LABELS FOR IN-MOLD FORMING AND
MOLDED RESIN PRODUCTS HAVING THE
SAME
CROSS REFERENCE TO RELATED 5
APPLICATION
This is a Continuation Application of PCT Application No. PCT/JP01/05105, filed on Jun. 15, 2001, which was not published under PCT Article 21(2) in English. ^
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application Nos. 2000-181257, filed on Jun. 16, 2000 and 2000-226451, filed on Jul. 27, 2000, the entire contents of which are incorporated herein by reference. 15
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to labels used in in-mold forming. The present invention further relates to molded 20 resin products to which such labels are applied.
2. Discussion of the Background
In-mold forming is a known method of manufacturing labeled molded resin products by integrated molding. In this ^ method, a label is placed in advance on the inner wall of a mold, a moldable resin such as polyethylene or propylene based resin is melted and directly fed into the mold, and the label is attached by injection, vacuum, differential pressure, or foam molding (see Japanese Unexamined Patent Publi- 3Q cation (KOKAI) Showa No. 58-69015 and European Patent Publication No. 254923). Known forms of such labels used in in-mold forming are gravure printed resin films, polychromatic offset printed synthetic paper (for example, see Japanese Examined Patent Publication (KOKOKU) Heisei 3J No. 2-7814 and Japanese Unexamined Patent Publication (KOKAI) Heisei No. 2-84319), and aluminum labels comprising aluminum foil on the rear side of which is laminated a high-pressure low-density polyethylene or an ethylenevinyl acetate copolymer and on the front side of which gravure printing is conducted.
However, in the manufacturing of labeled containers by hollow molding using these conventional in-mold forming labels, when the portion of the container to which the labels are attached is highly curved or undulated, there is a problem 45 during expansion of the parison being extruded from the die by the injection of air in that air present between the label secured in the mold and the parison forms air pockets known as "blisters." Since labeled containers having blisters are of little commercial value, there is a need to prevent blister 50 formation.
In response to such problems, Japanese Examined Patent Publication (KOKOKU) Heisei No. 6-70736 and Japanese Examined Utility Model Publication (JIKKO) Heisei No. 7-54109 propose that special through-holes be provided in 55 the label to suppress blistering.
However, when the shape of the container involved is cylindrical (meaning containers designed to have true circular cross-sections when viewed from the top or bottom, including the case where there is some deviation from a true 60 circular form due to dimensional error in the mold, contraction of resin in the mold, or the like), as shown in the sectional view of FIG. 1, when label (1) occupies a large amount of the area along the perimeter of container (2), preventing blistering necessitates either providing large- 65 diameter through-holes or increasing the number of throughholes per unit area to facilitate the escape of air. However,
when large-diameter holes are made, labeled containers of poor appearance due to conspicuous through-holes are obtained. When the number of through-holes per unit area is increased, due to the presence of numerous through-holes in the label in the area of the suction pad (normally about 10 to 30 mm in diameter) of the automatic label feeder, problems are encountered in the course of picking up stacked labels in that the labels cannot be picked up by suction, the labels fall off along the way, or two labels are picked up at once. There are also problems in that, depending on the size and positioning of suction holes in the mold in which the label is secured, the label cannot be secured in the proper position.
To minimize these problems, it is necessary to form suitable through-holes in the label by trial and error in combining the shape of the container and label, the size and positioning of the suction pads, and the size and positioning of the suction holes in the mold. Thus, for conventional labels, it has not been possible to widely employ various container and label shapes, or the broad use thereof has not been possible with feeding units and molds.
Japanese Examined Patent Publication (KOKOKU) Heisei No. 4-71699 proposes the prevention of blistering by the use of a film having minute ventilation holes. However, when ventilation is increased excessively to prevent blistering, the above-described problems with label feeding with an automatic label feeder tend to occur. Thus, this label is also precluded from use in various shapes on a variety of differently shaped containers, or is precluded from wide use in feeders and molds.
In light of the above-described problems of prior art, the object of the present invention is to provide a label for in-mold forming permitting the attachment of labels while effectively inhibiting blistering on molded resin articles having a variety of shapes. A further object of the present invention is to provide a label for in-mold forming permitting smooth suction by automatic label feeding devices and reliable securing of labels, thereby affording high manufacturing efficiency with in-mold labels. Astill further object of the present invention is to provide a labeled molded resin article that is attractive in appearance and can be manufactured economically.
SUMMARY OF THE INVENTION
The present inventors conducted extensive research, resulting in the discovery that by imparting a prescribed degree of air permeability to labels and adjusting the centerline average roughness of the surface of the heat seal resin layer to within a prescribed range, it was possible to effectively prevent blistering in a manner permitting the reliable and smooth feeding of labels to various automatic label feeders and molds; the present invention was devised on that basis.
That is, the present invention provides a label for in-mold forming comprising a thermoplastic resin film base layer and a heat-seal resin layer, wherein a surface of the heat-seal resin layer has a centerline average roughness of 0.5 to 5 micrometers and the label has an air permeability of 10 to 20,000 seconds.
In the label for in-mold forming of the present invention, the value obtained by dividing the air permeability by the centerline average roughness is desirably from 10 to 4,000 seconds/micrometer. Further, the outer surface of the heat seal resin layer is desirably embossed. In the label for in-mold forming of the present invention, holes and/or slits are desirably present in the form of a grid-like pattern. When
slits are present, the length of the slits is desirably from 0.5 to 20 mm and the pitch is desirably from 5 to 25 mm. Further, the thermoplastic resin film base layer comprising the label for in-mold forming of the present invention is desirably comprised of a film that has been stretched in at 5 least one direction. Further, the thermoplastic resin film base layer is desirably comprised of a microporous stretched resin film comprising organic and/or inorganic finepowder. The heat seal resin layer is desirably comprised of polyethylene with a degree of crystallinity of 10 to 60 percent, a number 10 average molecular weight of 10,000 to 40,000, and a melting point of 50 to 130° C.
The present invention further provides a labeled molded resin article in which the label for in-mold forming is integrally adhered to a molded resin article by thermal :5 fusion. A preferable resin article is prepared by vacuum molding or differential pressure molding. The portion of the molded resin article where the label for in-mold forming has been thermally fused desirably comprises a curved surface, particularly a curved surface with a radius of curvature of 20 200 mm or less.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a sectional view showing a cylindrical container 25 having an adhered label.
FIG. 2 is a sectional view of a form of the label for in-mold forming of the present invention.
FIG. 3 is a sectional view of an example of a desirable configuration of the thermoplastic resin film base layer of 30 the label for in-mold forming of the present invention.
FIG. 4 shows patterns of through-holes.
FIG. 5 shows patterns of slits.
FIG. 6 shows a further pattern of slits. 35 FIG. 7 is a sectional view descriptive of the method of
in-mold forming.
FIG. 8 is a sectional view of the container employed in
example (c).
40
DETAILED DESCRIPTION OF PREFERRED
EMBODIMENTS
The label for in-mold forming and labeled molded resin article of the present invention are described in detail below. 4J
FIG. 2 is a sectional view of a typical form of the label for in-mold forming of the present invention. Label for in-mold forming (1) of the present invention comprises a thermoplastic resin film base layer (3) and a heat-seal resin layer (4). The surface of thermoplastic resin film base layer (3) 50 may be printed (5) as shown in the figure. The centerline average roughness of the surface of heat-seal resin layer (4) is adjusted to from 0.5 to 5 micrometers. The centerline average roughness can be adjusted, for example, by embossing the surface of heat-seal resin layer (4) to form embossed 55 valleys (6) and peaks (7). The air permeability of the label for in-mold forming of the present invention is adjusted to from 10 to 20,000 seconds. The air permeability is adjusted, for example, by forming through-holes or slits (cut lines) (8) through the label as shown in the figure. 60
The thermoplastic resin film base layer constituting the label for in-mold forming of the present invention is a film-like layer comprised of thermoplastic resin and is the layer functioning as the base material of the label for in-mold forming of the present invention. Examples of 65 materials employed in the thermoplastic resin film layer are films of: polypropylene, propylene-ethylene copolymer,
high-density polyethylene, medium-density polyethylene, polymethyl-l-pentene, ethylene-cyclic olefin copolymers, other polyolefin resins, polyethylene terephthalate resins, polyvinyl chloride resins, nylon 6, nylon 6,6, nylon 6,10, nylon 6,12, other polyamide resins, ABS resins, and ionomer resins. Of these, the preferred materials are polypropylene, high-density polyethylene, polyethylene terephthalate, and other thermoplastic resins with melting points ranging from 130 to 280° C. These resins may be employed singly or in combinations of two or more.
The chief component thermoplastic resin desirably has a melting point that is 15° C. or more higher than the melting point of the polyolefin resin constituting the heat seal resin layer. Among resins satisfying this condition, propylene based resin is desirable from the perspectives of resistance to chemicals and cost. Examples of such propylene based resins are isotactic or syndiotactic stereoregular propylene homopolymers; and copolymers of the chief component propylene with alpha-olefins such as ethylene, 1-butene, 1-hexene, 1-heptene, 4-methyl-l-pentene, and the like. These copolymers may be in the form of two-element systems, three-element systems, four-element systems, random copolymers, and block copolymers.
In addition to the thermoplastic resin, inorganic finepowders, organic finepowders, and the like may be suitably blended into the thermoplastic resin film base layer.
The type of inorganic finepowder or organic finepowder is not specifically limited.
Examples of inorganic finepowders are heavy calcium carbonate, precipitated calcium carbonate, baked clay, talc, barium sulfate, diatomaceous earth, magnesium oxide, zinc oxide, titanium dioxide, and silicon oxide. Of these, heavy calcium carbonate, baked clay, and talc are preferred from the viewpoints of cost and easiness of forming.
Examples of organic finepowders are polyethylene terephthalate, polybutylene terephthalate, polyamide, polycarbonate, polyethylene napththalate, polystyrene, melamine resins, polyethylene sulfide, polyimide, polyethyl ether ketone, and polyphenylene sulfide. Among these, the use of immiscible finepowder(s) with a higher melting point than the thermoplastic resin employed is desirable.
One of the above-listed finepowders may be selected and employed singly in the thermoplastic resin film base layer, or two or more may be selected and employed in combination. When employing two or more in combination, organic finepowder(s) and inorganic finepowder(s) may be employed in combination.
A film comprising 8 to 80 weight percent of the abovedescribed organic or inorganic finepowder in a thermoplastic resin, a film stretched by a known method in one or two directions, a film the surface of which is coated with a latex comprising an inorganic filler, and a film on which aluminum has been vapor deposited or applied may be suitably employed as the thermoplastic resin film base layer.
From the viewpoints of printing properties, preventing heat shrinkage, and the like, it is desirable to employ a thermoplastic resin film base layer in the form of a microporous stretched resin film having a biaxiallystretched film core layer (A) comprising 5 to 30 weight percent of inorganic finepowder, 3-20 weight percent of high-density polyethylene, and 92 to 50 weight percent of propylene based resin, on one side of which is present a surface layer (B) in the form of a monoaxially-stretched film with a resin composition of 35 to 65 weight percent of inorganic finepowder, 0 to 10 weight percent of high-density polyethylene, and 55-35 weight percent of propylene based
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