U.S. patent number 3,841,893 [Application Number 05/298,721] was granted by the patent office on 1974-10-15 for charge control agents for liquid developers.
This patent grant is currently assigned to Rank Xerox, Ltd.. Invention is credited to Satoru Honjo, Hajime Miyatuka, Sadao Osawa.
United States Patent |
3,841,893 |
Honjo , et al. |
October 15, 1974 |
CHARGE CONTROL AGENTS FOR LIQUID DEVELOPERS
Abstract
Liquid developer for developing an electrostatic latent image
present on an electrostatographic imaging surface comprising an
insulating liquid having dispersed therein positively charged
marking particles and also containing at least one charge control
agent selected from the group consisting of vinyltriethoxysilane,
.gamma.-glycidoxypropyltrimethoxysilane, and
.beta.-(3,4-epoxycyclohexyl)ethyltrimethoxysilane.
Inventors: |
Honjo; Satoru (Tokyo,
JA), Miyatuka; Hajime (Asaka, JA), Osawa;
Sadao (Kawaguchi, JA) |
Assignee: |
Rank Xerox, Ltd. (London,
EN)
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Family
ID: |
27283243 |
Appl.
No.: |
05/298,721 |
Filed: |
October 13, 1972 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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121537 |
Mar 5, 1971 |
3729419 |
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Foreign Application Priority Data
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Mar 12, 1970 [JA] |
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45-20984 |
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Current U.S.
Class: |
430/118.6;
430/115 |
Current CPC
Class: |
G03G
9/135 (20130101); C10M 2223/045 (20130101); C10M
2207/121 (20130101); C10M 2207/282 (20130101); C10M
2219/083 (20130101); C10N 2010/00 (20130101); C10N
2010/14 (20130101); C10M 2207/283 (20130101); C10M
2223/047 (20130101); C10M 2207/286 (20130101); C10M
2223/042 (20130101); C10N 2010/02 (20130101); C10M
2207/129 (20130101); C10M 2219/082 (20130101); C10M
2207/281 (20130101); C10N 2010/04 (20130101); C10M
2219/066 (20130101); C10M 2223/04 (20130101); C10M
2207/122 (20130101); C10M 2223/041 (20130101); C10N
2010/08 (20130101); C10M 2207/125 (20130101); C10N
2010/10 (20130101); C10M 2219/068 (20130101); C10N
2040/20 (20130101) |
Current International
Class: |
G03G
9/135 (20060101); G03G 9/12 (20060101); G03g
009/04 (); G03g 013/10 () |
Field of
Search: |
;117/37LE ;96/1LY
;252/62.1 ;106/20 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Sofocleous; Michael
Parent Case Text
This is a division, of application Ser. No. 121,537, filed Mar. 5,
1971 now U.S. Pat. No. 3,729,419.
Claims
What is claimed is:
1. A method of developing an electrostatic latent image of negative
polarity present on an imaging surface comprising contacting said
imaging member with an electrostatographic liquid developer
comprising an insulating carrier liquid and uniformly dispersed
therein finely divided positively charged electroscopic marking
particles, said liquid developer further comprising an amount of a
charge control agent which is soluble in said carrier liquid and
present in an amount of from about 0.5 to about 2.0 percent by
volume of the developer, said agent being selected from the group
consisting of vinyltriethoxysilane,
.gamma.-glycidoxy-propyltrimethoxysilane, and
.beta.-(3,4-epoxycyclohexyl)ethylitrimethoxysilane and mixtures
thereof sufficient to provide a stable positive charge on the
electroscopic marking particles.
2. A method of developing an electrostatic latent image according
to claim 1 wherein said liquid developer further comprises a
resinous fixing agent.
3. A method of developing an electrostatic latent image according
to claim 1 wherein said charge control agent is
vinyltriethoxysilane.
4. A method of developing an electrostatic latent image according
to claim 1 wherein said charge control agent is
.gamma.-glycidoxypropyltrimethoxysilane.
5. A method of developing an electrostatic latent image according
to claim 1 wherein said charge control agent is
.beta.-(3,4-epoxycyclohexyl)ethyltrimethoxysilane.
6. A method of developing an electrostatic latent image according
to claim 1 wherein said electroscopic marking particles are present
in the liquid developer in an amount of from about 2 to about 20
grams per liter.
Description
BACKGROUND OF THE INVENTION
This invention relates to liquid developers for use in
electrostatographic imaging systems, and more particularly, to
improved liquid developers with novel charge control agents.
The formation and development of images on the surface of
photoconductor material by electrostatic means is well known. The
basic electrostatographic process as taught by C. F. Carlson in
U.S. Pat. No. 2,297,691 involves placing a uniform electrostatic
charge on a photoconductive insulating layer, exposing the layer to
a light and shadow image to dissipate the charge on the areas of
the layer exposed to the light and developing the resulting
electrostatic latent image by depositing on the image a finely
divided electroscopic marking material referred to in the art as
"toner." The toner will normally be attracted to those areas of the
layer which retain a charge thereby forming a toner image
corresponding to the electrostatic latent image. The powder image
may then be transferred to a support surface such as paper and
permanently affixed to the support by any suitable means such as
heat fixing or solvent fixing. Alternatively, the powder image may
be fixed to the photoconductive layer if elimination of the powder
transfer step is desired. In addition, instead of latent image
formation by uniform charging followed by imagewise exposure, the
latent image may be formed by directly charging the layer in image
configuration. Other methods are known for applying electroscopic
particles to the imaging surface. Included within this group are
the "cascade" development technique disclosed by E. N. Wise in U.S.
Pat. No. 2,618,552; the powder cloud development technique
disclosed by C. F. Carlson in U.S. Pat. No. 2,221,776; and the
magnetic brush process disclosed, for example, in U.S. Pat. No.
2,874,063.
Development of an electrostatic latent image may also be achieved
with liquid rather than dry developer materials. In conventional
liquid development, more commonly referred to as electrophoretic
development, an insulating liquid vehicle having finely divided
solid material dispersed therein contacts the imaging surface in
both charged and uncharged areas. Under the influence of the
electric field associated with a charged image pattern, the
suspended particles migrate toward the charged portions of the
imaging surface separating out of the insulating liquid. This
electrophoretic migration of charged particles results in the
deposition of the charged particles on the imaging surface in image
configuration. Electrophoretic development of an electrostatic
latent image may, for example, be obtained by pouring the developer
over the image bearing surface, by immersing the imaging surface in
a pool of the developer or by presenting the liquid developer on a
smooth surface roller and moving the roller against the imaging
surface. The liquid development technique has been shown to provide
developed images of excellent quality and to provide particular
advantages over other development methods in offering ease in
handling.
Typically, the electrostatographic liquid developers are generally
dispersions comprising a highly insulating liquid referred to as
the carrier liquid and dispersed therein submicron size marking
particles which may comprise a pigment. In addition, fixing agents
such as resinous materials to assist in fixing the toner particles
to the support member and suspending or stabilizing agents may be
added to insure uniform suspension of the marking particles
throughout the insulating liquid.
To formulate the developer, the marking particles are first
dispersed within the continuous phase of any resinous material.
Conventional ballmill, three roll mill or sand mill may be employed
to provide a homogeneous mixture of resinous material and pigment
which is sometimes referred to as a paste or concentrate which may
be subsequently diluted with carrier liquid or dispersed in a large
volume of a carrier liquid to form the liquid developer. In
addition, if desired to improve the dispersion stability of the
developer, other additives such as surface active agents may be
added.
Furthermore, if desired, one may use concentrated dispersions
commercially available such as printing ink, tars or pitches in
which the pigment particles are already dispersed in a resinous
vehicle. Stable dilute dispersions of these can be prepared merely
by dissolving the paste in carrier liquids by means of, for
example, ultrasonic devices.
While a satisfactory degree of dispersion and dispersion stability
may be readily achieved in general most liquid developers other
necessary characteristics of the liquid developer are frequently
difficult to achieve and to maintain for an adequate period of
time. Since development is achieved by the migration of charged
particles through the insulating liquid in response to the charge
pattern on the imaging surface charge of proper polarity and
magnitude should be maintained on the charged particles. In
practice, however, considerable difficulty has been experienced in
maintaining this polarity and magnitude of charge on the individual
marking particles. The reasons for the alteration in polarity and
magnitude of charge on the charged particles are many and include
internal and external influences on the liquid developer. In order
to control the polarity and the magnitude of charge on the
individual marking particles, the practice of adding charge control
agents to the liquid developer has been employed. Very often these
control agents may also function for stabilizing or fixing
properties. The choice of materials, particularly resinous
materials, suitable for charge control agents is rather limited.
Conventionally, alkyd resins and linseed oil have served the dual
purpose in liquid developers of functioning not only as the vehicle
for the pigments, but also as the desired charge control agent to
impart a positive charge to the dispersed particles. However, the
suitability of these liquid developers is limited by the specific
materials and compositions which are capable of producing the
necessary charge control and the flexibility in developer
formulation is thereby limited. These limitations are even more
strict for printing inks, tars or pitches.
In addition, other additives frequently are employed to improve the
electrophoretic performance of liquid developer. Typically, these
additives are soluble in the carrier liquid and exhibit a marked
charged controlling capability without reducing the volume
resistivity of the liquid developer to a value lower than the
critical threshold. However, only a limited number of compounds
such as cobalt naphthenate, and copper oleate are capable of
meeting these requirements. Thus, there is a continuing need for
additional and more effective charge controlling agents for
electrostatographic liquid developers.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide liquid
developers which overcome the above noted deficiencies.
It is another object of this invention to provide novel charge
control agents for liquid developers.
It is another object of this invention to provide liquid developers
of high electrical resistivity including positively charged toner
particles.
It is another object of this invention to provide a liquid
developer capable of maintaining the desired polarity and magnitude
of charge on the individual marking particles.
It is another object of this invention to provide liquid developers
of increased flexibility in compositions which are easy to
formulate.
It is another object of this invention to provide an imaging method
capable of producing clear high density prints.
It is another object of this invention to provide a liquid
development method capable of consistent print quality.
The above objects and others are accomplished, generally speaking,
by employing as a charge controlling agent in electrostatographic
liquid developers selected organosilicon compounds. More
specifically, liquid developers of the present invention are
characterized in that they contain at least one compound selected
from the group consisting of vinyltriethoxysilane,
.gamma.-glycidoxypropyltrimethoxysilane, and
.beta.-(3,4-epoxycyclohexyl)ethyltrimethoxysilane in amounts of
from about 0.5 to about 2.0 percent by volume of the developer.
Since generally speaking, organosilicon compounds are sufficiently
polar to dissolve in alcohol, acetone or water thereby markedly
decreasing the volume resistivity of the developer it is quite
surprising that the three recited organosilicon materials are
capable of functioning as superior charge controlling agents for
electrostatographic liquid developers. This capability is believed
to be due to the fact that the materials according to this
invention are readily soluble in many nonpolar solvents such as
cyclohexane, kerosene, toluol, xylol and isoparaffinic
hydrocarbons.
A particularly important feature of the present invention lies in
the fact that it provides liquid developer capable of excellent
performance without requiring specialized complicated manufacturing
processes since the charge control function of the charge control
agents of this invention may be achieved merely by adding the
recited compounds to the dispersion of marking particles in the
insulating liquid. Furthermore, since the developer of the present
invention includes only positively charged toner, an image of
improved optical density may be obtained. In addition, since the
charge control agents of the present invention are so effective in
controlling the electrophoretic performance of the liquid developer
a wider selection of other additives and particularly resinous
materials is possible. The resinous materials which in the past
were unacceptable since they would not function alone adequately in
their charge controlling properties can now be used in conjunction
with the charge control agents of this invention to provide
superior liquid developers. Furthermore, the charge control agents
of the present invention may be used to improve the electrophoretic
performances of developers made from commercially available
printing inks, tars, or pitches. Since the charge control agents of
the present invention may be readily mixed with the liquid
developer the range of raw materials capable of use in liquid
developers may in some instances be greatly enlarged.
The organosilicon compounds may be present in the liquid developer
in any suitable amount. If too small an amount is incorporated in
the liquid developer, the charge controlling effect is inadequate.
On the other hand, if too large an amount of charge control agent
is added to the liquid developer, the volume resistivity of the
developer may be lowered to a degree such that on contact with the
developer, an electrostatic charge pattern may be discharged. In
addition, in some cases, coagulation of marking particles may
occur. Typically, the charge control agent is present in an amount
of from about 0.5 to about 2.0 percent by volume of the developer.
The charge control agents of the present invention may be added to
any suitable electrostatographic liquid developers. Typically, the
liquids employed have relatively high insulating values generally
having a volume resistivity greater than about 10.sup.10 ohm-cm so
as not to effect the electrostatic charge pattern on the insulating
layer and low dielectric constant of less than about 3.5. Typical
specific vehicles include hydrocarbons such as benzene, xylene,
hexane, naphtha, kerosene, cyclohexane, Decalin, isoparaffinic
hydrocarbons and halogenated hydrocarbons such as carbon
tetrachloride, trichloroethylene, and chloroform. Typical
electroscopic marking particles include among others, charcoal,
carbon black, magnesium oxide, lithopone, cadmium yellow, chrome
yellow, cobalt blue, cadmium red, burnt siena, Hansa yellow, rose
bengal and phthalocyanine which are present in an amount of from
about 2 to about 20 grams per liter. The electroscopic marking
particles are conventionally dispersed and suspended in the liquid
by stirring or agitation and where a highly uniform and stable
suspension is desired, this suspension may be passed through a
colloid mill. As discussed above, if desired, suspending or
dispersing agent may be added for their well known functions.
The liquid developer according to the present invention may be
employed to develop an electrostatic charge pattern present on any
suitable imaging surface. Basically, any material capable of
holding the charge pattern may be employed. Typical materials
include dielectric layers and photoconductors. A particularly
preferred material for use in automatic copiers is a photosensitive
paper comprising photoconductive pigment particles in an insulating
binder layer. Typically, this paper comprises zinc oxide
photoconductive particles present in an insulating binder layer
which is overcoated on the paper substrate. The particular imaging
member and particular development technique may be readily
determined by one skilled in the art. The photosensitive paper
described above, for example, may be substituted with
photoconductive materials made from cadmium sulfide, zinc sulfide,
zinc selenide, cadmium selenide, titanium dioxide, phthalocyanine
and polyvinylcarbazole.
DESCRIPTION OF PREFERRED EMBODIMENTS
The following preferred examples further define and describe the
preferred materials and methods of the present invention. Examples
II, III and V are presented for comparative purposes. Unless
otherwise indicated, all parts and percentages are by weight.
EXAMPLE I
An electrostatic latent image present on an electrophotographic
member which has been uniformly charged and exposed to a light and
shadow pattern in conventional manner is developed by contacting
the surface with a liquid developer formed in the following manner:
To 1,000 ml of kerosene, 5 grams of black offset printing ink "Jet
King G process H Black" (commercially available from Toyo Ink
Manufacturing Company) is added and dispersed therein by means of
an ultrasonic dispersing device. To this dispersion 1.0 percent by
volume of developer of vinyltriethoxysilane (available from
Shin-etsu Chemical Industry under the tradename "KBE 1003+") is
added to provide a liquid developer wherein the carbon black is
positively charged. When applied to the surface of the
electrophotographic plate, a black tar image having high optical
density is obtained. Upon repeated development, no change in print
quality is observed.
EXAMPLE II
The procedure of Example I is repeated except that the
vinyltriethoxysilane is omitted from the liquid developer. While
the toner particles remain positively charged in this liquid
developer, the electrophoretic performance of the developer
fluctuates from portion to portion of the original printing
ink.
EXAMPLE III
An electrostatic latent image of negative polarity is formed on an
electrophotographic plate by charging the plate negatively and
exposing it to a light and shadow pattern in conventional manner.
The electrostatic latent image is developed with a liquid developer
made in the following manner: Two grams of channel black and 50
grams of an alkyd resin purchased from Japan Reichold Chemical
Industry under the tradename "Beckosol EL 8002" are blended in a
500 ml ball mill jar for about two days to prepare a concentrated
paste which is subsequently dispersed in about 2,000 ml of an
isoparaffinic solvent (Isopar H, available from Humble Oil and
Refining Company). The majority of the toner particles in this
liquid developer acquire a positive charge. However, particles
bearing a negative charge are also present and when the developer
is applied to the electrophotographic plate a low density toner
image with hallow and streaks around high contrast image areas is
obtained.
EXAMPLE IV
The procedure of Example III is repeated except that about 1.0
percent by volume of the developer of
beta-(3,4-epoxycyclohexyl)ethyltrimethoxysilane (available as "KBM
303" from Shin-etsu Chemical Industries) is added to the liquid
developer described in Example III. Development of the
electrostatic latent image on the electrophotographic plate
provides print of reduced hallow and streaks as well as increased
image density.
EXAMPLE V
An electrostatic latent image present on an electrophotographic
plate which has been conventionally uniformly negatively charged
and exposed to a light and shadow pattern is developed with a
liquid developer prepared in the following manner: A homogeneous
paste is prepared by blending about 200 grams of R--4 varnish
available from Toyo Ink Manufacturing Company and about 10 grams of
channel black in a three roll mill. Fifty grams of this paste are
dispersed in 2,000 mil of kerosene in an ultrasonic dispersing
device. When used to develop the electrostatic latent image present
on the electrophotographic member, the electrophoretic performance
of this liquid developer is observed to change depending on the
manufacturing conditions of the developer. In general, a very
unclear low density image is produced.
EXAMPLE VI
The procedure of Example I is repeated except that 1.5 percent by
volume of the developer of .gamma.-glycidoxypropyltrimethoxysilane
("KBM 403" available from Shin-etsu Chemical Industries) is added
to the liquid developer. When employed as a liquid developer in the
development of electrostatic latent images present on
electrophotographic layers, a stable positively charged
electrophoretic developer is observed to provide consistent print
quality with a marked reduction in performance fluctuation.
Although specific materials and operational techniques are set
forth in the above exemplary embodiments using the charge control
agents and techniques of this invention, they are merely intended
as illustrations of the present invention. There are other
materials and techniques than those listed above which may be
substituted for those in the examples with similar results. Other
modifications of the present invention will occur to those skilled
in the art upon a reading of the present disclosure which
modifications are intended to be included within the scope of this
invention.
* * * * *