RETROREFLECTIVE INKS AND FABRICS
Field Of The Invention
The invention relates the field of inks suitable for printing onto textiles.
More particularly, the invention relates to inks suitable for printing retroreflective patterns onto fabrics.
Background Of The Invention
Retroreflective surfaces redirect light from environmental sources such as
automobile headlights and overhead streetlights into the eyes of others.
Retroreflectorized objects are therefore more visible under low light conditions
than nonreflectorized objects. In order to promote public safety, objects
commonly encountered in motor vehicle traffic that are often made
retroreflective. For example, traffic signs, emergency response vehicles, vehicle
license plates, bicycles, and the like are made retroreflective to make them more
conspicuous, especially at nighttime and during inclement weather. In a similar
fashion, various articles of clothing are sometimes made retroreflective to make
the wearer more visible to others.
Retroreflective compositions for use on fabrics and other objects are
known in the art. For example, retroreflective coating compositions are
disclosed in Palmquist et al. U.S. Pat. No. 2,963,378; Nellessen, U.S. Pat. Nos.
3,099,637; 3,228,897; and 3,420,597; Longlet et al. U.S. Pat. No. 3,535,01 9;
Bingham U.S. Pat. Nos. 4, 1 03,060; Re. 30,892; and 4,263,345; Fouche Jr.
U.S. Pat. No. 4, 1 87,332; and Rizika et al. U.S. Patent No. 5,650,21 3.
Commercially available retroreflective compositions include SCOTCHLITE textile
ink (Minnesota Mining and Manufacturing Co., St. Paul, MN) and ILLUMITE
textile ink (Reflective Technologies, Inc., Cambridge, MA).
Conventional retroreflective compositions are useful for rendering various
objects more visible. They are, however, expensive and difficult to work with.
For example, conventional retroreflective compositions generally comprise
translucent beads hemispherically coated with a reflectorizing substance such as
metallic aluminum. E.g., Rizika et al. U.S. Patent No. 5,650,21 3. Such beads
are not only relatively costly to manufacture but also result in the retroreflective
compositions being unstable. That is, when such beads are dispersed in
commonly used liquid carriers, the resulting mixture becomes unusable within a
period of a few days. Because this mixture has a relatively short shelf life,
conventional retroreflective compositions are sold as two or three separated
precursor components. Prior to use, these precursor components must be mixed
together to form a retroreflective ink.
Conventional retroreflective compositions are also not optimized for
printing onto textiles because they often clog printing screens, require a
relatively high curing temperature, and are compatible only for printing onto
darker fabrics as the retroreflective compositions themselves typically have a
dark gray color. Moreover, many of the available retroreflective compositions
are not suitable for use on garments because coating of such compositions onto
a fabric often renders the fabric inflexible or rough to the touch.
Summary Of The Invention
A easy to use retroreflective ink has been developed. The components of
this ink are stable relative to one another, allowing the ink to be stored for
relatively long periods in premixed form. This ink is also adapted for use on
garments and is particularly suited for use in automated printing processes.
Accordingly, the invention features a retroreflective ink composed of a
multitude of components including a non-volatile matrix material, a volatile
component, and a plurality of beads exhibiting retroreflective qualities but not
having a reflective coating. In some variations of the foregoing, the beads
comprising this ink can have a mean diameter of about 1 0-40 microns (e.g.,
about 25 to 35 microns, less than 30 microns, and about 25 microns), can be
clear (i.e., transparent or colorless) or tinted to a predetermined color, solid,
spherical or nonspherical in shape, and/or comprised of a glass such as silica.
In one aspect of the invention, the beads comprise about 55-60% the ink
volume when all of the volatile carrier (e.g., water) has been removed from the
ink. In another aspect of the invention, the non-volatile matrix material (e.g., an
acrylic copolymer) comprises about 40-45 % of the ink volume when all of the
volatile carrier has been removed from the ink. In some embodiments, the
volatile component comprises about 45-50% by volume of the ink.
Also within the invention is a retroreflective ink containing numerous
components including a non-volatile matrix material, a volatile component, and a
plurality of beads, but not containing any pigment particles.
The invention additionally features a fabric having an ink of the invention
thereon. Also within the invention are methods of making a retroreflective
fabric, the methods including the step of printing a fabric with a retroreflective
ink of the invention.
In another aspect, the invention features a retroreflective ink including a
mixture having both 409 AG Reflective Clear LF Base and Grancill PWX Binding
and Finishing Agent.
As used herein, the word "retroreflective" is an adjective that indicates
that an object or substrate reflects rays of light in directions close to opposite
the direction of the incident rays (e.g., along their originating path) with this
property being maintained over wide variations of incident ray directions.
As used herein, the word "ink" means a fluid useful for depositing a
substance onto a substrate, e.g., a retroreflective composition onto a fabric.
As used herein, an object has a "reflective coating" when it has applied
thereon one or more layers of a reflective material such as a metallic material
(e.g., aluminum) or a non-metallic material (e.g., an organic compound) . For
example, spherical beads having with metallic aluminum hemispherically
covering their surfaces have a reflective coating.
As used herein, the word "colorless" is an adjective that describes an
object having no readily observable tint or hue. For example, common glass
having no exogenously added tinting agent or dye is colorless. By "tinted" is
meant having an added color or hue. For example, retroreflective beads are
tinted when a coloring agent or dye is added to impart a color to the beads.
As used herein, the phrase "pigment particle" means is particulate solid
(although not a "spherical bead") which is insoluble in, and essentially physically
and chemically unaffected by, the vehicle in which it is incorporated. Typically,
pigment particles are used to impart a color in the substance in which they are
incorporated.
As used herein, the word "fabric" means a woven material such as a
textile. Fabrics can be composed of natural or synthetic materials such as
cotton, nylon, polyester and the like, and are often fashioned into garments such
as article of clothing.
Unless otherwise defined, all technical terms used herein have the same
meaning as commonly understood by one of ordinary skill in the art to which
this invention belongs. Although methods and materials similar or equivalent to
those described herein can be used in the practice or testing of the present
invention, suitable methods and materials are described below. All publications,
patent applications, patents, and other references mentioned herein are
incorporated by reference in their entirety. In the case of conflict, the present
specification, including definitions will control. In addition, the particular
embodiments discussed below are illustrative only and not intended to be
limiting.
Detailed Description
The invention encompasses retroreflective inks comprising a non-volatile
matrix material, a volatile component, and a plurality of beads.
Components of the Retroreflective Ink
Beads suitable for use in the compositions of the invention are
commercially available. For example, spherical beads are available from Potter's
Industries (Valley Forge, PA) and Light Bead (Arlington, MA) . In preferred
embodiments of the invention, the beads are roughly spherical in shape,
composed of glass (e.g., silica), and have a diameter of approximately 1 0 to 200
microns (e.g., 1 0, 1 2, 14, 1 6, 1 8, 20, 22, 24, 25, 26, 28, 30, 32, 34, 35, 40,
50, 60, 70, 80, 90, 1 00, 1 10, 1 20, 1 30, 140, 1 50, 1 60, 1 70, 1 80, 1 90, or
200 microns) . Although the beads can be a heterogenous mixture of beads of
varying diameter, in preferred embodiments, the beads are a fairly homogenous
mixture of beads having a mean diameter of approximately 25 to 35 microns.
For screen printing, preferred embodiments feature smaller beads because
smaller beads flow more easily through the pores of the screen mesh and are
less apt to cause clogging. The particular mean diameter of the bead can be
selected by one of ordinary skill in the art according to the mesh count of the
screen. For example, beads having a mean diameter of approximately 25
microns are suitable for use with screens having a mesh count in the range of
1 10 threads per inch (tpi). Likewise, smaller diameter beads (e.g., 1 5 to 20
microns) would be suitable for use with finer mesh counts. By varying the
composition of the glass used to make the beads, the beads can have an index
of refraction ranging from 1 .7 to 2.5. In preferred embodiments, in order to
ensure sufficient retroreflectivity, the beads have a mean index of refraction of
at least about 1 .9 (e.g., 1 .9, 2.O., 2.1 , 2.2., 2.3, 2.4, 2.5) . In preferred
embodiments, the beads are translucent and not colored.
In some applications, however, the glass comprising the beads is tinted a
particular color so that the beads have a tint (e.g., a red, orange, yellow, green,
blue, or violet hue). In preferred embodiments the beads are solid. In other
embodiments, however, they can also be hollow, or perforated (e.g., with pores
of varying diameter such as 1 , 2, 5, 1 0, 20 microns in diameter).
The beads within the subject invention may have a roughly spherical
shape. In alternate embodiments, the beads may have other shapes. For
example, the beads may be polygonal, cone-shaped, star-shaped, of an irregular
shape, etc. The beads may even comprise a mixture of two or more differently-
shaped beads. Preferred shapes of the beads are those that enhance
retroreflectivity.
The non-volatile matrix material featured in the invention is any suitable
material that facilitates coating of the beads onto a substrate (i.e., the object to
which the ink of the invention is applied such as textiles, fabric, paper, leather,
plastic, glass, metals, wood, rubber, synthetic rubber, composites, etc.).
Suitable compositions for use as the non-volatile matrix material are known in
the art. For example, matrix materials typically used in conventional (non-
retroreflective) textile inks may be used.
In preferred embodiments, the non-volatile matrix material takes the form
of a transparent or translucent non-volatile film-forming emulsion. Exemplary
non-volatile matrix materials suitable for use on fabric such as those used to
make clothing include, but are not limited to acrylic, vinylidene chloride,
butadiene, acrylonitrile or urethane polymers, or any of suitable mixture of the
foregoing. Materials suitable for use as or preparation of the non-volatile matrix
are commercially available from chemical suppliers such as Sigma-Aldrich (St.
Louis, MO) . In a particularly preferred embodiment, the non-volatile matrix
material is an acrylic copolymer. Still other materials suitable for use as the non-
volatile matrix material can be selected by one skilled in the art based on the
properties desired for a particular application. For example, various oils, resins,
solvents can be used as the non-volatile matrix material in certain applications.
The volatile component of the invention is a liquid component conducive
to evaporation. The volatile component can be any suitable liquid or
combination of two or more liquids such as volatile organic solvents. Materials
suitable for use as or preparation of the volatile component are commercially
available from chemical suppliers (e.g., Sigma-Aldrich). In a particularly preferred
embodiment, the volatile component is water. Water that has been distilled,
deionized, and/or filtered to remove contaminants is preferred. Still other
materials suitable for use as the volatile component can be selected by one
skilled in the art based on the properties desired for a particular application.
While the foregoing comprise the minimal elements typically needed to
fabricate the inks of the invention, other components can be added to the ink
depending on the particular qualities desired. For example, although the
preferred inks of the invention are colorless and do not contain insoluble coloring
agents such as pigment particles, such particles or, alternatively, soluble coloring
dyes can be added to the ink so that a substrate treated with the ink takes on a
pre-selected color or hue. Additionally, in certain embodiments, texturizing
agents may be added to the inks where it is desired to impart a particular
surface quality to the substrate to which the ink is applied. For example, sand
particles may be added to the ink so that the substrate to which the ink is
applied exhibits a high friction surface. Still other ink additives may be included.
These can be selected by one skilled in the art depending on what particulars
qualities are desired. For example, to further adapt the inks for use in a screen
printing process, materials such as lubricants, surfactants, dispersants,
thickeners, defoamers, stretch additives (i.e., agents that impart elasticity),
binding agents (i.e., agents that help adhere solid particulates to substrates),
finishing agents, low crocking agents, cross link agents (e.g., CX100, Zeneca
Industries, Wilmington, MA), low cure additives (i.e., agents that reduce the
time and/or temperature of curing), fixers and/or ammonium hydroxide can be
added.
Preparation of the Retroreflective Ink
In various preferred embodiments of the invention, the retroreflective ink
is prepared for use by mixing the beads, non-volatile matrix material, volatile
component, and, optionally, the aforementioned additives together to form an
ink. Appropriate amounts of each of the foregoing components are added
together in a predetermined ratio then mixed to form the ink. Mixing can be
accomplished by any means known in the art, e.g., using a high speed mixer or
blender.
The precise ratio selected will depend on the particular application for
which the ink will be used and can be selected by one of skill in the art based on
the characteristics of each component. For example, in a particularly preferred
embodiment suitable for use in screen printing fabrics, a bead-matrix mixture is
prepared where the mixture comprises by volume about 55-60% beads and
about 40-45 % non-volatile matrix material. The volatile component is added to
the bead-matrix material in an amount so that the volatile component is present
at about 45-50% the volume of the ink (i.e., the total volume of the beads,
matrix material, and volatile component). That is, the volatile component is
added to the bead-matrix material mixture in a ratio of about 1 :2 by volume.
After mixing the foregoing components together to form the ink, the ink is
stored in an airtight container so that the volatile component does not
appreciably evaporate prior to use.
Applying Retroreflective Inks to Substrates
The inks of the invention can be applied to substrates by any suitable
method known in the art. For example, the inks can by manually applied to a
piece of fabric by simply dispensing (e.g., using a pipet) a quantity of the ink
onto the fabric. Other suitable methods for applying the inks to a substrate
include coating (e.g., Floating Knife or Knife Over Roll method), stenciling, ink jet
printing, and web or rotary screen printing. In commercial processes where a
large number of fabric articles to be treated with the inks of the invention, the
preferred method of application is screen printing.
In one exemplary embodiment, a rotary screen printing process is used to
apply the ink to a substrate. In this method, the ink is pumped into the inner
portion of a perforated cylindrical screen and forced out onto a substrate through
the tiny screen perforations. The screen perforations can be made in the form of
a predetermined image, so that the ink becomes deposited onto the substrate in
a repeating pattern of the predetermined image. Thus, for example, where it is
desired to render a pre-existing image printed on a fabric retroreflective, a
transparent version of the retroreflective ink of the invention is printed directly
over the pre-existing image using a screen duplicating the image. To add a
retroreflective tint to the image, a dye or coloring agent is added to the
retroreflective ink before it is printed onto the image.
Substrates printed with a retroreflective ink of the invention are cured by
applying heat for a predetermined period of time to the substrate. The exact
amount of heat added and time needed to effect a cure will depend upon the
particular retroreflective ink and substrate used. This can be determined without
undue experimentation. In a typical application, the temperature of the ink is
raised to 325 degrees F. With the addition of low cure additive this curing
temperature can be reduced to 225 degrees F. Low temperature curing is
preferred when fabrics with low melting points are used as the substrate (e.g.,
synthetic materials such as polyester or nylon).
Example
A retroreflective ink of the invention was prepared by mixing 3 parts of
409 AG REFLECTIVE CLEAR LF base (International Coatings Corporation,
Cerritos, CA) with 1 part Grancill PWX binding and finishing agent (Grant
Industries, Elmwood Park, NJ 07407) . 409 AG REFLECTIVE CLEAR LF base
includes water as a volatile component, uncoated roughly spherical glass beads
having a mean diameter of about 25 microns, and a matrix material. 409 AG
Reflective Clear LF base is made by mixing approximately 2 pounds of uncoated
roughly spherical glass beads into each gallon of a textile ink base sold by
International Coatings Corporation (400 series Waterbase #402LF) and then
adjusting the viscosity using a volatile component to approximately 0.090 to
0.1 1 0 centistokes (i.e., a specific gravity compatible with screen printing and for
maintaining bead suspension) . Grancill PWX includes water as a volatile
component, binding agents that help adhere solid particle to a substrate, and
finishing agents that facilitate the use of the ink in screen printing applications.
CX100 cross link (Zeneca Industries) was then added in a quantity of 2% of the
total volume. This ink was screen printed onto a fabric in a predetermined
pattern. The printed fabric exhibited low daytime noticeability, while
manifesting readily detectible retroreflectivity under low light conditions (e.g.,
under typical nightime lighting) .
From the foregoing, it can be appreciated that the retroreflective inks and
related methods of the invention provide compositions and processes for
enhancing the visibility various objects under low visibility conditions.
Other Embodiments
While the above specification contains many specifics, these should not
be construed as limitations on the scope of the invention, but rather as examples
of preferred embodiments thereof. Many other variations are possible.
Accordingly, the scope of the invention should be determined not by the
embodiments illustrated, but by the appended claims and their legal equivalents.