JPH04241948A - Ink jet recording head - Google Patents

Abstract

PURPOSE:To stably emit ink and to easily clean a liquid repelling treatment surface, in an ink jet recording head constituted so that liquid repelling treatment is applied to the end surface having ink emitting orifices provided thereto of the head to stabilize the emission of ink, by specifying the relation between a liquid repelling treatment agent and the ink and more enhancing liquid repelling effect. CONSTITUTION:In an ink jet recording head equipped with the ink emitting orifices 2 communicating with an ink chamber 1 and emitting ink 4 to the recording sheet arranged in opposed relation to the ink emitting orifices 2, liquid repelling treatment bringing the sweepback contact angle thetar of the ink to 30 deg. or more is applied to the head end surfaces 12, 13 having the ink emitting orifices 2 provided thereto.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to an inkjet recording head that discharges ink onto a recording sheet according to image information, and more specifically, the present invention relates to an inkjet recording head of a type in which the opening surface of the ink discharge openings is treated to be liquid repellent. Regarding improvements.

0002

2. Description of the Related Art Inkjet recording, as is already well known, is a recording method in which ink droplets are ejected from an ink discharge port, and the ink droplets are attached to a recording sheet to form dots. In this recording method, parameters such as ink droplet ejection direction, ejection speed, and ink droplet particle size are closely related to image quality, so it is necessary to maintain these parameters in a stable state at all times. strongly requested.

However, in the inkjet recording method, when ink droplets are ejected, ink droplets called splashes are generated, which adhere to the ink ejection orifice surface of the recording head and wet the area around the ink ejection orifices. In some cases, the above-mentioned parameters may fluctuate greatly due to the fine ink ejection orifices being blocked, resulting in a decrease in image quality or, in extreme cases, an inability to eject ink droplets.

[0004] Therefore, in order to always obtain stable image quality, it is required to actively control the degree of ink wetting around the ink ejection ports so that the above parameters do not fluctuate.

[0005] From this point of view, Japanese Patent Application Laid-open No. 59-1948
In a number of inventions such as No. 64, it has been proposed to perform liquid repellent treatment on the opening surface of the ink ejection opening. That is, according to these proposals, the adhered ink is retained in the form of droplets by applying a liquid-repellent treatment to the opening surface, thereby preventing the adhered ink from flowing out and covering the area around the ink ejection opening. .

[0006]

[Problems to be Solved by the Invention] However, in these proposals, it may not be possible to obtain a sufficient improvement effect simply by applying liquid repellent treatment to the opening surface of the ink ejection port.
The problem is that the effect can only be obtained when a specific liquid repellent treatment agent and a specific ink are combined. Therefore, a new challenge for this type of inkjet recording head is how to identify an effective combination of liquid repellent treatment agent and ink.

The present invention has been made to address these problems, and its purpose is to specify the relationship between a liquid repellent agent and ink, and to create an inkjet recording head with a higher liquid repellent effect. Our goal is to provide the following.

[0008]

[Means for Solving the Problems] In order to achieve the above object, the inventors of the present invention first focused on the static contact angle of the ink with respect to the liquid-repellent surface, and determined that the ink from the recording head is absorbed by the difference in the static contact angle. We conducted an experiment to examine how the discharge changes. Here, the static contact angle of ink refers to the angle θ0 between the ink surface and the treated surface a when an ink droplet i is formed on the liquid-repellent treated surface a, as shown in FIG. It is used to express the liquid repellent effect of

In this experiment, an inkjet recording head with 128 ink ejection ports opened at a pitch corresponding to a resolution of 400 DPI was used, and five different types of liquid-repellent films were formed on the surface where the ink ejection ports were formed. Ink was continuously ejected from each head and the stability of ink droplet ejection was observed. The ink used in the experiment is an aqueous ink composed of 60 wt% water, 38 wt% diethylene glycol, and 2 wt% dye, and has a viscosity of 2 cp and a surface tension of 40 dyne/cm.

[0010] Table 1 below shows the experimental results. In Table 1, continuous discharge means 30 seconds of discharge and 30 seconds of rest.
The recovery operation is an operation of wiping the opening surface of the ink ejection port once with a rubber blade back and forth.

[0011]

[Table 1]

As shown in Table 1, all of the five types of liquid-repellent films formed have a static contact angle θ0 of 60° or more and should be difficult to wet with ink. Disturbances in direction and fluctuations in dot size were observed, and it was found that ink pooled around the ink ejection ports and that ink covered the ink ejection ports. That is, according to this result, no relationship could be found between the static contact angle θ0 of the ink and the stability of ink ejection.

Next, the inventor of the present application focused on the dynamic contact angle of the ink with respect to the liquid-repellent surface, that is, the receding contact angle, and determined the receding contact angle for each of the five types of liquid-repellent films used in the above experiment. was measured. Here, the receding contact angle refers to the angle θr formed between the ink surface and the treated surface when the ink i is removed from the liquid-repellent treated surface a, as shown in FIG.

Table 2 below shows a comparison between the static contact angle θ0 and the receding contact angle θr. In addition, a contact angle meter (model CA-D, manufactured by Kyowa Interface Science Co., Ltd.) was used to measure the actual receding contact angle θr, and when the ink on the liquid-repellent surface was pulled back by the droplet forming orifice (see Figure 4). The receding contact angle θr formed at
was measured.

[0015]

[Table 2]

The results shown in Tables 1 and 2 revealed the following facts. ■Even if liquid-repellent treatment is applied, the effects vary greatly depending on the type of treated film. ■Retreating contact angle θr is 3
If it is below 0°, no liquid repellent effect can be expected. (2) When the receding contact angle θr is 30° or more, there is a liquid repellent effect, and even if ink accumulates around the ink discharge port, the liquid repellent effect can be enjoyed again by wiping. (2) When the receding contact angle θr is 40° or more, the liquid repellent effect is particularly remarkable.

[0017]The inventor of the present application has proposed the present invention based on the results of the above experiment. That is, the inkjet recording head of the present invention is provided with an inkjet recording head that is provided with an ink discharge port that communicates with an ink chamber and that discharges ink toward a recording sheet that is disposed opposite to the ink discharge port. The receding contact angle θr of the ink is 3 on the end face of the head where
It is characterized by having been subjected to a liquid repellent treatment of 0° or more.

[0018] In such technical means, the inkjet recording head that performs liquid-repellent treatment may be one that ejects ink droplets from the ink ejection opening by any energy application means, for example, by electrostatic energy. It may be of a type that sucks ink droplets toward the recording sheet, or it may be of a type that ejects ink onto a recording sheet by utilizing boiling of the ink film surface due to application of thermal energy.

[0019]

[Operation] According to the above technical means, a liquid repellent treatment that is more effective in combination with ink is applied to the opening surface of the ink ejection port, so that ink pools are not formed around the ink ejection port. Furthermore, the ink ejection openings are not covered with ink, and the ejection speed, directionality, and particle size of ink droplets are stabilized.

Furthermore, by setting the receding contact angle of the ink to a certain value or more, the ink releasability when wiping off the ink adhering to the opening surface of the ink ejection port is improved.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The ink jet recording head of the present invention will be described in detail below with reference to the accompanying drawings.

FIGS. 1 and 2 show a specific example of an ink jet recording head to which the present invention can be applied. , is an inkjet recording head of a type that ejects ink droplets from an ink ejection port 2 by utilizing the pressure of a vapor bubble generated by film surface boiling of ink 4.

This recording head has a pair of insulating substrates 5 and 6 bonded together to form an ink chamber 1, an ink discharge port 2, and an ink channel 3 that communicates and connects these. A heater 7 is provided for applying thermal energy. The ink chamber 1, ink discharge port 2, and ink flow path 3 are located on one insulating substrate 5 in which a recess 8 corresponding to the ink chamber 1 and a groove 9 having a triangular cross section corresponding to the ink flow path 3 are carved. 128 ink channels 3 are arranged in parallel at a pitch of 63.5 μm to correspond to a resolution of 400 DPI. Further, a polyimide layer 10 is formed on the contact surface of the other flat insulating substrate 6 for the purpose of ensuring flatness and heat storage, and the heaters 7 are arranged on the surface of this layer 10 at the same pitch as the ink channels 3. 128 heaters 7 are arranged in parallel, and each heater 7 is connected to positive and negative electrodes (not shown) for energization. Incidentally, reference numeral 11 is an ink supply port for continuously supplying ink 4 to the ink chamber 1.

In this inkjet recording head, when the individual heaters 7 are energized appropriately according to the image information and the heaters 7 generate heat, the ink 4 in contact with the heaters 7 in the ink flow path 3 boils on the film surface and rapidly boils. steam bubble grows,
The pressure of the bubble pushes out the ink 4 in the ink flow path 3 from the ink ejection port 2, and the pushed out ink 4
The ink becomes ink droplets and is ejected onto a recording sheet (not shown) to perform printing.

The liquid-repellent film 14 is formed on the ink discharge port opening surfaces of such a recording head, that is, the end surfaces 12 and 13 of the insulating substrates 5 and 6. The following two types were carried out.

Processing film ■: N2 gas is fed from the ink supply port 2 at a flow rate of about 1 liter/min, and while being ejected from the ink discharge port 2, 1% trichlorotrifluoro of perfluoroalkylsilane C8F17CH2CH2Si(OCH3)3 is The end surfaces 12 and 13 of the insulating substrates 5 and 6 were immersed in the ethane solution for 20 seconds, taken out from the solution and dried, the N2 gas was turned off, and the final temperature was 120°C for 30 seconds.
It was cured and baked by heating for several minutes.

Processing film ■: N2 gas is fed from the ink supply port 2 at a flow rate of about 1 liter/min, and while being ejected from the ink discharge port 2, a silicone resin (Toray
Manufactured by Dow Corning Silicone Company: Product name SR241
The end surfaces 1 of the insulating substrates 5 and 6 are placed in a 10% toluene solution of
Nos. 2 and 13 were immersed for 20 seconds, taken out from the solution and dried, the N2 gas was turned off, and finally, they were cured and baked by heating at 120° C. for 30 minutes.

Each liquid repellent film 14 formed in this way
, using the water-based ink described above, the static contact angle θ0
When the receding contact angle θr was measured, the following results were obtained. Treated film ■ Static contact angle: 86° Receding contact angle: 54° Treated film ■ Static contact angle: 65
° Receding contact angle: 42°

[0029] As a result of conducting an ink ejection test using the recording heads on which each treated film 14 was formed, the ejection directionality of the ink 4 was stable in all the recording heads, and continuous ejection was performed for a long time. Even in this case, no ink accumulation occurred around the ink discharge port 2. This confirmed the effectiveness of this example.

In this example, the liquid-repellent film was explained when using a specific water-based ink, but other inks such as oil-based inks may also be used if the receding contact angle θr is 3.
A similar effect can be obtained by applying liquid repellency treatment to the opening surface of the ink ejection port so that the angle is 0° or more.

[0031] The liquid repellent agent may be silicone resin, silicone oil,
Any material may be selected, such as a fluorine-based polymer, a silane coupling agent, an organic titanium compound, or a monomer gas plasma polymerized film.

[0032]

As explained above, according to the inkjet recording head of the present invention, more effective liquid repellent treatment can be applied to the opening surface of the ink ejection opening, and the ejected ink droplets can be Since the ejection speed, directionality, and particle size are stabilized, it becomes possible to form a high-quality recorded image.

Furthermore, by setting the receding contact angle θr of the ink to a certain value or more, the ink releasability from the opening surface of the ink ejection port is improved, so there is no ink left behind after cleaning the opening surface. In addition to being able to reproduce the initial ink ejection state with a simple cleaning operation, it is also possible to reduce the number of times of cleaning, thereby making it possible to improve the recording speed.

Furthermore, since the state of ink droplet ejection is stabilized, it is possible to obtain a good recorded image even if the repetition rate of ink ejection is increased.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an inkjet recording head to which the present invention can be applied.

FIG. 2 is a view taken in the direction of arrow A in FIG. 1;

FIG. 3 is a diagram showing the static contact angle between ink and a liquid-repellent surface.

FIG. 4 is a diagram showing the receding contact angle between ink and a liquid-repellent surface.

[Explanation of symbols]

1 Ink chamber 2 Ink discharge port 3 Ink channel 4 Ink 5, 6 Insulating substrates 12, 13 Insulating substrate end face (head end face) 14 Liquid repellent treatment film

Claims (1)

[Claims] Claims: 1. An inkjet recording head comprising an ink discharge port communicating with an ink chamber and discharging ink toward a recording sheet disposed opposite to the ink discharge port; teeth,
An inkjet recording head characterized by being subjected to a liquid repellent treatment such that the receding contact angle θr of ink is 30° or more.