FILM WINDING CORE, AND WOUND FILM BODY USING SAME

Abstract

A film winding core (10) of the present invention includes a core body (12) and a plurality of film supporting portions (14). The core body (12) has a tubular shape. The plurality of film supporting portions (14) are provided around the core body (12). The film supporting portions (14) protrude from the outer peripheral surface (12p) of the core body (12) respectively at a plurality of positions in a rotational direction of the core body (12) so that a film (18) is supported away from the outer peripheral surface (12p) of the core body (12). Each of the film supporting portions (14) is made of a material that can be deformed when the film (18) is wound on the film winding core (10).

Description

TECHNICAL FIELD

The present invention relates to a film winding core and a wound film body using the core.

BACKGROUND ART

A long film is produced by a known method such as extrusion molding and wound on a cylindrical core for storage and shipment. The film thus wound on the cylindrical core is distorted (deformed) during storage, which may cause difficulties in unwinding the film. For example, Patent Literature 1 points out such a problem.

Patent Literature 1 describes a core configured to prevent the distortion of a belt-like article resulting from the contraction of the wound article. Specifically, after the belt-like article is wound on the core in close contact with the outer periphery of the core, the core is contracted in the radial direction thereof. Then, after the core is expanded in the radial direction to increase the contact between the outer periphery of the core and the belt-like article, the belt-like article is unwound from the core.

CITATION LIST

Patent Literature

Patent Literature 1: JP 2009-113877 A (FIG. 5 to FIG. 10)

SUMMARY OF INVENTION

Technical Problem

Since the core described in Patent Literature 1 has a relatively complex mechanism, it is not suitable for sale to customers in the form of a roll of film wound on the core.

It is an object of the present invention to provide a simple technique for preventing defects in unwinding the film.

Solution to Problem

The present invention provides a film winding core on which a long film is to be wound. This film winding core includes: a core body having a tubular shape; and a plurality of film supporting portions provided around the core body. The film supporting portions protrude from an outer peripheral surface of the core body respectively at a plurality of positions in a rotational direction of the core body so that the film is supported away from the outer peripheral surface of the core body, and each of the film supporting portions is made of a material that can be deformed when the film is wound on the film winding core.

In another aspect, the present invention provides a wound film body including: the film winding core of the present invention; and a film wound on the film winding core of the present invention.

Advantageous Effects of Invention

To the inventors' knowledge, a film is distorted based on the following mechanism. Depending on the production method of the film, a long film has not a little thickness unevenness (variations in the thickness) in a width direction. When such a film is wound on a conventional cylindrical core, a thick portion of the film expands outward more than a thin portion thereof. Then, tension is concentrated on the thick portion, and the thick portion is stretched in the longitudinal direction. On the other hand, sufficient tension is not applied to the thin portion, and so-called “gapping” occurs in some cases. “Gapping” refers to the formation of a gap between the inner layer and the outer layer of the wound film. In the case where the film is wound on the core and then the wound film is stored in a temperature environment in which the film contracts, a gapped portion of the film contracts in the longitudinal direction to eliminate the gap. As a result, distortion between the thick portion and the thin portion increases. This makes a difference in the longitudinal length between the thick portion and the thin portion.

This distortion is memorized in the film. Therefore, the film is unwound from the core while keeping the distortion. Then, sufficient tension is not applied to the thick portion, which causes a slack in the thick portion. This phenomenon is most obvious when the tension applied to the film is not high enough to unwind the film. The slack in the film causes errors in feeding the film, and reduces the yield of film-related products and the availability of the film.

According to the present invention, the plurality of film supporting portions are provided around the core body. Since the film supporting portions protrude from the outer peripheral surface of the core body, the film is supported by the film supporting portions. Therefore, it is possible to prevent the film from coming into close contact with the core body between two film supporting portions that are adjacent to each other in the rotational direction. Thus, it is possible to prevent as much as possible the distortion from being memorized in the film. In addition, the film supporting portions are made of a material that can be deformed when the film is wound. The deformation of the film supporting portions can alleviate or offset the influence of the uneven thickness of the film.

As described above, according to the core of the present invention, the distortion caused by the uneven thickness can be suppressed. Therefore, the bend or slack in the film can be prevented during unwinding of the film. As a result, stable feeding of the film can be achieved during unwinding thereof, and thus the incidence of manufacturing defects (feeding errors) can be reduced significantly. The yield of film-related products and the availability of the film are also improved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a film winding core according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of the core shown in FIG. 1, taken along the line II-II.

FIG. 3 is a cross-sectional view of a wound film body using the core shown in FIG. 1.

FIG. 4 is a schematic view showing a preferable protrusion height of film supporting portions.

FIG. 5A is a cross-sectional view of a core according to a modification.

FIG. 5B is a cross-sectional view of a core according to another modification.

FIG. 5C is a cross-sectional view of a core according to still another modification.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Hereinafter, in this description, the film winding core is simply referred to as a “core”.

As shown in FIG. 1 and FIG. 2, a core 10 is composed of a core body 12, a pair of bearing portions 16, and a plurality of film supporting portions 14. As shown in FIG. 3, a wound film body 100 includes the core 10 and a long film 18 wound on the core 10. The core 10 can be rotated about a rotational axis O. The rotational axis O is an axis passing through the center of the core body 12.

The core body 12 has a tubular shape. For example, the core body 12 can be formed of a tubular member with both ends open. The cross-sectional shape of the core body 12 is not particularly limited. The shape may be a circle as in the present embodiment, or it may be a polygon. In this core 10, the film 18 is supported directly by the film supporting portions 14. Furthermore, as described later, the influence of the uneven thickness of the film 18 is cancelled out by the film supporting portions 14. Therefore, a high dimensional accuracy is not required for the core body 12.

The material of the core body 12 is not particularly limited. The core body 12 can be made of resin, metal, ceramic, glass, or a combination of these. Desirably, the core body 12 is not easily deformed when the film 18 is wound on the core 10. Typically, the core body 12 can be obtained by molding a thermoplastic resin, such as polycarbonate, polypropylene, polyethylene, acrylonitrile-butadiene-styrene copolymer, polyester (for example, polyethylene terephthalate, polyethylene naphthalate or the like), polystyrene, or polyvinyl chloride, by a known method, for example, by injection molding.

The film supporting portions 14 are portions provided around the core body 12, and protrude radially outwardly from the outer peripheral surface 12p of the core body 12 respectively at a plurality of positions in the rotational direction of the core body 12 so that the film 18 is supported away from the outer peripheral surface 12p of the core body 12. According to the film supporting portions 14, the close contact between the film 18 and the core body 12 can be avoided between the film supporting portions 14 that are adjacent to each other in the rotational direction. Thus, it is possible to prevent the distortion from being memorized in the film 18.

The film supporting portions 14 are made of a material that can be deformed when the film 18 is wound on the core 10. In the present embodiment, the film supporting portions 14 are made of an elastically deformable material. When the film supporting portions 14 are elastically deformable, sufficient friction can be generated between the film supporting portions 14 and the film 18. Therefore, free rotation of the core 10 can be prevented when the film 18 is wound and unwound. In addition, since the film supporting portions 14 have appropriate elastic and cushioning properties, the influence of the uneven thickness of the film 18 can be alleviated or offset effectively.

Typically, at least one material selected from the group consisting of sponge, rubber, and foam can be used as a material for the film supporting portions 14. These materials are all inexpensively available and easy to process. These materials also allow sufficient friction to act between the film 18 and the film supporting portions 14. For example, since urethane foam has the above-mentioned properties in a well-balanced manner, it is recommended as the material for the film supporting portions 14. Materials having appropriate impact resilience are, for example, natural rubber, nitrile rubber, silicone rubber, and foams of these. Besides these materials, polyethylene, EVA (ethylene-vinylacetate copolymer), EPDM (ethylene-propylene-diene rubber), fluorine rubber, and foams of these also can be used. The film supporting portions 14 can be fixed to the core body 12 by a known method such as bonding or welding.

The entire film supporting portion 14 does not have to be made of any one of the above materials. Only a portion of the film supporting portion 14, for example, a portion in contact with the film 18 may be made of any one of the above materials.

In the present embodiment, the film supporting portions 14 are arranged at regular intervals (regular angular intervals) in the rotational direction of the core body 12. The film supporting portions 14 arranged at regular intervals in the rotational direction improves the uniformity of load on the film 18 in the longitudinal direction of the film 18. This has an advantage in suppressing the distortion.

As shown by a dashed line in FIG. 4, an imaginary polygon PL having a minimum area required to surround all the film supporting portions 14 in a cross-section perpendicular to the rotational axis O is defined. The positions of the film supporting portions 14, the number of the film supporting portions 14, the height h of the film supporting portions 14 protruding from the outer peripheral surface 12p of the core body 12 can be adjusted so that the core body 12 fits within this polygon PL. When these requirements are satisfied, the film 18 can be prevented from being strongly pressed against the core body 12. For example, a core 10A shown in FIG. 5A has the film supporting portions 14 provided at regular intervals at eight positions thereon in the rotational direction.

The film supporting portions 14 are provided so as to extend from one side of the core body 12 to the other side thereof. The longitudinal direction of the film supporting portion 14 is parallel to the rotational axis O of the core 10, and is perpendicular to the longitudinal direction of the film 18. This configuration allows a uniform supporting force to be applied to the film 18 in the width direction of the film 18.

In the present embodiment, the film supporting portion 14 has a semicircular column shape. This shape allows the film supporting portion 14 to have a reasonably large surface area for supporting the film 18. This is preferred from the viewpoint of preventing a local deformation of the film 18. A core 10B shown in FIG. 5B is provided with film supporting portions 24 having a hollow semicircular column shape. A core 10C shown in FIG. 5C is provided with film supporting portions 34 having a rectangular column shape. These film supporting portions 24 and 34 also can be suitably employed because they perform the same action as the film supporting portions 14. In particular, since the film supporting portions 24 having a hollow structure as shown in FIG. 5B can be easily elastically deformed, the effect of alleviating or offsetting the influence of the uneven thickness of the film 18 can be expected sufficiently. In the cross-section perpendicular to the rotational axis O, the outer peripheral surface of the film supporting portion 14 or 24 has a smaller curvature than that of the outer peripheral surface 12p of the core body 12.

The bearing portions 16 are portions which are mounted on both sides of the core body 12 and into which a shaft (not shown) used to rotate the core 10 is to be inserted. The core 10 can be rotated smoothly by the bearing portions 16. The bearing portions 16 have the same contour as the core body 12. However, the bearing portions 16 have a larger diameter than that of the core body 12, which means that the bearing portions 16 may extend beyond the core body 12.

In the present embodiment, the bearing portions 16 are each constituted by a disc-shaped flange having a bearing hole 16h. The bearing portions 16 may be integrated with the core body 12, or may be detachable from the core body 12. In the former case, the bearing portions 16 can be integrated with the core body 12 by a known method such as welding or bonding. In the latter case, fitting structures can be provided between the core body 12 and the bearing portions 16. In the case where the bearing portions 16 are detachable, this one pair of bearing portions 16 can be shared by many cores 10. Therefore, the cost of the core 10 can be reduced. In addition, since the weight of the wound film body 100 can be reduced by removing the bearing portions 16 therefrom, a reduction in the transportation cost for delivery to a customer also can be expected. The bearing portions 16 are not essential components, of course. The shaft can be inserted directly into the core body 12 so as to rotate the core 10.

As used in this description, the “bearing portion 16” may not have a function of supporting the shaft, to be exact. The term “bearing portion” is used in the sense of “a portion having a through-hole (bearing hole 16h) for mounting the core 10 on the shaft”.

Since the core 10 of the present embodiment does not have a mechanically movable portion, it can be produced at low cost.

As shown in FIG. 3, the wound film body 100 has a polygonal shape, typically a regular polygonal shape, as a whole, in the cross-section perpendicular to the rotational axis O (or in plan view). In the wound film body 100, gaps SH are formed between the outer peripheral surface 12p of the core body 12 and the film 18. Portions of the film 18 wound on the core 10 that are not supported by the film supporting portions 14 are slightly slackened toward the core body 12. In this state, the film 18 may be completely separated from the core body 12 or may be in contact with the outer peripheral surface 12p unless the effect of suppressing the distortion decreases significantly.

The material, structure and dimensions of the film 18 to be wound on the core 10 are not particularly limited. However, the use of the core 10 of the present embodiment for winding a film having thickness unevenness inherent thereto is very effective in suppressing the distortion. For example, a film produced using an extruder equipped with a T-die has an approximately uniform width-direction thickness distribution in any portion of the film measured in the longitudinal direction. For example, it is assumed that there is a thickness difference of about 1 μm between one end of the film and the other end thereof in the width direction. When this film is wound 1000 turns on a conventional cylindrical core, a diameter difference of about 2 mm is created between one end of the resulting wound film body and the other end thereof. Even such slight thickness unevenness increases the diameter difference in the resulting wound film body as the number of winding turns increases. As a result, the distortion due to the uneven thickness is memorized in the film, which increases the probability of unwinding defects (typically feeding errors).

The core 10 of the present embodiment is particularly effective in winding a film which is hard to remove distortion once the distortion is memorized in the film. Such a film has flexibility, and typically it has a thickness of micrometer order (for example, 2 to 100 μm).

Generally, there are few cases where the film having an uneven thickness itself has a great influence on the quality of a final product, for example, a secondary battery. As described above, even if a film has thickness variations of about ±1 μm from a target thickness of 20 μm, such variations in the thickness of the film are unlikely to have an influence on the quality of the final product as long as the other properties of the film meet the standards. Indeed, if the film has a completely uniform thickness, it is expected that unwinding defects caused by thickness unevenness rarely occur. However, it is very difficult and impractical to reduce the variations of ±1 μm to ±0.1 μm by improving the production method of the film. According to the present invention, it is possible to prevent defects caused by the uneven thickness of the film by improving the core, instead of improving the film itself.

The film produced using an extruder equipped with a T-die is, for example, a porous resin membrane. Examples of the porous resin membrane include porous membranes made of polyolefin, fluorine resin, polyurethane, polyamide, polyester, polyimide, polyamide-imide, epoxy, and the like. Examples of polyolefin include polyethylene and polypropylene. Examples of fluorine resin include polytetrafluoroethylene. A porous resin membrane made of polyimide, polyamide-imide or epoxy may be a thermosetting membrane. These porous resin membranes can be widely used for applications such as a separator for an electrochemical device, a waterproof gas permeable membrane, a dust collecting filter, and a low dielectric substrate.

The film 18 may or may not have an adhesive layer. However, a film having no adhesive layer is more suitable for use with the core 10 of the present embodiment. Generally, once a film having an adhesive layer adheres to something, a high tension is required to remove the film. Therefore, even if the film is slightly distorted, such distortion is unlikely to cause feeding errors. In contrast, a film having no adhesive layer, more specifically, a film having slidable front and back surfaces, is often unwound at a low tension and a high speed for use. The higher the unwinding speed, the higher the probability of a feeding error. Therefore, it is particularly recommended to use the core 10 of the present embodiment as a core for a film having no adhesive layer.

Claims

1. A film winding core on which a long film is to be wound, comprising:

a core body having a tubular shape; and

a plurality of film supporting portions provided around the core body, the film supporting portions protruding from an outer peripheral surface of the core body respectively at a plurality of positions in a rotational direction of the core body so that the film is supported away from the outer peripheral surface of the core body, and each of the film supporting portions being made of a material that can be deformed when the film is wound on the film winding core.

2. The film winding core according to claim 1, wherein the material is an elastically deformable material.

3. The film winding core according to claim 1, wherein the material comprises at least one selected from the group consisting of sponge, rubber, and foam.

4. The film winding core according to claim 1, wherein the film supporting portions are arranged at regular intervals in the rotational direction.

5. The film winding core according to claim 1, wherein the positions of the film supporting portions, the number of the film supporting portions, and a height of the film supporting portions protruding from the outer peripheral surface of the core body are adjusted so that the core body fits within a polygon having a minimum area required to surround all the film supporting portions in a cross-section perpendicular to a rotational axis of the film winding core.

6. The film winding core according to claim 1, wherein

the film supporting portions are each provided so as to extend from one side of the core body to the other side of the core body, and

a longitudinal direction of the film supporting portion is parallel to a rotational axis of the film winding core.

7. The film winding core according to claim 1, wherein the film supporting portion has a shape of a semicircular column, a rectangular column, or a hollow semicircular column.

8. The film winding core according to claim 1, further comprising a pair of bearing portions which are mounted on both sides of the core body and into which a shaft used to rotate the film winding core is to be inserted.

9. The film winding core according to claim 8, wherein the bearing portions are constituted by a pair of flanges each having a bearing hole and being detachable from the core body.

10. A wound film body comprising:

the film winding core according to claim 1; and

a long film wound on the film winding core.

11. The wound film body according to claim 10, wherein the film is a film produced using an extruder equipped with a T-die.

12. The wound film body according to claim 11, wherein the film is a porous resin membrane.