molar ratio
of 65 : 35 (manufactured by The Goodyear Tire & Rubber Co. and
sold under the name `Pliolite VTL`) was subjected to thermal fusion
and, after cooling, pulverized to the grain size of less than 150
mesh with a ball-mill, whereby there was prepared a toner.
Subsequently, 10 parts by weight of the thus prepared toner was
uniformly dispersed in 150 parts by weight of a carrier liquid
comprising Naphtha No. 6 and Isopar H mixed at the weight ratio of
2 : 8, whereby there was obtained the desired liquid developer for
electrophotography. Furthermore, the example was repeated using
Solprene instead of Pliolite VTL, but there was obtained the same
good result as the example described above.
Example 4
A dispersant comprising 1 part by weight of the fine grains having
the 2nd resinous layer such as obtained in Example 2, 2 parts by
weight of the 3rd resin, viz.,
lauryl-methacrylate-hydroxymethacrylate resin copolymer of Example
2 and 10 parts by weight of a solvent consisting of Naphtha No. 6
and Isopar H mixed at the weight ratio of 7 : 3 was spray-dried by
means of a spray-dryer to form a layer consisting of the dispersed
3rd resin on the top of the foregoing 2nd resinous layer, whereby
there was prepared a toner provided with three resinous layers, of
which the outermost layer is the resin-dispersed layer.
Subsequently, 1 part by weight of the thus prepared toner was
dispersed in 100 parts by weight of Isopar H, whereby there was
obtained the desired liquid developer for electrophotography.
Next, the respective liquid developers prepared as above were
applied to an electrophotographic copying material (manufactured by
K.K. RICOH and sold under the name `BS-1`) which had been impressed
with an electrostatic latent image, and development was effected
thereby. As a result, the respective developers proved capable of
forming quite clear copied images. Moreover, even when these liquid
developers were preserved for a long period of time or were
repeatedly employed for development, there was observed no coming
off of the resinous layer coated on the pigment particles, and
accordingly, such properties as dispersibility, polarity-control or
developing efficiency thereof were quite effectively maintained to
be the same as that at the initial stage subsequent to manufacture
thereof.
* * * * *