CN1782001A - Ink composition, printing method using the same and printed image obtained using the same, and ink set and ink head - Google Patents

Abstract

The object of the present invention is to provide an ink composition capable of obtaining a high-quality recorded image with excellent discharge stability when an inkjet recording method is used, a recording method using the composition, a recorded image, an ink set, and an inkjet head . The difference between the dynamic surface tension (mN/m) and the static surface tension (mN/m) of the ink composition (60) measured by the maximum bubble pressure method at a temperature of 24-26°C is 0-7 (mN/m). The ink composition is stored in the ink ejection tank (50) of the inkjet head (1), and the ink composition is supplied from the ink tank (50) to the ink cartridge (40) provided with the discharge port (31), and voltage is applied to the On the separator (12) made of piezoelectric material, pressure is applied from the separator (12) to the ink composition (60) stored in the ink tank (40), thereby discharging the ink composition ( 60) A liquid droplet that adheres to a recording material to record an image.

Description

Ink composition, recording method using same, and recorded image, ink set, and inkjet head

This application is a divisional application with the filing date of September 18, 2003, the application number of 03165009.0, and the title of "ink composition, recording method using it and recorded image, ink set and inkjet head".

technical field

The present invention relates to an ink composition suitable for an inkjet recording method, a recording method and a recorded image using the ink composition, an ink set and an ink head.

Background technique

The inkjet recording method is a method of releasing and flying droplets of an ink composition (hereinafter also simply referred to as "ink") by kinetic energy or thermal energy, and making such droplets adhere to a recording material such as paper to record an image. Methods.

Heretofore, the characteristics of the ink used in the inkjet recording method (hereinafter also referred to as "inkjet ink") can be expressed by physical properties such as surface tension or viscosity. Attempts have been made to adjust the drying properties of inks or to improve the quality of formed images by limiting these physical properties.

For example, there has been proposed an inkjet recording method which defines an ink droplet by the product of a Weber number including surface tension as a parameter, and a Reynolds number including viscosity as a parameter. Keeping the product of the Weber number and the Reynolds number within a certain range can achieve high-quality images (see Japanese Examined Patent Publication JP-B2 2968010). An inkjet recording method using an ink of a specific range of surface tension has also been proposed (see Japanese Examined Patent Publication JP-B2 63-65034 (1988)).

The surface tension used in the technology described in JP-B2 2968010 and JP-B2 63-65034 is the surface tension when the liquid surface reaches an equilibrium state, that is, the static surface tension. The surface tension commonly used as an index of ink properties for inkjet is also a static surface tension (e.g. Akio Kinoshita et al., "Tokushu Kinou Inki no Jissai Gijutu (Practical Techniques for Inks with Special Functions)", Popular Edition 1st Edition, CMC Co. , Nov. 15, 1999, pp. 6-7). In this way, the static surface tension among the surface tensions is often used to express the characteristics of the inkjet ink.

However, it is difficult to fully express the characteristics of inks only by static surface tension.

In an inkjet recording apparatus for recording an image by the inkjet recording method, the ink cartridge of the inkjet head is filled with ink, ink droplets are discharged from the discharge port at the front end of the ink cartridge in a continuous manner, adhere to a recording material, and an image is recorded. When the ink is continuously discharged, at the same time as the ink droplets are discharged, a new surface of the ink, that is, a new meniscus is formed at the discharge port, and, for example, when the discharge port starts to form a new surface, immediately before discharge, at the moment of discharge The surface tension of the ink is different when the ink droplet lands on the recording material, when it flies out, or when the ink droplet permeates into the recording material such as paper. For example, the surface tension of the slow-moving state when the discharge port starts to form a new surface or ink droplets penetrate into the recording material such as paper, and the surface tension of the fast-moving state at the time of discharge are constantly changing. Here, the slowly moving state can be regarded as a static state, and it is considered that the surface tension changes from a static state to a dynamic state every now and then. Therefore, in order to fully express the characteristics of inkjet inks, it is necessary to consider the dynamic surface tension, which is the surface tension during the process of the liquid surface reaching an equilibrium state.

The importance of dynamic surface tension has been described in various references. For example, Schwartz, J. evaluated the static surface tension and dynamic surface tension of aqueous coatings, pointed out that dynamic surface tension is an important factor for aqueous coatings to form coating films, and low dynamic surface tensions can effectively form uniform and excellent coating films (see "Importance of Low Dynamic Surface Tension in Aqueous Coatings").

Medina, S.W. and Sutovich, M.N. discuss the importance of dynamic surface tension in high-speed printing, and propose that static surface tension is the surface tension when the liquid surface reaches an equilibrium state, which is an effective representation of the performance of ink in a slow moving state (such as ink droplets penetrating paper, etc.), but not an index that effectively represents the performance of ink in a fast-moving state (such as when printing at high speed). On the other hand, they suggested that the dynamic surface tension means the ability of the surfactant contained in the ink to continuously generate a new ink surface toward the discharge port, or to migrate to the interface between the ink droplet continuously attached to the recording material and the recording material index of. That is, the surface active agent reduces its surface tension by being adsorbed on the newly formed surface of the ink, or at the interface between the ink droplet and the recording material, and therefore, the The higher the migration ability of the interface, the higher the effect of reducing the surface tension of the ink in the fast moving state, thus, the dynamic surface tension of the ink is reduced (see "Surfactant used to prepare VOC Comoliant water-based ink").

Also proposed are an ink composition suitable for an inkjet recording method, and a recording method using the ink composition, which has a definite relationship between dynamic surface tension and viscosity. This technology shows that in the range where the ink composition satisfies the condition of [dynamic surface tension (dyne/cm) at the time of life 0 milliseconds] + [viscosity (cP)] = 42 to 49, satisfactory printing characteristics can be obtained (see Japanese Examined Patent Publication JP-B2 2516218).

But, in the technology that JP-B2 2516218 records, the conditional equation that adds viscosity value with dynamic surface tension determines dynamic surface tension, but because the unit of dynamic surface tension and viscosity value is different, promptly dimension is different, so, like this The value of the conditional equation is meaningless.

The technique also showed that surfactants do not contribute to the reduction of dynamic surface tension. However, it is known that surfactants generally significantly contribute to the wettability of inkjet inks on the inner wall of ink cartridges or the performance of inks on recording materials, and are not only main components of inks but also important factors for controlling dynamic surface tension. For example, Schwartz, J., in the aforementioned article "The Importance of Low Dynamic Surface Tension in Aqueous Coatings," uses certain surfactants to alter the static and dynamic surface tensions and evaluates their effect on coating film formation, stating that The reduction of dynamic surface tension can effectively reduce the shrinkage of the coating film, the occurrence of holes in the coating film and the trapped air bubbles in it.

Additionally, this technique only determines dynamic surface tension, not static surface tension. As described above, in the inkjet recording method, the surface tension of the ink changes from dynamic to static every moment, and therefore, it is necessary to sufficiently represent the dynamic surface tension and the static surface tension of the ink for inkjet.

In addition, this technique only determined the dynamic surface tension of the fast-moving state, especially the dynamic surface tension of 0 ms, but not the slow-moving state. As described above, in the inkjet recording method, the surface tension of the ink often changes between the surface tension of the slowly moving state and the surface tension of the fast moving state, so the dynamic surface tension of the fast moving state and the dynamic surface tension of the slowly moving state Both tension and tension are important for fully expressing the characteristics of the inkjet ink.

Contents of the invention

An object of the present invention is to provide a composition having excellent discharge stability and providing high-quality recorded images when used in an inkjet recording method by determining the relationship between dynamic surface tension and static surface tension, using the ink A recording method and a recording image of the composition, and an ink set and an ink head.

Another object of the present invention is to provide an inkjet film having excellent discharge stability and providing high quality when used in an inkjet recording method by determining the relationship between the dynamic surface tension of a fast-moving state and that of a slow-moving state. An ink composition for recording images, a recording method and image recording using the composition, and an ink set and an inkjet head.

The invention provides an ink composition, which contains at least one colorant and a medium, the dynamic surface tension measured by the maximum bubble pressure method (maximum bubble pressure method) at a temperature of 24 to 26 ° C and the dynamic surface tension at a temperature of 24 to 26 ° C The static surface tension measured below satisfies the relationship of the following formula (1):

0≤[Dynamic surface tension (mN/m)]-[Static surface tension (mN/m)]≤7(mN/m)

(1)

According to the present invention, the ink composition is designed to keep the difference between the dynamic surface tension and the static surface tension measured at a temperature range of 24-26° C. within a certain range. In the inkjet recording device for recording images using this inkjet recording method, when the ink composition droplets are continuously discharged, the discharge port provided at the front end of the ink cartridge in the inkjet head continuously generates a new surface of the ink composition, so that the ink composition Object movement is fast, and dynamic surface tension has a large influence. On the other hand, in the ink cartridge (inkchamber), after the ink composition is discharged, the reduced ink composition can be replenished from the ink tank by capillary action, and the replenishment volume corresponds to the reduced volume due to discharge, so the ink composition moves slowly. , can be regarded as static, thus the static surface tension has a great influence. That is, since both the dynamic surface tension and the static surface tension exert an influence on discharge, it is necessary to consider the balance between the dynamic surface tension and the static surface tension in order to achieve stable discharge of ink composition droplets. In addition, when an image is recorded by the ink composition droplet attaching to the recording material, the ink composition also shows that the droplet moves fast when it lands on the recording material, but gradually slows down thereafter, and when the recording material is absorbent When recording the material, the ink composition penetrates into the recording material. That is, the surface tension may change from dynamic to static, and if the difference between the dynamic surface tension and the static surface tension is large, it takes a long time for the ink composition on the recording material to dry, resulting in blotting. Therefore, as described above, by keeping the difference between the dynamic surface tension and the static surface tension within a certain range, if the inkjet recording method is used, an ink composition can be obtained which exhibits excellent ejection stability and excellent recording performance. Printing is suppressed on materials and provides high quality recorded images.

In addition, in the present invention, the bubble frequency for measuring the dynamic surface tension is preferably 0.5 to 35 Hz.

According to the present invention, the ink composition is designed so that the difference between the dynamic surface tension and the static surface tension measured at the bubble frequency of 0.5-35 Hz is within a certain range. Thereby, an ink composition can be obtained which, when used in an inkjet recording method, exhibits excellent discharge stability and suppresses the occurrence of printing on a recording material, whereby a high-quality recorded image can be obtained.

Furthermore, in the present invention, the preferred static surface tension is 20 to 50 mN/m.

According to the invention, the static surface tension is 20-50 mN/m. A static surface tension of less than 20 mN/m results in excessively high permeability so that the ink composition spreads laterally on the absorbent recording material and the outline of the formed image appears unclear. In addition, a static surface tension exceeding 50 mN/m also reduces the permeability on the recording material, thereby reducing the dryness. In addition, the ink composition exhibits reduced wettability on the inner wall of the ink cartridge, hindering the supply of the ink composition to the ink cartridge, so that the ink composition cannot fill the ink cartridge smoothly and cannot be stably discharged in the form of droplets. Therefore, as mentioned above, the static surface tension is kept at 20-50mN/m, and the difference between the measured dynamic surface tension and the static surface tension is kept within a certain range, and an ink composition can be obtained. METHOD When the composition is used, it exhibits excellent discharge stability and suppresses the occurrence of printing on a recording material, thereby obtaining a high-quality recorded image.

Furthermore, in the present invention, it is preferable that water is included in the ink composition as a medium.

According to the present invention, since water is contained as a medium in the ink composition, it is possible to suppress the occurrence of printing on the recording material and improve the drying performance.

Furthermore, in the present invention, it is preferable that the ink composition further includes a surfactant.

According to the present invention, since the ink composition further contains a surfactant, it is easy to control the dynamic surface tension and the static surface tension.

In addition, in the present invention, preferred media include glycol ethers and/or polyols.

According to the present invention, since the medium contains glycol ethers and/or polyols including low vapor pressure, a wetting effect can be obtained, thereby improving discharge stability.

In addition, in the present invention, preferred colorants include dyes.

According to the present invention, since the colorant includes a dye, clogging of the discharge port can be suppressed, thereby improving discharge stability.

In addition, in the present invention, preferable colorants include pigments.

According to the present invention, since the colorant includes a pigment, it is possible to obtain a recorded image having excellent light resistance and water resistance.

In addition, in the present invention, preferred colorants include pigments having hydrophilic groups.

According to the present invention, since the colorant includes a pigment having a hydrophilic group, a recorded image having excellent light resistance and water resistance can be obtained. Also, since the pigment has a hydrophilic group, it can exist in a stable dispersed state in the aqueous ink composition. Therefore, the occurrence of clogging can be suppressed, and an ink composition capable of obtaining a recorded image having excellent light resistance and water resistance without deteriorating discharge stability can be obtained.

In addition, in the present invention, preferred surfactants include nonionic surfactants.

According to the present invention, since the surfactant includes a nonionic surfactant which is not easily affected by the coexisting electrolyte, the difference between the dynamic surface tension and the static surface tension can be kept within a certain range regardless of whether electrolyte is added to the ink composition.

In addition, in the present invention, it is preferable to contain a surfactant having a critical micelle concentration or higher.

According to the present invention, the concentration of the surfactant is at or above the critical micelle concentration. The surface tension of a surfactant-containing solution decreases as the surfactant increases up to the critical micelle concentration, but remains essentially constant at or above the critical micelle concentration. Therefore, as mentioned above, due to the presence of surfactants at or above the critical micelle concentration, it is possible to make full use of the effect of surfactants and control the values of dynamic surface tension and static surface tension by surfactants basically remains unchanged, an ink composition with uniform properties can be obtained.

In addition, in the present invention, it is preferable that the pigment includes at least one of C.I. Pigment Blue 15:3 and C.I. Pigment Blue 15:4.

According to the present invention, since the pigment includes at least one of C.I. Pigment Blue 15:3 and C.I. Pigment Blue 15:4, an ink combination capable of obtaining a recorded image excellent in cyan color developability can be obtained. thing.

In addition, in the present invention, it is preferable that the pigment includes at least one pigment selected from C.I. Pigment Red 122, C.I. Pigment Red 209, and C.I. Pigment Violet 19.

According to the present invention, since the pigment includes at least one pigment selected from C.I. Pigment Red 122, C.I. Pigment Red 209, and C.I. Pigment Violet 19, an ink composition capable of producing a high-quality magenta recorded image can be obtained.

In addition, in the present invention, it is preferable that the pigment includes at least one pigment selected from C.I. Pigment Yellow 74, C.I. Pigment Yellow 138, C.I. Pigment Yellow 150, and C.I. Pigment Yellow 180.

According to the present invention, since the pigment includes at least one pigment selected from the group consisting of C.I. Pigment Yellow 74, C.I. Pigment Yellow 138, C.I. Pigment Yellow 150, and C.I. Pigment Yellow 180, an ink composition capable of producing high-quality yellow recorded images can be obtained .

The present invention also provides a recording method, which is a recording method for recording an image by attaching an ink composition to a recording material, wherein the ink composition employs any one of the above-mentioned ink compositions of the present invention.

According to the present invention, any one of the ink compositions of the present invention described above is used in a recording method for recording an image by attaching the ink composition to a recording material, thereby providing a stable high-quality recorded image.

The present invention also provides a recording method for recording an image, the method comprising: pressurizing the ink composition, discharging the ink composition droplets, and making the droplets adhere to the recording material, wherein the ink composition is the above-mentioned Any ink composition of the present invention.

According to the present invention, since the ink composition is pressurized, the ink composition droplets are discharged, and the droplets adhere to the recording material to record an image, that is, in the inkjet recording method, any one of the above-mentioned inventions ink composition, thereby enabling stable discharge and providing stable high-quality recorded images.

In addition, in the present invention, the ink composition uses at least one of the following ink compositions: the ink composition wherein the pigment includes at least one of C.I. Pigment Blue 15:3 and C.I. Pigment Blue 15:4; wherein the pigment includes selected The ink composition of at least one pigment from C.I. Pigment Red 122, C.I. Pigment Red 209 and C.I. Pigment Violet 19, and wherein the pigment comprises a pigment selected from C.I. Pigment Yellow 74, C.I Pigment Yellow 138, C.I. Pigment Yellow 150 and C.I. Pigment Yellow 180 Ink composition of at least one pigment.

According to the present invention, since the ink composition uses at least one ink composition capable of obtaining a recorded image excellent in cyan color development, an ink composition capable of obtaining a recorded image excellent in magenta color development, and an ink composition capable of obtaining It is an ink composition for recording images with excellent yellow color development properties. Therefore, by superimposing the above three ink compositions, it is possible to realize a high-density black recording image.

The present invention also provides a recorded image recorded by the above recording method.

According to the present invention, since an image is recorded using the recording method, a high-quality recorded image can be obtained.

The present invention also provides a kind of ink set (ink set), it comprises:

An ink composition, wherein the pigment comprises at least one pigment in C.I Pigment Blue 15:3 and C.I. Pigment Blue 15:4;

An ink composition, wherein the pigment comprises at least one pigment selected from C.I. Pigment Red 122, C.I. Pigment Red 209 and C.I. Pigment Violet 19; and

An ink composition, wherein the pigment includes at least one pigment selected from C.I. Pigment Yellow 74, C.I. Pigment Yellow 138, C.I. Pigment Yellow 150, and C.I. Pigment Yellow 180.

According to the present invention, since the ink set includes an ink composition capable of obtaining a recorded image excellent in cyan color-developing property; an ink composition excellent in magenta color-developing property for recording an image; and an ink composition excellent in yellow color-developing property The ink composition of the image, therefore, by superimposing the above three ink compositions, a high-density black recorded image can be realized.

The present invention also provides an inkjet head (ink head), comprising:

An ink tank (ink tank) for storing any of the above-mentioned ink compositions of the present invention;

Ink cartridge (ink chamber) has an outlet for discharging ink composition droplets and receives ink composition from the ink tank;

a piezoelectric element deformable in response to the application of a voltage, provided in at least a portion of the ink cartridge, thereby applying pressure to an ink composition contained in the ink cartridge; and

The electrodes that apply voltage to the piezoelectric element.

According to the present invention, the inkjet head stores any ink composition of the present invention through the ink tank; the ink composition provided by the ink tank is contained with the ink cartridge, and the ink cartridge has a discharge port for discharging ink composition droplets; applying a voltage; and applying pressure to the ink composition contained in the ink cartridge using a piezoelectric element that strains in response to the applied voltage, the piezoelectric element being provided in at least a portion of the ink cartridge. Accordingly, it is possible to obtain a piezoelectric inkjet head capable of discharging ink composition droplets from discharge ports in response to a voltage applied to the piezoelectric element. Also, since the ink tank stores any one of the ink compositions of the present invention, ink composition droplets can be stably discharged from the discharge port. By using such an inkjet head, a piezoelectric inkjet recording device with high reliability can be realized.

The present invention also provides an inkjet head, comprising:

An ink tank for storing any one of the above-mentioned ink compositions of the present invention;

an ink cartridge having an outlet for discharging droplets of ink composition and receiving ink composition from an ink reservoir;

a heat generating member provided in at least a portion of the ink cartridge, adapted to heat the ink composition in the ink cartridge to generate air bubbles therein, thereby applying pressure to the ink composition; and

An electrode provided for applying voltage to a heating element.

According to the present invention, the inkjet head stores any ink composition of the present invention through the ink tank; the ink cartridge is equipped with the ink composition from the ink tank, and the ink cartridge has a discharge port for discharging ink composition droplets; applying a voltage; and heating the ink composition in the ink cartridge using a heating element provided in at least a portion of the ink cartridge to generate air bubbles, thereby applying pressure to the ink composition. Accordingly, there can be obtained a thermal ink-jet type ink-jet head capable of discharging liquid droplets of an ink composition from a discharge port in response to a voltage applied to a heat-generating element. Also, since the ink tank stores any one of the ink compositions of the present invention, ink composition droplets can be stably discharged from the discharge port. Such an inkjet head can realize a thermal inkjet type inkjet recording device with high reliability.

The present invention also provides a recorded image in which ink composition droplets are discharged through a piezoelectric inkjet head and adhered to a recording material for recording.

According to the present invention, since the recorded image is formed by the ink composition droplets being discharged by the piezoelectric inkjet head and attached to the recording material, the inkjet head can stably discharge the ink composition droplets as described above, therefore, it is possible Stably obtain high-quality recorded images.

The present invention also provides a recorded image in which droplets of the ink composition are discharged through a thermal inkjet type inkjet head and adhered to a recording material.

According to the present invention, since the recorded image is formed by the ink composition droplets being discharged from the thermal inkjet type inkjet head and attached to the recording material, the inkjet head can stably discharge the ink composition droplets as described above, so it can be stabilized. to obtain high-quality recorded images.

The invention provides an ink composition comprising at least one colorant and a medium, wherein:

Among the dynamic _surface tensions measured by the maximum bubble pressure method _at a temperature of 24-26°C, the difference d( =σ ₁₀ -σ ₁ ) satisfy the following formula (2):

0mN/m≤d≤7mN/m         (2)

According to the present invention, the ink composition is designed to be the dynamic surface tension (σ ₁₀ ) when the bubble frequency is 10 Hz and the dynamic surface tension when the bubble frequency is 1 Hz in the dynamic surface tension measured by the maximum bubble pressure method at a temperature of 24 to 26 ° C. The difference d (=σ ₁₀ −σ ₁ ) of the tension (σ ₁ ) is within a certain range. In an inkjet recording device for recording images by an inkjet recording method, when ink composition droplets are continuously discharged, a new surface of the ink composition is continuously generated at the discharge port at the front end of the ink cartridge in the inkjet head, so that the ink composition moves rapidly , and has a large influence on the high-frequency dynamic surface tension of about 10 Hz, which corresponds to the dynamic surface tension of the fast-moving state. On the other hand, in the ink cartridge, after the ink composition is discharged, the ink composition is replenished from the ink tank by capillary action, the volume of which corresponds to the reduced amount of the discharge, so the ink composition moves slowly, for low frequency dynamics of about 1 Hz Surface tension has a large influence, the dynamic surface tension corresponding to the dynamic surface tension of the slowly moving state. That is, when discharging, due to the influence of both high-frequency dynamic surface tension and low-frequency dynamic surface tension, in order to realize stable discharge of ink composition droplets, it is necessary to consider high-frequency dynamic surface tension and low-frequency dynamic surface tension. Balance of dynamic surface tension. Also, when the droplet is attached to the recording material to record an image, the ink composition shows a rapid movement of the droplet on the recording material at the moment, but then gradually slows down. When the recording material is an absorbent recording material, the ink The composition slowly penetrates into the recording material. That is, the dynamic surface tension of the ink composition changes from the dynamic surface tension of the fast-moving state to the dynamic surface tension of the slow-moving state, and when the difference between the high-frequency dynamic surface tension and the low-frequency dynamic surface tension is large, the recording material The ink composition on the surface takes longer to dry, resulting in blots. Excess penetration can also cause rear penetration. Therefore, as mentioned above, the difference d (=σ ₁₀ -σ ₁ ) between the dynamic surface tension (σ ₁₀ ) with a bubble frequency of 10 Hz and the dynamic surface tension (σ ₁ ) with a bubble frequency of 1 Hz is designed within the above-mentioned certain range, Thereby, when the ink composition is used in an inkjet recording method, it is possible to obtain an ink composition which is excellent in discharge stability, and can suppress imprinting on a recording material, thereby providing a high-quality recorded image.

In addition, in the present invention, it is preferable that the dynamic surface tension (σ ₁₀ ) at a bubble frequency of 10 Hz and the dynamic surface tension (σ ₁ ) at a bubble frequency of 1 Hz are in the range of 20 to 70 mN/m.

According to the present invention, the dynamic surface tension (σ ₁₀ ) when the bubble frequency is 10 Hz and the dynamic surface tension (σ ₁ ) when the bubble frequency is 1 Hz are in the range of 20-70 mN/m. When σ ₁₀ and σ ₁ are less than 20 mN/m, the permeability to the absorbent recording material becomes too high, so that the ink composition attached to the absorbent recording material diffuses from the drop point to the surrounding area, thereby forming an image outline Not clear. When σ ₁₀ and σ ₁ exceed 70 mN/m, the penetrating power of the absorbent recording material becomes too low, so that the drying property on the absorbent recording material decreases. The ink composition also showed poor wettability with the inner wall of the ink tank, hindering the supply of the ink composition to the ink tank, so that the ink composition was difficult to fill the ink tank smoothly and could not be stably discharged in the form of droplets. In addition, it is difficult to form a new generation surface of the ink composition having a desired shape at the discharge port at the front end of the ink cartridge, that is, it is difficult to control the meniscus, so it is impossible to discharge the ink composition droplets continuously at high speed. Therefore, the dynamic surface tension (σ ₁₀ ) when the bubble frequency is 10Hz and the dynamic surface tension (σ ₁ ) when the bubble frequency is 1Hz are designed to be 20-70mN/m, and the difference between σ ₁₀ and σ ₁ d(=σ ₁₀ -σ ₁ ) Within the above-mentioned certain range, when the ink composition is used in an inkjet recording method, an ink composition excellent in discharge stability can be obtained, and it can suppress imprinting on a recording material, thereby providing high quality recorded image.

In addition, in the present invention, it is preferable that the ink composition further includes a surfactant.

According to the present invention, since the ink composition also includes a surfactant, the dynamic surface tension of the ink composition can be easily controlled, including the dynamic surface tension (σ ₁₀ ) with a bubble frequency of 10 Hz and the dynamic surface tension (σ 10 ) with a bubble frequency of 1 Hz. Tension (σ ₁ ).

In addition, in the present invention, it is preferable that the medium contains water.

According to the present invention, since the medium contains water, it is possible to suppress the occurrence of marks on the absorbent recording material and improve the drying property.

In addition, in the present invention, it is preferable that the medium contains at least one of glycol ethers and polyols.

According to the present invention, since the medium contains at least one of low vapor pressure glycol ethers and polyols, a wetting effect can be obtained and discharge stability can be improved.

In addition, in the present invention, it is preferable that the colorant includes a dye.

According to the present invention, since the colorant includes a dye, the occurrence of nozzle clogging can be suppressed, improving discharge stability.

In addition, in the present invention, it is preferable that the colorant includes a pigment.

According to the present invention, since the colorant includes a pigment, a recorded image having excellent light resistance and water resistance can be obtained.

In addition, in the present invention, it is preferable that the colorant includes a pigment having a hydrophilic group.

According to the invention, colorants include pigments having hydrophilic groups. Thereby, recorded images having excellent light resistance and water resistance can be obtained. Also since the pigment has a hydrophilic group, it can be stably dispersed in an aqueous ink composition. Accordingly, the occurrence of nozzle clogging can be suppressed, so an ink composition for recording images having excellent light resistance and water resistance is obtained without reducing discharge stability.

In addition, in the present invention, it is preferable that the surfactant includes a nonionic surfactant.

According to the present invention, since the surfactant includes a nonionic surfactant that is hardly affected by the coexisting electrolyte, the dynamic surface tension (σ ₁₀ ) at a bubble frequency of 10 Hz and the dynamic surface tension (σ ₁ ) at a bubble frequency of 1 Hz are The difference d (=σ ₁₀ −σ ₁ ) of can be kept within a certain range regardless of whether electrolyte is added to the ink composition.

In addition, in the present invention, it is preferable to contain a surfactant having a critical micelle concentration or higher.

According to the invention, a surfactant is present at or above a critical micelle concentration. The surface tension of a solution containing a surfactant decreases as the surfactant increases up to the critical micelle concentration, but remains essentially constant at or above the critical micelle concentration. Therefore, due to the presence of surfactants at or above the critical micelle concentration, as described above, it is possible to take full advantage of the effect of the surfactant and use it to control the dynamic surface with a bubble frequency of 10 Hz. The tension (σ ₁₀ ) and the dynamic surface tension (σ ₁ ) at a bubble frequency of 1 Hz are kept substantially constant so that an ink composition with uniform properties can be obtained.

In addition, in the present invention, it is preferable that the pigment includes at least one of C.I. Pigment Blue 15:3 and C.I. Pigment Blue 15:4.

According to the present invention, since the pigment includes at least one of C.I. Pigment Blue 15:3 and C.I. Pigment Blue 15:4, an ink composition for recording images excellent in cyan color development can be obtained.

In addition, in the present invention, it is preferable that the pigment includes at least one pigment selected from C.I. Pigment Red 122, C.I. Pigment Red 209, and C.I. Pigment Violet 19.

According to the present invention, since the pigment includes at least one pigment selected from C.I. Pigment Red 122, C.I. Pigment Red 209, and C.I. Pigment Violet 19, an ink composition for recording images excellent in magenta color development can be obtained.

In addition, in the present invention, it is preferable that the pigment includes at least one pigment selected from C.I. Pigment Yellow 74, C.I. Pigment Yellow 138, C.I. Pigment Yellow 150, and C.I. Pigment Yellow 180.

According to the present invention, since the pigment includes at least one pigment selected from the group consisting of C.I. Pigment Yellow 74, C.I. Pigment Yellow 138, C.I. Pigment Yellow 150, and C.I. Pigment Yellow 180, a recorded image excellent in yellow color development can be obtained. ink composition.

In addition, in the present invention, it is preferable that the pigment includes carbon black.

According to the present invention, since the pigment includes carbon black, an ink composition for recording an image excellent in black color developability can be obtained.

The present invention also provides a recording method for recording an image by attaching an ink composition to a recording material, the ink composition of the method being any one of the above-mentioned ink compositions of the present invention.

According to the present invention, the recording method for recording an image by attaching an ink composition to a recording material uses any one of the above-mentioned ink compositions of the present invention, thereby stably providing a high-quality recorded image.

The present invention also provides a recording method for recording an image by applying pressure to the ink composition to discharge droplets of the ink composition and attaching the droplets to a recording material to record an image, wherein the ink combination used The substance is any one of the above-mentioned ink compositions of the present invention.

According to the present invention, a recording method for recording an image by applying pressure to an ink composition to discharge droplets of the ink composition and attach the droplets to a recording material, that is, an inkjet recording method, employs any of the ink compositions of the present invention described above. One, thereby enabling stable discharge and providing high-quality recorded images.

In addition, in the present invention, it is preferred that the ink composition uses at least one of the following ink compositions: an ink combination in which the pigment includes at least one of C.I. Pigment Blue 15:3 and C.I. Pigment Blue 15:4 Pigment Red 122, C.I. Pigment Red 209, and C.I. Pigment Violet 19, wherein the pigment includes at least one pigment selected from C.I. Pigment Yellow 74, C.I. Pigment Ink composition of Yellow 138, C.I. Pigment Yellow 150 and C.I. Pigment Yellow 180 pigments.

According to the present invention, the ink composition uses at least one of an ink composition capable of obtaining a recorded image excellent in cyan color development, an ink composition excellent in magenta color development in a recorded image, and an ink composition capable of obtaining a recorded image excellent in yellow color development. ink composition. Therefore, by stacking the above three ink compositions, a high-density black recorded image can be realized. Therefore, various colors can be expressed using the above-mentioned three ink compositions, so that a color recorded image excellent in color developability can be provided.

In addition, in the present invention, the ink composition uses at least one of the following ink compositions: the ink composition wherein the pigment includes at least one of C.I. Pigment Blue 15:3 and C.I. Pigment Blue 15:4, wherein the Pigment Red 122, C.I. Pigment Red 209 and C.I. Pigment Violet 19, wherein the pigment includes at least one pigment selected from C.I. Pigment Yellow 74, C.I. Pigment Yellow 138, C.I. An ink composition of pigments of Pigment Yellow 150 and C.I Pigment Yellow 180, and an ink composition in which the pigment includes carbon black.

According to the present invention, the ink composition uses at least one of an ink composition capable of forming a high-quality cyan recorded image, an ink composition capable of forming a high-quality magenta recorded image, an ink composition capable of forming a high-quality yellow recorded image, and an ink composition capable of forming a high-quality Ink composition for high quality black recorded images. Therefore, by superimposing the three ink compositions of an ink composition capable of producing a high-quality cyan recorded image, an ink composition capable of producing a high-quality magenta recorded image, and an ink composition capable of producing a high-quality yellow recorded image, a high-density ink can be realized. The image is recorded in black. Therefore, with the 4 ink compositions in which an ink composition capable of forming a high-quality black recorded image is added to the above 3 ink compositions, various colors can be represented, thereby providing a color recorded image with excellent color generation.

The present invention also provides a recorded image recorded by the above recording method.

According to the present invention, since an image is recorded by this recording method, a high-quality recorded image can be obtained.

The present invention also provides a kind of ink set, it comprises:

An ink composition, wherein said pigment comprises at least one of C.I. Pigment Blue 15:3 and C.I. Pigment Blue 15:4;

An ink composition, wherein the pigment comprises at least one pigment selected from C.I. Pigment Red 122, C.I. Pigment Red 209 and C.I. Pigment Violet 19; and

An ink composition, wherein the pigment includes at least one pigment selected from the group consisting of C.I. Pigment Yellow 74, C.I. Pigment Yellow 138, C.I. Pigment Yellow 150, and C.I. Pigment Yellow 180.

According to the present invention, the ink set includes an ink composition capable of forming a high-quality cyan recorded image, an ink composition capable of forming a high-quality magenta recorded image, and an ink composition capable of forming a high-quality yellow recorded image. Therefore, a high-density black recorded image can be realized by superimposing the above three ink compositions. That is, the ink set containing the above three kinds of ink compositions was excellent in color balance. Therefore, by using an ink set including the above three ink compositions, it is possible to express various colors, and thus it is possible to provide a color recorded image in which high-quality colors are formed.

The present invention also provides a kind of ink set, it comprises:

An ink composition, wherein said pigment comprises at least one pigment in C.I. Pigment Blue 15:3 and C.I. Pigment Blue 15:4;

An ink composition, wherein the pigment comprises at least one pigment selected from C.I. Pigment Red 122, C.I. Pigment Red 209 and C.I. Pigment Violet 19;

An ink composition, wherein the pigment comprises at least one pigment selected from C.I. Pigment Yellow 74, C.I. Pigment Yellow 138, C.I. Pigment Yellow 150, and C.I. Pigment Yellow 180; and

An ink composition wherein the pigment includes carbon black.

According to the present invention, the ink set includes an ink composition capable of forming a high-quality cyan recorded image, an ink composition capable of forming a high-quality magenta recorded image, an ink composition capable of forming a high-quality yellow recorded image, and an ink composition capable of forming a high-quality recorded image in yellow. Ink composition that produces high-quality black recorded images. Therefore, high density can be achieved by superimposing the above three ink compositions: the ink composition capable of producing high-quality cyan recorded images, the ink composition capable of producing high-quality magenta recorded images, and the ink composition capable of producing high-quality yellow recorded images. black record image. Therefore, the color balance of the ink set including the above three compositions was excellent. Therefore, an ink set comprising four ink compositions in which an ink composition capable of producing a high-quality black recorded image is added to the above three ink compositions can express various colors, thereby providing a color recorded image excellent in color development.

The present invention also provides a kind of inkjet head, it comprises:

An ink tank for storing any of the above-mentioned ink compositions of the present invention;

an ink cartridge having an outlet for ejecting droplets of the ink composition and receiving the ink composition from the ink tank;

a piezoelectric element deformable in response to an applied voltage, the piezoelectric element being provided in at least a portion of the ink cartridge so as to apply pressure to the ink composition in the ink cartridge; and

The electrodes that apply voltage to the piezoelectric element.

According to the present invention, the inkjet head stores any ink composition of the present invention through the ink tank, and holds the ink composition supplied from the ink tank through an ink cartridge having a droplet discharge port for discharging the ink composition; A voltage is applied to the element; pressure is applied to the ink composition in the ink cartridge through the piezoelectric element, which deforms according to the applied voltage and is provided in at least a part of the ink cartridge. Thus, there is obtained a piezoelectric inkjet head that discharges ink composition droplets from discharge ports in accordance with the voltage applied to the piezoelectric element. Also, since the ink tank stores any one of the ink compositions of the present invention, droplets of the ink composition can be stably discharged from the discharge port. By using such an inkjet head, a piezoelectric inkjet recording device with high reliability can be realized.

The present invention also provides a kind of inkjet head, it comprises:

An ink tank for storing any one of the above-mentioned ink compositions of the present invention;

an ink cartridge having an outlet for discharging droplets of the ink composition and receiving the ink composition from the ink tank;

a heat generating element provided in at least a portion of the ink cartridge, the element being adapted to heat the ink composition in the ink cartridge to generate air bubbles therein to apply pressure to the ink composition; and

An electrode equipped to apply voltage to a heating element.

According to the present invention, the inkjet head stores any one of the ink composition of the present invention through the ink tank; holds the ink composition supplied from the ink tank through an ink cartridge having a discharge port for discharging ink composition droplets; The element applies a voltage; the ink composition in the ink cartridge is heated by a heating element provided in at least a part of the ink cartridge to generate air bubbles, thereby applying pressure to the ink composition. Thus, a thermal inkjet type inkjet head is obtained which discharges liquid droplets of the ink composition from the discharge port in accordance with the voltage applied to the heat generating element. Also, since the ink tank stores any one of the ink compositions of the present invention, droplets of the ink composition can be stably discharged from the discharge port. If such an inkjet head is used, a highly reliable thermal inkjet type inkjet recording device can be realized.

The present invention also provides a recorded image recorded by attaching droplets of the ink composition discharged through a piezoelectric inkjet head to a recording material.

According to the present invention, since the ink composition droplets discharged by the piezoelectric inkjet head adhere to the recording material to form a recorded image, the piezoelectric inkjet head can stably discharge the ink composition droplets as described above, thereby enabling Stably obtain high-quality recorded images.

The present invention also provides a recorded image in which droplets of the ink composition discharged from a thermal inkjet type inkjet head adhere to a recording material.

According to the present invention, since the ink composition droplets discharged from the thermal inkjet inkjet head adhere to the recording material to form a recorded image, the thermal inkjet inkjet head can stably discharge the ink composition droplets as described above, Thus, a high-quality recorded image can be stably obtained.

Description of drawings

The objects, features and advantages of the present invention will be more clearly explained from the following detailed description and accompanying drawings.

1 is an exploded perspective view of a simplified structure of an inkjet head according to a second embodiment of the present invention;

Fig. 2 is a partially enlarged view of the top plate structure of the inkjet head shown in Fig. 1;

Fig. 3 is a cross-sectional view of the inkjet head shown in Fig. 1 viewed from the extending direction of the ink cartridge;

Figure 4 is an exploded perspective view of a simplified structure of an inkjet head according to a third embodiment of the present invention;

Fig. 5 is a partial plan view of the structure of the inkjet head shown in Fig. 4; and

Fig. 6 is a schematic cross-sectional view of a state in which ink composition droplets 61 are discharged from the ink cartridge.

Detailed ways

Preferred embodiments of the present invention will be described in detail with reference to the following drawings.

The ink composition of the first embodiment of the present invention includes at least one colorant and an organic solvent as a medium, and the dynamic surface tension measured by the maximum bubble pressure method at a temperature of 24 to 26°C, and at a temperature of 24 to 26°C The static surface tension measured below satisfies the relationship of the following formula (1):

0≤[Dynamic Surface Tension (mN/m)]-[Static Surface Tension (mN/m)]≤7(mN/m) (1)

The maximum bubble pressure method used to measure the dynamic surface tension will be described below.

The maximum bubble pressure method is a method for measuring surface tension. This method is to insert a thin tube into the liquid, and generate bubbles from the front end of the thin tube, thereby forming a liquid-gas interface in the liquid. When the pressure difference between the inside and outside of the bubble reaches the maximum When, that is, when the radius of the bubble is equal to the radius r of the capillary, the pressure difference value ΔP is measured, and then the surface tension σ is calculated from this value. The surface tension σ was obtained from the following formula (A).

σ＝ΔP·r/2 (A)

The bubble frequency is the number of bubbles generated per unit time. By changing the bubble frequency, the dynamic change of the surface tension can be obtained, that is, the dynamic surface tension. By measuring the dynamic surface tension, changes in the dynamic properties of liquids can be evaluated. In this embodiment, the dynamic surface tension is measured at a bubble frequency in the range of 0.5 to 35 Hz.

For example, a ring method called the di Nuit method, a suspended plate method, or the like is employed as a method for measuring the static surface tension. In this embodiment, the static surface tension is determined using the suspension plate method.

The ink composition of this embodiment is suitable for an inkjet recording method. In this inkjet recording method, a pressure is applied to an ink composition to discharge ink composition droplets, and the droplets are attached to a recording material to record an image.

In an inkjet recording device for recording an image by an inkjet recording method, when ink composition droplets are continuously discharged, a new surface of the ink composition is continuously generated through the discharge port provided at the front end of the ink cartridge in the inkjet head, thereby The ink composition moves quickly and the influence of dynamic surface tension is large. On the other hand, in the ink cartridge, after the ink composition is discharged, the ink composition is discharged from the ink tank due to capillary action, and the discharge amount corresponds to the volume reduced by the discharge, so that the ink composition moves slowly, which can be regarded as static , thus the static surface tension has a great influence. Then, since both dynamic surface tension and static surface tension exert an influence on discharge, in order to achieve stable discharge of ink composition droplets, it is necessary to consider the balance of dynamic surface tension and static surface. When an ink composition droplet adheres to a recording material to record an image, the ink composition moves rapidly at the moment when the droplet lands on the recording material, but gradually slows down thereafter. When the recording material is an absorbent recording material, the ink composition penetrates into the recording material. That is, since the surface tension changes from dynamic surface tension to static surface tension, a large difference between the dynamic surface tension and the static surface tension requires the ink composition to dry on the recording material for a long time, resulting in imprinting or excessive penetration , causing ink bleeding on the back.

As described above, the ink composition of the present embodiment satisfies the above formula (1 ), that is, the difference between the dynamic surface tension and the static surface tension measured at a temperature of 24 to 26°C is designed within a certain range, so that an ink composition used in the inkjet recording method can be obtained, and the composition shows Excellent ejection stability and suppresses the occurrence of markings on recording materials, thereby providing high-quality recorded images. Therefore, using the ink composition of the present embodiment in the inkjet recording method, it is possible to achieve stable discharge and stably provide high-quality recorded images.

Reasons for limiting the design range of the ink composition of this embodiment will be described below.

If the difference between the dynamic surface tension (mN/m) and the static surface tension (mN/m) measured at a temperature of 24 to 26°C exceeds 7mN/m, the balance between the dynamic surface tension and the static surface tension deteriorates, and the droplet cannot be stabilized. discharge. Also, drying of the recording material takes time and produces blots, thereby deteriorating image quality. Therefore, the selected range should be equal to or less than 7mN/m.

If the difference between the dynamic surface tension (mN/m) and the static surface tension (mN/m) measured at a temperature of 24 to 26°C is less than 0mN/m, the static surface tension becomes high, which reduces the impact of the ink composition on the composition of the inkjet head. The wettability of the components, therefore, the filling of the ink cartridge with the ink composition becomes difficult. Therefore, the selected range should be equal to or greater than 0mN/m.

The static surface tension of the ink composition containing at least one colorant and one organic solvent is preferably 20 to 50 mN/m, more preferably 20 to 45 mN/m.

When the static surface tension is less than 20 mN/m, the permeability becomes too high, causing the ink composition to spread laterally on the absorbent recording material, thereby resulting in unclear outlines of images. On the other hand, when the static surface tension exceeds 50 mN/m, the permeability to the recording material decreases and the dryness decreases. In addition, the wettability of the ink composition and the inner wall of the ink cartridge is reduced, hindering the supply of the ink composition to the ink cartridge, and making it difficult to fill the ink composition with the ink composition, so that ink composition droplets cannot be stably discharged. Therefore, the selected range is 20-50mN/m.

The viscosity of the ink composition containing at least one colorant and an organic solvent is preferably equal to or less than 20 mPa.s, more preferably equal to or less than 15 mPa.s at a measurement temperature of 25°C. When used in an inkjet recording method, when the viscosity of the ink composition exceeds 20 mPa.s, ink composition droplets cannot be stably discharged. Therefore, the selected range is equal to or less than 20mPa.s.

The ink composition of the present embodiment preferably contains water as a medium in addition to a colorant and an organic solvent. Such a composition can suppress the occurrence of marks on the recording material and improve drying properties.

The content of water in the ink composition is preferably 30 to 95% by weight, more preferably 30 to 85% by weight. When the water content is less than 30% by weight, the amount of the organic solvent increases, and stabilization of ink additives soluble or dispersible in water becomes difficult. In addition, when the organic solvent component is excessively increased, the viscosity increases significantly, eventually exceeding the proper viscosity range of the ink composition. In addition, when the water content exceeds 95% by weight, the amount of the organic solvent is too small to maintain the wettability of the ink composition. Therefore, the selected range is 30 to 95% by weight.

Colorants can be dyes, pigments or mixtures thereof. The dye or pigment may be a substance containing a dye or a pigment, or a substance to which a dye or pigment is attached.

Clogging can be suppressed by using a dye as a colorant, thereby improving discharge stability. Recorded images excellent in light resistance and water resistance can also be obtained by using a pigment as a colorant.

In order to reproduce various colors in the color inkjet recording method, an ink composition of 3 colors can be used, which are cyan (abbreviated as C), magenta (abbreviated as M) and yellow (abbreviated as Y), by combining these Various colors can be expressed by mixing the ink composition. However, since it is difficult to reproduce black by mixing three colors, a black (abbreviated as B) ink composition is generally used to express black. By changing the color of the colorants contained, cyan, magenta, yellow or black ink compositions can be obtained.

The dye is not particularly limited, but when the ink composition contains water, it is preferable to use a water-soluble dye such as acid dye, direct dye, reactive dye or food dye. Among these water-soluble dyes, those excellent in water resistance, light resistance or safety are preferably used.

Specific examples of dyes include the following dyes, but the dyes are not limited to these examples. In the following examples, dyes are represented by color index (C.I. for short).

Dyes used in cyan ink compositions include acid dyes such as C.I. Acid Blue 7, 9, 29, 45, 92 and 249; direct dyes such as C.I. Direct Blue 1, 2, 6, 15, 22, 25, 71, 76 , 79, 86, 90, 98, 163, 165, 199 and 202; reactive dyes, such as C.I. reactive blue 1, 2, 7, 14, 15, 23, 32, 38, 41, 63, 80 and 95, etc. Among these dyes, at least one dye selected from C.I. Acid Blues 7 and 9, and C.I. Direct Blue 199 is preferably used.

Dyes that can be used in magenta ink compositions include acid dyes such as C.I. , 106, 111, 114, 115, 134, 186, 249, 254 and 289; direct dyes such as C.I. Direct Red 1, 4, 9, 13, 17, 20, 28, 31, 39, 80, 81, 83, 89, 225 and 227, C.I. Direct Orange 26, 29, 62 and 102; reactive dyes such as C.I. Reactive Red 1, 14, 17, 25, 26, 32, 37, 44, 46, 55, 58, 60, 66, 74, 79, 96, 97, 141, 147, 180 and 181 etc. Among these dyes, at least one dye selected from C.I. Acid Red 52 and 289, and C.I. Reactive Red 58, 141 and 180 is preferably used.

Dyes that can be used in yellow ink compositions include acid dyes such as C.I. Acid Yellow 1, 7, 17, 23, 42, 44, 79 and 142; direct dyes such as C.I. Direct Yellow 1, 12, 24, 26, 33 , 44, 50, 86, 120, 132, 142 and 144; reactive dyes such as C.I. Reactive Yellow 1, 5, 11, 13, 14, 20, 21, 22, 25, 40, 47, 51, 55, 65 and 67 etc. Among these dyes, at least one dye selected from C.I. Acid Yellow 17 and 23, and C.I. Direct Yellow 86 is preferably used.

Dyes that can be used in black ink compositions include food dyes such as C.I. Food Black 2; direct dyes such as C.I. and 171; reactive dyes, such as C.I. Reactive Black 3, 4, 7, 11, 12 and 17, etc. Among these dyes, at least one of C.I. Food Black 2 and C.I. Direct Black 154 is preferably used.

These dyes are used within the range of being stable and soluble at normal temperature. Since such a range is different for each dye, the content of the dye in the ink composition is not particularly limited, but is preferably 0.1 to 10% by weight.

As for the pigment, any pigment dispersible in a solution can be used, but it is preferable to use a pigment excellent in light resistance or safety.

Specific examples of pigments include the following pigments, but the pigments are not limited to these. In the following examples, pigments are indicated by Color Index (C.I.) numbers.

Examples of pigments used in the cyan ink composition include C.I. Pigment Blue 1, 2, 15, 16, 17, 21, 22, 60 and 64 and the like.

Examples of pigments used in the magenta ink composition include C.I. Pigment Red 2, 3, 5, 16, 23, 31, 49, 57, 63, 122, and 209, and C.I. Pigment Violet 19, and the like.

Examples of pigments used in the yellow ink composition include C.I Pigment Yellow 1, 2, 3, 5, 12, 74, 138, 150, and 180 and the like.

Examples of the pigment used in the black ink composition include carbon black such as channel black, furnace black, thermal black or lamp black, and the like.

Among these pigments, at least one of C.I. Pigment Blue 15:3 and Pigment Blue 15:4 is preferably used in the cyan ink composition. For the magenta ink composition, it is preferable to use at least one pigment selected from C.I. Pigment Red 122, C.I. Pigment Red 209 and C.I. Pigment Violet 19. And for the yellow ink composition, it is preferable to use at least one pigment selected from C.I. Pigment Yellow 74, C.I. Pigment Yellow 138, C.I. Pigment Yellow 150 and C.I. Pigment Yellow 180. For black ink compositions, at least one pigment selected from the above-mentioned carbon blacks is preferably used.

By using these pigments, it is possible to obtain an ink composition capable of realizing a recorded image excellent in color developability of each color. When using an ink set composed of three ink compositions of cyan, magenta, and yellow of these pigments, by superimposing the three ink compositions, a high-density black recording image can be obtained, which is close to that obtained by using a black ink composition The recorded image formed. Therefore, it is possible to express color without using a black ink composition.

When the ink composition contains water, the pigment preferably has one or more hydrophilic groups selected from, for example, carboxyl, hydroxyl, amino and sulfonic acid groups and the like. Such a hydrophilic group can be directly added to the surface of the pigment by chemical modification, or introduced by hydrophilization by covering the surface of the pigment with a polymer having such a hydrophilic group. Such hydrophilic groups may also be salts.

Pigments with hydrophilic groups can be stably dispersed in aqueous ink compositions. Therefore, by using a pigment having a hydrophilic group as a colorant, the occurrence of clogging can be suppressed, thereby obtaining a recorded image excellent in light resistance and water resistance without impairing discharge stability.

These pigments are used within the range in which they can be stably dispersed at normal temperature. Since such a range varies for each pigment, the content of the pigment in the ink composition is not particularly limited, but is preferably 0.1 to 10% by weight.

Specific examples of organic solvents, for example, amides, such as dimethylformamide or dimethylacetamide; polyalcohols, such as polyethylene glycol, polypropylene glycol, ethylene glycol, diethylene glycol, disulfide Glycol (thiodiglycol), propylene glycol, triethylene glycol, 1,5-pentanediol, 1,4-butanediol, 1,2-hexanediol, 1,3-propanediol, glycerin and 1,2,6- Hexatriol; ethers of polyhydric alcohols, such as glycol ethers, such as ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, triglycerides Alcohol monobutyl ether, propylene glycol monoethyl ether, tetraethylene glycol monomethyl ether and ethylene glycol monophenyl ether, etc.; sulfur-containing compounds, such as sulfolane or dimethyl sulfoxide, etc.; nitrogen-containing compounds, such as 2-pyrrolidone, N-methyl Pyrrolidone or ε-caprolactam, etc.; oxygen-containing compounds, such as γ-butyrolactone, etc.; multifunctional compounds, such as dimethylaminoethanol, diethylaminoethanol, triethanolamine or morpholine, etc., but the organic solvent is not limited for such instances.

Among these organic solvents, glycol ethers or polyols are preferably used because such solvents have low vapor pressure, and when such solvents are contained in the ink composition, a wetting effect is obtained to improve discharge stability. Among the glycol ethers, it is more preferable to use diethylene glycol monobutyl ether, propylene glycol monobutyl ether, triethylene glycol monobutyl ether or tetraethylene glycol monobutyl ether as organic solvents, and their vapor pressure at 25 °C is 0.01 mm Mercury column or lower, and has excellent wetting effect. Among polyols, it is more preferable to use glycerin, 1,2-hexanediol or 1,5-pentanediol, which have a vapor pressure of 0.01 mmHg or less at 25°C and have an excellent wetting effect .

The content of the organic solvent in the ink composition is preferably 3 to 70% by weight, more preferably 3 to 50% by weight. When the content of the organic solvent is less than 3% by weight, the ink composition may dry rapidly, making it difficult to maintain wettability. And when the content of the organic solvent exceeds 70% by weight, the water-soluble or water-non-dispersible ink additives may not exist stably. In addition, depending on the kind of solvent used, the viscosity showed a significant increase and exceeded the proper viscosity range of the ink composition. Therefore, the selected range is 3 to 70% by weight. However, when the ink composition has water as the main component, its content is preferably 3 to 40% by weight, more preferably 3 to 30% by weight. However, when the ink composition has water as the main component, when the organic solvent content exceeds 40% by weight, although it depends on the kind of the colorant used, it leads to a decrease in printing quality and a long drying time. Therefore, the selected range is 3 to 40% by weight.

The ink composition of the present embodiment preferably further includes a surfactant. Such a configuration can easily control the above-mentioned dynamic surface tension and static surface tension.

The surfactant can be any one of nonionic surfactant, anionic surfactant, cationic surfactant or a combination thereof. The type of surfactant, such as nonionic, cationic or anionic surfactant, should be selected according to the type of electrolyte contained in the ink composition. For example, if the ink composition contains anionic substances, a nonionic or anionic surfactant is used. Among these surfactants, nonionic surfactants are preferred because they are not easily affected by coexisting electrolytes and can keep the difference between dynamic surface tension and static surface tension within a predetermined range regardless of whether the ink composition is Electrolyte is added.

Specific examples of nonionic surfactants include surfactants represented by the following general formulas (I), (II), (III), (IV), (V) and (VI), but nonionic Surfactants are not limited to these examples.

HO(CH ₂ CH ₂ O) _p (CH ₂ CH ₂ CH ₂ O) _q (CH ₂ CH ₂ O) _r H (V)

In the general formula (I), m represents an integer or fraction of 0-30; n represents an integer or fraction of 0-30; the sum (m+n) of m and n represents an integer or fraction of 0-30.

In the general formula (II), k represents an integer or fraction of 11-13; l represents an integer or fraction of 3-30.

In the general formula (III), h represents an integer or fraction of 0 to 11; i represents an integer or fraction of 0 to 11; j represents an integer or fraction of 3 to 50; the sum of h and i (h+i) represents 9 An integer or fraction of ~11.

In the general formula (IV), w represents an integer or fraction of 0 to 11; x represents an integer or fraction of 5 to 9; y represents an integer or fraction of 2.5 to 5; z represents an integer or fraction of 0 to 9; w and The sum (w+z) of z represents an integer of 9-11 or a fraction.

In general formula (V), p represents an integer or a fraction of 0-78; q represents an integer or a fraction of 2-15; r represents an integer or a fraction of 0-18.

In the general formula (VI), the sum (s+t) of s and t represents an integer or fraction of 1-30, and the sum (u+v) of u and v represents an integer or fraction of 1-10.

The surfactant is preferably contained in the ink composition at or above the critical micelle concentration. The surface tension of surfactant-containing solutions decreases as surfactant increases up to the critical micelle concentration, but remains essentially constant above the critical micelle concentration. Therefore, when using the above-mentioned critical micelle concentration or a surfactant higher than the critical micelle concentration, the effect of the surfactant can be fully brought into play, and the dynamic surface tension and static surface tension controlled by the surfactant can be kept at a constant value. , so as to obtain an ink composition with uniform properties.

Although the critical micelle concentration of various surfactants is different, for any nonionic surfactant, anionic surfactant and cationic surfactant, its critical micelle concentration is about 0.001～3% by weight ( Measurement temperature: 25°C).

When a pigment is used as a colorant, the ink composition of the present embodiment preferably contains a binder resin. By containing the binder resin, the peeling of the pigment from the recording material can be prevented.

As the binder resin, one or more resins selected from polyester resins, acrylic resins, styrene-acrylic copolymer resins, polyester-acrylic copolymer resins, and the like can be used.

In addition to colorants, organic solvents, water, surfactants, and binder resins, the ink composition of this embodiment may also contain other additives such as antifungal agents, pH regulators, chelating agents, antirusting agents agent) or UV absorbers.

For the antifungal agent, it is preferable to use sodium dehydroacetate, sodium benzoate, sodium sorbinate or the like.

As the pH adjuster, it is preferable to use triethanolamine, sodium hydroxide, sodium carbonate, sodium nitrate, potassium nitrate, or the like.

For example, using 0.5 to 15% by weight of colorant, 3 to 70% by weight of organic solvent, 29 to 95% by weight of water and 0.001 to 5% by weight of surfactant, an ink composition can be obtained which contains at least one colorant and an organic solvent, and its dynamic surface tension measured by the maximum bubble pressure method at a temperature of 24 to 26 ° C and the static surface tension measured at a temperature of 24 to 26 ° C satisfy the relationship of the above formula (1).

Fig. 1 is an exploded perspective view illustrating the structure of an ink jet head 1 constituting a second embodiment of the present invention, and Fig. 2 is a partially enlarged view illustrating the structure of a top plate 10 constituting the ink jet head 1 shown in Fig. 1 . For simplicity and easy understanding, the driving electrodes 13 shown in FIG. 2 are omitted in FIG. 1 .

The inkjet head 1 is composed of the following parts: a top plate 10 made of piezoelectric material, which has a bottom wall portion 11 and a plurality of partitions 12; a cover plate 20, which is mounted on the upper surface of the partitions 12; a nozzle plate 30, It is provided at one end of the partition 12 having a plurality of discharge ports 31; a back panel (not shown) provided at the other end of the partition 12; A plurality of partitions 12 are arranged parallel to each other at predetermined intervals on the bottom wall portion 11, and a plurality of ink cartridges 40 are constituted by the plurality of partitions 12, the bottom wall portion 11, the cover plate 20, the nozzle plate 30, and the back plate (not shown). . The cover plate 20 is formed by a common ink supply channel 21 communicating with the ink cartridge 40 and an ink supply tube 22 connecting the common ink supply channel 21 and the opening 51 of the ink tank 50 . The ink tank 50 stores the ink composition 60 of the first embodiment, and the ink composition 60 is supplied to each ink cartridge 40 through the common ink supply path 21 .

As shown in FIG. 2 , on the surface of the ink chamber 40 facing the bottom wall portion 1 of the top plate 10 and the plurality of spacers 12 , drive electrodes 13 for applying a voltage to the plurality of spacers 12 are formed. The piezoelectric material constituting the plurality of spacers 12 is polarized in the direction indicated by arrow 70, so that the plurality of spacers 12 function as piezoelectric elements.

The inkjet head 1 having such a structure is a piezoelectric inkjet head capable of discharging ink composition 60 droplets from the discharge port 31 according to the voltage applied to the plurality of spacers 12 as piezoelectric elements. .

Hereinafter, the operation principle of the inkjet head 1 when the ink composition 60 is discharged from the ink cartridge 40 will be described. FIG. 3 is a cross-sectional view of the ink jet head 1 shown in FIG. 1 viewed from the direction in which the ink cartridge 40 extends. Hereinafter, the operation when the ink composition 60 is discharged from the ink cartridge 40b will be described.

When the voltage is not applied to the separators 12a and 12b constituting the ink cartridge 40b, that is, between the drive electrode 13b of the ink cartridge 40b and the drive electrode 13a of the ink cartridge 40a adjacent to the ink cartridge 40b, and between the drive electrode 13b of the ink cartridge 40b and the ink cartridge 40c adjacent to the ink cartridge 40b When no potential difference is generated between the drive electrodes 13c, the ink cartridge 40b is filled with the ink composition 60 supplied from the ink tank 50 by capillary action. Similarly, the ink cartridges 40a, 40c are also in a state of being filled with the ink composition 60 .

When a voltage is applied to the drive electrodes 13a and 13c, a potential difference is generated between the drive electrode 13b and the drive electrode 13a, and between the drive electrode 13b and the drive electrode 13c, thereby applying voltage to the separators 12a and 12b constituting the ink cartridge 40b. voltage. This voltage generates electric fields in the directions of arrows 71 and 72 in the spacers 12a and 12b, respectively, and such electric fields cause deformation in the spacers 12a and 12b constituting the ink cartridge 40b, thereby producing convex deformation on the side of the ink cartridge 40b. Accordingly, a pressure wave is generated, and a large pressure is applied to the ink composition 60 filled in the ink cartridge 40, thereby discharging ink composition 60 droplets from the discharge port 31 shown in FIG. 1 .

When the application of voltage to the drive electrodes 13a and 13c is terminated, the partitions 12a and 12b return to their original shape, restoring the original volume of the ink cartridge 40, thereby supplying the ink corresponding to the recovery from the ink tank 50 through the common ink supply channel 21 shown in FIG. 1 . volume of the ink composition, the ink cartridge 40b returns to the initial state filled with the ink composition 60.

As described above, since the ink tank 50 stores the ink composition 60 of the fourth embodiment, and such ink composition 60 is supplied to the ink cartridge 40 and discharged from the discharge port 31 as liquid droplets, the inkjet head 1 of the embodiment can Liquid droplets of the ink composition 60 are stably discharged from the discharge port 31 . By using such an inkjet head, a highly reliable piezoelectric inkjet recording device can be realized, and a high-quality recorded image can be stably obtained.

In this embodiment, the separator 12 constituting the ink cartridge 40 is made of piezoelectric material and acts as a piezoelectric element, but this structure is not limited, and it can also be made of non-piezoelectric material to form the ink cartridge. It is also possible to install piezoelectric elements inside or outside the partition.

Fig. 4 is an exploded perspective view schematically illustrating the structure of an ink jet head 2 constituting a third embodiment of the present invention, and Fig. 5 is a partial plan view showing the structure of the ink jet head 2 shown in Fig. 4 . For simplicity and easy understanding, the cover plate 20 and the ink tank 50 shown in FIG. 4 are omitted in FIG. 5 . The ink-jet head 2 of this embodiment is similar to the ink-jet head 1 of the second embodiment, and therefore corresponding parts are denoted by the same numerals, and explanations will be omitted.

It should be noted that the top plate 100 includes a base plate 101 and a plurality of spacers 102 arranged parallel to each other at predetermined intervals on the base plate 101 and a heater 103 as a heat generating body installed on the surface of the ink cartridge 40 facing the base plate 101 and , drive electrodes 104 and 105 that apply a voltage to the heater 103 .

The inkjet head 2 configured in this way is a thermal inkjet type inkjet head capable of discharging ink composition 60 droplets from the discharge port 31 in accordance with a voltage applied to the heater 103 as a heat generating body.

Hereinafter, the working principle of the inkjet head 2 when the ink composition 60 is discharged from the ink cartridge 40 will be explained. FIG. 6 is a diagram illustrating a state in which liquid droplets 61 of the ink composition 60 are discharged from the ink cartridge 40 . FIG. 6 shows the sectional structure of the inkjet head 2 along the section line I-I.

When no voltage is applied to the heater 103, the state is similar to the state where no voltage is applied to the spacer 12 in the inkjet head 1 of the second embodiment, and the ink cartridge 40 is in a state filled with the ink composition 60.

When the driving electrodes 104 and 105 apply a voltage to the heater 103 , the heater 103 generates heat, which heats the ink composition 60 filled in the ink cartridge 40 and generates air bubbles 62 . Therefore, a pressure wave is generated, a large pressure is applied to the ink composition 60 filled in the ink cartridge 40 , and the liquid droplets 61 of the ink composition 60 are discharged from the discharge port 31 .

When the voltage applied to the heater 103 was terminated, the ink composition 60 in the ink cartridge 40 was cooled, the air bubbles 62 disappeared, and the ink composition 60 was supplied from the ink tank 50 through the shared ink supply channel 21 shown in FIG. With the restored volume, the ink cartridge 40 returns to the original state filled with the ink composition 60 .

Like the inkjet head 1 of the second embodiment, the inkjet head 2 of the present embodiment stores the ink composition 60a of the fourth embodiment in the ink tank 50, and such ink composition 60a is supplied to the ink cartridge 40, and from The discharge port 31 discharges the liquid droplets 61 a, and therefore, the liquid droplets 61 a of the ink composition 60 can be stably discharged from the discharge port 31 . By using such an inkjet head, a highly reliable thermal inkjet type inkjet recording device can be realized, and a high-quality recorded image can be stably provided.

Example

The present invention will be further illustrated below by examples, but the present invention is not limited by these examples. In these embodiments, image recording is also referred to as printing or printing.

<Ink composition>

In the process of preparing the ink composition, the kind and quantity of the coloring agent, organic solvent and surfactant and the content of binder resin and water are changed as shown in Table 1 to obtain the relational expression satisfying the important conditions of the present invention (1) The ink compositions of Examples 1 to 7 and the ink compositions of Comparative Examples 1 to 4 that do not satisfy the relational expression (1) of the present invention. In Table 1, the units of values in each column are expressed in parts by weight, and the total amount of each ink composition in Examples 1 to 7 and Comparative Examples 1 to 4 is 100 parts by weight. Furthermore, in Table 1, TEGBE represents triethylene glycol monobutyl ether; PEG400 represents polyethylene glycol with a molecular weight of 400; Fluorinated surfactant 1 represents a surfactant represented by the following chemical formula (VII); Active agent 2 represents a surfactant represented by the following chemical formula (VIII):

In Examples 1 to 7 and Comparative Examples 1 to 4, the dynamic surface tension and the static surface tension of the ink composition were measured as follows.

<Dynamic Surface Tension>

Measurement was performed with a surface tensiometer (BP-4: manufactured by Kyowa Kaimen Kagaku Co.) at a bubble frequency of 0.5 to 35 Hz.

<Static Surface Tension>

The measurement was performed with a static surface tensiometer (CBVP-A3: manufactured by Kyowa Kaimen Kagaku Co.).

Table 2 shows the measured value of dynamic surface tension and static surface tension of each ink composition of Examples 1 to 7 and Comparative Examples 1 to 4, the d value represented by the following formula (B), and the temperature and air bubble frequency at the time of measurement.

d(mN/m)＝[Dynamic Surface Tension (mN/m)]-[Static Surface Tension (mN/m)] (B)

Table 1 (where R is the margin) combination Example comparative example 1 2 3 4 5 6 7 1 2 3 4 dye CI Direct Blue 199 2.5 CI Pigment Blue 15:3 3 CI Pigment Blue 15:4 3 CI Pigment Red 122 5 CI Pigment Yellow 74 4 CI Pigment Yellow 180 4 carbon black 5 5 CI Pigment Blue 17 2 CI Pigment Red 58 3 CI Pigment Yellow 13 2 Diethylene glycol 8 8 8 5 5 8 8 2 5 20 10 Glycerol 5 7 8 10 8 8 9 5 5 17 10 1,5-pentanediol 2 5 2 2 5 2 18 5 TEGBE 8 8 8 5 5 3 6 4 8 PEG400 1 10 15 15 10 General formula (I) (m+n=10) 1 General formula (II) (k=11～13, 1=15) 1 1.0 General formula (III) (h+i=9～11, j=9) 1.5 General formula (IV) (w+z=9～11, x=9, y=5) 1.5 General formula (V) (p=12, q=8, r=4) 1 Fluorinated Surfactants 1 1 0.5 Fluorinated Surfactant 2 1.5 1 0.5 binder resin polyester resin none 1 1.5 2 1 1.5 1 1 1.5 2 2 water R R R R R R R R R R R

Table 2 Example comparative example 1 2 3 4 5 6 7 1 2 3 4 Dynamic Surface Tension (mN/m) 31.9 31.9 34.5 34.7 34.4 34.8 34.6 31.4 29.5 29.5 28.6 Static Surface Tension (mN/m) 27.9 27.8 30.4 30.8 30.4 31.0 30.1 23.3 20.5 20.5 20.4 d(mN/m) 4 4.1 4.1 3.9 4 3.8 4.5 8.1 9 9 8.2 Measuring temperature (°C) 25.6 25.6 25.3 25.6 25.1 25.0 24.8 24.7 25.7 24.8 24.6 Determination of bubble frequency (Hz) 15 14 14 15 16 16 15 15 16 16 16

Each ink composition obtained in Examples 1 to 7 and Comparative Examples 1 to 4 was filled into an ink tank of an inkjet recording apparatus using a commercially available inkjet recording apparatus (AJ2000: produced by SharpKabushiki Kaisha ) obtained after modification, and continuously printed at a printing density of 5% on ordinary copy paper (trade name: SF4AM3) produced by Sharp Kabushiki Kaisha at a printing speed of 7 pages per minute of A4 paper. In this test, when the ink tank is empty, the ink composition is refilled, printing is continued until the ink composition droplet cannot be discharged from the nozzle and no more printing is possible, and the number of sheets completely printed up to this point is counted to obtain the printable value. The number of sheets was used as an evaluation index of discharge stability. If the number of printable sheets exceeds 200, it is rated as good (◯), if the number of sheets is 150 to 200, it is rated as good (△), and if it is less than 150, it is rated as poor (×).

In addition, each ink composition of Examples 1 to 7 and Comparative Examples 1 to 4 was filled into an ink tank of an inkjet recording device, which was a commercially available inkjet recording device (AJ2000: produced by SharpKabushiki Kaisha) via The reformed ones were printed with specific patterns on plain copy paper (trade name: SF4AM3) produced by Sharp Kabushiki Kaisha to form images for evaluation. After the evaluation image is placed for one day, if there is no imprint, the pattern line width is set to 100, and the pattern line width of each evaluation image is measured to obtain a relative value, which is used as an index for evaluating image quality. If the relative value of the line width is less than 150 and there is almost no imprint, the result is rated as good (○), if the relative line width is 150 to 250, and there are some imprints, it is rated as good (△), if the relative line width exceeds 250, and When there were a large number of blots, it was rated as poor (x).

The results of these evaluations are listed in Table 3.

table 3 Example comparative example 1 2 3 4 5 6 7 1 2 3 4 discharge stability ○ ○ ○ ○ ○ ○ ○ x x x x Image Quality ○ ○ ○ ○ ○ ○ ○ x x x x

In the ink compositions of Examples 1 to 7 satisfying the relational expression (1) which is an important condition of the present invention, both discharge stability and image quality were good. On the other hand, in the ink compositions of Comparative Examples 1 to 4, the difference between the dynamic surface tension and the static surface tension was more than 7 and exceeded the range of the formula (1), and the discharge stability and image quality were poor.

As described above, by designing so as to satisfy the relational expression (1), it is possible to obtain an ink composition which, when used in an inkjet recording method, exhibits excellent discharge stability and suppresses marking of a recording material, thereby providing High quality recorded images.

<ink set>

As shown in Table 4, the ink compositions of Examples 2 to 6 and Comparative Examples 1 to 3 were mixed as cyan, magenta and yellow ink compositions to obtain: Example ink set 1, wherein the cyan ink composition contained At least one pigment in C.I. Pigment Blue 15:3 and C.I. Pigment Blue 15:4, the magenta ink composition contains at least one pigment selected from C.I Pigment Red 122, 209 and C.I. Pigment Violet 19, and the yellow ink composition contains at least one A pigment selected from C.I. Pigment Yellow 74, 138, 150, and 180; comparative example ink sets 1 to 3, wherein all cyan, magenta, and yellow ink compositions contain pigments different from the above-mentioned pigments; and comparative example ink sets 4, wherein all the cyan, magenta and yellow ink compositions contain pigments other than the above-mentioned pigments.

Table 4 blue Magenta yellow Example ink set 1 Embodiment 2C.I. pigment blue 15:3 Embodiment 4C.I. Pigment Red 122 Example 5C.I. Pigment Yellow 74 Comparative Example Ink Set 1 Comparative Example 1C.I. Pigment Blue 17 Embodiment 4C.I. Pigment Red 122 Embodiment 6C.I. Pigment Yellow 180 Comparative Example Ink Set 2 Embodiment 3C.I. pigment blue 15:4 Comparative Example 2C.I. Pigment Red 58 Embodiment 6C.I. Pigment Yellow 180 Comparative Example Ink Set 3 Embodiment 3C.I. pigment blue 15:4 Embodiment 4C.I. Pigment Red 122 Comparative Example 3C.I. Pigment Yellow 13 Comparative Example Ink Set 4 Comparative Example 1C.I. Pigment Blue 17 Comparative Example 2C.I. Pigment Red 58 Comparative Example 3C.I. Pigment Yellow 13

Using the respective ink sets of Example Ink Set 1 and Comparative Example Ink Sets 1 to 4 obtained, on the inkjet recording apparatus, the inkjet recording apparatus was a commercially available inkjet recording apparatus (AJ2000: produced by SharpKabushiki Kaisha) modified The resultant was printed on gloss paper (trade name: AJ-K4AG) at a printing ratio of cyan, magenta, and yellow ink compositions of 1:1:1, thereby forming a black image. Also, the ink composition of Example 7 was used as a black ink composition to obtain the same image.

The ^resulting image was measured with a spectrophotometer (X-Rite 938: manufactured by X-Rite ^{Inc.) to obtain the lightness index L* and chromaticity} index a ^* and b ^* .

The test results were evaluated in the following manner. In the black image formed with the ink composition of Example 7, the chromaticity indices a ^* and b ^* were taken as A1 and B1, respectively, and in the black images formed with the ink set 1 of Example and the ink sets 1 to 4 of Comparative Examples, The chromaticity indexes a ^* and b ^* are taken as A2 and B2 respectively, and the value of Δa ^* b ^* represented by the following formula (C) is obtained as an evaluation index of black reproducibility:

Δa ^* b ^* ＝{(A1-A2) ² +(B1-B2) ² } ^1*2 (C)

Cases where the value of Δa ^* b ^* was equal to or less than 20 (Δa ^* b ^* ≤20) were rated as good (◯), while cases exceeding 20 (Δa ^* b ^* >20) were rated as poor (×). The evaluation results are listed in Table 5.

table 5 Evaluation Results Example ink set 1 ○ Comparative Example Ink Set 1 x Comparative Example Ink Set 2 x Comparative Example Ink Set 3 x Comparative Example Ink Set 4 x

Table 5 shows that the black images formed with Example ink set 1 have a higher density than the black images formed with Comparative example ink sets 1 to 4, which is close to that of the black images formed with the ink composition of Example 7. Image density.

As mentioned above, the cyan ink composition containing at least one pigment in C.I. Pigment Blue 15:3 and C.I. Pigment Blue 15:4, the product containing at least one pigment selected from C.I. Pigment Red 122, 209 and C.I. A red ink composition, and a yellow ink composition containing at least one pigment selected from C.I. Pigment Yellow 74, 138, 150 and 180, and a high-density black image can be obtained by superimposing these three ink compositions.

The ink composition according to the fourth embodiment of the present invention contains at least one colorant and a medium, and the dynamic surface tension (σ ₁₀ ) and the dynamic surface tension (σ ₁ ) difference d(σ ₁₀ -σ ₁ ) at a bubble frequency of 1 Hz satisfies the following formula (2):

0mN/m≤d≤7mN/m         (2)

The maximum bubble pressure method used to measure the dynamic surface tension will be described below.

The maximum bubble pressure method is a method for measuring surface tension. The method is to insert a thin tube into the liquid, and bubbles are generated from the front end of the thin tube, thereby forming a liquid-gas interface in the liquid. When the pressure difference between the inside and outside of the bubble When the maximum is reached, that is, when the radius of the bubble is equal to the radius r of the capillary, the pressure difference value (ΔP) is measured, and the surface tension (σ) is then obtained from this value. The surface tension (σ) was obtained from the following formula (A).

σ＝ΔP·r/2 (A)

The bubble frequency is the number of bubbles generated per unit time. By changing the bubble frequency, the dynamic surface tension from the slow moving state to the fast moving state can be obtained. By calculating the dynamic surface tension from the slowly moving state to the fast moving state, the change of the dynamic properties of the liquid can be evaluated.

The ink composition of this embodiment can be used in a recording method for recording an image by attaching the ink composition to a recording material, for example, in an inkjet recording method or a recording method using a handwriting implement such as a pen. High-quality recorded images can be stably obtained using the ink composition of the present embodiment.

Among the recording methods, the ink composition of the present embodiment is preferably used in an inkjet recording method. In this inkjet recording method, droplets of the ink composition are discharged by applying pressure to the ink composition, and such droplets adhere to a recording material to record an image. In the inkjet recording method, using the ink composition of the present embodiment can achieve stable discharge and provide a high-quality recorded image stably.

In an inkjet recording device for recording an image using an inkjet recording method, when ink composition droplets are continuously discharged, a new surface of the ink composition is continuously generated from the discharge port installed at the front end of the ink cartridge in the inkjet head, so , the ink composition moves rapidly, and in the state of rapid movement, at a high frequency of about 10 Hz corresponding to the dynamic surface tension, the influence of the dynamic surface tension is large. On the other hand, in the ink cartridge, after the ink composition is discharged, the ink tank supplies the ink composition by capillary action, and its supply amount is equivalent to the volume reduced by the discharge, so the ink composition moves slowly, which is opposite to the slow moving dynamic surface. Tension corresponds to a large influence of dynamic surface tension at low frequencies of about 1 Hz. Therefore, since both the high-frequency dynamic surface tension and the low-frequency dynamic surface tension exert an influence on the discharge, it is necessary to consider the balance between the high-frequency dynamic surface tension and the low-frequency dynamic surface tension in order to achieve stable ink composition droplets. discharge. In addition, when the image is recorded by the ink composition droplets being attached to the recording material, the ink composition moves rapidly at the moment when the droplets land on the recording material, but gradually slows down thereafter. When the recording material is an absorbent recording material, The ink composition slowly penetrates into the recording material. That is, due to the dynamic surface tension of the ink composition, the dynamic surface tension of the fast-moving state changes to the dynamic surface tension of the slow-moving state, and the difference between the high-frequency dynamic surface tension and the low-frequency dynamic surface tension increases, and the ink composition The drying time of the material on the recording material is prolonged, resulting in blots or excessive penetration, resulting in backside bleed.

As described above, the ink composition of this embodiment is designed so that, among dynamic surface tensions measured by the maximum bubble pressure method at a measurement temperature of 24 to 26°C, the dynamic surface tension (σ ₁₀ ) at a bubble frequency of 10 Hz and the bubble frequency The difference d(=σ ₁₀ -σ ₁ ) of the dynamic surface tension (σ ₁ ) at 1 Hz satisfies the above formula (2), even if the difference between the dynamic surface tension at the high frequency of 10 Hz and the dynamic surface tension at the low frequency of 1 Hz Within a certain range, therefore, in the inkjet recording method, when using the ink composition of the present embodiment, excellent discharge stability can be obtained, and marking of the recording material can be suppressed, thereby providing an ink composition for recording images with high quality. .

The reasons for limiting the design range of the ink composition of the present embodiment will be described below.

When the difference d (=σ ₁₀ −σ ₁ ) between σ ₁₀ and σ ₁ exceeds 7 mN/m, the balance between the dynamic surface tension at high frequency and the dynamic surface tension at low frequency becomes poor, and droplets cannot be discharged stably. Also, drying on the recording material takes time and produces blots, thereby deteriorating image quality. Therefore, choose equal to or less than 7mN/m.

If the difference d (=σ ₁₀ -σ ₁ ) between σ ₁₀ and σ ₁ is less than 0 mN/m, the dynamic surface tension at low frequency becomes high, the wettability of the ink composition to the components constituting the inkjet head decreases, and the ink composition It becomes difficult to refill the ink cartridges. Therefore, choose equal to or greater than 0mN/m.

The dynamic surface tension (σ ₁₀ ) at a bubble frequency of 10 Hz and the dynamic surface tension (σ ₁ ) at a bubble frequency of 1 Hz are preferably 20 to 70 mN/m, more preferably 20 to 50 mN/m.

When σ ₁₀ and σ ₁ are less than 20 mN/m, the permeability to the absorbent recording material becomes too high, so when attached to the absorbent recording material, the ink composition spreads from the landing point to the surrounding area, forming a Image outlines are not clear. On the other hand, when σ ₁₀ and σ ₁ exceed 70 mN/m, the permeability to the absorbent recording material becomes too low, and the drying property on the absorbent recording material decreases. In addition, the wettability of the ink composition and the inner wall of the ink cartridge becomes poor, preventing the supply of the ink composition to the ink cartridge, making it difficult to fill the ink composition into the ink cartridge, so that ink composition droplets cannot be discharged stably. In addition, it is difficult to form the new surface of the ink composition in the discharge port provided at the front end of the ink cartridge into a desired shape, that is, it is difficult to control the meniscus, and continuous high-speed discharge of ink composition droplets becomes impossible. Therefore, the selected range is 20-70mN/m.

The viscosity of the ink composition of this embodiment is preferably equal to or less than 20 mPa·s, more preferably equal to or less than 15 mPa·s at 25°C. An ink composition having a viscosity exceeding 20 mPa·s at 25° C. cannot be stably discharged in the form of ink composition droplets when used in an inkjet recording method. Therefore, the selected viscosity range is equal to or less than 20 mPa·s.

As the medium, water or an organic solvent or the like can be used.

The medium preferably contains water. Thus, occurrence of marks on the absorbent recording material can be suppressed, and drying property is improved.

The water content in the ink composition is preferably 30 to 95% by weight, more preferably 30 to 85% by weight. When the water content is less than 30% by weight, the amount of organic solvent in the ink composition is too large, making it difficult for ink additives dissolved or dispersed in water to exist stably in the ink composition. In addition, an excessive increase in the organic solvent component will lead to a significant increase in viscosity, which will eventually exceed the proper viscosity range of the ink composition. In addition, when the water content exceeds 95% by weight, the amount of the organic solvent is excessively reduced, so that the wettability of the ink composition cannot be maintained. Therefore, the selected range is 30 to 95% by weight.

Specific examples of organic solvents, for example, amides, such as dimethylformamide and dimethylacetamide, etc.; polyols, such as polyethylene glycol, polypropylene glycol, ethylene glycol, diethylene glycol, sulfur Diethylene glycol, propylene glycol, triethylene glycol, 1,5-pentanediol, 1,4-butanediol, 1,2-hexanediol, 1,3-propanediol, glycerol and 1,2,6- Hexatriol, etc.; ethers of polyols, such as ethylene glycol ethers, such as ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, triethylene glycol monomethyl ether Butyl ether, propylene glycol monoethyl ether, tetraethylene glycol monomethyl ether and ethylene glycol monophenyl ether, etc.; sulfur-containing compounds, such as sulfolane or dimethyl sulfoxide, etc.; nitrogen-containing compounds, such as 2-pyrrolidone, N-methylpyrrolidone or ε-caprolactam, etc.; oxygen-containing compounds, such as γ-butyrolactone, etc.; multifunctional compounds, such as dimethylaminoethanol, diethylaminoethanol, triethanolamine and morpholine, etc., but organic solvents are not limited to these instance. These organic solvents may be used alone or in combination of two or more.

Among these organic solvents, glycol ethers or polyols are preferably used because such solvents have low vapor pressure, and when such solvents are contained in the ink composition, wettability is obtained, thereby improving discharge stability Therefore, the medium preferably contains at least one of glycol ethers and polyols. Among glycol ethers and polyols, as diethylene glycol monobutyl ether, propylene glycol monobutyl ether, triethylene glycol monobutyl ether or tetraethylene glycol monobutyl ether as glycol ethers, or as polyols Glycerin, 1,2-hexanediol or 1,5-pentanediol, because they have a vapor pressure of 0.05 mmHg or less at 25°C and have excellent wetting effects, so, use They are more preferred as media.

The content of the organic solvent in the ink composition is preferably 3 to 70% by weight, more preferably 3 to 50% by weight. When the content of the organic solvent is less than 3% by weight, the ink composition dries quickly, making it difficult to maintain wettability. And when the content of the organic solvent exceeds 70% by weight, the water-soluble or water-dispersible additive cannot stably exist in the ink composition. In addition, depending on the kind of the organic solvent used, the increase of the viscosity is remarkable, and exceeds the proper viscosity range of the ink composition. Therefore, the selected range is 3 to 70% by weight. However, when the ink composition contains water as a main component, the content of the organic solvent in the ink composition is preferably 3 to 40% by weight, more preferably 3 to 30% by weight. Although depending on the kind of coloring agent used, when the ink composition contains water as a main component and the organic solvent content exceeds 40% by weight, it leads to a decrease in the print quality of the resulting recorded image and a prolonged drying time of the ink composition . Therefore, the selection range is 3 to 40% by weight.

As the coloring agent, dyes, pigments or mixtures thereof can be used. The dye or pigment may be a substance containing a dye or a pigment or a substance to which a dye or pigment is attached.

When a dye is used in a colorant, the occurrence of clogging can be suppressed, thereby improving the stability of discharge. Recorded images excellent in light fastness and water resistance can also be obtained when a pigment is used in the colorant.

In order to reproduce various colors in the color inkjet recording method, an ink composition of 3 colors is used, which are cyan (abbreviated as C), magenta (abbreviated as M) and yellow (abbreviated as Y), through which Mixing of ink compositions expresses various colors. However, since it is difficult to reproduce black by mixing three colors, black (abbreviated as B) ink composition is generally used to express black. By changing the color of the colorants contained, cyan, magenta, yellow or black ink compositions can be obtained.

There is no particular limitation on the dye, but when the ink composition contains water, it is preferable to use a water-soluble dye such as acid dye, direct dye, reactive dye or food dye. Among these water-soluble dyes, those excellent in water resistance, light resistance or safety are preferably used.

Specific examples of dyes include the following dyes, but the dyes are not limited to these examples. In the following examples, dyes are indicated by color index (abbreviated C.I.) numbers.

The dyes that can be used in the cyan ink composition, for example, can enumerate acid dyes, such as C.I. Acid Blue 7, 9, 29, 45, 92 and 249; direct dyes, such as C.I. 22, 25, 71, 76, 79, 86, 90, 98, 163, 165, 199, and 202; reactive dyes such as C.I. Reactive Blue 1, 2, 7, 14, 15, 23, 32, 38, 41, 63 , 80 and 95. Among these dyes, at least one selected from C.I. Acid Blues 7 and 9, and C.I. Direct Blue 199 is preferably used.

As the dye used in the magenta ink composition, for example, acid dyes such as C.I. Acid Red 1, 8, 13, 14, 18, 26, 27, 35, 37, 42, 52, 82, 87, 89 , 92, 97, 106, 111, 114, 115, 134, 186, 249, 254 and 289; direct dyes such as C.I. Direct Red 1, 4, 9, 13, 17, 20, 28, 31, 39, 80, 81, 83, 89, 225 and 227, C.I. Direct Orange 26, 29, 62 and 102; reactive dyes such as C.I. Reactive Red 1, 14, 17, 25, 26, 32, 37, 44, 46, 55, 58, 60, 66, 74, 79, 96, 97, 141, 147, 180 and 181 etc. Among these dyes, at least one dye selected from C.I. Acid Red 52 and 289, and C.I. Reactive Red 58, 141 and 180 is preferably used.

As the dye used in the yellow ink composition, for example, acid dyes such as C.I. Acid Yellow 1, 7, 17, 23, 42, 44, 79 and 142; direct dyes such as C.I. Direct Yellow 1, 12, 24 , 26, 33, 44, 50, 86, 120, 132, 142 and 144; reactive dyes such as C.I. Reactive Yellow 1, 5, 11, 13, 14, 20, 21, 22, 25, 40, 47, 51, 55, 65 and 67. Among these dyes, at least one selected from C.I. Acid Yellow 17 and 23, and C.I. Direct Yellow 86 is preferably used.

As the dye used in the black ink composition, for example, food dyes such as C.I. Food Black 2; direct dyes such as C.I. Direct Black 19, 22, 32, 38, 51, 56, 71, 74, 75, 77 , 154, 168 and 171; reactive dyes, such as C.I. reactive black 3, 4, 7, 11, 12 and 17, etc. Among these dyes, at least one of C.I. Edible Black 2 and C.I. Direct Black 154 is preferably used.

Use these dyes within a stable soluble range at normal temperatures. Since such a range is different for each dye, the content of the dye in the ink composition is not particularly limited, but is preferably 0.1 to 10% by weight.

As for the pigment, any pigment dispersible in solution may be used, but it is preferable to use a pigment excellent in light fastness and water resistance.

Specific examples of the pigment include the following pigments, but the pigment is not limited to these examples. In the following examples, the color index (C.I.) number of the dye is used.

Examples of the pigment used in the cyan ink composition include C.I. Pigment Blue 1, 2, 15, 16, 17, 21, 22, 60, and 64.

Examples of the pigment used in the magenta ink composition include C.I. Pigment Red 2, 3, 5, 16, 23, 31, 49, 57, 63, 122, and 209, and C.I. Pigment Violet 19.

Examples of the pigment used in the yellow ink composition include C.I. Pigment Yellow 1, 2, 3, 5, 12, 74, 138, 150, and 180.

Examples of the pigment used in the black ink composition include carbon black such as channel black, furnace black, thermal black, or lamp black.

Among these pigments, at least one of C.I. Pigment Blue 15:3 and C.I. Pigment Blue 15:4 is preferably used in the cyan ink composition. For the magenta ink composition, it is preferable to use at least one pigment selected from C.I. Pigment Red 122, C.I. Pigment Red 209 and C.I. Pigment Violet 19. And for the yellow ink composition, it is preferable to use at least one pigment selected from C.I. Pigment Yellow 74, C.I. Pigment Yellow 138, C.I. Pigment Yellow 150 and C.I. Pigment Yellow 180. For the black ink composition, it is preferable to use at least one pigment selected from the above-mentioned carbon blacks. The use of these pigments provides an ink composition capable of producing high-quality recorded images in cyan, magenta, yellow or black.

The cyan, magenta and yellow three-color ink compositions that use these preferred pigments are superimposed, that is, the cyan ink composition that adopts at least one pigment in C.I. Pigment Blue 15:3 and C.I. Pigment Blue 15:4; A magenta ink composition selected from C.I. Pigment Red 122, C.I. Pigment Red 209 and C.I. Pigment Violet 19; and using at least one selected from C.I. Pigment Yellow 74, C.I. With the yellow ink composition, a high-density black recorded image close to a recorded image formed with the black ink composition can be obtained. That is, the ink set containing the above three ink compositions provided excellent color balance. Therefore, using an ink set containing these 3 ink compositions, or an ink set of 4 ink compositions, that is, an ink set of these 3 ink compositions and a black ink composition using carbon black, various colors can be expressed , thereby providing a color recorded image excellent in color development.

When the ink composition contains water, the pigment preferably contains one or more hydrophilic groups selected from, for example, carboxyl, hydroxyl, amino and sulfonic acid groups. Such hydrophilic groups can be directly added to the pigment surface by chemical modification, or added to the pigment surface by covering the pigment surface with a polymer containing such hydrophilic groups, thereby obtaining hydrophilicity. Such hydrophilic groups may also be in the form of salts.

Pigments containing hydrophilic groups can be stably dispersed in aqueous ink compositions. Therefore, by using a pigment having a hydrophilic group as a colorant, the occurrence of clogging can be suppressed, and a recorded image excellent in light resistance and water resistance can be obtained without impairing discharge stability.

These pigments are used within a stable dispersible range at normal temperature. Since such a range is different for each dye, the content of the pigment in the ink composition is not particularly limited, but is preferably 0.1 to 10% by weight.

The ink composition of this embodiment preferably further contains a surfactant. Therefore, the dynamic surface tension of the ink composition, including the dynamic surface tension (σ ₁₀ ) at a bubble frequency of 10 Hz and the dynamic surface tension (σ ₁ ) at a bubble frequency of 1 Hz, can be easily controlled.

The surfactant may be any one of nonionic surfactants, anionic surfactants, cationic surfactants, and zwitterionic surfactants. The type of surfactant is selected according to the type of electrolyte contained in the ink composition, such as nonionic, cationic and anionic surfactants. For example, if the ink composition contains anionic substances, a nonionic or anionic surfactant is used. Such surfactants may be used in combination. In this case, the types of surfactants, such as nonionic, anionic or cationic surfactants, may be the same or different.

Among these surfactants, nonionic surfactants are preferred because they are not easily affected by coexisting electrolytes, and can make the dynamic surface tension (σ ₁₀ ) at a bubble frequency of 10 Hz and the dynamic surface tension (σ 10 ) at a bubble frequency of ₁ Hz ) difference d(=σ ₁₀ −σ ₁ ) remains within a certain range regardless of whether an electrolyte is added to the ink composition.

Specific examples of nonionic surfactants include surfactants represented by the following general formulas (IX), (X), (XI), (XII), (XIII) and (XIV), but nonionic Surfactants are not limited by these examples.

In general formula (IX), m represents an integer or fraction of 0-30; n represents an integer or fraction of 0-30; and the sum (m+n) of m and n represents an integer or fraction of 0-30.

In general formula (X), k represents the integer or fraction of 11-13; l represents the integer or fraction of 3-30.

In the general formula (XI), h represents an integer or fraction of 0 to 11; i represents an integer or fraction of 0 to 11; j represents an integer or fraction of 3 to 50; the sum of h and i (h+i) represents 9 An integer or fraction of ~11.

In the general formula (XII), w represents an integer or fraction of 0 to 11; x represents an integer or fraction of 5 to 9; y represents an integer or fraction of 2.5 to 5; z represents an integer or fraction of 0 to 9; w and The sum (w+z) of z represents an integer of 9-11 or a fraction.

In general formula (XIII), p represents an integer or fraction of 0-78; q represents an integer or fraction of 2-15; r represents an integer or fraction of 0-18.

In the general formula (XIV), s represents an integer or fraction of 0-30; t represents an integer or fraction of 0-30; but the sum (s+t) of s and t represents an integer or fraction of 0-30. In addition, u represents an integer or fraction of 0-10; v represents an integer or fraction of 0-10, but the sum (u+v) of u and v represents an integer or fraction of 0-10.

The surfactant is preferably contained in the ink composition at or above the critical micelle concentration. The surface tension of surfactant-containing solutions decreases with increasing surfactant up to the critical micelle concentration, but remains essentially constant above the critical micelle concentration. Therefore, using a surfactant at or above the critical micelle concentration as described above, it is possible to fully utilize the effect of the surfactant to make the dynamic surface tension of the bubble frequency 10 Hz controlled by the surfactant and the bubble frequency 1 Hz The dynamic surface tension of is maintained at a substantially constant value, resulting in an ink composition with uniform properties.

Although the critical micelle concentration of various surfactants is different, the critical micelle concentration of any nonionic surfactant, anionic surfactant, cationic surfactant and zwitterionic surfactant is about 0.001 at 25°C ~3% by weight.

When a pigment is used as a colorant, the ink composition of the present embodiment preferably contains a binder resin. The presence of the binder resin prevents the peeling of the pigment from the recording material.

As the binder resin, one or more resins selected from polyester resins, acrylic resins, styrene-acrylic copolymer resins, and polyester-acrylic copolymer resins may be used.

The ink composition of the present embodiment may further contain other additives such as antifungal agents, pH adjusters, chelating agents, rust inhibitors, or ultraviolet absorbers, in addition to colorants, media, surfactants, and binder resins.

As an antifungal agent, it is preferable to use sodium dehydroacetate, sodium benzoate, sodium sorbate, or the like.

As the pH adjuster, it is preferable to use triethanolamine, sodium hydroxide, sodium carbonate, sodium nitrate, potassium nitrate, or the like.

For example, an ink composition containing at least one colorant and medium, and in which the dynamic surface tension (σ ₁₀ ) at a bubble frequency of 10 Hz and the dynamic surface tension (σ ₁ ) at a bubble frequency of 1 Hz satisfy the formula (2 ) difference d(=σ ₁₀ −σ ₁ ).

The ink composition according to the fourth embodiment of the present invention is used in the ink jet head 1 shown in FIGS. 1 to 3 . Since the ink tank 50 stores the ink composition 60a of the fourth embodiment described above, and such ink composition 60a is supplied to the ink cartridge 40 and discharged in the form of droplets from the discharge port 31, the inkjet head 1 of this embodiment can be stabilized. Droplets of the ink composition 60a are discharged from the discharge port 31 in a steady manner. Such an inkjet head can realize a piezoelectric inkjet recording device with high reliability, which can stably provide high-quality recorded images.

The ink composition according to the fourth embodiment of the present invention is used in the ink jet head 2 shown in FIGS. 4 to 6 . Like the inkjet head 1 of the second embodiment, since the ink tank 50 stores the ink composition 60a of the fourth embodiment, such ink composition 60a is supplied to the ink cartridge 40 and is discharged from the discharge port 31 in the form of droplets 61a. discharge, therefore, the inkjet head 2 of the present embodiment can stably discharge the ink composition 60 a droplet 61 a from the discharge port 31 . Such an inkjet head can realize a thermal inkjet type inkjet recording device with high reliability, and can stably provide high-quality recorded images.

Example

The present invention will be illustrated in more detail by examples below, but the present invention is not limited by these examples. In these embodiments, image recording is sometimes referred to as printing or printing.

<Ink composition>

When preparing the ink composition, as shown in Table 6, the types and contents of the colorant, organic solvent and surfactant, and the content of the binder resin and water are changed to obtain the ink compositions of Examples 8-14 , where the dynamic surface tension (σ ₁₀ ) at a bubble frequency of 10 Hz and the dynamic surface tension (σ ₁ ) at a bubble frequency of 1 Hz have a difference d(=σ ₁₀ −σ ₁ ) satisfying formula (2), and the An ink composition, wherein d does not satisfy formula (2). In Table 6, the units of values in each column are expressed in parts by weight, and the total amount of each ink composition in Examples 8 to 14 and Comparative Examples 5 to 8 is 100 parts by weight, respectively. In addition, in Table 6, TEGBE represents triethylene glycol monobutyl ether; PEG400 represents polyethylene glycol with a molecular weight of 400; general formula (IX) represents a surfactant represented by general formula (IX); general formula (X) represents The surfactant represented by general formula (X); General formula (XI) represents the surfactant represented by general formula (XI); General formula (XII) represents the surfactant represented by general formula (XII); General formula (XIII) represents the surfactant represented by general formula (XIII); Fluorosurfactant 1 represents the surfactant represented by chemical formula (XV); Fluorosurfactant 2 represents the surfactant represented by chemical formula (XVI) agent. The surfactant concentration in the ink composition is equal to or higher than the critical micelle concentration in Examples 8-14 and Comparative Examples 5-7, but less than that in Comparative Example 8.

The dynamic surface tensions of Examples 8 to 14 and Comparative Examples 5 to 8 were measured with a surface tensiometer (BP-4: produced by Kyowa Kaimen Kagaku Co.) at a bubble frequency of 0.5 to 35 Hz.

_Table 7 _shows the difference d(mN/ m) (=σ ₁₀ -σ ₁ ) and the measurement temperature (°C) at this time.

Table 6 combination Example comparative example 8 9 10 11 12 13 14 5 6 7 8 dye CI Direct Blue 199 2.5 CI Pigment Blue 15:3 3 CI Pigment Blue 15:4 3 CI Pigment Red 122 5 CI Pigment Yellow 74 4 CI Pigment Yellow 180 4 carbon black 5 5 CI Pigment Blue 17 2 CI Pigment Red 58 3 CI Pigment Yellow 13 2 Diethylene glycol 8 8 8 5 5 8 8 2 5 20 10 Glycerol 5 7 8 10 8 8 9 5 5 17 10 1,5-pentanediol 2 5 2 2 5 2 18 5 TEGBE 8 8 8 5 5 3 6 4 8 PEG400 1 10 15 15 10 General formula (IX) (m+n=10) 1 1 General formula (X) (k=11～13, 1=15) 1 1.0 0.001 General formula (XI) (h+i=9～11, j=9) 1.5 General formula (XII) (w+z=9～11, x=9, y=5) 1.5 General formula (XIII) (p=12, q=8, r=4) 1 Fluorosurfactant 1 1 Fluorosurfactant 2 1.5 1 binder resin polyester resin none 1 1.5 2 1 1.5 1 1 1.5 2 2 water R R R R R R R R R R R

R: Margin

Table 7 Dynamic surface tension σ ₁₀ (mN/m) at 10Hz Dynamic surface tension σ ₁ (mN/m) at 1Hz d(mN/m) Measuring temperature (°C) Example 8 31.9 26.7 5.2 25.3～25.7 Example 9 31.9 26.7 5.2 25.2～25.6 Example 10 34.5 29.5 5 24.9～25.3 Example 11 34.7 29.6 5.1 24.7～25.2 Example 12 34.4 29.1 5.3 24.8～25.2 Example 13 34.8 29.7 5.1 25.0～25.4 Example 14 34.6 29.5 5.1 25.3～25.7 Comparative Example 5 31.4 24.3 7.1 25.1～25.6 Comparative example 6 29.5 22.0 7.5 25.1～25.6 Comparative Example 7 29.5 22.2 7.3 25.0～25.5 Comparative Example 8 38.9 25.5 13.4 24.8～25.2

The discharge stability of the obtained ink compositions of Examples 8 to 14 and Comparative Examples 5 to 8 when used in an inkjet recording method and the image quality of the obtained recorded images were evaluated as follows.

<Discharge stability>

The obtained ink compositions of Examples 8 to 14 and Comparative Examples 5 to 8 were respectively filled into ink tanks of an inkjet recording apparatus, which is a commercially available inkjet recording apparatus (AJ2000: produced by SharpKabushiki Kaisha) Obtained through transformation, so that the inkjet head 1 shown in Figure 1 can be installed, with the printing speed of 7 pages per minute of A4 paper, the ordinary copy paper (trade name: SF4AM3) produced continuously in Sharp KabushikiKaisha with printing density 5% to print on. In this test, when the ink tank is empty, the ink composition is refilled, printing is continued until the ink composition droplet cannot be discharged from the nozzle and no more printing is possible, and the number of sheets completely printed up to this point is counted to obtain the printable value. The number of sheets was used as an index for evaluating the discharge stability. If the number of printable sheets exceeds 200, it is rated as good (◯), if the number is 150 to 200, it is rated as good (△), and if it is less than 150, it is rated as poor (×).

<Image Quality>

In addition, the obtained ink compositions of Examples 8 to 14 and Comparative Examples 5 to 8 were respectively filled into ink tanks of an inkjet recording device, which is a commercially available inkjet recording device (AJ2000: by Sharp Kabushiki Kaisha) modified so that the inkjet head 1 shown in FIG. 1 can be mounted to print a specific pattern on plain copy paper (trade name: SF4AM3) produced by Sharp Kabushiki Kaisha to obtain an image for evaluation. Leave the evaluated image for one day, set the pattern line width to 100, measure the relative value of the pattern line width of each evaluation image, and use it as an index for evaluating image quality. If the relative line width is less than 150 and there is almost no imprint, the result is rated as good (○); if the relative line width is 150-250, and there are some imprints, it is rated as good (△); if the relative line width exceeds 250, and there is A large amount of imprinting was rated as poor (x).

The above evaluation results are listed in Table 8.

Table 8 Example comparative example 8 9 10 11 12 13 14 5 6 7 8 discharge stability ○ ○ ○ ○ ○ ○ ○ x x x △ Image Quality ○ ○ ○ ○ ○ ○ ○ x x x x

In the ink compositions of Examples 8 to 14, the difference d(=σ ₁₀ −σ ₁ ) between the dynamic surface tension (σ ₁₀ ) at a bubble frequency of 10 Hz and the dynamic surface tension (σ ₁ ) at a bubble frequency of 1 Hz satisfies the formula ( 2), its discharge stability and image quality are good. On the other hand, in the ink compositions of Comparative Examples 5 to 8, their difference d was greater than 7 and exceeded the range of formula (2), and the discharge stability and image quality were poor or good.

As mentioned above, the difference d(=σ ₁₀ -σ ₁ ) between the dynamic surface tension (σ ₁₀ ) at a bubble frequency of 10 Hz and the dynamic surface tension (σ ₁ ) at a bubble frequency of 1 Hz satisfies formula (2), and it is possible to obtain An ink composition for use in an inkjet recording method, which exhibits excellent discharge stability and suppresses the occurrence of markings on a recording material, providing high-quality recorded images.

<ink set>

As shown in Table 9, the ink compositions of Examples 9 to 13 and Comparative Examples 5 to 7 were mixed as cyan, magenta and yellow ink compositions to obtain C.I. Pigment Blue 15:3 and C.I. Pigment Blue 15 Cyan ink composition of at least one pigment in 4, containing at least one magenta ink composition selected from C.I. Pigment Red 122,209 and C.I. Pigment Violet 19 pigment, containing at least one selected from C.I. Pigment Yellow 74, The yellow ink composition of 138,150 and 180 pigments constitutes embodiment ink group 2; Make comparative example ink group 5～7, wherein any kind of pigment in cyan, magenta and yellow ink composition is different from above-mentioned pigment; Comparative Ink Set 8 was prepared in which all of the cyan, magenta, and yellow ink compositions contained pigments other than those described above.

Table 9 blue Magenta yellow Example ink set 2 Embodiment 9C.I. pigment blue 15:3 Example 11C.I. Pigment Red 122 Example 12C.I. Pigment Yellow 74 Comparative Example Ink Set 5 Comparative Example 5C.I. Pigment Blue 17 Example 11C.I. Pigment Red 122 Embodiment 13C.I. Pigment Yellow 180 Comparative Example Ink Set 6 Embodiment 10C.I. Pigment blue 15:4 Comparative Example 6C.I. Pigment Red 58 Embodiment 13C.I. Pigment Yellow 180 Comparative Example Ink Set 7 Embodiment 10C.I. Pigment blue 15:4 Example 11C.I. Pigment Red 122 Comparative Example 7C.I. Pigment Yellow 13 Comparative Example Ink Set 8 Comparative Example 5C.I. Pigment Blue 17 Comparative Example 6C.I. Pigment Red 58 Comparative Example 7C.I. Pigment Yellow 13

Using the obtained Example Ink Set 2 and Comparative Example Ink Sets 5 to 8 respectively, and using an inkjet recording device, the inkjet recording device is a commercially available inkjet recording device (AJ2000: produced by Sharp KabushikiKaisha) obtained through modification, A black image was formed by printing on glossy paper (trade name: AJ-K4AG) at a printing ratio of cyan, magenta, and yellow ink compositions of 1:1:1. Furthermore, the ink composition of Example 14 was used as the black ink composition to obtain the same image.

Each of the obtained black images was measured with a spectrophotometer (X-Rite 938: manufactured by X-Rite Inc.) to obtain a lightness index L ^* and chromaticity in the L ^* a ^* b ^* color system (CIE: 1976) Index a ^* , b ^* .

The test results were evaluated as follows. In the black image formed with the ink composition of Example 14, the chromaticity indices a ^* and b ^* were taken as A1 and B1, respectively, and in the black images formed with the ink set 2 of Example and the ink sets 5 to 8 of Comparative Examples, The chromaticity indices a ^* and b ^* are taken as A2 and B2 respectively, and the Δa ^* b ^* value represented by the following formula (C) is obtained as an evaluation index of black reproducibility:

Δa ^* b ^* ＝{(A1-A2) ² +(B1-B2) ² } ^1/2 (C)

Cases where the value of Δa ^* b ^* was equal to or less than 20 (Δa ^* b ^* ≤20) were rated as good (◯), while cases exceeding 20 (Δa ^* b ^* >20) were rated as poor (×). The evaluation results are listed in Table 10.

Table 10 Evaluation Results Example ink set 2 ○ Comparative Example Ink Set 5 x Comparative Example Ink Set 6 x Comparative Example Ink Set 7 x Comparative Example Ink Set 8 x

Table 10 shows that, compared with the black image formed by the superposition of the three ink compositions contained in the ink groups 5-8 of the comparative example, the black image formed by the superposition of the three ink compositions contained in the ink group 2 of the example ink has more High density, which is close to that of the black image formed with the ink composition of Example 14. Therefore, it can be concluded that Example ink set 2 has better black reproducibility and excellent color balance than Comparative Example ink sets 5-8.

As mentioned above, the cyan ink composition containing at least one pigment in C.I Pigment Blue 15:3 and C.I Pigment Blue 15:4, the cyan ink composition containing at least one selected from C.I. Pigment Red 122, 209 and C.I. Pigment Violet 19 pigment The magenta ink composition and the yellow ink composition containing at least one pigment selected from C.I. Pigment Yellow 74, 138, 150 and 180 are superimposed to obtain an ink set with excellent color balance.

It can be implemented in various other ways without departing from the spirit or essential features of the present invention. Therefore, it can be considered that these schemes are illustrative rather than restrictive in all respects, and the scope of the present invention is indicated by the claims rather than the above description, therefore, all changes falling within the scope of the claims include within the scope of the present invention.

Claims (27)

1. An ink composition, containing at least a coloring agent, a medium and a tensio-active agent, wherein, Among the dynamic surface tensions measured by _the maximum bubble pressure method at a temperature of 24 to 26°C _, the difference d(=σ ₁₀ -σ ₁ ) satisfy the following formula (2): 0mN/m≤d≤7mN/m 2. The ink composition according to claim 1, wherein the dynamic surface tension (σ ₁₀ ) at a bubble frequency of 10 Hz and the dynamic surface tension (σ ₁ ) at a bubble frequency of 1 Hz are in the range of 20 to 70 mN/m. 3. The ink composition according to claim 1, wherein the medium contains water. 4. The ink composition according to claim 1, wherein the medium contains at least one of glycol ethers and polyols. 5. The ink composition of claim 1, wherein the colorant comprises a dye. 6. The ink composition of claim 1, wherein the colorant comprises a pigment. 7. The ink composition of claim 3, wherein the colorant comprises a pigment having a hydrophilic group. 8. The ink composition according to claim 1, wherein the surfactant comprises a nonionic surfactant. 9. The ink composition according to claim 1, wherein the surfactant is contained at or above the critical micelle concentration. 10. The ink composition of claim 6, wherein the pigment comprises at least one of C.I. Pigment Blue 15:3 or C.I. Pigment Blue 15:4. 11. The ink composition according to claim 6, wherein the pigment comprises at least one pigment selected from C.I. Pigment Red 122, C.I. Pigment Red 209, and C.I. Pigment Violet 19. 12. The ink composition according to claim 6, wherein the pigment comprises at least one pigment selected from the group consisting of C.I Pigment Yellow 74, C.I Pigment Yellow 138, C.I Pigment Yellow 150, and C.I. Pigment Yellow 180. 13. The ink composition of claim 6, wherein the pigment comprises carbon black. 14. A method of image recording, comprising: attaching the ink composition to the recording material, Wherein the ink composition uses the ink composition described in claim 1. 15. A method of image recording, comprising: applying pressure to the ink composition to expel droplets of the ink composition; and Attach the droplet to the recording material, Wherein the ink composition uses the ink composition described in claim 1. 16. The recording method according to claim 14, wherein, for the ink composition, at least the ink composition according to claim 10, the ink composition according to claim 11 and the ink composition according to claim 12 are used . 17. The recording method according to claim 15, wherein, for the ink composition, at least the ink composition according to claim 10, the ink composition according to claim 11 and the ink composition according to claim 12 are used . 18. The recording method according to claim 14, wherein, for the ink composition, at least the ink composition according to claim 10, the ink composition according to claim 11, and the ink composition according to claim 12 are used And the ink composition described in claim 13. 19. The recording method according to claim 15, wherein, for the ink composition, at least the ink composition according to claim 10, the ink composition according to claim 11, and the ink composition according to claim 12 are used And the ink composition described in claim 13. 20. A recorded image recorded by the recording method according to claim 14. 21. A recorded image recorded by the recording method according to claim 15. 22. An ink set comprising: The ink composition described in claim 10; The ink composition of claim 11; and The ink composition described in claim 12. 23. An ink set comprising: The ink composition described in claim 10; The ink composition described in claim 11; The ink composition of claim 12, and The ink composition described in claim 13. 24. An inkjet head comprising: An ink tank for storing the ink composition of claim 1; an ink cartridge having an outlet for ejecting ink composition droplets and receiving ink composition from the ink tank; a piezoelectric element deformable in response to an applied voltage and provided in at least a portion of the ink cartridge for applying pressure to an ink composition contained in the ink cartridge; and The electrodes that apply voltage to the piezoelectric element. 25. An inkjet head comprising: An ink tank for storing the ink composition of claim 1; an ink cartridge having an outlet for ejecting ink composition droplets and receiving a supply of ink composition from the ink tank; a heat generating element provided in at least some of the ink cartridges for heating the ink composition contained in the ink cartridge to cause bubbles to apply pressure to the ink composition; and An electrode that applies voltage to a heating element. 26. A recorded image recorded by attaching droplets of the ink composition discharged from the inkjet head according to claim 24 to a recording material. 27. A recorded image recorded by attaching droplets of the ink composition discharged from the inkjet head according to claim 25 to a recording material.

Images