Heat-shrinkable film, and heat-shrinkable ring-shaped label and package using same

Abstract

The purpose of the present invention is to provide a heat-shrinkable film that has a reduced natural shrinkage rate and improved shrink finish. This heat-shrinkable film is composed of polyester and / or polystyrene and satisfies the following (1) to (4): (1) the shrinkage rate in the main shrinkage direction when treated in hot water at 70°C for 10 seconds is 3% or less; (2) the shrinkage rate in the main shrinkage direction when treated in hot water at 80°C for 10 seconds is more than 10% and not more than 50%; (3) the shrinkage rate in the main shrinkage direction when treated in silicon oil at 120°C for 10 seconds is 50-80%; and (4) the natural shrinkage rate (dimensional change rate) in the main shrinkage direction of the film after aging for 168 hours in an atmosphere of 50°C and 40% relative humidity is 1% or less.

Description

Heat-shrinkable film, and heat-shrinkable annular label and packaging using the same

[0001] The present invention relates to a heat-shrinkable polyester and / or polystyrene film, and annular labels and packaging materials produced using the same. More specifically, the present invention relates to a heat-shrinkable film suitable for label applications that exhibits minimal change in physical properties due to aging, and a packaging material to which an annular label is attached.

[0002] In recent years, heat-shrinkable films have come to be widely used for label packaging, cap seals, and stacked packaging, which combine the protection of glass bottles, PET bottles, and the like with product labeling. However, when heat-shrinkable films are stored in an outdoor warehouse without temperature control during high summer temperatures, the film shrinks and undergoes dimensional changes (so-called natural shrinkage), resulting in narrower product widths and tighter rolls. Similarly, when stored in a warehouse with high temperatures, the shrinkage rate in the main shrinkage direction decreases, necessitating changes in the temperature conditions for heat-shrinking when heat-shrinking and attaching the film to containers such as PET bottles after label cutting, which makes it difficult to attach the film efficiently. For this reason, heat-shrinkable films are generally stored under low-temperature conditions at temperatures below 25°C. However, low-temperature storage is undesirable not only in terms of delivery and cost, but also from the standpoint of increased environmental impact due to increased power consumption.

[0003] To address these issues, the present applicant has disclosed, for example, in Patent Documents 1 and 2, heat-shrinkable polyester films that do not undergo natural shrinkage and exhibit only a small decrease in shrinkage rate in the main shrinkage direction, even when stored in an outdoor warehouse without temperature control during high summer temperatures. These films can be beautifully and efficiently attached to containers such as PET bottles as labels without changing the temperature conditions during heat shrinkage. However, while the heat-shrinkable films in Patent Documents 1 and 2 have a high shrinkage rate at 120°C, they have a low shrinkage rate (at most 35% in the examples) in the normal shrinkage temperature range of 100°C or less. Depending on the shape of the container to be covered (the design to be shrunk), a high shrinkage rate of 50% or more may be required. In this case, the shrinkage temperature must be raised, but this approach can approach the film's melting temperature, causing the film to melt before adhering to the container, resulting in a poor appearance. In other words, there has been a need for a heat-shrinkable film that does not require low-temperature storage and can achieve the required shrinkage rate when shrunk at a relatively low temperature range of 100°C or less.

[0004] Patent No. 5408250 Patent No. 5664548

[0005] The present invention aims to suppress the natural shrinkage that is a problem with conventional heat-shrinkable films and to improve the shrink finish.

[0006] [1] A heat-shrinkable film made of polyester and / or polystyrene, satisfying the following (1) to (4): (1) a shrinkage rate of 3% or less in the main shrinkage direction when treated in 70°C hot water for 10 seconds, (2) a shrinkage rate of more than 10% but not more than 50% in the main shrinkage direction when treated in 80°C hot water for 10 seconds, (3) a shrinkage rate of 50% or more but not more than 80% in the main shrinkage direction when treated in 120°C silicone oil for 10 seconds, and (4) a natural shrinkage rate (dimensional change rate) in the main shrinkage direction of the film after aging for 168 hours in an atmosphere at a temperature of 55°C and a relative humidity of 40% of 1% or less. [2] The heat-shrinkable film according to [1], characterized in that, after aging for 168 hours in an atmosphere at a temperature of 55°C and a relative humidity of 40%, a tensile test is conducted on 10 samples in the longitudinal direction of the film using a tensile tester with a chuck distance of 100 mm, and the number of initial breaks, which is the number of breaks at 5% tension, is 4 or less. [3] The heat-shrinkable film according to [1] or [2], characterized in that the glass transition onset temperature is 65°C or higher and 110°C or lower when the temperature is raised from room temperature at 10°C / min using temperature-modulated differential scanning calorimetry (MDSC). [4] The heat-shrinkable film according to any one of [1] to [3], characterized in that the reversible heat capacity difference ΔCp is 0.22 J / g K or lower from 30°C to 70°C when the temperature is raised from room temperature at 10°C / min using temperature-modulated differential scanning calorimetry (MDSC), and the reversible heat capacity difference ΔCp is 0.25 or higher and 0.4 or lower from 30°C to 80°C. [5] The heat-shrinkable film according to any one of [1] to [4], wherein the polyester heat-shrinkable film is composed of ethylene terephthalate units in an amount of 40 mol% or higher of 100 mol% of the total resin components constituting the polyethylene. [6] The heat-shrinkable film according to any one of [1] to [5], wherein the heat-shrinkable film made of polyester is substantially free of butanediol, diethylene glycol, and ε-caprolactone.[7] The heat-shrinkable film according to any one of [1] to [6], wherein the heat-shrinkable polyester film contains at least one monomer capable of becoming an amorphous component selected from the group consisting of neopentyl glycol, 1,4-cyclohexanedimethanol, and isophthalic acid. [8] The heat-shrinkable polystyrene film according to any one of [1] to [4], wherein the polystyrene is a styrene-diene copolymer. [9] The heat-shrinkable polystyrene film according to [8], wherein the styrene content is 50% by mass or more based on 100% by mass of the resin components constituting the film.

[10] A heat-shrinkable annular label using the heat-shrinkable film according to any one of [1] to [9] as a base material, the edges of which are bonded to form a ring.

[11] A package produced by covering at least a portion of the outer periphery of an object with the heat-shrinkable annular label according to

[10] , and then heat-shrinking the label.

[0007] The heat-shrinkable film of the present invention can suppress natural shrinkage and improve shrinkage finish. Therefore, the present invention can provide a heat-shrinkable label that does not undergo natural shrinkage even when stored in an outdoor warehouse without temperature control during high summer temperatures, and that has good shrinkage finish regardless of the shape or design of the container.

[0008] The heat-shrinkable film of the present invention will be described below. The present invention is a heat-shrinkable film made of polyester and / or polystyrene, which satisfies the following (1) to (4): (1) When treated in hot water at 70°C for 10 seconds, the shrinkage rate in the main shrinkage direction is 3% or less; (2) When treated in hot water at 80°C for 10 seconds, the shrinkage rate in the main shrinkage direction is more than 10% and not more than 50%; (3) When treated in silicone oil at 120°C for 10 seconds, the shrinkage rate in the main shrinkage direction is 50% or more and not more than 80%; and (4) After aging for 168 hours in an atmosphere at a temperature of 55°C and a relative humidity of 40%, the natural shrinkage rate (dimensional change rate) in the main shrinkage direction of the film is 1% or less.

[0009] 1. Properties of Heat-Shrinkable Film 1.1. 70°C Shrinkage (Before Aging) The heat-shrinkable film of the present invention must have a shrinkage rate of 3% or less in the main shrinkage direction when treated in 70°C hot water for 10 seconds. A 70°C shrinkage rate of more than 3% is undesirable because it increases the natural shrinkage rate (dimensional change rate) when aged at a temperature of 55°C and a relative humidity of 40%, as described below. To reduce the natural shrinkage rate, a 70°C shrinkage rate of 2.5% or less is more preferable, and a rate of 2.0% or less is even more preferable. On the other hand, a preferred lower limit for the 70°C shrinkage rate is -3%. A negative shrinkage rate indicates that the film stretches. To suppress the natural shrinkage rate, a negative 70°C shrinkage rate is acceptable, but is undesirable because the film stretches when shrink-wrapped onto a bottle or other packaging object, which can lead to defects such as wrinkles. The lower limit for the 70°C shrinkage rate is more preferably -2.5%, and even more preferably -2%. In the present invention, a 70°C shrinkage rate of 0% is the most preferable.

[0010] 1.2. 80°C Shrinkage (Before Aging) The heat-shrinkable film of the present invention must have a shrinkage rate in the main shrinkage direction of more than 10% and not more than 50% when treated in 80°C hot water for 10 seconds. An 80°C shrinkage rate of 10% or less is not preferred because, when heat-shrunk and attached to a container such as a PET bottle as a label, shrinkage is insufficient, causing wrinkles and a poor appearance. Furthermore, an 80°C shrinkage rate of more than 50% is not preferred because the shrinkage rate at the start of shrinkage increases, causing rapid shrinkage when heat-shrunk and attached to a label, resulting in distortion of the label design, etc. The 80°C shrinkage rate is preferably 11% to 49%, more preferably 12% to 48%, and even more preferably 13% to 47%.

[0011] 1.3. Difference in 80°C Shrinkage Rate Before and After Aging It is preferable that the difference between the 80°C shrinkage rate in the main shrinkage direction after aging at a temperature of 55°C and a relative humidity of 40% and the 80°C shrinkage rate before aging does not exceed 10%. A difference of 10% or less in the 80°C shrinkage rate before and after aging is preferable because the heat-shrinkable film can be used without changing the heating conditions for heat shrinking and installation, even after storage in a hot and humid environment such as a warehouse in summer. The difference in 80°C shrinkage rate is preferably 9% or less, more preferably 8% or less.

[0012] 1.4. 120°C Shrinkage Rate (Before Aging) The heat-shrinkable film of the present invention must have a shrinkage rate in the main shrinkage direction of 50% or more and 80% or less when immersed in a silicone oil bath at 120°C for 10 seconds. A 120°C shrinkage rate of less than 50% is not preferable because when the film is heat-shrunk and attached to a packaging object such as a PET bottle as a label, shrinkage is insufficient, causing wrinkles and deteriorating the appearance. A higher upper limit for the shrinkage rate allows attachment to containers with more complex shapes, but the upper limit in the technical level of the present invention is 80%. The 120°C shrinkage rate is preferably 53% or more, more preferably 55% or more.

[0013] 1.5.55°C Natural Shrinkage Rate (After Aging) The heat-shrinkable film of the present invention has a natural shrinkage rate (dimensional change rate) of 1% or less in the main shrinkage direction of the film after aging for 168 hours at a temperature of 55°C and a relative humidity of 40%. If the natural shrinkage rate exceeds 1%, the dimensions of the film will change between immediately after production and after storage, resulting in problems such as dimensional differences during processing steps such as printing and increased tendency for roll tightening. The natural shrinkage rate in the main shrinkage direction is preferably 0.9% or less, more preferably 0.8% or less. Furthermore, the lower limit of the natural shrinkage rate is preferably 0%, but in consideration of the level of production technology, the lower limit may be 0.2%.

[0014] 1.6. Number of Initial Breaks (After Aging) The heat-shrinkable film of the present invention preferably has an initial break number, which is the number of breaks before 5% tension in the longitudinal direction of the film after aging for 168 hours at a temperature of 55°C and a relative humidity of 40%, of 10 samples. If the number of initial breaks after aging in the longitudinal direction of the film is more than 4, the film may break when the film roll is unwound for printing or the like after storage in a warehouse and tension is applied, which is undesirable, resulting in a process abnormality. The lower limit of the number of initial breaks after aging in the longitudinal direction is preferably 0, but in practice it may be 1 or less.

[0015] 1.7. Glass Transition Onset Temperature (Before Aging) The heat-shrinkable film of the present invention preferably has a glass transition onset temperature of 65°C or higher and 110°C or lower, as measured by temperature-modulated differential scanning calorimetry (MDSC), as described below. The shrinkage onset temperature of a heat-shrinkable film depends on the glass transition onset temperature. Therefore, if the glass transition onset temperature is lower than 65°C, it becomes difficult to maintain a reversible heat capacity difference ΔCp of 0.22 J / g·K or less from 30°C to 70°C, as described below, and the 70°C shrinkage rate in the main shrinkage direction tends to exceed 3% and the natural shrinkage rate tends to exceed 1%, which is undesirable. On the other hand, if the glass transition onset temperature exceeds 110°C, it becomes difficult to maintain a reversible heat capacity difference ΔCp of 0.25 J / g·K or higher from 30°C to 80°C, as described below, and it tends to be difficult to achieve an 80°C shrinkage rate in the main shrinkage direction of more than 10%. The glass transition onset temperature is preferably 66°C or higher and 109°C or lower, more preferably 67°C or higher and 108°C or lower.

[0016] 1.8. Reversible Heat Capacity Difference ΔCp (Before Aging) The heat-shrinkable film of the present invention preferably has a reversible heat capacity difference ΔCp from 30°C to 70°C, as measured by temperature-modulated differential scanning calorimetry (MDSC) described below, of 0.22 J / g·K or less, and a reversible heat capacity difference (ΔCp) from 30°C to 80°C of 0.25 J / g·K or more and 0.4 J / g·K or less. ΔCp is thought to be related to the amount of mobile amorphous molecular chains in the heat-shrinkable film; the larger the ΔCp during the temperature rise process, the greater the amount of mobile amorphous molecular chains. In studying conventional heat-shrinkable films, these mobile amorphous molecular chains are thought to correspond to the molecular chains that contribute to thermal shrinkage during heating. In the present invention, the inventors have also extensively studied this as an indicator for increasing the 80°C shrinkage rate in the main shrinkage direction. However, the inventors have discovered that this ΔCp also contributes to the 70°C shrinkage rate (and natural shrinkage rate) in the main shrinkage direction, which are important in the present invention. It is believed that ΔCp during the temperature rise process indicates amorphous molecular chains that can move within the respective temperature ranges of 30°C to 70°C and 30°C to 80°C. In the present invention, the inventors have discovered that the following molecular structure can be adopted to achieve a concept that was not present in conventional heat-shrinkable films, namely, maintaining a low 70°C shrinkage while achieving a high 80°C shrinkage in the nearby temperature range. That is, to maintain a low 70°C shrinkage, which contributes to the natural shrinkage, it is important to reduce the amount of mobile amorphous molecular chains in the 30°C to 70°C range, while to achieve a high 80°C shrinkage in the temperature range relatively close to 70°C, it is important to increase the amount of mobile amorphous molecular chains in the 30°C to 80°C range.

[0017] If the ΔCp from 30°C to 70°C exceeds 0.22 J / g·K, the number of mobile amorphous molecular chains in this temperature range will be too large, which will lead to an increase in the 70°C shrinkage rate in the main shrinkage direction that is likely to exceed 3%, and ultimately to an increase in the natural shrinkage rate that is likely to exceed 1%, which is undesirable. The ΔCp from 30°C to 70°C is more preferably 0.215 J / g·K or less, and even more preferably 0.21 J / g·K or less. On the other hand, the lower limit of the ΔCp from 30°C to 70°C is 0 J / g·K, and this value is most preferred. However, in the present invention, if the ΔCp from 30°C to 70°C is 0 J / g·K, it will be difficult to maintain the ΔCp from 30°C to 80°C below at 0.25 J / g·K or more, so it is preferable that the ΔCp be at least 0.05 J / g·K. In practice, a ΔCp from 30°C to 70°C of 0.1 J / g·K or more is sufficient.

[0018] If the ΔCp from 30°C to 80°C is less than 0.25 J / g·K, fewer molecular chains contribute to shrinkage upon heating, making it difficult to achieve an 80°C shrinkage rate of more than 10% in the main shrinkage direction, and the heat shrinkage rate required for label attachment is reduced, which is undesirable. On the other hand, if the ΔCp from 30°C to 80°C exceeds 0.4 J / g·K, the ΔCp from 30°C to 70°C is likely to exceed 0.22 J / g·K, which in turn makes the 70°C shrinkage rate in the main shrinkage direction more likely to exceed 3% and the natural shrinkage rate more likely to exceed 1%, which is undesirable. The ΔCp from 30°C to 80°C is preferably 0.255 J / g·K to 0.395 J / g·K, and more preferably 0.26 J / g·K to 0.39 J / g·K.

[0019] 1.9. Enthalpy Relaxation Amount (After Aging) The heat-shrinkable film of the present invention preferably has an enthalpy relaxation amount after aging of 2.5 J / g or less, as measured by temperature-modulated differential scanning calorimetry (MDSC) described below. The enthalpy relaxation amount indicates the degree of deterioration of the film during aging, and if it exceeds 2.5 J / g or less, the natural shrinkage rate tends to increase and the shrinkage rate after aging tends to decrease. The lower the enthalpy relaxation amount, the more preferable it is, so 0 J / g or less is most preferable, but 0.1 J / g·K is considered to be the lower limit in terms of the technical level of the present invention. Even if the lower limit of the enthalpy relaxation amount is 0.5 J / g, it is sufficient for practical use.

[0020] 2. Raw Materials and Layer Structure of the Heat-Shrinkable Film The heat-shrinkable film of the present invention is a polyester film, a polystyrene film, or a polyester-polystyrene film. A polyester film is a film made primarily of polyester. A polystyrene film is a film made primarily of polystyrene. A polyester-polystyrene film may be a film made primarily of a mixture of polyester and polystyrene. The mixing ratio of polyester to polystyrene is not particularly limited, and is preferably 10:90 to 90:10, more preferably 30:70 to 70:30, and even more preferably 40:60 to 60:40 by mass. Alternatively, the heat-shrinkable film may be a laminated film formed by laminating two of the above polyester films. The "main raw materials" mentioned above mean that, of 100% by mass of the resin components constituting the heat-shrinkable film, preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably substantially 100% by mass is polyester and / or polystyrene. The term "substantially 100% by mass" means that other resin components may be included as long as the basic properties of the film of the present invention are not impaired. For example, other resins may be included as components of additives described below.

[0021] 2.1. Composition of Heat-Shrinkable Polyester Film The polyester resin constituting the heat-shrinkable polyester film may be a homopolymer or a copolymer. When two or more polyesters are mixed, the mixture may be a mixture of copolymer polyesters, or a mixture of copolymer polyesters and homopolyesters of the desired composition. The polyester resin homopolymer is not limited to the following as long as it satisfies the above physical properties. Examples include polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT), polycyclohexylene dimethylene terephthalate (PCT), polycyclohexane dimethylene isophthalate (PCHT), polyethylene naphthalate (PEN), and polybutylene naphthalate (PBN). Polyethylene terephthalate, polyethylene-2,6-naphthalate, and polytrimethylene terephthalate are preferred from the perspective of balancing physical properties and cost. Known components can be used as the diol and dicarboxylic acid components constituting the polyester homopolymer. As long as the above physical properties are satisfied, the polyester resin may be a copolymer in which a part of the diol component or dicarboxylic acid component constituting the homopolymer of the polyester resin is replaced with a copolymer component such as those listed below.

[0022] The heat-shrinkable polyester film of the present invention may be a polyester homopolymer satisfying the above-mentioned physical properties, or a copolymerized polyester resin (copolymer) in which a portion of the diol component or dicarboxylic acid component constituting the polyester homopolymer is replaced with a copolymerization component such as the following. The copolymerization component may be one type or a combination of two or more types. A suitable polyester raw material for producing the heat-shrinkable film of the present invention is a polyethylene terephthalate unit. In one embodiment, the polyester raw material is primarily composed of ethylene terephthalate units. The primary component of the ethylene terephthalate unit is preferably 40 mol% or more, more preferably 50 mol% or more, even more preferably 55 mol% or more, even more preferably 70 mol% or more, and most preferably 75 mol% or more, based on 100 mol% of all resin components constituting the polyester. In the case of a homopolymer, the polyester is substantially composed of ethylene terephthalate units, but other resin components may be contained, for example, as additives described below, as long as they do not impair the basic properties of the film of the present invention.

[0023] In a preferred embodiment, diol components suitable as the polyhydric alcohol component include ethylene glycol, which constitutes the polyethylene terephthalate unit, as well as aliphatic diols, alicyclic diols, and aromatic diols, which may be used alone or in combination of two or more. Examples of aliphatic diols include propylene glycol, 1,6-hexanediol, 1,10-decanediol, neopentyl glycol, 2-methyl-2-ethyl-1,3-propanediol, 2-diethyl-1,3-propanediol, and 2-ethyl-2-n-butyl-1,3-propanediol. Examples of alicyclic diols include 1,3-cyclohexanedimethanol and 1,4-cyclohexanedimethanol. Examples of aromatic diols include ethylene oxide adducts of bis(4'-β-hydroxyethoxyphenyl)sulfone and other bis(methylol) compounds; and xylylene glycol.

[0024] In a preferred embodiment, dicarboxylic acid components suitable as the polycarboxylic acid component include terephthalic acid, which constitutes the ethylene terephthalate unit, as well as aromatic dicarboxylic acids, aliphatic dicarboxylic acids, and alicyclic dicarboxylic acids, which may be used alone or in combination of two or more. Examples of aliphatic dicarboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, sebacic acid, pimelic acid, suberic acid, undecanoic acid, dodecanedicarboxylic acid, brassylic acid, tetradecanedicarboxylic acid, thapsic acid, nonadecanedicarboxylic acid, docosanedicarboxylic acid, and substituted derivatives thereof, as well as 4,4'-dicarboxycyclohexane and substituted derivatives thereof. Examples of aromatic dicarboxylic acids include phthalic acid, isophthalic acid, orthophthalic acid, 5-sodium isophthalic acid, and 2,6-naphthalenedicarboxylic acid. Examples of the alicyclic dicarboxylic acid include 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, tetrahydrophthalic acid, hexahydrophthalic acid, and methyltetrahydrophthalic acid.

[0025] In one embodiment, the heat-shrinkable polyester film, particularly the polyethylene terephthalate film, preferably contains a monomer capable of forming an amorphous component to improve its properties. Specific examples of the monomer capable of forming an amorphous component include aromatic dicarboxylic acids such as neopentyl glycol, 1,4-cyclohexanedimethanol, isophthalic acid, and orthophthalic acid; aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid, and decanedicarboxylic acid; and alicyclic dicarboxylic acids, 1,4-cyclohexanedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,3-propanediol, 2,2-diethyl-1,3-propanediol, 2-n-butyl-2-ethyl-1,3-propanediol, 2,2-isopropyl-1,3-propanediol, 2,2-di-n-butyl-1,3-propanediol, and hexanediol. Among these, neopentyl glycol, 1,4-cyclohexanedimethanol, and isophthalic acid are preferred. These may be used alone or in combination of two or more.

[0026] From the viewpoint of achieving the effects of the present invention, it is preferable to adjust resin components other than the main component constituting the polyester (e.g., ethylene terephthalate unit). When two or more dicarboxylic acids are used in combination, the terephthalic acid component is preferably 70 mol% or more, more preferably 80 mol% or more, even more preferably 90 mol% or more, and even more preferably 95 mol% or more, based on 100 mol% of the polycarboxylic acid components constituting the polyester. When two or more diol components are used in combination, the ethylene glycol component is preferably 50 mol% or more, more preferably 60 mol% or more, even more preferably 70 mol% or more, even more preferably 80 mol% or more, and particularly preferably 90 mol% or more, based on 100 mol% of the polyhydric alcohol components constituting the polyester.

[0027] In one embodiment, when an aliphatic dicarboxylic acid (e.g., adipic acid, sebacic acid, decanedicarboxylic acid, etc.) is contained in the polyester, the total content of the aliphatic dicarboxylic acids is preferably less than 3 mol% based on 100 mol% of the dicarboxylic acid components constituting the polyester. Heat-shrinkable films obtained using polyesters containing 3 mol% or more of these aliphatic dicarboxylic acids may have insufficient film stiffness during high-speed application.

[0028] In the present invention, in order to maintain the glass transition onset temperature (Tg) at 65°C or higher and to obtain the effects of the present invention, it is preferable not to use resin raw materials with low Tg, and specifically, the film is substantially free of at least one or all of those selected from the group consisting of butanediol, diethylene glycol, and ε-caprolactone. Here, "substantially free" means that these compounds are present in a total amount of preferably 2 mol% or less, or even substantially 0 mol%, of the resin components constituting the heat-shrinkable film. "Substantially 0 mol%" means that these compounds are allowed within a range that does not impair the properties of the film, and they may be present, for example, as additives.

[0029] It is also preferable that the polyester does not contain trivalent or higher polycarboxylic acids (e.g., trimellitic acid, pyromellitic acid, and anhydrides thereof), since heat-shrinkable films obtained using polyesters containing these polycarboxylic acids may have difficulty achieving the required high shrinkage percentage.

[0030] The polyester used in the present invention preferably does not contain a diol having 8 or more carbon atoms (e.g., octanediol, etc.) or a polyhydric alcohol having a valence of 3 or more (e.g., trimethylolpropane, trimethylolethane, glycerin, diglycerin, etc.). A heat-shrinkable film obtained using a polyester containing such a diol or polyhydric alcohol may have difficulty in achieving the required high shrinkage percentage.

[0031] 2.2. Structure of Heat-Shrinkable Polystyrene-Based Film The polystyrene resin constituting the heat-shrinkable polystyrene-based film may be a homopolymer or a copolymer. When two or more types of polystyrene are mixed, the mixture may be a mixture of copolymer polystyrenes, or a mixture of copolymer polystyrene and homopolystyrene of a desired composition. In the heat-shrinkable polystyrene-based film, the styrene content is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and even more preferably 90% by mass or more, based on 100% by mass of the resin components constituting the film, and may be substantially 100% by mass. Here, "substantially 100% by mass" has the same meaning as in polyester-based films.

[0032] Polystyrene-based resins are polymers composed of a styrene-based monomer as an essential monomer (monomer) component. That is, they are polymers containing at least one structural unit derived from a styrene-based monomer per molecule. The styrene-based monomer is not particularly limited as long as it satisfies the above-described physical properties of the present invention, but examples include alkylstyrenes, halogen-substituted alkylstyrenes, halogenated styrenes, alkoxystyrenes, carboxyalkylstyrenes, alkyl ether styrenes, and alkylsilylstyrenes. Examples of alkylstyrenes include styrene, α-methylstyrene, m-methylstyrene, p-methylstyrene, p-ethylstyrene, p-isobutylstyrene, and p-t-butylstyrene. Examples of halogen-substituted alkylstyrenes include p-, m-, or o-chloromethylstyrene. Examples of halogenated styrenes include p-, m-, or o-chlorostyrene, p-, m-, or o-bromostyrene, p-, m-, or o-fluorostyrene, and o-methyl-p-fluorostyrene. Examples of alkoxystyrenes include p-, m-, or o-methoxystyrene, and p-, m-, or o-ethoxystyrene. Examples of carboxyalkylstyrenes include p-, m-, and o-carboxymethylstyrene. Examples of alkyl ether styrenes include p-vinylbenzyl propyl ether. Examples of alkylsilylstyrenes include p-trimethylsilylstyrene. The above styrene monomers may be used alone or in combination of two or more.

[0033] The polystyrene-based resin is not particularly limited as long as it satisfies the above-mentioned physical properties of the present invention, but examples thereof include homopolymers of styrene-based monomers such as general-purpose polystyrene, which is a homopolymer of styrene, copolymers composed solely of two or more styrene-based monomers as monomer components, copolymers such as styrene-diene copolymers and styrene-polymerizable unsaturated carboxylic acid ester copolymers, mixtures of polystyrene and synthetic rubber (e.g., polybutadiene, polyisoprene, etc.), high-impact polystyrenes such as polystyrene obtained by graft-polymerizing styrene onto synthetic rubber, and polystyrene obtained by dispersing a rubber-like elastomer in a continuous phase of a polymer containing a styrene-based monomer (e.g., a copolymer of a styrene-based monomer and a (meth)acrylic acid ester monomer) and graft-polymerizing the copolymer onto the rubber-like elastomer. The polystyrene-based resins may be used alone or in combination of two or more.

[0034] In addition, in a preferred embodiment, the heat-shrinkable film of the present invention is composed of a styrene-diene copolymer in order to satisfy the above-mentioned physical properties of the present invention. In this case, the heat-shrinkable film of the present invention and the shrink label using the same can have excellent shrink properties. The styrene-diene copolymer is a copolymer composed of a styrene monomer and a diene (particularly, a conjugated diene) as essential monomer components. That is, it is a polymer containing at least a structural unit derived from a styrene monomer and a structural unit derived from a diene (particularly, a conjugated diene) in one molecule.

[0035] The diene is not particularly limited, but conjugated dienes are preferred, such as 1,3-butadiene, isoprene (2-methyl-1,3-butadiene), 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene, and chloroprene. Among these, 1,3-butadiene is particularly preferred from the viewpoints of stretchability, heat shrinkability, and interlaminar strength. That is, the styrene-diene copolymer is preferably a styrene-butadiene copolymer. The dienes may be used alone or in combination of two or more.

[0036] The monomer components constituting the styrene-diene copolymer may further contain a monomer component other than the styrene-based monomer and the diene. Examples of the monomer component other than the styrene-based monomer and the diene include vinyl-based monomers, polymerizable unsaturated carboxylic acid esters, and polymerizable unsaturated carboxylic acid anhydrides. The copolymerization form of the styrene-diene copolymer is not particularly limited, and examples include random copolymers, block copolymers, and graft copolymers. Among these, block copolymers are preferred, and examples include styrene block (S)-diene block (D) type, S-D-S type, D-S-D type, and S-D-S-D type.

[0037] Examples of the styrene-diene block copolymer (styrene-diene block copolymer) include styrene-butadiene block copolymers (SBC) such as styrene-butadiene-styrene block copolymer (SBS), styrene-isoprene block copolymers such as styrene-isoprene-styrene block copolymer (SIS), and styrene-butadiene-isoprene block copolymers such as styrene-butadiene-isoprene-styrene block copolymer (SBIS), among which styrene-butadiene block copolymers are preferred. These block copolymers may be used alone or in combination of two or more.

[0038] The styrene-butadiene block copolymer is not particularly limited as long as it has a styrene block in which only a styrene-based monomer is polymerized and a butadiene block in which only butadiene is polymerized. Examples of the styrene-butadiene block copolymer include styrene-butadiene block copolymers having styrene blocks at both ends, such as styrene-butadiene-styrene block copolymer (SBS) and styrene-butadiene-styrene-butadiene-styrene block copolymer (SBSBS); styrene-butadiene block copolymers having styrene blocks and butadiene blocks at their respective ends, such as styrene-butadiene copolymer (SB) and styrene-butadiene-styrene-butadiene copolymer (SBSB); and styrene-butadiene block copolymers having butadiene blocks at both ends, such as butadiene-styrene-butadiene copolymer (BSSB). Of these, styrene-butadiene block copolymers having styrene blocks at both ends are preferred, and SBS is more preferred. These styrene-butadiene block copolymers may be used alone or in combination of two or more.

[0039] In the present invention, a heat-shrinkable polyester-polystyrene film is also a preferred embodiment. The polyester corresponds to the heat-shrinkable polyester film described above, and the polystyrene corresponds to the heat-shrinkable polystyrene film described above, so their explanations are omitted here. The polyester-polystyrene film may be a film (single-layer film) manufactured from a mixed resin obtained by mixing the respective raw resins, or may be a two-type two-layer or two-type three-layer laminate film obtained by laminating a polyester film and a polystyrene film, which have been formed separately.

[0040] 2.3 Other Additives Various additives, such as waxes, antioxidants, antistatic agents, crystal nucleating agents, viscosity reducers, heat stabilizers, coloring pigments, color inhibitors, and ultraviolet absorbers, may be added to the polyester or polystyrene resin forming the heat-shrinkable film of the present invention, as needed.

[0041] It is preferable to add a lubricant to the resin forming the heat-shrinkable film of the present invention to improve the workability (slipperiness) of the film. Any lubricant can be selected. Examples include inorganic particles such as silica, alumina, titanium dioxide, calcium carbonate, kaolin, and barium sulfate; organic particles such as acrylic resin particles, melamine resin particles, silicone resin particles, and cross-linked polystyrene particles; polyolefin waxes such as polyethylene wax and oxidized polyethylene wax; and various waxes such as fatty acid amides, fatty acid esters, paraffin wax, polytetrafluoroethylene (PTFE) wax, and carnauba wax. The average particle size of the microparticles is preferably in the range of 0.05 to 3.0 μm. The average particle size of the microparticles is measured using a Coulter counter. The lubricant can be incorporated into the resin forming the heat-shrinkable film of the present invention by adding it at any stage of the production of polyester raw materials or polystyrene raw materials.

[0042] 2.4. Layer Structure The layer structure of the heat-shrinkable film of the present invention may be any structure, such as a single layer, two-type two-layer structure, or two-type three-layer structure, and the number of layers may be greater than these. In the case of a single layer, polyester raw material alone or polystyrene raw material alone may be used, or the two may be mixed. When polyester raw material and polystyrene raw material are mixed, a void-containing (white) film can be obtained if a compatibilizer is not used, and a transparent film can be obtained if a compatibilizer is used. Furthermore, in the case of a multilayer structure such as two-type two-layer structure or two-type three-layer structure, for example, a polystyrene raw material may be used for the core layer and a polyester raw material for the skin layer, or the raw materials of the core layer and the skin layer may be interchanged. In the case of a laminate structure of polyester and polystyrene, it is preferable to use an adhesive or a compatibilizer. Examples of such adhesives and compatibilizers include polyester-based resins, polyolefin-based resins, acrylic resins, polycarbonate resins, etc. These may be used alone or in combination of two or more types.

[0043] 3. Method for Producing Heat-Shrinkable Film 3.1. Method for Producing Heat-Shrinkable Film The heat-shrinkable film of the present invention can be obtained by melt-extruding the above-mentioned raw materials using an extruder to form an unstretched film, and then stretching the unstretched film by a predetermined method described below. The following description will be given taking as an example a heat-shrinkable film formed by transverse uniaxial stretching or by sequential biaxial stretching in which longitudinal stretching is followed by transverse stretching, and in which the transverse direction (width direction) is the main shrinkage direction. However, as long as the above-mentioned physical properties of the present invention are satisfied, the film may be formed by longitudinal uniaxial stretching or by sequential biaxial stretching in which longitudinal stretching is followed by transverse stretching, or by simultaneous biaxial stretching in which longitudinal and transverse directions are simultaneously stretched.

[0044] 3.1.1. Extrusion Conditions, Unstretched Film Formation Conditions When melt-extruding the raw resin, it is preferable to dry the polyester or polystyrene raw material using a dryer such as a hopper dryer or paddle dryer, or a vacuum dryer. After drying the polyester or polystyrene raw material, it is melted and extruded into a film using an extruder at a temperature of 200 to 300°C. Any existing method, such as a T-die method or a tubular method, can be used for extrusion. An unstretched film can be obtained by quenching the extruded sheet-like molten resin. A suitable method for quenching the molten resin is to cast the molten resin from a die onto a rotating drum and rapidly cool and solidify it to obtain a substantially unoriented resin sheet.

[0045] 3.1.2. Longitudinal Stretching When transverse uniaxial stretching is employed in the production of the heat-shrinkable film of the present invention, the longitudinal stretching ratio is 1 (unstretched). When a longitudinal-transverse sequential biaxial stretching method is employed, the longitudinal stretching ratio is preferably 1.05 to 5. A longitudinal stretching ratio of more than 5 is undesirable because breakage is likely to occur in the subsequent transverse stretching. The upper limit of the longitudinal stretching ratio is preferably 4.9, more preferably 4.8 or less.

[0046] When stretching in the longitudinal direction, it is preferable to preheat a substantially unoriented film to Tg or higher and Tg + 40°C or lower. If the longitudinal stretching temperature is lower than Tg, the stretching stress during longitudinal stretching may become too large, which may cause the film to break. On the other hand, if the longitudinal stretching temperature exceeds Tg + 30°C, the film may easily stick to the roll and may wind around the roll. The longitudinal stretching temperature is preferably Tg + 2°C or higher and Tg + 38°C or lower, more preferably Tg + 4°C or higher and Tg + 36°C or lower. Note that either one-stage stretching or two or more multi-stage stretching can be used for longitudinal stretching.

[0047] In the present invention, after longitudinal stretching to a longitudinal stretching ratio of 2 or more, it is preferable to relax the film (relaxation) by utilizing the difference in roll speeds. This relaxation treatment can reduce the thermal shrinkage in the longitudinal direction caused by longitudinal stretching, and is particularly effective when the transverse direction is the main shrinkage direction. The relaxation rate is preferably 5% to 60%. If the relaxation rate is below 5%, the effect of relaxation in reducing the longitudinal shrinkage rate is almost lost. On the other hand, if the relaxation rate exceeds 60%, the proportion of the film that is relaxed (shrunk) during the process becomes large, which may result in the film not shrinking sufficiently and winding around the roll. The relaxation rate is more preferably 7% to 58%, and even more preferably 9% to 56%.

[0048] The relaxation temperature is preferably Tg or higher and Tg + 40°C or lower. If the relaxation temperature is lower than Tg, it is highly likely that the longitudinal shrinkage required for relaxation will not be achieved, and the film may wind around the roll. On the other hand, if the relaxation temperature exceeds Tg + 40°C, the film will tend to stick to the roll, and there is also a risk of the film winding around the roll. The relaxation temperature is preferably Tg + 2°C or higher and Tg + 38°C or lower, more preferably Tg + 4°C or higher and Tg + 36°C or lower.

[0049] 3.1.3. Transverse Stretching In the production of the heat-shrinkable film of the present invention, the transverse stretching ratio is preferably 3.0 times or more and 6.0 times or less. If the transverse stretching ratio is less than 3.0 times, thickness unevenness in the transverse direction tends to worsen, which is not preferred. Furthermore, if the transverse stretching ratio exceeds 6 times, breakage tends to occur, which is not preferred. The transverse stretching ratio is more preferably 3.5 times or more and 5.5 times or less.

[0050] When performing transverse stretching, an intermediate preheating treatment may be performed before transverse stretching. In particular, when performing longitudinal-transverse stretching, it is preferable to heat the film as an intermediate preheating treatment until the film temperature falls within the range of Tg + 10°C or more and Tg + 100°C or less. By performing such a preheating treatment, it is possible to reduce the shrinkage rate in the longitudinal direction, which is the non-shrinkage direction, caused by longitudinal stretching. If the film temperature in the preheating treatment is less than Tg + 10°C, this is not preferable because it hardly achieves the effect of reducing the shrinkage rate in the longitudinal direction. Furthermore, if it exceeds Tg + 100°C, the molecular orientation of the film decreases, making it more likely to break early, which is also not preferable. It is more preferable that the film temperature in the longitudinal preheating treatment be Tg + 20°C or more and Tg + 90°C or less.

[0051] When performing transverse stretching, it is preferable to adjust the surface temperature of the film to be Tg°C or higher and Tg + 40°C or lower. When performing the above-mentioned preheating treatment, a cooling step may be provided before the subsequent transverse stretching step. When producing a film by the longitudinal-transverse stretching method, it is preferable to adjust the surface temperature of the film to be Tg°C or higher and Tg + 40°C or lower when performing transverse stretching, rather than transversely stretching the film that has been preheated as described above. If the film temperature at the start of transverse stretching remains above Tg + 40°C, the transverse shrinkage of the film will be low, and the shrinkability when made into a label will be insufficient, which is undesirable. Furthermore, if the film temperature during transverse stretching falls below Tg due to film quenching, the stress during stretching will increase, making the film more susceptible to breakage, which is not desirable. The transverse stretching temperature is more preferably Tg + 2°C or higher and Tg + 35°C or lower, and even more preferably Tg + 4°C or higher and Tg + 34°C or lower.

[0052] 3.1.4. Heat Setting In the production of the heat-shrinkable film of the present invention, it is preferable to perform a heat treatment (heat setting) while holding the film after stretching. Heat setting facilitates achieving a ΔCp of 0.22 J / g·K or less from 30°C to 70°C, making it possible to adjust the shrinkage rate and reduce the natural shrinkage rate. The heat setting temperature is preferably Tg + 5°C or higher and Tg + 40°C or lower. A heat setting temperature lower than Tg + 5°C makes it difficult to achieve a ΔCp of 0.22 J / g·K or less from 30°C to 70°C, which in turn increases the 70°C shrinkage rate and natural shrinkage rate in the main shrinkage direction, making the film more susceptible to wrinkling during storage, which is undesirable. On the other hand, if the heat setting temperature exceeds Tg+40°C, it becomes difficult to maintain ΔCp at 0.25 J / g·K or more from 30°C to 80°C, and the shrinkage rate in the main shrinkage direction at 80°C or 120°C decreases, which is undesirable because it tends to deteriorate the appearance due to insufficient shrinkage when used as a heat shrinkable film. The heat setting temperature is more preferably Tg+7°C or higher and Tg+35°C or lower, and even more preferably Tg+10°C or higher and Tg+30°C or lower.

[0053] The heat setting treatment time is preferably 5 seconds or more and 40 seconds or less. If the treatment time is less than 5 seconds, the actual film temperature cannot keep up with the treatment temperature, making it difficult to obtain the full effect of the heat setting treatment, and the natural shrinkage rate tends to increase, which is undesirable. If the treatment time exceeds 40 seconds, the zone length of the heat setting treatment zone must be increased, which increases the production cost, which is undesirable. The treatment time is more preferably 7 seconds or more and 35 seconds or less.

[0054] 3.1.5. Relaxation Treatment in the Main Shrinkage Direction In the production of the heat-shrinkable film of the present invention, it is preferable to perform a relaxation treatment in the same direction after stretching in the shrinkage direction. The inventors conducted extensive research to determine the ability to maintain a high 80°C shrinkage (ΔCp from 30°C to 80°C) while reducing the 70°C shrinkage and natural shrinkage (ΔCp from 30°C to 70°C), which is particularly important in the present invention. As a result, they found that by performing a relaxation treatment in the main shrinkage direction under the specified conditions described below, it is possible to keep the ΔCp in these opposing temperature ranges within the specified ranges.

[0055] For example, when the main shrinkage direction is the horizontal direction, relaxation treatment can be performed by narrowing the tenter width while the film is heated to shrink the film. The relaxation treatment is preferably performed at a relaxation rate of 1% or more and 20% or less, as shown in the following formula 1. A relaxation rate of less than 1% is not preferred because the natural shrinkage rate cannot be sufficiently reduced. A relaxation rate of more than 20% is also not preferred because the 80°C shrinkage rate drops significantly. The relaxation rate is more preferably 2% or more and 19% or less. Relaxation rate = {(tenter width before relaxation - tenter width after relaxation) / tenter width before relaxation} x 100 (%) Formula 1

[0056] The relaxation treatment can be carried out either simultaneously with the heat setting treatment or after the heat setting treatment, but it is more preferable to carry out the treatment after the heat setting treatment. When the relaxation treatment is carried out after the heat setting treatment, it is preferably carried out at a temperature lower than the heat setting temperature and in the range of Tg or higher and Tg + 30°C or lower. The present inventors have surprisingly discovered that treatment under such conditions makes it possible to specifically reduce the ΔCp from 30°C to 70°C while maintaining a high ΔCp from 30°C to 80°C. Although the detailed mechanism behind this has not been clarified, the present inventors speculate that by carrying out relaxation at a temperature lower than the heat setting temperature at constant length (without relaxation), only amorphous molecular chains that move in the relatively low temperature range of 30°C to 70°C are relaxed (ΔCp from 30°C to 70°C is reduced), while molecular chains that shrink in the relatively high temperature range of 30°C to 80°C are maintained, and only molecular chains that contribute to natural shrinkage can be selectively relaxed. The preferred temperature range for the relaxation treatment is Tg+3°C or higher and Tg+25°C or lower.

[0057] 4. Annular Labels and Packages Packages using the heat-shrinkable film of the present invention are formed by covering at least a portion of the outer periphery of an object to be packaged with the heat-shrinkable film of the present invention and then heat-shrinking the film. Examples of objects to be packaged include plastic food storage bottles, polyethylene containers used for shampoos and conditioners, various bottles, cans, plastic containers for confectionery and lunch boxes, and paper boxes. Furthermore, labels obtained from heat-shrinkable films do not necessarily have to cover the entire container; they may only cover a portion of the container, such as a bottle cap (cap seal). They may also be preforms that have not yet been completely attached to the container. Typically, when labels obtained from heat-shrinkable films are heat-shrunk to cover such objects, the labels are heat-shrunk by approximately 2 to 15% before being attached to the object.

[0058] Labels can be produced by coating one side of a rectangular film with an organic solvent slightly inward from the edge, then immediately rolling the film and overlapping and gluing the edges together to form a label; alternatively, by coating one side of a rolled film with an organic solvent slightly inward from the edge, then immediately rolling the film and overlapping and gluing the edges together to form a tubular body, which is then cut into a circular label. Preferred organic solvents for adhesive use are cyclic ethers such as 1,3-dioxolane or tetrahydrofuran. Other suitable organic solvents include aromatic hydrocarbons such as benzene, toluene, xylene, and trimethylbenzene; halogenated hydrocarbons such as methylene chloride and chloroform; and phenols such as phenol, as well as mixtures of these.

[0059] This application claims the benefit of priority based on Japanese Patent Application No. 2024-070729, filed on April 24, 2024. The entire contents of the specification of Japanese Patent Application No. 2024-070729, filed on April 24, 2024, are incorporated herein by reference.

[0060] Next, the present invention will be specifically explained using examples and comparative examples, but the present invention is not limited to the aspects of these examples and can be appropriately modified within the scope of the present invention.

[0061] <Method for Evaluating Heat-Shrinkable Film> [Thickness] Using a micrometer (Militron 1254D manufactured by Finepfluh), measurements were taken at five points, and the average value was calculated.

[0062] [Glass transition temperature (Tg)] The sample film was weighed at 5.0±0.2 mg and placed in a PerkinElmer aluminum pan (flat dish shape), and the pan was sealed with a lid. When sealing the sample in the pan, the film was stacked and punched into a circle (4.5 mm diameter) to ensure good adhesion to the pan bottom. "Good adhesion to the pan bottom" means that when the sample is sealed in the pan, the film sample is not bent inside the pan and is firmly pressed down with the lid, leaving no space between the stacked films. While wrinkles may be present in the film before punching, it is preferable to smooth out the wrinkles before punching the sample. The shape and size of the punched sample (punch) are not limited to the above, as long as the sample fits into the pan bottom without bending. The sample was measured using a temperature-modulated differential scanning calorimeter (DSC) "DSC8500" (manufactured by PerkinElmer) in StepScan mode from 20°C to 200°C at an average heating rate of 2.7°C / min, a step temperature (second temperature) of 1.3°C, and an isothermal time of 0.2 min, to obtain reverse heat flow. In the reverse heat flow obtained by the measurement, the first signal that changed stepwise from the baseline during the heating process was determined as the glass transition onset temperature Tg. Specifically, an extension of the heat flow baseline was drawn, and the intersection with the tangent at the inflection point (Tg) was determined. The value on the horizontal axis at this intersection was read, and the lower value was taken as the glass transition temperature Tg.

[0063] [70°C and 80°C Shrinkage (Before Aging)] A heat-shrinkable film was cut into a 10 cm x 10 cm square and immersed in warm water at a predetermined temperature ±0.5°C for 10 seconds without load to allow it to heat shrink. The film was then immersed in water at 25°C ±0.5°C for 10 seconds, and after being pulled out of the water, the dimensions of the film in the longitudinal and transverse directions were measured, and the heat shrinkage ratio was calculated according to the following formula 2. The direction with the larger heat shrinkage ratio was designated as the main shrinkage direction. Heat shrinkage ratio = {(length before shrinkage - length after shrinkage) / length before shrinkage} × 100 (%) Formula 2

[0064] [80°C Shrinkage (After Aging)] After leaving the heat-shrinkable film in a 55°C environment for 168 hours, it was cut into a 10 cm x 10 cm square and immersed in warm water at 80°C ± 0.5°C for 10 seconds under no load to cause heat shrinkage, then immersed in water at 25°C ± 0.5°C for 10 seconds and pulled out of the water, and the dimensions of the film in the longitudinal and transverse directions were measured, and the heat shrinkage ratio was calculated in accordance with the above formula 2. The direction with the larger heat shrinkage ratio was defined as the main shrinkage direction.

[0065] [120°C Shrinkage (Before Aging)] A heat-shrinkable film was cut into a 10 cm x 10 cm square and immersed in silicone oil at 120°C ± 0.5°C for 10 seconds under no load to cause heat shrinkage, then immersed in water at 25°C ± 0.5°C for 10 seconds and pulled out of the water, and the dimensions of the film in the longitudinal and transverse directions were measured, and the heat shrinkage ratio was calculated in accordance with the above formula 2. The direction with the larger heat shrinkage ratio was defined as the main shrinkage direction.

[0066] [Natural Shrinkage at 55°C] A sample was taken at a length of 20 mm in a direction perpendicular to the main shrinkage direction of the film and 240 mm in the main shrinkage direction, and a mark was made so that the length in the main shrinkage direction was 200 mm. The length between the markings was taken as the length (mm) before aging. The film was aged for 168 hours in an environment of a temperature of 55°C and a relative humidity of 40%, and the length between the markings was taken as the length (mm) after aging, and the natural shrinkage was calculated using the following formula 3. The measurement was performed twice, and the average value of these measurements was calculated as the natural shrinkage. Natural shrinkage = {(length before aging - length after aging) / length before aging} x 100 (%) Formula 3

[0067] [Number of Initial Breaks] A film sample cut to 20 cm in the longitudinal direction and 30 cm in the width direction was aged for 168 hours under an environment of 55°C and 40% relative humidity, and then a rectangular sample of 140 mm in the longitudinal direction and 20 mm in the width direction was obtained. The aged film was subjected to a tensile test at a temperature of 23°C and a tensile speed of 200 mm / min, with both ends of the test piece in the longitudinal direction held in a universal tensile tester (Shimadzu Corporation, Autograph AG-I) (one-side chuck engagement position 20 mm, chuck distance 100 mm). Ten samples were taken from one aged film sample, and a tensile test was performed on each sample. The number of samples that broke at 5% elongation or less in the longitudinal direction of the film was determined and recorded as the number of initial breaks.

[0068] [Reversible Heat Capacity Difference ΔCp] The reverse heat flow of a sample film was measured in the same manner as in the glass transition temperature measurement described above, and the reversible heat capacity Cp of the heat flow at each temperature of 30°C and 70°C or 80°C was determined using analysis software (Pyris Manager) for a PerkinElmer DSC8500, and ΔCp was calculated using the following equation 4. ΔCp = (Cp at 70°C or 80°C) - (Cp at 30°C) (J / (g K)) Equation 4

[0069] [Enthalpy Relaxation Amount] The non-reverse heat flow obtained by measuring a sample film in the same manner as in the glass transition temperature measurement described above was determined using analysis software (Pyris Manager) for a PerkinElmer DSC8500. The enthalpy relaxation amount (J / g) was calculated from the area of ​​the peak indicating enthalpy relaxation, which appeared as a peak-like signal at a position of Tg±10° C. from the baseline of the non-reverse heat flow. Specifically, a line was drawn connecting the low-temperature side and the high-temperature side of the peak's starting point, and the area of ​​the peak and the part surrounded by this line was calculated as the enthalpy relaxation amount (J / g).

[0070] [Shrinkage Finish] The edges of the heat-shrinkable film were welded with dioxolane or tetrahydrofuran to obtain a cylindrical label (a label with the main shrinkage direction of the heat-shrinkable film as the circumferential direction). This label was passed through a steam tunnel adjusted to 85°C, and then passed through a hot air tunnel adjusted to 200°C to heat-shrink it. The shrinkage finish of the label was visually evaluated on a three-point scale according to the following criteria. The defects described below refer to jumping, wrinkles, insufficient shrinkage, folding of the label edge, whitening from shrinkage, etc. ○ (Good): Good finish (3 or fewer defects) × (Bad): Poor finish (4 or more defects)

[0071] <Polyester Raw Materials> The following polyesters A to G were prepared as polyester raw materials. Polyester A: 100 mol% terephthalic acid / / 100 mol% ethylene glycol (polyethylene terephthalate) with 8000 ppm of silica added as a lubricant. Polyester B: 100 mol% terephthalic acid / / 100 mol% ethylene glycol (polyethylene terephthalate). Polyester C: 100 mol% terephthalic acid / / 70 mol% ethylene glycol / 30 mol% neopentyl glycol (copolymer polyester). Polyester D: 100 mol% terephthalic acid / / 100 mol% butanediol (polybutylene terephthalate). Polyester E: 100 mol% terephthalic acid / / 70 mol% ethylene glycol / 30 mol% 1,4-cyclohexanedimethanol (copolymer polyester). Polyester F: 99 mol% terephthalic acid / 1 mol% isophthalic acid / / 100 mol% ethylene glycol (polyester mechanically recycled from PET bottles).

[0072] <Polystyrene Raw Material> The following polystyrene resins A and B were prepared as polystyrene raw materials. Polystyrene resin A (polystyrene A): 92% by weight of styrene / 8% by weight of butadiene (copolymer) Polystyrene resin B (polystyrene B): 70% by weight of styrene / 30% by weight of butadiene (copolymer)

[0073] (Example 1) Polyester A, polyester B, and polyester C were mixed in a mass ratio of 5:20:75, melted at 275°C using an extruder, and taken up while being cooled on a chill roll set at a surface temperature of 25°C to obtain an unstretched film.

[0074] The obtained unstretched film was introduced into a longitudinal stretching machine having a plurality of roll groups arranged in series, and preheated with a preheating roll until the film temperature reached 92° C., after which it was stretched in the longitudinal direction by 4.1 times by utilizing the difference in rotation speed between a low-speed rotating roll set at a surface temperature of 92° C. and a high-speed rotating roll set at a surface temperature of 92° C. Subsequently, the obtained film immediately after longitudinal stretching was passed through a heating furnace set at 110° C., and subjected to a 45% relaxation treatment in the longitudinal direction by utilizing the difference in speed between the rolls at the entrance and exit of the heating furnace.

[0075] The obtained longitudinally stretched film was then introduced into a transverse stretching machine (tenter), and while both ends of the film were held with clips, the film was preheated to a film temperature of 140°C. The film was then cooled to a surface temperature of 100°C, and then stretched 4.3 times in the width direction at a film temperature of 100°C. Next, a heat treatment was performed at 100°C, and in the subsequent zone, a 10% relaxation treatment was performed in the width direction at a film temperature of 90°C. Next, both edges of the film were cut and removed, and the biaxially stretched film of approximately 20 μm was wound into a roll. The properties of the obtained film were evaluated by the methods described above.

[0076] Example 2 A biaxially stretched film of about 20 μm was obtained by film production in the same manner as in Example 1, except that the relaxation treatment after transverse stretching was changed to 3%. The properties of the obtained film were evaluated by the methods described above.

[0077] Example 3: An unstretched film was obtained in the same manner as in Example 1. The unstretched film was introduced into a longitudinal stretching machine with multiple roll groups arranged in series and preheated using preheating rolls until the film temperature reached 92°C. The unstretched film was then stretched in the longitudinal direction by 1.2 times using the difference in rotation speed between a low-speed rotating roll set at a surface temperature of 92°C and a high-speed rotating roll set at a surface temperature of 92°C. The longitudinally stretched film was then introduced into a transverse stretching machine (tenter) and, with both ends of the film held by clips, preheated to a film temperature of 130°C. The film was then cooled to a surface temperature of 90°C and stretched 4.3 times in the width direction at a film temperature of 90°C. The film was then subjected to a heat treatment at 110°C and a 10% relaxation treatment in the width direction. The biaxially stretched film was then wound into a roll with a thickness of approximately 20 μm, with both edges of the film trimmed and removed. The properties of the resulting film were evaluated using the methods described above.

[0078] Example 4 After obtaining an unstretched film in the same manner as in Example 1, the obtained unstretched film was introduced into a transverse stretching machine (tenter), and while both ends of the film were held with clips, the film was preheated to a film temperature of 100°C, and then stretched 4.3 times in the width direction at a set temperature of 90°C. Next, a heat treatment was performed at 110°C, and in the subsequent zone, a 10% relaxation treatment was performed in the width direction at a film temperature of 90°C. Next, both edges of the film were cut and removed, and a biaxially stretched film of approximately 20 μm was wound into a roll. The properties of the obtained film were evaluated by the methods described above.

[0079] Example 5 Polystyrene A and polystyrene B were mixed in a mass ratio of 40:60 and melted at 230°C using an extruder. 780 ppm by mass of erucic acid amide and 350 ppm by mass of ethylene bisstearic acid amide were mixed as lubricants. An unstretched laminated film was obtained by taking up the film while cooling it on a chill roll set at a surface temperature of 30°C. The unstretched film obtained was introduced into a longitudinal stretching machine having a plurality of rolls arranged in series, preheated with a preheating roll until the film temperature reached 95°C, and then stretched 1.15 times in the longitudinal direction by utilizing the difference in rotation speed between a low-speed rotating roll set at a surface temperature of 95°C and a high-speed rotating roll set at a surface temperature of 95°C. The longitudinally stretched film obtained was then introduced into a transverse stretching machine (tenter), preheated to 110°C with both ends of the film held by clips, and then stretched 4.7 times in the width direction at a film temperature of 100°C. The film was then heat-treated at 120°C, and then in the subsequent zone, it was relaxed by 10% in the width direction at a film temperature of 100°C. The biaxially stretched film having a thickness of approximately 40 µm was then wound into a roll, with both edges of the film being trimmed and removed. The properties of the resulting film were evaluated by the methods described above.

[0080] Example 6 Polystyrene A and polystyrene B were mixed in a mass ratio of 50:50 and melted at 230°C using an extruder. 780 ppm by mass of erucamide and 350 ppm by mass of ethylenebisstearamide were mixed as lubricants. An unstretched laminated film was obtained by taking up the film while cooling it on a chill roll set at a surface temperature of 30°C. The unstretched film obtained was introduced into a transverse stretching machine (tenter), and while both ends of the film were held with clips, it was preheated to a film temperature of 95°C. It was then stretched 4.8 times in the width direction at a film temperature of 90°C. It was then heat-treated at 125°C, and in the subsequent zone, it was relaxed 7% in the width direction at a film temperature of 100°C. Both edges of the film were then trimmed and removed, and the uniaxially stretched film of approximately 40 μm was wound into a roll. The properties of the obtained film were evaluated using the methods described above.

[0081] Example 7: The raw materials for Layer A were a mixture of polyester A, polyester B, and polyester C in a mass ratio of 5:20:75, and the raw materials for Layer B were a mixture of polystyrene A and polystyrene B in a mass ratio of 40:60. The mixed raw materials for Layers A and B were melted in separate extruders, with the polyester at 270°C and the polystyrene at 230°C. The molten resins were joined in the middle of the flow path by a feed block, extruded from a T-die, and taken up while cooled on a chill roll set at a surface temperature of 30°C to obtain an unstretched laminated film. When laminating Layers A and B, a separately melted polyester elastomer was placed between each layer. The film was configured so that both surface layers were Layer A and the central layer was Layer B (a two-type, three-layer structure of A / B / A), and the extrusion rate was adjusted so that the thickness ratio of Layer A to Layer B was B / A / B = 15 / 70 / 15. The resulting unstretched film was introduced into a longitudinal stretching machine with multiple roll groups arranged in series, and preheated using a preheating roll until the film temperature reached 95°C. The film was then stretched 4.1 times in the longitudinal direction by utilizing the difference in rotation speed between a low-speed rotating roll set at a surface temperature of 95°C and a high-speed rotating roll set at a surface temperature of 95°C. The resulting film immediately after longitudinal stretching was passed through a heating furnace set at 96°C and subjected to a 40% longitudinal relaxation treatment by utilizing the difference in speed between the rolls at the inlet and outlet of the heating furnace. The resulting longitudinally stretched film was then introduced into a transverse stretching machine (tenter), and, with both ends of the film held by clips, preheated to a film temperature of 125°C. The film was then cooled to a surface temperature of 100°C, and stretched 4.2 times in the width direction at a film temperature of 98°C. The film was then heat-treated at 100°C, and in the subsequent zone, it was relaxed 5% in the width direction at a film temperature of 85°C. The biaxially stretched film was then wound into a roll with both edges cut off and removed, and the properties of the resulting film were evaluated by the methods described above.

[0082] Example 8: Polyester A, polyester E, and polyester F were mixed in a mass ratio of 5:65:30 to form the raw materials for Layer A, and polystyrene A and polystyrene B were mixed in a mass ratio of 50:50 to form the raw materials for Layer B. The mixed raw materials for Layer A and Layer B were melted in separate extruders, with the polyester at 270°C and the polystyrene at 230°C. The molten resins were joined in the middle of the flow path using a feed block, extruded from a T-die, and taken up while cooled on a chill roll set at a surface temperature of 30°C to obtain an unstretched laminated film. When laminating Layer A and Layer B, a separately melted polyester elastomer was placed between each layer. The film was configured so that both surface layers were Layer A and the central layer was Layer B (a two-type, three-layer structure of A / B / A), and the extrusion rate was adjusted so that the thickness ratio of Layer A to Layer B was B / A / B = 15 / 70 / 15.

[0083] The resulting unstretched film was introduced into a transverse stretching machine (tenter), and while both ends of the film were held with clips, the film was preheated to a temperature of 90°C, and then stretched 4.5 times in the width direction at a film temperature of 85°C. Next, a heat treatment was performed at 120°C, and in the subsequent zone, a 5% relaxation treatment was performed in the width direction at a film temperature of 100°C. Next, both edges of the film were cut and removed, and an approximately 30 μm uniaxially stretched film was wound into a roll. The properties of the resulting film were evaluated by the methods described above.

[0084] Comparative Example 1: The raw materials for Layer A were a mixture of polyester A, polyester B, and polyester C in a mass ratio of 5:20:75, melted at 270°C using an extruder, and taken up while cooled on a chill roll set at a surface temperature of 30°C to obtain an unstretched laminated film. The resulting unstretched film was introduced into a longitudinal stretching machine having a series of rolls arranged in a continuous manner, preheated with a preheating roll until the film temperature reached 78°C, and then stretched 3.64 times in the longitudinal direction by utilizing the difference in rotation speed between a low-speed rotating roll set at a surface temperature of 78°C and a high-speed rotating roll set at a surface temperature of 78°C. The resulting film immediately after longitudinal stretching was passed through a heating furnace set at 93°C and subjected to a 30% relaxation treatment in the longitudinal direction by utilizing the difference in speed between the rolls at the entrance and exit of the heating furnace. The obtained longitudinally stretched film was then introduced into a transverse stretching machine (tenter), and while both ends of the film were held with clips, the film was preheated to a film temperature of 150°C. The film was then cooled to a surface temperature of 100°C, and then stretched 4 times in the width direction at a film temperature of 95°C. The film was then heat-treated at 125°C at a fixed length without relaxation. Both edges of the film were then cut and removed, and a biaxially stretched film of approximately 20 μm was wound into a roll. The properties of the obtained film were evaluated by the methods described above.

[0085] Comparative Example 2: The raw materials for Layer A were a mixture of polyester A, polyester C, and polyester D in a mass ratio of 5:50:45, melted at 270°C using an extruder, and taken up while cooled on a chill roll set at a surface temperature of 30°C to obtain an unstretched laminated film. The resulting unstretched film was introduced into a longitudinal stretching machine having a series of rolls arranged in series, preheated with a preheating roll until the film temperature reached 73°C, and then stretched 3.8 times in the longitudinal direction by utilizing the difference in rotation speed between a low-speed rotating roll set at a surface temperature of 73°C and a high-speed rotating roll also set at a surface temperature of 73°C. The resulting film immediately after longitudinal stretching was passed through a heating furnace set at 95°C and subjected to a 40% relaxation treatment in the longitudinal direction by utilizing the difference in speed between the rolls at the entrance and exit of the heating furnace.

[0086] The obtained longitudinally stretched film was then introduced into a transverse stretching machine (tenter), and while both ends of the film were held with clips, the film was preheated to a film temperature of 140°C. The film was then cooled to a surface temperature of 100°C, and then stretched 4 times in the width direction at a film temperature of 95°C. The film was then heat-treated at 100°C at a fixed length without relaxation. Both edges of the film were then cut and removed, and the biaxially stretched film of approximately 20 μm was wound into a roll. The properties of the obtained film were evaluated by the methods described above.

[0087] Comparative Example 3 Polystyrene A and polystyrene B were mixed in a mass ratio of 40:60 and melted at 230°C using an extruder. 780 ppm by mass of erucic acid amide and 350 ppm by mass of ethylene bisstearic acid amide were mixed as lubricants. The film was taken up while cooled on a chill roll set at a surface temperature of 30°C to obtain an unstretched laminated film. The obtained unstretched film was introduced into a longitudinal stretching machine having a plurality of roll groups arranged in series, preheated with a preheating roll until the film temperature reached 90°C, and then stretched to 1.15 times in the longitudinal direction by utilizing the difference in rotation speed between a low-speed rotating roll set at a surface temperature of 78°C and a high-speed rotating roll set at a surface temperature of 90°C. Subsequently, the obtained longitudinally stretched film was introduced into a transverse stretching machine (tenter), and while both ends of the film were held with clips, the film was preheated until the film temperature reached 100°C, and then stretched 4.5 times in the width direction at a film temperature of 75°C. The film was then heat-treated at 90°C at a fixed length without relaxation, and the biaxially stretched film was wound into a roll with both edges cut off. The properties of the resulting film were evaluated by the methods described above.

[0088] Comparative Example 4 A film was produced in the same manner as in Example 7, except that the conditions shown in Table 1 were changed, and the properties of the obtained film were evaluated by the methods described above.

[0089]

[0090]

[0091] In Comparative Example 1, stretching was performed at a high temperature, and the subsequent relaxation treatment was omitted. As a result, the 70°C shrinkage rate and natural shrinkage rate in the main shrinkage direction were high, and the dimensional stability in the low temperature range was insufficient. In Comparative Example 2, polybutylene terephthalate (PBT) was included as the polyester raw material, and the relaxation treatment after stretching was omitted. As a result, the shrinkage rates at 80°C and 120°C in the main shrinkage direction were both low, and the heat shrinkability as a label was insufficient. In Comparative Example 3, a polystyrene-based resin was used, the transverse stretching temperature was a low 75°C, and the relaxation treatment was omitted. As a result, the shrinkability was insufficient, and the shrinkage rate at 120°C in particular tended to be low and the natural shrinkage rate also tended to be high. In Comparative Example 4, heat treatment (fixed length) was not performed, and the temperature during the relaxation treatment was high. As a result, the relaxation of the amorphous molecular chains was insufficient, and as a result, the shrinkage rate before aging was outside the specified range.

[0092] The heat-shrinkable film of the present invention can be widely used for label packaging, cap seals, integrated packaging, and the like.

Claims

1. A heat-shrinkable film made of polyester and / or polystyrene that satisfies the following (1) to (4): (1) When treated in 70°C hot water for 10 seconds, the shrinkage rate in the main shrinkage direction is 3% or less; (2) When treated in 80°C hot water for 10 seconds, the shrinkage rate in the main shrinkage direction is more than 10% and not more than 50%; (3) When treated in 120°C silicone oil for 10 seconds, the shrinkage rate in the main shrinkage direction is 50% or more and not more than 80%; (4) After aging for 168 hours in an atmosphere at a temperature of 55°C and a relative humidity of 40%, the natural shrinkage rate (dimensional change rate) in the main shrinkage direction of the film is 1% or less.

2. The heat-shrinkable film according to claim 1, characterized in that after aging for 168 hours in an atmosphere of 55°C and 40% relative humidity, a tensile test is conducted on 10 samples in the longitudinal direction of the film using a tensile tester with a chuck distance of 100 mm, and the number of initial breaks, which is the number of breaks that occur when the film is stretched by 5%, is 4 or less.

3. The heat-shrinkable film according to claim 1, characterized in that the glass transition onset temperature is 65°C or higher and 110°C or lower when the temperature is increased from room temperature at a rate of 10°C / min using temperature-modulated differential scanning calorimetry (MDSC).

4. A heat-shrinkable film according to claim 1, characterized in that when heated from room temperature at a rate of 10°C / min using temperature-modulated differential scanning calorimetry (MDSC), the reversible heat capacity difference ΔCp from 30°C to 70°C is 0.22 J / g·K or less, and the reversible heat capacity difference ΔCp from 30°C to 80°C is 0.25 or more and 0.4 or less.

5. The heat-shrinkable film made of the polyester according to claim 1, wherein 40 mol % or more of the total resin components constituting the polyethylene are ethylene terephthalate units, out of 100 mol %.

6. The heat-shrinkable film according to claim 5, wherein the heat-shrinkable polyester film is substantially free of butanediol, diethylene glycol, and ε-caprolactone.

7. The heat-shrinkable film according to claim 5, wherein the heat-shrinkable polyester film contains at least one monomer capable of becoming an amorphous component selected from the group consisting of neopentyl glycol, 1,4-cyclohexanedimethanol, and isophthalic acid.

8. The heat-shrinkable film made of polystyrene according to claim 1, wherein the polystyrene is a styrene-diene copolymer.

9. The heat-shrinkable film according to claim 8, wherein the polystyrene heat-shrinkable film has a styrene content of 50% by mass or more out of 100% by mass of the resin components constituting the film.

10. A heat-shrinkable annular label using the heat-shrinkable film according to any one of claims 1 to 9 as a base material, with the edges bonded to form a ring.

11. A package characterized by covering at least a part of the outer periphery of an object with the heat-shrinkable annular label according to claim 10 and then heat-shrinking it.

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