CN111137020A

CN111137020A - Ink-jet printer

Info

Publication number: CN111137020A
Application number: CN201910998438.6A
Authority: CN
Inventors: 根崎大; 古川普弘
Original assignee: Kishu Giken Kogyo Co Ltd
Current assignee: Kishu Giken Kogyo Co Ltd
Priority date: 2018-11-01
Filing date: 2019-10-21
Publication date: 2020-05-12
Anticipated expiration: 2039-10-21
Also published as: JP2020069746A; JP6604613B1; CN111137020B

Abstract

The invention provides an ink jet printer capable of promoting the vaporization of a solvent without using extra electric power to improve the viscosity of ink. In an ink jet printer, a branch pipe (5j) branched from a pipe (5c) is attached to the pipe (5c) connecting a recovery tank (51) and an ink cartridge (2). A static mixer (10) for stirring and mixing the ink and air by the flow of the transferred ink is connected in series to the branch pipe (5 j). When the viscosity of the ink supplied to the print head (3) is lower than a predetermined value, the switching valve (66) is switched to the branch pipe (5j) side, and the ink recovered by the recovery tank (51) is guided to the static mixer (10) and passes through the static mixer (10), thereby promoting the vaporization of the ink solvent.

Description

Ink-jet printer

Technical Field

The present invention relates to a continuous ink jet printer, and more particularly, to an ink jet printer including a mechanism for increasing the viscosity of ink recovered in a recovery tank.

Background

In a continuous ink jet printer, ink droplets for printing among ink droplets ejected from nozzles of a print head are deflected and fly to be ejected onto a surface of a print object. On the other hand, ink droplets not subjected to the flight trajectory correction and not related to printing are stored in a recovery tank (setter) and recovered into the ink cartridge through a pipe. The ink recovered by the recovery tank is transported into the ink cartridge together with air, wherein the air is discharged from the ink cartridge.

In general, a highly volatile solvent such as methyl ethyl ketone is used for ink used in a continuous ink jet printer, and when the ink is collected in an ink cartridge, a large amount of solvent vapor is discharged into the atmosphere, thereby increasing the viscosity of the ink. Therefore, insufficient solvent is replenished to prevent the viscosity of the ink from increasing.

On the other hand, depending on the usage environment of the printer, the temperature may be the lowest in the morning and may increase rapidly by the middle of the day. In this case, as the ink characteristics, since the viscosity decreases as the temperature increases, the viscosity of the ink set to an appropriate value at the start of operation becomes lower than the appropriate value in the afternoon. If the viscosity of the ink is lower than an appropriate value, a part of the ink droplets separates in flight, and the printed image produces streaks, resulting in deterioration of the quality of printing.

In addition, it is known that: in some cases, a nozzle having a small diameter is replaced with a nozzle having a large diameter depending on the application, but in this case, it is necessary to increase the viscosity of the ink to be used. Therefore, when the nozzle to be used is replaced with a nozzle having a large diameter, if only the nozzle is replaced, the viscosity of the ink becomes lower than an appropriate value, and the print quality cannot be maintained for the same reason as described above.

As a method for increasing the viscosity of the ink which has been reduced, the applicant has previously proposed a method for promoting vaporization of the solvent by heating the ink recovered in the recovery tank (see patent document 1).

Patent document

Patent document 1: japanese patent laid-open No. 2008-137198

Disclosure of Invention

According to the method described in patent document 1, although the viscosity of the ink can be increased by adding a heating member to the piping of the ink jet printer, it is necessary to supply power to the heating member to vaporize the solvent, and extra power is required in addition to printing, and therefore improvement is required from the viewpoint of energy saving.

The present invention has been made in view of the above conventional problems, and an object thereof is to provide an ink jet printer capable of promoting vaporization of a solvent and increasing viscosity of ink without requiring additional electric power.

In order to achieve the above object, an ink jet printer according to the present invention includes:

an ink cartridge that stores ink;

a print head that ejects ink supplied from the ink cartridge toward a surface of a printed object;

a recovery tank that recovers ink that is not used for printing from among inks ejected from nozzles of the print head; and

a pump that transfers ink from the ink tank toward the print head and transfers ink recovered by the recovery tank toward the ink tank,

a branch pipe branched from a pipe connecting the recovery tank and the ink cartridge is mounted on the pipe,

a static mixer for stirring and mixing the ink and air by the flow of the transferred ink is connected in series to the branch pipe.

Here, it is preferable that a switching valve for switching ink transfer is installed at a branching portion of the branch pipe, and when the viscosity of the ink is lower than a predetermined value, the ink recovered by the recovery tank is transferred to the ink cartridge via the branch pipe.

Preferably, the inkjet printer according to the present invention further includes:

a pressure sensor that is attached to a middle of a pipe that transfers ink of the ink cartridge to the print head, and that detects a pressure of the ink;

a speed detection mechanism which is built in the print head and detects a speed of the ink droplet ejected from the nozzle; and

and a controller that calculates the viscosity of the ink supplied to the print head based on the pressure detected by the pressure sensor and the velocity of the ink droplet detected by the velocity detection unit, and controls the operation of the switching valve based on the calculated value.

Preferably, the storage device of the controller stores data indicating a relationship between the ink pressure and the velocity of the ink droplet and the ink viscosity in advance.

Effects of the invention

When the ink jet printer according to the present invention is used, vaporization of the ink solvent can be promoted and the viscosity of the ink can be increased by adding a static mixer to the piping of the ink. In addition, the static mixer does not have a heating part and a moving part, so that extra power is not consumed.

Drawings

Fig. 1 is a piping diagram of an inkjet printer according to an embodiment of the present invention.

Fig. 2 is a block diagram showing a configuration of a control system of an inkjet printer according to an embodiment of the present invention.

Fig. 3 is a graph illustrating the effect of the embodiment of the present invention.

Description of the symbols:

1-an ink jet printer; 2-ink cartridge; 3-a print head; 4-a pump; 5. 5a to 5 i-piping; 5 j-branch; 9-a controller; 10-a static mixer; 21-a cartridge body; 22-a cover; 41-44-membrane unit; 51-a recovery tank; 52-54-filter; 55-a buffer; 56-check valve; 57-a throttle valve; 61-65-opening/closing valve; 66-a switching valve; 67-ink discharge valve; 71-a pressure sensor; 72-temperature sensor; 73-liquid level detection sensor; 74-ink droplet velocity detection mechanism; 81. 82-a replenishment cartridge; 83-coacervation cartridge; 91-CPU; 92-ROM; 93-RAM; 94-input and display panel; 95-a storage device; 96-bus; i-ink.

Detailed Description

An ink jet printer according to an embodiment of the present invention will be described below with reference to the drawings.

< ink jet Printer constitution >

Fig. 1 shows a piping diagram of an inkjet printer according to the present embodiment. In addition, fig. 2 shows a block diagram of a control system of the printer. Since the main object of the present invention is to increase the viscosity of ink, printing-related components that are not involved in increasing the viscosity of ink are omitted in fig. 1 and 2.

As shown in the piping diagram of fig. 1, an inkjet printer (hereinafter, simply referred to as "printer") 1 includes: an ink cartridge 2 that stores ink I; a print head 3 that ejects ink to print on a surface of a print target; a pump 4 that outputs ink; pipes 5a to 5i (hereinafter, also collectively referred to as "pipes 5") which connect these members; a branch pipe 5j branched from the pipe 5 c; opening/closing valves 61-65, which are disposed in the middle of the pipe 5 and open/close the pipe; a switching valve 66 for selecting either the pipe 5c or the branch pipe 5 j; sensors 71 to 73 for detecting various states of the ink;

cartridges

81 and 82 for ink and solvent supply; and a static mixer 10 connected in series with the branch pipe 5 j.

As shown in fig. 2, the operation of the printer 1 is controlled by the controller 9. Therefore, the input side of the controller 9 is connected to sensors 71 to 73 shown in fig. 1, and also connected to a droplet speed detection mechanism 74, and the output side is connected to a motor 45 that rotationally drives the pump 4, on/off valves 61 to 65 that open and close the pipe 5, and a switching valve 66.

The ink cartridge 2 includes: a rectangular parallelepiped box main body 21 made of reinforced plastic or the like and having an open upper surface; and a flat plate-like cover 22 made of reinforced plastic or the like and provided to cover the upper surface of the cartridge main body 21.

As shown in fig. 1, the cover 22 is formed with a plurality of holes through which the tubes 5 pass and holes through which the temperature sensor 72 and the liquid level detection sensor 73 pass. Further, a condensation box 83 is attached to the tip of the pipe 5i, and collects vapor of the ink solvent released through the pipe 5i, and condenses and liquefies the vapor of the ink solvent, thereby recovering the ink solvent.

The hole formed in the cover 22 is sealed with a pipe or the like. These holes may be provided in either the cartridge main body 21 or the cover 22, but in the present embodiment, the holes are provided in the cover 22 in view of ease of handling.

The opening of the case main body 21 and the lid 22 are fastened with a gasket interposed therebetween using bolts and nuts (not shown), whereby the case main body 21 and the lid 22 are sealed.

In the present embodiment, as the ink, an ink obtained by adding 5 to 10% of a chromium complex salt as a black dye to 70 to 90% of methyl ethyl ketone as a solvent and adding a little cyclohexane 5 to 10% and isopropyl alcohol 0.1 to 1% thereto is used.

The configuration and operation of the print head 3 will be briefly described. The ink jet printer is roughly classified into a continuous type and an on-demand type, and in the present invention, the continuous type is used.

The structure of the print head of a continuous ink jet printer is well known and therefore will not be described with reference to the drawings. In this method, ink is pressurized by a pump 4, and ejected from a nozzle provided in a print head 3, and ink droplets are charged at positions where the ejected ink is separated into ink droplets, and the trajectory of the charged ink droplets is bent by a deflection electrode and made to collide with a predetermined position on a print surface, thereby forming dots.

In the continuous printer, ink that is not used for printing out of ink droplets ejected from the print head 3 is collected by the collection tank 51, and returned to the ink cartridge 2 through the pipe 5c to be reused as described later.

A pump 4 is disposed in the middle of a pipe 5a connecting the ink cartridge 2 and the print head 3, and transfers ink in the cartridge to the print head 3. In the present embodiment, as the pump 4, a diaphragm pump in which 4 diaphragm units 41 to 44 are integrated and these diaphragm units are rotationally driven by 1 motor 45 (see fig. 2) is used.

The diaphragm unit 41 is used to transfer the ink in the ink cartridge 2 to the print head 3, and the

diaphragm units

42 and 43 are used to transfer the ink recovered by the recovery tank 51 to the ink cartridge 2.

The diaphragm unit 44 is used for stirring ink in the ink cartridge 2 by circulating the ink, and is used when supplying ink or a solvent stored in the

replenishment cartridge

81 or 82 to the ink cartridge 2.

Filters

52, 53, and 54 provided in the middle of the

pipes

5a and 5c remove impurities in the ink, and a check valve 56 prevents the ink from flowing backward. The check valve 56 incorporates a spring, and prevents ink from being transferred by the action of the spring when the pressure of the ink does not exceed a predetermined value, and transfers the ink only when the pressure of the ink exceeds the predetermined value. In addition, a damper 55 and a throttle 57 are attached to the pipe 5. Hereinafter, their functions will be explained.

In addition to the above components, opening and closing valves 61 to 65, a switching valve 66, and an ink discharge valve 67 are disposed in the middle of the

pipes

5a, 5c, 5d, 5e, 5f, and 5 g. The opening/closing valves 61 to 65 are solenoid valves, and open/close the piping 5 to transfer ink or stop the transfer in accordance with an instruction from the controller 9 in fig. 2.

The switching valve 66 is constituted by an electromagnetic valve, transfers the ink collected in the collection tank 51 to the ink cartridge 2 via either the pipe 5c or the branch pipe 5j, and selects either the pipe 5c or the branch pipe 5j according to an instruction from the controller 9 in fig. 2. When the branch pipe 5j is selected, the ink passes through the static mixer 10 and then returns to the pipe 5 c. Hereinafter, the function of the static mixer 10 will be explained.

When the printer 1 is maintained and inspected, the ink discharge valve 67 is manually opened and closed to discharge ink remaining in the pipe 5 a.

The pressure sensor 71 connected to the pipe 5a detects the pressure of the ink flowing through the pipe 5 a. Further, the temperature sensor 72 attached to the cover 22 of the ink cartridge 2 detects the temperature of the ink in the ink cartridge 2. The liquid level detection sensor 73 attached to the cap 22 of the ink cartridge 2 uses a plurality of conductive rods having different lengths, and detects the height of the liquid level of the ink by whether or not the conductive rods are electrically connected.

Although not shown, the print head 3 incorporates an ink droplet speed detection mechanism 74 (see fig. 2) that detects the speed of ink droplets ejected from the nozzles. The ink droplet velocity detection means 74 detects the velocity of the ink droplet by detecting the voltage induced by a pair of electrodes provided along the flight path of the ink droplet.

The controller 9 in fig. 2 controls the operation of the motor 45 for rotationally driving the pump 4, the opening/closing valves 61 to 65, and the switching valve 66 based on output signals of the pressure sensor 71, the temperature sensor 72, the liquid surface detection sensor 73, and the ink droplet speed detection sensor 74.

As shown in fig. 2, the controller 9 is constituted by a CPU91, a ROM92, a RAM93, an input and display panel 94, a storage device 95, and a bus 96.

The CPU91 generates instruction signals necessary for controlling the operations of the respective sections of the printer 1. The ROM92 stores programs necessary for the CPU91 to operate. The RAM93 temporarily stores data required during execution of programs.

The storage device 95 is constituted by a hard disk drive, a flash memory, and the like, and stores data necessary for controlling the printer 1. The input and display panel 94 is configured by a liquid crystal display or the like, inputs contents of printing, setting values, and the like, and displays the input data, contents of printing, and the like. The bus 96 transmits data signals, address signals, and control signals of the CPU 91.

< description of ink flow >

Next, the flow of ink in the printer 1 will be described based on fig. 1 described above. The arrows given along the piping 5 in fig. 1 indicate the direction in which the ink flows.

The ink I stored in the ink cartridge 2 is sucked by the diaphragm unit 41 and transferred to the print head 3 through the pipe 5 a. A buffer 55 and a check valve 56 are disposed downstream of the diaphragm unit 41 of the pipe 5a, and a pipe 5b is branched from the pipe 5a immediately before the buffer 55 and the check valve, and the tip of the pipe 5b is connected to the ink cartridge 2.

The ink output from the diaphragm unit 41 reaches the check valve 56 after the pulsation flow is removed by the buffer 55. The check valve 56 keeps the pressure of the ink supplied to the print head 3 at a constant value, and when the pressure of the ink removed by the buffer 55 due to the pulsating flow is lower than a value determined by the spring force of the spring, the check valve 56 is always closed, and therefore the ink returns to the ink cartridge through the branch pipe 5 b. The throttle valve 57 provided in the middle of the branch pipe 5b adjusts the flow rate of the ink recovered to the ink cartridge 2.

The pressure sensor 71 attached to the pipe 5a on the downstream side of the check valve 56 detects the pressure of the ink supplied to the print head 3. The ink pressure detected by the pressure sensor 71 is used to adjust the viscosity of the ink.

In order to keep the quality of an image or the like printed by the printer 1 constant, the velocity of ink droplets ejected by the print head 3 needs to be kept at a constant value. The ink droplet speed detection mechanism 74 built in the print head 3 is used in this case.

The pressure of the ink transferred through the pipe 5a and the velocity of the ink droplets are in a proportional relationship, and when the pressure for maintaining the velocity increases, it is determined that the viscosity of the ink increases, and the solvent is replenished from the replenishment cartridge 82.

The on-off valve 61 provided in the middle of the pipe 5a opens the flow path of the pipe 5a when the pump 4 is driven to start printing by the printer, and closes the flow path of the pipe 5a when the operation of the pump 4 is stopped after the printing is finished.

A part of the ink droplets ejected from the print head 3 is used for printing, and the other ink droplets are recovered by the recovery gutter 51. The ink collected in the collection tank 51 is transferred by the

diaphragm units

42 and 43 through the pipe 5c and returned to the ink cartridge 2.

A branch pipe 5j is attached to a middle portion of the pipe 5c, and a static mixer 10 is connected in series to the branch pipe 5 j. By switching the switching valve 66 attached to the branch portion of the pipe 5c, the ink recovered by the recovery tank 51 is transferred to the ink cartridge 2 through either the pipe 5c or the branch pipe 5 j.

The use of 2

diaphragm units

42 and 43 for transferring ink in the pipe 5c is a result of taking into account the ink transfer capability of the diaphragm units, and when the transfer capability of the diaphragm units is large, ink can be transferred using 1 diaphragm unit.

The pipe taken out from the lower part of the print head 3 and the ink cartridge 2 are connected by a pipe 5d, and an opening/closing valve 62 is disposed in the middle of the pipe 5 d. The pipe 5d is used to discharge air remaining in the print head 3 when the printer 1 is powered on, and opens the on-off valve 62 to transfer ink containing air and return the ink to the ink cartridge 2.

Pipes

5e and 5h for transferring the ink taken out from the ink supply cartridge 81 to the ink cartridge 2 by using the diaphragm unit 44 are provided, and an opening/closing valve 63 is attached to a middle portion of the pipe 5 e.

Similarly,

pipes

5f and 5h for transferring the solvent taken out of the solvent replenishment cartridge 82 to the ink cartridge 2 by using the diaphragm unit 44 are provided, and an opening/closing valve 64 is attached to a middle portion of the pipe 5 f.

Further,

pipes

5g and 5h for returning the ink taken out from the ink cartridge 2 to the ink cartridge 2 by using the diaphragm unit 44 are provided, and an opening/closing valve 65 is attached to a middle portion of the pipe 5 g. The pipe 5g is used for stirring the ink in the ink cartridge 2.

Since the 3

pipes

5e, 5f, and 5g described above also serve as the diaphragm unit 44 for ink transfer, the

pipes

5e, 5f, and 5g are joined together and connected to the pipe 5 h.

When ink is replenished to the ink cartridge 2, the opening/closing valve 63 is opened and the opening/

closing valves

64 and 65 are closed in accordance with an instruction from the controller 9, and the diaphragm unit 44 is driven to transfer the ink in the replenishing cartridge 81 to the ink cartridge 2.

When the solvent is replenished to the ink cartridge 2, the opening/closing valve 64 is opened and the opening/

closing valves

63 and 65 are closed in accordance with an instruction from the controller 9, and the diaphragm unit 44 is driven to transfer the solvent in the replenishment cartridge 82 to the ink cartridge 2.

When the ink components contain a pigment, the ink tends to sink and settle down with time, and therefore, the ink in the ink cartridge 2 needs to be constantly stirred. When ink is to be stirred, the opening/closing valve 65 is opened and the opening/

closing valves

63 and 64 are closed in accordance with an instruction from the controller 9, so that the diaphragm unit 44 is driven to suck ink in the ink cartridge 2 through the pipe 5g and discharge the ink in the pipe 5h to the ink cartridge 2.

< adjustment of viscosity of ink >

In the present embodiment, when the viscosity of the ink supplied to the print head 3 is lower than a predetermined value, the ink viscosity is increased by promoting the vaporization of the ink solvent. As a method for increasing the viscosity of the ink, a static mixer 10 is disposed in the middle of a pipe for transferring the ink recovered by the recovery tank 51 to the ink cartridge 2, and the evaporation of the solvent is promoted by flowing the ink through the static mixer 10.

The static mixer 10 is: a static mixer that does not have a driving unit and performs stirring by using a flow of a fluid is provided with a plurality of members obtained by twisting a rectangular plate by 180 degrees. The fluid passing through the mixer is sequentially stirred and mixed by a plurality of members having different twisting directions.

In general, a static mixer is used for mixing a high-viscosity fluid (adhesive, food), heat exchange of the fluid, and heat equalization, and is not used for promoting vaporization of an ink solvent. The inventors of the present invention have tried to pass the ink recovered in the recovery tank through a static mixer, and as a result, have found that a significant effect is exerted on the vaporization of the ink solvent.

Fig. 3 shows the amount of solvent consumed when the ink recovered by the recovery tank 51 is passed through the static mixer 10 and when the ink recovered by the recovery tank 51 is not passed through the static mixer 10. The solvent consumption is: the amount of solvent replenished per unit time to maintain the concentration of ink circulating in the printer at a constant value. If the vaporization of the solvent is promoted, the solvent consumption is inevitably increased.

In the experiment, an ink obtained by adding a chromium complex salt as a black dye to methyl ethyl ketone as a solvent was used, and the pump 4 was driven at a rotation speed of 160rpm to pass the ink through the static mixer 10. The solvent consumption shown on the right side of fig. 3 is an average of 2 experiments.

On the other hand, the left side of fig. 3 shows the amount of solvent consumed when the ink is not passed through the static mixer. The solvent consumption is: average of 5 experiments performed while driving the pump 4 at 178rpm using the same ink.

As is apparent from the experimental results, by passing the ink through the static mixer, the solvent consumption amount increased by about 45% as compared with the case where the ink was not passed through the static mixer.

The structure of the static mixer is not limited to the structure in which a plurality of members obtained by twisting the rectangular plate are arranged as described above. Any structure may be employed as long as it is a structure in which stirring is performed by a flow of a fluid.

Next, the procedure for increasing the viscosity of the ink will be described with reference to fig. 1 and 2.

As a prerequisite for promoting the vaporization of the ink solvent, the ink viscosity needs to be measured. The method for measuring the viscosity of the ink comprises the following steps: the method of directly measuring the viscosity of ink described in patent document 1 and the method of indirectly measuring the viscosity of ink based on the pressure of ink supplied to a print head. In any of the methods, the effect of promoting the vaporization of the ink solvent is not changed, but in the present embodiment, the latter method is adopted in view of the simplification of the configuration of the detection means.

Specifically, the speed of the ink droplets ejected from the nozzles of the print head 3 is detected by the ink droplet speed detection means 74, and the pressure of the ink supplied to the print head 3 is detected by the pressure sensor 71. Data indicating the relationship between the ink droplet velocity and the ink pressure and the ink viscosity detected by the viscosity detection means is stored in advance in the storage device 95 of the controller 9.

The CPU91 of the controller 9 calculates a value corresponding to the velocity of the ink droplets detected by the ink droplet velocity detection means 74 and the pressure detected by the pressure sensor 71 based on the data stored in the storage device 95, and sets the value as the viscosity of the ink.

When the calculated ink viscosity is lower than a predetermined value, the controller 9 switches the switching valve 66 to the branch pipe 5j side, and guides the ink recovered by the recovery tank 51 to the static mixer 10 to pass through the static mixer 10, thereby promoting the vaporization of the ink solvent.

As shown in fig. 3, by passing the ink through the static mixer 10, vaporization of the ink solvent is promoted, and as a result, the viscosity of the ink increases.

When the ink viscosity corresponding to the pressure detected by the pressure sensor 71 and the speed detected by the speed detection mechanism 74 exceeds a predetermined value and is determined to be appropriate, the controller 9 switches the switching valve 66 so that the ink is transferred to the ink cartridge 2 through the pipe 5 c.

As described above, the static mixer has a remarkable effect of promoting vaporization of the ink solvent, and is therefore most suitable as a mechanism for increasing the viscosity of the ink. Further, since the ink passes through the static mixer by the driving force of the pump as the ink transfer mechanism, unnecessary power is not consumed.

Although the above embodiment has been described with respect to the case where methyl ethyl ketone is used as the ink solvent, it goes without saying that similar effects are exhibited when another solvent is used in order to promote vaporization of the solvent.

Claims

1. An ink-jet printer is characterized in that,

the inkjet printer includes:

an ink cartridge that stores ink;

2. The inkjet printer of claim 1,

a switching valve for switching ink transfer is installed at a branching portion of the branch pipe, and when the viscosity of the ink is lower than a predetermined value, the ink recovered by the recovery tank is transferred to the ink cartridge via the branch pipe.

3. The inkjet printer of claim 2,

the inkjet printer further includes:

4. The inkjet printer of claim 3,

data indicating the relationship between the pressure of the ink and the velocity of the ink droplet and the viscosity of the ink is stored in advance in the storage device of the controller.