Magnetic tape and process of making a magnetic tape

DETAILED DESCRIPTION OF THE INVENTION In practicing the invention, an aqueous dispersion of the magnetic particles containing the dissolved CSZ monomer is applied to the backing, the particles are magnetically oriented, the coated film is dried and the polymerization of the CSZ monomer is completed by a mild heat treatment.
The drying and curing may be effected in a single heat treatment, as, for instance, by passing the wet film under a bank of infrared lamps or through a tunnel oven.
The temperature attained in the heat treatment is not critical and may be varied widely.
The drying may be effected at from room temperature to about 150.
degree.
C.
, about 80.
degree.
- 120.
degree.
C.
being optimum.
While the polymerization proceeds to a large extent concurrently with the drying, it is usually preferred to assure completion by a further heat treatment which can be at the same or a higher temperature, up to that at which the backing film might begin to soften or deform.
For most systems 1-5 minutes at 75.
degree.
-150.
degree.
C.
is suitable.
While the magnetic particles may be any of those known in the art such as chromium dioxide, zinc ferrous ferrite, etc.
, iron oxide particles are the most widely used.
They should be finely divided, uniformly dispersed in the coating medium, inert to the dispersing agent, binder and backing, and magnetically oriented.
Also, their density per unit area on the tape should be as high as possible while the thickness of the coating should be as small as possible consistent with acceptable functional properties.
To maximize these opposing desiderata the coating composition should contain the maximum possible proportion of magnetic particles and the minimum proportion of binder that is consonant with the need for sufficient fluidity for application of a uniform layer on the backing and the production of a finished coating that has the requisite smoothness, toughness, flexibility, adherence to the backing and abrasion resistance.
This means that the volume ratio of pigment (magnetic particles) to binder (CSZ polymer) should be as high as possible without undue sacrifice of film properties