Olefin-based heat-shrinkable multilayer film

Abstract

This invention provides an olefin-based heat-shrinkable multilayer film that is easy to bond with solvents and separate by specific gravity, and has excellent heat shrinkage properties and transparency. [Solution] An olefin-based heat-shrinkable multilayer film comprising an intermediate layer made of a polyolefin resin, a first surface layer made of a polystyrene resin on one surface side of the intermediate layer, and a second surface layer made of a polystyrene resin on the other surface side, wherein (a) the molecular weight distribution (Mw / Mn) of the polyolefin resin constituting the intermediate layer is 4.0 or less, (b) when heat shrinkage is performed at 100°C for 10 seconds, the heat shrinkage rate in the main shrinkage direction is A1, and A1 is a value in the range of 50 to 80%, (c) the haze value is a value of 1 to 9%, and (d) when the thickness of the intermediate layer is t1, the thickness of the first surface layer is t2, and the thickness of the second surface layer is t3, the thickness ratio (t2+t3) / (t1) is a value in the range of 0.1 to 0.5.

Description

[Technical Field]

[0001] This invention relates to an olefin-based heat-shrinkable multilayer film (hereinafter sometimes simply referred to as a heat-shrinkable film). In particular, this invention relates to an olefin-based heat-shrinkable multilayer film that is easy to bond with solvents and separate by specific gravity, and has excellent heat shrinkage properties and transparency. [Background technology]

[0002] In recent years, a wide variety of heat-shrinkable films have been widely used for purposes such as packaging glass or plastic bottles with heat-shrinkable film to improve the appearance of packaged goods and to serve as both a protective layer and a label for the product. Polyvinyl chloride resins, polystyrene resins, polyester resins, polyolefin resins, and the like are known as the main components of such heat-shrinkable films.

[0003] However, while heat-shrinkable films made from polyvinyl chloride resin have excellent heat-shrinkability, they also have environmental problems such as being prone to generating chlorine gas during combustion. On the other hand, heat-shrinkable films made primarily from polystyrene or polyester resins, while exhibiting relatively good heat shrinkability, suffer from poor recyclability due to the small difference in specific gravity between them and the PET resin that makes up PET bottles, making specific gravity separation using water or other means difficult. In contrast, heat-shrinkable films made of polyolefin resin have the advantage of a large difference in specific gravity from PET bottles, making specific gravity separation using water or other means relatively easy. However, the difficulty in solvent bonding the film itself means that conventional tubular heat-shrinkable film manufacturing equipment cannot be used as is.

[0004] Therefore, for example, it has been proposed to incorporate cyclic olefin resins as one of the constituent components of polyolefin resins (see Patent Document 1). More specifically, the density is 0.94 g / cm³. 3A laminate is formed by providing a layer consisting of an olefin resin and an adhesive resin as an intermediate layer, and a surface layer and a back layer made of styrene resin on the front and back surfaces of this intermediate layer, respectively, with the thickness ratio of each layer of this laminate being (surface layer + back layer) / intermediate layer = 1 / 1 to 1 / 6, and this laminate is stretched 2 to 6 times in at least one axial direction to form a heat-shrinkable laminated film.

[0005] Furthermore, a heat-shrinkable laminated porous film equipped with a porous polyolefin resin layer has also been proposed (see Patent Document 2). More specifically, the heat-shrinkable laminated porous film comprises a pair of front and back layers mainly composed of at least one selected from the group consisting of copolymer resins (A) of styrene hydrocarbons and conjugated diene hydrocarbons, and a porous layer provided between the pair of front and back layers, mainly composed of a resin composition containing a polyolefin resin (B) and a filler (C), and is stretched in at least one direction to have a predetermined range of porosity. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2000-309071 (Claims, etc.) [Patent Document 2] Japanese Patent Publication No. 2018-153984 (Claims, etc.) [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] However, in the case of heat-shrinkable laminated films such as those described in Patent Document 1, when cyclic olefin resins are incorporated, the resulting film becomes hard and brittle, leading to problems such as easy tearing during secondary processing such as printing, and easy delamination between layers. Furthermore, when cyclic olefin resins were incorporated as the main component of heat-shrinkable films, a problem was observed where compatibility with other resins decreased, leading to a reduction in the transparency of the film. Furthermore, because cyclic olefin resins are relatively expensive, incorporating them as a component material increases the manufacturing cost of heat-shrinkable films, resulting in an economic disadvantage.

[0008] Furthermore, in the case of heat-shrinkable laminated porous films such as those described in Patent Document 2, there was a problem in that it was difficult to control the porosity value, and consequently the specific gravity, during manufacturing. As a result, the specific gravity values ​​varied, making it difficult to separate specific gravity values ​​during recycling. Furthermore, problems such as a decrease in the transparency, thermal shrinkage, and mechanical properties of the film were also observed.

[0009] The present invention has been made in view of the above-mentioned problems, and its purpose is to provide a heat-shrinkable multilayer film that is easy to bond with solvents and separate by specific gravity, and has excellent heat shrinkability and transparency. [Means for solving the problem]

[0010] According to the present invention, an olefin-based heat-shrinkable multilayer film is provided that includes an intermediate layer made from a polyolefin resin, a first surface layer made from at least a polystyrene resin on one surface side of the intermediate layer, and a second surface layer made from at least a polystyrene resin on the other surface side of the intermediate layer, and satisfies the following configurations (a) to (d), thereby solving the above-mentioned problems. (a) The molecular weight distribution (Mw / Mn) of the polyolefin resin constituting the intermediate layer shall be 4.0 or less. (b) When the material is immersed in 100°C water (hereinafter sometimes referred to as boiling water) for 10 seconds, the thermal shrinkage rate in the main shrinkage direction, A1, shall be within the range of 50 to 80%. (c) The haze value measured in accordance with JIS K 7136:2000 shall be between 1% and 9%. (d) 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) shall be within the range of 0.1 to 0.5. Thus, by satisfying at least configuration (a) to (d), solvent adhesion and specific gravity separation are facilitated, and excellent heat shrinkability can be obtained. In particular, by restricting the molecular weight distribution (Mw / Mn) of the polyolefin resin constituting the intermediate layer within a predetermined range, not only excellent heat shrinkability but also excellent lightness and transparency (low haze), etc. can be obtained. Furthermore, by setting the ratio of the thickness (t1) of the intermediate layer to the total thickness (t2 + t3) of the first surface layer and the second surface layer before the stretching treatment within a predetermined range, not only the usability of the heat shrinkable film is improved, but also excellent heat shrinkability and mechanical properties, etc. can be obtained.

[0011] Also, when forming the olefin-based heat shrinkable multilayer film, it is preferable that the crystal melting enthalpy (ΔH) measured by DSC for the intermediate layer is set to a value of 135 mJ / mg or less. By setting the crystal melting enthalpy (ΔH) measured by DSC in the intermediate layer to a value within a predetermined range in this way, the variation in the specific gravity of the film due to the intermediate layer is suppressed, and not only excellent heat shrinkability can be obtained, but also further weight reduction of the film can be achieved.

[0012] Also, when forming the olefin-based heat shrinkable multilayer film, it is preferable that the polystyrene resin contains 50% by weight or more of a styrene-butadiene copolymer with respect to the total amount (100% by weight). By thus making the polystyrene resin constituting the first surface layer and the second surface layer contain a predetermined amount of styrene-butadiene copolymer (SBC), the transparency is further improved, and delamination between layers can be more effectively suppressed.

[0013] Also, when forming the olefin-based heat shrinkable multilayer film, it is preferable that the intermediate layer contains linear low-density polyethylene as the polyolefin resin. By containing linear low-density polyethylene as the polyolefin resin constituting the intermediate layer in this way, it is possible to suppress variations in the specific gravity of the film and achieve further weight reduction.

[0014] Also, when forming an olefin-based heat-shrinkable multilayer film, it is preferable that the weight-average molecular weight (Mw) of the polyolefin resin constituting the intermediate layer is within the range of 150,000 to 250,000, and the number-average molecular weight (Mn) of the polyolefin resin constituting the intermediate layer is within the range of 50,000 to 100,000. By restricting the weight-average molecular weight (Mw) and number-average molecular weight (Mn) of the polyolefin resin constituting the intermediate layer to predetermined ranges in this way, it is possible to obtain further excellent heat shrinkability and excellent lightness, transparency, etc.

[0015] Also, when forming an olefin-based heat-shrinkable multilayer film, it is preferable that the polystyrene resin constituting the first surface layer and the second surface layer, or either one of them, contains a styrene-based elastomer. By the styrene-based resin constituting the first surface layer and the second surface layer containing a styrene-based elastomer, particularly a hydrogenated styrene-based elastomer, in this way, it is possible to obtain further excellent transparency and effectively suppress interlayer peeling.

[0016] Also, when forming an olefin-based heat-shrinkable multilayer film, it is preferable that the thickness after the stretching treatment is within the range of 10 to 60 μm. By setting the thickness of such a heat-shrinkable film to a value within a predetermined range in this way, not only is the usability improved, but it also has further excellent transparency and can obtain excellent heat shrinkability, mechanical properties, etc.

[0017] Also, when forming an olefin-based heat-shrinkable multilayer film, it is preferable that the specific gravity measured in accordance with JIS K 7112-1:2023 (former JIS K 7112:1999) is 0.95 or less.

Brief Description of the Drawings

[0018] [Figure 1] Figures 1(a) to 1(c) are diagrams provided to illustrate the form and method of use of the heat-shrinkable film, respectively. [Figure 2] Figure 2 is a chart showing the molecular weight distribution of each resin (types A to E) that constitutes the intermediate layer in a heat-shrinkable film. [Figure 3] Figure 3 shows the DSC charts (first heating cycle and second cycle after cooling to room temperature) for each resin (types A to E) that constitutes the intermediate layer in the heat-shrinkable film. [Figure 4] Figure 4 is provided to illustrate the relationship between the enthalpy of crystalline melting of the intermediate layer and the thermal shrinkage rate in the TD direction in a heat-shrinkable film. [Figure 5] Figure 5 illustrates the relationship between the enthalpy of crystalline melting in the intermediate layer and the haze in a heat-shrinkable film. [Figure 6] Figure 6 illustrates the relationship between the enthalpy of crystalline melting of the intermediate layer and its specific gravity in a heat-shrinkable film. [Figure 7] Figure 7 illustrates the relationship between the SBC content in the surface layer of a heat-shrinkable film and the haze. [Figure 8] Figure 8 illustrates the relationship between the thickness ratio (t2 + t3) of the surface layer and the thickness of the intermediate layer (t1) in a heat-shrinkable film, and the haze. [Modes for carrying out the invention]

[0019] [First Embodiment] The first embodiment is an olefin-based heat-shrinkable multilayer film 10, as illustrated in Figures 1(a) to (c), comprising an intermediate layer 10a made of a polyolefin resin, a first surface layer 10b made of at least a polystyrene resin on one surface side of the intermediate layer 10a, and a second surface layer 10c made of at least a polystyrene resin on the other surface side of the intermediate layer 10a, and satisfying the following configurations (a) to (d). (a) The molecular weight distribution (Mw / Mn) of the polyolefin resin constituting the intermediate layer shall be 4.0 or less. (b) When the material is shrunk by immersion in 100°C water for 10 seconds, the thermal shrinkage rate in the main shrinkage direction, A1, shall be within the range of 50 to 80%. (c) The haze value measured in accordance with JIS K 7136:2000 shall be between 1% and 9%. (d) 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) shall be within the range of 0.1 to 0.5. Figure 1(a) shows the basic structure of the olefin-based heat-shrinkable multilayer film 10, which consists of three layers. Figure 1(b) shows a configuration in which a decorative layer 10d is provided on the outside (bottommost layer in the drawing) of the second surface layer 10c of the olefin-based heat-shrinkable multilayer film 10. Furthermore, Figure 1(c) shows the olefin-based heat-shrinkable multilayer film 10 with the decorative layer 10d shown in Figure 1(b) applied to a PET bottle.

[0020] 1.Basic configuration (1) Middle class As illustrated in Figures 1(a) to (c), the olefin-based heat-shrinkable multilayer film 10 is characterized by having an intermediate layer 10a made from a polyolefin resin between the first surface layer 10b and the second surface layer 10c. The reason for this is that polyolefin resins can exhibit properties as heat-shrinkable films by utilizing crystallization based on stretching and other processes. Furthermore, polyolefin resins offer excellent transparency (haze) and lightweight properties (specific gravity), allowing for accurate and rapid recycling using specific gravity separation via a designated cyclone system. Therefore, among polyolefin resins, polyethylene resins in particular have superior transparency, crystallinity (heat shrinkage rate), and lightness (specific gravity) compared to polypropylene and the like.

[0021] (2) First surface layer / Second surface layer As illustrated in Figures 1(a) to (c), the olefin-based heat-shrinkable multilayer film 10 is characterized by having a first surface layer 10b made of at least a polystyrene resin on one surface side of the intermediate layer 10a, and a second surface layer 10c made of at least a polystyrene resin on the other surface side of the intermediate layer 10a. The reason for this is that the intermediate layer, which is derived from polyolefin resin, has low surface energy, making solvent bonding and paintability difficult, and thus potentially inconvenient to use. In other words, by forming a first surface layer and a second surface layer made of polystyrene resin, which have excellent solvent adhesion and paintability, on both sides of the intermediate layer made of polyolefin resin, the solvent adhesion and paintability of the intermediate layer made of polyolefin resin can be easily improved.

[0022] (3)Multilayer structure As illustrated in Figures 1(a) to (c), it is advisable to use a multilayer olefin-based heat-shrinkable multilayer film 10 that basically includes an intermediate layer 10a derived from a polyolefin resin, a first surface layer 10b derived from a polystyrene resin, and a second surface layer 10c also derived from a polystyrene resin. The reason for this is that, although a two-layer structure may be acceptable in practice for olefin-based heat-shrinkable multilayer films, a three-layer structure is generally easier to manufacture and, furthermore, makes it easier to obtain uniform heat shrinkage properties regardless of whether it is the front or back side.

[0023] Furthermore, in constructing the olefin-based heat-shrinkable multilayer film of the present invention, it is preferable that there is no adhesive layer (including a primer layer) between the intermediate layer, the first surface layer, and the second surface layer. The reason for this is the ease with which olefin-based heat-shrinkable multilayer films can be controlled, such as by managing the desired specific gravity, thickness, and heat shrinkage rate. Conversely, if an adhesive layer (including a primer layer) is included between the intermediate layer, the first surface layer, and the second surface layer, it becomes difficult to control the specific gravity, which can lead to a decrease in lightweight properties, or the thickness may become excessively large, making it difficult to manage and control the thermal shrinkage rate. Furthermore, the manufacturing process may involve an increase in the number of steps involved, making it difficult to provide stable and economical olefin-based heat-shrinkable multilayer films.

[0024] 2.Specific configuration (1) Ingredients of the middle layer The type of polyolefin resin constituting the intermediate layer is preferably determined considering the transparency, thermal shrinkage rate, molecular weight distribution, etc., of the resulting film, but basically, polymers derived from olefin hydrocarbons such as ethylene and propylene as monomer components can be used. Furthermore, the polyolefin resin may be a homopolymer or a copolymer. If it is a copolymer, the copolymerization ratio of olefin hydrocarbons such as ethylene, butene, hexene, etc. is preferably 50% by weight or more (synonymous with mass%, and the same applies hereinafter), but may be 70% by weight or more, or 90% by weight or more. Therefore, examples of such polyolefin resins include polyethylene resin, 1-hexene copolymer, ethylene-propylene copolymer, and the like, with linear low-density polyethylene (LLDPE) being particularly preferred.

[0025] Furthermore, there are no particular restrictions on the catalyst used when polymerizing polyolefin resins; Ziegler-Natta catalysts, metallocene catalysts, and others can be used. However, since polyolefin resins with excellent stereoregularity and mechanical strength can be easily obtained, it is also preferable to use polyolefin resins (such as isotactic or syndiotactic) produced using metallocene catalysts. Furthermore, the polyolefin resin used may have any crystallinity or melting point, but depending on the physical properties and application of the resulting film, a polyolefin resin composition may be used that is a blend of two polyolefin resins with different properties within a specific range.

[0026] (2) Molecular weight distribution of the polyolefin resin constituting the intermediate layer Furthermore, it is preferable that the weight-average molecular weight (Mw) of such olefin resin be within the range of 150,000 to 250,000. The reason for this is that having such a weight-average molecular weight (Mw) makes it easier to obtain olefin-based heat-shrinkable multilayer films with low haze and controlled heat shrinkage. Furthermore, it is preferable that the number-average molecular weight (Mn) of such olefin resin be within the range of 50,000 to 100,000. The reason for this is that olefin resins, by having such a number-average molecular weight (Mn), make it easier to obtain olefin-based heat-shrinkable multilayer films with low haze and controlled heat shrinkage. Figure 2 shows charts (Types A-E) illustrating the molecular weight distribution of each resin constituting the intermediate layer.

[0027] Therefore, since olefin resins have such weight-average molecular weight (Mw) and number-average molecular weight (Mn), making it easier to control haze, thermal shrinkage, etc., it is preferable that the molecular weight distribution (Mw / Mn) be 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 within a predetermined range further improves transparency, crystallinity (thermal shrinkage rate), and other properties.

[0028] As shown in Figure 3, DSC charts (after the first heating cycle and after cooling to room temperature) for each olefin resin (types A to E) constituting the intermediate layer can be obtained. In other words, the weight-average molecular weight (Mw) and number-average molecular weight (Mn) of olefin resins, and furthermore, the molecular weight distribution (Mw / Mn) based on them, can be measured using high-temperature GPC. More specifically, for example, using HLC-8321GPC / HT (manufactured by Tosoh Corporation), with dichlorobenzene as the solvent and a column temperature of 145°C, the weight-average molecular weight (Mw) of olefin resins can be calculated by comparing the results with a calibration curve using standard styrene particles.

[0029] (3) Crystal melting enthalpy (ΔH) measured by DSC of the intermediate layer A key feature is that the enthalpy of fusion (ΔH) of the intermediate layer, as measured by DSC, is set to a value of 135 mJ / mg or less. The reason for this is that by controlling the enthalpy of fusion, commonly known as the heat of fusion, it becomes easier to obtain a desirable thermal shrinkage rate, and transparency also improves. More specifically, when such crystalline melting enthalpy exceeds 135 mJ / mg, the thermal shrinkage rate under shrinkage conditions of, for example, 100°C for 10 seconds decreases significantly. Furthermore, when the enthalpy of crystalline melting exceeds 135 mJ / mg, transparency tends to decrease. However, if the enthalpy of crystalline melting becomes excessively small, the crystallinity decreases, which can conversely make it difficult to control the thermal shrinkage rate. Therefore, it is preferable that the enthalpy of crystalline melting measured by DSC of the intermediate layer be in the range of 100 to 130 mJ / mg, and more preferably in the range of 110 to 125 mJ / mg. Furthermore, the enthalpy of crystalline melting in the intermediate layer can be measured using a DSC (differential scanning calorimetry).

[0030] Here, referring to Figure 4, the relationship between the crystalline melting enthalpy (ΔH) of the polyolefin resin constituting the intermediate layer and the thermal shrinkage rate in the TD direction (100°C, 10 seconds), which is the main shrinkage direction, will be explained based on data from Example 1, etc. Specifically, the horizontal axis represents the enthalpy of crystalline melting of the polyolefin resin, and the vertical axis represents the thermal shrinkage rate (%) in the TD direction. From the characteristic curve in Figure 4, it can be seen that there is a negative linear correlation between the enthalpy of fusion and the thermal shrinkage rate (%) in the TD direction. This suggests that by controlling the enthalpy of fusion to 135 mJ / mg or less, the thermal shrinkage rate in the TD direction can be controlled to a desired range (e.g., 50% or more).

[0031] Furthermore, referring to Figure 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 from Example 1, etc. Specifically, the horizontal axis represents the enthalpy of crystalline melting of polyolefin resins, and the vertical axis represents the haze (%). As shown in Figure 5, although there is no significant linear correlation between the enthalpy of fusion and haze (%), it can be said that if the enthalpy of fusion is in the range of 110 to 135 mJ / mg, approximately equivalent haze values ​​can be obtained.

[0032] Furthermore, referring to Figure 6, the relationship between the enthalpy of crystalline melting (ΔH) of the polyolefin resin constituting the intermediate layer and the specific gravity when the thickness ratio of the heat-shrinkable film is changed will be explained based on the data from Example 1, etc. Specifically, the horizontal axis represents the enthalpy of crystalline melting of polyolefin resins, and the vertical axis represents the specific gravity when the thickness ratio (before stretching) of the heat-shrinkable film is changed. From the two characteristic curves A and B in Figure 6, which show the results when the thickness ratio is changed, it can be seen that there is a positive linear correlation between the enthalpy of fusion and the specific gravity when the thickness ratio is changed. By controlling the enthalpy of fusion to 135 mJ / mg or less, the specific gravity of the heat-shrinkable film can be controlled to a low value of 0.95 or less. Based on the data from Example 1, etc., characteristic curves A and B were obtained. Characteristic curve A is the case where the total thickness (t2+t3) of the surface layer made of polystyrene resin is relatively thick at 48 μm, and the thickness (t1) of the intermediate layer made of polyolefin resin is relatively thin at 112 μm. In other words, the heat-shrinkable film exhibits the predetermined behavior because the relative amount of polystyrene resin, which has a relatively high specific gravity, is greater than that of polyolefin resin, which has a relatively low specific gravity. On the other hand, characteristic curve B represents the case where the total thickness (t2+t3) of the surface layer made of polystyrene resin is relatively thin at 32 μm, and the thickness (t1) of the intermediate layer made of polyolefin resin is relatively thick at 128 μm. In other words, the heat-shrinkable film exhibits the predetermined behavior because the relative amount of polystyrene resin, which has a relatively high specific gravity, is less than that of polyolefin resin, which has a relatively low specific gravity.

[0033] (4) Thickness of the intermediate layer When the thickness of the intermediate layer before stretching is (t1), it is generally preferable that the thickness (t1) be within the range of 50 to 200 μm. The reason for this is that by controlling the thickness of such an intermediate layer to a predetermined range, not only is usability improved, but the specific gravity is controlled to a value below the desired value, and excellent thermal shrinkage and transparency can be obtained. More specifically, if the thickness of such an intermediate layer is less than 50 μm, it may become difficult to adjust the specific gravity, or the handling properties may be significantly reduced. On the other hand, if the thickness of such an intermediate layer exceeds 200 μm, transparency may decrease, it may become difficult to achieve a uniform thickness, and delamination may become more likely. Therefore, it is more preferable to set the thickness of such an intermediate layer to a value in the range of 80 to 150 μm, and even more preferable to set it to a value in the range of 100 to 130 μm. Furthermore, the thickness of the intermediate layer after stretching can be reduced in thickness depending on the stretching conditions, and the preferred range can be said to be thinner than the thickness mentioned above.

[0034] (5) Composition components of the first surface layer and the second surface layer 1 The polystyrene resin constituting the first surface layer and the second surface layer, or either one thereof, preferably contains 50% by weight or more of styrene-butadiene copolymer (SBC) based on the total amount (100% by weight). This is because if the SBC content falls below 50% by weight, the transparency of the resulting film may decrease significantly. Therefore, it is more preferable to have an SBC content of 60% by weight or more, and even more preferable to have an SBC content of 70% by weight or more, relative to the total amount (100% by weight) of at least one of the first and second surface layers. The types of residual components other than SBC in the first and second surface layers are not particularly limited, but typically include polymers other than styrene-butadiene copolymer (SBC) and compatibilizers, as described later.

[0035] Furthermore, it is preferable that the polystyrene resin constituting the first surface layer, the second surface layer, or either one thereof, contains a styrene elastomer. The reason for this is that by including a styrene-based elastomer as a type of styrene-butadiene copolymer (SBC), adhesion between the intermediate layer is improved, effectively suppressing delamination, and furthermore, a good thermal shrinkage rate is easily obtained. Therefore, when a styrene-based elastomer is included, it is generally preferable that the styrene-based elastomer content be in the range of 1 to 30% by weight, more preferably in the range of 2 to 20% by weight, and even more preferably in the range of 3 to 10% by weight, relative to the total amount (100% by weight) of at least one layer of the first surface layer and the second surface layer. As for the styrene-based elastomer, one or more types of styrene-butadiene block copolymer, styrene-butadiene / butylene-styrene triblock copolymer, styrene-ethylene-butylene-styrene block copolymer, and styrene-ethylene / butylene-styrene triblock copolymer (each styrene-based copolymer contains a thermoplastic elastomer) are preferred.

[0036] (6) Compounding components of the first and second surface layers 2 Furthermore, it is preferable that the polystyrene-based resin constituting the first surface layer and the second surface layer, or either one thereof, is a polymer other than the styrene-based elastomer mentioned above, and further contains a compatibilizer. The reason for this is that the inclusion of a compatibilizer improves adhesion between the intermediate layer and the surrounding material, effectively suppressing delamination and making it easier to obtain a good thermal shrinkage rate. Therefore, when a compatibilizer is included, it is generally preferable that the compatibilizer content be in the range of 1 to 30% by weight, more preferably in the range of 2 to 20% by weight, and even more preferably in the range of 3 to 10% by weight, relative to the total amount (100% by weight) of at least one layer of the first surface layer and the second surface layer.

[0037] Furthermore, various compounds and polymers can be used as compatibilizers as long as they exhibit the required compatibility. However, for example, polymers other than the styrene-based elastomers mentioned above are preferred as compatibilizers (hydrogenated elastomer resins, etc.) because they are compatible with the styrene-based elastomers and exhibit good compatibility. In other words, as styrene-based compatibilizers (hydrogenated elastomer resins), 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 styrene-ethylene-butylene-styrene block copolymers having functional groups. Hydrogenated elastomers, 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, and oligomers of styrene-ethylene / butylene-styrene triblock copolymers, either individually or in combination of two or more of these, as well as combinations of these with various tackifiers, etc., are preferred. Therefore, these styrene-based compatibilizers are more effectively used to adjust compatibility, heat resistance, transparency, etc., and if the butadiene portion is contained within the molecule, it is more preferable that it is hydrogenated, and furthermore, it is preferable that it has a functional group (carboxyl group, hydroxyl group, etc., hereinafter the same). Furthermore, when using these styrene-based compatibilizers, the adjustment of compatibilities, heat resistance, fluidity, etc., becomes more effective. Therefore, it is preferable to set the styrene content contained therein to a value in the range of 10 to 80% by weight of the total amount, more preferably to a value in the range of 30 to 75% by weight, and even more preferably to a value in the range of 50 to 70% by weight. Furthermore, when a tackifier is added to a styrene-based compatibilizer to facilitate plasticization and improve compatibility, it is preferable that the tackifier is added in an amount of 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 that the total thickness (t2 + t3) of the first and second surface layers be within the range of 10 to 80 μm. The reason for this is that by controlling the total thickness to a predetermined range, not only is usability improved, but the specific gravity is controlled to a value below the desired value, and excellent thermal shrinkage and transparency can be obtained. More specifically, if the total thickness of the material is less than 10 μm, it may become difficult to adjust the specific gravity, or the handling properties may be significantly reduced. On the other hand, if the total thickness exceeds 80 μm, transparency may decrease, it may become difficult to achieve a uniform thickness, and it may become difficult to adjust the specific gravity. Therefore, it is more preferable that the sum of the thickness of the first surface layer before stretching and the thickness of the second surface layer before stretching be in the range of 20 to 60 μm, and even more preferable that it be in the range of 30 to 50 μm. Furthermore, the thickness of the first and second surface layers after the stretching process will be reduced in thickness according to the stretching conditions, and will be thinner than the thickness mentioned above.

[0039] Furthermore, the thickness of the first surface layer (t2) before or after stretching, and the thickness of the second surface layer (t3), may differ, taking into consideration the intended use and usability of the film. Therefore, when the thickness of the second surface layer (t3) is greater than the thickness of the first surface layer (t2) in the ratio of the thickness of the first surface layer (t2) to the thickness of the second surface layer (t3), it is preferable that the ratio (t2 / t3) be in the range of 0.1 to 0.9, more preferably in the range of 0.2 to 0.8, and even more preferably in the range of 0.3 to 0.7. Of course, in the ratio of the thickness of the first surface layer (t2) to the thickness of the second surface layer (t3), if the thickness of the second surface layer (t3) is thinner than the thickness of the first surface layer (t2), it is preferable that the ratio be greater than 1.1, more preferably within the range of 1.2 to 5, and even more preferably within the range of 1.5 to 4.

[0040] However, considering the intended use and ease of use of the film, as well as the uniformity of the heat shrinkage rate and ease of manufacturing, it is also preferable to make the thickness of the first surface layer (t2) and the thickness of the second surface layer (t3) before stretching substantially equal. In other words, it is preferable to set the ratio (t2 / t3) to a value in the range of greater than 0.9 to 1.1, more preferably to a value in the range of 0.95 to 1.05, and even more preferably to a value in the range of 0.99 to 1.01.

[0041] (8) Additives The structure of the olefin-based heat-shrinkable multilayer film is as described above, but as long as the objectives of the present invention described above are not impaired, other known resins, antioxidants, heat stabilizers, antistatic agents, antiblocking agents, slip agents, nucleating agents, ultraviolet absorbers, colorants, etc. may be appropriately included as needed. Furthermore, while the addition of antistatic agents, antiblocking agents, and slip agents is particularly effective in improving blocking resistance, excessive addition can inhibit solvent adhesion, so careful consideration must be given to the amount added.

[0042] 3.Characteristics (1) Thermal shrinkage The heat shrinkage rate in the main shrinkage direction (TD direction) when immersed in 100°C water, i.e., boiling water, for 10 seconds is defined as A1, and this is characterized by setting A1 to a value within the range of 50 to 80%. The reason for this is that if the thermal shrinkage coefficient A1 falls outside this range, the types and average molecular weights of usable polyolefin resins, polystyrene resins, etc., may be excessively limited. Therefore, when shrinking is performed under the condition of immersion in 100°C water for 10 seconds, it is more preferable that the thermal shrinkage rate A1 in the main shrinkage direction (TD direction) be in the range of 55 to 75%, and even more preferable that it be in the range of 58 to 65%.

[0043] (2) Haze value This invention is characterized by setting the haze value of the olefin-based heat-shrinkable multilayer film before heat shrinkage to 10% or less, as measured in accordance with JIS K 7136:2000. By specifically limiting the haze value to a predetermined range, the transparency of the shrink film can be controlled quantitatively, and its good transparency further enhances its versatility. More specifically, if the haze value of the film before heat shrinkage exceeds 10%, its transparency decreases, which may make it difficult to apply to decorative purposes. On the other hand, if the haze value of the film before heat shrinkage becomes excessively small, it becomes difficult to control stably, which can lead to a significant decrease in production yield. Therefore, it is more preferable to set the haze value of the film before heat shrinkage to a value in the range of 1 to 9%, and even more preferable to set it to a value in the range of 2 to 8%.

[0044] Here, referring to Figure 7, we will explain the relationship between the SBC content (weight %) and the haze value (%) in the polystyrene resin of the surface layer. In other words, the relationship between the SBC content and the haze value will be explained based on data from Example 1, etc. Specifically, the horizontal axis shows the SBC content (by weight %), and the vertical axis shows the haze (%). As shown in the characteristic curve in Figure 7, there is a curvilinear correlation between the amount of SBC (by weight) blended into the total amount (100% by weight) of polystyrene resin, the remaining amount being general-purpose polystyrene, and the haze value, indicating a significant decrease. This suggests that by controlling the SBC content to 50% by weight or more, more preferably 60% by weight 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, and is characterized by being set to a value of 0.95 or less. The reason for this is that when the specific gravity exceeds 0.95, the separation process can become excessively time-consuming and laborious. However, if the specific gravity becomes excessively low, the types and average molecular weights of usable polyolefin resins, polystyrene resins, etc., 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 preferable that the thickness of the olefin-based heat-shrinkable multilayer film after stretching is within the range of 10 to 60 μm. The reason for this is that by setting the thickness of such heat-shrinkable multilayer film within a predetermined range, not only is usability improved, but transparency is further enhanced, and superior heat shrinkage and mechanical properties can be obtained. Therefore, it is more preferable to set the thickness of such heat-shrinkable multilayer film to a value in the range of 20 to 55 μm, and even more preferable to set it to a value in 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, it is preferable that the thickness ratio (t2+t3) / (t1) is within the range of 0.1 to 0.5. The reason for this is that, although it depends on the type of raw materials, by setting the ratio of the thickness of the intermediate layer (t1) to the total thickness of the first and second surface layers (t2+t3) within a predetermined range, the haze value and specific gravity can be controlled to be small, and not only is it easier to use, but excellent heat shrinkage properties can also be obtained. Therefore, it is more preferable to set the thickness ratio to a value within the range of 0.2 to 0.48, and even more preferable to set it to a value within the range of 0.25 to 0.45.

[0048] (6) Relationship between the total thickness of the first and second surface layers and the thickness ratio with respect to the intermediate layer 2 Here, referring to Figure 8, we will explain the relationship between the thickness ratio (t2+t3) / (t1) of each layer before stretching and the haze of the heat-shrinkable multilayer film. Specifically, the horizontal axis shows the values ​​(-) for different thickness ratios of the heat-shrinkable multilayer film before stretching (equivalent to Example 18), and the vertical axis shows the haze (%) of the heat-shrinkable multilayer film before stretching. Judging from the characteristic curve in Figure 8, as the thickness ratio increases in the range of 0.1 to 0.5, the resulting haze value gradually increases, and when the thickness ratio exceeds 0.5, it tends to become significantly higher. Therefore, in order to reduce the haze value of such a heat-shrinkable multilayer film to 10% or less, it is preferable to set the thickness ratio to a value of approximately 0.5 or less. Although not shown in the diagram, it has been found that by setting the thickness ratio within the range of 0.1 to 0.5, the specific gravity of the heat-shrinkable multilayer film can be easily controlled to a value of 0.95 or less.

[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 comprises at least a first to third step.

[0050] 1. Preparation of raw materials and melting process First, as raw materials, 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 linear low-density polyethylene (LLDPE), which is suitable as an olefin resin, or polystyrene-butadiene copolymer (containing a predetermined amount of SBC, etc.), which is suitable as a polystyrene resin, as such raw materials. Next, it is preferable to weigh the raw materials into each of the two stirring containers and heat them using the stirring containers until they become uniform and melted.

[0051] 2. Process for creating the raw material sheet Next, the uniformly mixed raw materials are dried to an extremely dry state, and then, typically, extrusion molding is performed to create a raw material sheet of a predetermined thickness. More specifically, for example, by extruding the material at an extrusion temperature of 220°C using an extruder (manufactured by Tanabe Plastic Machinery Co., Ltd.) with an L / D ratio of 24 and an extrusion screw diameter of 50 mm, a raw material sheet of a predetermined thickness (usually 100-250 μm) can be obtained. Specifically, molten LLDPE was placed in an extruder to form an intermediate layer and melt-kneaded at 180-220°C. Meanwhile, a polystyrene-butadiene copolymer containing a predetermined amount of SBC, etc., was 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 180-220°C.

[0052] Next, it is preferable to set the extrusion amount of each extruder so that the ratio of the thicknesses of each layer (t2+t3) / (t1) is typically 0.1 to 0.5, and to co-extrude downward from a 3-layer die kept at 210°C to obtain a raw material sheet consisting of a predetermined laminate. Furthermore, while it is preferable that the thicknesses of the first surface layer and the second surface layer be substantially equal, it is also preferable that they be different, taking into consideration the intended use.

[0053] 3. Process for creating olefin-based heat-shrinkable multilayer films Next, the obtained raw material sheet (a multilayer laminate) was moved on and between rolls using a shrink film manufacturing apparatus while being heated and pressed, and stretched to, for example, a stretch ratio of 200-800% in the TD direction and 90-120% in the MD direction, thereby creating an olefin-based heat-shrinkable multilayer film. More specifically, the standard stretch ratios are typically set to approximately 500% in the TD direction and approximately 100% in the MD direction.

[0054] 4. Inspection process for olefin-based heat-shrinkable multilayer film (optional process) It is preferable to continuously or intermittently measure the following properties of the prepared olefin-based heat-shrinkable multilayer film and to provide a predetermined inspection process (optional process). In other words, by measuring the following characteristics through a predetermined inspection process and confirming that they fall within a predetermined range, an olefin-based heat-shrinkable multilayer film with more uniform specific gravity separation and heat shrinkage properties can be produced. 1) Visual inspection of the appearance of olefin-based heat-shrinkable multilayer films 2) Measurement of thickness variation 3) Measurement of tensile modulus 4) Measurement of tear strength 5) Measurement of viscoelastic properties using SS curves

[0055] [Third Embodiment] The third embodiment is an embodiment relating to a method for using an olefin-based heat-shrinkable multilayer film. Therefore, any known method of using shrink film can be suitably applied. For example, when implementing a method for using an olefin-based heat-shrinkable multilayer film, first, the olefin-based heat-shrinkable multilayer film is cut to an appropriate length and width, and a long cylindrical object is formed. Next, the long cylindrical object is fed into an automatic labeling device (shrink labeler) and cut to the required length. Next, it is fitted onto the PET bottle or similar container that has been filled with its contents.

[0056] Next, as a heat treatment for the olefin-based heat-shrinkable multilayer film fitted onto PET bottles, etc., it is passed through a hot air tunnel or steam tunnel at a predetermined temperature. Then, by using radiant heat such as infrared rays provided in these tunnels, and by blowing heated steam at around 90°C to 100°C from the surroundings, the olefin-based heat-shrinkable multilayer film is uniformly heated and thermally shrunk. Therefore, as shown in Figure 1(c), the heat-shrinkable olefin-based multilayer film 10 can be adhered to the outer surface of the PET bottle 20 after heat shrinkage, allowing for the rapid production of a labeled container.

[0057] In other words, the olefin-based heat-shrinkable multilayer film of the present invention is an olefin-based heat-shrinkable multilayer film that includes a surface layer derived from a polystyrene resin, as detailed in the first embodiment, and is characterized by satisfying at least the following configurations (a) and (b). By doing so, the heat-shrinkable film becomes easier to handle, and for example, after being attached to a PET bottle, it can improve the ability to prevent the label from tearing during transportation and storage. 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 Figure 1(c), a predetermined decorative layer 10d can be directly or indirectly provided on the second surface layer 10c of the olefin-based heat-shrinkable multilayer film 10', which is the surface facing the PET bottle 20. In other words, the effect can be achieved that the letters, symbols, figures, patterns, etc. of such decorative layer 10d can be sufficiently recognized from the outside through the olefin-based heat-shrinkable multilayer film 10'. [Examples]

[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 in Example 1, etc., without any particular reason. The polyolefin resin, polystyrene resin, etc. used in Example 1 and the like are as follows.

[0059] (1) Olefin resin 1) Type A Ethylene-1-hexene copolymer produced by 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 ch 4 , Mw: 20.2×10 4 , Mw / Mn: 3.1 <P

[0060] 2) Type B Ethylene-1-hexene copolymer produced by a metallocene catalyst Density: 0.91 g / cm 3 , MFR: 1.8 g / 10 min, melt tension: 104 mN Melting 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 a metallocene catalyst Density: 0.92 g / cm 3 , MFR: 2.0 g / 10 min, melt tension: 200 mN Melting enthalpy (ΔH): 110 mJ / mg Mn: 7×10 4 , Mw: 23.8×10 4 , Mw / Mn: 3.4

[0062] 4) Type D Ethylene-1-butene copolymer produced by a Ziegler-Natta catalyst Density: 0.92 g / cm 3 , MFR: 0.2 g / 10 min , Melting 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 using Ziegler-Natta catalysts Density: 0.92g / cm 3 , MFR:1g / 10min Enthalpy of fusion (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 with a styrene / butadiene weight ratio of 85 / 15 and molecular weights of 24,000 and 125,000 for the styrene block portion.

[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 olefin-based heat-shrinkable multilayer films In the first stirring vessel, 100 parts by weight (synonymous with parts by mass, and the same applies hereinafter) of ethylene-1-hexene copolymer produced with a type A metallocene catalyst was placed as an olefin resin for the intermediate layer, and the mixture was stirred while being heated at 220°C to obtain a homogeneous solution. Meanwhile, in the second stirring vessel, 87.7 parts by weight of Type F polystyrene resin for the surface layer, 10 parts by weight of Type L as a compatibilizer, and 2.3 parts by weight of AB as an antiblocking agent were placed, and the mixture was stirred while heating at 220°C to obtain a homogeneous solution.

[0072] Next, each was supplied to an extruder (manufactured by Tanabe Plastic Machinery Co., Ltd.) with an L / D ratio of 24 and an extrusion screw diameter of 50 mm, under conditions of an extrusion temperature of 220°C, and extrusion molding was performed to obtain a three-layered raw material sheet with a thickness of 160 μm. In other words, before stretching, the thickness of each layer of the obtained raw sheet was 16 μm for the surface layer and 128 μm for the intermediate layer, for a total thickness of 160 μm.

[0073] Next, the obtained raw material sheet (a multilayer laminate) was subjected to a shrink film manufacturing apparatus, moving it on and between rolls while heating and pressing, and stretched to a stretch ratio of 500% in the TD direction and 100% in the MD direction, thereby creating 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) added to the olefin resin, which is the main component used in the obtained heat-shrinkable film, was evaluated according to the following criteria. ◎: The amount of SBC included is 60% by weight or more. ○: The amount of SBC included is 50% by weight or more. △: The amount of SBC included is 40% by weight or more. ×: The amount of SBC included is less than 40% by weight.

[0075] (2) Evaluation 2: Enthalpy of fusion (ΔH) Using DSC, the crystalline melting enthalpy of the intermediate layer constituting the olefin-based heat-shrinkable multilayer film was determined at a heating rate of 10°C / min.

[0076] (3) Rating 3: Specific gravity The specific gravity of the olefin-based heat-shrinkable multilayer film was determined from the ratio of the density measured by the density gradient tube method in accordance with JIS K 7112-1:2023 to the density of water at 23°C.

[0077] (4) Rating 4: Haze value The haze value of the obtained heat-shrinkable film was measured in accordance with JIS K 7136:2000.

[0078] (5) Rating 5: Heat shrinkage rate (100℃, 10 seconds) Cut the film into a 100mm x 100mm square so that one side is parallel to the direction of film flow, and immerse it in a hot water bath maintained at 100°C for 10 seconds. Next, immediately after 10 seconds, it was immersed for 10 seconds in a separately prepared 25°C water bath. Next, the film was quickly removed from the hot water bath, and its length in the direction of principal shrinkage was measured to determine its thermal shrinkage rate.

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

[0080] [Example 2] 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 was used as the polystyrene resin for the surface layer; 10 parts by weight of type L was used as a compatibilizer; and 2.3 parts by weight of type AB was used as an antiblocking agent. Then, for each thickness of the obtained raw material sheet, the surface layer was made 24 μm thick and the intermediate layer 112 μm thick, for a total thickness of 160 μm. A heat-shrinkable film was then prepared and evaluated in the same manner as in Example 1, except that it was stretched using this material.

[0081] [Example 3] In Example 3, a three-layer raw material sheet with thicknesses of 16 / 128 / 16 μm was prepared in the same manner as in Example 1, except that 100 parts by weight of type A, an ethylene-1-hexene copolymer produced by 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 a compatibilizer, and 2.3 parts by weight of type AB as an antiblocking agent. A heat-shrinkable film was then produced and evaluated using this sheet.

[0082] [Example 4] In Example 4, a three-layer raw material sheet with thicknesses of 24 / 112 / 24 μm was prepared in the same manner as in Example 2, except that 100 parts by weight of type A, an ethylene-1-hexene copolymer produced by 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 a compatibilizer, and 2.3 parts by weight of type AB as an antiblocking agent. A heat-shrinkable film was then produced and evaluated using this sheet.

[0083] [Example 5] In Example 5, a three-layer raw material sheet with thicknesses of 16 / 128 / 16 μm was prepared in the same manner as in Example 1, except that 100 parts by weight of type A, an ethylene-1-hexene copolymer produced by 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 a compatibilizer, and 2.3 parts by weight of type AB as an antiblocking agent. A heat-shrinkable film was then produced and evaluated using this sheet.

[0084] [Example 6] In Example 6, a three-layer raw material sheet with thicknesses of 24 / 112 / 24 μm was prepared in the same manner as in Example 2, except that 100 parts by weight of type A, an ethylene-1-hexene copolymer produced by 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 a compatibilizer, and 2.3 parts by weight of type AB as an antiblocking agent. A heat-shrinkable film was then produced and evaluated using this sheet.

[0085] [Example 7] In Example 7, a three-layer raw material sheet with thicknesses of 16 / 128 / 16 μm was prepared in the same manner as in Example 1, except that 100 parts by weight of type A, an ethylene-1-hexene copolymer produced by 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 a compatibilizer, and 2.3 parts by weight of type AB as an antiblocking agent. A heat-shrinkable film was then produced and evaluated using this sheet.

[0086] [Example 8] In Example 8, a three-layer raw material sheet with thicknesses of 24 / 112 / 24 μm was prepared in the same manner as in Example 2, except that 100 parts by weight of type A, an ethylene-1-hexene copolymer produced by 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 a compatibilizer, and 2.3 parts by weight of type AB as an antiblocking agent. A heat-shrinkable film was then produced and evaluated using this sheet.

[0087] [Example 9] In Example 9, a three-layer raw material sheet with thicknesses of 16 / 128 / 16 μm was prepared in the same manner as in Example 1, except that 100 parts by weight of type A, an ethylene-1-hexene copolymer produced by 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 a compatibilizer, and 2.3 parts by weight of type AB as an antiblocking agent. A heat-shrinkable film was then produced and evaluated using this sheet.

[0088] [Example 10] In Example 10, a three-layer raw material sheet with thicknesses of 24 / 112 / 24 μm was prepared in the same manner as in Example 2, except that 100 parts by weight of type A, an ethylene-1-hexene copolymer produced by 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 a compatibilizer, and 2.3 parts by weight of type AB as an antiblocking agent. A heat-shrinkable film was then produced and evaluated using this sheet.

[0089] [Example 11] In Example 11, a three-layer raw material sheet with thicknesses of 16 / 128 / 16 μm was prepared in the same manner as in Example 1, except that 100 parts by weight of type A, an ethylene-1-hexene copolymer produced by 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 a compatibilizer, and 2.3 parts by weight of type AB as an antiblocking agent. A heat-shrinkable film was then produced and evaluated using this sheet.

[0090] [Example 12] In Example 12, a three-layer raw material sheet with thicknesses of 24 / 112 / 24 μm was prepared in the same manner as in Example 2, except that 100 parts by weight of type A, an ethylene-1-hexene copolymer produced by 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 a compatibilizer, and 2.3 parts by weight of type AB as an antiblocking agent. A heat-shrinkable film was then produced and evaluated using this sheet.

[0091] [Example 13] In Example 13, a three-layer raw material sheet with thicknesses of 16 / 128 / 16 μm was prepared in the same manner as in Example 1, except that 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 a compatibilizer, and 2.3 parts by weight of Type AB as an antiblocking agent. A heat-shrinkable film was then produced and evaluated using this sheet.

[0092] [Example 14] In Example 14, a three-layer raw material sheet with thicknesses of 24 / 112 / 24 μm was prepared in the same manner as in Example 2, except that 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 a compatibilizer, and 2.3 parts by weight of Type AB as an antiblocking agent. A heat-shrinkable film was then produced and evaluated using this sheet.

[0093] [Example 15] In Example 15, a three-layer raw material sheet with thicknesses of 16 / 128 / 16 μm was prepared in the same manner as in Example 1, except that 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 a compatibilizer, and 2.3 parts by weight of Type AB as an antiblocking agent. A heat-shrinkable film was then produced and evaluated using this sheet.

[0094] [Example 16] In Example 16, a three-layer raw material sheet with thicknesses of 24 / 112 / 24 μm was prepared in the same manner as in Example 2, except that 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 a compatibilizer, and 2.3 parts by weight of Type AB as an antiblocking agent. A heat-shrinkable film was then produced and evaluated using this sheet.

[0095] [Example 17] In Example 17, a three-layer raw material sheet with thicknesses of 16 / 128 / 16 μm was prepared in the same manner as in Example 1, except that 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 the polystyrene resin for the surface layer, 5 parts by weight of Type P was used as a compatibilizer, and 2.3 parts by weight of Type AB was used as an antiblocking agent. A heat-shrinkable film was then produced and evaluated.

[0096] [Example 18] In Example 18, a three-layer raw material sheet with thicknesses of 24 / 112 / 24 μm was prepared in the same manner as in Example 2, except that 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 the polystyrene resin for the surface layer, 5 parts by weight of Type P was used as a compatibilizer, and 2.3 parts by weight of Type AB was used as an antiblocking agent. A heat-shrinkable film was then produced and evaluated.

[0097] [Example 19] In Example 19, a three-layer raw material sheet with thicknesses of 24 / 112 / 24 μm was prepared, with 100 parts by weight of Type A resin produced using a metallocene catalyst as the intermediate olefin resin, 97.2 parts by weight of Type F resin as the surface layer polystyrene resin, and 2.3 parts by weight of Type AB as an antiblocking agent. A heat-shrinkable film was then produced using this sheet and evaluated.

[0098] [Example 20] In Example 20, a three-layer raw material sheet with thicknesses of 24 / 112 / 24 μm was prepared, with the following components used: 100 parts by weight of Type A resin produced using a metallocene catalyst as the intermediate layer olefin resin; 23.18 parts by weight of Type F resin and 69.53 parts by weight of Type K resin as the surface layer polystyrene resin; 5 parts by weight of Type P resin as a compatibilizer; and 2.3 parts by weight of Type AB resin as an antiblocking agent. A heat-shrinkable film was then produced using this sheet and evaluated.

[0099] [Example 21] In Example 21, a three-layer raw material sheet with thicknesses of 24 / 112 / 25 μm was prepared, with the following components used: 100 parts by weight of Type A resin produced using a metallocene catalyst as the intermediate olefin resin, 95.2 parts by weight of Type F resin as the surface layer polystyrene resin, 2.5 parts by weight of Type P as a compatibilizer, and 2.3 parts by weight of Type AB as an antiblocking agent. A heat-shrinkable film was then produced using this sheet and evaluated.

[0100] [Comparative Example 1] In Comparative Example 1, a three-layer raw material sheet with thicknesses of 24 / 112 / 24 μm was prepared, except that 100 parts by weight of Type D resin produced using a Ziegler-Natta catalyst was used as the intermediate olefin resin, 92.7 parts by weight of Type F resin was used as the surface layer polystyrene resin, 5 parts by weight of Type P resin was used as a compatibilizer, and 2.3 parts by weight of Type AB resin was used as an antiblocking agent. A heat-shrinkable film was then produced using this sheet and evaluated. As a result, it is presumed that Comparative Example 1 uses Type D olefin resin in the intermediate layer, which has a crystal melting enthalpy (ΔH) exceeding 135 mJ / mg and a broad molecular weight distribution. However, the stretching process resulted in unevenness and a specific gravity exceeding 0.95.

[0101] [Comparative Example 2] In Comparative Example 2, a three-layer raw material sheet with thicknesses of 16 / 128 / 16 μm was prepared, except that 100 parts by weight of Type E, manufactured using a Ziegler-Natta catalyst, was used as the olefin resin for the intermediate layer, 92.7 parts by weight of Type F, the polystyrene resin for the surface layer, 5 parts by weight of Type P as a compatibilizer, and 2.3 parts by weight of Type AB as an antiblocking agent. A heat-shrinkable film was then produced using this sheet and evaluated. As a result, it is presumed that Comparative Example 2, which uses Type E olefin resin in the intermediate layer, has a crystal melting enthalpy (ΔH) exceeding 135 mJ / mg and a broad molecular weight distribution, and therefore showed a tendency for the thermal shrinkage rate in the TD direction to be considerably low at 45% (less than 50%).

[0102] [Comparative Example 3] In Comparative Example 3, a three-layer raw material sheet with thicknesses of 24 / 112 / 24 μm was prepared, except that 100 parts by weight of Type E, manufactured using a Ziegler-Natta catalyst, was used as the olefin resin for the intermediate layer, 92.7 parts by weight of Type F, the polystyrene resin for the surface layer, 5 parts by weight of Type P as a compatibilizer, and 2.3 parts by weight of Type AB as an antiblocking agent. A heat-shrinkable film was then produced using this sheet and evaluated. As a result, it is presumed that Comparative Example 3, because it uses Type E, an olefin resin with a crystal melting enthalpy (ΔH) exceeding 135 mJ / mg and a broad molecular weight distribution, for its intermediate layer, showed a tendency for the thermal shrinkage rate in the TD direction to be considerably low at 46% (less than 50%).

[0103] [Comparative Example 4] In Comparative Example 4, a three-layer raw material sheet with thicknesses of 16 / 128 / 16 μm was prepared, except that 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 was used as the polystyrene resin for the surface layer, 5 parts by weight of type P was used as a compatibilizer, and 2.3 parts by weight of type AB was used as an antiblocking agent. A heat-shrinkable film was then produced using this sheet and evaluated. As a result, it is presumed that Comparative Example 4 uses Type K polystyrene resin with a low SBC content as the main component. However, stretching treatment caused whitening, resulting in a considerably high haze value of 12.1%.

[0104] [Comparative Example 5] In Comparative Example 5, a three-layer raw material sheet with thicknesses of 24 / 112 / 24 μm was prepared, except that 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 was used as the polystyrene resin for the surface layer, 5 parts by weight of type P was used as a compatibilizer, and 2.3 parts by weight of type AB was used as an antiblocking agent. A heat-shrinkable film was then produced using this sheet and evaluated. As a result, it is presumed that Comparative Example 5 uses Type K polystyrene resin with a low SBC content as the main component. However, whitening occurred during the stretching process, resulting in a considerably high haze value of 19.1%.

[0105] [Table 1]

[0106] [Table 2]

[0107] [Table 3] [Industrial applicability]

[0108] According to the olefin-based heat-shrinkable multilayer film of the present invention, by setting the resin composition of the three layers constituting the olefin-based heat-shrinkable multilayer film to a specific range, it exhibits excellent heat shrinkability, transparency, and interlayer peelability, and in PET bottles and the like, it can heat shrink uniformly, exhibit excellent decorative properties, and does not break during printing or center sealing. Furthermore, even without substantially incorporating relatively expensive cyclic olefin resins, when applied to PET bottles and the like, it now exhibits uniform heat shrinkage and excellent decorative properties.

[0109] Furthermore, because its specific gravity is low (0.95 or less), even when used as a heat-shrinkable film for PET bottles, it is now possible to easily and quickly recover and recycle only the olefin-based heat-shrinkable multilayer film by using a designated cyclone device or the like to separate it by specific gravity.

[0110] Furthermore, when solvents such as cyclohexane and tetrahydrofuran are used as adhesive solvents, the solvent adhesion is excellent, and center sealing can be easily performed using conventional solvent bonding methods, eliminating the need to add additional secondary processing equipment. Therefore, the olefin-based heat-shrinkable multilayer film of the present invention can be suitably applied to various PET bottles, outer covering materials for lunch boxes, and the like, significantly expanding its versatility, and its industrial applicability is extremely high. [Explanation of symbols]

[0111] 10,10',10'': Olefin-based heat-shrinkable multilayer film 10a: Middle layer 10b: First surface layer 10c: Second surface layer 10d: Decorative layer 20: PET bottles

Claims

1. An olefin-based heat-shrinkable multilayer film comprising an intermediate layer derived from a polyolefin resin, a first surface layer on one surface side of the intermediate layer which is derived from at least a polystyrene resin, and a second surface layer on the other surface side of the intermediate layer which is derived from at least a polystyrene resin, and characterized in that it satisfies the following configurations (a) to (d). (a) The molecular weight distribution (Mw / Mn) of the polyolefin resin constituting the intermediate layer shall be 4.0 or less. (b) When shrinkage is caused by immersion in 100°C water for 10 seconds, the thermal shrinkage rate in the main shrinkage direction is A1, and A1 is within the range of 50 to 80%. (c) The haze value measured in accordance with JIS K 7136:2000 shall be between 1% and 9%. (d) 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) shall be within the range of 0.1 to 0.

5.

2. The olefin-based heat-shrinkable multilayer film according to claim 1, characterized in that the crystalline enthalpy of melting (ΔH) of the intermediate layer, as measured by DSC, is 135 mJ / mg or less.

3. The olefin-based heat-shrinkable multilayer film according to claim 1 or 2, characterized in that the polystyrene resin contains 50% by weight or more of a styrene-butadiene copolymer based on the total amount.

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

5. The olefin-based heat-shrinkable multilayer film according to claim 1 or 2, characterized in that the weight-average molecular weight of the polyolefin resin constituting the intermediate layer is in the range of 150,000 to 250,000, and the number-average molecular weight of the polyolefin resin constituting the intermediate layer is in the range of 50,000 to 100,000.

6. The olefin-based heat-shrinkable multilayer film according to claim 1 or 2, characterized in that the polystyrene-based resin constituting the first surface layer and the second surface layer, or either one thereof, contains a styrene-based elastomer.

7. The olefin-based heat-shrinkable multilayer film according to claim 1 or 2, characterized in that the thickness after stretching is 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 specific gravity measured in accordance with JIS K 7112-1:2023 is 0.95 or less.

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