EP-4741464-A1 - INKJET INK AND INKJET RECORDING APPARATUS

Abstract

An ink includes: a quinacridone pigment; a pigment dispersion resin; and an aqueous medium. Maximum absorbance at a wavelength of 300 nm or more and 350 nm or less in an ultraviolet-visible light absorption spectrum of a 25-fold diluted solution of a supernatant liquid obtained by centrifuging the ink at 23°C and 140,000 rpm for 3 hours is 0.16 or more and 0.40 or less, and absorbance at 429 nm is 0.002 or less. In the ink, the number of coarse particles having a particle diameter of 500 nm or more is 4.0 × 10 8 /mL or less. A 50-fold diluted solution of the supernatant liquid has a phosphorus concentration of 1.0 ppm or more and 16.0 ppm or less.

Inventors

• SATO, SATOSHI

Assignees

• KYOCERA Document Solutions Inc.

Dates

Publication Date

20260513

Application Date

20251104

Claims (3)

1. An inkjet ink, comprising: a quinacridone pigment; a pigment dispersion resin; and an aqueous medium, maximum absorbance at a wavelength of 300 nm or more and 350 nm or less in an ultraviolet-visible light absorption spectrum of a 25-fold diluted solution of a supernatant liquid obtained by centrifuging the inkjet ink at 23°C and 140,000 rpm for 3 hours being 0.16 or more and 0.40 or less, absorbance at 429 nm being 0.002 or less, the number of coarse particles having a particle diameter of 500 nm or more being 4.0 × 10 8 /mL or less, and a 50-fold diluted solution of the supernatant liquid having a phosphorus concentration of 1.0 ppm or more and 16.0 ppm or less.
2. The inkjet ink according to claim 1, wherein the pigment dispersion resin includes an adsorbed resin adsorbed on the quinacridone pigment and an unadsorbed resin that is not adsorbed on the quinacridone pigment, and a ratio of the unadsorbed resin in the pigment dispersion resin is 20 mass% or more and 50 mass% or less.
3. An inkjet recording apparatus (1), comprising: a conveying unit (6) that conveys a recording medium; and a line type recording head (4) that ejects an ink onto the recording medium, the ink including the inkjet ink according to claim 1 or 2.

Description

Field The present disclosure relates to an inkjet ink including a quinacridone pigment, and an inkjet recording apparatus. Background Japanese Patent Application Laid-open No. 2000-273383 and Japanese Patent Application Laid-open No. 2002-167534 disclose inkjet inks for recording an image on a recording medium such as paper. Inkjet inks desired to have high ejection stability when ejected from a nozzle of a recording head. In the inkjet ink disclosed in Japanese Patent Application Laid-open No. 2000-273383, a pigment derivative is blended in order to improve ejection stability. In the inkjet ink disclosed in Japanese Patent Application Laid-open No. 2002-167534, ejection stability is improved on the basis of the increase rate of the average particle diameter of a coloring agent when concentrated. Summary According to an embodiment of the present disclosure, there is provided an inkjet ink, including: a quinacridone pigment; a pigment dispersion resin; and an aqueous medium. Maximum absorbance at a wavelength of 300 nm or more and 350 nm or less in an ultraviolet-visible light absorption spectrum of a 25-fold diluted solution of a supernatant liquid obtained by centrifuging the inkjet ink at 23°C and 140,000 rpm for 3 hours is 0.16 or more and 0.40 or less, and absorbance at 429 nm is 0.002 or less. In the inkjet ink, the number of coarse particles having a particle diameter of 500 nm or more is 4.0 × 108/mL or less. A 50-fold diluted solution of the supernatant liquid has a phosphorus concentration of 1.0 ppm or more and 16.0 ppm or less. an inkjet recording apparatus according to an embodiment of the present disclosure includes: a conveying unit that conveys a recording medium; and a line type recording head that ejects an ink onto the recording medium. The ink includes the above inkjet ink. Brief Description of Figures Fig. 1 is a diagram showing an inkjet recording apparatus according to an embodiment of the present disclosure; andFig. 2 is a diagram showing the lower surface of the recording head of the inkjet recording apparatus. Detailed Description In Japanese Patent Application Laid-open No. 2000-273383 and Japanese Patent Application Laid-open No. 2002-167534, the effects of coarse particles generated during the dispersion of the pigments, intermediates generated during the synthesis of pigments, catalysts used for synthesizing pigments, and the like are not considered in relation to ejection stability. Further, inkjet inks are desired to have high rubfastness in the image formed on a recording medium and high redispersibility in a cleaning solution during the maintenance of the ejection surface of the recording head. In view of the circumstances as described above, it is an object of the present disclosure to provide an inkjet ink having ejection stability, rubfastness, and cleanability. Embodiments of the present disclosure will be described. [Inkjet ink] An inkjet ink according to an embodiment of the present disclosure (hereinafter, also referred to simply as an "ink") includes a quinacridone pigment; a pigment dispersion resin and an aqueous medium. In the ink according to this embodiment, the pigment dispersion resin includes an adsorbed resin adsorbed on the quinacridone pigment, and an unadsorbed resin that is not adsorbed on the quinacridone pigment and is free in the aqueous medium, and the quinacridone pigment and the adsorbed resin constitute the pigment dispersion. In the ink according to this embodiment, by controlling the amounts of the unadsorbed resin, an intermediate generated during the synthesis of a quinacridone pigment (hereinafter, also referred to simply as an "intermediate"), coarse particles, and a phosphorus-containing catalyst used for synthesizing a quinacridone pigment, it is possible to realize a configuration having ejection stability, rubfastness, and cleanability. Note that in the present disclosure, the coarse particles refer to particles having a particle diameter of 500 nm or more. The amount of the unadsorbed resin in the ink according to this embodiment can be known using the ultraviolet-visible light absorption spectrum of a 25-fold diluted solution of a supernatant liquid obtained by centrifuging the ink at 23°C and 140,000 rpm for 3 hours (hereinafter, also referred to simply as a "supernatant liquid"). That is, it can be seen that the higher the maximum absorbance of the peak appearing in the wavelength range of 300 nm or more and 350 nm or less in this ultraviolet-visible light absorption spectrum, the greater the amount of the unadsorbed resin in the ink. In the ink according to this embodiment, the amount of the unadsorbed resin is controlled such that the maximum absorbance at a wavelength of 300 nm or more and 350 nm or less in this ultraviolet-visible light absorption spectrum is 0.16 or more and 0.40 or less. Further, in the ink according to this embodiment, the ratio of the unadsorbed resin in the pigment dispersion resin is favorably controlled to