Inkjet recording method and inkjet recording apparatus

Abstract

To provide an ink jet recording method capable of recording an image with a tertiary color, less causing color shift even with use of a recording apparatus having a large-capacity ink storage portion provided with an inlet port.SOLUTION: The ink jet recording method includes the step of recording an image, with use of an ink jet recording apparatus that includes: a plurality of aqueous inks; an ink storage portion that independently stores the aqueous inks; a recording head having formed therein an ejection port through which each aqueous ink is ejected; and a tube through which each aqueous ink is supplied from the ink storage portion to the recording head. The ink storage portion is provided with an inlet port through which the aqueous ink is injected, the tube is formed of a resin material, a cyan ink contains a phthalocyanine pigment, and both of a yellow ink and a magenta ink each contain an azo pigment.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an inkjet recording method and an inkjet recording apparatus used therein. [Background technology]

[0002] In recent years, inkjet recording methods have been used when printing business documents including characters and charts on recording media such as plain paper. In addition, due to an increase in the number of home workers and SOHOs, there is also a demand for compact devices that can record documents faster than before. With the increase in frequency of use for such business purposes, there is a strong demand from the market for ink storage units with larger capacities in order to record larger volumes of documents. For example, an inkjet recording device equipped with an ink storage unit capable of storing a large amount of ink has been proposed (Patent Document 1).

[0003] The following configurations can be given as examples of ink supply means in a recording device equipped with a large-capacity ink storage unit. That is, a means is known in which an ink supply tube connects a recording head mounted on a carriage to an ink storage unit installed in a location separate from the carriage, and ink is supplied from the ink storage unit to the recording head through the tube. By employing such a supply means, it is possible to increase the capacity of the ink storage unit while adopting a simple configuration. Furthermore, by providing an inlet in the ink storage unit, ink can be replenished to the ink storage unit through the inlet, which is useful when using a larger amount of ink.

[0004] Furthermore, with the aim of expanding the use of inkjet recording methods for business documents, water-based inks containing pigments have come to be widely used as coloring materials capable of recording dark, clear images (Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2017-001391 A Summary of the Invention [Problem to be solved by the invention]

[0006] The present inventors have studied the configuration of an inkjet recording device necessary for increasing productivity and an inkjet recording method using the same. Specifically, they have prepared an inkjet recording device having an ink storage section (main tank) with an inlet and a recording head with a sub-tank, with the main tank and the sub-tank connected by an ink supply tube. Then, using this inkjet recording device, they recorded an image with an ink set composed of pigment inks as proposed in Patent Document 1. As a result, they found that a new problem occurs in that color shift gradually occurs in a tertiary color image when each color ink is ejected for a long period of time.

[0007] Therefore, an object of the present invention is to provide an inkjet recording method capable of recording a tertiary color image with little color shift even when using a recording device equipped with a large-capacity ink storage section provided with an injection port. Another object of the present invention is to provide an inkjet recording device used in the inkjet recording method. [Means for solving the problem]

[0008] That is, according to the present invention, there is provided an inkjet recording method using an inkjet recording apparatus including a plurality of water-based inks including cyan ink, magenta ink, and yellow ink, ink containers for respectively accommodating the water-based inks, a recording head formed with ejection ports for ejecting the water-based inks supplied from the ink containers, and tubes for supplying the water-based inks from the ink containers to the recording head, the method comprising the steps of: applying the water-based inks ejected from the ejection ports to a recording medium to record an image, the ink containers being provided with injection ports for injecting the water-based inks, the tubes being formed of a resin material, the cyan ink containing a phthalocyanine pigment, and the yellow ink and the magenta ink each containing an azo pigment. the magenta ink further contains a quinacridone pigment, and the content (mass%) of the azo pigment in the magenta ink is 80 mass% or less based on the content (mass%) of all pigments in the magenta ink. The present invention provides an ink-jet recording method comprising the steps of: Effect of the Invention

[0009] According to the present invention, it is possible to provide an inkjet recording method that is capable of recording tertiary color images with little color shift, even when using a recording device equipped with a large-capacity ink storage section with an injection port. [Brief description of the drawings]

[0010] [Figure 1] 1 is a perspective view illustrating an embodiment of an inkjet recording apparatus of the present invention. [Diagram 2] FIG. 2 is a schematic diagram illustrating an example of an ink supply system. [Diagram 3] FIG. 2 is a schematic diagram for explaining a method for measuring the air permeability of a tube. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The present invention will be described in more detail below with reference to preferred embodiments. In the present invention, when the compound is a salt, the salt is present in the ink in the form of dissociation into ions, but for convenience, it is expressed as "containing a salt." In addition, water-based ink for inkjet printing may be simply referred to as "ink." Physical property values ​​are values ​​at room temperature (25°C) unless otherwise specified.

[0012] The inventors first prepared an inkjet recording device equipped with a main tank, which is a large-capacity ink storage unit with an inlet, and observed changes in the device when images were recorded using this inkjet recording device for a long period of time. As a result, it was found that pigments aggregate on the inner surface of a tube (ink supply tube) that supplies ink from the main tank to the recording head, or aggregate inside the tube, due to long-term use. Further detailed observation revealed that the degree of occurrence of such a phenomenon differs depending on the color of the ink. Specifically, it was found that pigments adhere firmly to the inner surface of the tube corresponding to magenta ink, and the inner diameter of the tube corresponding to magenta ink becomes narrower than the inner diameters of the tubes corresponding to cyan ink and yellow ink.

[0013] In the early stages of using the recording device, no adhesion or aggregation of pigments occurred in the tubes corresponding to the three ink colors. However, in the case of a recording device equipped with a main tank with an inlet, the liquid components in the main tank tend to evaporate due to opening and closing of the inlet or by keeping the ink contained for a long period of time, which promotes the concentration of the ink and aggregation of the pigments. Furthermore, compared to dye ink, pigment ink tends to interact with thermoplastic resin, which is a common resin tube material, so that pigments tend to adhere to the inner surface of the tube. Therefore, if a recording device equipped with a large-capacity main tank equipped with an inlet is used for a long period of time, the situation in which ink and pigment aggregates flow and remain in the tube will be repeated.

[0014] Among them, the general-purpose quinacridone pigment used as the coloring material for magenta ink is quite prone to aggregation. Therefore, as the recording device is used for a long period of time, the aggregated pigment adheres to the inner surface of the tube corresponding to the magenta ink, and the inner diameter of the tube is likely to become narrow. In contrast, the general-purpose phthalocyanine pigment used as the coloring material for cyan ink and the general-purpose azo pigment used as the coloring material for yellow ink are much less prone to aggregation than the quinacridone pigment. Therefore, the flow rate and speed of the ink flowing in the tube corresponding to the magenta ink are likely to decrease significantly as the recording device is used for a long period of time, compared to the flow rate and speed of the ink flowing in the tube corresponding to the cyan ink and the yellow ink. As a result, the amount of magenta ink discharged during image recording gradually decreases compared to the cyan ink and the yellow ink, and it is thought that this causes a "color shift" in which the tone of the tertiary color changes to a greenish hue.

[0015] The high coagulation of quinacridone pigments is due to their planar structure. Furthermore, since the surface of this planar structure is hydrophobic, it easily interacts with the inner surface of the tube, causing a chain reaction of adhesion. As a result, it is considered that the inner diameter of the tube corresponding to the magenta ink containing the quinacridone pigment is likely to be specifically narrow. On the other hand, it is preferable to use a quinacridone pigment in order to express a suitable color tone for magenta. Therefore, the present inventors have investigated a method for recording images with high productivity while expressing the conventional magenta color tone and preventing color shift of tertiary colors. As a result, they have found that an azo pigment can be used in the magenta ink, and have arrived at the present invention.

[0016] Pigments such as quinacridone and quinacridone solid solutions, which are general-purpose pigments used in magenta inks, and diketopyrrolopyrrole and dioxazine, which are pigments often used in magenta inks, tend to aggregate easily. The quinacridone skeleton, diketopyrrolopyrrole skeleton, and dioxazine skeleton have a high degree of planarity at the portion where multiple rings including an aromatic ring are condensed, so that the area where the flat surfaces attract each other is large. In addition, since they have imino groups and carbonyl groups, they tend to form strong hydrogen bonds between molecules. Furthermore, the highly planar portions of these pigments also increase the contact area with the inner surface of the tube, so that the pigments are chain-attached to the inner surface of the tube due to the long-term circulation and retention of the ink.

[0017] On the other hand, azo pigments that have a three-dimensionally rotatable structure (azo bond) have molecules that can freely rotate around the azo bond as the axis of rotation. In other words, azo pigments are not highly planar, so they are less likely to stack strongly between molecules and to aggregate. As a result, the pigments are less likely to adhere to the inner surface of the tube even after long-term use, so the inner diameter of the tube is less likely to narrow, and the flow rate and flow speed of the cyan ink, yellow ink, and magenta ink in the tube can be kept equal. This makes it possible to record tertiary color images with less color shift, even when using a recording device equipped with a large-capacity ink storage unit with an injection port.

[0018] <Inkjet recording method and inkjet recording apparatus> The inkjet recording method of the present invention uses an inkjet recording device including a plurality of water-based inks, an ink storage section, a recording head having an ejection port for ejecting the water-based ink, and a tube. The plurality of water-based inks include cyan ink, magenta ink, and yellow ink. The ink storage section is a member that stores the water-based inks and is provided with an inlet for injecting the water-based ink. The recording head is provided with an ejection port for ejecting the water-based ink supplied from the ink storage section. The tube is a member that connects the recording head and the ink storage section and supplies the water-based ink from the ink storage section to the recording head, and is formed of a resin material. The inkjet recording method of the present invention includes a step of applying the water-based ink ejected from the ejection port of the recording head to a recording medium to record an image. The inkjet recording device of the present invention includes a plurality of water-based inks, an ink storage section, a recording head having an ejection port for ejecting the water-based ink, and a tube. The ink storage section of the inkjet recording device is provided with an inlet for injecting the water-based ink, and the tube is formed of a resin material.

[0019] (Inkjet recording device) FIG. 1 is a perspective view showing a schematic diagram of an embodiment of an inkjet recording apparatus of the present invention. The inkjet recording apparatus of this embodiment is a so-called serial type inkjet recording apparatus that performs a recording operation by reciprocating a recording head in an X direction (main scanning direction). A recording medium 101 is intermittently transported in a Y direction (sub-scanning direction) by a transport roller 107. A recording unit 102 mounted on a carriage 103 is reciprocally scanned in an X direction (main scanning direction) that is a direction perpendicular to the Y direction that is the transport direction of the recording medium 101. A recording operation is performed by transporting the recording medium 101 in the Y direction and reciprocating scanning of the recording unit 102 in the X direction. The recording unit 102 is composed of an inkjet type recording head 203 (FIG. 2) that ejects ink from a plurality of ejection ports, and a subtank 202 (FIG. 2) as a second ink storage section, and is mounted on the carriage 103. The carriage 103 is supported so as to be movable along a guide rail 105 arranged along the X direction, and is fixed to an endless belt 106 that moves in parallel with the guide rail 105. The endless belt 106 reciprocates due to the driving force of a motor, thereby causing the carriage 103 to scan back and forth in the X direction.

[0020] A main tank 201 (FIG. 2) is housed inside each of the main tank housing sections 108 and 109 as a first ink housing section. The main tank 201 housed in the main tank housing sections 108 and 109 and the sub tank 202 of the recording unit 102 are connected by an ink supply tube 104. Ink is supplied from the main tank 201 to the sub tank 202 (FIG. 2) through the ink supply tube 104, and then ejected from the ejection opening of the recording head 203. The main tank 201, the ink supply tube 104, and the sub tank 202 can be provided in numbers corresponding to the types of ink. The main tank in the main tank housing section 108 and the sub tank constituting the recording unit 102 are connected by a color ink tube 111. The main tank in the main tank housing section 109 and the sub tank constituting the recording unit 102 are connected by a black ink tube 112. It is preferable that the main tank 201 and the sub tank 202 are connected by an ink supply tube 104 without passing through any other ink storage section.

[0021] The main tank housing portions 108 and 109 are provided with an ink inlet 210 for injecting ink into the main tank 201 from outside the inkjet recording device. When using the inkjet recording device for the first time or when the amount of ink has decreased, ink is injected from an ink bottle into the main tank placed inside the inkjet recording device. The user can open the ink inlet 210 and inject ink into the ink tank 201. In other words, the main tank is left inside the inkjet recording device and is not replaced itself.

[0022] 2 is a schematic diagram showing an example of an ink supply system. Ink (shown by hatching) stored in a main tank 201 is supplied to a sub tank 202 via an ink supply tube 104, and then supplied to a print head 203. A gas introduction tube 204 serving as an air communication section is connected to the main tank 201. When printing is performed and ink is consumed, ink is supplied from the main tank 201 to the sub tank 202, and the ink in the main tank 201 decreases. Then, air is introduced into the main tank 201 from the gas introduction tube 204, one end of which is open to the atmosphere, so that the internal negative pressure for holding the ink is kept substantially constant in the ink supply system.

[0023] The ink supply tubes 104, including the color ink tubes 111 and the black ink tube 112, are connected to the sub-tanks 202 that constitute the recording unit 102 mounted on the carriage 103. For this reason, the ink supply tubes 104 are routed around inside the device following the reciprocating scanning of the carriage 103. Therefore, the material that constitutes the ink supply tubes 104 must be selected to have flexibility that can withstand the frequent reciprocating scanning of the carriage 103. For this reason, the ink supply tubes 104 are formed from a resin material.

[0024] The ink supply tube is a member formed by molding a resin material into a tubular shape. The resin material constituting the tube may be a single resin material or a combination of two or more resin materials. It may also be a resin material containing various additives. The structure of the tube may be a single-layer structure or a laminated structure. As the resin material, a thermoplastic elastomer is preferable because it has excellent moldability, rubber elasticity, and flexibility. Examples of the thermoplastic elastomer include olefin-based, urethane-based, ester-based, styrene-based, and vinyl chloride-based resins. Among them, a styrene-based thermoplastic elastomer is preferable because it has particularly excellent flexibility and rubber elasticity. Examples of additives to be mixed into the resin material include softeners, lubricants, surfactants, antioxidants, antiaging agents, adhesion promoters, and pigments.

[0025] The inner diameter and wall thickness of the tube are appropriately set in consideration of productivity such as molding, bending rigidity when routed through a recording device, ink supplyability, gas barrier properties, etc. The inner diameter of the tube is preferably 1 mm or more and 5 mm or less, and more preferably 1 mm or more and 3 mm or less. The wall thickness of the tube is preferably 0.5 mm or more and 5 mm or less, and more preferably 0.5 mm or more and 3 mm or less.

[0026] When the gas barrier property of the ink supply tube is low, that is, when the air permeability is high, liquid components such as water are likely to evaporate from the ink in the tube. When the liquid components evaporate, the action of electrostatic repulsion for dispersing the pigment is likely to weaken, which may cause the pigment dispersion state to become unstable, and the aggregated pigment may easily adhere to the inner surface of the tube, which may reduce the degree of suppression of the color tone change of the tertiary color. Therefore, it is preferable that the air permeability of the tube is 60 μL / day or less. On the other hand, a tube with low gas barrier property has high rigidity, but it is preferable that the tube has flexibility that can withstand being pulled around inside the recording device. For this reason, it is preferable that the air permeability of the tube is 10 μL / day or more.

[0027] The air permeability of the tube can be measured according to the following method. FIG. 3 is a schematic diagram for explaining a method for measuring the air permeability of the tube. As shown in FIG. 3, one end of a tube 301 cut to an arbitrary length is sealed with a pinch cock 302, and the other end is connected to one tip of an L-shaped 1 mL measuring pipette 303. The other tip of the measuring pipette 303 is inserted into a container 304 containing water. In the above state, the tube is left in an environment with a temperature of 40° C. and a relative humidity of 20%, and the scale of the measuring pipette is read at regular intervals to measure the amount of air that has permeated into the tube. The air permeability of the tube in the present invention is the amount per 100 mm of tube length, and is expressed in units of μL / day. The target temperature for determining the air permeability of the tube is set to 40° C. in order to confirm that sufficient effects can be obtained even in a normal temperature environment by evaluating the tube under more severe conditions than the normal temperature environment (normal temperature, 25° C.) in which the inkjet recording device is used.

[0028] In order to increase the number of recordable sheets and thereby realize high productivity, it is preferable that the main tank 201 has a large maximum ink capacity V1 (mL). Specifically, the maximum ink capacity V1 (mL) of the main tank 201 is preferably 60 mL or more and 300 mL or less, and more preferably 100 mL or more and 250 mL or less. In addition, it is preferable that the initial ink filling amount of the main tank 201 is about 95% based on the maximum ink capacity.

[0029] It is also preferable that the subtank 202 has a large maximum ink capacity V2 (mL) in order to reduce the frequency of ink supply from the main tank 201 and to stably supply ink to the recording head 203. However, for example, assuming a serial system as shown in FIG. 1 in which the subtank 202 is mounted on the carriage 103, it is preferable that the maximum ink capacity V2 (mL) of the subtank 202 is not too large. In other words, if too much ink is stored in the subtank 202, the recording unit 102 becomes large, the moving speed of the carriage 103 decreases, and it becomes necessary to increase the strength of the endless belt 106 and the motor that move the carriage 103. Therefore, it is preferable that the maximum ink capacity V2 (mL) of the subtank 202 is 1 mL or more and 20 mL or less, and more preferably 2 mL or more and 10 mL or less.

[0030] The housings of the main tank 201 and the sub tank 202 are formed of thermoplastic resins such as polyester, polycarbonate, polyethylene, polypropylene, polystyrene, polyphenylene ether, and mixtures or modified products thereof. An ink absorber capable of generating negative pressure for retaining ink may be disposed inside the housing. Compressed fibers of polypropylene, polyurethane, or the like are preferable as the ink absorber. Alternatively, the ink may be directly stored inside the housing without disposing an ink absorber. From the viewpoint of realizing high-speed recording, it is preferable that the sub tank 202 does not have an absorber for impregnating and storing ink, and that the ink is directly stored inside the housing constituting the sub tank 202.

[0031] The recording unit 102 is composed of a recording head 203 and a subtank 202. The subtank 202 may be attached to the recording unit 102, which is a head cartridge in which the recording head 203 is built, and the recording unit 102 with the subtank 202 attached may be attached to the carriage 103. Furthermore, the recording unit 102 integrally composed of the subtank 202 and the recording head 203 may be attached to the carriage 103. Among these, it is preferable to adopt a configuration in which the recording unit 102 with the subtank 202 attached is set in the carriage 103 as shown in Figures 1 and 2.

[0032] The ink ejection method of the recording head 203 may be a method of applying mechanical energy to the ink or a method of applying thermal energy to the ink. Among these, it is preferable to adopt a method of ejecting ink by applying thermal energy to the ink.

[0033] Any recording medium may be used as the target for recording an image. In particular, it is preferable to use permeable paper such as recording media without a coating layer, such as plain paper or uncoated paper, or recording media with a coating layer, such as glossy paper or art paper.

[0034] (Water-based ink) The inkjet recording method of the present invention includes a step of recording an image by applying a plurality of water-based inks including a cyan ink, a magenta ink, and a yellow ink to a recording medium by ejecting the water-based inks from ejection openings of a recording head. All of the water-based inks are pigment inks containing a pigment as a coloring material. The components constituting the inks will be described below.

[0035] [Colorant] A pigment is used as the coloring material. The content (mass%) of the pigment in the ink is preferably 0.1% by mass or more and 15.0% by mass or less, and more preferably 1.0% by mass or more and 10.0% by mass or less, based on the total mass of the ink. The content of the pigment in each ink is preferably in the order of most to least: magenta ink, yellow ink, and cyan ink.

[0036] The pigment dispersion method is not particularly limited. For example, resin-dispersed pigments dispersed by a resin dispersant, pigments dispersed by a surfactant, and microencapsulated pigments in which at least a part of the pigment particle surface is coated with a resin or the like can be used. Self-dispersed pigments in which a functional group containing a hydrophilic group such as an anionic group is bonded to the pigment particle surface, and pigments in which an organic group containing a polymer is chemically bonded to the pigment particle surface (resin-bonded self-dispersed pigments) can also be used. Pigments with different dispersion methods may be used in combination. Among them, resin-dispersed pigments dispersed by a resin dispersant are preferred. It is more preferred to use a water-soluble resin as the resin dispersant.

[0037] The cyan ink contains a phthalocyanine pigment such as a copper phthalocyanine pigment. Examples of the phthalocyanine pigment include CI Pigment Blue 15, 15:1, 15:3, 15:4, and 15:6. Of these, CI Pigment Blue 15:3 is preferred. These phthalocyanine pigments can be used alone or in combination of two or more.

[0038] Both the yellow ink and the magenta ink contain an azo pigment. Examples of the azo pigment used in the yellow ink include CI Pigment Yellow: 1, 3, 12, 13, 14, 17, 55, 62, 65, 73, 74, 81, 83, 93, 97, 100, 104, 127, 151, 154, 155, 174, 180, and 183. Of these, CI Pigment Yellow 74 is preferred. These azo pigments can be used alone or in combination of two or more. Examples of azo pigments used in magenta inks include CI Pigment Red: 4, 9, 12, 14, 23, 31, 32, 49:1, 49:2, 57, 63:1, 112, 146, 147, 150, 170, 175, 176, 184, 185, 187, 188, 208, 210, 245, 268, and 269. Of these, CI Pigment Red 150 is preferred. These azo pigments may be used alone or in combination of two or more.

[0039] The magenta ink preferably further contains a quinacridone pigment as a coloring material other than the azo pigment. Examples of the quinacridone pigment include CI Pigment Red: 122, 192, 202, 206, 207, 209, and 282; CI Pigment Violet: 19, and the like. The quinacridone pigment may be a quinacridone solid solution formed from two or more of these quinacridone pigments. Among these, a solid solution containing CI Pigment Violet 19 and CI Pigment Red 122 is preferable. By containing the quinacridone pigment together with the azo pigment, a more preferable color tone of magenta can be expressed. As described above, the quinacridone pigment is prone to aggregation, but when the azo pigment is present, the aggregation of the pigment is more easily suppressed compared to a magenta ink containing only the quinacridone pigment as a pigment. Therefore, even if a quinacridone pigment is used, the effect of preventing the pigment from agglomerating to the inner surface of the magenta ink tube from adhering is not lost, and a more preferable color tone can be expressed as the magenta ink.

[0040] The content (mass%) of the azo pigment in the magenta ink is preferably 20% by mass or more, more preferably 30% by mass or more, based on the content (mass%) of all pigments in the magenta ink. If the proportion of the azo pigment is too low, the aggregated quinacridone pigment may easily adhere to the inner surface of the magenta ink tube, and the degree of suppression of the color tone change of the tertiary color may decrease. In addition, the content (mass%) of the azo pigment in the magenta ink is preferably 80% by mass or less, more preferably 70% by mass or less, based on the content (mass%) of all pigments in the magenta ink. If the proportion of the azo pigment is too high, it may be somewhat difficult to express a preferable color tone of magenta.

[0041] It is preferred that the cyan ink contains CI Pigment Blue 15:3, the magenta ink contains CI Pigment Red 150 and a quinacridone solid solution, and the yellow ink contains CI Pigment Yellow 74. Furthermore, it is particularly preferred that the quinacridone solid solution of the magenta ink is a solid solution containing CI Pigment Violet 19 and CI Pigment Red 122. Combining the pigments of each ink as described above is particularly preferred because it makes it difficult for aggregated pigments to adhere to the inner surface of the magenta ink tube, making it possible to more effectively suppress changes in the hue of the tertiary color, and also resulting in an excellent balance of the hue of each ink.

[0042] [resin] The ink preferably contains a resin. The resin can be added to the ink (i) to stabilize the dispersion state of the pigment, that is, as a resin dispersant or its auxiliary. Also, the resin can be added to the ink (ii) to improve various properties of the image to be recorded. The state of the resin in the ink may be a state in which it is dissolved in an aqueous medium, or a state in which it is dispersed as resin particles in an aqueous medium. In this specification, "the resin is water-soluble" means that when the resin is neutralized with an alkali equivalent to the acid value, it does not form particles whose particle size can be measured by a measurement method such as a dynamic light scattering method. The content (mass%) of the resin in the ink is preferably 0.1% by mass or more and 5.0% by mass or less, and more preferably 0.1% by mass or more and 3.0% by mass or less, based on the total mass of the ink.

[0043] Examples of the resin include acrylic resin, polyester resin, urethane resin, urea resin, polysaccharides, and polypeptides. Among them, acrylic resin is preferred from the viewpoint of ejection characteristics from the ejection port of the recording head. As the acrylic resin, one having a unit with an anionic group and a unit without an anionic group as a constituent unit is preferred. Examples of the form of the acrylic resin include random copolymer, block copolymer, graft copolymer, and combinations thereof.

[0044] Examples of monomers that become units constituting the acrylic resin upon polymerization include monomers having an anionic group and monomers having no anionic group. Usually, a monomer having an anionic group becomes a hydrophilic unit upon polymerization, and a monomer having no anionic group becomes a hydrophobic unit upon polymerization.

[0045] Examples of the monomer having an anionic group include monomers having a carboxylic acid group such as (meth)acrylic acid, itaconic acid, maleic acid, and fumaric acid; anhydrides and salts of these monomers; and examples of the cation constituting the salt of the monomer having an anionic group include lithium cation, sodium cation, potassium cation, ammonium cation, and organic ammonium cation.

[0046] Examples of monomers not having an anionic group include monomers having an aromatic group, such as styrene, α-methylstyrene, benzyl (meth)acrylate, 2-vinylpyridine, 4-vinylpyridine, and 1-vinylimidazole; and (meth)acrylic acid esters, such as ethyl (meth)acrylate, methyl (meth)acrylate, (iso)propyl (meth)acrylate, (n-, iso-, and t-)butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate.

[0047] The acid value of the resin is preferably 40 mgKOH / g or more and 300 mgKOH / g or less, and more preferably 100 mgKOH / g or more and 250 mgKOH / g or less. In particular, it is more preferably 100 mgKOH / g or more and 200 mgKOH / g or less. The weight average molecular weight of the resin is preferably 3,000 or more and 50,000 or less, and more preferably 5,000 or more and 15,000 or less. The weight average molecular weight of the resin is a value measured by gel permeation chromatography in terms of polystyrene.

[0048] [Random Copolymer] The ink preferably contains a water-soluble random copolymer containing a unit derived from (meth)acrylic acid and a unit not having an anionic group derived from at least one of a monomer having an aromatic group and a (meth)acrylic acid ester. Among them, a water-soluble random copolymer containing a unit derived from (meth)acrylic acid and a unit derived from at least one of a monomer of styrene and α-methylstyrene is preferred. Such a random copolymer is suitable as a resin dispersant for dispersing a pigment because it easily interacts with the pigment. The acid value of the random copolymer is preferably 100 mgKOH / g or more and 250 mgKOH / g or less, more preferably 100 mgKOH / g or more and 200 mgKOH / g or less. The content (mass %) of the random copolymer in the ink is preferably 0.1 mass % or more and 3.0 mass % or less based on the total mass of the ink.

[0049] [Block Copolymer] Moreover, it is preferable that the ink further contains a block copolymer. In particular, it is preferable that the magenta ink contains a block copolymer. As the block copolymer, a water-soluble resin containing an A block having no anionic group and a B block having an anionic group is preferable. The A block (hydrophobic block) is a polymer block composed of units derived from a monomer having no anionic group. Moreover, the B block (hydrophilic block) is a polymer block composed of units derived from a monomer having an anionic group. Each block may be composed of units derived from one or more types of monomers, and in particular, it is more preferable that each block is composed of units derived from only one type of monomer.

[0050] The block copolymer is preferably a water-soluble resin containing the following A block (hydrophobic block) and B block (hydrophilic block). The A block is preferably composed of a unit derived from a monomer having an aromatic group such as benzyl methacrylate. The B block is preferably composed of a unit derived from a (meth)acrylic acid ester such as butyl methacrylate and a unit derived from a monomer having an anionic group such as (meth)acrylic acid. Such a block copolymer has functions separated within its molecular structure, and is efficiently adsorbed to the pigment and its resin dispersant while exerting steric repulsion for a long period of time, so that the dispersed state of the pigment can be stably maintained. For this reason, the pigment aggregated on the inner surface of the tube is less likely to adhere, and the change in the color tone of the tertiary color can be more effectively suppressed. The acid value of the block copolymer is preferably 80 mgKOH / g or more and 200 mgKOH / g or less, and more preferably 100 mgKOH / g or more and 150 mgKOH / g or less. The block copolymer can be synthesized according to a polymerization method that has been commonly used in the past. Specific examples of the polymerization method include a living radical polymerization method and a living anionic polymerization method. The content (mass %) of the block copolymer in the ink is preferably 0.1 mass % or more and 3.0 mass % or less based on the total mass of the ink.

[0051] Assume that each of the multiple inks contains a resin. In this case, it is preferable that the mass ratio of the resin content (mass%) to the total pigment content (mass%) in the magenta ink is greater than the mass ratio of the resin content (mass%) to the total pigment content (mass%) in the cyan ink. It is also preferable that the mass ratio of the resin content (mass%) to the total pigment content (mass%) in the magenta ink is greater than the mass ratio of the resin content (mass%) to the total pigment content (mass%) in the yellow ink. By satisfying the above-mentioned relationship between the three types of ink, the pigments that have aggregated are less likely to adhere to the inner surface of the magenta ink tube, and changes in the tone of the tertiary color can be more effectively suppressed.

[0052] [Aqueous medium] The ink is an aqueous ink containing at least water as an aqueous medium. The ink can contain water or an aqueous medium that is a mixed solvent of water and a water-soluble organic solvent. As the water-soluble organic solvent, any of those usable for inkjet inks, such as alcohols, (poly)alkylene glycols, glycol ethers, nitrogen-containing compounds, and sulfur-containing compounds, can be used. The content (mass%) of the water-soluble organic solvent in the ink is preferably 3.0% by mass or more and 50.0% by mass or less based on the total mass of the ink. As the water, it is preferable to use deionized water or ion-exchanged water. The content (mass%) of water in the ink is preferably 50.0% by mass or more and 95.0% by mass or less based on the total mass of the ink.

[0053] [Surfactants] The ink may contain various types of surfactants. Examples of the surfactants include hydrocarbon surfactants, fluorine surfactants, and silicone surfactants. These surfactants may be any of nonionic surfactants, anionic surfactants, cationic surfactants, and amphoteric surfactants. The content (mass %) of the surfactant in the ink is preferably 0.1% by mass or more and 5.0% by mass or less, and more preferably 0.2% by mass or more and 1.5% by mass or less, based on the total mass of the ink.

[0054] [Other ingredients] The ink may further contain water-soluble organic compounds that are solid at 25° C., such as urea or its derivatives, trimethylolpropane, and trimethylolethane. The content (mass %) of the water-soluble organic compounds in the ink is preferably 0.1 mass % or more and 10.0 mass % or less, based on the total mass of the ink. In addition to the above components, the ink may contain various additives such as antifoaming agents, pH adjusters, viscosity adjusters, rust inhibitors, preservatives, antifungal agents, antioxidants, and reduction inhibitors, as necessary. EXAMPLES

[0055] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited by the following examples as long as it does not exceed the gist of the invention. The terms "parts" and "%" used to describe the amounts of components are based on mass unless otherwise specified. The acid value of the resin was measured by potentiometric titration using potassium hydroxide-methanol titrant. The weight average molecular weight of the resin is a value calculated in terms of polystyrene measured by gel permeation chromatography (GPC).

[0056] <Resin preparation> (Resin 1-4) Water-soluble resins 1 to 4 were synthesized by polymerizing the monomers shown in Table 1 by a conventional method. The acid value of resins 1 to 4 was 120 mgKOH / g, and the weight average molecular weight was 8,000. The obtained resins 1 to 4 were dissolved in ion-exchanged water by adding potassium hydroxide in an amount equimolar to the acid value of the resins, to prepare aqueous solutions of each resin with a resin content of 10.0%. The monomers in Table 1 are St: styrene, BzMA: benzyl methacrylate, nBA: n-butyl acrylate, AA: acrylic acid, and MAA: methacrylic acid.

[0057] TIFF0007665439000001.tif52170

[0058] (Resin 5) Resin 5, a water-soluble block copolymer, was synthesized according to the description of JP 2018-150518 A. Resin 5 has an A block composed of units derived from benzyl methacrylate and a B block composed of units derived from butyl methacrylate and units derived from methacrylic acid. Resin 5 had an acid value of 120 mg KOH / g and a weight average molecular weight of 10,000. The obtained resin 5 was dissolved in ion-exchanged water by adding potassium hydroxide in an amount equimolar to the acid value thereof to prepare an aqueous solution of resin 5 having a resin 5 content of 10.0%.

[0059] <Preparation of pigment dispersion> The components (unit: parts) shown in the upper part of Table 2 were mixed to obtain a mixture. In Table 2, "solid solution pigment" is a solid solution containing CI Pigment Violet 19 and CI Pigment Red 122. The obtained mixture was dispersed using a sand grinder for 1 hour, and then centrifuged to remove coarse particles. After pressure filtration using a microfilter (manufactured by Fujifilm) with a pore size of 3.0 μm, an appropriate amount of ion-exchanged water was added to obtain each pigment dispersion. The lower part of Table 2 shows the contents of pigment and resin (resin dispersant) in the pigment dispersion.

[0060] TIFF0007665439000002.tif102170

[0061] <Ink Preparation> Each ink was prepared by mixing the components (unit: %) shown in the upper rows of Tables 3-1 to 3-4, thoroughly stirring, and then filtering under pressure using a cellulose acetate filter (manufactured by Advantec) with a pore size of 3.0 μm. In Tables 3-1 to 3-4, the number average molecular weight of polyethylene glycol is "1,000." Also, "Acetylenol E100" is the trade name of a nonionic surfactant (acetylene glycol ethylene oxide adduct) manufactured by Kawaken Fine Chemicals. The properties of the prepared inks are shown in the lower rows of Tables 3-1 to 3-4.

[0062] TIFF0007665439000003.tif156170

[0063] TIFF0007665439000004.tif152170

[0064] TIFF0007665439000005.tif163170

[0065] TIFF0007665439000006.tif156170

[0066] <Preparing the tube> Tubes 1 to 5 were prepared, each having an inner diameter of 2 mm and an outer diameter of 4 mm, and were formed using a styrene-based thermoplastic elastomer, a lubricant, and a softener. Tube 6, a commercially available glass tube, and Tube 7, a commercially available aluminum tube, were also prepared. The air permeability of tubes 1 to 5 was measured in an environment of 40°C using the method described above. The air permeability of the tube is the value per tube length L = 100 mm, and is expressed in units of "μL / day." The properties of the prepared tubes are shown in Table 4.

[0067] TIFF0007665439000007.tif69170

[0068] <Evaluation> An inkjet recording apparatus having the main components shown in FIG. 1 and incorporating an ink supply system having the configuration shown in FIG. 2 was prepared. This recording apparatus is a serial type recording apparatus in which a recording head 203 is incorporated and a recording unit 102 having a sub-tank 202 is mounted on a carriage 103. In addition, a tube of the type shown in Table 5 was used as the ink supply tube 104. The maximum ink capacity V1 of the main tank was 150 mL, and the maximum ink capacity V2 of the sub-tank was 5 mL. The main tank 201 was filled with each color of ink of the type shown in Table 5. When the remaining ink amount decreased during the evaluation, the ink was replenished from the inlet of the main tank 201. In this embodiment, the recording duty of a solid image recorded under the condition that two ink droplets with a mass of 5 ng per droplet are applied to a unit area of ​​1 / 600 inch x 1 / 600 inch is defined as 100%. In the present invention, in the evaluation criteria for each item shown below, "AAA", "AA", "A", and "B" were considered acceptable levels, and "C" was considered unacceptable. The evaluation results are shown in Table 5.

[0069] (Tertiary color tone change) Using the above-mentioned inkjet recording device, yellow ink, cyan ink, and magenta ink were applied to the recording medium in this order in a layered manner, and a tertiary color image was recorded in which the recording duty of each ink was 30% and the total recording duty was 90%. As the recording medium, a product name "HR-101" (plain paper, manufactured by Canon) was used. The obtained image was designated "Evaluation Image 1". Next, the following solid image was recorded on 10 sheets, and then the recording was paused for 1 hour, and this cycle was repeated to record a total of 5,000 sheets of solid images. The recorded solid image was an A4-sized recording medium on which yellow ink, cyan ink, and magenta ink were applied to the recording medium in this order in a layered manner, and the recording duty of each ink was 5%, and the total recording duty was 15%. As the recording medium, a product name "GF-500" (plain paper, manufactured by Canon) was used. Then, a tertiary color image was recorded under the same conditions as Evaluation Image 1. The obtained image was designated "Evaluation Image 2".

[0070] The tertiary color images of the evaluation images 1 and 2 obtained above were measured using a fluorescence spectrodensitometer (product name "FD-7", manufactured by Konica Minolta) to measure the L * a * b * L based on the display system * , a * , and b * The measurement value for evaluation image 1 is L1 * , a1 * , and b1 * The measured value in evaluation image 2 is L2 * , a2 * , and b2 * From the measured values, ΔE = {(L2 * -L1 * ) 2 +(a2 * -a1 * ) 2 +(b2 * -b1 * ) 2} 1 / 2The color difference ΔE was calculated according to the formula above, and the change in the tertiary color tone was evaluated according to the following evaluation criteria. The smaller the ΔE, the more the color tone change is suppressed.

[0071] In this evaluation, a large number of prints was set in order to use a large amount of ink and to allow a long time to pass from the start of the evaluation. In other words, the number of times ink was injected into the main tank from the injection port was increased, and the contact time between the ink and air during ink injection was lengthened, creating conditions that made it easy for the viscosity of the ink contained in the main tank to increase. In addition, the long evaluation time created conditions that made it easy for the amount of air to permeate into the tube to increase. AAA: ΔE was less than 0.5. AA: ΔE was greater than or equal to 0.5 and less than 1.0. A: ΔE was greater than or equal to 1.0 and less than 1.5. B: ΔE was 1.5 or greater but less than 2.0. C: ΔE was 2.0 or more.

[0072] (Magenta shade) Using the above inkjet recording device, a solid image with a recording duty of 100% was recorded on an A4-sized recording medium using all the nozzles for magenta ink. The recording medium used was "Red Label Superior" (plain paper, manufactured by Canon). A colorimeter (manufactured by Konica Minolta under the trade name "FD-7") was used to measure the b * The values ​​were measured, and the magenta color tone was evaluated according to the following evaluation criteria. AA:b * The value was below -5. A:b * The value was greater than -5 and less than -3. B:b * The value was greater than -3 and less than 1. C:b * The value was greater than 1.

[0073] TIFF0007665439000008.tif255170

[0074] In the comparative example where ΔE was large in the evaluation of "change in tertiary color tone," the tone of evaluation image 2 was shifted to a greener hue than that of evaluation image 1. From this, it can be said that in the examples where ΔE was small, the decrease in the ejection amount caused by the blockage of the magenta ink tube was suppressed.

Claims

1. an inkjet recording method comprising a step of applying the water-based inks ejected from the ejection ports to a recording medium to record an image using an inkjet recording device comprising: a plurality of water-based inks including a cyan ink, a magenta ink, and a yellow ink; ink containers for storing the respective water-based inks; a recording head having ejection ports for ejecting the water-based inks supplied from the ink containers; and a tube for supplying the water-based ink from the ink container to the recording head, the ink container is provided with an inlet for injecting the water-based ink; The tube is made of a resin material, the cyan ink contains a phthalocyanine pigment, the yellow ink and the magenta ink each contain an azo pigment, the magenta ink further contains a quinacridone pigment, an inkjet recording method, wherein a content (% by mass) of the azo pigment in the magenta ink is 80% by mass or less based on a content (% by mass) of all pigments in the magenta ink;

2. An inkjet recording method using an inkjet recording device comprising: a plurality of water-based inks including cyan ink, magenta ink, and yellow ink; ink storage sections for storing each of the water-based inks; a recording head having an ejection port formed therein for ejecting the water-based ink supplied from the ink storage section; and a tube for supplying the water-based ink from the ink storage section to the recording head, the method comprising the steps of: applying the water-based ink ejected from the ejection port to a recording medium to record an image, the ink container is provided with an inlet for injecting the water-based ink; The tube is made of a resin material, the cyan ink contains a phthalocyanine pigment, the yellow ink and the magenta ink each contain an azo pigment, The plurality of water-based inks further contain a resin, the content (mass %) of the resin in each of the plurality of water-based inks is 0.1 mass % or more and 5.0 mass % or less based on the total mass of the ink; 13. The inkjet recording method, wherein the resin in the magenta ink contains a block copolymer.

3. An inkjet recording method using an inkjet recording device comprising: a plurality of water-based inks including cyan ink, magenta ink, and yellow ink; ink storage sections for storing each of the water-based inks; a recording head having an ejection port formed therein for ejecting the water-based ink supplied from the ink storage section; and a tube for supplying the water-based ink from the ink storage section to the recording head, the method comprising the steps of: applying the water-based ink ejected from the ejection port to a recording medium to record an image, the ink container is provided with an inlet for injecting the water-based ink; The tube is made of a resin material, the cyan ink contains a phthalocyanine pigment, the yellow ink and the magenta ink each contain an azo pigment, The plurality of water-based inks further contain a resin, a mass ratio of the content (mass%) of the resin to the content (mass%) of all pigments in the magenta ink is a mass ratio of the resin content (% by mass) to the total pigment content (% by mass) in the cyan ink and a mass ratio of the resin content (% by mass) to the total pigment content (% by mass) in the yellow ink are both greater than the mass ratio of the resin content (% by mass) to the total pigment content (% by mass) in the cyan ink, 13. The inkjet recording method, wherein the resin in the magenta ink contains a block copolymer.

4. 4. The ink-jet recording method according to claim 1, wherein the air permeation amount (μL / day) of the tube at a temperature of 40° C. is 60 μL / day or less.

5. 5. The ink-jet recording method according to claim 1, wherein the air permeation amount (μL / day) of the tube at a temperature of 40° C. is 10 μL / day or more.

6. 6. The ink jet recording method according to claim 1, wherein a resin material constituting the tube is a styrene-based thermoplastic elastomer.

7. 7. The ink-jet recording method according to claim 1, wherein the inner diameter of the tube is from 1 mm to 5 mm.

8. 8. The ink-jet recording method according to claim 1, wherein the wall thickness of the tube is from 0.5 mm to 5 mm.

9. The maximum ink capacity V of the ink storage unit １ The ink-jet recording method according to any one of claims 1 to 8, wherein (mL) is 60 mL or more and 300 mL or less.

10. the inkjet recording apparatus further comprises a second ink container provided in the recording head, 10. The ink jet recording method according to claim 1, wherein the ink containing section and the second ink containing section are connected by the tube without passing through any other ink containing section.

11. The second ink storage section has a maximum ink storage capacity V ２ The ink jet recording method according to claim 10, wherein (mL) is 1 mL or more and 20 mL or less.

12. 12. The inkjet recording method according to claim 1, wherein the pigment content (mass %) in each of the plurality of water-based inks is from 0.1 mass % to 15.0 mass % based on the total mass of the ink.

13. 13. The inkjet recording method according to claim 1, wherein the plurality of water-based inks are arranged in the order of greatest pigment content from greatest to least pigment content as follows: the magenta ink, the yellow ink, and the cyan ink.

14. the phthalocyanine pigment in the cyan ink comprises C.I. Pigment Blue 15:3; The azo pigment in the magenta ink comprises C.I. Pigment Red 150; 14. The ink-jet recording method according to any one of claims 1 to 13, wherein the azo pigment in the yellow ink contains C. I. Pigment Yellow 74.

15. The inkjet recording method according to any one of claims 2 to 14, wherein the magenta ink further contains a quinacridone pigment.

16. 16. The ink-jet recording method according to claim 15, wherein the quinacridone pigment in the magenta ink comprises a solid solution containing C. I. Pigment Violet 19 and C. I. Pigment Red 122.

17. 17. The inkjet recording method according to claim 15, wherein a content (% by mass) of the azo pigment in the magenta ink is 20% by mass or more based on a content (% by mass) of all pigments in the magenta ink.

18. 18. The inkjet recording method according to claim 15, wherein a content (% by mass) of the azo pigment in the magenta ink is 80% by mass or less based on a content (% by mass) of all pigments in the magenta ink.

19. The plurality of water-based inks further contain a resin, 19. The inkjet recording method according to claim 1, wherein the content (mass %) of the resin in each of the plurality of water-based inks is from 0.1 mass % to 5.0 mass % based on the total mass of the ink.

20. The plurality of water-based inks further contain a resin, a mass ratio of the content (mass%) of the resin to the content (mass%) of all pigments in the magenta ink is 19. The inkjet recording method according to claim 1, wherein the mass ratio of the resin content (mass%) to the total pigment content (mass%) in the cyan ink is greater than both the mass ratio of the resin content (mass%) to the total pigment content (mass%) in the yellow ink and the mass ratio of the resin content (mass%) to the total pigment content (mass%) in the cyan ink.

21. 21. The inkjet recording method according to claim 19, wherein the resin in the magenta ink is a block copolymer.

22. the block copolymer is a water-soluble resin including an A block which is a hydrophobic block and a B block which is a hydrophilic block, the A block contains a unit derived from a monomer having an aromatic group, The ink jet recording method according to claim 21, wherein the B block contains a unit derived from a (meth)acrylic acid ester and a unit derived from a monomer having an anionic group.

23. an inkjet recording apparatus comprising: a plurality of water-based inks including a cyan ink, a magenta ink, and a yellow ink; ink containers for containing the respective water-based inks; a recording head having an ejection port for ejecting the water-based ink supplied from the ink container; and a tube for supplying the water-based ink from the ink container to the recording head, the ink container is provided with an inlet for injecting the water-based ink; The tube is made of a resin material, the cyan ink contains a phthalocyanine pigment, the yellow ink and the magenta ink each contain an azo pigment, the magenta ink further contains a quinacridone pigment, an inkjet recording apparatus, wherein a content (mass %) of the azo pigment in the magenta ink is 80 mass % or less based on a content (mass %) of all pigments in the magenta ink;

24. An inkjet recording device comprising: a plurality of water-based inks including cyan ink, magenta ink, and yellow ink; ink containers for accommodating each of the water-based inks; a recording head having an ejection port for ejecting the water-based ink supplied from the ink container; and a tube for supplying the water-based ink from the ink container to the recording head, the ink container is provided with an inlet for injecting the water-based ink; The tube is made of a resin material, the cyan ink contains a phthalocyanine pigment, the yellow ink and the magenta ink each contain an azo pigment, The plurality of water-based inks further contain a resin, the content (mass %) of the resin in each of the plurality of water-based inks is 0.1 mass % or more and 5.0 mass % or less based on the total mass of the ink; 2. An inkjet recording apparatus, wherein the resin in the magenta ink contains a block copolymer.

25. An inkjet recording device comprising: a plurality of water-based inks including cyan ink, magenta ink, and yellow ink; ink containers for accommodating each of the water-based inks; a recording head having an ejection port for ejecting the water-based ink supplied from the ink container; and a tube for supplying the water-based ink from the ink container to the recording head, the ink container is provided with an inlet for injecting the water-based ink; The tube is made of a resin material, the cyan ink contains a phthalocyanine pigment, the yellow ink and the magenta ink each contain an azo pigment, The plurality of water-based inks further contain a resin, a mass ratio of the content (mass%) of the resin to the content (mass%) of all pigments in the magenta ink is a mass ratio of the resin content (% by mass) to the total pigment content (% by mass) in the cyan ink and a mass ratio of the resin content (% by mass) to the total pigment content (% by mass) in the yellow ink are both greater than the mass ratio of the resin content (% by mass) to the total pigment content (% by mass) in the cyan ink, 2. An inkjet recording apparatus, wherein the resin in the magenta ink contains a block copolymer.

Images