JP7845889B2 - How to print with an inkjet printer - Google Patents

Description

This invention relates to a printing method for an inkjet printer. More specifically, this invention relates to a printing method for an inkjet printer that prints by ejecting pigment-containing inks, such as process color inks and white inks, for forming an image on a medium, and pigment-free inks, such as clear topcoat inks, which are ejected onto the surface of the pigment-containing inks and serve as an overcoat layer to coat the surface of the image formed by the pigment-containing inks and provide gloss, onto the medium using an inkjet method.

Furthermore, the clear inks mentioned above are generally known to come in two types: gloss (shiny) and matte (non-glossy).

Furthermore, in this specification and the claims, "inks containing pigments" will be collectively referred to as "pigment inks" as appropriate, and "inks not containing pigments" will be collectively referred to as "pigment-free inks" as appropriate.

Furthermore, in this specification and the claims, "media" includes not only recording media such as various types of paper, such as ordinary paper, but also various materials such as sheets made from resin materials like polyvinyl chloride (PVC) and polyester, metal plates made from aluminum and iron, glass plates, and relatively thick plate materials such as wooden boards.

Furthermore, in this specification and in the claims, "inkjet method" means a printing method using inkjet technology by various conventionally known methods, including various continuous methods such as binary deflection methods and continuous deflection methods, and various on-demand methods such as thermal methods and piezoelectric element methods. "Inkjet printer" comprehensively means an apparatus that performs printing using the inkjet technology described above.

In general, an inkjet printer is known in which the overall operation is controlled by a computer system, and which is equipped with a table (platform) on which media such as recording paper is placed, and a carriage is arranged above the media placed on the table and is movable relative to the table in a predetermined direction, and an inkjet head that ejects ink from ink ejection nozzles using an inkjet method is mounted on this carriage, and ink is ejected from the ink ejection nozzles of this inkjet head onto the media using an inkjet method to perform the desired printing.

In this specification and within the claims, the direction of carriage movement (transport direction) in such inkjet printers will be appropriately referred to as the "main scanning direction."

Furthermore, in the inkjet printer described above, the media-holding table is configured to be relatively movable relative to the carriage in a direction perpendicular to the main scanning direction, thereby enabling printing on the desired location on the media placed on the table.

In this specification and the claims, the direction of table movement (transport direction) perpendicular to the "main scanning direction" will be appropriately referred to as the "sub-scanning direction."

Incidentally, as an example of the inkjet printer described above, there is a known inkjet printer that has, for example, a first inkjet head equipped with a first ink ejection nozzle for ejecting process color ink, which is a pigment ink that has photocurability (for example, UV curability, which hardens when exposed to ultraviolet light) and whose hardening is accelerated when irradiated with light as a first type of ink by an inkjet method, and a second inkjet head equipped with a second ink ejection nozzle for ejecting clear ink, which is a pigment-free ink that has photocurability (for example, UV curability, which hardens when exposed to ultraviolet light) and whose hardening is accelerated when irradiated with light as a second type of ink by an inkjet method. The first and second inkjet heads are transported in the main scanning direction, and the table on which the media is placed is transported in the sub-scanning direction, and printing is performed by irradiating the process color ink ejected onto the media from the first ink ejection nozzle and the clear ink ejected onto the media from the second ink ejection nozzle with light to accelerate their hardening.

According to the inkjet printer disclosed in Japanese Patent Publication No. 5452188, when performing a clear print using a UV-curable, pigment-free clear ink for a topcoat over a color print of an image using a process color ink (a pigment ink with UV curing properties), the printing was performed using the method shown in Figures 1(a), 1(b), 1(c), 1(d), and 1(e).

Specifically, first, while the table 102 on which the media 100 is placed is transported in the direction from the print start position to the print end position (forward direction) in the sub-scanning direction, the first inkjet head 104 is moved relative to the media 100 in the main scanning direction. Process color ink, which is pigment ink, is ejected from the first ink ejection nozzle of the first inkjet head 104 toward the media 100, and ultraviolet (UV) light is irradiated (see Figure 1(a)). This forms an image 106 on the media 100 by color printing using the process color ink (see Figure 1(b)).

Once image formation on the media 100 is complete, the table 102 is transported in the direction from the end of printing to the start of printing in the sub-scanning direction (reverse direction), and a pull-back process is performed to temporarily return the media 100 to the start of printing (see Figure 1(c)).

Subsequently, while transporting the table 102 again in the direction from the print start position to the print end position (forward direction) in the sub-scanning direction, the second inkjet head 108 is moved relative to the media 100 in the main scanning direction. Clear ink, which is a pigment-free ink, is ejected from the second ink ejection nozzle of the second inkjet head 108 toward the media 100, and ultraviolet light is irradiated (see Figure 1(d)). This forms a topcoat 110 on the media 100 by clear printing using the clear ink (see Figure 1(e)).

However, in printed materials (outputs) produced by the inkjet printing method disclosed in the aforementioned Japanese Patent Publication No. 5452188, while the topcoat formed with clear ink (a pigment-free ink) can suppress the fading of images formed with process color inks (pigment-based inks), pigment-free inks, which do not contain pigments that absorb light energy, are more prone to cracking than pigment-based inks. Therefore, if the printed material is placed outdoors, it may be affected by sunlight and rain, and as time passes after printing, many cracks may develop in the topcoat formed with clear ink (a pigment-free ink).

For example, according to the test results of an outdoor weather resistance test (described later) conducted by the present inventor, when the peak illuminance when irradiating with ultraviolet light was set to 1800 mW/ ^cm² , the irradiation time for one transport of the first inkjet head 104 and the second inkjet head 108 in the main scanning direction was set to 0.036 sec, and the cumulative light amount for one transport was 65 mJ/ ^cm² , when the condition was observed after 750 hours from the start of the outdoor weather resistance test, it was found that numerous cracks had formed, as shown in Figure 2.

For the outdoor weather resistance test, a "Xenon Weather Meter NX25Z" manufactured by Suga Test Instruments Co., Ltd. was used, and irradiation and rainfall were repeated. The light source was set to emit light of a desired wavelength using a filter, and the radiant intensity was set to 60 W/ ^cm² .

Furthermore, the integrated light intensity was calculated using the formula: "Integrated light intensity (mJ/ ^cm² ) = Peak illuminance (mW/ ^cm² ) × Irradiation time (sec) for one transport in the main scanning direction".

Furthermore, it has been conventionally known that cracks in topcoats, as described above, are caused by factors such as light (especially ultraviolet light), heat (temperature changes), rain, and oxygen.

Patent No. 5452188

This invention has been made in view of the above-mentioned problems of the prior art, and its objective is to provide an inkjet printer printing method that suppresses the occurrence of cracking in the topcoat formed by the pigment-free ink over time in printed materials (final products) in which a topcoat is formed by printing with a light-curable pigment ink on top of an image formed by printing with a light-curable pigment ink.

To achieve the above objective, the inkjet printer printing method according to the present invention involves ejecting photocurable pigment ink from a pigment ink ejection nozzle onto a media placed on a table while irradiating it with light. During the transport operation of the table relative to the pigment ink ejection nozzle, non-pigmented ink is ejected from a non-pigmented ink ejection nozzle onto the pigment ink ejected onto the media.

Therefore, according to the inkjet printer printing method of the present invention, when light irradiation is performed and photocurable pigment ink is ejected onto the media from the pigment ink ejection nozzle onto the media, photocurable pigment-free ink is ejected onto the media from the pigment-free ink ejection nozzle during the transport operation of the table on which the media is placed. As a result, a state is created on the media where the pigment ink and pigment-free ink are mixed. Therefore, the effect of the pigment contained in the pigment ink extends to the topcoat made of pigment-free ink, and even if the printed material (final product) is placed outdoors and exposed to sunlight and rain, the occurrence of cracking of the topcoat made of pigment-free ink over time is suppressed.

Here, since pigments absorb light energy, it is known that including pigment particles in the ink is effective in improving light resistance. Therefore, topcoats formed with pigment-free ink are prone to cracking.

However, according to the inkjet printer printing method of the present invention, unlike conventional techniques where the media is pulled back after printing with process color ink (pigment ink) and then clear ink (non-pigment ink) is printed, the pigment ink and non-pigment ink are printed onto the media at the same time without pulling the media back. Therefore, a state in which the pigment ink and non-pigment ink are mixed can be created.

In other words, before the image formed with pigment ink on the media has completely hardened, the topcoat is printed with pigment-free ink. This allows the weather-resistant effect of the pigment in the pigment ink to extend to the topcoat formed with the pigment-free ink, thereby suppressing the occurrence of cracks in the topcoat.

In other words, the inkjet printer printing method according to the present invention comprises a table on which media is placed, a pigment ink ejection nozzle for ejecting photocurable pigment ink onto the media placed on the table, a pigment-free ink ejection nozzle for ejecting photocurable non-pigment ink onto the media placed on the table, a transport means for relatively moving the pigment ink ejection nozzle and the non-pigment ink ejection nozzle and the table to transport the media relative to the pigment ink ejection nozzle and the non-pigment ink ejection nozzle, and a light irradiation means for irradiating the pigment ink and the non-pigment ink ejected onto the media with light, wherein, during the transport operation of the media by the transport means when ejecting the pigment ink from the pigment ink ejection nozzle onto the media placed on the table, the non-pigment ink ejection nozzle ejects the non-pigment ink onto the pigment ink ejected onto the media during the transport operation.

Therefore, according to the inkjet printer printing method of the present invention, printing is performed at the same time between printing with pigment ink and printing with non-pigment ink without pulling the media back. As a result, the non-pigment ink is ejected onto the pigment ink before the pigment ink hardens, creating a state where the pigment ink and non-pigment ink are mixed. This allows the effects of the pigment contained in the pigment ink to extend to the topcoat made with non-pigment ink, thereby suppressing the occurrence of cracks in the topcoat formed with non-pigment ink.

Furthermore, in the inkjet printer printing method according to the present invention described above, the light irradiation means is an ultraviolet irradiation lamp.

The peak illuminance of ultraviolet irradiation using the above-mentioned ultraviolet irradiation lamp is set to be between 1200 mW/ ^cm² and 1800 mW/ ^cm² .

Therefore, according to the inkjet printer printing method of the present invention, by setting the peak illuminance of ultraviolet irradiation to an appropriate value, the occurrence of cracks in the topcoat formed with pigment-free ink can be further suppressed.

Furthermore, the inkjet printer printing method according to the present invention is characterized in that, in the inkjet printer printing method according to the present invention described above, the media on which the pigment-free ink has been ejected onto the pigment ink is heated to a temperature of 60°C to 80°C.

Therefore, according to the inkjet printer printing method of the present invention, by heating the media at an appropriate temperature, the occurrence of cracks in the topcoat formed with pigment-free ink can be further suppressed.

As described above, the present invention provides the excellent effect of suppressing the occurrence of cracks in the topcoat formed by the pigment-free ink over time in printed materials (final products) in which a topcoat is formed by printing a topcoat with a light-curable pigment-free ink over an image formed by printing with a light-curable pigment ink.

Figures 1(a), (b), (c), (d), and (e) are schematic diagrams illustrating the printing method of a conventional inkjet printer. Figure 2 is an explanatory diagram showing the results of an outdoor weather resistance test of printed materials (deliverables) printed using a conventional inkjet printer printing method. Figure 3 is a schematic perspective diagram illustrating an example of an inkjet printer that implements the printing method of the inkjet printer according to the present invention. Figure 4 is a schematic perspective view illustrating the inkjet printer shown in Figure 3 with the main unit case removed. Figure 5 is a schematic plan view of the inkjet printer shown in Figure 3 with the main body case removed, showing the table positioned furthest downstream in the sub-scanning direction. Figure 6 is a schematic plan view of the inkjet printer shown in Figure 3 with the main body case removed, showing the table positioned furthest upstream in the sub-scanning direction. Figure 7 is a schematic diagram illustrating the arrangement of the inkjet head and light irradiation device in a plan view of the inkjet printer shown in Figure 3. Figures 8(a) and 8(b) are schematic explanatory diagrams illustrating the printing method of the inkjet printer of the present invention. Figure 9 is an explanatory diagram showing the results of an outdoor weather resistance test of printed materials (outputs) printed by the inkjet printer printing method according to the present invention. Figure 10 is an explanatory diagram showing the results of a comparative experiment in an outdoor weather resistance test.

The following describes in detail an example of an embodiment of the inkjet printer printing method according to the present invention, with reference to the attached drawings.

(I) Description of the overall configuration of an inkjet printer implementing the inkjet printer printing method according to the present invention.

Figure 3 shows a schematic perspective diagram illustrating an example of an inkjet printer implementing the printing method according to the present invention.

Furthermore, Figure 4 shows a schematic perspective diagram illustrating the inkjet printer shown in Figure 3 with the main unit case removed.

Furthermore, Figure 5 is a schematic plan view of the inkjet printer shown in Figure 3 with the main body case removed, showing the table positioned furthest downstream in the sub-scanning direction.

Furthermore, Figure 6 is a schematic plan view of the inkjet printer shown in Figure 3 with the main body case removed, showing the table positioned furthest upstream in the sub-scanning direction.

Furthermore, Figure 7 shows a schematic diagram illustrating the arrangement of the inkjet head and light irradiation device in a plan view of the inkjet printer shown in Figure 3.

In the following explanation, the Y direction in the XYZ Cartesian coordinate system refers to the main scanning direction, which is the direction of movement of the carriage 32 (described later). The X direction in the XYZ Cartesian coordinate system refers to the sub-scanning direction, which is perpendicular to the Y direction (main scanning direction) in the XY plane. The Z direction in the XYZ Cartesian coordinate system refers to the height direction, which is perpendicular to the XY plane.

Furthermore, for the sake of clarity in the following explanation, the Y direction (main scanning direction) will be defined as the left side of the page containing Figure 3 being the left direction and the right side being the right direction; the X direction (sub-scanning direction) will be defined as the front direction of the page containing Figure 3 being the front direction and the top direction being the back direction; and the Z direction (height direction) will be defined as the down direction of the page containing Figure 3 being the down direction and the top direction being the up direction.

Furthermore, in the sub-scanning direction, the rear side will be appropriately referred to as the "upstream side," and the front side will be appropriately referred to as the "downstream side."

Furthermore, in the sub-scanning direction, the direction from upstream to downstream is referred to as the "forward direction," while the direction from downstream to upstream is referred to as the "reverse direction."

Furthermore, the directions described above are merely for illustrative purposes and do not in any way limit the installation configuration of the inkjet printer, nor do they limit the present invention in any way.

Reference numeral 10 indicates a so-called flatbed type inkjet printer. Compared to home inkjet printers, it is a large inkjet printer with a longer scanning surface in the main scanning direction, and is used, for example, in commercial applications.

The operation of this inkjet printer 10 is controlled by a control device 92, which is configured as a computer system, such as a microcomputer. The control device 92 performs printing on the media 5 according to the print data.

This print data may be supplied from an external source and taken into the control device 92 of the inkjet printer 10, or it may be generated by the control device 92 of the inkjet printer 10.

In this embodiment, the control device 92 is shown as being located inside the main body case 12 (see Figure 3), but it goes without saying that the control device 92 may also be located outside the main body case 12.

This inkjet printer 10 comprises a base member 60, a main body case 12 attached to the base member 60, a carriage movement mechanism 20, a table movement mechanism 38, an inkjet head unit 30, and a maintenance device 70.

Furthermore, the inkjet printer 10 includes a carriage movement mechanism 20 and a main frame 14 that supports the inkjet head unit 30.

The table movement mechanism 38 includes a first slide rail 51 and a second slide rail 52 that support the table unit 40 (described later) so as to be movable in the sub-scanning direction, a table unit 40 having a table 48 which is a mounting base on which the media 5 is placed, and a movement device 41 that moves the table unit 40 in the sub-scanning direction.

Here, the inkjet head unit 30 is positioned above the table unit 40 inside the main body case 12.

This inkjet head unit 30 comprises an inkjet head 34, a carriage 32 on which the inkjet head 34 is mounted, a light irradiation device 80L attached to the carriage 32 on the left side of the inkjet head 34, and a light irradiation device 80R attached to the carriage 32 on the right side of the inkjet head 34.

Furthermore, a front cover 13C is provided in the center of the front of the main case 12, a left cover 13L is provided on the left side of the front of the main case 12, and a right cover 13R is provided on the right side of the front of the main case 12.

These front cover 13C, left cover 13L, and right cover 13R are configured to be openable and closable relative to the main case 12, and the front cover 13C is provided with a window 13W.

This window 13W is formed, for example, from a transparent acrylic plate, allowing the worker to see inside the main case 12 through the window 13W.

The base member 60 is attached to the lower part of the main body case 12 and supports the main body case 12.

More specifically, the base member 60 is composed of a bottom wall 61 that forms the bottom surface, a left wall 62 located to the left and above the bottom wall 61, a right wall 63 located to the right and above the bottom wall 61, a left side wall 64 connecting the bottom wall 61 and the left wall 62 and extending in the vertical direction Z, and a right side wall 65 connecting the bottom wall 61 and the right wall 63 and extending in the vertical direction Z.

The table unit 40 described above is configured to move along the bottom wall 61 in the sub-scanning direction.

The main frame 14 is supported by the left wall 62 and right wall 63 described above and is mounted on the base member 60.

This main frame 14 has a left base wall 15L extending upward from the left wall 62 of the base member 60, a right base wall 15R extending upward from the right wall 63 of the base member 60, and a support wall 16 connecting the upper end of the left base wall 15L and the upper end of the right base wall 15R.

Furthermore, the left base wall 15L is located to the left of the table unit 40, and the right base wall 15R is located to the right of the table unit 40.

Furthermore, the support wall 16 is formed to extend in the main scanning direction and is positioned above the base member 60.

Furthermore, the inkjet printer 10 has an opening 14H that penetrates in the sub-scanning direction, which is formed by being surrounded by the support wall 16 of the main frame 14 and the base member 60.

This opening 14H is set to be large enough for the table unit 40 to pass through when the table unit 40 moves in the sub-scanning direction.

Furthermore, the inkjet printer 10 is provided with a guide rail 18 that extends in the main scanning direction and is positioned above the opening 14H, along the front surface of the support wall 16.

These guide rails 18 will be positioned above the table unit 40.

Furthermore, the carriage 32 of the inkjet head unit 30 is slidably mounted on the guide rail 18, and the carriage 32 is guided to move in the main scanning direction by the guide rail 18.
The carriage movement mechanism 20 is a mechanism that moves the carriage 32 relative to the media 5 placed on the table 48 of the table unit 40 in the main scanning direction.

The configuration of the carriage movement mechanism 20 is not particularly limited, but in this embodiment, the carriage movement mechanism 20 is configured to include a left pulley 21, a right pulley 22, an endless belt 23, and a carriage motor 24.

Here, the left pulley 21 is located to the left of the left end of the guide rail 18, and the right pulley 22 is located to the right of the right end of the guide rail 18.

The left pulley 21 and the right pulley 22 are fixed to the support wall 16, and the belt 23 is wrapped around the left pulley 21 and the right pulley 22.

Furthermore, in this embodiment, the carriage motor 24 is connected to the right pulley 22, but it may also be connected to the left pulley 21.

In this embodiment, the carriage motor 24 is driven, causing the right pulley 22 to rotate, which in turn causes the belt 23 to travel between the left pulley 21 and the right pulley 22.

The carriage 32 is attached to the belt 23 so as to be slidably engaged with the guide rail 18.

The carriage 32 is positioned above the table 48. The carriage motor 24 drives the belt 23, causing the carriage 32 to move in the main scanning direction. As a result, the inkjet head 34 and light irradiation devices 80L and 80R mounted on the carriage 32 also move in the main scanning direction.

The inkjet head 34 is configured to include a pigment inkjet head 34a equipped with a pigment ink ejection nozzle for ejecting pigment ink, and a pigment-free inkjet head 34b equipped with a pigment-free ink ejection nozzle for ejecting non-pigment ink.

More specifically, in the main scanning direction, the pigment inkjet head 34a is positioned on the right, and the pigment-free inkjet head 34b is positioned on the left.

Here, the pigment inkjet head 34a includes, as pigment ink ejection nozzles, a color ink ejection nozzle 34a-1 for ejecting black (K) process color ink, a color ink ejection nozzle 34a-2 for ejecting yellow (Y) process color ink, a color ink ejection nozzle 34a-3 for ejecting red (M) process color ink, and a color ink ejection nozzle 34a-4 for ejecting blue (C) process color ink.

Furthermore, the pigment-free inkjet head 34b includes clear ink ejection nozzles 34b-1 and 34b-2 for ejecting clear ink (Cl), a pigment-free ink, and primer ejection nozzles 34b-3 and 34b-4 for ejecting primer (Pr).

These color ink ejection nozzles 34a-1, 34a-2, 34a-3, 34a-4, clear ink ejection nozzles 34b-1, 34b-2, and primer ejection nozzles 34b-3, 34b-4 are each configured as nozzle rows with multiple nozzles arranged in the sub-scanning direction.

Furthermore, the interiors of the color ink ejection nozzles 34a-1, 34a-2, 34a-3, 34a-4, the clear ink ejection nozzles 34b-1, 34b-2, and the primer ejection nozzles 34b-3, 34b-4 are set to negative pressure (a pressure lower than atmospheric pressure).

In this embodiment, for example, photocurable inks are used as process color inks, clear inks, and primers. Such photocurable inks include, for example, UV-curable inks that harden when exposed to ultraviolet light.

Here, process color ink, which is a pigment ink, is used to form a printed image on media 5. Such process color inks contain a colorant such as a pigment, a photopolymerizable monomer, and a photopolymerization initiator system, and optionally contain various other additives, such as photosensitizers, polymerization inhibitors, scavengers, antioxidants, UV absorbers, plasticizers, surfactants, leveling agents, thickeners, dispersants, defoamers, preservatives, and solvents.

Furthermore, clear ink, which is a pigment-free ink, is dispensed onto the surface of process color inks and white inks (white inks contain pigments; white inks will be described in detail later), forming a topcoat that acts as an overcoat layer covering the process color inks and white inks. Such clear inks do not contain colorants such as pigments, but contain photopolymerizable monomers and photopolymerization initiators, and, if necessary, various additives similar to those found in process color inks.

Furthermore, primers are used to improve the adhesion between media 5 and process color inks or white inks. These primers do not contain colorants such as pigments, but contain photopolymerizable monomers and photopolymerization initiators, and, if necessary, various additives similar to those found in process color inks. Primer colors include, for example, transparent, white, and gray.
The light irradiation devices 80L and 80R are devices that irradiate light (for example, ultraviolet light) onto the photocurable ink (for example, ultraviolet ink) dispensed onto the media 5.

In this embodiment, the process color ink, clear ink, and primer, which are photocurable inks, are UV-curable inks that harden when exposed to ultraviolet light. Furthermore, UV irradiation lamps are used as the light irradiation devices 80L and 80R.

The light irradiation device 80L is positioned to the left of the pigment-free inkjet head 34b, while the light irradiation device 80R is positioned to the right of the pigment inkjet head 34a. These light irradiation devices 80L and 80R are fixed to the carriage 32.

Therefore, the light irradiation devices 80L and 80R can move along the guide rail 18 via the carriage 32 in the main scanning direction as the carriage moves.

The front edge 80a of the light irradiation devices 80L and 80R is located further forward than the furthest forward nozzle positions of the color ink ejection nozzles 34a-1, 34a-2, 34a-3, and 34a-4 in the pigment inkjet head 34a, and the clear ink ejection nozzles 34b-1, 34b-2 and primer ejection nozzles 34b-3 and 34b-4 in the pigment-free inkjet head 34b.

On the other hand, the rear edge 80b of the light irradiation devices 80L and 80R is located further back than the furthest rear nozzle positions of the color ink ejection nozzles 34a-1, 34a-2, 34a-3, and 34a-4 in the pigment inkjet head 34a, and the clear ink ejection nozzles 34b-1, 34b-2 and primer ejection nozzles 34b-3 and 34b-4 in the pigment-free inkjet head 34b.

Therefore, the light irradiation devices 80L and 80R can irradiate light onto the process color ink, clear ink, and primer ejected from the color ink ejection nozzles 34a-1, 34a-2, 34a-3, and 34a-4 of the pigment inkjet head 34a, and the clear ink ejection nozzles 34b-1, 34b-2, and primer ejection nozzles 34b-3, and 34b-4 of the non-pigment inkjet head 34b, over overlapping areas in the transport direction of the table 48.
Next, the table moving mechanism 38 is a mechanism that moves the table 48 of the table unit 40 in the sub-scanning direction.

The table unit 40 comprises a table 48, a table carriage 47 that supports the table 48 so as to be movable in the sub-scanning direction, and a heating device 96 positioned directly beneath the table 48 within the table carriage 47.

This table carriage 47 is supported by the first slide rail 51 and the second slide rail 52.

The table 48 is formed in a rectangular shape, with a length in the sub-scanning direction shorter than the length in the main scanning direction, and the media 5 is placed on its upper surface.

Furthermore, the length of table 48 in the sub-scanning direction may be longer than the length in the main scanning direction, or the lengths in the sub-scanning direction and the main scanning direction may be the same.

These tables 48 are positioned below the support wall 16 and below the inkjet head unit 30, and are configured to be movable in the sub-scanning direction by the moving device 41.

The moving device 41 is positioned on the base member 60 and comprises a front pulley 42, a rear pulley 43, an endless belt 44, and a drive motor 45.

Here, the front pulley 42 is provided on the front side of the bottom wall 61 of the base member 60, while the rear pulley 43 is provided on the rear side of the bottom wall 61.

The belt 44 is wrapped around the front pulley 42 and the rear pulley 43, and the drive motor 45 is connected to the rear pulley 43. However, the drive motor 45 may also be connected to the front pulley 42.

In this embodiment, the drive motor 45 is driven, causing the rear pulley 43 to rotate, which in turn causes the belt 44 to travel between the front pulley 42 and the rear pulley 43.

Since the table carriage 47 of the table unit 40 is attached to the belt 44, when the belt 44 is driven by the drive motor 45, the table unit 40 moves along the first slide rail 51 and the second slide rail 52 in the sub-scanning direction.

In other words, the moving device 41 can move the table 48 back and forth in the sub-scanning direction (i.e., the forward and reverse directions).

Here, Figure 5 shows the state where the table 48 is located at the furthest downstream side, i.e., the furthest forward side, in the sub-scanning direction, and Figure 6 shows the state where the table 48 is located at the furthest upstream side, i.e., the furthest rear side, in the sub-scanning direction.

In other words, the table 48 can be transported by the moving device 41 in the forward direction from the upstream side to the downstream side in the sub-scanning direction, and can also be transported by the moving device 41 in the reverse direction from the downstream side to the upstream side in the sub-scanning direction.

Note that in Figures 5 and 6, the carriage movement mechanism 20 and other components have been omitted from the illustration to improve the visibility of the drawings.
Furthermore, the inkjet printer 10 includes an ink cartridge storage section 19, which stores ink and houses ink cartridges (not shown) connected to the inkjet head 34.

This ink cartridge housing 19 is located at the rear of the main body frame 14, on the left wall 62 of the base member 60.

In this embodiment, the case where three ink cartridge storage units 19 are arranged in the main scanning direction is shown, but the number of ink cartridge storage units 19 is not limited to three.

Furthermore, the ink cartridge is configured to be inserted into the ink cartridge housing 19 through an opening 19H formed in the left base wall 15L of the main frame 14.

Next, the maintenance device 70 includes a wiping device that wipes the nozzle surface where the pigment ink ejection nozzle of the pigment inkjet head 34a is located and the nozzle surface where the non-pigment ink ejection nozzle of the non-pigment inkjet head 34b is located, and a cleaning device that forcibly sucks ink from the pigment ink head ejection nozzle of the pigment inkjet head 34a and the non-pigment ink ejection nozzle of the non-pigment inkjet head 34b.

The maintenance device 70 is mounted on the right wall 63 of the base member 60, in front of the main frame 14.

Furthermore, the maintenance device 70 is positioned to the right of the table unit 40 and below the inkjet head unit 30.

The front end 70F of the maintenance device 70 is located downstream in the sub-scanning direction, i.e., forward, than the upstream end 48B of the table 48 in the sub-scanning direction when the table 48 is at its most downstream position in the sub-scanning direction.

The inkjet printer 10 is equipped with a partition wall 90 to restrict access from outside the movement space of the table 48 (for example, on the left wall 62 of the base member 60) to inside the movement space of the table 48 (for example, on the bottom wall 61 of the base member 60).

This partition wall 90 is composed of a plate-like member and is located below the support wall 16, and is positioned to the side of the table 48 in the main scanning direction (to the left in this embodiment).

Furthermore, as described above, the inkjet printer 10 is equipped with a control device 92, and the operator can control the operation of the inkjet printer 10 by operating various controls provided on the operation panel 94.

In other words, although detailed illustrations are omitted, the control panel 92 is equipped with various controls for performing operations, including controls for selecting print data when printing to media 5, and a display unit for showing the operation status of said controls.

(II) Description of the printing method of the inkjet printer according to the present invention

In the above configuration, the inkjet printer 10's overall operation is controlled by the control device 92. However, since the general operation of the inkjet printer 10 when printing on the media 5 can be handled using the conventional techniques disclosed in the patent documents cited above, a detailed explanation of that operation will be omitted. Therefore, the following explanation will focus only on matters related to the implementation of the present invention, with reference to Figures 8(a)(b) to 10.

Figures 8(a) and 8(b) show schematic diagrams illustrating the printing method of the inkjet printer according to the present invention.

Furthermore, Figure 9 shows an explanatory diagram illustrating the results of an outdoor weather resistance test of printed materials (outputs) printed using the inkjet printer printing method according to the present invention.

Furthermore, Figure 10 shows an explanatory diagram illustrating the results of comparative experiments in outdoor weather resistance tests.

The inkjet printer printing method according to the present invention involves the following steps: While irradiating with ultraviolet light using light irradiation devices 80L and 80R, process color ink, which is an ultraviolet-curable pigment ink, is ejected from the pigment ink ejection nozzle of the pigment inkjet head 34a onto the media 5 placed on the table 48. During the transport operation in which the table 48 is transported relative to the pigment ink ejection nozzle, clear ink, which is an ultraviolet-curable pigment-free ink, is ejected from the pigment-free ink ejection nozzle of the pigment-free inkjet head 34b onto the image formed by the process color ink ejected onto the media 5.

Specifically, in the inkjet printer printing method according to the present invention, while transporting the table 48 on which the media 5 is placed in the direction from the printing start position to the printing end position (forward direction) in the sub-scanning direction, the carriage 32 is moved relative to the media 5 in the main scanning direction, and ultraviolet light is irradiated by light irradiation devices 80L and 80R. Process color ink, which is pigment ink, is ejected from the pigment ink ejection nozzle of the pigment inkjet head 34a toward the media 5 to form an image 97, and clear ink, which is pigment-free ink, is ejected from the pigment-free ink ejection nozzle of the pigment-free inkjet head 34b toward the image 97 to form a top coat (see Figure 8(a)).

As a result, an image 97 is formed on the media 5 using process color ink, which is a pigment ink, and a topcoat 98 is formed on the image 97 formed on the media 5 using clear ink, which is a pigment-free ink (see Figure 8(b)).

In other words, in the inkjet printer printing method according to the present invention, during the same transport operation as when the carriage 32 is transported in the main scanning direction to form an image 97 on the media 5 using process color ink, clear ink is ejected from the pigment-free ink ejection nozzle of the pigment-free inkjet head 34b onto the image 97 formed on the media 5.

This results in a state where the process color ink and clear ink are mixed to some extent on the media 5. Therefore, the effects of the pigments in the process color ink extend to the topcoat formed by the clear ink. As a result, even if the media 5, on which the printed image 97 and topcoat 98 are formed, is placed outdoors and exposed to sunlight and rain, the occurrence of cracks in the topcoat over time is suppressed.

Here, since pigments absorb light energy, it is known that including pigment particles in the ink is effective in improving light resistance. Therefore, topcoats formed with clear ink that does not contain pigment are prone to cracking.

Furthermore, the inclusion of pigments makes it difficult for the crosslinking density to become high, resulting in a less rigid coating film. This is known to reduce the likelihood of cracking.

However, the inkjet printer printing method according to the present invention differs from the conventional printing method described in the "Background Art" section (the conventional printing method involves printing an image with process color ink, then withdrawing the media, and subsequently printing a top coat with clear ink). Because the process color ink (pigment ink) and the clear ink (pigment-free ink) are printed onto the media 5 at the same time without withdrawing the media 5, a state in which the process color ink (pigment ink) and the clear ink (pigment-free ink) are mixed can be created.

In other words, because the clear ink is printed on the image 97 formed on the media 5 with process color ink before the image 97 has completely hardened, a state is created on the media 5 where the process color ink and the clear ink are mixed. This allows the weather-resistant effect of the pigments in the process color ink to extend to the topcoat 98 formed by the clear ink, thereby suppressing the occurrence of cracks in the topcoat 98.

Here, according to the test results of an outdoor weather resistance test conducted by the present inventor (using the same method as described in the "Background Art" section above), when the peak illuminance of ultraviolet irradiation by the light irradiation devices 80L and 80R was set to 1200 mW/ ^cm² to 1800 mW/ ^cm² , the irradiation time for one transport of the pigment inkjet head 34a and the non-pigment inkjet head 34b in the main scanning direction was set to 0.036 sec, and the cumulative light amount for one transport was 43 mJ/ ^cm² to 65 mJ/ ^cm² , no cracks were observed after 1000 hours from the start of the outdoor weather resistance test, as shown in Figure 9.

Furthermore, while a higher peak intensity of UV irradiation increases the curing rate of pigment ink, if the curing rate of pigment ink becomes too high, mixing between the pigment ink (e.g., process color ink) and the pigment-free ink (e.g., clear ink) will not proceed properly, making the topcoat formed by the pigment-free ink more prone to cracking.

For example, according to the test results of an outdoor weather resistance test conducted by the present inventor (using the same method as described in the "Background Art" section above), when the peak illuminance of ultraviolet irradiation by the light irradiation devices 80L and 80R was set to 2400 mW/ ^cm² , the irradiation time for one transport of the pigment inkjet head 34a and the non-pigment inkjet head 34b in the main scanning direction was set to 0.036 sec, and the cumulative light amount for one transport was 86 mJ/ ^cm² , when the condition was observed 750 hours after the start of the outdoor weather resistance test, crack formation was observed as shown in Figure 10.

For these reasons, it is preferable that the peak illuminance during ultraviolet irradiation be between 1200 mW/ ^cm² and 1800 mW/ ^cm² .

Here, cracks in the topcoat can also occur due to internal strain (internal stress) caused by repeated expansion and contraction of the printed material (final product) due to temperature changes. However, after printing the topcoat, for example, by heating the printed media 5, which is the final product, to a temperature of 60°C to 80°C using a heating device 96, residual monomers and photopolymerization initiators in the media 5 are volatilized. This reduces the internal stress difference between the areas where volatilization has progressed and those where it has not, thereby suppressing cracks caused by internal stress.

(III) Explanation of the effects and advantages of the inkjet printer printing method according to the present invention.

As described above, according to the inkjet printer printing method of the present invention, in a printed product (deliverable) in which a top coat is formed by printing a top coat with a light-curable, pigment-free ink for topcoat, such as clear ink, on top of an image formed by printing a pigment ink such as a light-curable Proscolor ink, even if the printed product is placed outdoors and exposed to sunlight and rain, it is possible to suppress the occurrence of cracks in the top coat formed with the pigment-free ink over time.
(IV) Description of other embodiments and variations

The embodiments described above are merely illustrative, and the present invention can be implemented in various other forms. That is, the present invention is not limited to the embodiments described above, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention.

For example, the above-described embodiment may be modified as shown in (IV-1) to (IV-6) below.

(IV-1) In the embodiments described above, Proscolor ink was used as an example of pigment ink, and clear ink was used as an example of non-pigment ink. However, pigment inks and non-pigment inks are not limited to these. For example, white ink may be used as the pigment ink.

Here, the white ink contains a colorant such as a white pigment, a photopolymerizable monomer, and a photopolymerization initiator system, and optionally includes other various additives, such as photosensitizers, polymerization inhibitors, scavengers, antioxidants, UV absorbers, plasticizers, surfactants, leveling agents, thickeners, dispersants, defoamers, preservatives, and solvents.

(IV-2) In the above-described embodiment, detailed explanations were omitted, but the pigment ink ejection nozzle and the non-pigment ink ejection nozzle were provided on separate inkjet heads. However, this is not the only configuration. For example, an inkjet head equipped with both pigment ink ejection nozzles and non-pigment ink ejection nozzles may be used.

(IV-3) In the embodiments described above, detailed explanations have been omitted, but the inkjet printer 10 may complete printing one band in a single movement of the carriage 32 in the main scanning direction, i.e., in a single pass (main scanning operation), or it may complete printing one band in multiple passes.

(IV-4) In the above-described embodiment, the case in which the printed material (output) is heated by a heating device 96 provided in the inkjet printer 10 was explained, but of course, it is not limited to this. For example, a heating means such as a heating device may be prepared separately from the inkjet printer 10, and the printed material (output) may be heated by such a heating means.

(IV-5) In the embodiments described above, the case where ultraviolet curing is used as the photocuring property was explained. However, the wavelength of light used for photocuring is not limited to ultraviolet light, and of course, light of an appropriate wavelength may be used depending on the relationship between the ink and the lighting device.

(IV-6) Of course, the embodiments described above, as well as the various other embodiments and modifications shown in (IV-1) to (IV-5) above, may be combined as appropriate.

This invention is suitable for use in inkjet printers that print by ejecting pigment-containing inks, such as process color inks and white inks, for forming images on media, and pigment-free inks, such as clear inks for topcoats, which are ejected onto the surface of the pigment-containing inks and act as an overcoat layer to coat the surface of the image formed by the pigment-containing inks, thereby providing gloss.

5 Media 10 Inkjet printer 12 Main case 13C Front cover 13L Left cover 13R Right cover 13W Window 14 Main frame 14H Opening 15L Left base wall 15R Right base wall 16 Support wall 18 Guide rail 19 Ink cartridge storage area 19H Opening 20 Carriage movement mechanism (transportation means)
21, 22 Pulley 23 Belt 24 Carriage motor 30 Inkjet head unit 32 Carriage 34 Inkjet head 34a Pigment inkjet head 34a-1, 34a-2, 34a-3, 34a-4 Color ink ejection nozzle 34b Pigment-free inkjet head 34b-1, 34b-2 Clear ink ejection nozzle 34b-3, 34b-4 Primer ejection nozzle 38 Table moving mechanism (transportation means)
40 Table unit 41 Moving device 42, 43 Pulley 44 Belt 45 Drive motor 47 Table carriage 48 Table 48B End 51 First slide rail 52 Second slide rail 60 Base member 61 Bottom wall 62 Left wall 63 Right wall 64 Left side wall 65 Right side wall 70 Maintenance device 70F Front end 80L, 80R Light irradiation device (light irradiation means, ultraviolet irradiation lamp)
80a Front edge 80b Rear edge 90 Partition wall 92 Control device 94 Operation panel 96 Heating device 97 Image 98 Top coat 100 Media 102 Table 104 First inkjet head 106 Image 108 Second inkjet head 110 Top coat

Claims (2)

A table for placing media,
A pigment ink dispensing nozzle for dispensing photocurable pigment ink onto the media placed on the table,
A pigment-free ink dispensing nozzle for dispensing a photocurable pigment-free ink onto the media placed on the table,
A conveying means for moving the pigment ink ejection nozzle and the non-pigment ink ejection nozzle and the table relative to each other, thereby conveying the media relative to the pigment ink ejection nozzle and the non-pigment ink ejection nozzle,
A printing method for an inkjet printer, comprising a light irradiation means for irradiating light onto the pigment ink and the non-pigment ink ejected onto the media,
When the pigment ink is discharged from the pigment ink discharge nozzle onto the media placed on the table, during the media transport operation by the transport means, the non-pigment ink is discharged from the non-pigment ink discharge nozzle onto the pigment ink discharged onto the media during the transport operation.
The peak illuminance of ultraviolet irradiation by the aforementioned light irradiation means is 1200 mW/ ^cm² to 1800 mW/cm² ^.
A printing method for an inkjet printer, characterized by the following features. A table for placing media,
A pigment ink dispensing nozzle for dispensing photocurable pigment ink onto the media placed on the table,
A pigment-free ink dispensing nozzle for dispensing a photocurable pigment-free ink onto the media placed on the table,
A conveying means for moving the pigment ink ejection nozzle and the non-pigment ink ejection nozzle and the table relative to each other, thereby conveying the media relative to the pigment ink ejection nozzle and the non-pigment ink ejection nozzle,
A light irradiation means for irradiating light onto the pigment ink and the non-pigment ink ejected onto the media.
A printing method for an inkjet printer having,
When the pigment ink is discharged from the pigment ink discharge nozzle onto the media placed on the table, during the media transport operation by the transport means, the non-pigment ink is discharged from the non-pigment ink discharge nozzle onto the pigment ink discharged onto the media during the transport operation.
A printing method for an inkjet printer, characterized by heating the media on which the non-pigment ink has been ejected onto the pigment ink at a temperature of 60°C to 80°C.