Aliphatic-aromatic polyesters and their use

Abstract

The present application provides an aliphatic-aromatic polyester and application thereof, the aliphatic-aromatic polyester comprises diacid residue and diol residue; the diacid residue comprises terephthalic acid residue and at least one aliphatic diacid residue; the diol residue comprises 1,4-butanediol residue; the mass percentage content of the number average molecular weight of the aliphatic-aromatic polyester and the oligomer with the number average molecular weight determined by GPC being less than or equal to 1000 satisfies the following relationship: Mn / q is 50000-110000; wherein, Mn is the number average molecular weight of the aliphatic-aromatic polyester, and q is the mass percentage content of the oligomer with the number average molecular weight determined by GPC being less than or equal to 1000. The shrink film prepared from the aliphatic-aromatic polyester has excellent heat shrinkage performance.

Description

Technical Field

[0001] This invention belongs to the field of polymer compound technology, specifically relating to an aliphatic-aromatic polyester and its applications. Background Technology

[0002] Shrink film is a type of plastic film that shrinks and adheres tightly to packaged goods upon heating, utilizing its heat-shrinking properties to wrap, protect, and enhance the appearance of the product. Its core principle is that during production, the polymer is stretched at high temperatures, causing the molecular chains to align along the stretching direction. After the molecular chains deorient and return to their original state, a shrinking force is generated, causing the film to adhere tightly to the product surface. Shrink film is widely used in food packaging, daily chemical products, industrial products, electronic products, and pharmaceutical packaging. Currently, shrink films are mainly made of materials such as polyvinyl chloride (PVC), polyethylene (PE), polyethylene terephthalate-1,4-cyclohexanediol (PETG), and polyolefins (POF). Among these, PE has high shrinkage force, low-temperature resistance, and puncture resistance, while PETG has high transparency, high shrinkage rate, and good printability. However, none of the above-mentioned traditional shrink films are biodegradable.

[0003] To alleviate the environmental problems caused by the abandonment of traditional shrink films, people have begun to use biodegradable polyesters, such as polybutylene terephthalate (PBAT), to replace the above-mentioned traditional materials and improve the biodegradability of shrink films. However, commercially available biodegradable polyesters generally have the problem of low heat shrinkage performance.

[0004] Therefore, developing a polyester with good heat shrinkage properties is an urgent problem to be solved in this field. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide an aliphatic-aromatic polyester and its applications. This aliphatic-aromatic polyester solves the problem of insufficient heat shrinkage properties in existing biodegradable polyesters.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides an aliphatic-aromatic polyester comprising diacid residues and diol residues; wherein the diacid residues comprise terephthalic acid residues and at least one aliphatic diacid residue; wherein the diol residues comprise 1,4-butanediol residues; and wherein the number-average molecular weight of the aliphatic-aromatic polyester and the mass percentage of oligomers with a number-average molecular weight ≤1000 as determined by GPC in the aliphatic-aromatic polyester satisfy the following relationship: Mn / q is 50000~110000; wherein Mn is the number-average molecular weight of the aliphatic-aromatic polyester, and q is the mass percentage of oligomers with a number-average molecular weight ≤1000 as determined by GPC.

[0008] In this invention, the ratio of the number-average molecular weight to the oligomer content of the aliphatic-aromatic polyester is controlled within a specific range, so that the shrink film prepared from the aliphatic-aromatic polyester has excellent heat shrinkage properties.

[0009] In this invention, the aliphatic-aromatic polyester has a low number-average molecular weight, resulting in weak entanglement of polymer molecular chains, insufficient shrinkage force after material orientation, and poor heat shrinkage performance. Conversely, a high number-average molecular weight hinders the thermal motion of molecular chains, which also leads to poor heat shrinkage performance. Furthermore, heat shrinkage requires higher temperatures and times, resulting in higher energy consumption and increased costs.

[0010] In this invention, the oligomers are linear or cyclic low-molecular-weight polymers produced during the reaction of diacids and diols. The oligomers can act as plasticizers and nucleating agents in aliphatic-aromatic polyesters, affecting their crystallization properties and consequently their shrinkage rate. The content of oligomers with a number-average molecular weight ≤1000, as determined by GPC, within a specific range is beneficial for obtaining films with superior heat-shrinkage properties.

[0011] It should be noted that the term "residue" refers to any organic structure introduced into the polymer molecular chain by the relevant monomer through a polycondensation reaction, that is, an organic structure derived from the relevant monomer; for example, a diacid residue refers to a structure in an aliphatic polyester derived from a diacid monomer.

[0012] In this invention, terephthalic acid and / or terephthalic acid derivatives are introduced into the polyester molecular chain through a polymerization reaction to form terephthalic acid residues; aliphatic diacids and / or aliphatic diacid derivatives are introduced into the polyester molecular chain through a polymerization reaction to form aliphatic diacid residues.

[0013] In this invention, the terephthalic acid derivatives include dialkyl terephthalates, which, by way of example, include but are not limited to dimethyl terephthalate, diethyl terephthalate, and diisopropyl terephthalate; the aliphatic diacid derivatives include dialkyl terephthalates, which, by way of example, include but are not limited to dimethyl terephthalate, diethyl terephthalate, dipropyl terephthalate, diisopropyl terephthalate, dibutyl terephthalate, and dihexyl terephthalate.

[0014] In this invention, Mn / q is 50000~110000, for example, it can be 50000, 52000, 55000, 58000, 60000, 62000, 65000, 68000, 70000, 72000, 75000, 78000, 80000, 82000, 85000, 88000, 90000, 92000, 95000, 98000, 100000, 100200, 100500, 100800, 110000 or any two of them, preferably Mn / q is 85300~105000.

[0015] Preferably, the number-average molecular weight of the aliphatic-aromatic polyester is 51,000 to 100,000, for example, it can be 51,000, 52,000, 55,000, 58,000, 60,000, 62,000, 65,000, 68,000, 70,000, 72,000, 75,000, 78,000, 80,000, 82,000, 85,000, 88,000, 90,000, 92,000, 95,000, 98,000, 100,000 or any two of these ranges, and more preferably, the number-average molecular weight is 75,550 to 86,900.

[0016] Preferably, the mass percentage of oligomers with a number average molecular weight ≤1000 as determined by GPC in the aliphatic-aromatic polyester is ≤2%, for example, it can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.72%, 0.75%, 0.78%, 0.8%, 0.82%, 0.84%, 0.86%, 0.88%, 0.9%, 0.92%, 0.94%, 0.96%, 0.98%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, or any two of these ranges; more preferably, it is 0.7~1.12%.

[0017] Preferably, the molecular weight distribution index (PDI) of the aliphatic-aromatic polyester is 1.45 to 1.75, for example, it can be 1.45, 1.46, 1.47, 1.48, 1.49, 1.5, 1.51, 1.52, 1.53, 1.54, 1.55, 1.56, 1.58, 1.6, 1.62, 1.64, 1.66, 1.68, 1.7, 1.72, 1.74, 1.75 or any two of them, preferably 1.52 to 1.67.

[0018] In this invention, the aliphatic-aromatic polyester has a high molecular weight distribution index, which can lead to uneven shrinkage due to differences in the response of different chain lengths, thus affecting the overall performance. Conversely, a low molecular weight distribution index results in a high shrinkage initiation temperature and requires more precise control of the shrinkage behavior, increasing the processing difficulty of the material.

[0019] In this invention, Mn, q, and PDI can all be obtained by gel permeation chromatography. Aliphatic-aromatic polyesters with different Mn, q, or PDI can be obtained by adjusting the type and content of raw materials, branching structure, and preparation method. The raw materials include diacids, diols, and other additives (such as branching agents, chain extenders, etc.). The preparation method includes polymerization processes (such as continuous or batch methods), reaction temperature, reaction time, and reaction pressure.

[0020] Preferably, the dicarboxylic acid residues comprise the following residues:

[0021] a1) contains 32-55 mol% terephthalic acid residues based on a total molar percentage of 100 mol% of a1) and a2); a2) contains 45-68 mol% aliphatic dicarboxylic acid residues based on a total molar percentage of 100 mol% of a1) and a2).

[0022] In this invention, 32-55 mol% of terephthalic acid residues can be, for example, 32 mol%, 34 mol%, 36 mol%, 38 mol%, 40 mol%, 42 mol%, 44 mol%, 46 mol%, 48 mol%, 49 mol%, 50 mol%, 52 mol%, 54 mol%, 55 mol%, or any combination thereof, more preferably 42-50 mol%.

[0023] In this invention, 45-68 mol% of aliphatic dicarboxylic acid residues can be, for example, 45 mol%, 46 mol%, 48 mol%, 50 mol%, 51 mol%, 52 mol%, 54 mol%, 56 mol%, 58 mol%, 60 mol%, 62 mol%, 64 mol%, 66 mol%, 68 mol%, or any combination thereof, more preferably 50-58 mol%.

[0024] In this invention, the aliphatic dicarboxylic acid residues include C2~C22 straight-chain dicarboxylic acid residues, such as C2, C4, C6, C8, C10, C12, C14, C16, C18, C20, C22 straight-chain dicarboxylic acid residues, etc.

[0025] Preferably, the aliphatic dicarboxylic acid residue includes at least one of succinic acid residue, adipic acid residue, azelaic acid residue, sebacic acid residue or tridecanoic acid residue, and preferably includes at least succinic acid residue.

[0026] In this invention, the diol residues also include C2~C13 straight-chain diol residues, such as C2, C3, C5, C6, C8, C9, C10, C12, C13 straight-chain diol residues, etc.

[0027] Preferably, the diol residue further includes at least one selected from the following: 1,2-ethylene glycol residue, 1,2-propanediol residue, 1,3-propanediol residue, 1,5-pentanediol residue, 1,6-hexanediol residue, 1,7-heptanediol residue, 1,8-octanediol residue, 1,9-nonanediol residue, 1,10-decanediol residue, 1,11-undecanediol residue, 1,12-dodecanediol residue, or 1,13-tridecanediol residue.

[0028] In this invention, the molar percentage of butanediol residues in the diol residues is ≥40%.

[0029] In this invention, according to ISO 1133-2-2011 standard, the melt index of the aliphatic-aromatic polyester is 1.0~10.0 g / 10min, preferably 3.0~8.0 g / 10min, under the conditions of 190℃ and 2.16 kg.

[0030] In this invention, the method is carried out according to method A in GB / T14190-2017 standard. The aliphatic-aromatic polyester has a terminal carboxyl group content of ≤50 mol / t, preferably ≤25 mol / t, and more preferably ≤15 mol / t.

[0031] In this invention, the preparation method of the aliphatic-aromatic polyester is not particularly limited, and any method capable of preparing the specific aliphatic-aromatic polyester of this invention is acceptable; preferably, the preparation method of the aliphatic-aromatic polyester includes the following steps:

[0032] (1) The dicarboxylic acid is reacted with the diol to obtain the esterified product;

[0033] (2) The esterified product obtained in step (1) is subjected to a prepolymerization reaction to obtain a prepolymerized product;

[0034] (3) The prepolymer obtained in step (2) is subjected to polycondensation reaction to obtain the aliphatic-aromatic polyester.

[0035] In this invention, the dicarboxylic acid in step (1) is terephthalic acid and / or a terephthalic acid derivative, as well as an aliphatic dicarboxylic acid and / or an aliphatic dicarboxylic acid derivative; the dicarboxylic acid may be used alone or as a mixture of at least two; the diol includes 1,4-butanediol and may also include other aliphatic diols.

[0036] In this invention, the source of the dicarboxylic acid is not particularly limited. It can be derived from bio-based dicarboxylic acids (i.e., the raw material for preparation is biomass resources) or from petroleum-based dicarboxylic acids (i.e., the raw material for preparation is petroleum resources).

[0037] In this invention, the molar ratio of diacid to diol in step (1) is 1:(2.5~4.0), where the specific values ​​of (2.5~4.0) can be, for example, 2.5, 2.8, 3.0, 3.3, 3.5, 3.8, 4.0, etc.; more preferably, it is 1:(2.8~3.2). The higher the content of diol, the more complete the reaction of diacid, but the higher the cost of preparing aliphatic-aromatic polyester.

[0038] Preferably, the raw materials for the reaction in step (1) further include a branching agent; the mass content of the branching agent is 0~3wt%, preferably 0.01~2wt%, more preferably 0.05~1wt%, and particularly preferably 0.08~0.20wt%, based on the total mass of the aliphatic-aromatic polyester as 100% (i.e., based on the theoretical mass of the aliphatic-aromatic polyester calculated based on the mass of the dicarboxylic acid and diol).

[0039] In this invention, the branching agent is a branching agent having at least three reactive functional groups (such as hydroxyl, carboxyl, etc.). Specifically, the branching agent includes at least one of tartaric acid, citric acid, malic acid, trimethylolpropane, trimethylolethane, pentaerythritol, polyether triol, glycerol, 1,3,5-benzotriic acid, 1,2,4-benzotriic acid, 1,2,4-benzotriic anhydride, 1,2,4,5-benzotetrate, or pyromellitic dianhydride; preferably trimethylolpropane, pentaerythritol, or glycerol; particularly preferably glycerol.

[0040] In this invention, the reaction in step (1) includes an isothermal esterification reaction or a gradient-temperature esterification reaction; the isothermal esterification reaction refers to the reaction at a constant temperature, wherein the temperature of the isothermal esterification reaction is 165~240℃, the pressure is 0.65~1.15 bar, and the time is 1~5h, preferably the temperature is 188~232℃, the pressure is 0.8~1.0 bar, and the time is 2~4h; the gradient-temperature esterification reaction refers to the reaction being carried out at a temperature A for a period of time before being raised to a temperature B and then the reaction is continued for a period of time; specifically, the gradient-temperature esterification reaction includes a first-stage reaction and a second-stage reaction carried out sequentially, wherein the temperature of the first-stage reaction is 165~212℃, the pressure is 0.85~1.2 bar, and the time is 1.5~3.5h; and the temperature of the second-stage reaction is 220~240℃, the pressure is 0.65~0.84 bar, and the time is 0.5~2.5h. In this invention, the content of terminal carboxyl groups in the esterification product of step (1) is 410~620 mol / t.

[0041] In this invention, after the reaction described in step (1), there is also a step of removing excess diol by distillation. The removed diol can be purified by distillation and reused as a raw material. The purity of the purified diol is ≥95%.

[0042] In this invention, step (1) can be carried out in a mixing device, where a dicarboxylic acid and a diol are mixed to obtain a slurry, and then heated to carry out the reaction.

[0043] In this invention, the prepolymerization reaction in step (2) can be carried out in a prepolymerization reactor, such as a tube bundle reactor, a cascade reactor (Kesselkaskade), or a bubble cap tower, especially a downflow cascade reactor, which may also have a degassing unit; the temperature of the prepolymerization reaction is 225~260℃, the pressure is 0.3~0.65 bar, and the time is 60~200 min, preferably the temperature is 235~245℃, the pressure is 0.35~0.55 bar, and the time is 90~130 min.

[0044] In this invention, the end carboxyl group content of the prepolymer product is 30~70 mol / t, more preferably 40~60 mol / t.

[0045] In this invention, the raw materials for the reactions in steps (1) and (2) each independently include a catalyst; the total mass of the catalyst is 0.001~1 wt%, preferably 0.03~0.2 wt%, based on 100% of the total mass of the aliphatic-aromatic polyester (i.e., the theoretical mass of the aliphatic-aromatic polyester calculated based on the mass of the diacid and diol); the catalyst includes zinc compounds, aluminum compounds, and titanium compounds, preferably titanium compounds. Compared with tin compounds, antimony compounds, cobalt compounds, and lead compounds commonly used in the literature, titanium compounds (such as tetrabutyl titanate or tetraisopropyl titanate) have lower residual amounts and lower toxicity in the product or downstream products. Catalyst toxicity is particularly important in biodegradable polyesters because they can directly enter the environment through composting bags or covering films.

[0046] In this invention, the mass of the catalyst in the raw materials of the reaction in step (1) is 58-72% of the total mass of the catalyst.

[0047] In this invention, the reactor for the polycondensation reaction in step (3) can be a rotary reactor or a cage reactor; the temperature of the polycondensation reaction is 235~260℃, the pressure is 0.2~5mbar, and the time is 45~155min, preferably the temperature is 240~250℃, the pressure is 0.5~3mbar, and the time is 60~90min.

[0048] In this invention, other additives may be added during the reaction in step (3) according to actual needs; the other additives include, but are not limited to, catalyst passivators, color stabilizers, activators, etc.

[0049] The catalyst passivator includes, but is not limited to, phosphorus compounds; the phosphorus compounds include, but are not limited to, one or more of phosphorous acid, phosphoric acid, and phosphite; based on 100 wt% of the prepolymer product, the mass of the catalyst passivator is 0.001~0.1 wt%, preferably 0.01~0.05 wt%. For example, when a highly active titanium compound is selected as the catalyst, a catalyst passivator can be added, wherein the molar ratio of Ti to P is (1.1~1.5):1, and particularly preferably the molar ratio of Ti to P is (1.1~1.3):1.

[0050] The color stabilizer includes, but is not limited to, phosphorus compounds; the phosphorus compounds include, but are not limited to, one or more of phosphoric acid, phosphorous acid, triphenyl phosphite, triphenyl phosphate, sodium hypophosphite, and sodium phosphite; the use of color stabilizers generally leads to a decrease in the condensation rate. Therefore, triphenyl phosphate, which has no adverse effect on the condensation rate, is preferred as a color stabilizer. The color stabilizer is 0.001 to 1.5 wt%, preferably 0.01 to 1.0 wt%, based on 100 wt% of the prepolymer; when the catalyst is selected from titanium compounds, the molar ratio of Ti to P is 1:(0.3 to 1.0), particularly preferably 1:(0.5 to 1.0).

[0051] The activator includes, but is not limited to, phosphorus compounds; the phosphorus compounds include, but are not limited to, one or more of disodium hydrogen phosphate, calcium hypophosphite, calcium phosphite, calcium phosphate, sodium hypophosphite, sodium phosphite, triphenyl phosphite, triphenyl phosphate, trimethyl phosphate, triethyl phosphate, tripropyl phosphate, and tributyl phosphate. Based on 100 wt% of the prepolymer product, the activator comprises 0.001–1.5 wt%, preferably 0.01–1.0 wt%; when the catalyst is selected from titanium compounds, the molar ratio of Ti to P is (1.0–1.5):1, particularly preferably (1.1–1.3):1.

[0052] More preferably, a combination of color stabilizers and activators is used, for example, a combination of triphenyl phosphate and disodium hydrogen phosphate.

[0053] In this invention, the polycondensation reaction may be followed by a chain growth reaction, in which the product obtained from the polycondensation reaction (polycondensation product) is reacted with a chain grower to obtain a chain growth product.

[0054] In this invention, the chain extender includes one or more of isocyanates, peroxides, epoxides, oxazolines, oxazines, caprolactam, or carbodiimides.

[0055] In this invention, the isocyanate can be an aromatic diisocyanate and / or an aliphatic diisocyanate. The aromatic diisocyanate can be toluene 2,4-diisocyanate, toluene 2,6-diisocyanate, diphenylmethane 2,2′-diisocyanate, diphenylmethane 2,4′-diisocyanate, diphenylmethane 4,4′-diisocyanate, naphthalene 1,5-diisocyanate, or xylene diisocyanate; particularly preferred are diphenylmethane 2,2′-diisocyanate, diphenylmethane 2,4′-diisocyanate, or diphenylmethane 4,4′-diisocyanate. The aromatic diisocyanate can also be a polynuclear aromatic diisocyanate, such as tris(4-isocyanate-phenyl)methane with three rings, which can be formed during the production of diisocyanates with one or two rings. The aliphatic diisocyanate may be a straight-chain or branched alkylene diisocyanate containing 2 to 20 carbon atoms or a cycloalkylene diisocyanate containing 3 to 20 carbon atoms; exemplary, the aliphatic diisocyanate includes hexamethylene diisocyanate, pentamethylene diisocyanate, isophorone diisocyanate, or methylene di(4-isocyanate cyclohexane) diisocyanate. Hexamethylene diisocyanate is particularly preferred.

[0056] In this invention, based on the total mass of the polycondensation product, the mass of the isocyanate can be 0.05~2wt%, particularly preferably 0.1~1.5wt%.

[0057] In this invention, the peroxide may be one or more of the following: benzoyl peroxide, 1,1-di(tert-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-di(tert-butylperoxy)methylcyclododecane, n-butyl 4,4-di(butylperoxy)valerate, dicumyl peroxide, tert-butyl peroxybenzoate, dibutyl peroxide, α,α-di(tert-butylperoxy)diisopropylbenzene, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, 2,5-dimethyl-2,5-di(tert-butylperoxy)hex-3-yne, or tert-butylperoxycumene.

[0058] In this invention, based on the total mass of the polycondensation product, the mass of the peroxide can be 0.1 to 2 wt%, particularly preferably 0.2 to 1 wt%.

[0059] In this invention, the epoxide may be one or more of the following: diglycidyl ether, hexamethylene diglycidyl ether, sorbitol diglycidyl ether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, diglycerol polyglycidyl ether, glycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether, resorcinol diglycidyl ether, neopentyl glycol diglycidyl ether, ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, dipropylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and polybutylene glycol diglycidyl ether, or copolymers containing epoxy groups based on styrene, acrylates, and / or methacrylates.

[0060] In this invention, based on the total mass of the polycondensation product, the mass of the epoxide can be 0.1~2wt%, preferably 0.2~1wt%.

[0061] In this invention, the oxazoline may be selected from one or more of 2,2′-bis(2-oxazoline), bis(2-oxazolinyl)methane, 1,2-bis(2-oxazolinyl)ethane, 1,3-bis(2-oxazolinyl)propane, 1,4-bis(2-oxazolinyl)butane, 1,4-bis(2-oxazolinyl)benzene, 1,2-bis(2-oxazolinyl)benzene, or 1,3-bis(2-oxazolinyl)benzene. The oxazine may be selected from one or more of 2,2′-bis(2-dioxazine), bis(2-dioxazinyl)methane, 1,2-bis(2-dioxazinyl)ethane, 1,3-bis(2-dioxazinyl)propane, 1,4-bis(2-dioxazinyl)butane, 1,4-bis(2-dioxazinyl)benzene, 1,2-bis(2-dioxazinyl)benzene, or 1,3-bis(2-dioxazinyl)benzene. The carbodiimide may be selected from one or more of N,N′-di-2,6-diisopropylphenylcarbodiimide, N,N′-di-o-tolylcarbodiimide, N,N′-diphenylcarbodiimide, N,N′-dioctyldecylcarbodiimide, N,N′-di-2,6-dimethylphenylcarbodiimide, N-tolyl-N′-cyclohexylcarbodiimide, N,N′-di-2,6-di-tert-butylphenylcarbodiimide, N,N′-di-2,4,6-triisobutylphenylcarbodiimide, diisopropylcarbodiimide, dimethylcarbodiimide, diisobutylcarbodiimide, dioctylcarbodiimide, tert-butylisopropylcarbodiimide, di-β-naphthylcarbodiimide, or di-tert-butylcarbodiimide.

[0062] In this invention, based on the total mass of the polycondensation product, the mass of each of the oxazoline, oxazine, caprolactam and carbodiimide is independently 0.1 to 2 wt%, preferably 0.2 to 1 wt%.

[0063] In this invention, the chain growth reaction is carried out at a temperature of 170~245℃, more preferably 180~235℃; the reaction is carried out under ultra-high atmospheric pressure or atmospheric pressure, depending on the system used.

[0064] In this invention, the chain growth reaction can be carried out in an extruder, a continuous kneader (List reactor), or a static mixer. The extruder can be a single-screw extruder or a twin-screw extruder; the static mixer can use SMR, SMX, or SMXL components, or combinations thereof. Examples of List reactors are single-screw DISCOTHERM B, twin-screw CRP, or ORP reactors. Preferably, the chain growth reaction is carried out in an extruder for a chain growth reaction time of 2–15 min, more preferably 4–13 min.

[0065] In this invention, the aliphatic-aromatic polyester can also be prepared by the following method, which includes the following steps:

[0066] (S1-1) An aliphatic diacid and / or an aliphatic diacid derivative are mixed with 1,4-butanediol and a branching agent, and esterified at 160~200℃ and 0.80~1.40 bar for 1~5 h to obtain esterified product A;

[0067] (S1-2) Terephthalic acid and / or terephthalic acid derivatives are mixed with 1,4-butanediol and a catalyst, and esterified at 205~255℃ and 0.40~0.80 bar for 0.5~4h to obtain esterified product T;

[0068] (S2) The esterification product A obtained in step (S1-1) and the esterification product T obtained in step (S1-2) are mixed with the catalyst and subjected to prepolymerization reaction at 225~260℃ and 0.3~0.65bar for 60~200min to obtain the prepolymer product;

[0069] (S3) The prepolymer obtained in step (S2) is subjected to polycondensation reaction at 235~260℃ and 0.2~5mbar for 45~155min to obtain the aliphatic-aromatic polyester.

[0070] In this invention, the molar ratio of the aliphatic diacid and / or aliphatic diacid derivative to 1,4-butanediol in step (S1-1) is 1:(2.5~3.2), specifically 1:2.5, 1:2.8, 1:3.2, etc. The molar ratio of terephthalic acid and / or terephthalic acid derivative to 1,4-butanediol in step (S1-2) is 1:(2.8~4.0), specifically 1:2.8, 1:3.0, 1:3.5, 1:4.0, etc.

[0071] In this step (S1-1), the mass of the branching agent and the mass of the catalyst in steps (S1-2) and (S2) are each independently selected from the same range as in steps (1) and (2); other auxiliaries may also be added in step (S3), and the specific content and type of auxiliaries are selected from the same range as in step (3); and after the polycondensation reaction in step (S3), a chain growth reaction may also be carried out, and the specific parameters are selected from the same range as in step (3).

[0072] In a second aspect, the present invention provides a shrink film prepared from the aliphatic-aromatic polyester described in the first aspect.

[0073] In this invention, the mass percentage of aliphatic-aromatic polyester in the shrink film is ≥50%, more preferably ≥65%.

[0074] In this invention, a second polymer, a third polymer, additives, etc., may be added to the shrink film as needed.

[0075] In this invention, the second polymer comprises at least one selected from polylactic acid (PLA), polybutylene succinate (PBS), polybutylene adipate succinate (PBSA), polybutylene sebacate succinate (PBSSe), and polybutylene sebacate succinate (PBSe); the mass percentage of the second polymer in the shrink film is 1-20%, preferably 4-10%. According to standard ISO 1133-2-2011, at 190°C and 2.16 kg, the melt flow rate of the second polymer is 0.5-50 g / 10 min.

[0076] In this invention, the third polymer includes at least one selected from starch, cellulose, chitin, chitosan, alginate, protein, gelatin, natural rubber, lignin, or derivatives of the aforementioned substances. The mass percentage of the third polymer in the shrink film is 1-25%, preferably 2-10%.

[0077] In this invention, the proteins include, but are not limited to, gluten, zein, casein, and collagen; the lignin includes unpurified lignin, purified hydrolyzed lignin, and alkalized lignin. Starch can also be used in allosteric and gelling forms or as a filler. The starch can represent a continuous phase or a dispersed phase, or it can be in a co-continuous form.

[0078] In this invention, the additives can be added as needed, including but not limited to at least one of antioxidants, lubricants, light stabilizers, and release agents. The mass percentage of the additives in the shrink film is 0-1%.

[0079] In this invention, the types of additives are not limited too much; conventional additives can be used. For example, the antioxidants include, but are not limited to, any one of antioxidant 1010, antioxidant 1076, antioxidant 168, antioxidant 164, antioxidant DLTP, or antioxidant TPP.

[0080] The light stabilizers include, but are not limited to, at least one of hindered amine light stabilizers (such as light stabilizer 770, light stabilizer 622, light stabilizer 944, etc.), benzophenone light stabilizers (such as UV531), or benzotriazole light stabilizers.

[0081] The lubricant includes, but is not limited to, at least one of esters (such as polyethylene glycol esters, polyol esters), lignite salts, ethylene bis-stearamide, or polyethylene wax.

[0082] The release agent includes, but is not limited to, at least one of the following: inorganic release agents (such as talc, mica powder, clay, etc.), organic release agents (such as fatty acids, paraffin wax, glycerin, petrolatum, etc.), or polymeric release agents (such as silicone oil, polyethylene glycol, low molecular weight polyethylene, etc.).

[0083] In this invention, the shrink film can be prepared using a blown film process.

[0084] Preferably, with a thickness of 40±2μm, the shrinkage rate of the shrink film is ≥65% in the transverse direction and ≥35% in the longitudinal direction; more preferably, the transverse shrinkage rate is ≥76% and the longitudinal shrinkage rate is ≥44%.

[0085] The aliphatic-aromatic polyester and the shrink film prepared from the aliphatic-aromatic polyester described in this invention are both biodegradable.

[0086] For the purposes of this invention, a substance or mixture of substances is considered "biodegradable" if it exhibits a biodegradability of at least 90%, as defined in DIN EN 13432.

[0087] According to DIN EN 13432, during composting, CO2-free air is introduced into the maturing compost, and the compost is subjected to a specific temperature process. Here, biodegradability is defined as the percentage degree of biodegradation expressed as the ratio of the net amount of CO2 released by the sample (minus the amount of CO2 released by compost without the sample) to the maximum amount of CO2 that the sample can release (calculated from the carbon content in the sample). After only a few days of composting, biodegradable polyesters and biodegradable polyester compositions typically show obvious signs of degradation, such as fungal growth, lysis, and perforation.

[0088] Other methods for determining biodegradability are also described in ASTM D5338 and ASTM D6400.

[0089] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0090] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0091] The aliphatic-aromatic polyester provided by the present invention, by controlling the ratio of the number-average molecular weight and oligomer content of the aliphatic-aromatic polyester within a specific range, enables the shrink film prepared from the aliphatic-aromatic polyester to have excellent heat shrinkage properties. Detailed Implementation

[0092] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0093] In this invention, all materials used can be purchased commercially or prepared using conventional methods. Unless otherwise specified, the materials used in this invention are as follows.

[0094] Terephthalic acid: purchased from Zhuhai INEOS Chemical Co., Ltd.

[0095] Succinic acid: purchased from Shandong Landian Biotechnology Co., Ltd.

[0096] 1,4-Butanediol: Purchased from Meike Chemical Co., Ltd.

[0097] 1,3-Propanediol: Purchased from Anhui Huaheng Biotechnology Co., Ltd.

[0098] Glycerin: Purchased from Aladdin.

[0099] Tetrabutyl titanate: Purchased from Jianyi Chemical Import & Export Co., Ltd.

[0100] In this invention, the test methods for the composition of dicarboxylic acid residues, number-average molecular weight (Mn), PDI, and mass percentage (q) of oligomers with a number-average molecular weight ≤1000 as determined by GPC in aliphatic-aromatic polyesters are as follows.

[0101] 1. Composition of dicarboxylic acid residues

[0102] pass 1 The test was performed using the 1H NMR method; specifically, 20 mg of the aliphatic-aromatic polyester sample was dissolved in 0.6 mL of deuterated chloroform, and then its concentration was determined at room temperature using a Bruker AV 500 nuclear magnetic resonance spectrometer. 1¹H NMR; the characteristic peaks of terephthalic acid residues and aliphatic dicarboxylic acid residues are integrated, and the molar content of each residue in the aliphatic-aromatic polyester is obtained by the percentage of the peak area. Specifically, taking terephthalic acid residues and succinic acid residues as examples, the characteristic chemical shift of terephthalic acid residues is about 8.10 ppm, representing 4 hydrogen atoms on the benzene ring, and the characteristic chemical shift of succinic acid residues is about 2.63 ppm, representing 4 hydrogen atoms on the two methylene-CH₂-CH₂- atoms in succinic acid. The integrated area of ​​terephthalic acid residues is I1, and the integrated area of ​​succinic acid residues is I2. Then, the molar percentage content of terephthalic acid residues in the aliphatic-aromatic polyester is I1 / (I1+I2)×100%.

[0103] 2. Mn and PDI

[0104] The tests were performed using gel permeation chromatography (GPC). Specifically, a chromatographic system was used at 40°C with three tandem columns (particle diameters of 5 μm and porosities of 500 Å, 1000 Å, and 10000 Å, respectively) and a refractive index detector. Chloroform was used as the eluent (elution flow rate of 1 mL / min), and polystyrene was used as the reference standard. The instrument model was Waters 1515GPC. The sample preparation method was as follows: aliphatic-aromatic polyesters were directly dissolved in chromatographic grade THF to prepare a 1 mg / mL solution for testing, and the Mn and PDI of the aliphatic-aromatic polyesters were obtained.

[0105] 3. Mass percentage (q) of oligomers with a number average molecular weight ≤1000 as determined by GPC.

[0106] The test was performed using gel permeation chromatography (GPC). Specifically, an aliphatic-aromatic polyester sample (approximately 3-4 g) (F1) was placed in a 200 mL flask with 30 mL of chloroform. After the aliphatic-aromatic polyester was completely dissolved, 100 mL of a 1:1 (v / v) mixture of methanol and acetone was added. After stirring for 2 h, the mixture was filtered through a filter with an 8 μm pore size. The polymer residue on the filter was then washed with acetone, and the methanol / acetone mixture was heated under an air stream at 70 °C until it was completely evaporated. The weight of the residual solid component was recorded (F2). The solid component sample (approximately 10 mg) was dissolved in 10 mL of chloroform and analyzed by GPC. The mass percentage (P1) of low molecular weight polymers with a number average molecular weight ≤1000 was determined using the molecular weight distribution curve recorded by the GPC instrument. The mass percentage of oligomers with a number average molecular weight ≤1000 was then calculated according to the following equation: q = (P1 × F2) / F1 × 100%.

[0107] Example 1

[0108] This embodiment provides an aliphatic-aromatic polyester, the preparation method of which includes the following steps:

[0109] (1) 20 kg succinic acid, 26.5 kg terephthalic acid, 90 kg 1,4-butanediol, 90 g glycerol and 30 g tetrabutyl titanate were physically mixed. After the mixture was completed, the mixture was transferred to an esterification reactor and esterified at 200 °C and 1.1 bar for 2 h. Then the temperature was raised to 230 °C and the pressure was reduced to 0.8 bar. The esterification reaction was continued for 1 h to obtain the esterified product.

[0110] (2) The esterification product obtained in step (1) is transferred to a prepolymerization reactor, 20 g of tetrabutyl titanate is added to it, and the prepolymerization reaction is carried out at 238°C and 0.55 bar for 120 min to obtain the prepolymerization product.

[0111] (3) The prepolymer obtained in step (2) is transferred to a polycondensation reactor and polycondensed at 245°C and 1.5 mbar for 85 min to obtain the aliphatic-aromatic polyester.

[0112] Example 2

[0113] This embodiment provides an aliphatic-aromatic polyester, the preparation method of which includes the following steps:

[0114] (1) 20 kg succinic acid, 26.5 kg terephthalic acid, 75 kg 1,4-butanediol, 120 g glycerol and 28 g tetrabutyl titanate were physically mixed. After the mixture was completed, the mixture was transferred to an esterification reactor and esterified at 190 °C and 1.1 bar for 2 h. Then the temperature was raised to 225 °C and the pressure was reduced to 0.8 bar. The esterification reaction was continued for 1 h to obtain the esterified product.

[0115] (2) The esterification product obtained in step (1) is transferred to a prepolymerization reactor, 16 g of tetrabutyl titanate is added to it, and the prepolymerization reaction is carried out at 235°C and 0.60 bar for 130 min to obtain the prepolymerization product.

[0116] (3) The prepolymer obtained in step (2) is transferred to a polycondensation reactor and polycondensed at 245°C and 1.6 mbar for 90 min to obtain the aliphatic-aromatic polyester.

[0117] Example 3

[0118] This embodiment provides an aliphatic-aromatic polyester, the preparation method of which includes the following steps:

[0119] (1) 20 kg succinic acid, 26.5 kg terephthalic acid, 46 kg 1,4-butanediol, 37 kg 1,3-propanediol, 90 g glycerol and 34 g tetrabutyl titanate were physically mixed. After the mixture was completed, the resulting mixture was transferred to an esterification reactor and esterified at 210 °C and 1.1 bar for 2.5 h. Then the temperature was raised to 235 °C and the pressure was reduced to 0.8 bar. The esterification reaction was continued for 1 h to obtain the esterified product.

[0120] (2) The esterification product obtained in step (1) is transferred to a prepolymerization reactor, 24 g of tetrabutyl titanate is added to it, and the prepolymerization reaction is carried out at 240°C and 0.60 bar for 120 min to obtain the prepolymerization product.

[0121] (3) The prepolymer obtained in step (2) is transferred to a polycondensation reactor and polycondensed at 243°C and 1.3 mbar for 90 min to obtain the aliphatic-aromatic polyester.

[0122] Example 4

[0123] This embodiment provides an aliphatic-aromatic polyester, the preparation method of which includes the following steps:

[0124] (1) 20 kg succinic acid, 26.5 kg terephthalic acid, 100 kg 1,4-butanediol, 55 g glycerol and 36 g tetrabutyl titanate were physically mixed. After the mixture was completed, the mixture was transferred to an esterification reactor and esterified at 200 °C and 1.0 bar for 2.5 h. Then the temperature was raised to 230 °C and the pressure was reduced to 0.8 bar. The esterification reaction was continued for 1.5 h to obtain the esterified product.

[0125] (2) The esterification product obtained in step (1) is transferred to a prepolymerization reactor, 22 g of tetrabutyl titanate is added to it, and the prepolymerization reaction is carried out at 235°C and 0.32 bar for 130 min to obtain the prepolymerization product.

[0126] (3) The prepolymer obtained in step (2) is transferred to a polycondensation reactor and polycondensed at 242°C and 1.6 mbar for 70 min to obtain the aliphatic-aromatic polyester.

[0127] Example 5

[0128] This embodiment provides an aliphatic-aromatic polyester, the preparation method of which includes the following steps:

[0129] (1) 20 kg succinic acid, 26.5 kg terephthalic acid, 75 kg 1,4-butanediol, 120 g glycerol and 36 g tetrabutyl titanate were physically mixed. After the mixture was completed, the mixture was transferred to an esterification reactor and esterified at 200 °C and 1.0 bar for 2 h. Then the temperature was raised to 225 °C and the pressure was reduced to 0.65 bar. The esterification reaction was continued for 1 h to obtain the esterified product.

[0130] (2) The esterification product obtained in step (1) is transferred to a prepolymerization reactor, 25 g of tetrabutyl titanate is added to it, and the prepolymerization reaction is carried out at 240°C and 0.60 bar for 90 min to obtain the prepolymerization product.

[0131] (3) The prepolymer obtained in step (2) is transferred to a polycondensation reactor and polycondensed at 242°C and 1.4 mbar for 60 min to obtain the polycondensation product;

[0132] (4) Add 400g of hexamethylene diisocyanate to the polycondensation product obtained in step (3) and carry out a chain growth reaction at 190°C for 7 minutes to obtain an aliphatic-aromatic polyester.

[0133] Example 6

[0134] This embodiment provides an aliphatic-aromatic polyester, the preparation method of which includes the following steps:

[0135] (1) 20 kg succinic acid, 26.5 kg terephthalic acid, 75 kg 1,4-butanediol, 120 g glycerol and 28 g tetrabutyl titanate were physically mixed. After the mixture was completed, the mixture was transferred to an esterification reactor and esterified at 190 °C and 1.1 bar for 2 h. Then the temperature was raised to 225 °C and the pressure was reduced to 0.8 bar. The esterification reaction was continued for 1 h to obtain the esterified product.

[0136] (2) The esterification product obtained in step (1) is transferred to a prepolymerization reactor, 12 g of tetrabutyl titanate is added to it, and the prepolymerization reaction is carried out at 230°C and 0.60 bar for 110 min to obtain the prepolymerization product.

[0137] (3) The prepolymer obtained in step (2) is transferred to a polycondensation reactor and polycondensed at 248°C and 1.8 mbar for 110 min to obtain the aliphatic-aromatic polyester.

[0138] Example 7

[0139] This embodiment provides an aliphatic-aromatic polyester, the preparation method of which includes the following steps:

[0140] (1) 20 kg succinic acid, 26.5 kg terephthalic acid, 90 kg 1,4-butanediol, 100 g glycerol and 32 g tetrabutyl titanate were physically mixed. After the mixture was completed, the mixture was transferred to an esterification reactor and esterified at 200 °C and 1.1 bar for 2.5 h. Then the temperature was raised to 233 °C and the pressure was reduced to 0.9 bar. The esterification reaction was continued for 1.5 h to obtain the esterified product.

[0141] (2) The esterification product obtained in step (1) is transferred to a prepolymerization reactor, 22 g of tetrabutyl titanate is added to it, and the prepolymerization reaction is carried out at 242℃ and 0.50 bar for 120 min to obtain the prepolymerization product.

[0142] (3) The prepolymer obtained in step (2) is transferred to a polycondensation reactor and polycondensed at 245°C and 1.2 mbar for 90 min to obtain the aliphatic-aromatic polyester.

[0143] Example 8

[0144] This embodiment provides an aliphatic-aromatic polyester, the preparation method of which includes the following steps:

[0145] (1) 20 kg succinic acid, 26.5 kg terephthalic acid, 100 kg 1,4-butanediol, 120 g glycerol and 34 g tetrabutyl titanate were physically mixed. After the mixture was completed, the mixture was transferred to an esterification reactor and esterified at 190 °C and 1.0 bar for 3 h. Then the temperature was raised to 235 °C and the pressure was reduced to 0.8 bar. The esterification reaction was continued for 2 h to obtain the esterified product.

[0146] (2) The esterification product obtained in step (1) is transferred to a prepolymerization reactor, 24 g of tetrabutyl titanate is added to it, and the prepolymerization reaction is carried out at 240°C and 0.55 bar for 110 min to obtain the prepolymerization product.

[0147] (3) The prepolymer obtained in step (2) is transferred to a polycondensation reactor and polycondensed at 245°C and 1.1 mbar for 90 min to obtain the aliphatic-aromatic polyester.

[0148] Example 9

[0149] This embodiment provides an aliphatic-aromatic polyester, the preparation method of which includes the following steps:

[0150] (1) 20 kg succinic acid, 33 kg terephthalic acid, 88 kg 1,4-butanediol, 145 g glycerol and 28 g tetrabutyl titanate were physically mixed. After the mixture was completed, the mixture was transferred to an esterification reactor and esterified at 230 °C and 0.7 bar for 3 h to obtain the esterification product.

[0151] (2) The esterification product obtained in step (1) is transferred to a prepolymerization reactor, 12 g of tetrabutyl titanate is added to it, and the prepolymerization reaction is carried out at 235°C and 0.60 bar for 90 min to obtain the prepolymerization product.

[0152] (3) The prepolymer obtained in step (2) is transferred to a polycondensation reactor and polycondensed at 245°C and 1.6 mbar for 90 min to obtain the aliphatic-aromatic polyester.

[0153] Example 10

[0154] This embodiment provides an aliphatic-aromatic polyester, the preparation method of which includes the following steps:

[0155] (1) 28 kg succinic acid, 21 kg terephthalic acid, 82 kg 1,4-butanediol, 140 g glycerol and 25 g tetrabutyl titanate were physically mixed. After the mixture was completed, the mixture was transferred to an esterification reactor and esterified at 180 °C and 1.0 bar for 3 h. Then the temperature was raised to 235 °C and the pressure was reduced to 0.8 bar. The esterification reaction was continued for 1 h to obtain the esterified product.

[0156] (2) The esterification product obtained in step (1) is transferred to a prepolymerization reactor, 15 g of tetrabutyl titanate is added to it, and the prepolymerization reaction is carried out at 235°C and 0.60 bar for 70 min to obtain the prepolymerization product.

[0157] (3) The prepolymer obtained in step (2) is transferred to a polycondensation reactor and polycondensed at 242°C and 2.0 mbar for 150 min to obtain the aliphatic-aromatic polyester.

[0158] Example 11

[0159] This embodiment provides an aliphatic-aromatic polyester, the preparation method of which includes the following steps:

[0160] (1-1) 20 kg of succinic acid, 40 kg of 1,4-butanediol and 90 g of glycerol were physically mixed. After the mixture was completed, the resulting mixture was transferred to an esterification reactor and esterified at 180 °C and 1.1 bar for 3 h to obtain esterification product A.

[0161] (1-2) 26.5 kg of terephthalic acid, 50 kg of 1,4-butanediol and 35 g of tetrabutyl titanate were physically mixed. After the mixture was completed, the resulting mixture was transferred to an esterification reactor and esterified at 235 °C and 0.60 bar for 2 h to obtain esterification product T.

[0162] (2) After mixing the esterification product A and esterification product T obtained in steps (1-1) and (1-2), the mixture is transferred to a prepolymerization reactor, 20 g of tetrabutyl titanate is added, and the mixture is prepolymerized at 240°C and 0.40 bar for 105 min to obtain the prepolymer.

[0163] (3) The prepolymer obtained in step (2) is transferred to a polycondensation reactor and polycondensed at 243°C and 1.3 mbar for 80 min to obtain the aliphatic-aromatic polyester.

[0164] Comparative Example 1

[0165] This comparative example provides an aliphatic-aromatic polyester, the preparation method of which includes the following steps:

[0166] (1) 20 kg succinic acid, 26.5 kg terephthalic acid, 60 kg 1,4-butanediol and 28 g tetrabutyl titanate were physically mixed. After the mixture was completed, the mixture was transferred to an esterification reactor and esterified at 170 °C and 1.0 bar for 2 h. Then the temperature was raised to 230 °C and the pressure was reduced to 0.8 bar. The esterification reaction was continued for 1 h to obtain the esterified product.

[0167] (2) The esterification product obtained in step (1) is transferred to a prepolymerization reactor, 12 g of tetrabutyl titanate is added to it, and the prepolymerization reaction is carried out at 230°C and 0.70 bar for 100 min to obtain the prepolymerization product.

[0168] (3) The prepolymer obtained in step (2) is transferred to a polycondensation reactor and polycondensed at 245°C and 1.4 mbar for 130 min to obtain the aliphatic-aromatic polyester.

[0169] Comparative Example 2

[0170] This comparative example provides an aliphatic-aromatic polyester, the preparation method of which includes the following steps:

[0171] (1) 20 kg succinic acid, 26.5 kg terephthalic acid, 75 kg 1,4-butanediol, 100 g glycerol and 36 g tetrabutyl titanate were physically mixed. After the mixture was completed, the mixture was transferred to an esterification reactor and esterified at 200 °C and 1.0 bar for 3 h. Then the temperature was raised to 230 °C and the pressure was reduced to 0.65 bar. The esterification reaction was continued for 2 h to obtain the esterified product.

[0172] (2) The esterification product obtained in step (1) is transferred to a prepolymerization reactor, 25 g of tetrabutyl titanate is added to it, and the prepolymerization reaction is carried out at 242℃ and 0.50 bar for 100 min to obtain the prepolymerization product.

[0173] (3) The prepolymer obtained in step (2) is transferred to a polycondensation reactor and polycondensed at 244°C and 1.3 mbar for 70 min to obtain the polycondensation product;

[0174] (4) Add 260g of hexamethylene diisocyanate to the polycondensation product obtained in step (3) and carry out a chain growth reaction at 200℃ for 5 minutes to obtain an aliphatic-aromatic polyester.

[0175] Comparative Example 3

[0176] This comparative example provides an aliphatic-aromatic polyester, the preparation method of which includes the following steps:

[0177] (1) 20 kg succinic acid, 26.5 kg terephthalic acid, 90 kg 1,4-butanediol, 70 g glycerol and 25 g tetrabutyl titanate were physically mixed. After the mixture was completed, the mixture was transferred to an esterification reactor and esterified at 215 °C and 0.8 bar for 2 h. Then the temperature was raised to 210 °C and the pressure was reduced to 0.86 bar. The esterification reaction was continued for 1 h to obtain the esterified product.

[0178] (2) The esterification product obtained in step (1) is transferred to a prepolymerization reactor, 18 g of tetrabutyl titanate is added to it, and the prepolymerization reaction is carried out at 215°C and 0.70 bar for 100 min to obtain the prepolymerization product.

[0179] (3) The prepolymer obtained in step (2) is transferred to a polycondensation reactor and polycondensed at 233°C and 1.7 mbar for 65 min to obtain the aliphatic-aromatic polyester.

[0180] Comparative Example 4

[0181] This comparative example provides an aliphatic-aromatic polyester, the preparation method of which includes the following steps:

[0182] The aliphatic-aromatic polyester described in Example 6 was subjected to contact purification treatment with a THF aqueous solution. The concentration of the THF aqueous solution was 40 wt%, the contact purification treatment temperature was 55°C, and the time was 2 h. After filtration and drying, the aliphatic-aromatic polyester was obtained.

[0183] The specific values ​​of the dicarboxylic acid residue composition, Mn, q, Mn / q, and PDI of the aliphatic-aromatic polyesters provided in Examples 1-11 and Comparative Examples 1-4 are shown in Tables 1-3; " / " indicates that the composition was not present or was not tested.

[0184] The aliphatic-aromatic polyesters provided in the examples and comparative examples were used to prepare films with a thickness of 40±2μm using a blown film extruder with a screw diameter of 40mm, a blown film temperature of 120~170℃, a die gap of 1mm, a flow rate of 25±0.5 kg / h, and a blow-up ratio of 3.0. Transverse (TD) and longitudinal (MD) shrinkage rates were tested according to standard ASTM D2732-14 (test temperature 140℃, test time 120s). Specific test results are shown in Tables 1-3.

[0185] Table 1

[0186]

[0187] Table 2

[0188]

[0189] Table 3

[0190]

[0191] As shown in Tables 1-3, the aliphatic-aromatic polyester provided by this invention, by controlling the ratio of the number-average molecular weight to the oligomer content of the aliphatic-aromatic polyester within a specific range, results in a shrink film with excellent heat shrinkage properties. The aliphatic-aromatic polyester has a TD shrinkage rate ≥65% and a MD shrinkage rate ≥35%.

[0192] As can be seen from Examples 1, 2 and Examples 4, 5, the Mn and q of the aliphatic-aromatic polyester within a certain range are beneficial to further improve the heat shrinkage performance of the shrink film.

[0193] As can be seen from Examples 1 and 2 and Examples 7 and 8, the molecular weight distribution index of the aliphatic-aromatic polyester is within a specific range, which is beneficial to further improve the heat shrinkage performance of the shrink film.

[0194] As can be seen from Examples 1, 2 and Examples 9, 10, the aliphatic-aromatic polyester uses a dicarboxylic acid with a specific composition, which is beneficial to further improve the heat shrinkage performance of the shrink film.

[0195] As can be seen from Comparative Examples 1 to 4, the ratio of the number-average molecular weight of the aliphatic-aromatic polyester to the mass percentage of oligomers with a number-average molecular weight ≤1000 as determined by GPC in the aliphatic-aromatic polyester is not within the specific range of the present invention, resulting in a decrease in the shrinkage rate of the obtained shrink film and a deterioration in its heat shrinkage performance.

[0196] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An aliphatic-aromatic polyester, characterized in that, The aliphatic-aromatic polyester comprises dicarboxylic acid residues and diol residues; The diacid residues include the following residues: a1), based on the total molar percentage of a1) and a2) as 100 mol%, 32~55 mol% of terephthalic acid residues; a2), based on the total molar percentage of a1) and a2) as 100 mol%, 45~68 mol% of aliphatic dicarboxylic acid residues; The diol residues include 1,4-butanediol residues; The number-average molecular weight of the aliphatic-aromatic polyester and the mass percentage of oligomers with a number-average molecular weight ≤1000 as determined by GPC in the aliphatic-aromatic polyester satisfy the following relationship: Mn / q is 50,000~110,000; where Mn is the number average molecular weight of aliphatic-aromatic polyester, and q is the mass percentage of oligomers with a number average molecular weight ≤1000 as determined by GPC. The number-average molecular weight of the aliphatic-aromatic polyester is 68,000 to 100,000.

2. The aliphatic-aromatic polyester according to claim 1, characterized in that, The Mn / q ratio is 85300~105000.

3. The aliphatic-aromatic polyester according to claim 1, characterized in that, The mass percentage of oligomers with a number average molecular weight ≤1000 as determined by GPC in the aliphatic-aromatic polyester is ≤2%.

4. The aliphatic-aromatic polyester according to claim 1, characterized in that, The molecular weight distribution index of the aliphatic-aromatic polyester is 1.45~1.

75.

5. The aliphatic-aromatic polyester according to claim 1, characterized in that, The aliphatic dicarboxylic acid residue includes at least one of succinic acid residue, adipic acid residue, azelaic acid residue, sebacic acid residue, or tridecanoic acid residue.

6. The aliphatic-aromatic polyester according to claim 1, characterized in that, The diol residues further include at least one of the following: 1,2-ethylene glycol residue, 1,2-propanediol residue, 1,3-propanediol residue, 1,5-pentanediol residue, 1,6-hexanediol residue, 1,7-heptanediol residue, 1,8-octanediol residue, 1,9-nonanediol residue, 1,10-decanediol residue, 1,11-undecanediol residue, 1,12-dodecanediol residue, or 1,13-tridecanediol residue.

7. A shrink film, characterized in that, The shrink film is prepared from the aliphatic-aromatic polyester according to any one of claims 1 to 6.

8. The shrink film according to claim 7, characterized in that, With a thickness of 40±2μm, the shrinkage rate of the shrink film is ≥65% in the transverse direction and ≥35% in the longitudinal direction.

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