Polyester film for electronic tag and preparation method thereof

Abstract

The invention relates to a polyester film for an electronic tag and a preparation method thereof.According to the polyester film for the electronic tag, a five-layer co-extrusion structure is adopted, a maze effect is formed through nano clay, the gas diffusion path is prolonged by 10-20 times, the symmetrical core layer design is adopted, stress balance is achieved, the bending rigidity is improved, and the service life of the electronic tag is prolonged. According to the preparation method of the polyester film for the electronic tag, a synchronous two-way stretching technology is adopted, the problem of inconsistent directional shrinkage after two-way stretching is solved, a staged heat setting process is adopted, segmented temperature control is matched with slow cooling, residual internal stress is reduced, the thermal expansion coefficient is reduced by adding the carbon nanotubes, and therefore the overall performance is improved, and the service life is prolonged.

Description

Technical Field

[0001] The present invention relates to a polyester film for electronic tags and a preparation method thereof. Background Art

[0002] The applications of polyester films in electronic tags mainly include: substrates for RFID antennas, isolation layers of electronic tags, protective layers of tags, and substrates for flexible electronic circuits.

[0003] However, the polyester films produced by the prior art for electronic tags have defects in dimensional stability, with a relatively high thermal shrinkage rate, and inconsistent shrinkage rates in different directions after biaxial stretching. In a high-temperature and high-humidity environment, there will still be a thermal shrinkage of 0.5%-1.5%, resulting in deformation of the electronic tag antenna and circuit offset, affecting the transmission performance of RFID signals; during surface treatment, corona treatment is usually used, but this corona treatment method has a short aging time, insufficient adhesion of the coating, and high modulus leads to brittleness, and the functional additives migrate and fail, thus affecting the overall stability and service life. Summary of the Invention

[0004] The technical problem to be solved by the present invention is: in order to overcome the deficiencies of the prior art, the present invention provides a polyester film for electronic tags and a preparation method thereof.

[0005] The technical solution adopted by the present invention to solve its technical problems is: a polyester film for electronic tags, comprising a functional layer, a core layer, a barrier layer, a core layer, and an adhesive layer arranged in sequence from top to bottom. The functional layer comprises PET, an antistatic agent, and a UV stabilizer. The core layer comprises high-crystalline PET. The barrier layer comprises a PET and nano-clay composite material. The adhesive layer comprises PETG and a maleic anhydride graft.

[0006] Preferably, the antistatic agent is polyether ester amide and carbon nanotubes. The UV stabilizer comprises benzotriazoles, triazines, and nano-cerium oxide. The PET and nano-clay composite material comprises a PET matrix, organic montmorillonite, and a compatibilizer.

[0007] Preferably, the ratio of polyether ester amide to carbon nanotubes is 15:1. The ratio of benzotriazoles, triazines, and nano-cerium oxide is 6:2:1. The ratio of the PET matrix, organic montmorillonite, and compatibilizer is 96:3.5:0.5. The ratio of PETG and maleic anhydride graft is 95:5. The core layer further comprises nano-diamond.

[0008] A preparation method of a polyester film for electronic tags as described above, comprising the following steps:

[0009] a. Raw material preparation: DMT with a purity of ≥99.9%, EG with a purity of ≥99.8%, the main catalyst antimony trioxide, the co-catalyst cobalt acetate, the stabilizer triphenyl phosphate, the matting agent silica, the antioxidant, and the color toner;

[0010] b. Transesterification reaction: Dimethyl terephthalate and EG are added to the esterification kettle at a molar ratio of 1:2.3, and 70% of the total amount of the main catalyst and the co-catalyst is added. The reaction temperature is gradually increased from 180°C to 220°C, the reaction pressure is gradually reduced from atmospheric pressure to 50 kPa, and the reaction time is 2 - 3 h;

[0011] c. Pre-polycondensation: The reaction temperature is raised to 250 - 260°C, the reaction pressure is further reduced to 10 - 20 kPa, and the remaining 30% of the catalyst is added;

[0012] d. Final polycondensation: The reactor is switched, and the material is transferred to the disk reactor for the final polycondensation reaction;

[0013] e. Melt extrusion: Using an extruder, through five independent die heads, it is simultaneously extruded from top to bottom in the order of the functional layer, the core layer, the barrier layer, the core layer, and the adhesive layer to form a five-layer structure;

[0014] f. Sheet casting: The melt-extruded material is formed into an amorphous thick sheet by rapid cooling and forming;

[0015] g. Biaxial stretching: Using a tenter frame to simultaneously stretch the thick sheet longitudinally and transversely. The longitudinal stretching includes three stages: preheating, stretching, and relaxation;

[0016] h. Heat setting: Heat setting is carried out using a staged heat setting process, including a preheating stage, a high-temperature setting stage, an annealing stage, a slow cooling stage, and a forced cooling stage;

[0017] i. Surface treatment: After activation by atmospheric pressure plasma, acrylic monomers are grafted, and a micro-scale raised structure is formed by UV imprinting;

[0018] j. Rewinding: Rewinding is achieved using a center winder.

[0019] Preferably, in step e, the thickness ratios of the functional layer, the core layer, the barrier layer, the core layer, and the adhesive layer are 2:3:1:3:2 respectively. The melt pressure of the functional layer, the core layer, and the adhesive layer is 8 - 12 MPa, the melt pressure of the barrier layer is 12 - 15 MPa. The screw of the extrusion die head corresponding to the functional layer is a barrier screw with a length-diameter ratio of 32:1. The screw of the extrusion die head corresponding to the core layer is a separating type BM screw with a length-diameter ratio of 36:1. The screw of the extrusion die head corresponding to the barrier layer is a high-shear double-thread screw with a length-diameter ratio of 40:1. The screw of the extrusion die head corresponding to the adhesive layer is a tapered screw with a length-diameter ratio of 28:1.

[0020] Preferably, in step e, the steps of the melt extrusion process include raw material drying, screw plasticization, melt filtration, metering pump conveying, multi-layer die confluence, and melt lamination.

[0021] Preferably, in the raw material drying step, PET is dried with hot air at 160 - 180°C for 4 - 6 h to make the moisture ≤ 50 ppm, and the nano-clay is dried under vacuum at 120°C for 2 h; in the melt filtration step, the functional layer, core layer, and adhesive layer are filtered with a 20-μm sintered metal filter mesh, and the barrier layer is filtered with a 10-μm double-layer filter mesh.

[0022] Preferably, in step g, the temperature in the preheating stage is 80 - 95°C. The stretching stage includes low-temperature stretching and high-temperature stretching. The temperature of low-temperature stretching is 95 - 110°C, and the stretching ratio is 1.5 - 2.0 times; the temperature of high-temperature stretching is 110 - 125°C, and the stretching ratio is 1.8 - 2.2 times; the temperature in the relaxation stage is 100 - 110°C, and the stretching ratio is -0.5 - 0%.

[0023] Preferably, in step h, the temperature in the preheating stage is 200°C, and the residence time is 4 - 6 s; the temperature in the high-temperature shaping stage is 230°C, and the residence time is 8 - 10 s; the temperature in the annealing stage is 210°C, and the residence time is 6 - 8 s; the slow cooling stage is a stepped temperature, the temperature drops from 190°C to 100°C, and the residence time is 10 - 15 s; the temperature in the forced cooling stage is below 50°C, and the residence time is 3 - 5 s.

[0024] Preferably, in step i, the surface treatment steps include atmospheric pressure plasma activation, acrylic monomer spraying, UV imprinting of microstructures, and post-curing. Among them, the working gas for plasma activation is a mixed gas of argon and oxygen, the mixing ratio of argon and oxygen is 9:1, the discharge power is 300 - 500 W, the electrode spacing is 1 - 2 mm, the treatment speed is 5 - 15 m / min. In the UV imprinting of microstructures, a nickel template with a micro-column array is used, the diameter of the micro-column is 5 μm, the height is 8 μm, the spacing between adjacent micro-columns is 10 μm, and the imprinting pressure is 0.2 - 0.5 MPa.

[0025] The beneficial effects of the present invention are as follows: for the polyester film for electronic tags, by adopting a five-layer co-extrusion structure, the nano-clay forms a "labyrinth effect", and the gas diffusion path is extended by 10 - 20 times. By adopting a symmetric core layer design, stress balance is achieved, and the bending stiffness is improved. For the preparation method of the polyester film for electronic tags, the synchronous biaxial stretching technology is adopted to solve the problem of inconsistent directional shrinkage rates after biaxial stretching. The staged heat setting process is adopted, with segmented temperature control and slow cooling, reducing the residual internal stress. By adding carbon nanotubes, the thermal expansion coefficient is reduced, thereby improving the overall performance and service life. Detailed implementation manners

[0026] A polyester film for electronic tags, comprising a functional layer, a core layer, a barrier layer, a core layer and an adhesive layer arranged in sequence from top to bottom. The functional layer comprises PET, an antistatic agent and a UV stabilizer. The core layer comprises highly crystalline PET. The barrier layer comprises a PET and nanoclay composite material. The adhesive layer comprises PETG and a maleic anhydride graft.

[0027] Preferably, the antistatic agent is polyether ester amide and carbon nanotubes. The UV stabilizer comprises benzotriazoles, triazines and nano cerium oxide. The PET and nanoclay composite material comprises a PET matrix, organic montmorillonite and a compatibilizer.

[0028] Preferably, the ratio of polyether ester amide to carbon nanotubes is 15:1. The ratio of benzotriazoles, triazines to nano cerium oxide is 6:2:1. The ratio of the PET matrix, organic montmorillonite and compatibilizer is 96:3.5:0.5. The ratio of PETG and maleic anhydride graft is 95:5. The core layer further comprises nano diamond.

[0029] PET is polyethylene terephthalate, which is a high molecular polymer.

[0030] PETG is a transparent, amorphous copolyester. The commonly used comonomer is 1,4-cyclohexanedimethanol, and its full name is polyethylene terephthalate-1,4-cyclohexanedimethanol ester.

[0031] Highly crystalline PET is a functional material with significantly improved crystallinity of polyethylene terephthalate through molecular structure design and process regulation.

[0032] The molecular chains in the crystalline region are arranged closely, and the ability to resist thermal motion is stronger.

[0033] The tensile strength of ordinary PET is 160 MPa, the elastic modulus is 3.5 GPa, and the puncture strength is 120

[0034] N / mm;

[0035] While the tensile strength of highly crystalline PET is 210 MPa, the elastic modulus is 5.2 GPa, and the puncture strength is 180 N / mm.

[0036] Test of dimensional stability and resistance change:

[0037] Test equipment: measuring tools, resistance measuring device

[0038] Test method: Place the sample label film in an environment of 85 °C and 85% humidity for 500 h, and measure the change in antenna width and the change rate of resistance.

[0039] Test samples:

[0040] Sample A: A label film using ordinary PET film;

[0041] Sample B: A label film using highly crystalline PET film;

[0042] Test data comparison table

[0043] Material type Line width change (μm) Resistance change rate Ordinary PET ±8.2 12％ High-crystalline PET ±2.5 3％

[0044] After experimental test comparison, the label film using highly crystalline PET has better dimensional stability, a smaller change rate of resistance value, and better performance.

[0045] Here, nano-diamond is added to the core layer. Actually, the proportion of nano-diamond is about 0.1%, mainly to improve the thermal conductivity and optimize the heat dissipation performance.

[0046] The antistatic agents are polyether ester amide and carbon nanotubes. Here, the technical solution of a composite antistatic system of polyether ester amide and carbon nanotubes is adopted. Through the synergistic effect of the molecular-level conductive network and the nano-level conductive path, a long-lasting and efficient antistatic performance is provided for the electronic label film.

[0047] The conductive mechanism of polyether ester amide is ionic conduction. After absorbing moisture, proton migration occurs. The typical addition amount is 2 - 5wt%, and dispersion can be achieved only by melt blending;

[0048] The conductive mechanism of carbon nanotubes is electron conduction, with delocalized electrons in the π bond. The typical addition amount is 0.1 - 0.5wt%, and dispersion needs to be achieved through high shear;

[0049] The coordination effect of polyether ester amide and carbon nanotubes is manifested as: realizing dual-path conduction, with a 30% reduction in the total addition amount, and the compatibility of carbon nanotubes in PET can be improved through polyether ester amide.

[0050] Moreover, carbon nanotubes have ultra-high modulus and a three-dimensional network structure. Through the physical constraint effect and the network inhibition mechanism, the dimensional thermal stability of the film can be significantly improved.

[0051] The UV stabilizers include benzotriazoles, triazines, and nano-ceria. Here, through the organic-inorganic synergistic effect, broad-spectrum and weather-resistant UV protection is provided for the electronic label film, while maintaining high transparency and material compatibility.

[0052] The specific substance of benzotriazoles is Tinuvin 326, with an action wavelength range of 300 - 380nm. As the main absorber, it captures UVB and short-wave UVA.

[0053] The specific triazine substance is Cyasorb UV-1164, with an operating wavelength range of 290 - 400 nm, mainly used to broaden the absorption range and enhance high-temperature resistance.

[0054] Nano-ceria can achieve full-band reflection, mainly used to reflect residual ultraviolet rays and prevent deep degradation.

[0055] UV long-wave cut-off test:

[0056] Test equipment: UV-visible spectrophotometer, xenon aging chamber;

[0057] Test samples:

[0058] Sample A: An electronic tag of 10 cm * 10 cm, with a film thickness of 12 μm, and the above three UV stabilizers are added to the film;

[0059] Sample B: An electronic tag of 10 cm * 10 cm, with a film thickness of 12 μm, and the above three UV stabilizers are added to the film;

[0060] Test pretreatment: Equilibrate for 24 h in an environment with a temperature of 23 °C and a humidity of 50%;

[0061] Test method: Record data at 5 nm wavelength intervals

[0062] Test standard: ISO 4892-3;

[0063] Test data comparison table

[0064] Parameter Sample B Sample A UV cut-off wavelength 380 nm 400 nm

[0065] Yellowing index test:

[0066] Test equipment: Color difference meter, QUV accelerated aging chamber;

[0067] Test samples:

[0068] Sample A: An electronic tag of 7.5 cm * 2.5 cm, with the film stacked to be opaque, and the above three UV stabilizers are added to the film;

[0069] Sample B: An electronic tag of 7.5 cm * 2.5 cm, with the film stacked to be opaque, and the above three UV stabilizers are not added to the film;

[0070] Test standard: ASTM D1925;

[0071] Test method: Circulate in the aging chamber, measure and record data every 100 h

[0072] Test data comparison table

[0073] Parameter Sample B Sample A Yellowness index 8.5 1.2

[0074] Transmittance test:

[0075] Test equipment: haze meter and circular fixture;

[0076] Test samples:

[0077] Sample A: An electronic label of 5 cm * 5 cm, with a single-layer film thickness of 12 μm, and the above three UV stabilizers are added to the film;

[0078] Sample B: An electronic label of 5 cm * 5 cm, with a single-layer film thickness of 12 μm, and the above three UV stabilizers are not added to the film;

[0079] Test method: Test in a darkroom environment, measure 3 times and take the average value;

[0080] Test standard: ASTM D1003;

[0081] Test data comparison table

[0082] Parameter Sample B Sample A Transmittance 89％ 86％

[0083] Damp heat resistance test:

[0084] Test equipment: thermostatic and humidistatic chamber, electrical property tester;

[0085] Test samples:

[0086] Sample A: A complete electronic label of 10 cm * 5 cm, and the above three UV stabilizers are added to the film of the electronic label;

[0087] Sample B: A complete electronic label of 10 cm * 5 cm, and the above three UV stabilizers are not added to the film of the electronic label;

[0088] Test standard: IEC 60068-2-78;

[0089] Failure criterion: Surface resistance change > 50%, coating peeling area > 5%.

[0090] Test method: Regularly detect the resistance and regularly observe the appearance change.

[0091] Test data comparison table

[0092]

[0093]

[0094] Through the above tests and data comparison, the samples added with the above three UV stabilizers show obvious advantages in several properties such as UV cut-off wavelength, yellowness index and damp heat resistance.

[0095] The PET and nanoclay composite material includes a PET matrix, organophilic montmorillonite, and a compatibilizer. Through the synergistic effect of the nano-effect of the nanoclay and the PET matrix, the barrier property, rigidity, and dimensional stability of the electronic tag film are significantly improved.

[0096] The PET matrix is used to provide mechanical strength and processability, and the addition ratio is 95-97%;

[0097] The organophilic montmorillonite is used to form a "labyrinth effect" to achieve path barrier, and the addition ratio is 3-5%;

[0098] The compatibilizer is used to improve the bonding at the interface between the clay and the PET, and the addition ratio is 1-2%.

[0099] The adhesive layer includes PETG and a maleic anhydride grafted product. Here, through the flexibility of PETG and the high reactivity of the maleic anhydride grafted product, strong adhesion between the electronic tag film and the metal coating and printing ink is achieved.

[0100] In the PEGT matrix, it contains more than 30% of cyclohexanedimethanol, mainly to provide flexibility and low-temperature adhesiveness, and the addition amount ranges from 85-95%;

[0101] The grafting rate of the maleic anhydride grafted product is 1.2-1.8%, mainly to introduce carboxyl groups to enhance the polar binding force, and the addition amount ranges from 3-8%;

[0102] Actually, the adhesive layer also includes 2-5% of an elastomer toughening agent and an anti-hydrolysis agent;

[0103] The elastomer toughening agent is hydrogenated SBS, mainly used to reduce the modulus and improve the anti-bending fatigue property;

[0104] The anti-hydrolysis agent is carbodiimide, mainly used to inhibit the cleavage of ester bonds in a humid and hot environment.

[0105] A method for preparing a polyester film for an electronic tag as described above includes the following steps:

[0106] a. Raw material preparation: DMT with a purity ≥ 99.9%, EG with a purity ≥ 99.8%, a main catalyst antimony trioxide, a co-catalyst cobalt acetate, a stabilizer triphenyl phosphate, a matting agent silica, an antioxidant, and a color toner;

[0107] DMT is dimethyl terephthalate, and here it is pre-dried with hot nitrogen at 80°C for 4 hours, and the moisture content is less than 50 ppm;

[0108] EG is ethylene glycol, and here it is pre-dehydrated with a molecular sieve, and the oxygen content is less than 1 ppm;

[0109] Antimony trioxide is used as the main catalyst, mainly to promote the transesterification reaction.

[0110] Cobalt acetate is used as a co-catalyst, mainly to reduce the reaction activation energy and synergistically enhance the effect with the main catalyst.

[0111] Triphenyl phosphate is used as a stabilizer, mainly to inhibit thermal degradation.

[0112] Silica is used as a matting agent, mainly to control the surface roughness.

[0113] The antioxidant is actually pentaerythritol tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], mainly to achieve melt antioxidant performance.

[0114] The toner is actually ultramarine blue, mainly to neutralize yellowing.

[0115] Here, antimony trioxide needs to be pre-dispersed. It is pre-dispersed into EG at an addition ratio of 10%, and then treated with ultrasonic waves at 40 KHz for 30 min.

[0116] b. Transesterification reaction: Dimethyl terephthalate and EG are added to the esterification kettle at a molar ratio of 1:2.3, and 70% of the total amount of the main catalyst and the co-catalyst is added. The reaction temperature is gradually increased from 180 °C to 220 °C in a gradient manner, and the reaction pressure is gradually reduced from atmospheric pressure to 50 kPa. The reaction time is 2 - 3 h;

[0117] c. Pre-polycondensation: The reaction temperature is increased to 250 - 260 °C, the reaction pressure is further reduced to 10 - 20 kPa, and the remaining 30% of the catalyst is added;

[0118] d. Final polycondensation: The reactor is switched, and the material is transferred to the disk reactor for the final polycondensation reaction;

[0119] e. Melt extrusion: An extruder is used to simultaneously extrude through five independent die heads from top to bottom in the order of the functional layer, the core layer, the barrier layer, the core layer, and the adhesive layer to form a five-layer structure;

[0120] f. Sheet casting: The melt-extruded material is formed into an amorphous thick sheet by means of rapid cooling and molding;

[0121] Sheet casting is to quickly cool and form the molten PET into an amorphous thick sheet through die head extrusion.

[0122] The sheet casting step includes melt output, die head extrusion, electrostatic adsorption, rapid cooling by a chill roll, and thickness measurement feedback. Here, a coat-hanger die head design is adopted, and the width of the die lip is 1.5 - 2.5 m, and the opening adjustment range is 0.5 - 3 mm.

[0123] Here, an infrared thickness gauge can be used to achieve on-line thickness detection, a white light interferometer can be used to detect surface roughness, and the birefringence method can be used to detect internal stress.

[0124] g. Biaxial stretching: A tenter is used to simultaneously stretch the thick sheet longitudinally and transversely. The longitudinal stretching includes three stages: preheating, stretching, and relaxation.

[0125] h. Heat setting: Stage-wise heat setting process is adopted for heat setting, including preheating stage, high-temperature setting stage, annealing stage, slow cooling stage, and forced cooling stage.

[0126] i. Surface treatment: After activation by atmospheric pressure plasma, acrylic monomers are grafted, and a micron-scale raised structure is formed by UV imprinting.

[0127] j. Rewinding: A center winder is used to achieve rewinding.

[0128] Preferably, in step e, the thickness ratios of the functional layer, core layer, barrier layer, core layer, and adhesive layer are 2:3:1:3:2 respectively. The melt pressures of the functional layer, core layer, and adhesive layer are 8 - 12 MPa, and the melt pressure of the barrier layer is 12 - 15 MPa. The screw of the extrusion die head corresponding to the functional layer is a barrier screw with a length-diameter ratio of 32:1. The screw of the extrusion die head corresponding to the core layer is a separating type BM screw with a length-diameter ratio of 36:1. The screw of the extrusion die head corresponding to the barrier layer is a high-shear double-thread screw with a length-diameter ratio of 40:1. The screw of the extrusion die head corresponding to the adhesive layer is a tapered screw with a length-diameter ratio of 28:1.

[0129] Preferably, in step e, the steps of the melt extrusion process include raw material drying, screw plasticization, melt filtration, metering pump transportation, multi-layer die head convergence, and melt lamination.

[0130] The main functions of the functional layer are surface functionalization and environmental protection.

[0131] The core layer located below the functional layer mainly plays the functions of mechanical support and dimensional stability.

[0132] The barrier layer mainly realizes gas barrier and water vapor barrier.

[0133] The core layer located below the barrier layer mainly plays a role in balancing stress in a symmetric structure.

[0134] The adhesive layer mainly plays the role of interfacial adhesion and improves printing adaptability.

[0135] The barrier layer is compounded with nano-montmorillonite, and the layer spacing of montmorillonite is 1.2 - 1.8 nm, and the aspect ratio > 200.

[0136] A symmetric core layer is set here, which can achieve stress balance, isotropic thermal shrinkage rate, a 30% increase in bending stiffness, and can also achieve crystallization regulation. The core layers on the upper and lower sides are cooled synchronously, making the crystallinity difference less than 2%.

[0137] The extrusion screw used for the functional layer is a barrier screw, with temperature changes of 250°C - 265°C - 270°C - 260°C, and a melt viscosity of 350 Pa·s;

[0138] The extrusion screw used for the core layer is a separating BM screw, with temperature changes of 270°C - 280°C - 285°C - 275°C, and a melt viscosity of 420 Pa·s;

[0139] The extrusion screw used for the barrier layer is a high-shear double-thread screw, with temperature changes of 275°C - 285°C - 280°C - 265°C, and a melt viscosity of 500 Pa·s;

[0140] The extrusion screw used for the adhesive layer is a variable-pitch screw, with temperature changes of 230°C - 240°C - 245°C - 235°C, and a melt viscosity of 500 Pa·s;

[0141] Preferably, in the raw material drying step, PET is dried with hot air at 160 - 180°C for 4 - 6 h, so that the moisture content ≤ 50 ppm, and the nano-clay is dried under vacuum at 120°C for 2 h; in the melt filtration step, the functional layer, the core layer, and the adhesive layer are filtered with a 20-μm sintered metal filter mesh, and the barrier layer is filtered with a 10-μm double-layer filter mesh.

[0142] The temperature gradient between layers is controlled such that the temperature difference between the functional layer and the core layer is less than 8°C, which can be adjusted by raising the temperature of the die head section of the functional layer by 3 - 5°C;

[0143] The temperature difference between the core layer and the barrier layer is less than 5°C, and the temperature difference between the core layer and the adhesive layer is less than 10°C.

[0144] Preferably, in step g, the temperature in the preheating stage is 80 - 95°C. The stretching stage includes low-temperature stretching and high-temperature stretching. The temperature of low-temperature stretching is 95 - 110°C, the stretching ratio is 1.5 - 2.0 times, the temperature of high-temperature stretching is 110 - 125°C, the stretching ratio is 1.8 - 2.2 times, and the temperature in the relaxation stage is 100 - 110°C, and the stretching ratio is -0.5 - 0%.

[0145] Here, through bidirectional synchronous stretching, two-dimensional orientation of molecular chains is achieved, improving the mechanical properties and dimensional stability of the film.

[0146] In the preheating stage, the temperature is uniformly raised above Tg to eliminate the internal stress in the cast film;

[0147] In the low-temperature stretching stage, the formation of induced crystal nuclei is avoided, the molecular chain breakage is prevented, and the initial orientation is achieved;

[0148] In the high-temperature stretching stage, the crystal structure is improved and the necking phenomenon is eliminated;

[0149] In the relaxation stage, the local stress is released and the properties are balanced.

[0150] Preferably, in step h, the temperature in the preheating stage is 200 °C, the residence time is 4 - 6 s, the temperature in the high-temperature shaping stage is 230 °C, the residence time is 8 - 10 s, the temperature in the annealing stage is 210 °C, the residence time is 6 - 8 s, the slow cooling stage is a stepped temperature, the temperature drops from 190 °C to 100 °C, the residence time is 10 - 15 s, and the temperature in the forced cooling stage is below 50 °C, and the residence time is 3 - 5 s.

[0151] The function of the preheating stage is to activate the molecular chain movement, eliminate the stretching stress, and induce the formation of crystal nuclei;

[0152] The function of the heat setting stage is to improve the crystal structure and lock the molecular chain orientation;

[0153] The function of the annealing stage is to release the local stress and homogenize the crystal size;

[0154] The function of the slow cooling stage is to reduce the internal stress by means of gradient cooling, inhibit the non-equilibrium crystallization, and reduce the thermal shrinkage anisotropy;

[0155] The function of the forced cooling stage is to quickly lock the crystal morphology and quickly shape.

[0156] Preferably, in step i, the surface treatment steps include atmospheric pressure plasma activation, acrylic monomer spraying, UV imprinting of microstructures, and post-curing. Among them, the working gas for plasma activation is a mixed gas of argon and oxygen, the mixing ratio of argon and oxygen is 9:1, the discharge power is 300 - 500 W, the electrode spacing is 1 - 2 mm, the treatment speed is 5 - 15 m / min. In the UV imprinting of microstructures, a nickel template with a micro-column array is used, the micro-column diameter is 5 μm, the height is 8 μm, the spacing between adjacent micro-columns is 10 μm, and the imprinting pressure is 0.2 - 0.5 MPa.

[0157] Here, by combining plasma surface modification and UV imprinting, functional microstructures are constructed on the surface of the polyester film for electronic tags, and antistatic enhancement, coating adhesion improvement, and optical property regulation can be achieved synchronously.

[0158] The working gas here uses a combination of argon and oxygen. Argon can generate highly active free radicals, and oxygen can introduce polar groups such as carboxyl groups.

[0159] The spacing of the discharge electrodes is set to 1 - 2 mm, which can avoid arcs and ensure uniform glow discharge.

[0160] By means of UV imprinted microstructures, the surface area can be increased, thereby enhancing the hygroscopicity and reducing the surface resistance.

[0161] Adhesion test of metal coating:

[0162] Testing equipment: universal material testing machine, digital microscope;

[0163] Test samples:

[0164] Sample A: An electronic tag film of 150 mm * 150 mm, with a thickness of 12 μm, vacuum-evaporated with copper on the surface, and the bonding method is that the copper foil and the film are cured with epoxy resin glue, and the surface is untreated;

[0165] Sample B: An electronic tag film of 150 mm * 150 mm, with a thickness of 12 μm, vacuum-evaporated with copper on the surface, and the bonding method is that the copper foil and the film are cured with epoxy resin glue, and the surface is only treated with plasma;

[0166] Sample C: An electronic tag film of 150 mm * 150 mm, with a thickness of 12 μm, vacuum-evaporated with copper on the surface, and the bonding method is that the copper foil and the film are cured with epoxy resin glue, and the surface is treated with a combination of plasma and UV imprinting technology;

[0167] Testing method: Fix the film end, peel the copper foil at an angle of 180°, record the force value curve, and take the average value in the steady state stage.

[0168] Testing standards: ASTM D1876 and ASTM D3359;

[0169] Failure mode determination criterion: When the copper foil is completely separated from the film and there is no residual metal on the PET surface, it is interfacial peeling;

[0170] When there is interfacial peeling in some areas and coating fracture in some areas, it is mixed failure; when the copper foil itself fractures or the PET substrate tears, it is cohesive failure.

[0171] Sample type Peel strength (N / cm) RSD (%) Failure energy (Joule / square meter) Sample A 0.1 20.0 5.2 Sample B 1.8 16.7 18.6 Sample C 4.2 9.5 42.3

[0172] Through testing, the film treated with a combination process of plasma and UV imprinting on the surface has significant advantages in the experimental tests of peel strength, relative standard deviation, and failure energy data.

[0173] Rewinding is the last key process in film production, which directly affects the appearance quality, interlayer structure, and subsequent processing performance of the product.

[0174] The winding process steps include film flattening, tension detection, static elimination, surface defect scanning, core fitting, constant-tension winding, taper control, and unwinding and packaging.

[0175] Here, the dynamic balance of the air shaft is used to correct the eccentricity of the core, and the eccentricity is controlled within 0.1 mm.

[0176] The winding tension is adjusted by the closed-loop control of the servo motor and the tension sensor, and the tension is controlled between 50 - 80 N / m.

[0177] The surface "zero indentation" is achieved by protecting the wound film with release paper.

[0178] The end face flatness is adjusted by the automatic deviation correction system, and the end face flatness is controlled within ±0.3 mm.

[0179] The hardness of the film roll is achieved by taper tension control, and the hardness of the film roll is controlled between 50 - 55 Shore A.

[0180] The initial tension here is set to 50 N / m to prevent damage to the functional layer.

[0181] Compared with the prior art, for the polyester film for electronic tags, by adopting a five-layer co-extrusion structure, the nano-clay forms a "labyrinth effect", and the gas diffusion path is extended by 10 - 20 times. By adopting a symmetric core layer design, stress balance is achieved, and the bending stiffness is improved. For the preparation method of the polyester film for electronic tags, the synchronous biaxial stretching technology is adopted to solve the problem of inconsistent directional shrinkage rate after biaxial stretching. The stagewise heat setting process is adopted, with segmented temperature control and slow cooling, reducing the residual internal stress. By adding carbon nanotubes, the coefficient of thermal expansion is reduced, thereby improving the overall performance and service life.

[0182] Inspired by the ideal embodiments of the present invention described above, through the above description, relevant staff can make various changes and modifications completely within the scope not deviating from the technical idea of this invention. The technical scope of this invention is not limited to the content in the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A polyester film for electronic tags, characterized in that, It includes a functional layer, a core layer, a barrier layer, a core layer, and an adhesive layer arranged successively from top to bottom. The functional layer includes PET, an antistatic agent, and a UV stabilizer. The core layer includes highly crystalline PET. The barrier layer includes a PET and nanoclay composite material. The adhesive layer includes PETG and a maleic anhydride graft.

2. The polyester film for electronic tags according to claim 1, characterized in that, The antistatic agent is polyether ester amide and carbon nanotubes. The UV stabilizer includes benzotriazoles, triazines, and nanoceria. The PET and nanoclay composite material includes a PET matrix, organically modified montmorillonite, and a compatibilizer.

3. The polyester film for electronic tags according to claim 2, wherein The ratio of polyether ester amide to carbon nanotubes is 15:

1. The ratio of benzotriazoles, triazines, and nanoceria is 6:2:

1. The ratio of the PET matrix, organically modified montmorillonite, and compatibilizer is 96: 3.5:0.

5. The ratio of PETG and maleic anhydride graft is 95:

5. The core layer also includes nanodiamonds.

4. A method for preparing a polyester film for an electronic tag according to any one of claims 1-3, characterized in that, It includes the following steps: a. Raw material preparation: DMT with a purity ≥ 99.9%, EG with a purity ≥ 99.8%, the main catalyst antimony trioxide, the co-catalyst cobalt acetate, the stabilizer triphenyl phosphate, the delustering agent silica, the antioxidant, and the colorant. b. Transesterification reaction: Dimethyl terephthalate and EG are added to the esterification kettle at a molar ratio of 1:2.3, and 70% of the total amount of the main catalyst and the co-catalyst is added. The reaction temperature is gradually increased from 180°C to 220°C in a gradient manner, and the reaction pressure is gradually reduced from atmospheric pressure to 50 kPa. The reaction time is 2 - 3 h. c. Pre-polycondensation: The reaction temperature is raised to 250 - 260°C, and the reaction pressure is further reduced to 10 - 20 kPa, and the remaining 30% of the catalyst is added. d. Final polycondensation: The reactor is switched, and the material is transferred to a disk reactor for the final polycondensation reaction. e. Melt extrusion: Using an extruder, through five independent dies, it is simultaneously extruded from top to bottom in the order of the functional layer, the core layer, the barrier layer, the core layer, and the adhesive layer to form a five-layer structure. f. Sheet casting: The melt-extruded material is formed into an amorphous thick sheet by means of rapid cooling and molding. g. Biaxial stretching: A tenter frame is used to simultaneously stretch the thick sheet longitudinally and transversely. The longitudinal stretching includes three stages: preheating, stretching, and relaxation. h. Heat setting: Heat setting is carried out using a staged heat setting process, including a preheating stage, a high-temperature setting stage, an annealing stage, a slow cooling stage, and a forced cooling stage. i. Surface treatment: After activation by atmospheric pressure plasma, acrylic monomers are grafted, and a microscale raised structure is formed by UV imprinting. j. Rewinding: Rewinding is achieved using a center winder.

5. The preparation method of the polyester film for electronic tags according to claim 4, characterized in that, In step e, the thickness ratios of the functional layer, the core layer, the barrier layer, the core layer, and the adhesive layer are 2:3:1:3:2 respectively. The melt pressures of the functional layer, the core layer, and the adhesive layer are 8 - 12 MPa, and the melt pressure of the barrier layer is 12 - 15 MPa. The screw of the extrusion die head corresponding to the functional layer is a barrier screw with a length-diameter ratio of 32:

1. The screw of the extrusion die head corresponding to the core layer is a separating type BM screw with a length-diameter ratio of 36:

1. The screw of the extrusion die head corresponding to the barrier layer is a high-shear double-thread screw with a length-diameter ratio of 40:

1. The screw of the extrusion die head corresponding to the adhesive layer is a tapered screw with a length-diameter ratio of 28:

1.

6. The preparation method of the polyester film for electronic tags according to claim 4, characterized in that, In step e, the steps of the melt extrusion process include raw material drying, screw plasticization, melt filtration, metering pump transportation, multi-layer die head confluence, and melt lamination.

7. The preparation method of the polyester film for electronic tags according to claim 6, characterized in that, In the raw material drying step, PET is dried with hot air at 160 - 180 °C for 4 - 6 h to make the moisture ≤ 50 ppm, and the nano-clay is dried under vacuum at 120 °C for 2 h. In the melt filtration step, the functional layer, the core layer, and the adhesive layer are filtered with a 20-μm sintered metal filter screen, and the barrier layer is filtered with a 10-μm double-layer filter screen.

8. The preparation method of the polyester film for electronic tags according to claim 4, characterized in that, In step g, the temperature in the preheating stage is 80 - 95 °C. The stretching stage includes low-temperature stretching and high-temperature stretching. The temperature of low-temperature stretching is 95 - 110 °C, and the stretching ratio is 1.5 - 2.0 times. The temperature of high-temperature stretching is 110 - 125 °C, and the stretching ratio is 1.8 - 2.2 times. The temperature in the relaxation stage is 100 - 110 °C, and the stretching ratio is -0.5 - 0%.

9. The preparation method of the polyester film for electronic tags according to claim 4, characterized in that, In step h, the temperature in the preheating stage is 200 °C, and the residence time is 4 - 6 s. The temperature in the high-temperature shaping stage is 230 °C, and the residence time is 8 - 10 s. The temperature in the annealing stage is 210 °C, and the residence time is 6 - 8 s. The slow cooling stage is a stepped temperature, and the temperature drops from 190 °C to 100 °C, with a residence time of 10 - 15 s. The temperature in the forced cooling stage is below 50 °C, and the residence time is 3 - 5 s.

10. The preparation method of the polyester film for electronic tags according to claim 4, characterized in that, In step i, the surface treatment steps include atmospheric pressure plasma activation, acrylic monomer spraying, UV imprinting of microstructures, and post-curing. Among them, the working gas for plasma activation is a mixed gas of argon and oxygen, and the mixing ratio of argon and oxygen is 9:

1. The discharge power is 300 - 500 W, the electrode spacing is 1 - 2 mm, and the treatment speed is 5 - 15 m / min. In the UV imprinting of microstructures, a nickel template with a micro-column array is used. The diameter of the micro-columns is 5 μm, the height is 8 μm, the spacing between adjacent micro-columns is 10 μm, and the imprinting pressure is 0.2 - 0.5 MPa.