Claims:1. A process for preparing silica microbeads, the process comprising:
a) mixing 93-95% w/w silica powder, 3-7% w/w binder, 0.5-1.5% w/w sliding agent and water to obtain a mixture, the silica powder and the water in weight ratio of 1:1 to 1: 1.8;
b) extruding the mixture;
c) spheronizing the extrudate to obtain spheronized particles; and
d) sintering the spheronized particles at a temperature in the range of 600 °C to 1050 °C for a time period in the range of 1-10 hours at a heating rate of 15-30 °C per min to obtain the silica microbeads.

2. The process as claimed in claim 1, wherein the mixture is extruded from an extrusion screen having an aperture size in the range of 0.2-1 mm.

3. The process as claimed in any of claims 1 and 2, wherein the extrusion screen is in the shape of a dome or a cone.

4. The process as claimed in any of claims 1 to 3, wherein the mixture is extruded at a rate of 100-150 rpm.

5. The process as claimed in any of claims 1 to 4, wherein the extrudate is in the form of cylindrical wires of a diameter in the range of 0.2 – 1 mm .

6. The process as claimed in any of claims 1 to 5, wherein the process further comprises drying the extrudate at 100 to 500°C for 30-60 mins prior to the spheronization.

7. The process as claimed in any of claims 1 to 6, wherein the process further comprises heating the spheronized particles at the temperature in the range of 400-500 °C for 30-90 mins prior to the sintering.

8. The process as claimed any of claims 1 to 7, wherein the binder is selected from the group consisting of hydroxypropyl methylcellulose, polyethylene glycol, carboxymethyl cellulose, partially pregelatinized starch and a combination thereof.

9. The process as claimed in any of claims 1 to 8, wherein the sliding agent is selected from the group consisting of sodium sulphate, potassium sulphate, calcium sulphate, eutectic compounds of sodium, potassium or calcium sulphate and a combination thereof.

10. The process as claimed in any of claims 1 to 9, wherein the spheronization is performed for 100-200 sec at a spheronizer speed in the range of 200-300 rpm and a spheronizer load in the range of 200-750 g.

11. The process as claimed in any of claims 1 to 10, wherein the sintering is performed at the temperature in the range of 800-1000 °C for 1-2 hours.

12. The process as claimed in any of claims 1 to 11, wherein average particle size of the silica microbeads obtained is in the range of 100-1000 microns.

13. Silica microbeads having:
an average particle size in the range of¬¬¬ 100-1000 microns
crush strength in the range of ¬¬120-5500 grams;
surface area in the range of 0.4643-10 m2/g;
tap density in the range of 0.5008-1.0872 g/cc; and
pore volume in the range of 0.00252-0.01 cm3/g.

14. The silica microbeads as claimed in claim 13 having the average particle size in the range of 100-700 microns.

15. The silica microbeads as claimed in any of claims 13 and 14 having the crush strength in the range of 300-2000 grams.

16. A personal care composition comprising the silica microbeads as claimed in any of claims 13 to 15.

, Description:FIELD OF THE INVENTION

The present disclosure relates to silica microbeads and a process for preparing them. The present disclosure also relates to personal care compositions containing said silica microbeads.

BACKGROUND OF THE INVENTION

Microbeads are used in a wide range of cosmetic products, including exfoliators, body washes, shower gels, toothpaste, face washes, and various abrasive cleaning products.

Plastic microbeads are tiny balls of polyethylene and other plastics derived from petrochemicals, including polypropylene and polystyrene. However, the use of plastic microbeads poses a significant risk to the environment as well as human and animal health. Due to this reason, plastic microbeads have been banned in several countries.

Silica microbeads are an ideal replacement of the plastic microbeads. Not only are they compatible with other ingredients in the cosmetic composition, they are also environment friendly. Further, they can easily be removed in wastewater treatment plants.

US 2010/0247914 discloses porous silica-based particles and process for preparing them. It also discloses cosmetic compositions containing the disclosed silica-based particles. The spray dried silica microbeads obtained from an already known process suffer from various drawbacks. For example, conventionally obtained silica microbeads lack the required crush strength, affecting their stability.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 depicts a Thermo-Gravimetric Analysis (‘TGA’) profile and selected sintering cycles of the silica microbeads with hydroxypropyl methylcellulose (‘HPMC’).

FIGs 2(a), (b), and (c) depict microstructural features of the silica microbeads, sintered at 600°C, 900°C and 1000°C respectively.
FIGs.2(d), (e), and (f) depict Scanning Electron Microscopy (‘SEM’) micrographs of spherical silica microbeads.

SUMMARY

The present disclosure relates to a process for preparing silica microbeads. The process comprises mixing 93-95% w/w silica powder, 3-7% w/w binder, 0.5-1.5% w/w sliding agent, and water to obtain a mixture, the silica powder and the water are in a weight ratio of 1:1 to 1: 1.8; extruding the mixture; spheronizing the extrudate to obtain spheronized particles; and sintering the spheronized particles at a temperature in the range of 600 °C to 1050 °C for a time period in the range of 1-10 hours at a heating rate of 15-30 °C per min to obtain the silica microbeads.

The present disclosure also relates to silica microbeads having average particle size in the range of 100-1000 microns; crush strength in the range of 120-5500 grams; surface area in the range of 0.4643-10 m2/gram; tap density in the range of 0.5008-1.0872 gram/cc; and pore volume in the range of 0.00252-0.01 cm3/gram.

The present disclosure also relates to a personal care composition comprising the silica microbeads described above.

DETAILED DESCRIPTION

For the purpose of promoting an understanding of the principles of the disclosure, reference will now be made to embodiments and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the disclosure is thereby intended, such alterations and further modifications in the disclosed composition and method, and such further applications of the principles of the disclosure therein being contemplated as would normally occur to one skilled in the art to which the disclosure relates.

It will be understood by those skilled in the art that the foregoing general description and the following detailed description are exemplary and explanatory of the disclosure and are not intended to be restrictive thereof.

Reference throughout this specification to “one embodiment” “an embodiment” or similar language means that a particular feature, or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. Thus, appearances of the phrase “in one embodiment”, “in an embodiment” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment. The present disclosure relates to silica microbeads and a process for preparing the same. The disclosed silica microbeads are suitable for various applications. The silica microbeads are particularly suitable for cosmetic, skin care and personal care compositions. The present disclosure also relates to cosmetic and personal care compositions comprising the disclosed microbeads.

A process for preparing silica microbeads is disclosed. The process comprises mixing 93-95% w/w silica powder, 3-7% w/w binder, 0.5-1.5% w/w sliding agent and water to obtain a mixture, the silica powder and the water in weight ratio of 1:1 to 1: 1.8; extruding the mixture; spheronizing the extrudate to obtain spheronized particles; and sintering the spheronized particles at a temperature in the range of 600 °C to 1050 °C for a time period in the range of 1-10 hours at a heating rate of 15-30 °C per min to obtain the silica microbeads.

In an embodiment, the silica powder has an average particle size in the range of 5-15 nm.

Any suitable binder may be used in the process. Examples of the binder suitable for use in the process include but are not limited to HPMC, polyethylene glycol, carboxymethyl cellulose, partially pregelatinized starch and a combination thereof. In an embodiment, the binder is HPMC.

Any suitable sliding agent may be used in the process. Examples of the sliding agent suitable for use in the process include but are not limited to sodium sulphate, potassium sulphate, calcium sulphate, eutectic compounds of sodium, potassium or calcium sulphate and a combination thereof. In an embodiment, the sliding agent is sodium sulphate.

The silica powder, water, the binder and the sliding agent can be mixed together sequentially in any order or simultaneously. In an example, the silica powder and water are mixed prior to addition of the binder and the sliding agent.

In accordance with an embodiment, the silica powder and water are present in the weight ratio in the range of 1:1 to 1: 1.4. In accordance with an embodiment, the silica powder and water are present in the weight ratio of 1:1.

The extrudate may be in the form of granules, pellets, strands, or cylindrical wires. In accordance with a specific embodiment, the extrudate is in the form of cylindrical wires of a diameter in the range of 0.2-1 mm.

Any suitable extruder may be used for extruding the mixture. For example, the extruder can be a single screw extruder or a twin-screw extruder. In a specific embodiment, the extruder is a single screw extruder. In another embodiment, the extruder is a twin-screw extruder. The size of an extrusion screen for extruding the mixture depends on the desired diameter of the extrudate. In accordance with an embodiment, the mixture is extruded from the extrusion screen having an aperture size in the range of 0.2-1 mm. In accordance with an embodiment, the extrusion screen is in the shape of a dome or a cone. The mixture is extruded at a rate of 100-150 rpm. In a specific embodiment, the mixture is extruded at a rate of 10-20 meter/min.

The extrudate may be subjected to drying prior to the spheronization. In accordance with an embodiment, the extrudate is subjected to drying at a temperature of 100 to 500 °C for 30-60 mins prior to the spheronization. In an embodiment, the temperature is in the range of 100 to 200 °C. In a specific embodiment, the temperature is 100 °C.

In accordance with an embodiment, the spheronization is performed for 100-200 sec at a spheronizer speed in the range of 200-300 rpm and a spheronizer load in the range of 200-750 g.

The spheronized particles obtained after the spheronization step, are then subjected to sintering. The temperature for sintering is selected based on glass transition or melting temperature of the spheronized particles. In accordance with a specific embodiment, the sintering is performed at the temperature in the range of 800-1000 °C for 1-2 hours.

In accordance with an embodiment, the spheronized particles are subjected to heating at the temperature in the range of 400-500 °C for 30-90 mins prior to the sintering to reduce the impurities in the spheronized particles.

The silica microbeads in accordance with the present disclosure have an average particle size in the range of 100-1000 microns, crush strength in the range of 120-5500 grams; surface area in the range of 0.4643-10 m2/g; tap density in the range of 0.5008-1.0872 g/cc; and pore volume in the range of 0.00252-0.01 cm3/g.

In accordance with an embodiment, the average particle size of the silica microbeads is in the range of 100-700 microns.

In accordance with an embodiment, the crush strength of the silica microbeads is in the range of 300-2000 grams.

In accordance with an embodiment, the silica microbeads have a highly porous structure with an interconnected capillary network similar to a sponge.

The present disclosure also relates to personal care compositions comprising the disclosed silica microbeads. Examples, of the personal care compositions include but are not limited to cosmetic and skin care compositions or formulations such as moisturizers, creams, lotions, nail polishes, make-up preparations, lipsticks, wipes, scrubs and exfoliating compositions, hair products such as shampoos, and conditioners, shaving creams, gels and foams, body washes, soaps, and toothpastes.

EXAMPLES

The following examples are provided to explain and illustrate the preferred embodiments of the present disclosure and do not in any way limit the scope of the disclosure as described:

Example 1: Extrusion, spheronization and sintering of silica

A wet mix was formed by mixing of the silica powder and water in the ratio of 1: 1:1 % w/w, 5 wt. % HPMC binder and 0.5 – 1.5 % sodium sulfate. The wet mix so obtained was extruded in a single screw extruder (USSE-60). The extrusion screen aperture was 0.5 mm and the extrusion rate was 100-150 rpm. After the extrusion, the extrudate so obtained was dried at a temperature of 100 ºC.

The dried extrudate was subjected to spheronization (in Spheronizer ‘USPH 250’) to obtain spheronized particles. The spheronizer plate groove size was 2/2.5 mm, and the spheronizer speed was 300 rpm for 250 sec.

The spheronized particles were then subjected to sintering. Temperature for the sintering was selected based on the glass transition/melting temperature and TGA profile of the silica and HPMC microbeads as depicted in FIG.1 Accordingly, the sintering temperature was varied from 600 to 1050 °C.

Example 2: Evaluation of mechanical properties of silica microbeads

Mechanical properties of the obtained silica microbeads were measured using CT3 texture analyser from Brookfield instruments. Crush strength/force of particle is directly proportional to area and hardness (yield strength is considered). The crush strength of the silica microbeads was analysed in compression mode and Chang, Etsion and Bogy (CEB) model-based values were measured.

Example 3: Sintering behaviour of the silica microbeads at 900 °C and 1000 °C

Various samples (v1 to v4) of the silica powder were prepared as given in Table 1.

Table 1: Preparation of the silica powder samples

Property
Without CTAB (Cetyl trimethylammonium bromide), without Sulphate With CTAB, without Sulphate Without CTAB, With Sulphate With CTAB, With Sulphate
Variant 1(v1) Variant 2(v2) Variant 3(v3) Variant 4(v4)
Oil absorption (ml/100g) 200 215 180 201.3
Particle size, d50 (?m) 10.9 9.5 9.8 9.93
pH value 6.1 4.8 6.6 6.51
Conductivity ?S/cm 15 124 330 186
Sulphate content % Not detectable Not detectable 0.43 0.20
Tamped density (g/cc) 0.2675 0.2008 0.2478 0.2197

The samples v1-v4 were then used to prepare the silica microbeads. Tables 2 and 3 provide mechanical and physical properties and crush strength of the silica microbeads so obtained.

Table 2: Mechanical and physical properties of the silica microbeads sintered at 900 °C and 1000°C

Type of silica microbeads Crush strength of the silica microbeads(grams) Weight loss % Shrinkage by Vol. %
900 °C 1000 °C 900 °C 1000 °C 900 °C 1000 °C
Sintered microbeads obtained from v1 73-230 147-286 42.12097095 41.52584909 24.09638554 50
Sintered microbeads obtained from v2 44-86 103-321 19.78695933 20.11070111 24.3902439 31.12244
Sintered microbeads obtained from v3 122-342 153-583 43.32090371 43.39428277 48.19277108 72.1428
Sintered microbeads obtained from v4 127-324 210-5414 34.17366947 32.64259774 32.22222222 69.1489

Table 3: Crush strength of the silica microbeads obtained

Type of silica microbeads
Crush strength (grams)
900 °C 1000 °C
Sintered microbeads obtained from v1 73-230 147-286
Sintered microbeads obtained from v2 44-86 103-321
Sintered microbeads obtained from v3 122-342 153-583
Sintered microbeads obtained from v4 127-324 210-5414

Few samples of the silica microbeads were prepared after sintering in the temperature range of 600-1050 °C. Table 5 includes the nomenclature for the silica microbeads prepared.

Table 4. Sintering temperature with nomenclature of the silica microbeads

S No. 5 wt. % HPMC based Silica microbead codes
Sintering temperature °C Silica microbead size (mm)

0.125-0.3 0.3-0.5 0.5-1
Sample /Silica microbead nomenclature
1 600 5S60 5M60 5L60
2 650 5S65 5M65 5L65
3 700 5S70 5M70 5L70
4 750 5S75 5M75 5L75
5 800 5S80 5M80 5L80
6 850 5S85 5M85 5L85
7 900 5S90 5M90 5L90
8 1050 5S105 5M105 5L105
9 0 5S00 5M00 5L00
10 Commercial HPMC - colour 0.25- 0.6 mm MCC
11 Commercial HPMC- white 0.7 mm MCW

Table 5: The mechanical properties of different silica microbeads sintered at a temperature in the range of 600-1050°C

S.No. Sample / Silica microbead Nomenclature Silica microbead size - 300 ?m Silica microbead size - 500 ?m Stability in Cream
Crush Strength-Force (g) Crush Strength-Force (g)
1 5M60 33 70 -
2 5M65 41 340 -
3 5M70 191 455 good
4 5M75 168 386 good
5 5M80 600 702 good
6 5M85 345 962 good
7 5M90 630 1500 good
8 5M105 950 1884 good
9 5M00 20 41 -
10 MCC 63 544 -
11 MCW 260 850 good

FIGs. 2(a), (b) and (c) depict microstructural features of the silica microbeads, sintered at 600 °C, 900°C and 1000 °C respectively. FIGs 2(d), (e) and (f) depict Scanning Electron Microscopy (‘SEM’) micrographs of spherical silica microbeads. As observed from the FIGs. 2 (a) to (c), as sintering temperature increases, the number of contacts and corresponding contact area between the primary particles also increases. Further, the morphology of the microbeads is spherical, which is very effective for scrubbing/feeling.

Example 4: Preparation and analysis a cream base with the silica microbeads

A cream base was prepared with the silica microbeads and their mechanical properties were analysed.
Table 6: Composition of the cream base
Phase Ingredients %
A Caprylic Capric triglyceride 15
Beeswax 2
Sheabutter 2
Stearic acid 2
Cetyl alcohol 2
Lanolin 7
Glyceryl Monostearate, PEG 100 Stearate 2
B Xanthan Gum 0.3
DI Water QS
Glycerol 5
Propylene glycol 3
Avalure Flex 6 1
C Silica microbeads 1%-10%
D Germaben II 0.5

Table 7: Comparison of physical and mechanical propertied of the silica microbeads obtained from v1, v4 with commercial silica microbeads

Type of beads wt. % beads in cream Crush strength of the silica microbeads soaked in the cream (grams) Particle size d50 (microns) Tap density (g/cc) surface area (m²/g) Pore Volume (cm³/g)
Day1 Day28
Sintered microbeads obtained from v1 5 98-565 166-439 373 0.7133 44.1979 0.358652
Sintered microbeads
obtained from v4 5 375-958 386-1230 358 1.08 0.4643 0.00252
Commercial silica 5 ~15 15- 22 320 0.25 190 …

Example 5: Sensory analysis of cream with the silica microbeads

Dated: 31/01/2019
No of Panellist: 10 (6 Female & 4 Male)

A cream base blended with 5% sintered silica microbeads obtained from v4 having size less than 300µm and competitor beads were subjected to a sensory test by 10 panellists and the performance was evaluated based on following parameters:
- Shape & size of beads
- Feel during application
- Scrubbing efficacy of beads
- Reddening during & after application
- Overall preferred

The results were evaluated in accordance with the criteria for scoring as given below-
5: Like very much
4: Like moderately
3: Neither like nor dislike
2: Dislike moderately
1: Dislike very much

Sample 1: 5% competitor’s silica microbeads
Sample 2: 5%, sintered silica microbeads obtained from v4

Table 8: Summary of responses of the panellists to Sample 1 and 2

Criteria Size & Shape of beads Feel during application Scrubbing efficacy Reddening on skin Overall
Samples 1 2 1 2 1 2 1 2 1 2
No. of panellist preferring one sample over the other 3 7 2 7 3 6 No No 3 7

Based on the responses in Table 8 it can be concluded that Sample 2 with sintered silica microbeads obtained from v4 is found to have performed better over the competitor in most of the criteria.

INDUSTRIAL APPLICABILITY

The silica microbeads prepared by the disclosed process are suitable for use in various types of personal care compositions. The disclosed silica microbeads can be easily incorporated in the personal care compositions. Further, the disclosed silica microbeads are compatible with other ingredients present in the compositions. Also, the silica microbeads are environment friendly and can be easily removed in waste water treatment plants. They do not pose any risk to the human and animal health.

The disclosed silica microbeads exhibit high absorption capacity and enable formation of compact, sustainable and economical powder formulations. Due to their improved flowability and reduced caking tendency, the disclosed silica microbeads facilitate incorporation of temperature sensitive ingredients in the personal care compositions and enable the incorporation of incompatible ingredients in the compositions. The silica microbeads also allow easier processing of liquid ingredients into powder formulation. The silica microbeads have controlled porosity and can act as carriers of liquid ingredients.