METHOD OF WRAPPING AND WRAPPED OBJECT

Abstract: A wrapping material which is heat-bondable on both surfaces, and heat-shrinkable and gas-barring if desired, so as to wrap an article in the form of a cylinder in such manner that overlapping parts of the material are heat-bonded to each other as at a pasted part of an envelope, and open parts formed at both ends of a line of pasted part are sealed by heat-bonding, when the article is to be overlapped, whereby the package thus formed is tough at heat-bonded pasted part, free of liquid leakage, not conspicuous in surface roughness, looks neat owing to absence of bent parts at both sealed ends, is excellent in strength and appearance at sealed parts, and, after all, is high in commercial value. When the wrapping material is not only self-adhesive but heat-bondable at a temperature of heat-shrinking treatment and exposed to an atmosphere of heating for heat-shrinking after subjected to temporary bonding by self-adhesiveness of the material, a completely heat-bonded package can be obtained by the heat-shrinking treatment without an additional application of heat-bonding treatment to said temporarily bonded parts.

Description: TECHNICAL FIELD The present invention relates to a method for packaging an object comprising wrapping a packaging material sheet being heat-sealable on both sides thereof around the object as to form a tubular shape, heat sealing overlapping opposite ends of the sheet to a lap seal whereby a tube is formed and heat sealing both opening portions of the tube at each end of the lap seal line without thereby forming a folded portion as well as to a resulting package. This method may generally be performed by wrapping an object with a packaging material such as a wrapping film, forming an overlap portion of the packaging material on any one surface, for example, bottom surface, of the object, lap-heat-sealing the overlap portion and heat-sealing opening portions formed on opposite ends of the lap-heat-sealed portion. BACKGROUND ART Hitherto, various methods have been proposed and practically employed for overwrap-packaging an object with a plastic film. For instance, packaging methods of the type which seals three sides of a package include one adapted to heat-seal all the three sides of a package by melt-cut sealing or band sealing (heat-sealing using a heating bar, heating continuous belt or heating disk edge to form a band-like sealed portion), one adapted to fin-heat-seal one of the three sides of a package and to melt-cut-seal or band-seal the two remaining sides thereof, and one adapted to electrostatic-seal one side of a package in a lap seal fashion and to melt-cut-seal or band-seal the two remaining sides thereof. In addition, there is known a packaging method using a stretched film wherein one side of a package is lap-heat-sealed and the two remaining sides thereof are folded onto the bottom surface of the package and fixed thereto by heat sealing. Such conventional methods, however, involve a problem that where packages each having a heat-sealed portion resulting from melt-cut sealing on the bottom surface thereof are transported or displayed in a stacked fashion, the melt-cut-sealed portion on the bottom surface of an upper package is brought into close contact with the top surface of the underlying package and rubbed thereby due to vibration or the like and is hence prone to rupture. Although rupture of such kind is hard to occur if a package is fin-heat-sealed on the bottom surface thereof, another problem arises that since the fin-heat-scaled portion of the package is considerably thick and forms a projection on the bottom surface of the package, stacking this package on an object having, for example, a soft surface would frequently leave a mark of the sealed portion on the top surface of the underlying object. With the package which is electrostatic-sealed on the bottom surface thereof in a lap seal fashion, the problem of the aforementioned marking will not arise because the sealed portion is thin and does not project so much. However, such a package suffers a problem that the sealed portion is likely to be unsealed since it is not fusion-bonded and a problem that if the package contains a liquid such as water or juice, such a liquid is easy to leak from the package. Further, in this case another problem is present that since the packaging material must be an electrostatically chargeable film, such a film is easy to collect dust due to static electricity and is inevitably poor in antifog properties. Further, with the package using a stretched film wherein one side of the package is lap-heat-sealed and the two remaining sides thereof are folded onto the bottom surface of the package and fixed thereto by heat sealing, there is a drawback that the portions folded onto the bottom surface of the package are wrinkled and, hence, openings are left in the wrinkled portion to frequently permit a liquid to leak therethrough. In addition such a wrinkled portion degrades the appearance of the package. A method according to the introductory sentence is known from the document GB 2 203 927 A. From the document US 3,679,048 it is known to apply heat shrink treatment to packages similar to those according to the document GB 2 203 927 A. DISCLOSURE OF THE INVENTION The present invention has been attained as a result of intensive efforts to solve the foregoing various problems. According to the present invention, such problems are all solved by using in a method according to the first part of claim 1 a packaging material, e.g. a wrapping film, being self-tacky on both of its sides and by forming a provisional lap seal and provisional seals at the opening portions of the tube by tacking together the opposite ends of the sheet and the packaging material at the opening portions prior to heat sealing. The present invention uses packaging material, e.g. a film, which is heat-sealable on both sides thereof and self-tacky on both of its sides. Preferably, such a material is heat-shrinkable, or both stretchable and heat-shrinkable. Then the resulting package may be subjected to a heat shrink treatment after being sealed. Alternatively, if a packaging material having on each side thereof a surface layer being self-tacky and heat sealable is used, whereby the heat sealability of the surface layer is exhibited within a temperature range suited for heat shrinkage of the packaging material, a provisional lap seal may be formed on a bottom surface of the object by compressing an overlap portion of the packaging material and, after having formed the provisional lap seal and the provisional seals at the opening portions of the tube, the obtained provisional package may be subjected to a heat shrink treatment under heat shrink conditions of the packaging material, thereby at the same time heat sealing the provisional lap seal and the provisional seals at the opening portions. Expressed in other terms, where the packaging material is also heat-shrinkable, the packaging material is after its provisional sealing subjected to a heating environment for heat shrinkage, thereby obtaining a package with its provisionally-sealed portion completely heat-sealed by the heat shrink treatment without the need of an additional heat-sealing treatment. In a particular embodiment of the invention after obtaining the provisional package and prior to the heat shrink treatment a line of perforations is provided in a portion of the packaging material contacting the object or in a portion between the object and at least one of the provisional seals at the opening portions. The packaging material, e.g. film, may be a single-layered film but preferably a multilayered film comprising a core layer and a sealant layer having heat-sealability on each side of the core layer. A film for the core layer may be imparted with gas barrier property, good modulas of elasticity, or other preferable characteristics suitable for the purpose of individual package. Examples of the film material forming each layer include polyolefin resins, vinyl chloride resins, polyamide resins and ethylene-vinyl alcohol resins. Nevertheless, any other materials may be used without particular limitations as far as they meet the above-mentioned requirements. To be described next is a method for producing a package according to the present invention using the aforementioned packaging material. An object to be packaged is wrapped with the aforementioned packaging material in such a manner as to form a tubular shape, followed by heat sealing of the overlapped ends of the packaging material by applying a heating bar heated to such a temperature as to allow heat sealing of the packaging material or by placing the overlapped ends onto a hot plate. The peripheral edge of each opening portion formed at each end of the tubular shape is flatly collapsed and then heat-sealed by melt-cut sealing, band sealing or the like. Since the packaging material has self-tackiness, the overlap portion and the opening portions at opposite ends which are formed when the object is tubularly wrapped with the packaging material are provisionally sealed by merely compressing the same. Hence, such provisionally-sealed portions will not be unsealed or shifted easily. This allows those opening portions to be heat-sealed directly or the overlap portion on the bottom surface of the package to be sealed directly, by means of a hot plate or the like. Further, where the packaging material to be used is besides being self-tacky and heat-sealable heat shrinkable whereby at the same time the heat-seal layer is heat-sealable within a temperature range suitable for heat shrinkage, the overlap portion on the bottom surface of the package and the opening portions at opposite ends are collapsed to achieve provisional sealing, and then the package is directly subjected to the heat shrink treatment without any particular heat-sealing process, thereby obtaining a shrink package with the packaging material completely heat-sealed while heat-shrinked during the heat shrink treatment. If desired, suitable unsealability can be imparted to the package by providing the packaging material with a V-shaped notch or a cut line of perforations in a portion thereof contacting the object or in a portion thereof between each opening portion sealed and the object. Self-tackiness as referred to in claims 1 and 6 is exhibited by the packaging material when surfaces thereof are brought into mutual and close contact with each other. BEST MODE FOR CARRYING OUT THE INVENTION The present invention will now be described more specifically by way of examples thereof. EXAMPLE 1 As a packaging material there was used a stretchable, heat-shrinkable, polyolefin-based, multilayered film having a width of 25 cm and a thickness of 13 µ (KOHJINKORAP, a product of Kohjin Co., Ltd.),, the heat shrinkage percentage of the film being 40% in both longitudinal and transverse direction at 100°C. The film was wrapped around a polypropylene tray having a length of 10 cm in the longitudinal direction, a length of 18 cm in the transverse direction and a height of 1.5 cm, on which 160 g of pickles were placed, as an object to be packaged, in the transverse direction of the tray. The film was then cut to have an overlap portion having a width of about 30 mm and extending centrally of the bottom surface of the tray. The resulting wrapped object was placed upon a hot plate at 100°C for one second to allow heat sealing of the overall area of the overlap portion in a lap heat seal fashion. In turn, an opening portion formed at each end of the lap heat sealed portion was collapsed, then heat-sealed at a location adjacent an end of the tray by melt-cut sealing using a knife of 1.5 mmR at 180°C. The resulting package was heated for two seconds by passing it through a hot-air tunnel heated at 110°C to give a shrink package. Packages of the type thus obtained were stacked one upon another up to six stages within a cardboard box, then subjected to a vibration test for 40 minutes by placing the box on a flat board adapted to reciprocate 50 times per minute at an amplitude of 20 cm. As a result, the lap-heat-sealed area on the bottom surface of each of the packages was found to be uniformly transparent and smooth with no rupture of seal. Further, the melt-cut-sealed portion of each selvage exhibited a clear-cut appearance, and the package did not permit the juice of pickles to leak therefrom no matter how inclined. The shrink package thus obtained was a commercial package which was excellent in appearance, strength and liquid-tight property. EXAMPLE 2 As a packaging material there was used an ethylene-vinyl alcohol-based multilayered film of barrier properties having a width of 27 cm and a thickness of 14 µm, the film comprising a 2 µm-thick EVOH film layer and a 6 µm-thick polyethylene film layer laminated on each side of the EVOH film layer. The film was wrapped around a polypropylene tray having a length of 12 cm in the longitudinal direction, a length of 20 cm in the transverse direction and a height of 2.0 cm, on which 200 g of chilled hamburger was placed, as an object to be packaged, in the transverse direction of the tray. The film was then cut to have an overlap portion having a width of about 20 mm and extending centrally of the bottom surface of the tray. The resulting wrapped object was directly placed upon a hot plate at 100°C for two seconds to allow heat-sealing of the overall area of the overlap portion in a lap heat seal fashion. In turn, an opening portion formed at each end of the lap-heat-sealed portion was pressed to be collapsed, then heat-sealed at a location adjacent an end of the tray using a 5 mm-wide bar sealer heated at 110°C. The package thus obtained was subjected to the same test as in Example 1 for 40 minutes. As a result, the lap-heat-sealed area on the bottom surface of the package was found to be uniformly transparent and smooth with no rupture of seal. Further, the bar-sealed portion in each selvage portion was found to be sealed securely. Consequently, the package thus obtained was a commercial package which was excellent in appearance, strength and barrier properties. Example 3 As a packaging material there was used a stretchable, heat-shrinkable, polyethylene-based, multilayered film, the film comprising a 10.4 µm-thick core layer formed of a linear low-density polyethylene resin having a melting point of 126°C (a main peak by DSC measurement) and a heat shrinkage initiating temperature of 80°C and, laminated on each side of the core layer, a 1.3 µm-thick, self-tacky, heat-sealable layer formed of a mixture of 49% by weight of a linear low-density polyethylene resin having a melting point of 80°C (the same as the above), 49% by weight of the linear low-density polyethylene resin as used in the core layer and 2% by weight of a tackifier (ARKON P115, a product of Arakawa Chemical Co.), the heat-seal initiating temperature of the heat-seal layer being 70°C. The film was wrapped around a lunch box of polypropylene filled with a variety of lunch foods (Makunouchi Bento), as an object to be packaged, in the transverse direction of the lunch box. The film was cut to have an overlap portion of 15 mm in width on the bottom surface of the lunch box. The overlapped ends of the wrapping film were stuck to each other by the self-tackiness of the film. In turn, a tubular opening portion formed at each end of the box was pressed from above and from below to be closed by self-tackiness of the film, thereby obtaining a provisional package. A cut line of perforations was then provided to the packaging material by applying thereto a rotary perforation cutter at a location spaced by 5 mm from the lunch box between each closed end of the packaging material and the lunch box. The thus obtained provisional package was passed through a 100°C hot air shrink tunnel for two seconds. The resulting package was a complete package with its provisionally sealed portions at the bottom surface and opposite ends thereof being securely heat-sealed by the heat of the shrink tunnel. The thus obtained package was subjected to a vibration test for 40 minutes in the same manner as in Example 1. As a result, the package was found to have the overlap portion and closed end portions securely sealed with no rupture of seal. When this package was held by hands and the opposite end portions thereof were pulled outwardly by hands, the packaging material was cut easily along the cut line of perforations to allow removal of the lunch box with ease. COMPARATIVE EXAMPLE 1 Using a packaging material and an object to be packaged which were completely identical with those used in Example 1, the film was wrapped around the tray in the transverse direction of the tray and the film was heat-sealed by melt-cut sealing so as to have a seal line extending centrally of the bottom surface of the tray. In turn, an opening portion formed at each end of the tray by the heat-sealing on the bottom was collapsed, then heat-sealed at a portion adjacent an end of the tray by melt-cut sealing. The resulting package was heated for six seconds by passing it through a hot-air tunnel heated at 120°C to give a shrink package. Packages of the type thus obtained were stacked one upon another up to six stages within a cardboard box, then subjected to a vibration test for 40 minutes by placing the box on a flat board adapted to reciprocate 50 time per minute. As a result, some packages were each found to have a pinhole-like rupture in a portion of the heat-sealed portion in the bottom surface of the package because of friction with the top surface of the underlying package due to vibration. When these packages were inclined at various angles, juice was found to ooze from the pinhole. The shrink package thus obtained was one which was incomplete in strength and in liquid-tight properties. COMPARATIVE EXAMPLE 2 As a packaging material there was used an electrostatic-chargeable, heat-shrinkable, polypropylene-based film of 28 cm in width and 15 µ in thickness (KOHJINPOLYSET, a product of Kohjin Co., Ltd.). The film was wrapped around a polypropylene tray having a length of 10 cm in the longitudinal direction, a length of 18 cm in the transverse direction and a height of 1.5 cm, on which 160 g of pickles were placed, as an object to be packaged, in the transverse direction of the tray. The film was cut to have an overlap portion having a width of about 30 mm and extending centrally of the bottom surface of the tray. The overall area of the overlap portion on the bottom was allowed to be electrostatic-sealed in a lap seal fashion. In turn, an opening portion formed at each end of the electrostatic-lap-sealed area was collapsed, then heat-sealed at a location adjacent an end of the tray by melt-cut sealing. The resulting package was heated for six seconds by passing it through a hot-air tunnel heated at 160°C to give a shrink package. Packages of the type thus obtained were stacked one upon another up to six stages within a cardboard box, then subjected to a vibration test for 40 minutes by placing the box on a flat board adapted to reciprocate 50 times per minute at an amplitude of 20 cm. As a result, the electrostatic-lap-sealed area on the bottom surface of some packages was found to have some exfoliation though seemed to be transparent and smooth. Variously inclining these packages resulted in ooze of juice of pickles therefrom. The thus obtained shrink package was one which had a problem of sealability and liquid-tight properties at the electrostatic-sealed portion on the bottom surface thereof. COMPARATIVE EXAMPLE 3 In a manner similar to that of Example 1 except that the packaging material was 34 cm wide, a tubularly wrapped object was given as having a lap-heat-sealed portion on the bottom surface thereof. An opening portion formed at each end of the heat-sealed area was collapsed and folded onto the bottom surface. The wrapped object with its packaging material thus folded was placed upon a hot plate heated at 100°C to fix the folded portions to the bottom surface of the package by fusion bonding, thereby achieving sealing. The package thus obtained was found to have a bottom surface exhibiting not so good appearance. Further, variously inclining this package resulted in ooze of juice of the packaged object from the folded and fixed portion on the bottom surface thereof. This package when displayed as a commercial article had a degraded value on a commercial basis due to its appearance. INDUSTRIAL APPLICABILITY According to the present invention, in overwrapping an object to be packaged, the object is wrapped with a packaging material in such a manner as to form a tubular shape, which packaging material is heat-sealable on both sides thereof and, as required, has heat shrinkability or gas-barrier properties; the overlap portion of the packaging material is heat-sealed in a lap seal fashion; and an opening portion formed at each end of the lap seal line is heat-sealed. The lap-heat-sealed portion of the package thus obtained has a satisfactory strength with liquid leakage prevented, and the unevenness of this portion is inconspicuous. Further, respective sealed portions at both ends of the package exhibit a good appearance because of the absence of a folded portion. The resulting package is excellent in seal strength and appearance and hence highly valuable on a commercial basis. Further, where the packaging material is self-tacky and, at the same time, heat-sealable within the temperature range for heat shrinkage, exposing the package provisionally sealed by self-tackiness to a heating environment for heat shrinkage will give a package with heat sealing completely achieved during the heat shrink treatment without the need of an additional heat-sealing process for the provisionally-sealed portion.

Claims: A method for packaging an object comprising: wrapping a packaging material sheet being heat sealable on both sides thereof around the object as to form a tubular shape, heat sealing overlapping opposite ends of the sheet to a lap seal whereby a tube is formed and heat sealing both opening portions of the tube at each end of the lap seal line without thereby forming a folded portion , characterized in that a packaging material being self-tacky on both of its sides is used and a provisional lap seal and provisional seals at the opening portions of the tube are formed by tacking together the opposite ends of the sheet and the packaging material at the opening portions prior to heat sealing. The method of Claim 1, characterized in that the packaging material is heat-shrinkable and the resulting package is subjected to a heat shrink treatment after being sealed. The method of Claim 1, characterized in that the opening portion formed at each end of the lap seal line is sealed by melt-cut sealing. The method of Claim 1, characterized in that a packaging material having on each side thereof a surface layer being self-tacky and heat sealable is used, whereby the heat sealability of the surface layer is exhibited within a temperature range suited for heat shrinkage of the packaging material, that the provisional lap seal is formed on a bottom surface of the object by compressing an overlap portion of the packaging material, and that after having formed the provisional lap seal and the provisional seals at the opening portions of the tube, the obtained provisional package is subjected to a heat shrink treatment under heat shrink conditions of the packaging material, thereby at the same time heat sealing the provisional lap seal and the provisional seals at the opening portions. The method of Claim 4, characterized in that after obtaining the provisional package and prior to the heat shrink treatment a line of perforations is provided in a portion of the packaging material contacting the object or in a portion between the object and at least one of the provisional seals at the opening portions. A package comprising an object and a packaging material being heat sealable on both sides thereof and obtainable by wrapping a sheet of the packaging material around the object as to form a tubular shape, heat sealing overlapping opposite ends of the sheet to a lap seat whereby a tube is formed and heat sealing both opening portions of the tube at each end of the lap seal line without thereby forming a folded portion, characterized in that the packaging material is self-tacky on both of its sides and that a provisional lap seal and provisional seals at the opening portions of the tube are formed by tacking together the opposite ends of the sheet and the packaging material at the opening portions prior to heat sealing. The package of Claim 6, characterized in that the packaging material is heat-shrinkable and the resulting package is subjected to a heat shrink treatment after being sealed. The package of Claim 6, characterized in that the opening portion formed at each end of the lap seal line is sealed by melt-cut sealing. The package of Claim 7, characterized in that the heat sealability of the surface layers on both sides of the packaging material is exhibited within a temperature range suited for heat shrinkage of the packaging material, and that the provisional lap seal and the provisional seals at the opening portions of the tube are heat sealed during a heat shrinkage treatment. The package of Claim 6, characterized in that a line of perforations for unsealing the package is provided in a portion of the packaging material contacting the object or in a portion between the object and the sealed portion at each end of the object.

Inventors: TAKAHASHI MASUMI, TAKAHASHI, MASUMI
Applicants: KOHJIN CO, KOHJIN CO. LTD.
Application year: 1992
Main classification: B65D75
IPC codes: B65D75, B32B27, B65D65