Toner composition

The present invention relates to an improved toner composition for electrophotography comprising an improved polyaniline charge control agent.

FIELD OF THE INVENTION 
The present invention relates to an toner composition for use in 
electrophotography comprising an improved charge control agent. 
BACKGROUND OF THE INVENTION 
In electrophotography an image comprising an electrostatic field pattern, 
usually of non-uniform strength, (also referred to as an electrostatic 
latent image) is formed on an insulative surface of an electrophotographic 
element. The insulative surface comprises a photoconductive layer and an 
electrically conductive substrate. The electrostatic latent image may be 
formed by imagewise photo-induced dissipation of the strength of portions 
of an electrostatic field of uniform strength previously formed on the 
insulative surface. Typically, the electrostatic latent image is then 
developed into a toner image by contacting the latent image with a toner 
composition generally containing a pigment. The toner image is then 
transferred onto a transfer medium such as paper and fixed thereon by 
heating and/or pressure. The last step involves cleaning residual toner 
from the electrophotographic element. 
Dry toner compositions used in electrophotography are divided into 
one-component compositions composed of a toner generally comprising a 
binder resin having a colorant dispersed therein and two-component 
compositions composed of a toner and a carrier. Charge control agents are 
generally melt mixed with the toner resin to control the level and range 
or distribution of charge of the toner during use. The desired level of 
chargeability is dependent on the method of development and development 
hardware. Charge control agents are often selected to achieve the desired 
charge level. High positive charge levels are often desired in 
electrophotography. It is also desired to have a narrow range of charge on 
the toner particles to avoid wrong sign toner particles and also to 
improve performance of the toner composition. Extraparticulate inorganic 
fine particles such as fumed silica are frequently added to toner 
compositions to improve fluidity and anti-caking properties. 
Monomeric charge control agents are known in the art such as amines and 
quaternary ammonium salts for positive charge toners and metal complex 
dyes for negative charge toners. These charge control agents are generally 
blended into the melted toner resin which is then cooled and ground into 
fine particles. Unfortunately, monomeric charge control agents exhibit 
fast charge decay after prolonged use. Polymeric charge control agents do 
not exhibit this fast decay after prolonged use. It is therefore desired 
to utilize polymeric charge control agents in toner particles to improve 
charge stability. 
Hitachi Japanese patent 2120865 dated May 8, 1990 discloses color toner 
beads comprising resin, conductive polyaniline and carbon black as a 
charge control agent. The carbon black is weakly charging and therefore 
the toner will have a low average positive charge and further, will have a 
broad range of charged particles making the toner susceptible to wrong 
sign toner particles. Therefore, there still is a need in the art for a 
suitable polymeric charge control agent for use in positively charged 
toner compositions. 
It is therefore an object of the present invention to provide an improved 
toner composition comprising an improved polymeric charge control agent. 
Other objects and advantages will become apparent from the following 
disclosure. 
SUMMARY OF THE INVENTION 
The present invention relates to an improved particulate toner composition 
for use in electrophotography comprising toner and base treated 
polyaniline which functions as a charge control agent. The base treated 
polyaniline is non-conductive. Optionally, the composition may also 
comprise a colorant, a carrier, inorganic fine particles and other 
additives known to those skilled in the art. Surprisingly, the base 
treated polyaniline provides the toner composition with a large average 
charge and also a narrow distribution of charge level on the individual 
toner particles to improve the performance of the toner composition. 
A more thorough disclosure of the present invention is presented in the 
detail description which follows.

DETAILED DESCRIPTION OF THE INVENTION 
The present invention relates to an improved particulate, dry toner 
composition for use in electrophotography comprising toner and base 
treated polyaniline. The key ingredient in the composition of the present 
invention is the based treated polyaniline. As used herein "base treated 
polyaniline" shall mean unsubstituted or substituted polyaniline which has 
been contacted with a base. The polyaniline for use in the present 
invention can be unsubstituted or optionally substituted with a variety of 
substituents which do not interfer with the charge control ability such as 
(i) N-substituted such as N-alkyl where alkyl is C.sub.1 -C.sub.10 or 
N-phenyl or (ii) substituted on the aromatic ring with substituents such 
as C.sub.1 -C.sub.10 alkyl, phenyl, halo, benzyl or C.sub.1 -C.sub.10 
alkylsiloxane. 
The polyanilines will suitably have a molecular weight (Mn) of about 4000 
to about 400,000. 
Polyanilines are commercially available and also can be synthesized by art 
known procedures. The base used to treat the polyaniline suitably has a 
concentration of about 0.1 to about 8 molar, preferably about 0.1 to about 
2 molar and pit of about 8 or greater, preferably greater than about 9, 
more preferably about 10. Very high pit may cause some degradation of the 
polyaniline. Preferably the base is a Bronsted base, preferably ammonium 
hydroxide or an alkaline base. The preferred base anion is hydroxy. 
The polyaniline is conveniently suspended in water and contacted with the 
liquid base (base dissolved in a suitable solvent, preferably water) for a 
short period of time of about 10-300 minutes with stirring. The 
polyaniline is then removed from the liquid base by filtration or 
centrifugation, rinsed several times with suitable solvent such as water 
to remove base and dried in a vacuum oven at room temperature e.g. 
20.degree. C. The base-treated polyaniline is electrically non-conductive 
having a conductivity less than 1.times.10.sup.8- seimens/cm, preferably 
less than 1.times.10.sup.-10 seimens/cm. 
A variety of toner particles known to those skilled in the art can be used 
in the toner composition of the present invention. Toner particles 
generally comprise a resin and optionally a colorant. 
As a resin for the toner particles to be used in the present invention, 
there may be employed homopolymers of styrene and its derivatives and 
copolymers thereof such as polystyrene, poly-p-chorostyrene, 
polyvinyltoluene, styrene-p-chlorostyrene copolymer, styrene-vinyltoluene 
copolymer; copolymers of styrene and acrylic acid ester such as 
styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, 
styrene-n-butyl acrylate copolymer, styrene-2-ethylhexyl acrylate 
copolymer; copolymers of styrene and methacrylic acid ester such as 
styrene-methyl methacrylate, styrene-ethyl methacrylate, styrene-n-butyl 
methacrylate, styrene-2-ethylhexyl methacrylate; multi-component 
copolymers of styrene, acrylic acid ester and methacrylic acid ester; 
styrene copolymers of styrene with other vinyl monomers such as 
styrene-acrylonitrile copolymer, styrene-vinyl methyl ether copolymer, 
styrene-butadiene copolymer, styrene-vinyl methyl ketone copolymer, 
styrene-acrylonitrile-indene copolymer, styrene-maleic acid ester 
copolymer; polymethyl methacrylate, polybutyl methacrylate, polyvinyl 
acetate, polyester, epoxy resin, polyvinyl butyral, polyacrylic acid 
resin, phenolic resin, aliphatic or alicyclic hydrocarbon resin, petroleum 
resin, chlorine paraffin, either individually or as a mixture. 
Suitable resins for the toner particles for use with pressure fixing 
electrophotography, are low molecular weight polyethylene, low molecular 
weight polypropylene, ethylene-vinyl acetate copolymer, ethylene-acrylic 
acid ester copolymer, higher fatty acid and polyester resin. Other types 
of suitable resins for toner particles in the composition of the present 
invention will be known to those skilled in the art. 
Optional colorants for the toner particles include a pigment or a dye as 
the colorant. For example, carbon black, solvent black, phthalocyanine 
blue, Ultramarine, quinacridone, benzidine yellow may be utilized. 
The resin, base-treated polyaniline and colorant components of the toner 
can be conveniently melt mixed together such as by melt-blending the 
components in a mixer such as a Rheomix twin screw mixer. The solidified 
melt is ground to desired size (size classified) to form a free-flowing 
powder of toner particles. Alternatively, the toner components can be 
solution blended in a volatile solvent such as dichloromethane and then 
atomized in a spray dryer to produce toner particles, as is well known. 
Alternatively, the base-treated polyaniline can be added with an 
extraparticulate as a flowing agent. 
Toner particles may have an average diameter between about 0.5 microns 
(.mu.m) and about 50 .mu.m, a value in the range from about 8.0 to about 
20 .mu.m being preferable for many currently used machines. However, 
larger or smaller particles may be needed for particular methods of 
development or development conditions. 
If desired, the toner of the present invention may further contain known 
additives such as release agents. 
The toner composition of the present invention will generally comprise 
about 90 to about 99.9 weight % of the toner and about 0.1 to about 10 
weight of the base-treated polyaniline preferably about 3 to 6 weight % of 
base-treated polyaniline. 
The toner particles of the invention may be used alone in monocomponent 
developers or may be mixed with a suitable carrier vehicle known to those 
skilled in the art for use in dual component developers. The carrier 
vehicles which can be used to form developer compositions can be selected 
from various materials. Such materials include carrier core particles and 
core particles overcoated with a thin layer of film-forming resin to 
establish the correct triboelectric relationship and charge level with the 
toner employed. Suitable carriers for two component toner compositions 
include iron powder, glass beads, crystals of inorganic salts, ferrite 
powder, nickel powder an these powders having thereon a resin coating such 
as epoxy or fluorocarbon resins. 
The toner composition of the present invention may also contain other known 
additives such as waxes and siloxane oils. 
The toner composition with extraparticulates can be made by admixing the 
components (toner and extraparticulates) together in a blender. 
The following examples are detailed descriptions of compositions of the 
present invention. The descriptions fall within the scope of, and serve to 
exemplify, the more generally described compositions set forth above. The 
examples are presented for illustrative purposes only, and are not 
intended as a restriction on the scope of the invention. 
Charging Experiments 
I. Components 
1. Toner--poly(styrene-co-butylmethacrylate). 
2. Polyaniline--polyaniline. 
3. Base-treated polyaniline is polyaniline which has been contacted with 
1.0 molar ammonium hydroxide (pH=10) for period of 5 hours, then dried and 
ground into particles &lt;40 nanometers. 
4. Toner Composition is dual component comprising (i) 97.5 weight % of 140 
micron steel carrier beads and (ii) 2.5 weight % of toner which comprises 
6 weight % polyaniline and 94 weight % poly(styrene-co-butylmethacrylate) 
II. Test Procedure 
The toner composition was rolled in a metal can for indicated period of 
time. Aliquots of the composition were then transferred to a Faraday cage, 
known as a blow-off cage, and the toner was blown away from the carrier 
and out of the cage using forced air. The charge on the toner was obtained 
from the charge (Q) an weight (M) change of the cage and was reported as 
Q/M 
______________________________________ 
TONER CHARGE (uc/g) 
Toner + 
Rolling Time Toner + base treated 
(min) Toner Polyaniline 
polyaniline 
______________________________________ 
0 0 -4 +3 
5 -3 -9 +5 
10 -7 -13 +7 
30 -21 -18 +13 
60 -37 -23 +16 
120 -44 -31 +20 
180 -38 -37 +21 
______________________________________ 
______________________________________ 
TONER CHARGE (uc/g) 
Rolling Time Toner + base treated 
Minutes N-ethyl polyaniline 
______________________________________ 
0 15 
5 20 
10 22 
30 26 
60 27 
90 27 
120 28 
180 27 
______________________________________ 
The results of the test suprisingly show that the base treated polyanilines 
of the present invention provide substantially greater positive charge 
control than conductive polyaniline. The greater positive charge control 
provides the toner composition with a large average positive charge which 
improves the performance of the toner composition. 
Although this invention has been described with respect to specific 
embodiments, the details thereof are not to be construed as limitations 
for it will be apparent that various embodiments, changes, and 
modifications may be resorted to without departing from the spirit and 
scope thereof, and it is understood that such equivalent embodiments are 
intended to be included within the scope of this invention.