Preparation of nano-sized UV absorbers

Abstract

The invention relates to an improved process for the manufacture of nano-sized organic UV absorbers having a mean particle size distribution (D.sub.v50) determined by light scattering of less than 200 nm.

Claims

1. A process for the preparation of a milled suspension comprised of an aqueous dispersion of a nano-sized insoluble organic UV absorber having a particle size Dv50 determined by light scattering of less than 200 nm, wherein the process comprises the steps of: (a) providing a suspension of coarse particles of an insoluble organic UV absorber having a particle size Dv90 determined by laser diffraction in the range of 75 to 90 μm in a mixture of water and a C.sub.8-C.sub.10 alkyl polyglucoside; and (b) milling the suspension in the absence of an anti-foam agent in a ball mill using yttrium-stabilized zirconium oxide grinding beads until the insoluble organic UV absorber has a particle size Dv50 of less than 200 nm to thereby obtain the milled suspension, wherein the insoluble organic UV absorber is a compound of formula (I): ##STR00003## wherein R.sup.1 is a C.sub.1-C.sub.18 alkyl group which is optionally substituted by phenyl.

2. The process according to claim 1, wherein step (b) is practiced until the particle size Dv50 of the nano-sized insoluble organic UV absorber is 50 to 150 nm.

3. The process according to claim 1, wherein the compound of formula (I) is a compound of formula (Ia): ##STR00004##

4. The process according to claim 1, wherein step (a) comprises a step of: (i) suspending the coarse particles of the insoluble organic UV absorber in a mixture of water and the C.sub.8-C.sub.10 alkyl polyglucoside to obtain the suspension.

5. The process according to claim 4, wherein step (i) comprises an additional step (ia) prior to step (b), wherein step (ia) includes degassing the suspension.

6. The process according to claim 4, wherein the process further comprises the subsequent steps of: (c) removing the grinding beads from the milled suspension, followed by (d) adding a mixture of a thickener and propylene glycol to the milled suspension.

7. The process according to claim 6, wherein the thickener is selected from the group consisting of xanthan gum, gellan gum and carboxymethylcellulose.

8. The process according to claim 7, wherein the propylene glycol and xanthan gum are present in a weight-ratio (w/w) of the propylene glycol to the xanthan gum of 3:1 to 1:3.

9. The process according to claim 1, wherein the suspension consists of: a) 45-55 wt.-%, based on the total weight of the suspension, of the coarse particles of the insoluble organic UV absorber, b) 10-20 wt.-%, based on the total weight of the suspension, of the C.sub.8-C.sub.10 alkyl polyglucoside, and c) 25-40 wt.-% of water, based on the total weight of the suspension, wherein the ingredients a) to c) sum to 100 wt.-%.

10. The process according to claim 9, wherein the suspension consists of: a) 48-52 wt.-%, based on the total weight of the suspension, of the coarse particles of the insoluble organic UV absorber, b) 13-17 wt.-%, based on the total weight of the suspension, of the C.sub.8-C.sub.10 alkyl polyglucoside, and c) 30-35 wt.-%, based on the total weight of the suspension, of water.

11. The process according to claim 1, wherein grinding beads have a diameter of 0.1-0.5 mm.

Description

EXAMPLE 1

Milling

(1) a) 22 kg of purified water was added into a 100 l vessel at 30-35° C. Afterwards 9.8 kg Green APG 0810 were added. Then 33 kg Grandsorb UV360 having a coarse particle size Dv90 of 86 μm (measured by laser diffraction with a Malvern Mastersizer 3000, powder measurement, air pressure 0.2 bar) was slowly added over a time period of 30 minutes followed by degassing the resulting suspension for 2 h under gentle stirring at 65° C. The resulting suspension was then cooled down to 25-30° C. Afterwards 50 kg of the resulting suspension was milled in a LMZ 4 using yttrium-stabilized zirconium oxide grinding beads (0.3 mm, 95% ZrO.sub.2, 5% Y.sub.2O.sub.3 from Tosoh Ceramic, Japan) until a particle size Dv50 of about 100 nm (measured by light scattering with a Coulter Delsa Nano S, at an adjusted concentration of 3 mg/ml) was obtained. Only little foam formation during the milling was observed, which was well tolerated by the milling process. After removal of the grinding beads, a suspension consisting of 161 g of propyleneglycol and 80.5 g of xanthan was slowly added under gentle stirring at about 40° C. resulting in the final product form.

(2) b) The same experiment as outlined in a) was repeated with Grandsorb UV360 having a coarse particle size Dv90 of 262 μm. In this case uncontrolled foaming shortly after the start of the milling was observed which led to the termination of the milling process.

(3) c) The same experiment as outlined in a) was repeated with PlantaCare 2000 UP. In this case more foaming compared to Green APG 0810 during milling was observed, which was however still tolerable to run the process to the end.

EXAMPLE 2

Analytics of Alkyl Polyglucosides

(4) The respective samples have been dissolved in a mixture of tetrahydrofurane/water (50/50), approx. 1 mg/ml, and were analysed by HPLC mass spectrometry using a reversed-phase YMC Pro C.sub.4 column with a water/acetonitrile gradient with 0.1% methanesulfonic acid (5.fwdarw.90% acetonitrile over 15 min). Detection was performed on an Agilent 6130 single MSD operating in ES positive mode. TIC and EIC were used to determine the relative distribution of the compounds of interest. The relative distribution of the alkyl monoglucosides is outlined in table 1. All % are area-%.

(5) TABLE-US-00001 TABLE 1 Relative distribution of the alkyl mono glucosides Relative amount [%] Alkyl (8-16) C8-C10 Sample Glucoside* polyglucoside° C.sub.8 monoglucoside 20.8 44.1 C.sub.10 monoglucoside 16.6 54.7 C.sub.12 monoglucoside 41.5 1.2 C.sub.14 monoglucoside 20.1 n.d. C.sub.16 monoglucoside 0.9 n.d. *Commercially available as Plantacare UP 2000 at Cognis; approx. absolute amount as determined by HPLC-MS of C.sub.8/C.sub.10/C.sub.12/C.sub.14/C.sub.16 alkyl monoglucoside~77% (area %) °Commercially available as Green APG 0810 at Shanghai Fine Chemicals; approx. absolute amount as determined by HPLC-MS of C.sub.8/C.sub.10 alkyl monoglucoside~78% (area %) n.d.: not detected