Process for thermoremanent duplication of magnetic recording master tape onto slave tape with reduced dimensional changes of slave tape

DETAILED DESCRIPTION What is claimed is: 1.
A process for thermoremanent duplication of magnetic signals of a magnetic recording master tape on a magnetic recording slave tape consisting of a polyester film base and a layer of a ferromagnetic material coated thereon, which comprises the following steps of i.
heating said slave tape above the Curie point of said ferromagnetic material, ii.
contacting said master tape and said slave tape, iii.
cooling said slave tape below its Curie point while contacted with said master tape, iv.
separating said master tape and said slave tape, and then v.
heat-treating said slave tape without stretch at a temperature of at least 40.
degree.
C.
but less than the Curie point of said ferromagnetic material for at least 0.
1 second.
2.
The process of claim 1 wherein the heat-treating temperature is 70.
degree.
C.
to a point 10.
degree.
C.
lower than the Curie point of said ferromagnetic material.
3.
The process of claim 1 wherein said polyester is a member selected from polyesters at least 90 mol% of which recurring units consist of ethylene 2,6-naphthalene dicarboxylate, ethylene terephthalate and 1,4-cyclohexane terephthalate.
4.
The process of claim 1 wherein said ferromagnetic material is a chromium dioxide-type ferromagnetic material.
5.
The process of claim 1 wherein said stretchless heat-treatment comprises continuously feeding the slave tape after thermoremanent duplication into a heat-treating zone by means of a roller unit, allowing it to pass through the zone, and then withdrawing it from the zone, wherein the slave tape is fed at an overfeed rate (k), as defined by the following equation, of 0 to 2% ##EQU3## in which V.
sub.
1 is the rate of feeding the slave tape into the heat-treating zone, and V.
sub.
2 is the rate of withdrawing the slave tape from the heat-treating zone.
6.
The process of claim 5 wherein the overfeed rate is 0.
02 to 2%.
7.
The process of claim 1 wherein said stretchless heat-treatment is performed immediately after the thermoremanent duplication