TWI709495B - Printing method - Google Patents

Abstract

The present invention provides a technology that can inhibit the retransfer of the photocurable ink after transfer to an intermediate transfer body, etc., and inhibit the photocuring of the ink on the intermediate transfer body, and can perform multi-layer printing well. In the printing method of the present invention, the printing pattern of the photocurable ink is transferred from the intermediate transfer body 3 to the object to be printed B, and the first light is irradiated to the printing pattern transferred to the object to increase the viscosity of the photocurable ink. , The second light is irradiated to the printed pattern with increased viscosity to harden the photocurable ink. The first light includes light of a first wavelength, and the second light includes light of a second wavelength having a wavelength shorter than the first wavelength with a higher intensity than the first light. The photocurable ink includes: a polymer material, which is cured by polymerization; a first photopolymerization initiator, which reacts with light of the first wavelength; and a second photopolymerization initiator, which does not interact with the first wavelength The light reacts with the light of the second wavelength.

Description

Printing method

The present invention relates to a printing technology for printing by transferring a printing pattern formed on an intermediate transfer body using a photocurable ink to an object to be printed.

The photocurable ink prepared from the polymer material and the photopolymerization initiator in the printing ink is cured by light irradiation for a short period of time, and can usually be cured more quickly than by curing by drying or heating. Therefore, the printed matter just after printing can be immediately supplied to the next step, which is suitable for high-speed printing processing. For example, the technology described in Japanese Patent Laid-Open No. 2017-196887 (Patent Document 1) is about a kind of printing pattern formed on the surface of the printing cloth (intermediate transfer body) overlapped on the surface of the printed matter. Multi-color printing method. In this technology, in order to prevent the color mixing of the ink or the uncured ink on the printed matter from being transferred to the printing cloth, a photocurable ink is used to irradiate ultraviolet rays for each color of printing, thereby curing the ink.

In addition, in this technique, in order to prevent the ink on the printing cloth from being irradiated with light and starting to harden, a member for shielding light is arranged between the light source and the printing cloth.

Furthermore, as the photocurable ink, one containing a plurality of photopolymerization initiators is proposed. For example, Japanese Patent Laid-Open No. 2003-251910 (Patent Document 2) describes the following: In a printing system that combines inkjet printing and photocuring, in order to improve the adhesion of the ink film to the substrate, follow And use two or more polymerization initiators with different absorption wavelengths. However, in inkjet printing that directly ejects ink to the printed matter, the above-mentioned ink retransfer problem does not occur in principle.

[The problem to be solved by the invention]

The technique described in Patent Document 1 described above includes the following problems to be solved. First, the shielding of the light from the light source to the ink on the printing cloth cannot be said to be sufficient in the above-mentioned prior art. The reason is that it is impossible to shield the light incident on the surface of the printed cloth due to reflection or transmission at the printed object. Especially when the printed object is a transparent body such as glass, it is unavoidable that the light reflected on the surface or transmitted through the interior is diffracted to the surface of the printed cloth. If such light is irradiated to the ink on the printing cloth, the surface of the ink hardens on the printing cloth, so there is a problem that the transferability to the printed matter is reduced.

Second, in multi-layer printing in which a plurality of printed patterns are overlapped on the printed matter, in order to obtain higher adhesion between the layers, it is more desirable to overlap with the transferred ink maintaining a certain degree of viscosity. On the other hand, when the ink transferred to the printed matter maintains a low viscosity, when the ink on the printed matter comes into contact with the intermediate transfer body or surrounding components, it may be transferred to these components again. In order to prevent such retransfer, the transferred ink preferably has a sufficiently high viscosity at least on its surface. That is, it is required that the ink after transfer be maintained in a state that is higher than the viscosity immediately after transfer and lower than that in the fully cured state, and has a moderate viscosity. However, in the technique described in Patent Document 1, it is difficult to control such a hardened state.

In Patent Document 2 related to inkjet printing, there is no disclosure that helps eliminate this problem. [Technical means to solve the problem]

The present invention was made in view of the above-mentioned problems, and its object is to provide a technique for appropriately controlling the viscosity of the photocurable ink after transfer to the printed matter, thereby suppressing the retransfer to the intermediate transfer body, etc. In addition, photocuring of the ink on the intermediate transfer body can be suppressed, and multilayer printing can be performed well.

In order to achieve the above object, one aspect of the printing method of the present invention includes: the first step is to form a printing pattern of photocurable ink on the surface of the intermediate transfer body; the second step is to make the intermediate transfer body Abutting on the object to be printed, transfer the printing pattern on the surface of the intermediate transfer body to the object to be printed; the third step is to irradiate the printing pattern transferred to the object to be printed with first light to harden the light The viscosity of the flexible ink increases; and the fourth step is to irradiate the printed pattern with increased viscosity with a second light to harden the photocurable ink.

Here, the first light includes light of a first wavelength, and the second light includes light of a second wavelength having a wavelength shorter than the first wavelength at a higher intensity than the first light. Furthermore, the photocurable ink includes: a polymer material, which is cured by polymerization; a first photopolymerization initiator, which reacts with the light of the first wavelength; and a second photopolymerization initiator, which does not Reacts with the light of the first wavelength and reacts with the light of the second wavelength. The first light may be one that does not substantially include light of the second wavelength.

In the present invention, the so-called photopolymerization initiator "reacts with light" means that the photopolymerization initiator is irradiated with light to produce chemical changes such as promoting the polymerization reaction of the polymer material. In addition, "the first light does not substantially include 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. That is, the second photopolymerization initiator is not changed by the first light irradiation.

For the invention constructed as above, in the third and fourth steps, the photocurable ink (hereinafter sometimes referred to as "ink") transferred from the intermediate transfer body to the printed matter in the first and second steps Irradiate light. Among them, in the third step, only the first photopolymerization initiator reacts, and the second photopolymerization initiator does not react. Therefore, the ink becomes a low degree of polymerization and its viscosity increases.

Even if the exposure amount in the third step becomes large and the first photopolymerization initiator has completely reacted, the second photopolymerization initiator does not substantially react. Therefore, the maximum viscosity of the ink that can be reached in the third step can be controlled according to the content of the first photopolymerization initiator, and there is no need to adjust the viscosity according to the exposure amount. Therefore, it is easy to maintain the ink controllability after the third step at an appropriate viscosity.

Moreover, even if the ink on the intermediate transfer body is irradiated with the first light, it is possible to surely prevent the viscosity of the ink from increasing to a certain level or more. Therefore, it can be avoided that the transferability of the ink from the intermediate transfer body to the printed matter is greatly reduced.

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

In this way, in the present invention, the ink after being transferred to the printed matter can be maintained at an intermediate viscosity that does not reach full curing, and the viscosity at this time can be controlled according to the content of the first photopolymerization initiator. Therefore, by maintaining the appropriate viscosity of the photocurable ink after transfer to the printed matter, retransfer to the intermediate transfer body can be suppressed, and photocuring of the ink on the intermediate transfer body can be suppressed. In addition, the adhesion between the layers during multilayer printing can be achieved in a good state. Furthermore, by using additional irradiation with the second light, the ink can be cured more reliably. [Effects of Invention]

According to the present invention, the ink contains two kinds of photocuring initiators with different reaction wavelengths, and the first light with a relatively long wavelength is irradiated to increase the viscosity, and then the second light with a shorter wavelength is irradiated to further harden the ink. Therefore, the viscosity of the ink after the first light irradiation can be controlled, the retransfer to the intermediate transfer body, etc. can be suppressed, and the photohardening of the ink on the intermediate transfer body can be suppressed. Moreover, multilayer printing can also be performed well.

The above and other objects and novel features of the present invention can be understood more completely by referring to the accompanying drawings and reading the following detailed description. However, the drawings are exclusively used for explanation, rather than limiting the scope of the present invention.

FIG. 1 is a schematic diagram showing a schematic configuration example of a printing system that can realize the printing method of the present invention. The printing system 100 is a system for printing on the surface of an object to be printed. The to-be-printed object is, for example, a glass bottle or a resin bottle that has a substantially cylindrical shape. The printing system 100 prints on the surface of the object to be printed, more specifically, the side surface as a cylindrical surface. Here, in order to uniformly show the directions in each figure, as shown in Fig. 1, an XYZ orthogonal coordinate system is set. For example, the XY plane can be regarded as a horizontal plane and the Z axis can be regarded as a vertical axis. Hereinafter, the (-Z) direction shall be vertically downward.

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

The printing process of the printing system 100 includes the following steps, namely, (1) By using the plate platform unit 1 and the ink filling unit 2 to form an ink pattern using photocurable ink; (2) Transfer the ink pattern to the transfer unit 3; (3) Transfer the ink pattern from the transfer unit 3 to the printed matter; and (4) The ink is cured by light from the pre-curing unit 4 and the main curing unit 5. Hereinafter, using a cylindrical glass bottle or resin bottle (hereinafter referred to as "bottle") B in which the printed matter is used, the structure and operation of each part of the device will be described in order.

Figure 2 is a diagram showing the composition of the plate platform unit and the ink filling unit. The plate platform unit 1 includes a platform 11 on which a plate (for example, an intaglio) P for forming an ink pattern is placed on the upper surface. The platform 11 is installed on the base portion 13 via the alignment mechanism 12. The alignment mechanism 12 moves the platform 11 in the XYZ direction and the direction of rotation around the Z axis according to the control command from the control unit 9. For example, a cross 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 on the pedestal of the printing system 100 and can move back and forth 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. The base portion 13 is moved in the (-Y) direction and (+Y) direction by the actuation of the drive mechanism. The position (the position shown by the solid line in FIG. 2) in the movable range of the base 13 that is most deviated to the (-Y) direction side is the rest position of the base 13. As the driving mechanism, for example, an appropriate mechanism such as a combination of a rotary motor and a ball screw mechanism, a linear motor, a linear motion guide, and an air cylinder can be used.

Aiming cameras 15 and 15 are arranged above the platform 11 in a state of being positioned at a static position. The alignment cameras 15 and 15 photograph the alignment marks provided on the periphery of the plate P or the upper surface of the plate P placed on the platform 11, and send the image data to the control unit 9. The control unit 9 detects the position of the plate P on the platform 11, and moves the alignment mechanism 12 as necessary, thereby adjusting the position of the plate P to an appropriate position.

The base portion 13 is provided with an ink filling unit 2 and a transfer unit 3 along a path that moves in the (+Y) direction from the rest position. The ink filling unit 2 includes a nozzle 21. The nozzle 21 is arranged so as to face the upper surface of the plate P placed on the table 11 passing directly below it. The ink supply unit 22 controlled by the control unit 9 supplies the nozzle 21 with photocurable ink (hereinafter sometimes referred to as "ink"). The supplied ink is ejected from an ejection port provided at the lower end of the nozzle 21, and is coated on the upper surface of the plate P.

The photocurable ink contains pigments as color developers, polymer materials and photopolymerization initiators. The polymer material constitutes a firm polymer layer through polymerization reaction, and includes at least one of a monomer and an oligomer. The photopolymerization initiator is a reactive species generated by chemical changes after being irradiated with light to promote the polymerization reaction of polymer materials.

A scraper 23 is provided on the (+Y) direction side of the nozzle 21. The doctor blade 23 slides and rubs along the surface of the plate P to which the ink is supplied to scrape the ink. Thereby, the ink is filled in the recesses provided on the upper surface of the plate P, on the other hand, the remaining ink other than this is removed to form an ink pattern.

In this way, the plate P filled with ink moves 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 printing cloth cylinder 30 and a motor 33 for rotating it. In more detail, the printing cloth cylinder 30 includes, for example, a printing cloth cylinder 31 that is a metal cylinder, and a printing cloth 32 wound on the surface thereof, and is formed into a substantially cylindrical shape as a whole. The printing cloth cylinder 30 is supported by a frame not shown to rotate freely, and is driven to rotate around the central axis shown by the single-dot chain line in FIG. 1 by a motor 33 controlled by the control unit 9.

The printing cloth 32 is a resin material with elasticity, for example, made of silicone resin, and can carry an ink pattern on its surface. The printed cloth 32 has a sufficiently large thickness compared to the possible unevenness on the surface of the bottle B to be printed. As shown in FIG. 2, when the plate P placed on the platform 11 passes a position directly below the printing cloth cylinder 30, the surface of the printing cloth 32 abuts the upper surface of the plate P. At this time, the ink filled in the recesses of the plate P moves to the surface of the printing cloth 32. In this way, the ink pattern on the plate P is transferred to the printing cloth 32.

In this way, the ink pattern temporarily transferred (primary transfer) to the printing cloth 32 will be secondarily transferred to the surface of the bottle B that is the final printed matter. That is, the printing cloth 32 functions as an intermediate transfer body that temporarily supports the ink pattern that is finally transferred to the printed matter.

3A and 3B are diagrams showing the structure of the bottle holding unit. More specifically, FIG. 3A is a side view of the bottle holding unit 6 viewed in the Y direction, and FIG. 3B is a side view of the bottle holding unit 6 viewed in the X direction.

The bottle holding unit 6 rotatably holds the bottle B, which is a printing object whose side surface B2 becomes the printing target surface, about its central axis. The bottle holding unit 6 has a support frame 60 formed by combining a bottom plate 61 and a pair of side plates 62 and 62 extending upward from both ends of the X direction side. A connecting member 621 is attached to one of the side plates 62, and the connecting member 621 is free to rotate. In addition, a spring member 622 is provided on the other side plate 62. The neck B1 of the bottle B is connected to the connecting member 621. On the other hand, the bottom portion B3 of the bottle B is elastically pushed toward the neck B1 by the spring member 622. Thereby, the bottle B is held in a posture in which its central axis is substantially horizontal. In addition, the connecting member 621 can be rotationally driven by a motor (not shown) to rotate the bottle B around its central axis.

As shown in FIGS. 1, 3A, and 3B, the bottle B is assisted by supporting rollers 631 to 634 whose X direction is the axial direction. The support rollers 631 to 634 are rotatably supported by the side plates 62, respectively. Among them, a pair of supporting rollers 631 and 632 are arranged under the bottle B and abut against the side surface B2 of the bottle B from below, thereby restricting the displacement of the bottle B in the direction of gravity, that is, the (-Z) direction. In addition, another pair of support rollers 633, 634 are arranged on the (+Y) direction side of the bottle B, and abut against the (+Y) side of the bottle B, thereby restricting the movement of the bottle B in the (+Y) direction Bit. On the other hand, the side surface in the (-Y) direction of the side surface B2 of the bottle B is in a state of being opened largely.

The bottom plate 61 of the support frame 60 is mounted on the base portion 66 via the alignment mechanism 65. The alignment mechanism 66 moves the support frame 60 in the XYZ direction and the direction of rotation around the Z axis according to the control command from the control unit 9. For example, a cross-roller bearing mechanism can be used as the alignment mechanism 65.

The base portion 66 is engaged with the guide rails 67 and 67 extending along the Y direction on the pedestal of the printing system 100 and can move back and forth along the guide rail 67 in the Y direction. More specifically, a driving mechanism (not shown) controlled by the control unit 9 is connected to the base portion 66. The base portion 67 is moved in the (-Y) direction and (+Y) direction by the actuation of the drive mechanism. Therefore, the bottle B held in the bottle holding unit 6 can move horizontally within a specific movable range in the Y direction. As the driving mechanism, for example, an appropriate mechanism such as a combination of a rotary motor and a ball screw mechanism, a linear motor, a linear motion guide, and an air cylinder can be used.

As shown in FIG. 3B, when the bottle holding unit 6 moves the bottle B to the vicinity of the (-Y) direction side end in its movable range, the (-Y) direction side surface of the bottle B is pressed against the surface of the printing cloth 32. Thereby, the ink pattern carried on the surface of the printing cloth 32 is transferred to the side surface B2 of the bottle B. The displacement of the bottle B caused by the reaction force from the printing cloth 32 generated by pressing the bottle B against the printing cloth 32 can be prevented by the supporting rollers 631 to 634.

In addition, the description is omitted in FIGS. 3A and 3B, but as described below, the bottle B held in the bottle holding unit 6 is also provided with an alignment camera 68 for detecting its position (FIG. 6 ). The control unit 9 operates the alignment mechanism 66 based on the shooting 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 printing cloth 32 to an appropriate position.

As shown in FIG. 1, a pre-curing unit 4 and a full-curing unit 5 are arranged along the movement path of the bottle B using the bottle holding unit 6. These units are used to irradiate light (ultraviolet rays, UV (Ultraviolet, ultraviolet) light) to the ink pattern formed by the photocurable ink transferred to the bottle B to harden the ink. However, the functions of the two are different, and the details will be described below.

The pre-curing unit 4 does not completely harden the ink, and has the function of increasing the viscosity of the ink pattern transferred to the bottle B to the extent that it does not interfere with the subsequent steps. Therefore, the intensity of the emitted light can be relatively low, and for example, an LED (Light Emitting Diode) capable of outputting ultraviolet light can be used as a light source. The pre-curing unit 4 irradiates the ink just after transfer to the bottle B with light. Therefore, as shown in FIG. 3B, the pre-curing unit 4 is arranged at a position opposite to the surface of the bottle B positioned to abut on the surface of the printing cloth 32.

On the other hand, the formal hardening unit 5 has a function of hardening the ink whose viscosity has increased. Therefore, as the light source, one with a large output such as a UV lamp is preferable. The formal curing unit 5 is arranged at a position farther away from the printed cloth 32 than the pre-curing unit 4. The purpose is to prevent the strong light emitted from the formal curing unit 5 from irradiating the ink pattern on the printing cloth 32.

Fig. 4 is a flowchart showing an embodiment of the printing method of the present invention. More specifically, FIG. 4 shows an example of printing processing to which the printing method of the present invention is applied. The printing process is realized by the control unit 9 executing a pre-stored program and causing each part of the device to perform specific actions. In addition, FIGS. 5 and 6 are diagrams schematically showing the movement of various parts during the execution of the printing method of FIG. 4. Furthermore, in FIGS. 5 to 7, the dotted arrow indicates the direction of movement of the component.

In this printing process, first, the plate P and the bottle B are set in the printing system 100. Specifically, the plate P is loaded into the system and set on the platform 11 (step S101), and the alignment adjustment of the plate P is performed based on the shooting result of the alignment camera 15 (step S102). Then, the platform 11 starts to move in the (+Y) direction. The nozzle 21 of the ink filling unit 2 applies the photocurable ink IK to the upper surface of the plate P, and scrapes the remaining ink with the doctor blade 23, thereby filling the ink on the plate surface. (Step S103). The platform 11 further moves and passes through the position directly below the rotating printing cloth cylinder 60, thereby transferring the ink pattern formed on the plate P to the surface of the printing cloth 32 (step S104).

FIG. 5 schematically shows the state of each part after the plate P is placed on the table 11 until the alignment adjustment and ink filling are performed, and the ink pattern is transferred to the printing cloth 32. As shown in the lower part of FIG. 5, finally, all the ink patterns IP formed on the plate P are transferred to the printing cloth 32.

Simultaneously with the processing for the plate P as described above, the bottle holding unit 6 executes the processing for the bottle B. That is, after setting the bottle B to be printed (step S105), as shown in FIG. 6, the bottle B is photographed by the camera 68, and the alignment adjustment of the bottle B is performed based on the photographing result (step S106). Then, the bottle holding unit 6 is moved in the (-Y) direction to make the bottle B abut on the surface of the printing cloth 32 (step S107).

As shown in FIG. 6, the printing cloth 32 to which the ink pattern IP is transferred abuts and rotates together with each other, thereby sequentially transferring the ink patterns IP on the surface of the printing cloth 32 to the bottle B. Furthermore, for the sake of explanation, FIG. 5 shows the steps from the loading of the plate P to the ink pattern transfer to the printing cloth 32, and FIG. 6 shows the steps from the loading of the bottle B to the ink transfer to the bottle B. , These steps are recorded as independent steps. However, in actual processing, the ink pattern transfer to the printing cloth 32 and the ink pattern transfer from the printing cloth 32 to the bottle B can be continuously performed during the same rotation of the printing cloth 32.

Here, the surface of the bottle B abuts against the support rollers 631 to 634. When the ink pattern IP reaches a position where it abuts the support rollers 631 to 634 along with the rotation of the bottle B, uncured ink may be transferred from the bottle B to the support rollers 631 to 634. In addition, when the bottle B rotates more than one revolution, the ink pattern IP on the surface of the bottle B may be transferred to the printing cloth 32 again. Such conditions will disturb the ink pattern on the surface of the bottle B, and will contaminate the printing cloth 32 or the supporting rollers 631-634 due to the ink.

In order to prevent the above-mentioned problems, a pre-hardening treatment is performed by ultraviolet irradiation with a relatively low exposure amount (step S108). That is, as shown in FIG. 6, light (ultraviolet rays) UV1 is irradiated from the pre-curing unit 4 toward the surface of the bottle B immediately after receiving the transfer of the ink pattern IP from the printing cloth 32. As described below, the light UV1 irradiated from the pre-curing unit 4 has the following properties: the viscosity of the ink is increased by polymerizing part of the polymer material contained in the ink, but the ink is not cured as a whole.

In this way, by increasing the viscosity of the ink, the adhesion of the ink to other objects is reduced. Therefore, when the surface of the bottle B carrying the ink comes into contact with the supporting rollers 631 to 634 or the printing cloth 32, the ink can be prevented from being transferred to the supporting rollers 631 to 634 or the printing cloth 32. At the end of the pre-curing time, the ink is not completely cured. In order to completely harden, the 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 in a state where the bottle B and the printing cloth 32 are far apart. The light UV2 at this time is irradiated with a sufficient exposure amount to completely harden the ink.

The bottle B after the printing process is carried out in this way is carried out to the outside (step S110). When there is a bottle to be printed next (YES in step S111), return to steps S102 and S105, and execute the above process repeatedly from the alignment adjustment of plate P and the loading of bottle B. Furthermore, when it is necessary to change the version P, just return to step S101.

Next, the operation in the case of overlapping printing will be described. In some cases, the bottle B to which the ink pattern has been transferred may be printed by overlapping the ink pattern. For example, there is a case where the printing layer becomes thicker by overlapping ink patterns of the same color, or a case where multi-color printing is performed by overlapping ink patterns of different colors.

In the case of such overlapping printing, it is preferable that the ink pattern transferred to the bottle B is not completely cured. The reason is that when the layer of the new ink pattern is overlapped with the layer of the completely hardened ink pattern, the adhesion between the layers may deteriorate. On the other hand, when the viscosity of the transferred ink pattern is too low, the inks of different colors are mixed with each other or retransfer of the ink from the bottle B to the printing cloth 32 occurs, which reduces the printing quality.

In the printing process of this embodiment, the above-mentioned pre-curing is used to make the viscosity of the transferred ink moderate, thereby preventing these problems. That is, the new ink pattern is transferred to the bottle B where the transferred ink pattern has been pre-hardened. Thereby, multiple layers of overlap printing can be performed well. Specifically, it can be done as follows.

Fig. 7 is a diagram schematically showing the movement of each part in overlapping printing. First, consider the case of overlapping ink patterns of the same color. If the circumferential length of the ink pattern transferred to the printing cloth 32 is greater than the circumference of the bottle B, the bottle B will rotate more than one revolution until all the ink patterns are transferred. As a result, the pattern transferred in the second rotation is superimposed on the pattern transferred in the first rotation to be transferred.

That is, as shown in FIG. 7, the ink pattern IP1 remaining on the surface of the printing cloth 32 after the ink pattern IP1 is transferred during the first rotation of the bottle B is transferred during the second rotation of the bottle B or later To bottle B. At this time, by transferring the new ink pattern IP2 to the area on the surface of the bottle B where the ink pattern IP1 has been transferred, double-layer overlapping printing is realized. By making the Y-direction length of the plate P sufficiently larger than the circumference of the bottle B, such overlapping printing can be easily performed. Furthermore, in FIG. 7, in order to improve the visibility of the figure, the ink pattern IP1 transferred in the first circle and the ink pattern IP2 transferred in the second circle are shown in different densities.

In this case, the ink immediately after transfer is irradiated with light UV1 from the pre-curing unit 4 to perform the pre-curing. Therefore, it is possible to prevent the ink from being transferred from the bottle B to the printing cloth 32 again. In addition, since the ink is not completely cured, there is no problem in adhesion to the newly transferred ink. Then, a formal hardening treatment is performed after the overlap printing is completed, so that the entire transferred ink patterns IP1 and IP2 can be completely hardened. In this way, good quality overlap printing can be performed.

On the other hand, when printing with different colors or different types of inks overlapped, it is necessary to switch the plate P and the ink. In this case, the plate P and ink can also be switched in the printing system 100 of FIG. 1. However, in terms of the productivity of continuous printing, it is advantageous to prepare a plate platform unit 1, an ink filling unit 2, a transfer unit 3, and a pre-curing unit that have been specialized into one ink according to the number of types of ink. Group 4, while transporting bottle B between these units, overlap printing in sequence.

In this case, the multi-color overlay printing can also be completed by the following method, that is, in the stage of using one ink to pre-curing, switch bottle B and repeat the transfer process to form multiple layers, and then Perform formal hardening treatment collectively.

However, in the printing process, the ink just after transfer to the bottle B must be irradiated with light for pre-curing. Therefore, the pre-curing unit 4 must be arranged near the printed cloth 32. Therefore, there are cases where the light UV1 emitted from the pre-curing unit 4 leaks and is diffracted to the printing cloth 32, causing the ink carried on the printing cloth 32 to be irradiated with light.

8A and 8B are diagrams illustrating the problem of light leakage to the printed cloth. As shown in FIG. 8A, in order to reduce the light directly irradiated from the pre-curing unit 4 to the printed cloth 32, it is only necessary to provide an appropriate light-shielding member S between the two. However, when the surface of bottle B has light reflectivity or when the material of bottle B itself has light transmittance, as shown by the dotted arrow, light UV1 sometimes enters the printing cloth 32 through the surface or inside of bottle B . Especially when the raw material of bottle B is transparent material, the influence is more significant. In addition, when the printing cloth 32 is made of silicone resin, it has a certain degree of ultraviolet transmittance. There is a possibility that the viscosity of the ink on the printing cloth 32 may increase due to the unexpected light irradiation.

As long as the ink transfer from the printing cloth 32 to the bottle B and the light irradiation of the transferred ink can be carried out separately, it is possible to avoid the ink on the printing cloth 32 by not irradiating the light before the transfer is completed. Light irradiation. However, the productivity of this printing process is low. Therefore, as a practical problem, it is unavoidable that the ink transfer from the printing cloth 32 to the bottle B and the light irradiation for pre-curing temporarily overlap.

Fig. 8B is a diagram schematically showing the relationship between the exposure amount and the viscosity of the ink. As shown by the solid line, as the exposure amount represented by the product of the intensity of the irradiation light and the irradiation time increases, the viscosity of the ink also increases. However, if the ink is completely hardened, the viscosity will not rise above it. During the pre-curing stage, the following appropriate viscosity must be maintained, that is, the viscosity is high to the extent that the ink is not retransferred to the printing cloth 32, etc., and the adhesion between the layers is not reduced. However, as described above, when light may be incident on the ink while being carried on the printing cloth 32, it is actually impossible to manage the viscosity of the ink by adjusting the exposure amount in the pre-curing process.

Therefore, as shown by the dotted line, it is more desirable to increase the viscosity of the ink to a proper viscosity by light irradiation, and even if the exposure is increased beyond that, the viscosity will not change as if the viscosity increases. In order to achieve such a viscosity change, in this embodiment, the ink contains two polymerization initiators with different light absorption characteristics. In addition, between the pre-curing unit 4 and the formal curing unit 5, light with different spectral distributions is generated. The details are as follows.

Fig. 9 is a diagram showing ink and UV light used in this embodiment. The photocurable ink of this embodiment contains a first photopolymerization initiator that also has absorption characteristics for relatively long wavelengths, and a second photopolymerization initiator that absorbs only light on the shorter wavelength side. Moreover, the light UV1 irradiated from the pre-curing unit 4 uses light that contains a lot of components of the wavelength λ1. The components of the wavelength λ1 have higher absorption characteristics in the first photopolymerization initiator, but are used in the second photopolymerization. Almost no absorption in the starter. Furthermore, it is more desirable that the light UV1 does not substantially contain a wavelength component that makes the second photopolymerization initiator absorbability. That is, the light UV1 for pre-curing preferably contains only components on the longer wavelength side than the absorption wavelength region of the second photopolymerization initiator.

On the other hand, with regard to the light UV2 emitted from the main curing unit 5, a component containing a large amount of the wavelength λ2 in which the second photopolymerization initiator exhibits higher absorption and having a higher emission intensity than the light UV1 is used. In addition, the first photopolymerization initiator does not necessarily have to be absorbing at this wavelength. However, generally speaking, materials with higher absorption on the long-wavelength side also have higher absorption for shorter-wavelength light.

In this way, the first photopolymerization initiator reacted with the light UV1 for precuring, but the second photopolymerization initiator did not react. Here, as long as the content of the first photopolymerization initiator in the ink is sufficiently smaller than the amount required to harden the ink as a whole, the ink will not be completely cured even if all the first photopolymerization initiators react. Therefore, relative to the increase in cumulative exposure, the increase in viscosity saturates. The viscosity at this time can be controlled according to the content of the first photopolymerization initiator.

10A to 10D are diagrams schematically showing the mechanism of ink curing by light irradiation. As shown in FIG. 10A, the ink pattern IP immediately after transfer contains a polymer material and the first and second photopolymerization initiators. As shown in FIG. 10B, when the ink pattern IP transferred to the bottle surface B2 is irradiated with light UV1 from the pre-curing unit 4, the first photopolymerization initiator reacts, thereby starting the polymerization reaction of the polymer material. 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 transfer, but it is not completely cured.

As shown in FIG. 10C, by irradiating light UV2 containing more components of shorter wavelength from the main curing unit 5, in addition to the first photopolymerization initiator, the second photopolymerization initiator also reacts. Thereby, the polymerization reaction of the polymer proceeds further, the polymer is firmly cross-linked in the pattern, and the ink becomes a completely hardened state.

The viscosity change during this period is shown schematically in Figure 10D. By irradiating the ink pattern with light UV1, the viscosity of the ink increases, but even if the light irradiation continues, the increase in viscosity is saturated. According to the content of the first photopolymerization initiator, the viscosity at this time can be set to an appropriate viscosity. Then, by subsequently irradiating light UV2, the viscosity of the ink rises again, and finally stops rising due to the overall hardening. In order to meet the required specifications for the mechanical strength of the ink pattern at this time, the content of the polymer material and the second photopolymerization initiator in the ink is specified in advance. As for the second photopolymerization initiator, it is preferable to contain at least an amount required to completely cure the entire ink.

This phenomenon occurs not only on the bottle B receiving the ink transfer from the printing cloth 32, but also on the printing cloth 32 that is diffracted by light from the bottle B. That is, the ink carried on the printing cloth 32 changes its viscosity when light is irradiated. However, the increase in the viscosity of the ink in the exposure using the light UV1 is originally limited, and the exposure amount on the printing cloth 32 is sufficiently small compared to the ink directly irradiated by the light on the bottle B. Therefore, it is possible to prevent the viscosity of the ink on the printing cloth 32 from increasing to the extent that transferability to the bottle B becomes a problem. Therefore, the measures for shielding the light incident from the pre-curing unit 4 to the printed cloth 32 can also be omitted. Of course, it is preferable to adopt a mechanism (for example, a light-shielding plate) for the pre-curing unit 4 to shield the light leakage to the printed cloth 32 side, in order to be safe.

On the other hand, when the light UV2 irradiates the ink on the printing cloth 32, it may cause the ink to harden. However, when the light UV2 is irradiated, the printed cloth 32 is separated from the bottle B far, if necessary, there is no restriction on the position of the shading member provided between them. Therefore, it is possible to easily prevent the exposure of the ink on the printing cloth 32 caused by the light UV2 from becoming a major problem.

Among the various materials known as photoreaction initiators, those that have higher light absorption characteristics on the relatively short wavelength side and can be preferably used as the "second photopolymerization initiator", for example, benzoin derivatives, two Benzophenone and so on. In addition, as those that also have light absorption properties on the longer wavelength side and can be used as the "first photopolymerization initiator", for example, there are Michelone and phosphine oxide-based compounds.

In the previous general view, in order to efficiently perform the photocuring of the ink, a photopolymerization initiator that is sensitive to light in a wider band is added in an amount more than the amount required for complete curing of the ink. Its purpose is to efficiently absorb the irradiated light and promote the polymerization reaction of polymer materials.

On the other hand, in the printing process of the above-mentioned embodiment, a small amount of photopolymerization initiator (first photopolymerization initiator) having broad-band light absorption characteristics and light absorption characteristics shifted to the shorter wavelength side are combined. A larger amount of photopolymerization initiator (second photopolymerization initiator) is added to the ink. In addition, the ink is precured by irradiating the ink transferred to the printed matter with light of a wavelength at which only the first photopolymerization initiator has sensitivity. The amount of the first photopolymerization initiator that reacts with the irradiated light at this time is small and does not completely harden the ink. Therefore, even if the light exposure at this time is too large, the viscosity of the ink can be prevented from increasing beyond the proper range.

In addition, a part of the irradiated light may be incident on the untransferred ink on the printing cloth (intermediate transfer body). However, the resulting increase in the viscosity of the untransferred ink is also limited, which can avoid the decrease in transferability to the printed matter. In addition, by performing overlap printing in a state where the ink maintains an appropriate viscosity due to the pre-curing, the adhesion of the inks between the overlapped layers becomes good. Moreover, it can also prevent the ink transferred to the printed matter from being transferred to surrounding members.

As explained above, in the above embodiment, the printing cloth 32 functions as the "intermediate transfer body" of the present invention, and the ink pattern IP corresponds to the "printing pattern" of the present invention. In addition, the light UV1 emitted from the pre-curing unit 4 corresponds to the "first light" of the present invention, and the wavelength λ1 is an example of the "first wavelength" of the present invention. On the other hand, the light UV2 emitted from the main curing unit 5 corresponds to the "second light" of the present invention, and the wavelength λ2 is an example of the "second wavelength" of the present invention.

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

In addition, the present invention is not limited to the above-mentioned embodiments, and various changes can be made in addition to the above-mentioned contents without departing from the spirit thereof. For example, the printing system 100 of the above embodiment has a pre-curing unit 4 and a formal curing unit 5 for appropriately increasing the viscosity of the ink after transfer. On the other hand, for example, in a printing system based on overlap printing, it is also configured to use a combination of one or more printing devices and one formal hardening device, and the one or more printing devices execute In the step before pre-curing, the one formal curing device receives the printed matter from the printing devices to the pre-curing, and performs formal curing.

In addition, in the printing system 100 of the above embodiment, the plate platform unit 1 moves the plate P relative to the fixed printing cloth cylinder 30, and the bottle holding unit 6 moves the bottle B relative to the fixed printing cloth cylinder 30, thereby performing printing processing. In the mutual positioning. However, the movement of these units only needs to be realized relatively. Which unit is made movable is not limited to the above-mentioned content and is arbitrary.

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

In addition, the light source of the pre-curing unit 4 in the above embodiment is a UV-LED, and the light source of the formal 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.

In addition, the bottle holding unit 6 of the above-mentioned embodiment has a configuration in which the bottle B as a to-be-printed material is sandwiched by the connecting member 621 and the spring member 622, and the bottle B is supported by the supporting rollers 631 to 634. However, the holding form of the printed matter is not limited to this but is arbitrary. For example, it may also be a structure in which an appropriate rotating chuck mechanism is used to hold the printed matter.

In addition, the printed matter in the above embodiment is a substantially cylindrical bottle B, but the printed matter is not limited to this. For example, it is also possible to use the above-mentioned printing processing system 100 to perform printing processing for a cylindrical printed matter with open ends or a printed matter provided with unevenness on the cylindrical surface.

Above, as explained in the specific embodiments, in the printing method of the present invention, for example, the content of the first photopolymerization initiator in the photocurable ink may be less than that required to harden the polymer material as a whole. the amount. According to this structure, even if the amount of exposure by the first light increases, the ink will not be completely cured, and an appropriate viscosity can be maintained. Therefore, a printing process that is less sensitive to exposure can be constructed.

In addition, for example, the printed matter may be translucent. In this case, it is actually impossible to control the light that penetrates the inside of the printed matter and enters the intermediate transfer body. However, as described above, the variation of the exposure amount in the present invention has less influence on the viscosity. Therefore, it is possible to avoid the problems that lead to the retransfer of the ink or the deterioration of the printing quality such as poor transfer.

In addition, for example, the present invention may also be configured such that the intermediate transfer body has a printing cloth made of elastic resin whose surface shape is a cylindrical surface, and the printing cloth carrying a printing pattern on the surface abuts against the object to be printed and rotates, The printing pattern is transferred to the printed matter. According to this structure, by providing a printing cloth temporarily supporting the printed pattern, it is also possible to easily cope with the change of the printed pattern or the printed matter. In addition, the surface of the printing cloth with elasticity can follow the unevenness of the surface of the printed matter, so printing can be performed well on the printed matter that is not a complete cylinder.

Moreover, in the printing method of the present invention, the transfer in the second step and the light irradiation in the third step can also be performed simultaneously at least for a period of time. Part of the light used in the light irradiation used in the third step may cause the ink viscosity in the second step to change. However, in the present invention, the problem is eliminated by studying the photopolymerization initiator and the wavelength of the irradiated light, even when the two steps are performed at the same time, there is no problem.

In addition, the printing method of the present invention may be configured to perform the processing from the first step to the third step multiple times on the same to-be-printed object to transfer a plurality of layers of printing patterns to the to-be-printed object, and then perform the fourth step. According to this structure, the newly transferred printing pattern overlaps the ink that was transferred in the previous step and the viscosity has increased moderately. Therefore, the adhesion between the layers can be improved. Then, after the transfer of the plural layers, the second light is collectively irradiated, thereby curing the entire printed pattern to obtain the final printed matter.

Above, the invention has been described according to specific embodiments, but the description is not intended to be interpreted in a limited sense. By referring to the description of the invention, those skilled in the art can understand various modifications of the embodiments disclosed in the same manner as other embodiments of the invention. Therefore, it is considered that the scope of the attached patent application does not deviate from the true scope of the invention, and includes the modification or embodiment. [Industrial availability]

The present invention can be applied to all printing techniques for printing on the surface of a cylindrical printed object such as a glass bottle or a resin bottle, and is especially effective when the printed object is transparent and has translucency.

1: Edition platform unit 2: Ink filling unit 3: Transfer unit 4: Pre-hardening unit 5: Formal hardening unit 6: Bottle holding unit 9: Control unit 11: Platform 12: Alignment mechanism 13: Base 14: Rail 15: Point the camera 21: Nozzle 22: Ink supply department 23: scraper 30: Printing cloth roller 31: Printing cloth roller 32: Printing cloth (intermediate transfer body) 33: Motor 60: Support frame 61: bottom plate 62: side panel 65: alignment mechanism 66: Base 67: Rail 68: Point at the camera 100: printing system 621: connecting member 622: Spring member 631: back-up roller 632: Support Roll 633: Support Roll 634: Support roller B: Bottle (printed matter) B1: neck B2: side B3: bottom face IK: Light-curing ink IP: ink pattern (printed pattern) IP1: Ink pattern (printed pattern) IP2: Ink pattern (printed pattern) P: version S: Shading member S101: Step 1 S102: Step 1 S103: Step 1 S104: Step 2 S105: Step 2 S106: Step 2 S107: Step 2 S108: Step 3 S109: Step 4 S110: Step S111: Step UV1: first light UV2: second light

FIG. 1 is a schematic diagram showing a schematic configuration example of a printing system that can realize the printing method of the present invention. Figure 2 is a diagram showing the composition of the plate platform unit and the ink filling unit. Fig. 3A is a diagram showing the structure of a bottle holding unit. Fig. 3B is a diagram showing the structure of the bottle holding unit. Fig. 4 is a flowchart showing an embodiment of the printing method of the present invention. FIG. 5 is a diagram schematically showing the movement of various parts during the execution of the printing method of FIG. 4. FIG. 6 is a diagram schematically showing the movement of various parts during the execution of the printing method of FIG. 4. Fig. 7 is a diagram schematically showing the movement of each part in overlapping printing. Fig. 8A is a diagram illustrating the problem of light leakage to the printed cloth. Fig. 8B is a diagram illustrating the problem of light leakage to the printed cloth. Fig. 9 is a diagram showing ink and UV light used in this embodiment. Fig. 10A is a diagram schematically showing the mechanism of ink curing by light irradiation. Fig. 10B is a diagram schematically showing the mechanism of ink curing by light irradiation. Fig. 10C is a diagram schematically showing the mechanism of ink hardening by light irradiation. Fig. 10D is a diagram schematically showing the mechanism of ink curing by light irradiation.

1: Edition platform unit

2: Ink filling unit

3: Transfer unit

4: Pre-hardening unit

5: Formal hardening unit

6: Bottle holding unit

9: Control unit

11: Platform

21: Nozzle

30: Printing cloth roller

31: Printing cloth roller

32: Printing cloth

33: Motor

100: printing system

631: back-up roller

632: Support Roll

633: Support Roll

634: Support roller

B: Bottle

P: version

Claims (7)

A printing method, which includes: The first step is to form a printing pattern of photocurable ink on the surface of the intermediate transfer body; The second step is to make the intermediate transfer body abut against the object to be printed, and transfer the printing pattern on the surface of the intermediate transfer body to the object to be printed; The third step is to irradiate the printing pattern transferred to the printing object with first light to increase the viscosity of the photocurable ink; and The fourth step is to irradiate the printed pattern with increased viscosity with a second light to harden the photocurable ink; and The above-mentioned first light includes light of the first wavelength, The second light includes light having a second wavelength shorter than the first wavelength with a higher intensity than the first light, and The above-mentioned photocurable ink contains: Polymer material, which is cured by polymerization; A first photopolymerization initiator that reacts with the light of the first wavelength; and The second photopolymerization initiator does not react with the light of the first wavelength but reacts with the light of the second wavelength. The printing method of claim 1, wherein the first light does not substantially include the light of the second wavelength. The printing method of claim 1 or 2, wherein the content of the first photopolymerization initiator in the photocurable ink is less than the amount required to harden the polymer material as a whole. The printing method of claim 1 or 2, wherein the above-mentioned to-be-printed object has light transmittance. The printing method of claim 1, wherein the intermediate transfer body has a printing cloth made of elastic resin whose surface shape is a cylindrical surface, The printing cloth having the printing pattern on its surface abuts on the printing object and rotates, so that the printing pattern is transferred to the printing object. The printing method of claim 1, wherein the transfer in the second step and the light irradiation in the third step are performed simultaneously for at least a period of time. The printing method of claim 1, wherein the processes from the first step to the third step are performed multiple times on the same printed matter to transfer the plurality of layers of the printing patterns to the printed matter, and then the fourth step.

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