Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1998-07-24
2001-05-22
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C523S210000
Reexamination Certificate
active
06235829
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to hydrophobic modification of chargeable pigment particles and non-polar suspensions of such pigment particles.
BACKGROUND OF THE INVENTION
Stable suspensions of chargeable pigment particles are desirable in certain applications wherein the formation of images (permanent or latent) requires charging or discharging the pigment particles. Such applications include liquid toners, ink jet inks using solvents and electrostatic paints.
The preparation of such suspensions has been documented in literature. To stabilize hydrophilic pigments in non-polar solvents, steric barriers are introduced to provide stabilization. Common strategies to do so include the use of ionic surfactants or polymeric dispersants which adsorb on the pigment (e.g., U.S. Pat. Nos. 5,536,615 and 5,482,809); dendrimers (e.g., U.S. Pat. No. 5,558,968) or non-polymeric resins (e.g., U.S. Pat. No. 5,521,046) to modify the pigment surface. Though polymeric dyes (U.S. Pat. Nos. 5,521,271 and 5,563,024) have been disclosed as alternatives to pigments for use in such applications, their inferior lightfastness and weatherability, coupled with their relatively high production costs, have restricted their usage.
Stable suspensions of chargeable pigment particles in non-polar solvents is difficult to prepare, mainly for two reasons. First, many chargeable pigment particles contain surface polar functional groups like carboxylic acid. In addition to rendering the pigment chargeable, these polar functional groups also make the pigment hydrophilic. In non-polar systems containing non-polar solvents, the hydrophilicity of the pigment particles causes them to be attracted to each other rather than to the non-polar solvent, resulting in flocculation and destabilization of the pigment suspension.
Second, in contrast to the possibility of applying both steric and electrostatic interactions to combat flocculation in polar systems, mainly steric interaction can be applied in non-polar systems. In most cases, surfactants are used to provide steric stabilization in suspending such particles. The polar ends of the surfactants adsorb onto the hydrophilic pigment surface, and the hydrophobic portion is solvated by the non-polar solvent. This mode of weak attachment leads to flocculation and degradation of the non-polar suspension. A disadvantage of using physically adsorbed surfactants or dispersants in suspensions is that under external stress, like a high electric field, some of these suspensions or formulations become unstable. This is due to the dissociation or desorption of a surfactant or resin from the pigment particle surface.
The use of dendrimers that are covalently bonded to pigment surfaces partially addresses the problem of desorption, but the process of assembling such a complex molecular architecture on the pigment surface translates into a lengthy preparation and high production cost.
A need therefore exists for a method of making a non-polar suspension of chargeable pigment particles that does not suffer from problems such as desorption, and is available as a lower cost alternative to the use of dendrimers and the like.
SUMMARY OF THE INVENTION
The foregoing needs have been fulfilled to a great extent by the present invention which provides a method for making a non-polar suspension of chargeable pigment particles comprising (1) forming a suspension of pigment particles in a non-polar solvent, wherein the pigment particles are inherently ionic or are chargeable and possess surface anchoring groups on the surface of the pigment particles; and (2) contacting the pigment particles with a polymeric resin comprising a hydrophobic region and a reactive group that reacts with the surface-anchoring groups on the surface of the pigment particle. Preferably, the reactive groups form a covalent bond between the pigment and the polymeric resin.
The present invention further provides a non-polar suspension of inherently ionic or chargeable pigment particles having surface-anchoring groups on the surface of the particles. The suspension comprises the pigment particles suspended in a non-polar solvent, wherein the pigment particles have on their surface a polymeric resin that comprises a hydrophobic region and a reactive group that reacts with the surface-anchoring groups on the pigment surface.
The present invention further provides a method of hydrophobically modifying chargeable pigment particles having a first functional group, the method comprising contacting the pigment particles with a polymer having a hydrophobic region and a second functional group in such a way as to form a covalent bond between the first and second functional groups.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention provides a method for making a non-polar suspension of chargeable pigment particles comprising (1) forming a suspension of pigment particles in a non-polar solvent, wherein the pigment particles are inherently ionic or are chargeable and possess surface anchoring groups on the surface of the pigment particles; and (2) contacting the pigment particles with a polymeric resin comprising a hydrophobic region and a reactive group that reacts with the surface-anchoring groups on the surface of the pigment particle. The surface anchoring group and the polymeric resin can form a covalent or hydrogen bonding, preferably a covalent bond. The polymeric resin preferably comprises a maleic anhydride group.
The present invention also provides a non-polar suspension of inherently ionic or chargeable pigment particles having surface-anchoring groups on the surface of the particles. The suspension comprises the pigment particles suspended in a non-polar solvent, wherein the pigment particles have on their surface a polymeric resin that comprises a hydrophobic region and a reactive group that reacts with the surface-anchoring groups on the pigment surface.
The pigment particles for modification according to the present invention advantageously have two desirable properties: chargeability and susceptibility to being modified. Chargeability is imparted by the reactive or functional groups present on the pigment. Thus, chargeable pigments can be divided into two categories. The first category includes pigments that are inherently ionic in character. Examples of this type of pigment include complexes of transitional metals, e.g., iron blue; and ionic compounds, e.g., calcium sulfate. Some pigments contain residual ionic species on their surface, as a result of an inefficient washing process. Although such pigments may be used in the present process, since the ionic species on the pigment surface are not bound tightly on the surface, they may be lost or washed off during the process steps, and hence chargeability of such pigments may not be satisfactory and may vary from batch to batch.
The second category of chargeable pigments includes pigments that are not inherently ionic and yet possess chargeable groups on the surface. These groups include, but are not limited to, carboxylic groups, hydroxyl groups including phenolic hydroxyl groups, alkyl hydroxyl groups, and alkenyl hydroxyl groups, amino groups which may be primary, secondary, tertiary or quaternary ammonium groups, quinoline groups, and other functional groups that contain heteroatoms such as nitrogen, oxygen, or sulfur. Examples of pigments possessing such groups include oxidized carbon black. A particularly suitable oxidized carbon black pigment is FX™ 200 supplied by Degussa Company (Ridgefield Park, N.J.). Those of ordinary skill in the art know that oxidized carbon black contains carboxyl, hydroxyl, keto, aldehyde, and/or other chargeable groups. Other examples of pigments include Hansa Yellow, Dinitroaniline Orange, Naphthol Red, Red Lake C, Lithol Red, Rubine Red, Dianisidine Blue, Alizarin Lake, and Nickel Azo Yello, which bear hydroxyl groups, and Disperse Yellow 9, Disperse Black 1, and Solvent Brown, which bear amino groups.
The second property desirable in a pigment is its susceptibility or reactivity to permit surface mo
Cain Edward J.
Leydig , Voit & Mayer, Ltd.
Marconi Data Systems Inc.
LandOfFree
Modification of chargeable pigment particles does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Modification of chargeable pigment particles, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Modification of chargeable pigment particles will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2554871