US-12624504-B2 - Process for producing an aqueous polymer dispersion from a vinyl aromatic compound and a conjugated aliphatic diene

US12624504B2US 12624504 B2US12624504 B2US 12624504B2US-12624504-B2

Abstract

The invention relates to a process for producing an aqueous polymer dispersion by means of radically initiated aqueous emulsion polymerisation by polymerising, in an aqueous medium, in accordance with a monomer feed process: (a) 40 to 75 parts by weight styrene; (b) 24.9 to 59.9 parts by weight butadiene; (c) 0.1 to 10 parts by weight of at least one ethylenically unsaturated carboxylic acid; and (d) 0 to 15 parts by weight other monomers, wherein the parts by weight of monomers (a) to (d) add up to 100 parts by weight, which process comprises the following steps: a) creating a template of a seed latex and 1 to 10 parts by weight monomers, based on the total monomer amount; b) starting the polymerisation at a temperature ≥80° C. in this template; and c) subsequently steadily metering monomers and emulsifier into this reaction mixture; c1) wherein at a time when 40 to 55% of the total metering time of the monomers has elapsed and 40 to 55 parts by weight of the monomer amounts to be metered in are metered in, the metering rate of the emulsifier for a period P2 that lasts at most for 30 minutes is increased to 10 to 100 times the average metering rate of the emulsifier during the period P1, wherein the period P1 is the preceding length of time beginning with the start of the emulsifier metering; c2) and at a time when 60 to 85% of the total metering time of the monomers has elapsed and 60 to 85 parts by weight of the monomer amount to be metered in are metered in, the metering rate of the emulsifier for a period P4 that lasts at most 30 minutes is increased to 10 to 120 times the average metering rate of the emulsifier of the period P1 and with the proviso that the aqueous polymer dispersion has a solids content of ≥58 wt. %. The invention also relates to the dispersion obtained according to the process, and to the use thereof as a binder, adhesive, sizing agent for fibres, for producing coatings or for producing a paper coating slip.

Inventors

Carmen-Elena Cimpeanu
Christian Jehn-Rendu
Justin Andrew BORDLEY
Claudia Wood

Assignees

BASF SE

Dates

Publication Date: 20260512
Application Date: 20230206
Priority Date: 20220214

Claims (13)

1 . A process for producing an aqueous polymer dispersion by free-radically initiated aqueous emulsion polymerization, characterized in that, in an aqueous medium, (a) 40 to 75 parts by weight of styrene, (b) 24.9 to 59.9 parts by weight of butadiene, (c) 0.1 to 10 parts by weight of at least one ethylenically unsaturated carboxylic acid and (d) 0 to 15 parts by weight of one or more other monomers, where the parts by weight of monomers (a) to (d) add up to 100 parts by weight, are polymerized by a monomer feed process comprising the following steps: a) initially charging a seed latex and 1 to 10 parts by weight of monomers based on the total amount of monomers, b) initiating the polymerization at a temperature ≥80° C. in this initial charge, c) and then constantly metering monomers and emulsifier into this reaction mixture, c1) characterized in that, at a time when 40% to 55% of the total monomer metering time has elapsed and 40 to 55 parts by weight of the amount of monomers to be metered in have been metered in, the metering rate of the emulsifier is increased for a period P2 of not longer than 30 minutes to 10 to 150 times the average metering rate of the emulsifier during the period P1, where the period P1 is the preceding period of time commencing with the start of emulsifier metering, c2) and, at a time when 60% to 85% of the total monomer metering time has elapsed and 60 to 85 parts by weight of the amount of monomers to be metered in have been metered in, the metering rate of the emulsifier is increased for a period P4 of not longer than 30 minutes to 10 to 150 times the average metering rate of the emulsifier in period P1, with the proviso that the aqueous polymer dispersion has a solids content of ≥58% by weight.
2 . The process as claimed in claim 1 , characterized in that the ethylenically unsaturated carboxylic acid is selected from acrylic acid, methacrylic acid and itaconic acid.
3 . The process as claimed in claim 1 , characterized in that 0.1 to 15 parts by weight of other monomer (d) are polymerized.
4 . The process as claimed in claim 1 , characterized in that the other monomer (d) is selected from acrylamide, methacrylamide, acrylonitrile, methacrylonitrile, N-methylolacrylamide, N-methyl (meth)acrylamide, vinyl esters of saturated C to C18 carboxylic acids, esters of acrylic acid and of methacrylic acid with monohydric C to C18 alcohols, allyl esters of saturated carboxylic acids, vinyl ethers, vinyl ketones, dialkyl esters of ethylenically unsaturated carboxylic acids, N-vinylpyrrolidone, N-vinylpyrrolidine, N-vinylformamide, N,N-dialkylaminoalkylacrylamides, N,N-dialkylaminoalkylmethacrylamides, N,N-dialkylaminoalkyl acrylates, N,N-dialkylaminoalkyl methacrylates, vinyl chloride and vinylidene chloride, and mixtures thereof.
5 . The process as claimed in claim 1 , characterized in that the following are polymerized in the aqueous medium: (a) 40 to 75 parts by weight of styrene, (b) 24.8 to 59.8 parts by weight of butadiene, (c) 0.1 to 10 parts by weight of at least one ethylenically unsaturated carboxylic acid and d1) 0.1 to 5 parts by weight of acrylamide and/or methacrylamide, d2) 0 to 10 parts by weight of one or more other monoethylenically unsaturated monomers, where the parts by weight of monomers (a) to (d) add up to 100 parts by weight.
6 . The process as claimed in claim 1 , characterized in that the aqueous polymer dispersion has a solids content of ≥59% by weight.
7 . The process as claimed in claim 1 , characterized in that the monomers are metered in at a constant mass flow rate over a period of at least 100 minutes.
8 . The process as claimed in claim 1 , characterized in that the emulsifier is selected from alkali metal and ammonium salts of C 8 -C 22 -alkyl sulfates, sulfuric monoesters of ethoxylated alkanols, sulfuric monoesters of ethoxylated alkylphenols, and bis(phenylsulfonic acid) ethers or the alkali metal or ammonium salts thereof that bear a C4-C24-alkyl group on one or both aromatic rings.
9 . The process as claimed in claim 1 , characterized in that 0.1 to 5 parts by weight of emulsifier based on 100 parts by weight of monomers are metered in constantly in a mixture with at least one monomer.
10 . The process as claimed in claim 1 , characterized in that polymerization is effected at a temperature in the range from ≥80° C. to ≤115° C.
11 . The process as claimed in claim 1 , characterized in that the seed latex used is a styrene polymer and/or methyl methacrylate polymer having a glass transition temperature ≥50° C. as claimed in DIN EN ISO 11357-2 (2013-09).
12 . An aqueous polymer dispersion obtainable by the process as claimed in claim 1 that has a solids content of ≥58% by weight and a Brookfield viscosity of <1000 mPa·s measured at 100 rpm with spindle 3 at 23° C.
13 . A paper coating slip comprising (i) inorganic pigments and (ii) an aqueous polymer dispersion as claimed in claim 12 and optionally further auxiliaries.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a National stage application (under 35 U.S.C. § 371) of PCT/EP2023/052823, filed Feb. 6, 2023, which claims benefit of European Application No. 22156655.7, filed Feb. 14, 2022, both of which are incorporated herein by reference in their entirety. The invention relates to a process for producing an aqueous polymer dispersion having a polymodal particle distribution of the polymer particles by copolymerizing a vinylaromatic compound and a conjugated aliphatic diene. The invention also relates to the aqueous polymer dispersions produced by the process and to the use of these as binder for adhesives, sizing agents, fibers, coating compositions and paper coating slips. Binders for paper coating slips that are based on copolymers of vinylaromatic compounds and aliphatic dienes are often chosen for applications such as packaging board. Because of ever-increasing production speeds of the paper machines, there are rising demands on the rheology of the coating slip. In spite of the high pigment content, which is of course coarser than the binder polymer, the latter has a strong influence on the rheology of a coating slip. It would be possible to lower the viscosity of the coating slip by greater dilution, but what is desired is the exact opposite. Thus, modern dispersions are supposed to have a high solids content and nevertheless to have low viscosity at high speeds. Conventional polymer emulsions having a monomodal particle size distribution generally have a solids content of ≤50% by weight. Above a solids content of 50%, the dispersions generally have an unacceptable viscosity. Peter C. Hayes states that, in the case of high solids contents of coating slips with styrene-butadiene binders, running characteristics are improved by relatively small particles of the binder (“Styrene-butadiene and styrene-acrylic latexes in paper coating applications”, Coating Material: Pigment Binders & Additives Short Course, Orange Beach, AL, United States, Mar. 11-13, 2002, pages 115-123, TAPPI PRESS, Atlanta, 2002). U.S. Pat. Nos. 4,567,099 and 4,474,860 teach the use of a blend of two styrene/butadiene dispersions of different particle size for paper coating applications. However, the mixing of two dispersions typically leads to dilution of the overall dispersion since dispersions with small particle size can be produced only with a relatively low solids content. It is only by subsequent concentration of the blend that higher solids contents are achieved. Such concentration, i.e. subsequent removal of water, is energy-intensive and takes a long time. Moreover, two dispersions have to be produced beforehand, which means a poor space-time yield for the overall product. U.S. Pat. No. 5,726,259 teaches the production of a bimodal styrene/butadiene latex binder for paper coating slips. The latex binder is produced by initiating the polymerization with an in situ seed, adding the monomers in portions by 10 monomer additions and, after 43% of the total amount of monomers has been metered in and 44% of the total metering time has elapsed, a further in situ seed is produced and hence the growth of a second particle population is initiated. This affords polymer dispersions having a solids content of 50% by weight. U.S. Pat. No. 4,780,503 describes a process for producing a bimodal polymer dispersion, wherein further lauryl ether sulfate is metered in at a juncture of 43-53% monomer conversion. According to this teaching, dispersions having a relatively high solids content are obtained. However, a reaction time of 10 hours is specified, which suggests a reaction temperature <80° C. Such long reaction times are uneconomic. WO2020/249406 teaches the production of a bimodal styrene/butadiene/acrylic acid dispersion by, after metering in 17% to 25% of the total amount of monomers, adding a large amount of emulsifier all at once, hence initiating the growth of a second particle population. The dispersions thus obtained have low odor, but only a solids content of 53% by weight. It was therefore an object of the present invention to find a process for producing styrene/butadiene polymer dispersions having a solids content of at least 58% that has an improved space-time yield. The polymer dispersion obtained thereby is to have a viscosity <1000 mPas, Brookfield, 100 rpm, spindle 3 at 23° C., such that, incorporated into paper coating slips, it has good rheological characteristics even at high shear forces. It is preferably to be polymodal. The object is achieved in accordance with the invention by a process for producing an aqueous polymer dispersion by free-radically initiated aqueous emulsion polymerization, which comprises polymerizing, in an aqueous medium, (a) 40 to 75 parts by weight of styrene,(b) 24.9 to 59.9 parts by weight of butadiene,(c) 0.1 to 10 parts by weight of at least one ethylenically unsaturated carboxylic acid and(d) 0 to 15 parts by weight of other monomers,where the