JPH03189165A - Ink jet recording method - Google Patents

Abstract

PURPOSE:To obtain a high gradation and high clarity image by a method wherein when an image is formed by making a plurality of ink drops shoot the same pixel on a material to be recorded, following ink drops are made to shoot while a dot on the material to be recorded formed with a preceding ink drop is enlarging. CONSTITUTION:In order to make a following ink drop shoot during an enlarging period of a preceding ink drop, in the case where a pixel is formed by, for instance, two ink drops, after discharging a first ink drop, a second and a third pulses are made off, and a second ink drop is discharged by using a fourth pulse. At that time, the second ink drop shoots during a third enlarging period (A3) of a dot by the first ink drop. Further, in the case where a third ink drop is made to shoot, after discharging the second ink drop, two pulses are made off. Thereafter, if the third ink drop is discharged, it shoots during an enlarging period of A2'. If this information is incorporated into a discharge driver and printing is performed, a high clarity and high gradation image is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an inkjet recording method, and particularly to an inkjet recording method in which one pixel is formed by a plurality of droplets.

[Prior Art] Various methods are known for achieving good gradation expression in inkjet recording.

For example, the size of ejected droplets is changed by various means and the pixel area is thereby changed (area gradation method), and a collection of several dots is treated as one pixel, and gradation is expressed by changing the number of printed dots. Method ('a degree pattern method, dither method, etc.)
, a method of printing using ink with different densities (dark and light ink method), in which multiple ink droplets land on the same spot on the recording material to form a single dot, and depending on the number of ink droplets that land, There is a method of expressing gradation by changing the dot area and density (multi-droplet method).

Among these, the multi-droplet method has high resolution and
It is expected to be a method with 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, or even if the same number of ink droplets is used, the dot diameter and There were drawbacks such as variations in density, and when viewed as an image, the number of gradations was small and clarity was lacking.Also,
When the number of ink droplets is increased in an attempt to increase the dot density, the dot diameter becomes larger and the resolution is lowered. Furthermore, if a subsequent ink droplet lands before the ink layer formed by the preceding ink droplet on the recording material permeates into the recording material or disappears by evaporation, ink splatter occurs.
There was also the problem that this caused the image to become smudged.

An object of the present invention is to provide a high-gradation, highly clear image in multi-droplet inkjet recording by modulating only the dot diameter while keeping the dot 00 (optical density) constant.

[Means for Solving the Problems] In order to achieve such an object, the present invention is an advanced technology in inkjet recording in which an image is formed by landing a plurality of ink droplets on the same pixel on a recording material. The method is characterized in that a subsequent ink droplet is landed while the dot formed by the ink droplet on the recording material is expanding.

[Function] The inventors have found that by changing the time interval at which a plurality of ink droplets land on a recording material, the diameter and density of the formed dots will differ even if the number of ink droplets is the same. It was revealed.

The present invention was completed based on this knowledge.

In other words, after the ink droplet lands on the recording material, it takes a few microseconds.
Expansion and contraction are repeated on the recording material to be opened for several hundred μsec. Such vibrations are due to the viscosity of the ink.

Although it is thought that it depends on the physical properties such as surface tension and the landing speed of the ink droplets, according to the observations of the present inventors, the curve roughly resembles that shown in FIG. 2.

Further investigation by the present inventors revealed that the appearance of the next ink droplet when it lands changes depending on which state of the vibration curve in FIG. 2 the first ink droplet is in.

FIG. 3 shows the difference in the spread of ink droplets due to the difference in landing timing. The figure shows an ink droplet viewed from the side. For example, as shown in FIG. 3(A), if the next ink droplet 1 lands when the first ink droplet is in A (expansion phase) in FIG. Sa becomes thinner. On the other hand, as shown in Figure 3 (B), when the first ink drop is in B (systolic phase) in Figure 2, the next ink drop 1
When the dot lands, the dot diameter expands only a little, and the thickness of the ink layer 2 increases.

Further investigation revealed that if the subsequent ink droplet lands during the dot expansion period caused by the preceding ink droplet, the thickness of the ink droplet on the recording material will be approximately constant regardless of the number of ink droplets. Ta. If the thickness of the ink layer is constant, the dot OD will be constant, so if the subsequent ink droplets are made to land only during the expansion phase of the ink droplet, ideally, only the dot diameter will be modulated with the dot 0[1 constant. gradation can be realized.

Also, if a subsequent ink droplet lands during the contraction phase of the ink droplet,
It was also observed that a lot of ink splatter occurred. Since this splatter is less likely to occur during the expansion stage of the ink droplets, the resulting image has a clean background.

As mentioned above, in the conventional multi-droplet method, printing is performed completely ignoring the timing of the ink droplets, whereas in the present invention, the dots formed by the preceding ink droplets are enlarged. By allowing the subsequent ink droplets to land only when the image is on, it has become possible to obtain images with high gradation, high clarity, and a clean background.

In the present invention, any inkjet recording method such as a continuous method or an on-demand method can be used as an ejection method, but a bubble jet method having multiple nozzles capable of high-speed printing is particularly preferable, and a high-density printing (for example, 14 A recording method that can perform dot/ID11 or higher) is more desirable.

Further, both water-based inks and oil-based inks can be used in the present invention, but water-based inks are preferred from the viewpoint of odor, safety, and the like.

Furthermore, recording materials include so-called coated paper with an ink-receiving layer on the surface, so-called plain paper such as high-quality paper, letter paper, and copy paper, transbearing range film, etc.
Any material generally used in inkjet recording can be used in the present invention. Preferably, if a recording material with a Bekk smoothness (JISP8119) of 500 seconds or more is used, a higher definition image can be obtained.

[Example] The present invention will be explained in more detail with reference to Examples below.

The head and ink used in this example are as follows.

Head 128 nozzles, density 15.7 dots 7mm, bubble jet method.

Ejection frequency 50kHz, ink droplet flying speed 16m/sec
c.

Distance between discharge raw paper 1jl 0.5+am Ink Propylene oxide added glycerin (average molecular weight 800) 5%
Butanol 1% Triethylene glycol 25% C,1, Direct Black 19 2% Water
67% The above composition was mixed and dissolved, and then filtered through a filter to obtain an ink.

The vibration of landed ink droplets was measured as follows.

Ink is ejected from the head, the number of ink droplets forming one dot is varied, and the appearance of the ink droplets when they land is observed using an optical microscope.
Observations were made using a device that combines a strobe lighting system and a paper feeding system. As a result, the contraction period of the ink droplets was as shown in Table 1.

Table 1 Unit: μ5ec m: Unmeasured When ejecting continuously at an ejection frequency of 50 kHz, the impact timing is at intervals of 20 usec, as shown in FIG.

FIG. 1 shows the vibration of a dot formed by successively ejected ink droplets.

In order to make a subsequent ink droplet land during the expansion period of the preceding ink droplet, for example, when forming a pixel with two ink droplets as shown in FIG. It is sufficient to turn off the third pulse and use the fourth pulse to eject the S2 ink droplets. At this time, the second ink droplet will land during the third expansion period of the dot caused by the first ink droplet (A3 in FIG. 1). Furthermore, when a third ink droplet is to be landed, as shown in FIG. 1, after ejecting the second ink droplet, turn off the second pulse, and then eject the third ink droplet. It will arrive during the expansion period of /2. - For boat fishing, ejection pulses may be selected in the same manner for the fourth and subsequent ink droplets so that the subsequent ink droplets land during the expansion period of the preceding ink droplet. In this embodiment, when there are three or more preceding ink droplets, the first expansion period of the dot is 0 to 21 μs.
Since it is more than ec, the fourth ink droplet and above are consecutively 20
It is sufficient to eject at intervals of μsec.

To summarize the above, the relationship between the number of ink droplets forming one pixel and the ejection pulse is shown in Table 2.

Table 2 [Comparative Example] Using the same head and ink as in the example, printing was performed using the number of ink droplets forming one pixel and the ejection pulse as shown in Table 3.

Table 3 When this information was incorporated into the ejection driver and printed, a highly clear and high gradation image was obtained.

The above embodiment is an example of implementing the present invention, and the recording method according to the present invention is not limited to this embodiment.

That is, when the number of ink droplets is two or three, the subsequent ink droplet lands during the contraction period of the preceding ink droplet.

The resolution of the obtained image was slightly inferior to that of the image of the example, and particularly fine parts were blurred.

[Effects of the Invention] As explained above, according to the present invention, an image with excellent resolution and gradation can be obtained.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram explaining the method of the present invention, FIG. 2 is a diagram showing the vibration of ink droplets on the recording material, FIG. 3 is a diagram showing the difference in spread of ink droplets depending on the landing timing, and FIG. The figure is a diagram showing the timing of ejection and landing of ink droplets. 1...Next ink drop, 2...Ink layer. Figure 1 Figure 2 (A)

Claims (1)

[Claims] 1) In inkjet recording in which an image is formed by landing multiple ink droplets on the same pixel on a recording material,
An inkjet recording method characterized in that a subsequent ink droplet is landed while a dot formed by a preceding ink droplet on a recording material is expanding.