A polyester heat shrinkable film with low melt resistivity and its production process

Abstract

The present invention provides a polyester heat shrinkable film with low melt resistivity and a production process thereof, and relates to the technical field of polymer packaging materials. A polyester heat shrinkable film with low melt resistivity, wherein the raw materials for preparing the film include, in parts by weight, 70 to 108 parts of modified low-resistivity polyester, 20 to 36 parts of low-density polyethylene, 6 to 11 parts of 1,4-butanediol, 2 to 7 parts of a viscosity reducer, and 3 to 6 parts of diisononyl cyclohexane-1,2-dicarboxylate; the raw materials for preparing the modified low-resistivity polyester include polyethylene terephthalate, a polyester modifier, diethyltoluenediamine, and pentaerythritol phosphate; the raw materials for preparing the polyester modifier include terephthalic acid, 1,6-hexanediol, calcium stearate, and diethylene glycol. The polyester heat shrinkable film with low melt resistivity provided by the present invention has good mechanical properties, and the resistivity of the polyester melt is as low as 0.65 to 0.88×10 6 Ω·m, which can provide continuous production of chill rolls at a line speed of 90~140m / min.

Description

Technical Field

[0001] The invention relates to the technical field of polymer packaging materials, in particular to a polyester heat shrinkable film with low melt resistivity and a production process thereof. Background Art

[0002] Heat-shrinkable polyester film (abbreviated as heat shrink film) is a new type of heat-shrinkable packaging material, and market demand has been growing rapidly in recent years. Due to its high shrinkage, excellent transparency, non-toxicity, odorlessness, good mechanical properties, excellent printing properties, low autogenous shrinkage, relatively long shelf life, and environmentally friendly characteristics, PET heat-shrink film has successfully replaced polyvinyl chloride (PVC) heat-shrinkable film as the most ideal shrink packaging material.

[0003] However, to achieve a high transverse shrinkage ratio for heat shrink film, production typically employs uniaxial stretching or a very low longitudinal stretching ratio to maintain a high transverse stretch ratio. This results in the production speed of heat shrink film being limited by the linear speed of the chill roller. Currently, increasing the linear speed of the chill roller used in heat shrink film production significantly degrades the electrostatic adsorption effect of the cast sheet, leading to the appearance of electrostatic adsorption bubbles or lines on the film surface, and even discharge and film breakage, impacting production stability. Therefore, high production speeds cannot be achieved, typically between 40 and 80 m / min. Simply increasing the electrostatic adsorption voltage or adjusting the location of the electrostatic adsorption can lead to product breakdown and other problems, presenting certain risks and limitations.

[0004] In general, the heat shrinkable film produced by the existing technology has the problem of poor electrostatic adsorption effect of the casting sheet, which leads to limited production speed and product surface defects. Summary of the Invention

[0005] In order to solve the above-mentioned problems existing in the prior art, the present invention provides a polyester heat shrinkable film with low melt resistivity and a production process thereof, and achieves the following invention objectives: reducing the resistivity of the polyester melt of the heat shrinkable film to increase the linear speed of the quenching roller, avoiding electrostatic adsorption bubbles or electrostatic adsorption lines during the stretching process, and achieving high-speed continuous production while maintaining film performance.

[0006] To achieve the above objectives, the technical solutions adopted are as follows:

[0007] The invention provides a polyester heat shrinkable film with low melt resistivity. The raw materials for preparing the film include, by weight, 70 to 108 parts of modified low-resistivity polyester, 20 to 36 parts of low-density polyethylene, 6 to 11 parts of 1,4-butanediol, 2 to 7 parts of a viscosity reducer, and 3 to 6 parts of diisononyl cyclohexane-1,2-dicarboxylate.

[0008] The low-density polyethylene used in the present invention has a density of 0.91-0.925 g / cm³.

[0009] The viscosity reducer used in the present invention is any one of dearomatized D60, D80 and D110.

[0010] The modified low-resistivity polyester comprises raw materials, in parts by weight, including 53-77 parts of polyethylene terephthalate, 26-35 parts of a polyester modifier, 4-9 parts of diethyltoluenediamine, and 3-7 parts of pentaerythritol phosphate.

[0011] The polyester modifier comprises raw materials, in parts by weight, comprising 48 to 61 parts of terephthalic acid, 45 to 59 parts of 1,6-hexanediol, 2 to 3.8 parts of calcium stearate, and 4 to 7 parts of diethylene glycol.

[0012] The present invention also provides a production process for a polyester heat shrinkable film with low melt resistivity, comprising the following steps:

[0013] 1. Preparation of polyester modifier

[0014] (1) Terephthalic acid, 1,6-hexanediol, and calcium stearate were added to the reactor and the temperature was increased gradually, first at 140°C for 1-2 hours, then at 180°C for 2-4 hours, and finally at 220°C for 4-5 hours; nitrogen was continuously introduced for protection during the reaction.

[0015] (2) Add catalyst and diethylene glycol, reduce the pressure to a vacuum degree of <-0.097 MPa, raise the temperature to 230-240°C, and react for 2-4 hours to obtain a modifier melt. Extrude and pelletize the melt to obtain a polyester modifier.

[0016] The catalyst is zirconium acetylacetonate, and the addition amount is 0.05~0.3% of the mass of terephthalic acid.

[0017] 2. Preparation of modified low resistivity polyester

[0018] Polyethylene terephthalate, polyester modifier, diethyltoluenediamine, and pentaerythritol phosphate were mixed and added to an internal mixer. The mixture was mixed for 35-45 minutes at a temperature of 230-250°C to obtain a modified low-resistivity polyester melt. The modified low-resistivity polyester melt was pelletized to obtain a modified low-resistivity polyester for later use.

[0019] 3. Cast sheet extrusion

[0020] The modified low-resistivity polyester, low-density polyethylene, 1,4-butanediol, viscosity reducer, and cyclohexane-1,2-dicarboxylic acid diisononyl ester are mixed according to the raw material ratio and added into a twin-screw extruder, heated and melted to form a melt, and the melt enters the die head through a filter and a metering pump, extruded into a cast sheet, cooled and then stretched.

[0021] The heating melt temperature of the twin-screw extruder is 235~255℃, and the die head temperature is 245~260℃.

[0022] Multi-layer co-extrusion equipment can also be used to extrude double-layer or three-layer cast sheets. Any color masterbatch can be added to different cast sheet layers to prepare heat shrinkable films of different colors; functional materials such as light-blocking agents, ultraviolet absorbers, and opening agents can also be added to multi-layer cast sheets.

[0023] 4. Stretch and shape

[0024] The cooled cast film is introduced into the stretching equipment and preheated. The high-voltage electrostatic generator voltage is adjusted to 8-10kV, and the chill roll speed is adjusted to 90-140m / min. The film is stretched in the main shrinkage direction at a ratio of 1.5-6.0 times. The stretched film is then cold-set, corona-treated, and then pulled and reeled to obtain the semi-finished heat shrink film. Preheat temperature: 110-140°C; chill roll temperature: 25°C.

[0025] The beneficial effects of the present invention are as follows:

[0026] The polyester heat shrinkable film with low melt resistivity provided by the present invention has a polyester melt resistivity as low as 0.65~0.88×10 6 Ω·m, which can be used for continuous production at a line speed of 90-140 m / min for the chill roller; the polyester heat shrinkable film with low melt resistivity provided by the present invention has a shrinkage rate of up to 80% or more in the main shrinkage direction and a tensile strength of 128-140 MPa, which not only retains the mechanical properties of heat shrinkable films produced by conventional production methods but also enables high-speed continuous production. DETAILED DESCRIPTION

[0027] To make the purpose, technical solutions and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0028] Example 1 A polyester heat shrinkable film with low melt resistivity

[0029] A polyester heat shrinkable film with low melt resistivity is prepared from the following raw materials in parts by weight: 100 parts of modified low-resistivity polyester, 32 parts of low-density polyethylene, 6 parts of 1,4-butanediol, 2 parts of a viscosity reducer, and 5 parts of diisononyl cyclohexane-1,2-dicarboxylate.

[0030] In this embodiment, dearomatized D60 is used as the viscosity reducer.

[0031] The modified low-resistivity polyester is prepared from raw materials including, by weight, 53 parts of polyethylene terephthalate, 29 parts of a polyester modifier, 6 parts of diethyltoluenediamine, and 5 parts of pentaerythritol phosphate;

[0032] The polyester modifier is prepared by using raw materials including, by weight, 48 parts of terephthalic acid, 50 parts of 1,6-hexanediol, 2.3 parts of calcium stearate, and 7 parts of diethylene glycol.

[0033] A production process for polyester heat shrinkable film with low melt resistivity:

[0034] Step 1: Preparation of polyester modifier

[0035] (1) Terephthalic acid, 1,6-hexanediol, and calcium stearate were added to the reactor and subjected to a gradient temperature reaction: first, the reaction was carried out at 140°C for 1 h, then at 180°C for 2 h, and finally at 220°C for 5 h; nitrogen was continuously introduced during the reaction.

[0036] (2) Add diethylene glycol and a catalyst, control the vacuum degree to <-0.097 MPa, raise the temperature to 240°C, react for 2 hours, and obtain a modifier melt; extrude and pelletize the melt to obtain a polyester modifier.

[0037] The catalyst is zirconium acetylacetonate, and the added amount is 0.2% of the mass of terephthalic acid.

[0038] Step 2: Preparation of modified low resistivity polyester

[0039] Polyethylene terephthalate, polyester modifier, diethyltoluenediamine and pentaerythritol phosphate were mixed and added into an internal mixer, and mixed for 35 minutes at a mixing temperature of 240° C. to obtain a modified low-resistivity polyester melt; the modified low-resistivity polyester melt was granulated to obtain a modified low-resistivity polyester for later use.

[0040] Step 3: Casting sheet extrusion

[0041] The modified low-resistivity polyester, low-density polyethylene, 1,4-butanediol, viscosity reducer, and cyclohexane-1,2-dicarboxylic acid diisononyl ester are mixed according to the raw material ratio and added into a twin-screw extruder, heated and melted to form a casting melt, and the casting melt enters the die head through a filter and a metering pump, and the casting sheet is extruded and cooled for stretching.

[0042] The twin-screw extruder was heated to a melt temperature of 245°C and a die head temperature of 255°C.

[0043] Step 4: Stretch and shape

[0044] The cooled cast film is introduced into the stretching equipment and preheated. The high-voltage electrostatic generator voltage is adjusted to 8kV, and the chill roller linear speed is adjusted to 115m / min. The film is stretched at a ratio of 3.5 times in the main shrinkage direction. The stretched film is then cold-set, corona-treated, and then pulled and reeled to obtain the semi-finished heat shrink film. The preheating temperature is controlled at 130°C; the chill roller temperature is controlled at 25°C.

[0045] Example 2 A polyester heat shrinkable film with low melt resistivity

[0046] A polyester heat shrinkable film with low melt resistivity is prepared from the following raw materials in parts by weight: 108 parts of modified low-resistivity polyester, 20 parts of low-density polyethylene, 8 parts of 1,4-butanediol, 2 parts of a viscosity reducer, and 5 parts of diisononyl cyclohexane-1,2-dicarboxylate.

[0047] In this embodiment, dearomatized D80 is used as the viscosity reducer.

[0048] The modified low-resistivity polyester is prepared from raw materials including, by weight, 55 parts of polyethylene terephthalate, 26 parts of a polyester modifier, 9 parts of diethyltoluenediamine, and 7 parts of pentaerythritol phosphate;

[0049] The polyester modifier is prepared by using raw materials including, by weight, 50 parts of terephthalic acid, 45 parts of 1,6-hexanediol, 2 parts of calcium stearate, and 4 parts of diethylene glycol.

[0050] A production process for polyester heat shrinkable film with low melt resistivity:

[0051] Step 1: Preparation of polyester modifier

[0052] (1) Terephthalic acid, 1,6-hexanediol, and calcium stearate were added to the reactor and subjected to a gradient temperature reaction: first, react at 140°C for 2 h, then at 180°C for 4 h, and finally at 220°C for 4 h; nitrogen was continuously introduced during the reaction.

[0053] (2) Add diethylene glycol and a catalyst, control the vacuum degree to <-0.097 MPa, raise the temperature to 230°C, react for 4 hours, and obtain a modifier melt; extrude and pelletize the melt to obtain a polyester modifier.

[0054] The catalyst is zirconium acetylacetonate, and the added amount is 0.1% of the mass of terephthalic acid.

[0055] Step 2: Preparation of modified low resistivity polyester

[0056] Polyethylene terephthalate, polyester modifier, diethyltoluenediamine and pentaerythritol phosphate were mixed and added into an internal mixer, and mixed for 45 minutes at a mixing temperature of 230° C. to obtain a modified low-resistivity polyester melt; the modified low-resistivity polyester melt was granulated to obtain a modified low-resistivity polyester for later use.

[0057] Step 3: Casting sheet extrusion

[0058] Modified low-resistivity polyester, low-density polyethylene, 1,4-butanediol, viscosity reducer, and diisononyl cyclohexane-1,2-dicarboxylate were mixed according to the raw material ratio and added to a twin-screw extruder. The mixture was heated and melted to form a casting melt. The casting melt passed through a filter and a metering pump into the die head, where the casting melt was extruded and cooled for stretching. The twin-screw extruder had a heating and melting temperature of 235°C and a die head temperature of 260°C.

[0059] Step 4: Stretch and shape

[0060] The cooled cast film is introduced into the stretching equipment and preheated. The high-voltage electrostatic generator voltage is adjusted to 8kV, and the chill roller linear speed is adjusted to 125m / min. The film is stretched at a ratio of 4.4 times in the main shrinkage direction. The stretched film is then cold-set, corona-treated, and then pulled and reeled to obtain the semi-finished heat shrink film. The preheating temperature is controlled at 110°C; the chill roller temperature is controlled at 25°C.

[0061] Example 3 A polyester heat shrinkable film with low melt resistivity

[0062] A polyester heat shrinkable film with low melt resistivity is prepared from the following raw materials in parts by weight: 100 parts of modified low-resistivity polyester, 20 parts of low-density polyethylene, 11 parts of 1,4-butanediol, 7 parts of a viscosity reducer, and 3 parts of diisononyl cyclohexane-1,2-dicarboxylate.

[0063] In this embodiment, dearomatized D80 is used as the viscosity reducer.

[0064] The modified low-resistivity polyester is prepared from raw materials including, by weight, 77 parts of polyethylene terephthalate, 35 parts of a polyester modifier, 6 parts of diethyltoluenediamine, and 4 parts of pentaerythritol phosphate;

[0065] The polyester modifier is prepared by using raw materials including, by weight, 55 parts of terephthalic acid, 59 parts of 1,6-hexanediol, 3.5 parts of calcium stearate, and 7 parts of diethylene glycol.

[0066] A production process for polyester heat shrinkable film with low melt resistivity:

[0067] Step 1: Preparation of polyester modifier

[0068] (1) Terephthalic acid, 1,6-hexanediol, and calcium stearate were added to the reactor and subjected to a gradient temperature reaction: first, react at 140°C for 2 h, then at 180°C for 4 h, and finally at 220°C for 4 h; nitrogen was continuously introduced during the reaction.

[0069] (2) Add diethylene glycol and a catalyst, control the vacuum degree to <-0.097 MPa, raise the temperature to 230°C, react for 3 hours, and obtain a modifier melt; extrude and pelletize the melt to obtain a polyester modifier.

[0070] The catalyst is zirconium acetylacetonate, and the added amount is 0.05% of the mass of terephthalic acid.

[0071] Step 2: Preparation of modified low resistivity polyester

[0072] Polyethylene terephthalate, polyester modifier, diethyltoluenediamine and pentaerythritol phosphate were mixed and added into an internal mixer, and mixed for 40 minutes at a mixing temperature of 250° C. to obtain a modified low-resistivity polyester melt; the modified low-resistivity polyester melt was granulated to obtain a modified low-resistivity polyester for later use.

[0073] Step 3: Casting sheet extrusion

[0074] The modified low-resistivity polyester, low-density polyethylene, 1,4-butanediol, viscosity reducer, and cyclohexane-1,2-dicarboxylic acid diisononyl ester are mixed according to the raw material ratio and added into a twin-screw extruder, heated and melted to form a casting melt, and the casting melt enters the die head through a filter and a metering pump, and the casting sheet is extruded and cooled for stretching.

[0075] The twin-screw extruder was heated to a melt temperature of 255°C and a die head temperature of 250°C.

[0076] Step 4: Stretch and shape

[0077] The cooled cast film is introduced into the stretching equipment and preheated. The high-voltage electrostatic generator voltage is adjusted to 10kV, and the chill roller linear speed is adjusted to 90m / min. The film is stretched in the main shrinkage direction at a ratio of 1.5 times. The stretched film is then cold-set, corona-treated, and then pulled and reeled to obtain the semi-finished heat shrink film. The preheating temperature is controlled at 120°C; the chill roller temperature is controlled at 25°C.

[0078] Example 4 A polyester heat shrinkable film with low melt resistivity

[0079] A polyester heat shrinkable film with low melt resistivity is prepared from the following raw materials in parts by weight: 70 parts of modified low-resistivity polyester, 36 parts of low-density polyethylene, 10 parts of 1,4-butanediol, 3 parts of a viscosity reducer, and 6 parts of diisononyl cyclohexane-1,2-dicarboxylate.

[0080] In this embodiment, dearomatized D110 is used as the viscosity reducer.

[0081] The modified low-resistivity polyester is prepared from raw materials including, by weight, 68 parts of polyethylene terephthalate, 35 parts of a polyester modifier, 4 parts of diethyltoluenediamine, and 3 parts of pentaerythritol phosphate;

[0082] The polyester modifier is prepared by using raw materials including, by weight, 61 parts of terephthalic acid, 55 parts of 1,6-hexanediol, 3.8 parts of calcium stearate, and 7 parts of diethylene glycol.

[0083] A production process for polyester heat shrinkable film with low melt resistivity:

[0084] Step 1: Preparation of polyester modifier

[0085] (1) Terephthalic acid, 1,6-hexanediol, and calcium stearate were added to the reactor and subjected to a gradient temperature reaction: first, react at 140°C for 2 h, then at 180°C for 4 h, and finally at 220°C for 4 h; nitrogen was continuously introduced during the reaction.

[0086] (2) Add diethylene glycol and a catalyst, control the vacuum degree to <-0.097 MPa, raise the temperature to 230°C, react for 3 hours, and obtain a modifier melt; extrude and pelletize the melt to obtain a polyester modifier.

[0087] The catalyst is zirconium acetylacetonate, and the added amount is 0.3% of the mass of terephthalic acid.

[0088] Step 2: Preparation of modified low resistivity polyester

[0089] Polyethylene terephthalate, polyester modifier, diethyltoluenediamine and pentaerythritol phosphate were mixed and added into an internal mixer, and mixed for 40 minutes at a mixing temperature of 240° C. to obtain a modified low-resistivity polyester melt; the modified low-resistivity polyester melt was granulated to obtain a modified low-resistivity polyester for later use.

[0090] Step 3: Casting sheet extrusion

[0091] The modified low-resistivity polyester, low-density polyethylene, 1,4-butanediol, viscosity reducer, and cyclohexane-1,2-dicarboxylic acid diisononyl ester are mixed according to the raw material ratio and added into a twin-screw extruder, heated and melted to form a casting melt, and the casting melt enters the die head through a filter and a metering pump, and the casting sheet is extruded and cooled for stretching.

[0092] The twin-screw extruder was heated to a melt temperature of 240°C and a die head temperature of 245°C.

[0093] Step 4: Stretch and shape

[0094] The cooled cast film is introduced into the stretching equipment and preheated. The high-voltage electrostatic generator voltage is adjusted to 10kV, and the chill roller linear speed is adjusted to 140m / min. The film is stretched at a ratio of 6.0 in the main shrinkage direction. The stretched film is then cold-set, corona-treated, and then pulled and reeled to obtain the semi-finished heat shrink film. The preheating temperature is controlled at 140°C; the chill roller temperature is controlled at 25°C.

[0095] Performance Testing

[0096] (1) Resistivity test

[0097] The modified low-resistivity polyester melt obtained in step 2 of Examples 1-4 was heated to 270°C. Using a high-insulation resistance meter, a high voltage was applied to the high-voltage electrode with a fixed measurement area and distance between the high-voltage electrode and the measuring electrode, generating a melt resistance. The melt resistivity at that temperature was calculated as: ρ = R × s / L. Excess current was conducted to the ground via the grounding electrode and did not affect the test results. The test results are shown in Table 1.

[0098] Table 1 Resistivity test results

[0099] Test subjects Example 1 Example 2 Example 3 Example 4 Resistivity (Ω·m) <![CDATA[0.67×10 6 ]]> <![CDATA[0.65×10 6 ]]> <![CDATA[0.73×10 6 ]]> <![CDATA[0.88×10 6 ]]>

[0100] (2) Heat shrink film performance test

[0101] The mechanical properties of the semi-finished heat shrinkable films obtained in Examples 1 to 4 were tested using the following method. The test results are shown in Table 2.

[0102] Tensile strength: Prepare specimens and conduct tests according to the test method provided in "Determination of tensile properties of plastics Part 3: Test conditions for film and sheeting" (GB / T1040.3-2006).

[0103] Shrinkage rate: Place the heat shrinkable film in a 90℃ water bath for 10 seconds. Calculate the shrinkage rate according to the method provided in "Test Method for Shrinkage Performance of Heat Shrinkable Films" (GB / T 34848-2017): Shrinkage rate R = (L0-L) / L0×100%; R: shrinkage rate (%); L0: initial length of the sample (mm); L: length of the sample after shrinkage (mm).

[0104] Table 2 Mechanical properties test results

[0105] Test subjects Example 1 Example 2 Example 3 Example 4 Film thickness (µm) 45±1 45±1 45±1 45±1 Tensile strength (MPa) 140 133 136 128 Shrinkage in the main shrinkage direction (%) 58.4 65.6 23.7 80.2

[0106] It can be seen from the data in Table 1 that the low melt resistivity polyester heat shrinkable film provided by the present invention has a resistivity of the modified low resistivity polyester melt as low as 0.65~0.88×10 6 Ω·m, which can be used for continuous production of the chill roller at a line speed of 90~140m / min; the data in Table 2 show that the polyester heat shrinkable film with low melt resistivity provided by the present invention has a wide shrinkage range, with the shrinkage in the main shrinkage direction being greater than 20% and up to more than 80%, and the tensile strength is between 128~140MPa.

[0107] In summary, the polyester heat shrinkable film with low melt resistivity provided by the present invention not only retains the mechanical properties of conventionally produced heat shrinkable films, but also achieves high-speed continuous production by reducing the resistivity of the polyester melt.

[0108] 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 scope of protection of the present invention.

Claims

1. A polyester heat shrinkable film with low melt resistivity, characterized in that: The heat shrinkable film is prepared from the following raw materials, calculated by weight: 70-108 parts of modified low-resistivity polyester, 20-36 parts of low-density polyethylene, 6-11 parts of 1,4-butanediol, 2-7 parts of viscosity reducer, and 3-6 parts of diisononyl cyclohexane-1,2-dicarboxylate; The modified low-resistivity polyester is prepared from raw materials including polyethylene terephthalate, a polyester modifier, diethyltoluenediamine, and pentaerythritol phosphate, wherein the mass ratio of the polyethylene terephthalate, the polyester modifier, the diethyltoluenediamine, and the pentaerythritol phosphate is (53-77): (26-35): (4-9): (3-7); The polyester modifier: the raw materials for preparation include terephthalic acid, 1,6-hexanediol, calcium stearate, diethylene glycol, The mass ratio of terephthalic acid, 1,6-hexanediol, calcium stearate, and diethylene glycol is (48-61): (45-59): (2-3.8): (4-7); The viscosity reducer is any one of dearomatized D60, D80 and D110.

2. The process for producing a polyester heat shrinkable film with low melt resistivity according to claim 1, wherein: The invention comprises the steps of preparing a polyester modifier, preparing a modified low-resistivity polyester, extruding a cast sheet, and stretching and shaping. The stretching and shaping comprises introducing the cast sheet into a stretching device, stretching the cast sheet at a ratio of 1.5 to 6.0 by adjusting the linear speed of a quenching roller, and cold-setting the stretched cast sheet to obtain a heat shrinkable film.

3. The process for producing a polyester heat shrinkable film with low melt resistivity according to claim 2, wherein: The linear speed of the cooling roller is 90-140 m / min.

4. The process for producing a polyester heat shrinkable film with low melt resistivity according to claim 2, wherein: The polyester modifier is prepared by adding terephthalic acid, 1,6-hexanediol, and calcium stearate into a reactor for gradient temperature reaction, then adding a catalyst and diethylene glycol, and reacting at 230-240° C. for 2-4 hours to obtain the polyester modifier.

5. The process for producing a polyester heat shrinkable film with low melt resistivity according to claim 2, wherein: The modified low-resistivity polyester is prepared by mixing polyethylene terephthalate, a polyester modifier, diethyltoluenediamine, and pentaerythritol phosphate, and kneading the mixture at 230-250° C. for 35-45 minutes to obtain the modified low-resistivity polyester.

6. The process for producing a polyester heat shrinkable film with low melt resistivity according to claim 4, wherein: The gradient temperature reaction is first carried out at 140° C. for 1 to 2 hours, then at 180° C. for 2 to 4 hours, and finally at 220° C. for 4 to 5 hours. The catalyst is zirconium acetylacetonate, and the addition amount is 0.05 to 0.3% of the mass of terephthalic acid.

7. The process for producing a polyester heat shrinkable film with low melt resistivity according to claim 2, wherein: The casting sheet extrusion comprises adding modified low resistivity polyester, low density polyethylene, 1,4-butanediol, viscosity reducer and diisononyl cyclohexane 1,2-dicarboxylate into a twin-screw extruder, heating and melting to form a melt, and extruding the melt through a die to obtain a casting sheet.

8. The process for producing a polyester heat shrinkable film with low melt resistivity according to claim 7, wherein: The twin-screw extruder has a heating melt temperature of 235-255°C and a die head temperature of 245-260°C.