WO2011020022A1

WO2011020022A1 - Temperature control in gravure and flexographic printing by aqueous fluid injection into the ink

Info

Publication number: WO2011020022A1
Application number: PCT/US2010/045477
Authority: WO
Inventors: Richard M Jones
Original assignee: Sun Chemical Corporation
Priority date: 2009-08-13
Filing date: 2010-08-13
Publication date: 2011-02-17

Abstract

A method of maintaining a flexographic or gravure press at a constant and controlled temperature is presented In exemplary embodiments of the present invention, a volatile fluid can be injected into ink as it circulates through a portion of the printing press. In exemplary embodiments of the present invention the volatile fluid can be water, and can, for example, be injected into a doctor-bladed chamber from which the ink transfers to an anilox or other ink-carrying roller In exemplary embodiments of the present invention the avoidance of large temperature run-up can be thus avoided, and the concomitant consequent damage to ink, print, and press from the use of highly pigmented inks in presses that do not possess adequate tempering by other means In exemplary embodiments of the present invention such fluid injection can be in addition to, or as an alternative to, any built-in tempering.

Description

TEMPERATURE CONTROL IN GRAVURE AND FLEXOGRAPHIC PRINTING BY AQUEOUS FLUID INJECTION INTO THE INK

CROSS-REFERENCE TO RELATED APPLICATIONS:

The present application claims priority to U.S. Provisional Patent Application 61/233,614, filed on August 13, 2009, the disclosure of which is hereby

incorporated herein by reference.

TECHNICAL FIELD:

The present invention relates to ink and related technologies, and in particular to a method for the temperature control of inks on press.

BACKGROUND OF THE NVENTION:

Various mechanical means of tempering a printing press or ink are known. For example, US 6,688,225 describes a doctor-bladed chamber that is cooled by chilled fluid flow through an enclosed chamber at the rear of the unit.

Similar traditional approaches to controlling ink and press temperatures range from tempering the ink with cooling coils in the sump to tempering the press by circulation of coolant throughout the interior of driven rolls. However in order to implement such methods in existing un-cooled printing presses, both of these extremes require expensive redesigns, which are totally unsuited to many existing presses.

Moreover, attempts to cool a press or the ink using circulation of coolant does not allow for precise control of the cooling. There is every indication that tempering inks and presses by circulated coolant can often be overdone, which in the end affects ink transfer. This is due to the large mass of metal and volume of ink in a printing press that must be chilled, and the slowness by which it reaches equilibrium compared with the demands of high speed printing. Thus, such a method can cause the ink and press to see-saw in temperature from overcooled to under-cooled, depending upon the response time to an adjustment or setting.

What is needed in the art are methods and systems to control the temperature of inks on press without complicated retrofits, and in a manner that is direct and that can be precisely controlled.

SUMMARY OF THE INVENTION:

A method of maintaining a flexographic or gravure press at a constant and controlled temperature is presented. In exemplary embodiments of the present invention, a volatile fluid can be injected into ink as it circulates through a portion of the printing press. In exemplary embodiments of the present invention the volatile fluid can be water, and can, for example, be injected into a doctor-bladed chamber from which the ink transfers to an anilox or other ink-carrying roller. In exemplary embodiments of the present invention the avoidance of large temperature run-up can be thus avoided, and the concomitant consequent damage to ink, print, and press from the use of highly pigmented inks in presses that do not possess adequate tempering by other means. In exemplary embodiments of the present invention such fluid injection can be in addition to, or as an alternative to, any built-in tempering. If the former (i.e., in addition to built- in tempering), such fluid injection can, for example, serve as a "fine-tuning" component that works in conjunction with the existing cooling system to provide, for example, precise temperature control.

Other aspects, advantages and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS:

Fig. 1 is a plot of temperature v. run time of an exemplary anilox roll during prolonged running of a heavy water-based flexographic ink;

Fig. 2 is a plot of temperature v. press run time for three exemplary water injection rates for a single waterbased ink formulation according to exemplary embodiments of the present invention; and

Fig. 3 is a plot of magenta print density v. press run time with and without water injection according to exemplary embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION:

The matters exemplified in the following description such as, for example, detailed constructions, processes and elements are provided to assist in a comprehensive understanding of the embodiments of the invention. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. Also, descriptions of well- known functions and constructions are omitted for clarity and conciseness. Furthermore, the terms used herein are defined according to the functions of exemplary embodiments of the present invention. Thus, the terms may vary depending on a user's or operator's intention and usage.

In exemplary embodiments of the present invention, the injection of a volatile liquid, which by its latent heat of vaporization lowers temperature, can be a much more cost effective approach to controlling temperature in gravure and flexographic printing than complex cooling systems and apparatuses. As noted, there is every indication that tempering inks and presses by circulated coolant can be often overdone, which in the end can affect the transfer of ink more than is the case with the proposed inventive volatile injection. This is due to the large mass of metal and volume of ink in a printing press that must be chilled, and the slowness by which it reaches equilibrium compared with the demands of high speed printing, and is in general a function of the run length and other factors. As is known, being low in temperature can affect ink rheology just as being high in temperature can, as shown in Fig.3, discussed below.

On the other hand, injection of volatile liquid into flexographic or gravure ink cools the zone of highest temperature (the doctor blade/engraved cylinder interface) directly. In exemplary embodiments of the present invention the volatile fluid can be injected into the doctor blade/engraved cylinder interface directly, or, for example, can be injected into the ink inlet stream. In addition, the inventive injection has a smaller footprint, faster cooling effect, and is more energy efficient than built-in press tempering. When the volatile liquid is water, there is no emission or explosion hazard.

In exemplary embodiments of the present invention the volatile liquid can be, for example, water, or can be, for example, alcohol or a combination of alcohol and water. In exemplary embodiments of the present invention isopropanol or ethanol can be used. Other liquids can be used as well, subject to appropriate limits on VOCs and fire hazard considerations.

It is noted that the footprint refers to the physical size of the unit(s) on the pressroom floor that provide(s) press temperature control (in square footage or other area measure). If, for example, chillers are being used for the rolls, or, for example, if the ink line is being tempered, refrigeration unit(s) and coolant lines needed to implement such cooling can occupy considerable space around the press. In contrast, a water injection feed unit for each ink line is compact and easily fits within the existing footprint of the ink pumping stations. When it is considered that seven or more ink stations would typically be present, the space savings advantage is considerable.

The heating of the printing press by friction leads to a cascading series of events, all of which are unfavorable. First the ink is damaged, then the printed stock, and finally the press itself. In the first and second instances, printers suffer from having to replace ink and misprinted stock, and in the third, the printer faces increased overhead and downtime for repairs. With low-cost, add-on, water or other volatile liquid injectors governed by ink temperature, viscosity, pH, dielectric constant, impedance, or conductivity measurements, the delivery of inks that tend to higher pigment loading or higher viscosity is much more palatable and easier to sell to printers. In fact, the alternative - a recommendation to temper the press or the ink by conventional means may be entirely too capital intensive to allow for the consideration of retrofitting existing un-tempered presses. Not only is the cost of such retrofitting prohibitive, conventional presses do not have the coolant chambers required, and there is often no room for them, even if a complex addition were contemplated. Either way, for the reasons discussed above, standard cooling approaches are indirect and can have a much longer time to equilibrium.

In exemplary embodiments of the present invention the injected fluid can preferably have a low boiling point and high latent heat of vaporization, so as to thus carry off heat as fast as it is generated. In exemplary embodiments of the present invention the fluid should also preferably cause no VOC or fire hazard. In exemplary embodiments of the present invention the fluid can be, preferably, water, or, alternatively, a water-alcohol solution, or, for example, plain alcohol. In exemplary embodiments of the present invention ethanol or isopropanol can be used, for example. It is noted that while water is an obvious choice when dealing with water-based inks, it is less obvious for inks that are not extendable with water. However, it is known that fountain solution water is emulsified into lithographic ink and that this ink prints even better than without water emulsification. Thus, the same emulsification can be expected for the heavy flexographic and gravure inks with injected water. Thus, exemplary embodiments of the present invention can be universally applicable to a wide variety of inks and presses.

Alternatively, although water is a preferred fluid, in exemplary embodiments of the present invention many other fluids could be used in the injection process. In some cases it may even be advantageous to use other fluids or blends of fluids alone or in combination with water to control temperature and cooling in such a way that water alone would not allow. Thus, for example, a combination buffer ions and water can be used if ink viscosity is better suited to such an approach.

In exemplary embodiments of the present invention a process whereby a flexographic or gravure high-speed press is maintained at the appropriate temperature by fluid injection into the ink stream can thus be used for a variety of ink types and presses. In exemplary embodiments of the present invention the inventive process can, for example, be used in other types of printing presses where cooling is advantageous, including, for example, lithography, screen, etc.

As noted, in exemplary embodiments of the present invention the injection fluid should preferably have low boiling point and high latent heat of evaporation, such as is found in, for example, water and low carbon chain alcohols, for example. Though a guideline for a general range of fluid injection rate can be developed to encompass a wide range of press conditions and inks, in exemplary embodiments of the present invention an optimized rate or range can be determined for each specific press configuration and ink. This can be done, for example, by running the printing press with different rates of injection of the volatile fluid, and measuring the temperature. In general, the precise fluid and injection rate is a function of many factors, and is press, ink, ambient temperature specific. Thus, to optimize the method in exemplary embodiments of the present invention, the method can be calibrated to the specific context in which ink temperature control is desired.

In exemplary embodiments of the present invention frictional heat is removed by evaporation of all or a portion of the injected fluid. Thus, controlling the rate of injection controls the temperature. In exemplary embodiments of the present invention the volume of injected liquid can be controlled or limited so as not to compromise print quality. In fact, it can greatly improve print quality. Monitoring temperature, viscosity, pH, dielectric constant, impedance, or conductivity, depending on the type of ink, can be used, for example, to control the rate of addition. The inventive process can be used for any type of ink or press, whether the press is configured for tempering or not. In exemplary embodiments of the present invention, the injected fluid can, for example, be directed to the sump or, for example, into the ink lines.

As flexographic and gravure press speeds increase and ink transfer decreases as a result of increasing temperature, inks with increased pigment loading are being employed to hold print density. This leads to higher heat in the press as ink flow is relied on to remove heat, most notably at the doctor blade-anilox roll frictional seal, for example. Studies have shown, for example, that the temperature at the doctor blade/anilox juncture can reach as high as 200° C.

Fig. 1 shows an example of the increased temperature of an exemplary anilox roll with prolonged running of a heavy water-based flexographic ink (for example, 0.35 Pa-sec, 100 s^"1, 25° C). The example shown is the result of prolonged running on a flexographic press of highly pigmented water based inks using three lots of base epoxy acrylate of differing water compatibility, and with no cooling of the press or the ink. In such a setup, long before the maximum temperatures are reached, printing defects can occur, such as, for example, poor transfer, poor trapping, and irreversible ink damage. Such effects tend to manifest once a temperature of 30-40 C° is reached.

Fig. 2 shows the ability to control the temperature of the press with water injection into the ink. Depicted are the results of the injection of water into the ink stream at three rates for a single water-based ink formulation, according to an exemplary embodiment of the present invention.

Depending upon the rate of fluid injection, the press reaches an equilibrium temperature as a result of excess heat going into the latent heat of water evaporation. Ink damage from overheating, print defects from variance of ink properties, and press damage are thus all avoided or greatly reduced by this simple process.

Finally, Fig. 3 depicts a printing defect where the print optical density (solid print area, 100%) rises throughout the first three hours of running followed by a fall. This defect is related to press temperature and is very objectionable, inasmuch as it makes all trapped colors vary as well. When water (or other volatile fluid) injection is practiced according to the present invention, these strong shifts in color density can be avoided.

As can be seen with reference to Fig. 3, for this press and ink combination a 66 ml/hr/gal water injection is a bit insufficient as the optical density begins a slow rise after three hours. At the other extreme, a 122 ml/hr/gal water injection is a bit excessive, as the optical density falls after three hours. The ideal rate and anilox temperature for this ink/press/speed combination was found to be about 100 ml/hr/gal and 31⁰C. These conditions led to constant color printing for at least six hours. It is understood that these conditions were found to be ideal for this particular press configuration and ink type, but variations on these conditions can be, and in general will be, utilized to optimize performance under different press conditions and/or when using different inks or substrates, according to various exemplary embodiments of the present invention. A general rule of thumb for water injection, for example, is to inject sufficient water to replace that lost from the ink by evaporation.

As noted above, the traditional way to moderate flexographic and gravure press temperature is by fluid heat exchange. For example, to cool the ink, copper coils through which glycol coolant is pumped, have been used, and for the press, for example, air, water, or more commonly oil, for example, that has passed through a heat exchanger is pumped through the interior spaces of rotating equipment. As also noted above, these approaches are both costly and require a large footprint to implement, and in many cases are simply not applicable (and certainly not practical) to existing press installations (as there are no, and often no room for, cooling chambers).

In contrast to these conventional approaches, the injection of water or other volatile fluids into the ink stream is low cost and small footprint solution.

In exemplary embodiments of the present invention, the technique of injection can be as simple as periodic addition of water or aqueous solution into the ink sump. In exemplary embodiments of the present invention the technique can be controlled as a feedback loop based on one or more of temperature, viscosity, pH, dielectric constant, impedance, or conductivity of the ink. In exemplary embodiments of the present invention, the ink can be, for example, unmodified or can, for example, contain materials designed to emulsify the water into the ink, such as, for example surfactants. In exemplary embodiments of the present invention the ink can accept the fluid in solution, or, for example, can be subject to shear forces following injection of the fluid to achieve a uniform dispersion. For example, in-line devices such as stirrers or static mixers can be used, but good results do not necessarily require such mixing. In exemplary embodiments of the present invention mixing as may be required can also be achieved by injection of the fluid into the ink pump intake, whereupon the mixing occurs within the pump body.

In general, in exemplary embodiments of the present invention, the time required to return a high temperature to controlled lower temperature is on the order of minutes. Thus, during the course of a print run, any thermal disruption can be accommodated. In contrast, in conventional tempering, an ink or a press can become either overcooled or undercooled leading to poor ink transfer (and other print problems), and requiring hours to readjust.

The examples presented in Figs. 1 -3 represent actual print trials of UniQure™ inks as used in the WetFlex™ process. They consist of an epoxy acrylate difunctional monomer, a glycol diacrylate monomer, water, a urethane dispersion, pigment, and the typical wetting agents. Other inks such as, for example, water-based flexo, solvent-based gravure, and 100% active flexo could similarly be used, for example. Either solution or emulsion would be acceptable, but preferably the emulsion would be small droplet, as in lithographic ink.

It is noted that while Sun Chemical's UniQure™ inks are described in the context of certain examples, many and various other inks could also be used with the disclosed process, including, but not limited to, other inks containing dissolved water. The compositional details of UniQure™ inks are disclosed in, for example, the following patents assigned to Sun Chemical, which are hereby incorporated herein by this reference: US 7479511 , EP 1504067, EP 1792956, US 7226959 and EP 1392780. The present invention has been described using various details and with reference to various exemplary and preferred embodiments thereof. However, it will be appreciated that those skilled in the art, upon consideration of the present disclosure, may make modifications and/or improvements on this invention that fall within the scope and spirit of the invention.

Claims

WHAT IS CLAIMED:

1. A method of maintaining a flexographic or gravure press at a constant and controlled temperature, comprising:

injecting a volatile fluid into the ink as it circulates through a portion of the press.

2. The method of claim 1 , wherein said portion of the press is a doctor- bladed chamber.

3. The method of claim 1 , wherein the ink circulates through a portion of the press and transfers to an ink-carrying roller.

4. The method of claim 3, wherein the ink-carrying roller is an anilox.

5. The method of any of claims 1 -4, wherein said volatile fluid is water and wherein it is injected into said ink at a rate of between 50 and 150 ml/hour/gal.

6. The method of any of claims 1 -5, wherein said volatile fluid is water, and wherein it is injected into said ink at a temperature between 25° C and 35° C.

7. The method of any of claims 1 -6, wherein the optical density of inks is decreased as a result of the injection of the volatile fluid.

8. The method of claim 1 , wherein said injection of a volatile fluid comprises periodic addition of water or aqueous solution into an ink sump.

9. The method of claim 1 , wherein said injection of a volatile fluid is controlled using a feedback loop based on at least one of temperature, viscosity, pH, dielectric constant, impedance, and conductivity of the ink.

10. The method of claim 1 , wherein the volatile fluid is one of water, alcohol or a combination thereof, and the ink is unmodified.

11. The method of claim 1 , wherein the volatile fluid is one of water, alcohol or a combination thereof, and the ink contains materials designed to emulsify the fluid into the ink.

12. The method of any of claims 1 -11 , further comprising mixing the ink using in-line stirrers or static mixers.

13. The method of any of claims 1 -13, wherein the fluid is injected into an ink pump intake, and wherein the ink is mixed with the volatile fluid in a pump body.

14. The method of any of claims 1 -13, where the ink is highly pigmented.

15. A method of accommodating thermal disruption during the course of a print run, comprising injecting a volatile fluid into an ink according to the method of any of claims 1 -14.

16. The method of claim 1 , wherein the volatile fluid lowers ink temperature by its latent heat of vaporization.

17. The method of clam 16, wherein said volatile fluid has a low boiling point and a high latent heat of vaporization.

18. The method of claim 11 , wherein said materials are surfactants.

19. The method of claim 1 , wherein the ink is water-based or non water- based.

20. The method of claim 1 .wherein the fluid is a combination of buffer ions and water.

21. The method of claim 1 , wherein the injected fluid is directed to one of a sump and ink lines.

22. The method of claim 1 , wherein an optimized rate or range is determined for a specific printing press configuration and ink.

23. The method of claim 22, wherein said optimization is effected by running the printing press with different rates of injection of the volatile fluid, and measuring the temperature.

24. The method of claim 1 , wherein the ink accepts the fluid in solution.

25. The method of claim 1 , wherein the ink is subjected to shear forces following injection of the fluid to achieve a uniform dispersion.

26. The method of claim 25, wherein in-line devices such as stirrers or static mixers are used to supply said shear forces.