METHOD FOR PRODUCING AN AQUEOUS POLYMER DISPERSION FROM A VINYL AROMATIC COMPOUND AND A CONJUGATED ALIPHATIC DIENE

Abstract

The present invention relates to a process for preparing an aqueous polymer dispersion by radically initiated aqueous emulsion polymerization, which comprises polymerizing

TABLE-US-00001 (a) 40 to 75 parts by weight of at least one vinylaromatic compound, (b) 24.9 to 59.9 parts by weight of at least one conjugated aliphatic diene, (c) 0.1 to 10 parts by weight of at least one monomer containing acid groups, an (d) 0 to 20 parts by weight of at least one other monoethylenically unsaturated monomer, where the amounts of the monomers (a) to (d) add up to 100 parts by weight,
in an aqueous medium by a monomer feed process, with the proviso that monomers and emulsifier are metered continuously and following a period P1, when 15 to 30% of the total monomer metering time has elapsed and 15 to 30 wt % of the total monomer amount has been metered in, the metering rate of the emulsifier is increased for a period P2 lasting no longer than 30 minutes to 10 to 100 times the average metering rate of the emulsifier in the period P1,
and also to the aqueous polymer dispersions prepared by the process and to the use thereof as a binder, adhesive, fiber sizing agent, for producing coatings or for producing a paper coating slip.

Claims

1.-18. (canceled)

19. A process for preparing an aqueous polymer dispersion having a polymodal particle distribution of the polymer particles, with a first population of large polymer particles and a second population of small polymer particles, by radically initiated aqueous emulsion polymerization, which comprises polymerizing TABLE-US-00035 (a) 40 to 75 parts by weight of at least one vinylaromatic compound, (b) 24.9 to 59.9 parts by weight of at least one conjugated aliphatic diene, (c) 0.1 to 10 parts by weight of at least one monomer containing acid groups, and (d) 0 to 20 parts by weight of at least one other monoethylenically unsaturated monomer, where the amounts of the monomers (a) to (d) add up to 100 parts by weight, in an aqueous medium by a monomer feed process, with the proviso that monomers and emulsifier are metered continuously and following a period P1, when 15 to 30% of the total monomer metering time has elapsed and 15 to 30 wt % of the total monomer amount has been metered in, the metering rate of the emulsifier is increased for a period P2 lasting no longer than 30 minutes to 10 to 100 times the average metering rate of the emulsifier in the period P1.

20. The process according to claim 19, wherein the vinylaromatic compound is styrene and/or methylstyrene and the conjugated aliphatic diene is 1,3-butadiene and/or isoprene.

21. The process according to claim 19, wherein the polymerization is initiated in an initial charge which contains up to 20 parts by weight of the total monomers and subsequently monomers and emulsifier are metered continuously.

22. The process according to claim 19, wherein the emulsifier is selected from alkali metal salts and ammonium salts of C.sub.8-C.sub.22 alkyl sulfates and of sulfuric monoesters with ethoxylated C.sub.12-C.sub.18 alkanols (EO degree: 2 to 40) and of sulfuric monoesters with ethoxylated C.sub.4-C.sub.9 alkylphenols (EO degree: 10 to 40), and from bis(phenylsulfonic acid) ethers and/or the alkali metal salts or ammonium salts thereof which carry a C.sub.4-C.sub.24 alkyl group on one or both aromatic rings.

23. The process according to claim 19, wherein the emulsifier and at least one monomer are metered together as a mixture.

24. The process according to claim 19, wherein 0.1 to 5 parts by weight of emulsifier per 100 parts by weight of monomers are metered continuously in a mixture with at least one monomer.

25. The process according to claim 19, wherein during the period P2 the metering rate of the emulsifier is 20 to 90 times the average metering rate of the emulsifier in the period P1.

26. The process according to claim 19, wherein polymerization takes place in the presence of at least one inorganic peroxide and also at least one organic peroxide.

27. The process according to claim 19, wherein no reducing agent that can form a red/ox initiator system with the organic or inorganic peroxides is present during the monomer feed.

28. The process according to claim 19, wherein polymerization takes place at a temperature in the range from ≥80° C. to ≤115° C.

29. The process according to claim 19, wherein the polymerization is initiated in an initial charge containing up to 2 parts by weight of finely divided polystyrene per 100 parts by weight of total monomers and then monomers and emulsifier are metered continuously.

30. The process according to claim 19, wherein no chain transfer agent selected from aliphatic and/or araliphatic halogen compounds, organic thio compounds and substituted thiols is used during the polymerization.

31. An aqueous polymer dispersion obtained by the process according to claim 19.

32. The aqueous polymer dispersion according to claim 31, wherein the fraction of the first population is 60 to 95 wt % and the fraction of the second population is 5 to 40 wt %, based on the total polymer of the dispersion.

33. The use of the aqueous polymer dispersion according to claim 31 as a binder, adhesive, fiber sizing agent, for producing coatings or for producing paper coating slips.

34. A paper coating slip comprising (i) inorganic pigments and (ii) an aqueous polymer dispersion according to claim 31 and also optionally further auxiliaries.

35. Paper or card coated with a paper coating slip according to claim 34.

36. A method for coating paper or card, by providing an aqueous polymer dispersion according to claim 31; and producing a paper coating slip with the aqueous polymer dispersion, at least one pigment and optional further auxiliaries; and applying the paper coating slip to at least one surface of paper or card.

Description

EXAMPLES

[0133] Unless otherwise apparent from the context, the indications in percent always mean percent by weight. The indication of a content relates to the content in aqueous solution or dispersion. Where water was used within the examples, it was demineralized water.

[0134] Measurement Methods

[0135] Particle Size:

[0136] The size of the particles in the polymer dispersion and also the particle size distribution were determined using an analytical ultracentrifuge (AUC) with turbidity-based optical system and Mie correction for transmitted intensities per size. With turbidity detection, all components from 30 nm to 5 μm in diameter undergo measurement.

[0137] The method uses a homogeneous starting sedimentation. The method was carried out according to the guidelines of ISO 13318-1, with the specific set-up being described in W. Mächtle, L. Börger, “Analytical Ultracentrifugation of Polymers and Nanoparticles” chapter 3, Springer Science and Business Media, Berlin 2006. The evaluation starts from a spherical solid particle morphology of skeletal density which is dictated by the comonomer composition. The results are reported in volume metric in sphere-equivalent diameters.

[0138] For the measurement, the dispersions are diluted to a concentration of 4 g (solids)/liter with a 0.05 wt % aqueous surfactant solution and subjected to the measurement under the same conditions.

[0139] The weight fraction of a particle population is obtained directly from the integral of the measurement. Below, the fraction of all particles from 36 to 75 nm is considered for the population of the small particles, and the fraction of all particles from 80 to 180 nm is considered for the population of the large particles.

[0140] Determining the Viscosity of the Dispersion:

[0141] The viscosity of the dispersion was determined according to ASTM D2196 with a Brookfield viscometer with RV spindles at 100 rpm and a temperature of 23° C.

[0142] Determining the Viscosity of the Coating Slip:

[0143] The viscosity at high shear rates was measured using a high-pressure capillary viscometer (ACAV high-shear viscometer A2, manufacturer: ACA Systems). Prior to the measurement, the sample is filtered through a 100 μm sieve and then its density is determined. The measurement is carried out at a temperature of 23° C.

[0144] Solids Content:

[0145] Solids contents of the polymer dispersions were determined by distributing 0.5 to 1.5 g of the polymer dispersion in a metal lid with a diameter of 4 cm and then drying it in a forced-air drying cabinet at 140° C. for 30 minutes. The ratio of the mass of the sample after drying under the above conditions to the mass at sampling gives the solids content of the polymer dispersion.

[0146] Starting materials used in the examples were as follows: [0147] Emulsifier A: sodium lauryl sulfate as a 15 wt % solution (Disponil® SDS from BASF) [0148] Emulsifier B: ethoxylated sodium lauryl ether sulfate as a 28 wt % solution (Texapon® NSO P from BASF) [0149] Complexing agent: EDTA as a 2 wt % solution (Trilon® BX from BASF) [0150] Seed latex: polystyrene seed in the form of a 29.7 wt % dispersion with a particle size of around 30 nm (determined by analytical ultracentrifuge) [0151] Initiator A: 7 wt % solution of sodium peroxodisulfate (NaPS) [0152] Initiator B: 10 wt % solution of tert-butyl hydroperoxide [0153] Reducing agent: 13 wt % solution of acetone bisulfite [0154] Degraded starch: commercial 72 wt % aqueous glucose syrup having a DE (dextrose equivalent) value of 28

[0155] Unless indicated otherwise, the water was deionized water. In all of the examples, the feeds were metered at a uniform volume flow rate.

[0156] Preparation of the Emulsion Polymers

[0157] The quantities below in pphm (parts per hundred monomer) are based on 100 parts by weight of total monomer.

Example 1 Emulsion Polymerization of Styrene/Butadiene/Acrylic Acid

[0158] Initial Charge:

TABLE-US-00005 360.01 g of water 192.86 g of a 7 wt % aqueous solution of itaconic acid (0.6 pphm) 45.45 g of a 29.7 wt % dispersion of a polystyrene latex with a mean particle size of 30 nm (0.6 pphm) 18.00 g of a 15 wt % solution of sodium lauryl sulfate (emulsifier A) (0.12 pphm) 11.25 g of a 2 wt % solution of EDTA (complexing agent) (0.01 pphm) 4.50 g of acrylic acid (0.2 pphm) 47.48 g of styrene (2.11 pphm)

[0159] Addition:

TABLE-US-00006 86.79 g of a 7 wt % solution of sodium peroxodisulfate (initiator A) (0.27 pphm)

[0160] Feed 1:

TABLE-US-00007 90.00 g of acrylic acid (4.0 pphm) 40.18 g of a 28 wt % solution of ethoxylated sodium lauryl ether sulfate (emulsifier B) (0.5 pphm) 36.00 g of a 15 wt % solution of sodium lauryl sulfate (0.24 pphm) 22.50 g of 15 wt % sodium hydroxide solution (0.15 pphm) 503.69 ml of water

[0161] Feed 2:

TABLE-US-00008 1364.63 g of styrene (60.65 pphm)

[0162] Feed 3:

TABLE-US-00009 729.9 g of butadiene (32.44 pphm)

[0163] Feed 4:

TABLE-US-00010 273.21 g of a 7 wt % solution of sodium peroxodisulfate (initiator A) (0.85 pphm)

[0164] Feed 5:

TABLE-US-00011 180.00 g of a 10 wt % solution of tert-butyl hydroperoxide (initiator B) (0.8 pphm)

[0165] Feed 6 (Emulsifier Shot):

TABLE-US-00012 150.00 g of a 15 wt % solution of sodium lauryl sulfate (1.00 pphm)

[0166] Feed 7:

TABLE-US-00013 51.75 g of a 10 wt % solution of tert-butyl hydroperoxide (initiator B) (0.23 pphm)

[0167] Feed 8:

TABLE-US-00014 66.98 g of a 13.1 wt % solution of acetone bisulfite (0.39 pphm)

[0168] The components of the initial charge were charged to a 6 l pressure reactor and mixed. The initial charge was heated to 90° C. When 90° C. were reached, the initiator A (addition 1) was added slowly and the polymerization commenced.

[0169] Started immediately thereafter were feeds 1, 2, 3 and 4 (time: 0 minutes). Feeds 1, 2 and 3 took place over a period of 4 hours. Feed 4 took place over a period of 4 hours and 15 minutes.

[0170] Feed 5 was commenced after 30 minutes after the start of feeds 1, 2, 3 and 4 (time: 30 minutes) and took place over 3 hours.

[0171] Feed 6 was commenced after 50 minutes after the start of feeds 1, 2, 3 and 4 (time: 50 minutes) and took place over 20 minutes.

[0172] 15 minutes before the end of feeds 1, 2, 3 and 4 (time: 225 minutes) the polymerization temperature is increased to 100° C. After the end of the metered addition of feed 4, the polymerization mixture was stirred for a further 30 minutes. The polymerization mixture was then heated to a temperature of 90° C. and thereafter 71.59 ml of water (3.19 pphm) and 15.00 g of 15 wt % sodium hydroxide solution (0.10 pphm) were added.

[0173] Feeds 7 and 8 were started subsequently and took place over a further 2 hours. After the end of feeds 7 and 8, the polymerization mixture was cooled to room temperature and admixed with 144.00 g of 15 wt % sodium hydroxide solution (0.96 pphm).

[0174] The solids content of the dispersion was 53 wt %.

[0175] The polymer dispersion was analyzed using an analytical ultracentrifuge:

[0176] Bimodal Particle Size Distribution:

[0177] The smaller particle population had its peak maximum at 55 nm. The fraction as a proportion of the total polymer was 20 wt %.

[0178] The larger particle population had its peak maximum at 117 nm. The fraction as a proportion of the total polymer was 80 wt %.

Inventive Example 2 (Delayed Butadiene Addition)

[0179] The emulsion polymerization was carried out as in inventive example 1, with the difference that feed 3 was not started until 30 minutes after the start of feeds 1, 2 and 4 (time: 30 minutes) and took place over 3.5 hours.

[0180] Feed 6 was commenced 60 minutes after the start of feeds 1, 2 and 4 (time: 60 minutes) and took place over 20 minutes. In feed 1 an increased amount of sodium hydroxide solution was used (0.25 pphm).

[0181] The solids content of the dispersion was 53 wt %.

[0182] The polymer dispersion was analyzed using an analytical ultracentrifuge:

[0183] Bimodal Particle Size Distribution:

[0184] The smaller particle population had its peak maximum at 50 nm. The fraction as a proportion of the total polymer was 27 wt %.

[0185] The larger particle population had its peak maximum at 120 nm. The fraction as a proportion of the total polymer was 73 wt %.

Inventive Example 3 (Delayed Butadiene Addition)

[0186] The emulsion polymerization was carried out as in inventive example 1, with the difference that feed 3 was not started until 30 minutes after the start of feeds 1, 2 and 4 (time: 30 minutes) and took place over 3.5 hours.

[0187] Feed 6 was commenced 40 minutes after the start of feeds 1, 2 and 4 (time: 40 minutes) and took place over 20 minutes. In feed 1 an increased amount of sodium hydroxide solution was used (0.25 pphm).

[0188] The solids content of the dispersion was 53 wt %.

[0189] The polymer dispersion was analyzed using an analytical ultracentrifuge:

[0190] Bimodal Particle Size Distribution:

[0191] The smaller particle population had its peak maximum at 56 nm. The fraction as a proportion of the total polymer was 24 wt %.

[0192] The larger particle population had its peak maximum at 118 nm. The fraction as a proportion of the total polymer was 76 wt %.

Inventive Example 4

[0193] The emulsion polymerization was carried out as in inventive example 1, with the difference that feed 6 was not started until 40 minutes after the start of feeds 1, 2, 3 and 4 (time: 40 minutes) and was metered over 20 minutes. In feed 1 an increased amount of sodium hydroxide solution was used (0.25 pphm).

[0194] The solids content of the dispersion was 53 wt %.

[0195] The polymer dispersion was analyzed using an analytical ultracentrifuge:

[0196] Bimodal Particle Size Distribution:

[0197] The smaller particle population had its peak maximum at 58 nm. The fraction as a proportion of the total polymer was 30 wt %.

[0198] The larger particle population had its peak maximum at 118 nm. The fraction as a proportion of the total polymer was 70 wt %.

Inventive Example 5

[0199] The emulsion polymerization was carried out as in inventive example 1, with the difference that feed 6 comprised 90.00 g of a 15 wt % solution of sodium lauryl sulfate (0.6 pphm), metered in over a period of 20 minutes.

[0200] The solids content of the dispersion was 53 wt %.

[0201] The polymer dispersion was analyzed using an analytical ultracentrifuge:

[0202] Bimodal Particle Size Distribution:

[0203] The smaller particle population had its peak maximum at 56 nm. The fraction as a proportion of the total polymer was 16 wt %.

[0204] The larger particle population had its peak maximum at 116 nm. The fraction as a proportion of the total polymer was 84 wt %.

Inventive Example 6

[0205] The emulsion polymerization was carried out as in inventive example 1, with the difference that the seed latex used in the initial charge was 75.75 g of a 29.7 wt % dispersion of a polystyrene latex having a mean particle size of 30 nm (1.0 pphm).

[0206] The solids content of the dispersion was 53 wt %.

[0207] The polymer dispersion was analyzed using an analytical ultracentrifuge:

[0208] Bimodal Particle Size Distribution:

[0209] The smaller particle population had its peak maximum at 50 nm. The fraction as a proportion of the total polymer was 10 wt %.

[0210] The larger particle population had its peak maximum at 100 nm. The fraction as a proportion of the total polymer was 90 wt %.

Comparative Example C1 (without Emulsifier Shot)

[0211] Initial Charge:

TABLE-US-00015 360.01 g of water 11.25 g of a 2 wt % solution of EDTA (complexing agent) (0.01 pphm) 18.00 g of a 15 wt % solution of sodium lauryl sulfate (emulsifier A) (0.12 pphm) 192.86 g of a 7 wt % aqueous solution of itaconic acid (0.6 pphm) 45.45 g of a 29.7 wt % dispersion of a polystyrene latex with a mean particle size of 30 nm (0.6 pphm) 4.50 g of acrylic acid (0.2 pphm) 47.48 g of styrene (2.11 pphm)

[0212] Addition:

TABLE-US-00016 86.79 g of a 7 wt % solution of sodium peroxodisulfate (initiator A) (0.27 pphm)

[0213] Feed 1:

TABLE-US-00017 90.00 g of acrylic acid (4.0 pphm) 40.18 g of a 28 wt % solution of ethoxylated sodium lauryl ether sulfate (emulsifier B) (0.5 pphm) 36.00 g of a 15 wt % solution of sodium lauryl sulfate (0.24 pphm) 37.5 g of 15 wt % sodium hydroxide solution (0.15 pphm) 597.91 ml of water

[0214] Feed 2:

TABLE-US-00018 1252.13 g of styrene (55.65 pphm)

[0215] Feed 3:

TABLE-US-00019 842.4 g of butadiene (37.44 pphm)

[0216] Feed 4:

TABLE-US-00020 273.21 g of a 7 wt % solution of sodium peroxodisulfate (initiator A) (0.85 pphm)

[0217] Feed 5:

TABLE-US-00021 180.00 g of a 10 wt % solution of tert-butyl hydroperoxide (initiator B) (0.8 pphm)

[0218] Feed 6:

TABLE-US-00022 51.75 g of a 10 wt % solution of tert-butyl hydroperoxide (initiator B) (0.23 pphm)

[0219] Feed 7:

TABLE-US-00023 66.98 g of a 13.1 wt % solution of acetone bisulfite (0.39 pphm)

[0220] The components of the initial charge were charged to a 6 l pressure reactor and mixed. The initial charge was heated to 90° C. When 90° C. were reached, the initiator A (addition 1) was added slowly and the polymerization commenced.

[0221] Started immediately thereafter were feeds 1, 2 and 4 (time: 0 minutes). Feeds 1 and 2 took place over a period of 4 hours.

[0222] Feed 3 started 30 minutes after the start of feeds 1, 2 and 4 (time: 30 minutes) and took place over 3.5 hours.

[0223] Feed 4 took place over a period of 4 hours and 15 minutes.

[0224] Feed 5 was commenced after 30 minutes after the start of feeds 1, 2 and 4 (time: 30 minutes) and took place over 3 hours.

[0225] 15 minutes before the end of feeds 1, 2 and 3 (time: 225 minutes) the polymerization temperature was increased to 100° C. After the end of the metered addition of feed 4, the polymerization mixture was stirred for a further 30 minutes. The polymerization mixture was then heated to a temperature of 90° C. and thereafter 71.59 ml of water and 15.00 g of 15 wt % sodium hydroxide solution (0.10 pphm) were added.

[0226] Feeds 6 and 7 were started subsequently and took place over a further 2 hours. After the end of feeds 6 and 7, the polymerization mixture was cooled to room temperature and subsequently admixed with 144.00 g of 15 wt % sodium hydroxide solution (0.96 pphm).

[0227] A monomodal dispersion was obtained. The solids content of the dispersion was 53 wt %.

[0228] The mean particle size D.sub.50 (determined by means of AUC) of the dispersion particles: 128 nm.

Comparative Example C2 (without Emulsifier Shot)

[0229] Initial Charge:

TABLE-US-00024 360.01 g of water 11.25 g of a 2 wt % solution of EDTA (complexing agent) (0.01 pphm) 18.00 g of a 15 wt % solution of sodium lauryl sulfate (emulsifier A) (0.12 pphm) 192.86 g of a 7 wt % aqueous solution of itaconic acid (0.6 pphm) 189.39 g of a 29.7 wt % dispersion of a polystyrene latex with a mean particle size of 30 nm (2.50 pphm) 4.50 g of acrylic acid (0.2 pphm) 47.48 g of styrene (2.11 pphm)

[0230] Addition:

TABLE-US-00025 86.79 g of a 7 wt % solution of sodium peroxodisulfate (initiator A) (0.27 pphm)

[0231] Feed 1:

TABLE-US-00026 90.00 g of acrylic acid (4.0 pphm) 40.18 g of a 28 wt % solution of ethoxylated sodium lauryl ether sulfate (emulsifier B) (0.5 pphm) 36.00 g of a 15 wt % solution of sodium lauryl sulfate (0.24 pphm) 37.5 g of 15 wt % sodium hydroxide solution (0.25 pphm) 547.96 ml of water

[0232] Feed 2:

TABLE-US-00027 1252.13 g of styrene (55.65 pphm)

[0233] Feed 3:

TABLE-US-00028 842.4 g of butadiene (37.44 pphm)

[0234] Feed 4:

TABLE-US-00029 273.21 g of a 7 wt % solution of sodium peroxodisulfate (initiator A) (0.85 pphm)

[0235] Feed 5:

TABLE-US-00030 180.00 g of a 10 wt % solution of tert-butyl hydroperoxide (initiator B) (0.8 pphm)

[0236] Feed 6:

TABLE-US-00031 51.75 g of a 10 wt % solution of tert-butyl hydroperoxide (initiator B) (0.23 pphm)

[0237] Feed 7:

TABLE-US-00032 66.98 g of a 13.1 wt % solution of acetone bisulfite (0.39 pphm)

[0238] The components of the initial charge were charged to a 6 l pressure reactor and mixed. The initial charge was heated to 90° C. When 90° C. were reached, the initiator A (addition 1) was added slowly and the polymerization commenced.

[0239] Started immediately thereafter were feeds 1, 2 and 4 (time: 0 minutes). Feeds 1 and 2 took place over a period of 4 hours.

[0240] Feed 3 started 30 minutes after the start of feeds 1, 2 and 4 (time: 30 minutes) and took place over 3.5 hours.

[0241] Feed 4 took place over a period of 4 hours and 15 minutes.

[0242] Feed 5 was commenced after 30 minutes after the start of feeds 1, 2 and 4 (time: 30 minutes) and took place over 3 hours.

[0243] 15 minutes before the end of feeds 1, 2 and 3 (time: 225 minutes) the polymerization temperature was increased to 100° C. After the end of the metered addition of feed 4, the polymerization mixture was stirred for a further 30 minutes. The polymerization mixture was then heated to a temperature of 90° C. and thereafter 71.59 ml of water and 15.00 g of 15 wt % sodium hydroxide solution (0.10 pphm) were added.

[0244] Feeds 6 and 7 were started subsequently and took place over a further 2 hours. After the end of feeds 6 and 7, the polymerization mixture was cooled to room temperature and subsequently admixed with 129.00 g of 15 wt % sodium hydroxide solution (0.86 pphm).

[0245] The dispersion has coagulated.

TABLE-US-00033 TABLE 1 Start of metering of emulsifier shot by time, and amount of monomer metered in, in the individual examples Commencement Start from Start from “Emulsifier of “emulsifier y % total z % of total shot” x times shot” after monomer monomer the metering Ex. x min metering time amount* rate in P1 1 50 20.83 20.83 16.66 2 60 25 21.42 16.66 3 40 16.66 15.42 16.66 4 40 16.66 16.66 16.66 5 50 20.83 20.83 10 6 50 20.83 20.83 16.66 C1 none — — — *without monomers in the initial charge

[0246] Production of Coating Slips S1 to S6 and SC1

[0247] Coating slips were produced with the dispersions obtained from the examples, these slips consisting of 100 parts by weight of precipitated calcium carbonate (Opacarb A 40), 9.5 parts by weight of binder (example dispersion, solids), 0.5 part by weight of calcium stearate (Ombrelub), 0.25 part by weight of thickener (Sterocoll FS) and 0.1 part of dispersant (Sokalan CP 10). All weight figures are based on the respective solids content of the components.

[0248] The solids content of the coating slip was 66 wt % and the pH was 8.8.

[0249] The viscosity at high shear rates was measured using a capillary viscometer (ACAV).

TABLE-US-00034 TABLE 2 Viscosity of coating slip at high shear rates Viscosity at a shear Viscosity at a shear Dispersion rate of 500 000 s.sup.−1 rate of 620 000 s.sup.−1 Ex. ex. [mPa s] [mPa s] S1 1 118 109 S2 2 115 114 S3 3 124 123 S4 4 114 108 S5 5 115 110 S6 6 106 100 SC1 C1 150 not measurable

[0250] As can be seen from the table, all of inventive coating slips S1 to S6 formulated with the dispersions of the invention have a low viscosity at high shear rates and therefore have very good rheological behavior. The coating slip formulated with the monomodal dispersion of comparative example C1 resulted in significantly higher viscosities and is no longer measurable at a shear rate of 620 000 s.sup.−1.