Preparation method of high-transmittance low-haze PETG heat-shrinkable label film

Abstract

This invention discloses a method for preparing a high-transmittance, low-haze PETG heat-shrinkable label film, comprising: extruding and plasticizing PETG resin through a hopper into an extruder; obtaining clean core layer PETG melt and surface layer PETG melt after metering by a metering pump, filtration by a fine filter, and filtration by a high-precision melt filter; forming an ABA three-layer structure material flow through a distributor, and casting it into an ABA-structured PETG sheet through a casting die and casting mechanism; adding a coating liquid to a coating machine and uniformly coating it onto the surface of the PETG sheet to obtain a coated PETG sheet, wherein the uniform coating is double-sided coating; and subjecting the coated PETG sheet to a transverse stretching system, a traction system, a winding system, a slitting system, and inspection to obtain a high-transmittance, low-haze PETG heat-shrinkable label film. This invention utilizes a nitrogen atmosphere to enhance the protection of the extruded melt and uses a high-precision melt filter for efficient impurity removal to form a high-transmittance, low-haze PETG heat-shrinkable label film.

Description

Technical Field

[0001] This invention belongs to the field of PETG heat-shrinkable label film technology, specifically relating to a method for preparing a high-transmittance, low-haze PETG heat-shrinkable label film. Background Technology

[0002] Heat shrink label film can completely wrap around a PET bottle during use, giving the bottle a 360° label design. By printing exquisite patterns and vibrant colors, it creates a visually impactful packaging effect, highlighting the perfect image and attractiveness of the product on the supermarket shelf, and achieving brand differentiation and product marketing.

[0003] PETG material is environmentally friendly and non-toxic, with high shrinkage and good mechanical properties, making it the primary substrate film for PET bottled beverage labels. PETG is PET modified with comonomers CHDM or NPG. The addition of comonomers disrupts the regularity of PET chain segments, reducing its crystallinity. Because PETG film is less prone to crystal formation during manufacturing, PETG heat-shrink label films exhibit superior optical properties. However, the manufacturing process of PETG heat-shrink label films typically involves the addition of opening slip agents and other additives, and some waste materials such as edge fibers are recycled. These additives, impurities, and crystal formation can all negatively impact the film's light transmittance and increase its haze.

[0004] Therefore, influenced by young people's consumption concepts of novelty and uniqueness, some beverages are designed with special shapes or colors. In order to ensure the perfect presentation of the effect, the transparency of PETG heat shrink label film is required to be very high, and ordinary PETG heat shrink label film cannot meet the requirements. Summary of the Invention

[0005] To address the problems in the existing technology, this invention provides a method for preparing a high-transmittance, low-haze PETG heat-shrinkable label film. This method solves the problem that the transmittance of existing PETG heat-shrinkable label films cannot meet the high requirements of the market. It utilizes a nitrogen atmosphere to enhance the protection of the extruded melt and uses a high-precision melt filtration device for efficient impurity removal to form a high-transmittance, low-haze PETG heat-shrinkable label film.

[0006] To achieve the above technical objectives, the technical solution of the present invention is as follows:

[0007] A method for preparing a high-transmittance, low-haze PETG heat-shrinkable label film includes the following steps: Step 1: PETG resin is fed into the first extruder through a hopper for extrusion and plasticization. After metering by a metering pump, filtration by a fine filter, and filtration by a high-precision melt filter, a clean core layer PETG melt is obtained. The hopper is in a nitrogen atmosphere. The extrusion and plasticization temperature of the first extruder is 255-270℃. The temperature of the metering pump is 265-270℃, the temperature of the fine filter is 265-270℃, and the temperature of the melt pipeline is 265-270℃. The operating temperature inside the high-precision melt filter is 268-270℃. Step 2: PETG resin is fed into the second extruder through a hopper for extrusion and plasticization. After metering by a metering pump, filtration by a fine filter, and filtration by a high-precision melt filter, a clean surface layer of PETG melt is obtained. The hopper is in a nitrogen atmosphere. The extrusion and plasticization temperature of the second extruder is 255-270℃; the temperature of the metering pump is 265-270℃; the temperature of the fine filter is 265-270℃; and the temperature of the melt pipeline is 265-270℃. The operating temperature inside the high-precision melt filter is 268-270℃. Step 3: The surface layer PETG melt is piped into the corresponding flow channel of the die pre-distributor, splitting into two streams to form upper and lower surface layers, i.e., the surface layer stream; the core layer PETG melt is piped into the middle flow channel of the die pre-distributor to form the middle layer, i.e., the core layer stream; the surface layer stream and the core layer stream are distributed to form an ABA three-layer structure stream, which is then cast into an ABA structure PETG sheet through the casting die and casting mechanism; the temperature of the die pre-distributor is 265-270℃, the temperature of the casting die is 265-270℃, and the temperature of the casting roller of the casting mechanism is 28℃; Step 4: Add the coating liquid to the coating machine and coat it evenly on the surface of the PETG sheet to obtain the coated PETG sheet. The even coating is done by double-sided coating. Step 5: The coated PETG sheet is subjected to a transverse stretching system, a traction system, and a winding system to obtain a semi-finished product. Then, it is subjected to a slitting system and inspection to obtain a high light transmittance and low haze PETG heat shrink label film. The transverse stretching system has a transverse stretching ratio of 5.0 and a stretching temperature of 85-98℃.

[0008] The aforementioned PETG sheets use the same PETG material for both the surface and core layers, without adding any additives or using recycled materials, and the extrusion process and parameters are completely identical. Since the core and surface layers are made of completely identical materials, there are no minor performance differences caused by different raw materials between layers that could lead to variations in light refraction and scattering between film layers, affecting the overall light transmittance and increasing film haze. Therefore, by not adding additives and not using recycled materials, the purity of the PETG material is ensured, preventing additive components, impurities in recycled materials, and degradation products from becoming light scattering centers, interfering with the normal propagation of light within the film, and thus reducing film transmittance and increasing haze.

[0009] The hopper operates under a nitrogen atmosphere. A nitrogen manifold is installed inside the hopper and located at the bottom, near the extruder inlet. Furthermore, the nitrogen manifold has evenly distributed vents facing the extruder inlet. Multiple nitrogen manifolds are provided, such as 4, 6, or 8. During operation, the nitrogen atmosphere in the hopper is uniformly supplied through the nitrogen manifold. At this time, the PETG pellets in the hopper are in a nitrogen atmosphere, and as nitrogen is uniformly introduced, the air between the PETG pellets is replaced by nitrogen and discharged through the exhaust port at the top of the hopper. To ensure that the PETG pellets in the extruder feed inlet and the downstream screw channel of the extruder are free of oxygen, the hopper is purged with nitrogen before use to ensure that the atmosphere in the hopper and the extruder is nitrogen. As the PETG pellets are conveyed forward in the extruder screw channel, the PETG pellets are compacted, and most of the nitrogen in the gaps around the pellets is squeezed out and returned to the hopper through the extruder feed inlet, ensuring that the PETG pellets are in a nitrogen-protected atmosphere.

[0010] The PETG pellets are encapsulated in nitrogen within the hopper after being purged with nitrogen. This nitrogen gas displaces and removes any air trapped within the pellets, preventing oxygen from entering the extruder screw. During the high-temperature, high-shear melting and plasticizing process of PETG, the nitrogen protection effectively prevents thermal and oxygen degradation. Simultaneously, nitrogen purging removes moisture adsorbed on the surface of the PETG pellets, reducing the likelihood of hydrolysis. This treatment method effectively prevents PETG pellet deterioration and significantly improves its stability.

[0011] The coating solution is prepared from nano-silica and water-based polyester, with the following mass ratio: 50 parts nano-silica dispersion, 15 parts water-based polyester, 1 part curing agent, and 34 parts water. The nano-silica dispersion contains 20% silica by mass, with a silica particle size of 30 nm. The nano-silica dispersion used is VK-SP30W from Zhejiang Zhitai Nanomaterials Co., Ltd., the water-based polyester is MD-1245 from Toyobo (Japan), and the curing agent is Bayhydur® 401-70. The coating solution is added to a coating machine and applied to the surface of PETG sheets, with a coating thickness of 250-300 nm. Therefore, the 250-300 nm thick coating on the PETG sheet surface, after transverse stretching, reduces the coating thickness to 50-60 nm. Since the refractive index of silica is close to that of PETG, the direct impact on the optical properties of the thin film is minimal. Therefore, the coating film on the PETG surface not only does not affect the transmission of light inside the film, but the surface layer has an extremely limited, even negligible, influence on light. Moreover, the coating forms an uneven structure on the film surface, thus producing an effect similar to an opening agent, ensuring the subsequent processing and use of the film.

[0012] Both the surface layer PETG melt and the core layer PETG melt are filtered by a fine filter and a high-precision melt filter. This process deeply filters the PETG melt, further removing small impurity particles from the melt, resulting in a purer film with higher light transmittance and lower haze. The PETG melt, after being melted and plasticized in the extruder, enters the high-precision melt filter from the top after being filtered by the fine filter. Under the combined action of nitrogen pressure and gravity, the PETG melt flows downwards through the filter screen inside the high-precision melt filter, removing small impurity particles and improving the homogenization of the PETG melt. The nitrogen pressure is 0.2-0.4 MPa. The PETG resin used in steps 1 and 2 is a modified PETG resin, specifically CHDM modified PETG or NPG modified PETG; wherein, the CHDM modified PETG is one of Embrace™ copolyester, Embrace™ LV copolyester, GN001, S2008 from SK Corporation of Korea, and K2012 from SK Corporation of Korea; the NPG modified PETG is one of FG718H from Yizheng Chemical Fiber, HSF from Jiangsu Suolide, and W501 from Jiangyin Huahong.

[0013] As can be seen from the above description, the present invention has the following advantages: 1. This invention solves the problem that the light transmittance of existing PETG heat shrink label films cannot meet the high requirements of the market. It utilizes a nitrogen atmosphere to enhance the protection of the extruded melt and uses a high-precision melt filtration device for efficient impurity removal to form a PETG heat shrink label film with high light transmittance and low haze.

[0014] 2. This invention utilizes the consistency of materials between the core layer and the surface layer to form a homogenized heat-shrinkable label film, eliminating the need for recycled materials and additives, thus preventing performance differences between the surface layer and the core layer. At the same time, coating the surface with a film made of nano-silica and water-based polyester not only does not affect the light transmittance and haze, but also improves the abrasion resistance and opening performance of the heat-shrinkable label film.

[0015] 3. This invention utilizes the filter screen cutting and flow shearing of a high-precision melt filtration device to filter impurities in the melt and remove nitrogen gas from the melt, ensuring that there are no air bubbles in the subsequent sheet. Detailed Implementation

[0016] The present invention will be described in detail with reference to the embodiments, but the claims of the present invention are not intended to limit the scope of the invention.

[0017] A method for preparing a high-transmittance, low-haze PETG heat-shrinkable label film includes the following steps: Step 1: PETG resin is fed into the first extruder through a hopper for extrusion and plasticization. After metering by a metering pump, filtration by a fine filter, and filtration by a high-precision melt filter, a clean core layer PETG melt is obtained. The hopper is in a nitrogen atmosphere. The extrusion and plasticization temperature of the first extruder is 255-270℃. The temperature of the metering pump is 265-270℃, the temperature of the fine filter is 265-270℃, and the temperature of the melt pipeline is 265-270℃. The operating temperature inside the high-precision melt filter is 268-270℃. Step 2: PETG resin is fed into the second extruder through a hopper for extrusion and plasticization. After metering by a metering pump, filtration by a fine filter, and filtration by a high-precision melt filter, a clean surface layer of PETG melt is obtained. The hopper is in a nitrogen atmosphere. The extrusion and plasticization temperature of the second extruder is 255-270℃; the temperature of the metering pump is 265-270℃; the temperature of the fine filter is 265-270℃; and the temperature of the melt pipeline is 265-270℃. The operating temperature inside the high-precision melt filter is 268-270℃. Step 3: The surface layer PETG melt is piped into the corresponding flow channel of the die pre-distributor, splitting into two streams to form upper and lower surface layers, i.e., the surface layer stream; the core layer PETG melt is piped into the middle flow channel of the die pre-distributor to form the middle layer, i.e., the core layer stream; the surface layer stream and the core layer stream are distributed to form an ABA three-layer structure stream, which is then cast into an ABA structure PETG sheet through the casting die and casting mechanism; the temperature of the die pre-distributor is 265-270℃, the temperature of the casting die is 265-270℃, and the temperature of the casting roller of the casting mechanism is 28℃; Step 4: Add the coating liquid to the coating machine and coat it evenly on the surface of the PETG sheet to obtain the coated PETG sheet. The even coating is done by double-sided coating. Step 5: The coated PETG sheet is subjected to a transverse stretching system, a traction system, and a winding system to obtain a semi-finished product. Then, it is subjected to a slitting system and inspection to obtain a high light transmittance and low haze PETG heat shrink label film. The transverse stretching system has a transverse stretching ratio of 5.0 and a stretching temperature of 85-98℃.

[0018] The hopper is equipped with multiple nitrogen manifolds, which can be 4, 6, or 8. In this embodiment, 4 nitrogen manifolds are used. The diameter of the nitrogen manifolds is 7-8 mm, and in this embodiment, the diameter is 7 mm. Each nitrogen manifold has 2-4 vent holes for releasing nitrogen. In this embodiment, there are 3 vent holes. The diameter of the vent holes is 10-12 mm, and in this embodiment, the diameter is 10 mm.

[0019] The nitrogen pressure in the high-precision melt filter device is 0.2-0.4 MPa, and the filtration accuracy decreases from 15 μm to 10 μm.

[0020] The coating solution is prepared from nano-silica and water-based polyester, with the following mass ratio: 50 parts nano-silica dispersion, 15 parts water-based polyester, 1 part curing agent, and 34 parts water. The nano-silica dispersion contains 20% silica by mass, and the silica particle size is 30 nm. The nano-silica dispersion used is VK-SP30W from Zhejiang Zhitai Nanomaterials Co., Ltd., the water-based polyester is MD-1245 from Toyobo (Japan), and the curing agent is Bayhydur® 401-70. The coating solution is added to a coating machine to coat the surface of PETG sheets, with a coating thickness of 250-300 nm. The coating machine used is a product of BNM (Korea).

[0021] The PETG resin used in Examples 1-3 was NPG-modified PETG produced by Jiangsu Suolide Co., Ltd., with the model number HSF.

[0022] Example 1 A method for preparing a high-transmittance, low-haze PETG heat-shrinkable label film includes the following steps: Step 1: PETG resin is fed into the first extruder through a hopper for extrusion and plasticization. After metering by a metering pump, filtration by a fine filter, and filtration by a high-precision melt filter, a clean core layer PETG melt is obtained. The hopper is in a nitrogen atmosphere. The extrusion and plasticization temperature of the first extruder is 255-270℃. The temperature of the metering pump is 265-270℃, the temperature of the fine filter is 265-270℃, and the temperature of the melt pipeline is 265-270℃. The operating temperature inside the high-precision melt filter is 268-270℃. Step 2: PETG resin is fed into the second extruder through a hopper for extrusion and plasticization. After metering by a metering pump, filtration by a fine filter, and filtration by a high-precision melt filter, a clean surface layer of PETG melt is obtained. The hopper is in a nitrogen atmosphere. The extrusion and plasticization temperature of the second extruder is 255-270℃; the temperature of the metering pump is 265-270℃; the temperature of the fine filter is 265-270℃; and the temperature of the melt pipeline is 265-270℃. The operating temperature inside the high-precision melt filter is 268-270℃. Step 3: The surface layer PETG melt is piped into the corresponding flow channel of the die pre-distributor, splitting into two streams to form upper and lower surface layers, i.e., the surface layer stream; the core layer PETG melt is piped into the middle flow channel of the die pre-distributor to form the middle layer, i.e., the core layer stream; the surface layer stream and the core layer stream are distributed to form an ABA three-layer structure stream, which is then cast into an ABA structure PETG sheet through the casting die and casting mechanism; the temperature of the die pre-distributor is 265-270℃, the temperature of the casting die is 265-270℃, and the temperature of the casting roller of the casting mechanism is 28℃; Step 4: Add the coating liquid to the coating machine and coat it evenly on the surface of the PETG sheet to obtain a coated PETG sheet. The uniform coating is double-sided coating; the coating thickness is 280 nm. Step 5: The coated PETG sheet is subjected to a transverse stretching system, a traction system, and a winding system to obtain a semi-finished product. Then, it is subjected to a slitting system and inspection to obtain a high light transmittance and low haze PETG heat shrink label film. The transverse stretching system has a transverse stretching ratio of 5.0 and a stretching temperature of 85-98℃.

[0023] The thickness ratio of the three layers in the PETG sheet is ABA (surface layer: core layer: surface layer) = 10:80:10.

[0024] Example 2 A method for preparing a high-transmittance, low-haze PETG heat-shrinkable label film includes the following steps: Step 1: PETG resin is fed into the first extruder through a hopper for extrusion and plasticization. After metering by a metering pump, filtration by a fine filter, and filtration by a high-precision melt filter, a clean core layer PETG melt is obtained. The hopper is in a nitrogen atmosphere. The extrusion and plasticization temperature of the first extruder is 255-270℃. The temperature of the metering pump is 265-270℃, the temperature of the fine filter is 265-270℃, and the temperature of the melt pipeline is 265-270℃. The operating temperature inside the high-precision melt filter is 268-270℃. Step 2: PETG resin is fed into the second extruder through a hopper for extrusion and plasticization. After metering by a metering pump, filtration by a fine filter, and filtration by a high-precision melt filter, a clean surface layer of PETG melt is obtained. The hopper is in a nitrogen atmosphere. The extrusion and plasticization temperature of the second extruder is 255-270℃; the temperature of the metering pump is 265-270℃; the temperature of the fine filter is 265-270℃; and the temperature of the melt pipeline is 265-270℃. The operating temperature inside the high-precision melt filter is 268-270℃. Step 3: The surface layer PETG melt is piped into the corresponding flow channel of the die pre-distributor, splitting into two streams to form upper and lower surface layers, i.e., the surface layer stream; the core layer PETG melt is piped into the middle flow channel of the die pre-distributor to form the middle layer, i.e., the core layer stream; the surface layer stream and the core layer stream are distributed to form an ABA three-layer structure stream, which is then cast into an ABA structure PETG sheet through the casting die and casting mechanism; the temperature of the die pre-distributor is 265-270℃, the temperature of the casting die is 265-270℃, and the temperature of the casting roller of the casting mechanism is 28℃; Step 4: Add the coating liquid to the coating machine and coat it evenly on the surface of the PETG sheet to obtain a coated PETG sheet. The uniform coating is double-sided coating; the coating thickness is 300 nm. Step 5: The coated PETG sheet is subjected to a transverse stretching system, a traction system, and a winding system to obtain a semi-finished product. Then, it is subjected to a slitting system and inspection to obtain a high light transmittance and low haze PETG heat shrink label film. The transverse stretching system has a transverse stretching ratio of 5.0 and a stretching temperature of 85-98℃.

[0025] The thickness ratio of the three layers in the PETG sheet is ABA (surface layer: core layer: surface layer) = 12.5:75:12.5.

[0026] Example 3 A method for preparing a high-transmittance, low-haze PETG heat-shrinkable label film includes the following steps: Step 1: PETG resin is fed into the first extruder through a hopper for extrusion and plasticization. After metering by a metering pump, filtration by a fine filter, and filtration by a high-precision melt filter, a clean core layer PETG melt is obtained. The hopper is in a nitrogen atmosphere. The extrusion and plasticization temperature of the first extruder is 255-270℃. The temperature of the metering pump is 265-270℃, the temperature of the fine filter is 265-270℃, and the temperature of the melt pipeline is 265-270℃. The operating temperature of the high-precision melt filter is 268-270℃. Step 2: PETG resin is fed into the second extruder through a hopper for extrusion and plasticization. After metering by a metering pump, filtration by a fine filter, and filtration by a high-precision melt filter, a clean surface layer of PETG melt is obtained. The hopper is under a nitrogen atmosphere. The extrusion and plasticization temperature of the second extruder is 255-270℃; the temperature of the metering pump is 265-270℃; the temperature of the fine filter is 265-270℃; and the temperature of the melt pipeline is 265-270℃. The operating temperature of the high-precision melt filter is 268-270℃. Step 3: The surface layer PETG melt is piped into the corresponding flow channel of the die pre-distributor, splitting into two streams to form upper and lower surface layers, i.e., the surface layer stream; the core layer PETG melt is piped into the middle flow channel of the die pre-distributor to form the middle layer, i.e., the core layer stream; the surface layer stream and the core layer stream are distributed to form an ABA three-layer structure stream, which is then cast into an ABA structure PETG sheet through the casting die and casting mechanism; the temperature of the die pre-distributor is 265-270℃, the temperature of the casting die is 265-270℃, and the temperature of the casting roller of the casting mechanism is 28℃; Step 4: Add the coating liquid to the coating machine and coat it evenly on the surface of the PETG sheet to obtain a coated PETG sheet. The uniform coating is double-sided coating; the coating thickness is 250 nm. Step 5: The coated PETG sheet is subjected to a transverse stretching system, a traction system, and a winding system to obtain a semi-finished product. Then, it is subjected to a slitting system and inspection to obtain a high light transmittance and low haze PETG heat shrink label film. The transverse stretching system has a transverse stretching ratio of 5.0 and a stretching temperature of 85-98℃.

[0027] The thickness ratio of the three layers in the PETG sheet is ABA (surface layer: core layer: surface layer) = 15:70:15.

[0028] Comparative Example 1 A method for preparing a PETG heat-shrinkable label film includes the following steps: Step 1: PETG resin is fed into the first extruder through a hopper for extrusion and plasticization. After metering by a metering pump and filtration by a fine filter, a clean core layer PETG melt is obtained. The extrusion and plasticization temperature of the first extruder is 255-270℃; the temperature of the metering pump is 265-270℃, the temperature of the fine filter is 265-270℃, and the temperature of the melt pipeline is 265-270℃. The PETG resin is NPG-modified PETG produced by Jiangsu Suolide Co., Ltd., and its model is HSF. Step 2: PETG resin and open-face slip masterbatch are fed into a second extruder through a hopper for extrusion and plasticization. After metering by a metering pump and filtration by a fine filter, a surface layer of PETG melt is obtained. The extrusion and plasticization temperature of the second extruder is 255-270℃; the temperature of the metering pump is 265-270℃, the temperature of the fine filter is 265-270℃, and the temperature of the melt pipeline is 265-270℃; the open-face slip masterbatch is TA10-08 MB13 from Sucarno GmbH, Switzerland, and its mass percentage is 1.5%; the PETG resin is NPG-modified PETG produced by Jiangsu Suolide Co., Ltd., and its model is HSF. Step 3: The surface layer PETG melt is piped into the corresponding flow channel of the die pre-distributor, splitting into two streams to form upper and lower surface layers, i.e., the surface layer stream; the core layer PETG melt is piped into the middle flow channel of the die pre-distributor to form the middle layer, i.e., the core layer stream; the surface layer stream and the core layer stream are distributed to form an ABA three-layer structure stream, which is then cast into an ABA structure PETG sheet through the casting die and casting mechanism; the temperature of the die pre-distributor is 265-270℃, the temperature of the casting die is 265-270℃, and the temperature of the casting roller of the casting mechanism is 28℃; Step 4: The PETG sheet is subjected to a transverse stretching system, a traction system, and a winding system to obtain a semi-finished product. Then, it is subjected to a slitting system and inspection to obtain a PETG heat shrink label film. The transverse stretching system has a transverse stretching ratio of 5.0 and a stretching temperature of 85-98℃.

[0029] The thickness ratio of the three layers in the PETG sheet is ABA (surface layer: core layer: surface layer) = 12.5:75:12.5.

[0030] Comparative Example 2 A method for preparing a PETG heat-shrinkable label film includes the following steps: Step 1: PETG resin and scrap filaments are fed into the first extruder through a hopper for extrusion and plasticization. After metering by a metering pump and filtration by a fine filter, a clean core layer PETG melt is obtained. The extrusion and plasticization temperature of the first extruder is 255-270℃; the temperature of the metering pump is 265-270℃, the temperature of the fine filter is 265-270℃, and the temperature of the melt pipeline is 265-270℃. The scrap filaments are recycled from the edge-cutting mechanism in the transverse stretching system, and account for 10% by mass. The PETG resin is NPG-modified PETG produced by Jiangsu Suolide Co., Ltd., model HSF. Step 2: PETG resin and open-face slip masterbatch are fed into a second extruder through a hopper for extrusion and plasticization. After metering by a metering pump and filtration by a fine filter, a surface layer of PETG melt is obtained. The extrusion and plasticization temperature of the second extruder is 255-270℃; the temperature of the metering pump is 265-270℃, the temperature of the fine filter is 265-270℃, and the temperature of the melt pipeline is 265-270℃; the open-face slip masterbatch is TA10-08 MB13 from Sucarno GmbH, Switzerland, and its mass percentage is 1.5%; the PETG resin is NPG-modified PETG produced by Jiangsu Suolide Co., Ltd., and its model is HSF. Step 3: The surface layer PETG melt is piped into the corresponding flow channel of the die pre-distributor, splitting into two streams to form upper and lower surface layers, i.e., the surface layer stream; the core layer PETG melt is piped into the middle flow channel of the die pre-distributor to form the middle layer, i.e., the core layer stream; the surface layer stream and the core layer stream are distributed to form an ABA three-layer structure stream, which is then cast into an ABA structure PETG sheet through the casting die and casting mechanism; the temperature of the die pre-distributor is 265-270℃, the temperature of the casting die is 265-270℃, and the temperature of the casting roller of the casting mechanism is 28℃; Step 4: The PETG sheet is subjected to a transverse stretching system, a traction system, and a winding system to obtain a semi-finished product. Then, it is subjected to a slitting system and inspection to obtain a PETG heat shrink label film. The transverse stretching system has a transverse stretching ratio of 5.0 and a stretching temperature of 85-98℃.

[0031] The thickness ratio of the three layers in the PETG sheet is ABA (surface layer: core layer: surface layer) = 12.5:75:12.5.

[0032] Comparative Example 3 A method for preparing a PETG heat-shrinkable label film includes the following steps: Step 1: PETG resin is fed into the first extruder through a hopper for extrusion and plasticization. After metering by a metering pump and filtration by a fine filter, a clean core layer PETG melt is obtained. The extrusion and plasticization temperature of the first extruder is 255-270℃; the temperature of the metering pump is 265-270℃, the temperature of the fine filter is 265-270℃, and the temperature of the melt pipeline is 265-270℃. The PETG resin is a CHDM-modified Embrace™ copolyester from Eastman Corporation, USA. Step 2: PETG resin and open-face slip masterbatch are fed into a second extruder through a hopper for extrusion and plasticization. After metering by a metering pump and filtration by a fine filter, a surface layer of PETG melt is obtained. The extrusion and plasticization temperature of the second extruder is 255-270℃; the temperature of the metering pump is 265-270℃, the temperature of the fine filter is 265-270℃, and the temperature of the melt pipeline is 265-270℃; the open-face slip masterbatch is TA10-08 MB13 from Sucanor, Switzerland, and its mass percentage is 1.5%; the PETG resin is CHDM-modified Embrace™ copolyester from Eastman, USA. Step 3: The surface layer PETG melt is piped into the corresponding flow channel of the die pre-distributor, splitting into two streams to form upper and lower surface layers, i.e., the surface layer stream; the core layer PETG melt is piped into the middle flow channel of the die pre-distributor to form the middle layer, i.e., the core layer stream; the surface layer stream and the core layer stream are distributed to form an ABA three-layer structure stream, which is then cast into an ABA structure PETG sheet through the casting die and casting mechanism; the temperature of the die pre-distributor is 265-270℃, the temperature of the casting die is 265-270℃, and the temperature of the casting roller of the casting mechanism is 28℃; Step 4: The PETG sheet is subjected to a transverse stretching system, a traction system, and a winding system to obtain a semi-finished product. Then, it is subjected to a slitting system and inspection to obtain a PETG heat shrink label film. The transverse stretching system has a transverse stretching ratio of 5.0 and a stretching temperature of 85-98℃.

[0033] The thickness ratio of the three layers in the PETG sheet is ABA (surface layer: core layer: surface layer) = 12.5:75:12.5.

[0034] Comparative Example 4 A method for preparing a PETG heat-shrinkable label film includes the following steps: Step 1: PETG resin is fed into the first extruder through a hopper for extrusion and plasticization. After metering by a metering pump and filtration by a fine filter, a clean core layer PETG melt is obtained. The extrusion and plasticization temperature of the first extruder is 255-270℃; the temperature of the metering pump is 265-270℃, the temperature of the fine filter is 265-270℃, and the temperature of the melt pipeline is 265-270℃. The PETG resin is CHDM-modified S2008 from SK Corporation of Korea. Step 2: PETG resin and open-face slip masterbatch are fed into a second extruder through a hopper for extrusion and plasticization. After metering by a metering pump and filtration by a fine filter, a surface layer of PETG melt is obtained. The extrusion and plasticization temperature of the second extruder is 255-270℃; the temperature of the metering pump is 265-270℃, the temperature of the fine filter is 265-270℃, and the temperature of the melt pipeline is 265-270℃; the open-face slip masterbatch is TA10-08 MB13 from Sucarno, Switzerland, and its mass percentage is 1.5%; the PETG resin is CHDM-modified S2008 from SK Corporation, South Korea. Step 3: The surface layer PETG melt is piped into the corresponding flow channel of the die pre-distributor, splitting into two streams to form upper and lower surface layers, i.e., the surface layer stream; the core layer PETG melt is piped into the middle flow channel of the die pre-distributor to form the middle layer, i.e., the core layer stream; the surface layer stream and the core layer stream are distributed to form an ABA three-layer structure stream, which is then cast into an ABA structure PETG sheet through the casting die and casting mechanism; the temperature of the die pre-distributor is 265-270℃, the temperature of the casting die is 265-270℃, and the temperature of the casting roller of the casting mechanism is 28℃; Step 4: The PETG sheet is subjected to a transverse stretching system, a traction system, and a winding system to obtain a semi-finished product. Then, it is subjected to a slitting system and inspection to obtain a PETG heat shrink label film. The transverse stretching system has a transverse stretching ratio of 5.0 and a stretching temperature of 85-98℃.

[0035] The thickness ratio of the three layers in the PETG sheet is ABA (surface layer: core layer: surface layer) = 12.5:75:12.5.

[0036] Comparative Example 5 A method for preparing a PETG heat-shrinkable label film includes the following steps: Step 1: PETG resin is fed into the first extruder through a hopper for extrusion and plasticization. After metering by a metering pump and filtration by a fine filter, the core layer PETG melt is obtained. The extrusion and plasticization temperature of the first extruder is 255-270℃; the temperature of the metering pump is 265-270℃, the temperature of the fine filter is 265-270℃, and the temperature of the melt pipeline is 265-270℃. The PETG resin is NPG-modified PETG produced by Jiangsu Suolide Co., Ltd., and the model is HSF. Step 2: PETG resin and open-face slip masterbatch are fed into a second extruder through a hopper for extrusion and plasticization. After metering by a metering pump and filtration by a fine filter, a surface layer of PETG melt is obtained. The extrusion and plasticization temperature of the second extruder is 255-270℃; the temperature of the metering pump is 265-270℃, the temperature of the fine filter is 265-270℃, and the temperature of the melt pipeline is 265-270℃; the PETG resin is NPG-modified PETG produced by Jiangsu Suolide Co., Ltd., and the model is HSF. Step 3: The surface layer PETG melt is piped into the corresponding flow channel of the die pre-distributor, splitting into two streams to form upper and lower surface layers, i.e., the surface layer stream; the core layer PETG melt is piped into the middle flow channel of the die pre-distributor to form the middle layer, i.e., the core layer stream; the surface layer stream and the core layer stream are distributed to form an ABA three-layer structure stream, which is then cast into an ABA structure PETG sheet through the casting die and casting mechanism; the temperature of the die pre-distributor is 265-270℃, the temperature of the casting die is 265-270℃, and the temperature of the casting roller of the casting mechanism is 28℃; Step 4: Add the coating liquid to the coating machine and coat it evenly on the surface of the PETG sheet to obtain a coated PETG sheet. The uniform coating is double-sided coating; the coating thickness is 280 nm. The coating solution is prepared from nano-silica and water-based polyester, with the following mass ratio: 50 parts nano-silica dispersion, 15 parts water-based polyester, 1 part curing agent, and 34 parts water. The nano-silica dispersion contains 20% silica by mass, and the silica particle size is 30 nm. The nano-silica dispersion used is VK-SP30W from Zhejiang Zhitai Nanomaterials Co., Ltd., the water-based polyester is MD-1245 from Toyobo (Japan), and the curing agent is Bayhydur® 401-70. The coating solution is added to a coating machine to coat the surface of PETG sheets, with a coating thickness of 250 nm. The coating machine used is a product of BNM (Korea).

[0037] Step 5: The coated PETG sheet is subjected to a transverse stretching system, a traction system, and a winding system to obtain a semi-finished product. Then, it is subjected to a slitting system and inspection to obtain a high light transmittance and low haze PETG heat shrink label film. The transverse stretching system has a transverse stretching ratio of 5.0 and a stretching temperature of 85-98℃.

[0038] The thickness ratio of the three layers in the PETG sheet is ABA (surface layer: core layer: surface layer) = 12.5:75:12.5.

[0039] Performance testing The PETG heat-shrinkable label films prepared in Examples 1-3 and Comparative Examples 1-5 were used as test samples for performance testing, and the results are as follows:

[0040] The data comparison above shows that the surface melt and core melt in this technical solution both use hoppers under a nitrogen atmosphere, and the nitrogen atmosphere in the extruder and metering pump is maintained, which improves the stability of PETG material. Combined with the impurity removal of the high-precision melt filter device, the purity of PETG material is improved, ensuring the high light transmittance and low haze of the PETG heat shrink label film. At the same time, the use of silica as a coating liquid provides good opening properties without affecting the light transmittance and haze, solving the problem of PETG sheets not containing opening agents. Finally, a PETG heat shrink label film with high light transmittance and low haze is obtained.

[0041] It is understood that the above detailed description of the present invention is for illustrative purposes only and is not intended to limit the technical solutions described in the embodiments of the present invention. Those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention to achieve the same technical effects; as long as the usage requirements are met, they are all within the protection scope of the present invention.

Claims

1. A method for preparing a high light transmission low haze PETG heat shrink label film, characterized by: Includes the following steps: Step 1: PETG resin is fed into the first extruder through a hopper for extrusion and plasticization. After being metered by a metering pump, filtered by a fine filter and a high-precision melt filter, a clean core layer PETG melt is obtained. The hopper is in a nitrogen atmosphere. Step 2: PETG resin is fed into the second extruder through a hopper for extrusion and plasticization. After being metered by a metering pump, filtered by a fine filter and a high-precision melt filter, a clean surface layer of PETG melt is obtained. The hopper is in a nitrogen atmosphere. Step 3: The surface layer PETG melt is fed into the corresponding flow channel of the die head pre-distributor through a pipe, and divided into two streams to form two surface layers, namely the surface layer stream; the core layer PETG melt is fed into the middle flow channel of the die head pre-distributor through a pipe to form the middle layer, namely the core layer stream; the surface layer stream and the core layer stream are fed into the distributor to form an ABA three-layer structure stream, which is then cast into an ABA structure PETG sheet through the casting die and casting mechanism. Step 4: Add the coating liquid to the coating machine and coat it evenly on the surface of the PETG sheet to obtain the coated PETG sheet. The even coating is done by double-sided coating. Step 5: The coated PETG sheet is subjected to a transverse stretching system, a traction system, and a winding system to obtain a semi-finished product. Then, it is subjected to a slitting system and inspection to obtain a high-transmittance, low-haze PETG heat-shrinkable label film.

2. The method for preparing the high transmittance, low haze PETG heat-shrinkable label film according to claim 1, characterized in that: The extrusion plasticizing temperature of the first extruder in step 1 is 255-270℃; the temperature of the metering pump is 265-270℃, the temperature of the fine filter is 265-270℃, and the temperature of the melt pipeline is 265-270℃; the operating temperature inside the high-precision melt filter is 268-270℃.

3. The method for preparing the high transmittance, low haze PETG heat-shrinkable label film according to claim 1, characterized in that: The extrusion plasticizing temperature of the second extruder in step 2 is 255-270℃; the temperature of the metering pump is 265-270℃, the temperature of the fine filter is 265-270℃, and the temperature of the melt pipeline is 265-270℃; the operating temperature inside the high-precision melt filter is 268-270℃.

4. The method for preparing the high transmittance, low haze PETG heat-shrinkable label film according to claim 1, characterized in that: The surface layer and core layer of the PETG resin in both steps 1 and 2 are made of the same PETG material.

5. The method for preparing the high light transmittance, low haze PETG heat-shrinkable label film according to claim 1, characterized in that: The hoppers in steps 1 and 2 are operated under a nitrogen atmosphere. A nitrogen manifold is installed inside the hopper and is located at the bottom of the hopper, close to the extruder inlet.

6. The method for preparing the high light transmittance, low haze PETG heat-shrinkable label film according to claim 1, characterized in that: The temperature of the pre-distributor of the die head in step 3 is 265-270℃, the temperature of the casting die head is 265-270℃, and the temperature of the casting roller of the casting mechanism is 28℃.

7. The method for preparing the high transmittance, low haze PETG heat-shrinkable label film according to claim 1, characterized in that: The transverse stretching system in step 5 has a transverse stretching ratio of 5.0 and a stretching temperature of 85-98℃.

8. The method for preparing the high light transmittance, low haze PETG heat-shrinkable label film according to claim 1, characterized in that: The coating solution is prepared by using nano-silica and water-based polyester.

9. The method for preparing a high-transmittance, low-haze PETG heat-shrinkable label film according to claim 8, characterized in that: The mass ratio of the coating liquid is: 50 parts of nano silica dispersion, 15 parts of water-based polyester, 1 part of curing agent, and 34 parts of water.

10. The method for preparing the high transmittance, low haze PETG heat-shrinkable label film according to claim 1, characterized in that: The PETG resin used in steps 1 and 2 is a modified PETG resin, specifically CHDM modified PETG or NPG modified PETG; wherein, the CHDM modified PETG is one of Embrace™ copolyester, Embrace™ LV copolyester, GN001, S2008 from SK Corporation of Korea, and K2012 from SK Corporation of Korea; the NPG modified PETG is one of FG718H from Yizheng Chemical Fiber, HSF from Jiangsu Suolide, and W501 from Jiangyin Huahong.

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