Description

The present invention relates to a process for the solidification of hexyl 2-[4-(diethylamino)-2- hydroxybenzoyl]benzoate (INCI diethylamino hydroxybenzoyl hexyl benzoate, DHHB), wherein the process comprises a step (a) of applying a shear rate of at least 400 s ¹ to liquid hexyl 2-[4- (diethylamino)-2-hydroxybenzoyl]benzoate.

Hexyl 2-[4-(diethylamino)-2-hydroxybenzoyl]benzoate (INCI diethylamino hydroxybenzoyl hexyl benzoate), also referred to as DHHB, is an UV-A filter belonging to the group of benzo- phenone derivatives. It is sold under the tradename Uvinul A Plus by BASF. It has a melting point of ~54 °C.

It is known in the art that solvent-free DHHB melt is hard to crystallize. An undercooled melt can stay in a metastable liquid state for weeks, until it finally crystallizes. An economical solidifi cation process like flaking or pastillation on a cooling belt is not possible with such a very slowly crystallizing product. Only methods like crystallizing DHHB in tubs or drums and afterwards crushing it are applicable. However, these methods have a bad space time yield and lead to non-uniform particle shapes and sizes, which can lead to drawbacks, e.g., regarding its caking properties.

It was therefore an object of the present invention to provide an improved process for the so lidification of DHHB. In particular, it was an object of the present invention to provide a process, which has economic advantages in comparison to the prior art methods. Moreover, it was an object to provide the solidified DHHB in uniform particle shapes and sizes, preferably exhibiting a good flowability.

It has surprisingly been found that at least one of the afore-mentioned objects can be achieved by the process of the present invention. In particular, the present invention relates to a process for the solidification of hexyl 2-[4-(diethylamino)-2-hydroxybenzoyl]benzoate (INCI diethylamino hydroxybenzoyl hexyl benzoate, DHHB), wherein the process comprises a step (a) of applying a shear rate of at least 400 s ¹ to liquid hexyl 2-[4-(diethylamino)-2-hydroxybenzoyl]benzoate.

It has surprisingly been found by the inventors of the present invention that applying a shear rate to a DHHB melt or subcooled melt can provoke a crystallization of DHHB, and therefore strongly accelerate the crystallization.

In a preferred embodiment, the melt has a temperature from more than 54 to 70 °C, preferably from more than 54 to 65 °C or the subcooled melt has a temperature from 15 to 54 °C, prefera bly from 20 to 35 °C.

In a preferred embodiment, the applied shear rate is at least 500 s ¹ , preferably at least 1000 S ¹ or at least 2000 s ¹ . An apparatus, which generates very high shear rates, is an ex truder. In a preferred embodiment, the process of the present invention is therefore performed in an extruder, a scraped surface heat exchanger, a cooling disc crystallizer, or a stirred vessel with scraping agitator.

According to one preferred embodiment, the step (a) is performed in an extruder and the process of the present invention comprises in a preferred embodiment the steps of (a1) heating hexyl 2-[4-(diethylamino)-2-hydroxybenzoyl]benzoate until a liquid melt is ob tained;

(a2) feeding the liquid hexyl 2-[4-(diethylamino)-2-hydroxybenzoyl]benzoate into an extruder; (a3) extruding the liquid hexyl 2-[4-(diethylamino)-2-hydroxybenzoyl]benzoate.

In another preferred embodiment, the step (a) is performed in a scraped surface heat ex changer, a cooling disc crystallizer, or a stirred vessel with scraping agitator and the process of the present invention comprises the steps of

(a1 r) heating hexyl 2-[4-(diethylamino)-2-hydroxybenzoyl]benzoate until a liquid melt is ob tained;

(a2r) cooling the liquid hexyl 2-[4-(diethylamino)-2-hydroxybenzoyl]benzoate to obtain a sub cooled melt of hexyl 2-[4-(diethylamino)-2-hydroxybenzoyl]benzoate;

(a3r) feeding the subcooled melt of hexyl 2-[4-(diethylamino)-2-hydroxybenzoyl]benzoate into an apparatus, preferably a scraped surface heat exchanger, a cooling disc crystallizer, or a stirred vessel with scraping agitator; and

(a4r) applying shearing on the subcooled melt of hexyl 2-[4-(diethylamino)-2-hydroxyben- zoyl]benzoate.

In the following, preferred embodiments regarding the process of the invention are provided. It is to be understood that the preferred embodiments mentioned above and those still to be illus trated below are preferred alone as well as in combination with each other.

As indicated above, the process of the invention comprises a step (a) of applying a shear rate of at least 400 s ¹ to liquid hexyl 2-[4-(diethylamino)-2-hydroxybenzoyl]benzoate, in order to pro voke crystallization.

In a preferred embodiment, the liquid hexyl 2-[4-(diethylamino)-2-hydroxybenzoyl]benzoate is provided as a melt or a subcooled melt. It is to be understood that depending on the used appa ratus the liquid hexyl 2-[4-(diethylamino)-2-hydroxybenzoyl]benzoate is provided either as a melt or as a subcooled melt.

In a preferred embodiment, the melt has a temperature from more than 54 to 70 °C, preferably from more than 54 to 65 °C or the subcooled melt has a temperature from 15 to 54 °C, prefera bly from 20 to 35 °C.

The application of the shear rate is decisive for the time period until nucleation starts and initi ates solidification. Preferably, the shear rate is adapted such that nucleation starts within less than 2 hours, more preferably within less than 1 hour. In a preferred embodiment, the applied shear rate is at least 500 s ¹ , preferably at least 1000 s ¹ or at least 2000 s ¹ . In a more preferred embodiment, the applied shear rate is at least 5000 s ¹ . Preferred shear rates are in the range of from 1000 to 100000, preferably from 2000 to 50000, more preferably from 8000 to 30000. Such high shear rates further reduce the time period until nucleation starts, thereby increasing the efficiency of the solidification process.

As used herein, the term “shear rate” refers to the rate at which progressive shearing defor mation is applied to the liquid DHHB. In general, the shear rate may be determined for a fluid flowing between two parallel plates, one moving at a constant speed and the other one station ary based on the following equation: y = v/h wherein “y” is the shear rate measured in reciprocal seconds, “v” is the velocity of the moving plate, measured in meters per second, and “h” is the distance between the two parallel plates, measured in meters. Based on this principle, the rotational speed and the dimensions of an ap paratus used for the application of the shear rate predetermine the shear rate.

The solidification of DHHB may be further enhanced by applying temperatures below the melt ing point, i.e. temperatures of less than 54 °C. In a preferred embodiment, the step (a) of the process of the invention is performed in an apparatus, which is cooled to a temperature of less than 54 °C, preferably 40 °C or less. Particularly preferred are temperatures in the range of from 20 °C to 35 °C, e.g. about 30 °C.

A suitable apparatus for the process of the invention is an extruder. In a preferred embodi ment, the process of the invention is therefore performed in an extruder. The extruder may be used for partial or complete solidification. Complete solidification may take place within minutes, preferably within 30 minutes, more preferably within 20 minutes. Suitable extruders include sin gle screw and twin screw extruders. Preferred is a twin screw extruder with co-rotating or coun ter-rotating screws. The extruder may be equipped with heating means and cooling means as required. The screw speed, i.e. the rotational speed of the extruder (screw speed, measured in rpm), will be adapted in order to apply the required shear rate. A skilled person is aware that the shear rate also depends amongst other things on the screw diameter and the distance between screw and wall. In particular, a high screw speed, a high screw diameter and a small distance between screw and wall results in a high shear rate and vice versa.

As indicated above, the step (a) of the process is preferably performed in an apparatus, which is cooled to a temperature of less than 54 °C, preferably less than 40 °C. Thus, it is preferred that the barrel temperature of the extruder is less than 54 °C, preferably less than 40 °C. For this purpose, a cryostat may be used.

It is preferred that the DHHB is introduced into the extruder in liquid form. Thus, it is preferred that the DHHB is heated prior to the feeding into the extruder. Accordingly, in a preferred em bodiment, the process of the invention comprises the steps of

(a1) heating hexyl 2-[4-(diethylamino)-2-hydroxybenzoyl]benzoate until a liquid melt is ob tained;

(a2) feeding the liquid hexyl 2-[4-(diethylamino)-2-hydroxybenzoyl]benzoate into an extruder; (a3) extruding the liquid hexyl 2-[4-(diethylamino)-2-hydroxybenzoyl]benzoate.

In one preferred embodiment, in step (a1), a temperature of more than 54 °C is applied. Pref erably, the liquid melt in step (a1) is obtained at a temperature from more than 54 to 80 °C, more preferably from 60 to 75 °C. In another preferred embodiment, the step (a2) is performed under heating of the feed to a temperature of more than 54 °C. Preferably, the liquid hexyl 2-[4- (diethylamino)-2-hydroxybenzoyl]benzoate in step (a2) is fed at a temperature from more than 54 to 75 °C, more preferably from more than 54 to 70 °C, even more preferably from 54 to 65 °C. In yet another preferred embodiment, the step (a3) is performed at a barrel temperature of less than 54 °C, preferably less than 40 °C. Preferably, the liquid hexyl 2-[4-(diethylamino)-2- hydroxybenzoyl]benzoate in step (a3) is extruded at a temperature from 10 to 54 °C, more pref erably from 11 to 50 °C. In another preferred embodiment, in step (a3) the liquid hexyl 2-[4-(di- ethylamino)-2-hydroxybenzoyl]benzoate has a temperature from 10 to 30 °C, more preferably from 12 to 25 °C, even more preferably from 14 to 22 °C, and in particular from 15 to 21 °C.

In another preferred embodiment, the step (a3) is performed at least under atmospheric pres sure, preferably at pressures higher than atmospheric pressure to ensure efficient extrusion from the extrusion head.

The extrusion step (a3) may provide the DHHB in various forms.

In one preferred embodiment, the extrusion step (a3) provides the hexyl 2-[4-(diethylamino)-2- hydroxybenzoyl]benzoate in the form of solidified strands.

In another preferred embodiment, the extrusion step (a3) provides the hexyl 2-[4-(diethyla- mino)-2-hydroxybenzoyl]benzoate in the form of a suspension, which is solidified by a further step of

(a4i) cooling the suspension on a cooling belt or on a drum flaker at a temperature of less than 54 °C, preferably less than 40 °C to obtain a solidified melt.

More preferably, in step (a4i), the suspension is cooled at a temperature in the range of from 20 to 30 °C, in particular at room temperature. The resulting solidified melt may then be broken into flakes or particles in further step following the step (a4i). Thus, in a preferred embodiment, the process further comprises the step of

(a5i) breaking the solidified melt into flakes or particles.

In another preferred embodiment, the extrusion step (a3) provides the hexyl 2-[4-(diethyla- mino)-2-hydroxybenzoyl]benzoate in the form of a suspension, which is solidified by a further step of

(a4ii) forming drops of the suspension and cooling them on a cooling belt at a temperature of 25 °C or less to obtain solidified pastilles.

In a preferred embodiment, the extruder is a single screw extruder or a twin screw extruder, preferably a twin screw extruder.

In a further preferred embodiment, the process of the invention is performed as a continuous process, wherein the liquid hexyl 2-[4-(diethylamino)-2-hydroxybenzoyl]benzoate is continuously fed into the extruder and the hexyl 2-[4-(diethylamino)-2-hydroxybenzoyl]benzoate is continu ously collected from the extruder in the form of solidified strands or in the form of a suspension.

Any apparatus providing sufficient shear rate is suitable, such as a rheometer, scraped surface heat exchanger, a cooling disc crystallizer, or a stirred vessel with scraping agitator. In a pre ferred embodiment, the process of the invention is therefore performed in a rheometer, a scraped surface heat exchanger, a cooling disc crystallizer, or a stirred vessel with scraping agi tator, more preferably a scraped surface heat exchanger, a cooling disc crystallizer, or a stirred vessel with scraping agitator. In this connection, the liquid hexyl 2-[4-(diethylamino)-2-hydroxybenzoyl]benzoate in step (a) of the process is preferably provided as a subcooled melt.

The subcooled melt preferably has a temperature from 15 to 54 °C, more preferably from 15 to 40 °C, even more preferably from 20 to 35 °C, and in particular from 20 to 30 °C.

The apparatus preferably has a temperature from 15 to 54 °C, more preferably from 15 to 40 °C, even more preferably from 20 to 35 °C, and in particular from 20 to 30 °C.

The subcooled melt may be provided according to any known method.

When a scraped surface heat exchanger, a cooling disc crystallizer, or a stirred vessel with scraping agitator is used, it is preferred that the DHHB is introduced into the scraped surface heat exchanger, the cooling disc crystallizer, or the stirred vessel with scraping agitator as sub cooled melt. Thus, it is preferred that the DHHB is first heated and then cooled prior to the feed ing into the suitable apparatus, e.g. a scraped surface heat exchanger, a cooling disc crystal lizer, or a stirred vessel with scraping agitator.

In a preferred embodiment, the process of the invention comprises the steps of (a1 r) heating hexyl 2-[4-(diethylamino)-2-hydroxybenzoyl]benzoate until a liquid melt is ob tained;

(a2r) cooling the liquid hexyl 2-[4-(diethylamino)-2-hydroxybenzoyl]benzoate to obtain a sub cooled melt of hexyl 2-[4-(diethylamino)-2-hydroxybenzoyl]benzoate;

(a3r) feeding the subcooled melt of hexyl 2-[4-(diethylamino)-2-hydroxybenzoyl]benzoate into an apparatus, preferably a scraped surface heat exchanger, a cooling disc crystallizer, or a stirred vessel with scraping agitator; and

(a4r) applying shearing on the subcooled melt of hexyl 2-[4-(diethylamino)-2-hydroxyben- zoyl]benzoate.

In one preferred embodiment, in step (air), a temperature of more than 54 °C is applied. Pref erably, the liquid melt in step (air) is obtained at a temperature from more than 54 to 80 °C, more preferably from 60 to 75 °C. In another preferred embodiment, in step (a2r) the subcooled melt preferably has a temperature from 15 to 54 °C, more preferably from 15 to 40 °C, even more preferably from 20 to 35 °C, and in particular from 20 to 30 °C. In another preferred em bodiment, the step (a4r) is performed at a temperature of less than 54 °C, preferably less than 40 °C, more preferably less than 35 °C, and in particular less than 30 °C. In yet another pre ferred embodiment, the step (a4r) is performed at a temperature from 15 to 54 °C, more prefer ably from 15 to 40 °C, more preferably from 20 to 35 °C, and in particular from 20 to 30 °C.

In another preferred embodiment, the step (a4r) is performed at least under atmospheric pres sure.

The shearing step (a4r) may provide the DHHB in various solidified forms.

The present invention is further illustrated by the following examples.

Examples

Comparative example

Solidification of DHHB was tested under the following conditions Table 1

The results show that the solidification kinetics for DHHB are very slow.

Example 1

Solidification of DHHB in a rheometer Shearing was applied to a subcooled melt of DHHB having a temperature of 25 °C by a rotat ing cone.

Start of nucleation was determined by observing the shear rate and the viscosity. Nucleation starts when the shear rate drops and the viscosity increases.

It was observed that with increasing shear rates, the time period until nucleation started short- ened. The nucleation then initiates the solidification of the DHHB. The results for different shear rates are summarized in Table 2.

Table 2 Example 2

Solidification of DHHB in an extruder

An extruder without a die head was used. For melting the DHHB, a heating cabinet at a tem- perature of 70 °C was used. The feeding unit was heated at a temperature of 60 °C. The ex truder was cooled using a cryostat. The rotational speed of the screw was adapted as indicated in table 3. The throughput of the extruder and the temperature of the extrusion mass were adapted as indicated in table 3. The results for the solidification time are provided in table 3.

Table 3: