U.S. patent number 3,922,381 [Application Number 05/479,298] was granted by the patent office on 1975-11-25 for chemically treated carrier particles for use in electrophotographic process.
This patent grant is currently assigned to Addressorgrap Multigraph Corporation. Invention is credited to Pabitra Datta.
United States Patent |
3,922,381 |
Datta |
November 25, 1975 |
**Please see images for:
( Certificate of Correction ) ** |
Chemically treated carrier particles for use in electrophotographic
process
Abstract
Carrier particles for use in an electrophotographic process are
prepared by applying a perfluoro acid to the surface of the carrier
particle. The resulting carriers are long lived and capable of
imparting a positive triboelectric charge to electroscopic powders
mixed therewith.
Inventors: |
Datta; Pabitra (Lyndhurst,
OH) |
Assignee: |
Addressorgrap Multigraph
Corporation (Cleveland, OH)
|
Family
ID: |
23903425 |
Appl.
No.: |
05/479,298 |
Filed: |
June 14, 1974 |
Current U.S.
Class: |
430/111.35;
427/216; 430/111.2; 399/252; 427/215; 430/121.1; 430/122.2 |
Current CPC
Class: |
G03G
9/1138 (20130101); G03G 9/10 (20130101) |
Current International
Class: |
G03G
9/10 (20060101); G03G 9/113 (20060101); G03G
013/08 (); G03G 013/09 (); B05D 005/12 (); C03C
017/28 () |
Field of
Search: |
;117/1R,1M,17.5
;252/62.1P ;96/15D ;427/18,19,20,215,216,220 ;428/403,404,406 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Bowers, Jr.; Charles L.
Assistant Examiner: Miller; John R.
Attorney, Agent or Firm: Kondzella; Michael A.
Claims
I claim:
1. A carrier for use in electrophotographic development of latent
electrostatic images capable of inducing an electrostatic charge in
a toner mixed therewith which comprises a member selected from the
group consisting of metallic particles and siliceous particles to
the surface of which is adhered a member selected from the group
consisting of perfluorinated and substantially perfluorinated
carboxylic acids containing from 3 to 18 carbon atoms and esters
and amides thereof.
2. A composition according to claim 1 wherein the carrier comprises
a monomolecular layer of said acid, ester or amide adhered to the
surface of said particles by chemical adsorption.
3. A composition according to claim 1 wherein said acid is
perfluorooctanoic acid.
4. A composition according to claim 1 wherein said acid is
perfluoropropionic acid.
5. A composition according to claim 1 wherein said acid is
perfluorobutyric acid.
6. A composition according to claim 1 wherein said acid is
perfluorodecanoic acid.
7. A composition according to claim 1 wherein said acid is 11 - H -
eicosafluoroundecanoic acid.
8. A composition according to claim 1 wherein said acid is
perfluoroglutaric acid.
9. A composition according to claim 1 wherein said amide is
perfluoroacetamide.
10. A composition according to claim 1 wherein said electrostatic
charge is of a positive polarity.
11. A composition according to claim 1 wherein said particles are
magnetic.
12. A composition according to claim 1 wherein said particles are
non-magnetic.
13. A composition according to claim 1 wherein said particles are
iron.
14. A composition according to claim 1 wherein said particles are
spherical iron beads.
15. A composition according to claim 1 wherein said particles are
phosphated iron.
16. A process for developing a latent electrostatic image which
comprises
mixing an electroscopic powder with a carrier comprising a member
selected from the group consisting of metallic particles and
siliceous particles to the surface of which is adhered a member
selected from the group consisting of perfluorinated and
substantially perfluorinated carboxylic acids containing from 3 to
18 carbon atoms and esters and amides thereof to impart opposite
electrostatic charges to said electroscopic powder and said
carrier, whereby said electroscopic powder is attracted to said
carrier and
transferring said electroscopic powder from said carrier to said
latent electrostatic image.
17. A process according to claim 16 wherein said transferring step
is accomplished by means of cascade development.
18. A process according to claim 16 wherein said transferring step
is accomplished by means of magnetic brush development.
Description
BACKGROUND OF THE INVENTION
This invention relates to carriers for use in developer
formulations which charge electroscopic powders triboelectrically.
These carriers are useful in electrophotographic processes for
developing latent electrostatic images in which a colored toner
carried by the carrier particle is caused to be attracted from the
carrier particle to develop the latent electrostatic image.
In the electrophotographic process it is necessary to use a carrier
for the toner in order to produce an electrostatic charge upon the
toner particles. Various kinds of developing processes are known
including cascade, powder cloud and magnetic brush processes. In
each of these processes it is necessary that the carrier used have
certain triboelectric properties so that it is capable of imparting
to the toner particles an electrostatic charge of the proper
polarity and magnitude. Where uncoated carrier particles are used
it has been necessary to select a toner having the desired
triboelectric properties. Recently, it has been found that the
carrier particles can be coated with various types of polymeric
coatings to permit variation in the triboelectric properties
thereof. One such method is disclosed in U.S. Pat. No. 3,811,880 to
Luther C. Browning, assigned to the same assignee as this
invention.
Although polymeric coatings of this type enable a certain degree of
control of the triboelectric properties of the developer mix, it
has been found that in use in the environment of
electrophotographic reproduction machines such carrier particles
are subject to aging which limits their effectiveness. Wearing away
and removal of part of the polymeric coating upon the surface of
the carrier particles is another problem encountered. This may
result in undesired abrasion of the photoconductive surface used
for imaging and also cause bias shorting.
Another problem inherent in the use of polymeric coatings for
carrier particles is the phenomenon known as "bound toner." Through
a mechanism which is not clearly understood prolonged usage of
developer mixes including polymeric coated carrier particles
results in toner being adhered onto the surface of the coated
carrier causing a decrease in the effectiveness of the toning
process and hence in the overall development of the images being
reproduced.
OBJECTS
It is accordingly an object of this invention to provide carriers
for toners which are not subject to the disadvantages mentioned
above.
Another object of this invention is to provide carrier particles
which have an enhanced longevity.
Another object of this invention is to provide carrier particles
which are capable of imparting desired triboelectric properties to
various types of toners.
Other objects and advantages of this invention will become apparent
in the following detailed disclosure and description.
SUMMARY OF THE INVENTION
Chemically treated carrier particles can be used in developer mixes
in order to increase the useful life of the developer and also to
provide desired triboelectric properties. A chemical treatment for
the purpose of adhering a perfluoro carboxylic acid to the surface
of a carrier matrix has been found to result in carriers having a
longevity which is significantly greater than untreated carrier
particles or carrier particles coated with various kinds of
polymers. A more efficient carrier with respect to triboelectric
properties, a carrier having low surface energy and a low
coefficient of friction and a carrier which does not need to be
replenished as frequently as other types of carriers is thereby
provided.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a series of curves showing variation in image density as
a function of the number of copies produced for various types of
carriers.
FIG. 2 is a series of curves showing bound toner as a function of
the number of copies produced for various types of carriers.
DETAILED DESCRIPTION OF THE INVENTION
It has been found that the various problems encountered with
previously available carriers are generally obviated by the use of
a carrier particle to the surface of which is adhered a perfluoro
carboxylic acid or derivative thereof. The perfluoro acids
contemplated by this invention are those perfluorinated and
substantially perfluorinated carboxylic acids, both aliphatic and
aromatic, which have carbon chains of from 3 to 18 carbon atoms in
length. Exemplary of such acids are perfluoropropionic acid,
perfluorobutyric acid, perfluorovaleric acid, perfluoroadipic acid,
perfluoroheptanoic acid, perfluorooctanoic acid, perfluorononanoic
acid, perfluorodecanoic acid, 11 - H - eicosafluoroundecanoic acid,
as well as the higher molecular weight aliphatic acids and aromatic
acids such as perfluorobenzoic acid. Polycarboxylic acids can also
be used, for example, perfluorosuccinic acid or perfluoroglutaric
acid. Derivatives of perfluoro carboxylic acids such as esters and
amides can also be used.
As carrier matrix materials it is possible to use a wide variety of
substances, for example glass beads, ceramic beads, grains of sand
or metallic particles. Non-metallic matrix materials are useful
where a cascade development system is utilized although metallic
matrices can also be used in cascade development. Where a magnetic
brush developing system is used it is necessary that the matrix be
magnetic. For this purpose various irons and steels have been used,
for example, spherical steel beads and irregularly shaped iron
powders.
The desired chemical treatment can be accomplished in a number of
ways. In general, it is merely necessary to mix the carrier matrix
material with a solution of the perfluoro carboxylic acid.
Ordinarily, adherence of the perfluoro acid to the powder or bead
occurs in a dilute solution of the perfluoro acid in a suitable
solvent such as an alcohol, ketone or hydrocarbon at room
temperature in a matter of hours. It is desirable that the matrix
material being used be thoroughly cleaned and dried prior to
treatment with the perfluoro acid and that the product resulting
from treatment of the matrix material with the perfluoro acid
solution be thoroughly dried before use.
The matrix particles treated with a perfluoro acid according to
this invention are believed to constitute a monomolecular film of
the acid adhered to the surface of the matrix particle, although
thicker films may be produced if desired. Adherence of the
perfluoro acid to the carrier matrix is believed to be by chemical
adsorption.
The resulting carriers are found to have a longer useful life than
prior art carriers in the environment of electrophotographic
development. Because these carriers have a low surface energy,
reduced toner filming, characterized as "bound toner" is realized.
In addition the adherence of the film of perfluoro carboxylic acid
to the carrier matrix material reduces flaking, chipping and
spalling of the carrier.
Further, as pointed out above, the triboelectric properties of the
carriers of this invention are such that most toners will be
charged with a positive polarity when used with these carriers.
Even polytetrafluoroethylene (Teflon) and polyethylene can be
charged positively using the carriers of this invention. Since most
commercially available toners are less electronegative than Teflon
or polyethylene they are charged with a positive polarity almost
without exception.
With the outstanding triboelectric properties of the carriers of
this invention and the physical properties mentioned above, namely
the low surface energy, the low coefficient of friction and the
pronounced adherence of the perfluoro carboxylic acid to the
carrier matrix material these carriers represent a significant
improvement over carriers which have been previously used. In
addition to the long life of the carriers themselves the particular
combination of properties increases the life of the photoconductor
used in the electrophotographic process and also results in very
high quality copies being produced.
The durability and effectiveness of these carriers is greatly
enhanced because of the extremely thin film of perfluoro carboxylic
acid upon the surface of the carrier matrix material.
Another advantage of the carriers of this invention is that the
toner filming or "bound toner" determined using various
commercially available toners with these carriers is considerably
less than in the case of carrier particles which have been coated
with low surface energy polymers such as polyvinylidene fluoride or
silicones, which show little if any improvement over uncoated
carrier matrix material. The low percentage of "bound toner"
indicates that the carriers of this invention can be used much more
successfully than previously available carriers since their
efficiency is not reduced by toner filming upon the carrier
particles to the same extent as prior art carriers.
This invention will be better understood by reference to the
following examples which are intended to illustrate but not to
unnecessarily limit the scope of this invention which is defined in
the claims appended hereto.
EXAMPLE 1
A 4 kilogram quantity of 150.mu. average particle size spherical
steel beads was cleaned with trichloroethane in an ultrasonic
cleaner and then dried in a fluidized oven at 80.degree.C. The
cleaned and dried steel beads were then poured into a solution of 4
g. of perfluorooctanoic acid (PFOA) in 800 g. of methanol and
stirred for 2 hours. The alcoholic solution was then decanted and
the steel beads were washed with an equivalent amount of methanol
and dried in a fluidized bed oven at 60.degree.C for 1 hour.
EXAMPLE 2
A quantity of 4 kilograms of 150.mu. average particle size
spherical steel beads was cleaned with trichloroethane in an
ultrasonic cleaner and then dried in a fluidized oven at
80.degree.C.
The cleaned and dried steel beads were mixed with a toner
containing polymers prepared from styrene and acrylic monomers,
polyvinyl butyral and carbon black in a weight ratio of 40:1. Zinc
oxide coated paper was charged negatively by means of a corona
discharge using a potential of 5000 volts, exposed through a
photographic transparency and toned with a hand-held magnetic brush
using this developer. Reversal copies were produced.
Triboelectric properties of this toner were determined in the
following manner:
A sheet of toner about 1 mm. thick was formed upon a steel plate by
melting the toner onto the metal. The resulting toner sheet was
then gently rubbed in the carrier and the carrier was removed by
shaking or lightly vacuuming the toner sheet.
The triboelectric interaction between the toner sheet and carrier
deposited a surface charge on the toner sheet. This surface charge
caused a voltage drop across the toner sheet which was then
measured with a non-contact voltmeter such as a Monroe Electronics
"Isoprobe."
For a sheet of dielectric of area A, thickness t, dielectric
constant K, and bulk resistivity .rho., with a surface charge
density of +(.sigma..sub.c) on the top surface and -(.sigma..sub.c)
on the bottom surface the equivalent circuit is a capacitor of
capacity
in parallel with a resistance
with a voltage across the plates of: ##EQU1## where .epsilon..sub.o
is the permitivity of free space.
The surface charge density .sigma..sub.c associated with the
toner-carrier triboelectric interaction was thus easily calculated
from the measured voltage drop across the toner sheet, the
dielectric constant and the thickness of the sheet.
The sheet thickness was determined by measuring the thickness of
the sheet plus metal plate with calipers and substracting the
measured thickness of the bare metal plate. The sheet dielectric
constant was determined in the standard manner by (1) measuring the
capacitance of the sheet placed between electrodes of known area
and, (2) dividing that value by the calculated unloaded capacitance
of the electrodes separated by a space equal to the sheet
thickness.
Toner sheets made by carefully melting the toner powder onto the
plate were often found to have edges slightly lower than the
centers. In order to avoid any inaccuracies occasioned by the
method of sheet preparation care was taken to measure the voltage
only in the regions where the thickness was uniform and easy to
measure.
Using the above described technique this toner was found to have a
surface charge density .sigma..sub.c of -0.18 .times.
10.sup.-.sup.10 coulomb per square centimeter when charged with
steel beads.
EXAMPLE 3
The PFOA treated steel beads prepared according to Example 1 in the
amount of 50 g. were mixed with 0.75 g. of the toner of Example 2.
Zinc oxide coated paper was charged negatively by means of a corona
discharge using a potential of 5000 volts, exposed through a
photographic transparency and toned with a hand-held magnetic brush
using this developer. The surface charge density was found to be
+1.8 .times. 10.sup.-.sup.10 coulomb per square centimeter.
Positive copies were produced.
EXAMPLE 4
A 1500 g. quantity of PFOA treated steel beads prepared according
to Example 1 were mixed with 22.5 g. of the toner of Example 2. The
resulting developer was poured into the toning unit of an
Addressograph-Multigraph Model 2000 electrostatic copying machine.
Copies of a photographic transparency were made using zinc oxide
coated paper. The optical density of the copies produced was
determined by means of a MACBETH RD-519 densitometer.
A curve showing optical density as a function of the number of
copies produced was plotted and is shown as Curve A in FIG. 1.
Using this developer 180,000 copies were produced before any
adverse effect upon copy quality was observed.
Fresh developer was added and the machine was run continuously for
240 hours. One hour of running time is equivalent to the production
of 1200 copies. Every 12 to 24 hours a small amount of developer
was removed from the toning unit and examined microscopically for
toner filming.
No toner adhered to the surface of the carrier beads (bound toner)
was observed prior to 192 hours running time. Percentage of bound
toner was determined using the analytical technique described in
Denshi Shashin (Electrophotography) 10, 14 (1971). The analytical
results were plotted and are shown in Curve F of FIG. 2 which shows
the percentage of bound toner determined as a function of the
number of copies produced.
EXAMPLE 5
A developer consisting of 1500 g. of cleaned and dried 150.mu.
average particle size steel beads and 22.5 g. of a toner containing
polyamide resin, maleic modified rosin, polyketone resin,
polyethylene, lithium stearate, carbon black and a positive
orienting dye was tested according to the procedure of Example
4.
Curve B of FIG. 1 shows the optical densities observed and Curve G
of FIG. 2 shows the bound toner determinations. The surface charge
density was found to be +1.0 .times. 10.sup.-.sup.10 coulomb per
square centimeter. About 12,000 copies could be produced before the
copy density became unsatisfactory.
EXAMPLE 6
The toner of Example 5 was mixed with PFOA treated steel beads
prepared according to the procedure of Example 1 and copies were
produced according to the procedure of Example 4.
The results are shown in Curve C of FIG. 1. The surface charge
density was found to be +6.2 .times. 10.sup.-.sup.10 coulomb per
square centimeter. Copy quality was maintained for 240,000
copies.
EXAMPLE 7
A developer consisting of 50 g. of cleaned and dried 150.mu.
average particle size steel beads and 0.75 g. of a toner containing
copolymers of styrene and butyl methacrylate, carbon black and a
negative orienting dye was tested according to the procedure of
Example 2.
The surface charge density was found to be -1.0 .times.
10.sup.-.sup.10 coulomb per square centimeter. Reversal copies were
produced.
EXAMPLE 8
The toner of Example 7 was mixed with PFOA treated steel beads
prepared according to the procedure of Example 1 and tested
according to the procedure of Example 2.
The surface charge density was found to be +4.9 .times.
10.sup.-.sup.10 coulomb per square centimeter. Positive copies were
produced.
EXAMPLE 9
A developer consisting of 50 g. of cleaned and dried 150.mu.
average particle size steel beads and 0.75 g. of a toner containing
copolymers of styrene and n-butyl methacrylate, maleic modified
rosin, polyvinyl stearate and carbon black was tested according to
the procedure of Example 2.
The surface charge density was found to be -0.4 .times.
10.sup.-.sup.10 coulomb per square centimeter. Reversal copies were
produced.
EXAMPLE 10
A developer consisting of 1500 g. of PFOA treated steel beads
prepared according to the procedure of Example 1 and 22.5 g. of the
toner of Example 9 was tested according to the procedure of Example
4.
The surface charge density was found to be +1.3 .times.
10.sup.-.sup.10 coulomb per square centimeter. Positive copies were
produced with copy quality being maintained for 120,000 copies.
EXAMPLE 11
The procedure of Example 1 was followed except that iron powder
having a particle size range of 75.mu. to 200.mu. was used.
EXAMPLE 12
The procedure of Example 2 was followed except that the iron powder
of Example 11 was used.
The surface charge density was found to be -0.5 .times.
10.sup.-.sup.10 coulomb per square centimeter and reversal copies
were produced. Similar results were obtained with the toners of
Examples 7 and 9.
EXAMPLE 13
The procedure of Example 2 was followed except that the carrier
used was the PFOA treated iron powder of Example 11.
The surface charge density was found to be +1.8 .times.
10.sup.-.sup.10 coulomb per square centimeter. Positive images were
produced. Similar results were observed with the toners of Examples
7 and 9.
EXAMPLE 14
The procedure of Example 4 was followed except that the developer
consisted of the iron powder of Example 11 and 22.5 g. of the toner
of Example 5.
The surface charge density was found to be +1.15 .times.
10.sup.-.sup.10 coulomb per square centimeter. Copy quality began
to fall off after about 15,000 copies. The optical densities are
shown in Curve D of FIG. 1. Microscopic examination revealed toner
filming.
EXAMPLE 15
The procedure of Example 4 was followed using the carrier of
Example 11 and the toner of Example 5.
The optical densities are shown in Curve E of FIG. 1. Copy quality
was maintained for 240,000 copies. The surface charge density was
found to be +1.4 .times. 10.sup.-.sup.10 coulomb per square
centimeter.
Other iron carrier matrix materials were used with similar effect.
Various sizes of irregular shaped iron particles from about 50.mu.
to 200.mu. were found to be effective as were spherical iron beads
from about 150.mu. to 500.mu..
In addition to PFOA other perfluorinated and substantially
perfluorinated acids and derivatives thereof were found to impart a
positive charge to various toners. Exemplary of such other
perfluoro acids are perfluoropropionic acid, perfluorobutyric acid,
perfluorodecanoic acid and perfluoroglutaric acid. An example of a
substantially perfluorinated acid is 11- H - eicosafluoroundecanoic
acid. An example of an acid derivative which can be used in this
invention is perfluoroacetamide.
The carriers of this invention generally were effective to impart a
positive charge to toners of widely varying types. In addition
these carriers charged sheets of polyethylene,
polytetrafluoroethylene (Teflon) and polymethacrylates
positively.
EXAMPLE 16
A 300 g. quantity of BONDERITE 860 (Parker Rust Proof Division,
Hooker Chemical Corporation, Detroit, Mich.), a phosphating agent
for producing a corrosion-inhibiting finish on metals, was mixed
with 4800 g. of cold water and the mixture heated on a hot plate to
80.degree. C. and then poured into a 2 gallon stainless steel
container of a pony mixer and stirred for 1 minute.
Spherical steel beads of 150.mu. average particle size in a
quantity of 5 kilograms were added and mixed for 10 minutes, then
decanted and washed with cold water until the solution was clear
and dried in a fluidized oven at 100.degree. C. for 2 hours.
The resistivity of the resulting phosphated steel beads was found
to be about 1 .times. 10.sup.10 to 1 .times. 10.sup.11 ohms
compared to a resistivity of about 1 .times. 10.sup.7 ohms for the
untreated beads.
EXAMPLE 17
A quantity of 4 kilograms of the phosphated steel beads prepared
according to Example 16 was poured into a solution of 4 g. of PFOA
in 800 g. of methanol and stirred for 2 hours. The alcoholic
solution was then decanted and the PFOA treated beads were washed
with an equivalent amount of methanol and dried in a fluidized bed
oven at 60.degree.C for 1 hour.
EXAMPLE 18
The procedure of Example 2 was followed using the phosphated steel
beads of Example 16.
Reversal images were produced using the toners of Examples 2, 7 and
9.
EXAMPLE 19
The procedure of Example 2 was followed using the PFOA treated
phosphated steel beads of Example 17.
Positive copies were produced using the toners of Examples 2, 7 and
9.
EXAMPLE 20
The procedure of Example 4 was followed using the PFOA coated
phosphated steel beads of Example 17.
Copy quality was maintained for 200,000 copies.
EXAMPLE 21
A 2 kilogram quantity of 650 micron average particle size Ottawa
sand was poured into a solution of 5 grams of PFOA in 400 grams of
methanol and mixed for 2 hours. The alcoholic solution was then
decanted and the sand particles washed with an equivalent amount of
methanol and dried in a fluidized bed oven at 60.degree.C for 1
hour.
EXAMPLE 22
Ottawa sand (650 micron particle size) in a quantity of 50 grams
was mixed in a plastic bag with 0.5 gram of the toner of Example
2.
The toner was found to have a surface charge density of -0.3
.times. 10.sup.-.sup.10 coulomb per square centimeter. Zinc oxide
coated paper was charged negatively by means of a corona discharge
using a potential of 5,000 volts, exposed through a photographic
transparency and toned by cascading the above described developer
mixture across the surface of the exposed zinc oxide paper.
Reversal copies were produced.
EXAMPLE 23
The carrier particles of Example 21 were mixed with the toner of
Example 2 and tested according to the procedure of Example 22.
The surface charge density was found to be +2.0 .times.
10.sup.-.sup.10 coulomb per square centimeter. Positive copies were
produced.
EXAMPLE 24
The procedure of Example 22 was followed except that the toner of
Example 5 was used.
The surface charge density was found to be +2.7 .times.
10.sup.-.sup.10 coulomb per square centimeter. Copies of relatively
low optical density were produced.
EXAMPLE 25
The procedure of Example 23 was followed using the toner of Example
5.
The surface charge density was found to be +11 .times.
10.sup.-.sup.10 coulomb per square centimeter. Positive copies of
good optical density were produced.
EXAMPLE 26
The procedure of Example 22 was followed using the toner of Example
9.
The surface charge density was found to be +0.53 .times.
10.sup.-.sup.10 coulomb per square centimeter. Copies having a
significant amount of background and some reversal characteristics
were produced.
EXAMPLE 27
The procedure of Example 23 was followed except that the toner of
Example 9 was used.
The surface charge density was found to be +2.0 .times.
10.sup.-.sup.10 coulomb per square centimeter. Positive copies of
good optical density were produced.
It can thus be seen that the carriers of this invention can be used
to produce good positive copies using a variety of toners and by
any desired development method; such as magnetic brush development
or cascade development. Particularly noteworthy is the apparent
ability of the carriers of this invention to impart a positive
charge to most types of toners.
This invention has been described with respect to a limited number
of specific embodiments. However, it is intended that alternative
compositions and methods can be used and it is to be understood
that this invention is not to be limited except in accordance with
the claims appended hereto.
* * * * *