Winding core and magnetic recording medium producing method

Abstract

A winding core 10 according to the present invention has a cylindrical outer peripheral surface and arranged in a manner that when a web is wound around the outer peripheral surface and so a predetermined pressure acts on the outer peripheral surface, the deformation distortion γ(=ΔR/R) of the outer peripheral surface along the radial direction thereof is equal to or less than 0.001. In this case, ΔR represents the maximum deformation amount along the radial direction of the outer peripheral surface of the winding core and R the diameter of the outer peripheral surface of the winding core upon no occurrence of deformation.

Description

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a winding core and a magnetic recording medium producing method and, more particularly, relates to a winding core and a magnetic recording medium producing method which can reduce the probability of the occurrence of the failure of a web in the producing process etc. of the magnetic recording medium.

[0003] 2. Description of the Related Art

[0004] The producing process of a magnetic recording medium includes a process of setting a winding core (supply roller) around which a long belt-shaped supporting member is wound to a coating apparatus, a process of coating magnetic material or non-magnetic material on one surface of the supporting member while feeding the supporting member from the winding core, and a process of winding the supporting member having been coated around a winding core (take-up roller), etc. The supporting member thus wound around the supply roller is formed by polyethylene terephthalate (PET) etc.

[0005] FIG. 4 shows a conventional example of a winding core used as a supply roller or a take-up roller. The winding core 80 includes a cylindrical portion 81 having a cylindrical outer peripheral surface. An annular pivoting member 83 is fitted in and screwed to the both end portions of the cylindrical portion 81. A web (including a supporting member being not coated thereon or a supporting member subjected to a coating process or other predetermined processing, etc. in the specification) W as a long belt-shaped supporting member is wound around the winding core 80. There is a case that the web with the length of 9000 to 10000 m is wound around the winding core 80.

[0006] However, since the thickness of the magnetic recording medium has become thinner in order to cope with the tendency of the high density of the magnetic recording medium, the following new problem arises. That is, as shown by an enlarged view in FIG. 4, when the web W is wound around the winding core 80 to increase the laminated wound number around the cylindrical portion 81, there arises a case that the web W wound near the outer peripheral surface of the cylindrical portion 81. In other words, the web W at the lower layer is bent at some portions and deformed as if it is buckled. To be more concrete, the web W is deformed in a manner that projections protruding in the outer diameter direction or not-shown projections protruding in the inner diameter direction from the plane in parallel to the outer peripheral surface of the cylindrical portion 81 are formed at some portions on the web W along the axial direction of the cylindrical portion 81. Such deformation occurs not only at the web W of the lowest layer but also the web W over plural layers. For example, there arises a case that such deformation occurs over the range of about 5% of the entire distance H of the winding core 80, around which winding operation of the web W has been completed, from the outer peripheral surface of the cylindrical portion 81 to the most outer peripheral surface of the web W.

[0007] Since the failure portion at which such deformation occurred must be disposed, the productivity of the magnetic recording media is degraded.

SUMMARY OF THE INVENTION

[0008] The invention has been made in view of the aforesaid problem of the conventional art, and an object of the invention is to provide a winding core which does not cause the deformation failure of a web even when the thin web is wound around the winding core to increase the laminated wound number thereof and to provide a magnetic recording medium producing method which does not cause the deformation failure of the web around the winding core.

[0009] The inventors of the invention have found that when the web W is wound around the winding core 80 to increase the laminated wound number thereof, there is a case that the outer peripheral surface of the cylindrical portion 81 deforms in the inner diameter direction of the cylindrical portion, which becomes a cause for raising the deformation of the web W. That is, the cylindrical portion is deformed by the winding fastening force of the web W in a manner that the diameter of the outer peripheral surface of the cylindrical portion 81 of the winding core 80, in particular, the diameter of the outer peripheral surface at the center portion along the axial direction of the cylindrical portion 81 becomes smaller as compared with the non-deformation case.

[0010] Then, the inventors investigated wholeheartedly the aforesaid fact and have thought the following configurations 1 to 4.

[0011] Configuration 1: A winding core comprising a cylindrical outer peripheral surface and, when a web is wound around the outer peripheral surface and so a pressure of 300 Pa acts on the outer peripheral surface, deformation distortion γ along a radial direction of the outer peripheral surface, represented by a following expression [1], is equal to or less than 0.001

γ=ΔR/R  [1]

[0012] where, in the expression [1], AR represents a maximum deformation amount along the radial direction of the outer peripheral surface of the winding core and R represents a diameter of the outer peripheral surface of the winding core upon no occurrence of deformation.

[0013] Configuration 2: In a method of producing a magnetic recording medium including a process of winding a web around a winding core, the web is wound around the winding core so that a following expression [2] is satisfied when the web is wound around an outer peripheral surface of the winding core and so a pressure of 300 Pa acts on the outer peripheral surface

ΔR/R≦ 0.001  [2]

[0014] where, in the expression [2], ΔR represents a maximum deformation amount along a radial direction of the outer peripheral surface of the winding core and R represents a diameter of the outer peripheral surface of the winding core upon no occurrence of deformation.

[0015] Configuration 3: In a winding core having a cylindrical outer peripheral surface, wherein a pressure acts on the outer peripheral surface when a web is wound around the outer peripheral surface, a deformation coefficient β of the winding core, represented by a following expression [3], is equal to or less than 6.0×10−11

β=ΔR×P/R2  [3]

[0016] where, in the expression [3], ΔR represents a maximum deformation amount (m) along a radial direction of the outer peripheral surface of the winding core, P represents a pressure (N/m2) acting on the outer peripheral surface of the winding core and R represents a diameter (m) of the outer peripheral surface of the winding core upon no occurrence of deformation.

[0017] Configuration 4: In a method of producing a magnetic recording medium including a process of winding a web around a winding core, the web is wound around the winding core so that a following expression [4] is satisfied

ΔR×P/R2≦6.0×10−11  [4]

[0018] where, in the expression [4], ΔR represents a maximum deformation amount (m) along a radial direction of an outer peripheral surface of the winding core, P represents a pressure (N/m2) acting on the outer peripheral surface of the winding core and R represents a diameter (m) of the outer peripheral surface of the winding core upon no occurrence of deformation.

[0019] According to the winding core of the configurations 1 and 3, even when the long web is wound around the winding core and so a large pressure due to the winding fastening force of the web acts on the outer peripheral surface of the winding core, the winding core scarcely deforms in the radial inner direction thereof. Thus, the deformation failure of the web scarcely occurs and so an amount of the web which must be disposed can be reduced remarkably.

[0020] Incidentally, in the configurations 1 and 3, although the means for satisfying the expression [1] and/or the expression [3] is not limited, as such means, the invention may provide a reinforcement member for improving the rigidity of the winding core in the radial direction thereof, a solid-core portion in the winding core, the processing on the surface of the winding core for improving the rigidity thereof, etc.

[0021] According to the producing method of a magnetic recording medium of the configurations 2 and 4, the deformation failure of the web scarcely occurs and so an amount of the web which must be disposed can be reduced remarkably. Thus, the productivity of the magnetic recording medium can be improved.

[0022] Incidentally, in the configurations 2 and 4, various methods may be employed in order to wind the web around the winding core so as to satisfy the expression [2] and/or the expression [4]. For example, it is considered that the winding core described in the configurations 1 and 3 may be employed as a supply portion and a take-up portion. Alternatively, it is considered to control the tension of the web.

[0023] The gist of the configurations 2 and 4 resides in that the entirety of the winding core is thought as if it is an elastic member having elasticity along the radial direction thereof, then the deformation coefficient β which is different from the elastic coefficient but similar thereto is defined and the deformation coefficient is set to be equal to or less than a predetermined value.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] FIG. 1A and 1B are partially cut-away views showing an embodiment of the present invention;

[0025] FIG. 2 is a schematic diagram showing an apparatus for executing the invention;

[0026] FIG. 3 is a graph showing the relation between deformation coefficients and failure occurrence probabilities in an example and a comparative example, and

[0027] FIG. 4 is a partially cut-away view showing a conventional winding core.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0028] The embodiment of the invention will be explained based on the accompanying drawings. FIG. 1A and 1B show a winding core 10 according to the embodiment of the invention. As shown in FIG. 1A, the winding core 10 is configured in a manner that an annular supporting portion 12 is fitted at the both ends of the cylindrical portion 11 thereof. The supporting portion 12 has a small-diameter cylindrical portion 12a which protrudes from the both ends of the cylindrical portion 11 and has a diameter smaller than that of the cylindrical portion 11. A pivoting member 13 is fitted and fixed by a screw etc. to the projection end of the small-diameter cylindrical portion 12a.

[0029] An inner peripheral surface supporting member 15 serving as a reinforcement member for improving the rigidity of the winding core 10 in the diameter direction thereof is fitted at the inner peripheral surface at the center portion along the axial direction of the cylindrical portion 11.

[0030] As shown in FIG. 1B which is a diagram seen toward an arrow B in FIG. 1A, the inner peripheral surface supporting member 15 is arranged in a manner that a center hole 17 and lightening portions 18 are provided at a circular-plate shaped member 16 whose outer peripheral surface fits against the inner peripheral surface of the cylindrical portion 11.

[0031] Since the winding core 10 shown in FIG. 1 is provided with the inner peripheral surface supporting member 15, the following expressions [1] and [2] are satisfied.

γ=ΔR/R  [1]

ΔR/R≦0.001  [2]

[0032] In the expressions [1] and [2], γ represents the deformation distortion along the radial direction of the winding core, ΔR represents the maximum deformation amount along the radial direction of the outer peripheral surface of the winding core and R represents the diameter of the outer peripheral surface of the winding core upon no occurrence of deformation.

[0033] According to the winding core 10 thus configured, even when the long web is wound around the winding core and so a large pressure due to the winding fastening force of the web(for example 300 Pa) acts on the outer peripheral surface of the winding core, the cylindrical portion 11 scarcely deforms in the radial inner direction. Thus, the web hardly deforms.

[0034] The winding core according to the invention is not limited to the aforesaid embodiment and the winding core may be subjected to suitable deformation, improvement etc.

[0035] For example, as the inner peripheral surface supporting member, a member including a ring member whose outer peripheral surface fits against the inner peripheral surface of the cylindrical portion and a plurality of bridging rods for supporting the ring member etc. may be employed.

[0036] Further, in order to improve the rigidity in the radial direction of the winding core, the cylindrical portion may be formed by material with high rigidity (for example, Young's modulus of 125 GPa) instead of using the reinforcement member. Alternatively, a member with a high rigidity may be wound around the cylindrical portion instead of using the reinforcement member.

[0037] Young's modulus of bakelite which is an example of the material of the conventional winding core is 7 GPa.

[0038] FIG. 2 is a diagram showing the configuration of a coating apparatus for carrying out the producing method of the magnetic recording medium according to the invention. Incidentally, other apparatus etc. may be employed and applied to the invention.

[0039] The coating apparatus 30 includes a coating section 31 and a calendar section 32. In the coating section 31, the web W is supplied from a supply portion 33 which is formed by winding the web on the outer peripheral surface of the winding core 10 shown in FIG. 1. The web W thus supplied is transferred by driving rollers 34 such as suitable transfer rollers, suction drums with grooves etc. and passed through a first dry zone 36, a back coating portion 37 and a second dry and heat processing zone 38.

[0040] Aramid or PET etc. may be employed as the material of the supporting member (web), but the material of the supporting member is not limited thereto.

[0041] The web W passed through the coating section 31 is subjected to the calendar processing by the calendar section 32. That is, the web W is subjected to the calendar processing in a manner that the web is sandwiched and transferred between calendar rollers 40 and 41 and calendar rollers 41 and 42.

[0042] The web W having passed the calendar section 32 is wound in a roll shape by a take-up portion 43 having the winding core 10 shown in FIG. 1.

[0043] According to the aforesaid producing method of the magnetic recording medium using the coating apparatus 30, since the deformation failure of the web W hardly occurs at the supply portion 33 and the take-up portion 43, an amount of the web W which must be disposed can be reduced remarkably. Thus, the productivity of the magnetic recording medium can be improved.

Embodiment

[0044] The remarkable effects of the invention will be explained based on the embodiment of the invention.

[0045] As the winding core of the take-up portion 43 of the coating apparatus 30 shown in FIG. 2, three winding cores each having the configuration shown in FIG. 1 and a deformation coefficient β of 1.5×10−11 are prepared and three winding cores each having the configuration shown in FIG. 1 and a deformation coefficient β of 4.5×10−11 are prepared. The web of 10000 m is wound around these winding cores and then observation was made as to the deformation failure of the web. The observation result is shown in the graph of FIG. 3.

[0046] As a comparative example, three winding cores each not having the inner peripheral surface supporting member 15 shown in FIG. 1 but having a deformation coefficient β of 7.0×10−11 are prepared and three winding cores each not having the inner peripheral surface supporting member 15 shown in FIG. 1 but having a deformation coefficient β of 1.3×10−10 are prepared. The web of 10000 m is wound around these winding cores and then observation result of the deformation failure of the web is also shown in the graph of FIG. 3.

[0047] In FIG. 3, the failure occurrence probability represents a % range with respect to the entire distance H (see FIG. 4) from the outer peripheral surface of the cylindrical portion to the most outer peripheral surface of the web where the deformation failure of the web occurred. The diameter of the outer peripheral surface of each of the winding cores is 300 mm.

[0048] As shown in FIG. 3, when the deformation coefficient β is equal to or less than 2.0×10−1, the failure occurrence probability is almost 0. When the deformation coefficient β exceeds 2.0×10−11, the failure occurrence probability increases gradually, and the failure occurrence probability becomes 1% when the deformation coefficient is 6.0×10−11. Further, when the deformation coefficient β exceeds 6.0×10−11, the failure occurrence probability increases rapidly. For example, when the deformation coefficient β is 1.3×10−10, the failure occurrence probability becomes 5% or more.

[0049] When the failure occurrence probability is 1% or less, an amount of the web which must be disposed can be reduced remarkably and so the productivity of the magnetic recording medium can be improved.

[0050] As described above, according to the invention, even when the long web is wound around the winding core and so a large pressure acts on the outer peripheral surface of the winding core, the winding core scarcely deforms in the radial inner direction thereof. Thus, the deformation failure of the web scarcely occurs and so an amount of the web which must be disposed can be reduced remarkably.

[0051] Therefore, according to the invention, the productivity of the magnetic recording medium can be improved.

Claims

1. A winding core comprising a cylindrical outer peripheral surface for winding a web, wherein when a predetermined pressure acts on said outer peripheral surface by winding web, deformation distortion γ of said outer peripheral surface along radial direction thereof satisfies following expressions:γ=ΔR/R≦0.001,andγ≦0.001,wherein ΔR represents a maximum deformation amount along said radial direction of said outer peripheral surface of said winding core and R represents a diameter of said outer peripheral surface of said winding core upon no occurrence of deformation.

2. A winding core comprising a cylindrical outer peripheral surface for winding a web, wherein when a pressure acts on said outer peripheral surface by winding said web, deformation coefficient β of said winding core satisfies following expressions:β=ΔR×P/R2and,β≦6.0×10−11,wherein ΔR represents a maximum deformation amount (m) along a radial direction of said outer peripheral surface of said winding core, P represents a pressure (N/m2) acting on said outer peripheral surface of said winding core and R represents a diameter (m) of said outer peripheral surface of said winding core upon no occurrence of deformation.

3. The winding core according to claim 1, comprising a supporting portion which fits an outer surface thereof fits to an inner surface of said winding core.

4. A method for producing a magnetic recording medium comprising a step of winding a web around a winding core, wherein when a predetermined pressure acts on an outer peripheral surface of said winding core by winding said web, a following expression is satisfied at said outer peripheral surface:ΔR/R≦0.001,wherein ΔR represents a maximum deformation amount along a radial direction of said outer peripheral surface and R represents a diameter of said outer peripheral surface of said winding core upon no occurrence of deformation.

5. A method for producing a magnetic recording medium comprising a step of winding a web around a winding core, wherein a following expression is satisfied at an outer peripheral surface of said winding core:ΔR×P/R2≦6.0×10−11,wherein ΔR represents a maximum deformation amount (m) along a radial direction of an outer peripheral surface, P represents a pressure (N/m2) acting on said outer peripheral surface of said winding core and R represents a diameter (m) of said outer peripheral surface of said winding core upon no occurrence of deformation.