Incremental printing of symbolic information – Ink jet – Medium and processing means
Reexamination Certificate
2001-01-08
2002-10-22
Gordon, Raquel Yvette (Department: 2853)
Incremental printing of symbolic information
Ink jet
Medium and processing means
Reexamination Certificate
active
06467897
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to compositions including an energy curable fluid vehicle and surface modified, nanometer-sized particles. The inventive compositions have utility in a wide range of applications, but are particularly suitable for use as printing inks, including ink jet printing inks.
BACKGROUND OF THE INVENTION
Inks are widely used in a variety of printing and coating processes including, for example offset, intaglio, rotogravure, ink jet, flexographic, screen, and spraying techniques. It would be desirable for the inks to remain in a free flowing fluid state during the fluid deposition step, yet undergo rapid self-fixing shortly thereafter to produce durable, non-smearable features on a final receptor material. In many instances, it is desirable to be able to build thickness without substantial spreading of the fluid. The art continuously searches for novel methods to control and improve the rheological characteristics of fluid inks, particularly the rate of self-fixing, which in turn yields better print quality, efficiency and higher speed in the various printing and coating processes.
Ink jet imaging techniques have become very popular in commercial and consumer applications. Ink jet printers operate by ejecting a fluid (e.g., ink) onto a receiving substrate in controlled patterns of closely spaced ink droplets. By selectively regulating the pattern of ink droplets, ink jet printers can produce a wide variety of printed features, including text, graphics, images, holograms, and the like. Moreover, ink jet printers are capable of forming printed features on a wide variety of substrates, including not just flat films or sheets, but also three-dimensional objects as well.
Thermal ink jet printers and piezo ink jet printers are the two main types of ink jet systems in widespread use today. For both approaches, the jetted fluid must meet stringent performance requirements in order for the fluid to be appropriately jettable and for the resultant printed features to have the desired mechanical, chemical, visual, and durability characteristics. In particular, fluids must have relatively low viscosity when jetted, yet must be able to form accurate, durable images on the desired receiving substrate. For example, a typical fluid for thermal ink jetting must typically have a viscosity in the range of 3 to 5 millipascal·seconds (mPa·s) at 25° C., while piezo ink jet fluids must typically have a viscosity in the range of 10 to 30 mPa·s at the printhead temperature. The need to use low viscosity fluids (e.g., inks) may make it challenging to obtain printed features with sufficient thickness and resolution to achieve good mechanical, chemical, visual, and durability characteristics.
Phase change inks (e.g., wax based) have been used for a variety of printing processes including piezo ink jet printing. Typically these inks include a dye or pigment mixed with a vehicle made of wax and/or a thermoplastic polymer that is solid at room temperature, but fluid at the printhead temperature (typically greater than 100° C.). Since such inks solidify rapidly when printed on the substrate, they give consistent image quality that is independent of the type of substrate used. However, the durability of such phase change ink compositions is typically poor, since they may scratch off easily. This is especially the case when the inks are printed onto non-porous plastic surfaces. Further, due to the waxy nature of the vehicle used in conventional phase change inks, the inks typically have poor adhesion to many substrates.
Organic solvent-based and water-based jettable inks are also well known. A typical water-based ink generally comprises a colorant, which may be a dye and/or a pigment, one or more organic co-solvents, and one or more additives that are included to enhance the performance of the ink. Representative examples of such additives include one or more colorants, slip modifiers, thixotropic agents, tack promoting agents, tack reducing agents, foaming agents, antifoaming agents, flow or other rheology control agents, waxes, oils, plasticizers, binders, antioxidants, fungicides, bactericides, organic and/or inorganic filler particles, leveling agents, opacifiers, antistatic agents, dispersants, and the like.
Printed, and especially ink jet printed compositions also require good dot gain characteristics. Dot gain refers to the degree to which a printed feature spreads out upon application to a substrate. If a printed feature (e.g., a dot or line) spreads out too much on the substrate, the resultant image may tend to have poor resolution. On the other hand, if a printed feature spreads insufficiently upon application to the substrate, then poor image density may result. Dot gain characteristics depend upon factors including the nature of the ink composition, printing conditions, and the nature of the substrate. Some inks show favorable dot gain characteristics on some substrates, but not on others.
It would be desirable to provide ink compositions that have consistently good dot gain characteristics with a wide variety of different porous and nonporous substrates.
It is known that inorganic oxide filler can be incorporated into radiation curable ink compositions in order to increase mechanical and durability properties such as hardness, modulus, abrasion resistance, and refractive index as compared to unfilled systems. The presence of such particles is also believed to decrease not only shrinkage upon curing, but also the coefficient of thermal expansion of the resultant cured composition. Unfortunately, however, incorporating conventional inorganic oxide filler into fluid compositions generally causes the compositions to phase separate, settle, clog printheads during use, lose of optical transparency, and the like with even relatively minor weight loadings of the particles. Such an increase in viscosity is a serious drawback for applications, such as ink jetting, in which relatively low viscosity is necessary for the compositions to be jettable.
Accordingly, it also would be highly desirable to find a way to improve mechanical and durability properties of radiation cured ink compositions without experiencing one or more of the drawbacks of conventional fillers.
SUMMARY OF THE INVENTION
The present invention relates to compositions that incorporate surface modified, nanometer sized, inorganic oxide particles into energy curable fluids. The surface modification aspect allows the compatibility between the particles and fluid to be controllably adjusted to achieve a wide range of Theological characteristics. When cured, the presence of the particles also helps improve physical properties such as hardness, modulus, abrasion resistance, refractive index, and the like. The compositions are particularly well-suited for forming printed, radiation cured features on substrates such as paper, signs, walkways, roadways, motor vehicles, boats, aircraft, furniture, equipment, and the like.
Although the compositions are useful in many applications, they are especially useful for ink jet printing applications. The nanometer size of the particles allows the compositions to be ink jetted without clogging the printhead nozzles. The size of the particles is also below light scattering range so that the particles do not interfere with optical clarity or light transparency. Accordingly, although optical additives such as colorants or the like may be incorporated into the formulations, transparent coatings reinforced with the nanometer-sized particles are easily prepared. The surface-treated particles may also be functionalized with energy curable moieties, which allows the particles to react with the energy curable fluid vehicle during curing. This provides the cured compositions with additional reinforcement if desired.
Embodiments of the invention may be formulated with surface modified particles that are only marginally compatible with the fluid vehicle. A wide range of rheological properties can be achieved with this approach. Some embodiments of such compositions are highly thixotr
Eliason Kevin M.
Kolb Brant U.
Kumar Kanta
Lee Jennifer L.
Nerad Bruce A.
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