EP1294797A1

EP1294797A1 - Magnetic or magnetisable bonding agent composition

Info

Publication number: EP1294797A1
Application number: EP01951586A
Authority: EP
Inventors: Benedikt Raether; Ulrike Hees
Original assignee: Emtec Magnetics GmbH
Current assignee: Emtec Magnetics GmbH
Priority date: 2000-06-16
Filing date: 2001-06-13
Publication date: 2003-03-26
Also published as: KR20030031497A; NO20026009D0; CN1436204A; WO2001096455A1; DE10029699A1; JP2004503641A; AU2001272472A1; NO20026009L

Abstract

The invention relates to a bonding agent composition containing at least one block copolymer which can be produced by means of radical polymerisation, at least two blocks of different monomer compositions, and at least one magnetic or magnetisable pigment. The invention also relates to a method for producing such a bonding agent composition and the use thereof.

Description

description

Magnetic or magnetizable binder composition

The invention relates to a binder composition, at least comprising a block copolymer which can be prepared by free-radical polymerization and having at least two blocks of different monomer compositions and at least one magnetic or magnetizable pigment, a process for the preparation of such a binder composition and the use thereof.

Binder compositions which contain a polymer or a mixture of two or more polymers as a binder and additionally at least one magnetic or magnetizable pigment dispersed in the binder composition are often used for the production of magnetic or magnetizable layers, for example for the production of magnetic paints, but in particular used for the production of magnetic recording media. Such magnetic recording media occupy a wide space in the context of the permanent storage of information, in particular data. The structure of such magnetic recording media usually has a non-magnetic carrier material and at least one magnetizable layer based on at least one polymeric binder and at least one magnetic or magnetizable pigment dispersed therein, which is adherently attached to this carrier material.

In the course of an ever increasing proportion of information processing and storage in daily life, there is a need for magnetic recording media which store the highest possible density of information in the smallest possible space and which can store and reproduce it as reliably and permanently as possible, i.e. over a long period of time , In particular, the quality of the recording and the reproduction as well as the aging resistance of such magnetic recording media are therefore high demands. The fulfillment of the requirements mentioned, however, depends to a large extent on the nature of the polymeric binder in the magnetic recording medium. In particular, the ability of the binder to stably disperse the magnetic or magnetizable pigments dispersed therein is of great importance. In order to meet the above requirements, the aim is to increase the stability of dispersions of magnetic pigments in polymeric binders and, for example to improve the magnetic properties, in particular the remanence, to increase the packing density of the magnetic pigments in the magnetic layer.

As a rule, the increase in the pigment content is accompanied by a decrease in the binder content in the magnetic layer. However, the measures listed above actually make it more difficult to divide the pigments in the course of the dispersion process. In addition, losses in dispersion stability can usually be found. The flexibility and elasticity required for magnetic recording media, as well as a corresponding tensile strength of the magnetic layer, are generally impaired by a reduction in the proportion of binder.

In addition, corresponding magnetic recording media, in particular when they are in direct contact with mechanical devices for reading the data or information stored on the recording media, must have the lowest possible friction values and high abrasion and wear resistance. The mechanical properties mentioned should also be guaranteed in extreme climatic conditions, for example at high temperature and high air humidity. However, many binders known to date from the prior art are unable to meet these requirements. In many cases, the wetting and dispersion of the pigments, particularly in the case of very finely divided magnetic pigments, is adversely affected. Any sintering in the dispersing process is not broken up sufficiently or a re-agglomeration of the pigment particles not sufficiently prevented. This can lead to poor magnetic values of the recording medium.

In order to avoid the disadvantages described above, small-molecular dispersants have often been added to the dispersion in small amounts in order to facilitate the dispersing process. However, such low molecular weight dispersants have disadvantages. For example, they can sweat easily in unfavorable climatic conditions such as high air humidity and temperature, that is, they can come to the surface of the magnetic recording medium, which leads to deposits on all tape-carrying parts, but especially on the magnetic head, in recording and playback devices. In addition, such deposits increase friction, which can block the magnetic recording medium when it is passed through a reader or writer.

Another problem arises with polymeric binders which disperse a magnetic or magnetizable pigment, with regard to compatibility problems between the binder or a binder mixture and the magnetic or magnetizable pigment dispersed therein. Since such pigments generally have a hydrophilic surface, the compatibility of the binders can be improved, for example, by introducing hydrophilic structural elements into the binder. However, this can lead to the hydrophilicity of the magnetic recording layer increasing to such an extent that the magnetic layer swells when exposed to moisture, in particular moisture associated with high temperature, as a result of which the magnetic layer can swell and exudate certain low-molecular constituents.

In the past, polycondensates or polyaddition products have mainly been used as polymers for binders which can disperse a magnetic or magnetizable pigment. Again and again attempts have been started to use free-radically polymerized binders, which are then in shape statistical copolymers were used.

The use of polyaddition or polycondensation products essentially allows the chemical and physical properties of the binder used to be influenced, since polyaddition or polycondensation reactions, if the reaction is carried out appropriately, enable block-wise construction of a corresponding binder. However, the disadvantage of such binders is the fact that with increasing control over the material properties, a higher, usually multi-stage, synthesis effort has to be carried out. In particular in the case of polyaddition products, which are frequently prepared by reacting isocyanates with corresponding compounds which are reactive toward isocyanates, the handling of the toxic isocyanates should be mentioned as a disadvantage. Furthermore, such polymers generally have a high polydispersity that is difficult to control.

In contrast, the production of statistical copolymers by radical polymerization represents a significant simplification of the process. However, the resulting products are difficult to control in their physical or chemical properties, and it is generally not possible to set such properties in a targeted manner.

For example, US Pat. No. 5,695,884 describes a thermoplastic polyurethane which has at least one sulfonate group. The sulfonate group is introduced into the polyurethane via a polyester polyol containing sulfonate groups, which in turn contains the sulfonate group as a sulfophthalic acid derivative. The disadvantage of this procedure is the high number of reaction stages that are required to arrive at the final polymeric binder.

DE-A 40 39 749 relates to a branched polyurethane with urea groups at the chain ends free of OH groups and a molecular weight between 30,000 and 200,000. However, the binder described has none Block structure, is difficult to control in its properties and also requires a not inconsiderable amount of synthesis.

The known processes for the radical production of polymers therefore do not allow a sufficiently targeted adjustment of the degree of polymerization, block length distribution, polydispersity and block structure. This means that valuable properties such as dispersing effect, flow behavior or mechanical strength cannot be set at all or only incompletely. The known binders which can be prepared by free-radical polymerization therefore either require the additional use of low-molecular-weight dispersants, the negative properties already mentioned above being useful, or the incorporation of monomers with functional groups which act as ionic or other polar anchor groups and with the pigment surface can interact. However, this is not a satisfactory solution to the problem mentioned above. On the one hand, the incorporation of such monomers which have a polar group can only be controlled incompletely in the known binders which can be prepared by free-radical polymerization, and on the other hand are monomers with anchor groups which have a desired Adjustment of the interaction of the binder with the pigment surface enable, often difficult to access.

There has therefore been a need for binder compositions which do not have the above-mentioned disadvantages of the prior art. It is therefore an object of the present invention to provide binder compositions which have binders which are easy to produce by free-radical polymerization, but which have an excellent dispersing action, excellent physical and mechanical properties and a suitable long-term behavior. The object of the invention was achieved by a binder composition which contains at least one block copolymer which can be prepared by free-radical polymerization and a magnetic or magnetizable pigment. The present invention therefore relates to a binder composition comprising at least one block copolymer which can be prepared by free-radical polymerization and has at least two blocks of different monomer compositions and at least one magnetic or magnetizable pigment.

In the context of the present invention, a “binder composition” is understood to mean a mixture which contains at least one block copolymer which can be prepared by free-radical polymerization and which has at least two blocks of different monomer compositions, and additionally at least one magnetic or magnetizable pigment.

In the context of the present invention, a “block copolymer” is understood to mean a polymer which has at least two polymer blocks characterized by a different monomer composition. In the context of the present invention, a “different monomer composition” means the finding that at least two regions of the block copolymer have at least two blocks with a different monomer composition. It is possible within the scope of the present invention that the transition between two blocks runs continuously, that is to say that between two blocks there is a zone which has a statistical or regular sequence of the monomers constituting the blocks. However, it is also provided in the context of the present invention that the transition between two blocks is essentially discontinuous. An “essentially discontinuous transition” is understood to mean a transition zone which has a significantly shorter length than at least one of the blocks separated by the transition zone. In a preferred embodiment of the present invention, the chain length of such a transition zone is less than 1/10, preferably less than 1/20, of the block length of at least one of the blocks separated by the transition zone.

Under a "different monomer composition" is in the frame The present invention understood the finding that the monomers constituting the respective block differ in at least one feature, for example in their interlinking, in their conformation or constitution. In the context of the present invention, block copolymers are preferably used which have at least two blocks whose monomer composition differs at least through the constitution of the monomers.

In a preferred embodiment, the block copolymers which can be used in the present invention have a polydispersity of less than about 5, for example less than about 4 or less than about 3.

The molecular weight of the block copolymers which can be used in the context of the present invention is generally at least about 1,000, but preferably higher, for example 2,000, 4,000, 8,000 or 10,000. Depending on the desired mechanical properties of the products which can be produced with the aid of the binder composition according to the invention, block copolymers which have a molecular weight of more than 20,000, for example more than 40,000, more than 60,000 or more than 80,000, can be used in the context of the present invention. It may be advantageous to use block copolymers whose molecular weight exceeds 100,000.

In the context of the present text, the “molecular weight” is understood to mean the value for M _w as can be obtained from GPC under the following conditions: eluent: THF, standard: polystyrene, Waters system, UV detector: Waters 410, RI detector : Waters 481, pump: 510; Columns: cross-linked polystyrene (measuring range: 500 - 100,000 g / mol) from PSS (Mainz).

The block copolymers which can be used in the binder compositions according to the present invention are produced by free radicals

Polymerization. A method for producing the in the invention Depending on the desired number of blocks, block copolymers which can be used in binder compositions run at least in two stages. Depending on the desired number of blocks, however, more stages can be run through. If, for example, a block copolymer with four blocks is to be produced, four steps are usually required to produce a corresponding polymer. The same applies to higher or lower number of blocks. The number of stages required is generally identical to the number of blocks obtained in the block copolymer. The block copolymer preferably has two to six blocks. '

In the context of a preferred embodiment of the invention, the block copolymer is produced by a process comprising at least the following steps (i) and (ii):

(i) reaction under free-radical conditions of a reaction mixture comprising at least one free-radically polymerizable monomer (a), at least one free-radical initiator, and a compound of the formula (I)

wherein Rj to R ₄ each independently represent hydrogen, an unsubstituted or substituted alkyl radical, cycloalkyl radical, aralkyl radical, an unsubstituted or a substituted aromatic hydrocarbon radical, with the proviso that at least two of the radicals Rj. to ι are unsubstituted or substituted aromatic hydrocarbon radical, or the radicals Ri and R ₂ or R ₃ and R each stand in pairs for a substituted or unsubstituted aromatic hydrocarbon with 6 to 18 C atoms and a functional group which, in conjugation to the CC double bond in the general formula (I), has a multiple bond between a C atom and a hetero atom, being a

Reaction product (A) is obtained and

(ii) reaction of the reaction product (A) obtained in step (i) under free radical conditions with at least one free-radically homo- or copolymerizable monomer (b), a reaction product (B) being obtained.

In step (i) of the process described above, all radically convertible monomers can be used as monomer (a).

For example, compounds (a) which are free-radically homo- or copolymerizable and which have a hydrophilic group, e.g. include a carboxyl group, sulfonic acid group or phosphoric acid group. In this case, the monomers (a) are hydrophilic, free-radically homo- or copolymerizable monomers, i.e. monomers whose solubility in water is higher than that of styrene.

Mixtures of various hydrophilic monomers can of course also be used as monomers (a) in the context of the present invention.

Within the scope of a further embodiment of the present invention, however, it is also possible to use monomers which can be polymerized by free radicals and which have a water solubility which corresponds to or is even lower than that of styrene.

Mixtures can also be used in accordance with the above-mentioned process polymerize from at least one hydrophilic monomer and at least one hydrophobic monomer. The following are specifically mentioned as monomers (a):

Ci to C ₂ o-alkyl and hydroxy alkyl esters of monoethylenically unsaturated C ₃ to C] _. o-Monocarboxylic acids or C - to C ₈ -dicarboxylic acids, for example methyl methacrylate, ethyl methacrylate, propyl methacrylate (all isomers), butyl methacrylate (all isomers), 2-ethylhexyl methacrylate, isobornyl methacrylate, methyl acrylate, ethyl acrylate, propyl acrylate (all isomers), all Isomers), 2-ethyl-hexyl acrylate, isobornyl acrylate, benzyl acrylate, phenyl acrylate, stearyl acrylate, maleic acid diethyl ester, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, and furthermore (meth) acrylic esters from alkoxylated ci to C 2 to ₈ -alkylene with alkali Ethylene oxide, propylene oxide, butylene oxide or mixtures thereof are reacted; Benzyl methacrylate, phenyl methacrylate, stearyl methacrylate, methacrylonitrile, styrene, α-methylstyrene, acrylonitrile, functionalized methacrylates; Acrylates and styrenes, selected from glycidyl methacrylate, 2-hydroxyethyl methacrylate, hydroxypropyl methacrylate (all isomers), hydroxybutyl methacrylate (all isomers), cyclohexyl methacrylate, cyclohexyl acrylate, hexyl methacrylate and hexyl acrylate (all isomers), diethylaminoethyl methacrylate methacrylate, triethyl methacrylate, triethyl acrylate methacrylate, triethyl methacrylate, , 2-hydroxyethyl methacrylate, diethylammoethyl acrylate, triethylene glycol acrylate, methacrylamide, N-tert-butyl methacrylamide, Nn-butyl methacrylamide, N-methylol-meth-acrylamide, N-ethylol methacrylamide, N-tert-butylacrylamide, N-butylacrylamide, N- Methylolacrylamide, N-ethylolacrylamide, vinylbenzoic acid (all isomers), diethylaminostyrene (all isomers), α-methylvinylbenzoic acid (all isomers), diethylamino-α-methylstyrene (all isomers), p-methylstyrene, p-vinylbenzenesulfonic acid, trimethoxysilylpropyl methacrylate, Triethoxysilylpropyl methacrylate, tributoxysilylpropyl methacrylate, diethoxymethylsilylpropylme thacrylate, dibutoxymethylsilyl propyl methacrylate, diisopropoxymethyl silyl propyl methacrylate, dimethoxysilyl propyl methacrylate, diethoxysilyl propyl methacrylate, dibutoxysilyl propyl methacrylate, diisopropoxysilyl propyl methacrylate, trimethoxysilyl Diethoxymethylsilylpropylacrylat, Dibutoxymethylsilylpropylacrylat, Diisopropoxy- methylsilylpropylacrylat, Dimethoxysilylpropylacrylat, butyrate Diethoxysilylpropylacrylat, Dibutoxysilylpropylacrylat, Diisopropoxysilylpropylacrylat, vinyl acetate and vinyl chloride, vinyl chloride, vinyl fluoride, vinyl bromide, vinyl alcohol, vinyl ethers of d- to C ₁₈ alcohols, vinyl ethers of alkoxylated Ci- to C ₁₈ alcohols and vinyl ethers of polyalkylene oxides such as polyethylene oxide, polypropylene oxide or polybutylene oxide, monoethylenically unsaturated C ₃ - to Cio-monocarboxylic acids, their alkali metal salts and / or ammonium salts, for example acrylic acid, methacrylic acid, dimethylacrylic acid, ethyl acrylic acid, allyl acetic acid or vinyl _4- acetic acid unsaturated mono Cs-dicarboxylic acids, their half esters, anhydrides, alkali metal salts and / or ammonium salts, for example maleic acid, fumaric acid, itaconic acid, mesaconic acid, methylene malonic acid, citraconic acid, maleic acid ydrid, itaconic anhydride or methylmalonic anhydride; further sulfonic acid groups or their salts, for example their monoethylenically unsaturated monomers containing alkali metal or ammonium salts, for example allylsulfonic acid, styrenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid (AMPS), methallylsulfonic acid, vinylsulfonic acid, 3-sulfopropyl acrylate or methacrylic acid sulfopropyl ester, furthermore phosphonic acid groups or their salts, for example their monoethylenically unsaturated monomers containing alkali metal or ammonium salts, for example vinylphosphonic acid, allylphosphonic acid or acrylamidoethyl propanephosphonic acid, furthermore amides and N-substituted amides of monoethylenically unsaturated C ₃ to C 10 -monocarboxylic acids or C - To Cs-dicarboxylic acids, for example acrylamide, N-alkyl acrylamides or N, N-dialkyl acrylamides each having 1 to 18 C atoms in the alkyl group such as N-methyl acrylamide, N, N-dimethylacrylamide, N-tert-butylacrylamide or N-octadecyl acrylamide, Mal monomethylhexylamide, maleic acid monodecylamide, diethylaminopropylmethacrylamide or acrylamidoglycolic acid; furthermore alkylamidoalkyl (meth) acrylates, for example dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, ethylaminoethyl acrylate, diethylaminoethyl methacrylate, dimethylaminopropyl acrylate or dimethylaminopropyl methacrylate; Farther Vinyl esters, vinyl formate, vinyl acetate or vinyl propionate, which may also be saponified after the polymerization; furthermore N-vinyl compounds, for example N-vinylpyrrolidone, N-vinylcaprolactam, N-vinylformamide, N-vinyl-N-methylformamide, 1-vinylimidazole or 1-vinyl-2-methylimidazole; furthermore vinyl ethers of Ci to -C ₈ alcohols, vinyl ethers of alkoxylated C to Cis alcohols and vinyl ethers of polyalkylene oxides such as polyethylene oxide, polypropylene oxide or polybutylene oxide, styrene or its derivatives such as α-methylstyrene, indene, dicyclopentadiene, monomers, the amino or imino groups such as dimethylaminoethyl methacrylate, diethylaminoethyl acrylate, diethylaminopropyl methacrylamide or allylamine, monomers which carry quaternary ammonium groups, such as, for example, as salts, as are obtained by reacting the basic amino functions with acids such as hydrochloric acid, sulfuric acid, nitric acid, formic acid or acetic acid or in acetic acid quaternized form (examples of suitable quaternizing agents are dimethyl sulfate, diethyl sulfate, methyl chloride, ethyl chloride or benzyl chloride), such as dimethylaminoethyl acrylate hydrochloride, diallyldimethylammonium chloride, dimethylaminoethyl acrylate methyl chloride, dimethylaminoethylaminopropyl methacrylamide methosulfate , Vinylpyridiπiumsalze or 1-Vinylimidazoliumsalze; Monomers in which the amino groups and / or ammonium groups are only released after the polymerization and subsequent hydrolysis, such as, for example, N-vinylformamide or N-vinylacetamide and mixtures of two or more of the above-mentioned monomers.

In a preferred embodiment, the first monomer (a) is styrene or one or more of the above-mentioned styrene derivatives, acrylic or methacrylic acid, a C 1 -C 4 -alkyl or -hydroxyalkyl acrylate or -methacrylate, vinyl acetate, one of the above-mentioned vinyl ethers or a mixture of two or more thereof, a substituted or unsubstituted N-vinylpyrrolidone, a mixture of two or more thereof, or a mixture of this first monomer (a) with at least one further radically homo- or copolymerizable monomer (a). According to the invention, a compound of the formula (I) is used in the preparation of the reaction product (A)

used, wherein Ri to R _{4 have} the meaning given above. In the context of the present invention, a “heteroatom” is understood to mean an atom other than carbon which is capable of forming multiple bonds (double or triple bonds) with a carbon atom.

In a preferred embodiment of the invention, 1,1-diphenylethene, 1,1-dinaphthylethene, 4,4'-vinylidene-bis (N, N'-dimethylaniline), 4,4'- Vinylidenbis (aminobenzene), cis-stilbene, trans-stilbene, methyl α-phenylacrylate, methyl α-phenylmethacrylate, α-phenylacrylonitrile, α-phenylmethacrylonitrile or a mixture of two or more thereof. In a further preferred embodiment of the invention, 1,1-diphenylethene is used as the compound of the general formula (I).

Also suitable as a compound of the general formula (I) are substituted diphenylethenes which are either on one or both aromatic hydrocarbon radicals with electron-withdrawing or electron-donating substituents, e.g. tert-butyl, benzyl or CN groups are substituted, or an alkoxydiphenylethene such as e.g. Methoxy, ethoxy or tert-butyloxydiphenylethene, and the analogous thio or amino compounds, can be used.

Step (i) of the above process is carried out in the presence of at least one free radical initiator. The initiator should preferably be soluble in the solvent used or at least in the monomers used for the polymerization. In general, however, everyone can Radical chain polymerization conventionally used azo and / or peroxo compounds can be used.

Suitable initiators are described, for example, in WO 98/01478 on p. 10, lines 17-34, which in this regard are included in full in the context of the present application.

In a preferred embodiment for stage (i) of the above-mentioned process, a comparatively large amount of free-radical initiator is added, the proportion of free-radical initiator in the reaction mixture preferably being 0.5 to 50% by weight, more preferably 1 to 20 % By weight, based in each case on the total amount of the monomer (a) and the initiator, is. The ratio of initiator to compound of the general formula (I) is preferably 3: 1 to 1: 3, more preferably 2: 1 to 1: 2, and in particular 1.5: 1 to 1: 1.5.

The step (i) reaction described above can be carried out in an aqueous environment or substantially anhydrous in the preparation of the binder composition of the present invention.

If the reaction described in stage (i) is carried out in the aqueous phase, the term “aqueous phase” in the context of the present text is understood to mean a phase which contains 10 to 100% by weight of water. If the water content of the aqueous phase is less than 10%, it is preferred in the context of the present invention if the aqueous phase is a mixture of water and one or more water-miscible solvents such as THF, methanol, ethanol, propanol, butanol, acetone, methyl Contains ethyl ketone or the like. However, it is also possible to carry out the reaction in step (i) in the presence of a mixture of water and a water-immiscible solvent, such as an aromatic solvent, for example toluene.

The above reaction in step (i) can be carried out, for example, in the presence of a base be performed. As a result, organic or inorganic, preferably low molecular weight bases can be used. Examples of suitable bases are NaOH, KOH, ammonia, diethanolamine, mono-, di- or triethylamine, dimethylethanolamine or a mixture of two or more thereof. Good results can be achieved, for example, with ammonia, di- or triethylamine or a mixture of two or more of them.

However, it is also possible to carry out the reaction according to stage (i) in an organic solvent or solvent-free (“in bulk”), for example in the melt,

10 perform. If, in the context of the present invention, one speaks of a reaction regime in an organic solvent or solvent-free, this is understood to mean a reaction regime which in the presence of less than 10% by weight, preferably less than 5% by weight or less than 1 wt .-% water runs off. In a further embodiment of the present invention

15, at least one block copolymer is used in the binder composition according to the invention, in the preparation of which step (i) was carried out in an organic solvent or solvent-free, the water content of the reaction mixture being less than 0.5% by weight, for example less than 0.3% by weight % or less than 0.1% by weight. In a further embodiment of the

In the present invention, the reaction of stage (i) is carried out anhydrous, that is to say with a water content of less than 0.001% by weight. Such water contents can be achieved, for example, by using commercially available solvents, as are usually used as organic solvents in radical polymerizations.

25

Suitable solvents in the context of the present invention are in principle all polar and non-polar organic solvents in which the corresponding and preferably also the resulting polymers are soluble, if appropriate at elevated temperature. Suitable solvents are, for example, C ₃ - to Cio-

30. alkanes, cyclohexane, decalin, acetone, methyl ethyl ketone, diisobutyl ketone, tetrahydrofuran, dioxane, benzene, toluene, glycols such as ethylene glycol, triethylene glycol, partially or completely end group-capped glycol ethers such as ethylene glycol monomethyl ether, ethyl acetate, methanol or ethanol or the higher homologues of the alkanols with up to 18 C atoms (optionally as cosolvent) or mixtures of two or more thereof.

The reaction in stage (i) is generally carried out at temperatures above room temperature and below the decomposition temperature of the monomers, a temperature range from 50 to 150 ° C., more preferably 70 to 120 ° C. and in particular 80 to 110 ° C. being chosen.

The reaction in step (i) is generally carried out at pressures from 1 to 300 bar, for example from about 1.5 to 100 or about 2 to about 20 bar.

Although there are no restrictions with regard to the molecular weight distribution, a reaction product can be obtained in the reaction according to (i) which has a molecular weight distribution M _w / M _n measured using gel permeation chromatography using polystyrene as standard of = 4, preferably = 3 , more preferably = 2, in particular = 1.5 and in some cases also = 1.3. The molecular weights of the reaction product (A) can be controlled within wide limits by the choice of the ratios of monomers (a) to compounds (I) to radical initiator. The content of compound (I) in particular determines the molecular weight in such a way that the greater the proportion of compound (I), the lower the molecular weight obtained.

The reaction product obtained in the reaction according to step (i) is, for example, directly processed further to produce the block copolymers contained in the binder composition according to the invention. However, it is also possible within the scope of the present invention to temporarily store the reaction product according to stage (i) first and to process it only at a later point in time. During further processing, the reaction product according to stage (i) serves as a macroinitiator for a further implementation, as is defined below as stage (ii). In the following stage (ii), the reaction product of stage (i) is reacted with a further free-radically homo- or copolymerizable monomer or a mixture of two or more such monomers. In such a reaction according to stage (ii), the reaction product of stage (i) is accordingly reacted with at least one freely selectable, radically homo- or copolymerizable monomer (b) which differs in at least one of the properties already defined above from that in stage (i) used monomers (a) differs. If a mixture of two or more monomers has already been used in the reaction according to stage (i), a further monomer (b) can be used in stage (ii), but it is equally possible to use a mixture of two or more monomers (b). The only decisive factor in this connection is that the monomers which were used in stage (i) differ from the monomers which are used in stage (ii) in that the block obtained in the course of the reaction in stage (i) differs from the block obtained in step (ii) in at least one of the properties mentioned above.

In principle, the monomers already mentioned in the context of the explanation of the monomers (a) are suitable as monomers (b).

The reaction in stage (ii) is in principle carried out under the usual conditions for free-radical polymerization, it being possible for the reaction in stage (i) to be carried out in the aqueous phase, in a solvent or without solvent.

Steps (i) and (ii) can be carried out separately from one another both spatially and temporally in the context of the method described, step (i) and then step (ii) being carried out first. Steps (i) and (ii) can also be carried out in succession in only one reaction vessel, ie at least one monomer (a) is first used in the presence of a compound of the general formula (I) depending on the desired Application or the desired properties partially or completely free-radically polymerized and then at least one monomer (b) added and also free-radically polymerized.

However, it is also possible in the context of the present invention that a monomer mixture comprising at least one monomer (a) and at least one monomer (b) is used from the start and is reacted in the presence of the compound (I).

It is assumed that the compound (I) first reacts with the at least one monomer (a) and then the reaction product (A) formed therefrom also reacts with the monomer (b) above a certain molecular weight.

Depending on how the reaction is carried out, it is possible according to the invention to produce functionalized polymers, block or multiblock and gradient copolymers, star-shaped polymers, graft copolymers and branched copolymers on the end groups.

It is also provided that the polymer (B) obtained in stage (ii) is reacted with a further monomer (c) in a further reaction stage (iii), the monomer (c) likewise being selected, for example, from the list already mentioned above can be. The implementation takes place as already described for stages (i) and (ii). The process according to the invention can accordingly be carried out with an arbitrary number of stages with a corresponding arbitrary number of monomers, essentially limited only by the reaction conditions and the material properties of the resulting polymer.

Depending on the desired number of blocks in the block copolymer, the binder Polymers to be used in the composition, the reaction product from stage (ii), the polymer (B), are reacted in a further reaction stage (iii) with a further monomer (c) or a mixture of two or more further monomers (c). The monomer (c) or the mixture of two or more monomers (c) can be selected, for example, from the list of the monomers (a) already mentioned above. Implementation takes place as already described for stages (i) and (ii). This reaction procedure makes it possible to produce a block copolymer with an essentially arbitrarily high number of blocks, for example 5, 10, 20, 50 or 100 blocks.

In this context, it is irrelevant whether all blocks have different monomer compositions, or whether a block sequence is formed in which two or more different monomers are composed in a specific order or are statistically repeated. The only decisive factor is that at least two of the blocks have a different monomer composition as defined above.

The process for producing a block copolymer, as used in a binder composition according to the invention, can therefore be carried out in one step

(iii) the reaction product (B) obtained in step (ii) under radical

Conditions are reacted in the presence of at least one, radically homo- or copolymerizable monomer (c), these

If necessary, the reaction is repeated several times in succession with the same or different monomers (c).

It is possible in a simple manner using a readily accessible compound of the general formula (I) to provide block copolymers which have, for example, an anchor group block, such as one based on (meth) acrylic acid, allylsulfonic acid, styrene sulfonic acid, 2-acrylamido-2 -methylpropanesulfonic acid (AMPS), methallylsulfonic acid, vinyl sulfonic acid, acrylic acid-3- sulfopropyl ester or 3-sulfopropyl methacrylic acid-based block, the block having at least a length of 1 monomer unit, and a further, preferably hydrophobic polymer block, such as a block based on vinyl aromatic monomers, such as styrene or substituted styrenes, and have non-aromatic vinyl compounds, such as vinyl acetate, and higher (> C ₄ ) alkyl (meth) acrylates. According to the described method, however, it is also possible, using a compound of the general formula (I), to provide block copolymers which have a hydrophobic and subsequently an anchor group block.

In the context of the present invention, an anchor group block is understood to mean a block which interacts attractively with the surface of a pigment.

Furthermore, it has been shown that monomers which have an electron-rich olefinically unsaturated double bond can also be radically homo- or copolymerized by the process described. Examples of such compounds are the vinyl ethers, vinyl esters, for example vinyl acetate, or the N-vinyl compounds, as have already been mentioned above.

In the context of the process mentioned, the monomers can be copolymerized essentially in any order without, for example, a particular sequence of hydrophilic and hydrophobic monomers having to be observed.

Polymers of the following structure can also be prepared, for example, which can be used in the binder compositions according to the invention: poly ((meth) acrylic acid stat (meth) acrylate b (styrene stat (meth) acrylate)), the term " (meth) acrylate ", alkyl esters of methacrylic acid and acrylic acid.

The following block copolymers should be mentioned: Poly (styrene-b-acrylic acid), poly (styrene-b-acrylic acid methyl ester), poly (styrene-b-acrylic acid methyl ester), poly (styrene-b-methacrylic acid), poly (styrene-b-methacrylic acid methyl ester), poly (styrene -b-methacrylic acid ethyl ester), poly (hydroxyethyl acrylate-b-methacrylic acid), poly (N-vinylpyrrolidone-b-acrylic acid methyl ester), poly (N-vinylpyrrolidone-b-acrylic acid ethyl ester), poly (N-vinylpyrrolidone-b-methacrylic acid methyl ester) ), Poly (N-vinylpyrrolidone-b-methacrylic acid ethyl ester),

Poly (N-vinylpyrrolidone-b-styrene), poly (N-vinylpyrrolidone-b-vinyl acetate), poly (N-vinylpyrrolidone-b-α-methylstyrene), poly (N-vinylformamide-b-methacrylic acid methyl ester), poly ( N-vinylformamide-b-methacrylic acid ethyl ester), poly (N-vinylformamide-b-vinyl acetate), poly (N-vinylformamide-b-acrylic acid methyl ester) or poly (N-vinylformamide-b-acrylic acid ethyl ester).

The following can also be used according to the present invention:

Poly (methacrylic acid methyl ester-b- (styrene-stat-acrylonitrile)), poly (n-butyl acrylate-b-styrene-bn-butyl acrylate), poly (styrene-bn-butyl acrylate-b-styrene), poly (styrene-bn-butyl acrylate) -b-styrene-bn-butyl acrylate), poly (methyl methacrylate-b-styrene-b-methyl-methacrylate-b-styrene), poly (n-butyl acrylate-b-styrene-bn-butyl acrylate-b-styrene) and like.

Also suitable are: poly ((styrene-s-styrenesulfonic acid sodium salt) -b-methyl methacrylate), poly ((styrene-s-styrenesulfonic acid sodium salt) -b-propyl methacrylate), poly ((styrene-s-styrenesulfonic acid sodium salt) ) -b-butyl methacrylate), poly ((styrene-s-styrenesulfonic acid sodium salt) -b-ethyl methacrylate), poly ((styrene-s-styrenesulfonic acid sodium salt) -b-propyl acrylate), poly ((styrene-s- styrenesulfonic acid sodium salt) -b-methyl acrylate), poly ((styrene-s-styrenesulfonic acid sodium salt) -b-butyl acrylate), poly ((styrene-s-styrenesulfonic acid sodium salt) -b-ethyl acrylate), poly ( (styrene-s-acrylamido-2-methylpropanesulfonic acid sodium salt) -b-methyl methacrylate), poly ((styrene-s-acrylamido-2-methylpropanesulfonic acid sodium salt) -b-propyl methacrylate), poly ((styrene-s-acrylamido) -2-methylpropanesulfonic acid sodium salt) - b-butyl methacrylate), poly ((styrene-s-acrylamido-2-methylpropanesulfonic acid) Sodium salt) -b-ethyl methacrylate), poly ((styrene-s-acrylamido-2-methylpropanesulfonic acid sodium salt) -b-propyl acrylate), poly ((styrene-s-acrylamido-2-methylpropanesulfonic acid sodium salt) -b -methyl acrylate), poly ((styrene-s-acrylamido-2-methylpropanesulfonic acid sodium salt) -b-butyl acrylate), poly ((styrene-s-acrylamido-2-methylpropanesulfonic acid sodium salt) -b-ethyl acrylate), poly ((styrene -s-acrylonitrile -s-acrylamido-2-methylpropanesulfonic acid sodium salt) -b-styrene); Poly ((styrene-s-styrenesulfonic acid sodium salt) -b-styrene), poly ((styrene-s-acrylonitrile-s-styrenesulfonic acid sodium salt) -b-styrene), poly ((styrene-s-acrylamido-2 -methylpropanesulfonic acid sodium salt) -b-styrene), poly ((styrene-s-acrylonitrile-s-acrylamido-2-methylpropanesulfonic acid sodium salt) -b-methyl methacrylate); Poly ((styrene-s-styrenesulfonic acid sodium salt) -b-methyl methacrylate), poly ((styrene-s-acrylonitrile-s-styrenesulfonic acid sodium salt) -b-methyl methacrylate), poly ((styrene-s-acrylamido) -2-methylpropanesulfonic acid sodium salt) -b-methyl methacrylate), poly ((styrene-s-acrylonitrile-s-acrylamido-2-methylpropanesulfonic acid sodium salt) -b-ethyl methacrylate); Poly ((styrene-s-styrenesulfonic acid sodium salt) -b-ethyl methacrylate), poly ((styrene-s-acrylonitrile-s-styrenesulfonic acid sodium salt) -b-ethyl methacrylate), poly ((styrene-s-acrylamido-2-methylpropanesulfonic acid) -Sodium salt) -b-ethyl methacrylate), poly ((styrene-s-acrylonitrile-s-acrylamido-2-methylpropanesulfonic acid sodium salt) -b-propyl methacrylate); Poly ((styrene-s-styrenesulfonic acid sodium salt) -b-propyl methacrylate), poly ((styrene-s-acrylonitrile-s-styrenesulfonic acid sodium salt) -b-propyl methacrylate), poly ((styrene-s-acrylamido) -2-methylpropanesulfonic acid sodium salt) -b-propyl methacrylate), poly ((styrene-s-acrylonitrile-s-acrylamido-2-methylpropanesulfonic acid sodium salt) -b-butyl methacrylate); Poly ((styrene-s-styrenesulfonic acid sodium salt) -b-butyl methacrylate), poly ((styrene-s-acrylonitrile-s-styrenesulfonic acid sodium salt) -b-butyl methacrylate), poly ((styrene-s-acrylamido -2-methylpropanesulfonic acid sodium salt) -b-butyl methacrylate), poly ((styrene-s-acrylonitrile-s-acrylamido-2-methyl-propanesulfonic acid sodium salt) -b-methyl acrylate); Poly ((styrene-s-styrenesulfonic acid- sodium salt) -b-methyl acrylate), poly ((styrene-s-acrylonitrile-s-styrenesulfonic acid-

Sodium salt) -b-methyl acrylate), poly ((styrene-s-acrylamido-2-methylpropanesulfonic acid sodium salt) -b-methyl acrylate), poly ((styrene-s-acrylonitrile-s-acrylamido-2-methylpropanesulfonic acid sodium salt) b-ethyl acrylate); Poly ((styrene-s-styrenesulfonic acid sodium salt) -b-ethyl acrylate), poly ((styrene-s-acrylonitrile-s-styrenesulfonic acid-sodium salt) -b-ethyl acrylate), poly ((styrene-s-acrylamido-2-methylpropanesulfonic acid sodium salt) -b -ethyl acrylate), poly ((styrene-s-acrylonitrile-s-acrylamido-2-methylpropanesulfonic acid sodium salt) -b-propyl acrylate); Poly ((styrene-s-styrene-sulfonic acid sodium salt) -b-propyl acrylate), poly ((styrene-s-acrylonitrile-s-styrenesulfonic acid sodium salt) -b-propyl acrylate), poly ((styrene-s-acrylamido) -2-methylρro-pansulfonic acid sodium salt) -b-propyl acrylate), poly ((styrene-s-acrylonitrile-s-acrylamido-2-methylpropanesulfonic acid sodium salt) -b-butyl acrylate); Poly ((styrene-s-styrenesulfonic acid sodium salt) -b-butyl acrylate), poly ((styrene-s-acrylonitrile-s-styrene-sulfonic acid sodium salt) -b-butyl acrylate) and poly ((styrene-s-acrylamido-2 -methyl-propanesulfonic acid sodium salt) -b-butyl acrylate).

In addition to the structures listed, the block copolymers according to the invention can also have hydroxyethyl methacrylate and / or hydroxyethyl acrylate units in one or more blocks, the proportion of the monomer units mentioned per block not exceeding 20 mol%.

A binder composition according to the invention can, for example, have only one of the above-mentioned block copolymers. However, it is also provided in the context of the present invention that a binder composition according to the invention has two or more of the block copolymers mentioned.

To prepare the binder composition, the block copolymer can be used directly as a polymer dispersion (aqueous dispersion), or the block copolymers obtained are dried and dissolved in a suitable solvent or solvent mixture and also used to prepare the binder composition according to the invention.

In addition to the block copolymers mentioned, a binder composition according to the invention can also comprise further polymers. Suitable other Polymers are, for example, statistical copolymers produced by radical polymerization. Also suitable as further polymers are, for example, polyaddition or polycondensation products such as polyesters, polyethers, polycarbonates, polylactones, polyamides or polyurethanes. In addition to the polymers described above, or a mixture of two or more such polymers, the binder compositions according to the invention comprise a magnetic pigment, or a mixture of two or more magnetic pigments. Magnetic pigments include oxidic pigments such as γ-Fe ₂ O ₃ , Fe ₃ O ₄ , FeO _x (1.33 <X <1.5), co-modified γ-Fe ₂ O ₃ , co-modified Fe ₃ O ₄ , Co-modified FeO _x (1.33 <X <1.5), CrO ₂ , metallic pigments such as Fe, Co and Ni or their alloys, barium ferrite or strontium ferrite.

As is generally customary, further elements or compounds can be admixed to these pigments. As a rule, these pigments are anisotropic magnetic pigments.

Preferred are, for example, acicular or spindle-shaped co-modified or unmodified γ-Fe ₂ O ₃ , acicular or spindle-shaped co-modified or unmodified Fe ₃ O, acicular or spindle-shaped co-modified or unmodified FeO _x (1.33 <X <1.5 ), CrO ₂ or metallic pigments such as Fe, Co and Ni or their alloys. The particle size is generally 0.04 to 2 μm and the ratio of the central longitudinal axis to the central transverse axis (aspect ratio) is 2 to 20. In the context of a preferred embodiment of the present invention, magnetic pigments are used whose particle size is in a range from 0.07 to 0.8 μm and their aspect ratio is 2 to 20. Metal pigments or their alloys and mixtures which contain at least one further magnetic pigment in addition to metal pigments are particularly preferred.

In addition, the binder compositions according to the invention can also contain fillers, dispersing agents, other additives such as lubricants, carbon black or contain non-magnetic inorganic or organic pigments.

As a lubricant, 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.

Examples of suitable non-magnetic inorganic pigments are carbon black, graphite, metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides and metal sulfides. Examples include TiO ₂ (rutile or anatase), TiO _x , cerium oxide, tin oxide, tungsten oxide, antimony oxide, ZnO, ZrO ₂ SiO ₂ , Cr ₂ O ₃ , α-Al ₂ O ₃ , β-Al ₂ O ₃ , γ -Al ₂ O ₃ , α-Fe ₂ O ₃ , goethite, corundum, silicon nitride, titanium carbide, magnesium oxide, boron nitride, molybdenum sulfide, copper oxide, MgCO ₃ , CaCO ₃ , BaCO ₃ , SrCO ₃ , BaSO ₄ , silicon carbide and titanium carbide. These compounds can be present either individually or in combination with one another and are not restricted in shape and size. The compounds do not have to be in pure form but can be surface-treated with other compounds. Organic fillers such as polyethylene or polypropylene can also be used.

The binder compositions according to the invention can be obtained by mixing the above-mentioned polymers with magnetic or magnetizable pigments. The present invention therefore also relates to a process for the preparation of a binder composition according to the invention, in which a block copolymer which can be prepared by free-radical polymerization and having at least two blocks of different monomer compositions is dispersed with at least one magnetic or magnetizable pigment.

For the preparation of the binder compositions according to the invention, therefore, a block copolymer which can be prepared by free-radical polymerization and has at least two blocks of different monomer composition, or a Mixture of two or more such block copolymers with a magnetic pigment, or a mixture of two or more magnetic pigments, for example in admixture with one or more solvents and optionally together with fillers, dispersing aids, further 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 binder composition according to the invention, that is to say in particular the pigments and the polymeric binders, are first mixed with a little solvent to form a dough-like mass and then intimately mixed with one another, for B. by kneading, mixed and then dispersed. For example, in a dispersing apparatus, e.g. B. a pot ball mill or an agitator mill, from the magnetic pigment and the other pasted ingredients of the binder composition or a solution of the binder used, preferably in an organic solvent, with the addition of lubricant and possibly small amounts of a dispersant, the binder composition according to the invention are prepared.

The present invention thus also relates to a process for the preparation of a binder composition in which a block copolymer which can be prepared by free-radical polymerization and at least two blocks of different monomer composition and at least one magnetic or magnetizable inorganic or organic pigment or at least one magnetic or magnetizable inorganic or organic pigment are mixed is already present during the production of the block copolymer which can be prepared by radical polymerization.

The binder compositions according to the invention can be used within the scope of their

Use for the production of magnetic recording media, for example, can be applied to customary rigid or flexible carrier materials, the thickness of which is generally about 0.5 to about 200 μm. Suitable as carrier materials For example, there are films made of linear polyesters such as polyethylene terephthalate or polyethylene naphthalate, which in particular have thicknesses of approximately 4 to approximately 150 μm, for example approximately 5 to approximately 36 μm.

The invention also relates to a magnetic recording medium, at least comprising a binder composition according to the invention or a binder composition produced by a method according to the invention.

The magnetic recording media according to the invention can be produced in a known manner. The binder composition prepared in a dispersing apparatus, for example a pot ball mill or an agitator mill, from the magnetic pigment and a solution of the binders, preferably in an organic solvent, with the addition of lubricants and possibly small amounts of dispersant and other customary additives, is optionally after Mixing a crosslinker filtered and with the usual coating machine, eg. B. applied by means of a ruler or an extruder on the non-magnetic carrier. The coating can be done on one or both sides of the carrier.

It is possible to apply the binder composition according to the invention in multiple layers, it being possible for the type and / or amount of the magnetic or magnetizable pigments in the individual layers to be the same or different. It is also possible to apply a so-called adhesive layer or one or more binder-containing layers which do not contain any magnetic or magnetizable pigments directly to the support. A layer structure is also possible, in which layers which contain magnetic or magnetizable pigments alternate with layers without magnetic or magnetizable pigments. If several magnetic and / or non-magnetic layers are applied, the magnetic recording media can be produced either by the known wet-on-dry method or by according to the known wet-on-wet method. All devices known from the prior art as being suitable can be used.

Magnetic alignment is usually carried out before the liquid binder composition is dried on the carrier. The latter expediently takes place in about 10 to about 200 s at temperatures of about 50 to about 90 ° C. The magnetic layers can be used on conventional machines

Passing between heated and polished rollers, if necessary

Application of pressure and temperatures from about 25 to about 100 ° C, preferably 60 to about 90 ° C, smoothed and compressed. In the case of crosslinking binders, it has proven to be very advantageous to carry out the calendering before the crosslinking is complete, since the polymers carrying OH groups are very thermoplastic in the uncrosslinked state, without sticking together. The thickness of the magnetic layer is generally about 0.1 to about 20 μm, preferably about 0.2 to about 8 μm.

In the case of the production of magnetic tapes, the coated foils are cut in the longitudinal direction and in the customary widths, which are usually determined by inches. In the production of round recording media, the desired shape is punched out.

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.

Magnetic recording media include all known rigid or flexible, analog or digital recording media, e.g. To understand audio or video tapes, data tapes, floppy disks, magnetic cards or the like.

Another object of the invention is a magnetic recording medium containing an inventive or manufactured according to the invention Binder composition.

In the context of a preferred embodiment of the invention, the magnetic recording medium according to the invention contains a ferromagnetic metal pigment or a ferromagnetic metal alloy pigment as the magnetic or magnetizable pigment. In the context of a further preferred embodiment of the invention, the binder composition contains at least one further magnetic or non-magnetic pigment.

The magnetic recording medium according to the invention can be used, for example, as a video tape, audio tape, data tape, floppy disk, hard disk or magnetic card.

The present invention will now be explained below with the aid of a few examples.

Examples

example 1

Synthesis of a polymeric reaction product from methyl methacrylate and styrene

125 g of 25% ammonia solution in 125 g of water were placed in the oil bath and kept at 90.degree. 6 g of 1,1-diphenylethene, dissolved in 125 g of methyl methacrylate, and 4.73 g of ammonium peroxodisulfate, dissolved in 22.4 g of water, were then added dropwise through 2 dropping funnels in the course of 60 minutes. Then again 4.73 g of ammonium peroxodisulfate, dissolved in 22.4 g of water, were added dropwise within one hour. The mixture was then kept at 90 ° C. for a further hour. 65 g of styrene were added to this batch and the oil bath temperature was increased to 100 ° C. for 4 hours.

Example 2 Synthesis of a polymeric reaction product from methacrylic acid and hydroxyethyl acrylate

112 g of water and 112 g of 25% ammonia solution were introduced and heated to 90 ° C. 9.46 g of ammonium peroxodisulfate, dissolved in 45 g of water, were then added dropwise in 30 minutes and 6 g of 1,1-diphenylethene, dissolved in 107.5 g of methacrylic acid.

9.46 g of ammonium peroxodisulfate, dissolved in 45 g of water, were then added dropwise again over the course of 30 minutes.

After the addition, the mixture was kept at 90 ° C. for 5 hours. Then 1 mol of hydroxyethyl acrylate was added and the mixture was kept at 90 ° C. for 5 hours.

Example 3

Synthesis of a polymeric reaction product from methacrylic acid methyl ester and hydroxyethyl acrylate

360 g of water were introduced and kept at 90 ° C. Then 10 g of 1,1-diphenylethene, dissolved in 200 g of methyl methacrylate, and 10.3 g of ammonium peroxodisulfate, dissolved in 100 g of water, were mixed in parallel within 60 minutes and 9.2 g of 25% strength ammonia solution in 100 g of water dissolved, added dropwise within 90 minutes. The mixture was then kept at 90 ° C. for a further 3 hours. 25 g of hydroxyethyl acrylate were then added to 100 g of the dispersion described above and the batch was kept at 90 ° C. for 6 hours.

Example 4

Synthesis of a polymeric reaction product from methyl methacrylate, Acrylonitrile and styrene

360 g of water were introduced and kept at 90 ° C. 10 g of 1,1-diphenylethene, dissolved in 200 g of methyl methacrylate, and 10.3 g of ammonium peroxodisulfate, dissolved in 100 g of water, were then mixed in parallel within 60 minutes and 9.2 g of 25% strength ammonia solution in 100 g of water dissolved, added dropwise within 90 minutes. The mixture was then kept at 90 ° C. for a further 3 hours.

17.2 g of styrene and 1 g of acrylonitrile were then added to 100 g of the dispersion described above and the batch was kept at 90 ° C. for 6 hours.

Example 5

Synthesis of a polymeric reaction product from n-butyl acrylate and styrene

360 g of water were placed in the oil bath and heated to 90.degree. 11.1 g of 1,1-diphenylethene, dissolved in 256 g of n-butyl acrylate, and 10.7 g of sodium peroxide sulfate, dissolved in 100 g of water, were then added dropwise through 3 dropping funnels in the course of 180 minutes, and 2.3 were added in the course of 120 minutes g of sodium hydroxide, dissolved in 100 g of water, are added dropwise. The oil bath was held at 90 ° C for a total of 6 hours. After the aqueous phase had been separated off, styrene was added to the remaining polymer and the oil bath was kept at 115 ° C. for 6 hours. 169 g of n-butyl acrylate were then added and the oil bath was kept at 115 ° C. for 6 hours.

Example 6

Synthesis of a polymeric reaction product from methyl methacrylate and styrene 180 g of water were placed and kept at 90 ° C. Then 3 g of cis-stilbene, dissolved in 50 g of methyl methacrylate, and 5 g of 25% ammonia solution, dissolved in 50 g of water, were added dropwise in three minutes from three dropping funnels, and 5.0 g of ammonium peroxodisulfate, dissolved in 50 g of water , added dropwise in 90 minutes. The mixture was then kept at 90 ° C. for a further 4.5 hours. This gave a polymer with M _w = 54,200 g / mol and a polydispersity of 2.4.

70 g of the polymer dispersion described above were heated to 115 ° C. and 50 g of styrene were metered in. The mixture was then kept at 115 ° C. for 6 hours.

Example 7

Synthesis of a polymeric reaction product from methyl methacrylate and styrene.

180 g of water were placed and kept at 90 ° C. Then, in parallel from three dropping funnels, 3 g of trans-stilbene, dissolved in 50 g of methyl methacrylate, and 5 g of 25% ammonia solution, dissolved in 50 g of water, were added dropwise in 60 minutes and 5.1 g of ammonium peroxodisulfate, dissolved in 50 g of water , added dropwise in 90 minutes. The mixture was then kept at 90 ° C. for a further 4.5 hours. This gave a polymer with M _w = 46,800 g / mol and a polydispersity of 2.9.

A polymer with M _w = 168,000 g / mol and a polydispersity of 4.2 was obtained.

Example 8

Synthesis of a polymeric reaction product from methyl methacrylate 180 g of water were placed and kept at 90 ° C. Then 5 g of 4,4'-vinylidenebis (N, N'-dimethylaniline), dissolved in 100 g of methyl methacrylate, and 4.6 g of 25% ammonia solution, dissolved in 100 g of water, were in parallel from three dropping funnels within 60 Was added dropwise and 5.1 g of ammonium peroxodisulfate, dissolved in 100 g of water, were added dropwise within 90 minutes.

The mixture was kept at 90 ° C. for a further 4 hours. A polymer with M _w = 2,150 g / mol and a polydispersity of 1.2 is obtained.

Example 9

Synthesis of a polymeric reaction product from methyl methacrylate

360 g of water were introduced and kept at 90 ° C. Subsequently, 10 g of 1,1-diphenylethene, dissolved in 200 g of methyl methacrylate, and 10.3 ammonium peroxodisulfate, dissolved in 100 g of water, were dissolved in 100 g of water within 60 minutes and 9.2 g of 25% ammonia solution , added dropwise within 90 minutes. The mixture was then kept at 90 ° C. for a further 3 hours.

Example 10

For the dispersion experiments, the polymer (polymer 1) prepared according to Example 1 was dried and dissolved in the solvents (mixtures) described below.

Dispergierbeispiele

example 1

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 1, 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 kneader type HKD 10, from IKA-Maschinenbau, Staufen).

A mixture of 145 parts by weight of THF and 145 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 9 hours. 1 part by weight of butyl stearate, 5.2 parts by weight of a 50% strength by weight solution of the reaction product of 3 moles of tolylene diisocyanate with 1 mole 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 satinized in a steel / steel calender with 6 columns at 85 ° C and a pressure of 200 kg / cm and then cut into 1/2 inch wide video tapes. Nergleichsbeispiel

The procedure was as described above, but the polymer 1 according to the invention was replaced by a commercially available VC copolymer with sulfonate anchor groups (Νippon Zeon).

Table 1 shows the measurement results obtained.

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 the roller board

The higher the gloss value, the better the pigment distribution. RF level:

The high-frequency level was 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 in 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 over a length of 100 mm with a force of 2 N and a speed of 20 mm / s over a steel pin (diameter 2.5 mm, wrapping 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 2

a) Upper class

A mixture of 100 parts by weight of a ferromagnetic metal pigment (Hc = 180 kA / m; SSA = 58 m ² / 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 Polymers according to the invention 1, 3.5 parts by weight of a commercially available polyurethane with polar anchor groups (Morton company), 2 parts by weight of stearic acid, 1 part by weight of myristic acid, 15 parts by weight of tetrahydrofuran and 15 parts by weight of dioxane kneaded for 2 hours in a batch kneader (IKA high-performance kneader type HKD 10, company IKA Maschinenbau, Staufen).

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% solution of the reaction product of 3 moles of tolylene diisocyanate with 1 mole of trimethylolpropane in tetrahydrofuran and portions of a mixture of 44 parts by weight of tetrahydrofuran were then added to the dispersion with vigorous stirring 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 dispersion was obtained for the top layer.

Comparative Example 2 a)

The procedure was as described above, but the polymer 1 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 1, 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 with polar anchor groups (Tg = 35 ° C; Morton), 2 parts by weight of stearic acid, 27 parts by weight Parts of tetrahydrofuran and 27 parts by weight of dioxane were kneaded in a batch kneader for 3 hours. A mixture of 234 parts by weight of tetrahydrofuran and 234 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 15 hours. 6.3 parts by weight of a 50% solution of the reaction product of 3 moles of tolylene diisocyanate 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 dispersion was obtained.

Comparative Example 2b)

Apply top and bottom layers

The dispersions were applied wet-on-wet to the front of a back-coated polyethylene terephthalate film. Before drying, the coated film 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 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 2. Table 2

Gloss and friction measurements were carried out as described in Example 1.

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 distribution in the upper and lower layers. In addition, the very low friction values ensure good running and abrasion behavior in the recorder.

The following examples show the use of the described binders in magnetic storage media: example 1

A magnetic dispersion of the following composition was produced:

Magnetic pigment 100 parts by weight

(acicular cobalt-containing iron powder; needle length 150 nm; pH = 9.5; BET surface area: 55 m ² / g; Hc: 132 kA m; saturation magnetization: 126.6 emu / g)

Inorganic support pigment 10 parts by weight (aluminum oxide; pH = 8.5; BET surface area: 6 m ² / g;

Primary grain size: 0.3 μm)

Carbon black 1 part by weight

(Primary grain size: 60 nm; pH = 8.0; DBPA adsorption:

65 cmVlOO g) binder with polymer 1, as described above 10 parts by weight

Binder B 10 parts by weight

(Polyester polyurethane; Tg = 50 ° C; 50 meq NaSO ₃ - / kg)

Stearic acid 1 part by weight

Butyl stearate 1 part by weight of tetrahydrofuran 230 parts by weight

Dioxane 230 parts by weight

The dispersion was prepared in the customary manner, with grinding being carried out in a horizontal stirred ball mill. Binder B and lubricant were only added after a gloss level of 120 (60 °) had been reached. It was then filtered through a filter with a pore size of 2 μm.

Before the coating, 6 parts by weight of a 50% crosslinking solution were stirred in (2,6-functional isocyanate based on TMP / TDI). The coating was carried out by means of a knife coater on a 14 μm thick PET film which had previously been provided with a back coating. Magnetic layer thickness: 2.5 μm. After calendering (2 steel / steel and 3 PU / steel rolls; 60 ° C; 200 kp / cm), the coated block was stored at 60 ° C for 3 days.

The material was cut into tapes of 1/2 inch width, which were then wound into Magstar cassettes after cleaning via fleece and blade.

Nergleichsbeispiel:

Like example 1, but using 10 parts by weight of binder B instead of binder with polymer 1. Achieved gloss value: 110 (60 °).

Durability Test

2 cassettes each were 2 days at 31 ° C and 85% rel. Humidity stored and then subjected to an eight-hour endurance test in an IBM 3590 drive in the same climate ("locate rewind test").

The cassettes of the comparative example showed a clear increase in errors; the resistance of the layer was not sufficient.

Claims

claims

1. A binder composition containing at least one block copolymer which can be prepared by radical polymerization and has at least two blocks of different monomer composition, and at least one magnetic or magnetizable pigment.

2. Binder composition according to claim 1, characterized in that the block copolymer has two to six blocks.

3. Binder composition according to claim 1 or 2, characterized in that the block copolymer was produced by a process at least comprising the following steps (i) and (ii):

where Ri to Rj. each independently for

Hydrogen, an unsubstituted or substituted alkyl radical, cycloalkyl radical, aralkyl radical, an unsubstituted or a substituted aromatic radical

Are hydrocarbon radicals, with the proviso that at least two of the radicals bis bis represent an unsubstituted or a substituted aromatic hydrocarbon radical, or the radicals Rj and R ₂ or R ₃ and R ₄ each in pairs for a substituted or unsubstituted aromatic hydrocarbon having 6 to 18 C atoms and a functional group which, in conjugation to the CC double bond in the general formula (I), has a multiple bond between a C atom and a hetero atom has, stand, a reaction product (A) is obtained and

(ii) reaction of the reaction product (A) obtained in step (i) under free radical conditions with at least one free-radically homo- or copolymerizable monomer (b), where a

Reaction product (B) is obtained.

4. Binder composition according to claim 3, wherein the proportion of free radical initiator to the at least one monomer (a) 0.5 to 50 wt .-%, based on the total amount of the initiator and the monomer

(a).

5. Binder composition according to claim 3 or 4, wherein as a compound of the general formula (I) 1,1-diphenylethene, an alkoxydiphenylethene, 1,1-dinaphthylethene, 4,4'-vinylidenebis (N, N'-dimethylaniline), 4, 4'-vinylidenebis (aminobenzene), cis-stilbene, trans-stilbene, methyl α-phenylacrylate, methyl α-phenylmethacrylate, α-phenylacrylonitrile, α-phenylmethacrylonitrile or a mixture of two or more thereof.

6. Binder composition according to one of claims 3 to 5, wherein the reaction mixture as a first monomer (a) styrene, acrylic or methacrylic acid, a C 1 to C ₄ alkyl or hydroxyalkyl acrylate or methacrylate, vinyl acetate, a substituted or unsubstituted N-vinyl pyrrolidone, a mixture of two or more thereof, or a mixture of such a first monomer (a) with at least one further radically homo- or copolymerizable monomer.

7. Binder composition according to one of claims 3 to 6, characterized in that 10% by weight of water or less are present in the reaction mixture during the reaction.

8 binder composition according to one of claims 1 to 7, characterized in that the block copolymer was prepared by a process at least comprising the following step (iii):

(iii) the reaction product (B) obtained in step (ii) is reacted under free radical conditions in the presence of at least one free-radically homo- or copolymerizable monomer (c), this reaction optionally being repeated several times in succession with the same or different monomers (c) becomes.

9. A process for the preparation of a binder composition in which a block copolymer which can be prepared by free-radical polymerization and at least two blocks of different monomer composition, and at least one magnetic or magnetizable inorganic or organic pigment or at least one magnetic or magnetizable inorganic or organic pigment are mixed during the preparation of the block copolymers which can be prepared by radical polymerization are present.

10. Use of a binder composition according to any one of claims 1 to 8 or a binder composition prepared according to claim 9 for the production of magnetic recording media.

11. Magnetic recording medium containing a binder A composition according to any one of claims 1 to 8 or made according to claim 9.

12. The magnetic recording medium according to claim 11, wherein the magnetic or magnetizable pigment is a ferromagnetic

Metal pigment or a ferromagnetic metal alloy pigment.

13. A magnetic recording medium according to claim 11 or 12, wherein the binder composition contains at least one further magnetic or non-magnetic pigment.

14. Magnetic recording medium according to one of claims 11 to 13, characterized in that it is a video tape, an audio tape, a data tape, a floppy disk, or a magnetic card.