A polyester heat-shrinkable film containing recycled materials and a preparation method thereof

Abstract

The present invention provides a polyester heat-shrinkable film containing recycled materials and a preparation method thereof, belonging to the technical field of polymer synthetic films. The raw materials of the polyester heat-shrinkable film include recycled PET polyester particles, PET polyester chips, and a modified masterbatch; the modified masterbatch is prepared from polyethylene terephthalate-1,4-cyclohexanedimethanol ester, triphenyl phosphite, polyethylene glycol block copolymer, nano-silica, and hyperbranched polyester amine; the polyethylene glycol block copolymer is prepared from polyethylene glycol and γ-valerolactone under the action of a catalyst; the hyperbranched polyester amine is prepared from trimethylolpropane, methyl crotonate, and diethylenetriamine. The product of the present invention has excellent properties such as excellent unidirectional anti-shrinkage performance and low haze.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer synthetic membranes, and particularly relates to a polyester heat-shrinkable film containing recycled materials and a preparation method thereof. Background Art

[0002] Heat-shrinkable films are usually used for the storage, transportation, and outer packaging of various foods and beverages, electronics and electrical appliances, and pharmaceutical and daily chemical products. Their characteristic is that they can significantly reduce in size after heating, and they are a widely used plastic packaging material. At present, countries around the world pay more and more attention to environmental protection and circular economy. Many countries and regions have issued various directives or documents, putting forward requirements for the proportion of recycled components in plastic products. Therefore, the plastic packaging products industry must also pay attention to and increase the proportion of recycled materials in products. With the progress of technology, heat-shrinkable films made of various materials such as PETG, PET, and PP have emerged one after another, gradually replacing PVC materials, especially in scenarios where recyclable packaging is required, and their advantages in recycling are significant.

[0003] Due to the inconsistent quality and different aging conditions of PET recycled materials, or some recycled materials having been processed multiple times, resulting in a wide molecular weight distribution, the PDI is usually greater than 2.5. According to the existing PET heat-shrinkable film preparation process, if too much recycled material is added, microscopically, there will be insufficient entanglement of chain segments and low molecular chain orientation degree, resulting in a decline in the mechanical properties of the film, causing poor unidirectional anti-shrinkage performance, high haze and other adverse phenomena. This is disadvantageous for packaging high-curvature containers, especially for precision packaging industries such as heat-shrinkable labels.

[0004] Chinese Patent CN117165043A discloses a functional masterbatch for recyclable heat-shrinkable films and a preparation method thereof. The heat-shrinkable film prepared by this method has a relatively high tensile strength, and the characteristic is that the biaxial shrinkage rate is relatively high. Chinese Patent CN117836137B discloses a recyclable heat-shrinkable film for recyclable containers, which has a relatively high shrinkage rate. When heated to 100 °C, the entire recyclable shrink label can shrink by 1% to 90%, but it does not mention whether it can not shrink in a single direction, and only states that its product can be recycled, and does not mention adding recycled materials in its preparation process.

[0005] At present, there is little research on unidirectional anti-shrinkage polyester films containing recycled materials in the market. The PET heat-shrinkable films containing recycled materials prepared by the existing technology generally have poor unidirectional anti-shrinkage performance and high haze. Summary of the Invention

[0006] In order to solve the above problems existing in the prior art, the present invention provides a polyester heat-shrinkable film containing recycled materials and a preparation method thereof, achieving the following invention objectives: preparing a polyester heat-shrinkable film with a high proportion of recycled materials, excellent unidirectional anti-shrinkage performance, low haze, and high tensile strength.

[0007] To achieve the above object, the technical solution adopted is as follows:

[0008] A polyester heat-shrinkable film containing recycled materials, the raw materials of which include recycled PET polyester particles, PET polyester chips, and a modified masterbatch;

[0009] The modified masterbatch is prepared from polyethylene terephthalate-1,4-cyclohexanedimethanol ester, triphenyl phosphite, polyethylene glycol block copolymer, nano-silica, and hyperbranched polyester amine.

[0010] The hyperbranched polyester amine is prepared from trimethylolpropane, methyl crotonate, and diethylenetriamine.

[0011] The polyethylene glycol block copolymer is prepared from polyethylene glycol and γ-valerolactone under the action of a catalyst.

[0012] The weight ratio of the recycled PET polyester particles, PET polyester chips, and the modified masterbatch is: 600 - 750 parts of recycled PET polyester particles, 250 - 300 parts of PET polyester chips, and 70 - 85 parts of the modified masterbatch.

[0013] Furthermore, the mass ratio of the polyethylene terephthalate-1,4-cyclohexanedimethanol ester, triphenyl phosphite, polyethylene glycol block copolymer, nano-silica, and hyperbranched polyester amine is (80 - 95):(10 - 18):(8 - 12):(5 - 10):(3 - 8).

[0014] Furthermore, the molar ratio of the trimethylolpropane, methyl crotonate, and diethylenetriamine is 1:(2 - 4):(0.3 - 0.5).

[0015] Furthermore, the molar ratio of the polyethylene glycol and γ-valerolactone is 1:(3 - 5).

[0016] Furthermore, the catalyst is stannous octoate, and the addition amount is 0.1% - 0.4% of the mass of the polyethylene glycol.

[0017] A preparation method of a polyester heat-shrinkable film containing recycled materials, including the steps of preparing a polyethylene glycol block copolymer, preparing a hyperbranched polyester amine, preparing a modified masterbatch, melt blending, casting into a film, and stretching and shaping;

[0018] Furthermore, the preparation of the hyperbranched polyester amine: includes the synthesis of dendritic molecules and the amidation reaction steps; the synthesis of the dendritic molecules: adding trimethylolpropane and methyl crotonate into a reactor, introducing nitrogen for protection, starting stirring and heating, the reaction temperature is 50 - 60°C, and the reaction time is 4 - 8 hours;

[0019] Further, for the amidation reaction: after the synthesis reaction of the dendrimer is completed, diethylenetriamine is added dropwise to the reactor. After the addition is completed, heating is started, and the temperature is raised to 80-90 °C, and the reaction continues for 6-10 hours;

[0020] Further, for the preparation of the modified masterbatch: polyethylene terephthalate-1,4-cyclohexanedimethanol ester, triphenyl phosphite, polyethylene glycol block copolymer, nano-silica, and hyperbranched polyester amine are kneaded, and the kneading is carried out for 30-40 min at a temperature set at 220-230 °C.

[0021] Further, for the preparation of the polyethylene glycol block copolymer: polyethylene glycol and γ-valerolactone are added to the reactor, stirring is started, nitrogen protection is introduced, the temperature is raised to 110-130 °C, a catalyst is added, and after reacting for 6-8 hours, a polyethylene glycol block copolymer is obtained.

[0022] The number-average molecular weight of the polyethylene glycol block copolymer is 5000-15000 g / mol.

[0023] Further, for the melt blending: recycled PET polyester particles, PET polyester chips, and the modified masterbatch are melt-extruded through a twin-screw extruder; the temperature of the preheating section hopper of the twin-screw extruder is 80-90 °C, the plasticizing and melting section is 250-260 °C, and the die extrusion section is 270-275 °C.

[0024] Further, for the recycled PET polyester particles, the ash content is less than 0.1%, and the impurity content is less than 0.2%.

[0025] Further, the PET polyester chips are new PET polyester materials.

[0026] Further, for the stretching and setting: it includes longitudinal stretching and transverse stretching; longitudinal stretching: the stretching ratio is 0.5-4.5 times, and the stretching temperature is 80-100 °C; transverse stretching: the stretching temperature is 95-110 °C, and the stretching ratio is 2.5-5.5 times.

[0027] Compared with the prior art, the present invention has achieved the following beneficial effects:

[0028] A polyester heat-shrinkable film containing recycled materials prepared by the present invention has a longitudinal shrinkage rate as low as 2.1%-3.1% and a transverse shrinkage rate of up to 72%-76% on the basis of a recycled material content of 60%-70%, and the haze is less than 5%. Description of the Drawings

[0029] Appendix Figure 1 It is the nuclear magnetic resonance hydrogen spectrum (H-NMR) diagram of the "preparation of polyethylene glycol block copolymer" step of the present invention.

[0030] AppendixFigure 2 This is the infrared spectrum (FTIR) diagram before the reaction in the step of "preparation of hyperbranched polyesters and polyamines" of the present invention.

[0031] Appendix Figure 3 This is the infrared spectrum (FTIR) diagram after the reaction in the step of "preparation of hyperbranched polyesters and polyamines" of the present invention. Detailed implementation manners

[0032] To make the objectives, technical solutions and advantages of the present invention clearer, the following will further describe the implementation manners of the present invention in detail. It should be understood that the specific implementation manners described herein are only used to illustrate and explain the present invention and are not used to limit the present invention.

[0033] Example 1 A method for preparing a polyester heat shrinkable film containing recycled materials

[0034] Step 1: Preparation of polyethylene glycol block copolymer

[0035] Add polyethylene glycol and γ-valerolactone into a dry reactor, start stirring, introduce nitrogen for protection, heat up to 130 °C, add stannous octoate, and after reacting for 6 hours, obtain a polyethylene glycol block copolymer. The number-average molecular weight of the polyethylene glycol block copolymer is 5000 g / mol.

[0036] The molar ratio of the amounts of polyethylene glycol and γ-valerolactone used is 1:3.

[0037] The addition amount of stannous octoate is 0.2% of the mass of polyethylene glycol.

[0038] Step 2: Preparation of hyperbranched polyesters and polyamines

[0039] ① Synthesis of dendritic molecules: Add trimethylolpropane and methyl crotonate into a dry reactor according to the ratio, introduce nitrogen for protection, start stirring and heating, control the stirring rate at 300 rpm, and control the temperature at 55 °C, and react for 5 hours.

[0040] ② Amidation reaction: After the synthesis reaction of dendritic molecules is completed, keep stirring on, dropwise add diethylenetriamine into the reactor, start heating after dropping is completed, heat up to 80 °C, and keep the reaction at this temperature for 10 hours.

[0041] The molar ratio of the amounts of trimethylolpropane (TMP), methyl crotonate (MC) and diethylenetriamine (DETA) used is 1:2.0:0.5.

[0042] ③ Purification: Cool the reaction solution obtained in step ② to room temperature, slowly pour it into ethanol at -5°C, and stir for 30 minutes. Filter the stirred reaction solution by suction filtration, and the obtained solid product is dried to obtain a white powdery hyperbranched polyester amine. The drying temperature is 50°C, the vacuum is ≤ -0.065 MPa, and the drying time is 12 hours.

[0043] Step 3: Preparation of modified masterbatch

[0044] Mix PETG, triphenyl phosphite, polyethylene glycol block copolymer, nano-silica, and hyperbranched polyester amine evenly, then add them to a mixer and mix for 35 minutes at a temperature of 226°C. The melt after mixing is fed into a twin-screw granulator through a hot melt gear pump. After extrusion and pelletizing by the twin-screw granulator, a modified masterbatch with a particle size of 3 mm is obtained.

[0045] The weight ratio of the raw materials used is: polyethylene terephthalate-1,4-cyclohexanedimethanol ester (PETG) 80 parts, triphenyl phosphite 13 parts, polyethylene glycol block copolymer 10 parts, nano-silica 10 parts, hyperbranched polyester amine (HPEA) 3 parts.

[0046] Step 4: Melt blending

[0047] Mix the recycled PET polyester particles, PET polyester chips (new PET polyester materials), and modified masterbatch evenly, and convey them through a hopper to a twin-screw extruder for melt extrusion. The temperature settings for each section of the twin-screw extruder are: the hopper temperature of the preheating section is 80°C, the conveying section is 225°C, the plasticizing and melting section is 260°C, the vacuum exhaust section is 250°C, the homogenizing and metering section is 255°C, and the die head extrusion section is 270°C. The die head is a hanger-type flat die head with a die lip gap of 1.5 mm.

[0048] The weight ratio of the raw materials used is: recycled PET polyester particles 600 parts, PET polyester chips 300 parts, modified masterbatch 85 parts.

[0049] The recycled PET polyester particles have an ash content of less than 0.1% and an impurity content of less than 0.2%, and are purchased from Foshan Yaotaiyuansu Industry Co., Ltd.

[0050] Step 5: Cast film forming

[0051] The melt extruded from the die head contacts the surface of a rapidly rotating quenching roll vertically in a curtain shape, and the melt is extended into a film by the quenching roll; cooling water is connected in the quenching roll, and the temperature of the cooling water is controlled at 20°C. After cooling, the film is peeled off from the surface of the quenching roll and enters the stretching and shaping section.

[0052] Step 6: Stretching and shaping

[0053] After the diaphragm is peeled off from the surface of the quenching roll, it is successively introduced into the longitudinal stretching machine and the transverse stretching machine through the traction roll group.

[0054] The control parameters of the longitudinal stretching machine are: stretching multiple 0.5 times, temperature 88 °C.

[0055] The control parameters of the transverse stretching machine are: stretching multiple 2.5 times, temperature 95 °C.

[0056] After stretching, heat setting is carried out on the diaphragm. The temperature of the diaphragm is raised to 190 °C by infrared heating, and then cooled down to 170 °C in a gradient manner, with each 10 °C as a gradient, and the temperature of each gradient lasts for 5 seconds; after heat setting, it is cooled to room temperature, and after trimming and winding, a polyester heat-shrinkable film containing recycled materials is obtained.

[0057] Example 2 A preparation method of a polyester heat-shrinkable film containing recycled materials

[0058] Step 1: Preparation of polyethylene glycol block copolymer

[0059] Add polyethylene glycol and γ-valerolactone into a dry reactor, start stirring, introduce nitrogen for protection, heat up to 115 °C, add stannous octoate, and after reacting for 7.5 hours, obtain a polyethylene glycol block copolymer. The molar ratio of PEG to γ-valerolactone is 1:3.8.

[0060] The addition amount of stannous octoate is 0.1% of the mass of polyethylene glycol.

[0061] The prepared polyethylene glycol block copolymer: the number average molecular weight is 9000 g / mol.

[0062] Step 2: Preparation of hyperbranched polyester amine

[0063] ① Synthesis of dendritic molecules: Add trimethylolpropane and methyl crotonate into a dry reactor according to the ratio, introduce nitrogen for protection, start stirring and heating, control the stirring rate at 200 rpm, and control the temperature at 60 °C, and react for 8 hours.

[0064] ② Amidation reaction: After the synthesis reaction of dendritic molecules is completed, keep stirring on, dropwise add diethylenetriamine into the reactor, start heating after dropping is completed, heat up to 85 °C, and keep the temperature for reaction for 7.5 hours.

[0065] The molar ratio of the usage amounts of trimethylolpropane (TMP), methyl crotonate (MC) and diethylenetriamine (DETA) is 1:4.0:0.3.

[0066] ③Purification: Cool the reaction solution obtained in step ② to room temperature, slowly pour it into ethanol at -5°C, and stir for 30 minutes. Filter the stirred reaction solution by suction filtration, and the obtained solid product is dried to obtain a white powdery hyperbranched polyester amine. The drying temperature is 50°C, the vacuum is ≤ -0.065 MPa, and the drying time is 12 hours.

[0067] Step 3: Preparation of modified masterbatch

[0068] Mix PETG, triphenyl phosphite, polyethylene glycol block copolymer, nano-silica, and hyperbranched polyester amine evenly, then add them to a mixer and knead for 30 min at a temperature of 230°C. Feed the kneaded melt to a twin-screw granulator through a hot melt gear pump, and after extrusion and pelletizing by the twin-screw granulator, a modified masterbatch with a particle size of 2.5 mm is obtained.

[0069] The weight part ratio of the raw materials used is as follows: polyethylene terephthalate-1,4-cyclohexanedimethanol ester (PETG) 85 parts, triphenyl phosphite 10 parts, polyethylene glycol block copolymer 8 parts, nano-silica 8 parts, hyperbranched polyester amine (HPEA) 6 parts.

[0070] Step 4: Melt blending

[0071] Mix the recycled PET polyester particles, PET polyester chips, and modified masterbatch evenly, and convey them to a twin-screw extruder through a hopper for melt extrusion. The temperature settings of each section of the twin-screw extruder are as follows: the temperature of the preheating section hopper is 90°C, the conveying section is 235°C, the plasticizing and melting section is 250°C, the vacuum exhaust section is 240°C, the homogenizing and metering section is 265°C, and the die head extrusion section is 275°C. The die head is a hanger-type flat die head, and the die lip gap is 1.5 mm.

[0072] The weight part ratio of the raw materials used is as follows: recycled PET polyester particles 650 parts, PET polyester chips 260 parts, modified masterbatch 78 parts.

[0073] The recycled PET polyester particles have an ash content of less than 0.1% and an impurity content of less than 0.2%, and are purchased from Foshan Yaotaiyuansu Industry Co., Ltd.

[0074] Step 5: Cast film forming

[0075] The melt extruded from the die head vertically contacts the surface of a rapidly rotating quenching roll in a curtain shape, and the melt is extended into a film by the quenching roll; cooling water is connected in the quenching roll, and the temperature of the cooling water is controlled at 15°C. After cooling, the film is peeled off from the surface of the quenching roll and enters the stretching and shaping section.

[0076] Step 6: Stretching and shaping

[0077] After the film is peeled off from the surface of the quenching roll, it is sequentially introduced into a longitudinal stretching machine and a transverse stretching machine through a set of traction rolls.

[0078] The control parameters of the longitudinal stretching machine are: stretching multiple 4.3 times, temperature 100 °C.

[0079] The control parameters of the transverse stretching machine are: stretching multiple 2.8 times, temperature 100 °C.

[0080] After stretching is completed, heat setting is carried out on the diaphragm. The temperature of the diaphragm is raised to 190 °C by infrared heating, and then cooled down to 170 °C in a gradient manner. Each 10 °C is a gradient, and the temperature of each gradient lasts for 5 seconds; after heat setting is completed, it is cooled to room temperature. After edge trimming and winding, a polyester heat shrinkable film containing recycled materials is obtained.

[0081] Example 3 Preparation method of a polyester heat shrinkable film containing recycled materials

[0082] Step 1: Preparation of polyethylene glycol block copolymer

[0083] Add polyethylene glycol and γ-valerolactone into a dry reactor, start stirring, introduce nitrogen for protection, heat up to 110 °C, add stannous octoate, and after reacting for 8 hours, obtain a polyethylene glycol block copolymer. The number average molecular weight of the polyethylene glycol block copolymer is 11000 g / mol. The molar ratio of the dosage of polyethylene glycol to γ-valerolactone is 1:4.2.

[0084] The addition amount of stannous octoate is 0.4% of the mass of polyethylene glycol.

[0085] Step 2: Preparation of hyperbranched polyester amine

[0086] ① Synthesis of dendritic molecules: Add trimethylolpropane and methyl crotonate into a dry reactor according to the ratio, introduce nitrogen for protection, start stirring and heating, control the stirring rate at 500 rpm, and control the temperature at 60 °C, and react for 4 hours.

[0087] ② Amidation reaction: After the synthesis reaction of dendritic molecules is completed, keep stirring on, add diethylenetriamine dropwise to the reactor, and start heating after dropping is completed, heat up to 80 °C, and keep the reaction at this temperature for 8.5 hours.

[0088] The molar ratio of the dosage of trimethylolpropane (TMP), methyl crotonate (MC) to diethylenetriamine (DETA) is 1:3.3:0.4.

[0089] ③ Purification: Cool the reaction solution obtained in step ② to room temperature, slowly pour it into ethanol at -5 °C, and stir for 30 minutes. Filter the stirred reaction solution, and the obtained solid product is dried to obtain a white powdery hyperbranched polyester amine. The drying temperature is 50 °C, the vacuum ≤ -0.065 MPa, and the drying time is 12 hours.

[0090] Step 3: Preparation of Modified Masterbatch

[0091] Mix PETG, triphenyl phosphite, polyethylene glycol block copolymer, nano-silica, and hyperbranched polyester amine evenly, then add them to a mixer and knead for 40 minutes at a temperature of 223°C. Feed the kneaded melt to a twin-screw granulator through a hot melt gear pump. After extrusion and pelletizing by the twin-screw granulator, a modified masterbatch with a particle size of 3.3 mm is obtained.

[0092] The weight ratio of the raw materials used is as follows: 90 parts of polyethylene terephthalate-1,4-cyclohexanedimethanol ester (PETG), 16 parts of triphenyl phosphite, 9 parts of polyethylene glycol block copolymer, 6 parts of nano-silica, and 8 parts of hyperbranched polyester amine (HPEA).

[0093] Step 4: Melt Blending

[0094] Mix the recycled PET polyester particles, PET polyester chips, and modified masterbatch evenly, and convey them to a twin-screw extruder through a hopper for melt extrusion. The temperature settings for each section of the twin-screw extruder are as follows: the temperature of the preheating section hopper is 90°C, the conveying section is 230°C, the plasticizing and melting section is 255°C, the vacuum exhaust section is 250°C, the homogenizing and metering section is 260°C, and the die head extrusion section is 275°C. The die head is a hanger-type flat die head with a die lip gap of 1.5 mm.

[0095] The weight ratio of the raw materials used is as follows: 700 parts of recycled PET polyester particles, 280 parts of PET polyester chips, and 74 parts of modified masterbatch.

[0096] The recycled PET polyester particles have an ash content of less than 0.1% and an impurity content of less than 0.2%, and are purchased from Foshan Yaotaiyuansu Industry Co., Ltd.

[0097] Step 5: Cast Film Forming

[0098] The melt extruded from the die head contacts the surface of a rapidly rotating quenching roll vertically in a curtain shape, and the melt is extended into a film by the quenching roll; cooling water is connected in the quenching roll, and the temperature of the cooling water is controlled at 18°C. After cooling, the film is peeled off from the surface of the quenching roll and enters the stretching and shaping section.

[0099] Step 6: Stretching and Shaping

[0100] After the film is peeled off from the surface of the quenching roll, it is sequentially introduced into a longitudinal stretching machine and a transverse stretching machine through a set of traction rolls.

[0101] The control parameters of the longitudinal stretching machine are: stretching ratio 3.9 times, temperature 80°C.

[0102] The control parameters of the transverse stretching machine are: stretching ratio 3.2 times, temperature 105°C.

[0103] After stretching, the diaphragm is heat-set. The temperature of the diaphragm is raised to 190 °C by infrared heating, and then cooled down to 170 °C in a gradient manner, with each 10 °C as a gradient and each gradient temperature lasting for 5 seconds. After heat-setting, it is cooled to room temperature. After trimming and winding, a polyester heat-shrinkable film containing recycled materials is obtained.

[0104] Example 4 A method for preparing a polyester heat-shrinkable film containing recycled materials

[0105] Step 1: Preparation of polyethylene glycol block copolymer

[0106] Polyethylene glycol and γ-valerolactone are added to a dry reactor. Stirring is started, nitrogen is introduced for protection, the temperature is raised to 120 °C, and stannous octoate is added. After reacting for 6.5 hours, a polyethylene glycol block copolymer is obtained. The number-average molecular weight of the polyethylene glycol block copolymer is 15000 g / mol.

[0107] The molar ratio of the amounts of polyethylene glycol and γ-valerolactone used is 1:5.

[0108] The addition amount of stannous octoate is 0.3% of the mass of polyethylene glycol.

[0109] Step 2: Preparation of hyperbranched polyester amine

[0110] ① Synthesis of dendritic molecule: Trimethylolpropane and methyl crotonate are added to a dry reactor according to the ratio. Nitrogen is introduced for protection, stirring is started and heated, the stirring rate is controlled at 400 rpm, and the temperature is controlled at 50 °C. The reaction lasts for 6 hours.

[0111] ② Amidation reaction: After the synthesis reaction of the dendritic molecule is completed, stirring is kept on, diethylenetriamine is added dropwise to the reactor, and after the addition is completed, heating is started, the temperature is raised to 90 °C, and the reaction is kept at this temperature for 6 hours.

[0112] The molar ratio of the amounts of trimethylolpropane (TMP), methyl crotonate (MC) and diethylenetriamine (DETA) used is 1:2.6:0.5.

[0113] ③ Purification: The reaction solution obtained in step ② is cooled to room temperature and slowly poured into ethanol at -5 °C, and stirred for 30 minutes. The stirred reaction solution is filtered by suction, and the obtained solid product is dried to obtain a white powdery hyperbranched polyester amine. The drying temperature is 50 °C, the vacuum is ≤ -0.065 MPa, and the drying time is 12 hours.

[0114] Step 3: Preparation of modified masterbatch

[0115] Mix PETG, triphenyl phosphite, polyethylene glycol block copolymer, nano-silica, and hyperbranched polyester amine evenly, then add them to a mixer and knead for 40 min at a temperature of 220 °C. Feed the kneaded melt into a twin-screw granulator through a hot melt gear pump. After extrusion and pelletization by the twin-screw granulator, a modified masterbatch with a particle size of 3.5 mm is obtained.

[0116] The weight ratio of the raw materials used is as follows: polyethylene terephthalate-1,4-cyclohexanedimethanol ester (PETG) 95 parts, triphenyl phosphite 18 parts, polyethylene glycol block copolymer 12 parts, nano-silica 5 parts, and hyperbranched polyester amine (HPEA) 5 parts.

[0117] Step 4: Melt blending

[0118] Mix the recycled PET polyester particles, PET polyester chips, and modified masterbatch evenly, and convey them to a twin-screw extruder through a hopper for melt extrusion. The temperature settings for each section of the twin-screw extruder are as follows: the temperature of the preheating section hopper is 90 °C, the conveying section is 233 °C, the plasticizing and melting section is 257 °C, the vacuum exhaust section is 245 °C, the homogenizing and metering section is 265 °C, and the die head extrusion section is 273 °C. A hanger-type flat die head is selected for the die head, and the die lip gap is 1.5 mm.

[0119] The weight ratio of the raw materials used is as follows: recycled PET polyester particles 750 parts, PET polyester chips 250 parts, and modified masterbatch 70 parts.

[0120] The recycled PET polyester particles have an ash content of less than 0.1% and an impurity content of less than 0.2%, and are purchased from Foshan Yaotaiyuanshu Industry Co., Ltd.

[0121] Step 5: Cast film formation

[0122] The melt extruded from the die head contacts the surface of a rapidly rotating quenching roll vertically in a curtain shape, and the melt is extended into a film through the quenching roll; cooling water is connected in the quenching roll, and the temperature of the cooling water is controlled at 16 °C. After cooling, the film is peeled off from the surface of the quenching roll and enters the stretching and shaping section.

[0123] Step 6: Stretching and shaping

[0124] After the film is peeled off from the surface of the quenching roll, it is sequentially introduced into a longitudinal stretching machine and a transverse stretching machine through a traction roll group.

[0125] The control parameters of the longitudinal stretching machine are: stretching ratio 4.5 times, temperature 95 °C.

[0126] The control parameters of the transverse stretching machine are: stretching ratio 5.5 times, temperature 110 °C.

[0127] After stretching, the diaphragm is heat-set. The temperature of the diaphragm is raised to 190 °C by infrared heating, and then gradually cooled to 170 °C, with each 10 °C as a gradient and the temperature of each gradient lasting for 5 seconds. After heat-setting, it is cooled to room temperature. After trimming and winding, a polyester heat-shrinkable film containing recycled materials is obtained.

[0128] Comparative Example 1

[0129] Step 1, melt blending

[0130] The recycled PET polyester particles and PET polyester chips are mixed evenly and conveyed to a twin-screw extruder through a hopper for melt extrusion. The temperature of each section of the twin-screw extruder is set as follows: the temperature of the hopper in the preheating section is 90 °C, the conveying section is 230 °C, the plasticizing and melting section is 255 °C, the vacuum exhaust section is 250 °C, the homogenizing and metering section is 260 °C, and the die head extrusion section is 275 °C. The die head is a hanger-type flat die head with a die lip gap of 1.5 mm.

[0131] The weight ratio of the raw materials used is: 600 parts of recycled PET polyester particles and 300 parts of PET polyester chips.

[0132] Step 2, casting into film

[0133] The melt extruded from the die head contacts the surface of the rapidly rotating quenching roll vertically in a curtain shape, and the melt is extended into a film through the quenching roll; cooling water is connected in the quenching roll, and the temperature of the cooling water is controlled at 18 °C. After cooling, the diaphragm is peeled off from the surface of the quenching roll and enters the stretching and setting section.

[0134] Step 3, stretching and setting

[0135] After the diaphragm is peeled off from the surface of the quenching roll, it is sequentially introduced into a longitudinal stretching machine and a transverse stretching machine through a traction roll group.

[0136] The control parameters of the longitudinal stretching machine are: stretching ratio 3.9 times, temperature 80 °C.

[0137] The control parameters of the transverse stretching machine are: stretching ratio 3.2 times, temperature 105 °C.

[0138] After stretching, the diaphragm is heat-set. The temperature of the diaphragm is raised to 190 °C by infrared heating, and then gradually cooled to 170 °C, with each 10 °C as a gradient and the temperature of each gradient lasting for 5 seconds. After heat-setting, it is cooled to room temperature. After trimming and winding, a polyester heat-shrinkable film containing recycled materials is obtained.

[0139] Performance testing

[0140] (I) Mechanical property and optical property testing

[0141] The mechanical and optical properties of the products prepared in Examples 1-4 and Comparative Example 1 were tested, and the test results and test reference standards are shown in Table 1.

[0142] Table 1 Test Results of Mechanical and Optical Properties

[0143] Analyzing the data in Table 1, it can be seen that the transverse shrinkage rate of Examples 1-4 is 72% - 76%, the longitudinal shrinkage rate is 2.1% - 3.1%, the longitudinal tensile strength is 82 MPa - 95 MPa, the transverse elongation at break is 354% - 389%, and the transverse tensile strength is 137 MPa - 150 MPa. The data shows that the polyester heat shrinkable film containing recycled materials obtained by the present invention has excellent unidirectional anti-shrinkage performance and mechanical properties. At the same time, due to its low haze, it can well meet the requirements of the fine packaging industry. In Comparative Example 1, for the heat shrinkable film obtained without adding the modified masterbatch during the preparation of the heat shrinkable film, its tensile strength, shrinkage rate, and elongation at break all decreased to varying degrees compared with Examples 1-4. The longitudinal shrinkage is high, and the haze data is also higher than that of Examples 1-4. This shows that the modified masterbatch provided by the present invention has a significant effect on improving the mechanical and optical properties of the PET polyester heat shrinkable film containing recycled materials.

[0144] (2) Anti-aging Performance Test

[0145] The products prepared in Examples 1-4 and Comparative Example 1 were subjected to light aging treatment according to GB / T 43297-2023.

[0146] Parameters of the xenon lamp aging chamber: Irradiation intensity: 0.5 W / m² @ 340 nm, chamber temperature: 50°C ± 2°C, relative humidity: 50% ± 10%, irradiation time: 240 hours.

[0147] After the irradiation, the mechanical and optical properties of the products prepared in Examples 1-4 and Comparative Example 1 were tested, and the test results are shown in Table 2;

[0148] Table 2 Test Results of Mechanical and Optical Properties after Aging Test

[0149] Analysis of the data in Table 2 shows that after the aging treatment of Examples 1 to 4, the transverse shrinkage rate is 69% to 72%, the longitudinal shrinkage rate is 2.6% to 3.7%, the longitudinal tensile strength is 79 MPa to 90 MPa, the longitudinal elongation at break is 87% to 90%, the transverse tensile strength is 130 MPa to 139 MPa, the haze is 3.8% to 4.5%, and the attenuation of optical and mechanical properties is small; after the aging treatment of Comparative Example 1, the transverse tensile strength drops to 55 MPa, the longitudinal tensile strength drops to 48 MPa, and the haze increases to 10.7%; it shows that the PET polyester heat shrinkable film containing recycled materials provided by the present invention has excellent anti-aging performance.

[0150] The polyethylene glycol block copolymer obtained in the step of "preparation of polyethylene glycol block copolymer" of the present invention can be confirmed by nuclear magnetic resonance hydrogen spectrum (H-NMR). The nuclear magnetic resonance hydrogen spectrum (H-NMR) diagram is as attached Figure 1 shown. The product can be determined by the characteristic peaks of polyethylene glycol (PEG) and γ-valerolactone.

[0151] The hyperbranched polyesteramine obtained in the step of "preparation of hyperbranched polyesteramine" of the present invention can be confirmed by infrared spectroscopy (FTIR) detection. The infrared spectroscopy (FTIR) diagrams before and after the reaction are as attached Figures 2-3 shown. It can be seen from the infrared spectroscopy (FTIR) diagram that after the reaction is completed, the ester group signal at 1720 cm -1 weakens, and the amide bond signal at 1650 cm -1 strengthens, indicating that the hyperbranched polyesteramine is obtained.

[0152] Unless otherwise specified, the ratios described in the present invention are all mass ratios, and the percentages described in the present invention are all mass percentages. Obviously, there are many specific implementation methods that can be changed under the concept of the present invention. It should be stated here that any changes made under the inventive concept of the present invention will fall within the protection scope of the present invention.

Claims

1. A polyester heat-shrinkable film containing recycled materials, characterized in that: The raw materials include recycled PET polyester particles, PET polyester chips, and modified masterbatch; the weight ratio of the recycled PET polyester particles, PET polyester chips, and modified masterbatch is: 600 - 750 parts of recycled PET polyester particles, 250 - 300 parts of PET polyester chips, and 70 - 85 parts of modified masterbatch; The modified masterbatch is prepared from polyethylene terephthalate-1,4-cyclohexanedimethanol ester, triphenyl phosphite, polyethylene glycol block copolymer, nano-silica, and hyperbranched polyester amine; the mass ratio of the polyethylene terephthalate-1,4-cyclohexanedimethanol ester, triphenyl phosphite, polyethylene glycol block copolymer, nano-silica, and hyperbranched polyester amine is (80 - 95):(10 - 18):(8 - 12):(5 - 10):(3 - 8); The polyethylene glycol block copolymer is prepared by reacting polyethylene glycol with γ-valerolactone under the action of a catalyst; The hyperbranched polyester amine is prepared from trimethylolpropane, methyl crotonate, and diethylenetriamine, and the preparation method includes the synthesis of dendritic molecules and the amidation reaction steps; the synthesis of dendritic molecules: add trimethylolpropane and methyl crotonate into a reactor, introduce nitrogen for protection, start stirring and heating, the reaction temperature is 50 - 60 °C, and the reaction time is 4 - 8 hours; The amidation reaction: after the synthesis reaction of dendritic molecules is completed, add diethylenetriamine dropwise into the reactor, start heating after dropping, raise the temperature to 80 - 90 °C, and continue to react for 6 - 10 hours.

2. A polyester heat-shrinkable film containing recycled materials according to claim 1, characterized in that: The molar ratio of trimethylolpropane, methyl crotonate, and diethylenetriamine is 1:(2 - 4):(0.3 - 0.5).

3. The polyester heat-shrinkable film containing recycled materials according to claim 1, wherein: The molar ratio of polyethylene glycol and γ-valerolactone is 1:(3 - 5); the catalyst is stannous octoate, and the addition amount is 0.1% - 0.4% of the mass of polyethylene glycol.

4. The preparation method of a polyester heat shrinkable film containing recycled material according to any one of claims 1-3, characterized in that: It includes the preparation of polyethylene glycol block copolymer, the preparation of hyperbranched polyester amine, the preparation of modified masterbatch, melt blending, casting into film, and stretching and setting steps; the melt blending: melt extrude the recycled PET polyester particles, PET polyester chips, and modified masterbatch through a twin-screw extruder; the temperature of the preheating section hopper of the twin-screw extruder is 80 - 90 °C, the plasticizing and melting section is 250 - 260 °C, and the die head extrusion section is 270 - 275 °C.

5. The preparation method of a polyester heat-shrinkable film containing recycled materials according to claim 4, characterized in that: The preparation of polyethylene glycol block copolymer: add polyethylene glycol and γ-valerolactone into a reactor, start stirring, introduce nitrogen for protection, raise the temperature to 110 - 130 °C, add the catalyst, and after reacting for 6 - 8 hours, obtain the polyethylene glycol block copolymer.

6. The preparation method of a polyester heat-shrinkable film containing recycled material according to claim 4, characterized in that: The preparation of the modified masterbatch: knead polyethylene terephthalate-1,4-cyclohexanedimethanol ester, triphenyl phosphite, polyethylene glycol block copolymer, nano-silica, and hyperbranched polyester amine, knead for 30 - 40 min, and set the temperature at 220 - 230 °C.

7. The preparation method of a polyester heat shrinkable film containing recycled materials according to claim 4, wherein: The stretching and setting: includes longitudinal stretching and transverse stretching; Longitudinal stretching: the stretching multiple is 0.5 to 4.5 times, and the stretching temperature is 80 to 100 °C; Transverse stretching: the stretching temperature is 95 to 110 °C, and the stretching multiple is 2.5 to 5.5 times.

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