Stock material or miscellaneous articles – Magnetic feature
Reexamination Certificate
1998-02-17
2001-11-20
Dixon, Merrick (Department: 1774)
Stock material or miscellaneous articles
Magnetic feature
C428S375000
Reexamination Certificate
active
06319624
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a resin roll for calendering a magnetic recording medium and to a manufacturing method therefore.
2. Description of the Background Art
Generally, it is a wide spread practice in the manufacturing of a magnetic recording medium to apply a magnetic layer on a base film and to perform calendering thereafter.
Generally, in the process of manufacturing a magnetic recording medium, the magnetic recording medium is calendered by being passed between a mirror-surfaced metal roll and an elastic roll such as a resin roll disposed in opposing relationship thereto. A high nip pressure is applied to the recording medium to eliminate voids in the magnetic layer, to make the surface of the magnetic recording medium smooth and to increase the density of the magnetic layer. In this case, the magnetic layer side of the magnetic recording medium is brought into contact with the metal roll.
The signal density of the magnetic recording medium has been significantly improved recently. In order to obtain a highly dense magnetic recording medium, it is necessary to apply a magnetic coating filled with magnetic powder to a high density on the base film so as to increase the magnetic flux density. However, if the amount of the magnetic powder is increased, it becomes difficult to eliminate voids in the magnetic layer generated when the solvent is dried, and also it has been difficult to obtain sufficient surface smoothness of the magnetic layer under the conventional conditions for calendering, because hardness of the magnetic coating could have been increased.
Accordingly, in order to make smooth the surface of the above described magnetic layer filled with magnetic powder to a high density and to completely eliminate voids, it is necessary to apply higher temperature and higher nip pressure in the calendering step.
Accordingly, there has been a demand for a resin roll for calendering which can be used at higher temperature and which can provide greater pressure.
The following characteristics are required of the resin roll for calendering.
(1) A roll with satisfactory high surface smoothness.
(2) Hardness, especially high surface hardness.
(3) Heat resistance, especially heat resistance to render the roll less likely to deform due to thermal expansion or melting that would result from autogenous heat.
(4) Compression strength to withstand the high nip pressure applied by the metal roll and to remain free of cracking or breaking.
(5) A roll free of pin holes.
However, in the conventional resin roll for calendering a magnetic recording medium, the roll properties are limited, so that the nip width, that is, the nip area tends to be unavoidably large. Therefore, in terms of applied pressure, that is, pressure per unit area acting on the nip surface, satisfactory pressure per unit area to meet the recent demand for high density magnetic recording medium could not be obtained. Furthermore, in order to improve efficiency in processing, when heating is performed at a higher temperature or when the press load is increased to obtain larger pressure per unit area, the nip width, that is, the nip area is further enlarged, making it difficult to obtain the effective pressure per unit area at the nip surface.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a resin roll for calendering a magnetic recording medium in which the nip width is smaller than that of the prior art under a similar load, and the nip width is not increased, even when under high load at a high temperature, thus providing substantially larger pressure per unit area, whereby the surface is smooth and surface hardness is high, which provides compression strength and heat resistance and is free of pin holes.
Another object of the present invention is to provide a method of manufacturing the above described high performance resin roll for calendering a magnetic recording medium at low cost with high efficiency.
Still another object of the present invention is to provide a calendering apparatus employing the above described high performance resin roll as an elastic roll.
The above described objects of the present invention are attained by a resin roll for calendering a magnetic recording medium including a metal roll core and a thermosetting resin outer layer, wherein a surface portion of the thermosetting resin outer layer has a storage elastic modulus (E′) from 5×10
10
to 5×10
11
dyn/cm
2
at a temperature in the range from 50° to 150° C. at a frequency of 10 hertz (Hz). More specifically, according to the present invention, the storage elastic modulus (E′) of the surface portion of the thermosetting resin outer layer of the resin roll for calendering at a temperature of use is increased, whereby the nip width can be made smaller, and since the high storage elastic modulus (E′) of the surface portion is maintained even at a high temperature, a small nip width can be maintained.
Preferably, the storage elastic modulus (E′) at the surface portion of the thermosetting resin outer layer of the roll should be at least 6×10
10
dyn/cm
2
, and more preferably, it should be at least 8×10
10
dyn/cm
2
. Preferably, it should be at most 2×10
11
dyn/cm
2
, and more preferably, it should be at most 1.5×10
11
dyn/cm
2
.
The conditions for measurement for temperature and frequency described above are set as close as possible to the conditions for use of the resin roll for calendering. The temperature is normally in the range from 50° to 150° C., which is preferably 50° to 180° C. and, more preferably, 50° to 200° C.
The frequency is set to 10 hertz. This value is selected for the following reasons. If the outer periphery of the resin roll for calendering is set to 1 m and the running speed to 300 m/min, for example, the rate rotation of the roll is 300 rpm, and the frequency corresponding to this rate of rotation is 5 Hz. However, if the resin roll for calendering is pinched between two metal rolls, the surface portion of the roll passes twice the nip per one rotation, and hence the frequency is set to 10 Hz.
In the foregoing, if the storage elastic modulus (E′) at the surface portion of the thermosetting resin outer layer of the resin roll for calendering is not higher than 5×10
10
dyn/cm
2
, the nip width becomes too large, resulting in similar pressure per unit area as that of the prior art, and hence it is not preferable. If the storage elastic modulus (E′) exceeds 5×10
11
dyn/cm
2
, the nip width becomes smaller and larger pressure per unit area can be obtained. However, since the storage elastic modulus (E′) is too large, ups and downs of the material to be processed cannot be absorbed by the roll surface, hindering uniform calendering. Therefore, it is not preferable.
The thermosetting resin constituting the outer layer of the resin roll for calendering includes, for example, epoxy resin, polyurethane resin, polyisocyanurate resin, cross linked polyesteramide resin, unsaturated polyester resin and diallylphthalate resin. In view of durability, heat resistance and moldability, epoxy resin and cross linked polyesteramide resin are preferable, and specifically, epoxy resin is desired.
The aforementioned metal roll core is made of a metal such as iron, steel, stainless steel or aluminum.
From another view point, the resin roll for calendering a magnetic recording medium in accordance with the present invention includes a metal roll core and a thermosetting resin outer layer, wherein an expression (1−&ngr;
2
)/E′ representing relation between storage elastic modulus (E′) and the Poisson's ratio (&ngr;) with respect to Hertz's equation representing nip width of the surface portion of the thermosetting outer layer is within the range of
5×10
−12
cm
2
/dyn<(1−&ngr;
2
)/E′<2×10
−11
cm
2
/dyn
under the condition that the temperature is 50° to 150° C. and the frequency is 10 Hz.
In the ab
Abe Tatsuyuki
Nakayama Kenjiro
Watanabe Atsuo
Birch & Stewart Kolasch & Birch, LLP
Dixon Merrick
Yamauchi Corporation
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