Note: Descriptions are shown in the official language in which they were submitted.
915,366
--1--
STABILIZED LATENT SENSITIZING COMPOSITION
The present invention relates to humidity-
stable, latent sensitizing cornpositions and latent sensi-
tizing inks prepared Erom these compositions. ~ore
particularly, stabili~ed, latent, Elexographic sensitizing
compositions are described.
Impact or pressure-sensitive self-marking carbon-
less transer papers have been known for a number of
years. The most common type of carbonless impact transfer
paper comprises sheets having coated on the back surface
~reverse surface) thereof tiny microscopic capsules
containing liquid fill and haviny chemically reac-tive
color-forming metal chelating compounds conventionally
referred to as dye precursors thereln. These coatings are
commonly referred to as CB coatings. The other surface of
15 the sheet, generally the top surface or front surface
(obverse surface), has a dry coating of a coreactant
metal~containing chemical for the dye precursor. These
sensitizing coatings are commonly referred to as CF
coatings. When the CF and CB coatings are brought into
20 contact, such as in a multi-sheet form, and pressure is
applied so as to rupture the capsules on the CB surface
and cause the dye precursor to migrate onto the CF
coating, a chemical chelating reaction takes place and a
colored complex is formed in the area oE the ruptured
25 capsules. The dye precursor in the capsules can be one of
the known dye precursor metal chelatin~ materials such as
2-
the N,N'~di-substituted dithiooxamide chelating agents
which will form colored complexes with a transition metal
cations. A particular substituted dithiooxamide
derivative which has been ound useful is the combination
of N,N'di-benzyl-dithiooxamide (DBDTO) and N,N'-
bis(2-octanoyl oxyethyl) dithiooxamide (DOEDTO). These
materials are usually present in an organic solvent, such
as cyclohexane, within the microcapsule and are generally
present in amounts of about 4% to 8% by weight of the
capsule fill.
The CF sensitizing coating used with these dye
precursor CB materials contains a coreactant chemical
which is a transition metal salt. Nickel salts are
preferred since they tend to provide fairly colorless
coatings prior to reaction. Other metal catlons, such as
mercury, cadmium, leadr zinc, copper, cobalt and silver
will also produce images. However, certain of these
compounds such as cobalt, cadmium and zinc cation con-
taining compounds react with the dithiooxamide derivatives
to produce very nearly colorless products. Consequently,
where the use of white paper is desired, they form images
haviny very little, if any, contrast with the background
of the paper itself. The transition metal sal~ may be the
salt of an organic or inorganic acid. Thus~ nickel salts
of, for example, nitric or sulfuric acid can be used.
More preferably, the salts of organic acids are used.
Nickel rosinate and nickel-2-ethylhexoate are two widely
--3--
used color forming transition metal salts.
Becaùse the CF and CB imaging compositions are
generally relatively colorless when applied to sheets and
form color only aEter reaction takes place, these
/ 5 materials are commonly referred to as latent sensiti2ing
: composltlons.
Previously, the application of these latent
sensiti2ing materials involved the coating o the complete
surface of substrates using aqueous coating compositions
and techniques. These techniques do not lend themselves
to the application of the latent materials in selected,
patterned areas. Accordingly, it is desired to provide
latent, sensitizing compositions, particularly latent CF
sensitizing compositions containing transition metal
salts, which can be applied to selected, patterned areas
of a substrate by conventional printing and coating
techniques.
one such sensitizing composition is described in
U.S~ Patent 4,111,4~2, issued September 5, 1978. It has
20 been found, however, that such compositions, which by
necessity must remain "open" and receptive to the dye
precursor material released by the capsules on a CB sheet,
also may exhibit reduced imaging speed and intensity on
prolonged storage due to interaction with atmospheric
25 moisture, Further, in certain circumstances, transer of
the sensitizing composition to the overlying CB sheet may
occur. This "back transfer" can then cause objectionable
6~
coloration on ~he overlying CB sheet.
According to the present invention there is provided a latent, stabi-
lized, sensitizing composition characterized in that said composi-tion comprises a
solution of a color--forming, transition metal salt of an inorganic or organic acid
and a stabilizing amount oE di-terpene stabiliæing agent in a substantially non-
aqueous liquid vehicle, wherein said inorganic acid is one which will provide
salts with transition metals which dissociate in the non-aqueous liquid vehicle to
provide the transition metal for the color-forming reaction, or said organic acid
is selected from aliphatic and aromatic mono- and di carboxylic: acids, substituted
aliphatic or aromatic rnonocarboxylic acids and heterocyclic monocarbo~ylic acids.
The present invention overcomes the difficulties encountered by prior
art compositions by providing a transition metal salt color-forming component in
combination with a stabilizing agent for said color-forming component such that
the composition is stable in a substantially non-aqueous vehicle and is not degra-
ded significantly by the effects o~ atmospheric moisture following applica-tion to
a substrate. Inks formulated utilizing these compositions do not exhibit objec-
tionable back trans~er. The stabilized imaging composition comprises a blend of
(1) a color-forming transition metal sal-t and, (2) a diterpene stabilizing agent,
dissolved in a substantially non-aqueous (i.e. less than 50% by weight water),
liquid vehicle. These latent compositions are referred to herein as "stable" or
"stabilized" in that they retain a greater percent of their initial image speed
and intensity over time, particularly when exposed to conditions of high relative
humidity following application to a substrate, than do compositions not having the
stabilizing agent.
While not wishing to be bound by any particular theory or mechanism, it
is believed that the transition metal salts may undergo hydrolysis in the presence
of atmospheric moisture forming undesirable side products which reduce the concen-
--4--
tration of the color-forming component a~ailable. It is beli.eved that the
stabilizing
~4a-
agents used in the present invention tend to inhibit the
hydrolysis or its undesirable effects and allow the
imaging composition to substantially main-tain its initial
imaging characteristics even under conditions of high
humidity. More specifically, it is believed that the
diterpene stabilizing agents may react with free
transition metal ions which may be form~d by hydrolysis or
dissociation of the color-forming transition metal salt to
form a more stable, nickel diterpenatel which in itself is
a color-forming compound. Thus, by addition of an
appropriate amount of the diterpene stabilizing agent,
stabilized sensitizing compositions can be provided and
various liquid, latent, sensitizing compositions can be
formulated, such as flexographic inks, gravure inks,
off-set in~s, lithographic inks and other coating and
printing compositions.
The color-forming transition metal salts useful
in the present invention can be the transition metal salts
of organic or inorganic acids. The preferred transition
metal salts are the nickel salts, although copper iron and
other transition metals can be used to advantage. Inor-
ganic acids which can be used to form the transition metal
salts are acids which will provide salts with transition
- metals which dissociate to provide the transition metal
for the color-forming reaction. Exemplary inorganic acids
are nitric acidr sulfuric acid, hydrochloric acid and the
like.
--6--
The organic acids which are useful in ~orming
the transition metal salts of the present invention are
th~ aliphatic and aromatic mono- and di- carboxylic acids,
substituted aliphatic and aromatic monocarboxylic acids,
and heterocyclic monocarboxylic acids. Monocarboxylic
aliphatic acids containing about 6 to 10 carbon atoms are
preferred. Nickel-2-ethylhexoate is a particularly
preferred color-forming transition metal salt. Otber
nickel salts which have been investigated are nickel
stearate, nickel rosinate, nickel laurate, nickel acetate,
nickel-2-ethylhexoate, nickel decanoate, nickel cyclo-
hexoate, nickel~2-ethyl~utyrate, nickel caproate, nickel
behenate, nickel-12-hydroxystearate, nickel benzoate,
nickel o-chlorobenzoate, nickel p-chlorobenzoate, nickel
3, 4-dihydroxybenzoate, nickel p-ethoxybenzoate, nickel
2-dimethyl aminobenzoate, nickel m-aminobenzoate, nickel
salicylate, nickel succinate, nickel sebacate, nickel
terephthalate, nickel camphorate, nickel 3-pyridine-
carboxylate, nickel oleate, nickel itaconate, nickel
fumarate, nickel n-octoate, nickel 3-hydroxy-2~naphthoate,
nickel linoleate, nickel undecylenate. As noted herein-
above, nickel-2-ethylhexoate is preferred for use in
certain ink formulations since it provides superior
properties with respect to solubility in the alcohol
vehicles used in flexographic inks, ini~ial image speed,
and a low order of toxicityO Nickel rosinate also has
particularly desirable imaging properties, bu~ is soluble
--7-
at rela~ively low levels in many conventional ink
vehicles.
The diterpene stabilizing agents which impart
the improved humidity resistance to the sensitiæing
5 compositions of the present invention are components
containing resin acids, alkali metal or alkaline earth
metal salts of the resin acids, mixtures of such resin
acids and their salts, and rosin compositions comprising a
major fraction of resin acids, e.g., at least 25~ by
10 weight and preferably greater than 75% by weight, free
resin acids. Representative rosin composition~ meeting
these requirements are the tall oil rosins, such a~ are
commercially available from the Glidden Chemical Company
B under the trade name "Sylvaros", such as Sylvaros R Tall
15 oil Rosin which contains about 85% free resin acids,
(22-25% of abietic acid) an acid number of about 161 165
and a softening point of about 81-85C. Tall oil rosin is
oft~n used because of its cost and ready commercial
availability.
The known resin acids are abietic acid, pimaric
acid, the isomers of abietic and pimaric acids, ellio-
tinoic acid and sandaracopimaric ~cid. See for example
"Encyclopedia of Chemical Technology", Second Edition,
(1968) published by Interscience Publishers, at Volume ~7,
25 pages 482 & 433. Exemplary salts are the sodium, potassium
and calcium salts of these resin acids, particularly salts
of abietic acid.
~ f~^R~e ~? ~ r/~
--8-
The diterpene stabilizing agent provides
increasing stabilizing effect even at very low concen-
trations. It has been found that the stabilizing effect
increases with increasing concentration of the stabilizing
agent up to a ratio of about 1.75 parts stabilizing agent
to 1 part transition metal ion, e.g., nickel ion. At
weight ratios above this level, the effectiveness is only
marginally increased. Amounts in excess of this level,
for example, in a ratio of about 6 to 1 can be used, but
may not be economically feasible. Depending on the
composition to be formulated, amounts of the diterpene
stabilizing agent in excess of the 1.75 ratio may not
affect the composition properties significantly. In the
preparation of flexographic inks, which are generally very
low viscosity inks, the amount of diterpene agent can vary
widely without affecting the properties of the ink. In
other formulations, e.g., off-set inks, a weight ratio
somewhat above the 1.75 ratio~ may in fact be necessary to
impart desirable viscosity and ~ack properties to the ink
formulation. Thus, widely varying amounts of the
stabilizing agent can be employed to advan-tage depending
on the use for which the imaging composition is intended~
In terms of weight ratio of commonly used
components, a weight ratio of diterpene stabilizing agents
to nickel-2-ethylhexoate of about 0.33 or above provides
the most desirable stabilizing effectO
6~
~ , ,
The stabilized sensitizing compositions of the
present invention can be advantageously used in formu-
lating various liquid, latent, sensiti7ing compositions.
Generally the stabilized imaging compositions are dis-
solved or dispersed in a vehicle having propertiessuitable for the particular application method contem-
plated Representative ink and paint vehicles include the
aromatic, aliphatic, chlorinated or nitrated hydrocarbons,
such as toluene, VM&P perchloroethylene, 2-nitropropane;
ketones such as methyl ethyl ketone; esters such as ethyl
acetate and butylcorbitol acetate, ethers such as diethyl
ether; amides such as dimethylformamide; alcohols
particularly the low molecular weight alcohols such as
methanol, ethanol and diacetone alcohol; and glycols such
as polypropyleneglycol.
The compositions oE the present invention can be
utilized to provide a variety of printing inks. In one
embodiment of the present invention an ink comprising a
vehicle component which is a non polymeric, oleophilic,
organic acid anion (that is, an anion of a proton donating
acid) having a cationic counter-ion, a transition metal
salt color-forming component, and a diterpene stabilizing
component comprising a resin acid~ alkali metal or
alkaline metal earth resin acid salt or mixtures thereof.
2~ These resin acid components aid in providing acceptable
tack and viscosity to the ink like a conventional ink
vehicle, yet surprisingly, also aid the ink in maintaining
--10--
i~aging speed on exposure to atmospheric moisture which
would otherwise reduce imaging speed. Thus, the diterpene
stabilizing component provides la-tent inks having improved
imaging properties over latent ink not having this com-
ponent. These inks can be conveniently formulated so thatthey can be applied to selected areas of substrates by a
variety of conventional printing methods, particularly
offset and gravure methods.
These latent, sensitizing inks comprise, based
on the weight of the total ink composition, about 5 to 55%
by weiyht vehicle component which is a non-polymeric,
oleophilic, organic, acid anion having a cationic counter
ion, a stabilizing amount, e.g. 20 to 30% by weight, of
diterpene stabilizing component, up to about 30% by weight
thinner and up to about 70% by weight particulate filler.
The ink al50 includes as one of the above components, or
as an additional component, at least about 5% by weight of
at least one color-generating component. The ratio of
filler to the vehicle component is from about 0.1:1 to
6:1.
Other conventional ingredients such as
additional tack and viscosity modifiers, antioxidants,
wetting agents, optical brighteners and the like can be
added as necessary.
The non-polymeric vehicle components described
above are preferably the aliphatic, aromatic and alicyclic
carboxylic and sulfonic acids containing at least 6 carbon
~9~L6~
atoms and the cation containing salts of these acids.
These vehicle components have sufEiciently oleophilic
moieties to provide acceptable inking q~alities and
; promote rapid and intense development of the sensiti~ed
5 areas when used in the formulations of this invention.
They are particularly effective with the metal complexing
color-generating/color-activating components such as the
metal/dithiooxamide ~DT0~/polyhydric phenol combinations
which require a cosolYent reaction medium Eor rapid,
10 intense development of the sensitized area. Exemplary of
these vehicle components are the rosin, stearic, oleic,
2-ethylhexoic, 2-phenylbutyric, benzoic~ hydrocinnamic
acids and dinonylnaphthalene sulfonic acids as well as the
corresponding cation salts of these acids.
The described vehicle components are generally
oily liquids or crystalline or amorphous waxy solids and
when dispersed or dissolved in a thinner exhibit the
desirable binding and viscosity modifying characteristics
of conventional polymeric binders with respect to tack,
20 adhesion, and the like, which are essential to the
suitability of the inks Eor application by conventional
printing methods.
In one embodiment, the vehicle component is a
color~generating vehicle component which is an oleophilic,
25 organic acid anion containing at least 6 carbon atoms and
having a transition metal counter-ion. The transition
metal counter~ion forms a color~d complex when ccntacted
-12-
with a color-activating metal complexing agent, such as
dithiooxamide tDTO) and its derivatives and the polyhydric
phenols
The oleophilic anion moiety aids in providing
good inking qualities and in promoting the subsequent
development of the latent, sensitized ink.
In this embodiment the vehicle component also
- acts as the color-generating component. Because of this
dual characteristic of the vehicle component, these inks
are particularly effective to provide greater concentra-
tions of available color-generating component per unit
area of the substrate to which the ink is applied than is
possible using color-generating components carried in
conventional polymeric, film-forming vehicles. Thus,
these inks can provide latent sensi-tized areas which can
be more quickly and intensely developed by contact with
color-activating components than is possible by
formulating inks having color-generating components in
conventional ink vehicles, such as conventional
20 lithographic inks containing varnish.
The transition metal counter ion of these color~
generating vehicle components is preferably selec~ed from
among nickel, copper, iron and cobalt. Generally nickel
and iron are preerred because of the dark color these
25 metals produce with conventional color-activating
coreactants such as DTO and its derivatives or the
polyhydric phenols. Representative color-generating
6~
-13~
vehicle components which can be used in the present
invention are the nickel, iron, and copper derivatives of
aliphatic, aromatic and alicyclic carboxylic and sulfonic
acids containiny at least 6 carbon atoms and combinations
thereof. Thus, nickel rosinate, nickel calcium rosinate,
nickel-2-ethylhexoate, nickel stearate, nickel
2 phenylbutyrate, nickel oleate, nickel benzoate, nickel
hydrocinnamate, nickel dinonylnaphthalene sulfonate, as
well as the corresponding copper and iron salts o the
above compounds, and mixtures of two or more of the above
compounds are useful.
An essential ingredient of an offset or gravure
ink according ~o the present invention is a particulate
filler which can be dispersed in the liquid ink vehicleO
These fillers are necessary to maintain the sensitized
area suitably receptive to the color-activating material
used to develop the latent ink. These fillers can be an~
of the conventional pigments and extenders which are known
in the printing art. The fillers can be chosen so as to
be nearly transparent when dispersed in the ink vehicle or
can be colored if desired. Thus, when applied to a
substrate, the latent, undeveloped ink can be transparent
so as to be invisible or can have a color which closely
matches or which contrasts with the substrate to which the
ink is applied, depending upon the end use o the
sensitized substrates.
,
,
g~6~
The filler must be chosen with some care
depending on the particular printing method to be employed
in its application. Thus, for certain printing tech-
niques, such as wet offset printing, an oil-receptive,
hydrophobic filler should be used to provide superivr
results. Inks formulated in this manner ~an also be used
to advantage in dry offset printing. A simple oil
absorption test can be used to determine whether the
fillers are suitably oil-receptive. An oil absorption
test such as ASTM D-281-31 can be used. The results of
these tests are generally expressed as parts by weight of
oil absorbed per 100 parts by weight of filler~ It has
been found that a filler tested using linseed oil
according to ASTM D-281-31 should have an oil absorption
value of at least about 5 in order to be suitable for wet
offset printing. For dry offset printing, a relatively
non-hydrophobic fillerr such as the colloidal silicas sold
commercially under the trade name Cab-O-Sil (Cabot
Corporation) may be used if desired.
The ultimate particle size of the filler in the
final ink composition should be less than about 10
micrometers and preferably less than about 5 micrometers
in order to be readily applied by conventional printing
presses.
Representative fillers which can be used are
fumed alumina, alumina hydrate, and trihydrater powdered
and fumed anhydrous and particulate colloidal silica, such
-~ ~r~
6~
-15-
! ~ as the commercially available "Aerosils" and "Cab-O-Sils"
(available from Deguss, Inc. and Cabot Corporation,
respectively), calcium and magnesium carbonate, barium
sulfate, kaolin clay, attapulgite clay, bentonite clay,
zeolites, zinc oxide, ureaformaldehyde pigment, and the
like.
The filler can comprise up to about 70% by
weight of the ink composition. The larger amounts of
filler may be necessary on non-absorptive, smooth papers,
whereas lower amounts of the filler can be used where the
paper readily absorbs the ink or has a rough surface which
aids in keeping the inked surface receptive to the
coreactant. For most applications~ the filler preferably
comprises about 5 to about 25 percent by weight of the ink
composition.
Within the range of compositions disclosed
above, it has been found that the ratio of filler to the
aforementioned vehicle component is important. In order
to obtain the desired printing characteristics along with
superior imaging speed and image intensity when the
sensitized areas are contacted with a color-activating
component, the ratio of filler to vehicle component should
be from about 0.1:1 to about 6:1 and preferably about
0.1:1 to about 4:1. When filler amounts below the 0.1:1
ratio are used t the sensitized areas may develop with less
speed and intensity. Ratios above about 6~1 are generally
not satisfactory for use on conventional printing presses.
~ tr~ k
6 0
-16-
Certain of the filler components can function as
color-generating components. The acidified clays, e.g.,
kaolin, attapulgite and bentonite clays, and the natural
and synthetic zeolites can be used to provide both the
color-generating and filling function in the ink
composition since they possess the ability to provide an
intense color when contacted with the color-activating
basic chromogenic materials, i.e. the leuco dyes, which
are well known in the carbonless paper art. Generally
when these fillers are used as color-generating components
the weight percent of the filler should be about 15% by
weight or greater to obtain satisfactory color development
in the sensitized areas.
The thinners which are used in combination with
the aforementioned vehicle components in the inks of the
present invention are materials which are known in the
printing art. These materials are solvents, diluents, and
low viscosity oils which are added to ink to reduce their
consistency and tack, thereby modifying the rheological
properties of the ink as required for use in a particular
printing method. Typical thinner materials are liquid
hydrocarbons, castor oils, dialkyl phthalates, trialkyl
phosphates such as tributyl phosphate, alkyl carboxylates,
low molecular weight alcohols, fatty alcohols, and the
like. The amount and type of thinner to be used in any
particular composition varies, depending primarily upon
vehicle component and the oil-receptive filler employed.
~ ~9~
-17-
A sufficient amount of the thinner is incorporated into
the formulation to provide the proper viscosity and tack
for the particular printing method employed. Determina-
tion o~ ink tack values as is conventional in the art can
be used to determine the proper amount of thinner to be
added. Generally up to about 30% by weight of thinner can
be used. Preferably the amount of thinner is about 10 to
about 25~ by weight of the total ink composition~
Although the use in this invention of the afore~
mentioned vehicle components in combination with thinners
eliminates the need for conventional varnishes in order to
obtain satisfactory inking properties, varnishes can be
used in the formulations if desired to modify further the
tack, viscosity and other rheological properties where
these properties are difficult to obtain with normal com-
binations of the vehicle component and thinner. Useful
varnishes are the drying oils and other naturally
occurring and synthetic polymers known in the art such as
the phenolics, linseed oils, alkyds, and modified alkyds,
nitrocellulose, tung oil, cellulose acetate, ethyl
cellulose, and the like. Up to about 40~ by weight of
varnish, based on the weight of the total ink compositionJ
may be used. Preferably the varnish comprises less than
about 10% by weight of the ink composition since these
varnishes tend to inhibit subsequent development of the
latent inks due to their film-forming properties.
~9~6~1
Agents which inhibit the effect of oxygen on the
components of the ink, i.e. antioxidants, can also be
added to stabilize the ink components and the sensitized
areas after development. Useful antioxidants are well
known in the printing ink art, and any of the known
antioxidants which do not react with the color-generating
component can be used. If an antioxidant which reacts
with the color-generating component is used~ the ink may
be undesirably "desensitized" or a colored reaction
10 product may be formed which causes undesirable coloring of
the sensitized area.
~ xemplary of the antioxidants which can be used
are thiourea, hydroquinone, hindered phenols such as
alkylated hydroxytoluene, and the like. Preferably the
15 antioxidant comprises less than 10~ by weight and most
preferably less than about 2.5~ by weight of the total ink
composition.
Other conventional ink additives can be added to
the ink formulation if desired, such as lubricants,
20 optical brighteners, dyes, waxes, buffers, wetting agents
and odorants and the like, to improve the applicationv
performance and aesthetic qualities of the ink. Generally
these additives comprise less than about 2~ by weight of
the ink composition and most preferably comprise less than
25 about 0.5~ by weight of ~he total ink composition.
When the filler is, or contains, one of the
aforementioned acidified clays or zeolites, the filler
9~
--19--
itsel can be a color-generating component in lieu of or
in addition to a color-generating vehicle component. If
both the vehicle and filler contain a color-generating
component, the latent, sensitizing ink may be developed by
a plurality of distinct color-activating components.
In addition to or in lieu of the above-noted
color-yenerating components, an additional color-
generating component or mixture of color-generating
components can be incorporated into the ink formulation.
Thus, the ink formulation can comprise a transition metal
salt such as the nitrates, sulfates or halides of the
transition metals. A preferred -transition metal salt is
nickel nitrate.
If more than one color generating component is
used in the ink formulation, care must be taken to see
that the components do not prematurely react with each
other. Thus generally a transition metal salt and a DTO
derivatiVe would not be incorporated in the same
formulation. Similarly an acidified clay and a leuco dye
wsuld not be combined. Typically, the ink may contain a
transition metal ion and an acidified clay so that the ink
can be developed by either a DTO or other metal complexing
compound or by a leuco dye or both.
As noted previouslyl the inks can contain
ingredients, such as varnish, to modify further the tack,
viscosity and other rheological properties of the ink~
Additional conventional ingredients such as antioxidants,
-20-
lubricants, optical brighteners, dyes, waxes, buffers,
wetting agents, odorants and the like can be added as
necessary and generally comprise in total less than about
10% by weight of the total composition. For example, the
ink may require up to about 7~ by weight antioxidant.
However, the amount is generally about 2.5% by weight or
less, with the remaining additives ranging up to about 2%
by weight and preferably about 0.5% or less by weight.
A preferred ink formulation would comprise about
5 to 55~, and preferably about 30 to 45%, by weight
vehicle component which is a non-polymeric, oleophilic,
organic acid anion having a cationic counter ion, such as
nickel-2-ethylhexoate, a stabilizing amount of diterpene
stabilizing component, about 5 ~o 15% by weight
particulate fillerr up to about 30~ by weight thinner, and
about 0.5% by weight antioxidant. The ink must include at
least about 5% by weight transition metal salt color
generating component.
The inks of the type described above can be
prepared using conventional ink milling equipment.
Generally the ink is prepared by admixing all of the
ingredients and blending to form a homogeneous mixture of
working consistency suitable for an ink mill. In some
cases the amount of particulate filler may be such that
only a portion of the filler can be added before the ink
is milled. The admixture is then dispersed in a conven-
tional agitating means to form a homogeneous dispersion.
-21-
The particle size in the final mixture should be about l0
micrometers, or less~ for ease of application by conven-
tional printing methods. Other liquid ingredients as
previously noted can be added to the milled ink to adjust
the tack, viscosity and other rheological properties of
the ink as required.
In addition to the inks described above, flexo-
graphic inks can also be formulated. Flexographic
printing techniques are particularly well adapted to the
manufacture of forms and other printed products and latent
flexographic inks can be provided in accordance with the
present invention. Flexographic printing generally
involves the use of a rotary press comprising usually one
or more hard and/or rubber blanketed rolls to apply a
flexographic ink over the entire surface of a paper
substrate, such as in tinting a substrate or to provide a
pattern or other message on the substrate~ Flexographic
inks generally comprise a low viscosity, polar vehicle,
typically a denatured alcohol vehicle such as methanol or
ethanol which may or may not contain some water, having
dissolved or dispersed therein various dyes, pigments, and
resins, etc. to provide an acceptable flexographic ink.
Due to the large amount of low viscosity liquid vehicle
these inks tend to be very low viscosity and water like.
In attempting to provide latent, sensitizing compositions
for flexographic prin~ing a color-forming component must
be incorporated in the ink vehicle together with other
-22-
colored dyes and pigments if desired. Merely adding a
conventional color-forming material such as a transition
metal salt to alcohol or other conventional flexographic
ink vehicle does not provide satisfactory inks since a
loss in the speed of image formation after several days
exposure to 80% relative humidity at 80 F is realized~
Under more extreme conditions, a loss in imaging intensity
may also be exhibited. ~owever, the stabilized imaging
composition o the present invention provide means for
formulating stabilized, latent, sensitizing flexographic
inks.
It has been found by the present inventor that
in formulating flexographic inks and certain other liquid
sensitizing compositions some additional problems may be
encountered which are peculiar to these compositions.
This is believed due to the tendency of the transition
metal salt to dissociate and form a transition metal
diterpenate, such as nickel diterpenate, to an extent
which may exceed the solubility product constant of the
transition metal diterpenate in the vehicle and cause
precipitation of the nickel diterpenate. This tendency
has been overcome in the present invention by the addition
of a solubilizing acid comprising the family of acids
which have the following properties;
l. The solubilizing acid must itself be soluble
in the vehicle.
-23-
2. The solubillzing acid should be of suf-
ficient strength or have a sufficiently high dissocia-
tion constant in the vehicle to drive the resin acid
equilibrium to a less dissociated level so as not to
exceed the solubility product constant in the vehicle
of the transition metal diterpenate, e.g. nickel
diterpenate, and cause precipitation of the
transition metal diterpenateO
3. The transition metal salt of the
solubilizing acid must be soluble in the vehicle at
least to the point where the transition metal is
suppressed from precipitating as the diterpenate. In
other words, the solubility product constant of the
transition me~al salt of the solubilizing acid in the
vehicle must be high enough so that a sufficient
amount of the solubilizing acid can be added to
suppress formation of transition metal diterpenate in
excess of its ~olubility product constant in the
vehicle.
From the foregoing discussion, it can be seen
that the solubilizing acid must be chosen so that the
solubility product constant of the transition metal saIt
of the solubilizing acid in the vehicle is not below the
solubility product constant of the transition metal
diterpenate in the vehicle.
The proper selection of an acid according to the
above criteria will allow the use of the stabilized
.
-24-
imaying compositions in formulating flexographic inks and
other sensitizing compositions. In effect, the use of
these acids will allow sufficient diterpene stabilizing
agent to be added to stabilize the transition metal
color-forming salt without causing precipitation of the
transition metal diterpenate which may be formed through
dissociation of the transition metal salt. ~ number of
acids which meet the criteria described above in varying
degrees have been found. Exemplary of such acids are
o-chlorobenzoic acid, benzoic acid, salicylic acid,
2-naphthalene sulfonic acid, benzene sulfonic acid, nitric
acid, lactic acid, acetic acid r and citric acid. For
reasons discussed hereinafter, the preferred solubilizing
acids for-formulating flexographic inks are the
o-chlorobenæoic acid, benzoic acid and salicylic acid,
with o-chlorobenzoic acid being the most preferred.
The amount of the acid necessary to suppress the
precipitation of the transition metal diterpenate varies
depending on the acid used. In effect, the correct amount
of acid must be chosen to provide a "solubility window'i.
That is, as stated above, a sufficient amount of the acid
must be added to prevent precipitation of the transition
metal diterpenate, but not so much as to cause
precipitation of the transition metal salt of the
solubilizing acid. This "solubility window" varies with
each acid but can be readily determined by routine tests.
For example, a formulation comprising the stabilized
~ ~.f~g3L610
-25-
imaging composition described hereinabove in an alcohol
vehicle can be formulated and various amounts of the
solubilizing acid added to determine when precipitation
occurs. For example, a solution comprising 10~ nickel-
2-ethylhexoate, 3.3% by weight tall oil rosin as a
; solution in anhydrous ethyl alcohol can be prepared and
various weight percents of the various acids added to
determine the "solubility window". Results of these tests
indicate that ~he "solubility window" for this particular
formulation when benzoic acid is used as the acid, is
between about 0.8 and 1.5% acid based on the total weight
of the co~position. Thus, with formulations containing
less than about 0.8% by weight benzoic acid, the nickel
diterpenate will precipitate out of solution. With
formulations containing above about 1.5% by weight benzoic
acid, nickel benzoate will precipitate out of solution.
Salicylic acid in a similar formulation provides
a "solu~ility window'l between about 0.7% and 1.2% by
weight.
o-chlorobenzoic acid on the other hand, is
rather unique in that amoun~s in excess of about 2.8% by
weight in the above formulation are required to prevent
the precipitation of nickel diterpenate. This then
represents the lower edge of the "solubility window" for
o-chlorobenzoic acid in this formulation. On the other
hand, amounts greatly in excess of this amount of
o-chlorobenzoic acid can be added with no resultlng
- ,
-26-
precipi-tation of the nickel salt of _-chlorobenzoic acid.
Thus, the "solubility window" for _-chlorobenzoic acid in
this formulation is extremely wide once the lower level
has been reached. o-chlorobenzoic acid is unique in
; 5 another respect in that the nickel salts of this acid are
extremely soluble in water. Thus, if alcohol vehicles
containing some water, as opposed to anhydrous alcohols,
are used, no undesirable precipita~es will be formed. For
these reasons, o-chlorobenzoic acid is the preferred
10 solubilizing acid or many sensitizing compositions
including flexographic ink formulations.
As noted above, in formulating various
sensitizing compositions, an organic vehicle is normally
used as the major vehicle component. In practice,
15 concentrates or syrups are often prepared by dissolving or
dispersing the stabilized imaging composition and the
solubilizing acid described above in a vehicle, such as an
alcohol vehicle. This concentrate or syrup is then
diluted at the point of use by the printer or other user
20 to provide the flexographic ink or other sensitizing
composition. Dilution is performed by adding an amount of
the vehicle, such as ethanol, to provide a composition
having a solids content of about 5-15% by weight,
depending on the particular printing or coating equipment
25 employed and the substrate to be printed or coated. In i
addition to the latent, stabilized, imaging concentrates
described herein, conventional color concentrates can be
-27-
added to provide a colored latent composition Eor tinting
or printing.
Preparation of the coating compositions is
accomplished by formulating a concentrate or syrup com-
5 prising (1) a color-forming transition metal salt as
described above, (2) a diterpene stabilizing agent, (3) a
solubilizing acid, and (4) a solvent for the above
componentsO Generally the solvent will be an organic
solvent~ for example an alcohol such as methanol or
10 ethanol, naphtha or one of a number of other common
solvents or vehicles described hereinabove.
The concentrate is generally formulated to
provi~e a solution of about 80% or more solids and
containing about 40 to 75~ by weight color-forming
15 transition metal salt. This concentrate is diluted by the
printer by adding a sufficient amount of liquid vehicle
particularly adapted to the coating technique to be
employed to allow the desired amount oE transition metal
salt to be applied to the substrate. It is generally
20 desired to provide about 0.0085 lbs. of nickel ion per
1300 square feet o paper (about 3.2 x 10 2 grams nickel
ion per square meter of paper).
Flexographic inks formulated ascording to the
present invention can be applied to paper substrates with
25 conventional 1exographic printing or tinting equipment~
These substrates can be imaged using conventional CB
- sheets containing encapsulated dithiooxamide-based dye
9~6~
-28-
precursors as known in the art. Upon exposure to
atmospheric moisture, e.g. seven days at 80 relative
humidity and 80 F the image speed is retained at a
satisfactory level. Other coating compositions can be
readily formulated and applied by other conventional
techniques.
The sensitizing compositions o~ this invention
can be applied to selected areas of substrat~s such as
paper by conventional printing techniques, including
lithography, flexography, letterpress, dry offset, rubber
plate, intaglio, silk screen, rotogravure, and the like.
Applying these ink compositions with conventional printing
equipment makes it practical to pattern or spot coat
substrates, and thus, selectively sensitize paper or
other substrates for business forms applications where
there is a desire to have an image appear only on certain
portions of a form or on certain sheets of a multi-sheet
form, such as invoice and purchase order forms where price
or cost information is needed only on certain sheets of
the multi-sheet form.
The sensitized areas of the substrates can then
be developed by contacting the sensitized area, or a
portion of the area, with a color-activating component.
Typically, the color-activating component is contained as
an encapsulated component on a sheet of paper, e.g~ a CB
(coated back) sheet, so that when the CB sheet i5 placed
in contact with the sensitized sheet and the capsules
6~
~29
ruptured, as by writing or typing on the obverse surface
of the CB sheet, the color-activating component contacts
the sensitized area, or a portion thereof, containing the
color-generating component and a visible image is formed.
Alternatively, the sensitized areas can be
contacted with a crayon, or developing solution contained
in a marking pen, which contains a color-activating
component and the sensitized area visibly developed
Business forms which are multi-sheet forms can
comprise one or more CB sheets overlying and in register
with one or more sensitized CF (coated front) sheets,
Thus a multi-sheet form may have a CB sheet as the top
sheet overlying one or more sheets in register which are
CB sheets having at least a part of the obverse surface
sensitized. Writing or typiny on the obverse surface of
the top sheet causes like information to be recorded in
the obverse sensitized portions of the underlying sheets
which are in register with the written or typed
information entered on ~he top sheet of the multi-sheet
form.
In addition to the latent, sensitizing composi-
tion applied to the surface of the sheets, conventional
printing can be applied to the sheets in the sensiti~ed or
unsensitized areas to provide forms for business entries,
paper based feedback systems for educational use and the
like.
~9~
~30-
The following examples further illustrate the
present invention. In these Examples, all parts and
percents are by weight, unless otherwise indicated.
EXAMPLE 1
An ink for sensitizing selected areas of paper
with a latent coreactant was prepared having the following
formulation:
Wt %
Nickel-2-ethylhexoate 36.0
10 Hydrophilic Silica Filler 14.2
Tall Oil Rosin 25.2
Butylated Hydroxy Toluene 0.5
Hydrocarbon Oil 24.1
The nickel-2-ethylhexoate, tall oil rosin and antioxidant
were dissolved in the hydrocarbon oil. The filler was
then dispersed in the solution and the final dispersion
carried out in a conventional heated, agitated kettle.
The composition had a tack of 12.3 and a viscosity of
100,000 centipoise and could be sa~isfactor-ily printed on
a wet offset or dry offset press.
The ink was applied to 16 lb. (7.~ kg) bond
paper in selected areas oE the sheet. ~fter drying at
room temperature, the sensitized sheets were developed by
placing a sheet coated with an encapsulated dithiooxamide
derivative ('l3M" Brand Carbonless Paper, Type 200 CB
-31-
[coated back] she~et) so that the capsule coating and the
inked surfaces were in direct contact. The sheets were
run through a steel pressure roll to develop uniformly a
1.2 cm wide strip of the sensitized sheet. The developed
area had an acceptable blue-purple color as determined by
optical density measurements.
Sensitized sheets were also developed by placing
a sheet coated with an encapsulated dithiooxamide
derivative (CB sheet described above) so that the capsule
10 coating and the inked surfaces were in direct contact.
Images were produced on the sensitized sheet by writing on
the obverse surface of the CB sheet with a ball-point pen
using normal hand pressure. Similarly, typing on the
obverse surface of the CB sheet produced an image on the
15 sensitized sheet. In both cases image formation was very
rapid.
Sensitized sheets were exposed to 80~ relative
humidity at B0F. for a period of 1~ da~s with a decrease
in image intensity from a value of about 32 to a value of
20 about 41 while under the same conditions a similar ink
without the stabilizing component showed an image
intensity decreasing from about 34 ~o about 63 (30 second
image time).
-32-
EXAMPLE 2
An ink for sensiti~ing selected areas of paper
with a latent coreactant was prepared having the following
formulation:
Wt%
Nickel-2-ethylhexoate 36.0
Hydrophilic Silica Filler 13.7
Tall Oil Rosin 13.g
Sodium Abietate 9.7
10 Butylated Hydroxy Toluene 0.5
Hydrocarbon Oil 26.2
The nickel-2-ethylhexoate, tall oil rosin, sodium abietate
and antioxidant were dissolved in the hydrocarbon oil.
The filler was then dispersed in ~he solution and the
final dispersion carried out in a conventional heated,
agitated kettle. The composition had a tack of 13.0, a
.~ viscosity of 192,000 centipoise and could be satisfac-
torily printed on a wet offset or dry offset press and was
satisfactorily developed by a CB sheet as described in
Example 1,
Sensitized sheets wer~ exposed to 80% relative
humidity at 32C for a period of 12 days with a decrease
in image intensity from a value of about 34 to about 46
while under the same conditions a similar ink without the
s~abilizing component showed a decrease in image intensity
from about 34 to about 63 (30 second image time).
~9~6al
--33--
EXAMPLE 3
A stabilized flexographic ink was prepared in a
heated kettle by dissolving 51.4 parts nickel
~-ethylhexoate in 16.2 parts cf anhydrous ethyl alcohol.
Subsequently 15.4 parts of o-chlorobenzoic acid was
diæsolved followed by 17.0 parts tall oil rosin. The
composition was an 83.8~ solids syrup.
A flexographic ink was prepared by diluting the
concentrate prepared above with anhydrous ethyl alcohol.
The 83.8~ solids syrup was combined with 1.8 parts o a
colored flexographic ink and 86.6 parts of ethyl alcohol
to provide a tinted flexographic ink. The ink was applied
¦ to forms paper on a laboratory flexographic rotary press
to provida a coating weight of about 0.7 lbs. ink per 1300
ft2 of substrate ~318g/120m2)~
The CF coated sheet, when dried, provided rapid
intense imaging with a conv~ntional CB sheet containing
substituted dithiooxamide in cyclohexane as the
microcapsule fill. Initial 30 second speed image tests
(reflectance 30 seconds after imaging~ gave values of
; about 28 to 30. A clear control ink without the
stabilizing agent of the present invention provided a 30
second speed image of about 32. After 7 days aging a 80
R.~. and 27~C the 30 second speed image value for the
control ink had increased to a reflectance value of about
72, whereas the sheet coated with the stabilized
flexographic ink had only increased to a value of less
34-
; than about 40. This demonstrates that the stabilized inks
of the present invention are resistant to the effscts of
atmospheric moisture.
EXAMPLE 4
.
A stabilized flexographic ink was prepared by
dissolving 42.2 parts of nickel-2-ethylhexoate and 29.5
parts of tall oil ro~in in 28.3 parts of a hydrocarbon oil
(Magiesol 52) to give a 71.7~ solids syrup.
The 71.7% solids syrup was combined with 89.9
10 parts of VM&P naphtha (flash point ~8F). The ink was
applied to forms paper on a laboratory flexographic rotary
press to provide a coating weight of approximately 0.7 lbs
ink per 1300 ft2 of substrate (318 g/120 m2).
The CF coated sheet, when dried, provided rapid
intense imaging with a conventional CB sheet containing
substituted dithiooxamide in cyclohexane as ~he
microcapsule fill. Initial 4 second .speed image tests
(reflectance 4 seconds after imaging) gave values of 53O5
compared to the value for a control ink, without the
20 stabilizing agent of the present inventiont of 52.5.
After 4 days aging at 80% RH and 27C, the 4 second speed
image value for the control ink had increased to a
reflectance value o about 80.5, whereas the sheet coated
with the stabilized flexographic ink had only increased to
25 67.
-35-
The concentrated syrup described in Example 4,
above, may be diluted with a variety o~ solvents, such as
: pe~chloroethylene, diacetone alcohol, butyl carbitol
acetate, methyl ethyl ketone, ethyl acetate, toluene,
polypropyleneglycol 1025, dimethylformamide, diethyl
ether, 2-nitro propane, or various mixtures thereof, with
: ~ comparable results.
