JP7389672B2 - Tablet printing equipment and tablet printing equipment maintenance methods - Google Patents

Description

The present invention relates to a tablet printing device that prints on the surface of a tablet, and a method for maintaining the tablet printing device.

Characters and codes are printed on the surface of tablets, which are a form of pharmaceutical products, to identify the product. Such characters and codes may be printed by stamping, but there is a problem in that the visibility of stamping is low. In particular, in recent years, the types of tablets have diversified due to the spread of generic drugs. For this reason, in order to make tablets easier to identify, technology that uses an inkjet method to print clearly on the surface of tablets is attracting attention.

Patent Document 1 describes an example of a conventional apparatus that prints on the surface of a tablet using an inkjet method.

International Publication No. 2016/159096

In an inkjet tablet printing device, ink droplets (hereinafter simply referred to as "ink droplets") are ejected from a plurality of nozzles provided on the ejection surface of a head toward the tablet while transporting the tablet. In such an inkjet printing device, an ink surface is arranged inside each nozzle. For this reason, in nozzles that are used less frequently, the ink solvent evaporates from the liquid surface, causing rise of the meniscus, aggregation of ink components, concentration of ink components, etc. within the nozzle. This reduces the fluidity of the ink and causes the problem of ink clogging.

To solve such problems, common inkjet printing apparatuses use a maintenance method called purge processing, which pressurizes the ink in the head and ejects the ink from all nozzles at once. By applying pressure and ejecting ink through purge processing, the agglomeration of the ink components causing the ink and the concentrated ink are ejected out of the nozzle.

On the other hand, the printing rate of tablet printing devices is about 8%, which is lower than that of other printing devices. Therefore, there are long periods during which ink is not ejected from many nozzles. That is, compared to other printing devices, the fluidity of ink tends to decrease, and the number of nozzles in which ink clogging occurs increases.

Therefore, in order to eliminate ink clogging by conventional purge processing in a tablet printing device, it is necessary to increase the purge time or the number of purges. In other words, it consumes a larger amount of ink than other printing devices.

However, the edible inks used in tablet printing equipment are very expensive compared to the inks used in media such as ordinary paper and film.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a technique that can efficiently eliminate ink clogging while suppressing ink consumption.

In order to solve the above problems, a first invention of the present application is an inkjet tablet printing device that prints on the surface of a tablet, and includes an inkjet head having a plurality of nozzles capable of ejecting ink; a pressure adjustment section capable of adjusting the pressure within the head; a heater capable of raising the temperature of the ink ejected from the nozzle inside the head to a first temperature and a second temperature; the head; the pressure adjustment section; and a control unit that controls the heater, and the control unit includes a printing step of discharging the ink at the first temperature from some of the nozzles onto the surface of the tablet, and adjusting the pressure. a recovery step of ejecting the ink at the second temperature from all the nozzles by increasing the pressure in the head by a part, and the second temperature is lower than the first temperature. The temperature is also higher than 2℃ and lower than 15℃ ,
The ink ejected in the recovery step stays on the lower surface of the head without dripping from the head.

A second invention of the present application is the tablet printing apparatus of the first invention , in which the control section includes, in the recovery step, a step of: a) heating the ink in the head to the second temperature by the heater; , b) stopping the heater after the step a), and c) increasing the pressure inside the head after the step b) to eject the ink from all the nozzles. ,including.

A third invention of the present application is the tablet printing apparatus of the first invention or the second invention , wherein the head communicates with each of the plurality of nozzles arranged on the lower surface of the head, and the internal pressure and an ink storage chamber communicating with the plurality of individual ink chambers, and the heater is disposed inside the ink storage chamber.

A fourth invention of the present application is a method for maintaining a head having a plurality of nozzles for ejecting ink in an inkjet tablet printing apparatus that prints on the surface of a tablet, the method comprising: A) ink in the head; B) After the step A), increasing the pressure within the head to eject the ink from all the nozzles. , the second temperature is a temperature higher than the first temperature, which is the temperature of the ink in the head when printing on the tablet, by 2° C. or more and 15° C. or less,
The ink ejected in step B) does not drip from the head but stays on the lower surface of the head.

A fifth invention of the present application is the maintenance method of the fourth invention , wherein in step A), while moving the head from a printing position to a maintenance position, the temperature of the ink in the head is adjusted to the second temperature. The step B) includes B1) confirming that the temperature of the ink in the head has reached the second temperature and stopping the temperature increase of the ink; and B2) the step B1). After that, the method includes a step of increasing the pressure inside the head to eject the ink from all the nozzles, and B3) wiping off the ink remaining on the lower surface of the head.

According to the first to ninth inventions of the present application, in the recovery process, the temperature of the ink is set to a second temperature higher than the first temperature during the printing process. This reduces the viscosity of the ink and reduces the pressure loss within the nozzle. As a result, the amount of ink ejected in the recovery process can be suppressed.

In particular, according to the second invention and the seventh invention of the present application, the amount of ink ejected in the recovery process can be significantly suppressed compared to normal purge processing.

In particular, according to the third invention and the eighth invention of the present application, the recovery step can be performed at an appropriate ink temperature.

1 is a diagram showing the configuration of a tablet printing device. It is a partial perspective view of a tablet conveyance mechanism. FIG. 3 is a bottom view of the head. FIG. 2 is a block diagram showing connections between a control unit and various parts within the tablet printing device. FIG. 3 is a partial side view of the printing section. FIG. 3 is a longitudinal cross-sectional view of the cap. FIG. 2 is a schematic diagram showing the configuration of a head and an ink supply mechanism. 7 is a flowchart showing the flow of temperature management within the head before the start of a printing process. It is a flowchart showing the flow of a recovery process. FIG. 3 is a diagram showing the relationship between ink temperature and viscosity.

Embodiments of the present invention will be described below with reference to the drawings. In addition, in the following description, the direction in which a plurality of tablets are conveyed will be referred to as the "transportation direction", and the direction perpendicular and horizontal to the transportation direction will be referred to as the "width direction".

<1. Overall configuration of tablet printing device>
FIG. 1 is a diagram showing the configuration of a tablet printing apparatus 1 according to an embodiment of the present invention. This tablet printing device 1 is a device that prints images such as a product name, product code, company name, logo mark, etc. on the surface of each tablet 9 while conveying a plurality of tablets 9 that are pharmaceuticals. As shown in FIG. 1, the tablet printing apparatus 1 of this embodiment includes a tablet conveyance mechanism 10, a printing section 20, a drying mechanism 30, and a control section 100.

The tablet transport mechanism 10 is a mechanism that holds and transports a plurality of tablets 9, which are objects to be printed. The tablet conveyance mechanism 10 includes a pair of pulleys 11 and an annular conveyance belt 12 stretched between the pair of pulleys 11. A plurality of tablets 9 loaded into the tablet printing apparatus 1 are arranged at equal intervals and supplied to the outer peripheral surface of the conveyor belt 12 by a carry-in mechanism 51 composed of a vibrating feeder, a conveyor drum, and the like. One of the pair of pulleys 11 is rotated by power obtained from the transport motor 13. As a result, the conveyor belt 12 rotates in the direction of the arrow in FIG. At this time, the other of the pair of pulleys 11 rotates as the conveyor belt 12 rotates.

FIG. 2 is a partial perspective view of the tablet transport mechanism 10. As shown in FIG. 2, the conveyor belt 12 is provided with a plurality of suction holes 14. The plurality of suction holes 14 are arranged at equal intervals in the transport direction and the width direction. Further, as shown in FIG. 1, the tablet conveyance mechanism 10 includes a suction mechanism 15 that sucks out gas from the space inside the conveyance belt 12. When the suction mechanism 15 is operated, the space inside the conveyor belt 12 becomes a negative pressure lower than atmospheric pressure. The plurality of tablets 9 are suction-held in the suction holes 14 by the negative pressure.

In this way, the tablet conveyance mechanism 10 conveys the plurality of tablets 9 by rotating the conveyor belt 12 while holding the plurality of tablets 9 in the plurality of suction holes 14 at regular intervals. A plurality of tablets 9 are conveyed in the horizontal direction below four heads 21, which will be described later.

Further, as shown in FIG. 1, the tablet conveyance mechanism 10 has a blow mechanism 16 inside the conveyance belt 12. When the blow mechanism 16 is operated, among the plurality of suction holes 14 of the conveyor belt 12, only the suction hole 14 facing the discharge mechanism 52 has a positive pressure higher than atmospheric pressure. As a result, the suction of the tablet 9 in the suction hole 14 is released, and the tablet 9 is transferred from the conveyor belt 12 to the delivery mechanism 52. The carry-out mechanism 52 carries out the tablets 9 delivered from the conveyor belt 12 to the outside of the tablet printing apparatus 1, for example, by using another conveyor belt.

The printing unit 20 is a part that records an image on the surface of the tablet 9 transported by the transport belt 12 using an inkjet method. As shown in FIG. 1, the printing section 20 of this embodiment has four heads 21. The four heads 21 are located above the conveyor belt 12 and arranged in a line along the conveyance direction of the tablets 9. The four heads 21 eject ink droplets of different colors (for example, cyan, magenta, yellow, and black) toward the surface of the tablet 9. Then, a multicolor image is recorded on the surface of the tablet 9 by superimposing the monochrome images formed by these colors. Note that the ink ejected from each head 21 is an edible ink manufactured from raw materials approved by the Japanese Pharmacopoeia, the Food Sanitation Law, etc.

FIG. 3 is a bottom view of one head 21. In FIG. 3, the conveyor belt 12 and the plurality of tablets 9 held by the conveyor belt 12 are shown by two-dot chain lines. As shown in an enlarged view in FIG. 3, a plurality of nozzles 211 capable of ejecting ink droplets are provided on the lower surface of the head 21. In this embodiment, a plurality of nozzles 211 are two-dimensionally arranged on the lower surface of the head 21 in the transport direction and the width direction. The nozzles 211 are arranged with their positions shifted in the width direction. In this way, by arranging the plurality of nozzles 211 two-dimensionally, the positions of the nozzles 211 in the width direction can be made close to each other. However, the plurality of nozzles 211 may be arranged in a line along the width direction.

As a method for ejecting ink droplets from the nozzle 211, for example, a so-called piezo method is used in which the ink in the nozzle 211 is pressurized and ejected by applying voltage to a piezoelectric element to deform it. However, the ink droplet ejection method may be a so-called thermal method in which the ink droplets are ejected by energizing a heater to heat and expand the ink in the nozzle 211 .

The drying mechanism 30 is a mechanism that dries the ink adhering to the surface of the tablet 9. The drying mechanism 30 is provided around the conveyor belt 12 at a position downstream of the printing section 20 in the conveyance direction. The drying mechanism 30 includes, for example, a hot air supply mechanism that blows heated gas (hot air) toward the tablets 9 conveyed by the conveyor belt 12. The ink attached to the surface of the tablet 9 is dried by hot air and fixed on the surface of the tablet 9.

The control section 100 is a means for controlling the operation of each section within the tablet printing apparatus 1. FIG. 4 is a block diagram showing connections between the control section 100 and each section within the tablet printing apparatus 1. As conceptually shown in FIG. 4, the control unit 100 is constituted by a computer having a processor 101 such as a CPU, a memory 102 such as a RAM, and a storage unit 103 such as a hard disk drive. A computer program P for executing print processing is installed in the storage unit 103.

Further, as shown in FIG. 4, the control unit 100 communicates with the above-mentioned transport motor 13, suction mechanism 15, blow mechanism 16, four heads 21, drying mechanism 30, carry-in mechanism 51, and carry-out mechanism 52, respectively. Possibly connected. The control unit 100 is also communicably connected to a head moving mechanism 22, a cleaning unit 24, a wiping unit 25, and an ink supply mechanism 70, which will be described later. The control unit 100 temporarily reads the computer program P and data stored in the storage unit 103 into the memory 102, and the processor 101 performs arithmetic processing based on the computer program P, thereby controlling the operation of each of the above units. do. As a result, printing processing for the plurality of tablets 9 and maintenance processing to be described later proceed.

<2. About the head movement mechanism and cap>
Next, the head moving mechanism 22 and the cap 23 will be explained with reference to FIGS. 5 and 6. FIG. 5 is a partial side view of the printing section 20 seen from the position of the outlined arrow V in FIG. FIG. 6 is a longitudinal sectional view of the cap 23.

As shown in FIG. 5, the internal space of this tablet printing device 1 is divided into a printing area A1 and a retreat area A2. The printing area A1 is a printing space where printing is performed on the tablet 9 while the tablet 9 is transported by the tablet transport mechanism 10 described above. The evacuation area A2 is a evacuation space in which the head 21 is evacuated and on standby before or after printing, and in which equipment that does not need to be in the same space as the tablets 9 is accommodated.

A partition wall 60 is provided between the print area A1 and the retreat area A2 to partition the two areas. The partition wall 60 has an opening 61 through which the head 21 passes. The opening 61 may be always open, or may be provided with a shutter mechanism that opens when the head 21 passes.

As described above, the printing section 20 has four heads 21. Further, as shown in FIG. 5, the printing section 20 includes a head moving mechanism 22 and a cap 23 for each head 21. That is, the printing unit 20 of this embodiment includes four heads 21, four head moving mechanisms 22 corresponding to each head 21, and four caps 23 corresponding to each head 21.

The head moving mechanism 22 is a mechanism that moves the head 21 between the printing position P1 and the standby position P2. The head moving mechanism 22 of this embodiment includes an arm 221 and an arm moving mechanism 222.

The arm 221 is a member extending in the width direction. The head 21 is fixed to the tip of the arm 221 on one side in the width direction. The arm moving mechanism 222 moves the arm 221 in the vertical direction and the width direction according to a command from the control unit 100. As a result, the arm 221 and the head 21 move together in the vertical direction and the width direction.

The arm moving mechanism 222 is realized, for example, by combining a horizontal direction (width direction) moving mechanism and a vertical moving mechanism. These moving mechanisms are realized by, for example, a mechanism that converts rotational motion of a motor into linear motion via a ball screw, a linear motor, an air cylinder, or the like.

As shown in FIG. 5, the head moving mechanism 22 moves the head 21 in the vertical direction and the width direction between the printing position P1 and the standby position P2. The head 21 prints on the tablet 9 at the printing position P1. When the head 21 is placed at the printing position P1, the plurality of nozzles 211 face the tablets 9 held on the conveyor belt 12. At the standby position P2, the plurality of nozzles 211 of the head 21 are covered by the cap 23.

The standby position P2 is a lower position than the printing position P1. Therefore, when moving the head 21 from the printing position P1 to the standby position P2, the head moving mechanism 22 moves the head 21 from the printing position P1 into the retreat area A2 in the width direction and places it at the intermediate position P3. Afterwards, it is lowered to the standby position P2.

When moving the head 21 from the standby position P2 to the printing position P1, the head moving mechanism 22 moves the head 21 in the reverse order. That is, the head moving mechanism 22 raises the head 21 from the standby position P2 to the intermediate position P3, and then moves the head 21 into the printing area A1 in the width direction to the printing position P1.

Note that the intermediate position P3 may be higher than the printing position P1. In that case, the head moving mechanism 22 raises the head 21 from the printing position P1 to the same height as the intermediate position P3, and then moves the head 21 in the width direction at the height to the intermediate position P3 within the retreat area A2. After that, it may be lowered to the standby position P2.

In that case, when moving the head 21 from the standby position P2 to the printing position P1, the head moving mechanism 22 raises the head 21 from the standby position P2 to the intermediate position P3, and then moves the head 21 into the printing area A1. Then, the head 21 is lowered and placed at the printing position P1.

The cap 23 is a substantially rectangular parallelepiped-shaped housing with an open top surface. The cap 23 is fixed at a predetermined position within the retreat area A2. The cap 23 covers the plurality of nozzles 211 of the head 21 arranged at the standby position P2. In this way, by covering the nozzle 211 with the cap 23 while the head 21 is not in use, the ink inside the nozzle 211 can be prevented from drying.

In this embodiment, the cap 23 includes a cleaning unit 24 and a wiping unit 25.

The cleaning unit 24 is a unit for cleaning the plurality of nozzles 211 of the head 21. As shown in FIGS. 5 and 6, the cleaning unit 24 includes a cleaning nozzle 241 and a cleaning liquid supply section 242.

The cleaning nozzle 241 discharges the cleaning liquid supplied from the cleaning liquid supply section 242 toward the plurality of nozzles 211 inside the cap 23 . Specifically, as shown in FIG. 6, the cleaning nozzle 241 has a plurality of discharge ports 240 that discharge the cleaning liquid upward. By cleaning the plurality of nozzles 211 of the head 21 with the cleaning unit 24, fine particles and the like attached to the nozzles 211 in the print area A1 can be removed. Note that the cap 23 does not need to be equipped with the cleaning unit 24.

The wiping unit 25 is a unit for wiping the ejection surface (lower surface) of the head 21 including the plurality of nozzles 211. The wiping unit 25 has a blade 251 and a blade moving mechanism 252.

The blade 251 is a member for wiping off ink droplets and cleaning liquid adhering to the lower surface of the head 21. For the blade 251, a plate-shaped member made of flexible rubber or the like is used, for example. Note that only the tip portion 250 of the blade 251 that contacts the head 21 may be formed of a flexible member.

The blade moving mechanism 252 is a mechanism that rotationally moves the blade 251. The blade moving mechanism 252 includes, for example, a drive source such as a motor, and a power transmission mechanism that transmits the rotational motion of the motor to the blade 251. When the blade moving mechanism 252 is operated, the blade 251 rotates between a storage position Q1 shown by a solid line in FIG. 6 and a wiping position Q2 shown by a two-dot chain line in FIG.

When the head 21 is placed at the standby position P2 and the plurality of nozzles 211 are covered by the cap 23, the blade 251 is placed at the storage position Q1. In the storage position Q1, the entire blade 251 is stored inside the cap 23.

On the other hand, when the blade 251 wipes ink droplets and cleaning liquid on the lower surface of the head 21, the head moving mechanism 22 raises the head 21 to a wiping position P4 higher than the standby position P2, and moves the lower surface of the head 21 to the cap 23. pull away from Then, the blade 251 is rotated from the storage position Q1 to the wiping position Q2. At the wiping position Q2, the tip 250 of the blade 251 contacts the lower surface of the head 21. Thereafter, the head moving mechanism 22 horizontally moves the head 21 in the width direction. As a result, ink droplets, cleaning liquid, and the like adhering to the plurality of nozzles 211 and their surroundings on the lower surface of the head 21 are wiped away by the tip portion 250 of the blade 251.

Note that the wiping position P4 where the lower surface of the head 21 is wiped may be the same as the intermediate position P3, or may be different from the intermediate position P3.

<3. Regarding the ink supply mechanism and head configuration>
Next, the ink supply mechanism 70 that supplies ink to the head 21 and the configuration of the head 21 will be described with reference to FIG. 7. FIG. 7 is a schematic diagram showing the configuration of the head 21 and the ink supply mechanism 70. As described above, the printing section 20 has four heads 21. The printing unit 20 includes an ink supply mechanism 70 for each head 21 that supplies ink to the head 21. That is, the printing unit 20 of this embodiment further includes four ink supply mechanisms 70.

As shown in FIG. 7, each ink supply mechanism 70 has an ink storage section 71, a pressure adjustment mechanism 72, and a pipe 73.

The ink storage section 71 is a container that stores ink to be supplied to the head 21. The ink storage section 71 has a pressure sensor 711 for detecting the pressure within the ink storage section 71 .

The pressure adjustment mechanism 72 is a mechanism for adjusting the pressure inside the ink storage section 71. Since the pressure adjustment mechanism 72 adjusts the pressure inside the ink storage section 71, the pressure adjustment mechanism 72 can indirectly adjust the pressure inside the head 21 when the ink storage section 71 and the head 21 communicate with each other. That is, the pressure adjustment mechanism 72 constitutes a pressure adjustment section that can adjust the pressure inside the head 21.

In this embodiment, the ink storage section 71 is a tank with a constant capacity. The pressure adjustment mechanism 72 then adjusts the pressure within the ink storage section 71 by adjusting the air pressure of the gas layer above the ink storage section 71 . However, the ink storage section 71 may be a so-called ink bag in which a flexible container is filled with ink. In that case, the pressure adjustment mechanism 72 may adjust the pressure inside the ink storage section 71 by adjusting the pressure applied from the outside across the ink storage section 71, which is an ink bag, for example.

The piping 73 communicates and connects the lower end of the ink storage section 71 and an ink supply port 81 of the head 21, which will be described later. For example, a solenoid valve 731 that controls communication of the pipe 73 is inserted into the pipe 73. When the pressure inside the ink storage section 71 becomes greater than the pressure inside the head 21 with the electromagnetic valve 731 open, ink is supplied from the ink storage section 71 to the head 21 . Note that a check valve may be inserted into the pipe 73 together with the solenoid valve 731 or in place of the solenoid valve 731. Further, a filter may be inserted into the pipe 73 to remove solid components, foreign matter, etc. from the ink.

Each head 21 has a casing 80, an ink supply port 81 provided in the casing 80, an ink storage chamber 82, a plurality of individual channels 83, a plurality of individual ink chambers 84, and a plurality of nozzles 211. Although six individual channels 83, six individual ink chambers 84, and six nozzles 211 are shown in FIG. 7 for convenience, the actual head 21 includes a large number of nozzles 211 and the same number of individual channels 83. and an individual ink chamber 84 are provided.

The ink supply port 81 is a communication port that communicates the ink storage chamber 82 with the outside. The downstream end of the piping 73 of the ink supply mechanism 70 is connected to the ink supply port 81 . As a result, ink supplied from the ink storage section 71 via the pipe 73 is temporarily stored in the ink storage chamber 82 via the ink supply port 81.

The ink storage chamber 82 temporarily stores ink to be supplied to each individual ink chamber 84. Inside the ink storage chamber 82, a heater 821 for heating the ink and a temperature sensor 822 for detecting the temperature of the ink are provided.

The heater 821 is a heating mechanism for raising the temperature of ink within the head 21. The control unit 100 controls the heater 821 based on the ink temperature detected by the temperature sensor 822. Thereby, the heater 821 can raise the temperature of the ink in the head 21 to a temperature such as a first temperature and a second temperature, which will be described later. That is, the heater 821 can raise the temperature of the ink ejected from the plurality of nozzles 211 to the first temperature and the second temperature.

The individual flow paths 83 are ink flow paths that connect the ink storage chamber 82 and each individual ink chamber 84. When the pressure within the individual ink chamber 84 becomes lower than the pressure within the ink storage chamber 82, ink is supplied from the ink storage chamber 82 to the individual ink chamber 84 via the individual flow path 83.

The individual ink chamber 84 is an ink storage section provided for each nozzle 211. The individual ink chamber 84 is secondarily filled with the ink supplied into the head 21 . The lower ends of the individual ink chambers 84 communicate with the nozzles 211, respectively.

The nozzle 211 communicates the individual ink chamber 84 with an external space. When ink is not ejected, the liquid level of the ink forms a meniscus inside the nozzle 211 . Further, the lower end portion of the nozzle 211 is arranged to be exposed on the lower surface of the casing 80.

A pressure generating element 841 is arranged on the wall surface of each individual ink chamber 84 . The pressure generating element 841 is an actuator that increases the pressure inside the individual ink chamber 84 . The head 21 of this embodiment is a so-called piezo type ejection head. Therefore, a piezoelectric element is used as the pressure generating element 841 of this embodiment. When an ejection signal, which is an electrical signal, is sent from the control unit 100 to the pressure generating element 841, the pressure generating element 841 is deformed, and the ink filled in the individual ink chamber 84 is pressurized. Then, as the pressure within the individual ink chamber 84 increases, the ink within the individual ink chamber 84 is ejected as droplets from the nozzle 211. Note that the head 21 is not limited to the piezo type, and may be an ejection head of another type.

<4. Regarding temperature control inside the head during the printing process and recovery process>
Next, temperature control within the head 21 before the start of the printing process and during the recovery process in the tablet printing apparatus 1 will be described with reference to FIGS. 8 and 9. FIG. 8 is a flowchart showing the flow of temperature management within the head 21 before the start of the printing process. FIG. 9 is a flowchart showing the flow of the recovery process.

The control unit 100 can cause the tablet printing device 1 to perform at least a printing process and a recovery process. In the printing process, the control unit 100 causes ink at the first temperature to be ejected from some nozzles 211 onto the surface of the tablet 9 while transporting the tablet 9 . Thereby, the printing process is performed on the surface of the tablet 9. On the other hand, in the recovery process, the control unit 100 increases the pressure within the head 21 and causes all the nozzles 211 to eject ink at the second temperature. That is, in the recovery process, the control unit 100 implements a maintenance method called a so-called purge process. In addition to the printing process and the recovery process, the control unit 100 may be able to execute other processes, such as a cleaning process for cleaning the lower surface of the head 21, for example.

First, with reference to FIG. 8, the flow of temperature management within the head 21 before the start of the printing process will be described. As shown in FIG. 8, at the start of the printing process, first, a pre-printing temperature raising process including steps S111, S112, and S113 and a pre-printing moving process including steps S121 and S122 are performed in parallel.

In the pre-print temperature raising process (steps S111 to S113), the control unit 100 first drives the heater 821 to start raising the temperature of the ink in the head 21 to the first temperature (step S111). When the temperature rise is started, the control unit 100 monitors whether the ink temperature detected by the temperature sensor 822 has reached the first temperature (step S112).

In step S112, if the control unit 100 determines that the ink temperature has not reached the first temperature, the process returns to step S112 and waits (step S112/No). In step S112, when determining that the ink temperature has reached the first temperature (step S112/Yes), the control unit 100 performs feedback control of the heater 821 to maintain the ink temperature in the head 21 at the first temperature. (step S113).

On the other hand, in the pre-print movement process (steps S121 to S122), the control unit 100 first operates the head movement mechanism 22 to move the head 21 to the printing position P1 (step S121). After starting the movement, the control unit 100 monitors whether the head 21 has reached the printing position P1 (step S122). In step S122, if the control unit 100 determines that the head 21 has not reached the printing position P1, the process returns to step S122 (step S122/No).

When the control unit 100 starts feedback control in step S113 and determines that the head 21 has reached the printing position P1 in step S122 (step S122/Yes), the process proceeds to step S13 and the printing process is started ( Step S13).

Here, the first temperature is the ink temperature within the head 21 during the printing process. In the printing process, the ink temperature within the head 21 is maintained at the first temperature by feedback control. Therefore, in the printing process, the control unit 100 causes ink at the first temperature to be ejected from some nozzles 211 of the head 21 onto the surface of the tablet 9.

Next, the flow of the recovery process will be explained with reference to FIG. As shown in FIG. 9, when the recovery process is started, first, a pre-purge temperature raising process including step S211 and step S212 and a pre-purge moving process including step S221 and step S222 are performed in parallel.

In the pre-purge temperature raising process (steps S211 to S212), the heater 821 raises the temperature of the ink in the head 21 to a second temperature higher than the first temperature. First, the control unit 100 drives the heater 821 to start raising the temperature of the ink in the head 21 to the second temperature (step S211). When the temperature increase starts, the control unit 100 monitors whether the ink temperature detected by the temperature sensor 822 has reached the second temperature (step S212).

In step S212, if the control unit 100 determines that the ink temperature has not reached the second temperature (step S212/No), the process returns to step S212 and waits.

On the other hand, in the pre-purge movement process (steps S221 to S222), the control unit 100 first operates the head movement mechanism 22 to move the head 21 to the standby position P2 (step S221). After starting the movement, the control unit 100 monitors whether the head 21 has reached the standby position P2 (step S222). In step S222, if the control unit 100 determines that the head 21 has not reached the standby position P2, the process returns to step S222 (step S222/No).

If the control unit 100 determines in step S212 that the ink temperature has reached the second temperature (step S212/Yes), and determines that the head 21 has reached the standby position P2 in step S222 (step S222 /Yes), the process advances to step S23. Then, the control unit 100 stops the heater 821 from increasing the temperature of the ink in the head 21 (step S23). That is, the control unit 100 confirms that the temperature of the ink in the head 21 has reached the second temperature and stops increasing the temperature of the ink.

Note that when it is determined that the ink temperature has reached the second temperature in step S212 (step S212/Yes), if it is not determined that the head 21 has reached the standby position P2 in step S222, the control The unit 100 may perform feedback control of the heater 821 to maintain the temperature of the ink within the head 21 at the second temperature.

After stopping the temperature increase of the ink by the heater 821, the control unit 100 increases the pressure inside the head 21 and causes all the nozzles 211 to eject ink (step S24).

As a specific procedure performed by the control section 100 in step S24, for example, first, the electromagnetic valve 731 is closed to cut off communication between the ink storage section 71 and the head 21. Then, the pressure within the ink storage section 71 is increased by the pressure adjustment mechanism 72. Thereafter, by opening the electromagnetic valve 731, the pressure inside the head 21 suddenly increases.

In step S24, as the pressure inside the head 21 increases, ink at the second temperature is ejected from the nozzle 211. At this time, the amount of ink ejected in step S24 is smaller than the amount of ink ejected in general purge processing. Therefore, the ink ejected in step S24 remains on the lower surface of the head 21.

In this way, in step S24, the purge process is performed at the standby position P2. That is, the standby position P2 is a maintenance position where a purge process is performed. Further, by performing steps S211 to S212 and steps S221 to S222 in parallel, the head 21 is moved from the printing position P1 to the standby position P2, which is the maintenance position, and the inside of the head 21 is A step of raising the temperature of the ink to a second temperature is being performed.

After step S24, the control unit 100 wipes the lower surface of the head 21 with the wiping unit 25 (step S25). Specifically, after the head moving mechanism 22 moves the head 21 to the wiping position P4, the blade moving mechanism 252 moves the blade 251 to the wiping position Q2. Then, by moving the head 21 in the width direction by the head moving mechanism 22, the blade 251 comes into contact with the lower surface of the head 21 and wipes off the ink accumulated on the lower surface of the head 21.

Note that the head 21 may be placed at the wiping position P4 in step S24. In that case, in the pre-purge movement process (steps S221 to S222), the head 21 is placed at the wiping position P4 instead of the standby position P2. That is, the maintenance position where the purge process is performed is the wiping position P4.

When the wiping process of step S25 is completed, the recovery process of the head 21 is completed. After this, when performing a printing process, the head 21 is placed at the printing position P1. Moreover, when the printing process is not performed after this, the head 21 is arranged at the standby position P2.

As described above, in this tablet printing apparatus 1, the temperature of the ink discharged from the nozzle 211 in the recovery process (second temperature) is higher than the temperature of the ink discharged from the nozzle 211 in the printing process (first temperature). The temperature is high.

In the nozzle 211 that is used infrequently, the solvent evaporates from the ink surface or there is no flow of ink within the nozzle 211, resulting in an increase in the meniscus, aggregation of ink components, concentration of ink components, etc. The fluidity of the ink decreases, and the pressure loss within the nozzle 211 increases.

Therefore, in the recovery process, the temperature of the ink in the head 21 is set to a second temperature higher than the first temperature, which is the ink temperature in the printing process. The ink at the second temperature has a lower viscosity than the ink at the first temperature. Therefore, when performing the purge process, it is possible to reduce the viscosity of the ink, improve the fluidity of the ink, and reduce the pressure loss inside the nozzle 211. This makes it possible to eliminate ink clogging in the nozzle 211 even when the amount of ink ejected in the purge process is smaller than that in the normal purge process.

That is, by making the temperature of the ink higher in the recovery process than in the printing process, the amount of ink consumed in the recovery process can be suppressed.

In this embodiment, the first temperature is around 32°C, and the second temperature is around 40°C. The second temperature is preferably a temperature higher than the first temperature by 2° C. or more and 15° C. or less.

When the temperature of the ink increases by 2° C. or more, the viscosity of the ink decreases to such an extent that the ejection condition changes. For this reason, it is preferable that the second temperature is higher than the first temperature by at least 2°C. On the other hand, if the second temperature is set too high, there is a possibility that the temperature inside the head 21 will not decrease to the first temperature after the recovery process. In this case, it becomes necessary to provide a cooling period for lowering the temperature of the ink in the head 21 after the recovery step and before the printing step, or to provide a temperature lowering mechanism. For this reason, it is preferable that the difference between the first temperature and the second temperature is 15° C. or less.

Here, FIG. 10 is a diagram showing the relationship between temperature and viscosity of the edible ink used in this embodiment. In FIG. 10, the horizontal axis is temperature [° C.], and the vertical axis is ink viscosity [mPa·s]. The measuring device used to measure the viscosity of the ink shown in FIG. 10 is VISCOMETER DV-IIPro manufactured by BROOKFIELD.

In the tablet printing apparatus 1 of this embodiment, the viscosity of the ink suitable for the printing process is 3.9±0.2 mPa·s. For this reason, the first temperature is set at around 32°C. On the other hand, in the purge step, the viscosity is preferably 3.2±0.2 mPa·s, which is about 20% lower than that in the printing step. For this reason, the second temperature is set at around 40°C.

Specifically, in this embodiment, the amount of ink ejected during the purge process is small enough to stay on the lower surface of the head 21 without dripping from the head 21. For example, in a tablet printing apparatus 1 having a head 21 of the same size as a conventional printing apparatus, which typically ejects about 60 cc of ink in a purge process, the amount of ink ejected in the purge process of step S24 is set to be about 1 cc. be able to.

<5. Modified example>
Although the main embodiments of the present invention have been described above, the present invention is not limited to the above embodiments.

In the embodiment described above, the position of the cap 23 is fixed and the lower surface of the head 21 is covered with the cap 23 by lowering the head 21. However, the lower surface of the head 21 may be covered with the cap 23 by providing the cap 23 with a vertical movement mechanism and raising the cap 23.

Further, in the above embodiment, the printing section 20 was provided with four heads 21. However, the number of heads 21 included in the printing section 20 may be one to three, or five or more.

Further, in the above embodiment, one head 21 has a two-stage structure including one ink storage chamber and a plurality of individual ink chambers 84, but the present invention is not limited to this. For example, one head may include a common ink flow path, a plurality of ink storage chambers to which ink is supplied from the common ink flow path, and a plurality of individual ink chambers communicating with each of the ink storage chambers. It may have a tiered structure. Also, the head may have other structures.

Further, in the above embodiment, there is one head 21 that ejects the same type of ink at the same location in the transport direction, but the present invention is not limited to this. A head unit that ejects the same type of ink at the same location in the transport direction may be configured by combining a plurality of heads.

Moreover, although the tablet printing apparatus 1 of the above embodiment includes one printing section that prints on the surface of the tablet 9, the present invention is not limited to this. The tablet printing device may include two printing units: a printing unit that prints on one side of the tablet, and a printing unit that prints on the other side (back side) of the tablet.

In addition, "tablets" to be treated in the present invention include, for example, uncoated tablets, orally disintegrating tablets (OD tablets), film-coated tablets (FC tablets), sugar-coated tablets, and scored tablets, but are not necessarily tablets as pharmaceuticals. is not limited to. The tablet printing apparatus of the present invention may print on tablets as health foods and tablet confections such as ramune.

Further, the detailed configuration of the tablet printing device 1 may be different from each figure of the present application. Furthermore, the elements appearing in the above-described embodiments and modifications may be combined as appropriate to the extent that no contradiction occurs.

1 Tablet printing device 9 Tablet 20 Printing section 21 Head 71 Ink storage section 72 Pressure adjustment mechanism 82 Ink storage chamber 84 Individual ink chamber 85 Nozzle 100 Control section 211 Nozzle 251 Blade 821 Heater 822 Temperature sensor 841 Pressure generating element P1 Printing position P2 Standby Position P3 Wiping position

Claims (5)

An inkjet tablet printing device that prints on the surface of a tablet,
an inkjet head having multiple nozzles capable of ejecting ink;
a pressure adjustment section that can adjust the pressure within the head;
a heater capable of heating the ink ejected from the nozzle inside the head to a first temperature and a second temperature;
a control unit that controls the head, the pressure adjustment unit, and the heater;
has
The control unit includes:
a printing step of ejecting the ink at the first temperature from some of the nozzles onto the surface of the tablet;
a recovery step in which the pressure in the head is increased by the pressure adjustment unit to eject the ink at the second temperature from all the nozzles;
is executable,
The second temperature is a temperature higher than the first temperature by 2°C or more and 15°C or less ,
In the tablet printing device , the ink ejected in the recovery step does not drip from the head but stays on the lower surface of the head . The tablet printing device according to claim 1,
In the recovery step, the control unit includes:
a) raising the temperature of the ink in the head to the second temperature by the heater;
b) stopping the heater after step a);
c) after step b), increasing the pressure within the head to eject the ink from all the nozzles;
tablet printing equipment, including; The tablet printing device according to claim 1 or 2,
The head is
a plurality of the nozzles arranged on the lower surface of the head;
a plurality of individual ink chambers communicating with each of the nozzles and having an actuator for increasing internal pressure;
an ink storage chamber communicating with the plurality of individual ink chambers;
has
The tablet printing apparatus, wherein the heater is disposed inside the ink storage chamber. A method for maintaining a head having a plurality of nozzles for ejecting ink in an inkjet tablet printing device that prints on the surface of a tablet, the method comprising:
A) raising the temperature of the ink in the head to a second temperature;
B) after step A), increasing the pressure within the head to eject the ink from all the nozzles;
including;
The second temperature is a temperature higher than the first temperature, which is the temperature of the ink in the head when printing on the tablet, by 2° C. or more and 15° C. or less,
A maintenance method in which the ink ejected in step B) does not drip from the head but stays on the lower surface of the head. The maintenance method according to claim 4,
In step A), while moving the head from a printing position to a maintenance position, increasing the temperature of the ink in the head to the second temperature,
The step B) is
B1) confirming that the temperature of the ink in the head has reached the second temperature and stopping the temperature increase of the ink;
B2) After the step B1), increasing the pressure within the head to eject the ink from all the nozzles as ejection targets;
B3) wiping off the ink remaining on the lower surface of the head;
including maintenance methods.

Images