Note: Descriptions are shown in the official language in which they were submitted.
iO80~i3~
Background of the_Invention
With the increased use of bond paper copiers, development
powders have enjoyed an increased popularity over liquid
toners. Along with the increased use of development powders,
magnetic brush units are ~ecoming increasingly popular and
units using cascading methods are still frequently employed.
Such units usually have a carrier powder, such as iron powder,
which serves as the carrier material. Inexpensive, untreated
carrier powders cannot be used in magnetic brush systems
since such carrier powders may have insufficient stability
toward rusting, lack color stability, or triboelectric charge
properties which are adversely effected by variable humidity
conditions. In order to solve these problems, those in
the art have resorted to chemical plating and coating of
the carrier particles with polymers, oils, waxes and the
like.
Prior art developer materials, which are employed
in automatic copy machines, have carrier filming problems
due to the mechanical rubbing of the carrier surface with
the soft toner resins. The gradual accumulation of permanently
attached film impairs the normal triboelectric charging
of the toner particles in the toner mix. As I result, the
toner is either less highly charged or sometimes oppositèly
charged giving rise to poor copy quality with a high degree
of background.
}n the literature, several ways of treating, coating
and electroplating the carrier partizle ha-e been suggested
to overcome the filming problems. Examples of such carrier
particle modifications are found in U.S. Patents 3,725,118;
3,736,257; 3,778,262; 3,795,618 and 3,849,127. Most of
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the prior art coating methods result in high cost and have
other dis~dvantages such as yielding improper triboelectric
charge properties and imparting a very high eleetrieal resistanee
to the carrier that reduces its development electrode effect
and results in poorly filled-in large image areas.
Summarv of the Invention
In the art of electrostatographic imaging pcoeessing,
an electrostatic latent image is formed on a recording surface
of a photoconductor. The electrostatic image may then be
developed by finely-divided toner particles electrostatically
attached to the surface of carrier particles. Preferab
the earrier particles are iron powder or beads.
It has been found that a simple fluorotelomer adsorption
treatment of iron powder from a solvent produces a treated
carrier particle which has good stability to rusting under
high relative humidity, a constant triboeleetric eharge
property under all conditions when mixed w1th standard toners,
very low dusting of the toner in a magnetic brush unit and
allows the use of lower reverse biased voltage during development
whieh improves copy guality and the reliability of maehine
performance.
~y using the fluorotelomer treated earrier partieles
of this invention, an improved eleetrophotoqraphic proeess
is obtained, wherein a latent electrostatic image is contacted
with a developer mixture which includes the treated carrier
'' particles.
- The method of producing fluorotelomer treated carrier
partieles involves dispersing a fluorotelomer in an organie
solvent such as trichlorotrifluoroethane in a concentration
of 0.01 to 10~. The eore material is plaeed into the solution,
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the core material being selected from either metal, sand, or glass.
The solution is decanted and allowed to dry a~ter which the treated
carrier particles is heated to a temperature of 250 to 350 degrees
centigrade. It will be appreciated that this treatment is appre-
ciably simpler than previously disclosed methods of treating
or coating core particles.
In one particular aspect the present invention provides a
carrier particle for a development powder comprising a core selected
from the group consisting of metal, sand and glass, said core being
coated with fluorotelomer having a molecular weight of 3,000 to
30,000.
In another particular aspect the present invention provides
in a method of producing a fluorotelomer coated carrier particle for
use in a development powder, the steps comprising: a) dispersing a
quantity of fluorotelomer compound in an organic solvent in a weight
- - concentration of 0.01 to 10%; b) placing a quantity of core material
into said dispersion; c) mixing the core material and dispersion;
d) decanting the solvent, and e) heating the treated carrier
partlcles to a temperature slightly above the melting point of the
telomer.
In a further particular aspect the present invention provides
an electrostatographic imaging process comprising the steps of
forming an electrostatic latent image on a recording surface and
contacting said electrostatic latent image with a development powder
; comprising finely-divided toner particles electrostatically attached
to the surface of carrier particles, said carrier particles com-
prising a core material being coated with a fluorotelomer having a
molecular weight of 3,000 to 30,000.
Description of the Preferred Embodiment
The core of the carrier particle formed by the present
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invention may be a~y material which can react chemically with the
fluorotelomer compounds of this inventlon. Thus, by way of example,
the material of the core of the carrier particle may be sand, glass
beads, metallic beads or metallic powders. As used in this specif-
ication, including the appended claims, the term metal and metallic
is intended to $nclude elemental metals as well as their oxides,
carbides and other forms of metallic compounds and alloys which have
a solid form.
The core of carrier particles of the preferred embodiment is
a ferromagnetic material such as iron or steel. Other suitable
ferromagnetic materials such as magnetic oxides and alloys of
copper-nickel-iron, for example, also may be employed. The size of
the core may be between 40 and 1000 microns with the preferred size
range being between 50 and 400 microns.
The fluorotelomer may be selected from a number of short
chain fluoro compounds having a molecular weight of 3,000 to 30,000.
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Fluorotelomers are white, waxy short-chain compounds of tetrafluoro-
ethylene having a particle size of 5 - 30~ and a sharp melting point.
It should be noted that fluorotelomers are different from long
chain polymers
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such as polytetrafluoroethylene available from DuPont under
the trademark TEFLON. Examples of commercially available
fluorotelomers are VYDAX AR, VYDAX 5100, VYDAX~550 and VYDAX
looo lDuPont Petroleum Chemicals, Wilmington, Delaware 198983
which are telomers dispersed in an appropriate solvent.
The first three have the same telomers dispersed in trichloro-
trifluoroethane, the difference being in solid content.
The weight percent of flourotelomers in these formulations
are as follows: VYDAX AR - 20~, VYDAX 5100 - 10~ and VYDA
550 - 5~. The particular telomer used in these formulations
has density of 2.16 gm/cc at 25 aegrees centigrade, a softening
point of 265 degrees centigrade, a sharp melting point of
300 degrees centigrade and a molecular weight of approximately
3,700. The VYDAX~ 000 is a 7.5~ dispersion of a fluorotelomer
in CCl2F - CClF2 which fluorotelomer has a density of 2.il gm/cc
at 25 degrees centigrade, a softening point of 322 degrees
centigrade, a melting point of 325 degrees centigrade and
a molecular weight of approximately 25,000. Other properties
of these commercially available materials are given in DuPont
Bulletin V-3 and Bulletin Y-i. Also see M.L. Miller nThe
Structure of Polymers" - Reinhold Publishing Corp. (1966).
~ lany organic solvents may be employed for the purpose
of dispersing a telomer. Examples of such solvents are
trichlorotrifluoroethane, (which is the preferred solvent),
trichloroethane, methyl chloride, perchloroethylene, trichloro-
ethylene, toluene benzene, or combinations thereof.
As a core material, ANCOR STEEL 1000S (-80/+230
mesh) Hoegenaes, Inc., Riverton, New Jersey was used. Spherical
iron powder from Nuclear Metals Division Whittaker, Concord,
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Massachusetts also have been used with success. Other core
materials which have been successfully employed include cobalt and
nickel.
Commercial toners may be used in conjunction with
fluorotelomer treated carrier particles. Examples of such
commerical toners are ISC lOOg-14A toner made by Imaging
Systems Corp., (hereinafter referred to as ISC toner) Toner
~67-146 made by Phillip A. Hunt Chemical Corp., and IBM
Toner ~ 1162058. A non-commercial toner used in combiantion
with fluorotelomer treated carrier particle was a composition
or 45.5 parts styrene-butylmethacrylate copolymer, 45.5
parts PLIOLITE VTL (Goodyear Chemicals) 6 parts mogul-L
(Cabot Corp.) and 3 parts nigrosine base ~B ~GAF Corp.).
This non-commercial toner is hereinafter referred to as
; PB toner. The prepared toner concentrate in the developer
mix is between 1 and 3%, the balance being fluorotelomer
treated powder.
One of the fluorotelomer treatment of the carrier
particle is accomplished by dispersing a fluorotelomer in
an organic solvent such as trichlorotrifluoroethane. The
core material is added to the dispersion and mixed on rollers
for about 30 to 45 minutes. Subsequently t:e mixture is filtered
and dried. The treated core material is heated to slightly
above the melting point of the telomer. The heatlng step
melts the telomer and causes it to coat the carrier particles
so that upon cooling, a protective layer is provided. The
coating thickness may be 1/2 to 25 microns with the preferred
coating thickness being 1-5 microns. -
In some instances it may be desirable to carry outthis heating step in a protective atmosphere. For example,
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1080534
where a copier uses toner density control based on light
reflectance, it is important to uniformly maintain the color
of the carrier. When the heating step is conducted in air,
oxidation of the surfaces occurs which results in color
variations. Thus to prevent such color changes, a protective
atmosphere may be used. Examples of such protective atmospheres
are hydrogen, helium, argon, exothermic gas and endothermic
gas.
Preferably the fluorotelomer treated carrier particle
is mixed with a toner at a ratio of 98:2 respectively.
These ratios are based on weight as are all ratio and percentage
figures in this specification. The developer powder is
evaluated using the foilowing tests:
A. Faraday Cup measurement: these are carried out
as a function of fluorotelomer treatment and exposure
to various humidity conditions. It yields a charge
; to mass measurement that indicates the effectiveness
of the treatment.
B. Step tablet measurements: this gives an indication
as to toning characteristics of the developer powder.
Electrically insulated spots of 1 cm in diameter
are back charged in potentials of increasing voltage
in increments of 10 V. These spots are developed
to completion with the development powders from a
manual magnetic brush. The spots are evaluated for
print density fill in and other visually observable
characteristics.
C. Machine evaluation of the developer powdee in
a plain paper copier such as the PBC Copier,
Copier Division, Pitney-Bowes, Inc., Danbury, Conn.
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1108053'.~
Ideally one would like to have no drop in charge
to mass ratio at high relative hùmidity.
Example I
A control sample having no protective coating was
first prepared for purposes of comparison wherein 100 grams
of A~CO~ STEEL 1000 iron powder (Hoeganaes Corp.), Riverton,
N.J., having a mesh size of -l00/+250 is heated to 300 degrees
centigrade for 30 minutes in air. After cooling in the
atmosphere it was found that the iron turns blue due to
sùrface oxidation. A 2.4~ toner mixture using ISC toner
was made and the charge to mass (C/M) was measured at 10
coul/gm. By comparison, unheated Ancor Steel 1000 powder
gives a C/M of 10.5 ~ coul/gm.
Example II
A quantity of 4 kg of ANCOR STEEL 1000 iron powder
was placed in a dispersion of 20.5 gram~ of Vydax AR in
700 CC FREO F (trichlorotrifluoroethane) and 100 CC FREON-ll
~trichlorofluoromethane). The ingredients were mixed for
1/2 hour on rollers and filtered. The solvent was evaporated
until the iron powder was dry. A small batch of 2.4~ ISC
toner mixture was made using 100 gm. of the dried mixture
and the C/M was mèasured in at 15 ~coul/gram. The rest
of the treated iron powder was heated to 3D0 degrees centigrade
for 15 minutes to melt the telomer in order to form a coating.
It was cooled and aqain a 2.4% ISC toner nixture was made.
The C/M was measured as 24~ c ul/gram.
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Example III
A 4 ~g quantity of ANCOR sTEeL 1000 powder was added
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~i to a dispersion of 8 grams VYDAX 550 in 700 CC FREON TF
solvent and 100 CC FREON-ll solvent and mixed for 1/2 hour
on rollers. This mixture was then filtered and dried. Again,
a 100 gm batch of 2.4% ISC toner ~ixture was made and the
C/M was measured at 15~coul/gram. The rest of the treated
iron powder was heated to 300 degrees centigrade for 15
minutes, cooled and again a 2 . 4% ISC toner mixture was made.
The C/M was mea~ured as 24 ~ coul/~ram.
Examples IV - VI ~
The following various concentrates of VYDAX AR
in the solvent of Examples II and III were produced and
coated on iron powder.
IV) 0.16% of VYDAX AR.
V) 0.28% of VYDAX AR.
VI) 1.0% of VYDA ~AR.
Groups of 2.4~ ISC toner mixture were made with treated
iron powders from IV, V, VI above and they had C/~ ratios of
20.3, 21.8 and 22.2 ~ coul/gram respectively.
Example VII
O~e half gram of VYDA ~l000 was dispersed in 250
CC FREON TF and to that was added 100 gms. of iron powder.
The treated iron was heated to 325 degrees centigrade for
ten minutes. A 2. 4% ISC toner mixture was found to have
a C/M of 16 ~ coul/gram.
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Example VIII
Two grams of VYDAX 1000 in 250 CC of FREON TF was
used in treating 100 grams of iron powder. The treated
iron powder was heated to 325 degrees centigrade for ten
minutes. A 2.4~ ISC toner mixture was found to have a C/M
of 25 ~coul/gram.
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Example IX
Four kg of ANCOR STEEL 1000 powder and 20.5 grams_
VYDAX Ar were placed in 700 CC FREON TF and 100 CC FREON-ll
and mixed for 1/2 hour on rollers. The mixture was then
filtered and dried. A small 10 gm. batch of 2.4% PB toner
mixture was made and the C/i~ measured at 15 coul/gram.
The balance of the treated iron powder was heated to 300
degrees centigrade for 15 minutes and cooled. A 2.4% PB
toner mixture was made. The C/N was measured as 24 ~ coul/gram.
Example X
Four kg of ANCOR STEEL 1000 and 20.5 grams of VYDAX
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Ar were added to a blend of 700 CC FREON TF and 100 CC FREON-ll
and mixed for 1/2 hour on rollers. The mixture was filtered
and dried. A ten gram batch with 2.4~ ISC toner mixture
was made with the dried mixture and the C/M was measured
at 15~ coul/gram. The rest of the treated iron powder was
heated in argon atmosphere to 300 degrPes centigrade for
15 minutes and coolad. Again, a 2.4% ISC toner mixture
was made. The C/M was measured as 24 ~ coul/gram.
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Example XI
The same procedure as Example X was followed except
that the mixture was heated in a hydrogen atmosphere instead
o argon. The C/M was again measured as 24 ~ coul/gram.
Example XII
The same procedure as in Example X and XI were followed
except that the mixture was heated in nitrogen instead of
argon or hydrogen. Once more the C/M was measured as 24
coul/gram.
; This coated carrier material was used to make a 2%
developer mixture with Hunt toner 67-689. This development
powder was evaluated in a Minolta PPC 1000 copier and good
results were achieved.
Example XIII
The same procedures as in Examples XI-XII were followed
except that the mixture was heated in helium. The C/M was
again measured as 24 ~ coul/gram.
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Example XIV
One hundred grams of Cobalt powder -150/1270 mesh
was treated with 0.5 gram VYDAX AR in 25 CC of FREON 11.
After 30 minutes of mixing, the mixture was decanted and
the cobalt powder dried at 80 degrees centigrade -100 degrees -
~j centigrade for ten minutes. The dried powder was further
heated to 575 degrees fahrenheit -600 degrees fahrenheit
~ in a furnace for 5-10 minutes and cooled. The C/M of treated
I cobalt powder was determined when mixed with toner at 2.4%
concentrate and was found to be 23.7 ~ coul/gram. The unheated
cobalt powder under the same conditions gave a C/M of 10.2
cou~/gram.
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Example XV
Treatment conditions similar to that or Example XIV
were repeated except that nickel powder was used instead
of cobalt. The C/M of heated nickel powder was 15.2 ~ coul/gram
and the C/M of unheated nickel powder was 7.1~ coul/gram.
Development powders produced in accordance with the
above Examples I-XV were utilized in a PBC Copier in accordance
with standard techniques. Copies produced in those runs
showed good fill-in, good resolution and low background.
The copier in each instance was operated at -100 volts bias
instead of the standard level of 150 volts. The lower bias
is possible because of the characteristics resulting from
the fluorotelomer treatment. Additionally, iron pull-out
was reduced to 10~ of what was previously experienced without
any treatment of the carrier particles.
As stated previously, the primary advantages to giving
carrier powders a fluorotelomer teeatment are to reduce
oxidation, obtain a constant triboelectric charge and to
achieve low dusting. During the tests to determine the
effectiveness of the various fluoroterlomer coated carrier
materials disclosed in Examples I-XV, another advantage
was found. All the tests utilized a copier which uses
a photoconductive belt having a zinc oxide coating. It
was found that the life of the photoconductive belt was
e~tended considerably when used in cooperation with solid
toners having carrier powders treated in accordance with
the instant invention. Although the reason for the extended
life of the belt is not known, it is believed that the fluoro-
telomer coating~ have a lubricating e~fect.
It will be appreciated that the ratios of carrier
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po~der to toner ~isclosed in the above examples are for
devclopmcllt l-owdcrs ncwly char~cd to a copier and that the
development powder llad to be replenished with toner and
carrier particles in proper proportion as the same were consumed.
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