Heat-sealable composite films

Details Heat-sealable composite films Heat-sealable composite films

1996-10-07

2002-12-17

Nakarani, D. S. (Department: 1773)

Stock material or miscellaneous articles

Structurally defined web or sheet

Including components having same physical characteristic in...

C428S215000, C428S327000, C428S336000, C428S516000, C428S519000, C428S910000

Reexamination Certificate

active

06495246

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a composite film suited for overwrap packaging and a method for producing the film.
BACKGROUND OF THE INVENTION
As packaging materials, a variety of types of film, particularly polypropylene film and polyethylene terephthalate film, both of which are particularly satisfactory in clarity, rigidity and other characteristics, are in use today. Furthermore, a film coated with a vinylidene chloride copolymer which has a heat sealing property as well as a gas barrier property with respect to oxygen and water vapor is in use for the overwrap packaging of various commercial items such as food products, tobacco products, cassette tapes and so on.
Meanwhile, a stretched film such as biaxially oriented polypropylene film is poor in heat sealability. Therefore, development work is in progress on a stretched laminated film comprising a base polymer layer composed of polypropylene or the like and a heat-sealable surface polymer layer of an olefinic polymer. However, the laminate film having an olefinic polymer ply is unsatisfactory in mechanical properties so that it is hardly compatible with an automatic overwrapping machine which is operated at a high speed of, for example, not less than 300 units of packaging load per minute. Thus, if such a laminated film is fed to an automatic overwrapping machine, where it is exposed to both heat and pressure, the slidability and releasability of the film with respect to the machine hardware such as the metal guide plate are markedly decreased. Therefore, overwrap packaging cannot be carried out at a high speed so that the packaging efficiency is remarkably sacrificed.
To improve the slidability of film, it is practiced to add an antiblocking agent, e.g. microfine particles of an inorganic substance such as silica, alumina, synthetic zeolite, etc., those of an organic substance such as polyethylene, or a mineral or petroleum wax to the olefinic polymer [cf. Japanese Patent application No. 71830/1991 (JP-A-3-71830)].
However, even when such an additive is incorporated, the releasability of film with respect to the metal guide plate is unsatisfactory in the sealing stage where the film is subjected to both heat and pressure. Therefore, packaging at a speed over 300 units of packaging load/minute is not feasible.
Also known is a film comprising a polypropylene base layer and an ethylene homopolymer or copolymer covering layer containing a fatty acid amide as a slidability improver or lubricant. However, even with the formation of such a fatty acid amide-containing covering layer, the releasability of film with respect to the metal guide plate in the heat-sealing stage is poor and, therefore, high-speed packaging can not be realized.
To overcome the above disadvantages, Japanese Patent Publication No. 56864/1988 (JP-B-63-56864) proposes a multi-layer film comprising a polypropylene layer and a laminatable layer made of ethylene homopolymer or copolymer, the laminatable layer containing a higher fatty amine, a dispersed thermoplastic resin incompatible with ethylene homopolymer or copolymer and a dialkylpolysiloxane. This film is suited for wrapping cigaret cartons.
Japanese Patent application Laid-open No. 133050/1984 (JP-A-59-133050) discloses an oriented or a stretched multi-layer polypropylene film comprising a polypropylene base layer containing a C
8-24
monocarboxylic acid amide and a polyolefin surface or skin layer containing a finely divided powder of silica and silicone oil.
Furthermore, Japanese Patent application Laid-open No. 60745/1990 (JP-A-2-60745) discloses a biaxially oriented film comprising a polypropylene-containing base layer and, as laminated to at least one side thereof, a surface layer made from a random copolymer containing ethylene and propylene as constituent units and a diorganopolysiloxane gum. Japanese Patent application Laid-open No. 205440/1991 (JP-A-3-205440) discloses a biaxially oriented film comprising the same base layer as above and, as laminated thereto, a surface layer containing the same copolymer as above, finely divided insoluble silicone rubber and a diorganopolysiloxane gum.
These films are generally well slidable and compatible with high-speed packaging. However, when any of these films is fed to an automatic overwrapping machine for packaging the load at a speed of 300 units of load/minute, the following troubles are encountered. Thus, because of its low-temperature slidability or insufficient antistatic property, the film tends to be electrostatically stuck to a member such as the metal guide plate of the automatic overwrapping machine and cannot be cut to the required size and, hence, cause a jam in the machine, thus preventing high-speed continuous packaging. If an attempt is made to improve the slidability of film by increasing the amount of the incompatible thermoplastic resin or silica powder to the copolymer containing ethylene and propylene as constituent units, the clarity of the film is sacrificed. On the other hand, an organopolysiloxane of high degree of polymerization can hardly be dispersed uniformly in the copolymer so that the film quality as a whole cannot be critically controlled.
SUMMARY OF THE INVENTION
Therefore, it is an object of this invention to provide a composite film with which product s can be packaged at high speed.
It is a further object of this s invention to provide a composite film which is remarkably improved in clarity, slidability, releasability and antistaticity and with which products can be packaged on an automatic overwrapping machine at high speed.
It is still another object of this invention to provide a method for producing a composite film having the above-mentioned desirable characteristics.
The inventors of this invention found after a great deal of research done to accomplish the above objects that when a first covering layer on one side and a second covering layer on the other side of a base resin layer of a laminate film are respectively formed from resin compositions comprising herein-defined components, there is obtained a composite film which is improved markedly in slidability, releasability, clarity and antistaticity and compatible with high-speed packaging.
Thus, the composite film of the present invention comprises a base resin layer, a first covering layer of a resin composition (1) comprising the following components (A), (B), (C) and (D) as laminated to one side of the base resin layer and a second covering layer of a resin composition (2) comprising the following components (A) and (D) as laminated to the other side of the base resin layer.
(A) a heat-sealable olefinic polymer
(B) a diorganopolysiloxane
(C) a fine-powdered heat-resistant resin
(D) a higher fatty acid amide
The method for producing a composite film according to the present invention comprises laminating a first covering layer of a resin composition (1) comprising the following components (A), (B), (C) and (D) to one side of a base resin layer and a second covering layer of a resin composition (2) comprising the following components (A) and (D) to the other side of the base resin layer.
(A) a heat-sealable olefinic polymer
(B) a diorganopolysiloxane
(C) a fine-powdered heat-resistant resin
(D) a higher fatty acid amide
DETAILED DESCRIPTION OF THE INVENTION
The resin which constitutes the above-mentioned base resin layer includes, for example, polyolefin resins such as polyethylene, polypropylene, ethylene-propylene copolymer, etc.; vinyl alcohol series polymers such as polyvinyl alcohol, ethylene-vinyl alcohol copolymer, etc.; polyvinyl chloride; vinylidene chloride series polymers; styrenic polymers such as polystyrene, styrene-acrylonitrile copolymer, styreneacrylonitrile-butadiene copolymer, etc.; polyesters such as polyethylene terephthalate, polybutylene terephthalate, etc.; nylons or polyamides such as nylon 6, nylon 11, nylon 12, nylon 66, nylon 6/66, nylon 66/610, nylon 6/11, etc.; polyacrylonitrile; and polycarbonates.
The base resin layer is preferably made of polyolefin resin (particularly a polypropylene series r

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