Polyester copolymer, shrinkable film, and manufacturing method therefor

Abstract

The present invention relates to: a polyester copolymer capable of being stretched at a relatively low temperature and providing a shrinkable film exhibiting a higher shrinkage rate in the TD direction; a shrinkable film comprising same; and a manufacturing method therefor.

Description

Polyester copolymer, shrink film and method for producing the same

[0001] Cross-citation with related application(s)

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2024-0048557, filed April 11, 2024, the entire contents of which are incorporated herein by reference.

[0003] The present invention relates to a polyester copolymer capable of providing a shrink film that is stretchable at a relatively low temperature and exhibits a higher shrinkage ratio in the width direction, a shrink film comprising the same, and a method for producing the same.

[0004] Shrink films, which shrink by heat, are used for applications such as labels and packaging containers for plastics, glass bottles, batteries, or electrolytic capacitors, shrink wrapping, and shrink labels. Polyvinyl chloride (PVC), polystyrene, or polyester films are used as such shrink films.

[0005] However, films made of polyvinyl chloride are classified as subject to environmental regulations because they generate substances that cause hydrogen chloride gas and dioxin when incinerated, and when the film is used as a shrink label for PET containers, there is the inconvenience of having to separate the label and container when collecting them in order to recycle the container.

[0006] Polystyrene films offer excellent workability during shrinkage processes and a pleasing product appearance. However, their poor chemical resistance necessitates the use of special ink formulations for printing. Furthermore, they lack room-temperature storage stability, leading to dimensional changes and spontaneous shrinkage.

[0007] Accordingly, as the use of PET containers increases, the use of shrink films manufactured from polyester resins that do not require a separate label separation process during recycling is increasing, while not having the environmental and chemical resistance issues of the aforementioned polyvinyl chloride (PVC) and polystyrene films.

[0008] Such polyester shrink film can be manufactured, for example, by melt-extruding a polyester resin at a temperature higher than its melting point, and then stretching the melt-extruded product in the transverse direction (TD direction) at a temperature higher than the glass transition temperature of the resin.

[0009] Regarding these transverse direction (TD) stretching conditions, in the past, in order to suppress fracture and stretching unevenness during stretching, it was common to conduct stretching at a temperature about 10℃ higher than the inherent glass transition temperature of the polyester resin (e.g., the second glass transition temperature, Tg2, measured during the second heating process in DSC analysis). However, this high-temperature stretching process caused limitations in the stretching conditions for manufacturing polyester shrinkable films, a decrease in the energy efficiency of the entire process, and a decrease in the shrinkage rate in the transverse direction. To overcome this, a method of adding a large amount of copolymerization monomer was used in the past, but this has the disadvantage of reducing the crystallinity of the polyester, making the recycling process with PET difficult.

[0010] Accordingly, there is a continuous demand for the development of technology for a manufacturing process of a polyester resin or a shrink film using the same that can provide a shrink film that can be stretched at a relatively low temperature, thus exhibiting excellent stretching processability and high energy efficiency, as well as a higher shrinkage ratio in the width direction.

[0011] Accordingly, the present invention provides a polyester copolymer that is stretchable at a lower temperature, enabling the production of a shrink film by stretching in a wider range in the width direction, and enabling the production of a shrink film exhibiting a higher shrinkage ratio in the width direction.

[0012] The present invention also provides a shrink film comprising the polyester copolymer, which can be manufactured at a lower temperature with high energy efficiency and exhibits an excellent shrinkage ratio in the width direction, and a method for manufacturing the same.

[0013] Accordingly, the present invention comprises a residue of a dicarboxylic acid component including an aromatic dicarboxylic acid; and

[0014] A polyester copolymer comprising residues of a diol component including ethylene glycol and diethylene glycol,

[0015] At least one of the residues of the above dicarboxylic acid component and the residues of the above diol component comprises a residue having a cycloalkyl group or a branched residue,

[0016] A polyester copolymer is provided in which, when analyzing a non-stretched film obtained by melt-extruding the polyester copolymer, the first glass transition temperature (Tg1) measured in the first heating process is 2°C or more lower than the second glass transition temperature (Tg2) measured in the second heating process after cooling.

[0017] The present invention also provides a shrink film comprising the polyester copolymer.

[0018] In addition, the present invention comprises a step of melt-extruding the polyester copolymer of the present invention at a temperature of 200°C or more and 300°C or less; and

[0019] A method for producing a shrink film is provided, comprising the step of stretching the molten extrudate in the transverse direction (TD direction) at a temperature that is 5°C lower than the second glass transition temperature and 15°C higher than the second glass transition temperature.

[0020]

[0021] Hereinafter, a polyester copolymer, a shrink film comprising the same, and a method for producing the same according to specific embodiments of the invention will be described in more detail. First, several terms will be defined as follows.

[0022] First, unless otherwise specified herein, terminology is used solely for the purpose of describing specific embodiments and is not intended to limit the invention. In addition, unless the context clearly dictates otherwise, singular forms include plural forms. As used herein, the word "comprising" specifies a particular feature, region, integer, step, operation, element, and / or component, but does not exclude the presence or addition of other specific features, regions, integers, steps, operations, elements, components, and / or groups.

[0023] Additionally, in the present specification, the term 'residue (of a component such as a dicarboxylic acid or diol)' means a certain portion or unit derived from a specific component (compound) and included in the result of a chemical reaction when the specific component (compound) participates in the chemical reaction. Specifically, the 'residue' of the dicarboxylic acid component or the 'residue' of the diol component, respectively, means a portion derived from the dicarboxylic acid component or a portion derived from the diol component in a polyester copolymer formed by an esterification reaction or a condensation polymerization reaction.

[0024]

[0025] Meanwhile, a polyester copolymer according to one embodiment of the invention is a polyester copolymer comprising a residue of a dicarboxylic acid component including an aromatic dicarboxylic acid; and a residue of a diol component including ethylene glycol and diethylene glycol.

[0026] At least one of the residues of the above dicarboxylic acid component and the residues of the above diol component comprises a residue having a cycloalkyl group or a branched residue,

[0027] In the DSC analysis of the unstretched film obtained by melt-extruding the above polyester copolymer, the first glass transition temperature (Tg1) measured in the first heating process has a value that is 2℃ or more lower than the second glass transition temperature (Tg2) measured in the second heating process after cooling.

[0028] The inventors of the present invention continued their research to develop a polyester resin for shrinkable films that is stretchable from a temperature close to or lower than the glass transition temperature and exhibits a higher shrinkage ratio in the width direction.

[0029] In this continuous research process, the inventors have basically discovered that a polyester copolymer manufactured using an aromatic dicarboxylic acid component such as terephthalic acid and a diol component, wherein ethylene glycol and diethylene glycol are used as the diol component, and a component having a cycloalkyl group and / or a branched component as part of the dicarboxylic acid and diol components, and wherein the contents of residues derived from these components and diethylene glycol respectively satisfy a certain relationship, can provide a polyester copolymer whose first glass transition temperature (Tg1) measured in an unstretched film state obtained by melt-extruding the copolymer is 2°C or more lower than its second glass transition temperature (Tg2), thereby completing the invention.

[0030] At this time, the first glass transition temperature (Tg1) and the second glass transition temperature (Tg2) are thermal properties derived from the DSC analysis process of the unstretched film melt-extruded from the polyester copolymer, respectively. For example, the first glass transition temperature (Tg1) corresponds to the glass transition temperature derived from the first temperature increase peak measured and confirmed in the first temperature increase process during the DSC analysis, and the second glass transition temperature (Tg2) corresponds to the glass transition temperature derived from the second temperature increase peak measured and confirmed in the additional second temperature increase process after the first temperature increase and decrease. In addition, with respect to polyester resins or copolymers, the second glass transition temperature is generally defined as the glass transition temperature unique to each resin or copolymer.

[0031] In particular, since the second glass transition temperature (Tg2) has a value that is 2°C or higher than the first glass transition temperature (Tg1), the width direction stretching can be performed at a wider temperature ranging from a temperature that is substantially the same as or lower than the second glass transition temperature corresponding to the unique glass transition temperature of the copolymer of one embodiment to a temperature that is about 15°C higher than the second glass transition temperature (i.e., a temperature ranging from Tg2-5(°C) to Tg2+15(°C)), and in particular, it was confirmed that the width direction stretching can be performed well from the above-mentioned low temperature, so that a shrink film having a high width direction shrinkage ratio can be manufactured.

[0032] Therefore, when applying the polyester copolymer according to this embodiment, the temperature range for stretching is expanded starting from a lower temperature, so not only is the manufacturing process of the shrink film excellent, but the energy efficiency of the process can also be improved. Furthermore, since a shrink film having a high shrinkage ratio in the width direction can be manufactured using the copolymer according to this embodiment, such a shrink film can be very preferably used for labels for various containers, etc.

[0033] Meanwhile, unlike the copolymer of one embodiment, if the copolymer does not contain a residue having a cycloalkyl group or a branched residue, or if the contents of these residues and diethylene glycol residues do not satisfy a certain relationship described below, it was confirmed that the first glass transition temperature (Tg1) becomes higher than the second glass transition temperature (Tg2), or the first and second glass transition temperatures become substantially the same. In this case, it is necessary to conduct stretching at a temperature sufficiently higher than not only the second glass transition temperature but also the first glass transition temperature, for example, at least 8°C or 10°C higher than Tg2, and it was confirmed that at a lower stretching temperature, unevenness or breakage of stretching may occur, so that the shrink film cannot be properly manufactured, or the shrinkage ratio in the width direction of the shrink film may be insufficient.

[0034] In contrast, when using a copolymer of one embodiment, stretching can be performed well without occurrence of breakage or stretching unevenness in a lower and wider temperature range, and through such stretching process, a shrink film exhibiting a high widthwise shrinkage ratio can be manufactured.

[0035] Dicarboxylic acid components

[0036] In the copolymer of the above embodiment, the dicarboxylic acid component refers to a main monomer that constitutes a polyester copolymer together with a diol component, and the residue of the dicarboxylic acid component may refer to a unit derived from a monomer of the dicarboxylic acid component and remaining in the copolymer.

[0037] In the polyester copolymer of the above embodiment, the dicarboxylic acid component and its residues may include 70 mol% or more, or 80 mol% or more, or 90 mol% or more and 100 mol% or less of terephthalic acid and its residues, based on 100 mol% of the total. By virtue of the residues of terephthalic acid and the high content thereof, the basic physical properties of the polyester copolymer, such as heat resistance, chemical resistance, and weather resistance, may be improved.

[0038] The above dicarboxylic acid component may further include, in addition to terephthalic acid, an aromatic dicarboxylic acid component, an alicyclic dicarboxylic acid component, an aliphatic dicarboxylic acid component, or a mixture thereof. In this case, the dicarboxylic acid component other than terephthalic acid may be included in an amount of 20 mol% or less, or 15 mol% or less, or 10 mol% or less, based on 100 mol% of the total dicarboxylic acid component.

[0039] At this time, examples of the additional dicarboxylic acid component include at least one selected from the group consisting of dimethyl terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, diphenyl dicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, sebacic acid, succinic acid, isodecylsuccinic acid, maleic acid, maleic anhydride, fumaric acid, adipic acid, glutaric acid, azelaic acid, 4,4'-stilbenedicarboxylic acid, 2,5-furandicarboxylic acid, 2,5-thiophenedicarboxylic acid, regenerated isophthalic acid, regenerated terephthalic acid, etherified derivatives thereof, and esterified derivatives thereof, and various dicarboxylic acids known to be usable for producing other polyester copolymers can be used.

[0040] Meanwhile, the copolymer of the above embodiment may further include a dicarboxylic acid residue having a cycloalkyl group and / or a branched dicarboxylic acid residue as the residue of the dicarboxylic acid component. By including these residues, the elongation properties and shrinkage in the width direction of the polyester copolymer may be further improved.

[0041] Specific examples of dicarboxylic acids and branched dicarboxylic acids having such cycloalkyl groups include carboxylic acids having a cycloalkyl group having 4 to 16 carbon atoms or a branched alkyl group having 3 to 10 carbon atoms, and more specific examples include at least one selected from the group consisting of cyclohexane dicarboxylic acid, hydroxycyclohexane carboxylic acid, and etherified derivatives and esterified derivatives thereof.

[0042] In a specific embodiment, the copolymer of one embodiment may primarily comprise residues derived from cyclohexane dicarboxylic acid or the like, together with residues of an aromatic dicarboxylic acid such as terephthalic acid, so as to enable the production of a shrink film having first and second glass transition temperatures satisfying the relationships described above, being stretchable at a wider temperature, and having an improved widthwise shrinkage ratio.

[0043] Dior ingredients

[0044] Meanwhile, in the polyester copolymer of the above-described embodiment, the diol component refers to a main monomer that constitutes the polyester copolymer together with the above-described dicarboxylic acid component, and the residue of the diol component may refer to a unit derived from the monomer of the diol component and remaining in the copolymer.

[0045] In the polyester copolymer of the above embodiment, the diol component and its residues may basically include residues derived from ethylene glycol and diethylene glycol.

[0046] In addition, the copolymer of the above embodiment may further include a diol residue having a cycloalkyl group and / or a branched diol residue, together with the residues of ethylene glycol and diethylene glycol. By including these residues, the elongation properties and shrinkage ratio in the width direction of the polyester copolymer may be further improved.

[0047] Specific examples of such diols and branched diols having a cycloalkyl group include diols having a cycloalkyl group having 4 to 16 carbon atoms or a branched alkyl group having 3 to 10 carbon atoms, and more specific examples include at least one selected from the group consisting of cyclohexane dimethanol, 1,2-cyclohexanediol, 1,4-cyclohexanediol, neopentylglycol, 2-methyl-1,3-propanediol, 2-methylene-1,3-propanediol, 2-ethyl-1,3-propanediol, 2-isopropyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 3-methyl-2,4-pentanediol, and etherified derivatives and esterified derivatives thereof.

[0048] Additionally, the copolymer of the above embodiment may further comprise, as an additional diol residue, a residue of an alicyclic diol, such as an isosorbide residue.

[0049] In addition, the copolymer of the above embodiment can be produced using an additional diol component, for example, an additional chain diol component, in addition to the ethylene glycol, diethylene glycol, diol having a cycloalkyl group, and / or branched diol component described above, within a range satisfying the relationship of Formula 1 described below. Examples of such diols are not particularly limited, and diols having an alkyl group having 3 to 8 carbon atoms, etc. can be used without particular limitation. Specific examples of such additional diol components include at least one selected from the group consisting of bis-2-hydroxyethyl terephthalate, isosorbide, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 2,3-butanediol, 1,6-hexanediol, 4-(hydroxymethyl)cyclohexylmethyl 4-(hydroxymethyl)cyclohexanecarboxylate, 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol, recycled cyclohexanedimethanol, recycled ethylene glycol, recycled bis-2-hydroxyethyl terephthalate, recycled diethylene glycol, etherified derivatives thereof, and esterified derivatives thereof.

[0050] Meanwhile, the polyester copolymer of the above-described embodiment is a polyester copolymer in which the sum of the content of the dicarboxylic acid residue having the cycloalkyl group and the branched dicarboxylic acid residue based on 100 mol% of the total dicarboxylic acid residues included therein and the content of the diol residue having the cycloalkyl group and the branched diol residue based on 100 mol% of the total diol residues is x (mol%),

[0051] When the content of the diethylene glycol residue is y (mol%) based on 100 mol% of the total diol residue, it is preferable to satisfy the relationship of the following equation 1:

[0052] [Formula 1]

[0053] 20 ≤ 1.23 * x (mol%) + 0.82 * y (mol%) ≤ 45

[0054]

[0055] The copolymer of one embodiment satisfying the relationship of the above Equation 1 can have optimized contents of each of the diethylene glycol residue, the residue having a cycloalkyl group, and the branched residue included therein. As a result of optimizing these contents, it was confirmed that the copolymer of one embodiment, in a melt-extruded, unstretched film state, can satisfy optimized thermal properties in which the second glass transition temperature (Tg2) is 2℃ or higher than the first glass transition temperature (Tg1). Therefore, the copolymer of one embodiment satisfying the relationship of the above Equation 1 can be well stretched in the width direction without causing fracture or uneven stretching in a wide temperature range from a temperature similar to or lower than Tg2 to a temperature 15℃ higher than Tg2. In addition, through this stretching process, a shrinkable film exhibiting an improved shrinkage ratio at high temperatures can be provided.

[0056] In order for the copolymer of the above embodiment to more appropriately satisfy more desirable thermal properties, for example, thermal properties in which Tg2 becomes higher than Tg1, the total content defined by x+y (mol%), i.e., the sum x (mol%) of the content of the dicarboxylic acid residue having the cycloalkyl group and the branched dicarboxylic acid residue based on 100 mol% of the total dicarboxylic acid residues, and the content of the diol residue having the cycloalkyl group and the branched diol residue based on 100 mol% of the total diol residues,

[0057] The total sum of the content y (mol%) of the diethylene glycol residues based on 100 mol% of the total diol residues can be 15 to 40 mol%, 16 to 39 mol%, or 20 to 40 mol%.

[0058] In this way, the elongation properties of the copolymer and the shrinkage ratio in the width direction of the shrink film manufactured therefrom can be further improved.

[0059] According to a more specific example of the copolymer of the above-described embodiment, the residue of the dicarboxylic acid component comprises 90 to 100 mol% of the aromatic dicarboxylic acid residue and 10 mol% or less, or 0 to 10 mol%, of the dicarboxylic acid residue having the cycloalkyl group or the branched dicarboxylic acid residue, based on the total 100 mol% thereof.

[0060] The residue of the diol component may include 60 to 85 mol% of the ethylene glycol residue, 1 to 25 mol% of the diethylene glycol residue, and 35 mol% or less, or 0 to 33 mol%, of the diol residue having the cycloalkyl group or the branched diol residue, based on 100 mol% of the total.

[0061] Within the content range of each of these residues, as the content of the residue derived from a monomer having a diethylene glycol, a cycloalkyl group, or a branched structure is adjusted to satisfy the above formula 1, etc., the copolymer of the above embodiment can satisfy more desirable glass transition temperature characteristics, and further, it can be possible to provide a shrink film that satisfies more improved widthwise shrinkage ratio and other mechanical and thermal properties.

[0062] polyester copolymer

[0063] As described above, the polyester copolymer of one embodiment can satisfy thermal properties in which the first glass transition temperature (Tg1) of an unstretched film obtained by melt-extruding the copolymer is lower than the second glass transition temperature (Tg2) by 2°C or more, or by 2 to 10°C, or by 2 to 8°C, or by 2.5 to 8°C, or by 3 to 7.5°C, by including residues of a dicarboxylic acid and / or diol component in a specific composition.

[0064] At this time, the first glass transition temperature (Tg1) and the second glass transition temperature (Tg) are thermal properties derived from the DSC analysis process of the unstretched film melt-extruded from the polyester copolymer, respectively. For example, the first glass transition temperature (Tg1) corresponds to the glass transition temperature derived from the first temperature increase peak measured and confirmed in the first temperature increase process during the DSC analysis, and the second glass transition temperature (Tg2) corresponds to the glass transition temperature derived from the second temperature increase peak measured and confirmed in the additional second temperature increase process after the first temperature increase and temperature decrease. The temperature increase and temperature decrease conditions during the DSC analysis can follow the DSC analysis conditions of general polyester resins, and are specifically summarized in the examples described below.

[0065] In a more specific example, the first glass transition temperature (Tg1) may be 55 to 85°C, or 57 to 83°C, and the second glass transition temperature (Tg2) may be 60 to 90°C, or 60 to 88°C. As a result, the copolymer may exhibit better stretching processability, etc., and it becomes possible to manufacture a shrink film exhibiting superior mechanical and thermal properties.

[0066] Meanwhile, the polyester copolymer of the above-described embodiment can be produced by copolymerizing the above-described dicarboxylic acid component and diol component. In this case, the copolymerization can be performed sequentially through an esterification reaction and a polycondensation reaction.

[0067] The above esterification reaction is carried out in the presence of an esterification reaction catalyst, and an esterification reaction catalyst including a zinc-based compound may be used. Specific examples of such zinc-based catalysts include zinc acetate, zinc acetate dihydrate, zinc chloride, zinc sulfate, zinc sulfide, zinc carbonate, zinc citrate, zinc gluconate, or mixtures thereof.

[0068] The above esterification reaction can be carried out at a pressure of 0 to 10.0 kg / cm2 and a temperature of 150 to 300°C. The esterification reaction conditions can be appropriately adjusted depending on the specific characteristics of the polyester to be produced, the ratio of each component, or process conditions. Preferably, the esterification reaction can be carried out at a pressure of 0 to 5.0 kg / cm2, more preferably a pressure of 0.1 to 3.0 kg / cm2; and a temperature of 200 to 300°C, more preferably 240 to 280°C.

[0069] And, the above esterification reaction can be performed in batch or continuous manner, and each raw material can be input separately, but it is preferable to input it in the form of a slurry in which a diol component is mixed with a dicarboxylic acid component. And, a diol component such as isosorbide, which is a solid at room temperature, can be dissolved in water or ethylene glycol and then mixed with a dicarboxylic acid component such as terephthalic acid to make a slurry. Alternatively, a slurry can also be made by mixing a dicarboxylic acid component such as terephthalic acid and other diol components after isosorbide is melted at 60℃ or higher. In addition, water can be additionally added to the mixed slurry to help increase the fluidity of the slurry.

[0070] In addition, the polycondensation reaction may be carried out at a temperature of 150 to 300°C, preferably 200 to 290°C; and a reduced pressure of 600 to 0.01 mmHg, preferably 200 to 0.05 mmHg, more preferably 100 to 0.1 mmHg. By applying the reduced pressure conditions of the polycondensation reaction, glycol, which is a by-product of the polycondensation reaction, can be removed from the system. Accordingly, if the polycondensation reaction is performed outside the reduced pressure condition range of 400 to 0.01 mmHg, the removal of the by-product may be insufficient. In addition, if the polycondensation reaction occurs outside the temperature range of 150 to 300°C, if the polycondensation reaction proceeds below 150°C, the glycol, which is a by-product of the polycondensation reaction, cannot be effectively removed from the system, so that the intrinsic viscosity of the final reaction product decreases, which may deteriorate the properties of the polyester resin produced. In addition, if the reaction proceeds above 300°C, the appearance of the polyester resin produced is likely to turn yellow. In addition, the polycondensation reaction may proceed for a necessary time until the intrinsic viscosity of the final reaction product reaches an appropriate level, for example, for an average residence time of 1 to 24 hours.

[0071] In addition, the polycondensation reaction may use a polycondensation catalyst including a titanium compound, a germanium compound, an antimony compound, an aluminum compound, a tin compound, or a mixture thereof.

[0072] Examples of the titanium-based compounds include tetraethyl titanate, acetyltripropyl titanate, tetrapropyl titanate, tetrabutyl titanate, 2-ethylhexyl titanate, octylene glycol titanate, lactate titanate, triethanolamine titanate, acetylacetonate titanate, ethylacetoacetic ester titanate, isostearyl titanate, titanium dioxide, and the like. Examples of the germanium-based compounds include germanium dioxide, germanium tetrachloride, germanium ethylene glycol, germanium acetate, copolymers using these, or mixtures thereof. Preferably, germanium dioxide can be used, and as such germanium dioxide, both crystalline and amorphous can be used, and glycol-soluble can also be used.

[0073] The polyester copolymer of one embodiment manufactured by the method described above can satisfy a specific relationship between the first and second glass transition temperatures, thereby enabling the provision of a shrink film having an improved shrinkage in the width direction by stretching in the width direction over a wide temperature range from relatively low temperatures.

[0074] According to another embodiment of the invention, a shrink film comprising the copolymer of the above-described embodiment is provided.

[0075] Such shrink films can exhibit a high transverse direction (TD) shrinkage ratio of 50% or more, or 55 to 90%, or 60 to 80%, when treated in water at 95°C for 30 seconds, for example. Therefore, the shrink films can be very preferably used for purposes such as labels for various containers.

[0076] In addition, the shrink film of the other embodiment can be manufactured by stretching in the width direction in a wide temperature range from a temperature relatively similar to or lower than Tg2 to a temperature lower than the melting point, or up to Tg2+15°C, since it is manufactured with the copolymer of one embodiment. For example, such a shrink film can be manufactured by a method including the steps of melt-extruding the polyester copolymer of one embodiment at a temperature higher than the melting point, or higher than 200°C, or higher than 200°C and lower than 300°C; and stretching the melt-extruded product in the width direction (TD direction; Transverse Direction) at a temperature that is 5°C lower than the second glass transition temperature to 15°C higher than the second glass transition temperature, or at a temperature equal to or higher than the second glass transition temperature by 15°C.

[0077] At this time, the widthwise stretching step can be performed at a stretching ratio of 3 to 8 times, similar to a stretching process of a general shrink film.

[0078] These shrink films can be manufactured by stretching in the width direction over a relatively low and wide temperature range without stretching unevenly or breaking, thereby exhibiting excellent processability and process energy efficiency. Furthermore, these shrink films exhibit superior overall properties along with a higher width-wise shrinkage ratio, making them ideal for use as labels for various containers and the like.

[0079] The polyester copolymer according to the present invention described above enables the production of a shrink film by stretching in the width direction over a wide temperature range from a relatively low temperature, compared to conventional polyester resins for producing shrink films.

[0080] Additionally, these shrink films can exhibit improved shrinkage in the width direction. Therefore, these shrink films can be preferably applied as label films for various containers, etc.

[0081] Hereinafter, preferred examples are presented to aid understanding of the present invention. However, the following examples are provided solely to facilitate understanding of the present invention and are not intended to limit the scope of the present invention.

[0082]

[0083] Examples 1 to 10 and Comparative Examples 1 to 5

[0084] The polyester copolymers of the examples and comparative examples were manufactured by the following manufacturing method.

[0085] In a 10 L reactor connected to a column and a condenser that can be cooled by water, each monomer selected from terephthalic acid (TPA), 1,4-cyclohexane dicarboxylic acid (CHDA), 1,4-cyclohexane dimethanol (CHDM), diethylene glycol (DEG), neopentyl glycol (NPG), isosorbide (ISB), or ethylene glycol (EG) was charged so that the compositions and contents shown in Tables 1 and 2 below remained in the 5 L reactor, and a Ti catalyst (0.2 g), phosphoric acid (10.0 g), blue toner (0.005 g), and red toner (0.003 g) were each charged.

[0086] Next, nitrogen was injected into the reactor so that the pressure of the reactor was 1.0 kgf / cm above atmospheric pressure. 2 The reactor was pressurized to a high pressure (absolute pressure: 1495.6 mmHg). Then, the temperature of the reactor was raised to 240℃, and after the pressurization, the temperature of the reactor was raised to 260℃. After that, the mixture inside the reactor was observed with the naked eye, and the esterification reaction was performed until the mixture became transparent. During this process, by-products were discharged through the column and condenser. When the esterification reaction was completed, the nitrogen inside the pressurized reactor was discharged to the outside to lower the pressure of the reactor to normal pressure, and the mixture inside the reactor was transferred to a 7 L reactor capable of vacuum reaction.

[0087] And, the pressure of the reactor was lowered from atmospheric pressure to 5 Torr (absolute pressure: 5 mmHg) over 30 minutes, and at the same time, the temperature of the reactor was raised to 270℃ over 1 hour, and the polycondensation reaction was performed while maintaining the pressure of the reactor below 1 Torr (absolute pressure: 1 mmHg). In the early stage of the polycondensation reaction, the stirring speed is set to high, but as the polycondensation reaction progresses, if the stirring force becomes weak due to the increase in the viscosity of the reactants or the temperature of the reactants rises above the set temperature, the stirring speed can be appropriately adjusted. The polycondensation reaction was performed until the intrinsic viscosity (IV) of the mixture (melt) inside the reactor became 0.70 dl / g. When the intrinsic viscosity of the mixture inside the reactor reached the desired level, the mixture was discharged outside the reactor to be stranded, which was solidified with a cooling liquid and granulated to an average weight of about 12 to 14 mg, thereby obtaining about 5 kg of a polyester resin (copolymer).

[0088] Through the above-described process, polyester copolymers of examples and comparative examples were manufactured, and their physical properties are shown together in Tables 1 and 2 below.

[0089]

[0090]

[0091]

[0092] Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Example 9 Example 10 Residue (mol%) TPA 100.0100.096.5 100.095.996.4 100.0100.0100.0100.0100.0 CHDA 3.5 4.13.6 CHDM 10.010.26.8 9.35.74.9 24.4 10.22.1 DEG 12.114.6 14.8 14.9 16.3 17.0 13.75.3 19.0 23.1 NPG 9.77.1 ISB 2.0 EG 7 7.9 75.2 78.4 75.8 78.0 78.16 1.974.8 73.974.8 DSC (℃) 1st Tg (Tg1)67.364.264.564.462.961.868.973.560.158.32nd Tg(Tg2)71.169.167.969.466.966.671.276.163.862.1Extensibility2nd Tg + 10OOOOOOOOOO2nd Tg + 8OOOOOOOOOO2nd Tg + 6OOOOOOOOOO2nd Tg + 4OOOOOOFractureFractureFractureO2nd Tg + 2FractureOOFractureOO---OExtensibility Temperature(℃)2nd Tg+42nd Tg+22nd Tg+22nd Tg+42nd Tg+22nd Tg+22nd Tg+62nd Tg+62nd Tg+295℃ TD Shrinkage (%) (30sec dipping) 61% 76% 73% 73% 72% 72% 77% 72% 75% 74%

[0093] Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Residue (mol%) TPA 99.8 100.0 100.0 100.0 100.0 CHDA 0.2 CHDM 4.5 8.2 11.7 3 1.3 DEG 10.5 7.6 5.7 11.9 7.5 NPG 32.7 ISB EG 8 5.0 8 4.2 8 2.6 5 6.8 5 9.8 DSC (℃) 1st Tg (Tg1) 72.1 74.9 76.3 72.4 70.8 2nd Tg (Tg2) 72.3 74.7 7.1 72.9 7 1.1 Elongation 2nd Tg + 10 OOO Break O 2nd Tg + 8 Break Break Break- Break 2nd Tg + 6----- 2nd Tg + 4----- 2nd Tg + 2-----Extensible temperature 2nd Tg+102nd Tg+102nd Tg+102nd Tg+102nd Tg+1095℃ TD shrinkage rate (%) (30sec dipping) 47% 48% 59% - 75%

[0094]

[0095] Experimental example

[0096] The physical properties of the copolymers manufactured in the above examples and comparative examples were evaluated as follows, and the results are summarized and presented in Tables 1 and 2 above.

[0097] 1) First and second glass transition temperatures (Tg1, Tg2):

[0098] A polyester copolymer was extruded through a die at a temperature of 230°C to 290°C, and then cooled to 20°C to 50°C to produce an unstretched film, which was used as a sample. A differential scanning calorimeter (DSC, DSC 1 from Mettler Toledo) was filled with the sample (resin), and the glass transition temperature (Tg1) was obtained from the heat flow obtained while heating at 10°C / min to 280°C, and then maintained at 280°C for 5 minutes, cooled to 30°C at -300°C / min, and then heated at 10°C / min to 280°C, and the glass transition temperature (Tg2) was obtained from the heat flow obtained.

[0099]

[0100] 2) Evaluation of ductility:

[0101] A polyester copolymer was extruded through a die at a temperature of 230°C to 290°C and then cooled to 20°C to 50°C to produce an unstretched film. Thereafter, the unstretched film was kept at 65°C to 90°C for 4 minutes and then stretched 5 times in the transverse direction at the same temperature to produce a polyester film. When a break occurred in the middle or edge of the unstretched film during stretching at different temperatures, it was described as “broken” at that temperature, and when stretching was possible without a break, it was evaluated as “O.”

[0102] The minimum temperature at which no fracture occurred was evaluated as the elongation temperature.

[0103]

[0104] 3) Shrinkage in width direction (TD direction):

[0105] A 5 x 5 cm sample was obtained by cutting a stretched film without breakage, and the sample was immersed in 95°C hot water and maintained for 30 seconds. The length of the sample before and after shrinkage was measured, and the shrinkage in the width direction was evaluated according to the following equation 2.

[0106] [Formula 2]

[0107] ((Sample length in width direction before shrinkage - Sample length in width direction after shrinkage) / Sample length in width direction before shrinkage) x 100 (%)

[0108]

[0109] Referring to Tables 1 and 2 above, it was confirmed that the unstretched film obtained by melt-extruding the copolymer of the example exhibited a characteristic in which Tg2 was 2°C or higher than Tg1, whereas the unstretched film obtained by melt-extruding the copolymer of the comparative example did not exhibit the corresponding characteristic.

[0110] In addition, it was confirmed that the unstretched film obtained by melt-extruding the copolymer of the example satisfying the characteristic that Tg2 is 2℃ or higher than Tg1 was able to be stretched well without occurrence of breakage, etc. from a low temperature comparable to Tg2 to a temperature 10℃ to 15℃ higher than Tg2, and could be manufactured as a shrink film showing a high width direction shrinkage rate compared to the comparative example.

Claims

1. A residue of a dicarboxylic acid component containing an aromatic dicarboxylic acid; and A polyester copolymer comprising residues of a diol component including ethylene glycol and diethylene glycol, At least one of the residues of the above dicarboxylic acid component and the residues of the above diol component comprises a residue having a cycloalkyl group or a branched residue, A polyester copolymer having a first glass transition temperature (Tg1) measured in the first heating process during DSC analysis of an unstretched film obtained by melt-extruding the above polyester copolymer, which is 2℃ or more lower than the second glass transition temperature (Tg2) measured in the second heating process after cooling.

2. In the first paragraph, a polyester copolymer in which the residue of the dicarboxylic acid component contains 70 mol% or more of residues of terephthalic acid.

3. In the first paragraph, the residue of the dicarboxylic acid component further comprises a residue of at least one dicarboxylic acid selected from the group consisting of dimethyl terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, diphenyl dicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, sebacic acid, succinic acid, isodecylsuccinic acid, maleic acid, maleic anhydride, fumaric acid, adipic acid, glutaric acid, azelaic acid, 4,4'-stilbenedicarboxylic acid, 2,5-furandicarboxylic acid, 2,5-thiophenedicarboxylic acid, regenerated isophthalic acid, regenerated terephthalic acid, etherified derivatives thereof, and esterified derivatives thereof.

4. In the first paragraph, the residue having a cycloalkyl group or a branched residue is a polyester copolymer having a cycloalkyl group having 4 to 16 carbon atoms or a branched alkyl group having 3 to 10 carbon atoms.

5. A polyester copolymer in claim 1, wherein the residue or branched residue having a cycloalkyl group is at least one residue selected from the group consisting of cyclohexane dicarboxylic acid, cyclohexane dimethanol, 1,2-cyclohexanediol, 1,4-cyclohexanediol, neopentylglycol, 2-methyl-1,3-propanediol, 2-methylene-1,3-propanediol, 2-ethyl-1,3-propanediol, 2-isopropyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 3-methyl-2,4-pentanediol, hydroxycyclohexane carboxylic acid, and etherified derivatives and esterified derivatives thereof.

6. In the first paragraph, the residue of the diol component further comprises at least one residue selected from the group consisting of bis-2-hydroxyethyl terephthalate, isosorbide, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 2,3-butanediol, 1,6-hexanediol, 4-(hydroxymethyl)cyclohexylmethyl 4-(hydroxymethyl)cyclohexanecarboxylate, 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol, recycled cyclohexanedimethanol, recycled ethylene glycol, recycled bis-2-hydroxyethyl terephthalate, recycled diethylene glycol, etherified derivatives thereof, and esterified derivatives thereof.

7. In paragraph 1, The sum of the content of the dicarboxylic acid residues and branched dicarboxylic acid residues having the cycloalkyl group based on 100 mol% of the total dicarboxylic acid residues and the content of the diol residues and branched diol residues having the cycloalkyl group based on 100 mol% of the total diol residues is x (mol%), A polyester copolymer satisfying the relationship of the following formula 1, where the content of the diethylene glycol residue is y (mol%) based on 100 mol% of the total diol residues: [Formula 1] 20 ≤ 1.23 * x (mol%) + 0.82 * y (mol%) ≤ 45 8. A polyester copolymer in the 7th paragraph, wherein the total sum of x+y (mol%) is 15 to 40 mol%.

9. In the 8th paragraph, the residue of the dicarboxylic acid component comprises 90 to 100 mol% of the aromatic dicarboxylic acid residue and 10 mol% or less of the dicarboxylic acid residue having the cycloalkyl group or the branched dicarboxylic acid residue, based on the total 100 mol% thereof. A polyester copolymer comprising, based on 100 mol% of the total, the residues of the diol component, 60 to 85 mol% of the ethylene glycol residues, 1 to 25 mol% of the diethylene glycol residues, and 35 mol% or less of the diol residues having a cycloalkyl group or branched diol residues.

10. In the first paragraph, the first glass transition temperature (Tg1) is 55 to 85 ℃, The above second glass transition temperature (Tg2) is 60 to 90 ℃, A polyester copolymer having a first glass transition temperature (Tg1) that is 2 to 8°C lower than the second glass transition temperature.

11. A shrink film comprising a polyester copolymer according to any one of claims 1 to 10.

12. A shrink film having a shrinkage ratio in the transverse direction (TD direction) of 50% or more when treated in water at 95°C for 30 seconds in accordance with claim 11.

13. A step of melt-extruding the polyester copolymer of any one of claims 1 to 10 at a temperature of 200°C or higher and 300°C or lower; and A method for producing a shrink film, comprising the step of stretching the molten extrudate in the transverse direction (TD direction) at a temperature that is 5°C lower than the second glass transition temperature and 15°C higher than the second glass transition temperature.

14. A method for manufacturing a shrink film, wherein the widthwise stretching step in the 13th paragraph is performed at a stretching ratio of 3 to 8 times.