U.S. patent number 3,900,588 [Application Number 05/445,389] was granted by the patent office on 1975-08-19 for non-filming dual additive developer.
This patent grant is currently assigned to Xerox Corporation. Invention is credited to Donald J. Fisher.
United States Patent |
3,900,588 |
Fisher |
August 19, 1975 |
Non-filming dual additive developer
Abstract
An imaging technique and composition for developing
electrostatographic latent images is given whereby a developer
composition is employed comprising toner, a substantially smearless
polymeric additive, and an abrasive material.
Inventors: |
Fisher; Donald J. (Pittsford,
NY) |
Assignee: |
Xerox Corporation (Stamford,
CT)
|
Family
ID: |
23768711 |
Appl.
No.: |
05/445,389 |
Filed: |
February 25, 1974 |
Current U.S.
Class: |
430/119.81;
430/108.1; 430/101; 427/469 |
Current CPC
Class: |
G03G
9/08717 (20130101); G03G 9/09725 (20130101); G03G
9/08715 (20130101); G03G 9/09708 (20130101); G03G
9/0906 (20130101); G03G 9/10 (20130101) |
Current International
Class: |
G03G
9/09 (20060101); G03G 9/10 (20060101); G03G
9/097 (20060101); G03G 9/087 (20060101); G03g
009/02 (); G03g 013/08 () |
Field of
Search: |
;117/17.5 ;252/62.1
;96/1SD |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Sofocleous; Michael
Claims
What is claimed is:
1. An imaging process comprising the steps of:
a. forming an electrostatic latent image on an imaging surface;
b. developing said latent image by bringing an electrostatographic
developing mixture within the influence of said latent image, said
developing mixture comprising particles, said particles including
(1) finely divided electroscopic toner material, (2) a minor
portion, based upon the weight of said toner material of a stable,
tough, substantially smearless, polymeric additive having an
average particle size less than about the average particle size of
said finely divided toner material, and (3) a minor proportion
based on the weight of said toner material of a finely divided,
nonsmearable, abrasive material of a hardness greater than said
polymeric additive and toner materials;
c. removing the residual developed image from said imaging surface
by a force which causes the toner, polymeric additive and abrasive
materials of said developing mixture to be wiped across at least a
portion of said imaging surface; and
d. repeating the process sequence at least one additional time.
2. The imaging process of claim 1 wherein said particles include
carrier particles which are grossly larger than said finely divided
toner material.
3. The imaging process of claim 1 wherein said force is applied via
a cleaning blade.
4. The imaging process of claim 1 wherein said force is applied via
a cleaning web.
5. The imaging process of claim 1 wherein said force is applied via
a cleaning brush.
Description
BACKGROUND OF THE INVENTION
This invention relates to imaging systems, and more particularly,
to improved electrostatographic developing materials, their
manufacture and use.
The formation and development of images on the surface of
photoconductive materials 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 layers exposed to the light and developing the resulting
electrostatic latent image by depositing on the image a finely
divided electroscopic 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. This powder image may then be
transferred to a support surface such as paper. The transferred
image may substantially be permanently affixed to the support
surface as by heat. Instead of latent image formation by uniformly
charging the photoconductive layer and then exposing the layer to a
light and shadow image, one may form the latent image by directly
charging the layer in image configuration. The powder image may be
fixed to the photoconductive layer if the powder image transfer
step is not desired. Other suitable fixing means such as solvent or
overcoating treatment may be substituted for the foregoing heat
fixing step.
Several methods are known for applying the electroscopic particles
to the electrostatic latent image to be developed. One development
method, as disclosed by E. N. Wise in U.S. Pat. No. 2,618,552 is
known as "cascade" development. In this method, a developer
material comprising relatively large carrier particles having
finely divided toner particles electrostatically coated thereon is
conveyed to and rolled or cascaded across the electrostatic image
bearing surface. The composition of the carrier particles is so
selected as to triboelectrically charge the toner particles to
their desired polarity. As the mixture cascades or rolls across the
latent image bearing surface, the toner particles are
electrostatically deposited and secured in positive development
processes to the charged portion of the latent image and are not
deposited on the uncharged or background portions of the image.
Most of the toner particles accidentally deposited in the
background areas are removed by the rolling carrier, due
apparently, to the greater electrostatic attraction between the
toner and the carrier than between the toner and the discharged
background. The carrier and excess toner are then recycled. This
technique enhances development of line copy images.
Another method for developing electrostatic images is the "magnetic
brush" process as disclosed, for example, in U.S. Pat. No.
2,874,063. In this method, a developer material containing toner
particles and magnetically attractable carrier particles are
carried by a magnet. The magnetic field of the magnet causes
alignment of the magnetically attractable carrier particles into a
brushlike configuration. This "magnetic brush" is engaged with the
electrostatic image bearing surface and the toner particles are
drawn from the brush to the latent image by electrostatic
attraction.
Still another technique for developing electrostatic latent images
is the "powder cloud" process as disclosed, for example, by C. F.
Carlson in U.S. Pat. No. 2,221,776.
Other development methods such as "touchdown" development as
disclosed by R. W. Gundlach in U.S. Pat. No. 3,166,432 may be used
where suitable.
Generally, commercial electrostatographic development systems
utilize automatic machines. Since automatic electrostatographic
imaging machines should operate with a minimum of maintenance, the
developer employed in the machines should be capable of being
recycled through many thousands of cycles. In automatic xerographic
equipment, it is conventional to employ an electrostatographic
plate which is charged, exposed and then developed by contact with
a developer mixture. In some automatic machines, the toner image
formed on the electrostatographic plate is transferred to a
receiving surface and the electrostatographic plate is then cleaned
for reuse. Transfer is effected by a corona generating device which
imparts an electrostatic charge to attract the powder from the
electrostatographic plate to the recording surface. The polarity of
charge required to effect image transfer is dependent upon the
visual form of the original copy relative to the reproduction and
to the electroscopic characteristics of the developing material
employed to effect development. For example, where a positive
reproduction is to be made of the positive original, it is
conventional to employ a positive corona to effect transfer of a
negatively charged toner image to the recording surface. When a
positive reproduction from a negative original is desired, it is
conventional to employ positively charged toner which is repelled
by the charged areas on the plate to the discharged areas thereon
to form a positive image which may be transferred by negative
polarity corona. In either case, a residual powder image usually
remains on the image after transfer. Because the plate may be
reused for a subsequent cycle, it is necessary that the residual
image be removed to prevent further charging and redevelopment of
the same image. In a positive to positive reproduction process
described above, the residual powder is tightly retained on the
plate surface by a phenomenon not fully understood which prevents
complete transfer of the powder to the support surface,
particularly in the image area. Incomplete transfer of toner
particles is undesirable because image density of the ultimate copy
is reduced and highly abrasive photoreceptor cleaning techniques
are required to remove the residual toner from the photoreceptor
surface. This imaging process is ordinarily repeated from each copy
reproduced by the machine any time during the reusable life of the
developer and the electrophotographic plate surface.
Various electrostatographic plate cleaning devices such as the
"brush" and the "web" cleaning apparatus are known in the prior
art. A typical brush cleaning apparatus is disclosed by L. E.
Walkup et al in U.S. Pat. No. 2,832,977. The brush type cleaning
means usually comprises one or more rotating brushes, which remove
residual powder from the plate into a stream of air which is
exhausted through a filtering system. A typical web cleaning device
is disclosed by W. E. Graff, Jr. et al. in U.S. Pat. No. 3,186,838.
As disclosed by Graff, Jr. et al., removal of the residual powder
on the plate is effected by passing a web of fibrous materials over
the plate surface. Another useful system for removing residual
toner particles from the surface of a photoreceptor comprises a
flexible cleaning blade which wipes, scrapes, or otherwise removes
the residual toner from the photoreceptor surface as the surface
moves past the blade.
The foregoing cleaning systems do not, however, remove all types of
toner particles from all types of reusable photoreceptors. This is
not a shortcoming of the cleaning system by itself. If a particular
toner would not tend to form an adherent residual film on a
particular photoreceptor, the cleaning systems described would
effectively remove all residual toner. However, many commerical
toners of their very nature do tend to form a residual film on
reusable photoreceptors and such films are undesirable because
their presence adversely affects the quality of the undeveloped and
developed images. The toner film problem is particularly acute in
high speed copying and duplicating machines where contact between
the developer and the imaging surface occurs a great many more
times and at a higher velocity than in conventional
electrostatographic systems. Ultimately, the toner buildup becomes
so great that effective copying or duplicating is impaired.
In such systems there is a continuing need to have developers which
exhibit high, long term triboelectric stability, while at the same
time assisting in the elimination of buildup of toner film.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to provide a
developer composition which assists in the elimination of toner
film buildup.
It is another object of the invention to provide a developer
composition which improves solid area print density.
It is a further object of the invention to provide a developer
composition which reduces background density of copies.
It is yet another object of the invention to provide a developer
composition having enhanced and stabilized triboelectric
characteristics.
Other objects and advantages will be found from a full and complete
understanding of the invention.
The above objects and others are surprisingly accomplished by
providing an electrostatographic developing composition comprising
particles; said particles including (1) a finely divided
electroscopic toner material; (2) a minor portion, based upon the
weight of said toner material, of a stable, tough, substantially
smearless, polymeric additive, and (3) a minor portion, based upon
the weight of said toner material, of a finely divided nonsmearable
abrasive material having a hardness greater than said polymeric
additive and said toner material.
Thus, the developer composition of the present invention comprises
three constituents, a toner material and a dual additive comprising
a substantially smearless polymeric material and a finely divided
abrasive type material.
Other objects of the invention are accomplished through a cyclic
imaging and development process comprising forming an electrostatic
latent image on an imaging surface and forming a developed image by
contacting said imaging surface with an electrostatographic
developing mixture comprising particles, said particles including
(1) finely divided electroscopic toner material, (2) a minor
proportion based on the weight of said toner of a tough, stable,
substantially smearless polymeric additive material, and (3) a
minor proportion based on the weight of said toner material of a
finely divided, nonsmearable, abrasive material of a hardness
greater than said friction-reducing and toner materials; removing
at least a portion of at least any residual developed image from
said imaging surface by a force which causes the developer mixture
to be wiped across at least a portion of said imaging surface; and
repeating the process sequence at least one additional time.
The toner material of the present invention may be any
electroscopic toner material which preferably is pigmented or dyed.
Typical toner materials include polystyrene resin, acrylic resin,
polyethylene resin, polyvinyl chloride resin, polyacrylamide resin,
methacrylate resin, polyethylene terephthalate resin, polyamide
resin, and copolymers, polyblends, and mixtures thereof. Vinyl
resins having a melting point or melting range starting at least
about 110.degree.F are especially suitable for use in the toner of
this invention. These vinyl resins may be a homopolymer or a
copolymer of two or more vinyl monomers. Typical monomeric units
which may be employed to form vinyl polymers include: styrene,
vinyl naphthalene, mono-olefins, such as, ethylene, propylene,
butylene, isobutylene and the like, vinyl esters, such as vinyl
acetate, vinyl propionate, vinyl benzoate, vinyl butryrate and the
like, esters of alphamethylene aliphatic monocarboxylic acids such
as methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl
acrylate, dodecyl acrylate, n-octyl acrylate, methyl methacrylate,
ethyl methacrylate, butyl methacrylate and the like; vinyl ethers
such as vinyl methyl ether, vinyl isobutyl ether, vinyl ethyl
ether, and the like; vinyl ketones such as vinyl methyl ketone,
vinyl hexyl ketone, methyl isopropyl ketone and the like; and
mixtures thereof. Suitable materials employed as the toner will
usually have an average molecular weight between about 3,000 to
about 500,000.
Any suitable pigment or dye may be employed as the colorant for the
toner particles. Toner colorants are well known and include, for
example, carbon black, nigrosine dye, aniline blue, Calco Oil Blue,
chrome yellow, ultramarine blue, duPont Oil Red, quinoline yellow,
methylene blue chloride, phthalocyanine blue, Malachite Green
Oxalate, lamp black, Rose Bengal and mixtures thereof. The pigment
or dyes should be present in the toner in a sufficient quantity to
render it highly colored so that it will form a clearly visible
image on a recording member. Thus, for example, where conventional
xerographic copies of typed documents are desired, the toner may
comprise a black pigment such as carbon black or a black dye such
as Amaplast Black Dye available from the National Aniline Products,
Incorporated. Preferably, the pigment is employed in an amount of
from about 1 percent to about 30 percent, by weight, based on the
total weight of the colored toner. If the toner colorant employed
is a dye, substantially smaller quantities of the colorant may be
used.
The additives may be introduced into the ultimate developer
material in any suitable manner to form a physical mix of additive
particles with developing material particles. Thus, for example,
the additive particles may be initially mixed with carrier
particles or toner particles and thereafter introduced into the
developer mix. Generally, when the additives are physically mixed
with toner or carrier particles, satisfactory results are achieved
when about 0.11 to about 15 percent additives based on the weight
of the toner particles is employed. Greater cleaning efficiency at
reduced cleaning pressures is achieved when the additives are
present in an amount from about 0.1 percent to about 5 percent
based on the weight of the toner in the final developer
mixture.
Any suitable stable, tough, smearless, solid, polymeric additive
having a Rockwell hardness (ASTM Test D/785) of at least about R-10
may be employed in the developer of this invention. Undesirable
filming of the additive is inhibited by employment of tough
additive particles having a Rockwell hardness of about R-10. If
desired, additive materials having a Rockwell hardness as high as
about R-120 may be utilized to form the developer of this
invention. Generally, the additive particles have an average
particle size less than about the particle size of the toner
particles. An average particle size from about 0.05 to about 30
microns is preferred because more copies of higher quality images
may be obtained. Particularly good results are obtained with an
average particle size range from about 0.20 micron to about 8
microns because efficient cleaning is achieved without adversely
affecting image density as a result of additive particles present
in transferred toner images. The additives of this invention may be
of any suitable shape. Typical shapes include flake, cylindrical,
spherical, granular and irregular paricles. Optimum results are
obtained with additive particles having a spherical shape because
more effective removal of residual toner particles at lower
cleaning pressures is achieved, particularly with a blade cleaning
system.
Generally, polymeric additive materials more electronegative than
sulfur are preferred because a greater number of higher quality
images can be obtained on reusable photoreceptors with scraping
devices such as doctor blades. Whether a material is more
electronegative than sulfur may be determined by known techniques
such as by determining the position of the additive material
relative to sulfur in a triboelectric series. The materials in a
triboelectric series are arranged in such a way that each material
is charged with positive electricity when contacted with any
material below it in the series and with negative electricity when
contacted with any material above it in the series. Thus any
material which acquires a negative charge when contacted with
sulfur may be considered more electronegative than sulfur and
obviously would be below sulfur in the triboelectric series.
Typical stable, solid, polymeric additive materials below sulfur in
the triboelectric series include: polyvinylidene fluoride,
polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinyl
fluoride, polyvinylchloride, polyvinylidine chloride, polyethylene,
polypropylene, chlorinated polyethylene, chlorinated polyether,
copolymers of tetrafluoroethylene and chlorotrifluoroethylene,
copolymers of tetrafluoroethylene and hexafluoropropylene,
copolymers of tetrafluoroethylene and vinylidine fluoride,
copolymers of chlorotrifluoroethylene and vinylidine fluoride,
copolymers of vinyl chloride and vinyl fluoride, copolymers of
vinyl chloride and polyethylene, copolymers of vinyl chloride and
polypropylene and mixtures of any of the above homopolymers or
copolymers. Homopolymers or copolymers of fluoro-olefins detailed
above are preferred because a greater number of high quality copies
can be obtained on a reusable photoreceptor surface.
The combination of the resin component, colorant, polymeric
additive and abrasive additive, whether the resin component is a
homopolymer, copolymer or blend, should have a blocking temperature
of at least about 110.degree.F. When the toner is characterized by
a blocking temperature less than about 110.degree.F. the toner
particles tend to agglomerate during storage and machine operation
and also from undesirable films on the surface of reusable
photoreceptors which adversely affect image quality.
The toner compositions of the present invention may be prepared by
any well-known toner mixing and comminution technique. For example,
the ingredients may be thoroughly mixed by blending, mixing and
milling the components and thereafter micropulverizing the
resulting mixture. Another well-known technique for forming toner
particles is to spray-dry a ball-milled toner composition
comprising a colorant, a resin and a solvent. When the toner
mixtures of this invention are to be employed in a cascade
development process, the toner should have an average particle size
by weight percent less than about 30 microns and preferably between
about 4 and about 20 microns for optimum results.
Preferably, the additives of this invention are selected from
materials having a lower critical surface tension than the critical
surface tension of the toner employed therewith. Normally, a
difference in critical tension value of at least about 2 dynes per
centimeter between the toner and the additive is preferred for
optimum cleaning and image quality. Good results are obtained with
developer material comprising colored toner particles having a
critical surface tension value greater than about 24 dynes per
centimeter in combination with additives having a critical surface
tension value less than about 33 dynes per centimeter. Typical
polymeric materials having a critical surface tension value less
than about 33 dynes per centimeter include: polyvinylidine
fluoride, polytetrafluoroethylene, polychlorotrifluoroethylene,
polyvinyl fluoride, copolymers of tetrafluoroethylene and
chlorotrifluoroethylene, copolymers of tetrafluoroethylene and
hexafluoropropylene, copolymers of chlorotrifluoroethylene and
vinylidene fluoride, and mixtures thereof. Excellent results are
obtained with polyvinylidine fluoride. Developers containing
polyvinylidine fluoride additives form the greatest number of dense
background free images on reusable imaging surfaces.
A number of pigmented or dyed electroscopic toner material having a
critical surface tension value greater than about 24 dynes per
centimeter are described in the patent literature. Typical toner
materials having a critical surface tension value greater than
about 24 dynes per centimeter include polystyrene resin, acrylic
resin, polyethylene resin, polyvinyl chloride resin, polyacrylamide
resin, methacrylate resin, polyethylene terephthalate resin,
polyamide resin, polyamide epichlorohydrin resin, resinous
condensation product of 2,2 bis (4-hydroxy-isopropoxy-phenyl) -
propane and fumaric acid, and copolymers, polyblends and mixtures
thereof.
The critical surface tension values of many solid surfaces are well
known. For further details as to the determination of the critical
surface tension of a solid surface, reference is made to the
discussion in the Journal of Colloid Science, Vol. 7, 1952
beginning at page 109. The critical surface tension values employed
herein are based on measurements made between about 20.degree.C and
about 25.degree.C.
With no intention of being bound by any theory of action, is is
believed that the use of a tough, stable, substantially smearless
polymeric additive material with a nonsmearing abrasive reduces
toner impaction and assists in enhancing the long term
triboelectric properties of the developer. It is this which is
believed to help in forming and maintaining good high density image
quality while reducing background.
Contemplated abrasive materials include colloidal silica, surface
modified organophilic silica, aluminum silicate, surface treated
aluminum silicate, titanium dioxide, alumina, calcium carbonate,
antimony trioxide, barium titanate, calcium titanate or strontium
titanate, CaSiO.sub.3, MgO, ZnO, ZrO.sub.2 etc. and mixtures
thereof.
The particularly preferred materials are these which have been
surface modified to impart hydrophobic characteristics thereto. For
example, hydrophobic silicas are prepared by reacting freshly
prepared colloidal silica with at least one organosilicon compound
having hydrocarbon groups as well as hydrolyzable groups attached
to its silicon atom. In one technique, the reactants and steam are
pneumatically introduced in parallel flow into a fluidized bed
reactor heated to about 400.degree.C. The organosilicon compound
reacts with silanol groups on the surface of the SiO.sub.2
particles and chemical attachment between the silicon atom in the
organosilicon compound and the silicon atom in the SiO.sub.2 occurs
through an oxygen atom. Any suitable hydrocarbon or substituted
hydrocarbon organic group directly attached to a silicon atom in
the organosilicon compound may be employed in preparing the
modified silica. The organic group is preferably one which imparts
hydrophobic characteristics to the abrasive material to improve the
stability of developer materials under varying humidity conditions.
The organic groups may comprise saturated or unsaturated
hydrocarbon groups or derivatives thereof. Saturated organic groups
include methyl, ethyl, propyl, butyl, chloropropyl and chloromethyl
groups. Examples of typical organosilicon compounds include:
dimethyl dichlorosilane, trimethyl chlorosilane, methyl
trichlorosilane, vinyl triethoxy silane. The type of organo groups
can influence the triboelectric characteristics of the developer.
For example, aminopropylsilane treated with silica can be used in a
reversal type developer.
The particle size of the abrasive additive should a fall within the
submicron range of from about 1 to about 500 millimicrons and
preferably, between about 10 to about 100 millimicrons.
Concerning the comparative hardness of the abrasive type material,
this material must be harder than both the toner material and the
polymeric additive material. While most of the materials disclosed
can be considered to be very hard materials falling within Mohs'
hardness scale, it is to be understood that any material of less
hardness than talc of Mohs' hardness scale can also be employed so
long as it is harder than the toner material and polymeric additive
material. Materials softer than talc are conveniently classified
according to the Shore durometer penetration technique and placed
within either scale A, B, C and D of this test procedure.
The chemical composition of the abrasive additive is not critical
so long as it does not introduce deleterious contaminents or
adversely affect the imaging and development aspects of an
electrostatographic system. In addition, there is no particular
criticality surrounding the shape of each abrasive particle since
both spherical and irregularly shaped additives function
effectively. Preferred materials are Aerosil R972, a hydrophobic
silica available from DeGussa Incorporated, New York, New York and
Kaophile-2, a hydrophobic aluminum silicate, available from Georgia
Kaolin Company Elizabeth, New Jersey.
The composition of the present invention finds utility in all known
electrostatographic development systems. This includes systems
which employ a carrier material such as magnetic brush development
and cascade development as well as systems which do not necessarily
employ a carrier material such as powder cloud development, fiber
brush development and touchdown development.
Suitable coated and uncoated carrier materials and consumable
carrier materials which are known, are useful with this
invention.
Many typical carriers are described in U.S. Pat. No. 2,618,552. An
ultimate coated particle diameter between about 50 microns to about
2000 microns is preferred because the carrier particles then
possess sufficient density and inertia to avoid adherence to the
electrostatic images during the cascade development process.
Adherence of carrier beads to electrostatic drums is undesirable
because of the formation of deep scratches on the surface during
the image transfer and drum cleaning steps. Also, print deletion
occurs when large carrier beads adhere to xerographic imaging
surfaces. For magnetic brush development, carrier particles having
an average particle size less than about 8000 microns are
satisfactory. Generally speaking, satisfactory results are obtained
when about 1 part toner is used with about 10 to about 1000 parts
by weight of carrier in the cascade and magnetic brush
developers.
Concerning the broad relative proportions of the toner material
versus the additive materials, the polymeric additive material
should be present in an amount of about 0.1 percent to about 10
percent by weight based upon the toner. A particularly preferred
ratio is from about 0.1 percent to about 5 percent by weight of
polymeric additive material based on the weight of toner.
Generally, it has been found that from about 0.01 percent to about
5 percent by weight of abrasive material based on the weight of the
toner material will achieve the desired results. A particularly
preferred range is from about 0.1 to about 1 percent by weight.
The toner compositions of the instant invention may be employed to
develop electrostatic latent images on any suitable electrostatic
latent image bearing surface including conventional photoconductive
surfaces. Well known photoconductive materials include: vitreous
selenium, organic or inorganic photoconductors embedded in a
nonphotoconductive matrix, organic or inorganic photoconductors
embedded in a photoconductive matrix or the like. Representative
patents in which photoconductive materials are disclosed include:
U.S. Pat. No. 2,803,542 to Ullrich, U.S. Pat. No. 2,970,906 to
Bixby, U.S. Pat. No. 3,121,006 to Middleton, U.S. Pat. No.
3,121,007 to Middleton and U.S. Pat. No. 3,151,982 to Corrsin.
In U.S. Pat. No. 2,986,521, Wielicki, there is taught a reversal
type developer powder for electrostatic printing comprising
electroscopic material, i.e. toner, coated with a finely divided
colloidal silica. The toner material must have (1) a positive
triboelectric relationship with respect to the silica and (2) the
silica coated toner must be repelled from negatively charged areas
of an imaging surface. The only positively stated purpose or
utility for the silica is to reduce tackiness and improve the free
flowing characteristics of the developer powder.
In copending U.S. Ser. No. 31,353, filed on Apr. 23, 1970 in the
name of Chatterji, it is taught that the inclusion at a minor
proportion of similar polymeric additives in an electrostatic
developer overcomes certain problems associated with the use of
prior art toner materials.
In U.S. Pat. No. 3,522,850 issued to Stephen F. Royka et al., it is
taught to employ a dry lubricant when employing a blade cleaner in
an electrostatographic imaging system. This patent, however, does
not teach the use of a combination of additives to control tribo
and improve print density.
In U.S. Pat. No. 3,720,617 issued to Chatterji et al., it is taught
to employ silica as an additive in an electrostatographic imaging
system. This patent does not teach or recognize the enhance
properties possible with the use of the additional polymeric
additive of this invention.
In Ser. No. 188,570 filed Oct. 12, 1971, in the name of Jugle et
al., now abandoned in favor of continuing application Ser. No.
443,659 filed Feb. 19, 1974, it is taught to use a smearable
additive and an abrasive to control the coating of the smearable
additive on the photoreceptor during repeated cyclic imaging. This
patent does not teach or recognize the enhance properties by using
a nonsmearable additive in conjunction with an abrasive additive,
nor does it recognize that toner impaction can be reduced by the
unique technique given in this specification.
The following examples further define, describe and compare
exemplary methods of preparing the development system components of
the present invention and of utilizing them in a development and
cleaning process. Parts and percentages are by weight unless
otherwise indicated.
EXAMPLE I
The vitreous selenium drum of an automatic copying machine is
corona charged to a positive voltage of about 800 volts and exposed
to a light-and-shadow image to form an electrostatic latent image.
The selenium drum is then rotated through a cascade development
station. A control developer comprising 1 part toner having a
critical surface tension value of about 30 dynes per centimeter and
containing a styrene-butyl methacrylate copolymer and about 10
percent by weight carbon black is prepared by the method disclosed
in Example I of U.S. Pat. No. 3,079,342 and about 100 parts steel
core carrier beads prepared by the process disclosed in U.S. Pat.
No. 2,618,551 is employed in the developer station. The toner
particles have an average particle size of about 10 microns and the
carrier beads have an average particle size of about 450 microns.
After the electrostatic latent image is developed in the developing
station, the resulting toner image is transferred to a sheet of
paper at a transfer station. The residual toner particles remaining
on the selenium drum after passage through the transfer station is
removed by means of a cleaning blade comprising a rectangular strip
of about 3/32 inch thick polyurethane elastomer having an edge
spring biased against the photoreceptor surface. The trailing face
of the cleaning blade is positioned to form an acute angle of about
22 with the line of tangency extending through the line of blade
contact. Sufficient pressure is applied to the blade to obtain
maximum removal of the toner particles from the drum surface. The
drum surface is rotated at a surface speed of about 10 inches per
second past the cleaning blade and 500 copies are made. After only
a few copies are made, the copies and drum surface are examined for
quality and condition, respectively, The copies made at the start
and near the termination of the test are characterized by high
background, streak marks, and irregular image density. Large
portions of the drum are covered by a continuous toner film and
occasional streaks and scratch marks. The electrical properties of
the drum are measured and found to be erratic along the surface due
to the toner deposits and scratches.
EXAMPLE II
The procedure of Example I is repeated under substantially the same
conditions except that about 1 part of polyvinylidene fluoride
particles and 0.25 part of hydrophobic silica are added to about
100 parts toner particles. The polyvinylidene fluoride (Kynar
201-Pennwalt Chemical Corporation) particles have a spherical
shape, a particle size range from about 0.3 micron to about 0.4
micron, Shore D hardness (ASTM Test D676) of about 70-80 (Rockwell
hardness 80-95). The silica is Aerosil R972. A fresh vitreous
selenium drum is also substituted for the drum employed in Example
I. After about 5,000 cycles, the copies, the drum surface, and the
carrier particles are examined for quality and conditions,
respectively. The copies formed throughout the test are
characterized by high density print quality and substantially no
background toner deposits. The electrical properties of the drum
are measured and are found to exhibit substantially the same
responses before and after the test. The drum surface shows no
signs of toner-filming, streaks, or scratches. After long term use,
the carrier triboelectric properties are xerographically enhanced
over a sample without silica.
The expression "developer material" as employed herein is intended
to include electroscopic toner material or combinations of toner
material and carrier material.
Although specific materials and conditions are set forth in the
foregoing examples, these are merely intended as illustrations of
the present invention. Various other suitable toner components,
additives, colorants and development techniques such as those
listed above may be substituted for those in the examples with
similar results. Other materials may also be added to the toner or
carrier to sensitize, synergize or otherwise improve the imaging
properties or other desirable of the system.
Other modifications of the present invention will occur to those
skilled in the art upon a reading of the present disclosure. These
are intended to be included within the scope of this invention.
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