Patent Application
20110111142
This disclosure relates to a label and a method for preparing the same. More particularly, it relates to a label with preventing the possibility of decreased marking efficiency or quality change with time due to the presence of oxidation residues inside a base film of the label when subjected to laser marking and at the same time having improved scratch resistance, and a method for preparing the same.
On a label, information concerning the related product, such as date and place of production, manufacturer, or the like, is marked for consumers to recognize them.
Labels are attached on various products. For example, the label may be affixed to a container or bottle containing detergents, chemicals, oils or beverages. Also, it may be used as a vehicle identification label. Further, it may be used in a variety of electronic products, semiconductors or medical instruments requiring prevention of forgery or alteration in order to ensure product reliability, allow quality management, improve product image, and so forth.
The labels can be produced in various ways. One of them is the laser marking technique.
Different marking mechanisms are available for laser marking of labels. One generally known example of laser marking uses a color pigment or interference pigment when irradiating laser (Japanese Patent Publication No. 2004-029726).
This disclosure is directed to providing a label capable of preventing decreased marking distinctness and quality change with time due to the presence of oxidation residues inside a base film of the label, when performing laser marking using a metal or metal oxide that experiences color change upon oxidization by laser, and, at the same time, having improved endurance including scratch resistance, chemical resistance and heat resistance, and a method for preparing the same.
In one general aspect, there are provided a label including: a first base film; a first ink layer formed on an outer side of the first base film and including a metal or metal oxide experiencing color change upon oxidization by laser; and a resin coating layer formed on the first ink layer to protect the first ink layer and transmitting laser wholly or partly to the first ink layer, and a method for preparing the same.
In accordance with the present disclosure, when performing laser marking using a metal or metal oxide that changes from its original color to another color by being oxidized by a laser, decreased marking distinctness or quality change with time due to the presence of oxidation residues inside a base film of the label may be prevented and endurance of the label including scratch resistance, chemical resistance and heat resistance may be improved. Accordingly, the label according to the present disclosure is widely applicable to various containers, vehicle identification labels, and products requiring prevention of forgery or alteration.
In the present disclosure, a side on which a release film is formed based on a first base film is defined as an “inner side” of the first base film, and the opposite side is defined as an “outer side” of the first base film.
In the present disclosure, a metal or metal oxide is used that changes from its original color to another color by being oxidized (i.e., change in oxidation number or change from incompletely oxidized state to completely oxidized state) by laser when laser is irradiated to a label. For example, if Ti4O7 is used as such pigment, its color changes from black to white (TiO2) upon irradiation of laser.
Since the laser irradiation may induce such color change resulting form the change in oxidation state, a metal which experiences color change upon oxidization (e.g., Cu, Fe, Al, Ni, Mg, Ag or Sb as well as Ti) or a metal oxide [e.g., Fe2O2, Cu2O, Ag2O, Al2O2 or Mg2O as well as TinO2n-1 (n is an integer from 1 to 10)] may be used for marking of a label using laser. In case of TinO2n-1, if n is an integer from 2 to 4, the metal oxide exhibits black color before laser irradiation. Especially, if n is 4, i.e., if Ti4O7 is used, the black color is more distinct.
The inventors have noted that, when the various metals or metal oxides are oxidized by laser irradiation and experience color change, oxidation residues may be formed as they are not completely oxidized to the desired oxides.
That is to say, when an ink layer is provided on an inner side of a first base film, fine oxidation residues may be formed upon laser irradiation, causing reduced marking efficiency and oxidation residues itself may cause quality change of the label with time due to the presence of oxidation residues in the laminate on the inner side of the first base film.
In accordance with the present disclosure, the location of the ink layer to be marked is controlled to prevent the decreased marking distinctness and quality change with time due to the presence of oxidation residues in the laminate structure on the inner side of the first base film.
That is to say, by forming the ink layer to be marked above the first base film (on the outer side of the first base film), not below the first base film (on the inner side of the first base film), formation of the oxidation residue may be reduced and, even when the oxidation residues are formed, decreased marking distinctness or quality change with time of the label may be prevented.
Also, in accordance with the present disclosure, to prevent, for example, scratching of the ink layer formed on the first base film, a resin coating layer is formed on the first ink layer to protect the first ink layer while the laser passing through a part or the whole of the resin coating layer is transmitted to the ink layer to allow marking of the ink layer. For reference, the resin coating layer may be partly removed upon laser irradiation by the laser energy. This means that part of the irradiated laser is used to remove the resin coating layer. In this case, the initially irradiated laser is transmitted not wholly but partly.
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Now, each layer of the label according to the embodiments of the present disclosure will be described in detail.
First, the first base film may be a heat-resistant film since heat is produced when laser is irradiated thereto. As specific examples, the first base film may be a polyolefin-, polyester (PET or PEN)- or polyimide-based film. Especially, the first base film may be a PET film. When a PET film is used, the film may have various colors as well as superior dimension stability and processability.
The thickness of the first base film is not particularly limited and may be adjusted adequately depending on the laser intensity. As a specific example, when a YAG laser (1,064 nm) is used, the first base film may have a thickness of 12 to 150 μm. If the thickness of the first base film is less than 12 μm, carbonization may occur during the laser irradiation due to instant heating. And, if the thickness exceeds 150 μm, workability of roll-to-roll printing may be not good.
If required, the first base film may be formed as a self-destructive film by half cutting, forming multiple small through-holes or forming a porous structure in order to prevent forgery or alteration. For example, the first base film may be half-cut previously by 10-50% of the film thickness, or a roll with diamond particles, needles or brushes attached thereon may be passed across the film to form through-holes of an irregular or regular linear pattern. In that case, forgery or alteration may be prevented since the film is broken when a label attached to the product is forcibly detached.
The first base film may have the same color as the marking color. In this case, the film may be given the desired color through the master batch method.
As described earlier, the first ink layer which is to be laser marked comprises a metal or metal oxide that changes from its original color to another color by being oxidized by a laser to reveal desired characters or pattern.
The laser is not specially limited. Specifically, a low-output YAG laser (1,064 nm) may be used. In general, when laser light is focused on a material, heat is produced as the absorbed light energy is converted to thermal energy.
This heat induces the oxidation of the metal or metal oxide and thus the color change of the ink layer. Accordingly, the desired color can be obtained by adequately selecting the metal or metal oxide and the laser irradiation intensity. Non-limiting examples of the metal oxidized upon laser irradiation may include Ti, Fe, Ag, Cu, Ni, Al or Sb. When an incompletely oxidized metal oxide, e.g., Ti4O7, is used, the output of laser irradiation may be decreased as compared to when the corresponding metal is used.
The first ink layer may be made of an acrylate urethane-based resin and comprise the metal or metal oxide. If necessary, the first ink layer may be configured a single layer or multiple layers. If the ink layer is configured as a single layer, production cost may be reduced and, stability of quality and convenience of processing may be attained.
The first ink layer may also be configured as multiple layers. In this case, a second-color ink layer may be formed of a metal or metal oxide with good laser absorption efficiency, such as Cu, Fe, Al, Ni or Ag. Since the second-color ink layer reinforces concealing effect, the laser marking efficiency may be enhanced even when a first-color ink layer is printed with minimum thickness.
The metal or metal oxide particles of the first ink layer may have a particle size greater than 0 μm and not greater than 1 μm. A well-controlled particle size ensures uniform quality during the laser marking. The smaller the particle size of the pigment particles, the denser they are in the ink layer and the better color change is attained upon oxidation.
The thickness of the first ink layer is not particularly limited. It may be greater than 0 μm and equal to or less than 5 μm. If the ink layer is thicker than 5 μm, workability may be not good and the resulting label may be too thick. More specifically, the first ink layer may be 0.5-2 μm thick.
The first ink layer may be printed by various printing techniques. For example, gravure printing, microgravure printing, reverse kiss coating, or the like may be employed. These printing techniques may reduce production cost because they allow mass production.
The resin coating layer is a coating layer formed on the first ink layer. While transmitting laser wholly or partly to the first ink layer, it protects the first ink layer from external impact or scratching.
The resin coating layer may be formed by coating a resin having excellent hardness on the first ink layer. That is to say, the resin coating layer may be a hard coating layer.
The resin coating layer may have a surface pencil hardness of at least 4H to ensure good scratch resistance.
The resin coating layer may be formed of a resin that is cured by application of energy, such as a UV-curable resin cured by light, a thermocurable resin cured by heat, or an EB-curable resin cured by electron beam. These resins may comprise an acryl-based polymer, a urethane-based polymer, an epoxy-based polymer, a silicone polymer, a silica polymer, or the like.
Particularly, the resin coating layer may comprise a photopolymerizable resin, a photoinitiator, a solvent, an additive, or the like. The photopolymerizable resin may be an oligomer, a monomer, a blend thereof, or a photopolymerizable prepolymer such as a cation-polymerizable prepolymer.
As non-limiting examples, the photoinitiator may be one or more selected from a group consisting of benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin n-butyl ether, benzoin isobutyl ether, acetophenone, dimethylaminoacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 2,2-diethoxy-2-phenylacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1-hydroxycyclohexyl phenyl ketone, 2-methyl-1 [4-(methylthio)phenyl]-2-morpholinopropan-1-one, 4-(2-hydroxyethoxy)phenyl 2-hydroxy-2-propyl ketone, benzophenone, p-phenylbenzophenone, 4,4′-d iethylaminobenzophenone, dichlorobenzophenone, 2-methylanthraquinone, 2-ethylanthraquinone, 2-tert-butylanthraquinone, 2-aminoanthraquinone, 2-methylthioxanthone, 2-ethylthioxanthone, 2-chlorothioxanthone, 2,4-dimethylthioxanthone, 2-4-diethylthioxanthone, benzyl dimethyl ketal, acetophenone dimethyl ketal and p-dimethylaminobenzoic acid ester.
If the photoinitiator is one for a cation-polymerizable prepolymer, it may be one or more compounds selected from a group consisting of, for example, onium including aromatic sulfonium, aromatic oxosulfonium or aromatic iodonium, tetrafluoroborate, hexafluorophosphate, hexafluoroantimonate and hexafluoroarsenate.
The photoinitiator may be used in an amount of 0.2 to 10 parts by weight based on 100 parts by weight of the photopolymerizable resin. If the photoinitiator content is below 0.2 part by weight, a desired addition effect of the photoinitiator may not be attained. And, a content exceeding 10 parts by weight may not be effective.
The solvent may be an aliphatic hydrocarbon such as hexane, heptane, cyclohexane, etc., an aromatic hydrocarbon such as toluene, xylene, etc., a halogenated hydrocarbon such as methylene chloride, ethylene chloride, etc., an alcohol such as methanol, ethanol, propanol, butanol, etc., a ketone such as acetone, methyl ethyl ketone, 2-pentanone, isophorone, etc., an ester such as ethyl acetate, butyl acetate, etc., or a cellosolve such as ethyl cellosolve, etc.
The additive may be an antioxidant, UV absorbent, photostabilizer, leveling agent, antifoaming agent, matting agent, or the like. Specifically, it may be silica, alumina, talc, clay, calcium carbonate, magnesium carbonate, barium sulfate, aluminum hydroxide, titanium dioxide, zirconium oxide, or the like.
The resin coating layer may be coated with a thickness of 4 to 12 μm in dry state. If the thickness is less than 4 μm, desired surface pencil hardness and UV curability may not be attained. And, if it exceeds 12 μm, burring may occur upon laser irradiation.
The agglutinant layer is formed on one side of the first base film or on one side of the second base film or the release film which will be described later.
The agglutinant layer should maintain its adhesion force upon laser irradiation and have printability, thermal stability, chemical resistance and oil resistance. When considering these factors, the agglutinant layer may comprise an acryl-, silicone- or urethane-based agglutinant agent.
As a specific example, the agglutinant may be one having low initial agglutinant force to allow easy removal when the film is falsely attached to an undesired spot and, after being heated to a certain temperature (80-90° C.), having increased adhesion force. In this case, workability is improved during attachment of the film and, after attachment, the film may be induced to tear or break when the film is forcibly detached.
For example, when the agglutinant layer comprises an acryl-based agglutinant with excellent heat resistance, a low-viscosity or high-viscosity adhesive may be used. Gravure coating may be employed when a low-viscosity acryl-based agglutinant is used. And, when a high-viscosity acryl-based agglutinant is used, S knife coating (also known as comma coating) may be employed. The agglutinant may be coated in an amount of 10 to 15 g/m2 in wet state.
The second base film reinforces stiffness of the marking film, provides color contrast with the first base film or the first ink layer, and, depending on situations, may provide fragility to the film. The second base film is an additional base film provided supplement the first base film.
As specific examples, the second base film may be a polyolefin (OPP or PE)-, polyester (PET or PEN)- or polyimide (PI)-based film. More specifically, it may be a PET film. When considering workability, heat resistance and processability, the second base film may have a thickness of 12 to 100 μm.
The second base film may have the same color as the marking color in order to provide color contrast with the first ink layer. That is to say, by using a second base film having a color contrasted with that of the coating layer, the marked pattern or characters may be seen distinctly. For example, if it is configured such that the first ink layer is black and white characters are marked upon laser irradiation, the white characters may be seen more clearly when the second base film is white.
Further, the first base film and/or the second base film may be made self-destructive by half cutting, forming multiple small through-holes or forming a porous structure in order to prevent forgery or alteration.
In that case, forgery or alteration may be prevented since the film is broken when a label attached to the product is forcibly detached.
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A label 700 illustrated in
A label 800 illustrated in
A label 900 illustrated in
A label 1000 illustrated in
A label 1100 illustrated in
A label 1200 illustrated in
A label 1300 illustrated in
The release film is formed on the innermost side of the label. The release film is removed before the label is attached to the product, such that the agglutinant layer contacts directly with the product. The release film may be a silicone-coated PET film or a fluorine-coated fluorine film (in case a silicone-based adhesive is used). The release film may comprise a curing agent such as an epoxy-based silane crosslinking agent as well as an additive such as a Pt catalyst. Further, silicone may be added to the release film in order to provide releasability corresponding to the adhesion force of the agglutinant layer.
If required, the label may further comprise an additional ink layer (second ink layer) in addition to the first ink layer on the inner side of the first base film. Further, an adhesive layer for bonding the second base film with the first base film or bonding the first base film with the ink layer may be provided. The adhesive layer provides adhesion even after the laser irradiation and has printability, adhesion stability, chemical resistance and oil resistance.
As described above, the present disclosure thoroughly solves the problem of decreased marking efficiency resulting from the fine oxidation residues remaining in the film after the laser irradiation. By providing the ink layer on the first base film and forming the resin coating layer thereon to protect the ink layer, marking efficiency is improved and the risk of color change or film fracture during the preparation process is minimized because the laser needs not have strong intensity. In addition, by forming the resin coating layer for protecting the ink layer using a high-hardness resin or a curable resin, film strength and scratch resistance may be improved.
Further, high-quality printing is possible using an ink for single-layer laser printing. The single-layer printing reduces production cost. In addition, the label is free from various contaminants and may be used semi-permanently since it has superior chemical resistance, heat resistance, or the like. Besides, a self-destructive film may be provided by half-cutting the film or forming multiple small through-holes thereon in order to prevent forgery or alteration.
The examples and experiments will now be described. The following examples and experiments are for illustrative purposes only and not intended to limit the scope of this disclosure.
[Preparation of Labels of Example and Comparative Example]
The label described with reference to
For comparison, a label of Comparative Example was prepared by forming a first ink layer 120 comprising Ti4O7 as a pigment between a first base film 110 and an agglutinant layer 140, without a resin coating layer 130.
Thus prepared labels of Example and Comparative Example were subjected to marking by irradiating YAG laser.
[Determination of Whiteness]
After performing marking for the labels of Example and Comparative Example, a spectrophotometer was used to determine lightness (L*) and color difference (AE) of the marked white portion. For reference, an L* value of “+” represents white, and a value of “−” represents black. The color difference (ΔE) considers not only the lightness (L*) but also chromaticity (a*b*) as determined by hue and saturation, and is calculated automatically.
The label of Example exhibited an L* value of 94.04, whereas the label of Comparative Example exhibited an L* value of 90.56. This means that the label of Example was whiter, i.e., had better laser marking efficiency, than the label of Comparative Example.
The color difference (ΔE) of the Example label and the Comparative Example label was 4.53. For reference, if ΔE is 0 to 0.5, the difference is hardly distinguishable. If ΔE is 0.5 to 1.5, there is slight difference. And, if E is larger than 1.5, the difference is appreciable.
When the labels of Example and Comparative Example were allowed to stand in the air for a day, the label of Comparative Example showed color change at the marked portion.
It can be concluded that the difference in whiteness and color change results from the presence or absence of oxidation residues.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2008-0045796 | May 2008 | KR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/KR2009/002597 | 5/15/2009 | WO | 00 | 11/15/2010 |
