Process for reproducibly preparing uniform dry ink compositions comprising water-soluble cationic dyestuffs

The present invention concerns our discovery that a water-soluble cationic dye and binder composition may be dissolved in a solvent, and, optionally, a magnetic material may be uniformly dispersed within said solvent solution. The resulting solution or mixture is agitated with a hot water solution comprising an ionizable salt whereby there is essentially no partitioning of the cationic dyestuff into the aqueous phase. During the intermixing step, the solvent is driven off, thereby providing a solid mixture of ink which may be pulverized and used in a wide variety of printing processes.

The present invention relates to dry ink compositions and, more 
particularly, to dry ink compositions comprising cationic dyes which are 
useful in magnetic printing processes. 
BACKGROUND OF THE INVENTION 
Printing compositions comprising pigments or dyes have long been known in 
the art. Conventionally, printing inks have comprised solvents and one or 
more colorants whereby the inks have been applied by conventional printing 
processes. In recent years, dry ink compositions have come into wide use 
through the development of processes such as transfer printing, 
electrostatic printing and magnetic printing. Thus, industry has spent a 
substantial amount of time and effort to develop processes which are 
useful to prepare dry ink compositions. 
THE PRIOR ART 
Dry ink compositions which are presently available usually comprise a 
binder in which is dispersed a colorant. Such inks were initially made by 
selecting a solvent for the binder and the colorant (the colorant being 
dissolvable or dispersable in the solvent) and then evaporating the 
mixture to produce a solid product. However, the product which was 
obtained was generally unsatisfactory because the colorant was 
non-uniformly dispersed throughout the solid matrix. U.S. Pat. Nos. 
3,830,750 and 4,105,572 contain background information relating to the 
production of dry ink compositions. 
Basically, two general processes are presently in use for producing such 
compositions. These are melt extrusion techniques and spray drying 
techniques. Melt extrusion involves the preparation of a heat-softened 
resin which is mixed with a colorant to form a dispersion of material that 
is then cooled and pulverized to provide a powdered ink composition. This 
technique is generally unsatisfactory with respect to cationic dyestuffs, 
however, because these dyestuffs tend to be heat sensitive or subject to 
oxidative degradation. Furthermore, certain resins which do not extrude 
well or which thermally degrade cannot be satisfactorily intermixed with 
cationic dyes using this technique. For example, very high molecular 
weight polyvinyl chloride and high molecular weight ethyl cellulose resins 
do not process well using melt extrusion techniques. 
The other basic technique, spray drying, involves the preparation of a 
solution or dispersion of dye and binder in a solvent which is then 
sprayed into a drying chamber. In the drying chamber the solvent 
evaporates leaving fine particles of ink. Spray drying is not particularly 
desirable for several reasons. It involves the use of large and expensive 
equipment; there are pollution, fire and health hazards associated with 
the evaporation of the commonly used organic solvents in the heated drying 
chamber; and rigorous cleaning of the apparatus is required if different 
dye colors are to be prepared using a single unit. Furthermore, 
particularly with respect to cationic dyes, heat stability problems may be 
encountered during the drying process. 
A third technique which has not found wide acceptance is disclosed in U.S. 
Pat. No. 3,679,612. This invention was directed to the production of 
substantially spherical ink particles which were intended for use in 
electrostatic printing processes. The process involved the dissolution of 
a binder in a solvent, after which a colorant was dissolved or dispersed 
in the solution. The resulting solution or mixture was then dispersed in 
an inert non-solvent. The solvent preferably had a lower boiling point 
than the non-solvent so that, when the intermixed material was heated, the 
solvent evaporated leaving a solid material behind. The solid was then 
dried using a spray drying process. A preferred system comprised methylene 
chloride as the solvent and water as the non-solvent. 
This technique has been shown to be useful to prepare ink compositions 
comprising disperse dyes when water is the non-solvent because disperse 
dyes do not partition into the water. However, it has proved to be 
generally inapplicable to cationic dyes, because these dyes tend to be 
water soluble. Upon dispersing a solution or dispersion of a cationic dye 
and binder in an aqueous non-solvent, the cationic dye often partitions 
into the non-solvent. The solid which is produced thus has a non-uniform 
character and frequently is encrusted with dry dye powder. Thus, it is 
difficult, if not impossible, to use this method to prepare dry ink 
compositions wherein the color contents are adequately controlled. 
Accordingly, one objective of the present invention is to provide a process 
for preparing dry ink compositions comprising a cationic dye and a binder. 
Yet another objective of the present invention is to provide a process for 
preparing magnetic toners whereby the toner comprises a magnetic material, 
a binder and a uniformly dispersed cationic dye. 
These and other objectives of the present invention will become apparent 
from the detailed description of the preferred embodiments which follow. 
SUMMARY OF THE INVENTION 
The present invention concerns our discovery that a water-soluble cationic 
dye and binder composition may be dissolved in a solvent, and, optionally, 
a magnetic material may be uniformly dispersed within said solvent 
solution. The resulting solution or mixture is agitated with a hot water 
solution comprising an ionizable salt whereby there is essentially no 
partitioning of the cationic dyestuff into the aqueous phase. During the 
intermixing step, the solvent is driven off, thereby providing a solid 
mixture of ink which may be pulverized and used in a wide variety of 
printing processes. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In one embodiment the present invention comprises a process for producing a 
dry ink composition comprising a cationic dye, said process comprising the 
steps of preparing an organic phase comprising a solution of at least one 
water-soluble cationic dye and a binder in a suitable organic solvent, 
said organic phase optionally comprising magnetic particles substantially 
uniformly suspended therein, said solvent having a boiling point lower 
than that of water or being capable of forming an azeotrope with water, 
said azeotrope having a boiling point lower than that of water; 
intermixing said organic phase with an aqueous solution comprising an 
ionizable salt, sufficient ionizable salt being present to substantially 
prevent partition of said dye into said aqueous solution, the temperature 
of said aqueous solution being not less than said boiling point, said 
solvent being volatilized during intermixing thereby causing a 
substantially homogeneous solid mixture comprising said dye, binder and 
optional magnetic particles to precipitate; separating and drying said 
solid mixture; and pulverizing said solid mixture to obtain a desired 
particle size range. 
In a second embodiment the present invention comprises a dry ink 
composition comprising at least one water-soluble cationic dye, a binder 
and, optionally, magnetic particles, said composition having been obtained 
by preparing an organic phase comprising a solution of said dye and binder 
in a suitable organic solvent, said optional magnetic particles being 
substantially uniformly suspended therein, said solvent having a boiling 
point lower than that of water or being capable of forming an azeotrope 
with water, said azeotrope having a boiling point lower than that of 
water; intermixing said organic phase with an aqueous solution comprising 
an ionizable salt, sufficient ionizable salt being present to 
substantially prevent partition of said dye into said aqueous solution, 
the temperature of said aqueous solution being not less than said boiling 
point, said solvent being volatilized during intermixing thereby causing a 
substantially homogeneous solid mixture comprising said dye, binder and 
optional magnetic particles to precipitate; separating and drying said 
solid mixture; and pulverizing said solid mixture to obtain a desired 
particle size range. 
Applicants have discovered that inks comprising cationic dyes and binder 
may be uniformly prepared so as to be useful in a wide variety of transfer 
printing and magnetic printing processes. The problems normally 
encountered with the partitioning of cationic dyes into water, and the 
non-uniform inks resulting therefrom, are avoided. Furthermore, the 
problems encountered when cationic dyes are subjected to the conditions of 
the aforementioned spray drying or melt extrusion techniques are avoided, 
and the resulting toners are substantially less expensive than toners 
produced by these commonly used techniques. In addition, the present 
invention is also remarkably useful to produce toners which are usable to 
produce images having fine, sharp detail. Such toners are particularly 
adaptable to transfer print difficult-to-print substrates such as 
polyvinyl chloride. 
The solvent which is selected should be suitable to dissolve both the 
binder resin and the dye. This solvent may be miscible or immiscible with 
the hot water quenching bath with which it will ultimately be mixed; 
however, it should have a boiling point which is lower than that of water 
or, alternatively, it should form an azeotrope with water, in which case 
the azeotrope should have a boiling point which is lower than that of 
water. These boiling characteristics are desirable because residual 
solvent is detrimental in the final product, causing caking of the toner 
and vapor formation during the heating which is necessary to effect dye 
transfer. The presence of such vapors during transfer can lead to 
indistinct images. Solvents which have given very satisfactory results are 
acetone, methylene chloride, methanol, ethanol, tetrahydrofuran, 
chloroform and methyl ethyl ketone. 
Optionally, a magnetic material such as particles of finely divided iron, 
iron oxide or chromium dioxide will be present. When such particles are 
included in the solvent solution, the viscosity of said solution should be 
adjusted such that the particulate matter remains suspended. Too low a 
viscosity simply results in the magnetic material settling out. Preferably 
the viscosity is controlled by adjusting the binder/solvent ratio. 
A wide variety of resins will be adaptable to practice the present 
invention including polyvinyl chloride, polyacrylate, polyvinylidene 
chloride, polyethylene, polystyrene, copolymers of vinyl acetate and 
ethylene, melamine formaldehyde resins, organo polysiloxane resins, 
aldehyde resins, ketone resins, cellulose resins, epoxy resins, epoxy 
modified resins, phenol/formaldehyde resins, acrylic resins, and many 
others. Resins of these types comprise both thermoplastic and 
thermosetting resins. Examples of those resins which will be suitable are 
set forth in U.S. Pat. No. 3,679,612, said listing being provided by way 
of illustration and not by way of limitation. 
Where the resulting ink composition will be used in transfer printing 
processes, other considerations should also be taken into account in 
selecting the resin or binder. For example, certain binders such as 
polyvinyl alcohol or polyvinyl acetate will interfere with or impede the 
migration of the cationic dyes when they are subjected to the transfer 
printing process. Accordingly, a binder should be selected which does not 
cause this effect. Examples of binders which have given superior results 
are polyvinyl acetals, such as polyvinylbutyral; cellulose ethers, such as 
ethylcellulose and methylcellulose; and mixtures thereof. Such binders, 
however, are not restricted to use only for transfer printing processes. 
The solvent composition may also contain other ingredients. For example, 
solutions comprising cationic dyes and binders have shown a tendency to 
gel when aged for several hours. Such gelling may be avoided by adding a 
basic stabilizer which does not substantially affect the color of the dye. 
Amines, and particularly tertiary amines, have provided good results. One 
such tertiary amine is N,N,N',N'-tetramethylethylene diamine which has 
served not only as an anti-gelling agent but also as a dispersant for the 
magnetic particles, when present. Typically, the stabilizer is used at a 
level of from about 0.1 to about 5% of the total weight of the solvent 
composition. 
Anti-static additives may also be included to improve the properties of the 
dry ink compositions. Such compounds are well known in the art and include 
additives such as monomeric and polymeric quaternary ammonium salts. 
Virtually any ionizable salt can be used to practice the present invention, 
provided that it does not interact unfavorably with the dye. This salt is 
dissolved in water at a level which is suitable to substantially prevent 
partition of the cationic dye between the organic solvent phase and the 
aqueous phase. As a general rule, it is preferable to select ionizable 
salts that comprise an anion which is identical or very similar to that of 
the cationic dye. In this way, a detrimental exchange of the anion of the 
cationic dye is precluded. Although instances where detrimental results 
have been obtained due to this phenomenon are rare, the possibility 
exists. Accordingly, the use of an ionizable salt with a common or very 
similar anion is recommended, chloride or sulfate salts being preferred 
because they represent the counter ion in most cationic dyes. 
The quantity of salt which is utilized will depend to a great extent on the 
partitionability of the cationic dye. Some cationic dyes will tend to 
partition more readily than others, and the solvent which is used may also 
affect the amount of partitioning; accordingly, a greater quantity of salt 
would be required to prevent partitioning in such circumstances. 
Generally, about one pound of ionizable salt for each one gallon of water 
is preferred, although the quantity of salt which is selected is largely a 
matter of choice to the artisan. 
When practicing the present invention, the intermixing of the solvent and 
non-solvent will be accomplished when the temperature of the aqueous 
non-solvent is above that of the solvent. Preferably, the water induces 
the solvent to volatilize rapidly, thereby causing a rapid and uniform 
precipitation of the solid ink composition. 
Once the solid has precipitated, it may be separated by decantation or 
filtration, dried, and then pulverized by conventional techniques to 
produce an ink which is usable in the desired process. The objective, of 
course, is to provide a solid material which has the dye uniformly 
distributed throughout so that even deposition of dye is achieved during 
the selected printing process.

The advantages and utility of the present invention will become apparent 
from the examples which follow. 
EXAMPLE I 
A control toner comprising basic red 22 dye (Atacryl Red ALB; unspecified 
counter ion) was prepared in the following manner. A solution was prepared 
comprising 2295 ml of methlyene chloride, 450 ml of methanol, 423 g of 
polyvinylbutyral binder, 31.5 g of basic red 22 dye and 13.5 g of 
N,N,N',N'-tetramethylethylene diamine stabilizer by stirring for about 2 
hours. When all of the components were dissolved, 477 g of iron oxide 
(MO-7029 from Pfizer) was suspended to form a mixture whose viscosity was 
such that the solid particles did not settle out. The suspended material 
was quickly poured into a bath of rapidly stirred water maintained at 
about 90.degree. C., thereby causing the methylene chloride to flash off. 
The solid material settled to the bottom of the bath and was separated; 
however, a substantial amount of dye partitioned into the water as 
evidenced by a deep red color. Furthermore, the precipitated material, 
when separated, contained a crust of dye particles, indicating that the 
dye was not uniformly dispersed throughout the solid. This material gave 
generally unsatisfactory results when used as a toner. 
EXAMPLE II 
A second sample was prepared by dissolving 100 g of polyvinylbutyral 
binder, 10 g of the same basic red 22 dye and 2 g of 
N,N,N',N'-tetramethylethylene diamine in 2295 ml of methylene chloride and 
450 ml of methanol. After a solution was obtained, 105 g of iron oxide was 
suspended to form a mixture. 
A rapidly stirred hot water bath was prepared at 90.degree. C., the bath 
containing 2 pounds of sodium chloride and 1 pound of calcium chloride for 
every 3 gallons of water. The solvent suspension was quickly poured into 
this water solution, thereby inducing precipitation of the solid. In this 
instance, however, virtually none of the dye partitioned into the water as 
evidenced by the lack of color of the aqueous solution. Furthermore, when 
separated, the solid material had dye uniformly dispersed throughout and 
had essentially no dye crust as had been the case for Example I. 
EXAMPLES III-VII 
Examples III-VII illustrate experiments which establish the superiority of 
the present invention over the prior art process where a room-temperature 
quenching bath comprising no ionizable salt was used. A solvent 
composition containing the indicated ingredients was prepared for each 
example and 100 ml of each composition was poured into each of the 
following quenching baths: 
a. 320 ml of a solution comprising water and 80 g of sodium chloride at 
90.degree. C. 
b. 320 ml of water at 90.degree. C. 
c. 320 ml of a solution comprising water and 80 g of sodium chloride at 
25.degree. C. 
d. 320 ml of water at 25.degree. C. 
After intermixing was complete, the 25.degree. C. samples (samples c and d) 
were warmed to a temperature sufficient to drive off the solvent and 
precipitate the toner. The ultraviolet absorbance of each aqueous phase 
was then measured at a wavelength corresponding to a UV maximum for the 
dye. Comparison of the results indicated, in all instances, that less 
partitioning occurred for samples that were intermixed with the hot, 
salt-containing water solution. 
EXAMPLE III 
The solvent mixture comprised the following ingredients: 
______________________________________ 
Ingredient Weight (grams) 
______________________________________ 
Ethyl cellulose 154 
Basic red 22 (Sandocryl Red BBL; unspecified 
12 
counter ion) 
Magnetic oxide (Pfizer MO-7029) 
160 
N,N,N',N'--Tetramethylethylene diamine 
4 
Acetone 1,200 
______________________________________ 
After intermixing the solvent solution and precipitating the toner, the 
absorbance of samples from each aqueous bath was measured at 370 nm, as 
follows: 
______________________________________ 
Sample Absorbance (370 nm) 
______________________________________ 
IIIa 0.935 
IIIb 1.477 
IIIc 1.255 
IIId 2.030 
______________________________________ 
The hot salt bath (IIIa) is seen to have less partitioned dye than any of 
the other three samples. 
EXAMPLE IV 
The solvent mixture comprised the following ingredients: 
______________________________________ 
Ingredient Weight (grams) 
______________________________________ 
Ethyl cellulose 154 
Basic red 22 (Sandocryl Red BBL; unspecified 
12 
counter ion) 
Magnetic oxide (Pfizer MO-7029) 
160 
N,N,N',N'--Tetramethylethylene diamine 
2 
Methylene chloride 1,200 
______________________________________ 
After intermixing the solvent solution and precipitating the toner, the 
absorbance values were measured as described for Example III. 
______________________________________ 
Sample Absorbance (370 nm) 
______________________________________ 
IVa 0.692 
IVb 1.710 
IVc 2.400 
IVd 1.260 
______________________________________ 
As before, the hot salt bath (IVa) gave superior results. 
EXAMPLE V 
The solvent mixture comprised the following ingredients: 
______________________________________ 
Ingredient Weight (grams) 
______________________________________ 
Polyvinyl acetate 194 
Basic green 4 (chloride counter ion) 
8 
Magnetic oxide (Pfizer MO-7029) 
160 
N,N,N',N'--Tetramethylethylene diamine 
2 
Methylene chloride 1,000 
______________________________________ 
The absorbance values for these solutions were measured at 474 nm. 
______________________________________ 
Sample Absorbance (475 nm) 
______________________________________ 
Va 0.191 
Vb 1.095 
Vc 0.316 
Vd 0.317 
______________________________________ 
The hot salt bath (Va) was again superior. 
EXAMPLE VI 
The solvent mixture comprised the following ingredients: 
______________________________________ 
Ingredient Weight (grams) 
______________________________________ 
Ethyl cellulose 154 
Basic blue 66 (Atacryl Blue LLB; 
10 
unspecified counter ion) 
Magnetic oxide (Pfizer MO-7029) 
160 
N,N,N',N'--Tetramethylethylene diamine 
2 
Tetrahydrofuran 550 
Acetone 600 
Ethanol 600 
______________________________________ 
The absorbance values were recorded at 380 nm to give the following: 
______________________________________ 
Sample Absorbance (380 nm) 
______________________________________ 
VIa 0.055 
VIb 2.79 
VIc 0.133 
VId 2.59 
______________________________________ 
Again, the hot salt bath (VIa) gave superior results. 
EXAMPLE VII 
The solvent mixture comprised the following ingredients: 
______________________________________ 
Ingredient Weight (grams) 
______________________________________ 
Ethyl cellulose 154 
Basic blue 66 (Atacryl Blue LLB; 
10 
unspecified counter ion) 
Magnetic oxide (Pfizer MO-7029) 
160 
N,N,N',N'--Tetramethylethylene diamine 
2 
Chloroform 1,000 
______________________________________ 
The absorbance values were measured as described for Example VI, again 
indicating the superiority of the hot salt bath (VIIa). 
______________________________________ 
Sample Absorbance (380 nm) 
______________________________________ 
VIIa 0.066 
VIIb 0.107 
VIIc 0.206 
VIId 0.490 
______________________________________ 
EXAMPLE VIII 
This example illustrates that the same aqueous non-solvent may be used to 
prepare toners comprising different dyes without adverse results. Two 
different solvent mixtures were prepared as follows: 
______________________________________ 
Weight 
Ingredient Toner VIIIa 
Toner VIIIb 
______________________________________ 
Ethyl cellulose -- 1.57 lbs. 
Polyvinylbutyral 3.15 lbs. 1.57 lbs. 
Basic blue 26 18.2 g -- 
(chloride counter ion) 
Basic yellow 13 -- 63.8 g 
(chloride counter ion) 
Magnetic oxide (Pfizer MO-7029) 
3.55 lbs. 3.55 lbs. 
N,N,N',N'--Tetramethylethylene 
28.0 g 28.0 g 
diamine 
Methylene chloride 24.69 lbs. 24.9 lbs. 
Methanol 3.09 lbs. 3.09 lbs. 
______________________________________ 
A 40-gallon water bath containing 40 pounds of sodium chloride was heated 
to 90.degree. C. and toner VIIIa was quickly poured in with rapid 
stirring. After the solvent was removed, the precipitated toner was 
separated and the bath was filtered. No coloration was observed. The bath 
was reheated to 90.degree. C. and toner VIIIb was added in the same 
manner. Examination of the recovered toner showed no color contamination, 
and no dye partitioned into the water solution. 
The present invention is not restricted solely to the descriptions and 
illustrations provided above but encompasses all modifications envisaged 
by the following claims.