SURFACE-REACTED CALCIUM CARBONATE FOR USE AS ANTI-CAKING AGENT

Abstract

The present invention relates to the use of a surface-reacted calcium carbonate as anti-caking agent, wherein the surface-reacted calcium carbonate is a reaction product of natural ground or precipitated calcium carbonate with carbon dioxide and at least one acid in an aqueous medium, wherein the carbon dioxide is formed in situ by the acid treatment and/or is supplied from an external source, and to a composition comprising said anti-caking agent, as well as to a method for the production of such a composition.

Claims

1. Use of a surface-reacted calcium carbonate as anti-caking agent, wherein the surface-reacted calcium carbonate is a reaction product of natural ground or precipitated calcium carbonate with carbon dioxide and at least one acid in an aqueous medium, wherein the carbon dioxide is formed in situ by the acid treatment and/or is supplied from an external source.

2. Use according to claim 1, wherein the natural ground calcium carbonate is selected from calcium carbonate containing minerals, preferably selected from the group consisting of marble, chalk, dolomite, limestone, and mixtures thereof.

3. Use according to claim 1, wherein the precipitated calcium carbonate is selected from the group consisting of precipitated calcium carbonates having aragonitic, vateritic or calcitic mineralogical crystal forms, and mixtures thereof.

4. Use according to claim 1, wherein the surface-reacted calcium carbonate has a specific surface area of from 1 m.sup.2/g to 200 m.sup.2/g, preferably from 20 m.sup.2/g to 180 m.sup.2/g, more preferably from 30 m.sup.2/g to 160 m.sup.2/g, even more preferably from 40 m.sup.2/g to 150 m.sup.2/g, and most preferably from 50 m.sup.2/g to 140 m.sup.2/g, measured using nitrogen and the BET method according to ISO 9277.

5. Use according to claim 1, wherein the surface-reacted calcium carbonate particles have a volume median grain diameter d.sub.50 of from 0.1 to 50 μm, preferably from 0.5 to 25 μm, more preferably from 0.8 to 20 μm, even more preferably from 1 to 10 μm, and most preferably from 4 to 8 μm.

6. Use according to claim 1, wherein the surface-reacted calcium carbonate has an intra-particle intruded specific pore volume within the range of 0.150 to 1.300 cm.sup.3/g, preferably of 0.300 to 1.250 cm.sup.3/g, and most preferably of 0.400 to 1.210 cm.sup.3/g, calculated from a mercury intrusion porosimetry measurement.

7. Use according to claim 1, wherein the at least one acid is selected from the group consisting of hydrochloric acid, sulphuric acid, sulphurous acid, phosphoric acid, citric acid, oxalic acid, acetic acid, formic acid, and mixtures thereof, preferably the at least one acid is selected from the group consisting of hydrochloric acid, sulphuric acid, sulphurous acid, phosphoric acid, oxalic acid, and mixtures thereof, and more preferably the at least one acid is phosphoric acid or a mixture of phosphoric acid and citric acid.

8. Use according to claim 1, wherein the anti-caking agent is used in a composition selected from the group consisting of a food composition, a feed composition, a nutraceutical composition and a cosmetic composition, and preferably the composition is selected from a food composition or a feed composition.

9. Use according to claim 8, wherein the food composition is food salt, curing salt, salt substitute, milk powder, skimmed milk powder, cream powder, egg powder, whey fat powder, protein powder, vending machine powder, grated cheese, sugar, powdered food flavour, spice, seasoning, packet soup mixture, baking mixture, pudding powder, mousse powder, or sauce powder.

10. Use according to claim 8, wherein the feed composition is pet food, milk replacer for animals, or mineral salt for animals.

11. Method for controlling, reducing or preventing caking of a particulate composition, the method comprising the step of adding to a particulate composition a surface-reacted calcium carbonate, wherein the surface-reacted calcium carbonate is a reaction product of natural ground or precipitated calcium carbonate with carbon dioxide and at least one acid in an aqueous medium, wherein the carbon dioxide is formed in situ by the acid treatment and/or is supplied from an external source.

12. A composition comprising an anti-caking agent, wherein the anti-caking agent contains surface-reacted calcium carbonate, wherein the surface-reacted calcium carbonate is a reaction product of natural ground or precipitated calcium carbonate with carbon dioxide and at least one acid in an aqueous medium, wherein the carbon dioxide is formed in situ by the acid treatment and/or is supplied from an external source, wherein the composition is selected from the group consisting of a food composition, a feed composition, a nutraceutical composition and a cosmetic composition.

13. Composition according to claim 12, wherein the surface-reacted calcium carbonate is present in the composition in an amount between 0.1 and 10 wt.-%, preferably in an amount between 0.2 and 5 wt.-%, more preferably in an amount between 0.3 and 3 wt.-%, and most preferably in an amount between 0.5 and 2.5 wt.-%, based on the total weight of the composition.

14. Method for the production of a composition, the method comprising the step of mixing a surface-reacted calcium carbonate with a composition selected from the group consisting of a food composition, a feed composition, a nutraceutical composition and a cosmetic composition, wherein the surface-reacted calcium carbonate is a reaction product of natural ground or precipitated calcium carbonate with carbon dioxide and at least one acid in an aqueous medium, wherein the carbon dioxide is formed in situ by the acid treatment and/or is supplied from an external source.

Description

DESCRIPTION OF THE FIGURES

[0125] FIG. 1 shows a scanning electron microscope (SEM) micrograph of amorphous silica precipitate.

[0126] FIG. 2 shows a magnified section of FIG. 1.

[0127] FIG. 3 shows a scanning electron microscope (SEM) micrograph of surface-reacted calcium carbonate particles.

EXAMPLES

1. Measurement Methods

[0128] In the following, measurement methods implemented in the examples are described.

BET Specific Surface Area (SSA)

[0129] The BET specific surface area is measured via the BET process according to ISO 9277 using nitrogen, following conditioning of the sample by heating at 250° C. for a period of 30 minutes. Prior to such measurements, the sample is filtered within a Büchner funnel, rinsed with deionised water and dried at 110° C. in an oven for at least 12 hours.

Particle Size Distribution

[0130] The volume median particle size d.sub.50 of surface-reacted calcium carbonate was evaluated using a Malvern Mastersizer 2000 Laser Diffraction System (Malvern Instruments Plc., Great Britain). The d.sub.50 or d.sub.98 value, measured using a Malvern Mastersizer 2000 Laser Diffraction System, indicates a diameter value such that 50% or 98% by volume, respectively, of the particles have a diameter of less than this value. The raw data obtained by the measurement are analysed using the Mie theory, with a particle refractive index of 1.57 and an absorption index of 0.005.

[0131] The weight median particle size of all other particulate materials, e.g. natural ground or precipitated calcium carbonate is determined by the sedimentation method, which is an analysis of sedimentation behaviour in a gravimetric field. The measurement is made with a Sedigraph™ 5100, Micromeritics Instrument Corporation. The method and the instrument are known to the skilled person and are commonly used to determine grain size of fillers and pigments. The measurement is carried out in an aqueous solution of 0.1 wt.-% Na.sub.4P.sub.2O.sub.7. The samples are dispersed using a high speed stirrer and supersonicated.

Porosity/Pore Volume

[0132] The porosity or pore volume was measured using a Micromeritics Autopore IV 9500 mercury porosimeter having a maximum applied pressure of 414 MPa (60 000 psi), equivalent to a Laplace throat diameter of 0.004 μm. The equilibration time used at each pressure step was 20 seconds. The sample material was sealed in a 5 ml chamber powder penetrometer for analysis. The data were corrected for mercury compression, penetrometer expansion and sample material compression using the software Pore-Comp (Gane, P. A. C., Kettle, J. P., Matthews, G. P. and Ridgway, C. J., “Void Space Structure of Compressible Polymer Spheres and Consolidated Calcium Carbonate Paper-Coating Formulations”, Industrial and Engineering Chemistry Research, 35(5), 1996, p 1753-1764.).

2. Materials

Anti-Caking Agents

[0133] Monocalcium phosphate (MCP-M fine), (ICL Food Specialities, Distributor Omya AG, Switzerland; d.sub.50=2.9 μm, d.sub.98=10 μm).

[0134] Natural ground calcium carbonate (GCC) (Kemalpasa, Turkey, Omya Calcipur 110-KP, Omya AG, Switzerland; d.sub.50=2.2 μm, d.sub.98=9 μm).

[0135] Amorphous silica precipitate comprising agglomerates of primary nano-scale particles (silica), (d.sub.50=15 μm (secondary particles)).

[0136] Calcium citrate (Ca-citrate), (produced as described in U.S. Pat. No. 5,149,552; SSA=6.2 m.sup.2/g).

[0137] Surface-reacted calcium carbonate (SRCC1) (d.sub.50=7.3 μm, d.sub.98=16.6 μm, SSA=52.1 m.sup.2 g.sup.−1) prepared according to Example 1.

[0138] Surface-reacted calcium carbonate (SRCC2) (d.sub.50=30.4 μm, d.sub.98=64.6 μm, SSA=139.5 m.sup.2g.sup.−1) prepared according to Example 2.

Particulate Composition

[0139] Sea salt (Migros M classic, Migros, Switzerland).

3. Examples

Example 1—Preparation of Surface-Reacted Calcium Carbonate SRCC1

[0140] In a mixing vessel, 330 litres of an aqueous suspension of natural ground calcium carbonate was prepared by adjusting the solids content of a ground limestone calcium carbonate from Omya SAS, Orgon, having a weight based median particle size of 1.3 μm, as determined by sedimentation, such that a solids content of 10 wt.-%, based on the total weight of the aqueous suspension, was obtained.

[0141] Whilst mixing the suspension at a speed of 12.7 m/s, 10.6 kg of an aqueous solution containing 30 wt.-% phosphoric acid, based on the total weight of the aqueous solution, was added to said suspension over a period of 12 minutes at a temperature of 70° C. After the addition of the acid, the slurry was stirred for additional 5 minutes, before removing it from the vessel and drying. During acid treatment carbon dioxide was formed in situ in the aqueous suspension.

[0142] The resulting surface-reacted calcium carbonate SRCC1 had an intra-particle intruded specific pore volume of 0.871 g/cm.sup.3 for the pore diameter range of 0.004 to 0.4 μm, a volume median grain diameter (d.sub.50) of 7.3 μm and a d.sub.98 of 16.6 μm as measured by laser diffraction (Malvern Mastersizer 2000) and a specific surface area of 52.1 m.sup.2g.sup.−1.

Example 2—Preparation of Surface-Reacted Calcium Carbonate SRCC2

[0143] In a mixing vessel, 10 litres of an aqueous suspension of natural ground calcium carbonate was prepared by adjusting the solids content of a ground limestone calcium carbonate from Omya SAS, Orgon, having a weight based median particle size of 1.2 μm, as determined by sedimentation, such that a solids content of 10 wt.-%, based on the total weight of the aqueous suspension, was obtained.

[0144] Whilst mixing the suspension, 1.8 kg of an aqueous solution containing 30 wt.-% phosphoric acid, based on the total weight of the aqueous suspension, was added to said suspension over a period of 10 minutes at a temperature of 70° C. Additionally, starting 2 minutes after the start of phosphoric acid addition, 53 g citric acid was added in form of a solution containing 50 wt.-% citric acid, over a period of 20 seconds. After the addition of the phosphoric acid and the citric acid, the slurry was stirred for additional 5 minutes, before removing it from the vessel and drying. During the acid treatment carbon dioxide was formed in situ in the aqueous suspension.

[0145] The resulting surface-reacted calcium carbonate SRCC2 had an intra-particle intruded specific pore volume of 1.206 g/cm.sup.3 for the pore diameter range of 0.004 to 0.8 μm, a volume median grain diameter (d.sub.50) of 30.4 μm and a d.sub.98 of 64.6 μm as measured by laser diffraction (Malvern Mastersizer 2000) and a specific surface area of 139.5 m.sup.2g.sup.−1.

Example 3—Caking Trials—Sea Salt

[0146] Sea salt was used as particulate composition. As can be gathered from Tables 2 and 3 below, samples were prepared by mixing the particulate composition with 1.0 wt.-% of the respective anti-caking agent, based on the total weight of the sample. As reference example, the respective particulate composition without a caking-agent was used.

[0147] 10 g of each sample were put into a porcelain dish and were placed in a climate chamber (ratioTEC Prüfsysteme GmbH, Germany) for five days. The parameters of the climate chamber are given in Table 1 below.

TABLE-US-00001 TABLE 1 Parameters of the climate chamber. Time Temperature in ° C. Relative Humidity in % 0 h .sup.   15 69 12 h     14 93 1 day.sup.  12 80 2 days 13 79 3 days 12 85 4 days 13 90

[0148] After each day the consistency of the particulate compositions was evaluated visually.

[0149] The results of the caking trials are listed in Tables 2 and 3 below.

TABLE-US-00002 TABLE 2 Particulate compositions with comparative anti-caking agents. No anti- 1.0% MCP- 1.0% 1.0% 1.0% Ca- Day caking agent M fine GCC silica citrate 1 5 5 5 2 3 2 5 5 5 3 3 3 5 5 5 3 3 4 5 5 5 4 5

TABLE-US-00003 TABLE 3 Particulate composition with inventive anti-caking agents. Day 1.0% SRCC 1 1.0% SRCC 2 1 3 1 2 3 1 3 3 1 4 3 4

[0150] The numbers have the following meaning:

1=powder
2=between powder and compact
3=half compact
4=compact with a little separate pieces of salt
5=compact.

[0151] As can be seen from the results compiled in Tables 2 and 3, the samples comprising the inventive anti-caking agents maintain their powdered form or remain at least in a half-compacted state, i.e. the caking is reduced. The results clearly show that the compositions have a good separation efficacy in comparison to the comparative compositions comprising conventional anti-caking agents like monocalcium phosphate (MCP-M fine), ground calcium carbonate (GCC) or calcium citrate (Ca citrate).

[0152] Only the composition comprising 1 wt.-% of amorphous silica precipitate, based on the total weight of the compositions, shows comparable good anti-caking properties. However, anti-caking agents such as amorphous silica precipitate suffer from the drawback that they are in form of aggregates or secondary particles, which in turn consist of primary nano-scale particles. Therefore, a composition comprising such an anti-caking agent may have to be labelled in the future as containing nano-scale particles on the final package, which is undesirable.

[0153] Scanning electron microscope (SEM) micrograph pictures of the amorphous silica are shown in FIGS. 1 and 2. FIG. 2 is a magnified section of FIG. 1, which reveals that primary nano-size particles are agglomerated to bigger secondary particles having a particles size in the micrometre range. For comparison, FIG. 3 shows a SEM micrograph of a surface-treated calcium carbonate according to the present invention. The porous surface structure of the surface-reacted calcium carbonate is clearly visible and it can be gathered from FIG. 3 that nano-size particles are not present.

[0154] The results of the caking trials confirm that surface-reacted calcium carbonate according to the present invention provide good anti-caking properties at already low amounts.

Example 4—Caking Trials—Flavor Seasoning

[0155] Cheese and onion snack seasoning (Saporesse Plus YEL001-274, obtained from Synergy Corby Ltd., Corby, Northamptonshire, UK) was used as particulate composition. As can be gathered from Tables 5 and 6 below, samples were prepared by mixing the particulate composition with 1.0 wt.-% of the respective anti-caking agent, based on the total weight of the sample. As reference example, the respective particulate composition without a caking-agent was used.

[0156] 10 g of each sample were put into a porcelain dish and were placed in a climate chamber (ratioTEC Prüfsysteme GmbH, Germany) for five days. The parameters of the climate chamber are given in Table 4 below.

TABLE-US-00004 TABLE 4 Parameters of the climate chamber. Time Temperature in ° C. Relative Humidity in % 0 h .sup.   12 79 1 day.sup.  12 78 2 days 13 76 3 days 13 77 4 days 13 76

[0157] After each day the consistency of the particulate compositions was evaluated visually.

[0158] The results of the caking trials are listed in Tables 5 and 6 below.

TABLE-US-00005 TABLE 5 Particulate compositions with comparative anti-caking agents. No anti- 1.0% MCP- 1.0% 1.0% 1.0% Ca- Day caking agent M fine GCC silica citrate 1 5 4 4 4 3 2 5 4 5 4 3 3 5 3 5 4 3 4 5 3 5 4 5

TABLE-US-00006 TABLE 6 Particulate composition with inventive anti-caking agents. Day 1.0% SRCC 1 1.0% SRCC 2 1 3 2 2 3 2 3 3 2 4 3 2

[0159] The numbers have the following meaning:

1=powder
2=between powder and compact
3=half compact
4=compact with a little separate pieces of salt
5=compact.

[0160] As can be seen from the results compiled in Tables 5 and 6, the samples comprising the inventive anti-caking agents maintain their powdered form or remain at least in a half-compacted state, i.e. the caking is reduced. The results clearly show that the compositions have a good separation efficacy in comparison to the comparative compositions comprising conventional anti-caking agents like monocalcium phosphate (MCP-M fine), ground calcium carbonate (GCC) or calcium citrate (Ca citrate).

[0161] The results of the caking trials confirm that surface-reacted calcium carbonate according to the present invention provide good anti-caking properties at already low amounts.