JPH09272198A - Ink-jet print apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease generation of stripe fluctuation in an image by making the diameter of the formed ink dot invariant regardless of inks used when a plurality of inks with different concn. are used for performing gradation print. SOLUTION: The amt. of jetting of each ink is made different by changing respectively the width of a driving pulse applied on an electricity-heat convertor for each head for jetting each ink with a different concn. and thereby, a dot with a fixed diameter of √2x+α to a picture element with an area of x×x is formed by the jetted ink at any time when the ink is jetted from any head. As the result, the formed dot always covers the hole picture element to prevent a gap between the dots from being generated in an image and to accordingly suppress generation of stripe fluctuation caused by this gap.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inkjet printing apparatus, and more particularly to an inkjet printing apparatus for performing gradation printing.

[0002]

2. Description of the Related Art Generally, a method of printing a gradation image with ink dots in a printing apparatus such as an ink jet printer is to drive an ink jet head and change a voltage or a pulse width applied to eject ink. , A so-called analog modulation method of changing the diameter of ink dots formed on recording paper, a digital modulation method of performing gradation printing by changing the number of dots to be printed in a predetermined matrix without changing the diameter of ink dots, and Is known as a digital / analog modulation method in which the number of dots in a matrix and the diameter thereof are changed by combining an analog modulation method and a digital modulation method.

However, in the analog modulation method in which the diameter of an ink dot is changed in each pixel, the effect of ink ejection on the immediately preceding pixel is affected by, for example, the heat storage effect of the head associated with ink ejection, and fine dot diameter control is possible. Often relatively difficult. Further, in the inkjet method, the range of dot diameters that can be controlled is also limited, and it is difficult to output a relatively multi-valued image with 256 gradations, for example, only by this method.

On the other hand, in the digital modulation method using a matrix, for example, in order to express 256 gradations, a 16 × 16 matrix is required, and as a result, the area occupied by one pixel becomes large, and the actual printed image is substantially reduced. There is a problem that the dynamic resolution is lowered and it is difficult to output a high resolution image.

Therefore, in order to obtain a stable high gradation image,
It is general to use the analog modulation method as described above and output a gradation image by performing binarization processing such as an error diffusion method in order to avoid a substantial reduction in resolution.

However, even in this method, there is a problem that when the density difference between the ink dot and the background (recording paper surface) is large, the ink dot is conspicuous especially in the highlight portion and the image becomes rough. It was

On the other hand, in order to improve the gradation characteristics, especially in the highlight portion, a method of outputting an image using a plurality of inks of different densities for the same color has been proposed.

[0008]

However, in the method of outputting a gradation image by using a plurality of inks having different densities for the same color, when the inks of different densities are ejected under the same conditions, The dot diameter of the ink on the recording paper is often different due to the difference in the physical property values. Specifically, when an ink having a low density, for example, an ink obtained by diluting an ink having a high density is used, the dot diameter thereof tends to be smaller than when an ink having a high density is used. As a result, even if full-scale printing (so-called solid printing) or similar printing is performed with low density ink, the dot diameter is small,
The recording paper surface may not be completely covered with ink dots.

In general, an ink jet head of a so-called multi-nozzle type having a plurality of ejection openings for one type of ink is used for the purpose of improving the printing speed. In many cases, there is some variation in the formation of individual discharge ports and their relative positions, although they are manufactured. In such a head, ejection failure such as deflection of the ejection direction or reduction of ejection amount may occur, and the ink landing position may slightly deviate from the original position.

In such a case, when the above-described low-density ink is used, the gaps between the ink dots, that is, the portions where the recording paper surface is exposed become particularly noticeable, and such portions cause a print image to be printed. In, a streak-like pattern (hereinafter, also referred to as streak unevenness) will be observed.

The present invention has been made in order to solve the above problems, and an object of the present invention is to provide one of the plurality of inks in the case of gradation printing using a plurality of inks having different densities. An object of the present invention is to provide an inkjet printing apparatus capable of reducing the occurrence of streak unevenness by making the diameter of ink dots formed on a print medium constant regardless of the ink used.

[0012]

According to the present invention, there is provided:
In an inkjet printing apparatus that prints by using a plurality of inkjet heads that respectively discharge inks having different densities and discharges the inks from the plurality of inkjet heads onto a print medium, It is characterized by comprising dot diameter setting means for substantially equalizing the diameters of the dots formed on the print medium.

More preferably, the dot diameter setting means makes the diameters of the dots formed by making the ink ejection amounts of the plurality of ink jet heads different from each other substantially.

Further, the dot diameter setting means substantially changes the diameter of each dot by changing the weight ratio of the organic solvent contained in the ink in the composition of the ink ejected by each of the plurality of ink jet heads. It is characterized by making them equal.

According to the above construction, for example, the ejection amount or the ink component can be made different for each head which ejects the inks having different densities, so that the dots formed on the print medium by the respective ejected inks. It is possible to make the diameters of the dots substantially equal to each other, whereby it is possible to prevent the reduction of the dot diameter caused by the difference in the density of the ejected ink in advance, and it is possible to suppress the generation of gaps between the dots.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION In one embodiment of the present invention, the diameter of an ink dot formed on a print medium such as recording paper is determined as follows.

FIG. 1 is a diagram schematically showing dots formed in this embodiment. As shown in the figure, when dots are formed in a square portion of xx which is assumed to be one pixel, the diameter is set to √2x + α, and in the present embodiment, it is always possible to use any of a plurality of inks having different densities. This diameter is realized. Here, of the diameter √2x + α, α is provided so that even if the landing position is slightly deviated, the deviation is absorbed and the diameter is not changed, and the value of α is about 10% of x. Is.

That is, as described above, when a plurality of inks having different densities are used, the diameter itself varies relatively beyond the range that can be absorbed by α, but in the present embodiment, the densities of the inks to be used are changed. By changing the dot diameter according to the variation caused by the above, the diameter is set to the value of √2x + α as described above. The diameter thus realized does not create a gap in dot formation in solid printing as described above.

The methods for changing the dot diameter of the ink are roughly classified into the following two methods.

The first is a method of changing the ink ejection amount, and the second is a method of changing the physical properties of the ink. Generally, the diameter of an ink dot formed is determined by the ejection amount and the properties of the ink and the print medium. For example,
The larger the ejection amount, the larger the dot diameter. Further, even if the ejection amount is the same, the dot diameter formed becomes larger when the wettability of the ink with respect to the print medium is higher. That is, the dot diameter of the ink can be controlled by the above two methods.

Generally, as the ink used in ink jet printing, a water-based ink is often used in consideration of ejection performance and the like. The composition of this water-based ink comprises an ink dye, a surfactant, water, and an organic solvent as an additive. As an additive, usually moisturizing, antiseptic,
Glycerin, glycol, for antioxidant and pH adjustment
Urea, IPA and the like are used, but not limited to these and can be appropriately selected. Therefore, the wettability of the ink is determined by the above ink composition.

On the other hand, as a concrete method of changing the ink ejection amount, which is the first method, a method of changing a voltage or a pulse width applied for ejecting ink, or a method of ejecting a plurality of inks respectively This can be realized by a method in which the structure is changed for each ink and the ejection amount unique to the head is changed. In the present embodiment, either method may be used, but from the viewpoint of ejection stability, it is preferable to use a head designed specifically for the ejection amount determined according to the dot diameter to be realized. That is.

More specifically, when n (n is 2 or more) different density inks are used for the same color, the ink amount when ejecting the highest density ink is V ₁ .
Assuming that the ink ejection amount is V ₂ , ..., V _n as the ink density decreases, the dot diameters of those dot diameters are established by establishing the relationship of V ₁ ≤V ₂ ≤ ... ≤V _n. Is a constant value √2x + α.

On the other hand, when the dot diameter is changed depending on the physical property value of the ink, changing the content ratio of the surfactant to the ink dye changes the wettability of the ink, resulting in controlling the dot diameter of the ink. Is effective.

Specifically, when the ejection amount is the same, the surfactant content ratios are set to W ₁ and W in the order of increasing ink density.
_The dot diameter can be made constant by setting the relationship W ₁ ≤W ₂ ≤ ... ≤W _n by setting ₂ , ..., W _n .

According to the present embodiment described above, it is possible to suppress the occurrence of streak unevenness caused by the periodic exposure of the recording paper surface.

[0027]

An embodiment of the present invention will be described below in detail with reference to the drawings.

(Embodiment 1) FIG. 2 is a diagram showing a schematic structure of an ink jet printer embodying the present invention. In the present embodiment, cyan ink heads 21a, 21b, which eject inks of three different densities, respectively, for four color inks of cyan (C), magenta (M), yellow (Y), and black (K), respectively. 21c, heads 22a, 22b, 22c for magenta ink, heads 23a, 23b, 23c for yellow ink and heads 24a, 24b, 24c for black ink are used. These heads have three units 1a and 1b for each density.
And mounted in the form of 1c. Each inkjet head has 64 ejection ports, and is provided with an electrothermal converter for generating thermal energy used for ejecting ink, corresponding to each ejection port. FIG.
Shows a view of each head as viewed from the surface side on which the ejection ports are arranged.

The carriage 2 on which the head units 1a, 1b and 1c are integrally mounted is slidably engaged with the guide shafts 7a and 7b, so that the driving force of the carriage motor 6 causes the carriage 2 to move along the guide shafts 7a and 7b. You can move. A transport path of the recording paper 3 as a print medium is provided in a part of the moving range of the carriage. That is, a pair of paper feed rollers 4 (only one of which is shown) is provided at each of two positions in a direction orthogonal to the movement direction of the carriage 2, and each roller pair is driven by the paper feed motor 5. The recording paper 3 is conveyed in a direction orthogonal to the moving direction of the carriage 2.

Ink ejection in each ink jet head and driving of the carriage motor 6 and the paper feed motor 5 are performed by the head driving unit 11 and the head moving driving unit 1, respectively.
It is controlled by the control unit / image processing unit 10 via the control unit 2 and the recording paper moving drive unit 13.

Of the four types of ink used in this embodiment,
Taking cyan (C) as an example, the composition ratio of each ink of three levels and the reflection density when each ink is printed on inkjet printing coated paper (LC-201 manufactured by Canon Inc.) (Dainippon Screen Stock Co., Ltd.) (Measurement by DM-800 manufactured by company) is shown in Table 1 below.

[0032]

[Table 1]

The cyan heads 21a, 21b and 21c for ejecting these inks are driven as follows. The image data of 256 gradations of cyan (C) is
The reflection density of 1.5, 0.
In consideration of 75 and 0.3, the data is converted into binary data by the control unit / image processing unit 10 by the multi-valued error diffusion method, and the head drive unit 11 uses each of the heads 21a based on this data.
Drive ~ 21c. At this time, the pulse width of the head drive pulse is 3.0 μm in the ink C ₁ head 21a.
sec, 3.8 μ in the ink C ₂ head 21b
sec, 5.0 μ in the ink C ₃ head 21C
sec. As a result, the amount of ink ejected from each head is V ₁ = 40 pl, V ₂ = 42 p
1, V ₃ = 44 pl.

The following Table 2 shows the voltage of the drive pulse as 2
The results of measuring the diameters of the ink dots when the pulse width is set to 3.0 μsec and when the pulse width is set as described above for each ink head at 0 V are shown.

[0035]

[Table 2]

By varying the drive pulse width of the head for each of the inks having different densities in this way, the diameters of the dots formed by the ink ejected from the respective heads are set to a range of about 90 μm, which is a substantially equal value. be able to.

By performing the same process for magenta (M), yellow (Y), and black (K) in the same manner, it is possible to reduce streak unevenness in a full-color print image.

(Embodiment 2) As in Embodiment 1 above, C,
A gradation image is output by using inks of three different densities for each of M, Y, and K colors.

In the first embodiment, the ejection amount is changed by modulating the width of the drive pulse to make the dot diameter constant, whereas in the present embodiment, the ejection amount is changed by changing the structure of the head. To make the dot diameter constant. That is, in the head used in this example, the distance between the heater as the electrothermal converter and the ejection port at the tip of the ink path is different.

Drive voltage 20 for each head
V, drive frequency 6 kHz, drive pulse width 3.0 μsec
Table 3 below shows the ink discharge amount under the condition of.

[0041]

[Table 3]

That is, the maximum density of each ink C ₁ , M
Heads a shown in Table 3 as heads for ₁ , Y ₁ and K ₁ .
, The head b as a head for each of the inks C ₂ , M ₂ , Y ₂ and K ₂ having an intermediate density, and each ink C having a minimum density.
_The head c is used as a head for ₃ , M ₃ , Y ₃ , and K ₃ , respectively. Then, the distance from the heater to the ejection port is set in the order of the head c, the head b, and the head a. The dot diameter of each cyan head at this time is also shown in Table 3.

As described above, by varying the head discharge structure to change the ink ejection amount, it is possible to change the ink density according to each ink concentration and to always obtain a desired dot diameter for each ink. As a result, streak unevenness is not noticeable. A toned image can be obtained.

(Embodiment 3) Embodiment 1 is also applied to this embodiment.
A gradation image is printed in the same manner as in Example 1. Here, the same head and drive voltage are used, but the ink used has the composition shown in Table 4 below. In Table 4, cyan (C) is shown for simplicity.

[0045]

[Table 4]

As shown in Table 4, the content ratio W of the surfactant to the dye is W ₁ = 1/4, W ₂ = 5/4, W ₃ =
5, which satisfies the relationship of W ₁ <W ₂ <W ₃ .

Using these inks, a driving frequency of 6 kHz
By ejecting under the conditions of z, drive voltage 20 V, and drive pulse width 3.0 μsec, the respective dot diameters can be made approximately the same size.

In this way, by outputting for each color of C, M, Y, K, it is possible to obtain an image in which streak unevenness is reduced.

(Others) The present invention is particularly provided with a means (for example, an electrothermal converter or a laser beam) for generating thermal energy as energy used for ejecting ink even in the ink jet recording system. In the recording head and the recording apparatus of the type in which the state of the ink is changed by the heat energy, an excellent effect is brought about. This is because according to such a method, it is possible to achieve higher density and higher definition of recording.

The typical configuration and principle are described in, for example, US Pat. Nos. 4,723,129 and 4,740.
It is preferable to use the basic principle disclosed in the specification of Japanese Patent No. 796. This method is a so-called on-demand type,
Although it can be applied to any type of continuous type, in particular, in the case of the on-demand type, it can be applied to a sheet holding liquid (ink) or an electrothermal converter arranged corresponding to the liquid path. By applying at least one drive signal corresponding to the recorded information and giving a rapid temperature rise exceeding the nucleate boiling, heat energy is generated in the electrothermal transducer, and film boiling occurs on the heat acting surface of the recording head. Liquid (ink) corresponding to this drive signal on a one-to-one basis.
This is effective because air bubbles inside can be formed. The liquid (ink) is ejected through the ejection opening by the growth and contraction of the bubble to form at least one droplet. When the drive signal is formed into a pulse shape, the growth and shrinkage of the bubble are performed immediately and appropriately, so that the ejection of a liquid (ink) having particularly excellent responsiveness can be achieved, which is more preferable. As the pulse-shaped drive signal, those described in US Pat. Nos. 4,463,359 and 4,345,262 are suitable. If the conditions described in US Pat. No. 4,313,124 of the invention relating to the rate of temperature rise on the heat acting surface are adopted, more excellent recording can be performed.

As the constitution of the recording head, in addition to the combination constitution of the discharge port, the liquid passage, and the electrothermal converter (the straight liquid passage or the right-angled liquid passage) as disclosed in the above-mentioned specifications, US Pat. No. 4,558,333, US Pat. No. 4,558,333, which discloses a configuration in which a heat acting portion is arranged in a bending region.
A configuration using the specification of Japanese Patent No. 59600 is also included in the present invention. In addition, Japanese Unexamined Patent Publication No. 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 opening for absorbing a pressure wave of thermal energy is provided. The effect of the present invention is effective even if the configuration corresponding to the ejection portion is disclosed in JP-A-59-138461. That is, according to the present invention, recording can be surely and efficiently performed regardless of the form of the recording head.

Further, the present invention can be effectively applied to a full line type recording head having a length corresponding to the maximum width of a recording medium which can be recorded by the recording apparatus. Such a recording head may have a configuration that satisfies the length by a combination of a plurality of recording heads or a configuration as one recording head integrally formed.

In addition, even in the case of the serial type as described above, the recording head fixed to the apparatus main body or the electric connection with the apparatus main body or the ink from the apparatus main body is attached to the apparatus main body by being attached to the apparatus main body. The present invention is also effective when a replaceable chip-type recording head that can be supplied or a cartridge-type recording head in which an ink tank is provided integrally with the recording head itself is used.

It is preferable to add a recording head ejection recovery unit, a preliminary auxiliary unit, and the like as the configuration of the recording apparatus of the present invention since the effects of the present invention can be further stabilized. If these are specifically mentioned, the recording head is heated using capping means, cleaning means, pressurizing or suction means, an electrothermal transducer, another heating element or a combination thereof. Pre-heating means for performing the pre-heating and pre-discharging means for performing the discharging other than the recording can be used.

Regarding the type and number of recording heads to be mounted, for example, only one is provided corresponding to a single color ink, or a plurality of inks having different recording colors and densities are supported. A plurality of pieces may be provided. That is, for example, the recording mode of the recording apparatus is not limited to the recording mode of only the mainstream color such as black, but it may be either the recording head is integrally formed or a plurality of combinations may be used. The present invention is also extremely effective for an apparatus provided with at least one of full-color recording modes by color mixing.

In addition, 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 lower and which softens or liquefies at room temperature may be used. In general, the ink jet system generally controls the temperature of the ink itself within a range of 30 ° C. or more and 70 ° C. or less to control the temperature so that the viscosity of the ink is in a stable ejection range. Sometimes, the ink may be in a liquid state. In addition, the temperature rise due to thermal energy is positively prevented by using it as the energy of the state change from the solid state of the ink to the liquid state, or in order to prevent the evaporation of the ink, it is solidified and heated in the standing state. You may use the ink liquefied by. In any case, by applying heat energy such as ink that is liquefied by applying heat energy according to the recording signal and liquid ink is ejected or that begins to solidify when it reaches the recording medium. The present invention can be applied to the case where an ink having a property of being liquefied for the first time is used. In this case, the ink is
JP-A-54-56847 or JP-A-60-7
As described in Japanese Patent Publication No. 1260, it is also possible to adopt a form in which the sheet is opposed to the electrothermal converter in a state where it is held as a liquid or solid substance in the concave portion or through hole of the porous sheet. In the present invention, the most effective one for each of the above-mentioned inks is to execute the above-mentioned film boiling method.

In addition, the form of the ink jet recording apparatus of the present invention is not only used as an image output terminal of an information processing apparatus such as a computer, but also for a copying apparatus combined with a reader or the like, and a facsimile apparatus having a transmission / reception function. It may take a form.

[0058]

As described above, according to the present invention,
For example, the ejection amount or the ink component can be different for each head that ejects inks having different densities, so that the diameters of the dots formed on the print medium by the ejected inks can be made substantially equal. As a result, it is possible to prevent in advance the reduction of the dot diameter caused by the difference in the density of the ejected ink, and it is possible to suppress the occurrence of gaps between the dots.

As a result, it is possible to reduce streak unevenness in a printed image, and it is possible to obtain an image with high image quality at all gradations.

[Brief description of drawings]

FIG. 1 is a diagram illustrating dot formation according to an embodiment of the present invention.

FIG. 2 is a diagram showing a schematic configuration of an inkjet printer embodying the present invention.

[Explanation of symbols]

 1a, 1b, 1c Head unit 2 Carriage 3 Recording paper 4 Paper feed roller 5 Paper feed motor 6 Carriage motor 7a, 7b Guide shaft 10 Control unit / Image processing unit 11 Head drive unit 12 Head movement drive unit 13 Recording paper movement unit Drive part

Claims (10)

[Claims] 1. An inkjet printing apparatus that uses a plurality of inkjet heads for respectively ejecting inks having different densities, and ejects the inks from the plurality of inkjet heads onto a print medium to perform printing. An ink jet printing apparatus, comprising: dot diameter setting means for substantially equalizing the diameters of the dots formed on the print medium by the ejected ink. 2. The ink jet printing apparatus according to claim 1, wherein the dot diameter setting means sets the diameters set to be equal to cover the pixels on which the dots are formed. 3. The dot diameter setting means sets the diameters of dots formed by making the ink ejection amounts of the plurality of ink jet heads different from each other to be substantially equal to each other. The inkjet printing apparatus described in 1. 4. The inkjet printing apparatus according to claim 3, wherein the dot diameter setting unit sequentially increases the ink ejection amount as the density of the ink ejected from each of the plurality of inkjet heads decreases. 5. The dot diameter setting means changes the pulse width of a drive pulse applied to an electrothermal converter that generates thermal energy used for ink ejection of each of the plurality of ink jet heads to vary ejection amounts. The inkjet printing apparatus according to claim 3, wherein the inkjet printing apparatus is provided. 6. The ink jet printing apparatus according to claim 3, wherein the dot diameter setting unit changes the ink ejection amount by changing the structure of each of the plurality of ink jet heads. 7. The dot diameter setting means ejects each ink by changing the distance between an electrothermal converter that generates thermal energy used for ink ejection of each of the plurality of inkjet heads and an ink ejection port. The inkjet printing apparatus according to claim 6, wherein the amount is different. 8. The dot diameter setting means substantially changes the diameter of each dot by changing the weight ratio of the organic solvent contained in the ink in the composition of the ink ejected by each of the plurality of inkjet heads. The ink jet printing apparatus according to claim 1 or 2, wherein 9. The dot diameter setting means increases the content ratio of the surfactant to the ink dye in the organic solvent, as the ink discharged from the plurality of inkjet heads has a lower concentration. Claim 8
5. The inkjet printing apparatus according to claim 1. 10. The inkjet printing apparatus according to claim 8, wherein each of the plurality of inkjet heads has a thermal energy generator that generates thermal energy used to eject ink.