Phosphorylated polymer dispersants for inks

Details Phosphorylated polymer dispersants for inks Phosphorylated polymer dispersants for inks

1999-08-04

2002-08-13

Zitomer, Fred (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C106S031130, C106S031250, C526S274000, C526S320000, C526S333000

Reexamination Certificate

active

06433117

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to monomers comprising a phosphate functionality, copolymers comprising these monomers and aqueous dispersions comprising such copolymers.
BACKGROUND OF THE INVENTION
Thermal ink jet printers vaporize ink in print heads by resistive heating. Vaporized ink is expelled through orifices toward substrates and any ink remaining in the print head is cooled before the next round of heating and vaporization. This process of vaporization and cooling, known as firing, usually occurs at high frequency in print heads drastically changing ink from water-rich to solvent-rich compositions around resistors. These changes may cause flocculation of insoluble particles, such as pigments. Additives such as polymer binders, thickeners, organic cosolvents and surfactants, in addition to the firing process described above, may further increase flocculation during printing. Flocculation of ink and plugged print heads are undesirable characteristics in the ink jet printer industry.
To avoid flocculation, dispersants added to inks increase the length of time insoluble particles remain in a dispersed state (i.e., increasing dispersion stability of an ink). However, the effectiveness of dispersants are dependent, in part, on the composition of inks and the environment under which inks are stored or used. Development of new polymer dispersants, which maintain particles in a dispersed state during various chemical and physical conditions are desirable characteristics.
One goal of ink jet printing technology is to spray ink onto a substrate, such as paper, and form discrete characters. It is well known that ink placed in contact with a substrate may ink bleed and/or color bleed. Ink bleed refers to the spreading out of ink on a substrate. Color bleed refers to ink mixing at ink boundaries between two or more ink droplets.
SUMMARY OF THE INVENTION
The present invention relates to copolymer dispersants having one or more phosphate functionality, which are able to maintain aqueous dispersions in dispersed states, in part, under differing pH conditions. Copolymers of the present invention are preferably used as dispersants and are prepared from ethylenically unsaturated monomers having a phosphate functionality that provides electrostatic interaction and a structure that provides steric interaction between insoluble particles in aqueous dispersions. These inventive copolymers may be used to produce aqueous dispersions having a distinct pH (in part, due to the pKas of the phosphate functionality) within a wide pH range. Inks of the present invention (including an inventive copolymer) may be used to reduce color bleed and increase print quality. A copolymer of the present invention is prepared using one or more ethylenically unsaturated monomers including a phosphate monomer having the general formula:
CH
2
═C(R
3
)C(O)OX
a
(C
2
H
4
O)
b
—(C
3
H
6
O)
c
—R
4
where a=0 or 1; when a=1, X is an akyl, aryl, or alkaryl diradical connecting group of 1-9 carbon atoms; b and c are independently selected from the range of 0-100 provided that b and c are not simultaneously 0; R
3
is H or CH
3
; and R
4
is selected from the group consisting of PO
3
H
2
, alcohol and epoxy.
The present invention also provides aqueous dispersions, preferably an aqueous ink for use in ink jet printers, comprising an aqueous carrier, a colorant, and a copolymer dispersant comprising at least one polymerized phosphate monomer.
The present invention provides for articles comprising a substrate having a first and a second major surface and a layer, preferably a noncontiguous layer (e.g., one or more drops of ink), of aqueous dispersion attached to the substrate. The aqueous dispersion comprising a colorant and an inventive copolymer dispersant comprising at least one polymerized phosphate monomer.
As used herein, with respect to the present invention, the following shall apply:
“phosphate monomer” refers to an ethylenically unsaturated monomer of the present invention having the general formula:
CH
2
═C(R
3
)C(O)OX
a
(C
2
H
4
O)
b
—(C
3
H
6
O)
c
—R
4
wherein a=0 or 1; when a=1, X is an akyl, aryl, or alkaryl diradical connecting group of 1-9 carbon atoms; b and c are independently selected from the range of 0-100 provided that b and c are not simultaneously 0; R
3
is H or CH
3
; and R
4
is selected from the group consisting of PO
3
H
2
, an alcohol group or an epoxy group. The alcohol and/or epoxy group may be converted into phosphate functionalites as described herein.
“polymerized phosphate monomer” refers to a unit of a polymer including the structure:
CH
2
═C(R
3
)C(O)OX
a
(C
2
H
4
O)
b
—(C
3
H
6
O)
c
—PO
3
H
2
prepared from the above described phosphate monomer.
“polymerized monomer” refers to a unit of a polymer prepared from a monomer.
DETAILED DESCRIPTION OF THE INVENTION
Copolymers of the present invention are preferably used as dispersants and may comprise one or more polymerized phosphate monomers. Aqueous dispersions, such as inks, comprising such copolymer have good dispersion stability and may be used in ink jet printers, preferably thermal ink jet printers. Inks of the present invention may be adapted to meet the requirements of a particular ink jet printer, such as to provide a balance of light stability, smear resistance, viscosity, surface tension, optical density, and pluggage resistance as desired for the particular application. The aqueous dispersion of the present invention may also be suitable for other applications such as paints or protective coatings.
Copolymer Dispersants
Copolymer dispersants of the present invention comprise one or more polymerized phosphate monomers, which are prepared from phosphate monomers having the general formula:
CH
2
═C(R
3
)C(O)OX
a
(C
2
H
4
O)
b
—(C
3
H
6
O)
c
—R
4
where a=0 or 1; when a=1, X is an akyl, aryl, or alkaryl diradical connecting group of 1-9 carbon atoms; b and c are independently selected from the range of 0-100 provided that b and c are not simultaneously 0; R
3
is H or CH
3
; and R
4
is selected from the group consisting of PO
3
H
2
, an alcohol group or an epoxy group.
When R
4
is an alcohol group and an epoxy group, these monomers maybe phosphorylated with phosphorylating agents such as POCl
3
, polyphophoric acid, preferably P
2O
5
prior to a polymerization process. Alternatively, monomers having an R
4
selected from an alcohol group or an epoxy group may be incorporated into a copolymer of the present invention and then the copolymer is treated with one or more phosphorylating agents to form one or more phosphate functionalities where the epoxy group(s) or the alcohol group(s) use to be.
The polymerization of phosphate monomers creates copolymers having structures that are either random or comb. A comb structure, as used herein, refers to a copolymer of the present invention including polymerized phosphate monomers wherein b plus c are 3 or greater (i.e., the monomers stick out from the copolymer chain creating a copolymer having a comb structure). Not to be held to any particular theory, the length of phosphate monomer is thought to sterically hinder agglomeration of insoluble particles in a dispersion. A random structure, as used herein, refers to a copolymer of the present invention including polymerized monomers wherein b plus c are less than 3. Copolymers of the present invention may include from 5 weight percent to 90 weight percent, preferably 5 weight percent to 60 weight percent, most preferably 20 weight percent to 60 weight percent of polymerized phosphate monomer.
Copolymers of the present invention may be prepared from hydrophilic monomers such as ethylenically unsaturated monomers having acid or acid precursor groups. Examples of useful monomers include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, itaconic acid monoester, maleic acid, maleic acid monoester, fumaric acid, fumaric acid monoester, and the like.
Copolymers of the present invention may be prepared from hydrophobic monomers such as unsaturated monomers select

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