Inkjet recording method and inkjet recording device

Abstract

To provide an inkjet recording method having good ink discharge stability while using a recording head having a mechanism of heating ink and capable of recording an image excellent in abrasion resistance on a non-absorbent recording medium.SOLUTION: There is provided an inkjet recording method by discharging an aqueous ink from a recording head, followed by applying to a recording medium to record an image, which comprises a step of discharging an aqueous ink heated to a temperature TH(°C) from a recording head to apply to the recording medium and a step of heating the recording medium to which the aqueous ink is applied to a temperature TF(°C), wherein the aqueous ink contains a pigment and polyester resin particles and the glass transition temperature TG(°C) of the polyester resin particles, the temperature TH(°C) and the temperature TF(°C) satisfy the relationships of the following expressions: TG(°C)>TH(°C) (1), TF(°C)≥TH(°C)+10°C (2) and TF(°C)≥TG(°C)-10°C (3).SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] In recent years, inkjet recording methods have been increasingly used in the sign and display field, such as for recording posters and large-sized advertisements. In this field, polyvinyl chloride sheets and polyethylene terephthalate (PET) sheets are often used as recording media due to their durability and cost. These recording media have no or almost no aqueous ink absorption layer on the recording surface, and are known as non-absorbent recording media (recording media that do not absorb aqueous ink) or low-absorbent recording media (recording media that have low absorbency for aqueous ink). Conventionally, solvent-based inks and curable inks have been used to record images on these recording media. However, there is a growing need for aqueous inks that use aqueous media to reduce environmental impact and odor.

[0003] Images used in the field of signs and displays are required to have excellent abrasion resistance. To meet this requirement, for example, an ink containing acrylic resin particles and a method of applying this ink to a low- to non-absorbent recording medium to record an image and then heating the recorded image have been proposed (Patent Document 1). Also proposed is an ink containing alkyl polyols with a boiling point within a predetermined range, which can record images with excellent abrasion resistance while suppressing adhesion to the recording head (Patent Document 2).

[0004] On the other hand, when an image is recorded using a recording head that ejects water-based ink using thermal energy, a temperature difference occurs between the recording elements (ejection heaters) that generate thermal energy and the recording elements that are used more frequently. This temperature difference can cause a difference in the amount of ink ejected from the ejection ports corresponding to the recording elements, resulting in unevenness in the recorded image. To resolve this difference in the amount of ink ejected, a method has been proposed for recording an image while controlling the temperature of the recording head and the ink within the recording head (hereinafter also referred to as "temperature control"), for example (Patent Document 3). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-220352 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-251049 [Patent Document 3] Japanese Patent Application Laid-Open No. 2016-002738 Summary of the Invention [Problem to be solved by the invention]

[0006] However, it was found that when the ink proposed in Patent Document 1 is ejected onto a recording medium from a recording head that ejects ink using thermal energy, the recorded image is more likely to become uneven, and the scratch resistance of the uneven areas is reduced. It was also found that when the ink proposed in Patent Document 1 is ejected from a temperature-controlled recording head, the recorded image is less likely to become uneven, and the scratch resistance of the image is improved. However, it was found that when ink is continuously ejected from a temperature-controlled recording head for a long period of time, the ink is more likely to solidify near the ejection ports, and the ejection stability of the ink is reduced.

[0007] Therefore, an object of the present invention is to provide an inkjet recording method that uses a recording head having a mechanism for heating the ink, yet has good ink ejection stability and is capable of recording images with excellent abrasion resistance on a low- to non-absorbent recording medium. Another object of the present invention is to provide an inkjet recording apparatus used in this inkjet recording method. [Means for solving the problem]

[0008] That is, according to the present invention, there is provided an ink-jet recording method in which an aqueous ink is ejected from an ink-jet recording head by the action of thermal energy and applied to a recording medium to record an image, and the ink is heated to a temperature T H (°C) from the recording head to apply the water-based ink to the recording medium; and F (°C), wherein the water-based ink contains a pigment and polyester resin particles, the ratio of the weight-average molecular weight to the number-average molecular weight of the polyester resin particles is 6.0 or less, and the glass transition temperature T G (℃), the temperature T H (℃), and the temperature T F (°C) satisfies the relationships of the following formulas (1) to (3), the amount of heat ((W·h) / g) applied to the water-based ink applied to the recording medium is 2 (W·h) / g or more, and the recording medium is in a state where the ink temperature is within 30 msec from the start of contact in the Bristow method. 1 / 2 Water absorption up to 10mL / m 2 An inkjet recording method is provided, characterized in that: T G (℃)>T H (℃) (1) T F (℃)≧T H (℃)+10℃ (2) T F (℃)≧T G (℃)-10℃ (3) [Effects of the Invention]

[0009] According to the present invention, it is possible to provide an inkjet recording method that uses a recording head having an ink heating mechanism, yet has good ink ejection stability and is capable of recording images with excellent abrasion resistance on a low to non-absorbent recording medium. Furthermore, according to the present invention, it is possible to provide an inkjet recording apparatus used in this inkjet recording method. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a perspective view schematically illustrating an embodiment of an inkjet recording apparatus of the present invention. [Figure 2] 1 is a side view schematically illustrating an embodiment of an inkjet recording apparatus of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention will be described in further detail below with reference to preferred embodiments. In the present invention, when the compound is a salt, the salt is present in the ink as dissociated ions, but for convenience it will be expressed as "containing a salt." Furthermore, aqueous inkjet inks may be simply referred to as "ink." Unless otherwise specified, physical property values ​​are those at room temperature (25°C) and normal pressure (1 atmosphere).

[0012] In addition, in this specification, unless otherwise specified, the term "unit" refers to a unit structure corresponding to one monomer. When written as "(meth)acrylic acid" and "(meth)acrylate", they mean "acrylic acid, methacrylic acid" and "acrylate, methacrylate", respectively. Polyester resins commonly used in aqueous inkjet inks are composed of units derived from polyhydric alcohols and units derived from polycarboxylic acids. A structure containing an ester bond (-COO-) and composed of units derived from polyhydric alcohols and units derived from polycarboxylic acids is sometimes called an "ester unit".

[0013] Furthermore, in this specification, low-absorption to non-absorption recording media may be collectively referred to as "non-absorption recording media." A low-absorption to non-absorption recording medium is determined by measuring the time from the start of contact to the time of contact in the Bristow method for 30 msec. 1 / 2 Water absorption up to 10mL / m 2 It is defined as follows:

[0014] The present inventors have investigated the cause of ink solidification near the ejection orifice when the ink proposed in Patent Document 1 (hereinafter referred to as "ink containing acrylic resin particles A") is ejected continuously for a long period of time from a temperature-controlled recording head. When an ejection orifice where ink had solidified and failed to eject was observed, it was found that some of the acrylic resin particles A in the ink had fused and blocked the ejection orifice. At this time, the glass transition temperature (T G (℃)) is the temperature of the temperature-controlled print head (the temperature of the ink in the print head (T H (°C)). Therefore, the glass transition temperature (T G Near the nozzle of the print head, which is temperature-controlled to a temperature above 200°C, the liquid components in the ink evaporate rapidly, concentrating acrylic resin particles A. At that time, it is thought that some of the concentrated acrylic resin particles melt and solidify at the nozzle.

[0015] Therefore, the glass transition temperature (T G (℃) is the temperature of the ink in the print head (T H Inks were prepared using acrylic resin particles B, which had a temperature slightly higher (about 20°C higher) than the standard temperature (°C), and acrylic resin particles C, which had a temperature sufficiently higher (about 50°C higher). These inks were used to evaluate the ejection stability from the recording head. As a result, it was found that the ejection stability of the ink containing acrylic resin particles B did not improve, but that the ejection stability of the ink containing acrylic resin particles C did improve. In other words, in the case of acrylic resin particles, in order to ensure the ejection stability of the ink, it is necessary to keep the temperature of the ink inside the recording head (T H (°C) GIt is necessary to use acrylic resin particles having a viscosity of 1000 MPa (°C).

[0016] Next, the glass transition temperature (T G The recording medium to which the ink containing the above three types of acrylic resin particles having different fixing temperatures (T F (°C)), the ink was thoroughly dried, and the scratch resistance of the image was confirmed. As a result, it was found that the scratch resistance of the image recorded using the ink containing acrylic resin particles C did not reach a sufficient level. When the film formation state of the recorded image was observed using an electron microscope, it was found that the acrylic resin particles C were not sufficiently fused together.

[0017] Furthermore, the fixing temperature T F When the recording medium was heated to a temperature of 1000°C, vinyl chloride sheet, a typical example of a non-absorbent recording medium, shrunk due to the heat. This caused unevenness in the recording material, and the image on the raised areas was rubbed off by external force, resulting in a decrease in scratch resistance. In other words, it was found that when using a recording medium such as vinyl chloride sheet, and at a fixing temperature (T F (° C.)), it has been found that ink containing acrylic resin particles cannot achieve both ink ejection stability and scratch resistance of the recorded image.

[0018] Next, we focused on the type of resin particles, aiming to achieve both ink ejection stability from a temperature-controlled recording head and scratch resistance of the recorded image. Specifically, we focused on polyester resin particles, which are expected to have a narrower softening temperature range than acrylic resin particles. Typical polyester resins are produced by alternating the reaction of a polycarboxylic acid component (monomer A) with a polyhydric alcohol component (monomer B). Therefore, compared to acrylic resins produced by copolymerization, their molecular weight distribution is narrower, and the monomer units in the resin are often in an "ABABAB" state. In other words, polyester resins are thought to have a narrower softening temperature range than acrylic resins because of their sharp molecular weight distribution and highly uniform composition. In the present invention, polyester resin particles with a weight-average molecular weight (Mw) to number-average molecular weight (Mn) ratio of 6.0 or less (narrow) are used. If the Mw / Mn ratio exceeds 6.0, the molecular weight distribution will be too broad, and the softening temperature of the resin particles will not fall within the desired range, making it impossible to achieve both ink ejection stability and image abrasion resistance.

[0019] The inventors have investigated the temperature of the ink in the print head (T H (°C)) is slightly higher (about 20°C higher) than G (℃)) was prepared and verified. Specifically, using this ink, the fixing temperature (T F The ink jetting stability and scratch resistance of the printed image were evaluated at a temperature of approximately 90°C. As a result, it was found that, unlike when ink containing acrylic resin particles was used, both jetting stability and scratch resistance were achieved.

[0020] If the glass transition temperature is the same, the softening temperature range of acrylic resin particles is wider than that of polyester resin particles. In other words, compared to polyester resin particles, acrylic resin particles have a lower softening start temperature and a higher softening end temperature. Therefore, in order to suppress the fusion of acrylic resin particles in the ink in a temperature-controlled recording head, the softening start temperature must be adjusted to the temperature of the ink in the recording head (TH It is necessary to use acrylic resin particles with a glass transition temperature (T G (℃) is the temperature of the ink in the print head (T H (℃), the softening end temperature is also higher, and the T F On the other hand, the softening temperature of polyester resin particles is also higher than the glass transition temperature (T G (°C)) is higher than that of the same acrylic resin particles. Furthermore, the softening end temperature of polyester resin particles is higher than the glass transition temperature (T G (°C)) is lower than that of the same acrylic resin particles. For these reasons, when ink containing polyester resin particles is used, the glass transition temperature (T G It is believed that the ejection stability and the scratch resistance of the image were improved compared to when an ink containing acrylic resin particles with a similar temperature (°C) was used.

[0021] However, from the viewpoint of achieving both high levels of ejection stability and abrasion resistance, even when polyester resin particles are used, the fixing temperature (T F (℃) and the temperature of the ink in the print head (T H Specifically, it is necessary to make the difference between the temperature of the temperature-controlled print head (the temperature of the ink ejected from the print head (T H (°C)) and the heating temperature T F (°C) must satisfy the relationship of the following formula (2). T F (℃)≧T H (℃)+10℃ (2)

[0022] Fixing temperature (T F (℃) and the temperature of the ink in the print head (T H If the difference in the fixing temperature (T F (℃)) at which sufficient fusion occurs. G When polyester resin particles having a fixing temperature (TF (℃) and the temperature of the ink in the print head (T H If the difference in the temperature of the ink in the print head (T H (℃) at which fusion does not occur. G (℃)), the fixing temperature (T F (°C), sufficient fusion is not achieved, and the scratch resistance of the image decreases.

[0023] Furthermore, from the viewpoint of improving the scratch resistance of the image, the heating temperature T F (℃) and the glass transition temperature T G (°C) must satisfy the relationship of the following formula (3). T F (℃)≧T G (℃)-10℃ (3)

[0024] In order to investigate the influence of an aqueous medium (water and a water-soluble organic solvent) on the fusibility of resin particles, the inventors measured the SP values ​​(unit: (cal / cm)) of resin particles and aqueous medium calculated by the Fedors method. 3 ) 1 / 2 ) and measured the change in glass transition temperature (°C). The glass transition temperature (°C) of the resin particles was measured using a differential scanning calorimeter (DSC). Using the glass transition temperature (°C) of the powdered resin (glass transition temperature of the resin itself) as the standard, the glass transition temperature (°C) of the resin when the powdered resin and an aqueous medium were mixed in a 1:1 mass ratio was measured and compared. As the resins, resin particles formed from acrylic resin (acrylic resin particles) and resin particles formed from polyester resin (polyester resin particles) were used.

[0025] As a result of the investigation, it was found that water lowers the glass transition temperature of the resin by 10°C or more, and that the water-soluble organic solvents commonly used in water-based inkjet inks tend to lower the glass transition temperature of the resin more than water. In order to improve the scratch resistance of the image, it is important to sufficiently fuse the polyester resin particles. As mentioned above, the aqueous medium used in water-based inkjet inks is the T G (°C) by 10°C or more. F (℃) and the glass transition temperature T G It is important for the resin particles to be sufficiently fused together that the temperature (° C.) satisfies the relationship of the above formula (3).

[0026] Furthermore, in order to ensure that the ink dries sufficiently, the amount of heat ((W·h) / g) applied to the ink applied to the recording medium must be at least 2 (W·h) / g. If the amount of heat applied to the ink is less than 2 (W·h) / g, the ink applied to the recording medium will not dry sufficiently, resulting in insufficient scratch resistance for the recorded image.

[0027] <Inkjet recording method and inkjet recording apparatus> The inkjet recording method of the present invention is a method of recording an image by ejecting a water-based ink from an inkjet recording head by the action of thermal energy and applying the ink to a recording medium. H (°C) onto a recording medium by ejecting the water-based ink from a recording head; and heating the recording medium onto which the water-based ink has been applied to a temperature T F (°C). The aqueous ink contains a pigment and polyester resin particles, and the ratio of the weight average molecular weight to the number average molecular weight of the polyester resin particles is 6.0 or less. The glass transition temperature T G (℃), temperature T H (℃), and temperature T F(°C) satisfies the relationships of the following formulas (1) to (3). The inkjet recording apparatus of the present invention is an apparatus used in an inkjet recording method in which an aqueous ink is ejected from an inkjet recording head by the action of thermal energy and applied to a recording medium to record an image, and is an apparatus suitable for use in the above-mentioned recording method. It is not necessary to provide a step of applying a coating liquid that does not contain a coloring material in addition to the ink, or a step of curing the image by irradiation with active energy rays or the like. The inkjet recording method and inkjet recording apparatus of the present invention (hereinafter also simply referred to as "recording method and recording apparatus") will be described in detail below. T G (℃)>T H (℃) (1) T F (℃)≧T H (℃)+10℃ (2) T F (℃)≧T G (℃)-10℃ (3)

[0028] FIG. 1 is a perspective view that schematically shows an embodiment of an inkjet recording apparatus of the present invention. FIG. 2 is a side view that schematically shows an embodiment of an inkjet recording apparatus of the present invention. As shown in FIGS. 1 and 2, the recording apparatus of this embodiment includes an inkjet recording head 22 that ejects ink. The recording head 22 is a recording head that ejects ink by the action of thermal energy. A recording head that ejects ink by the action of thermal energy is a thermal recording head that applies thermal energy to ink by applying electric pulses to electrothermal conversion elements, thereby ejecting ink from ejection openings. This thermal recording head heats the water-based ink that is ejected from the recording head and applied to the recording medium at a temperature T H (℃). H (°C) is preferably 40°C or higher. H (°C) is preferably 70°C or less.

[0029] [Heating process] In the recording method of the present invention, the recording medium to which the ink has been applied is heated to a temperature T F The method includes a step of heating (heat treatment) the recording medium to (° C.) by heating the recording medium to which the ink has been applied, thereby accelerating the formation of a film of polyester resin particles and enabling the recording of an image with excellent scratch resistance.

[0030] The means for heating the recording medium is not particularly limited, and examples thereof include known heating means such as a heater, an air blowing means using an air blower such as a dryer, and a heating means combining these. That is, the inkjet recording apparatus heats the recording medium on which ink has been applied to a temperature T F (°C). Examples of the heating means include the above-mentioned warming means, air blowing means, and a combination of these. Examples of the heat treatment method include a method of applying heat from the side opposite (backside) to the recording surface (ink-applied surface) of the recording medium using a heater, a method of applying warm or hot air to the recording surface of the recording medium, and a method of heating from the recording surface or backside using an infrared heater. A combination of these methods may also be used. In order to improve the scratch resistance of the image, it is preferable to heat the recording medium to a heating temperature (image temperature) T F (°C) is preferably 90°C or less. In addition, the heating temperature (image temperature) T F (°C) is preferably 50°C or higher. In order to further improve the scratch resistance of the image, the heating temperature T H (°C) is set to 40°C or higher, and the heating temperature (image temperature) T F (°C) is preferably 90°C or less. The heating temperature of the recording medium to which the ink has been applied may be read by a sensor incorporated in a position corresponding to the heating means of the recording device, or may be determined from the relationship between the amount of heat and the temperature of the recording medium, which is determined in advance depending on the type of ink and recording medium.

[0031] The amount of heat ((W·h) / g) applied to the ink applied to the recording medium must be 2 (W·h) / g or more. When a heat amount of 2 (W·h) / g or more is applied to the ink, the ink applied to the recording medium dries sufficiently, improving the scratch resistance of the recorded image. The amount of heat ((W·h) / g) applied to the ink applied to the recording medium is preferably 10 (W·h) / g or less. The amount of heat applied to the ink can be measured as follows. First, the power A (W) applied to the heating means that heats the recording medium is measured. Then, the recording area B (m ) per unit time of the recording device is measured. 2 / h), and the ink consumption per unit area used for this printing, C (g / m 2 From these values, the amount of heat ((W·h) / g) applied to the ink applied to the recording medium is calculated based on the following formula (4). Amount of heat applied to ink applied to recording medium ((W·h) / g) =A(W) / B(m 2 / h) / C(g / m 2 ) (4)

[0032] In the recording device shown in FIGS. 1 and 2, a heater 25 supported by a frame (not shown) is disposed downstream in the sub-scanning direction A from the position where the recording head 22 reciprocates in the main scanning direction B. The recording medium 1 to which ink has been applied can be heated by the heater 25. Specific examples of the heater 25 include a sheath heater and a halogen heater. The heater 25 is covered by a heater cover 26. The heater cover 26 is a member for efficiently irradiating the heat generated by the heater 25 onto the recording medium 1. The heater cover 26 also serves as a member for protecting the heater 25. The recording medium 1 to which ink ejected from the recording head 22 has been applied is wound up by a take-up spool 27 to form a roll-shaped wound medium 24.

[0033] (Recording medium) In the recording method and recording device of the present invention, a non-absorbent recording medium (a low to non-absorbent recording medium) is used as the recording medium. The low to non-absorbent recording medium is a recording medium that is absorbed within 30 msec from the start of contact in the Bristow method described in JAPAN TAPPI Paper Pulp Test Method No. 51, "Liquid Absorbency Test Method for Paper and Paperboard." 1 / 2 Water absorption up to 10mL / m 2 In the present invention, a recording medium that satisfies the above-mentioned condition of water absorption amount is defined as a "low to non-absorbent recording medium." Inkjet recording media (glossy paper, matte paper, etc.) having a coating layer (ink receiving layer) formed of inorganic particles, and plain paper having no coating layer, have a water absorption amount of 10 mL / m or more. 2 It is an "absorbent recording medium" that exceeds this.

[0034] Examples of low to non-absorbent recording media that can be used include plastic films, recording media in which a plastic film is bonded to the recording surface of a substrate, and recording media in which an organic resin coating layer is provided on the recording surface of a substrate containing cellulose pulp. Of these, plastic films are preferred, and recording media in which an organic resin coating layer is provided as an organic resin layer on the recording surface of a substrate containing cellulose pulp are also preferred.

[0035] When the ink used in the recording method and recording apparatus of the present invention is applied to a non-absorbent recording medium, components such as water and water-soluble organic solvents volatilize, concentrating the polyester resin particles. This promotes fusion between the concentrated polyester resin particles, improving the abrasion resistance of the recorded image. In contrast, when the ink is applied to a recording medium with high liquid component absorption, fusion between the polyester resin particles is less likely to be promoted, resulting in insufficient improvement in the abrasion resistance of the image. Note that the recording medium in this specification does not refer to a transfer medium, but rather to a recording medium on which an image is recorded as a recorded product.

[0036] (water-based ink) The ink contains a pigment and polyester resin particles. Each component of the ink will be described in detail below.

[0037] [Colorant] The ink contains a pigment as a coloring material. The content (mass %) of the pigment in the ink is preferably 0.1% to 15.0% by mass, and more preferably 1.0% to 10.0% by mass, based on the total mass of the ink.

[0038] Specific examples of pigments include inorganic pigments such as carbon black and titanium oxide, and organic pigments such as azo, phthalocyanine, quinacridone, isoindolinone, imidazolone, diketopyrrolopyrrole, dioxazine, and perinone. Of the pigments, carbon black and organic pigments are preferably used.

[0039] Examples of pigment dispersion methods include resin-dispersed pigments, which use a resin as a dispersant, and self-dispersed pigments, in which hydrophilic groups are bonded to the pigment particle surface. Other examples include resin-bonded pigments, in which organic groups containing a resin are chemically bonded to the pigment particle surface, and microencapsulated pigments, in which the pigment particle surface is coated with a resin or the like.

[0040] As the resin dispersant for dispersing the pigment in the aqueous medium, it is preferable to use one that can disperse the pigment in the aqueous medium by the action of an anionic group, and it is preferable to use a water-soluble resin as the resin dispersant.

[0041] Examples of the resin dispersant include acrylic resins, urethane resins, etc. Among these, acrylic resins are preferred, and acrylic resins composed of units derived from (meth)acrylic acid or (meth)acrylic acid esters are more preferred.

[0042] The acrylic resin is preferably one having a hydrophilic unit and a hydrophobic unit as constituent units. Among these, a resin having a hydrophilic unit derived from (meth)acrylic acid and a hydrophobic unit derived from at least one of a monomer having an aromatic ring and a (meth)acrylic acid ester is preferred. A resin having a hydrophilic unit derived from (meth)acrylic acid and a hydrophobic unit derived from at least one of a styrene and an α-methylstyrene monomer is particularly preferred. These resins are likely to interact with pigments, and can therefore be suitably used as resin dispersants for dispersing pigments.

[0043] The hydrophilic unit is a unit having a hydrophilic group such as an anionic group. The hydrophilic unit can be formed, for example, by polymerizing a hydrophilic monomer having a hydrophilic group. Specific examples of hydrophilic monomers having a hydrophilic group include acidic monomers having a carboxylic acid group, such as (meth)acrylic acid, itaconic acid, maleic acid, and fumaric acid, and anionic monomers such as anhydrides and salts of these acidic monomers. Examples of cations constituting the salts of acidic monomers include ions of lithium, sodium, potassium, ammonium, and organic ammonium. The hydrophobic unit is a unit not having a hydrophilic group such as an anionic group. The hydrophobic unit can be formed, for example, by polymerizing a hydrophobic monomer not having a hydrophilic group such as an anionic group. Specific examples of hydrophobic monomers include monomers having an aromatic ring, such as styrene, α-methylstyrene, and benzyl (meth)acrylate; and (meth)acrylic acid ester monomers, such as methyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate.

[0044] Self-dispersing pigments can be used in which anionic groups such as carboxylic acid groups, sulfonic acid groups, and phosphonic acid groups are bonded to the surface of pigment particles directly or via another atomic group (-R-). The anionic group can be either an acid type or a salt type. If the anionic group is a salt type, it can be either partially dissociated or completely dissociated. When the anionic group is a salt type, examples of the cation that serves as the counter ion include alkali metal cations, ammonium, and organic ammonium. Specific examples of the other atomic group (-R-) include linear or branched alkylene groups having 1 to 12 carbon atoms; arylene groups such as phenylene and naphthylene; carbonyl groups; imino groups; amide groups; sulfonyl groups; ester groups; and ether groups. Furthermore, combinations of these groups may also be used.

[0045] [Polyester Resin Particles] The ink contains polyester resin particles. The content (mass%) of the polyester resin particles 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 (mass%) of the polyester resin particles in the ink is preferably 1.5 times or more, more preferably 1.7 times or more, and preferably 5.0 times or less, relative to the content (mass%) of the pigment. If the mass ratio is less than 1.5 times, the amount of polyester resin particles is too small compared to the pigment, making it difficult to improve adhesion to the recording medium. In addition, the polyester resin particles may not sufficiently cover the pigment, resulting in reduced scratch resistance of the image. The polyester resin particles are present in the ink in a dispersed state, i.e., in the form of a resin emulsion. It is preferable that the polyester resin particles do not encapsulate a colorant.

[0046] In this specification, "resin particles" refers to a resin that does not dissolve in the aqueous medium that constitutes the ink, and specifically refers to a resin that can exist in the aqueous medium in the form of particles whose particle diameter can be measured by dynamic light scattering. On the other hand, "water-soluble resin" refers to a resin that can dissolve in the aqueous medium that constitutes the ink, and specifically refers to a resin that can exist in the aqueous medium in the form of particles whose particle diameter cannot be measured by dynamic light scattering. "Resin particles" can also be referred to as "water-dispersible resin (water-insoluble resin)."

[0047] Whether a resin is a "resin particle" can be determined according to the following method. First, a liquid containing the resin to be determined (resin content: 10% by mass) is prepared. Next, the prepared liquid is diluted 10 times (by volume) with ion-exchange water to prepare a sample. Then, when the particle size of the resin in the sample is measured by dynamic light scattering, if particles having the particle size are measured, the particles are determined to be "resin particles" (water-dispersible resin). On the other hand, if particles having the particle size are not measured, the resin is determined not to be a "resin particle" (a "water-soluble resin"). The measurement conditions can be, for example, Set Zero: 30 seconds, number of measurements: 3, measurement time: 180 seconds, shape: spherical, refractive index: 1.59. A particle size distribution measurement device such as a particle size analyzer using dynamic light scattering (e.g., the "Nanotrac UPA-EX150" manufactured by Nikkiso) can be used. Of course, the particle size distribution measurement device and measurement conditions are not limited to those described above.

[0048] For other resins such as polyester resin particles and resin dispersants, whether they are resin particles or not is determined according to the above method. However, for the purpose of simple determination, it is preferable to use a liquid (resin content: 10% by mass) containing a resin neutralized with an alkali (sodium hydroxide, potassium hydroxide, etc.) equivalent to the acid value for other resins.

[0049] [Constituent materials of polyester resin] Polyester resins are typically composed of units derived from polyhydric alcohols and units derived from polycarboxylic acids. Unreacted hydroxy groups or carboxylic acid groups are present at the terminals of the polyester resin. The total proportion (mass%) of units derived from polyhydric alcohols and units derived from polycarboxylic acids in the polyester resin is preferably 90.0 mass% or more. It is more preferably 95.0 mass% or more, and may even be 100.0 mass%.

[0050] (1) Polyhydric alcohol Examples of polyhydric alcohols include dihydric to tetrahydric polyhydric alcohols. Examples of polyhydric alcohols include polyhydric alcohols having an aliphatic group, polyhydric alcohols having an aromatic group, and sugar alcohols. Examples of polyhydric alcohols include dihydric alcohols such as ethylene glycol (1,2-ethanediol), neopentyl glycol (2,2-dimethyl-1,3-propanediol), 1,3-propanediol, 1,4-butanediol, benzenediol, and 2,2-bis(4-hydroxyphenyl)propane (bisphenol A); trihydric alcohols such as glycerin, trimethylolethane, and trimethylolpropane; and tetrahydric alcohols such as pentaerythritol. Oligomers (low-molecular-weight polymers having a molecular weight of 1,000 or less) can also be used as polyhydric alcohols. Dihydric alcohols are preferred as polyhydric alcohols. The proportion (mass %) of units derived from polyhydric alcohols in the polyester resin is preferably 40.0% by mass or more and 60.0% by mass or less.

[0051] (2) Polycarboxylic acids Examples of polycarboxylic acids include dicarboxylic to tetracarboxylic acids. Examples of polycarboxylic acids include polycarboxylic acids having an aliphatic group, polycarboxylic acids having an aromatic group, and nitrogen-containing polycarboxylic acids. Examples of polycarboxylic acids include dicarboxylic acids such as glutaric acid, adipic acid, terephthalic acid, isophthalic acid, and 2,6-naphthalenedicarboxylic acid; tricarboxylic acids such as trimellitic acid; and tetracarboxylic acids such as ethylenediaminetetraacetic acid. Oligomers (low-molecular-weight polymers having a molecular weight of 1,000 or less) can also be used as polycarboxylic acids. Dicarboxylic acids are preferably used as polycarboxylic acids. The proportion (mass%) of units derived from polycarboxylic acids in the polyester resin is preferably 40.0 mass% or more and 60.0 mass% or less.

[0052] [Physical properties of polyester resin particles] The ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the polyester resin particles (the polyester resin constituting the polyester resin particles) is 6.0 or less, preferably 5.0 or less, and more preferably 4.0 or less. Furthermore, the ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is preferably 1.5 or more, and more preferably 2.0 or more. If the Mw / Mn ratio exceeds 6.0, the molecular weight distribution is too broad, and the softening temperature of the resin particles does not fall within the desired range, failing to achieve both ink ejection stability and image abrasion resistance.

[0053] The weight-average molecular weight of the polyester resin particles (the polyester resin constituting the polyester resin particles) is preferably 30,000 or more and 70,000 or less. If the weight-average molecular weight is less than 30,000, the molecular chains of the polyester resin are too short, making entanglement difficult, which may reduce the effect of improving the scratch resistance of the image. On the other hand, if the weight-average molecular weight is more than 70,000, the molecular chains of the polyester resin are too long, making molecular motion difficult and entanglement difficult, which may reduce the effect of improving the scratch resistance of the image. The number-average molecular weight of the polyester resin particles (the polyester resin constituting the polyester resin particles) is preferably 5,000 or more and 30,000 or less. The weight-average molecular weight (Mw) and number-average molecular weight (Mn) in this specification are values ​​calculated in terms of polystyrene as measured by gel permeation chromatography.

[0054] The glass transition temperature (Tg) is an index showing the melting property of resin particles, and means the temperature at which the resin particles start to change from a crystalline state to an amorphous state. G The glass transition temperature (°C) is preferably 50°C or higher, more preferably 60°C or higher, and is preferably 90°C or lower, more preferably 80°C or lower. The glass transition temperature of the polyester resin particles can be measured for the resin particles themselves using a thermal analyzer such as a differential scanning calorimeter (DSC).

[0055] Glass transition temperature T of polyester resin particles G (°C) and the heating temperature T of the ink ejected from the recording head H The glass transition temperature T (°C) of the polyester resin particles must satisfy the relationship of the following formula (1): G (℃) is the temperature T H It is important that the temperature is higher than (℃). G (℃) is T H If the temperature is below 100° C., some of the polyester resin particles tend to fuse together near the ejection openings of the recording head, resulting in insufficient ejection stability of the ink. T G (℃)>TH (℃) (1)

[0056] The inventors observed the scraped portions of the image after evaluating the abrasion resistance using an electron microscope. As a result, it was found that in addition to fused polyester resin particles, many pigment particles were scattered in the scraped portions. Next, the film properties of the image recorded with the ink containing no pigment and the image recorded with the ink containing no polyester resin particles were analyzed and compared. As a result, it was found that the coefficient of friction of the surface of the image recorded with the ink containing no polyester resin was higher.

[0057] Considering only abrasion resistance, it is considered ideal for the image surface to be composed of a resin film with a low coefficient of friction. Therefore, in order to preferentially migrate pigments to the interior of ink dots applied to non-absorbent recording media, further investigation was conducted, focusing on the amount of anionic groups (μmol / g) on ​​the resin particles and pigments. It is believed that in ink dots applied to non-absorbent recording media, water and water-soluble organic solvents remain on the non-absorbent recording medium for a certain period of time. During this time, liquid components evaporate from the ink dot surface, and the relative dielectric constant of the liquid component on the ink dot surface becomes lower than the relative dielectric constant of the liquid component inside the ink dot. It is believed that at this time, pigment particles with a relatively large amount of anionic groups preferentially migrate to the interior of the ink dot.

[0058] Further investigations revealed that the scratch resistance of images is improved when the amount of anionic groups in the pigment is somewhat greater than the amount of anionic groups in the polyester resin particles. Specifically, the pigment is dispersed in the ink by the action of the anionic groups, and the amount of anionic groups in the pigment (μmol / g) is preferably 6.0 times or more the amount of anionic groups in the polyester resin particles (μmol / g). The amount of anionic groups in the pigment (μmol / g) is preferably 20.0 times or less, and more preferably 10.0 times or less, the ratio of the amount of anionic groups in the polyester resin particles (μmol / g).

[0059] The anionic groups of a pigment refer to the anionic groups bonded directly or via other atomic groups to the pigment particle surface in the case of a self-dispersing pigment, or to the anionic groups of the dispersant in the case of a pigment dispersed with a dispersant such as a resin dispersant. The amount of anionic groups of a pigment (μmol / g) refers to the amount of anionic groups per unit mass of the pigment itself in the case of a self-dispersing pigment, or the amount of anionic groups per unit mass of the pigment and dispersant combined in the case of a pigment dispersed with a dispersant. The amounts of anionic groups of both the resin particles and the pigment can be measured by colloid titration. In the examples described below, the amounts of anionic groups of the resin particles and the pigment were measured by colloid titration using potential difference using an automatic potentiometric titrator (product name "AT-510" manufactured by Kyoto Electronics Manufacturing Co., Ltd.) equipped with a streaming potential titration unit (PCD-500). Methyl glycol chitosan was used as the titration reagent.

[0060] [Analysis of polyester resin particles] The composition of the polyester resin constituting the resin particles can be analyzed, for example, by the following method. First, a sample is prepared by dissolving the resin particles in an organic solvent, such as tetrahydrofuran, that can dissolve the resin particles. The resin particles dissolved in the organic solvent can be in the form of an aqueous dispersion or in a dry state. The prepared sample can be analyzed using analytical methods such as nuclear magnetic resonance (NMR) spectroscopy and matrix-assisted laser desorption / ionization mass spectrometry (MALDI-MS) to determine the types and proportions of the units (monomers) constituting the resin. Furthermore, the resin particles can be analyzed by pyrolysis-gas chromatography to detect the units (monomers) constituting the resin. If insoluble matter that does not dissolve in the organic solvent is generated during sample preparation, the resulting insoluble matter can also be analyzed by pyrolysis-gas chromatography to detect the units (monomers) constituting the resin.

[0061] [Wax particles] The ink preferably further contains wax particles. Images recorded using ink containing wax particles exhibit better abrasion resistance because the dynamic friction coefficient of the surface is reduced and stress applied by abrasion can be released. The melting point of the wax forming the wax particles is 1 / 2 the heating temperature T F (℃). F If the temperature is below 100°C, the wax may melt when heated and become less likely to be present near the surface of the image, which may weaken the effect of improving the scratch resistance of the image. The melting point of the wax can be measured in accordance with the test method described in 5.3.1 (Melt Point Test Method) of JIS K2235:1991 (Petroleum Wax).

[0062] The wax forming the wax particles can be a synthetic wax. The synthetic wax can be at least one wax selected from the group consisting of Fischer-Tropsch wax, polyolefin wax, and α-olefin-maleic anhydride copolymer. These synthetic waxes tend to have a narrower molecular weight distribution than natural waxes such as paraffin wax and carnauba wax. For this reason, synthetic waxes tend to have a lower molecular weight distribution than natural waxes such as paraffin wax and carnauba wax. F This method can be suitably used because it is easy to precisely control the melting point of the wax so that the wax particles do not melt relative to the temperature (°C).

[0063] The content (mass %) of wax particles in the ink is preferably 0.1% by mass or more and 5.0% by mass or less, based on the total mass of the ink. Furthermore, the content (mass %) of polyester resin particles in the ink is preferably 2.0 times or more and 30.0 times or less, in mass ratio, relative to the content (mass %) of wax particles. If the mass ratio is less than 2.0 times, the wax particles tend to inhibit film formation of the polyester particles, slightly weakening the strength of the ink film and potentially weakening the effect of improving the scratch resistance of the image. On the other hand, if the mass ratio is more than 30.0 times, the wax particles will be too few relative to the polyester resin particles, resulting in fewer wax particles present on the surface of the image and potentially weakening the effect of improving the scratch resistance of the image.

[0064] [Aqueous medium] The ink is an aqueous ink containing at least water as the aqueous medium. The ink can contain water or an aqueous medium that is a mixed solvent of water and a water-soluble organic solvent. Deionized water or ion-exchanged water is preferably used as the water. The water content (mass %) in the ink is preferably 50.0% to 95.0% by mass, based on the total mass of the ink. The water-soluble organic solvent content (mass %) in the ink is preferably 3.0% to 50.0% by mass, more preferably 5.0% to 30.0% by mass, based on the total mass of the ink. As the water-soluble organic solvent, any solvent usable in inkjet inks, such as alcohols, (poly)alkylene glycols, glycol ethers, nitrogen-containing compounds, and sulfur-containing compounds, can be used. While the term "water-soluble organic solvent" generally refers to a liquid, in the present invention, for convenience, the term "water-soluble organic solvent" also includes those that are solid at 25°C.

[0065] The water-soluble organic solvent affects the drying property of the ink and the glass transition temperature T GThe present inventors investigated the optimal water-soluble organic solvent to achieve both ink ejection stability and image abrasion resistance at a higher level. As a result, they found that if the boiling point of the water-soluble organic solvent is too low, the ink ejection stability tends to decrease. For example, if the boiling point of the water-soluble organic solvent is 120°C or lower, ejection failure occurs in some ejection ports when an image is recorded by ejecting ink from a temperature-controlled print head for a long period of time. It is thought that if the boiling point of the water-soluble organic solvent is too low, it becomes difficult to ensure the moisture retention of the ink near the ejection ports of the temperature-controlled print head, and the resin in the ink is likely to solidify.

[0066] On the other hand, it was found that if the boiling point of the water-soluble organic solvent is too high, the scratch resistance of the recorded image tends to decrease. For example, if the boiling point of the water-soluble organic solvent is 310°C or higher, the scratch resistance of the image may decrease. Even when heated for a long time at the upper limit temperature (approximately 90°C) at which the thermal shrinkage of the vinyl chloride sheet stops, some of the high-boiling water-soluble organic solvent remains on the image, which is thought to have reduced the scratch resistance of the image.

[0067] Furthermore, when a water-soluble organic solvent whose SP value is close to the SP value of the polyester resin particles is used, the glass transition temperature T G Specifically, when the difference between the SP value of the water-soluble organic solvent and the SP value of the polyester resin particles (hereinafter also referred to as "ΔSP value") is 4.0 or less, the glass transition temperature T G (℃) drops significantly.

[0068] [First water-soluble organic solvent] The ink preferably contains a first water-soluble organic solvent whose boiling point is 120°C or higher and 220°C or lower. Of all the water-soluble organic solvents in the ink, the content (mass %) of the first water-soluble organic solvent is preferably the highest. When the ink applied to a non-absorbent recording medium is heated, the liquid components in the ink evaporate, and the polyester resin and water-soluble organic solvent are concentrated in the ink dots. At this time, the glass transition temperature T of the polyester resin particles that have come into contact with the water-soluble organic solvents having similar SP values ​​is G (°C) is significantly reduced, promoting fusion between polyester resin particles. When the boiling point of the first water-soluble organic solvent is 220°C or lower, the first water-soluble organic solvent is easily volatilized from the resin film formed by fusion, which is thought to further improve the scratch resistance of the image. On the other hand, when the boiling point of the water-soluble organic solvent is less than 120°C, the ink's moisture retention is likely to decrease, and ejection stability may be slightly reduced.

[0069] Examples of the first water-soluble organic solvent having a boiling point of 120°C or higher and 220°C or lower include 1,3-propanediol (214°C), 2-methyl-1,3-propanediol (214°C), diethylene glycol monoethyl ether (202°C), ethylene glycol (198°C), diethylene glycol monomethyl ether (194°C), 1,2-butanediol (193°C), propylene glycol (188°C), 3-methoxy-3-methylbutanol (174°C), diethylene glycol dimethyl ether (160°C), 2-ethoxyethanol (136°C), 2-methoxyethanol (125°C), and propylene glycol monomethyl ether (120°C).

[0070] From the viewpoint of further improving the scratch resistance of the recorded image, the difference (ΔSP value) between the SP value of the first water-soluble organic solvent and the SP value of the polyester resin particles is preferably 4.0 or less, more preferably 3.5 or less. The ΔSP value is preferably 0.1 or more, more preferably 0.5 or more. Furthermore, the content (mass %) of the first water-soluble organic solvent in the ink is preferably 1.0 to 4.0 times the content (mass %) of the polyester resin particles. When the mass ratio is less than 1.0, the glass transition temperature T G On the other hand, if the mass ratio is more than 4.0 times, the glass transition temperature T G If the temperature (° C.) is decreased, some of the polyester resin particles may be more likely to melt, which may reduce the effect of improving the ejection stability of the ink.

[0071] When multiple water-soluble organic solvents corresponding to the first water-soluble organic solvent are used, the "SP value" of the first water-soluble organic solvent can be understood in terms of the "average SP value." This "average SP value" is the value calculated and integrated for each water-soluble organic solvent by multiplying the SP value of a given water-soluble organic solvent by the proportion (mass %) of that water-soluble organic solvent in the total amount of water-soluble organic solvents in the ink. For example, the average SP value of the water-soluble organic solvents (total 15.0 parts by mass) with the composition shown below is "(12.8 x 10.0 / 15.0) + (13.5 x 5.0 / 15.0) = 12.8." The numbers in parentheses are the SP values ​​(units omitted) of each water-soluble organic solvent. 1,2-butanediol (12.8): 10.0 parts by mass 1,2-propanediol (13.5): 5.0 parts by mass

[0072] [Second water-soluble organic solvent] A detailed analysis of an image recorded with ink containing only the first water-soluble organic solvent as the water-soluble organic solvent revealed that there were areas where the polyester resin particles were not sufficiently fused. In the ink applied to a non-absorbent recording medium, the first water-soluble organic solvent volatilized before it was fully compatible with the polyester resin particles, causing the polyester resin particles to melt at a temperature lower than the glass transition temperature T G This is thought to be because it was difficult to sufficiently lower the temperature (°C). Therefore, the present inventors discovered that the abrasion resistance of the resulting image can be further improved by using a water-soluble organic solvent having a boiling point higher than that of the first water-soluble organic solvent. That is, the ink preferably contains a second water-soluble organic solvent whose boiling point is greater than 220°C and less than or equal to 310°C. Furthermore, the difference (ΔSP value) between the SP value of the second water-soluble organic solvent and the SP value of the polyester resin particles is preferably 4.0 or less, more preferably 3.5 or less. The ΔSP value is preferably 0.1 or more, more preferably 0.5 or more. When multiple water-soluble organic solvents corresponding to the second water-soluble organic solvent are used, the "SP value" of the second water-soluble organic solvent can be appropriately understood in terms of the "average SP value," as in the case of the first water-soluble organic solvent.

[0073] Examples of the second water-soluble organic solvent having a boiling point greater than 220°C and equal to or less than 310°C include 2-hydroxyethyl-2-pyrrolidone (309°C), trimethylolpropane (296°C), glycerin (290°C), triethylene glycol (288°C), sulfolane (287°C), diethylene glycol (246°C), 2-pyrrolidone (245°C), dipropylene glycol (232°C), diethylene glycol mono-2-ethylhexyl ether (229°C), and 1,2-hexanediol (223°C).

[0074] [SP value of water-soluble organic solvents] The SP value (δ) in the present invention is a value calculated by the Fedors method based on the following formula (A) [unit: (cal / cm 3 ) 1 / 2 ]. ΔE of the resin vapand V can be determined by referring to the description in, for example, Coating Times No. 193 (1992).

[0075] TIFF2023039913000001.tif18170 (In the above formula (A), ΔE vap represents the molar heat of vaporization of the compound (cal / mol), and V represents the molar volume of the compound at 25°C (cc / mol).

[0076] The SP value of a general-purpose water-soluble organic solvent in water-based inkjet inks, measured by the Fedors method, is expressed in units of (cal / cm 3 ) 1 / 2The following are abbreviated as follows: Glycerin (16.4), 1-hydroxy-2-pyrrolidone (16.4), 1,3-propanediol (16.1), trimethylolpropane (15.9), 1,4-butanediol (15.0), diethylene glycol (15.0), ethylene glycol (14.8), 1,3-butanediol (14.8), 2-methyl-1,3-propanediol (14.8), 1,2,6-hexanetriol (14.5), urea (14.4), ethyleneurea (14.2), 1,5-pentanediol (14.2), 1-(hydroxymethyl) ...5-pentanediol (14.2), 1-(hydroxymethyl)-2-pyrrolidone (16.4), 1,5-pentanediol (14.2), 1-(hydroxymethyl)-2-pyrrolidone (16.4), 1,5-pentanediol (14.2), 1-(hydroxymethyl)-2-pyrrolidone (16.4), 1,5-pentanediol (14.2), 1-(hydroxymethyl)-2-pyrrolidone (16.4), 1-(2-hydroxyethyl)-2-pyrrolidone (13.5), 3-methyl-1,5-pentanediol (13.4), 2-ethylpropane-1,3-diol (13.2), 2-methylpentane-2,4-diol (13.1), tetramethylene sulfoxide (12.9), 1-(3-hydroxypropyl)-2-pyrrolidone ( 12.9), tetraethylene glycol (12.8), polyethylene glycol with a number average molecular weight of 200 (12.8), 1,2-butanediol (12.8), 2-pyrrolidone (12.6), 1-(4-hydroxybutyl)-2-pyrrolidone (12.5), 1,2-pentanediol (12.2), 3-methylsulfolane (12.1), ethylene glycol monomethyl ether (12.0), n-propanol (11.8), 1,2-hexanediol (11.8), isopropanol (11.6), N-methyl-2-pyrrolidone (11.5), ethylene glycol monomethyl ether (12.0), Ethylene glycol monoethyl ether (11.5), 1,3-dimethyl-2-imidazolidinone (11.4), n-butanol (11.3), diethylene glycol monomethyl ether (11.2), 2-butanol (11.1), isobutanol (11.1), diethylene glycol monoethyl ether (10.9), triethylene glycol monoethyl ether (10.6), polyethylene glycol with a number average molecular weight of 600 (10.5), diethylene glycol monobutyl ether (10.5), 3-methoxy-3-methylbutanol (10.5), triethylene glycol monobutyl ether (10.3), tetraethylene glycol monobutyl ether (10.2), polyethylene glycol with a number average molecular weight of 1000 (10.1), gamma-butyrolactone (9.9), 3-methoxy-N,N-dimethylpropionamide (9.2), tetraethylene glycol dimethyl ether (8.5), triethylene glycol butyl methyl ether (8.4), ethylene glycol dimethyl ether (7.6). The SP value of the water-soluble organic solvent contained in the ink is 5.0 (cal / cm. 3 ) 1 / 2 Above, 20.0(cal / cm 3 ) 1 / 2 It is preferable that:

[0077] [Other ingredients] The ink may contain various additives, such as surfactants, pH adjusters, antifoaming agents, rust inhibitors, preservatives, antifungal agents, antioxidants, antireducing agents, and chelating agents, as needed. These components (other components) are different from water-soluble organic solvents, and therefore the boiling point and SP value do not need to be taken into consideration. When a surfactant is contained, the content (mass %) of the surfactant in the ink is preferably 0.1% to 5.0% by mass, and more preferably 0.1% to 2.0% by mass, based on the total mass of the ink. [Example]

[0078] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples as long as the gist of the invention is not exceeded. The terms "parts" and "%" used to describe the amounts of components are based on mass unless otherwise specified.

[0079] <Method of measuring physical properties> (Weight average molecular weight and number average molecular weight of resin) The weight-average molecular weight (Mw) and number-average molecular weight (Mn) of the resin (particles) were measured according to the following procedure. The resin was added to tetrahydrofuran, dissolved at 25°C for 24 hours, and then filtered through a membrane filter to prepare a sample. The resin content in the sample was adjusted to approximately 0.3%. The prepared sample was analyzed by gel permeation chromatography according to the conditions shown below, and the number-average molecular weight was calculated using a molecular weight calibration curve created using standard polystyrene resins. The standard polystyrene resins used were "TSK Standard Polystyrene F-850, F-450, F-288, F-128, F-80, F-40, F-20, F-10, F-4, F-2, F-1, A-5000, A-2500, A-1000, A-500" (manufactured by Tosoh). HPLC equipment: Product name "2695 Separations Module" (Waters) Refractive index (RI) detector: Product name "2414 detector" (manufactured by Waters) Column: 4 columns, product name "GPC KF-806M" (Showa Denko) Eluent: tetrahydrofuran ·Flow rate: 1.0mL / min Oven temperature: 40℃ Sample injection volume: 100 μL

[0080] (glass transition temperature of resin) A liquid containing resin particles was dried at 60°C, and 2 mg of the resulting resin particles was placed in an aluminum container and sealed to prepare a sample for measurement. A differential scanning calorimeter (trade name "Q1000", manufactured by TA Instruments) was used to perform thermal analysis of the prepared sample according to the temperature program shown below, creating a temperature rise curve. In the created temperature rise curve (horizontal axis: temperature, vertical axis: heat quantity), the temperature at the intersection of a straight line extending from the low-temperature side curve to the high-temperature side through two points on the curve, and a tangent drawn at the point where the gradient of the step-like change in the curve is maximum, was determined as the glass transition temperature (T G )" [Temperature Program]: (1) Heat up to 200°C at 10°C / min (2) Decrease the temperature from 200°C to -50°C at a rate of 5°C / min. (3) Heat from -50°C to 200°C at 10°C / min

[0081] (Determining whether the resin is a resin particle, particle size) The liquid containing the resin was diluted with ion-exchanged water to prepare a sample with a resin content of approximately 1.0%. The particle size of this sample (cumulative 50% particle size D on a volume basis) was measured using a particle size distribution analyzer that uses dynamic light scattering under the following measurement conditions: 50 ) was measured. The particle size distribution analyzer used was a Nanotrac WAVEII-Q (manufactured by Microtrac Bell). If particles with a particle size were measured using this measurement method, the resin was determined to be a "resin particle" (a "water-dispersible resin"). On the other hand, if particles with a particle size were not measured using this measurement method, the resin was determined not to be a "resin particle" (a "water-soluble resin"). [Measurement conditions]: SetZero:30s Measurement count: 3 times Measurement time: 180 seconds ·Shape: true spherical Refractive index: 1.6 ·Density: 1.0

[0082] <Preparation of pigment dispersion> (Pigment dispersions 1-3) A water-soluble resin, styrene / acrylic acid copolymer (composition (mole) ratio = 84.6 / 15.4), was dissolved in ion-exchanged water with the addition of sodium hydroxide in an amount equal to the acid value, to prepare an aqueous solution of resin dispersant with a resin content of 25.0%. The acid value of this water-soluble resin was 120 mg KOH / g. A mixture of the components, the types and amounts (unit: %) shown in Table 1, was placed in a sand grinder and dispersed for 1 hour. The mixture was then centrifuged to remove coarse particles, and pressure-filtered using a 3.0 μm pore-size microfilter (manufactured by Fujifilm). An appropriate amount of ion-exchanged water was added to obtain each pigment dispersion. The amount of anionic groups in the pigments is shown in Table 1.

[0083] TIFF2023039913000002.tif66170

[0084] (Pigment dispersion 4) Pigment (CI Pigment Black 7) Dispersion 4 was prepared using a water-insoluble resin as a resin dispersant, following the description of "Preparation of Black Pigment Dispersion 1" in Patent Document 2 (JP 2012-251049 A). The water-insoluble resin used as the resin dispersant was a methacrylic acid / styrene macromer / 2-ethylhexyl methacrylate / styrene / methoxypolyethylene glycol monomethacrylate copolymer. The resulting pigment dispersion had a pigment content of 30.0%, a resin content of 6.0%, and an anionic group content of 398 μmol / g.

[0085] <Preparation of aqueous dispersion of resin particles> (Resin particles 1 to 8) A mixture of monomers of the types and amounts (parts) shown in Table 2 was placed in a reaction vessel equipped with a stirrer installed inside the autoclave. The temperature was raised to 220°C, and an esterification reaction was carried out according to the "stirring speed" and "reaction time" shown in Table 2. The temperature was raised to 240°C, and the pressure inside the autoclave was reduced to 13 Pa over 90 minutes. The esterification (dehydration condensation) reaction was continued by maintaining the reduced pressure of 240°C and 13 Pa for 5 hours, and then nitrogen gas was introduced into the autoclave to return the pressure to normal. After the temperature inside the reaction vessel was lowered to 220°C, a catalyst (tetra-n-butyl titanate) and 1.0 part of trimellitic acid were added, and the mixture was heated at 220°C for 2 hours to carry out the transesterification reaction. The amount of catalyst (mol) was 3 x 10 -4 × total amount (mol) of polycarboxylic acids used. Nitrogen gas was then introduced into the autoclave to create a pressurized state, and a sheet-like resin was taken out. The resin taken out was cooled to 25°C and then crushed in a crusher to obtain a polyester resin. The meanings of the monomer abbreviations in Table 2 are as follows: EG: Ethylene glycol NPG: Neopentyl glycol tPA: Terephthalic acid iPA: Isophthalic acid

[0086] A stirrer (product name "Tornado Stirrer Standard SM-104", manufactured by AS ONE) was placed in a 2-L beaker. 200 g of polyester resin and methyl ethyl ketone (MEK) were placed in the beaker and stirred at 30°C to dissolve the polyester resin. Next, 15.9 g of a 5% aqueous potassium hydroxide solution was added and stirred for 30 minutes. While stirring at 30°C, 500 g of deionized water was added dropwise at a rate of 20 mL / min. After heating to 60°C, MEK and some of the water were distilled off. After cooling to 25°C, the mixture was filtered through a 150-mesh wire screen, and deionized water was added to obtain aqueous dispersions of resin particles 1 to 8 (resin content: 30.0%). The properties of the resin particles in the resulting aqueous dispersions are shown in Table 2.

[0087] TIFF2023039913000003.tif77170

[0088] (Resin particles 9) An aqueous dispersion of commercially available polyester resin particles (trade name "Eliteru KT-8803", manufactured by Unitika, resin content 30.0%) was used as "aqueous dispersion of resin particles 9." The amount of anionic groups in resin particles 9 was 398 μmol / g, the number average molecular weight was 15,000, and the glass transition temperature T G The temperature was 65°C and the SP value was 11.9.

[0089] (Resin particles 10-12) 1,160 mL of water was heated to 90°C in a reactor. 1.39 g of potassium persulfate as a polymerization initiator was mixed with 160 mL of water to prepare an initiator solution. 32 mL of the prepared initiator solution was added to the reactor and stirred. Separately, a monomer mixture was prepared by mixing 1.6 g of isooctylthioglycolate as a monomer chain transfer agent (type and amount (g) shown in Table 3) and 9.98 g of a 30% aqueous solution of an emulsifier with 159.4 mL of water. The emulsifier used was Rhodafac RS 710 (manufactured by Rhodia Novecare). The prepared monomer mixture was added dropwise to the reactor over 30 minutes, and simultaneously, 129.4 g of the initiator solution was added dropwise to the reactor over 30 minutes and stirred. The resulting reaction mixture was stirred and maintained at 90°C for 3 hours. After cooling to 50°C, the pH was adjusted to 8.5 by adding 50% aqueous potassium hydroxide solution. After the contents were cooled to ambient temperature, they were filtered through a 200-mesh filter and deionized water was added to obtain a dispersion of resin particles 10 to 12 (resin content 30.0%). The properties of the resin particles in the obtained dispersion are shown in Table 3. The meanings of the abbreviations for the monomers in Table 3 are as follows: St: Styrene HMA: Hexyl methacrylate EGDMA: Ethylene glycol dimethacrylate αMSt: α-methylstyrene BzA: Benzyl acrylate ·MAA: methacrylic acid

[0090] TIFF2023039913000004.tif48170

[0091] <Preparation of wax particles> The content of the following commercially available wax particles was adjusted with deionized water to prepare an aqueous dispersion of wax particles (wax particle content: 30.0%). Aqueous dispersion of wax particles 1: Fischer-Tropsch wax (product name "EMUSTAR-6315", manufactured by Nippon Seiro, melting point 113°C) Aqueous dispersion of wax particles 2: Carvana wax (product name "Cellosol 524", manufactured by Chukyo Yushi, melting point 83°C) Aqueous dispersion of wax particles 3: oxidized polyethylene wax (product name "AQUACER515", manufactured by BYK Japan, melting point 135°C)

[0092] <Ink Preparation> Each ink was prepared by mixing the components (unit: %) shown in Tables 4-1 to 4-4, thoroughly stirring, and then filtering under pressure using a membrane filter (trade name "HDCII filter", manufactured by Pall) with a pore size of 4.5 μm. The properties of each ink prepared are shown in the lower part of Tables 4-1 to 4-4. Details of each component in Tables 4-1 to 4-4 are also shown below. In Tables 4-1 to 4-4, the numbers in parentheses next to the water-soluble organic solvent are the boiling point (°C) and SP value of the water-soluble organic solvent. When multiple second water-soluble organic solvents are contained, the "SP value V2 of the second water-soluble organic solvent" is a value weighted by the mass ratio of the contents. Zonyl FS-3100: Product name, fluorosurfactant, manufactured by Chemours BYK333: Product name, silicone surfactant, manufactured by BYK Japan BYK349: Product name, silicone surfactant, manufactured by BYK Japan Surfynol DF-110D: Product name, acetylene diol surfactant, manufactured by Nissin Chemical Industry Co., Ltd.

[0093] TIFF2023039913000005.tif231170

[0094] TIFF2023039913000006.tif232170

[0095] TIFF2023039913000007.tif229170

[0096] TIFF2023039913000008.tif255156

[0097] <Evaluation> Recording apparatuses 1 and 2 equipped with inkjet recording heads as shown below, and recording media 1 and 2 were prepared. Recording media 1 was used for recording a sample at 30 msec from the start of contact in the Bristow method. 1 / 2 Water absorption up to 10mL / m 2 On the other hand, recording medium 2 was measured at 30 msec from the start of contact in the Bristow method. 1 / 2 Water absorption up to 10mL / m 2 In the present invention, the evaluation criteria for each item shown below were "AAA", "AA", "A", and "B", with "C" being an unacceptable level. The evaluation results are shown in Tables 5-1 and 5-2. A recording device 1 (trade name "Pixus Pro-2000", manufactured by Canon) is equipped with a recording head that ejects ink by the action of thermal energy, and has a mechanism for heating the ink in the recording head. Recording device 2 (product name "PX-G5300", manufactured by Seiko Epson) is equipped with a recording head that ejects ink by the action of physical energy, and does not have a mechanism for heating the ink in the recording head. Recording medium 1: Product name "Scotchcal Graphic Film IJ1220", manufactured by 3M, material: polyvinyl chloride Recording medium 2: High-quality dedicated paper, product name "HR-101S", manufactured by Canon

[0098] (Discharge stability) Each ink was filled into an ink cartridge and installed in an inkjet recording device. Under conditions of 25°C temperature and 50% relative humidity, with 32 ng of ink applied to a 1 / 600 inch x 1 / 600 inch unit area, and the conditions shown in Tables 5-1 and 5-2, 100 solid images measuring 27 cm x 38 cm were continuously printed on A3-sized recording media. After printing 100 sheets, a nozzle check pattern was printed and the percentage of ejection ports where ejection failure occurred was confirmed, and the ink ejection stability was evaluated according to the evaluation criteria shown below. A: The percentage of ejection ports where ejection failure occurred was 0% of all ejection ports. B: The proportion of ejection ports where ejection failure occurred was less than 80% of all ejection ports. C: The proportion of ejection ports where ejection failure occurred was 80% or more of all ejection ports.

[0099] (Abrasion resistance) Each ink was filled into an ink cartridge and installed in an inkjet recording device. A 27 cm x 38 cm solid image was recorded on an A3-size recording medium under the conditions of 25°C temperature and 50% relative humidity, with 32 ng of ink applied to a 1 / 600 inch x 1 / 600 inch unit area, as shown in Tables 5-1 and 5-2. A rubbing test was performed using a Gakushin-type abrasion tester (manufactured by Tester Sangyo Co., Ltd.) conforming to JIS L0849. A white cotton cloth (as specified in JIS L0803) was rubbed against the surface of the recorded image 150 times with a 500 g load. The image was visually inspected after the rub test, and its abrasion resistance was evaluated according to the following criteria. AAA: No scratches were observed on the image after 300 strokes. AA: Scratch marks were observed on the image after 300 reciprocal strokes, but no scratch marks were observed on the image after 150 reciprocal strokes. A: Scratch marks were observed on the image after 150 reciprocal strokes, but no scratch marks were observed on the image after 50 reciprocal strokes. B: Scratches were observed on the image after 50 reciprocal passes, but the white background of the recording medium was not visible. C: Scratches were observed on the image after 50 reciprocal passes, and the white background of the recording medium was visible.

[0100] TIFF2023039913000009.tif214170

[0101] TIFF2023039913000010.tif240170

[0102] The disclosure of this embodiment includes the following methods and configurations. (Method 1) An inkjet recording method in which a water-based ink is ejected from an inkjet recording head by the action of thermal energy and applied to a recording medium to record an image, temperature T H(°C) from the recording head to apply the water-based ink to the recording medium; and F (°C), the water-based ink contains a pigment and polyester resin particles; the ratio of the weight average molecular weight to the number average molecular weight of the polyester resin particles is 6.0 or less; The glass transition temperature T G (℃), the temperature T H (℃), and the temperature T F (°C) satisfies the relationships of the following formulas (1) to (3), the amount of heat ((W·h) / g) applied to the water-based ink applied to the recording medium is 2 (W·h) / g or more; The recording medium is in a state where the temperature is within 30 msec from the start of contact in the Bristow method. 1 / 2 Water absorption up to 10mL / m 2 An inkjet recording method characterized by the following: T G (℃)>T H (℃) (1) T F (℃)≧T H (℃)+10℃ (2) T F (℃)≧T G (℃)-10℃ (3) (Method 2) The temperature T H (°C) is 40°C or higher, The temperature T F The inkjet recording method according to Method 1, wherein (°C) is 90°C or less. (Method 3) The water-based ink further contains a first water-soluble organic solvent having a boiling point of 120°C or higher and 220°C or lower, 3. The inkjet recording method according to Method 1 or 2, wherein the content (% by mass) of the first water-soluble organic solvent is the highest among all the water-soluble organic solvents in the aqueous ink. (Method 4) The difference between the SP value of the first water-soluble organic solvent and the SP value of the polyester resin particles is 4.0 or less, 4. The inkjet recording method according to claim 3, wherein the content (mass %) of the first water-soluble organic solvent in the aqueous ink is 1.0 times or more and 4.0 times or less in mass ratio to the content (mass %) of the polyester resin particles. (Method 5) The water-based ink further contains a second water-soluble organic solvent having a boiling point of more than 220°C and not more than 310°C, 5. The inkjet recording method according to any one of Methods 1 to 4, wherein the difference between the SP value of the second water-soluble organic solvent and the SP value of the polyester resin particles is 4.0 or less. (Method 6) The pigment is dispersed in the aqueous ink by the action of an anionic group, 6. The inkjet recording method according to any one of Methods 1 to 5, wherein the amount (μmol / g) of the anionic groups in the pigment is 6.0 times or more the amount (μmol / g) of the anionic groups in the polyester resin particles. (Method 7) The inkjet recording method according to any one of Methods 1 to 6, wherein the weight average molecular weight of the polyester resin particles is 30,000 or more and 70,000 or less. (Method 8) An inkjet recording method described in any one of Methods 1 to 7, wherein the content (mass%) of the polyester resin particles in the aqueous ink is 1.5 times or more by mass relative to the content (mass%) of the pigment. (Method 9) The aqueous ink further contains wax particles formed of at least one wax selected from the group consisting of Fischer-Tropsch wax, polyolefin wax, and α-olefin-maleic anhydride copolymer; 9. The inkjet recording method according to any one of Methods 1 to 8, wherein the content (mass%) of the polyester resin particles in the aqueous ink is 2.0 times or more and 30.0 times or less in mass ratio to the content (mass%) of the wax particles. (Configuration 1) An inkjet recording apparatus for use in an inkjet recording method in which a water-based ink is ejected from an inkjet recording head by the action of thermal energy and applied to a recording medium to record an image, comprising: The water-based ink is discharged from the recording head and applied to the recording medium at a temperature T H (°C), and a mechanism for heating the recording medium to a temperature T F (°C), the water-based ink contains a pigment and polyester resin particles; the ratio of the weight average molecular weight to the number average molecular weight of the polyester resin particles is 6.0 or less; The glass transition temperature T G (℃), the temperature T H (℃), and the temperature T F (°C) satisfies the relationships of the following formulas (1) to (3), the amount of heat ((W·h) / g) applied to the water-based ink applied to the recording medium is 2 (W·h) / g or more; The recording medium is in a state where the temperature is within 30 msec from the start of contact in the Bristow method. 1 / 2 Water absorption up to 10mL / m 2 An inkjet recording apparatus characterized by the following: T G (℃)>T H (℃) (1) T F (℃)≧T H (℃)+10℃ (2) T F (℃)≧T G (℃)-10℃ (3)

Claims

1. An inkjet recording method in which a water-based ink is ejected from an inkjet recording head by the action of thermal energy and applied to a recording medium to record an image, comprising: Temperature T Ｈ (°C) from the recording head to apply the water-based ink to the recording medium; and Ｆ and heating to (°C), the water-based ink contains a pigment and polyester resin particles; the ratio of the weight average molecular weight to the number average molecular weight of the polyester resin particles is 6.0 or less; The glass transition temperature T Ｇ (°C), the temperature T Ｈ (°C), and the temperature T Ｆ (°C) satisfies the relationships of the following formulas (1) to (3), the amount of heat ((Wh) / g) applied to the aqueous ink applied to the recording medium is 2 (Wh) / g or more; The recording medium is １／２ Water absorption up to 10 mL / m ２ An inkjet recording method characterized by the following: T Ｇ (℃)>T Ｈ (℃) ・・・(1) T Ｆ (℃)≧T Ｈ (℃)+10℃ ・・・(2) T Ｆ (℃)≧T Ｇ (℃)-10℃ ・・・(3)

2. The temperature T Ｈ (°C) is 40°C or higher, The temperature T Ｆ 2. The ink jet recording method according to claim 1, wherein the temperature (°C) is 90°C or lower.

3. the water-based ink further contains a first water-soluble organic solvent having a boiling point of 120°C or higher and 220°C or lower; The inkjet recording method according to claim 1 , wherein the content (% by mass) of the first water-soluble organic solvent is the highest among all the water-soluble organic solvents in the aqueous ink.

4. a difference between the SP value of the first water-soluble organic solvent and the SP value of the polyester resin particles is 4.0 or less; 4. The inkjet recording method according to claim 3, wherein the content (mass %) of the first water-soluble organic solvent in the aqueous ink is 1.0 to 4.0 times the content (mass %) of the polyester resin particles in terms of mass ratio.

5. the water-based ink further contains a second water-soluble organic solvent having a boiling point of more than 220°C and not more than 310°C, 5. The inkjet recording method according to claim 1, wherein the difference between the SP value of the second water-soluble organic solvent and the SP value of the polyester resin particles is 4.0 or less.

6. the pigment is dispersed in the aqueous ink by the action of an anionic group, 5. The inkjet recording method according to claim 1, wherein the amount (μmol / g) of the anionic group in the pigment is 6.0 times or more the amount (μmol / g) of the anionic group in the polyester resin particles.

7. 5. The ink jet recording method according to claim 1, wherein the weight average molecular weight of the polyester resin particles is 30,000 or more and 70,000 or less.

8. 5. The inkjet recording method according to claim 1, wherein the content (mass %) of the polyester resin particles in the aqueous ink is 1.5 times or more the content (mass %) of the pigment in terms of mass ratio.

9. the aqueous ink further contains wax particles formed of at least one wax selected from the group consisting of Fischer-Tropsch wax, polyolefin wax, and α-olefin-maleic anhydride copolymer; 5. The inkjet recording method according to claim 1, wherein the content (mass %) of the polyester resin particles in the aqueous ink is 2.0 times or more and 30.0 times or less in mass relative to the content (mass %) of the wax particles.

10. An inkjet recording apparatus for use in an inkjet recording method in which a water-based ink is ejected from an inkjet recording head by the action of thermal energy and applied to a recording medium to record an image, The water-based ink that is ejected from the recording head and applied to the recording medium is heated to a temperature T Ｈ (°C), and a mechanism for heating the recording medium to which the water-based ink has been applied to a temperature T Ｆ (°C), the water-based ink contains a pigment and polyester resin particles; the ratio of the weight average molecular weight to the number average molecular weight of the polyester resin particles is 6.0 or less; The glass transition temperature T Ｇ (°C), the temperature T Ｈ (°C), and the temperature T Ｆ (°C) satisfies the relationships of the following formulas (1) to (3), the amount of heat ((Wh) / g) applied to the aqueous ink applied to the recording medium is 2 (Wh) / g or more; The recording medium is １／２ Water absorption up to 10 mL / m ２ An inkjet recording apparatus characterized by the following: T Ｇ (℃)>T Ｈ (℃) ・・・(1) T Ｆ (℃)≧T Ｈ (℃)+10℃ ・・・(2) T Ｆ (℃)≧T Ｇ (℃)-10℃ ・・・(3)

Images