Heat-shrinkable polyester film, heat-shrinkable label, and package

Abstract

Provided is a heat-shrinkable polyester film that not only has a high heat shrinkage in the main shrinkage direction, but also has a good heat shrinkability of recycled PET resin even when recycled together with used beverage PET bottles. A heat-shrinkable polyester film containing, in 100 mol% of a dicarboxylic acid component, 95 mol% or more and 100 mol% or less of a dicarboxylic acid, 0 mol% or more and 5 mol% of isophthalic acid, and containing, in 100 mol% of all ester units, 85 mol% or more and 98 mol% or less of terephthalic acid ethylene glycol ester units, and containing, in 100 mol% of a polyol component, 2 mol% or more and 15 mol% or less of diethylene glycol, has a prescribed hot water heat shrinkage, and has a melting peak temperature, a crystallization exotherm, and a melting exotherm determined by melting the film after melting and quenching using a differential scanning calorimeter (DSC), and then re-warming, within prescribed ranges.

Description

Technical Field

[0001] This invention relates to heat-shrinkable polyester films, and more specifically, to heat-shrinkable polyester films, heat-shrinkable labels, and packaging bodies that can be recycled without problems even when mixed with PET bottles in the recycling process of PET bottles. Background Technology

[0002] In recent years, stretch films (so-called heat-shrinkable films) made of polyvinyl chloride (PVC), polystyrene (PS), and polyester resins have been widely used in labeling, sealing, and assembly packaging of glass bottles and PET bottles, serving both protective and labeling purposes. Among these heat-shrinkable films, PVC-based films suffer from low heat resistance and the potential to produce hydrogen chloride gas and dioxins when burned. Furthermore, PPS films have poor solvent resistance, require specially formulated inks for printing, and need to be burned at high temperatures, resulting in unpleasant odors and large amounts of black smoke. Therefore, polyester-based heat-shrinkable films, with their high heat resistance, ease of burning, and excellent solvent resistance, are widely used for shrink labels, and their usage is trending towards increasing use as the volume of PET containers increases.

[0003] Commonly used heat-shrinkable polyester films are those that shrink significantly in the width direction. This film is stretched using a tenter frame or similar method to create a wide master roll. This master roll is then cut to any width and simultaneously wound into rolls of any length to form the film roll product. To allow for design and product labeling, the film is submitted to the printing process in roll form. After printing, it is again cut to the necessary width, wound into rolls, and then sealed using solvent bonding at the center to form a tubular bag, which is then wound into a roll (forming the label roll).

[0004] The tubular bag is made by rolling up the label, which is then cut to the necessary length as it is unrolled, forming a ring label. The ring label is then attached to the packaged item by hand covering or other methods, and shrinks and solidifies into a label by passing through a steam or hot air passage.

[0005] In recent years, environmental concerns have increased. For example, PET bottle containers are being recycled, recycled as PET resin, and used in various plastic products. Due to these increased environmental concerns, the use of recycled PET resin has increased, and the recycling rate of PET bottles has also increased.

[0006] For PET bottles used in beverages, the empty PET bottle containers are recycled to form recycled PET resin. However, the labels that are designed for beverage PET bottles are usually not recycled.

[0007] For PET, the raw material used in PET bottles, the polystyrene-based heat-shrinkable film label described in Patent Document 1 is incompatible with PET. Therefore, if polystyrene-based heat-shrinkable film is mixed in during the process of producing recycled PET resin, the transparentness of the recycled PET resin will be lost, which is not preferable.

[0008] The laminated film of polyester and polystyrene described in Patent Document 2 also mixes PET and incompatible polystyrene, and is therefore not preferred.

[0009] Patent document 3 is an invention of a polyester-based heat-shrinkable film, but since it mixes cyclic olefins and the like to contain voids, it mixes PET and incompatible olefin-based raw materials in the same way as above, which is not preferred.

[0010] Patent document 4 describes an invention of a transparent polyester heat-shrinkable film that does not contain materials incompatible with PET, thus preserving transparency during the production of recycled PET resin. However, polyester heat-shrinkable films are typically produced using amorphous PET raw materials with added amorphous monomers to exhibit heat-shrinkable properties. The raw materials used in PET bottles are homopolymer PET, which is crystalline. Therefore, if amorphous polyester heat-shrinkable films are mixed in during the production of recycled PET resin, the resulting recycled PET resin is difficult to reuse as homopolymer PET raw material and cannot be used again to manufacture PET bottles. Furthermore, due to the difference in density between crystalline and amorphous materials, the amorphous material is not uniformly extruded during the process of mixing the two materials to produce recycled resin. This can easily lead to problems such as pulses and fiber breakage at the die after melt extrusion, making it undesirable.

[0011] Existing technical documents

[0012] Patent documents

[0013] Patent Document 1: Japanese Patent No. 5286763

[0014] Patent Document 2: International Publication No. WO2020 / 021948

[0015] Patent Document 3: Japanese Patent No. 5625912

[0016] Patent Document 4: Japanese Patent No. 5633808 Summary of the Invention

[0017] The problem the invention aims to solve

[0018] The object of the present invention is to provide a heat-shrinkable polyester film that not only has a high heat shrinkage rate in the main shrinkage direction, but also yields good heat shrinkage of recycled PET resin even when recycled together with used beverage PET bottles.

[0019] Solution for solving the problem

[0020] The present invention, which solves the above problems, has the following technical features.

[0021] 1. A heat-shrinkable polyester film, characterized in that it contains 95 mol% and 100 mol% of dicarboxylic acid and 0 mol% and 5 mol% of isophthalic acid in 100 mol% of dicarboxylic acid components, and contains 85 mol% and 98 mol% of ethylene terephthalate units in 100 mol% of all ester units, and contains 2 mol% and 15 mol% of diethylene glycol in 100 mol% of polyol components, wherein the heat-shrinkable polyester film satisfies the following conditions (1) to (5).

[0022] (1) The hot water thermal shrinkage rate when the film is immersed in hot water at 90°C for 10 seconds is more than 40% and less than 70% in the width direction of the film.

[0023] (2) The hot water thermal shrinkage rate when the film is immersed in hot water at 90°C for 10 seconds is greater than -5% and less than 15% in the length direction of the film.

[0024] (3) Using a differential scanning calorimeter (DSC), the film was heated to 300°C to melt it, then rapidly cooled, and then heated to 300°C again. The resulting endothermic peak temperature based on melting was above 245°C and below 260°C.

[0025] (4) The heat of crystallization based on the film was obtained by heating the film to 300°C to melt it, then rapidly cooling it, and then heating it to 300°C again using a differential scanning calorimeter (DSC). The heat of crystallization was above 10 mJ / mg.

[0026] (5) The heat of melting based on the film was obtained by heating it to 300°C using a differential scanning calorimeter (DSC), then rapidly cooling it, and then heating it back to 300°C. The heat of melting was above 10 mJ / mg.

[0027] 2. The heat-shrinkable polyester film according to 1, characterized in that the density of the film is 1.33 g / cm³. 3 Above and 1.39 g / cm 3 the following.

[0028] 3. The heat-shrinkable polyester film according to 1 or 2, characterized in that the haze at a film thickness of 20 μm is 2% or more and 10% or less.

[0029] 4. A heat-shrinkable label that uses the heat-shrinkable polyester film described in any one of 1. to 3. above.

[0030] 5. A packaging body, characterized in that it is formed by covering at least a portion of the outer periphery of the packaged object with the heat-shrinkable label described in 4. above and causing it to heat-shrink.

[0031] 6. The heat-shrinkable polyester film according to any one of 1 to 3 above, characterized in that it is used for heat-shrinkable labels and subsequently for recycled PET bottle raw materials.

[0032] The effects of the invention

[0033] The heat-shrinkable polyester film of the present invention not only has a high heat shrinkage rate in the main shrinkage direction, but also uses raw materials whose composition is similar to that used in PET bottles for beverages. Furthermore, the melting point, heat release, and heat absorption determined by differential scanning calorimetry (hereinafter sometimes referred to as DSC) are similar to those of the raw materials used in PET bottles. Therefore, even if the heat-shrinkable polyester film and PET bottles are recycled at the same time, recycled PET resin can be obtained. Attached Figure Description

[0034] Figure 1 Examples of measurements of the endothermic peak temperature, heat release based on crystallization, and heat endothermic based on melting of thin films using DSC in this invention.

[0035] Figure 2 An example (top view) of the TD (width-direction stretching) pattern in the process of manufacturing the heat-shrinkable polyester film of the present invention. Detailed Implementation

[0036] The heat-shrinkable polyester film of the present invention will be described in detail below. It should be noted that the manufacturing method of the heat-shrinkable polyester film is as described in detail below; however, heat-shrinkable films are typically obtained by conveying and stretching using rollers or the like. In this case, the conveying direction of the film is referred to as the length direction, and the direction orthogonal to the aforementioned length direction is referred to as the film width direction. Therefore, the width direction of the heat-shrinkable polyester film shown below refers to the direction perpendicular to the roll-up / unroll-down direction, and the length direction of the film refers to the direction parallel to the roll-up / unroll-down direction.

[0037] The heat-shrinkable polyester film of the present invention is characterized in that it contains 85 mol% to 98 mol% of ethylene terephthalate units in 100 mol% of all ester units, 95 mol% to 100 mol% of dicarboxylic acid and 0 mol% to 5 mol% of isophthalic acid in 100 mol% of dicarboxylic acid components, and 2 mol% to 15 mol% of diethylene glycol in 100 mol% of polyol components, wherein the heat-shrinkable polyester film satisfies the following conditions (1) to (5).

[0038] (1) The hot water thermal shrinkage rate when the film is immersed in hot water at 90°C for 10 seconds is more than 40% and less than 70% in the width direction of the film.

[0039] (2) The hot water thermal shrinkage rate when the film is immersed in hot water at 90°C for 10 seconds is greater than -5% and less than 15% in the length direction of the film.

[0040] (3) Using a differential scanning calorimeter (DSC), the film was heated to 300°C to melt it, then rapidly cooled, and then heated to 300°C again. The resulting endothermic peak temperature based on melting was above 245°C and below 260°C.

[0041] (4) The heat of crystallization based on the film was obtained by heating the film to 300°C to melt it, then rapidly cooling it, and then heating it to 300°C again using a differential scanning calorimeter (DSC). The heat of crystallization was above 10 mJ / mg.

[0042] (5) The heat of melting based on the film was obtained by heating it to 300°C using a differential scanning calorimeter (DSC), then rapidly cooling it, and then heating it back to 300°C. The heat of melting was above 10 mJ / mg.

[0043] The inventors analyzed the raw material composition of commercially available beverage PET bottles (from Coca-Cola, Suntory, Itoen, Kirin, and Asahi) using 1H-NMR (varian assay, UNITY 50). The dicarboxylic acid component contained 97-98.5 mol% and isophthalic acid 1.5-3 mol% per 100 mol%. Furthermore, the ester component contained 97-99 mol% of ethylene terephthalate units per 100 mol%, and the polyol component contained 1-3 mol% of diethylene glycol. It is believed that isophthalic acid was intentionally added to prevent whitening of the PET bottle neck during molding. Diethylene glycol is considered to be a byproduct of the raw material polymerization.

[0044] Therefore, heat-shrinkable polyester films are preferred because they facilitate recycling with PET bottles when the dicarboxylic acid component uses dicarboxylic acid and isophthalic acid, and the ester unit uses only ethylene terephthalate and diethylene glycol.

[0045] Furthermore, the weight ratio of PET bottles to labels was compared using 500ml beverage PET bottles. If the weight ratio of PET bottle is set to 1, the label weight ratio is 0.05 to 0.2, indicating a low label weight ratio. Thus, the inventors discovered that although the label weight ratio is low when PET bottles and labels are mixed for recycling, the composition and characteristics of the label become the main reasons for variations in resin size and other properties during the recycling process.

[0046] In heat-shrinkable polyester films, to obtain high shrinkage, other polycarboxylic acid components and other polyol components are widely used, for example, in copolymerization of homopolymers (PET) containing polyethylene terephthalate. Neopentyl glycol and 1,4-cyclohexanediol are widely considered as polyol components used in this copolymerization. When films are copolymerized with these components, a different raw material composition is formed than that of the raw materials for beverage PET bottles, thus reducing the recyclability with PET bottles, and therefore is not preferred.

[0047] As for the polymerization method of polyethylene terephthalate (hereinafter sometimes simply referred to as PET), any manufacturing method can be used, such as direct polymerization, which involves the direct reaction of terephthalic acid and ethylene glycol, as well as other dicarboxylic acid components and glycol components as needed; and transesterification, which involves the transesterification reaction of dimethyl terephthalate (which may contain methyl esters of other dicarboxylic acids as needed) and ethylene glycol (which may contain other glycol components as needed).

[0048] Examples of dicarboxylic acid components other than terephthalic acid that constitute polyester include aromatic dicarboxylic acids such as isophthalic acid, naphthalene dicarboxylic acid, and phthalic acid; aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid, and decane dicarboxylic acid; and alicyclic dicarboxylic acids. In the heat-shrinkable polyester film of the present invention, isophthalic acid, which is the same component as the raw material of PET bottles, is preferably used. The content of isophthalic acid is 0 mol% or more in 100 mol% of the polycarboxylic acid component, preferably 1 mol% or more, and more preferably 1.5 mol% or more to form the same composition as the raw material of PET bottles. Since the label weight is 5-20% relative to the PET bottle, a content of 15 mol%, which is 5 times that of the PET bottle, is not preferred. Isophthalic acid is amorphous; if there is a high content of isophthalic acid, the amorphousness increases, which can cause problems such as pulses when mixed with PET bottles or used to produce recycled PET raw materials, and is therefore not preferred. The isophthalic acid content is 5 mol% or less, preferably 4 mol% or less, and more preferably 3 mol% or less, the same as that in PET bottle raw materials.

[0049] In the polyester polyol component of the film constituting the present invention, diethylene glycol is required to be 2 mol% or more and 15 mol% or less in 100 mol% of the polyol component.

[0050] If the diethylene glycol content is less than 2 mol%, it is difficult to exhibit the shrinkage properties required for a heat-shrinkable film, and therefore it is not preferred. The diethylene glycol content is preferably 3 mol% or more, more preferably 4 mol% or more.

[0051] On the other hand, regarding the upper limit, as mentioned above, the label weight is 5% to 20% of the PET bottle weight. Therefore, even when mixed with PET bottles in the recycling process, the diethylene glycol content is 1 / 5 to 1 / 20 or less. As mentioned above, the diethylene glycol content in the PET bottle raw material is 1% to 3 mol%, so if the diethylene glycol content in the recycled PET resin is 15 mol% or less, the diethylene glycol content in the PET bottle resin is within the range when the recycled PET resin is formed. The diethylene glycol content is preferably 13 mol% or less, more preferably 11 mol% or less.

[0052] Preferably, the product does not contain diols with 8 or more carbon atoms (e.g., octanediol) or polyols with 3 or more carbon atoms (e.g., trimethylolpropane, trimethylolethane, glycerol, diglycerol, etc.). For heat-shrinkable polyester films obtained using polyesters containing these diols or polyols, it is difficult to achieve the necessary high shrinkage.

[0053] Various additives, such as waxes, antioxidants, antistatic agents, crystal nucleating agents, detackifiers, heat stabilizers, pigments for coloring, color-resistant agents, and ultraviolet absorbers, can be added to the resin in which the heat-shrinkable polyester film of the present invention is formed, as needed.

[0054] In the resin forming the heat-shrinkable polyester film of the present invention, fine particles are preferably added as a lubricant to improve the workability (slipability) of the film. Any type of fine particle can be selected; for example, inorganic fine particles include silica, alumina, titanium dioxide, calcium carbonate, kaolin, and barium sulfate; organic fine particles include, for example, acrylic resin particles, melamine resin particles, silicone resin particles, and cross-linked polystyrene particles. The average particle size of the fine particles can be appropriately selected as needed, within the range of 0.05 to 3.0 μm (when measured using a Coulter counter).

[0055] As a method for compounding the aforementioned particles into the resin that forms a heat-shrinkable polyester film, the particles can be added at any stage of the polyester resin manufacturing process. Preferably, they are added in the form of a slurry dispersed in ethylene glycol or the like during the esterification stage, or after the transesterification reaction and before the start of the polycondensation reaction, to carry out the polycondensation reaction. Alternatively, it is preferable to use a compounding extruder with venting holes to mix the slurry of particles dispersed in ethylene glycol or water with the polyester resin raw material, or to use a compounding extruder to mix dried particles with the polyester resin raw material.

[0056] When the heat-shrinkable polyester film of the present invention is treated in hot water at 90°C under no-load conditions for 10 seconds, the heat shrinkage rate of the film in the main shrinkage direction (i.e., the heat shrinkage rate in hot water at 90°C), calculated from the length before and after shrinkage using Formula 1, is preferably 40% or more and 70% or less.

[0057] Heat shrinkage rate = {(length before shrinkage - length after shrinkage) / length before shrinkage} × 100 (%) Equation 1

[0058] If the hot water shrinkage rate in the main shrinkage direction at 90°C is less than 40%, the shrinkage will be small when used for beverage labeling or as film for boxed meal packaging. This will result in wrinkles and loosening of the label after heat shrinkage, making it undesirable. A hot water shrinkage rate of 43% or more is more preferred, 46% or more is particularly preferred, and 50% or more is most preferred.

[0059] Even if the hot water thermal shrinkage rate in the main shrinkage direction at 90°C is higher than 70%, there is no problem. However, in this invention, it is not possible to obtain a film with a hot water thermal shrinkage rate of higher than 70% at 90°C. Therefore, the upper limit is set to 70%.

[0060] The heat-shrinkable polyester film of the present invention preferably has a hot water shrinkage rate of -5% or more and 15% or less in the longitudinal direction orthogonal to the main shrinkage direction at 90°C. If the hot water shrinkage rate in the longitudinal direction at 90°C is less than -5%, the label will elongate and the label height in the PET bottle will increase when used for beverage labeling, which is therefore undesirable. A hot water shrinkage rate in the longitudinal direction at 90°C is more preferably -4% or more, and particularly preferably -3% or more.

[0061] If the shrinkage rate in hot water at 90°C along the length direction is greater than 15%, the label will shorten when used for beverage labeling, resulting in a shorter label height in the PET bottle, which is undesirable. Furthermore, it also contributes to label deformation after shrinkage. A shrinkage rate in hot water at 90°C along the length direction is more preferably 13% or less, further preferably 11% or less, particularly preferably 8% or less, and most preferably 5% or less.

[0062] The heat-shrinkable polyester film of the present invention preferably exhibits an endothermic peak temperature of 245°C or higher and 260°C or lower, obtained by heating to 300°C using a differential scanning calorimeter (DSC) to melt the film, cooling it, and then heating it back to 300°C. The peak temperature of the heat of melting for PET bottles, measured using the same method, is in the range of 250-260°C. Therefore, if the peak temperature of the heat of melting differs significantly from that of PET bottles, adverse problems such as pulses may occur during the melt extrusion process when producing recycled PET resin, which is undesirable. More preferably, the temperature is 247°C or higher and 260°C or lower; particularly preferably, it is 250°C or higher and 255°C or lower.

[0063] The heat-shrinkable polyester film of the present invention preferably exhibits a heat release based on crystallization of 10 mJ / mg or more, obtained by melting the film at 300°C using DSC, cooling it, and then heating it back to 300°C. The heat release from PET bottles measured using the same method is in the range of 25 to 55 mJ / mg. If the heat-shrinkable polyester film has a high amorphous content, no heat release will be shown, thus causing problems such as pulses during the melt extrusion process when manufacturing recycled PET resin, which is therefore undesirable.

[0064] Therefore, the heat release based on crystallization is preferably 10 mJ / mg or more, more preferably 20 mJ / mg or more, and particularly preferably 25 mJ / mg or more.

[0065] There is no specific upper limit for the heat released by crystallization, but for polyester raw materials, it should not exceed 60 mJ / mg.

[0066] The heat-shrinkable polyester film of the present invention preferably exhibits a melting-based heat absorption of 10 mJ / mg or more, obtained by melting the film at 300°C using DSC, cooling it, and then heating it back to 300°C. The heat absorption of PET bottles measured using the same method is shown in the range of 30–65 mJ / mg. If the heat-shrinkable polyester film has a high amorphous content, no heat absorption will be shown, which can cause problems such as pulses during the melt extrusion process when manufacturing recycled PET resin, and is therefore not preferred.

[0067] Therefore, the heat of melting is preferably 10 mJ / mg or more, more preferably 20 mJ / mg or more, and particularly preferably 30 mJ / mg or more.

[0068] There is no specific upper limit for the heat absorbed by melting, but for polyester raw materials, it should not exceed 70 mJ / mg.

[0069] The heat-shrinkable polyester film of the present invention preferably has a density of 1.33 g / cm³. 3 The above. Density has been reported extensively as an indicator of crystallinity. Therefore, a low density indicates low crystallinity and a high content of amorphous material.

[0070] If the density is less than 1.33 g / cm³ 3 This results in problems such as pulses during the melt extrusion process when producing recycled PET resin, making it undesirable. A more preferred value is 1.34 g / cm³. 3 Above, with a preferred concentration of 1.35 g / cm³ 3 above.

[0071] On the other hand, if the density is too high, crystallization will occur, and the shrinkage characteristics described above will not be obtained, which is therefore not preferred. A density of 1.38 g / cm³ is more preferable. 3 The following is a preferred concentration: 1.37 g / cm³3 the following.

[0072] The thickness of the heat-shrinkable polyester film of the present invention is not particularly limited, but for heat-shrinkable films used for labeling and lunchbox packaging, 15 to 50 μm is preferred. If the film thickness is less than 15 μm, the elasticity of the film is significantly reduced, and wrinkles are easily formed during rolling, so it is not preferred. On the other hand, even if the film thickness is thick, there is no problem with the film roll, and from a cost point of view, thinner film is preferred. The film thickness is more preferably 17 to 45 μm, and particularly preferably 20 to 40 μm.

[0073] The heat-shrinkable polyester film of the present invention preferably has a haze value of 2% or more and 10% or less when the film thickness is 20 μm. Since heat-shrinkable films are designed for aesthetic purposes, a haze value higher than 10% would prevent the contents from being clearly visible when forming labels for PET bottles, reducing the design flexibility and therefore is not preferred. A haze value of 8% or less, and particularly preferably 6% or less, when the film thickness is 20 μm, is more preferably preferred.

[0074] Even if the haze is less than 2% when the film thickness is 20μm, there is no problem. In this invention, if the haze value is less than 2%, the sliding properties of the film will deteriorate. Therefore, the lower limit is set to 2%.

[0075] The heat-shrinkable polyester 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 stretching the unstretched film in the width direction. It should be noted that the polyester can be obtained by polycondensing the aforementioned suitable dicarboxylic acid component and diol component using a known method. Furthermore, fragmented polyester is typically used as the raw material for the film.

[0076] When melting and extruding the raw material resin, it is preferable to use a hopper dryer, paddle dryer, or vacuum dryer to dry the polyester raw material. After drying, the polyester raw material is melted in an extruder at a temperature of 230–270°C and extruded in a thin film. During extrusion, any existing method can be used, such as the T-die method or the tubular method.

[0077] Next, by rapidly cooling the extruded sheet of molten resin, an unstretched film can be obtained. It should be noted that, as a method for rapidly cooling the molten resin, a suitable approach is to cast the molten resin from the spinneret onto a rotating drum and rapidly cool and solidify it to obtain a substantially unoriented resin sheet.

[0078] Furthermore, by stretching the obtained unstretched film in the width direction under specified conditions as described below, the heat-shrinkable polyester film of the present invention can be obtained. The preferred stretching method for obtaining the heat-shrinkable polyester film of the present invention will be described below.

[0079] Conventional heat-shrinkable polyester films are manufactured by stretching an unstretched film in the desired shrinkage direction. In this invention, by also stretching in the length direction, production speed is increased and productivity is improved, thus biaxial stretching is performed within the stretch ratio range described later.

[0080] For length-direction stretching, it is preferable to use rollers with varying speeds for roller stretching. The rollers are preheated to a surface temperature of Tg or higher but below Tg+20°C, and stretched at a ratio of 1.1 to 1.3 times the rated value. If the surface temperature is below Tg, the tensile stress increases, leading to breakage, which is undesirable. Furthermore, if the temperature is above Tg+20°C, the film adheres to the roller, causing film damage, which is also undesirable. The roller surface temperature is preferably Tg+3°C or higher but below Tg+17°C, and particularly preferably Tg+5°C or higher but below Tg+15°C.

[0081] When the stretch ratio is less than 1.1, the improvement in productivity is small, so it is not preferred. A stretch ratio of 1.15 or higher is preferred, and 1.2 or higher is particularly preferred. If the stretch ratio in the length direction is higher than 1.3, the shrinkage rate in the length direction increases, so it is not preferred. A stretch ratio of 1.28 or lower is preferred, and 1.25 or lower is particularly preferred.

[0082] For stretching in the width direction, the film stretched in the length direction is guided to a tenter frame that can hold and heat both ends of the film with clamps. After the film is heated to a specified temperature by hot air, the distance between the clamps is increased while the film is being transported in the length direction, thereby stretching the film.

[0083] The preheating temperature for stretching the film along its length is preferably above Tg+30°C and below Tg+80°C. Temperatures below Tg+30°C are undesirable because insufficient preheating leads to increased tensile force and a higher risk of breakage. Furthermore, heating above Tg+80°C reduces the tensile force of the unstretched sheet in the width direction, resulting in poor thickness accuracy (thickness unevenness) in this direction. More preferably, the temperature is above Tg+40°C and below Tg+70°C.

[0084] The film temperature during width-direction stretching is preferably above Tg+5°C and below Tg+30°C. If the film temperature is below Tg+5°C, the tensile force is too high, which can easily cause the film to break, and therefore this is not preferred. If the film temperature exceeds Tg+30°C, the tensile force is too low, and therefore the width-direction thermal shrinkage rate measured at 90°C as described above is reduced, and therefore this is not preferred. More preferably, the temperature is above Tg+8°C and below Tg+25°C.

[0085] The stretching ratio in the width direction is preferably 3.4 times or more and 5 times or less. If the stretching ratio is less than 3.4 times, the stretching force is insufficient, and the thickness accuracy (so-called thickness unevenness) in the width direction of the film deteriorates. In addition, if the stretching ratio exceeds 5 times, the risk of breakage during film formation increases, and the equipment becomes larger, so it is not preferred. More preferably, it is 3.5 times or more and 4.8 times or less. In addition, although there is no particular limitation, heat treatment can be performed after stretching in the width direction to adjust the shrinkage rate.

[0086] When stretching in the width direction, it is preferable to perform the stretching in two or more stages. In this invention, a crystalline polyester raw material is weakly stretched in the length direction, and then the film is stretched in the width direction. The molecular orientation of the film is typically reduced in the stretching direction, and the molecular orientation in the direction orthogonal to the stretching is decreased. Therefore, by initially stretching in the width direction at a low stretching ratio of 1.2 to 1.7 times, the molecular orientation in the length direction of the film decreases, and the thermal shrinkage rate in the length direction can be reduced. Furthermore, if a first-stage stretching is performed in the width direction, followed by relaxation in the width direction at 5% to 20% (so-called TD relaxation) in a tenter frame, the molecules in the length direction also relax, and the effect of reducing the thermal shrinkage rate in the length direction is amplified. Preferably, after relaxation in the width direction, a fixed length is formed in a tenter frame, and then a second-stage stretching is performed at 2 to 4.2 times.

[0087] After the second stage of stretching, heat treatment is preferably performed within the tenter frame at a temperature above the stretching temperature and below the stretching temperature +18°C. If the heat treatment temperature is lower than the stretching temperature, the purpose of the heat treatment process, which relaxes the molecular chains, cannot be achieved. Furthermore, if the heat treatment temperature is higher than the stretching temperature +18°C, the heat shrinkage rate decreases, making it undesirable as a heat-shrinkable film. A stretching temperature of +1°C or higher and below the stretching temperature +15°C is more preferable.

[0088] Example

[0089] The present invention will be described in more detail below through embodiments, but the present invention is not limited in any way by the above embodiments, and appropriate changes can be made without departing from the spirit of the present invention.

[0090] In addition, the evaluation method for thin films is described below.

[0091] [Intrinsic Viscosity (IV)]

[0092] 0.2 g of polyester was dissolved in 50 ml of a mixed solvent of phenol and 1,1,2,2-tetrachloroethane (60 / 40 by weight), and the viscosity was measured using an Ostwald viscometer at 30 °C. The unit is dl / g.

[0093] [Composition Analysis]

[0094] Each sample was dissolved in a solvent prepared by mixing chloroform D (manufactured by Eurysop) and trifluoroacetic acid D1 (manufactured by Eurysop) in a 10:1 (volume ratio) to prepare a sample solution. The NMR spectra of the protons in the sample solution were measured using an NMR spectrometer "GEMINI-200" (manufactured by Varian) at 23°C for a cumulative total of 64 measurements. During the NMR measurements, the specified proton peak intensity was calculated, and the concentrations of the diacid and polyol components per 100 mol% were determined.

[0095] [Heat shrinkage rate (hot water heat shrinkage rate)]

[0096] The film was cut into 10cm×10cm squares and immersed in hot water at a specified temperature ±0.5℃ for 10 seconds under no load to shrink it. Then, it was immersed in water at 25℃±0.5℃ for 10 seconds. The film was then removed from the water and the longitudinal and transverse dimensions were measured. The heat shrinkage rate was calculated according to the following formula (1). The direction with the larger heat shrinkage rate was taken as the main shrinkage direction.

[0097] Heat shrinkage rate = {(length before shrinkage - length after shrinkage) / length before shrinkage} × 100 (%) Equation 1

[0098] [Tg (glass transition temperature)]

[0099] Tg was determined using a differential scanning calorimeter (DSC220) manufactured by Seiko Instruments Inc., according to JIS-K7121-1987. Specifically, 10 mg of an unstretched film was heated from -40 °C to 120 °C at a heating rate of 10 °C / min, and the endothermic curve was measured. Tangents were plotted before and after the inflection point of the obtained endothermic curve, and the intersection point was taken as the glass transition temperature (Tg; °C).

[0100] [Endothermic Peak Temperature] [Heat Absorption]

[0101] The DSC was determined using a Seiko Instruments Inc. differential scanning calorimeter (model: DSC220) according to JIS-K7121-1987. 5 mg of the prepared film was placed in a sample pan, the pan was covered, and the temperature was increased to 300°C at a rate of 10°C / min under a nitrogen atmosphere. This temperature was then maintained at 300°C for 2 minutes. The sample pan was then removed and quenched using liquid nitrogen. After quenching, the sample was brought back to room temperature and then heated again using a differential scanning calorimeter at a rate of 10°C / min to a temperature between 30°C and 300°C. The DSC was measured. The endothermic peak at which the sample melted was taken as the endothermic peak temperature. The heat absorbed during melting was calculated from the area of ​​the endothermic peak. In the absence of a melting peak, there was no melting peak temperature, and the heat absorbed was recorded as 0.

[0102] [Heat release]

[0103] The differential scanning calorimeter (DSC220) manufactured by Seiko Instruments Inc. was used, and the results were determined according to JIS-K7121-1987. 5 mg of the prepared film was placed into a sample pan, the pan was covered, and the temperature was increased to 300°C at a rate of 10°C / min under a nitrogen atmosphere. This temperature was then maintained at 300°C for 2 minutes. The sample pan was then removed and quenched using liquid nitrogen. After quenching, the sample was brought back to room temperature and then heated again to 30°C–300°C at a rate of 10°C / min using the differential scanning calorimeter. The DSC was measured. The heat of release was calculated from the area of ​​the exothermic peak. In cases where there was no exothermic peak, the temperature at which no exothermic peak occurred was recorded as 0.

[0104] [Thickness of the thin film]

[0105] The determination was performed using a dial gauge according to JIS K7130-1999 Method A.

[0106] [Density of the thin film]

[0107] The density of a sample approximately 3 mm square was determined using the density gradient tube method according to JIS-K-7112 and an aqueous solution of calcium nitrate.

[0108] [Haze of the thin film]

[0109] According to JIS K7361-1, the film was cut into a square shape with 10cm sides, and the haze was measured using a NDH2000 haze meter manufactured by Nippon Densho Co., Ltd. The measurement was performed at 3 locations, and the average value was taken as the actual haze measurement value. The haze converted to 20μm was calculated using the following formula (2).

[0110] Haze = Actual measured haze value × 20 / Film thickness (%) (20 μm)

[0111] [Shrinkage finish]

[0112] The end of the heat-shrinkable film was welded using a pulse sealer (manufactured by FUJI IMPULSE CO., LTD.) to obtain a cylindrical label with the width direction as the circumferential direction. The diameter in the shrinkage direction of the label is 68 mm. This label was covered on a commercially available 500-ml PET bottle (containing contents, trunk diameter 62 mm, minimum diameter of the neck 25 mm), and heat shrinkage was performed with steam using a steam channel (model; SH-1500-L) manufactured by Fuji Astec Inc. adjusted to 90°C (channel passing time 5 seconds). The shrinkage finishability of the label was visually evaluated according to the following criteria. A 5-grade evaluation was performed visually according to the following criteria. The defects described below refer to flying up, wrinkles, insufficient shrinkage, folding-in of the label end, shrinkage whitening, etc. A score of 3 or above is considered qualified.

[0113] 5: The best finishability (no defects)

[0114] 4: Good finishability (1 defect exists)

[0115] 3: 2 defects exist

[0116] 2: 3 to 5 defects exist

[0117] 1: Many defects exist (more than 6)

[0118] [Deviation of recycled PET resin]

[0119] The contents of the 500-ml sized PET bottle for which the above shrinkage finishability was evaluated were taken out, washed with water, and then the PET bottle and the label were shredded to a size of 8 to 10 mm using a shredder (model 48 manufactured by FUJITEX Co., Ltd.) to make fragments.

[0120] The obtained fragments were melted at 280°C using a granulator (SRH-V55 / 48 manufactured by Nippon Oil Co., Ltd.), and recycled PET resin was produced for 30 minutes with an extrusion rate of about 120 kg per hour. It was produced by cutting in such a way that the size of the recycled PET resin at this time formed a length of 3 ± 0.8 mm (2.2 to 3.8 mm) and the grain weight formed 30 ± 10 mg / each (20 to 40 mg / each). Then, 300 grains of recycled PET resin (900 grains in total) were sampled 5 minutes, 15 minutes, and 25 minutes after the start of granulation, and the size of the recycled PET resin was measured. The judgment was made using the following method, and ○ was considered qualified.

[0121] ○: Resin outside the size (length, grain weight) range is 10% or less of the whole, and there is no trouble during granulation due to pulses, etc.

[0122] △: Resin outside the size (length, particle weight) range accounts for less than 30% of the total, and granulation problems caused by pulses, etc., occur less than twice.

[0123] ×: Resin outside the size (length, particle weight) range accounts for more than 30% of the total, and granulation problems due to pulses, etc., occur more than 3 times.

[0124] <Manufacturing of Polyester Raw Materials>

[0125] [Synthesis example 1]

[0126] A stainless steel autoclave equipped with a stirrer, thermometer, and partial reflux cooler was used to add 100 mol% dimethyl terephthalate (DMT) as a dicarboxylic acid and 100 mol% ethylene glycol (EG) as a polyol, at a molar ratio of 2.2 times that of dimethyl terephthalate. Zinc acetate (0.05 mol% relative to the acid component) and antimony trioxide (0.225 mol% relative to the acid component) as a polycondensation catalyst were also added. The transesterification reaction was carried out simultaneously with the distillation removal of the generated methanol from the system. Polycondensation was then carried out at 280 °C under reduced pressure of 26.7 Pa to obtain polyester A with an intrinsic viscosity of 0.75 dl / g. The composition is shown in Table 1.

[0127] [Synthesis Examples 2 to 5]

[0128] Polyesters B to D, as shown in Table 1, were obtained using the same method as in Synthesis Example 1. During the manufacture of polyester B, SiO2 (manufactured by FUJI SILYSIA CHEMICAL LTD., SYLYSIA 266; average particle size 3 μm) was added as a lubricant at a ratio of 20,000 ppm relative to the polyester. It should be noted that the intrinsic viscosity of all polyesters was 0.75 dl / g.

[0129] It should be noted that each polyester is appropriately formed into fragments. The composition of each polyester is shown in Table 1.

[0130] [Table 1]

[0131]

[0132] ※DMT: Dimethyl terephthalate

[0133] IPA: Isophthalic acid

[0134] EG: Ethylene glycol

[0135] DEG: Diethylene glycol

[0136] NPG: Neopentyl Glycol

[0137] [Example 1]

[0138] Polyester A, polyester B, and polyester C were mixed in a weight ratio of 67:3:30 and fed into an extruder. The mixed resin was then melted at 273°C using a quadrupole screw, cooled to 260°C, and extruded from a T-die. The mixture was then quenched by winding it onto a rotating metal roller cooled to a surface temperature of 20°C, thereby obtaining an unstretched film with a thickness of 201 μm. The Tg of the unstretched film was 65°C.

[0139] The unstretched film is guided to a longitudinal stretching machine and preheated using rollers with a surface temperature of Tg+10℃ (75℃). The film is then stretched 1.2 times in the longitudinal (length) direction using the speed difference between the rollers. The uniaxially stretched film is then guided to a tenter frame. While holding the film at both ends with clamps, it is preheated to a temperature of Tg+45℃ (110℃). Then, at a film temperature of Tg+10℃ (75℃), it is stretched 1.5 times in the transverse direction in the first stage. Next, it is relaxed by 10% in the width direction at Tg+10℃ (75℃). The film, relaxed in the width direction, is stretched 3.1 times in the second stage at Tg+10℃ (75℃) (total stretching ratio 4.2 times). Finally, the film stretched in the width direction is heat-set at Tg+12℃ (77℃). The two edges of the stretched film were cut off, thereby continuously producing biaxially stretched films of approximately 40 μm in length, resulting in film rolls formed from heat-shrinkable polyester films. The properties of the obtained films were then evaluated using the method described above. The film-forming conditions are shown in Table 2, and the evaluation results are shown in Table 3.

[0140] The film has no practical problems in terms of shrinkage, finishing properties, and deviations in recycled PET.

[0141] [Example 2]

[0142] Polyester A, polyester B, and polyester C were mixed in a weight ratio of 77:3:20 and fed into an extruder to obtain an unstretched film with a thickness of 201 μm, similar to Example 1. The Tg of the unstretched film was 70°C.

[0143] The unstretched film was stretched in the same manner as in Example 1 to obtain a film roll formed from a heat-shrinkable polyester film with a thickness of 40 μm. However, the stretching temperature Tg differed from that in Example 1, and was therefore changed to Tg+10℃ (80℃), Tg+45℃ (115℃), and Tg+12℃ (82℃). The properties of the obtained film were evaluated using the above method. The film-forming conditions are shown in Table 2, and the evaluation results are shown in Table 3.

[0144] The film has no practical problems in terms of shrinkage, finishing properties, and deviations in recycled PET.

[0145] [Example 3]

[0146] Polyester A, polyester B, and polyester C were mixed in a weight ratio of 92:3:5 and fed into an extruder to obtain an unstretched film with a thickness of 201 μm, similar to Example 1. The Tg of the unstretched film was 74°C.

[0147] The unstretched film was stretched in the same manner as in Example 1 to obtain a film roll formed from a heat-shrinkable polyester film with a thickness of 40 μm. However, the stretching temperature Tg differed from that in Example 1, and was therefore changed to Tg+10℃ (84℃), Tg+45℃ (119℃), and Tg+12℃ (86℃). The properties of the obtained film were evaluated using the above method. The film-forming conditions are shown in Table 2, and the evaluation results are shown in Table 3.

[0148] The film has no practical problems in terms of shrinkage, finishing properties, and deviations in recycled PET.

[0149] [Example 4]

[0150] Polyester A, polyester B, polyester C, and polyester D were mixed in a weight ratio of 52:3:5:40 and fed into an extruder to obtain an unstretched film with a thickness of 201 μm, similar to Example 1. The Tg of the unstretched film was 74 °C.

[0151] The unstretched film was stretched in the same manner as in Example 1 to obtain a film roll formed from a heat-shrinkable polyester film with a thickness of 40 μm. However, the stretching temperature Tg differed from that in Example 1, and was therefore changed to Tg+10℃ (84℃), Tg+45℃ (119℃), and Tg+12℃ (86℃). The properties of the obtained film were evaluated using the above method. The film-forming conditions are shown in Table 2, and the evaluation results are shown in Table 3.

[0152] The film has no practical problems in terms of shrinkage, finishing properties, and deviations in recycled PET.

[0153] [Example 5]

[0154] Polyester A, polyester B, polyester C, and polyester D were mixed in a weight ratio of 57:3:30:10 and fed into an extruder to obtain an unstretched film with a thickness of 201 μm, similar to Example 1. The Tg of the unstretched film was 65°C.

[0155] The unstretched film was stretched in the same manner as in Example 1 to obtain a film roll formed from a heat-shrinkable polyester film with a thickness of 40 μm. The film-forming conditions are shown in Table 2, and the evaluation results are shown in Table 3.

[0156] The film has no practical problems in terms of shrinkage, finishing properties, and deviations in recycled PET.

[0157] [Example 6]

[0158] Polyester A, polyester B, polyester C, and polyester D were mixed in a weight ratio of 67:3:20:10 and fed into an extruder to obtain an unstretched film with a thickness of 201 μm, similar to Example 1. The Tg of the unstretched film was 70°C.

[0159] The unstretched film was stretched in the same manner as in Example 1 to obtain a film roll formed from a heat-shrinkable polyester film with a thickness of 40 μm. However, the stretching temperature Tg differed from that in Example 1, and was therefore changed to Tg+10℃ (80℃), Tg+45℃ (115℃), and Tg+12℃ (82℃). The properties of the obtained film were evaluated using the above method. The film-forming conditions are shown in Table 2, and the evaluation results are shown in Table 3.

[0160] The film has no practical problems in terms of shrinkage, finishing properties, and deviations in recycled PET.

[0161] [Comparative Example 1]

[0162] Polyester A, polyester B, and polyester C were mixed in a weight ratio of 47:3:50 and fed into an extruder. The mixed resin was then melted at 273°C using a quadrupole screw, cooled to 260°C, and extruded from a T-die. The mixture was then quenched by winding it onto a rotating metal roller cooled to a surface temperature of 20°C, thereby obtaining an unstretched film with a thickness of 201 μm. The Tg of the unstretched film was 58°C.

[0163] The unstretched film is guided to a longitudinal stretching machine and preheated using rollers with a surface temperature of Tg+10℃ (68℃). The film is then stretched 1.2 times in the longitudinal (length) direction using the speed difference between the rollers. The uniaxially stretched film is then guided to a tenter frame. While holding the film at both ends with clamps, it is preheated to a temperature of Tg+45℃ (103℃). Then, at a film temperature of Tg+10℃ (68℃), it is stretched 1.5 times in the transverse direction in the first stage. Next, it is relaxed by 10% in the width direction at Tg+10℃ (68℃). The film, relaxed in the width direction, is stretched 3.1 times in the second stage at Tg+10℃ (68℃) (total stretching ratio 4.2 times). Finally, the film stretched in the width direction is heat-set at Tg+12℃ (70℃). The two edges of the stretched film were cut off, thereby continuously producing biaxially stretched films of approximately 40 μm in length, resulting in film rolls formed from heat-shrinkable polyester films. The properties of the obtained films were then evaluated using the method described above. The film-forming conditions are shown in Table 2, and the evaluation results are shown in Table 3.

[0164] While the film has no practical problems in terms of shrinkage and finishing, the dimensional deviations of recycled PET resin when mixed with PET bottles are significant, leading to problems such as granulation difficulties caused by pulses.

[0165] [Comparative Example 2]

[0166] Polyester B, polyester C, and polyester D were mixed in a weight ratio of 3:7:90 and fed into an extruder to obtain an unstretched film with a thickness of 201 μm, similar to Example 1. The Tg of the unstretched film was 73°C.

[0167] The unstretched film was stretched in the same manner as in Example 1 to obtain a film roll formed from a heat-shrinkable polyester film with a thickness of 40 μm. However, the stretching temperature Tg differed from that in Example 1, and was therefore changed to Tg+10℃ (83℃), Tg+45℃ (118℃), and Tg+12℃ (85℃). The properties of the obtained film were evaluated using the above method. The film-forming conditions are shown in Table 2, and the evaluation results are shown in Table 3.

[0168] While the film has no practical problems in terms of shrinkage and finishing, the dimensional deviations of recycled PET resin when mixed with PET bottles are significant, leading to two problems during granulation due to pulses.

[0169] [Comparative Example 3]

[0170] Polyester A, polyester B, polyester C, and polyester E were mixed in a weight ratio of 12:3:5:80 and fed into an extruder to obtain an unstretched film with a thickness of 201 μm, similar to Example 1. The Tg of the unstretched film was 74 °C.

[0171] The unstretched film was stretched in the same manner as in Example 1 to obtain a film roll formed from a heat-shrinkable polyester film with a thickness of 40 μm. However, the stretching temperature Tg differed from that in Example 1, and was therefore changed to Tg+10℃ (83℃), Tg+45℃ (118℃), and Tg+12℃ (85℃). The properties of the obtained film were evaluated using the above method. The film-forming conditions are shown in Table 2, and the evaluation results are shown in Table 3.

[0172] It produces a film with good shrink-finishing properties, but the dimensional deviations of recycled PET resin mixed with PET bottles are significant, leading to problems such as multiple granulation issues caused by pulses.

[0173] [Table 2A]

[0174]

[0175] [Table 2B]

[0176]

[0177] [Table 3]

[0178]

[0179] Industrial availability

[0180] Although the heat-shrinkable polyester film of the present invention has a high heat shrinkage rate, the raw material composition used is similar to that used in PET bottles for beverages. Therefore, in the process of producing recycled PET resin by recycling PET bottles, even when mixed with heat-shrinkable polyester film used for labels, recycled PET resin can be produced with stable quality.

Claims

1. A heat-shrinkable polyester film, characterized in that, The heat-shrinkable polyester film contains 95 mol% to 100 mol% of dicarboxylic acid and 0 mol% to 5 mol% of isophthalic acid in 100 mol% of dicarboxylic acid components, and 85 mol% to 98 mol% of ethylene terephthalate units in 100 mol% of all ester units, and 2 mol% to 15 mol% of diethylene glycol in 100 mol% of polyol components. The heat-shrinkable polyester film satisfies the following conditions (1) to (5), where the length direction refers to the film conveying direction, and the width direction refers to the direction orthogonal to the length direction. (1) The hot water thermal shrinkage rate when the film is immersed in hot water at 90°C for 10 seconds is more than 40% and less than 70% in the width direction of the film. (2) The hot water thermal shrinkage rate when the film is immersed in hot water at 90°C for 10 seconds is greater than -5% and less than 15% in the length direction of the film. (3) Using a differential scanning calorimeter (DSC), the film was heated to 300°C to melt it, then rapidly cooled, and then heated to 300°C again. The resulting endothermic peak temperature based on melting was above 245°C and below 260°C. (4) The heat of crystallization based on the film was obtained by heating the film to 300°C to melt it, then rapidly cooling it, and then heating it to 300°C again using a differential scanning calorimeter (DSC). The heat of crystallization was above 10 mJ / mg. (5) The heat of melting based on the film was obtained by heating the film to 300°C using a differential scanning calorimeter (DSC) to melt it, then cooling it rapidly and heating it to 300°C again. The heat of melting was above 10 mJ / mg.

2. The heat-shrinkable polyester film according to claim 1, characterized in that, The density of the film is 1.33 g / cm³. 3 Above and 1.39 g / cm 3 the following.

3. The heat-shrinkable polyester film according to claim 1 or 2, characterized in that, The haze is above 2% and below 10% when the film thickness is 20μm.

4. A heat-shrinkable label using the heat-shrinkable polyester film according to any one of claims 1 to 3.

5. A packaging body, characterized in that, It is formed by covering at least a portion of the outer periphery of the packaged object with the heat-shrinkable label as described in claim 4 and causing it to heat-shrink.

6. The heat-shrinkable polyester film according to any one of claims 1 to 3, characterized in that, It was used in heat-shrinkable labels, and then in recycled PET bottle materials.

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