JP4482325B2 - Density detection method, density detection apparatus, and inkjet recording apparatus - Google Patents

Description

  The present invention relates to a density detection method and a density detection apparatus capable of accurately detecting ink density in ink jet recording, wet electrophotography, and the like, and an electrostatic ink jet recording apparatus using the density detection apparatus.

In order to stably record a high-quality image in image recording using ink such as an ink jet recording apparatus or wet electrophotographic image recording using toner ink, it is necessary to keep the density of the ink for image recording appropriate. It is essential.
In particular, in electrostatic ink jet image recording using ink that contains a color material and in which charged particles (hereinafter referred to as color material particles) are dispersed in a carrier liquid, the liquid is ejected by electrophoresis using an electrostatic force or the like. Since the ink droplets are ejected by moving the color material particles to the part (nozzle) to discharge the ink droplets, that is, the ink is concentrated, the ink droplets are ejected, so that stable and appropriate image recording is performed. For this purpose, the management of the ink density is important.

  In view of such a point, for example, Patent Document 1 discloses that, in electrostatic ink jet recording, in an ink circulation path that circulates between an ink tank, an ink jet head, and an ink tank, ink is transmitted using a light emitting element and a light receiving element. Inkjet that detects transmitted light, detects the amount of color material particles (toner particles) in the ink flow, that is, the ink density, and determines the amount of color material particles to be replenished in the ink flow according to this detection result A recording device is disclosed.

However, in such optical ink density detection, the detection part (cell) becomes dirty over time due to adhesion of coloring material particles, etc., resulting in an error in the ink density detection result. The ink density cannot be managed properly.
On the other hand, in Patent Document 2, in an ink jet recording apparatus or an electrophotographic image forming apparatus having such an optical ink density detecting means, an elastic body is in contact with the inner surface of the measuring section inside the detecting section. There has been disclosed a cleaning mechanism that houses a cleaning member and keeps the detection unit clean by reciprocating the cleaning member using an ink flow in the measurement unit.
Japanese Patent No. 2834100 Japanese Patent No. 3130879

By using such a cleaning mechanism, it is possible to reduce an ink density detection error caused by the contamination of the detection unit by ink, and to perform proper ink density detection stably. On the other hand, the cleaning mechanism disclosed in Patent Document 2 requires a flow path, a check valve, a valve, and the like that enable ink flow in the reciprocating direction in order to reciprocate the cleaning member. It becomes complicated. In addition, there is a concern that the cleaning function is deteriorated due to contamination of the cleaning member.
On the other hand, it is conceivable to clean the inside of the measurement unit with a mechanically driven wiper or the like, but there are problems such as an increase in the size of the detection unit, a reduction in design freedom, and a complicated mechanism.

  An object of the present invention is to solve the above-mentioned problems of the prior art. In an image recording apparatus using an ink such as an ink jet image recording such as an electrostatic ink jet or a wet electrophotographic image recording, an optical ink is used. Concentration detection method that can accurately detect the concentration of ink without using a cleaning member or the like, and whether or not the detection unit is soiled, and the concentration detection method are carried out. It is an object of the present invention to provide a density detecting device that performs recording, and an ink jet recording device that can record an image with ink having an appropriate density by using the density detecting device and can stably record a high-quality image.

In order to solve the above-mentioned problem, the concentration detection method of the present invention is a concentration detection method for measuring the transmitted light of a fluid to be measured and detecting the concentration of the fluid from the measurement result. A concentration detection method comprising: measuring a transmitted light at a plurality of detection points having different fluid passage lengths of measurement light in a fluid flow path; and detecting the concentration of the fluid from the measurement results of the plurality of transmitted light. I will provide a.
In such a concentration detection method of the present invention, it is preferable to use a pipe line having at least one region having different diameters and measure the transmitted light at each diameter position of the pipe line.

In addition, the concentration detection apparatus of the present invention detects the flow of the fluid to be measured in the concentration detection apparatus that detects the concentration of the fluid in the detection cell by making the measurement light incident on the detection cell and detecting the transmitted light. A first detection cell forming a path; a second detection cell having a measurement light passage length different from that of the first detection cell; and measurement light incident on the first detection cell and the second detection cell. A concentration detection apparatus comprising: detection means for detecting the transmitted light; and calculation means for detecting the concentration of the fluid using a plurality of measurement results obtained by the detection means. .
In such a concentration detection apparatus of the present invention, it is preferable that the first detection cell and the second detection cell are tubes having different cross-sectional shapes provided in series.

Furthermore, the ink jet recording apparatus of the present invention is an electrostatic ink jet recording apparatus that discharges, by electrostatic force, ink formed by dispersing charged fine particles in a dispersion medium. An electrostatic ink jet head that stores the ink, an ink tank that stores the ink, a circulation means that circulates the ink in a predetermined path including the ink jet head and the ink tank, and the ink circulation path by the circulation means An ink jet recording apparatus comprising the concentration detection apparatus according to the invention, in which a detection unit is disposed, is provided.
In such an ink jet recording apparatus of the present invention, the ink tank has a replenishing means for replenishing the ink tank with the diluent and the ink having a predetermined concentration, and the replenishing means is in accordance with the detection result of the ink density by the density detecting device. It is preferable to determine the replenishment amount of the dilution liquid and the ink having a predetermined concentration to the ink tank.

According to the density detection method and density detection apparatus of the present invention having the above-described configuration, for example, in optical ink density detection in an electrostatic ink jet recording apparatus, a wet electrophotographic recording apparatus, etc., a cleaning mechanism for the detection unit Even if the ink density is not present, it is possible to accurately detect the ink density regardless of the presence or absence of contamination on the ink density detection unit.
Further, according to the ink jet recording apparatus of the present invention using such a concentration detection apparatus of the present invention, an electrostatic ink jet using an ink containing a coloring material and in which charged fine particles are dispersed in a dispersion medium. Regardless of the presence or absence of contamination on the ink density detection unit, the recording apparatus accurately detects the ink density, replenishes the ink appropriately according to the accurate density detection result, and stably stabilizes the ink density. I can keep it. Therefore, the ink jet recording apparatus of the present invention can stably discharge ink droplets with ink having an appropriate concentration, and can stably record a high-quality image.

  Hereinafter, the density detection method, the density detection apparatus, and the ink jet recording apparatus of the present invention will be described in detail based on preferred embodiments shown in the accompanying drawings.

FIG. 1 shows a conceptual diagram of an example of an ink jet recording apparatus of the present invention.
The ink jet recording apparatus 10 uses an ink in which charged fine particles containing a color material (hereinafter referred to as color material particles) are dispersed in a carrier liquid (dispersion medium), and an electrostatic force is applied to the ink. This is an electrostatic ink jet recording apparatus that discharges droplets.
Such an ink jet recording apparatus 10 (hereinafter referred to as a recording apparatus 10) basically includes a holding means 12, a conveying means 14, a recording means 16, an ink circulating means 18, a solvent recovery means 20, a concentration detection of the recording medium P. Means 22 and ink replenishing means 24 are provided, and these are accommodated in a housing 26.
As will be described in detail later, the density detector 22 optically measures the ink density by the density detector of the present invention that implements the density detection method of the present invention. Further, as a preferred mode, the ink replenishing means 24 replenishes ink according to the density detection result by the density detecting means 22.

  The holding means 12 for the recording medium P includes a paper feed tray 30 that holds the recording medium P before recording, a feed roller 32, and a discharge tray 34 that holds the recording medium P after recording.

The paper feed tray 30 is a housing that can be attached to and detached from a predetermined loading unit set in the recording apparatus 10. In the illustrated example, the loading unit is set on the left side in the lower view in the housing 26, and the paper feed tray 3
0 is inserted into the housing 26 with the take-out portion of the recording medium P forward, and a predetermined loading portion in a state where the rear end portion (the end opposite to the take-out portion) slightly protrudes from the housing. Is loaded.
The feed roller 32 is a half-moon roller arranged corresponding to the take-out portion of the paper feed tray 30 loaded in the loading portion.

  In the paper feed tray 30, a plurality of recording media P before recording are stacked and accommodated. At the time of image recording, the recording medium P is taken out from the paper feed tray 30 one by one by the feed roller 32 and supplied to the recording medium P conveying means 14 described later.

The discharge tray 34 accommodates the recording medium P on which an image has been recorded. In the illustrated example, a part of the discharge tray 34 protrudes from the housing 26 and above the loading portion of the paper feed tray 30. It is arranged with the tip in the discharge direction tilted downward.
The recording medium P after recording is conveyed by the conveying means 14 and discharged from the discharge unit, and is sequentially stacked and accommodated in the discharge tray 34.

  The conveyance means 14 conveys the recording medium P supplied from the paper feed tray 30 to the discharge tray 34 by a predetermined path using electrostatic adsorption or the like, and includes a conveyance roller pair 36, a conveyance belt 38, and the like. , A roller 40 (40a, 40b, and 40c), a conductive platen 42, a charging device 44 and a discharging device 46 for the recording medium P, a separation claw 48, a guide 50, and a fixing roller pair 52. .

The conveyance roller pair 36 is provided at a position between the feed roller 32 and the conveyance belt 38 on the conveyance path of the recording medium P.
Next, the recording medium P taken out from the paper feed tray 30 by the feed roller 32 is nipped and conveyed by the conveyance roller pair 36, and is supplied to a predetermined position facing the charging device 44 (scorotron charger 44a) on the surface of the conveyance belt 38. Is done.

  The charging device 44 includes a scorotron charger 44a and a high voltage power supply 44b. The scorotron charger 44 a is disposed upstream of the recording unit 16 (head unit 60) (upstream in the conveyance direction of the recording medium P, hereinafter simply upstream) so as to face the conveyance belt 38. The negative terminal of the high voltage power supply 44b is connected to the scorotron charger 44a, and the positive terminal is grounded.

The conveyor belt 38 is an endless belt, and is stretched in a substantially triangular shape by three rollers 40.
The transport belt 38 has an insulating surface (electrostatic adsorption surface of the recording medium P) and a conductive back surface (contact surface with the roller 40). At least one of the rollers 40 is connected to a drive source (not shown), and is driven to rotate at a predetermined speed during recording, whereby the transport belt 38 also transports the recording medium P (arrow in the figure). Direction).
A plate-like conductive platen 42 is disposed in contact with the inner surface of the conveyor belt 38 at a position corresponding to the recording means 16 (head unit 60) inside the conveyor belt 38.

  In the illustrated example, the roller 40b is grounded. Therefore, the rollers 40a and 40c and the conductive platen 42 are also grounded via the back surface of the conveyor belt 38. As a result, the position of the transport belt 38 facing the recording unit 16 (head unit 60) functions as a counter electrode of the control electrode for discharging ink droplets in the electrostatic ink jet described later.

As described above, the recording medium P is supplied to the conveying roller pair 36 by the feed roller 32, and is supplied by the conveying roller pair 36 to a predetermined position facing the surface of the conveying belt 38 and the scorotron charger 44a. Further, the conveyance belt 38 is rotated by the rotation of the roller 40 serving as a driving source.
The surface of the recording medium P conveyed to this position is uniformly charged to a predetermined negative high potential (for example, about −1.5 kV) by the scorotron charger 44a. The surface of the conveyor belt 38 is insulative, and the recording medium P is electrostatically attracted to the surface of the conveyor belt 38 due to this negative high potential charge, and is conveyed in the same direction by the rotation of the conveyor belt 38 to be recorded. It is conveyed to the means 16 and used for image recording by electrostatic ink jet. The recording means 16 will be described in detail later.
Further, the negative high potential charged on the recording medium P acts as a bias voltage for ink droplet ejection in electrostatic ink jet, which will be described later, and the conveyance of the recording medium P by the conveying belt 38 is a recording in ink jet recording. Scanning conveyance (main scanning) of the medium P is performed.

On the downstream side of the recording unit 16, a static elimination device 46, a separation claw 48, a guide 50, and a fixing roller 52 are arranged toward the downstream side.
The static eliminator 46 includes a corotron static eliminator 46a and a high voltage power source 46b. The corotron static eliminator 46 a is disposed at a position facing the surface of the conveyor belt 38. One end of the high-voltage power supply 46b is connected to the corotron static eliminator 46a, and the other end is grounded.
The recording medium P after recording is neutralized by the corotron neutralizer 46a. Thereby, the recording medium P can be easily separated from the transport belt 38.

The recording medium P that has been neutralized by the neutralization device 46 is separated (separated) from the conveying belt 38 by the separation claw 48, guided by the guide 50, and supplied to the fixing roller pair 52.
The fixing roller pair 52 is a conveyance roller pair in which at least one is a heat roller. The recording medium P is nipped and conveyed by the fixing roller pair 52, and an image recorded by electrostatic ink jet is heated and fixed.
The recording medium P on which the image is fixed is discharged from the discharge portion by the fixing roller pair 52 and is sequentially stacked in the discharge tray 34.

As described above, the recording medium P charged by the charging unit 44 and adsorbed by the conveyance belt 38 is conveyed to the recording unit 16 by the conveyance belt 38 and an image is recorded.
The recording means 16 records an image on the recording medium P by electrostatic inkjet, and includes a head unit 60, a head driver 62, and a position detection device 64 for the recording medium P.

The recording apparatus 10 in the illustrated example records four full-color images of C (cyan), M (magenta), Y (yellow), and K (black), and the head unit 60 uses ink of each color. Have four recording heads 70 (see FIGS. 2 to 4).
Accordingly, in the illustrated recording apparatus 10, each of the C, M, Y, and K recording heads 70 is provided with an ink circulating means 18, a density detecting means 22, and an ink replenishing means 24 described later. In the illustrated example, these portions for the recording heads 70 of the respective colors are arranged, for example, in a direction perpendicular to the paper surface of FIG.

In the illustrated example, the recording head 70 has a row of ejection units (so-called nozzle row) corresponding to the entire area with respect to the width of the corresponding recording medium P (size in a direction orthogonal to the conveyance direction by the conveyance belt 38). Each recording head 70 is a so-called line head, and the recording heads 70 are arranged in the transport direction (column direction, which will be described later) of the recording medium P in such a manner that the columns (row direction, which will be described later) coincide with the width direction of the recording medium P. The
The ink jet recording apparatus of the present invention is not limited to the one using such a line head, and the recording head is intermittently transported, and the recording head is orthogonal to the transport direction in synchronization with the transport. It may be an ink jet recording apparatus that uses a so-called shuttle type recording head that scans in the direction of movement.

FIG. 2 shows a conceptual diagram of the recording head 70. 2A is a partially sectional perspective view, and FIG. 2B is a sectional view.
In the recording apparatus 10, as described above, the recording medium P charged to a negative high voltage (charging the bias voltage) by the charging unit 44 and electrostatically attracted to the conveyance belt 38 is conveyed by the conveyance belt 38. Under the control of the head driver 62, the ink droplets R are ejected on demand by modulating and driving the ejection units of the recording head 70 in accordance with the recording image, that is, the supplied image data, to turn on / off the ejection. Then, the target full-color image is recorded on the recording medium P.

  As described above, the recording head 70 is a line head having a row of ejection portions corresponding to the width of the recording medium P. As conceptually shown in FIG. FIG. 2 shows only a part of the ejection unit in order to clearly show the structure.

The recording head 70 (hereinafter referred to as the head 70) ejects ink droplets R by applying an electrostatic force to ink Q formed by dispersing color material particles (including color material and charged fine particles) in a carrier liquid. The electrostatic inkjet head includes a head substrate 72, a discharge substrate 74, and an ink guide 76.
In the head 70, the head substrate 72 and the discharge substrate 74 are arranged facing each other and spaced apart from each other by a predetermined distance, and an ink channel 78 for supplying the ink Q to each discharge port 96 is formed therebetween. The ink Q is circulated through a predetermined path including the ink flow path 78 by the ink circulation means 18, and at the time of recording, at a predetermined speed (for example, an ink flow of 200 mm / s) in the predetermined direction in the ink flow path 78, for example, , In the direction of arrow a in the figure.

The head substrate 72 is a sheet-like insulative substrate common to all ejection units, and a floating conductive plate 80 that is in an electrically floating state is provided on the surface thereof.
The floating conductive plate 80 generates an induced voltage that is induced in accordance with a drive voltage applied to a first control electrode 82 and a second control electrode 84 described later during image recording. In addition, the voltage value of the induced voltage automatically changes according to the number of operating channels. By this induced voltage, the color material particles contained in the ink Q in the ink flow path 78 are energized and migrate to the discharge substrate 74 side, that is, the concentration of the ink Q at the discharge port 96 described later is more preferably performed. Is called.

  The floating conductive plate 80 is not an essential component and is preferably provided as necessary. The floating conductive plate 80 may be disposed on the head substrate 72 side with respect to the ink flow path 78, and may be disposed, for example, inside the head substrate 72. The floating conductive plate 80 is preferably arranged on the upstream side of the ink flow path 78 from the position where the ejection unit is arranged. Further, a predetermined voltage may be applied to the floating conductive plate 80.

On the other hand, the ejection substrate 74 is a sheet-like insulating substrate that is common to all ejection sections, like the head substrate 72, and includes an insulating substrate 86, a first control electrode 82, a second control electrode 84, and a guard. An electrode 88 and insulating layers 90, 92, and 94 are provided. In addition, ink discharge ports 96 are opened through the discharge substrate 74 at positions corresponding to the respective ink guides 76, and the leading end portion 98 of the ink guide protrudes from the surface of the discharge substrate 74 to form the ink guide 76. Is inserted. As described above, the head substrate 72 and the discharge substrate 74 are arranged apart from each other, and the ink flow path 78 is formed therebetween.
In the head 70, the first control electrode 82, the second control electrode 84, the ejection port 96, the ink guide 76, and the like corresponding to each other constitute one ink ejection unit.

The first control electrode 82 and the second control electrode 84 are circular electrodes provided in a ring shape on the surfaces of the upper surface and the lower surface of the insulating substrate 86, respectively, so as to surround the periphery of the corresponding discharge ports 96. Yes (see FIG. 3 and FIG. 4). The surfaces of the insulating substrate 86 and the first control electrode 82 are covered with an insulating layer 92 that protects and planarizes the surface, and similarly, the surfaces of the insulating substrate 86 and the second control electrode 84 are covered with the insulating layer 92. An insulating layer 90 for planarizing the surface is covered. Further, a guard electrode 88 is formed on the insulating layer 92, and an insulating layer 94 for planarizing the surface is formed on the guard electrode 88 and the insulating layer 92.
Note that the first control electrode 82 and the second control electrode 84 are not limited to ring-shaped circular electrodes, and may be substantially circular electrodes, divided circular electrodes, parallel electrodes, for example, as long as the electrodes are disposed so as to face the ink guide 76. Any shape such as a substantially parallel electrode may be used.

  As shown in FIGS. 3 and 4, in the head 70, each ejection unit including the ink guide 76, the first control electrode 82 and the second control electrode 84, the ejection port 96, and the like is two-dimensionally arranged in a matrix. Has been placed.

Specifically, as shown in FIGS. 3B and 3C, the head 70 moves the columns of the ejection units arranged in the row direction (sub-scanning direction (horizontal direction in FIG. 3)) in the column direction (main direction). 3 rows (A row, B row, C row) in the scanning direction (vertical direction in FIG. 3). Note that FIG. 3 shows a total of 15 discharge units arranged in a matrix of 5 (1 column, 2 columns, 3 columns, 4 columns, 5 columns) in the row direction.
The head 70 is a line head, and has a row of ejection portions (nozzle row) corresponding to the width direction of the recording medium P in the row direction. Accordingly, the four heads 70 are arranged in the column direction with the row direction aligned with the direction perpendicular to the paper surface of FIG. 1, and the recording medium P is conveyed in the column direction (main scanning) by the conveyance belt 38.
The ejection units in each row are arranged at a predetermined interval in the column direction. In addition, each row is arranged so that the ejection units are shifted from each other by 1/3 pitch in the row direction so that their ejection units are located between the ejection units of other rows (between the row directions).

As shown in FIG. 3A, the guard electrode 88 is a sheet-like electrode in which regions corresponding to the discharge port 96 and the control electrode open in a circular shape. That is, the guard electrode 88 is formed between the control electrodes.
Further, as shown in FIG. 3B, the first control electrodes 82 of the discharge units arranged in the same column are connected to each other and arranged in the same row as shown in FIG. The second control electrodes 84 of the discharge unit are connected to each other.
Further, although not shown, the first control electrode 82 and the second control electrode 84 are each applied with a drive voltage (pulse voltage), and each electrode is modulated to drive ejection of the ink droplet R. It is connected to a pulse power supply for turning off.

At the time of image recording, the first control electrodes 82 arranged in the same column are simultaneously applied (on) with a driving voltage of the same voltage level. Similarly, the drive voltages are applied (on) to the second control electrodes 84 arranged in the same row simultaneously and at the same voltage level.
In addition, one row recorded on the recording medium P is divided into three groups corresponding to the number of rows of the second control electrodes 84 in the column direction, and each row of A row, B row, and C row It is recorded sequentially by dividing.
For example, in the example shown in FIG. 2, the A line, the B line, and the C line of the second control electrode 84 are sequentially turned on at a predetermined timing. Corresponding to this drive, the first control electrode 82 is modulated and driven (on / off) in accordance with image data (recorded image), so that one line on the recording medium P is obtained by three time-divided image recording. Minutes of images are recorded. As described above, since the recording medium P is conveyed in the column direction, image recording with a recording density three times the recording density (discharge portion density) of each row can be performed in the row direction (sub-scanning direction). it can.

  The control electrode is not limited to the two-layer electrode structure of the first control electrode 82 and the second control electrode 84, and may be a single-layer electrode structure or an electrode structure having three or more layers.

As described above, the guard electrode 88 has a ring-shaped portion corresponding to the first control electrode 82 and the second control electrode 84 formed around each discharge port 96 as shown in FIG. It is a sheet-like electrode common to all the discharge parts. That is, the guard electrode 88 is an electrode disposed between the control electrodes. The surfaces of the insulating layer 92 and the guard electrode 88 are covered with an insulating layer 94 that protects and flattens the surfaces.
A predetermined voltage is applied to the guard electrode 88 and plays a role of suppressing electric field interference generated between the ink guides 76 of the adjacent ejection portions.
The guard electrode 88 is not an essential component. Further, in order to shield the repulsive electric field from the first control electrode 82 or the second control electrode 84 toward the ink flow path 78, the discharge substrate 74 has a shield electrode on the ink flow path 78 side from the second control electrode 84. May be provided.

  The ink guide 76 is a ceramic flat plate having a convex end portion 96 having a predetermined thickness. In the illustrated example, the ink guides 76 of the ejection units in the same row are disposed on the same support 47 disposed on the floating conductive plate 80 on the head substrate 72 at a predetermined interval. The ink guide 76 passes through the ejection port 96 opened in the ejection substrate 74, and the tip portion 96 is located above the outermost surface of the ejection substrate 74 on the recording medium P side (the upper surface in the drawing of the insulating layer 94). It protrudes.

The leading end portion 96 of the ink guide 76 is formed in a substantially triangular shape (or trapezoidal shape) that gradually becomes thinner toward the holding means 17 of the recording medium P.
In addition, it is preferable that the metal is vapor-deposited in the front-end | tip part 96 (most advanced part). Although the metal vapor deposition of the tip portion 96 is not an essential element, there is an effect that the dielectric constant of the tip portion 96 is substantially increased and a strong electric field can be easily generated.

  The shape of the ink guide 76 is not particularly limited as long as the colorant particles in the ink Q can be migrated toward the tip portion 96 (that is, the ink Q is concentrated). For example, the tip portion 96 is convex. You may change freely, such as not having to. Further, in order to promote the concentration of ink, a notch serving as an ink guide groove for collecting the ink Q in the tip portion 96 by capillary action may be formed in the central portion of the ink guide 76 along the vertical direction in the drawing. .

  As described above, the second control electrodes 84 are sequentially turned on (driven (high voltage level (for example, 400 to 600 V) or high impedance state)) one row at a time at a predetermined timing, and all the remaining second electrodes are driven. The control electrode 84 is turned off (non-driven (ground level (ground state)). In addition, the first control electrode 82 is turned on in units of columns in accordance with image data (recorded image) in all columns at the same time. By setting the high voltage level or the ground level, ink ejection / non-ejection (ink ejection on / off) in each ejection unit is controlled.

That is, when the second control electrode 84 is on and the first control electrode 82 is on, the ink Q is ejected (ejection on) as the ink droplet R, and the first control electrode 82 and the second control electrode 84 are When at least one is off, ink is not ejected (ejection off).
Then, the ink droplets R ejected from each ejection unit are attracted to the recording medium P charged with a negative bias voltage, and adhere to a predetermined position of the recording medium P to form an image.

  As described above, when the row of the second lower control electrode 84 is sequentially turned on and the upper first control electrode 82 is turned on / off according to the image data, the first control electrode 82 is turned on according to the image data. Therefore, the first control electrode 82 frequently changes to the high voltage level or the ground level at the discharge portions on both sides of each discharge portion in the column direction. In this case, by biasing the guard electrode 88 to a predetermined guard potential, for example, the ground level, at the time of image recording, it is possible to eliminate the influence of the electric field of the adjacent ejection unit.

  In the head 70, it is not limited at all whether one or both of the first control electrode 82 and the second control electrode 84 perform on / off control of ink ejection. That is, ink is ejected when the difference between the voltage value at the time of ink on / off on the control electrode side and the voltage value on the recording medium P side is larger than a predetermined value, and ink is discharged when the difference is smaller than the predetermined value. What is necessary is just to set the voltage of the control electrode side and the recording medium P side suitably so that it may not discharge.

Therefore, in the head 70, the first control electrode 82 is sequentially turned on for each column and the second control electrode 84 is turned on in accordance with the image data. It is also possible to turn it off.
In this case, the column direction is turned on for each column of the first control electrodes 82, and the first control electrodes 82 of the discharge units in the columns on both sides thereof are always at the ground level with the respective discharge units in the column direction as the center. The first control electrodes 26 of the ejection portions in the rows on both sides serve as the guard electrode 88. As described above, when each column is sequentially turned on by the upper first control electrode 82 and the lower second control electrode 84 is driven in accordance with the image data, the adjacent ejection can be performed without providing the guard electrode 88. It is possible to improve the recording quality by eliminating the influence of the part.

  In this embodiment, the color material particles in the ink Q are positively charged and the recording medium side is charged to a negative high voltage. However, the present invention is not limited to this, and conversely, the color material particles in the ink are negatively charged. The recording medium P side may be charged to a positive high voltage. As described above, when the polarity of the color material particles is reversed from that in the present embodiment, the counter electrode 18, the charging unit 18 of the recording medium P, and the first control electrode 82 and the second control electrode 84 of each discharge unit are connected. What is necessary is just to make an applied voltage polarity etc. reverse to said example.

  The ink Q (ink composition) discharged by such a head 70 is obtained by dispersing color material particles (including color material and charged fine particles) in a carrier liquid.

The carrier liquid is preferably a dielectric liquid (nonaqueous solvent) having a high electric resistivity (10 ⁹ Ω · cm or more, preferably 10 ¹⁰ Ω · cm or more). If the electric resistance of the carrier liquid is low, the carrier liquid itself is charged by charge injection due to the drive voltage applied to the control electrode, and the colorant particles do not concentrate. In addition, a carrier liquid having a low electric resistance is not suitable for the present invention because there is a concern of causing electrical conduction between adjacent control electrodes.

The relative dielectric constant of the dielectric liquid used as the carrier liquid is preferably 5 or less, more preferably 4 or less, and still more preferably 3.5 or less. By setting the relative dielectric constant in such a range, an electric field effectively acts on the colorant particles in the carrier liquid, and migration easily occurs.
The upper limit value of the specific electric resistance of such a carrier liquid is preferably about 10 ¹⁶ Ωcm, and the lower limit value of the relative dielectric constant is preferably about 1.9. The reason why it is desirable that the electric resistance of the carrier liquid is in the above range is that if the electric resistance is low, ink ejection under a low electric field is deteriorated, and the reason why the relative dielectric constant is preferably in the above range is the reason. This is because, when the dielectric constant increases, the electric field is relaxed by the polarization of the solvent, and the color of the dots formed thereby becomes thin or causes blurring.

  The dielectric liquid used as the carrier liquid is preferably a linear or branched aliphatic hydrocarbon, alicyclic hydrocarbon, or aromatic hydrocarbon, and halogen-substituted products of these hydrocarbons. For example, hexane, heptane, octane, isooctane, decane, isodecane, decalin, nonane, dodecane, isododecane, cyclohexane, cyclooctane, cyclodecane, benzene, toluene, xylene, mesitylene, Isopar C, Isopar E, Isopar G, Isopar H, Isopar L, Isopar M (isopar: trade name of Exxon), Shellsol 70, Shellsol 71 (shellsol: trade name of Shell Oil), Amsco OMS, Amsco 460 solvent (trade name of Amsco: Spirits), Silicone oil (for example, KF-96L manufactured by Shin-Etsu Silicone) or the like can be used alone or in combination.

  The colorant particles dispersed in such a carrier liquid may be dispersed in the carrier liquid as the colorant itself as colorant particles, but preferably contain dispersed resin particles for improving fixability. When the dispersed resin particles are included, the pigment is generally coated with the resin material of the dispersed resin particles to form resin-coated particles, and the dye is colored with the dispersed resin particles to form colored particles. Is common.

As the color material, any pigments and dyes that have been conventionally used in inkjet ink compositions, printing (oil-based) ink compositions, or electrophotographic liquid developers can be used.
As the pigment used as the color material, regardless of inorganic pigments or organic pigments, those generally used in the technical field of printing can be used. Specifically, for example, carbon black, cadmium red, molybdenum red, chrome yellow, cadmium yellow, titanium yellow, chromium oxide, viridian, cobalt green, ultramarine blue, Prussian blue, cobalt blue, azo pigment, phthalocyanine pigment Conventionally known pigments such as quinacridone pigments, isoindolinone pigments, dioxazine pigments, selenium pigments, perylene pigments, perinone pigments, thioindigo pigments, quinophthalone pigments, metal complex pigments, and the like are not particularly limited. Can be used.
As dyes used as coloring materials, azo dyes, metal complex dyes, naphthol dyes, anthraquinone dyes, indigo dyes, carbonium dyes, quinoneimine dyes, xanthene dyes, aniline dyes, quinoline dyes, nitro dyes, nitroso dyes, benzoquinone dyes, naphthoquinone dyes And oil-soluble dyes such as phthalocyanine dyes and metal phthalocyanine dyes.

Furthermore, as the dispersed resin particles, for example, rosins, rosin-modified phenol resins, alkyd resins, (meth) acrylic polymers, polyurethane, polyester, polyamide, polyethylene, polybutadiene, polystyrene, polyvinyl acetate, polyvinyl alcohol, acetal modification of polyvinyl alcohol Products, polycarbonate and the like.
Among these, from the viewpoint of ease of particle formation, the weight average molecular weight is in the range of 2,000 to 1,000,000 and the polydispersity (weight average molecular weight / number average molecular weight) is 1.0 to 5 Polymers in the range of 0.0 are preferred. Furthermore, from the viewpoint of ease of fixing, a polymer having any one of a softening point, a glass transition point, and a melting point within a range of 40 ° C. to 120 ° C. is preferable.

  In the ink Q, the content of the color material particles (the total content of the color material particles or further dispersed resin particles) is preferably contained in the range of 0.5 to 30% by weight with respect to the whole ink, and more preferably. Is preferably contained in the range of 1.5 to 25% by weight, more preferably 3 to 20% by weight. If the content of the colorant particles is reduced, problems such as insufficient printed image density and difficulty in obtaining a strong image due to difficulty in obtaining the affinity between the ink Q and the surface of the recording medium P are likely to occur. On the other hand, when the content increases, it becomes difficult to obtain a uniform dispersion, or the ink Q is easily clogged with the inkjet head 10 or the like, and stable ink ejection is difficult to obtain. It is.

  The average particle diameter of the colorant particles dispersed in the carrier liquid is preferably 0.1 to 5 μm, more preferably 0.2 to 1.5 μm, and still more preferably 0.4 to 1.0 μm. . This particle size is determined by CAPA-500 (trade name, manufactured by Horiba, Ltd.).

After the colorant particles are dispersed in the carrier liquid (a dispersant may be used if necessary), the chargeant is added to the carrier liquid to charge the colorant particles, and the charged colorant The ink Q is obtained by dispersing particles in a carrier liquid. When dispersing the colorant particles, a dispersion medium may be added as necessary.
As an example of the charge control agent, various materials used in electrophotographic liquid developers can be used. Also, “Recent development and commercialization of electrophotographic development systems and toner materials”, pages 139 to 148, “The Basics and Applications of Electrophotographic Technology” edited by Electrophotographic Society, pages 497 to 505 (Corona Inc., published in 1988), Yuji Harasaki Various charge control agents described in “Electrophotography” 16 (No. 2), p. 44 (1977) can also be used.

The color material particles may be positively charged or negatively charged as long as they have the same polarity as the drive voltage applied to the control electrode.
The charge amount of the color material particles is preferably in the range of 5 to 200 μC / g, more preferably 10 to 150 μC / g, and still more preferably 15 to 100 μC / g.

In addition, since the electric resistance of the dielectric solvent may change due to the addition of the charge control agent, the distribution ratio P defined below is preferably 50% or more, more preferably 60% or more, and even more preferably 70% or more. And
P = 100 × (σ1−σ2) / σ1
Here, σ1 is the electrical conductivity of the ink Q, and σ2 is the electrical conductivity of the supernatant obtained by applying the ink Q to the centrifuge. The electrical conductivity was measured using an LCR meter (AG-4311 manufactured by Ando Electric Co., Ltd.) and an electrode for liquid (LP-05 type manufactured by Kawaguchi Electric Manufacturing Co., Ltd.) under the conditions of an applied voltage of 5 V and a frequency of 1 kHz. This is the measured value. Centrifugation was performed for 30 minutes using a small high-speed cooling centrifuge (Tomy Seiko Co., Ltd. SRX-201) under conditions of a rotational speed of 14500 rpm and a temperature of 23 ° C.
By using the ink Q as described above, migration of charged particles is likely to occur, and concentration is facilitated.

The electrical conductivity of the ink Q is preferably 100 to 3000 pS / cm, more preferably 150 to 2500 pS / cm, and still more preferably 200 to 2000 pS / cm. By setting the electric conductivity in the above range, the voltage applied to the control electrode does not become extremely high, and there is no fear of causing electrical continuity between adjacent recording electrodes.
The surface tension of the ink Q is preferably in the range of 15 to 50 mN / m, more preferably 15.5 to 45 mN / m, and still more preferably 16 to 40 mN / m. By setting the surface tension within this range, the voltage applied to the control electrode does not become extremely high, and the ink does not leak around the head to be contaminated.
Furthermore, the viscosity of the ink Q is preferably 0.5 to 5 mPa · sec, more preferably 0.6 to 3.0 mPa · sec, and still more preferably 0.7 to 2.0 mPa · sec.

As an example, such an ink Q can be prepared by dispersing color material particles in a carrier liquid to form particles, and adding a charge adjusting agent to the dispersion medium to cause the color material particles to be charged. Specific methods include the following methods.
(1) A method in which a color material or further dispersed resin particles are mixed (kneaded) in advance, and then dispersed in a carrier liquid using a dispersant as required, and a charge adjusting agent is added.
(2) A method in which a coloring material, or further dispersed resin particles and a dispersing agent are simultaneously added to a carrier liquid, dispersed, and a charge adjusting agent is added.
(3) A method in which a coloring material and a charge adjusting agent, or further dispersed resin particles and a dispersing agent are simultaneously added to a carrier liquid and dispersed.

The position detection device 64 is a conventionally known position detection unit such as a photosensor, and the recording medium P is transported to a predetermined position on the transport path by the transport belt 38 between the charging device 64 and the head unit 60. This is to detect this.
The detection result of the recording medium P by the position detection device 64 is supplied to the head driver 62.

The head driver 62 supplies a drive signal to each head 70 of the head unit 60.
Image data is input to the head driver 62 from an external device such as a scanner or a computer. The head driver 62 refers to the detection result of the recording medium P by the position detection device 64, and at the time when the recording medium P is transported to a predetermined position, each of the head drivers 62 corresponds to the transport timing of the recording medium P and the supplied image data. A drive signal for the control electrode is supplied to each head 70 (its pulse power supply) of the head unit 60. In response to this drive signal, the head 70 sequentially drives the second control electrodes 84 in each row and modulates and drives the first control electrodes 82 in each column according to image data as described above. As a result, ink of each color is ejected from the head 70 of each color, and an image corresponding to the image data is recorded on the recording medium P.

In the electrostatic ink jet using such an ink Q, a force is not applied to the entire ink to cause the ink to fly toward the recording medium as in the conventional ink jet system. A force is applied to the colorant particles, which are solid components dispersed in the ink, to cause the ink to fly. Hereinafter, the operation of discharging the ink droplet R in the recording unit 16 (head 70) will be described.
In the following example, the color material particles are positively charged. Therefore, when ejection is on, a positive drive voltage is applied to the first control electrode 82 and the second control electrode 84, and the recording medium P has A negative high voltage (bias voltage) is charged.

At the time of recording an image, the ink Q is circulated by the ink circulation means 18 described later, and flows in the ink flow path 78 from the right side in the figure to the left side (in the direction of arrow a in FIG. 1) at a predetermined speed.
Further, as described above, the recording medium P is charged to a negative high voltage by the charging device 44, electrostatically adsorbed to the transport belt 38, transported by the rotation of the transport belt 38, and transferred to the head unit of the recording unit 16. It reaches the facing position.
The negative high voltage charged on the recording medium P acts as a bias voltage in electrostatic inkjet, and the recording medium P and the conveyance belt 38 act as counter electrodes to the control electrode of the head 70 as described above. It is as follows.

  As described above, when the recording medium P is transported to a predetermined position by the transport belt 38, the head driver 62 supplies a drive signal to each head 70 according to the transport timing of the recording medium P and the image data. In response to this, each head 70 sequentially drives the second control electrode 84 in each row, and modulates and drives the first control electrode 82 in each column according to the image data, and the ink ejection is performed according to the image data. To modulate and turn on / off.

Here, when at least one of the first control electrode 82 and the second control electrode 84 is off, that is, in a state where only the bias voltage is applied, the ink Q has the bias voltage and the color material particles (charge) of the ink Q. Particle) and the Coulomb repulsive force between the coloring material particles, the coulomb repulsive force between the coloring material particles, the viscosity of the carrier liquid, the surface tension, the dielectric polarization force, etc., which are coupled to move the coloring material particles and the carrier liquid. As conceptually shown in FIG. 2 (B), a balanced meniscus shape slightly raised from the discharge port 96 is obtained.
In addition, the colorant particles move toward the recording medium P charged with a bias voltage by so-called electrophoresis due to the Coulomb attractive force or the like. That is, the ink Q is concentrated in the meniscus of the discharge port 96.

  From this state, a driving voltage (pulse voltage) for ejecting the ink droplet R is applied. That is, in the illustrated example, when both the first control electrode 82 and the second control electrode 84 are turned on, the drive voltage is superimposed on the bias voltage, and the previous coupling is further performed by the superposition of the drive voltage. The formed movement occurs, and the electrostatic force pulls the color material particles and the carrier liquid to the bias voltage (counter electrode) side, that is, the recording medium P side, the meniscus grows, and the so-called substantially conical ink liquid column is formed from the upper part. A tailor cone is formed. Similarly to the above, the color material particles are moved to the meniscus by electrophoresis, and the ink Q of the meniscus is concentrated and is in a substantially uniform high density state having a large number of color material particles.

When a finite time has passed after the start of the application of the drive voltage, the balance between the color material particles and the surface tension of the carrier liquid mainly breaks at the tip of the meniscus with high electric field strength due to the movement of the color material particles, The meniscus grows abruptly to form an elongated ink liquid column having a diameter of about several to several tens of μm, which is called a kite string.
Further, when a finite time elapses, the silk thread grows, and the growth of the silk thread, vibration caused by Rayleigh / Weber instability, uneven distribution of colorant particles in the meniscus, uneven distribution of electrostatic field on the meniscus, etc. As a result of this interaction, the kite string is divided, ejected / flyed as ink droplets R, and pulled by the bias voltage to land on the recording medium P.
The growth and splitting of the kite string, and further the movement of the color material particles to the meniscus (punch kite) occur continuously during the application of the drive voltage. When the application of the drive voltage is completed (at least one of the first control electrode 82 and the second control electrode 84 is turned off), the state returns to the meniscus state in FIG. 2B where only the bias voltage is applied.

As described above, the ink Q is circulated by the ink circulation means 18.
The ink circulating means 18 includes an ink tank 100, an ink supply path 102, and an ink recovery path 104, and the ink tank 100 to the ink supply path 102 to the head 70 (ink path 26) to the ink recovery path 104 to the ink tank 100. In this way, the ink Q in the ink tank 100 is circulated.
Note that a pump for circulating the ink Q along this path is built in the ink tank 100. The ink tank 100 preferably includes a stirring unit for preventing the sedimentation / deposition of the color material particles and a temperature adjusting unit for improving the stability of ink discharge.

In the ink supply path 102, a transmitted light measurement unit 110 of the density detection unit 22 is disposed.
The density detection unit 22 includes the transmitted light measurement unit 110 and the calculation unit 112. The density detection unit 22 measures the transmitted light of the ink Q circulated by the ink circulation unit 18, and thereby the density of the ink Q (for example, in the ink Q). % By weight of colorant particles) is detected. Here, the concentration detection means 22 is a concentration measurement device according to the present invention that performs the concentration detection method according to the present invention, and measures the transmitted light in a plurality of (two in the illustrated example) detection cells, thereby providing ink. The density of the ink Q is detected with high accuracy without any error caused by dirt or the like due to Q.

FIG. 5 shows a conceptual diagram of the concentration detection means 22.
The transmitted light measurement unit 110 of the concentration detection unit 22 includes a first detection cell 114 and a first measurement unit 118, and a second detection cell 116 and a second measurement unit 120.
Both the first detection cell 114 and the second detection cell 116 are circular transparent ink flow paths provided in the middle of the ink supply path 102. The second detection cell 116 has a smaller diameter than the first detection cell and is provided in series downstream of the first detection cell 114.

The first measuring means 118 receives the light source 118a that makes the measurement light incident on the first detection cell 114 and the light that is transmitted through the first detection cell 114 (the measurement light that has passed through the first detection cell 114) and measures the light. This is a known transmitted light measuring means composed of the element 118b. On the other hand, the second measuring means 120 is also a known transmitted light composed of a light source 120a that makes the measurement light incident on the second detection cell 116 and a light receiving element 120b that receives and measures the light transmitted through the second detection cell 116. It is a measuring means.
Both measuring means use the same light source and light receiving element, and both measure the transmitted light on the detection surface of the corresponding detection cell. That is, the length of the measurement light ink Q passing through the first detection cell 114 (first measurement means 118) is longer than the length of the measurement light ink Q passage through the second detection cell 116 (second measurement means 120).

  The measurement results of the transmitted light by the light receiving elements 118b and 120b are supplied to the calculation unit 112. The calculation unit 112 detects the concentration including the ink concentration and the contamination of the detection cell (flow path) for each detection cell from both measurement results, and compares them to detect the actual concentration of the ink Q. A first density detection unit 121a, a second density detection unit 121b, a comparison calculation unit 122, and a density detection unit.

The first density detection unit 121a processes the measurement result of the transmitted light by the light receiving element 118b (first measurement means 118), and detects the density including the density of the ink Q in the first detection cell 114 and the contamination of the detection cell. The resulting site. Further, the second density detector 121b processes the measurement result of the transmitted light by the light receiving element 120b (second measuring means 120), and the density including the density of the ink Q in the second detection cell 116 and the contamination of the detection cell. It is a site | part made into a detection result.
The comparison calculation unit 122 is a part that compares and calculates the density detection results of the first concentration detection unit 121a and the second concentration detection unit 121b, and the concentration detection unit 124 further compares the result of the comparison calculation by the comparison calculation unit 122 (or Further, it is a part that detects the density of the ink Q by using the measurement results of the light receiving elements 118b and 120b as necessary, and supplies it to an ink replenishing means 24 (its replenishment necessity determining unit 130) to be described later.

  The first concentration detection unit 121a and the second concentration detection unit 121b may be, for example, a digital detection result (output signal) of transmitted light by each light receiving element to be a concentration detection result, Alternatively, the measurement result of transmitted light by the light receiving element may be converted into light amount data or optical density to obtain a density detection result using an LUT or an arithmetic expression created in advance through experiments or the like. Alternatively, the density detection result may be obtained by converting the measurement result of the transmitted light by the measurement unit into the density of the ink Q using an LUT or an arithmetic expression created in advance through experiments or the like.

As described above, the density detector 22 detects the density of the ink Q by measuring the transmitted light of the ink Q (detection cell through which the ink Q flows).
As a matter of course, if the ink Q is circulated, color material particles and the like adhere to the detection cell and become gradually dirty. As a result, the measurement result of the transmitted light in the detection cell includes this stain, and an error corresponding to the stain of the detection cell also occurs in the density measurement result of the ink Q.

Here, since the first detection cell 114 and the second detection cell 116 are arranged in series, the same amount of ink Q flows through both detection cells. Almost equal. Further, as described above, the detection lengths of the ink Q are different between the two detection cells.
In this way, the transmitted light of the ink Q is measured by a plurality of detection cells in which the ink Q to be measured has the same amount of flow, that is, dirt is equivalent, and the passage length of the ink Q of the measurement light is different. Thus, the density of the ink Q can be detected with high accuracy regardless of the presence or absence or the state of the detection cell.

  As an example, in the comparison calculation unit 122, the second result of the light receiving element 120b processed by the second concentration detection unit 121b is obtained from the measurement result of the transmitted light of the first detection cell 114 by the light receiving element 118b processed by the first concentration detection unit 121a. The measurement result of the transmitted light of the detection cell 116 is subtracted, and the density detection unit 124 uses the LUT indicating the relationship between the subtraction result and the appropriate density of the ink Q, which is created in advance, from the subtraction result of the ink Q. A method for obtaining the concentration is exemplified.

Both the measurement results of the transmitted light in both detection cells include the absorption of the measurement light due to the contamination of the detection cell in addition to the absorption of the measurement light by the ink Q.
Here, the absorption of the measurement light by the detection cell is negligible, the inner diameter of the first detection cell 114 (that is, the passage length of the measurement light) is d ₁ , and the inner diameter of the second detection cell 116 is d ₂ . . At this time, the transmitted light of the first detection cell 114 is absorbed by the measurement light when it passes through the ink Q by the distance d ₁ from the measurement light, and the absorption of the measurement light due to contamination of the first detection cell 114. The light is reduced by minutes. Similarly, the transmitted light of the second detection cell 116 is obtained by measuring the absorption of the measurement light when passing through the ink Q by the distance d ₂ from the measurement light and the absorption of the measurement light due to the contamination of the second detection cell 116. Reduced light.

As described above, since the light source 118a and the light source 120a are the same, the amount of measurement light incident on both detection cells is equal. Further, as described above, the flow rates of the ink Q in the first detection cell 114 and the second detection cell 116 are the same, and the contamination of both is the same.
Accordingly, the result of subtracting the measurement result of the transmitted light of the second detection cell 116 from the measurement result of the transmitted light of the first detection cell 114 is the result of the ink Q from the measurement light by the distance d ₃ (= d ₁ -d ₂ ). transmitted light obtained by subtracting the absorption amount of the measurement light at the time that has passed, i.e., inner diameter assumes the detection cell at all no dirt d _3, the measurement result of the transmitted light at the time of flowing the ink Q in the detection cell Will be equal.

Accordingly, in correspondence with the detection cell of the inner diameter d ₃ , an LUT indicating the relationship between the measurement result of the transmitted light by the measuring means when the ink Q is flowing in the detection cell and the accurate density of the ink Q is provided. Preliminarily created and set in the density detection unit 124, and the density of the ink Q is detected from the subtraction result supplied from the comparison calculation unit 122 by using this LUT. Thus, it is possible to detect the accurate ink Q density regardless of the state.

In the transmitted light measurement unit 110 of the concentration detection unit 22 of the illustrated example, the measurement unit (light source and light receiving element) is not limited to being fixed at the position of the illustrated example. For example, it is usually retracted to another position. It may be moved to a measurement position as shown in the drawing when measuring the density of the ink Q. Moreover, it is not limited to having a plurality of detection units and measuring units individually, and one movable measuring unit may be used in combination with a plurality of detection units.
Alternatively, the density of the ink Q may be detected by measuring transmitted light at different positions in the cross-sectional direction of the detection cell to form a plurality of detection means having different ink passage lengths of the measurement light.

Although the transmitted light measurement unit 110 in the illustrated example has two detection means, the present invention is not limited to this, and is upstream of the first detection cell 114 and / or downstream of the second detection cell 116. If the same amount of ink Q flows and the passage length of the measurement light is different, such as by providing one or more detection cells, provide three or more detection cells and measurement means (detection means). You may make it perform density | concentration detection.
For example, when three detection means are provided, three combinations of the two detection means can be made. Therefore, three density detection results are obtained in the same manner as described above, and three average values and median values are obtained as the density detection results. And a method is exemplified.

Since the same amount of the same ink Q flows in the first detection cell 114 and the second detection cell 116, the contamination is basically the same. However, since there is a difference in flow rate between the two, there is a possibility that a slight difference occurs in the degree of contamination.
On the other hand, by providing a plurality of detection cells in this way, it is possible to cancel out the difference in dirt due to the difference in flow rate and perform more accurate dirt detection, that is, concentration measurement.

Further, the position of each detection cell is not limited to the position immediately upstream and downstream as in the illustrated example. For example, if the flow rate of the ink Q is the same and the fluid passage length of the measurement light is different, a plurality of detection cells may be arranged in parallel to measure the transmitted light. In order to more suitably equalize the contamination of the detection cells, the detection cells are preferably arranged in series and immediately upstream and / or immediately downstream.
Furthermore, the shape of the detection cell is not limited to the circular tube shown in the figure, and various cells such as a square columnar cell can be used as long as the light transmission property and the ink Q (fluid) passage length of the measurement light are different. Is possible.

As described above, the density detection result of the ink Q by the density detection unit 22 (density detection unit 124) is supplied to the ink replenishment unit 24 (replenishment necessity determination unit 130).
The ink replenishing unit 24 includes a replenishment necessity determining unit 130, a carrier liquid replenishing unit 132, and a high density ink replenishing unit 134.

The replenishment necessity determining unit 130 detects the density of the ink Q by the density detector 22 and the current ink circulation system (ink tank 100 to ink supply path 102 to head 70 to ink recovery path 104 to ink tank 100). The replenishment amount of high-concentration ink and carrier liquid so that the specified ink amount, the preset specified ink amount, the target ink concentration, and the ink Q in the ink circulation system are the target concentration and the specified ink amount. It is a part to do.
Note that the amount of ink Q in the ink circulation system is obtained by, for example, obtaining the ink discharge amount from the previous replenishment by counting the image data and the total number of discharges of all discharge units, or further evaporating the ink over time measured in advance. What is necessary is just to calculate | require and calculate quantity. Alternatively, the circulation of the ink Q may be stopped and the amount of ink in the ink tank 100 may be measured, or the amount of ink in the ink supply path 102, the head 70, and the ink recovery path 104 at the time of circulation can naturally be known. Therefore, it may be obtained by measuring the amount of ink in the ink tank 100 during circulation.

The carrier liquid replenishing unit 132 has a tank that is filled with the carrier liquid (diluted liquid) of the ink Q, and replenishes the ink tank 100 with the carrier liquid according to the replenishment amount determined by the replenishment necessity determination unit 130.
On the other hand, the high-density ink replenishment unit 134 has a tank that is filled with high-density ink (ink with a large amount of colorant particles), and the high-density ink is supplied according to the replenishment amount determined by the replenishment necessity determination unit 130. Refill the ink tank to 100. In this example, the density of the high density ink is not particularly limited, and the ink having the same density as the target density of the ink Q may be used as the ink having a predetermined density for replenishment. Replenishment may be performed using a plurality of inks having a predetermined density and different densities. Further, the replenishment may be performed only with a predetermined concentration of ink without using the carrier liquid.

In the electrostatic ink jet as in the recording apparatus 10, as described above, the ink Q is concentrated in the ejection portion, and the electrostatic force is applied here to eject the ink droplet R. In order to stabilize the image density and to set the image density to the target density, the density of the ink Q supplied to the head 70 (circulated through the circulation system) is extremely important.
On the other hand, according to the present invention, as described above, the density detection unit 22 measures the density of the ink Q with high accuracy regardless of the contamination of the detection cell, and the ink Q (carrier liquid and high density ink) is measured. ) Can be replenished. Therefore, in the recording apparatus 10 of the present invention, it is possible to stably discharge high-quality images by stably discharging ink droplets with the ink Q having an appropriate concentration.

In the recording apparatus 10 of the present invention, there are no particular limitations on the timing of ink Q density detection by the density detection means 22 and ink replenishment to the ink tank 100. For example, for every predetermined period or a predetermined number of images. It may be performed automatically every time recording is performed, or may be performed automatically by detecting the amount of ink Q by the above-described means, etc., and is performed according to an input instruction based on the judgment of an operator who observes the recorded image. Alternatively, both means may be provided and selectively performed.
The density detection and replenishment of the ink Q may be performed simultaneously for all the colors, or may be appropriately performed for each color.

A solvent recovery means 20 is disposed on the upper part (ceiling part) of the recording apparatus 10.
The solvent recovery means 20 recovers a carrier liquid that evaporates from the ink ejected from the head 70 onto the recording medium P, a carrier liquid that evaporates from the ink during image fixing, and the like. The exhaust fan 140, the activated carbon filter 142, It has. The activated carbon filter 142 is attached to the back surface of the upper surface (upper side in the drawing) of the housing 26, and the exhaust fan 140 is attached to the activated carbon filter 142.
The air containing the carrier liquid component inside the housing 22 is exhausted to the outside of the housing 22 through the activated carbon filter 142 by the exhaust fan 140. At that time, the dispersed solvent component contained in the air inside the housing 22 is adsorbed and removed by the activated carbon filter 142.

Hereinafter, the operation of the recording apparatus 10 will be described.
In the recording apparatus 10, when an image is recorded, the recording medium P stored in the paper feed tray 30 is taken out one by one by the feed roller 32, nipped and conveyed by the conveyance roller pair 36, and supplied to a predetermined position on the conveyance belt 38. Is done.
The recording medium P supplied on the conveyance belt 38 is charged to a negative high potential by the charging device 44 and electrostatically attracted to the surface of the conveyance belt 38. This negative high potential acts not only for electrostatic attraction to the conveyor belt 38 but also as a bias voltage in the electrostatic ink jet.

The recording medium P electrostatically attracted to the surface of the conveyance belt 38 is conveyed (main scanning) at a predetermined speed by the conveyance belt 38.
In synchronization with this, the head driver 62 refers to the detection result of the recording medium P by the position detection device 64, and outputs a driving signal for each control electrode according to the conveyance timing of the recording medium P and the supplied image data. This is supplied to each head 70 (its pulse power supply) of the head unit 60.
In response to this, the second control electrodes 84 in each row are sequentially driven, and the first control electrodes 82 in each column are modulated and driven in accordance with image data. The ink is discharged and an image corresponding to the image data is recorded on the recording medium P.

  The recording medium P after image recording is neutralized by the neutralization device 46, separated from the conveying belt 38 by the separation claw 48, and supplied to the fixing roller pair 52 along the guide 48. The recorded images are heated and fixed while being nipped and conveyed by the fixing roller pair 52 and are stacked in the discharge tray 28 and stocked.

In addition, the ink Q circulates through a predetermined circulation path from the ink tank 100 to the ink supply path 102 to the head 70 to the ink recovery path 104 to the ink tank 100 during recording or when the recording apparatus 10 is on standby for image recording. is doing.
Here, in the recording apparatus 10, for example, the density measurement unit 22 periodically measures the density of the ink Q, and according to the result, the ink tank 100 is replenished with the ink Q by the ink replenishment unit 24.

  As described above, at the time of measuring the density of the ink Q, the transmitted light measurement unit 110 measures the transmitted light emitted from the light source 118a and transmitted through the first detection cell 114 by the light receiving element 118b, and also emitted from the light source 120a. The transmitted light transmitted through the two detection cells 116 is measured by the light receiving element 120 b and supplied to the comparison unit 122 of the calculation unit 112.

The comparison unit 122 subtracts the measurement result of the transmitted light by the light receiving element 120b from the measurement result of the transmitted light by the light receiving element 118b, and sends the result to the density detection unit 124.
The density detection unit 124 uses an LUT indicating the relationship between the measurement result of the transmitted light in the detection cell having a preset inner diameter d ₃ and the density of the ink Q, and uses the ink Q from the subtraction result supplied from the comparison unit 122. Is detected and sent to the ink replenishing unit 24.

In the ink replenishment section 24, the replenishment amount determination means 130 determines whether the high-concentration ink and the carrier liquid are in accordance with the density detection result of the ink Q by the density detection means 22, the target ink Q density, the amount of ink Q in the circulation system, and the like. The replenishment amount is determined, and the carrier liquid and high concentration ink are replenished from the carrier liquid replenishment unit 132 and the high concentration ink replenishment unit 134 to the ink tank 100.
As described above, the density detection result of the ink Q by the density detection means 22 is a highly accurate one in which an error due to contamination of the detection cell is corrected. Therefore, the carrier liquid and the high density ink can be appropriately replenished. Therefore, high-quality image recording can be stably performed with the ink Q having an appropriate concentration.

  As described above, the density detection method, the density detection apparatus, and the ink jet recording apparatus of the present invention have been described in detail. However, the present invention is not limited to the above-described embodiment, and various types can be made without departing from the gist of the present invention. Of course, improvements and changes may be made.

It is a conceptual diagram of an example of the inkjet recording device of this invention. 2A and 2B are conceptual diagrams of a recording head of the ink jet recording apparatus illustrated in FIG. 1, in which FIG. (A), (B) and (C) are schematic diagrams for explaining the recording head shown in FIG. FIG. 3 is a schematic perspective view for explaining the recording head shown in FIG. 2. It is a conceptual diagram of the density | concentration measurement means of the inkjet recording device shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 (Inkjet) recording apparatus 12 Holding | maintenance means 14 Conveyance means 16 Recording means 18 Ink circulation means 20 Solvent recovery means 24 Concentration detection means 26 Ink replenishment means 26 Housing | casing 30 Paper feed tray 32 Feed roller 34 Discharge tray 36 Conveyance roller pair 38 Conveyance Belt 40 Roller 42 Conductive platen 44 Charging device 46 Neutralizing device 48 Separation claw 50 Guide 52 Fixing roller pair 60 Head unit 62 Head driver 64 Position detecting means 70 (Recording) Head 72 Head substrate 74 Discharge port substrate 76 Ink guide 78 Ink flow Path 80 Floating conductive plate 821 Control electrode 86 Second control electrode 86 Insulating substrate 88 Guard electrode 90, 92, 94 Insulating layer 96 Discharge port 98 Tip portion 100 Ink tank 102 Ink supply path 104 Ink recovery path 110 Measurement 112 arithmetic unit 114 first detection cell 116 second detection cell 118 first measurement unit 120 second measurement unit 121a first concentration detection unit 121b second concentration detection unit 122 comparison unit 124 concentration detection unit 130 replenishment necessity determination unit 132 carrier Liquid replenishment unit 134 High-density ink replenishment unit

Claims (6)

A concentration detection method for measuring transmitted light of a fluid to be measured and detecting the concentration of the fluid from the measurement result,
In the flow path of the fluid to be measured, the transmitted light is measured at three or more detection locations where the fluid passage length of the measurement light is different, and a plurality of combinations of the two detection locations are created, and the combined two locations of the transmitted light A concentration detection method , wherein the concentration of the fluid is detected for each combination from the measurement results, and an average value or a median value of the concentration detection results in each combination is used as the concentration detection result of the fluid . Diameter using a conduit having at least two positions of the different regions, the concentration detection method according to claim 1 for measuring the transmitted light at the position of each diameter of the pipe. In a concentration detector that detects the concentration of fluid in the detection cell by making measurement light incident on the detection cell and detecting the transmitted light,
Three or more detection cells forming a flow path of a fluid to be measured, detection means for entering measurement light into each of the three or more detection cells and detecting the transmitted light, and two detection cells A plurality of combinations are created, and the concentration of the fluid is detected for each combination of the detection cells from the measurement results in the two detection cells combined, and the average value or median value of the concentration detection results in each combination is detected as the fluid. And a calculating means for detecting the concentration as a concentration. The concentration detection apparatus according to claim 3, wherein the three or more detection cells are tubes having different cross-sectional shapes provided in series.   An electrostatic ink jet recording apparatus that discharges, by electrostatic force, ink obtained by dispersing charged fine particles in a dispersion medium, the electrostatic ink jet head that discharges ink by applying an electrostatic force; and 4. The ink tank for storing ink, a circulation means for circulating the ink in a predetermined path including the ink jet head and the ink tank, and the detection unit is disposed in an ink circulation path by the circulation means. Or an ink-jet recording apparatus comprising the density detection apparatus according to 4.   The replenishing means replenishes the ink tank with the diluted liquid and the ink having a predetermined concentration, and the replenishing means is configured to supply the diluted liquid to the ink tank and the predetermined density according to the detection result of the ink density by the density detecting device. The ink jet recording apparatus according to claim 5, wherein an ink replenishment amount is determined.

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