Stock material or miscellaneous articles – Composite – Of metal
Reexamination Certificate
2000-11-21
2003-04-29
Watkins, III, William P. (Department: 1772)
Stock material or miscellaneous articles
Composite
Of metal
C428S910000, C428S409000, C428S523000, C428S515000, C428S516000, C428S517000, C428S519000, C428S462000, C427S536000, C427S540000, C427S535000, C427S534000, C427S533000
Reexamination Certificate
active
06555240
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a highly transparent easily adhesive film and more specifically to a highly transparent easily adhesive film, which is a polypropylene film excellent in transparency and which is also excellent in the adhesion to a coated layer. The coated layer is excellent in the printability through the photogravure, relief printing, offset printing, flexography or the like, or capable of recording information through the ink jet recording technique.
A polypropylene film based on polypropylene, propylene copolymer or mixture thereof has widely been used as a film for packaging because of its excellent properties such as mechanical strength and transparency. On the other hand, it has been known that the polypropylene film has insufficient adhesion to a coated film applied onto the surface thereof. In this regard, the coated film is in general applied to the polypropylene film in order to impart various functions such as gas barrier properties, heat sealability and printability to the polypropylene film. This would be attributable to poor adhesive properties of the polypropylene film. There have been proposed a variety of means for eliminating this drawback, such as insertion of various anchor layers between the coated layer and the polypropylene film.
For instance, Japanese Examined Patent Publication No. Sho 45-32360 discloses a method, which makes use of a polyethyleneimine and a glycidyl type epoxy resin in such an anchor layer in order to improve the adhesive properties of a polypropylene film to a polyvinylidene chloride layer. The latter layer is applied to the polypropylene film for imparting gas barrier properties thereto. In addition, U.S. Pat. No. 3,023,126 discloses the use of an anchor layer comprising an isocyanate as a component thereof.
However, these methods have still been insufficient in the improvement of the adhesive properties of the polyolefin films and the use of only such an anchor layer has never permitted the printing operation with UV inks.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a highly transparent easily adhesive film, which can eliminate the foregoing drawbacks associated with the conventional techniques, more particularly, to provide the film which permits the production of a laminate film excellent in printability through, for instance, the photogravure, relief printing, offset printing and flexography, simply using an anchor layer. The film also has improved adhesion to a functional coated layer to be applied onto the anchor layer.
Another object of the present invention is to provide an adhesive sheet, which is an indicating label comprising a printable transparent film as a surface base material and which is used as a label for transparent containers. The adhesive sheet has an excellent ability of being printed through the conventional printing methods and is also excellent in adhesion to ink during the UV flexography, in transparency and is less susceptible to discoloration with light rays.
A still another object of the present invention is to provide a metal-deposited (for instance, aluminum-deposited) polyolefin film suitably used as, for instance, indicating labels.
According to a first aspect of the present invention, there is thus provided a laminate of films for printing, wherein an anchor layer containing an oxazoline group-modified resin is formed on the modified surface of a polyolefin film, at least one side of which is surface-modified.
According to a second aspect of the present invention, there is provided a laminate of films for printing, wherein at least one side of a longitudinally stretched polyolefin film is subjected to a corona discharge treatment, that an ethylene-acrylic acid type copolymer layer is formed on the corona discharge-treated surface, and that after the polyolefin film is stretched in the lateral direction, an anchor layer comprising a binder resin selected from the group consisting of acrylic resins, polyester resins and SBR resins and an oxazoline group-modified resin is applied onto the modified surface of the surface-modified polyolefin film, which has been subjected to the corona surface-treatment.
According to a third aspect of the present invention, there is further provided the foregoing laminate of films in which an adhesive layer is formed on the surface of the surface-modified polyolefin film opposite to the surface thereof to which the anchor layer is applied.
According to a fourth aspect of the present invention, there is provided the foregoing laminate of films in which an adhesive layer, for metal vapor-deposition, containing an anti-blocking agent is formed on the surface of the surface-modified polyolefin film opposite to the surface thereof to which the anchor layer is applied and a vapor-deposited metal layer is applied onto the adhesive layer.
According to a fifth aspect of the present invention, there is provided the foregoing laminate of films, in which the surface-modified polyolefin film is a surface-roughened polyolefin sheet and in which a vapor-deposited metal layer is present on the surface of the sheet opposite to that carrying the anchor layer.
According to a sixth aspect of the present invention, there is provided a method for preparing a laminate of films for printing. The method comprises the steps of subjecting, to a corona discharge treatment, at least one side of a longitudinally stretched polyolefin film; forming an ethylene-acrylic acid type copolymer layer on the corona discharge-treated surface of the polyolefin film; stretching the polyolefin film in the lateral direction; and then forming an anchor layer, which comprises a binder resin selected from the group consisting of acrylic resins, polyester resins and SBR resins and an oxazoline group-modified resin on the modified surface of the surface-modified polyolefin film, which has been subjected to the corona discharge treatment.
BEST MODE FOR CARRYING OUT THE INVENTION
A biaxially oriented polyolefin film in which at least one side thereof is surface-modified is preferably used in the present invention.
This biaxially oriented polyolefin film in which at least one side thereof is surface-modified is prepared as follows: A polyolefin composition is melt-extruded according to the usual method and then the melt-extruded composition is first oriented in its longitudinal direction to give a uniaxially oriented film. Thereafter, the longitudinally oriented polyolefin film is further oriented in the lateral direction. The thickness of the film obtained after the lateral orientation is not restricted to any particular range, but it preferably ranges from 15 to 100 &mgr;m. In general, the draw ratio: longitudinal/lateral orientation of the film preferably ranges from 2 to 10.
In the present invention, a layer is formed by applying ethylene-acrylic acid type copolymer paint onto at least one side of the film and then drying after the longitudinal orientation and before the lateral orientation to thus surface-modify the polyolefin film. In this respect, a film is in general longitudinally oriented while making use of the difference in the peripheral speed between rolls. For this reason, if the layer is applied before the longitudinal orientation of the film, the coated surface of the film comes in contact with the surface of these rolls during the longitudinal orientation. Accordingly, the film is not uniformly surface-modified and this in turn results in the reduction of adhesion to the anchor layer. On the other hand, the application of the layer after the lateral orientation of the film would leads to a decrease of the adhesion between the polyolefin composition and the ethylene-acrylic acid type copolymer.
In this respect, examples of methods for surface-modification are a corona discharge treatment and/or a flame treatment, with the corona discharge treatment being preferred. In addition, examples of the methods include surface-roughened methods (1) to (6) which will be described later.
As the polyolefin composition used in t
Katayama Koichi
Nishikori Yoshiharu
Ogawa Yuichi
Sakaushi Noboru
Christie Parker & Hale LLP
Oji Paper Co. Ltd.
Watkins III William P.
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