Magnetic recording medium

Abstract

There is provided a magnetic recording medium which comprises a substrate, a magnetic layer on one surface of a substrate and a backcoating layer on the other surface of the substrate, wherein the magnetic layer contains a magnetic metal powder having a major axis of not larger than 0.2 μm and an inorganic powder having a Mohs' hardness of at least 5, and the backcoating layer contains an inorganic powder having a particle size smaller than the size of the major axis of the magnetic metal powder and which has sufficiently reduced noise at high density recording and high output required in, for example, a small size video tape with high picture quality, the magnetic recording medium in the form of a magnetic tape having a total thickness of not larger than 14 μm inclusive of the substrate, the magnetic layer and the backcoating layer, and reliably maintained not to increase the noise after long term storage.

What is claimed:  
     
       1. A magnetic recording assembly which comprises a magnetic tape and a cassette casing, said magnetic tape comprising a substrate, a magnetic layer on one surface of said substrate and a backcoating layer on an opposite surface of said substrate, wherein said magnetic layer contains a magnetic metal powder having a major axis size of not larger than 0.2 μm to achieve high density recording at a center recording wavelength of 0.8 μm or less and an inorganic powder having a Mohs' hardness of at least 5, said magnetic layer having a thickness not greater than 3.0 μm, a surface roughness of not greater than 0.004 μm in terms of center line average roughness, and a squareness ratio of at least 0.85 under an applied magnetic field of 10 KOe and said backcoating layer contains a carbon black and an inorganic powder having a particle size smaller than said major axis size of said magnetic metal powder, and has a surface roughness of not greater than 0.01 μm in terms of center line, and a Mohs' hardness of at least 5, and said cassette casing is made of an ABS resin containing a pigment having a Moh's hardness of from 2 to 4. 
     
     
       2. A magnetic recording assembly which comprises a magnetic tape comprising a substrate, a magnetic layer on one surface of said substrate and a backcoating layer on a reverse surface of said substrate for recording information at a center recording wavelength of not larger than 0.8 μm, wherein said magnetic layer has a thickness not larger than about 3.0 μm and contains a magnetic metal powder having a major axis size of not larger than 0.2 μm and an inorganic powder having a Mohs' hardness of at least 5, and said backcoating layer contains carbon black and an inorganic powder having a particle size smaller than said major axis of said magnetic metal powder, and a Mohs' hardness of at least 5 and a cassette casing made of an ABS resin containing a pigment having a Mohs' hardness of from 2 to 4. 
     
     
       3. A magnetic recording assembly which comprises a magnetic tape, for recording information at a center recording wavelength of no greater than 0.8 μm, said magnetic tape comprising a substrate, a magnetic layer having a thickness not larger than about 3.0 μm which contains magnetic metal powder having a major axis of 0.2 μm or less and inorganic powder having a Moh's hardness of at least 5 on one surface of said substrate and a backcoating layer which contains carbon black and an inorganic powder having a particle size smaller than a major axis size of said magnetic metal powder and a Mohs' hardness of at least 5 on a reverse surface of said substrate, a hub, said magnetic tape being wound around said hub with said backcoating layer facing inside, and a cassette casing made of an ABS resin containing a pigment having a Mohs' hardness of from 2 to 4 in which said tape wound hub is placed. 
     
     
       4. A magnetic recording assembly which comprises a magnetic tape comprising a substrate, a magnetic layer on one surface of said substrate and a backcoating layer on an opposite surface of said substrate, for recording information at a center recording wavelength of not larger than 0.8 μm, wherein said magnetic layer has a thickness not larger than about 3.0 μm and has a surface roughness of not larger than 0.004 μm in terms of center line average roughness and a squareness ratio of at least 0.85 at an applied magnetic field of 10 KOe and contains magnetic metal powder having a major axis of 0.2 μm or less and an inorganic powder having a Mohs' hardness of at least 5, and said backcoating layer has a surface roughness of not larger than 0.01 μm in terms of center line average roughness and contains carbon black and an inorganic powder having a particle size smaller than said major axis size of said magnetic metal powder, and a Mohs' hardness of at least 5 and a cassette casing made of an ABS resin containing a pigment having a Mohs' hardness of from 2 to 4. 
     
     
       5. A magnetic recording assembly which comprises a magnetic tape comprising a substrate, a magnetic layer on one surface of said substrate and a backcoating layer on an opposite surface of said substrate, for recording information at a center recording wavelength of not longer than 0.8 μm, wherein said magnetic layer has a thickness not larger than about 3.0 μm and has a surface roughness of not larger than 0.004 μm in terms of center line average roughness and a coercive force of at least 1500 Oe and contains a magnetic metal powder having a major axis of 0.2 μm or less and inorganic powder having a Mohs' hardness of at least 5, and said backcoating layer has a surface roughness of not larger than 0.01 μm in terms of center line average roughness and contains carbon black and an inorganic powder having a particle size smaller than said major axis size of said magnetic metal powder, and a Mohs' hardness of at least 5 and a cassette casing made of an ABS resin containing a pigment having a Mohs' hardness of from 2 to 4. 
     
     
       6. A magnetic recording assembly comprising magnetic tape comprising a substrate, a magnetic layer on one surface of said substrate and a backcoating layer on an opposite surface of said substrate, wherein said magnetic layer has a thickness not larger than about 3.0 μm and contains a magnetic metal powder having a major axis of 0.2 μm or less to achieve high density recording at a center recording wavelength of 0.8 μm or less and an inorganic powder having a Mohs' hardness of at least 5, and said backcoating layer contains carbon black and an inorganic powder having a particle size smaller than said major axis size of said magnetic metal powder and a Mohs' hardness of at least 5, a total thickness of said tape being not larger than 14 μm and a cassette casing made of an ABS resin containing a pigment having a Mohs' hardness of from 2 to 4. 
     
     
       7. A magnetic recording medium which comprises a substrate, a magnetic layer on one surface of said substrate and a backcoating layer on a reverse surface of said substrate, wherein said magnetic layer has a thickness not larger than about 3.0 μm and contains a magnetic metal powder having a major axis of 0.2 μm or less to achieve high density recording at a center recording wavelength of 0.8 μm or less which comprises iron and at least 0.1% by weight of manganese based on a weight of said iron, and an inorganic powder having a Mohs' hardness of at least 5, and said backcoating layer contains carbon black and an inorganic powder having a particle size smaller than said major axis size of said magnetic metal powder, and a Mohs' hardness of at least 5 and a cassette casing made of an ABS resin containing a pigment having a Mohs' hardness of from 2 to 4. 
     
     
       8. A magnetic recording assembly which comprises a magnetic tape comprising a substrate, a magnetic layer on one surface of said substrate and a backcoating layer on an opposite surface of said substrate, wherein said magnetic layer has a thickness not larger than about 3.0 μm and contains a magnetic metal powder having a major axis of 0.2 μm or less to achieve high density recording at a center recording wavelength of 0.8 μm or less which comprises iron, manganese and an alkaline earth metal and an inorganic powder having a Mohs' hardness of at least 5, and said backcoating layer contains carbon black and an inorganic powder having a particle size smaller than said major axis size of said magnetic metal powder and a Mohs' hardness of at least 5 and has a surface roughness in terms of center line average surface roughness smaller than said major axis size of said magnetic metal powder and a cassette casing made of an ABS resin containing a pigment having a Mohs' hardness of from 2 to 4. 
     
     
       9. A magnetic recording medium which comprises a substrate, a magnetic layer on one surface of said substrate and a backcoating layer on an opposite surface of said substrate, wherein said magnetic layer has a thickness not larger than about 3.0 μm and contains a magnetic metal powder having a major axis of 0.2 μm or less to achieve high density recording at a center recording wavelength of 0.8 μm or less which comprises iron, manganese and an alkaline earth metal and an inorganic powder having a Mohs' hardness of at least 5 , and said backcoating layer contains carbon black and an inorganic powder  having a particle size smaller  larger than said major axis size of said magnetic metal powder and a Mohs' hardness of at least 5 and has a surface roughness in terms of center line average surface roughness smaller than said major axis size of said magnetic metal powder . 
     
     
       10. A magnetic recording assembly which comprises a magnetic tape comprising a substrate, a magnetic layer on one surface of said substrate and a backcoating layer on an opposite surface of said substrate, wherein said magnetic layer has a thickness not larger than about 3.0 μm and contains a magnetic metal powder having a major axis of 0.2 μm or less to achieve high density recording at a center recording wavelength of 0.8 μm or less, said backcoating layer contains carbon black and an inorganic powder having a particle size smaller than said major axis size of said magnetic metal powder and a Mohs' hardness of at least 5 and has surface roughness in terms of center line average surface roughness smaller than said major axis size of said magnetic metal powder, and a total thickness of said substrate, said magnetic layer and said backcoating layer is not larger than 14 μm and a cassette casing made of an ABS resin containing a pigment having a Mohs' hardness of from 2 to 4. 
     
     
       11. A magnetic recording assembly which comprises a magnetic tape comprising a substrate, a magnetic layer on one surface of said substrate and a backcoating layer on an opposite surface of said substrate for recording information at a center recording wavelength of not larger than 0.8 μm, wherein said magnetic layer has a thickness not larger than about 3.0 μm and contains a magnetic metal powder having a major axis of 0.2 μm or less to achieve high density recording at a center recording wavelength of 0.8 μm or less and an inorganic powder having a Mohs' hardness of at least 5, and said backcoating layer contains carbon black which comprises primary particles or agglomerates having a particle size larger than said major axis size of said magnetic metal powder and a cassette casing made of an ABS resin containing a pigment having a Mohs' hardness of from 2 to 4. 
     
     
       12. A magnetic recording assembly comprising a magnetic tape which comprises a substrate, a magnetic layer having a thickness not larger than about 3.0 μm and which contains magnetic metal powder having a major axis of 0.2 μm or less and inorganic powder having a Mohs' hardness of at least 5 on one surface of said substrate and a backcoating layer which contains carbon black which comprises primary particles or agglomerates having a particle size larger than said major axis size of said magnetic metal powder on an opposite surface of said substrate and which is used for recording information at a center recording wavelength of not longer than 0.8 μm, a hub around which said magnetic tape is wound with said backcoating layer facing inside and a cassette casing in which said tape wound hub is set made of an ABS resin containing a pigment having a Mohs' hardness of from 2 to 4. 
     
     
       13. A magnetic recording medium comprising a substrate, a magnetic layer on one surface of said substrate and a backcoating layer on an opposite surface of said substrate, wherein said magnetic layer contains a magnetic metal powder having a major axis of not larger than  0 . 2  μm and an inorganic powder having a Mohs' hardness of at least  5 , said magnetic layer having a thickness not greater than  3 . 0  μm, and said backcoating layer contains carbon black which comprises primary particles or agglomerates having a particle size larger than said major axis of said magnetic metal powder.  
     
     
       14. The magnetic recording medium according to  claim 9 , wherein said magnetic metal powder comprises iron, manganese and an alkaline earth metal.  
     
     
       15. The magnetic recording medium according to  claim 14 , wherein said magnetic layer includes an inorganic powder having a Mohs' hardness of at least  5 .  
     
     
       16. The magnetic recording medium according to  claim 15 , wherein said backcoating layer contains an inorganic powder.  
     
     
       17. The magnetic recording medium according to  claim 16 , wherein said inorganic powder has a particle size smaller than said major axis size of said magnetic metal powder.  
     
     
       18. The magnetic recording medium according to  claim 17 , wherein said inorganic powder has a Mohs' hardness of at least  5 .  
     
     
       19. The magnetic recording medium according to  claim 18 , wherein said inorganic powder has a surface roughness in terms of center line average surface roughness smaller than said major axis size of said magnetic metal powder.  
     
     
       20. The magnetic recording medium according to  claim 9 , wherein said magnetic layer includes an inorganic powder having a Mohs' hardness of at least  5 .  
     
     
       21. The magnetic recording medium according to  claim 9 , wherein said backcoating layer contains an inorganic powder.  
     
     
       22. The magnetic recording medium according to  claim 21 , wherein said inorganic powder has a particle size smaller than said major axis size of said magnetic metal powder.  
     
     
       23. The magnetic recording medium according to  claim 21 , wherein said inorganic powder has a Mohs' hardness of at least  5 .  
     
     
       24. The magnetic recording medium according to  claim 21 , wherein said inorganic powder has a surface roughness in terms of center line average surface roughness smaller than said major axis size of said magnetic metal powder.  
     
     
       25. The magnetic recording medium according to  claim 21 , wherein said inorganic powder is a metal oxide.  
     
     
       26. The magnetic recording assembly according to  claim 25 , wherein said metal oxide is at least one metal oxide selected from the group consisting of α-Fe 2   O   3    and Al   2   O   3   .    
     
     
       27. The magnetic recording medium according to  claim 9 , wherein said carbon black comprises primary particles or agglomerates.  
     
     
       28. The magnetic recording medium according to  claim 9 , wherein a total thickness of said substrate, said magnetic layer and said backcoating layer is not larger than  14  μm.  
     
     
       29. The magnetic recording medium according to  claim 9 , wherein said magnetic metal powder has a coating of an oxide of at least one metal selected from the group consisting of iron, aluminum and silicon.  
     
     
       30. The magnetic recording medium according to  claim 9 , wherein said magnetic layer has a squareness ratio of at least  0 . 85  under an applied magnetic field of  10  KOe.  
     
     
       31. The magnetic recording medium according to  claim 9 , wherein said magnetic layer has a surface roughness of not larger than  0 . 004  μm in terms of center average roughness.  
     
     
       32. The magnetic recording medium according to  claim 9 , wherein said backcoating layer has a surface roughness of not larger than  0 . 01  μm in terms of center average roughness.  
     
     
       33. The magnetic recording medium according to  claim 9 , wherein said carbon black comprises primary particles.  
     
     
       34. The magnetic recording medium according to  claim 9 , wherein said carbon black comprises agglomerates.  
     
     
       35. The magnetic recording medium according to  claim 9 , wherein said magnetic layer has a coercive force of at least  1500  Oe.  
     
     
       36. The magnetic recording medium according to  claim 9 , wherein said substrate is made of a biaxially oriented polyester.  
     
     
       37. The magnetic recording medium according to  claim 9 , wherein said magnetic tape is wound around a hub with said backcoating layer facing inside.  
     
     
       38. The magnetic recording medium according to  claim 37 , wherein said hub has a sink of less than  5  μm on the peripheral surface.  
     
     
       39. The magnetic recording medium according to  claim 9 , further comprising a cassette casing made of an ABS resin containing a pigment having a Mohs' hardness of from  2  to  4 .