A microporous adjustable low-density PETG heat shrinkable film and preparation method thereof

Abstract

The present invention discloses a microporous adjustable low-density PETG heat shrinkable film, comprising a core layer and upper and lower surface layers, characterized in that the upper and lower surface layers mainly comprise 100 parts by mass of modified polyethylene terephthalate (PETG) polyester chips and 1 to 3 parts of an opening agent, and the core layer mainly comprises 100 parts by mass of PETG polyester chips, 0 to 30 parts of white masterbatch, 10 parts of PET polyester chips and 2 to 5 parts of a foaming agent; the present invention also discloses a method for preparing the above heat shrinkable film, wherein the raw materials are mixed, extruded, melt-plasticized, die-casted, biaxially stretched, cooled and shaped, light-cured, pulled, trimmed, and rolled to obtain the composite film. The method of the present invention can control the density of the finally prepared PETG heat shrinkable film to 0.9 to 1.3 g / cm due to its ability to adjust the pore structure in a gradient manner. 3 .

Description

Technical Field

[0001] The invention belongs to the technical field of polymer new material processing, and particularly relates to a microporous adjustable low-density PETG heat shrinkable film and a preparation method thereof. Background Art

[0002] At present, the materials of heat shrinkable film are mainly divided into polystyrene (OPS), polyvinyl chloride (PVC), modified polyethylene terephthalate glycol (PETG) and polyethylene (PE), etc. Among them, PETG heat shrinkable film is widely used in the label field because of its advantages such as high heat shrinkage rate, excellent strength performance, good stiffness, good environmental performance and suitable for printing.

[0003] Due to the limitation of raw materials, the density of PETG heat shrink film is as high as 1.32g / cm 3 . In order to solve the problem of high density of PETG heat shrink film, the industry often adopts physical foaming, chemical foaming and heterogeneous material stretching and pore making methods to prepare PETG heat shrink film with pore structure; however, the existing foaming methods have certain shortcomings. First, the pore structure in the processed product is often evenly distributed; second, the saturation or foaming process needs to be precisely controlled. In view of this, there is an urgent need for a convenient and fast processing method to obtain ultra-thin and low-density PETG heat shrink film with a differentiated pore structure. Summary of the invention

[0004] In view of the defects and shortcomings of the prior art, the present invention provides a microporous adjustable low-density PETG heat shrinkable film and a preparation method thereof. The present invention controls the foaming process by pressurizing the opening of the melting pipe of the main extruder and adjusting the pressure and temperature gradient changes to make the pores grow in a gradient manner, thereby solving the problem that the existing chemical foaming technology cannot effectively prepare a film with a differentiated pore structure.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: a microporous adjustable low-density PETG heat shrinkable film, comprising a core layer and upper and lower surface layers, the upper and lower surface layers mainly comprising 100 parts by mass of modified polyethylene terephthalate PETG polyester chips and 1 to 3 parts of an opening agent, and the core layer mainly comprising 100 parts by mass of PETG polyester chips, 0 to 30 parts of white masterbatch, 10 parts of PET polyester chips and 2 to 5 parts of a foaming agent.

[0006] Preferably, the opening agent is nano-silicon dioxide or erucamide.

[0007] Preferably, the foaming agent is sodium bicarbonate with PETG as a carrier, potassium bicarbonate with PETG as a carrier, sodium bicarbonate with PET as a carrier, or potassium bicarbonate with PET as a carrier.

[0008] Preferably, the white masterbatch is titanium dioxide with PETG as a carrier or titanium dioxide with PET as a carrier.

[0009] Furthermore, the mass ratio of the upper surface layer, the core layer and the lower surface layer is 1:1 to 10:1.

[0010] Furthermore, the thickness of the microporous adjustable low-density PETG heat shrinkable film is 30 to 100 μm.

[0011] A method for preparing the above-mentioned microporous adjustable low-density PETG heat shrinkable film comprises the following steps:

[0012] Step (1), putting 100 parts by mass of modified polyethylene terephthalate (PETG) polyester chips and 1 to 3 parts of an opening agent as raw materials for the upper and lower surface layers into a high-speed mixing device for mixing at room temperature, the mixing speed being 300 to 600 rpm, and the mixing time being 3 to 10 minutes; putting 100 parts by mass of PETG polyester chips, 0 to 30 parts of white masterbatch, 10 parts of PET polyester chips and 2 to 5 parts of a foaming agent as raw materials for the core layer into a high-speed mixing device for mixing at room temperature, the mixing speed being 300 to 600 rpm, and the mixing time being 3 to 10 minutes;

[0013] Step (2), the ingredients of each layer are respectively put into a twin-screw vacuum extruder for melt plasticization according to the mixing of the core layer and the surface layer. The temperature of the twin-screw vacuum extruder is 250-280° C. The homogenizing section of the main extruder is pressurized (the width of the pressurized homogenizing section is 5 cm, the material flow time is 30 s, and the pressure along the material flow direction is gradiently changed by controlling the flow rate of the pressurized gas introduced), and the melt pipe is subjected to gradient temperature control (the temperature variable pipe section is 20 cm long, and the material flow time is 100 s, The pipeline is equipped with a heat exchange device to control the temperature to change in a gradient. After the melt is filtered out of impurities by a fine filter, the mass ratio of the upper surface layer, the core layer, and the lower surface layer is adjusted to 1:1 to 10:1 by the extruder speed device. The melt is collected into a three-layer melt structure of the upper surface layer, the core layer, and the lower surface layer through a distributor and melt-extruded from a three-layer composite die head (the die head temperature is 250°C to 270°C). The extruded melt is cast and cooled at 20 to 50°C on a quenching roller to form a casting sheet. During the quenching process, the linear speed of the quenching roller is controlled to be 70 to 90 m / min.

[0014] Step (3), biaxially stretching the cast sheet, wherein the longitudinal stretching conditions are: preheating at 80°C to 100°C, stretching the sheet to a ratio of 1.0 to 1.2 at 80°C to 100°C, and cooling and shaping the sheet at 70°C to 90°C after longitudinal stretching; and transverse stretching after longitudinal stretching, wherein the transverse stretching conditions are: preheating at 80°C to 120°C, stretching the sheet to a ratio of 4.0 to 6.0 at 80°C to 120°C, and cooling and shaping the sheet at 60°C to obtain a PETG heat shrinkable film;

[0015] Step (4), pulling, trimming, winding, packaging, and finished product.

[0016] Preferably, the pressurized gas used in the pressurized treatment process in step (2) is nitrogen, argon or carbon dioxide.

[0017] Furthermore, the pressure applied during the pressurization treatment in step (2) is 1 to 19 MPa, and the pressure change along the material flow direction is 0.6 to 1.2 MPa / s, which changes cyclically.

[0018] Furthermore, in step (2), the temperature of the melt pipe is controlled to be 260-270° C., and the temperature change along the material flow direction is 0.1-0.2° C. / s, which changes cyclically.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] (1) The present invention provides a method for preparing a microporous adjustable low-density PETG heat shrinkable film, which completes the foaming post-processing process by performing gradient pressure regulation control on the opening of the melt pipe of the main extruder and gradient temperature control on the melt pipe. The entire processing process is easy to operate and the process is relatively simple.

[0021] (2) The microporous adjustable low-density PETG heat shrinkable film prepared by the method of the present invention has a better differentiated pore structure.

[0022] (3) The method for preparing a microporous low-density PETG heat shrinkable film provided by the present invention can control the density of the finally prepared PETG heat shrinkable film to 0.9-1.3 g / cm due to the ability to adjust the pore structure by gradient. 3 .

[0023] (4) The method of the present invention can prepare a microporous adjustable low-density PETG heat shrinkable film without adding low shrinkage force raw materials, which can effectively reduce the shrinkage force and increase the applicable scenarios. DETAILED DESCRIPTION

[0024] The technical solution of the invention is further described below in conjunction with specific implementation methods. It should also be understood that the following embodiments are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention belong to the scope of protection of the present invention.

[0025] The current PETG heat shrinkable film generally undergoes melt extrusion, filtration, casting and other processes during the foaming production process, and the resulting cast sheet pore structure distribution is often relatively simple. By adopting the gradient pressure regulation in the homogenizing section of the main extruder or the gradient temperature change at the melt pipeline, the differential regulation of the pore structure can be ensured to obtain a microporous adjustable low-density PETG shrinkable film.

[0026] The invention provides a microporous adjustable low-density PETG heat shrinkable film, comprising a core layer and upper and lower surface layers, wherein the upper and lower surface layers mainly comprise 100 parts by mass of modified polyethylene terephthalate (PETG) polyester chips and 1 to 3 parts of an opening agent, and the core layer mainly comprises 100 parts by mass of PETG polyester chips, 0 to 30 parts of white master batches, 10 parts of PET polyester chips and 2 to 5 parts of a foaming agent.

[0027] Preferably, the opening agent is nano-silicon dioxide or erucamide.

[0028] Preferably, the foaming agent is sodium bicarbonate with PETG as a carrier, potassium bicarbonate with PETG as a carrier, sodium bicarbonate with PET as a carrier, or potassium bicarbonate with PET as a carrier.

[0029] Preferably, the white masterbatch is titanium dioxide with PETG as a carrier or titanium dioxide with PET as a carrier.

[0030] Furthermore, the mass ratio of the upper surface layer, the core layer and the lower surface layer is 1:1 to 10:1.

[0031] Furthermore, the thickness of the microporous adjustable low-density PETG heat shrinkable film is 30 to 100 μm.

[0032] A method for preparing the above-mentioned microporous adjustable low-density PETG heat shrinkable film comprises the following steps:

[0033] Step (1), putting 100 parts by mass of modified polyethylene terephthalate (PETG) polyester chips and 1 to 3 parts of an opening agent as raw materials for the upper and lower surface layers into a high-speed mixing device for mixing at room temperature, the mixing speed being 300 to 600 rpm, and the mixing time being 3 to 10 minutes; putting 100 parts by mass of PETG polyester chips, 0 to 30 parts of white masterbatch, 10 parts of PET polyester chips and 2 to 5 parts of a foaming agent as raw materials for the core layer into a high-speed mixing device for mixing at room temperature, the mixing speed being 300 to 600 rpm, and the mixing time being 3 to 10 minutes;

[0034] Step (2), the ingredients of each layer are respectively put into a twin-screw vacuum extruder for melt plasticization according to the mixing of the core layer and the surface layer. The temperature of the twin-screw vacuum extruder is 250-280° C. The homogenizing section of the main extruder is pressurized (the width of the pressurized homogenizing section is 5 cm, the material flow time is 30 s, and the pressure along the material flow direction is gradiently changed by controlling the flow rate of the pressurized gas introduced), and the melt pipe is subjected to gradient temperature control (the temperature variable pipe section is 20 cm long, and the material flow time is 100 s, The pipeline is equipped with a heat exchange device to control the temperature to change in a gradient. After the melt is filtered out of impurities by a fine filter, the mass ratio of the upper surface layer, the core layer, and the lower surface layer is adjusted to 1:1 to 10:1 by the extruder speed device. The melt is collected into a three-layer melt structure of the upper surface layer, the core layer, and the lower surface layer through a distributor and melt-extruded from a three-layer composite die head (the die head temperature is 250°C to 270°C). The extruded melt is cast and cooled at 20 to 50°C on a quenching roller to form a casting sheet. During the quenching process, the linear speed of the quenching roller is controlled to be 70 to 90 m / min.

[0035] Step (3), biaxially stretching the cast sheet, wherein the longitudinal stretching conditions are: preheating at 80°C to 100°C, stretching the sheet to a ratio of 1.0 to 1.2 at 80°C to 100°C, and cooling and shaping the sheet at 70°C to 90°C after longitudinal stretching; and transverse stretching after longitudinal stretching, wherein the transverse stretching conditions are: preheating at 80°C to 120°C, stretching the sheet to a ratio of 4.0 to 6.0 at 80°C to 120°C, and cooling and shaping the sheet at 60°C to obtain a PETG heat shrinkable film;

[0036] Step (4), pulling, trimming, winding, packaging, and finished product.

[0037] Preferably, the pressurized gas used in the pressurized treatment process in step (2) is nitrogen, argon or carbon dioxide.

[0038] Furthermore, the pressure applied during the pressurization treatment in step (2) is 1 to 19 MPa, and the pressure change along the material flow direction is 0.6 to 1.2 MPa / s, which changes cyclically.

[0039] Furthermore, in step (2), the temperature of the melt pipe is controlled to be 260-270° C., and the temperature change along the material flow direction is 0.1-0.2° C. / s, which changes cyclically.

[0040] Example 1

[0041] (1) weighing the upper and lower surface layer raw materials and the core layer raw materials according to the mass proportions, wherein the upper and lower surface layer raw materials mainly include: 100 parts of modified polyethylene terephthalate glycol ester PETG polyester chips and 2 parts of nano-silicon dioxide as an opening agent; the core layer raw materials mainly include: 100 parts of PETG polyester chips, 10 parts of white masterbatch (titanium dioxide with PET as a carrier), 10 parts of PET polyester chips and 3 parts of foaming agent (sodium bicarbonate with PETG as a carrier);

[0042] (2) placing the upper and lower surface layer raw materials into a high-speed mixing device and stirring at 500 rpm for 5 min at room temperature to obtain a mixed raw material for the upper and lower surface layers;

[0043] (3) placing the core layer raw material into a high-speed mixing device and stirring at 500 rpm for 5 min at room temperature to obtain a core layer mixed raw material;

[0044] (4) The ingredients of each layer are respectively put into a twin-screw vacuum extruder for melt plasticization according to the mixing of the core layer and the surface layer. The temperature of the twin-screw vacuum extruder is 250°C. Nitrogen is introduced into the homogenizing section of the main extruder for pressurization, and the flow rate of the introduced nitrogen is controlled so that the pressure change range is 1-13MPa, the pressure change rate is 0.8MPa / s, and the change is cyclical; the melt pipeline is subjected to gradient temperature control, the temperature change range is 260-270°C, and the temperature change rate is 0.1°C / s; after the melt is filtered out of impurities by a fine filter, the mass ratio of the upper surface layer, the core layer, and the lower surface layer is adjusted to 1:3:1 by the extruder speed device, and the melt is gathered into a three-layer melt structure of the upper surface layer, the core layer, and the lower surface layer through a distributor, and is melt-extruded from a three-layer composite die (the die head temperature is 250°C), and the extruded melt is cast and cooled at 30°C on a quenching roller to form a cast sheet. During the quenching process, the linear speed of the quenching roller is controlled to be 70m / min.

[0045] (5) biaxially stretching the cast sheet, wherein the longitudinal stretching conditions are: preheating at 90° C., stretching the sheet to a ratio of 1.0 at 90° C., and cooling and shaping the sheet at 80° C. after longitudinal stretching; and transverse stretching after longitudinal stretching, wherein the transverse stretching conditions are: preheating at 100° C., stretching the sheet to a ratio of 4.5 at 100° C., and cooling and shaping the sheet at 85° C. after transverse stretching to obtain a PETG heat shrinkable film;

[0046] The density of the PETG heat shrinkable film prepared above is 1.12 g / cm 3 .

[0047] Example 2

[0048] (1) weighing the upper and lower surface layer raw materials and the core layer raw materials according to the mass proportions, wherein the upper and lower surface layer raw materials mainly include: 100 parts of modified polyethylene terephthalate glycol ester PETG polyester chips and 2 parts of nano-silicon dioxide as an opening agent; the core layer raw materials mainly include: 100 parts of PETG polyester chips, 10 parts of white masterbatch (titanium dioxide with PET as a carrier), 10 parts of PET polyester chips and 3 parts of foaming agent (sodium bicarbonate with PETG as a carrier);

[0049] (2) placing the upper and lower surface layer raw materials into a high-speed mixing device and stirring at 500 rpm for 5 min at room temperature to obtain a mixed raw material for the upper and lower surface layers;

[0050] (3) placing the core layer raw material into a high-speed mixing device and stirring at 500 rpm for 5 min at room temperature to obtain a core layer mixed raw material;

[0051] (4) The ingredients of each layer are respectively put into a twin-screw vacuum extruder for melt plasticization according to the mixing of the core layer and the surface layer. The temperature of the twin-screw vacuum extruder is 250°C. Nitrogen is introduced into the homogenizing section of the main extruder for pressurization, and the flow rate of the introduced nitrogen is controlled so that the pressure change range is 1-10MPa, the pressure change rate is 0.6MPa / s, and the change is cyclic; the melt pipeline is subjected to gradient temperature control, the temperature change range is 260-270°C, and the temperature change rate is 0.1°C / s; after the melt is filtered out of impurities by a fine filter, the mass ratio of the upper surface layer, the core layer, and the lower surface layer is adjusted to 1:3:1 by the extruder speed device, and the melt is gathered into a three-layer melt structure of the upper surface layer, the core layer, and the lower surface layer through a distributor, and is melt-extruded from a three-layer composite die (the die head temperature is 250°C), and the extruded melt is cast and cooled at 30°C on a quenching roller to form a casting sheet. During the quenching process, the linear speed of the quenching roller is controlled to be 70m / min.

[0052] (5) biaxially stretching the cast sheet, wherein the longitudinal stretching conditions are: preheating at 90° C., stretching the sheet to a ratio of 1.0 at 90° C., and cooling and shaping the sheet at 80° C. after longitudinal stretching; and transverse stretching after longitudinal stretching, wherein the transverse stretching conditions are: preheating at 100° C., stretching the sheet to a ratio of 4.5 at 100° C., and cooling and shaping the sheet at 85° C. after transverse stretching to obtain a PETG heat shrinkable film;

[0053] The density of the PETG heat shrinkable film prepared above is 1.05 g / cm 3 .

[0054] Example 3

[0055] (1) weighing the upper and lower surface layer raw materials and the core layer raw materials according to the mass proportions, wherein the upper and lower surface layer raw materials mainly include: 100 parts of modified polyethylene terephthalate glycol ester PETG polyester chips and 2 parts of nano-silicon dioxide as an opening agent; the core layer raw materials mainly include: 100 parts of PETG polyester chips, 10 parts of white masterbatch (titanium dioxide with PET as a carrier), 10 parts of PET polyester chips and 3 parts of foaming agent (sodium bicarbonate with PETG as a carrier);

[0056] (2) placing the upper and lower surface layer raw materials into a high-speed mixing device and stirring at 500 rpm for 5 min at room temperature to obtain a mixed raw material for the upper and lower surface layers;

[0057] (3) placing the core layer raw material into a high-speed mixing device and stirring at 500 rpm for 5 min at room temperature to obtain a core layer mixed raw material;

[0058] (4) The ingredients of each layer are respectively put into a twin-screw vacuum extruder for melt plasticization according to the mixing of the core layer and the surface layer. The temperature of the twin-screw vacuum extruder is 250°C. Nitrogen is introduced into the homogenizing section of the main extruder for pressurization, and the flow rate of the introduced nitrogen is controlled so that the pressure change range is 1-19 MPa, the pressure change rate is 1.2 MPa / s, and the change is cyclical; the melt pipeline is subjected to gradient temperature control, the temperature change range is 260-270°C, and the temperature change rate is 0.1°C / s; after the melt is filtered out of impurities by a fine filter, the mass ratio of the upper surface layer, the core layer, and the lower surface layer is adjusted to 1:3:1 by the extruder speed device, and the melt is gathered into a three-layer melt structure of the upper surface layer, the core layer, and the lower surface layer through a distributor, and is melt-extruded from a three-layer composite die (the die head temperature is 250°C), and the extruded melt is cast and cooled at 30°C on a quenching roller to form a cast sheet. During the quenching process, the linear speed of the quenching roller is controlled to be 70m / min.

[0059] (5) biaxially stretching the cast sheet, wherein the longitudinal stretching conditions are: preheating at 90° C., stretching the sheet to a ratio of 1.0 at 90° C., and cooling and shaping the sheet at 80° C. after longitudinal stretching; and transverse stretching after longitudinal stretching, wherein the transverse stretching conditions are: preheating at 100° C., stretching the sheet to a ratio of 4.5 at 100° C., and cooling and shaping the sheet at 85° C. after transverse stretching to obtain a PETG heat shrinkable film;

[0060] The density of the PETG heat shrinkable film prepared above is 1.10 g / cm 3 .

[0061] Example 4

[0062] (1) weighing the upper and lower surface layer raw materials and the core layer raw materials according to the mass proportions, wherein the upper and lower surface layer raw materials mainly include: 100 parts of modified polyethylene terephthalate glycol ester PETG polyester chips and 2 parts of nano-silicon dioxide as an opening agent; the core layer raw materials mainly include: 100 parts of PETG polyester chips, 10 parts of white masterbatch (titanium dioxide with PET as a carrier), 10 parts of PET polyester chips and 3 parts of foaming agent (sodium bicarbonate with PETG as a carrier);

[0063] (2) placing the upper and lower surface layer raw materials into a high-speed mixing device and stirring at 500 rpm for 5 min at room temperature to obtain a mixed raw material for the upper and lower surface layers;

[0064] (3) placing the core layer raw material into a high-speed mixing device and stirring at 500 rpm for 5 min at room temperature to obtain a core layer mixed raw material;

[0065] (4) The ingredients of each layer are respectively put into a twin-screw vacuum extruder for melt plasticization according to the mixing of the core layer and the surface layer. The temperature of the twin-screw vacuum extruder is 250°C. Nitrogen is introduced into the homogenizing section of the main extruder for pressurization, and the flow rate of the introduced nitrogen is controlled so that the pressure change range is 1-19 MPa, the pressure change rate is 1.2 MPa / s, and the change is cyclical; the melt pipeline is subjected to gradient temperature control, the temperature change range is 260-270°C, and the temperature change rate is 0.2°C / s; after the melt is filtered out of impurities by a fine filter, the mass ratio of the upper surface layer, the core layer, and the lower surface layer is adjusted to 1:3:1 by the extruder speed device, and the melt is gathered into a three-layer melt structure of the upper surface layer, the core layer, and the lower surface layer through a distributor, and is melt-extruded from a three-layer composite die (the die head temperature is 250°C), and the extruded melt is cast and cooled at 30°C on a quenching roller to form a casting sheet. During the quenching process, the linear speed of the quenching roller is controlled to be 70m / min.

[0066] (5) biaxially stretching the cast sheet, wherein the longitudinal stretching conditions are: preheating at 90° C., stretching the sheet to a ratio of 1.0 at 90° C., and cooling and shaping the sheet at 80° C. after longitudinal stretching; and transverse stretching after longitudinal stretching, wherein the transverse stretching conditions are: preheating at 100° C., stretching the sheet to a ratio of 4.5 at 100° C., and cooling and shaping the sheet at 85° C. after transverse stretching to obtain a PETG heat shrinkable film;

[0067] The density of the PETG heat shrinkable film prepared above is 1.08 g / cm 3 .

[0068] Example 5

[0069] (1) Weighing the upper and lower surface layer raw materials and the core layer raw materials according to the mass proportions, wherein the upper and lower surface layer raw materials mainly include: 100 parts of modified polyethylene terephthalate glycol ester PETG polyester chips and 2 parts of nano-silicon dioxide as an opening agent; the core layer raw materials mainly include: 100 parts of PETG polyester chips, 10 parts of PET polyester chips and 3 parts of a foaming agent (sodium bicarbonate with PETG as a carrier);

[0070] (2) placing the upper and lower surface layer raw materials into a high-speed mixing device and stirring at 500 rpm for 5 min at room temperature to obtain a mixed raw material for the upper and lower surface layers;

[0071] (3) placing the core layer raw material into a high-speed mixing device and stirring at 500 rpm for 5 min at room temperature to obtain a core layer mixed raw material;

[0072] (4) The ingredients of each layer are respectively put into a twin-screw vacuum extruder for melt plasticization according to the mixing of the core layer and the surface layer. The temperature of the twin-screw vacuum extruder is 250°C. Nitrogen is introduced into the homogenizing section of the main extruder for pressurization, and the flow rate of the introduced nitrogen is controlled so that the pressure change range is 1-19 MPa, the pressure change rate is 1.2 MPa / s, and the change is cyclical; the melt pipeline is subjected to gradient temperature control, the temperature change range is 260-270°C, and the temperature change rate is 0.2°C / s; after the melt is filtered out of impurities by a fine filter, the mass ratio of the upper surface layer, the core layer, and the lower surface layer is adjusted to 1:3:1 by the extruder speed device, and the melt is gathered into a three-layer melt structure of the upper surface layer, the core layer, and the lower surface layer through a distributor, and is melt-extruded from a three-layer composite die (the die head temperature is 250°C), and the extruded melt is cast and cooled at 30°C on a quenching roller to form a casting sheet. During the quenching process, the linear speed of the quenching roller is controlled to be 70m / min.

[0073] (5) biaxially stretching the cast sheet, wherein the longitudinal stretching conditions are: preheating at 90° C., stretching the sheet to a ratio of 1.0 at 90° C., and cooling and shaping the sheet at 80° C. after longitudinal stretching; and transverse stretching after longitudinal stretching, wherein the transverse stretching conditions are: preheating at 100° C., stretching the sheet to a ratio of 4.5 at 100° C., and cooling and shaping the sheet at 85° C. after transverse stretching to obtain a PETG heat shrinkable film;

[0074] The density of the PETG heat shrinkable film prepared above is 1.01 g / cm 3 .

[0075] Comparative Example 1

[0076] (1) weighing the upper and lower surface layer raw materials and the core layer raw materials according to the mass proportions, wherein the upper and lower surface layer raw materials mainly include: 100 parts of modified polyethylene terephthalate glycol ester PETG polyester chips and 2 parts of nano-silicon dioxide as an opening agent; the core layer raw materials mainly include: 100 parts of PETG polyester chips, 10 parts of white masterbatch (titanium dioxide with PET as a carrier), 10 parts of PET polyester chips and 3 parts of foaming agent (sodium bicarbonate with PETG as a carrier);

[0077] (2) placing the upper and lower surface layer raw materials into a high-speed mixing device and stirring at 500 rpm for 5 min at room temperature to obtain a mixed raw material for the upper and lower surface layers;

[0078] (3) placing the core layer raw material into a high-speed mixing device and stirring at 500 rpm for 5 min at room temperature to obtain a core layer mixed raw material;

[0079] (4) The ingredients of each layer are put into a twin-screw vacuum extruder for melt plasticization according to the mixing of the core layer and the surface layer. The temperature of the twin-screw vacuum extruder is 250°C. After the melt is filtered through a fine filter to remove impurities, the mass ratio of the upper surface layer, the core layer, and the lower surface layer is adjusted to 1:3:1 through the extruder speed device. The melt is gathered into a three-layer melt structure of the upper surface layer, the core layer, and the lower surface layer through a distributor and melt-extruded from a three-layer composite die (the die temperature is 250°C). The extruded melt is cast and cooled at 30°C on a quenching roller to form a cast sheet. During the quenching process, the linear speed of the quenching roller is controlled to be 70m / min.

[0080] (5) biaxially stretching the cast sheet, wherein the longitudinal stretching conditions are: preheating at 90° C., stretching the sheet to a ratio of 1.0 at 90° C., and cooling and shaping the sheet at 80° C. after longitudinal stretching; and transverse stretching after longitudinal stretching, wherein the transverse stretching conditions are: preheating at 100° C., stretching the sheet to a ratio of 4.5 at 100° C., and cooling and shaping the sheet at 85° C. after transverse stretching to obtain a PETG heat shrinkable film;

[0081] The density of the PETG heat shrinkable film prepared above is 1.40 g / cm 3 .

[0082] Comparative Example 2

[0083] (1) Weighing the upper and lower surface layer raw materials and the core layer raw materials according to the mass proportions, wherein the upper and lower surface layer raw materials mainly include: 100 parts of modified polyethylene terephthalate glycol ester PETG polyester chips and 2 parts of nano-silicon dioxide as an opening agent; the core layer raw materials mainly include: 100 parts of PETG polyester chips, 10 parts of PET polyester chips and 3 parts of a foaming agent (sodium bicarbonate with PETG as a carrier);

[0084] (2) placing the upper and lower surface layer raw materials into a high-speed mixing device and stirring at 500 rpm for 5 min at room temperature to obtain a mixed raw material for the upper and lower surface layers;

[0085] (3) placing the core layer raw material into a high-speed mixing device and stirring at 500 rpm for 5 min at room temperature to obtain a core layer mixed raw material;

[0086] (4) The ingredients of each layer are put into a twin-screw vacuum extruder for melt plasticization according to the mixing of the core layer and the surface layer. The temperature of the twin-screw vacuum extruder is 250°C. After the melt is filtered through a fine filter to remove impurities, the mass ratio of the upper surface layer, the core layer, and the lower surface layer is adjusted to 1:3:1 through the extruder speed device. The melt is gathered into a three-layer melt structure of the upper surface layer, the core layer, and the lower surface layer through a distributor and melt-extruded from a three-layer composite die (the die temperature is 250°C). The extruded melt is cast and cooled at 30°C on a quenching roller to form a cast sheet. During the quenching process, the linear speed of the quenching roller is controlled to be 70m / min.

[0087] (5) biaxially stretching the cast sheet, wherein the longitudinal stretching conditions are: preheating at 90° C., stretching the sheet to a ratio of 1.0 at 90° C., and cooling and shaping the sheet at 80° C. after longitudinal stretching; and transverse stretching after longitudinal stretching, wherein the transverse stretching conditions are: preheating at 100° C., stretching the sheet to a ratio of 4.5 at 100° C., and cooling and shaping the sheet at 85° C. after transverse stretching to obtain a PETG heat shrinkable film;

[0088] The density of the PETG heat shrinkable film prepared above is 1.31 g / cm 3 .

[0089] The above is only an embodiment of the present invention, and does not limit the present invention in any form. The present invention can also have other forms of embodiments according to the above structures and functions, which are not listed one by one. Therefore, any simple modification, equivalent change and modification made by any technician familiar with the profession to the above embodiment according to the technical essence of the present invention without departing from the scope of the technical solution of the present invention still falls within the scope of the technical solution of the present invention.

Claims

1. A microporous adjustable low-density PETG heat shrinkable film, comprising a core layer and upper and lower surface layers, characterized in that: The upper and lower surface layers mainly include 100 parts by mass of modified polyethylene terephthalate (PETG) polyester chips and 1 to 3 parts of an opening agent, and the core layer mainly includes 100 parts by mass of PETG polyester chips, 0 to 30 parts of white masterbatch, 10 parts of PET polyester chips and 2 to 5 parts of a foaming agent; The method for producing a microporous low-density PETG heat shrinkable film comprises the following steps: Step (1), putting 100 parts by mass of modified polyethylene terephthalate (PETG) polyester chips and 1 to 3 parts of an opening agent as raw materials for the upper and lower surface layers into a high-speed mixing device for mixing at room temperature, the mixing speed being 300 to 600 rpm, and the mixing time being 3 to 10 minutes; putting 100 parts by mass of PETG polyester chips, 0 to 30 parts of white masterbatch, 10 parts of PET polyester chips and 2 to 5 parts of a foaming agent as raw materials for the core layer into a high-speed mixing device for mixing at room temperature, the mixing speed being 300 to 600 rpm, and the mixing time being 3 to 10 minutes; Step (2), the ingredients of each layer are respectively put into a twin-screw vacuum extruder for melt plasticization according to the mixing of the core layer and the surface layer, the temperature of the twin-screw vacuum extruder is 250-280°C, the homogenizing section of the main extruder adopts gradient pressure regulation control, the width of the pressurized homogenizing section is 5 cm, the material flow time is 30 s, the melt pipeline is subjected to gradient temperature control, the temperature variable pipeline section is 20 cm long, the material flow time is 100 s, after the melt is filtered through a fine filter to remove impurities, the mass ratio of the upper surface layer, the core layer, and the lower surface layer is adjusted to 1:1-10:1 by the extruder speed equipment, and the upper surface layer, the core layer, and the lower surface layer are collected through a distributor into a three-layer melt structure of the upper surface layer, the core layer, and the lower surface layer, and melt extruded from a three-layer composite die head, the die head temperature is 250-270°C, the extruded melt is cast and cooled at 20-50°C on a quenching roller to form a cast sheet, and the linear speed of the quenching roller during the quenching process is controlled to be 70-90 m / min; Step (3), biaxially stretching the cast sheet, wherein the longitudinal stretching conditions are: preheating at 80°C to 100°C, stretching the sheet to a ratio of 1.0 to 1.2 at 80°C to 100°C, and cooling and shaping the sheet at 70°C to 90°C after longitudinal stretching; and transverse stretching after longitudinal stretching, wherein the transverse stretching conditions are: preheating at 80°C to 120°C, stretching the sheet to a ratio of 4.0 to 6.0 at 80°C to 120°C, and cooling and shaping the sheet at 60°C to obtain a PETG heat shrinkable film; Step (4), pulling, trimming, winding, packaging, and finished product.

2. A microporous adjustable low-density PETG heat shrinkable film as claimed in claim 1, characterized in that: The opening agent is nano silicon dioxide or erucamide.

3. A microporous adjustable low-density PETG heat shrinkable film as claimed in claim 2, characterized in that: The foaming agent is sodium bicarbonate with PETG as a carrier, potassium bicarbonate with PETG as a carrier, sodium bicarbonate with PET as a carrier, or potassium bicarbonate with PET as a carrier.

4. A microporous adjustable low-density PETG heat shrinkable film as claimed in claim 1, characterized in that: The white masterbatch is titanium dioxide with PETG as a carrier or titanium dioxide with PET as a carrier.

5. A microporous adjustable low-density PETG heat shrinkable film as claimed in claim 2, characterized in that: The mass ratio of the upper surface layer, the core layer and the lower surface layer is 1:1 to 10:

1.

6. The microporous adjustable low-density PETG heat shrinkable film according to claim 1, characterized in that: The thickness of the microporous adjustable low-density PETG heat shrinkable film is 30-100 μm.

7. The microporous adjustable low-density PETG heat shrinkable film according to claim 1, characterized in that: The pressurized gas used in the gradient pressure control process in step (2) is nitrogen, argon or carbon dioxide.

8. The microporous adjustable low-density PETG heat shrinkable film according to claim 1, characterized in that: The pressure applied during the gradient pressure control process in step (2) is 1 to 19 MPa, and the pressure change along the material flow direction is 0.6 to 1.2 MPa / s, which changes cyclically.

9. The microporous adjustable low-density PETG heat shrinkable film according to claim 1, characterized in that: In step (2), the temperature of the melt pipe is controlled by gradient temperature change to be 260-270° C., and the temperature change along the material flow direction is 0.1-0.2° C. / s, and the change is cyclic.