JP7213041B2 - printing method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printing technique for printing by transferring a print pattern formed on an intermediate transfer body to a material to be printed using photocurable ink.

Among printing inks, a photocurable ink prepared by containing a polymer material and a photopolymerization initiator can be cured more rapidly by light irradiation for a short period of time than by drying or heating. Therefore, the printed material immediately after printing can be immediately supplied to the next process, which is suitable for high-speed printing. For example, the technique described in Patent Document 1 relates to a printing method that realizes multicolor printing by superimposing print patterns of multiple colors formed on the surface of a blanket (intermediate transfer member) on the surface of a printing material. In this technology, in order to prevent color mixing of inks and uncured ink on the printed material from being retransferred to the blanket, light curing ink is used, and the ink is cured by irradiating ultraviolet rays for each color printed. hardening it.

Further, in this technique, a member for shielding light is arranged between the light source and the blanket in order to prevent the ink on the blanket from being cured by being irradiated with light.

Photocurable inks containing a plurality of types of photopolymerization initiators have also been proposed. For example, in Patent Document 2, in a printing system that combines inkjet printing and photocuring, two or more types of polymerization initiators with different absorption wavelengths are used for the purpose of improving the adhesion and followability of the ink film to the substrate. The combined use of agents is described. However, in the case of ink-jet printing in which ink is directly ejected onto a printed material, the problem of retransfer of the ink described above does not occur in principle.

JP 2017-196887 A (eg paragraph 0092) JP 2003-251910 A (eg paragraph 0078)

The technique described in Patent Document 1 mentioned above includes the following problems to be solved. First, it cannot be said that the light emitted from the light source to the ink on the blanket is sufficiently shielded. This is because it cannot block light incident on the blanket surface due to reflection or transmission from the substrate. In particular, when the material to be printed is a transparent material such as glass, it is inevitable that the light reflected on the surface or transmitted through the material will reach the surface of the blanket. When the ink on the blanket is irradiated with such light, the surface of the ink is cured, thereby deteriorating the transferability to the printing material.

In order to obtain high adhesion between layers in multilayer printing in which a plurality of print patterns are superimposed on a printed material, it is desirable to superimpose in a state where the viscosity of the transferred ink is maintained at a certain level or less. On the other hand, if the ink transferred to the printing material remains in a low viscosity state, the ink on the printing material may be re-transferred to the intermediate transfer member or surrounding members when it comes into contact with those members. There is In order to prevent such retransfer, it is desirable that at least the surface of the transferred ink has a sufficiently high viscosity. In other words, the ink after transfer is required to maintain an appropriate viscosity that is higher than the viscosity immediately after transfer and lower than the viscosity in the completely cured state. However, with the technique described in Patent Document 1, it is difficult to control such a cured state.

Japanese Patent Application Laid-Open No. 2002-200010 relating to inkjet printing does not disclose anything that contributes to the resolution of such problems.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and is capable of appropriately controlling the viscosity of photocurable ink after being transferred to an object to be printed. It is an object of the present invention to provide a technology capable of suppressing the photocuring of the ink and performing good multi-layer printing.

In one aspect of the printing method according to the present invention, in order to achieve the above object, a first step of forming a print pattern with photocurable ink on the surface of an intermediate transfer member, and bringing a backup member into contact with the surface to be printed. a second step of bringing the intermediate transfer body into contact with the substantially cylindrical printed material supported by the intermediate transfer body to transfer the print pattern on the surface of the intermediate transfer body to the printed surface ; a third step of increasing the viscosity of the photo-curable ink by irradiating a first light onto the region before coming into contact with the backup member after being separated from the intermediate transfer member; and a fourth step of curing the photocurable ink by irradiating the second light.

Here, the photocurable ink includes a polymer material that is hardened by polymerization, a first photopolymerization initiator that reacts with light of a first wavelength contained in the first light, and and a second photopolymerization initiator that does not react and reacts to light of a second wavelength shorter than the first wavelength and contained in the second light, wherein the first light is the second light. The second light does not substantially contain any wavelength components, and the intensity of the second wavelength component of the second light is greater than that of the first light .

In the present invention, the photopolymerization initiator "reacts to light" means that the photopolymerization initiator undergoes a chemical change that accelerates the polymerization reaction of the polymer material upon exposure to light. Further, "the first light does not substantially contain the second wavelength component" means that the influence of the first light on the second photopolymerization initiator that reacts with the second wavelength component can be ignored. means. In other words, the second photopolymerization initiator is not changed by the first light irradiation.

In the invention configured as described above, the photocurable ink (hereinafter, sometimes simply referred to as "ink") transferred from the intermediate transfer member to the printing material in the first and second steps is transferred to the third and second steps. Light is applied in four steps. Among these, in the third step, only the first photopolymerization initiator reacts, and the second photopolymerization initiator does not react. As a result, the ink becomes less polymerized and its viscosity increases.

Even if the amount of exposure in the third step is increased and the first photopolymerization initiator is completely reacted, the second photopolymerization initiator is not substantially reacted. Therefore, the maximum viscosity of the ink that can be reached in the third step can be controlled by the content of the first photopolymerization initiator, and there is no need to adjust the viscosity by the amount of exposure. Therefore, it is easy to maintain an appropriate viscosity of the ink after the third step with good controllability.

Moreover, even if the ink on the intermediate transfer member is irradiated with the first light, it is possible to reliably avoid an increase in the viscosity of the ink beyond a certain level. Therefore, it is possible to avoid a significant deterioration in the transferability of the ink from the intermediate transfer member to the printing material.

On the other hand, in the fourth step, the ink is further cured by the second photopolymerization initiator that reacts with the irradiation of the second light containing more of the second wavelength component. As a result, the ink after transfer can be cured to a required hardness.

Thus, in the present invention, the ink after being transferred to the printing material can be maintained at an intermediate viscosity that does not reach complete curing, and the viscosity at that time can be adjusted by adding the first photopolymerization initiator. Controllable by quantity. Therefore, by maintaining an appropriate viscosity of the photocurable ink after transfer to the substrate, it is possible to suppress retransfer to the intermediate transfer body and to suppress photocuring of the ink on the intermediate transfer body. can. In addition, it is possible to achieve a good state of adhesion between layers during multi-layer printing. Further, the ink can be cured more reliably by additional irradiation using the second light.

According to the present invention, two types of photocuring initiators having different reaction wavelengths are contained in the ink, the viscosity is increased by irradiating the first light with a relatively long wavelength, and the second light with a shorter wavelength is applied. to cure the ink. Therefore, it is possible to control the viscosity of the ink after the irradiation of the first light, suppress retransfer to the intermediate transfer body, etc., and suppress photocuring of the ink on the intermediate transfer body. . Moreover, multilayer printing can also be carried out satisfactorily.

1 is a schematic diagram showing a schematic configuration example of a printing system capable of implementing a printing method according to the present invention; FIG. FIG. 3 is a diagram showing configurations of a plate stage unit and an ink filling unit; FIG. 4 is a diagram showing the configuration of a bottle holding unit; 1 is a flow chart showing an embodiment of a printing method according to the present invention; 5 is a diagram schematically showing the movement of each part in the process of executing the printing method of FIG. 4; FIG. 5 is a diagram schematically showing the movement of each part in the process of executing the printing method of FIG. 4; FIG. FIG. 10 is a diagram schematically showing movement of each part in overprinting; It is a figure explaining the problem of the leak of the light to a blanket. FIG. 3 shows the ink and UV light used in this embodiment; FIG. 4 is a diagram schematically showing a mechanism of ink curing by light irradiation;

FIG. 1 is a schematic diagram showing an example of a schematic configuration of a printing system capable of implementing a printing method according to the present invention. The printing system 100 is a system for printing on the surface of an object to be printed having a substantially cylindrical outer shape, such as a glass bottle or a resin bottle, more specifically, on the side surface which is a cylindrical surface. Here, an XYZ orthogonal coordinate system is set as shown in FIG. 1 in order to uniformly show the directions in each figure. For example, the XY plane can be considered as the horizontal plane and the Z axis as the vertical axis. In the following, the (-Z) direction is defined as vertically downward.

The printing system 100 includes a plate stage unit 1 , an ink filling unit 2 , a transfer unit 3 , a temporary curing unit 4 , a final curing unit 5 and a bottle holding unit 6 . These units are arranged in the above order from the (-Y) direction side to the (+Y) direction side. The printing system 100 further comprises a control unit 9 that controls the operation of each of these units.

Printing processing in the printing system 100 includes:
(1) Formation of an ink pattern using photocurable ink by the plate stage unit 1 and the ink filling unit 2;
(2) transferring the ink pattern to the transfer unit 3;
(3) transfer of the ink pattern from the transfer unit 3 to the substrate to be printed;
(4) ink curing by light irradiation from the temporary curing unit 4 and the main curing unit 5;
contains each step of In the following, the case where the object to be printed is a cylindrical glass bottle or a resin bottle (hereinafter simply referred to as "bottle") B will be taken up, and the configuration and operation of each part of the apparatus will be described in sequence.

FIG. 2 is a diagram showing the configuration of the plate stage unit and the ink filling unit. The plate stage unit 1 includes a stage 11 on which a plate (for example, an intaglio plate) P for forming an ink pattern is placed. A stage 11 is attached to a base portion 13 via an alignment mechanism 12 . The alignment mechanism 12 moves the stage 11 in XYZ directions and rotation directions around the Z axis in accordance with a control command from the control unit 9 . For example, a crossed roller bearing mechanism can be used as the alignment mechanism 12 .

The base portion 13 is engaged with a guide rail 14 extending in the Y direction from the pedestal of the printing system 100 and is reciprocally movable along the guide rail 14 in the Y direction. More specifically, a driving mechanism (not shown) controlled by the control unit 9 is connected to the base portion 13. By operating the driving mechanism, the base portion 13 moves in the (−Y) direction and the (+Y) direction. move to The position closest to the (−Y) direction (the position indicated by the solid line in FIG. 2) in the movable range of the base portion 13 is the home position of the base portion 13 .

Alignment cameras 15, 15 are arranged above the stage 11 positioned at the home position. Alignment cameras 15 and 15 take images of the periphery of the plate P placed on the stage 11 or the alignment marks provided on the upper surface of the plate P, and send image data to the control unit 9 . The control unit 9 detects the position of the plate P on the stage 11 and operates the alignment mechanism 12 as necessary to adjust the position of the plate P to the proper position.

An ink filling unit 2 and a transfer unit 3 are provided along the path along which the base portion 13 moves in the (+Y) direction from the home position. The ink filling unit 2 has a nozzle 21 facing the upper surface of the plate P placed on the stage 11 passing directly below. The nozzles 21 are supplied with photocurable ink (hereinafter sometimes simply referred to as “ink”) from an ink supply section 22 controlled by the control unit 9 . The supplied ink is ejected from ejection openings provided at the lower ends of the nozzles 21 and applied to the upper surface of the plate P. As shown in FIG.

Photocurable ink is made up of a pigment as a color developer, a polymer material (including at least one of monomers and oligomers) that forms a strong polymer layer through polymerization, and active species that are generated by chemical changes upon exposure to light. It contains a photopolymerization initiator that accelerates the polymerization reaction of the polymer material.

A doctor blade 23 is provided on the (+Y) direction side of the nozzle 21 . The doctor blade 23 rubs the surface of the plate P supplied with ink to scrape off the ink. As a result, the concave portions provided on the upper surface of the plate P are filled with the ink, and the remaining surplus ink is removed to form an ink pattern.

The plate P filled with ink in this way moves further in the (+Y) direction and reaches the arrangement position of the transfer unit 3 . As shown in FIGS. 1 and 2, the transfer unit 3 includes a blanket roll 30 and a motor 33 for rotating it. More specifically, the blanket roll 30 includes a blanket cylinder 31, which is, for example, a metal cylinder, and a blanket 32 wrapped around its surface, and has a generally cylindrical shape as a whole. The blanket roll 30 is rotatably supported by a frame (not shown) and driven to rotate about a central axis indicated by a dashed line in FIG. 1 by a motor 33 controlled by the control unit 9 .

The blanket 32 is made of an elastic resin material, such as silicon resin, and is capable of carrying an ink pattern on its surface. The blanket 32 has a thickness sufficiently larger than the irregularities that may occur on the surface of the bottle B, which is the object to be printed. As shown in FIG. 2, when the plate P placed on the stage 11 passes through the position directly below the blanket roll 30, the surface of the blanket 32 contacts the upper surface of the plate P. As shown in FIG. At this time, the ink filling the depressions of the plate P migrates to the surface of the blanket 32 . The ink pattern on the plate P is thus transferred to the blanket 32 .

The ink pattern thus once transferred (primary transfer) to the blanket 32 is secondarily transferred to the surface of the bottle B, which is the final object to be printed. Thus, the blanket 32 functions as an intermediate transfer member that temporarily carries the ink pattern to be finally transferred onto the substrate.

FIG. 3 is a diagram showing the structure of the bottle holding unit. More specifically, FIG. 3(a) is a side view of the bottle holding unit 6 as seen in the Y direction, and FIG. 3(b) is a side view of the bottle holding unit 6 as seen in the X direction.

The bottle holding unit 6 holds the bottle B, which is an object to be printed whose side surface B2 is the surface to be printed, so as to be rotatable around its central axis. As shown in FIG. It has a support frame 60 combined with a pair of side plates 62, 62 extending upwardly from the base. A connecting member 621 is rotatably attached to one of the side plates 62 . A spring member 622 is provided on the other side plate 62 . While the mouth portion B1 of the bottle B is connected to the connecting member 621, the bottom portion B3 of the bottle B is urged toward the mouth portion B1 by the spring member 622, so that the central axis of the bottle B is substantially horizontal. It is held in an upright position. Also, the connecting member 621 is rotationally driven by a motor (not shown), and can rotate the bottle B around its central axis.

As shown in FIGS. 1 and 3, the bottle B is supplementarily supported by backup rolls 631 to 634 whose axial direction is the X direction. Backup rolls 631 to 634 are rotatably supported on both side plates 62, respectively. Of these, a pair of backup rolls 631 and 632 are provided below the bottle B, and by contacting the side surface B2 of the bottle B from below, restrict the displacement of the bottle B in the direction of gravity, that is, in the (-Z) direction. . Another pair of backup rolls 633 and 634 are provided on the (+Y) direction side of the bottle B, and are in contact with the (+Y) direction side surface of the bottle B to prevent displacement of the bottle B in the (+Y) direction. regulate. On the other hand, of the side faces B2 of the bottle B, the (-Y) direction side face is in a wide open state.

A bottom plate 61 of the support frame 60 is attached to a base portion 66 via an alignment mechanism 65 . The alignment mechanism 66 moves the support frame 60 in the XYZ directions and rotation directions around the Z axis in accordance with a control command from the control unit 9 . For example, a crossed roller bearing mechanism can be used as alignment mechanism 65 .

The base portion 66 is engaged with guide rails 67, 67 extending in the Y direction from the base of the printing system 100, and is reciprocally movable along the guide rails 67 in the Y direction. More specifically, a drive mechanism (not shown) controlled by the control unit 9 is connected to the base portion 66. By operating the drive mechanism, the base portion 67 moves in the (-Y) direction and the (+Y) direction. move to Therefore, the bottle B held by the bottle holding unit 6 is horizontally movable within a predetermined movable range in the Y direction.

As shown in FIG. 3(b), when the bottle holding unit 6 moves the bottle B to the vicinity of the (-Y) direction side end of its movable range, the (-Y) direction side surface of the bottle B is covered with the blanket 32. pressed against the surface of As a result, the ink pattern carried on the surface of the blanket 32 is transferred to the side surface B2 of the bottle B. As shown in FIG. Backup rolls 631 to 634 prevent the bottle B from being displaced due to the reaction force from the blanket 32 caused by pressing the bottle B against the blanket 32 .

Although not shown in FIG. 3, an alignment camera 68 (FIG. 6) is provided for detecting the position of the bottle B held by the bottle holding unit 6, as will be described later. ing. The control unit 9 operates the alignment mechanism 66 based on the imaging result of the alignment camera 68 to adjust the position of the bottle B, more specifically, the relative position of the bottle B with respect to the blanket 32 to an appropriate position.

As shown in FIG. 1 , the temporary curing unit 4 and the main curing unit 5 are arranged along the movement path of the bottle B by the bottle holding unit 6 . All of these are for curing the ink by irradiating light (ultraviolet light, UV light) to the ink pattern of the photocurable ink transferred to the bottle B. FIG. However, although the details will be described later, the functions of the two are different.

The temporary curing unit 4 does not completely cure the ink, but has a function of increasing the viscosity of the ink pattern transferred to the bottle B to a level that does not hinder the execution of the post-process. Therefore, the intensity of emitted light may be relatively low, and it is possible to use, for example, a light source equipped with an LED (Light Emitting Diode) that outputs ultraviolet rays. The temporary curing unit 4 irradiates the ink immediately after being transferred to the bottle B with light. Therefore, as shown in FIG. 3(b), it is arranged at a position facing the surface of the bottle B which is positioned so as to contact the surface of the blanket 32. As shown in FIG.

On the other hand, the main curing unit 5 has a function of more firmly curing the ink with increased viscosity. For this reason, a high-output light source such as a UV lamp is suitable as the light source. The main curing unit 5 is arranged at a position farther from the blanket 32 than the temporary curing unit 4 is. This is to avoid the strong light emitted from the main curing unit 5 from irradiating the ink pattern on the blanket 32 .

FIG. 4 is a flow chart showing an embodiment of a printing method according to the invention. 5 and 6 are diagrams schematically showing the movement of each part in the execution process of the printing method of FIG. More specifically, FIG. 4 shows an example of printing processing to which the printing method according to the invention is applied. 5 to 7, dotted line arrows indicate the direction of movement of the member. This printing process is realized by causing the control unit 9 to execute a pre-stored program and cause each part of the apparatus to perform a predetermined operation.

In this printing process, the plate P and the bottle B are set in the printing system 100 first. Specifically, the plate P is carried into the system and set on the stage 11 (step S101), and the alignment of the plate P is adjusted based on the imaging result of the alignment camera 15 (step S102). Subsequently, the stage 11 starts moving in the (+Y) direction, the photocurable ink IK is applied to the upper surface of the plate P from the nozzles 21 of the ink filling unit 2, and the surplus ink is scraped off by the doctor blade 23. , the printing plate is filled with ink (step S103). The stage 11 moves further and passes directly under the rotating blanket roll 60, thereby transferring the ink pattern formed on the plate P to the surface of the blanket 32 (step S104).

FIG. 5 schematically shows the state of each part from when the plate P is placed on the stage 11 to when it undergoes alignment adjustment and ink filling, and when the ink pattern is transferred to the blanket 32 . As shown in the lower part of FIG. 5, all the ink patterns IP formed on the plate P are finally transferred onto the blanket 32 .

In parallel with the process for the plate P as described above, the process for the bottle B is executed in the bottle holding unit 6 . That is, when the bottle B, which is the object to be printed, is set (step S105), as shown in FIG. 6, the alignment camera 68 takes an image of the bottle B, and the alignment of the bottle B is adjusted based on the imaged result (step S105). S106). Then, the bottle holding unit 6 moves in the (-Y) direction and brings the bottle B into contact with the surface of the blanket 32 (step S107).

As shown in FIG. 6, the ink pattern IP on the surface of the blanket 32 is sequentially transferred to the bottle B by the blanket 32 to which the ink pattern IP has been transferred and the bottle B rotating with each other while being in contact with each other. 5 shows the steps from carrying in the plate P to transferring the ink pattern to the blanket 32, and FIG. 6 shows the steps from carrying in the bottle B to transferring the ink to the bottle B. These steps are described as independent. However, in actual processing, the ink pattern transfer to the blanket 32 and the ink pattern transfer from the blanket 32 to the bottle B can be performed continuously in the same revolution of the blanket 32 .

Here, the surface of the bottle B is in contact with the backup rollers 631 to 634, and when the ink pattern IP reaches the contact position with the backup rollers 631 to 634 as the bottle B rotates, the uncured ink is transferred to the bottle B. to the backup rollers 631-634. Further, when the bottle B rotates one round or more, the ink pattern IP on the surface of the bottle B may be re-transferred onto the blanket 32 . These disturb the ink pattern on the surface of the bottle B and contaminate the blanket 32 and the backup rollers 631 to 634 with the ink.

In order to prevent this problem, a pre-curing process is performed by irradiating ultraviolet light with a relatively low exposure (step S108). That is, as shown in FIG. 6, the temporary curing unit 4 irradiates light (ultraviolet rays) UV1 toward the surface of the bottle B immediately after receiving the transfer of the ink pattern IP from the blanket 32 . As will be described later, the light UV1 emitted from the temporary curing unit 4 increases the viscosity of the ink by polymerizing a part of the polymer material contained in the ink, but does not cure the entire ink. have.

This increase in viscosity of the ink reduces the adhesion to other objects, and when the surface of the bottle B carrying the ink comes into contact with the backup rolls 631 to 634 or the blanket 32, the ink is transferred to them. is prevented. At the end of temporary curing, the ink is not completely cured. In order to completely harden this, a main hardening process is performed (step S109). As shown in the lower part of FIG. 6, the main curing process is performed by irradiating the bottle B with light (ultraviolet rays) UV2 from the main curing unit 5 while the bottle B is largely separated from the blanket 32 . The irradiation of the light UV2 at this time is performed with an exposure amount sufficient to completely cure the ink.

The bottle B thus printed is transported outside (step S110), and if there is a bottle to be printed next (YES in step S111), the process returns to steps S102 and S105 to adjust the alignment of the plate P and The above process is repeated from the carrying-in of the bottle B. If it is necessary to change the plate P, the process may return to step S101.

Next, the operation for overprinting will be described. There is a case where another ink pattern is superimposed and printed on the bottle B to which the ink pattern has already been transferred. For example, there are cases where it is desired to thicken the print layer by overlapping ink patterns of the same color, or where it is desired to perform multicolor printing by overlapping ink patterns of different colors.

When such overprinting is performed, it is preferable that the ink pattern already transferred to the bottle B is not completely cured. This is because when a new ink pattern layer is overlaid on a completely cured ink pattern layer, the adhesion between the layers may deteriorate. On the other hand, if the viscosity of the transferred ink pattern is too low, the inks of different colors may be mixed with each other, or the ink may be retransferred from the bottle B to the blanket 32, thereby degrading the print quality. end up

In the printing process of the present embodiment, it is possible to prevent these problems from occurring by setting the viscosity of the transferred ink to an appropriate value through the temporary curing described above. That is, by transferring a new ink pattern to the bottle B in which the transferred ink pattern is pre-cured, it is possible to carry out excellent overlapping printing of multiple layers. Specifically, it can be done as follows.

FIG. 7 is a diagram schematically showing the movement of each part in overprinting. First, consider the case where ink patterns of the same color are superimposed. If the circumferential length of the ink pattern transferred to the blanket 32 is greater than the circumferential length of the bottle B, the bottle B will rotate more than once before all the ink patterns are transferred, resulting in Then, the pattern transferred in the second round is superimposed on the pattern transferred in the first round.

That is, as shown in FIG. 7, the ink pattern IP2 remaining on the surface of the blanket 32 after the ink pattern IP1 is transferred in the first round of the bottle B is transferred to the ink pattern IP2 in the second round of the bottle B or later. will be transferred to the bottle B in the circulation of . At this time, a new ink pattern IP2 is transferred to a region of the surface of the bottle B to which the ink pattern IP1 has already been transferred, thereby realizing two-layer overprinting. By making the length of the plate P in the Y direction sufficiently larger than the circumference of the bottle B, such overprinting can be easily performed. In addition, in FIG. 7, the ink pattern IP1 transferred in the first round and the ink pattern IP2 transferred in the second round are shown with different densities in order to improve visibility in the drawing.

In this case, the ink immediately after transfer is irradiated with the light UV1 from the temporary curing unit 4 and is temporarily cured, so retransfer of the ink from the bottle B to the blanket 32 is prevented. In addition, since this ink is not completely cured, there is no problem with the adhesion to newly transferred ink. By performing the main curing process after the overprinting, the entire transferred ink patterns IP1 and IP2 can be completely cured. In this way, it is possible to perform overprinting with good quality.

On the other hand, when printing different colors or types of ink in layers, it is necessary to switch the plate P and the ink. In this case, the plate P and the ink may be switched in the printing system 100 of FIG. However, as many sets of plate stage unit 1, ink filling unit 2, transfer unit 3, and temporary curing unit 4 as the number of types of ink are prepared, and bottles B are transported between them. Sequential overprinting is advantageous in terms of productivity in continuous printing.

In this case also, at the stage where one type of ink is used to temporarily cure, multiple layers are formed by switching the bottle B and repeating the transfer process, and then the main curing process is performed collectively to overlap. Printing can be completed.

By the way, in this printing process, it is necessary to irradiate the ink immediately after it has been transferred to the bottle B with light for temporary curing. Therefore, it is necessary to arrange the temporary curing unit 4 in the vicinity of the blanket 32 . Due to this, the light UV1 emitted from the temporary curing unit 4 may leak and wrap around the blanket 32, and the ink carried on the blanket 32 may be exposed to light irradiation.

FIG. 8 is a diagram for explaining the problem of light leakage into the blanket. As shown in FIG. 8(a), in order to reduce the amount of light directly directed toward the blanket 32 from the temporary curing unit 4, an appropriate light shielding member S may be provided between the two. However, when the surface of the bottle B has light reflectivity, or when the material of the bottle B itself has light transparency, the light UV1 may enter the blanket 32 through the surface or inside of the bottle B. . Especially when the material of the bottle B is a transparent material, the effect is remarkable. Moreover, when the blanket 32 is made of silicone resin, it itself has a certain degree of ultraviolet transmittance. Such unexpected light irradiation may increase the viscosity of the ink on the blanket 32 .

If the ink transfer from the blanket 32 to the bottle B and the light irradiation to the transferred ink can be performed separately, the light irradiation on the blanket 32 is prevented until the transfer is completed. It is possible to avoid exposing the ink to light. However, since the productivity of such a printing process is low, as a practical matter, it is unavoidable that the transfer of ink from the blanket 32 to the bottle B and the light irradiation for temporary curing overlap even temporarily.

FIG. 8B is a diagram schematically showing the relationship between the amount of exposure and the viscosity of ink. As indicated by the solid line, the viscosity of the ink increases as the amount of exposure, which is represented by the product of the intensity of the irradiation light and the irradiation time, increases. At the stage of temporary curing, it is necessary to maintain a proper viscosity that is high enough to prevent retransfer of the ink to the blanket 32 or the like, and does not reach a viscosity that reduces adhesion between layers. However, if there is a possibility that light will enter the ink while it is carried by the blanket 32 as described above, it is practically impossible to control the viscosity of the ink by adjusting the exposure amount in the temporary curing process.

Therefore, as indicated by the dotted line, the ideal viscosity change is such that the ink viscosity does not increase even if the exposure amount is increased after the ink viscosity has increased to an appropriate viscosity by light irradiation. In order to realize such a viscosity change, in the present embodiment, the ink contains two types of polymerization initiators with different light absorption characteristics, and the spectral distribution between the temporary curing unit 4 and the main curing unit 5 is I am trying to generate different lights. Specifically, it is as follows.

FIG. 9 is a diagram showing the ink and UV light used in this embodiment. The photocurable ink of the present embodiment contains a first photopolymerization initiator that absorbs up to relatively long wavelengths and a second photopolymerization initiator that absorbs only light on the shorter wavelength side. ing. The light UV1 emitted from the temporary curing unit 4 is light containing a large amount of a component with a wavelength λ1 that is highly absorbed by the first photopolymerization initiator but is hardly absorbed by the second photopolymerization initiator. be done. Furthermore, it is desirable that the light UV1 substantially does not contain wavelength components that the second photopolymerization initiator exhibits absorption properties. In other words, it is desirable that the temporary curing light UV1 contains only components on the longer wavelength side than the absorption wavelength region of the second photopolymerization initiator.

On the other hand, the light UV2 emitted from the main curing unit 5 contains a large amount of the component of the wavelength λ2 that the second photopolymerization initiator exhibits high absorption and has a higher emission intensity. It is not essential that the first photoinitiator be absorptive at this wavelength, but in general materials with high absorptivity at longer wavelengths are also highly absorptive at shorter wavelengths. have sex.

In this way, although the first photopolymerization initiator reacts with the light UV1 for temporary curing, the second photopolymerization initiator does not react. Here, if the content of the first photopolymerization initiator in the ink is made sufficiently smaller than the amount required to cure the entire ink, even if the first photopolymerization initiator has all reacted, The ink does not cure completely. Therefore, the increase in viscosity saturates with respect to the increase in integrated exposure amount. The viscosity at this time can be controlled by the content of the first photopolymerization initiator.

FIG. 10 is a diagram schematically showing the mechanism of ink curing by light irradiation. As shown in FIG. 10(a), the ink IK immediately after transfer contains the polymer material and the first and second photopolymerization initiators. As shown in FIG. 10(b), when the ink pattern IP transferred to the bottle surface B2 is irradiated with the light UV1 from the temporary curing unit 4, the first photopolymerization initiator reacts, thereby forming the polymer material. A polymerization reaction begins. However, since the content of the first photopolymerization initiator is small, the polymerization reaction is limited, and relatively low-molecular-weight polymers are dispersed in the ink. As a result, the viscosity increases compared to immediately after the transfer, but complete curing is not achieved.

As shown in FIG. 10(c), when the main curing unit 5 irradiates the light UV2 containing many shorter wavelength components, the second photopolymerization initiator is also produced in addition to the first photopolymerization initiator. As a result, the polymerization reaction of the polymer further proceeds, the polymer is strongly crosslinked within the pattern, and the ink is completely cured.

FIG. 10(d) schematically shows the change in viscosity during this period. By irradiating the ink pattern with the light UV1, the viscosity of the ink increases, but the increase in viscosity saturates even if the light irradiation is continued. Depending on the content of the first photopolymerization initiator, the viscosity at this time can be adjusted to an appropriate viscosity. Then, by irradiation with light UV2, the viscosity of the ink increases again, and the increase stops when the whole is finally cured. The contents of the polymer material and the second photopolymerization initiator in the ink are determined so that the mechanical strength of the ink pattern at this time satisfies the required specifications. As for the second photopolymerization initiator, it is desirable that the amount contained is at least the amount necessary to completely cure the entire ink.

These phenomena can occur not only on the bottle B to which ink has been transferred from the blanket 32 but also on the blanket 32 which receives the wraparound of light through the bottle B. FIG. That is, when the ink carried on the blanket 32 is exposed to light, its viscosity changes. However, the increase in ink viscosity is originally limited by the exposure with the light UV1, and the amount of exposure on the blanket 32 is sufficiently small compared to the ink on the bottle B that receives direct light irradiation. Therefore, the viscosity of the ink on the blanket 32 is prevented from increasing to the extent that the transferability to the bottle B becomes a problem. Therefore, measures for shielding the light from the temporary curing unit 4 entering the blanket 32 may be omitted. Of course, in order to be more thorough, it is preferable that the temporary curing unit 4 is provided with a means (for example, a light shielding plate) for shielding light from leaking to the blanket 32 side.

On the other hand, if the ink on the blanket 32 is irradiated with the light UV2, the ink may be cured. There is no positional restriction on providing the light shielding member between them. Therefore, exposure of the ink on the blanket 32 by the light UV2 can be easily avoided from becoming a serious problem.

Among various materials known as photoreaction initiators, those having high light absorption characteristics on the relatively short wavelength side and suitable for use as the "second photopolymerization initiator" include, for example, benzoin. Derivatives, benzophenone, etc. Examples of those that have light absorption properties up to longer wavelengths and can be used as the "first photopolymerization initiator" include Michler's ketone and acylphosphine oxide compounds.

According to the general idea so far, in order to efficiently perform photocuring of the ink, a photopolymerization initiator sensitive to light in a wide band is added in an amount equal to or greater than the amount necessary for complete curing of the ink. The purpose of this is to efficiently absorb the irradiated light and promote the polymerization reaction of the polymer material.

On the other hand, in the printing process of the above embodiment, a small amount of photopolymerization initiator (first photopolymerization initiator) having broadband light absorption characteristics and a larger amount of light having light absorption characteristics biased toward the shorter wavelength side A polymerization initiator (second photopolymerization initiator) is added to the ink. Then, the ink transferred to the printing material is irradiated with light having a wavelength to which only the first photopolymerization initiator is sensitive, so that the ink is preliminarily cured. The amount of the first photopolymerization initiator that reacts with the irradiation light at this time is small, and is not enough to completely cure the ink. Therefore, even if the amount of exposure in the light irradiation at this time becomes excessive, it is possible to prevent the viscosity of the ink from increasing beyond the appropriate range.

In addition, part of the irradiated light may enter the untransferred ink on the blanket (intermediate transfer body), but the increase in the viscosity of the untransferred ink is limited, and the transfer to the substrate is limited. A decline in quality can be avoided. In addition, by performing overprinting in a state in which the ink maintains an appropriate viscosity through temporary curing, the adhesion between the inks in the overlaid layers is improved. In addition, it is possible to prevent the ink transferred to the material to be printed from moving to surrounding members.

As described above, in the above embodiment, the blanket 32 functions as the "intermediate transfer member" of the invention, and the ink pattern IP corresponds to the "print pattern" of the invention. Further, the light UV1 emitted from the temporary curing unit 4 corresponds to the "first light" of the invention, and the wavelength λ1 is an example of the "first wavelength" of the invention. On the other hand, the light UV2 emitted from the main curing unit 5 corresponds to the "second light" of the invention, and the wavelength λ2 is an example of the "second wavelength" of the invention.

In the printing process (FIG. 4) in the above embodiment, steps S101 to S103 correspond to the "first process" of the invention, while steps S104 to S107 correspond to the "second process" of the invention. . Also, steps S108 and S109 correspond to the "third step" and "fourth step" of the present invention, respectively.

The present invention is not limited to the above-described embodiments, and various modifications other than those described above can be made without departing from the spirit of the present invention. For example, the printing system 100 of the above embodiment includes a temporary curing unit 4 and a main curing unit 5 for appropriately increasing the viscosity of ink after transfer. On the other hand, for example, in a printing system premised on overprinting, one or more printing apparatuses that perform the process up to temporary curing, and those printing apparatuses receive the printed material that has been temporarily cured and perform the main curing. It is also possible to have a configuration in combination with one main curing device to be executed.

Further, in the printing system 100 of the above-described embodiment, the plate stage 11 moves the plate P and the bottle holding unit 6 moves the bottle B with respect to the fixed blanket roll 30, respectively, so that they are positioned relative to each other in the printing process. . However, it is sufficient that these movements are relatively realized, and which unit is to be made movable is not limited to the above and is arbitrary.

In addition, the formation of the ink pattern in the above embodiment is performed by applying ink to an intaglio and scraping it off with a doctor blade. However, the method of forming the ink pattern is not limited to this and is arbitrary. For example, an ink pattern formed on a planographic plate using an inkjet printing device may be transferred to the blanket, or an ink pattern may be directly formed on the surface of the blanket using an inkjet printing device.

Further, the light source of the temporary curing unit 4 in the above embodiment is a UV-LED, and the light source of the main curing unit 5 is a UV lamp. However, the light source is not limited to these, and any light source can be used as long as it can emit light of the required wavelength and intensity.

Further, the bottle holding unit 6 of the above-described embodiment has a configuration in which the bottle B, which is the object to be printed, is sandwiched between the connecting member 621 and the spring member 622, and the bottle B is additionally supported by the backup rolls 631 to 634. . However, the form of holding the material to be printed is not limited to this and is arbitrary. For example, it may be configured to hold the printing material with an appropriate rotary chuck mechanism.

Further, although the object to be printed in the above embodiment is the substantially cylindrical bottle B, the object to be printed is not limited to this. For example, the print processing system 100 described above can be used to perform print processing on a cylindrical print substrate with both ends open and a print substrate with unevenness on a cylindrical surface.

As described above by exemplifying specific embodiments, in the printing method according to the present invention, for example, the content of the first photopolymerization initiator in the photocurable ink is such that the entire polymer material is cured. may be less than that required for According to such a configuration, it is possible to maintain an appropriate viscosity without completely curing the ink even when the exposure amount of the first light increases. Therefore, a printing process that is less sensitive to exposure dose can be constructed.

Further, for example, the material to be printed may have optical transparency. In this case, it is practically impossible to control the light that passes through the interior of the printing material and is incident on the intermediate transfer member. In addition, it is possible to avoid problems such as retransfer of ink and defective transfer, which may lead to deterioration of print quality.

Further, for example, in the present invention, the intermediate transfer member has a cylindrical surface and a blanket made of elastic resin. It may be configured to transfer to a substrate. According to such a configuration, by providing the blanket that temporarily supports the print pattern, it becomes possible to easily cope with changes in the print pattern and the material to be printed. Moreover, since the surface of the blanket having elasticity can follow the unevenness of the surface of the printing material, it is possible to print well even on the printing material which is not a perfect cylinder.

Further, in the printing method according to the present invention, the transfer in the second step and the light irradiation in the third step may be performed simultaneously at least for a period of time. Part of the light used in the light irradiation for the third step may cause a change in the ink viscosity in the second step, but in the present invention, this problem is solved by devising the photopolymerization initiator and the wavelength of the irradiation light. Therefore, there is no problem even if both steps are executed simultaneously.

Further, in the printing method according to the present invention, the processes from the first step to the third step are performed a plurality of times on the same material to be printed to transfer the print pattern of multiple layers to the material to be printed, and then the fourth process is performed. may be configured to According to such a configuration, the newly transferred print pattern is superimposed on the ink that has been transferred in the previous step and whose viscosity has increased appropriately. Therefore, the adhesion between the layers can be improved. Then, by collectively irradiating the second light after transferring the plurality of layers, the entire print pattern can be cured to obtain a final printed matter.

INDUSTRIAL APPLICABILITY The present invention can be applied to all printing techniques for printing on the surface of a cylindrical printing object such as a glass bottle or a resin bottle. effective for

3 transfer unit 4 temporary curing unit 5 main curing unit 32 blanket (intermediate transfer body)
100 printing system B bottle (printed material)
IP, IP1, IP2 Ink pattern (printing pattern)
P plate S101 to S103 1st step S104 to S107 2nd step S108 3rd step S109 4th step UV1 First light UV2 Second light

Claims (8)

a first step of forming a print pattern with photocurable ink on the surface of an intermediate transfer member;
The intermediate transfer body is brought into contact with a substantially cylindrical printed material supported by bringing a backup member into contact with the printed surface, and the print pattern on the surface of the intermediate transfer body is transferred to the printed surface . 2 steps;
a third step of increasing the viscosity of the photocurable ink by irradiating a first light onto a region of the printing surface that has separated from the intermediate transfer member and has not come into contact with the backup member ;
a fourth step of irradiating the print pattern with increased viscosity with a second light to cure the photocurable ink;
The photocurable ink is
a polymeric material that solidifies upon polymerization;
a first photopolymerization initiator that reacts with light of a first wavelength contained in the first light;
a second photopolymerization initiator that does not react to the first wavelength and reacts to light of a second wavelength shorter than the first wavelength and contained in the second light;
A printing method in which the first light does not substantially contain the second wavelength component, and the second light has a greater intensity of the second wavelength component than the first light. 2. The printing method according to claim 1, wherein in the third step, the surface to be printed is irradiated with the first light while the object to be printed and the intermediate transfer member are in contact with each other. 3. The printing method according to claim 1, wherein the content of the first photopolymerization initiator in the photocurable ink is less than the amount required to cure the polymer material as a whole. 4. The printing method according to any one of claims 1 to 3, wherein the material to be printed has optical transparency. the intermediate transfer body has a cylindrical surface and a blanket made of elastic resin;
5. The printing method according to any one of claims 1 to 4, wherein the blanket carrying the print pattern on its surface rotates while being in contact with the material to be printed, thereby transferring the print pattern to the material to be printed. 6. The printing method according to any one of claims 1 to 5, wherein the transfer in the second step and the light irradiation in the third step are performed simultaneously at least for a period of time. 2. The method of claim 1, wherein the processes from the first step to the third step are performed a plurality of times on the same material to be printed to transfer the print patterns of a plurality of layers to the material to be printed, and then the fourth step is performed. 7. The printing method according to any one of 6. The printing method according to any one of claims 1 to 7, wherein in the third step, the viscosity of the photocurable ink is increased to a viscosity at which transfer of the photocurable ink to the backup member does not occur.

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