Polyester-based heat-shrinkable film

Abstract

The purpose of the present invention is to provide a polyester-based heat-shrinkable film which is suitable for heat-shrinkable label applications and which is less apt to become loose after having been applied as labels and does not become distorted when applied as labels. This polyester-based heat-shrinkable film has ethylene terephthalate units, and the polyester resin components include the following amorphous components: 8-20 mol% of 1,4-cyclohexanedimethanol-derived constituent unit included in 100 mol% of the diol components; and an adipic-acid-derived constituent unit and an isophthalic-acid-derived constituent unit included in 100 mol% of the dicarboxylic acid components in such amounts that the molar ratio of the content of each of the constituent units to the content in mol% of the 1,4-cyclohexanedimethanol-derived constituent unit is 0.1-0.5. The polyester-based heat-shrinkable film has a hot-water shrinkage and a shrinkage stress which satisfy given ranges.

Description

Polyester heat-shrinkable film

[0001] The present invention relates to a polyester heat-shrinkable film suitable for heat-shrinkable label applications, a label, and a package using the label.

[0002] In recent years, stretched films (so-called heat-shrinkable films) made of polyvinyl chloride resins, polystyrene resins, polyester resins, etc. have been widely used for label packaging, cap seals, and integrated packaging, etc., which serve to protect glass bottles or plastic bottles and display product information. Among these heat-shrinkable films, polyvinyl chloride films have problems such as low heat resistance, generating hydrogen chloride gas when incinerated, and being a source of dioxins. Polystyrene films, on the other hand, have poor solvent resistance, require the use of inks with special compositions for printing, and require incineration at high temperatures, resulting in the generation of large amounts of black smoke accompanied by an unpleasant odor when incinerated. For these reasons, polyester-based heat-shrinkable films, which have high heat resistance, are easily incinerated, and have excellent solvent resistance, have been widely used as shrink labels, and their usage has tended to increase with the increase in PET (polyethylene terephthalate resin) bottle containers and the like.

[0003] As the polyester resin used in such polyester-based heat-shrinkable films, a copolymer polyester resin in which a third component as an amorphous component is copolymerized with a polyester consisting of an ester polymer of terephthalic acid and ethylene glycol is widely used.

[0004] As an example of such copolymerized polyester resins, Patent Document 1 discloses a heat-shrinkable film using a polyester resin copolymerized with 1,4-cyclohexanedimethanol as an amorphous component.

[0005] To date, heat-shrinkable polyester films that shrink significantly in the width direction have been widely used. Heat-shrinkable polyester films whose main shrinkage direction is the width direction are stretched at a high ratio in the width direction to exhibit shrinkage properties in the width direction, thereby exhibiting a sufficient shrinkage rate when heated.

[0006] When a label using a heat-shrinkable film is attached to a PET bottle, the label is generally shrunk by passing the PET bottle covered with the label through a steam tunnel filled with heated steam. When heated, the PET bottle expands due to heat, and when the PET bottle subsequently shrinks upon cooling, the attached label tends to loosen. Therefore, a label with excellent shrinkage properties, including a high shrinkage stress and excellent followability, is desirable.

[0007] To improve the shrinkage stress, it is desirable to increase the stretch ratio when stretching the film. Furthermore, typically, when a film passes through a steam tunnel, its temperature gradually increases from low to high. As the temperature increases, the shrinkage rate of the film increases, allowing it to be applied as a label without slack or wrinkles. However, when the present inventors conducted research on a polyester copolymerized with 1,4-cyclohexanedimethanol as an amorphous component, they unexpectedly observed that when the stretch ratio was increased to increase the value of the shrinkage stress in the main shrinkage direction, the shrinkage rate at 70°C in the direction perpendicular to the main shrinkage direction (longitudinal direction) became higher than the shrinkage rate at 80°C. In other words, they discovered that when applied as a label, as the film temperature increased, portions of the film became less likely to shrink, contrary to normal, resulting in the problem of distortion at the edge of the applied PET bottle label.

[0008] Patent No. 3378253

[0009] The present invention aims to solve the problems of the conventional technology described above and to provide a polyester-based heat-shrinkable film that is suitable for use as a heat-shrinkable label, is less likely to slacken after application, and does not distort when applied.

[0010] As a result of extensive investigations, the present inventors have found that the above-mentioned problems can be solved by the means described below, and have arrived at the present invention. That is, the present invention has the following configuration: [1] A polyester-based heat-shrinkable film having ethylene terephthalate units, and containing, as amorphous components in the total polyester resin components, 8 to 20 mol % of constitutional units derived from 1,4-cyclohexanedimethanol per 100 mol % of the diol component, and containing, per 100 mol % of the dicarboxylic acid component, constitutional units derived from adipic acid and constitutional units derived from isophthalic acid, each in a molar ratio of 0.1 to 0.5 relative to the mol % content of the constitutional units derived from 1,4-cyclohexanedimethanol, and satisfying the following (1) to (3): (1) When the film is immersed in 90°C hot water for 10 seconds, the hot water heat shrinkage rate is 40% to 70% in the width direction, which is the main shrinkage direction of the film. (2) Regarding the hot water heat shrinkage rate in the longitudinal direction of the film, which is the non-shrinkage direction, the value Δ is calculated by subtracting the hot water heat shrinkage rate when the film is immersed in hot water at 70°C for 10 seconds from the hot water heat shrinkage rate when the film is immersed in hot water at 80°C for 10 seconds, as shown in the following formula 1: ８０－７０ is between -3% and 1%. ８０－７０ = 80°C hot water heat shrinkage rate - 70°C hot water heat shrinkage rate (Equation 1) (3) The maximum shrinkage stress in the main shrinkage direction of the film measured with hot air at 90°C is 6 MPa or more and 14 MPa or less.

[0011] [2] The polyester-based heat-shrinkable film according to [1], wherein the shrinkage stress in the main shrinkage direction measured in hot air at 90°C has a shrinkage stress ratio 30 seconds after the start of measurement, expressed by the following formula 2, of 75% or more and 100% or less: Shrinkage stress ratio = (shrinkage stress after 30 seconds / maximum shrinkage stress) x 100 (%) (Formula 2)

[0012] [3] The polyester-based heat-shrinkable film according to [1] or [2], wherein the ethylene terephthalate units account for 50 mol % or more of 100 mol % of polyester constituent units.

[0013] [4] The polyester-based heat-shrinkable film according to any one of [1] to [3], wherein the dicarboxylic acid component constituting the polyester resin is an aliphatic dicarboxylic acid and an aromatic dicarboxylic acid.

[0014] [5] The polyester-based heat-shrinkable film according to any one of [1] to [4], wherein the diol component constituting the polyester resin is substantially ethylene glycol and 1,4-cyclohexanedimethanol.

[0015] [6] The polyester-based heat-shrinkable film according to any one of [1] to [5], which does not contain any amorphous components other than the constitutional units derived from 1,4-cyclohexanedimethanol, the constitutional units derived from adipic acid, and the constitutional units derived from isophthalic acid.

[0016] [7] The polyester-based heat-shrinkable film according to any one of [1] to [6], wherein the dicarboxylic acid component constituting the polyester resin is substantially terephthalic acid, isophthalic acid, or adipic acid.

[0017] [8] A label having perforations or notches obtained from the polyester heat-shrinkable film according to any one of [1] to [7].

[0018] [9] A package formed by covering at least a part of the outer periphery of an object to be packaged with the label according to [8] and heat-shrinking it.

[0019] The polyester-based heat-shrinkable film of the present invention is produced by forming a film of polyester having a specific composition using a specific manufacturing method, thereby reducing the difference in shrinkage rate at 70°C relative to the shrinkage rate at 80°C in a direction perpendicular to the main shrinkage direction, and can be used as a heat-shrinkable label that does not generate distortion.

[0020] Furthermore, the polyester heat-shrinkable film of the present invention has a high shrinkage stress and is excellent in conformity with the packaged item, so that it is less likely to sag when attached as a label.

[0021] Furthermore, the polyester heat-shrinkable film of the present invention has extremely high adhesive strength when bonded to both sides (or to the same side) using a solvent, and can be suitably used for various coated labels, including labels for PET bottles, etc.

[0022] Furthermore, packages wrapped with labels obtained using the polyester heat-shrinkable film of the present invention have a beautiful appearance.

[0023] The polyester used in the polyester-based heat-shrinkable film of the present invention has a chemical structure obtained by polycondensation of a polycarboxylic acid component and a polyhydric alcohol component, and in particular, the polyester has ethylene terephthalate units. The ethylene terephthalate units may account for preferably 50 mol% or more, more preferably 60 mol% or more, and even more preferably 65 mol% or more of 100 mol% of the constituent units of the polyester. The remainder may be composed of other resin components, and preferably constituent units derived from 1,4-cyclohexanedimethanol, adipic acid, and isophthalic acid.

[0024] The polycarboxylic acid component and the polydiol component each comprise one or more selected components. The polycarboxylic acid component is preferably a dicarboxylic acid component, and the polydiol component is preferably a diol component.

[0025] The dicarboxylic acid component constituting the polyester resin is not particularly limited, but the following dicarboxylic acids or their esters and dicarboxylic acid anhydrides can be used. Specific examples of dicarboxylic acids include aliphatic dicarboxylic acids, alicyclic dicarboxylic acids, and aromatic dicarboxylic acids. Examples of aliphatic dicarboxylic acids include adipic acid, sebacic acid, dimer acid, fumaric acid, maleic acid, and succinic acid. Examples of alicyclic dicarboxylic acids include 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, tetrahydrophthalic acid, hexahydrophthalic acid, and methyltetrahydrophthalic acid. Examples of aromatic dicarboxylic acids include terephthalic acid, isophthalic acid, orthophthalic acid, naphthalenedicarboxylic acid, 2,5-furandicarboxylic acid, and 5-sodiumsulfodimethylisophthalic acid, as well as esters and acid anhydrides thereof. Adipic acid is preferred as the aliphatic dicarboxylic acid. As the aromatic dicarboxylic acid, terephthalic acid, isophthalic acid, orthophthalic acid, naphthalenedicarboxylic acid, and 2,5-furandicarboxylic acid are preferred, with terephthalic acid, isophthalic acid, and naphthalenedicarboxylic acid being more preferred, and terephthalic acid and isophthalic acid being even more preferred. In the present invention, the use of an aliphatic dicarboxylic acid and an aromatic dicarboxylic acid in combination is also a preferred embodiment. In one embodiment, the dicarboxylic acid component may essentially consist of an aliphatic dicarboxylic acid and an aromatic dicarboxylic acid, and preferably may not contain any dicarboxylic acid components other than the above-mentioned preferred examples.

[0026] The diol component constituting the polyester resin is not particularly limited, but examples thereof include aliphatic diols, alicyclic diols, aromatic diols, etc. Specific examples include aliphatic diols such as ethylene glycol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, hexanediol, and diethylene glycol, alicyclic diols such as 1,4-cyclohexanedimethanol, and aromatic diols such as bisphenol A.

[0027] A preferred embodiment of the polyester of the present invention is a polyester containing 1,4-cyclohexanedimethanol and one or more aliphatic diols having 2 to 4 carbon atoms (e.g., ethylene glycol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, diethylene glycol, etc.) constituting the main chain of the polyester molecular chain, and the glass transition point (Tg) is adjusted to 60 to 80° C. Ethylene glycol is preferred as the aliphatic diol having 2 to 4 carbon atoms.

[0028] In the present invention, 1,4-cyclohexanedimethanol is essential as the diol component that forms the amorphous component from the viewpoints of improving heat resistance and imparting sufficient shrinkage properties. Specifically, the content of 1,4-cyclohexanedimethanol units is 8 to 20 mol%, preferably 10 to 18 mol%, and more preferably 12 to 18 mol% per 100 mol% of the diol component. If the content of 1,4-cyclohexanedimethanol units exceeds 20 mol%, the difference in shrinkage rate in the longitudinal direction at 70°C and 80°C becomes large, making the heat-shrinkable film prone to distortion when attached as a label. On the other hand, if the content of 1,4-cyclohexanedimethanol units is less than 8 mol%, the shrinkage stress becomes too high or the required shrinkage rate for a heat-shrinkable film cannot be achieved. In one embodiment, the diol component of the polyester according to the present invention may be essentially ethylene glycol and 1,4-cyclohexanedimethanol. In the present invention, "substantially" means that diethylene glycol, which is produced as a side reaction during the polycondensation reaction of ethylene glycol in the synthesis of the polyester, may be present within a range that does not impair the effects of the present invention.

[0029] In the present invention, it is preferable that the diol component that can become an amorphous component is only 1,4-cyclohexanedimethanol. However, amorphous components other than 1,4-cyclohexanedimethanol may be contained within a range that does not impair the effects of the present invention. Examples of such components include neopentyl glycol, 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.

[0030] It is preferable that the polyester does not contain a diol having six or more carbon atoms (e.g., hexanediol, etc.) or a polyhydric alcohol having three or more valences (e.g., trimethylolpropane, trimethylolethane, glycerin, diglycerin, etc.). A polyester-based heat-shrinkable film obtained using a polyester containing these diols or polyhydric alcohols will have difficulty achieving the required high shrinkage rate. It is also preferable that the polyester does not contain triethylene glycol or polyethylene glycol as much as possible.

[0031] In order to reduce the difference in shrinkage between 80°C and 70°C in the longitudinal direction due to the 1,4-cyclohexanedimethanol unit, the inventors conducted the following study. Generally, when a film is stretched in a uniaxial direction, not only is stress exerted in the stretching direction, but also a compressive force acts in a direction perpendicular to the stretching direction. Copolymer polyester resins having 1,4-cyclohexanedimethanol units as an amorphous component have excellent heat resistance, but when a film using this resin is heated and stretched in the width direction, it is thought that the compressive force acting in the direction perpendicular to the stretching direction (i.e., the longitudinal direction) also increases. When the compressive force increases, the molecular chains are fixed in a compressed state during stretching. When a heat-shrinkable film produced in this way is heated, the molecular chains relax and shrink, and the compressed molecular chains are also released and move in the direction of expansion, inhibiting shrinkage. This is thought to be the reason for the reverse tendency, that is, the shrinkage at 80°C is smaller than the shrinkage at 70°C in the longitudinal direction. Therefore, the present inventors have focused on the dicarboxylic acid unit of polyester and investigated components that reduce compression of molecular chains in the direction perpendicular to the stretching direction, leading to the completion of the present invention.

[0032] That is, by adding adipic acid units and isophthalic acid units as dicarboxylic acid components that form amorphous components in a molar ratio of 0.1 to 0.5 relative to the content (mol %) of 1,4-cyclohexanedimethanol units used in the diol, the difference between the 80°C shrinkage rate and the 70°C shrinkage rate in the non-shrinkage direction was reduced, resulting in a heat-shrinkable film that does not generate distortion when attached and does not impair heat resistance when used as a label. It is believed that this is because the mixture of aliphatic dicarboxylic acid components with different relaxation times and aromatic dicarboxylic acid components, terephthalic acid and isophthalic acid, which have different molecular structures, inhibits the packing of molecular chains that occurs in the direction perpendicular to the stretching direction during stretching, thereby reducing compression.

[0033] The ratio of the adipic acid unit to the content (mol %) of the 1,4-cyclohexanedimethanol unit is 0.1 to 0.5, preferably 0.2 to 0.4. A ratio of the adipic acid unit exceeding 0.5 is undesirable because it reduces the heat resistance of the film and decreases the shrinkage stress, making it more likely to become loose during application. Furthermore, the ratio of the isophthalic acid unit to the content (mol %) of the 1,4-cyclohexanedimethanol unit is 0.1 to 0.5, preferably 0.3 to 0.4. A ratio of the isophthalic acid unit exceeding 0.5 is undesirable because it reduces the heat resistance of the film and deteriorates film-forming properties, making it more likely to have uneven thickness. Furthermore, a ratio of the adipic acid unit to the isophthalic acid unit less than 0.1 is undesirable because it insufficiently reduces the difference in shrinkage rate between 70°C and 80°C.

[0034] When an aliphatic dicarboxylic acid having 6 or more carbon atoms other than adipic acid (e.g., sebacic acid, decanedicarboxylic acid, etc.) is contained in the polyester, the content is preferably less than 2 mol % (based on 100 mol % of the dicarboxylic acid component). Polyester-based heat-shrinkable films obtained using polyesters containing 2 mol % or more of these aliphatic dicarboxylic acids have insufficient film stiffness when applied at high speed.

[0035] 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 polyester-based heat-shrinkable films obtained using polyesters containing these polycarboxylic acids have difficulty achieving the required high shrinkage ratio.

[0036] Furthermore, in the polyester, the total amount of 1,4-cyclohexanedimethanol, adipic acid, and isophthalic acid (hereinafter collectively referred to as "monomer components capable of becoming amorphous components"), which can be formed as amorphous components, is 10 mol% or more, preferably 13 mol% or more, more preferably 15 mol% or more, and particularly preferably 16 mol% or more, based on 100 mol% of the polyhydric alcohol components or 100 mol% of the polycarboxylic acid components in the total polyester resin. A content of less than 10 mol% of the monomer components capable of becoming amorphous components is undesirable because it may result in the required shrinkage rate not being achieved or the shrinkage stress becoming too large. The upper limit of the total amount of the monomer components capable of becoming amorphous components is not particularly limited, but a preferred upper limit is 35 mol% in terms of polymerization costs and film formability. Other monomer components capable of becoming amorphous components may be included within a range that does not impair the effects of the present invention, and the total amount is preferably 10 mol% or less, more preferably 8 mol% or less, even more preferably 5 mol% or less, and even more preferably substantially absent (0 mol%).

[0037] Various additives may be added to the resin forming the polyester-based heat-shrinkable film of the present invention, as needed, such as waxes, antioxidants, antistatic agents, crystal nucleating agents, viscosity reducers, heat stabilizers, coloring pigments, color inhibitors, ultraviolet absorbers, etc. The content of these additives is not particularly limited, and they may be added within a range that does not impair the effects of the invention, for example, to the extent that the additives exert their effects.

[0038] It is preferable to add fine particles as a lubricant to the resin forming the polyester heat-shrinkable film of the present invention, which improves the workability (slipperiness) of the film. Any fine particles can be selected, but examples of inorganic fine particles include silica, alumina, titanium dioxide, calcium carbonate, kaolin, barium sulfate, etc., and organic fine particles include acrylic resin particles, melamine resin particles, silicone resin particles, cross-linked polystyrene particles, etc. The average particle size of the fine particles can be appropriately selected as needed within the range of 0.05 to 3.0 μm (as measured with a Coulter counter).

[0039] The method of incorporating the particles into the resin that forms the polyester-based heat-shrinkable film can be, for example, adding them at any stage in the production of the polyester-based resin, but it is preferable to add them as a slurry dispersed in ethylene glycol or the like at the stage of esterification or after the completion of the transesterification reaction and before the start of the polycondensation reaction, and then proceed with the polycondensation reaction. Also preferred is a method of blending a slurry of particles dispersed in ethylene glycol or water or the like with the polyester-based resin raw material using a vented extruder, or a method of blending dried particles with the polyester-based resin raw material using a kneading extruder.

[0040] The polyester heat-shrinkable film of the present invention may be subjected to corona treatment, coating treatment, flame treatment, or the like in order to improve the adhesiveness of the film surface.

[0041] The polyester heat-shrinkable film of the present invention has the following properties. (1) 90°C hot water heat shrinkage rate The polyester heat-shrinkable film of the present invention is immersed in 90°C hot water for 10 seconds under no load, and then immediately immersed in water at 25°C ± 0.5°C for 10 seconds. The heat shrinkage rate in the width direction of the film (i.e., 90°C hot water heat shrinkage rate) calculated from the lengths before and after shrinkage using the following formula 1 is 40% or more and 70% or less: Heat shrinkage rate = {(length before shrinkage - length after shrinkage) / length before shrinkage} × 100 (%) (Formula 1)

[0042] If the hot water heat shrinkage rate in the width direction at 90°C is less than 40%, the shrinkage amount is small, and when used as a label, wrinkles and sagging will occur in the label after heat shrinkage. The hot water heat shrinkage rate at 90°C is preferably 43% or more, more preferably 45% or more. Conversely, if the hot water heat shrinkage rate in the width direction at 90°C exceeds 70%, the label will not shrink gradually, and distortion will occur in the label after shrinkage. The hot water heat shrinkage rate at 90°C is preferably 65% ​​or less, more preferably 60% or less. In the present invention, the width direction of the film is the main shrinkage direction, and the longitudinal direction of the film is the direction perpendicular to the main shrinkage direction (sometimes referred to as the non-shrinkage direction).

[0043] (2) Difference Between 80°C Longitudinal Hot Water Shrinkage and 70°C Longitudinal Hot Water Shrinkage The polyester heat-shrinkable film of the present invention preferably has a hot water heat shrinkage in the longitudinal direction of the film at 80°C of 0% or more and 7% or less, measured in the same manner as above. If the hot water heat shrinkage in the longitudinal direction at 80°C is less than 0% (i.e., the film expands upon heating), it is not preferable because a good shrinkage appearance cannot be obtained when used as a bottle label. Conversely, if the hot water heat shrinkage in the longitudinal direction at 80°C is more than 7%, it is not preferable because distortion due to sink marks is likely to occur in the label after heat shrinkage. The hot water heat shrinkage in the longitudinal direction at 80°C is more preferably 0.5% or more and 6% or less, and particularly preferably 1% or more and 5% or less.

[0044] The polyester heat-shrinkable film of the present invention has a value (Δ ８０－７０ ) is -3% or more and 1% or less. If the difference in the longitudinal hot water heat shrinkage rate at 80°C and 70°C is less than -3% (i.e., the shrinkage is greater at 70°C), when used as a bottle label, the label is likely to become distorted after heat shrinkage, which is not preferable. On the other hand, if the difference in the longitudinal hot water heat shrinkage rate at 80°C and 70°C is 1% or more, wrinkles are likely to occur at the edges due to shrinkage, which is not preferable. Δ ８０－７０ = 80°C hot water heat shrinkage rate (%) - 70°C hot water heat shrinkage rate (%) (Equation 2)

[0045] (3) Maximum shrinkage stress in width direction when exposed to 90°C hot air The polyester heat-shrinkable film of the present invention has a maximum shrinkage stress in the width direction of the film measured using 90°C hot air of 6 MPa or more and 14 MPa or less. Preferably, the shrinkage stress 30 seconds after the start of measurement, as shown below, is 75% or more and 100% or less of the maximum shrinkage stress. The shrinkage stress is measured by the method described in the examples.

[0046] If the maximum shrinkage stress at 90°C in the film width direction is less than 6 MPa, the label may slacken and not adhere to the bottle when used as a bottle label, which is undesirable. The maximum shrinkage stress at 90°C is more preferably 7 MPa or more, and even more preferably 8 MPa or more. Conversely, if the maximum shrinkage stress at 90°C exceeds 14 MPa, the film may deform due to the shrinkage stress, which is undesirable as it tends to cause distortion in the label after heat shrinkage. The maximum shrinkage stress at 90°C is more preferably 13.5 MPa or less, and even more preferably 13 MPa or less.

[0047] (4) Shrinkage Stress Ratio The shrinkage stress 30 seconds after the start of measurement in 90°C hot air, as shown in the following formula 3, is preferably 75% to 100% of the maximum shrinkage stress. That is, the polyester heat-shrinkable film of the present invention exhibits unique heat shrinkage characteristics, exhibiting a shrinkage stress similar to the maximum heat shrinkage stress even 30 seconds after the start of heat shrinkage. If the shrinkage stress after 30 seconds / maximum shrinkage stress (hereinafter referred to as the stress ratio) is less than 75%, the label's ability to follow the bottle's expansion due to heating when the label is placed on the bottle and heat-shrunk is poor. Furthermore, when the bottle temperature drops after shrinkage and thermal expansion ceases, the label becomes loose, which is undesirable. The stress ratio is more preferably 80% or more, and even more preferably 85% or more. A larger stress ratio is preferable because it improves followability, but the upper limit is 100% because the shrinkage stress after 30 seconds cannot exceed the maximum shrinkage stress. Shrinkage stress ratio = (shrinkage stress after 30 seconds / maximum shrinkage stress) x 100 (%) (Equation 3)

[0048] The polyester heat-shrinkable film of the present invention has a thickness of 10 μm or more and 70 μm or less, but is not particularly limited thereto. The haze value of the polyester heat-shrinkable film is preferably 2% or more and 13% or less. A haze value of more than 13% is undesirable because it may result in poor transparency and poor appearance when producing labels. The haze value is more preferably 11% or less, and particularly preferably 9% or less. The smaller the haze value, the better. However, considering that a certain amount of lubricant must be added to the film to impart the necessary slipperiness for practical use, the lower limit is about 2%.

[0049] The refractive index (Ny) in the width direction of the polyester-based heat-shrinkable film of the present invention is preferably 1.615 or more and 1.670 or less. Ny indicates the molecular orientation in the stretching direction (width direction). By setting the refractive index in the width direction of the film within this range, sufficient shrinkage stress can be obtained. Furthermore, if Ny exceeds 1.670, oriented crystallization occurs, reducing the shrinkage rate, or the shrinkage stress becomes too high, causing wrinkles and distortion during shrinkage finish, which is not preferable. Ny is more preferably 1.620 or more and 1.665 or less, and particularly preferably 1.625 or more and 1.660 or less.

[0050] The polyester heat-shrinkable film of the present invention can be obtained by melt-extruding the above-mentioned polyester raw material using an extruder to form an unstretched film, and then uniaxially stretching and heat-treating the unstretched film by the predetermined method described below. The polyester can be obtained by polycondensing the above-mentioned suitable dicarboxylic acid component and diol component using a known method. Usually, two or more types of chip-like polyester are mixed and used as the raw material for the film.

[0051] When melt-extruding the raw material resin, it is preferable to dry the polyester raw material using a dryer such as a hopper dryer or a paddle dryer, or a vacuum dryer. After drying the polyester raw material in this way, it is melted at a temperature of 200 to 300°C using an extruder and extruded into a film. For extrusion, any known method such as a T-die method or a tubular method can be used.

[0052] The extruded sheet-like molten resin can then be rapidly cooled to obtain an unstretched film. A suitable method for rapidly cooling 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.

[0053] The unstretched film thus obtained is then stretched in the width direction under predetermined conditions as described below, and then heat-treated again to obtain the polyester-based heat-shrinkable film of the present invention. A preferred film-forming method for obtaining the polyester-based heat-shrinkable film of the present invention will now be described in detail.

[0054] [Method for Producing a Polyester-Based Heat-Shrinkable Film of the Present Invention] In producing a film by the transverse stretching method of the present invention, transverse stretching is performed in a tenter with both ends in the width direction held by clips at a temperature of Tg + 5°C or higher and Tg + 35°C or lower, at a stretching ratio of 4.2 to 6 times. By performing transverse stretching under such predetermined conditions, a film can be obtained that maintains a sufficient shrinkage ratio even after the heat treatment described below. The transverse stretching temperature is more preferably Tg + 12°C or higher, even more preferably Tg + 14°C or higher, more preferably Tg + 30°C or lower, and even more preferably Tg + 28°C or lower. On the other hand, the transverse stretching ratio is more preferably 4.4 times or higher, even more preferably 4.6 times or higher, more preferably 5.5 times or lower, and even more preferably 5 times or lower. A stretching ratio below 4.2 times is undesirable because it is difficult to obtain sufficient shrinkage stress. Furthermore, a stretching ratio exceeding 6.0 times requires large-scale equipment, increases equipment costs, and is prone to breakage during film production, so the upper limit is set at 6.0 times.

[0055] When stretching in the transverse direction, if the stretching temperature exceeds Tg + 35° C., the shrinkage rate in the width direction tends to decrease, but it is preferable to control the stretching temperature to Tg + 35° C. or lower, as this makes it easier to maintain a high shrinkage rate in the width direction. Furthermore, if the stretching temperature exceeds Tg + 35° C., thickness unevenness in the width direction tends to increase, but by controlling the stretching temperature to Tg + 35° C. or lower, thickness unevenness in the width direction can be reduced.

[0056] On the other hand, if the stretching temperature is lower than Tg+5°C, the orientation in the width direction becomes too large, making the film more likely to break during transverse stretching. However, by controlling the stretching temperature to Tg+5°C or higher, it is possible to reduce the risk of the film breaking during transverse stretching.

[0057] The film after transverse stretching must be finally heat-treated in a tenter with both ends in the width direction held with clips at a temperature of Tg + 10°C or higher and Tg + 40°C or lower for 1 second or longer and 10 seconds or shorter. If the heat treatment temperature is higher than Tg + 40°C, the shrinkage in the width direction decreases, and the heat shrinkage at 90°C becomes less than 40%, which is undesirable. If the heat treatment temperature is lower than Tg + 10°C, stress relaxation is not sufficient, and the resulting heat-shrinkable film will experience excessively large stress during shrinkage or a large stress ratio, which is undesirable. Furthermore, while a longer heat treatment time is preferable, if it is too long, the equipment will become large, so it is preferable to keep it to 9 seconds or shorter.

[0058] In the final heat treatment step, relaxation may be performed in the width direction within the tenter by reducing the widthwise distance within the tenter for a time of 0.1 to 9 seconds within a range of 1% to 15%, preferably 2% to 13%. The maximum stress during thermal shrinkage can be reduced by stress relaxation through relaxation, thereby reducing the stress ratio during shrinkage. Since a relaxation rate of 1% or less provides almost no stress relaxation effect, a relaxation rate of 1% or more is preferable. A relaxation rate of more than 15% is not preferable because it increases the load on the rail bending portion of the tenter equipment and significantly reduces the shrinkage rate in the main shrinkage direction.

[0059] The packaging of the present invention is formed by covering at least a portion of the outer periphery of an object to be packaged with a label having perforations or notches obtained from the polyester heat-shrinkable film of the present invention and then heat-shrinking the label. Examples of packaging objects include PET beverage bottles, various bottles, cans, plastic containers for confectionery and lunch boxes, and paper boxes. Typically, when a label made from a polyester heat-shrinkable film is heat-shrunk to cover such an object, the label is heat-shrunk by approximately 5 to 30% to be tightly attached to the packaging object. The label to be covered on the object to be packaged may or may not be printed.

[0060] 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, one side of a rolled film can be coated 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 can then be cut into labels. Preferred organic solvents for adhesive use are cyclic ethers such as 1,3-dioxolane or tetrahydrofuran. Other examples 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.

[0061] This application claims the benefit of priority based on Japanese Patent Application No. 2024-048182, filed on March 25, 2024. The entire contents of the specification of Japanese Patent Application No. 2024-048182, filed on March 25, 2024, are incorporated herein by reference.

[0062] Next, the present invention will be specifically explained using examples and comparative examples, but the present invention is not limited to the embodiments of these examples and can be appropriately modified within the scope of the present invention. In the following, for a film wound into a roll during film production, the winding direction is described as the longitudinal direction and the roll lateral direction is described as the width direction, and the film evaluation method is shown.

[0063] [Heat Shrinkage (Hot Water Heat Shrinkage)] The film was cut into a 10 cm x 10 cm square parallel to the unwinding direction of the roll, and immersed in hot water at a predetermined temperature ±0.5°C for 10 seconds under no load to cause heat shrinkage. 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 (1): Heat shrinkage ratio = {(length before shrinkage - length after shrinkage) / length before shrinkage} × 100 (%) (Formula 1)

[0064] [Difference in Shrinkage Rate] The hot water shrinkage rate in the longitudinal direction was measured at temperatures of 80°C and 70°C in the same manner as in the method for determining the heat shrinkage rate. The obtained shrinkage rates were used to obtain a value (Δ ８０－７０ ) was calculated. ８０－７０ = Heat shrinkage rate in the longitudinal direction at 80°C (%) - Heat shrinkage rate in the longitudinal direction at 70°C (%) (Equation 2)

[0065] [Shrinkage Stress] A sample measuring 200 mm in length and 20 mm in width was cut out from the heat-shrinkable film and measured using a tensile tester with a heating furnace (Tensilon (registered trademark of Orientec) manufactured by Toyo Baldwin Co., Ltd. (now Orientec). The heating furnace was preheated to 90°C, and the distance between chucks was 100 mm. The airflow from the heating furnace was stopped, the door of the heating furnace was opened, and the sample was attached to the chuck. The door of the heating furnace was then quickly closed and airflow was resumed. The shrinkage stress was measured for 30 seconds or more, and the shrinkage stress (MPa) after 30 seconds was determined. The maximum value during the measurement was defined as the maximum shrinkage stress (MPa). Furthermore, the ratio (percentage) of the shrinkage stress after 30 seconds to the maximum shrinkage stress was defined as the stress ratio (%) according to the following formula 3: Shrinkage stress ratio = (shrinkage stress after 30 seconds / maximum shrinkage stress) × 100 (%) (Formula 3)

[0066] [Haze] The haze of each unshrunk heat-shrinkable film was measured in accordance with JIS K 7136 using a haze meter "500A" (manufactured by Nippon Denshoku Industries Co., Ltd.) The measurement was carried out twice, and the average value was taken as the haze.

[0067] [Refractive Index] Using an Abbe Refractometer Model 4T manufactured by Atago Co., Ltd., the sample films before shrinkage were left to stand in an atmosphere of 23±2°C and 65±5% RH for 2 hours or more, and then the refractive index (Ny) in the width direction was measured.

[0068] [Shrinkage Distortion of Label] Cylindrical labels (labels with the width direction of the heat-shrinkable film as the circumferential direction) were prepared by adhering both ends of a heat-shrinkable film with dioxolane. The labels were placed on 500 ml PET bottles (body diameter 65 mm, minimum neck diameter 25 mm) and passed through a steam tunnel (model: SH-1500-L) manufactured by Fuji Astec Inc. at a zone temperature of 90°C for 2.5 seconds to heat-shrink the labels and attach them to the bottles. During attachment, the length of the neck was adjusted so that the 50 mm diameter portion was at one end of the label. To evaluate the finish after shrinkage, the distortion of the top of the attached label in a 360-degree direction was measured using a gauge, and the maximum distortion was determined. Distortion was evaluated according to the following criteria: ⊚: Maximum distortion less than 1.0 mm; ◯: Maximum distortion 1.0 mm or more but less than 2.0 mm; ×: Maximum distortion 2.0 mm or more.

[0069] [Label Adhesion] Labels were attached to PET bottles under the same conditions as those for the label shrinkage distortion described above. Label adhesion was evaluated according to the following criteria: ⊚: There was no slack between the attached label and the PET bottle, and the label did not move when the bottle cap was fixed and the label was twisted. ◯: The label did not move when the bottle cap was fixed and the label was twisted, but there was some slack between the label and the PET bottle. ×: The label shifted when the bottle cap was fixed and the label was twisted.

[0070] [Wrinkles on Label] Labels were attached to PET bottles under the same conditions as those for the shrinkage distortion of the labels described above, and the occurrence of wrinkles was evaluated according to the following criteria: ⊚: Zero (0) wrinkles of 2 mm or larger in size; ○: 1 to 2 wrinkles of 2 mm or larger in size; ×: 3 or more wrinkles of 2 mm or larger in size.

[0071] <Preparation of polyester raw material> A stainless steel autoclave equipped with a stirrer, thermometer, and partial reflux condenser was charged with 100 mol% dimethyl terephthalate (DMT) as a dibasic acid component and 100 mol% ethylene glycol (EG) as a glycol component, with the ethylene glycol being 2.2 times the molar ratio of dimethyl terephthalate. Using 0.05 mol% (relative to the acid component) of zinc acetate as an ester exchange catalyst, an ester exchange reaction was carried out while distilling off the resulting methanol. Subsequently, 0.025 mol% (relative to the acid component) of antimony trioxide was added as a polycondensation catalyst, and a polycondensation reaction was carried out at 280°C under reduced pressure of 26.6 Pa (0.2 Torr), yielding a polyester (A) with an intrinsic viscosity of 0.63 dl / g. This polyester was polyethylene terephthalate. Next, the same monomers and various catalysts as those used in the polyester (A) were charged, and SiO was used as a lubricant during production. ２ Polyester (E) was obtained by adding 7,000 ppm of PEG-14 (Sylysia 266 manufactured by Fuji Silysia Ltd.). Polyesters (B, C, D) shown in Table 1 were synthesized in the same manner as for polyester (A). In the table, TPA stands for terephthalic acid, IPA stands for isophthalic acid, AA stands for adipic acid, EG stands for ethylene glycol, CHDM stands for 1,4-cyclohexanedimethanol, and DEG stands for diethylene glycol. The intrinsic viscosities of polyesters B, C, D, and E were 0.70 dl / g, 0.68 dl / g, 0.66 dl / g, and 0.63 dl / g, respectively. Each polyester was appropriately formed into chips.

[0072] The compositions of the polyester raw materials used in the Examples and Comparative Examples, and the resin compositions and production conditions of the films in the Examples and Comparative Examples are shown in Tables 1 and 2, respectively.

[0073]

[0074]

[0075]

[0076] Example 1 The above-described polyester A, polyester B, polyester C, polyester D, and polyester E were mixed in a mass ratio of 15:50:15:15:5 and charged into an extruder. This mixed resin was melted at 275°C, extruded through a T-die, and quenched by being wound around a rotating metal roll cooled to a surface temperature of 30°C, to obtain an unstretched film having a thickness of 137 μm. The take-up speed of the unstretched film (rotational speed of the metal roll) was approximately 20 m / min. The Tg of the unstretched film was 68°C.

[0077] The unstretched film introduced into the tenter was preheated to 90°C, then heated to 85°C, and stretched 4.7 times in the width direction (transverse direction).

[0078] The transversely stretched film was introduced into a heat treatment zone, where it was heat treated at 90°C for 5 seconds. At the same time, it was relaxed by 3% in the width direction. It was then cooled, both edges were cut and removed, and the film was wound into a roll with a width of 500 mm, thereby continuously producing a biaxially stretched film with a thickness of 30 μm over a predetermined length. The properties of the resulting film were evaluated using the methods described above. The evaluation results are shown in Table 3. The film had good shrinkage finish.

[0079] Example 2 A film having a thickness of 30 μm was produced in the same manner as in Example 1, except that the mass ratio of Polyester A, Polyester B, Polyester C, and Polyester D was changed to 0:50:30:15. The evaluation results are shown in Table 3. The film had good shrink finish.

[0080] Example 3 A film having a thickness of 30 μm was produced in the same manner as in Example 1, except that the mass ratio of Polyester A, Polyester B, Polyester C, and Polyester D was changed to 35:50:5:5. The evaluation results are shown in Table 3. The film had good shrink finish.

[0081] Example 4 A film having a thickness of 30 μm was produced in the same manner as in Example 1, except that the mass ratio of Polyester A, Polyester B, Polyester C, and Polyester D was changed to 0:65:10:20. The evaluation results are shown in Table 3. The film had good shrink finish.

[0082] Example 5 A film having a thickness of 30 μm was produced in the same manner as in Example 1, except that the mass ratio of Polyester A, Polyester B, Polyester C, and Polyester D was changed to 0:65:28:2. The evaluation results are shown in Table 3. The film had good shrink finish.

[0083] Example 6 A film having a thickness of 30 μm was produced in the same manner as in Example 1, except that the mass ratio of Polyester A, Polyester B, Polyester C, and Polyester D was changed to 15:65:8:7. The evaluation results are shown in Table 3. The film had good shrink finish.

[0084] Example 7 A film having a thickness of 30 μm was produced in the same manner as in Example 1, except that the mass ratio of Polyester A, Polyester B, Polyester C, and Polyester D was changed to 40:35:10:10. The evaluation results are shown in Table 3. The film had good shrink finish.

[0085] Example 8 A film having a thickness of 30 μm was produced in the same manner as in Example 1, except that the mass ratio of Polyester A, Polyester B, Polyester C, and Polyester D was changed to 50:35:5:5. The evaluation results are shown in Table 3. The film had good shrink finish.

[0086] Example 9 A film having a thickness of 30 μm was produced in the same manner as in Example 1, except that the mass ratio of Polyester A, Polyester B, Polyester C, and Polyester D was changed to 35:35:15:10. The evaluation results are shown in Table 3. The film had good shrink finish.

[0087] Comparative Example 1 A film having a thickness of 30 μm was produced in the same manner as in Example 1, except that the mass ratio of Polyester A, Polyester B, Polyester C, and Polyester D was changed to 45:50:0:0. The evaluation results are shown in Table 3. There was a large difference in shrinkage between 80°C and 70°C, and distortion of the film was observed at the neck of the PET bottle when finished.

[0088] Comparative Example 2 A film having a thickness of 30 μm was produced in the same manner as in Example 1, except that the mass ratio of Polyester A, Polyester B, Polyester C, and Polyester D was changed to 0:75:10:10. The evaluation results are shown in Table 3. As in Comparative Example 1, there was a large difference in shrinkage between 80°C and 70°C, and distortion of the film was observed at the neck of the PET bottle when finished.

[0089] Comparative Example 3 A 30 μm thick film was produced in the same manner as in Example 1, except that the mass ratio of Polyester A, Polyester B, Polyester C, and Polyester D was changed to 65:20:5:5. The evaluation results are shown in Table 3. Because the shrinkage stress was too large, the film deformed during shrinkage, and the distortion caused the label to be attached at an angle, resulting in poor appearance.

[0090] Comparative Example 4 A 30 μm thick film was produced in the same manner as in Example 1, except that the raw materials were changed to a mass ratio of Polyester A, Polyester B, Polyester C, and Polyester D of 0:40:40:15. The label did not adhere well after attachment, and when the bottle was fixed and the label was twisted, it rotated and became misaligned.

[0091] Comparative Example 5 A film having a thickness of 30 μm was produced in the same manner as in Example 1, except that the heat treatment temperature in the final heat treatment step was changed to 110° C. The evaluation results are shown in Table 3. The shrinkage rate was insufficient, and wrinkles and slack were observed in the finished label.

[0092]

[0093]

[0094] The polyester heat-shrinkable film of the present invention has the above-mentioned excellent properties and can therefore be suitably used for labeling bottles, etc. Packages such as bottles obtained by using the polyester heat-shrinkable film of the present invention as a label have beautiful appearances.

Claims

1. A polyester-based heat-shrinkable film having ethylene terephthalate units, and containing, as amorphous components in the total polyester resin components, 8 to 20 mol % of constituent units derived from 1,4-cyclohexanedimethanol per 100 mol % of diol components, and containing, per 100 mol % of dicarboxylic acid components, constituent units derived from adipic acid and constituent units derived from isophthalic acid, each in a molar ratio of 0.1 to 0.5 relative to the mol % content of the constituent units derived from 1,4-cyclohexanedimethanol, and satisfying the following (1) to (3): (1) When the film is immersed in 90°C hot water for 10 seconds, the hot water heat shrinkage rate is 40% to 70% in the width direction, which is the main shrinkage direction of the film. (2) Regarding the hot water heat shrinkage rate in the longitudinal direction of the film, which is the non-shrinkage direction, the value Δ is calculated by subtracting the hot water heat shrinkage rate when the film is immersed in hot water at 70°C for 10 seconds from the hot water heat shrinkage rate when the film is immersed in hot water at 80°C for 10 seconds, as shown in the following formula 1: ８０－７０ is between -3% and 1%. ８０－７０ = 80°C hot water heat shrinkage rate - 70°C hot water heat shrinkage rate (Equation 1) (3) The maximum shrinkage stress in the main shrinkage direction of the film measured with hot air at 90°C is 6 MPa or more and 14 MPa or less.

2. The polyester heat-shrinkable film according to claim 1, wherein the shrinkage stress ratio measured in the main shrinkage direction in hot air at 90°C after 30 seconds from the start of measurement, expressed by the following formula 2, is 75% or more and 100% or less: Shrinkage stress ratio = (shrinkage stress after 30 seconds / maximum shrinkage stress) x 100 (%) (Formula 2) 3. The polyester-based heat-shrinkable film according to claim 1, wherein the ethylene terephthalate units account for 50 mol % or more of 100 mol % of the polyester constituent units.

4. The polyester-based heat-shrinkable film according to claim 1, wherein the dicarboxylic acid components constituting the polyester resin are an aliphatic dicarboxylic acid and an aromatic dicarboxylic acid.

5. The polyester-based heat-shrinkable film according to claim 1, wherein the diol component constituting the polyester resin is essentially ethylene glycol and 1,4-cyclohexanedimethanol.

6. The polyester-based heat-shrinkable film according to claim 1, which does not contain any amorphous components other than the constituent units derived from 1,4-cyclohexanedimethanol, the constituent units derived from adipic acid, and the constituent units derived from isophthalic acid.

7. The polyester-based heat-shrinkable film according to claim 1, wherein the dicarboxylic acid component constituting the polyester resin is substantially terephthalic acid, isophthalic acid, and adipic acid.

8. A label having perforations or notches obtained from the polyester heat-shrinkable film according to any one of claims 1 to 7.

9. A package formed by covering at least a portion of the outer periphery of an object to be packaged with the label according to claim 8 and then heat-shrinking it.

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