Olefin-based heat-shrinkable multilayer film

Abstract

Provided is an olefin-based heat-shrinkable multilayer film that is substantially free of a cyclic olefin-based resin, is easy to use for solvent bonding and gravity separation, and has excellent heat shrinkability and transparency.　The olefin-based heat-shrinkable multilayer film comprises a first surface layer and a second surface layer, which are derived from a polystyrene-based resin, and an intermediate layer derived from a polyolefin-based resin, wherein (a) the polystyrene-based resin contains at least 50 wt% of a styrene-butadiene copolymer, (b) the crystal melting enthalpy of the intermediate layer is set to a value of 135 mJ / mg or less, (c) the thermal shrinkage rate in the TD direction is 50-80% under the shrinkage conditions of 100°C and 10 seconds, (d) the haze value is 10% or less, and (e) the specific gravity is 0.95 or less.

Description

Olefin-based heat-shrinkable multilayer film

[0001] The present invention relates to an olefin-based heat-shrinkable multilayer film (hereinafter sometimes simply referred to as a heat-shrinkable film), and particularly to an olefin-based heat-shrinkable multilayer film that is substantially free of a cyclic olefin resin, is easy to solvent bond and gravity separate, and has excellent heat shrinkability, transparency, etc.

[0002] In recent years, a wide variety of heat-shrinkable films have been widely used for the purpose of packaging with heat-shrinkable films that protect glass bottles or plastic bottles and also display products in order to improve the appearance of the packaged products. Known base resins for such heat-shrinkable films include polyvinyl chloride resins, polystyrene resins, polyester resins, and polyolefin resins.

[0003] However, heat-shrinkable films made of polyvinyl chloride resins have excellent heat shrinkability, but have environmental problems such as the tendency to generate chlorine gas when burned. On the other hand, heat-shrinkable films made of polystyrene resins or polyester resins as the main raw materials have relatively good heat shrinkability, but have the problem that their specific gravity difference from the PET resin that makes up PET bottles is small, making gravity separation using water or the like difficult and resulting in poor recyclability. In contrast, heat-shrinkable films made of polyolefin resins have the advantage that their specific gravity difference from PET bottles is large, making gravity separation using water or the like relatively easy, but the film itself is difficult to solvent-bond, resulting in the problem that conventional cylindrical heat-shrinkable film manufacturing equipment cannot be used as is.

[0004] Therefore, it has been proposed to blend, for example, a cyclic olefin resin as one of the constituent components of a polyolefin resin (see Patent Document 1). More specifically, 3The heat-shrinkable laminated film is obtained by stretching the laminate at least uniaxially by 2 to 6 times, using an intermediate layer made of an olefin-based resin and an adhesive resin of less than 1 / 200 mm thick, and providing a surface layer and a back layer made of a styrene-based resin on the front and back surfaces of the intermediate layer, respectively, to form a laminate, the thicknesses of the layers of the laminate being in the relationship of (surface layer + back layer) / intermediate layer = 1 / 1 to 1 / 6.

[0005] A heat-shrinkable laminated porous film having a porous polyolefin-based resin layer has also been proposed (see Patent Document 2). More specifically, the heat-shrinkable laminated porous film has a pair of front and back layers whose main component is at least one selected from the group consisting of copolymer resins (A) of styrene-based hydrocarbons and conjugated diene-based hydrocarbons, and a porous layer disposed between the pair of front and back layers and whose main component is a resin composition containing a polyolefin-based resin (B) and a filler (C), and is stretched in at least one direction to have a porosity within a predetermined range.

[0006] JP 2000-309071 A (Claims, etc.) JP 2018-153984 A (Claims, etc.)

[0007] However, in the case of the heat-shrinkable laminate film of Patent Document 1 and the like, when a cyclic olefin resin is blended, the resulting film becomes hard and brittle, and there are problems that it is prone to tearing and delamination during secondary processing such as printing. Furthermore, when a cyclic olefin resin is blended into the main component of the heat-shrinkable film, there is also a problem that the compatibility with other resins decreases, and the transparency of the film is likely to decrease. Furthermore, since cyclic olefin resins are relatively expensive, blending them as a constituent material increases the production cost of the heat-shrinkable film, which is economically disadvantageous.

[0008] Furthermore, in the case of the heat-shrinkable laminated porous film of Patent Document 2 and the like, there is a problem in that it is difficult to control the porosity value and, in turn, the specific gravity during production, which results in variations in the specific gravity value, making it difficult to separate the films by specific gravity during recycling, and furthermore, there are problems such as deterioration in the transparency, heat shrinkability, and mechanical properties of the film.

[0009] The present invention has been made in light of the above-mentioned problems, and its object is to provide a heat-shrinkable multilayer film that is easy to solvent bond and gravity separate, and has excellent heat shrinkability, transparency, etc., without substantially incorporating a cyclic olefin resin.

[0010] According to the present invention, there is provided an olefin-based heat-shrinkable multilayer film that can solve the above-mentioned problems, comprising an intermediate layer derived from a polyolefin-based resin, a first surface layer (usually the top surface side) derived from at least a polystyrene-based resin on one surface side of the intermediate layer (usually the top surface side), and a second surface layer (usually the back surface side) derived from at least a polystyrene-based resin on the other surface side of the intermediate layer, and that satisfies the following characteristics (a) to (e): (a) the polystyrene-based resin contains 50 wt % or more of a styrene-butadiene copolymer based on the total weight of the film; and (b) the crystalline melting enthalpy (ΔH) of the intermediate layer, measured by DSC in accordance with JIS K 7121:2012 (corresponding to ISO 11357-2:2013), is 135 mJ / mg or less. (c) When the heat shrinkage percentage in the main shrinkage direction when shrunk for 10 seconds in boiling water at 100°C is defined as A1, A1 is set to a value within the range of 50 to 80%. (d) The haze value measured in accordance with JIS K 7136:2000 (corresponding to ISO 14782:1999) is set to 10% or less. (e) The specific gravity measured in accordance with JIS K 7112-1:2023 (corresponding to ISO 1183-1:2023) is set to 0.95 or less. Thus, by satisfying at least the requirements (a) to (e), solvent adhesion and specific gravity separation are facilitated, and excellent heat shrinkability, transparency, etc. can be obtained without substantially incorporating a cyclic olefin resin.

[0011] In constructing the olefin-based heat-shrinkable multilayer film of the present invention, it is preferable that the molecular weight distribution (Mw / Mn) of the polyolefin-based resin constituting the intermediate layer is set to a value of 4.0 or less as the configuration (f). By limiting the molecular weight distribution (Mw / Mn) of the polyolefin-based resin constituting the intermediate layer to a predetermined range in this way, it is possible to obtain excellent heat shrinkability, light weight, transparency (low haze), etc.

[0012] In constructing the olefin-based heat-shrinkable multilayer film of the present invention, the intermediate layer preferably contains linear low-density polyethylene as the polyolefin-based resin. By containing linear low-density polyethylene as the polyolefin-based resin constituting the intermediate layer in this manner, it is possible to suppress variations in the specific gravity of the film and achieve further weight reduction.

[0013] In constructing the olefin-based heat-shrinkable multilayer film of the present invention, it is preferable that the weight-average molecular weight of the polyolefin-based resin constituting the intermediate layer is set to a value within the range of 150,000 to 250,000. By limiting the weight-average molecular weight (Mw) of the polyolefin-based resin constituting the intermediate layer to a predetermined range in this way, it is possible to obtain excellent heat shrinkability, as well as excellent lightness, transparency, etc.

[0014] In constructing the olefin-based heat-shrinkable multilayer film of the present invention, it is preferable that the polystyrene-based resin constituting the first surface layer and / or the second surface layer contains a styrene-based elastomer. By using a styrene-based resin constituting the first surface layer and / or the second surface layer that contains a styrene-based elastomer, particularly a hydrogenated styrene-based elastomer, the transparency is further improved and interlayer delamination can be effectively suppressed.

[0015] In constructing the olefin-based heat-shrinkable multilayer film of the present invention, it is preferable that the polystyrene-based resin constituting the first surface layer and / or the second surface layer contains a compatibilizer. By containing a compatibilizer in the styrene-based resin constituting the first surface layer and / or the second surface layer, the film has excellent transparency and can effectively suppress delamination.

[0016] In constructing the olefin-based heat-shrinkable multilayer film of the present invention, it is preferable that the thickness of the film after stretching is set to a value within the range of 10 to 60 μm. By setting the thickness of the heat-shrinkable film to a value within the predetermined range, not only is the film easy to use, but also the film has even better transparency, and excellent heat shrinkability and mechanical properties.

[0017] In constructing the olefin-based heat-shrinkable multilayer film of the present invention, it is preferable to set the thickness ratio (t2+t3) / (t1) to a value within the range of 0.1 to 0.5, where t1 is the thickness of the intermediate layer before stretching, t2 is the thickness of the first surface layer before stretching, and t3 is the thickness of the second surface layer before stretching. By setting the ratio of the thickness of the intermediate layer (t1) to the sum (t2+t3) of the thicknesses of the first and second surface layers before stretching within this range, not only is the heat-shrinkable film easy to use, but excellent heat shrinkability, mechanical properties, etc. can also be obtained.

[0018] FIGS. 1(a) to 1(c) are diagrams each used to explain the configuration and usage of a heat-shrinkable film. FIG. 2 is a chart showing the molecular weight distribution of a resin constituting an intermediate layer in a heat-shrinkable film. FIG. 3 is a DSC chart of a resin constituting an intermediate layer in a heat-shrinkable film. FIG. 4 is a diagram used to explain the relationship between the crystalline melting enthalpy of an intermediate layer in a heat-shrinkable film and the thermal shrinkage rate in the TD direction. FIG. 5 is a diagram used to explain the relationship between the crystalline melting enthalpy of an intermediate layer in a heat-shrinkable film and the haze. FIG. 6 is a diagram used to explain the relationship between the crystalline melting enthalpy of an intermediate layer in a heat-shrinkable film and the specific gravity. FIG. 7 is a diagram used to explain the relationship between the SBC content in the surface layer of a heat-shrinkable film and the haze. FIG. 8 is a diagram used to explain the relationship between the ratio of the total thickness of the surface layer (t2 + t3) to the thickness of the intermediate layer (t1) and the haze in a heat-shrinkable film.

[0019] 1(a) to 1(c), the first embodiment is an olefin-based heat-shrinkable multilayer film 10 including an intermediate layer 10a derived from a polyolefin-based resin, a first surface layer 10b derived from at least a polystyrene-based resin on one surface side of the intermediate layer 10a, and a second surface layer 10c derived from at least a polystyrene-based resin on the other surface side of the intermediate layer 10a, the olefin-based heat-shrinkable multilayer film 10 being characterized by satisfying the following configurations (a) to (e): (a) the polystyrene-based resin contains 50 wt% or more of a styrene-butadiene copolymer based on the total weight of the polystyrene-based resin; and (b) the crystalline melting enthalpy (ΔH) of the intermediate layer, as measured by DSC in accordance with JIS K 7121:2012 (corresponding to ISO 11357-2:2013), is 135 mJ / mg or less. (c) When the heat shrinkage rate in the main shrinkage direction is A1 when shrunk for 10 seconds in boiling water at 100°C, A1 is set to a value within the range of 50 to 80%. (d) The haze value measured in accordance with JIS K 7136:2000 (corresponding to ISO 14782:1999) is set to 10% or less. (e) The specific gravity measured in accordance with JIS K 7112-1:2023 (corresponding to ISO 1183-1:2023) is set to 0.95 or less. Note that Figure 1(a) shows the basic structure of an olefin-based heat-shrinkable multilayer film 10 consisting of a three-layer structure. Figure 1(b) shows a structure in which a decorative layer 10d is provided on the outer side (the bottom layer in the drawing) of the second surface layer 10c of the olefin-based heat-shrinkable multilayer film 10. Furthermore, FIG. 1(c) is a diagram showing a state in which the olefin-based heat-shrinkable multi-layer film 10 provided with the decorative layer 10d of FIG. 1(b) is applied to a PET bottle.

[0020] 1. Basic Structure (1) Intermediate Layer As illustrated in Figures 1(a) to 1(c), the olefin-based heat-shrinkable multilayer film 10 is characterized by the provision of an intermediate layer 10a derived from a polyolefin-based resin between a first surface layer 10b and a second surface layer 10c. This is because polyolefin-based resins can exhibit the properties of a heat-shrinkable film by utilizing crystallization due to stretching or the like. Furthermore, polyolefin-based resins have excellent transparency (haze) and light weight (specific gravity), and therefore can be recycled accurately and quickly using a specific gravity separation device or the like using a specified cyclone device or the like. Therefore, among polyolefin-based resins, polyethylene-based resins in particular have superior transparency, crystallinity (heat shrinkage rate), light weight (specific gravity), and the like compared to polypropylene and the like.

[0021] 1(a) to 1(c), the olefin-based heat-shrinkable multilayer film 10 is characterized by having a first surface layer 10b derived from at least a polystyrene-based resin on one surface side of an intermediate layer 10a, and a second surface layer 10c derived from at least a polystyrene-based resin on the other surface side of the intermediate layer 10a. The reason for this is that an intermediate layer derived from a polyolefin-based resin has low surface energy, which makes it difficult to achieve solvent adhesion and paintability, and can make the film difficult to use. In other words, by forming a first surface layer and a second surface layer derived from a polystyrene-based resin, which have excellent solvent adhesion and paintability, on both sides of the intermediate layer derived from a polyolefin-based resin, the solvent adhesion, paintability, etc. of the intermediate layer derived from a polyolefin-based resin can be easily improved.

[0022] 1(a) to 1(c), it is advantageous to use an olefin-based heat-shrinkable multilayer film 10 having a multilayer structure that basically includes an intermediate layer 10a derived from a polyolefin-based resin, a first surface layer 10b derived from a polystyrene-based resin, and a second surface layer 10c also derived from a polystyrene-based resin. The reason for this is that, although a two-layer structure may be practically acceptable for an olefin-based heat-shrinkable multilayer film, a three-layer structure is basically easy to manufacture and, further, makes it easier to obtain uniform heat shrinkability, etc., regardless of whether it is on the front or back.

[0023] In constructing the olefin-based heat-shrinkable multilayer film of the present invention, it is preferable not to include an adhesive layer (including a primer layer) between the intermediate layer and the first and second surface layers. The reason for this is to achieve the desired specific gravity, thickness, and heat shrinkage rate management and control for the olefin-based heat-shrinkable multilayer film. Conversely, if an adhesive layer (including a primer layer) is included between the intermediate layer and the first and second surface layers, it may become difficult to manage the specific gravity, resulting in a decrease in lightness, or the film may become excessively thick, making it difficult to manage and control the heat shrinkage rate. Moreover, it may increase the number of manufacturing steps, making it difficult to provide a stable and economical olefin-based heat-shrinkable multilayer film.

[0024] 2. Specific Structure (1) Ingredients of the Intermediate Layer The type of polyolefin resin constituting the intermediate layer is preferably determined taking into consideration the transparency, heat shrinkage, molecular weight distribution, etc. of the resulting film. Basically, however, polymers containing olefin hydrocarbons such as ethylene and propylene as monomer components can be used. The polyolefin resin may be a homopolymer or a copolymer. In the case of a copolymer, the copolymerization ratio of the olefin hydrocarbon, such as ethylene, butene, or hexene, is preferably 50% by weight or more (same as "mass %" below), and may be 70% by weight or more, or even 90% by weight or more. Therefore, examples of such polyolefin resins include polyethylene resins, 1-hexene copolymers, and ethylene-propylene copolymers. Linear low-density polyethylene (LLDPE) is particularly preferred.

[0025] Furthermore, there are no particular limitations on the catalyst used when polymerizing the polyolefin resin, and Ziegler-Natta catalysts, metallocene catalysts, etc. can be used. However, it is also preferable to use polyolefin resins (isotactic, syndiotactic, etc.) obtained using metallocene catalysts, as this makes it easier to obtain polyolefin resins with excellent stereoregularity, mechanical strength, etc. Furthermore, the polyolefin resin used may have any crystallinity or melting point, and a polyolefin resin composition in which two polyolefin resins with different properties are blended in specific ranges may be used depending on the physical properties and application of the resulting film.

[0026] (2) Molecular Weight Distribution of Polyolefin Resin Constituting the Intermediate Layer It is preferable to set the weight-average molecular weight (Mw) of such an olefin resin to a value within the range of 150,000 to 250,000. This is because such a weight-average molecular weight (Mw) makes it easier to obtain an olefin-based heat-shrinkable multilayer film with low haze and a controlled heat shrinkage rate. It is also preferable to set the number-average molecular weight (Mn) of such an olefin-based resin to a value within the range of 50,000 to 100,000. This is because such a number-average molecular weight (Mn) of the olefin-based resin makes it easier to obtain an olefin-based heat-shrinkable multilayer film with low haze and a controlled heat shrinkage rate. Note that Figure 2 shows charts (Types A to E) showing the molecular weight distribution of the resin constituting the intermediate layer.

[0027] Therefore, since the haze, heat shrinkage, etc. can be easily controlled by the olefin resin having such a weight average molecular weight (Mw) and number average molecular weight (Mn), it is preferable that the molecular weight distribution (Mw / Mn) is also set to a value of 4.0 or less. The reason for this is that controlling the molecular weight distribution (Mw / Mn) of the polyolefin resin constituting the intermediate layer further improves the transparency, crystallinity (heat shrinkage), etc.

[0028] As shown in Figure 3, the weight average molecular weight (Mw) and number average molecular weight (Mn) of the olefin resin, as well as the molecular weight distribution (Mw / Mn) based on these, can be measured using high-temperature GPC. More specifically, for example, using an HLC-8321GPC / HT (manufactured by Tosoh Corporation), dichlorobenzene is used as a solvent, and the column temperature is 145°C, and the weight average molecular weight (Mw) of the olefin resin can be calculated by comparing with a calibration curve based on standard styrene particles.

[0029] (3) Crystalline Melting Enthalpy (ΔH) of the Intermediate Layer Measured by DSC The intermediate layer is characterized by having a crystalline melting enthalpy (ΔH) measured by DSC of 135 mJ / mg or less. The reason for this is that controlling the crystalline melting enthalpy, commonly referred to as the heat of fusion, makes it easier to obtain a desirable heat shrinkage rate and also improves transparency. More specifically, if the crystalline melting enthalpy exceeds 135 mJ / mg, for example, the heat shrinkage rate under shrinkage conditions of 100°C and 10 seconds is significantly reduced. Moreover, if the crystalline melting enthalpy exceeds 135 mJ / mg, transparency also tends to decrease. However, if the crystalline melting enthalpy is excessively small, crystallinity will be reduced, which may make it difficult to control the heat shrinkage rate. Therefore, the crystalline melting enthalpy of the intermediate layer measured by DSC is preferably set to a value within a range of 100 to 130 mJ / mg, and more preferably a value within a range of 110 to 125 mJ / mg. The crystalline melting enthalpy of the intermediate layer can be measured using a DSC (differential scanning calorimeter) in accordance with JIS K 7121:2012 (corresponding to ISO 11357-2:2013).

[0030] Here, referring to Figure 4, based on the data of Example 1 and the like, the relationship between the crystalline melting enthalpy (ΔH) of the polyolefin resin constituting the intermediate layer and the thermal shrinkage rate in the transverse direction (100°C, 10 seconds) will be explained. That is, the horizontal axis represents the crystalline melting enthalpy of the polyolefin resin, and the vertical axis represents the thermal shrinkage rate in the transverse direction (%, 100°C, 10 seconds). From the characteristic curve in Figure 4, it can be seen that there is a negative linear correlation between the crystalline melting enthalpy and the thermal shrinkage rate in the transverse direction (%), and that by controlling the crystalline melting enthalpy to 135°C or less, the thermal shrinkage rate in the transverse direction can be controlled within a desired range.

[0031] 5, the relationship between the crystalline melting enthalpy (ΔH) of the polyolefin resin constituting the intermediate layer and the haze (%) will be explained based on the data of Example 1, etc. That is, the horizontal axis represents the crystalline melting enthalpy of the polyolefin resin, and the vertical axis represents the haze (%). From the characteristic curve in FIG. 5, no significant correlation is observed between the crystalline melting enthalpy and the haze (%), and it can be said that approximately the same haze value can be obtained if the crystalline melting enthalpy is in the range of 110 to 140°C.

[0032] Furthermore, referring to Figure 6, the relationship between the crystalline melting enthalpy (ΔH) and specific gravity of the polyolefin resin constituting the intermediate layer will be explained based on the data of Example 1, etc. That is, the horizontal axis shows the crystalline melting enthalpy of the polyolefin resin, and the vertical axis shows the specific gravity. From the characteristic curve in Figure 6, it can be said that there is a positive linear correlation between the crystalline melting enthalpy and the specific gravity, and that by controlling the crystalline melting enthalpy to 135°C or less, the specific gravity can be controlled to a low value of 0.95 or less. Note that, while characteristic curves A and B were obtained based on the data of Example 1, etc., characteristic curve A is presumably due to the fact that the total thickness (t2 + t3) of the surface layer made of polystyrene-based resin is relatively thick, and the relative amount of polystyrene-based resin with a relatively high specific gravity in the entire film is greater than that of polyolefin-based resin with a relatively low specific gravity. Conversely, it is presumed that characteristic curve B is due to the fact that the total thickness (t2 + t3) of the polystyrene-based resin is relatively thin, and the relative amount of polystyrene-based resin, which has a relatively high specific gravity, is less than the amount of polyolefin-based resin, which has a relatively low specific gravity, in the entire film.

[0033] (4) Thickness of Intermediate Layer When the thickness of the intermediate layer before stretching is (t1), it is usually preferable to set the thickness (t1) to a value within the range of 50 to 200 μm. This is because controlling the thickness of the intermediate layer within a predetermined range not only improves usability, but also controls the specific gravity to a value below the desired value, and achieves excellent heat shrinkability, transparency, and the like. More specifically, if the thickness of the intermediate layer is less than 50 μm, it may be difficult to adjust the specific gravity or the handling may be significantly reduced. On the other hand, if the thickness of the intermediate layer is greater than 200 μm, it may decrease transparency, make it difficult to achieve a uniform thickness, and even be prone to interlayer delamination. Therefore, it is more preferable to set the thickness of the intermediate layer to a value within the range of 80 to 150 μm, and even more preferable to set it to a value within the range of 100 to 130 μm.

[0034] (5) Component 1 of the First Surface Layer and the Second Surface Layer The polystyrene resin constituting the first surface layer, the second surface layer, or either one of them preferably contains 50 wt% or more of styrene-butadiene copolymer (SBC) relative to the total amount (100 wt%). The reason for this is that if the SBC content is less than 50 wt%, the transparency of the resulting film may be significantly reduced. Therefore, the SBC content is more preferably 60 wt% or more, and even more preferably 70 wt% or more, relative to the total amount (100 wt%) of at least one of the first surface layer and the second surface layer. The types of residual components other than SBC in the first surface layer and the second surface layer are not particularly limited, but typically include polymers other than styrene-butadiene copolymer (SBC) and compatibilizers, as described below.

[0035] Furthermore, it is preferable that the polystyrene-based resin constituting the first surface layer, the second surface layer, or either one of them contains a styrene-based elastomer. The reason for this is that the inclusion of a styrene-based elastomer as a type of styrene-butadiene copolymer (SBC) improves adhesion with the intermediate layer, effectively suppresses delamination, and further facilitates achieving a favorable heat shrinkage rate. Therefore, when a styrene-based elastomer is contained, the content of the styrene-based elastomer is typically preferably within a range of 1 to 30 wt %, more preferably within a range of 2 to 20 wt %, and even more preferably within a range of 3 to 10 wt %, relative to the total weight (100 wt %) of at least one of the first surface layer and the second surface layer. Examples of the styrene-based elastomer include styrene-butadiene block copolymers, styrene-butadiene / butylene-styrene triblock copolymers, styrene-ethylene-butylene-styrene block copolymers, and styrene-ethylene / butylene-styrene triblock copolymers (each of which includes a thermoplastic elastomer), either alone or in combination.

[0036] (6) Component 2 of the First and Second Surface Layers Furthermore, it is preferable that the polystyrene-based resin constituting the first and / or second surface layer is a polymer other than the styrene-based elastomer and further contains a compatibilizer. This is because the inclusion of a compatibilizer improves adhesion with the intermediate layer, effectively suppresses delamination, and facilitates obtaining a good thermal shrinkage rate. Therefore, when a compatibilizer is contained, the content of the compatibilizer is typically preferably within a range of 1 to 30 wt %, more preferably within a range of 2 to 20 wt %, and even more preferably within a range of 3 to 10 wt %, relative to the total weight (100 wt %) of at least one of the first and second surface layers.

[0037] As the compatibilizer, various compounds and polymers can be used as long as they exhibit the desired compatibility, but for example, a polymer other than the above-mentioned styrene-based elastomer that is compatible with the styrene-based elastomer and exhibits good compatibility is preferred as a styrene-based compatibilizer (such as a hydrogenated elastomer resin). That is, examples of the styrene-based compatibilizer (hydrogenated elastomer resin) include hydrogenated elastomers of styrene-butadiene block copolymers, hydrogenated elastomers of styrene-butadiene / butylene-styrene triblock copolymers, hydrogenated elastomers of styrene-ethylene-butylene-styrene block copolymers, hydrogenated elastomers of styrene-butadiene block copolymers having functional groups (carboxyl groups, hydroxyl groups, etc., hereinafter the same), hydrogenated elastomers of styrene-butadiene / butylene-styrene triblock copolymers having functional groups, and hydrogenated elastomers of styrene-ethylene-butylene-styrene block copolymers having functional groups. Preferred are hydrogenated elastomers of polymers, hydrogenated elastomers of styrene-ethylene / butylene-styrene triblock copolymers having functional groups, hydrogenated elastomers of styrene-ethylene / butylene-styrene triblock copolymers, oligomers of styrene-butadiene block copolymers, oligomers of styrene-butadiene / butylene-styrene triblock copolymers, oligomers of styrene-ethylene-butylene-styrene block copolymers, oligomers of styrene-ethylene / butylene-styrene triblock copolymers, and further, oligomers of these various tackifiers, etc., used alone or in combination of two or more. Therefore, when these styrene-based compatibilizers contain a butadiene moiety in the molecule, it is more preferable that the butadiene moiety has been hydrogenated, since this more effectively adjusts compatibility, heat resistance, transparency, etc., and it is also preferable that the butadiene moiety has a functional group (such as a carboxyl group or a hydroxyl group; the same applies hereinafter). Furthermore, when these styrene-based compatibilizers are used, the compatibility, heat resistance, flowability, and the like can be more effectively adjusted, and therefore the styrene content contained therein is preferably set to a value within a range of 10 to 80% by weight, more preferably a value within a range of 30 to 75% by weight, and even more preferably a value within a range of 50 to 70% by weight, based on the total weight.In order to facilitate plasticization and improve compatibility in the styrene-based compatibilizer, it is preferable that a tackifier is blended in an amount of usually 10 to 100 parts by weight per 100 parts by weight of the main component of the compatibilizer.

[0038] (7) Thickness of the First and Second Surface Layers When the thickness of the first surface layer before stretching is t2 and the thickness of the second surface layer before stretching is t3, it is generally preferable to set the total thickness (t2 + t3) of the first and second surface layers to a value within the range of 10 to 80 μm. This is because controlling this total thickness within a predetermined range not only improves usability, but also controls the specific gravity to a value below the desired value, and achieves excellent heat shrinkability, transparency, and the like. More specifically, if this total thickness is less than 10 μm, it may be difficult to adjust the specific gravity or the handleability may be significantly reduced. On the other hand, if this total thickness exceeds 80 μm, it may be difficult to achieve a uniform thickness or adjust the specific gravity. Therefore, it is more preferable that the total thickness of the first surface layer before the stretching treatment and the second surface layer before the stretching treatment is a value within the range of 20 to 60 μm, and even more preferable that it is a value within the range of 30 to 50 μm.

[0039] The thickness (t2) of the first surface layer and the thickness (t3) of the second surface layer before stretching may be different, taking into consideration the application and ease of use of the film. Therefore, when the thickness (t3) of the second surface layer is made thicker than the thickness (t2) of the first surface layer (in the ratio (t2) / thickness (t3) of the first surface layer, the ratio (t2 / t3) is preferably set to a value within the range of 0.1 to 0.9, more preferably a value within the range of 0.2 to 0.8, and even more preferably a value within the range of 0.3 to 0.7. Of course, when the thickness (t3) of the second surface layer is made thinner than the thickness (t2) of the first surface layer (in the ratio (t2) / thickness (t3) of the second surface layer, the ratio is preferably set to a value exceeding 1.1, more preferably a value within the range of 1.2 to 5, and even more preferably a value within the range of 1.5 to 4.

[0040] However, taking into consideration the application and ease of use of the film, as well as the uniformity of the thermal shrinkage rate and ease of production, it is also preferable that the thickness of the first surface layer (t2) / the thickness of the second surface layer (t3) before the stretching treatment be substantially equal. That is, it is preferable that the ratio (t2 / t3) be a value greater than 0.9 but not greater than 1.1, more preferably a value in the range of 0.95 to 1.05, and even more preferably a value in the range of 0.99 to 1.01.

[0041] (8) Additives The olefin-based heat-shrinkable multilayer film has the above-mentioned structure, but may contain, as needed, known resins other than those mentioned above, antioxidants, heat stabilizers, antistatic agents, antiblocking agents, slip agents, nucleating agents, ultraviolet absorbers, colorants, etc., within the scope of not impairing the above-mentioned object of the present invention. Of these, the addition of antistatic agents, antiblocking agents, slip agents, etc. is particularly effective in improving blocking resistance, but excessive addition impairs solvent adhesion, so the amount added must be carefully considered.

[0042] 3. Specific Configuration (1) Heat Shrinkage Ratio When shrunk in boiling water at 100°C for 10 seconds, the heat shrinkage ratio A1 in the main shrinkage direction (TD) is set to a value within the range of 50 to 80%. The reason for this is that if the heat shrinkage ratio A1 is outside this range, the types and average molecular weights of usable polyolefin-based resins and polystyrene-based resins may be excessively limited. Therefore, when shrunk in boiling water at 100°C for 10 seconds, the heat shrinkage ratio A1 in the main shrinkage direction (TD) is preferably set to a value within the range of 55 to 75%, and even more preferably to a value within the range of 58 to 65%.

[0043] (2) Haze Value The haze value of the olefin-based heat-shrinkable multilayer film before heat shrinkage, measured in accordance with JIS K 7136:2000 (equivalent to ISO 14782:1999), is characterized by being 10% or less. By specifically limiting the haze value to a value within a predetermined range, the transparency of the shrink film can be easily controlled quantitatively, and since the transparency is good, versatility can be further enhanced. More specifically, if the haze value of the film before heat shrinkage exceeds 10%, transparency may decrease, making it difficult to apply to decorative applications, etc. On the other hand, if the haze value of the film before heat shrinkage is excessively small, stable control may be difficult, resulting in a significant decrease in production yield. Therefore, as the configuration (m), it is more preferable that the haze value of the film before heat shrinkage be within the range of 1 to 9%, and even more preferably within the range of 2 to 8%.

[0044] Here, with reference to FIG. 7 , the relationship between the SBC content (wt %) blended into the polystyrene-based resin of the surface layer and the haze value (%) will be described. That is, based on the data of Example 1 and the like, the relationship between the SBC content (wt %) and the haze value (%) will be described. That is, the horizontal axis represents the SBC content, and the vertical axis represents the haze. From the characteristic curve in FIG. 7 , it can be seen that there is a curvilinear correlation between the SBC content (wt %) blended into the total amount (100 wt %) of the polystyrene-based resin and the haze value, and that by controlling the SBC content to 50 wt % or more, more preferably 60 wt % or more, the haze can be controlled to a low value of 10% or less.

[0045] (3) Specific Gravity The specific gravity of the olefin-based heat-shrinkable multilayer film after stretching is measured in accordance with JIS K 7112-1:2023 (corresponding to ISO 1183-1:2023), and is characterized by being 0.95 or less. The reason for this is that if the specific gravity exceeds 0.95, gravity separation may require excessive time and effort. However, if the specific gravity is too low, the types and average molecular weights of polyolefin-based resins and polystyrene-based resins that can be used may be excessively limited. Therefore, it is more preferable to set the specific gravity to a value within the range of 0.91 to 0.945, and even more preferable to set it to a value within the range of 0.92 to 0.94.

[0046] (4) Thickness It is usually preferable that the thickness of the olefin-based heat-shrinkable multilayer film after stretching is set to a value within the range of 10 to 60 μm. The reason for this is that by setting the thickness of such a heat-shrinkable multilayer film to a value within the specified range, not only is it easy to use, but it also has better transparency, and excellent heat shrinkability and mechanical properties. Therefore, it is more preferable that the thickness of such a heat-shrinkable multilayer film is set to a value within the range of 20 to 55 μm, and even more preferably to a value within the range of 30 to 50 μm.

[0047] (5) Relationship between the Total Thickness of the First and Second Surface Layers and the Thickness Ratio of the Intermediate Layer 1 When the thickness of the intermediate layer before stretching is t1, the thickness of the first surface layer before stretching is t2, and the thickness of the second surface layer before stretching is t3, the thickness ratio (t2 + t3) / (t1) is preferably set to a value within a range of 0.1 to 0.5. The reason for this, although it depends on the type of raw material, is that by setting the ratio of the thickness of the intermediate layer (t1) to the total thickness (t2 + t3) of the first and second surface layers within a predetermined range, the haze value and specific gravity can be controlled to a low level, improving usability and achieving excellent heat shrinkability. Therefore, it is more preferable to set the thickness ratio (t2 + t3) / (t1) to a value within a range of 0.2 to 0.48, and even more preferably a value within a range of 0.25 to 0.45.

[0048] (6) Relationship 2 between the Total Thickness of the First and Second Surface Layers and the Thickness Ratio of the Intermediate Layer Referring now to Figure 8, the relationship between the thickness ratio (t2 + t3) / (t1) of each layer before stretching and the haze (%) of the heat-shrinkable multilayer film is described. Specifically, the horizontal axis represents the thickness (t2 + t3) / (t1) ratio of the heat-shrinkable multilayer film (corresponding to Example 18) before stretching, and the vertical axis represents the haze value of the heat-shrinkable multilayer film before stretching. Judging from the characteristic curve in Figure 8, it appears that increasing the thickness ratio (t2 + t3) / (t1) tends to significantly increase the resulting haze value. Therefore, in order to maintain the haze value of the heat-shrinkable multilayer film at 10% or less, it is preferable to set the thickness ratio (t2 + t3) / (t1) to a value of approximately 0.5 or less. Although not shown, it has been found that the specific gravity of the heat-shrinkable multilayer film can be easily controlled to a value of 0.95 or less by setting the ratio of thickness (t2+t3) / (t1) to a value within the range of 0.1 to 0.5.

[0049] [Second embodiment] The second embodiment is a method for producing an olefin-based heat-shrinkable multilayer film according to the first embodiment, characterized in that it includes at least first to third steps.

[0050] 1. Raw Material Preparation and Melting Process First, an olefin-based resin is prepared for the intermediate layer, and a polystyrene-based resin is prepared for the first surface layer. Therefore, it is preferable to prepare such raw materials as linear low-density polyethylene (LLDPE), which is suitable as an olefin-based resin, or polystyrene-butadiene copolymer (containing a predetermined amount of SBC, etc.), which is suitable as a polystyrene-based resin. Next, each raw material is weighed and placed into two stirring vessels, and the materials are heated and melted in each stirring vessel until homogeneous.

[0051] 2. Raw Sheet Preparation Process Next, the uniformly mixed raw materials are each dried to an absolute dry state, and then typically extrusion-molded to produce a raw sheet of a predetermined thickness. More specifically, for example, extrusion molding is performed using an extruder (manufactured by Tanabe Plastic Machinery Co., Ltd.) with an L / D of 24 and an extrusion screw diameter of 50 mm at an extrusion temperature of 220°C to obtain a raw sheet of a predetermined thickness (usually 100 to 250 μm). That is, molten LLDPE or the like is placed in an extruder for forming the intermediate layer and melt-kneaded at 180 to 220°C. Meanwhile, polystyrene-butadiene copolymers containing a predetermined amount of SBC or the like are placed in an extruder for forming the first surface layer on the front side and an extruder for forming the second surface layer on the back side, respectively, and melt-kneaded at 180 to 220°C.

[0052] Next, the extrusion rates of the extruders are set so that the thickness ratio of each layer, (t2 / t3) / (t1), is usually 0.1 to 0.5, and the mixture is co-extruded downward through a three-layer die maintained at 210° C. to form a raw sheet consisting of the desired laminate. It is also preferable that the thicknesses of the first surface layer and the second surface layer are substantially equal, but it is also preferable that they are different in consideration of the application, etc.

[0053] 3. Process for Producing Olefin-Based Heat-Shrinkable Multilayer Film Next, the obtained raw sheet (multilayer laminate) was stretched, for example, to a TD stretch ratio of 200 to 800% and an MD stretch ratio of 90 to 120% using a shrink film manufacturing device by moving the sheet over and between rolls while being heated and pressed, to produce an olefin-based heat-shrinkable multilayer film. More specifically, the standard stretch ratios are usually about 500% in the TD direction and about 100% in the MD direction.

[0054] 4. Inspection step (optional step) of olefin-based heat-shrinkable multilayer film It is preferable to provide a predetermined inspection step (optional step) in which the following properties are measured continuously or intermittently for the produced olefin-based heat-shrinkable multilayer film. That is, by measuring the following properties in the predetermined inspection step and confirming that they fall within the predetermined ranges, it is possible to obtain an olefin-based heat-shrinkable multilayer film having more uniform specific gravity separability, heat shrinkability, etc. 1) Visual inspection of the appearance of the olefin-based heat-shrinkable multilayer film 2) Measurement of thickness variation 3) Measurement of tensile modulus 4) Measurement of tear strength 5) Measurement of viscoelastic properties using an SS curve

[0055] [Third Embodiment] The third embodiment relates to a method for using an olefin-based heat-shrinkable multilayer film. Therefore, any known method for using a shrink film can be suitably applied. For example, when carrying out the method for using an olefin-based heat-shrinkable multilayer film, the olefin-based heat-shrinkable multilayer film is first cut to an appropriate length and width and formed into a long cylindrical object. The long cylindrical object is then fed to an automatic label attachment device (shrink labeler) and further cut to the required length. The long cylindrical object is then fitted onto a PET bottle or the like filled with a content.

[0056] Next, the olefin-based heat-shrinkable multilayer film wrapped around the PET bottle or the like is heat-treated by passing it through a hot air tunnel or steam tunnel at a predetermined temperature. These tunnels provide radiant heat such as infrared rays or heated steam at about 90°C to 100°C, which is blown onto the olefin-based heat-shrinkable multilayer film from the surrounding area, thereby uniformly heating and heat-shrinking the film. Thus, as shown in FIG. 1(c), the olefin-based heat-shrinkable multilayer film 10 after heat shrinkage can be brought into close contact with the outer surface of a PET bottle 20, allowing a labeled container to be quickly obtained.

[0057] That is, according to the olefin-based heat-shrinkable multilayer film of the present invention, as described in detail in the first embodiment, it is an olefin-based heat-shrinkable multilayer film including a surface layer derived from a polystyrene-based resin, and is characterized by satisfying at least the configurations (a) and (b). This improves the handleability of the heat-shrinkable film, and improves the resistance to breakage of the label during transportation and storage after attachment to a PET bottle, for example. Furthermore, the olefin-based heat-shrinkable multilayer film of the present invention is characterized by a low haze value and high transparency. Therefore, as shown in FIG. 1( c), even if a predetermined decorative layer is provided directly or indirectly on the second surface layer of the olefin-based heat-shrinkable multilayer film, which is the surface facing the PET bottle or the like, it is possible to achieve the effect of ensuring that letters, symbols, figures, patterns, etc. on the decorative layer are fully recognizable.

[0058] The olefin-based heat-shrinkable multilayer film of the present invention will be described in detail below based on examples. However, the scope of the present invention is not limited by the description of Example 1 or the like without any particular reason. The polyolefin-based resins, polystyrene resins, etc. used in Example 1 and the like are as follows.

[0059] (1) Olefin resin 1) Type A Ethylene-1-hexene copolymer produced with a metallocene catalyst Density: 0.92 g / cm 3 , MFR: 2.0 g / 10 min Melting enthalpy (ΔH): 126 mJ / mg Mn: 6.6×10 4 , Mw: 20.2×104 , Mw / Mn: 3.1

[0060] 2) Type B Ethylene / 1-hexene copolymer produced by metallocene catalyst Density: 0.91 g / cm 3 , MFR: 1.8 g / 10 min, melt tension: 104 mN, fusion enthalpy (ΔH): 115 mJ / mg, Mn: 8.2 × 10 4 , Mw: 21.6×10 4 , Mw / Mn: 2.6

[0061] 3) Type C Ethylene / 1-hexene copolymer produced by metallocene catalyst Density: 0.92 g / cm 3 , MFR: 2.0 g / 10 min, melt tension: 200 mN, fusion enthalpy (ΔH): 110 mJ / mg, Mn: 7.0×10 4 , Mw: 23.8×10 4 , Mw / Mn: 3.4

[0062] 4) Type D Ethylene / 1-butene copolymer produced by Ziegler-Natta catalyst Density: 0.92 g / cm 3 , MFR: 0.2 g / 10 min, molecular weight distribution: 19.5, fusion enthalpy (ΔH): 140 mJ / mg, Mn: 2.0×10 4 , Mw: 44.2×10 4 , Mw / Mn: 22.1

[0063] 5) Type E Ethylene / 1-butene copolymer produced by Ziegler-Natta catalyst Density: 0.92 g / cm 3 , MFR: 1 g / 10 min Melting enthalpy (ΔH): 138 mJ / mg Mn: 6.4 × 10 4 , Mw: 26.2×10 4 , Mw / Mn: 4.1

[0064] (2) Polystyrene resin and other compounding components 1) Type F: A styrene-butadiene block copolymer having a weight ratio of styrene / butadiene of 85 / 15 and molecular weights of the styrene block portion of 24,000 and 125,000.

[0065] 2) Type K: A mixture of styrene-butadiene block copolymer and polystyrene resin (weight ratio: 50:50)

[0066] 3) Type AB High Impact Polystyrene Resin (HIPS)

[0067] 4) Type L Compatibilizer (SEBS1): Styrene-butadiene block copolymer (hydrogenated elastomer resin), styrene content 53% by weight,

[0068] 5) Type M Compatibilizer (SEBS2): Styrene-butadiene / butylene-styrene triblock copolymer (hydrogenated elastomer resin), styrene content 68% by weight

[0069] 6) Type N Compatibilizer (SEBS3): Styrene-ethylene-butylene-styrene block copolymer (hydrogenated elastomer resin), styrene content 43% by weight

[0070] 7) Type P Compatibilizer (SEBS4): Styrene-ethylene / butylene-styrene triblock copolymer (hydrogenated elastomer resin), styrene content 68% by weight

[0071] Example 1 1. Preparation of an Olefin-Based Heat-Shrinkable Multilayer Film In a first stirring vessel, 100 parts by weight (same as parts by mass, and the same applies hereinafter) of an ethylene-1-hexene copolymer produced with a Type A metallocene catalyst was placed as the olefin-based resin for the intermediate layer, and the mixture was stirred while heated at 220°C to form a uniform solution. Meanwhile, in a second stirring vessel, 87.7 parts by weight of Type F as the polystyrene-based resin for the surface layer, 10 parts by weight of Type L as the compatibilizer, and 2.3 parts by weight of AB as the antiblocking agent were placed, and the mixture was stirred while heated at 220°C to form a uniform solution.

[0072] Next, each was fed to an extruder (manufactured by Tanabe Plastic Machinery Co., Ltd.) with an L / D of 24 and an extrusion screw diameter of 50 mm at an extrusion temperature of 220°C, and extrusion molding was performed to obtain a raw sheet having a thickness of 160 μm for the three structures. That is, the thickness of each of the obtained raw sheets before stretching was 16 μm for the surface layer and 128 μm for the middle layer, for a total thickness of 160 μm.

[0073] Next, the obtained raw sheet (multilayer laminate) was stretched using a shrink film manufacturing device by moving it over and between rolls while being heated and pressed, so that the stretching ratio in the TD direction was 500% and the stretching ratio in the MD direction was 100%, thereby producing an olefin-based heat-shrinkable multilayer film with a thickness of 50 μm.

[0074] 2. Evaluation of Olefin-Based Heat-Shrinkable Multilayer Films (1) Evaluation 1: Amount of Styrene-Butadiene Copolymer The amount of styrene-butadiene copolymer (SBC) blended into the olefin-based resin, which was the main component used in the obtained heat-shrinkable film, was evaluated according to the following criteria: ◎: The amount of SBC blended was 60% by weight or more. ○: The amount of SBC blended was 50% by weight or more. △: The amount of SBC blended was 40% by weight or more. ×: The amount of SBC blended was less than 40% by weight.

[0075] (2) Evaluation 2: Crystalline Melting Enthalpy (ΔH) In accordance with JIS K 7121:2012 (corresponding to ISO 11357-2:2013), the crystalline melting enthalpy of the intermediate layer constituting the olefin-based heat-shrinkable multilayer film was measured during the second heating process at a heating rate of 10°C / min using a DSC (DSC7000X, manufactured by Hitachi High-Tech Corporation).

[0076] (3) Evaluation 3: Specific Gravity The specific gravity of the olefin-based heat-shrinkable multilayer film was determined from the ratio of the density measured by a density gradient tube method in accordance with JIS K 7112-1999 to the density of water at a temperature of 23°C.

[0077] (4) Evaluation 4: Haze Value The haze value of the obtained heat-shrinkable film was measured in accordance with JIS K 7105.

[0078] (5) Evaluation 5: Heat Shrinkage (100°C, 10 seconds) A film was cut into a 100 mm x 100 mm square with one side parallel to the machine direction of the film, and this was immersed in a hot water bath maintained at 100°C for 10 seconds. Then, immediately after 10 seconds, the film was immersed in a separately prepared water bath at 25°C for 10 seconds. Next, the film was quickly removed from the hot water bath, and the length of the film in the main shrinkage direction was measured to determine the heat shrinkage.

[0079] (6) Evaluation 6: Mw / Mn The weight average molecular weight (Mw) and number average molecular weight (Mn) of the olefin resin, which was the main component used in the obtained heat-shrinkable film, were measured, and the molecular weight distribution Mw / Mn was calculated.

[0080] (7) Evaluation 7: Peelability Using the same resin as that used to produce the olefin-based heat-shrinkable multilayer film, a single-layer surface layer sheet having a thickness of 60 μm and a single-layer intermediate layer sheet having a thickness of 160 μm were produced using an extruder with an L / D of 24 and an extrusion screw diameter of 50 mm at an extrusion temperature of 220°C. The resulting surface layer sheet and intermediate layer surface layer sheet were then cut into two long samples each measuring 100 mm in MD and 15 mm in TD. The two long samples were then heat-sealed using a heat sealer at 200°C, 0.2 MPa, and 2 seconds, and then left at room temperature for 24 hours to produce test samples. The obtained test samples were subjected to a precision universal testing machine (Shimadzu Corporation: Autograph AGX-10kNV2D) to measure the peel strength by a T-test peel at a speed of 200 mm / min, and the releasability was evaluated according to the following criteria. The results are shown in Table 4. ○: Peel strength is 3.0 N / mm 2 △: Peel strength is 3.0 N / mm or more 2 x: Peel strength is less than 0.3 N / mm 2 is less than.

[0081] In Example 2, 100 parts by weight of Type A, an ethylene-1-hexene copolymer produced using a metallocene catalyst, was used as the olefin resin for the intermediate layer, 87.7 parts by weight of Type F as the polystyrene resin for the surface layer, 10 parts by weight of Type L as the compatibilizer, and 2.3 parts by weight of Type AB as the antiblocking agent. The obtained raw sheets were then stretched to a total thickness of 160 μm, with the surface layer being 24 μm and the intermediate layer being 112 μm, respectively, in the same manner as in Example 1, except that a heat-shrinkable film was prepared and evaluated in the same manner as in Example 1.

[0082] Example 3 In Example 3, 100 parts by weight of Type A, which is an ethylene-1-hexene copolymer produced using a metallocene catalyst, was used as the olefin resin for the intermediate layer, 87.7 parts by weight of Type F as the polystyrene resin for the surface layer, 10 parts by weight of Type N as the compatibilizer, and 2.3 parts by weight of Type AB as the antiblocking agent were used. In the same manner as in Example 1, except for this, a raw sheet having a three-layer structure with a thickness of 16 / 128 / 16 μm was prepared, and this was subjected to a stretching treatment to prepare a heat-shrinkable film, which was then evaluated in the same manner as in Example 1.

[0083] Example 4 In Example 4, 100 parts by weight of Type A, which is an ethylene-1-hexene copolymer produced using a metallocene catalyst, was used as the olefin resin for the intermediate layer, 87.7 parts by weight of Type F as the polystyrene resin for the surface layer, 10 parts by weight of Type N as the compatibilizer, and 2.3 parts by weight of Type AB as the antiblocking agent were used. In the same manner as in Example 2, except for this, a raw sheet having a three-layer structure with a thickness of 24 / 112 / 24 μm was prepared, and this was subjected to a stretching treatment to prepare a heat-shrinkable film, which was evaluated in the same manner as in Example 1.

[0084] Example 5 In Example 5, 100 parts by weight of Type A, which is an ethylene-1-hexene copolymer produced using a metallocene catalyst, was used as the olefin resin for the intermediate layer, 87.7 parts by weight of Type F as the polystyrene resin for the surface layer, 10 parts by weight of Type P as the compatibilizer, and 2.3 parts by weight of Type AB as the antiblocking agent were used. In the same manner as in Example 1, except for this, a raw sheet having a three-layer structure with a thickness of 16 / 128 / 16 μm was prepared, and this was subjected to a stretching treatment to prepare a heat-shrinkable film, which was evaluated in the same manner as in Example 1.

[0085] Example 6 In Example 6, 100 parts by weight of Type A, which is an ethylene-1-hexene copolymer produced using a metallocene catalyst, was used as the olefin resin for the intermediate layer, 87.7 parts by weight of Type F as the polystyrene resin for the surface layer, 10 parts by weight of Type P as the compatibilizer, and 2.3 parts by weight of Type AB as the antiblocking agent were used. In the same manner as in Example 2, except for this, a raw sheet having a three-layer structure with a thickness of 24 / 112 / 24 μm was prepared, and this was subjected to a stretching treatment to prepare a heat-shrinkable film, which was evaluated in the same manner as in Example 1.

[0086] Example 7 In Example 7, 100 parts by weight of Type A, which is an ethylene-1-hexene copolymer produced using a metallocene catalyst, was used as the olefin resin for the intermediate layer, 87.7 parts by weight of Type F as the polystyrene resin for the surface layer, 10 parts by weight of Type M as the compatibilizer, and 2.3 parts by weight of Type AB as the antiblocking agent were used. In the same manner as in Example 1, except for this, a raw sheet having a three-layer structure with a thickness of 16 / 128 / 16 μm was prepared, and this was subjected to a stretching treatment to prepare a heat-shrinkable film, which was then evaluated in the same manner as in Example 1.

[0087] Example 8 In Example 8, 100 parts by weight of Type A, which is an ethylene-1-hexene copolymer produced using a metallocene catalyst, was used as the olefin resin for the intermediate layer, 87.7 parts by weight of Type F as the polystyrene resin for the surface layer, 10 parts by weight of Type M as the compatibilizer, and 2.3 parts by weight of Type AB as the antiblocking agent were used. In the same manner as in Example 2, except for this, a raw sheet having a three-layer structure with a thickness of 24 / 112 / 24 μm was prepared, and this was subjected to a stretching treatment to prepare a heat-shrinkable film, which was evaluated in the same manner as in Example 1.

[0088] Example 9 In Example 9, 100 parts by weight of Type A, which is an ethylene-1-hexene copolymer produced using a metallocene catalyst, was used as the olefin resin for the intermediate layer, 92.7 parts by weight of Type F as the polystyrene resin for the surface layer, 5 parts by weight of Type M as the compatibilizer, and 2.3 parts by weight of Type AB as the antiblocking agent were used. In the same manner as in Example 1, except for this, a raw sheet having a three-layer structure with a thickness of 16 / 128 / 16 μm was prepared, and this was subjected to a stretching treatment to prepare a heat-shrinkable film, which was evaluated in the same manner as in Example 1.

[0089] Example 10 In Example 10, 100 parts by weight of Type A, which is an ethylene-1-hexene copolymer produced using a metallocene catalyst, was used as the olefin resin for the intermediate layer, 92.7 parts by weight of Type F as the polystyrene resin for the surface layer, 5 parts by weight of Type M as the compatibilizer, and 2.3 parts by weight of Type AB as the antiblocking agent were used. In the same manner as in Example 2, a three-layer raw sheet having a thickness of 24 / 112 / 24 μm was prepared, and this was subjected to a stretching treatment to prepare a heat-shrinkable film, which was evaluated in the same manner as in Example 1.

[0090] Example 11 In Example 11, 100 parts by weight of Type A, which is an ethylene-1-hexene copolymer produced using a metallocene catalyst, was used as the olefin resin for the intermediate layer, 92.7 parts by weight of Type F as the polystyrene resin for the surface layer, 5 parts by weight of Type P as the compatibilizer, and 2.3 parts by weight of Type AB as the antiblocking agent were used. Except for this, a raw sheet having a three-layer structure with a thickness of 16 / 128 / 16 μm was prepared in the same manner as in Example 1. The sheet was then stretched to prepare a heat-shrinkable film, which was then evaluated in the same manner as in Example 1.

[0091] Example 12 In Example 12, 100 parts by weight of Type A, which is an ethylene-1-hexene copolymer produced using a metallocene catalyst, was used as the olefin resin for the intermediate layer, 92.7 parts by weight of Type F as the polystyrene resin for the surface layer, 5 parts by weight of Type P as the compatibilizer, and 2.3 parts by weight of Type AB as the antiblocking agent were used. In the same manner as in Example 2, a three-layer raw sheet having a thickness of 24 / 112 / 24 μm was prepared, and this was subjected to a stretching treatment to prepare a heat-shrinkable film, which was evaluated in the same manner as in Example 1.

[0092] Example 13 In Example 13, 100 parts by weight of Type B produced using a metallocene catalyst was used as the olefin resin for the intermediate layer, 92.7 parts by weight of Type F as the polystyrene resin for the surface layer, 5 parts by weight of Type P as the compatibilizer, and 2.3 parts by weight of Type AB as the antiblocking agent were used. Except for this, a three-layer raw sheet having a thickness of 16 / 128 / 16 μm was prepared in the same manner as in Example 1. The sheet was then stretched to prepare a heat-shrinkable film, which was then evaluated in the same manner as in Example 1.

[0093] Example 14 In Example 14, 100 parts by weight of Type B produced using a metallocene catalyst was used as the olefin resin for the intermediate layer, 92.7 parts by weight of Type F as the polystyrene resin for the surface layer, 5 parts by weight of Type P as the compatibilizer, and 2.3 parts by weight of Type AB as the antiblocking agent were used. In the same manner as in Example 2, except for this, a three-layer raw sheet having a thickness of 24 / 112 / 24 μm was prepared, and this was subjected to a stretching treatment to prepare a heat-shrinkable film, which was evaluated in the same manner as in Example 1.

[0094] Example 15 In Example 15, 100 parts by weight of Type C produced using a metallocene catalyst was used as the olefin resin for the intermediate layer, 92.7 parts by weight of Type F as the polystyrene resin for the surface layer, 5 parts by weight of Type P as the compatibilizer, and 2.3 parts by weight of Type AB as the antiblocking agent were used. Except for this, a three-layer raw sheet having a thickness of 16 / 128 / 16 μm was prepared in the same manner as in Example 1. The sheet was then stretched to prepare a heat-shrinkable film, which was then evaluated in the same manner as in Example 1.

[0095] Example 16 In Example 16, 100 parts by weight of Type C produced using a metallocene catalyst was used as the olefin resin for the intermediate layer, 92.7 parts by weight of Type F as the polystyrene resin for the surface layer, 5 parts by weight of Type P as the compatibilizer, and 2.3 parts by weight of Type AB as the antiblocking agent were used. Except for this, a raw sheet having a three-layer structure with a thickness of 24 / 112 / 24 μm was prepared in the same manner as in Example 2. This was then stretched to prepare a heat-shrinkable film, which was then evaluated in the same manner as in Example 1.

[0096] Example 17 In Example 17, 100 parts by weight of Type A produced using a metallocene catalyst was used as the olefin resin for the intermediate layer, 46.35 parts by weight of Type F and 46.35 parts by weight of Type K were used as polystyrene resins for the surface layer, 5 parts by weight of Type P was used as the compatibilizer, and 2.3 parts by weight of Type AB was used as the antiblocking agent. A three-layer raw sheet having a thickness of 16 / 128 / 16 μm was prepared in the same manner as in Example 1, and this was then subjected to a stretching treatment to prepare a heat-shrinkable film, which was then evaluated in the same manner as in Example 1.

[0097] Example 18 In Example 18, 100 parts by weight of Type A produced using a metallocene catalyst was used as the olefin resin for the intermediate layer, 46.35 parts by weight of Type F and 46.35 parts by weight of Type K were used as polystyrene resins for the surface layer, 5 parts by weight of Type P was used as the compatibilizer, and 2.3 parts by weight of Type AB was used as the antiblocking agent. A three-layer raw sheet having a thickness of 24 / 112 / 24 μm was prepared in the same manner as in Example 2, and this was then subjected to a stretching treatment to prepare a heat-shrinkable film, which was then evaluated in the same manner as in Example 1.

[0098] Example 19 In Example 19, 100 parts by weight of Type A produced using a metallocene catalyst was used as the olefin resin for the intermediate layer, 97.2 parts by weight of Type F as the polystyrene resin for the surface layer, and 2.3 parts by weight of Type AB as the antiblocking agent were used. A three-layer raw sheet having a thickness of 24 / 112 / 24 μm was prepared, and this was subjected to a stretching treatment to prepare a heat-shrinkable film, which was evaluated in the same manner as in Example 1.

[0099] [Example 20] In Example 20, 100 parts by weight of Type A produced using a metallocene catalyst was used as the olefin resin for the intermediate layer, 23.18 parts by weight of Type F and 69.53 parts by weight of Type K were used as polystyrene resins for the surface layer, 5 parts by weight of Type P was used as the compatibilizer, and 2.3 parts by weight of Type AB was used as the antiblocking agent. A three-layer raw sheet having a thickness of 24 / 112 / 24 μm was prepared, and this was subjected to a stretching treatment to prepare a heat-shrinkable film, which was evaluated in the same manner as in Example 1.

[0100] Example 21 In Example 21, 100 parts by weight of Type A produced using a metallocene catalyst was used as the olefin resin for the intermediate layer, 95.2 parts by weight of Type F as the polystyrene resin for the surface layer, 2.5 parts by weight of Type P as the compatibilizer, and 2.3 parts by weight of Type AB as the antiblocking agent were used. A three-layer raw sheet having a thickness of 24 / 112 / 25 μm was prepared, and this was subjected to a stretching treatment to prepare a heat-shrinkable film, which was evaluated in the same manner as in Example 1.

[0101] Comparative Example 1 In Comparative Example 1, 100 parts by weight of Type D produced using a Ziegler-Natta catalyst was used as the olefin resin for the intermediate layer, 92.7 parts by weight of Type F as the polystyrene resin for the surface layer, 5 parts by weight of Type P as the compatibilizer, and 2.3 parts by weight of Type AB as the antiblocking agent were used. A three-layer raw sheet having a thickness of 24 / 112 / 24 μm was prepared, which was then stretched to produce a heat-shrinkable film, which was evaluated in the same manner as in Example 1. As a result, in Comparative Example 1, unevenness occurred upon stretching, and the specific gravity exceeded 0.95, presumably because the intermediate layer used was Type D, an olefin resin with a crystalline melting enthalpy (ΔH) exceeding 135 mJ / mg and a wide molecular weight distribution.

[0102] Comparative Example 2 In Comparative Example 2, 100 parts by weight of Type E produced using a Ziegler-Natta catalyst was used as the olefin resin for the intermediate layer, 92.7 parts by weight of Type F as the polystyrene resin for the surface layer, 5 parts by weight of Type P as the compatibilizer, and 2.3 parts by weight of Type AB as the antiblocking agent were used. A three-layer raw sheet having a thickness of 16 / 128 / 16 μm was prepared, which was then stretched to produce a heat-shrinkable film, which was evaluated in the same manner as in Example 1. As a result, in Comparative Example 2, the heat shrinkage rate in the TD direction tended to be quite low, at 45% (less than 50%), presumably because the intermediate layer used was Type E, an olefin resin with a crystalline melting enthalpy (ΔH) exceeding 135 mJ / mg and a wide molecular weight distribution.

[0103] Comparative Example 3 In Comparative Example 3, 100 parts by weight of Type E produced using a Ziegler-Natta catalyst was used as the olefin resin for the intermediate layer, 92.7 parts by weight of Type F as the polystyrene resin for the surface layer, 5 parts by weight of Type P as the compatibilizer, and 2.3 parts by weight of Type AB as the antiblocking agent were used. A three-layer raw sheet having a thickness of 24 / 112 / 24 μm was prepared, which was then stretched to produce a heat-shrinkable film, which was evaluated in the same manner as in Example 1. As a result, in Comparative Example 2, the heat shrinkage rate in the TD direction tended to be quite low, at 46% (less than 50%), presumably because the intermediate layer used Type E, an olefin resin with a crystalline melting enthalpy (ΔH) exceeding 135 mJ / mg and a wide molecular weight distribution.

[0104] Comparative Example 4 In Comparative Example 4, 100 parts by weight of Type A was used as the olefin resin for the intermediate layer, 92.7 parts by weight of Type K as the polystyrene resin for the surface layer, 5 parts by weight of Type P as the compatibilizer, and 2.3 parts by weight of Type AB as the antiblocking agent, and the rest of the raw sheet had a three-layer structure having a thickness of 16 / 128 / 16 μm, which was then stretched to produce a heat-shrinkable film, which was evaluated in the same manner as in Example 1. As a result, it is presumed that Comparative Example 4 uses Type K, which contains a small amount of SBC as the polystyrene resin, as the main component, but whitening occurred due to the stretching, resulting in a considerably high haze value of 12.1%.

[0105] Comparative Example 5 In Comparative Example 5, 100 parts by weight of Type A was used as the olefin resin for the intermediate layer, 92.7 parts by weight of Type K as the polystyrene resin for the surface layer, 5 parts by weight of Type P as the compatibilizer, and 2.3 parts by weight of Type AB as the antiblocking agent, and the rest of the raw sheet had a three-layer structure of 24 / 112 / 24 μm in thickness, which was then stretched to produce a heat-shrinkable film, which was evaluated in the same manner as in Example 1. As a result, it is presumed that Comparative Example 5 uses Type K, which contains a small amount of SBC as the polystyrene resin, as the main component, but whitening occurred due to the stretching, resulting in a considerably high haze value of 19.1%.

[0106]

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[0109]

[0110] According to the olefin-based heat-shrinkable multilayer film of the present invention, the resin compositions of the three layers constituting the olefin-based heat-shrinkable multilayer film are set within specific ranges without substantially blending a cyclic olefin-based resin, and therefore the film has excellent heat shrinkability, transparency, and interlayer peelability, and when used in PET bottles, it undergoes uniform heat shrinkage, exhibits excellent decorative properties, and is not susceptible to breakage during printing or center sealing processing.

[0111] Furthermore, since the specific gravity is small, at 0.95 or less, even if the olefin-based heat-shrinkable multilayer film is still in use as a heat-shrinkable film for PET bottles, it can be peeled off from the PET bottle by utilizing specific gravity separation using a specified cyclone device or the like, and can be easily and quickly recovered and recycled.

[0112] Furthermore, when solvents such as cyclohexane and tetrahydrofuran are used as adhesive solvents, the solvent adhesion is good, and center sealing can be easily performed using a conventional solvent adhesion method, eliminating the need for additional secondary processing equipment. Moreover, the polystyrene-based resin constituting the first surface layer and / or the second surface layer contains a predetermined amount of styrene-based elastomer, which makes it possible to effectively increase the peel strength (T-peel strength).

[0113] Therefore, as explained above, the olefin-based heat-shrinkable multilayer film of the present invention can be suitably applied to various PET bottles, outer wrapping materials for lunch boxes, etc., thereby significantly expanding its versatility and making it highly applicable in industry.

[0114] 10, 10', 10'': Olefin-based heat-shrinkable multilayer film 10a: First surface layer 10b: Intermediate layer 10c: Second surface layer 10d: Decorative layer 20: PET bottle

Claims

1. An olefin-based heat-shrinkable multilayer film comprising an intermediate layer derived from a polyolefin-based resin, a first surface layer derived from at least a polystyrene-based resin on one surface side of the intermediate layer, and a second surface layer derived from at least a polystyrene-based resin on the other surface side of the intermediate layer, and satisfying the following characteristics (a) to (e): (a) the polystyrene-based resin contains 50% by weight or more of a styrene-butadiene copolymer based on the total weight of the intermediate layer; (b) the crystalline melting enthalpy (ΔH) of the intermediate layer, as measured by DSC in accordance with JIS K 7121:2012 (corresponding to ISO 11357-2:2013), is 135 mJ / mg or less; and (c) when shrunk in boiling water at 100°C for 10 seconds, the thermal shrinkage ratio A1 in the main shrinkage direction is within the range of 50 to 80%. (d) The haze value measured in accordance with JIS K 7136:2000 (corresponding to ISO 14782:1999) is 10% or less. (e) The specific gravity measured in accordance with JIS K 7112-1:2023 (corresponding to ISO 1183-1:2023) is 0.95 or less.

2. The olefin-based heat-shrinkable multilayer film according to claim 1, characterized in that, as component (f), the molecular weight distribution (Mw / Mn) of the polyolefin-based resin constituting the intermediate layer is set to a value of 4.0 or less.

3. The olefin-based heat-shrinkable multi-layer film according to claim 1 or 2, characterized in that the intermediate layer contains linear low-density polyethylene as the polyolefin-based resin.

4. The olefin-based heat-shrinkable multilayer film according to claim 1 or 2, characterized in that the weight-average molecular weight of the polyolefin-based resin constituting the intermediate layer is set to a value within the range of 150,000 to 250,000.

5. The olefin-based heat-shrinkable multilayer film according to claim 1 or 2, characterized in that the number average molecular weight of the polyolefin-based resin constituting the intermediate layer is set to a value within the range of 50,000 to 100,000.

6. An olefin-based heat-shrinkable multilayer film as described in claim 1 or 2, characterized in that the polystyrene-based resin constituting the first surface layer and / or the second surface layer contains a styrene-based elastomer.

7. The olefin-based heat-shrinkable multi-layer film according to claim 1 or 2, characterized in that the thickness after stretching is set to a value within the range of 10 to 60 μm.

8. An olefin-based heat-shrinkable multilayer film according to claim 1 or 2, characterized in that the thickness ratio (t2+t3) / (t1) is a value within the range of 0.1 to 0.5, where t1 is the thickness of the intermediate layer before stretching, t2 is the thickness of the first surface layer before stretching, and t3 is the thickness of the second surface layer before stretching.

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