WATER BASED MAGNETIC INKS AND THE MANUFACTURE THEREOF

ENCRES MAGNETIQUES A BASE D'EAU, ET MODE DE FABRICATION

English Abstract

WATER BASED MAGNETIC INKS AND THE MANUFACTURE THEREOF
Abstract of the Disclosure
Finely divided magnetic particles are rendered water-dispensible through
the aid of a combination of one or more nonionic wetting agents and one or
more cationic surface active agents. The magnetic material particles, as
used in a magnetic ink, are 50 to 300 .ANG. in size and are pre-coated with a
long chain unsaturated aliphatic fatty acid about C8 to C24, such as oleic
acid, linoleic acid, linolenic acid, myristolenic acid, or palmitoleic acid,
to maintain desired size particles while preventing agglomeration during
preparation and initial water dispension.

Claims

The embodiments of the invention in which an exclusive property or privilege
is claimed are defined as follows:
1. A process for preparing an aqueous magnetic ink which consists essentially
of dispersing magnetic particles in water in the presence of surface active
agents consisting essentially of about 5 to 10 weight percent of a nonionic
wetting agent based on weight of magnetic particles and about 2 to 15 weight
percent of cationic surface active agent based on weight of magnetic particles,
said nonionic wetting agent providing a surface tension between magnetic parti-
cles and water of 24 to 35 dynes per centimeter and said cationic surfactant
imparting a zeta potential of about +30 to +100 millivolts to the magnetic
particles.
2. The process of claim 1, wherein the magnetic particles are first coated
with an agent to prevent agglomeration thereon and then are dispersed in said
water.
3. The process of claim 2, wherein said agent is a C8 to C24 unsaturated ali-
phatic fatty acid.
4. The process of claim 3, wherein said acid is oleic acid, linoleic acid,
linolenic acid, myristolenic acid or palmitoleic acid.
5. The process of claim 2, wherein the magnetic particles are 50 to 300 A.
6. The process of claim 1, wherein the nonionic wetting agent is an alkyl
aryl polyether alcohol, wherein the alkyl chain contains 8 to 45 carbon atoms,
and contains about 8 to 15 mols ethylene oxide per mol.
7. The process of claim 6, wherein the alkyl aryl polyether alcohol is of
the formula:
<IMG>
wherein R is the alkyl chain and x is an integer from 9 to 10.
8. The process of claim 2, wherein the cationic surfactant is an alkylamine.
9. The process of claim 2, wherein the cationic surfactant is a quarternary
ammonium compound.
10. The process of claim 2, wherein the cationic surfactant is a quarternary
sulfonium compound.

11. The process of claim 2, wherein the cationic surfactant is a quarternary
phosphonium compound.
12. The process of claim 9 wherein the cationic surfactant is an ethoxylated
quarternary ammonium compound.
13. The process of claim 9, wherein the compound is of the formula:
<IMG>
wherein R and R1 are the same or different C8 to C24 straight or branched chain
alkyl groups and X is a suitable anion including a halogen ion.
14. The process of claim 13, wherein R and R1 are C12 to C18 alkyl groups.
15. The process of claim 2, wherein the magnetic particles are magnetite.
16. An aqueous magnetic ink consisting essentially of a dispersion of magnetic
particles in water in the presence of surface active agents consisting essen-
tially of about 5 to 10 weight percent of a nonionic wetting agent based on
weight of magnetic particles and about 2 to 15 weight percent of a cationic
surface active agent based on weight of magnetic particles, said nonionic
wetting agent providing a surface tension between magnetic particles and water
of 24 to 36 dynes per centimeter and said cationic surfactant imparting a zeta
potential of about +30 to +100 millivolts to the magnetic particles.
17. The ink of claim 16, wherein said wetting agent and surface active agent
are coated on the magnetic particles.
18. The ink of claim 17, wherein the magnetic particles are pre-coated with
an anti-agglomeration agent.
19. The ink of claim 18, wherein said agent is a C8 to C24 unsaturated aliph-
atic fatty acid.
20. The ink of claim 19, wherein said acid is oleic acid, linoleic acid, lino-
lenic acid, myristolenic acid or palmitoleic acid.
21. The ink of claim 18, wherein the magnetic particles are 50 to 300 A.
22. The ink of claim 18, wherein the nonionic wetting agent is an alkyl aryl
polyether alcohol, wherein the alkyl chain contains 8 to 45 carbon atoms, and
contains about 8 to 15 mols ethylene oxide per mol.
11

23. The ink of claim 22, wherein the alkyl aryl polyether alcohol is of the
formula:
<IMG>
wherein R is the alkyl chain and x is an integer from 9 to 10.
24. The ink of claim 18, wherein the cationic surfactant is an alkylamine.
25. The ink of claim 18, wherein the cationic surfactant is a quarternary
ammonium compound.
26. The ink of claim 18, wherein the cationic surfactant is a quarternary
sulfonium compound.
27. The ink of claim 18, wherein the cationic surfactant is a quarternary
phosphonium compound.
28. The ink of claim 25, wherein the cationic surfactant is an ethoxylated
quarternary ammonium compound.
29. The ink of claim 25, wherein the compound is of the formula:
<IMG>
wherein R and R1 are the same or different C8 to C24 straight or branched
chain alkyl groups, and X is a suitable anion including a halogen ion.
30. The ink of claim 29, wherein R and R1 are C12 to C18 alkyl groups.
31. The ink of claim 18, wherein the magnetic particles are magnetite.
12

Description

~062854
1 Background of the Invention
Magnetic inks are known formed of magnetic material dis-
persed in a liquid carrier.
The magnetic material is typically magnetite (Fe304),~f -
Fe203 and the 1ike. The magnetic material, in extremely finely div-
ided form of the order of submicron size, is more or less permanently
suspended in a liquid carrier with the aid of dispersing agents,
surfactants, and the like to form a colloidal magnetic fluid, typic-
ally referred to as a ferrofluid.
The liquid carrier employed is usually a non-aqueous sol-
vent, often an organic solvent of the non-polar type. Examples of
non-aqueous solvents usable in the preparation of ferrofluids are
aliphatic hydrocarbons, such as heptane, decane, mineral oil,
kerosene, and the like, halogenated hydrocarbons such as carbon
tetrachloride, trichloroethylene and the like, aromatic solvents
such as benzene, toluene and the like, silicone oils, etc.
The dispersing aid is included in the ferrofluid formulation
to prevent aggregation of magnetic material particles in the non-
aqueous solvent, which could lead to flocculation and deposition
out of suspension of magnetic material. The dispersing aid, which
may be one or more surfactants, wetting agents and the like, is
applied to coat the surfaces of the individual magnetic particles
so as to form a coating around the individual magnetic particles to
prevent agglomeration or flocculation due to attraction therebetween.
Aliphatic carboxylic acids having about 8 to 24 carbon atoms are
known as dispersing aids for magnetic material, such as magnetite,
to be colloidally suspended in non-aqueous solvents. In this
regard, see U.S. 3,531,413 and U.S. 3,764,540.
For certain applications of magnetic inks it is desirable
to employ water as the carrier fluid for the magnetic material in
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1 place of the more commonly used non-aqueous solvents. The present
invention is directed to the preparation of colloidal suspensions of
magnetic material, such as magnetite, in an aqueous medium, and the
ferrofluid so produced.
Accordingly, it is an object of the present invention to
provide a method for forming a colloidal suspension of magnetic
particles, particularly magnetite, in water.
Another object of this invention is to provide an aqueous
based magnetic ink.
A further object of this invention is to provide a specific
combination of dispersing aids which can be employed to colloidally
disperse magnetite in water.
Summary of the Invention
In accordance with the present invention, finely divided
magnetic particles are rendered water-dispersible through the aid
of a combination of one or more non-ionic wetting agents and one or
more cationic surface active agents.
In a preferred embodiment of this invention, the magnetic
material particles are 50 to 300 A in size, more preferably 75 to
200 A, and are pre-coated with a long chain unsaturated aliphatic
fatty acid about C8 to C24, such as oleic acid, linoleic acid,
linolenic acid, myristolenic acid, or palmitoleic acid, to maintain
desired size particles while preventing agglomeration during pre-
paration thereof and initial water dispersion. Other aids to pre-
vent agglomeration could be employed in this invention.
This non-ionic wetting agent is selected to provide a
bridge between the lyophilic disperse phase, i.e., magnetite, and
the aqueous dispersion medium.
The cationic surface active agent is selected to impart a0 relatively large charge on the magnetite particles, say of the
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1 order of a zeta potential of +30 to +100 mV. Quartenary ammon-
ium salts, amines and quartenary sulfonium or phosphonium compounds
are exemplary of the kinds of cationic surface active agents used
in the present invention.
Detailed Description of the Invention
Magnetic inks are used in magnetic ink jet printing where
a stream of ink is supplied under pressure and periodically inter-
rupted to produce droplets, which impinge upon a sheet of moving
paper. To obtain printing on the paper by the ink, it is necessary
that the droplets be spaced substantially uniform distances from
each other, be of uniform size, and be formed at a high rate such
as about 10 per second.
Magnetic ink is preferably isotropic and virtually free of
remanence. Magnetic ink suitable for ink jet printing is described
in this invention.
In order to prepare an aqueous based magnetic pringing ink,
it is necessary to have available magnetic particles of small size
characterized by high magnetic moment. Using magnetite as an
example, the particle size range should be about 50 to 300 A, pre-
ferably about 75 to 200 A. Magnetic moment, bearing in mind the
above disclosed use for aqueous magnetic inks of the present
invention, should desirably be within the range of about 65 to 80
emu.lgram of dried, e.g., air or vacuum, magnetic material, prefer-
ably about 70 emu./gram. Dispersed magnetite of size and magnetic
moment disclosed above, is available from a number of commercial
sources such as Sherritt Gordon Mines, Ltd., Canada, or may be
prepared in a manner well known in the art. For example, the follow-
ing general process may be employed.
Ferric chloride and ferrous chloride are dissolved in
separate bodies of water to form solutions thereof. The solutions
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1 are m;xed in amounts to mainta;n the molar ratio Fe 3/Fe 2 slightly
under the theoretical value of 2.0 without de-aerating the solutions.
Oxygen in the solution will oxidize some ferrous ions to ferric ions.
Magnetitie, Fe304, can be formed by chemical precipitation of the
ferrous-ferric mixture with base, such as ammonium hydrozide. In
order to favor a high rate of magnetite nucleation coupled with a
slow rate of particle growth, chemical precipitation can be carried
out at low temperatures, for example, in an ultrasonic bath main-
tained at about 5 to 12C. The pH of the mixture during chemical
precipitation for deposition of magnetite is maintained between
about 8.9 and 10.2, preferred pH is 9.5, with the amount of hydroxide
used being adjusted accordingly.
In order to aid in the prevention of agglomeration of mag-
netite during and immediately subsequent to chemical precipitation,
a dispersing aid is added to the precipitation mixture within a few
seconds of hydroxide addition. Ancillary to agglomeration prevention,
the dispersing aid will also help maintain desired small particle
size. The dispersing aid is selected from those materials known to
prevent inter-particle attraction between individual magnetite
particles. As discussed above, 8 to 24 carbon atom aliphatic mono-
carboxylic acids can be employed for this purpose. Finally, the
carboxylic acid coated magnetic particles in aqueous suspension are
heated to about 60 to 100C, to increase the magnetic moment thereof
and the pH of the mixture is decreased from about 8 to 6 to aid in
precipitation of the coated magnetite particles. Then, the particles
are rinsed with distilled water to remove NH4Cl salt and separation
can be carried out in any conventional manner, such as by use of
the ultracentrifuge.
Once magnetite particles of the preferred 75 to 200 A size
have been obtained or prepared as above, they are rendered water
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1 dispersible to form a colloidal dispersion in water by dispersing
them in combination with the two-component dispersing aid of the
invention. Both non-ionic and cationic are absorbed on the surface
of the magnetite particles.
The amount and type of non-ionic wetting agent is selected
to provide an interfacial tension between magnetite particles and
water of about 24 to 36 dynes/cm, preferably about 30 to 34 dynes
per cm. Generally, about 5 to 10 weight percent based on magnetite
of non-ionic wetting agent will be sufficient, preferably about 7
weight percent.
As noted above, the non-ionic wetting agent is selected to
provide a bridge between the lyophilic disperse phase, i.e., magne-
tite, and the dispersion medium of water. Non-ionics based on poly-
oxyethylene, due to the hydrophilic nature of the polyoxyethylene
chains, are suitable for use in the present invention. Alkylaryl-
polyether alcohols or alkylphenol ethers of polyethylene glycol
wherein the alkyl chain is of C25 to C45 and containing from 8 to 15
oxyethylene units can be employed, for example, of the formula:
R ~ OCH2CH2 ) xH
wherein R is the alkyl chain and x designates the number of oxyethy-
lene units present. The octyl or nonyl compounds wherein x is 9
or 10, are preferred due to their excellent water solubility and
reasonable viscosity, for example, nonyl phenol or tertiary octyl
phenol polyoxyethylenated with 9 to 10 moles of ethylene oxide.
The amount and type of cationic surface active agent is
selected to impart a zeta potential of about +30 to +100 mv, pre-
ferably about +60 to +90 mv, to the magnetite particles.
Usable cationics are quarternary compounds and amines, such
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1 as the quarternary ammonium salts, alkyl amines, quarternary
sulfonium compounds, quarternary phosphonium compounds and ethoxy-
lated quarternary ammonium compounds.
These cationics will generally be used in the concentration
of 2-15 based on magnetite, preferably 6% by weight.
As examples of quarternary ammonium salts, there may be
mentioned compounds of the formula:
CH3 +
R N - CH3 X-
Rl
wherein R and Rl are the same or different and are about 8 to 24 car-
bon atom branched or straight chain alkyl or benzyl radicals and
preferably R and Rl are C12 to C18 groups. A minor amount of unsat-
uration may be present in R and Rl. X is a suitable anion such as a
halogen ion.
As examples of sulfonium compounds, there may be mentioned
compounds of the formula:
R
R S+ X
L R _ l
As examples of phosphonium cationics there may be mentioned
compounds of the formula:
¦ R i
LR P - R Cl
R
In the above sulfonium and phosphorium compounds the R
groups are the same or different Cl to C24 alkyl groups, with pre-
ferably two of the R groups being methyl and the other(s) being at
least C8.
As examples of amine cationics, there may be mentioned
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106Z8S4
long chain alkylamines. Since there surfactants are pH sensitive, care must
be exercised in their use.
EXAMPLE
This example illustrates the preparation of a magnetic ink in accordance
with the present invention.
As the magnetite particles, magnetite prepared by any prior art method
coated with unsaturated fatty acid such as oleate, is used.
Oleate-coated magnetite particles (190 grams) are added to a suitable
mixing apparatus such as an attritor along with a solution of 2 grams of
potassium hydroxide and 2 grams of Ardefoam** (mineral and silicone oils
available from the Armak Chemical Division of Alzona, Inc., of Chicago,
Illinois, to act as a bubble breaker during the magnetic printing operation~.
Thereafter, a solution of cationic and nonionic surfactants is added thereto.
This solution is prepared by first dissolving 30 grams of Triton** N-101
(a polyoxyethylenated nonyl phenol containing 9 to 10 moles ethylene oxide
per mol available from Rohm and Haas Co.,) in 100 ml. of water. Then 10
grams of Arquad** 2H-75 (a dimethyldialkyl quarternary ammonium compound of
575 molecular weight wherein the dialkyl groups are 24% saturated hexadecyl,
75% saturated octadecyl and 1% unsaturated octadecenyl and having 75%* acti-
vity (available from Armak Chemical Division). Following 2 hours in the
attritor, the mixture is heated in a boiling bath of water for 3 hours, after
which it is cooled to room temperature and centrifuged for 45 minutes at 3000
rpm. The fluid remaining after decantation is useable as a magnetic ink.
Typical data for the magnetic ink is as follows:
Magnetic moment - 25-30 emu/gram
* Weight percentages in this specification are based 100% activity of
non-ionic and cationic compounds.
** Trade Mark
Y09-74-007 -8-

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1 Weight of ink - 400-450 grams
Viscosity - 11-17 cps
Surface Tension - 28-35 dynes/cm
pH - 6 - 8
Resistivity - 80-140 ~ cm
While the invention has been described in detail and with
reference to specific embodiments thereof, it will be apparent to one
skilled in the art that various changes and modifications can be made
therein without departing from the spirit and scope thereof.