Heat-shrinkable multilayer film

Abstract

To provide a heat-shrinkable multilayer film that is less likely to be loosened after heat shrinkage.SOLUTION: A heat-shrinkable multilayer film has a substrate and an adjacent layer. The substrate has a first face and a second face. The adjacent layer is laminated on at least one of the first and second faces of the substrate and contains thermoplastic resin. The substrate contains long-chain branched polypropylene of 3 mass% or more and less than 20 mass%.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to heat-shrinkable multilayer films. [Background technology]

[0002] Patent Document 1 discloses a heat-shrinkable multilayer film. The heat-shrinkable multilayer film disclosed in Patent Document 1 is formed by laminating an outermost layer containing a resin (A) having an alicyclic structure in its molecule and having a thickness of 1 μm or less, and an intermediate layer containing a thermoplastic resin (B) other than (A). According to Patent Document 1, this provides a heat-shrinkable multilayer film with small natural shrinkage during storage and large shrinkage rate upon heating. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-276516 Summary of the Invention [Problem to be solved by the invention]

[0004] Such heat-shrinkable multilayer films are also used as shrink labels or packaging materials to be attached to plastic or metal containers, taking advantage of their heat shrinkability. Therefore, in addition to having a sufficient shrinkage rate when heated, the films are also required to be less likely to become loose after heat shrinkage. However, Patent Document 1 does not take these points into consideration.

[0005] An object of the present invention is to provide a heat-shrinkable multilayer film that is less likely to become loose after heat shrinkage. [Means for solving the problem]

[0006] A heat-shrinkable multilayer film according to a first aspect includes a substrate and an adjacent layer. The substrate has a first surface and a second surface. The adjacent layer is laminated to at least one of the first surface and the second surface of the substrate and contains a thermoplastic resin. The substrate contains 3% by mass or more and less than 20% by mass of long-chain branched polypropylene.

[0007] A heat-shrinkable multilayer film according to a second aspect is the heat-shrinkable multilayer film according to the first aspect, wherein the substrate contains more than 20% by mass of an alicyclic petroleum resin.

[0008] A heat-shrinkable multilayer film according to a third aspect is the heat-shrinkable multilayer film according to the first or second aspect, in which the adjacent layer contains a cyclic olefin resin.

[0009] A heat-shrinkable multilayer film according to a fourth aspect is the heat-shrinkable multilayer film according to any one of the first aspect to the third aspect, in which the thickness of the substrate is 10 μm to 60 μm.

[0010] A heat-shrinkable multilayer film according to a fifth aspect is the heat-shrinkable multilayer film according to any one of the first to fourth aspects, further comprising a surface layer laminated on an adjacent layer and containing a thermoplastic resin.

[0011] A heat-shrinkable multilayer film according to a sixth aspect is the heat-shrinkable multilayer film according to the fifth aspect, in which adjacent layers are laminated on the first and second surfaces of the substrate, and surface layers are laminated on each adjacent layer. [Effects of the Invention]

[0012] According to the above-mentioned viewpoint, a heat-shrinkable multilayer film that is less likely to loosen after heat shrinkage is provided. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a cross-sectional view showing an example of a heat-shrinkable multilayer film according to an embodiment. [Figure 2] 1 is a cross-sectional view showing an example of a heat-shrinkable multilayer film according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, one embodiment of a heat-shrinkable multilayer film 100 according to the present disclosure will be described. This heat-shrinkable multilayer film 100 comprises a sheet-like substrate having a first side and a second side, and an adjacent layer laminated to at least one of the first side and the second side of the substrate. Therefore, as shown in FIG. 1, the heat-shrinkable multilayer film 100 can take either an embodiment in which an adjacent layer 2 is laminated to both sides of the substrate 1, or an embodiment in which the adjacent layer 2 is laminated to one side of the substrate 1, as shown in FIG. 2. Furthermore, the heat-shrinkable multilayer film 100 may also comprise a surface layer 3 laminated to the adjacent layer 2. Each component will be described in detail below. Furthermore, a film formed from each material may be referred to as a film.

[0015] <1. Base material> The substrate 1 contains a thermoplastic resin. More specifically, the substrate 1 mainly contains a propylene-based resin as the thermoplastic resin, and further contains a polypropylene having a long-chain branched structure. Furthermore, the substrate 1 may contain an alicyclic petroleum resin. This will be explained below.

[0016] <1-1. Propylene-based resin> From the viewpoint of exhibiting heat shrinkability, the propylene-based resin is preferably a binary or ternary random copolymer containing propylene as the main component and an α-olefin as a copolymerization component. Specific examples of the α-olefin include ethylene, 1-butene, 1-hexene, and 1-octene, and the resin may contain two or more types of α-olefins. The proportion of the α-olefin as a copolymerization component is preferably 1 to 10 mol %. Furthermore, the propylene-based resin may be a mixture of different propylene-α-olefin random copolymers.

[0017] Commercially available propylene-based resins such as those mentioned above include, for example, Adsyl (manufactured by Basell) and Novatec (manufactured by Japan Polypropylene Corporation).

[0018] The deflection temperature under load (0.45 MPa) of the propylene-based resin is preferably 110° C. or lower, and more preferably 90° C. or lower. When the propylene-based resin is a mixed resin containing two or more propylene-based resins with different deflection temperatures under load, the deflection temperature under load of the propylene-based resin refers to an apparent deflection temperature under load calculated by summing the products of the deflection temperatures under load of each propylene-based resin and the blending ratio (weight ratio).

[0019] The base material 1 preferably contains 40% by mass or more and 80% by mass or less of the above-mentioned propylene-based resin, and more preferably 50% by mass or more and 76% by mass or less, relative to 100% by mass of the resin components constituting the base material 1.

[0020] <1-2. Long-chain branched polypropylene> Long-chain branched polypropylene is polypropylene with a long-chain branched structure, also known as a comb structure, and examples thereof include metallocene polypropylene. Long-chain branched polypropylene has a structure that makes it easier for molecules to entangle with each other, resulting in excellent shape retention. This helps to suppress the return of the alicyclic petroleum resin (described below) after thermal shrinkage, thereby maintaining the shape retention of the substrate 1 as a whole. Furthermore, long-chain branched polypropylene has high melt tension and strain hardening properties, allowing the thickness of the substrate 1 to be precisely controlled.

[0021] An example of a commercially available product of the long-chain branched polypropylene described above is Waymax (manufactured by Japan Polypropylene Corporation).

[0022] The base material 1 preferably contains 3% by mass or more, more preferably 5% by mass or more, and even more preferably 10% by mass or more of the long-chain branched polypropylene described above, relative to 100% by mass of the resin components constituting the base material 1. On the other hand, from the viewpoint of maintaining appropriate heat shrinkability and ensuring transparency, the base material 1 preferably contains less than 20% by mass, more preferably 15% by mass or less of the long-chain branched polypropylene described above, relative to 100% by mass of the resin components constituting the base material 1.

[0023] <1-3. Alicyclic petroleum resin> Alicyclic petroleum resins are petroleum resins having an alicyclic structure. Petroleum resins are resins obtained by polymerizing the C4-C5 fraction or the C5-C9 fraction remaining after pyrolysis of naphtha to obtain ethylene, propylene, butadiene, etc., in a mixed state. Examples of such resins include aromatic petroleum resins, aliphatic petroleum resins, aromatic hydrocarbon resin-based petroleum resins, alicyclic saturated hydrocarbon resin-based petroleum resins, copolymers of the above-mentioned petroleum resins, and hydrogenated products of these petroleum resins. Among these, the alicyclic petroleum resins already mentioned are preferred from the viewpoints of suppressing softening of the film at temperatures below 100°C and improving transparency. Specific examples include hydrogenated products of alicyclic saturated hydrocarbon resin-based petroleum resins and aromatic petroleum resins.

[0024] Commercially available alicyclic petroleum resins such as those mentioned above include, for example, Regalite (manufactured by Eastman Co.), Imave (manufactured by Idemitsu Kosan Co.), and Alcon (manufactured by Arakawa Chemical Industries Co., Ltd.).

[0025] The softening point of the alicyclic petroleum resin is preferably 80°C or higher and 170°C or lower, and more preferably 110°C or higher and 155°C or lower. If the softening point is lower than 80°C, the heat resistance of the film may decrease, and the petroleum resin component may easily bleed out to the surface in a high-temperature atmosphere. On the other hand, if the softening point is higher than 170°C, molding processability such as extrusion film formability and stretching processability may be impaired. A softening point of the alicyclic petroleum resin of 110°C or higher is preferable because it can suppress natural shrinkage of the film. A softening point of the alicyclic petroleum resin of 155°C or lower is preferable because it can be uniformly stretched in the stretching step that imparts heat shrinkability to the film. Furthermore, a softening point of 120°C or higher and 140°C or lower can particularly exhibit good heat shrinkability. The softening point of the alicyclic petroleum resin can be measured by a method in accordance with JIS K2207:2006.

[0026] The number average molecular weight of the alicyclic petroleum resin is preferably 700 or more and 1300 or less. If the number average molecular weight of the alicyclic petroleum resin is less than 720, the heat resistance of the film may decrease, and the petroleum resin component may easily bleed out to the surface in a high-temperature atmosphere. On the other hand, if the number average molecular weight of the alicyclic petroleum resin exceeds 1300, molding processability such as stretchability may deteriorate. The number average molecular weight of the alicyclic petroleum resin can be confirmed by gel permeation chromatography (GPC).

[0027] The base material 1 preferably contains more than 20% by mass of the above-mentioned alicyclic petroleum resin relative to 100% by mass of the resin components constituting the base material 1, more preferably 21% by mass or more, and even more preferably 30% by mass or more.

[0028] <1-4. Thickness of base material> The thickness of the substrate 1 is, for example, preferably 10 μm or more and 60 μm or less, more preferably 15 μm or more and 50 μm or less, and even more preferably 15 μm or more and 40 μm or less.

[0029] The base material 1 contains a relatively large amount of alicyclic petroleum resin, which improves the heat shrinkability and gloss of the heat shrinkable multilayer film. However, alicyclic petroleum resins tend to shrink back after heat shrinkage, which causes the heat shrinkable multilayer film to loosen after heat shrinkage. The base material 1 contains long-chain branched polypropylene, which has excellent shape retention, which suppresses the shrinkage and loosening caused by the alicyclic petroleum resin. As a result, the heat shrinkable multilayer film 100 including the base material 1 is less likely to loosen after heat shrinkage while maintaining excellent heat shrinkability.

[0030] <2. Adjacent Layer> The adjacent layer 2 is a layer adjacent to at least one of the first and second surfaces of the substrate 1, and contains a thermoplastic resin. The adjacent layer 2 may mainly contain a cyclic olefin resin as the thermoplastic resin, and may further contain an ethylene resin. This will be explained below.

[0031] <2-1. Cyclic olefin resin> The cyclic olefin resin reduces the crystallinity of the thermoplastic resin, increasing the heat shrinkage rate of the adjacent layer 2 and improving the stretchability during film formation. Furthermore, some of the cyclic olefin resin in the adjacent layer 2 is mixed into the substrate 1 during the film formation process. This bonds with the alicyclic petroleum resin contained in the substrate 1, increasing the interlayer adhesive strength between the adjacent layer 2 and the substrate 1.

[0032] The cyclic olefin resin is preferably a cyclic olefin copolymer (COC), such as (a) a copolymer of ethylene or propylene with a cyclic olefin, (b) a copolymer of an α-olefin with a cyclic olefin, (c) a hydrogenated product of the above copolymer, and (d) a graft-modified product of (a) to (c) with an unsaturated carboxylic acid or a derivative thereof.

[0033] As the α-olefin, for example, a linear or branched α-olefin having 2 to 20 carbon atoms can be used, and examples thereof include 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, etc. Two or more of these may be used in combination.

[0034] The cyclic olefin is not particularly limited, and examples thereof include norbornene and derivatives thereof, such as norbornene, 6-methylnorbornene, 6-ethylnorbornene, 5-propylnorbornene, 6-n-butylnorbornene, 1-methylnorbornene, 7-methylnorbornene, 5,6-dimethylnorbornene, 5-phenylnorbornene, and 5-benzylnorbornene, as well as tetracyclododecene and derivatives thereof, such as tetracyclododecene, 8-methyltetracyclo-3-dodecene, 8-ethyltetracyclo-3-dodecene, and 5,10-dimethyltetracyclo-3-dodecene.

[0035] Commercially available products of the above-mentioned cyclic olefin resins include APEL (manufactured by Mitsui Chemicals, Inc.), TOPAS COC (manufactured by Polyplastics Co., Ltd.), and ZEONOR (manufactured by Zeon Corporation).

[0036] The number average molecular weight of the cyclic olefin resin measured by GPC is preferably 1000 or more and 1 million or less. By keeping it within the above range, film formation becomes easy.

[0037] The glass transition temperature of the cyclic olefin resin is preferably 20°C or higher and 130°C or lower, and more preferably 50°C or higher and 100°C or lower. When the glass transition temperature is 20°C or higher, the heat resistance of the film surface is improved, which can prevent blocking between containers on the mounting line and keep the natural shrinkage within a good range. When the glass transition temperature is 130°C or lower, the thermal shrinkage in the transverse direction can be sufficiently increased.

[0038] The adjacent layer 2 preferably contains 70% by mass or more of the above-mentioned cyclic olefin resin relative to 100% by mass of the resin components constituting the adjacent layer 2.

[0039] <2-2. Ethylene-based resins> Examples of ethylene-based resins include branched low-density polyethylene resins, ethylene-vinyl acetate copolymers, ionomer resins, and mixtures thereof. Furthermore, the adjacent layer 2 preferably contains a linear low-density polyethylene resin. Examples of linear low-density polyethylene resins include copolymers of ethylene and α-olefins. Examples of α-olefins include 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, and 1-octene. The copolymer may be a random copolymer or a block copolymer.

[0040] Commercially available linear low-density polyethylene resins such as those described above include Evolue (manufactured by Prime Polymer Co., Ltd.), Yumerit (manufactured by Ube Maruzen Polyethylene Co., Ltd.), and Novatec (manufactured by Japan Polyethylene Co., Ltd.). Commercially available low-density polyethylene resins include Sumikasen (manufactured by Sumitomo Chemical Co., Ltd.) and Novatec (manufactured by Japan Polyethylene Co., Ltd.).

[0041] The adjacent layer 2 preferably contains 30% by mass or less of the above-mentioned ethylene-based resin relative to 100% by mass of the resin component constituting the adjacent layer 2.

[0042] <2-3. Thickness> The thickness of the thermoplastic resin of the adjacent layer 2 is, for example, preferably 1 μm or more and 5 μm or less, and more preferably 1.5 μm or more and 4.5 μm or less.

[0043] <3.Surface layer> The heat-shrinkable multilayer film 100 may further include a surface layer 3. The surface layer 3 is a layer adjacent to the adjacent layer 2, is formed of a thermoplastic resin, and may further contain fine particles. Examples of the thermoplastic resin that can be used include styrene-based resins, polyester-based resins, ethylene-based resins, cyclic olefin-based resins, etc., or a mixture of at least one of these.

[0044] <3-1. Styrene-based resin> Examples of the styrene-based resin that can be used include styrene-butadiene copolymer and hydrogenated styrene-based thermoplastic elastomer. Examples of commercially available styrene-based resins include Clearen (manufactured by Denka Co., Ltd.).

[0045] <3-2. Polyester resin> The polyester resin is not particularly limited, but glycol-modified polyethylene terephthalate is preferred.

[0046] <3-3. Ethylene-based resins> Examples of the ethylene-based resin include linear low-density polyethylene resin, branched low-density polyethylene resin, ethylene-vinyl acetate copolymer, ionomer resin, and mixtures thereof. Commercially available products include those already exemplified in the description of the adjacent layer.

[0047] <3-4. Cyclic olefin resin> Details of the cyclic olefin resin are as described above. When a cyclic olefin resin is used for the surface layer 3, glossiness can be increased and surface properties can be improved. When the surface layer 3 is made of the above-mentioned cyclic olefin resin, glossiness can be increased and surface properties can be improved. Furthermore, in this embodiment, since the adjacent layer 2 also contains a cyclic olefin resin, the interlayer adhesive strength with the adjacent layer 2 is improved.

[0048] <3-5. Fine particles> The surface layer 3 may contain fine particles. The fine particles can be added, for example, to improve the anti-blocking performance of the heat-shrinkable multilayer film. These fine particles can be either organic or inorganic. Examples of organic fine particles include acrylic resin fine particles, styrene resin fine particles, styrene-acrylic resin fine particles, urethane resin fine particles, and silicone resin fine particles. Acrylic resin fine particles are particularly preferred from the viewpoint of compatibility with cyclic olefin resins, and polymethyl methacrylate crosslinked fine particles are even more preferred.

[0049] Commercially available organic fine particles such as those described above include, for example, Techpolymer (manufactured by Sekisui Plastics Co., Ltd.), Finesphere (manufactured by Nippon Paint Co., Ltd.), Ganz Pearl (manufactured by Aica Kogyo Co., Ltd.), and Art Pearl (manufactured by Negami Chemical Industries Co., Ltd.).

[0050] Examples of inorganic fine particles that can be used include silica, zeolite, and alumina.

[0051] The surface layer 3 preferably contains 0.01 parts by weight or more and 0.10 parts by weight or less of the above-mentioned fine particles relative to 100% by mass of the resin component constituting the surface layer 3, and more preferably 0.03 parts by weight or more and 0.08 parts by weight or less.

[0052] <3-6. Thickness> The thickness of the surface layer 3 is, for example, preferably 0.1 μm or more and 3 μm or less, more preferably 0.2 μm or more and 2 μm or less, and even more preferably 0.3 μm or more and 1 μm or less.

[0053] <4. Thickness of heat-shrinkable multilayer film> The overall thickness of the heat-shrinkable multilayer film 100 is, for example, preferably 15 μm or more and 80 μm or less, more preferably 20 μm or more and 70 μm or less, and even more preferably 25 μm or more and 45 μm or less. When the overall thickness of the heat-shrinkable multilayer film 100 is within the above-mentioned range, excellent heat shrinkability is obtained and loosening after heat shrinkage is effectively suppressed. Furthermore, the thickness ratio of the substrate 1 to one adjacent layer 2, substrate / adjacent layer, is preferably in the range of 9:1 to 5:1, more preferably 8:1 to 6:1. By setting the thickness within the above range, an excellent shrink finish can be achieved as a heat-shrinkable multilayer film.

[0054] <5. Other ingredients> The substrate 1, the adjacent layer 2, and the surface layer 3 may each contain additives such as antioxidants, heat stabilizers, ultraviolet absorbers, light stabilizers, lubricants, antistatic agents, flame retardants, antibacterial agents, fluorescent brighteners, and colorants, as necessary.

[0055] <6. Heat shrinkage rate of heat-shrinkable multilayer film> When the heat-shrinkable multilayer film 100 is immersed in 100°C hot water for 10 seconds, then immersed in 20°C water for 10 seconds, and then removed, the heat shrinkage rate in the main shrinkage direction (TD direction) is preferably 64% or more and preferably 76% or less. Furthermore, when the heat-shrinkable multilayer film 100 is immersed in 100°C hot water for 10 seconds, then immersed in 20°C water for 10 seconds, the heat shrinkage rate in the direction perpendicular to the main shrinkage direction (MD direction) is preferably 5% or more and preferably 20% or less. When the heat shrinkage rate is within the above-mentioned range, problems such as poor shrinkage do not occur, and the film can be suitably used, particularly as a heat-shrinkable multilayer film to be attached to a container.

[0056] <7. Glossiness of heat-shrinkable multilayer film> Since the heat-shrinkable multilayer film 100 can be used as a base film for a heat-shrinkable label, it is preferable that the glossiness of the appearance is 140 or more. This glossiness is measured at an incident angle of 45° using a VG-2000 model manufactured by Nippon Denshoku Industries Co., Ltd. according to a method conforming to ASTM D523.

[0057] 8. Manufacturing method of heat-shrinkable multilayer film Although there are no particular limitations on the method for producing the heat-shrinkable multilayer film 100, a method in which each layer is simultaneously formed by coextrusion is preferred. When the coextrusion method is coextrusion using a T-die, the lamination method may be any of a feed block method, a multi-manifold method, or a method combining these.

[0058] Specific examples of methods for producing the heat-shrinkable multilayer film 100 include a method in which the raw materials constituting the above-mentioned substrate, adjacent layer, and surface layer are each fed into an extruder, extruded into a sheet through a die, cooled and solidified by a take-up roll, and then uniaxially or biaxially stretched. Examples of stretching methods that can be used include roll stretching, tenter stretching, and a combination of these. The stretching temperature varies depending on the softening temperature of the resin constituting the heat-shrinkable multilayer film 100, the shrinkage properties required of the heat-shrinkable multilayer film 100, and the like, but is preferably 65°C or higher, more preferably 70°C or higher, and preferably 120°C or lower, more preferably 115°C or lower.

[0059] The stretching ratio in the main shrinkage direction varies depending on the resin constituting the heat-shrinkable multilayer film 100, the stretching means, the stretching temperature, etc., but is preferably 3 times or more, more preferably 4 times or more, and is preferably 7 times or less, more preferably 6 times or less.

[0060] <9. Features> In the heat-shrinkable multilayer film 100, the substrate 1, which is the thickest and contributes most to the overall heat shrinkability, contains a relatively large amount of an alicyclic petroleum resin with excellent heat shrinkability and also contains a long-chain branched polypropylene with high melt tension, thereby providing a heat-shrinkable multilayer film with excellent heat shrinkability and little loosening after heat shrinkage.

[0061] Furthermore, in the heat-shrinkable multilayer film 100, the adjacent layer 2 contains a cyclic olefin resin as a main component, thereby providing a highly glossy appearance. Furthermore, the adjacent substrate 1 contains an alicyclic petroleum resin, which has a similar structure to the cyclic olefin resin, thereby improving interlayer adhesion with the substrate 1 and providing a heat-shrinkable multilayer film with high interlayer adhesive strength. [Example]

[0062] Examples of the present disclosure will be described in detail below, but the present disclosure is not limited to these examples.

[0063] <1. Preparation of Examples and Comparative Examples> Heat-shrinkable multilayer films according to Examples 1 to 7 and Comparative Examples 1 to 3 were produced as follows. The heat-shrinkable multilayer films according to Examples 1 to 6 and Comparative Examples 1 and 2 had a three-layer structure, as shown in Fig. 1, including a substrate and adjacent layers laminated on both sides of the substrate, with the surface layers of Fig. 1 omitted. On the other hand, the heat-shrinkable multilayer films according to Example 7 and Comparative Example 3 had a five-layer structure, as shown in Fig. 1, including a substrate, adjacent layers laminated on both sides of the substrate, and surface layers laminated on each adjacent layer.

[0064] The components shown in Table 1 were used as raw materials for the substrate, adjacent layer, and surface layer, and these were mixed in the ratios shown in Table 1 to obtain raw material compositions for the substrate, adjacent layer, and surface layer of Examples 1 to 7 and Comparative Examples 1 to 3. A propylene copolymer was used as the main component of the substrate. Weymax (manufactured by Japan Polypropylene Corporation) was used as the long-chain branched polypropylene for the substrate. Arcon P125 (manufactured by Arakawa Chemical Industries, Ltd.) was used as the alicyclic petroleum resin for the substrate. In Examples 5 and 6, an aromatic petroleum resin was used instead of the alicyclic petroleum resin.

[0065] The ethylene-based resin for the adjacent layer was linear low-density polyethylene. The cyclic olefin-based resin for the adjacent layer was cyclic olefin copolymer (COC). The surface layer was also formed using the same cyclic olefin copolymer (COC).

[0066] Subsequently, the raw material compositions constituting the substrate, adjacent layer, and surface layer were melted using separate extruders at a barrel temperature of 180°C for the substrate, 210°C for the adjacent layer, and 210°C for the surface layer, and extruded through a T-die and cooled and solidified using rolls cooled to 30°C to produce an unstretched sheet. This was stretched 5 times in the TD direction using a tenter-type stretching machine at a temperature of 90°C, to produce each heat-shrinkable multilayer film.

[0067] The thickness of the heat-shrinkable multilayer films of Examples 1 to 6 and Comparative Examples 1 and 2 was 40 μm in total, consisting of a 32 μm substrate thickness and a 4 μm adjacent layer thickness, and the thickness of the heat-shrinkable multilayer films of Example 7 and Comparative Example 3 was 41 μm in total, consisting of a 32 μm substrate thickness, a 4 μm adjacent layer thickness, and a 0.5 μm surface layer thickness.

[0068] [Table 1] The units of the materials constituting the surface layer, adjacent layer, and substrate are % by mass.

[0069] <2. Evaluation> The above-mentioned Examples 1 to 7 and Comparative Examples 1 to 3 were evaluated as follows.

[0070] <2-1. Glossiness> The gloss at an incident angle of 45° was measured for Examples 1 to 7 and Comparative Examples 1 to 3 using a VG-2000 model manufactured by Nippon Denshoku Industries Co., Ltd. according to a method in accordance with ASTM D523.

[0071] <2-2. Visual Inspection> The presence or absence of appearance defects was inspected by visual inspection. If ground glass-like unevenness was visually confirmed and the sample was not transparent, it was judged to have an appearance defect, and if no unevenness was visually confirmed and the sample was transparent, it was judged to have no appearance defect.

[0072] <2-3. Shrinkage rate> Three measurement samples measuring 100 mm length x 100 mm width (the TD direction of the film is the longitudinal direction, and the MD direction is the transverse direction) were cut out from any position of each of the heat-shrinkable multilayer films according to Examples 1 to 7 and Comparative Examples 1 to 3. Each measurement sample was immersed in warm water at 100°C for 10 seconds, and then in water at 20°C for 10 seconds. After being removed from the water, the length L1 in the TD direction and the length L2 in the MD direction of each measurement sample were measured, and the heat shrinkage in each direction was calculated according to the following formula, and the average value for the three samples was calculated. Heat shrinkage rate (%) = {(100-Ln) / 100} x 100 (n=1, 2)

[0073] <2-4. Amount of looseness> Using the heat-shrinkable multilayer films of Examples 1 to 7 and Comparative Examples 1 to 3, cylindrical bodies of the same dimensions were fabricated, with the TD direction of the film as the circumferential direction. The fabricated cylindrical bodies were wrapped around empty containers of the same dimensions, shrunk in a hot air shrink tunnel at 100°C, and attached to the containers. Immediately after attachment, it was confirmed that each cylindrical body was tightly attached to the container. Thereafter, the containers with the cylindrical bodies were left standing at an air temperature of 20°C for 24 hours, and the cylindrical bodies were cut open and removed from the containers, and their circumferential lengths (length along the wrapping direction) were measured. The outer circumference of the container was 280 mm. If the measured deviation in length of the cylindrical body (amount of slack, mm) from this was 1.3 mm or less, it was determined that slack was suppressed, and if it exceeded 1.3 mm, it was determined that slack had occurred.

[0074] <3. Evaluation Results> The evaluation results are shown in Table 2 below. [Table 2]

[0075] According to the above results, in Examples 1 to 4 and 7, the shrinkage rates in the TD and MD were within the preferred ranges, and the amount of slack after heat shrinkage was suitably suppressed. Furthermore, the gloss was relatively high, and there was no poor appearance. In terms of the shrinkage rate and the amount of slack after heat shrinkage, Examples 5 and 6 also achieved relatively favorable results, but the gloss decreased. This is thought to be due to the use of an aromatic petroleum resin instead of an alicyclic petroleum resin. In Comparative Examples 1 and 3, which did not contain long-chain branched polypropylene, the amount of slack after heat shrinkage increased. This confirmed that long-chain branched polypropylene suppresses the amount of slack after heat shrinkage. On the other hand, in Comparative Example 2, the heat shrinkage rate in the TD was lower than the lower limit of the preferred range, and poor appearance was confirmed, along with low gloss. This is thought to be due to the relatively high content of long-chain branched polypropylene at 20% by mass. [Explanation of symbols]

[0076] 1 Base material 2 Adjacent layers 3 Surface layer 100 Heat-shrinkable multilayer film

Claims

1. a substrate having a first surface and a second surface; an adjacent layer laminated on at least one of the first surface and the second surface of the substrate and containing a thermoplastic resin; Equipped with The base material contains 3% by mass or more and less than 20% by mass of long-chain branched polypropylene and more than 20% by mass of alicyclic petroleum resin. Heat-shrinkable multilayer film.

2. the adjacent layer contains a cyclic olefin resin, The heat-shrinkable multilayer film according to claim 1 .

3. The thickness of the substrate is 10 μm to 60 μm. The heat-shrinkable multilayer film according to claim 1 or 2.

4. a surface layer laminated on the adjacent layer and containing a thermoplastic resin; Further provided with The heat-shrinkable multilayer film according to any one of claims 1 to 3.

5. the adjacent layers are laminated on the first and second surfaces of the substrate, The surface layer is laminated on each of the adjacent layers. The heat-shrinkable multilayer film according to claim 4.

Images