Printing apparatus and applications therefor

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.

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.RTM. 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.

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 3/8
 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 3/8 inch to about 5/8 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 1/2 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:
 ##STR1##
 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".times.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 1/2 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.