Olefin-based heat-shrinkable film

Abstract

Provided is an olefin-based heat-shrinkable film that accurately and stably achieves a desired heat shrinkage rate and exhibits good recyclability in a well-balanced manner. The olefin-based heat-shrinkable film contains a polyolefin-based copolymer and satisfies the following characteristics (1)-(3). (1) When immersed in hot water at 100°C for 10 seconds, the heat shrinkage rate in the main shrinkage direction is 50% or greater. (2) The polyolefin-based copolymer has a crystal melting enthalpy of 120 mJ / mg or less as measured by DSC. (3) The polyolefin-based copolymer has a density of 0.912 g / cm3 or less as measured in accordance with JIS K7112-1 (2023).

Description

Olefin-based heat-shrinkable film

[0001] This invention relates to an olefin-based heat-shrinkable film (hereinafter sometimes simply referred to as a heat-shrinkable film). More specifically, it relates to an olefin-based heat-shrinkable film that, whether single-layer or multi-layer, can accurately and stably control the desired heat shrinkage rate by defining the crystal melting enthalpy, etc., measured using DSC, and further exhibits good recyclability in a well-balanced manner.

[0002] Conventionally, heat-shrinkable films have been derived from styrene-based resins and PET-based resins, and due to their excellent mechanical properties and transparency, they have been widely used as base films for labels on PET bottles and other products made from PET-based resins. However, PET-based heat-shrinkable films have problems such as poor lightness, difficulty in specific gravity separation from the PET-based resins that make up PET bottles, and the fact that the PET-based heat-shrinkable films themselves tend to aggregate, resulting in poor recyclability.

[0003] Therefore, olefin-based heat-shrinkable films are attracting attention because they are inexpensive, economically efficient, have a relatively low specific gravity, and are highly recyclable. Specifically, ethylene-based heat-shrinkable films derived from a predetermined ethylene polymer composition have been proposed (see, for example, Patent Document 1). That is, the density of the predetermined ethylene polymer is 0.88 to 0.94 g / cm³. 3 The melt flow rate (190°C, 2.16 kgf (21.6 N)) is 0.1 to 200 g / 10 min, the ratio to the specified melt flow rate (210°C, 10 kgf) is 1 to 20, and the molecular weight distribution ratio (Mw / Mn) is 2 to 4. Furthermore, the ethylene-based heat shrinkable film derived from the specified ethylene polymer has a heat shrinkage rate of 8% or more at 70°C, 15% or more at 80°C, and 30% or more at 90°C.

[0004] Furthermore, a method for producing an ethylene-based heat-shrinkable film derived from an ethylene polymer composition containing a plurality of predetermined ethylene polymers has been proposed (see, for example, Patent Document 2). More specifically, the method for producing a heat-shrinkable polyolefin film is characterized by a. forming an unoriented polyolefin film structure, and b. stretching the polyolefin film at a selected stretching speed, a predetermined stretching ratio, and stretching temperature, wherein the polyolefin film structure consists of an ethylene polymer with a polymer density of less than 0.915 g / cc.

[0005] Furthermore, an ethylene-based heat-shrinkable film derived from an ethylene polymer composition containing a plurality of predetermined ethylene polymers has been proposed (see, for example, Patent Document 3). Such an ethylene-based heat-shrinkable film is characterized by being derived from an ethylene polymer composition containing a first ethylene polymer and a second ethylene polymer, having the following characteristics (i) to (iii): (i) The first ethylene polymer and the second ethylene polymer each show one or more melting peaks when measured using differential scanning calorimetry (DSC). (ii) The density of the first ethylene polymer is 0.87 to 0.93 g / cc (g / cm³). 3 It is identical to the above, and the same applies hereinafter.) and is contained in an amount of 20 to 80% by weight of the total weight. (iii) The density of the second ethylene polymer is 0.89 to 0.96 g / cc, and the density difference with respect to the first ethylene polymer is 0 to 0.05 g / cc.

[0006] Furthermore, the density is 0.94 g / cm³. 3 A heat-shrinkable laminated film has been proposed in which an intermediate layer is made of an olefin resin of less than 100% and an adhesive resin, and a surface layer and a back layer made of styrene resin are provided on the front and back surfaces of this intermediate layer, respectively (see, for example, Patent Document 4). The thickness of each layer of such a heat-shrinkable laminated film satisfies the relationship (surface layer + back layer) / intermediate layer = 1 / 1 to 1 / 6, and is characterized by being produced by stretching it 2 to 6 times in one axis direction.

[0007] Japanese Patent Publication No. 11-152377 (Claims, etc.), Japanese Patent Publication No. 2000-504771 (Claims, etc.), Japanese Patent Publication No. 2000-507644 (Claims, etc.), Japanese Patent Publication No. 2000-309071 (Claims, etc.)

[0008] However, the ethylene-based heat-shrinkable film described in Patent Document 1 has problems such as the fact that the predetermined range for the melt flow rate (190°C, 2.16 kgf (21.6 N)) is too wide, and the value of the heat shrinkage rate is strictly defined for each temperature (70°C, 80°C, 90°C), making it difficult to manufacture and difficult to achieve a balanced and stable heat shrinkage.

[0009] Furthermore, the method for manufacturing ethylene-based heat-shrinkable film described in Patent Document 2 requires stretching at a predetermined stretching speed, predetermined stretching ratio, and stretching temperature, and the polyolefin film structure must be formed from an ethylene polymer with a predetermined density (less than 0.915 g / cc). While the manufacturing conditions are strictly defined, there is a problem in that the heat shrinkage rate of the resulting ethylene-based heat-shrinkable film tends to vary.

[0010] Furthermore, the ethylene-based heat-shrinkable film described in Patent Document 3 required a uniform blending of predetermined first and second ethylene polymers. As a result, the density, density difference, and heat shrinkage rate of the resulting ethylene-based heat-shrinkable film were low and prone to variation. For example, even under shrinkage conditions of 105°C for 10 seconds, the heat shrinkage rate was at most 52%. In other words, it was difficult to obtain the desired heat shrinkage rate and recyclability in a balanced and stable manner.

[0011] Furthermore, the heat-shrinkable laminated film described in Patent Document 4 required the creation of a three-type, five-layer structure, with an intermediate layer made of an olefin resin and a predetermined adhesive resin, and a surface layer and a back layer made of a styrene resin on top of it. As a result, it was difficult to accurately control the ratio of each layer, which meant that the specific gravity and heat shrinkage rate of each layer were low and prone to variation during manufacturing, making it difficult to accurately and stably control the desired heat shrinkage rate. Moreover, because it was difficult to lower the specific gravity of the entire film, some of it would sink after printing, resulting in problems with recyclability.

[0012] Furthermore, in the olefin resins used in ethylene-based heat-shrinkable films described in Patent Documents 1 to 4, no attention was paid to the influence of density and other factors in relation to values ​​such as crystal melting enthalpy measured by DSC. As a result, in all cases, the problem arose that it was not possible to obtain an olefin-based heat-shrinkable film that could accurately and stably control the desired heat shrinkage rate and exhibit good recyclability in a well-balanced manner.

[0013] Therefore, the present inventors have discovered that by satisfying at least characteristics (1) to (3) in an olefin-based heat-shrinkable film containing a specific polyolefin copolymer, the enthalpy of crystalline melting of the polyolefin copolymer can be defined using DSC, thereby controlling the heat shrinkage rate to a desired range and further exhibiting good recyclability, thus completing the present invention. In other words, the present invention aims to efficiently provide an olefin-based heat-shrinkable film that, whether single-layer or multi-layer, can achieve a uniform heat shrinkage rate with high accuracy and stability by defining the enthalpy of crystalline melting, etc., measured using DSC, while also being effectively lightweight, well-balanced, and easy to recycle.

[0014] The present invention provides an olefin-based heat-shrinkable film derived from a polyolefin copolymer, characterized by satisfying the following characteristics (1) to (3), thereby solving the above-mentioned problems. (1) The heat shrinkage rate in the main shrinkage direction (TD direction) when the olefin-based heat-shrinkable film is immersed in 100°C hot water for 10 seconds is 50% or more. (2) The crystalline melting enthalpy of the polyolefin copolymer, as measured by DSC, is 120 mJ / mg or less. (3) The density of the polyolefin copolymer, as measured in accordance with JIS K 7112-1:2023 (corresponding to ISO 1183-1:2023), is 0.912 g / cm³. 3 The following values ​​shall be used. By satisfying these predetermined characteristics, it is possible to efficiently and stably obtain an olefin-based heat-shrinkable film that accurately and stably controls the desired heat shrinkage rate and exhibits a good balance and excellent recyclability.

[0015] Furthermore, when constructing the olefin-based heat-shrinkable film of the present invention, it is preferable that the polyolefin copolymer has a melt flow rate (MFR) of 3.8 g / 10 min or less, as measured in accordance with JIS K 7210-1:2014 (corresponding to ISO 1133-1:2011), as characteristic (4). By further satisfying characteristic (4) in the polyolefin copolymer constituting the olefin-based heat-shrinkable film, it becomes easier to adjust the enthalpy of crystalline melting and the melting point, making it easier to further satisfy the conditions of characteristics (1) to (3).

[0016] Further, in constituting the olefin-based heat-shrinkable film of the present invention, the polyolefin-based copolymer is preferably a copolymer obtained from an olefin monomer and an α-olefin monomer as raw materials. By using such a polyolefin-based copolymer obtained from an olefin monomer and an α-olefin monomer as raw materials, adjustment of crystal melting enthalpy, melting point and the like is facilitated, making it easier to further satisfy the characteristics (1) to (3). It should be noted that if the olefin monomer and α-olefin monomer are an ethylene monomer and an α-ethylene monomer, it can be said that it becomes easier to further satisfy the characteristics (1) to (3).

[0017] Further, in constituting the olefin-based heat-shrinkable film of the present invention, as the characteristic (5), it is preferable that the polyolefin-based copolymer has a first melting point peak within a range of 75 to 100°C and a second melting point peak within a range of 95 to 130°C in DSC measurement. By adjusting the temperature ranges of these melting point peaks in this way, where the polyolefin-based copolymer has at least these two melting point peaks, adjustment of crystal melting enthalpy and the like is further facilitated, making it easier to further satisfy the characteristics (1) to (3).

[0018] Further, in constituting the olefin-based heat-shrinkable film of the present invention, as the characteristic (6), it is preferable that the difference between the temperature T1 of the first melting point peak and the temperature T2 of the second melting point peak is a value within a range of 13 to 40°C. By adjusting the temperature difference between these two melting point peaks of the polyolefin-based copolymer in this way, adjustment of crystal melting enthalpy and the like is further facilitated, making it easier to further satisfy the characteristics (1) to (3).

[0019] Further, in constituting the olefin-based heat-shrinkable film of the present invention, as the characteristic (7), it is preferable that the haze measured in accordance with JIS K 7136:2000 (equivalent to ISO 14782:1999) is a value of 15% or less. By adjusting the value of haze, which is an indicator of transparency, in this way, usability and the like are further improved while satisfying the characteristics (1) to (3).

[0020] In addition, when configuring the olefin-based heat-shrinkable film of the present invention, it is preferable that the thickness is a value within the range of 20 to 100 μm. By setting the thickness of the olefin-based heat-shrinkable film to a value within the predetermined range as described above, while satisfying characteristics (1) to (3), the production of the heat-shrinkable film itself can also be further improved.

[0021] In addition, when configuring the olefin-based heat-shrinkable film of the present invention, as characteristic (8), it is preferable that the natural shrinkage rate after storage at 30°C for 30 days is a value of 4.0% or less. By adjusting the natural shrinkage rate of the olefin-based heat-shrinkable film within the predetermined range as described above, while satisfying characteristics (1) to (3), the storage stability and usability of the heat-shrinkable film can also be further improved.

[0022] Figure 1(a) is a schematic cross-sectional view of an example of a single-layer olefin-based heat-shrinkable film of the present invention, Figure 1(b) is a schematic cross-sectional view of an example of a multilayer olefin-based heat-shrinkable film of the present invention, Figure 1(c) is a schematic cross-sectional view of another example of a multilayer olefin-based heat-shrinkable film of the present invention, and Figure 1(d) is a diagram provided to illustrate an example of how to use the olefin-based heat-shrinkable film of the present invention. Figure 2 is a diagram provided to illustrate the relationship between the enthalpy of fusion of a polyolefin copolymer and the heat shrinkage rate of the heat-shrinkable film. Figure 3 is a diagram provided to illustrate the method for calculating the enthalpy of fusion in an example DSC chart for illustrating two melting point peaks. Figure 4 is a diagram provided to illustrate the relationship between the density of a polyolefin copolymer and the heat shrinkage rate of the heat-shrinkable film. Figure 5 is a diagram provided to illustrate the relationship between the density of a polyolefin copolymer and the enthalpy of fusion. Figure 6 is an example of DSC charts measured for various polyolefin copolymers (corresponding to Examples 1 to 13 and Comparative Examples 1 to 4). Figure 7 is provided to illustrate the relationship between the temperature (T1) of the first melting point peak (low-temperature melting point) of the polyolefin copolymer and the thermal shrinkage rate of the heat-shrinkable film. Figure 8 is provided to illustrate the relationship between the temperature (T2) of the second melting point peak (high-temperature melting point) of the polyolefin copolymer and the thermal shrinkage rate of the heat-shrinkable film. Figure 9 is provided to illustrate the relationship between the difference (T2-T1) between the temperatures of the first melting point peak (T1) and the second melting point peak (T2) of the polyolefin copolymer and the thermal shrinkage rate of the heat-shrinkable film. Figures 10(a) to 10(c) are provided to illustrate an example of the molecular weight distribution of the polyolefin copolymer in Example 1, etc.

[0023] [First Embodiment] The present invention relates to an olefin-based heat-shrinkable film 10, 10' derived from a polyolefin copolymer, as illustrated in Figures 1(a) to (c), characterized in that it satisfies the following characteristics (1) to (3): (1) The heat shrinkage rate in the main shrinkage direction when the olefin-based heat-shrinkable film is immersed in 100°C hot water for 10 seconds is 50% or more. (2) The crystalline melting enthalpy of the polyolefin copolymer, as measured by DSC, is 120 mJ / mg or less. (3) The density of the polyolefin copolymer, as measured in accordance with JIS K 7112-1:2023 (corresponding to ISO 1183-1:2023), is 0.912 g / cm³. 3 The following values ​​shall apply. Below, we will specifically describe the olefin-based heat-shrinkable film that satisfies characteristics (1) to (3), and the polyolefin copolymer used as a raw material for it.

[0024] 1. Polyolefin Copolymer (1) Enthalpy of Melt As a characteristic (2) of the present invention, the polyolefin copolymer is characterized in that the enthalpy of melt (ΔH) of melt, as measured by DSC, is 120 mJ / mg or less. The reason for this is that by controlling the enthalpy of melt, as measured on the DSC chart, to be within this numerical range, a desirable thermal shrinkage rate can be easily obtained.

[0025] Figure 2 shows the relationship between the enthalpy of fusion of the polyolefin copolymer, measured by DSC, and the thermal shrinkage rate of the polyolefin heat-shrinkable film. The X-axis represents the enthalpy of fusion of the polyolefin copolymer (mJ / mg), and the Y-axis represents the thermal shrinkage rate (%) of the polyolefin heat-shrinkable film after heat treatment at 100°C for 10 seconds. These data correspond to Example 1 and Comparative Example 1, which will be described later. As shown in the characteristic curve L1 in Figure 2, it is understood that by controlling the enthalpy of fusion of the polyolefin copolymer, measured by DSC, to a predetermined numerical range, i.e., 120 mJ / mg or less, a desirable thermal shrinkage rate of 50% or more can be obtained in the polyolefin heat-shrinkable film. More specifically, by setting the enthalpy of fusion to 120 mJ / mg or less, the thermal shrinkage rate at 100°C for 10 seconds can be increased, for example. Conversely, if the enthalpy of fusion exceeds 120 mJ / mg, the thermal shrinkage rate decreases significantly, and the material may even fracture during thermal shrinkage. This is thought to be because controlling the enthalpy of fusion within a predetermined range lowers the degree of crystallinity, which in turn increases the number of molecular chains that contribute to orientation during stretching.

[0026] However, if the value of the enthalpy of fusion becomes excessively small, the crystallinity becomes too low, which reduces the mechanical properties of the film and causes it to tear during stretching, making manufacturing difficult. Therefore, it is more preferable to set the enthalpy of fusion to a value in the range of 70 to 120 mJ / mg, even more preferable to set it to a value in the range of 80 to 110 mJ / mg, and even more preferable to set it to a value in the range of 90 to 100 mJ / mg.

[0027] The enthalpy of crystalline melting can be measured in accordance with JIS K 7121:2012 (equivalent to ISO 3146) using a DSC (Differential Scanning Calorimeter) under the conditions shown in Example 1, which will be described later. Here, a specific method for measuring the enthalpy of crystalline melting (ΔH) will be explained with reference to Figure 3. Figure 3 shows a schematic example of a DSC curve obtained in the second scan of the DSC curve. In the section of the DSC curve obtained in the second scan of the DSC curve obtained when evaluating the melting point peak as described above, the section from 140°C to 180°C is a straight line because the phase transition is completely completed. The point where this straight line intersects the DSC curve again when extended to 20°C is defined as the melting start point. The point where the baseline becomes a straight line again is defined as the melting end point. A straight line is then drawn from this melting start point to this melting end point. Therefore, as shown in Figure 3, the enthalpy of crystalline melting (ΔH) is automatically calculated by the accompanying analysis software using the area of ​​the region enclosed by the straight line from the melting start point to the melting end point and the DCS curve. This enthalpy of crystalline melting can be adjusted to a desired range by appropriately adjusting, for example, the composition ratio of the monomer components constituting the polyolefin copolymer, or the manufacturing conditions (such as the degree of elongation). For example, if the polyolefin copolymer is a polyethylene-α-olefin copolymer, the value of the enthalpy of crystalline melting obtained can be adjusted by adjusting the ethylene content and / or α-olefin content.

[0028] (2) The monomer components used as raw materials for the polyolefin copolymer are not particularly limited in type, but typically include random copolymers such as ethylene-α-olefin random copolymers, propylene-α-olefin random copolymers, and butylene-α-olefin random copolymers, as well as block copolymers such as propylene-ethylene block copolymers. Particularly preferred are polyethylene copolymers, and especially ethylene-α-olefin copolymers, because they easily satisfy the density, which is characteristic (3) of the present invention. These polyolefin copolymers have at least two crystalline parts with different melting temperatures, and the enthalpy of crystalline melting can be controlled by controlling the melting points of these crystalline parts, and it is thought that this control contributes to achieving a desirable thermal shrinkage rate. Therefore, it is thought that the control of the melting point described later also contributes to achieving a desirable thermal shrinkage rate.

[0029] Furthermore, as the α-olefin, α-olefins having 2 to 20 carbon atoms are preferred, α-olefins having 2 to 10 carbon atoms are more preferred, and α-olefins having 4 to 8 carbon atoms are even more preferred. More specifically, ethylene, propylene, butene-1, hexene-1, octene-1, etc. are preferred. The polyolefin copolymer is preferably a polyethylene copolymer, and is particularly preferably linear low-density polyethylene (LLPDE), with LLDPE having butene-1, hexene-1, or octene-1 as the α-olefin component being particularly preferred. This is because such LLDPE can more reliably achieve preferred thermal shrinkage rate, density, etc.

[0030] Furthermore, while there are no particular restrictions on the catalyst used when obtaining polyolefin copolymers by polymerization, Ziegler-Natta catalysts and metallocene catalysts can be used because they offer good handling during polymerization. Moreover, since polyethylene resins with excellent stereoregularity and mechanical strength can be easily obtained, it is even more preferable to use a predetermined amount of metallocene catalyst to produce a stereoregular polyethylene copolymer (such as isotactic or syndiotactic).

[0031] (3) Density As part of the configuration (3) of the present invention, the density of the polyolefin copolymer is 0.912 g / cm³ 3 The following characteristics apply. The reason for this is that by setting the density within a predetermined range, it becomes easier to adjust the heat shrinkage rate within a predetermined range. Furthermore, with such a density, the time and effort required for specific gravity separation of the heat shrink film can be reduced, and moreover, it becomes easier to lighten the heat shrink film as a whole or the container packaged with the heat shrink film as a whole. Moreover, if the density is too high, the possibility of breakage increases during stretching in film manufacturing.

[0032] Here, referring to Figure 4, the relationship between the density of the polyolefin copolymer and the thermal shrinkage rate of the heat-shrinkable film is explained. The X-axis represents the density of the polyolefin copolymer (g / cm³). 3 The graph shows the thermal shrinkage rate (%) when the heat-shrinkable film is heat-treated at 100°C for 10 seconds. The first melting point peak of the polyolefin copolymer used in Example 1 and Comparative Example 1, and the thermal shrinkage rate of the heat-shrinkable film obtained using such polyolefin copolymer are plotted. From the characteristic curve L2 in Figure 4, it can be seen that there is a correlation between the density of the polyolefin copolymer and the thermal shrinkage rate of the heat-shrinkable film. That is, the density of the polyolefin copolymer is set to a value within a predetermined numerical range, for example, 0.912 g / cm³. 3It is understood that a preferable heat shrinkage rate of 50% or more can be obtained by controlling as follows. However, if the density of the polyolefin copolymer is excessively low, the mechanical strength, heat resistance, punchability and the like of the film decrease, and the enthalpy of fusion also correspondingly decreases, which may make it difficult to adjust the heat shrinkage rate within a predetermined range. Therefore, in consideration of values such as the heat shrinkage rate and the enthalpy of fusion, the suitable range of the density of the polyolefin copolymer is set to 0.885 to 0.911 g / cm 3 It is preferably a value within the range of 0.890 to 0.910 g / cm 3 More preferably, it is a value within the range of 0.895 to 0.908 g / cm 3 It is even more preferable to set the value within this range. Such density can be measured in accordance with JIS K 7112-1:2023 (corresponding to ISO 1183-1:2023), and more specifically, can be measured based on the method shown in Example 1 and the like described later.

[0033] Next, with reference to FIG. 5, the relationship between the density of the polyolefin copolymer and the crystal fusion enthalpy is shown. The X-axis represents the density (g / cm 3 ) of the polyolefin copolymer, and the Y-axis represents the crystal fusion enthalpy (mJ / mg) of the polyolefin copolymer. From the characteristic curve L3 in FIG. 5, it can be seen that the density (g / cm 3 ) of the polyolefin copolymer and the crystal fusion enthalpy (mJ / mg) have a strong proportional relationship. Specifically, it can be understood that as the density increases, the crystal fusion enthalpy increases linearly as a linear function.

[0034] (4) Melt Flow Rate Also, as part of the structure (4) of the present invention, with respect to the melt flow rate (MFR) of the polyolefin copolymer, it is preferable that the value of the MFR (190°C, 2.16 kg load) measured in accordance with JIS K 7210-1:2014 (corresponding to ISO 1133-1:2011) be 3.8 g / 10 min or less. The reason for this is that if such an MFR exceeds a predetermined range, the predetermined heat shrinkage rate may not be obtained when actually using it as a heat shrinkable film. In addition, having such an MFR within a predetermined range makes it easier to extrude in film manufacturing. For example, if the MFR exceeds 3.8, it becomes difficult to form a film by casting. However, if such an MFR becomes excessively small, although there is an effect from density, the values ​​of melting enthalpy and heat shrinkage rate also tend to be low. Therefore, it is more preferable to set the MFR to a value within the range of 0.1 to 3.7 g / 10 min, even more preferable to set it to a value within the range of 0.5 to 3.5 g / 10 min, and even more preferable to set it to a value within the range of 0.8 to 3.0 g / 10 min.

[0035] (5) Melting point 1. A polyolefin copolymer may have one melting point peak in the DSC chart obtained by DSC measurement, but it is preferable to have multiple melting point peaks (at least a first melting point peak and a second melting point peak).

[0036] Here, the significance of these two melting point peaks will be explained again with reference to Figure 3. Figure 3 shows a schematic example of a DSC chart obtained by performing DSC measurement (dynamic scan) on a polyolefin copolymer constituting a heat-shrinkable film. That is, it is preferable that at least a first melting point peak and a second melting point peak appear on such a DSC chart and that each is identified. The reason for this is that having such two melting point peaks makes it easier to adjust the value and distribution of the crystal melting enthalpy, which is the sum of the melting enthalpy of the first and second melting point peaks. Therefore, it becomes easier to satisfy at least properties (1) to (3), and consequently, it is possible to exhibit suitable heat shrinkability as a heat-shrinkable film.

[0037] Figure 6 shows the DSC charts of the type A to G polyolefin copolymers used in Examples 1 to 7 and the type H to K polyolefin copolymers used in Comparative Examples 1 to 4, obtained by DSC measurement (dynamic scan). From these DSC charts of polyolefin copolymers, it can be confirmed that each polyolefin copolymer in Examples 1 to 7 and Comparative Examples 1 to 4 has at least two melting point peaks. In Examples 1 to 7, etc., the value of the enthalpy of crystalline melting and the value of the thermal shrinkage can be controlled with high precision by controlling the temperatures (T1 and T2) and distribution of these multiple melting point peaks.

[0038] (6) Melting Point 2 More specifically, it is preferable that the temperature of the first melting point peak (T1) of the polyolefin copolymer is in the range of 75 to 100°C, and the temperature of the second melting point peak (T2) is in the range of 95 to 130°C. Here, the temperature of the first melting point peak T1 refers to the temperature of the lowest melting point peak among the multiple melting point peaks. That is, the temperature of the first melting point peak T1 is lower than the temperature of the second melting point peak T2, so T1 < T2. Also, the temperature of the second melting point peak T2 refers to the temperature of the highest melting point peak among the multiple melting point peaks. It has been found that by limiting the temperature range of these melting point peaks, it becomes easier to adjust the enthalpy of crystal melting in the polyolefin copolymer, and it becomes easier to satisfy properties (1) to (3). It can be said that the lower the temperature of the first melting point peak, the higher the thermal shrinkage rate can be. This is thought to be because the partial melting and recrystallization of the film during stretching significantly affects the thermal shrinkage rate.

[0039] Referring to Figure 7, the relationship between the temperature of the first melting point peak of the polyolefin copolymer (low-temperature melting point: T1) and the thermal shrinkage rate of the polyolefin heat-shrinkable film is shown. The X-axis represents the first melting point peak (°C) of the polyolefin copolymer, and the Y-axis represents the thermal shrinkage rate (%) when the heat-shrinkable film is heat-treated at 100°C for 10 seconds. The first melting point peak of the polyolefin copolymer used in Example 1 and Comparative Example 1, and the thermal shrinkage rate of the heat-shrinkable film obtained using such polyolefin copolymer are plotted. From the characteristic curve L7 in Figure 7, it can be seen that there is a negative linear relationship between the low-temperature melting point of the polyolefin copolymer and the thermal shrinkage rate of the heat-shrinkable film. For example, from the characteristic curve L7, it can be seen that by controlling the low-temperature melting point to a value within the range of 75 to 100°C, the thermal shrinkage rate can be adjusted to a suitable value of 50 to 70%. In other words, by controlling the temperature of the first melting point peak (T1) to a value within a predetermined numerical range, a predetermined thermal shrinkage rate can be obtained with high precision and stably. Therefore, in order to obtain a predetermined thermal shrinkage rate, it is more preferable to set the temperature of the first melting point peak (T1) to a value within the range of 77 to 97°C, and even more preferable to set it to a value within the range of 80 to 95°C.

[0040] Next, referring to Figure 8, the relationship between the temperature of the second melting point peak of the polyolefin copolymer (high-temperature melting point: T2) and the thermal shrinkage rate is shown. The X-axis shows the temperature (°C) of the second melting point peak of the polyolefin copolymer, and the Y-axis shows the thermal shrinkage rate (%) of the heat-shrinkable film after a heat treatment at 100°C for 10 seconds, with data for Example 1 and Comparative Example 1 plotted on the X-axis. From the characteristic curves L8 and L'8 in Figure 8, it can be seen that there is a certain correlation between the high-temperature melting point of the polyolefin copolymer and the thermal shrinkage rate of the heat-shrinkable film, although there is some variation. For example, if the density of the polyolefin copolymer is 0.912 g / cm³ 3Under the following conditions, it can be understood from the characteristic curve L8 that by controlling the high-temperature melting point to a value within the range of 95 to 130°C, the thermal shrinkage rate can be adjusted to a suitable range of 50 to 70%. On the other hand, the density of the polyolefin copolymer is 0.912 g / cm³. 3 When the temperature is increased, it can be seen from characteristic curve L'8 that the thermal shrinkage rate can be adjusted by controlling the high-temperature melting point, but it is understood that the thermal shrinkage rate decreases significantly as the high-temperature melting point increases. In other words, by controlling the temperature of the second melting point peak (T2) to a predetermined numerical range, it becomes easier to adjust the enthalpy of crystalline melting in the polyolefin copolymer, and a predetermined thermal shrinkage rate can be obtained with high precision and stability. Therefore, assuming that the temperature of the second melting point peak on the high-temperature side (T2) is higher than the temperature of the first melting point peak (T1), it is more preferable to set it to a value in the range of 96 to 127°C, and even more preferable to set it to a value in the range of 97 to 125°C.

[0041] Furthermore, adjusting the temperature of the second melting point peak (T2) is also involved in controlling the temperature difference between the two melting point peaks (T2-T1), which will be described later, and is also useful for obtaining a predetermined thermal shrinkage rate with high accuracy and stability. First, these melting point peak temperatures can be measured in accordance with JIS K 7121:2012 (corresponding to ISO 11357-2:2013) using a DSC (Differential Scanning Calorimeter) and the conditions shown in Example 1, which will be described later. These melting point peak temperatures can be adjusted, for example, by adjusting the composition ratio and / or type of monomer components constituting the polyolefin copolymer. For example, if the polyolefin copolymer is a polyethylene-α-olefin copolymer, the temperatures of these melting point peaks can be adjusted by adjusting the ethylene content and / or α-olefin content or by adjusting the type of α-olefin.

[0042] (7) Melting point 3 Furthermore, it is preferable that the difference (T2-T1) between the temperature of the first melting point peak (T1) and the temperature of the second melting point peak (T2) be within the range of 13 to 40°C. The reason for this is that by controlling the temperature difference (T2-T1) of these melting point peaks to a predetermined range, it becomes easier to adjust the crystal melting enthalpy, etc., and it becomes easier to satisfy characteristics (1) to (3). Accordingly, it is more preferable that the temperature difference (T2-T1) of these melting point peaks be within the range of 14 to 35°C, and even more preferable that it be within the range of 15 to 30°C.

[0043] Referring to Figure 9, the relationship between the difference (T2-T1) between the temperature of the first melting point peak (T1) and the temperature of the second melting point peak (T2) of the polyolefin copolymer and the thermal shrinkage rate is shown. The X-axis shows the difference (T2-T1, °C) between the temperature of the first melting point peak (T1) and the temperature of the second melting point peak (T2) of the polyolefin copolymer, and the Y-axis shows the thermal shrinkage rate (%) when the heat shrinkable film is heated at 100 °C for 10 seconds. The difference for the polyolefin copolymers used in Example 1 and Comparative Example 1, and the thermal shrinkage rate of the heat shrinkable film obtained using such polyolefin copolymers are plotted. From the characteristic curve L9 in Figure 9, it can be seen that the difference (T2-T1) between the temperature of the first melting point peak (T1) and the temperature of the second melting point peak (T2) of the polyolefin copolymer and the thermal shrinkage rate of the heat shrinkable film also have a positive quadratic relationship, although there is some variation. Therefore, it is understood that by controlling this difference (T2 - T1) to a predetermined numerical range, a predetermined thermal shrinkage rate can be obtained accurately and stably.

[0044] (8) The average molecular weight or the weight-average molecular weight (Mw) of the polyolefin copolymer is preferably in the range of 50,000 to 500,000. This is because having such a weight-average molecular weight (Mw) makes it easier to obtain a heat-shrinkable film with low haze and controlled heat shrinkage. Therefore, it is more preferable that the weight-average molecular weight (Mw) be in the range of 70,000 to 400,000, even more preferable that it be in the range of 100,000 to 300,000, and even more preferable that it be in the range of 150,000 to 280,000.

[0045] On the other hand, it is preferable that the number-average molecular weight (Mn) of such polyolefin copolymer is in the range of 30,000 to 150,000. This is because having such a number-average molecular weight (Mn) in the polyolefin copolymer makes it easier to obtain a heat-shrinkable film with low haze and controlled heat shrinkage. Therefore, it is more preferable that the number-average molecular weight (Mn) be in the range of 40,000 to 130,000, and even more preferable that it be in the range of 50,000 to 100,000.

[0046] Here, Figure 10 shows an example of the molecular weight distribution of polyolefin copolymers used in the examples and comparative examples, as measured by high-temperature GPC. As shown in Figure 10, controlling the molecular weight distribution makes it easier to control haze, thermal shrinkage, etc., so it is preferable to set the molecular weight distribution (Mw / Mn) to a value of 7.0 or less. This is because controlling the molecular weight distribution (Mw / Mn) to 7.0 or less further improves transparency, crystallinity (thermal shrinkage), etc. However, if the molecular weight distribution (Mw / Mn) becomes excessively small, the applicable polymerization methods, usable monomer species, yield, etc. may be excessively limited. Therefore, it is more preferable to set the molecular weight distribution (Mw / Mn) to a value in the range of 1.8 to 7.0, even more preferable to set it to a value in the range of 2.0 to 6.0, and even more preferable to set it to a value in the range of 2.5 to 5.0.

[0047] Furthermore, the weight-average molecular weight (Mw) and number-average molecular weight (Mn) of polyolefin copolymers, as well as the molecular weight distribution (Mw / Mn) based on them, can be measured using high-temperature GPC. More specifically, for example, using an 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 polyethylene resins can be calculated by comparing it with a calibration curve using standard styrene particles.

[0048] 2. Polyolefin-based heat shrinkable film (1) Heat shrinkage rate One of the characteristics of the present invention is that the polyolefin-based heat shrinkable film has a heat shrinkage rate (hereinafter sometimes referred to as heat shrinkage rate A1) of 50% or more in the main shrinkage direction (usually the TD direction) when immersed in hot water at 100°C for 10 seconds. The reason for this is that by controlling such a heat shrinkage rate within a predetermined range, the range of applications for the polyolefin-based heat shrinkable film is expanded, the thickness can be controlled within a predetermined range during manufacturing, and the usability is improved. However, if such a heat shrinkage rate is excessively high, the applicable manufacturing methods, usable monomer species, yield, etc. may be excessively limited. Therefore, it is more preferable to set such a heat shrinkage rate to a value in the range of 55% to 80%, even more preferable to set it to a value in the range of 57% to 80%, and even more preferable to set it to a value in the range of 60% to 70%.

[0049] (2) Natural shrinkage rate Also, as a characteristic (8) of the present invention, it is preferable that the natural shrinkage rate in the main shrinkage direction (TD direction) of the polyolefin-based heat shrink film when stored for a long period of time under the conditions of 30°C for 30 days is 4.0% or less. The reason for this is that by having such a natural shrinkage rate of 4.0% or less, the storage conditions are not excessively restricted, and the predetermined heat shrinkage rate can be obtained more reliably and reproducibly when actually used. However, if such a natural shrinkage rate is excessively small, the types of olefin monomer species that can be used and the average molecular weight are excessively restricted. In addition, other parameters such as the heat shrinkage rate obtained by restricting manufacturing conditions such as the stretching temperature may also be restricted. Therefore, it is more preferable that such a natural shrinkage rate be in the range of 0.1 to 3.9%, even more preferable that it be in the range of 0.2 to 3.5%, and even more preferable that it be in the range of 0.3 to 3.0%. The natural shrinkage rate can be measured as the shrinkage rate when left at 30°C for 30 days, in accordance with the method detailed in Example 1, etc.

[0050] (3) The specific gravity of the heat-shrinkable film, measured in accordance with JIS K 7112-1:2023 (equivalent to ISO 1183-1:2019) (measurement temperature: 23°C, sometimes considered equivalent to density; the same applies hereinafter), is preferably set to a value of 0.95 or less. The reason for this is that by setting the specific gravity of the heat-shrinkable film within a predetermined range, not only is specific gravity separation during the recycling of PET bottles made easier, but the values ​​of enthalpy of fusion and heat shrinkage rate also become easier to adjust. However, if such specific gravity becomes excessively small, the types of polyethylene-based resin compositions that can be used may be excessively limited, the mechanical strength of the polyethylene-based heat-shrinkable film may decrease, or the natural shrinkage rate may become excessively large. Therefore, it is more preferable to set such specific gravity to a value in the range of 0.85 to 0.93, and even more preferable to set it to a value in the range of 0.90 to 0.92. Furthermore, this specific gravity is a weight ratio to water, and in the case of the present invention, it is a characteristic that can be considered virtually identical to density.

[0051] (4) Haze Furthermore, it is preferable that the haze of the heat-shrinkable film (typically for a thickness of 40 μm) measured in accordance with ISO 14782:2021 (corresponding to ISO 14782:1999) be 15% or less. The reason for this is that by specifically limiting the haze of such a film to a predetermined range, the transparency of the heat-shrinkable film can be controlled quantitatively, and the good transparency further enhances its versatility. More specifically, if the haze of the film before heat shrinkage exceeds 15%, the transparency decreases, and it may become difficult to apply it to decorative purposes, etc. On the other hand, if the haze of the film before heat shrinkage becomes excessively small, it becomes difficult to control it stably, and the production yield may decrease significantly. Therefore, it is more preferable to set the haze of the heat-shrinkable film to a value in the range of 0.1 to 13%, even more preferable to set it to a value in the range of 0.3 to 10%, and particularly preferable to set it to a value in the range of 0.5 to 5.0%.

[0052] (5) Thickness It is preferable that the thickness of the heat shrinkable film be within the range of 20 to 100 μm. The reason for this is that by controlling the thickness to a predetermined range, not only is the usability improved, but the specific gravity is controlled to a value below the desired value, and excellent heat shrinkability and transparency can be obtained. More specifically, if the thickness of the heat shrinkable film is less than 20 μm, it may become difficult to adjust the specific gravity, or the handling may be significantly reduced. On the other hand, if the thickness of the heat shrinkable film exceeds 100 μm, the transparency may decrease, or it may become difficult to achieve a uniform thickness. Therefore, it is more preferable that the thickness of the heat shrinkable film be within the range of 25 μm to 60 μm, and even more preferable that it be within the range of 30 to 50 μm.

[0053] (6) Layer structure The heat shrinkable film may also be a single layer formed from a polyolefin copolymer, as shown in Figure 1(a). That is, by using such a single layer, the heat shrinkable film can exhibit predetermined heat shrinkability, etc., by satisfying at least properties (1) to (3), and furthermore, properties (4) to (8), and moreover, it is inexpensive and has the advantage of simplifying and facilitating the manufacturing process, including the inspection process. On the other hand, the layer structure of such a heat shrinkable film may be composed of multiple polyolefin copolymer layers or different layers, but this case will be described in detail in the second embodiment.

[0054] (7) The manufacturing method and the method for manufacturing the heat shrink film will be described in detail in the third embodiment described later.

[0055] (8) Method of Use Furthermore, the method of use of the olefin-based heat shrink film 10' illustrated in Figure 1(d) will be described in detail in the fourth embodiment described later.

[0056] [Second Embodiment] As a second embodiment, a polyolefin-based heat shrinkable film (hereinafter sometimes simply referred to as a multilayer heat shrinkable film) is provided, comprising at least a layer derived from the polyolefin-based copolymer that constitutes the heat shrinkable film described in the first embodiment, and consisting of multiple layers as shown in Figures 1(b) to (c). The polyolefin-based copolymer that constitutes a part of the multilayer heat shrinkable film is the same as the polyolefin-based copolymer in the first embodiment, so a further explanation will be omitted.

[0057] (1) Multilayer structure The multilayer heat shrinkable film has a multilayer structure comprising at least a first layer formed from the polyolefin copolymer. The first layer is a base layer of the heat shrinkable film, and is preferably a base layer (corresponding to an intermediate layer in the case of three or more layers) that constitutes 50% by weight or more, preferably 60% by weight or more, more preferably 70% by weight or more, and even more preferably 80% by weight or more of the total amount of the heat shrinkable film. The reason for this is that by having the base layer constitute each layer containing the polyolefin copolymer in such weight proportions, it becomes easier to adjust the specific gravity of the entire heat shrinkable film, and consequently, the adjustment of the enthalpy of fusion and the heat shrinkage rate can be adjusted accurately and stably.

[0058] Furthermore, in the case of a multilayer structure, the other layers may be a second layer and / or a third layer, which may be formed from the same or different polyolefin copolymers, or they may be layers formed from other compositions, particularly other resin compositions. For example, a second layer and / or a third layer, formed from the same or different polyolefin copolymers, may be laminated on one side of the first layer, or a layer formed from other compositions, particularly other resins or resin compositions, may be laminated. That is, the heat-shrinkable film may be a two-layer film consisting of such a first layer and a second layer laminated on one side of the first layer, or it may be a three-layer film in which the second and third layers are formed on both sides of the first layer.

[0059] Therefore, it is preferable to improve the thermal shrinkage rate at low temperatures by such a second layer and / or third layer, particularly by a second layer and / or third layer having the composition described later. It is also preferable that such a second layer and / or third layer exhibit functions such as reducing the natural shrinkage rate or controlling rigidity. Furthermore, such a second layer and / or third layer can also further strengthen the solvent sealing properties and / or printability on the film surface. In addition, there may be one or more other layers between the first layer and the second layer. Such other layers are preferably, for example, an adhesive layer, an adhesion-improving layer, a thickness-adjusting layer, or a type of printing layer.

[0060] As described above, although such multilayer heat-shrinkable films may include other layers, it is preferable that the weight percentage of the first layer be 99% by weight or less, more preferably 95% by weight or less, even more preferably 90% by weight or less, and even more preferably 85% by weight or less, relative to the total amount of the heat-shrinkable film (100% by weight).

[0061] (2) The composition of the second and third layers. Preferably, the second and third layers are layers formed from the same or different styrene-based block copolymer resin composition or cyclic polyolefin-based resin composition. The reason for this is that layers formed from such resin compositions can achieve a desirable haze in the heat-shrinkable film, and can also achieve a desirable heat shrinkage rate at low temperatures and a desirable natural shrinkage rate in the heat-shrinkable film. More specifically, a film laminated on the first layer with such a resin composition layer can achieve a haze of 10% or less. Furthermore, a heat shrinkage rate of 55% or more can be achieved by heat treatment at 10°C for 10 seconds. Moreover, it is easy to achieve a natural shrinkage rate of 3.5% or less in the direction perpendicular to the main shrinkage direction when stored for a long period of time at 30°C for 30 days.

[0062] Furthermore, the same or different styrene-based block copolymer resin compositions constituting the second and third layers are preferably resin compositions mainly composed of styrene-butadiene copolymer (SBC) (hereinafter also referred to as "SBC resin compositions"). This is because SBC can impart solvent sealing properties to the film surface, and furthermore, it can provide low-temperature shrinkage and / or stiffness. In addition, SBC can also contribute to improved transparency. Therefore, the SBC content in such SBC resin compositions is preferably 70% by weight or more, more preferably 80% by weight or more, and even more preferably 85% by weight or more, based on the total amount of the SBC resin composition.

[0063] Furthermore, the second and third layers may each be made of the same or different resins consisting solely of SBC, but it is preferable that other components are included in the resin composition in addition to SBC in order to improve film properties such as impact resistance and / or antiblocking properties. Accordingly, the SBC content in the SBC resin composition is preferably 99% by weight or less, more preferably 95% by weight or less, and even more preferably 90% by weight or less, based on the total amount (100% by weight) of the SBC resin composition. The density of such SBC is usually 1 to 1.05 g / cm³. 3 The value is preferably within the range of 1.01 to 1.04 g / cm³. 3 It is more preferable that the value be within this range. The reason for this is that if the SEC has such a predetermined density, it becomes easier to control the specific gravity (which is considered the same as density) to a small value when a heat-shrinkable film is formed from it.

[0064] Furthermore, the second and third layers preferably further contain hydrogenated styrene-based thermoplastic elastomer (SEBS). This is because SEBS has high compatibility with the olefin copolymer forming the first layer, and SEBS can improve the interlayer adhesion of the heat-shrinkable film. In other words, if the SEBS content is too low, the interlayer adhesion may decrease. On the other hand, if the SEBS content is too high, the cost will increase, which may be economically disadvantageous. Therefore, the SEBS content in such an SBC resin composition is preferably in the range of 1 to 20% by weight, and more preferably in the range of 5 to 15% by weight, relative to the total amount (100% by weight) of the SBC resin composition. Furthermore, the density of such SEBS is usually 0.95 to 1.05 g / cm³. 3 It is preferable that the value be within the range of 1 to 1.04 g / cm³. 3 It is more preferable to set the value within this range. The reason for this is that if SEBS has such a predetermined density, it becomes easier to control its specific gravity (which is virtually identical to density) to a desired relatively small value when it is used to construct a heat-shrinkable film.

[0065] Furthermore, the same or different styrene-based block copolymer resin compositions constituting the second and third layers preferably further contain an antiblocking agent to prevent film blocking. This is because the antiblocking agent can effectively prevent blocking without significantly altering the properties of the heat-shrinkable film. Such an antiblocking agent may be an organic or inorganic antiblocking agent, but is preferably a styrene-based antiblocking agent, for example, high-impact polystyrene (HIPS). The density of such an antiblocking agent is, for example, 1 to 1.05 g / cm³. 3 It is preferable to set the value within this range. This is because such a density makes it easier to adjust the specific gravity of the entire film to a lower level. Such an antiblocking agent may be melted in the film manufacturing process of the present invention, that is, its shape may be such that it cannot be recognized as a predetermined antiblocking agent within the film.

[0066] Furthermore, by adjusting the content ratio of the antiblocking agent, it is possible to achieve both desirable antiblocking properties and good film heat shrinkage. However, if the content ratio of the antiblocking agent is too high, it tends to be disadvantageous in terms of cost, and in addition, the stretchability and heat shrinkage rate of the film may decrease. Moreover, if the content ratio of the antiblocking agent is too high, the haze of the film may become significantly high. Therefore, it is preferable to set the content ratio of the antiblocking agent in such an SBC resin composition to a value in the range of 0 to 5% by weight relative to the total amount (100% by weight) of the SBC resin composition, and more preferably to a value in the range of 1 to 3% by weight.

[0067] Furthermore, the polyolefin resin composition constituting the second and third layers is preferably a resin composition containing a predetermined amount of cyclic polyolefin copolymer (COC), such as an ethylene-cycloolefin copolymer (hereinafter also referred to as "COC resin composition"). This is because incorporating such COC can impart solvent sealing properties to the film surface and further improve low-temperature shrinkage and / or stiffness. Moreover, COC can also contribute to improving the transparency of the heat-shrinkable film. Therefore, it is preferable that the amount of COC in such COC resin composition be 60% by weight or more, more preferably 65% ​​by weight or more, and even more preferably 70% by weight or more, based on the total amount. However, the second and third layers may be formed from a resin consisting only of COC, but it is also preferable that the resin composition contains a mixture of other components in addition to COC. Therefore, in the case of a mixture, it is preferable that the COC content in the COC resin composition be 90% by weight or less, more preferably 85% by weight or less, and even more preferably 80% by weight or less, relative to the total amount.

[0068] (3) Thickness of the second and third layers The thickness (weight percentage) of the second and third layers may be the same or different, but it is generally preferable to have a value in the range of 5 to 20% by weight, and more preferably in the range of 10 to 15% by weight, relative to the total amount (100% by weight) of the heat shrinkable film. The reason for this is that such thickness allows the second and / or third layers to exhibit desired properties. Specifically, for example, they can exhibit impact resistance, transparency, or gloss. Furthermore, such thickness allows the specific gravity of the entire heat shrinkable film to be set to a desired value, for example, a specific gravity of 0.95 or less can be achieved.

[0069] (4) Heat shrinkage rate It is preferable that the heat shrinkage rate in the main shrinkage direction (TD direction) when the multilayer heat shrinkable film is immersed in hot water at 100°C for 10 seconds is 50% or more. The reason for this is that having such a heat shrinkage rate within a predetermined range makes it possible to provide packaging that is suitable for container shapes where such a heat shrinkage rate is required. Accordingly, it is more preferable that the heat shrinkage rate in the main shrinkage direction (TD direction) when immersed in hot water at 100°C for 10 seconds be in the range of 55 to 80%, even more preferable that it be in the range of 57 to 80%, and even more preferable that it be in the range of 60 to 75%.

[0070] (5) Natural shrinkage rate When the multilayer heat-shrinkable film is stored for a long period of time at 30°C for 30 days, it is preferable that the natural shrinkage rate in the direction perpendicular to the main shrinkage direction be 4.0% or less. The reason for this is that a natural shrinkage rate of 4.0% or less makes it possible to more reliably obtain the predetermined heat shrinkage rate when actually using the film. However, if the natural shrinkage rate is excessively small, the types of polyethylene resins that can be used and the average molecular weight may be excessively limited. Therefore, it is more preferable that the natural shrinkage rate be in the range of 0.1 to 4.0%, even more preferable that it be in the range of 0.3 to 3.8%, and even more preferable that it be in the range of 0.3 to 3.5%. The natural shrinkage rate can be measured as the shrinkage rate when left at 30°C for 30 days, according to the method described in detail in Example 1, etc.

[0071] (6) Specific gravity, or the specific gravity of the multilayer heat shrink film measured in accordance with JIS K 7112-1:2023 (corresponding to ISO 1183-1:2023) (measurement temperature: 23°C, the same applies hereafter), is preferably set to a value of 0.95 or less. The reason for this is that by setting such a specific gravity within a predetermined range, not only is specific gravity separation during the recycling of PET bottles made easier, but overall weight reduction is made easier. However, if such a specific gravity is excessively low, the types of polyethylene-based resin compositions that can be used may be excessively limited, the mechanical strength of the polyethylene-based heat shrink film may decrease, or the natural shrinkage rate may become excessively large. Therefore, it is more preferable to set such a specific gravity to a value in the range of 0.85 to 0.95, and even more preferable to set it to a value in the range of 0.90 to 0.94.

[0072] (7) Haze It is preferable that the haze of the multilayer heat shrinkable film (typically equivalent to a thickness of 40 μm), measured in accordance with JIS K 7136:2000, be 15% or less. The reason for this is that by specifically limiting such haze to a predetermined range, the transparency of the multilayer heat shrinkable film can be controlled quantitatively, and the good transparency further enhances its versatility. More specifically, if the haze of the multilayer heat shrinkable film before heat shrinking exceeds 15%, the transparency decreases, and it may become difficult to apply it to decorative purposes, etc. On the other hand, if the haze of the multilayer heat shrinkable film before heat shrinking becomes excessively small, it becomes difficult to control it stably, and the production yield may decrease significantly. Therefore, it is more preferable that the haze of the multilayer heat shrinkable film be in the range of 0.3 to 15%, even more preferable that it be in the range of 0.5 to 10%, and even more preferable that it be in the range of 0.5 to 4%.

[0073] (8) Thickness It is preferable that the thickness of the multilayer heat shrinkable film be within the range of 20 to 100 μm. The reason for this is that by controlling the thickness to a predetermined range, not only is the usability improved, but the specific gravity is controlled to a value below the desired value, and excellent heat shrinkability and transparency can be obtained. More specifically, if the thickness is less than 20 μm, it may become difficult to adjust the specific gravity, or the handling may be significantly reduced. On the other hand, if the thickness exceeds 100 μm, the transparency may decrease, or it may become difficult to achieve a uniform thickness. Therefore, it is more preferable that the thickness be within the range of 25 μm to 60 μm, and even more preferable that it be within the range of 30 to 50 μm.

[0074] Furthermore, in the case of a three-layer structure having a first layer (base layer) and second and third layers (two surface layers) laminated on two sides of the first layer, the ratio (total weight of the second and third layers) / (total weight of the first layer) is preferably 1 / 1.5 to 1 / 6, and particularly preferably 1 / 2 to 1 / 5. This makes it easier to achieve a density with excellent recyclability. The weight ratio of these layers can be appropriately adjusted, for example, by adjusting the amount of raw materials fed into the extruder.

[0075] [Third Embodiment] The third embodiment is an invention relating to a method for manufacturing the heat-shrinkable film described in the first embodiment, or to a method for manufacturing the multilayer heat-shrinkable film described in the second embodiment.

[0076] 1. Preparation of raw materials and melting process First, a polyolefin copolymer is prepared as the raw material. Therefore, it is preferable to prepare linear low-density polyethylene (LLDPE), which is suitable as a polyolefin copolymer, as the raw material. Next, the raw materials are weighed and added to a stirring container, and it is preferable to heat each in a stirring container until it becomes uniform and melts.

[0077] 2. Process for creating the raw material sheet Next, the uniformly mixed raw materials are dried to an oven-dry state, and then, typically, extrusion molding is performed to create a raw material sheet of a predetermined thickness. More specifically, the extrusion temperature is usually preferably in the range of 190°C to 230°C, and more preferably in the range of 200°C to 220°C. Also, the screw diameter (D) of the extruder is preferably in the range of 15 mm to 35 mm, and more preferably in the range of 20 mm to 30 mm. Accordingly, considering the length (L) and screw diameter (D) of the extruder, the L / D is preferably in the range of 20 to 40, and more preferably in the range of 25 to 35. Then, by extrusion molding using such an extruder, it is usually preferable to form a raw material sheet with a width in the range of 30 μm to 1000 mm, more preferably in the range of 50 μm to 300 μm, and more preferably in the range of 100 μm to 200 μm.

[0078] Furthermore, it is preferable to use, for example, a three-layer extruder as the extruder. This is because, when manufacturing a heat-shrinkable film consisting of a single layer of polyolefin copolymer, a predetermined base sheet can be created by feeding the same polyolefin copolymer into all three raw material inlets of the three-layer extruder. Also, when manufacturing a multilayer heat-shrinkable film using such a three-layer extruder, a predetermined base sheet can be created by feeding the polyolefin copolymer into the raw material inlet for forming the first layer (base layer) of the three raw material inlets of the three-layer extruder, while feeding the compositions that form the surface layers into the raw material inlets for forming the second and third layers (surface layers). In other words, a two-type, three-layer base sheet can be formed using a three-layer extruder in this way.

[0079] 3. Process for creating polyolefin heat shrinkable film Next, it is preferable to stretch the obtained raw sheet by moving it on and between rolls while heating and pressing using a shrink film manufacturing apparatus. More specifically, it is preferable that the stretching ratio in the TD direction be in the range of 300 to 700%, more preferably in the range of 350 to 660%, and even more preferably in the range of 400 to 600%. On the other hand, the stretching ratio in the MD direction is usually preferably in the range of 80 to 120%, more preferably in the range of 85 to 115%, and even more preferably in the range of 90 to 110%. In other words, by stretching in this way, not only single-layer polyolefin heat shrinkable films can be created. Furthermore, it is preferable to combine preheating and fixing treatments in such stretching treatments. Accordingly, it is usually preferable that the preheating temperature be in the range of 80 to 100°C, and even more preferably in the range of 85 to 95°C. Furthermore, the stretching temperature is usually preferably in the range of 80°C to 100°C, and more preferably in the range of 85°C to 95°C. Next, it is also preferable to perform a relaxation operation after stretching. The heat-fixing temperature in such a relaxation operation is usually preferably in the range of 80°C to 100°C, and more preferably in the range of 85°C to 95°C. Then, through such a relaxation operation, the stretching ratio in the TD direction is usually preferably in the range of 250°C to 650%, and more preferably in the range of 350°C to 550%. On the other hand, the stretching ratio in the MD direction is usually preferably in the range of 80°C to 120%, and more preferably in the range of 90°C to 110%. Moreover, in such a relaxation operation, only the stretching ratio in the TD direction may be changed, and the stretching ratio in the MD direction may not be changed.

[0080] 4. Inspection Process for Polyolefin Heat Shrinkable Film (Optional Process) It is preferable to continuously or intermittently measure the following properties of the prepared polyolefin heat shrinkable film and to provide a predetermined inspection process (optional process). That is, by measuring the following properties through the predetermined inspection process and confirming that they fall within a predetermined range, a polyolefin heat shrinkable film with more uniform specific gravity separation and heat shrinkability can be obtained. 1) Visual inspection of the appearance of the polyolefin heat shrinkable film 2) Measurement of thickness variation 3) Measurement of tensile modulus 4) Measurement of tear strength 5) Measurement of viscoelastic properties using SS curve

[0081] [Fourth Embodiment] The fourth embodiment is an embodiment of a method for using polyolefin heat shrink film. Therefore, known methods for using shrink film can be suitably applied to any of them. For example, when implementing a method for using polyolefin heat shrink film, first, the polyolefin heat shrink film is cut to an appropriate length and width and formed into a long cylindrical object. Next, the long cylindrical object is supplied to an automatic labeling device (shrink labeler) and further cut to the required length. Then, it is fitted onto a container filled with contents. Examples of such containers include, but are not limited to, resin containers (e.g., PET resin containers, particularly PET bottles, and polyolefin resin containers, particularly PP bottles) or glass containers (e.g., glass bottles).

[0082] Next, the polyolefin heat-shrinkable film fitted onto the container is subjected to a heat treatment by passing it through a hot air tunnel or steam tunnel at a predetermined temperature. Then, by blowing radiant heat such as infrared rays, or heated steam at about 90°C, from the surroundings into these tunnels, the polyolefin heat-shrinkable film is uniformly heated and heat-shrinked. As a result, the film can be tightly attached to the outer surface of the container, and a labeled container can be quickly obtained.

[0083] In other words, the polyolefin-based heat-shrinkable film of the present invention, by including the specific polyolefin copolymer detailed in the first and second embodiments, can achieve a high heat shrinkage rate and improve recyclability due to its low specific gravity. Furthermore, it can also achieve a low natural shrinkage rate during storage before heat shrinking and high transparency.

[0084] Next, the present invention will be described in more detail by reference to examples. However, the present invention is not limited by the following examples, and can be implemented with appropriate modifications, all of which are included within the technical scope of the present invention.

[0085] [Example 1] 1. Preparation of polyolefin copolymer First, prepare the polyolefin copolymer to be used in Example 1, etc. The polyolefin copolymer to be used in Example 1, etc. is as follows.

[0086] 1) Type A (used in Example 1) Ethylene-1-hexene copolymer produced by a Ziegler-Natta catalyst Density: 0.900 g / cm³ 3 MFR (190°C, 2.16 kgf (21.6 N), the same applies hereafter): 0.8 g / 10 min. Temperature of the first melting peak T1: 86.7°C, temperature of the second melting peak T2: 110.6°C. Melting difference: 23.9°C. Crystal melting enthalpy (ΔH): 92 mJ / mg. Mw: 26.8 × 10⁻⁶ 4 Mn: 6.4 × 10 4 , Mw / Mn: 4.2

[0087] 2) Type B (used in Example 2) Ethylene-1-hexene copolymer produced by a metallocene catalyst: Density: 0.901 g / cm³ 3 MFR: 2.0 g / 10 min. Temperature of the first melting point peak T1: 81.0°C, Temperature of the second melting point peak T2: 97.2°C. Melting point difference: 16.2°C. Crystal melting enthalpy (ΔH): 96 mJ / mg. Mw: 17.2 × 10⁻⁶ 4 Mn: 6.8 × 10 4 , Mw / Mn: 2.5

[0088] 3) Type C (used in Example 3) Ethylene-1-octene copolymer produced by a metallocene catalyst: Density: 0.903 g / cm³ 3 MFR: 1.2 g / 10 min. Temperature of the first melting point peak T1: 93.4°C, Temperature of the second melting point peak T2: 114.7°C. Melting point difference: 21.3°C. Crystal melting enthalpy (ΔH): 94.7 mJ / mg. Mw: 20.9 × 10⁻⁶ 4 Mn: 6.6 × 10 4 , Mw / Mn: 3.2

[0089] 4) Type D (used in Example 4) Ethylene-1-octene copolymer produced by a metallocene catalyst: Density: 0.903 g / cm³ 3 MFR: 3.8 g / 10 min. Temperature of the first melting point peak T1: 91.1°C, Temperature of the second melting point peak T2: 113.1°C. Melting point difference: 22°C. Crystal melting enthalpy (ΔH): 90.8 mJ / mg. Mw: 15.5 × 10⁻⁶ 4 Mn: 5.6 × 10 4 , Mw / Mn: 2.8

[0090] 5) Type E (used in Example 5) Ethylene-1-hexene copolymer produced by a metallocene catalyst: Density: 0.904 g / cm³ 3 MFR: 2.0 g / 10 min, temperature of the first melting point peak T1: 91.1°C, temperature of the second melting point peak T2: 110.4°C, melting difference: 19.3°C, enthalpy of fusion (ΔH): 96 mJ / mg, Mw: 18.1 × 10⁻⁶ 4 Mn: 7.2 × 10 4 , Mw / Mn: 2.5

[0091] 6) Type F (used in Example 6) Ethylene-1-octene copolymer produced by a metallocene catalyst: Density: 0.905 g / cm³ 3 MFR: 0.8 g / 10 min. Temperature of the first melting point peak T1: 97.9°C, Temperature of the second melting point peak T2: 122.9°C. Melting difference: 25.0°C. Crystal melting enthalpy (ΔH): 101 mJ / mg. Mw: 25.9 × 10⁻⁶ 4 Mn: 5.1 × 10 4 Mw / Mn: 5

[0092] 7) Type G (used in Example 7) Ethylene-1-hexene copolymer produced by a metallocene catalyst: Density: 0.910 g / cm³ 3 MFR: 1.7 g / 10 min, temperature of the first melting point peak T1: 99.0°C, temperature of the second melting point peak T2: 112.6°C, melting point difference: 13.6°C, enthalpy of fusion (ΔH): 115 mJ / mg, Mw: 21.7 × 10⁻⁶ 4 Mn: 8.1 × 10 4 , Mw / Mn: 2.7

[0093] 8) Type H (used in Comparative Example 1) Density of ethylene-1-hexene copolymer produced by a metallocene catalyst: 0.913 g / cm³ 3 MFR: 2.0 g / 10 min, temperature of the first melting point peak T1: 101.2°C, temperature of the second melting point peak T2: 113.8°C, melting point difference: 12.6°C, enthalpy of fusion (ΔH): 122 mJ / mg, Mw: 20.1 × 10⁻⁶ 4 Mn: 8.7 × 10 4 , Mw / Mn: 2.3

[0094] 9) Type I (used in Comparative Example 2) Density of ethylene-1-hexene copolymer produced by a metallocene catalyst: 0.916 g / cm³ 3 MFR: 2.0 g / 10 min, temperature of the first melting point peak T1: 104.0°C, temperature of the second melting point peak T2: 116.0°C, melting point difference: 12.0°C, enthalpy of fusion (ΔH): 126 mJ / mg, Mw: 20.5 × 10⁻⁶ 4 Mn: 6.6 × 10 4 , Mw / Mn: 3.1

[0095] 10) Type J (used in Comparative Example 3) Ethylene-1-hexene copolymer produced by a metallocene catalyst: Density: 0.918 g / cm³ 3 MFR: 3.8 g / 10 min. Temperature of the first melting point peak T1: 104.6°C, temperature of the second melting point peak T2: 115.3°C, melting point difference: 10.7°C. Crystal melting enthalpy (ΔH): 129 mJ / mg. Mw: 17.1 × 10⁻⁶ 4 Mn: 6.9 × 10 4 , Mw / Mn: 2.5

[0096] 11) Type K (used in Comparative Example 4) Ethylene-1-butene copolymer produced by a Ziegler-Natta catalyst: Density: 0.920 g / cm³ 3 MFR: 1.0 g / 10 min, temperature of the first melting point peak T1: 109.3°C, temperature of the second melting point peak T2: 123°C, melting point difference: 13.7°C, enthalpy of fusion (ΔH): 138 mJ / mg, Mw: 26.5 × 10⁻⁶ 4 Mn: 6.4 × 10 4 , Mw / Mn: 4.2

[0097] 2. Evaluation of Polyolefin Copolymers Next, the prepared polyolefin copolymers were evaluated as follows. Table 1 shows the evaluation results obtained. In this invention, if multiple melting peaks exist, the temperature of the lowest-temperature melting peak was considered as the melting point.

[0098] (1) Evaluation 1: Density The density of the polyolefin copolymer was measured by the density gradient tube method in accordance with JIS K 7112-1:2023 (equivalent to ISO 1183-1:2019).

[0099] (2) Evaluation 2: Enthalpy of Melt (ΔH) The enthalpy of melt (ΔH) of the polyolefin copolymer was measured using a DSC (DSC7000X manufactured by Hitachi High-Tech Corporation) in accordance with JIS K 7121:2012 (equivalent to ISO 11357-2:2013) at a heating rate of 10 seconds / min.

[0100] (3) Evaluation 3: Melting Point Peak The melting point (°C) of polyolefin copolymers was measured using a DSC in accordance with JIS K 7121:2012 (equivalent to ISO 11357-2:2013). Specifically, the analysis of the melting point peak was performed using the analysis software "Software for NEXTA" attached to the DSC "DSC7000X" manufactured by Hitachi High-Tech Corporation. As shown in Figure 3, at least two melting points were measured on the DSC chart for each of the polyolefin copolymers used. The lowest melting point was defined as the temperature T1 of the first melting point peak, and the highest melting point was defined as the temperature T2 of the second melting point peak. In addition, the difference in temperatures between these melting point peaks was calculated.

[0101] (4) Evaluation 4: The weight-average molecular weight (Mw) and number-average molecular weight (Mn) of the polyolefin copolymer were measured using a high-temperature GPC (HLC-8321GPC / HT) manufactured by Tosoh Corporation, and their molecular weight distribution ratio (Mw / Mn) was calculated.

[0102] (5) Evaluation 5: MFR The MFR of the polyolefin copolymer was measured in accordance with JIS K 7210-1:2014 (equivalent to ISO 1133-1:2011) (measurement temperature: 190°C, load: 2.16 kgf (21.6 N)).

[0103] 3. Preparation of Olefin-Based Heat Shrinkable Film A polyolefin copolymer produced with a type A metallocene catalyst was placed in a stirring vessel and stirred while being heated at 220°C until it became a uniform liquid state. Next, it was supplied to an extruder (manufactured by Labotec Co., Ltd.) with an L / D ratio of 30 and an extrusion screw diameter of 25 mm at an extrusion temperature of 210°C, and extrusion molding was performed to obtain a raw material sheet with a thickness of 160 μm. Next, using a shrink film manufacturing apparatus, the obtained raw material sheet was stretched under conditions such as a preheating temperature of 90°C, a stretching temperature of 90°C, a stretching ratio of 100% in the MD direction, and a stretching ratio of 500% in the TD direction. Immediately thereafter, a relaxation operation was performed using a shrink film manufacturing apparatus at a heat-fixing temperature of 90°C to change the stretching ratio in the MD direction to 100% and the stretching ratio in the TD direction to 450%, thereby creating a heat-shrinkable film with a thickness of 40 μm (hereinafter sometimes referred to as the heat-shrinkable film of Example 1).

[0104] Furthermore, each of the polyolefin copolymers of types B to N (Examples 2 to 13) was obtained in the same manner as the polyolefin copolymer of type A described later, and each olefin-based heat-shrinkable film was prepared. In addition, each of the polyolefin copolymers of types H to K (Comparative Examples 1 to 4) was obtained in the same manner as the polyolefin copolymer of type A described later, and each olefin-based heat-shrinkable film was prepared.

[0105] 4. Evaluation of Single-Layer Olefin Heat Shrinkable Films, etc. (1) Evaluation 6: Heat Shrinkage Rate in the TD Direction (100°C, 10 seconds) A stretched film was cut into a 10 cm x 10 cm square so that one side was parallel to the film flow direction, and this was immersed in a water bath heated to 100°C ± 0.5°C for 10 seconds. Next, after 10 seconds had elapsed since immersing the film in the hot water in the water bath, it was immediately immersed in a separate water bath containing water maintained at 25°C for 10 seconds, and the length in the main shrinkage direction (TD direction) of the film was measured in each case, and the heat shrinkage rate in the TD direction was calculated using the following formula (Evaluation 1). Heat shrinkage rate (%) = 100 × (Length before shrinkage - Length after shrinkage) / (Length before shrinkage)

[0106] (2) Evaluation 7: Recycling Test (Floating Test) Ten heat-shrinkable films (length in the TD direction: 10 mm, length in the MD direction: 10 mm) were floated on the surface of water (23°C) contained in a container, and a recycling test (floating test) was conducted to see if the heat-shrinkable films remained floating on the water for 60 seconds or more, and were evaluated according to the following criteria. ○: All 10 heat-shrinkable films floated on the water. ×: Nine or fewer heat-shrinkable films floated on the water.

[0107] (3) Evaluation 8: Haze In accordance with JIS K 7136:2000 (equivalent to ISO 14782:1999), the haze of the heat shrink film (thickness: approximately 40 μm) was measured, and the measured values ​​were evaluated according to the following criteria. The evaluation results obtained are shown in Table 1. ◎: Haze is 4% or less. ○: Haze is greater than 4% and 10% or less. △: Haze is greater than 10% and 15% or less. ×: Haze is greater than 15%.

[0108] (4) Evaluation 9: Natural Shrinkage A roll of heat-shrinkable film was prepared. Two markings were then made at 300 mm intervals (S1) along the main shrinkage direction (TD direction) of the heat-shrinkable film as an initial value, and the film was left to stand naturally at 30°C for 30 days. After standing, the distance between the markings that had shortened due to natural shrinkage (mm, S2) was measured using calipers or an optical microscope, and the natural shrinkage rate was calculated using the following formula (1). The obtained evaluation results are shown in Table 2.

[0109]

[0110] The natural shrinkage rate was evaluated according to the following criteria based on the values ​​obtained. The evaluation results are shown in Table 1. ◎: Natural shrinkage rate is 3% or less. ○: Natural shrinkage rate is greater than 3% and 3.5% or less. △: Natural shrinkage rate is greater than 3.5% and 4% or less. ×: Natural shrinkage rate is greater than 4%.

[0111] (5) Evaluation 10: Specific Gravity The specific gravity (at 23°C) of the obtained heat shrink film was measured in accordance with JIS K 7112-1:2023 and evaluated according to the following criteria. The evaluation results are shown in Table 1. ◎: Specific gravity is 0.93 or less ○: Specific gravity is greater than 0.93 and 0.94 or less △: Specific gravity is greater than 0.94 and 0.95 or less ×: Specific gravity is greater than 0.95

[0112]

[0113] [Examples 2-7] In Examples 2-7, single-layer olefin-based heat-shrinkable films were prepared using the same method as in Example 1, except that type A was replaced with polyolefin copolymers of types B-G, respectively. These films were then evaluated according to evaluations 1-9. The obtained evaluation results are shown in Table 1.

[0114] [Comparative Examples 1-4] In Comparative Examples 1-4, single-layer olefin-based heat-shrinkable films were prepared in the same manner as in Example 1, except that type H-K polyolefin copolymers were used instead of type A polyolefin copolymer in Example 1. These films were then evaluated according to evaluations 1-9. The obtained evaluation results are shown in Table 1.

[0115] [Example 8] 1. Preparation of a multilayer olefin-based heat shrinkable film As the polyolefin copolymer constituting the first layer (substrate layer) of the film, the type A polyolefin copolymer described above was prepared. Next, as compositions constituting the second and third layers (surface layers) of the film, a styrene-based block copolymer (SBC) resin composition and a cyclic polyolefin copolymer (COC) resin composition were prepared. More specifically, as the styrene-based block copolymer (SBC) resin composition, a resin composition having the composition of SBC 87.7% by weight, hydrogenated elastomer 10% by weight, and antiblocking agent 2.3% by weight was prepared. As the cyclic polyolefin copolymer (COC) resin composition, a material with a glass transition temperature Tg = 67°C and an MFR of 14.1 / 10 min under conditions of 260°C 2.16 kgf (21.6 N) was prepared. Such SBC is a styrene-butadiene copolymer (density 1.025 g / cm³) with a styrene / butadiene weight ratio of 85 / 15 and molecular weights of 24,000 and 125,000 for the styrene block portion. 3 Furthermore, the hydrogenated elastomer is a copolymer in which the butadiene units of the styrene-butadiene block copolymer are hydrogenated, and the ratio of styrene units to butadiene units is 70 / 30. In addition, the antiblocking agent is HIPS (high-impact polystyrene resin).

[0116] Next, the polyolefin copolymer and the SBC resin composition were supplied to an extruder (manufactured by Labotec Co., Ltd.) with an L / D ratio of 30 and an extrusion screw diameter of 25 mm at an extrusion temperature of 210°C, and extrusion molding was performed to obtain a raw material sheet with a thickness of 160 μm. In this extrusion molding, the polyolefin copolymer was fed into a raw material supply port for forming the base layer (first layer), and the SBC resin composition was fed into two raw material supply ports for forming two surface layers (second layers) laminated on each of the two surfaces of the base layer, thereby forming a layer structure of two types and three layers. As a result, a raw material sheet was formed comprising a base layer formed from the polyolefin copolymer, an SBC resin composition surface layer laminated on one side of the base layer, and an SBC resin composition surface layer laminated on the other side of the base layer.

[0117] Next, using a shrink film manufacturing apparatus, the obtained raw sheet was stretched at a preheating temperature of 90°C and a stretching temperature of 90°C, with a stretch ratio of 100% in the MD direction and a stretch ratio of 500% in the TD direction. Immediately thereafter, a relaxation operation was performed using the shrink film manufacturing apparatus at a heat-fixing temperature of 90°C to change the stretch ratio in the MD direction to 100% and the stretch ratio in the TD direction to 450%, thereby creating a heat-shrinkable film with a thickness of 50 μm.

[0118] 2. Evaluation of Multilayer Olefin Heat Shrinkable Films The obtained multilayer olefin heat shrinkable films were evaluated by measuring the heat shrinkage rate and other parameters in the same manner as in Example 1. The evaluation results are shown in Table 2.

[0119]

[0120] [Examples 9-13] In Examples 9-13, multilayer olefin-based heat-shrinkable films were prepared and evaluated using the same method as in Example 8, except that the base layer and surface layer were changed to the resins (Types A, B, C, F) shown in Table 2. The evaluation results are shown in Table 2.

[0121] [Comparative Example 5] In Comparative Example 5, a multilayer olefin-based heat-shrinkable film was prepared and evaluated using the same method as the heat-shrinkable film in Example 8, except that the base layer and surface layer were changed to the resin (Type H) shown in Table 2. The evaluation results are shown in Table 2.

[0122] According to the present invention, an olefin-based heat-shrinkable film that satisfies predetermined characteristics (1) to (3) is provided, and even if it is a single layer, by defining the crystal melting enthalpy etc. measured using DSC, it is possible to accurately and balancedly exhibit the desired heat shrinkage rate and good recyclability. Furthermore, according to the present invention, a multilayer olefin-based heat-shrinkable film is also provided, comprising a first layer formed from a predetermined polyolefin-based copolymer and a layer formed from a styrene-based block copolymer resin composition or a cyclic polyolefin-based resin composition laminated on at least one surface of the first layer, and by satisfying predetermined characteristics (1) to (3), it is possible to exhibit a well-balanced desired heat shrinkage rate and good recyclability.

[0123] Therefore, such polyolefin-based heat-shrinkable films can achieve a high heat shrinkage rate even at relatively low temperatures, such as 100°C, in a well-balanced and precise manner, making them suitable as packaging films where high shrinkage rates at low heating temperatures are required. Moreover, since these olefin-based heat-shrinkable films can achieve a low specific gravity, for example, when recycling PET bottles, the specific gravity separation from the PET bottles can be performed accurately and quickly using a predetermined cyclone device or the like. In addition, among these characteristics (1) to (3), the ability to control the heat shrinkage rate at low temperatures by adjusting the enthalpy of crystal melting is something that could not have been anticipated at all from conventional technology.

[0124] Furthermore, the ethylene-based heat-shrinkable film described in Patent Document 1 improves the heat shrinkage rate by lowering the transverse uniaxial stretching temperature to a low temperature of 55°C, but this makes it prone to spontaneous shrinkage during storage at room temperature, resulting in problems such as the raw material becoming tightly rolled and wrinkled. In addition, the manufacturing method described in Patent Document 2 has the problem of being difficult to manufacture due to the narrow range of stretching temperatures and strict manufacturing conditions. In contrast, the polyolefin-based heat-shrinkable film of the present invention, as described above, can achieve the desired heat shrinkage rate by defining the crystal melting enthalpy, and also offers the manufacturing advantage of being less prone to spontaneous shrinkage.

[0125] Furthermore, the method for producing polyolefin-based heat-shrinkable films of the present invention makes it possible to stably produce polyolefin-based heat-shrinkable films, particularly polyethylene-based heat-shrinkable films, in both single-layer and multi-layer configurations as described above. Therefore, the polyolefin-based heat-shrinkable films of the present invention, particularly polyethylene-based heat-shrinkable films, can be suitably applied to various PET bottles, outer covering materials for lunch boxes, and the like, significantly expanding their versatility. Since they are also easily recyclable, their industrial applicability is extremely high.

[0126] 10, 10': Polyolefin heat shrinkable film 10a: First layer 10b: Second layer 10c: Third layer 20: PET bottle

Claims

1. An olefin-based heat-shrinkable film derived from a polyolefin copolymer, characterized in that it satisfies the following characteristics (1) to (3): (1) The heat shrinkage rate in the main shrinkage direction when the olefin-based heat-shrinkable film is immersed in 100°C water for 10 seconds is 50% or more. (2) The crystalline melting enthalpy of the polyolefin copolymer, as measured by DSC, is 120 mJ / mg or less. (3) The density of the polyolefin copolymer, as measured in accordance with JIS K 7112-1:2023, is 0.912 g / cm³. 3 The following values ​​should be used.

2. The olefin-based heat-shrinkable film according to claim 1, characterized in that the polyolefin copolymer has a property (4) of 3.8 g / 10 min or less, as measured in accordance with JIS K 7210-1:2014.

3. The olefin-based heat-shrinkable film according to claim 1 or 2, characterized in that the polyolefin copolymer is a copolymer made from an olefin monomer and an α-olefin monomer as raw materials.

4. The olefin-based heat-shrinkable film according to claim 3, characterized in that the polyolefin copolymer has, as characteristic (5), a first melting point peak at 75 to less than 100°C and a second melting point peak at 95 to 130°C in DSC measurement.

5. The olefin-based heat-shrinkable film according to claim 4, characterized in that the difference between the temperature T1 of the first melting point peak and the temperature T2 of the second melting point peak is within the range of 13 to 40°C as a property (6) of the polyolefin-based copolymer.

6. The olefin-based heat-shrinkable film according to claim 1 or 2, characterized in that, as a property (7), the haze measured in accordance with JIS K 7136:2000 is 15% or less.

7. The olefin-based heat-shrinkable film according to claim 1 or 2, characterized in that the thickness is within the range of 20 to 100 μm.

8. The olefin-based heat-shrinkable film according to claim 1 or 2, characterized in that, as property (8), the natural shrinkage rate when stored at 30°C for 30 days is 4.0% or less.

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