Fine white particles comprising polymer-encapsulated titanium oxide

Patent metadata

Field	Value
Publication number	US-11174405-B2
Application number	US-201716463515-A
Country	US
Kind code	B2
Filing date	Nov 30, 2017
Priority date	Nov 30, 2016
Publication date	Nov 16, 2021
Grant date	Nov 16, 2021

Abstract

The present invention relates to white fine particles from which a white ink that is capable of satisfying both of high hiding power and good bending resistance in a printed material can be obtained, and further relates to white fine particles from which an ink that is capable of satisfying not only excellent fixing properties even when printed on a non-liquid absorbing printing medium such as a resin film, but also suppression of increase in viscosity of the ink and at the same time good deinking properties at a high level can be obtained. The present invention provides [1] white fine particles containing titanium oxide and a polymer component with which the titanium oxide is encapsulated, in which a titanium atomic fraction of a surface of the respective white fine particles as measured at a photoelectron takeoff angle of 45° by X-ray photoelectron spectroscopy (XPS) is not more than 7 atomic %, [2] a water-based ink containing the aforementioned white fine particles, in which the titanium atomic fraction of the surface of the respective white fine particles as measured at a photoelectron takeoff angle of 45° by XPS is not more than 5 atomic %, and [3] a process for producing a dispersion of white fine particles, including step 1 of mixing titanium oxide and a polymer dispersant to obtain a titanium oxide dispersion and step 2 of adding a polymerizable monomer to the thus obtained titanium oxide dispersion to subject the polymerizable monomer to polymerization reaction, thereby obtaining the dispersion of the white fine particles, in which a titanium atomic fraction of a surface of the respective white fine particles as measured at a photoelectron takeoff angle of 45° by XPS is not more than 7 atomic %.

First claim

The invention claimed is:

1. White fine particles comprising titanium oxide and a polymer component with which the titanium oxide is encapsulated, in which a titanium atomic fraction of a surface of the respective white fine particles as measured at a photoelectron takeoff angle of 45° by X-ray photoelectron spectroscopy (XPS) is not more than 7 atomic %,
wherein a mass ratio of the titanium oxide to the polymer component [titanium oxide/polymer component] is not less than 10/90 and not more than 70/30,
the polymer component comprises a polymer comprising a constitutional unit derived from at least one polymerizable monomer selected from the group consisting of a (meth) acrylate and an aromatic group-containing monomer, in addition to an underlying polymer dispersant comprising a constitutional unit derived from at least one compound selected from the group consisting of (meth)acrylic acid and an alkyl (meth)acrylate,
the polymer dispersant is a vinyl polymer that is produced by copolymerizing a monomer mixture comprising (a) a salt-forming group-containing monomer and (b) a hydrophobic monomer, and
the content of the constitutional unit derived from (a) the salt-forming group-containing monomer in the whole constitutional units of the polymer dispersant is not less than 30% by mass and not more than 85% by mass.

2. The white fine particles according to claim 1 , wherein the white fine particles comprise the titanium oxide and the polymer component with which the titanium oxide is encapsulated, in which a titanium atomic fraction of a surface of respective particles of the titanium oxide as measured at a photoelectron takeoff angle of 20° by X-ray photoelectron spectroscopy (XPS) is not less than 30 atomic %, and a titanium atomic fraction of a surface of the respective white fine particles as measured at a photoelectron takeoff angle of 20° by X-ray photoelectron spectroscopy (XPS) is not more than 2 atomic %.

3. The white fine particles according to claim 1 , wherein a mass ratio of precipitated particles (precipitated component) to non-precipitated particles (non-precipitated component) [precipitated component/non-precipitated component] as measured by subjecting the white fine particles to centrifugal separation under the following conditions is from 100/0 to 95/5:
Conditions of centrifugal separation:
A water dispersion of the white fine particles having a solid content of 20% by mass is subjected to centrifugal separation using a centrifuge in a 25° C. atmosphere at a relative centrifugal acceleration of 170 G for 1 hour.

4. The white fine particles according to claim 1 , wherein the titanium oxide is untreated, or surface-treated with at least one material selected from the group consisting of alumina, silica, zinc oxide and zirconia.

5. The white fine particles according to claim 1 , wherein the titanium oxide is titanium oxide whose surface is subjected to no surface treatment.

6. The white fine particles according to claim 1 , wherein an average primary particle size of the titanium oxide is not less than 30 nm and not more than 500 nm.

7. The white fine particles according to claim 1 , wherein a volume median particle size (D 50 ) of the white fine particles is not less than 50 nm and not more than 680 nm.

8. The white fine particles according to claim 1 , wherein the polymer component comprises a constitutional unit derived from a (meth)acrylic monomer.

9. The white fine particles according to claim 1 , wherein the polymer dispersant is in the form of a water-insoluble polymer.

10. The white fine particles according to claim 1 , a polymer coating rate represented by the formula (1) is not less than 93% and not more than 100%:
Polymer coating rate (%)={1−(titanium atomic fraction of surface of respective white fine particles)/(titanium atomic fraction of surface of titanium oxide)}×100  (1).

11. A water-based ink comprising the white fine particles according to claim 1 , in which the titanium atomic fraction of the surface of the respective white fine particles as measured at a photoelectron takeoff angle of 45° by X-ray photoelectron spectroscopy (XPS) is not more than 5 atomic %.

12. The water-based ink according to claim 11 for use in ink-jet printing.

13. A process for producing a dispersion of white fine particles formed by encapsulating titanium oxide with a polymer component, comprising the following steps 1 and 2:
Step 1: mixing the titanium oxide and a polymer dispersant to obtain a titanium oxide dispersion; and
Step 2: adding a polymerizable monomer to the titanium oxide dispersion obtained in the step 1 to subject the polymerizable monomer to polymerization reaction, thereby obtaining the dispersion of the white fine particles,
in which a titanium atomic fraction of a surface of the respective white fine particles as measured at a photoelectron takeoff angle of 45° by X-ray photoelectron spectroscopy (XPS) is not more than 7 atomic %, and the titanium oxide is untreated, or surface-treated with at least one material selected from the group consisting of alumina, silica, zinc oxide and zirconia.

14. The process for producing a dispersion of white fine particles according to claim 13 , wherein a mass ratio of the titanium oxide to the polymer dispersant [titanium oxide/polymer dispersant] in the step 1 is not less than 75/25 and not more than 99/1.

15. The process for producing a dispersion of white fine particles according to claim 13 , wherein the polymerizable monomer used in the step 2 is at least one monomer selected from the group consisting of a (meth)acrylate monomer and an aromatic group-containing monomer.

16. The process for producing a dispersion of white fine particles according to claim 13 , wherein subjecting a titanium oxide mixture comprising the titanium oxide, the polymer dispersant and an aqueous medium to dispersing treatment in the step 1.

Assignees

• Kao Corp

Inventors

• Yoshida Tomohide
• Ueda Yasufumi

Classifications

• C09D11/322 Primary

  Pigment inks · CPC title

• C01P2004/64

  Nanometer sized, i.e. from 1-100 nanometer · CPC title

• B41M5/00

  Duplicating or marking methods; Sheet materials for use therein (by using light-sensitive materials G03; electrography, magnetography G03G {; repeatedly usable boards or tablets for writing or drawing B43L1/00}) · CPC title

• C09C3/10

  Treatment with macromolecular organic compounds {(C09C3/006 takes precedence)} · CPC title

• C01P2004/52

  highly monodisperse size distribution · CPC title