Method for the preparation of electrostatographic toner of controlled shape by evaporative limited coalescence

A method is described for the preparation of electrostatographic toner particles which involves the use of carnauba wax for treating the surface of a pigment employed The method involves recrystallizing carnauba wax from its natural state by dissolution in ethyl acetate and cooling to precipitate needle like structures The structures so obtained are then added to a mixture comprising a pigment, a polymer material, a solvent and optionally a charge control agent which mixture serves as the organic phase in a limited coalescence process. The toner particles produced in accordance with this method are non spherical in nature and evidence excellent fluidity and anti-blocking properties.

FIELD OF THE INVENTION 
This invention relates to a method for the preparation of polymeric powders 
suitable for use as electrostatographic toner, and more particularly, to a 
method for the preparation of toner particles of controlled shape in which 
carnauba wax is employed for controlling sphericity of the particles. 
BACKGROUND OF THE INVENTION 
Electrostatic toner polymer particles are commonly prepared by suspension 
polymerization in a process commonly referred to as "limited coalescence". 
In this process, polymer particles having a narrow size distribution are 
obtained by forming a solution of a polymer in a solvent that is 
immiscible with water, dispersing the solution so formed in an aqueous 
medium containing a solid colloidal stabilizer and removing the solvent by 
evaporation The resultant particles are then isolated, washed and dried. 
In the practice of this technique, toner particles are prepared from any 
type of polymer that is soluble in a solvent that is immiscible with 
water. Thus, the size and size distribution of the resulting particles can 
be predetermined and controlled by the relative quantities of the 
particular polymer employed, the solvent, the quantity and size of the 
water insoluble particulate suspension stabilizer and the size to which 
the solvent-polymer droplets are reduced by the agitation employed. 
Suspension polymerization techniques of this type have been described in 
numerous patents pertaining to the preparation of electrostatographic 
toner particles because such techniques typically result in the formation 
of toner particles having a substantially uniform size and uniform size 
distribution. Representative suspension polymerization processes employed 
in toner preparation are described in U.S. Pat. Nos. 4,314,932, 4,360,611, 
4,415,644, and 4,789,617. 
U.S. Pat. No 4,789,617 is representative of the prior art in this field and 
describes a process for the preparation of electrostatographic toner 
particles by solution polymerization. This process involves dispersing a 
polymerizable monomer, a colorant and a low softening point compound in an 
aqueous medium heated to a temperature above the polymerization 
temperature to form particles of the monomer composition and then adding a 
water insoluble polymerization initiator to the aqueous medium to effect 
solution polymerization. This results in the formation of polymerization 
toners which are spherical in nature, of required fluidity, and evidence 
excellent anti-blocking characteristics and sharp particle size 
distribution. These toners contain large amounts of a low softening point 
compound having a softening point within the range of 
40.degree.-130.degree. C. Examples of the low softening point compound 
employed are paraffins, waxes, low molecular weight polyolefins, modified 
waxes having an aromatic group, natural waxes, and long chain carboxylic 
acids having a long hydrocarbon chain including 12 or more carbon atoms. 
Among the waxes described are beeswax, carnauba wax and montan wax. The 
low softening point compounds employed are used in an amount ranging from 
50- 3000 parts by weight to 100 parts by weight of polymerizable monomer. 
The net result of this prior art technique is the production of spherical 
toner particles of sharp particle size distribution which evidence 
excellent fluidity and anti-blocking properties. 
The shape of the toner particles prepared in accordance with the foregoing 
prior art technique and that of the aforementioned representative patents 
is generally spherical, especially when the size of the particles is 
smaller than 10 microns. This is of particular concern to those skilled in 
the art since it is also known that particle size and shape have a bearing 
upon the electrostatic toner transfer properties. Thus, for example, the 
transfer efficiency of toner particles has been found to improve as the 
sphericity of the particles is reduced Accordingly, workers in the art 
have long sought to modify the shape of the evaporative limited 
coalescence type toners independently of pigment or binder choice in order 
to enhance the transfer properties of the toner. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, this end has been successfully 
attained by a novel process in which carnauba wax is introduced into the 
organic phase of the limited coalescence process in a limited amount. It 
has surprisingly been found that the use of this limited amount of this 
specific wax, i.e., carnauba wax, which is highly surface active in 
nature, results in the formation of non-spherical toner particles once the 
solvent is removed. The toner particle shape is controlled or modified by 
the limited amount of this specific wax independently of the toner polymer 
(resin, binder matrix) and optional pigment used to form the toner. 
Further, it has been determined that the degree of non-sphericity is 
directly related to the wax concentration The resulting non-spherical 
shape of the carnauba wax containing particles enhances electrostatic 
transfer efficiency of the toner particles from the developed 
electrostatic latent image to a receiver such as plain paper. Also, since 
carnauba wax is an essentially colorless substance, it does not affect the 
hue of toners in which it is included with the toner pigment. 
Viewed from one aspect, the present invention is directed to a method for 
the preparation of electrostatographic toner. The method comprises the 
steps of dissolving carnauba wax in ethyl acetate heated to a temperature 
of at least 75.degree. C. and cooling the solution, so resulting in the 
precipitation of the wax in the form of very fine needles a few microns in 
length; recovering the wax needles and mixing therewith a polymer 
material, a solvent and optionally a pigment and a charge control agent to 
form an organic phase; dispersing the organic phase in an aqueous phase 
comprising a particulate stabilizer and homogenizing the mixture; and 
evaporating the solvent and washing and drying the resultant product. 
Viewed from another aspect, the present invention is directed to a process 
for preparing electrostatographic toner by dispersing an organic phase in 
an aqueous phase to yield a layer of particulate suspension stabilizer on 
the surface of a polymer The improvement in the process comprises adding 
carnauba wax in ethyl acetate to a polymer material, a pigment and 
optionally a charge control agent to form the organic phase in the 
aforementioned limited coalescence process. 
These and other features and advantages of the invention will be better 
understood taken in conjunction with the following detailed description 
and claims. 
DETAILED DESCRIPTION OF THE INVENTION 
In accordance with the present invention, a solution of carnauba wax in 
ethyl acetate is prepared. Carnauba wax is a natural product extracted 
from the leaves of the Brazilian palm tree. It is a hard wax normally 
found in large brittle chunks which must be converted into a form useful 
in the practice of the invention. The first step then in the process 
involves dissolving the wax in its natural form in ethyl acetate heated to 
a temperature of about 75.degree. C. Following this, the solution is 
cooled and in the cooling process the wax precipitates in the form of very 
fine needles of a few microns in length. 
The next step in the inventive process involves mixing the wax needles so 
obtained with a pigment, a polymer material (binder, resin, toner matrix), 
ethyl acetate and optionally a charge control agent to form an organic 
phase in which the pigment concentration ranges from about 2.0 to 30.0%, 
by weight, based on the weight of the total solids present, and the 
pigment to wax ratio ranges from about 1:1 to 1:0.05. The charge control 
agent is employed in an amount ranging from 0 to 10 parts per hundred, 
based on the total weight of solids present, with a preferred range from 
0.2 to 3.0 parts per hundred. The ethyl acetate solvent is employed in an 
amount ranging from about 250 to 900% based upon the total weight of 
solids present This mixture is permitted to stir overnight and then 
dispersed in an aqueous phase comprising a particulate stabilizer. 
The particulate stabilizer selected for use herein may be selected from 
among highly cross-linked polymeric latex materials of the type described 
in U.S. Pat. Nos. 4,965,131 which issued on Oct. 23, 1990 to M. Nair et 
al., or SiO.sub.2. 
These stabilizers typically have colloidal dimensions. The size and 
concentration of these stabilizers controls and predetermines the size of 
the final toner particles. In other words, the smaller the size and/or the 
higher the concentration of such particles, the smaller the size of the 
final toner particles. The particulate stabilizer is generally used in an 
amount ranging from about 1-15 parts, by weight, of the final product. 
Any suitable promoter that is water soluble and affects the 
hydrophilic/hydrophobic balance of the solid dispersing agent in the 
aqueous solution may be employed in order to drive the solid dispersing 
agent, that is, the particulate stabilizer, to the polymer/solvent 
droplet-water interface. It will be appreciated by those skilled in the 
art that the promoter is required only when silica is employed as the 
stabilizing agent. When latex is employed for this purpose, the 
hydrophobic/hydrophilic characteristics are provided by the polymers 
employed. Typical of such promoters are sulfonated polystyrenes, 
alginates, carboxy methyl cellulose, tetramethyl ammonium hydroxide or 
chloride, diethylaminoethylmethacrylate, water soluble complex resinous 
amine condensation products such as the water soluble condensation 
products of diethanol amine and adipic acid, water soluble condensation 
products of ethylene oxide, urea and formaldehyde and polyethyleneimine. 
Also effective for this purpose are gelatin, casein, albumin, gluten and 
the like or nonionic materials such as methoxycellulose. The promoter is 
generally used in an amount from about 0.2 to about 0.6 parts per 100 
parts of aqueous solution. 
Various additives generally present in electrostatographic toner may be 
added to the polymer prior to dissolution in the solvent or in the 
dissolution step itself, such as charge control agents. Suitable charge 
control agents are disclosed for example in U.S. Pat. Nos. 3,893,935; 
4,079,014; 4,323,634 and British Patent Nos. 1,501,085 and 1,420,839. 
Charge control agents are generally employed in small quantities such as 
from about 0 to about 10 parts per hundred based upon the weight of the 
final toner product, and preferably from about 0.2 to about 3.0 parts per 
hundred based on the weight of the toner. 
The resultant mixture is then subjected to mixing and homogenization. In 
this process, the particulate stabilizer forms an interface between the 
organic globules in the organic phase and the aqueous phase. Due to the 
high surface area associated with small particles, the coverage by the 
particulate stabilizer is not complete. Coalescence continues until the 
surface is completely covered by the particulate stabilizer. Thereafter, 
no further growth of the particles occurs. Accordingly, the amount of the 
particulate stabilizer is inversely proportional to the size of the toner 
obtained. The relationship between the aqueous phase and the organic 
phase, by volume, may range from 1.5:1 to approximately 9:1. This 
indicates that the organic phase is typically present in an amount from 
about 10% to 40% of the total homogenized volume. 
Following the homogenization treatment, the solvent present is evaporated 
and the resultant product washed and dried. 
As indicated, the present invention is applicable to the preparation of 
polymeric toner particles from any type of polymer that is capable of 
being dissolved in a solvent that is immiscible with water and includes 
compositions such as, for example, olefin homopolymers and copolymers, 
such as, polyethylene, polypropylene, polyisobutylene and 
polyisopentylene; polyfluoroolefins, such as polytetrafluoroethylene and 
polytrifluorochloroethylene; polyamides, such as polyhexamethylene 
adipamide, polyhexamethylene sebacamide, and polycaprolactam; acrylic 
resins, such as polymethylmethacrylate, polymethylacrylate, 
polyethylmethacrylate and styrene-methylmethacrylate; ethylene-methyl 
acrylate copolymers, ethylene-ethyl acrylate copolymers, ethylene-ethyl 
methacrylate copolymers, polystyrene and copolymers of styrene with 
unsaturated monomers, cellulose derivatives, polyesters, polyvinyl resins 
and ethylene-allyl alcohol copolymers and the like. 
Pigments suitable for use in the practice of the present invention should 
be capable of being dispersed in the polymer, insoluble in water and yield 
strong permanent color. Typical of such pigments are the organic pigments 
such as phthalocyanines, lithols and the like and inorganic pigments such 
as TiO.sub.2, carbon black and the like. Typical of the phthalocyanine 
pigments are copper phthalocyanine, mono-chlor copper phthalocyanine, and 
hexadecachlor copper phthalocyanine. Other organic pigments suitable for 
use herein include anthraquinone vat pigments such as vat yellow 
6GLCL1127, quinone yellow 18-1, indanthrone CL1106, pyranthrone CL1096, 
brominated pyranthrones such as dibromopyranthrone, vat brilliant orange 
RK, anthramide brown CL1151, dibenzanthrone green CL1101, flavanthrone 
yellow CL1118; azo pigments such as toluidine red CL69 and hansa yellow; 
and metallized pigments such as azo yellow and permanent red. The carbon 
black may be any of the known types such as channel black, furnace black, 
acetylene black, thermal black, lamp black and aniline black. The pigments 
are employed in an amount sufficient ti give a content thereof in the 
toner from about 1 to 40%, by weight, based upon the weight of the toner, 
and preferably within the range of 4 to 20%, by weight. 
The hard wax chosen for use in the practice of the present invention is 
carnauba wax, a naturally occurring wax which has a melting point of 
83.degree. C. The wax is available from commercial sources and is employed 
in an amount ranging from 0.1% to 40%, by weight, based upon the weight of 
the final toner. Studies have revealed that the use of greater than 40 
weight per cent results in the formation of a mixture which is too viscous 
and yields a brittle product whereas the lower limit of 0.1% is dictated 
by practical considerations. 
The invention will be more fully understood by reference to the following 
exemplary embodiment which is set forth solely for purposes of exposition 
and is not to be construed as limiting.

EXAMPLE 1 
In a pint jar, 200 milliliters of 1/8" stainless steel media were placed 
together with 15 grams of carbon black pigment (REGAL 300 manufactured by 
Cabot Corp.), 7.5 grams of butyl acetate-styrene copolymer (PICCOTONER 
1221 manufactured by Hercules Powder Co.), 2 2.5 grams of 33% carnauba wax 
in ethyl acetate and 140.0 grams of ethyl acetate. The wax had been 
dissolved in ethyl acetate at about 75.degree. C. and recovered in the 
form of fine needles as a precipitate by cooling the resultant solution 
and then redissolved in ethyl acetate to form the 33% solution. 
The resultant mixture was then milled for 3 days to yield a concentrate. 
Next, 74.0 grams of the concentrate was added to 426.0 grams of ethyl 
acetate containing 88.0 grams of a butyl acetate-styrene copolymer 
(PICCOTONER 1221) in solution. This mixture was comprised of 6% pigment, 
3.0% carnauba wax and 91% binder copolymer and comprised the organic phase 
in this evaporative limited coalescence process. The organic phase was 
then added to an aqueous phase comprising 1500 milliliters of a buffer 
solution having a pH of 10 containing 54.0 grams of a latex dispersion 
comprising 3% solids in water. This mixture was the subjected to very high 
shear using a Polytron sold by Brinkman followed by a Microfluidizer. Upon 
exiting, the solvent was removed from the particles so formed by stirring 
overnight at room temperature in an open container to yield elongate 
particles which were of the order of 7 microns volume average and entirely 
non. spherical. 
EXAMPLE 2 
The procedure of Example 1 was repeated with the exception that the 
carnauba wax was omitted from the mixture. The resultant particles were 
completely spherical in nature and were approximately 7 microns in size. 
EXAMPLE 3 
The procedure of example 1 was repeated with the exception that the carbon 
black pigment was replaced by NOVAPERM YELLOW HR 11-1400 manufactured by 
Hoechst Celanese Co. The resultant particles were totally non-spherical in 
nature and approximately 7 microns in size. 
EXAMPLE 4 
The procedure of example 1 was repeated with the exception that the carbon 
black pigment was replaced with the cyan pigment bridged aluminum 
phthalocyanine. The resultant toner particles were totally non-spherical 
and 7 microns in size. 
EXAMPLE 5 
The procedure of example 1 was repeated with the exception that the pigment 
was omitted. The resultant toner particles were found to be entirely 
non-spherical in nature. 
EXAMPLE 6 
The procedure of example 5 was repeated with the exception that the 
carnauba wax was omitted. The resultant toner particles were perfectly 
spherical in nature. 
While the invention has been described in detail with reference to certain 
preferred embodiments, it will be understood that variations may be made 
by one skilled in the art without departing from the spirit and scope of 
the invention. Thus, for example, different polymer compositions and 
pigments may be utilized throughout the examples for those employed.