JP2005225118A - Plastic label - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a plastic label which is excellent in blocking resistance, tough, and flexible. <P>SOLUTION: In the plastic label 1, a printing layer 3 is formed on at least one side of a base film 2. The thickness of the base film 2 is 30-150 μm. At least one side of the base film is irradiated with electron beams under conditions of a voltage of 50-500 kV and a dosage of 5-50 kGy. In the base film 2 shown in Fig., by being irradiated with electron beams in the arrow direction, the density of a region 2a is maximized, the density of a region 2b is somewhat reduced, and the density of a region 2c is minimized. In the base film 2, a density gradient corresponding to the degree of crosslinking is formed in the thickness direction (depth direction). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a plastic label, and more particularly to a plastic label having both waist strength and flexibility.

  Conventionally, a shrink label using a heat-shrinkable film as a base film is used as a label to be attached to a container such as a polyethylene terephthalate container (so-called PET bottle). As a heat-shrinkable film, a heat-shrinkable polyolefin film is used in that it has a low specific gravity and is relatively inexpensive, and in particular, a polyethylene heat-shrinkable film is excellent in impact resistance and heat seal strength. It is preferably used. However, it is not always satisfactory in terms of waist strength, blocking property, and film strength, and has problems such as large natural shrinkage and poor fit during heat shrinkage.

  On the other hand, a polyethylene-based heat-shrinkable film in which an electron beam is irradiated onto the film and electron beam cross-linked has been proposed (for example, see Patent Document 1). According to the film of Patent Document 1, since the film is strong, troubles during packaging by an automatic packaging machine can be avoided, but there is a problem that the flexibility of the film is impaired.

  On the other hand, there has been proposed a stretch shrink label for containers in which molecular orientation is imparted to a linear low density polyethylene film obtained using a metallocene catalyst, and the stretch property and a certain amount of shrink property are combined (for example, patent document). 2). However, when the base film of the stretch shrink label is composed of a single layer of the metallocene linear low-density polyethylene film, there is a problem that it is impossible to achieve both the restorability after heat shrinkage and the blocking resistance. That is, a certain type of metallocene linear low density polyethylene film can be stretched at a low temperature. For example, a high shrinkage rate can be obtained by heating at 80 ° C., and an excellent restorability can be obtained even after heat shrinkage. In the layer, it is normally sticky, and blocking occurs when it is rolled up as a film. Moreover, although another metallocene linear low density polyethylene film is excellent in blocking resistance, the single layer has remarkably poor resilience after heat shrinkage.

JP-A-8-267679 JP 2000-025112 A

An object of the present invention is to provide a plastic label that is excellent in blocking resistance, strong, and flexible.
Another object of the present invention is to provide a plastic label which, in addition to the above properties, can prevent spontaneous shrinkage, and is excellent in shrinkability during heating and cutting suitability.
Still another object of the present invention is to provide a plastic label that is excellent in scratch resistance and blocking resistance, is firm, and has excellent stretchability and flexibility.

  As a result of intensive studies to achieve the above object, the present inventors have changed the degree of cross-linking in the thickness direction by irradiating an electron beam, so that labels having different surface and internal characteristics can be obtained without changing the constituent components. The present invention has been completed by finding out that it can be obtained.

  That is, the present invention is a plastic label in which a printed layer is provided on at least one surface of a base film, wherein the base film has a thickness of 30 to 150 μm, a voltage of 50 to 500 kV and a dose on at least one surface. A plastic label that is irradiated with an electron beam under a condition of 5 to 50 kGy is provided. The base film may be a film having a gel fraction of 10 to 65% and a cross-linking density gradually decreasing from the surface of the base film toward the inside.

  Since the plastic label of the present invention is not easily blocked, has a strong stiffness, and has flexibility, it can be used in a wide range of applications. For example, as a shrink label that suppresses natural shrinkage and is excellent in heat shrinkage rate and cutting suitability, as a stretch label that is hard to be scratched and exhibits excellent stretch properties, and as a stretch shrink label that also has the above characteristics Available.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as necessary. FIG. 1 is a schematic sectional view showing an example of the plastic label of the present invention. This label 1 is composed of a printing layer 3 provided on one surface of a base film 2. The base film 2 is irradiated with an electron beam from the direction of the arrow, and each region obtained by dividing the film into three equal parts (dotted line portions) in the thickness direction is indicated by 2a, 2b, and 2c in order from the surface irradiated with the electron beam. .

  The plastic label 1 of the present invention only needs to be made of a plastic base film, and may be any of stretch labels, shrink labels, stretch shrink labels, heat-sensitive adhesive labels, roll labels, tack labels, in-mold labels, and the like.

  Examples of the base film 2 include plastic films such as an olefin resin film, a polyester film made of polyethylene terephthalate, a styrene resin film made of a styrene-butadiene block copolymer, and a vinyl chloride resin film. The base film can be formed of one kind or two or more kinds of materials, and may be either a single layer or multiple layers. Preferred base films include single-layer or multilayer olefin resin films.

  Examples of the olefin resin film include polyethylene (low density polyethylene (LDPE), linear low density polyethylene (LLDPE), metallocene polyethylene, high density polyethylene, etc.), ethylene copolymer (for example, ethylene- (meta)). Polyethylene resins such as acrylic ester copolymers, ethylene- (meth) acrylic acid copolymers, ethylene-vinyl acetate copolymers (EVA), ethylene-vinyl alcohol copolymers, ionomers, etc.); polypropylene, polypropylene modified Examples thereof include polypropylene resins such as resins; and films made of mixtures thereof. In particular, in the present invention, a single-layer or multi-layer polyethylene-based resin (particularly preferably polyethylene) film is preferably used.

  A conventional surface treatment such as corona discharge treatment or plasma treatment may be applied to the surface of the base film 2 on the printing layer 3 side in order to improve printability. In the present invention, the printability of the surface subjected to electron beam irradiation is improved. In addition, various additives such as a lubricant, a filler, a heat stabilizer, an antioxidant, an ultraviolet absorber, an antistatic agent, a flame retardant, a colorant, and an anti-blocking agent are added to the base film 2 as necessary. May be.

  The base film 2 has a thickness of 30 to 150 μm. The thickness of the base film 2 can be appropriately selected according to the type of label. For example, the shrink label is preferably about 40 to 100 μm, and the stretch label is preferably about 60 to 120 μm. When the thickness of the film 2 is greater than 150 μm, it is difficult to obtain a sufficient crosslinking density by electron beam irradiation. When the thickness is less than 30 μm, the crosslinking reaction tends to proceed excessively, causing discoloration of the film, generation of gas, and bubbles. May occur.

  The printing layer 3 can be formed by printing a desired image and characters on at least one surface of the base film 2 by a conventional printing method such as gravure printing. In addition, the surface of the base film 2 on which the electron beam irradiation has been performed has good adhesion of the printing ink.

  The plastic label of the present invention may be provided with other resin layers in addition to the base film 2 and the print layer 3.

  The plastic label of the present invention is characterized in that at least one surface of the base film is irradiated with an electron beam under conditions of a voltage of 50 to 500 kV and a dose of 5 to 50 kGy. The cross-linking reaction of the polymer constituting the base film proceeds by electron beam irradiation. Under the above conditions, a base film in which the cross-linking density gradually decreases from the film surface toward the inside is obtained. In the base film in the present invention, a density gradient according to the degree of crosslinking is formed in the thickness direction (depth direction) of the base film. The crosslinking density formed by electron beam irradiation can be confirmed by an electron micrograph of a cross section in the thickness direction of the film after electron beam irradiation, or by a gel fraction (based on JIS K 6769).

  Since the label made of such a base film has a high cross-linking density on the surface, blocking is unlikely to occur, the waist is strong, and the internal cross-linking density is lower than the surface, so that flexibility can be exhibited. If the voltage is less than 50 kV, the distance that the electron beam reaches is too short, so that the film tends to be insufficiently modified. If the voltage is 500 kV or more, the electron beam is uniformly irradiated on the entire film to form the density gradient as described above. It becomes difficult. When the dose is less than 5 kGy, the crosslinking reaction of the polymer does not proceed sufficiently, so that the crosslinking density of the surface tends to be low. When the dose exceeds 50 kGy, the crosslinking density of the whole film is too high and the film becomes hard and the flexibility tends to decrease. The electron beam irradiation may be performed only on one side of the base film or on both sides. Preferably, both surfaces of the film are irradiated under conditions of a voltage of 80 to 400 kV and a dose of 10 to 30 kGy.

  In FIG. 1, since the base film 2 is irradiated with the electron beam from the arrow direction, the crosslinking density gradually decreases from the film surface toward the inside. That is, a density gradient corresponding to the degree of crosslinking is formed in the thickness direction (depth direction) of the base film. More specifically, in the base film 2 shown in FIG. 1, the region 2a has the highest density, the region 2b has the lowest density, and the region 2c has the lowest density by the electron beam irradiation from the arrow direction. Yes. The density gradient of the base film 2 can be adjusted by the electron beam irradiation conditions (voltage, dose, irradiation direction, etc.).

The crosslinking density after electron beam irradiation can be expressed by, for example, a gel fraction. The gel fraction is measured according to JIS K 6769. Specifically, the gel fraction in the present invention is the insoluble fraction obtained by shaking and dissolving a sample of dry weight W ₁ (g) collected from the base film after electron beam irradiation in a large excess of organic solvent, and filtering it out. When the dry weight of is W ₂ (g), it is calculated by the following formula. The organic solvent can be appropriately selected according to the resin constituting the base film so that a portion crosslinked by electron beam irradiation is substantially insoluble. For example, when the base film is a polyethylene resin film or the like, a xylene solvent is used. The sampling of the base film needs to be performed so as to be uniform in the film thickness direction.
Gel fraction (% by weight) = (W ₂ / W ₁ ) × 100

  The gel fraction of the base film 2 is, for example, about 10 to 65%, preferably about 30 to 50%. If the gel fraction is less than 10%, it may be difficult to process due to lack of elasticity, and if it exceeds 65%, flexibility tends to be inferior. The gel fraction of the base film can be adjusted by the type of polymer constituting the film, the thickness of the film, the irradiation conditions (voltage, dose, irradiated surface, etc.) of the electron beam.

  Moreover, the plastic label of this invention is advantageous at the point which can modify a film characteristic after base film shaping | molding as mentioned above. That is, the density gradient can be imparted to the outer layer and the inner layer after film formation on the base film 2 composed of a single layer or multiple layers. Specifically, the base film 2 made of a single layer has a core layer made of a low-density polymer by irradiating both surfaces with an electron beam, and an outer layer made of a high-density polymer laminated on both sides of the core layer. Can be formed.

  The plastic label 1 having the above-described configuration has high density on the surface irradiated with the electron beam, so that stickiness can be suppressed, firmness is improved, handling is improved, and the inner side is lower in density than the surface, so flexibility Is excellent.

  When the plastic label is a stretch label, since it has the above-described configuration, it is particularly advantageous in that it has excellent stretch characteristics and scratch resistance. As the stretch label, for example, a base film printed on at least one surface is used, and the base film has a self-stretching property. The base film is obtained by subjecting a film obtained by melt-extruding a resin composition from a T die or a ring die and cooling with a cooling roll to electron beam irradiation under the above-mentioned conditions, unstretched or stretched as necessary. It can manufacture by giving. A stretch label can be produced by forming a printing layer on at least one surface of the base film by gravure printing or the like.

  After printing, usually cut into a long strip with the desired width, round the label with the print side on the inside, and bond both sides with adhesive, solvent, heat fusion, etc. A cylindrical stretch label can be obtained by cutting to a desired length as required. After supplying the cylindrical stretch label thus obtained to the automatic label mounting device and cutting it to the required length, the label is expanded by the diameter expansion arm of the device and externally fitted to a container or the like, Next, the diameter is reduced by releasing the external force, and the container is used in close contact with a container or the like by an elastic contraction force.

  According to the stretch label which has the said structure, since the inside of a film is low density, it is excellent in an expansion-contraction characteristic. For this reason, it can be mounted on a container or the like with high adhesiveness while exhibiting good restoration properties. On the other hand, since the film surface has been densified by electron beam irradiation, the cylindrical stretch label can be cut reliably, and it has excellent scratch resistance, and the surface is not easily scratched. It can be produced efficiently.

  In addition, when the plastic label is a shrink label, it has the above-described configuration, and is particularly advantageous in that it has excellent heat shrinkability and cutability, can prevent natural shrinkage, and improves moldability. As the shrink label, for example, a base film printed on at least one surface thereof is used, and the base film has heat shrinkability. The base film can be produced by melt-extruding the resin composition from a T die or an annular die, cooling the film with a cooling roll, subjecting the film to electron beam irradiation under the above conditions, and further subjecting it to a stretching treatment. . A shrink label can be manufactured by forming a printing layer on at least one surface of the base film by gravure printing or the like.

  After printing, it is usually cut into long strips with the desired width, the label is rolled into a cylindrical shape with a former with the printed surface inside, and both sides are bonded with an adhesive, solvent, heat fusion, etc. And it can be set as a cylindrical shrink label by cut | disconnecting to desired length as needed. The cylindrical shrink label obtained in this way is supplied to an automatic label mounting device, cut to the required length, externally fitted into a container, etc., and contracted by heating at a predetermined temperature into a container, etc. Used in close contact.

  According to the shrink label having the above configuration, since the inside of the film has a low density, it can exhibit excellent heat shrinkability and can be attached to a container or the like with high adhesion. On the other hand, since the film surface has been densified by electron beam irradiation, the cylindrical shrink label can be reliably cut, and natural shrinkage can be prevented. Inconveniences such as being impossible can be avoided, and handling is improved. Moreover, since the film whose surface is densified has an appropriate rigidity, the molding processability is improved, and in particular, the film can be easily stretched.

  When the plastic label is a stretch shrink label, it can have the advantages of both the stretch label and the shrink label described above. Hereinafter, a stretch shrink label will be described as an example of the plastic label of the present invention in detail.

  FIG. 2 is a schematic sectional view showing another example of the plastic label of the present invention. This label 1 'is composed of a printed layer 3' provided on one surface of a base film 2 '. The base film 2' has a three-layer structure of outer layer 5, core layer 4 and outer layer 5. doing. Further, both surfaces of the label 1 are irradiated with electron beams. This label 1 'corresponds to a stretch shrink label.

  For the core layer 4 and the outer layers 5 and 5 constituting the base film 2 ′, for example, an exemplary film can be used as the base film 2, and among them, the base film 2 ′ (the core layer 4 and the outer layers 5 and 5 can be used. ) Is preferably an olefin resin film. Examples of the olefin resin film include polyolefins such as polyethylene (low density polyethylene (LDPE), linear low density polyethylene (LLDPE), metallocene polyethylene, high density polyethylene, etc.), polypropylene, and ethylene-α-olefin copolymer resin. An ethylene copolymer (for example, an ethylene- (meth) acrylic acid ester copolymer, an ethylene- (meth) acrylic acid copolymer, an ethylene-vinyl acetate copolymer (EVA), an ethylene-vinyl alcohol copolymer, Ionomers, etc.); polypropylene-modified resins, etc .; and films made of mixtures thereof. A preferred base film 2 'is formed of linear low density polyethylene (LLDPE).

  LLDPE is a copolymer of ethylene and a small amount of α-olefin, and examples of the α-olefin include 4 to 4 carbon atoms such as 1-butene, 1-hexene, 4-methyl-1-pentene, and 1-octene. About 8 α-olefins are used. LLDPE includes polymers obtained using a Ziegler catalyst, polymers obtained using a metallocene catalyst, and the base film 2 'can be obtained by any method, but can be obtained using a metallocene catalyst. More preferred is a polymer (metallocene LLDPE).

  The metallocene catalyst is usually a metallocene transition metal compound (a metal complex comprising titanium, zirconium or hafnium and a ligand such as cyclopentadienyl, indenyl, tetrahydroindenyl, fluoronyl) and an organoaluminum compound (for example, , Alkylaluminum such as triethylaluminum, chain or cyclic alumoxane such as methylalumoxane, etc.) or a boron compound. This catalyst may be used by being supported on a carrier such as silica gel, zeolite, or diatomaceous earth.

  Particularly preferred metallocene LLDPE includes LLDPE obtained using a single-site metallocene catalyst having a uniform active site among metallocene catalysts. Such polyethylene can be produced, for example, by the method described in JP-A-9-297539.

  Among these, polyethylene or the like is preferable as the resin constituting the core layer 4, and a resin having barrier properties such as ethylene-vinyl alcohol (EVOH) can also be used. As the resin constituting the outer layer 5, polyethylene is preferably used. The density of polyethylene is appropriately selected in consideration of heat shrinkability, restoring property, blocking property, etc. Generally, when both the core layer 4 and the outer layer 5 are made of polyethylene, the outer layer 5 is more than the core layer 4. Often used in combination to increase the density of the polyethylene. Metallocene LLDPE and LLDPE are particularly preferably used.

  The thickness of the core layer 4 is, for example, about 20 to 120 μm, preferably about 30 to 90 μm. Moreover, the thickness of the outer layers 5 and 5 is each about 2-20 micrometers, for example, Preferably it is about 5-15 micrometers. The total thickness of the base film 2 ′ is 30 to 150 μm, preferably about 50 to 100 μm. Further, the thickness of the core layer 4 is, for example, 40 to 95%, preferably about 50 to 90% of the total thickness of the base film 2 '. When the thickness of the core layer 4 is less than 40%, the film is easily broken during the stretching treatment, and when it exceeds 95%, blocking tends to occur.

  In order to improve the printability, the surface of the outer layers 5 and 5 on the printed layer 3 'side may be subjected to conventional surface treatment such as corona discharge treatment or plasma treatment. In addition, the core layer 4 and the outer layers 5 and 5 may be provided with a lubricant, a filler, a heat stabilizer, an antioxidant, an ultraviolet absorber, an antistatic agent, a flame retardant, a colorant, an antiblocking agent, etc., as necessary. Various additives may be added.

  The core layer 4 and the outer layers 5 and 5 can each be composed of a plurality of layers. Moreover, you may provide another resin layer between the core layer 4 and the outer layers 5 and 5 in the range which does not impair rigidity, heat shrinkability, a restoring property, etc.

  The base film 2 'can be produced by a conventional method used for producing a laminated film, such as a coextrusion method. For example, the base film 2 ′ shown in FIG. 2 includes a resin composition containing a resin that forms the core layer 4 and a resin composition containing a resin that forms the outer layers 5 and 5. Is melt-extruded using a feed block 2 type 3 layer type extruder, cooled by a cooling roll, and then irradiated with an electron beam on both surfaces of the film, and subjected to stretching treatment (uniaxial stretching or biaxial stretching). Can be obtained. An annular die can be used instead of the T die.

  Electron beam irradiation is usually performed on the surface of at least one surface of the film under the conditions of a voltage of 50 to 500 kV and a dose of 5 to 50 kGy using a conventional electron beam irradiation apparatus in the pre-process of the stretching treatment. The base film used for the stretch shrink label is preferably subjected to electron beam irradiation on both surfaces under conditions of a voltage of 80 to 200 kV and a dose of 10 to 30 kGy. The base film 2 'shown in FIG. 2 has a configuration in which both surfaces are irradiated with an electron beam, so that a low-density core layer 4 and high-density outer layers 5 and 5 are provided on both sides thereof. .

  The gel fraction of the base film 2 ′ can be calculated by the above-described method, and is, for example, about 10 to 65%, preferably about 30 to 50%. When the gel fraction exceeds 65%, the flexibility tends to be inferior, and when it is less than 10%, there is a lack of waist and processing may be difficult.

Stretching can be performed by either a tenter method or a tube method. The stretching treatment is usually performed at a temperature of about 60 to 90 ° C., preferably about 70 to 85 ° C., and 2.5 to 6.0 times, preferably 3.0 to 5.0 times in the width direction (lateral direction; TD direction). It is performed by stretching to a certain extent. Although stretching is preferably uniaxial stretching, stretching may be performed in the length direction (longitudinal direction; MD direction) as necessary.
The base film 2 ′ thus obtained exhibits heat shrinkability in the width direction (direction subjected to stretching treatment) and also has self-stretchability.

  In the label 1 ′ (stretch shrink label) as described above, the core layer 4 of the base film 2 ′ is formed at a low density. Therefore, the extension followability is imparted, and molding processability such as a stretching process is facilitated. In addition, elasticity (restorability) is maintained even after shrinkage, and heat shrinkability can be significantly improved.

  For example, after the base film 2 ′ is immersed in warm water at 100 ° C. for 10 seconds, the heat shrinkage rate (hereinafter referred to as “heat shrinkage rate A” in one direction X (the direction in which the stretching process has been performed; the width direction in the above case)). Is sometimes 25% or more (about 25 to 80%). According to the present invention, for example, it is possible to achieve a shrinkage rate of 1.2 times or more, preferably about 2 times that of the conventional product.

  In addition, the restoration rate after holding the base film 2 ′ in the state X stretched 1.25 times in the direction X for 3 seconds (hereinafter sometimes referred to as “restoration rate A”) is, for example, 8.0% or less ( 0% to 8.0%), and after the base film 2 'was immersed in warm water at 100 ° C for 10 seconds and then stretched 1.25 times in the direction X for 3 seconds, the restoration rate ( Hereinafter, the “restoration rate B” may be 10.0% or less (0 to 10.0%), for example. For this reason, for example, a container having a curved surface can be easily mounted with good adhesion, and even if the container is slightly deformed after opening, the label mounting position does not shift.

The thermal contraction rate A is a contraction rate in one direction X after the base film 2 'is immersed in warm water of 100 ° C. for 10 seconds, and is obtained by the following formula.
Thermal contraction rate A (%) = [{(original length in direction X) − (length after immersion in direction X)} / (original length in direction X)] × 100

In addition, the restoration rate A is a ratio of restoration when the tensile force is released after holding the base film 2 'in one direction X for 1.25 times the original length for 3 seconds. In other words, it is obtained by the following formula.
Restoration rate A (%) = [{(length after releasing tensile force in direction X) − (original length in direction X)} / (original length in direction X)] × 100

Further, the restoration rate B is obtained by immersing the base film 2 'in warm water at 100 ° C. for 10 seconds and then holding it for 3 seconds in a state where it is extended 1.25 times the original length in one direction X. The ratio that is restored when the tensile force is released is determined by the following formula.
Restoration rate B (%) = [{(length after releasing tensile force in direction X) − (length after immersion in direction X)} / (length after immersion in direction X)] × 100

  The larger the value of the heat shrinkage rate A, the higher the heat shrinkability, and the smaller the values of the restoration rates A and B, the better the restoreability. The heat shrinkage rate A, the restoration rate A, and the restoration rate B are appropriately selected from the types of resins constituting the core layer 4 and the outer layers 5 and 5, the stretching ratio, temperature, stretching conditions such as electron beam irradiation conditions, and the like. Can be adjusted. In the present invention, the heat shrinkage rate can be remarkably improved by electron beam irradiation under the above-mentioned conditions. For example, the heat shrinkage rate A can be increased to about 1.2 to 2 times that before irradiation by electron beam irradiation.

  Moreover, in this invention, since the electron beam irradiation surface (at least one outer layer 5 and 5) is densified, it is excellent in extension followability and can avoid the fracture | rupture at the time of an extending | stretching process. In addition, blocking can be prevented, scratch resistance is high, and the label surface is not easily damaged, so that it is excellent in handleability.

  Furthermore, F10 value of the base film 2 ′ [tensile strength (unit MPa) when the film test piece is stretched by 10% in the tensile test; conforming to test conditions JIS K 7113, test piece size 200 mm × 15 mm, marked line The distance between 100 mm, test speed 50 mm / min, temperature 23 ° C., 50% RH] is usually 0.1 to 100 MPa in the main stretching direction in the case of a uniaxially stretched film, and the F10 value in the case of a biaxially stretched film is The width direction and the length direction are, for example, about 0.1 to 50 MPa, preferably about 2 to 30 MPa. If the value is too small, it will be difficult to process due to lack of elasticity, and conversely if too large, it will be easily broken by impact and will tend to hinder the work of attaching to a container or the like.

  Further, the base film 2 'has excellent natural shrinkage prevention properties, and specifically, shrinkage in the main stretching direction (direction corresponding to the circumferential direction of the container) when left at 30 ° C for 30 days. The rate (natural shrinkage rate) is 2% or less (preferably 1.8% or less). Usually, there is no practical problem if the natural shrinkage of the base film 2 'is 2% or less, and it is said that practical use is difficult if it exceeds 3%.

  The print layer 3 ′ can be formed on the surface of at least one of the outer layers 5 and 5 in the same manner as the print layer 3. In addition, since the surfaces of the outer layers 5 and 5 are all irradiated with an electron beam, the adhesion of the printing ink is good.

  Examples of the article to be attached with the plastic label of the present invention include plastic containers such as PET bottles and containers such as glass bottle-shaped containers.

  As a method for attaching the plastic label to the container (attachment), a known or conventional method can be applied. FIG. 3 is a perspective view showing a state when the plastic label of FIG. 2 is attached to an attachment. As shown in FIG. 3, when the plastic label is a stretch shrink label made of the base film 2 ', the base film 2 is usually cut into a long strip having a desired width, with the printing surface facing inward. After the end portions are overlapped and bonded by a solvent, an adhesive, heat, or the like so that the direction X of ′ becomes the circumferential direction and the direction Y of the base film 2 ′ perpendicular to the direction X becomes the length direction. If necessary, cut into a desired length to form a cylindrical stretch shrink label.

  A stretch shrink label formed in a cylindrical shape is supplied to an automatic label mounting apparatus and cut into a required length. In the present invention, the stretch shrink label formed in a cylindrical shape can be cut well. In general, a film having a high degree of crosslinking is difficult to cut, and problems such as abrasion of the cutter blade are likely to occur. However, in the present invention, only the label surface is highly crosslinked, and the inner side (inner layer) retains flexibility. Therefore, such a problem can be avoided.

  After the cylindrical label is cut to a required length, the label is stretched so as to have a large diameter by a diameter-expanding arm of an automatic label mounting device, and the container 6 is usually filled with the contents, and its body portion is After externally fitting into a container slightly larger than the periphery of the label, the diameter-enlarging arm of the label mounting device is removed, and then heated with hot air of a predetermined temperature (for example, about 80 to 200 ° C.), radiant heat such as steam or infrared rays. By doing so, the stretch shrink label can be attached to the container.

  According to such a stretch shrink label, it heat shrinks when it is externally fitted to an object to be attached, so that it can conform to the shape of the shoulder portion of the container and can be in close contact. Further, since this label has self-shrinkage, the label itself is reduced in diameter even if the mounted object is slightly deformed, and the mounting position is hardly shifted.

  The method of attaching the plastic label of the present invention to the container is not limited to the method of attaching a cylindrical label to the container, such as the above-described shrink label or stretch label, but a small label such as a tack label or a heat-sensitive adhesive label. It may be a method of sticking a piece of label on a part of the surface of the container or a method of packaging (overlapping) so as to cover the entire container with a label made of a biaxially stretched film or the like.

Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples. The gel fraction of the obtained base film was measured by the following method.
(Gel fraction)
The gel fraction of the base film was measured according to JIS K 6769. That is, a dry weight W ₁ (g) sample uniformly collected in the thickness direction from a base film (polymer after electron beam irradiation) was dissolved in a large excess of xylene solvent by shaking and filtered, and the dry weight of insoluble matter separated by filtration. Was W ₂ (g) and calculated according to the following formula.
Gel fraction (% by weight) = (W ₂ / W ₁ ) × 100

Example 1
Metallocene LLDPE (trade name “Umerit 1540F”, manufactured by Ube Industries, Ltd .; density 0.914 g / cm ³ ) (a1), metallocene LLDPE (trade name “Evolue SP2040”, manufactured by Mitsui Chemicals, Inc .; density 0. 918 g / cm ³ ) (b1), a merging method is a feed block type 2 type 3 layer extruder, the layer configuration is (b1) / (a1) / (b1), and the thickness of the core layer (a1) [(B1) :( a1) :( b1) = 1: 4: 1 (thickness ratio)] and co-extruded from a T die at a temperature of 190 ° C. to form a laminate. . Both sides of the resulting laminate are irradiated with an electron beam under the conditions of a dose of 20 kGy and a voltage of 130 kV, then stretched four times in the width direction (TD direction) at about 85 ° C., and then heat-treated at 75 ° C. in a tension state. It fixed in the zone, took out outside the tenter, cooled, wound up on the core, and formed the base film (thickness 60 micrometers). The gel fraction of the base film was 35%. Moreover, it was confirmed by the electron micrograph of the cross section of the thickness direction of a base film that the density gradient was formed toward the inside from the surface of this base film.
A plastic label (stretch shrink label) was obtained by performing gravure printing with a design of 8 colors on one surface of the obtained base film to form a printed layer.

Example 2
In Example 1, a plastic label was obtained by the same operation as in Example 1 except that one side of the laminate was irradiated with an electron beam with a dose of 20 kGy and a voltage of 300 kV. The gel fraction of the base film was 40%. Moreover, it was confirmed by the electron micrograph of the cross section of the thickness direction of a base film that the density gradient was formed toward the inside from the surface of this base film.

Comparative Example 1
In Example 1, a plastic label was obtained by performing the same operation as in Example 1 except that the electron beam was not irradiated. The gel fraction of the base film was 0%. Moreover, it was confirmed by the electron micrograph of the cross section of the thickness direction of a base film that the surface and the inside of this base film were formed with uniform density.

Comparative Example 2
In Example 1, a laminate was formed by the same operation as in Example 1 except that an electron beam with a dose of 20 kGy and a voltage of 600 kV was irradiated, and the electron beam was irradiated. The obtained film was hard and could not be stretched under the same conditions as in Example 1. The gel fraction of this film was 70%. Moreover, it was confirmed by the electron micrograph of the cross section of the thickness direction of a base film that the surface and the inside of this base film were uniformly formed with high density.

(Evaluation test)
Thermal Shrinkage A test piece of 10 cm × 10 cm (length in the width direction (TD direction) × length in the length direction (MD direction)) was cut out from the base film formed in Example and Comparative Example 1, and this test piece Was immersed in warm water of 100 ° C. for 10 seconds, the lengths of the base film in the TD direction and the MD direction were measured, and the thermal shrinkage rates in the TD direction and the MD direction were determined by the above formula. The results are shown in Table 1.

Stretching property F10 value of the base film formed in Example and Comparative Example 1 [tensile strength (unit MPa) when the film test piece is stretched by 10% in the tensile test] in accordance with JIS K 7113, test piece Was measured under the conditions of 200 mm × 15 mm, distance between marked lines 100 mm, test speed 50 mm / min, temperature 23 ° C., 50% RH. The results are shown in Table 1.

Restoration rate (instantaneous strain)
A test piece of 10 cm × 1 cm (length in the TD direction × length in the MD direction) was cut out from the base film formed in Example and Comparative Example 1, and both ends of the test piece were placed in the TD direction of the base film at room temperature. In addition, after holding for 3 seconds in a state where the length was extended to 1.25 times, the tensile force was released and the length was measured, and the restoration rate was obtained by the above formula. The results are shown in Table 1.

Natural Shrinkage The base film formed in Example and Comparative Example 1 was stored in an atmosphere at 30 ° C. for 30 days, and the shrinkage in the width direction during the storage period (referred to as the natural shrinkage) was measured. The results are shown in Table 1.

Cutting suitability Three times the plastic labels obtained in Example and Comparative Example 1 were stacked, and the operation of cutting with a cutter was repeated 10 times. The results are shown in Table 1.

It is a schematic sectional drawing which shows an example of the plastic label of this invention. It is a schematic sectional drawing which shows the other example of the plastic label of this invention. It is a perspective view which shows the state at the time of mounting | wearing a to-be-mounted object with the plastic label of FIG.

Explanation of symbols

1, 1 'plastic label 2, 2a, 2b, 2c, 2' base film 3, 3 'printed layer 4 core layer 5 outer layer 6 container

Claims (2)

A plastic label in which a printed layer is provided on at least one surface of a base film, wherein the base film has a thickness of 30 to 150 μm and a voltage of 50 to 500 kV and a dose of 5 to 50 kGy on at least one surface. Plastic label that has been subjected to electron beam irradiation. The plastic label according to claim 1, wherein the gel fraction of the base film is 10 to 65%, and the crosslinking density gradually decreases from the surface of the base film toward the inside.

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