Embodiments of the present invention relate to apparatus and methods for flexographic printing.

Flexographic printing apparatus is a fast and economic process of printing high quality printed material. Flexographic printing apparatus uses flexible printing plates to form an image on a web material. The flexible printing plates are formed of a base surface with raised areas, the raised areas corresponding to the areas to be printed onto the web material. Flexographic printing apparatus is typically used for printing in the food, beverage, medical, cosmetic, printed publication and clothing industries. Flexographic printing apparatus is capable of printing on paper, paperboard, cardboard, corrugated cardboard, metallised paper, glassine, pressure sensitive paper, pressure sensitive films and coated films, polystyrene, polypropylene, polyethylene, polyester film, glass, textiles, metal foils and metal sheets. Typical applications include food bags, shopping bags, book covers, food and beverage cartons, product packaging, wallpaper, greetings cards and envelopes. A major drawback in flexographic printing concerns a loss of resolution in the printed image due to the effects of "dot gain". Dot gain is the effect whereby the raised areas of the printing plate are deformed when pressure is applied to their upper surface. The deformation of the raised areas may take several forms, the main forms being deformation by expansion, whereby the upper surface of the raised areas is expanded when in contact with the web material, and deformation by barrelling, whereby the shoulder of the raised areas barrels to form part of the upper surface of the raised areas when in contact with the web material. Known ways of addressing dot gain are to reduce the pressure applied to the flexible printing plate such that the raised areas are not compressed as much. Because of the flexible nature of the printing plate in a flexographic printing press a further issue may arise whereby contact is lost between the printing plate and the web material to be printed upon, as the printing plate moves relative to the web material. During printing, the raised areas of the flexible printing plate are compressed as the raised areas come into contact with the web material. The raised areas then subsequently return to their original form once the pressure applied to the printing plate is discontinued. As the raised areas of the printing plate are brought into contact with the web material, the leading edges of the raised areas are compressed and may be laterally deflected from their original position. This lateral deflection may cause the plate to recoil from the web material, causing missing areas of printing on the web material. This effect is sometimes termed "bouncing". One known way to address bouncing is for the operator to apply more pressure to the printing plate to damp the recoil effects of the flexible plate material; however this has the consequent effect of causing increased dot gain.

The drive for higher resolution printing has lead to the use of smaller raised areas on the printing plates, to form more complex images, this in turn exacerbates the effect of dot gain on the final image.

According to various, but not necessarily all, embodiments of the invention there is provided a temperature regulation arrangement for flexographic printing apparatus having an ink supply, an anilox roll, a printing plate and an impression cylinder, the arrangement comprising temperature control means operable to maintain the printing plate and/or ink from the ink supply at a predetermined temperature or within a predetermined temperature range during printing.

According to further embodiments of the invention there is provided flexographic printing apparatus comprising an ink supply, an anilox roll, a printing plate, an impression cylinder and a temperature regulation arrangement having temperature control means operable to maintain the printing plate and/or ink from the ink supply at a predetermined temperature or within a predetermined temperature range during printing.

The temperature control means may comprise an ink temperature control arrangement operable to control the temperature of ink from the ink supply at a predetermined temperature or within a predetermined temperature range. The temperature control means may comprise means to enable selection of the predetermined temperature or predetermined temperature range for the ink, which means may comprise a manually operable ink temperature control. The ink temperature control arrangement may comprise a thermostat or similarly operable device to help maintain the ink at a predetermined temperature or within a predetermined temperature range. The ink temperature control arrangement may be operable to control the temperature of the ink in the ink supply. The ink temperature control arrangement may be operable to control the temperature of the ink from the ink supply.

The ink temperature control arrangement may comprise a heat exchanger. The heat exchanger may be thermally connected to ink to be temperature controlled. The heat exchanger may be operable to transfer heat to or from ink to be temperature controlled. The heat exchanger may be conductively connected to ink to be temperature controlled. The heat exchanger may be convectively connected to ink to be temperature controlled. The heat exchanger may comprise a thermoelectric heat pump such as a Peltier cooler. Alternatively the heat exchanger may comprise a cyclic refrigeration unit or other suitable cooling arrangement.

Alternatively or in addition the ink temperature control arrangement may comprise an air conditioning unit arranged to control the temperature of the ink and surrounding environment. The ink may be located within a generally enclosed space in which the ink temperature control arrangement is operable to control the temperature of the ink and/or the air within the space. A housing may be provided to house and enclose the ink and/or the ink temperature control arrangement.

The temperature control means may comprise a printing plate temperature control arrangement operable to control the temperature of the printing plate at a predetermined temperature or within a predetermined temperature range, which may be the same temperature or temperature range as the predetermined temperature or predetermined temperature range for the ink. The temperature control means may comprise means to enable selection of the predetermined temperature or predetermined temperature range for the printing plate, which means may comprise a manually operable printing plate temperature control. The printing plate temperature control arrangement may comprise a thermostat or similar operable device to help maintain the printing plate temperature control arrangement at a predetermined temperature or within a predetermined temperature range.

The printing plate temperature control arrangement may comprise a heat exchanger. The heat exchanger may be thermally connected to the printing plate. The heat exchanger may be operable to transfer heat to or from the printing plate. The heat exchanger may be conductively connected to the printing plate. The heat exchanger may be convectively connected to the printing plate. The heat exchanger may be connected to the printing plate through a printing roll. The heat exchanger may comprise a thermoelectric heat pump such as a Peltier cooler. Alternatively the heat exchanger may comprise a cyclic refrigeration unit or other suitable cooling arrangement.

Alternatively or in addition the printing plate temperature control arrangement may comprise an air conditioning unit arranged to control the temperature of the printing plate and surrounding environment. The printing plate may be located within a generally enclosed space in which the printing plate temperature control arrangement is operable to control the temperature of the printing plate and/or the air within the space. A housing may be provided to house and enclose the printing plate and/or the printing plate temperature control arrangement. The ink temperature control arrangement and the printing plate temperature control arrangement may be independently operable. Alternatively the ink temperature control arrangement and the printing plate temperature control arrangement may be co-operable. The ink temperature control arrangement and the printing plate temperature control arrangement may be separate arrangements or may comprise a single arrangement within the temperature control means.

The ink supply may comprise an ink transfer arrangement such as an ink roll, or ink pump system. The temperature control means may comprise an ink transfer temperature control arrangement operable to control the temperature of the ink transfer arrangement and/or the ink in or from the ink transfer arrangement. The ink transfer temperature arrangement may be separate or part of one or more of the ink temperature control arrangement and/or the printing plate temperature control arrangement.

The temperature control means may comprise an anilox roll temperature control arrangement operable to control the temperature of the anilox roll. The anilox roll temperature control arrangement may be part of one or more of the ink temperature control arrangement and/or the printing plate temperature control arrangement.

The temperature control means may control the predetermined temperature or predetermined temperature range for the ink and/or printing plate at between 0°C and 70°C. The predetermined temperature or predetermined temperature range may be between 5°C and 35°C. The predetermined temperature or predetermined temperature range may be between 10°C and 25°C. In certain embodiments the predetermined temperature or predetermined temperature range may be between 10°C and 16°C. In alternative embodiments the predetermined temperature or predetermined temperature range may be between 15°C and 25°C.

According to a still further embodiment of the invention, there is provided a method for the regulation of the temperature of flexographic printing apparatus, wherein the temperature of the printing plate and/or ink from the ink supply is maintained at a predetermined temperature or within a predetermined temperature range.

A predetermined temperature or predetermined temperature range for the ink from the ink supply may be set using ink temperature control means, which may comprise means operable to enable selection of the predetermined temperature or predetermined temperature range for the ink. The predetermined temperature or predetermined temperature range may be set by adjustment of a manually operable ink temperature control. A thermostat or similarly operable device may be used to maintain the ink at a predetermined temperature or within a predetermined temperature range.

A predetermined temperature or predetermined temperature range for the printing plate may be set using printing plate temperature control means, which may comprise means operable to enable selection of the predetermined temperature or predetermined temperature range for the printing plate. The predetermined temperature or predetermined temperature range may be set by adjustment of a manually operable printing plate temperature control. A thermostat or similarly operable device may be used to maintain the printing plate at a predetermined temperature or within a predetermined temperature range. The predetermined temperature or predetermined temperature range for the printing plate may be the same temperature or temperature range as the predetermined temperature or predetermined temperature range for the ink. The predetermined temperature or predetermined temperature range for the ink and/or printing plate may be set between 0°C and 70°C. The predetermined temperature or predetermined temperature range may be set between 5°C and 35°C. The predetermined temperature or predetermined temperature range may be set between 10°C and 25°C. In certain embodiments the predetermined temperature or predetermined temperature range may be set between 10°C and 16°C. In alternative embodiments the predetermined temperature or predetermined temperature range may be set between 15°C and 25°C.

The method may comprise the use of the temperature regulation arrangement as described in any of paragraphs 6 to 17 above. For a better understanding of various examples of embodiments of the present invention reference will now be made, by way of example only, to the accompanying drawings, in which:

Fig. 1 is a diagrammatic side view of one central impression flexographic printing press according to the present invention.

Fig. 2 is an enlarged diagrammatic perspective view of an area of the surface of an anilox roll. Fig. 3 is a diagrammatic side view of a printing plate.

Fig. 4 is a diagrammatic side view of a central impression flexographic printing press according to the present invention with an alternative ink transfer arrangement. Fig. 5 is a diagrammatic side view of a first alternative flexographic printing press to which the present invention is applied.

Fig. 6 is a diagrammatic side view of a second alternative flexographic printing press to which the present invention is applied.

The present invention provides a temperature regulation arrangement 10 for flexographic printing apparatus 12 having an ink supply 14, an anilox roll 16, a printing plate 18 and an impression cylinder 20, the arrangement comprising temperature control means 22 operable to maintain the printing plate 18 and/or the ink from the ink supply 14 at a predetermined temperature during printing.

The present invention further provides flexographic printing apparatus 12 comprising an ink supply 14, an anilox roll 16, a printing plate 18, an impression cylinder 20, and a temperature regulation arrangement 10 having temperature control means 22 for maintaining the printing plate 18 and/or the ink supply 14 at a predetermined temperature during printing.

In an example of the invention, shown in Fig. 1 , a printing unit 100, comprising an ink supply 14, anilox roll 16 and a printing plate 18, is shown arranged in relation to the impression cylinder 20, which in this case is a central impression cylinder 20. A number of printing units 100 may be located around the circumference of the central impression cylinder 20. The ink supply 14 comprises an ink transfer arrangement comprising an ink containment vessel 42 with an outlet pipe 44 and an inlet pipe 46 to transfer ink to and from an ink chamber 48. The ink provided in the ink supply 14, may be any suitable type of ink known for use in flexographic printing, such as solvent based ink, water based ink, electron beam curable ink, ultraviolet curable ink or a two-part chemically curable ink. The ink chamber 48 is located adjacent to an anilox roll 16. The ink chamber 48 has an opening 50 bounded by two scrapers 40, which are usually formed of a rigid material, such as metal. These scrapers 40 are often called doctor blades. The opening 50 is in close proximity to the surface 36 of the anilox roll 16.

Fig. 2 shows a typical, and enlarged, perspective view of an area of the surface 36 of an anilox roll 16. The anilox roll 16 is generally formed of a cylinder 34, which is typically plated with chrome or ceramic, with an anilox roll surface 36 which has been engraved or otherwise treated to form cells 38 into which the ink, from the ink supply 14, is transferred. The cells 38 are generally of an inverted truncated or non-truncated pyramidal form and may typically have a base with 3, 4 or 6 sides. In the example shown in Fig. 2, the cells 38 have an inverted truncated hexagonal pyramidal form. In other examples the cells 38 may be joined to adjacent cells 38 via shallow channels to provide a more even pick up of ink from the ink supply 14. The number of cells 38, engraved into the anilox roll surface 36 is typically between 100 and 1000 cells per inch. The two doctor blades 40 are in contact with the surface 36 of the anilox roll 16 to form a seal arrangement such that ink is metered into the cells 38 in the anilox roll surface 36 of the anilox roll 16, without excess ink being lost from the chamber 48 or being deposited on the anilox roll surface 36 of the anilox roll 16, such that each cell 38 contains a specific quantity of ink.

The anilox roll 16 is further in proximity to, but not in contact with, a printing roll 52, which is sometimes referred to as a plate cylinder. The printing plate 18 is disposed on the printing roll 52. Fig. 3 shows a typical cross section of a printing plate 18. The printing plate 18 is formed of a flexible material such as a polymeric material and provides a relief with raised areas 54 suitable for coating with ink from the anilox roll 16. In this embodiment the printing plate 18 is formed of a photopolymer material. Photopolymer printing plates 18 are formed by selectively UV curing the material in specific areas corresponding to the raised areas 54 of the photopolymer printing plate 18, such that those areas correspond to the areas of the final image where ink is to be deposited. Such UV curing of photopolymer printing plates 18 and the process of forming such plates is well known in the art. In other embodiments the printing plates 18 may be formed of moulded rubber or other suitable material.

The raised areas 54 project from the upper face 55 of the base 56 of the printing plate 18. The raised areas 54 are generally of circular cross-section and may be generally cylindrical or frustoconical in form, with an axis substantially perpendicular to the base 56 of the printing plate 18. The circular cross-section thereby provides a generally circular top surface 58 onto which ink is transferred from the cells 38 of the anilox roll 16. The heights of the raised areas 54, substantially perpendicular to the base 56 of the printing plate 18 are such that when positioned substantially perpendicular to the anilox roll surface 36 the raised areas 54 are generally in contact with the anilox roll surface 36, to enable ink transfer from the cells 38 of the anilox roll 16 to the raised areas 54 of the relief of the printing plate 18. This provides a top surface 58 coated in ink, which, when subsequently positioned in contact with a web material 60, prints a dot of ink onto the web material 60 for each of the raised areas 54 of the printing plate 18. The pattern of the print is determined by the pattern of raised areas 54 on the printing plate 18. The lower face 57 of the base 56 is adhered to the printing roll 52 to be fixed in position in relation to the printing plates 18 of further printing units 100 of the flexographic printing apparatus 12.

The printing plate 18 is positioned to be in contact with or in close proximity to the impression cylinder 20. When the printing roll 52 is rotated such that the axes of the raised areas 54 of the printing plate 18 are substantially perpendicular to the surface of the impression cylinder 20, the top surface 58 of the raised areas 54, which are coated with ink, will be in contact with the web material 60, which is disposed between the top surfaces 58 of the raised areas 54 of the printing plate 18 and the surface of the impression cylinder 20, such that ink is transferred to the web material 60. The web material 60 is a material suitable for printing upon, which includes but is not limited to paper, paperboard, cardboard, corrugated cardboard, metallised paper, glassine, pressure sensitive paper, pressure sensitive films and coated films, polystyrene, polypropylene, polyethylene, polyester film, glass, textiles, metal foils and metal sheets. The separation of the printing plate 18 from the impression cylinder 20 will be set with knowledge of the thickness of the web material 60, to be printed upon.

In an alternative embodiment, the raised relief of the printing plate 18 is formed of a solid area or solid areas suitable for printing solid colour blocks onto a web material 60 to be printed to. Each printing plate may be used to print a different colour ink. Typically in flexographic printing apparatus 12 incorporating printing plates 18 with solid areas for printing, between 4 and 10 printing plates 18 are arranged on separate printing units 100, each printing unit 100 comprising at least an ink supply 14, an anilox roll 16 and a printing plate 18.

The top surfaces 58 of the raised areas 54 of the printing plate 18 are in contact with a web material 60, which is rotated upon a central impression cylinder 20. Each printing plate 18 in the flexographic printing apparatus 12 is in contact with the web material 60 between the printing plate 18 and the central impression cylinder 20 at various points around the central impression cylinder 20. The central impression cylinder 20 accommodates multiple printing units 100 around the circumference of the central impression cylinder 20, each printing unit 100 having a printing plate 18 in contact with the web material 60 between the printing plate 18 and the central impression cylinder 20.

On each separate printing plate 18 a different set of raised areas 54 are formed corresponding to a different area or areas of the final image to be formed on the web material 60. These raised areas 54 provide the pattern for the final image to be printed on the web material 60. Typically the ink for each printing plate 18 provides a specific different colour for the final image, and dependent on the colours required, these may have to be specifically mixed by an operator. It is also possible to overprint colours to provide mixed colours from those of the inks provided for each printing plate 18.

In the embodiment shown in Fig. 3, the raised areas 54 are formed of small raised areas 54, suitable for printing half tone images (images formed by the interlacing of dots of ink), such that a quad colour system (CYMK) may be used to form a full colour image. By providing small raised areas 54 to form halftone images a final full colour image can be formed by using only four printing plates 18, each with a complementary arrangement of small raised areas 54 for picking up and depositing a different colour ink on the web material 60 such that the dots of ink deposited on the web material 60 are positioned in an overlapping or interlaced manner to form, to the naked eye, a composite full colour image. This has the benefit of requiring only four colour inks to be used, these generally being cyan (C), magenta (M), yellow (Y) and black (K), to form the full colour image. These four colours may be chosen from a standard colour index. When using these four standard colours there is no requirement for an operator to mix specific colours for each different print job, as the same standard four colours can be used to print any image which would appear as a full colour image when presented to the naked eye.

Temperature control means 22 is provided to control the temperature of the printing plate 18 and ink from the ink supply 14. The temperature control means 22 comprises an ink temperature control arrangement and a printing plate temperature control arrangement which are combined into a single temperature control arrangement 84. A predetermined temperature or predetermined temperature range for ink from the ink supply 14 and printing plate 18 is set by the use of a temperature control 82 which may be in the form of a keypad input, dial, via computer control or other user input. The temperature control arrangement 84 comprises a heat exchanger convectively connected to the ink from the ink supply 14 to be temperature controlled and the printing plate 18 to be temperature controlled. A thermostat 86 is used to maintain the temperature of the ink from the ink supply 14 and the temperature of the printing plate 18. The thermostat 86 being operatively connected to the temperature control arrangement 84 such that the temperature control arrangement 84 can be switched on or off in response to a rise or fall in the monitored temperature.

The temperature control arrangement 84, is a single convective cooling arrangement such as an air conditioning unit 84. In this embodiment, pipes from the ink supply 14, which are preferably made of conductive material such as metal, but can be formed of other materials such as plastic and rubber materials, pass through a housing 90 of the air conditioning unit 84, to be convectively cooled, whilst further convective cooling is applied to an enclosure or housing 92 in which at least the printing plate 18 is located.

The present invention still further provides a method for the regulation of the temperature of flexographic printing apparatus 12, wherein the temperature of the printing plate 18 and/or ink from the ink supply 14 is maintained at a predetermined temperature or within a predetermined temperature range.

The temperature of the printing plate 18 and/or ink from the ink supply 14 is to be maintained at a predetermined temperature or within a predetermined temperature range such that the physical effects of a varying temperature upon the printing plate 18, at least, are minimised. Variations in temperature in flexographic printing apparatus 12 may be introduced through the frictional interaction of components, such as the anilox roll 16 and the printing plate 18, within the flexographic printing apparatus 12, through the use of motorised drive systems for the components of the flexographic printing apparatus 12, which may introduce heat into the flexographic printing apparatus 12, through drying apparatus within the flexographic printing press 12, which may be used to evaporate the solvent from the ink on the web material 60, or by other means. An increase in the temperature of the components of the flexographic printing apparatus 12, such as the anilox roll 16 and the printing plate 18, may alter the relative position between the components which may lead to increased frictional effects and thus a further increase in temperature of the components. Conversely, a decrease in the temperature of the components, such as the anilox roll 16 and the printing plate 18, may alter the relative position between the components which may lead to decreased frictional effects and thus a further decrease in temperature of the components. By minimising the variation of temperature at and/or on the printing plate 18, at least, the effects of temperature variation, such as distortion due to heat expansion or contraction, are minimised. By minimising the effects of temperature variation, such as expansion or contraction of the components of the flexographic printing apparatus 12, especially the printing plate 18, the relative location of, and thus the registration between, the components in the system may be maintained with more accuracy. With accurate temperature maintenance, the registration between the components may be kept substantially constant.

The components of the flexographic printing apparatus 12 are initially set to be optimally positioned relative to the other components of the flexographic printing apparatus 12 at the regulated operating temperature. That is the components are positioned to minimise dot gain and bouncing. During operation of the flexographic printing apparatus 12, any positional deviation between components, for example because of the effects of expansion or contraction of the components due to increases or decreases in temperature of the components, leads to increased dot gain or missing print. Further, positional deviation between components may also introduce, increase or decrease bouncing in the flexographic printing apparatus 12. Therefore, by minimising the positional deviation between components, for example by reducing the effects of expansion or contraction of the components, a reduction in the effects of dot gain and bouncing in the flexographic printing apparatus 12 may be observed. The reduction of the effects of dot gain and bouncing leads to less variation in the quality of the printing on the web material 60.

By regulating the temperature of ink from the ink supply 14, the ink may also act as a heat transfer medium to help maintain the printing plate 18 at a set temperature, or within a set temperature range.

Further, the temperature ranges may be chosen for optimum viscosity of the ink in relation to the process, such that the effects of ink drying on the elements of the apparatus, especially on the raised areas 54 of the printing plate 18, are minimised. Different solvent levels in the ink can be chosen to affect both the viscosity of the ink, at a given temperature, and the rate of drying of the ink. Inks with higher solvent levels require longer dying times, at a given temperature. Such solvent levels will be apparent to the person skilled in the art. It is desirable to minimise or prevent the ink drying on the components of the flexographic printing apparatus 12, as this can lead to a build up of tacky or dried ink, which may be later transferred to other components, including the web material 60, which may affect the quality of the printing. Inks with higher solvent levels will require a greater degree of heat input to dry the ink on the web material 60, by evaporating the solvent content of the ink. This is often done by using a heater close to the web material 60. Such heaters introduce further temperature rises within the flexographic printing press 12, and therefore lead to increased expansion of components of the flexographic printing apparatus 12, in particular the printing plate 18.

Generally a temperature for ink from the ink supply 14 and/or the printing plate 18 will be between 0°C and 70°C. The range may be between 5°C and 35°C, and may be between 10°C and 25°C. Depending on the constitution of the ink, a range between 10°C and 16°C or a range between 15°C and 25°C may be suitable. By keeping the range of operational temperature as small as possible the process may be optimised such that the effects of temperature deviation on the ink from the ink supply 14, the printing plate 18 and on the other components of the apparatus are minimised. By keeping the temperature of the ink from the ink supply 14, the printing plate 18 and the components of the flexographic printing apparatus 12 at a constant temperature, or within a small range of temperatures, the effects of temperature variations on the ink, the printing plate 18 and other components are minimised. Thus, by maintaining operational temperatures at a set temperature, or within a set temperature range, the viscosity of the ink and the drying of the ink can be accurately controlled. By accurate control of the viscosity of the ink, the quality of the printing can be controlled. Further, the effects of heat expansion and contraction in the components of the apparatus, as described above, are minimised.

In use, a predetermined temperature or predetermined temperature range is set by the user via the temperature control 82, which may be in the form of a keypad input, dial, via computer control or other user input, in relation to ink from the ink supply 14 and the printing plate 18. A thermostat 86 monitors the temperature of the ink from the ink supply 14 and/or the printing plate 18 and is operatively connected to the temperature control arrangement 84.

When the temperature of the ink from the ink supply 14 and/or the printing plate 18 is above a predetermined temperature, the temperature control arrangement 84 will be switched on to operatively cool the ink from the ink supply 14 and/or the printing plate 18. When the temperature of the ink from the ink supply 14 and/or the printing plate 18 falls below a predetermined temperature, the temperature control arrangement 84 will be switched off or may be operable to introduce heat to maintain the temperature at the predetermined temperature or within the predetermined temperature range. In this way the ink from the ink supply 14 and/or the printing plate 18 is maintained at a predetermined temperature or within a predetermined temperature range.

When the printing process begins, ink is pumped or drawn from the ink containment vessel 42, through an outlet pipe 44. The outlet pipe 44 passes through a heat exchanger, such as an air conditioning unit 84. A temperature control 82 is used to set a predetermined temperature for the ink from the ink supply 14 and printing plate 18. A thermostat 86 is used to monitor the temperature and is used to facilitate the control of the air conditioning unit 84. If the temperature is too low then the air conditioning unit 84 is switched off and if the temperature is too high then the air conditioning unit 84 is switched on. The ink is cooled by virtue of convective cooling from the air conditioning unit 84 acting on the outlet pipe 44, and further by the conduction of heat between the outlet pipe 44 and the ink flowing through the outlet pipe 44.

The ink then passes into the ink chamber 48 where it may subsequently pass through an opening 50 to the anilox roll surface 36 on the anilox roll 16. The ink covers the surface 36 of the anilox roll 16 and enters the cells 38 in the surface 36 of the anilox roll 16, to fill the cells 38 with ink. Ink in the ink chamber 48 which has not passed through the opening 50 may be circulated to return through an inlet pipe 46, which also passes through the air conditioning unit 84 back to the ink containment vessel 42. In alternative embodiments, the returning ink may not pass through the air conditioning unit 84. This circulation of the ink allows for better temperature distribution in the ink. Further, the air conditioning unit 84 may be directed to maintain the air inside of an enclosure or housing 92, in which the ink chamber 48 and printing plate 18 are located, at a constant temperature, or within a temperature range.

The various components such as the anilox roll 16, printing roll 52 and impression cylinder 20 may be driven, and the drive may be provided by one or more motors. Alternatively a friction drive mechanism may be used where the web material 60 is driven to traverse between the printing plate 18 on the printing roll 52 and the impression cylinder 20, and the friction between the web material 60 and the printing plate 18 causes rotation of the printing roll 52. This may further drive the other components of the flexographic printing apparatus, such as the anilox roll 16.

The anilox roll 16, printing roll 52 and impression cylinder 20 may be driven synchronously, such that their surfaces move at the same speed, preventing slippage between the surfaces of adjacent components, thus reducing component wear and improving printing quality. As the anilox roll 16 rotates its surface is in contact with the printing plate 18, which is disposed on the printing roll 52. As the anilox roll 16 is rotated such that the filled cells 38, on the surface 36 of the anilox roll 16, are brought into contact with the raised areas 54 of the printing plate 18, the ink is transferred from the cells 38 of the anilox roll 16 to the top surface 58 of the raised areas 54 of the printing plate 18. The regulation in ink temperature helps to regulate the temperature of the printing plate 18 through conduction of heat between the ink and the printing plate 18.

As the printing plate 18 is rotated, which may be effected through drive of the printing roll 52, the raised areas 54, which have a top surface 58 coated with ink, come into contact with the web material 60 that is to be printed upon, with the web material 60 located or sandwiched between the printing plate 18 and an impression cylinder 20. In an alternate embodiment, illustrated in Fig. 4, ink is provided as an ink supply 14, which in this example is contained in an ink reservoir 24, such as an ink pan, vat or trough, into which an ink roll 26 is positioned to operate as an ink transfer arrangement. The ink roll 26 comprises a cylindrical body 28 which is operable to rotate about its central axis 30, the central axis 30 being the axis along the line between the centres of the bases of the cylindrical body 28. The ink roll 26 has at least a portion of the surface 32 of the cylindrical body 28 in contact with the ink supply 14 in the ink reservoir 24, such that the ink is transferred from the ink supply 14 to the ink roll 26. The surface 32 of the ink roll 26 is often coated to aid ink pick up. A typical coating material would be an elastomer, such as rubber. The ink roll 26 then rotates in contact with the anilox roll 16.

In the embodiment of Fig. 4, any excess ink on the anilox roll surface 36, not in the cells 38 below the level of the anilox roll surface 36, is removed by a doctor blade 40. This provides for metered containment of ink in the cells 38 of the anilox roll 16, such that each cell 38 contains a specific quantity of ink. The anilox roll 16 and printing plate 18 can take the forms previously described above and shown in Figs. 2 and 3 respectively. The interaction between the anilox roll 16, printing plate 18 and impression cylinder 20 may be substantially as described above.

In the embodiment of Fig. 4, temperature control means 22 is provided to control the temperature of the printing plate 18 and ink from the ink supply 14. The temperature control means 22 comprises an ink temperature control arrangement 64 and a printing plate temperature control arrangement 74 which are separate arrangements, arrangeable to provide different temperature control to the ink from the ink supply 14 and the printing plate 18.

In relation to ink from the ink supply 14 a predetermined temperature or predetermined temperature range for the ink from the ink supply 14, is set by the use of an ink temperature control 62, which may be in the form of a keypad input, dial, via computer control or other user input.

The ink temperature control arrangement 64 comprises a heat exchanger convectively connected to the ink to be temperature controlled. A first thermostat 66 is used to maintain the temperature of the ink from the ink supply 14. The first thermostat 66 being operatively connected to the ink temperature control arrangement 64 such that the ink temperature control arrangement 64 can be switched on or off in response to a rise or fall in the monitored temperature.

In relation to the printing plate 18, a predetermined temperature or predetermined temperature range for the printing plate 18, is set by the use of a printing plate temperature control 72, which may be in the form of a keypad input, dial, via computer control or other user input.

The printing plate temperature control arrangement 74 comprises a heat exchanger convectively connected to the printing plate 18 to be temperature controlled.

A second thermostat 76 is used to maintain the temperature of the printing plate 18. The second thermostat 76 being operatively connected to the printing plate temperature control arrangement 74 such that the printing plate temperature control arrangement 74 can be switched on or off in response to a rise or fall in the monitored temperature.

In embodiments where the ink temperature control arrangement 64 and the printing plate temperature control arrangement 74 are to be convectively connected to the ink to be temperature controlled and the printing plate 18 to be temperature controlled, these temperature control arrangements may be separate convective cooling arrangements and may be convective cooling arrangements such as air conditioning units.

In an alternative embodiment of the method of the present invention, a first thermostat 66 monitors the temperature of the ink from the ink supply 14 and is operatively connected to the ink temperature control arrangement 64. A second thermostat 76 monitors the temperature of the printing plate 18 and is operatively connected to the printing plate temperature control arrangement 74. The temperatures suitable for operation of the apparatus may be as previously described above, and may be set by the user via temperature controls 64, 74, which may be in the form of keypad inputs, dials, via computer control or other user inputs, in relation to ink from the ink supply 14 and the printing plate 18.

The thermostat 66 is used to monitor the temperature of the ink from the ink supply 14 and when the temperature of the ink from the ink supply 14 is above a predetermined temperature, the ink temperature control arrangement 64 will be switched on to operatively cool the ink from the ink supply 14. When the temperature of the ink from the ink supply 14 falls below a predetermined temperature, the ink temperature control arrangement 64 will be switched off or may be operable to introduce heat to maintain the temperature at the predetermined temperature or within the predetermined temperature range. In this way the ink from the ink supply 14 is maintained at a predetermined temperature or within a predetermined temperature range.

The thermostat 76 is used to monitor the temperature of the printing plate 18 and when the temperature of the printing plate 18 is above a predetermined temperature, the printing plate temperature control arrangement 74 will be switched on to operatively cool the printing plate 18. When the temperature of the printing plate 18 falls below a predetermined temperature, the printing plate temperature control arrangement 74 will be switched off or may be operable to introduce heat to maintain the temperature at the predetermined temperature or within the predetermined temperature range. In this way the printing plate 18 is maintained at a predetermined temperature or within a predetermined temperature range. Using the apparatus of Fig. 4, when the printing process begins the surface of the cylindrical body 28 of the ink roll 26 rotates about a central axis 30 of the cylindrical body 28 such that at least a portion of the surface 32 of the ink roll 26 is in contact with the ink supply 14 in the ink reservoir 24. Ink is thereby transferred from the ink supply 14 to the ink roll 26. The ink roll 26 is further in contact with the anilox roll 16. Within the ink reservoir 24, an ink temperature control arrangement 64, such as a heat exchanger 64, is present to convect heat to/from the ink in the ink supply 14. In alternative embodiments the heat exchanger 64 may be arranged to convect heat from the walls of the ink reservoir 24. In further embodiments the heat exchanger may conductively cool or heat the ink in the ink reservoir 24 either by a heat exchanger in the ink supply 14 or conductively connected to the ink reservoir 24. Ink is then transferred from the surface 32 of the ink roll 26 onto the surface 36 of the anilox roll 16. The ink covers the surface 36 of the anilox roll 16 and enters the cells 38 in the surface 36 of the anilox roll 16, to fill the cells 38 with ink. As the anilox roll 16 rotates, its surface 36 is in close contact with a doctor blade 40. The doctor blade 40 shears the ink from the surface 36 of the anilox roll 16, leaving the ink within the cells 38.

As the anilox roll 16 rotates it is also in contact with the printing plate 18, which is disposed on the printing roll 52. As the filled cells 38 are rotated to be in contact with the raised areas 54 of the printing plate 18, the ink is transferred from the cells 38 of the anilox roll 16 to the top surface 58 of the raised areas 54 of the printing plate 18. The heat exchangers 64, 74, which may be air conditioning units may be directed to maintain the temperature of the air inside an enclosure or housing similar to that shown for Fig. 1 . Alternatively the heat exchangers 64, 74 may be directed to maintain the temperature of the air inside the flexographic printing apparatus 12. For applications of the present invention it is expected that the predetermined temperatures or predetermined temperature ranges may vary according to the composition of the ink. The predetermined temperatures or predetermined temperature ranges may vary according to the materials used in the construction of at least one of the anilox roll 16, the printing plate 18, the impression cylinder 20.

The appropriate predetermined temperatures or predetermined temperature ranges for a given composition of the ink and construction of the components of the flexographic printing apparatus will be apparent to the person skilled in the art, when presented with the benefits of the present invention to regulate temperatures to address dot gain and bouncing problems in flexographic printing apparatus 12. Although embodiments of the present invention have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the invention as claimed. Although the present invention has been described such that the temperature control arrangement 84 is noted to be connected convectively to the ink from the ink supply 14 to be temperature controlled and/or the printing plate 18 to be temperature controlled, it will be appreciated that the temperature control arrangement 84 may be conductively connected to the ink from the ink supply 14 to be temperature controlled and/or the printing plate 18 to be temperature controlled.

Although the present invention has been described such that the ink temperature control arrangement 64 and/or the printing plate temperature control arrangement 74 are noted to be connected convectively to the ink from the ink supply 14 to be temperature controlled and/or the printing plate 18 to be temperature controlled it will be appreciated that the ink temperature control arrangement 64 and/or the printing plate temperature control arrangement 74 may be conductively connected to the ink from the ink supply 14 to be temperature controlled and/or the printing plate 18 to be temperature controlled.

Although the present invention has been described such that if the temperature monitored by the or at least one of the thermostats 66, 76, 86 or other temperature measurement devices is too low then the or at least one of the temperature control arrangements 64, 74, 84, is switched off and if the temperature monitored by the or at least one of the thermostats 66, 76, 86 or other temperature measurement devices is too high then the or at least one of the temperature control arrangements 64, 74, 84, is switched on, or operated to provide cooling, it will be understood that the or at least one of the temperature control arrangements 64, 74, 84 could be used to provide heat rather than, or in addition to, cooling such that if the temperature monitored by the or at least one of the thermostats 66, 76, 86 or other temperature measurement devices is too low then the or at least one of the temperature control arrangements 64, 74, 84 is switched on, or operated to provide heat, and if the temperature monitored by the or at least one of the thermostats 66, 76, 86 or other temperature measurement devices is too high then the or at least one of the temperature control arrangements 64, 74, 84 is switched off.

Although the present invention has been described whereby the temperature control means 22 is provided to regulate the temperature of the printing plate 18 and ink from the ink supply 14, either dependently or independently from each other, it will be appreciated that the temperature control means 22 may be provided to regulate the temperature of one only of a printing plate 18 or ink from the ink supply 14. Although the present invention has been described whereby the temperature control arrangements such as the ink temperature control arrangement 64, printing plate temperature control arrangement 74 and combined temperature control arrangement 84 are heat exchangers such as air conditioning units, it will be appreciated that other temperature control arrangements may be used, such as Peltier cooling devices, which may be affixed, for example, to the outer surfaces of components to be cooled. Further other devices such as cyclic refrigeration units may be used to help maintain a temperature at a constant value or within a desired range.

Although the present invention has been described such that the ink from the ink supply 14 and the printing plate 18 are temperature controlled to prevent variations in temperature from affecting the final print quality, it will be appreciated that other components of the flexographic printing apparatus 12, such as the ink roll 26 and/or the anilox roll 16 may be temperature controlled in a manner similar to those described above in relation to the ink from the ink supply 14 and the printing plate 18.

Although the present invention has been described in relation to printing units 100 being provided around the circumference of a central impression cylinder 20, it will be apparent that in alternative flexographic printing apparatus 12, printing units 100 may be in a stacked arrangement, each printing unit 100 having a printing plate 18 in contact with a web material 60 disposed between the printing plate 18 and an impression cylinder 20. A separate impression cylinder 20 is used for each printing unit 100. In the stack arrangement the printing units 100 are arranged in a vertical stack, or a number of vertical stacks as in Fig. 5 where each print unit 100 is an arrangement as shown in Figs. 1 and 4, but with the central impression cylinder 20 being replaced with an individual impression cylinder 20. In a further alternative flexographic printing apparatus 12, as shown in Fig. 6, each printing unit 100 is in a line, allowing for thicker materials, such as cardboard, to be passed through the press, as there is no requirement for the web material 60 to be bent during printing. Although the present invention has been described in relation to temperature control of a single printing unit 100, it is to be understood that a flexographic printing apparatus 12 may consist of multiple printing units 100, each of which may comprise temperature regulation arrangements 10 as described. Alternatively the flexographic printing apparatus 12 may comprise a temperature regulation arrangement 10 to control the temperature of multiple printing units 100. For example the inlet pipes 46 and outlet pipes 44 of multiple printing units 100, as shown singly in Fig. 1 , may all pass through a single temperature control arrangement 84 and that the temperature control arrangement 84 may provide convective cooling to the entire flexographic printing apparatus 12, thus maintaining the temperature of multiple printing plates 18 within the flexographic printing apparatus 12.

Features described in the preceding description may be used in combinations other than the combinations explicitly described.

Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not. Although features have been described with reference to certain embodiments, those features may also be present in other embodiments whether described or not.

Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.