JP2002046287A - Ink jet recording apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve an accuracy for detecting an ink viscosity. SOLUTION: The ink jet recording apparatus has a nozzle body for jetting ink particles, a pressure reducing valve for reducing an ink to be supplied to the nozzle body to a predetermined pressure, and a pressure supply source including a pump, a pressurized air or the like for pressurizing the ink to be supplied to the nozzle body via the pressure reducing valve. The viscosity of the ink supplied to the nozzle is detected on the basis of a change of the ink pressure at the downstream side of the pressure supply source which drops after pressurizing the supply ink by the pressure supply source is stopped.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to adjustment of ink viscosity of an ink jet recording apparatus.

[0002]

2. Description of the Related Art Since the viscosity (concentration) of an ink greatly affects the printing performance of an ink jet recording apparatus, an operation is performed while controlling the viscosity. A method to detect and calculate the flight time (velocity) of the ink particles ejected from the nozzle, a method to count and calculate the time when a certain amount of ink is ejected from the nozzle, and an ink circulation path to supply ink to the nozzle Separately, there is a path and load for measuring the ink viscosity, and a method of measuring the flow rate of ink flowing through the path. Alternatively, a method has been used in which a reference liquid level is set in an ink container, the same amount of ink as the ink particles used for printing is supplied, and then the solvent is supplied to the reference liquid level.

[0003]

However, whichever method is used, the detection error is large, the accumulated error over a long period of time, the variation in the viscosity (density) of the replenished ink, and the influence on the measured value are affected. Adjustment of viscosity (concentration) has not been performed well due to changes in dimensions and characteristics of the parts to be given.
In addition, since a dedicated component or device for measurement is required, there is a problem that the cost is increased. SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and has an object to provide a simple ink composition which has good ink viscosity detection accuracy and good adjustment of viscosity, and does not require a dedicated component.

[0004]

SUMMARY OF THE INVENTION The present invention relates to an ink jet recording apparatus provided with a pump for pressurizing ink supplied to a nozzle body via a pressure reducing valve and a pressurized supply source including pressurized air. After the pressurization of the supply ink by the pressure supply source is stopped, the viscosity of the ink supplied to the nozzles is detected based on a change in the ink pressure on the downstream side of the pressurization supply source that falls.

[0005]

Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the same portions are denoted by the same reference numerals, and overlapping description will be omitted as appropriate. First, the ink circulation path of the inkjet recording apparatus will be described with reference to FIG. The ink 2 in the ink container 1 is sucked by a supply pump 3 as a pressurized supply source, and is pressure-fed toward the nozzle body 10. The pressurized supply source for supplying the pressurized ink may be pressurized air or the like. The ink 2 is sent to the nozzle body 10 via the electromagnetic valve 4, the pressure reducing valve 7, and the filter 8.
The ink particles 11 ejected from the nozzle body 10 are used for forming a print. Ink particles not used for print formation
The ink container 1 is collected by the gutter 12 and is collected by the collection pump 12.
Collected inside. On the downstream side of the pressurized supply source, a solenoid valve 4,
In addition to the pressure reducing valve 7, the filter 8, the nozzle body 10, and the like, an accumulator 5, a pressure sensor 6 on the accumulator side, and a pressure sensor 9 on the pressure reducing valve side are provided. The accumulator 5 and the pressure sensor 6 on the accumulator side are arranged between the solenoid valve 4 and the pressure reducing valve 7. The pressure sensor 9 on the pressure reducing valve side is a pressure reducing valve 7.
And the nozzle body 10. Accumulator 5
Is to absorb and store the pressure (energy) of the ink. Ink 2 pressurized and fed by supply pump 3 of a pressurized supply source
Is sent to the pressure reducing valve 7 while the pressure of the ink is absorbed and accumulated in the accumulator 5. The ink 2, which has been reduced in pressure to a pressure suitable for printing by the pressure reducing valve 7, is sent to the nozzle body 10 after the foreign matter which causes clogging of the nozzle 10 is removed by the filter 8, and is sent to the nozzle body 10.
It is gushing out. By the circulation of the ink, the viscosity of the ink in the ink container 1 rises and becomes hard. The ink particles which are not used for printing and return to the ink container 1 are volatilized by the solvent, and the remaining portion is occupied by the resin, so that the viscosity naturally increases. Therefore, the rising viscosity is detected, and a solvent is supplied to the ink container 1 in accordance with the detected value, so that the ink viscosity is adjusted to be suitable for printing. The solvent 15 in the solvent container 14 is sucked up by the solvent supply pump 16, and a predetermined amount of the solvent corresponding to the detected ink viscosity is supplied to the ink container 1 through the electromagnetic valve 17. Here, the ink viscosity detection will be described in detail with reference to FIG. The pump 3 is pressurized. Then, when pressure is applied until the detection value of the pressure sensor 6 reaches PLMAX from PL, the pump 3 is stopped and the electromagnetic valve 4 is closed. Since the ejection of the ink particles from the nozzle body 10 continues even after the electromagnetic valve 4 is closed, the pump 3
The pressure downstream of the pressurized supply naturally drops. When the detection value of the pressure sensor 6 has decreased to PH, measurement of time is started, and the elapsed time until the detection value becomes PL is measured. This elapsed time depends on the viscosity of the ink. It is short when the viscosity is low, and becomes longer as the viscosity increases. The difference in the ink viscosity becomes the length of the elapsed time because the ejection amount of the ink particles ejected from the nozzle body 10 differs depending on the difference in the viscosity. When the viscosity is low, the elapsed time is short with a large injection, and when the viscosity is high, the elapsed time is long with a small injection. Since the relationship between the pressure change and the elapsed time on the downstream side of the pressurized supply source has a very close relationship with the ink viscosity, the ink viscosity can be accurately detected by knowing the relationship between the pressure change and the elapsed time. . When the ink viscosity lower limit value μL (low), the elapsed time TL is short, and when the ink viscosity reference value μM (medium), the elapsed time TM is intermediate. And
When the ink viscosity upper limit value is μH (high), the elapsed time TH
Is longer. As described above, the ink viscosity (upper limit value, reference value, lower limit value) can be detected by measuring the time spent for a predetermined pressure change in which the detected pressure value changes from PH to PL. The detection of the ink viscosity can be calculated from the pressure change on the downstream side of the pressure supply source and the time spent for the pressure change, so that the ink viscosity can be detected with high accuracy. Also, since no special components or devices for viscosity detection are required, the configuration is simpler than conventional ones, and it is advantageous in terms of cost. Further, since no special parts constituting the detection device are required, there is no decrease in the detection accuracy due to variations in the special parts, and the detection accuracy is good. Since the adjustment of the ink viscosity is performed based on accurate ink viscosity detection, the ink viscosity can be maintained in an appropriate state. The accumulator 5 is provided to further enhance the accuracy of detecting the ink viscosity. By the pressurization of the pump 3, the ink pressure on the downstream side of the pump 3 increases to PMAX while being absorbed and accumulated in the accumulator 5. By stopping the pump 3 and closing the solenoid valve 4, the pressure on the downstream side of the pump 3 decreases. Since the pressure drop drops while discharging the pressure stored in the accumulator 5, the pressure drop from PH to PL is different from the pressure drop in a short time without the accumulator 5. become longer. By making the elapsed time longer, unlike the case where the elapsed time is short, each elapsed time (TL, TM, TH) can be easily distinguished, and the detection accuracy is improved. The reason why the elapsed time measurement start pressure is set to PH is to increase the detection accuracy. PMAX has high and low variations among individual products, and when the elapsed time starts from this pressure point, a variation portion causes a measurement error. The measurement start point was lowered to PH in order to remove the variation error and to increase the detection accuracy. As shown in FIG. 2, the nozzle supply pressure is set sufficiently lower than the detection pressure PL which is the lowest pressure of the detection pressure for detecting the ink viscosity. The pressure detection of the ink viscosity detection is performed on the upstream side of the pressure reducing valve 7 opposite to the nozzle supply pressure side. At the time of detecting the ink viscosity, the lowest pressure PH of the pressure reducing valve 7 is set sufficiently higher than the nozzle supply pressure, so that the ink viscosity can be detected while the operation of the ink jet recording apparatus is continued. Further, when the accumulator 5 is not provided, the pressure drop of the ink is extremely high, and if the pressure drops below and the nozzle supply pressure cannot be maintained, the operation of the ink jet recording apparatus is stopped. In order to suppress this operation stop, the accumulator 5
Preparation is necessary. Considering the variation in detection accuracy among individual products, the upper limit of ink viscosity (μ
L), the ink viscosity reference value (μM), the ink viscosity upper limit value (μH), and the elapsed time (TL, TM, TH) are desirably set to values having a margin. The reason that the solvent 15 in the solvent container 14 is added to the ink container 1 by the above-described ink viscosity detection is that when the viscosity is high, a predetermined amount of solvent corresponding to the detected value is added to adjust the viscosity to an appropriate value. No adjustment is made when the viscosity is low. It takes a little time before the adjusted ink in the ink container 1 is supplied to the nozzle body 10. With this in mind, it is desirable to frequently adjust the ink viscosity so as not to be too low or too high. Since the above-described relationship between the ink pressure change and the elapsed time can be regarded as a gradient change, a change in the ink viscosity can be detected by detecting the change in the gradient. Specifically, from a certain pressure (high pressure side) to a certain pressure
The time during which the pressure drops to (low pressure side) is measured, and the time change is regarded as the ink viscosity change. The relationship between the ink ejection amount of the nozzle body 10 and the ink viscosity has been described above, but will be described in more detail here. Considering the flow in a circular pipe, if the flow is laminar, the velocity is u, the vertical direction to the flow is the y-coordinate, and the viscosity is μ. The force, the shear stress

[0006]

(Equation 1)

Is expressed by the following equation. Generally Re <2 × 10
In the range of 3, the flow becomes laminar, and the pressure loss and the viscosity are in a proportional relationship. To express this relationship as an equation, next, considering the pressure loss Δp in a circular pipe (in this case, a pipe), the friction loss coefficient is λ, the pipe length is L, the pipe diameter is d, the fluid density is ρ, and the flow velocity is v. Then

[0008]

(Equation 2)

Is represented by the following equation. Also, if Re is small in a smooth circular tube, from Poiseuille's law

[0010]

(Equation 3)

Is represented by the following equation. Where kinematic viscosity ν = μ / ρ
It is. The discharge flow rate Q from the pipe nozzle is represented by a flow coefficient c,
Nozzle opening area is A, primary pressure is p1, secondary pressure is p
If it is 2, it can be expressed by the following equation, and it can be seen that the ejection flow rate from the nozzle changes according to the ink viscosity.

[0012]

(Equation 4)

[0013]

As described above, according to the present invention, it is possible to obtain an ink jet recording apparatus with high inspection accuracy.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an ink circulation path of an inkjet recording apparatus according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of ink viscosity detection according to an embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Ink container, 2 ... Ink, 3 ... Supply pump, 4 ... Solenoid valve, 5 ... Accumulator, 6 ... Pressure sensor, 7 ... Pressure reducing valve, 8 ... Filter, 9 ... Pressure sensor, 10 ... Nozzle, 1
DESCRIPTION OF SYMBOLS 1 ... Ink particle, 12 ... Gutter, 13 ... Recovery pump, 1
4 ... Solvent container, 15 ... Solvent, 16 ... Solvent supply pump, 1
7 ... Solenoid valve.

Claims (5)

[Claims] A nozzle for ejecting ink particles, a pressure reducing valve for reducing the pressure of the ink supplied to the nozzle to a predetermined pressure, a pump for pressurizing the ink supplied to the nozzle via the pressure reducing valve, An ink jet recording apparatus provided with a pressurized supply source including pressurized air or the like, wherein the nozzle is stopped based on a change in ink pressure downstream of the pressurized supply source after the pressurization of the supply ink by the pressurized supply source is stopped. An ink jet recording apparatus for detecting the viscosity of ink supplied to a printer. 2. A nozzle for ejecting ink particles, a pressure reducing valve for reducing the pressure of the ink supplied to the nozzle to a predetermined pressure, a pump for pressurizing the ink supplied to the nozzle via the pressure reducing valve, In an ink jet recording apparatus provided with a pressurized supply source including pressurized air, etc., after the pressurization of the supply ink by the pressurized supply source is stopped, a change in the ink pressure on the downstream side of the pressurized supply source is detected. An ink jet recording apparatus for adjusting the viscosity of ink supplied to a nozzle based on a detection value. 3. A nozzle for ejecting ink particles, a pressure reducing valve for reducing the pressure of the ink supplied to the nozzle to a predetermined pressure, a pump for pressurizing the ink supplied to the nozzle via the pressure reducing valve, In an ink jet recording apparatus provided with a pressurized supply source including pressurized air or the like, a pressure sensor for detecting a pressure of supply ink supplied from the pressurized supply source is provided downstream of the pressurized supply source. An ink jet recording apparatus for adjusting the viscosity of ink supplied to a nozzle based on a change in ink pressure on the downstream side of the pressurized supply source detected by the pressure sensor after the pressurization of the supplied ink by the source is stopped. . 4. A nozzle for ejecting ink particles, a pressure reducing valve for reducing the pressure of the ink supplied to the nozzle to a predetermined pressure, a pump for pressurizing the ink supplied to the nozzle via the pressure reducing valve, An ink jet recording apparatus provided with a pressurized supply source including pressurized air or the like, wherein the ink pressure on the downstream side of the pressurized supply source that descends after the pressurization of the supplied ink by the pressurized supply source is stopped is a predetermined value. An ink jet recording apparatus for detecting the viscosity of ink to be supplied to a nozzle based on the time spent until the following. 5. A nozzle for ejecting ink particles, a pressure reducing valve for reducing the pressure of ink supplied to the nozzle to a predetermined pressure, a pump for pressurizing ink supplied to the nozzle via the pressure reducing valve, In an ink jet recording apparatus provided with a pressurized supply source including pressurized air, etc., a pressure sensor for detecting a pressure of supply ink supplied from the pressurized supply source to a downstream side of the pressurized supply source and absorbing a pressure of the downstream side are absorbed. An accumulator that accumulates, based on the time spent until the ink pressure on the downstream side of the pressurized supply source, which descends after stopping pressurization of the supply ink by the pressurized supply source, becomes equal to or lower than a predetermined value. An ink jet recording apparatus for detecting the viscosity of ink supplied to a printer.