Patent Application
20100178438
The present invention relates to a shrinkable label having a hologram layer. More specifically, it relates to a shrinkable label that provides a sharp holographic expression even after shrink processing with relatively large deformation. It also relates to a container with the shrinkable label attached thereto.
Labels each having a hologram (holographic labels) are currently used for the purpose typically of imparting a graphical design function or of preventing forgery. Known holographic labels generally employed are wrapping labels and tack labels which are prepared by applying or transferring a hologram foil to a base paper or a non-shrinkable plastic base film. These labels, however, are difficult to be in intimate contact with articles having irregular complicated dimensions (shapes), because they do not so satisfactorily fit such irregular complicated dimensions. Examples of the articles having irregular complicated dimensions include PET plastic bottles.
In contrast, some of holographic labels using heat-shrinkable base materials are improved in fitting ability (Patent Documents 1 to 3). These labels, however, are also wrapping labels each having a pressure-sensitive adhesive layer. When they are applied typically to dry cells, they shrink and deform only at upper and lower ends thereof so as to fit the dimensions of the dry cells at the upper and lower ends, but their bodies carrying a hologram hardly shrink.
Specifically, there has been obtained no holographic label which includes a hologram carried by a shrinkable film (especially by a tubular shrinkable label) that can fit complicated dimensions of bottles.
Patent Document 1: Japanese Unexamined Patent Application Publication (JP-A) No. 2003-177672
Patent Document 2: Japanese Unexamined Patent Application Publication (JP-A) No. 2003-330351
Patent Document 3: Japanese Unexamined Patent Application Publication (JP-A) No. 2004-230571
To fit such bottle dimensions, so-called “tubular shrinkable labels” have been used. These tubular (cylindrical) shrinkable labels undergo large shrinkage so as to fit the bottle dimensions. The present inventors attempted to adopt the known holographic labels typically to tubular shrinkable labels, and, as a result, found that the hologram layer does not conform to or follow the shrinkage and suffers from problems such as whitening upon shrinkage. Independently, inks that can satisfactorily conform to shrink processing have been used for known tubular shrinkable labels (see, for example, PCT International Publication Number WO 2007/007803). The present inventors also attempted to adopt these inks to holographic labels and, as a result, found that the hologram is lost as a result of shrink processing.
Accordingly, an object of the present invention is to provide a shrinkable label having a hologram, which provides a holographic expression even when adopted to a tubular shrinkable label that undergoes relatively large shrinkage and which satisfactorily conforms to shrinkage. Another object of the present invention is to provide a container with a holographic label, as prepared by attaching the shrinkable label to the container.
After intensive investigations to achieve the objects, the present inventors have found that the use of a hologram layer prepared from a resin composition having a specific resinous formulation can give a shrinkable label that satisfactorily conforms to shrink processing with relatively large deformation and provides a sharp holographic expression even after the shrink processing. The present invention has been made based on these findings.
Specifically, the present invention provides, in an embodiment, a shrinkable label which includes a shrinkable film, and a hologram layer present on or above at least one side of the shrinkable film, in which the hologram layer is formed by curing a resin composition which is cationically curable by the action of an active energy ray. The resin composition contains one or more oxetane compounds including a monofunctional oxetane compound, and one or more bifunctional or higher-functional epoxy compounds, in which the total of the oxetane compounds and the bifunctional or higher-functional epoxy compounds occupies 60 percent by weight or more of the resin composition, and the monofunctional oxetane compound occupies 30 percent by weight or more of the oxetane compounds.
In the shrinkable label, the shrinkable film preferably has a percentage of thermal shrinkage (in hot water at 70° C. for 10 seconds) in its principal orientation direction of from 10% to 30% and preferably has a percentage of thermal shrinkage (in hot water at 80° C. for 10 seconds) in its principal orientation direction of from 30% to 70%.
The shrinkable label may have a shrinkage rate (in hot water at 80° C.) in its principal orientation direction of from 1% to 20% per 0.2 second.
The shrinkable label may have a shrinkage stress in its principal orientation direction of 1.0 to 6.0 newtons per square millimeter (N/mm2), where the shrinkage stress is determined while immersing 80% of a test piece of the shrinkable label in hot water at 80° C. for 10 seconds.
The shrinkable label may be a tubular shrinkable label.
In another embodiment, the present invention provides a container with a label, prepared by placing the shrinkable label around a container and allowing the label to shrink to thereby come into intimate contact with the container.
The shrinkable label according to an embodiment of the present invention suffers from neither whitening of the hologram layer upon shrinkage nor hologram loss even after shrink processing with relatively large shrinkage. The shrinkable label therefore exhibits both satisfactory shape conformity (dimensional conformity) and a sharp holographic expression even when applied to an article having complicated dimensions, and is thereby advantageous especially as a label typically for PET plastic bottles.
Some embodiments of the present invention will be illustrated in detail below.
A shrinkable label according to an embodiment of the present invention has a multilayer structure and includes a shrinkable film and, on or above at least one side thereof, a hologram layer. It should be noted, however, that the hologram layer does not have to spread over a whole side of the shrinkable label, and the shrinkable label has only to at least partially include a multilayer structure of the shrinkable film and the hologram layer. The shrinkable film and the hologram layer may lie on each other directly without the interposition of another layer or may lie over each other with the interposition of one or more other layers. Exemplary other layers include adhesive layers and anchor coat layers. Each of these layers may be a single layer or a multilayer including two or more layers.
The hologram layer in the shrinkable label is formed by curing a resin composition that is curable by the action of an active energy ray. The hologram layer formed from such a resin composition that is curable by the action of an active energy ray is advantageously adoptable even to a base material, such as a shrinkable film, which thermally deforms upon usage. In contrast, a hologram layer formed from a heat-curable resin composition is unsuitable to be adopted to the base material which will thermally deform. Of active energy rays, the resin composition for the formation of the hologram layer is preferably curable by the action of an ultraviolet ray or near-ultraviolet ray. The absorption wavelength of the resin composition is preferably from 200 to 460 nm. As used herein the term “resin composition” also means and includes a “composition for the formation of a resin” (resin precursor composition).
A resin composition curable by the action of an active energy ray (active-energy-ray-curable resin composition) for the formation of the hologram layer should have certain flexibility so as to satisfactorily conform to shrink processing and, in contrast, should have certain rigidity or hardness so as keep its dimensions to maintain the hologram. Such an active-energy-ray-curable resin composition which has satisfactory flexibility and satisfactory rigidity in good balance and is usable in the shrinkable label herein is a cationically polymerizable (cationically curable) resin composition containing one or more oxetane compounds and one or more epoxy compounds.
The resin composition cationically curable by the action of an active energy ray (hereinafter referred to as “cationically curable resin composition”) for the formation of the hologram layer in the shrinkable label contains one or more oxetane compounds including a monofunctional oxetane compound; and one or more bifunctional or higher-functional epoxy compounds as essential components. As used herein the terms “oxetane compounds” and “epoxy compounds” do not include silicones having oxetanyl group and/or epoxy group.
Oxetane compounds for use in the cationically curable resin composition are compounds each having at least one oxetanyl group per molecule and may each be either a monomer or an oligomer. Typically, the oxetane compounds described in Japanese Unexamined Patent Application Publication (JP-A) No. H08 (1996)-85775 and Japanese Unexamined Patent Application Publication (JP-A) No. H08 (1996)-134405 can be used herein.
Of oxetane compounds, preferred examples as compounds having one oxetanyl group per one molecule (monofunctional oxetane compounds) include, but are not limited to, phenoxy-modified oxetanes and ethylcyclohexane-ring-containing oxetanes. Specific examples of monofunctional oxetanes include 3-ethyl-3-[(phenoxy)methyl]oxetane, 3-ethyl-3-(hexyloxymethyl)oxetane, 3-ethyl-3-(2-ethylhexyloxymethyl)oxetane, 3-ethyl-3-(hydroxymethyl)oxetane, and 3-ethyl-3-(chloromethyl)oxetane. Among them, 3-ethyl-3-[(phenoxy)methyl]oxetane and 3-ethyl-3-(hydroxymethyl)oxetane are especially preferred from the viewpoints of coatability (printability) and the curability of the resulting resin composition layer (coated layer).
Exemplary compounds having two or more oxetanyl groups per one molecule (bifunctional or higher-functional oxetane compounds) include bifunctional oxetane compounds such as 1,4-bis[[(3-ethyloxetan-3-yl)methoxy]methyl]benzene and bis[(3-ethyloxetan-3-yl)methyl]ether; and multifunctional oxetane compounds such as oxetanylsilsesquioxane, oxetanyl silicate, and phenol novolac oxetanes. Among these compounds, preferred are those each having two or three functional groups, and more preferred are those each having two functional groups from the viewpoints of satisfactory curability and printability. Among them, bis[(3-ethyloxetan-3-yl)methyl]ether is especially preferred from the viewpoints of the printability of the resin composition and the curability of the resin composition layer.
The oxetane compounds can be prepared from an oxetane alcohol and a halide (e.g., xylene dichloride) according to a known procedure. The oxetane alcohol may be prepared typically from trimethylolpropane and dimethyl carbonate. Already-available oxetane compounds can also be used herein, and exemplary commercially available oxetane compounds include monofunctional oxetane compounds such as “ARON OXETANE OXT-101”, “ARON OXETANE OXT-211”, “ARON OXETANE OXT-212”, and “ARON OXETANE OXT-213” each supplied by Toagosei Co., Ltd.; bifunctional oxetane compounds such as “ARON OXETANE OXT-121”, “ARON OXETANE OXT-221”, and “ARON OXETANE OXT-223” each supplied by Toagosei Co., Ltd.; and multifunctional oxetane compounds such as “ARON OXETANE OX-SQ-H”, “ARON OXETANE OX-SC”, and “ARON OXETANE PNOX-1009” each supplied by Toagosei Co., Ltd.
The one or more oxetane compounds should include one or more monofunctional oxetane compounds in an amount of 30 percent by weight or more. The compounding ratio (weight ratio) of the monofunctional oxetane compounds to bifunctional or higher-functional oxetane compounds [(monofunctional oxetane compounds):(bifunctional or higher-functional oxetane compounds)] in the oxetane compounds is from 30:70 to 100:0 and is preferably from 40:60 to 90:10. The conformity to shrink processing becomes better with an increasing compounding ratio of the monofunctional oxetane compounds. Specifically, if the compounding ratio of the monofunctional oxetane compounds is less than the above range, the resin composition may not satisfactorily conform to shrink processing and may thereby cause problems such as “ink cracking”. In contrast, with an increasing compounding ratio of bifunctional or higher-functional oxetane compounds, the resin composition may tend to be cured more rapidly, so as to improve the productivity.
Bifunctional or higher-functional epoxy compounds (hereinafter also simply referred to as “epoxy compounds”) for use in the cationically curable resin composition may be known epoxy compounds each having at least two epoxy groups per molecule. Examples of usable epoxy compounds include aliphatic epoxy compounds, alicyclic epoxy compounds, and aromatic epoxy compounds. Among them, glycidyl-containing compounds and epoxycyclohexane-ring-containing compounds are preferred from the viewpoint of higher reaction rate. Exemplary aliphatic epoxy compounds include epoxidized linseed oil. Exemplary alicyclic epoxy compounds include 3,4-epoxycyclohexylmethyl 3′,4′-epoxycyclohexanecarboxylate and bis-(3,4-epoxycyclohexyl) adipate. Exemplary aromatic epoxy compounds include bisphenol-A glycidyl ether, glycidyl ether condensates of bisphenol-A, and epichlorohydrin-modified derivatives of novolac resins and of cresol resins.
The bifunctional or higher-functional epoxy compounds can be synthesized according to a common procedure such as synthesis from epichlorohydrin and bisphenol-A. Such bifunctional or higher-functional epoxy compounds are also commercially available typically as “Celloxide 2021”, “Celloxide 2021P”, “Celloxide 2080”, and “EPOLEAD GT400” each from Daicel Chemical Industries, Ltd.
The compounding ratio (weight ratio) of the oxetane compounds (total amount of monofunctional, and bifunctional or higher-functional oxetane compounds) to the epoxy compounds [(oxetane compounds):(epoxy compounds)] in the cationically curable resin composition is preferably from 90:10 to 40:60, and more preferably from 80:20 to 45:55. The resin composition, if containing oxetane compounds in an amount larger than the above range, may suffer from a low initial curing reaction rate, and it may take much time for the resin composition to be cured. This may invite insufficient productivity or may cause the resin composition to remain uncured in a regular curing process. The resin composition, if containing epoxy compounds in an amount larger than the above range, may have an excessively high viscosity to impede uniform application through coating procedure such as gravure printing or flexographic printing. In addition, this resin composition may often suffer from termination of the curing reaction to give a cured article having a low molecular weight, and the resulting cured resin layer after curing may become fragile.
The total amount of the oxetane compounds and the epoxy compounds in the cationically curable resin composition is 60 percent by weight or more (for example, from 60 to 99 percent by weight), and is preferably from 70 to 99 percent by weight, and more preferably from 90 to 99 percent by weight, based on the total amount of the cationically curable resin composition. These ranges are preferred from the viewpoints typically of coatability and curability.
In the cationically curable resin composition, the oxetane compound component contributes to the formation of a high-molecular-weight tough cured resin layer (hologram layer) because this component is resistant to the termination of the curing reaction. However, it also acts to retard a curing initiation reaction, and this prolongs the curing process time. As a result, the process time of hologram processing (e.g., the time within which a hologram foil or hologram master film is laid over the layer) is prolonged to cause insufficient productivity and/or the hologram may be broken upon removal of the hologram master film or hologram foil. Additionally, when curing is performed within a short time, the resin composition layer may not be cured sufficiently and the resulting cured resin layer (hologram layer) may have insufficient toughness. In contrast, the epoxy compound component undergoes a rapid initiation reaction, but it is also susceptible to termination to thereby give a cured article having a low molecular weight. The resulting cured resin layer (hologram layer) may often show a low film strength. The combination use of these two components can give a resin composition having both a satisfactory curing rate (curing speed) (productivity) and sufficient toughness after curing. This also improves curability and thereby improves the adhesion between the cured resin layer (hologram layer) and the base film (shrinkable film).
The cationically curable resin composition preferably further contains one or more photopolymerization initiators (photoinitiators) for the development of curability by the action of an active energy ray. Though not limited, preferred photopolymerization initiators include photocationic initiators. Exemplary photocationic initiators include, but are not limited to, diazonium salts, diaryliodonium salts, triarylsulfonium salts, silanol/aluminum complexes, sulfonic acid esters, and imidosulfonates. Among them, diaryliodonium salts and triarylsulfonium salts are preferred from the viewpoint of reactivity. The content of photopolymerization initiators is preferably from 0.5 to 7 percent by weight, and more preferably from 1 to 5 percent by weight based on the total weight of the resin composition, though not critical.
The cationically curable resin composition preferably further contains one or more sensitizers (intensifiers) according to necessity so as to improve the production efficiency. The sensitizers for use herein can be chosen from already-available sensitizers in consideration typically of the type of the active energy ray to be used. Exemplary sensitizers include (1) amine sensitizers including aliphatic amines, aromatic amines, and amines having a nitrogen-containing ring, such as piperidine; (2) allyl sensitizers, and urea sensitizers such as o-tolylthiourea; (3) sulfur compound sensitizers such as sodium diethyl dithiophosphate; (4) anthracene sensitizers; (5) nitrile sensitizers such as N,N-di-(substituted)-p-aminobenzonitrile compounds; (6) phosphorus compound sensitizers such as tri-(n-butyl)phosphine; (7) nitrogen compound sensitizers such as N-nitrosohydroxylamine derivatives and oxazolidine compounds; and (8) chlorine compound sensitizers such as carbon tetrachloride. Among them, anthracene sensitizers are preferred for their high sensitizing activities, of which thioxanthone and 9,10-dibutoxyanthracene are more preferred. Though not critical, the content of the sensitizers is preferably from 0.1 to 5 percent by weight, and especially preferably from 0.3 to 3 percent by weight, based on the total weight of the resin composition.
The cationically curable resin composition may further contain one or more silicone compounds (silicone oils) so as to improve the curing rate (curing speed), adhesion, and slippage. Though not limited, the silicone compounds for use herein may be polysiloxanes having a siloxane-bond main chain (principal chain). Examples thereof include straight silicone compounds having no other substituents than methyl group and phenyl group, such as dimethyl silicones, methyl phenyl silicones, and methyl hydrogen silicones; and modified silicone compounds having one or more substituents other than methyl group and phenyl group in their side chains or terminals.
Exemplary substituents in the modified silicones include epoxy group, fluorine atom, amino group, carboxyl group, aliphatic hydroxyl group (alcoholic hydroxyl group), aromatic hydroxyl group (phenolic hydroxyl group), (meth)acryloyl-containing substituents, and substituents having a polyether chain. Exemplary modified silicones containing such substituents include epoxy-modified silicones, fluorine-modified silicones, amino-modified silicones, (meth)acrylic-modified silicones, polyether-modified silicones, carboxyl-modified silicones, carbinol-modified silicones, phenol-modified silicones, and diol-modified silicones. The compounds described in PCT International Publication Number WO 2007/007803, for example, can be used as such modified silicone compounds.
The amount of the silicone compounds is preferably from 0.1 to 3 parts by weight, and more preferably from 0.5 to 2.5 parts by weight, per 100 parts by weight of the total amount of the oxetane compounds and the epoxy compounds.
The cationically curable resin composition may further contain one or more resins from the viewpoint of providing further satisfactory scratch resistance, abrasion resistance, and waterproof, and modifying the viscosity. Examples of such resins include polyester resins, polyurethane resins, vinyl resins, acrylic resin, cellulosic resins, and polybutadiene resins. Each of different resins may be incorporated alone or in combination.
Where necessary, the cationically curable resin compositions may further contain one or more lubricants. Examples of the lubricants herein include waxes and wax-like compounds, including polyolefinic waxes such as polyethylene waxes; fatty acid amides; fatty acid esters; paraffin waxes; polytetrafluoroethylene (PTFE) waxes; and carnauba waxes.
The content of a solvent, if contained in the cationically curable resin composition, is preferably 5 percent by weight or less, more preferably 1 percent by weight or less, and most preferably substantially zero (i.e., the resin composition most preferably contains substantially no solvent), where the solvent is not involved in the reaction and is used mainly as a dispersant. As used herein the term “solvent” refers to one that is generally used typically in inks for gravure printing or flexographic printing so as to improve the coating workability of coating compositions (inks) or the compatibility and dispersibility of components in the coating compositions. Exemplary “solvents” include organic solvents such as toluene, xylenes, methyl ethyl ketone, ethyl acetate, methyl alcohol, ethyl alcohol, isopropyl alcohol, and cyclohexane; and water. Reactive diluents taken into the resin composition after curing are not included in this category (solvents). The resin composition can develop satisfactory coatability and dispersibility among components even when containing no solvent and thereby needs a minimum amount of a solvent. This eliminates the need of removing the solvent, allows high-speed production and cost reduction, and reduces the environmental load.
The cationically curable resin composition may be a transparent resin composition containing no pigment component, or a resin composition colored by one or more colorants within ranges not impeding development of a sharp holographic expression. The colorants can be chosen from pigments and dyestuffs generally used in printing inks without limitation. Among them, pigments are preferably used. Exemplary pigments usable herein include organic or inorganic coloring pigments including cyan (blue) pigments such as copper phthalocyanine blue; red pigments such as condensed azo pigments; yellow pigments such as azo lake pigments; carbon black; aluminum flake; and mica. One or more pigments according to the intended use may be suitably chosen from among them. Extender pigments can also be used as the pigments, for the purpose typically of gloss modification. Exemplary extender pigments include alumina, calcium carbonate, barium sulfate, silica, and acrylic beads. The amount of such pigments is preferably from 1 to 20 parts by weight, and more preferably from 1 to 5 parts by weight, per 100 parts by weight of the total amount of the oxetane compounds and the epoxy compounds. These ranges are preferred from the viewpoint of not impeding holographic expression (holographic display).
In addition to the above components, the cationically curable resin composition may further contain any of other resin components and additives such as dispersants, antioxidants, flavors, deodorants, and stabilizers within ranges not adversely affecting the advantages of the present invention. These are added for the purpose of imparting other function(s) to the resin composition.
When to be applied, for example, by gravure printing, the viscosity (23±2° C.) of the cationically curable resin composition is preferably from 10 to 2000 millipascal second (mPa·s), and more preferably from 20 to 1000 mPa·s, though not critical. The resin composition, if having a viscosity of more than 2000 mPa·s, may show insufficient gravure printability to cause defects such as “blur” (poor coverage), and satisfactory decorativeness may not be imparted to the resulting label. In contrast, the resin composition, if having a viscosity of less than 10 mPa·s, may become insufficiently stable during storage and may often suffer from problems such as sedimentation of additives. The viscosity of the resin composition can be controlled, for example, by adjusting or modifying the compounding ratios of respective components and/or by adding thickeners or viscosity decreasers.
The cationically curable resin composition may be prepared by blending or mixing the respective components.
Exemplary devices for the mixing include mixers such as butterfly mixer, planetary mixer, pony mixer, dissolver, tank mixer, homomixer, and homodisperser; and mills such as roll mill, sand mill, ball mill, bead mill, and line mill; and kneaders. The mixing time (residence time) in the mixing is preferably from 10 to 120 minutes. The resulting resin composition may be subjected to filtration before use, where necessary.
The cationically curable resin composition is useful not only for the formation of the hologram layer but also for use as a transparent ink (clear ink), because the resin composition can impart activities such as abrasion resistance, scratch resistance, and solvent resistance to an article to be applied.
The shrinkable film for use in the shrinkable label is a layer which serves as a base of the label and which bears strength properties and shrinking properties. One or more resins for use in the shrinkable film can be chosen suitably according typically to required properties and cost. Exemplary resins include, but are not limited to, polyester resins, olefinic resins, styrenic resins, poly(vinyl chloride)s, polyamide resins, aramids, polyimides, poly(phenylene sulfide)s, and acrylic resins. Above all, the shrinkable film is preferably made from a polyester film, a polystyrenic film, or a laminated film of these films. Exemplary polyester resins usable herein include poly(ethylene terephthalate) (PET) resins, poly(ethylene-2,6-naphthalenedicarboxylate)s (PENs), and poly(lactic acid)s (PLAs), of which polyethylene terephthalate) (PET) resins are preferred. Preferred exemplary styrenic resins include regular polystyrenes, styrene-butadiene copolymers (SBSs), and styrene-butadiene-isoprene copolymers (SBISs).
The shrinkable film for use herein may be a single-layer film, or a multilayer film including two or more film layers according typically to required properties and intended use. When it is a multilayer film, the multilayer film may include two or more different film layers made from two or more different resins, respectively.
The shrinkable film is preferably a monoaxially, biaxially, or multiaxially oriented film, so as to exhibit shrinking properties. When the shrinkable film is a multilayer film including two or more film layers, at least one film layer of the multilayer film is preferably oriented. If all the film layers are not oriented, the shrinkable film may not exhibit sufficient shrinking properties. The shrinkable film is often a monoaxially or biaxially oriented film and is generally a film intensively oriented in a film width direction (a direction to be a label circumferential direction). In other words, the shrinkable film is generally a film substantially monoaxially oriented in the width direction.
The shrinkable film may be prepared according to a common procedure such as film formation using a molten material or film formation using a solution. Independently, commercially available shrinkable films are also usable herein. Where necessary, the surface of the shrinkable film may have been subjected to a common surface treatment such as corona discharge treatment and/or primer treatment. The lamination of the shrinkable film, if having a multilayer structure, can be performed according to a common procedure such as coextrusion or dry lamination. The orientation of the shrinkable film may be performed by biaxial drawing in a longitudinal direction (lengthwise direction; machine direction (MD)) and in a width direction (cross direction; transverse direction (TD)) or by monoaxial drawing in a longitudinal or cross direction. The drawing can be performed according to any of roll drawing, tenter drawing, or tube drawing. The drawing is often performed by conducting drawing in a longitudinal direction according to necessity and thereafter drawing in a cross direction each at a temperature of from about 70° C. to about 100° C. The draw ratio in the longitudinal drawing may be from about 1.01 to about 1.5 times, and preferably from about 1.05 to about 1.3 times. The draw ratio in the crosswise drawing may be from about 3 to about 6 times, and preferably from about 4 to about 5.5 times.
Though not critical, the thickness of the shrinkable film is preferably from 10 to 100 μm, more preferably from 20 to 80 μm, and furthermore preferably from 30 to 60 μm. The shrinkable film may be a three-layer film including a core layer and surface layers. In this case, the ratio in thickness among the core layer and the surface layers [(surface layer)/(core layer)/(surface layer)] is preferably from 1/2/1 to 1/10/1.
The shrinkable film for use in the shrinkable label is preferably one having a relatively small shrinkage stress and a relatively low shrinkage rate. These conditions are preferred from the viewpoints of maintaining the shape of the hologram upon shrink processing and of ensuring the conformity of the hologram layer to shrink processing. To satisfy these conditions, the shrinkable film is preferably a multilayer film including at least one layer of polyester resin and at least one layer of styrenic resin. Among such films, a multilayer shrinkable film including a styrenic resin core layer, and polyester resin surface layers is especially preferred. This multilayer shrinkable film is preferred because the polyester resin shows good adhesion to the hologram layer, and the styrenic resin exhibits satisfactory shrinking properties. Such shrinkable films are also commercially available, and examples thereof include multilayer films including polyester resin surface layers and a styrenic resin core layer, such as “DL” supplied by Mitsubishi Plastics, Inc. and “HGS” supplied by GUNZE Limited; polystyrenic films such as “BONSET” supplied by CI Kasei Co., Ltd.; and polylactic acid) films such as “ECOLOJU” supplied by Mitsubishi Plastics, Inc.
Though not critical, the percentage of thermal shrinkage (in hot water at 70° C. for 10 seconds) of the shrinkable film for use herein in its principal orientation direction is preferably from 10% to 30%, and more preferably from 15% to 25%. Also though not critical, the percentage of thermal shrinkage (in hot water at 80° C. for 10 seconds) of the shrinkable film in its principal orientation direction is preferably from 30% to 70%, and more preferably from 35% to 65%. If the shrinkable film has a percentage of thermal shrinkage in its principal orientation direction exceeding the above range, the hologram layer may not satisfactorily conform to shrink processing and may cause whitening and/or unsatisfactory expression of the hologram. If the shrinkable film has a percentage of thermal shrinkage in its principal orientation direction less than the above range, the resulting label may not satisfactorily fit the dimensions of an article to be applied, and the resulting container with the label may not be well finished. As used herein the term “principal orientation direction” refers to a direction in which the drawing process has been mainly performed (i.e., a direction in which the percentage of thermal shrinkage is largest) and, when the shrinkable label is a tubular shrinkable label, it is generally a width direction of the film.
The percentage of thermal shrinkage (80° C. for 10 seconds) of the shrinkable film in a direction perpendicular to the principal orientation direction is preferably from about −3% to about 15%, though not critical.
The transparency of the shrinkable film for use herein, when being a transparent film, is preferably less than 10, more preferably less than 5.0, and furthermore preferably less than 2.0, in terms of haze (%) determined in accordance with JIS K 7105. The shrinkable film, if having a haze of 10 or more, may cloud a print and thereby cause insufficient decorativeness when the print is to be seen through the shrinkable film.
The shrinkable label according to an embodiment of the present invention is prepared by forming a hologram layer on the shrinkable film through curing of the cationically curable resin composition. The hologram layer may be formed mainly through the following steps (i) to (iv) of: (i) applying the cationically curable resin composition to the shrinkable film; (ii) laying a transfer hologram over the resin composition layer formed in the step (i); (iii) curing the resin composition layer by the action of an active energy ray (to give a “cured resin layer”); and (iv) removing the transfer hologram. The steps (i) to (iv) are preferably performed as a series of steps with the applying step (coating step) from the viewpoint of satisfactory productivity. Though not critical, the process speed herein is preferably from 20 to 150 meters per minute (m/min), and more preferably from 25 to 100 m/min.
Preferred procedures to apply the resin composition to the shrinkable film in the step (i) include gravure printing, flexographic printing, serigraph, and rotary letterpress, of which gravure printing and flexographic printing are more preferred. These procedures are preferred from the viewpoints typically of cost, productivity, and decorativeness of the resulting print. The coating step may be performed at any stage (time) not critical and may be performed as an in-line coating or an off-line coating. The in-line coating is provided during the production processes of the shrinkable film, for example, before drawing or after monoaxial longitudinal drawing. The off-line coating is provided after the formation of the shrinkable film. Among them, the off-line coating is preferred from the viewpoints of productivity and workability such as curing workability.
The transfer hologram for use in the step (ii) may be in any form such as a roll or film, but it is preferably one in a film form, such as hologram master film or hologram foil, for the sake of convenience. The laying (lamination) of, for example, a hologram master film over the resin composition layer may be performed according to or using a device or procedure generally used in lamination of such films, such as nip roller or air blast. Among them, air blast is preferred from the viewpoint of suppressing the generation of shearing stress upon overlaying (lamination).
In the step (iii), curing of the (uncured) resin composition layer is performed through active-energy-ray curing using a device such as ultraviolet (UV) lamp, ultraviolet light emitting diode (UV LED), or ultraviolet laser. From the viewpoint of curability, the active energy ray to be applied is preferably an ultraviolet ray (near-ultraviolet ray) having a wavelength of from 200 to 460 nm; and the application (irradiation) is preferably performed at an irradiation intensity of from 150 millijoules per square centimeter (mJ/cm2) to 1000 mJ/cm2 for an irradiation time of from 0.1 to 3 seconds, while these ranges may vary depending on the formulation of the resin composition and are not critical.
The hologram layer (cured resin layer) is preferably provided as a surface-most layer (such as an outermost layer or innermost layer) in the shrinkable label. Exemplary multilayer structures of the shrinkable label include, but are not limited to, (hologram layer)/(shrinkable film layer)/(print layer); (hologram layer)/(print layer)/(shrinkable film layer)/(print layer); and (hologram layer)/(anchor coat layer)/(shrinkable film layer)/(print layer). In addition, a print layer may be partially provided over the surface hologram layer. The hologram layer for use herein has good adhesion with the shrinkable film and thereby exhibits satisfactory activities even when it is arranged directly on the surface of the shrinkable film. The lamination structure, however, is not limited thereto, and the hologram layer may be provided over the shrinkable film with the interposition of one or more other layers such as adhesive layer.
The thickness of the hologram layer in the shrinkable label is not critical but is preferably from 0.3 to 5 μm, and more preferably from 0.5 to 3 μm. The hologram layer, if having a thickness of more than 5 μm, may cause curing failure and/or shrinking failure. In contrast, when the hologram layer is formed to have a thickness of less than 0.3 μm, the hologram layer may not have depressions and protrusions in sufficient heights as a result of holographic processing to form a hologram, and the resulting hologram may not be formed stably.
The shrinkable label may further include one or more layers such as print layers, in addition to the shrinkable film and the hologram layer. Exemplary print layers include design print layers which indicate, for example, a product name, an illustration, a design, or handling precautions; and white backing print layers. Such a print layer is formed by applying a layer of printing ink, and, where necessary, drying and/or curing the applied layer. The printing ink herein contains a binder resin, a pigment, and, where necessary, a solvent as components. Though not critical, the thickness of the print layer (as a single layer) is preferably from 0.1 to 15 μm, and more preferably from 0.5 to 10 μm. The shrinkable label may include such a print layer partially and/or may include two or more print layers. The print layer(s) may be formed according to a known or common coating procedure not limited, but is preferably formed typically through gravure printing or flexographic printing. The printing step is preferably performed before the step of forming the hologram layer, through not limited thereto. When a print layer is to be formed partially over the hologram layer, the printing step is performed after the step of forming the hologram layer.
The shrinkable label may further include one or more other layers according to necessity. Exemplary other layers include protective layer, adhesive layer, ultraviolet-absorbing layer, overlaminate layer, anchor coat layer, primer coat layer, nonwoven fabric layer, and paper layer.
The shrinkage stress (primary shrinkage stress) (in hot water at 80° C.) of the shrinkable label in its principal orientation direction is preferably from 1.0 to 6.0 N/mm2, and more preferably from 1.5 to 5.0 N/mm2. The shrinkable label, if having a shrinkage stress of more than 6.0 N/mm2, may not satisfactorily conform to shrinking and may thereby suffer from whitening (ink cracking). The shrinkable label, if having a shrinkage stress of less than 1.0 N/mm2, may not sufficiently fit the dimensions of an article to be applied upon shrink processing and may not be well finished, or the ink coat may not sufficiently shrink to thereby suffer from shrinkage failure such as wrinkles or curls. The “thermal shrinkage stress (primary shrinkage stress)” herein is a maximum value of shrinkage stress as determined while immersing 80% of a test piece of the shrinkable label in hot water at 80° C. for 10 seconds and measuring shrinkage stress with a tensile tester.
The shrinkage rate (in hot water at 80° C.) of the shrinkable label in its principal orientation direction is preferably from 1% to 20% per 0.2 second, and more preferably from 2% to 15% per 0.2 second. The shrinkable label, if having a shrinkage rate of more than 20% per 0.2 second, may not satisfactorily conform to shrinking and may thereby suffer from whitening (ink cracking). The shrinkable label, if having a shrinkage rate of less than 1% per 0.2 second, may not be produced with good productivity, because it may take much time to perform shrink processing. The shrinkage stress and the shrinkage rate of the shrinkable label are close to those of the shrinkable film contained therein.
The thickness of the shrinkable label is not critical but is preferably from 10 to 150 μm, and more preferably from 20 to 120 μm.
The shrinkable label is not limited in its form (shape) and can be, for example, a tubular label or a wrapping label. However, the shrinkable label is preferably a shrinkable label of tubular form (tubular shrinkable label; cylindrical shrinkable label) so as to exhibit the advantages of the present invention. Specifically, the shrinkable label according to the present invention provides a beautiful holographic expression even when it shrinks and deforms to a large extent as a result of shrink processing. In this connection, there are common labels having a hologram layer formed by using a regular active-energy-ray-curable resin composition other than the resin composition for use in the present invention. These common labels are difficult to be used as tubular labels, although some of them are usable as wrapping labels in which the labels shrink and deform to a relatively small degree.
The shrinkable label, when used as a tubular shrinkable label, is formed into a round tube (cylinder) so that the principal orientation direction (generally, a width direction of the sheet) is to be a circumferential direction of the label. Specifically, a long continuous shrinkable label is formed into a tube, and a solvent, such as tetrahydrofuran (THF), and/or an adhesive (these components are hereinafter referred to as “solvent or another component”) is applied to an inner surface of one lateral end of the label to form a band about 2 to 4 mm wide in a longitudinal direction. The label is then cylindrically wound so that the portion where the solvent or another component is applied is laid over the outer surface of the other lateral end of the label at a position of 5 to 10 mm inside from the other lateral end, affixed and adhered (center-sealed). Thus, the tubular shrink label is obtained as a continuous long tubular sheet. In this process, it is desirable that neither hologram layer nor print layer is arranged in a portion where the solvent or another component is applied (center-seal portion) so that two adjacent portions of the base shrinkable film are directly bonded with each other in the portion.
The shrinkable label may have perforations for tearing the label. In this case, perforations with predetermined lengths and intervals (pitches) may be formed in a longitudinal direction. The perforations can be arranged according to a common procedure. They can be arranged, for example, by pressing a disk-like blade peripherally having cutting edges and non-cutting portions alternately, or by using laser. The step of arranging perforations can be carried out as appropriate in a suitable stage, such as after the printing step, or before or after the step of processing the label to form a tubular label. Though may be arranged on the hologram layer, the perforations are preferably arranged in a portion of the base shrinkable film where the hologram layer is not provided.
[Container with Label]
The shrinkable label is attached to a container to give a container with the label. Exemplary containers for use in the container with the label include soft-drink bottles such as PET plastic bottles; home-delivery milk containers; containers for foodstuffs such as seasonings; alcoholic drink bottles; containers for pharmaceutical preparations; containers for chemicals such as detergents and aerosols (sprays). Preferred materials for the container include, but are not limited to, plastics such as poly(polyethylene terephthalate)s (PETs); and paper. Though not critical, the container preferably has a cylindrical or rectangular bottle shape.
The way to attach the shrinkable label to the container may be, but is not limited to, the following procedure. When the shrinkable label is a tubular shrinkable label, a continuous tubular shrinkable label is cut, the cut label is attached to a predetermined container, is allowed to shrink through heat treatment to come into intimate contact with the container, and thereby yields the container with the label. More specifically, the continuous long tubular shrinkable label is fed to an automatic labeling machine (shrink labeler), cut to a required length, fitted onto a container filled with a content, subjected to thermal shrinkage by allowing the article to pass through a hot-air tunnel or steam tunnel at a predetermined temperature or by heating the article with radial heat such as infrared rays to come into intimate contact with the container, and thus yields the container with the label. Though being shrinkable by the application of hot air (at 60° C. to 300° C.), the shrinkable label is preferably allowed to shrink by the application of steam (water vapor), because it is desirable to allow the label to shrink uniformly and relatively gradually. The heating treatment is preferably performed at a temperature of from 60° C. to 100° C., and more preferably from 65° C. to 95° C. Upon the attachment to the container, a portion of the shrinkable label where the hologram layer is formed (hologram-formed portion) thermally shrinks preferably by a rate of from about 3% to about 25%, and more preferably by a rate of from about 5% to about 20%.
(1) Percentage of Thermal Shrinkage (in Hot Water at 70° C. for 10 Seconds) and Percentage of Thermal Shrinkage (in Hot Water at 80° C. for 10 Seconds)
A method for measuring a percentage of thermal shrinkage (in hot water at 70° C. for 10 seconds) will be described below. A percentage of thermal shrinkage (in hot water at 80° C. for 10 seconds) can be measured by the following method, except for changing the temperature of the hot water from 70° C. to 80° C.
A square sample piece of 50 mm in a principal orientation direction and 50 mm in a perpendicular direction to the principal orientation direction was prepared from a shrinkable film to be tested.
The sample piece was subjected to a heat treatment (under no load) in hot water at 70° C. for 10 seconds, the sizes (in a width direction) of the sample before and after the heat treatment were read out, and a percentage of thermal shrinkage was calculated according to the following formula. The test was repeated a total of five times, and the average of five data was defined as the percentage of shrinkage.
The principal orientation direction of shrinkable films (shrinkable labels) prepared according to the examples and comparative example below is the width direction of the films.
Percentage of Thermal Shrinkage(%)=(L0−L1)/L0×100
L0: Size (in the principal orientation direction) of the sample before the heat treatment;
L1: Size (in the same direction as L0) of the sample after the heat treatment
The determination method of the percentage of thermal shrinkage in the principal orientation direction has been described above. The percentage of thermal shrinkage in a perpendicular direction to the principal orientation direction can be calculated according to the determination method, except for measuring sizes in a perpendicular direction to the principal orientation direction.
When a principal orientation direction is unknown, the principal orientation direction may be determined by measuring percentages of thermal shrinkage in different directions at intervals typically of 10° and defining a direction, in which the percentage of shrinkage has a maximum, as the principal orientation direction.
(2) Shrinkage Stress (in Hot Water at 80° C.)
A roughly rectangular sample piece of 200 mm in a principal orientation direction and 15 mm in a perpendicular direction to the principal orientation direction was sampled from each of the shrinkable labels prepared according to the examples and comparative example. The sample piece was secured by chucks of a tensile tester (supplied by Shimadzu Corporation, “Autograph AGS-50G”, capacity of load cell: 500 N) at a chuck-interval of 100 mm so that the principal orientation direction stands the tensile direction. While maintaining the chuck interval at 100 mm, the sample piece was immersed in hot water at 80° C. for 10 seconds so that the sample piece in a portion from the lower end up to 80 mm of the 100-mm chuck interval was immersed in the hot water. A shrinkage stress (N/mm2) generated in this process was measured, and the maximum value of the shrinkage stress was defined as the shrinkage stress (primary shrinkage stress) of the sample.
(3) Shrinkage Rate (in Hot Water at 80° C.)
A strip sample piece of 100 mm in the principal orientation direction and 5 mm in a perpendicular direction to the principal orientation direction was sampled for measurements from each of the shrinkable labels prepared according to the examples and comparative example.
The sample piece was immersed in a hot bath at 80° C., how the size in its principal orientation direction (initial measurement length: 88 mm) changed with time during immersion was measured (sampling time (interval): 0.1 second), from which how the percentage of thermal shrinkage changed with time was calculated. The rate of change (unit: percentage (%) per 0.2 second) of the percentage of thermal shrinkage with respect to the time was calculated from measured percentages of thermal shrinkage at three subsequent measurement points, and the maximum value thereof was defined as the “shrinkage rate (in hot water at 80° C.)” of the sample.
(4) Surface Curability (Initial Tack Test)
In the procedures of the examples and comparative example, a curing process of a resin composition layer was performed by the application of an ultraviolet ray (under two different conditions of ultraviolet irradiation process speed of 70 m/min and 100 m/min), and immediately after the curing process, the surface of a cured resin layer was touched by finger. Whether the resin composition remaining uncured stuck to the finger was visually observed, and the surface curability (initial tack test) was evaluated according to the following criteria:
No resin composition sticks to the finger even after curing at a process speed of 100 m/min: Good surface curability (Good)
The resin composition does not stick to the finger after curing at a process speed of 70 m/min but it sticks to the finger after curing at a process speed of 100 m/min: Usable level (Tolerable)
The resin composition sticks to the finger even after curing at a process speed of 70 m/min: Poor surface curability
(5) Adhesion (Tape Peel Test)
Tests were performed in accordance with Japanese Industrial Standards (JIS) K 5600, except for not providing cross cuts on samples. Specifically, a Nichiban Tape (18 mm in width) was affixed to the surface of the hologram layer of each of the shrinkable labels prepared according to the examples and comparative example, the tape was thereafter peeled off at an angle of 90 degrees, and how much area the hologram layer remained on the label was observed in a region of 5 mm long and 5 mm wide. The adhesion (adhesiveness) of the sample was determined according to the following criteria:
90% or more of the hologram layer remains: Good adhesion (Good)
80% or more and less than 90% of the hologram layer remains: Somewhat poor adhesion but at usable level (Tolerable)
Less than 80% of the hologram layer remains: Poor adhesion (Poor)
(6) Shrinkage Whitening Test (Conformity to Processing)
A strip sample piece of 100 mm in length and 50 mm in width was sampled from each of the shrinkable labels prepared according to the examples and comparative example so that the principal orientation direction (width direction of the label) be the longitudinal direction of the sample piece.
The sample was secured at both ends (at a distance of 100 mm) in its longitudinal direction by a jig. The jig was configured to secure the sample piece at an interval of 80 mm, and the secured sample piece was therefore loose before heat treatment. The sample secured at both ends by the jig was subjected to a heat treatment (heat shrink processing) by immersing the same in hot water at 90° C. for 10 seconds so as to thermally shrink by 20%.
The sample after the heat shrink processing was evaluated according to the following criteria:
The sample does not suffer from whitening: Good process conformity (Good)
The sample slightly suffers from whitening: Usable level (Tolerable)
The sample suffers from whitening: Poor process conformity (Poor)
(7) Holographic Expressivity
Each of the shrinkable labels prepared according to the examples and comparative example was thermally shrunk by 10% or 20% by the procedure of the shrinkage whitening test, the resulting pattern was visually observed, and the holographic expressivity of each sample was evaluated according to the following criteria.
To thermally shrink the sample by 10%, the jig interval in the heat shrink processing in the shrinkage whitening test was changed to 90 mm.
A clear optical interference pattern (holographic pattern) is observed: Good holographic expressivity (Good)
An optical interference pattern is observed but at a low brightness: Usable level (Tolerable)
An optical interference pattern is not clearly observed: Poor holographic expressivity (Poor)
The present invention will be illustrated in further detail with reference to several examples below. It should be noted, however, that these examples are never construed to limit the scope of the present invention. Table 1 shows the formulations (weight ratios) of a component A and a component B in resin compositions; and evaluations of the resin compositions and shrinkable labels each prepared according to the examples and comparative example. The details of the components in Table 1 are shown in Table 2.
A cationically curable resin composition was prepared by blending 3-ethyl-3-[(phenoxy)methyl]oxetane (supplied by Toagosei Co., Ltd. under the trade name “ARON OXETANE OXT-211”) as a component A (monofunctional oxetane compound), 3,4-epoxycyclohexylmethyl 3′,4′-epoxycyclohexanecarboxylate (supplied by Daicel Chemical Industries, Ltd. under the trade name “Celloxide 2021P”) as a component C (epoxy compound), a photocationic initiator, and a silicone compound in amounts (parts by weight) given in Table 1. No solvent was used herein.
A shrinkable film used herein as a base film was a multilayer shrinkable film (supplied by Mitsubishi Plastics, Inc. under the trade name “DL”). The multilayer shrinkable film “DL” has a thickness of 40 μm, a percentage of thermal shrinkage (70° C. for 10 seconds) of 20.3%, and a percentage of thermal shrinkage (80° C. for 10 seconds) of 37.1% and includes polyester resin surface layers and a styrenic resin core layer.
The cationically curable resin composition was applied to one side of the shrinkable film through entire gravure printing to give a resin composition layer 3 μm thick. The gravure printing was performed by using a bench gravure printing machine (supplied by Nissho Gravure Co., Ltd. under the trade name “GRAVO PROOF MINI”) and a photogravure cylinder (gravure plate) of 80 lines, with a plate depth of 27 μm.
Next, a hologram transfer foil (supplied by Coburn Japan Corporation under, the trade name “Hologram Transparent OPP Laminate Film”) was laid over the resin composition layer. Subsequently, the resin composition layer was cured by applying light to the resin composition layer side under conditions of a conveyor speed of 70 m/min and at 240 watts per centimeter (W/cm) using an ultraviolet irradiator (supplied by Fusion UV Systems Japan KK under the trade name “LIGHT HAMMER 10”; output 100%, D valve). Thereafter the hologram transfer foil was removed to give a shrinkable label having a hologram layer. The shrinkable label had a shrinkage rate (in hot water at 80° C.) of 5.6% per 0.2 second and a shrinkage stress of 4.7 N/mm2, wherein the shrinkage stress was determined while immersing 80% of a test piece of the shrinkable label in hot water at 80° C. for 10 seconds.
In the above procedure, the process speeds were 50 m/min in the printing process, 70 m/min in the curing process, and 50 m/min in the process of laminating and removing the hologram foil. The evaluation of the surface curability was conducted also while performing the curing process at a process speed of 100 m/min.
The above-prepared shrinkable label (having a label thickness of 42 μm and a hologram layer thickness of 2 μm) was evaluated on the surface curability (initial tack test), adhesion (tape peel), process conformity (shrinkage whitening test), and holographic expressivity.
As is demonstrated in Table 1, the prepared resin composition and shrinkable label had superior properties.
Independently, the above-prepared shrinkable label was wound into a tube (cylinder) so that the hologram layer faced outward and the width direction of the film stood the circumferential direction. The wound label was center-sealed with tetrahydrofuran (THF) and thereby yielded a tubular shrinkable label. At last, the tubular shrinkable label was attached to a container (supplied by Toyo Seikan Kaisha, Ltd.; 500-ml heat-resistant rectangular PET plastic bottle), heated and shrunk in a steam tunnel at an atmospheric temperature of 90° C. so that the hologram-bearing portion shrunk by 5% to 15%, and thereby yielded a container with a label. The resulting container with the label was well finished.
A cationically curable resin composition and a shrinkable label were prepared by the procedure of Example 1, except for further using bis[(3-ethyloxetan-3-yl)methyl]ether (supplied by Toagosei Co., Ltd. under the trade name “ARON OXETANE OXT-221”) as a component B (bifunctional oxetane compound) and employing the compounding ratios of respective components as given in Table 1. The shrinkage rate (in hot water at 80° C.) and the shrinkage stress (shrinkage stress as determined while immersing 80% of a test piece of the shrinkable label in hot water at 80° C. for 10 seconds) of the shrinkable label according to Example 2 were close to those of the shrinkable label according to Example 1.
As is demonstrated in Table 1, the prepared resin composition and shrinkable label had superior properties. Independently, a container with the label was prepared by the procedure of Example 1 to find that the prepared container with the label was well finished.
A cationically curable resin composition and a shrinkable label were prepared by the procedure of Example 1, except for employing the compounding ratios of respective components as given in Table 1. The shrinkage rate (in hot water at 80° C.) and the shrinkage stress (shrinkage stress as determined while immersing 80% of a test piece of the shrinkable label in hot water at 80° C. for 10 seconds) of the shrinkable label according to Example 3 were close to those of the shrinkable label according to Example 1.
As is demonstrated in Table 1, the prepared resin composition and shrinkable label had superior properties. Independently, a container with the label was prepared by the procedure of Example 1 to find that the prepared container with the label was well finished.
A cationically curable resin composition and a shrinkable label were prepared by the procedure of Example 1, except for not using the component A, as is shown in Table 1.
As is demonstrated in Table 1, the prepared shrinkable label was inferior in properties.
The present invention is applicable to a shrinkable label which has a hologram layer and which provides a sharp holographic expression even after shrink processing with relatively large deformation, and it is also applicable to a container with the shrinkable label attached thereto.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-187388 | Jul 2007 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2008/062390 | 7/9/2008 | WO | 00 | 1/13/2010 |
