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Description  |
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This invention relates to an ink composition suitable for use with jet
printers for inscribing onto surfaces which are non-absorbent or not
readily wet by water.
In the copending applications Ser. No. 571,215, filed Apr. 24, 1975, and
entitled "Printing Ink Composition for Jet Printing on Glazed Ceramic
Surfaces", and Ser. No. 590,802, filed June 27, 1975, and entitled
"Printing Ink Composition for Jet Printing on Glazed Ceramic Surfaces",
description is made of compositions suitable for meeting the
specifications for jet printing ink for use with present technology. Such
ink compositions depend upon the use of a vehicle having a water base in
which the various components of the ink composition are soluble. While
water based jet printing ink compositions are suitable for jet printing
onto paper or other surfaces onto which the ink can be readily absorbed
for fast drying, they have not been found to be suitable for use in jet
printing onto non-porous, non-absorbent surfaces such as glass, metals,
plastics, ceramics or the like surfaces, or surfaces coated and/or
laminated with plastic, metal, glass or synthetic resinous materials, or
surfaces which are characterized by hydrophobic, water repellent
properties, such as an oily, lubricated, or surfaces having a coating of
lubricant or parting compound which remains on the surface after molding.
There are a number of reasons why such water based jet printing inks have
been found to be unsuitable for use in jet printing onto such surfaces.
Included is the inability of such water based ink compositions to wet out
such surfaces with the result that surface tension causes the ink to
collect into droplets and produce characters of very poor definition.
In the absence of absorption into the surface for establishing a strong,
physical bond, reliance must be had upon chemical forces to establish a
strong bonded relationship between the dried ink composition and the
non-absorbent, non-porous surface onto which it is applied. The necessary
chemical bond is incapable of being established between water based ink
compositions and the surface with the result that the applied characters
can literally be wiped or washed off of the surface. Finally, by reason of
the lack of absorption into the surface, drying depends upon evaporation
of the water, with the result that the ink characters dry so slowly as to
reduce their utility for present high character speed technology in jet
printing.
Attempts have been made to overcome deficiencies such as rapid drying,
surface tension, and adhesion by replacement of water with alcohol.
However, while such alcoholic inks reduce some of the inefficiencies, such
as rate of drying and high surface tension, they remain insufficient from
the standpoint of adhesion of the dried ink characters onto surfaces of
the types described.
Thus it is an object of this invention to produce a jet printing ink
composition which is characterized by fast drying, low surface tension and
good wet-out and adhesion to non-porous, non-absorbent surfaces, and it is
a further object of this invention to produce jet printing inks of the
type described which are further characterized by the requirements of an
ink composition suitable for jet printing, namely, a viscosity within the
range of 1.5 to 10 cps, a resistivity below 2000 ohm-cm, a velocity of
sound of 1200-1700 m/sec, and insolubles of less than 5 microns in size,
as well as good rub resistance and fast drying.
More specifically, it is an object of this invention to produce a jet
printing ink composition formulated of a vehicle having an organic solvent
base, good wet-out of non-porous -- non-absorbent surfaces, and good
adhesion when dried to such non-absorbent -- non-porous surfaces, such as
surfaces of metals represented by iron, steel, tin plate, copper and the
like; surfaces formed of plastic or synthetic resinous materials such as
polyethylene, cellulose resins, epoxy resins, vinyl polymers and
copolymers, polyesters, polyamides, polyacrylic or polyalkylacrylic
resins, acetal resinous polymers, phenolic resins, butadiene-styrene
copolymer resins and the like; glass, glazed ceramics and the like
surfaces, as well as surfaces having a coating of such materials, or
coated with residual parting or lubricating compound used in molding
products having a surface to be printed or coded with ink composition by
the jet printing technique.
Ink compositions suitable for printing on such surfaces to provide a water
insoluble, rub resistant, well bonded imprint are well known but such
known ink compositions are not compatible with the jet printing process
from the standpoint of viscosity, resistance, and particulate matter, as
heretofore described.
It has been found, in accordance with the practice of this invention, that
the desired objectives in a printing ink composition suitable for jet
printing onto surfaces of the types described can be prepared when use is
made of a vehicle formulated predominantly of a ketone, in the form of an
aliphatic ketone, represented by acetone, methyl ethyl ketone, methyl
isobutyl ketone, and preferably an aliphatic ketone having up to 10 carbon
atoms in straight chain arrangement, or an alicyclic ketone such as
cyclopentanone, cyclohexanone, methyl isobutyl ketone or other alicyclic
ketone having up to 10 carbon atoms.
Ketone based jet printing ink compositions of this invention are
characterized by lower surface tension by comparison with water based inks
and they are better able to wet out hydrophobic surfaces and avoid
gathering of the applied ink composition into droplets on the surface. The
presence of such ketones, as a predominant proportion of the diluent,
enables the applied ink composition, while wet, to act upon the surfaces
formed of synthetic resinous materials or plastics to cause softening or
swelling whereby stronger and more permanent adhesion of the dried ink
characters can be obtained to the printed surface. In addition, such
ketone solvent components are highly volatile thereby to permit rapid
drying when applied to non-porous -- non-absorbent surfaces.
Unlike the strongly hydrogen bonded diluents, such as alcohol and water,
wherein the desired conductivity levels can be obtained merely by the
addition of the dye component, the ketones embodied in the formulation of
the jet printing ink compositions of this invention are only moderately
hydrogen bonded solvents such that it becomes necessary to incorporate a
solvent soluble, ionizable salt into the ink composition in order to
acquire the necessary conductivity.
Representative of solvent soluble ionizable salts that may be used are the
alkali metal and alkaline earth metal halides, such as sodium, potassium
and ammonium chloride, ammonium nitrate, alkali metal thiocyanates such as
sodium, potassium and ammonium thiocyanate, alkali metal alkylates such as
sodium, potassium or ammonium acetates. The desired results are secured
when the soluble ionizable salts are present in the ink composition in an
amount of at least 0.25% by weight of the ink composition. No added
benefit is derived when the amount of ionizable salt exceeds 2% by weight.
In the preferred practice of the invention, it is desirable to make use of
the ionizable salt component in an amount within the range of 0.5 to 1.0%
by weight of the ink composition.
The jet printing ink should produce an ink image which, upon drying, is
water insoluble, yet the ink composition itself should be water tolerant
to enable operation under highly humid conditions without undesirable
effect on the stability of the ink system. In fact, the conductivity of
the jet ink composition of this invention is benefitted by the presence of
a small amount of water, either added intentionally or absorbed from the
air when operating under high humidity conditions. The amount of water
present in the ink composition should not exceed 10% by weight of the ink
composition and it is preferred to restrict the amount of water to within
the range of 0 to 5% by weight.
Further improvement of the jet printing ink of this invention, from the
standpoint of adhesion in the substrate can be achieved by the formulation
of the jet printing ink composition to include a vinyl acetate copolymer
resinous component selected from the group consisting of vinyl acetate --
vinyl chloride copolymer, such as is available from Union Carbide Chemical
Company under the trade designations VINYLITE VYHH, VYHD, VYLF, VYNS,
VYNW, VAGH, VAGD, VMCH, VMCC, VMCA and VERR; and vinyl acetate -- crotonic
acid copolymers such as the type marketed by Monsanto Chemical Company
under the designations Gelva C3V10, C3V20, C3V30, C5V10, and C5V16.
The desired improvement in adhesion is not obtained by the use of vinyl
acetate homopolymer, vinyl chloride homopolymer, while other vinyl acetate
copolymers such as vinyl acetate - ethylene copolymer are not sufficiently
soluble in the ketone based ink composition to enable their use.
Although not essential to the ink composition, the presence of vinyl
acetate copolymer provides for improved adhesion. When present, it is
undesirable to formulate the jet printing ink with more than 6% by weight
of the resinous binder component. In general, the vinyl acetate copolymer
is formulated into the ink composition in an amount within the range of 0
to 6% by weight and preferably within the range of 2 to 4% by weight.
Even when such additional resinous binder component is present in the
printing ink composition, good adhesion is not obtained on surfaces formed
of polyester resins (Dacron), polyamide resins (Nylon),
polytetrafluoroethylene resins (Teflon), or silicone resins. Because the
ink is applied by liquid spray from a jet nozzle, the character of the
surface is not important in that the jet printing ink composition of this
invention can be printed onto surfaces which are flat, concave, convex,
terraced, embossed, rippled, and the like. The ink jet stream can reach
into surface irregularities where conventional printing means fail.
Having described the basic concepts of the invention, illustration will now
be made of examples of ink compositions representative of the practice of
this invention.
EXAMPLE 1
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Methylethyl ketone 80.7%
N-Methyl-2-Pyrrolidone 2.0
Diethylene Glycol Ethyl Ether
2.1
Water 5.0
Vinyl acetate - vinyl chloride
copolymer (Vinylite VMCH)
2.3
Polyvinyl butyral (Vinylite XYHL)
.9
Solvent soluble ionizable salt
(potassium thiocyanate) 1.0
Rhodamine B Base 1.0
Ethyl Alcohol 5.0
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The ingredients are merely combined to form a solution. The ink composition
has good imaging characteristics and good rub resistance when printed onto
metal or plastic surfaces by jet printing.
EXAMPLE 2
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Methyl Isobutyl ketone 78.7%
N-Methyl-2-Pyrrolidone 2.0
Diethylene Glycol Ethyl Ether
2.1
Water 5.0
Ethyl Alcohol 7.0
Vinyl acetate - vinyl chloride
copolymer (Vinylite VMCH)
2.3
Polyvinyl butyral (Vinylite XYHL)
.9
Solvent soluble ionizable salt
(potassium thiocyanate) 1.0
Rhodamine B Base 1.0
______________________________________
The ingredients are combined into a solution in any order. The ink
composition, which is similar to that of Example 1, except for the
substitution of methyl isobutyl ketone for methyl ethyl ketone, has
improved adhesion to can lids heavily coated with a mold release
lubricant.
EXAMPLE 3
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Methyl Isobutyl ketone 63.2%
Methylethyl ketone 17.0
vinyl acetate - vinul chloride
copolymer (Vinylite VMCH)
4.0
N-Methyl-2-Pyrrolidone 2.0
Diethylene Glycol Ethyl Ether
2.8
Methyl Alcohol 9.5
Solvent soluble ionizable salt
(potassium thiocyanate) .5
Methyl Violet Base 1.0
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This example illustrates an ink composition of this invention in which
water is absent as a component. It has a viscosity of 2.55 cps, a
resistance of 2500 ohm-cm and is easily jet printable.
EXAMPLE 4
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Methyl Isobutyl ketone 63.5%
Methyl Ethyl ketone 15.0
Vinyl acetate - vinyl chloride
copolymer (Vinylite VMCH)
3.7
N-Methyl-2-Pyrrolidone 2.0
Diethylene Glycol Ethyl Ether
2.5
Water 5.0
Methyl Alcohol 6.5
Solvent soluble ionizable salt
(potassium thiocyanate) .8
Methyl Violet Base 1.0
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This ink composition, which is similar to that of Example 3, except for the
addition of 5.0% by weight water, has a viscosity of 2.56 cps, and a
resistance of 660 ohm-cm. Jet printing was good and the dried printed
image has good rub resistance on all surfaces including surfaces having a
coating of a mold release agent.
EXAMPLE 5
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Methyl Isobutyl ketone 76.5%
Polyvinyl acetate - crotonic
acid copolymer (Gelva C5V10)
5.0
Nevillac Hard Resin 2.0
Ethylene Glycol Ethyl Ether
2.5
N-Methyl-2-Pyrrolidone 2.5
Water 5.0
Methyl Alcohol 5.0
Solvent soluble ionizable salt
(potassium thiocyanate)
.75
Methyl Violet Base .75
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The ingredients are combined as in the previous example to form a solution.
The ink composition has good jet printing characteristics and good
adhesion to metal and plastic surfaces, including surfaces coated with a
mold release agent.
The jet printing ink compositions of Examples 1 to 5 meet the requirements
for jet printability, namely, a viscosity within the range of 1.5 to 10
cps and preferably within the range of 2.0 to 6.0 cps; ink resistivity
below 2000 ohm-cm and preferably below 1000 ohm-cm; surface tension below
28 dyne/cm; a velocity of sound of the ink composition, insuring proper
nozzle resonance, of 1200-1700 m/sec. The ink compositions are filtered to
remove insolubles greater than 5 microns and preferably greater than 2
microns in size.
Rub resistance of the dried ink composition is measured by rubbing the
dried ink image with the thumb wet and dry. For good rub resistance, the
dried characters should resist removal by three hard rubs wet and dry.
The coloring component of the ink compositions of this invention is limited
to dyestuffs which are soluble in ketone, with or without small amounts of
water when present, alcohol when present, and the dissolved ionizable
salt. Representative of such ketone soluble dyestuffs are Methyl Violet
Base Dyes (C. I. solvent Violet 8), Rhodemine B Base Dyes (C. I. solvent
Red 49), and the like. It is sufficient to make use of a dye component or
mixture of dye components in a concentration of 0.25% by weight or more
and preferably in an amount within the range of 0.5 to 2.0% by weight.
In the above examples, the N-methyl-2-pyrrolidone and ethanol aid dye
solubility and promote water tolerance of the ink composition. They may be
replaced by other pyrrolidones and lower alcohols. When present, the
pyrrolidones are employed in an amount within the range of 0 to 4% and
preferably 1 to 3% by weight of the ink composition, and the lower C.sub.1
to C.sub.5 alcohols are employed within the range of 0 to 8% and
preferably 2 to 6% by weight of the ink composition.
The diethylene glycol ethyl or other glycol ethers serve as an agent to
control drying rate. For this purpose, such glycol ethers may be employed
in an amount within the range of 0 to 4% by weight and preferably 1 to 3%
by weight.
It will be understood that changes may be made in the details of
formulation of the ink composition without departing from the spirit of
the invention, especially as defined in the following claims.
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Description |
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