Abstract:
The present invention relates to a novel printing apparatus and methods for using the same. The present invention further relates to a method of curing photocurable inks, as used in ink jet printers and other printing apparatus, by exposing the photocurable ink to a radiation source, particularly a flat excimer lamp.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of priority to provisional patent application Ser. No. 60/121,560, filed on Feb. 25, 1999. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a novel printing apparatus and methods for using the same. The present invention further relates to a method of curing photocurable inks, as used in ink jet printers and other printing apparatus, by exposing the photocurable ink to a radiation source, particularly a flat excimer lamp. 
     BACKGROUND OF THE INVENTION 
     Many commercially available photoinitiators, including IRGACURE® 369, are presently used in ink compositions to accelerate ink drying in “radiation-drying printing.” As used herein, the term “radiation-drying printing” refers to any printing method which utilizes radiation as a drying means. Radiation-drying printing includes, for example, off-set printing operations, such as on a Heidelberg press, flexographic printing, and flat-bed printing. Commercially available photoinitiator systems have a number of shortcomings. First, most of the commercially available photoinitiator systems require a relatively large amount of photoinitiator in the ink composition to fully cure/dry the ink composition. This leads to undesirable extractables within the ink composition. Second, most of the commercially available photoinitiator systems require a high energy radiation source to induce photocuring. Moreover, even with the high energy radiation source, often the cure results are unsatisfactory. Third, many commercially available photoinitiator systems are highly reactive to oxygen and must be used under a nitrogen blanket. Fourth, even with a large amount of photoinitiator and a high energy light source, the commercially available photoinitiator systems require a dry/cure time only accomplished by multiple passes, as many as 15 passes, under a light source, which significantly limits the output of a radiation-drying printing apparatus. 
     What is needed in the art is a new printing apparatus, which enables substantially instantaneous drying/curing of a photocurable ink without the need for a large amount of photoinitiator in the ink or a high energy radiation source for drying/curing. What is also needed in the art is a method of significantly increasing the output of a radiation-drying printing apparatus due to a reduction in ink drying/curing time. 
     SUMMARY OF THE INVENTION 
     The present invention addresses some of the difficulties and problems discussed above by the discovery of a new printing apparatus, which enables instantaneous drying/curing of a photocurable ink composition. The printing apparatus may be used to dry/cure any photocurable ink composition and finds particular utility with ink compositions containing one or more energy-efficient photoinitiators. 
     The present invention is also directed to methods of using the above-described printing apparatus to print an ink composition onto a substrate. The method comprises printing an ink onto a substrate; and drying/curing the ink with a source of radiation. In one embodiment, the radiation source is a flat excimer lamp. 
     These and other features and advantages of the present invention will become apparent after a review of the following detailed description of the disclosed embodiments and the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     FIG. 1 depicts a printing apparatus of the present invention. 
     FIG. 2 depicts a flat excimer lamp used in the printing apparatus of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is directed to a printing apparatus for printing photocurable ink compositions onto a substrate. The printing apparatus comprising means for applying a photocurable ink composition onto a substrate and means for drying/curing the photocurable ink composition. The means for drying/curing the photocurable ink composition comprises a lamp. The printing apparatus of the present invention enables rapid drying/curing of photocurable ink compositions, resulting in water resistant, cured print. 
     FIG. 1 depicts a printing apparatus  10  of the present invention. The printing apparatus comprises a printing means  11 , which applies a photocurable ink composition  12  onto a substrate  13 . The printing apparatus further comprises a drying/curing means  14  for drying/curing the photocurable ink composition  12  on the substrate  13 . 
     In one embodiment of the present invention, the printing apparatus comprising means for applying a photocurable ink composition onto a substrate and means for drying/curing the photocurable ink composition, wherein the excimer lamp is a low energy “flat lamp.” As used herein, the term “flat lamp” is used to describe a lamp having a thickness substantially less than the width and the length of the lamp. Suitable flat lamps include, but are not limited to, flat excimer lamps available from Heraeus Noblelight GmbH (Hanau, Germany). 
     FIG. 2 depicts a flat excimer lamp  20  used in one example of the printing apparatus of the present invention. The flat excimer lamp has a flat lower surface  21 , which comes into close contact with a substrate  22 . The flat excimer lamp has side surfaces  23  and an upper surface  24 . 
     The configuration of the flat excimer lamp enables optimum usage of the radiation emitted by the lamp. Unlike conventional lamps, having various sizes and shapes, a significant amount of radiation from the flat lamp reflects directly off of a printed substrate surface. Further, conventional lamps have various sizes and shapes, which prevent incorporation of the lamp into a printing apparatus. However, the flat lamp requires a relatively low volume of space for operation. In addition, the geometry of the flat lamp allows a large portion of the surface area of the flat lamp to be in close contact with the surface of a printed substrate. The flat lamp may be used in conjunction with a conventional printing apparatus or incorporated into a printing apparatus. 
     The dimensions of the flat excimer lamp may vary depending upon the desired position of the lamp relative to the printing means. Desirably, the flat lamp has a width of from about 3 inches to about 9 inches; a length of from about 6 inches to about 16 inches; and a thickness of from about ⅜ inch to about 1 inch. More desirably, the flat lamp has a width of from about 3 inches to about 7 inches; a length of from about 8 inches to about 14 inches; and a thickness of from about ⅜ inch to about ⅝ inch. Even more desirably, the flat lamp has a width of about 5 inches; a length of about 12 inches; and a thickness of about ½ inch. 
     In one embodiment of the present invention, the lamp emits ultraviolet radiation at a wavelength of from about 4 to about 400 nanometers. Desirably, the radiation will have a wavelength of from about 100 to about 420 nanometers, and more desirably will have a wavelength of from 222 to about 420 nanometers. Even more desirably, the radiation will have a wavelength of from about 222 to about 308 nanometers. The radiation desirably will be radiation from a 308 nm 15 W flat excimer lamp, available from Heraeus Noblelight GmbH (Hanau, Germany). 
     Although the radiation source is desirably a flat excimer lamp, other radiation sources may also be used in the present invention. Other suitable lamps include, but are not limited to, non-flat excimer lamps, mercury lamps, and other specialty doped lamps. Suitable lamps are disclosed in copending U.S. Provisional Patent Application Ser. No. 60/111,950, the subject matter of which has been incorporated into U.S. patent application Ser. No. 09/407,007, filed on Sep. 28, 1999, both of which are assigned to Kimberly Clark Worldwide, Inc., the entirety of which is incorporated herein by reference. 
     The choice of a specific radiation source allows for the effective tuning of the radiation source to a particular photocurable ink composition. The ink composition may contain one or more photoinitiators, which absorb energy at a wavelength corresponding to the wavelength of the radiation source. Suitable photoinitiators include, but are not limited to, photoinitiators disclosed in copending Provisional Patent Applications Nos. 60/082,143, 60/087,866, 60/102,153, 60/111,950, and 60/121,302, the subject matter of all of which has been incorporated into U.S. patent application Ser. No. 09/407,007, filed on Sep. 28, 1999; U.S. patent application Ser. No. 08/998,464; and U.S. Pat. No. 5,739,175; all of which are assigned to Kimberly Clark Worldwide, Inc., the entirety of which is incorporated herein by reference. 
     The excimer lamp of the printing apparatus of the present invention emits radiation at a specific wavelength band, which results in the photoinitiators to more efficiently utilize the radiation in the emission spectrum of the radiating source corresponding to the “tuned” wavelength band, even though the intensity of such radiation may be much lower than, for example, radiation from a narrow band emitter, such as an excimer lamp. For example, it may be desirable to utilize a flat excimer lamp, or other radiation emission source, that emits radiation having a wavelength of approximately 222 nm or 308 nm with one or more photoinitiators. Further, it may be desirable to utilize an excimer lamp, or other radiation emission source, that emits radiation having a wavelength of approximately 360 nm or 420 nm with one or more photoinitiators. 
     In a further embodiment, the present invention is directed to a method of printing an ink composition onto a substrate using an ink jet printing apparatus as described above. The method comprises applying a photocurable ink composition onto a substrate, and drying/curing the photocurable ink composition. The means for drying/curing the photocurable ink composition may comprise a flat excimer lamp as described above. 
     The printing apparatus of the present invention and the method of printing using the printing apparatus of the present invention has been described above in terms of the means for applying a photocurable ink composition onto a substrate and the means for drying/curing the photocurable ink composition. In addition to the means for applying a photocurable ink composition and the means for drying/curing the photocurable ink composition, the printing apparatus may further comprise other components including, but not limited to, a paper feeder, a printed sheet sorter, etc. In one embodiment of the present invention, the printing apparatus further comprises a housing means for enclosing the means for applying a photocurable ink composition onto a substrate and the means for drying/curing the photocurable ink composition. 
     Although the printing apparatus of the present invention finds particular applicability in the area of ink jet printing, the printing apparatus of the present invention may be used in any radiation-drying printing process. As used herein, “radiation-drying printing” refers to any printing method, which utilizes radiation as a drying means. Radiation-drying printing includes, for example, off-set printing operations, such as on a Heidelberg press, flexographic printing, and flat-bed printing. 
     The printing apparatus of the present invention enables increased output due to the efficient drying/curing of the printed substrate. Further, the increased output may be obtained while using a minimal amount of photoinitiator and a low energy light source. The printing apparatus of the present invention enables rapid curing times from 5-10 times faster than the curing times of ink compositions using conventional equipment. The printing apparatus of the present invention enables print speeds, which were at one time thought to be unobtainable. For example, in an open air printing process using a Heidelberg print press and a 15 W flat excimer lamp for photocuring, desirably the printed sheet output is greater than 6,000 sheets per hour. More desirably, the printed sheet output is greater than 8,000 sheets per hour. Even more desirably, the printed sheet output is greater than 10,000 sheets per hour. 
     While the specification has been described in detail with respect to specific embodiments thereof, it will be appreciated that those skilled in the art, upon attaining an understanding of the foregoing, may readily conceive of alterations to, variations of, and equivalents to these embodiments. Accordingly, the scope of the present invention should be assessed as that of the appended claims and any equivalents thereto. 
     The present invention is further described by the examples which follow. Such examples, however, are not to be construed as limiting in any way either the spirit or scope of the present invention. In the examples, all parts are parts by weight unless stated otherwise. 
     EXAMPLE 1 
     Ink Jet Printing of an UV Curable Acrylate Resin Using a Flat Lamp 
     A printing apparatus comprising an Epson Stylus Color Printer, Model 740, in combination with an excimer lamp was used to print ink compositions onto a paper substrate according to the following method. 
     The water-based inks were removed by syringe from an Epson color ink jet cartridge, Model S020191). The empty cartridge was flushed with a clear flexographic resin until the resin from the cartridge was colorless. A 9:1 wt/wt mixture of Satomer SR335 (N-lauryl acrylate) and Flexo Resin was prepared. One percent of a photoinitiator having the following structure was added to the mixture:                           
     Three inks were prepared from the above mixture: a magenta ink using 5 wt % Intrasperse Red-Violet RH; a yellow ink using 5 wt % Disperse Yellow 42; and a cyan ink using 5 wt % Victoria Blue BO. Each ink was placed within the ink cartridge, which was positioned inside the Epson printer. 
     Using a paint program, three 2″×2″ squares for each ink were printed onto a transparency film and exposed to a flat lamp available from Heraeus Noblelight GmbH (Hanau, Germany) and having a width of about 5 inches; a length of about 12 inches; and a thickness of about ½ inch. An instantaneous cure was observed. 
     EXAMPLE 2 
     Ink Jet Printing of an UV Curable Acrylate Resin Using a Cylindrical Excimer Lamp 
     Example 1 was repeated except a cylindrical 308 nm excimer lamp was used in place of the flat lamp. A good cure was observed.