Regenerated PET (polyethylene terephthalate) film manufactured by using regenerated fragments

Abstract

The present invention provides: a regenerated fragment having an intrinsic viscosity and DEG unit content within specific ranges and having excellent film-forming properties; according to the present invention, the regenerated PET film has characteristics of excellent breaking strength, excellent elongation at break and significantly low thermal shrinkage, and solves the problems of low breaking strength, low elongation at break and high thermal shrinkage of the traditional regenerated PET film.

Description

Technical Field

[0001] The present disclosure relates to a recycled chip including waste PET and having an adjusted intrinsic viscosity and DEG unit content, and a PET film prepared from the recycled chip. Background Art

[0002] Plastic waste causes various problems such as water pollution, ecosystem damage, and soil pollution caused by landfilling due to poor biodegradability and large porosity. In addition, even when plastic is incinerated, it releases carbon dioxide and toxic gases that cause air pollution, making it more difficult to handle.

[0003] In this case, in order to handle plastic waste, plastics made from biomass or biodegradable plastics are currently being manufactured, but these plastics are difficult to commercialize due to high costs and complex manufacturing processes, and do not achieve the fundamental purpose of handling plastic waste.

[0004] Among the technologies for handling plastic waste, the technology that can recycle a large amount of plastic waste may be the plastic waste recycling technology. The recycling technology of PET, which accounts for a large part of plastic waste, has made remarkable technological developments since 2000, and the market scale has been continuously expanding. In addition, in recent years, due to China's import control of plastic waste, the recycled PET industry has developed rapidly.

[0005] The recycling process of waste PET (recycled PET) is to use recycled PET after processes such as sorting, removing foreign substances, cleaning, and metal separation to manufacture clothing, packaging containers, household appliances, automobiles, and films. However, since the physical properties of such recycled PET are not as good as those of PET products produced from virgin PET, the goal of recycling waste PET is mainly to minimize the environmental load rather than completely recycle the materials.

[0006] For example, since waste PET is manufactured by crushing old products that have undergone primary processing and is distributed as recycled PET flakes, the film processability is significantly reduced. In addition, compared with virgin PET films, the PET films thus produced generally have poor mechanical properties and thermal stability.

[0007] In this case, a new technology is needed to enable recycled PET films to have excellent film processability even when containing a large amount of waste PET. In addition, a technology for producing a PET film is also needed, which has physical properties equivalent to or better than those of virgin PET films produced from virgin PET, and thus has commercially useful properties.

[0008] [Prior Art Documents]

[0009] [Patent Documents]

[0010] Korean Patent Application No. 10-2013-0035897A

[0011] Korean Patent Application No. 10-2022-0003140A. Summary of the Invention

[0012] Technical Problem

[0013] One aspect of the present disclosure provides a recycled PET film having an intrinsic viscosity (IV) of 0.55 dL / g or greater, thereby achieving excellent breaking strength to solve the problem of poor mechanical properties of conventional recycled PET films.

[0014] One aspect of the present disclosure provides a recycled PET film having an IV of 0.62 dL / g or less to solve the problem of irregular travel of unstretched recycled PET films in conventional processes for producing films from waste PET.

[0015] One aspect of the present disclosure provides a recycled PET film comprising a molding modifier to solve the problem of irregular travel of unstretched recycled PET films in conventional processes for producing films from waste PET.

[0016] One aspect of the present disclosure provides a recycled PET film having a DEG unit content of 3 mol% or less, and thus can achieve a significantly lower thermal shrinkage rate than conventional recycled PET films produced from waste PET, to solve the problem of poor thermal properties of conventional recycled PET films.

[0017] In one or more embodiments, the recycled PET film may have an elongation at break of 20 kgf / mm 2 or greater, 25 kgf / mm 2 or greater, preferably 27 kgf / mm 2 or greater.

[0018] In one or more embodiments, the thermal shrinkage rate of the recycled PET film at 200 °C may be 5% or less in the MD direction and 1% or less in the TD direction.

[0019] Solution to the Problem

[0020] The recycled PET film of the present disclosure can be produced using recycled chips including waste PET and virgin chips including virgin PET, wherein the recycled PET film may have an intrinsic viscosity (IV) of 0.55 dL / g to 0.62 dL / g and a DEG unit content of 3 mol% or less.

[0021] In one or more embodiments, the recycled chips may have an intrinsic viscosity (IV) of 0.60 dL / g to 0.65 dL / g.

[0022] In one or more embodiments, the weight-average molecular weight of the waste PET can be from 40,000 g / mol to 70,000 g / mol.

[0023] In one or more embodiments, the recycled PET film can have a DEG unit content of from 0.5 mol% to 2 mol%.

[0024] In one or more embodiments, as measured by ASTM D882, the breaking strength of the recycled PET film can be 20 kgf / mm in both the MD and TD directions 2 to 30 kgf / mm 2 .

[0025] In one or more embodiments, the thermal shrinkage rate of the recycled PET film at 200 °C can be 5% or less in the MD direction and 1% or less in the TD direction.

[0026] In one or more embodiments, the recycled PET film can have a melting point of from 245 °C to 255 °C.

[0027] In one or more embodiments, the recycled PET film can have an acid value (COOH value) of from 25 eq / ton to 45 eq / ton.

[0028] In one or more embodiments, the recycled PET film can comprise from 30 wt% to 95 wt% of waste PET and from 5 wt% to 70 wt% of virgin PET.

[0029] In one or more embodiments, the recycled PET film can contain from 10 ppm to 200 ppm of metal ions derived from virgin debris from manufacturing including molding modifiers.

[0030] In one or more embodiments, the recycled PET film can satisfy the following formulas 1 to 3.

[0031] [Formula 1]

[0032] 10 ≤ [Mg] ≤ 100

[0033] [Formula 2]

[0034] 0.1 ≤ [Na] ≤ 10

[0035] [Formula 3]

[0036] 1 ≤ [P] ≤ 10

[0037] (In Formulas 1 to 3, [Mg] represents the concentration (ppm) of magnesium ions contained in the recycled PET film, [Na] represents the concentration (ppm) of sodium ions contained in the recycled PET film, and [P] represents the concentration (ppm) of phosphate ions contained in the recycled PET film.)

[0038] In one or more embodiments, the recycled PET film may contain 100 ppm to 1,000 ppm of an anti-blocking agent.

[0039] The method for preparing recycled PET according to the present invention may include producing recycled chips including waste PET, producing virgin chips including virgin PET, and producing a recycled PET film including the recycled chips and the virgin chips.

[0040] In one or more embodiments, when producing the recycled PET film, the weight ratio of the recycled chips to the virgin chips contained therein may be from 30:70 to 95:5. For example, the weight ratio of the recycled chips to the virgin chips may be from 50:50 to 90:10, from 55:45 to 90:10, or from 60:40 to 80:20.

[0041] In one or more embodiments, virgin chips containing 150 ppm to 14,000 ppm of a molding modifier may be produced.

[0042] In one or more embodiments, virgin chips containing 150 ppm to 20,000 ppm of an anti-blocking agent may be produced.

[0043] Advantageous Effects of the Invention

[0044] The recycled PET film according to an embodiment of the present invention, by having an intrinsic viscosity satisfying 0.55 dL / g to 0.62 dL / g, may have excellent tensile strength and elongation at break, and a recycled PET film including a large amount of waste PET may be produced by making the unstretched recycled PET film travel more uniformly.

[0045] The recycled PET film according to an embodiment of the present invention, by having a DEG unit content satisfying 3 mol% or less, may have more excellent heat resistance and a significantly reduced thermal shrinkage rate compared to a conventional recycled PET film.

[0046] The recycled PET film according to an embodiment of the present invention, by having a DEG unit content satisfying 0.5 mol% or more, may achieve a glass transition temperature of 81 °C or lower and a melting point of 255 °C or lower, which may further improve the film-forming performance of recycled PET and enable the production of a recycled PET film with low thermal energy in the method for preparing the recycled PET film.

[0047] Therefore, the recycled PET film according to the embodiments of the present invention can achieve environmental protection advantages by recycling waste PET; can provide excellent mechanical strength and heat resistance by controlling the intrinsic viscosity, and thus can be used as a substitute for virgin PET in related fields; and can be more advantageous than traditional recycled PET in terms of customer satisfaction. Detailed Description

[0048] Best Mode for Carrying Out the Invention

[0049] The recycled PET film and its preparation method according to the present invention will be described in more detail below. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which this disclosure belongs. In the following description, well-known functions and configurations will not be described, as they may unnecessarily obscure the understanding of the present disclosure.

[0050] Unless otherwise specified in the context, the singular forms used in this specification may also include the plural forms.

[0051] In addition, the numerical ranges used in this specification include all values including the upper and lower limits within the range, increments logically derived from the form and span of the defined range, all double limits, and all possible combinations of the upper and lower limits of the numerical ranges defined in different forms. Values outside the numerical range that may occur due to experimental errors or rounded values also belong to the defined numerical range unless otherwise defined in the specification of the present disclosure.

[0052] As used herein, the terms "comprises" and / or "comprising" or "includes" and / or "including" are open-ended and synonymous with "provided with", "containing", "having", or "characterized by", and do not exclude additional, unrecited elements, materials, or method steps.

[0053] The term "acidity" as used herein may refer to the equivalent weight of the PET carboxyl end groups (*-COOH) contained in the recycled PET, recycled chips, or PET film.

[0054] The term "unstretched recycled PET film" as used herein may refer to a molten recycled PET sheet obtained by a T-die or a recycled PET sheet in an unstretched state during PET film production.

[0055] For example, traditional waste PET, such as fibers, containers, labels, pipes, bottles, and films, etc., is made into recycled PET molded products through processes such as compression, inorganic particle separation, cleaning, color classification, drying, pulverization, non-solvent solution cleaning, drying, metal particle separation, etc.

[0056] However, such waste PET products have undergone one or more molding processes, and thus have different PDIs, crystallinities, physical properties, glass transition temperatures, melting points, etc. Moreover, due to the residual grade, compared with the molded products produced from virgin PET, their physical properties are poor.

[0057] For example, since the process of preparing recycled PET film from waste PET includes multiple processes such as heat treatment, cooling, stretching, and drying, etc., which are carried out in a short period of time. Traditionally, even if it contains a large amount of virgin PET, such as 50 wt% or more, the produced recycled PET film still exhibits poor physical properties. For example, it shows poor mechanical properties and thermal properties and cannot be used for commercial applications.

[0058] In view of the above problems existing in traditional recycled PET films, through research, it is found that by controlling the intrinsic viscosity (IV) of recycled fragments including waste PET, the film-forming performance of recycled PET films can be significantly improved. Moreover, surprisingly, the recycled PET films produced in this way also have excellent mechanical properties.

[0059] In addition, it is further found that according to the DEG unit content of the PET resin (waste PET and virgin PET) contained in the recycled PET film, by controlling the DEG unit content, the recycled PET film can significantly improve the thermal shrinkage rate and can maintain mechanical properties.

[0060] Therefore, the recycled PET film according to the embodiments of the present invention, due to its significantly improved mechanical strength and low thermal shrinkage rate, can be highly environmentally friendly by recycling waste PET and can be used as a substitute for virgin PET films used in fields such as display substrates and electronic substrate protective films.

[0061] The recycled PET film of the present disclosure will be described in detail below.

[0062] The recycled PET film of the present disclosure can be made from recycled fragments including waste PET and virgin fragments including virgin PET.

[0063] In one or more embodiments, the recycled PET film can have an intrinsic viscosity (IV) of 0.55 dL / g to 0.62 dL / g and a DEG unit content of 3 mol% or less.

[0064] In another embodiment, the recycled PET film may have an intrinsic viscosity of 0.57 dL / g to 0.59 dL / g, and the recycled PET film with an intrinsic viscosity satisfying this range may be preferred because of its excellent elongation at break and its breaking strength within a practical range.

[0065] The intrinsic viscosity of the recycled PET film may be determined by the weight-average molecular weight or crystallinity of the waste PET and virgin PET contained in the recycled PET film. In addition, since the recycled PET film having an intrinsic viscosity within the above range may have a lower crystallinity than the virgin PET film, the film produced therefrom may have a significant elongation at break.

[0066] The recycled PET film with an intrinsic viscosity lower than 0.55 dL / g may have a higher elongation at break due to a significantly reduced crystallinity, but may have a significantly reduced breaking strength.

[0067] In addition, the recycled PET film with an intrinsic viscosity greater than 0.62 dL / g may have reduced mechanical properties due to its low film-forming property, and thus the PET film with an intrinsic viscosity within the above range may be more preferred.

[0068] According to one or more embodiments, the recycled chips may have an intrinsic viscosity (IV) of 0.60 dL / g to 0.65 dL / g.

[0069] The recycled chips with an intrinsic viscosity within the above range may be preferred because their intrinsic viscosity is lower than that of the virgin PET resin, as such recycled chips may enable the unstretched recycled PET film to travel at a constant speed during the processing of the recycled PET film, and the intrinsic viscosity of the PET film produced therefrom may satisfy 0.62 dL / g or lower.

[0070] The intrinsic viscosity of the recycled chips may depend on the molecular weight, polymer structure, and repeat unit content of the waste PET and virgin PET contained therein. For example, the value of the intrinsic viscosity may vary according to the weight-average molecular weight of the waste PET contained in the recycled chips.

[0071] According to one or more embodiments, the weight-average molecular weight of the waste PET may be 40,000 g / mol to 70,000 g / mol, 45,000 g / mol to 65,000 g / mol, or preferably 50,000 g / mol to 60,000 g / mol.

[0072] Since the recycled chips including the waste PET having a weight-average molecular weight within the above range may have an IV within the above range, such recycled chips may have excellent PET film processability, and the PET film produced therefrom may have excellent elongation at break and breaking strength, and thus may be preferred.

[0073] In one or more embodiments, the polydispersity index (PDI) of the waste PET can be from 1.0 to 3.0, preferably from 1.5 to 2.5. In addition, the waste PET may be a product obtained by crushing various waste PET products having different weight-average molecular weights, so the PDI value is relatively high; however, since the waste PET is recycled flakes produced by mixing these waste PET products, the deterioration of the physical properties of the recycled PET film caused by the high PDI of the waste PET can be reduced or suppressed.

[0074] In one or more embodiments, the waste PET and virgin PET contained in the recycled PET film may contain diethylene glycol as a comonomer unit in addition to ethylene and ethylene terephthalate.

[0075] In one or more embodiments, the DEG unit content of the waste PET contained in the recycled PET film can be from 0.5 mol% to 3.0 mol%. For example, the DEG unit content of the waste PET contained in the recycled PET film can be from 0.5 mol% to 2.9 mol%, from 0.5 mol% to 2.8 mol%, from 0.5 mol% to 2.7 mol%, from 0.5 mol% to 2.6 mol%, from 0.5 mol% to 2.5 mol%, from 0.6 mol% to 2.4 mol%, from 0.6 mol% to 2.3 mol%, from 0.6 mol% to 2.2 mol%, from 0.6 mol% to 2.1 mol%, from 0.6 mol% to 2.0 mol%, from 0.7 mol% to 1.9 mol%, from 0.7 mol% to 1.8 mol%, from 0.7 mol% to 1.7 mol%, from 0.8 mol% to 1.6 mol%, from 0.8 mol% to 1.5 mol%, from 0.8 mol% to 1.4 mol%, from 0.9 mol% to 1.3 mol%, from 1.0 mol% to 1.3 mol%, or from 1.1 mol% to 1.3 mol%.

[0076] Depending on the waste PET, virgin PET, and the content of the DEG units contained therein, the properties of the recycled PET film such as crystallinity, glass transition temperature, cooling temperature, thermal shrinkage rate, elongation, and tensile strength may vary. In addition, an increase in the DEG unit content results in a decrease in crystallinity, which may lead to a decrease in the glass transition temperature and melting point, as well as a decrease in the breaking strength.

[0077] According to one or more embodiments, the recycled PET film can have a DEG unit content of from 0.5 mol% to 2 mol%, preferably from 1 mol% to 2 mol%.

[0078] The recycled PET film with a DEG unit content within the above range can achieve a lower thermal shrinkage rate than traditional recycled PET films including waste PET, and can also achieve a glass transition temperature and a melting point that result in excellent film-forming properties of recycled PET, and thus can be preferred.

[0079] For example, a recycled PET film containing PET (waste PET and virgin PET) with a DEG unit content exceeding 3 mol% may have an increased elongation at break, but the tensile strength may decrease significantly, so it cannot be used as a substitute for virgin PET film.

[0080] In addition, for a recycled PET film containing PET (waste PET and virgin PET) with a DEG unit content of 0.5 mol% or less, the film-forming properties of the recycled PET may decrease due to a significant reduction in elongation and an increase in melting point; therefore, it is more preferred that the DEG unit content of the recycled PET film satisfies 0.5 mol% to 3 mol%.

[0081] According to one or more embodiments, the recycled PET film may have an acid value (COOH value) of 25 eq / ton to 45 eq / ton, for example, 32 eq / ton to 39 eq / ton.

[0082] Surprisingly, the recycled PET film with an acid value within the above range can achieve more significant film-forming properties through the interaction with the intrinsic viscosity within the above range, and has excellent transparency, low thermal shrinkage rate, and excellent tensile strength and elongation at break, and thus can be preferred.

[0083] According to one or more embodiments, the recycled PET film may include 40 wt% to 95 wt% of waste PET and 5 wt% to 60 wt% of virgin PET, and preferably may include 60 wt% to 95 wt% of waste PET and 5 wt% to 40 wt% of virgin PET.

[0084] By including waste PET and virgin PET within the above wt% range as the PET resin component, the recycled PET film can accommodate more waste PET than traditional recycled PET films, and thus is more environmentally friendly. In addition, the intrinsic viscosity and DEG unit content can be controlled within the above range by using recycled chips containing waste PET.

[0085] As described above, the recycled PET film can simultaneously exhibit excellent elongation at break and tensile strength, and also has a low thermal shrinkage rate, such that the recycled PET film has sufficient physical properties and can be used as a substitute for virgin PET film.

[0086] According to one or more embodiments, the thickness of the recycled PET film may be 10 μm to 200 μm, for example, 10 μm to 125 μm, for example, 10 μm to 100 μm; however, the thickness of the recycled PET film may be adjusted according to its application field and may be any thickness as long as it does not reduce the physical properties.

[0087] The recycled PET films having the thickness in the above range may be different from each other depending on the degree of stretching of the unstretched recycled PET film drawn out from the T-die in the method for preparing the PET film described below in the MD and TD directions. In addition, the recycled PET film having a thickness in the above range may be preferred because it can have minimal surface scratches, pinholes or holes.

[0088] In addition, the recycled PET film having a thickness within the above range may be a single layer film or a laminated film, and the thickness may be increased with lamination, but is not particularly limited.

[0089] For example, the laminated film may be a film having two or more recycled PET film layers, and may have a laminated structure including a single PET film layer and different types of layers (e.g., a layer containing no recycled polyester, or a layer containing a different type of resin).

[0090] According to an embodiment, the recycled PET film may contain 10 ppm to 200 ppm of metal ions derived from the produced virgin fragments including the molding modifier, and may include, for example, 10 ppm to 100 ppm, such as 30 ppm to 80 ppm.

[0091] In the prepared primary fragments containing the molding modifier, the molding modifier may contain metal ions, for example, the metal ions may be Mg 2+ 、Na + , Ca 2+ 、P0 4 3- or Li + .

[0092] The molding modifier can be, for example, one selected from magnesium hydroxide, magnesium acetate, sodium acetate, sodium hydroxide, calcium acetate, lithium acetate, calcium phosphate, magnesium oxide, magnesium hydroxide, magnesium alcoholate, manganese acetate, zinc acetate, trimethyl phosphate and triethyl phosphate, or a mixture of two or more thereof.

[0093] According to one or more embodiments, the molding modifier may include a magnesium compound, a sodium compound, and a phosphorus compound, and may include, for example, magnesium acetate, sodium acetate, and trimethyl (ethyl) phosphate.

[0094] According to one or more embodiments, the recycled PET film may satisfy Formulas 1 to 3 below.

[0095] [Formula 1]

[0096] 10 ≤ [Mg] ≤ 100

[0097] [Formula 2]

[0098] 0.1 ≤ [Na] ≤ 10

[0099] [Formula 3]

[0100] 1 ≤ [P] ≤ 50

[0101] (In Formulas 1 to 3, [Mg] represents the concentration (ppm) of magnesium ions contained in the recycled PET film, [Na] represents the concentration (ppm) of sodium ions contained in the recycled PET film, and [P] represents the concentration (ppm) of phosphate ions contained in the recycled PET film.)

[0102] In another embodiment, in Formulas 1 to 3, [Mg] can be 10 to 80, [Na] can be 0.1 to 5, and [P] can be 1 to 10.

[0103] When the recycled PET film contains magnesium ions, sodium ions, and phosphate ions within the concentration (ppm) ranges of Formulas 1 to 3, even if the metal ion content is extremely small, significant film-forming performance can be achieved, and metal ion aggregation can be prevented. Therefore, the PET film produced therefrom can simultaneously achieve significant transparency, low color difference values, and low surface characteristics.

[0104] Furthermore, through a recycled PET film made from recycled chips with adjusted intrinsic viscosity, DEG unit content, and acidity, excellent processability can be achieved, and by further including a molding modifier, further improved film-forming performance can be achieved. Surprisingly, due to excellent compatibility with recycled chips having an intrinsic viscosity within the above range, the effect of the molding modifier can be further enhanced.

[0105] The recycled PET film according to one or more embodiments may contain 100 ppm to 1,000 ppm of an anti-blocking agent, particularly 300 ppm to 1,000 ppm, more particularly 500 ppm to 900 ppm.

[0106] The recycled PET film containing an anti-blocking agent within the above range may have further improved recycled PET film-forming performance during the preparation process. In addition, the recycled PET film produced in this way is not easily adhered to each other during winding, significantly reduces defects caused by scratches, and has uniform processability, and thus can be preferred.

[0107] In one or more embodiments, the anti-blocking agent can be inorganic particles, organic particles, or a mixture thereof. For example, it can be NaF, MgF 2 , CaF 2, BaF 2 , SiO 2 , BaSO 4 , CeF 3 , Al 2 O 3 , ZrO 2 , TiO 2 , ZnS, ZnSe and Ta 2 O 5 or more of the above. For example, the anti-blocking agent including SiO 2 can achieve excellent film-forming properties, but is not limited thereto, and any anti-blocking agent recognizable by those skilled in the art can be used.

[0108] The recycled PET film may further include one or more additives selected from lubricants, stabilizers, plasticizers, UV stabilizers, heat stabilizers, fillers, pigments, blowing agents, viscosity regulators, processing aids, flame retardants, reinforcing agents, and dispersants. Not limited to the above examples, any additives known to those skilled in the art can be used.

[0109] The physical properties of the recycled PET film according to the embodiments will be described in more detail below.

[0110] The recycled PET film according to the embodiments, by having an intrinsic viscosity and a DEG unit content within the above ranges, can have excellent elongation at break and tensile strength, and in terms of thermal properties, can have a significantly reduced thermal shrinkage rate.

[0111] In addition, by further adding a molding modifier to the recycled PET film, the film-forming property can be further improved, thereby obtaining a recycled PET film with excellent transparency, reduced pinhole defects, and reduced surface unevenness.

[0112] Measured according to ASTM D882, the tensile strength of the recycled PET film according to the embodiments can be 10 kgf / mm 2 to 30 kgf / mm 2 , preferably 20 kgf / mm 2 to 30 kgf / mm 2 .

[0113] The recycled PET film having a tensile strength within the above range can have a tensile strength superior to that of a conventional recycled PET film and a tensile strength similar to that of a virgin PET film, and thus can be used as a substitute for a virgin PET film in fields requiring high tensile strength.

[0114] As measured according to ASTM D882, the elongation at break of the recycled PET film according to another embodiment may be 130% to 170% in the MD direction and 100% to 140% in the TD direction, preferably 150% to 170% in the MD direction and 110% to 140% in the TD direction.

[0115] The recycled PET film having an elongation at break within the above range may be due to having an intrinsic viscosity satisfying the range of 0.55 dL / g to 0.62 dL / g. In addition, since the elongation at break is within the above range, the elongation at break of the recycled PET film is superior to that of virgin PET, and the elongation at break is improved compared to conventional recycled PET. Therefore, it can be more advantageously used as a flexible material.

[0116] According to one or more embodiments, the thermal shrinkage rate of the recycled PET film at 200 °C may be 5% or less in the MD direction and 1% or less in the TD direction, and preferably 3% or less in the MD direction, more preferably 2% or less in the MD direction, and 0.1% to 0.5% in the TD direction.

[0117] The recycled PET film having a thermal shrinkage rate within the above range still has excellent dimensional stability even in a high-temperature environment, and thus can be used in various fields including display substrates, electronic product protective films, food containers, etc.

[0118] The method for preparing the recycled PET film of the present disclosure will be described in detail below.

[0119] Disclosed herein is a method for preparing a PET film, comprising: producing recycled chips including waste PET; producing virgin chips including virgin PET; and producing a recycled PET film including the recycled chips and the virgin chips.

[0120] According to one or more embodiments, the recycled chips may have an intrinsic viscosity of 0.60 dL / g to 0.65 dL / g.

[0121] The recycled chips having an intrinsic viscosity within the above range may have excellent film-forming properties as described above, and the recycled PET film produced from such recycled chips may have an intrinsic viscosity (IV) of 0.55 dL / g to 0.61 dL / g, thereby achieving excellent tensile strength and excellent elongation at break.

[0122] The waste PET may be any waste polyester-based polymer, for example, it may be selected from one or more of polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polypropylene terephthalate (PTT), polyethylene naphthalate (PEN).

[0123] In addition, recycled PET can be a used polyester-based copolymer and can be produced, for example, by polymerizing one or more selected from terephthalates and C 1 -C 12 alkyl diols. However, without being limited to the above examples, any polyester-based copolymer known to those skilled in the art can be used.

[0124] In one or more embodiments, when producing a recycled PET film, the weight ratio of recycled chips to virgin chips included can be from 30:70 to 95:5, such as 50:50 to 95:5, 70:30 to 95:5, or 80:20 to 90:10.

[0125] A method for preparing a recycled PET film including recycled chips and virgin chips in a weight ratio within the above range can be significantly environmentally friendly by recycling and reusing a large amount of waste PET. In addition, the recycled PET film prepared by this method can achieve physical properties comparable to those of virgin PET films and can be used as a substitute for virgin PET films in related fields, thereby achieving further significant environmental protection.

[0126] In one or more embodiments, the method for preparing a recycled PET film can further include a molding modifier and an anti-blocking agent. The molding modifier can be introduced during the preparation process of the recycled chips to produce recycled chips containing metal ions from the molding modifier, and the molding modifier can be introduced during the preparation process of the virgin chips to produce virgin chips containing metal ions.

[0127] For example, since the produced recycled PET film may have further improved metal ion dispersibility, it may be preferable to introduce the molding modifier during the preparation of the virgin chips.

[0128] The molding modifier can be, for example, one or a mixture of two or more selected from magnesium hydroxide, magnesium acetate, sodium acetate, sodium hydroxide, calcium acetate, lithium acetate, calcium phosphate, magnesium oxide, magnesium hydroxide, magnesium alkoxide, manganese acetate, zinc acetate, trimethyl phosphate, and triethyl phosphate.

[0129] The molding modifier can be a substance that can achieve excellent film-forming properties of the recycled PET film even when added in a relatively small amount, and preferably includes magnesium acetate, sodium acetate, and trimethyl (ethyl) phosphate.

[0130] In one or more embodiments, the virgin chips can contain 150 ppm to 14,000 ppm, preferably 150 ppm to 10,000 ppm, more preferably 1,000 ppm to 6,000 ppm of the molding modifier.

[0131] For example, a shaping modifier can be introduced during the production of virgin flakes, and the virgin flakes thus produced containing metal ions from the shaping modifier can contain metal ions with excellent dispersibility and can therefore be preferred.

[0132] In the virgin flakes produced and containing the shaping modifier within the above range, the concentration (ppm) of the shaping modifier contained may vary depending on the amount (wt%) of the virgin flakes introduced during the production of the recycled PET film, but can still satisfy the concentration (ppm) range of the shaping modifier introduced during the preparation of the virgin flakes.

[0133] For example, the recycled PET film of the present invention can be produced to include 100 ppm to 700 ppm of a shaping modifier, such as 100 ppm to 500 ppm, such as 100 ppm to 300 ppm; however, the amount of the shaping modifier included is not limited as long as the metal ion concentration in the recycled PET film thus produced satisfies 10 ppm to 200 ppm.

[0134] In one or more embodiments, in the above method for preparing recycled PET, an anti-blocking agent can be added together with the shaping modifier during the production of recycled flakes, virgin flakes, and the recycled PET film. In another embodiment, including the anti-blocking agent in the virgin flakes can result in high-quality recycled flakes, virgin flakes, and shaping modifier, and the recycled PET film thus produced can contain an anti-blocking agent with excellent dispersibility.

[0135] According to one or more embodiments, the virgin flakes can contain 150 ppm to 20,000 ppm, preferably 1,000 ppm to 20,000 ppm, more preferably 1,500 ppm to 18,000 ppm of an anti-blocking agent; however, the amount of the anti-blocking agent is not particularly limited and can vary depending on the wt% of the virgin flakes introduced during the preparation of the recycled PET film.

[0136] In one or more embodiments, producing the recycled PET film can include stretching the unstretched recycled PET film 3 to 5 times in the TD and MD directions.

[0137] For example, an unstretched PET film melt-extruded from a T-die (260 °C to 280 °C) can be driven to a casting roll while leveling it, cooled to 80 °C, and stretched 3 to 5 times longitudinally (MD) by a longitudinal stretching machine. Then, the recycled PET film stretched in the MD direction is stretched 4 to 5 times in the transverse (TD) direction using a transverse stretching machine, thereby producing a recycled PET film with a thickness of 10 μm to 100 μm.

[0138] For example, the stretching process in the MD direction can be carried out at a temperature of 80°C to 120°C, preferably 100°C to 120°C, and the elongation ratio is 3.8 to 4.8 times, preferably 4.0 to 4.5 times; however, the temperature and elongation ratio are not limited to the above examples. Additionally, the stretching process in the TD direction can be carried out at a temperature of 200°C to 240°C, preferably 210°C to 240°C, more preferably 220°C to 235°C, and can be stretched at the same elongation ratio as in the MD direction.

[0139] The PET film and its preparation method according to the present invention will be described in more detail below with reference to examples. However, the following examples are for illustrative purposes only to describe the present disclosure in detail; thus, the present disclosure is not limited to these examples and can be implemented in various forms. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. Additionally, the terms used herein are only for effectively describing specific embodiments and are not intended to limit the present disclosure.

[0140] Preparation of recycled fragments

[0141] [Measurement methods]

[0142] 1. Measurement of intrinsic viscosity (IV)

[0143] Weigh 2.0 g of the sample using an electronic scale and place it in a 100 mL conical flask with a glass stopper. Add 25 mL of o-chlorophenol (OCP) using a pipette. Next, place the conical flask in a molten bath at 100°C and dissolve it for 1 hour at a rotation speed of 150 rpm. Then, take out the completely dissolved sample solution in the conical flask from the bath and cool it at room temperature. Next, using the entire pipette, introduce 7.5 mL of the sample solution cooled in a constant temperature bath at 25°C into a Cannon-Fenske viscometer and let it stand for 20 minutes to achieve temperature equilibrium. Next, let the sample solution in the Cannon-Fenske viscometer flow once, and then from the second time, let it flow freely, and record the efflux time by measuring the time required for the solution to flow from the upper scale line to the lower scale line of the viscometer. Using the Huggins Equation, the value of the intrinsic viscosity can be obtained.

[0144] 2. Measurement of DEG unit content

[0145] Place 0.0015 g of HD and 0.037 g of DEG in a 100 mL round-bottom flask, dissolve them in methanol, take 1 μL of the dissolved solution, and perform gas chromatography analysis using a gas chromatograph (Agilent, 6890N) to obtain a chromatogram. Next, dissolve 0.15 g of HD and 0.06 g of zinc acetate in methanol in a beaker, and place 30.0 mL of the dissolved reaction solution in a polytetrafluoroethylene container; then place the polytetrafluoroethylene container containing the reaction solution in a pressure tube and seal the pressure tube. Then, place the sealed pressure tube in an oven at 210 °C and react for 30 minutes. After the reaction is completed and cooled to room temperature, remove the polytetrafluoroethylene container from the pressure tube. Separate the dissociation solution in the polytetrafluoroethylene container using a 0.45 μm separation membrane, take 1 μL of the separated reaction solution, and obtain a chromatogram by gas chromatography. Then, calculate the DEG contained in the reaction solution by comparing the obtained DEG chromatogram with the chromatogram of the reaction solution.

[0146] 3. Measurement of glass transition temperature and melting point

[0147] Place 0.1 mg of the sample in a differential scanning calorimeter (DSC, Perkin Elmer, DSC7, heating rate: 0.8 °C / s) to obtain the glass transition temperature (Tg) and melting point (Tm) values of the sample.

[0148] [Preparation Examples 1 to 7]

[0149] Use a kneading device (Errema) to produce recycled chips from waste PET with the characteristics shown in Table 1 below.

[0150] Then measure the intrinsic viscosity and DEG unit content of the produced recycled chips by the above method, and the results are shown in Table 1 below.

[0151] [Table 1]

[0152]

[0153] As shown in Table 1, recycled chips of Preparation Examples 1 to 5 were produced from waste PET products with different intrinsic viscosities. It was found that the recycled chips produced in this way had the intrinsic viscosity and DEG unit content shown in Table 1.

[0154] As waste PET is processed into recycled chips through a kneading device, the intrinsic viscosity of the recycled chips has become lower than that of the waste PET. However, it was found that the intrinsic viscosity of the original waste PET is still the most important influencing factor.

[0155] As can be seen from Table 1, Preparation Examples 6 and 7 have the same intrinsic viscosity as Preparation Example 3; at the same time, it was also found that among the recycled fragments of waste PET products with different melting points prepared, the lower melting point of the waste PET led to an increase in the content of DEG units in the recycled PET copolymer contained therein.

[0156] This phenomenon may be due to the increase in the content of DEG units in the waste PET, resulting in an increase in the irregularity of the waste PET, thereby causing a decrease in crystallinity.

[0157] Preparation of Recycled PET Film

[0158] [Measurement Method]

[0159] 4. Measurement of Elongation at Break and Tensile Strength

[0160] The measurement was carried out in accordance with ASTM D882 standard, and the sample was elongated at a rotating head rate of 500 mm / min. The maximum tensile strength at the break of the sample was measured, and the maximum elongation was measured, from which the tensile strength at break and the elongation at break were obtained.

[0161] 5. Measurement of Thermal Shrinkage Rate

[0162] The measurement was carried out in accordance with ASTM D2305 standard. Each sample was heated in an oven at 150 °C and 200 °C for 15 minutes respectively. Then, according to the dimensional change test disclosed in ASTM D2305, the thermal shrinkage rates of the heated samples at 150 °C and 200 °C were measured.

[0163] [Examples 1 to 4 and Comparative Examples 1 and 5]

[0164] The virgin PET was loaded into a mixing equipment (Errema), and then the loaded virgin PET was mixed with a molding modifier containing the metal compounds, magnesium acetate (MgAc), sodium acetate (NaAc) and triethyl phosphate (TEP) shown in Table 2 according to their respective concentrations. Then, SiO 2 was added to the virgin PET to make virgin fragments.

[0165] Subsequently, 80 wt% of the recycled fragments of the preparation example and 20 wt% of the virgin fragments shown in Table 2 were melt-mixed at 260 °C. After the mixing was completed, the obtained mixture was poured into a T-die head maintained at 275 °C (error range: ±15 °C), and then the obtained unstretched recycled PET film was stretched 4.5 times in the MD and TD directions to obtain a recycled PET film with a thickness of 12 μm.

[0166] Then, the recycled PET film produced in this way was measured by the following measurement methods, and the results are shown in Table 3 below.

[0167] [Table 2]

[0168]

[0169] [Table 3]

[0170]

[0171] In Table 3, referring to Examples 1 to 3, it was found that an increase in the intrinsic viscosity led to an increase in the breaking strength and a decrease in the elongation at break. This result indicates that the increase in the intrinsic viscosity was due to an increase in the brittleness of the PET film, and the increase in brittleness was due to an increase in the crystallinity of the recycled PET film. For the same reason, referring to Comparative Examples 1 and 2 in Table 3, it was found that a decrease in the intrinsic viscosity led to a significant decrease in the breaking strength. Additionally, it can be seen from Comparative Example 3 that as the intrinsic viscosity increased, the breaking strength increased, but the elongation at break decreased significantly. This result indicates that Comparative Examples 1 to 3 cannot be widely applied to fields that require excellent flexibility.

[0172] Furthermore, it was also found that the crystallinity of the recycled PET film was related to the DEG unit content of the waste PET and virgin PET contained therein, and this finding can be confirmed in Comparative Examples 4 and 5 in Table 3 above.

[0173] It was found that the elongation at break of the recycled PET film in Comparative Example 4 (with a DEG unit content of 0.3 mol%) decreased significantly compared to Example 3. Additionally, it was also found that the breaking strength of Comparative Example 5 decreased significantly and the heat shrinkage rate increased significantly.

[0174] This indicates that the mechanical properties of the recycled PET film according to the present invention, such as the breaking strength and the elongation at break, can be controlled by the intrinsic viscosity and the DEG unit content of the waste PET and virgin PET contained therein; and if the intrinsic viscosity of the recycled PET film produced thereby is in the range of 0.55 dL / g to 0.62 dL / g, the recycled PET film can simultaneously have excellent breaking strength and excellent elongation at break.

[0175] Furthermore, as the DEG unit content of the PET film according to the present invention increases, the breaking strength of the PET film may decrease significantly, while the elongation at break may increase.

[0176] For example, an increase in the DEG unit content of the recycled PET film may cause a sharp increase in the heat shrinkage rate, resulting in a significant decrease in the dimensional stability of the recycled PET film; this indicates that the DEG unit content of the recycled PET film needs to be in the range of 0.5 mol% to 3 mol% in order for the recycled PET film to simultaneously have excellent mechanical properties and excellent thermal characteristics.

[0177] Although the present disclosure has been described with reference to specific embodiments and comparative examples, it should be understood that these embodiments are only to be considered as descriptive and not for the purpose of limitation. In addition, those of ordinary skill in the art should understand that various changes in form and detail can be made without departing from the spirit and scope of the present disclosure.

[0178] Therefore, the inventive concept should not be limited to the embodiments described herein, but rather encompasses all modifications, equivalents, and alternatives falling within the spirit and scope of the appended claims.

Claims

1. A recycled PET film, which is produced from recycled chips including waste PET and virgin chips including virgin PET, wherein, the recycled PET film has an intrinsic viscosity (IV) of 0.55 dL / g to 0.62 dL / g and a DEG unit content of 3 mol% or less.

2. The recycled PET film according to claim 1, wherein the recycled chips have an intrinsic viscosity (IV) of 0.60 dL / g to 0.65 dL / g.

3. The recycled PET film according to claim 1, wherein the waste PET has a weight average molecular weight of 40,000 g / mol to 70,000 g / mol.

4. The recycled PET film according to claim 1, wherein the recycled PET film has a DEG unit content of 0.5 mol% to 2 mol%.

5. The recycled PET film according to claim 1, wherein the breaking strength of the recycled PET film is 20 kgf / mm in both the MD and TD directions as measured by ASTM D882 2 to 30 kgf / mm 2 .

6. The recycled PET film according to claim 1, wherein the thermal shrinkage rate of the recycled PET film at 200 °C is 5% or less in the MD direction and 1% or less in the TD direction.

7. The recycled PET film according to claim 1, wherein the melting point of the recycled PET film is 245 °C to 255 °C.

8. The recycled PET film according to claim 1, wherein the acid value (COOH value) of the recycled PET film is 25 eq / ton to 45 eq / ton.

9. The recycled PET film according to claim 1, wherein the recycled PET film contains 30 wt% to 95 wt% of the waste PET and 5 wt% to 70 wt% of the virgin PET.

10. The recycled PET film according to claim 1, wherein the recycled PET film contains 10 ppm to 200 ppm of metal ions derived from the virgin chips including a molding modifier.

11. The recycled PET film according to claim 10, wherein the recycled PET film satisfies Formulas 1 to 3: [Formula 1] 10 ≤ [Mg] ≤ 100 [Formula 2] 0.1 ≤ [Na] ≤ 10 [Formula 3] 1≤[P]≤10 wherein, in Formulas 1 to 3, [Mg] is the concentration (ppm) of magnesium ions contained in the recycled PET film, [Na] is the concentration (ppm) of sodium ions contained in the recycled PET film, and [P] is the concentration (ppm) of phosphorus ions contained in the recycled PET film.

12. The recycled PET film according to claim 1, wherein the recycled PET film contains 100 ppm to 1,000 ppm of an anti-blocking agent.

13. A method for manufacturing a recycled PET film, the method comprising: preparing recycled chips including waste PET; preparing virgin chips including virgin PET; and and preparing a recycled PET film including the recycled chips and the virgin chips.

14. The method according to claim 13, wherein when preparing the recycled PET film, the weight ratio of the recycled chips to the virgin chips included can be 30:70 to 95:

5.

15. The method according to claim 13, wherein the preparation of the virgin chips includes 150 ppm to 14,000 ppm of a molding modifier.

16. The method according to claim 13, wherein the preparation of the native chips comprises an anti-sticking agent in an amount of 150 ppm to 20,000 ppm.

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