Printing System

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Patent Application No. 14/821 ,043 filed August 7, 2015, which is incorporated herein in its entirety by this reference thereto.

FIELD

The invention relates to inkjet printing. More particularly, the invention relates to spot gloss and gloss control in an inkjet printing system.

BACKGROUND

Inkjet printing involves depositing droplets of liquid ink onto a printing medium from one or more printer heads. The printer heads are coupled with a container containing ink. Ink is ejected from one or more nozzles of the print heads when a piezoelectric crystal in the print head is actuated. The piezoelectric crystal generates a pulse in the ink so that the ink expels through the nozzle as a droplet. To create the image, a carriage which holds one or more print heads scans or traverses across the printing medium, while the print heads deposit ink as the printing medium moves.

Large format printing is performed to create signs, banners, museum displays, sails, bus boards, POP applications, and the like. Oftentimes consumers of large format prints prefer to choose a full or partial gloss finish to create striking displays. Gloss finishes come in various reflective intensities measured in Gloss Number. Gloss Number measures how much light is reflected at a given position. In today's art, gloss finishes are commonplace with solvent based SWF printers, but a high gloss finish is not available on today's UV printers due to the fact that the curing of the droplets of UV ink leaves a matte surface structure, rather than a very smooth finish.

Spot gloss allows one to put gloss coating on some parts of a printed image while leaving other parts uncoated. For instance, one may want to apply gloss coating to a company logo, and leave the rest of the image in a matte finish. If spot gloss is needed in inkjet printing, the background image normally is printed first, and then the printing media is reversed back through the printer carriage for a second run, or the media is removed and reloaded. This approach requires additional handling of the media, which decreases throughput and which can also result in registration errors. Alternatively, a multilayer technique can be used to print a layer of clear inks on a target area to create a spot gloss or a gloss overcoat. In this approach, a clear ink channel is required to achieve the spot gloss and/or a gloss overcoat.

SUMMARY

Embodiments of the invention provide a technique that effects spot gloss or gloss control and/or variations on one image without requiring clear inks. This is preferably accomplished by use of a multilayer printing process in which an image is first printed using a first set of color print heads and then cured, and in which the image is again printed using a second set of color print head, but where the image remains uncured for a predetermined interval to allow the ink drops applied to the media to spread and thus introduce a gloss effect. DRAWINGS

Figures 1A and 1 B are plan views showing a carriage for an inkjet printing system that provides spot gloss and gloss control according to the invention;

Figure 2 is a perspective view of an exemplary inkjet printer for use in connection with the invention; and

Figure 3 is a flow diagram showing a technique for spot gloss and gloss control in an inkjet printing system.

DESCRIPTION

Embodiments of the invention provide a technique that effects spot gloss or gloss control and/or variations on one image without requiring clear inks. Spot gloss concerns the selective application of gloss effects to portions of an image, i.e. spots such as an item or portion of the text, while gloss effects can also be applied to the entire image, i.e. the entire printed image is glossy. This is preferably accomplished by use of a multilayer printing process in which an image is first printed using a first set of color print heads and then cured, and in which the image is again printed using a second set of color print heads, but where the image remains uncured for a predetermined interval to allow the ink drops applied to the media to spread and thus introduce a gloss effect. Such multiple layers are readily generated using image editing software, such as Adobe Photoshop®.

Figures 1A and 1 B are plan views showing a carriage for an inkjet printing system that provides spot gloss and gloss control according to the invention. In the example of Figures 1A and 1 B, there are eight colors, every color has two or three printing heads, although there can be one or more than three printing heads for every color. To print a two layer image, the shroud 12 covering the emitting window of the UV lamp 10 can start with the second row of printing heads (Figure 1 A) or start with the middle of the second row (Figure 1 B). The length of the shroud can be adjusted to control the time allowed for the ink spreading to control the gloss level. In embodiments of the invention, the minimum length of the shroud could cover, for example, the second row of the printing heads.

In embodiments of the invention, the spreading of the ink drops can be controlled in any of two ways, e.g. the shroud blocks the UV light to allow the liquid ink to spread without intervention of UV light, or the shroud is a screened to allow a controllable amount UV light to pass through to partially pin the ink drops to control the spread of spreading.

As shown in Figures 1 A and 1 B, an ink jet printer for use in connection with embodiments of the herein disclosed invention includes a moving carriage that is operable to move back and forth (14) over a moving belt or table to deposit the inks on the media which, in turn, is moved by a belt, table, or roller. In embodiments of the invention, the belt, table, or roller moves the media in a direction (16) that is perpendicular to that of the carriage. Such printers are considered to be continuous printers because the carriage and media continue to move relative to each other as described above until printing of the desired image on the media is completed.

Figure 2 is a perspective view of an exemplary inkjet printer for use in connection with the invention. In Figure 2, the printing heads 30 and mercury arc UV lamp 32 are shown mounted on a carriage. The inkjet printer carriage contains multiple print heads 18/20 (Figure 1A) or 22, 24, 26 (Figure 1 B) which are used to deposit, for example, radiation-curable inks on the media. The print heads in the inkjet printer can be arranged in any of single row or, as shown in Figures 1 A and 1 B, multiple rows for each color. Figure 3 is a flow diagram showing a technique for spot gloss and gloss control in an inkjet printing system. The image to be printed on the media is processed as a two-layer or multilayer image. As mentioned above, this can be accomplished using known techniques, such as by use of such software as Adobe Photoshop®. The first layer is the normal image portion, i.e. the first layer is not given a gloss treatment. This layer is printed by a first set of print heads (100) and cured (1 10). The second layer contains the portion of the image that expresses the desired level of gloss, as well as those spots to which gloss is to be applied if the image has selectively predetermined areas that have more gloss relative to other areas of the image. This layer is printed by a second set of print heads (120), the ink is not immediately cured and is therefore allowed to spread to create a gloss effect (130). Once the desired gloss effect is achieved, the second ink layer is cured (140).

The time allowed for ink drop spreading is critical for the gloss. More time allowed for ink spreading results in more gloss achieved. The time, for example, can be less than a second to several minutes; the gloss level can be 10-100 gloss units. The curing of UV inks can be instantaneous or up to many seconds dependent on the UV energy available for curing.

In another embodiment of the invention, a screen shroud is used to pin the ink drops to convert them to a partial liquid or gel state to control the speed of ink drop spreading further and thereby vary the gloss.

Examples of UV inks can be found in US8889232B2 (Cong). A radiation curable ink composition (see Table 1 below) may comprise one or more of: an oligomer component;

a monomer component;

a photo-initiator component;

a colorant component; and • an additive component.

Table 1 : Ink Composition

Referring again to Figures 1 A and 1 B, in an embodiment of the invention, the first half of the printing heads for each color 18 is used to print the first layer. Once the inks are deposited on the media, the inks are immediately exposed to UV lamps 10 that, in an embodiment of the invention, are attached on the both ends of the carriage. The inks are then cured.

The second half of the printing heads of each color 20 are used to print the second layer. In embodiments of the invention, a part of the UV lamps is covered or screened 12, as shown in Figures 1A and 1 B. As such, there is no UV radiation or limited UV radiation output available to cure the second layer inks. As a result, the inks are given more time to spread on the media and thus give a varied gloss appearance to the first layer, dependent on the UV energy available through the covered or screened portion of the lamp. In embodiments of the invention, the length of the screening or blocking effect determines the amount of gloss achieved, where a longer time before the cure is completed produces a greater gloss effect because the ink droplets have greater time to spread before being completely cured.

In embodiments of the invention, screening can be applied by a shutter mechanism that is variably adjustable to produce selected gloss effects. Such shutter mechanism can be any of a mechanical shutter, for example that is operated by a user or an actuator; or an electronic shutter, such as an electronic panel having a selectable degree of opacity. In the case of a mechanical shutter, the amount of light allowed to pass there through to effect ink curing can be a function of the density of the shutter, e.g. by varying the density of a screen mesh, or a function of the length of the shutter, e.g. by selectably changing the length of the shutter to affect the length of time that the ink is allowed to spread before being cured.

In other embodiments of the invention, a variable gap between the curing lamps may be introduced into the carriage such that the gloss layer of ink initially passes through the gap and is thus not cured during the time it takes to clear the gap. In embodiments of the invention, the gap can be selectively variable, for example by operation of a drive mechanism that moves the curing lamps relative to each other to establish the gap. The size of the gap then determines the time required for curing the gloss layer and, hence, the amount of ink drop spread and resulting gloss effect. Some such embodiments move the UV lamps on both sides of carriage away each other on the carriage moving direction. In other embodiments, every UV lamp is sectioned, where the section used to cure the second layer can be moved away from the section used to cure the first layer image in the media moving direction to create gaps that achieve a similar effect of the shroud. In embodiments of the invention, a printer dialog may be provided to the user that allows the user to select a degree of gloss applied. For example, a slider control may be provided that adjusts the opacity, density, or length of the shutter or screen mechanism. Embodiments of the invention control gloss through mechanical, electronic, or software mechanisms installed on the printer. In practice, the gloss level setting is optimized to the type of UV inks used in the printer. Every UV ink formulation is different in terms of curing speed and properties, thereby different gloss settings are needed to be adjusted to fit the different UV inks.

Eventually, as the media advances through the printer, the second layer ink moves past the covered or screened part of the curing lamp and reaches a region where it is exposed to sufficient radiation to be cured. The covered or screened portion can be applied on either lamps or to single lamp to achieve different gloss effects. Further, as discussed above, the length of the covered or screened portion of the UV lamps can be adjusted based on the printing speed and desired gloss variation effects. A longer covered or screened lamp portion allows more time for the inks to flow before being cured. In this way, a higher level of gloss is achieved.

Embodiments of the invention can be used to control the gloss of an entire image in a printer that is setup for single layer printing. In such embodiments, the image is processed as one layer and the beginning portion of the lamp is covered or screened to control the rate at which ink drops spread and, thus vary the gloss of the image without printing the image via a multilayer process. In another embodiment, the first layer is blank and the second layer is the whole image. Because the gloss of the second layer can be controlled the gloss of the whole image can be controlled.

As discussed above, a portion of the UV lamp, such as a mercury arc lamp, that is used to cure ink after the ink is applied to the media by the second half of the printing heads is covered or screened such that no UV or a reduced amount of UV energy reaches the inks deposited on the media.

For UV LED lamps, in embodiments of the invention a portion of the LED lamp can be controlled to vary the energy output, such that similar effects to those achieved with mercury arc lamps can be obtained without requiring mechanical blocking or screening. As discussed above, a user printer dialog may be provided that allows the user to select the level of gloss provided. In embodiments of the invention, the printing heads for each color can be arranged in multiple rows. Two rows are shown in Figure 1 for purposes of description only. For example, if there are three heads per color, the second half of printing heads, i.e. the part that is used for gloss effect, starts from the middle of the second head.

Although the invention is described herein with reference to the preferred embodiment, one skilled in the art will readily appreciate that other applications may be substituted for those set forth herein without departing from the spirit and scope of the present invention. Accordingly, the invention should only be limited by the Claims included below.