U.S. patent number 3,833,366 [Application Number 05/307,748] was granted by the patent office on 1974-09-03 for carrier compositions.
This patent grant is currently assigned to Xerox Corporation. Invention is credited to Robert Joseph Hagenbach, Robert William Madrid.
United States Patent |
3,833,366 |
Madrid , et al. |
September 3, 1974 |
CARRIER COMPOSITIONS
Abstract
A carrier for electrostatographic developer mixtures is provided
comprising a core surrounded by a pre-coated partially cured thin
film of a silicone, over-coated with an unsaturated polyester, said
silicone chemically coupling said polyester to said core upon
curing.
Inventors: |
Madrid; Robert William
(Macedon, NY), Hagenbach; Robert Joseph (Rochester, NY) |
Assignee: |
Xerox Corporation (Rochester,
NY)
|
Family
ID: |
26975906 |
Appl.
No.: |
05/307,748 |
Filed: |
November 17, 1972 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
814437 |
Apr 8, 1969 |
|
|
|
|
Current U.S.
Class: |
430/111.1;
428/405; 430/123.58 |
Current CPC
Class: |
G03G
9/1136 (20130101); G03G 9/1137 (20130101); G03G
9/1131 (20130101); G03G 9/1135 (20130101); Y10T
428/2995 (20150115) |
Current International
Class: |
G03G
9/113 (20060101); G03g 009/02 (); G03g
013/08 () |
Field of
Search: |
;117/17.5,1S,124E,124F,72,75,1B,1M,1C ;252/62.1 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Sofocleous; Michael
Parent Case Text
This is a continuation of application Ser. No. 814,437, now
abandoned, filed in the United States on Apr. 8, 1969.
Claims
We claim:
1. In an electrostatographic developer mixture comprising
finely-divided toner particles electrostatically clinging to the
surface of free-flowing carrier particles, said carrier particles
comprising a core having a diameter between about 50 microns to
about 600 microns wherein the improvement comprises coating said
core with a first substantially continuous uniform layer comprising
an at least partially cured hydrolyzed ambifunctional silane,
silanol or siloxane, and a second substantially continuous uniform
over-layer comprising an unsaturated polyester resin, said
over-layer being capable of triboelectrifying the toner particles,
said core material being capable of reacting with the first layer
and of forming a bond therewith, and said first layer chemically
coupling said second layer to said core upon curing.
2. An electrostatographic developer mixture as defined in claim 1
wherein said first layer comprises the at least partially cured
hydrolyzed product of an ambifunctional organosilane, silanol, or
siloxane containing from 1 to 3 hydrolyzable groups attached to the
silicon atom and at least one functional organic group attached to
said silicon atom.
3. An electrostatographic developer mixture as defined in claim 1
wherein said unsaturated polyester resin is derived from the allyl
esters of unsaturated organic acids or anhydrides.
4. In an electrostatographic imaging process comprising the steps
of forming an electrostatic latent image on a surface and
developing said electrostatic latent image by contacting said
latent image with an electrostatostatographic developer mixture
comprising finely-divided toner particles electrostatically
clinging to the surface of free-flowing carrier particles, said
carrier particles comprising a core having a diameter between about
50 microns to about 600 microns wherein the improvement comprises
coating said core with a first substantially continuous uniform
layer comprising an at least partially cured hydrolyzed
ambifunctional silane, silanol or siloxane, and a second
substantially continuous uniform over-layer comprising an
unsaturated polyester resin, said over-layer being capable of
triboelectrifying the toner particles, said core material being
capable of reacting with the first layer and of forming a bond
therewith, and said first layer chemically coupling said second
layer to said core upon curing, whereby at least a portion of said
finely-divided toner particles are attracted to and held on said
surface in conformance to said electrostatic latent image.
5. An electrostatographic imaging process as defined in claim 4
wherein said first layer comprises the at least partially cured
hydrolyzed product of an ambifunctional organosilane, silanol, or
siloxane containing from 1 to 3 hydrolyzable groups attached to the
silicon atom and at least one functional organic group attached to
said silicon atom.
6. An electrostatographic imaging process as defined in claim 4
wherein said unsaturated polyester resin is derived from the allyl
esters of unsaturated organic acids or anhydrides.
Description
This invention relates in general to imaging systems and, more
particularly, to improved 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 xerographic 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 latent
electrostatic 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 latent
electrostatic image. This powder image may then be transferred to a
support surface such as paper. The transferred image may
subsequently 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 elimination of the powder image
transfer step is desired. Other suitable fixing means such as
solvent or overcoating treatment may be substituted for the
foregoing heat fixing step.
Many methods are known for applying the electroscopic particles to
the latent electrostatic 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 clinging to the
surface of the carrier particles is conveyed to and rolled or
cascaded across the latent electrostatic image-bearing surface. The
composition of the toner particles is so chosen as to have a
triboelectric polarity opposite that of carrier particles. As the
mixture cascades or rolls across the image-bearing surface, the
toner particles are electrostatically deposited and secured 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 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 particles and unused
toner particles are then recycled. This technique is extremely good
for the development of line copy images. The cascade development
process is the most widely used commercial xerographic development
technique. A general purpose office copying machine incorporating
this technique is described in U.S. Pat. No. 3,099,943.
Another technique for developing electrostatic images is the
"magnetic brush" process as disclosed, for example, in U.S. Pat.
Nos. 2,874,063. In this method, a developer material containing
toner and magnetic carrier particles is carried by a magnet. The
magnetic field of the magnet causes alignment of the magnetic
carriers in a brush-like configuration. This "magnetic brush" is
engaged with an electrostatic-image bearing surface and the toner
particles are drawn from the brush to the electrostatic image by
electrostatic attraction.
Carrier Material Criteria
The criteria for selection of suitable carrier materials are
extremely rigid in that these materials must exhibit a unique
balance of electrostatic properties. The carrier must be capable of
inducing a triboelectric charge on the toner particles opposite in
polarity to that of the image being developed in order to effect
deposition of the toner particles on the latent image. However, the
carrier must also exhibit sufficient electrostatic attraction for
the toner particles to enable the carrier to be an effective
scavenger for toner particles deposited on the discharged
background of the photoconductive insulating layer.
A property common to all carrier developers is a threshold force
which the image developing forces must exceed in order to effect
deposition. The retention force of the carrier is probably a
combination of coulomb attraction between the toner and carrier,
along with short-range "contact" forces. These retention forces
account for the high contrast characteristic of all carrier
developers as is desirable for line copy reproduction. It
contributes to relatively clean, dust-free background or non-image
areas, yet permits dense image development.
Residual charge is almost invariably present in the nominally
discharged or background areas of the latent image. Relatively low
as this charge density is, it may nevertheless be non-uniform, and
such irregularities will be a source of small fields capable of
trapping toner particles. This electrostatic "noise" in the
background areas of the latent image is one of the primary sources
of unwanted background toner.
As toner is removed from carrier by the development fields, the
carrier becomes more capable of accepting loosely held toner,
especially that not held by fields associated with the latent
image. Removal of toner from the carrier leaves upon it an
opposite, unbalanced charge that is not immediately neutralized.
Thus developer is intrinsically its own scavenging agent.
Thus it is of critical importance in obtaining a suitable carrier
material that it be capable of imparting charge to the toner
particles through triboelectrification and yet exhibit sufficient
electrostatic charge relative to the discharged portions of the
photoconductor to attract stray toner particles thereby maintaining
a clean background without interfering with the attraction of the
toner particles by the latent image. Thus, the triboelectric
relationship of the toner and carrier must be such that an
acceptable development of the xerographic image is produced, i.e.,
a dense image with low background. An excessively high
triboelectric relationship produces low density image with clean
background because of the inability of the electrostatic image to
attract sufficient toner particles from the carrier. A low
triboelectric relationship produces a so-called "dusty" developer
which will develop very low contrast electrostatic patterns but
will also produce high background densities. In order to obtain a
practical developer, these extremes must be avoided. In use, the
average triboelectric relationship for the developer decreases with
time because of cumulative physical damage to the carrier.
Therefore, the ideal carrier is a material exhibiting the proper
triboelectric relationship with the toner and is resistant to
physical damage and impaction which impairs this critical
relationship.
While ordinarily capable of producing good quality images,
conventional developing materials suffer serious deficiencies in
certain areas. The developing materials must flow freely to
facilitate accurate metering and even distribution during the
development and developer recycling phases of the
electrostatographic process. Some developer materials, though
possessing desirable properties such as proper triboelectric
characteristics, are unsuitable because they tend to cake, bridge
and agglomerate during handling and storage. Adherence of carrier
particles to reusable electrostatographic imaging surfaces causes
the formation of undesirable scratches on the surfaces during image
transfer and surface cleaning steps. The tendency of carrier
particles to adhere to imaging surfaces is aggravated when the
carrier surfaces are rough and irregular. The coatings of most
carrier particles deteriorate rapidly when employed in continuous
processes which require the recycling of carrier particles by
bucket conveyors partially submerged in the developer supply such
as disclosed in U.S. Pat. No. 3,099,943. Deterioration occurs when
portions of or the entire coating separates from the carrier core.
The separation may be in the form of chips, flakes or entire layers
and is primarily caused by fragile, poorly adhering coating
materials which fail upon impact and abrasive contact with machine
parts and other carrier particles. Carriers having coatings which
tend to chip and otherwise separate from the carrier core must be
frequently replaced thereby increasing expense and consuming time.
Print deletion and poor print quality occur when carrier having
damaged coatings are not replaced. Fines and grit formed from
carrier disintegration tend to drift and form unwanted deposits on
critical machine parts and this coating has a positive charge which
adds to the background on the selenium plate. Many carrier coatings
having high compressive and tensile strength either do not adhere
well to the carrier core or do not possess the desired
triboelectric characteristics. The triboelectric and flow
characteristics of many carriers are adversely affected when
relative humidity is high. For example, the triboelectric values of
some carrier coatings fluctuate with changes in relative humidity
and are not desirable for employment in xerographic systems,
particularly in automatic machines which require carriers having
stable and predictable triboelectric values. Another factor
affecting the stability of carrier triboelectric properties is the
susceptibility of carrier coatings to "toner impaction." When
carrier particles are employed in automatic machines and recycled
through many cycles, the many collisions which occur between the
carrier particles and other surfaces in the machine cause the toner
particles carried on the surface of the carrier particles to be
welded or otherwise forced into the carrier coatings. The gradual
accumulation of permanently attached toner material on the surface
of the carrier particles causes a change in the triboelectric value
of the carrier particles and directly contributes to the
degradation of copy quality by eventual destruction of the toner
carrying capacity of the carrier. Thus, there is a continuing need
for a better system for developing latent electrostatic images.
It is, therefore, an object of this invention to provide developing
materials which overcome the above noted deficiencies.
It is another object of this invention to provide developing
materials which flow freely.
It is a further object of this invention to provide carrier coating
materials which tenaciously adhere to carrier cores.
It is a still further object of this invention to provide carrier
coatings which are more resistant to chipping, flaking and the
like.
It is yet another object of this invention to provide carrier
coatings having stable triboelectric values.
It is a further object of this invention to provide carrier
coatings having high tensile and compressive strength.
It is still another object of this invention to provide toner
impaction resistant carrier coatings.
It is another object of this invention to provide developers having
physical and chemical properties superior to those of known
developer materials.
SUMMARY OF THE INVENTION
These, as well as other objects, are accomplished by the present
invention which provides a carrier for electrostatographic
developer mixtures comprising a core surrounded by a first layer
comprising a hydrolyzed ambifunctional organo silane, silanol or
siloxane and a second over-layer comprising an unsaturated
polyester resin, said first layer chemically coupling said second
layer to said core upon curing.
In general, the carriers of the present invention are prepared by
pre-coating carrier cores with a first layer comprising an
ambifunctional silicone-forming material such as organo silanes,
silanols or siloxanes having from 1 to 3 hydrolyzable groups,
hydrolyzing said material and at least partially curing the
ambifunctional silicone thus formed to bond said first layer to
said core. Thereafter, said pre-coated core is overcoated with an
unsaturated monomeric ester or polyester prepolymer and the
composite, multicoated core is finally cured to chemically couple
the resulting polyester to the core.
DESCRIPTION OF THE INVENTION
Core Materials
Any suitable well known coated or uncoated carrier material can be
employed as the core of the carriers of this invention. Typical
carrier materials include sodium chloride, ammonium chloride,
aluminum potassium chloride, Rochelle salt, sodium nitrate,
potassium chlorate, granular zircon, granular silicon, methyl
methacrylate, glass, silicon dioxide, flintshot, iron, steel,
ferrite, nickel, carborundum and mixtures thereof. Many of the
foregoing and other typical carriers are described by L. E. Walkup
in U.S. Pat. No. 2,618,551; L. E. Walkup et al. in U.S. Pat. No.
2,638,416 and E. N. Wise in U.S. Pat. No. 2,618,552. An ultimate
coated carrier particle diameter between about 50 microns to about
600 microns is preferred because the carrier particles then
possesses sufficient density and inertia to avoid adherence to the
electrostatic images during the cascade development process.
Adherence of carrier beads to an electrostatographic drum is
undesirable because of the formation of deep scratches on the drum
surface during the image transfer and drum cleaning steps,
particularly where cleaning is accomplished by a web cleaner such
as the web disclosed by W. P. Graff, Jr. et al. in U.S. Pat No.
3,186,838.
Pre-Coating Layer
The pre-coating layer surrounding the carrier core comprises an
ambifunctional silicon compound. The ambifunctional silicon
compounds useful in the present invention are those organo silanes,
silanols and siloxanes containing from 1 to 3 hydrolyzable groups
attached to a silicon atom and at least one functional organic
group attached to a silicon atom. Functional sites in the organic
groups attached to the silicon atom enable reaction to occur which
are typically organic in nature. Molecules having such functional
groups are generally referred to as organo-functional silicon
compounds, denoting that their chemical reactions occur in the
organic portion of the molecule. Compounds with both
silicon-functional and organo-functional groups are generally
referred to as ambifunctional silicon compounds and are the type of
silicon compounds employed herein.
Typical hydrolyzable groups included in such silicon compounds are,
for example, alkoxy groups such as methoxy, ethoxy, propyloxy and
the like, halo groups such as chloro, bromo and the like, acetoxy,
hydroxy and amino groups. Functional organic groups included in
such compounds are the radical residue of such compounds as amines,
glycidyl ethers, acrylates, methacrylates, vinyls and unsaturated
aliphatics containing from 2 to about 8 carbon atoms such as
butenyl, propenyl, hexenyl radicals and the like. If more than one
organic group is attached to a silicon atom, only one of the
organic groups need be functional. Hence, compounds such as
dimethyl vinyl chlorosilane are suitable. When more than one
functional group attached to the silicon atom is present, these
groups need not be identical. For example, vinyl allyl silicon
chlorides and bromides can be employed.
Exemplary of such ambifunctional silicon compounds are
n-(trimethoxysilylpropyl)ethylene diamine,
n-(dimethoxymethylsilylisobutyl) ethylene diamine,
gamma-methacryloxypropyl trimethoxysilane,
gamma-glycidoxypropyltrimethoxysilane, vinyltrichlorosilane, vinyl
triethoxy silane, vinyl trimethoxy silane,
vinyl-tris(beta-methoxy-ethoxy)silane, divinyl dichlorosilane,
dimethyl vinylchloro silane and the like. Also, the hydroxy silanes
(silanois) such as trimethyl silanol, dimethyl silanediol, diphenyl
silanediol and the like are useful.
Hydrolysis and/or condensation of the hydrolyzable groups attached
to the silicon atoms gives rise to the formation of siloxane
polymers generally called silicones. The corresponding partially
condensed siloxanes can be readily employed in lieu of silanes or
silanols. Hydrolysis can be promoted by pretreating the carrier
core with any suitable hydrolyzing medium such as water, a dilute
solution of acetic acid, sodium hydroxide, ammonium hydroxide,
triethylamine, dioxane or a dialkyl ether, or simply by mixing the
hydrolyzing medium with the silicon polymer prior to the coating
operation. The silanols are easily condensed to the corresponding
siloxanes by application of heat. Still further, two or more
silicon compounds as hereinabove defined can be co-hydrolyzed. In
such cases, siloxanes are formed representing each monomer
separately and usually products containing two or more kinds of
monomer units are also formed.
The resulting liquid hydrolyzates and/or condensates hereinafter
collectively referred to as "hydrolyzates" can be readily applied
to the carrier cores in any convenient manner such as by mixing,
dipping, spraying or other similar means of application. Any
suitable coating thickness can be employed. However, a coating
having a thickness at least sufficient to form a continuous film is
preferred because the carrier coating will then possess a uniform
distribution of potential cross-linking sites with both the core
and the over-coating. In addition, a coating of sufficient
thickness is necessary to resist abrasion and prevent pinholes
which adversely affect the triboelectric properties of the coated
carrier particles.
Once applied, the hydrolyzates are at least partially cured to
affect bonding between the carrier core and the precoated silicone
layer. Curing is conducted by heating the mixture of carrier cores
and hydrolyzates at temperatures ranging from about 100.degree.C.
to about 110.degree.C.
Although not considered critical, peroxide-type catalysts as
hereinafter further described as well as organic salts of certain
reactive metals such as cobalt, lead, zinc and iron as, for
example, zinc naphthenate, iron octoate, cobalt naphthenate and the
like have been found useful in hastening the cure.
Over-Coating Layer
Over-coating of the pre-coated core materials is accomplished with
monomer or prepolymer solutions which upon curing give rise to
cross-linked unsaturated polyesters. The unsaturated polyesters
useful as over-coating materials in the present invention are
preferably those unsaturated polyesters derived from the allyl
esters of unsaturated organic acids or anhydrides or the
prepolymers thereof. Most preferably, however, the unsaturated
polyesters are derived from the allyl esters of unsaturated cyclic
organic acids and anhydrides. Illustrative of such materials are
diallyl maleate, diallyl fumarate, diethylene glycol bis(allyl
carbonate), diallyl benzene phosphonate. Preferably, however,
materials such as diallyl phthalate, diallyl isophthalate and
diallyl chlorendate are employed since they are solids and there is
no chance of unreacted liquid monomer which may be accidentally
present, contaminating and destroying the xerographic properties of
the selenium plate. These latter materials can be readily prepared
by esterification of phthalic or isophthalic anhydride or
chlorendic anhydride with allyl alcohol. Chlorendic anhydride is
the diels-alder adduct, 1, 4, 5, 6, 7,
7-hexachlorobicyclo-(2.2.1)-5-heptene-2,3-dicarboxylic anhydride
prepared from hexachlorocyclopentadiene and maleic anhydride.
Similar useful adducts can be prepared by reaction of
hexachlorocyclopentadiene with such dienophiles as maleic acid,
citraconic anhydride, chloro maleic anhydride, itaconic anhydride
and the like.
While most of the allyl esters hereinabove described are useful
primarily as positive carrier coatings, diallyl chloroendate and
the other diels-alder adducts of hexachlorocyclopentadiene are
especially useful as reversal carrier coatings because of their
relative electronegativity.
These compounds can be polymerized alone under mild conditions
using only one of the allyl groups to form linear polyesters which
can undergo further polymerization to yield thermosetting, highly
cross-linked compounds. It is, therefore, unnecessary to add any
other polymerizing monomer such as a glycol although additional
monomers can be added if desired.
The allyl esters and prepolymers of the present invention undergo
thermal polymerization in the presence of a free radical initiator.
Since the materials easily undergo a vinyl type polymerization,
free radical initiators, such as peroxides and azo compounds, can
be employed. The action of the initiator can be modified by use of
activators and promoters. Peroxide type initiators which will
initiate polymerization at relatively low temperatures (30.degree.
to 60.degree.C.) are those such as acetyl benzoyl peroxide,
peracetic acid, methyl ethyl ketone peroxide, cumene hydroperoxide
and the like. For polymerization at intermediate temperatures
(60.degree.-100.degree.C.), peroxides such as tert.-butyl
hydroperoxide, methyl amyl ketone peroxide, tert.-butyl perbenzoate
and the like can be employed. At still higher temperatures (above
100.degree.C.), peroxides such as p-chlorobenzoyl peroxide,
ditert.-butyl peroxide, dibenzal diperoxide are suitably employed.
Azo compounds such as azo-bisisobutyronitrile,
dimethylazodiisobutyrate, azobis-1-phenylethane, alkali metal
azodisulfonates and the like have been found useful. Catalytic
activity is obtained when these free radical initiators are
employed in an amount from about 0.0001 to about 5.0 percent based
on the combined weight of the polymerizable ingredients.
It has been found in the present invention that better
cross-linking between the silicon compounds used as a pre-coat and
the unsaturated polyester over-coat can be promoted by selecting a
peroxide initiator which is an active polymerization catalyst for
both materials at the curing temperatures employed. Mixtures of
peroxides can be employed if desired. For example, benzoyl peroxide
is not a particularly effective catalyst for polymerization of
vinyltriethoxy silane, as low conversion to polymer is obtained.
Di-tert.-butyl peroxide is, however, a good catalyst for vinyl
triethoxysilane at higher temperatures and can be employed by
itself or in combination with another peroxide such as tert.-butyl
perbenzoate which is especially active in allyl ester
polymerization. A well established crosslinked network between the
silicone and polyester coatings can thus be obtained during
curing.
The rate of cure can be increased if desired through use of an
activator. Cobalt, in the form of its ethyl hexanoate or
naphthenate salt, is a good general purpose activator for use with
ketone peroxides. Activators cause rapid curing at room temperature
and tend to reduce surface tackiness. Concentrations as low as
about 30 ppm of cobalt have been found effective.
A promoter can also be added to the curing system if desired to
reduce the time usually required for gelling the resin. Pre-gelled
structures have sufficient rigidity to be handled, and thus can be
transferred to ovens to obtain final cure. Promoters used with acyl
peroxides include tertiary dialkyl aryl amines such as diethyl
aniline and aliphetic thiols as, for example, lauryl mercaptan.
Concentrations in the range of about 0.05 to about 0.5 percent by
weight of promoter have been found suitable.
In addition, inhibitors or antioxidants can be added to the
polyester to improve environmental stability. Inhibitors found
useful for this purpose are for example 5-butyl catechol,
2,6-di-tert.-butyl-p-cresol, hydroquinone, p-benzoquinone and
similar sterically hindered phenols.
The polyester overcoating can be applied to the precoated carrier
cores either as a monomeric solution or a prepolymer solution
together with initiator, activator, promoter and/or inhibitor. The
over-coating solution can be applied by mixing, dipping, spraying
and other similar liquid application methods. The coating solution
is generally applied hot, i.e., at about 100.degree.C. to about
130.degree.C. to promote rapid curing. Upon application of a
continuous thin film of solution to the pre-coated core particles,
the temperature is dropped below the softening point of the
polyester and the curing is continued until integrally coated core
particles having sufficient rigidity to be easily handled are
obtained. Thereupon, the coated core particles are finally cured,
generally in a vacuum oven at temperatures below the softening
point of the polyester.
Any suitable coating thickness can be employed. A coating having a
thickness at least sufficient to form a continuous film is
preferred because the composite carrier coating will then possess
sufficient thickness to resist abrasion and prevent pinholes which
adversely affect the triboelectric properties of the coated carrier
particles.
To achieve further variation in the properties of the final
resinous product, well known additives such as plasticizers,
reactive or non-reactive resins, dyes, pigments, wetting agents and
mixtures thereof can be admixed with the overcoating solution.
Toner Particles
The electrostatographic developer mixtures of the present invention
comprise finely-divided toner particles electrostatically clinging
to the surface of carrier particles prepared in the manner
hereinabove described. Generally, toner particles consist of a
carbon black dispersed in a resin; however, other pigments of dyes
can also be employed, including florescent materials. Toner can be
given special adhesive (or in some cases, non-adhesive) properties
to control transfer of still other material in an image pattern; it
can also be made inert to acids or solvents in order to serve as a
resist for selective etching applications. Toner particles,
however, must be of sufficient electric charge so that forces
exerted by the electrostatic image fields are sufficient to capture
the particles from the developer mass.
Employing the pre-coating and over-coating materials and procedures
described herein, a carrier is obtained which is composed of a
tough, internally cross-linked over-coating chemically coupled
through the pre-coat to the carrier core. These carriers have been
found extremely durable and resistant to impaction. The
surprisingly better results obtained from the employment of the
multi-layer carrier materials of the present invention may be
attributable to many factors. For example, the marked durability of
the carrier may be due to the fact that the ambifunctional organo
silicon pre-coating adheres extremely well to the carrier cores
tested and forms an extensive cross-link network with the polyester
over-coating forming, in essence, an integral structure tenaciously
bound to the carrier. Outstanding adhesion is obtained when the
organo silicon precoating of this invention is applied to glass or
similar siliceous particles. The unsaturated polyester
over-coatings of this invention exhibits a smooth, hard outer
surface which is highly resistant to chipping and flaking. The
smooth tough surface enhances the rolling action of the carrier
particles across the electrostatographic surfaces and produces the
tendency of the carrier particles to adhere to the surfaces.
Employment of the present carrier coatings unexpectedly extends
carrier life, particularly in respect to toner impaction
resistance. Additionally, the hydrophobic properties of the resins
of this invention especially those derived from diallyl chlorendate
appear to contribute in some unknown manner to the stability of the
triboelectric properties of the coated carrier over a wide relative
humidity range.
The following examples further define, describe and compare methods
of preparing the carrier materials of the present invention and of
utilizing them to develop electrostatic latent images. Parts and
percentages are by weight unless otherwise indicated.
EXAMPLE 1
Control Sample: Conventional Developer
A control sample containing one part colored toner particles having
an average particle size of about 10 to about 20 microns and 99
parts coated carrier particles available in the Xerox 813 Developer
sold by the Xerox Corporation, Rochester, New York is cascaded
across an electrostatic image-bearing surface. The resultant
developed image is transferred by electrostatic means to a sheet of
paper whereon it is fused by heat. The residual powder is removed
from the electrostatic imaging surface by a cleaning web of the
type disclosed by W. P. Graff, Jr. et al. in U.S. Pat. No.
3,186,838. After the copying process is repeated 8,000 times, the
developer mix is examined for the presence of carrier coating chips
and flakes. Numerous carrier chips and flakes are found in the
developer mix.
EXAMPLE 2
A coating solution (100 grams) having 2.22 grams of the hydrolysis
product of gamma-methacryloxypropyltrimethoxy silane (Dow Corning
Z-6030), prepared by mixing 1 g. of acetic acid (glacial)/100 g.
H.sub.2 O (distilled) with 10 g. of
methacryloxypropyltrimethoxysilane until both layers were
completely miscible and diluting 22.2 grams of the product to 100
gms. with distilled water, was admixed with 15 lbs. of 600 micron
glass carrier cores until said glass cores were uniformly coated.
The resulting mixture was heated at 110.degree.C. for about 30
minutes to partially cure said silane and affect a strong bond
between said silane and the free hydroxyl groups on the surface of
said glass cores.
Thereafter, 200 grams of an overcoating solution having the
following composition was admixed with the precoated glass cores at
about 110.degree.C.
17.2 parts diallyl phthalate polyester prepolymer (Dapon 35
manufactured by FMC Corporation)
1.6 parts DuPont Oil Red Dye
180.0 parts 1,4-dioxane (solvent)
1.2 parts benzoyl peroxide
0.06 parts cobalt naphthenate
Mixing was continued until a uniform overcoating had been applied
to the glass cores. The temperature was then dropped below the
softening point of the prepolymer and held at such temperature
(76.degree.C.) for about one-half hour. The coated cores were then
sufficiently rigid to be easily handled and were thereupon
transferred to a vacuum oven and post heated for 70 hours at 30 mm.
Hg and at a temperature about 5.degree.C. below the initial
softening point of the prepolymer.
The developing procedure of Example 1 is repeated with the
foregoing coated carrier substituted for the Xerox 813 carrier. The
copying process, however, is repeated 21,000 times rather than
8,000 times. An examination of the developer mix after test
termination reveals substantially no carrier coating chips or
flakes.
EXAMPLE 3
A coating solution of 1000 grams of the hydrolysis product of
vinyltriacetoxysilane (Dow Corning Z-6075) was admixed with 50 lbs.
of 600 micron glass carrier cores employing essentially the same
procedure described in Example 2.
Thereafter, 2000 grams of an overcoating solution having the
following composition was admixed with the pre-coated glass cores
at about 130.degree.C.
100 parts diallyl isophthalate (Dapon M manufactured by FMC
Corporation)
1659.5 parts methyl isobutyl ketone
6 parts n-butyl acetate
0.25 parts t-butyl perbenzoate
0.25 parts di-tert.-butyl peroxide
Essentially the same overcoating and curing procedure described in
Example 2 was employed except that curing was at 48.degree.C. for
one-half hour due to the lower softening point of Dapon M. The
developing procedure of Example 1 is repeated with the foregoing
coated carrier substituted for the Xerox 813 carrier. The copy
process, however, is repeated 21,000 times rather than 8,000 times.
An examination of the developer mix after test termination reveals
substantially no carrier coating chips or flakes.
EXAMPLE 4
A coating solution (27.5 grams) having 2.75 g. of the hydrolysis
product of vinyl silane (A-172 Union Carbide) was prepared by
mixing 1 g. of acetic acid (glacial)/100 g. H.sub.2 O (distilled)
with 10 g. of vinyl silane (A-172 Union Carbide) until both layers
were completely miscible and diluting 27.5 gms. of above to 100
gms. with distilled water, was admixed with 9 lbs. of 450 micron
glass carrier cores until said cores were uniformly coated. The
resulting mixture was heated at 110.degree.C. for about 30 minutes
to partially cure said silane and affect a strong bond between said
silane and said glass cores.
Thereafter, 200 grams of an overcoating solution having the
following composition was admixed with the precoated glass cores at
about 120.degree.C.
17.2 parts diallyl chlorendate
1.6 parts DuPont Oil Red Dye
180.0 parts 1,4-dioxane
1.2 parts benzoyl peroxide
0.03 parts 2,5-dimethylhexyl-2,5-di(peroxybenzoate)
0.03 parts 2,6-di-tert.-butyl-p-cresol
Essentially the same overcoating and curing procedure described in
Example 2 was employed to obtain about 20 grams of combined coating
materials (pre-coat and overcoat) applied to about 2500 grams of
glass cores. Carrier cores coated as above were designated carrier
A.
Two other coating solutions, B and C, containing 10 percent by
weight of polymeric material dissolved in appropriate solvents were
prepared. Solution B contains a polycarbonate resin ("Lexan" sold
by the General Electric Corporation) dissolved in ethylene
dichloride. Solution C contains a copolymer of 87 percent
vinylchloride and 13 percent vinylacetate dissolved in a mixture of
methyl ethyl ketone and toluene. The coating solutions are sprayed
onto two different batches of 450 micron glass carrier cores and
the resulting coated cores heated to drive off the solvent. About
20 grams of polymeric material is applied to about 2500 grams of
glass cores. About 99 parts of each carrier sample, A, B and C is
mixed with 1 part colored styrene copolymer toner particles having
an average particle size of about 10 to 20 microns and cascaded
across an electrostatic image-bearing surface. The developed image
is then electrostatically transferred to a receiving sheet. The
development and transfer steps are repeated at different relative
humidities in 10 percent increments from 20 percent to 80 percent.
The resolution in lines per millimeter of each of the transferred
images is plotted on a graph against the corresponding percent
relative humidity. The change in resolution between 20 and 80
percent relative humidity for samples B and C is more than 4 times
greater than the change in resolution for sample A.
EXAMPLE 5
Control Sample: Conventional Developer
A control sample containing one part pigmented toner particles
having an average particle size of about 10 to about 20 microns and
99 parts coated carrier particles available in the Xerox 813
Developer sold by the Xerox Corporation, Rochester, New York is
tumbled in a rotating cylindrical jar having an inside diameter of
about 2.25 and a surface speed of 140 feet per minute. Toner
impaction along with coating chips and flakes are observed within
about 50 hours after the test is initiated.
EXAMPLE 6
Coated carrier cores prepared as described in Example 2 were
subjected to the impaction testing procedure of Example 5
substituting said cores for the Xerox 813 carrier. Toner impaction
is discovered after about 100 hours after the test was initiated.
No ships or flakes are found.
EXAMPLE 7
Coated carrier cores were prepared as described in Example 3 using
250 micron steel carrier cores in lieu of the glass beads. The
coated steel cores were subjected to the impaction testing
procedure of Example 5 substituting said carrier for the Xerox 813
carrier. Toner impaction is discovered after about 100 hours after
the test was initiated. No chips or flakes are found.
EXAMPLE 8
Coated carrier cores were prepared as described in Example 4 with
respect to the preparation of Sample A. The coated glass cores were
subjected to the impaction test procedure of Example 5 substituting
said carrier cores for the Xerox 813 carrier. Toner impaction is
observed within about 150 hours after the test was initiated. No
chips or flakes are found.
Although specific materials and conditions were set forth in the
above exemplary processes in making an using the developer material
of this invention, these are merely intended as illustrations of
the present invention. Various other toners, carrier cores,
substituents and processes such as those listed above may be
substituted for those in 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. These
are intended to be included within the scope of this invention.
* * * * *