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EP-4036179-B1 - INK JET RECORDING METHOD AND INK JET RECORDING APPARATUS

EP4036179B1EP 4036179 B1EP4036179 B1EP 4036179B1EP-4036179-B1

Inventors

  • TAJIMA, TAKAHIRO
  • Kakikawa, Hiroshi
  • YAMAMOTO, MASASHI
  • YOSHIZAWA, ATSUHITO

Dates

Publication Date
20260506
Application Date
20220120

Claims (19)

  1. An ink jet recording method comprising a step of recording an image by applying a first ink and a second ink to a recording medium by using an ink jet recording apparatus such that an area where the first ink is applied and an area where the second ink is applied at least partially overlap each other, the ink jet recording apparatus including a recording head having ejection orifices configured to eject the first ink and the second ink, respectively, wherein the first ink comprises an alkaline buffer and a pigment particle that is a pigment dispersed by an effect of an anionic group, and the second ink comprises a fluorescent particle that is a particle including a coloring material that exhibits fluorescence, dispersed by an effect of an anionic group, characterized in that a density ρ 1 (g/cm 3 ) of the pigment particle is more than a density ρ 2 (g/cm 3 ) of the fluorescent particle.
  2. The ink jet recording method according to claim 1, wherein the pigment particles satisfy a relationship of a formula (1): A λ 2 / A λ 1 ≤ 0.5 where A λ1 is an absorbance of the pigment particle at a maximum absorption wavelength λ 1 (nm) of the pigment particle, and A λ2 is an absorbance of the pigment particle at a maximum fluorescence wavelength λ 2 (nm) of the fluorescent particle.
  3. The ink jet recording method according to claim 1 or 2, wherein the pigment particle comprises at least one type of pigment selected from a group consisting of carbon black, quinacridone, perinone, perylene, dioxazine, azo and phthalocyanine.
  4. The ink jet recording method according to any one of claims 1 to 3, wherein the pigment particle comprises quinacridone.
  5. The ink jet recording method according to any one of claims 1 to 4, wherein the pigment particle comprises a pigment formed of a molecule having a fused ring constituted of fusing of five or more rings.
  6. The ink jet recording method according to any one of claims 1 to 5, wherein the pigment particle is a pigment dispersed by a resin having an anionic group.
  7. The ink jet recording method according to any one of claims 1 to 6, wherein a content (% by mass) of the pigment particle in the first ink is 0.10% by mass or more to 10.00% by mass or less based on a total mass of the ink.
  8. The ink jet recording method according to any one of claims 1 to 7, wherein the density ρ 1 (g/cm 3 ) of the pigment particle is 1.45 g/cm 3 or more to 5.00 g/cm 3 or less.
  9. The ink jet recording method according to any one of claims 1 to 8, wherein pKa of the alkaline buffer at 25°C is 7.6 or more to 10.4 or less.
  10. The ink jet recording method according to any one of claims 1 to 9, wherein the alkaline buffer is a tertiary amine compound.
  11. The ink jet recording method according to any one of claims 1 to 10, wherein the content (% by mass) of the alkaline buffer in the first ink is 0.10% by mass or more to 15.00% or less based on a total mass of the ink.
  12. The ink jet recording method according to any one of claims 1 to 11, wherein the first ink further comprises a nonionic siloxane compound.
  13. The ink jet recording method according to any one of claims 1 to 12, wherein the fluorescent particle is a resin particle dyed with a coloring material that exhibits fluorescence.
  14. The ink jet recording method according to claim 13, wherein the coloring material that exhibits fluorescence is a basic dye.
  15. The ink jet recording method according to claim 13 or 14, wherein the coloring material that exhibits fluorescence is a compound with a xanthene skeleton.
  16. The ink jet recording method according to any one of claims 1 to 15, wherein a content (% by mass) of the fluorescent particle in the second ink is 0.10% by mass or more to 15.00% or less based on a total mass of the ink.
  17. The ink jet recording method according to any one of claims 1 to 16, wherein the density ρ 2 (g/cm 3 ) of the fluorescent particle is 1.00 g/cm 3 or more to 1.50 g/cm 3 or less.
  18. The ink jet recording method according to any one of claims 1 to 17, wherein the first ink and the second ink are applied to a unit area of the recording medium by performing main scanning of the recording head 4 times or more to 16 times or less.
  19. An ink jet recording apparatus comprising a first ink, a second ink, and a recording head having ejection orifices configured to eject the first ink and the second ink, respectively, wherein the ink jet recording apparatus is configured to record an image by applying the first ink and the second ink to a recording medium such that an area where the first ink is applied and an area where the second ink is applied at least partially overlap each other, the first ink comprises an alkaline buffer and a pigment particle that is a pigment dispersed by an effect of an anionic group, the second ink comprises a fluorescent particle that is a particle including a coloring material that exhibits fluorescence, dispersed by an effect of an anionic group, and a density ρ 1 (g/cm 3 ) of the pigment particle is more than a density ρ 2 (g/cm 3 ) of the fluorescent particle.

Description

BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to an ink jet recording method and an ink jet recording apparatus. Description of the Related Art Ink jet recording technologies have attracted attention since long. For example, US 5,888,284 discloses dye-based inks and ink sets and uses thereof in inkjet systems. In recent years, an ink jet recording method is used to record an image on a recording medium for a poster application and the like and frequency of usage thereof is greatly increasing. In such applications, there are demands for a wide expressible color gamut and high image fastness. To meet such demands, for example, an ink containing a fine resin particle dyed with a fluorescent dye is proposed (Japanese Patent Application Laid-Open No. 2008-063546). Moreover, there is proposed an ink set including an ink containing a pigment and an ink containing a dispersed particle that is a mixture of a fluorescent coloring material and a resin (Japanese Patent Application Laid-Open No. 2002-363455). The present inventors made studies on an ink containing a fluorescent particle (particle including a coloring material that exhibits fluorescence) to record an image with a wide expressible color gamut and excellent fastness. As a result, the present inventors found that, when the ink containing the fluorescent particle is used, the lightfastness of the recorded image tends to decrease. The coloring material that exhibits fluorescence absorbs short-wavelength light corresponding to an ultraviolet to visible range and emits light with a wavelength longer than the wavelength of the absorbed light. The coloring material having absorbed light transitions to an unstable excited state in which an energy state is high. Fluorescence refers to light emission that occurs when the coloring material returns from a singlet state in the excited state to a ground state. The singlet state is a very unstable state and a redox reaction is likely to occur. Accordingly, the coloring material that exhibits fluorescence is likely to degrade and has low lightfastness. Next, the present inventors made studies on addition of a pigment to an ink containing a fluorescent particle. As a result, the present inventors found that using the ink containing the pigment together with the fluorescent particle improves the lightfastness of the recorded image. The lightfastness of the image is assumed to have improved due to mixing with the pigment with excellent lightfastness. However, the present inventors also found that the fluorescence intensity of the image decreases. Such a decrease in the fluorescence intensity is assumed to occur because fluorescent light emitted from the fluorescent particle is scattered or absorbed by the pigment present on the fluorescent particle and the fluorescence intensity decreases. Moreover, it was found that, since both the fluorescent particle and the pigment are contained in the same ink, the contents of the fluorescent particle and the pigment are fixed and the expressible color gamut cannot be increased. Furthermore, the present inventors studied the ink containing a fine resin particle dyed with a fluorescent dye that is proposed in Japanese Patent Application Laid-Open No. 2008-063546. As a result, it was found that the fluorescence intensity of the image was improved but the expressible color gamut was still small. Moreover, the present inventors studied an image recorded by using the ink set proposed in Japanese Patent Application Laid-Open No. 2002-363455 and by applying the two types of inks to the recording medium such that the inks at least partially overlap each other. As a result, it was found that the expressible color gamut was increased but an increase in the fluorescence intensity of the image was difficult to achieve. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an ink jet recording method that enables recording of an image with a wide expressible color gamut and high fluorescence intensity. Moreover, another object of the present invention is to provide an ink jet recording apparatus that uses this ink jet recording method. Specifically, the present invention provides an ink jet recording method as defined in claim 1. This method comprises a step of recording an image by applying a first ink and a second ink to a recording medium by using an ink jet recording apparatus such that an area where the first ink is applied and an area where the second ink is applied at least partially overlap each other, the ink jet recording apparatus including a recording head having ejection orifices configured to eject the first ink and the second ink, respectively, wherein the first ink contains an alkaline buffer and a pigment particle that is a pigment dispersed by an effect of an anionic group, the second ink contains a fluorescent particle that is a particle including a coloring material that exhibits fluorescence, dispersed by an eff