Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2000-09-14
2002-08-13
Sanders, Kriellion A. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S537000, C524S539000, C524S540000, C524S612000
Reexamination Certificate
active
06433070
ABSTRACT:
The invention relates to a binder composition, at least containing an inorganic filler and a thermoplastic block copolyurethane having in each case at least one soft segment (A) and at least one hard segment (B), at least one hard segment (B) containing a structural element of the formula I
a process for the preparation of such a binder composition and its use, in particular for the production of magnetic recording media.
Various groups of substances are known to be suitable as binders in magnetic recording media. The polyurethanes, which in particular substantially improve the resilience of the magnetic recording media or of coatings of such magnetic recording media, have proven particularly advantageous to date. In the case of the polyurethanes, however, their poor hardness and abrasion resistance have frequently proven disadvantageous.
This problem is described, for example, in German Patent Application 19626824.9. Although the polyurethanes obtainable according to this publication have substantially improved values with respect to hardness and abrasion resistance, the stability of the recording might decline under specific conditions, for example at elevated storage or operating temperatures.
To counteract these problems, the polyurethanes used in magnetic recording media were provided, for example, with ionic anchor groups. Thus, EP-A 0 681 289 describes ionic phosphonates which are suitable for use in binders for magnetic recording media. The publication describes polyurethanes which contain such ionic phosphonates and their use in magnetic recording media. However, the disadvantage of such polyurethanes carrying ionic anchor groups is that, as a rule, they exhibit high water absorption, in particular at elevated temperatures and high atmospheric humidity. With increasing water absorption, however, the glass transition temperature of the magnetic recording medium is reduced, which as a rule can lead to increased abrasion and tack of the tapes and finally to deposits on the read head and to data loss when such polyurethanes are used in magnetic recording media, for example in tapes.
There was therefore a need for binders or binder compositions which can be used, for example, for the production of magnetic recording media and avoid the abovementioned disadvantages.
It is an object of the present invention to provide such binders or binder compositions.
We have found that this object is achieved by a binder composition which contains at least one inorganic filler and one thermoplastic block copolyurethane having at least one soft segment (A) and at least one hard segment (B).
The present invention therefore relates to a binder composition, at least containing an inorganic filler and a thermoplastic block copolyurethane or a mixture of two or more thermoplastic block copolyurethanes having at least one soft segment (A) and at least one hard segment (B), at least one hard segment having a structural element of the formula I
where R
1
and R
3
are identical or different, substituted or unsubstituted aromatic or heteroaromatic radicals of 4 to 40 carbon atoms and R
2
and R
4
are hydrogen or R
1
, R
2
, R
3
and R
4
are essentially completely fluorinated alkyl groups of 1 to 10 carbon atoms, R
5
and R
6
are identical or different, substituted or unsubstituted, linear or branched aliphatic or unsubstituted or substituted cycloaliphatic or unsubstituted or substituted aromatic radicals of 4 to 40 carbon atoms and n is from 1 to 100.
As used for the purposes of the present text, the term binder composition relates to compositions which contain at least one binder and at least one inorganic filler.
For the purposes of the present invention, a binder is understood as meaning a polymer or a mixture of two or more polymers which are substantially involved in the composition of the magnetic storage medium after chemical or physical drying is complete. In the context of the present invention, a binder may contain, for example, only one polymer, i.e. a specific type of polymer molecules, individual molecules of this type differing only in their different molecular weight which is established in a molecular weight distribution obtained by the chosen polymerization method. The chemical composition of such polymer molecules is essentially identical when only a single type of polymer molecule is present in the binder. However, the binder according to the present invention may also have two or more different types of polymer molecules. Different types of polymer molecules may differ, for example, in their molecular weight distribution, in their molecular weight or in their chemical composition. However, it is also possible for the different types of polymer molecules to differ in two or more of said properties.
For the purposes of the present invention, a hard segment is understood as meaning a segment of a thermoplastic polyurethane molecule, the hard segment having a glass transition temperature of at least about 50° C.
For the purposes of the present invention, a soft segment is understood as meaning a segment of a polyurethane molecule which is linked covalently to a hard segment and has a glass transition temperature which is below the temperature of use of a magnetic recording medium produced from the novel polymer, for example less than about 30° C., preferably less than about 20° C.
For the purposes of the present invention, an anchor group is understood as meaning a functional group which is capable of interacting with ionic or nonionic, polar compounds. In particular, anchor groups are understood as meaning those functional groups which are capable of interacting with the surface of inorganic filler materials, in particular with the surface of inorganic magnetic or magnetizable pigments.
In the text below, the thermoplastic block copolyurethanes used for the purposes of the present invention are referred to as thermoplastic polyurethanes or simply as polyurethanes for the sake of simplicity. Polyurethanes which do not have thermoplastic properties or are not block copolymers are expressly indicated as such below.
For the purposes of the present invention, an inorganic filler is understood as meaning a particulate filler which has a particle size of from about 100 nm to about 1 mm. Suitable inorganic fillers are, for example, chalk, titanium dioxide, silica and further minerals correspondingly processible to give particles, or metals, carbon black or in particular magnetic or magnetizable pigments, for example oxide pigments, such as &ggr;-Fe
2
O
3
, &ggr;-Fe
3
O
4
, CrO
2
, or Co-modified Fe
2
O
3
, or metallic pigments, such as Fe, Co and Ni. As is generally known, further elements or compounds can be mixed with said pigments.
The thermoplastic polyurethanes contained in the novel binder compositions have in each case at least one hard segment (B) which has at least one structural element of the formula I
Here, R
1
and R
3
are identical or different, substituted or unsubstituted aromatic or heteroaromatic radicals of 4 to 40 carbon atoms and R
2
and R
4
are hydrogen or R
1
, R
2
, R
3
and R
4
are essentially completely fluorinated alkyl groups of 1 to 10 carbon atoms.
In a preferred embodiment of the present invention, R
2
and R
4
are one or two of the following radicals:
In a further preferred embodiment of the present invention, R
2
and R
4
are identical. In another preferred embodiment of the invention, R
2
and R
4
are methoxyphenyl or trimethoxyphenyl. In a further preferred embodiment of the invention, R
2
and R
4
are hydrogen.
For the purposes of the present invention, R
5
and R
6
are identical or different, substituted or unsubstituted, linear or branched aliphatic or unsubstituted or substituted cycloaliphatic or unsubstituted or substituted aromatic radicals of about 4 to about 40 carbon atoms. Suitable aliphatic radicals are, for example, butylene, pentylene, hexylene, heptylene, octylene, nonylene, decylene and the higher homologs of this series, as can be obtained by extending said hydrocarbon chains by in each case one CH
2
group. Other suita
Bradshaw Richard
Hees Ulrike
Kohl Albert
Kress Ria
Maier Gerhard
Emtec Magnetics GmbH
Keil & Weinkauf
Sanders Kriellion A.
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