PROCESS FOR PREPARING A SURFACE TREATED CALCIUM CARBONATE MATERIAL

Abstract

The present invention relates to a process for preparing a surface treated calcium carbonate-comprising material, a surface treated calcium carbonate-comprising material obtained by the process, an article comprising the surface treated calcium carbonate-comprising material, a polymer composition and the use of the surface treated calcium carbonate-comprising material in polymer applications.

Claims

1-15. (canceled)

16. A process for preparing a surface treated calcium carbonate-comprising material for use in polymer applications comprising the steps of: a) providing water; b) providing at least one calcium carbonate-comprising material; c) providing at least one homopolymer (P) used as grinding aid agent prepared from the polymerisation reaction of acrylic acid or methacrylic acid or salts thereof, having i) an average molecular weight (Mw) as measured by gel permeation chromatography (GPC) from 3 000 to 5 000 g/mol, and ii) a Polydispersity Index (PI) as measured by gel permeation chromatography (GPC) of between 1.5 and 2.9, and iii) carboxylic acid functions that are totally or partially neutralized (1) by Na.sup.+ in an amount of 70 mol-% and (2) by Na.sup.+, K.sup.+, Li.sup.+ or combinations thereof in an additional amount from 10 to 30 mol-%; d) forming an aqueous suspension by mixing the water of step a), the at least one calcium carbonate-comprising material of step b) and the at least one homopolymer of step c); e) wet grinding the at least one calcium carbonate-comprising material in the aqueous suspension of step d) in the presence of the at least one homopolymer in at least one wet grinding step until the at least one calcium carbonate-comprising material has a weight median particle size d.sub.50 from 0.1 μm to 3 μm as determined by the sedimentation method; f) up-concentrating or dewatering the aqueous suspension obtained in step e) to achieve a higher solids content than that of step e) and the solids content achieved in step f) is at least 74 wt.-%, based on the total weight of the aqueous suspension; g) drying the aqueous suspension obtained in step f) to achieve a calcium carbonate-comprising material having a moisture content of ≤0.5 wt.-%, based on the total dry weight of the calcium carbonate-comprising material; and h) surface treating the calcium carbonate-comprising material obtained in step g) with at least one hydrophobizing agent.

17. The process according to claim 16, wherein the drying in step g) occurs by atomizing, spray drying, drying in a rotational oven, drying in a pond, jet-drying, fluid bed drying, freeze drying, fluidized spray drying, or fountain nozzle drying.

18. The process according to claim 16, wherein step d) of forming an aqueous suspension is carried out by (I) mixing simultaneously the water of step a), the at least one calcium carbonate-comprising material of step b) and the at least one homopolymer of step c); (II) mixing first the water of step a) with the at least one calcium carbonate-comprising material of step b) and then adding the at least one homopolymer of step c) into the mixture; (III) mixing first the water of step a) with the at least one homopolymer of step c) and then adding the at least one calcium carbonate-comprising material of step b) into the mixture; or (IV) mixing first the at least one homopolymer of step c) with the at least one calcium carbonate-comprising material of step b) and then adding the water of step a) into the mixture.

19. The process according to claim 16, wherein the aqueous suspension of step d) and/or e) has a solids content in the range from 40 to 70 wt.-%, based on the total weight of the aqueous suspension.

20. The process according to claim 16, wherein the aqueous suspension of step d) and/or e) has a solids content in the range from 50 to 70 wt.-%, based on the total weight of the aqueous suspension.

21. The process according to claim 16, wherein 100% of the neutralized carboxylic acid functions of the homopolymer of step c) are neutralized by Na.sup.+.

22. The process according to claim 16, wherein wet grinding step e) is carried out in that the homopolymer of step c) is present in an amount ranging from 500 to 5000 ppm, based on the total dry weight of the calcium carbonate-comprising material.

23. The process according to claim 16, wherein wet grinding step e) is carried out in that the homopolymer of step c) is present in an amount ranging from 800 to 4000 ppm, based on the total dry weight of the calcium carbonate-comprising material.

24. The process according to claim 16, wherein wet grinding step e) is carried out in that the homopolymer of step c) is present in an amount ranging from 1200 to 2000 ppm, based on the total dry weight of the calcium carbonate-comprising material.

25. The process according to claim 16, wherein the up-concentration or dewatering in step f) is carried out such as to achieve a higher solids content than that of step e), and the solids content achieved in step f) is at least 75 wt.-%, based on the total weight of the aqueous suspension.

26. The process according to claim 16, wherein the up-concentration or dewatering in step f) is carried out such as to achieve a higher solids content than that of step e), and the solids content achieved in step f) is in the range from 78 to 83 wt.-%, based on the total weight of the aqueous suspension.

27. The process according claim 16, wherein the up-concentration or dewatering in step f) is carried out by mechanical- and/or thermal up-concentration and/or combinations thereof, optionally in combination with vacuum.

28. The process according to claim 16, wherein the calcium carbonate-comprising material in the aqueous suspension obtained in step e) and/or step f) has a weight median particle size d.sub.50 from 0.1 μm to 2.8 μm, as determined by the sedimentation method.

29. The process according to claim 16, wherein the calcium carbonate-comprising material in the aqueous suspension obtained in step e) and/or step f) has a weight median particle size d.sub.50 from 0.6 μm to 2.5 μm, as determined by the sedimentation method.

30. The process according to claim 16, wherein the hydrophobizing agent is selected from an aliphatic carboxylic acid having a total amount of carbon atoms from C.sub.4 to C.sub.24; a mono-substituted succinic anhydride consisting of succinic anhydride mono-substituted with a group selected from a linear, branched, aliphatic and cyclic group having a total amount of carbon atoms from at least C.sub.2 to C.sub.30 in the substituent; a phosphoric acid ester blend of one or more phosphoric acid mono-ester and one or more phosphoric acid di-ester; polyhydrogensiloxane, an inert silicone oil, polydimethylsiloxane, and mixtures thereof; and an aliphatic aldehyde selected from aliphatic aldehydes having 6 to 14 carbon atoms and mixtures thereof.

31. The process according to claim 30, wherein the aliphatic aldehyde is selected from aliphatic aldehydes having 6 to 12 carbon atoms and mixtures thereof.

32. The process according to claim 30, wherein the aliphatic aldehyde is selected from polydimethylsiloxane, hexanal, heptanal, octanal, nonanal, decanal, undecanal, dodecanal, tridecanal, butadecanal and mixtures thereof.

33. The process according to claim 16, wherein the surface treated calcium carbonate-comprising material has a moisture pick-up of no more than 0.26 mg/m.sup.2, at a temperature of 23° C. (±2° C.).

34. A surface treated calcium carbonate-comprising material obtained by the process according to claim 16, wherein the surface treated calcium carbonate-comprising material comprises a treatment layer on the surface of the calcium carbonate-comprising material comprising the at least one hydrophobizing agent and reaction products thereof.

35. An article comprising the surface treated calcium carbonate-comprising material according to claim 34.

36. A polymer product comprising the surface treated calcium carbonate-comprising material according to claim 34.

37. A polyolefin polymer product comprising the surface treated calcium carbonate-comprising material according to claim 34.

38. The article according to claim 35, wherein the surface treated calcium carbonate-comprising material is present in an amount from 1 to 90 wt %.

39. The article according to claim 35, wherein the surface treated calcium carbonate-comprising material is present in an amount from 7 to 60 wt %.

40. A polymer composition comprising the surface treated calcium carbonate-comprising material according to claim 34 in an amount of from 50 to 85 wt.-%, based on the total weight of the polymer composition.

41. A masterbatch comprising the surface treated calcium carbonate-comprising material according to claim 34 in an amount of from 50 to 85 wt.-%, based on the total weight of the polymer composition.

42. The surface treated calcium carbonate-comprising material according to claim 34 suitable for use in polymer applications.

Description

EXAMPLES

A. Measurement Methods

[0209] The following measurement methods are used to evaluate the parameters given in the examples and claims.

pH Measurement

[0210] Any pH value was measured at 25° C. (+/−1° C.) using a Mettler-Toledo Seven Easy pH meter and a Mettler-Toledo InLab Expert Pro pH electrode. A three point calibration (according to the segment method) of the instrument was first made using commercially available buffer solutions having pH values of 4, 7 and 10 at 25° C. (from Aldrich). The reported pH values were the endpoint values detected by the instrument (signal differs by less than 0.1 mV from the average over the last 6 seconds).

Conductivity Measurement

[0211] Conductivity of a suspension was measured at 25° C. (+/−1° C.) using Mettler Toledo Seven Multi instrumentation equipped with the corresponding Mettler Toledo conductivity expansion unit and a Mettler Toledo InLab 731 conductivity probe, directly following stirring the suspension at 1500 rpm using a Pendraulik tooth disc stirrer. The instrument was first calibrated in the relevant conductivity range using commercially available conductivity calibration solutions from Mettler Toledo. The influence of temperature on conductivity was automatically corrected by the linear correction mode. Measured conductivities were reported for the reference temperature of 20° C. The reported conductivity values were the endpoint values detected by the instrument (the endpoint is when the measured conductivity differs by less than 0.4% from the average over the last 6 seconds).

Particle Size Distribution and Weight Median Grain Diameter

[0212] Particle size distribution (mass % particles with a diameter <X) and weight median grain diameter (d.sub.50) of particulate materials were determined via the sedimentation method, i.e. an analysis of sedimentation behaviour in a gravimetric field. The measurement was made with a Sedigraph™ 5100 at 25° C. (+/−1° C.). The method and the instrument are known to the skilled person and are commonly used to determine grain size of fillers and minerals. The measurement was carried out in an aqueous solution of 0.1% by weight of Na.sub.4P.sub.2O.sub.7. The samples were dispersed using a high speed stirrer and ultrasonic.

Viscosity Measurement

[0213] Brookfield viscosity was measured after 1 minute (if no other indication) of stirring by the use of a RVT model Brookfield™ viscometer at a rotation speed of 100 rpm (revolutions per minute) with the appropriate disc spindle 2, 3 or 4. Without further indication, the viscosity was measured at 25° C. (+/−1° C.).

Weight Solids (% by Weight) of a Material in Suspension

[0214] Weight solids was determined by dividing the weight of the solid material by the total weight of the aqueous suspension. The weight of the solid material was determined by weighing the solid material obtained by evaporating the aqueous phase of suspension and drying the obtained material to a constant weight.

Moisture Pick Up Susceptibility

[0215] The moisture pick up susceptibility of a material as referred to herein was determined in mg moisture/g after exposure to an atmosphere of 10 and 85% relative humidity, respectively, for 2.5 hours at a temperature of +23° C. (±2° C.). For this purpose, the sample was first kept at an atmosphere of 10% relative humidity for 2.5 hours, then the atmosphere was changed to 85% relative humidity at which the sample was kept for another 2.5 hours. The weight increase between 10 and 85% relative humidity was then used to calculate the moisture pick-up in mg moisture/g of sample.

Humidity (Moisture Content) of Calcium Carbonate

[0216] A 10 g powder sample was heated in an oven at 150° C. (+/−1° C.) until the mass was constant for 20 minutes. The mass loss was determined gravimetrically and is expressed as wt.-% loss based on the initial sample mass. This mass loss was attributed to the sample moisture content.

Average Molecular Weight (Mw) and Polydispersity (PI)

[0217] A test portion of the polymer solution corresponding to 90 mg of dry matter was introduced into a 10 ml flask. Mobile phase, with an additional 0.04 wt. % of dimethylformamide, was added, until a total mass of 10 g was reached. The composition of this mobile phase at pH 9 was as follows: NaHCO.sub.3: 0.05 mol/l, NaNO.sub.3: 0.1 mol/l, triethanolamine: 0.02 mol/l, 0.03 wt. % of NaN.sub.3. The gel permeation chromatography (GPC) equipment was equipped with an isocratic pump of the Waters™ 515 type, the flow rate was set to 0.8 ml/min., a Waters™ 717+sample changer, a kiln containing a precolumn of the “Guard Column Ultrahydrogel Waters™” type which was 6 cm in length and had an internal diameter of 40 mm, followed by a linear column of the “Ultrahydrogel Waters™” type which was 30 cm in length and had an internal diameter of 7.8 mm.

[0218] Detection was accomplished by means of a Waters™ 410 type differential refractometer. The kiln was heated to a temperature of 60° C. and the refractometer was heated to a temperature of 45° C. The GPC equipment was calibrated with a series of powders of sodium polyacrylate standards supplied and certified by Polymer Standard Service or American Polymers Standards Corporation. (maximum (M.sub.P) molecular weight of between 900 and 2.25.106 g/mol and a polydispersity index of between 1.4 and 1.8).

[0219] The calibration graph was of the linear type and took account of the correction obtained using the flow rate marker (dimethylformamide).

[0220] Acquisition and processing of the chromatogram were accomplished through use of the PSS WinGPC Scientific v. 4.02 application. The chromatogram obtained was incorporated in the area corresponding to molecular weights higher than 200 g/mol.

B. Materials Used

Calcium Carbonate-Comprising Material A

[0221] Natural CaCO.sub.3 marble from Italy, Avenza, having a d.sub.90 value of 50 μm, a d.sub.50 value of 10 μm, and a d.sub.20 value of 2 m.

Grinding Aid Agents

[0222] The grinding aid agents used are set out in the following table 1.

TABLE-US-00001 TABLE 1 Grinding aid agents used Grinding aid Mw PI Neutralization agent Composition [g/mol] (Mw/Mn) [mol %] A (comparative) Homopolymer 6 000 2.6 70% Na.sup.+, of acrylic acid 30% Ca.sup.2+ B (inventive) Homopolymer 3 600 2.0 100% Na.sup.+ of acrylic acid C (inventive) Homopolymer 3 770 2.0 90% Na.sup.+ of acrylic acid D (comparative) Homopolymer 6 000 2.6 100% NH.sub.4.sup.+ of acrylic acid

C. Test Results

2. Trials 1 to 4

Preparation of Pigment Particles Suspension

[0223] An aqueous suspension having solids content of 71 wt.-% (+/−1 wt.-%), based on the total weight of the suspension, was prepared by mixing tap water with 1 500 ppm of the respective grinding aid agent set out in table 2 and the calcium carbonate-comprising material A using a Ystral mixer (Dispermix, Ystral GmbH, Germany). Subsequently, the obtained mixture was wet ground in a 200-litre vertical attritor mill using zircon silicate beads of 0.6 to 1.0 mm diameter. The slurry temperature at the mill inlet was 20° C. and at the outlet between 50 and 70° C. The mill parameters where adjusted in order to reach a particle size distribution of at least 46% <2 μm.

[0224] The results are summarized in table 2 below.

TABLE-US-00002 TABLE 2 Wet grinding of a calcium carbonate-comprising material suspension with various grinding aid agents Grinding aid agent Specific Slurry Slurry PSD Grinding quantity surface solids Viscosity % < % < Trial aid agent [ppm] [m.sup.2/g] [wt.-%] [mPa .Math. s] 2 μm 1 μm pH 1 (comparative) A 1 500 5.9 71.7 237 46.7 27.0 9.0 2 (inventive) B 1 500 4.9 71.7 123 46.2 26.5 9.5 3 (inventive) C 1 500 5.1 71.8 88 46.0 27.0 9.3 4 (comparative) D 1 500 N/A 71.0 Viscosity N/A N/A N/A too high, not able to grind

[0225] In a subsequent stage, the suspensions were up-concentrated using a thermal pilot evaporator from EPCON™ brand. The evaporator was operated at a suspension temperature of 9500. Samples were taken at different solids contents and the viscosity was measured after cooling down of the suspensions to 2500. The target was to identify the solids content corresponding to a viscosity (at 2500) of approximately 500 mPa.Math.s. The results are shown in table 3 below.

TABLE-US-00003 TABLE 3 thermal up-concentration-viscosity at different solids concentrations Viscosity Trial Solids [wt.-%] [mPa .Math. s] at 25° C. 1A (comparative) 76.9 3 112 2A (inventive) 74.6   320 75.6   500 76.8   780 3A (inventive) 74.9   143 77.2   245 78.8   510

[0226] From table 3, it can be gathered that the viscosity of the aqueous suspensions prepared by using the inventive grinding aid agents is lower compared to a comparative suspension based on another homopolymer as grinding aid agent. Furthermore, it is to be noted that the comparative polymer D (see trial 4 in table 2) even did not allow grinding the mineral material.

[0227] The suspensions set out in table 3 were subsequently spray dried on a Niro drier operating at an atomizer speed of 16 680 rpm. The burner temperature was 40000 and the tower temperature was 13000.

[0228] Each of the dried calcium carbonate-comprising materials was subsequently surface treated with 1 0.2 wt.-% of stearic acid in a Laboratory mixer (Somakon MP-LB Mixer, Somakon Verfahrenstechnik, Germany). The dry calcium carbonate-comprising materials were activated for 10 min at 12000 and 2 000 rpm. Subsequently, the surface treatment agent was added and the corresponding blends were further mixed at 12000 under a stirring speed of 2 000 rpm for a period of 10 min.

[0229] The results for the moisture pick-up susceptibility are set out in table 4 below.

TABLE-US-00004 TABLE 4 moisture pick-up of surface treated calcium carbonate-comprising materials Grinding Grinding moisture pick up aid aid agent susceptibility-after Trial agent quantity [ppm] treatment [mg/m.sup.2] Based on 1A A 1500 0.27 (comparative) Based on 2A B 1500 0.24 (inventive) Based on 3A C 1500 0.25 (inventive)

[0230] From table 4, it can be gathered that both inventive grinding aid agents B and C lead to a lower moisture pick-up susceptibility of the final surface treated calcium carbonate-comprising material compared to a surface treated material prepared by using the same amount of a grinding aid agent based on a homopolymer.