JPH11268284A - Ink jet imaging method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink jet imaging method in which a clear image can be obtained using a high viscosity ink. SOLUTION: An image is formed by setting the advance contact angle θa and retract contact angle θr of ink, respectively, at 80-110 deg. and at 40 deg. or more for a surface subjected to ink repelling treatment and setting the advance and retract angles θa θr at 30 deg. or less for a surface subjected to ink affinity treatment using an ink jet printer subjected to ink repelling treatment on the periphery of ink jet port on the surface of nozzle plate in a head and ink affinity treatment on the circumferential fringe thereof, and an ink exhibiting viscosity of 4 cp or above at 25 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink-jet type image forming method capable of performing stable high-speed ejection even with high-viscosity ink and obtaining a clear image.

[0002]

2. Description of the Related Art An ink jet printer fills a nozzle with ink, applies a positive pressure to the ink, pushes the ink out of an ink chamber, and then applies a negative pressure to the ink to pull the ink back into the nozzle, thereby extruding the ink column. To eject ink droplets from the nozzles.
At this time, the ink meniscus is drawn deep into the nozzle, and the negative pressure fills the ink from the ink tank into the nozzle, preparing for the next ejection. When the negative pressure is reversed to a positive pressure, the meniscus is pushed out again and moves toward the outlet of the nozzle.

As described above, since the pressure applied for discharging ink remains and vibrates even after the ink is discharged,
When the ink pressure in the nozzle fluctuates, the ink meniscus vibrates as shown in FIG. This vibration is repeated several times, gradually attenuating, and the next ejection becomes possible. Also, depending on the type of head, when ink is ejected from one ink chamber,
The ejection pressure is also transmitted to the adjacent ink chamber, and the ink meniscus vibrates.

When a positive pressure is applied to the ink in the nozzle due to the pressure fluctuation, the ink may overflow from the discharge port. The ink that has overflowed to the surface of the nozzle plate is drawn into the nozzle by the next negative pressure.However, the ease with which the ink overflows and the ease with which the ink is drawn is determined by the wettability between the ink and the nozzle plate surface, that is,
The contact angle is relevant. As described above, the surface of the nozzle plate of the ink jet head is easily stained by overflowing ink, which hinders stable ejection and causes deterioration of an image.

[0005] There are various causes for the nozzle plate being stained with ink. The following are summarized: 1) The ink pressure fluctuation accompanying ejection as described above. That is, the ink overflowing from the nozzle due to the positive pressure is
It is not completely drawn into the nozzle by the negative pressure and remains on the surface of the nozzle plate. 2) Pressure transmission from the adjacent ink chamber. That is, the ink chambers on both sides of the ink chamber from which the ink was ejected vibrate and the ink overflows from the nozzles. 3) The tail of the ejected ink drops is torn off, and a minute ink mist adheres to the nozzle plate. Since the distance between the nozzles is close to about 1 mm, the ink mist scattered on the printing medium adheres to the surface of the nozzle plate. 5) The carriage equipped with the nozzle moves while moving in the direction perpendicular to the direction of travel of the printing medium. , A large change in acceleration occurs at the end of the operating range of the head carriage, and the shock causes ink to overflow from the nozzles.

The spilled ink and the adhering ink mist are accumulated on the nozzle plate to form an ink pool. When the pool touches the discharge port, the ink droplets to be discharged are pulled as shown in FIG. Bend the direction. Further, if the ink pool becomes larger and covers the discharge port, the ink splatters when the ink droplets are discharged by piercing the pool and contaminate the image. Further, if the ink pool covers the discharge port thickly, the ink is not discharged. Further, dust generated from paper, cloth, or the like, which is a printing material, easily adheres to the ink reservoir on the nozzle plate, and this may block the nozzle hole.

[0007] If ink accumulates around the discharge port in this manner, normal discharge cannot be performed. Therefore, it is necessary to draw the ink overflowing on the surface of the nozzle plate into the nozzle using a negative pressure between discharges. There is. In addition, ink that cannot be drawn into the nozzles or ink that has adhered from the outside needs to be moved to and held at a place distant from the ink ejection port, and occasionally wiped by wiping.

As described above, in an ink jet printer, it is important to keep the area around the ink discharge ports of the nozzle plate clean, and in order to prevent contamination by ink, the nozzle plate is subjected to an ink-repellent treatment. .

When the surface of the nozzle plate is treated with ink repellent, even if the meniscus of the ink comes out of the discharge port, it is difficult for the ink to overflow onto the nozzle plate or to spread. or,
Even if ink overflows, if the surface of the nozzle plate is treated with ink-repellent ink, the ink will be repelled and become a fine hemisphere, so the contact area with the nozzle plate will be small, it will be easy to move on the nozzle plate, and the head And the like, so that the next ink droplet is not disturbed by being separated from the ejection port due to vibration of the ink.

[0010]

However, inks for textile printing, pigment / dispersed dye inks, etc. are required to obtain high-speed discharge performance, dyeing properties, and dispersion stability, and thus various additives are added. In some cases, the viscosity of the ink increases and becomes 4 cp or more. When such a relatively high-viscosity ink is used, there is a problem that an image is still deteriorated even when a conventional nozzle plate subjected to an ink repellent treatment is used.

In recent years, the number of nozzles, the nozzle density, and the driving frequency have been increased in order to increase the printing speed, and frequent wiping by stopping the discharge cannot perform high-speed printing or stable printing. Since the ink jetting is performed, the overflow amount of ink and the ink mist tend to increase.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide an ink jet type image forming method capable of obtaining a clear image even when a relatively high-viscosity ink is used.

[0013]

SUMMARY OF THE INVENTION The object of the present invention is to provide an ink jet printer in which the periphery of an ink ejection port on the surface of a nozzle plate of a head is subjected to an ink-repellent treatment and the periphery thereof is subjected to an ink-philic treatment. Using an ink of 4 cp or more, the advancing contact angle of the ink to the ink-repellent surface is 80 to 110 °, and the receding contact angle is 40 °.
The above is achieved by an image forming method of an ink jet system in which an image is formed by setting an advancing contact angle and a receding contact angle of the same ink to the parent ink processing surface to 30 ° or less.

That is, the present inventors have arrived at the present invention based on the following considerations.

The ink that overflows to the nozzle surface is sucked into the nozzle by a negative pressure, and is repelled by the ink-repellent surface to be separated into a hemisphere and separated from the discharge port. I want to remove it. That is, stable ejection relates to the ease with which ink droplets are sucked and the ease with which ink droplets move, which are determined by the contact angle between the ink and the nozzle plate.

Generally, the angle formed by a stationary droplet with the solid surface is called an equilibrium contact angle θe or simply a contact angle θ (hereinafter, referred to as a contact angle θ).
θ). When the stationary droplet shown in FIG. 3A is moved by applying an external force, the equilibrium contact angle disappears as shown in FIG. 3B, and a forward contact angle θa and a receding contact angle θr appear.

Θ is the contact angle of a stationary droplet, and indicates whether or not the liquid easily wets the solid surface. Since a liquid having a large θ hardly wets the solid surface, the contact area is small and the solid surface is easy to move on the solid surface.However, when the droplet starts to move, a forward contact angle θa and a receding contact angle θr appear,
The mobility of the droplet is affected not by θ but by θa and θr. Usually, since it can be considered that θa ≒ θ, the mobility of the droplet can be estimated only by the value of θ. However, in the case of a high-viscosity ink droplet, the correlation with the mobility cannot be obtained, and the influence of θr is large. The inventor thought that it would receive it. Also, since the gravity acting on the ink droplet on the horizontal plane and the minute ink droplet of about 50 to 100 μm overflowing from the nozzle hole having a diameter of 20 to 40 μm can be ignored, the force constantly acting on the ink droplet on the nozzle plate is Since only the surface tension and the effect of the surface tension on the droplet are determined by the contact angle, the mobility of the droplet may be evaluated using the contact angle as a parameter.

Here, the advancing contact angle θa is a contact angle that appears when a droplet is advanced, and is a contact angle with respect to a solid surface that has not been wet with the liquid. The receding contact angle θ
r is a contact angle that appears when the liquid recedes, and is a contact angle with respect to a solid surface already wetted with the liquid.

Assuming that the surface tension of the liquid is σdyne / cm, σcosθa is a force acting in the direction of moving the droplet forward, and σcosθr is a force acting in the direction of retracting the droplet. Since the relationship of θa> θr always holds, the force that hinders the movement of the droplet is σ (cosθr−cosθa) erg / c
m ² (see FIG. 4). As shown in FIG.
When a large θr appears, the movement of the droplet is not hindered much, but when a small θr as shown in FIG. 5B appears, the movement of the droplet is hindered. That is, as θr decreases, the force that hinders the movement of the droplet increases, and the movement of the droplet becomes difficult.
In a system with a small θr, the rear end of the droplet spreads thinly and remains even when most of the droplet moves, so that the nozzle plate surface becomes dirty. The advancing contact angle θa is determined by the solid surface that is not wetted with ink and the ink, so that it becomes a substantially constant value if the nozzle plate and the ink are determined. Fluctuates greatly due to the interaction with For example, the ink component is adsorbed on the surface of the hydrophobic solid, and the hydrophobic surface is changed to a hydrophilic surface, or the hydrophobic functional group on the solid surface is sunk into the solid by the influence of the ink, and the hydrophilic group appears on the surface instead. Then, θr greatly decreases.

Specifically, the water θa relative to the water-repellent surface formed of a fluororesin or silicon resin shows a relatively stable large value of 110 to 120 ° regardless of the difference in the chemical structure of the water-repellent surface. However, θr is sensitive to the slight difference in the chemical structure of the water-repellent surface,
It is known that it fluctuates greatly. This is described in detail in the Journal of the Textile Society of Japan Vol 152, No 9, p 493, (1996).

Inks for ink jet printers include dyes, pigments, dispersants, nozzle drying inhibitors, defoamers,
Since additives such as surfactants, penetrants, and preservatives are added, these components may be adsorbed on the water-repellent surface and change it to a hydrophilic surface. For example, high pigment dispersion effect, or
When the ink contains a polymer surfactant or the like having a high nozzle drying prevention effect, θr may be extremely small. In such a system, the mobility of the ink droplet is deteriorated, and the trailing end of the ink droplet spreads thinly and remains on the nozzle plate.

FIG. 6 shows the relationship between the contact angle of the nozzle plate water-repellent with the silicone resin and the amount of the acrylic oligomer added to the ink. Although the change of θa is small, θ
It turns out that r changes greatly.

In addition, even if the ink droplets on the nozzle plate are temporarily trapped at a position distant from the nozzles and the carriage on which the head is mounted is subjected to severe movement, vibration, shock, speed change, etc., the trapped ink is discharged to the ink ejection port. By avoiding contact with, the number of times of wiping can be reduced. That is, the ink-repellent processing section 2 is formed around the discharge port, and the surrounding area is further surrounded by the ink-repellent processing section 3, and the ink droplets repelled by the ink-repellent processing section 2 as shown in FIG. Just trap it.

Based on these considerations, as a result of intensive studies, when ink having a viscosity of 4 cp or more at 25 ° C. is used, the area around the ink discharge ports on the surface of the nozzle plate of the head is subjected to an ink-repellent treatment, and the periphery is further treated as a parent. After the ink treatment, the forward contact angle of the ink to the ink-repellent treated surface is set to 80 to 11
0 °, the receding contact angle is 40 ° or more, and if the advancing contact angle and the receding contact angle of the ink with respect to the parent ink processing surface are 30 ° or less, the ink overflowing on the nozzle surface is always removed from around the ejection port, The present inventors have found that stable ink ejection performance can be obtained.

Japanese Patent Application Laid-Open No. 4-241948 describes that the ink repellent treatment is performed so that the receding contact angle of the ink becomes 30 ° or more, but there is no concept for defining the advancing contact angle.

JP-A-5-193146 discloses that a non-wetting area having a contact angle of 70 ° or more and a contact angle of 2
Providing a wettability region of 0 to 50 ° is the same as that of Example 7-178.
No. 918 describes that an ink-repellent region having a contact angle of 110 ° and a parent ink region having a contact angle of 20 ° are provided, respectively, but there is no concept of defining the forward contact angle and the receding contact angle.

Japanese Patent Application Laid-Open No. Hei 8-244234 discloses that a fluororesin having a perfluorohetero structure into which a silane coupling agent is introduced is used as a water-repellent material, the forward contact angle of the water-repellent portion is 90 to 95 °, and the receding portion is receded. It is described that the contact angle is 70 ° or more, but there is no idea to provide a hydrophilic portion.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments will be described below.

It is preferable that the advancing contact angle θa of the ink droplet with respect to the surface of the nozzle plate subjected to the ink-repellent treatment is large, and it is 80 to 110 ° in the present invention. If the angle is smaller than 80 °, the ink repellent effect cannot be obtained, the ink easily overflows from the discharge port, and the ink easily spreads on the nozzle plate and spreads.
If a is small, θr also becomes small, so that it is difficult for the ink droplet to move. A larger receding contact angle θr is preferable because the ink droplets easily move, and is preferably 40 ° or more, preferably 50 ° or more, and more preferably 60 ° or more in the present invention. If the receding contact angle is smaller than the present invention, the effect of hindering the movement of the ink droplets increases, and the overflowed ink is not completely absorbed in the nozzles, or the ink droplets remain near the nozzles.

The contact angle may be adjusted by selecting the composition of the ink-repellent film, ink additives (surfactant, polymer activator, water-soluble polymer, etc.).

In order to pull the ink droplets moved from the ink-repellent processing unit into the ink-repellent processing unit and trap them therein, it is necessary that this part is sufficiently wetted with the ink. or,
The ink droplets grown to about several mm trapped here are much larger than the minute ink droplets of about 50 μm near the ejection port, so they are easy to move and do not move even if the head moves violently until they are removed by wiping. Need to be anchored. From the point of ink wetting, the advancing contact angle is 30 ° or less. The receding contact angle is also set to 30 ° or less from the viewpoint of preventing ink movement.

As shown in FIG. 8, the ink-repellent processing section and the ink-affinity processing section on the nozzle plate surface have a nozzle diameter of 1 around the nozzle hole.
An ink-repellent portion having a diameter of 10 to 10 times is provided, and the surrounding portion is further surrounded by an ink-repellent portion. As a specific method, a nozzle plate is made of an ink-philic resin, an ink-repellent film is provided on one side thereof, and an excimer laser (oscillation wavelength: 248 nm, pulse width 1
Using 50 nsec), a mask having a desired nozzle hole pattern is applied to form the nozzle holes. Further, the side having the water-repellent film may be processed by laser while masking the nozzle hole and its peripheral portion to expose the nozzle plate resin. In this case, if the nozzle plate is formed of polyimide, polysulfone, or polyethersulfone, they themselves have a contact angle to water of about 50 to 70 °, but are irradiated with laser light to form -OH, -COOH, etc. on the surface. Is generated, and the surface is further roughened to make the contact angle 0 to 10 °.
Can be up to the extent. Preferably a polyimide resin, manufactured by Dupont; Kapton or Ube Industries, Ltd.
Manufactured by Ubirex etc. are excellent in dimensional stability, ink resistance and heat resistance.

For the ink-repellent treatment, a fluorine polymer or a silicone resin which is soluble in an organic solvent and can be applied is preferably used. Alternating copolymer of fluoroolefin and vinyl ether (FEVE, manufactured by Asahi Glass Co., Ltd .; Lumiflon;
Made by Dainippon Ink Co., Ltd .; Fluonate, manufactured by Central Glass Co., Ltd .; Cefral Coat, manufactured by Daikin Co., Ltd .; C-1
Etc.), an amorphous, highly water-repellent, solvent-soluble perfluorocyclopolymer (manufactured by Asahi Glass Co., Ltd .; Cytop, Dup)
ont company; Teflon AF, etc.), polymer having a perfluoro group in the side chain (Asahi Glass Co., Ltd .; Asahi Guard AG series, etc.), room temperature curing type silicone resin, room temperature curing type organic modified silicone resin, silicon hard coat material , Silane coupling agents, fluoroalkylsilanes, etc. (manufactured by Toray Dow Corning Silicone Co., Ltd .; SR2410, 2411, 2
107, 2115, fluoroalkylsilane manufactured by Toshiba Silicon; TSL-8233, 8257, etc.).

These ink-repellent materials are dissolved in an appropriate solvent and coated on a nozzle plate by dip coating, spin coating, or the like to a thickness of about 0.1 to 10 μm. After drying, the coating film is subjected to a heat treatment at 150 to 300 ° C. for about 1 hour to complement the crosslinking and the surface orientation of the water-repellent group.

Further, since the ink repellent layer is rubbed with a wiper, paper, cloth or the like, durability is required. In order to strongly bond the ink repellents and strongly adhere to the nozzle plate, use an ink repellent having a hydroxyl group or a carboxyl group to crosslink with an isocyanate curing agent or epoxy curing agent, or to react with moisture in the air. A silicon compound having a silanol group that crosslinks as a result may be employed.

The ink repellent layer preferably contains an ultraviolet absorber. Resins such as polyimide, polysulfone, and polyethersulfone have absorption in the ultraviolet, so a nozzle hole close to a perfect circle can be made with an excimer laser.However, the above-described ink-repellent material has no absorption in the ultraviolet, Excimer laser processing lowers the roundness and causes variations in the flight direction of ink droplets. Therefore,
It is improved by adding a salicylic acid-based, phenyl salicylate-based, benzophenone-based, or benzotriazole-based ultraviolet absorber.

In the present invention, a fixed amount of ink droplet is placed on a solid surface using a contact angle measuring device manufactured by Kyowa Interface Science Co., Ltd .; CA-X type. Adopt advancing and receding contact angles measured by expanding and contracting.

[0038]

The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

Example 1 << Ink-repellent treatment of nozzle plate >> 1 part by weight of C ₈ F ₁₇ CH ₂ CH ₂ Si (OCH ₃ ) ₃ 10 parts by weight of Si (OC ₂ H ₅ ) ₄ 10 parts by weight of γ-glycidoxypropyltrimethoxy A liquid composed of 1 part by weight of silane, 38 parts by weight of methanol, 30 parts by weight of water, and 20 parts by weight of acetic acid was applied to a polyimide plate having a thickness of 120 μm (Ube Industries, Ltd .; Upilex) by a spin coating method.
μm thickness and air dried for 30 minutes.
Heat treatment was performed at 0 ° C. for 1 hour. The excimer laser is irradiated from the side where the ink repellent layer is not provided, and 360 DPI
Thus, 64 nozzle holes having a diameter of 40 μm were formed.
Furthermore, a circular mask covering the area of five times the nozzle diameter is applied around the center of the nozzle hole on the surface provided with the ink-repellent film to protect the area around the ejection port, and then irradiated with excimer laser to excite the ink-repellent ink. The film was removed to form a parent ink area.

<< Ink Composition >> (viscosity 7 cp at 25 ° C.) 5 parts by weight of disperse dye [C. I. Disperse Yellow] Dispersant: manufactured by Kao Corporation; 0.5 parts by weight of Demol C (formalin condensate of sodium creosote oil sulfonate) 20 parts by weight of glycerin 0.1 parts by weight of sodium 2- (2-ethylhexyl) sulfosuccinate Part urea 3.0 parts by weight water 71.4 parts by weight << Measurement of contact angle >> An ink-repellent layer was provided on the nozzle plate resin, and when measured with the above ink, θa was 97 °,
θr was 75 °. The contact angle of the surface from which the ink-repellent film was removed by irradiating a laser (the surface of the ink-repellent surface) was measured. As a result, θa was 25 ° and θr was 25 °.

<< Ejection Test >> A nozzle plate provided with an ink repellent processing section and a parent ink processing section and a comparative nozzle plate provided only with the ink repellent processing section but not provided with a parent ink processing section were attached to a head made of a piezoelectric element. Continuous ejection was performed at 0.2 kHz. During the discharge, the discharge was interrupted from time to time, and the surface of the nozzle plate was observed and wiped. The ejection amount was measured with a precision balance, and the average ejection amount per ink drop was determined. At the same time, the discharge state was observed with a tool microscope.

As a result, in the head using the nozzle plate of the present invention, the average discharge amount per ink droplet from all the nozzles was uniform at 65 ng, and all the nozzles discharged continuously for 10 hours in a stable manner. No bending in direction was seen. However, in the head using the comparative nozzle plate, the average ejection amount per ink drop varies from nozzle to nozzle,
It was 55 to 65 ng, and the ejection direction of some ink droplets was bent when ejected for several minutes, and the nozzle plate was stained with ink. After 10 minutes, the ejection of several nozzles stopped.

[0043]

According to the ink jet system of the present invention,
High-viscosity ink can be discharged stably at high speed, and a clear image can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating vibration of an ink meniscus.

FIG. 2 is a model diagram showing an effect of an ink pool on an ejection direction.

FIG. 3 is a diagram illustrating each contact angle.

FIG. 4 is a diagram showing a force acting on a droplet during movement.

FIG. 5 is a diagram showing a relationship between θr and the movement of a droplet.

FIG. 6 is a diagram showing an example of a relationship between a contact angle of a nozzle plate subjected to a water-repellent treatment with a silicone resin and an amount of an acrylic oligomer added to ink.

FIG. 7 is a model diagram showing the behavior of an ink droplet on a nozzle plate according to the present invention.

FIG. 8 is a view showing an example of a nozzle plate surface according to the present invention.

FIG. 9 is a model diagram showing measurement of a contact angle.

[Explanation of symbols]

 1 Nozzle hole (ink ejection port) 2 Ink repellent processing section 3 Ink-friendly processing section

Claims (1)

[Claims] 1. An ink jet printer in which the periphery of an ink discharge port on the surface of a nozzle plate of a head is subjected to an ink repellent treatment and the periphery thereof is treated with an ink-repellent ink, and the ink repellent is applied using an ink having a viscosity of 4 cp or more at 25 ° C. An image is formed by setting the advancing contact angle of the ink to the ink treated surface to 80 to 110 °, the receding contact angle to 40 ° or more, and the advancing contact angle and the receding contact angle of the ink to the parent ink treated surface to 30 ° or less. An image forming method of an ink jet system, characterized in that: