Recyclable shrink film having linear shrinkage curve

Abstract

To provide an environmentally friendly heat-shrinkable film having shrinkage characteristics suitable for use in an empty container or a container with low rigidity.SOLUTION: A heat-shrinkable film contains copolyester including a diol component and a dicarboxylic acid component. The film is characterized by a heat-shrinkage curve corresponding to a coefficient of contraction in a main shrinkage direction as a function of temperature retention for 10 seconds. The heat-shrinkage curve has an inclination of less than 2.0 in units of 5°C in a whole range of 65-95°C.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a heat-shrinkable film. More specifically, the present invention relates to a heat-shrinkable film for shrink-to-fit labelling of packages such as food and beverage packaging.

Background Art

[0002] Heat-shrinkable films are known, for example, for covering and protecting articles, joining articles together, applying labels to articles, and providing tamper-evident protection, and are generally available.

[0003] Polyvinyl chloride (PVC) and polystyrene (PS), particularly oriented polystyrene (OPS), are commonly used in the manufacture of heat - shrinkable films. Typically, the polymer material is prepared, extruded into a film, biaxially and / or uniaxially stretched, and wound onto a roll. At a packaging facility, the film is unwound, printed, sewn together to form a tube, and applied around an article. Thereafter, the film is heated to the shrink temperature and shrinks to fit snugly around the article. In some applications, the container has food or beverage in it before the label is applied. In other applications, the shrink label is applied to an empty container. Heat - shrinkable films may have relatively high shrinkage rates and stresses to prevent the contents from deforming the container under the pressure of the shrink film. However, exposing a filled container, even partially, to heat can be undesirable or not possible because it may cause the food / beverage product to spoil. However, without contents, heat - shrinkable films with high shrinkage rates and stresses tend to deform or crush empty containers. PVC and OPS, which have a relatively low shrink - start temperature and low shrinkage rates and stresses, were preferred materials for shrink - film manufacture. However, these materials are generally not recyclable, and even when they are, the recycling process requires separating the PVS or OPS film from containers made of different materials before recycling the various materials. Therefore, PVC and OPS shrink films are not compatible with the significant shift, both within and outside the industry, towards environmentally friendly solutions.

[0004] Polyethylene terephthalate (PET) is commonly used in the food and beverage packaging industry. In particular, amorphous polyethylene terephthalate (APET) is preferred for its versatility, transparency, and recyclability, and is frequently used in the manufacture of food and beverage containers (e.g., food trays and containers, bowls, cups, bottles, etc.). Therefore, "monopolymer packaging" including PET bottles together with PET shrink films is advantageous. However, in order to be suitable for shrink film applications, it is necessary to reduce the crystallization ability of APET. Glycol-modified polyethylene terephthalate (commonly referred to as "PET-G" and "PETG") has a moderately low degree of crystallinity, but has relatively high shrinkage and stress and is not suitable for effective packaging / labeling of empty containers. Summary of the Invention Problems to be Solved by the Invention

[0005] Accordingly, an object of the present invention is to reduce the above problems and provide an improved alternative to existing products. In particular, an object of the present invention is to provide an environmentally friendly heat-shrinkable film having shrinkage characteristics suitable for use with empty containers or containers with low rigidity.

[0006] According to one aspect, a recyclable heat-shrinkable film comprising a copolyester comprising a diol component and a dicarboxylic acid component is provided. In an embodiment, the diol component is selected from at least one member selected from the group consisting of ethylene glycol, diethylene glycol, neopentyl glycol, propylene glycol, polyethylene glycol, tetraethylene glycol, and cyclohexanedimethanol. In an embodiment, the dicarboxylic acid component is selected from at least one member of the group consisting of isophthalic acid and terephthalic acid.

[0007] In an embodiment, the heat-shrinkable film has an A-B-A structure, where the "A" layer is the surface layer and the "B" layer is the core layer between the A surface layers.

[0008] According to another aspect, there is provided a recyclable heat-shrinkable film having a heat shrinkage curve corresponding to the shrinkage rate in the main shrinkage direction as a function of isothermal holding in water for 10 seconds, and the heat shrinkage curve having a gentle slope. In an embodiment, the slope is less than 2.0 at every 5 °C interval between 65 °C and 95 °C.

[0009] According to another aspect, there is provided a recyclable heat-shrinkable film which is a heat shrinkage curve corresponding to the shrinkage rate in the main shrinkage direction as a function of the holding temperature in water for 10 seconds, and the heat shrinkage curve having a substantially linear shape. In an embodiment, by linear regression analysis of the curve, a Pearson correlation coefficient of at least 0.95 is obtained for the entire curve between 60 °C and 95 °C.

[0010] According to another aspect, there is provided a recyclable heat-shrinkable film characterized by a low shrinkage rate. In an embodiment, the shrinkage rate is 10% or less per second when measured in air at 85 °C.

[0011] According to another aspect, there is provided a method for manufacturing a heat-shrinkable film having a heat shrinkage curve with a gentle gradient and substantially linear shape at a temperature between 60 °C and 95 °C. This method includes a step of preparing a copolyester from a constituent resin, a step of extrusion molding to obtain an unstretched film, and a step of further extrusion molding the film in a tenter frame extrusion process including a stretching zone and an annealing zone. In an embodiment, the temperature in the annealing zone is higher than the temperature in the stretching zone.

[0012] According to yet another aspect, there is provided a method of applying the heat-shrinkable film as described above. This method includes a step of applying the film onto and / or around an article, and a step of heating the film to at least its shrinkage start temperature.

[0013] In the drawings, like reference characters generally refer to the same parts throughout different views. Also, the drawings are not necessarily to scale; instead, emphasis is generally placed on illustrating the principles of the present invention. In the following description, various embodiments of the present invention will be described with reference to the following drawings:

Brief Description of the Drawings

[0014]

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Modes for Carrying Out the Invention

[0015] The claimed apparatus, compositions, systems, and methods are intended to encompass variations and adaptations developed using information from the embodiments described herein. Adaptations and / or modifications of the apparatus, compositions, systems, and methods described herein may be made by those of ordinary skill in the relevant art. In contrast to conventional heat-shrinkable films, when the shrinkage rate in the primary shrinkage direction of the films described herein is plotted as a function of temperature, the resulting curve is substantially linear. Further, the slope of the shrinkage rate-temperature curve for embodiments of the films described herein is generally lower than that of conventional shrinkable films. Thus, the gradual and controlled increase in heat shrinkage rate with increasing temperature produces desirable properties in the heat-shrinkable film.

[0016] In various examples, "shrink rate" (also referred to as "shrink percentage") refers to the amount of shrinkage that a heat-shrinkable film undergoes in the indicated direction during the shrinkage phase, expressed as a shrinkage rate compared to the film size in that direction prior to the shrinkage phase. ASTM D-2732 (Standard Test Method for Unrestrained Linear Thermal Shrinkage of Plastic Film and Sheeting) can be used to measure the shrink rate of the films described herein.

[0017] In various examples, "shrink stress" (also sometimes referred to as "shrink force") is the tension, force, or stress (e.g., force per area) exerted by a heat-shrinkable film during the shrinkage phase. Films with high shrink stress may be suitable for rigid articles, while low shrink stress is desirable for flexible, deformable, and / or hollow articles. Additionally, printed low shrink stress films have been found to exhibit improved shrink performance (e.g., low risk of discoloration, color density, deformation of printed images, and label defects). Shrink stress can be measured using ASTM D2838, DIN 53369:1076-02, or similar techniques. As an example, shrink stress can be the maximum tension exerted by the heat-shrinkable film over a temperature range.

[0018] In various examples, the "shrink start temperature" is the temperature at which a heat-shrinkable film begins to shrink. To minimize deformation and damage to the article to which the film is applied, it is desirable to have a low shrink start temperature. In the case of plastic articles such as polyethylene terephthalate (PET) bottles, the shrink start temperature of the heat-shrinkable film is preferably substantially lower than the glass transition temperature of the article to avoid or minimize deformation of the article. Additionally, the shrink start temperature of the film is preferably low enough not to damage or impair the contents within the article. The shrink start temperature can be measured using ASTM-D-2732 or similar techniques.

[0019] In certain examples, "intrinsic viscosity" (IV) is a property of the polymer used to manufacture the shrink film. IV can depend on the average molecular weight of the polymer, e.g., the higher the molecular weight, the higher the IV. In some cases, the lower the IV, the lower the shrink stress can be. IV can be measured using ASTM D4603-03 or similar techniques.

[0020] In various examples, the "glass transition temperature" (Tg) is the temperature at which an amorphous polymer transitions from a glassy state to a rubbery state. The Tg value can affect many physical properties of the polymer, and in particular, a decrease in the glass transition temperature can lead to a decrease in the shrinkage start temperature. However, if the Tg is too low, the film may become sticky or tacky and may not be suitable for packaging purposes. The glass transition temperature can be measured using thermomechanical analysis (TMA), dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), or similar techniques.

[0021] Generally, a heat-shrinkable film is a film that tends to shrink when heat is applied or when exposed to a high temperature (e.g., above the shrinkage start temperature). Heat-shrinkable films can be used for forming labels for various containers such as bottles, cap seals, and bundle packaging. For example, ink can be printed on a heat-shrinkable film to form an image and / or text. The printed heat-shrinkable film is formed into a tubular sleeve and placed over the container. When heat is applied, the sleeve shrinks and can be made to fit tightly over the container. The container can be filled with a desired product (e.g., a beverage) and sold to consumers. Heat-shrinkable films and related manufacturing methods are described in International Publication No. WO 2022 / 072477, published on April 7, 2022, the entire disclosure of which is incorporated herein by reference.

[0022] After use, the container and label can be subjected to a recycling process, crushed, shredded, and / or chopped into flakes or particles. The particles can be washed or de-inked by being subjected to a hot water wash process. The washed particles can be subjected to a drying and / or solidification process to heat the particles to remove moisture, make the particles crystallizable, and / or increase the molecular weight of the particles. However, in some cases, the high temperature of the drying and / or solidification process can cause the particles to become sticky and the particles may form lumps. These lumps can clog filters and screens and / or form bridges, preventing proper flow of the material in the recycling process.

[0023] A wide variety of polymer materials can be used in the manufacture of heat - shrinkable films. For example, polyvinyl chloride (PVC), polystyrene (PS), especially oriented polystyrene (OPS), are commonly used in the manufacture of heat - shrinkable films. PVC and OPS can provide a low shrink - start temperature and low shrink stress, but PVC and OPS films are generally not easily recyclable. For example, PVC films and OPS films are often used together with containers made of different materials, and in order to carry out proper recycling, it is necessary to separate different types of materials.

[0024] Polyethylene terephthalate (PET) is commonly used in the food and beverage packaging industry for the manufacture of containers and heat - shrinkable films. Amorphous polyethylene terephthalate (APET) is preferred for its versatility, transparency, and recyclability, and is frequently used in the manufacture of food and beverage containers (such as food trays, bowls, cups, and bottles). However, in order to be suitable for shrink - film applications, it is necessary to reduce the crystallization tendency of APET. Glycol - modified PET (commonly called copolyester, "PET - G", or "PETG") can preferably have a low degree of crystallinity, but films made of PETG can become sticky during the recycling process, especially when the shrink - start temperature and shrink stress are low, as described herein. For this reason, such films can be difficult or impossible to recycle.

[0025] Advantageously, compared to conventional films with low shrink stress, the heat - shrinkable films described herein are less likely to become sticky and / or less likely to form lumps during the recycling process. For example, the film can be mixed with similar materials (such as PET bottle flakes) and, unlike conventional films, can be subjected to solid - state forming and other recycling processes without forming lumps that would block the formation of closures or otherwise impede the proper flow of other materials.

[0026] Figure 1 is a schematic perspective view of a heat-shrinkable film 10 according to a particular embodiment. In these embodiments, the heat-shrinkable film has an A-B-A structure, where the "A" layers are the top and bottom layers and the "B" layer is the core layer between the A surface layers. As depicted in Figure 1, the heat-shrinkable film 10 includes a top layer 12, a bottom layer 14, and a core layer 16 (e.g., adhered) disposed between the top layer 12 and the bottom layer 14. In various embodiments, the top layer 12, the bottom layer 14, and the core layer 16 each include or are composed of a polyester such as PET, APET, one or more copolyesters (or referred to as copolyester or PETG), or combinations thereof. Each polyester and copolyester can have a diol component and a dicarboxylic acid component, and can be formed by subjecting the diol component and the dicarboxylic acid (DA) component to a transesterification reaction and then polymerizing. The diol component of a particular polyester (e.g., APET) can be or can include ethylene glycol (EG). In embodiments, one or both of the surface layers include an anti-blocking additive and / or a topical anti-static additive or coating.

[0027] The diol component in the copolyester consists of, for example, ethylene glycol (EG), diethylene glycol (DEG), neopentyl glycol (NPG, e.g., 2-dimethylpropane-1,3-diol), propylene glycol (PPG), cyclohexanedimethanol (CHDM, e.g., 1,4-cyclohexanedimethanol), tetraethylene glycol (TEG), 1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, 2,3-butanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 2,2-diethyl-1,5-pentanediol, 2,4-diethyl-1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,1-dimethyl-1,5-pentanediol, 1,2-octanediol, 1,3-octanediol, or a combination or inclusion thereof. In an embodiment, the approximate composition of the diol component in the copolyester resin used for the film is, with the total amount of glycol in the film formulation being 100 mol%, 50 mol% to 85 mol% of ethylene glycol, 10 mol% to 30 mol% of cyclohexanedimethanol, and 5 mol% to 25 mol% of diethylene glycol. In some examples, by including NPG in the diol component, higher shrinkage force, desirable shrinkage characteristics, and / or good anti-clamping performance (e.g., acceptable performance in the clamping performance test described herein) can be achieved. NPG can be lower in cost than other types of diol components. By including CHDM and / or DEG in the diol component, lower shrinkage force and desirable shrinkage characteristics can be achieved, but if the content of CHDM and / or DEG is too high, the anti-clamping performance may be insufficient or poor. When EG is included in the diol component, good anti-clamping performance is achieved, but if there is too much, the shrinkage characteristics may relatively deteriorate. In various examples, it may be desirable for the film to have a higher shrinkage rate in the transverse direction compared to the machine direction.

[0028] The dicarboxylic acid (DA) component in the copolyester can be composed of, for example, terephthalic acid (TA), isophthalic acid (IPA), dimethyl terephthalic acid, naphthalenedicarboxylic acid, orthophthalic acid, aromatic dicarboxylic acid, adipic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, aliphatic dicarboxylic acid or alicyclic dicarboxylic acid, or can include these. In one example, the dicarboxylic acid component in the polyester and copolyester is terephthalic acid (TA) or its ester. In an embodiment, the dicarboxylic acid component in the copolyester resin used for the film contains 0.05 mol% to 0.8 mol% of isophthalic acid and 99.0 mol% to 100 mol% of terephthalic acid.

[0029] In an embodiment, the film described herein is manufactured from a blend of an amorphous resin material and a crystallized resin material. In an embodiment, the amorphous resin has a Tg of up to about 75 °C and an intrinsic viscosity of about 0.65 dl / g to about 0.85 dl / g. In an embodiment, the crystallized resin has a Tg of up to about 80 °C and an intrinsic viscosity of about 0.70 dl / g to about 0.85 dl / g. In an embodiment, the Tg of the entire film is up to about 80 °C. In an embodiment, 60 mol% to 90 mol% of the entire film is made from the amorphous resin. In an embodiment where the film described herein features an A-B-A structure, the surface "A" layer preferably has slightly lower crystallinity to optimize the solvent seaming process.

[0030] Referring back to FIG. 1, the heat - shrinkable film 10 can have a thickness T, a length L, and a width W. The thickness T can be, for example, from about 15 microns to about 100 microns. In various examples, the core layer 16 can occupy from about 50% to about 90% of the total thickness T. The top layer 12 and the bottom layer 14 can occupy the remainder of the total thickness T and / or can have equal thicknesses. For example, the top layer 12 and the bottom layer 14 can each occupy from about 5% to about 25% of the total thickness T. The length L and the width W can vary depending on the manufacturing process, the packaging process, and / or how the film 10 is utilized. For example, the web of the heat - shrinkable film 10 in the manufacturing process can have a width W of up to about 20 m, and the web can be slit into narrower ribbons having a width W as low as about 0.01 m. Alternatively, in the case of the particles of the heat - shrinkable film 10 in the recycling process, as described herein, the length L and / or the width W (or the diameter of circular particles) can be from about 1 mm to about 50 mm, or from about 3 mm to about 15 mm.

[0031] In various examples, one or more layers or materials can be disposed on the top layer 12 or on the bottom layer, between the top layer 12 and the core layer 16, or between the bottom layer 14 and the core layer 16. For example, a coating, a primer, or an ink (e.g., a printed image or text) can be applied to the film 10. The top layer 12 and / or the bottom layer 14 can function as a contact medium printed with a washable primer and / or a washable ink, which can be removed during the recycling process as described herein. The top layer 12 and the bottom layer 14 can be formulated so as not to solidify with the PET flakes even when exposed to high temperatures in the recycling process. The core layer 16 can provide desirable shrinkage characteristics such as low shrinkage force and low shrinkage start temperature.

[0032] The heat-shrinkable film 10 can have any shape and, as shown in FIG. 1, need not be a flat rectangle. For example, referring to FIG. 2, the heat-shrinkable film 10 can be formed into a shrink sleeve 20 having a tubular shape (e.g., by forming a seam with a solvent). The shrink sleeve 20 can be placed over a bottle (or other container) and, when heat is applied (e.g., using steam, hot air, microwave energy, or infrared radiation), can shrink to form a snug fit around the bottle.

[0033] FIG. 3 is a schematic view of a manufacturing process 30 that can be used to manufacture a heat-shrinkable film (e.g., heat-shrinkable film 10) according to a particular embodiment. One or more extruders 32 can be used to co-extrude three layers for the heat-shrinkable film (e.g., top layer 12, bottom layer 14, and core layer 16). The process temperature of the extruder 32 can be from about 200° C. to about 300° C. The three layers are cast onto a chill roll 34 to cool and solidify the film. The web 36 of the film is inspected by one or more quality control sensors 38 and sent to a tenter frame 40. The tenter frame 40 can stretch the film in the transverse direction (a direction perpendicular to the machine direction) to a draw ratio of from about 1.5 to about 7, or about 5. Additionally or alternatively, one or more downstream rollers can stretch the film in the machine direction by pulling the web at a faster speed compared to the speed of the upstream roller. The stretching can be performed at a temperature above the glass transition temperature Tg of the heat-shrinkable film or one or more layers of the film. For example, the stretching can be performed at a temperature from about Tg to about Tg + 10° C. or + 15° C. One or more quality control sensors 42 can inspect the stretched film, and this film can be wound up to form a roll 44. In an embodiment, the process includes an annealing step after the film is stretched, and the annealing temperature is above the temperature at which the stretching is performed. In an embodiment, the annealing is performed at a temperature within the range of Tg + 10° C. to Tg + 25° C.

[0034] In subsequent steps (not shown), the heat-shrinkable film can be unwound from roll 44 and passed through a printing step of applying ink to the heat-shrinkable film. In some examples, one or more intermediate layers can be applied between the heat-shrinkable film and the ink. For example, a primer that can be dissolved or stripped with caustic soda can be applied to the heat-shrinkable film before applying the ink. The primer can facilitate the removal of the ink in a subsequent hot water wash step, as described herein. Additionally, or alternatively, the heat-shrinkable film can be formed into a tube (e.g., to form sleeve 20) and / or cut to a desired size.

[0035] Figure 4 is a schematic diagram of a recycling process 50 that can be used for recycling a heat-shrinkable film (e.g., heat-shrinkable film 10). Process 50 can begin with obtaining a used or residual packaging material 52 that includes the heat-shrinkable film and other recyclable materials such as PET containers or bottles. The residual packaging material 52 is fed to a shredder 54, which can shred, chop, and / or comminute the packaging material 52 to obtain particles 56 of those materials. In various examples, the particles 56 can include particles of the heat-shrinkable film that are at least partially covered with ink.

[0036] The particles 56 are fed to a washer 58, which can wash the particles 56 using a hot water wash process in which the particles 56 are immersed, mixed, and / or scrubbed in a warm liquid bath. The liquid bath can include water, caustic soda (e.g., in an amount of about 0.1 wt% to about 5 wt%), a detergent (e.g., in an amount of about 0.1 wt% to about 3 wt%), and other components (e.g., a defoamer or anti-foaming agent). The liquid bath can have a temperature of about 55°C to about 95°C, or about 85°C. The washer 58 can have a mixing device (e.g., a rotor blade operating at 500 rpm) to mix or agitate the particles 56 in the liquid bath. The output from the washer 58 can include washed particles 60 of the heat-shrinkable film (e.g., having little or no ink) and a stream 62 of ink, dirt, or other contaminants.

[0037] The washed particles 60 can be supplied to an oven or reactor 64, where the particles are heated to a temperature of about 170 °C to about 230 °C (e.g., under reduced pressure) to carry out a drying and solidification process. The drying and solidification process can remove water, crystallize the particles 60, and / or increase the molecular weight of the particles 60. The reactor 64 can produce treated particles 66, and the treated particles 66 can be used to form recycled products such as new heat-shrinkable films, containers, etc. In certain embodiments, the oven or reactor 64 can include a plurality of ovens or reactors and / or the washed particles 60 can be processed in two or more stages, which can include, for example, (i) a drying and crystallization stage, and (ii) a solidification stage. The drying and crystallization stage can be carried out at a temperature from about 130 °C to about 190 °C for up to about 180 minutes. The drying and crystallization stage can be carried out at atmospheric pressure or under reduced pressure. The solidification stage can be carried out at a temperature from about 170 °C to about 230 °C for about 90 minutes or more to achieve the desired molecular weight. The solidification stage can be carried out under reduced pressure (e.g., below atmospheric pressure) and / or in a nitrogen environment to avoid oxidation.

[0038] As described herein, in some examples, the high temperatures within reactor 64 may cause particles 60 to become sticky, which may cause particles 60 to bind to each other or to other materials (e.g., PET bottle flakes) and form agglomerates. The formation of agglomerates can potentially clog filters or screens and / or form bridges that impede proper flow of materials through recycling process 50. Advantageously, compared to conventional low shrink-force heat-shrinkable films, the heat-shrinkable films described herein (e.g., film 10) are less likely to become sticky and / or less likely to form agglomerates during recycling process 50, thus improving the recyclability of the film. For example, the particles of the heat-shrinkable films described herein may not melt and / or may not become tacky or sticky even when exposed to the temperatures and pressures within an oven or reactor 64. In various examples, the heat-shrinkable films described herein are formulated to resist adhesion to other materials when heated to a temperature of about 170°C to about 230°C, or about 210°C.

[0039] The heat-shrinkable film described in this specification is characterized by a unique amount of heat shrinkage. The shrinkage rate, as used herein, is the percent shrinkage in the Machine direction or "MD", which is the direction in which the film is stretched on the roller after extrusion, and the Transverse direction or "TD", also called the major shrinkage direction, since the film mainly shrinks in the TD direction when heated after being formed. In contrast to conventional heat-shrinkable films, when the TD shrinkage rate of the film described in this specification is plotted as a function of temperature, the resulting curve, herein referred to as the "TD shrink rate-temperature curve", is more linear. In embodiments, when performing a linear regression analysis on such a TD shrink rate-temperature curve for temperatures between 60 °C and 95 °C, the resulting Pearson correlation coefficient squared is greater than 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, or 0.99.

[0040] Furthermore, the slope of the TD shrink rate-temperature curve of embodiments of the film described in this specification is generally lower than that of conventional shrinkable films, and preferably less than 2.0 at every 5 °C interval between 65 °C and 95 °C.

[0041] In embodiments, the heat-shrinkable film described in this specification is characterized in that the heat shrinkage rate in the major shrinkage direction when held in water at 65 °C for 10 seconds is 0.25% to 1.0%.

[0042] In embodiments, the heat-shrinkable film described in this specification is characterized in that the heat shrinkage rate in the major shrinkage direction when held in water at 70 °C for 10 seconds is 3.0% to 5.0%.

[0043] In embodiments, the heat-shrinkable film described in this specification is characterized in that the heat shrinkage rate in the major shrinkage direction when held in water at 75 °C for 10 seconds is 11% to 15%.

[0044] In an embodiment, the heat-shrinkable film described in this specification is characterized in that the heat shrinkage rate in the main shrinkage direction is 15% - 25% when held in water at a temperature of 80°C for 10 seconds.

[0045] In an embodiment, the heat-shrinkable film described in this specification is characterized in that the heat shrinkage rate in the main shrinkage direction is 25% - 35% when held in water at a temperature of 85°C for 10 seconds.

[0046] In an embodiment, the heat-shrinkable film described in this specification is characterized in that the heat shrinkage rate in the main shrinkage direction is 25% - 45% when held in water at a temperature of 90°C for 10 seconds.

[0047] In an embodiment, the heat-shrinkable film described in this specification is characterized in that the heat shrinkage rate in the main shrinkage direction is 40% - 50% when held in water at a temperature of 95°C for 10 seconds.

Example

[0048] [Example - Shrinkage of Film in Water] The water bath shrinkage test is used as a standard type for quantifying shrinkage performance in the industry. A typical test is conducted in an isothermal water bath at 50°C - 100°C, and the residence time is 10 seconds - 1 minute depending on the application. The tests and opinions described below relate to the water bath shrinkage test performance of the embodiments described in this specification compared with commercially available PETG and PVC films. The water bath shrinkage performance characteristics were tested at both 30-second and 10-second residence times using the industry standard water bath test method (ASTM D - 2732).

[0049] The shrinkage rate - temperature curves in the TD direction and MD direction at a water bath temperature of 65°C to 95°C, in 5°C increments, and residence times of 30 seconds and 10 seconds are shown in FIGS. 5 and 6, respectively. The data are shown for two examples of a PVC film, a PETG film, and a film according to the embodiments described herein. The data were averaged and fitted with a linear trend line and correlation coefficient. Comparing the new film to the provision of a standard film, it can be seen that the shrinkage curve is significantly more linear in the shrinkage behavior, as seen in a higher R 2 value, i.e., a correlation coefficient of 0.93 or greater. The shrinkage curves of PVC and PETG also have higher gradient values than the curves of the film embodiments described herein, and these curves have a gradient in the TD or main shrinkage direction of less than 2.0 in 5°C increments. The rate of increase of the thermal shrinkage rate in the TD direction in the temperature range of 0.35×Tm°C to 0.40×Tm°C is 1% / °C to 4% / °C, and the rate of increase in the temperature range of 0.45×Tm°C to 0.50×Tm°C is 0.30% / °C to 0.70% (where Tm is the melting temperature of the film).

[0050] [Example - Film Shrinkage in Air] Compared with the tests in water bath, the test data using the modified ISO14616 test method show better consistency with the decoration performance of the film in a hot air / drying tunnel. The hot air shrinkage test was carried out using a conventional hot air shrinkage force tester, which inserts up to six individually prepared film samples into a controlled hot air environment and monitors the film shrinkage characteristics such as film shrinkage and shrinkage force over time to create a shrinkage curve. The shrinkage value is represented as a percentage value, and the shrinkage force is represented in Newtons (N). Continuous data are collected approximately every 0.3 - 0.4 seconds for each individual test station. The data collection method was changed so that the time when the sample starts to move into the heating chamber is set as t = 0 s instead of when the sample is completely immersed in the heating chamber. This change was necessary to identify the material behavior at high temperatures where the sample has to start shrinking before being completely immersed. In the following graph, t = 6 s is approximately the time when the sample is completely immersed in the heating chamber. The tests were carried out at a number of temperatures from 85 °C to 125 °C to better characterize the performance variations observed in downstream hot air / heat tunnel applications. The data collected in this test were subjected to point-to-point differential calculation with respect to time to characterize the shrinkage as an instantaneous shrinkage speed / velocity and were calculated as (S2 - S1) / (t2 - t1) (where t1 and t2 are time 1 and time 2 respectively, and S1 and S2 are the shrinkage percentages at t1 and t2 respectively). Next, the shrinkage speeds of individual stations were averaged over all samples to obtain a curve of the average shrinkage speed for each material.

[0051] Figure 7 is a graph of the shrinkage speed as a function of time at 85 °C in air for a PVC film, a PETG film, and an example film according to the embodiments described herein. Among these films, the standard PETG film had the highest peak shrinkage speed and the steepest slope of the curve (corresponding to shrinkage acceleration). This indicates that the film shrinks rapidly compared to the PVC film and the film according to the embodiments described herein.

[0052] Figure 8 is a graph of the shrinkage rate of a PVC film, a PETG film, and an example film according to the embodiments described herein as a function of time at 105° C. in air. The shrinkage rates experienced by all films were higher than at 85° C. The behavior of a standard PVC film appears to be similar to that of a PETG film, although the PETG film starts to shrink slightly earlier and the gradient value is slightly lower. The film according to the embodiments described herein has a relatively low and stable shrinkage rate comparable to standard PVC when tested at 85° C. As the test temperature increases, the shrinkage rate curve of the shrink film becomes higher and steeper, meaning that the decorative window for successful applications becomes narrower.

[0053] [Terms] The phraseology and terminology used herein are for illustrative purposes and should not be regarded as limiting.

[0054] As used herein in the specification and claims, the terms "approximately", the phrase "approximately equal to", and other similar phrases (e.g., "X has a value of approximately Y" or "X is approximately equal to Y") are to be understood to mean that a value (X) is within a predetermined range of another value (Y). The predetermined range can be, unless otherwise specified, plus or minus 20%, 10%, 5%, 3%, 1%, 0.1%, or less than 0.1%.

[0055] As used in this specification and the claims, the indefinite articles "a" and "an" should be understood to mean "at least one" unless clearly indicated otherwise. The phrase "and / or" as used in this specification and the claims is to be understood to mean "either or both" of the elements so joined, i.e., elements that may be present conjunctively in some cases and disjunctively in other cases. Multiple elements listed together with "and / or" are to be construed in the same manner, i.e., to mean "one or more" of the elements so joined. Other elements may optionally be present, whether or not they are specifically related to the elements specifically identified by the "and / or" clause. Thus, by way of non-limiting example, reference to "A and / or B", when used in combination with open-ended language such as "comprising", may in one embodiment refer to only A (optionally including elements other than B), in another embodiment refer to only B (optionally including elements other than A), and in yet another embodiment refer to both A and B (optionally including other elements), and so on.

[0056] As used in this specification and the claims, "or" shall be understood to have the same meaning as "and / or" as defined above. For example, when separating items in a list, "or" or "and / or" shall be construed as inclusive, i.e., including at least one of the number of elements or items in the list, but more than one, and optionally, further including items not listed. Terms that clearly indicate the contrary, such as "only one of", "exactly one of", or when used in the claims, "consisting of", shall refer to including exactly one of the number of elements or items in the list. Generally, the term "or" shall indicate an exclusive alternative (i.e., "one or the other but not both") only when preceded by terms indicating exclusivity such as "either", "one of", "only one of", "exactly one of". "Consisting essentially of" shall have its ordinary meaning as used in the field of patent law when used in the claims.

[0057] As used in this specification and the claims, the phrase "at least one" in reference to a list of one or more elements should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but need not necessarily include at least one of each and every element specifically recited in the list of elements, nor does it exclude any combinations of elements in the list of elements. This definition also allows that elements other than those specifically identified in the list of elements referred to by the phrase "at least one" may optionally exist, whether or not they are related to the specifically identified elements. Thus, by way of non-limiting example, "at least one of A and B" (or equivalently, "at least one of A or B", or equivalently, "at least one of A and / or B") can, in one embodiment, refer to at least one, optionally including more than one, A where B does not exist (and optionally including elements other than B), in another embodiment can refer to at least one, optionally including more than one, B where A does not exist (and optionally including elements other than A), and in yet another embodiment can refer to at least one, optionally including more than one, A and at least one, optionally including more than one, B (and optionally including other elements), etc.

[0058] The use of "including", "comprising", "having", "containing", "involving", and variations thereof means including the items listed thereafter and additional items.

[0059] In the claims, the use of ordinal numbers such as "first", "second", "third", etc. to modify claim elements does not in itself mean the priority, precedence, order, or temporal order in which acts of a method are performed with respect to other claim elements of a claim element. The ordinal numbers are used only as labels to distinguish a claim element having a certain name from another element having the same name (except for the use of the ordinal terms) for the purpose of distinguishing claim elements.

[0060] In this specification, for example, each numerical value shown in a table, chart, or graph is intended to represent the minimum or maximum value within the range of the corresponding parameter. Thus, when adding to the claims, the numerical value provides an explicit basis for claiming the range that may be above or below the numerical value in accordance with the teachings of this specification. For the numerical ranges described in this specification, various embodiments include any parameter value (e.g., an integer value or a decimal value) within the described range. For example, if the described range is 1 to 10, the value of each parameter can be greater than, less than, or equal to 1, 2, 3,..., or 10. Unless otherwise recited in the claims, each numerical value presented in this specification is not to be considered limiting in any way.

[0061] The terms and expressions used in this specification are used as terms and expressions for explanation and are not meant to be limiting. In using such terms and expressions, there is no intention to exclude equivalents of the features shown and described or a part thereof. In addition, although specific embodiments of the present invention have been described, it will be apparent to those skilled in the art that other embodiments incorporating the concepts disclosed herein may be used without departing from the spirit and scope of the present invention. The features and functions of various embodiments can be arranged in various combinations and permutations, all of which are considered to be within the scope of the disclosed present invention. Accordingly, the described embodiments are considered to be illustrative in all respects and not restrictive. Furthermore, the configurations, materials, and dimensions described herein are intended for illustration and are in no way limiting. Similarly, although a physical explanation has been given for the purpose of illustration, there is no intention to be bound by a specific theory or mechanism, nor is there any intention to limit the scope of the claims accordingly.

Claims

1. A heat-shrinkable film comprising a copolyester including a diol component and a dicarboxylic acid component, the diol component is at least one selected from the group consisting of ethylene glycol, diethylene glycol, neopentyl glycol, propylene glycol, polyethylene glycol, tetraethylene glycol, and cyclohexanedimethanol; the dicarboxylic acid component is at least one selected from the group consisting of isophthalic acid and terephthalic acid, 60 to 90 mol % of the copolyester is amorphous; The film is characterized by a heat shrinkage curve corresponding to the shrinkage in the main shrink direction as a function of a 10 second temperature hold; The heat shrinkage curve has a slope of less than 2.0 at all 5° C. increments from 65° C. to 95° C.

2. 10. The heat shrinkable film of claim 1, wherein the heat shrink curve is characterized by a squared Pearson correlation coefficient of at least 0.95 from 60°C to 95°C.

3. 2. The heat shrinkable film according to claim 1, wherein the heat shrinkage percentage in the main shrinkage direction when held at 65° C. for 10 seconds is a maximum of 1.0%.

4. 2. The heat shrinkable film according to claim 1, wherein the heat shrinkage rate in the main shrinkage direction when held at 70° C. for 10 seconds is 3.0% to 5.0%.

5. 2. The heat shrinkable film according to claim 1, wherein the heat shrinkage rate in the main shrinkage direction when held at 75° C. for 10 seconds is 11% to 15%.

6. 2. The heat shrinkable film according to claim 1, wherein the heat shrinkage rate in the main shrinkage direction when held at 80° C. for 10 seconds is 15% to 25%.

7. 2. The heat shrinkable film according to claim 1, wherein the heat shrinkage rate in the main shrinkage direction when held at 85° C. for 10 seconds is 25% to 35%.

8. 2. The heat shrinkable film according to claim 1, wherein the heat shrinkage rate in the main shrinkage direction when held at 90° C. for 10 seconds is 25% to 45%.

9. 2. The heat shrinkable film according to claim 1, wherein the heat shrinkage rate in the main shrinkage direction when held at 95° C. for 10 seconds is 40% to 50%.

10. 2. The heat shrinkable film of claim 1, wherein the film comprises an A-B-A layer structure comprising a surface A layer and a core B layer.

11. 10. The heat shrinkable film of claim 1, wherein the film has a glass transition temperature of up to 80°C.

12. 2. The heat shrinkable film of claim 1, wherein the diol component comprises 50 to 85 mol % ethylene glycol.

13. 2. The heat shrinkable film of claim 1, wherein the diol component comprises 10 to 30 mol % cyclohexanedimethanol.

14. 2. The heat shrinkable film according to claim 1, wherein the diol component comprises 5 to 25 mol % diethylene glycol.

15. 2. The heat shrinkable film according to claim 1, wherein the dicarboxylic acid component comprises 99 to 100 mol % terephthalic acid.

16. The heat shrinkable film according to claim 15, wherein the dicarboxylic acid component comprises 0.05 to 0.8 mol % of isophthalic acid.

17. 2. The heat shrinkable film according to claim 1, having a shrinkage stress of less than 9.0 MPa at 85°C.

18. 18. The heat shrinkable film according to claim 17, characterized in that the shrinkage rate is up to 10% per second at 85°C.

19. 2. The heat shrinkable film according to claim 1, wherein the molecular orientation angle in the main shrinkage direction is a maximum of 2.0°.

20. 20. The heat shrinkable film according to claim 19, wherein the molecular orientation angle in the main shrinkage direction is a maximum of 1.5°.

21. A heat-shrinkable film comprising a copolyester including a diol component and a dicarboxylic acid component, the diol component is at least one selected from the group consisting of ethylene glycol, diethylene glycol, neopentyl glycol, propylene glycol, polyethylene glycol, tetraethylene glycol, and cyclohexanedimethanol; the dicarboxylic acid component is at least one selected from the group consisting of isophthalic acid and terephthalic acid, 60 to 90 mol % of the copolyester is amorphous; The film is characterized by a heat shrinkage curve corresponding to the shrinkage in the main shrink direction as a function of a 10 second temperature hold; A heat shrinkable film, wherein said heat shrink curve is characterized by a squared Pearson correlation coefficient of at least 0.95 at temperatures between 60°C and 95°C.

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