Patent Description:
In order to facilitate even distribution of inorganic pigments into base compositions, the pigments are typically formed into finely divided powders. For example, the particle size of a pigment can be reduced by milling or micronizing the pigment during the finishing steps of the pigment manufacturing process.

Unfortunately, pigment powders tend to be dusty and exhibit poor flow characteristics. These issues can make the pigment powders difficult to bag and transport and create problems in forming, compounding and manufacturing end-use products. The poor flow characteristics of the pigment particles can make the amount of time and energy needed to sufficiently disperse the particles into base compositions excessively high. Dispersion of pigment powders into polymer compositions can be particularly problematic.

Increasing the ability of inorganic pigments to be dispersed into base compositions makes the pigments more suitable for end use applications. <CIT> describes particulate titanium dioxide having on the particles thereof an ester or partial ester of an organic hydroxyl compound containing <NUM> to <NUM> OH groups and an aliphatic saturated C<NUM> to C<NUM> monocarboxylic acid. <CIT> describes thermoplastic concentrates comprising inorganic pigments, such as titanium dioxide, treated with a partial ester polyol and unsaturated monocarboxylic acid treating agent, of the formula R(OH)xCOOR', wherein R is an alkyl or aryl radical containing from about <NUM> to about <NUM> carbon atoms, R' is an unsaturated alkyl radical containing from about <NUM> to about <NUM> carbon atoms, and x is a number from about <NUM> to about <NUM>.

The present disclosure may be understood more readily by reference to this detailed description as well as to the examples included herein. Numerous specific details are set forth in order to provide a thorough understanding of the examples described herein. However, it will be understood by those of ordinary skill in the art that the examples described herein can be practiced without these specific details. In other instances, methods, procedures and components have not been described in detail in order to avoid obscuring the related relevant feature being described. Also, the description is not to be considered as limiting the scope of the examples.

In accordance with this disclosure, a treated, particulate inorganic pigment, and a method of forming a treated, particulate inorganic pigment are provided. In another aspect, this disclosure includes a polymer composition that includes a treated, particulate inorganic pigment.

The treated, particulate inorganic pigment disclosed herein comprises a plurality of pigment particles, and a trimethylolpropane ester deposited on the surfaces of the pigment particles. As used herein and in the appended claims, "deposited" on the surfaces of the pigment particles means deposited directly or indirectly on the surfaces of the pigment particles unless stated otherwise.

For example, the pigment particles of the treated, particulate inorganic oxide pigment disclosed herein can be formed of a pigment selected from the group consisting of titanium dioxide, basic carbonate white lead, basic sulfate white lead, basic silicate white lead, zinc sulfide, composite pigments of zinc sulfide and barium sulfate, zinc oxide, antimony oxide, iron oxide, lead oxide, aluminum oxide, silicon dioxide, chromium oxide, zirconium oxide, calcium carbonate, calcium sulfate, china clay, kaolin clay, mica, diatomaceous earth, cadmium sulfide, cadmium selenide, lead chromate, zinc chromate, nickel titanate, and mixtures thereof. For example, the pigment particles can be formed of titanium dioxide. For example, the titanium dioxide can have a rutile crystalline structure or a combination of an anatase crystalline structure and a rutile crystalline structure. For example, the titanium dioxide can have a rutile crystalline structure. For example, the titanium dioxide can be formed by the sulfate or the chloride process. For example, the titanium dioxide can be formed by the chloride process.

In the sulfate process for manufacturing the titanium dioxide, for example, a titanium slag ore is dissolved in sulfuric acid to form titanyl sulfate. The titanyl sulfate is then hydrolyzed to form hydrous titanium dioxide. The hydrated titanium dioxide is heated in a calciner to grow titanium dioxide crystals to pigmentary dimensions.

In the chloride process for manufacturing the titanium dioxide, for example, a dry titanium dioxide ore is fed into a chlorinator together with coke and chlorine to produce a gaseous titanium halide (such as titanium tetrachloride). The produced titanium halide is purified and oxidized in a specially designed reactor at a high temperature to produce titanium dioxide particles having a desired particle size. Aluminum chloride or some other co-oxidant is typically added to the titanium halide in the oxidation reactor to facilitate rutile formation and control particle size. The titanium dioxide and gaseous reaction products are then cooled and the titanium dioxide particles are recovered.

The pigment particles of the treated inorganic oxide disclosed herein can be treated with various components as known in the art. For example, at least one inorganic coating can be deposited on the surfaces of the pigment particles. For example, at least one inorganic coating selected from the group consisting of metal oxide coatings, metal hydroxide coatings, and mixtures thereof can be deposited on the surfaces of the pigment particles. For example, at least one inorganic coating selected from the group consisting of silica coatings, alumina coatings, and mixtures thereof can be deposited on the surfaces of the pigment particles. The inorganic coating(s) can be used to impart one or more properties and/or characteristics to the pigment particles to make the pigment particles more suitable for specific end uses. For example, silica and/or alumina coatings can be used to help improve the wetting and dispersing properties of the pigment particles.

The trimethylolpropane ester deposited on the surfaces of the pigment particles is obtainable by reacting at least one saturated fatty acid with trimethylolpropane. The fatty acid(s) partially or fully esterifies the trimethylolpropane to form a trimethylolpropane ester.

For example, the fatty acid(s) used to form the trimethylolpropane ester can be a monobasic or dibasic, linear or branched, saturated fatty acid. For example, the fatty acid(s) can be a saturated, straight chain fatty acid. For example, the fatty acid(s) can be a saturated, branched chain fatty acid. For example, the fatty acid(s) can be a dimer acid. For example, the fatty acid(s) can have from <NUM> to <NUM> carbon atoms. For example, the fatty acid(s) can have from <NUM> to <NUM> carbon atoms. By way of further example, the fatty acid(s) can have from <NUM> to <NUM> carbon atoms.

For example, the fatty acid(s) used to form the trimethylolpropane ester can be selected from the group consisting of trimethyl hexanoic acid, octanoic acid, decanoic acid, dodecanoic acid, myristic acid, stearic acid, caprylic acid, capric acid, lauric acid, palmitic acid, arachic acid, behenic acid, adipic acid, sebacic acid, azelaic acid, and mixtures thereof. For example, the fatty acid(s) can be selected from the group consisting of stearic acid, caprylic acid, capric acid, lauric acid, and mixtures thereof.

As another example, the fatty acid(s) used to form the trimethylolpropane ester can be a fatty acid that has been reacted with a silicone compound to form a silicone modified fatty acid or a fatty acid modified silicone. As used herein and in the appended claims, "silicone modified fatty acid" and "fatty acid modified silicone" mean the same thing and may be used interchangeably. For example, fatty acid modified silicones suitable for use herein can have the following formula:
<CHM>
wherein R1, R2, R3 and R4 are each selected from a hydrogen moiety, a methyl (CH<NUM>) group and a higher alkyl group, and wherein R1, R2, R3 and R4 can be the same or different.

If two or more fatty acids are used to partially or fully esterify the trimethylolpropane, the type and characteristics of each fatty acid within the above parameters can vary.

For example, the trimethylolpropane ester is obtainable by reacting at least one fatty acid selected from the group consisting of stearic acid, caprylic acid, capric acid, lauric acid, a fatty acid modified silicone, and mixtures thereof with trimethylolpropane. For example, the trimethylolpropane ester is obtainable by reacting at least one fatty acid selected from the group consisting of stearic acid, caprylic acid, capric acid, lauric acid, a fatty acid modified silicone, and mixtures thereof with trimethylolpropane.

For example, the trimethylolpropane esters can be selected from the group consisting of trimethylolpropane trilaurate, trimethylol propane tricocoate, trimethylol propane tristearate, and mixtures thereof.

An example of a specific trimethylolpropane ester that can be used is shown below:
<CHM>.

Examples of suitable trimethylolpropane esters that include a silicone functional group (also called silicone multi-esters) and that are suitable for use as the trimethylolpropane ester disclosed herein are sold by Siltech Corporation in association with the trade name Silube® TMP D2 (branched silicones with C8/C10 fatty groups), Silube® TMP D219 (branched silicones with C18 fatty groups), and Silube® TMP D218 (branched silicones with branched C18 fatty groups).

An example of a trimethylolpropane ester made by reacting a fatty acid modified silicone (FAS) with trimethylolpropane (TMP) is shown below:
<CHM>
Examples of fatty acid modified silicones that can be the fatty acid modified silicone in the above formula (FAS) include the following:
<CHM>
<CHM>
wherein R1, R2, R3, R4, R5 and R6 can each be selected from a hydrogen moiety, a methyl (CH<NUM>) group and a higher alkyl group, and wherein R1, R2, R3, R4, R5 and R6 can be the same or different.

For example, the trimethylolpropane ester can be deposited on the surfaces of the pigment particles in an amount in the range of from about <NUM>% to about <NUM>% by weight, based on the total weight of the pigment particles. For example, the trimethylolpropane ester can be deposited on the surfaces of the pigment particles in an amount in the range of from about <NUM>% to about <NUM>% by weight, based on the total weight of the pigment particles. For example, the trimethylolpropane ester can be deposited on the surfaces of the pigment particles in an amount in the range of from about <NUM>% to about <NUM>% by weight, based on the total weight of the pigment particles. The exact amount of the trimethylolpropane ester deposited on the surfaces of the pigment particles will typically vary depending on the application.

If desired, two or more trimethylolpropane esters as described above can be deposited on the surfaces of the pigment particles.

The method of forming a treated, particulate inorganic pigment in accordance with this disclosure comprises providing a plurality of pigment particles, providing a trimethylolpropane ester, and depositing the trimethylolpropane ester on the surfaces of the pigment particles. The pigment particles used in the method are the pigment particles described above. The trimethylolpropane ester used in the method is the trimethylolpropane ester described above. For example, the pigment particles can be titanium dioxide particles.

For example, at the time the trimethylolpropane ester is deposited on the surfaces of the pigment particles, the pigment particles can have a primary particle size in the range of from about <NUM> microns to about <NUM> microns, typically in the range of from about <NUM> microns to about <NUM> microns. If desired, two or more trimethylolpropane esters as described above can be deposited on the surfaces of the pigment particles.

The trimethylolpropane ester can be deposited on the inorganic pigment, either directly on the surfaces of the pigment particles or on top of one or more components (for example, alumina and/or silica coatings) that have been deposited on the surfaces of the pigment particles, by any method known in the art. For example, the trimethylolpropane ester can be deposited on the surfaces of the pigment particles by milling the trimethylolpropane ester and pigment particles together in a fluid energy mill, by spraying the trimethylolpropane ester on the surfaces of the pigment particles, by mixing the trimethylolpropane ester with the pigment particles in dry form, or by mixing the trimethylolpropane ester and pigment particles together (optionally with a dispersing agent) in an aqueous slurry. For example, the trimethylolpropane ester can be deposited on the surfaces of the pigment particles by mixing the trimethylolpropane ester with the pigment particles in an aqueous slurry and subsequently drying the slurry. For example, the aqueous slurry can be the same aqueous slurry that has been used to coat at least one inorganic coating on the surfaces of the pigment particles. For example, once the trimethylolpropane ester is deposited on the surfaces of the pigment particles, the treated, particulate inorganic pigment can dried and milled (for example, steam milled).

For example, an agglomerated raw titanium dioxide slurry is formed using sodium hexametaphosphate as a dispersant. The slurry is sand milled to reduce the particle size of the titanium dioxide to in the range of from about <NUM> microns to about <NUM> microns (for example, such that about <NUM>% of the particles are less than <NUM> microns). Next, the milled slurry is heated to about <NUM>, treated with concentrated acid, allowed to digest and subsequently treated with caustic to form hydroxyl sites on the surfaces of the pigment particles. The pigment is then washed to remove salts. The washed pigment is then treated with <NUM>% to <NUM>% by weight trimethylolpropane esters, based on the total weight of the pigment. The trimethylolpropane ester treated pigment is then dried and subsequently steam milled (micronized).

The polymer composition disclosed herein includes at least one polymer, and the treated, particulate inorganic pigment as described above.

Examples of polymers to which the treated, particulate inorganic pigment can be added to form the polymer composition include polyolefins such as polyethylene (for example, low density polyethylene) and polypropylene, acrylic resins such as poly(methyl methacrylate), polyester resins such as polyethylene terephthalate, polyamide resins, styrenic resins such as acrylonitrile-butadiene-styrene copolymer, polyvinyl chloride, polycarbonate resins, and mixtures thereof. For example, the polymer(s) can be selected from the group consisting of polyolefins, acrylic resins, polyester resins, polyamide resins, styrenic resins, polyvinyl chloride, polycarbonate resins, and mixtures thereof. For example, the polymer(s) can be selected from the group consisting of polyethylene, polypropylene, poly(methyl methacrylate), polyethylene terephthalate, polyamide resins, acrylonitrile-butadiene-styrene copolymer, polyvinyl chloride, polycarbonate resins, and mixtures thereof.

The treated, particulate inorganic pigment can be admixed with the polymer to form the polymer composition by any method known in the art. For example, the treated, particulate inorganic pigment can be added to a slurry containing the polymer and mixed therein.

The amount of the treated, particulate inorganic pigment included in the polymer composition can vary depending on the type of polymer composition. For example, the treated, particulate inorganic pigment can be included in the polymer composition in an amount in the range of from about <NUM>% to about <NUM>% by weight based on the total weight of the polymer composition. For example, the treated, particulate inorganic pigment can be included in the polymer composition in an amount in the range of from about <NUM>% to about <NUM>% by weight based on the total weight of the polymer composition.

For example, a treated, particulate titanium dioxide pigment can be mixed with the subject polymer together with a dispersant to prepare a <NUM>% by weight titanium dioxide-containing polymeric master batch concentrate. The mixing process can be carried out, for example, via mastication of the mixture in the mixing bowl of a Plasticorder™ Model PL-<NUM> as sold by C. Brabender Instruments, Inc. , at <NUM> and a mixing speed of <NUM> rpm.

The treatment of an inorganic pigment with a trimethylolpropane ester as disclosed herein significantly improves the bulk density of the pigment which improves the flow properties, processability and dispersibility of the pigment, particularly in polymer compositions. The trimethylolpropane esters used herein are very stable and have low volatility and good biodegradable and eco-toxicity properties.

The hydrophobic nature of the treated pigment makes it very suitable for use in polymer compositions. For example, the polymer composition disclosed herein has a reduced grit content. Due to the trimethylolpropane ester, the treated, particulate inorganic pigment can be dispersed in base compositions including polymer compositions using less time and energy than the particulate inorganic pigments used heretofore.

The following examples illustrate specific aspects consistent with the present disclosure but do not limit the scope of the disclosure or the appended claims. Concentrations and percentages are by weight unless otherwise indicated.

Particulate titanium dioxide pigment formed by the chloride process and containing <NUM>% alumina in its crystalline lattice was dispersed in water in the presence of <NUM>% by weight, based on the weight of the pigment, sodium hexametaphosphate (a dispersant) and an amount of sodium hydroxide sufficient to adjust the pH of the aqueous solution to a minimum value of <NUM>. An amount of titanium dioxide sufficient to form an aqueous slurry having a solids content of <NUM>% by weight was utilized. The titanium dioxide slurry was then subjected to sand milling (using a zircon sand-to-pigment weight ratio of <NUM>:<NUM>) until <NUM>% of the pigment particles were smaller than <NUM> microns, as determined utilizing a Microtrac™ X100 Particle Size Analyzer.

The slurry was then heated to <NUM>, acidified to a pH of <NUM> using concentrated sulfuric acid, and allowed to digest at <NUM> for <NUM> minutes. Next, the pH of the slurry was adjusted to <NUM> using a <NUM>% by weight aqueous sodium hydroxide solution, and the slurry was further digested for <NUM> minutes at <NUM>. The pH of the slurry was finally readjusted to <NUM>, as necessary, and the dispersion was filtered while hot. The resulting filtrate was washed with water, which had been preheated to <NUM>, in an amount equal to the weight of recovered pigment.

Next, a polyol ester, specifically a trimethylolpropane ester having <NUM> carbon atoms ("TMP-C12") was added to the washed filter cake in an amount of <NUM>% by weight based on the weight of the titanium dioxide. The resulting pigment was oven dried at <NUM> overnight and the dried pigment was crushed to yield dry pigment powder.

The dried pigment was then steam micronized, utilizing a steam to pigment weight ratio of <NUM>:<NUM>, with a steam injector pressure set at <NUM> psi and micronizer ring pressure set at <NUM> psi. The resulting treated pigment sample was evaluated in titanium dioxide/polyethylene concentrates, according to the following procedure.

First, <NUM> grams of the pigment were mixed with <NUM> grams of low density polyethylene as manufactured by the Dow Chemical Co. (Dow™ <NUM>) and <NUM>% by weight, based on the weight of the polyethylene, of an <NUM>/<NUM> mixture of tris(<NUM>,<NUM>-di-tertbutylphenyl) phosphite and octadecyl-<NUM>-(<NUM>,<NUM>-di-tertbutyl-<NUM>-hydroxyphenyl)propionate, to prepare a <NUM>% by weight titanium dioxide-containing polyethylene concentrate, via mastication of the mixture in the mixing bowl of a Plasticorder™ Model PL-<NUM> as sold by C. Brabender Instruments, Inc. , at <NUM> and a mixing speed of <NUM> rpm.

Instantaneous torque and temperature values were then recorded for a nine minute period to ensure equilibrium mixing conditions were attained. Equilibrium torque values were determined via averaging the measured instantaneous torque values for a two minute period after equilibrium mixing conditions had been achieved.

The resulting polymer concentrate was cooled and ground into pellets. The melt flow index value was determined on the resulting pellet concentrate using ASTM method D1238, procedure B. Maximum extruder processing pressure was determined by extruding <NUM> grams of the <NUM>% concentrate through a <NUM> mesh screen filter using a <NUM> inch barrel, <NUM>/<NUM> length to diameter extruder attached to the aforementioned Brabender™ Plasticorder, at an average processing temperature of approximately <NUM> and at <NUM> rpm, while recording instrument pressure values at the extruder die.

The amount of inorganic residue left on the <NUM> mesh screen filter, reported as pigment grit content in parts-per-million based on pigment, was determined gravimetrically via heating the post-extrusion screen in a muffle furnace at <NUM> for twenty minutes, cooling the screen to room temperature, then subsequently weighing the screen, with comparison to its weight prior to use.

Blown film tests were carried out to determine how well the titanium dioxide had dispersed in the low density polyethylene (Dow™ <NUM>) formulation. The pigment was first processed into a master batch with a titanium dioxide loading of <NUM> as described above. The master batch was then let down to <NUM>% in low density polyethylene and blown into film using a Killion™ blown film extruder. The extruder had three zones, wherein zone one was maintained at <NUM>° C, zone two was maintained at <NUM> and zone three was maintained at <NUM>, and two dies wherein die one was maintained at <NUM> and die two was maintained at <NUM> at <NUM> rpm with a film tower speed of <NUM>. A three foot sample was collected and separated into three <NUM> foot by <NUM> foot films. The nibs on the films were counted and reported in nibs per square foot.

The same procedure was repeated using titanium dioxide produced according to the procedure set forth above, but instead of using TMP-C12, trimethylol propane without a fatty acid ester ("TMP") was used to form Comparative Example 1a, polymethylhydrosiloxane ("PHMS") was used to form Comparative Example 1b, and <NUM>-ethyl hexyl laurate ("<NUM>-EHL") was used to form Comparative Example 1c. The results of the tests are provided in Tables 1a and 1b below.

As shown by the results, the titanium dioxide/polyethylene polymer concentrate incorporating titanium dioxide treated with a polyol ester (TMP-C12 triester) exhibited improved properties compared to the comparative samples, as indicated by a higher melt flow index, lower equilibrium torque value, lower maximum extruder pressure, lower grit content and lower nibs in the blown film.

A titanium dioxide filter cake was prepared in the manner described in Example <NUM>. Next, a trimethylolpropane ester having <NUM> carbon atoms ("TMP-C18") was added to the washed filter cake in an amount of <NUM>% by weight, based on the weight of the titanium dioxide in the filter cake. The resulting pigment was oven dried at <NUM> overnight and the dried pigment was crushed to yield dry pigment powder.

The dried pigment was steam micronized, utilizing a steam to pigment weight ratio of <NUM>:<NUM>, with a steam injector pressure set at <NUM> psi and micronizer ring pressure set at <NUM> psi.

Next, the same overall procedure was repeated using titanium dioxide produced according to the procedure outlined above but instead of using TMP-C18, polymethylhydrosiloxane (PHMS) was used to form Comparative Example 2a.

The resulting treated pigment samples were evaluated in titanium dioxide/polyethylene concentrates, according to the same procedure described above in Example <NUM>. The results of the tests are shown below.

The results show improved results can be obtained by the polyol ester treated pigment at various polyol ester chain lengths. The described titanium dioxide/polyethylene polymer composition, comprising a pigment having an organic surface treatment coating comprising TMP-C18 also exhibited improved properties versus the comparative sample, as indicated by a higher bulk density, lower equilibrium torque value, lower maximum extruder pressure and lower nibs in the blown film.

Example <NUM> is not covered by the subject matter of the claims, and is included for reference purposes. A titanium dioxide filter cake was prepared in the same manner described in Example <NUM> above. Next, pentaerythritol tetra stearate ("PETS ester") was added to the washed filter cake in an amount of <NUM>% by weight, based on the weight of the titanium dioxide in the filter cake. The resulting pigment was oven dried at <NUM> overnight and the dried pigment was crushed to yield dry pigment powder.

The dried pigment was steam micronized, utilizing a steam to pigment weight ratio of <NUM>:<NUM>, with a steam injector pressure set at <NUM> psi and micronizer ring pressure set at <NUM> psi. The resulting treated pigment sample was evaluated in titanium dioxide/polyethylene concentrates, according to the procedure described in Example <NUM> above. The same procedure was then repeated using titanium dioxide produced according to the procedure described in Example <NUM> above but instead of using PETS ester, polymethylhydrosiloxane (PHMS) was used to form Comparative Example 3a. The results are shown by Tables 3a and 3b below.

The titanium dioxide/polyethylene polymer concentrate, comprising a pigment having an organic surface treatment coating comprising PETS ester also showed improvements versus the comparative sample by indicating a higher bulk density, a lower equilibrium torque value and lower nibs in the blown film.

A titanium dioxide filter cake was prepared in the manner described in Example <NUM>. Next, a polyol ester including a silicone functional group ("Silube® D2," sold by Siltech Corporation) was added to the washed filter cake in an amount of <NUM>% by weight, based on the weight of the titanium dioxide in the filter cake. The resulting pigment was oven dried at <NUM>° C overnight and the dried pigment was crushed to yield dry pigment powder. The dried pigment was then steam micronized, utilizing a steam to pigment weight ratio of <NUM>:<NUM>, with a steam injector pressure set at <NUM> psi and micronizer ring pressure set at <NUM> psi.

Next, the same overall procedure was then repeated using titanium dioxide produced according to the procedure described in Example <NUM> above but instead of using "Silube® D2," polymethylhydrosiloxane (PHMS) was used to form Comparative Example 4a.

The resulting treated pigment samples were evaluated in titanium dioxide/polyethylene concentrates, according to the same procedure described above in Example <NUM>. The results are shown by Tables 4a and 4b below.

The results show that improved results can also be obtained by using a pigment treated with a polyol ester having a silicone functional group (for example, formed with a fatty acid modified silicone). The titanium dioxide/polyethylene polymer concentrate, comprising a pigment having an organic surface treatment coating comprising a polyol ester having a branched silicone with C8/C10 fatty groups ("Silube® D2"), also showed improvements versus the comparative sample by indicating a higher bulk density, a lower maximum extruder pressure, a lower grit content and lower nibs in the blown film.

Claim 1:
A treated, particulate inorganic pigment, comprising:
a plurality of pigment particles; and
a trimethylolpropane ester deposited on the surfaces of said pigment particles, wherein said trimethylolpropane ester is obtainable by reacting at least one fatty acid with trimethylolpropane, said fatty acid(s) being selected from saturated, straight chain fatty acids and saturated, branched chain fatty acids, said fatty acid fully esterifying the trimethylolpropane to form a trimethylolpropane ester.