Primed substrates comprising radiation cured ink jetted images

Details Primed substrates comprising radiation cured ink jetted images Primed substrates comprising radiation cured ink jetted images

2001-04-18

2004-04-13

Kelly, Cynthia H. (Department: 1774)

Stock material or miscellaneous articles

Ink jet stock for printing

Hardened, cured, or cross-linked ink receptive layer

C428S032100, C428S032340

Reexamination Certificate

active

06720042

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to primed substrates comprising radiation cured ink jetted images and methods of ink jet printing radiation curable inks that employ applying a primer. The imaged articles are durable for outdoor usage. A variety of polymeric sheets may be primed including various sheeting for signage and commercial graphic films for advertising and promotional displays.
BACKGROUND OF INVENTION
A variety of print methods have been employed for imaging various sheet materials. Commonly employed print methods include gravure, off-set, flexographic, lithographic, electrographic, electrophotographic (including laser printing and xerography), ion deposition (also referred to as electron beam imaging [EBI]), magnetographics, ink jet printing, screen printing and thermal mass transfer. More detailed information concerning such methods is available in standard printing textbooks.
One of ordinary skill in the art appreciates the differences in these various print methods and recognizes that a combination of ink and receiving substrate that results in high image quality in one printing method often exhibits an entirely different image quality with another print method. For example, in contact printing methods such as screen printing, a blade forces the ink to advance and wet the receiving substrate. Image defects are typically due to a subsequent recession of the ink contact angle with the substrate. In the case of non-contact printing methods such as ink jet printing, the individual ink drops are merely deposited on the surface. In order to achieve good image quality, the ink drops need to spread, join together, and form a substantially uniform, leveled film. This process requires a low advancing contact angle between the ink and the substrate. For any given ink/substrate combination, the advancing contact angle is typically significantly greater than the receding contact angle. Accordingly, ink/substrate combinations that result in good image quality when printed with contact methods such as screen printing, often exhibit insufficient wetting when imaged with non-contact printing methods such as ink jet printing. Insufficient wetting results in low radial diffusion of the individual ink drops on the surface of the substrate (also referred to as “dot gain”), low color density, and banding effects (e.g. gaps between rows of drops).
Another important difference between screen printing and ink jet printing is the physical properties of the ink. Screen printing ink compositions typically contain over 40% solids and have a viscosity of at least two orders of magnitude greater than the viscosity of ink jet printing inks. It is not generally feasible to dilute a screen printing ink to make it suitable for ink jet printing. The addition of large amounts of low viscosity diluents drastically deteriorates the ink performance and properties, particularly the durability. Further, the polymers employed in screen printing inks are typically high in molecular weight and exhibit significant elasticity. In contrast, ink jet ink compositions are typically Newtonian.
Ink jet printing is emerging as the digital printing method of choice due to its good resolution, flexibility, high speed, and affordability. Ink jet printers operate by ejecting, onto a receiving substrate, 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, holograms, and the like. The inks most commonly used in ink jet printers are water-based or solvent-based. Water-based inks require porous substrates or substrates with special coatings that absorb water.
On the other hand, solvent-based inks typically contain about 90% organic solvents. Since manufacturers prefer to reduce solvent emissions, the evaporation of large quantities of solvent during ink drying is undesirable. Further, the drying process can be the rate-limiting step for ink jet printing, reducing production rates. In order to avoid the problems associated with water-based and solvent-based inks, radiation-curable ink compositions comprising polymerizable ingredients have been developed. The polymerizable ingredients not only function as a solvent by reducing the viscosity of the composition prior to curing, but also function as a binder when cured, and optionally as a crosslinking agent. In the uncured state, these compositions have low viscosities and are readily ink jettable. The polymerizable ingredients readily react upon exposure to a suitable radiation source (e.g. ultraviolet light, electron beam) to form a crosslinked polymer network. The use of radiation curing allows the inks to “dry instantly” per se in view of the rapidity in which the composition can be radiation cured.
One problem, however, with radiation curable ink jet inks is that ink compositions do not uniformly adhere to all substrates. Accordingly, the ink composition is typically modified for optimized adhesion on the substrate of interest. Further, good wetting and flow onto various substrates is controlled by the ink/substrate interaction. Preferably, the interaction results in a sufficiently low advancing contact angle of the ink on the substrate, as previously described. Accordingly, for the same ink composition, the image quality (e.g. color density and dot gain) tends to vary depending on the substrate being printed. Substrate treatments such as solvent wiping, blowing, corona, flame and UV pre-treatment have been suggested in “Practical Considerations for Using UV Reactive Inks in Piezo DOD Print”, IS&T NIP 15: 1999 International Conference on Digital Printing Technologies. Further, in the case of ink jet printing onto polymeric materials, WO 99/29788 describes pretreatment by flame, plasma etch or corona treatment to raise the surface energy. As a practical matter, however, many ink jet printing operations are not equipped to pre-treat substrates prior to imaging in this manner. Hence, industry would find advantage in substrates and methods of ink jet printing that address this problem.
SUMMARY OF THE INVENTION
The present invention relates to an article comprising a sheet or polymeric material having a primed surface portion and a radiation cured ink jetted image disposed on said primed surface portion. The substrate, primer and ink are chosen such that the article is durable for outdoor usage. The polymeric material is thermoplastic or thermosetting. Preferred polymeric sheet materials include acrylic-containing films, poly(vinyl chloride)-containing films, poly(vinyl fluoride)-containing films, urethane-containing films, melamine-containing films, polyvinyl butyral-containing films, polyolefin-containing films, polyester-containing films and polycarbonate-containing films. A preferred sheet comprises a retroreflective viewing surface.
The image exhibits an improvement in overall print quality in comparison to the same imaged sheet lacking such primer. The ink and primer exhibit at least about 80% adhesion according to ASTM D 3359-95A. The image preferably has a black color density of at least about 1.5 and a final ink dot size of at least [(2)
1/2
]/dpi wherein dpi is the print resolution is dots per linear inch.
In one embodiment, the primed surface portion comprises at least one film-forming resin comprising an acrylic resin, a polyvinyl resin, a polyester, a polyacrylate, a polyurethane and mixtures thereof. Acrylic resins, polyurethane resins and mixtures thereof are preferred.
In another embodiment, the primed surface portion comprises crosslinked poly(meth)acrylate.
In another embodiment, the primed surface portion comprises at least one colorant.
The article is useful as an intermediate or as a finished product for signage and commercial graphic films.
In other embodiments, the present invention relates to methods of ink jet printing that employ the use of a primer.
In one embodiment, the method comprises applying at least one of a water-based primer composition or a solvent-based prim

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