CORK STOPPER COATED WITH RESIN LAYER

Abstract

A cork stopper coated with a resin layer having a columnar cork stopper body formed by a compression molding of a cork granule with a binder resin, and a resin coating layer covering an outer circumferential surface of the cork stopper from an end side to another end of the cork stopper body along an axial direction. The cork stopper body and the resin coating layer constitute a core portion, and the core portion, when being pressed in a hollow tubular portion with a tightening allowance of 1.5 mm, experiencing a compression stress of 100N to 300N in case of a moisture content ratio of the core portion being 6 percent by weight and experiencing a compression stress 100N to 150N smaller than that in case of a moisture content ratio of the core portion being 2 percent by weight.

Description

TECHNICAL FIELD

The present invention relates to a cork stopper coated with a resin layer for plugging the mouth portion of a container for beverages like whisky or wine.

BACKGROUND ART

A cork stopper coated with a resin (rubber) layer integrated at one end with a flange portion doubling as a handle is widely used as a cork stopper for plugging the mouth portion of a container for beverages like whisky or wine, referring to Patent Literature 1 to 4. A cork stopper body of the cork stopper coated with a resin layer is formed in a columnar shape by the compression molding of a cork granule and a binder resin, or formed in a columnar shape by boring natural cork bark. A coating layer of resin is formed for preventing a corky smell from diffusing into the beverage in the container, preventing cork dust from falling into the container, preventing a color change on the cork surface caused by the invasion of beverage into a cork layer, and the like. A stable openability of the cork stopper regardless of a storage condition and a usage condition of the container is demanded when the cork stopper is coated with a layer made of resin. In the Patent Literature, the friction coefficient of the surface of the coated layer is appropriately determined by executing a silicone treatment or a roughening treatment on the coated layer surface.

In a production method of a cork stopper in Patent Literature 5 proposed by the applicant of the present application, a cork granule is pressed in a direction orthogonal to the longitudinal direction, i.e. the axial direction, of the columnar body, namely in the centripetal direction when the columnar cork stopper is molded under compression with binder resin. The cork stopper obtained by such a compression molding, having a coating layer of resin, has excellent flexibility in the diametrical direction and the sealing ability is improved by its conformability to the container mouth. Thereby, good features such as an easy openability and the prevention of damage at the time of opening are obtained.

CITATION LIST

Patent Literature

PTL 1 JP-S63-147456-U1

PTL 2 WO2004/020300

PTL 3 JP-2004-231244-A

PTL 4 WO2011/155515

PTL 5 JP-2010-099909-A

SUMMARY OF INVENTION

Technical Problem

In the case of the above-mentioned cork stopper coated with a resin layer, the friction coefficient is optimized for improving the openability of the cork stopper by a silicone treatment or a roughening treatment on the surface of the coating layer. However, such treatment for optimizing the friction of coefficient adds to production procedures and increases the production cost. When the stress of the cork changes, the openability of the cork stopper is not kept stable even if the friction coefficient is controlled. It is difficult to simultaneously achieve improvement in the openability and prevention of popping of the cork stopper. In addition, when the cork stopper coated with a resin layer is used for a container for beverages such as whisky or wine, the moisture content ratio of the core portion varies from two to six percent by weight, depending on the change of seasons. When the moisture content ratio is low, the compression stress of the cork stopper pressed into the mouth of the beverage container becomes large, thereby deteriorating openability. Therefore, it is desired to maintain a good openability in which the variation of the compression stress is less regardless of the change of seasons. As a result of verification by the inventors of the present application, the cork stopper disclosed in Patent Literature 5 is superior in the stability of the stress at the time of closing the container mouth with the cork stopper molded under pressure along the axial direction.

The present invention is proposed in view of the above-mentioned problems and has an object to provide a new cork stopper coated with a resin layer having a stable openability while keeping the unique sealing ability of the cork stopper. In addition, the inventors endeavored to apply their insights from the aforementioned results to a cork stopper coated with a resin layer, and as a result of numerous considerations, a cork stopper coated with a resin layer which has a stable openability and hardly pops out was easily obtained. Thus, the object of the present invention is to provide such a new cork stopper in view of the verified results.

Solution To Problem

In one embodiment of the present invention, the cork stopper coated with a resin layer comprises a columnar cork stopper body formed by a compression molding of a cork granule with a binder resin and a resin coating layer covering an outer circumferential surface of the cork stopper from an end side to another end of the cork stopper body along an axial direction. The cork stopper body and the resin coating layer constitute a core portion, and the core portion, when being pressed in a hollow tubular portion with a tightening allowance of 1.5 mm, experiences a compression stress of 100N to 300N in the case of a moisture content ratio of the core portion being 6 percent by weight and experiences a compression stress 100N to 150N smaller than that in the case of a moisture content ratio of the core portion being 2 percent by weight.

Generally, when the cork stopper coated with a resin layer is used for a container for beverages such as whisky or wine, the moisture content ratio of the core portion varies from two to six percent by weight, depending on the change of seasons. When the moisture content ratio is low, the compression stress of the cork stopper pressed into the mouth of the beverage container becomes large, thereby deteriorating openability. In the case of a cork stopper coated with a resin layer of an embodiment of the present invention, the compression stress is as small as 100N to 300N when the moisture content ratio of the core portion is 6 percent by weight, and the difference from the case when the moisture content ratio of the core portion is 2 percent by weight is as small as 100 to 150N. Therefore, openability is kept stable regardless of the change of seasons. If the compression stress at a moisture content ratio of 6 percent by weight in the core portion is smaller than 100N, the sealing ability becomes deteriorated. If the compression stress at a moisture content ratio of 6 percent by weight in the core portion is larger than 300N, the compression stress becomes large when the moisture content ratio changes to 2 percent by weight, thereby deteriorating the openability.

In the cork stopper coated with a resin layer as mentioned above, the cork stopper body can be formed by a compression molding executed in a centrifugal direction. In the cork stopper coated with a resin layer in an embodiment of the present invention, the cork stopper body is molded under compression in the centripetal direction, thereby having superior flexibility in the diametrical direction. When such a cork stopper coated with a resin layer is pressed to plug the container mouth portion, the cork stopper elastically contacts the inside of the mouth portion with flexibility and is elastically compressed with the resin coating layer interposed between the cork stopper and the inside of the mouth portion, thereby obtaining a stable sealing ability. The strength in the longitudinal direction (in the axial direction) of the cork stopper body, coupled with the binding force of the binder resin, becomes large, thereby preventing breakage of the cork stopper at the time of opening or closing.

In the cork stopper coated with a resin layer as mentioned above, the cork stopper body can have an attachment hole configured to attach a flange portion, the attachment hole extending from the end side to the other end side of the cork stopper body along an axial direction.

In the cork stopper of an embodiment, the flange portion is attached to the attachment hole and the cork stopper is easily closed or opened using the flange portion as a handle.

In such a case, the cork stopper coated with a resin layer can comprise an expanding portion with a diameter larger than an outer diameter of another portion of the core portion, the expanding portion extending from a region corresponding to a bottom of the attachment hole to the other end of the cork stopper.

In such a configuration, the expanding portion prevents the stopper from popping out.

Further, the expanding portion can be formed by heating the core portion.

When the core portion is heated, the cork stopper body thermally expands. In an embodiment of the present invention, the core portion from the region corresponding to the bottom of the attachment hole to the other end is solid and the cork stopper body is molded under compression in the centripetal direction, thus thermal expansion enlarges the diameter of the core portion. Therefore, the expanding portion is easily formed by heating.

In the cork stopper coated with a resin layer as mentioned above, the resin coating layer can be made of a polyethylene terephthalate. When the cork stopper coated with a resin layer is used for a beverage container, the resin coating layer contacts liquid. The resin coating layer is made of a polyethylene terephthalate with a high barrier property, so that a corky smell is prevented from diffusing into the beverage in the container. Polyethylene terephthalate is harmless and hygienic, thereby being suitable for a resin layer of a cork stopper for beverages.

In the cork stopper coated with a resin layer as mentioned above, the resin of the coating layer can include a lubricant.

In the above-mentioned embodiment, the resin of the coating layer includes a lubricant, so that the friction coefficient of the coating layer surface is easily controlled and a stable openability is obtained.

Advantageous Effects of Invention

The present invention is able to provide a cork stopper coated with a resin layer with a stable openability while keeping the unique sealing ability of the cork stopper.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram of a longitudinal section showing one embodiment of a cork stopper coated with a resin layer of an embodiment of the present invention.

FIG. 2 is a flow chart diagrammatically showing a production method of the above-mentioned cork stopper.

FIG. 3 is a table showing the measurement result of the compression stress depending on the moisture content ratio when a stopper that is coated with a resin layer of an embodiment of the present invention is pressed into a hollow tubular part with a tightening allowance of 1.5 mm, compared with that of a conventional stopper coated with a resin layer.

DESCRIPTION OF EMBODIMENTS

The embodiments of the present invention are explained referring to the attached drawings. FIG. 1 is a diagram of a longitudinal section showing one embodiment of the cork stopper coated with a resin layer of an embodiment of the present invention. A cork stopper coated with a resin layer 1 is comprised of a columnar cork stopper body 2 obtained by a compression molding of a cork granule and a binder resin, a resin coating layer 3 coated on the outer circumferential surface of the cork stopper body 2 from an end 2a side (in the vicinity of the end 2a) to the other end 2b in the direction of the axis L, and a flange portion 5 integrally formed with the end 2a of the cork stopper body 2. The cork stopper body 2 and the resin coating layer 3 constitute a core portion 4. The cork stopper body 2 is formed by molding under pressure in the centripetal direction and has an attachment hole 20 for attaching the flange portion 5 formed from the end 2a side to the other end 2b side along the direction of the axis L. An expanding portion 41 having an outer diameter larger than that of the other portions is formed from the region corresponding to a bottom portion 20a of the attachment hole 20 to the other end 2b of the core portion 4. The bottom portion 20a of the attachment hole 20 is concavely curved. The reference numeral 20b in the figure shows the start point of the concave bottom portion 20a. The expanding portion 41 is formed from the region corresponding to the start point 20b and extending to the other end 2b of the core portion 4.

The flange portion 5 is made of glass and comprises a disk-like flange body 50 and a columnar projecting portion 51 projecting downward from the center of the flange body 50. The projecting portion 51 is pressed in the attachment hole 20 of the cork stopper body 2 in such a manner that the lower surface of the flange body 50 abuts the upper surface of the cork stopper body 2. The abutting surface and the pressed surface are coated with an adhesive agent, thus the cork stopper body 2 and the flange portion 5 are integrally fixed. A washer 6 made of polyethylene is fitted around the outer circumference of the cork stopper body 2 so as to contact the lower surface of the flange body 50. A part of the cork stopper body 2 to which the washer 6 is provided is not coated with the resin coating layer 3. The washer 6 is provided between an upper open edge portion 70a of a mouth portion 70 and the lower surface of the flange body 50, preventing direct contact of the open edge portion 70a and the lower surface of the flange body 50, when the core portion 4 of the stopper coated with a resin layer of this embodiment is pressed into the mouth portion 70 (hollow tubular portion) of a container 7 for whisky (two-dotted line) for closing the mouth portion 70. In this specification the term “close” means to plug the mouth portion 70 of the container 7 with the cork stopper coated with a resin layer 1. The container 7 made of glass does not contact the flange portion 5 made of glass and a consumer is able to plug the mouth portion without causing unpleasantness.

In the explanation referring to FIG. 1, the end 2a side is an upper end and the other end 2b side is the lower end. The flange portion 5 is made of glass in the above-mentioned embodiment; however, the flange portion 5 can be made of hard resin or metal. In FIG. 1 the shapes of the expanding portion 41 and the mouth portion 70 of the container 7 are enlarged for easy explanation.

The production method of a cork stopper coated with a resin layer 1 is explained further referring to FIG. 2. At step S1, a mixture of a cork granule and binder is produced. The cork granule is made by crushing natural cork bark and granulating the crushed cork. The binder is a resin adhesive agent. At step S2, the cork stopper body 2 is manufactured in such a manner that the mixture obtained in at step S1 is molded under compression in the centripetal direction (in the direction perpendicular to the axis L of the cork stopper body 2) based on the method disclosed in Patent Literature 5. The obtained cork stopper body 2 is compressed in the centripetal direction, so that excellent flexibility in the diametrical direction is obtained as mentioned above and a large strength along the axis L, coupled with the binding force of the binder resin, is obtained. At step 3S, the attachment hole 20 is formed in the cork stopper body 2. The attachment hole 20 is formed by boring the cork stopper body 2 from the end 2a side (the upper side in FIG. 1) to the other end 2b side along the axis L.

At step S4, the resin coating layer 3 is formed on the outer circumferential surface (referred to as the circumferential surface hereinafter) of the cork stopper body 2 from the end 2a side to the other end 2b. For providing the resin coating layer 3, a urethane adhesive agent is applied on the circumferential surface of the cork stopper body 2. Then, the circumferential surface of the cork stopper body 2 is covered with a heated polyethylene terephthalate film and then is pressed into a mold. The polyethylene terephthalate film in an extended condition is thermally attached on the circumferential surface of the cork stopper body 2. Thus, the resin coating layer 3 is formed by a polyethylene terephthalate bonded on the entire circumferential surface of the cork stopper body 2 and the core portion 4 is formed with the cork stopper body 2 and the resin coated layer 3. Polyethylene terephthalate is preferably used for the resin of the resin coating layer for a beverage container because polyethylene terephthalate is harmless, hygienic and excellent in preventing the diffusion of a corky smell into the beverage in the container. However, the resin is not limited to polyethylene terephthalate. Polyethylene, nylon, polybutylene terephthalate, ethylene-vinyl acetate copolymer, or the like can be selectively used depending on the usage. The resin of the resin coating layer 3 desirably includes a lubricant. The lubricant can be a resin lubricant such as a spherical silicone resin and a spherical polyethylene resin, or an inorganic lubricant such as silica, clay and talc.

At step S5, silicone is applied and heated on the circumferential surface (zone 1 in FIG. 1) of the core portion 4 on the side of the other end 2b, from the start point 20b of the bottom 20a of the attachment hole 20 to the other end 2b. A coating layer of silicone is formed on the zone Z1 of the core portion 4 by heating. A region of the cork stopper body 2 corresponding to the zone Z1 axially expands by such heating. The region is solid and the cork stopper body 2 is formed by a compression molding in the centripetal direction, so that the region expands in a diametrical direction by thermal expansion, and the expanding portion 41 is formed at the region of the core portion 4 corresponding to the zone Z1 as shown in FIG. 1. At step S6, the washer 6 is fitted at a predetermined position and the flange portion 5 is attached after forming the expanding portion 41 along with the silicone film. The end (the upper end) 2a of the cork stopper body 2 and the circumferential surface of the projecting portion 51 of the flange portion 5 are applied with an adhesive agent, then the projecting portion 51 is pressed into the attachment hole 20 as mentioned above, and the adhesive agent is hardened, thereby attaching the flange portion 5. Thus, the production procedure of the resin cork stopper 1 is finished.

At step S5, heating is executed after silicone is applied; however, heating can be executed without applying silicone.

During the manufacturing of the resin cork stopper 1, a tightening allowance is generally required for the cork stopper of a container for beverages such as whisky, so that an outer diameter D1 of a columnar portion 40 of the core portion 4 other than the expanding portion 41 is set 1.5 mm larger than the smallest inner diameter of an inner diametrical face 70b of the mouth portion 70 of the container 7. Namely, when the cork stopper coated with a resin layer 1 is pressed into the mouth portion 70 of the container 7 shown in FIG. 1 for plugging the mouth portion 70, the columnar portion 40 is elastically deformed by compression along the shape of the inner diametrical face 70b of the mouth portion 70 shown with two-dotted lines. The inner diametrical face 70b of the mouth portion 70 and the columnar portion 40 elastically contact each other to be sealed by the restorative elasticity of the elastic deformation, thereby preventing leakage of liquid in the container 7. The resin coating layer 3 covers the circumferential surface of the cork stopper body 2, so that a corky smell is prevented from diffusing into the beverage in the container 7. The elastic contact portion of the inner diametrical face 70b of the mouth portion 70 and the columnar portion 40 includes the resin coating layer 3 therebetween, thereby achieving sealing performance completely. When the resin coating layer 3 includes the above-mentioned lubricant so as to control friction resistance with the inner diametrical face 70b of the mouth portion 70, the compression stress at the time of closing the mouth portion is easily controlled and stable openability is obtained.

The cork stopper coated with a resin layer produced as mentioned above and the conventional cork stopper coated with a resin layer disclosed in Patent Literatures 1, 2 and 4 include moisture of 2.0 percent by weight (moisture content ratio) at the time of production and the moisture content ratio changes from 2.0 to 6.0 percent by weight depending on the conditions thereafter. When the moisture content ratio changes, the compression stress when the cork stopper plugs the mouth portion of the container by being pressed therein also changes. FIG. 3 shows the measurement result of the compression stress depending on the moisture content ratio when the stopper coated with a resin layer of an embodiment of the present invention is pressed into the hollow tubular part with a tightening allowance of 1.5 mm, in comparison with that of a conventional cork stopper coated with a resin layer. In FIG. 3, the product compressed in an axial direction (a vertical direction) is a conventional cork stopper coated with a resin layer produced in such a manner that a columnar body is formed by a compression molding of a cork granule and binder in the axial direction and the circumferential surface is coated with resin layer. The product compressed in a radial direction (a centripetal direction) is a cork stopper coated with a resin layer of the embodiment of the present invention in which a columnar body produced by the method disclosed in Patent Literature 5 is coated with a resin layer. The former is called a conventional product and the latter, a cork stopper coated with a resin layer of an embodiment of the present invention, is referred to as “Inventive Product”.

As shown in FIG. 3, the values of the compression stress of the Inventive Product when the moisture content ratio is 2.0 percent by weight and 6.0 percent by weight are lower than those of a conventional cork stopper, thus the openability of the Inventive Product is superior to that of a conventional cork stopper. The Inventive Product is smaller than the conventional cork stopper in the change amount of the compression stress between the moisture content ratio of 2.0 percent by weight and 6.0 percent by weight. Therefore, the change caused by circumstances and the seasons in the openability of the Inventive Product is smaller than that of a conventional cork stopper, thus the Inventive Product is superior to the conventional cork stopper in its suitability as a cork stopper.

Several examinations were executed for moisture content ratios in the range of 2.0 to 6.0 percent by weight. It was found that, in view of sealing ability, the openability and popping of the cork stopper, in the case of pressing the core portion into the hollow tubular portion with a tightening allowance of 1.5 mm, the compression stress should be 100N to 300N when the moisture content ratio of the core portion 4 is 6 percent by weight and should be 100N to 150N smaller than that when the moisture content ratio of the core portion is 2 percent by weight. It was also found that the excellent features of the cork stopper coated with a resin layer of the embodiment of the present invention were based on the fact that the cork stopper body was formed by a compression molding in the centripetal direction, and the friction coefficient of the surface of the core portion was easily controlled, unlike those of a conventional cork stopper coated with a resin layer.

When the cork stopper coated with a resin layer 1 plugs the container 7, a part of the expanding portion 41, as shown in FIG. 1, abuts or elastically contacts the inside of a shoulder portion 71 of which the diameter gradually enlarges from the mouth portion 70 of the container 7 to a container main body (not shown in the Figure). An anchoring effect is achieved between the expanding portion 41 and the shoulder portion 71 by abutting or by elastic contact of the expanding portion 41 and the inside of the shoulder portion 71, thereby preventing the popping of the cork stopper and keeping stable the plugged condition of the cork stopper coated with a resin layer 1. When the cork stopper coated with a resin layer 1 is closed or opened, the expanding portion 41 passes through the smallest diameter portion D2 of the inner diametrical face 70b of the mouth portion 70 so that the expanding portion 41 is largely compressed under elasticity in the centripetal direction. By the reaction force of the elastic compression, large force is required for closing or opening the cork stopper. Considering the operational ability of closing or opening the cork stopper and preventing the popping of the cork stopper, the expanding width of the expanding portion 41, namely the result of the calculation formula (the largest outer diameter D3 of the expanding portion 41 minus the outer diameter D1 of the columnar portion 40 multiplied by 0.5 thereafter), is preferably 0.1 mm to 0.3 mm. The expanding width of the expanding portion 41 is less than 0.1 mm, thereby reducing the effectiveness in preventing the popping of the cork stopper. When the expanding width of the expanding portion 41 exceeds 0.3 mm, the burden applied to the fingers of an operator at the time of closing or opening becomes large. The coating layer of silicone is formed on the surface (the zone Z1) of the expanding portion 41, thereby allowing the cork stopper to be opened or closed smoothly and preventing noise at the time of closing or opening.

The expanding portion 41 extends from the region corresponding to the start point of 20b of the attachment hole 20 to the other end 2b of the core portion 4, namely the entire area of the zone Z1. Thus, the largest outer diameter D3 of the expanding portion 41 becomes larger than the outer diameter D1 of the columnar portion 40. In addition, the relation of the diameters in relation to the outer diameter D4 corresponding to the deepest portion of the bottom 20a of the attachment hole 20 of the expanding portion 41 is stated as follows: D3>D4>D1. However, the expanding portion 41 can be formed in a zone Z2 expanding from the deepest portion of the bottom 20a of the mounting hole 20 to the other end 2b. When the expanding portion 41 is formed in the zone Z2, at step S5, the zone Z2 is applied with silicone and heated, or the zone Z2 is heated without applying silicone, thereby forming the expanding portion 41 in the zone Z2 by thermal expansion.

In the above-mentioned embodiments, a cork stopper coated with a resin layer is used for a container for whisky. The container may also be used for beverages such as brandy, wine, champagne, Japanese sake or juice. The shape of the cork stopper coated with a resin layer 1 in FIG. 1 is an example and the embodiment of the present invention is not limited to such a shape. In the Figure, the core portion 4 has the expanding portion 41. However, the core portion 4 can be constituted with a straight body without the expanding portion 41 as long as the moisture content ratio and the compression stress of the core portion 4 are in the above-mentioned relationship. In the above-mentioned embodiment, the excellent features of the above-mentioned relationship between the moisture content ratio and the compression stress of the core portion are based on the compression molding of the cork stopper body in the centripetal direction. However, the present invention includes the case wherein the above-mentioned features of the relationship between the moisture content ratio and the compression stress of the core portion are obtained by other compression molding.

REFERENCE CHARACTERS LIST

• 1 cork stopper coated with a resin layer
• 2 cork stopper body
• 2a end
• 2b other end
• 20 attachment hole
• 20a bottom
• 3 resin coating layer
• 4 core portion
• 41 expanding portion
• 5 flange portion
• 70 mouth portion of beverage (hollow tubular portion)
• L axis

Claims

1. A cork stopper coated with a resin layer comprising: a columnar cork stopper body formed by a compression molding of a cork granule with a binder resin; and a resin coating layer covering an outer circumferential surface of the cork stopper from an end side to another end of the cork stopper body along an axial direction,

the cork stopper body and the resin coating layer constituting a core portion, and

the core portion, when being pressed into a hollow tubular portion with a tightening allowance of 1.5 mm, experiencing a compression stress of 100N to 300N in case of a moisture content ratio of the core portion being 6 percent by weight and experiencing a compression stress 100N to 150N smaller than that in case of a moisture content ratio of the core portion being 2 percent by weight.

2. The cork stopper coated with the resin layer as set forth in claim 1, wherein the cork stopper body is formed by a compression molding executed in a centrifugal direction.

3. The cork stopper coated with the resin layer as set forth in claim 1, wherein the cork stopper body has an attachment hole configured to attach a flange portion, the attachment hole extending from the end side to the other end side of the cork stopper body along the axial direction.

4. The cork stopper coated with the resin layer as set forth in claim 3, wherein the cork stopper coated with the resin layer further comprises an expanding portion with a diameter larger than an outer diameter of another portion of the core portion, the expanding portion extending from a region corresponding to a bottom of the attachment hole to the other end of the cork stopper body.

5. The cork stopper coated with the resin layer as set forth in claim 4, wherein the expanding portion is formed by heating the core portion.

6. The cork stopper coated with the resin layer as set forth in claim 1, wherein the resin coating layer is made of polyethylene terephthalate.

7. The cork stopper coated with the resin layer as set forth in claim 1, wherein the resin of the coating layer includes a lubricant.

8. The cork stopper coated with the resin layer as set forth in claim 2, wherein the cork stopper body has an attachment hole configured to attach a flange portion, the attachment hole extending from the end side to the other end side of the cork stopper body along the axial direction.

9. The cork stopper coated with the resin layer as set forth in claim 8, wherein the cork stopper coated with the resin layer further comprises an expanding portion with a diameter larger than an outer diameter of another portion of the core portion, the expanding portion extending from a region corresponding to a bottom of the attachment hole to the other end of the cork stopper body.

10. The cork stopper coated with the resin layer as set forth in claim 9, wherein the expanding portion is formed by heating the core portion.