Polyester film and packaging material

Abstract

The polyester film of the present invention comprises a laminate of alternating first and second layers, wherein the first layer contains lactic acid residues, and the second layer contains terephthalate residues and adipic acid residues. In a film noise level evaluation by rotating the film 180 degrees at 800 rpm for more than 30 seconds, the polyester film has an average equivalent noise level of less than 78 dB and a Young's modulus of 280 kgf / mm². 2 The polyester film exhibits excellent flexibility, which improves noise reduction while ensuring transparency.

Description

Technical Field

[0001] One example relates to a multilayer polyester film with improved noise levels. This invention relates to a packaging material using a biodegradable polyester film with improved noise levels. Background Technology

[0002] As is well known, polylactic acid resin is a reusable and environmentally friendly material that is biodegradable in a short period of time and leaves almost no harmful components.

[0003] However, when this polylactic acid resin is processed into film form, it generates a lot of noise, which has become a limitation to its practical commercialization.

[0004] To compensate for the shortcomings of polylactic acid resin, a method of imparting film flexibility by blending polylactic acid with aliphatic-aromatic copolyesters is used. However, in this case, due to the low compatibility between polylactic acid and aliphatic-aromatic copolyesters, the transparency of the film is significantly reduced, making it difficult to use for packaging applications that require transparency.

[0005] The aforementioned background technology is technical information that the inventors retained in order to derive this invention, or that they obtained during the process of deriving this invention. It cannot be said to be conventional technology that was disclosed to the general public before the application of this invention.

[0006] As relevant prior art, it includes Korean Patent No. 10-0904144 (Patent Document 1) and Korean Patent No. 10-2404216 (Patent Document 2), etc. Summary of the Invention

[0007] The problem the invention aims to solve

[0008] The purpose of this embodiment is to provide a polyester film that improves noise performance, ensures transparency, and has biodegradable properties.

[0009] The purpose of this embodiment is to provide a packaging material comprising the polyester film.

[0010] means for solving problems

[0011] One embodiment for achieving the stated purpose provides a polyester film comprising a laminate of alternating first and second layers, wherein the first layer comprises lactic acid residues and the second layer comprises terephthalate residues and adipic acid residues.

[0012] In the film noise level evaluation by rotating the film 180 degrees at 800 rpm for more than 30 seconds, the average equivalent noise level of the polyester film in the implementation example is less than 78 dB.

[0013] The Young's modulus of the polyester film in the example can be 280 kgf / mm². 2 the following.

[0014] In the evaluation of film noise level, when the thickness of the laminate is 16 μm, the noise level of the polyester film in the implementation example can be below 63 dB under 250 Hz conditions.

[0015] The haze of the laminate can be below 10%.

[0016] The haze of the polyester film in the example can be below 10%.

[0017] When the thickness of the laminate is 16 μm, in the film noise level evaluation, the noise level of the polyester film in the implementation example can be below 53 dB under 500 Hz conditions.

[0018] The laminated body can be formed by alternating layers of the first layer and the second layer for more than 30 layers.

[0019] The first layer may also contain hydroxyalkanoate residues.

[0020] Based on 100 parts by weight of the lactic acid residues, the first layer may contain 1 to 7 parts by weight of the hydroxyalkanoate residues.

[0021] The second layer may comprise polybutylene adipate-co-terephthalic acid resin.

[0022] The ratio of the thickness of the first layer to the thickness of the second layer can be from 1:0.2 to 1.5.

[0023] The polyester film of the embodiment may also include a surface layer.

[0024] The surface layer can be disposed on one side and the other side of the laminate.

[0025] The surface layer may comprise: a first resin containing lactic acid residues; and inorganic particles.

[0026] The polyester film of the embodiment includes a laminate in which a first layer and a second layer are alternately stacked, wherein the first layer contains lactic acid residues and the second layer contains terephthalate residues and adipic acid residues; when the noise level of the film is evaluated by rotating it 180 degrees at 800 rpm for more than 30 seconds, the noise level of the polyester film can be below 80 dB under the conditions of 250 Hz, 500 Hz, 1000 Hz, 2000 Hz, 4000 Hz and 8000 Hz.

[0027] Another implementation of the above-described objective provides a packaging material comprising the aforementioned polyester film.

[0028] The packaging material can be food packaging material or disposable product packaging material.

[0029] Invention Effects

[0030] An example could be a polyester film that is biodegradable while reducing noise generation. Another example could be a polyester film and a packaging material using the same, wherein the polyester film can suppress noise generation in the human audible range (especially in the low frequencies), is environmentally friendly, relatively transparent, and possesses adequate mechanical strength and flexibility. Attached Figure Description

[0031] Figure 1 , Figure 2A and Figure 2B This is a conceptual diagram illustrating an example of a polyester film, showing a cross-section of the implementation.

[0032] Figure 3 This is a conceptual diagram illustrating a noise measurement method applicable to noise level evaluation in an implementation example.

[0033] Explanation of reference numerals in the attached figures

[0034] 100: Polyester film

[0035] 50: Layered body

[0036] 52: First floor

[0037] 54: Second layer

[0038] 70: Surface

[0039] 10: Pole

[0040] 12: Fixing part

[0041] 14: Noise Analyzer

[0042] d: distance Detailed Implementation

[0043] Hereinafter, implementation examples will be described in detail with reference to the accompanying drawings to enable those skilled in the art to readily implement the present invention. However, implementation examples may take many different forms and are not limited to the embodiments described herein. Throughout this specification, similar parts are given the same reference numerals.

[0044] In this specification, the term "these combinations" included in the Markush form of the description refers to a mixture or combination of one or more of the groups of structural elements described in the Markush form of the description, which means including one or more of the groups of said structural elements.

[0045] In this specification, the reference to "A and / or B" means "A, B, or A and B".

[0046] Throughout this specification, the terms "first" and "second" are used to distinguish between the same terms. Furthermore, unless the context clearly indicates otherwise, singular expressions include plural expressions.

[0047] Unless otherwise specified in this specification, ppm is based on weight.

[0048] The accompanying drawings may be enlarged or omitted for illustrative purposes, therefore the scope of protection of the invention claims of the implementation examples shall not be limited.

[0049] As a typical biodegradable polymer, polylactic acid (PLA) resin has attracted much attention as a film material that can replace existing petroleum-based polyester films. However, PLA films produce a loud crackling sound during use, which is a drawback that hinders their use as packaging materials. In particular, when PLA-containing films are used in food packaging materials closely related to daily life, such as biscuit bags and bread bags, the crackling sound can become noise, causing an unpleasant experience for users.

[0050] Noise pollution, often referred to as "noise pollution," has become a social problem that needs to be reduced. Furthermore, consumers are reluctant to choose products that generate unnecessary noise. Therefore, it is crucial to provide biodegradable films that do not produce unnecessary noise, replacing existing petrochemical-based films with environmentally friendly biodegradable films.

[0051] The inventors conducted various attempts to prepare films with low noise generation while achieving biodegradability, and as a result, presented implementation examples. Through these implementation examples, the inventors reduced the hissing sound of biodegradable polyester films and obtained mechanical strength exceeding a specified level, confirming their suitability for use as packaging materials for food and other products, and presented these implementation examples.

[0052] Figure 1 , Figure 2A and Figure 2B These are conceptual diagrams illustrating one example of a polyester film, showing cross-sections of the implementation. Figure 3 This is a conceptual diagram illustrating a noise measurement method applicable to noise level evaluation in an implementation example. The following refers to... Figures 1 to 3 The implementation example will be explained in more detail.

[0053] One embodiment of the polyester film 100 includes a laminate 50 in which a first layer 52 and a second layer 54 are alternately stacked, wherein the first layer 52 contains lactic acid residues and the second layer 54 contains terephthalate residues and adipic acid residues (see reference). Figure 1 ).

[0054] Another embodiment of the polyester film 100 includes the laminate 50 described above and a surface layer 70 disposed on one or both sides of the laminate (see reference). Figure 2A and Figure 2B ).

[0055] Layered bodies

[0056] The laminate 50 is a laminate containing alternating layers of a first layer and a second layer of distinct polymer resin.

[0057] The first layer 52 contains lactic acid residues.

[0058] The first layer 52 may contain polylactic acid based resin (PLA based resin).

[0059] Unlike petroleum-based resins, polylactic acid (PLA) resins are based on biomass, which helps reduce carbon dioxide emissions. Furthermore, they are biodegradable, meaning they decompose faster in landfills due to moisture and microorganisms compared to petroleum-based resins, making them more environmentally friendly.

[0060] Based on the first layer as a whole, the polylactic acid resin content can be 50% by weight or more, and its content can also be 80% by weight or more, 85% by weight or more, 90% by weight or more, 93% by weight or more, 95% by weight or more, or 97% by weight or more. In addition, its content can be 99.9% by weight or less or 99% by weight or less.

[0061] Polylactic acid resins may contain L-lactic acid residues, D-lactic acid residues, D,L-lactic acid residues, or combinations thereof.

[0062] Based on the polylactic acid (PLA) resin as a whole, the content of L-lactic acid residues in the PLA resin can be 80 mol% or more, specifically 83 mol% or more, 85 mol% or more, 88 mol% or more, 90 mol% or more, or 92 mol% or more. Alternatively, the L-lactic acid content can be 99 mol% or less, 97 mol% or less, 95 mol% or less, or 93 mol% or less. Under these conditions, the heat resistance properties of the film can be further improved.

[0063] Based on the polylactic acid (PLA) resin as a whole, the content of D-lactic acid residues in the PLA resin can be greater than 0 mol%, 0.5 mol%, or 1 mol%. Alternatively, the D-lactic acid content can be less than 5 mol% or less than 3 mol%. In this case, the stretching processability of the film can be further improved.

[0064] The weight-average molecular weight (Mw) of the polylactic acid resin can be from 100,000 g / mol to 1,000,000 g / mol, for example, from 100,000 g / mol to 800,000 g / mol, from 100,000 g / mol to 500,000 g / mol, or from 100,000 g / mol to 300,000 g / mol. The weight-average molecular weight (Mw) can be determined by gel permeation chromatography (GPC). When the weight-average molecular weight (Mw) of the polylactic acid resin meets the aforementioned range, it can help improve the mechanical properties of the film.

[0065] The first layer 52 may also contain hydroxy alkyl ester residues.

[0066] Hydroxyalkanoate residues can be derived from polyhydroxyalkanoate resins (PHA resin).

[0067] The first layer 52 may contain polylactic acid resin and polyhydroxyalkanoate resin.

[0068] Polyhydroxyalkanoate resins are semi-crystalline thermoplastic polyester compounds that can be produced through chemical synthesis or by microorganisms (bacteria or algae) and are used in the preparation of biodegradable plastics.

[0069] The polyhydroxyalkanoate resin may contain one or more residues selected from the group consisting of poly[3-hydroxybutyrate] (P3-HB), poly[4-hydroxybutyrate] (P4-HB), poly[3-hydroxyvalerate] (PHV), poly[3-hydroxybutyrate]-co-poly[3-hydroxyvalerate] (PHBV), poly[3-poly[3-hydroxyhexanoate] (PHC), poly[3-hydroxyheptanoate] (PHH), poly[3-hydroxyoctanoate] (PHO), poly[3-hydroxynonanoate] (PHN), poly[3-hydroxydecanoate] (PHD), poly[3-hydroxydodecanoate] (PHDD), and poly[3-hydroxytetradecanoate] (PHTD).

[0070] Specifically, the polyhydroxyalkanoate resin may contain any one selected from the group consisting of 3-hydroxybutyrate residues (3HB residues), 4-hydroxybutyrate residues (4HB residues), and combinations thereof.

[0071] Based on the polyhydroxyalkanoate resin as a whole, the polyhydroxyalkanoate resin may contain more than 50 mol% of 3HB residues, or more than 55 mol% or 60 mol% of 3HB residues. The content of the residues may be less than 100 mol%, or less than 80 mol% or 70 mol%.

[0072] Based on the polyhydroxyalkanoate resin as a whole, the polyhydroxyalkanoate resin may contain less than 50 mol% of 4HB residues, or less than 45 mol% or less, or less than 640 mol% of 4HB residues. The content of the residues may be more than 0 mol%, or more than 20 mol% or more, or more than 30 mol%.

[0073] The polyhydroxyalkanoate resin may contain 4HB residues and 3HB residues, and based on the total amount of the polyhydroxyalkanoate resin, it may contain 30 mol% to 35 mol% of 4HB residues. In this case, mechanical properties can be improved by adjusting the crystallinity of the film.

[0074] The first layer 52 can be prepared using a resin blend of the polylactic acid resin and the polyhydroxyalkanoate resin. This helps to impart a predetermined level of biodegradability and appropriate mechanical properties to the polyester film.

[0075] Based on 100 parts by weight of lactic acid residues, the hydroxyalkanoate residues contained in the first layer 52 can be from 1 to 7 parts by weight, or from 2 to 6 parts by weight. If a resin containing said residues is applied within this range, it can impart film strength and help control crystallinity during biaxial stretching, and can provide a film with a further reduction in overall noise level by adjusting the physical properties of the relatively hard first layer.

[0076] The resin suitable for the first layer 52 can have a melt viscosity of 5000P or higher or 7000P or higher at a temperature of 210°C, and can be below 14000P or below 12000P. Under these conditions, stable processability can be achieved when the laminate is prepared by extrusion.

[0077] The first layer 52 may also contain inorganic particles. The inorganic particles may, by way of example, act as an anti-blocking agent, but are not limited thereto.

[0078] Inorganic particles suitable for the first layer may exemplary comprise silicon dioxide (SiO2), calcium carbonate (CaCO3), indium tin oxide (ITO), aluminum hydroxide (Al2(OH)3), zinc oxide (ZnO), titanium dioxide (TiO2), or barium sulfate (BaSO4).

[0079] The inorganic particles may have a D50 of 1 μm or more, or 1.5 μm or more. The D50 may also be less than 3 μm or less than 2 μm.

[0080] Based on the overall composition of each layer, the inorganic particles contained in the first layer or the surface layer can be less than 2000 ppm or less than 1500 ppm. When the inorganic particles are contained in the surface layer, they can act as an anti-blocking agent.

[0081] In addition, when the first layer contains inorganic particles containing calcium carbonate, it can help reduce noise generation in polyester films.

[0082] As needed, the first layer 52 may also include conventional electrostatic agents, antistatic agents, antioxidants, heat stabilizers, ultraviolet blocking agents, anti-blocking agents, or combinations thereof.

[0083] The second layer 54 contains terephthalate residues and adipic acid residues.

[0084] The second layer 54 is mainly composed of aliphatic-aromatic copolyester resin, and specifically contains adipic acid residues and terephthalate residues.

[0085] The aliphatic-aromatic copolyester resin may contain aliphatic dicarboxylic acid residues as adipic acid and aromatic dicarboxylic acid residues as terephthalic acid, and may also contain diol residues.

[0086] The aliphatic dicarboxylic acid may, by way of example, also include succinic acid, sebacic acid, glutaric acid, malonic acid, oxalic acid, azelaic acid, or azelaic acid.

[0087] The aromatic dicarboxylic acid may, by way of example, also include isophthalic acid, naphthal-2,6-dicarboxylic acid, dibenzenesulfonic acid dicarboxylic acid, diphenyl ether dicarboxylic acid, diphenoxyethane dicarboxylic acid, or cyclohexane dicarboxylic acid.

[0088] The diol residue may be any residue selected from ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, propylene glycol, neopentanediol, 2-methyl-1,3-propanediol, diethylene glycol and other alkylene glycols, 1,4-cyclohexanediol, 1,4-cyclohexanediol, polyethylene glycol and mixtures thereof.

[0089] Based on the overall acid content, the resin contained in the second layer 54 may contain 30 mol% or more, 40 mol% or more, 45 mol% or more, or 50 mol% or more of aliphatic components. Alternatively, based on the overall acid content, the aliphatic components may be less than 80 mol%, less than 70 mol%, or less than 60 mol%. In this case, the biodegradability of the polyester film can be further improved.

[0090] The resin suitable for the second layer 54 may, for example, be polybutylene terephthalate (PBAT) resin, in which case it may help reduce the noise level and improve processability during film preparation.

[0091] The resin suitable for the second layer 54 can have a melt viscosity of 3000P or higher or 4000P or higher at a temperature of 210°C, and can be below 9000P or below 7000P. Under these conditions, stable processability can be achieved when the laminate is prepared by extrusion.

[0092] The weight-average molecular weight (Mw) of the aliphatic-aromatic copolyester resin can be, for example, from 50,000 g / mol to 400,000 g / mol, from 50,000 g / mol to 300,000 g / mol, from 50,000 g / mol to 200,000 g / mol, or from 50,000 g / mol to 100,000 g / mol. The weight-average molecular weight (Mw) can be determined by gel permeation chromatography (GPC). In this case, it exhibits excellent compatibility with resins suitable for the first layer, as well as excellent processability.

[0093] As needed, the second layer 54 may also contain conventional electrostatic agents, antistatic agents, antioxidants, heat stabilizers, UV blockers, anti-blocking agents, or combinations thereof.

[0094] Compared to the first layer 52, the second layer 54 has a softer feature.

[0095] A relatively stiff first layer and a relatively soft second layer are alternately stacked to form a laminate 50. The mechanical properties of the laminate as a whole can be maintained above a specified level through the first layer, and noise generated during the use of the film can be reduced through the interaction between the first and second layers. In particular, compared with polylactic acid films, films that provide a significant reduction in equivalent noise level and low-frequency noise level are available.

[0096] Furthermore, due to the multilayered nature of the laminate, the optical properties of the polyester film are improved. In particular, compared to a single-layer film formed by blending resins for the first layer and resins for the second layer, it exhibits a reduced haze value. Therefore, the implemented example provides a film with excellent light transmittance under visible light.

[0097] The total number of layers in the laminate 50 can be 4 or more, 6 or more, 10 or more, 30 or more, 34 or more, or 36 or more. The laminate can have fewer than 424 layers, fewer than 324 layers, or fewer than 224 layers. When it is difficult to distinguish between the first layer and adjacent surface layers by applying the same resin as the first layer to the surface layer described later, the total number of layers in the laminate is based on the number of layers determined assuming the existence of the first layer.

[0098] The laminate 50 can provide a multilayer polyester film that maintains the mechanical strength of the polyester film above a specified level and improves the noise level by alternately stacking the first layer 52 and the second layer 54 in a multilayer structure.

[0099] The laminate can consist of 36 or more alternating layers of the first and second layers, or 36 to 144 alternating layers. In this case, when the polyester film is used for general bagging applications such as snack bags, the noise generated can be substantially reduced.

[0100] In the laminate 50, the average thickness ratio of the first layer 52 to the second layer 54 can be from 1:0.2 to 1.5. The average thickness ratio of the first layer to the second layer can be from 1:0.3 to 1.3. When the average thickness ratio of the individual layers of the first and second layers meets the above ranges, noise reduction effect can be obtained while maintaining a film strength above an appropriate level.

[0101] The laminate 50 is essentially completely biodegradable after a predetermined period of time in the presence of microorganisms and moisture, thus possessing environmentally friendly characteristics.

[0102] In the evaluation of film noise level during a 180-degree rotation at 800 rpm for more than 30 seconds, the average equivalent noise level of the laminate 50 can be below 78 dB. The average equivalent noise level can be below 77.5 dB, 76 dB, 74.5 dB, or 73 dB. The average equivalent noise level can be above 72 dB.

[0103] The film noise level evaluation can be performed using a noise analyzer 14. The sample film (or laminate) is cut to A4 size, and the long end of the sample is clamped and fixed to a rod 10 located inside a box configured for external noise isolation using a fixing part 12 (e.g., a clamp). Noise is generated by rotating the rod. The distance (d) between the end of the measuring part of the noise analyzer and the film is approximately 10 cm. Noise generation is measured by rotating the rod 180 degrees at 800 RPM for at least 30 seconds (refer to...). Figure 3 ).

[0104] For example, a film cut to A4 size is prepared in a box made of polycarbonate measuring 650(W)×450(D)×500(H)mm, and a digital noise analyzer (model name: CR-162C) from Cirrus Research PIC (UK) is configured (see reference). Figure 3 The noise analyzer is placed approximately 10 cm from the prepared film. The film is clamped at both ends and rotated 180 degrees. Noise is emitted at 800 RPM for at least 30 seconds, and the noise level is measured. Data analysis is based on applicable noise tools software. The program can evaluate the noise level and equivalent noise level over 30 seconds at each specific frequency. For example, the noise level and equivalent noise level can be measured in the range of 31.5 Hz to 16000 Hz.

[0105] The evaluation of the average equivalent noise level is based on the value measured at any thickness selected from 15 μm to 30 μm for the laminate or the polyester film.

[0106] When the thickness of the laminate is 16 μm, in the film noise level evaluation, at 250 Hz, the noise level of the laminate 50 can be below 63 dB, below 62 dB, below 61 dB, or below 60 dB. This means that it has a relatively low noise level at frequencies that represent low frequencies.

[0107] When the thickness of the laminate is 16 μm, in the film noise level evaluation, at 500 Hz, the noise level of the laminate 50 can be below 53 dB, below 52 dB, below 51 dB, or below 50 dB. This means that the noise level in the relatively low-frequency range, which people perceive as noisy, is relatively low.

[0108] When the thickness of the laminate is 16 μm, in the film noise level evaluation at 1000 Hz, the laminate 50 can be below 59 dB, below 57 dB, below 56 dB, or below 55 dB. This means that the noise level is low in the lower frequency range.

[0109] When the thickness of the laminate is 16 μm, in the film noise level evaluation at 2000 Hz, the laminate 50 can be below 67 dB, below 66 dB, below 65 dB, below 64 dB, or below 63.5 dB. This is generally considered to be high-frequency noise, which essentially means a reduction in noise level.

[0110] When the thickness of the laminate is 16 μm, in the film noise level evaluation at 4000 Hz, the laminate 50 can be below 75 dB, below 74 dB, below 73 dB, below 72 dB, or below 71 dB. This is generally considered to be a high-frequency noise level and is also the region in the film that generates the most noise, which essentially means a reduction in noise level.

[0111] When the thickness of the laminate is 16 μm, under 8000 Hz conditions, the laminate 50 can be below 72 dB, below 71 dB, below 70.5 dB, below 70 dB, below 69 dB, or below 68 dB. This means a reduction in noise generation at relatively high frequencies.

[0112] When the thickness of the laminate is 16 μm, at 16000 Hz, the laminate 50 can have a noise level below 63 dB, below 62 dB, below 60 dB, or below 58 dB. This means a reduction in high-frequency noise generation.

[0113] The haze of the laminate 50 can be less than 10%, less than 9%, or less than 8%. The haze can be more than 2% or more than 4%. This is a suitable optical property, sufficient for use as a packaging material, and exhibits particularly superior properties compared to a simple blend of a resin with lactic acid residues and an aliphatic-aromatic copolyester resin. When the two resins are simply blended, turbidity occurs due to poor compatibility. In this embodiment, by using the structure of the laminate, the reduction in optical properties due to poor compatibility of the two resins can be suppressed, and excellent optical physical properties are obtained. The haze is based on a value measured using a haze meter (model name: SEP-H) from Nihon Semitsu Kogaku.

[0114] surface layer

[0115] The polyester film 100 of the embodiment may also include a surface layer 70.

[0116] Surface layer 70 may be disposed on one or the other side of the laminate (see reference) Figure 2A ).

[0117] The surface layer 70 can be disposed on one or the other side of the laminate (see reference). Figure 2B ).

[0118] The surface layer 70 can be made of the resin of the first layer 52. The surface layer 70 can also be made of the resin of the second layer 54. In this case, the processability of the polyester film can be further improved, and the entire film can be endowed with biodegradable properties.

[0119] When the resin of the first layer is applied, the surface layer 70 can further improve the mechanical properties and processability of the polyester film.

[0120] Surface layer 70 may contain inorganic particles in the same manner as the first layer, as previously described, and additives may be applied as needed.

[0121] Based on the thickness of 100 of the laminate 50, the thickness of the surface layer 70 can be in the range of 5 to 25. The thickness of the surface layer 70 can be 0.8 μm or more, 1.2 μm or more, or 2 μm or more, and there is no particular limit to the upper limit of the thickness.

[0122] If the surface layer is applicable to both the upper and lower parts of the laminate, then the thickness of the surface layer as described above refers to the thickness of one side of the surface layer.

[0123] When the surface layer 70 is applied to the polyester film 100, it can provide a film with excellent surface strength and controlled overall tactile feel and anti-slip properties.

[0124] Polyester film

[0125] In the film noise level evaluation by rotating the film 180 degrees at 800 rpm for more than 30 seconds, the average equivalent noise level of the polyester film 100 in the implementation example can be 78 dB or less. The average equivalent noise level can be 77.5 dB or less, 76 dB or less, 74.5 dB or less, or 73 dB or less. The average equivalent noise level can be 72 dB or more.

[0126] For example, with a thickness of about 25 μm as a reference, when all measurements are performed under the same conditions, the average equivalent noise level of ordinary polyester film based on petroleum-based materials is about 80.3 dB, while the average equivalent noise level of polyester film suitable for polylactic acid resin is about 83 dB to 85 dB, showing a difference in level.

[0127] The implementation example provides an average equivalent noise level applicable to biodegradable polymers such as polylactic acid resin, while substantially suppressing or reducing noise generation. In other words, compared to polyester films (based on petroleum-based materials) suitable for product packaging materials, the implementation example provides a biodegradable polyester film that further suppresses noise.

[0128] The evaluation of the average equivalent noise level or noise level is based on the value measured at any thickness selected from 10 μm to 30 μm for the laminate or the polyester film.

[0129] In the aforementioned film noise level evaluation, under 250Hz conditions, the noise level of the polyester film 100 of the embodiment can be below 63dB, below 62dB, below 61dB, or below 60dB. This means that it has a relatively low noise level at frequencies that exhibit low bass.

[0130] In the aforementioned film noise level evaluation, under 500Hz conditions, the noise level of the polyester film 100 in the implementation example can be below 53dB, below 52dB, below 51dB, or 50dB. This means that the noise level in the relatively low-frequency range, where people perceive noise, is relatively low.

[0131] In the aforementioned film noise level evaluation, under 1000 Hz conditions, the polyester film 100 of the implementation example can be below 59 dB, below 57 dB, below 56 dB, or below 55 dB. This means that the noise level is low in the lower frequency range.

[0132] In the aforementioned film noise level evaluation, under 2000 Hz conditions, the polyester film 100 of the example can be below 67 dB, below 66 dB, below 65 dB, below 64 dB, or below 63.5 dB. This is generally considered to be high-frequency noise, which essentially means a reduction in noise level.

[0133] In the aforementioned film noise level evaluation, under 4000Hz conditions, the polyester film 100 of the implementation example can be below 75dB, below 74dB, below 73dB, below 72dB, or below 71dB. This is generally considered to be a high-frequency noise level and is also the region in the film where the greatest noise is generated, which essentially means a reduction in noise level.

[0134] In the aforementioned film noise level evaluation, under 8000Hz conditions, the polyester film 100 of the implementation example can be below 72 dB, below 71 dB, below 70.5 dB, below 70 dB, below 69 dB, or below 68 dB. This means a reduction in the generation of relatively high-frequency noise.

[0135] In the aforementioned film noise level evaluation, at 16000Hz, the polyester film 100 of the implementation example can be below 63dB, below 62dB, below 60dB, or below 58dB. This means a reduction in the generation of high-frequency noise.

[0136] The haze of the polyester film can be 10% or less. Alternatively, the haze can be 6.5% or more and 9.5% or less. Furthermore, the haze can be 7% or more and 9% or less. When these haze ranges are achieved, transparency is obtained, thus making it suitable for various applications requiring light transmission. The haze is measured using a haze meter (model name: SEP-H) from Nihon Semitsu Kogaku.

[0137] The Young's modulus of the polyester film 100 in the example can be 280 kgf / mm². 2The Young's modulus described below is based on the standard test method (ASTM D882) for the tensile properties of plastic films, and it means the average Young's modulus of the film in the longitudinal (MD) direction and the transverse (TD) direction.

[0138] The Young's modulus can be 280 kgf / mm². 2 Below, 275kgf / mm 2 Below, 270kgf / mm 2 Below, 220kgf / mm 2 Below, 200kgf / mm 2 Below or 160 kgf / mm 2 The Young's modulus can be 80 kgf / mm². 2 Above, 100kgf / mm 2 Above, 120kgf / mm 2 Above, 125kgf / mm 2 Above or 150 kgf / mm 2 The above. Young's modulus is one of the indicators of the flexibility of polyester film. Although flexible films are considered to generate less noise, according to the inventors' repeated experiments, the level of Young's modulus and the degree of noise generation of the film are not necessarily constantly correlated. However, it does indicate that the film as a whole has more flexible properties.

[0139] The tensile strength of the polyester film 100 in the example can be 3 kgf / mm. 2 Above, 4kgf / mm 2 Above, 5kgf / mm 2 Above or 7kgf / mm 2 The above can be 17 kgf / mm 2 Below, 15kgf / mm 2 Below or 12 kgf / mm 2 The tensile strength described below refers to the average value when the tensile strengths in the MD and TD directions differ. The polyester film may have a tensile strength suitable for use as a packaging material.

[0140] The elongation of the polyester film 100 in the embodiment can be 60% or more, 70% or more, or 75% or more, and can be less than 120%. When the elongation in the MD direction and the TD direction are different, the elongation refers to their average value. The polyester film can have elongation characteristics suitable for use as a packaging material.

[0141] The heat shrinkage rate of the polyester film 100 in the embodiment can be less than 5%, less than 4%, or less than 3%. The heat shrinkage rate can be 0.5% or more. This means that the polyester film has dimensional stability above a predetermined level, and the embodiment can have stable heat shrinkage rate characteristics.

[0142] The thickness of the polyester film 100 in the embodiment can be less than 1000 μm, less than 800 μm, less than 600 μm, less than 400 μm, less than 200 μm, less than 100 μm, or less than 60 μm. The thickness can be more than 10 μm or more than 15 μm. In this case, it can have a thickness suitable for use as a packaging material.

[0143] The polyester film 100 of the embodiment includes a laminate of alternating first and second layers, wherein the first layer contains lactic acid residues and the second layer contains terephthalate residues and adipic acid residues; when the noise level of the film is evaluated by rotating it 180 degrees at 800 rpm for more than 30 seconds, the noise level of the polyester film 100 can be below 80 dB, below 77 dB, or below 75 dB. In this case, the noise level means the value measured at 250 Hz, 500 Hz, 1000 Hz, 2000 Hz, 4000 Hz, and 8000 Hz, respectively.

[0144] The polyester film 100 exhibits low overall noise across a wide range of frequencies, primarily from bass to treble, thus providing an environmentally friendly polyester film with above-a-predetermined mechanical strength while remaining relatively quiet.

[0145] Preparation method of polyester film

[0146] Another embodiment of the method for preparing a polyester film includes: a step of preparing a composition; a step of obtaining an unstretched sheet; and a step of obtaining a polyester film.

[0147] The step of preparing the composition is to prepare a first resin composition containing lactic acid residues and a second resin composition containing terephthalate residues and adipic acid residues (hereinafter referred to as the "first step").

[0148] The step of obtaining the unstretched sheet is to obtain an unstretched sheet comprising an alternating layer of a first layer containing the first resin and a second layer containing the second resin by melt extruding the first resin composition and the second resin composition respectively (hereinafter referred to as the "second step").

[0149] The step of obtaining the polyester film is to obtain the polyester film by stretching and heat-fixing the laminated sheet (hereinafter referred to as the "third step").

[0150] The specific description of the polyester film and the laminate is repeated above, so its detailed description is omitted.

[0151] The first resin composition may include the resin, inorganic particles, and additives as described above in the first layer. The second resin composition may include the resin and additives as described above in the second layer.

[0152] The melt viscosity of the first and second resin layers at 210°C is the same as described above. If a resin with this melt viscosity is used in the first and second resin compositions, it will facilitate the use of extrusion to prepare the laminate.

[0153] The first resin composition and the second resin composition may undergo a moisture removal step in the first step and / or the second step, preferably reducing the moisture content to below 150 ppm.

[0154] In the second step, a conventional film lamination unit, such as a feed block, can be used. Exemplarily, the film lamination unit may have a structure in which molten resin corresponding to the first and second layers is discharged in a stacked manner, and may also include a portion for discharging resin from the surface layer. When the first resin composition or the second resin composition is applied to the surface layer, processability can be improved. The thickness ratio of each layer of the laminate and the thickness ratio of the surface layer can be controlled by controlling the amount of molten resin discharged, etc.

[0155] The thickness ratio and other parameters are the same as described above. Considering the stretching process described later, the thickness of each layer can be controlled to suit the requirements.

[0156] The second step can be achieved by thinning the unstretched sheet by processes such as pressing it tightly against a cooling roller after melt extrusion.

[0157] The third step includes stretching the sheet along both the longitudinal and transverse directions. A heat-setting step may also be included after the stretching.

[0158] The stretching can be applied to biaxial stretching or differential biaxial stretching. Specifically, the stretching can be performed by the following steps: after preheating to 50°C to 80°C, stretching 2 to 4 times along the longitudinal direction (MD) at a temperature of 40°C to 100°C, and stretching 3 to 6 times along the transverse direction (TD) at a temperature of 50°C to 150°C.

[0159] The heat-fixing step can be performed at temperatures of 50°C to 150°C, 70°C to 150°C, 100°C to 150°C, or 110°C to 140°C.

[0160] Through the stretching and heat-fixing, the polyester film can improve its mechanical strength and dimensional stability while maintaining a thin thickness.

[0161] Packaging materials

[0162] Another example of packaging material includes the aforementioned polyester film. The specific description of the polyester film is repeated above, therefore its detailed description is omitted.

[0163] Packaging materials may include, for example, disposable packaging materials, food packaging materials, etc., and may include the polyester film directly, as well as aluminum foil, colored layers, etc.

[0164] The packaging material is environmentally friendly because it uses a biodegradable resin, reducing carbon dioxide emissions and being almost completely biodegradable under certain conditions. Furthermore, it utilizes polylactic acid resin, which is currently under research as an existing biodegradable film, while reducing noise levels, maintaining mechanical strength above specified levels, and ensuring an appropriate level of haze, making it highly suitable as a packaging material.

[0165] The implementation examples are described in more detail below through specific embodiments. These embodiments are merely examples to aid in understanding the implementation examples, and the scope of protection of this invention is not limited thereto.

[0166] 1. Preparation of polyester films according to Examples 1 and 2

[0167] As the first resin composition, a mixed resin comprising 93.9 parts by weight of a polylactic acid polymer, 6 parts by weight of a polyhydroxyalkanoate polymer and 0.1 parts by weight of calcium carbonate, based on 100 parts by weight of the first resin, is used.

[0168] In the first resin, the D-lactide content of the polylactic acid polymer is about 1 mol% to about 3 mol%, the melt viscosity is about 7000 P to about 12000 P (poise) at a temperature of 210°C, the 4HB content of the polyhydroxyalkanoate polymer is 30 mol% to 35 mol%, and the calcium carbonate uses particles with D50 = 1.5 μm.

[0169] As the second resin, 100 parts by weight of polybutylene adipate-co-terephthalic acid resin was used, based on 100 parts by weight of the second resin, having a melt viscosity of about 4000P to about 7000P (poise) at a temperature of 210°C, and having an aliphatic component content of 50 mol in the acid component.

[0170] The first resin was dried in a dehumidifying dryer at a temperature of 60°C for more than 8 hours, and the second resin was dried in a dehumidifying dryer at a temperature of 80°C for more than 2 hours to remove moisture.

[0171] Two extruders and multi-layer feed blocks stacked alternately in a preset number of layers are used. The first resin is melt-extruded using an extruder at a temperature of 210°C, and the second resin is melt-extruded using an extruder at a temperature of 210°C. The discharge ratio (volume ratio) of the first resin to the second resin is 70:30.

[0172] In a multi-layer feed block, a first resin composition is branched into 36 layers, and a second resin composition is branched into 36 layers, then alternately stacked, and the first and second layers are stacked into 72 layers respectively. A surface layer, approximately 10% of the overall thickness, is provided on the outermost layer of both the upper and lower surfaces, and the first resin composition is applied to the surface layer to have the same composition as the first layer. Then, after passing through a 780mm die, it is pressed against a cooling roller cooled to 20°C to obtain an unstretched multi-layer sheet of 73 layers, including the outermost layer (the portion adjacent to the surface layer and the first layer is considered as one layer).

[0173] Unstretched multilayer sheets were longitudinally stretched 3.0 times at 65°C and transversely stretched 4.0 times at 85°C, and then heat-fixed at 120°C with a relaxation rate of 1% to prepare a 20 μm biaxially stretched multilayer film (Example 1).

[0174] Example 2 was prepared in the same manner as Example 1, and after stretching and heat-fixing, it was prepared to have a thickness of 25 μm.

[0175] 2. Preparation of polyester films according to Examples 3 to 5

[0176] In Example 3, the first resin composition and the second resin composition are used in the same manner as described above, and the discharge ratio (volume ratio) of the first resin composition to the second resin composition is 50:50.

[0177] In the multi-layer feed block, the first resin composition is branched into 36 layers, the second resin composition is branched into 36 layers and then stacked alternately, and the first layer and the second layer are stacked into 72 layers respectively. The outermost layers of the upper and lower surfaces are respectively provided with a surface layer accounting for about 8% of the overall thickness, and the first resin composition is applied to the surface layer to have the same composition as the first layer.

[0178] Other processes were carried out in the same manner as in Example 1 to prepare a 20 μm biaxially stretched multilayer film (Example 3).

[0179] Example 4 was carried out in the same manner as Example 3 to prepare a 25 μm biaxially stretched multilayer film.

[0180] In Example 5, in a multilayer feed block, a first resin composition is branched into 15 layers, and a second resin composition is branched into 15 layers, which are then alternately stacked. The first and second layers are stacked into 30 layers respectively. A surface layer is provided on the outermost layer of the upper and lower surfaces, and the first resin composition is applied to the surface layer to have the same composition as the first layer. A 31-layer film with a thickness of 20 μm is prepared.

[0181] 3. Preparation of polyester films of Comparative Examples 1 to 4

[0182] As Comparative Example 1, a polylactic acid polymer with a D-lactide content of about 1% to about 3 mol% was used, exhibiting a melt viscosity of about 7000 P to about 12000 P at a temperature of 210°C. Moisture was removed by drying in a dehumidifying dryer at 80°C for 6 hours. The resin for the first resin layer was melt-extruded using an extruder at 210°C. After passing through a 780 mm die, it was pressed against a cooling roller cooled to 20°C to obtain a single-layer unstretched sheet. The single-layer unstretched sheet obtained in this manner was longitudinally stretched 3.0 times at 65°C and transversely stretched 3.8 times at 85°C. A biaxially stretched single-layer film of approximately 20 μm was then prepared by applying a heat-fixing temperature of 120°C and a relaxation rate of about 1%.

[0183] As Comparative Example 2, a blend of 80% by weight of a polylactic acid polymer and 20% by weight of a second resin, as used in Example 1, was blended in a twin-screw extruder at 200°C. After drying in a dehumidifying dryer at 60°C for 8 hours, it was melt-extruded at approximately 210°C to prepare a 30 μm single-layer unstretched sheet. This unstretched sheet was used as the film of Comparative Example 2.

[0184] In Comparative Example 3, 10% by weight of polyhydroxyalkanoate and 90% by weight of polylactic acid polymer used in the first resin were manually mixed and then co-blended and processed into chips in a twin-screw extruder at 200°C. The chips were then dried in a dehumidifying dryer at 60°C for no more than 8 hours. Next, the chips were melt-extruded using a single-screw extruder at 210°C, passed through a 780mm die, and then pressed against a cooling roller cooled to 20°C to obtain a single-layer unstretched sheet. This single-layer unstretched sheet was then stretched longitudinally by 3.0 times at 65°C and transversely by 3.8 times at 85°C. Finally, a biaxially stretched multilayer film of approximately 20 μm was prepared by applying a heat-fixing temperature of 120°C and a relaxation rate of approximately 1%.

[0185] In Comparative Example 4, the resin used as the first layer was a polylactic acid polymer with a D-lactide content of approximately 1 mol% to 3 mol%, and a melt viscosity of approximately 7000 P to 12000 P at 210°C. The resin used as the second layer was polybutylene terephthalate (PBAT) resin with a melt viscosity of approximately 4000 P to approximately 7000 P at 210°C, and an aliphatic component content of 50 mol% in the acid component. The first resin was dried in a dehumidifying dryer at 60°C for no more than 8 hours, and the second resin was dried in a dehumidifying dryer at 80°C for no more than 2 hours to remove moisture. Two extruders and two layers of alternating multilayer feed blocks were used. The resin of the first resin was melt-extruded in an extruder at 210°C, and the resin of the second resin was melt-extruded in an extruder at 210°C. The discharge ratio (volume ratio) of the first resin to the second resin was 70:30. In a multilayer feed block, the first resin branch consists of 36 layers, the second resin branch consists of 36 layers, and the first and second resins are alternately stacked. The outermost layer on the upper / lower surface is composed of approximately 20% of the overall thickness of the first resin. Then, after passing through a 780mm die, it is pressed against a cooling roller cooled to 20°C to obtain an unstretched multilayer sheet with 73 layers (the portion of the first layer in direct contact with the surface layer is not distinguished and is therefore considered as one layer), including the outermost layer. This unstretched multilayer sheet is then longitudinally stretched 3.0 times at 65°C and laterally stretched 4.0 times at 85°C. Finally, a 20μm biaxially stretched multilayer film is prepared by applying a heat-fixing temperature of 120°C and a relaxation rate of 1%.

[0186] 4. Evaluation of physical properties

[0187] Noise level evaluation of thin films

[0188] A film, cut to A4 size (210mm × 297mm), was prepared in a 650(W) × 450(D) × 500(H) mm box made of polycarbonate. A digital noise analyzer (model name: CR-162C) from Cirrus Research PIC (UK) was used. The noise analyzer was placed approximately 10cm away from the prepared film, with both ends clamped, and rotated 180 degrees at 800 rpm for more than 30 seconds while measuring the noise. Data analysis used the equivalent noise level and frequency-differentiated noise level modes of the NoiseTools software program. The noise level and equivalent noise level at a specific frequency over 30 seconds were evaluated using the program, and the results are shown in the table below.

[0189] Mechanical performance evaluation

[0190] Film specimens were prepared according to the standard test method for tensile properties of plastic films (ASTM D882). These specimens were cut to lengths of 150 mm and widths of 15 mm, and then mounted at 50 mm intervals. A tensile testing machine and an Instron 5566A were used to test the specimens at a tensile speed of 200 mm / min. The slope of the straight line from the initial testing point to when the elongation reached 3% was measured and used as Young's modulus (kgf / mm²). 2 ).

[0191] Tensile strength is the maximum strength under tension (kgf / mm²). 2 Elongation is the percentage increase (%) of the sample at break compared to its initial value, and is measured using the same equipment.

[0192] Haze

[0193] Measurements were taken using a hazemeter (model name: SEP-H) from Nihon Semitsu Kogaku, Japan, according to ASTM D1003 standard.

[0194] The results of each measurement are summarized in Table 1 and Table 2 below.

[0195] Table 1

[0196]

[0197]

[0198] *The inorganic particles in the composition are calcium carbonate.

[0199] Table 2

[0200]

[0201] *The inorganic particles in Comparative Examples 1 and 4 are silicon dioxide.

[0202] Comparative Example 1 is a film made solely of polylactic acid (PLA) resin, which again confirmed that it has an equivalent noise level of over 80 dB and exhibits somewhat noisy characteristics. The Young's modulus value is also relatively high, and the film's flexibility is somewhat insufficient.

[0203] Unlike Comparative Example 1, Comparative Example 2 was a film made by blending polybutylene terephthalate (PBAT) with polylactic acid (PLA) resin. Although the flexibility was improved, the equivalent noise level remained at 80 dB, resulting in high noise and a significant increase in haze. This was determined to be due to the poor usability of the two resins.

[0204] Comparative Example 3 is a film made of a poly(hydroxyl alkyl acrylate) resin (PHA) blended with a polylactic acid (PLA) resin, with a Young's modulus of 300 kgf / mm². 2 The above points indicate a lack of flexibility, and the haze value is also considered to be too high.

[0205] Unlike Comparative Example 3, Comparative Example 4 uses an alternating laminated structure of polylactic acid (PLA) and polybutylene terephthalate (PBAT) instead of a film of polyhydroxyalkanoate (PHA) blended with PLA. Compared to the other comparative examples, it has a low haze value and therefore an advantage in terms of light transmittance. However, it still has a high equivalent noise level and Young's modulus.

[0206] In the embodiments, the equivalent noise level of the film tends to decrease, and the haze value is confirmed to be low.

[0207] In Examples 1 to 4, it was confirmed that the equivalent noise level of each polyester film was below 80 dB and the Young's modulus was 300 kgf / mm². 2 The following conditions apply, provided that the fog level does not exceed 10%.

[0208] The resins used in the embodiments and comparative examples are all prepared from biodegradable resins, thus possessing biodegradable properties. In addition, they reduce the noise generation level, a drawback of existing biodegradable resin films, thereby improving their usability as packaging materials, etc.

[0209] While the preferred embodiments of the present invention have been described in detail above, the scope of protection of the present invention is not limited thereto. Various modifications and improvements made by those skilled in the art using the basic concepts of the present invention as defined in the claims also fall within the scope of protection of the present invention.

Claims

1. A polyester film, wherein, This includes laminates in which the first and second layers are alternately stacked. in, The first layer contains lactic acid residues, and the first layer is prepared using a resin blend of polylactic acid resin and polyhydroxyalkanoate resin. The second layer contains terephthalate residues and adipic acid residues. The laminated body is formed by alternating layers of the first layer and the second layer, with a total of 4 to 424 layers. In a film noise level evaluation conducted by rotating the film 180 degrees at 800 rpm for more than 30 seconds, the average equivalent noise level of the polyester film was below 78 dB, and the Young's modulus was 280 kgf / mm². 2 the following.

2. The polyester film according to claim 1, wherein, When the thickness of the laminate is 16 μm, the noise level in the film noise level evaluation is below 63 dB under 250 Hz conditions.

3. The polyester film according to claim 1, wherein, The haze of the polyester film is below 10%.

4. The polyester film according to claim 1, wherein, When the thickness of the laminate is 16 μm, the noise level under 500 Hz conditions is below 53 dB in the film noise level evaluation.

5. The polyester film according to claim 1, wherein, The laminate is formed by alternating layers of the first layer and the second layer for more than 30 layers.

6. The polyester film according to claim 1, wherein, The first layer contains hydroxy alkyl ester residues.

7. The polyester film according to claim 6, wherein, Based on 100 parts by weight of the lactic acid residues, the first layer comprises 1 to 7 parts by weight of the hydroxyalkanoate residues. The second layer comprises polybutylene adipate-co-terephthalic acid resin.

8. The polyester film according to claim 1, wherein, The ratio of the thickness of the first layer to the thickness of the second layer is 1:0.2 to 1.

5.

9. The polyester film according to claim 1, wherein, The polyester film also includes a surface layer. The surface layers are respectively disposed on one side and the other side of the laminate. The surface layer includes: The first resin contains lactic acid residues; and Inorganic particles.

10. A polyester film, wherein, This includes laminates in which the first and second layers are alternately stacked. in, The first layer contains lactic acid residues, and the first layer is prepared using a resin blend of polylactic acid resin and polyhydroxyalkanoate resin. The second layer contains terephthalate residues and adipic acid residues. The laminated body is formed by alternating layers of the first layer and the second layer, with a total of 4 to 424 layers. When the noise level of the film is evaluated by rotating it 180 degrees at 800 rpm for more than 30 seconds, the noise level of the polyester film is below 80 dB under the conditions of 250 Hz, 500 Hz, 1000 Hz, 2000 Hz, 4000 Hz and 8000 Hz.

11. A packaging material, wherein, Includes the polyester film according to claim 1.

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