EP1325049A1

EP1325049A1 - Polyurethane, method for the production thereof and binding agent produced therefrom

Info

Publication number: EP1325049A1
Application number: EP01983534A
Authority: EP
Inventors: Ulrike Hees; Hans-Guenter Bohrmann; Benedikt Raether; Ria Kress; Albert Kohl
Original assignee: Emtec Magnetics GmbH
Current assignee: Emtec Magnetics GmbH
Priority date: 2000-10-13
Filing date: 2001-10-09
Publication date: 2003-07-09
Also published as: US6914118B2; AU2002215013A1; US20040127675A1; WO2002031012A1; DE10050710A1

Abstract

The invention relates to a polyurethane containing at least one anionic active group L, whereby the active group L is covalently bonded to a polyurethane section comprising at least one nitrogen atom in said polyurethane.

Description

description

Polyurethane, process for its production and binders made therefrom

The invention relates to an anchor group-containing polyurethane, a process for its production, its use and binders and moldings produced therefrom. A binder 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 covalently bonded to a polyether segment in the polyurethane having at least one nitrogen atom. In particular, the invention relates to the use of binders containing such polyurethanes or moldings produced from such binders for the production of magnetic recording media.

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.

No. 4,496,678 relates to viscosity-stabilized dispersions in which a polyether diol containing sulfonic acid groups acts as a stabilizing component in a polyurethane. No mention is made here of polyether sections bearing sulfonic acid groups and amino groups. US 5 747 630 relates to a polyurethane binder for a magnetic recording medium. The polyurethane binders described have, for example, polyether segments which have a cationic amino group with a sulfonic acid counterion. Polyether sections containing amino groups and having a covalently bonded acid group are not mentioned in the publication.

DE - C 28 33 845 relates to a magnetic recording material made from a carrier or base material and a magnetizable layer formed thereon from fine magnetic particles which are dispersed in a binder made from polyester or polyurethane. A suitable polyurethane has, for example, a metal sulfonate group content of 10 to 1000 equivalents per 10 ⁶ g of polymer. Polyurethanes with polyether segments which have both amino groups and acid groups are not described in the publication.

Polyurethanes with anchor groups are 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. ,

Furthermore, DE-A 100 05 647.4 describes a binder composition, at least containing a polyurethane with a structural unit according to general formula I defined therein

(I) wherein n is a number from 1 to 10, the radicals R ¹ each independently of one another for a polyurethane having 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 a linear or branched, saturated or unsaturated alkyl radical with 2 to 44 C atoms, X for an optionally aromatically substituted alkyl radical with 2 to 14 C atoms, Y for a polymer obtainable by polymerization, polyaddition or polycondensation with a molecular weight M _w of 150 up to 5000 and m stands for a value from 1 to 300, the radicals R ² each independently represent H or a linear or branched, saturated or unsaturated aliphatic hydrocarbon radical having 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 hydrocarbon radical with 6 to about 20 C atoms or an optionally substituted aromatic hydrocarbon radical with 6 to 18 C atoms, the radicals R ³ for a linear or branched, saturated or unsaturated Alkyl radical with 2 CA. or a saturated or unsaturated cycloalkyl radical with 4 to 44 C atoms, Z represents a linear or branched, saturated or unsaturated optionally substituted alkyl radical with 8 to 44 C atoms, an optionally substituted cycloalkyl radical with 4 to 44 C atoms, one optionally substituted araliphatic hydrocarbon radical having 6 to 40 carbon atoms or a polymer which can be obtained by polymerization, polyaddition or polycondensation and has a molecular weight M _w of 150 to 5000, Z being connected to the total molecule via suitable functional groups, or a partial or customs salt thereof, and at least one magnetic or magnetizable pigment, 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 with 1 to 20 C atoms, a saturated or unsaturated, optionally substituted cycloaliphatic hydrocarbon radical with 4 to 20 C atoms or an optionally substituted araliphatic hydrocarbon radical with 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 ₂ , -. NHR ³ or SH group, in which R ^{3 is} a linear or branched, saturated or unsaturated, optionally aromatically substituted alkyl radical having 1 to 44 carbon atoms, is incorporated in the polyurethane, or a salt thereof, and at least one magnetic or magnetizable Pigment.

In the light of the prior art cited above, the present invention was based on the object of providing a new polymer which is suitable for the production of magnetic recording media.

The invention relates to a polyurethane having at least one anionic anchor group L, the anchor group L being covalently bonded to a polyether segment in the polyurethane having at least one nitrogen atom.

In the context of the present invention, a “polyether segment having at least one nitrogen atom” is understood to mean a segment which has at least two ether groups and at least one nitrogen atom. The at least one nitrogen atom can be arranged, for example, between two or more ether groups. However, it is also possible for the at least one nitrogen atom to be arranged at the end of the polyether segment. Such a nitrogen atom can be used, for example, with two in the context of the present invention or more carbon atoms. Corresponding carbon atoms can belong to an alkyl group or to functional groups such as carboxyl groups or urea groups. Accordingly, the nitrogen atom is an amino N atom, an amido N atom or a urea N atom.

In the context of the present invention, a binder is understood to mean a composition which contains at least one thermoplastic polyurethane defined herein. The binder according to the invention preferably contains a mixture of two or more such polyurethanes or a mixture of at least one polyurethane with further polymers, the polymers or polyurethanes, after chemical or physical drying, substantially maintaining stable dispersions and sufficient mechanical stability of one of the binders produced magnetic recording medium are involved.

In the context of the present invention, a thermoplastic block copolyurethane is understood to mean a polyurethane which has a block-by-block structure A-B-A, these individual blocks being present in micro-phase separation. 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 is understood to mean a segment of a thermoplastic block copolyurethane 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 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 20 ° C.

In the context of the present invention, an anchor group is understood to mean an anionic group which is able to interact 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 covalently bound to a polyether segment in the polyurethane having at least one amino group.

A polyurethane according to the invention can have a statistical structure, i. H. 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, 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 the context of a further preferred embodiment of the present invention, the polyurethane according to the invention is a block copolyurethane. The polyurethane according to the invention can have anchor groups L both in a soft segment and in a hard segment. According to the invention, however, the number of anchor groups located in a hard segment of the thermoplastic polyurethane is greater than the number of anchor groups located in one soft segment (A) or several soft segments (A). In a preferred embodiment of the invention, the number of anchor groups in the total number of hard segments (B) in the polyurethane is at least five times, preferably at least 10 times, the total number of anchor groups in the soft segments (A). In a further preferred embodiment of the invention, the thermoplastic polyurethane according to the invention has essentially no anchor groups in the soft segment (A) or the soft segments (A).

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

In the context of a further preferred embodiment of the invention, at least one anchor group L is covalently bonded to at least one polyether segment in the polyurethane having at least one nitrogen atom. In the context of a further embodiment, the anchor group L is covalently bonded directly or via a corresponding spacer to at least one nitrogen atom in the polyether segment.

Suitable compounds for building up such a polyether segment are, for example, polyether compounds which have terminal amino groups. Such polyether compounds can be functionalized, for example, by the corresponding amino groups with, for example, acrylamidopropanesulfonic acid (AMPS) in the sense of a Michael addition such that the terminal amino groups each have a spacer on the amino N atom with the sulfonic acid group as anchor group L are covalently linked. Such aminopolyethers equipped with at least one anchor group L can then be converted, for example, by reaction with corresponding polyisocyanates to give polyureas or (in the presence of polyols) polyurea polyurethanes. For the sake of simplicity, polyurea polyurethanes are also referred to as polyurethanes in the context of the present invention.

Compounds particularly suitable for building up the polyether segments containing at least one nitrogen atom are, for example, compounds of the general formula II

H ₂ N-CH ₂ -CH (R) -O (- [CH ₂ -CH (R)] ₀ -O) "- CH ₂ -CH (R) -NH- (CH ₂ ) _m -SO ₃ H ( II),

wherein R is H or a linear or branched alkyl radical having 1 to 4 carbon atoms, in particular CH ₃ , n is a number from 1 to about 100 and m is a number from 2 to 10 and o is 1 or 2, or their alkali metal salts. Such products are sold, for example, by the Raschig company under the name Poly EPS 520Na.

If a soft segment in the context of a polyurethane according to the invention has a polyether segment with at least one nitrogen atom and at least one anchor group L, the molecular weight (M _w ) of the polyether segment is at least about 700, but preferably more, for example at least about 800, 900 or about 1000 g / mol. The upper limit for the molecular weight is about 100,000, but preferably less, in particular from 5,000 to 25,000.

If a hard segment in the context of a polyurethane according to the invention

Has polyether segment with at least one nitrogen atom and at least one anchor group L, the molecular weight (M _w ) of Polyether segment at least about 60, but preferably more, for example at least about 100, 200 or 300 g / mol. The upper limit for the molecular weight is about 500 to 1000, in particular about 600. The molecular weight should be rather low, since it is otherwise a soft segment. However, too low molecular weights mean that the polyether segment defined above is no longer soluble in common solvents, such as THF or dioxane.

In a preferred embodiment, the invention relates to a thermoplastic polyurethane of the general formula I.

Y- (AB (L) _m -A-) _n Y (I)

or a polyurethane of the general formula Ia

Y- (AB (L) _m -) _n Y (Ia)

or a polyurethane of the general formula II

Y- (AB (L) _r -AZ-) _n -AB (L) _m -AY (II),

where A, B and L have the meaning given above, Z for the rest of a compound XZX which is at least difunctional with respect to Y to form a covalent bond, Y for a functional group which is reactive towards the functional groups X of compound Z to form a covalent bond, X represents at least one functional group reactive towards the functional groups Y to form a covalent bond, n for a number from 1 to 10, m for a number from 1 to 10 and r for a number from 0 to 10, the number of anchor groups L in the entire block copolyurethane is 1 to n * m (formulas I and Ia) or 1 to n * r + m (formula II). Basically suitable as soft segments (A) are, for example, polyesters, polyethers, polyacetals, polycarbonates, polyester ethers and the like, such as polyester polyurethanes.

If the polyurethane according to the invention has soft segments and hard segments, the polyether segment containing at least one nitrogen atom can be arranged in the soft segment or in the hard segment or in both segments.

The compounds mentioned which are suitable for use as soft segments (A) have at least one functional group Y. In a preferred embodiment of the invention, the compounds suitable as soft segments (A) have at least two functional groups Y. In a further preferred embodiment of the invention, the functional groups Y are attached at the ends to the compounds suitable for use as soft segment (A).

Basically, Y stands for a functional group capable of reacting with an NCO group to form a covalent bond. In a preferred embodiment of the invention, Y is OH, NH ₂ , NHR, 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 ,

In a further preferred embodiment of the invention, Y represents an OH, NH ₂ or NHR group, in particular an OH group. In the further course of the text, suitable connections are described for the production of soft segments (A). 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, have a different functional group which is reactive toward NCO groups, for example, carry one of the other functional groups named for Y, insofar as a corresponding connection exists or can be produced.

Polyesters 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 groups. The polyester polyols can be obtained in a simple manner by esterification of linear or branched, saturated or unsaturated aliphatic or correspondingly suitable aromatic dicarboxylic acids with 4 to about 15 C atoms, preferably 4 to about 10 C atoms with glycols, preferably glycols with about 2 to about Produce 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 e.g. Trimellitic acid. 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-l, 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-l, 5, 2,2-dimethylpropanediol-1,3, 1,4-cyclohexanedimethanol, 1,4-diethanolcyclohexane, 2-methyl-2-butyl-l, 3-propanediol, 2,2-dimethyl-l, 4-butanediol, hydroxypivalic acid neopentyl glycol ester, triethylene glycol, methyl diethanolamine or aromatic aliphatic or arornatic-cycloaliphatic diols with 8 to about 30 C atoms, it being possible to use heterocyclic ring systems or preferably isocyclic ring systems such as naphthalene or in particular benzene derivatives such as bisphenol A as aromatic structures, twice symmetrically ethoxylated bisphenol A, twice symmetrically propoxylated bisphenol A, more ethoxylated or propo xylated 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 with 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 polyester polyols mentioned 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 production of the polyester polyols are, for example, α, α-dimethyl-γ-propiolactone, β-butyrolactone and ε-caprolactone. The polyether polyols are also suitable for use as soft segments (A) in the production of the above-mentioned thermoplastic polyurethanes. Polyether polyols are understood to mean essentially linear substances with ether bonds in the sense of the above-mentioned terminal OH groups. Suitable polyether 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 and amino alcohols such as N. - Consider methylethanolamine. In principle, however, all of the 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 polyether polyols and their preparation are mentioned, for example, in EP-B 0 416 386.

A polyurethane according to the invention has at least one anchor group L which is covalently bonded to a polyether segment in the polyurethane having at least one nitrogen atom. The preparation of suitable polyethers has been described above, for example. However, those polyethers which each have a nitrogen atom at the end of the polyether segment, in particular in the form of an amino group, are also suitable. Both polyether segments are suitable here which only have at least one nitrogen atom at the terminal. However, polyether segments which are attached to at least one are also suitable Chain end have a nitrogen atom and within the polyether chain another nitrogen atom or more nitrogen atoms.

Within the scope of a further embodiment of the present invention, such polyethers bearing nitrogen atoms are also suitable which do not carry the nitrogen atom within the backbone of the polyether segment but as a side chain.

In the context of the present invention, polycarbonates, for example, can also be used as soft segments (A). In a preferred embodiment of the invention, polycarbonates are used which are essentially linear and have at least two, preferably terminal, OH groups. Corresponding polycarbonate polyols are prepared, for example, by reacting one of the above-mentioned functional alcohols or a mixture of two or more such functional alcohols with phosgene. Suitable polycarbonate polyols, for example those based on 1,6-hexanediol and their preparation, are described, for example, in US Pat. No. 4,131,731.

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 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, for example, polyesters are used as soft segment (A), which can be obtained from a reaction of adipic acid or isophthalic acid and or a mixture thereof with 1,6-hexanediol or 1,4-cyclohexanedimethanol or a mixture thereof.

In a preferred embodiment of the invention, the soft segments (A) have glass transition temperatures from about -50 ° C. to about 20 ° C. In a further preferred embodiment of the invention, the glass transition temperatures of the soft segments (A) 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 (A) should have a molecular weight of about 500 to about 25,000 g / mol. In a preferred embodiment of the invention, soft segments (A) are used which have a molecular weight of approximately 2000 to approximately 10,000 g / mol, for example approximately 3000 to approximately 7000 g / mol.

Compounds of the abovementioned classes of compounds suitable for use as soft segments (A) can already be present in a molecular weight range suitable for use as soft segments (A). However, it is equally possible to use compounds of the abovementioned classes of compounds for the production of soft segments (A) which have a molecular weight which is below the molecular weight or the desired molecular weight suitable for use as soft segment (A). 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 Y are suitable for this purpose, for example, dicarboxylic acids, difunctional epoxy compounds or diisocyanates, diisocyanates being used in a preferred embodiment of the present invention.

To increase the molecular weight mentioned above, such di- or higher-functional compounds are used which lead to a glass transition temperature of the extended soft segment (A) which is within the desired range. In a preferred embodiment of the invention, compounds for increasing the molecular weight are therefore used in the production of the soft segments (A) diisocyanates, in particular, for example, those having 6 to about 30 carbon atoms 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) , Also suitable as diisocyanates in the context of the present invention are aromatic diisocyanates such as tolylene-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 as well as mixtures of two or more of the diisocyanates mentioned. In a preferred embodiment of the invention, diisocyanates are used which have an aromatic molecular component.

The soft segments (A) can optionally carry one or more anchor groups L. The production of soft segments (A) with anchor groups L takes place 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 (B) 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 (A) contained in the thermoplastic polyurethane have none Anchor groups L on.

To produce the hard segments (B), diisocyanates are reacted with compounds which are functional towards isocyanate groups. The selection of diisocyanates and corresponding compounds which are functional towards isocyanate groups is carried out in such a way that the corresponding hard segment has a glass transition temperature as defined in the introduction, the isocyanates mentioned above with regard to the soft segment being preferred.

If necessary, isocyanates with a functionality of more than 2 can be used in minor amounts of up to about 5% by weight, based on the total amount of the diisocyanates used to prepare the hard segment (B). Suitable isocyanates for this purpose are, for example, the trimerization products of functional isocyanates such as 1,4-butylene diisocyanate, 1,5-pentamethylene diisocyanate or 1,6-hexamethylene diisocyanate.

As functional compounds for the production of the hard segments (B), preference is given to using compounds which have at least two functional groups which are reactive toward isocyanates with the formation of a covalent bond. Suitable functional groups are, for example, those as already mentioned above in the context of the explanation of the functional groups Y. In a preferred embodiment of the invention, difunctional alcohols are used to produce the hard segments (B). 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 stepwise extension of the carbon chain of the compounds mentioned, and for example 2,2, 4- trimethylpentanediol-1,5,2,2-dimethylpropanediol-1,3,4-cyclohexanedimethanol, 1,4-diethanolcyclohexane, 2-methyl-2-butyl-1,3-propanediol, 2,2-dimethyl 1,4-butanediol, hydroxypivalic acid neopentylglycol ester, triethylene glycol, methyldieth-mol-imine or aromatic-aliphatic or aromatic-cycloaliphatic diols with 8 to about 30 carbon atoms, with aromatic structures being heterocyclic ring systems or preferably isocyclic ring systems such as naphthalene or in particular benzene derivatives Bisphenol A can be used. In a preferred embodiment of the present invention, compounds which have a molecular weight of less than about 200 g / mol, in particular less than about 150 g / mol, are used to produce the hard segments (B). Particularly suitable in this context are the low molecular weight aliphatic functional alcohols, for example ethylene glycol, propylene glycol, butylene glycol, neopentyl glycol, neodiol (2-butyl-2-ethyl-1,3-propanediol) and the like short-chain aliphatic, linear or branched compounds.

The at least one anchor group L can be introduced into the hard segment (B) in different ways. On the one hand, the anchor groups L can be incorporated by covalently incorporating a compound or a mixture of two or more compounds which are suitable for introducing an anchor group into corresponding functional groups contained in the hard segment (B) in the course of a polymer-analogous reaction. If this way of introducing anchor groups (L) is to be labeled, it is necessary for the hard segment (B) to contain, for example, free hydroxyl groups or amino groups. Using appropriate compounds which are suitable for reaction with the functional groups contained in the hard segment (B) and additionally have a functional group which is suitable as an anchor group (L), it is possible in this way Functionalized hard segments (B) are obtained which, depending on the reaction procedure during the polymer-analogous reaction, have one or more anchor groups (L). If the hard segment (B) has, for example, one hydroxyl group or two or more hydroxyl groups, functionalization of these hydroxyl groups is possible by polymer-analogous reaction of the hard segment (B) with a sulton, for example propane sultone. In this case, sulfonic acid groups are introduced as anchor groups L. It is also possible, for example, to react hydroxyl groups contained in the hard segment (B) with correspondingly functionalized carboxylic acids, for example halocarboxylic acids such as chloroacetic acid, in order to achieve functionalization of the hard segment with one or more corresponding anchor groups. Carboxylic acid anhydrides are also suitable for the functionalization of functional groups contained in the hard segment (B). A corresponding polymer-analogous reaction of functional groups contained in the hard segment, for example hydroxyl groups, with carboxylic acid anhydrides leads to hard segments (B) which have a carboxylic acid group as anchor group L. Epoxy compounds having corresponding anchor groups, for example, are also suitable for connecting corresponding anchor groups to functional groups contained in the hard segment (B). Furthermore, the anchor groups can be introduced into the polymer backbone by Michael addition with suitable groups.

Before the polymer-analogous reaction of the functional groups contained in the hard segment (B) with a corresponding compound suitable for forming anchor groups, the functional groups contained in the hard segment (B) can be reacted, for example, with alkylene oxides having 2 to 4 carbon atoms. In a preferred embodiment of the invention, functional hydroxy groups contained in the hard segment (B) are reacted with about 1 to about 30 mol of alkylene oxide, in particular propylene oxide, per hydroxyl group. A further possibility for equipping the hard segments (B) with anchor groups L is that a compound functionalized with an anchor group L is already used when the hard segment (B) is being built up, and thus during the synthesis of the hard segment (B) into the hard segment (B) is installed. Corresponding compounds functionalized with an anchor group L therefore have at least two functional groups which are reactive towards an isocyanate group with the formation of a covalent bond, for example the functional groups Y already mentioned. Correspondingly suitable compounds are, for example, dimethylolpropionic acid or further difunctional compounds which are reactive with isocyanates and have a group which interacts with inorganic surfaces, for example pigment surfaces, such as SO ₃ Na, for example the Tegomer DS3135 which was previously sold by Goldschmidt.

In a further preferred embodiment, the hard segment B can also contain a polyether segment which has at least one nitrogen atom and to which an anchor group L is covalently bonded. The polyether segments already mentioned are suitable, for example, as the polyether segment having at least one nitrogen atom.

The number of anchor groups L per hard segment (B) 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 (B) (represented in the general formula I, formula Ia, where n is the number 1 or in the general formula II, where n is the number 0), the number is m in formula I formula Ia, which indicates the number of anchor groups L in the hard segment (B), for a number from 1 to about 10. In a preferred embodiment of the invention, m stands for 1. If the thermoplastic polymer has more than one hard segment (B ), represented, for example, in the general formula I / formula Ia, where n for a number greater than 1 stands, it is not absolutely necessary in the context of the present invention that each hard segment (B) 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 (B) 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 accordingly, provided that it has two or more hard segments (B), in each case have hard segments (B) without anchor groups L, with one anchor group L or with two or more anchor groups L, at least one of the hard segments (B) must carry at least one anchor group L. The formula notation B (L), as used for example in formula I / formula Ia and formula II, is therefore not to be understood as meaning that each hard segment (B) must carry 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.

The parameters m and r, as used in formula I / formula Ia and II, therefore do not have to stand for an integer, but can assume values that encompass the entire range of numbers within the limits for r and m.

Corresponding to the conditions in polymer synthesis, the parameter n also does not necessarily have to stand for an integer, since molecules with different molecular weights are generally formed in polymer syntheses and therefore the number n can be different for molecules formed during polymer synthesis. 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 (B) contains the anchor groups L already defined.

In a preferred embodiment of the invention, the hard segments (B) 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 about 20 ° C. to about 90 ° C. In a further preferred embodiment of the invention, the glass transition temperatures of the hard segments (B) 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 (B) should have a molecular weight of about 350 to about 30,000 g / mol. In a preferred embodiment of the invention, hard segments (B) are used which have a molecular weight of about 1,000 to about 20,000 g / mol, for example about 2,000 to about 15,000 g / mol or about 3,000 to about 12,000 g / mol.

The soft segments (A) and the hard segments (B) are produced in accordance with 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. If various of the compounds mentioned, which can be used as a soft segment, are to be connected to one another due to the molecular weight of the individual compounds being too low, this also takes place, depending on the functional compound used for chain extension, also according to the usual rules known in organic chemistry for the respective functional ones Groups. The soft segments (A) are produced in such a way that a soft segment (A) is formed which has at least two functional groups Y, one group Y being able to react with an isocyanate 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 (A) which carry Y OH groups as functional groups 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 (A) which differ, for example, in their functionality from isocyanate groups. It is therefore entirely possible within the scope of the present invention that the soft segments (A) used have a functionality with respect to isocyanate 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 (A) used are polyester polyols, polyether 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 (B) in the context of the present invention are prepared in such a way that polyurethane prepolymers which can be used as hard segments and have at least two isocyanate groups are present after the preparation. In a preferred embodiment of the invention, the compounds which can be used as hard segments have at least two isocyanate groups as terminal isocyanate groups. The thermoplastic polyurethanes according to the invention are produced by reacting the compounds which can be used as soft segments (A) with the compounds which can be used as hard segments (B). In the context of the present invention, compounds which can be used as soft segments (A) have a structure YAY, where Y has the meaning given above and A stands for one of the structures described above which can be used as soft segment (A). Compounds which can be used in the context of the present invention as hard segments (B) accordingly have a structure OCN-B (L) m-NCO and are accordingly reactive toward the structures forming the soft segments with the formation of a covalent bond. 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 (B) have to have one or more anchor groups. It is only necessary to add a sufficient number of compounds bearing anchor groups L, so that each thermoplastic polyurethane has at least one hard segment which carries at least one anchor group L; a structure AB (L) -A is preferred.

The present invention therefore also relates to a process for producing a thermoplastic polyurethane according to the invention, in which at least one at least one functional linear or branched polyurethane prepolymer with NCO end groups, for example a compound OCN-B (L) _m -NCO, is used as the hard segment (B) at least one linear or branched soft segment (A) having at least one functional group reactive towards NCO groups, for example a compound YAY, is reacted.

The reaction of the compounds YAY and OCN-B (L) _m -NCO can be carried out in a manner known per se, preferably at temperatures from about 0 to about 120 ° C. The ratio of the two components is advantageously so chosen so that the ratio of Y to NCO groups is about 2 to about 1. 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.

At least one of the thermoplastic polyurethanes present in the binder according to the invention has a molecular weight of approximately 3000 to approximately 150,000, for example approximately 8,000 to approximately 100,000 or approximately 10,000 to approximately 60,000.

If appropriate, other, low molecular weight compounds may also be present during the reaction. Such connections can act as chain extenders, for example. Primary amino compounds with two to about 20, for example 2 to about 12, carbon atoms are suitable for this purpose. For example, these are ethylamine, n-propylamine, i-propylamine, n-propylamine, sec-propylamine, tert-butylamine, 1-aminoisobutane, substituted amines having 1 to about 20 carbon atoms, such as 2- (N, N-dimethylamino) ) -l-aminoethane, aminomercaptans such as 1-amino-2-mercaptoethane, aliphatic amino alcohols having 1 to about 20, preferably 1 to about 12, carbon atoms, for example methanolamine, l-amino-3,3-dimethylpentane-5- ol, 2-aminohexane-2 ', 2 "-diethanolamine, l-amino-2,5-dimethylcyclohexan-4-ol, 2-amino-l-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-trimethylcyclohexane-1 -ol, 1-amino- 1-cyclopentane-methanol, 2-amino-2-ethyl-1,3-propanediol, aromatic-aliphatic or aromatic-cycloaliphatic amino alcohols with 6 to about 20 C atoms, the aromatic structures being heterocyclic ring systems or preferably isocyclic ring systems such as naphthalene or in particular benzene derivatives such as 2-aminobenzyla alcohol, 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 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-methylmorpholine. 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 from 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.

If the compound Y-A-Y is used in excess, for example in twice the molar amount, to the corresponding compound forming the hard segment in the preparation of the thermoplastic polyurethanes according to the invention, a thermoplastic polyurethane is formed which has functional groups as end groups

Y wears. For the production of thermoplastic polyurethanes according to the general

Formula II can these compounds containing end groups reactive towards isocyanate groups with compounds which are functional towards such groups

Connections with chain extension are implemented. Corresponding functional compounds of the general formula X-Z-X show as functional

Groups X on the functional groups Y reactive groups. Examples of such functional groups X are primarily the isocyanate groups used in a preferred embodiment of the present invention become. Depending on the type of functional group Y, however, X can also stand for other functional groups reactive towards Y, for example for epoxy groups, carboxylic acid groups, carboxylic ester groups, carboxylic anhydrides or for double bonds which can be reacted with Y in the course of a Michael addition.

In a preferred embodiment of the invention, Z has as functional groups X at least two epoxy, OH, NCO or COOH groups or a mixture of two or more thereof which is not reactive with one another.

The invention also relates to a binder containing at least one thermoplastic polyurethane according to the invention.

The binder according to the invention contains at least one thermoplastic polyurethane which has at least one hard segment (B), at least one of the hard segments (B) carrying at least one anchor group L. In a preferred embodiment of the present invention, the binder 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 in the binder according to the invention is about 50 ± 5% by weight, the rest of which can consist of conventional polymers suitable for use in binders, for example polyurethanes. In addition to the thermoplastic polyurethanes mentioned, which carry an anchor group L in at least one hard segment (B), the binder 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 binders according to the invention contain at least one further binder in addition to the thermoplastic polyurethane or thermoplastic polyurethanes already mentioned.

In addition to the thermoplastic polyurethanes of the formula I / formula Ia or formula II or mixtures thereof, the binders according to the invention can also contain a further polymer or a mixture of two or more further polymers. The other polymers which can be used in the binder 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 acetopropionate 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 binders according to the invention generally contain the thermoplastic polyurethanes in an amount of up to about 100% by weight. Further binders can be present in the binder according to the invention in a proportion of up to about 90% by weight, for example up to about 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. 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, when mixtures of two or more polymers are used to prepare the dispersing or lamination binders. In this case, the ratio of hard segments with anchor groups to hard segments without anchor groups should be set so that the above-mentioned values are maintained.

In a preferred embodiment of the invention, polymers according to the invention suitable for use as dispersing binders have a glass transition temperature (T _g ) of approximately 55 to approximately 65 ° 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 the context of 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

Part of it. The usual oxidic pigments come as magnetic pigments

Pigments such as γ-Fe ₂ O ₃ , Fe ₃ O, FeO _x (l, 33 <x <l, 5), CrO ₂ , co-modified γ-Fe ₂ O ₃ ,

Co-modified Fe ₃ O, Co-modified FeO _x (1.33 <X <1.5), ferromagnetic metal pigments or metal alloy pigments, barium ferrite or strontium ferrite in

Consideration. The metal pigment or metal alloy pigment comprises a metal, such as e.g. Fe, Co, Ni or a combination of two or more of these metals as

Main component, and if necessary. other metal components such as AI, 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 binders according to the invention may also contain fillers, dispersing aids, further 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, that is to say 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 binders according to the invention can be applied, for example, to customary rigid or flexible carrier materials. Suitable carrier materials are, for example, films made 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. The invention therefore also relates to a shaped body, in particular a self-supporting shaped body, for example in film form or as a composite of a plurality of layers or film-shaped bodies, at least comprising a binder according to the invention or a binder produced by a method according to the invention.

The invention also relates to the use of a binder according to the invention or a binder 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 the end user area, e.g. B. Digital audio tape; Data storage tapes; disks; Floppy disk; ZIP disk; Magnetic stripe.

The invention is explained in more detail below by examples.

Examples

example 1

A polyurethane block consisting of 1 mol, ω-polypropylene glycol diamine sulfopropyl Na salt, 8 mol l, 3-bis (l-methyl-l-isocyanatoethyl) benzene (TMXDI, m-tetramethylxylylene diisocyanate), 6 mol neopentyl glycol and 2 mol ethanolamine is with 11.1 mol of a polyester diol with the molecular weight 802, consisting of adipic acid, isophthalic acid and 1,4-cyclohexanedimefhanol, and with 11.1 mol of 4,4'-diphenylmethane diisocyanate in tetrahydrofuran as a solvent with the addition of dibutyltin dilaurate as a catalyst at 60 ° C implemented until an NCO content of 0% is reached.

Production of the polyurethane block:

1952 g l, 3-bis- (l-methyl-l-isocyanatoethyl) benzene are dissolved in 7360 g tetrahydrofuran. With stirring

1439 g of a 40% strength solution of anhydrous α, ω-polypropylene glycol diamine sulfopropyl Na salt in tetrahydrofuran were quickly added.

After 10 minutes the stirring is stopped and after the white has stopped

Filtered precipitation. Become the filtrate

624 g of neopentyl glycol and

Given 1.7 g of dibutyltin dilaurate. With an NCO content of 0.74%

122.2 g of ethanolamine added.

Example 2

A polyurethane block consisting of 1 mole of α, ω-polypropylene glycol diamine sulfopropyl Na salt, 8 moles of l, 3-bis (l-methyl-l-isocyanatoethyl) benzene, 6 moles of neopentyl glycol and 2 moles of ethanolamine is mixed with 11.1 moles a polyester diol with molecular weight 802, consisting of adipic acid, isophthalic acid and 1,4-cyclo- hexanedimethanol, and with 11.655 mol of 4,4'-diphenylmethane diisocyanate in tetrahydrofuran as a solvent with the addition of dibutyltin dilaurate as a catalyst at 60 ° C. until a defined viscosity (1000 mPas (based on 40% strength solution)) is reached). The polyurethane block is produced analogously to example 1.

Manufacture of the binder:

To the polyurethane block described above

8903.2 g of polyester with the molecular weight of 802, consisting of adipic acid, isophthalic acid and 1,4-cyclohexanedimethanol, 2914.6 g of 4,4'-diphenylmethane diisocyanate and

14294.1 g of tetrahydrofuran were added and the mixture was stirred at 60 ° C. until the viscosity was 1000 mPas. The isocyanate still present at this point in time is destroyed by adding an equivalent amount of dibutylamine, thus interrupting the further reaction.

Example 3:

In a stirred ball mill, 2.07 kg of ceramic balls with a

Filled in diameter between 1.0 and 1.25 mm, 4553 g of a solvent mixture of tetrahydrofuran and methyl iso-butyl ketone consisting of 85 parts of tetrahydrofuran and 15 parts of methyl iso-butyl ketone, 650 g of a solution of the polymer according to the invention, 25% strength in tetrahydrofuran, 650g of a commercially available polyurethane, 25% in THF, 1400g of a ferromagnetic iron powder with a coercive field strength of 130 kA / m, 14g of a conductive carbon black, 127.4g of a spherical aluminum oxide and 25.4g of a mixture of fatty acids and fatty acid esters , The mixture was dispersed for 5 hours until the gloss point was constant at 125. After filtration through a filter with a pore size of 2 μm, a homogeneous, finely divided and settable dispersion was obtained. Immediately before coating, the dispersion was extracted with vigorous stirring with 0.012 part of a solution of a triisocyanate, based on 1 part of the dispersion 3 moles of tolylene diisocyanate and 1 mole of trimethylolpropane, 50% in tetrahydrofuran, were added.

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 pigment. After passing through the magnetic field, the coated film web was dried at 80 ° C. and smoothed by passing it between heated steel rolls with a roll temperature of 60 ° C. under pressure (line pressure 200 kg / cm).

Comparative example

The procedure was as described above, but the polymer according to the invention was replaced by a commercial binder having sulfonate anchor groups.

The dispersions produced according to the example are stable in storage, easy to process and the tapes produced in this way meet the requirements in every respect.

The dispersions prepared according to the comparative example have only a limited shelf life. The tapes have lower video levels due to the poorer surface and reproducibly show deposits on the video head.

Table 1

The measured values (Table 1) mean:

Gloss:

The reflection is measured at a 60 ° angle 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 pigment distribution is better, the higher the gloss value. The lowering of the gloss value with slight movement of the dispersion (roller board) indicates reagglomeration and thus storage instability of the dispersion.

RF level:

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

S / NfLuminanzI:

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. Abrasion on the video head:

The abrasion was assessed visually on a scale from 1 to 6 (very good to very bad).

Claims

claims

1. Polyurethane with at least one anionic anchor group L, the anchor group L being covalently bonded to a polyether segment having at least one nitrogen atom in the polyurethane.

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 soft segment (A) and at least one hard segment (B).

4. Polyurethane according to claim 3, characterized in that at least one hard segment (B) has at least one anionic anchor group L.

5. Polyurethane according to claim 3 or 4, characterized in that it has a structure according to the general formula I Y- (AB (L) _m -A-) _n Y (I) or the general formula Ia

Y- (AB (L) _ra -) _n Y (Ia) or the general formula II

Y- (AB (L) _r -AZ-) _n -AB (L) _m -AY (II), where A, B and L have the meaning given above, Z for the

The rest of a compound XZX which is at least functional with respect to Y to form a covalent bond, Y for a functional group which is reactive towards the functional groups X of the compound Z to form a covalent bond, X for at least one reactive with the functional groups Y to form a covalent bond functional group, n is a number from 1 to 10, m is a number from 1 to 10 and r is a number from 0 to 10, the number of anchor groups L in the entire polyurethane 1 to n * m (formulas I and Ia ) or 1 to n * r + m (formula II).

6. Polyurethane according to claim 5, characterized in that Y is OH, NH ₂ , NHR, 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.

7. Polyurethane according to one of claims 1 to 6, characterized in that the anchor group L is covalently connected to at least one nitrogen atom in the polyether segment.

8. binder, at least containing a thermoplastic polyurethane according to any one of claims 1 to 7.

9. Magnetic dispersion, at least containing a polyurethane according to one of claims 1 to 7 or a binder according to claim 8 and at least one magnetic or magnetizable pigment.

10. A process for the preparation of a polyurethane according to any one of claims 1 to 7, characterized in that at least one linear or branched polyetheramine bearing at least one covalently bonded anionic group L is used which is difunctional with respect to NCO groups.

11. Magnetic calibration medium, at least containing a polyurethane according to one of claims 1 to 7 or a binder according to claim 8 or one Magnetic dispersion according to claim 9 or a polyurethane produced according to claim 10.

12. Magnetic recording medium according to claim 11, characterized in that it is designed as an at least two-layer composite film.

13. Use of a polyurethane according to one of claims 1 to 7 or produced according to claim 10, or a binder according to claim 8, or a magnetic dispersion according to claim 9 for the production of magnetic recording media.

14. Use of a polyether having at least one nitrogen atom and at least one covalently bonded anionic group for the production of polyurethanes.

15. Use of a polyether having at least one nitrogen atom and at least one covalently bonded anionic group for the production of magnetic recording media.