JP2016079359A - Inkjet ink and inkjet recording system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink that can decrease the size of convex curl in a recording medium on which an image is formed by using an ink and is excellent in print density.SOLUTION: The inkjet ink includes a pigment dispersion and a vehicle. The pigment dispersion comprises a pigment and a pigment dispersion resin. The vehicle includes a humectant, a first penetrant, a second penetrant, and a surfactant. The surfactant is a nonionic surfactant. The first penetrant is 1-2-octanediol or 2,4-diethyl-1,5-pentanediol. The humectant contains propylene glycol or 1,3-propanediol having a content of not less than 25 mass% to not more than 100 mass% based on the total mass of the humectant. Each of the humectant, the first penetrant, the second penetrant and the surfactant is dissolved in the vehicle. The vehicle has a surface tension of not less than 30.0 mN/m to not more than 35.0 mN/m.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an inkjet ink and an inkjet recording system.

  In recent years, rapid progress in inkjet recording technology has made it possible to obtain high-definition inkjet photographs comparable to silver salt photographs.

  As printing speed increases, line-type recording heads (long heads) may be used. Examples of the inkjet printing method include a multi-pass method and a single-pass method. The multi-pass method is a method in which ink is ejected from the recording head while the recording head is reciprocated several times on the recording medium. The single pass method is a method in which ink is ejected from the recording head by passing the recording head once on the recording medium. The single pass method has an advantage that the printing speed can be increased.

  Therefore, from the viewpoint of speeding up printing, an image forming apparatus combining a line-type recording head and a single-pass method has been studied. However, when an image is formed on a recording medium using a line-type recording head and a single pass method, the recording head cannot pass over the recording medium because it passes only once on the recording medium. For this reason, particularly when plain paper is used as the recording medium, the density (printing density) of the formed image is liable to decrease and ink bleeding tends to occur. In addition, the ink is excessively permeated into the recording medium, and the phenomenon of see-through is easily caused that the image can be seen through on the surface (back surface) on which the image of the recording medium is not formed. As described above, when an image is formed on a recording medium using a line type recording head and a single pass method, there is a problem that the image quality of the formed image tends to be extremely inferior.

  By the way, water-based ink is often used as ink-jet ink. When an image is formed on a recording medium using aqueous ink, the occurrence of curling in the recording medium becomes a problem. The shape of the curl generated is a convex curl for several seconds after the image is formed (a curl that is convex in the direction from the image non-formation surface of the recording medium to the image formation surface). Thereafter, it gradually deforms into a concave curl (a curl convex in the direction from the image forming surface to the non-image forming surface of the recording medium). When such curl occurs in the recording medium, various problems occur during high-speed printing. For example, when the deformation of the recording medium due to the convex curl is large, the recording medium may not be satisfactorily attracted to the transport plate when printing on the second surface (back surface) of the recording medium in double-sided printing. Further, when the convex curl is generated, the concave curl is generated as time passes, so that the quality of the obtained printed matter may be deteriorated.

  In order to suppress the occurrence of such curling, an inkjet ink containing polyoxypropylene diglyceryl ether and alkylalkanediol as a water-soluble organic solvent has been proposed (Patent Document 1). However, inks made of such a hydrophilic skeleton material tend to suppress the occurrence of concave curls, but tend to cause convex curls.

  An ink-jet ink containing propylene glycol as a wetting agent has been proposed (Patent Document 2). However, 2,2,4-trimethyl-1,3-pentanediol is used in manufacturing the ink. Since 2,2,4-trimethyl-1,3-pentanediol is a high penetrant that is solid at room temperature, it is difficult to suppress the occurrence of convex curls.

JP 2010-59344 A JP 2004-43518 A

  Therefore, there has been a demand for an ink-jet ink that can both suppress the occurrence of convex curl in a recording medium when an image is formed using ink and can form an image with an excellent print density.

  The present invention has been made in view of the above problems, and can reduce the size of convex curl in a recording medium when an image is formed using ink, and can form an image with an excellent print density. Provided is an inkjet ink that can be used. Furthermore, by using such an ink, even when an image is formed by a line head type recording head, the size of the convex curl on the recording medium can be reduced, and an image with excellent print density can be obtained. An inkjet recording system that can be obtained is provided.

  The inkjet ink according to the present invention includes a pigment dispersion and a vehicle. The pigment dispersion includes a pigment and a pigment dispersion resin. The vehicle includes a humectant, a first penetrant, a second penetrant, and a surfactant. The surfactant is a nonionic surfactant. The first penetrant is 1,2-octanediol or 2,4-diethyl-1,5-pentanediol. The humectant contains propylene glycol or 1,3-propanediol at a content of 25% by mass to 100% by mass with respect to the total mass of the humectant. In the vehicle, the humectant, the first penetrant, the second penetrant, and the surfactant are each dissolved. The surface tension of the vehicle is 30.0 mN / m or more and 35.0 mN / m or less.

  An ink jet recording system according to the present invention includes a transport unit that transports a recording medium and an ink jet recording head. The ink jet recording head includes a nozzle row having a plurality of nozzles arranged in a direction orthogonal to the conveyance direction of the recording medium. A plurality of the nozzle rows are arranged side by side in the conveyance direction of the recording medium. By ejecting the above ink from the plurality of nozzles of the ink jet recording head, dots are formed on the recording medium transported by the transport unit.

  According to the present invention, the size of convex curl in a recording medium when an image is formed using ink can be reduced, and an image can be formed with an excellent print density.

It is a figure which shows the molecular structure of a cellulose. It is a figure which shows the generation mechanism of curl. It is a figure which shows the structure of an inkjet recording device provided with a line head type recording head. It is the figure which looked at the conveyance belt of the inkjet recording device shown in FIG. 3 from upper direction. FIG. 4A is a diagram illustrating a discharge unit of the line head type recording head illustrated in FIG. 3. (B) is BB sectional drawing of (a). 1 is a block diagram illustrating a configuration of an ink jet recording apparatus including a line head type recording head. FIG. It is a figure which shows a part of dot row formed on the recording head used for an inkjet recording device provided with a line head type recording head, and a recording medium.

  Hereinafter, embodiments of the present invention will be described.

[First Embodiment: Ink-jet ink]
The first embodiment of the present invention is an inkjet ink (hereinafter may be abbreviated as “ink”). The ink according to this embodiment contains a pigment dispersion and a vehicle. The pigment dispersion is composed of a pigment and a pigment dispersion resin. The vehicle includes a humectant, a first penetrant, a second penetrant, and a surfactant. In the vehicle, the humectant, the first penetrant, the second penetrant, and the surfactant are each dissolved. The surface tension of the vehicle is 30.0 mN / m or more and 35.0 mN / m or less.

  When the ink according to the present embodiment is a water-based ink to which water is added, the vehicle means an ink component excluding the added water and a pigment dispersion described later.

  In the ink of this embodiment, each component is dissolved in the vehicle contained in the ink, and the vehicle has a predetermined surface tension. Therefore, it is possible to achieve both the suppression of the occurrence of convex curl in the recording medium when an image is formed using ink and the formation of an image with an excellent print density. The reason will be described below.

  First, in order to facilitate understanding, a mechanism for generating convex curls will be described. Paper fibers that are recording media are composed of cellulose having the molecular structure shown in FIG. The cellulose molecules give strength to the paper by intermolecular hydrogen bonding. When the recording medium is plain paper, cellulose fibers constituting the plain paper are intertwined with each other. When the ink is water-based ink, when the ink is ejected onto the recording medium, the cellulose fiber on the surface of the recording medium gets wet. Thereby, as shown in FIG. 2, the hydroxyl group which the component (for example, water and a humectant) contained in an ink cut | disconnects the intermolecular hydrogen bond of a cellulose fiber, and a cellulose fiber swells. The swollen cellulose fiber is elongated by loosening of the entanglement between the fibers. As a result, a difference occurs between the lengths of the cellulose fibers on the surface (front surface) from which the ink of the recording medium is discharged and the cellulose fibers on the back surface thereof. Such a difference in the length of the cellulose fibers between the front surface and the back surface of the recording medium causes a convex curl of the recording medium. Thereafter, when the ink is dried, the swollen cellulose fibers contract, and the hydroxyl groups generated by the breakage of the hydrogen bonds form hydrogen bonds again at positions different from those before ink discharge. As a result, the convex curl of the recording medium changes to a concave curl.

  By adjusting the surface tension of the vehicle contained in the ink within a predetermined range (35.0 mN / m or less) from the above-described convex curl generation mechanism, the occurrence of convex curl can be suppressed. When the surface tension of the vehicle contained in the ink decreases, the permeability of the ink into the recording medium tends to increase. When the ink permeability increases, the difference between the wetness (swelled state) of the surface (front surface) of the recording medium on which the ink is ejected and the wetness of the back surface thereof decreases. As a result, it is considered that the difference in length between the cellulose fiber on the front surface of the recording medium and the cellulose fiber on the back surface thereof is reduced, and the occurrence of convex curl is suppressed.

  In addition, since the moisturizer, the first penetrating agent, the second penetrating agent, and the surfactant are dissolved in the vehicle, the occurrence of convex curl can be suppressed. When the components in the vehicle are separated or suspended, each component contained in the ink is easily separated when the ink wets and penetrates the recording medium. When the components are separated, only the ink component having high permeability (low surface tension) penetrates the recording medium first. As a result, the penetrability of the entire ink into the recording medium is reduced, and the difference between the wetness (swelled state) of the surface (front surface) on which the ink is ejected and the wetness of the back surface thereof increases. As a result, it is considered that the difference between the length of the cellulose fiber on the surface of the recording medium and the length of the cellulose fiber on the back surface becomes large. Conversely, the dissolution of each component in the ink reduces the difference between the length of the cellulose fiber on the surface of the recording medium and the length of the cellulose fiber on the back surface, thereby suppressing the occurrence of convex curl. It is thought.

  On the other hand, if the surface tension of the vehicle contained in the ink is too small, the ink permeability to the recording medium becomes too high, and the print density tends to decrease or the showthrough occurs. This is because the ink easily penetrates into the recording medium, and the pigment contained in the ink hardly stays on the surface of the recording medium. In addition, if the surface tension of the vehicle contained in the ink is excessive, unevenness in density occurs in the formed image, resulting in a decrease in print density.

  For the reasons described above, the ink of this embodiment has each component dissolved in the vehicle, and the vehicle has a predetermined surface tension (30.0 mN / m or more and 35.0 mN / m or less). It is possible to achieve both curling of curling and forming an image with an excellent print density.

  Hereinafter, the pigment dispersion and vehicle contained in the ink of this embodiment will be described. An ink preparation method will also be described.

<1. Pigment dispersion>
The pigment dispersion is composed of a pigment and a pigment dispersion resin. The pigment dispersion is preferably composed of a pigment (hereinafter sometimes referred to as pigment particles) and a pigment dispersion resin that covers the pigment particles. That is, the pigment dispersion is preferably composed of pigment particles and a pigment-dispersed resin layer (a film made of a pigment-dispersed resin) that exists so as to cover the surface of the pigment particles. Hereinafter, the manufacturing method of a pigment, pigment dispersion resin, and a pigment dispersion is demonstrated.

<1-1. Pigment>
As the pigment, for example, a yellow pigment, an orange pigment, a red pigment, a blue pigment, a violet pigment, or a black pigment can be used. Examples of yellow pigments include C.I. I. Pigment yellow (74, 93, 95, 109, 110, 120, 128, 138, 139, 151, 154, 155, 173, 180, 185, or 193). Examples of the orange pigment include C.I. I. Pigment orange (34, 36, 43, 61, 63, or 71). Examples of red pigments include C.I. I. Pigment red (122 or 202). Examples of blue pigments include C.I. I. Pigment blue (15, more specifically 15: 3). Examples of purple pigments include C.I. I. Pigment violet (19, 23, or 33). Examples of black pigments include C.I. I. Pigment black (7).

  The pigment content in the ink is preferably 4% by mass or more and 8% by mass or less with respect to the total mass of the ink. When the pigment content is 4% by mass or more, an image having a desired image density is easily obtained. Further, when the pigment content is 8% by mass or less, the fluidity of the ink is ensured, whereby an image having a desired image density is easily obtained, and the permeability of the ink to the recording medium is easily secured.

In order to improve the color density, hue, or stability of the ink, the volume median diameter (D ₅₀ ) of the pigment is preferably 30 nm or more and 200 nm or less, and more preferably 70 nm or more and 130 nm or less.

<1-2. Pigment-dispersed resin>
The pigment dispersion resin contained in the ink is preferably coated with a pigment (pigment particles). Aggregation of the pigment particles can be suppressed by forming a film (layer) made of the pigment dispersion resin on the surface of the pigment particles (adsorbing to the pigment particles). In the ink, a pigment dispersion resin (non-adsorbed resin) that is not adsorbed by the pigment particles may exist. The pigment dispersion resin preferably has an anionic property.

  The pigment dispersion resin can be appropriately selected from known pigment dispersion resins. Specific examples of the pigment dispersion resin include styrene-acrylic resin, styrene-maleic acid copolymer, styrene-maleic acid half ester copolymer, vinylnaphthalene-acrylic acid copolymer, or vinylnaphthalene-maleic acid copolymer. Is mentioned. The styrene-acrylic resin is a resin including a unit derived from styrene and a unit derived from acrylic acid, methacrylic acid, acrylic ester, or methacrylic ester. Examples of the styrene-acrylic resin include a styrene-acrylic acid-alkyl acrylate ester copolymer, a styrene-methacrylic acid-methacrylic acid alkyl ester-acrylic acid alkyl ester copolymer, a styrene-acrylic acid copolymer, and a styrene- Examples thereof include a maleic acid-acrylic acid alkyl ester copolymer, a styrene-methacrylic acid copolymer, and a styrene-methacrylic acid alkyl ester copolymer. Among these pigment-dispersed resins, styrene-acrylic resins are preferred, and styrene-methacrylic acid-alkyl methacrylate-alkyl acrylate copolymers are more preferred because they are easy to prepare and have excellent pigment dispersion effects. A methacrylic acid-methyl methacrylate-butyl acrylate-styrene copolymer is particularly preferred.

  Moreover, it is preferable that the acid value of pigment dispersion resin is 50 mgKOH / g or more and 300 mgKOH / g or less. If the acid value of the pigment-dispersed resin is too small, the dispersibility of the pigment tends to be low, and it becomes difficult to make the pigment fine particles, so that it is difficult to obtain good colorability and color developability. When the acid value of the pigment dispersion resin is excessive, the storage stability of the ink tends to be low.

  The acid value of the pigment dispersion resin can be adjusted by changing the amount of the monomer used when the pigment dispersion resin is synthesized. For the synthesis of the pigment dispersion resin, a monomer having an acidic functional group (for example, a carboxy group) (for example, acrylic acid or methacrylic acid) is used. By increasing the amount of the monomer having an acidic functional group, the acid value of the pigment dispersion resin can be increased.

  The mass average molecular weight (Mw) of the pigment dispersion resin is preferably, for example, 10,000 or more and 160000 or less. When the mass average molecular weight of the resin is too small, it is difficult to obtain an image having a desired image density when forming an image on a recording medium. In addition, when the mass average molecular weight is excessive, the viscosity of the ink is high, so that the viscosity of the ink is likely to be further increased due to volatilization of the solvent, and ink ejection from the nozzle is likely to occur. For this reason, when the mass average molecular weight of the resin is excessive, it is difficult to form a good image. Further, if the mass average molecular weight of the pigment-dispersed resin fat is too small, there may be a case where the recording medium after the image formation is exposed. On the other hand, if the mass average molecular weight of the pigment-dispersed resin is excessive, the intermittent ejection property of the ink may be impaired.

  The mass average molecular weight (Mw) can be measured by gel filtration chromatography. The molecular weight of the pigment dispersion resin can be adjusted by changing the polymerization conditions of the pigment dispersion resin (the amount of polymerization initiator used, the polymerization temperature, the polymerization time, etc.). The amount of the radical polymerization initiator is preferably 0.001 mol or more and 5 mol or less, and more preferably 0.01 mol or more and 2 mol or less, per mol of the monomer mixture. The polymerization temperature is preferably 50 ° C. or higher and 70 ° C. or lower. The polymerization time is preferably 10 hours or more and 24 hours or less.

  The content of the pigment dispersion resin is preferably in the range of 15 to 100 parts by mass with respect to 100 parts by mass of the pigment. If the content of the pigment-dispersed resin is too small, the recording medium after image formation may be show through. On the other hand, if the content of the pigment-dispersed resin is excessive, the osmotic dry viscosity described later increases, and it becomes difficult for the ink to spread on the recording medium, and an image having a desired density may not be obtained.

  The proportion of the pigment dispersion resin (adsorption resin) adsorbed on the pigment particles in the pigment dispersion resin in the ink is preferably 95% by mass or more and 100% by mass or less.

<1-3. Method for producing pigment dispersion>
A pigment dispersion can be obtained by coating a pigment (pigment particles) with a pigment dispersion resin. As a method for producing the pigment dispersion, a known method can be used. As a suitable method, for example, using a media type wet disperser such as Nano Glen Mill (manufactured by Asada Iron Works Co., Ltd.), MSC Mill (manufactured by Nippon Coke Industries Co., Ltd.), Dino Mill (manufactured by Shinmaru Enterprises Co., Ltd.) Examples thereof include a method of kneading a pigment and a pigment dispersion resin in an appropriate liquid medium such as water to obtain a pigment dispersion (specifically, a pigment dispersion containing the pigment dispersion). In the processing by the media type wet disperser, beads having a small particle diameter are used. The particle size of the beads is not particularly limited, but is, for example, 0.5 mm or more and 1.0 mm or less. Moreover, although the material of a bead is not specifically limited, For example, it is preferable to use hard materials, such as glass and a zirconia.

  The amount of the liquid medium used for producing the pigment dispersion is preferably, for example, a liquid medium having a mass of 0.1 to 5 times the total mass of the pigment and the pigment dispersion resin. It is more preferable to use a liquid medium having a mass of 0.5 to 4 times.

The dispersion conditions for producing the pigment dispersion are preferably adjusted such that the volume median diameter (D ₅₀ ) of the pigment dispersion is 70 nm to 130 nm (preferably 80 nm to 120 nm). For example, by changing the diameter of the beads, the degree of dispersion of the pigment and the amount of free resin (amount of pigment dispersion resin not coated with the pigment) can be adjusted. Specifically, the smaller the bead diameter, the finer the pigment. Moreover, the coating amount of the pigment dispersion resin with respect to a pigment can be increased, so that the diameter of a bead is small.

The volume median diameter (D ₅₀ ) can be determined, for example, for a solution obtained by diluting a pigment dispersion containing a pigment dispersion 300 times with ion-exchanged water (“Zeta” manufactured by Sysmex Corporation). Sizer ").

<2. Vehicle>
The vehicle included in the ink of the present embodiment contains a humectant, a first penetrating agent, a second penetrating agent, and a surfactant. Further, the vehicle may contain a known additive (for example, a dissolution stabilizer) as necessary. Hereinafter, the humectant, the first penetrant, the second penetrant, the surfactant, and the dissolution stabilizer will be described. The vehicle manufacturing method, vehicle dissolution state, and vehicle surface tension will also be described.

<2-1. Moisturizer>
The humectant is used for the purpose of stabilizing the viscosity of the ink by suppressing the volatilization of the liquid component from the ink. Further, the viscosity of the ink can be adjusted by adjusting the amount of the humectant.

  The humectant contains propylene glycol or 1,3-propanediol at a content of 25% by mass to 100% by mass with respect to the total mass of the humectant. One propylene glycol or 1,3-propanediol may be used alone, or a mixture of propylene glycol and 1,3-propanediol may be used.

  Propylene glycol or 1,3-propanediol is not too high in viscosity and boiling point. Therefore, when the ink permeates the recording medium and the water contained in the ink is evaporated, the dry viscosity of the ink can be within a suitable range. Since such ink has excellent permeability to the recording medium, it is considered that the occurrence of convex curl of the recording medium on which an image is formed using the ink is suppressed.

  Further, when the content of propylene glycol or 1,3-propanediol with respect to the total mass of the humectant is 25% by mass or more and 100% or less, the effect of suppressing the convex curl of the recording medium on which the image is formed is maintained. be able to. Therefore, for example, by containing another moisturizer with a high viscosity that contributes to the improvement of the print density at a content of 75% by mass or less with respect to the total mass of the moisturizer, while improving the print density of the ink, The effect of suppressing the occurrence of convex curl in the recording medium tends to be maintained.

  In addition to propylene glycol and 1,3-propanediol, the humectant may further contain another humectant with a content of 75% by mass or less based on the total mass of the humectant. Examples of other humectants include polyethylene glycol, polypropylene glycol, ethylene glycol, butylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, tripropylene glycol, 1,2,6-hexanetriol, thiodiglycol, 1, Examples include 3-butanediol, 1,5-pentanediol, or glycerin. As another moisturizing agent, glycerin or 1,3-butanediol is preferable from the viewpoint that the above-described viscosity is high and the printing density can be improved. Another moisturizer may be used alone or in combination of two or more.

  The content of the humectant is preferably 5% by mass or more and 35% by mass or less with respect to the total mass of the ink.

<2-2. First penetrant>
The vehicle contains a first penetrant. The first penetrant is a high penetrant and is used for the purpose of improving the penetrability in the longitudinal direction (thickness direction) of the recording medium. As the first penetrant, 1,2-octanediol or 2,4-diethyl-1,5-pentanediol is used. 1,2-octanediol or 2,4-diethyl-1,5-pentanediol may be used alone, or 1,2-octanediol and 2,4-diethyl-1,5-pentanediol May be used in combination.

  1,2-octanediol and 2,4-diethyl-1,5-pentanediol are liquid at room temperature (eg, 25 ° C.). When the first penetrant that is solid at the temperature (room temperature) at the time of preparing the ink is used, when the water in the ink evaporates from the recording medium in image formation, a part of the first penetrant tends to precipitate. . Such precipitation tends to hinder the penetration of the ink into the recording medium. When the penetration of ink is hindered, a convex curl is likely to occur in a recording medium on which an image is formed using the ink. Therefore, from the viewpoint of suppressing the occurrence of convex curl, 1,2-octanediol or 2,4-diethyl-1,5-pentanediol that is liquid at room temperature (for example, 25 ° C.) is preferably used as the first penetrant. Used.

<2-3. Second penetrant>
The vehicle contains a second penetrant. The second penetrant is used for the purpose of improving the penetrability (wetting property) in the lateral direction (direction perpendicular to the thickness) of the recording medium. As the second penetrant, polyhydric alcohol monoalkyl ether is preferably used. By using a polyhydric alcohol monoalkyl ether as the second penetrant, the penetrability in the longitudinal direction (thickness direction) of the recording medium due to the first penetrant and the width of the recording medium due to the second penetrant. The balance between permeability (direction perpendicular to the thickness) and permeability (wetability) can be improved. As a result, the ink can be permeated in a well-balanced manner in the vertical direction and the horizontal direction of the recording medium, and an image having a desired print density tends to be obtained during image formation.

  Examples of the polyhydric alcohol monoalkyl ether include ethers of polyhydric alcohol and monoalkyl having 1 to 4 carbon atoms. Specific examples of the polyhydric alcohol monoalkyl ether include triethylene glycol monobutyl ether, diethylene glycol monopropyl ether, triethylene glycol monoethyl ether, triethylene glycol monomethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoisopropyl ether, or diethylene glycol monoisobutyl ether. Is mentioned. Among these, triethylene glycol monobutyl ether or diethylene glycol monoethyl ether is preferable because of excellent ink permeability to a recording medium such as paper, ink moisture retention, and ink storage stability. As the polyhydric alcohol monoalkyl ether, one kind may be used alone, or two or more kinds may be mixed and used.

The content of the polyhydric alcohol monoalkyl ether is 2.0% by mass or more and 10.0% by mass or less with respect to the total mass of the ink. When using an ink having a low content of polyhydric alcohol monoalkyl ether, the permeability of the ink into the recording medium tends to be low. Therefore, it is difficult to obtain an image having a desired image density during image formation. When an ink having an excessive content of polyhydric alcohol monoalkyl ether is used, it is difficult to suppress a change in the viscosity of the ink and a change in the dispersion state of the pigment when the ink is stored for a long time in a high temperature environment.
<2-4. Surfactant>
The vehicle contains a surfactant. The surfactant is used for the purpose of improving the compatibility and dispersion stability of the components contained in the ink and for the purpose of improving the permeability (wetting property) of the ink to the recording medium. A nonionic surfactant is used as the surfactant.

  By using a nonionic surfactant, separation or suspension of the vehicle tends to be suppressed. Therefore, when the ink gets wet and penetrates into the recording medium, separation of the surfactant from the ink is suppressed, and each component contained in the ink becomes difficult to separate. Thereby, it is possible to prevent only the ink solvent having high permeability from penetrating into the recording medium first. As a result, the permeability of the entire ink into the recording medium is improved, and the occurrence of convex curl in the recording medium on which an image is formed using these inks can be suppressed.

  Preferable examples of the nonionic surfactant include polyalkylene glycol alkyl ether acrylate-alkyl acrylate-polyalkylene glycol acrylate-lauryl acrylate-alkyl methacrylate copolymer. More preferable examples of the nonionic surfactant include polyethylene glycol methyl ether acrylate-butyl acrylate-polypropylene glycol acrylate-lauryl acrylate-methyl methacrylate copolymer.

  Another preferred example of the nonionic surfactant is a compound represented by the following formula (1).

In formula (1), R ₁ and R ₂ each independently represents an alkyl group having 1 to 6 carbon atoms. EO represents an ethyleneoxy group, and m is a number of 5 or more and 6 or less indicating the average added mole number of EO. PO represents a propyleneoxy group, and n is a number of 1 or more and 2 or less indicating the average added mole number of PO.

  The content of the surfactant is preferably 0.3% by mass or more and 0.8% by mass or less with respect to the total mass of the ink. If the content of the surfactant is too small, convex curl is likely to occur in a recording medium on which an image is formed using ink. When the content of the surfactant is excessive, it is difficult to obtain a desired print density.

<2-5. Dissolution stabilizer>
The vehicle may contain a dissolution stabilizer as necessary. The dissolution stabilizer is used for the purpose of compatibilizing the components contained in the ink and stabilizing the dissolved state of the ink. Examples of the dissolution stabilizer include 2-pyrrolidone, N-methyl-2-pyrrolidone, and γ-butyrolactone. One of these dissolution stabilizers may be used alone, or two or more thereof may be used in combination. When the ink contains a dissolution stabilizer, the content of the dissolution stabilizer is preferably 1.0% by mass or more and 20.0% by mass or less, and 3.0% by mass or more and 15% by mass or less with respect to the total mass of the ink. More preferably, it is 0.0 mass% or less.

<2-6. Vehicle Manufacturing Method>
The vehicle stirs the humectant, the first penetrant, the second penetrant, the surfactant, and if necessary, the dissolution stabilizer using a stirrer (for example, “One-One Motor BL-600” manufactured by ASONE Corporation). Can be obtained.

<2-7. Dissolved state of vehicle>
In the vehicle, the humectant, the first penetrant, the second penetrant, and the surfactant are each dissolved. The dissolved state of the vehicle can be confirmed by visually observing the vehicle. In the vehicle, the humectant, the first penetrant, the second penetrant, and the surfactant are dissolved in a dissolved state in which neither separation nor suspension of the vehicle is observed (dissolved state in which the vehicle is transparent). Means.

  When the vehicle is separated or suspended, each component contained in the ink is easily separated when the ink wets and penetrates the recording medium. When the components are separated, only the component having high permeability (low surface tension) penetrates the recording medium first. As a result, the penetrability of the entire ink into the recording medium is reduced, and a convex curl is likely to occur on the recording medium on which an image is formed using the ink. Therefore, it is preferable that the humectant, the first penetrating agent, the second penetrating agent, and the surfactant are each dissolved in the vehicle.

<2-8. Vehicle surface tension>
The surface tension of the vehicle is 30.0 mN / m or more and 35.0 mN / m or less. When the surface tension of the vehicle is excessive, the permeability of the ink to the recording medium is lowered, and the convex curl is likely to occur on the recording medium on which an image is formed using the ink. If the surface tension of the vehicle is too small, the ink easily penetrates into the recording medium, so that the pigment contained in the ink does not stay on the surface of the recording medium, and the print density of the formed image tends to decrease.

  The surface tension of the vehicle means the surface tension measured at 25 ° C. unless otherwise specified. The surface tension can be measured, for example, according to the Wilhelmy method (plate method). In the measurement of the surface tension by the Wilhelmy method, for example, an “automatic surface tension meter DY-300” manufactured by Kyowa Interface Science Co., Ltd. can be used as the surface tension meter.

<3. Ink production method>
The method for producing the ink is not particularly limited as long as the pigment dispersion and the vehicle (humectant, first penetrant, second penetrant, surfactant) can be mixed uniformly. As a specific example of the ink production method, there is a method in which each component of the ink is agitated by a stirrer and mixed uniformly, and then, for example, foreign matters and coarse particles are removed by a filter having a pore diameter of 5 μm or less. When manufacturing the ink, a dissolution stabilizer and known additives (antioxidants, viscosity modifiers, pH adjusters, antiseptic mold agents) may be added to the ink as necessary. .

  The ink according to this embodiment is preferably used as a water-based ink by adding water. When the ink of this embodiment is a water-based ink, the water content in the ink is preferably 20% by mass or more and 70% by mass or less, and 25% by mass or more and 60% by mass or less with respect to the total mass of the ink. It is more preferable.

  The inkjet ink according to the first embodiment has been described above. According to the inkjet ink of the present embodiment, it is possible to obtain an image having excellent print density while suppressing the occurrence of convex curl in a recording medium on which an image is formed using the ink.

[Second Embodiment: Inkjet Recording System]
The second embodiment of the present invention is an ink jet recording system. The ink jet recording system of this embodiment includes a transport unit that transports a recording medium, and an ink jet recording head (hereinafter may be referred to as “recording head”). In the ink jet recording system of the present embodiment, the ink of the first embodiment is used. Hereinafter, the ink jet recording system of the present embodiment will be described with reference to the drawings.

  FIG. 3 is a diagram illustrating a configuration of an inkjet recording apparatus 100 for implementing the inkjet recording system according to the present embodiment. 4 is a view of the conveyance belt 5 of the inkjet recording apparatus 100 shown in FIG. 3 as viewed from above.

  As shown in FIG. 3, a paper feed tray 2 is provided on the left side of the inkjet recording apparatus 100. The paper feed tray 2 accommodates recording paper P (recording medium). A paper feed roller 3 and a paper feed driven roller 4 are provided at one end of the paper feed tray 2. The paper feed roller 3 takes out the stored recording paper P one by one from the uppermost recording paper P one by one, and transports and feeds the recording paper P to a later-described transport belt (transport section) 5. The paper feed driven roller 4 is pressed against the paper feed roller 3 and rotated.

  A transport belt 5 is rotatably disposed on the downstream side (right side in FIG. 3) of the paper feed roller 3 and the paper feed driven roller 4 in the paper transport direction. The conveyor belt 5 is stretched between a belt driving roller 6 and a belt driven roller 7 that is driven to rotate. The belt driving roller 6 is disposed on the downstream side in the paper conveyance direction. The belt driven roller 7 is arranged on the upstream side in the paper conveyance direction, and rotates following the belt driving roller 6 via the conveyance belt 5. When the belt driving roller 6 is rotationally driven in the clockwise direction, the recording paper P is transported in the paper transporting direction X indicated by the arrow.

  A discharge roller 8 and a discharge driven roller 9 are provided on the downstream side of the transport belt 5 in the sheet transport direction. The discharge roller 8 is driven clockwise in the drawing to discharge the recording paper P on which an image is recorded out of the apparatus housing. The discharge driven roller 9 is pressed against the upper part of the discharge roller 8 and rotates. A paper discharge tray 10 is provided on the downstream side of the discharge roller 8 and the discharge driven roller 9. On the paper discharge tray 10, the recording paper P discharged outside the apparatus housing is stacked.

  Above the transport belt 5, recording heads 11C, 11M, 11Y, and 11K are disposed. Each of the recording heads 11 </ b> C to 11 </ b> K is supported at a height such that a predetermined interval is formed with respect to the upper surface of the transport belt 5. The recording heads 11 </ b> C to 11 </ b> K record images on the recording paper P that is transported on the transport belt 5. These recording heads 11C to 11K are filled with inks of four different colors (cyan, magenta, yellow and black). A color image is formed on the recording paper P by ejecting the respective inks from the recording heads 11C to 11K.

  As shown in FIG. 4, the recording heads 11 </ b> C to 11 </ b> K are arranged in a direction (vertical direction in FIG. 4) orthogonal to the paper transport direction X of the recording paper P. The recording heads 11C to 11K include nozzle rows N1 and N2 (described later with reference to FIG. 7) having a plurality of nozzles 12 (described later with reference to FIG. 5). A plurality of nozzle arrays N1 and N2 are arranged in parallel in the conveyance direction X of the recording paper P. The recording heads 11C to 11K are also called line head type recording heads or long ink jet recording heads. The recording heads 11 </ b> C to 11 </ b> K are long recording heads formed with a length equal to or larger than the width of the conveyance belt 5, and have a recording area equal to or larger than the width of the recording paper P to be conveyed. The image for one line can be collectively recorded on the recording paper P conveyed.

  In the ink jet recording apparatus 100 in which the ink jet recording system of the present embodiment is implemented, a plurality of nozzles 12 are arranged in the longitudinal direction of the main bodies of the recording heads 11C to 11K, so that a recording area equal to or larger than the width of the recording paper P is formed. The recording heads 11C to 11K configured to include the recording heads 11C to 11K are used. However, for example, by arranging a plurality of short recording head units having a plurality of nozzles 12 in the width direction of the transport belt 5, an image can be recorded over the entire width of the transported recording paper P. A recording head can also be used.

  Examples of the ink ejection method of the recording heads 11C to 11K include a piezo method and a thermal ink jet method. In the piezo method, ink is pushed out using a piezo element (not shown). In the thermal ink jet method, bubbles are generated by a heating element and ink is ejected under pressure.

  Next, the configuration of the ejection unit 30 provided in each of the recording heads 11C to 11K will be described with reference to FIGS. 5 (a) and 5 (b). Fig.5 (a) is a figure which shows the discharge unit 30, FIG.5 (b) is BB sectional drawing of Fig.5 (a).

  As shown in FIGS. 5A and 5B, the discharge unit 30 includes a nozzle 12, an actuator 31, a diaphragm 31 a, a hole 32, a pressurizing chamber 33, and a nozzle channel 34. Have. The hole 32, the pressurizing chamber 33, the nozzle flow path 34, and the nozzle 12 are connected. Further, the pressurizing chamber 33 of each discharge unit 30 is connected to the common flow path 201 through the hole 32. Ink is supplied from an ink tank (not shown) to the common flow path 201 by, for example, a pump.

  The actuator 31 is made of a piezoelectric element, for example. When a voltage is applied to the piezoelectric element (actuator 31), the piezoelectric element is deformed by the inverse piezoelectric effect. The deformation of the piezoelectric element is transmitted to the pressurizing chamber 33 through the diaphragm 31a. Thereby, the pressurizing chamber 33 is compressed. The ink sent from the common channel 201 to the pressurizing chamber 33 through the hole 32 is pressurized by the actuator 31 in the pressurizing chamber 33 and is ejected from the nozzle 12 through the nozzle channel 34.

  FIG. 6 is a block diagram showing a configuration of an ink jet recording apparatus 100 for carrying out the ink jet recording method of the present embodiment. Portions common to FIGS. 3 and 4 are denoted by the same reference numerals and description thereof is omitted. The ink jet recording apparatus 100 includes a control unit 20. For example, an interface 21, a ROM 22, a RAM 23, an encoder 24, a motor control circuit 25, a recording head control circuit 26, and a voltage control circuit 27 are connected to the control unit 20.

  The interface 21 transmits / receives data to / from a host device such as a personal computer (not shown). The control unit 20 converts the image signal received via the interface 21 into image data by performing scaling processing or gradation processing as necessary. And a control signal is output to the various control circuits mentioned later.

  The ROM 22 stores, for example, a control program used to drive the recording heads 11C to 11K to record an image. The RAM 23 stores the image data subjected to scaling processing or gradation processing by the control unit 20 in a predetermined area.

  The encoder 24 is connected to the belt driving roller 6 on the paper discharge side. The belt driving roller 6 drives the conveyance belt 5. The encoder 24 outputs (transmits) a pulse train in accordance with the rotational displacement amount of the rotation shaft of the belt driving roller 6. The control unit 20 calculates the rotation amount by counting the number of pulses transmitted from the encoder 24 and grasps the feed amount (paper position) of the recording paper P. The control unit 20 outputs a control signal to the motor control circuit 25 and the recording head control circuit 26 based on the signal from the encoder 24.

  The motor control circuit 25 drives the recording medium transport motor 28 by an output signal from the control unit 20. The belt driving roller 6 is rotated by driving the recording medium conveying motor 28. As shown in FIG. 3, the belt driving roller 6 rotates the transport belt 5 in the clockwise direction of FIG. 3 to transport the recording paper P in the paper transport direction X indicated by the arrow.

  The recording head control circuit 26 transfers the image data stored in the RAM 23 to the recording heads 11 </ b> C to 11 </ b> K based on the output signal from the control unit 20. Based on the transferred image data, ink ejection from the recording heads 11C to 11K is controlled. The recording process on the recording paper P is performed by such control and the control of the conveyance of the recording paper P by the conveyance belt 5 driven by the recording medium conveyance motor 28.

  The voltage control circuit 27 generates an alternating electric field by applying a voltage to the belt driven roller 7 on the sheet feeding side based on an output signal from the control unit 20. The sheet is electrostatically attracted to the transport belt 5 by the generated alternating electric field. The electrostatic adsorption is released by grounding the belt driven roller 7 or the belt driving roller 6 based on an output signal from the control unit 20. In the present embodiment, a voltage is applied to the belt driven roller 7 on the sheet feeding side. However, the voltage may be applied to the belt driving roller 6 on the paper discharge side.

  Here, in the ink jet recording apparatus 100 for implementing the ink jet recording system of the present embodiment, as shown in FIG. 4, the nozzle rows of the recording heads 11C to 11K are in the paper transport direction X (the left-right direction in FIG. 4). Two rows are arranged in parallel. By ejecting the ink of the first embodiment from the plurality of nozzles 12 in the two nozzle rows arranged in the transport direction, dots are formed on the recording paper P transported by the transport belt (transport section) 5.

  A method of forming dots using the inkjet recording apparatus 100 for implementing the inkjet recording system of the present embodiment will be specifically described with reference to FIG. 7 illustrates the recording head 11C as an example of the recording heads 11C to 11K illustrated in FIGS. 3 and 4, but the other recording heads 11M to 11K are also described in the same manner.

  As shown in FIG. 7, the recording head 11C has nozzle rows N1 and N2 each including a plurality of nozzles arranged in parallel in the transport direction (paper transport direction X indicated by an arrow). That is, as the nozzles for forming each dot row in the transport direction, each of the nozzle rows N1 and N2 (for example, the nozzles 12a and 12a 'in the dot row L1) is provided with a total of two nozzles. For convenience of explanation, only 16 nozzles of 12a to 12p and 12a ′ to 12p ′ corresponding to the dot rows L1 to L16 are shown in the nozzles constituting the nozzle rows N1 and N2. ing. However, actually, a larger number of nozzles are arranged in a direction orthogonal to the transport direction.

  Then, an image is formed on the recording paper P by sequentially using the nozzle arrays N1 and N2. For example, one row of dot rows D1 in the width direction of the recording paper P (left and right direction in FIG. 7) is formed by ejecting ink from the nozzle row N1 (solid line arrows in FIG. 7). Subsequently, the recording paper P is moved by a predetermined amount in the transport direction, and the next one row of dot rows D2 is formed by ejecting ink from the nozzle row N2 (broken arrows in FIG. 7). Further, the recording paper P is moved by a predetermined amount in the transport direction, and the next one row of dot rows D3 is formed again by ejecting ink from the nozzle row N1. Hereinafter, the dot rows D4 and thereafter are similarly formed by alternately using the nozzle rows N1 and N2.

  In the present embodiment, the dot rows are formed by alternately using the nozzle rows N1 and N2. However, for example, in FIG. 7, the first dot row D1 for the first row is divided into odd-numbered nozzles (nozzles 12a, 12c, 12e...) In the nozzle row N1 and even-numbered nozzles in the nozzle row N2 ( Nozzles 12b ′, 12d ′, 12f ′...), And the next one row of dot rows D2 is an even-numbered nozzle (nozzles 12b, 12d, 12f...) In the nozzle row N1. And odd-numbered nozzles (nozzles 12a ′, 12c ′, 12e ′...) In the nozzle row N2 may be used. That is, as long as two nozzles corresponding to the same dot row are alternately used, the nozzles constituting the nozzle rows N1 and N2 may be used in any order.

  The inkjet recording system according to the second embodiment has been described above. In the ink jet recording system of the present embodiment, by using the ink of the first embodiment, even when an image is formed with a line head type recording head, while suppressing the occurrence of convex curl in the recording medium, An image with excellent print density can be obtained.

  Examples of the present invention will be described below. However, the present invention is not limited to the following examples.

<1. Preparation of ink>
In preparing the ink, first, a pigment dispersion (pigment dispersion containing a pigment dispersion) PD1 and a vehicle were prepared. Hereinafter, a method for preparing the pigment dispersion PD1, a method for preparing the vehicle, a method for measuring the surface tension of the vehicle, and a method for observing the dissolved state of the vehicle will be described. In addition, an ink preparation method using the prepared ink and vehicle will be described.

<1-1. Preparation Method of Pigment Dispersion Liquid PD1>
With a content shown in Table 1, a pigment, a pigment dispersion resin R1, an ethylene oxide adduct of acetylenic diol (“Orphine E1010” manufactured by Nissin Chemical Industry Co., Ltd.), and water (ion-exchanged water) with a capacity of 0.6 L I put it in a vessel. Further, an amount of potassium hydroxide (KOH) necessary for neutralization of the pigment dispersion resin R1 described later was added into the vessel. The contents of the vessel were dispersed using a media-type wet disperser (“Dynomill” manufactured by Shinmaru Enterprises Co., Ltd.).

  As the pigment, phthalocyanine blue 15: 3 (“Lionol Blue FG-7330” manufactured by Toyo Ink Manufacturing Co., Ltd.) was used.

  As the pigment dispersion resin R1, methacrylic acid (MAA) -methyl methacrylate (MMA) -butyl acrylate (BA) -styrene (ST) copolymer (mass average molecular weight (Mw) 20000, acid value 100) was used. .

  Since the pigment dispersion resin R1 is a water-soluble resin (alkali-soluble resin), the neutralization of the pigment dispersion resin R1 was performed by neutralization with an equal amount of 105% KOH aqueous solution. The amount of K (potassium) added was calculated based on the mass of the pigment dispersion resin R1. Moreover, the mass of water (ion-exchange water) was calculated including the mass of water contained in the KOH aqueous solution and the mass of water generated by the neutralization reaction.

Subsequently, the medium (zirconia beads) was filled in the vessel, and the dispersion conditions were adjusted so that the volume median diameter (D ₅₀ ) of the desired pigment dispersion was obtained. The vessel (zirconia beads having a diameter of 0.5 mm) was filled in the vessel so that the volume was 70% of the vessel capacity, and the contents of the vessel were removed while cooling with water at 10 ° C. and a peripheral speed of 8 m / sec. Dispersed. As a result, a pigment dispersion in which the volume median diameter (D ₅₀ ) was 100 nm (when D ₅₀ was measured a plurality of times, all D ₅₀ values were in the range of 80 nm to 120 nm) A pigment dispersion PD1 containing a pigment dispersion coated with resin R1 was obtained.

The volume median diameter (D ₅₀ ) was determined using a dynamic light scattering particle size distribution apparatus (“Zetasizer Nano” manufactured by Sysmex Corporation) for a solution obtained by diluting the pigment dispersion PD1 300 times with ion-exchanged water. It was measured.

<1-2. Vehicle Preparation Method>
Next, the humectant, the first penetrant, the second penetrant, the surfactant, and other raw materials (2-pyrrolidone) are rotated using a stirrer (“Three-One Motor BL-600” manufactured by ASONE Corporation). The mixture was uniformly mixed by stirring at 400 rpm. As a result, a vehicle was obtained. The details of the raw material of the vehicle and the content of the raw material will be described later.

<1-3. Measurement Method of Vehicle Surface Tension>
The surface tension of the obtained vehicle was measured according to the Wilhelmy method. The measurement temperature was 25 ° C.

<1-4. Method for observing vehicle dissolution state>
The dissolution state of the obtained vehicle was visually observed and evaluated according to the following criteria.
○ (Good): No separation or suspension of the vehicle is observed (the raw materials are dissolved in the vehicle and are transparent)
× (Poor): Vehicle separation or suspension observed

<1-5. Ink Preparation Method>
Pigment dispersion liquid PD1 obtained as described above, vehicle (humectant, first penetrant, second penetrant, surfactant, and other raw materials), and ion-exchanged water were mixed with an agitator (manufactured by ASONE CORPORATION). Using “Three-One Motor BL-600”), the mixture was stirred and mixed uniformly at a rotation speed of 400 rpm. Subsequently, in order to remove foreign matters and coarse particles, the mixed solution was filtered using a filter having a pore diameter of 5 μm. As a result, an ink was obtained. The details of the ink raw material and the content of the raw material will be described later.

<2. Evaluation method>
For each of the obtained inks, the print density and curling properties (convex curling properties) were evaluated. Hereinafter, a method for evaluating the print density and curling property will be described.

<2-1. Evaluation method of print density>
Using the inkjet recording apparatus 100 (see FIG. 3), the recording head 11C was filled with ink (sample). Subsequently, a solid image of 10 cm × 10 cm was formed on A4 plain paper (PPC paper, “C ² ” manufactured by Fuji Xerox Co., Ltd.) under a normal temperature and normal humidity (25 ° C., 60% RH) environment. The amount of ink ejected from the recording head 11C was controlled to be 11 pL per ink drop, and an image was formed under the same conditions for each ink.

The plain paper on which the image was formed was allowed to stand at room temperature and normal humidity (25 ° C., 60% RH) all day and night, and then the image density was measured with a portable reflection densitometer (“RD-19” manufactured by Sakata Inx Engineering). . The average value of the image densities at 10 locations in the image was taken as the density value. The obtained density value was evaluated according to the following criteria.
○ (Good): Density value is 1.10 or more x (Poor): Density value is less than 1.10

<2-2. Curling evaluation method>
A solid image was formed on the center of A4 plain paper by the same method as the above-described evaluation method of the print density. Immediately after the image formation, A4 plain paper was allowed to stand on a horizontal table. At that time, the sheet was left to stand so that the surface on which the solid image of plain paper was formed and the surface of the table faced each other. The height of the four corners of plain paper was measured with the surface of the table as a reference, and an average value (average value of the heights of four locations) was obtained. The average value obtained was evaluated according to the following criteria.
○ (Good): Average height of the four corners of plain paper is 10 mm or less × (Poor): Average height of the four corners of plain paper is more than 10 mm

  If the average height of the four corners of plain paper is 10 mm or less, when a suction fan of 0.8 KPa is used during printing, suction by the conveyance belt and correction of the paper using the decurling mechanism It is considered that the recording medium on the second side (back side) in double-sided printing can be adsorbed.

<3. Types of surfactants and evaluation results>
Hereinafter, the type of the surfactant used for preparing the ink was changed, and the influence on the printing density of the ink and the curling property (convex curling property) of the recording medium was examined. By changing the type of the surfactant, the surface tension of the vehicle and the dissolution state of the vehicle can be changed. Therefore, the influence of the surface tension of the vehicle and the dissolved state of the vehicle on the ink printing density and the curling property (convex curling property) of the recording medium was also examined.

  Inks (A-1) to (A-4) and (B-1) to (B-3) having the compositions shown in Table 2 were prepared by the above method and used as samples.

  As the surfactants shown in Table 2, in the inks (A-1), (A-2), (A-3), and (A-4), the nonionic surfactants S1, S2, S3, and S4 are used. Each was used. In the inks (B-1), (B-2), and (B-3), orphine, surfinol, and polyflow were used. Hereinafter, the nonionic surfactants S1 to S4, orphine, surfinol, and polyflow will be described.

(Nonionic surfactant S1)
As nonionic surfactant S1, polyethylene glycol methyl ether acrylate (PEGA) -butyl acrylate (BA) -polypropylene glycol acrylate (PPGA) -lauryl acrylate (LA) -methyl methacrylate (MMA) copolymer (PEGA / BA) / PPGA / LA / MMA monomer ratio of 60/10/10/12/8) was used. The nonionic surfactant S1 had a mass average molecular weight (Mw) of 5000. Nonionic surfactant S1 was soluble in water.

The mass average molecular weight (Mw) was measured under the following conditions using gel filtration chromatography (“HLC-8020GPC” manufactured by Tosoh Corporation). The calibration curves are 8 types of F-40, F-20, F-4, F-1, A-5000, A-2500, A-1000, and n-propylbenzene from TSKgel standard polystyrene manufactured by Tosoh Corporation. Created by selecting.
(Measurement conditions for mass average molecular weight)
Column: “TSKgel SuperMultipore HZ-H” (4.6 mm ID × 15 cm semi-micro column) manufactured by Tosoh Corporation
・ Number of columns: 3 ・ Eluent: Tetrahydrofuran ・ Flow rate: 0.35 mL / min ・ Sample injection volume: 10 μL
・ Measurement temperature: 40 ℃
・ Detector: IR detector

(Nonionic surfactant S2)
As the nonionic surfactant S2, a copolymer represented by the following formula (1) was used. Nonionic surfactant S2 was soluble in water.

In formula (1-1), R ₁₁ represents an n-propyl group, R ₁₂ represents an n-propyl group, EO represents an ethyleneoxy group, and m ₁ represents a number of 5 indicating the average number of moles of EO added. It is. PO represents a propyleneoxy group, and n ₁ is a number of 1 indicating the average added mole number of PO.

(Nonionic surfactant S3)
As the nonionic surfactant S3, a copolymer represented by the following formula (2) was used. Nonionic surfactant S3 was soluble in water.

In formula (1-2), R ₂₁ represents an n-propyl group, R ₂₂ represents an n-pentyl group, EO represents an ethyleneoxy group, and m ₂ represents a number of 6 representing the average number of moles of EO added. It is. PO represents a propyleneoxy group, and n ₂ is a number of 2 indicating the average added mole number of PO.

(Nonionic surfactant S4)
As the nonionic surfactant S4, a copolymer represented by the following formula (3) was used. Nonionic surfactant S4 was soluble in water.

In formula (1-3), R ₃₁ represents an n-butyl group, R ₃₂ represents a methyl group, EO represents an ethyleneoxy group, and m ₃ represents a number of 6 indicating the average number of moles of EO added. . PO represents a propyleneoxy group, and n ₃ is a number of 1 indicating the average added mole number of PO.

(Olfin)
As the surfactant, an ethylene oxide adduct of acetylenic diol (“Olfin E1010” manufactured by Nissin Chemical Industry Co., Ltd.) was used. Olfine E1010 was soluble in water.

(Surfinol)
As a surfactant, acetylenic diol derivative (“Surfinol 104” manufactured by Nissin Chemical Industry Co., Ltd.) Surfinol 104 was hardly dissolved in water and phase-separated.

(Polyflow)
As the surfactant, an acrylic polymer / amphiphilic oligomer (“Polyflow KL800” manufactured by Kyoeisha Chemical Co., Ltd., active ingredient concentration: 93 mass%) was used. Polyflow KL800 was hardly dissolved in water and suspended (white turbidity).

  In the process of preparing each of the inks (A-1) to (A-4) and (B-1) to (B-3), the surface tension of the vehicle was measured, and the dissolution state of the vehicle was observed. Further, the print density and the convex curl property were evaluated for each of the prepared inks (A-1) to (A-4) and (B-1) to (B-3). Table 3 shows the vehicle surface tension, vehicle dissolution state, print density evaluation, and convex curl evaluation of these inks.

  Table 3 showed the following. In the inks (A-1) to (A-4), the surface tension of the vehicle was 30.0 mN / m or more and 35.0 mN / m or less, and each component was dissolved in the vehicle. Therefore, the printing densities of the inks (A-1) to (A-4) are good, and the convex curl of the recording medium on which an image is formed using these inks is also suppressed.

  On the other hand, in the ink (B-1), the surface tension of the vehicle was as high as 37.0 mN / m. Therefore, the permeability of the ink (B-1) to the recording medium is reduced, and the recording medium on which an image is formed using the ink (B-1) is evaluated as a threshold value (“good (good)”. It is considered that the convex curl exceeding the upper limit of the average height of the four corners of plain paper: 10 mm) occurred.

  In the inks (B-2) and (B-3), the surface tension of the vehicle was 35.0 mN / m or less, but separation or suspension of the vehicle was observed. Since the inks (B-2) and (B-3) contain a low-solubility surfactant, the surfactant is easily separated from the ink when the ink wets and penetrates the recording medium. When the surfactant is separated, each component contained in the ink is easily separated, and it is considered that only the ink solvent having high penetrability penetrates the recording medium first. As a result, the penetrability of the inks (B-2) and (B-3) as a whole into the inside of the recording medium is lowered, and the recording medium on which an image is formed using these inks has a threshold (“◯ (good It is considered that a convex curl exceeding the upper limit of the average value of the heights of the four corners of plain paper evaluated as “)” was generated.

<4. Surfactant Content and Evaluation Results>
Hereinafter, the content of the surfactant used for preparing the ink was changed, and the influence on the printing density of the ink and the curling property (convex curling property) of the recording medium was examined.

  Inks (A-5) to (A-7) and (B-4) to (B-5) having the compositions shown in Table 4 were prepared by the method described above and used as samples. The inks were prepared so that the surfactant contents contained in these inks had values shown in Table 5, respectively.

  In the process of preparing each of the inks (A-5) to (A-7) and (B-4) to (B-5), the surface tension of the vehicle was measured, and the dissolution state of the vehicle was observed. Further, the print density and the convex curl property were evaluated for each of the prepared inks (A-5) to (A-7) and (B-4) to (B-5). Table 5 shows the surface tension of the vehicle of these inks, the dissolution state of the vehicle, the evaluation of the print density, and the evaluation of the convex curl property.

  Table 5 showed the following. In the inks (A-5) to (A-7), the surface tension of the vehicle was 30.0 mN / m or more and 35.0 mN / m or less, and the raw materials were dissolved in the vehicle. Therefore, the printing densities of the inks (A-5) to (A-7) are good, and the convex curl of the recording medium on which an image is formed using these inks is also suppressed.

  In the ink (B-4), the surface tension of the vehicle exceeded 35.0 mN / m. For this reason, in a recording medium on which an image is formed using ink (B-4), the threshold value (the upper limit value of the average value of the heights of the four corners of plain paper evaluated as “◯ (good)”) is exceeded. Convex curl occurred.

  In the ink (B-5), the surface tension of the vehicle was less than 30.0 mN / m. For this reason, the ink (B-5) penetrated too much into the recording medium, and the ink (B-5) was inferior in print density.

  From the above, as shown in Table 3 and Table 5, the surface tension of the vehicle is 30.0 mN / m or more and 35.0 mN / m or less, and each component (humectant, first penetrant, It was shown that the ink in which 2 penetrant and surfactant) are dissolved is excellent in convex curl property and print density. Further, it has been shown that an ink containing a vehicle containing a nonionic surfactant as a surfactant is excellent in convex curl properties and print density.

<5. Types of first penetrant and evaluation results>
Hereinafter, the type of the first penetrant used for ink preparation was changed, and the influence on the printing density of the ink and the curling property (convex curling property) of the recording medium was examined.

  Inks (A-8) to (A-9) and (B-6) to (B-8) having the compositions shown in Table 6 were prepared by the method described above and used as samples. As the first penetrant, 1,2-octanediol, 2,4-diethyl-1,5-pentanediol (DEPG), 2-ptyl-2-ethyl-1,3-propanediol (shown in Table 7) BEPG) and 2,2,4-trimethyl-1,3-pentanediol (TMPDO) were used.

  1,2-octanediol, 2,4-diethyl-1,5-pentanediol (DEPG), 2-ptyl-2-ethyl-1,3-propanediol (BEPG), and 2 used as the first penetrant Table 7 shows the chemical structure and physical properties of 2,2,4-trimethyl-1,3-pentanediol (TMPDO).

  In the process of preparing each of the inks (A-8) to (A-9) and (B-6) to (B-8), the surface tension of the vehicle was measured, and the dissolution state of the vehicle was observed. Further, for each of the prepared inks (A-8) to (A-9) and (B-6) to (B-8), the print density and the convex curl property were evaluated. Table 8 shows the surface tension of the vehicle, the dissolved state of the vehicle, the evaluation of the print density, and the evaluation of the convex curl of these inks.

  Table 8 shows the following. In the inks (A-8) to (A-9), the first penetrant contained in the ink is liquid at room temperature (25 ° C.), and the surface tension of the vehicle is 30.0 mN / m or more and 35.0 mN / m or less. Met. Therefore, the printing densities of the inks (A-8) to (A-9) are good, and the convex curl of the recording medium on which an image is formed using these inks is also suppressed.

  In the ink (B-6), the first penetrant contained in the ink was liquid at room temperature (25 ° C.), but the surface tension of the vehicle exceeded 35.0 mN / m. Since a vehicle having a high surface tension is used, it is considered difficult to reduce the surface tension of the ink containing the vehicle to a suitable value. As a result, on the recording medium on which an image is formed using the ink (B-6), the threshold value (upper limit value of the average height of the four corners of plain paper evaluated as “◯ (good)”: 10 mm) is set. It is thought that the convex curl that exceeds was generated.

  In the inks (B-7) to (B-8), the surface tension of the vehicle was 30.0 mN / m or more and 35.0 mN / m or less, but the first penetrant contained in the ink was room temperature (25 ° C.). It was a solid. When water in the ink evaporates from the recording medium during image formation, a part of the first penetrant is precipitated, and the penetration of the ink into the recording medium is likely to be hindered. As a result, in the recording medium on which the image is formed using the inks (B-7) to (B-8), the average value of the heights of the four corners of the plain paper evaluated as “◯ (good)”. It is considered that convex curls exceeding the upper limit: 10 mm) occurred.

  From the above, the ink containing a vehicle containing 1,2-octanediol or 2,4-diethyl-1,5-pentanediol as the first penetrant is a recording medium on which an image is formed using the ink. It was shown that not only the convex curl is suppressed, but also the image density is excellent.

<6. Types of moisturizers and evaluation results>
In the following, the type of moisturizing agent used in the preparation of the ink was changed, and the influence on the print density of the ink and the curling property (convex curling property) of the recording medium was examined.

  Inks (A-10) to (A-11) and (B-9) to (B-10) having the compositions shown in Table 9 were prepared by the above method and used as samples. As the humectant, one of glycerin, propylene glycol, 1.3-propanediol, and 1.3-butanediol shown in Table 10 was used.

  In the process of preparing each of the inks (A-10) to (A-11) and (B-9) to (B-10), the surface tension of the vehicle was measured, and the dissolution state of the vehicle was observed. In addition, for each of the prepared inks (A-10) to (A-11) and (B-9) to (B-10), the print density and the convex curl property were evaluated. Table 11 shows the vehicle surface tension, vehicle dissolution state, print density evaluation, and convex curl evaluation of these inks.

  Table 11 showed the following. In the inks (A-10) to (A-11), propylene glycol or 1,3-propanediol was used as a humectant. Propylene glycol or 1,3-propanediol does not have too high a viscosity and a boiling point as shown in Table 10. Therefore, when the ink permeates the recording medium and the water contained in the ink is evaporated, the dry viscosity of the ink can be within a suitable range. As a result, the printing densities of inks (A-8) to (A-9) were good, and the convex curl of the recording medium on which an image was formed using these inks was also suppressed.

  In the inks (B-9) to (B-10), glycerin or 1,3-butanediol was used as a humectant. When glycerin or 1,3-butanediol is used alone, as shown in Table 10, since the viscosity of these humectants is high, when the ink permeates the recording medium and evaporates the water contained in the ink. In addition, the dry viscosity of the ink tends to increase. As a result, in the recording medium on which an image is formed using the inks (B-9) to (B-10), the average value of the heights of the four corners of plain paper evaluated as “◯ (good)” It is considered that the convex curl exceeding the upper limit: 10 mm) occurred.

  From the above, it has been shown that an ink containing a vehicle containing propylene glycol or 1,3-propanediol as a humectant suppresses convex curl in a recording medium on which an image is formed using the ink.

<7. Propylene glycol or 1,3-propanediol content and evaluation results>
On the other hand, as shown in Table 11 above, when a humectant with high viscosity (glycerin or 1,3-butanediol) is used, the print density tends to be improved. Accordingly, by mixing a high-moisture moisturizer (glycerin or 1,3-butanediol) with propylene glycol or 1,3-propanediol, it is possible to suppress the convex curl of the recording medium on which the image is formed, and the print density. We studied to achieve both improvement. Hereinafter, the content of propylene glycol or 1,3-propanediol is changed with respect to the total mass of the humectant used in the preparation of the ink to give the ink print density and the curl property (convex curl property) of the recording medium. The impact was examined.

  Inks (A-12) to (A-14) and (B-11) having the compositions shown in Table 12 were prepared by the method described above and used as samples. As the humectant, a humectant in which glycerin and propylene glycol were mixed in the contents shown in Table 12 was used.

  In the course of preparing each of the inks (A-12) to (A-14) and (B-11), the surface tension of the vehicle was measured, and the dissolution state of the vehicle was observed. Further, the print density and the convex curl property were evaluated for each of the prepared inks (A-12) to (A-14) and (B-11). Table 12 shows the vehicle surface tension, vehicle dissolution state, print density evaluation, and convex curl evaluation of these inks.

  Next, inks (A-15) to (A-17) and (B-12) having the compositions shown in Table 13 were prepared by the method described above and used as samples. As the humectant, a humectant in which glycerin and 1,3-propanediol were mixed at the contents shown in Table 13 was used.

  In the process of preparing each of the inks (A-15) to (A-17) and (B-12), the surface tension of the vehicle was measured, and the dissolution state of the vehicle was observed. Further, for each of the prepared inks (A-15) to (A-17) and (B-12), the print density and the convex curl property were evaluated. Table 13 shows the vehicle surface tension, vehicle dissolution state, print density evaluation, and convex curl evaluation of these inks.

  Tables 12 and 13 showed the following. In the inks (A-12) to (A-17), the content of propylene glycol or 1,3-propanediol relative to the total mass of the humectant was 25% by mass or more and 100% or less. Therefore, the printing densities of the inks (A-12) to (A-17) are good, and the convex curl of the recording medium on which an image is formed using these inks is also suppressed.

In the inks (B-11) to (B-12), the content of propylene glycol or 1,3-propanediol relative to the total mass of the humectant was less than 25 mass.
When the content of glycerin with high viscosity increases, the viscosity of the entire humectant also increases, so when the ink penetrates the recording medium and the water contained in the ink is evaporated, the dry viscosity of the ink tends to increase. . As a result, in the recording medium on which the image is formed using the inks (B-11) to (B-12), the average value of the heights of the four corners of the plain paper evaluated as “◯ (good)”. It is considered that the convex curl exceeding the upper limit: 10 mm) occurred.

  From the above, ink containing a vehicle containing 1,3-propanediol or propylene glycol with a content of 25% by mass or more and 100% or less with respect to the total mass of the humectant forms an image using the ink. It was shown that not only the convex curl was suppressed but also the print density was excellent in the recorded medium.

  The present invention is not limited to the above-described embodiments and examples. For example, the present invention can be modified as follows.

  The configuration of the ink (for example, components, dimensions, material, or shape) can be arbitrarily changed or omitted without departing from the spirit of the present invention.

  In the above-described embodiment, the color printer including the recording heads 11C to 11K corresponding to the four colors of inks has been described as an example. However, the present invention can be applied to a monochrome ink jet printer having a single recording head in exactly the same manner. The present invention can also be applied to a multifunction peripheral (a complex image forming apparatus). The multifunction machine has functions of, for example, a scanner, a copier, a printer, and a facsimile machine. Further, the ink of the present invention may be used for purposes other than image formation (for example, data recording).

  For example, the number of nozzles constituting the nozzle arrays N1 and N2 of the recording heads 11C to 11K and the nozzle interval can be appropriately set according to the specifications of the apparatus. In the above-described embodiment, the two nozzle rows N1 and N2 are arranged in parallel in the transport direction. However, it is also possible to arrange three or more nozzle rows in parallel and form dot rows using the nozzles of each nozzle row in sequence. As the number of nozzle rows increases, the appearance frequency of defective dots in the dot rows also decreases, and white streaks become less noticeable.

  The ink-jet ink according to the present invention is suitable for use in forming an image such as a color printer.

2 Feed tray 3 Feed roller 4 Feed driven roller 5 Conveyor belt (conveyor)
6 Belt drive roller 7 Belt driven roller 8 Discharge roller 9 Discharge driven roller 10 Discharge tray 11C, 11M, 11Y, 11K Recording head (inkjet recording head)
12, 12a to 12p, 12a ′ to 12p ′ Nozzle 20 Control unit 30 Discharge unit 31 Actuator 31a Diaphragm 32 Hole 33 Pressurization chamber 34 Nozzle flow channel 100 Inkjet recording apparatus D1 to D4 dot row (row direction)
L1 to L16 dot row (transport direction)
N1, N2 nozzle array P Recording paper (recording medium)

Claims (3)

An inkjet ink comprising a pigment dispersion and a vehicle,
The pigment dispersion is composed of a pigment and a pigment dispersion resin,
The vehicle includes a humectant, a first penetrant, a second penetrant, and a surfactant;
The surfactant is a nonionic surfactant,
The first penetrant is 1,2-octanediol or 2,4-diethyl-1,5-pentanediol;
The moisturizer contains propylene glycol or 1,3-propanediol at a content of 25% by mass to 100% by mass with respect to the total mass of the moisturizer,
In the vehicle, the humectant, the first penetrant, the second penetrant, and the surfactant are each dissolved.
An ink-jet ink, wherein the vehicle has a surface tension of 30.0 mN / m or more and 35.0 mN / m or less.   The inkjet ink according to claim 1, wherein the second penetrant is a polyhydric alcohol monoalkyl ether. An ink jet recording system comprising a transport unit for transporting a recording medium and an ink jet recording head,
The inkjet recording head is
Comprising a nozzle row having a plurality of nozzles arranged in a direction orthogonal to the conveyance direction of the recording medium,
A plurality of the nozzle rows are arranged in parallel in the conveyance direction of the recording medium,
An ink jet recording system that forms dots on the recording medium transported by the transport unit by ejecting the ink according to claim 1 or 2 from the plurality of nozzles of the ink jet recording head.

Images