| PATENT NUMBER | This data is not available for free |
| PATENT GRANT DATE | 19.09.2000 |
| PATENT TITLE |
Method for treating pigment particles to improve dispersibility and particle size distribution |
| PATENT ABSTRACT | Surface treated pigment particles made by contacting a dispersion of pigment particles with a halosilane or organohalosilane, elevating the temperature to form a siloxane on the surface of the particles and recovering the surface treated particles as a presscake or as dry particles. |
| PATENT INVENTORS | This data is not available for free |
| PATENT ASSIGNEE | This data is not available for free |
| PATENT FILE DATE | January 23, 1997 |
| PATENT REFERENCES CITED |
Document No. XP002062908, Publication Date Mar. 1993, Derwent, Abstract. Document No. XP002062909, Publication Date Dec. 1989, Derwent, Abstract. Document No. XP002062910, Publication Date Feb. 1992, Derwent, Abstract. Document No. XP002062912, Publication Date Mar. 1992, Derwent, Abstract. Document No. XP002062913, Publication Date Nov. 1991, Derwent Abstract. |
| PATENT CLAIMS |
What is claimed is: 1. A method for preparing surface treated pigment particles, said method consisting of (1) contacting a dispersion of pigment particles with a surface treating agent selected from the group consisting of halosilanes and organohalosilanes, at a temperature from about 0 to about 40.degree. C. while maintaining the particles in dispersion with high shear stirring, (2) heating the resulting dispersion to a temperature from about 40 to about 70.degree. C. while maintaining high shear stirring, (3) allowing the dispersion to cool to a temperature from about 15 to about 30.degree. C., and (4) recovering the resulting surface treated particles. 2. The method of claim 1, wherein the surface treated particles are recovered as a presscake. 3. The method of claim 1, wherein the surface treated particles are recovered as dry particles. 4. The method of claim 1, wherein the surface treating agent is added to the dispersion in an amount less than about 15% by weight of the pigment particles. 5. The method of claim 1, wherein the pigment particles are organic pigment particles. 6. The method of claim 2, wherein the pigment particles are organic pigment particles. 7. The method of claim 3, wherein the pigment particles are organic pigment particles. 8. The method of claim 1, wherein the pigment particles are inorganic pigment particles. 9. The method of claim 2, wherein the pigment particles are inorganic pigment particles. 10. The method of claim 3, wherein the pigment particles are inorganic pigment particles. 11. The method of claim 1, wherein the pigment particles are carbon black. 12. The method of claim 2, wherein the pigment particles are carbon black. 13. The method of claim 3, wherein the pigment particles are carbon black. 14. A method for preparing a pigment concentrate, consisting of (1) contacting a dispersion of pigment particles with a surface treating agent selected from the group consisting of halosilanes and organohalosilanes, at a temperature from about 0 to about 40.degree. C. while maintaining the particles in dispersion with high shear stirring, (2) heating the resulting dispersion to a temperature from about 40 to about 70.degree. C. while maintaining high shear stirring, (3) allowing the dispersion to cool to a temperature from about 15 to about 30.degree. C., (4) recovering the resulting surface treated particles as a presscake and (5) adding an organic vehicle to the resulting presscake. 15. A method for preparing a pigment concentrate, consisting of (1) contacting a dispersion of pigment particles with a surface treating agent selected from the group consisting of halosilanes and organohalosilanes, at a temperature from about 0 to about 40.degree. C. while maintaining the particles in dispersion with high shear stirring, (2) heating the resulting dispersion to a temperature from about 40 to about 70.degree. C. while maintaining high shear stirring, (3) allowing the dispersion to cool to a temperature from about 15 to about 30.degree. C., (4) recovering the resulting surface treated particles as dry particles and (5) adding an organic vehicle to the resulting surface treated dry particles. 16. A method for preparing a pigment dispersion, consisting of (1) contacting a dispersion of pigment particles with a surface treating agent selected from the group consisting of halosilanes and organohalosilanes, at a temperature from about 0 to about 40.degree. C. while maintaining the particles in dispersion with high shear stirring, (2) heating the resulting dispersion to a temperature from about 40 to about 70.degree. C. while maintaining high shear stirring, (3) allowing the dispersion to cool to a temperature from about 15 to about 30.degree. C., (4) recovering the resulting surface treated particles as a presscake, (5) adding an organic vehicle to the resulting presscake to form a pigment concentrate, and (6) dispersing the concentrate with one or more solvents selected from the group consisting of ketones, alcohols, alkanols, water, ethers, glycols, low polar organic solvents and non-polar organic solvents. 17. A method for preparing a pigment dispersion, consisting of (1) contacting a dispersion of pigment particles with a surface treating agent selected from the group consisting of halosilanes and organohalosilanes, at a temperature from about 0 to about 40.degree. C. while maintaining the particles in dispersion with high shear stirring, (2) heating the resulting dispersion to a temperature from about 40 to about 70.degree. C. while maintaining high shear stirring, (3) allowing the dispersion to cool to a temperature from about 15 to about 30.degree. C., (4) recovering the resulting surface treated particles as dry particles (5) adding an organic vehicle to the resulting surface treated dry particles to form a pigment concentrate, and (6) dispersing the concentrate with one or more solvents selected from the group consisting of ketones, alcohols, alkanols, water, ethers, glycols, low polar organic solvents and non-polar organic solvents . |
| PATENT DESCRIPTION |
FIELD OF THE INVENTION This invention relates generally to the field of pigments, and in particular to pigment particles that have been modified to enhance their use in various formulations, such as inks, paints, coatings and the like. BACKGROUND OF THE INVENTION Pigments that are used in polar environments must be readily dispersible, and must exhibit highly polar surface characteristics. The degree of polarity may extend to the degree of being hydrophilic. Accordingly, it is important for certain applications to be able to render hydrophilic or to increase the hydrophilicity of the surface of pigment particles. It is desired to make pigments that have a small particle size distribution, are highly dispersible in many kinds of solvents including water, require little or no grinding energy and exhibit good chemical resistance. Preferably such pigments should be made by an environmentally safe procedure. It is well known that polysiloxane materials have many useful attributes, such as surface tension energy reduction, high heat resistance, high chemical resistance, surface active properties, and dispersing ability, while being essentially nontoxic. Polysiloxanes are also useful because they exhibit good weatherability when used as coating materials and adhesives. A U.S. Pat. No. 5,364,633 disclosed the use of modified poly(dimethylsiloxane)s, which have hydrophilic or ionic moieties on their chains, as surfactants to entrap water-soluble and water-insoluble substances. The patent uses long poly(alkyleneoxide) chains with hydroxyl moieties at the end as the hydrophilic functions. Such compounds are quite costly to design and produce. Two Japanese published patent applications, JP4036370 and JP2218723, disclose coating inorganic pigments by using modified poly(dimethylsiloxane)s as chemically bound dispersing agents. They have functional group(s), such as amino, hydroxyl, alkoxyl or isocyanate, in one molecular terminal, and react with surface hydroxyl groups of the pigments to form a covalent bond. The surface coated pigments disperse well in non-aqueous solvent, especially silicon oil. They require severe reaction conditions and high production cost. There are many ways to produce siloxane coated dry pigments. However many such approaches require high power grinding to minimize the particle size of the pigment because of adhesion or cross-linking between the particles. Accordingly, a need exists for pigments that have one or more of the following properties: (1) exhibit a small particle size distribution, (2) have a high dispersibility in high polar solvents, including water, alcohols, ketones, ethers, and the like, (3) have a high dispersibility in low polar solvents, including oils and varnishes, (4) require little or no grinding energy, (5) have high chemical resistance and high color strength, and (6) can be manufactured in an environmentally safe manner. SUMMARY OF THE INVENTION In accordance with the present invention, surface treated pigment particles may be obtained. In each of the several embodiments of the present invention, the desired pigment particles are first suspended in an appropriate medium and then treated while in suspension, with a silane that can hydrolyze to form a siloxane. The treating is achieved by suspending the pigment in a suspension medium, using high shear mixing, and adding the silane to the suspension. The suspension is maintained with high shear mixing and is heated at an elevated temperature for a sufficient period of time to allow the silane to convert to the siloxane and to form a coating on the surface of the pigment particles. The coated particles may then be recovered by any of several techniques. If the pigment particles are coated in an organic suspension or a mixed aqueous organic suspension, the solvent that is used to form the suspension may be removed directly by drying or may be replaced by solvent washing with a more volatile solvent that then may be removed by drying. Similarly, if the pigment particles are coated in an aqueous suspension, the water that is used to form the suspension may be removed directly by drying or may be replaced by solvent washing with a more volatile solvent that then may be removed by drying. The treated pigment particles may also be recovered in the form of a presscake, without forming dry, intermediate pigment particles. Pigments, in any form, such as slurry, presscakes or dry, can be used as sources for use in the present invention. The coated pigments that result from the present invention require little or no grinding energy to be finely powdered. By way of appropriate selection of moieties attached on a silicon atom, the coated pigments may be formulated to disperse well in water as well as in high polar organic solvents. Furthermore, excellent dispersibility of the coated pigments in low polar organic solvents, vegetable oils, common drying oils, naphthenic oils and paraffinic oils is exhibited by using selected organohalosilanes that have hydrophobic moieties. Thus, in one embodiment, the invention provides a method for preparing surface treated pigment particles, said method comprising (1) contacting a dispersion of pigment particles with a surface treating agent selected from the group consisting of halosilanes and organohalosilanes, at a temperature from about 0 to about 40.degree. C. while maintaining the particles in dispersion with high shear stirring, (2) heating the resulting dispersion to a temperature from about 40 to about 70.degree. C. while maintaining high shear stirring, (3) allowing the dispersion to cool to a temperature from about 15 to about 30.degree. C., and (4) recovering the resulting surface treated particles. The surface treating agent may be added to the dispersion in an amount less than about 15% by weight of the pigment particles. The present invention also provides a pigment dispersion comprising (a) pigment particles having on their surface a polysiloxane surface treating agent, said particle having a particle size from about 0.04 micrometer to about 2 micrometer, and (b) a vehicle. The vehicle may be one or more solvents selected from the group consisting of ketones, alcohols, alkanols, water, ethers, glycols, low polar organic solvents and non-polar organic solvents. DESCRIPTION OF THE PREFERRED EMBODIMENTS Typically, the coating of the pigments is carried out by the reaction of halosilanes with water The reaction is completed by an interfacial polymerization because of incompatibility of the silanes to water. The coating is carried out by Van der Waals attraction between the resulting siloxane and the surface of the pigment. It is believed that there is no covalent bonding that occurs between the surface of the pigment particle and the resulting siloxane formed from the halosilane. The coated pigments that are made in accordance with the present invention are useful in paints, thermal ink ribbons, dry jet inks (solid ink for ink jet), ink jet inks (liquid ink), oil based inks, solvent based inks, water-based inks, thermally curable inks (by dehydration of silanol groups above 200.degree. C.), presscakes for all types of inks, toner for xerography, coloring material for fabrics, coloring material for thermoplastics, display panels. The chemistry behind the use of the water reactive halosilanes in the present invention is shown below: 1) Monohalosilane 2 R.sup.1 R.sup.2 R.sup.3 SiCl+H.sub.2 O.fwdarw.R.sup.1 R.sup.2 R.sup.3 SiOSiR.sup.3 R.sup.2 R.sup.1 +2 HCl 2) Dihalosilane ##STR1## or ##STR2## 3) Trihalosilane ##STR3## 4) Tetrahalosilane ##STR4## R, R.sup.1, R.sup.2, R.sup.3 : Any kind of moiety which does not involve heteroatoms. Two or three aromatic rings or moieties larger than those should not be involved in the monohalo and dihalo silanes. 5) Titanium tetrachloride TiCl.sub.4 +4 H.sub.2 O.fwdarw.Ti(OH).sub.4 +4 HCl Even if organic solvents are used to purify the pigments, the interfacial reaction occurs the same as if conducted in water because the organic solvent-treated pigments maintain a water layer on their surface. High shear mixing, with heat, is required to coat the pigment effectively. The coating mechanism is successful because of the relative affinities among siloxane, water (optionally with organic solvents) and the pigment surface. Since the siloxane has poor compatibility with water, it deposits on the surface of the pigments and the water prevents the agglomeration of the coated pigments. After drying, as with air drying at room temperature or 40 degrees C., the coated pigments separate easily. Pigments The pigments that are of use in the present invention include but are not limited to the following: Metallized Azo Reds: Red 49:1 (Barium salt), Red 49:2 (Calcium salt), Red 63:1 (Calcium salt) Toluidine reds Naphthol reds Pyrazolones Rhodamines Quiacridones: Red B, Red Y, Magenta B, Magenta and violet Phthalocyanine blues, including copper phthalocyanine blue Alkali Blue Phthalocyanine greens Carbazole violets Monoarylide Yellow Diarylide Yellow Red Lake C Lithol reds: calcium and barium salts Lithol rubine Bon Maroon Perylene pigments Red 2B: Calcium, Barium and Magnesium salts Chrome Yellow Chrome Orange Molybdate orange Orange 36, Diarylide orange, Dianisidine orange, tolyl orange and Dinitraniline orange Carbon black, titanium dioxide, and iron compounds Such pigments may have a wide range of particle sizes, as from about 0.02 micrometer to about 100 micrometer, preferably from about 0.04 micrometer to about 5 micrometer, and more preferably from 0.04 micrometer to 2 micrometer. Some of the commercially available pigments in dry form and in presscake form are resinated during the manufacturing processes, for example lithol rubine, to increase color strength and to control its particle size. The present invention is applicable to both organic pigments and inorganic pigments and to carbon black. Coating The coating may be formed by use of any of the silanes discussed above, which react to form siloxanes on the surface of the particles. Additionally, titanium tetrachloride may be used to modify the pigment particle surface. The Organic Media Any of a wide variety of organic media may be used for purposes of the present invention. An organic solvent may be used alone or in combination with water, depending upon the pigment condition before the surface treatment is carried out, such as slurry form in water, presscake form or dry form. The coating environment of the pigments started from a slurry (water) or presscake is a mixture of organic solvent(s) and water. The Washing Solvent Organic solvents that have relatively low boiling points around 100.degree. C. or less are typically used as the solvent for washing. Such solvents include n-propanol or ethanol. Area of Application The present invention is useful for making coated pigment particles that may find use in a wide variety of applications, such as ink for ink jet (continuous and drop-on-demand system), dry jet ink (solid ink for ink jet), thermal ink ribbon, oil based ink, solvent based ink, water based ink, water based paint and coatings, presscake for inks, toner for xerography, coloring material for fabrics, coloring material for plastics and display panels, and the like. EXAMPLES The present invention is further illustrated by the following non-limiting examples. For the examples, the following equipment, reagents and procedures were used, unless otherwise specified. Process Equipment A 1.2 L stainless steel container equipped with a disperser from Premier Mill Corp., Laboratory Dispersator, Series 2000, Model 90 (one horse power with a 2.5 inch blades) and a hot plate was used for all processes. A mixer from Charles Ross and Son Company, Model LDM-1QT, equipped with a heater and a vacuum pump was used for preparing ink concentrates from dry coated pigments with varnish as well as from coated pigment in presscake form by flushing water with the varnish. Particle Size Distribution Analysis A laser beam scattering particle size analyzer from HORIBA, Model LA-900 (range of particle size detection: 0.04 micrometer to 1000 micrometer), was used for the particle size distribution study on the surface treated pigments (in dry form and in presscake form) which were redispersed in a solvent. Ethanol was chosen as the solvent for the particle size analysis in the analyzer. Relative refractive indexes for the measurements were set at 1.41 for carbon black, copper phthalocyanine blue, lithol rubine, diarylid yellow and alkali blue (refractive index of carbon black: 1.92/refractive index of ethanol: 1.36) because of difficulty in getting the refractive index for the pigments, and at 1.84 for titanium dioxide (refractive index of titanium dioxide: 2.50/refractive index of ethanol: 1.36). Pigments for Surface Treatment Three presscakes, Copper Phthalocyanine Blue G/S (BL2101-PC), Lithol Rubine (LR5133-PC) and Diarylid Yellow (YA1933-PC) from Magruder Color Co. Inc., were used, as indicated in the examples A presscake, Alkali Blue (NB D6152), from BASF, was also used as indicated in the examples. Carbon Black, Elftex-8 in dry form from Cabot Corporation, Special Black Division and AJACK BLACK 5021, which was a pre-ground carbon black slurry, from Dispersion Solution Inc. were also used as indicated in the examples. Titanium dioxide in dry form from Nanophase was also used as indicated in the examples. Surface Coating Agents and Solvents Monoalkyltrichlorosilanes and dialkyldichlorosilanes were from Gelest, Inc. All other surface coating agents and all solvents were from Aldrich Chemical Company. Surface Coating Procedures 1. Treatment in Water A slurry (10 wt. % pigment) was reconstituted from a presscake (36 grams of pigment in dry weight) with water in the container. It was mixed well with the disperser at app. 1000 rpm for 20 min. A halosilane was added to the slurry slowly at high speed dispersing condition between 2000 rpm and 3000 rpm. After the addition of the silane the mixture was heated up to about 60 degrees C. with keeping the high speed dispersing condition at 3000 rpm for 30 min. Then the hot plate was removed from the reaction set and the mixture was cooled off by air with mixing at 2000 rpm. The surface treated pigment slurry was split by two and put in two 1 quart jars. About 200 grams of ethanol was added to the slurry in the jar and they were shaken by hands. After the treated pigments settled, the supernatant was decanted and the slurry was air-dried on watch glasses for overnight to 3 days. The addition of ethanol caused elimination of a certain amount of water from the slurry and accelerated the evaporation speed of water from it. The dried surface treated pigments were broken off by using a spatula in a 8 oz glass jar and redispersed in solvent(s) with sonication for 5 to 10 minutes to test their stability in solvent(s) and their particle size distributions. 2. Treatment in a Mixture of Organic Solvent and Water This is a method that allows for the purification of pigments in a slurry with impurities, such as salts, unreacted starting materials for the pigment production and organic materials. A slurry which contained 10 wt. % of pigment in water was reconstituted from a presscake in the container by stirring at 1000 rpm for 20 min. Xylene which is 1/6 of total water in the slurry was added slowly with stirring at 500 rpm. The phase separation was observed after about 5 min. The pigment was transferred to the xylene rich phase with a certain amount of water. A typical ratio of the ingredients in the xylene base paste is shown in Table 1. TABLE 1 ______________________________________ Percentage of Ingredients in Xylene Paste Weight Ingredients Percent ______________________________________ Copper Phthalocyanine 27.6 Blue Pigment Xylene 41.8 Water 30.6 Total 100.0 ______________________________________ The xylene paste which involved 36 grams of the pigment in dry weight was dispersed in 316 grams of xylene in the container with the disperser at 1000 rpm for 20 min. Then a halosilane was added slowly at room temperature in the high shear dispersing condition between 2000 rpm and 3000 rpm. After the addition of the silane compound the mixture was kept at 60 degrees C. for 30 minutes at 3000 rpm. The heater was removed from the reaction set and the mixture was cooled in air at 2000 rpm. The mixture then was treated as mentioned above in the section of "1. Treatment in Water" and the siloxane coated dry pigment was prepared. 3. Dry Pigments Dry pigments, such as carbon black, were dispersed in water with high shear dispersing condition at 1500 rpm to 2000 rpm for 30 minutes with heat around 60.degree. C. to prepare the 15 wt. % pigment loaded slurry. Then it was cool down to the room temperature with mixing at the same speed. The further surface treatments in the water or in the mixture of the organic solvent(s) and water, and the preparation of the siloxane coated dry pigment is shown above in both sections of "1. Treatment in water" and "2. Treatment in a mixture of organic solvent(s) and water". Preparation of Pigment Dispersion Approximately 1 wt. % pigment loaded dispersion was prepared in a 20 mL glass vial. It was sonicated for 20 minutes. Solvents for the pigment dispersions were water, ethanol, methylethylketone(MEK), toluene and soy oil. Testing Procedure of Stability of Pigment Dispersion After preparation, as described above, the dispersions were kept still on an experimental bench for 24 hours and the stability of the pigment dispersions was evaluated by observing the amount of settled pigment and the color of the supernatants. The dispersions were classified by four degrees of stability, as shown in Table 2. TABLE 2 ______________________________________ Explanation of Degree of Pigment Dispersion Stability Degree of Stability Explanation ______________________________________ E Suspended very well with no settling G Suspended well with a little settling P Poorly suspended with a large settling VP Totally settled ______________________________________ Preparation of Presscake Made From Coated Pigment Presscakes were prepared by filtration of the coated pigments in water-based slurries. Evaluation of Water Content in Presscake About 2 grams of the presscake was weighed in an aluminum cup and was set in a drying oven at 110.degree. C. for 18 hours to 24 hours. The water content was calculated from its weight loss. Evaluation of Pigment for Chemical Resistance The coated dry pigment was mixed with an acid fountain solution (pH: 4.64) and an alkaline fountain solution (pH: 9.98) individually in 20 ml glass vials to constitute about 1 weight percent dispersions. They were sonicated for a few minutes and kept still at room temperature for 24 hours. The color of the supernatants then was evaluated as being the chemical resistance. A stronger color showed poor chemical indicative of resistance, as being directly related to "bleeding" of an ink caused by a fountain solution during a printing process. This is important test for ionic pigments, such as Lithol Rubine and Alkali Blue. Evaluation of Pigment in Oil Based Ink The coated dry copper phthalocyanine blue pigment was mixed by hand with a varnish as shown in Table 3, at a ratio of 40/59 (pigment/varnish), by weight, to make an ink concentrate. The mixture was set in a mixer from Charles Ross and Son Company, Model LDM-1QT, equipped with a heater and mixed at 70.28 rpm for 30 minutes at 40.degree. C. After the ink concentrate was allowed to cool, at room temperature, one part of an anti-oxidant (10 weight percent of BHT in Aged Linseed Oil) was added and mixed at the same speed for 10 minutes. TABLE 3 ______________________________________ Ingredients of Varnish* Ingredients Weight Percent ______________________________________ Aged Linseed Oil 71.43 Pentrex 859HV from Harcules 22.86 Acryloid-R DM-55 from Rhom and Haas 5.71 Total 100.00 ______________________________________ *: The varnish was prepared in nitrogen atmosphere. The ink concentrate was mixed by hand with a heat set let-down varnish as shown in Table 4 a ratio of 42/58 (ink concentrate/varnish), by weight, to prepare a heat set ink. The ink was mulled 200 revolutions with a 10 LB weight by using a Hoover Automatic Muller Model M5 from Hoover Muller Color Corporation. TABLE 4 ______________________________________ Formulation of Heat Set Let-down Varnish Ingredients Weight Percent ______________________________________ Exoset HS-126-G* 65.5 Exoset Q.S. 128 FF* 10.3 Capsule Softening Vehicle NVFG-380* 5.2 Poly/PTFE Compound from Lawter 5.2 International Inc. Exoset FF Varnish X-200-82A* 12.1 COVI-OX T-70 from Henkel Corp. 1.7 Total 100.0 ______________________________________ *: From Walsh Manufacturing Company. An off-set color swatching press from Little Joe Color Swatcher Inc., was employed for printing inks on sheets of coated stock paper. They were heatset at 250.degree. F. by using a heater from SQG Industries. Five samples were prepared for each ink. The color quality of the inks, such as L, a and b values, was measured by using a spectrophotometer from Hunter Lab, Model 45/0 Color Quest. The gloss of the printed ink was evaluated by using a gloss meter from Hunter Lab (ProGloss) at 60 degree. A densitometer from Macbeth, Model RD918, was employed to measure the density of the samples. All data were the average of the five printed samples. A Laray viscometer was employed for the Theological analysis of the heatset inks, such as Viscosity, Yield Value and Shortness Factor. |
| PATENT EXAMPLES | This data is not available for free |
| PATENT PHOTOCOPY | Available on request |
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