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Description  |
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FIELD OF THE INVENTION
The present invention relates to ink jet compositions, generally, and in
particular to jet ink compositions that are especially useful for marking
on food items, especially fruits and vegetables.
BACKGROUND OF THE INVENTION
Presently, most marking of information on food items, such as fruit, is
done by use of direct contact printing or labeling with stickers. Both
techniques present their own difficulties. Good print quality using direct
contact printing is difficult to achieve when printing on nonuniform,
irregular surfaces, as are presented when one attempts to print on
oranges, apples, grapefruit, and the like. Placing labels on such fruits
or vegetables can be difficult for the same reasons, and further requires
the consumer to remove the label before consuming a food item, such as an
apple, or the like.
It is often useful to place variable information on food items. One example
of such a need, generally in the case of fruits or vegetables, or citrus
fruit in particular, is the desire by suppliers to mark the fruit with the
"Price Look-Up" (PLU) Code. This PLU code is important at the retail level
for entering the proper price, based on fruit size. A quick, easy manner
of placing such information on food items is presently desired. Also,
desirable for brand recognition, is the ability to make images on the food
item, as by ink printing a corporate logo or the like.
Ink jet printing would offer the advantage of increased speed of marking
food products and the opportunity to put variable information on food
items, such as fruits and vegetables.
Ink jet printing is a well-known technique by which printing is
accomplished without contact between the printing device and the substrate
on which the printed characters are deposited. Ink jet printing systems
are generally of two types: continuous stream and drop-on-demand. In
continuous stream ink jet systems, ink is emitted in a continuous stream
under pressure through at least one orifice or nozzle. The stream is
perturbed, causing it to break up into droplets at a fixed distance from
the orifice. At this break-up point, the droplets are charged in
accordance with digital data signals. These drops are then passed through
an electrostatic field which adjusts the trajectory of each droplet. The
droplets are either directed back to a gutter for recirculation or to a
specific location on the substrate to create the desired character matrix.
In drop-on-demand systems, a droplet is expelled under pressure from a
valve directly to a position on the substrate in accordance with the
digital data signals. A droplet is not formed or expelled unless it is to
be jetted to the substrate. Since drop-on-demand systems require no ink
recovery, charging, or deflection, the system is much simpler than the
continuous stream system.
A problem associated with the direct marking of food items, such as
packaged fruit, however, is that the information on the fruit must remain
readable under a variety of conditions and must be stable, even in the
presence of moisture. Because packaged or boxed fruit is often subjected
to changing temperature and humidity conditions during transport, the
surface of the fruit can develop condensation or sweat. The printed
information on the surface of the fruit must remain readable even under
such temperature and humidity extremes and sudden changes therein. The
appearance of the printed image must not bleed, disappear, fade, or
transfer to other fruit placed in contact therewith, under any of the
conditions and environmental changes that fruit may encounter. For
example, FD&C Blue #1 (CI Number 42090) is a major colorant in making
violet or blue citrus inks. However, its sensitivity to water makes a
printed image formed therefrom on citrus "bleed" when condensation occurs
without the proper added ingredients. This is true to varying degrees with
all FD&C dyes, due to their water solubility.
To attempt to address this need for noncontact printing on fruits and
vegetables, some have suggested the use of ink jet printing. The problem,
however, has been that ink used in such a fashion must meet the
aforementioned rigid requirements, but also must be capable of being
printed by use of existing ink jet printing equipment. Further, the
printed image must be of food grade quality, edible and compliant with all
applicable regulatory requirements such as those set forth by the U.S.
Food and Drug Administration in the Code of Federal Regulations (CFR). In
PCT publication number WO92/14795 the use of certain ink jet formulations
has been mentioned in which a necessary component of the ink is methyl
ethyl ketone ("MEK"). However, the use of such a solvent for marking
fruits or vegetables is not desirable because it is not deemed acceptable
for such food contact and therefore does not comply with certain
governmental regulations, such as the regulations in the CFR that relate
to acceptable ingredients for making inks for marking fruits and
vegetables (Part 73, Chapter 1, Volume 21 of the CFR).
The aforementioned PCT application also suggests the use of ink
compositions that employ acetone in a mixture with water or an alkanol
and/or an alkyl ester, for ink jet printing onto a foodstuff. A cellulosic
material is used as a thickening and binding agent. The formulation may
optionally contain shellac or a rosin ester or certain other film-forming
resins. The PCT publication expressly states that problems related to
precipitation of dyestuffs and spreading of printed messages were
experienced when the alcohol content was beyond 50%. Although acetone may
be a suitable alternative to make an ink, its high evaporation rate makes
long-term printer operation a problem. This problem is caused by the
requirement of accurately maintaining the solvent balance of the ink while
running in the printer. The required make-up would need to be robust
enough to keep the solvents in the ink properly in equilibrium. This is
especially true if the ink were required to operate at different
environmental conditions of temperature and humidity.
An ink using acetone and water as the carrier, as suggested in the PCT
publication, that would operate at ambient conditions of temperature and
humidity, is difficult to employ in practice. Such an ink is even more
difficult to use if it includes an alcohol or combination of alcohols,
because of the problems in designing a suitable make-up solvent. If alkyl
esters are included or substituted for the alcohols in the ink (with
acetone still present), the job becomes even more complicated. The
elimination of acetone from the ink makes the creation of a make-up much
simpler.
Accordingly, there remains a need for a high quality ink jet composition
that can be used to print by ink jet printing onto the surfaces of fruits
and vegetable items, that will fulfill the rigid requirements as discussed
above and yet be suitable for such a food-contact use, and thus comply
with the list of acceptable ingredients as provided by governmental
authorities such as the U.S. FDA.
Such an ink must be capable of providing printed images with exceptionally
good moisture resistance, while employing components that are suitable for
food contact, such as FD&C water-soluble dyes.
SUMMARY OF THE INVENTION
Surprisingly, it has been discovered that it is not necessary to have
acetone as part of the solvent or carrier medium for ink compositions to
be applied to food items and that elimination of such a solvent provides
an improved ink for such a purpose. The carrier of the present invention
comprises ethanol, optionally in combination with a denaturing agent, such
as methanol.
Additionally, it has been found that wood rosin resins, especially
hydrogenated and highly hydrogenated wood rosin resins provide exceptional
adhesion of the ink to the surface of citrus fruits.
The present invention thus provides an ink composition for use in jet
printing on food items, especially fruits and vegetables, and a method of
forming printed images on such food items by use of such compositions.
The compositions of the present invention comprise a colorant, a binder and
a carrier. The composition is also characterized as being free of methyl
ethyl ketone and acetone.
The binders may be comprised of a cellulose derivative that is soluble or
dispersible in the carrier medium and/or at least one component selected
from the group consisting of hydrogenated wood rosin, shellac, and
ethylcellulose.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The formulated jet inks of the present invention will exhibit the following
characteristics: (1) a viscosity from about 1 to about 10 centipoise (cps)
at 25.degree. C., (2) an electrical resistivity from about 50 to about
2,500 ohms-cm.sup.-1, (3) a sonic velocity from about 1,000 to about 1,700
m/sec., and (4) a surface tension below 30 dynes/cm.
The Carrier
The carrier of the present invention comprises a lower alcohol, such as
ethanol. The lower alcohol may be a mixture of lower alcohols, such as the
denatured alcohol SDA-3A (ethanol with 5% methanol added as denaturant),
as is allowed by the U.S. FDA for this type of application. Thus, a
preferred carrier comprises ethanol and a denaturing agent, typically
methanol, and typically present in an amount of about 5%, based on the
total combined weight of ethanol and methanol.
The carrier may also include an alkyl ester, preferably ethyl acetate.
Water may also usually be present in the carrier. Deionized water is
preferred, for reasons of purity. The ethyl acetate, if present, is
usually present in an amount from about 5 to about 40 percent. The lower
alcohol, usually ethanol or a mixture of ethanol and methanol, is
typically present in an amount from about 5 to about 85 percent. The
water, if present, is usually present in an amount from about 0.5 to about
5 percent.
All percentages expressed herein are percentages by weight, unless
otherwise specified, and are based on the total weight of the ink
composition unless stated otherwise.
The Colorant
The composition of the invention also contains an image--forming component
which is soluble or dispersed in the solvent/carrier medium. The image
forming component can be in any suitable form having regard to the purpose
to which the image in the substrate is to be put. It is preferred that the
colorant be one which forms a visible image on the substrate, for example
a dyestuff or a pigment.
Useful colorants include the dyes: FD&C Blue #1; FD&C Blue #2; FD&C Green
#3; FD&C Red #2; FD&C Red #3; FD&C Red #40; FD&C Yellow #5; FD&C Yellow
#6. Also, Lakes (defined as aluminum salts of FD&C water soluble dyes) can
be used. They are available in powder form or predispersed in a suitable
liquid vehicle. The Lakes that are available are for FD&C Blue #1; FD&C
Blue #2; FD&C Red #3; FD&C Red #40; FD&C Yellow #5; FD&C Yellow #6.
Colorants from the Generally Recognized As Safe ("GRAS") List or specified
in Part 73 of Volume 21, C.F.R. Chapter 1 are especially preferred.
"Natural" colorants obtained from plants or extracts of insects, are also
suitable. Preferably, the colorant is a water-soluble dye.
The colorant is usually present in an amount from about 0.1% to about 20%
by weight of the ink composition, with an amount of from about 0.5 to
about 1.5% being preferred.
Binder Resin
As indicated, the binder resin of the present invention preferably
comprises a rosin resin, more preferably a wood rosin resin, and most
preferably a hydrogenated wood rosin resin. The most preferred
hydrogenated wood rosin resin is one that is characterized as being highly
hydrogenated, such as that sold by Hercules Incorporated under the
trademark Foral.RTM. AX.
The rosins or rosin derivatives that may be used include those listed in
.sctn. 172.615 of 21 CFR. Those include glycerol esters of partially
dimerized rosin, glycerol esters of partially hydrogenated gum or wood
rosin, glycerol esters of polymerized rosin, glycerol esters of tall oil
rosin, glycerol esters of wood rosin, partially hydrogenated methyl esters
of rosin, and pentaerythritol esters of partially hydrogenated gum or wood
resin.
In another embodiment, the binder may comprise a cellulose derivative,
preferably ethyl cellulose, along with shellac and/or a wood rosin resin.
The wood rosin may be a wood rosin or a hydrogenated wood rosin. The
preferred ethyl cellulose is described in Section 172.868 of Chapter 1 of
Volume 21 C.F.R.
Other film-forming resins also may be used to add adhesion of the ink
droplet to the substrate and to provide a measure of protection to the
dried droplet against abrasion and the action of water or other solvents
contacting the dried droplet. Any material that is capable of acting as a
binder from Part 184, Chapter 1, 21 CFR--direct food substances affirmed
as generally recognized as safe (GRAS List) may be employed. Such resins
can be used only in food grade forms.
In accordance with the present invention, then, it is possible to use a
rosin resin as the only binder, preferably a wood rosin resin. Most
preferably, the wood rosin resin is hydrogenated. The wood rosin resin is
preferably present in an amount from about 2 to about 25 percent based on
the total weight of the ink composition.
The film-forming cellulose derivative, preferably ethylcellulose, when
present, is usually present in an amount from about 0.2 to about 10
percent.
Shellac may be used in combination with the cellulose derivative alone as
the binder, or in combination with the rosin resin alone, as the binder.
Alternatively, shellac may be used in combination with both the cellulose
derivative and the rosin resin, especially with ethyl cellulose and wood
rosin resin, preferably hydrogenated wood rosin resin.
The Humectant
As stated above, the humectant prevents the ink jet tip from drying, and
the nozzle/valve from clogging. It can also act as a viscosity control
agent. Propylene glycol and any other suitable compound from the GRAS List
that has the desired properties can be used. Ink viscosity can be
tailor-made using this viscous material. Propylene glycol is preferred.
The humectant should be present in an amount from about 0.5% to about 4% by
weight of the ink composition, with an amount of from about 1.0 to about
2.0 being preferred.
Other Optional Components
Other components may also be included in the ink compositions of the
present invention to impart characteristics desirable for ink jet printing
applications. Volume 21, Chapter 1, Part 73.1 of the CFR under "Inks for
Marking Fruits and Vegetables".
The compositions of the present invention may also contain conductivity
agents. If present, they are present in amounts of from about 0.2% to
about 2.0%. Examples of suitable conductivity agents are food grade
ammonium, sodium or potassium salts of organic acids, such as sodium
acetate, potassium lactate or sodium propionate. The use of ammonium
chloride as a conductive agent is preferable.
A pH control agent may also be used in the ink composition from the GRAS
List to insure that the components of the ink composition remain soluble
throughout the range of water and throughout the ink's stated shelf life.
For this purpose, it is desirable to maintain the pH of the ink at about
7.0-10.5, e.g., about 7.5 and 10. A pH of 9.0 being optimal. The pH is
dependent upon the components which are employed in the composition.
Although use can be made of inorganic bases such as sodium hydroxide and
potassium hydroxide, their presence in the printed character leads to poor
water resistance after drying. It is preferred to make use of an organic
base which can be eliminated by evaporation. Best use is made of a pH
adjusting agent that evaporates rapidly to accelerate development of water
resistance upon aging. Thus, use can be made of ammonium hydroxide or
ammonium chloride for controlling pH within the desired range.
Typically, the pH control agent is present in an amount form about 0.10% to
about 5.0% by weight of the ink composition. The optimal amount will vary
depending upon the specific components of the ink composition.
The present invention may also comprise other additives, which may be any
substance that can enhance the ink with regard to (i) improved solubility
of other components, (ii) improved print quality, (iii) improved adhesion
of the ink to the media, and (iv) control of wetting characteristics,
which may be related to such properties as surface tension and viscosity,
among other properties. Again, because the principal application of the
inks of the present invention involve direct food contact, any such
additional components should be appropriate for food contact uses, such as
those components listed in Volume 21, Chapter 1, Part 73.1 of the CFR or
Part 184 of the same volume and chapter.
It is preferred to use all components in the composition which are food
grade or edible.
Manufacture
The ink compositions of the present invention can be made by conventional
means. Preferably, the colorant is dissolved or dispersed in the solvent
medium. The colorant may be in a dry, aqueous or other suitable solvent
form. The colorant is incorporated into the solvent medium for present use
using any suitable mixing technique. The colorant may also be available in
the form of a particulate solid or pigment, which can be used as such for
direct dissolution in the solvent medium. Many forms of suitable dyestuff,
notably water soluble food grade dyestuffs, are commercially available and
may be used in their commercially available purity.
All references cited herein are expressly incorporated herein in their
entirety.
The following Examples are illustrative of an ink jet composition of the
present invention and are not to be construed as limitations on the scope
of the invention.
EXAMPLE 1
The following formulation was made by mixing the components in the order
listed:
______________________________________
Material %
______________________________________
Ethyl acetate (Fisher Scientific)
27.0
Ethyl cellulose STD #4 (DOW)
1.8
SDA-3A Alcohol (Petro Products)
49.0
Shellac supplied in 50% ethanol
(Bradshaw - Praeger) 15.0
FD&C Blue #1 Dye (Warner - Jenkinson)
0.3
FD&C Red #3 Dye (Warner - Jenkinson)
1.1
NH.sub.4 OH (Fisher Scientific)
1.4
NH.sub.4 Cl (5% in water solution)
3.4
Propylene Glycol (Fisher Scientific)
1.0
100.0
______________________________________
The ink when applied by ink jet printing to lemons was reddish brown in
color and found to be storage stable after six cycles of transferring the
fruit from refrigerator to room temperature, without degradation of the
printed image.
EXAMPLE 2
The following formulation was made by mixing the components in the order
listed:
______________________________________
Material %
______________________________________
SDA-3A 200 Proof 81.5
Ethyl Cellulose 1.5
Foral AX 12.0
FD&C Blue #1 0.6
NH.sub.4 OH 1.4
NH.sub.4 Cl 5% solution
2.0
Propylene Glycol 1.0
Total 100
Viscosity 3.67
Resistivity 1263
pH 8.5
______________________________________
This blue ink when printed on lemons appears green. The formulation resists
condensation cycles from a refrigerator to room temperature, without
degradation of the printed image.
EXAMPLE 3
The following formulation was made by mixing the components in the order
listed:
______________________________________
Material %
______________________________________
Ethyl Acetate 30.8
Ethylcellulose 1.3
Hercules Staybelite Ester
4.0
SDA-3A Alcohol 37.8
Shellac 14.5
FD&C Blue Dye #1 0.4
FD&C Red Dye #3 0.2
Ammonium Hydroxide 0.5
Ammonium Chloride (20% in water)
1.5
100.0
______________________________________
This blue ink when printed on lemons appears green. The formulation resists
condensation cycles from a refrigerator to room temperature, without
degradation of the printed image.
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