Special copolyester for high-speed stretch film and preparation method of special copolyester

Abstract

The invention relates to the technical field of organic polymers, and discloses a special copolyester for a high-speed stretch film and a preparation method thereof.The special copolyester is prepared from, by mass, 50-60 parts of terephthalic acid, 20-30 parts of ethylene glycol, 5-20 parts of a polymerizable eutectic solvent, 0.02-0.03 part of a catalyst and 0.002-0.003 part of a stabilizer; the copolyester is prepared by polymerizing terephthalic acid, ethylene glycol, the polymerizable eutectic solvent, the catalyst and the stabilizer, and the polymerizable eutectic solvent has relatively high conductivity after polymerization, so that the melt resistivity of the polyester can be improved, and the toughness and transparency of the polyester can be improved; the problems of polyester crystallization and yellowing caused by electrostatic agents such as metal compounds can be avoided; the copolyester is low in melt resistivity, simple and feasible in preparation method and suitable for high-speed film drawing production.

Description

Technical Field

[0001] The invention relates to the technical field of organic polymers, in particular to a copolyester specially used for high-speed stretching film and a preparation method thereof. Background Art

[0002] Biaxially oriented polyester film (BOPET) has the characteristics of high strength, good rigidity, transparency, high gloss, etc. It is widely used in packaging printing, heat shrinkage, thermal transfer, optics, solar backplane, medical film, other industries, etc. It is made of polyethylene terephthalate (PET) as raw material, extruded by an extruder, and then stretched by a transverse stretching machine and a longitudinal stretching machine.

[0003] PET is a crystalline polymer. The crystallization of the cast sheet is closely related to the cooling speed and uniformity of the melt. Therefore, the tighter the melt is attached to the cooling drum surface from the die head, the better the heat conduction and the faster the melt cooling speed. At this time, the thick sheet has a small crystallinity and fine and uniform spherulites, which is conducive to the improvement of longitudinal stretch orientation and uniform and stable quality of the finished film. In actual production, high-voltage static electricity is generally used to make the melt closely attached to the cooling drum. The melt has strong molten conductivity, so the thick sheet has a good attachment effect and the melt cools quickly, which is conducive to obtaining a thick sheet with a smooth surface, low crystallinity and stable size.

[0004] The current mainstream preparation method is to improve the melt conductivity of the melt by adding electrostatic agents such as metal compounds during the PET polymerization process. For example, Publication No. CN108192085A discloses a method for changing the conductivity of PET products for high-speed films, Publication No. CN1425703A discloses a method for preparing polyester, and Publication No. CN116003750A discloses a polyester for high-speed films and a preparation method thereof. The present invention finds that the use of metal compound electrostatic regulators will cause crystallization of polyester during the polymerization process and deterioration of the color value of polyester chips, resulting in reduced quality of the polyester produced. Summary of the invention

[0005] Aiming at the problem in the prior art that polyester for high-speed film made by using metal compound-type electrostatic regulators has the problem that the color value of polyester chips is easily deteriorated during the polymerization process, the present invention provides a polyester specially used for high-speed stretching film. The polyester is prepared by polymerization of terephthalic acid, ethylene glycol, a polymerizable low eutectic solvent, a catalyst and a stabilizer. The polymerizable low eutectic solvent used in the polyester has strong conductivity after polymerization, can improve the melt resistivity of the polyester, can improve the toughness and transparency of the polyester, and can avoid the problems of polyester crystallization and yellowing caused by electrostatic agents such as metal compounds.

[0006] The specific technical scheme of the present invention is: A special copolyester for high-speed stretching film comprises the following raw materials by weight: 50-60 parts of terephthalic acid, 20-30 parts of ethylene glycol, 5-20 parts of a polymerizable low eutectic solvent, 0.02-0.03 parts of a catalyst, and 0.002-0.003 parts of a stabilizer.

[0007] Preferably, the polymerizable low eutectic solvent is prepared by polymerization reaction of a polymerizable monomer, a hydrogen bond acceptor, a cross-linking agent and an initiator, and the polymerization temperature is 60-70°C.

[0008] Preferably, the molar ratio of the polymerizable monomer to the hydrogen bond acceptor is 1:10-20, the molar ratio of the crosslinking agent to the polymerizable monomer is 1:10-20, and the molar ratio of the initiator to the polymerizable monomer is 1:20-100.

[0009] Preferably, the polymerizable monomer includes one or more of acrylamide, N-isopropylacrylamide, N,N-dimethylacrylamide, acrylic acid, methacrylic acid and hydroxyethyl methacrylate; the hydrogen bond acceptor includes one of a quaternary ammonium salt and betaine; the cross-linking agent includes one of N,N-methylenebisacrylamide and ethylene glycol dimethacrylate; and the initiator includes potassium persulfate and dibenzoyl peroxide.

[0010] Preferably, the catalyst includes one or more of antimony trioxide, antimony acetate, antimony glycolate and titanium glycolate.

[0011] Preferably, the stabilizer includes one or more of trimethyl phosphate, dimethyl phosphate, triphenyl phosphate and diphenyl phosphate.

[0012] The present invention provides a special copolyester for high-speed stretch film, which is prepared by copolymerization of terephthalic acid, ethylene glycol, a polymerizable low eutectic solvent, a catalyst and a stabilizer. The hydrogen bond donor or acceptor of the polymerizable low eutectic solvent contains a polymerizable group, and it still has strong conductivity after polymerization, so it can be used as an electrostatic regulator to adjust the molecular chain structure of PET polyester, which can significantly improve the melt resistivity of polyester; the polymerizable low eutectic solvent structure is a soft segment, and the internal bonding mainly relies on hydrogen bonds and van der Waals forces. After copolymerization, it can effectively reduce the crystallization rate of polyester, give polyester better toughness and transparency, and avoid the use of metal compounds and other electrostatic agents caused by polyester crystallization and yellowing problems. In addition, the polymerizable low eutectic solvent is simple to prepare, has the advantages of 100% atomic utilization and low cost, and is very suitable for industrial production applications.

[0013] A method for preparing the above-mentioned copolyester for high-speed stretch film comprises the following steps: injecting terephthalic acid, ethylene glycol, a polymerizable low eutectic solvent and a catalyst into a container for esterification reaction, and then adding a stabilizer for polycondensation reaction after the esterification reaction is completed to prepare the copolyester for high-speed stretch film.

[0014] Preferably, the conditions for the esterification reaction include: temperature 240-260° C., pressure 0.2-0.4 MPa.

[0015] Preferably, the polycondensation reaction includes: a temperature of 250 to 285° C., a vacuum degree of 40 to 100 Pa, and a reaction time of 1.5 to 2.5 h.

[0016] Preferably, the conditions of the polycondensation reaction also include: first evacuating to 90-100 Pa and heating to 250-265° C. for 30-50 min, then evacuating to below 40 Pa and heating to 275-285° C. for 60-120 min.

[0017] Compared with the prior art, this application has the following technical effects: The copolyester provided by the present invention is prepared by polymerization of terephthalic acid, ethylene glycol, a polymerizable low eutectic solvent, a catalyst and a stabilizer. The polymerizable low eutectic solvent has strong conductivity after polymerization, can improve the melt resistivity of the polyester, can improve the toughness and transparency of the polyester, and can avoid the problems of polyester crystallization and yellowing caused by electrostatic agents such as metal compounds. The copolyester has low melt resistivity and a simple and easy preparation method, and is suitable for high-speed film drawing production. DETAILED DESCRIPTION

[0018] The present invention will be further described below in conjunction with the embodiments.

[0019] Embodiment 1: A method for preparing a copolyester specially used for high-speed stretching film, comprising the following preparation methods: (1) preparing a polymerizable low eutectic solvent: weighing 0.5 mol of acrylic acid (36 g) and 0.125 mol of choline chloride (17.5 g), mixing them at 80° C. to form a completely transparent and uniform low eutectic solvent, cooling the low eutectic solvent to room temperature, adding 3.9 g of N,N-methylenebisacrylamide and 1.4 g of potassium persulfate, and stirring until completely dissolved to obtain a polymerizable low eutectic solvent; (2) Preparation of special copolyester for high-speed stretch film: 50 parts of terephthalic acid, 24 parts of ethylene glycol, 5 parts of polymerizable low eutectic solvent and 0.02 parts of catalyst (ethylene glycol antimony) were added to a 2.5L polymerization reactor, and the esterification reaction was carried out at 0.25MPa and 245°C for 120 minutes. After the esterification reaction was completed, 0.002 parts of stabilizer (triphenyl phosphate) was added and stirred for 10 minutes, and then vacuumed at 260-270°C for 50 minutes for pre-polycondensation reaction, and then the final polycondensation was carried out at an absolute pressure of less than 40Pa and 275°C for 115 minutes. After the reaction was completed, the copolyester for high-speed stretch film was extruded, pelletized and dried.

[0020] Embodiment 2: A method for preparing a copolyester specially used for high-speed stretching film, comprising the following preparation methods: (1) preparing a polymerizable low eutectic solvent: weighing 0.5 mol of acrylic acid (36 g) and 0.125 mol of choline chloride (17.5 g), mixing them at 80° C. to form a completely transparent and uniform low eutectic solvent, cooling the low eutectic solvent to room temperature, adding 3.9 g of N,N-methylenebisacrylamide and 1.4 g of potassium persulfate, and stirring until completely dissolved to obtain a polymerizable low eutectic solvent; (2) Preparation of special copolyester for high-speed stretch film: 50 parts of terephthalic acid, 24 parts of ethylene glycol, 10 parts of polymerizable low eutectic solvent and 0.02 parts of catalyst (ethylene glycol antimony) were added to a 2.5L polymerization reactor, and the esterification reaction was carried out at 0.25MPa and 245°C for 120 minutes. After the esterification reaction was completed, 0.002 parts of stabilizer (triphenyl phosphate) was added and stirred for 10 minutes, and then vacuumed at 260-270°C for 50 minutes for pre-polycondensation reaction, and then the final polycondensation was carried out at an absolute pressure of less than 40Pa and 275°C for 115 minutes. After the reaction was completed, the copolyester for high-speed stretch film was extruded, pelletized and dried.

[0021] Embodiment 3: A method for preparing a copolyester specially used for high-speed stretching film, comprising the following preparation methods: (1) preparing a polymerizable low eutectic solvent: weighing 0.5 mol of acrylic acid (36 g) and 0.125 mol of choline chloride (17.5 g), mixing them at 80° C. to form a completely transparent and uniform low eutectic solvent, cooling the low eutectic solvent to room temperature, adding 3.9 g of N,N-methylenebisacrylamide and 1.4 g of potassium persulfate, and stirring until completely dissolved to obtain a polymerizable low eutectic solvent; (2) Preparation of special copolyester for high-speed stretch film: 50 parts of terephthalic acid, 24 parts of ethylene glycol, 15 parts of polymerizable low eutectic solvent and 0.02 parts of catalyst (ethylene glycol antimony) were added to a 2.5L polymerization reactor, and the esterification reaction was carried out at 0.25MPa and 245°C for 120 minutes. After the esterification reaction was completed, 0.002 parts of stabilizer (triphenyl phosphate) was added and stirred for 10 minutes, and then vacuumed at 260-270°C for 50 minutes for pre-polycondensation reaction, and then the final polycondensation was carried out at an absolute pressure of less than 40Pa and 275°C for 115 minutes. After the reaction was completed, the copolyester for high-speed stretch film was extruded, pelletized and dried.

[0022] Embodiment 4: A method for preparing a copolyester specially used for high-speed stretching film, comprising the following preparation methods: (1) preparing a polymerizable low eutectic solvent: weighing 0.5 mol of acrylic acid (36 g) and 0.125 mol of choline chloride (17.5 g), mixing them at 80° C. to form a completely transparent and uniform low eutectic solvent, cooling the low eutectic solvent to room temperature, adding 3.9 g of N,N-methylenebisacrylamide and 1.4 g of potassium persulfate, and stirring until completely dissolved to obtain a polymerizable low eutectic solvent; (2) Preparation of special copolyester for high-speed stretch film: 50 parts of terephthalic acid, 24 parts of ethylene glycol, 20 parts of polymerizable low eutectic solvent and 0.02 parts of catalyst (ethylene glycol antimony) were added to a 2.5L polymerization reactor, and the esterification reaction was carried out at 0.25MPa and 245°C for 120 minutes. After the esterification reaction was completed, 0.002 parts of stabilizer (triphenyl phosphate) was added and stirred for 10 minutes, and then vacuumed at 260-270°C for 50 minutes for pre-polycondensation reaction, and then the final polycondensation was carried out at an absolute pressure of less than 40Pa and 275°C for 115 minutes. After the reaction was completed, the copolyester for high-speed stretch film was extruded, pelletized and dried.

[0023] Embodiment 5: A method for preparing a copolyester specially used for high-speed stretching film, comprising the following preparation methods: (1) preparing a polymerizable low eutectic solvent: weighing 0.45 mol of acrylic acid (32.4 g) and 0.15 mol of choline chloride (20.9 g), mixing them at 80° C. to form a completely transparent and uniform low eutectic solvent, cooling the low eutectic solvent to room temperature, adding 3.9 g of N,N-methylenebisacrylamide and 1.4 g of potassium persulfate, and stirring until completely dissolved to obtain a polymerizable low eutectic solvent; (2) Preparation of special copolyester for high-speed stretch film: 50 parts of terephthalic acid, 24 parts of ethylene glycol, 10 parts of polymerizable low eutectic solvent and 0.02 parts of catalyst (ethylene glycol antimony) were added to a 2.5L polymerization reactor, and the esterification reaction was carried out at 0.25MPa and 245°C for 120 minutes. After the esterification reaction was completed, 0.002 parts of stabilizer (triphenyl phosphate) was added and stirred for 10 minutes, and then vacuumed at 260-270°C for 50 minutes for pre-polycondensation reaction, and then the final polycondensation was carried out at an absolute pressure of less than 40Pa and 275°C for 115 minutes. After the reaction was completed, the copolyester for high-speed stretch film was extruded, pelletized and dried.

[0024] Embodiment 6: A method for preparing a copolyester specially used for high-speed stretching film, comprising the following preparation methods: (1) preparing a polymerizable low eutectic solvent: weighing 0.4 mol of acrylic acid (28.8 g) and 0.2 mol of choline chloride (27.9 g), mixing them at 80° C. to form a completely transparent and uniform low eutectic solvent, cooling the low eutectic solvent to room temperature, adding 3.1 g of N,N-methylenebisacrylamide and 1.1 g of potassium persulfate, and stirring until completely dissolved to obtain a polymerizable low eutectic solvent; (2) Preparation of special copolyester for high-speed stretch film: 50 parts of terephthalic acid, 24 parts of ethylene glycol, 10 parts of polymerizable low eutectic solvent and 0.02 parts of catalyst (ethylene glycol antimony) were added to a 2.5L polymerization reactor, and the esterification reaction was carried out at 0.25MPa and 245°C for 120 minutes. After the esterification reaction was completed, 0.002 parts of stabilizer (triphenyl phosphate) was added and stirred for 10 minutes, and then vacuumed at 260-270°C for 50 minutes for pre-polycondensation reaction, and then the final polycondensation was carried out at an absolute pressure of less than 40Pa and 275°C for 115 minutes. After the reaction was completed, the copolyester for high-speed stretch film was extruded, pelletized and dried.

[0025] Embodiment 7: A method for preparing a copolyester specially used for high-speed stretching film, comprising the following preparation methods: (1) preparing a polymerizable low eutectic solvent: weighing 0.5 mol of acrylic acid (36 g) and 0.125 mol of choline chloride (17.5 g), mixing them at 80° C. to form a completely transparent and uniform low eutectic solvent, cooling the low eutectic solvent to room temperature, adding 3.9 g of N,N-methylenebisacrylamide and 1.4 g of potassium persulfate, and stirring until completely dissolved to obtain a polymerizable low eutectic solvent; (2) Preparation of special copolyester for high-speed stretch film: 50 parts of terephthalic acid, 24 parts of ethylene glycol, 10 parts of polymerizable low eutectic solvent and 0.02 parts of catalyst (ethylene glycol antimony) were added to a 2.5L polymerization reactor, and the esterification reaction was carried out at 0.25MPa and 245°C for 120 minutes. After the esterification reaction was completed, 0.002 parts of stabilizer (triphenyl phosphate) was added and stirred for 10 minutes, and then vacuumed at 260-270°C for 50 minutes for pre-polycondensation reaction, and then the final polycondensation was carried out at an absolute pressure of less than 40Pa and 275°C for 115 minutes. After the reaction was completed, the copolyester for high-speed stretch film was extruded, pelletized and dried.

[0026] Embodiment 8: A method for preparing a copolyester specially used for high-speed stretching film, comprising the following preparation methods: (1) preparing a polymerizable low eutectic solvent: weighing 0.5 mol of acrylic acid (36 g) and 0.125 mol of choline chloride (17.5 g), mixing them at 80° C. to form a completely transparent and uniform low eutectic solvent, cooling the low eutectic solvent to room temperature, adding 3.9 g of N,N-methylenebisacrylamide and 1.4 g of potassium persulfate, and stirring until completely dissolved to obtain a polymerizable low eutectic solvent; (2) Preparation of special copolyester for high-speed stretch film: 50 parts of terephthalic acid, 30 parts of ethylene glycol, 10 parts of polymerizable low eutectic solvent and 0.02 parts of catalyst (ethylene glycol antimony) were added to a 2.5L polymerization reactor, and the esterification reaction was carried out at 0.25MPa and 245°C for 120 minutes. After the esterification reaction was completed, 0.002 parts of stabilizer (triphenyl phosphate) was added and stirred for 10 minutes, and then vacuumed at 260-270°C for pre-polycondensation for 50 minutes, and then the final polycondensation was carried out at an absolute pressure of less than 40Pa and 275°C for 115 minutes. After the reaction was completed, the copolyester for high-speed stretch film was extruded, pelletized and dried.

[0027] Comparative Example 1: The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 is a polyester for a large glossy film, and no polymerizable low eutectic solvent is added in Comparative Example 1, and the following steps are included: In a 2.5L polymerization reactor, 50 parts of terephthalic acid, 24 parts of ethylene glycol and 0.02 parts of catalyst (ethylene glycol antimony) were added to carry out esterification reaction at 0.25MPa and 245°C for 120 minutes. After the esterification reaction, 0.002 parts of stabilizer (triphenyl phosphate) were added and stirred for 10 minutes. Then, vacuum was drawn at 260-270°C for pre-polycondensation reaction for 50 minutes. Then, the final polycondensation reaction was carried out at an absolute pressure of less than 40Pa and 275°C for 115 minutes. After the reaction was completed, the polyester for glossy film was extruded, pelletized and dried.

[0028] Comparative Example 2: The difference between Comparative Example 2 and Example 1 is that a metal compound electrostatic regulator magnesium acetate is used, which comprises the following steps: 50 parts of terephthalic acid, 24 parts of ethylene glycol, 0.008 parts of magnesium acetate and 0.02 parts of catalyst (ethylene glycol antimony) are added to a 2.5L polymerization reactor, and an esterification reaction is carried out at 0.25MPa and 245°C for 120 minutes. After the esterification reaction is completed, 0.002 parts of stabilizer (triphenyl phosphate) are added and stirred for 10 minutes, and then a vacuum is drawn at 260-270°C for a preliminary polycondensation reaction for 50 minutes, and then a final polycondensation reaction is carried out at an absolute pressure of less than 40Pa and 275°C for 115 minutes. After the reaction is completed, the polyester for glossy film is extruded, pelletized and dried.

[0029] Comparative Example 3: The difference between Comparative Example 3 and Example 1 is that the amount of the polymerizable low eutectic solvent is too low, and the method comprises the following steps: (1) preparing a polymerizable low eutectic solvent: weighing 0.5 mol of acrylic acid (36 g) and 0.125 mol of choline chloride (17.5 g), mixing them at 80° C. to form a completely transparent and uniform low eutectic solvent, cooling the low eutectic solvent to room temperature, adding 3.9 g of N,N-methylenebisacrylamide and 1.4 g of potassium persulfate, and stirring until completely dissolved to obtain a polymerizable low eutectic solvent; (2) Preparation of special copolyester for high-speed stretch film: 50 parts of terephthalic acid, 24 parts of ethylene glycol, 2 parts of polymerizable low eutectic solvent and 0.02 parts of catalyst (ethylene glycol antimony) were added to a 2.5L polymerization reactor, and the esterification reaction was carried out at 0.25MPa and 245°C for 120 minutes. After the esterification reaction was completed, 0.002 parts of stabilizer (triphenyl phosphate) was added and stirred for 10 minutes, and then vacuumed at 260-270°C for 50 minutes for pre-condensation reaction, and then the final condensation reaction was carried out at an absolute pressure of less than 40Pa and 275°C for 115 minutes. After the reaction was completed, the copolyester for high-speed stretch film was extruded, pelletized and dried.

[0030] Comparative Example 4: The difference between Comparative Example 4 and Example 1 is that the amount of the polymerizable low eutectic solvent is too high, and the method comprises the following steps: (1) preparing a polymerizable low eutectic solvent: weighing 0.5 mol of acrylic acid (36 g) and 0.125 mol of choline chloride (17.5 g), mixing them at 80° C. to form a completely transparent and uniform low eutectic solvent, cooling the low eutectic solvent to room temperature, adding 3.9 g of N,N-methylenebisacrylamide and 1.4 g of potassium persulfate, and stirring until completely dissolved to obtain a polymerizable low eutectic solvent; (2) Preparation of special copolyester for high-speed stretch film: 50 parts of terephthalic acid, 24 parts of ethylene glycol, 25 parts of polymerizable low eutectic solvent and 0.02 parts of catalyst (ethylene glycol antimony) were added to a 2.5L polymerization reactor, and the esterification reaction was carried out at 0.25MPa and 245°C for 120 minutes. After the esterification reaction was completed, 0.002 parts of stabilizer (triphenyl phosphate) was added and stirred for 10 minutes, and then vacuumed at 260-270°C for pre-polycondensation for 50 minutes, and then the final polycondensation was carried out at an absolute pressure of less than 40Pa and 275°C for 115 minutes. After the reaction was completed, the copolyester for high-speed stretch film was extruded, pelletized and dried.

[0031] Test example: The properties of the copolyesters for high-speed stretch film prepared in Examples 1 to 8 and Comparative Examples 1 to 4 were tested; The test items include: intrinsic viscosity, chromaticity b value and melt resistivity.

[0032] The intrinsic viscosity is tested with reference to the capillary viscometer method disclosed in GBT14190-2008 Test Method for Fiber-Grade Polyester Chips (PET). The unit of intrinsic viscosity is dL / g, where the mass ratio of phenol to 1,2-dichlorobenzene is 50:50 or 60:40, and the result is accurate to three decimal places. The chromaticity b value is tested with reference to the drying method disclosed in GBT14190-2008 Test Method for Fiber-Grade Polyester Chips (PET); the melt resistivity is tested with reference to a test method for polymer melt resistivity disclosed in CN107907746B, using a melt resistivity tester, the test conditions are 275°C, the melt weight is 4.5g, and the smaller the melt resistivity, the better the antistatic effect; The test results are shown in Table 1.

[0033] Table 1 Test results Intrinsic viscosity (dL / g) Chromaticity b value Melt resistivity (S / m) Example 1 0.617 0.7 <![CDATA[2.1╳10 7 ]]> Example 2 0.612 0.5 <![CDATA[1.3╳10 7 ]]> Example 3 0.605 0.3 <![CDATA[8.6╳10 6 ]]> Example 4 0.597 0.4 <![CDATA[4.7╳10 6 ]]> Example 5 0.612 0.9 <![CDATA[9.5╳10 6 ]]> Example 6 0.610 0.7 <![CDATA[8.3╳10 6 ]]> Example 7 0.611 0.4 <![CDATA[1.2╳10 7 ]]> Example 8 0.614 0.7 <![CDATA[1.5╳10 7 ]]> Comparative Example 1 0.604 3.5 Over range Comparative Example 2 0.605 8.3 <![CDATA[4.8╳10 7 ]]> Comparative Example 3 0.618 1.5 <![CDATA[6.3╳10 7 ]]> Comparative Example 4 0.589 0.2 <![CDATA[3.2╳10 6 ]]> The copolyesters prepared in Examples 1 to 8 and Comparative Examples 1 to 2 were processed into BOPET films in the following steps: The steps are as follows: The polyester slices for the film were dried and melt-extruded to form a polyester thick sheet. After the thick sheet was left for one day, it was stretched in a biaxial stretching machine to prepare a BOPET film. Under the conditions of preheating temperature of 100°C and preheating time of 20s, the maximum tensile strain rate when the synchronous stretching ratio was 5.0╳5.0 was 235%; then the BOPET film was tested for performance, and the test items included: light transmittance, haze, tensile strength and elongation at break; The light transmittance is tested according to the method disclosed in GB / T 8807-1988 Test method for specular gloss of plastics, with an incident angle of 45°; the haze is tested according to the method disclosed in GB / T 2410-2008 Determination of light transmittance and haze of transparent plastics; The tensile strength and elongation at break were tested according to the methods published in GB / T 1040.1-2006 Determination of tensile properties of plastics Part 1: General Principles and GB / T 1040.3-2006 Test methods for tensile properties of plastics. Type 2 specimens were used, with a specimen width of 15 mm, an initial fixture spacing of 100 mm, a test speed of (100±10) mm / min, and the longitudinal and transverse directions were tested respectively; the number of specimens was 5 each, and the results were taken as the arithmetic mean. The test results are shown in Table 2.

[0034] Table 2 Test results of BOPET film Light transmittance (%) Haze(%) Tensile strength(MPa) Elongation at break (%) Example 1 92.5 2 120.4 220 Example 2 92.3 1.7 114.8 243 Example 3 92.2 1.4 105.6 261 Example 4 92.2 1.3 92.2 275 Example 5 92.3 1.8 116.5 232 Example 6 92.4 2.3 115.1 228 Example 7 92.3 1.8 111.3 234 Example 8 92.1 1.5 115.2 248 Comparative Example 1 90 5 150.7 100 Comparative Example 2 88 7 146.4 98 Comparative Example 3 91.4 2.8 131.8 150 Comparative Example 4 92.8 0.9 82.1 289 As shown in Table 1 and Table 2, the added amounts of the polymerizable low eutectic solvents of the copolyesters for high-speed stretching films and BOPET films prepared in Examples 1 to 4 are different. It is found that with the increase of the added amount, the conductivity of the copolyester for high-speed stretching films shows an increasing trend, the elongation at break of the BOPET film shows an increasing trend, and the tensile strength of the BOPET film shows a decreasing trend. In addition, the results of the excessive and insufficient amounts of the polymerizable low eutectic solvents in Comparative Examples 3 and 4 are tested, and the results show that when the amount of the polymerizable low eutectic solvent is too low, the solution resistivity cannot be significantly reduced, and when the amount is too high, the mechanical properties of the polyester film will be reduced.

[0035] Compared with Example 2, Examples 5 and 6 used polymerizable low eutectic solvents of the same content but different ratios. The results showed that the content of choline chloride would affect the melt resistivity of polyester chips. The higher the content of choline chloride, the lower the melt resistivity. Compared with Example 2, Examples 7 and 8 used terephthalic acid and ethylene glycol in different ratios. The results showed that the ratio of terephthalic acid to ethylene glycol had no significant effect on the properties of polyester.

[0036] Comparative Example 1 is a PET polyester without using a polymerizable low eutectic solvent. The results of Comparative Example 1 and the example show that the melt resistivity of the example is significantly lower than that of Comparative Example 1, and the elongation at break of the example is significantly higher than that of Comparative Example 1. The melt resistivity of the copolyester prepared in the example is significantly reduced and the toughness is significantly improved.

[0037] Comparative Example 2 is a copolyester made using magnesium acetate, a metal compound electrostatic regulator. The results of Comparative Example 2, Example 1 and Comparative Example 1 show that the use of metal compounds such as magnesium acetate can reduce the resistivity of the polyester solution, but the chromaticity b value of the polyester deteriorates significantly, and the color of the polyester turns yellow, requiring additional addition of a colorant for adjustment before it can meet the use requirements.

[0038] In summary, the introduction of a polymerizable low eutectic solvent can effectively reduce melt resistivity, improve hue, increase film transmittance, reduce haze and increase elongation at break, thereby preparing a high-speed stretching-specific copolyester with excellent performance and processing speed.

[0039] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent transformation made to the above embodiment based on the technical essence of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A copolyester for high-speed stretch film, characterized in that: The raw materials include, by mass ratio, 50-60 parts of terephthalic acid, 20-30 parts of ethylene glycol, 5-20 parts of a polymerizable low eutectic solvent, 0.02-0.03 parts of a catalyst, and 0.002-0.003 parts of a stabilizer.

2. The high-speed stretch film-specific copolyester according to claim 1, characterized in that: The polymerizable low eutectic solvent is prepared by polymerization reaction of a polymerizable monomer, a hydrogen bond acceptor, a cross-linking agent and an initiator, and the polymerization temperature is 60-70°C.

3. The high-speed stretch film-specific copolyester according to claim 2, characterized in that: The molar ratio of the polymerizable monomer to the hydrogen bond acceptor is 1:10-20, the molar ratio of the crosslinking agent to the polymerizable monomer is 1:10-20, and the molar ratio of the initiator to the polymerizable monomer is 1:20-100.

4. The special copolyester for high-speed stretch film according to claim 2 or 3, characterized in that: The polymerizable monomer includes one or more of acrylamide, N-isopropylacrylamide, N,N-dimethylacrylamide, acrylic acid, methacrylic acid and hydroxyethyl methacrylate; the hydrogen bond acceptor includes one of a quaternary ammonium salt and betaine; the crosslinking agent includes one of N,N-methylenebisacrylamide and ethylene glycol dimethacrylate; and the initiator includes potassium persulfate and dibenzoyl peroxide.

5. The copolyester for high-speed stretch film according to claim 2, characterized in that: The catalyst comprises one or more of antimony trioxide, antimony acetate, antimony glycolate and titanium glycolate.

6. The copolyester for high-speed stretch film according to claim 1, characterized in that: The stabilizer includes one or more of trimethyl phosphate, dimethyl phosphate, triphenyl phosphate and diphenyl phosphate.

7. A method for preparing the copolyester for high-speed stretching film according to any one of claims 1 to 6, characterized in that: The following steps are involved: Terephthalic acid, ethylene glycol, a polymerizable low eutectic solvent and a catalyst are injected into a container for esterification reaction. After the esterification reaction is completed, a stabilizer is added to carry out polycondensation reaction to prepare a copolyester specially used for high-speed stretch film.

8. The method according to claim 7, characterized in that: The conditions of the esterification reaction include: temperature 240-260° C., pressure 0.2-0.4 MPa.

9. The method according to claim 7, characterized in that: The polycondensation reaction includes: temperature of 250-285°C, vacuum degree of 40-100 Pa, and reaction time of 1.5-2.5 h.

10. The method according to claim 7, characterized in that: The conditions of the polycondensation reaction also include: first evacuating to 90-100 Pa and heating to 250-265°C for a reaction time of 30-50 min, then evacuating to below 40 Pa and heating to 275-285°C for a reaction time of 60-120 min.