JPH10324009A - Image forming system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a smoother image by superposing an ink dot of second group having lower viscosity than the ink of first group on an ink dot of first group. SOLUTION: The image forming system forms an image using a plurality of normal color inks and a photoink having lower density of coloring matter and higher viscosity than the plurality of normal color inks. Normal color ink dots are shown by hatched circles and photoink dots are shown by plain circles. At first, normal color ink dots are printed and then photoink dots are printed between adjacent normal color ink dots. When black color is represented, for example, normal color ink dots of black are printed at first and then dots of black photoink corresponding to the black ink are printed between adjacent black ink dots. Consequently, black ink dots can be blurred with black photoink.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus that forms a color image by using a plurality of color inks.

[0002]

2. Description of the Related Art Conventionally, there are various types of color image forming apparatuses typified by an ink jet printer and the like. In these image forming apparatuses, a plurality of color inks such as yellow (Y), magenta (M), cyan (C), and black (K) are used, and a full-color image is formed by using these inks. .

Further, in a conventional image forming apparatus, in order to form a smoother image, an ink (photo ink) having a lower color material density than each of the above inks is sometimes used. In this case, the original inks are collectively referred to as normal inks with respect to the photo inks. In such an image forming apparatus, for example, cyan (C) ink and cyan photo (Cp) ink are used, and dots of these inks are formed as shown in FIG.
An image was formed by partially overlapping. The hatched portion in FIG. 29 is an overlapping portion of two ink dots.

[0004]

However, FIG.
Even if the dots of the photo ink are partially overlapped with the normal ink, the spread of each ink on the printing paper in the overlapping portion of the dots is poor, and the degree of mixing of both inks on the printing paper is low, There has been a problem that the outline of each dot in the overlapping portion is emphasized and unsightly.

The present invention has been made to solve such a problem, and an object of the present invention is to provide an image forming apparatus capable of forming a smooth image.

[0006]

According to the present invention, there is provided an image forming apparatus, comprising: a first group of ink dots corresponding to a plurality of colors; A second group of ink dots having a low density of material on a print sheet, wherein the second group of inks comprises:
The printer head has a lower viscosity than the ink of the first group, and the printer head prints by overlapping the dots of the first group of ink with the dots of the second group of ink.

According to the first aspect of the present invention, an image is formed by overlapping dots of the first group of ink with ink of the second group having a lower viscosity than the ink of the first group. Can be.

[0008] This makes it possible for the dots of the second group of ink to bleed the dots of the ink of the first group on the printing paper, thereby forming a smoother image.

According to a second aspect of the present invention, in addition to the configuration of the first aspect of the present invention, the printer head further includes a dot diameter control unit for controlling a diameter of a dot to be printed by the printer head. Features.

According to the second aspect of the present invention, the first aspect is provided.
In addition to the effect of the invention described in the above, the diameter of the dots of the first or second group of inks printed by the print head can be changed.

Thus, when the first group of inks are oozed by the second group of inks, the first ink can be oozed to a desired degree.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an ink jet printer according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a perspective view showing a schematic configuration of an ink jet printer 1 according to a first embodiment of the present invention. The inkjet printer 1 includes a recording sheet 2 that is a recording medium such as a print sheet or a plastic thin plate;
Printer head 3 which is an ink jet type printer head, and carriage 4 which holds printer head 3
Swinging shafts 5 and 6 for reciprocating the carriage 4 in parallel with the recording surface of the recording sheet 2, a driving motor 7 for reciprocatingly driving the carriage 4 along the swinging shafts 5 and 6, and a driving motor 7 1 includes an idle pulley 8 for changing the rotation of the carriage into a reciprocating motion of the carriage, and a timing belt 9.

In the present embodiment, print paper is usually paper used in image forming apparatuses such as printers and copiers, and is, for example, PPC paper.

The ink jet printer 1 prevents the recording sheet 2 from floating by pressing the recording sheet 2 between the platen 10 and the platen 10 which also serves as a guide plate for guiding the recording sheet 2 along the transport path. The paper holding plate 11, the discharge roller 12 for discharging the recording sheet 2, the spur roller 13, and the recovery system 14 for cleaning the nozzle surface of the printer head 3 which discharges ink and recovering the ink discharge portion to a good state. And a paper feed knob 15 for manually conveying the recording sheet 2. The recovery system 14 includes a suction unit 16 that suctions the nozzles of the printer head 3 and a wiping device 17 that rubs the surface of the printer head 3 having the nozzles.

The recording sheet 2 is fed to a recording section where the printer head 3 and the platen 10 face each other by a paper feeding device such as a manual feed or a cut sheet feeder.
At this time, the rotation amount of a paper feed roller (not shown) is controlled,
The conveyance to the recording unit is controlled.

The printer head 3 uses a piezoelectric element (PZT) as an energy source for flying ink.
A voltage is applied to the piezoelectric element, causing distortion. This distortion changes the volume of the channel in the printer head 3 filled with ink. Due to this change in volume, ink is ejected from nozzles provided in the channel, and recording on the recording sheet 2 is performed.

The carriage 4 performs a main scan of the recording sheet 2 in the traverse direction (a direction traversing the recording sheet 2) by the drive motor 7, the idle pulley 8, and the timing belt 9, and the printer head 3 attached to the carriage 4 1
Record the image for the line. Each time recording of one line is completed, the recording sheet 2 is fed in the vertical direction and sub-scanned, and an image is recorded on the next line.

The image is recorded on the recording sheet 2 in this manner. The recording sheet 2 that has passed through the recording unit is discharged by a discharge roller 12 disposed downstream of the recording sheet and a spur roller 13 pressed against the discharge roller 12.

FIG. 2 is a perspective view for explaining the configuration around the carriage 4. As shown in FIG. Around the carriage 4, an ink cartridge 403 for storing ink, a casing 401 for storing the ink cartridge 403, a casing lid 405, and an ink supply pin for supplying ink to the printer head 3 while making the ink cartridge 403 detachable. 402, an urging clutch 406 for fixing the casing lid 405 to the casing 401 when the casing lid 405 is closed, an urging clutch stop 407, and a direction in which the ink cartridge 403 is stored (the direction of arrow D3).
And a leaf spring 408 that holds the ink cartridge 403 together with the casing lid 405 while pushing the ink cartridge 403 in the opposite direction. The ink cartridge 403 has an air communication hole 404 formed therein. The main scanning is performed by moving the carriage 4 in the direction of arrow D1 shown in the figure, and ink droplets are ejected in the direction of arrow D2. The printer head 3 is held on the bottom of the carriage 4.

FIGS. 3 to 5 are diagrams for explaining the configuration of the printer head 3. FIG. 3 is a plan view showing a part of the surface of the printer head 3 having nozzles. FIG. 4 is a cross-sectional view taken along the line IV-IV of FIG. 3, and FIG.
It is a line sectional view.

Referring to FIG. 3 to FIG.
Are the nozzle plate 301, the partition 302, the diaphragm 30
3. It has a configuration in which the substrate 304 and the substrate 304 are integrally stacked. The nozzle plate 301 is made of metal, synthetic resin, or the like, has nozzles 307, and has an ion-repellent layer on the surface 318. The partition wall 302 is formed of a thin film, and is fixed between the nozzle plate 301 and the diaphragm 303.

The nozzle plate 301 and the partition 302
A plurality of ink channels 306 for accommodating the ink 305 and an ink inlet 309 for connecting each ink channel 306 to the ink supply chamber 308 are formed between them. The ink supply chamber 308 is connected to an ink tank (not shown).
05 is supplied to the ink channel 306.

Each ink channel 3 is provided on the vibration plate 303.
In addition, a plurality of piezoelectric elements 313 corresponding to 06 are included. The piezoelectric element 313 is formed by processing the vibration plate 303. The processing of the diaphragm 303 is performed first.
Are fixed to a substrate 304 having a wiring portion 317 with an insulating adhesive, and then separated by a dicer process.
5, 316 are formed and the diaphragm 303 is divided. By this division, the piezoelectric element 313 corresponding to each ink channel 306, the piezoelectric element column 314 located between the adjacent piezoelectric elements 313, and the wall 310 surrounding these are separated.

The wiring portion 317 on the substrate 304 is connected to the ground and all the piezoelectric elements 313 in the printer head 3 are connected.
And a common electrode side wiring portion 311 connected to each of the piezoelectric elements 313 in the printer head 3 individually. The common electrode side wiring portion 311 on the substrate 304 is connected to a common electrode in the piezoelectric element 313. The individual electrode side wiring portion 312 is connected to an individual electrode in the piezoelectric element 313. Further, the individual electrode side wiring section 312 is connected to the head ejection drive section 105 (see FIG. 7) of the control section of the inkjet printer 1.

The operation of the printer head 3 having such a configuration is controlled by the control unit of the ink jet printer 1. Printer head ejection drive unit 10 of control unit
From 5, a predetermined voltage as a print signal is applied between the common electrode and the individual electrode provided inside the piezoelectric element 313, and the piezoelectric element 313 is deformed in a direction to push the partition 302. The deformation of the piezoelectric element 313 is transmitted to the partition 302, whereby the ink 305 in the ink channel 306 is pressurized, and the ink droplet is formed through the nozzle 307 to the recording sheet 2.
(See FIG. 1).

The degree of deformation of the piezoelectric element 313 changes as the voltage applied to the piezoelectric element 313 by the head ejection drive unit 105 changes. Accordingly, by controlling the voltage applied by the head ejection drive unit 105, the amount of ink ejected by one deformation of the piezoelectric element 313 can be controlled, and the diameter of the dot printed on the recording sheet 2 can be controlled. Can be changed.

FIG. 6 shows a nozzle of the printer head 3 shown in FIG.
FIG. Referring to FIG.
Head 3 is made of yellow, magenta and cyan inks
(Y) head 3Y, magenta (m)
Head 3M and cyan (c) head 3C
You. The printer head 3 is provided with a magenta photo-in
And magenta, which eject cyan photo ink respectively
Photo (mp) head 3Mp, and cyan photo (c)
p) Head 3Cp and black ink ejection
Black (k) head 3K. In addition,
The photo ink of the present embodiment includes magenta and cyan inks.
An ink with a lower concentration of colorant and lower viscosity than ink
It is. Then, for each of the heads 3Y to 3K,
Nozzles 307Y, 307M, 307C, 307Mp, 3
07Cp, 307K₁, 307K _TwoIs provided.
The black head 3K has twice the size of other color heads.
Nozzles are provided and adjacent nozzles 307K₁And no
Chisel 307K_TwoAre staggered up and down from each other
ing. The double-headed arrow in FIG.
Indicates the main scanning direction.

FIG. 7 is a block diagram showing a schematic configuration of the control unit of the ink jet printer 1. As shown in FIG. The control unit of the inkjet printer 1 includes a CPU 101 and a RAM 102
, A ROM 103, a data receiving unit 104, a head ejection driving unit 105, a head movement driving unit 106, a paper feed driving unit 107, a recovery motor driving unit 108, and various sensor units 109.

The CPU 101 for controlling the whole executes a program stored in the ROM 103 by using the RAM 102 as necessary. This program controls the head ejection drive unit 105, the head movement drive unit 106, the paper feed drive unit 107, and various sensor units 109 based on the image data read from the data reception unit 104, and prints an image on the recording sheet 2. And a recovery system motor drive unit 108 and various sensor units 109 when necessary, and the printer head 3 is controlled using the recovery system 14 (see FIG. 1).
And a portion for restoring the nozzle surface to a good state. The data receiving unit 104 is connected to a host computer or the like, and receives image data to be recorded.

Based on the control of the CPU 101, the head ejection drive unit 105 controls the piezoelectric element 313 of the printer head 3.
, The head movement drive unit 106 drives the drive motor 7 that moves the carriage 4 that holds the printer head 3 in the traverse direction, and the paper feed drive unit 107 drives the paper feed roller. Further, based on the control of the CPU 101, the recovery motor drive unit 108 drives a motor or the like necessary to recover the nozzle surface of the printer head 3 to a good state.

FIG. 8 is a block diagram showing a configuration of the CPU 101 of FIG. 7 and its peripherals. The CPU 101 inputs data r, g, and b corresponding to red, green, and blue, respectively, from a data receiving unit (image source input unit) 104, and performs a gradation correction unit 151 that performs gradation correction. A color conversion unit 152 that converts r, g, and b data to which tone correction has been performed into c, m, and y data (corresponding to cyan, magenta, and yellow inks); And the cp, mp (corresponding to each ink of cyan photo and magenta photo) data and the gray component in the three-color data after conversion are separated (under color removal and also called UCR) and replaced with a black signal. Black generation + UCR section 153 that outputs data k corresponding to black, and dither processing section 1 that performs dither processing on data output from black generation + UCR section 153
54. The data subjected to the dither processing is input to the head ejection drive unit 105. Each color data of cyan, magenta, yellow, and black subjected to the dither processing is data of five gradations. For cyan, the upper two tones are expressed by using cyan ink, and the lower three tones are expressed by cyan photo ink. For magenta, the upper two tones are expressed using magenta ink, and the lower three tones are expressed using magenta photo ink. The head ejection drive unit 105 is provided for each color head 3C.
To 3K.

FIG. 9 is a block diagram showing the configuration of the dither processing unit 154, the head ejection drive unit 105, and the printer head 3 of FIG. Referring to FIG. 9, head discharge driving unit 105 includes c head driving circuit 120c, m head driving circuit 120m, y head driving circuit 120y, and cp
Head drive circuit 120cp, mp head drive circuit 12
0mp and a k-head drive circuit 120k. As described with reference to FIG. 6, the printer head 3 includes a c head 3C, an m head 3M, a y head 3Y, a cp head 3Cp, and an mp head 3Mp connected to these drive circuits 120c to 120k, respectively. And a k-head 3K.

In the ink jet printer 1 according to the present embodiment, each of the head driving circuits 120c and 120c
m, 120y, 120cp, 120mp, 120k, the respective color heads 3C, 3M, 3Y,
By controlling the voltage applied to the 3Cp, 3Mp, and 3K piezoelectric elements 313, the amount of ink ejected from each color head is controlled. Thereby, the dot diameter to be printed can be changed according to the gradation.

FIG. 10 is a diagram showing the composition of yellow ink (Y ink) used in the ink jet printer according to the present embodiment.

FIG. 11 is a diagram showing the composition of the magenta ink (M ink) used in the ink jet printer according to the present embodiment.

FIG. 12 shows a cyan ink (C ink) used in the ink jet printer according to the present embodiment.
FIG. 3 is a diagram showing the composition of

FIG. 13 is a diagram showing the composition of the black ink (K ink) used in the ink jet printer according to the present embodiment.

In the present embodiment, as described above,
In addition to the above YMCK inks, the above M ink, C
Ink photo ink is used. Here, the YMCK color inks are collectively referred to as “normal color inks” with respect to the photo inks.

The photo inks used in this embodiment are light magenta inks shown in FIGS. 14 and 15, respectively.
Each of the light cyan inks contains a penetrant described later. Therefore, for convenience, the light magenta and light cyan inks that do not contain a penetrant are referred to as “Mpo ink” and “Cpo ink”, and light magenta is used as a photo ink in the present embodiment by containing a penetrant. , Light cyan ink are referred to as “Mp ink” and “Cp ink”, respectively.

FIG. 14 shows a light magenta ink (Mp) used in the ink jet printer 1 according to the present embodiment.
FIG. 3 is a diagram showing the composition of the o-ink). Also, FIG.
FIG. 3 is a diagram illustrating a composition of a light cyan ink (Cpo ink) used in the inkjet printer 1 according to the present embodiment.

Here, a penetrant was added to each of the above-mentioned Mpo and Cpo inks to prepare Mp and Cp inks whose permeability to print paper was increased. In addition, as a penetrant, lower alcohols, such as ethanol and isopropyl alcohol, are mentioned, for example, In this Embodiment, ethanol was used as an example.

Further, the ink jet printer according to the present invention may further include a head for discharging the respective photo inks (Yp ink, Kp ink) of the Y ink and the K ink whose compositions are shown in FIGS. 10 and 13, respectively. it can.

Therefore, the light yellow ink (Ypo ink) and the light black ink (K
po ink), the above-mentioned penetrant is added, and Yp ink,
The Kp ink was adjusted.

FIG. 16 is a diagram showing the composition of a light yellow ink (Ypo ink) that can be used in the ink jet printer 1 according to the present embodiment. FIG.
7 is an inkjet printer 1 according to the present embodiment.
FIG. 5 is a view showing a composition of a light black ink (Kpo ink) that can be used in the above.

Here, when a penetrant was added to each ink, the ink was prepared by reducing the weight of water in each ink composition shown in FIGS. 14 to 17 by the weight of the penetrant added. Therefore, in this case, the value of wt% (wt%) for the other compositions does not change.

In each of the above Mpo, Cpo, Ypo, and Kpo inks, the change in permeability to print paper was examined by changing the content of ethanol as a penetrant. The penetrability to the printer paper was determined by measuring the spread of the image of the dots of the ink droplets dropped on the printer paper using the optical measuring device shown in FIG. 18 and determining the dot diameter.

FIG. 18 shows an optical measuring device 500 for optically measuring the spread of ink droplets dropped on print paper.
FIG. In the optical measuring device 500, ink contained in the container 504 is supplied to the syringe 503, and an appropriate amount of ink is supplied from the syringe 503 to the paper table 5.
The droplets are dropped toward the print paper 502 placed on the print paper 01. Lamp 505 and C
A CD video camera 506 is provided. Then, an image of the ink dots dropped on the print paper 502 was captured by the CCD video camera 506, and the image was analyzed to measure the change over time in the dot diameter.

First, in FIG. 19, 1 μl of Kp ink (K
This shows how the dot diameter changes over time in an ink obtained by adding 1.2 wt% of ethanol as a penetrant to a po ink. In FIG. 19, the horizontal axis is the time after the ink is dropped, and the vertical axis is the diameter of the dot of the dropped ink.

Referring to FIG. 19, about 20
During the second (sec), the diameter of the dot increases with the passage of time, but after about 20 seconds from the dropping of the ink,
The diameter of the dot remains at 7 mm and hardly changes. It should be noted that the change with time of the diameter of the dot measured with the ethanol content of 1.2 wt% was the same for the other photo inks (Mp, Cp, Yp).

It should be noted that M added with ethanol (penetrant)
Each ink of po, Cpo, Ypo, and Kpo is the original Mp
The viscosity was lower than that of each of the inks o, Cpo, Ypo, and Kpo. Therefore, in order to investigate the change in the permeability to the print paper with respect to the change in the viscosity due to the change in the content of ethanol in each of the inks Mp, Cp, Yp, and Kp, the diameter of the dot dropped on the printer paper is examined. Was measured.

FIG. 20 shows the change in dot diameter with respect to the viscosity of the ink for 1 μl of Kp ink (ink obtained by adding a penetrant to Kpo ink). In FIG. 20, the unit of viscosity on the horizontal axis is centipoise (cp). The dot diameter in FIG. 20 is the diameter of the dot 30 seconds after ink dropping. Here, the reason why the measurement time is set to “after 30 seconds” is that, as described with reference to FIG. 19, the diameter of the dot of the dropped ink is considered to be substantially constant without increasing any further. Note that the viscosity of the Kpo ink containing no penetrant is 2 cp, and the data having a lower viscosity is the ink obtained by adding the penetrant ethanol to the Kpo ink as described above.

FIG. 20 further shows, as a comparison,
17 also shows data of ink in which the viscosity of Kpo PEG # 400 was increased from the composition shown in FIG. 17 and the viscosity was increased by reducing the water of the same wt%. That is, in FIG. 20, Kpo ink (corresponding to data of viscosity 2 cp) and
Kpo ink with ethanol added (viscosity 2 cp)
PEG # 4 of Kpo Ink)
The dot diameter of the ink is shown for the case where the wt% of 00 is increased (corresponding to each data whose viscosity exceeds 2 cp). Then, wt% of ethanol is shown in parentheses below each data, and PEG # 400 after the increase is shown.
Are shown in [] of each data. The wt% of PEG # 400 before the increase was 4.5% (FIG. 1).
7).

Referring to FIG. 20, without adding ethanol, the wage of PEG # 400 was determined from the composition shown in FIG.
For Kpo ink without changing t% (corresponding to data having a viscosity of 2 cp), the diameter of the ink dot is
5 mm. Looking at a region having a viscosity of 2 cp or less, as the wt% of ethanol increases and the viscosity of the ink decreases, the diameter of the dot of the ink increases. Looking at the region having a viscosity of 2 cp or more, the dot diameter of the ink decreases as the viscosity of the ink increases by increasing the wt% of PEG # 400. That is, as the viscosity decreases, the ink is more likely to penetrate the print paper.

Similarly, for Mp, Cp, and Yp, the dot diameter with respect to the viscosity of the ink was measured by changing the wt% of ethanol and PEG # 400. As a result, the result that the ink was more likely to penetrate into the printing paper as a result was obtained.

On the other hand, the normal color ink YM
Similarly, when the dot diameter of each ink of CK was measured 30 seconds after the ink was dropped, it was about 4 mm. Therefore, Mp, C to which the penetrant is added
It can be said that each of the inks p, Yp, and Kp has higher permeability to print paper than the normal color ink.

The ink jet printer 1 of the present embodiment
Is a normal color ink (Y,
M, C, K inks) and photo inks (Mp, Cp inks) are used. Further, Yp ink and Kp ink can be further used as the photo ink. In image formation using such inks, it is preferable to print the ink in a dot pattern as shown below. A preferred ink dot pattern in the present embodiment will be described with reference to FIGS.

FIG. 21 is a view for explaining the types of dots for explaining the dot patterns of the present embodiment shown in FIGS. 22 to 26. Referring to FIG. 21, dots made of any of the normal color inks Y, M, C, and K are indicated as “normal color ink dots” by symbols with oblique lines in a circle. Also, dots made of any of the photo inks Yp, Mp, Cp, and Kp are indicated by circle symbols as “dots of photo ink”.

FIG. 22 is a diagram showing a first dot pattern. In this pattern, first, dots of normal color ink are printed, and then dots of photo ink are printed between adjacent dots of normal color ink. For example, when expressing black, dots of K ink, which is a normal color ink, are printed first, and dots of Kp ink are printed between adjacent dots of K ink.

FIG. 23 is a diagram showing a second dot pattern. In this pattern, first, dots of photo ink are printed, and then dots of normal color ink are printed between adjacent dots of photo ink.

FIG. 24 is a diagram showing a third dot pattern. In this pattern, normal color ink dots and photo ink dots are alternately printed in order from the left end of the print paper.

FIG. 25 is a diagram showing a fourth dot pattern. In this pattern, first, dots of normal color ink are printed. Then, between adjacent dots of normal color ink, photo ink dots having a larger dot diameter than the previously printed normal color ink dots are printed. In the printer head 3 of the ink jet printer 1 according to the present embodiment, as described above, the dot diameter of the ink to be printed is changed by changing the voltage applied to the piezoelectric element 313 by the head ejection drive unit 105. be able to.
That is, the head ejection drive unit 105 constitutes a dot diameter control unit that controls the printer head to change the diameter of the dots printed.

FIG. 26 is a diagram showing a fifth dot pattern. In this pattern, first, dots of normal color ink are printed. Then, between adjacent normal color inks, photo ink dots having a smaller dot diameter than the previously printed normal ink color dots are printed.

When an image is formed in accordance with the patterns described with reference to FIGS. 21 to 26, the dots of the normal color ink are superimposed on the dots of the photo ink. Since the photo ink used here has a penetrating agent added, it has a lower viscosity than the normal color ink and has a higher permeability to the printing paper. Therefore, when an image is formed such that the dots of the normal color ink and the dots of the photo ink partially overlap, the end portions of the dots of the normal color ink exude to the dots of the photo ink, so that the image is formed as in the related art. In the image, the outline of the dot of each ink is not emphasized in the overlapping portion of the dot. Thereby, the formed image becomes smoother.

The dot diameter control unit constituted by the head ejection driving unit 105 can change the dot diameter printed by the head, so that the bleeding of the dots of the normal color ink by the photo ink can be performed to a desired degree. Can be adjusted.

Here, in order to verify the smoothness obtained by using the photo-ink to which the penetrant was added together with the normal color ink, “ΔD” indicating the smoothness of the image with respect to the ink dot diameter was used. Was measured. "Δ
"D" means the optical density (color density) of the paper surface on which the ink is printed, measured using a reflection type optical densitometer (DENSITO ME
TER), the maximum value (ODmax _. ) And the minimum value ( _Omax ) of the optical density indicated by the output waveform of the densitometer when measured continuously _.
D _min. ). That is, when the measurement is performed by the optical densitometer, an output signal having a waveform as shown in FIG. 27 is obtained. Then, from the waveform, the OD _max. And O of the optical density (vertical direction in FIG. 27) of the paper surface on which the ink is printed are obtained _.
D _min. Is obtained. Then, according to the following equation, “Δ
D "was obtained.

[0067] _{ΔD = |. OD max -OD min} |. "ΔD" is from that obtained in the manner described above, "Δ
It can be said that the smaller the value of "D", the smoother the image. In the present embodiment, “Sakura DENSITO METE” is used as a reflection type optical densitometer.
R PDA5 "(manufactured by Sakura (now Konica)) was used for the measurement.

FIG. 28 shows K as a normal color ink.
Is obtained by printing using the fifth dot pattern shown in FIG. 26 using Kp as the photo ink.
The measurement result of measuring ΔD with respect to the diameter of the ink dot is shown. As described above, the diameter of the dot of the Kp ink is changed by changing the value of wt% of ethanol or PEG # 400. Also, FIG.
The print pattern described above is one in which unevenness in print density is most likely to appear among the five dot patterns exemplified in the present embodiment.

Referring to FIG. 28, as the dot diameter of the Kp ink used increases, the value of ΔD decreases. In other words, it can be seen that the image becomes smoother as the content of the penetrant in the Kp ink, which is a photo ink, increases and the viscosity of the ink decreases. Therefore, when Kp ink is used as the photo ink, it is understood that the smoothness of the image is affected by the change in the viscosity of the photo ink.

When an image is actually formed, the image quality can be evaluated by the value of ΔD as in the following ○, Δ, ×.

ΔD ≦ 0.1: Evaluation “○” (smooth high gradation) 0.1 <ΔD ≦ 0.15: Evaluation “Δ” (smoothness that does not cause any practical problem) 0.15 <ΔD: Evaluation “× (Practically, there is a problem of noise and the like.) Further, with respect to other photo inks, printing was performed using the fifth dot pattern together with the corresponding normal ink, and ΔD was measured. Here, the content of the penetrant (ethanol) was 2 wt% as the photo ink,
The adjustment was made in three ways of 4 wt% and 7 wt%, and Examples 1 to 3, respectively. Within this range, the viscosity of the ink decreased as the amount of the penetrant increased in any of the inks. Further, in order to further clarify the effect of the addition of the penetrant, as Comparative Example 1, a normal ink and a light-colored ink corresponding to each were used (Mpo having the composition shown in FIGS. 14 to 17). , Cpo, Yp
o, Kpo inks, which do not contain penetrants)
Printing was performed using the fifth dot pattern, ΔD was measured, and the above-described evaluations of ○, Δ, and × were performed. Table 1 shows the results.

[0072]

[Table 1]

Referring to Table 1, when any of the Mp, Cp, and Kp inks used the ink to which the penetrant was added, ΔD was larger than that of Comparative Example 1 in which the penetrant was not added. Was low, and the image quality was smooth.
In general, when any one of the Mp, Cp, and Kp inks is used, the image tends to be smoother as the wt% of the penetrant increases.
Therefore, with these inks, it can be said that the lower the viscosity of the photo ink, the smoother the formed image. In addition, as for Yp, it is basically difficult to measure the optical density of Y and Yp, so that it was impossible to measure the smoothness of the image.

The embodiment disclosed this time is to be considered in all respects as illustrative and not restrictive. The scope of the present invention is shown by above-mentioned not description but claim, and it is intended that the meaning of a claim and equality and all the changes within the range are included.

[Modifications] The above embodiment can be modified as follows.

(1) As the penetrant, a substance other than lower alcohols that lowers the viscosity of the ink is used. That is,
Penetrants are not limited to lower alcohols,
Any substance that lowers the viscosity of the ink may be used.

(2) A nozzle for discharging white ink other than the RGB color is added. Thereby, the color reproducibility of the lightest density of the highlight can be improved, and the sharpness of the image increases.

(3) A nozzle for discharging a brown ink other than the RGB color is added. As a result, the reproducibility of colors such as human skin color is improved, and the depth of the image is increased.

(4) A nozzle for discharging a gray color ink in addition to the RGB color is added. This improves the reproducibility of the monochrome halftone gradation.

[Brief description of the drawings]

FIG. 1 is a perspective view illustrating a schematic configuration of an inkjet printer according to an embodiment of the present invention.

FIG. 2 is a perspective view illustrating a configuration around a carriage in FIG. 1;

FIG. 3 is a plan view showing a part of a surface having nozzles of the printer head of FIG. 1;

FIG. 4 is a sectional view taken along line IV-IV in FIG. 3;

FIG. 5 is a sectional view taken along line VV in FIG. 4;

FIG. 6 is a plan view of the printer head of FIG. 1;

FIG. 7 is a block diagram illustrating a schematic configuration of a control unit of the inkjet printer of FIG. 1;

FIG. 8 is a block diagram showing a configuration of the CPU of FIG. 7 and peripheral components thereof;

FIG. 9 is a block diagram illustrating a configuration of a dither processing unit, a printer head ejection drive unit, and each color head of FIG. 8;

FIG. 10 is a diagram illustrating a composition of a Y ink according to the embodiment of the present invention.

FIG. 11 is a diagram showing a composition of M ink in the embodiment of the present invention.

FIG. 12 is a diagram illustrating a composition of C ink according to an embodiment of the present invention.

FIG. 13 is a diagram showing a composition of K ink in the embodiment of the present invention.

FIG. 14 is a diagram showing the composition of the Mpo ink according to the embodiment of the present invention.

FIG. 15 is a diagram illustrating a composition of a Cpo ink according to an embodiment of the present invention.

FIG. 16 is a diagram illustrating a composition of a Ypo ink according to an embodiment of the present invention.

FIG. 17 is a diagram showing a composition of a Kpo ink according to an embodiment of the present invention.

FIG. 18 is a diagram showing an optical measurement device used in the embodiment of the present invention.

FIG. 19 is a diagram showing a change over time in the diameter of a dot of Kp ink in the embodiment of the present invention.

FIG. 20 is a diagram showing a dot diameter with respect to a content of a penetrant added to a Kpo ink in an embodiment of the present invention.

FIG. 21 is a diagram for explaining types of dots for explaining the dot patterns of the embodiment of the present invention shown in FIGS. 22 to 26;

FIG. 22 is a diagram showing a first dot pattern according to the embodiment of the present invention.

FIG. 23 is a diagram showing a second dot pattern according to the embodiment of the present invention.

FIG. 24 is a diagram showing a third dot pattern in the embodiment of the present invention.

FIG. 25 is a diagram showing a fourth dot pattern according to the embodiment of the present invention.

FIG. 26 is a diagram showing a fifth dot pattern in the embodiment of the present invention.

FIG. 27 is a diagram showing an example of an output waveform of the reflection type optical densitometer in the present embodiment.

FIG. 28 is a diagram illustrating the smoothness of an image with respect to the dot radius of photo ink in the embodiment of the present invention.

FIG. 29 is a diagram illustrating an example of a dot pattern in image formation in a conventional image forming apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ink-jet printer 2 Recording sheet 3 Printer head 3Y Y head 3M M head 3CC head 3KK head 3Mp Mp head 3Cp Cp head 4 Carriage

Claims (2)

[Claims] An ink dot of a first group corresponding to a plurality of colors and a dot of an ink of a second group having a lower color material density than the ink of the first group are printed on printing paper. Wherein the second group of inks has a lower viscosity than the first group of inks, and wherein the printer head comprises a first group of ink dots and a second group of inks. An image forming apparatus for printing by superimposing ink dots of a group. 2. The image forming apparatus according to claim 1, further comprising a dot diameter control unit that controls the printer head to change a diameter of a dot to be printed.