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Claims  |
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We claim:
1. A binderless ink composition, suitable for use in ink jet printing
operations and capable of bonding to synthetic polymeric resin surfaces by
softening and swelling the surface layers of the polymeric resin to allow
penetration of the ink, which comprises a solution of:
(1) a colorant selected from the group consisting of (a) a reactive
thermotropic dye capable of exhibiting a visible color change upon
exposure to steam at a temperature of at least about 215.degree. F. and
(b) a combination of dyes of different color capable of exhibiting a
visible color change upon exposure to water or steam at a temperature of
at least about 120.degree. F.;
(2) a solvent consisting essentially of from about 10 to about 35 percent
of water, from about 6 to about 25 percent of an aliphatic alcohol having
1 to 3 carbon atoms or mixtures thereof and from about 25 to about 75
percent of an organic compound selected from the group consisting of
aliphatic and cyclic ketones, amides, acetals, ethers and esters;
(3) from about 8 to about 17 percent of a surfactant and
(4) from about 0 to about 10 percent of an aliphatic hydrocarbon having
from 8 to 12 carbon atoms, the total percentage of the components
amounting to 100%.
2. An ink composition as claimed in claim 1, wherein said colorant is a
reactive thermotropic dye.
3. An ink composition as claimed in claim 1, wherein said colorant is a
combination of dyes of different color.
4. An ink composition as claimed in claim 2 or 3, wherein said organic
compound is 2-heptanone, said aliphatic alcohol is methanol or mixture
thereof with ethanol, said surfactant is sodium lauryl sulfate and said
aliphatic hydrocarbon is 1-decene.
5. An ink composition as claimed in claim 4, wherein said thermotropic dye
is a phenazine dye.
6. An ink composition as claimed in claim 4, wherein said combination of
dyes is an extractible/nonextractible dye pair.
7. A binderless ink composition, suitable for use in ink jet printing
operations and capable of bonding to synthetic polymeric resin surfaces by
softening and swelling the surface layers of the polymeric resin to allow
penetration of the ink which comprises a solution of 1% of a reaction
pehenazine dye capable of exhibiting a color change upon exposure to steam
at a temperature of at least about 215.degree. F., 57% 2-heptanone, 12%
methanol, 3% 1-decene, 13% sodium lauryl sulfate, and 14% water.
8. An ink composition as claimed in claim 7 wherein said dye is Janus Blue.
9. A binderless ink composition, suitable for use in ink jet printing
operations and capable of bonding to synthetic polymeric resin surfaces by
softening and swelling the surface layers of the polymeric resin to allow
penetration of the ink which comprises a solution of 1% of a combination
of dyes of different color of which one is extractible upon exposure to
water or steam at a temperature of at least about 120.degree. F., 57%
2-heptanone, 12% methanol, 3% 1-decene, 13% sodium lauryl sulfate and 14%
water.
10. An ink composition as claimed in claim 9 wherein said dye combination
is 0.6% Victoria Blue and 0.4% Palacet Yellow.
11. A method of indicating sterilization of articles having synthetic
polymeric resin surfaces which comprises applying markings to a surface of
said article using a binderless ink composition comprising a solution of:
(1) a colorant selected from the group consisting of (a) a reactive
thermotropic dye capable of exhibiting a visible color change upon
exposure to steam at a temperature of at least about 215.degree. F. and
(b) a combination of dyes of different color capable of exhibiting a
visible color change upon exposure to water or steam at a temperature of
at least about 120.degree. F.;
(2) a solvent consisting essentially of from about 10 to about 35 percent
of water, from about 6 to about 25 percent of an aliphatic alcohol having
1 to 3 carbon atoms or mixtures thereof and from about 25 to about 75
percent of an organic compound selected from the group consisting of
aliphatic and cyclic ketones, amides, acetals, ethers and esters;
(3) from about 8 to about 17 percent of a surfactant;
(4) from about 0 to about 10 percent of an aliphatic hydrocarbon having 8
to 12 carbon atoms; the total components amounting to 100%, and exposing
the marked articles to water or steam at sufficient temperature for a
sufficient time to effect a visible color change in said markings.
12. A method as claimed in claim 11, wherein said articles are polymeric
resin coated metal containers.
13. A method as claimed in claims 11 or 12 wherein said organic compound is
1-heptanone, said aliphatic alcohol is methanol, or mixture thereof with
ethanol, said surfactant is sodium lauryl sulfate and said aliphatic
hydrocarbon is 1-decene.
14. A method as claimed in claims 11, 12 or 13 wherein said markings are
applied by jet ink printing of said ink composition.
15. A method of indicating steam sterilization of articles having polymeric
resin surfaces which comprises:
applying ink jet printed markings to at least one surface of said article
employing a binderless ink composition which swells and softens the
polymeric resin to allow penetration of the ink, said ink composition
comprising a solution of (1) a reactive phenazine dye, (2) a solvent
consisting essentially of from about 10 to about 25 percent of water, from
about 6 to about 25 percent of an aliphatic alcohol having 1 to 3 carbon
atoms or mixtures thereof and from about 25 to about 75 percent of an
organic compound selected from the group consisting of 2-butanone,
2-pentanone, 2-hexanone, 2-octanone, 2,4-pentandione, furan, dioxane,
ethyl acetate, propyl acetate, butyl acetate, diemthyl acetamide, and
mixtures thereof: (3) from about 8 to about 17 percent of a surfactant and
(4) from about 0 to about 10 percent of an aliphatic hydrocarbon having
from 8 to 12 carbon atoms;
and exposing the marked articles to steam at a temperature of at least
about 215.degree. F. for a period of time sufficient to effect a visible
color change in said markings.
16. A method as defined in claim 15 wherein said ink composition comprises
1% Janus Blue, 57% 2-heptanone, 12% methanol, 3% 1-decene, 13% sodium
lauryl sulfate and 14% water.
17. A method of indicating sterilization of articles having polymeric resin
surfaces which comprises:
applying ink jet printed markings to at least one surface of said article
employing a binderless ink composition which swells and softens the
polymeric resin to allow penetration of the ink, said ink composition
comprising a solution of (1) a pair of extractible/non-extractible dyes of
different color; (2) a solvent consisting essentially of from about 10 to
about 25 percent of water, from about 6 to about 25 percent of an
aliphatic alcohol having 1 to 3 carbon atoms or mixtures thereof and from
about 25 to about 75 percent of an organic compound selected from the
group consisting of 2-butanone, 2-pentanone, 2-hexanone, 2-octanone,
2,4-pentandione, furan, dioxane, ethyl acetate, propyl acetate, butyl
acetate, dimethyl acetamide, and mixtures thereof; (3) from about 8 to
about 17 percent of a surfactant and (4) from about 0 to about 10 percent
of an aliphatic hydrocarbon having from 8 to 12 carbon atoms;
and exposing the marked articles to water at a temperature of at least
about 120.degree. F. for a period of time sufficient to extract said
extractible dye from said printed markings and thereby effect a visible
color change in said markings.
18. A method as defined in claim 17 wherein said ink comprises 0.6%
Victoria Blue, 0.4% Palacet Yellow, 57% 2-heptanone, 12% methanol, 3%
1-decene, 13% sodium lauryl sulfate and 14% water.
19. A method as claimed in claims 11, 15, or 17 wherein said articles are
polymeric resin coated metal containers. |
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Description |
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BACKGROUND OF THE INVENTION
1. Prior Art
The prior art appears to be best exemplified by the following patents which
were developed in a search:
______________________________________
Hainsworth 2,798,855 July 9, 1957
Hainsworth 2,798,856 July 9, 1957
Carumpalos 3,288,718 Nov. 29, 1966
Edenbaum 3,311,084 March 28, 1967
Edenbaum 3,360,339 Dec. 26, 1967
Verses 3,704,096 Nov. 28, 1972
Chapman 3,862,824 Jan. 28, 1977
Banczak 4,021,252 May 3, 1977
______________________________________
2. Field of the Invention
Metal cans constitute a very widely utilized medium for the protective
packaging of a great variety of products, many millions of cans being used
daily for packaging of foods, beverages and many other materials. For many
years, the common metal can was constructed of tinplated steel, and was
customarily referred to in the industry as an ETP can, the initials
standing for "electro-tin-plated." Containers of this type are referred to
by the public at large as "tin cans." In recent years, however, the metal
can industry has developed organic polymeric resinous coatings for metal
cans which offer substantially the same protection to the steel as
traditional thin coating of metallic tin. These organic resin based
coatings have been applied both as a top coat over the traditional thin
tin coating and as the sole protective coating composition applied
directly to the steel can body and/or end components to yield both resin
coated ETP cans and resin coated untinned steel cans which are now
referred to in the industry as "tin-free steel" or TFS cans. This
invention is directed primarily to ink compositions suitable for printing
identifying indicia on the resin coated surfaces of metal cans including
TFS and coated ETP cans as well as coated aluminum cans and can components
by means of ink jet printing techniques.
Manufacturing and processing concerns which package various products in
metal cans have found it highly desirable to print, at some point on the
can surface, a series of coded symbols which carry information of interest
primarily to the packager, including the particular machine on which the
can was packed, the date and time of packing and perhaps even the identity
of the machine operator. Such data are useful in case it is necessary to
trace any particular can or cans after they have been packed.
Many of the products packaged in metal cans are subjected to conditions of
high temperature and high moisture during pasteurization or sterilization
procedures carried out before or after the can is filled with product and
sealed. In order to be commercially satisfactory, the coded indicia
printed on the cans must be capable of withstanding these processing
conditions as well as being resistant to rubbing abrasion.
Another area of interest and need in the art relates to printable
sterilization indicators. Such compositions have heretofore utilized
pigment combinations, have been applied by contact printing techniques and
have been used primarily in determining whether proper sterilization heat
has been applied to objects used in medical and surgical procedures. In
the manufacturing and processing concerns which package various items in
metal cans discussed above, it is highly desirable, in addition to
providing coded symbols carrying information of value to the packager,
that some means are provided for visually determining when items have been
sterilized and/or pasteurized.
The provision of an ink composition which is adapted to a jet printing
technique, which is suitable for application to polymer coated surfaces,
abrasion resistant and resistant to the high temperature and high moisture
during pasteurization or sterilization (while at the same time undergoing
a visible and permanent color change when subjected to such processing
conditions) is the primary object of this invention. Another object of
this invention is to provide a jet ink composition capable of forming
markings which show a distinct difference in color among unsterilized and
completely sterilized packages.
Further objects of this invention will be apparent from the description of
the invention which follows.
SUMMARY OF THE INVENTION
The objectives of this invention are achieved by ink compositions which
contain no tackifying resinous binder and in which the solvent system is
composed of a homogeneous blend of water, a lower aliphatic alcohol, an
oxygenated aliphatic or cyclic ketone, ester or ether and, optionally, an
aliphatic hydrocarbon, the only other essential components being a soluble
colorant or colorant combination and a surfactant which serves the dual
functions of homogenizing agent and electrolyte.
The solvent system is so selected as to soften and swell the organic
polymer substrate sufficiently to allow penetration of the colorant into
the sub-surface structure thereof, whereby the indicia printed on the
substrate become highly resistant to abrasion and to conditions of high
temperature and humidity encountered in steam pasteurization and
sterilization processes.
The colorant is so selected as to produce a visible color change upon
exposure to water or steam at elevated temperature by one of two
mechanisms, i.e., through use of a colorant which reacts under process
conditions or through use of a combination of dyes one of which is an
extractible dye.
DETAILED DESCRIPTION OF THE INVENTION
The ink compositions of the present invention employ the mechanisms of
penetration of the organic coating and adhesion to the metal as disclosed
in copending application Ser. No. 634,507 filed Nov. 24, 1975 entitled
"Binderless Ink For Jet Printing" of Raymond L. Germonprez, a joint
inventor herein. As disclosed in said copending application, unlike
conventional inks which contain a tackifying, film-forming, resinous
binder which serves to bind the colorant to the substrate as an adherent
film is formed on the substrate surface upon evaporation of the volatile
ink solvents, the inks of the copending application and of the present
invention do not form a film over the surface of the polymeric coating
which covers the surface of a TFS or ETP can. The inks of the present
invention contain solvents which temporarily soften and swell the
polymeric resin coating of the TFS can sufficently to allow the colorant
component of the ink to penetrate the surface layers of the polymeric
coating. Upon removal of the ink solvents by evaporation, the colorant
component of the ink remains embedded in the resinous polymeric can
coating, primarily within the coating rather than on the surface thereof.
The protective coating of the TFS or coated ETP can thereby serves not
only as the substrate for supporting the printed indicia, but also as the
binder for the ink which, because of the penetration of the colorant into
the internal structure of the coating, becomes an integral part of the
coating and is substantially immune to abrasion, in contrast to normal
inks which remain as a surface film on the coating with little or no
penetration thereof.
In order to be effective in the process of the present invention, the ink
solvents must be capable of penetrating any waxy or oily lubricating film
residues which remain on the surface of the coated TFS can as a result of
the processing steps utilized in stamping and shaping the can components
from sheet or roll stock, and must effect temporary softening and swelling
of the polymeric resin can coating sufficient to allow penetration of the
colorant into the swollen body of the coating. The ink solvents, however,
must not dissolve or disrupt the can coating, destroy its adhesion to the
metal can surface or in any other way deleteriously affect the protective
poroperties of the coating.
In the selection of the ink solvents, therefore, consideration must be
given to achieving the desired effects on the can coating as well as
obtaining the proper solubility for the colorant and other components of
the ink and also achieving the desired viscosity and evaporative
characteristics, as will be discussed hereinafter.
With regard to the ink solvent effects on the can coating, satisfactory
solvents or mixtures of solvents may be selected for use with each of the
types of protective coatings customarily utilized on TFS or coated ETP
cans, including epoxy resins, polyvinyl chloride, acrylic resins,
polyamide-epoxy resin, polyamides, melamine modified alkyds, etherified
melamine formaldehyde-styrene resins and butadiene-styrene co-polymers.
Ketones, aldehydes and acetals are effective solvents for inks used for
printing on coatings of the polyvinyl chloride, epoxy, acrylic and
styrene-butadiene co-polymer types. Esters and ethers are also effective
with epoxy and acrylic type coatings, dimethyl acetamide and halogenated
alcohols are effectively used with polyamide resin coatings and
polyamide-epoxy resins, while aromatic organic solvents are satisfactory
for inclusion in inks for printing on the modified alkyd resins and
melamine formaldehyde resins when used as coatings on tin-free steel or
ETP can components. In general, the preferred solvents, particularly for
use with the epoxy and acrylic type resin coatings predominant in the
coated can field are oxygenated organic compounds of either aliphatic,
heterocyclic or aromatic type, selected in a particular case for giving
rise to the proper degree of softening and swelling of the substrate
coating during the jet printing operation.
Especially preferred as solvents herein are aliphatic ketones, for example
2-butanone, 2-pentanone, 2-hexanone, 2-octanone, 2,4-pentanedione, etc.;
cyclic ethers such as furan, dioxane, etc.; aliphatic esters including
ethyl acetate, propyl acetate, butyl acetate; amides including dimethyl
acetamide, etc. Mixtures of such preferred compounds may also be employed.
The properties of the solvent and the characteristics which are imparted to
the ink by the solvent are of paramount importance in the present
invention. It has been previously pointed out that the overall ink
composition must be of relatively low viscosity. Satisfactory results are
readily obtainable with inks having a viscosity as high as about 5 cps. at
68.degree. F., and it is possible to operate with ink having a viscosity
approaching 10 cps., although the jet printing process becomes
increasingly difficult to control as the ink viscosity increases. A
viscosity of about 1.90 cps. is considered optimal.
The propensity for the solvent to wet the substrate, as measured by the
property of surface tension of the solvent and of the ink composition
incorporating it is of great importance and must be carefully controlled.
Water, for example, will not properly wet the surface of a TFS can because
of its undesirably high surface tension (72 dyne cm. at standard
temperature) and inks having a water base are not satisfactory for use in
metal can printing, although such inks have been employed in jet printing
of paperboard, for example, since paperboard surfaces are readily wet by
water. On the other hand, oxygenated solvents such as ketones, alcohols,
ethers and esters, which have surface tensions much lower than water, may
wet TFS cans so readily that the coated metal surface is flooded by the
solvent, which spreads out and merges with other droplets to obscure the
limits of any indicia printed by use of these solvents. The inks of the
present invention, as used on a TFS can surface are compounded to have
surface tensions at 68.degree. F., of between about 22 and 35 dyne cm.,
the lower portion of this range being generally preferred.
In order to be effective in the formulation of a jet printing ink for metal
cans, the solvent medium must readily dissolve sufficient amounts of the
dye, the electrolyte and any desirable optional components to achieve the
desired level of conductivity and visual impact of the ink composition.
Further, since some degree of evaporation of solvent will occur in the ink
supply and ink return systems, thereby increasing the solids concentration
of the composition in these areas, the solvent must have a reserve solvent
power sufficient to prevent precipitation in this situation.
Although evaporation of the solvent from the ink supply and return systems
is generally undesirable, it is important that the solvent evaporate
sufficiently rapidly from the printed image area in order to leave the
printed indicia smearproof and moistureproof fairly promptly after the
printing operation is carried out. The solvent blend must achieve a
satisfactory balance in evaporative properties between these opposed
objectives.
As previously mentioned, in order for an ink to perform satisfactorily in
an ink jet printing system, the ink must have a high degree of
conductance, or conversely, a low specific resistivity. Since most organic
solvent ink systems are deficient in this respect, the compositions of
this invention include as components thereof a moderate amount of water
and an electrolyte, thereby greatly increasing the conductance of the ink
and its ability to accept an electrical charge on the droplets as they are
projected at the substrate target to be printed. The addition of water to
a basically organic-solvent-system ink tends to reduce the solution
stability of the system, and it has been found desirable to include an
organic surface active agent in the ink in order to restore and maintain
the stability of the ink composition. In this connection, it is most
convenient to employ as the electrolyte, a highly ionized surface active
agent such as sodium lauryl sulfate, which thereby serves the dual purpose
of providing the conductance to the ink and, at the same time, lending
solution stability to the overall ink system, which now includes both
water and an organic solvent of somewhat limited compatibility therewith.
It is, of course, obvious that separate components may serve these
individual roles, the surface active agent being of a non-ionic type and
the electrolyte being a salt such as lithium chloride, which has a
relatively high solubility in solvent systems such as those utilized
herein. In the preferred compositions, however, a single component
displaying surface active properties and also being strongly ionized is
utilized. Anionic surfactants such as sodium lauryl sulfate, alpha methyl
sodium lauryl sulfate are most desirable, and various cationic surfactants
may also be used, although the wetting properties of the cationics are
somewhat less satisfactory in the ink systems of this invention than those
of the anionic surfactants.
Colorants or dyes suitable for use in the ink compositions of this
invention are of two types hereafter described as (a) reactive and (b)
extractible/non-extractible pairs. cl A. REACTIVE DYES
Suitable dyes of this type are those which undergo a visible and permanent
color change when exposed to temperatures above about 215.degree. F. in
the presence of steam and which are soluble in the liquid ink base and
compatible with the components thereof.
A preferred class of dyes are those which may be classified as substituted
phenazines and diazotization products thereof derived by diazotization of
safranines, e.g., 3,7-diamino- 2,8-dimethyl-5-phenyl-phenazinium chloride,
with naphthols, phenols, aminobenzenes, etc. Representative dyes may be
represented by the formula:
##STR1##
wherein R.sub.1 and R.sub.2 are lower alkyl radicals or hydrogen, X is an
anion, for example, Cl.sup.-, Br.sup.- ; R.sub.3 is an aromatic
hydrocarbon radical, for example phenyl, tolyl, xylyl, etc., and Y is an
aromatic hydrocarbon radical or substituted aromatic hydrocarbon radical,
for example, 3-hydroxy-naphthyl, p- dimethyl aminophenyl;
p-hydroxyl-phenyl; 2-hydroxyl-4-ethyl amino-5-methylphenyl;
1,2-dihydroxypropyl-4-aminophenyl, etc.
Exemplary of such dyes are those available commercially as Janus Green B
(C.I. Blue 11050); Janus Blue or Indoine Blue (C.I. 12211); Janus Black
(C.I. 11825); Copying Black SK (C.I. 11957) and Copying Black 1059/1427
(C.I. 11090).
Although the mechanism by which the reactive dyes undergo a color change
are not known with certainty, it is believed that they undergo a chemical
reduction of the azo linkage under the conditions of the sterilization or
pasteurization resulting in a residual color forming moiety similar to
that of Safranine O(3,7-diamino-2,8-dimethyl-5-phenyl-phenazinium
chloride). Such a reaction may also involve a reduction generated on the
metal surface.
It is contemplated that other reactive dyes not specifically enumerated,
but of sufficient compatibility, solubility and reactivity under the
described conditions to undergo a color change, may also be employed.
In general, the dyes are present in the composition in amounts varying from
about 0.1% to about 5% by weight of the composition.
The preferred dyes are the diazo-phenazine class of dyes enumerated above
which have been found to exhibit a dark blue color upon application to the
substrate and to undergo a color change ranging from pink to red after
being subjected to a temperature of at least about 215.degree. F. in the
presence of steam for periods of time ranging from about 5 to about 30
minutes.
B. EXTRACTIBLE/NON-EXTRACTIBLE DYE PAIRS
Suitable dyes of this type are those which function in combination to
undergo a visible and permanent color change when exposed to temperatures
above about 120.degree. F. in the presence of water or steam. In addition
to such color transition characteristics, the dyes must also be soluble in
the liquid ink base and be compatible with components thereof.
As contemplated herein, pairs of dyes having differing solubilities or
extractability in water are employed. For example, a specific combination
may contain a water-extractible red dye and a relatively
non-water-extractible blue dye. The extractible dye is employed in a
weight ratio sufficient to give a discernible color change upon its
extraction, preferably at least about 2:1 of extractible to
non-extractible dye. Upon exposure to water at about 120.degree. F. or
higher the red dye is leached out or extracted and the substrate color
thus changes from purple to a permanent and visible blue color. The
leaching step which is critical to the successful operation of the
invention is not observed when water at temperatures below about
120.degree. F. is employed. Additionally, no change in color or leaching
takes place when the organic coating penetrated is fully cured or
cross-linked.
Particularly good results have been obtained when using Victoria Blue as
the non-extractible blue dye and Methyl Red as the more soluble leachable
red dye. Other suitable extractible/non-extractible combinations may be
illustrated by Victoria Blue/Palacet Yellow in which a green to blue color
change occurs upon extraction of Palacet Yellow.
Preferably extractible dye pairs are employed which change color at
temperatures as low as about 120.degree. F. others which change color at
somewhat higher temperatures may be employed if desired. The temperature
at which the dye becomes extractible is believed to be both a function of
its water-solubility as well as of the complexity of the dye molecule and
therefore will vary depending on the particular dye involved.
It will be obvious that other extractible/non-extractible dye pairs of the
same or different color combinations, although not specifically enumerated
hereinabove but of sufficient compatibility, solubility, etc. with the
components of the ink composition to function as desired, may be employed.
In general, the dyes will be present in the composition in amounts varying
from about 0.1% to about 5% by weight of the composition with the soluble
dye being present at levels sufficiently high to give a discernible color
change upon its extraction. In other words, the relative proportions may
be such that the dyes blend to form an intermediate color or one dye may
so predominate that only its color is visible in the blend. As long as
there is a visible color change upon extraction, such combinations are
useful herein.
The following examples are illustrative of ink compositions according to
this invention which are effective thermotropic jet inks.
EXAMPLE I
The following composition was formulated:
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Weight %
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2-heptanone 57
methyl alcohol 12
1-decene 3
sodium lauryl sulfate 13
water 14
Janus Blue 1
______________________________________
TFS cans, coated with an epoxy resin coating, were printed with the ink of
the above composition by known ink jet printing techniques with excellent
results, both as to the legibility of the printed indicia and their
durability when subjected to steam sterilization procedures customarily
employed in the canned food and beverage industry and to abrasion tests
which substantially obliterate indicia printed with standard, commercially
available inks. Subjecting the cans to sterilization in the presence of
steam at 240.degree. F. for about 20 minutes resulted in a visible color
change from blue to red.
In the above composition, other aliphatic ketones ranging in molecular
structure from 2-butanone to 2-octanone may be substituted for 2-heptanone
with substantially comparable results, although 2-heptanone is preferred
as having the optimum combination of evaporative and wettability
properties. Higher molecular weight ketones are somewhat slower to
evaporate, thus limiting the speed of the printing operation, whereas the
lower molecular weight ketones evaporate so rapidly that the ink does not
achieve optimum penetration into the interior structure of the polymeric
resin coating on the metal can surface. Amides or acetals of comparable
molecular weight may also be used. Other suitable oxygenated aliphatic or
cyclic solvents which may be substituted in whole or in part for the
2-heptanone in the above composition include ethers such as the propyl and
butyl ethers, furans and dioxans, and esters such as ethyl, propyl and
butyl acetate.
The function of the decene in the above composition is to cut through or
penetrate the thin layer of oily material which serves as a lubricant on
the resin coated metal surfaces of can components in the can forming
operations. Other effective grease-cutting aliphatic hydrocarbon solvents
having carbon chains of between 8 and 12 carbons, including decane,
dodecene, nonane, octane or isoctane may be substituted, if desired,
although decene is preferred as having the optimum evaporative properties.
A solvent of this nature is not necessary if the substrate being printed
does not have an oily surface. Molded plastic products and many plastic
resin coated substrates are free of such oily residues and decene type
solvents are not required in the ink composition in printing on such
substrates.
The methyl alcohol component lends homogeneity to the composition and may
enhance conductivity. It may range from about 6 to about 25 percent by
weight in the composition, the lower limit being established by the
necessity to keep the dye and 2-heptanone in solution and the upper limit
to prevent separation of the surfactant. Ethyl alcohol, n-propyl alcohol
or isopropyl alcohol may be substituted in whole or in part for the methyl
alcohol utilized in the above composition. Methyl alcohol is preferred
because of the lesser effect which variations in the concentration of this
solvent have on the conductivity of the ink. Inks wherein ethyl or propyl
alcohols are used are relatively sensitive in this respect and frequently
show a high specific resistivity (poor conductance) if the concentration
of the alcoholic component is increased by even a comparatively slight
degree.
The presence of water in the ink composition assures sufficient
electrolytic strength so that the ink performs properly in the jet
printing operation. The percentage of water should not exceed about 35%,
however, or the composition will not wet the substrate sufficiently to
enable the desired degree of drop spreading and penetration.
EXAMPLE 2
The following ink composition was formulated:
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Weight %
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2-heptanone 57
methyl alcohol 12
1-decene 3
sodium lauryl sulfate 13
water 14
Victoria Blue 0.6
Palacet Yellow 0.4
______________________________________
The procedure of Example 1 was repeated and comparable results were
obtained, the markings undergoing a visible change in color from blue
green to blue.
It will be seen from the above that the compositions of the invention, in
addition to their use as jet inks, are also valuable sterilization
indicators which can provide multiple functions in the packaging industry.
For example, use of the compositions to imprint indicia on metal cans
permits the packager to determine upon visual inspection of any given
batch of cans that the containers have been exposed to minimum retort
conditions of the character encountered during food processing.
Additionally, the presence of such visible indicia permits the ready
rejection of individual containers that have not been processed and
traceability of the origin of the container in the event of defects either
in the container or its contents. Additionally, provision of a
thermotropic ink usable in jet printing provides for obtaining the
above-mentioned functions more rapidly, permits faster code or character
changes and eliminates damage to the containers caused by many of prior
contact printing methods.
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