WO2009079572A1

WO2009079572A1 - Hybrid printing press and method

Info

Publication number: WO2009079572A1
Application number: PCT/US2008/087210
Authority: WO
Inventors: Faye Transvalidou; Robert O'boyle; Martin Darby
Original assignee: Sun Chemical Corporation
Priority date: 2007-12-19
Filing date: 2008-12-17
Publication date: 2009-06-25

Abstract

A printing press has one or more analog printing stations and one or more digital printing stations sequentially arranged on a central impression (CI) drum. Preferably, the analog stations are disposed upstream of the digital stations. A curing unit can be disposed after the last printing station. Preferably, the printing press is operated without curing between adjacent printing stations and the inks are selected to realize wet trapping between printing stations.

Description

HYBRID PRINTING PRESS AND METHOD

BACKGROUND OF THE INVENTION

Printing methods can generally be divided into two basic methods, analog and digital. The analog methods are those printing methods that use an image transfer system, i.e., a method that transfers ink from a surface, usually a cylinder, bearing a fixed image to a substrate in contact with the surface. Examples of these analog printing methods include, but are not limited to flexographic, gravure, offset, and screen printing. Digital methods do not involve transferring ink from a surface bearing a fixed image to a substrate in contact with it. Digital methods include, but are not limited to, electrophotography and all inkjet technologies such as piezoelectric, thermal, continuous, hot melt, etc. Each analog and digital method has its own advantages and disadvantages, and each requires different types of printing presses.

For example, variable data printing, that is printing substantially different content from one imaging frame to the next is hard or impossible on a conventional analog technology press such as flexographic or gravure presses that utilize expensive prefabricated image plates or cylinders to print the exact same image content on consecutive frames. In addition, these conventional analog printing techniques are not cost effective on very short runs because of the preparation time and plate making expense required. On the other hand, digital printing presses and ink systems have difficulty in reproducing customer brand colors, as well as difficulty with solid applications such as 1^st down and backing whites, although they are less expensive for very short runs because they allow the avoidance of expensive make-ready procedures. Digital presses using UV curing ink technology also have difficulty in printing extensible films.

Tandem in-line presses have existed for some time. For example, Paper Converting Machine Company built a tandem press in 1989 that used two 4 color stations in-line. This allowed a decreased changeover time by running one project on one of the press sections while the other section was being changed over to run the next project, but added cost by having two press sections when only one press section was required. Also, it increased the registration error between any two printed colors. There was also a substantial cost associated with having and supporting two overhead dryer sections (one between press sections and one after the last press section), and the arrangement was quite sensitive to operator adjustments.

High quality printing on extensible web materials has been done by flexographic printing on central impression (CI) presses. The flexographic process offers distinct cost advantages and flexibility compared to other types of analog printing such as gravure, and the advantage of using a CI drum as opposed to an in-line flexographic press is that the web is stable during the printing process. The stability of the web allows for higher quality printing on a variety of substances including extensible films. Unfortunately, the number of colors that can be printed on a single CI drum is limited.

To address the foregoing, US 6,220,157 describes a printing press which includes multiple in-line central impression cylinders or drums and means for obtaining registration of the images which are printed on the cylinders. US 6,864,756 describes a web apparatus in which multiple digital print heads are arranged around a bidirectional rotatable impression drum.

Multicolor analog printing processes typically require the sequential printing of a plurality of superposed single color ink layers. When high quality image reproduction is desired, it is important to avoid mixing of the previously applied ink layer with a subsequently applied ink layer because that layer mixing typically results in undesirable color rendition. The art has addressed this problem in a number of different ways. One is to dry or cure each applied ink layer prior to the application of the next superposed ink layer, but while this technique is effective, it also requires complete drying after applying each ink layer. Drying takes time and energy to accomplish, and as a result, productivity is reduced and production costs increase. In an effort to speed up the printing process, "wet trapping" was developed. Wet trapping is a process whereby the ink layer deposited or applied at each inking station is not dried before the next ink layer is deposited to produce a coloristic or visual effect. One description of wet trapping can be found in US 6,772,683. Layer registration, however, remains a problem.

An attempt to marry analog and digital printing was attempted roughly 15 years ago. The Agfa Dotrix press ( http://www.agfa.com/en/gs/ products_services/ all_products/dotrix_inkjetpress.jsp?t=2) arranged flexographic printing in-line with digital printing in a stack-type press. That arrangement limited press speed and has reportedly not achieved printer acceptance after many years in the market. Another in-line arrangement is described in US 2007/02400592 Al. It has now been found that analog and digital printing can be married and good image quality achieved if all of the printing stations are arranged on a central impression (CI) drum and preferably operated without intermediate drying between printing stations, and preferably wet trapping is employed prior to the final printing station.

SUMMARY OF THE INVENTION

In accordance with the present invention, one or more analog printing stations and one or more digital printing stations are sequentially arranged on a central impression (CI) drum and preferably operated without curing between adjacent printing stations. As used herein, the term "curing" includes but is not limited to drying. Preferably, the analog stations are disposed upstream of the digital stations. A curing unit can be disposed after the last printing station. The inks are preferably selected to realize wet trapping between printing stations.

The invention will be better understood by those of ordinary skill in this art from the following description in which Figure 1 is a schematic of one CI press configured with one possible arrangement of printing stations.

DESCRIPTION OF THE INVENTION

A hybrid printing press in accordance with the present invention has one or more analog printing stations and one or more digital printing stations sequentially arranged on a central impression (CI) drum. The drum may be duplicated as a part of a CI press which has multiple drums for printing on both sides of the substrate. Such a combination of both analog and digital print technologies on a single drum offers increased flexibility, the possibility of eliminating substrate pre-treatment or pre-print steps, and allows for the ability to simultaneously or sequentially apply protective coatings, barrier coatings, special effect or decorative inks or incorporate intelligent features on the substrate being printed.

Figure 1 shows one possible press configuration. As will become clear from the ensuing description, there are many other possible embodiments of the invention. A central impression (CI) drum or cylinder 1 has at least two printing stations located around its circumference, one of which is analog and one of which is digital. In the embodiment shown, there are six analog printing units 2 and five digital printing units 3 disposed on the cylinder. In other embodiments, the number of analog printing units 2 and digital printing units 3, as well as the ratio of analog to digital units, can be varied as desired. Different types of analog or digital printing units, or both, can be combined if desired. Conventional analog and digital printing units are employed and therefore, a detailed description of them is unnecessary and is omitted here. A substrate 4 to be printed, which can be, for instance and without limitation, paper or an extensible web, is guided onto the CI cylinder 1 and then encounters the printing units sequentially, as shown by the arrows. Preferably, the analog printing unit(s) is/are upstream of the digital unit(s).

Useable substrates include virtually any material suitable for a web-based or roll- to-roll printing processes. This includes but is not limited to papers, woven and non-woven textiles, metallic foils, flexible films and polymer films, including coated, uncoated, treated and untreated variations (i.e., corona-, plasma-, or chemically-treated) of polyethylene, polypropylene, polyvinyl chloride, Polyvinylidene chloride, polyvinyl butyrate, polyethylene terephthalate, polyethylene terephthalate glycol, polycarbonate, polystyrene, polylactic acid, polyethylene naphthenate, polyimides (e.g. that sold by DuPont under the trademark Kapton used in manufacturing of flexible electronics), polyamides, etc. and any combination of these polymers and composites containing such polymers (lamination structures, coated or coextruded films with multiple layers to modify the barrier properties, surface characteristics or other physicochemical characteristics of the substrate, polymer coated papers like polyethylene coated paper, foils, cavitated films, woven or non woven substrates, etc.). The hybrid press is not be limited to use with unprinted substrates, but could be used to print onto pre-printed substrates as well.

The hybrid press is also not limited to use with pigmented or dye-containing printing inks but can also be used to print any printable pigmented, non- pigmented, functional or decorative coating such as overprint varnishes, barrier coatings, primers, adhesives, conductive materials, dielectrics, reactive or precursor-type materials that would react (e.g., polymerize etc.) or become activated by the electron beam to provide a needed functionality to a subsequent online or offline process, etc.

As shown in the drawing, there are preferably no curing stations between printing units. However, conventional printing units having integral or non- integral curing stations can be employed but such curing stations would preferably not be operated during a hybrid press run. An advantage of the instant hybrid press is that even though it combines two or more printing methods on a single drum, it is available for use in certain applications which employ only one printing method. In these cases, the other printing station(s) on the hybrid press can be deactivated and the hybrid press used as a single method printing press.

If desired, any number of additional analog printing units 2 or digital printing units 3, or both, can be provided in-line downstream of the CI cylinder. Digital units so disposed are illustrated in the Figure. Preferably, only digital units are provided downstream.

Also provided downstream of the last CI printing unit is one or more curing stations 5. Any curing methods or units in any configuration on the press can be employed. Examples of these curing methods include, but are not limited to: EB (electron beam); ultraviolet (UV); heat set; thermocuring; infrared (IR); forced air; etc. While it can be provided on the CI cylinder 1 itself, the curing station 5 is preferably disposed in line downstream of the cylinder 1. This permits, for example, the hybrid press to be configured to wet-trap (wet-on-wet printing) multiple layers of inks/coatings which would all be cured in a final (preferably EB) curing stage, but the hybrid press could also be fitted with inter-station curing/drying units using any combination of curing methods. In the drawing, an EB curing station 5 is illustrated.

On the hybrid press, inter-station curing is preferably unnecessary. The inks/coatings used in the two or more printing methods will preferably be substantially compatible to allow "wet" trapping. In the preferred embodiment, the press is configured such that multiple layers of inks/coatings are wet-trapped and then cured in one final curing stage using EB (electron beam) curing. Use of two printing methods enables the simultaneous writing in one pass of images/graphics/patterns of different scales (resolution) and a single curing step for all. Use of the process and inks described in US 6,772,683 and PCT/US03/14293 or a similar EB curing process and ink set as the analog (e.g. flexographic) component of the hybrid press enables removal of photoinitiators from the formulation as opposed to UV curable flexographic inks which require a photoinitiator for reaction initiation. The EB approach can be more suitable for food packaging applications than a similar system with UV curable inks because of the higher degree of reaction completion, lower amounts of residual monomer, potential for lower migratables/extractables and lower odor. All these characteristics are very desirable for indirect contact food packaging and personal care/pharmaceutical applications.

Most current print applications use ink cured by ultra-violet (UV) radiation on a conventional or inkjet technology press. UV lamps, even when thermally managed, emit a sizeable component in the IR region, substantially heating the substrate. This is a concern for many flexible substrates used in packaging applications, especially thin extensible films used for laminations and shrink films which become distorted or can be destroyed by the high heat generated by UV lamps. UV curing depends on ink film thickness and the presence of pigments, and ink formulators tailor the ink to provide uniform curing through the ink layer. EB curing is substantially independent of ink film thickness and provides a higher degree of through-cure. Also, EB curing offers the advantage of not emitting IR radiation and thus does not generate the heat commonly emitted from UV lamps.

In particular for food and pharmaceutical applications, the use of inks curable by electron beam can be of lower odor than UV inks which, for example, contain photoinitiators. Electron beam curing offers higher degrees of polymerization and potentially lower extractables/migratables. One general example of such ink can be of the general composition mentioned in WO 97/31071 (Radiation Curable Ink Composition) concerning a UV-curable ink with polyfunctional alkoxylated monomers, where the photoinitiator package is removed and the viscosity and surface tension are adjusted to the desired printing specifications. Curing of these monomers and oligomers without using significant amounts of external heat is necessary to enable fast printing on flexible substrates that usually have lower dimensional stability and tolerance to thermal treatment than would be desirable for conventional commercial printing equipment that utilizes hot air or IR dryers. Electron beam curing is one method suitable for such technologies because it does not rely on application of external heat to cure the materials applied to form the desired structure. As mention above, curing using UV lamps can generate a large amount of heat that can affect the dimensional stability of a web under tension.

The hybrid printing press of the present invention permits the combination of two or more printing methods on a single drum, at least one being a conventional analog printing method and at least one being a conventional digital printing method. The analog methods include any print method that uses an image transfer system (i.e. a print method that transfers ink from a substrate, most often a cylinder, bearing a fixed image to a substrate in contact with the substrate). Examples of these print methods include, but are not limited to: flexographic; gravure; offset; and screen printing. The digital writing component can include, but is not limited to, electrophotography, and all inkjet technologies such as piezoelectric, thermal, continuous, hot melt, etc. Many different embodiments of the hybrid press are within the scope of the present invention. One preferred embodiment is drawn to a hybrid wide web (a substrate having a width >33 cm) printing press in which a conventional impact printing method (e.g., flexographic, modified gravure, screen or offset) employing central impression (CI) geometry is combined with a digital nonimpact direct writing method (e.g., inkjet) on a single drum. CI is a preferred geometry for the analog component of this press because it eliminates the color- to-color misregistration which is a problem with in-line and stack configurations. By imposing the substrate on the central impression drum, one minimizes the travel distance and misregistration opportunities between subsequent ink applications. The CI geometry keeps the substrate from "wandering" through the multiple rollers of the transport system that would otherwise be required.

The use of an inkjet writing component in the hybrid design is a preferred embodiment because it allows the printing of variable content and increased resolution (micron scale) that is impossible with a conventional plate-based printing system (e.g., flexographic printing). In packaging, for example, flexographic printing can be used for images of lower resolution or to print parts of the image that are substantially the same in each frame. By adding the digital component in a single hybrid press, one can customize the images on each frame.

This increases the efficiency and flexibility of the press beyond the capability of a conventional flexographic press and combines the strengths of both printing methods, while minimizing the deficiencies of each one. The writable width of the ink jet printing component of the hybrid press is substantially dependent on the application but would preferably be able to accommodate virtually the entire width of the substrate. It should be understood that any of the printing methods employed by the hybrid press can be direct or indirect, i.e., if necessary, there can be a number of intermediate transfer cylinders between the analog image cylinder and the substrate or the digital device and the substrate.

While food or pharmaceutical packaging applications have been mentioned above, another important aspect of the instant technology is that the digital writing component or both writing components can be used to apply localized functional coatings with micron scale resolution, form two-dimensional or three- dimensional structures or devices on the flexible substrate in a roll-to-roll mode such as sensors (freshness, time-temperature), "smart" components (electronic article surveillance), RFIDs, etc. The hybrid press configuration can also be used to produce light management films (RGB filters for displays), and the like. As long as the formulations used to form such coatings, structures or devices on the flexible substrate are not harmed by a electron beam or contain reactive components that rely on the energy of the electron beam to form a functional product, the preferred EB method can be used.

For graphic arts applications in packaging and commercial printing, combining an EB curable digital writing system with an EB CI analog (e.g. flexographic) printing method on a single press offers the following advantages: • Availability of flexographic stations on the press to apply other coatings or treatments on the flexible substrates that can be functional in nature (barrier layers, primers, adhesion promoters, coatings to produce other desirable effects, and the like). This eliminates the need for pre-press or offline coatings, decreases cost, and storage requirements, and increases efficiency. • Ability to utilize some of the inkjet writing heads or arrays for special effect coatings (glossy overcoats, metallic highlights), or functional coatings (surface modifiers, adhesives or release materials, brand protection materials, anti- theft or anti-tempering features), thus eliminating the need for storage, transport and higher cost for offline processing.

• High quality printing of whites, solids, and line colors.

• Higher efficiency and flexibility; faster turnaround for proofs that can be done utilizing the inkjet writing component only.

• Extending the economic viability of digital printing for larger print runs.

A field where variable printing is becoming increasingly important is that of packaging materials, where images of increasingly high quality are incorporated on the package and used to display a customized marketing message. Manufacturing of such customized packaging and marketing materials is prohibitively expensive using conventional printing methods like flexography and lithography. Incorporating a digital printing system and a central impression press together enables the resulting hybrid technology to take advantage of both print methods, maximizing the advantages of each while minimizing the deficiencies.

One preferred application, for example, concerns the production of highly customizable flexible packaging substrates using radiation curable inks, preferably electron beam curable inks. Several units mounted on the CI cylinder can be used to print, for example, a barrier coating or a white background on a part of the image/graphics that remain the same on each frame. The digital writer can then be used to print the variable part of the image or provide additional functional coatings, e.g. coatings that when cured will reduce the permeability or increase gloss or the chemical resistance of the print. Furthermore, the existence of the digital writer on the proposed hybrid press can enable printing the image on the substrate and simultaneously include intelligent package features.

InkJet printing is a preferred method because it is useful in many other fields including consumer imaging such as photoprinting, commercial printing of customized advertising/marketing products (point of purchase displays), printing on flexible and rigid substrates for packaging; printing on flexible substrate to form thin film or microscopic electronic devices, like thin film batteries and anti theft tags, optical components (filters for flexible displays), functional coatings that can be useful in a variety of applications, sensors, and the like.

Manufacturing of optical components (filters) for displays is conventionally done by dyeing, lithography, pigment dispersion and electrodeposition methods, all of which have the disadvantage of being multi-step processes where one color is applied at each process run. Normally the pixel matrix containing the colored material that forms the individual color lenses is pre-patterned to adequate resolution and dimensions for the targeted application. Sequentially writing the matrix pattern using the analog component (e.g. gravure or flexographic) of a hybrid press and filling the pixel wells by inkjet and curing in one step can further increase the efficiency in production.

It will be appreciated that the end use applications for the printed matter produced by the hybrid press are any application requiring deposition of thin films of coatings or patterned materials to form a functional coating or structure or a device. These include, but are not limited to packaging films (including food packaging), shrink sleeves, optical filters, decorative displays, POP displays, printable electronics, RFID, security devices, medical devices, intelligent packaging, sensors, photovoltaics, etc.

Another application is to include an inkjet writing head or array dedicated to provide online evaluation of curing uniformity and/or curing performance by writing a cure monitor patch, for example, at an edge of the substrate being printed although it could be placed elsewhere. This patch of color changing ink will substantially change optical properties (color or opacity) when cured properly. An online sensor can continuously monitor the optical properties of the patch post-cure to ensure that the appropriate level of curing has been achieved and can confirm adequate operation of the electron beam unit. This provides an added safety feature that is not available in existing energy curable press systems. Inadequately cured prints can be identified and removed before they leave the press room further limiting exposure risks for press workers and consumers.

It is also understood that the hybrid press can be a subsystem of a process used in the manufacturing of flexible packaging, printable electronics, etc. Other units accomplishing secondary operations (slitting, laser-cutting, etc.) can be attached to the press either before or after the printing process described herein.

It will therefore be appreciated that Figure 1 exhibits only one preferred embodiment of the hybrid press and is not meant to exclude other possible configurations. For example, the location or number of printing units could be altered, the digital units might not be directly on the CI cylinder but could be fitted elsewhere on the press (e.g. before or after the CI cylinder), inter-station curing units could be fitted between print units, printing units utilizing additional printing methods could be added to the press, etc. Thus, various changes and modification can be made without departing from the spirit and scope of this invention.

Claims

What is claimed is:

1. A hybrid printing press comprising a central impression drum having at least one analog printing station and at least one digital printing station sequentially arranged thereon.

2. The hybrid printing press of claim 1, wherein the central impression drum has at least two analog printing stations arranged thereon.

3. The hybrid printing press of any one of the preceding claims, wherein the central impression drum has at least two digital printing stations arranged thereon.

4. The hybrid printing press of any one of the preceding claims, wherein the central impression drum has at least two analog printing stations arranged thereon.

5. The hybrid printing press of any one of the preceding claims, having at least one curing unit disposed downstream of the central impression drum.

6. The hybrid printing press of claim 5, wherein said curing unit is an electron beam curing unit.

7. The hybrid printing press of any one of the preceding claims, wherein at least one analog printing station is a flexographic printing station.

8. The hybrid printing press of any one of the preceding claims, wherein at least one digital printing station is an inkjet printing station.

9. The hybrid printing press of any one of the preceding claims, having at least one additional printing station disposed downstream of the last central impression drum printing station.

10. The hybrid printing press of any one of the preceding claims, wherein at least one central impression press digital printing station is disposed downstream of a central impression drum analog printing station.

11. The hybrid printing press of any one of the preceding claims, wherein at least one central impression press digital printing station is disposed downstream of all central impression drum analog printing stations.

12. The hybrid printing press of any one of the preceding claims, wherein at least one central impression press digital printing station is disposed to print at an edge of a substrate being printed.

13. The hybrid printing press of any one of the preceding claims, further comprising a sensor disposed to sense the optical properties of a printing on the substrate.

14. A method of printing comprising conveying a substrate to be printed to a hybrid printing press comprising a central impression press having at least one analog printing station and at least one digital printing station sequentially arranged thereon, applying a coating to the substrate at each of said at least one analog printing station and at least one digital printing station, removing said coated substrate from the central impression drum.

15. A method of printing according to claim 14, wherein the coatings of the coated substrate removed from the central impression press are cured.

16. A method of printing according to claim 15, wherein said curing is effected by electron beam.

17. A method of printing according to any one of the preceding claims 14 to 16, wherein the central impression press has at least two analog or digital printing stations, and a coating is applied to the substrate at said at least two printing stations.

18. A method of printing according to any one of the preceding claims 14 to 17, wherein said coatings are selected such that each subsequently applied coating wet traps the proceeding coating.

19. A method of printing according to any one of the preceding claims 14 to 18, wherein said coatings are not cured between adjacent coating stations.]

20. A method of printing according to any one of the preceding claims 14 to 19, wherein flexographic printing is effected at an analog printing station.

21. A method of printing according to any one of the preceding claims 14 to 20, wherein inkjet printing is effected at a digital printing station.

22. A method of printing according to any one of the preceding claims 14 to 21, wherein at least one printing station applies a cure monitor to the substrate.

23. A method of printing according to claim 22, further comprising monitoring the optical properties of the cure monitor.

24. A printing made by the process of any one of the preceding claims 14 to 22.