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BACKGROUND OF THE INVENTION
This invention is directed to an aqueous printing ink composition and a
method for improving aqueous printing.
The printing process involves the distribution of ink in a uniform film,
the provision of a substrate having a uniform surface, and the transfer of
the ink to the substrate in a prescribed pattern. The final transfer of
ink from the printing surface to the substrate is accomplished by means of
pressure; the final force on the ink film is heavy pressure against a
porous surface followed by a tension sufficient to split the ink film.
Flexographic printing is a form of "relief" printing in which an impression
is taken from the raised portions of a printing surface. Flexographic
printing machines are essentially high-speed web or sheet-fed rotary
presses, which print with liquid inks from curved plates, usually made of
rubber or other elastomeric or plastic material, attached to a cylinder.
An important advantage of flexographic printing is that a uniform film of
ink can be printed even on rough papers, because the surface of the rubber
plate is sufficiently resilient to be forced into the hollows in the
paper.
Flexographic printing can be employed to produce a wide variety of printed
material, including waxed or decorative wrappers, aluminum foil, plastic
films, newsprint and corrugated papers and cartons. The inking system used
in flexographic printing consists essentially of an enclosed duct to limit
the evaporation of the solvent, and a simple train of aligned rollers. Ink
control is usually obtained by pressure on the end bearings of the inking
rollers, which tends to force the rollers apart at the center. Because of
this procedure, continuous fine control and correct alignment of rollers
is considered to be essential to produce acceptable printing. Although the
pressure on the inking rollers may vary appreciably in letter press
printing, in contradistinction, flexographic printing requires maintenance
of pressure on inking rollers at practically zero. Because of the
importance of maintaining such critical inking roller pressure,
flexographic inks must be carefully tailored to possess appropriate
viscosity or fluidity. In addition, the ink must be sufficiently volatile
or penetrative to dry within seconds or less, adhere well to the printing
surface, and be odorless when dry. The ink must also be free of any
solvents or components which would attack the rubber or plastic printing
plates or rollers.
In the case of pigmented inks, which are extensively used because of the
color effects and eye appeal of the printed product, the ink should be
stable and any pigment which settles out should be readily dispersible by
stirring. A considerable amount of research has been expended in
attempting to maintain satisfactory flow properties in the inks while at
the same time maximizing the degree of pigmentation and improving the ink
transfer properties. And at the same time, it is highly desirable to
employ water-based inks to avoid organic solvent emissions.
Another widely used printing technique is intaglio printing, which involves
taking impressions from recesses engraved or etched below the surface of a
plate or cylinder. Presently, the most important type of such printing is
rotogravure printing from polished copper electrodeposited on an iron,
steel or aluminum base. The design is etched into the copper by
photoengraving techniques. Gravure inks rely for drying mainly on solvent
evaporation, and therefore, gravure inks usually contain large amounts of
hydrocarbon solvents. Not only are these solvents highly flammable,
forming explosive mixtures with the atmosphere, but the vapors are also
extremely toxic. Because these undesirable properties involve significant
expenditures for flameproof electrical equipment, hoods and duct work for
containment, and recovery of the solvents, an aqueous rotogravure ink
which has suitable ink transfer properties has been needed in the printing
field.
DESCRIPTION OF PRIOR ART
U.S. Pat. No. 4,014,833 to A. L. Story, assigned to the same common
assignee as the present invention, discloses an aqueous printing ink with
polyethylene oxide in small amounts. Also, U.S. Pat. No. 3,461,092 to A.
L. Story, similarly assigned, discloses a solid particulate printing ink
composition and process for producing same.
Further, U.S. Pat. No. 4,231,911, to the same inventor and assignee as the
present invention, relates to an abrasion resistant protective coating
composition for foamed plastic substrates, especially those having
printing ink decorations thereon.
SUMMARY OF THE INVENTION
The present invention relates to an aqueous printing ink composition which
is comprised of a physical mixture of polyurethane resin, polyethylene
resin and water as the vehicle. The pigments, and colorants, are added to
the vehicle in minor amounts. The invention involves the use of a resinous
vehicle to produce a family of water-based inks with enhanced physical and
mechanical properties. The printing inks exhibit superior abrasion
resistance and also good adhesion to various substrates, including metal
and plastics, the latter in the form of films and foams.
A primary object of the present invention is to provide an aqueous printing
ink composition having improved applicating and transfer properties, and
method of improving such properties in various printing techniques.
Another object of the present invention is to provide an aqueous pigmented
flexographic ink which produces stronger imprints having increased color,
brilliance and clarity.
Still another object of the present invention is to provide an aqueous
pigmented flexographic ink which has increased scuff resistance and
substantially no objectionable emissions on drying.
Various other objects and advantages will become apparent from the
following detailed description.
DESCRIPTION OF THE PREFERRED EMBODIMENT
This invention is directly concerned with an ink vehicle composition which
facilitates producing an ink exhibiting good adhesion, lubricity and
abrasion resistance when applied to a substrate by a printing technique
such as flexography. More specifically, the vehicle composition comprises
a physical mixture of a water-borne aliphatic polyurethane resin and a
water-based low molecular weight polyethylene resin. The polyurethane and
polyethylene may be mixed together in a solids ratio ranging from 9:1 to
1:1, although the latter ratio is preferred.
An especially-desirable component for preparing the subject vehicle
composition consists of an oxidized homopolymer of polyethylene resin and
preferably Allied Chemical Polyethylene--Product No. AC-316--having a
softening point of 140.degree. C. (284.degree. C.) (ASTM-E-28), a hardness
(dmm) of less than 0.5 (ASTM D-5), a density (g/cc) of 0.98 (ASTM D-1505),
a viscosity (cps) at 149.degree. C. (300.degree. F.) (Brookfield) of
30,000, and an acid number (mgKOH/g) of 16. The subject material is Food
and Drug Administration approved for use in connection with packaging
products. Also, Allied Chemical Polyethylene Product No. AC-392--which is
equivalent to AC-316 may be used for the stated purposes, both materials
being manufactured and sold by Allied Chemical Corporation.
The basic formulation for the AC-316 Product of the polyethylene emulsion
non-ionic type is as follows:
______________________________________
PBW
______________________________________
AC Polyethylene 316
40.0
GAF Igepal CO-630 10.0
KOH 90% Flake 1.0
Na.sub.2 S.sub.2 O.sub.5
0.4
______________________________________
The preferred polyurethane resin is Neorez R-960 which is an aqueous
colloidal dispersion of an aliphatic urethane manufactured and sold by
Polyvinyl Chemical Industries. This product has wet properties of solids
34.+-.1, PH of 7.5 to 8.5, viscosity (cps) of 400 to 800, density
(lbs/gal) of 8.8, excellent mechanical stability, and will pass 5 cycles
in its freeze-thaw stability. This product also has the following
performance properties:
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CURE SCHEDULE
______________________________________
Air Dry 6 hrs
Force Dry 10 min at 200.degree. F.
Hardness 4 H
Tensil Strength 5000 psi
Cure 10 min at 200.degree. F.
Taber Abrasion 28 mg loss
Chemical Resistance Excellent
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As a non-ionic emulsifier, a preferred material is GAF Igepal No. CO-630,
which is a surfactant with a mole ratio of 9 units of ethylene oxide,
which units provide 65% of the ethylene oxide contained therein. This
material is a polyoxyethylated nonylphenol--more particularly
nonylphenoxypoly (ethyleneoxy) ethanol. Such surfactant has a non-ionic
character making it useful with either anionic or cationic agents.
Various other non-ionic type emulsifiers can be used such as GAF Igepal
CO-610 and CO-710, both of which are generally similar to Product CO-630.
Among the various types of anionic emulsifiers which can be used are
morpholine oleate, potassium oleate, and sodium oleate.
A low molecular weight alcohol is normally used in the composition to
provide three distinct advantages. The alcohol is readily compatible with
the emissible from the water-based composition in all proportions. The
alcohol provides: (a) long term shelf stability for the composition, (b)
printability or lubricity to the system so that it can be flexographically
printable, and (c) a depressant of the surface tension and/or coefficient
of friction of the system so that it can be more easily printable.
The surface tension of the composition can be further depressed by addition
of small amounts of water-miscible silicone fluids. Products such as LE-45
and L-77, which are silicone fluids made and sold by Union Carbide
Corporation, can be added to impart higher lubricity to the system, and
also serve as a surface tension depressant. It is preferred to add small
amounts of silicone fluid, an addition of LE-45 in the amount of less than
1 percent by weight based on the entire system being particularly
desirable.
If desired, an ultraviolet tracer can be added to the system, as is
conventionally known in the art, so that it can be determined where the
material has been printed or applied. This is especially important where
the system is basically colorless and transparent, and used in thin film
applications.
In preparing a limited quantity of the subject ink composition, such as
approximately one gallon, the following constituents are taken by weight
and intermixed as set forth hereinbelow:
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AMOUNT
COMPONENT MATERIAL (by Weight)
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A Polyethylene Resin
1660.00 gm
(AC-316)
B Polyurethane Resin
1470.00 gm
(R-960)
C Water 700.00 gm
D Isopropanol 767.50 gm
E Silicone Fluid
7.60 gm
(LE-45)
F Silicone Fluid
0.23 gm
(L-77)
TOTAL 3605.33 gm
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With regard to the listed constituents, the following information provides
more detailed specifications of the percent by weight of solids content of
the preferred commercial materials as supplied:
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COMPONENT PERCENT SOLIDS NATURE
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A 30.0 Water Emulsion
B 33.3 Water Dispersion
E 30.0 Water Emulsion
F 100.0 --
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Components E and F are both optional for use in improving lubricity and/or
reducing the surface tension of the final product depending upon the
selected printing process for applying the ink. Where the printing process
consists of the flexographic method, these optional constituents are
valuable additions to achieve best results where only prescribed surface
areas are to be left uncoated.
The preferred procedure for mixing the aforesaid constituents with
continuous stirring consists of taking the polyurethane resin (b) and
mixing it with the water fraction (c). The latter mixture then is added to
the aqueous polyethylene emulsion (a) as the stirring is continued. The
low molecular weight alcohol and preferably isopropanol (D) is then added
to the mixture with stirring. The optional silicone fluids, components E
and/or F, are then added to the mixture with further continuous stirring.
Component E is added on the basis of 0.2 percent by weight of the mixture
of components A through D. Component F is added on the basis of the
mixture of components A through D.
Component E consists of a Union Carbide silicone emulsion designed for use
in a wide variety of release and lubricant applications. Such materials
are dimethylpolysiloxanes having low surface tension and excellent
lubricity for use in the manufacture of printing inks. They serve to
facilitate pigment dispersion, impart slip to the ink to improve
performance, and assist the printing process by minimizing ink buildup.
Component E is a very stable emulsion for addition to printing inks to
decrease ink smearing and set-off. The addition of Component E to the
aqueous ink system which is also water-dilutable improves flow and
leveling properties of the composition.
As stated, the polyurethane resin and polyethylene resin are present in a
solids ratio ranging from 1:9 to 1:1, the preferred ratio being 1:1. The
composition also includes a low molecular weight alcohol as a printing
additive ranging from 0 to 30 percent by weight, based upon the three
primary constituents of polyethylene, polyurethane and water, with
isopropyl alcohol being added. The foregoing physical mixture is taken as
the basis for the major component in the subject printing ink compositions
as designated as "Base Component.
The following examples of aqueous printing ink compositions have been
formulated in accordance with the present invention, and are
representative of such materials having special utility.
EXAMPLE I
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BLACK INK PERCENT BY WT.
______________________________________
Base Component 64
Elftex 8 Carbon Black
14
Wax MP 22 1
Antifoam Agent AF-75
1
Clay Pigment 80 10
Water 10
TOTAL 100%
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EXAMPLE II
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YELLOW INK PERCENT BY WT.
______________________________________
Base Component 62
Benzidine Yellow 274-2861
16
Wax MP 22 1
Antifoam Agent AF-75
1
Clay Pigment 80 10
Water 10
TOTAL 100%
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EXAMPLE III
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BLUE INK PERCENT BY WT.
______________________________________
Base Component 60
Phthalocyanine Blue 55-3295
15
Wax MP 22 1
Antifoam Agent AF-75
1
Clay Pigment 80 10
Water 13
TOTAL 100%
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The Base Component of each of the examples has been described hereinabove
as an aqueous physical mixture of primarily polyurethane resin and
polyethylene resin. It is included in major amount in each of the
formulations.
In the case of the black ink, Alftex 8 Carbon Black is a black ink
component having good strength, blue tone and excellent dispersion and
printability properties, particularly useful for offset inks for news
printing. It is available from Cabot Corporation, Special Blacks Division,
Boston, Mass.
In the case of the yellow ink, the Benzidine Yellow, Product No. 274-2861,
is a colorant pigment available from Sun Chemical Company, Pigments
Division, Cincinnati, Ohio. The blue ink colorant, Phthalocyanine
Blue-Product No. 55-3295, is available from the same source.
The Benzidine Yellow is a diarylide yellow toner AAOT, having a color index
name of Pigment Yellow 14, and a color index number of 21095. It is a
powder having a specific gravity of 1.47, a bulk of 0.0815 gallon per
pound, and an oil absorption of 44.8. It exhibits very good to excellent
resistance to bleeding or degrading in a wide variety of chemical agents
or solvents.
The Phthalocyanine Blue is described as a blue pigment having a green
shade, a color index name of Pigment Blue 15, and a color index number of
74160. It is a bright blue powder having a specific gravity of 1.57, a
bulk of 0.0765 gallon per pound, and an oil absorption of 35. It exhibits
excellent resistance to bleeding or degrading in a wide variety of
chemical agents or solvents.
The colorant pigment ranges from about 10 to 20 weight percent of the
composition, whatever colorant is used.
The wax component of all examples, Product No. MP 22, is a synthetic
micronized wax which can be further defined as a basic chain hydrocarbon
synthetic wax. It provides excellent slip and good rub properties and is
economical for use in most ink and coating formulations. It has a maximum
particulate size of about 13 microns and an average particle size of about
4 microns. This product has a density of 0.94 gm/cm.sup.3 at 77.degree.
F., a melting point of 215.degree.-223.degree. F., a congealing point of
197.degree.-205.degree. F., and a penetration of 1-3 at 77.degree. F. This
product MP 22, is available from Micro Powders, Inc., Yonkers, N.Y.
The wax component may be an exudative wax such as an animal, vegetable or
mineral wax.
The antifoam agent, Product No. AF-75, is a silicone antifoam emulsion
available from General Electric Company, Waterford, N.Y. It is a 10
percent solids antifoam emulsion of polydimethylsiloxane useful for
defoaming aqueous systems. It is a low viscosity emulsion assuring ease of
handling and dilution. It has a density of 8.4 lbs/gal, a specific gravity
of 1.02, a viscosity of 2500 cps at 25.degree. C. (max) and a white color.
The clay pigment 80 is a fine powder filler having an average equivalent
particle diameter of about 0.8 microns. It has a specific gravity of 2.60,
a refractive index of 1.50 to 1.60, and a bulking value of 21.7 pounds per
gallon. It exhibits a screen residue of 0.01.degree. on a 325 U.S. mesh
screen, and has a particle size distribution of 80-82% finer than 2
microns and 3-6% coarser than 5 microns. The clay pigment serves as a
filler or bodying agent and ranges from 5 to 15 weight percent of the
composition. This product is available from J. M. Huber Corporation,
Macon, Ga.
Obviously, other colorants can be employed to formulate a much wider
variety of ink colors, the foregoing being exemplary of the invention.
The subject water-based inks can be useful for high-speed printing on
vending cups. While the inks are especially useful for printing on
thermoplastic materials, they can also be used for printing on paper or
metals. The inks offer distinctively improved adhesion to plastic
materials, and offer relatively high-gloss and excellent abrasion
resistance. If desired, the inks once deposited on the substrates in the
form of printing or decoration can be overcoated with the base component
only to provide a very shiny appearance and further improved scuff and
abrasion resistance. The inks can also be printed on sheet metals as well
as film and foam type plastic materials with very good adhesion. The inks
possess good lubricity when applied to the various substrates by known
printing techniques, such as flexography.
Various modifications of the present invention can be resorted to within
the spirit and scope of the appended claims.
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