WET SURFACE TREATMENT OF SURFACE-MODIFIED CALCIUM CARBONATE

Abstract

The present invention relates to a process for the surface treatment of a surface-modified calcium carbonate, a surface-treated calcium carbonate obtained by the process as well as the use of the surface-treated calcium carbonate in a polymer composition, in paper making, paper coatings, agricultural applications, paints, adhesives, sealants, construction applications, pharma applications and/or cosmetic applications, or for cross-linking of rubber, in sheet moulding compounds, in bulk moulding compounds, in cross-linkable polyolefin system formulations, preferably for pipes and cables, in cross-linkable polyvinyl chloride, in unsaturated polyesters and in alkyd resins, and the use of the surface-treated calcium carbonate and a curing agent for crosslinking of cross-linkable compounds.

Claims

1. A process for the surface treatment of a surface-modified calcium carbonate, the process comprising the steps of: a) providing an aqueous suspension of at least one surface-modified calcium carbonate having solids content in the range from 5 to 80 wt.-%, based on the total weight of the aqueous suspension; b) adjusting the pH-value of the aqueous suspension of step a) to a range from 7.5 to 12; c) adding at least one surface treatment agent to the aqueous suspension obtained in step b) in an amount ranging from 0.05 to 10 mg surface treatment agent per m.sup.2 of the accessible surface area of the surface-modified calcium carbonate as provided in step a), the at least one surface treatment agent is selected from the group consisting of mono- or di-substituted succinic anhydride containing compounds, mono- or di-substituted succinic acid containing compounds, mono- or di-substituted succinic acid salts containing compounds; unsaturated fatty acids, salts of unsaturated fatty acids; unsaturated esters of phosphoric acid, salts of unsaturated phosphoric acid esters; abietic acid, salts of abietic acid and mixtures thereof; d) mixing the aqueous suspension obtained in step c) at a temperature in the range from 30 to 120 C.; and e) drying the aqueous suspension during or after step d) at a temperature in the range from 40 to 160 C. at ambient or reduced pressure until the moisture content of the obtained surface-treated calcium carbonate is in the range from 0.001 to 20 wt.-%, based on the total weight of the surface-treated calcium carbonate.

2. The process according to claim 1, wherein the pH-value in step b) is adjusted by adding at least one base to the aqueous suspension of step a).

3. The process according to claim 1, wherein the process comprises a further step f) of adding at least one base to the aqueous suspension of step c) to readjust the pH-value to the range from 7.5 to 12, preferably from 8 to 11.5 and most preferably from 8.5 to 11 during or after step d).

4. The process according to claim 1, wherein the mono- or di-substituted succinic anhydride containing compounds, mono-or di-substituted succinic acid containing compounds or mono- or di-substituted succinic acid salts containing compounds comprise substituent(s) R.sup.1 and/or R.sup.2 comprising a cross-linkable double bond.

5. The process according to claim 1, wherein the solids content of the aqueous suspension of step a) is in the range from 10 to 70 wt.-%, preferably in the range from 15 to 60 wt.-% and most preferably in the range from 15 to 40 wt.-%, based on the total weight of the aqueous suspension; and/or the specific surface area of the surface-modified calcium carbonate as measured by the BET nitrogen method is in the range from 20 to 250 m.sup.2/g, preferably in the range from 25 to 200 m.sup.2/g and most preferably in the range from 35 to 150 m.sup.2/g.

6. The process according to claim 2, wherein the at least one base added in step b) is selected from the group consisting of calcium hydroxide, magnesium hydroxide, calcium hydrogen carbonate, sodium hydroxide, potassium hydroxide, lithium hydroxide, ammonium hydroxide, primary, secondary and tertiary amines and mixtures thereof, preferred is calcium hydroxide.

7. The process according to claim 1, wherein the pH-value of the aqueous suspension of step a) is adjusted in process step b) to the range from 7.8 to 11.5 and more preferably to the range from 8 to 11.

8. The process according to claim 1, wherein the amount of the at least one surface treatment agent added in step c) is in the range from 0.07 to 9 mg surface treatment agent per m.sup.2 of the accessible surface area of the surface-modified calcium carbonate, preferably in the range from 0.1 to 8 mg surface treatment agent per m.sup.2 of the accessible surface area of the surface-modified calcium carbonate and most preferably in the range from 0.11 to 5 mg surface treatment agent per m.sup.2 of the accessible surface area of the surface-modified calcium carbonate.

9. The process according to claim 1, wherein the at least one surface treatment agent is a) selected from the group consisting of sodium, potassium, calcium, magnesium, lithium, strontium, primary amine, secondary amine, tertiary amine and/or ammonium salts, whereby the amine salts are linear or cyclic, of mono- or di-substituted succinic acids, whereby one or both acid groups can be in the salt form, preferably both acid groups are in the salt form; unsaturated fatty acids, preferably oleic acid and/or linoleic acid; unsaturated esters of phosphoric acid; abietic acid and/or mixtures thereof, preferred are completely neutralized surface treatment agents; and/or b) maleinized polybutadiene having a Brookfield viscosity at 25 C. in the range from 1000 to 300000 mPas, and/or an acid number in the range from 10 to 300 mg potassium hydroxide per g maleinized polybutadiene and/or an iodine number in the range from 100 to 1000 g iodine per 100 g maleinized polybutadiene; and/or polyisobutylene succinic anhydride having a Brookfield viscosity at 25 C. in the range from 1000 to 300000 mPa s and/or an acid number in the range from 10 to 80 mg potassium hydroxide per g polyisobutylene succinic anhydride.

10. The process according to claim 1, wherein step d) is carried out at a temperature in the range from 45 to 115 C., preferably from 50 to 105 C. and more preferably in the range from 80 to 100 C. and/or for a period of time ranging from 1 second to 60 minutes.

11. The process according to claim 1, wherein step e) is carried out until the moisture content of the obtained surface-treated calcium carbonate is in the range from 0.005 to 15 wt.-%, preferably in the range from 0.01 to 10 wt.-% and more preferably from 0.05 to 5 wt.-%, based on the total weight of the surface-treated calcium carbonate.

12. The process according to claim 1, wherein step e) is carried out at a temperature in the range from 50 to 155 C., preferably from 70 to 150 C. and more preferably from 80 to 145 C.

13. The process according to claim 3, wherein the at least one base added in step f) is selected from the group consisting of lithium hydroxide, sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide and/or mixtures thereof.

14. The process according to claim 1, wherein the process comprises a further step g) after or during step e) of deagglomerating the surface-treated calcium carbonate of step d) or e), preferably step g) is carried out during step e).

15. The process according to claim 1, wherein all process steps are fully or partially batch or continuous processes, wherein a batch process is preferred for steps a) to d) and f) and a continuous process is preferred for step e).

16. A surface-treated calcium carbonate obtained by a process according to claim 1.

17. A product comprising the surface-treated calcium carbonate according to claim 16, wherein the product is a polymer composition, paper, a paper coating, an agricultural product, paint, an adhesive, a sealant, a construction product, a pharmaceutical product, or a cosmetic product.

18. A product comprising the surface-treated calcium carbonate according to claim 16, wherein the product is rubber, a sheet moulding compound, a bulk moulding compound, a cross-linkable polyolefin, a pipe, a cable, a cross-linkable polyvinyl chloride, an unsaturated polyester, or an alkyd resin, wherein the surface-treated calcium carbonate has been surface treated with at least one surface treatment agent being selected from the group consisting of mono- or di-substituted maleic anhydride containing compounds, fully or partially neutralized mono- or di-substituted succinic anhydride containing compounds, unsaturated fatty acids, salts of unsaturated fatty acids, unsaturated esters of phosphoric acid, salts of unsaturated phosphoric acid esters, abietic acid, salts of abietic acid and mixtures thereof.

19. A product comprising the a surface-treated calcium carbonate according to claim 16 and a curing agent for crosslinking of cross-linkable compounds, preferably rubber, polyolefin system formulations, polyvinyl chloride, unsaturated polyesters and alkyd resins, wherein the curing agent is a peroxide or a curing agent based on sulphur.

Description

EXAMPLES

[0321] 1 Measurement Methods

[0322] In the following the measurement methods implemented in the examples are described.

[0323] Moisture Content of Calcium Carbonate A 10 g powder sample was heated in an oven at 150 C. until the mass is 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 has been attributed to the sample humidity.

[0324] Moisture Pick Up Susceptibility

[0325] 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 is changed to 85% relative humidity at which the sample is 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.

[0326] The moisture pick up susceptibility in mg/g divided by the specific surface area in m.sup.2/g (calculated based on the specific surface area BET) corresponds to the normalized moisture pick up susceptibility expressed in mg/m.sup.2 of sample.

[0327] Volatile Onset Temperature

[0328] The volatile onset temperature was determined by analysis of the thermogravimetric analysis (TGA) curve. TGA analysis described hereafterbegin to evolve, as observed on a TGA curve, plotting the mass of remaining sample (y-axis) as a function of temperature (x-axis), the preparation and interpretation of such a curve being defined hereafter. TGA analytical methods provide information regarding losses of mass and volatile onset temperatures with great accuracy, and is common knowledge; it is, for example, described in Principles of Instrumental analysis, fifth edition, Skoog, Holler, Nieman, 1998 (first edition 1992) in Chapter 31 pages 798 to 800, and in many other commonly known reference works. TGA was performed using a Mettler Toledo TGA 851 based on a sample of 500+/50 mg and scanning temperatures from 25 to 550 C. at a rate of 20 C./minute under an air flow of 70 ml/min.

[0329] The skilled man will be able to determine the volatile onset temperature by analysis of the TGA curve as follows: the first derivative of the TGA curve is obtained and the inflection points thereon between 150 and 350 C. are identified. Of the inflection points having a tangential slope value of greater than 45 relative to a horizontal line, the one having the lowest associated temperature above 150 C. is identified. The temperature value associated with this lowest temperature inflection point of the first derivative curve is the volatile onset temperature.

[0330] Hydrophobicity

[0331] Various mixtures of different water and ethanol were prepared. The reported data are based on volume/volume ratios. The different steps are listed hereafter: [0332] a) A 100 mL glass beaker was filled with 50 ml of a water/ethanol mixture. [0333] b) Through a sieve (mesh size: approximately 1 mm) 0.5 g of the coated mineral material was added on the top of the liquid surface. [0334] c) After 30 seconds the amount of material which sank to the bottom of the beaker was identified (visual estimation).

[0335] The procedure was repeated with different water/ethanol blends until the composition was identified where 50% of the material sinks to the bottom of the beaker.

[0336] pH

[0337] The pH of a suspension was measured at 232 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 20 C. (from Aldrich). The reported pH values are the endpoint values detected by the instrument (the endpoint is when the measured signal differs by less than 0.1 mV from the average over the last 6 seconds).

[0338] Solids Content

[0339] The solids content (also known as dry weight) was determined using a Moisture Analyser HR73 from the company Mettler-Toledo, Switzerland, with the following settings: temperature of 120 C., automatic switch off 3, standard drying, 5 to 20 g of product.

[0340] Specific Surface Area BET The specific surface area was measured via the BET method according to ISO 9277:2010 using nitrogen, following conditioning of the sample by heating at 250 C. for a period of 30 minutes. Prior to such measurements, the sample was filtered within a Buchner funnel, rinsed with deionised water and dried overnight at 90 to 100 C. in an oven. Subsequently the dry cake was ground thoroughly in a mortar and the resulting powder placed in a moisture balance at 130 C. until a constant weight was reached. The specific surface area was measured before any surface treatment. We assume that the surface treatment does not alter the BET surface area.

[0341] Particle Size Distribution (Volume % Particles with a Diameter<X), d.sub.50 Value (Volume Median Grain Diameter) and d.sub.98 Value of a Particulate Material:

[0342] Volume median grain diameter d.sub.50 was evaluated using a Malvern Mastersizer 2000 Laser Diffraction System (Malvern Instruments Plc., Great Britain) using the Mie theory, with a particle refractive index of 1.57 and an absorption index of 0.005. The method and instrument are known to the skilled person and are commonly used to determine particle sizes of fillers and other particulate materials.

[0343] Brookfield Viscosity

[0344] The Brookfield viscosity was measured one hour after the production and after one minute of stirring at 25 C.1 C. at 100 rpm by the use of a Brookfield viscometer type RVT equipped with an appropriate disc spindle, for example spindle 2 to 5.

[0345] Iodine Number

[0346] The iodine number was measured according to DIN 53241/1.

[0347] Acid Number

[0348] The acid number was measured according to ASTM D 974.

[0349] Intra Particle Intruded Specific Pore Volume

[0350] The intra-particle intruded specific pore volume has been calculated from a mercury intrusion porosimetry measurement using a Micromeritics Autopore IV 9500 mercury porosimeter having a maximum applied pressure of mercury 414 MPa (60000 psi), equivalent to a Laplace throat diameter of 0.004 p.m. The equilibration time used at each pressure step is 20 seconds. The sample material is sealed in a 5 cm.sup.3 chamber powder penetrometer for analysis. The data are 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, p1753-1764.).

[0351] The total pore volume seen in the cumulative intrusion data can be separated into two regions with the intrusion data from 214 m down to about 1-4 m showing the coarse packing of the sample between any agglomerate structures contributing strongly. Below these diameters lies the fine interparticle packing of the particles themselves. If they also have intraparticle pores, then this region appears bi modal. The sum of these three regions gives the total overall pore volume of the powder, but depends strongly on the original sample compaction/settling of the powder at the coarse pore end of the distribution. The sum of these three regions gives the total overall pore volume of the powder, but depends strongly on the original sample compaction/settling of the powder at the coarse pore end of the distribution.

[0352] By taking the first derivative of the cumulative intrusion curve the pore size distributions based on equivalent Laplace diameter, inevitably including pore-shielding, are revealed. The differential curves clearly show the coarse agglomerate pore structure region, the interparticle pore region and the intraparticle pore region, if present. Knowing the intraparticle pore diameter range it is possible to subtract the remainder interparticle and interagglomerate pore volume from the total pore volume to deliver the desired pore volume of the internal pores alone in terms of the pore volume per unit mass (specific pore volume). The same principle of subtraction, of course, applies for isolating any of the other pore size regions of interest.

[0353] 2 Starting Materials

[0354] 2.1 Surface Treatment Agent

TABLE-US-00001 TABLE 1 Surface treatment agents. Treatment agent Name Supplier Properties 1 Ricon 130MA08 (low Cray Valley Viscosity: 6 500 3 500 mPa .Math. s molecular weight (25 C.) (*) polybutadiene Acid number: 40.1-51.5 meq functionalized with KOH/g(*) maleic anhydride) Iodine number: 114 3 (**) 2 Ricon 156MA17 (low Cray Valley Viscosity: 140 000 mPa * s molecular weight (55 C.) (*) polybutadiene Acid number: 91.6-103 meq functionalized with KOH/g (*) maleic anhydride) Iodine number: 121 4 (**) 3 Linoleic acid (CAS Aldrich 60-33-3) order number: 62240-1L-F (*) according to the technical data sheet from the supplier; (**) measured by applicant.

[0355] Samples of the treatment agents 1 to 3 according to Table 1 were completely neutralized as follows: Said treatment agents were each individually contacted with demineralized water in a 50/50 wt.-% ratio and heated under steering to 90 C. (+/5 C.). Upon continuous stirring and heating the suspension was adjusted with a 30 wt.-% aqueous solution of sodium hydroxide to a pH of 11 (+/0.3). The addition of sodium hydroxide was stopped once the pH was stable at 11+/0.3 units for 20 minutes.

[0356] In Table 3 the surface treatment agents which have been completely neutralized with sodium hydroxide prior surface coating of the surface-modified calcium carbonate (MCC) are marked with the ending Na after the name according to Table 1.

[0357] 2.2 Surface-Modified Calcium Carbonate (=MCC)

TABLE-US-00002 TABLE 2 Surface-modified calcium carbonates Intra-particle intruded BET surface specific pore volume area d.sub.50 Humidity Sample (cm.sup.3/g) [mg/m.sup.2] [m] [wt.-%] A 0.864 139 4.53 6.77 B 0.281 37 2.42 1.58

[0358] Experiments:

[0359] Dry treatment process

[0360] 400 g of surface modified calcium carbonate A were mixed for 10 minutes at 120 C. in the MTI mixer (at 3 000 rpm). The surface treatment agent (according to Table 1) was added and the blend was mixed for further 10 minutes at 120 C. and 3 000 rpm. After cooling down to room temperature the sample was removed from the mixer and stored in a sealed container.

[0361] Wet Treatment Process

[0362] 400 g of sample A were mixed with 1 600 g deionized water in order to obtain an aqueous suspension of approximately 20 wt.-%, based on the total weight of the suspension. The suspension was stirred with a VISCO JET CRACK steered of 12 cm diameter (300 to 500 rpm; VISCO JET Rhrsysteme GmbH, Germany) at room temperature. The pH was adjusted with an aqueous solution of the base according to Table 3. The pH adjustment was stopped when the targeted pH was stable within +/0.2 units for 5 minutes, the reported pH values are the end values.

[0363] The suspension was heated to 90 C. (+/5 C.) under constant stirring. The surface treatment agent as specified in Table 3 was added over a period of approximately 3 minutes. The blend was further stirred for 30 minutes at 90 C. The suspension was then dried in an oven for 10 hours at 120 C. to a moisture content of below 1 wt.-%. The resulting dry crumbles were de-agglomerated in an IKA A 11 basic analytical mill for 5 minutes and stored afterwards in a sealed container.

TABLE-US-00003 TABLE 3 Summary and results. Surface treatment Base for the Surface treatment agent dosage Treatment Suspension pH Trial MCC agent [wt.-%] process pH adjustment Hydrophobicity 1 (comp.) A Ricon 130MA08 2 dry n.d. 80/20 2 (comp.) A Ricon 130MA08-Na 2 dry n.d. NaOH 90/10 3 (comp.) A Ricon 130MA08 2 wet 7 90/10 4 (comp.) A Ricon 130MA08-Na 2 wet 7 75/25 5 (inventive) A Ricon 130MA08 2 wet 10.5 Ca(OH).sub.2 75/25 6 (comp.) A Ricon 130MA08-Na 2 wet >12 Ca(OH).sub.2 85/15 7 (inventive) A Ricon 130MA08-Na 2 wet 10.5 NaOH 60/40 8 (inventive) A Ricon 156MA17-Na 2 wet 10.5 Ca(OH).sub.2 55/45 9 (inventive) A Ricon 130MA08-Na 4 wet 10.3 Ca(OH).sub.2 65/35 10 (comp.) A Linoleic acid 2 dry n.d. 70/30 11 (inventive) A Linoleic acid-Na 2 wet 11 Ca(OH).sub.2 55/45 12 (comp.) B Ricon 130MA08-Na 2 wet >12 Ca(OH).sub.2 95/5 13 (inventive) B Ricon 130MA08-Na 2 wet 8 75/25 Comp. = Comparative Example, n.d. = not determined.