Stock material or miscellaneous articles – Composite – Of polyamidoester
Reexamination Certificate
1995-09-22
2002-04-23
Resan, Stevan A. (Department: 1773)
Stock material or miscellaneous articles
Composite
Of polyamidoester
C428S690000, C428S690000, C428S690000, C428S900000
Reexamination Certificate
active
06376083
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic recording medium, which comprises a magnetic layer having ferromagnetic powder dispersed in a binder and placed on a non-magnetic support member which has excellent electromagnetic transfer characteristics, high durability and preservation property (shelf life).
Magnetic recording medium is widely used in such applications as recording tape, video tape, floppy disk, etc. In a magnetic recording medium, a magnetic layer having ferromagnetic powder dispersed in a binder is laminated on a non-magnetic support member.
The magnetic recording medium must be at high level in electromagnetic transfer characteristics, running durability, running performance, etc. Specifically, an audio tape for recording and reproducing music must have high level of original sound reproducing ability. A video tape must have high electromagnetic transfer characteristics such as high ability to reproduce the original image.
With the requirement to have high electromagnetic transfer characteristics, the magnetic recording medium also must have good running durability. In general, abrasive material and lubricating material are added in the magnetic layer.
However, in order to obtain high running durability by adding abrasive material, it is necessary to increase the adding quantity to some extent, and this means that filling ratio of the ferromagnetic powder has to be lowered. In case abrasive material having large grain size is used to obtain good running durability, the abrasive material tends to protrude excessively on the surface of the magnetic layer. Therefore, the improvement of the running durability often leads to deterioration of the electromagnetic transfer characteristics.
When the running durability is improved by adding lubricant, the quantity of the added lubricant must be increased. This often makes the binder more easily plasticized and may lower the durability of the magnetic layer.
In improving the durability and electromagnetic transfer characteristics, the binder, which is one of the principal components of the magnetic layer, plays naturally an important role. Vinyl chloride resin, cellulose resin, urethane resin, acrylic resin, etc. as used in the past, cause poor wear-resistant property of the magnetic layer, and this leads to contamination of the running components of the magnetic tape.
To solve this problem, a method is adopted to increase the hardness of the magnetic layer using a hard binder. Polyurethane resin or polyurethane urea resin are used as the binder having such high hardness, and it is known that these compounds can be obtained through polymerization of long chain diol or diamine having weight average molecular weight of 500 to 5,000, low molecular diol having molecular weight of less than 500, chain extender of diamine, and organic diisocyanate in an organic solvent.
It is known that polar groups such as sulfonic acid, carboxylic acid, etc. are introduced into polyurethane to improve dispersion property of the ferromagnetic powder.
For example, the introduction of short chain diol having a polar group such as —SO
3
M into a chain extender is described in JP-(B) 61-18809, and the introduciton of a polar group with a chain extender is described in JP-(A) 64-72318. However, short chain diol having polar group has very strong hydrophilic property, and it has lower solubility in organic solvent compared with long chain diol and diisocyanate. This leads to uneven polymerization, and polymerization often occurs in lumps. Because polar group-containing segments are present in polyurethane molecules, association between molecules often occurs, and this leads to lower solubility and insufficient dispersion property.
The use of polyester urethane resin containing —SO
3
M is disclosed in JP-(B) 58-41656 (U.S. Pat. No. 4,152,485), and JP-(A) 5-250652 describes the introduction of polar group by formation of polyurethane resin using a part or all of polyhydroxy compound having metal salt of sulfonic acid. Further, JP-(A) 59-198530 (U.S. Pat. No. 4,643,949) discloses the use of sulfonic acid-containing polycarbonate polyurethane. However, the long chain diol containing polar group used in these patent publications is used by 11 mol % at the lowest, and long chain diol not containing polar group is contained by more than 20 mol %. These long chain diols have hydrophilic ester linkage, and this results in lower solubility in solvents and insufficient dispersion property. Ester linkage is easily hydrolyzed and causes poor performance in long-term storage.
JP-(A) 61-190717 describes polyol consisting of polyether polyol. As polyether long chain diol, polyethyleneglycol, polypropyleneglycol, or polytetra-methyleneglycol are known, while all of these have very low glass transition temperature (Tg) and are low in strength.
Also, JP-(A) 59-198530 describes polycarbonate urethane containing sulfonic acid. But, polycarbonate is expensive and has high hydrophilic property. It is low in preservation property and has low solubility in organic solvents.
Under such circumstances, there have been strong demands on a magnetic recording medium, which has high electromagnetic transfer characteristics and long-term preservation property with most of the resins having high hardness and has excellent durability under wide range of temperature and humidity conditions.
SUMMARY OF THE INVENTION
To solve the above problems, the magnetic recording medium according to the present invention comprises at least one magnetic layer having ferromagnetic powder dispersed by a binder placed on a non-magnetic support member, whereby a polyurethane resin or a polyurethane urea resin consisting of 5 mol % or less of a long chain diol having weight average molecular weight of 800 to 5,000, a short chain diol having weight average molecular weight of 50 to 500 and/or a short chain diamine and an organic diisocyanate is contained as the binder, said long chain diol has one polar group selected from —COOM, —SO
3
M, —OSO
3
M, —OPO(OM)
2
, or —PO(OM)
2
(where M represents a hydrogen atom, an alkali metal ion, or an ammonium ion) in the molecule, and the polar group is contained in the polyurethane by 1 to 5 mol %.
The present invention also provides a magnetic recording medium as described above, wherein said magnetic layer is arranged on a non-magnetic layer where non-magnetic powder is dispersed in a binder.
It also provides a magnetic recording medium as described above, wherein a polyurethane resin contains a long chain diol given by the following formula (1) by 1 to 5 mol %:
where R represents a polyalkyleneglycol residual group.
Further, the present invention provides a magnetic recording medium as described above, wherein a polyurethane resin contains a short chain diol and/or diamine having a cyclohexane ring given by the following formulae (2) or (3):
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The binder for the magnetic recording medium of the present invention comprises polyurethane resin, polyurethane urea resin and/or polyurea resin. Diol or diamine used as chain extender comprises a short chain diol or a short chain diamine as principal components, and a long chain diol having weight average molecular weight of 800 to 5,000 is normally used in these resins by 5 mol % or less to polyurethan urea resin and/or polyurea resin. Further, by introducing a polar group into the long chain diol, the polar group can be introduced evenly, and this solves the problems of localization or easy association of polar group.
Conventionally, the long chain diol is contained in polyurethane by 10 mol % or more, while it is contained by 5 mol % or less, or preferably by 1 to 5 mol % in the present invention. A short chain diol or diamine for forming resin with higher hardness is used by 95 mol % or more, and this leads to higher strength of film and to high Tg. Thus, the film is not easily peeled off even when the magnetic head slides along and may be partially heated to high temperature.
When the long chain diol used in the present invention has weight average
Hashimoto Hiroshi
Murayama Yuichiro
Okita Tsutomu
Satake Masaki
Fuji Photo Film Ltd.
Resan Stevan A.
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