JP2795740B2 - Ink jet recording device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to an ink jet recording apparatus using an ink jet recording head for discharging droplets with energy from a discharge energy generating means.

[Conventional technology]

Conventionally, this type of ink jet recording apparatus has an ink jet recording head that discharges droplets with energy from a discharge energy generating unit, and a relative moving unit that relatively moves a recording medium and the ink jet recording head. And the recording medium are arranged to face each other to perform image formation.

FIG. 9 is a block diagram showing a conventional example of an ink jet recording apparatus.
It is called "recording head". ), 42 'are pressure generating means, 7'
Is a recording medium, and the ink 43 'in the recording head 1 is extruded by the pressure generated by the pressure generating means 42' to cause ink droplets to adhere on the recording medium 7 'in the direction of arrow A by the recording medium conveying means (not shown). It is conveyed to form an image.

[Problems to be solved by the invention]

In the above-described conventional ink jet recording apparatus, there is an electric field between the recording medium and the recording head, and the motion of the droplet when the droplet is charged is affected by the electric force,
In some cases, the droplet does not land on an intended place on the recording medium, causing image disorder. In particular, when the humidity of the recording medium changes, the electric field between the recording medium and the recording head changes, and the electric force with respect to the movement of the droplet changes, so that the landing position changes and the image disturbance is amplified. There is a problem.

The present invention has been made in view of the above problems, and has as its object to provide an ink jet recording apparatus that does not adversely affect the movement of a droplet.

[Means for solving the problem]

An inkjet recording apparatus of the present invention includes: an inkjet recording head that ejects liquid droplets; a relative moving unit that relatively moves a recording medium and the inkjet recording head; a humidity detecting unit that detects a humidity of the recording medium; A potential difference adjusting unit that adjusts a potential difference between a medium and the inkjet recording head, wherein a value of the potential difference by the potential difference adjusting unit changes according to a humidity value of the recording medium detected by the humidity detecting unit. Let it.

Preferably, the relative movement means is an electrostatic suction conveyance means, and more preferably, the ink jet recording head is a full line type having a plurality of discharge ports over the entire width of the recording area of the recording medium, or The recording head ejects ink from ejection ports using thermal energy, and has an electrothermal converter as a means for generating thermal energy.

[Action]

When the relative moving unit relatively moves the recording medium and the ink jet recording head, the humidity detecting unit detects the humidity of the recording medium, and based on the detection result, the potential difference adjusting unit detects the humidity between the recording medium and the ink jet recording head. The potential difference is adjusted so that the ink droplets on the recording medium fly accurately from the inkjet recording head.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a configuration diagram schematically showing a first embodiment of the ink jet recording apparatus of the present invention.

1BK, 1y, 1m, and 1c are bubble jet ink jet recording heads (hereinafter, “recording heads”) corresponding to black, yellow, magenta, and cyan ink colors, respectively. A resistor is used to discharge ink droplets from a discharge port by bubbles generated in the ink by utilizing thermal energy generated when the heating resistor is energized, and is fixed to the block 2. Each print head has 4736 ejection openings arranged at a density of 400 dpi (dots per inch).

Reference numeral 3 denotes a capping unit, for example, in a standby mode.
At the time of recording, the block 2 is pulled up to a position A indicated by a dashed line in the figure, and the unit 3 is capped with the unit 3 opposed to the block 2 pulled up. Also, the capping unit 3
At the time of the circulation recovery, the recovery pump (not shown) is fed from the ink supply system, and serves as a tray for the waste ink pushed out from the discharge port. The waste ink is guided to a waste ink tank (not shown).

Reference numeral 4 denotes a charging / adsorbing belt for supporting and transporting the recording sheet 7, and is disposed opposite to each of the recording heads Bk, 1y, 1m, and 1c at a predetermined interval.
It is charged by 31 and driven by a drive source (not shown). Reference numeral 5 denotes a back platen that is disposed to face each recording head via the charging suction belt 4.

Reference numeral 6 denotes a paper feed cassette which stores recording sheets 7 such as plain paper and is detachably attached to the apparatus main body. Reference numeral 8 denotes a pickup roller which feeds out and feeds only one uppermost recording sheet 7; The recording sheet 7 sent out from the pickup roller 8 is conveyed to a conveyance path 10 by a pair of conveyance rollers 9, and is conveyed onto the charging adsorption belt 4 by a pair of conveyance rollers 11 disposed on the exit side of the conveyance path 10. .

Reference numerals 13 and 14 denote heaters and fans for drying and fixing ink droplets adhered onto the recording sheet 7 by hot air by recording, 15 a discharge roller for discharging the fixed recording sheet 7 to the outside of the apparatus, and 16 a discharged recording. This is a tray for sequentially storing the sheets 7. Numeral 32 denotes a brush-like electrode for injecting electric charge from a power supply 35 onto the recording sheet 7, and a humidity measuring means 33 is disposed near the brush-like electrode.

 Next, the operation of the embodiment shown in FIG. 1 will be described.

First, the recording operation will be described. When a recording start operation is performed, a recording sheet 7 of a designated size is sent out of the sheet cassette 6 by the pickup roller 8. The fed recording sheet 7 is conveyed by conveying rollers 9 and 11, rotates while being charged by a charging roller 31 so as to have a surface potential of about +2 kV, and has a planar shape by a back platen 5. It is placed on the suction belt 4. At this time, the recording sheet 7
The humidity is measured by the humidity measuring means 33, and the voltage applied to the brush-like electrode 32 is controlled according to the measured value (to be described later in detail). As the leading end of the recording sheet 7 arrives at the lower part of each of the recording heads 1c, 1m, 1y, 1Bk,
The energy generator of each recording head is driven according to image data via a drive circuit (not shown). With this drive,
Ink droplets corresponding to the image information are ejected from the ejection port to the recording sheet 7.
And recording is performed.

If the recording sheet 7 has poor hygroscopicity, the droplets adhering to the surface do not dry and are rubbed to cause printing stains.
Forcible drying is performed by 13 and the fan 14 to fix. The recording sheet 7 on which the fixing has been completed is discharged to a tray 16 by a discharge roller 15.

As described above, recording heads 1Bk, 1y, 1m, and 1m corresponding to cyan, magenta, yellow, and black inks respectively.
A color image is formed by giving a recording signal corresponding to each of the recording heads 1Bk, 1y, 1m, and 1c to 1c.

Next, the ejection principle of the ink jet recording head used in the apparatus of this embodiment will be described.

An ink jet recording head applied to an ink jet recording apparatus generally has a fine liquid discharge port (orifice), a liquid flow path, an energy action section provided in a part of the liquid flow path, and a liquid acting on the action section. An energy generating means for generating energy for forming droplets is provided.

As an energy generating means for generating such energy, a recording method using an electromechanical transducer such as a piezo element, irradiating a laser or an electromagnetic wave, etc., absorbs energy in a liquid there and generates heat, There are a recording method using an energy generating means for discharging and flying a droplet by the action of the heat generation, and a recording method using an energy generating means for discharging the liquid by heating the liquid with an electrothermal converter.

Among them, a recording head used in an ink jet recording method in which a liquid is discharged by thermal energy has a high density of liquid discharge ports (orifices) for discharging a recording droplet to form a flying droplet. Therefore, it is possible to record at a high resolution. Further, a recording head using an electrothermal transducer as an energy generating means can easily be made compact as a whole as a recording head.

Furthermore, it is possible to make full use of the advantages of IC technology and micro-machining technology, which have made remarkable progress in recent semiconductor technology and improve reliability, and it is easy to make them longer and more planar (two-dimensional). For example, it is possible to provide an ink jet recording head that can be easily formed into multiple discharge ports / high-density mounting, has high productivity in mass production, and has a low manufacturing cost.

In general, an ink jet recording head manufactured through a semiconductor manufacturing process using an electrothermal converter as an energy generating means is provided with a liquid flow path corresponding to each discharge port, and the liquid flow path is provided for each of the liquid flow paths. An electrothermal converter is provided as means for applying thermal energy to the liquid filling the flow path and discharging the liquid from the corresponding orifice to form a droplet for flight. The liquid is supplied from a common liquid chamber communicating with the flow path.

FIG. 2 shows a schematic configuration of the above-described ink jet recording head. The recording head passes through a semiconductor manufacturing process such as etching, vapor deposition, sputtering, etc.
Electrothermal transducer 103, electrode 104, liquid path wall 105 formed on 2
The top plate 106 is configured.

The recording liquid 112 is supplied from a liquid storage chamber (not shown) through a liquid supply pipe 107 into a common liquid chamber 108 of the recording head 101. In the figure, reference numeral 109 denotes a liquid supply pipe connector. The liquid 112 supplied into the common liquid chamber 108 is supplied into a liquid flow path (liquid path) 110 by a capillary phenomenon, and a discharge port surface 111 at the tip of the liquid path.
To form a meniscus, which is stably maintained.
Here, when electricity is supplied to the electrothermal converter 103, the liquid on the electrothermal converter surface is heated, and a bubbling phenomenon occurs.

With the above-described configuration, a multi-ejection port ink jet recording head is formed with a high-density ejection port arrangement such as an ejection port density of 400 dpi.

The application of a voltage to the brush-like electrode according to the value measured by the measuring means will be described with reference to FIG.

The ink 43 in the recording heads 1Bk, 1y, 1m, and 1c is pressure generating means.
The droplets are ejected at a pressure of 42 and fly and adhere to the recording sheet 7.

A conductive rubber is provided around the metal core with respect to the electrostatic attraction belt 4, and a charging roller 31 applying a voltage of about +2 kV (applied by the power supply 34) is brought into contact with the metal core, and a positive charge is formed on the electrostatic attraction belt 4. Put on. By bringing the recording sheet 7 into close contact with the charging and attracting belt 4, a negative charge is induced on the recording sheet 7 on the side of the charging and attracting belt, and
Then, an attraction force of the charging attraction belt is generated. Positive charges are induced on the side of the recording sheet 7 that is not on the side of the charge adsorption belt (the side facing the recording heads 1Bk, 1y, 1m, and 1c), and the recording head
A potential difference is generated between 1Bk, 1y, 1m, 1c and the recording sheet 7, and an electric field is formed.

The strength of this potential difference, that is, the strength of the electric field,
And the decay rate of the surface potential of the charging and adsorbing belt 4, which vary depending on the surrounding environment, and the conventional configuration cannot control the strength of the electric field. The deviation of the landing position of the falling droplet could not be controlled, causing unintended image disturbance.

In the present invention, the humidity measuring means 33 and the brush-like electrode 32
And a variable power supply 35 that changes according to the value measured by the humidity measuring means 33, and the recording sheet 7 and the recording heads 1Bk, 1y, 1m, 1c.
The strength of the electric field between them is about zero (-100V / mm
~ 100V / mm).

The relationship between the measured humidity and the value of the dielectric constant of the recording sheet 7 is measured in advance and is tabulated as shown in FIG. 4, and the dielectric constant of the recording sheet 7 can be estimated from the measured humidity value.
Further, the relationship between the dielectric constant and the magnitude of the potential induced on the recording sheet 7 is also known in advance. By utilizing these known relations and changing the voltage applied by the variable power supply 35 according to the humidity as shown in FIG. 5, the electric field between the recording sheet 7 and the recording head as shown in FIG. The intensity of the irrespective of humidity.

The location where the humidity measuring means 33 is arranged is not limited to the vicinity of the recording heads 1Bk, 1y, 1m, 1c as shown in FIG. May be arranged in the vicinity of the recording sheet 7.

Although the relationship between humidity and the voltage applied to the variable power supply 35 was derived from the relationship between humidity and dielectric constant, the present invention is not limited to this, and takes into account the relationship between humidity and the surface potential decay rate on the recording medium. Is also good.

Although the electric field between the recording sheet 7 and the recording heads 1Bk, 1y, 1m, 1c is controlled so that the intensity becomes about zero, the present invention is not limited to this. Plus 100 V / mm to plus 3
The ink droplets may be controlled to be in the range of 00 V / mm and have a means for negatively charging the ink droplets, and the ink droplets may be pulled toward the recording sheet by an electric force. Since the intensity of the electric field can be controlled by the configuration of this embodiment, the electric force acting on the droplet can be controlled, and unintended image disturbance due to the fluctuation of the electric force can be prevented.

Although the case of positive charging has been described, the present invention is not limited to this. The same applies to the case of negative charging.

Although the object to be measured in the examples was humidity, the present invention is not limited to this, and has a means for measuring the dielectric constant of the recording sheet, the one related to the strength of the electric field between the recording head and the recording sheet. Alternatively, the relationship between the measured value and the applied voltage may be tabulated to determine the optimum applied voltage. The measurement target is, for example, temperature.

In the configuration of the first embodiment, the power supply to be controlled is described as a constant voltage power supply, but is not limited to this, and may be a constant current power supply.

 FIG. 7 is a block diagram showing a second embodiment of the present invention.

In the first embodiment, the voltage applied to the brush-like electrode 32 is a variable power supply 35.
37, a variable power supply 36 for varying the voltage applied to the metal core of the charging roller 31 is provided, and the variable power supply 36 is controlled according to the value of the humidity measuring means 33.
It is clear that the power supply for both the brush-like electrode 32 and the charging roller 31 may be controlled.

 FIG. 8 is a block diagram showing a third embodiment of the present invention.

In the present embodiment, the voltage of the variable power supply 38 applied to the ink 43 is controlled by the value of the humidity measuring means 33.
In this case, there is an advantage that the time required for control is shorter than in the first and second embodiments because there is no field-back sequence.

The present invention brings about an excellent effect particularly in a recording head and a recording apparatus of a bubble jet method proposed by Canon Inc. among ink jet recording methods.

Regarding the representative configuration and principle, it is preferable to use the basic principle disclosed in, for example, US Pat. Nos. 4,723,129 and 4,740,796. This method can be applied to both the so-called on-demand type and the continuous type. In particular, in the case of the on-demand type, it corresponds to a sheet or a liquid path holding a liquid (ink) and By applying at least one drive signal that gives a rapid temperature rise above boiling. This is effective because heat energy is generated in the electrothermal converter and, as a result, bubbles in the liquid (ink) can be formed in one-to-one correspondence with the drive signal. By discharging the liquid (ink) through the discharge opening by the growth and contraction of the bubble, at least one droplet is formed. If this drive signal is formed into a pulse shape, the growth and shrinkage of the bubble are performed immediately and appropriately.
In particular, liquid (ink) discharge with excellent responsiveness can be achieved,
More preferred. As the pulse-shaped drive signal, those described in US Pat. Nos. 4,463,359 and 4,434,262 are suitable. Further, if the conditions described in US Pat. No. 4,313,124 relating to the invention relating to the temperature rise rate of the heat acting surface are adopted, more excellent recording can be performed.

As a configuration of the recording head, in addition to a combination configuration (a linear liquid flow path or a right-angle liquid flow path) of a discharge port, a liquid path, and an electric heat exchanger as disclosed in each of the above-mentioned specifications, a heat acting section U.S. Pat.
The configurations described in 4558333 and US Pat. No. 4,459,600 may be used. In addition, JP-A-59-123670 discloses a configuration in which a common slit is used as a discharge portion of the electrothermal converter for a plurality of electrothermal converters, and an aperture for absorbing a pressure wave of thermal energy. The present invention is also effective as a configuration based on JP-A-59-138461 which discloses a configuration corresponding to a discharge unit.

Further, as a full-line type recording head having a length corresponding to the width of the maximum recording medium on which the recording layer value can be recorded, the length of the recording head is determined by a combination of a plurality of recording heads as disclosed in the above specification. The present invention can exhibit the above-mentioned effects more effectively, although it may be either a configuration satisfying the above or a configuration as a single recording head formed integrally.

In addition, a replaceable chip-type recording head that can be electrically connected to the apparatus main body and supplied with ink from the apparatus main body by being attached to the apparatus main body, or provided integrally with the recording head itself The present invention is also effective when a cartridge type recording head is used.

It is preferable to add recovery means for the printhead, preliminary auxiliary means, and the like provided as components of the printing apparatus of the present invention since the effects of the present invention can be further stabilized. Specifically, for the recording head, a capping unit, a cleaning unit, a pressurizing or suction unit, an electrothermal transducer is a separate heating element or a preheating unit using a combination thereof, Performing a preliminary ejection mode in which ejection is performed separately from printing is also effective for performing stable printing.

Further, the printing mode of the printing apparatus is not limited to the printing mode of only the mainstream color such as black, but may be a printing head integrally formed or a combination of a plurality of printing heads. The present invention is extremely effective for an apparatus having at least one of the full colors.

In the embodiments of the present invention described above, the ink is described as a liquid. However, an ink which solidifies at room temperature or below and which softens or becomes liquid at room temperature, or which is generally used in an ink jet. It may be softened or liquid in a temperature range of 30 ° C. or more and 71 ° C. or less, which is the temperature range of the temperature adjustment performed. That is, any ink may be used as long as the ink is in liquid form for the use recording signal added character. In addition, the temperature rise due to thermal energy can be positively prevented by using it as energy for changing the state of the ink from the solid state to the liquid state, or ink that solidifies in a standing state to prevent evaporation of the ink can be used. In any case, thermal energy such as ink that liquefies and is ejected as an ink liquid by application according to the recording signal of thermal energy, or that already starts to solidify when it reaches the recording medium, is used. The use of an ink that liquefies for the first time is also applicable to the present invention. In such a case, as described in JP-A-54-56847 or JP-A-60-71260, the ink is held in a liquid state or a solid state in a porous sheet concave portion or through hole, It is good also as a form which opposes an electrothermal transducer. In the present invention, the most effective one for each of the above-mentioned inks is to execute the above-mentioned film boiling method.

〔The invention's effect〕

As described above, the present invention controls the electric potential difference between the recording medium and the ink jet recording head based on the detection result of the humidity detecting means to reduce the fluctuation of the electric field between the two, thereby providing an electric power Thus, there is an effect that the image quality can be kept constant regardless of the humidity of the recording medium, and disturbance of image quality can be eliminated.

[Brief description of the drawings]

FIG. 1 is a configuration diagram schematically showing a first embodiment of an ink jet recording apparatus of the present invention, FIG. 2 is a diagram showing a structure of an ink jet recording head, and FIG. 3 is a control unit of the embodiment of FIG. FIG. 4 is a graph showing a change in dielectric constant of the recording sheet with respect to humidity, and FIG.
FIG. 6 is a graph showing the strength of the electric field between the recording sheet and the ink jet recording head in the embodiment of FIG. 1, and FIGS. 7 and 8 are respectively graphs showing the second embodiment of the present invention. FIG. 9 is a block diagram showing a third embodiment, and FIG. 9 is a block diagram showing a conventional example. 2 ... block, 3 ... capping unit, 4 ... electrostatic adsorption belt, 5 ... back platen, 6 ... paper feed cassette, 7 ... recording sheet, 8 ... pickup roller, 9,11 ... transport roller 31, a charging roller, 32, a brush-like electrode, 33, a humidity measuring means, 34, 37, a power supply, 35, 36, 38, a variable power supply.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B41J 2/01

Claims (4)

(57) [Claims] An ink jet recording head for ejecting liquid droplets; a relative moving means for relatively moving a recording medium and the ink jet recording head; a humidity detecting means for detecting a humidity of the recording medium; A potential difference adjusting unit for adjusting a potential difference between the inkjet recording head and the recording medium, wherein the potential difference adjusting unit changes the value of the potential difference according to the humidity value of the recording medium detected by the humidity detecting unit. Characteristic inkjet recording device. 2. The ink jet recording apparatus according to claim 1, wherein the relative moving means is an electrostatic attraction conveying means. 3. The ink jet recording apparatus according to claim 1, wherein the ink jet recording head is of a full line type having a plurality of ejection ports over the entire width of the recording area of the recording medium. 4. An ink jet recording head according to claim 1, wherein said ink jet recording head discharges ink from said discharge port by utilizing thermal energy, and has an electrothermal converter as a means for generating thermal energy. An ink jet recording apparatus according to any one of the preceding claims.