GB1596999A

GB1596999A - Titanium dioxide pigment slurries for paint

Info

Publication number: GB1596999A
Application number: GB53164/77A
Authority: GB
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1976-12-22
Filing date: 1977-12-21
Publication date: 1981-09-03
Also published as: MX148379A; IT1114193B; NL7714259A; CA1087775A; FR2375308B1; IE46124B1; FR2375308A1; JPS5388826A; IE46124L; BR7708564A; DE2757227A1

Description

(54) TITANIUM DIOXIDE PIGMENT SLURRIES FOR PAINT (71) We, E. I. DU PONT DE NEMOURS AND COMPANY, a Corporation organised and existing under the laws of the State of Delaware, of Wilmington, Delaware 19898, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to titanium dioxide pigment.

The present invention is concerned with the preparation of titanium dioxide as an aqueous slurry suitable for incorporation in water-based acrylic paint systems to impart high-gloss characteristics to the dried paint film.

In recent years substantial research has been undertaken to develop titanium dioxide slurries that were suitable for use in paper and water-based paint manufacture. The economics and ease of use of'such slurries has been a substantial incentive for the development of titanium dioxide slurries.

This invention provides another step forward in the development of titanium dioxide slurries. This invention-provides a slurry of very high solids content that can be used to prepare high gloss water-based acrylic paint formulations.

According to the present invention, there is provided a titanium dioxide pigment aqueous slurry comprising (i) from 60 to 80 percent by weight of titanium dioxide, from 0.2 to 1 percent by weight based on the weight of the titanium dioxide of a sulfonate compound of the general formula: Formula I

wherein M is alkali metal; R, to R4 are each independently, H, -CH3 or -C2H5; X is -CN or -COOR5 wherein R5 is hydrogen or lower alkyl of 1 carbon atoms; Y is -COOH or -COONa, and a and b are, each independently, from 10 to 100; and (ii) from 0.1 to 0.6 percent by weight based on the weight of the titanium dioxide of 2 - amino - 2 - methyl - 1 - propanol.

In a particular embodiment of the invention, the sulfonate compound has the general formula: Formula II

in which a, b and Y are each as defined in Claim 1.

In a second aspect, the invention provides a process for producing a titanium dioxide pigment aqueous slurry which process comprises adding one to the other the aqueous solution defined below and such an amount of titanium dioxide to provide in the resulting mixture a titanium dioxide content of from 80 to 90 percent by weight of the mixture, the aqueous solution being an aqueous solution containing the sulfonate compound of Formula I as defined above and 2 - amino 2 - methyl - I - propanol in amounts, based on the weight of titanium dioxide in the mixture, of from 0.2 ,ó to 1% and 0.1% to 0.6%, respectively; grinding the mixture with a disc mill until the titanium dioxide is uniformly dispersed; and. if the titanium dioxide content of the mixture exceeds 80 percent by weight, adding sufficient water to reduce the titanium dioxide content to from 60 to 80 percent by weight of the finished slurry. Following the completion of the steps just referred to, water can, if so desired, of course, be added to the slurry to provide a lower titanium dioxide content within the 60 to 80 percent by weight range.

In one particular embodiment of the process just described, an aqueous solution comprising the sulfonate compound defined below and 2 - amino - 2 methyl - I - propanol in amounts respectively as specified above is combined with a titanium dioxide/water mixture in which the water amounts to from 10 to 200;, by weight of the slurry to form a mixture in which the titanium dioxide content is in the range from 80 to 90% by weight of such mixture: Formula ll

in which a, b and Y are each as defined above.

Preferred forms of the process of the invention comprise:- (a) drying and grinding in a confined vortex fluid energy mill titanium dioxide pigment prepared by the oxidation of titanium tetrachloride; (b) preparing a solution in an amount of water equal to from 10% to 20% by weight of the pigment slurry of from 0.2 to 1% by weight, based on the weight of titanium dioxide, of the sulfonate compound, and from 0.1 to 0.6It, by weight based on the weight of the titanium dioxide, of 2 - amino - 2 - methyl - I - propanol; (c) adding the titanium dioxide of step (a) to form a slurried mixture having a titanium dioxide content of from 80 to 90% by weight;; (d) grinding the slurried mixture with a disc mill until the titanium dioxide is uniformly dispersed and has a particle size average of less than 0.6 micron with not more than five mass percent of the particles having a size of greater than one micron; (e) adding sufficient water to reduce titanium dioxide content to from 75 to 79 percent by weight of the finished slurry; and (f) mixing the slurry until smooth and uniform.

The slurries of this invention are high-solids slurries and preferably contain from 70 to 80 percent by weight titanium dioxide. Most preferably, the solids content of the slurry will be from about 75 to 79 percent titanium dioxide. As will be appreciated from the Examples which follow, the compositions of this invention are high-gloss slurries. The term "high-gloss slurry" means that when the slurry is incorporated into an acrylic paint formulation and dried into a thin film the film is of high gloss. The high-gloss slurries of this invention can be prepared simply from a dry titanium dioxide which has not been subjected to special surface treatments prior to incorporation into water.Outstanding gloss levels in acrylic water-based paint systems have been achieved when a chloride process titanium dioxide is simultaneously dried and ground using a fluid energy mill of the confined vortex type such as is taught in U.S. Patent 3,840,188.

The titanium dioxide employed in the preparation of the slurry compositions of this invention will preferably be of uniformly small particle size with at least 95 mass percent of the particles having a size of one micron or less with the particle average size being less than 0.6 microns.

The titanium dioxide will normally be one which has no hydrous oxide aftertreatment as the presence of hydrous oxide reduces the gloss of the finished paint film. It is understood, however, that the presence of rutilizing agents such as cooxidized aluminum and the like which are normally present in titanium dioxide produced by oxidation of titanium tetrachloride will not obviate the advantages of the slurries of this invention.

To achieve outstanding properties of gloss the slurry is in general prepared by adding dry titanium dioxide to 13 to 20 percent by weight of water, preferably the titanium dioxide is added to 13 to 15 percent by weight of water. The high-solids slurry is then ground until uniform using a disc mill such as a Hockmeyer disperser manufactured by H. H. Hockmeyer, Inc. The grinding is continued until the slurry becomes uniform and then (if necessary or desired) sufficient water is added to reduce the solids content of the slurry to from 60 to 80 percent by weight.

When preparing the slurries of this invention the titanium dioxide content of the initial slurry should be at least 80 percent by weight so that the disc mill can impart sufficient shear into the system to assure reduction in agglomerate size of the titanium dioxide within the limits of this invention. Ideally, the particle size will be as fine as possible with the average particle size of less than 0.6 microns with not more than 5 mass percent of the titanium dioxide particles or agglomerates, as the case may be, having a particle size greater than one micron. Therefore, depending on the pigment base being employed, the grinding time and pigment concentration will be adjusted to achieve the desired particle size uniformity and distribution.It has also been discovered that addition of about five percent water to the system after the grinding step results in improved rheological properties of the slurry and handling and use of the finished slurry is markedly enhanced.

It has also been discovered that the use of the dispersant system used in the invention is necessary to achieve a titanium dioxide slurry which imparts outstanding gloss to a paint film derived from a water-based system. The dispersant system comprised of a 0.2 to 1 percent of a compound of formula I and from 0.1 to 0.6 percent of 2 - amino - 2 - methyl - 1 - propanol, based on the weight of titanium dioxide present will, when combined with the other processing conditions described herein, produce a titanium dioxide slurry with an unexpectedly high level of gloss in a dried paint film.

The following Examples are illustrative of the invention. All parts and percentages are by weight unless otherwise noted.

Example 1 Titanium dioxide produced by the oxidation of titanium tetrachloride and I percent aluminum oxide in aqueous slurry of about 55-75 percent by weight solids is fed to a fluid energy mill as described in the example of U.S. Patent 3,840,188 and dried and ground using a steam to pigment ratio of from 2.5 to 6 as described therein to produce dry titanium dioxide of uniform and small particle size.

Example 2 To 5,300 ml of water in a five-gallon container is added 150 ml of a compound of formula I in which M is Na, R, to R4 are hydrogen and X and Y are carboxyl groups, and 60 ml of 2 - amino - 2 - methyl propanol. To the above solution is added 30,000 g of titanium dioxide pigment obtained as described in Example 1.

Then a Hockmeyer disperser fitted with a four-inch blade rotating at 4,000 rpm is employed to grind the pigment. After grinding for 20 minutes, 3,000 ml of water is added to reduce the solids concentration in the slurry to about 76.7 percent by weight. The particle size of the solids is determined using a Micrometrics 5000 Analyzer which shows a mass percent of particles finer than: Mass % Size (,u)* 84 0.65 50 0.47 16 0.325 3.5 > 1 33 < 0.4 * 84 indicates that 84% of the particles are 0.65 y or smaller.

The slurry prepared in Example 2 is compared with a commercially available high-gloss titanium dioxide for gloss and hiding power as described below.

Air Dry Emulsion Gloss: An acrylic emulsion paint is prepared containing a 22.8 pigment volume concentration. The acrylic emulsion paint is drawn down to a film thickness of 0.008 inch and is allowed to dry for a minimum of three days and the gloss (60 ) of the paint film is then determined.

Oven Dry Emulsion Gloss: An acrylic emulsion paint is prepared containing a 25 pigment volume concentration. The acrylic emulsion paint is drawn down to a film thickness of 0.004 inch and is immediately placed into a 1 100C draft free oven for thirty minutes and the gloss (600) of the paint film is then determined.

Hiding Power: The above acrylic emulsion paint preparations are drawn down to a film thickness of 0.0025 inch on Morest 09 chart and dried for 24 hours. Hiding power of the paint prepared from the slurries of this invention is compared with that of the control. The relative hiding power (H.P.) of the slurries of this invention are calculated as follows: SX of Test Sample H.P.= x 100 SX of Control Sample SX -- Scattering power determined according to the method of D. B. Judd, "Optical Specifications of Light Scattering Materials", Journal of Research of the National Bureau of Standards, Vol. 19, 1937, li 287.

Emulsion Gloss Air Dry Oven Dry H.P.

Slurry of Example 2 62 75 102 Control 49 56 100 Example 3 2-Amino-2-methyl propanol (45 ml) and a compound of formula I in which M is Na, R1 to R4 are hydrogen and X and Y are carboxyl groups (114 ml) are added to 7,200 ml of water in a five-gallon container. To this mixture is added 22,700 g of the titanium dioxide pigment prepared in accordance with Example 1. The resultant slurry is then ground with a Hockmeyer disperser fitted with a four-inch blade for 20 minutes at 1,500 rpm. After this grinding the solids content of the slurry is reduced with 2,500 ml of water to give a final slurry with a solids concentration of 68.2.

The emulsion gloss and hiding power of the slurry of Example 3 is compared with that of a commercial gloss pigment with the following results: Emulsion Gloss Air Dry H.P.

Slurry of Example 3 64 99 Control 56 100 Example 4 Sixty milliliters of 2-amino-2-methyl propanol and 240 ml of a compound of formula I in which M is Na, R1 to R4 are hydrogen and X and Y are carboxyl groups are added to 5,300 ml of water in a five-gallon container. To the above mixture is added 30,000 g of a titanium dioxide pigment obtained as described in Example 1.

Then a Hochmeyer disperser fitted with a four-inch blade rotating at 2,000 rpm is employed to grind the pigment. After grinding for 20 minutes, 3,500 ml of water is added to reduce the solids concentration in the slurry of 77 percent by weight.

The particle size of the solids present in the slurry is determined using a Micrometrics 5000 Analyzer which shows a mass percent of particles finer than: Mass % Size (,u) 84 0.51 50 0.375 16 0.245 2.0 > 1 58 < 0.4 The gloss and hiding power of the slurry of Example 4 is compared with that of a commercial gloss pigment as described above with the following results: Emulsion Gloss Air Dry H.P.

Slurry of Example 4 64 99 Control 49 100 The following Examples are presented to demonstrate that the high-solids grind followed by dilution to a solids concentration within the range of 60 to 80 percent solids will produce a slurry which provides improved gloss when compared to the same pigment which is dried conventionally and incorporated directly into the paint system.

Example 5 Fifty-four milliliters of 2-amino-2-methyl propanol and 185 ml of a compound of formula I in which M is Na, R1 to R4 are hydrogen and X and Y are carboxyl groups are added to 2,930 ml of water. To the above mixture is added 18,000 g titanium dioxide pigment upon which has been precipitated 0.2 percent alumina.

Then a Hockmeyer disperser fitted with a four-inch blade rotating at 2,000 rpm is employed to grind the pigment. After grinding for 20 minutes 1,800 ml of water is added to reduce the solids content of the slurry to 79 percent by weight.

The particle size of the solids is determined using a Micrometrics 5000 Analyzer which shows a mass percent of particles finer than: Mass % Size (,u) 84 0.54 50 0.35 16 0.245 4.0 > 1 65 < 0.4 The air dried gloss and hiding power of the slurry of Example 5 is compared with that of a commercial gloss pigment as described above with the following results: Emulsion Gloss Air Dry H.P.

Slurry of Example 5 67/71 * 101 Control 60/49* 100 * repeat of gloss test.

Example 6 Fifty-four milliliters of 2-amino-2-methyl propanol and 145 ml of a compound of formula I in which M is Na, R1 to R4 are hydrogen and X and Y are carboxyl groups are added to 3,200 ml of water. To the above mixture is added 18,000 g of titanium dioxide which has not been surface treated. Then a Hockmeyer disperser fitted with a four-inch blade rotating at 2,000 rpm is employed to grind the pigment.

After grinding for 20 minutes 1,800 ml of water is added to reduce the solids content to 78.5 percent by weight.

The particle size of the solids in the slurry determined using a Micrometrics 5000 Analyzer which shows a mass percent of particles finer than: Mass % Size (,u) 84 0.43 50 0.31 16 0.225 2.0 > 1 80.0 < 0.4 The gloss, emulsion gloss and hiding power of the slurry of Example 6 is compared with a commercial gloss pigment as described above with the following results: Emulsion Gloss Air Dry Oven Dry H.P.

Slurry of Example 6 66/73* 73 97 Control 60/64* 56 100 * repeat of gloss test.

WHAT WE CLAIM IS: 1. A titanium dioxide pigment aqueous slurry comprising (i) from 60 to 80

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

The following Examples are presented to demonstrate that the high-solids grind followed by dilution to a solids concentration within the range of 60 to 80 percent solids will produce a slurry which provides improved gloss when compared to the same pigment which is dried conventionally and incorporated directly into the paint system.

Example 5 Fifty-four milliliters of 2-amino-2-methyl propanol and 185 ml of a compound of formula I in which M is Na, R1 to R4 are hydrogen and X and Y are carboxyl groups are added to 2,930 ml of water. To the above mixture is added 18,000 g titanium dioxide pigment upon which has been precipitated 0.2 percent alumina.

Then a Hockmeyer disperser fitted with a four-inch blade rotating at 2,000 rpm is employed to grind the pigment. After grinding for 20 minutes 1,800 ml of water is added to reduce the solids content of the slurry to 79 percent by weight.

The particle size of the solids is determined using a Micrometrics 5000 Analyzer which shows a mass percent of particles finer than: Mass % Size (,u)

84 0.54

50 0.35

16 0.245 4.0 > 1

65 < 0.4 The air dried gloss and hiding power of the slurry of Example 5 is compared with that of a commercial gloss pigment as described above with the following results: Emulsion Gloss Air Dry H.P.

Slurry of Example 5 67/71 * 101 Control 60/49* 100 * repeat of gloss test.

Example 6 Fifty-four milliliters of 2-amino-2-methyl propanol and 145 ml of a compound of formula I in which M is Na, R1 to R4 are hydrogen and X and Y are carboxyl groups are added to 3,200 ml of water. To the above mixture is added 18,000 g of titanium dioxide which has not been surface treated. Then a Hockmeyer disperser fitted with a four-inch blade rotating at 2,000 rpm is employed to grind the pigment.

After grinding for 20 minutes 1,800 ml of water is added to reduce the solids content to 78.5 percent by weight.

The particle size of the solids in the slurry determined using a Micrometrics 5000 Analyzer which shows a mass percent of particles finer than: Mass % Size (,u)

84 0.43

50 0.31

16 0.225 2.0 > 1 80.0 < 0.4 The gloss, emulsion gloss and hiding power of the slurry of Example 6 is compared with a commercial gloss pigment as described above with the following results: Emulsion Gloss Air Dry Oven Dry H.P.

Slurry of Example 6 66/73* 73 97 Control 60/64* 56 100 * repeat of gloss test.

WHAT WE CLAIM IS: 1. A titanium dioxide pigment aqueous slurry comprising (i) from 60 to 80

percent by weight of titanium dioxide, from 0.2 to 1 percent by weight based on the weight of the titanium dioxide of a sulfonate compound of the general formula: Formula I

wherein M is alkali metal; R1 to R4 are, each independently, H, -CH3 or -C2H5; X is -CN or -COOR5 wherein R5 is hydrogen or lower alkyl of 1-4 carbon atoms; Y is -COOH or-COONa, and a and bare, each independently, from 10 to 100; and (ii) from 0.1 to 0.6 percent by weight based on the weight of the titanium dioxide of 2 - amino - 2 - methyl - 1 - propanol.
2. A titanium dioxide pigment aqueous slurry comprising from 60% to 80 -" of titanium dioxide and the following constituents by weight on the basis of the weight of titanium dioxide, namely from 0.1 to 0.6% of 2 - amino - 2 - methyl - 1 propanol and from 0.2 to 1% of a sulfonate compound of the general formula: Formula II

in which a, b and Y are each as defined in Claim 1.
3. A slurry as claimed in Claim 1 or Claim 2 which contains from 70 to 80 percent by weight of titanium dioxide.
4. A slurry as claimed in any one of Claims 1 to 3 which contains from 75 to 79 percent by weight titanium dioxide.
5. A slurry as claimed in any preceding claim in which the titanium dioxide is chloride process titanium dioxide which has been dried and ground simultaneously in a fluid energy mill.
6. A slurry as claimed in any preceding claim, wherein the titanium dioxide is in a particulate form in which the particle average size is less than 0.6 micron with not more than 5 mass percent of the particles having a size greater than 1 micron.
7. A titanium dioxide pigment aqueous slurry substantially as described in any one of Examples 2 to 6.
8. A process for producing a titanium dioxide pigment aqueous slurry as claimed in Claim I which process comprises adding one to the other the aqueous solution defined below and such an amount of titanium dioxide to provide in the resulting mixture a titanium dioxide content of from 80 to 90 percent by weight of the mixture, the aqueous solution being an aqueous solution containing the sulfonate compound defined in Claim 1 and 2 - amino - 2 - methyl - 1 - propanol in amounts, based on the weight of titanium dioxide in the mixture, of from 0.2 , to 1% and 0.1% to 0.6%, respectively; grinding the mixture with a disc mill until the titanium dioxide is uniformly dispersed; and, if the titanium dioxide content of the mixture exceeds 80 percent by weight, adding sufficient water to reduce the titanium dioxide content to from 60 to 80 percent by weight of the finished slurry.
9. A process as claimed in Claim 8, wherein an aqueous solution comprising the sulfonate compound defined below and 2 - amino - 2 - methyl - 1 - propanol in amounts respectively as specified in Claim 8 is combined with a titanium dioxide/water mixture in which the water amounts to from 10 to 20% by weight of the slurry to form a mixture in which the titanium dioxide content is in the range from 80 to 90% by weight of such mixtures:- Formula II

in which a, b and Y are each as defined in Claim 1.
10. A process for producing a high solids content titanium dioxide pigment aqueous slurry which process comprises: (a) drying and grinding, in a confined vortex fluid energy mill titanium dioxide pigment prepared by the oxidation of titanium tetrachloride; (b) preparing a solution in an amount of water equal to from 10% to 20% by weight of the pigment slurry of from 0.2 to 1% by weight, based on the weight of titanium dioxide, of a sulfonate compound as defined in Claim 1 or Claim 2, and from 0.1 to 0.6% by weight based on the weight of the titanium dioxide, of 2 amino - 2 - methyl - I - propanol; (c) adding the titanium dioxide of step (a) to form a slurried mixture having a titanium dioxide content of from 80 to 90% by weight; ; (d) grinding the slurried mixture with a disc mill until the titanium dioxide is uniformly dispersed and has a particle size average of less than 0.6 micron with not more than five mass percent of the particles having a size of greater than one micron; (e) adding sufficient water to reduce titanium dioxide content to from 75 to 79 percent by weight of the finished slurry; and (f) mixing the slurry until smooth and uniform.
11. A process as claimed in Claim 8 and substantially as hereinbefore described in any one of Examples 2 to 6.
12. A titanium dioxide pigment aqueous slurry whenever obtained by a process as claimed in any one of Claims 8 to 11.
13. A high gloss emulsion paint which comprises a water-based acrylic coating composition pigmented with a slurry as claimed in any one of Claims I to 7 and 12.