MXPA97010143A - Durable pigments for plasti - Google Patents

Abstract

The present invention relates to an inorganic pigment coated with alumina comprising an inorganic pigment material containing at least about 0.75 weight percent alumina, based on the weight of the pigment material, having a first predominantly alumina coating boehmite on the inorganic pigment, a second coating predominantly of amorphous alumina on the first coating and a third coating predominantly of boehmite alumina on the second coating, the first coating is carried out in a discrete range and the second and third coatings are brought to out continually

Description

DURABLE PIGMENTS FOR PLASTICS BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improved inorganic pigments, coated with alumina, and to a method for multiple coating of inorganic pigments containing alumina in order to make them durable, of low reactivity chemistry and photochemistry and good optical properties and dispersion capacity in plastic applications. More specifically, the present invention relates to an improved alumina-containing titanium dioxide pigment, having a first boehmite alumina coating, a second amorphous alumina coating on the first boehmite alumina coating, and a third boehmite alumina coating on the second amorphous alumina coating. 2. Description of the Prior Art Methods of coating and surface treatment of inorganic pigments, such as titanium dioxide, which are used to achieve improved performance characteristics in plastic compositions are already known in the art. Dispersion capacity, resistance to manufacturing processes and P1503 / 97MX good optical properties are typically achieved by the surface treatment of the pigment, while the durable characteristic and the low chemical and photochemical reactivity are usually obtained by coating the pigment with silica, alumina and other metal oxide coatings. When precipitated using prior art practices, these metal oxide coatings tend to cause the pigments to disperse with more difficulty in plastics. Pigments coated with metal oxides tend to contain more adsorbed water, which can cause problems of thickening of the coating and degassing in the production of plastics with coated pigments. Typically, these problems have not been solved with a single pigment. In this way, the persons in charge of plastic mixtures have generally had to choose between a durable characteristic, which can be achieved with coated pigments, and dispersion capacity, resistance to manufacturing processes and good optical properties, which can be achieved with pigments treated and not treated. For example, U.S. Patent No. 3,523,810 discloses a process for coating titanium pigments with 0.5 percent to 10 percent boehmite alumina at a pH between 7 and 9, at temperatures between 70 ° and F1503 / 97MX 100 ° C. A pigment of this type only with boehmite and not with amorphous alumina can have good optical properties and dispersibility but can not achieve good long-lasting characteristics. Similarly, U.S. Patent No. 4,022,636 describes the addition of two alumina coatings to the titanium dioxide pigments, an amorphous coating at a pH of about 2 followed by a boehmite coating at a pH of about 8. , to achieve a pigment with good performance in plastics. However, this process does not have the elements required to form the dense alumina required for the manufacture of durable plastics. Also, U.S. Patent No. 4,416,699 discloses a method for coating a pigment with between 2 percent and 6 percent alumina to achieve the resistance to powder degradation, brightness and dispersibility required for the color grades of dioxide. titanium. However, this process contains alumina levels higher than those allowed for the optimum performance of titanium dioxide pigments in plastic applications. Examples of inorganic pigment coating processes for which the benefits of improved performance have been attributed include the coating processes set forth in U.S. Pat.

P1503 / 97MX No. 2,671,031. This patent shows the precipitation of a coating of hydrous aluminum oxide on titanium dioxide, followed by thermal treatment between 500 ° C and 800 ° C to reduce the powder disintegration of the pigment. The present invention does not involve the thermal process. U.S. Patent No. 2,780,558 discloses a process for coating pigment materials or colorants with added alumina as an alcoholate compound. The present invention includes multiple coatings of aggregate alumina as an inorganic salt. In U.S. Patent No. 3,146,119 the claimed process requires the precipitation of a layer of titanium dioxide on the pigment, prior to the precipitation of an alumina layer. The present invention does not require a coating of titanium dioxide. U.S. Patent No. 3,409,454 discloses a titanium dioxide pigment coated with alumina and a process for obtaining same, wherein the alumina is precipitated on the pigment under alkaline conditions (pH greater than 10) for improved pigment dispersibility in plastics. The present invention includes an acid coating and digestion process, followed by an alkaline coating step. U.S. Patent No. 3,529,985 discloses a pigment coated with titanium dioxide wherein the first coating of P1503 / 97MX metal oxide is calcined at a temperature of at least 450 ° C after the addition of the second coating to improve the durable characteristic and the optical properties. The present invention does not require a calcination step. U.S. Patent No. 3,853,575 discloses the production of titanium dioxide pigments coated with alumina, wherein the alumina coating is provided by the addition of an alkali alumina salt to an aqueous solution of titanium dioxide. The present invention discloses an acidic coating and digestion process followed by an alkaline coating step. U.S. Patent No. 4,239,548 discloses a titanium dioxide pigment with improved photochemical stability, achieved by a first coating of phosphate and cerium rals on the pigment and a second coating of phosphate and aluminum rals on the first coating. The present invention does not include the use of cerium. U.S. Patent No. 5,114,486 discloses a process for coating titanium dioxide pigments with zinc, phosphate and aluminum ions to improve the ability to withstand manufacturing processes. The present invention does not include the use of zinc. None of the aforementioned patents suggests or shows the coating of inorganic pigments with a P1 03 / 97MX first layer of boehmite alumina, a second layer of amorphous alumina and a third layer of boehmite alumina, to produce the coated pigments that are the subject of this application.

SUMMARY OF A NATION It is an object of the present invention to provide durable inorganic pigments coated with alumina with good optical properties, dielectability and chemical stability in plastic applications. A further object is to provide improved inorganic pigments, preferably titanium dioxide pigments, which have deposited thereon a first boehmite alumina coating, a second amorphous alumina coating and a third boehmite alumina coating. A further object of the present invention is to provide a process by which the inorganic pigments coated with alumina are produced.

DESCRIPTION OF PREFERRED EMBODIMENTS The present invention relates to an inorganic pigment coated with alumina comprising an inorganic pigment material containing at least about 0.75 weight percent alumina, based on the weight of the pigment material, which has a P1 03 / 97MX first coating predominantly of boehmite alumina on the inorganic pigment, a second coating predominantly of amorphous alumina on the first coating and a third coating predominantly of boehmite alumina on the second coating; the first coating is carried out in a discrete range and the second and third coatings are carried out continuously. Advantageously, the amine-coated inorganic pigment contains from about 0.75 percent to about 2 percent by weight of alumina based on the weight of the pigment. Preferably, the inorganic pigment coated with alumina contains from about 1 percent to about 1.5 percent by weight of alumina based on the weight of the pigment material and more, preferably, the inorganic pigment coated with alumina contains about 1.3 percent by weight of alumina based on the weight of the pigment material. Advantageously, the inorganic pigment coated with alumina used is titanium dioxide. The process for preparing the inorganic pigments of coated alumina of the present invention advantageously comprises the steps of: (a) grinding an aqueous suspension containing P1503 / 97MX inorganic pigment material, wherein the pigment material contains at least about 0.75 weight percent alumina based on the weight of the pigment material, in the presence of a dispersing agent, to carry out the distribution of a particle size in the pigment, where no more than about 40 percent of the pigment particles are greater than 0.49 microns, measured with a Microtrac 9200 FRA; (b) removing the grinding media from the aqueous suspension; (c) adding to the suspension a first amount of an alumina coating agent, advantageously, together with a second amount of a dispersing agent and adjusting the pH of the suspension to a level of at least about 1.5 to form a first coating predominantly of alumina boehmite on the pigment; (d) digesting the suspension at a temperature of from about 50 ° C to about 70 ° C for a time of about 5 to 60 minutes; (e) increasing the pH of the suspension to a level in the range of about 3 to about 5; (f) adding to the suspension a second amount of an alumina coating agent with simultaneous addition of a pH adjusting agent to form a P1S03 / 97MX second coating predominantly of amorphous alumina on the first coating, while maintaining the pH of the suspension within a range of about 3 to about 5; (g) digesting the suspension at a temperature of about 50 ° C to about 70 ° C for a time of about 10 to about 90 minutes; (h) adjusting the pH of the suspension to a level in the range of about 7 to about 9 and digesting the suspension at a temperature of about 50 ° C to about 70 ° C for a time of about 5 to about 60 minutes, to forming a third coating predominantly of boehmite alumina on the second coating; and (i) recovering the alumina coated pigment to provide a plastic grade pigment. Advantageously, the pigment material in step (a) contains from about 0.75 percent to about 2.0 percent by weight of alumina based on the weight of the pigment material. Preferably the pigment material in step (a) contains about 1.3 weight percent alumina based on the weight of the pigment material. In advantageous manner, the pigment material is titanium dioxide. Advantageously, the dispersing agent in steps (a) and P1 03 / 97MX (c) is selected from the group consisting of phosphates, polyols and amines. Preferably the dispersing agent is sodium hexametaphosphate. The dispersing agent in step (a) is advantageously present in an amount in the range of about 0.05 percent to about 0.5 percent by weight, based on the weight of the pigment material. Preferably, the amount of the dispersing agent is about 0.15 percent by weight based on the weight of the pigment material. When a dispersing agent is used in step (c), it is advantageously present in an amount in the Lango from about 0.05 percent to about 0.5 percent by weight, based on the weight of the pigment material. Preferably the dispersing agent is present in step (c) in an amount of about 0.15 percent by weight based on the weight of the pigment material. In the present invention from about 0.1 percent to about 20 percent of the particles of said pigment are 0.49 microns or less, measured with a Microtrac 9200 FRA. Advantageously from about 5 percent to about 10 percent , .three of said pigment particles are 0.49 microns or less and preferably about 7 percent of the pigment particles are 0.49 microns.

P1503 / 97MX or minors Advantageously, the grinding medium of step (a) is sand. Preferably the temperature during the steps from c to h is maintained within the range of about 50 ° C to about 70 ° C and more preferably the temperature is maintained at about 60 ° C. Advantageously, the alumina coating agent is an inorganic salt of alkaline or acid aluminum. Preferably the alumina coating agent is sodium aluminate. In the present process of the invention, the amount of alumina coating agent added in step (c) is sufficient to provide the first coating in an amount within the range of from about 0.2 percent to about 0.5 percent and, preferably, the aggregate alumina coating agent is sufficient to provide a first coating in an amount of about 0.35 weight percent. Advantageously, the alumina coating agent added in step (f) is sufficient to provide the second coating in an amount within a range of from about 0.2 percent to about 1.2 percent by weight based on weight P1503 / 97MX of the pigment material. Preferably, the aggregate alumina coating agent is sufficient to provide the second coating in an amount within a range of from about 0.5 percent to about 1.0 percent by weight and, more preferably, the aggregate alumina coating agent is sufficient to provide the second coating in an amount of about 0.75 weight percent. Advantageously, the pH of the suspension during step (a) is about 10. The pH of said suspension in step (c) is advantageously adjusted to a level in the range of about 1 to about 3, preferably pH The euepeneion is adjusted to approximately 1.5. Advantageously the pH of the suspension in step (e) is adjusted to about 3 and the pH of the suspension in step (f) is maintained at about 5.75. The pH of the suspension in the stage (h) is advantageously adjusted to a level within a range of about 7 to about 9 and, preferably, the pH of the suspension is adjusted to about 7.8. Advantageously, the pH adjusting agent in steps (c) and (f) is a mineral acid, preferably sulfuric acid. Preferably the pH adjusting agent in steps (e) and (h) is an alkaline base of metal hydroxide. From P1503 / 97MX preference the pH adjusting agent is sodium hydroxide. Advantageously, the suspension is digested in step (d) from about 5 to about 60 minutes and, preferably, the euepeneion is digested for about 15 minutes. Advantageously the suepeneion is digested in step (g) for about 10 to about 90 minutes and, more preferably, the suepeneion is digested for about 30 minutes. Advantageously, the suspension is digested in step (h) for about 5 to about 60 minutes and, preferably, the suspension is digested for about 15 minutes. Advantageously, the pigment developed from alumina is recovered by filtering, drying and grinding.

EXAMPLE 1 An aqueous solution comprising 1800 g of TiO2 with 1.3% by weight calculated alumina, while AI2O3 was dispersed with 0.15% sodium hexametaphosphate and ground in sand to obtain a particle size distribution of 7% particles They have a size smaller than 0.49 micron. The sand was removed after grinding. The suspension was diluted after a volume of 4.5 L, 2.54 g of Calgon was added and the temperature was adjusted to E1503 / 97MX 60 ° C. 11.5 mL, 1.4696 g / mL of alumina were added as sodium aluminate. The pH was adjusted to 3.5 with 5.0 mL of sulfuric acid and the solution was digested for 15 minutes. The pH of the eeolution was then adjusted to 5.75 with 5.0 mL of eodium hydroxide. 45.8 mL, 1.4696 g / mL, of alumina were added as sodium aluminate with concurrent addition of 13.3 mL of sulfuric acid to maintain the pH at 5.5 -6.0. The suspension was digested for 30 minutes. The pH was then adjusted to 7.8 with 4.3 mL of eodium hydroxide and digested for 15 minutes. The samples were then filtered, dried and micronized with 0.35% T P. The results are reported in Table 1.

EXAMPLE 2 The treatment of Example 1 was repeated. The pigment was micronized with 0.40% TMP / 0.3% TEA. Reference 1 was a pigment (durable) treated intenemente. Reference 2 was an untreated pigment for pláceicoe. Reference 3 was a standard grade plastic pigment.

P1503 / 97MX TABLE 1 * The lower numbers indicate less reactivity in eetae pruebae and, therefore, are preferred.

Claims (48)

1. NOVELTY OF THE INVENTION Having decribed the present invention, it is a novelty and, therefore, the property contained in the following EIVINDICATIONS is claimed as property: 1. An inorganic pigment coated with alumina comprising an inorganic pigment material containing at least about 0.75 weight percent alumina, with bae on the pee of the pigment material, having a first coating predominantly of boehmite alumina on the inorganic pigment, a second coating predominantly of amorphous alumina on the first coating, and a third coating predominantly of alumina boehmite on the second reverend; the first coating is carried out in a discrete range and the second and third coatings are carried out continuously.
2. 2. The inorganic pigment coated with alumina of claim 1, wherein the inorganic pigment contains from about 0.75 percent to about 2 percent by weight of alumina based on the weight of the pigment.
3. 3. The inorganic pigment coated with alumina of claim 2, wherein the pigment material contains from about 1 percent to about P1503 / 97MX 1. 5 percent by weight of alumina based on the weight of the pigment material.
4. 4. The inorganic pigmented alumina pigment of claim 3, wherein the pigment material contains about 1.3 percent by weight of alumina based on the weight of the pigment material.
5. 5. The inorganic pigment coated with alumina of claim 1, wherein the pigment material is titanium dioxide.
6. 6. A process for preparing inorganic pigments coated with alumina, comprising the steps of: (a) grinding an aqueous euepension containing inorganic pigment material, wherein the pigment material contains at least about 0.75 weight percent alumina based on the weight of the pigment material, in the presence of a dispersing agent, to obtain a particle size distribution in the pigment so that no more than about 40 percent of the pigment particles are greater than 0.49 micron , measures with a Microtrac 9200 FRA; (b) removing the milling media from the aqueous suepeneion; (c) adding a first quantity of an alumina coating agent to the suspension and adjusting the pH of P15Q3 / 97MX suspeneion at a level of at least about 1.5 to form a first coating predominantly of boehmite alumina on the pigment; (d) digesting the suepeneion at a temperature of from about 50 ° C to about 70 ° C for a time of about 5 to about 60 minutes; (e) increasing the pH of the euspension to a level in the range of about 3 to about 5; (f) adding to the suspension a second amount of an alumina coating agent with eimultaneous addition of a pH adjusting agent to form a second coating predominantly of amorphous alumina on the first coating, while maintaining the pH of the suspeneion within a range of between approximately 5 to 7; (g) digesting the suspension at a temperature of about 50 ° C to about 70 ° C for a time of about 10 to 90 minutes; (h) adjusting the pH of the suspeneion to a level in the range of about 6 to about 9 and digesting the suspension at a temperature of between about 50 ° C and 70 ° C for a time of about 5 to about 60 minutes, for form a third reverend predominantly of boehmite alumina over the second reverend; P1503 / 97MX (i) recover the pigment revealed from alumina to provide a plastically grade pigment. The process of claim 6, wherein the pigment material in step (a) contains from about 1 percent to about 1.5 percent by weight of alumina based on the weight of the pigment material. 8. The process of claim 7, wherein the pigment material contains about 1.3 weight percent alumina with bae in the weight of the pigment material. 9. The process of claim 6, wherein the pigment material is titanium dioxide. 10. The process of claim 6, wherein a second amount of a dispersion agent is added in step (c). The process of claim 10, wherein the die scattering agent in steps (a) and (c) ee selects from the group that you connected of phosphate, polyols and amines. 12. The process of claim 11, wherein the dieting agent is sodium hexametaphosphate. The process of claim 6, wherein the dispersing agent in step (a) is present in an amount in the range of about 0.05 percent P1503 / 97MX at about 0.5 weight percent based on the weight of the pigment material. The process of claim 13, wherein the amount of the dispersing agent is about 0.15 percent by weight based on the weight of the pigment material. The process of claim 10, wherein the dyeing agent in step (c) is present in an amount in the range of about 0.05 percent to about 0.50 percent in pee based on the weight of the pigment material . 16. The process of claim 15, wherein the dispersing agent is present in an amount of about 0.30 percent in pee with bae in the pee of the pigment material. 17. The process of claim 6, wherein from about 0.1 percent to about 20 percent of the pigment particles are 0.49 microns or less, measured with a Microtrac 9200 FRA. The process of claim 17, wherein from about 5 percent to about 10 percent of the pigment particles are 0.49 microns or less. The process of claim 18, wherein no more than about 7 percent of the particles of P1503 / 97MX pigment are 0.49 micron or less. The process of claim 6, wherein the grinding medium of step (a) is sand. 21. The process of claim 6, wherein the temperature during the stages of the c to the h ee remains within the range of between about 50 ° C and 70 ° C. 22. The process of claim 6, wherein the temperature ee maintains at about 60 ° C. 23. The process of claim 6, wherein the alumina revetment agent is an inorganic salt of alkali or acid aluminum. The process of claim 23, wherein the alumina coating agent is sodium aluminate. 25. The process of claim 6, wherein the amount of alumina release agent added in step (c) is sufficient to provide the first coating, in an amount within the range of from about 0.1 percent to about 1 percent by weight of boehmite alumina based on the weight of the pigment material. 26. The process of claim 25, wherein the alumina coating agent added in step (c) is efficient to provide a first release. [150 V97MX in an amount within the range of between about 0.2 and 0.5 percent in peeo, based on peeo of the pigment material. The process of claim 26, wherein the aggregate alumina coating agent is sufficient to provide the first coating in an amount of about 0.35 percent by weight based on the weight of the pigment material. The process of claim 6, wherein the alumina coating agent added in the step (f) is sufficient to provide the second coating in an amount within a range of between about 0.2 and 1.2 percent by weight, with bae by weight of the pigment material. The process of claim 28, wherein the aggregate alumina coating agent is sufficient to provide the second coating in an amount within a range of between about 0.5 and 1.0 weight percent based on the weight of the coating material. pigment. 30. The process of claim 29, wherein the aggregate alumina coating agent is sufficient to provide the second release in an amount of about 0.75 percent by weight based on the peel of the pigment material. P1503 / 97MX 31. The process of claim 6, wherein the pH of the suspension during step (a) is about 10. The process of claim 6, wherein the pH of the suspension in step (c) is adjusted to a level within the range of between about 1 and 3. The process of claim 32, wherein the pH of the suspension is adjusted to a level of about 1.5. 34. The process of claim 6, wherein the pH of the suspeneion in step (e) ee is adjusted to about 3. 35. The process of claim 6, wherein the pH of the euspension in step (f) is maintained at about 5.75. 36. The process of claim 6, wherein the pH of the suspension in step (h) is adjusted to a level within the range of between about 7 and. 37. The process of claim 36, wherein the pH of the suspension is set at about 8. 38. The process of claim 6, wherein the pH adjusting agent in steps (c) and (f) is a mineral acid. 39. The process of claim 38, wherein the pH adjusting agent is sulfuric acid. P1503 / 97MX 40. The process of claim 6, wherein the pH adjusting agent in steps (e) and (h) is an alkaline base of metal hydroxide. 41. The process of claim 40, wherein the pH adjusting agent is sodium hydroxide. 42. The process of claim 6, wherein the euepeneion is digested in step (d) for about 10 to about 45 minutes. 43. The process of claim 42, wherein the euepension is digested for approximately 15 minutes. 44. The process of claim 6, wherein the suspension is digested in step (g) for about 20 to about 70 minutes. 45. The process of claim 44, wherein the suspension is digested for approximately 30 minutes. 46. The process of claim 6, wherein the suspension is digested in step (h) for about 10 to about 45 minutes. 47. The process of claim 46, wherein the suspeneion is digested for approximately 15 minutes. 48. The process of claim 6, wherein the pigment developed from alumina is recovered by filtering, drying and grinding. Elñ03 / 97MX