CN113211996B

CN113211996B - Tablet printing apparatus and maintenance method for tablet printing apparatus

Info

Publication number: CN113211996B
Application number: CN202110164802.6A
Authority: CN
Inventors: 中野信行; 山下和人; 蒲隆
Original assignee: Screen Holdings Co Ltd
Current assignee: Screen Holdings Co Ltd
Priority date: 2020-02-06
Filing date: 2021-02-05
Publication date: 2022-10-28
Anticipated expiration: 2041-02-05
Also published as: KR20210100533A; KR102418940B1; CN113211996A; TWI761036B; JP7389672B2; JP2021122558A; TW202130521A

Abstract

The invention provides a tablet printing apparatus and a maintenance method of the tablet printing apparatus, which can restrain the consumption of ink and effectively eliminate ink blockage in the tablet printing apparatus. The tablet printing apparatus includes: an ink jet type print head having a plurality of nozzles capable of ejecting ink; a pressure adjustment unit capable of adjusting the pressure in the print head; a heater capable of heating ink to a first temperature and a second temperature inside the print head; and a control unit for controlling the respective units. The control section can execute: a printing step of discharging ink at a first temperature from a part of the nozzles onto the surface of the tablet; and a recovery step of raising the pressure in the print head to discharge ink at the second temperature to all the nozzles as discharge targets. The second temperature is a higher temperature than the first temperature. In this way, the viscosity of the ink is reduced and the pressure loss in the nozzle is reduced in the recovery step, and the amount of ink discharged in the recovery step can be suppressed.

Description

Tablet printing apparatus and maintenance method for tablet printing apparatus

Technical Field

The present invention relates to a tablet printing apparatus that prints on a surface of a tablet and a maintenance method for the tablet printing apparatus.

Background

Characters or codes for identifying products are printed on the surface of a tablet, which is one form of a pharmaceutical product. Such characters and codes are sometimes printed by imprinting, but imprinting has a problem of low visibility. In particular, in recent years, the types of tablets have been diversified due to the spread of pharmaceuticals. Therefore, in order to easily identify the tablet, a technique of clearly printing the surface of the tablet by an ink jet method is attracting attention.

Patent document 1 describes an example of a conventional apparatus for printing on the surface of a tablet by an ink jet method.

Documents of the prior art

Patent document

Patent document 1: international publication No. 2016/159096

Disclosure of Invention

Problems to be solved by the invention

In an ink jet type tablet printing apparatus, droplets of ink are discharged toward a tablet from a plurality of nozzles provided on a discharge surface of a print head while the tablet is conveyed. Hereinafter, the "droplet of ink" is simply referred to as "ink droplet". In such an ink jet type printing apparatus, a liquid surface of ink is disposed inside each nozzle. Therefore, in the nozzle which is used less frequently, the solvent of the ink evaporates from the liquid surface, and the rise of the meniscus, the aggregation of the ink components, the concentration of the ink components, and the like occur in the nozzle. This reduces the fluidity of the ink, and causes a problem of ink clogging.

In order to solve such a problem, a maintenance method called a purge process is used in a general ink jet type printing apparatus, in which ink in a print head is pressurized and discharged from all nozzles at once. The ink is discharged by applying pressure by the cleaning process, and the ink, which causes aggregation and concentration of the ink components, is discharged to the outside of the nozzle.

On the other hand, the tablet printing apparatus has a printing rate of about 8%, and the printing rate is lower than that of other printing apparatuses. Therefore, in the large number of nozzles, the period during which ink is not discharged is long. That is, in the tablet printing apparatus, the fluidity of the ink is easily lowered and the number of nozzles in which ink clogging occurs is increased as compared with the case of other printing apparatuses.

Therefore, in the tablet printing apparatus, in order to eliminate the ink clogging by the conventional cleaning process, it is necessary to increase the cleaning time or the number of times of cleaning. That is, a larger amount of ink is consumed than other printing apparatuses.

However, edible inks used in tablet printers are very expensive compared to inks used in media such as ordinary paper or photographs.

The present invention has been made in view of such circumstances, and an object thereof is to provide a technique capable of efficiently eliminating ink clogging while suppressing the amount of ink consumed.

Means for solving the problems

In order to solve the above problems, a first aspect of the present invention provides an ink jet type tablet printing apparatus for printing on a surface of a tablet, comprising: an inkjet print head having a plurality of nozzles capable of ejecting ink; a pressure adjustment unit capable of adjusting the pressure in the print head; a heater capable of heating the ink discharged from the nozzle to a first temperature and a second temperature inside the print head; and a control unit that controls the print head, the pressure adjustment unit, and the heater, wherein the control unit is capable of executing: a printing step of discharging the ink at the first temperature from a part of the nozzles onto a surface of the tablet; and a recovery step of raising the pressure in the print head by the pressure adjustment unit to discharge the ink at the second temperature, which is higher than the first temperature, to all the nozzles as discharge targets.

A second aspect of the present invention is a maintenance method for a print head having a plurality of nozzles for ejecting ink in an inkjet tablet printing apparatus for printing on a surface of a tablet, the maintenance method including the steps of: a) Raising the temperature of the ink in the print head to a second temperature; and B) after the step a), raising the pressure in the print head to discharge the ink to all the nozzles as discharge targets, wherein the second temperature is higher than a first temperature which is a temperature of the ink in the print head when the tablet is printed.

Effects of the invention

According to the first and second aspects of the present invention, in the recovery step, the temperature of the ink is set to the second temperature higher than the first temperature in the printing step. This reduces the viscosity of the ink, thereby reducing the pressure loss in the nozzle. As a result, the amount of ink discharged in the recovery step can be suppressed.

Drawings

Fig. 1 is a diagram showing the structure of a tablet printing apparatus.

Fig. 2 is a partial perspective view of the tablet transport mechanism.

Fig. 3 is a bottom view of the printhead.

Fig. 4 is a block diagram showing connections between the control unit and each unit in the tablet printing apparatus.

Fig. 5 is a partial side view of the printing portion.

Fig. 6 is a longitudinal sectional view of the cap.

Fig. 7 is a schematic diagram showing the configuration of the print head and the ink supply mechanism.

Fig. 8 is a flowchart showing a flow of temperature management in the print head before the start of the printing process.

Fig. 9 is a flowchart showing the flow of the recovery process.

Fig. 10 is a graph showing a relationship between the temperature and the viscosity of the ink.

In the figure:

1-tablet printing device, 9-tablet, 20-printing section, 21-print head, 71-ink storage section, 72-pressure adjustment mechanism, 82-ink storage chamber, 84-individual ink chamber, 100-control section, 211-nozzle, 251-blade, 821-heater, 822-temperature sensor, 841-pressure generation element, P1-printing position, P2-standby position, P4-wiping position.

Detailed Description

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, a direction in which a plurality of tablets are conveyed is referred to as a "conveying direction", and a direction perpendicular and horizontal to the conveying direction is referred to as a "width direction".

< 1. Integral Structure of tablet printing apparatus >

Fig. 1 is a diagram showing a configuration of a tablet printing apparatus 1 according to an embodiment of the present invention. The tablet printer 1 is a device that prints images such as product names, product codes, company names, logos, and the like on the surfaces of the tablets 9 while conveying a plurality of tablets 9 as a pharmaceutical product. As shown in fig. 1, the tablet printing apparatus 1 of the present embodiment includes a tablet conveying mechanism 10, a printing unit 20, a drying mechanism 30, and a control unit 100.

The tablet conveying mechanism 10 is a mechanism that conveys a plurality of tablets 9 as a printing object while holding them. The tablet conveying mechanism 10 includes a pair of pulleys 11 and an endless conveyor belt 12 extending between the pair of pulleys 11. The plurality of tablets 9 loaded into the tablet printing apparatus 1 are arranged at equal intervals by a loading mechanism 51 composed of a vibrating feeder, a conveying roller, or the like, and are supplied to the outer peripheral surface of the conveying belt 12. One of the pair of pulleys 11 is rotated by power obtained from a conveying motor 13. Thereby, the conveyor belt 12 rotates in the direction of the arrow in fig. 1. At this time, the other of the pair of pulleys 11 is driven to rotate in accordance with the rotation of the conveyor belt 12.

Fig. 2 is a partial perspective view of the tablet conveying 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 conveying direction and the width direction. As shown in fig. 1, the tablet conveying mechanism 10 includes a suction mechanism 15 for sucking gas from a space inside the conveyor belt 12. When the suction mechanism 15 is operated, the space inside the conveyor belt 12 becomes a negative pressure lower than the atmospheric pressure. The plurality of tablets 9 are held by suction through the suction holes 14 by the negative pressure.

In this way, the tablet conveying mechanism 10 holds the plurality of tablets 9 at a constant interval to the plurality of suction holes 14, and conveys the plurality of tablets 9 by the rotation of the conveyor belt 12. A plurality of tablets 9 are conveyed in the horizontal direction below the four printing heads 21 described later.

As shown in fig. 1, the tablet conveying mechanism 10 includes an air blowing mechanism 16 inside the conveyor belt 12. When the air blowing mechanism 16 is operated, only the adsorption holes 14 facing the carry-out mechanism 52 out of the adsorption holes 14 of the conveyor belt 12 have a positive pressure higher than the atmospheric pressure. Thereby, the adsorption of the tablet 9 by the adsorption hole 14 is released, and the tablet 9 is delivered from the conveyor belt 12 to the carrying-out mechanism 52. The carrying-out mechanism 52 carries out the tablet 9 delivered from the conveyor 12 to the outside of the tablet printing apparatus 1 by using another conveyor, for example.

The printing unit 20 is a portion for recording an image on the surface of the tablet 9 conveyed by the conveyor belt 12 by an ink jet method. As shown in fig. 1, the printing unit 20 of the present embodiment includes four printing heads 21. The four print heads 21 are positioned above the conveyor belt 12 and arranged in a line along the conveying direction of the tablets 9. The four print heads 21 eject ink droplets of mutually different colors toward the surface of the tablet 9. The four print heads 21 eject ink droplets of, for example, cyan, magenta, yellow, and black colors. Then, a multicolor image is recorded on the surface of tablet 9 by superimposing monochromatic images formed of these respective colors. In addition, edible ink manufactured from a material approved by the japanese pharmacopoeia, food sanitation law, or the like is used as the ink discharged from each print head 21.

Fig. 3 is a bottom view of one of the print heads 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 fig. 3 in an enlarged manner, a plurality of nozzles 211 capable of ejecting ink droplets are provided on the lower surface of the print head 21. In the present embodiment, the plurality of nozzles 211 are two-dimensionally arranged in the conveyance direction and the width direction on the lower surface of the print head 21. The nozzles 211 are arranged in a staggered manner in the width direction. In this way, if the plurality of nozzles 211 are arranged 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 aligned in a row along the width direction.

As a method of ejecting ink droplets from the nozzle 211, for example, a so-called piezoelectric method is used, in which ink in the nozzle 211 is ejected while being pressurized by applying a voltage to a piezoelectric element to deform the piezoelectric element. However, the ink droplets may be ejected by a so-called thermal method in which the ink in the nozzle 211 is heated and expanded by energizing a heater.

The drying mechanism 30 is a mechanism for drying 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 portion 20 in the conveying direction. In the drying mechanism 30, for example, a hot air supply mechanism is used that blows heated gas (hot air) toward the tablets 9 conveyed by the conveyor belt 12. The ink adhering to the surface of the tablet 9 is dried by hot air and fixed to the surface of the tablet 9.

The control unit 100 controls the operation of each unit in the tablet printing apparatus 1. Fig. 4 is a block diagram showing connections between the control unit 100 and each unit in 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 a printing process is installed in the storage unit 103.

As shown in fig. 4, the control unit 100 is communicably connected to the conveyance motor 13, the suction mechanism 15, the air blowing mechanism 16, the four print heads 21, the drying mechanism 30, the carrying-in mechanism 51, and the carrying-out mechanism 52. The control unit 100 is also communicably connected to the print head moving mechanism 22, the flushing unit 24, the wiping unit 25, and the ink supply mechanism 70, which will be described later. The control unit 100 temporarily reads out the computer program P and data stored in the storage unit 103 to the memory 102, and controls the operations of the above-described units by causing the processor 101 to perform arithmetic processing based on the computer program P. Thereby, the printing process and the maintenance process described later are performed on the plurality of tablets 9.

< 2 > relating to a head moving mechanism and a cap

Next, the print head moving mechanism 22 and the cap 23 will be described with reference to fig. 5 and 6. Fig. 5 is a partial side view of the printing portion 20 as viewed from the position of the hollow arrow V in fig. 1. Fig. 6 is a longitudinal sectional view of the cap 23.

As shown in fig. 5, the internal space of the tablet printing apparatus 1 is divided into a printing area A1 and a retreat area A2. The printing area A1 is a printing space for printing the tablets 9 while conveying the tablets 9 by the tablet conveying mechanism 10. The retreat region A2 is a retreat space for retreating and waiting the print head 21 before or after printing and accommodating an apparatus which is not necessarily in the same space as the tablet 9.

A partition wall 60 that partitions the printing area A1 and the escape area A2 is provided therebetween. The partition wall 60 has an opening 61 for passing the print head 21. The opening 61 may be opened all the time, or may be attached to a shutter mechanism that is opened when the print head 21 passes through.

As described above, the printing portion 20 has the four printing heads 21. In addition, as shown in fig. 5, the printing portion 20 has a head moving mechanism 22 and a cap 23 at each print head 21. That is, the printing section 20 of the present embodiment includes four printing heads 21, four head moving mechanisms 22 corresponding to the respective printing heads 21, and four caps 23 corresponding to the respective printing heads 21.

The head moving mechanism 22 is a mechanism for moving the print head 21 between the print position P1 and the standby position P2. The head moving mechanism 22 of the present embodiment includes an arm 221 and an arm moving mechanism 222.

The arm 221 is a member extending in the width direction. The print head 21 is fixed to the front end of one side in the width direction of the arm 221. The arm moving mechanism 222 moves the arm 221 in the vertical direction and the width direction in accordance with a command from the control unit 100. Thereby, the arm 221 and the print head 21 move in the vertical direction and the width direction as a unit.

The arm moving mechanism 222 is realized by combining a moving mechanism in the horizontal direction (width direction) and a moving mechanism in the vertical direction, for example. 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 print head 21 performs printing on the tablet 9 at the print position P1. When the print head 21 is disposed at the printing position P1, the plurality of nozzles 211 face the tablets 9 held on the conveyor belt 12. In the standby position P2, the plurality of nozzles 211 of the print head 21 are covered with the cap 23.

The standby position P2 is lower than the printing position P1. Therefore, when the print head 21 is moved from the print position P1 to the standby position P2, the print head moving mechanism 22 moves the print head 21 from the print position P1 into the retreat region A2 in the width direction, disposes the print head at the intermediate position P3, and then lowers the print head to the standby position P2.

When the print head 21 is moved from the standby position P2 to the printing position P1, the print head moving mechanism 22 moves the print 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 to the printing position P1 in the width direction within the printing area A1.

The intermediate position P3 may be a position higher than the printing position P1. In this 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 to the intermediate position P3 in the retreat region A2 in the width direction at the height. Then, the apparatus may be lowered to the standby position P2.

In this case, when the print head 21 is moved from the standby position P2 to the printing position P1, the print head moving mechanism 22 raises the print head 21 from the standby position P2 to the intermediate position P3, then moves the print head 21 in the width direction into the printing area A1, and then lowers the print head 21 to be disposed at the printing position P1.

The cap 23 is a substantially rectangular parallelepiped case whose upper surface is open. The cap 23 is fixed at a predetermined position within the escape area A2. The cap 23 covers the plurality of nozzles 211 of the print head 21 disposed at the standby position P2. In this way, by covering the nozzles 211 with the caps 23 while the print head 21 is not in use, the ink inside the nozzles 211 can be prevented from drying.

In the present embodiment, the cap 23 includes a flushing unit 24 and a wiping unit 25.

The flushing unit 24 is a unit for flushing the plurality of nozzles 211 of the print head 21. As shown in fig. 5 and 6, the rinse unit 24 includes a rinse nozzle 241 and a rinse liquid supply part 242.

The rinse nozzle 241 discharges the rinse liquid supplied from the rinse liquid supply unit 242 toward the plurality of nozzles 211 inside the cap 23. Specifically, as shown in fig. 6, the rinse nozzle 241 has a plurality of discharge ports 240 for discharging the rinse liquid upward. By flushing the plurality of nozzles 211 of the print head 21 with the flushing unit 24, the fine powder and the like adhering to the nozzles 211 in the printing area A1 can be removed. The cap 23 may not include the flushing unit 24.

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

The blade 251 is a member for wiping off ink droplets and a rinse solution adhering to the lower surface of the print head 21. The scraper 251 is a plate-like member made of, for example, flexible rubber. Further, the blade 251 may be formed of a flexible member only at the tip end portion 250 that contacts the print head 21.

The squeegee movement mechanism 252 is a mechanism for rotationally moving the squeegee 251. The squeegee movement mechanism 252 has a drive source such as a motor and a power transmission mechanism that transmits the rotational motion of the motor to the squeegee 251, for example. When the blade moving mechanism 252 is operated, the blade 251 is rotationally moved 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. 6.

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

On the other hand, when the blade 251 wipes ink droplets and a rinse liquid on the lower surface of the print head 21, the head moving mechanism 22 raises the print head 21 to the wiping position P4 higher than the standby position P2, and separates the lower surface of the print head 21 from the cap 23. Then, the blade 251 is rotationally moved from the storage position Q1 to the wiping position Q2. In the wiping position Q2, the leading end portion 250 of the blade 251 contacts the lower surface of the print head 21. After that, the print head moving mechanism 22 horizontally moves the print head 21 in the width direction. Thereby, the plurality of nozzles 211 attached to the lower surface of the print head 21 and ink droplets, rinse liquid, and the like around them are wiped by the tip portion 250 of the blade 251.

The wiping position P4 at which the lower surface of the print head 21 is wiped may be the same position as the intermediate position P3 or may be different from the intermediate position P3.

< 3 > Structure of ink supply mechanism and print head

Next, the structure of the ink supply mechanism 70 for supplying ink to the print head 21 and the print head 21 will be described with reference to fig. 7. Fig. 7 is a schematic diagram showing the structure of the print head 21 and the ink supply mechanism 70. As described above, the printing portion 20 has the four printing heads 21. The printing unit 20 includes an ink supply mechanism 70 for supplying ink to the print head 21 for each print head 21. That is, the printing unit 20 of the present embodiment further includes four ink supply mechanisms 70.

As shown in fig. 7, the ink supply mechanism 70 includes an ink storage portion 71, a pressure adjustment mechanism 72, and a pipe 73.

The ink storage portion 71 is a container for storing ink to be supplied to the print head 21. The ink storage portion 71 has a pressure sensor 711 for detecting the pressure inside the ink storage portion 71.

The pressure adjustment mechanism 72 is a mechanism for adjusting the pressure inside the ink storage section 71. The pressure in the ink storage section 71 is adjusted by the pressure adjusting mechanism 72, and the pressure in the print head 21 can be indirectly adjusted by the pressure adjusting mechanism 72 when the ink storage section 71 communicates with the print head 21. That is, the pressure adjusting mechanism 72 constitutes a pressure adjusting portion that can adjust the pressure in the print head 21.

In the present embodiment, the ink storage portion 71 is a tank having a constant capacity. The pressure adjusting mechanism 72 adjusts the pressure in the ink reservoir 71 by adjusting the gas pressure of the gas layer above the ink reservoir 71. However, the ink reservoir 71 may be a so-called ink bag in which a flexible container is filled with ink. In this case, the pressure adjusting mechanism 72 may adjust the pressure in the ink storage portion 71 by adjusting the pressure applied from the outside through the ink storage portion 71 as an ink bag, for example.

The pipe 73 connects the lower end of the ink reservoir 71 to an ink supply port 81 of the print head 21, which will be described later. For example, an electromagnetic valve 731 that controls communication of the pipe 73 is inserted into the pipe 73. In a state where the electromagnetic valve 731 is opened, if the pressure in the ink storage portion 71 is higher than the pressure in the print head 21, ink is supplied from the ink storage portion 71 to the print head 21. Further, a check valve may be inserted into the pipe 73 together with the solenoid valve 731 or in place of the solenoid valve 731. A filter for removing solid components, foreign substances, and the like in the ink may be inserted into the pipe 73.

The print head 21 includes a housing 80, an ink supply port 81 provided in the housing 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. Note that, although six individual channels 83, individual ink chambers 84, and nozzles 211 are shown in fig. 7 for convenience, a plurality of nozzles 211, the same number of individual channels 83, and the same number of individual ink chambers 84 are provided in the actual print head 21.

The ink supply port 81 is a communication port for communicating the ink storage chamber 82 with the outside. An end portion of the ink supply mechanism 70 on the downstream side of the pipe 73 is connected to the ink supply port 81. Thus, the ink supplied from the ink storage portion 71 through the pipe 73 is stored in the ink storage chamber 82 through the ink supply port 81 at a time.

The ink storage chamber 82 stores ink for supply to each of the ink chambers 84 at once. The ink storage chamber 82 is provided therein with a heater 821 for heating ink and a temperature sensor 822 for detecting the temperature of ink.

The heater 821 is a heating mechanism for raising the temperature of the ink in the print head 21. The control section 100 controls the heater 821 based on the temperature of the ink detected by the temperature sensor 822. The heater 821 can thereby raise the temperature of the ink in the print head 21 to a first temperature, a second temperature, and the like, which will be described later. That is, the heater 821 can raise the temperature of the ink discharged from the plurality of nozzles 211 to the first temperature and the second temperature.

The individual flow path 83 is a flow path of ink connecting the ink storage chamber 82 and each individual ink chamber 84. If the pressure in the individual ink chamber 84 is lower than the pressure in the ink storage chamber 82, ink is supplied from the ink storage chamber 82 to the individual ink chamber 84 through the individual flow path 83.

The individual ink chamber 84 is a reservoir for ink provided for each nozzle 211. The individual ink chambers 84 are filled with ink supplied into the print head 21 twice. The lower end portions of the individual ink chambers 84 communicate with the nozzles 211, respectively.

The nozzle 211 communicates the individual ink chamber 84 with the space outside. When ink is not discharged, the liquid surface of the ink forms a meniscus inside the nozzle 211. The lower end of the nozzle 211 is exposed to the lower surface of the housing 80.

Pressure generating elements 841 are disposed on the wall surfaces of the respective ink chambers 84. The pressure generating member 841 is an actuator that raises the pressure inside the individual ink chamber 84. The print head 21 of the present embodiment is a so-called piezoelectric discharge print head. Therefore, the pressure generating element 841 of the present embodiment uses a piezoelectric element. When a discharge signal, which is an electric signal, is transmitted 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, the pressure in the individual ink chamber 84 rises, and the ink in the individual ink chamber 84 is discharged as droplets from the nozzle 211. The print head 21 is not limited to the piezoelectric type, and may be a discharge print head of another type.

< 4. Temperature management in print head in printing process and recovery process >

Next, with reference to fig. 8 and 9, the temperature control in the print head 21 before the start of the printing process and during the recovery process in the tablet printing apparatus 1 will be described. Fig. 8 is a flowchart showing a flow of temperature management in the print head 21 before the printing process is started. Fig. 9 is a flowchart showing the flow of the recovery process.

The control unit 100 can cause the tablet printing apparatus 1 to perform at least the printing step and the recovery step. In the printing step, the control unit 100 causes the tablet transport mechanism 10 to transport the tablet 9 and discharges ink at a first temperature from a part of the nozzles 211 onto the surface of the tablet 9. Thereby, the surface of tablet 9 is subjected to printing treatment. On the other hand, in the recovery step, the control unit 100 raises the pressure in the print head 21 to discharge ink at the second temperature to all the nozzles 211 as discharge targets. That is, in the recovery step, the control unit 100 performs a maintenance method called a cleaning process. The control unit 100 may perform other processes such as a flushing process for flushing the lower surface of the print head 21, in addition to the printing process and the recovery process.

First, a flow of temperature management in the print head 21 before the start of the printing process will be described with reference to fig. 8. As shown in fig. 8, when the printing process is started, first, the pre-printing temperature raising process including step S111, step S112, and step S113 and the pre-printing movement process including step S121 and step S122 are performed simultaneously.

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

In step S112, if the control unit 100 determines that the temperature of the ink has not reached the first temperature (No in step S112), the process returns to step S112 to stand by. If it is determined in step S112 that the temperature of the ink has reached the first temperature (Yes in step S112), the control unit 100 starts the feedback control of the heater 821 to maintain the temperature of the ink in the print head 21 at the first temperature (step S113).

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

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

Here, the first temperature is the temperature of the ink in the print head 21 in the printing process. In the printing process, the temperature of the ink in the print head 21 is maintained at the first temperature by feedback control. Therefore, in the printing step, the control unit 100 discharges the ink at the first temperature from a part of the nozzles 211 of the print head 21 onto the surface of the tablet 9.

Next, the flow of the recovery process will be described with reference to fig. 9. As shown in fig. 9, when the recovery process is started, first, the temperature increase process before cleaning including steps S211 and S212 and the movement process before cleaning including steps S221 and S222 are performed simultaneously.

In the pre-cleaning temperature raising step (steps S211 to S212), the ink in the print head 21 is raised to a second temperature higher than the first temperature by the heater 821. First, the control unit 100 drives the heater 821 to start the temperature rise of the ink in the print head 21 to the second temperature (step S211). When the temperature rise is started, the control unit 100 monitors whether the temperature of the ink detected by the temperature sensor 822 reaches the second temperature (step S212).

If the control unit 100 determines in step S212 that the temperature of the ink has not reached the second temperature (step S212/No), it returns to step S212 to wait.

On the other hand, in the pre-cleaning movement step (steps S221 to S222), first, the control unit 100 operates the head movement mechanism 22 to move the print head 21 to the standby position P2 (step S221). After the start of the movement, the control unit 100 monitors whether or not the print head 21 reaches the standby position P2 (step S222). If the control unit 100 determines in step S222 that the print head 21 has not reached the standby position P2 (step S222/No), the process returns to step S222.

When the control unit 100 determines in step S212 that the temperature of the ink reaches the second temperature (step S212/Yes) and determines in step S222 that the print head 21 reaches the standby position P2 (step S222/Yes), the process proceeds to step S23. Then, the control section 100 stops the temperature rise of the ink in the print head 21 by the heater 821 (step S23). That is, the control unit 100 stops the temperature rise of the ink after confirming that the temperature of the ink in the print head 21 reaches the second temperature.

When it is determined in step S212 that the temperature of the ink has reached the second temperature (step S212/Yes) and it is not determined in step S222 that the print head 21 has reached the standby position P2, the control unit 100 may perform feedback control of the heater 821 so as to maintain the temperature of the ink in the print head 21 at the second temperature.

After stopping the temperature rise of the ink by the heater 821, the control unit 100 increases the pressure in the print head 21 and discharges the ink to all the nozzles 211 (step S24).

As a specific step performed by the control unit 100 in step S24, for example, the electromagnetic valve 731 is first closed to block communication between the ink storage unit 71 and the print head 21. Then, the pressure in the ink reservoir 71 is increased by the pressure adjustment mechanism 72. After that, the solenoid valve 731 is opened, so that the pressure in the print head 21 is raised at a burst.

In step S24, the ink at the second temperature is discharged from the nozzles 211 due to the pressure rise in the print head 21. In this case, the amount of ink discharged in step S24 is smaller than the amount of ink discharged in the normal cleaning process. Therefore, the ink discharged in step S24 remains on the lower surface of the print head 21.

In this way, in step S24, the cleaning process is performed at the standby position P2. That is, the standby position P2 is a maintenance position where the cleaning process is performed. Further, by simultaneously performing steps S211 to S212 and steps S221 to S222, the process of moving the print head 21 from the printing position P1 to the standby position P2 as the maintenance position and raising the temperature of the ink in the print head 21 to the second temperature is performed before the cleaning process.

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

In step S24, the print head 21 may be disposed at the wiping position P4. In this case, in the pre-cleaning movement step (steps S221 to S222), the print head 21 is disposed at the wiping position P4, not the standby position P2. That is, the maintenance position where the cleaning process is performed is the wiping position P4.

When the wiping process of step S25 ends, the recovery process of the print head 21 ends. When the printing process is performed later, the print head 21 is disposed at the printing position P1. When the printing process is not performed thereafter, the print head 21 is disposed at the standby position P2.

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

In the nozzle 211 which is used less frequently, the solvent evaporates from the ink surface, and the ink in the nozzle 211 does not flow, and the rise of the meniscus, aggregation of the ink components, concentration of the ink components, and the like occur, so that the fluidity of the ink is lowered, and the pressure loss in the nozzle 211 is increased.

Therefore, in the recovery step, the temperature of the ink in the print head 21 is set to a second temperature higher than the first temperature, which is the temperature of the ink in the printing step. The ink at the second temperature has a lower viscosity than the ink at the first temperature. Therefore, when the cleaning process is performed, the viscosity of the ink can be reduced, the fluidity of the ink can be improved, and the pressure loss in the nozzle 211 can be reduced. Thus, even when the amount of ink discharged in the purge process is smaller than that in the normal purge process, the ink clogging in the nozzles 211 can be eliminated.

That is, by setting the temperature of the ink higher than that in the printing step in the recovery step, the amount of ink consumed in the recovery step can be suppressed.

In the present embodiment, the first temperature is about 32 ℃, and the second temperature is about 40 ℃. Preferably, the second temperature is a temperature higher than the first temperature by a difference of 2 ℃ (inclusive) to 15 ℃ (inclusive).

If the temperature of the ink is increased by a difference of 2 ℃ or more (inclusive), the viscosity of the ink is lowered to such an extent that the discharge state is changed. Therefore, it is preferred that the second temperature is at least 2 ℃ (inclusive) higher than the first temperature. On the other hand, if the second temperature is made too high, the temperature inside the print head 21 may not decrease to the first temperature after the recovery process. In this way, it is necessary to provide a cooling period for cooling the ink in the print head 21 after the recovery process and before the printing process, or to provide a cooling mechanism. Therefore, the difference between the first temperature and the second temperature is preferably 15 ℃ (inclusive) or less.

Here, fig. 10 is a graph showing a relationship between the temperature and the viscosity of the edible ink used in the present embodiment. In fig. 10, the horizontal axis represents temperature [ ° c ], and the vertical axis represents the viscosity [ mPa · s ] of the ink. The instrument used for measuring the viscosity of the ink of FIG. 10 was VISCOMETER DV-IIPro manufactured by BROOKFIELD.

In the tablet printing apparatus 1 of the present embodiment, the viscosity of the ink suitable for the printing process is 3.9 ± 0.2mPa · s. Therefore, the first temperature is set to about 32 ℃. In contrast, in the cleaning step, the viscosity is preferably set to be about 20% lower than that in the printing step, and 3.2 ± 0.2mPa · s. Thus, the second temperature is around 40 ℃.

Specifically, in the present embodiment, the ink discharged in the cleaning process is small enough to be retained on the lower surface of the print head 21 without being dropped from the print head 21. For example, in the tablet printing apparatus 1 having the print head 21 of the same size as a conventional printing apparatus which discharges about 60cc of ink in the normal purge process, the discharge amount of ink in the purge step of step S24 can be set to about 1 cc.

< 5. Modification

The main embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments.

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

In the above embodiment, the printing unit 20 is provided with four printing heads 21. However, the number of the printing heads 21 included in the printing unit 20 may be one to three, or may be more than four.

In the above-described embodiment, the two-layer structure including one ink storage chamber and a plurality of individual ink chambers 84 is employed in one print head 21, but the present invention is not limited thereto. For example, a three-layer structure may be adopted in which 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 the respective ink storage chambers are provided in one print head. In addition, the printhead may be of other configurations.

In the above-described embodiment, the number of print heads 21 that discharge the same type of ink at the same position in the transport direction is one, but the present invention is not limited to this. The print head unit that discharges the same kind of ink at the same position in the transport direction may be configured by combining a plurality of print heads.

Further, the tablet printing apparatus 1 of the above-described embodiment includes one printing portion that prints on the surface of the tablet 9, but the present invention is not limited thereto. The tablet printing apparatus may include two printing portions, i.e., a printing portion for printing on one surface of the tablet and a printing portion for printing on the other surface (back surface) of the tablet.

The "tablet" to be treated in the present invention includes, for example, a non-coated tablet, an orally disintegrating tablet (OD tablet), a film-coated tablet (FC tablet), a sugar-coated tablet, a cut line tablet, and the like, but is not necessarily limited to a tablet as a pharmaceutical. The tablet printing apparatus of the present invention may print tablets, such as tablets and soda candies, which are health care products.

The detailed configuration of the tablet printing apparatus 1 may be different from those shown in the drawings of the present application. In addition, the respective elements appearing in the above-described embodiments and modifications may be appropriately combined within a range not to cause contradiction.

Claims

1. An inkjet tablet printing apparatus that prints on a surface of a tablet, comprising:

an inkjet print head having a plurality of nozzles capable of ejecting ink;

a pressure adjustment unit capable of adjusting the pressure in the print head;

a heater capable of heating the ink discharged from the nozzle to a first temperature and a second temperature inside the print head; and

a control unit for controlling the print head, the pressure adjustment unit, and the heater,

the control unit may perform:

a printing step of discharging the ink at the first temperature from a part of the nozzles onto a surface of the tablet; and

a recovery step of raising the pressure in the print head by the pressure adjustment unit to discharge the ink at the second temperature to all the nozzles as discharge targets,

the second temperature is higher than the first temperature.

2. The tablet printing apparatus of claim 1,

the ink discharged in the recovery step is retained on the lower surface of the print head.

3. Tablet printing device according to claim 1 or 2,

the second temperature is higher than the first temperature by a difference of 2 ℃ to 15 ℃.

4. The tablet printing apparatus according to claim 1 or 2,

the control unit includes, in the recovery step, the steps of:

a) Heating the ink in the print head to the second temperature by the heater;

b) Stopping the heater after the step a); and

c) After the step b), the pressure in the print head is increased to discharge the ink to all the nozzles as discharge targets.

5. The tablet printing apparatus according to claim 1 or 2,

the print head includes:

a plurality of nozzles arranged on a lower surface of the print head;

a plurality of individual ink chambers which communicate with each of the nozzles and have an actuator for increasing the pressure inside; and

an ink storage chamber communicating with the individual ink chambers,

the heater is disposed inside the ink storage chamber.

6. A maintenance method for a print head having a plurality of nozzles for ejecting ink in an ink jet tablet printing apparatus for printing on a surface of a tablet, the maintenance method comprising the steps of:

a) Raising the temperature of the ink in the print head to a second temperature; and

b) After the step A), the pressure in the print head is increased to discharge the ink from all the nozzles as discharge targets,

the second temperature is higher than a first temperature which is a temperature of the ink in the print head when the tablet is printed.

7. The maintenance method according to claim 6,

the ink discharged in the step B) is accumulated on the lower surface of the print head.

8. The maintenance method according to claim 6 or 7,

9. The maintenance method according to claim 6 or 7,

in the step a), the temperature of the ink in the print head is raised to the second temperature while moving the print head from the printing position to the maintenance position,

the step B) includes the following steps:

b1 Confirming that the temperature of the ink in the print head reaches the second temperature, and stopping the temperature rise of the ink;

b2 After the step B1), raising the pressure in the print head to discharge the ink to all the nozzles as discharge targets; and

b3 The ink accumulated on the lower surface of the print head is wiped off.