Note: Descriptions are shown in the official language in which they were submitted.
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WATER-BASED PAD PRINTING INK COMPOSITION
FIELD OF THE INVENTION
The present invention relates generally to a transfer-pad printing ink
composition preferably comprising a waterborne vinyl resin, an opacifier, a
S release agent, a dispersant and a colorant. The ink composition is particularly
suited for use with silicone rubber transfer pads to print alphanumeric patternson curved or spherical articles such as ophthalmic lenses. The ink formulation
is compatible with the pad surface so the pad precisely transfers the design to
a surface that is receptive to the ink which is removable with water.
BACKGROUND TO THE INVENTION
Pad or transfer-pad printing is a well established method for
transferring ink in the form of a thin design to a shaped surface such as one
having a rounded or otherwise irregular contour. This technique differs from
traditional printing in that it does not rely on a typeface in transferring the
design. Pad printing has been used commercially for many applications such
as (I) printing patterns on light bulbs, watch faces, and golf balls, (2) printing
circuits on dielectric substrates, (3) imprinting bar codes, and (4) marking glass
or plastic ophthalmic lenses for subsequent identification in prescription-filling
optical laboratories.
There are a number of commercial transfer-pad printing systems
available. For example, systems are obtainable from Trans Tech America,
Inc., Schaumberg, IL. Markem Corporation, Keene, NH; Tampo Print GmbH,
~unich and Stuttgart, Germany. Transfer-pad printing devices are described,
for example, in 4,060,031, 4,282,807, 4,615,266, 4,779,531, 4,803,922 and
4,856,670. Though these systems are automated and geared to accurately
transfer the pattern from a printing block (cliché), which contains the ink
design to be transferred, a critical step in the process involves accurately
picking up the ink design from the cliché, without altering the design as it lays
- on the pad prior to transfer to a receiving surface.
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Reproducing the design on a cliché on a substrate depends upon the
ability of the ink composition deposited in the cliché to effectively wet the
surface of the transfer-pad. If the ink composition does not properly wet the
pad surface, the pad will not completely pick up the ink in the design provided
5 in the cliché. Alternatively, the pad may pick up the ink design by suction ofa sufficient mass only to have the design break up (or bead up) on the pad
because of an incompatibility between the ink and the pad surface prior to
transference of the design to the desired surface. To address this problem, WO
92/20005 described a modified transfer-pad printing composition comprising
10 either a latex or a solution coating composition which includes a monomeric or
polymeric hydroxylated and/or carboxylated surface active wetting agent.
Following transfer of the ink composition, printing is complete when
the ink dries to form the design. In this regard, some commercially available
organic solvent-based inks must be dried and cured at elevated temperatures.
15 The volatile organic compounds in organic solvent-based inks raise
environmental concerns not only because of their presence but also because
acetone or another organic solvent is required to remove the print thereby
further aggravating the problem. Finally, it has also been observed that some
organic solvent-based inks cause a phenomenon referred to as "ghosting,"
20 where the ink composition leaves an impression on the surface of a plastic
substrate after the ink (e.g., design) has been wiped off.
SUMMARY OF THE INVENTION
The present invention is based in part on the discovery of a transfer-pad
aqueous ink composition comprising a marking ink in a waterborne vinyl resin
25 dispersion that is compatible with pad surfaces including those made of
silicone rubber. The ink composition, in the shape of an alphanumeric or any
geometric pattern, can be precisely imprinted on the pad surface; thereafter, the
design can be precisely transferred to another surface that is receptive to the
ink.
... . . .
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W O97/41180 PCT~US97/06805
In one aspect, the invention is directed to an aqueous coating
composition suitable for use in~ transfer-pad printing that comprises a water
soluble polymer; an opacifier; and a dispersant.
Preferably, the soluble polymer is a vinyl resin and the ink composition
includes a colorant to enhance the appearance of the finished pattern. When
the transfer pad is made of silicone rubber, the composition includes a release
agent.
In another aspect, the invention is directed to a transfer-pad printing
method of printing a pattern of a liquid coating from a cliché to a substrate
surface wherein the liquid coating comprises the above described aqueous ink
composition. In yet another aspect, the invention is directed to articles
including, for example, ophthalmic lenses, fabricated by this process.
In a preferred embodiment, the inventive aqueous ink composition does
not include an organic solvent which avoids the hazards associated with
organic solvent-based inks. In addition, the inventive ink composition
overcomes the deficiencies of conventional aqueous ink compositions which
have not been satisfactory. Specifically, prior art aqueous inks tend to bead upon the silicone rubber pad surface thereby breaking up the design sufficiently
so that the resultant imprinted product is a poor replica of the original design.
Furthermore, conventional aqueous marking ink solutions generally form very
light and not well defined imprints that ]ack body and substance. For these
reasons they fail to meet the requirements of a precision manufacturing
environment where readability, clarity, abrasion resistance, sturdiness and
moisture resistance are necessary.
A feature of the inventive water-dispersible ink is that it can dry at
room temperature (about 22~-25~C) in only a few seconds, or less time when
air assisted, to form good quality, well-defined prints that are comparable to
those formed from organic solvent-based inks. The prints are also abrasion
resistant so that articles (e.g., ophthalmic lenses) that are imprinted can be
- 30 safely packaged and shipped.
... . , ., " .. .
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Another feature of the invention is that the imprinted ink marks can be
readily removed by wiping with cold water.
A further feature is that the aqueous ink composition can imprint
patterns on ophthalmic lenses that are uncoated, coated for abrasion resistance
5 and/or anti-reflectivity. Plastic lenses are often coated with, for example, films
derived from polysiloxane, acrylate, epoxy, or urethane based compounds for
abrasion resistance and with multilayer films comprising silica, titania and/or
niobia for anti-reflectivity.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention is directed to water-based ink compositions for marking
irregular surfaces. The ink compositions can be employed to imprint any
article which can be imprinted by transfer-pad printing. The invention will be
illustrated with printing on ophthalmic lenses. In the case of ophthalmic
lenses, the markings are used in the production of lens products. Specifically,
15 the markings identify reference points on a lens, e.g., fitting cross, prism point,
near measurement etc., which guide laboratory personnel in grinding, polishing
and otherwise fitting the prescription to that required for the final eyeglass
product.
Ophthalmic lenses are fabricated from materials having superior
20 structural and optical properties. Crystalline quartz, fused silica, soda-lime
silicate glass, and plastics such as from polymers based on allyl diglycol
carbonate monomers (available as CR-39TM from PPG Industries, Inc.,
Hartford, CT), diacrylate or dimethacrylate compounds as described in U.S.
Patents 5,373,033 and 4,912,185, both incorporated herein, and which are
25 available as SPECTRALITETM from Sola Optical USA, Inc. Petaluma, CA,
and polycarbonates such as LEXANTM, available from General Electric Co.,
are preferred substrate materials for ophthalmic lenses (including sunglasses).
Preferred ophthalmic lenses also include l~-nin~ted lenses that are fabricated by
bonding two lens wafers (i.e., a front wafer and a back wafer) together with a
- 30 transparent adhesive. Laminated lens wafers are described, for example, in
U.S. Patents 5,149,181, 4,857,553, and 4,645,317 and U.K. Patent Application,
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wo 97/41180 PCT/US97/06805
GB 2,260,937A, all of which are incorporated herein. Suitable substrates
further include glass ophthalmic lenses, as described, for instance, in U.S.
- Patents 3,899,315 and 3,899,314, both of which are incorporated herein. As
used herein, the term "lens" refers to both single integral body and l~min~ttod
types.
The lens can be uncoated or coated for abrasion resistance or
antireflectivity. Ophthalmic lenses, particularly plastic ones, that are coated
with a polymeric abrasion or scratch resistance coating that may be about 1 lum
to about 12 ~m thick are also suitable substrates. The thickness of the
polymeric scratch resistance coating will depend, in part, on the substrate
materiah Generally, plastic materials such as polycarbonates will re~uire
thicker coatings.
Suitable lenses may also have an antireflection coating which refers to
a substantially transparent multilayer film that is applied to optical systems
(e.g., surfaces thereof) to substantially eliminate reflection over a relativelywide portion of the visible spectrum, and thereby increase the transmission of
light and reduce surface reflectance. Known anti-reflection coatings include
multilayer films comprising alternating high and low refractive index materials
(e.g., metal oxides) as described, for instance, in U.S. Patents 3,432,225,
3,565,509, 4,022,947, and 5,332,618, all of which are inco.porated herein. The
thickness of the AR coating will depend on the thickness of each individual
layer in the multilayer film and the total number of layers in the multilayer
film. The AR coating can include any number of layers. Preferably, the AR
coating for the ophthalmic lens has about 3 to about 12 layers, more preferably
about 4 to about 7 layers, and most preferably about 4 layers. Preferably, the
AR coating is about 100 to about 750 nm thick. For use with ophthalmic
lenses, the AR coating is preferably about 220 to about 500 nm thick. A
suitable anti-reflection coating is described in U.S. Patent Application Serial
No. 08/487,365 by Machol, entitled "Anti-reflection Coating", of common
- 30 assignee, filed on June 7, 1995, which is incorporated herein.
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However, before describing the invention in further detail, the following
terms will be defined.
The term "soluble polymer" refers to suitable water soluble polymers
that are compatible with the other components of the ink composition to form
5 an aqueous polymer mixture which produces a polymer composition with the
other components impregnated therein when the mixture is dried. Soluble
polymers include, for example, suitable urethanes, acrylates, epoxies, cellulose,
and vinyl derivatives. Specific examples, include, polyurethanes available as
N~OREZTM from Zeneca Resins, Wilmington, MA, styrene acrylates available
10 as JONCRYLTM from Johnson Wax Co., Racine, WI, hydroxypropylcellulose
available as KLUCELTM, cellulosic polymers available as AMBERGUMTM
both from Aqualon Co., Wilmington, DE, and aqueous vinyl polymer mixtures
that are available under the designations AW850, AW100, AW870, AW875
and WBVI00 from Union Carbide, Danbury, CT. Preferred soluble polymers
15 are thermoplastic. Preferred soluble polymers for the ink composition
comprise vinyl resins which are vinyl polymers or copolymers that are soluble
in water at room temperature. The presence of an aqueous colloidal dispersion
of said vinyl resins in the ink composition is critical in achieving the desiredflowability, printability and durability of the marlcing ink. The ink also has
20 good redispersibility characteristics and is easy to remove. Preferably, the
vinyl resin is a vinyl chloride copolymer. Suitable vinyl chloride copolymers
are available as a waterborne vinyl dispersant such as, for example, the
UCARTM waterborne vinyls (available from Union Carbide, Danbury, CT). A
preferred waterborne vinyl resin dispersion is AW-850TM, which contains
25 about 40% solids, is available from Union Carbide. The soluble polymer
typically comprises from about 10% to about 30%, preferably about 15% to
25%, and more preferably about 20% to 25% of the ink composition when
first formulated, that is, prior to drying. (All percentages herein are on a
weight basis). Another preferred waterborne vinyl resin dispersion is WBV
30 lO0 which contains about 50% solids. This soluble polymer comprises from
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about 10% to 30%, preferably about 15% to 25%, and more preferably 20% to
25% of the ink formulation.
The term "opacifier" or "opacifying agent" refers to any suitable
substance that imparts strength, durability and/or sharpness to the design or
pattern created on a substrate surface when the ink composition has dried. In
addition, it appears that the opacifying agent also improves the consistency andtexture of the ink so that it can be readily transferred from the cliché to the
articles surface by the transfer pad. Preferred opacifiers are inorganic
materials such, for example, titanium dioxide, aluminum oxides, aluminum
silicates, and silica. Titanium dioxide is preferred because it is less abrasiveand creates superior appearing, well-defined designs and marks. When a
colorant is used in the ink composition, the TiO2 opacifier creates a white
background which enhances the color of the colorant. The opacifying agent
typically comprises from about 5% to 45%, preferably from about 5% to 30%,
and more preferably from about lO% to 20% of the aqueous ink composition.
The term "dispersant" refers to any suitable substance which acts as a
wetting agent to disperse the ink cornponents especially the opacifier (and
colorant which is optional) to form an aqueous mixture wherein the
undissolved fine solid particles are uniformly distributed and separated.
Preferred dispersants include, for example, water-reducible alkyds, acrylics,
polyesters, epoxies, and mixtures thereof. DISPERSE-AYD W-22TM
(available from Daniel Products, Jersey City, N.J.) is a preferred dispersant.
The dispersant typically comprises from about 0.5% to 5.5%, preferably from
about 1% to 5%, and more preferably from about 1% to 2.5% of the aqueous
ink composition.
The term "release agent" refers to any suitable substance that acts as a
lubricant to render the aqueous ink composition more readily transferable from
the cliché to the silicone rubber transfer pad and from the pad to the substrate(e.g., lens) surface. Silicone rubber material is described, for example, in WO
- 30 92/20005. Suitable release agents include, for example, silicone fluids. A
preferred release agent is a silicone fluid available as SFI 188TM from General
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Electric Co., Waterford, NY. The release agent typically comprises from about
10% to 30%, preferably from about 12.5% to 27.5% and more preferably
about 15% to 20% of the aqueous ink composition.
The term "colorant" refers to suitable substances which impart color to
another material or mixture. Colorants are used as desired to render
uniqueness to the mark, e.g., "color coding." In addition, colorants provide
improved legibility with surface saver tapes in lens surfacing process.
Colorants typically comprise either nonsoluble inorganic and soluble organic
dyes. Preferred colorants include Erioglaucine (turquoise blue) and Tartrazine
(yellow) both available from Aldrich Chemical Co., Milwaukee, WI. When
present, the colorant comprises from about 0.25% to 7.5%, preferably from
about 0.5% to 5%, and more preferably from about 0.5% to 2.5% of the ink
composition.
METHODOLOGY
The inventive ink composition can be employed in conventional
transfer-pad devices which typically comprise a silicone rubber pad for
transferring an ink pattern from a cliché ink source and printing the design
onto the surface of an article (e.g., lens surface). Excess ink is removed from
the cliché with a doctor blade. Typically, the aqueous ink composition
comprises about 20% to 50% water, preferably about 25% to 45%, and more
preferably about 35% to 45%. The composition is thixotropic and has a
viscosity of about 1,000 cp to 20,000 cp, preferably about 5,000 cp to 15,000
cp, and more preferably about 7,500 cp to about 12,500 cp at room
temperature.
Markings on plastic ophthalmic lenses that identified reference points
on each lens were formed using Tampo Print Hermetic transfer-pad printing
device models 61 and 90. The devices were available from Trans Tech
America, Inc., Schaumberg, IL and adapted for fabricating ophthalmic lenses.
The following Examples 1-6 describe representative preferred
- 30 formulations of the inventive aqueous ink composition:
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Example 1: To 54.3 g of AW850 (soluble polymer) add 10.81 g of de-
ionized water under stir. To this add 1.63 g of DISPERS-AYD W22
(dispersant). 0.81 g Erioglaucine and 0.11 g Tartrazine (colorants) are then
added and the mixture is stirred for 15 minutes. Next add 14.12 g of titanium
dioxide and continue stirring for a further 2 hours. Finally, add 18.19 g of theSF1188 (release agent) and stir for 2 more hours. This formulation achieves a
teal colored ink.
Example 2: The same mixing procedure as Example 1 except replace
the AW850 with 54.3 g of WBV110.
Example 3: To 60.88 g of AW875 add 1.79 g of D~SPERS-AYD W22
under stir. 0.9 g Erioglaucine and 0. I l g Tartrazine are then added and the
mixture is stirred for 15 minutes. Next add 15.92 g of titanium dioxide and
continue stirring for a further 2 hours. Finally, add 20.52 g of the SF1188 and
stir for 2 more hours. The formulation achieves a teal colored ink.
Example 4: To 64.31 g of AW875 add 1.29 g of DISPERS-AYD
W22 under stir. 0.96 g of Tartrazine is then added and the mixture is stirred
for 15 minutes. Next add 15.43 g of titanium dioxide and continue stirring for
a further 2 hours. Finally, add 18.0 g of SF1188 and continue stirring for 2
hours. The formulation achieves a yellow colored ink.
Example 5: The same mixing procedure as Example 4 except replace
the AW850 with 64.31 g of WBVl lO.
Example 6: The same mixing procedure as Example 4 except replace
the AW850 with 64.31 g of AW875.
After lenses are transfer-pad printed with the aqueous ink composition,
the markings on the surfaces of the lenses formed when the ink composition
dried. At room temperature, drying occurred within a few seconds or less
when air is blown on the aqueous ink composition. The markings were easily
removable with water.
While the invention has been described in terms of various preferred
- 30 embodiments, the skilled artisan will appreciate the various modifications,
substitutions, and changes which may be made without departing from the
... . .. ... . . ...... . .
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spirit hereof. The descriptions of the subject matter in this disclosure are
illustrative of the invention and are not intended to be construed as limitations
upon the scope of the invention.
