This invention relates to pollution preventing microemulsion ink.
FIELD OF INVENTION:
The present invention relates to printing technology. Particularly, it relates to oil
based printing ink, wherein the ink is water washable, and oil-water
microemulsion. More particularly the microemulsion ink is free of Volatile
Organic Compounds (VOC) thereby eliminating the problems associated with the
conventional lithographic printing ink containing VOC. Additionally; the ink of
the present invention also eliminates using aliphatic solvents that imparts
pollution preventing property leading to zero pollution during the ink washing
process.
BACKGROUND OF TH INVENTION:
The main components of printing ink are pigments, binders, solvents and
additives. The pigments colour the ink and make it opaque. hydrocarbon and/or
alkyd resins are generally used as binders for binding the other ingredients of ink
together so that it forms a film; they also bind the ink to paper and contribute
gloss, resistance to heat, chemicals and water. Commonly employed binders could
be Acrylics, Alkyds , Cellulose derivatives , Rubber resins ,Ketones, Maleics,
Formaldehydes etc.
Solvents- make the ink flow so that it can be transferred to the printing surface
Additives- alter the physical properties of the ink to suit different situations
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High boiling point (Tb=240 C -320 C) hydrocarbons are chosen as solvents for
lithographic inks as the solvents used must be viscous and hydrophobic. Most of the
pollution of is essentially caused on account of presence of aliphatic solvents in
the ink and various volatile organic compounds, like methylene chloride and
toluene, in the wash solutions released during washing process. The VOCs
released during this process and during printing itself cause alarming levels of
pollution. The residual wash solution is further discharged into the waste streams
in large amounts aggravating pollution level. Severe shortage of petroleum, the
environmental and health problems caused by the inks containing volatile organic
compounds (VOCs), and prevalent strict regulations limiting the use of volatile
organic compounds, call for new solutions in printing chemistry and technology.
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Additionally, petroleum based ink also leave offensive odor on printing substrate that
makes it imperative to look for user and environment friendly and effective ink
formulation for printing ink.
Water based inks being one of the options glycol (water washable inks) was tried to
over come the drawbacks. Vegetable oil based inks also another option in view of
rising petrochemical crisis and environmental concerns. The soy bean oil based ink
was developed in 1985 and were marketed in 1987. Soy ink contains less VOC, less
alcohol and can be washed up without solvent. Their disadvantages include their high
cost compared to conventional ink as well as their disposal. American Newspaper
Publishers Association (ANP A) developed a series of ink formulations comprising a
blend of "gilsonite" and tall-oil fatty acids with carbon black pigment. The cost and
availability of tall oil and the difficulty of equipment clean-up caused by the gilsonite
limited the acceptance of these inks for commercial purposes. The other vegetable
oils tried were canola, cottonseed, safflower, and sunflower.
The discharge from washing operations m the currently prevalent printing
industries is a major cause of pollution. Most of this pollution is essentially caused
on account of presence of aliphatic solvents in the ink and various volatile organic
compounds, like methylene chloride and toluene, in the wash solutions. The
residual wash solution is discharged into the waste streams in large amounts. The
VOCs released during this process and during printing itself cause alarming levels
of pollution.
The prior art known to the applicant/inventors include following patents:
(i)US 5372635 (635), (ii) 5417749 (749), (iii) 5725646 (646), (iv) 6444021(021), (v)
6444022 (022), (vi) 6544322 (322), (vii) 7429292 (292), (viii) 7655082 (082), (ix)
7909924 (924), (x) 7985820 (820), (xi) 8013034 (034), (xii) CA2136362 (362), and
(xiii) PCT/US2007/022056.
From the claims of the above patents it is apparent that VOC is one of the required
componentsof the patent bearing numbers 322 ', 924', 034' 635' and 362' though at
low level in certain technologies. As such, the problems associated with VOC will get
inherited and are persistent.
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749' discloses a printing ink for waterless printing process using water-in -oil
microemulsion having 5 to 20% water, 0.5 to 3% surfactant.
The waterless printing process solved two issues: VOCs emanating from the
fountain solutions and control of the ink/water balance by the pressman. However,
the difference in surface energy between the image and non-image areas of the
conventional offset lithographic printing plate is typically 40 dynes/em is
dramatically reduced to 20 dynes/em in the case of the waterless printing plate.
Therefore the latitude between scumming and poor print density is considerably
narrowed and the issue of VOCs (emanating from the oil-based ink) still remains
in respect to waterless printing.
646' describes a way of stabilizing a waterbased ink composition without drying
up on a conventional multi roller ink train. Such composition eliminated the
principal disadvantages of conventional offset lithographic printing inks, viz. high
levels of VOCs emanating from the oil-based ink and the aqueous fountain
solution and the difficulty in controlling the ink/water balance, while preserving
the principal advantage of the conventional lithographic printing process, i.e. high
surface energy differential between the image and non-image areas of the printing
plate. It consists of using a rewetting agent, namely hydroxy ethyl ethylene urea.
Since this rewetting agent does not dry, it remains in the final film making it
susceptible to poor water resistance. Use of conventional rewetting agents, such as
glycols and glycol ethers not only imparts poor water resistance to the final film,
but also increases the tack of the formulations, thereby limiting its use on high
speed presses.
021' describes water washable color newspaper inks that contain a modified
soybean oil-based resin, a pigment, an acid neutralization agent, and a humectant.
This combination of ingredients causes the ink to readily disperse in water or
aqueous detergent solutions that are commonly used for cleaning. The modified
soybean oil-based resin provides the water washability when the oil is neutralized
in the ink formulation providing the washable characteristics of water. These
changes significantly expand coverage possible for newspaper inks.
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022' describes a water based lithographic ink comprising water; a modified rosin
polymer comprised of resins soluble in water regardless of the pH of the water,
resin rosin salts soluble in water at pH ranging from 7.5 to 10 and aqueous
emulsion resins; a modified linseed oil; and pigment. This modified linseed oil
comprises the reaction product of a polyglycol and linseed oil and provides an
alternative to the use of hydroxyethyl ethylene urea which use has the
disadvantage of slow drying and poor water resistance.
U.S. Patent Publication US 2002/0083865 describes a water based lithographic
ink composition containing water, a resin-bonded pigment, a nonionic surfactant,
a rewetting agent, and a polymerizable surfactant. This combination of ingredients
allows the lithographic ink to dry rapidly at a rate comparable to oil-based inks, to
emit minimal or no volatile organic compounds and to be water washable.
U.S. Pat. No. 6,709,503, describes a water based heatset offset lithographic ink
containing water, polyamide resins or fumarated rosin resins, hydroxyethylene
urea as a humectant, a modified linseed oil, a dibutylated benzoguanamine, a
pigment and p-toluene sulfonic acid.
292' discloses water washable lithographic printing ink, in particular lithographic
newspaper printing ink, containing a modified soybean oil-based resin can be
formulated to have good rheological properties in the absence of a humectant (i.e.
a rewetting agent), a surfactant and a polyol modified linseed oil. This makes the
preparation of the inks of the present invention more efficient and less costly. In
addition, the removal of humectants such as hydroxyethyl ethylene urea from
lithographic printing ink formulations allows for faster drying and better water
resistance. However, the cost of soybean oil makes this technology cost extensive.
In an attempt to eliminate volatile organic compounds (VOCs) in the pressroom,
water-based alternatives are being sought for ink formulations.
Pennaz and Schacht (1994) [Pennaz, T.J. Schacht, P.F. (1994), Ink composition,
US Patent 5,354,366 (October 11)] developed an ink system that consisted mainly
of an alkyd resin, a drying oil, a pigment and some other undisclosed components.
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The alkyd resin is low molecular weight polyester, containing pendant carboxylicacid
groups and is non volatile. During printing, the resin remains in acid form
and hence is hydrophobic, so that the ink is immiscible with water while printing
is done. However, when this ink is brought into contact with an aqueous base
during clean-up, emulsification of ink occurs owing to the reaction between the
pendant carboxylic acid groups in the ink and the base in the aqueous wash to
form a polymeric soap.
The pollution caused during ink washing necessitates developing alternate ink
with low VOC and non-polluting washing methods, which eliminates chemical
reaction and formation of polymeric soap. The ink washing commences in the
form of tiny jets of water-soluble material coming out vigorously from the
interface of the microemulsion ink drop and the wash liquid by the phenomena of
spontaneous emulsification. Thus, the oil-based microemulsions appear to provide
a prospective non polluting alternate system.
As mentioned herein before the environmental and health problems caused by the
inks Containing volatile organic compounds (VOCs) and the washing procedures call
for new solutions in printing chemistry and technology
The inventors have found out that an oil water microemulsion ink developed using
castor oil, an acidic esterified resin and surfactant not only takes care of
elimination of employing VOC but also imparts water washable property to the
ink. This in tum makes the ink pollution preventing. According to present
invention the washing of the microemulsion ink utilizes the principle of
spontaneous emulsification which is a physical process devoid of any salt
formation. In addition to being water based, the inks according to the present
invention are water washable .. Water washable as used herein means, regardless
of whether the inks contain water, they contain castor oil and high molecular
weight esterified acidic resin.
OBJECTNES OF THE INVENTION:
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The mam objective of the present invention is to provide a printing ink
avoiding/eliminating drawbacks associated with the existing printing ink.
Particularly, the invention provides a lithographic printing ink.
The other object of the present invention is to provide oil based printing ink.
Further, the ink is water washable, and oil-water microemulsion.
Still other object is to provide micro-emulsion oil base ink containing esterified
high molecular resin.
Yet other object of the present invention is to provide microemulsion ink that is
free of Volatile Organic Compounds (VOC), thereby eliminating the problems
associated with the conventional lithographic printing ink containing VOC.
Additionally, the ink of the present invention also eliminates using aliphatic
solvents that imparts pollution preventing property leading to zero pollution
during the ink washing
STATEMENT OF INVENTION:
Accordingly the present invention provides pollution preventing microemulsion
printing ink comprising (a) acidic esterified resin (b) surfactant (c) castor oil (d)
water, and (e) pigment
According to one of the embodiment the acidic esterified resin may be high
molecular weight esterified acidic resin. It may be esterified glycerol and the one
obtained from esterification of glycerol and higher fatty acids in presence of
castor oil.
According to other embodiment the esterified acidic resin may be added in the
range of---- to --- wt. %, preferably 79 to90 wt. %.
According to another embodiment the surfactant employed may be ionic, non
ionic or a combination thereof. The ionic surfactant used may be TX-100 and
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Sodium Lauryl Sulphate (SLS), non-ionic may be nonylphenol polyethylene
oxyether Span 85 (non-ionic sorbitol trioleate surfactant). ionic surfactant TX-100
may be preferred one. The surfactant may be added in the range of 0.1 to 7 wt. %.
preferably 0.1 to 1.5 wt. %.
According to yet other embodiment, the pigment employed may be and added in
the range of 5 to 40 % preferably 5 to 18 wt. %.
According still other embodiment, castor oil may be employed in the range of 5 to
90 preferably 5 to 18 wt.%
According to yet another embodiment 0.2 to 15.0% water in oil phase
microemulsion may be used in the ink.
DESCRIPTION OF THE FIGURES:
Figure 1 shows the effect of resin concentration in oil on the printing quality of
the ink.
Figure 2 shows the comparison of the conventional ink with that of the ink claimd
in the present invention.
Figure 3 and 4 depict the effect of different water in oil microemulsions on
printing quality.
Figure 5 shows effect of different w /o ratios on washability property of the ink
Figure 6 shows the effect of resin concentration on washability property of the
ink.
Figure 7 illustrates the effect of surfactant
DETAILED DESCRIPTION OF THE INVENTION:
In order that the invention may be readily understood, one embodiment of the
invention is illustrated by way of example in the accompanying drawings.
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Microemulsions are thermodynamically stable, transparent oil-water systems
stabilized by an interfacial layer of surface-active agent. The droplet of domain
size is about 0.01 Jlm, which makes it transparent. As apparent from the
description herein before, the proposed ink is free of VOC in addition to being
water washable microemulsion leading to absolutely zero pollution during
washing.
When a microemulsion drop is submerged in water, there exists a chemical
potential gradient for the water-soluble components of the ink which diffuse
towards the wash phase. In this process, the oil-soluble components are dragged
along. This mobilized oil phase is in the form of layers or jets streaking out into
the aqueous wash phase. Interfacial turbulence (drag effect of the spreading layer
of surfactant) and impingement of the jets of oil phase with wash phase cause the
oil phase to break into smaller drops, thus leading to spontaneous emulsification.
In spontaneous emulsification, the entire energy required for the emulsification
comes from the redistribution of material within the system, i.e. no external
mechanical work is required.
Ink constituents and their role:
The oil phase consisted of castor oil and an acidic resin. This phase was the major
phase in the oil based microemulsion. The water phase consisted of distilled water
preferably of density 0.914grnlml. The surfactant (ionic:TX-100 and Sodium
Lauryl Sulphate (SLS), non-ionic: Span 85) was added drop wise. After the
formulation of the microemulsion by stirring the oil and the water phase, a
colorant was added. The colorant used was a pigment. A pigment was chosen over
a dye because, unlike a dye, pigments do not bind with the oil phase and hence,
characteristics of the oil phase could be studied without any deviation of
properties.
The surfactant is critical to a microemulsion, as it binds and stabilizes the two
phases (oil and water) together. The resin is added to improve the binding,
rheological and mechanical properties of the ink. Its addition enhances the crosslinking
properties of the vehicular part of the ink. The viscosity is increased and in
general, the flow of the ink is better regulated. The resin used in this ink
formulation was an acidic resin made by esterification of glycerol and higher fatty
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acids in the presence of castor oil. It was a high molecular weight esterified acidic
resm.
Procedure for oil phase preparation:
The castor oil and resin were taken together in a beaker in the desired proportions.
The beaker was tightly covered with an aluminum foil to prevent escape of the
volatile components present in the resin and to keep the oil-resin ratio unchanged.
The mixture was then heated on a hot plate until it boiled, indicated by rigorous
bubble formation. A single oil phase was thus obtained on cooling the mixture.
Procedure for resin preparation:
The setup for resin preparation consisted of 500 ml three neck round bottom flask,
a small heating mantle and a packed bed column with a condenser at the top.
Water was used as coolant in both condensers. A weighed quantity of oil was
heated in the flask at 120°C for 30 min followed by addition of specified amount
of glycerol. The contents of the flask were heated to 240-245°C for 2.5 hrs to
allow monoglyceride formation. The contents were then allowed to cool down to
170 ± 5°C and charged with phthalic anhydride. A fall in temperature was
observed and the temperature was raised back to 170°C. After maintaining the
flask at 170°C for an hour, the temperature was further increased to 215-220°C
and maintained for 3 hrs. In the last phase of preparation, the flask was maintained
at 235-245°C for 2.5 hrs. Finally, the heater was switched off and the temperature
was allowed to fall. The resin was decanted when the temperature reached below
100°C.
Procedure for making a microemulsion
The procedure for making a preliminary oil-water microemulsion involves mixing
of weighed quantities of oil, water and the surfactant with a stirrer.
With the addition of resin to the oil phase of microemulsion, the stirring with high
rpm was used due to the highly viscous oil phase.
Procedure for washability testing of ink:
The washing of the ink from a rubber roller drum was performed as described
below. A weighed quantity of the ink sample was placed on the surface of the
roller drum over a measured area of 100 cm2
• The drum is rotated with an
electrically operated motor. An aqueous wash solution is allowed to flow through
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a nozzle continuously with a constant flow rate onto the rotating roller drum
coated with the ink until the washing of ink is completed or reaches a stage where
no further washing takes place. The wash solution used during the cleaning of the
roller drum is collected in a trough kept beneath the drum. The time required for
complete washing is recorded with a stopwatch. The volume of the wash solution
collected in a trough is measured with a measured cylinder.
Procedure for printability testing:
Rubber stamp pad test was performed for a preliminary selection of ink on the
basis of the following criteria:
• Penetration of the ink through paper
• Drying time, and
• Spreading of the ink on paper.
Screen printing was performed to ascertain and evaluate the printing
characteristics of the ink. A master slide (mesh) was taken and the ink was applied
uniformly over it and pressed using a squeegee to obtain the print. The same
above criteria served as analysis tools.
Various ink formulations as shown in table I were developed consisting of varying
water to oil ratios.
TABLE I
A. Preparation of ME with water percentage = 15%
Mass (gm) Weight%
Castor Oil 8.46 78.2
Water 1.74 15.0
TX-100 0.79 6.8
B. Preparation of ME with water percentage= 6.28%
Mass (gm) Weight%
Castor Oil 10.48 90.50
Water 0.73 6.28
TX-100 0.37 3.22
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C. Preparation of ME with water percentage= 5.3 ·~,
Mass (gml Welght%
Castor Oil 19.54 92.15
Water 1.028 4.84
TX-100 0.636 2.99
D. Preparation of ME with water percentage= 0.5 %
Mass {g_ml Weight%
Castor Oil 21.03 98.5
Water 0.11 0.5
TX-100 0.21 1.0
E. Preparation of ME with water : oil = 0.21%
Mass (gm) Weight%
Castor Oil 22.8 99.33
Water 0.5 0.21
TX-100 0.11 0.46
Ink formulations were consisted of only the basic constituents of ink (water, oil,
surfactant TX-100 and pigment). This was done to evaluate the effect of water-tooil
ratio on ink properties and hence, and arrive at desirable ratio for quality
printing and washing properties taking into account the drying time of the ink,
spreading of ink on paper and the ease of washing. After arriving at the water-tooil
ratio, the effect of resin and different surfactants on the ink properties was
studied and analyzed.
Stability.
All the microemulsions formed were found stable with changes in temperature
and pressure within the scope of the experimental conditions. Daily observations
of all the microemulsion ink samples proved that the microemulsion did not break
and hence is stable.
Observations were made with the naked eye and under a 400X to ensure that the
system is stable and does not break under the experimental conditions.
It may be noted that increasing the concentration of water phase in the
microemulsion increases in washability. Further, the working range of 0.2%-
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0.5% of water phase in the ink was proved to be the preferred (please see figure
5).
Resin percentage in the oil phase
Various percentages of resin in the oil phase ranging from 79 to 90wt.% were
studied for their washability and printability. The washability was found to be
easier for an ink that had a lower resin concentration, as the resin is viscous. But
the printability was very poor for low resin percentage inks since resin is
important for binding and rheological properties of the ink. Fig. 6 shows that
typically 79.5% and 90% resin in the oil phase gave good printability results.
However, higher resin percentage in the oil phase results in extremely low
washability. 79.5% resin appears to give the best printability results and
acceptable washability results.
As such, a 0.2% microemulsion with 79.5% resin in the oil phase is supposed to
be the most suitable ink formulation.
Surfactant systems:
A variety of surfactants were studied suitable. Their effect on the basic ink
properties of printability and washability was monitored. SLS (ionic surfactant,
NaC12H25S04), TX-100 (A non-ionic nonylphenol polyethyleneoxyether), Span-
85 (non-ionic sorbitol trioleate surfactant) and their mixtures were used in
different samples. It was done to ascertain if the use of a combination can improve
any of the properties of the microemulsion (printability or washability) and/or lead
to an overall reduction in the weight percentage of surfactant in the
microemulsion system, thereby making the ink more economical.
It was found for all the ink compositions that the washability of Span 85 based ink
is lesser that TX-100 based ink. Further, the washability of the Span-85 based
microemulsion ink falls much faster with an increase in the resin percentage as
compared to Triton X 100 based microemulsion ink. Fig.6 shows the variation in
washability rates of both these surfactants with the percentage resin in the varnish.
TX-100 is thus better surfactant for a microemulsion ink system. Figure 7
illustrates the efficiency of surfactants Triton X 100 and Span 85.
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The mixture ofTX-100 (in oil phase) and SLS (in water phase) was also studied
as a surfactant system. The resulting printability tests were however
unsatisfactory. The mixture of Span-85 (in oil phase) and SLS (in water phase) in
the similar fashion yielded in poor printability.
Thus, TX-1 00 alone appears to be the best surfactant system for the ink of the
present invention
The proposed microemulsion ink when was compared to conventionally used
printing ink indicates that the ink of the ink of the present ink showed less
spreading and more uniform application as compared to conventional one.
Based on the experimental work, it can be concluded that the microemulsion
system used in the inks is thermodynamically stable and it does not decompose on
keeping. A 0.2% water in oil phase microemulsion ink with Triton X 100 as the
surfactant and 79.5% resin in the oil phase was found to be the best formulation
among all the formulations made and tested.
It can also be safely concluded that the microemulsion ink system shows a definite
improvement in the washability as compared to the normal inks.
While the present subject matter has been described in detail with respect to
specific exemplary embodiments and methods thereof, it will be appreciated that
those skilled in the art, upon attaining an understanding of the foregoing, may
readily produce alterations to, variations of, and equivalents to such embodiments.
Accordingly, the scope of the present disclosure is by way of example rather than
by way of limitation, and the subject disclosure does not preclude inclusion of
such modifications, variations and/or additions to the present subject matter as
would be readily apparent to one of ordinary skill in the art.

WE CLAIM:
1. A pollution preventing microemulsion printing ink comprising (a) acidic
esterified resin (b) surfactant (c) castor oil (d) water, and (e) pigment.
2. The printing ink as claimed in claim 1 wherein the acidic esterified resin is
high molecular weight esterified acidic resin.
3. The printing ink as claimed in claim 2 wherein an esterified resin is
esterified glycerol and the one obtained fix)m esterification of glycerol and
higher fatty acids in presence of castor oil.
4. The printing ink as claimed in claim 1 wherein the esterified acidic resin is
added in the range of 79 to90 wt.%..
5. The printing ink as claimed in claim 1 wherein the surfactant employed is
ionic, non ionic or a combination thereof.
6. The printing ink as claimed in claims 1 and 5 wherein the ionic surfactant
used is TX-lOO and Sodium Lauryl Sulphate (SLS), non-ionic is
nonylphenol polyethylene oxyether Span 85 (non-ionic sorbitol trioleate
surfactant).
7. The printing ink as claimed in preceding claims wherein the ionic
surfactant is TX-100.
8. The printing ink as claimed in claim 1 wherein the surfactant is added in
the range of 0.1 to 7 wt. %. Preferably 0.1 to 1.5 wt. %.
9. The printing ink as claimed in claim 1 wherein the pigment is employed in
the range of 5 to 40%, preferably 5 to 18 wt.%.
10. The printing ink as claimed in claim 1 wherein the castor oil is employed
in the range of 5 to 90% preferably 5 to 18 wt.%.
11. The printing ink as claimed in claim 1 wherein 0.2 to 15.0% water in oil
phase microemulsion is used in the ink.