Stock material or miscellaneous articles – Circular sheet or circular blank – Recording medium or carrier
Reexamination Certificate
2001-05-14
2004-06-15
Resan, Stevan A. (Department: 1773)
Stock material or miscellaneous articles
Circular sheet or circular blank
Recording medium or carrier
C428S336000, C428S690000
Reexamination Certificate
active
06749917
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic recording medium for high-density recording containing ferromagnetic fine powder as a magnetic layer. In particular, the invention relates to a magnetic recording medium having good storage property and high durability.
As magnetic recording medium for the applications in audio equipment, video equipment, computer, etc., a magnetic recording medium is used, which has a magnetic layer containing ferromagnetic powder dispersed in a binder, and the magnetic layer is placed on a nonmagnetic support member.
In recent years, digital recording with less deterioration of recording quality compared with conventional analog recording has been used widely in practical application, also in the field of video tape recorder for home use. In general, more signals must be recorded in digital recording than in analog recording. The recording and reproducing system and recording medium used for digital recording must provide high picture quality and high tone quality and also must be designed in more compact size and must have space-saving property. In this respect, there are strong demands on high-density recording.
To achieve high-density recording, it is necessary to turn the recording signals to shorter wavelength and recording track must be designed narrower. For this purpose, ferromagnetic powder must be finer powder with high filling ratio and the recording medium must have smoother surface. Also, writing speed and reading speed to and from the recording medium must be increased. Attempts are now being made to increase the number of revolutions of cylinder or to increase carrier speed of tape.
In the equipment or devices using the magnetic recording medium, there is problem in that magnetic head is contaminated because the medium and the magnetic head slide against each other. In particular, in the device for high density recording, number of revolutions of the magnetic head is high. In a digital video tape recorder, number of revolutions of the magnetic head is as high as 9,600 rpm, and this is much higher compared with 1,800 rpm of an analog video tape recorder for household use, and 5,000 rpm of a video tape recorder for business use.
With the increase of sliding speed between the magnetic recording medium and the magnetic head, there are now strong demands on the development of a magnetic recording medium, which has high durability and high resistance to wear or damage and has high resistance to high speed sliding movement.
Not only for the tape-type magnetic recording medium, but also for disk-type magnetic recording medium, high-density magnetic recording medium is required, as typically represented by Zip (Iomega Inc.), which can be rotated at higher speed compared with the conventional type floppy disk. Thus, a magnetic recording medium with high durability and high resistance to wear and damage is required for this purpose.
To solve the above problems, for the purpose of providing a magnetic recording medium, which contains ferromagnetic metal powder dispersed in a binder and which has high durability in high density recording and can perform stabilized recording and reproduction, it is proposed to use a magnetic recording medium, which contains various types of lubricants in the magnetic layer. It is proposed to use various types of triester or tetraester compound as lubricant when ester is used as lubricant.
For instance, JP-88021255(B) describes the use of triester or tetraester lubricant obtained from trimethylolpropane, trimethylolethane or pentaerythritol. However, these lubricants have poor storage property, and the resistance to damage of the magnetic layer is low. In particular, the properties of this lubricant are not high enough for high-density recording medium such as digital recording tape.
Also, JP-59065931(A) describes a magnetic recording medium using a lubricant, which simultaneously uses triester of trimethylolpropane and other diester or tetraester and monoester. However, storage property of the magnetic layer is not sufficiently high, and the magnetic layer also has poor resistance to damage or wear. Further, these products are low in durability and have poor electromagnetic transfer characteristics.
JP-61139921(A) describes a magnetic recording medium, which uses fatty acid ester of polyhydric alcohol and phosphoric acid ester of phenoxydiethylene glycol as lubricants. But, this product has magnetic layer with low storage property and low resistance to damage. Further, the product has low durability and poor electromagnetic transfer characteristics.
Further, U.S. Pat. No. 4,696,869 (JP-95015748(B)) describes a magnetic recording medium, using ester or trimethylolpropane or ester of pentaerythritol and monoester as lubricants. However, the magnetic layer has low storage property and low resistance to damage. Further, this product has low durability and poor electromagnetic transfer characteristics in high-density recording.
Also, U.S. Pat. No. 5,258,223 (JP-2552958) proposes a magnetic recording medium, which can have higher electromagnetic transfer characteristics in short wavelength recording and which comprises a primer layer and a thin upper magnetic layer. In the prescription as disclosed, the product is not good enough in terms of durability. The storage property of the magnetic layer is low, and resistance to damage of the magnetic layer is not sufficient. Further, the product has low electromagnetic transfer characteristics in high-density recording.
SUMMARY OF THE INVENTION
The present invention provides a magnetic recording medium, which comprises a primer layer containing at least nonmagnetic powder on a support member and at least one layer of magnetic layer containing ferromagnetic powder dispersed in a binder, the magnetic layer being placed on the support member, wherein the primer layer comprises at least one type of compound expressed by the following general formula (1);
General formula (1)
where R
1
, R
2
, R
3
, and R
4
each represents an alkyl group having 2 to 7 carbon atoms.
Also, the present invention provides the magnetic recording medium as described above, wherein thickness of the magnetic layer is within the range of 0.05 to 1 &mgr;m.
Further, the present invention provides the magnetic recording medium as described above, wherein said medium is a disk-type magnetic recording medium.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention provides a high-density magnetic recording medium, comprising a lubricant of specific chemical structure for the purpose of achieving high durability and high resistance to damage and wear and good electromagnetic transfer characteristics.
In particular, it has been found in the present invention that, when a tetraester compound is added at least to a primer layer, and a magnetic layer is coated on the primer layer and dried, and processed by calender processing, very smooth magnetic layer can be obtained. Thus, a magnetic recording medium having high durability under high temperature and high speed operation can be obtained.
As the lubricant to be used in the present invention, it is preferable to use a tetraester compound expressed by the following general formula:
General formula (1):
where R
1
, R
2
, R
3
, and R
4
each represents an alkyl group having 2 to 7 carbon atoms, or more preferably having 3 to 5 carbon atoms. If the number of carbon atoms is less than the above value, the product is too volatile. When it is turned to high temperature during friction, surface of the magnetic layer is worn out, and durability is decreased. Hydrophilic property is increased, and durability is decreased under high temperature and high humidity environment. If the number of carbon atoms is more than the above value, viscosity increases. Fluid lubricating performance is decreased, and this leads to lower durability. For good preservation and stability, it is preferable that saturated hydrocarbon group is contained.
The hydrocarbon group may be either branched or direct chain, while the direct-chain group is more preferable
Harasawa Takeshi
Hashimoto Hiroshi
Resan Stevan A.
Stroock & Stroock & Lavan LLP
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