EP1346349A1

EP1346349A1 - Use of poly(meth)acrylate units containing sulphonate groups in binding agents for magnetic storage media

Info

Publication number: EP1346349A1
Application number: EP01989606A
Authority: EP
Inventors: Ulrike Hees; Hans-Guenter Bohrmann; Benedikt Raether; Ria Kress; Albert Kohl; Lothar Schulz
Original assignee: Emtec Magnetics GmbH
Current assignee: Emtec Magnetics GmbH
Priority date: 2000-12-22
Filing date: 2001-12-19
Publication date: 2003-09-24
Also published as: KR20020081340A; WO2002052549A1; US20040030047A1; DE10064299A1; CN1419689A; JP2004517171A

Abstract

The invention relates to a polyurethane comprising at least one anionic active group L. The anionic active group L is bound to a segment G in the polyurethane, said segment containing monomers that have been linked by radical polymerisation. The invention also relates to a binding agent composition containing an inventive polyurethane, to a method for the production thereof and to the use of polyurethanes of this type for producing magnetic recording media.

Description

Use of poly (meth) acrylate units with sulfonate groups in binders for magnetic storage media

The invention relates to an anchor group-containing polyurethane, a process for its production, its use and binder compositions and moldings produced therefrom. A binder composition according to the invention contains at least one polyurethane according to the invention which has at least one anionic anchor group L, the anchor group L being bonded to a segment G which contains monomers linked by free-radical polymerization in the polyurethane. In particular, the invention relates to the use of binder compositions containing such polyurethanes or moldings produced from such binder compositions for the production of magnetic recording media.

Magnetic recording media occupy a large space in the context of the permanent storage of information. Typically, a magnetic recording medium consists of a non-magnetic carrier material and at least one magnetizable layer based thereon, based on polymeric binders and magnetic pigments dispersed therein. Due to the ever increasing storage requirement for information and the associated increase in the information density on a specific storage medium, magnetic recording media are subject to ever increasing demands with regard to the quality of the recording and the reproduction as well as the aging resistance. In order to meet these requirements, the polymeric binder in which the magnetic pigments are dispersed is becoming increasingly important. The aim is to improve the stability of the magnetic dispersion, to avoid the occurrence of errors on the magnetic layer and to improve the magnetic properties, in particular the remanence, an increased packing density of the magnetic pigments in the magnetic layer, for example by A reduction in the proportion of binder combined with an increase in the proportion of pigment in this layer can be achieved.

However, the measures mentioned complicate both the division of the pigments in the dispersion process and the achievement of good dispersion stability. In addition, the magnetic layers have to be very flexible, have a high elasticity and have a high tensile strength. In addition, a reduction in the friction values and an increase in the abrasion and wear resistance of the magnetic layer are increasingly required to avoid level drops. These mechanical properties must also be guaranteed at high temperatures and high air humidity.

Various groups of substances are known to be suitable as polymers for the production of magnetic recording media. So far, the polyurethanes have proven to be particularly advantageous, which above all significantly improve the elasticity of the magnetic recording media or of coatings of such magnetic recording media. However, the low hardness and abrasion resistance of the polyurethanes have often proven to be disadvantageous.

The use of ionic groups such as metal sulfonate groups, metal salts of phosphonates and phosphate salts of amines improves the dispersing properties of such binders. Such effects have been described in various patents (US 5,747,630, JP 59-8127, JP 57-3134, JP 58-41564, JP 61-48122). The incorporation of low molecular weight, ionic groups into a slightly polar solvent-containing binder system is only possible to a limited extent because of the low solubility of the ionic groups. As described in DE 34 07 563, the Tegomer DS 3117 (from Th. Goldschmidt AG) is one of the few components that show good solubility in organic solvents. This sulfonate group-containing diol contains a long polyethylene glycol segment in the side chain, which increases the hydrophilicity of the binders synthesized therefrom and can lead to negative effects in the tape.

US 4,477,531 describes a magnetic recording medium with a polyurethane binder without reactive groups, made from a polyester, a glycol and a diisocyanate. A polyacrylate is only mentioned as an additional binder, that is, the compound is only mixed into it.

GB 1339930 describes a reaction product of monofunctional poly methacrylates with di-, tri- or tetraisocyanates. In the polymethacrylate segment, no sulfonate-containing groups or other functionalities are described which can lead to branching or a block-wise structure.

The structure of polyisocyanates which contain a block obtained by controlled radical polymerization has been described, for example, in US Pat. No. 3,788,996, US Pat. No. 4,032,689 or US Pat. No. 4,070,388. However, acidic or basic anchor groups are only introduced later here, which complicates the process.

EP-B 0 547 432 relates to magnetic recording media with a binder mixture of a polyurethane urea (meth) acrylate and a polyurethane. However, the (meth) acrylates mentioned here do not have anchor groups, so that additional aids have to be used to produce the magnetic recording media. No. 5,695,884 describes thermoplastic polyurethanes with metal sulfonate groups, the polyurethanes consisting of at least one polyester polyol, a low molecular weight diol and an organic diisocyanate.

EP-B 0 465 070 describes sulfonated and non-sulfonated thiol- and hydroxy-functionalized polyurethanes and graft copolymers produced therefrom, and the use of these polymers for magnetic recording media.

DE-C 28 33 845 relates to magnetic recording media with binders containing a polyester or a polyurethane with a metal sulfonate group content of 10 to 1000 equivalents / 10 ⁶ g of polymer, the polymer described being able to be used in mixtures with thermoplastic or thermosetting resins ,

EP-B 0 463 805 relates to hydroxy-functionalized polyurethanes with sulfonate groups which are modified with dithiocarbamate. Furthermore, EP-B 0 463 805 describes graft copolymers of hydroxy-functionalized polyurethanes having sulfonate groups with vinyl polymers and the use of the copolymers as magnetic recording media.

Polyurethanes with anchor groups are also described in DE-A 199 45 400.0, which relates to a thermoplastic block copolymer with at least one soft segment A and at least one hard segment B, the hard segment B having at least one anionic and / or at least one cationic anchor group L. In addition, DE-A 100 05 647.4 describes a binder composition, at least containing a polyurethane with a structural unit according to general formula I.

wherein n for a number from 1 to 10, the radicals R ¹ each independently of one another for a polyurethane with a molecular weight of at least about 1000, R ⁴ - Q-, R ⁴ -Q- (XO-) _m XQ- or R ⁴ - QYQ-, where Q is O, NH, NR ² or S, R ^{4 is} a linear or branched, saturated or unsaturated alkyl radical having 2 to 44 carbon atoms, X is an optionally aromatically substituted alkyl radical having 2 to 14 carbon atoms , Y stands for a polymer obtainable by polymerization, polyaddition or polycondensation with a molecular weight M _w of 150 to 5000 and m for a value of 1 to 300, the radicals R ² each independently of one another are H or a linear or branched, saturated or unsaturated aliphatic hydrocarbon radical with 1 to about 20 C atoms, a saturated or unsaturated, optionally substituted cycloaliphatic hydrocarbon radical with 4 to about 20 C atoms, an optionally substituted araliphatic A hydrocarbon radical with 6 to about 20 carbon atoms or an optionally substituted aromatic hydrocarbon radical with 6 to 18 carbon atoms, the radicals R ³ for a linear or branched, saturated or unsaturated alkyl radical with 2 carbon atoms or a saturated or unsaturated cycloalkyl radical with 4 to 44 carbon atoms, Z represents a linear or branched, saturated or unsaturated optionally substituted alkyl radical with 8 to 44 carbon atoms, an optionally substituted cycloalkyl radical with 4 to 44 carbon atoms, an optionally substituted araliphatic hydrocarbon radical with 6 up to 40 carbon atoms or a polymer with a molecular weight obtainable by polymerization, polyaddition or polycondensation M _w from 150 to 5000, where Z is connected to the entire molecule via suitable functional groups, or a partial or full salt thereof, and at least one magnetic or magnetizable pigment is known

Furthermore, DE-A 100 05 649.0 relates to a binder composition containing a polyurethane with a structural unit according to general formula I.

wherein R ^{1 is} H or a linear or branched, saturated or unsaturated aliphatic hydrocarbon radical having 1 to 20 C atoms, a saturated or unsaturated, optionally substituted cycloaliphatic hydrocarbon radical having 4 to 20 C atoms or an optionally substituted araliphatic hydrocarbon radical having 6 to 40 C atoms, R ^{2 represents} a linear or branched, saturated or unsaturated aliphatic hydrocarbon radical having 1 to 20 C atoms or a cycloaliphatic hydrocarbon radical having 4 to 20 C atoms or an optionally substituted aromatic hydrocarbon having 6 to 18 C atoms , X ¹ and X ² each independently represent an optionally substituted radical comprising at least two C atoms, at least one of the radicals X ¹ and X ² by reaction of an OH, NH ₎ , NHR ³ or SH group, wherein R ³ for a linear or branched, saturated or he is unsaturated, optionally aromatically substituted alkyl radical having 1 to 44 carbon atoms, into which polyurethane is incorporated, or a salt thereof, and at least one magnetic or magnetizable pigment. DE-A 100 50 710.7 relates to an anchor group-containing polyurethane, the anchor group being covalently bonded to a nitrogen atom-containing polyether segment in the polyurethane, a process for its production, its use and binders and moldings produced therefrom.

In the synthesis of abrasion-resistant polyurethanes, it is advantageous to incorporate polar functional groups in the polymer in a defined manner without being restricted to polar solvents such as water, for example when using low molecular weight diols with polar groups.

The present invention was therefore based on the object of providing a new polymer in which functionalized blocks can be incorporated into the polyurethane in various organic solvents.

The invention therefore relates to a polyurethane having at least one anionic anchor group L, the anchor group L being bonded to a segment G in the polyurethane which contains monomers linked by free-radical polymerization.

In the context of the invention, a “segment G which contains monomers linked by free-radical polymerization” is understood to mean a segment which comprises at least two monomer units, it being possible for these monomer units to be identical or different. Such a segment is built up from unsaturated monomers via controlled radical polymerization. In the context of the invention, segment G also has at least two further functional groups, in particular hydroxyl or thiol groups, amines or other groups which are reactive toward NCO groups and which can be the same or different and via which it is also incorporated into a polyurethane can be. In the context of the present invention, a binder composition is understood to mean a mixture of preferably two or more polymers which, after chemical or physical drying, are substantially involved in obtaining stable dispersions and in sufficient mechanical stability of a magnetic recording medium produced from the binder composition. According to the invention, however, a binder composition can also contain only one polymer and further additives.

In the context of the present invention, a binder is understood to mean a polymer or a mixture of two or more polymers.

In the context of the present invention, a thermoplastic block copolyurethane is understood to mean a polyurethane which has a block-like structure, for example A-B-A, these individual blocks being present in a micro-phase-separated manner. At a certain temperature or within a certain temperature range, the thermoplastic block copolyurethane has a softening point or a softening range. Above this softening point or range, the polyurethane is plastically deformable, and when it returns to temperatures below this softening point or range it retains the shape produced in the plastic state and behaves essentially like a duromer.

In the context of the present invention, a hard segment A is understood to mean a segment of a polyurethane molecule, preferably a thermoplastic polyurethane molecule, the hard segment having a glass transition temperature above at least about 20 to 40 ° C., preferably at least about 50 ° C. In the context of the present invention, a soft segment B is understood to mean a segment of a polyurethane molecule which is covalently connected to a hard segment and has a glass transition temperature of less than about 40 ° C.

An anchor group L is understood in the context of the present invention to be an anionic group which is capable of interactions with ionic or at least polar compounds. Anchor groups are understood in particular to mean functional groups which are able to interact with the surface of inorganic filler materials, in particular with the surface of inorganic magnetic or magnetizable pigments.

The polyurethanes according to the invention have at least one anionic anchor group L, the anchor group L being bonded to a segment G which contains monomers linked by free-radical polymerization in the polyurethane. In the context of the invention, a polyurethane is understood to be a mixture of individual polyurethane molecules. According to the invention, at least one molecule of the multiplicity of the molecules constituting the polyurethane has at least one anionic anchor group L, the anchor group L being bonded to a segment G which contains monomers linked by free-radical polymerization in the polyurethane. However, it is equally possible according to the invention that each of the molecules constituting the polyurethane has at least one anionic anchor group L.

A polyurethane according to the invention can have a statistical structure, ie it does not have to be a polyurethane built up in blocks. However, it is also provided in the context of the present invention that a polyurethane according to the invention has segments of different hardness exhibits, in particular at least one soft segment and at least one hard segment.

In the context of a preferred embodiment of the present invention, a polyurethane according to the invention has thermoplastic properties. In a further preferred embodiment of the present invention, the polyurethane according to the invention is a block copolyurethane.

According to the invention, the segment G with at least one anionic anchor group L can be built into the hard segment or the soft segment in a targeted manner. According to the invention, however, the number of anchor groups that are located in a hard segment A of the thermoplastic polyurethane is greater than the number of anchor groups that are located in a soft segment B or several soft segments B. In a preferred embodiment of the invention, the number of anchor groups that are in the total number of hard segments A in the polyurethane is at least five times, preferably at least 10 times as large as the total number of anchor groups in the soft segments B. In another In a preferred embodiment of the invention, the thermoplastic polyurethane according to the invention has essentially no anchor groups in the at least one soft segment B.

In a preferred embodiment of the compound, the polyurethane according to the invention contains, as anchor group L, a sulfonic acid group or a suitable salt of such a group.

Suitable compounds for building up such a segment G with at least one anionic anchor group L are suitable α, β-unsaturated monomers, for example correspondingly functionalized acrylates or methacrylates, acrylic amides or methacrylamides with polar functional groups or polar or non-polar vinyl monomers. Suitable functional groups are, for example, sulfonic acid groups or hydroxyl groups. By copolymerizing a hydroxy-functionalized monomer with a sulfonic acid-carrying monomer, it is possible, for example, to produce blocks which have a sulfonic acid group and can then be converted to polyurethanes via the free OH groups, for example by reaction with corresponding diisocyanates.

Monomers particularly suitable for building up a segment G with at least one anionic anchor group L are, for example, hydroxy (meth) acrylate, hydroxyalkyl (meth) acrylate, for example hydroxyethyl (meth) acrylate or hydroxypropyl (meth) acrylate, acrylamidopropanesulfonic acid (AMPS), methyl ( meth) acrylate and butyl (meth) acrylate. The blocks are preferably produced by controlled free-radical polymerization, for example using thioethanol. The composition of the blocks, which are built up from various copolymerizable monomers, can be estimated in a known manner via the copolymerization parameters.

In a preferred embodiment, the invention relates to a thermoplastic polyurethane with a structure of general form I.

- (A B,) ,, - (I) or, in a further embodiment, a polyurethane with branches of the general form II

- (A (B) _m ) _n - (II), where A is a hard segment and B is a soft segment, k and n are each a number from 1 to 10 and 1 and m are a number from 0 to 10 , where k, 1 and m for each repetition unit regardless of the next Repeat units can be selected and are preferably in at least one repeat unit of the polyurethane m or 1 for a number from 1 to 10. M and 1 preferably stand for a number from 1 to 10. A thermoplastic polyurethane of the general form II can be, for example, a polyurethane with a comb or star structure.

Structures which are possible according to the invention would thus be, for example: -BAB-, -ABBA-, -AAB-, -A (BA-) ₂ .

If the polyurethane according to the invention has soft segments and hard segments, segment G can be arranged in the soft segment or in the hard segment or in both segments.

In a preferred embodiment, the segment G is arranged in the hard segment A, so that the anionic anchor group L is also preferably present in the hard segment A. In particular, the polyurethane according to the invention therefore has the general form Ia

or Ha

- (A (L) _p (B) _m ) _n - (Ha), where A stands for a hard segment, B for a soft segment and L for an anchor group, and k and n each represent a number from 1 to 10, and 1 and m stands for a number from 0 to 10, k, 1 and m being selectable for each repeating unit independently of the next repeating unit, preferably in at least one repeating unit of the polyurethane according to the invention, m or 1 for a number from 1 to 10 and p for a Number greater than zero to 10 stands. M and 1 preferably represent a number from 1 to 10. The compounds mentioned which are suitable for use as hard segments A have at least one functional group X, where X represents a functional group which is reactive towards a functional group Y with the formation of a covalent bond. In a preferred embodiment of the invention, the compounds suitable as hard segments A have at least two functional groups X. In a further preferred embodiment of the invention, the functional groups X are attached at the ends to the compounds suitable for use as hard segment A.

Basically, X stands for a functional group which is capable of reacting preferably with an NCO group to form a covalent bond. In a preferred embodiment of the invention, X is OH, NH ₂ , NHR, NR ₂ , SH or COOH, where R is a linear or branched, saturated or unsaturated alkyl radical having 1 to 24 carbon atoms or an aryl radical having 6 to 24 carbon atoms -Atoms stands.

In a further preferred embodiment of the invention, X represents an OH, SH group or an amine, in particular an OH group. In the further course of the text, suitable connections for the production of hard segments A are described. For the sake of clarity, unless otherwise stated, the compounds are shown as OH-bearing compounds. However, in the context of the present invention it is equally possible to use corresponding compounds which, instead of the OH group shown in the further description, carry another functional group which is preferably reactive toward NCO groups, for example one of the other functional groups mentioned for X, provided that one corresponding connection exists or can be established. Polymers suitable for forming hard segments are, for example, polymers of derivatives of acrylic acid or methacrylic acid, in particular (meth) acrylamides, with polar groups or polar or non-polar vinyl monomers or a combination of two or more thereof or a combination of one or more of these monomers at least one less polar monomer.

Basically, polyester, polyether, polyacetals, polycarbonates, polyester ethers and the like, such as e.g. Polyester polyurethanes.

Polymers suitable for forming soft segments are, for example, predominantly linear polymers with terminal OH groups, preferably those with two or three, in particular with two OH end groups, which are then reacted, for example, with diisocyanates to form soft segment B. For example, polyester polyols are suitable which can be obtained in a simple manner by esterification of linear or branched, saturated or unsaturated aliphatic or correspondingly suitable aromatic dicarboxylic acids having 4 to about 15 C atoms, preferably 4 to about 10 C atoms with glycols, preferably glycols with about Have 2 to about 25 carbon atoms or by polymerizing lactones with about 3 to about 20 carbon atoms. Examples of dicarboxylic acids which can be used are glutaric acid, pimelic acid, suberic acid, sebacic acid, dodecanedioic acid and preferably adipic acid or succinic acid, or mixtures of two or more of the dicarboxylic acids mentioned. Suitable aromatic dicarboxylic acids are terephthalic acid, isophthalic acid, phthalic acid or mixtures of two or more of these dicarboxylic acids. Tricarboxylic acids such as trimellitic acid are also suitable. Mixtures of one or more of the aromatic di- or tricarboxylic acids mentioned with aliphatic or further aromatic dicarboxylic acids, for example with diphenic acid, pentadienoic acid, succinic acid or adipic acid, are also suitable. To prepare the polyester polyols, it may be advantageous to use appropriate acid derivatives such as carboxylic acid anhydrides or carboxylic acid chlorides instead of the dicarboxylic acids, if these are obtainable.

The polyester polyols suitable for use as a soft segment in the context of the present invention can be prepared by reacting dicarboxylic acids with corresponding glycols. Basically suitable glycols for the production of the polyester polyols are linear or branched, saturated or unsaturated, aliphatic or aromatic glycols. For example, these are diethylene glycol, 1,2-ethanediol, 1,3-propanediol, 2-methyl-1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7 -Heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol and the corresponding higher homologs, such as can be formed by gradually extending the carbon chain of the compounds mentioned, and for example 2,2,4-trimethylpentanediol-1 , 5, 2,2-dimethylpropanediol-1,3, 1,4-cyclohexanedimethanol, 1,4-diethanolcyclohexane, 2-methyl-2-butyl-1,3-propanediol, 2,2-dimethyl-1,4-butanediol , Hydroxypivalinsäu- neopentylglycolester, triethylene glycol, methyldiethanolamine or aromatic-aliphatic or aromatic-cycloaliphatic diols with 8 to about 30 carbon atoms, where heterocyclic ring systems or preferably isocyclic ring systems such as naphthalene or especially benzene derivatives such as bisphenol A can be used as aromatic structures symmetrically ethoxylated bisphenol A, double symmetrical I propoxylated bisphenol A, more ethoxylated or propoxylated bisphenol A derivatives or bisphenol F derivatives, the hydrogenation products of the bisphenol A and bisphenol F derivatives mentioned or the products of the corresponding reaction of a compound or a mixture of two or more of the compounds mentioned with an alkylene oxide having two to about 8 carbon atoms or a mixture of two or more such alkylene oxides. In a preferred embodiment of the invention, 1,2-ethanediol, 1,3-propanediol, 2-methyl-1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 2,2-dimethylpropanediol-1 , 3, 1, 4-cyclohexanedimethanol, 1, 4-diethanolcyclohexane and ethoxylated or propoxylated products of 2,2-bis (4-hydroxyphenylene) propane (bisphenol A). Depending on the desired properties of the thermoplastic polyurethanes equipped with the corresponding soft segments, the said polyester polyols can be used alone or as a mixture of two or more of the polyester polyols mentioned in different proportions to produce the thermoplastic polyurethanes. Suitable lactones for the preparation of the Polyesteφolyols are, for example, α, α-dimethyl-γ-propiolactone, ß-butyrolactone and ε-caprolactone.

The polyether polyols are also suitable for use as soft segments B in the production of the above-mentioned thermoplastic polyurethanes. Polyethene polyols are understood to mean essentially linear substances with ether bonds in the sense of the above-mentioned terminal OH groups. Suitable polyethene polyols can be prepared, for example, by polymerizing cyclic ethers such as tetrahydrofuran or by reacting one or more alkylene oxides having 2 to 4 carbon atoms in the alkylene radical with a starter molecule which has two active hydrogen atoms. Examples of suitable alkylene oxides are ethylene oxide, 1,2-propylene oxide, epichlorohydrin, 1,2-butylene oxide or 2,3-butylene oxide or mixtures of two or more thereof.

The alkylene oxides can be used individually, alternately in succession or as mixtures of two or more of the alkylene oxides mentioned. Examples of starter molecules are water, glycols such as ethylene glycol, propylene glycol, 1,4-butanediol, 1,5-pentanediol and 1,6-hexanediol, amines such as ethylenediamine, 1,6-hexamethylenediamine or 4,4'-diaminodiphenylmethane as well as amino alcohols such as methylethanolamine. Basically, however, everyone is Above-mentioned, at least functional compounds, as described for the construction of the soft segments, can be used as starter molecules. Suitable polyester polyols and polyethene polyols and their preparation are mentioned, for example, in EP-B 0 416 386.

In amounts of up to about 5% by weight, based on the total mass of the soft segments contained in the thermoplastic polyurethane, it is also possible, for example, to use aliphatic alcohols with three or more functional groups and 3 to about 15, preferably about 3 to about 10, carbon atoms be used in the manufacture of the soft segments. Correspondingly suitable compounds are, for example, trimethylolpropane, triethylolpropane, glycerol, pentaerythritol, sorbitol, mannitol and other sugar alcohols with up to about 10 OH groups per molecule. The corresponding derivatives of the compounds mentioned can also be used to produce the soft segments, as can be obtained by reaction with an alkylene oxide having 2 to about 4 carbon atoms or a mixture of two or more such alkylene oxides. In a further variant, carboxylic acids or derivatives thereof with three or more functional groups can also be used. The compounds mentioned can each be used alone or as a mixture of two or more of the compounds mentioned.

In a preferred embodiment of the invention, the soft segments B have glass transition temperatures from approximately -50 ° C. to approximately 40 ° C., in particular from -40 ° C. to 20 ° C. In a further particularly preferred embodiment of the invention, the glass transition temperatures of the soft segments B are in a range from approximately -30 ° C. to approximately 0 ° C. In order to ensure the desired mechanical properties of the thermoplastic polyurethane according to the invention, the soft segment B should have a molecular weight of about 500 to about 100,000 g / mol. In a preferred embodiment of the invention, soft segments B are used which have a molecular weight of approximately 1,500 to about 15,000 g / mol, for example about 2000 to about 10,000 g / mol, preferably about 3000 to 8000 g / mol.

Compounds of the abovementioned classes of compounds suitable for use as soft segments B can already be present in a molecular weight range suitable for use as soft segment B. However, it is equally possible to use compounds of the abovementioned classes of compounds for the production of soft segments B which have a molecular weight which is below the molecular weight or the desired molecular weight suitable for use as soft segment B. In this case, it is possible within the scope of the present invention to extend such compounds of the abovementioned classes of compounds by reaction with corresponding functional compounds until the required or desired molecular weight has been reached. Depending on the end group X, dicarboxylic acids, difunctional epoxy compounds or diisocyanates are suitable, for example, diisocyanates being used in a preferred embodiment of the present invention.

To increase the molecular weight mentioned above, those di- or higher-functional compounds are used which lead to a glass transition temperature of the extended soft segment B which is within the desired range. In a preferred embodiment of the invention, compounds for increasing the molecular weight in the production of the soft segments B, such as polyisocyanates, in particular diisocyanates and triisocyanates, in particular, for example, those having 6 to about 30 carbon atoms are therefore used in the case mentioned. The following may be mentioned in detail, for example: linear aliphatic diisocyanates such as 1,4-tetramethylene diisocyanate, 1,5-pentamethylene diisocyanate or 1,6-hexamethylene diisocyanate, aliphatic cyclic diisocyanates such as 1,4-cyclohexylene diisocyanate, dicyclohexylmethane diisocyanate or isophorone diisocyanate (IPDI). Furthermore within the scope of the present Aromatic diisocyanates such as toluene-2,4-diisocyanate (2,4-TDI), toluene-2,6-diisocyanate (2,6-TDI), the mixture of isomers of the latter two diisocyanates, m-tetramethylxylylene diisocyanate (TMXDI ), p-tetramethylxylylene diisocyanate, 1,5-naphthylene diisocyanate, 1,5-tetrahydronaphthylene diisocyanate, 2,2'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate and 4,4'-diphenylmethane diisocyanate (MDI) and mixtures of two or more of the diisocyanates mentioned. The tri-socyanates used can be biurets or allophanates. In a preferred embodiment of the invention, diisocyanates are used which have an aromatic molecular component.

The soft segments B can optionally carry one or more anchor groups L. The production of soft segments B with anchor groups L is carried out according to the usual rules of organic chemistry, for example as described in the further course of the text in the course of the production of the hard segments A carrying anchor groups. In a preferred embodiment of the present invention, however, the thermoplastic polyurethanes carry more anchor groups in the hard segment than in the soft segments. In a preferred embodiment of the invention, the ratio of anchor groups in the hard segments to anchor groups in the soft segments is at least about 5: 1, for example at least about 10: 1. In a further preferred embodiment of the invention, the soft segments B contained in the thermoplastic polyurethane have no anchor groups L.

The segment G with at least one anionic anchor group L and also the hard segment A are preferably produced via controlled free-radical polymerization of suitably functionalized monomers with thioethanol or thioacetic acid. Suitable monomers are, for example, derivatives of acrylic acid and methacrylic acid with polar groups, for example esterification products of acrylic acid and methacrylic acid with an alcohol component with Ci to C ₂₅ - Alkyl radical or alkyl radical substituted with a hetero atom such as O, S or N, or polar vinyl monomers or combinations of two or more of these monomers or combinations of one or more of these monomers with at least one less polar monomer. A hard segment A is produced in such a way that a compound functionalized with an anionic anchor group L is already used when building up the segment G and is therefore already incorporated into the hard segment A during the synthesis of the hard segment A. Suitable monomers for introducing the anchor group L are, for example, 2-acrylamido-2-methylpropanesulfonic acid and preferably its salts, particularly preferably its ammonium salts, or 3-sulfopropyl methacrylate Na salt. Monomers preferred for the preparation of the hard segment A and the segment G are selected from the group consisting of: 2-acrylamido-2-methylpropanesulfonic acid and preferably their salts, particularly preferably their ammonium salts, or 3-sulfopropyl methacrylate sodium salt, acrylamide, acyl nitrile, methacrylamide , Methacrylonitrile, N-vinylformamide, N- vinylpyrrolidone, N-vinylcaprolactam, N-vinylimidazole, methyl methacrylate (MMA), butyl methacrylate (BMA), ethyl acrylate, isopropyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, hydroxypropyl methacrylate, hydroxEMA methyl acrylate, hydroxEMA methyl acrylate, hydroxEMA methyl acrylate, hydroxEMA methyl acrylate, hydroxEMA methyl acrylate, hydroxEMA methyl acrylate, hydroxEMA methyl acrylate, hydroxEMA methacrylate, hydroxEMA , GMA, isobornyl acrylate, 2- (N, N-

Dimethylamino) ethyl methacrylate, vinyl acetate, vinyl propionate, vinyl chloride, styrene, alkylated styrenes, methoxystyrenes.

In a preferred embodiment of the invention, the hard segment A corresponds to the segment G.

The number of anchor groups L per hard segment A can vary within wide limits, with the solubility in common solvents such as THF or dioxane being the limiting factor. If a thermoplastic polyurethane according to the invention has only one hard segment A (represented in the general formula I or Ia, where n and k stand for the number 1 or in general) Formula II or Ha, where n stands for the number 1), the number p in formula la, which indicates the number of anchor groups L in the hard segment A, stands for a number greater than zero to 10. In a preferred embodiment of the invention p for 1. If the thermoplastic polymer has more than one hard segment A, for example represented in the general formula I or la, where n or k stand for a number greater than 1, it is not absolutely necessary in the context of the present invention that each hard segment A in the thermoplastic polymer carries an anchor group L or two or more anchor groups L. It is only necessary that at least one hard segment in the thermoplastic polymer carries an anchor group L. It is also provided in the context of the present invention that two or more hard segments A in a single thermoplastic polymer have a different number of anchor groups. A thermoplastic polyurethane which can be used in the context of the present invention can therefore, provided that it has two or more hard segments A, each have hard segments A without anchor groups L, with one anchor group L or with two or more anchor groups L, at least one of the hard segments A having at least one anchor group L must wear. The formula notation A (L), as it is used for example in formula Ia and formula Ila, is therefore not to be understood as meaning that each hard segment A must have an anchor group L. The only decisive factor is that at least one hard segment in the thermoplastic polyurethane carries at least one anchor group L. That is, based on the totality of the molecules, the number of anchor groups L can also assume a non-integer value less than 1.

The parameter p, as used in formulas Ia and Ila, therefore does not have to stand for an integer, but can assume values that encompass the entire range of numbers within the limits for p.

According to the conditions in polymer synthesis, the parameter n does not necessarily have to stand for an integer either, since usually at Polymer Synthesis Molecules with different molecular weights are formed and so the number n for molecules formed during polymer synthesis can be different. In the present case, the parameter n therefore expresses the average number of repeat units in the totality of the polymer molecules under consideration.

In a preferred embodiment of the invention, a hard segment A contains the anchor groups L already defined.

In a preferred embodiment of the invention, the hard segments A have glass transition temperatures of more than the use temperature of a magnetic storage medium produced from the polyurethanes according to the invention, for example from about 20 ° C. to about 90 ° C. In a further preferred embodiment of the invention, the glass transition temperatures of the hard segments A are in a range from approximately 20 ° C. to approximately 80 ° C., for example in a range from approximately 40 ° C. to approximately 70 ° C. In order to ensure the desired mechanical properties of the thermoplastic polyurethane according to the invention, the hard segments A should have a molecular weight (M _w ) of about 1000 to about 50,000 g / mol. In a preferred embodiment of the invention, hard segments A are used which have a molecular weight of about 1,500 to about 20,000 g / mol, for example about 3,000 to about 10,000 g / mol.

The production of the soft segments B and the hard segments A is carried out according to the usual rules of organic polymer chemistry. If a polyester, a polyether, a polycarbonate, a polyacetal or another compound which can be used as a soft segment is used as the soft segment, its production is carried out according to conventional polymer chemistry methods known to the person skilled in the art. Should various of the above-mentioned soft segments settable compounds are connected to each other due to a too low molecular weight of the individual compounds, this happens, depending on the functional compound used for chain extension, also according to the usual rules known in organic chemistry for the respective functional groups.

The soft segments B are produced in such a way that a soft segment B is formed which has at least two functional groups Y, one group Y being able to react with a reactive group X, preferably an OH group, to form a covalent bond. Suitable groups Y have already been mentioned in the course of this text. In a preferred embodiment of the invention, soft segments B, which carry isocyanate groups as functional groups Y, are used to produce the thermoplastic polyurethanes. The number of functional groups Y per soft segment should be at least about two. However, it is equally possible to use soft segments whose functionality is higher than two, for example about 3. It is also possible to use mixtures of two or more different soft segments B which differ, for example, in their functionality from reactive groups X. It is therefore entirely possible within the scope of the present invention that the soft segments B used have a functionality in relation to hydroxyl groups which is, for example, between 2 and 3, for example about 2.1 to about 2.5.

In a preferred embodiment of the invention, the soft segments B used are polyester polyols, polyethene polyols or polycarbonate polyols which, if appropriate, have been extended with diisocyanates, for example diphenylmethane diisocyanate or tolylene diisocyanate, until a corresponding molecular weight has been reached. In the context of a preferred embodiment, the compounds used as hard segments A in the context of the present invention are prepared in such a way that polymers having at least two reactive groups X, preferably OH groups, can be used as hard segments after the preparation. In a preferred embodiment of the invention, the compounds which can be used as hard segments have at least two OH groups as terminal groups.

In principle, the thermoplastic polyurethanes according to the invention can be produced in two different ways. In both cases, hard segment A is first produced by controlled radical polymerization. Within the scope of the invention, this hard segment block A has functional groups X. In the context of the present invention, a hard segment block A can be implemented with a soft segment block B with the formation of at least one covalent bond. Alternatively, the construction of the soft segment block B can take place directly during the implementation with the hard segment block A. Suitable compounds for reaction with the hard segment block A to build up a soft segment block B are those previously mentioned for building up the soft segment block B of the general form YBY. The structures given represent only a schematic representation of the structure of the compounds to be reacted with one another. The number of functional groups can differ from the structurally represented form in accordance with the above. As already explained above, not all of the compounds used to form hard segments A need to have one or more anchor groups. It is only necessary to add a sufficient number of compounds bearing anchor groups L, so that the thermoplastic polyurethane has at least one hard segment which carries at least one anchor group L. A structure BAB is preferred, the hard segment A carrying at least one anchor group L. The present invention therefore also relates to a method for producing a thermoplastic polyurethane according to the invention. In particular, it is a process for the production in which at least one functional segment A which is at least functional towards Y, in particular NCO groups, and comprises at least one segment G containing a polymer block composed of unsaturated monomers is reacted. In a preferred embodiment, segment G is a polyacrylate or a polymethacrylate block.

The implementation of a hard segment block with functional groups X and a soft segment block B with at least two functional groups Y can be carried out in a manner known per se, preferably at temperatures from approximately 0 to approximately 120 ° C. The ratio of the two components is advantageously chosen so that the ratio of X to Y groups is about 1 to about 2. Following the usual rules of polymer chemistry, the molecular weight of the thermoplastic polyurethanes obtained can be controlled within wide limits by appropriate variations in the ratio mentioned.

If appropriate, other, low molecular weight compounds may also be present as additives during the reaction. Such compounds can act, for example, as chain extenders or stopping reagents. Suitable for this purpose are, for example, primary amino compounds with two to about 20, for example 2 to about 12, carbon atoms. For example, these are ethylamine, n-propylamine, i-propylamine, sec-propylamine, n-butylamine, tert-butylamine, 1-aminoisobutane, substituted amines with two to about 20 carbon atoms, such as 2- (N, N-dimethylamino) ) - 1-Aminoethane, aminomercaptans such as l-amino-2-mercaptoethane, diamines, a-lipatic amino alcohols with 1 to about 20, preferably 1 to about 12, carbon atoms, for example methanolamine, l-amino-3,3-dimethyl pentan-5-ol, 2-aminohexan-2 ', 2 "-diethanolamine, l-amino-2,5-dimethylcyclohexan-4-ol, 2-amino-1-propanol, 2-amino-l-butanol, 3- Amino-l-propanol, l-amino-2- propanol, 2-amino-2-methyl-l-propanol, 5-amino-l-pentanol, 3-aminomethyl-3,5,5-trimethylcyclohexan-l-ol, 1-amino-l-cyclopentane-methanol, 2- Amino-2-ethyl-1,3-propanediol, aromatic-aliphatic or aromatic-cycloaliphatic amino alcohols having 6 to about 20 C atoms, heterocyclic ring systems or preferably isocyclic ring systems such as naphthalene or in particular benzene derivatives such as 2-aminobenzyl alcohol being used as aromatic structures, 3- (hydroxymethyl) aniline, 2-amino-3-phenyl-l-propanol, 2-amino-l-phenylethanol, 2-phenylglycinol or 2-amino-l-phenyl-l, 3-propanediol and mixtures of two or more of such connections.

The reaction can optionally be carried out in the presence of a catalyst. In a preferred embodiment, this is, for example, a tertiary amine such as triethylamine, tributylamine, diazabicyclo (2,2,2) octane, N-methylpyridine or N-methylmoφholin. Other suitable catalysts are organometallic compounds such as dibutyltin dilaurate and metal salts such as tin octoate, lead octoate or zinc stearate. The amount of catalyst present during the reactions is generally about 1 to about 500 ppm by weight.

The use of a solvent or diluent is usually not necessary. In a preferred embodiment, however, a solvent or a mixture of two or more solvents is used. Suitable solvents are, for example, hydrocarbons, in particular toluene, xylene or cyclohexane, esters, in particular ethyl glycol acetate, ethyl acetate or butyl acetate, amides, in particular dimethylformamide or N-methylpyrrolidone, sulfoxides, in particular dimethyl sulfoxide, ethers, in particular diisopropyl ether or methyl tert-butyl ether or preferably cyclic Ethers, especially tetrahydrofuran or dioxane. The invention also relates to a binder composition containing at least one thermoplastic polyurethane according to the invention.

The binder composition according to the invention contains at least one thermoplastic polyurethane which has at least one segment G, this segment G containing monomers linked by free-radical polymerization carrying at least one anchor group L. The binder composition according to the invention preferably contains at least one thermoplastic polyurethane which has at least one hard segment A and at least one soft segment B, the segment G being in the hard segment A or in the soft segment B or in A and B. In a preferred embodiment of the present invention, the binder composition according to the invention contains such a thermoplastic polyurethane or a mixture of two or more such thermoplastic polyurethanes in an amount of at least about 10% by weight, for example at least about 30 or 50% by weight. In a preferred embodiment of the invention, the amount of polyurethane according to the invention in the binder composition is about 50 ± 5% by weight, the remainder being made up of conventional polymers suitable for use in the binder composition, for example polyurethanes. In addition to the thermoplastic polyurethanes mentioned which carry an anchor group L in at least one hard segment A, the binder composition according to the invention can also contain a further thermoplastic polyurethane or a mixture of two or more further thermoplastic polyurethanes.

In the context of a further preferred embodiment of the present invention, the binder compositions according to the invention contain, in addition to the thermoplastic polyurethane already mentioned or the thermoplastic polyurethanes already mentioned, at least one further binder. In addition to the thermoplastic polyurethanes according to the invention or mixtures thereof, the binder compositions according to the invention may also contain a further polymer or a mixture of two or more further polymers. Other polymers which can be used in the binder composition according to the invention include, for example, non-thermoplastic polyurethanes, polyacrylates, polyester polyurethanes, poly (meth) acrylate urethanes, polymethacrylates, polyacrylamides, polymers or copolymers of vinyl monomers such as styrene, vinyl chloride, vinyl acetate, vinyl propionate, binders based on vinyl formals, cellulose-containing polymers such as cellulose esters, in particular cellulose nitrates, cellulose acetates, cellulose sulfonate propionate or cellulose acetobutyrate, phenoxy resins or epoxy resins, as can be obtained in a manner known per se, or mixtures of two or more thereof.

The binder compositions according to the invention generally contain the thermoplastic polyurethanes in an amount of up to about 100% by weight. Additional binders can be present in the binder composition according to the invention in a proportion of up to about 90% by weight, for example up to about 80, 70, 60, 50, 40 or 30% by weight or less.

The polyurethanes according to the invention can be used both as dispersing binders and as topcoat binders in a binder composition. If a polyurethane according to the invention is to be used as the dispersion binder, the number of anchor groups per hard segment in the polymer should be at least about 1, in particular about 1 to about 3. If a polyurethane according to the invention is to be used as the coating binder, the number of anchor groups per hard segment in the polymer should be about 0.1 to about 0.9, in particular about 0.2 to about 0.6. The same applies if mixtures of two or more polymers are used for the production of the dispersing or topcoat binders. In this case, the ratio of Hard segments with anchor groups to hard segments without anchor groups are set so that the above values are observed.

In a preferred embodiment of the invention, polymers according to the invention suitable for use as dispersing binders have a glass transition temperature (Tg) of approximately 50 to approximately 70 ° C. and a molecular weight of approximately 10,000 to approximately 25,000. In the context of a preferred embodiment of the invention, polymers according to the invention suitable for use as lacquer binders have a glass transition temperature (T _g ) of approximately 12 to approximately 30 ° C. and a molecular weight of approximately 40,000 to approximately 80,000.

In a preferred embodiment of the invention, the binders according to the invention contain a magnetic pigment or a mixture of two or more magnetic pigments and are suitable as a magnetic dispersion or as a constituent thereof. Magnetic pigments include the usual oxidic pigments such as γ-Fe ₂ O ₃ , Fe ₃ O ₄ , FeO _x (l, 33 <x <l, 5), CrO ₂ , co-modified γ-Fe ₂ O ₃ , Co modified Fe ₃ O ₄ , Co-modified FeO _x (1.33 <X <1.5), ferromagnetic metal pigments or metal alloy pigments, barium ferrite or strontium ferrite. The metal pigment or metal alloy pigment comprises a metal, such as Fe, Co, Ni or a combination of two or more of these metals as the main component, and optionally further metal components such as Al, Si, S, Sc, Ti, V, Cr, Cu, Y, Mo, Rh, Pd, Ag, Sn, Sb, Te, Ba, Ta, W, Re, Au, Hg, Pb, Fe, Bi, La, Ce, Pr, Nd, P, Co, Mn, Zn, Ni, Sr, B. As usual, other elements or compounds can be added to these pigments.

In addition, the binder compositions according to the invention may also contain fillers, dispersing aids, other additives such as lubricants, carbon black or non-magnetic inorganic or organic pigments. To produce the magnetic dispersions according to the invention it is therefore possible to use a thermoplastic polyurethane or a mixture of two or more of the abovementioned thermoplastic polyurethanes with a magnetic pigment or a mixture of two or more magnetic pigments, for example in a mixture with one or more solvents and, if appropriate, together with fillers and dispersing agents , other binders and other additives such as lubricants, carbon black or non-magnetic inorganic or organic pigments are dispersed together. In a preferred embodiment, the main components in the magnetic dispersion, in particular the pigments and the binder, are first mixed with a little solvent to form a dough-like mass and then intimately mixed with one another, e.g. B. by kneading, mixed and then dispersed.

For example, carboxylic acids with about 10 to about 20 carbon atoms, in particular stearic acid or palmitic acid or derivatives of carboxylic acids such as their salts, esters or amides, or mixtures of two or more thereof, can be used as lubricants.

Examples of suitable non-magnetic inorganic additives are aluminum oxide, silicon dioxide, titanium dioxide or zirconium dioxide, and non-magnetic organic pigments include polyethylene or polypropylene.

As part of their use in magnetic recording media, the binder compositions according to the invention can be applied, for example, to customary rigid or flexible carrier materials. Suitable carrier materials are, for example, films of linear polyesters such as polyethylene terephthalate or polyethylene naphthalate, which generally have thicknesses of approximately 4 to approximately 200 micrometers, in particular approximately 5 to approximately 36 micrometers. It has surprisingly been found that the use of the polyurethanes according to the invention leads, compared to pure polyurethanes, to pigmented binder films which dry with less tension from THF / MiBK solvent mixtures and thus lead to less cupping of the strips. Because of the hollow curvature of the tapes, abrasion can occur when contacting the magnetic head and the tape-head contact is disturbed, the tension-free drying of the films is of great interest.

The invention therefore also relates to a shaped body, in particular a self-supporting molded body, at least containing a binder composition according to the invention or a binder composition produced by a method according to the invention.

The invention also relates to the use of a binder composition according to the invention or a binder composition produced according to the invention for the production of magnetic recording media. The following are particularly worth mentioning as recording media:

Video cassettes, for both professional and consumer use; Audio cassettes, both for the professional and for the end user area, e.g. B. Digital audio tape; Data storage tapes; disks; Floppy disk; ZIP disk; Magnetic stripe.

In a preferred embodiment, such a recording medium has a double layer structure.

The invention is explained in more detail below by examples. EXAMPLES:

Synthesis of the polyacrylate block:

example 1

225.0 g of tetrahydrofuran and a freshly prepared solution of 25.74 g of 2-acrylamido-2-methylpropanesulfonic acid, 23.01 g of tributylamine and 26.25 g of tetrahydrofuran were placed in a stirring apparatus with 2 dosing pumps for the feeds and heated to boiling temperature. Then the two feeds, consisting of feed la (435.0 g methyl acrylate and 14.25 g 2-hydroxyethyl acrylate) and feed lb (4.13 g 2-mercaptoethanol, 0.75 g α, α '-Azoisobutyronitrile and 30.0 g tetrahydrofuran), added over 120 minutes. The further polymerization took place at an outside temperature of 80 ° C. and was terminated at a monomer content of <1% (gas chromatographic determination). The polymer solution was then diluted with 210.0 g of tetrahydrofuran, which gave a solids content of 50%.

Example 2

The OH-terminal, sulfonate group-hooked polyacrylate was prepared by radical polymerization of 1.99 mol of 2-acrylamido-2-methylpropanesulfonic acid tributylamine salt, 69.81 mol of methyl methacrylate and 1.97 mol of 2-hydroxyethyl acrylate with 0.08 mol of α, α'-Azoisobutyronitrile as a starter and 0.85 mol of 2-mercaptoethanol as a regulator. The polymerization was carried out 50% in tetrahydrofuran at 70 ° C.

Synthesis of the binder

Example 3

1 mol of an OH-terminated polyacrylate containing sulfonate groups (for example 1) and 11.25 mol of a polyester diol with a molecular weight of approximately 800, consisting of adipic acid, isophthalic acid and 1,4-cyclohexanedimethanol, were mixed with 11.88 mol of tetrahydrofuran in tetrahydrofuran. 4'-Diphenylmethane diisocyanate reacted at 60 ° C. At a viscosity of the 43% solution of 2000 mPas (at 60 ° C.), an amount of dibutylamine equivalent to the isocyanate still present was added.

Example 4

1 mol of an OH-terminated polyacrylate containing sulfonate groups (for example 1) and 11.25 mol of a polyester diol with a molecular weight of 800, consisting of adipic acid, isophthalic acid and 1,4-cyclohexanedimethanol, were mixed with 11.31 mol of 4,4 'in tetrahydrofuran. -Diphenylmethane diisocyanate reacted at 60 ° C. The reaction temperature is maintained until the amount of isocyanate groups present is zero.

Comparative measurements of hollow curvature

Example 5

Test recipe phase 1:

180 g pigment, 3.6 g stearic acid, 26 g dispersion binder in 28% solution in THF / MiBK (3: 1), dispersion in a stirrer mill.

Phase 2:

26 g binder, 24% solution in THF / MiBK (3: 1)

Hollow curvature of the squeegee films from the corresponding solutions with an 80 μm squeegee on PET film (film thickness: 24 or 75 μm): For the example according to the invention (polymethacrylate-containing binder) and the comparative example (Morthane CA 151), the hollow curvature was first measured after the dispersion according to phase 1 in the respective binder. The second binder, that is to say the binder containing polymethacrylate according to the invention or Morthane CA 152, was then added in phase 2, and the hollow curvature was again measured.

Table 1

Binder for phase 2:

Polybutyl methacrylate copolymer with 2-hydroxyethyl methacrylate and AMPS controlled polymerized with thioethanol. The binder was then obtained by reacting the polymethacrylate block with polyester VP9184 (BASF), 1,4-cyclohexanedimethanol and MDI.

dispersions

Example 6

In an agitator ball mill with a content of 1.5 l, filled with 2.7 kg ceramic balls with a diameter between 1.0-1.5 mm were with

- 4200 g of an organic solvent mixture consisting of 80% THF and 20% isobutyl methyl ketone

- 930 g of a solution of the polymer according to the invention, 15% in THF

- 500.4 g of a solution of a commercially available polyurethane with sulfonate anchor groups (Morton), 25% in THF 1200 g of a ferromagnetic metal pigment (Hc = 127 kA / m; SSA = 58 m ² / g; average particle size 170 nm, average particle diameter 25 nm)

- 110 g of α-aluminum oxide (average particle diameter 320 nm)

- 12 g of carbon black (BET = 60 m / g; primary particle size 30 nm) 12 g of stearic acid

- 9 g fatty acid ester as a lubricant

filled and dispersed for 6 hours. The dispersion produced in this way is homogeneous, finely divided, stable in settling and free from flocculate. The dispersion was then filtered under pressure through a filter (pore size 3 μm).

42 g of a 50% solution of the reaction product of 3 moles of toluene-2,4-diisocyanate (TDI) with 1 mole of trimethylolpropane in THF were added to the dispersion immediately before coating with vigorous stirring.

The dispersion was applied to a back-coated polyethylene terephthalate film with a dry layer thickness of 3 μm. Before drying, the coated web was passed through a straightening section consisting of a coil with a field strength of 200 kA / m to align the ferromagnetic pigments. After drying at 80 ° C, the film web was satinized in a steel steel calender with 6 columns at 85 ° C and a pressure of 200 kg / cm and then cut into Vτ inch wide video tapes.

Comparative example

The procedure was as described above, but the weight of the polyurethane according to the invention was replaced by a commercially available VC copolymer with sulfonate anchor groups (from Nippon Zeon).

The measurement results obtained are shown in Table 2. Table 2

The measured values (Table 2) mean:

Gloss:

A reflection at an angle of 60 ° is measured on the uncalendered layer.

Gloss 1: gloss value immediately after the end of the dispersion Gloss 2: gloss value after 24 hours of roller board. The higher the gloss value, the better the pigment distribution.

RF level:

The high-frequency levels were measured in a Betacam SP recorder (BVW 75 system, Sony company) against the reference band Sony RSB 01 SP. The higher the RF level, the better the band.

S / N (luminance:

The luminance signal was measured in a Betacam SP recorder (BVW 75 system, Sony company) against the reference band Sony RSB 01 SP. The higher the S / N value, the better the band. Coefficient of friction:

The coefficient of friction with the RAF test was determined with a sample length of 150 mm and a measuring distance of 100 mm. After air conditioning for 15 minutes at 40 ° C and 80% relative humidity, the piece of tape was stretched to a length of 100 mm with a force of 2 N and a speed of 20 mm / s using a steel pin (diameter 2.5 mm, wrap 90 ° ) pulled back and forth. The coefficient of friction was measured after 100 cycles in the above Climate. The smaller the value, the better the tape's running properties.

Example 7 Monolayer tape:

A mixture of 100 parts by weight of a ferromagnetic metal pigment (Hc = 117 kA m; SSA = 51 m ² / g, average particle length 170 nm, average particle diameter 25 nm), 10 parts by weight of α-aluminum oxide (average particle diameter 320 nm ), 2 parts by weight of carbon black (BET = 35 m ² / g; primary particle size = 50 nm), 9 parts by weight of the polymer according to the invention, 9 parts by weight of a commercially available polyurethane with sulfonate anchor groups (Morton), 2, 5 parts by weight of stearic acid, 15 parts by weight of tetrahydrofuran and 15 parts by weight of dioxane were kneaded for 2 hours in a batch kneader (IKA high-performance center type HKD 10, D A-Maschinenbau, Staufen).

A mixture of 145 parts by weight of THF and 145 parts by weight of dioxane was then added to the kneading mixture in portions in a dissolver with vigorous stirring, and the mixture was then dispersed in a stirrer mill for 9 hours. 1 part by weight of butyl stearate, 5.2 parts by weight of a 50% by weight solution of the reaction product of 3 mol of tolylene diisocyanate and 1 mol of trimethylolpropane in THF and a portion of a mixture of 40 Parts by weight of THF and 40 parts by weight of dioxane. After filtration through a filter with a pore size of 2 μm, a homogeneous, finely divided, settling-stable and flocculate-free coating-capable dispersion was obtained. The dispersion was applied to a back-coated polyethylene terephthalate film with a dry layer thickness of 3 μm. Before drying, the coated web was passed through a straightening section consisting of a coil with a field strength of 200 kA / m to align the ferromagnetic pigments. After drying at 80 ° C, the film web was satined in a steel / steel calender with 6 columns at 85 ° C and a pressure of 200 kg / cm and then cut into Vi inch wide video tapes.

Comparative example

The procedure was as described above, but the weight of the polyurethane according to the invention was replaced by a commercially available VC copolymer with sulfonate anchor groups (from Nippon Zeon). Table 3 shows the measurement results obtained.

Table 3

The measured values (Table 3) mean:

Gloss:

A reflection at an angle of 60 ° is measured on the uncalendered layer. Gloss 1: gloss value immediately after the end of the dispersion Gloss 2: gloss value after 24 hours of roller board.

The higher the gloss value, the better the pigment distribution.

RF level:

S / N (luminance):

The luminance signal was measured in a Betacam SP recorder (BVW 75 system, Sony company) against the reference band Sony RSB 01 SP. The higher the S / N value, the better the band.

Coefficient of friction:

The coefficient of friction with the RAF test was determined with a sample length of 150 mm and a measuring distance of 100 mm. After air conditioning for 15 minutes at 40 ° C and 80% relative humidity, the piece of tape was stretched to a length of 100 mm with a force of 2 N and a speed of 20 mm / s using a steel pin (diameter 2.5 mm, wrap 90 ° ) pulled back and forth. The coefficient of friction was measured after 100 cycles in the above-mentioned climate. The smaller the value, the better the tape's running properties.

Example 8

a) Upper class

A mixture of 100 parts by weight of a ferromagnetic metal pigment (Hc = 180 kA m; SSA = 58 m / g; average particle length 80 nm, average particle diameter 25 nm), 13 parts by weight of α-aluminum oxide (average particle diameter 220 nm) , 8.2 parts by weight of the polymer according to the invention, 3.5 parts by weight of a commercially available polyurethane with polar anchor groups (Morton), 2 parts by weight of stearic acid, 1 part by weight of myristic acid, 15 parts by weight Tetrahydrofuran and 15 parts by weight of dioxane were kneaded in a batch kneader (IKA high-performance kneader type HKD 10, company IKA Maschinenbau, Staufen) for 2 hours.

A mixture of 155 parts by weight of tetrahydrofuran and 155 parts by weight of dioxane was then added to the kneaded mixture in portions in a dissolver, with vigorous stirring, and the mixture was then dispersed for 10 hours using a stirrer mill. 1 part by weight of butyl stearate, 4 parts by weight of a 50% strength by weight solution of the reaction product of 3 moles of tolylene diisocyanate and 1 mole of trimethylolpropane in tetrahydrofuran and portions of a mixture of 44 parts by weight were then added to the dispersion with vigorous stirring Tetrahydrofüran and 44 parts by weight of dioxane. After filtration through a filter with a pore size of 2 μm, a homogeneous, finely divided, settling-stable and flocculate-free coating ready for coating was obtained.

Comparative Example 8a

The procedure was as described above, but the polyurethane according to the invention was replaced by a commercially available VC copolymer with sulfonate anchor groups (Nippon Zeon). b) lower class

A mixture of 100 parts by weight of α-iron oxide (average particle length 118 nm, average particle diameter 28 nm, SSA = 60 m ² / g; Toda company), 29 parts by weight of carbon black (average primary particle size 25 nm, SSA = 112 m ² / g), 13 parts by weight of the polymer according to the invention, 7.5 parts by weight of a commercially available polyurethane with polar anchor groups (Tg = 70 ° C; Morton company), 7.5 parts by weight of a second commercially available polyurethane polar anchor groups (Tg = 35 ° C; Morton company), 2 parts by weight of stearic acid, 27 parts by weight of tetrahydrofuran and 27 parts by weight of dioxane were kneaded in a batch keter for 3 hours.

A mixture of 234 parts by weight of tetrahydrofuran and 234 parts by weight of dioxane was then added in portions to the kneading compound in a dissolver, with vigorous stirring, and the mixture was then dispersed in a stirrer mill for 15 hours. 6.3 parts by weight of a 50% solution of the reaction product of 3 moles of toluenediisocyanate with 1 mole of trimethylolpropane in tetrahydrofuran was then added to the dispersion with vigorous stirring. After filtration through a filter with a pore size of 2 μm, a homogeneous, finely divided, settling-stable and flocculate-free, coating-ready dispersion was obtained.

Comparative Example 8b:

The procedure was as described above, but the polymer according to the invention was replaced by a commercially available VC copolymer with sulfonate anchor groups (Nippon Zeon).

Applying lower and upper layers:

The dispersions were applied wet-on-wet to the front of a back-coated polyethylene terephthalate film. Before drying, the coated film was aligned to align the ferromagnetic pigments through a straightening section consisting of a coil with a field strength of 200 kA / m. carried out. After drying at 80 ° C, the film web was satinized with a steel / steel calender with 6 columns at 80 ° C and a pressure of 200 kg / cm and then cut into 6.35 mm wide video tapes.

The measurement results obtained are listed in Table 4.

Table 4

Gloss, abrasion and friction measurements were carried out as described in Example 7.

The high-frequency level was measured in a DVC-MAZ device (AJ D-750, Panasonic) against the reference band Panasonic APOG 0715-15.

A comparison of the measurement results shows that the magnetic tapes according to the invention have improved level values due to better pigment division into the upper and lower layers. In addition, the very low friction values ensure good running and abrasion behavior in the recorder.

Claims

claims

1. Polyurethane with at least one anionic anchor group L, the anionic anchor group L being bonded to a segment G in the polyurethane which contains monomers linked by free-radical polymerization.

2. Polyurethane according to claim 1, characterized in that it has a block structure or thermoplastic properties or both.

3. Polyurethane according to claim 1 or 2, characterized in that it has at least one hard segment A and at least one soft segment B, wherein the segment G is in the hard segment A or in the soft segment B or in A and B.

4. Polyurethane according to claim 3, characterized in that at least one hard segment A has at least one segment G.

5. Polyurethane according to claim 3 or 4, characterized in that it has a structure according to the general shape

- (A _k B,) _n - (I) or

- (A (B) _m ) _n - (II), where A is a hard segment and B is a soft segment, k and n are each a number from 1 to 10 and 1 and m are a number from 0 to 10 stand, whereby k, 1 and m can be selected for each repetition unit independently of the next repetition unit.

6. Polyurethane according to claim 5, characterized in that 1 and m stand for a number from 1 to 10.

7. Polyurethane according to one of the preceding claims, characterized in that the monomers in segment G are derivatives of acrylic acid or methacrylic acid with polar groups or polar or non-polar vinyl monomers or a combination of two or more thereof or a combination of one of these monomers with one less are polar monomer.

8. Polyurethane according to one of the preceding claims, characterized in that the anionic anchor group L is a sulfonate.

9. A process for the production of a polyurethane as claimed in one of claims 1 to 8, characterized in that during the production at least one segment A which is functional at least with respect to NCO groups and comprises at least one segment G which comprises a polymer block composed of monomers linked by free-radical polymerization, is used.

10. The method according to claim 9, characterized in that the segment G is a polyacrylate or polymethacrylate block.

11. A binder composition containing at least one thermoplastic polyurethane according to one of claims 1 to 8 or a polyurethane produced according to claim 9 or 10.

12. Magnetic dispersion containing at least one polyurethane according to one of claims 1 to 8 or a polyurethane prepared according to claim 9 or 10 or a binder composition according to claim 11 and at least one magnetic or magnetizable pigment.

13. A magnetic recording medium containing at least one polyurethane according to one of claims 1 to 8 or a polyurethane according to claim 9 or 10 or a binder composition according to claim 11 or a magnetic dispersion according to claim 12.

14. Use of a polyurethane according to one of claims 1 to 8 or produced according to claim 9 or 10, or a binder composition according to claim 11, or a magnetic dispersion according to claim 12 for the production of magnetic recording media.