Heat-shrinkable film

Abstract

To provide a heat-shrinkable film having improved transparency and grease resistance.SOLUTION: A heat-shrinkable film has a surface layer comprising cyclic olefinic resin, ethylene resin, and petroleum resin. The surface layer contains the ethylene resin of 35 mass% or less and the petroleum resin of 5 mass% or more relative to 100 mass% of the total of the cyclic olefinic resin, ethylene resin, and petroleum resin.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Patent Document 1 discloses a heat-shrinkable multilayer film having front and back layers and an intermediate layer. The front and back layers contain 60 to 80 wt % of a cyclic olefin resin and 20 to 40 wt % of an ethylene resin. The intermediate layer contains a resin, and when the total resin components constituting the intermediate layer is taken as 100 mol %, it contains 35 to 70 mol % of a propylene component, 1 to 10 mol % of an ethylene component, and 1 to 10 mol % of a butene component. According to Patent Document 1, this configuration provides a heat-shrinkable film that has low density, excellent shrinkability, high rigidity, is resistant to delamination, and has excellent transparency. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2017-071064 Summary of the Invention [Problem to be solved by the invention]

[0004] Patent Document 1 states that a haze value of less than 7.0% for a heat-shrinkable film is within the acceptable range. The haze value is an index that indicates the degree of cloudiness of a heat-shrinkable film, and the lower the haze value, the higher the transparency. However, in some cases, it may be required to satisfy a higher transparency standard while also improving other aspects of appearance quality. Another criterion for evaluating appearance quality is grease resistance. If grease adheres to a heat-shrinkable film by touching it with a human hand before heat shrinking, the affected area may whiten after heat shrinking. Grease resistance indicates the degree to which whitening due to grease is suppressed, and the higher the resistance, the better.

[0005] The present disclosure aims to provide a heat-shrinkable film with improved transparency and grease resistance.

Means for Solving the Problems

[0006] The heat-shrinkable film according to one aspect of the present disclosure includes a surface layer composed of a cyclic olefin resin, an ethylene resin, and a petroleum resin. The surface layer contains 35% by mass or less of the ethylene resin and 5% by mass or more of the petroleum resin with respect to a total of 100% by mass of the cyclic olefin resin, the ethylene resin, and the petroleum resin.

[0007] The heat-shrinkable film may further include a core layer laminated adjacent to the surface layer. The core layer may contain a propylene resin and a petroleum resin.

[0008] In the heat-shrinkable film, the core layer may contain 10% by mass or more of the petroleum resin with respect to a total of 100% by mass of the propylene resin and the petroleum resin.

[0009] In the heat-shrinkable film, the core layer may further contain a cyclic olefin resin and an ethylene resin.

[0010] In the heat-shrinkable film, the core layer may contain long-chain branched polypropylene as the propylene resin.

[0011] In the heat-shrinkable film, the surface layer may be laminated adjacent to both surfaces of the core layer.

[0012] In the heat-shrinkable film, the cyclic olefin resin may include a first cyclic olefin resin having a glass transition temperature of Tg1 (°C) and a second cyclic olefin resin having a glass transition temperature of Tg2 (°C), and the difference between the glass transition temperatures Tg1 and Tg2 may be 10°C or more.

[0013] In the heat-shrinkable film, the glass transition temperatures Tg1 and Tg2 may satisfy Tg1 < 70°C and 70°C < Tg2.

[0014] In the heat-shrinkable film, the petroleum resin may include an alicyclic petroleum resin.

[0015] A heat-shrinkable label according to one aspect of the present disclosure includes any one of the heat-shrinkable films described above. [Effects of the Invention]

[0016] According to the above aspect, a heat-shrinkable film having improved transparency and oil resistance is provided. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a cross-sectional view showing a configuration of a heat-shrinkable film according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0018] <1. Overview> Hereinafter, one embodiment of a heat-shrinkable film according to the present disclosure will be described. The heat-shrinkable film is a film mainly composed of a thermoplastic resin, particularly an olefin-based resin, and is suitable for use as a packaging material attached to, for example, plastic containers. It is particularly suitable as a base film for heat-shrinkable labels attached to containers such as PET bottles. Therefore, heat-shrinkable labels including the heat-shrinkable film according to the present disclosure are also included within the scope of the present disclosure.

[0019] FIG. 1 shows a cross section of a heat-shrinkable film 1 according to this embodiment. As shown in FIG. 1, the heat-shrinkable film 1 includes a surface layer 2 and a core layer 3. The surface layer 2 is a layer adjacent to the core layer 3 and laminated on at least one surface of the core layer 3. In the example shown in FIG. 1, the surface layer 2 is laminated adjacent to both surfaces of the core layer 3. Note that the thickness of each layer shown in FIG. 1 does not necessarily reflect the actual dimensions. As will be described later, the surface layer 2 and the core layer 3 are mainly composed of an olefin-based resin. The olefin-based resin is a hydrocarbon having a carbon-carbon double bond, and examples thereof include ethylene-based resins, propylene-based resins, cyclic olefin-based resins, petroleum resins, and olefin-based elastomers.

[0020] The heat-shrinkable film 1 is configured so that its overall specific gravity is less than 1. This allows it to be separated by specific gravity from ester-based resins and styrene-based resins, which have specific gravities greater than 1, at recycling sites. This allows the heat-shrinkable film 1 to be used as a recycled material for olefin-based resins. In particular, when heat-shrinkable film 1 is used as a raw material to regenerate heat-shrinkable films 1 with substantially the same configuration, a resource cycle is established from heat-shrinkable film to heat-shrinkable film. Specifically, heat-shrinkable films 1 with a printed ink layer formed thereon and configured as heat-shrinkable labels can also be reused as raw materials for heat-shrinkable film 1 by undergoing a deinking process to remove the printed ink layer, thereby regenerating heat-shrinkable films with excellent transparency. Various known methods can be used for the deinking process, and are not limited thereto. For example, when a primer layer such as an acrylic resin is previously formed on the heat-shrinkable film 1 and a printed ink layer is then formed on top of that, the printed ink layer can be removed by immersing the film in a solution (e.g., an alkaline solution) in which the primer layer can be dissolved. Furthermore, even if no undercoat layer is provided, the printed ink layer can be removed by immersing the film in a solution (such as an alkaline solution) in which the binder resin of the printing ink can be dissolved. Therefore, the heat-shrinkable film 1 includes films made from virgin raw materials that have not been recycled, as well as films made from recycled olefin-based resins. Each layer of the heat-shrinkable film 1 will be described below.

[0021] <2. Surface layer> The surface layer 2 according to this embodiment contains an ethylene-based resin, a cyclic olefin-based resin, and a petroleum resin. Each of these resins will be described below.

[0022] [Ethylene-based resin] The ethylene-based resin improves the grease resistance of the heat-shrinkable film 1. If a cyclic olefin-based resin, which will be described later, is touched by a human hand before the heat-shrinkable film 1 is heat-shrunk and oil adheres to the resin, the area is likely to whiten (hereinafter also referred to as sebum whitening) after shrinkage. When the surface layer 2 contains an appropriate amount of ethylene-based resin, the heat-shrinkable film 1 is less likely to whiten due to sebum, and the grease resistance is improved.

[0023] Examples of the ethylene-based resin include linear low-density polyethylene, branched low-density polyethylene, ethylene-vinyl acetate copolymer, ionomer resin, and mixtures thereof. Further examples of the ethylene-based resin include copolymers of ethylene and α-olefins. Examples of α-olefins include, but are not limited to, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, and 1-octene. The copolymers may be random copolymers or block copolymers. The surface layer 2 preferably contains linear low-density polyethylene as the ethylene-based resin.

[0024] The density of the ethylene resin is 880 kg / m 3 It is preferable that the saturation is 940 kg / m or more. 3 Preferably, the melt flow rate (MFR) at 190°C is 0.1 g / 10 min or more and 30 g / 10 min or less, which improves compatibility with the cyclic olefin resin described below.

[0025] The Vicat softening temperature of the ethylene resin is preferably 90°C or higher and 110°C or lower. The Vicat softening temperature can be measured by a method in accordance with JIS K-7206 (1999). The melting point of the ethylene resin is preferably 95°C or higher and 120°C or lower.

[0026] Commercially available linear low-density polyethylene resins 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.).

[0027] When the total of the ethylene-based resin, cyclic olefin-based resin, and petroleum resin constituting the surface layer 2 is taken as 100% by mass, the surface layer 2 preferably contains 10% by mass or more of the ethylene-based resin, preferably 15% by mass or more, preferably 35% by mass or less, and more preferably 30% by mass or less. When the content of the ethylene-based resin is equal to or greater than the lower limit, the tendency of the cyclic olefin-based resin to whiten due to sebum is overcome, and the grease resistance of the heat-shrinkable film 1 is improved. When the content of the ethylene-based resin is equal to or less than the upper limit, the deterioration of the transparency of the heat-shrinkable film 1 due to the ethylene-based resin is suppressed.

[0028] [Cyclic olefin resin] Examples of cyclic olefin resins include (a) random copolymers of ethylene or propylene with cyclic olefins, (b) ring-opening polymers of the cyclic olefins or copolymers with α-olefins, (c) hydrogenated products of the polymers of (b), and (d) graft-modified products of (a) to (c) with unsaturated carboxylic acids and derivatives thereof, etc. Among these, random copolymers of cyclic olefins with ethylene, propylene, or α-olefins are preferred from the viewpoint of reducing the crystallinity of the heat-shrinkable film 1 and improving the stretchability, heat shrinkage rate, and transparency during production.

[0029] 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. Further examples include tetracyclododecene and derivatives thereof, such as tetracyclododecene, 8-methyltetracyclo-3-dodecene, 8-ethyltetracyclo-3-dodecene, and 5,10-dimethyltetracyclo-3-dodecene.

[0030] The number average molecular weight of the cyclic olefin resin measured by GPC (gel permeation chromatography) is preferably 1000 or more and 1 million or less. By setting the number average molecular weight within the above range, film formation becomes easy.

[0031] The glass transition temperature of the cyclic olefin resin is preferably 20°C or higher, more preferably 50°C or higher, and preferably 130°C or lower, and more preferably 100°C or lower. When the glass transition temperature is 20°C or higher, the heat resistance of the surface layer 2 is improved. Furthermore, in an attachment line for attaching heat-shrinkable labels containing the heat-shrinkable film 1 to containers, blocking between these containers can be suppressed. Furthermore, when the glass transition temperature is 50°C or higher, the natural shrinkage rate can be kept within a good range. When the glass transition temperature is 130°C or lower, the heat shrinkage rate in the main shrinkage direction can be sufficiently large. Furthermore, when the glass transition temperature is 100°C or lower, the heat shrinkage rate in the main shrinkage direction can be sufficiently large even at low temperatures.

[0032] The glass transition temperature can be measured by a method in accordance with ISO 3146. When the cyclic olefin resin is a mixed resin containing a plurality of cyclic olefin resins with different glass transition temperatures, the glass transition temperature of the mixed resin is an apparent glass transition temperature calculated based on the mass ratio and glass transition temperature of each cyclic olefin resin in the mixed resin.

[0033] The surface layer 2 preferably contains two types of cyclic olefin resins with different glass transition temperatures. If the cyclic olefin resins with a glass transition temperature Tg1 (°C) are designated as the first cyclic olefin resin (A1) and the cyclic olefin resin with a glass transition temperature Tg2 (°C) are designated as the second cyclic olefin resin (A2), the difference between Tg1 and Tg2 is preferably 10°C or more. Furthermore, it is preferable that Tg1 > 70°C, and Tg2 ≦ 70°C.

[0034] When the cyclic olefin resin is a mixed resin containing a first cyclic olefin resin (A1) and a second cyclic olefin resin (A2), the thermal properties of the mixed resin can be gradually expressed around the apparent glass transition temperature. This improves the processability of the heat-shrinkable film 1 during stretching. Furthermore, since the heat-shrinkable film 1 does not shrink rapidly during heat shrinkage, the occurrence of wrinkles due to heat shrinkage can be suppressed. Furthermore, by setting the difference between Tg1 and Tg2 to 10°C or more, the natural shrinkage rate of the heat-shrinkable film 1 can be suppressed while the heat shrinkage rate can be increased. These properties can be adjusted by adjusting the blending ratio of the first cyclic olefin resin (A1) and the second cyclic olefin resin (A2).

[0035] The density of the cyclic olefin resin is 1000 kg / m 3 It is preferable that the saturation is 1010 kg / m or more. 3 More preferably, it is 1050 kg / m or more. 3 It is preferable that the saturation is 1040 kg / m or less. 3 It is more preferable that the MFR at 230° C. is 1 g / 10 min or more, and more preferably 10 g / 10 min or less, thereby improving the compatibility with the above-mentioned ethylene-based resin.

[0036] Commercially available products of the cyclic olefin resin include APEL (manufactured by Mitsui Chemicals, Inc.), TOPAS (manufactured by Polyplastics Co., Ltd.), and ZEONOR (manufactured by Zeon Corporation).

[0037] When the total of the ethylene resin, cyclic olefin resin, and petroleum resin constituting the surface layer 2 is taken as 100% by mass, the surface layer 2 preferably contains 50% by mass or more of the cyclic olefin resin, more preferably 55% by mass or more, and preferably 75% by mass or less, and more preferably 70% by mass or less. When the content of the cyclic olefin resin is equal to or greater than the lower limit, the stretchability, heat shrinkability, and transparency of the heat-shrinkable film 1 are improved. On the other hand, cyclic olefin resins are susceptible to oils such as fatty acid esters, and can cause sebum blushing in areas of the heat-shrinkable film 1 where oils adhere after shrinkage. When the content of the cyclic olefin resin is equal to or less than the upper limit, the ethylene resin and the petroleum resin described below effectively suppress sebum blushing, improving the grease resistance of the heat-shrinkable film 1.

[0038] [Petroleum resin] Petroleum resins are resins derived from C4-C5 fractions (mainly C5 fractions) or C5-C9 fractions (mainly C9 fractions) remaining after thermal cracking of naphtha to remove compounds such as ethylene, propylene, and butadiene, and hydrogenated compounds thereof. 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, alicyclic petroleum resins are preferred from the viewpoints of suppressing softening of the heat-shrinkable film 1 at temperatures below 100°C and improving transparency. Specific examples of alicyclic petroleum resins include hydrogenated products of alicyclic saturated hydrocarbon resin-based petroleum resins and aromatic petroleum resins.

[0039] While petroleum resins effectively suppress the sebum blushing of cyclic olefin resins, a high content of petroleum resins tends to cause stickiness on the surface of the layer. The inventors have discovered that selecting an alicyclic petroleum resin as the petroleum resin in particular can effectively suppress sebum blushing while sufficiently suppressing surface stickiness. This is thought to be due to the high compatibility between alicyclic petroleum resins and structurally similar cyclic olefin resins. In addition, it has been confirmed that when alicyclic petroleum resins and cyclic olefin resins are contained in different layers, the bonds between the layers are strengthened, making interlayer delamination less likely to occur.

[0040] The number average molecular weight of the petroleum resin measured by the GPC method is preferably 500 or more, more preferably 600 or more, and is preferably 1000 or less, more preferably 900 or less. By setting the number average molecular weight within the above range, the rigidity of the heat-shrinkable film 1 is improved.

[0041] The softening point of the petroleum resin is preferably 80°C or higher, more preferably 110°C or higher, and preferably 170°C or lower, and more preferably 155°C or lower. If the softening point is lower than 80°C, the heat resistance of the heat-shrinkable film 1 may be reduced, and the petroleum resin component may be more likely to bleed out to the surface in a high-temperature atmosphere. If the softening point is higher than 170°C, molding processability such as extrusion film formability and stretching processability may be impaired. On the other hand, a softening point of 110°C or higher is preferable because natural shrinkage of the heat-shrinkable film 1 can be suppressed, and a softening point of 155°C or lower can be uniformly stretched in the stretching step. In particular, a softening point of 120°C or higher and 140°C or lower can exhibit good heat shrinkability. The softening point of the petroleum resin can be measured by a method in accordance with JIS K2207:2006.

[0042] The density of the above petroleum resin is 950 kg / m 3 It is preferable that the saturation is 980 kg / m or more. 3 More preferably, it is 1050 kg / m or more. 3 It is preferable that the saturation is 1020 kg / m or less. 3It is more preferable that the density is not more than 1000 kJ / g. When the density of the petroleum resin is within the above range, the rigidity of the heat-shrinkable film 1 is improved.

[0043] The refractive index of the petroleum resin at 20° C. is preferably 1.0 or more, more preferably 1.2 or more, and is preferably 2.0 or less, more preferably 1.8 or less. When the refractive index of the petroleum resin is within the above range, the transparency of the heat-shrinkable film 1 is improved.

[0044] When the total of the ethylene resin, cyclic olefin resin, and petroleum resin constituting the surface layer 2 is taken as 100% by mass, the surface layer 2 preferably contains 5% by mass or more, and preferably 25% by mass or less, of the petroleum resin. When the content of the petroleum resin is equal to or greater than the lower limit, the tendency of the cyclic olefin resin to whiten due to sebum is overcome, and the grease resistance of the heat-shrinkable film 1 is improved. When the content of the petroleum resin is equal to or less than the upper limit, the stickiness of the heat-shrinkable film 1 is suppressed.

[0045] [Fine particles] The surface layer 2 may further contain fine particles. The fine particles can be added, for example, to improve the anti-blocking performance of the heat-shrinkable film 1. As such fine particles, either organic or inorganic fine particles can be used. As organic fine particles, organic fine particles such as acrylic resin fine particles, styrene resin fine particles, styrene-acrylic resin fine particles, urethane resin fine particles, and silicone resin fine particles can be used. In particular, from the viewpoint of compatibility with cyclic olefin resins, acrylic resin fine particles are preferred, and polymethyl methacrylate crosslinked fine particles are more preferred.

[0046] 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.).

[0047] Examples of inorganic fine particles that can be used include silica, zeolite, and alumina.

[0048] The surface layer 2 preferably contains 0.01 parts by mass or more of the above-mentioned fine particles, more preferably 0.03 parts by mass or more, preferably 0.10 parts by mass or less, and more preferably 0.08 parts by mass or less, based on 100 parts by mass of the total thermoplastic resin constituting the surface layer 2.

[0049] <3. Core layer> The core layer 3 according to this embodiment contains a propylene-based resin and a petroleum resin as olefin-based resins. The core layer 3 may further contain an ethylene-based resin and a cyclic olefin-based resin. In particular, when the heat-shrinkable film 1 is recycled as a raw material for an olefin-based resin, it is preferable that this recycled raw material be used as a raw material for the core layer 3. That is, it is preferable that the core layer 3 contains all of the same olefin-based resins as the surface layer 2. Each resin will be described below.

[0050] [Propylene-based resin] The propylene-based resin improves both the rigidity and heat shrinkability of the heat-shrinkable film 1. Examples of such propylene-based resins include propylene copolymers, long-chain branched polypropylenes, and propylene-based elastomers. The core layer 3 may contain one or more of these. From the viewpoint of exhibiting heat shrinkability, the propylene copolymer is preferably a binary or ternary random copolymer containing propylene as the main component and an α-olefin as a copolymerization component. The proportion of the α-olefin as a copolymerization component is preferably 1 to 10 mol %. The propylene-based resin may also be a mixture of different propylene-α-olefin random copolymers. The α-olefin is as described above.

[0051] Commercially available propylene copolymers such as those mentioned above include, for example, Adsyl (manufactured by LyondellBasell) and Novatec (manufactured by Japan Polypropylene Corporation).

[0052] Long-chain branched polypropylene is polypropylene having 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 reversion of the petroleum resin after thermal shrinkage and maintain the shape retention of the core layer 3. Furthermore, long-chain branched polypropylene has high melt tension and strain hardening properties, allowing the thickness of the core layer 3 to be precisely controlled.

[0053] An example of a commercially available long-chain branched polypropylene is Waymax (manufactured by Japan Polypropylene Corporation).

[0054] The deflection temperature under load (0.45 MPa) of the propylene-based resin is preferably not more than 120° C., and more preferably not more than 90° C. 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 (mass ratio).

[0055] The MFR of the propylene-based resin at 230° C. is preferably 0.1 g / 10 min or more and 30 g / 10 min or less.

[0056] Propylene-based elastomers are resins obtained by imparting rubber elasticity to copolymers of propylene and ethylene or other α-olefins, but are not limited to these, and impart heat shrinkability and impact resistance to the heat-shrinkable film 1. In addition, they maintain the transparency of the core layer 3 and have excellent compatibility with propylene-based resins that are not configured as elastomers.

[0057] Examples of commercially available propylene-based elastomers include Tafmer (manufactured by Mitsui Chemicals, Inc.) and Thermorun (manufactured by Mitsubishi Chemical Corporation).

[0058] The core layer 3 preferably contains 50% by mass or more, more preferably 65% ​​by mass or more, and preferably 90% by mass or less, and more preferably 80% by mass or less of the propylene copolymer when the total amount of the thermoplastic resins constituting the core layer 3 is taken as 100% by mass. Furthermore, the core layer 3 preferably contains 15% by mass or less, more preferably 10% by mass or less of the long-chain branched polypropylene when the total amount of the thermoplastic resins constituting the core layer 3 is taken as 100% by mass. Furthermore, the core layer 3 preferably contains 10% by mass or less of the propylene-based elastomer when the total amount of the thermoplastic resins constituting the core layer 3 is taken as 100% by mass.

[0059] [Petroleum resin] The petroleum resin has been described above. The core layer 3 preferably contains the same petroleum resin as the surface layer 2. When the total of the propylene-based resin and petroleum resin constituting the core layer 3 is taken as 100% by mass, the core layer 3 preferably contains 10% by mass or more of the petroleum resin, more preferably 15% by mass or more, and preferably 45% by mass or less. By setting the content of the petroleum resin within the above range, the gloss and heat shrinkability of the heat-shrinkable film 1 are improved.

[0060] [Other resins] The core layer 3 may further contain an ethylene-based resin and a cyclic olefin-based resin. These resins are as already described in the description of the surface layer 2, and the core layer 3 may contain all of the same thermoplastic resins as the thermoplastic resins contained in the surface layer 2. The same type of thermoplastic resin may be different between the surface layer 2 and the core layer 3, as long as they have similar tendencies in properties. When the core layer 3 contains an ethylene-based resin and a cyclic olefin-based resin, the heat shrinkability of the heat-shrinkable film 1 is further improved.

[0061] <4. Other ingredients> The surface layer 2 and the core layer 3 may each contain additives such as antioxidants, heat stabilizers, UV absorbers, light stabilizers, lubricants, antistatic agents, flame retardants, antibacterial agents, fluorescent brighteners, and colorants, as needed.

[0062] <5. Thickness> The overall thickness of the heat-shrinkable film 1 is preferably 20 μm or more, more preferably 25 μm or more, and is preferably 60 μm or less, more preferably 50 μm or less. When the thickness of the surface layer 2 is taken as 1, the thickness of the core layer 3 is preferably 4 or more.

[0063] <6. Heat shrinkage rate of heat shrinkable film> When the heat-shrinkable film 1 is immersed in 70°C warm 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 is preferably 10% or more. Furthermore, when the heat-shrinkable film 1 is immersed in 80°C warm water for 10 seconds, then immersed in 20°C water for 10 seconds, the heat shrinkage rate in the main shrinkage direction is preferably 41% or more. Furthermore, when the heat-shrinkable film 1 is immersed in 90°C warm water for 10 seconds, then immersed in 20°C water for 10 seconds, the heat shrinkage rate in the main shrinkage direction is preferably 52% or more. When the heat shrinkage rate is within the above-mentioned range, problems such as poor shrinkage do not occur, and the heat-shrinkable film can be suitably used, particularly as a heat-shrinkable film to be attached to a container.

[0064] <7. Natural shrinkage rate of heat-shrinkable film> The natural shrinkage percentage in the main shrinkage direction of the heat-shrinkable film 1 when it is left standing for 7 days in an atmosphere at 40° C. is preferably less than 4.0%, and more preferably less than 3.0%. If the natural shrinkage percentage is less than 4.0%, the heat-shrinkable film 1 shrinks little during storage, and shrinkage defects are less likely to occur in the heat-shrinking step.

[0065] 8. Method for producing heat-shrinkable film Although there are no particular limitations on the method for producing the heat-shrinkable film 1, a method in which each layer is simultaneously formed by co-extrusion is preferred. When the co-extrusion method is co-extrusion using a T-die, the lamination method may be any of a feed block method, a multi-manifold method, or a method combining these.

[0066] Specific examples of methods for producing the heat-shrinkable film 1 include a method in which the raw materials constituting the surface layer 2 and the core layer 3 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 film 1, the shrinkage properties required of the heat-shrinkable film 1, and the like, but is preferably 65°C or higher, more preferably 70°C or higher, and preferably 125°C or lower, more preferably 115°C or lower.

[0067] The stretching ratio in the main shrinkage direction varies depending on the resin constituting the heat-shrinkable film 1, 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.

[0068] <9. Features> The heat-shrinkable film 1 according to the above embodiment has a surface layer 2 containing a cyclic olefin resin, an ethylene resin, and a petroleum resin in appropriate amounts, thereby achieving sufficient heat shrinkability as a heat-shrinkable film while also exhibiting high grease resistance and transparency. Furthermore, when the surface layer 2 contains two types of cyclic olefin resins with different glass transition temperatures, the natural shrinkage rate is suppressed to a preferred range while the heat shrinkage rate can be sufficiently increased. Furthermore, when the core layer 3 contains a thermoplastic resin similar to the thermoplastic resin contained in the surface layer 2, the heat-shrinkable film 1 and heat-shrinkable labels containing the same can be easily recycled into heat-shrinkable films. Furthermore, when the core layer 3 contains long-chain branched polypropylene, which contributes most to the heat shrinkability of the heat-shrinkable film 1, the heat-shrinkability of the heat-shrinkable film 1 is further improved, and reversion after heat shrinkage is suppressed, thereby improving shape retention. [Example]

[0069] Examples of the present disclosure will be described in detail below, but the present disclosure is not limited to these examples.

[0070] <1. Preparation of Examples and Comparative Examples> [Raw materials] The raw materials for the core layer and the surface layers laminated adjacent to both sides of the core layer were blended in the proportions (unit: mass %) shown in Table 1 to prepare resin compositions for the surface layers and core layers of Examples 1 to 6 and Comparative Examples 1 and 2. The raw materials in Table 1 used were as follows. COC1: Ethylene-norbornene copolymer resin (density 1010 kg / m 3 , MVR6.0cm 3 / 10min, glass transition temperature is 78℃) COC2: Ethylene-norbornene copolymer resin (density 1010 kg / m 3 , MVR6.0cm 3 / 10min, glass transition temperature is 65℃) LLDPE1: Linear low-density polyethylene (density 915 kg / m 3 , MFR1.0g / 10min, Vicat softening point 98℃) LLDPE2: Linear low-density polyethylene (density 913 kg / m 3 , MFR2.0g / 10min, Vicat softening point 96℃) Petroleum resin (softening point 125°C) Polypropylene random copolymer (random PP) (MFR 5.5g / 10min, Vicat softening point 111℃) Long-chain branched polypropylene (long-chain branched PP) (density 900 kg / m 3 , MFR 2.8g / 10min, deflection temperature under load (0.45MPa) 120℃) [Table 1]

[0071] [Extrusion molding] The resulting resin compositions were each placed in an extruder, melted at a barrel temperature of 210°C for the surface layer and 180°C for the core layer, extruded through a T-die, and cooled and solidified using rolls cooled to 30°C to produce a three-layer unstretched sheet in which the surface layers were laminated on both sides of the core layer. Each unstretched sheet was stretched 5 times in the TD direction using a tenter-type stretching machine at 90°C to produce a heat-shrinkable film with a total thickness of 40 μm and a layer thickness ratio of 1:5:1.

[0072] <2. Evaluation> The heat-shrinkable films according to Examples 1 to 6 and Comparative Examples 1 and 2 were evaluated as follows.

[0073] <2-1.Young's Modulus> Measurement samples measuring 250 mm lengthwise and 5 mm widthwise (the MD direction of the film is the longitudinal direction, and the TD direction is the transverse direction) and 250 mm lengthwise and 5 mm widthwise (the TD direction of the film is the longitudinal direction, and the MD direction is the transverse direction) were cut out from arbitrary locations of the heat-shrinkable films of Examples 1 to 6 and Comparative Examples 1 and 2. Using the measurement samples and a Strograph (VE-1D, manufactured by Toyo Seiki Seisaku-sho, Ltd.), the Young's moduli (GPa) in the MD and TD directions were measured according to ASTM D882.

[0074] <2-2. Heat shrinkage rate> Measurement samples measuring 100 mm long x 100 mm wide were cut out from any location of the heat-shrinkable films according to Examples 1 to 6 and Comparative Examples 1 and 2. Each sample was immersed in warm water at a predetermined temperature for 10 seconds, and then immersed in water at 20°C for 10 seconds. After being removed from the 20°C water, the length L of each sample in the main shrinkage direction was measured, and the heat shrinkage rate was calculated according to the following formula. Heat shrinkage rate (%) = {(100-L) / 100} x 100 The hot water used was 70°C, 80°C, and 90°C, and the average value calculated for three samples of the same heat-shrinkable film at each temperature was taken as the heat shrinkage rate of that heat-shrinkable film.

[0075] <2-3. Natural shrinkage rate> Three measurement samples measuring 100 mm long x 100 mm wide were cut out from any position of each of the heat-shrinkable films according to Examples 1 to 6 and Comparative Examples 1 and 2. Each sample was left to stand for 7 days in a low-temperature incubator (IL-82, manufactured by Yamato Scientific Co., Ltd.) adjusted to 40°C, and the shrinkage rate was calculated according to the same formula as for the heat shrinkage rate. The average value of the three samples of the same heat-shrinkable film was taken as the natural shrinkage rate of that heat-shrinkable film.

[0076] <2-4. Haze before shrinkage> Samples of the same size were cut out from the heat-shrinkable films according to Examples 1 to 6 and Comparative Examples 1 and 2, and the haze (%) was measured using a haze meter (NDH5000, manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with JIS K7136.

[0077] <2-5. Sebum whitening amount> Samples measuring 150 mm lengthwise and 250 mm widthwise (the MD direction of the film is the longitudinal direction, and the TD direction is the transverse direction) were cut out from the heat-shrinkable films of Examples 1 to 6 and Comparative Examples 1 and 2, and two longitudinal benchmark lines spaced 150 mm apart were marked horizontally. A finger with sebum from around the nose was used to touch each sample between the benchmark lines several times to deposit sebum onto each sample. Subsequently, each sample with sebum was attached to a jig and immersed in 80°C warm water for 7 seconds, allowing it to shrink so that the interval between the benchmark lines became 105 mm. The state of each sample after shrinkage was visually inspected, and the degree of sebum whitening was evaluated as Level 1, Level 2, or Level 3, in descending order. Level 1 indicates relatively high grease resistance, Level 2 indicates acceptable grease resistance, and Level 3 indicates grease resistance that does not meet the standard.

[0078] <2-6. Amount of looseness> Rectangular samples of the same size were cut from the heat-shrinkable films of Examples 1 to 6 and Comparative Examples 1 and 2. Both ends of each sample in the MD direction were sealed to produce cylindrical bodies with the same length and inner diameter. Each of the produced cylindrical bodies was placed over a cylindrical plastic container with the same configuration and dimensions (circumference 280 mm). This was then passed through a hot-air shrinkage tunnel at 100°C to heat-shrink the cylindrical body and attach it to the container. Immediately after heat shrinkage, it was confirmed that all of the cylindrical bodies were tightly attached to the container. The container with the cylindrical body was then left at 20°C for 24 hours, after which the cylindrical body was removed from the container and the circumferential length of the cylindrical body (i.e., the length in the TD direction) was measured. The difference between the circumferential length of the cylindrical body and the outer circumference of the container was taken as the slack (mm). A score of A was given if the slack was less than 1.0 mm, and a score of B was given if the slack was 1.0 mm or more but less than 1.5 mm. In other words, a score of A indicates that retraction after heat shrinkage was sufficiently suppressed, and a score of B indicates that retraction after heat shrinkage was within an acceptable range.

[0079] <3.Results> The results are shown in Table 2. [Table 2]

[0080] As shown in Table 2, there were no significant differences between the Examples and Comparative Examples in terms of Young's modulus (rigidity), heat shrinkage, natural shrinkage, and amount of slack. However, Comparative Examples 1 and 2, which did not contain a petroleum resin in the surface layer, resulted in inferior appearance quality compared to Examples 1 to 6. It is believed that Comparative Example 1 did not contain a petroleum resin in the surface layer but contained a relatively large amount of cyclic olefin resin, which prevented sufficient suppression of sebum blushing. Furthermore, Comparative Example 2 did not contain a petroleum resin in the surface layer but contained a relatively large amount of ethylene resin, which is believed to have deteriorated transparency (haze). In Examples 1 to 6, it was demonstrated that the inclusion of a petroleum resin in the surface layer effectively suppressed sebum blushing and deterioration of transparency. Furthermore, Examples 1 and 2, which contained two types of cyclic olefin resin in the surface layer, showed comparable heat shrinkage rates and more favorable natural shrinkage rates. It was confirmed that Example 1, which contained petroleum resin in the surface and core layers and further contained long-chain branched polypropylene in the core layer, also showed less slack after heat shrinkage than the others, demonstrating particularly favorable performance. [Explanation of symbols]

[0081] 1. Heat-shrinkable film 2 Surface layer 3 Core layer

Claims

1. A surface layer is formed from a cyclic olefin resin, an ethylene resin, and a petroleum resin, The surface layer contains 35% by mass or less of the ethylene-based resin and 5% by mass or more of the petroleum resin, relative to 100% by mass of the total of the cyclic olefin-based resin, the ethylene-based resin, and the petroleum resin. Heat shrinkable film.

2. Further, a core layer is laminated adjacent to the surface layer, The core layer contains a propylene-based resin and a petroleum resin. The heat-shrinkable film according to claim 1.

3. The core layer contains the petroleum resin in an amount of 10% by mass or more relative to 100% by mass of the total of the propylene-based resin and the petroleum resin. The heat-shrinkable film according to claim 2.

4. The core layer further contains a cyclic olefin-based resin and an ethylene-based resin. The heat-shrinkable film according to claim 2 or 3.

5. The core layer contains long-chain branched polypropylene as the propylene-based resin. The heat-shrinkable film according to any one of claims 2 to 4.

6. The surface layers are laminated adjacent to both surfaces of the core layer. The heat-shrinkable film according to any one of claims 2 to 5.

7. the cyclic olefin resin includes a first cyclic olefin resin having a glass transition temperature Tg1 (°C) and a second cyclic olefin resin having a glass transition temperature Tg2 (°C); The difference between the glass transition temperatures Tg1 and Tg2 is 10°C or more. The heat-shrinkable film according to any one of claims 1 to 6.

8. The glass transition temperatures Tg1 and Tg2 satisfy Tg1>70°C and 70°C≦Tg2. The heat-shrinkable film according to claim 7.

9. The petroleum resin includes an alicyclic petroleum resin. The heat-shrinkable film according to any one of claims 1 to 8.

10. A heat-shrinkable label comprising the heat-shrinkable film according to any one of claims 1 to 9.

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