Shrink label

Abstract

To provide shrink labels made of stretched polystyrene film (OPS) that are less prone to tearing even when thinned. [Solution] The shrink label of the present invention comprises a heat-shrinkable film. The heat-shrinkable film is a stretched film containing a styrene-diene copolymer. In a chromatogram obtained by gel permeation chromatography analysis of the styrene-diene copolymer, the ratio of the total area of ​​peaks with a number-average molecular weight of 50,000 or less is 4% or less, and the proportion of diene-derived constituent units contained in the styrene-diene copolymer is 23% by mass or more.

Description

Technical Field

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[0006]

[0001] The present invention relates to shrink labels.

Background Art

[0002] Shrink labels enable attachment that follows the shape of a container or the like by heat shrinkage, and are widely used for containers filled with various beverages, foods, toiletries, etc. (see, for example, Patent Document 1). In recent years, shrink labels are required to be thinner from an environmental perspective.

[0003] As a material for the heat-shrinkable film constituting the shrink label, a stretched polystyrene film (OPS) using a polystyrene-based resin may be used. The heat-shrinkable film made of OPS has the characteristic that it shrinks relatively gently and has a good finish after attachment to a container or the like. Also, when the material of the container is a polystyrene (PS)-based resin, using a heat-shrinkable film made of OPS has the advantage that the container and the shrink label can be recycled simultaneously and reused in the same way.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In a thin-walled shrink label made of OPS (for example, having a thickness of 30 μm or less), there is a problem that the shrink label is likely to break during conveyance in the process of attaching the shrink label to a container or the like, or during transportation by truck.

[0006] The objective of the present invention is to provide a shrink label made of stretched polystyrene film (OPS) that is less prone to tearing even when thinned. [Means for solving the problem]

[0007] The shrink label of the present invention comprises a heat-shrinkable film. The heat-shrinkable film is a stretched film containing a styrene-diene copolymer. In the chromatogram obtained by gel permeation chromatography analysis of the styrene-diene copolymer, the ratio of the total area of ​​peaks with a number-average molecular weight of 50,000 or less is 4% or less, and The proportion of diene-derived structural units contained in the styrene-diene copolymer is 23% by mass or more. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a shrink label made of stretched polystyrene film (OPS) that is less prone to tearing even when thinned. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic cross-sectional view showing a heat-shrinkable label used in the shrink label of the embodiment. [Modes for carrying out the invention]

[0010] Embodiments of the present invention will be described below with reference to the drawings. In the drawings, identical or common parts are denoted by the same reference numerals.

[0011] In this specification, "front side" means the outer side of the shrink label attached to the container, and "back side" means the inner side of the shrink label attached to the container. Furthermore, "circumferential direction" refers to the direction along the intersection line of the cylindrical shrink label with a virtual plane perpendicular to the axial direction of the cylindrical shrink label. Furthermore, the transverse direction (TD) refers to the direction corresponding to the width direction (short side) of the film roll, and the longitudinal direction (MD: machine direction) refers to the direction corresponding to the length direction (long side) of the film roll. Typically, the transverse direction (TD) is the primary shrinkage direction for heat-shrinkable film (shrink labels).

[0012] <Shrink label> A shrink label (heat-shrinkable tubular label) is a tubular label that shrinks in diameter when heated above a certain temperature and can be attached to an object (subject). The primary shrinkage direction of a shrink label is the circumferential direction of its tubular body (the tubular shrink label). For example, after the shrink label is fitted onto the object, it can be attached to the object by heating it to a predetermined heat shrinkage temperature (for example, by blowing hot air heated to about 100°C to 180°C onto the shrink label to about 65°C to 100°C).

[0013] While there are no particular limitations on the objects to which shrink labels are applied, typical examples include containers filled with beverages and other food products, and containers filled with cosmetics and shampoos. Shrink labels can be used, for example, as labels for various containers such as beverage containers, food containers, and detergent containers; as cap seals for sealing container caps; as outer coverings for various items such as electrical appliances, decorative items, tools, and general merchandise; as protective coverings for various items; and as binding materials for bundling multiple items together.

[0014] Shrink labels are equipped with a heat-shrinkable film and are primarily composed of a heat-shrinkable film. Shrink labels are manufactured, for example, by sealing the back surface of one end of a heat-shrinkable film cut to a predetermined width with the front surface of the other end in the width direction (TD) (a so-called center seal).

[0015] (Heat-shrinkable film) The heat-shrinkable film is a stretched film. The heat-shrinkable film 1 is produced, for example, by extruding a single-layer or multi-layer resin sheet made of a polystyrene-based resin using a T-die or the like, and then mainly stretching it in the transverse direction (TD) to impart heat shrinkability mainly in the transverse direction (TD) to form a film. When the film is uniaxially stretched, it mainly has heat shrinkability in one direction (the stretched direction). The stretching ratio in the transverse direction (TD), which is the main stretching direction (main shrinking direction), is, for example, about 2 to 6 times. The stretching ratio in the longitudinal direction (MD) orthogonal to the main shrinking direction is, for example, about 1.01 to 2 times.

[0016] The heat shrinkage rate of the heat-shrinkable film is not particularly limited, but the heat shrinkage rate in the transverse direction (TD: circumferential direction in a cylindrical body) is preferably 50% or more, more preferably 60% or more. The heat shrinkage rate in the longitudinal direction (MD) may be, for example, about -10 to 20% (minus indicates elongation rate). Here, the heat shrinkage rate is the shrinkage rate when a heat-shrinkable film (shrink film) cut into a 10 cm × 10 cm square in length and width is immersed in a 90°C warm water bath for 10 seconds.

[0017] The thickness (thickness before shrinkage) of the heat-shrinkable film is not particularly limited, but is, for example, 40 μm or less, and particularly preferably 15 to 30 μm. Especially when a conventional heat-shrinkable film (shrink label) made of a polystyrene-based resin is used for a small container, the effect of suppressing breakage of the present invention is useful when the film thickness is 30 μm or less, which is likely to cause breakage. The thickness of the heat-shrinkable film can be measured by a thickness measuring instrument such as a micrometer.

[0018] (Styrene-diene copolymer) The heat-shrinkable film used in this embodiment contains a styrene-diene copolymer as an essential component. The proportion of the styrene-diene copolymer contained in the heat-shrinkable film is preferably 70% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, and may be 100% by mass, based on the total mass (100% by mass) of the heat-shrinkable film. If the above content rate is less than 70% by mass, it is likely to break, making it difficult to process the film (such as printing and bag-making).

[0019] The styrene-diene copolymer is a kind of polystyrene resin, and is a copolymer composed of styrene-based monomers and dienes (especially conjugated dienes) as essential monomer components. That is, the styrene-diene copolymer is a polymer containing at least a structural unit derived from a styrene-based monomer and a structural unit derived from a diene (especially a conjugated diene) in the molecule (per molecule). In this specification, the structural unit derived from a styrene-based monomer is referred to as a "styrene-based unit", and the structural unit derived from a diene (diene-derived structural unit) is referred to as a "diene unit".

[0020] The styrene-based monomer is not particularly limited, and examples thereof include styrene, α-methylstyrene, m-methylstyrene, p-methylstyrene, p-ethylstyrene, p-isobutylstyrene, p-t-butylstyrene, chloromethylstyrene, and the like. Among them, styrene is preferable from the viewpoints of easy availability and material price. Note that only one kind of styrene-based monomer may be used, or two or more kinds may be used. The polystyrene resin is a polymer composed of a styrene-based monomer as an essential monomer (monomer) component. That is, it is a polymer containing at least a styrene-based unit in the molecule (per molecule).

[0021] The diene is not particularly limited, but conjugated dienes are preferred, such as 1,3-butadiene, isoprene (2-methyl-1,3-butadiene), 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene, and chloroprene. Among these, 1,3-butadiene is particularly preferred from the viewpoint of stretchability and shrinkage properties. That is, styrene-butadiene copolymer is preferred as the styrene-diene copolymer. Note that only one diene may be used, or two or more may be used.

[0022] The proportion of diene units contained in the styrene-diene copolymer is preferably 23% by mass or more, more preferably 24% by mass or more, and even more preferably 25% by mass or more, based on the total mass (100% by mass) of the styrene-diene copolymer. The tear-inhibiting effect of the present invention is easily obtained when the content of diene units is 23% by mass or more. Furthermore, if the styrene-diene copolymer contained in the heat-shrinkable film contains two or more types of styrene-diene copolymers, the content of styrene units and the content of diene units are, respectively, the content of all styrene-diene copolymers.

[0023] Furthermore, the content of diene units in the styrene-diene copolymer is preferably 40% by mass or less. That is, in the styrene-diene copolymer, the content of styrene units is preferably 60% by mass or more with respect to the total mass (100% by mass) of the styrene-diene copolymer.

[0024] For example, if a heat-shrinkable film is composed of multiple types of styrene-diene copolymers, the content of styrene units and the content of diene units can be determined by the content of each constituent unit in each styrene-diene copolymer and the content of each styrene-diene copolymer relative to the total amount in all styrene-diene copolymers constituting the heat-shrinkable film. Specifically, for example, a styrene-diene copolymer is a resin mixture composed only of a styrene-diene copolymer (PS1) in which the styrene unit content is s1 (mass%) and the diene unit content is d1 (mass%), and a styrene-diene copolymer (PS2) in which the styrene unit content is s2 (mass%) and the diene unit content is d2 (mass%), and if the content of PS1 in the above resin mixture (resin mixture of PS1 and PS2) (100 mass%) is W1 (mass%) and the content of PS2 is W2 (mass%), then the content of styrene units and diene units in the above resin mixture can generally be calculated from the following formula. Styrene unit content (mass%) = (s1 × W1 + s2 × W2) / 100 Diene unit content (mass%) = (d1 × W1 + d2 × W2) / 100

[0025] The analysis and measurement of the above-mentioned constituent units (styrene-based units and diene units) and their content are not particularly limited, but can be performed, for example, by nuclear magnetic resonance (NMR), gas chromatography-mass spectrometry (GCMS), etc.

[0026] The monomer components constituting the styrene-diene copolymer may further include monomer components other than styrene monomers and dienes. Examples of monomer components other than styrene monomers and dienes include vinyl monomers, polymerizable unsaturated carboxylic acid esters, and polymerizable unsaturated carboxylic anhydrides.

[0027] The copolymerization form of styrene-diene copolymers is not particularly limited, but examples include random copolymers, block copolymers, and graft copolymers. Among these, block copolymers are preferred, and examples include styrene block (S)-diene block (D) type, SDS type, DSD type, and SDSD type.

[0028] Examples of styrene-diene block copolymers (styrene-diene block copolymers) include styrene-butadiene block copolymers such as styrene-butadiene-styrene block copolymer (SBS), styrene-isoprene block copolymers such as styrene-isoprene-styrene block copolymer (SIS), and styrene-butadiene-isoprene block copolymers such as styrene-butadiene·isoprene-styrene block copolymer (SBIS). Among these, styrene-butadiene block copolymers are preferred. These block copolymers may be used individually or in combination of two or more.

[0029] The styrene-butadiene block copolymer can be any copolymer having alternating styrene blocks, where only styrene monomers are polymerized, and butadiene blocks, where only butadiene is polymerized. It is not particularly limited, but for example, Styrene-butadiene block copolymers having styrene blocks at both ends, such as styrene-butadiene-styrene block copolymer (SBS) and styrene-butadiene-styrene-butadiene-styrene block copolymer (SBSBS); Styrene-butadiene block copolymers having styrene blocks and butadiene blocks at their respective ends, such as styrene-butadiene copolymer (SB) and styrene-butadiene-styrene-butadiene copolymer (SBSB); Examples include styrene-butadiene block copolymers having butadiene blocks at both ends, such as butadiene-styrene-butadiene copolymer (BSB) and butadiene-styrene-butadiene-styrene-butadiene copolymer (BSBSB). Among these, styrene-butadiene block copolymers having styrene blocks at both ends are preferred, and SBS is more preferred. These styrene-butadiene block copolymers may be used individually or in combination of two or more types.

[0030] Styrene-diene block copolymers can be produced by known or conventional methods for producing block copolymers. Examples of methods for producing styrene-diene block copolymers include living polymerization (living radical polymerization, living anionic polymerization, living cation polymerization, etc.), which allows for easy control of the molecular weight, molecular weight distribution, and terminal structure of the styrene-diene block copolymer. Living polymerization can be carried out by known or conventional methods.

[0031] Furthermore, the heat-shrinkable film may contain resins other than styrene-diene copolymers (for example, polystyrene resins other than styrene-diene copolymers).

[0032] Polystyrene resins other than styrene-diene copolymers (polystyrene resins that do not contain diene units) are not particularly limited, but examples include homopolymers of styrene monomers (such as general-purpose polystyrene (GPPS), which is a homopolymer of styrene), copolymers composed of only two or more styrene monomers as monomer components, copolymers such as styrene-polymerizable unsaturated carboxylic acid ester copolymers, high-impact polystyrene (HIPS), graft-type high-impact polystyrene (graft HIPS), and styrene elastomers. Examples of HIPS include mixtures of polystyrene and synthetic rubber (e.g., polybutadiene or polyisoprene), and polystyrene obtained by graft polymerization of styrene onto synthetic rubber. Examples of grafted HIPS include polystyrene in which a rubbery elastic material is dispersed in a continuous phase of a polymer containing a styrene monomer (for example, a copolymer of a styrene monomer and a (meth)acrylic acid ester monomer), and the copolymer is graft polymerized onto the rubbery elastic material.

[0033] Polystyrene resins (including the styrene-diene copolymers mentioned above) may be hydrogenated. That is, the polystyrene resin may be a hydrogenated polystyrene resin (hydrogenated polystyrene resin). Examples of hydrogenated styrene-diene copolymers include hydrogenated styrene-butadiene-styrene block copolymer (SEBS), which is a resin obtained by adding hydrogen to SBS, and hydrogenated styrene-isoprene-styrene block copolymer (SEPS), which is a resin obtained by adding hydrogen to SIS.

[0034] Furthermore, the polystyrene resin (including the styrene-diene copolymer mentioned above) may have polar groups introduced into it. That is, the polystyrene resin may be a polystyrene resin with polar groups introduced into it (modified polystyrene resin). Note that the modified polystyrene resin includes hydrogenated polystyrene resin with polar groups introduced into it.

[0035] Modified polystyrene resins are polystyrene resins in which polar groups are introduced into a polystyrene resin as the main chain skeleton. The polar groups are not particularly limited, but examples include acid anhydride groups, carboxylic acid groups, carboxylic acid ester groups, carboxylic acid chloride groups, carboxylic acid amide groups, carboxylic acid bases, sulfonic acid groups, sulfonic acid ester groups, sulfonate chloride groups, sulfonic acid amide groups, sulfonic acid bases, isocyanate groups, epoxy groups, amino groups, imide groups, oxazoline groups, and hydroxyl groups.

[0036] The modified polystyrene resin is not particularly limited, but modified hydrogenated styrene-butadiene-styrene block copolymer (SEBS) and modified hydrogenated styrene-propylene-styrene block copolymer (SEPS) are preferred. Specifically, the modified polystyrene resin is preferably acid anhydride-modified SEBS, acid anhydride-modified SEPS, epoxy-modified SEBS, or epoxy-modified SEPS, and more preferably maleic anhydride-modified SEBS, maleic anhydride-modified SEPS, epoxy-modified SEBS, or epoxy-modified SEPS. The modified polystyrene resin may be used alone or in combination of two or more types.

[0037] Furthermore, the polystyrene resin is not particularly limited, but may be a flexible polystyrene resin. Examples of flexible polystyrene resins include styrene elastomers, styrene-diene copolymers, HIPS (high-impact polystyrene) with a high rubber component, and graft HIPS with a high rubber component. Among these, styrene elastomers and styrene-diene copolymers are preferred. The flexible polystyrene resin may be used alone or in combination of two or more types. The styrene elastomer may contain a diene component and may be a styrene-diene copolymer elastomer. Note that HIPS with a high rubber component refers to HIPS where the rubber component content exceeds 30% by mass relative to the total mass (100% by mass) of the HIPS. Similarly, graft HIPS with a high rubber component refers to graft HIPS where the rubber component content exceeds 30% by mass relative to the total mass (100% by mass) of the graft HIPS.

[0038] Flexible polystyrene resins include hydrogenated flexible polystyrene resins. While there are no particular limitations on hydrogenated flexible polystyrene resins, hydrogenated styrene elastomers and hydrogenated styrene-diene copolymers (particularly styrene-diene copolymers with a high hydrogenated diene component) are preferred.

[0039] Commercially available styrene-diene copolymers may be used, such as "Clearlen 530L" and "Clearlen 730L" from Denki Kagaku Kogyo Co., Ltd., "Styrolux S" and "Styrolux T" from Styroluxion Inc., and "679," "HF77," and "SGP10" from PS Japan Co., Ltd.

[0040] The heat-shrinkable film may contain resins other than polystyrene resins, as long as the effects of the present invention are not impaired. Examples of resins other than polystyrene resins include thermoplastic resins such as polyester resins, polyolefin resins, vinyl chloride resins, polycarbonate resins, and polyamide resins. Only one type of resin other than polystyrene resin may be used, or two or more types may be used.

[0041] Furthermore, the heat-shrinkable film 1 may contain additives such as lubricants, fillers, heat stabilizers, antioxidants, ultraviolet absorbers, antistatic agents, antifogging agents, flame retardants, colorants, pinning agents (alkaline earth metals), and softeners, to the extent that they do not impair the effects of the present invention.

[0042] (Molecular weight distribution of styrene-diene copolymers) In this embodiment, in the chromatogram (GPC chart) obtained by gel permeation chromatography (GPC) analysis of the styrene-diene copolymer constituting the heat-shrinkable film, the ratio of the total area of ​​peaks with a number-average molecular weight of 50,000 or less (ratio to the total area of ​​all peaks in the chromatogram) is 4% or less, preferably 3.5% or less, more preferably 2% or less, even more preferably 1% or less, and still more preferably 0.5% or less. In this case, the shrink label (heat-shrinkable film) is less likely to tear. The reason is not clear, but it is presumed that resins with small molecular weights are more likely to create starting points for tearing, and as the amount of these resins increases, the heat-shrinkable film becomes more prone to tearing.

[0043] Furthermore, in the above chromatogram, the ratio of the total area of ​​peaks with a number-average molecular weight exceeding 100,000 is preferably 70% or more, and more preferably 75% or more. In this case, it is considered more reliable that the shrink label (heat-shrinkable film) will not tear easily.

[0044] Furthermore, in the above chromatogram, the ratio of the total area of ​​peaks with a number-average molecular weight exceeding 200,000 is preferably 15% or less, and more preferably 10% or less. If the ratio exceeds 15%, flexibility decreases, making it difficult to process.

[0045] In the above chromatogram, the ratio of the total area of ​​peaks with a number-average molecular weight greater than 50,000 and less than or equal to 100,000 is preferably 15-30%, and more preferably 20-27%. In this case, the shrink label (heat-shrinkable film) is less likely to tear and is easier to process.

[0046] In the above chromatogram, the ratio of the total area of ​​peaks with a number-average molecular weight greater than 100,000 and less than or equal to 200,000 is preferably 60% or more, and more preferably 68% or more. In this case, the shrink label (heat-shrinkable film) becomes even less likely to tear. Furthermore, the ratio of the total area of ​​peaks with a number-average molecular weight between 100,000 and 200,000 is preferably 80% or less.

[0047] (Composition of heat-shrinkable film, etc.) The heat-shrinkable film may be a single-layer film or a laminated film obtained by co-extruding multiple resins. The laminated film may be a laminated film of different types of materials or a laminated film of the same type of material obtained by laminating films of the same type. As a laminated film of different types of materials, it may be a film obtained by stretching a co-extruded sheet consisting of two types and three layers (surface layer / center layer / surface layer), or it may be a film having two types and five layers, three types and five layers (surface layer / intermediate layer / center layer / intermediate layer / surface layer), or more types and number of layers.

[0048] Referring to Figure 1, it is preferable that the heat-shrinkable film 1 includes a central layer 11 and surface layers 12 provided on both sides of the central layer 11. In this case, the heat-shrinkable film 1, including the core layer 11 and the surface layer 12 as a whole, contains 70% by mass or more of a styrene-diene copolymer. Preferably, each of the core layer 11 and the surface layer 12 contains 70% by mass or more of a styrene-diene copolymer.

[0049] In a heat-shrinkable film including a central layer 11 and a surface layer 12 as shown in Figure 1, it is preferable that the surface layer 12 contains a lubricant. The inclusion of a lubricant in the surface layer 12 reduces the coefficient of friction on the surface of the heat-shrinkable film 1, increasing its slipperiness and thus suppressing tearing of the heat-shrinkable film 1 (shrink label). The core layer 11 may also contain a lubricant. The lubricant is not particularly limited, but for example, erucic acid amide, ethylenebisstearic acid amide, etc. can be used.

[0050] In the chromatogram (GPC chart) obtained by GPC analysis of the styrene-diene copolymer constituting both the central layer 11 and the surface layer 12, the area ratio of peaks with a number-average molecular weight of 50,000 or less is preferably 4% or less, preferably 3.5% or less, more preferably 2% or less, even more preferably 1% or less, and even more preferably 0.5% or less. In particular, it is more preferable that the styrene-diene copolymer GPC chart used for the surface layer 12 does not have a peak with a number average molecular weight of 50,000 or less. This is because the surface layer 12 is the part that is directly subjected to external forces such as friction, and if the amount of resin with a small molecular weight contained in the surface layer 12 increases, the surface layer 12 becomes the starting point for tearing, making it easier for the heat-shrinkable film 1 to tear.

[0051] The core layer 11 and the surface layer 12 may also contain resins other than styrene-diene copolymers, such as polystyrene resins that do not contain diene units (e.g., GPPS).

[0052] In this embodiment, it is preferable that the shrink label tears more than 100 times in the JSPS (Japan Society for the Promotion of Science) test described below (i.e., does not tear even after 100 JSPS tests). In the JSPS (Japan Society for the Promotion of Science) examination, a JSPS-type friction tester is used to apply a load by bringing a 500g stainless steel weight into contact with a heat-shrinkable film fixed to a movable table. The movable table is then moved back and forth until the heat-shrinkable film tears, and the number of reciprocations at which tearing occurs is measured. The more times tears occur during the JSPS (Japan Society for the Promotion of Science) testing, the less likely the shrink label (heat-shrinkable film) is to tear.

[0053] The shrink label of this embodiment is preferably attached to a container with an internal volume of 200 mL or less (preferably 100 mL or less) (specifically, it is fitted onto the outer circumference of the body of a bottle-shaped container made of plastic or the like, and then heat-shrunk to attach it).

[0054] Shrink labels made from stretched polystyrene (PS) resins such as styrene-diene copolymers (OPS) generally have lower strength than shrink labels made from polyester resins (PET, etc.). When used on containers with a volume exceeding 100 mL, the weight of the liquid inside the container can easily cause the label to tear when dropped or abraded. However, for relatively light containers (products) with a volume of 100 mL or less, such tearing is unlikely, and shrink labels made from OPS can be applied without problems. Thick OPS shrink labels, like PET shrink labels, are used for containers with a volume of 500 mL or more (such as PET bottles). On the other hand, while thin-walled shrink labels (e.g., 40 μm or less in thickness) are used for containers with a volume of 500 mL or more, thin-walled OPS shrink labels are not suitable for containers with a volume of 500 mL or more due to insufficient strength. However, for containers with an internal volume of 200 mL or less, especially small-volume containers of about 50 to 100 mL (lightweight plastic containers weighing 20 g or less, especially small containers made of PS resin weighing 10 g or less), there is room to use thin-walled shrink labels made of PS resin (e.g., OPS), and the provision of such labels has been desired. The present invention makes it possible to provide shrink labels made of PS resin that can be applied to such small-capacity containers.

[0055] Furthermore, the present invention also relates to a labeled container comprising a container (object: packaged item) and a shrink label of this embodiment attached to the container. Here, the internal volume of the container is preferably 200 mL or less, and more preferably 100 mL or less.

[0056] (Printing layer, etc.) In the shrink label of this embodiment, for example, if the heat-shrinkable film is a heat-shrinkable film 1 consisting of a central layer 11 and a surface layer 12 as shown in Figure 1, a printing layer for displaying a design may be provided on the back side of the heat-shrinkable film 1 (the surface layer 12 which becomes the back side). The printing layer may include a design printing layer that displays text, images, etc., and a background printing layer (for example, a solid white printing layer) that is laminated on the back side of the design printing layer to make the text, images, etc., look nice. Furthermore, when a printed layer is provided on the back surface of the heat-shrinkable film, a heat-shrinkable film with excellent light transmission (colorless and transparent or a slightly colored transparent film) is used. Furthermore, if the heat-shrinkable film 1 is a colored film such as a milky white film, a printed layer may be provided on the surface layer 12 that faces outwards. A slippery overcoat layer, a matte coat layer with a non-glossy effect, or the like may be appropriately provided on the surface of the printed layer.

[0057] In addition, the shrink label of this embodiment may have a dividing line for removing the shrink label from the container. Examples of dividing lines include perforations. The dividing line may be provided from the upper edge to the lower edge of the shrink label. [Examples]

[0058] (Examples 1-4, Comparative Examples 1-3) For Examples 1-4 and Comparative Examples 1-3, a heat-shrinkable film 1 with a two-type, three-layer structure was prepared, in which a surface layer 12 was formed on both sides of a central layer 11, as shown in Figure 1. The prepared (pre-shrinkage) heat-shrinkable film had a thickness of 20 μm, and the ratio of the surface layer 12: core layer 11: surface layer 12 thicknesses was 1:3.5:1. Furthermore, each heat-shrinkable film was confirmed to be an OPS film with suitable shrinkage properties, exhibiting a heat shrinkage rate of 30-50% at 80°C and 50-70% at 90°C.

[0059] In all of Examples 1-4 and Comparative Examples 1-3, the surface layer 12 is made of SBS resin containing a lubricant. The SBS resin constituting the surface layer 12 accounts for 36% by mass of the total resin constituting the heat-shrinkable film 1. On the other hand, in all of Examples 1-4 and Comparative Examples 1-3, the central layer 11 does not contain a lubricant.

[0060] The central layer 11 of Example 1 is made of a mixed resin of resin A (31% by mass), resin D (10% by mass), and resin E (23% by mass). The central layer 11 of Example 2 is made of a mixed resin of resin A (50% by mass) and resin B (14% by mass). The central layer 11 of Example 3 is made of resin A (64% by mass). The central layer 11 of Example 4 is made of a mixed resin of resin A (41% by mass) and resin E (23% by mass). The central layer 11 of Comparative Example 1 is made of a mixed resin of resin A (22% by mass), resin D (16% by mass), and resin E (36% by mass). The central layer 11 of Comparative Example 2 is composed of a mixed resin of Resin A (16% by mass), Resin B (29% by mass), and Resin C (19% by mass). The central layer 11 of Comparative Example 3 is composed of a mixed resin of Resin A (22% by mass), Resin D (36% by mass), and Resin E (16% by mass). Note that the ratios within the parentheses above are ratios with respect to the mass of the resin constituting the entire heat-shrinkable film 1. The blending ratios of each resin in the entire heat-shrinkable film 1 (central layer 11 and surface layer 12) of the above Examples and Comparative Examples are as shown in Table 1.

[0061] The above Resins A, B, D, and E are SBS (styrene-butadiene-styrene block copolymer). Resin C is GPPS (general-purpose polystyrene). The content ratios of diene units (butadiene units) in Resins A - D are as shown in Table 3.

[0062] <Molecular weight distribution measurement by GPC> Regarding the heat-shrinkable films used in each of the above Examples 1 - 4 and Comparative Examples 1 - 3, and the above Resins A - E (polystyrene resins), gel permeation chromatography (GPC) measurement was performed by RI (differential refractive index) detection under the following apparatus and conditions. 〔Measurement apparatus〕 GPC analyzer (manufactured by Waters, Waters2695) 〔Measurement conditions〕 Detector: manufactured by Waters, Waters2414 Separation column: manufactured by Showa Denko, Shodex KF-806 + KF-804 + KF-802.5 Solvent: tetrahydrofuran (flow rate: 1 mL / min, 40 °C)

[0063] Regarding the chromatogram (GPC chart) obtained by GCP measurement, the number average molecular weight of each peak was calculated (in terms of polystyrene conversion) from the calibration curve with standard polystyrene by the above GPC analyzer. Also, the area value of each peak in the GPC chart was calculated. From the number-average molecular weight and area value of each peak, the area ratio of peaks included in each range of number-average molecular weight (ratio of the total area of ​​peaks within each range) was determined. This range includes peaks with a number-average molecular weight greater than 200,000, those with a number-average molecular weight greater than 100,000 and those with a number-average molecular weight less than or equal to 200,000, and those with a number-average molecular weight of 50,000 or less. Table 1 shows the area ratios of each peak in the GPC charts obtained for the heat-shrinkable films of Examples 1-4 and Comparative Examples 1-3.

[0064] Table 2 shows the number-average molecular weight and area ratio of each peak in the GPC charts, which were similarly measured for resins A to E.

[0065] <JSPS Examination> The Japan Society for the Promotion of Science (JSPS) conducted a JSPS test on each of the heat-shrinkable films of Examples 1-4 and Comparative Examples 1-3 described above. In the JSPS (Japan Society for the Promotion of Science) test, a JSPS-type friction tester (manufactured by Daiei Kagaku Seiki Seisakusho Co., Ltd., a dye friction fastness tester) was used. A load was applied by bringing the surface of a weight (a 500g stainless steel weight) into contact with a heat-shrinkable film fixed to a movable table. The movable table was then moved back and forth until the heat-shrinkable film tore, and the number of reciprocations at which tearing occurred was measured. The "JSPS Test Results" column in Table 1 shows the results of the JSPS test (number of passes until the film broke).

[0066] <Usage Evaluation> Shrink labels were created using the heat-shrinkable film of Example 1. These labels were then attached (fitted and heat-shrinked) to polystyrene resin containers (capacity approximately 80 mL) using a shrink labeler and shrink heater on a beverage production line. The containers were then transported on the production line (conveyor belt), filled with 80 g of beverage using a filling device, and sealed for packaging. From approximately 10,000 containers produced, 1,000 were randomly selected from the packaging and visually inspected. No tears were found in the shrink labels, and the containers were deemed usable. Furthermore, when the shrink label of Comparative Example 1 was used on the same production line, frequent tearing occurred on the container surface.

[0067] [Table 1]

[0068] [Table 2]

[0069] [Table 3]

[0070] In Examples 1 to 4, the styrene-diene copolymer constituting the heat-shrinkable film has a composition within the scope of the present invention, where the ratio of the total area of ​​peaks with a number-average molecular weight of 50,000 or less on the GCP chart is 4% or less, and the proportion of diene units contained in the styrene-diene copolymer is 23% by mass or more. In Comparative Example 1, the styrene-diene copolymer constituting the heat-shrinkable film has a composition outside the scope of the present invention, with a ratio of more than 4% of the total area of ​​peaks with a number-average molecular weight of 50,000 or less in the GCP chart. Furthermore, in Comparative Examples 2 and 3, the proportion of diene units contained in the resin constituting the heat-shrinkable film is less than 23% by mass, and the composition is outside the scope of the present invention. From the results shown in Table 1, it can be seen that the heat-shrinkable films of Examples 1 to 4, which have compositions within the scope of the present invention, have a higher number of tearing cycles in the JSPS test compared to the heat-shrinkable films of Comparative Examples 1 to 3, which have compositions outside the scope of the present invention, and exhibit superior tear resistance.

[0071] Furthermore, in particular, Examples 2 and 3, where the area ratio of peaks with a number-average molecular weight of 50,000 or less in the GCP chart is less than 3% (1%, 0.5%), show that they can withstand more trials before tearing in the JSPS test compared to Examples 1 and 4, demonstrating extremely superior tear resistance.

[0072] Furthermore, in Examples 1 to 4, where the area ratio of peaks with a number-average molecular weight exceeding 200,000 in the GCP chart is 15% or less, there is a tendency for a higher number of trials before tearing in the JSPS (Japan Society for the Promotion of Science) test. In particular, Examples 2 and 3, where the area ratio is 10% or less, also show a higher number of trials before tearing in the JSPS test compared to Examples 1 and 4, indicating superior tear resistance.

[0073] Furthermore, in particular, Examples 2 and 3, where the area ratio of peaks with a number-average molecular weight between 100,000 and 200,000 in the GCP chart is 68% or more, showed a tendency to be extremely resistant to tearing, with more attempts required before tearing in the JSPS test compared to Examples 1 and 4.

[0074] The present invention is not limited to the embodiments described above and can be modified in various ways. Two or more embodiments selected from the various embodiments described above may be combined as appropriate, or at least one configuration (part of a configuration) selected from the various embodiments described above may be replaced with a part of a configuration of another embodiment. [Explanation of Symbols]

[0075] 1. Heat-shrinkable film 11 Central layer 12 Surface layer

Claims

1. A shrink label comprising a heat-shrinkable film, The heat-shrinkable film is a stretched film containing a styrene-diene copolymer. In the chromatogram obtained by gel permeation chromatography analysis of the styrene-diene copolymer, the ratio of the total area of ​​peaks with a number-average molecular weight of 50,000 or less is 4% or less, and The proportion of diene-derived structural units contained in the styrene-diene copolymer is 23% by mass or more. Shrink label.

2. The shrink label according to claim 1, wherein in the chromatogram, the ratio of the total area of ​​peaks with a number-average molecular weight greater than 100,000 is 70% or more.

3. The shrink label according to claim 1, wherein the thickness of the heat-shrinkable film is 15 to 30 μm, and it is attached to a container with an internal volume of 200 mL or less.

4. The heat-shrinkable film comprises a central layer and surface layers provided on both sides of the central layer. The shrink label according to claim 1, wherein the surface layer contains a lubricant.

5. A shrink label according to claim 1, wherein the number of times it tears in the following JSPS test is greater than 100. In the aforementioned JSPS (Japan Society for the Promotion of Science) test, a JSPS-type friction tester is used to apply a load by bringing a 500g stainless steel weight into contact with a heat-shrinkable film fixed to a movable table. The movable table is then moved back and forth until the heat-shrinkable film tears, and the number of reciprocations at which the tear occurs is measured.

6. A labeled container comprising a shrink label as described in claim 1 attached to a container, wherein the internal volume of the container is 200 mL or less.

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