Shrinkable label film with excellent shrinkability and loop rigidity

Abstract

Disclosed is a shrink label film that has improved low-temperature shrinkability and loop rigidity while maintaining improved seaming properties and transparency for a non-adhesive label with a specific gravity of less than 1. The present invention provides a shrink label film comprising a skin layer, a core layer, and a seal layer, wherein the skin layer and seal layer comprise a first polystyrene-based resin, and the core layer comprises 40 to 90 parts by weight of a copolymer of propylene and two or more olefins selected from ethylene and α-olefins, 5 to 30 parts by weight of a petroleum resin having a softening point of 120 to 140°C, and 5 to 30 parts by weight of a polyolefin elastomer, and wherein tie layers containing a second polystyrene-based resin are provided between the skin layer and the core layer and between the core layer and the seal layer.

Description

[Technical Field]

[0001] The present invention relates to a shrink label film, and more particularly to a shrink label film having excellent shrinkability and loop rigidity.

[0002] This application claims priority to and the benefit of Korean Patent Application No. 10-2022-0156659, filed on November 21, 2022, the entire text of which is incorporated herein by reference. [Background technology]

[0003] Various plastic containers, such as PET bottles, generally have labels with a printed layer attached to the outside. These labels are divided into adhesive labels and non-adhesive labels, which are classified according to whether or not an adhesive is used between the container and the label.

[0004] Adhesive labels are usually made using polypropylene materials, while non-adhesive labels are mainly made using polystyrene, polyester, polyvinyl chloride, etc. After use, polyethylene terephthalate (PET), polystyrene (PS), etc. containers with labels attached are crushed and pelletized, and then recycled as containers through a recycling process. In this process, the pelletized containers are placed in water and sorted according to their specific gravity.

[0005] Meanwhile, the Ministry of Environment has implemented a standard for grading packaging materials for ease of recycling (Ministry of Environment Notification No. 2019-255, implemented on December 30, 2019), which classifies non-adhesive labels with a specific gravity of less than 1 as having the highest recyclability grade, necessitating the development of non-adhesive labels with a specific gravity of less than 1.

[0006] In terms of the physical properties of non-adhesive labels, conventional materials such as PS, PET, and polyvinyl chloride (PVC) have a high specific gravity, so it is possible to consider using polyolefin materials with a specific gravity of less than 1. However, it is difficult to give polyolefin films shrinkability and seaming properties, so cyclic olefin copolymer (COC) is added to form the film.

[0007] In the case of labels, gravure printing is performed on the produced film, but if the tensile strength of the film in the machine direction (MD) is low, the tension applied to the roll will be low, resulting in lower productivity during printing. Also, if the film has high haze during printing, the clarity and aesthetic quality of the printed product will be reduced.

[0008] Meanwhile, in the case of beverage filling lines, aseptic lines, which are low-temperature sterilization systems, are the norm. In the labeling process of these lines, the heat source for heat shrinkage is steam, so the higher the shrinkage rate at low temperatures (100℃), the more diverse the types of beverages (bottles) that can be applied to. Materials with improved low-temperature shrinkability should be able to increase the stretch ratio at low-temperature stretching speeds (82~85℃).

[0009] Patent Document 1 discloses a multilayer oriented shrink film comprising one or more skin layers containing a polystyrene material and one or more core layers containing a polyolefin layer, but the strength and loop stiffness of the final film are low, and the low-temperature (100°C) shrinkability is poor due to stretching at high temperatures (110-130°C).

[0010] Patent Document 2 discloses a heat-shrinkable multilayer film composed of front and back layers containing a cyclic olefin resin and an ethylene resin, and an intermediate layer containing an olefin resin and a plastic resin. However, the film has a high haze and there is a limit to the stretching ratio, and the film breaks down when the stretching ratio is 5 times or more. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Korean Patent Publication No. 10-2008-0074177 [Patent Document 2] Japanese Patent Registration No. 6268136 Summary of the Invention [Problem to be solved by the invention]

[0012] The present invention provides a shrink label film that has improved low-temperature shrinkability and loop rigidity while maintaining improved seaming properties and transparency as a non-adhesive label with a specific gravity of less than 1. [Means for solving the problem]

[0013] In order to solve the above problems, the present invention provides a shrink label film comprising a skin layer, a core layer, and a seal layer, wherein the skin layer and the seal layer comprise a first polystyrene-based resin, and the core layer comprises 40 to 90 parts by weight of a copolymer of propylene and two or more olefins selected from ethylene and α-olefins, 5 to 30 parts by weight of a petroleum resin having a softening point of 120 to 140°C, and 5 to 30 parts by weight of a polyolefin elastomer, and wherein tie layers comprising a second polystyrene-based resin are provided between the skin layer and the core layer and between the core layer and the seal layer.

[0014] The first polystyrene resin is at least one selected from the group consisting of general-purpose polystyrene (GPPS), high impact polystyrene (HIPS), styrene-butadiene-styrene copolymer (SBS), styrene-isoprene-styrene copolymer (SIS), styrene-ethylene-butylene-styrene copolymer (SEBS), and styrene-butadiene copolymer (SBC).

[0015] The copolymer has a melting point (Tm) of 123 to 138°C and a melt index (230°C, 2.16 kg load) of 2 to 10 g / 10 min, and the two olefins are ethylene and 1-butene.

[0016] The present invention also provides a shrink label film, wherein the ethylene and 1-butene are each contained in an amount of 1 to 5% by weight of the copolymer.

[0017] The polyolefin elastomer has a density of 0.85 to 0.9 g / cm 3 and a propylene-ethylene rubber (PER) or propylene-butene rubber (PBR) having a melt index (230°C, 2.16 kg load) of 0.5 to 10 g / 10 min.

[0018] The second polystyrene resin is at least one selected from the group consisting of styrene-ethylene-butylene-styrene copolymer (SEBS), styrene-ethylene-propylene-styrene copolymer (SEPS), styrene-butadiene-styrene copolymer (SBS), styrene-isoprene-styrene copolymer (SIS), and styrene-butadiene copolymer (SBC).

[0019] The film has a density of 1 g / cm 3 The present invention provides a shrinkable label film having a shrinkage rate of 50% or more measured by the following method and a loop stiffness of 6 gf / 50 μm or more.

[0020] [Method for measuring shrinkage rate] The film stretched in the transverse direction (TD) was cut into a size of 50 mm x 50 mm, and immersed in a hot water bath at 100°C for 10 seconds each, after which the dimensions were measured. The transverse direction (TD) shrinkage was calculated using the following formula 1 and shown as the average shrinkage.

[0021]

number

[0022] [Loop stiffness measurement method] Using a LOOP STIFFNESS TESTER (TOYOSEIKI), the stretched film is cut into a size of 25mm x 150mm, and the left and right clamps (film fixing device) of the tester are fixed with a distance of 50mm. The part that protrudes outside the clamps is cut off, and the film is bent so that the gap between the clamps disappears. The load (gf) applied to the end of the loop-shaped test piece formed by bending the film is measured when the load device presses it at a speed of 60mm / min.

[0023] The present invention also provides a shrink label film characterized in that the film has a haze (ASTM D1003, thickness 50 μm) of less than 5%. [Effects of the Invention]

[0024] According to the present invention, in a shrink label film comprising a skin layer, a core layer, and a seal layer, a first polystyrene-based resin is used for the skin layer and the seal layer, and the core layer is composed of a copolymer of propylene with two or more olefins selected from ethylene and α-olefins, a petroleum resin, and a polyolefin elastomer, thereby providing a shrink label film with improved low-temperature shrinkability and loop rigidity while maintaining improved seaming properties and transparency as a non-adhesive label with a specific gravity of less than 1. [Brief explanation of the drawings]

[0025] [Figure 1] 1 is a schematic diagram illustrating a labeling process (shooting and shrinking) using a shrink label film and a sleeve manufacturing process. [Figure 2] 1 is a photograph showing the result of scanning electron microscope (SEM) cross-sectional photography of a film produced in Example 1 of the present invention. [Figure 3]FIG. 2 is a diagram illustrating the location where the presence or absence of adhesion of the film is confirmed in a test example of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0026] The present invention will be described in detail below through preferred embodiments. Prior to this, the terms and phrases used in this specification and claims should not be construed as being limited to their ordinary or dictionary meanings, but should be construed as meanings and concepts consistent with the technical concept of the present invention, based on the principle that the inventor can appropriately define the concepts of terms to best describe his or her invention. Therefore, it should be understood that the configuration of the embodiment described in this specification is merely the most preferred embodiment of the present invention and does not fully represent the technical concept of the present invention, and therefore, at the time of filing this application, various equivalents and modifications that can replace them may exist.

[0027] The present invention discloses a shrink label film comprising a skin layer, a core layer, and a seal layer, wherein the skin layer and the seal layer comprise a first polystyrene-based resin, and the core layer comprises 40 to 90 parts by weight of a copolymer of propylene and two or more olefins selected from ethylene and α-olefins, 5 to 30 parts by weight of a petroleum resin having a softening point of 120 to 140°C, and 5 to 30 parts by weight of a polyolefin elastomer.

[0028] The present invention provides a shrink label film that has improved low-temperature shrinkability and loop stiffness while maintaining improved seaming properties and transparency as a non-adhesive label with a specific gravity of less than 1.

[0029] Figure 1 is a schematic diagram illustrating the labeling process (shooting and shrinking) and sleeve manufacturing process using shrink label film. As shown in Figure 1, the seaming property is a physical property essential for bonding between films when manufacturing sleeves, the rigidity is a rigidity required for the film to have a certain value (approximately 4.5 gf) or more to ensure a smooth process of inserting the label into the bottle (shooting process), the transparency affects the appearance of the film when printing on it, and the shrinkage (TD direction) is a physical property necessary for the film to adhere to the bottle container when passing through a heat shrink tunnel after label shooting.

[0030] In the present invention, the first polystyrene-based resin used in each of the skin layer and the seal layer can basically impart shrinkage and seaming properties to the material, and while taking into consideration stretchability and transparency, can also realize improved low-temperature shrinkage and loop rigidity through the bonding relationship between the core layer and tie layer of a specific composition, which will be described later. In this respect, preferred examples include general-purpose polystyrene (GPPS), high impact polystyrene (HIPS), styrene-butadiene-styrene copolymer (SBS), styrene-isoprene-styrene copolymer (SIS), styrene-ethylene-butylene-styrene copolymer (SEBS), and styrene-butadiene copolymer (SBC). More preferred examples include styrene-butadiene copolymer (SBC) or a resin in which styrene-butadiene copolymer (SBC) is mixed with general-purpose polystyrene (GPPS).

[0031] However, cyclic olefin copolymer (COC), which has traditionally been used for the skin and seal layers, has limitations on stretch ratios, failing at stretch ratios of 5x or greater. Adding linear low-density polyethylene (LLDPE) could be considered to address this issue and lower the film's specific gravity, but this reduces the film's loop rigidity and increases haze. The present invention eliminates this linear low-density polyethylene and achieves a film specific gravity of less than 1 by changing the composition of the core layer (described below). In other words, while conventional shrink label films exhibited haze of 10% or greater when they contained linear low-density polyethylene in the skin and seal layers, eliminating this polyethylene can improve transparency to a haze of 3% or less.

[0032] In the present invention, it has been confirmed that the core layer most suitably contains a copolymer of propylene and two olefins selected from ethylene and α-olefins, a petroleum resin, and a polyolefin elastomer, in order to reduce the specific gravity of the film without compromising the improved physical properties achieved by using the first polystyrene-based resin in the skin layer and the seal layer, while maintaining the excellent loop rigidity, transparency, and seaming properties of the film, and in particular, to improve the low-temperature (100°C) shrinkage properties of the film.

[0033] The copolymer may be preferably an ethylene-propylene-α-olefin terpolymer, where the α-olefin has 4 to 10 carbon atoms, such as 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-heptene, 1-octene, 1-nonene, 1-decene, etc., and preferably 1-butene. In the case of the ethylene-propylene-α-olefin terpolymer, the contents of ethylene and the α-olefin may each be 1 to 5 wt %.

[0034] The copolymer preferably has a melting point (Tm) of 123 to 138°C and a melt index (230°C, 2.16 kg load) of 2 to 10 g / 10 min, more preferably a melting point (Tm) of 126 to 135°C and a melt index (230°C, 2.16 kg load) of 4 to 8 g / 10 min.

[0035] In the present invention, the petroleum resin constituting the core layer is a modifier added to improve the film's transparency, loop rigidity, and low-temperature shrinkability. Conventional core layer compositions using only elastomers or plastomers result in lower final film strength and loop rigidity due to their low density. Furthermore, they are unable to achieve high shrinkage rates of 50% or more, preferably 60% or more, at low temperatures (100°C) when stretched at high temperatures (110-130°C). Therefore, in the present invention, a petroleum resin with a specific softening point is added to the core layer to reduce the crystallinity of the core layer raw material, improving low-temperature stretchability and film shrinkability. Furthermore, the size of the copolymer's crystallites, located in the amorphous domain of the copolymer, is reduced, improving optical properties.

[0036] Such petroleum resins are pale yellow or dark brown thermoplastic resins with a molecular weight of 2,000 g / mol or less, obtained by polymerizing higher unsaturated hydrocarbons found in high-temperature pyrolysis oils such as naphtha using an acidic catalyst. In the present invention, petroleum resins with a softening point of 120 to 140°C, preferably 120 to 130°C, can be used in order to improve low-temperature shrinkage and loop rigidity.

[0037] In the case of aromatic petroleum resins, the main component may be a copolymer of styrene-vinyltoluene, α-methylstyrene, and indene. In the case of aliphatic petroleum resins, the main component may be a copolymer of isoprene, piperylene-2-methylbutene-1, etc., and the resin is produced from C5 oil, which is an oil produced in the olefin process of naphtha cracking. Aliphatic petroleum resins may also include petroleum resins produced from dicyclopentadiene. In addition, hydrogenated petroleum resins are resins formed by adding hydrogen to the aromatic petroleum resins and aliphatic petroleum resins, and may include petroleum resins produced from dicyclopentadiene and then hydrogenated.

[0038] In the present invention, the core layer contains a polyolefin elastomer (POE) to improve dispersion and fluidity by increasing the compatibility between the components, and to increase the elongation in the transverse direction (TD). In other words, if the elongation in the transverse direction (TD) of a shrink film is low, the label may tear when applied to labels for products such as carbonated beverages. However, in the present invention, by blending a polyolefin elastomer into the core layer, the elongation in the transverse direction (TD) can be improved by 50% or more compared to conventional films.

[0039] In consideration of this purpose, the polyolefin elastomer has a density of 0.85 to 0.9 g / cm 3 , and the melt index (230°C, 2.16 kg load) can be 0.5 to 10 g / 10 min, but preferably the density is 0.86 to 0.89 g / cm 3 , and the melt index (230°C, 2.16 kg load) may be 2 to 8 g / 10 min.

[0040] The polystyrene elastomer may be a copolymer of propylene and an olefin selected from ethylene and α-olefins. In this case, propylene-ethylene rubber (PER) or propylene-butene rubber (PBR), which have a lower melting point and higher compatibility than the propylene copolymer used as the base resin of the core layer, may be used to lower the stretchable temperature (improve low-temperature stretchability) and improve the stretching ratio. In this regard, the polyethylene elastomer is preferably a propylene-ethylene rubber copolymerized with 5 to 20 wt% ethylene or a propylene-butene rubber copolymerized with 10 to 30 wt% butene, more preferably a propylene-butene rubber copolymerized with 20 to 30 wt% butene.

[0041] In the present invention, the component combinations described above are combined in a specific range of component content ratios in each layer to achieve the desired improved seaming properties and transparency as well as improved loop stiffness and low-temperature shrinkability for shrink labels. To achieve this, the core layer contains 40 to 90 parts by weight of the copolymer, 5 to 30 parts by weight of the petroleum resin, and 5 to 30 parts by weight of the polyolefin elastomer. Preferably, the copolymer is contained in a range of 50 to 80 parts by weight, 5 to 25 parts by weight of the petroleum resin, and 10 to 25 parts by weight of the polyolefin elastomer.

[0042] If the content of the copolymer in the core layer is less than 40 parts by weight, transparency during stretching decreases, and if it exceeds 90 parts by weight, shrinkage of the film decreases. Furthermore, if the content of the petroleum resin exceeds 30 parts by weight, shrinkage and elongation of the film decrease. Furthermore, if the content of the polyolefin elastomer is less than 10 parts by weight, shrinkage and elongation of the film decrease, and if it exceeds 30 parts by weight, loop rigidity, transparency, and tensile strength of the film decrease.

[0043] Meanwhile, in the present invention, uneven flow may occur due to the difference in viscosity between the first polystyrene-based resin and the polyolefin. To solve this problem, the skin layer, core layer, and seal layer may each be made of a melt-blended composition, and the respective compositions may be laminated to produce a film. This improves dispersibility by melt-blending before film stretching due to the difference in fluidity between the raw materials of each layer, and also allows for a smooth stretching process after film formation.

[0044] Here, in the present invention, tie layers are provided between the skin layer and the core layer, and between the core layer and the seal layer, which prevents a decrease in interlayer adhesive strength due to the use of a first polystyrene-based resin in the skin layer and the seal layer, and further improves the loop rigidity and tensile properties of the film.

[0045] A polystyrene-based resin may be used as the component constituting the tie layer, taking into consideration compatibility with the components constituting the skin layer / seal layer and core layer, and maintaining improved transparency and low-temperature shrinkage. Examples of such polystyrene-based resins include styrene-ethylene-butylene-styrene copolymer (SEBS), styrene-ethylene-propylene-styrene copolymer (SEPS), styrene-butadiene-styrene copolymer (SBS), styrene-isoprene-styrene copolymer (SIS), and styrene-butadiene copolymer (SBC). Preferably, styrene-ethylene-butylene-styrene copolymer (SEBS) may be used.

[0046] The resin composition of each layer constituting the shrink label film of the present invention may further contain one or more additives, such as antioxidants, catalyst neutralizers, pigments, dispersants, weathering agents, antistatic agents, UV stabilizers, talc, etc., as needed, so long as the object of the present invention is not impaired. The amount of such additives used can be adjusted taking into account the total production volume and production process, within the range known to be usable for producing the shrink label film of the present invention without affecting its properties.

[0047] In the present invention, the film using the above components can be produced by a conventional method known in the art. For example, the components constituting each layer are mixed in the required amounts in a mixer, and then pelletized at 180 to 240°C using an extruder. The pellets are then melt-molded into a film using a multi-layer film-molding machine to produce a shrink label film.

[0048] In this case, a multilayer film molding machine is used to form a sheet having a thickness of 175 to 200 μm, with a skin layer:core layer:seal layer thickness ratio of, for example, 1:5 to 10:0.5 to 1.5. The sheet is then stretched at a stretching ratio of 3.5 to 5 times under conditions of a stretching section at 80 to 85°C, a preheating section at 95 to 100°C, and a heat setting section at 75 to 80°C, to produce a film having a final thickness of about 50 μm.

[0049] The shrink label film according to the present invention can provide a shrink label film having improved loop stiffness and low-temperature shrinkability while maintaining improved seaming properties and transparency as a non-adhesive label having a specific gravity of less than 1. More specifically, the shrink label film according to the present invention has a density of 1 g / cm 3 The shrinkage measured by the method described below may be 50% or more, preferably 60% or more, the loop stiffness may be 6 gf / 50 μm or more, preferably 6.5 gf / 50 μm or more, and the haze (ASTM D1003, thickness 50 μm) may be less than 5%, preferably less than 3%.

[0050] [Method for measuring shrinkage rate] The film stretched in the transverse direction (TD) was cut into a size of 50 mm x 50 mm, and immersed in a hot water bath at 100°C for 10 seconds each, after which the dimensions were measured. The transverse direction (TD) shrinkage was calculated using the following formula 1 and shown as the average shrinkage.

[0051]

number

[0052] [Loop stiffness measurement method] Using a LOOP STIFFNESS TESTER (TOYOSEIKI), the stretched film is cut into a size of 25mm x 150mm, and the left and right clamps (film fixing device) of the tester are fixed with a distance of 50mm. The part that protrudes outside the clamps is cut off, and the film is bent so that the distance between the clamps disappears. The load (gf) applied to the end of the loop-shaped test piece formed by bending the film so that the clamp distance disappears is measured by pressing it with a loading device at a speed of 60mm / min. [Example]

[0053] The present invention will be described in more detail with reference to the following specific examples and comparative examples. The specifications of the components used in the examples and comparative examples are summarized in Table 1 below, and the methods for measuring physical properties are as follows.

[0054] [Measurement method] - Density: Measured by the density gradient tube method of ASTM D1505. Melt index: Measured in accordance with ASTM D1238 under the temperature and load conditions described in Item 1 below. Melting point (Tm): Measured according to ASTM D3418. Using a differential scanning calorimeter (DSC, manufactured by TA Instruments), 10 mg of a specimen was pre-melted at 220°C for 5 minutes under a nitrogen gas atmosphere, and then the temperature was decreased to 40°C at a rate of 10°C / min. The temperature was then increased at a rate of 10°C / min, and the peak temperature of the maximum peak of the obtained melting endothermic curve was defined as the melting point (Tm). - Glass transition temperature (Tg): Measured according to ASTM D3418. Using a differential scanning calorimeter (DSC, TA Instruments), 10 mg of specimen was pre-melted at 220°C for 5 minutes under a nitrogen gas atmosphere, and then the temperature was decreased to -80°C at a rate of 10°C / min. The temperature was then increased at a rate of 10°C / min, and the midpoint between the heights of the onset and end points of the glass transition was calculated and defined as the glass transition temperature (Tg). - Softening point (VICAT): Measured according to the ASTM D1525 standard (ASTM E28 standard for petroleum resins). In the penetration test, a load of 1 kg or 5 kg is applied to a 3 mm thick specimen, and the temperature is raised uniformly at a rate of 50°C / hr. 2 The softening point was defined as the temperature at which a standard needle penetrated 1 mm into the paper piece.

[0055] [Table 1]

[0056] <Examples and Comparative Examples> Melt mixtures (using a twin-screw extruder) were prepared for each layer using the compositions shown in Table 2 below, and then the mixtures for each layer were molded into sheets with thicknesses of 175 to 200 μm using a multi-layer film extruder, with the skin layer / seal layer (total thickness of the same level), tie layer, and core layer thickness ratios set forth in Table 2. These sheets were then stretched at a stretching ratio of 3.8 to 4.8 times under conditions of a stretching zone of 80 to 85°C, a preheating zone of 98°C, and a heat setting zone of 78°C to produce films with a final thickness of 50 μm. The cross-sections of the films prepared in Example 1 were photographed using a scanning electron microscope (SEM), and the results are shown in Figure 2.

[0057] <Test example> The physical properties of the prepared film were measured by the following methods, and the results are shown in Table 2 below.

[0058] [Method of measuring physical properties] -Shrinkage rate: The film stretched in the transverse direction (TD) was cut into a size of 50 mm x 50 mm, and immersed in a hot water bath at 100°C for 10 seconds each, after which the dimensions were measured. The shrinkage rate in the transverse direction (TD) was calculated according to the following formula 1 and expressed as the average shrinkage rate.

[0059]

number

[0060] - Seaming: Solvent (toluene, chloroform, limonene, or α-pinene) was applied to a cotton swab to check for adhesion between the outer and rear surfaces of the stretched film (see Figure 3). Haze: Measured according to the ASTM D1003 standard. - Loop stiffness: Using a LOOP STIFFNESS TESTER (TOYOSEIKI), the stretched film was cut into a size of 25mm x 150mm and fixed with a 50mm gap between the left and right clamps (film fixing device) of the testing machine. The parts sticking out from the clamps were cut off and the film was bent so that the gap between the clamps disappeared. The load (gf) applied to the edge of the loop-shaped test piece formed by bending it was measured when the load device pressed it at a speed of 60mm / min. - Interlayer delamination: If delamination occurred between the skin layer and the core layer of the final stretched film, it was marked with "x", and if no delamination occurred, it was marked with "o".

[0061] [Table 2]

[0062] Referring to Table 2, it can be seen that when a first polystyrene-based resin is used for the skin layer and the seal layer according to the present invention and the core layer is composed of a copolymer of propylene and two or more olefins selected from ethylene and α-olefins, a petroleum resin, and a polyolefin elastomer, the low-temperature shrinkability and loop rigidity are improved while maintaining improved seaming properties and transparency. It can also be seen that these effects are significantly improved when PBR is used as the polyolefin elastomer for the core layer (Examples 2 and 4) or when a mixture of two or more first polystyrene-based resins is used for the skin layer and the seal layer (Examples 5 and 6).

[0063] In contrast, when a conventional cyclic olefin is used in the skin layer and seal layer (Comparative Example 1), good seaming and delamination properties are exhibited even without a tie layer, but the transparency, loop rigidity, and low-temperature shrinkage properties are generally inferior to those of the Examples.It can be seen that when a first polystyrene-based resin is used in the skin layer and seal layer but a tie layer is not used (Comparative Example 2), delamination occurs.

[0064] Furthermore, when a propylene homopolymer is used in the core layer (Comparative Example 3), it is difficult to form a film because the stretching temperature is insufficient and stretching is not possible. When the elastomer content in the core layer is excessive (Comparative Example 4), the density is low and transparency is improved, but the loop rigidity is reduced, making the film unsuitable for labeling processes. When the petroleum resin content in the core layer is excessive (Comparative Example 5), the transparency is reduced due to increased density and migration of low molecules, and the improvement in shrinkage and loop rigidity relative to increased content is not further apparent.

[0065] Although the preferred embodiments of the present invention have been described in detail above, the description of the present invention is for illustrative purposes only, and it should be understood by those skilled in the art that the present invention may be easily modified into other specific forms without changing the technical concept or essential features of the present invention.

[0066] Therefore, the scope of the present invention is indicated by the claims below rather than the above detailed description, and all modifications and variations derived from the meaning, scope and equivalent concepts of the claims should be interpreted as being included within the scope of the present invention.

Claims

1. A shrink label film comprising a skin layer, a core layer, and a seal layer, the skin layer and the seal layer comprise a first polystyrene-based resin; the core layer comprises 40 to 90 parts by weight of a copolymer of propylene and two or more olefins selected from ethylene and α-olefins, 5 to 30 parts by weight of a petroleum resin having a softening point of 120 to 140°C, and 5 to 30 parts by weight of a polyolefin elastomer; The shrink label film further comprises tie layers each containing a second polystyrene resin between the skin layer and the core layer and between the core layer and the seal layer.

2. 2. The shrink label film of claim 1, wherein the first polystyrene-based resin is at least one selected from the group consisting of general-purpose polystyrene (GPPS), high-impact polystyrene (HIPS), styrene-butadiene-styrene copolymer (SBS), styrene-isoprene-styrene copolymer (SIS), styrene-ethylene-butylene-styrene copolymer (SEBS), and styrene-butadiene copolymer (SBC).

3. The shrink label film according to claim 1, wherein the copolymer has a melting point (Tm) of 123 to 138°C and a melt index (230°C, 2.16 kg load) of 2 to 10 g / 10 min, and the two olefins are ethylene and 1-butene.

4. 2. The shrink label film of claim 1, wherein the ethylene and 1-butene are each contained in an amount of 1 to 5% by weight of the copolymer.

5. The polyolefin elastomer has a density of 0.85 to 0.9 g / cm ３ 2. The shrink label film according to claim 1, characterized in that the shrink label film is made of propylene-ethylene rubber (PER) or propylene-butene rubber (PBR) having a melt index (230°C, 2.16 kg load) of 0.5 to 10 g / 10 min.

6. 2. The shrink label film of claim 1, wherein the second polystyrene-based resin is at least one selected from the group consisting of styrene-ethylene-butylene-styrene copolymer (SEBS), styrene-ethylene-propylene-styrene copolymer (SEPS), styrene-butadiene-styrene copolymer (SBS), styrene-isoprene-styrene copolymer (SIS), and styrene-butadiene copolymer (SBC).

7. The film has a density of 1 g / cm ３ The shrinkable label film according to claim 1, characterized in that the shrinkage rate measured by the following method is 50% or more and the loop stiffness is 6 gf / 50 μm or more: [Method for measuring shrinkage rate] The film stretched in the transverse direction (TD) was cut into a size of 50 mm x 50 mm, and immersed in a hot water bath at 100°C for 10 seconds each, after which the dimensions were measured. The transverse direction (TD) shrinkage was calculated using the following equation 1 and expressed as an average shrinkage. [Equation 1] [Method for measuring loop stiffness] Using a LOOP STIFFNESS TESTER (manufactured by TOYOSEIKI), the stretched film was cut into a size of 25 mm x 150 mm, and the left and right clamps (film fixing device) of the tester were fixed with a gap of 50 mm. The portion protruding outside the clamps was cut off, and the film was bent so that the gap between the clamps disappeared. The load (gf) applied to the end of the loop-shaped test piece formed by bending the film so that the edge of the loop-shaped test piece was pressed with a loading device at a speed of 60 mm / min was measured.

8. 8. The shrink label film of claim 7, wherein the film has a haze (ASTM D1003, thickness 50 μm) of less than 5%.

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