Pigment ink composition

Details Pigment ink composition Pigment ink composition

2000-08-11

2002-07-16

Klemanski, Helene (Department: 1714)

Compositions: coating or plastic

Coating or plastic compositions

Marking

C106S031860, C106S031900

Reexamination Certificate

active

06419732

ABSTRACT:

This invention relates to an aqueous pigment ink composition suitable for use in inkjet recording and more particularly, to an aqueous pigment ink composition which keeps stable dispersion of the pigment and which can be printed on any recording material to form printed images having rub-off resistance and water fastness.
BACKGROUND OF THE INVENTION
Since conventional dye base inks commonly used in the inkjet recording technology undesirably lack light fastness and water fastness, pigment base inks featuring superior water fastness and light fastness are now used in part. Especially as to black ink, carbon black pigment ink has substituted for the dye base ink.
Since aqueous pigment ink uses inorganic pigment particles having good water fastness and light-fastness in themselves as the colorant, images printed on an object therewith are improved in water fastness and light-fastness over the dye base ink. However, since the pigment ink is not dissolved in water as is the dye ink, essentially the pigment ink merely rests on the object to be recorded. Then when the pigment ink is printed on the object to be recorded, typically a sheet of plain paper, the printed image is less resistant to water and removed by rubbing. On use of a marker filled with the pigment ink, images marked therewith are blurred or stained. An attempt would be made to add a binder to the pigment ink to bind pigment particles. Since the aqueous pigment ink is a dispersion of essentially water-insoluble pigment particles in water with the aid of a dispersant or the like, the addition of the binder can cause the particles to flocculate, exacerbating storage stability and often causing the inkjet head to be clogged.
SUMMARY OF THE INVENTION
An object of the invention is to provide a novel and improved pigment ink composition which is suited for use in the aqueous ink recording technology, especially the inkjet recording technology, forms printed images having rub-off resistance and water fastness, and has storage stability.
We have found that a pigment ink composition obtained by formulating in a specific proportion (I) an inorganic pigment, (II) an organosilicon compound (C) obtained by hydrolysis of (A) 100 parts by weight of a hydrolyzable silane containing an amino group-bearing organic group represented by the following general formula (1) or a partial hydrolyzate thereof and (B) 5 to 200 parts by weight of a hydrolyzable silane represented by the following general formula (2) or a partial hydrolyzate thereof, and (III) water is suited for use in the aqueous ink recording technology, especially the inkjet recording technology. When the pigment ink composition is printed on an object to be recorded, the printed images is bound to the object and have rub-off resistance and water fastness. Additionally, the composition remains stable during storage.
YR
1
m
SiR
2
3−m
  (1)
Herein R
1
is a substituted or unsubstituted monovalent hydrocarbon group of 1 to 8 carbon atoms, R
2
is an alkoxy or acyloxy group of 1 to 4 carbon atoms, Y is an amino group-bearing organic group, and m is equal to 0 or 1.
R
3
n
SiR
4
4−n
  (2)
Herein R
3
is a substituted or unsubstituted monovalent hydrocarbon group of 1 to 8 carbon atoms, R
4
is an alkoxy or acyloxy group of 1 to 4 carbon atoms, and n is equal to 0, 1 or 2.
Accordingly, the invention provides a pigment ink composition comprising (I) 10 parts by weight of the inorganic pigment, (II) 0.001 to 10 parts by weight of the above-mentioned organosilicon compound (C), and (III) 10 to 10,000 parts by weight of water.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Component (I) of the pigment ink composition according to the invention is an inorganic pigment which is typically selected from carbon black, titanium oxide, and iron oxide, but not limited thereto. Of these, carbon black is preferred. These inorganic pigments may be used as such although inorganic pigments are preferably surface modified with an organic substance adsorbing or bonding to the surface, for enhancing the dispersion and stability thereof in a medium. For example, a pigment is treated with an organoalkoxysilane for enhancing the dispersion with the aid of a dispersant as described in JP-A 11-61012. Carbon black particles are surface modified by graft polymerization from polymerization initiator groups that are introduced to particle surfaces on the basis of carboxyl or phenolic hydroxyl groups on particle surfaces as described in Carbon, No. 140, 322 (1989) and Surface, No. 28, 286 (1990).
Component (II) is an organosilicon compound (C) which serves to bind the pigment component in the pigment ink composition to an object to be recorded. This component is effective only in a minor amount and does not adversely affect the storage stability of the pigment ink composition.
The organosilicon compound (C) is obtained by hydrolysis of (A) a hydrolyzable silane containing an amino group-bearing organic group represented by the following general formula (1):
YR
1
m
SiR
2
3−m
  (1)
wherein R
1
is a substituted or unsubstituted monovalent hydrocarbon group of 1 to 8 carbon atoms, R
2
is an alkoxy or acyloxy group of 1 to 4 carbon atoms, Y is an amino group-bearing organic group, and m is equal to 0 or 1, or a partial hydrolyzate thereof, and (B) a hydrolyzable silane represented by the following general formula (2):
R
3
n
SiR
4
4−n
  (2)
wherein R
3
is a substituted or unsubstituted monovalent hydrocarbon group of 1 to 8 carbon atoms, R
4
is an alkoxy or acyloxy group of 1 to 4 carbon atoms, and n is equal to 0, 1 or 2, or a partial hydrolyzate thereof.
The hydrolyzable silane containing an amino group-bearing organic group represented by formula (1) is a component for rendering the system soluble in water, that is, for endowing the end organosilicon compound (C) with water solubility. The hydrolyzable silanes may be used alone or in admixture of two or more while partial hydrolyzates thereof are also useful.
YR
1
m
SiR
2
3−m
  (1)
In formula (1), R
1
represents substituted or unsubstituted monovalent hydrocarbon groups of 1 to 8 carbon atoms, for example, unsubstituted monovalent hydrocarbon groups such as alkyl, alkenyl, aryl and aralkyl groups, and substituted monovalent hydrocarbon groups in which some or all of the hydrogen atoms on the foregoing groups are replaced by halogen atoms or the like, such as halogenated alkyl groups. Illustrative, non-limiting, examples include —CH
3
, —CH
2
CH
3
, —CH
2
CH
2
CH
3
, —CH(CH
3
)
2
, —CH
2
CH
2
CH
2
CH
3
, —CH(CH
3
)CH
2
CH
3
, —CH
2
CH(CH
3
)CH
3
, —C(CH
3
)
3
, —C
6
H
5
, and —C
6
H
13
.
R
2
represents alkoxy or acyloxy groups of 1 to 4 carbon atoms. Illustrative, non-limiting, examples include —OCH
3
, —OCH
2
CH
3
, —OCH
2
CH
2
CH
3
, —OCH(CH
3
)
2
, —OCH
2
CH
2
CH
2
CH
3
, —OCH(CH
3
)CH
2
CH
3
, —OCH
2
CH(CH
3
)CH
3
, —OC(CH
3
)
3
, —OCOCH
3
, and —OCOCH
2
CH
3
.
Y is an amino group-bearing organic group. For example, it is represented by the following formula (3).
Herein, R
5
and R
6
represent hydrogen or monovalent hydrocarbon groups of 1 to 8 carbon atoms, and they may be the same or different. R
7
and R
8
represent divalent hydrocarbon groups of 1 to 8 carbon atoms, and they may be the same or different. The letter p is 0 or an integer of 1 to 3. It is noted that the monovalent hydrocarbon groups of 1 to 8 carbon atoms are the same as described above for R
1
; and alkylene groups are exemplary of the divalent hydrocarbon groups of 1 to 8 carbon atoms.
Illustrative, non-limiting, examples of the amino group-bearing organic group represented by Y are given below.
H
2
NCH
2
—, H(CH
3
)NCH
2
—, H
2
NCH
2
CH
2
—, H(CH
3
)NCH
2
CH
2
—H
2
NCH
2
CH
2
CH
2
—, H(CH
3
)NCH
2
CH
2
CH
2
—, (CH
3
)
2
NCH
2
CH
2
CH
2
—, H
2
NCH
2
CH
2
NHCH
2
—, H(CH
3
)NCH
2
CH
2
NHCH
2
CH
2
CH
2
—, (CH
3
)
2
NCH
2
CH
2
NHCH
2
CH
2
CH
2
—, H
2
NCH
2
CH
2
NHCH
2
CH
2
NHCH
2
CH
2
CH
2
—, H(CH
3
)NCH
2
CH
2
NHCH
2
CH
2
NHCH
2
CH
2
CH
2
—.
Of these, H
2
NCH
2
CH
2
CH
2
—, H
2
NCH
2
CH
2
NHCH
2
CH
2
CH
2
— and H
2

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