JPH04140148A - Ink jet recording method - Google Patents

Abstract

PURPOSE:To enable the recording of an image having high gradation and high sharpness by a method wherein, after the vibration of an ink droplet deposited precedently is substantially stopped on a recording material, a subsequent ink droplet is emitted onto the preceding ink droplet. CONSTITUTION:When a first ink droplet 1 is in an expansion stage A: if a subsequent ink droplet 2 strikes the first ink droplet, a dot size is expanded large and the thickness of an ink layer 3 becomes thinner. However, when the first ink droplet 1 is in a contraction stage B: if the subsequent ink droplet 2 strikes it, the dot size expands only a little and the thickness of the ink layer 3 becomes thicker. Since the thickness of an ink layer relates to the optical density (OD) of a dot and a dot size relates to the resolution, granularity and density of an image, the gradient of the image varies according to the striking timing of ink droplets even when the number of ink droplets per pixel is the same. Accordingly, if a plurality of ink droplets are emitted by taking advantage of the substantial vibration-stopping stage C, it becomes possible to obtain a stable dot size and dot density according to the number of ink droplets, whereby an image having high gradation and high resolution can be obtained.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an inkjet recording method.

[Prior Art] Various methods are known in order to achieve good gradation expression in inkjet printing. method (area gradient method), a collection of several dots is
Methods of creating gradations by changing the number of printed dots as pixels (density pattern method, dither method, etc.), methods of printing using inks of different densities (light and light ink method), and recording of multiple ink droplets per pixel. 1 by landing at almost the same position on the material.
There is a method of forming pixels and creating gradations by changing the dot area and density depending on the number of ink droplets that land (multi-droplet method). Among these, the multi-droplet method is expected to have high resolution, excellent gradation, and high-speed printing.

[Problems to be Solved by the Invention] However, with the conventional multi-droplet method, the desired gradation cannot be obtained even if the number of ink droplets is changed, and the dot diameter and density that occur even if the same number of ink droplets are used. However, when viewed as an image, there were problems such as a small number of tones and lack of sharpness.

An object of the present invention is to provide a method for recording high-gradation, high-definition images by precisely controlling dot diameter and dot density in multi-droplet inkjet recording.

[Means for Solving the Problems] In order to achieve such an object, the present invention provides an inkjet recording method in which an image is recorded by making a plurality of ink droplets land on the same pixel on a recording material. The method is characterized in that the subsequent ink droplets are allowed to land after the vibrations of the ink droplets that have landed in advance on the recording material have almost stopped.

[Function] According to the study of the present inventor, when the time interval at which a plurality of ink layers land on a recording material is changed, the diameter and dot density of the formed dots differ even if the number of ink droplets is the same. The present invention was completed based on this knowledge.

In other words, the ink droplet is approximately 10 minutes old after landing on the recording material.
It does not penetrate into the recording material for 0-200μsec,
It repeatedly expands and contracts on the recording material, and attenuates while vibrating. Such vibrations are thought to be determined by the physical properties of the ink, such as its viscosity and surface tension, and its landing speed, but according to the observations of the present inventors, the ink generally forms a curve as shown in FIG. 1.

That is, the ink droplet repeats an expansion phase (indicated by A in the figure) and a contraction phase (indicated by B in the figure), and eventually reaches a period in which vibration is substantially stopped as shown by C. Further investigation by the present inventor revealed that the appearance of the next ink droplet changes depending on which state the first ink layer is in on the vibration curve shown in FIG. 1.

For example, as shown in FIG. 2(A), the first ink droplet 1
When the ink droplet 2 is in the expansion phase (A) in Fig. 1, when the next ink droplet 2 lands, the dot diameter greatly expands and the thickness of the ink layer 3 becomes thinner, but as shown in Fig. 2 CB), If the next ink droplet 2 lands during Bl (systolic phase) in FIG. 1, the dot diameter will expand only a little and the thickness of the ink layer 3 will increase.

The thickness of the ink is related to the optical density (OD) of the dot,
Since the dot diameter is related to the resolution, graininess, and density of the image, even if the number of ink droplets per pixel is the same, the gradation will change depending on the landing timing of the ink droplets. The inventor investigated and found that in the conventional multi-droplet method, multiple ink droplets were landed during the period indicated by A or B in Fig. 1, that is, during the expansion phase or the contraction phase. It was found that as a result of variations in density, it was not possible to obtain images with high gradation and high resolution.

In contrast, in the present invention, a plurality of ink droplets are landed using the portion C in FIG. 1 (substantially the vibration stop period).
It becomes possible to obtain a stable dot diameter and dot density depending on the number of ink droplets, and an image with high gradation and high resolution can be obtained.

According to the inventor's detailed study, in order to obtain a stable dot diameter and dot density, the preceding ink droplet does not need to be completely stationary, and the amplitude shown in D in Fig. 1 is ,
After the maximum amplitude DO becomes 1710 or less,
I found that it is okay to have some vibration. However, it is desirable that the next ink droplet land before the previous ink droplet permeates into the recording material. If the landing timing of the subsequent ink droplets is too late, they will not be able to coalesce into ink droplets, which is not preferable for forming a good image.

The ejection method used in the present invention may be any inkjet method having multiple nozzles, but the bubble jet method is particularly preferable because it allows nozzles to be arranged at high density.

Further, the ink used in the present invention can be either water-based or oil-based, but water-based ink is preferred from the viewpoint of odor and safety.

Further, as the recording material used in the present invention, so-called coated paper having an ink-receiving layer on its surface, transparent range film, etc. are preferable.

[Example] The present invention will be specifically described below with reference to Examples. For comparison, the recording results obtained by the conventional method are also shown.

Recording is performed using the head, ink, and recording material below Ura Goya, and the appearance of a single droplet landing on the recording material is observed using an optical microscope and strobe device, and the dot system after landing is observed. Changes over time were measured.

Head 128 nozzles, density 14.2 dots/ff1I11, bubble jet method, droplet flight speed 10m/sec, droplet volume 25p, ejection frequency 10kHz, head scanning speed 0.35+o/s Ink diethylene glycol 20% (weight) %, same below) Ethyl alcohol 5% Water 72%C,
1. Direct Black 1543% The above composition was mixed and dissolved and filtered through a filter to obtain an ink.

Recording material Matsutoko) NM paper (manufactured by Mitsubishi Paper Industries) Further, recording was performed under the same conditions as in Example 1 except that the following heads were used. The performance of the head is the same as Example 1 except for the following.
is the same as

1 x 128 nozzles, density 14.2 dots/mm, droplet volume 12 ppr, ejection frequency 12.5 kHz, head scanning speed 0.22 m/s, 256 nozzles per inch, density 15.7 dots/mm , droplet volume 5 p°C, ejection frequency 16 kHz, head scanning speed 0.13 m/s K1IL 256 nozzles, density 15.7 dots/mm.

Droplet volume: 2.5 pQ, ejection frequency: 32 kHz, head scanning speed: 0.13 m/s For a comparative example, recording was performed using the conventional method of landing timing. The recording conditions were the same as in Example 1 except that the following head was used, and the performance of the head was the same as in Example 1 except for the following.

le school doctor Trot bread volume 259β, Discharge frequency 12.5kHz, Head scanning speed 0.44m/S Comparison balls Trotublet volume 12pI2, Discharge frequency 15kHz, Head scanning speed 0.26m/s comparison yoyu Dorotsu bread volume 5pρ, Discharge frequency 20kHz.

Head scanning speed: 0.16 m/s L Comparison A: Droplet volume: 2.5 pn, ejection frequency: 50 kHz, Head scanning speed: 0.20 m/s or more Prints full-color images using ink and paper. Ta. Table 1 shows the landing interval of successive ink droplets,
The measurement results of the time change of the dot system at the time of impact and the evaluation results of the obtained images are shown.

(Margins below) Table 1 Results of Examples and Comparative Examples c Image quality: Interval between successive ink droplets (μ5eC) Time after impact when the amplitude of ink droplet vibration becomes 1/10 or less (p5ec) A: Very Clear, B: Clear, C: Slightly unclear As is clear from Table 1, high-quality images are obtained in Examples 1 and 23.4, in which printing is performed after the ink droplet vibration has almost stopped upon landing. It can be seen that in Comparative Examples 1, 2, and 3.4, in which the subsequent ink droplets landed while the ink droplets were still vibrating, images of slightly inferior quality were obtained.

(Others) The present invention brings about excellent effects particularly in a bubble jet type recording head and recording apparatus, which is proposed by Canon Co., Ltd. among inkjet recording types. This is because such a system can achieve higher recording density and higher definition.

As for typical configurations and principles thereof, it is preferable to use the basic principles disclosed in, for example, US Pat. No. 4,723,129 and US Pat. No. 4,740,796. This method can be applied to both the so-called on-demand type and continuous type, but especially in the case of the on-demand type, it is necessary to arrange the liquid (ink) in accordance with the sheet and liquid path that hold it. The electrothermal converter that is
Generating thermal energy in the electrothermal transducer and producing film boiling on the thermally active surface of the recording head by applying at least one drive signal that corresponds to recorded information and provides a rapid temperature rise above nucleate boiling. As a result, bubbles in the liquid (ink) can be formed in a one-to-one correspondence with this drive signal, which is effective. The growth and contraction of the bubble causes liquid (ink) to be ejected through the ejection opening to form at least one droplet. If this drive signal is in the form of a pulse, bubble growth and contraction will occur immediately and appropriately.
Particularly responsive liquid (ink) ejection can be achieved,
More preferred. This pulse-shaped drive signal is described in U.S. Pat. No. 4,463,359 and U.S. Pat.
Those described in the specification are suitable. Furthermore, if the conditions described in the specification of US Pat. No. 4,313,124 concerning the temperature increase rate of the heat acting surface are adopted, it is possible to perform recording with an even higher temperature.

The configuration of the recording head includes, in addition to the combination configuration of ejection ports, liquid paths, and electrothermal converters (straight liquid flow path or right-angled liquid flow path) as disclosed in the above-mentioned specifications, a heat acting section. The present invention also includes configurations using US Pat. No. 4,558,333 and US Pat. No. 4,459,600, which disclose configurations in which the wafer is placed in a bending region. In addition, Japanese Patent Application Laid-Open No. 1989-5 discloses a configuration in which a common slit is used as a discharge part of a plurality of electrothermal converters.
No. 9-123670 and Japanese Patent Application Laid-Open No. 59/1989 which discloses a configuration in which a discharge portion is made to correspond to an opening that absorbs pressure waves of thermal energy.
The effects of the present invention are also effective even if the structure is based on the publication No.-138461. That is, regardless of the form of the recording head, according to the present invention, recording can be performed reliably and efficiently.

Furthermore, 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 that can be recorded by a recording apparatus.

Such a recording head may have either a configuration in which the length is satisfied by a combination of a plurality of recording heads, or a configuration as a single recording head formed integrally.

In addition, even with the serial type shown above, the recording head is fixed to the device body, or by being attached to the device body, electrical connection to the device body and ink supply from the device body are possible. The present invention is also effective when using a replaceable chip type recording head or a cartridge type recording head in which an ink tank is integrally provided in the recording head itself.

Further, it is preferable to add recovery means for the recording head, preliminary auxiliary means, etc., which are provided as a configuration of the recording apparatus, to the present invention, because the effects of the present invention can be further stabilized. Specifically, these include capping means for the recording head, cleaning means, pressure or suction means, preheating means using an electrothermal transducer or another heating element, or a combination thereof; It is also effective to perform a preliminary ejection mode in which ejection is performed separately from printing in order to perform stable printing.

In addition, regarding the type and number of recording heads installed, for example, in addition to one type that corresponds to single-color ink, there is also a plurality of recording heads that correspond to multiple inks with different recording colors and densities. It may be something that can be done. In other words, for example, the recording mode of the recording device is not only a recording mode of only the mainstream color such as black (although the recording head may be configured integrally or by a combination of multiple heads, it may also be a multiple color recording mode of different colors). The present invention is also extremely effective for devices equipped with at least one of color or full color by color mixture.

Additionally, in the embodiments of the present invention described above,
Although ink is described as a liquid, it is an ink that solidifies at room temperature or below, but softens or liquefies at room temperature, or in an inkjet method, the ink itself is
Generally, the temperature is adjusted within the range of 0°C or more and 70"C or less so that the viscosity of the ink is within the stable ejection range, so the ink is in a liquid state when the recording signal is applied. In addition, the temperature increase due to thermal energy can be actively prevented by using it as energy for changing the state of the ink from a solid state to a liquid state.
Alternatively, ink that solidifies when left unused is used to prevent ink evaporation, but in any case, the ink is liquefied by applying thermal energy in response to a recording signal, and the liquid ink is ejected, or the recording medium The present invention is also applicable to the case where an ink that is liquefied only by thermal energy is used, such as an ink that begins to solidify by the time it reaches . The ink for such cases is disclosed in Japanese Patent Application Laid-Open No. 54-56847 or Japanese Patent Application Laid-Open No. 60-7126.
As described in Japanese Patent No. 0, the porous sheet may be held as a liquid or solid in the recesses or through-holes of the porous sheet, facing the electrothermal converter. In the present invention, the most effective method for each of the above-mentioned inks is to implement the above-mentioned film boiling method.

In addition, the inkjet recording apparatus of the present invention may be used as an image output terminal for information processing equipment such as a computer, or may be used as a copying machine combined with a reader or the like, or as a facsimile machine having transmitting and receiving functions. It may also be something that is harvested.

[Effects of the Invention] As explained above, according to the present invention, it is possible to obtain a stable dot system and dot density, and it is possible to record an image with high gradation and high definition.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the vibration of an ink droplet on a recording material, and FIG. 2 is a diagram showing the difference in the spread of the ink droplet depending on the landing timing. 1... First ink droplet, 2... Second ink droplet, 3... Ink layer. Figure (A)

Claims (1)

[Claims] 1) In an inkjet recording method in which an image is recorded by landing a plurality of ink droplets on the same pixel on a recording material, the vibration of the ink droplets that landed in advance on the recording material An inkjet recording method characterized by causing subsequent ink droplets to land after the ink droplets have almost stopped. 2) The inkjet recording method according to claim 1, wherein the ink droplets are formed and ejected by applying thermal energy to the ink.