WO2015040015A2 - Aqueous polymer dispersion of aliphatic polycarbonate polymers - Google Patents

Abstract

The invention relates to an aqueous polymer dispersion of aliphatic polycarbonate polymers, to a method for producing said aqueous polymer dispersion, and to the use of said aqueous polymer dispersion in coating compositions, in particular as binders in paper coating slips, as sizing agents for paper, as paper strengthening agents, as binder compositions for nonwoven fabrics, in adhesives, or for formulating active ingredients. The aqueous polymer dispersion according to the invention contains: i) 5 to 50 wt%, in particular 8 to 40 wt%, with respect to the total weight of the dispersion, of at least one aliphatic polycarbonate polymer, in particular polypropylene carbonate; ii) 1 to 20 wt%, in particular 2 to 15 wt%, with respect to the total weight of the dispersion, of at least one partially or completely saponified polyvinyl alcohol; and iii) water, wherein the weight ratio of aliphatic polycarbonate polymers to the partially or completely saponified polyvinyl alcohol is in the range of 1 : 1 to 20 : 1, in particular in the range of 1.2 : 1 to 10 : 1.

Description

 The present invention relates to an aqueous polymer dispersion of aliphatic polycarbonate polymers, a process for their preparation and their use in coating compositions, in particular as binders in paper coating slivers, as sizing agents for paper, as paper strengthening agents, as binder compositions for nonwovens , in adhesives, or for the formulation of active ingredients.

Aliphatic polycarbonates such as polypropylene carbonate are of interest as biodegradable polymers for numerous applications. It would be desirable if the aliphatic polycarbonate were provided in the form of an aqueous polymer dispersion.

Unlike aqueous polymer dispersions whose polymer chains have a backbone built up from carbon atoms, aqueous dispersions of aliphatic polycarbonates can not be prepared by an emulsion polymerization process. Rather, such polymers are usually prepared by polycondensation of aliphatic diols with phosgene or by polyaddition of aliphatic oxiranes to CO2 in the presence of suitable catalysts in a non-aqueous polymerization medium and usually fall after removal of the solvent as solids. In order to obtain aqueous dispersions, solid polycarbonates would have to be dispersed in water. However, it must be taken into account that there is the risk of hydrolysis-induced molecular weight degradation in the case of polycarbonates owing to the hydrolysis-labile carbonate groups present in the polymer backbone.

Therefore, aqueous dispersions of aliphatic polycarbonates are usually prepared by mixing a solution of the polymer in an organic, preferably water-miscible solvent with the aqueous dispersing medium and then removing the organic solvent again. Such methods are described for example in US 3,238,173, US 3,726,824, WO 2006/136555,

WO 2007/074042 and WO 2012/140181. Complete removal of the organic solvent is difficult. For many applications, the comparatively large amounts of low molecular weight emulsifiers are disadvantageous.

In principle, it is also known to emulsify, using high shear forces, a melt of a thermoplastic polymer in the aqueous dispersing medium containing surface-active substances and then to cool it. Such methods are known, for example, from US 4320041, DE 41 15531, EP 1302502, EP 1514891 and WO 97/49762. WO 201 1/1 17308 describes a process for the preparation of aqueous dispersions of thermoplastic polymers, preferably aliphatic polyesters, in which the thermoplastic polymer is introduced by means of a mixing device into the aqueous dispersing medium which has at least one rotor-stator mixer. In the case of the polyalkylene carbonates, however, only dispersions having a low solids content and a comparatively large particle size of the dispersed polyalkylene carbonate particles can be produced by this process. With polycarbonates, however, there is a great risk that due to the drastic processing conditions, a reduction in molecular weight as a result of hydrolysis of the carbonate groups in the polymer backbone occurs.

The previously described or commercially available dispersions of aliphatic polycarbonates when used as a binder often have no satisfactory application profile. Especially when used in paper coating colors, the application profile is unsatisfactory. In comparison to conventional binders based on styrene-butadiene polymer dispersions (SB dispersions), the dry and wet pick resistance is unsatisfactory.

The object of the invention was therefore to provide an aqueous polymer dispersion based on aliphatic polycarbonates, which has good binder properties, in particular when used in paper coating slips.

This object is surprisingly achieved by the aqueous polymer dispersions based on aliphatic polycarbonates described below, in particular based on polypropylene carbonate, which contain a certain amount of a partially or completely saponified polyvinyl alcohol.

The invention therefore relates to aqueous polymer dispersions containing i) 5 to 50% by weight, in particular 8 to 40% by weight, based on the total weight of the dispersion, of at least one aliphatic polycarbonate polymer, in particular polypropylene carbonate;

ii) 1 to 20 wt .-%, in particular 2 to 15 wt .-%, based on the total weight of the dispersion, of at least one partially or fully saponified polyvinyl alcohol; and

iii) water,

wherein the weight ratio of the aliphatic polycarbonate polymer to that of a partially or fully saponified polyvinyl alcohol in the range of 1: 1 to 20: 1, in particular in the range of 1, 2: 1 to 10: 1. The aqueous aliphatic polycarbonate dispersions according to the invention are associated with a number of advantages. Thus, they generally have a low viscosity of at most 2000 mPa.s, in particular of at most 1500 mPa.s (determined by means of a rotational viscometer according to DIN EN ISO 2555 at 30 ° C and a shear rate of 100 sec ^-1 ). When used as a binder in paper-coating slivers, the aqueous polymer dispersions according to the invention have advantageous binder properties. In addition, they can easily be prepared by melt emulsification without the need for organic solvents. Accordingly, the aqueous polymer dispersions according to the invention preferably contain less than 0.5% by weight, in particular less than 0.1% by weight, of organically volatile compounds, based on the total weight of the polymer dispersion. Another advantage is that in addition to the partially or fully saponified polyvinyl alcohol no or only small amounts of surface-active substances are required to arrive at stable dispersions.

The invention also provides a process for the preparation of such aqueous polymer dispersion in which the aliphatic polycarbonate is emulsified in water at a temperature above the melting or softening temperature of the aliphatic polycarbonate in the presence of the polyvinyl alcohol.

The invention also provides the use of the aqueous polymer dispersions according to the invention as binders in coating compositions, as solvents for paper, as paper strengthening agents, as binder compositions for nonwovens, in adhesives, or for the formulation of active ingredients. In particular, the invention relates to the use of the novel aqueous polymer dispersions as binders in pigment-containing paper coating slips or paper coating slips.

The invention furthermore relates to a paper coating slip comprising an aqueous polymer dispersion according to the invention and at least one pigment.

In the aqueous polymer dispersions according to the invention, the aliphatic polycarbonate forms the disperse phase, whereas the water forms the coherent phase. In other words, in the aqueous polymer dispersions according to the invention, the aliphatic polycarbonate is in the form of finely divided particles. The weight-average particle diameter of the polymer particles (weight average, determined by light scattering) in these dispersions will generally not exceed a value of 10 μm, in particular 8 μm, especially 5 μm, and is typically in the range from 20 nm to 10 μm, in particular in the range from 50 nm to 8 μηη, especially in the range of 100 nm to 5 μηη. Preferably, less than 90 wt .-% of the polymer particles have a particle diameter of 25 μηη and especially 10 μηη not exceed. The particle size is determined in a manner known per se by light scattering on dispersions diluted with water (solids content 0.01 to 1% by weight). Preferably, the viscosity of the aqueous polymer dispersions of the invention, determined according to Brookfield at 30 ° C, at a value of at most 2 Pa-s, often at a maximum of 1, 5 Pa-s, z. B. in the range of 100 to 2000 mPa-s, in particular in the range of 200 to 1500 mPa-s (determined according to DIN EN ISO 2555 at a shear rate of 100 s- ¹ ).

The aqueous polymer dispersions according to the invention preferably contain less than 0.5% by weight, in particular less than 0.2% by weight, based on the total weight of the polymer dispersion, of organic volatile compounds, ie. H. Compounds which react at atmospheric pressure, i. 101, 3 kPa, have a maximum boiling point of 250 ° C (see ISO 1 1890-2: 2006 for details).

According to the invention, the aqueous polymer dispersion contains at least one aliphatic polycarbonate. Aliphatic polycarbonates are polymers which are predominantly composed of repeating units of the formula I defined below. They are also referred to as polyalkylene carbonates. In addition, the polyalkylene carbonates may also have repeating units of the formula II:

In the formulas I and II, A and A are an alkanediyl radical, in particular an alkan-1, 2-diyl radical, preferably having 2 to 10 C atoms and / or a cycloalkanediyl radical, in particular a cycloalkane-1,2 -diyl radical, preferably having 5 to 10 carbon atoms, wherein A and A within a polymer may also have different meanings. Preferably, A and A 'are independently selected from alkane-1, 2-diyl radicals, especially those having 2 to 4 carbon atoms, such as. B. 1, 2-ethanediyl, 1, 2-propanediyl, 1, 2-butanediyl, 1-methyl-1, 2-propanediyl and 2-methyl-1, 2-propanediyl. In particular, A is 1, 2-ethanediyl and / or 1, 2-propanediyl. In particular, A is 1, 2-ethanediyl and / or 1, 2-propanediyl.

In the preferred polycarbonates, more than 80 mol% and preferably more than 90% of all repeat units are those of the formula I. In particularly preferred polycarbonates more than 80 mol% and preferably more than 90% of all repeat units are those of the formula I, wherein is an alkanediyl radical, in particular an alkane-1, 2-diyl radical, preferably having 2 to 10 carbon atoms and in particular 2 to 4 carbon atoms. Repeating units of the formula I in which A is alkanediyl are also referred to as alkylene carbonate groups. Accordingly, a C 2 -C 10 -alkylene carbonate group is a repeating unit of the formula I in which A is an alkanediyl radical, in particular an alkane-1,2-diyl radical, having 2 to 10 carbon atoms and a C 2 -C 4 -alkylene carbonate group is a repeating unit of the formula I in which A is an alkanediyl radical, in particular an alkane-1,2-diyl radical, having 2 to 4 carbon atoms. In a preferred embodiment of the invention A is predominantly, ie at least 70 mol%, in particular at least 80 mol% or at least 90 mol%, based on all repeating units, for 1, 2-propanediyl. In this case, the aliphatic polycarbonate is polypropylene carbonate. Aliphatic polycarbonates are generally prepared by reacting aliphatic oxiranes, ie alkylene oxides having generally 2 to 10 C atoms or cycloalkylene oxides having generally 5 to 10 C atoms with CO.sub.2 in the presence of one or more suitable catalysts, see z. Inoue, macromol. Chem., Rapid Commun. 1, 775 (1980), Soga et al., Polymer Journal, 1981, 13, 407-10, US 4,789,727 and US 7,304,172. Particularly suitable are zinc and cobalt catalysts, as described, for example, in the aforementioned literature and in particular in US Pat. No. 4,789,727 and US Pat. No. 7,304,172.

Examples of suitable polyalkylene carbonates are the polyethylene carbonates known from EP-A 1264860, which are obtained by copolymerization of ethylene oxide and carbon dioxide in the presence of suitable catalysts, and in particular polypropylene carbonate (see, for example, WO 2007/125039), obtainable by copolymerization of propylene oxide and carbon dioxide in the presence of suitable catalysts. The polymer is also commercially available and is marketed, for example, by Empower Materials Inc. or Aldrich.

The number average molecular weight M _{n of} the polyalkylene carbonates, in particular of the polypropylene carbonates, is generally from 5000 to 500,000 daltons, in particular from 50,000 to 250,000 daltons. The weight-average molecular weight M _w is then usually in the range from 7000 to 5,000,000 daltons, in particular in the range from 70,000 to 500,000 daltons.

In a specific embodiment of the invention, the number average molecular weight M _{n of} the polypropylene carbonates is in the range of 50,000 to 250,000 daltons and especially in the range of 70,000 to 120,000 daltons. The weight-average molecular weight M _w is then usually in the range from 70,000 to 500,000 daltons, in particular in the range from 100,000 to 250,000 daltons. The proportion of the carbonate repeat units in the total amount of repeating units in the polymer is generally at least 80 mol%, in particular 90 mol%. The polydispersity (ratio of weight average (Mw) to number average (MN)) is usually between 1 and 80 and preferably between 2 and 10. The polypropylene carbonates used may contain up to 1% carbamate and urea groups.

Suitable aliphatic polycarbonates are also chain-extended polyalkylenecarbonates. Particularly suitable chain extenders for the polyalkylene carbonates are maleic anhydride, acetic anhydride, di- or polyisocyanates, di- or polyoxazolines or -oxazines or di- or polyepoxides. Examples of isocyanates are aromatic diisocyanates such as toluylene-2,4-diisocyanate, toluylene-2,6-diisocyanate,

2,2'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, naphthylene-1,5-diisocyanate or xylylene diisocyanate and aliphatic diisocyanates such as, in particular, 1,6-hexamethylene diisocyanate, isophorone diisocyanate or methylene bis (4-isocyanatocyclohexane). Particular preference is given to aliphatic diisocyanates and, among these, especially isophorone diisocyanate and in particular 1,6-hexamethylene diisocyanate. As bisoxazolines are 2,2'-bis (2-oxazoline),

Bis (2-oxazolinyl) methane, 1, 2-bis (2-oxazolinyl) ethane, 1, 3-bis (2-oxazolinyl) propane or 1, 4-bis (2-oxazolinyl) butane, especially 1,4-bis (2-oxazolinyl) benzene,

1, 2-bis (2-oxazolinyl) benzene or 1, 3-bis (2-oxazolinyl) benzene called. The chain extenders are preferably used in amounts of from 0.01 to 5, preferably from 0.05 to 2, particularly preferably from 0.08 to 1% by weight, based on the amount of polycarbonate. Chain-extended polyalkylene carbonates typically have a number-average molecular weight M _n of 30,000 to 500,000 daltons, preferably 60,000 to 250,000 daltons.

The polymer dispersions according to the invention also contain at least one polyvinyl alcohol. Polyvinyl alcohols are polymers which are predominantly, typically at least 70 mole percent, based on the total number of repeating units, of repeating units derived from vinyl alcohol, i. H. Repeating units of the formula -CH 2 -CHOH-. Polyvinyl alcohols are usually obtained by saponification of corresponding polyvinyl ester polymers, generally polyvinyl acetate or vinyl acetate copolymers. By saponification of the vinyl ester

Repeating units are the repeat units of the formula -CH2-CHOH- formed. Preference is given to polyvinyl alcohols in which at least 80 mol% of all repeating units, for. B. 80 to 100 mol%, in particular 80 to 99.9 mol%, the formula -CH2-CHOH- have.

The polyvinyl alcohol may be a so-called partially saponified polyvinyl alcohol or a fully saponified or fully saponified polyvinyl alcohol. Partially saponified polyvinyl alcohols are understood as meaning polypolyvinyl alcohols which in some cases have repeating units which are derived from vinyl esters. Fully saponified polyvinyl alcohols are understood as meaning polyvinyl alcohols which have less than 1% repeat units derived from vinyl esters. Preference is given to polyvinyl alcohols having a degree of hydrolysis or degree of hydrolysis of at least 80%, in particular at least 83%, z. B. 80 to 99.9%, in particular 83 to 99%, ie at least 80 mol%, in particular at least 83 mol%, z. 80 to 99.9 mol%, in particular 83 to 99 mol% of the vinyl ester units present in the polyvinyl ester polymer are present in the polyvinyl alcohol as repeating units of the formula -CH 2 -CHOH-. In a specific embodiment of the invention, the polyvinyl alcohol is a partially saponified polyvinyl alcohol having a saponification degree in the range of 80 to 99%, in particular in the range of 83 to 97%. The number average molecular weight M _{n of} the polyvinyl alcohols is usually in the

Range of 10,000 to 250,000 daltons, especially in the range of 20,000 to 150,000 daltons. The weight-average molecular weight M _w is then usually in the range from 12,000 to 750,000 daltons, in particular in the range from 25,000 to 45,000 daltons. Preference is given to polyvinyl alcohols whose 4 wt .-% solutions in water at a temperature of 20 ° C have a viscosity in the range of 10 to 150 mPa-s, determined by means of a rotational viscometer according to Brookfield (according to DIN EN ISO 2555).

The aqueous polymer dispersions according to the invention may additionally comprise one or more surface-active substances which are different from polyvinyl alcohol. However, the concentration of surface-active substances will generally not exceed 5% by weight, in particular 3% by weight, based on the total weight of the dispersion. Based on the aliphatic polycarbonate contained in the dispersion, the content of surface-active substances other than polyvinyl alcohol is generally at a maximum of 15% by weight, eg. B. in the range of 0.5 to 15 wt .-%, in particular in the range of 1 to 10 wt .-%.

The surfactants may be anionic, cationic, nonionic or zwitterionic. Preferably, the surfactants other than polyvinyl alcohol comprise one or more anionic surfactants and / or one or more nonionic surfactants and mixtures thereof. The surface-active substances may be emulsifiers or surfactants or else protective colloids. Emulsifiers or surfactants are generally low molecular weight or oligomeric substances which, unlike the polymeric protective colloids, have a (number-average) molecular weight of not more than 2000 daltons, in particular not more than 1500 daltons. In contrast, protective colloids generally have a molecular weight above 2000 daltons (number average), z. B. in the range of 2200 to 10 ⁶ daltons on. In preferred embodiments of the invention, the aqueous polymer dispersion contains at least one anionic surface-active substance, in particular at least one anionic emulsifier or surfactant. In these embodiments, the discrepancies persion, the at least one anionic surfactant, preferably in a concentration of 0.1 to 5 wt .-%, in particular in a concentration of 0.2 to 3 wt .-%, based on the total weight of the dispersion. Suitable anionic emulsifiers are, in particular, the salts of amphiphilic substances which have at least one anionic functional group, eg. B. at least one sulfonate, phosphonate, sulfate or phosphate group. These include, for example

 the salts, in particular the alkali metal and ammonium salts of the sulfuric acid semi-esters of aliphatic alcohols, in particular alkanols, as a rule

8 to 22 C atoms, in particular 10 to 20 C atoms (C8-C22 or C10-C20 alkyl sulfates),

 the salts, in particular the alkali metal and ammonium salts, of amphiphilic compounds which contain a sulfated oligoalkylene oxide group, in particular a sulfated oligoethylene oxide group (polyether sulfates), for example the salts, in particular the alkali metal and ammonium salts of sulfuric monoesters of alkoxylated aliphatic alcohols (alkyl polyether sulfates) , in particular the alkali metal and ammonium salts of sulfuric monoesters of alkoxylated alkanols (alkylpolyethersulfates), in which the aliphatic alcohols generally have 10 to 30, in particular 12 to 20, carbon atoms and the

The degree of alkoxylation is generally in the range from 2 to 50, in particular from 4 to 30, furthermore the salts, in particular the alkali metal and ammonium salts of sulfuric monoesters of alkoxylated, in particular ethoxylated, alkylphenols (alkylphenolpolyethersulfates) whose alkyl radicals are generally from 4 to 12 C Atoms (C 4 -C 12 -alkyl phenol polyether sulfates) and which generally have an alkoxylation degree in the range from 2 to 50,

 the salts, in particular the alkali metal and ammonium salts of amphiphilic compounds which have a phosphated oligoalkylene oxide group, in particular a phosphated oligoethylene oxide group (polyether phosphates), such as the salts, in particular the alkali metal and ammonium salts of Phosphorsäurehalbestern alkoxylated aliphatic alcohols, especially the Alkali metal and ammonium salts of Phosphorsäurehalbestern alkoxylated alkanols (alkyl polyether phosphates), wherein the aliphatic alcohols usually have 10 to 30, in particular 12 to 20 carbon atoms and the degree of alkoxylation usually in the range of 2 to 50, in particular from 4 to 30, further the salts, in particular the alkali metal and ammonium salts of Phosphorsäurehalbestern alkoxylated, in particular ethoxylated alkylphenols (Alkylphenolpolyetherphosphate) whose alkyl radicals usually 4 to 12 carbon atoms (C4-Ci2-Alkylphenolpolyetherphosphate), and in the Reg have an alkoxylation degree in the range of 2 to 50,

the salts, in particular the alkali metal and ammonium salts of alkylsulfonic acids, preferably having 12 to 20 C atoms (C 12-C 20 -alkyl sulfonates), the salts, in particular the alkali metal and ammonium salts of alkylaryl sulfonic acids (alkyl radical: C ₄ to Cie) and also

the salts, in particular the alkali metal and ammonium salts of dialkyl esters of sulfosuccinic acid (alkyl radical: C ₄ to Cie) and also

- The salts, in particular the alkali metal and ammonium salts of Alkylbiphe- nylethersulfonsäuren (alkyl radical: C ₄ to Cie) such. B. the product sold under the name Dowfax® 2A1 product.

Preferably, the surfactant is selected from the alkali metal salts and ammonium salts, especially the sodium salts, the aforementioned sulfuric monoesters of aliphatic alcohols, the alkali metal salts and ammonium salts, especially the sodium salts of the aforementioned sulfuric monoesters of alkoxylated, especially ethoxylated, aliphatic alcohols, the alkali metal salts and ammonium salts, especially the sodium salts of the aforementioned Alkylphenolpolyetherphos- phate and their mixtures. In particular, the at least one anionic surfactant is selected from alkali metal and ammonium salts, in particular the sodium salts of C 20 -C 20 -alkyl sulfates, C 10 -C 20 -alkyl polyether sulfates and C ₄ -C 10 -alkyl phenol polyether sulfates, where the latter two groups preferably have an alkoxylation degree, in particular one Have degree of ethoxylation in the range of 2 to 50 and especially in the range of 4 to 30.

The degree of alkoxylation or the degree of ethoxylation is understood as meaning the number-average number of alkylene oxide or ethylene oxide repeating units in the polyether group of the alkoxylated substances. Preferred alkylene oxide units in this context are, in particular, ethylene oxide units (CH ₂ CH ₂ -O) and 1,2-propylene oxide units (CH ₂ CH (CH ₃ ) -O).

In addition to the abovementioned constituents, the polymer dispersions according to the invention may contain customary additives, for example microbicides, defoamers and the like. However, the overall proportion of these additives usually constitutes less than 1% by weight, in particular less than 0.5% by weight, of the polymer dispersion.

The preparation of the aqueous polymer dispersions according to the invention is generally carried out by melt emulsification of the aliphatic polycarbonate. For this purpose, the aliphatic polycarbonate will be emulsified at a temperature above the melting or softening temperature of the aliphatic polycarbonate in water in the presence of the polyvinyl alcohol, preferably in an aqueous solution of the polyvinyl alcohol. In this case, one will choose the relative amounts of aliphatic polycarbonate and polyvinyl alcohol so that the inventive ratio of 20: 1 to 1 1 results. Preferably, the procedure is such that the aliphatic polycarbonate at a temperature above the melting or softening temperature of the aliphatic polycarbonate in an aqueous 1 to 25 wt .-%, in particular 2 to 20 wt .-% aqueous solution of the polyvinyl alcohol in a Rotor-stator mixer emul- giert and the resulting aqueous emulsion of the aliphatic polycarbonate quenched.

Such a process is known in principle from the above-cited WO 201 1/1 17308 and can be applied in an analogous manner to the preparation of the aqueous polymer dispersions according to the invention.

Rotor-stator mixers are familiar to the person skilled in the art and fundamentally comprise all types of dynamic mixers in which a high-speed, preferably rotationally symmetrical rotor in interaction with a stator forms one or more, essentially annular, annular work areas. In these work areas, the mix is exposed to strong shear and shear stresses, which often prevail in the annular gaps strong turbulence, which also favor the mixing process. In operation, the rotor-stator device is operated at a relatively high speed of typically 1000 to 20,000 rpm. This results in high peripheral speeds and a high shear rate, whereby the emulsion is exposed to high shear and shear stresses, which lead to an effective fragmentation of the melt and thus to a very effective emulsification. The rotor-stator mixers include, for example, sprocket dispersers, annular gap mills and colloid mills. Suitable rotor-stator devices preferably used for the method according to the invention are known from WO 201 1/1 17308, to which reference is hereby made.

Preference is given to those rotor-stator mixers which have means for generating cavitation forces. Such means may be rotor and / or stator arranged elevations which protrude into the mixing chamber and having at least one surface whose surface normal has a tangential portion, such as pins, teeth or knives or coaxial rings with radially arranged slots. Preferably, the rotor-stator mixer on the rotor side at least one rotationally symmetrically arranged sprocket and / or at least one rotationally symmetrical ring arranged with radial slots (tooth spaces) on. Such devices are also referred to as Zahnkranzdispergatoren or Zahnkranzdispergiermaschinen and are preferred for the inventive method. In particular, the rotor-stator mixer on both the rotor side and stator side at least one rotationally symmetrical sprocket and / or ring with radial Schlit- zen (tooth gaps), wherein the rotor and stator side arranged sprockets / rings are arranged coaxially and to form an annular gap mesh. To prepare the polymer dispersions of the invention, the aliphatic polycarbonate is emulsified in water at a temperature above the melting or softening temperature of the aliphatic polycarbonate in the presence of the polyvinyl alcohol. Water or the aqueous solution of the polyvinyl alcohol are hereinafter also referred to as emulsifying medium.

For this purpose, the aliphatic polycarbonate is usually heated to a temperature above the softening temperature and fed to a mixing device, which preferably comprises at least one rotor-stator device, preferably continuously. To the same extent, the required amount of water and polyvinyl alcohol and optionally other surface-active substances, preferably continuously supplied to the mixing device. Preferably, the polyvinyl alcohol is supplied as an aqueous solution. Preferably, any further surface-active substances are likewise supplied as aqueous solution. It has proved to be advantageous when emulsifying the aliphatic polycarbonate in a 1 to 25 wt .-%, in particular 2 to 20 wt .-% aqueous solution of the polyvinyl alcohol as the emulsifying medium. The amount of aqueous emulsifier is generally chosen so that set the desired concentrations of aliphatic polycarbonate and polyvinyl alcohol. However, it is also possible to use the aqueous emulsifying medium in a larger amount and then to concentrate the dispersion obtained. It is likewise possible first to prepare a more concentrated dispersion and to dilute it with further water or aqueous emulsifying medium. The mass ratio of polycarbonate fed to the total amount of aqueous emulsifying medium is typically in the range of 1:20 to 1.2: 1, often in the range of 1:10 to 1: 1, 1, and more preferably in the range of 1: 3 to 1: 1. With continuous addition of polycarbonate and aqueous emulsifying medium, the mass ratio of the supplied material flows in the aforementioned ranges. In the case of a multi-stage addition of emulsifying medium, the mass ratio of polycarbonate fed to the total quantity of aqueous emulsifying medium fed in the first to the penultimate stage can also be up to 4: 1 or up to 2.3: 1. Preferably, the supply of polycarbonate and aqueous emulsification medium occurs at a constant rate of addition, i. H. the mass ratio of polycarbonate, polyvinyl alcohol and emulsifying medium is constant throughout the process or does not deviate more than 10% from the preselected mass ratio.

The introduction of the aliphatic polycarbonate into the aqueous emulsifying medium typically takes place at a temperature of at least 5 K, often at least 10 K and in particular at least 20 K, z. In the range of 5 to 150 K, often in the range of 10 to 100 K and in particular in the range of 20 to 80 K above the melting point. or softening temperature of the aliphatic polycarbonate. This temperature is also referred to below as the mixing temperature. As a rule, the introduction of the aliphatic polycarbonate in the aqueous emulsifying medium at a temperature of at most 300 ° C, z. B. in the range of 50 to 300 ° C, often from 60 to 250 ° C and in particular from 100 to 200 ° C.

Because of the comparatively high mixing temperature, the introduction of the aliphatic polycarbonate into the aqueous emulsifying medium usually takes place at a pressure above atmospheric pressure, generally at a pressure in the range from 1 to 50 bar, frequently from 1.1 to 40 bar, in particular in the range from 1 , 5 to 20 bar.

The mixing process can be in one or more, z. B. 2, 3, 4 or 5 stages are performed, wherein at least one stage is performed in a rotor-stator mixer. In a multi-stage process, all stages are preferably carried out in rotor-stator mixers.

In a first embodiment of the invention, the mixing takes place in one stage, i. H. the mixing device comprises a rotor-stator mixer. In this case, the aliphatic polycarbonate and the aqueous emulsifying medium are generally supplied to the rotor-stator mixer in the amounts required for the preparation of the dispersion. For this purpose, it has been found useful to heat the aqueous emulsifying medium prior to feeding to the desired mixing temperature or a temperature of at least 20 K below the mixing temperature, preferably to a temperature in the range of +/- 20 K of the mixing temperature.

In a second, preferred embodiment of the invention, the mixing takes place in several stages, ie in a mixing device, the more, z. B. 2, 3, 4 or 5, in particular 3 or 4, serially interconnected rotor-stator mixer. It has proven useful in the first stage, ie in the first rotor-stator mixer to give the aliphatic polycarbonate and a subset of the emulsifying and there at a temperature above the melting or softening temperature of the polycarbonate with the subset of the aqueous emulsifying to mix. The subset of the emulsifying medium added to the first stage is usually from 10 to 60% by weight, in particular from 15 to 40% by weight, based on the total amount of emulsifying medium introduced into the mixing device. The introduction of the polycarbonate in the subset of the aqueous emulsifying medium is typically carried out at a temperature of at least 5 K, often at least 10 K and in particular at least 20 K, z. B. in the range of 5 to 150 K, often in the range of 10 to 100 K and in particular in the range of 20 to 80 K above the melting or softening temperature of the polycarbonate. In general, the mixing temperature in the first rotor-stator mixer is a maximum of 300 ° C, and is z. B. in the range of 50 to 300 ° C, often from 80 to 250 ° C and in particular from 100 to 200 ° C. Has to do this it is proven, the fed into the first rotor-stator mixer subset of emulsifying before feeding to the desired mixing temperature or a temperature of at least 20 K below the mixing temperature, preferably to a temperature in the range of +/- 20 K of the mixing temperature heat. The resulting in the first rotor-stator mixer aqueous dispersion is then transferred to another rotor-stator mixer and mixed there with a further subset or the remainder of the emulsifying. The second rotor-stator mixer, one or more, z. B. 1 or 2, further rotor-stator mixer, wherein the resulting in the second rotor-stator mixer dispersion in or optionally further rotor-stator mixer (s) (z), z. B. the third rotor-stator mixer, with the

Remainder or a further subset of the aqueous emulsifying be mixed. The temperature at which the dispersion produced in the first rotor-stator mixer in the second rotor-stator mixer is mixed with further emulsifying medium may be equal to, higher than or lower than the temperature in the first rotor-stator mixer. Preferably, it is below the temperature in the first rotor-stator mixer. In particular, it has proven useful if the mixing temperature in the first of the series-connected rotor-stator mixer at least 20 K, preferably at least 30 K, z. B. 20 to 200 K, in particular 30 to 120 K above the temperature in the last of the serially interconnected rotor-stator mixer. In particular, the temperature in the last of the serially interconnected rotor-stator mixer is at least 5 K, in particular at least 10 K, z. B. 5 to 200 K, in particular 10 to 150 K below the melting or softening temperature of the thermoplastic polymer. In a preferred embodiment of the invention, the aliphatic polycarbonate and the aqueous emulsifying medium containing the at least one surface-active substance are simultaneously, preferably continuously and in particular at a constant volume rate, the rotor-stator mixer or the rotor-stator mixers feed and remove the dispersion to the same extent.

However, it is also possible, in an upstream step, to prepare the aliphatic polycarbonate with the aqueous emulsifying medium which contains the polyvinyl alcohol and optionally further surface-active substance (s) to obtain a primary emulsion at a temperature above the melting or softening temperature of the aliphatic polycarbonate mix and feed this mixture to the rotor-stator mixer. This upstream step is preferably carried out in a kneader or extruder. The pre-emulsion thus obtained is then fed to the rotor-stator mixer (s). Preferably, the preemulsion is maintained at a temperature above the melting or softening temperature of the polymer. The initially obtained aqueous emulsion of the aliphatic polycarbonate in the aqueous emulsifying medium which is obtained in the mixing device is then subsequently quenched, ie quenched after leaving the mixing device, ie rapidly cooled to a temperature below the softening temperature of the aliphatic polycarbonate to agglomerate to avoid the polymer particles in the emulsion. The quenching can be carried out in a conventional manner, for example by suitable cooling devices and / or by dilution with cooled dispersant. In the case of a mixing device which has a plurality of rotor-stator mixers connected in series, the quenching can also take place in the second and optionally further rotor-stator mixers.

The polymer dispersions obtainable by the process according to the invention and the polymer dispersions according to the invention are suitable for a large number of applications which are usually suitable for aqueous polymer dispersions. The polymer dispersions obtainable by the process according to the invention and the aqueous dispersions of aliphatic polycarbonates according to the invention, in particular those in which the polycarbonate is a polypropylene carbonate, are particularly suitable for those applications in which a biodegradability of the polymer constituent is desirable. In particular, the aqueous dispersions are suitable as a binder component in aqueous binder compositions, in particular for binder compositions for papermaking, eg. Example, as a sizing agent for paper, as engine size or as a means for Oberflächenlei- mung, as a means for solidification of paper, as a binder for Papierstreicherei, and as a binder in non-pigmented coating compositions, for the production of barrier coatings on paper, cardboard or cardboard Binders for pigment-containing coating compositions, such as paints for interior and exterior applications, and also in binder compositions for fiber bonding and for the production of nonwovens. In addition, the aqueous dispersions are suitable in adhesives, for example as laminating adhesives, especially as laminating adhesives for laminating plastic films to laminar supports such as paper, cardboard, cardboard or plastic films, or for the formulation of active compounds, for example for the formulation of active compounds in the agrochemical sector or in the United States Pharmacy. The polymer dispersions according to the invention can also be used for the production of film materials. The polymer dispersions of the invention are particularly suitable for the production of pigment-containing paper coating slips, in particular as binders in paper coating slips.

An object of the invention is therefore also a paper coating slip comprising (i) at least one inorganic pigment and

(ii) at least one aqueous polymer dispersion according to the invention; and optionally one or more additives customary in paper coating slips.

Such paper coating slips are characterized in that they

 at least one aliphatic polycarbonate polymer;

 at least one partially or fully saponified polyvinyl alcohol;

 at least one pigment and

 Contain water,

wherein the weight ratio of aliphatic polycarbonate polymer to partially or fully saponified polyvinyl alcohol in the range of 1: 1 to 20: 1, in particular in the range of 1, 2: 1 to 10: 1.

The terms paper coating slip and paper coating color are used synonymously below. Paper coating slips are usually water-based liquid compositions and in addition to one or more pigments and at least one water-insoluble binder, usually an aqueous polymer dispersion, generally auxiliaries, for. As plasticizers, means for adjusting the required rheological properties and water retention, z. Thickeners, further optical brighteners, dispersants, surfactants, lubricants (for example calcium stearate and waxes), neutralizing agents for pH adjustment (eg NaOH or ammonium hydroxide), defoamers, deaerating agents, preservatives (eg. Biocides), flow control agents, dyes (especially soluble dyes), etc.

The pigments and the binder are usually dispersed in water. The paper coating slip generally contains one or more pigments in an amount of preferably at least 80% by weight, eg. B. 80 to 95 wt.%, Based on the total solids content. Particularly suitable are white pigments. Suitable white pigments are, for example, metal salt pigments such. Calcium sulfate, calcium aluminate sulfate, barium sulfate, magnesium carbonate and calcium carbonate, and mixtures thereof. In particular, the pigment comprises at least one carbonate pigment, in particular calcium carbonate. The calcium carbonate may be ground calcium carbonate (GCC), precipitated calcium carbonate (PCC), lime or chalk. Suitable calcium carbonate pigments are e.g. Available as Covercarb® 60, Hydrocarb® 60 or Hydrocarb® 90 ME. Other suitable white pigments are z. As silicic acids, aluminum oxides, aluminum hydrate, silicates, titanium dioxide, zinc oxide, kaolin, clay, talc or silica. Suitable further pigments are, for. Available as Capim® MP 50 (Clay), Hy- dragloss® 90 (Clay) or Talcum C10. The paper coating slip according to the invention contains at least one binder which comprises at least one polymer dispersion obtainable according to the invention or the combination of aliphatic polycarbonate polymers contained therein and partially or fully saponified Includes polyvinyl alcohol. The polymer dispersion prepared according to the invention or the combination of aliphatic polycarbonate polymer and partially or completely saponified polyvinyl alcohol contained therein can be used in the paper coating slip as the sole binder or in combination with one or more further binders. The most important tasks of binders in paper coating slips are to join the pigments to the paper and the pigments and to partially fill voids between pigment particles. For example, from 1 to 50 parts by weight, preferably from 1 to 25 parts by weight or from 5 to 15 parts by weight of an organic binder (solid, ie without water or other at 21 ° C.) are used per 100 parts by weight of pigments. 1 bar liquid solvent) and preferably 1 to 50 parts by weight, preferably 1 to 25 parts by weight or 5 to 15 parts by weight of the combination of aliphatic polycarbonate polymer and partially or fully saponified polyvinyl alcohol, based on 100 wt. Parts of pigment. In addition to the combination of aliphatic polycarbonate polymers and partially or completely saponified polyvinyl alcohol contained in the polymer dispersions according to the invention, the paper coating slips according to the invention may also contain other conventional binders. Further suitable binders are synthetic binders, in particular emulsion polymers preparable by emulsion polymerization, such as, for example, styrene-butadiene polymer dispersions (SB dispersions). Suitable binders are natural-based binders, in particular starch-based binders. By starch-based binders is meant in this context any native, modified or degraded starch. Native starches may consist of amylose, amylopectin or mixtures thereof. Modified starches may be oxidized starch, starch esters or starch ethers. Hydrolysis can reduce the molecular weight of the starch (degraded starch). The degradation products are oligosaccharides or dextrins into consideration. Preferred starches are corn, corn and potato starch. Particularly preferred are corn and maize starch, very particularly preferably corn starch.

Preferably, polymer dispersions prepared according to the invention are present as the sole synthetic binder or make up at least 80% by weight, based on the total mass of the synthetic binders. Suitable thickeners besides synthetic polymers (for example crosslinked polyacrylate), in particular celluloses, are preferably carboxymethylcellulose. Optical brighteners are z. As fluorescent or Phosphoreszensfarbstoffe, in particular stilbenes. It is preferably an aqueous paper coating slip; it contains water in particular already by the preparation form of the ingredients (aqueous polymer dispersions, aqueous pigment slurries). The desired solids content can be adjusted by adding more water. Typical solids contents of the paper coating slips are in the range of 30 to 75 wt .-%. The pH of the paper coating slip will preferably be from 6 to 10, in particular from 7 to 9.5.

One embodiment of the invention relates to a paper coating slip, wherein the polymers of the aqueous polymer dispersion prepared according to the invention, i. H. the combination of aliphatic polycarbonate polymer and polyvinyl alcohol, in an amount of 1 to 50 wt .-%, in particular from 5 to 40 wt .-% and especially in the range of 15 to 30 wt .-%, based on the total amount (100 wt .-%) of pigments, and wherein the pigments are preferably present in an amount of 80 to 95 wt .-%, based on the total solids content, and are preferably selected from the group consisting of calcium sulfate, calcium aluminate sulfate , Barium sulfate, magnesium carbonate, calcium carbonate, silicic acids, aluminum oxides, aluminum hydrate, silicates, titanium dioxide, zinc oxide, kaolin, alumina, talc and silicon dioxide and wherein the paper coating composition additionally contains at least one adjuvant which is selected from thickeners, further polymeric binders, Binders, optical brighteners, fillers, leveling agents, dispersants, surfactants, lubricants, neutralizing agents, defoamers, deaerating agents tents, preservatives and dyes.

The invention also relates to a paper or board coated with a paper coating slip according to the invention and to a method for painting paper or cardboard, wherein

an aqueous polymer dispersion is prepared or made available according to the invention; and

 with this polymer dispersion, at least one of the above-mentioned pigments, optionally with the addition of the optional further auxiliaries, a paper coating slip is produced;

- And the paper coating is applied to at least one surface of paper or cardboard.

The paper coating slip is preferably applied to uncoated base papers or uncoated cardboard. The amount is generally from 1 to 50 g, preferably from 5 to 30 g of solid (solid, that is to say without water or other solvents which are liquid at 21 ° C., 1 bar) per square meter.

The coating can be done by conventional application methods, for. Example by means of size press, film press, Bladecoater, air brush, squeegee, curtain coating (curtain coating) or spray coater. Depending on the pigment system, the aqueous dispersions can be used in paper coating slips for the base coat and / or for the top coat. Inventive paper coating slips have good performance properties. They have a good running behavior in paper coating processes and a high binding power. The coated papers and cartons have a good surface strength, in particular a very high wet and dry pick resistance. They are readily printable in the usual printing processes, such as high-pressure, intaglio, offset printing, digital printing, inkjet printing, flexographic printing, newspaper printing, letterpress printing, sublimation printing, laser printing, electrophotographic printing or a combination of these printing methods.

The following examples serve to illustrate the invention. Analysis: The particle size distribution was determined on a 1 wt .-% dilution of the dispersion by light scattering at 25 ° C.

The determination of the Brookfield viscosity of the dispersions was carried out at 30 ° C. according to EN ISO 2555 (1999) using a Physika MCR Couette geometry CC 27 rotational viscometer at shear rates of 100 sec ^-1 , unless stated otherwise.

feedstocks

For the following experiments, a polypropylene carbonate (hereinafter PPC) having a number average molecular weight of 140,000 daltons and a weight average molecular weight of 800,000 daltons was used (M _w / M _n = 5.7).

As Comparative Example 2, the copolyester used was a polybutylene terephthalate adipate prepared as follows: 538.3 g of terephthalic acid (27 mol%), 1280.2 g of adipic acid (73 mol%), 1405.9 g of 1,4-butanediol (130 Mole%) and 37 g of glycerol (1.5% by weight, based on the polymer) were mixed together with 1 g of tetrabutyl orthotitanate (TBOT), the molar ratio of alcohol component to acid component being 1.30. The reaction mixture was heated to a temperature of 210 ° C and at this temperature, the resulting water was distilled off over a period of 2 h. Subsequently, the temperature was raised to 240 ° C and gradually evacuated. Excess 1, 4-butanediol was distilled off in vacuo (<1 mbar) over a period of 2 h. The number average molecular weight of the resulting copolyester was 22600 g / mol, the weight average molecular weight at 76300 g / mol. The viscosity number VZ was 130. The melting temperature was 64 ° C. The zero shear viscosity ηο at 180 ° C was 164 Pas. The acid number was less than 1 mg KOH / g. The standard XSB binder used was the styrene-butadiene polymer dispersion Styronal® D818 from BASF SE.

Polyvinyl alcohol 1: degree of saponification 87-89%, viscosity (4% strength aqueous solution, 20 ° C.): 80-1 10 mPas (Poval 235 from Kuraray);

 Polyvinyl alcohol 2: degree of saponification 87-89%, viscosity (4% strength aqueous solution, 20 ° C.): 40-48 mPa.s (Poval 224E from Kuraray)

 Anionic surfactant 1: sodium salt of a sulfuric monoester of an ethoxylated alkanol (Emulphor FAS 30 from BASF SE)

Anionic surfactant 2: Aqueous 28% strength by weight solution of ethoxylated sodium dodecyl sulfate, Na salt (Hansanol® NS 243 from HANSA Group AG)

Production Examples Polycarbonate Dispersion 1:

As a rotor-stator mixer, a 3-stage in-line dispersing device was used, which had three rotor-stator mixing units arranged sequentially on a common rotor, the apparatus having helical elements in the first and third stages and in the second and third stages was provided with dental wrench-like shear elements.

Polypropylene carbonate was continuously drawn through the hopper in an amount of 0.85 kg / h into the single-screw extruder (Tech-Line E 16 T from Dr. Colin GmbH) and melted there at 180 ° C. The polymer melt was fed to the first stage of the dispersing apparatus (6000 rpm). The shear rate was 18850 1 / s and the polymer viscosity 35 Pa-s. At the same time, a 7% by weight aqueous solution of a partially saponified polyvinyl alcohol 1 containing 1% by weight of an anionic surfactant was fed into the three stages of the in-line dispersing apparatus such that solid contents of 34% by weight were obtained in the first and second stages .-% and 29 wt .-% resulted. In the third stage, the solids content was adjusted to 27% by weight. The temperature in each of the first and second stages was 180 ° C and in the third stage 160 ° C. The total residence time was 21 s. After leaving the third stage, the dispersion was quenched by means of a cooling bath to 50 ° C.

The dispersion obtained had a particle size distribution with a particle diameter dgo = 21 μηη. The pH of the dispersion was 4.83 and the viscosity (at 30 ° C, 100 1 / s) was 1.2 Pa s.

Polycarbonate dispersion 2: As a rotor-stator mixer, a 3-stage in-line dispersing device was used, which had three rotor-stator mixing units arranged sequentially on a common rotor, the apparatus having helical elements in the first and third stages and in the second and third stages was equipped with toothed ring-like shear elements.

Polypropylene carbonate was continuously drawn through the hopper in an amount of 0.85 kg / h in the single-screw extruder (Tech -ine E 16 T from Dr. Colin GmbH) and melted there at 180 ° C. The polymer melt was fed to the first stage of the dispersing apparatus (6000 rpm). The shear rate was 18850 1 / s and the polymer viscosity 35 Pa-s. At the same time, a 7% by weight aqueous solution of the partially saponified polyvinyl alcohol 2 containing 1% by weight of an anionic surfactant was fed to the three stages of the in-line dispersing apparatus so that solid contents of 23% by weight were obtained in the first and second stages .-% and 19 wt .-% resulted. In the third stage, the solids content was adjusted to 17% by weight. The temperature in each of the first and second stages was 180 ° C and in the third stage 160 ° C. The total residence time was 32 s. After leaving the third stage, the dispersion was quenched by means of a cooling bath to 50 ° C. The dispersion obtained had a particle size distribution with a particle diameter dgo = 7.5 μm. The pH of the dispersion was 4.85 and the viscosity (at 30 ° C, 100 1 / s) was 0.3 Pa-s.

Polycarbonate Dispersion 3: (Comparative Example 1)

To 100 parts by weight of a 10% strength by weight solution of PPC in ethyl acetate was added 0.32 g emulsifier solution 2 (corresponds to 0.9% by weight emulsifier, based on PPC). To this was added at 20 ° C 66 parts by weight of water and dispersed with the aid of an Ultraturrax at 24000 rpm ¹ until a stable emulsion was obtained (about 55 sec). Then the organic solvent and a subset of the water were removed at 35 ° C in vacuo. In this way, an aqueous dispersion of PPC having a polymer content of 22.2 wt .-% was obtained. The dispersion had a bimodal particle size distribution. About 78% by volume of the particles had a particle diameter dgo of 126 nm and about 22% by volume a particle diameter dgo of 599 nm, each determined by means of light scattering.

Polyester dispersion: (Comparative Example 2)

As a rotor-stator mixer was a 3-stage inline dispersing device, which had three sequentially arranged on a common rotor rotor-stator mixing units, wherein the device in the first and third stages with helical elements and in the second and third stages with Zahnkranzartigen shear elements was provided.

Polybutylene terephthalate adipate was continuously fed via the feed hopper in an amount of 1.47 kg / h into the single-screw extruder (Tech-Line E 16 T from Dr. Colin GmbH) and melted there at 157 ° C. The polymer melt was fed to the first stage of the disperser (6000 rpm). The shear rate was 18850 1 / s and the polymer viscosity was 22 Pas. Simultaneously, a 7 wt.% Aqueous solution of a partially saponified polyvinyl alcohol (Kuraray Poval 224E) was fed to the first two stages of the in-line disperser such that in the first and second stages in the second stage solid contents of 56 wt .-% and 47 wt .-% resulted. In the third stage, deionized water was fed and thus the solids content adjusted to 43 wt .-%. The temperature in each of the first and second stages was 157 ° C and in the third stage was 120 ° C. The total residence time was 32 s. After leaving the third stage, the dispersion was quenched by means of a cooling bath to 30 ° C.

The dispersion obtained had a particle size distribution with a particle diameter dgo = 3.18 μm. The pH of the dispersion was 4.86 and the viscosity (at 30 ° C, 100 1 / s) was 0.3 Pas.

Production of paper coating slips and papers (general requirement)

The coating composition is prepared in a stirring unit into which the individual components are fed in succession. The pigments are added in predispersed form (slurry). The other components are added after the pigments, with the order of the order in the given coating color recipe. The final solids content is adjusted by the addition of water.

Coating color recipe (parts by weight solid)

100 parts of finely divided calcium carbonate (Hydrocarb 60, Omya)

7 parts of coating color binders (polymer dispersions according to the invention)

0.37 parts thickener (Sterocoll® FS)

The solids content is 64% by weight. The pH is adjusted to about pH 9 with dilute sodium hydroxide solution.

The coating color was applied by means of a laboratory coater on one side to a base paper and dried by means of IR emitters. The weight of the applied coating layer was about 10 g / m ² . The coated paper was tested for surface strength using test methods known to those skilled in the art. The following test methods were used:

IGT dry picking strength (dry picking strength with the IGT test printing device - IGT dry)

 Strips were cut from the papers to be tested and printed with the IGT test printing device. The printing inks used are special test inks from Lorillieux, which transfer different tensile forces. The test strips are fed through the printing unit at a continuously increasing speed (maximum speed 200 cm / s). During the evaluation, the location on the sample print strip is determined at which 10 out breaks from the paper surface (picking points) have taken place after the start of printing. As a measure of the dry picking strength, the speed in cm / sec that was present at this place when printing and the test color used. The higher the speed of printing on the tenth picking point, the better the quality of a paper surface.

IGT wet picking strength (wet picking strength with the IGT proofing machine - IGT wet) Strips were cut from the papers to be tested and printed with the IGT proofing machine. The printing device has been set up so that the test strips are moistened with water before printing. As printing inks special test inks from the company Lorilleux are used which transmit different tensile forces. The pressure is carried out at a constant speed of 0.6 cm / s. Tears from the paper surface are visible as unprinted areas. To determine the wet pick resistance, the color density is determined with a color densitometer in comparison to the full color tone in%. The higher the specified color density, the better the wet pick resistance.

Offset test

 From the papers to be tested, samples having a size of 240 x 46 mm are cut out in the longitudinal direction. An appropriate amount of the ink is added to the inking roller and allowed to run for 1 minute. Then a pressure washer is used and colored for 30 s. The printing speed is 1 m / s. A strip of paper is returned to a print sample carrier with the printed paper strip in the starting position. After a specified period of time, the printing process is restarted without replacing the pressure disk. This process is repeated several times. After each print, the plucking on the printed side of the paper strip is visually inspected. In the table, the number of passes is indicated until the first time a plucking occurred. The higher the number of passes to the occurrence of the plucking, the better the suitability of the papers for offset printing.

The measurement results are summarized in Table 1. For comparison purposes, a coating color was prepared according to the above formulation with a conventional binder based on a styrene-butadiene dispersion (XSB binder).

Table 1: Measurement results for IGT dry and wet pick resistance and offset test

(IGT values normalized to standard = 100)

 As can be clearly seen, the values of the two PPC dispersions 1 and 2 according to the invention far outperform the conventional PPC dispersion 3 and also the polyester dispersion and the dispersion 2 even surpasses the standard XSB binder in IGT dry and offset -Test.

Claims

claims: Aqueous polymer dispersion containing  i) from 5 to 50% by weight, based on the total weight of the dispersion, of at least one aliphatic polycarbonate polymer,  ii) from 1 to 20% by weight, based on the total weight of the dispersion, of at least one partially or fully saponified polyvinyl alcohol; and  iii) water  wherein the weight ratio of aliphatic polycarbonate polymer to partially or fully saponified polyvinyl alcohol is in the range of 1: 1 to 20: 1. An aqueous polymer dispersion according to claim 1, wherein at least 90% of the repeating units of the aliphatic polycarbonate polymer are C ₂ -C ₄ -alkylene carbonate groups. An aqueous polymer dispersion according to claim 1 or 2, wherein the aliphatic polycarbonate polymer is a polypropylene carbonate. An aqueous polymer dispersion according to any one of the preceding claims, wherein the aliphatic polycarbonate polymer has a number average molecular weight in the range of 50,000 to 250,000 daltons. An aqueous polymer dispersion according to any one of the preceding claims, wherein the polyvinyl alcohol is a partially saponified or fully saponified polyvinyl alcohol having a degree of saponification of at least 80%. An aqueous polymer dispersion according to any one of the preceding claims additionally containing at least one anionic surfactant. An aqueous polymer dispersion according to claim 6, comprising the at least one anionic surfactant in a concentration of 0.1 to 5 wt .-%, based on the total weight of the dispersion. Aqueous polymer dispersion according to any one of the preceding claims having a viscosity according to Brookfield (20 ° C) of not more than 2000 mPa-s. Process for preparing an aqueous polymer dispersion according to one of the preceding claims, characterized in that the aliphatic polycarbonate is emulsified in water at a temperature above the melting or softening temperature of the aliphatic polycarbonate in the presence of the polyvinyl alcohol. 10. The method of claim 9, wherein the aliphatic polycarbonate emulsified at a temperature above the melting or softening temperature of the aliphatic polycarbonate in an aqueous 1 to 25 wt .-% solution of Polyvi- nylalkohols in a rotor-stator mixer, and the resulting aqueous emulsion of the aliphatic polycarbonate quenched. 1 1. A method according to claim 9 or 10, characterized in that the rotor-stator mixer is a Zahnkranzdispergiermaschine. 12. Use of an aqueous polymer dispersion according to one of claims 1 to 8 as a binder in coating compositions, as sizing agents for paper, as paper strengthening agents, as binder compositions for nonwovens, in adhesives, or for the formulation of active ingredients. 13. Use of an aqueous polymer dispersion according to any one of claims 1 to 8 as a binder in pigment-containing paper coating slips. 14. paper coating slip comprising an aqueous polymer dispersion according to any one of claims 1 to 8 and at least one pigment. 15. Paper coating slip containing  at least one aliphatic polycarbonate polymer;  at least one partially or fully saponified polyvinyl alcohol;  at least one pigment and  - Water,  wherein the weight ratio of aliphatic polycarbonate polymer to partially or fully saponified polyvinyl alcohol is in the range of 1: 1 to 20: 1. 16. Paper coating composition according to claim 14 or 15, which has at least one of the following features a) - g):  a) the aliphatic polycarbonate polymer is a polypropylene carbonate;  b) the aliphatic polycarbonate polymer has a number average molecular weight in the range of 50,000 to 250,000 daltons;  c) the polyvinyl alcohol is a partially or totally saponified polyvinyl alcohol having a saponification degree of at least 80%;  d) the paper coating color additionally contains at least one anionic surfactant; e) the paper coating color contains 1 to 50 parts by weight of the combination of aliphatic polycarbonate polymer and polyvinyl alcohol based on 100 parts by weight of pigment;  f) the pigment content is in the range of 80 to 95 wt .-%, based on the Total solids content of the paper coating color,  g) the pigment comprises at least one carbonate pigment.