Polymeric binders for ink jet inks

Details Polymeric binders for ink jet inks Polymeric binders for ink jet inks

2003-01-16

2004-06-01

Lipman, Bernard (Department: 1713)

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

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S245000, C526S281000, C526S287000

Reexamination Certificate

active

06743875

ABSTRACT:

This invention concerns polymeric binders which are suitable for use in ink jet inks. More specifically, this invention relates to polymeric binders formed by polymerization of a monomer mixture comprising a polymerizable surfactant monomer.
Certain ink jet inks comprise a liquid medium, a colorant, such as a pigment or dye, a binder or resin to aid in dispersing the pigment in the medium and to affix the colorant to the print surface. In order to create more durable print quality, particularly in terms of color-fastness and water- and rub-resistance of the printing ink, there has been interest in preparing ink jet inks in which the colorant is an insoluble pigment, rather than a water soluble dye. The latter are generally absorbed to some degree by the paper or other print medium, but due to their inherent water-solubility do not offer good waterfastness. Pigment-based inks are generally deposited on the surface of the print medium, making them susceptible to removal by water or abrasion. However, as a result of the physical properties of pigments, pigment based ink compositions have a tendency to have a low wet-rub resistance and low highlighter resistance.
The term “wet-rub,” as used herein, means applying abrasive pressure across the printed substrate with a wetted paper facial tissue and measuring any smear created thereby; wet-rub differs from waterfastness because abrasion is used. The term “highlighter resistance,” as used herein, means applying abrasive pressure across a printed substrate with a commercially available highlighting marker and measuring any smear created thereby; an example of such marker is Sanford Corp. Major Accent brand highlighting markers. The term “print quality”, as used herein, means an accumulative evaluation of the overall performance of an ink jet ink as measured by the appearance of a printed page of combined text and graphics, including edge sharpness, bleed, feathering, optical density, wet-rub resistance, highlighter resistance and print operability. The term “print operability”, as used herein, means an accumulative evaluation of printer performance, including print appearance and uniformity, page after page longevity of print quality and uniformity, nozzle drop outs, print head maintenance problems, and the ability to stop and restart printing.
Polymer binders have been added to ink jet ink compositions to improve durability, to improve print quality and to reduce color bleeding and feathering. However, the inclusion of such binders can result in increased printhead maintenance problems, including clogging of the nozzles and kogation, i.e. formation of film on or about the heater. Also, polymers may tend to form films on the nozzle plate. The addition of polymers to ink jet ink compositions also may cause decreased pigment dispersion stability and interference with bubble formation.
EP-A-0869 160 discloses an inkjet ink formulation with colorant, vehicle and resin emulsion containing ionic carboxylic groups on the surface of resin emulsion particles to cause disassociation of the colorant and resin particles. The resin has 1 to 40 wt. % “carboxylic acid groups”, and Tg of 0 to 120° C. Exemplified embodiments of the resin include copolymers of butyl acrylate, methyl methacrylate and (meth)acrylic acid, with 3 to 20 wt. % acid, Tg of 53 to 95° C. and particle size of 63 to 235 nm, utilizing high Tgs and low particle sizes.
EP-A-0747456 discloses a method for providing a waterborne coating composition, such as a paint, having improved color acceptance. The coating composition contains an emulsion-polymerized addition polymer formed from a mixture of monomers including a polymerizable surfactant monomer. There is no disclosure of the use of the addition polymer in an ink.
It is an object of the present invention to provide a polymeric binder for use with a colorant to form an ink jet ink that demonstrates an improved print quality, as expressed by an improvement in one or more properties used to determine print quality, which improvement is achieved without any significant detrimental effect on the other properties used to determine print quality.
In accordance with the present invention, there is provided a polymeric binder suitable for use in an ink composition, preferably an ink jet ink composition, comprising a colorant and a polymeric binder, wherein the polymeric binder is an emulsion-polymerized addition copolymer formed from a monomer mixture comprising ethylenically unsaturated monomers including from more than 4 to 15 wt % based on the weight of said mixture of at least one ethylenically unsaturated carboxylic acid functional monomer, and from 0.05 to 5 wt % based on the weight of said mixture of at least one polymerizable surfactant monomer comprising hydrophobic and hydrophilic functional groups, wherein said hydrophobic functional group comprises a polymerizable group within it.
In another aspect, there is provided an ink composition, preferably an ink jet composition, comprising a colorant and a polymeric binder, wherein the polymeric binder is an emulsion-polymerized addition copolymer formed from a monomer mixture comprising ethylenically unsaturated monomers including from more than 4 to 15 wt % based on the weight of said mixture of at least one ethylenically unsaturated carboxylic acid functional monomer, and from 0.05 to 5 wt % based on the weight of said mixture of at least one polymerizable surfactant monomer comprising hydrophobic and hydrophilic functional groups, wherein said hydrophobic functional group comprises a polymerizable group within it.
In yet another aspect of the present invention, there is provided the use of an emulsion-polymerized addition copolymer, formed from a monomer mixture comprising ethylenically unsaturated monomers including from more than 4 to 15 wt % based on the weight of said mixture of at least one ethylenically unsaturated carboxylic acid functional monomer and from 0.05 to 5 wt % based on the weight of said mixture of at least one polymerizable surfactant monomer comprising hydrophobic and hydrophilic functional groups, wherein said hydrophobic functional group comprises a polymerizable group within it, as a polymeric binder in an ink composition, preferably an ink jet composition, to improve the print quality of said ink composition.
Surprisingly, ink jet inks comprising a binder of the present invention demonstrate improved print quality over binders of similar composition but which do not comprise a polymerized surfactant monomer. In addition, ink jet inks of the present invention may demonstrate an improved optical density.
Polymerizable surfactant monomers are known in the art. They are surface active compounds having a polymerizable group, such as an allyl, acryl, methallyl or methacryl group (herein also referred to as (meth)acryl or (meth)allyl group), and which may be used as an emulsifier in an emulsion polymerization. Thus, the polymerizable surfactant functions as both a surfactant and as a comonomer. The polymerizable surfactant may be cationic, anionic or nonionic. Suitable polymerizable surfactant monomers comprising hydrophobic and hydrophilic functional groups, wherein said hydrophobicfunctional group comprises a polymerizable group within it include, for example, anionic surfactant monomers such as sulphates, phosphates, sulphosuccinate half esters, and sulphosuccinate diesters bearing copolymerizable reactive groups and nonionic surfactant monomers such as nonylphenoxy propenyl polyethoxylated alcohols (for example as Noigen RN-20 from Dai-ichi Corp). Preferred polymerizable surfactant monomers are nonylphenoxy propenyl polyethoxylated sulphate (for example as Hitenol from Dai-ichi Corp); sodium alkyl allyl sulphosuccinate (for example as Trem LF-40 from Henkel Corp); ammonium di-(tricyclo(5.2.1.0 2,6) dec-3-en-(8 or 9)oxyethyl) sulfosuccinate; and ammonium di-(tricyclo(5.2.1.0 2,6) dec-3-en-(8 or 9) sulfosuccinate. Additionally, the ammonium and metal salts of unsaturated C
6
to C
30
organic acids may be suitable, these may be used alone or in combination with

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